Active energy ray curable inkjet inks and printed materials

Abstract

We provide an active energy ray curing inkjet ink that excels in curability, adhesion, print quality, and ejection stability. [Solution] An active energy ray-curable inkjet ink comprising a polymerizable compound (excluding polymerizable compounds having siloxane bonds) (A) and a siloxane-based surface modifier, wherein the polymerizable compound (A) comprises 3 to 25% by mass of 5-methyl-3-vinyloxazolidine-2-one and a bifunctional or more functional acrylate compound, with the total content of both components being 45 to 85% by mass, and the siloxane-based surface modifier comprises 1 to 5% by mass of a siloxane-based surface modifier having an HLB value of 1.3 to 13.0, and further comprises a defined content of the polymerizable compound (A), monofunctional (meth)acrylate compound, and trifunctional or more functional (meth)acrylate compound.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to an active energy ray-curable inkjet ink and a printed material obtained by printing the active energy ray-curable inkjet ink onto a printing substrate. [Background technology]

[0002] In recent years, digital printing methods have been increasingly adopted in printing markets that prioritize productivity, such as the commercial printing market, the office printing market, and the specialty printing market. Reasons for this include the fact that digital printing does not require plate making, thus allowing for low-cost and short-time production of printed materials; the printing equipment is smaller and less expensive compared to that used in plate printing; and uniform printed materials can be easily obtained regardless of the skill level of the person performing the printing.

[0003] Among them, inkjet printing, a type of digital printing method, is superior to other digital printing methods in many respects, including low running costs, ease of full-color printing, and independence of the printing equipment's installation environment from affecting print quality. For this reason, there is a growing demand for the adoption of inkjet printing in the aforementioned printing market.

[0004] The inks used in the above-mentioned inkjet printing methods are diverse, including water-based, oil-based, solvent-based, and active energy ray-curing types. Among these, the demand for active energy ray-curing inks has been increasing in recent years due to their characteristics such as the ability to print high-quality materials on non-permeable printing substrates such as resin films and glass, their fast drying (curing) time, and the strength of the printed materials. In this disclosure, inks used in inkjet printing methods will also be simply referred to as "inkjet inks."

[0005] On the other hand, there has been a growing market demand for environmentally conscious products in recent years. From this perspective, light-emitting diode (LED) light sources are increasingly being adopted as the light source for the active energy rays used to cure active energy ray-curable inkjet inks. However, LED light sources have the characteristic of having a narrow wavelength range of emitted active energy rays, and improving curability becomes a challenge when used in combination with active energy ray-curable inkjet inks.

[0006] Furthermore, in recent years, advancements in inkjet head technology have led to the availability of inkjet heads capable of ejecting ink at high frequencies of 20 kHz or higher. Moreover, these active energy ray-curable inkjet inks are increasingly being used in line printers that install one or more of these inkjet heads to a length exceeding the width of the substrate.

[0007] In line printers equipped with active energy ray-curable inkjet inks, the active energy ray-curable inkjet ink ejected from the inkjet head onto the printing substrate must be cured by active energy rays irradiated from a light source located downstream of the inkjet head. Furthermore, printed images include not only images with high print density (for example, solid images (images printed at 100% print density to completely cover the surface of the printing substrate)) but also images with low print density, such as light-colored images. Thus, recent active energy ray-curable inkjet inks are required to be able to stably and quickly produce printed materials with excellent print quality, regardless of the type of printed image, and even when the wavelength range of the emitted active energy rays is narrow, such as with LED light sources.

[0008] However, attempting to improve the curability of active energy ray-curable inkjet inks presents a new challenge: the ink hardens before it can sufficiently wet and spread on the printing substrate, resulting in reduced print quality and adhesion. For example, Patent Document 1 discloses a radiation-curable inkjet composition containing vinylmethyl oxazolidinone and 2-(2-vinyloxyethoxy)ethyl (meth)acrylate as polymerizable compounds, while Patent Document 2 discloses a radiation-curable inkjet composition containing a predetermined amount of glycerin diacrylate and / or glycerin triacrylate. Furthermore, the inkjet compositions disclosed in Patent Documents 1 and 2 are said to produce printed materials with low viscosity but excellent abrasion resistance, and in the examples, curing of the above inkjet compositions using an LED light source is also performed.

[0009] Furthermore, Patent Document 3 discloses an active energy ray curable ink composition for LED light sources, comprising 2-(2-vinyloxyethoxy)ethyl (meth)acrylate and a polymerization accelerator (a sensitizer described later), with the content of monofunctional polymerizable compounds being below a certain amount. The ink composition disclosed in Patent Document 3 is said to exhibit excellent curability, adhesion, and hardness of printed materials even when irradiated with ultraviolet light from an LED light source.

[0010] Furthermore, Patent Document 4 discloses an active energy ray curable ink composition that includes an acylphosphine oxide compound as a photopolymerization initiator, and is further used in combination with a mercapto-modified (meth)acrylate and / or an anthracene compound. The ink composition disclosed in Patent Document 4 is said to have excellent storage stability and excellent curability when using an LED light source. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2021-042321 [Patent Document 2] Japanese Patent Application Laid-Open No. 2023-163470 [Patent Document 3] Japanese Patent Application Laid-Open No. 2022-184084 [Patent Document 4] Japanese Patent Application Laid-Open No. 2023-097118 [Summary of the Invention] [Problems to be Solved by the Invention]

[0012] However, as evaluated by the present inventors, it has been found that in the inkjet compositions specifically disclosed in the above Patent Documents 1 to 4, the print quality and adhesion may be insufficient depending on the printing conditions. In fact, in the examples of Patent Documents 1 and 2, although the curability and adhesion are evaluated, the evaluation is made using a coated film by a bar coater. In the examples of Patent Documents 3 and 4, a coated film by a spin coater is used. Therefore, in any of the patent documents, it is hard to say that the influence of wet spreading when actually printing using a printing device such as a line printer has been sufficiently studied.

[0013] As described above, conventionally, even when using an LED light source, it has been extremely difficult to obtain an active energy ray-curable inkjet ink that achieves both print quality and adhesion and curability, and further has good ejection stability.

[0014] Therefore, an object of one embodiment of the present invention is to provide an active energy ray-curable inkjet ink that is excellent in all of curability, adhesion, print quality, and ejection stability. [Means for Solving the Problems]

[0015] As a result of intensive studies by the present inventors, it has been found that all of the above-described problems can be solved simultaneously and at a high level by an active energy ray-curable inkjet ink having the following configuration.

[0016] That is, one embodiment of the present invention relates to an active energy ray-curable inkjet ink shown in the following [1] to [6], and a printed matter using the above active energy ray-curable inkjet ink shown in the following [7]. [1] An active energy ray-curable inkjet ink containing a polymerizable compound (excluding a polymerizable compound having a siloxane bond) (A) and a siloxane-based surface conditioner, where the total content of the polymerizable compound (A) is 45 to 95% by mass in the total amount of the inkjet ink, the polymerizable compound (A) includes 5-methyl-3-vinyloxazolidin-2-one and a polyfunctional acrylate compound, the content of the 5-methyl-3-vinyloxazolidin-2-one is 3 to 25% by mass in the total amount of the inkjet ink, the total content of the 5-methyl-3-vinyloxazolidin-2-one and the content of the polyfunctional acrylate compound is 45 to 85% by mass in the total amount of the inkjet ink, the siloxane-based surface conditioner includes a siloxane-based surface conditioner having an HLB value of 1.3 to 13.0, the content of the siloxane-based surface conditioner having an HLB value of 1.3 to 13.0 is 1 to 5% by mass in the total amount of the inkjet ink, the content of a monofunctional (meth)acrylate compound (excluding a monofunctional (meth)acrylate compound having a siloxane bond) is 1.0 times or less the content of the polyfunctional acrylate compound, An active energy ray-curable inkjet ink, wherein the content of a polyfunctional (meth)acrylate compound (excluding a polyfunctional (meth)acrylate compound having a siloxane bond) having three or more functional groups is 25% by mass or less in the total amount of the inkjet ink. [2] The active energy ray-curable inkjet ink according to [1], wherein the siloxane-based surface conditioner having an HLB value of 1.3 to 13.0 contains a (meth)acryloyl group. [3] The active energy ray curable inkjet ink according to [1] or [2], comprising an alkanediol diacrylate having 10 to 15 carbon atoms, as described above. [4] The active energy ray curable inkjet ink according to any one of [1] to [3], wherein the content of a polymerizable compound having one or more vinyl groups is 3 to 45% by mass of the total amount of the polymerizable compound (A). [5] The above-mentioned acrylate compound with two or more functions includes an alkanediol diacrylate, An active energy ray curable inkjet ink according to any one of [1] to [4], wherein the difference between the weighted average value of the HLB value of 5-methyl-3-vinyloxazolidine-2-one and the HLB value of the alkanediol diacrylate and the HLB value of a siloxane-based surface modifier having an HLB value of 1.3 to 13.0 is 0 to 3.5. [6] The active energy ray curable inkjet ink according to any one of [1] to [5], wherein when the content of 5-methyl-3-vinyloxazolidine-2-one is set to 1 by mass, the content of a siloxane-based surface modifier having an HLB value of 1.3 to 13.0 is 0.050 to 1.0 by mass. A printed material obtained by printing an active energy ray curable inkjet ink, as described in any of [7][1] to [6], onto a printing substrate. [Effects of the Invention]

[0017] An active energy ray curable inkjet ink, which is one embodiment of the present invention, exhibits excellent curability, adhesion, print quality, and ejection stability. [Modes for carrying out the invention]

[0018] The following describes in detail an active energy ray curable inkjet ink, which is one embodiment of the present invention (hereinafter also simply referred to as "the inkjet ink of this embodiment"). It should be noted that the present invention is not limited to the following embodiments, and includes modifications that do not alter the essence of the present invention. Furthermore, in this disclosure, the terms "(meth)acrylate," "(meth)acryloyl," and "(meth)acrylic acid" refer to "acrylate and / or methacrylate," "acryloyl and / or methacryloyl," and "acrylic acid and / or methacrylic acid," respectively.

[0019] First, we will explain the mechanism by which the above-mentioned effects are achieved by the configuration of the inkjet ink of this embodiment. However, the mechanism described below is a deduction by the inventors and does not limit the present invention in any way.

[0020] First, the inkjet ink of this embodiment contains a polymerizable compound (A) (excluding polymerizable compounds having siloxane bonds). Furthermore, the polymerizable compound (A) contains 3 to 25% by mass of 5-methyl-3-vinyloxazolidine-2-one. Generally, cyclic N-vinyl compounds are known to have a higher reaction rate with radicals derived from photopolymerization initiators than (meth)acrylate compounds. The reaction rate of 5-methyl-3-vinyloxazolidine-2-one is particularly high compared to other cyclic N-vinyl compounds. This is thought to be because, unlike N-vinylcaprolactam and N-vinylpyrrolidone, which are generally known cyclic N-vinyl compounds, 5-methyl-3-vinyloxazolidine-2-one has an oxygen atom in its ring structure. That is, electrons in the ring structure are attracted to this oxygen atom, making the vinyl group more readily react with radicals derived from photopolymerization initiators. Therefore, the inkjet ink of this embodiment containing a certain amount of 5-methyl-3-vinyloxazolidine-2-one exhibits excellent curability. Furthermore, it is believed that the intermolecular interactions, such as hydrogen bonds, formed by the nitrogen and oxygen atoms present in the 5-methyl-3-vinyloxazolidine-2-one improve adhesion to the printing substrate.

[0021] Furthermore, the inkjet ink of this embodiment contains a bifunctional or more acrylate compound as the polymerizable compound (A). Among the polymerizable groups that the polymerizable compound may have, the acryloyl group exhibits excellent reactivity. Moreover, by using a polymerizable compound that has multiple polymerizable groups, a three-dimensional crosslinked structure is formed by the polymerization reaction.

[0022] As described above, the inkjet ink of this embodiment uses polymerizable compounds that have excellent reactivity and adhesion, and their blending amounts are also specifically defined. That is, in the inkjet ink of this embodiment, the total amount of polymerizable compound (A) is 45 to 95% by mass of the total amount of inkjet ink, the amount of 5-methyl-3-vinyloxazolidine-2-one is 3 to 25% by mass of the total amount of inkjet ink, and the total amount of 5-methyl-3-vinyloxazolidine-2-one and the amount of the bifunctional or more acrylate compound is 45 to 85% by mass of the total amount of inkjet ink. Although the detailed principle is not clear, when a certain amount or more of 5-methyl-3-vinyloxazolidine-2-one and a bifunctional or more acrylate compound are used in this way, the polymerization reaction of the bifunctional or more acrylate compound is promoted by 5-methyl-3-vinyloxazolidine-2-one, and the curability and adhesion of the inkjet ink can be easily improved even with a small amount of radical generation.

[0023] On the other hand, in the inkjet ink of this embodiment, the content of monofunctional (meth)acrylate compounds (excluding monofunctional (meth)acrylate compounds having siloxane bonds) is 1.0 times or less the content of the above-mentioned bifunctional or multifunctional acrylate compounds. By keeping the content of monofunctional acrylate compounds within the above range, radicals generated from photopolymerization initiators, etc., react efficiently with 5-methyl-3-vinyloxazolidine-2-one, enabling further improvement in curability and adhesion.

[0024] Furthermore, in the inkjet ink of this embodiment, the content of trifunctional or greater (meth)acrylate compounds (excluding trifunctional or greater (meth)acrylate compounds having siloxane bonds) is 25% by mass or less of the total amount of the inkjet ink. By doing so, curing shrinkage that may occur when the inkjet ink is cured can be prevented, and both curability and adhesion can be achieved while maintaining good properties.

[0025] On the other hand, the inkjet ink of this embodiment contains a siloxane-based surface modifier with an HLB value of 1.3 to 13.0. Furthermore, the content of the siloxane-based surface modifier with an HLB value of 1.3 to 13.0 is 1 to 5% by mass of the total amount of inkjet ink. By setting the HLB value of the siloxane-based surface modifier to 1.3 or higher, a significant deterioration in ejection stability is prevented, and by setting the HLB value of the siloxane-based surface modifier to 13.0 or lower, wettability on the printing substrate is ensured, thereby improving the print quality of the printed material.

[0026] However, siloxane-based surface modifiers with an HLB value of 1.3 to 13.0 have a high orientation rate at the interface. Therefore, if a siloxane-based surface modifier with an HLB value of 1.3 to 13.0 is simply used, the siloxane-based surface modifier may orient itself at the interface within the inkjet head, potentially worsening ejection stability. Furthermore, after printing, the siloxane-based surface modifier may orient itself at the interface between the printing substrate and the inkjet ink, potentially worsening adhesion. In contrast, in the inkjet ink of this embodiment, a predetermined amount of 5-methyl-3-vinyloxazolidine-2-one is appropriately compatible with the siloxane-based surface modifier. As a result, during inkjet ink ejection, the orientation of the siloxane-based surface modifier at the interface is suppressed, significantly improving ejection stability. Similarly, even after the ink lands on the printing substrate, excessive orientation at the interface is suppressed, improving adhesion. Furthermore, although the principle is not entirely clear, when printed on a porous printing substrate such as coated paper, 5-methyl-3-vinyloxazolidine-2-one and a siloxane-based surface modifier with an HLB value of 1.3 to 13.0 orient together, which suppresses oxygen inhibition by air present in the pores, making it easier to maintain a high curing rate and also improving adhesion to the porous printing substrate.

[0027] As described above, the inkjet ink configuration of this embodiment is essential for solving the aforementioned problems. However, the mechanism for solving the aforementioned problems is a deduction by the inventors and does not limit the present invention in any way.

[0028] It should be noted that the inkjet inks specifically disclosed in the aforementioned Patent Documents 1 to 4 differ from the inkjet ink of this embodiment in that the content of siloxane-based surface modifiers with an HLB value of 1.3 to 13.0 is less than 1% by mass of the total amount of inkjet ink. On the other hand, Patent Document 1 uses 5-methyl-3-vinyloxazolidine-2-one (vinylmethyloxazolidinone) as an essential component, and in the examples, the above 5-methyl-3-vinyloxazolidine-2-one is used in combination with dipropylene glycol diacrylate, which is a bifunctional or more functional acrylate compound. However, no specific example is disclosed in which the content of 5-methyl-3-vinyloxazolidine-2-one is 25% by mass or less, and the total amount of the 5-methyl-3-vinyloxazolidine-2-one and the bifunctional or more functional acrylate compound is 45% by mass or more. Furthermore, Patent Document 2 does not disclose specific examples of inkjet inks that contain 5-methyl-3-vinyloxazolidine-2-one and have a content of 25% by mass or less of a trifunctional or more (meth)acrylate compound (excluding trifunctional or more (meth)acrylate compounds having a siloxane bond). Furthermore, Patent Documents 3 and 4 do not disclose specific examples using 5-methyl-3-vinyloxazolidine-2-one, and the specifications themselves do not mention 5-methyl-3-vinyloxazolidine-2-one at all. In particular, in the example of Patent Document 4, the only bifunctional or more acrylate compound included in the above specific example is "Miramer M240," and its amount is significantly less than the total amount of monofunctional (meth)acrylate compounds. Furthermore, regarding the configuration of the inkjet ink of this embodiment, which involves using a fixed amount of a siloxane-based surface modifier with an HLB value of 1.3 to 13.0, and using it in combination with 5-methyl-3-vinyloxazolidine-2-one and a bifunctional or higher acrylate compound, and further adjusting the amount of each component, and the effects of this configuration, there is no description or suggestion in the above-mentioned Patent Documents 1 to 4.

[0029] Next, each of the components constituting the inkjet ink of this embodiment will be described in detail below.

[0030] <Polymerizable compound> In this disclosure, a polymerizable compound refers to a compound that undergoes polymerization and / or crosslinking reactions by radicals generated from photopolymerization initiators, etc., as described later, and has the function of curing a composition containing the polymerizable compound. Any compound having the above-described properties can be used without particular limitation as the polymerizable compound. Specifically, monomers, oligomers, polymers, etc. can be used as polymerizable compounds. Here, "monomer" refers to a compound consisting of molecules that can become the smallest unit in a polymer obtained by polymerization and / or crosslinking reactions, and which has one or more polymerizable groups. On the other hand, both "oligomer" and "polymer" are polymers having polymerizable groups formed by the bonding of multiple monomers. The two are classified by their degree of polymerization; specifically, those with a degree of polymerization of 2 to 5 are "oligomers," and those with a degree of polymerization of 6 or more are "polymers." The monomers used to synthesize the oligomer may be compounds that do not have a functional group capable of reacting with a radical (a "polymerizable group" described later), but monomers used to impart photopolymerizable groups to the oligomer and polymer are not included in the monomers that constitute the oligomer and polymer. For example, a photopolymerizable urethane oligomer obtained by reacting a urethane oligomer having an isocyanate group at its terminus, which is a reaction product of 1,6-hexanediol and isophorone diisocyanate, with 2-hydroxyethyl acrylate is assumed to have 1,6-hexanediol and isophorone diisocyanate as monomers.

[0031] In this disclosure, "polymerizable group" refers to a functional group that can react with radicals, such as a (meth)acryloyl group and a vinyl group. Furthermore, "monofunctional" as described later refers to a compound having only one polymerizable group in one molecule, while "difunctional" and "trifunctional" refer to a compound having two polymerizable groups and a compound having three polymerizable groups in one molecule, respectively. Compounds with two or more functionalities are collectively referred to as "polyfunctional." On the other hand, as described later, in the inkjet ink of this embodiment, compounds having polymerizable groups can be used as siloxane-based surface modifiers, but these compounds, i.e., polymerizable compounds having siloxane bonds, are not included in the term "polymerizable compounds" in this disclosure.

[0032] The total amount of polymerizable compound (A) contained in the inkjet ink of this embodiment is 45 to 95% by mass of the total amount of inkjet ink, preferably 55 to 90% by mass, and particularly preferably 60 to 88% by mass. By keeping the total amount of polymerizable compound (A) within the above range, it becomes easy to prepare an inkjet ink that is excellent in terms of curability, adhesion, ejection stability, and print quality.

[0033] ≪5-methyl-3-vinyloxazolidine-2-one≫ As described above, the inkjet ink of this embodiment contains 5-methyl-3-vinyloxazolidine-2-one as a polymerizable compound. The content of 5-methyl-3-vinyloxazolidine-2-one is 3 to 25% by mass of the total amount of the inkjet ink.

[0034] As described above, 5-methyl-3-vinyloxazolidine-2-one exhibits particularly superior curing properties compared to other N-vinyl compounds. Furthermore, 5-methyl-3-vinyloxazolidine-2-one is an essential material in the inkjet ink of this embodiment because it also offers excellent adhesion, safety, and odor.

[0035] The content of 5-methyl-3-vinyloxazolidine-2-one is preferably 3 to 25% by mass, more preferably 4 to 25% by mass, and even more preferably 5 to 20% by mass, of the total amount of inkjet ink of this embodiment. By setting the content of 5-methyl-3-vinyloxazolidine-2-one within the above range and further combining it with a bifunctional or higher acrylate compound, an inkjet ink with excellent curability and adhesion can be obtained. Furthermore, as described above, by using it in combination with a siloxane-based surface modifier having an HLB value of 1.3 to 13.0, not only can excellent ejection stability and print quality be achieved simultaneously, but a high curing speed can also be achieved even on printing substrates that may be affected by oxygen inhibition due to air contained in the pores, such as coated paper, and adhesion to the above-mentioned pore-containing printing substrates can also be improved.

[0036] <<Acrylate compounds with two or more functions>> In this disclosure, an acrylate compound is a compound containing an acryloyl group as a polymerizable group. As described above, the inkjet ink of this embodiment contains a polymerizable compound that is bifunctional or more functional acrylate compound, that is, a polymerizable compound that has only an acryloyl group as a polymerizable group and contains two or more such acryloyl groups.

[0037] The total amount of 5-methyl-3-vinyloxazolidine-2-one and the total amount of the bifunctional or more functional acrylate compound is preferably 45 to 85% by mass of the total amount of inkjet ink, and more preferably 55 to 85% by mass. In the inkjet ink of this embodiment, by combining the total amount of 5-methyl-3-vinyloxazolidine-2-one and the total amount of the bifunctional or more functional acrylate compound within the above range, both curability and adhesion can be improved.

[0038] Specific examples of difunctional acrylate monomers (monomers having two acryloyl groups as polymerizable groups) included in acrylate compounds with two or more functions include 1,3-propanediol diacrylate, 1,4-butanediol diacrylate, 1,3-butylenediol diacrylate, 1,6-hexanediol diacrylate, ethylene oxide-modified 1,6-hexanediol diacrylate, propylene oxide-modified 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, and 1,10-decanediol diacrylate. Diacrylate, neopentyl glycol diacrylate, ethylene oxide-modified neopentyl glycol diacrylate, propylene oxide-modified neopentyl glycol diacrylate, 3-methyl-1,5-pentanediol diacrylate, 2,4-dimethyl-1,5-pentanediol diacrylate, 2-ethyl-2-butylpropanediol diacrylate, 2-ethyl-2-butylbutanediol diacrylate, ethylene oxide-modified cyclohexanemethanol diacrylate, ethylene glycol diacrylate, diethyl Examples include polyethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol 200 diacrylate, polyethylene glycol 300 diacrylate, polyethylene glycol 400 diacrylate, neopentyl glycol diacrylate hydroxypivalate, bisphenol A diacrylate, ethylene oxide-modified bisphenol A diacrylate, propylene oxide-modified bisphenol A diacrylate, bisphenol F diacrylate, ethylene oxide-modified bisphenol F diacrylate, propylene oxide-modified bisphenol F diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, ethylene oxide-modified isocyanurate diacrylate, tricyclodecane diacrylate, dimethylol tricyclodecane diacrylate, cyclohexanedimethanol diacrylate, trimethylolpropane diacrylate, neopentyl glycol-modified trimethylolpropane diacrylate, and dicyclopentanyl diacrylate.

[0039] Another example of a difunctional acrylate monomer is a polyfunctional acrylate compound (specific examples will be discussed later) having three or more polymerizable groups, in which two polymerizable groups are left intact and a primary or secondary organic amine is added to the remaining polymerizable groups (Michael addition).

[0040] Furthermore, specific examples of acrylate monomers with three or more functions (monomers having three or more acryloyl groups as polymerizable groups) that are included in acrylate compounds with two or more functions include trimethylolpropane triacrylate, trimethylolethane triacrylate, ethylene oxide-modified trimethylolpropane triacrylate, propylene oxide-modified trimethylolpropane triacrylate, glycerin triacrylate, ethylene oxide-modified glycerin triacrylate, propylene oxide-modified glycerin triacrylate, ethylene oxide-modified isocyanuric acid triacrylate, propylene oxide-modified isocyanuric acid triacrylate, propylene oxide-modified dipentaerythritol triacrylate, tetramethylolmethane triacrylate, pentaerythritol triacrylate, and dipentaerythritol triacrylate. Examples include lysritol triacrylate, tri(acryloyloxyethyl) isocyanurate, hydroxypivalaldehyde-modified dimethylolpropane triacrylate, sorbitol triacrylate, pentaerythritol tetraacrylate, sorbitol tetraacrylate, ditrimethylolpropane tetraacrylate, ethylene oxide-modified pentaerythritol tetraacrylate, propylene oxide-modified pentaerythritol tetraacrylate, tetramethylolmethane tetraacrylate, sorbitol pentaacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, sorbitol hexaacrylate, phosphazene alkylene oxide-modified hexaacrylate, ε-captolactone-modified dipentaerythritol hexaacrylate, and the like.

[0041] Furthermore, as the acrylate compound with two or more functions, a acrylate oligomer with two or more functions (an oligomer having two or more acryloyl groups as polymerizable groups) can also be used. From the viewpoint of balancing curability, discharge stability, and adhesion, the number of polymerizable groups contained in the above acrylate oligomer with two or more functions is preferably 2 to 6 per molecule. The number of polymerizable groups is more preferably 2 to 4, and particularly preferably 2. In addition, the mass-average molecular weight of the acrylate oligomer with two or more functions is preferably 400 to 6,000, and more preferably 500 to 4,500. The method for measuring the mass-average molecular weight is the same as in the case of the pigment-dispersed resin described later.

[0042] Examples of the above-mentioned bifunctional or more acrylate oligomers include urethane (meth)acrylate oligomers such as aliphatic urethane (meth)acrylate oligomers and aromatic urethane (meth)acrylate oligomers; acrylic (meth)acrylate oligomers; polyester (meth)acrylate oligomers; polyether (meth)acrylate oligomers; epoxy (meth)acrylate oligomers, etc. Furthermore, the above-mentioned oligomers may be modified, and examples of such modification include sulfonic acid modification, phosphoric acid modification, amino acid modification, mercapto modification, etc.

[0043] In one embodiment, it is preferable to use alkanediol diacrylate as the bifunctional or more functional acrylate compound. Compared to using only other bifunctional or more functional acrylate compounds, alkanediol diacrylate improves the curability and print quality of the inkjet ink it contains. In the inkjet ink of this embodiment, from the viewpoint of improving curability and print quality, alkanediol diacrylate having 10 to 15 carbon atoms is preferably used, and alkanediol acrylate having 10 to 12 carbon atoms is particularly preferably used. Among the difunctional acrylate monomers listed above, examples of alkanediolic diacrylates having 10 to 15 carbon atoms include 1,4-butanediol diacrylate, 1,3-butylenediolic diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, 3-methyl-1,5-pentanediol diacrylate, 2,4-dimethyl-1,5-pentanediol diacrylate, and 2-ethyl-2-butylpropanediol diacrylate.

[0044] The number of carbon atoms in the aforementioned alkanediol diacrylate also includes the number of carbon atoms in the acryloyl group. For example, "alkanediol diacrylate with 12 carbon atoms" refers to a compound consisting of two acryloyl groups and one alkylene group with 6 carbon atoms.

[0045] The inkjet ink of this embodiment preferably contains two or more alkanediol diacrylates having 10 to 15 carbon atoms, and more preferably two or more alkanediol diacrylates having 10 to 12 carbon atoms. In particular, it is especially preferable to include an alkanediol diacrylate consisting of a branched alkylene group and an alkanediol diacrylate consisting of an alkylene group without a branched structure. Although the detailed mechanism is unknown, by using a combination of an alkanediol diacrylate consisting of a branched alkylene group and an alkanediol diacrylate consisting of an alkylene group without a branched structure, it is possible to obtain an ink with excellent adhesion and ejection stability, as well as good solid filling and print quality.

[0046] Examples of combinations of alkanediol diacrylates consisting of branched alkylene groups and alkanediol diacrylates consisting of non-branched alkylene groups include: combinations of 1,3-butylenediol diacrylate and 1,4-butanediol diacrylate, 1,3-butylenediol diacrylate and 1,6-hexanediol diacrylate, 1,3-butylenediol diacrylate and 1,9-nonanediol diacrylate, and 3-methyl-1,5-pentanediol diacrylate and 1,4-butanediol diacrylate. Examples of combinations include those with relates, combinations of 3-methyl-1,5-pentanediol diacrylate and 1,6-hexanediol diacrylate, combinations of 3-methyl-1,5-pentanediol diacrylate and 1,9-nonanediol diacrylate, combinations of neopentyl glycol diacrylate and 1,4-butanediol diacrylate, combinations of neopentyl glycol diacrylate and 1,6-hexanediol diacrylate, and combinations of neopentyl glycol diacrylate and 1,9-nonanediol diacrylate. Among these, from the viewpoint of obtaining an inkjet ink that is excellent in all aspects of curability, adhesion, ejection stability, and print quality of printed materials, it is preferable to select one or more combinations selected from the group consisting of a combination of 1,3-butylenediol diacrylate and 1,4-butanediol diacrylate, a combination of 1,3-butylenediol diacrylate and 1,6-hexanediol diacrylate, a combination of 3-methyl-1,5-pentanediol diacrylate and 1,4-butanediol diacrylate, and a combination of 3-methyl-1,5-pentanediol diacrylate and 1,6-hexanediol diacrylate.

[0047] When using both an alkanediol diacrylate consisting of branched alkylene groups and an alkanediol diacrylate consisting of non-branched alkylene groups in combination, the WB / WN ratio is preferably 1.2 to 18, and particularly preferably 1.5 to 9.0, when WB / WN is defined as the content of the alkanediol diacrylate consisting of branched alkylene groups relative to the total amount of inkjet ink (WB%) and the content of the alkanediol diacrylate consisting of non-branched alkylene groups (WN%). By keeping the WB / WN ratio within this range, it becomes easier to obtain an inkjet ink with excellent adhesion, ejection stability, and print quality of printed materials.

[0048] <<Monofunctional (meth)acrylate compounds>> The inkjet ink of this embodiment may contain monofunctional (meth)acrylate compounds (excluding polymerizable compounds having siloxane bonds). However, in that case, the content of the monofunctional (meth)acrylate compounds (excluding polymerizable compounds having siloxane bonds) is preferably 1.0 times or less, more preferably 0.8 times or less, and particularly preferably 0.5 times or less, the content of the bifunctional or more functional acrylate compounds. By keeping the content of the monofunctional (meth)acrylate compounds within the above range, polymerization and / or crosslinking reactions can be carried out mainly with 5-methyl-3-vinyloxazolidine-2-one and bifunctional or more functional acrylate compounds, further improving curability and adhesion. Furthermore, the print quality also improves with improved curability. Furthermore, the content of monofunctional (meth)acrylate compounds (excluding polymerizable compounds having siloxane bonds) in the inkjet ink of this embodiment may be 0.0 times the content of bifunctional or more functional acrylate compounds. Here, "0.0 times" means that the target compound is substantially absent. Furthermore, "substantially absent" means that the target component is not intentionally added, and does not prevent contamination as an impurity, by-product, etc. Specifically, if the amount of contamination as an impurity, by-product, etc. is 0.1% by mass or less (preferably 0.05% by mass or less) of the total amount of inkjet ink, it shall be considered to be in the state of "substantially absent".

[0049] Furthermore, for similar reasons, namely to improve curability and adhesion, the content of monofunctional (meth)acrylate compounds (excluding polymerizable compounds having siloxane bonds) is preferably 20% by mass or less (0% by mass, i.e., may not be included) and particularly preferably 10% by mass or less (0% by mass, i.e., may not be included) in the total amount of inkjet ink of this embodiment.

[0050] Specific examples of monofunctional (meth)acrylate compounds include benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, ethylene oxide-modified 2-phenoxyethyl (meth)acrylate, propylene oxide-modified 2-phenoxyethyl (meth)acrylate, dicyclopentenyl (oxyethyl) (meth)acrylate, 2-methoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl (meth)acrylate, methoxydipropylene glycol (meth)acrylate, dipropylene glycol (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, propylene oxide-modified nonylphenol (meth)acrylate, ethylene oxide-modified o-phenylphenol (meth)acrylate, and ethylene oxide-modified nonylphenol (meth)acrylate. 2-Ethylhexyl (meth)acrylate, β-carboxyethyl (meth)acrylate, trimethylolpropaneformal (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isoamyl (meth)acrylate, isononyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, isodecyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, caprolactone (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 1,Examples of monofunctional (meth)acrylate monomers (monomers having one (meth)acryloyl group as a polymerizable group) include 4-cyclohexanedimethanol (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, (meth)acryloylmorpholine, 2-(diethylamino)ethyl (meth)acrylate, 2-(diisopropylamino)ethyl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, morpholinoethyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, and N-(meth)acryloyloxyethylhexahydrophthalimide.

[0051] Furthermore, other examples of monofunctional (meth)acrylate monomers include compounds obtained by retaining only one polymerizable group in a polyfunctional acrylate monomer (for example, the difunctional acrylate monomers and trifunctional or more acrylate monomers listed above) and adding a primary or secondary organic amine (Michael addition) to the remaining polymerizable group.

[0052] <Triple or more functional (meth)acrylate compounds> The inkjet ink of this embodiment may contain a trifunctional or higher (meth)acrylate compound (excluding polymerizable compounds having siloxane bonds). The inclusion of the trifunctional or higher (meth)acrylate compound in the inkjet ink of this embodiment improves its curability. However, in this case, the content of the trifunctional or higher (meth)acrylate compound (excluding polymerizable compounds having siloxane bonds) is preferably 25% by mass or less of the total inkjet ink, more preferably 2 to 20% by mass, and particularly preferably 2 to 15% by mass. By keeping the content of the trifunctional or higher (meth)acrylate compound within the above range, it is possible to suppress shrinkage during curing while improving curability, resulting in good adhesion. Furthermore, the ejection stability of the inkjet ink is also improved. Furthermore, the content of trifunctional or greater (meth)acrylate compounds (excluding polymerizable compounds having siloxane bonds) in the inkjet ink of this embodiment may be 0% by mass of the total amount of inkjet ink. Here, "0% by mass" means that the target compound is substantially not present.

[0053] Specific examples of (meth)acrylate compounds with three or more functions include the three or more functioning acrylate monomers listed above, as well as compounds in which the polymerizable groups of the three or more functioning acrylate monomers are replaced with methacryloyl groups (for example, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, etc.). Furthermore, if the inkjet ink of this embodiment contains a trifunctional or higher acrylate monomer, the trifunctional or higher acrylate monomer is encompassed by both "bifunctional or higher acrylate compounds" and "trifunctional or higher (meth)acrylate compounds."

[0054] <<Other polymerizable compounds>> The inkjet ink of this embodiment may contain polymerizable compounds other than those described above (referred to as "other polymerizable compounds" in this disclosure). Note that only one of these other polymerizable compounds may be used, or multiple polymerizable compounds may be used in combination.

[0055] Specific examples of the above-mentioned other polymerizable compounds include compounds obtained by replacing the polymerizable group with a methacryloyl group in the difunctional acrylate monomers listed above (e.g., 1,3-propanediol dimethacrylate, 1,4-butanediol dimethacrylate, etc.). In addition, compounds having one (meth)acryloyl group and one vinyl ether group can also be used as other polymerizable compounds. Specific examples of such compounds include 2-(2-vinyloxyethoxy)ethyl (meth)acrylate and 2-[2-(2-vinyloxyethoxy)ethoxy]ethyl (meth)acrylate.

[0056] Furthermore, as other examples of other polymerizable compounds, compounds having one vinyl group (excluding 5-methyl-3-vinyloxazolidin-2-one) can be mentioned. Specifically, N-vinylcaprolactam and N-vinylpyrrolidone can be mentioned.

[0057] When the inkjet ink of the present embodiment contains, as other polymerizable compounds, a compound having one or more vinyl groups (excluding 5-methyl-3-vinyloxazolidin-2-one), the total amount of the content of 5-methyl-3-vinyloxazolidin-2-one and the content of the compound having one vinyl group is preferably 3 to 45% by mass, more preferably 3 to 35% by mass, and particularly preferably 3 to 30% by mass in the total amount of the inkjet ink of the present embodiment. By setting the total amount within the above range, the polymerization reaction of the bifunctional or higher acrylate compound is promoted, and the curability and adhesion are improved. Further, with the improvement of curability, the print quality is also improved.

[0058] <Siloxane-based surface conditioner with an HLB value of 1.3 to 13.0> The inkjet ink of the present embodiment contains a siloxane-based surface conditioner having an HLB value of 1.3 to 13.0. By using a siloxane-based surface conditioner having an HLB value of 1.3 to 13.0, the wetting spreadability with respect to the printing substrate is improved, and the print quality is improved. Further, by using in combination a siloxane-based surface conditioner having an HLB value of 1.3 to 13.0 and 5-methyl-3-vinyloxazolidin-2-one, it becomes easy to improve the substrate adhesion and the ejection stability. Furthermore, since it is less likely to be affected by oxygen inhibition due to the air contained in the pores, a high curing rate is exhibited, and the adhesion to a printing substrate having pores such as coated paper can also be improved. The above HLB value is preferably 1.3 to 13.0, more preferably 1.6 to 11, and particularly preferably 2 to 9.

[0059] Furthermore, when the inkjet ink of this embodiment contains alkanediol diacrylate as the bifunctional or more functional acrylate compound, the difference between the weighted average value (weighted average HLB value) of the HLB value of 5-methyl-3-vinyloxazolidine-2-one and the HLB of the alkanediol diacrylate and the (weighted average) HLB value of the siloxane-based surface modifier is preferably 0 to 3.5, and particularly preferably 0 to 3.0. When the value of the above difference is within the above range, it is considered that 5-methyl-3-vinyloxazolidine-2-one, alkanediol diacrylate, and the siloxane-based surface modifier are all suitably compatible. As a result, it becomes easy to obtain an inkjet ink with excellent ejection stability, adhesion, and print quality of printed materials.

[0060] The expression "(weighted average) HLB value" above means that if there is only one compound, it represents the HLB value of that compound, and if there are two or more compounds, it represents the weighted average HLB value of those two or more compounds. Furthermore, the "weighted average HLB value" is obtained by first calculating the product of the HLB value of each compound and the mass ratio of that compound to the total amount of all compounds, and then summing these product values.

[0061] In this disclosure, the "HLB (Hydrophilic-Lipophilic Balance) value" is one of the parameters that represent the degree of hydrophilicity and hydrophobicity of a material. A smaller HLB value indicates higher hydrophobicity of the material, while a larger HLB value indicates higher hydrophilicity. There are two methods for determining the HLB value: calculation from the molecular structure and experimental measurement. In this disclosure, the HLB value of the siloxane-based surface modifier is the value calculated by experimental measurement using the method described below (measured HLB value).

[0062] [Method for measuring and calculating the HLB value of siloxane-based surface modifiers] (1) Dissolve 0.5 g of the target surfactant in 5 mL of ethanol. (2) At 25°C, titrate the mixture from (1) with a 2% phenol aqueous solution while stirring. The endpoint is reached when the mixture becomes cloudy and does not return to its original state when the 2% phenol aqueous solution is added dropwise. (3) When the amount of 2% phenol aqueous solution added dropwise to the endpoint is A [mL], the measured HLB value is calculated according to Equation 1 below. Note that if the solution is turbid at (1), the HLB value is assumed to be 1.1 or less.

[0063] Equation 1: Measured HLB value = 0.89 × A + 1.11

[0064] On the other hand, the Griffin method is used to calculate the HLB value of polymerizable compounds. The Griffin method is a method of calculating the HLB value using the formula (HLB value) = 20 × (sum of the formula weights of the hydrophilic parts in the target compound) ÷ (molecular weight of the target compound).

[0065] The content of the siloxane-based surface modifier having an HLB value of 1.3 to 13.0 is preferably 1 to 5% by mass, more preferably 1 to 4.5% by mass, and particularly preferably 1.5 to 4% by mass, of the total amount of inkjet ink in this embodiment. By adjusting the above content to 1 to 5% by mass, it is possible to achieve a high level of both ejection stability and print quality. Furthermore, even when printing on a printing substrate having pores, it becomes less susceptible to oxygen inhibition by air contained in the pores, making it easier to improve the curability and adhesion to the printing substrate having pores.

[0066] As described above, in the inkjet ink of this embodiment, the ejection stability and adhesion are improved by the compatibility of the siloxane-based surface modifier having an HLB value of 1.3 to 13.0 with 5-methyl-3-vinyloxazolidine-2-one. From this viewpoint, that is, from the viewpoint that the two are suitably compatible and curability, ejection stability, and adhesion are improved, the content mass of the siloxane-based surface modifier having an HLB value of 1.3 to 13.0, when the content mass of 5-methyl-3-vinyloxazolidine-2-one is set to 1, is preferably 0.050 to 1.0, and particularly preferably 0.10 to 0.40.

[0067] As siloxane-based surface modifiers with an HLB value of 1.3 to 13.0, for example, compounds having a dimethylsiloxane structure and modified versions thereof can be used. Among these, polyether-modified siloxane-based surface modifiers are particularly preferred. Furthermore, from the viewpoint of improving curability and adhesion, it is also preferable to use siloxane-based surface modifiers having a (meth)acryloyl group in the molecule ((meth)acrylic-modified siloxane-based surface modifiers). Particularly preferred are (meth)acrylic-polyether-modified siloxane-based surface modifiers having a polyether chain and a (meth)acryloyl group in the molecule.

[0068] Commercially available siloxane-based surface modifiers with an HLB value of 1.3 to 13.0 include, for example, TEGO® Wet 240, 250, 260, 270, 280, TEGO Glide 100, 432, 450, TEGO Twin 4000, 4100, 4200, TEGO Rad 2100, 2200N, 2250, 2300, 2330, 2500 from Evonik, and BYK®-345, 347, 349, 377, 3451, 3455, UV3500, UV3510, UV3530 from Bic Chemie, which can be preferably used. Among these, the siloxane-based surface modifiers with HLB values ​​of 2 to 9 are TEGO Wet 270, 280, TEGO Glide 100, 432, TEGO Twin 4000, 4100, 4200, TEGO Rad 2100, 2330, BYK-347, 377, 3455, UV3510, and UV3530. Furthermore, among the above specific examples, the siloxane-based surface modifiers containing a (meth)acryloyl group are TEGO Rad 2100, 2200N, 2250, 2300, 2330, 2500, BYK-UV3500, and UV3530.

[0069] <Other surface conditioning agents> The inkjet ink of this embodiment may contain surface modifiers other than siloxane-based surface modifiers with an HLB value of 1.3 to 13.0 (also referred to as "other surface modifiers" in this disclosure). Examples of the above-mentioned other surface modifiers include siloxane-based surface modifiers, fluorine-based surface modifiers, acetylene glycol-based surface modifiers, acetylene monool-based surface modifiers, etc., with an HLB value of less than 1.3 or greater than 13.0. These surface modifiers may be used individually or in combination of two or more.

[0070] <Photopolymerization initiator> The inkjet ink of this embodiment preferably contains a photopolymerization initiator. The photopolymerization initiator is a compound that serves as the starting point for polymerization and crosslinking reactions of polymerizable compounds. That is, the photopolymerization initiator absorbs energy from active energy rays, undergoes intramolecular cleavage, or is excited and further extracts hydrogen atoms from a hydrogen donor, thereby generating radicals. In this disclosure, "polymerizable initiator" also includes compounds that can function as the above-mentioned hydrogen donor, which are generally referred to as sensitizers.

[0071] As the photopolymerization initiator, one or more conventionally known compounds can be arbitrarily used. Specifically, acylphosphine oxide compounds, benzophenone compounds, indan compounds, thioxanthone compounds, hydroxyacetophenone compounds, alkylaminoacetophenone compounds, oxime ester compounds, aminobenzoate compounds, ketocoumarin compounds, anthracene compounds, etc., can be used. Of these, aminobenzoate compounds, ketocoumarin compounds, and anthracene compounds are generally classified as sensitizers.

[0072] Among these photopolymerization initiators, it is preferable to use one or more photopolymerization initiators selected from the group consisting of acylphosphine oxide compounds and thioxanthone compounds, because they provide inkjet inks with excellent curability and adhesion even when using light sources with a narrow wavelength range of irradiated active energy rays, such as LED light sources. It is particularly preferable to use at least one acylphosphine oxide compound.

[0073] ≪Acylphosphine oxide compounds≫ Specific examples of the above-mentioned acylphosphine oxide compounds include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, as well as polymers of these compounds. Examples of commercially available acylphosphine oxide compounds include "Omnirad TPO," "Omnirad TPO-L," "Omnirad TPO-H," "Omnirad 819," and "OMNIPOL TP" from IGM RESINS, and "Speedcure TPO," "Speedcure TPO-L," and "Speedcure BPO" from Lambson. Additionally, acylphosphine oxide compounds described in International Publication No. 2017 / 086224 and International Publication No. 2020 / 049378, as well as lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate, can also be used. In the inkjet ink of this embodiment, only one of the acylphosphine oxide compounds listed above may be used, or two or more may be used in combination.

[0074] Among these compounds, ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and / or polymers of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide are preferably used because they have a high affinity for 5-methyl-3-vinyloxazolidine-2-one and improve both curability and discharge stability.

[0075] When the inkjet ink of this embodiment contains an acylphosphine oxide compound, from the viewpoint of obtaining an inkjet ink that is excellent in curability, adhesion, ejection stability, and print quality, the amount of the compound added is preferably 4 to 15% by mass, and particularly preferably 5 to 12% by mass, of the total amount of the inkjet ink. Furthermore, from the viewpoint of obtaining an inkjet ink that is excellent in curability, adhesion, and ejection stability, the content of the acylphosphine oxide compound is preferably 0.4 to 4.0, and particularly preferably 0.5 to 2.5, when the content of 5-methyl-3-vinyloxazolidine-2-one is taken as 1.

[0076] Furthermore, from the viewpoint of improving curability and adhesion without degrading ejection stability and print quality, the total amount of ethoxyphenyl (2,4,6-trimethylbenzoyl)phosphine oxide and the total amount of ethoxyphenyl (2,4,6-trimethylbenzoyl)phosphine oxide polymers relative to the total amount of photopolymerization initiator contained in the inkjet ink of this embodiment is preferably 45 to 80% by mass, more preferably 50 to 80% by mass, and particularly preferably 50 to 70% by mass.

[0077] Furthermore, when the mass of 5-methyl-3-vinyloxazolidine-2-one is set to 1, the total mass of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and the polymer of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is preferably 0.33 to 2.0, and particularly preferably 0.37 to 1.6. By keeping the total mass within the above range, the affinity and compatibility of the above-mentioned compounds are improved, making it easier to obtain an inkjet ink with excellent curability, adhesion, and ejection stability.

[0078] ≪Thioxanthone compounds≫ Specific examples of thioxanthone compounds include 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 3-methoxythioxanthone, 2-carboxymethoxythioxanthone, 3-ethoxycarbonylmethoxythioxanthone, 3-butoxycarboxymethoxythioxanthone, 1,3-dimethyl-2-(2-ethylhexyloxy)thioxanthone, 2-[2,2-bis(ethoxycarbonyl)]ethylthioxanthone, 1-chloro-4-propoxythioxanthone, and polymers of these compounds. Furthermore, examples of commercially available thioxanthone compounds include "Omnirad ITX," "Omnirad DETX," "OMNIPOL TX," "OMNIPOL 3TX," and "OMNIPOL BL 728" from IGM RESINS, "SPEEDCURE ITX," "SPEEDCURE 2-ITX," "SPEEDCURE DETX," "SPEEDCURE LTX," "SPEEDCURE CPTX," and "SPEEDCURE 7010" from Lambson, and "Genopol TX-2" from RAHN. Of these commercially available products, "OMNIPOL TX," "SPEEDCURE 7010," and "Genopol TX-2" are the above-mentioned polymers. In the inkjet ink of this embodiment, only one of the listed thioxanthone compounds may be used, or two or more may be used in combination.

[0079] When the inkjet ink of this embodiment contains a thioxanthone compound, from the viewpoint of obtaining an inkjet ink that is excellent in curability, adhesion, ejection stability, and print quality, the amount of the compound added is preferably 0.5 to 8% by mass, and particularly preferably 1 to 5% by mass, of the total amount of the inkjet ink.

[0080] In one embodiment, the inkjet ink of this embodiment preferably uses both an acylphosphine oxide compound and a thioxanthone compound. In this case, from the viewpoint of achieving excellent curability and fineness of printed materials, the amount of acylphosphine oxide compound in the total inkjet ink, when the amount of thioxanthone compound is set to 1, is preferably 1 to 25, and particularly preferably 2 to 12. Furthermore, from the viewpoint of improving curability, the fineness of printed materials, and ejection stability, the content of acylphosphine oxide compounds in the total amount of inkjet ink is preferably 0.3 to 4, and particularly preferably 0.4 to 1.5, when the sum of the content of thioxanthone compounds and 5-methyl-3-vinyloxazolidine-2-one in the total amount of inkjet ink is taken as 1.

[0081] <<Other photopolymerization initiators>> Examples of commercially available photopolymerization initiators other than acylphosphine oxide compounds and thioxanthone compounds (also referred to as "other photopolymerization initiators" in this disclosure) are shown below.

[0082] Examples of commercially available benzophenone compounds include "Omnirad BP," "Omnirad BMS," "Omnirad 4PBZ," "OMNIRAD EMK," and "Esacure 1001M" from IGM RESINS.

[0083] An example of a commercially available indan-based compound is "SpeedCure XFs01" manufactured by LAMBSON.

[0084] Examples of commercially available hydroxyacetophenone compounds include "Omnirad 127," "Omnirad 184," "Omnirad 1173," "Omnirad 2959," and "Esacure KIP150" from IGM Resins.

[0085] Examples of commercially available alkylaminoacetophenone compounds include "Omnirad 907," "Omnirad 369," and "Omnirad 379" manufactured by IGM Resins.

[0086] Examples of commercially available oxime ester compounds include BASF's "IRGACURE OXE01," "IRGACURE OXE02," and "IRGACURE OXE04."

[0087] Examples of commercially available aminobenzoate compounds include "Omnirad EDB," "Omnirad EHA," "Esacure A198," and "Omnipol ASA" from IGM Resins; "SPEEDCURE EDB," "SPEEDCURE EHA," "SPEEDCURE BEDB," and "SPEEDCURE 7040" from Lambson; and "GENOPOL AB-1" and "GENOPOL AB-2" from Rahn AG.

[0088] Examples of commercially available ketocoumarin compounds include "Esacure 3644" manufactured by IGM Resins. Additionally, ketocoumarin compounds described in Japanese Patent Publication No. 2015-531753, Japanese Patent Publication No. 2019-527199, and Japanese Patent Publication No. 2021-509696 can also be used.

[0089] Examples of commercially available anthracene compounds include "Anthracure UVS-581" manufactured by Kawasaki Chemical Industries, Ltd.

[0090] In addition to those listed above, other photopolymerization initiators such as "Omnirad 651" and "Omnirad MBF" from IGM Resins can also be used.

[0091] In the inkjet ink of this embodiment, one of the commercially available products listed above may be used as a photopolymerization initiator, or two or more may be used in combination.

[0092] When the inkjet ink of this embodiment contains a photopolymerization initiator, the total amount of the photopolymerization initiator is preferably 3 to 20% by mass, more preferably 4 to 17% by mass, and particularly preferably 5 to 15% by mass, relative to the total amount of the inkjet ink. By keeping the total amount of the photopolymerization initiator within the above range, it is possible to achieve both curability, adhesion, and discharge stability.

[0093] <Coloring agents> When the inkjet ink of this embodiment contains a colorant, conventionally known dyes and pigments can be used as the colorant. Among these, the use of pigments is preferable from the viewpoint of improving the color development of printed materials (opacity in the case of white ink, and gloss in the case of metallic ink), as well as storage stability and ejection stability. Specific examples of organic and inorganic pigments that can be used as the above-mentioned pigments include: Red pigments: CI Pigment Red 5, 7, 12, 17, 48(Ca), 48(Mn), 49:2, 57(Ca), 57:1, 112, 122, 123, 147, 149, 150, 166, 168, 176, 177, 178, 179, 184, 188, 202, 209, 242, 254, 255, 264, 266, 269, 282; Orange pigments: CI Pigment Orange 5, 13, 34, 38, 43, 61, 62, 64; Yellow pigments: CI Pigment Yellow 1, 2, 3, 12, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 139, 147, 150, 151, 154, 155, 180, 185, 213; Green pigments: CI Pigment Green 7, 26, 36, 50, 58; Blue pigments: CI Pigment Blue 1, 2, 3, 15, 15:3, 15:4, 15:6, 16, 22, 60; Violet pigments, CI Pigment Violet 19, 23, 31, 37; As black pigments, CI Pigment Black 1, 6, 7, 32; As white pigments, CI Pigment White 4, 5, 6, 12, 18, 21, 25; and, Examples of metallic pigments include CI Pigment Metal 1 and 2. Furthermore, two or more of the pigments listed above may be used in combination.

[0094] When the inkjet ink of this embodiment contains a pigment, its content can be adjusted according to the color and intended use of the inkjet ink. For example, from the viewpoint of achieving both storage stability, ejection stability, and curability of the inkjet ink, the pigment content is preferably 0.5 to 15% by mass, and particularly preferably 1 to 10% by mass, except in the case of white ink and metallic ink. On the other hand, when the inkjet ink of this embodiment is a white ink, from the viewpoint of achieving both storage stability, ejection stability, curability, and opacity of the ink-cured film, the pigment content is more preferably 5 to 30% by mass, and even more preferably 15 to 25% by mass. Furthermore, when the inkjet ink is a metallic ink, from the viewpoint of achieving both storage stability, ejection stability, and glossiness of the ink-cured film, the pigment content is more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass.

[0095] Pigment derivatives When the inkjet ink of this embodiment contains a pigment, a pigment derivative can be used to ensure and improve the dispersion stability of the pigment, as well as the storage stability and ejection stability of the inkjet ink.

[0096] As the above-mentioned pigment derivatives, compounds in which substituents are introduced to the basic skeleton of the pigment can be used. In particular, it is preferable to use compounds in which substituents are introduced to the same basic skeleton as the pigment contained in the inkjet ink. For example, when using CI Pigment Blue 15:3 as the pigment, a compound in which substituents are introduced to the copper phthalocyanine skeleton can be preferably used, and when using CI Pigment Red 122 as the agent, a compound in which substituents are introduced to the quinacridone skeleton can be preferably used.

[0097] On the other hand, the substituents include a carboxylate group having a counterion (COO - ), and sulfonate groups having counterions (SO3 - ) are examples of counterions. In addition, hydrogen ions (H) are examples of counterions. + ), sodium ions, potassium ions, magnesium ions, calcium ions, primary amine cations, secondary amine cations, tertiary amine cations, quaternary ammonium cations, etc. can be used.

[0098] When the inkjet ink of this embodiment contains a pigment derivative, it is preferable that the substituent is a sulfonate group having a counterion selected from the group consisting of hydrogen ions, primary amine cations, secondary amine cations, and quaternary ammonium cations. By using a pigment derivative having such substituents, it becomes easy to obtain an inkjet ink with excellent storage stability and ejection stability.

[0099] When the inkjet ink of this embodiment contains a pigment and a pigment derivative, the amount of the pigment derivative varies depending on the type of pigment used in combination, but is preferably 0.5 to 10% by mass relative to the pigment content, and particularly preferably 1 to 8% by mass.

[0100] Pigment-dispersed resin When the inkjet ink of this embodiment contains a pigment, a pigment dispersion resin can be used to ensure and improve the dispersion stability of the pigment, as well as the storage stability and ejection stability of the inkjet ink.

[0101] The mass-average molecular weight of the pigment dispersion resin is preferably 3,500 to 60,000, more preferably 5,000 to 50,000, and even more preferably 10,000 to 45,000. Within this range, the compatibility of the pigment dispersion resin with the polymerizable monomer is good, improving the storage stability and discharge stability of the ink. In addition, the pigment is uniformly dispersed by the pigment dispersion resin, improving adhesion.

[0102] The above mass-average molecular weight can be determined by gel permission chromatography (GPC). Specifically, it is the value obtained as the polystyrene-equivalent molecular weight measured using a TSKgel column (manufactured by Tosoh Corporation) and a GPC equipped with an RI detector (for example, Tosoh Corporation's "HLC-8320GPC"), with DMF as the developing solvent.

[0103] From the viewpoint of suitably improving the dispersion stability of the pigments mentioned above, as well as the storage stability and ejection stability of the inkjet ink, the pigment dispersion resin is preferably a basic pigment dispersion resin.

[0104] In this disclosure, "basic pigment dispersion resin" refers to a dispersion resin in which basic groups serve as adsorption sites on the pigment surface. Examples of the basic groups include primary amino groups, secondary amino groups, tertiary amino groups, quaternary ammonium groups, and imino groups. Furthermore, organic groups bonded to the nitrogen atoms in the tertiary amino groups and quaternary ammonium groups may bond to each other to form a ring structure (a heterocyclic ring containing the nitrogen atoms). Examples of such rings include pyridine, pyrrolidine, pyrrolidone, imidazoline, and caprolactam.

[0105] Examples of the basic pigment dispersion resins mentioned above include acrylic resins having the basic group, (anhydride) maleic acid resins having the basic group, polyethyleneimine, polyallylamine, polydiallylamine, polyvinylimidazoline, and polyvinylpyrrolidone, as well as graft resins with these resins as the main chain. Examples of commercially available basic pigment dispersion resins include "Azisper-PB-821," "Azisper-PB-822," "Azisper-PB-824," and "Azisper-PB-881" from Ajinomoto Fine Techno Co., Ltd., and "DISPERBYK-162," "DISPERBYK-163," "DISPERBYK-168," "DISPERBYK-182," "DISPERBYK-184," "DISPERBYK-185," and "DISPERBYK-185" from Big Chemie Co., Ltd. Examples include "SPERBYK-2013", "DISPERBYK-2155", "BYKJET-9150", "BYKJET-9151", "BYKJET-9152", Lubrizol's "Solspers 24000", "Solspers 32000", "Solspers 33000", "Solspers 35000", "Solspers 39000", "Solspers 86000", "Solspers J200", and "Solspers X300", and BASF's "EFKA PX4701", "EFKA PX4703", and "EFKA PX4733".

[0106] In this disclosure, "acrylic resin" refers to a resin that uses one or more monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters as constituent monomers (styrene monomers may also be used). However, resins using (anhydride) maleic acid (maleic anhydride and / or maleic acid) as the monomer are not included in the above "acrylic resin". Furthermore, in this disclosure, "(anhydride) maleic acid resin" refers to a resin that uses at least (anhydride) maleic acid as a monomer constituting the resin. In addition, the (anhydride) maleic acid resin may also use one or more selected from the group consisting of α-olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, and styrene derivatives as the above monomer.

[0107] When the inkjet ink of this embodiment contains a basic pigment dispersion resin, its amine value is preferably 10 to 50 mgKOH / g, and particularly preferably 15 to 40 mgKOH / g. A basic pigment dispersion resin having an amine value within the above range has a sufficient number of adsorption sites and can therefore be strongly adsorbed to the pigment. As a result, the dispersion stability of the pigment, as well as the storage stability and ejection stability of the inkjet ink, are improved. Furthermore, since the adsorption sites (basic groups) do not inhibit the polymerization reaction of polymerizable compounds, the curability and adhesion of the inkjet ink are also improved.

[0108] The "amine value" mentioned above refers to the amount of potassium hydroxide (in mg) equivalent to the amount of acid needed to neutralize 1 g of resin. As an example of a method for measuring the amine value, the target resin is dissolved in a solvent mixture of ethanol or tetrahydrofuran and acetic acid, and then titrated using a 0.1 mol / L perchloric acid-acetic acid solution by potentiometric titration. The amine value can then be calculated by converting the titration volume read from the resulting titration curve to the amount of potassium hydroxide (in mg).

[0109] Furthermore, if the inkjet ink of this embodiment contains a basic pigment dispersion resin, its acid value is preferably 2 to 30 mg KOH / g, and particularly preferably 5 to 20 mg KOH / g. If the acid value of the basic pigment dispersion resin is within the above range, the adsorption of basic groups to the pigment surface is less likely to be inhibited, while the pigment dispersed by the basic dispersion resin is uniformly and stably dispersed within the inkjet ink, thereby improving the dispersion stability of the pigment, the storage stability of the inkjet ink, the ejection stability, and the adhesion.

[0110] The "acid value" mentioned above refers to the number of milligrams of potassium hydroxide required to neutralize 1 gram of resin, and can be determined by potentiometric titration in accordance with JIS K 0070. As an example of a specific measurement method, the target resin is dissolved in a solvent prepared by mixing diethyl ether and ethanol in a 1:1 mass ratio, and then titrated using a 0.1 mol / L potassium hydroxide-ethanol solution by potentiometric titration. The acid value can then be calculated using the titration volume read from the resulting titration curve.

[0111] When the inkjet ink of this embodiment contains a basic pigment dispersion resin, its content is preferably 15 to 120% by mass, and more preferably 20 to 80% by mass, relative to the total amount of pigment, except when the inkjet ink is a white ink. In the case of a white ink, the content is preferably 2 to 60% by mass, and more preferably 5 to 30% by mass, relative to the total amount of pigment. Using the ink within the above blending range improves the initial dispersibility of the pigment, the storage stability of the inkjet ink, and the adhesion.

[0112] Polymerization inhibitors To improve the ejection stability of the inkjet ink, and further to improve the hue stability and suppress curing wrinkles in printed materials, the inkjet ink of this embodiment may contain a polymerization inhibitor. Specific examples of such polymerization inhibitors include hindered phenol compounds, phenol compounds, hydroquinone compounds, phenothiazine compounds, phosphorus compounds, and nitrosophenylhydroxylamine compounds, which can be suitably used.

[0113] More specifically, examples of polymerization inhibitors that can be used in the inkjet ink of this embodiment include 4-methoxyphenol, tert-butylhydroquinone, 2,6-di-tert-butyl-4-methylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], hydroquinone, methylhydroquinone, phenothiazine, dicumylphenothiazine, triphenylphosphine, and aluminum salts of N-nitrosophenylhydroxylamine.

[0114] The polymerization inhibitor content is preferably 0.01 to 2% by mass, more preferably 0.05 to 1% by mass, and particularly preferably 0.1 to 0.8% by mass, based on the total mass of the inkjet ink. By adjusting the content to the above range, it becomes easier to improve the ejection stability of the inkjet ink while maintaining curability.

[0115] Organic solvents, water In the inkjet ink of this embodiment, an organic solvent and / or water may be used to reduce the viscosity of the inkjet ink, improve its wetting and spreading properties and adhesion to the printing substrate, and ensure ejection stability. When an organic solvent and / or water is included, the total amount contained therein is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, and particularly preferably 0.1 to 3% by mass, based on the total mass of the inkjet ink. Furthermore, from the viewpoint of ejection stability and wetting and spreading properties and adhesion to the printing substrate, when an organic solvent is used, it is preferable to use an organic solvent with a boiling point of 140 to 300°C.

[0116] Examples of organic solvents that can be used include alkylene glycol monoalkyl ether acetates, alkylene glycol diacetates, alkylene glycol monoalkyl ethers, alkylene glycol dialkyl ethers, alkanediols, lactams, lactones, other nitrogen-containing solvents, and other oxygen-containing solvents.

[0117] In particular, it is preferable to include at least one selected from the group consisting of alkylene glycol monoalkyl ethers, alkylene glycol dialkyl ethers, and alkylene glycol monoalkyl ether acetates. Tripropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol methyl ethyl ether, and diethylene glycol diethyl ether are especially preferred. In one embodiment, the organic solvent is preferably at least one selected from the group consisting of dipropylene glycol monomethyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol methyl ethyl ether, and diethylene glycol diethyl ether. By using these organic solvents, it is easy to improve adhesion and print quality while maintaining favorable storage stability and ejection stability of the inkjet ink.

[0118] Inert Resin The inkjet ink of this embodiment can improve adhesion to various printing substrates and may also contain an inert resin to adjust the viscoelasticity of the inkjet ink and improve ejection stability. As the inert resin, (meth)acrylic resin, urethane resin, vinyl chloride-vinyl acetate copolymer resin, ketone resin, etc. can be used. Among these, from the viewpoint of improving both adhesion and ejection stability, it is preferable that the inert resin contains (meth)acrylic resin and / or ketone resin.

[0119] When the inkjet ink of this embodiment contains an inert resin, its content is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, and particularly preferably 1 to 3% by mass, based on the total mass of the inkjet ink. By adjusting the above content within the above range, adhesion and discharge stability can be easily improved without worsening curability.

[0120] In this disclosure, "inert resin" refers to a resin that does not participate in polymerization reactions, contributes to adhesion to a printing substrate, and has solubility in inkjet inks.

[0121] <<Other additives>> The inkjet ink of this embodiment may, if necessary, further contain additives such as ultraviolet absorbers and fade inhibitors in addition to the components described above. These components can be any conventionally known compounds.

[0122] <Physical properties of inkjet inks> In this embodiment, the inkjet ink has a viscosity of 5 to 25 mPa·s at 25°C, and more preferably 7 to 20 mPa·s, from the viewpoint of improving ejection stability and print quality. If the viscosity is 5 mPa·s or higher, the inkjet ink can be ejected well from the inkjet head. If it is 25 mPa·s or lower, the ejection accuracy will not decrease, and ejection can be continued stably. Furthermore, from the viewpoint of providing high-frequency suitability and enabling stable ejection even at high-speed printing, the viscosity is particularly preferably 8 to 14 mPa·s. The viscosity can be measured using 1.1 mL of inkjet ink and an E-type viscometer (for example, "TVE25L" manufactured by Toki Sangyo Co., Ltd.) equipped with a cone with a cone angle of 1°34' (diameter 48 mm), under conditions of a 25°C environment and a rotation speed of 20 rpm.

[0123] Furthermore, from the viewpoint of improving ejection stability, print quality, and curability, the static surface tension of the inkjet ink at 25°C is preferably 20 to 45 mN / m, and particularly preferably 22 to 40 mN / m. The static surface tension used is the value measured by the plate method (Wilhelmi method). Specifically, for example, it can be measured at 25°C using an automatic surface tension meter "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. and a platinum plate.

[0124] <Method of manufacturing inkjet ink> The inkjet ink of this embodiment can be manufactured by conventionally known methods, for example, as follows. However, the method for manufacturing the inkjet ink of this embodiment is not limited to the method described below.

[0125] First, a pigment dispersion resin is dissolved in a polymerizable compound to produce a pigment dispersion resin varnish. Next, the pigment is gradually added to the stirred pigment dispersion resin varnish and mixed. After mixing for a certain period of time (premixing), a pigment dispersion liquid is produced by performing a dispersion treatment using a dispersion machine such as a paint shaker, sand mill, roll mill, or medialess disperser. It is preferable to use the above-mentioned bifunctional or more acrylate compound as the polymerizable compound used in the production of the pigment dispersion resin varnish, as this facilitates improvements in the dispersion stability of the pigment and the storage and ejection stability of the inkjet ink.

[0126] Subsequently, 5-methyl-3-vinyloxazolidine-2-one, a bifunctional or more acrylate compound, a siloxane-based surface modifier with an HLB value of 1.3 to 13.0, and, if necessary, other polymerizable compounds, photopolymerization initiators, surface modifiers, polymerization inhibitors, organic solvents, water, inert resins, and other additives are added to the pigment dispersion and thoroughly mixed. Then, the mixture is filtered to remove coarse particles, thereby obtaining the inkjet ink of this embodiment.

[0127] The amount of pigment present in the above-mentioned pigment dispersion is preferably 20 to 70% by mass, and particularly preferably 25 to 60% by mass, when using a white pigment. When using a pigment other than a white pigment, it is preferably 10 to 40% by mass, and particularly preferably 15 to 30% by mass, in the pigment dispersion.

[0128] <Printed material> An embodiment of the present invention is a printed material obtained by printing the inkjet ink of this embodiment onto a printing substrate, as described later; that is, a printing substrate on which images and / or characters are recorded. Therefore, "printed material" in this disclosure includes images and / or characters, which are made of a film (ink-cured film) obtained by curing the inkjet ink of this embodiment, and a printing substrate. The above-mentioned "image" also includes solid images and seamless images such as checkerboard patterns. Furthermore, the inkjet printing method shown below can be used as a method for manufacturing the above-mentioned printed material.

[0129] <Inkjet Printing Method> The inkjet ink of this embodiment described above is preferably used in an inkjet printing method. Furthermore, the inkjet printing method preferably includes, in this order, the steps of ejecting the inkjet ink of this embodiment from an inkjet head onto a printing substrate (Step I), and curing the inkjet ink ejected onto the printing substrate by irradiating it with active energy rays (Step II).

[0130] In the above inkjet printing method, a method may be employed in which the same inkjet ink is ejected and applied multiple times from the same inkjet head to the same location on the printing substrate, that is, a method in which step I is performed multiple times on the same location on the printing substrate (multi-pass printing method). However, in the case of the inkjet printing method using the inkjet ink of this embodiment, the effects of the above inkjet ink, such as excellent curability, print quality, and ejection stability, are fully demonstrated, and a method is preferred in which the same inkjet ink is ejected and applied only once from the same inkjet head to the same location on the printing substrate, from the viewpoint of obtaining printed materials with excellent print quality at high speed and stably. In other words, it is preferable to employ a method in which step I is performed only once on the same location on the printing substrate (one-pass printing method).

[0131] One-pass printing can be implemented, for example, by using a line printer. The printing speed (transport speed of the printing substrate) in this case is preferably 35 to 150 m / min, more preferably 50 to 125 m / min, and even more preferably 75 to 100 m / min, from the viewpoint of productivity and obtaining printed materials with good quality.

[0132] The inkjet ink in this embodiment is an inkjet printing ink. Therefore, as described above, an inkjet head is used as the inkjet ink ejection means in step I.

[0133] Methods for ejecting ink using an inkjet head include electrostatic induction, which ejects ink using electrostatic force; drop-on-demand (pressure pulse) method, which utilizes the vibration pressure of a piezoelectric element; acoustic inkjet method, which converts an electrical signal into an acoustic beam and irradiates the ink, using the resulting radiation pressure to eject the ink; and thermal inkjet method, which heats the ink to form bubbles and uses the resulting pressure to eject the ink. Among these, in one embodiment, from the viewpoint of ejection stability, the drop-on-demand (pressure pulse) method, which utilizes the vibration pressure of a piezoelectric element, is preferably used.

[0134] The drop volume of inkjet ink droplets ejected from the inkjet nozzle is preferably 1 to 50 pL (picoliters), more preferably 2 to 30 pL, and even more preferably 3 to 20 pL, from the viewpoint of print quality and ejection stability. Furthermore, the design resolution of the inkjet head is preferably 300 dpi or higher, more preferably 480 dpi or higher, and even more preferably 600 dpi or higher. Note that dpi represents the number of dots per 2.54 cm (1 inch). Inkjet ink ejection from the inkjet head may be performed at a high frequency of 20 kHz or higher.

[0135] Examples of inkjet heads that meet the above conditions include Kyocera's KJ4A-AA, KJ4A-TA, KJ4A-RH; Fujifilm's Samba G3L; Seiko Epson's S3200, S1600, S800, I3200, I1600; Konica Minolta's KM1024i, KM1024; and Ricoh's MH5320, MH5340, MH5240, MH5440, etc., all of which can be used suitably.

[0136] In one embodiment, the inkjet ink can be ejected while being heated by a heating device such as a heater provided in the inkjet head so that the inkjet ink has an appropriate viscosity. From the viewpoint of continuously and stably ejecting the inkjet ink, it is preferable to heat the inkjet ink so that the viscosity of the inkjet ink at the time of ejection is 15 mPa·s or less, and it is even more preferable to heat it so that it is 12 mPa·s or less.

[0137] On the other hand, in step II described above, the inkjet ink ejected onto the printing substrate hardens when irradiated with active energy rays, forming an ink-cured film.

[0138] In this disclosure, "active energy rays" refers to energy rays that can provide the energy necessary to generate radicals in the irradiated object (inkjet ink). Specific examples of active energy rays include ultraviolet light, electron beams, visible light, and infrared light. However, ultraviolet light is preferred because it easily improves the curability of the inkjet ink and offers a high degree of design flexibility for the inkjet ink and printing apparatus.

[0139] Furthermore, examples of ultraviolet light sources include high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, ultraviolet lasers, and LED light sources. Only one type may be used, or two or more types may be used in combination. For example, because the LED light source is small in size, it is easy to install multiple units side by side, or to use it in combination with a high-pressure mercury lamp or a metal halide lamp, which makes it easy to further improve curing performance. Also, when installing multiple LED light sources side by side, multiple types of LED light sources with different emission peak wavelengths may be used in combination.

[0140] Generally, ultraviolet light emitted from LED light sources has a narrow wavelength range and exhibits excellent directional propagation (i.e., poor diffusion), making it difficult to cure active energy ray-curable inkjet inks. However, the inkjet ink of this embodiment exhibits particularly excellent curability, making it suitable for combination with LED light sources.

[0141] In the inkjet printing method using the inkjet ink of this embodiment, when ultraviolet light is selected as the active energy ray and an LED light source is used as the light source for said ultraviolet light, the emission peak wavelength is preferably 260 to 450 nm, more preferably 280 to 420 nm, and particularly preferably 320 to 410 nm.

[0142] In Step II, when using an LED light source that emits ultraviolet light, from the perspective of fully exhibiting the above-described effects and obtaining a printed matter with excellent print quality including curability and fineness of the printed matter, the maximum illuminance of ultraviolet light on the printing substrate is 1,000 mW / cm 2 or more is preferable. The above maximum illuminance is more preferably 2,000 mW / cm 2 or more, and particularly preferably 3,000 mW / cm 2 or more. Also, the integrated light amount when irradiating the printing substrate varies depending on the types and contents of the polymerizable compound and the photopolymerization initiator contained in the inkjet ink. For example, it is preferably 50 mJ / cm 2 or more. The above integrated light amount is more preferably 100 mJ / cm 2 or more, and particularly preferably 150 mJ / cm 2 or more.

[0143] In the above Step I, after the droplets of the inkjet ink adhere to the printing substrate (that is, after the end of the above Step I), irradiation with active energy rays is started (that is, the above Step II is started). The time from the end of Step I to the start of Step II is preferably adjusted to 0.03 to 3 seconds. The above time is more preferably 0.04 to 2.5 seconds, and even more preferably 0.06 to 2 seconds. By adjusting the above time within the above range, the dot formation property of the inkjet ink becomes good, and a printed matter with excellent print quality can be obtained.

[0144] In the above inkjet printing method, the above Step II can be repeated a plurality of times. For example, immediately after applying the inkjet ink onto the printing substrate, after irradiating with active energy rays to partially cure the inkjet ink, the inkjet ink can be completely cured by irradiating with active energy rays again. By doing so, it becomes easy to obtain a printed matter with particularly excellent print quality including fineness of the printed matter. In the present disclosure, the above step of partially curing the inkjet ink is referred to as "pre-curing", and the above step of completely curing the inkjet ink is referred to as "main curing".

[0145] In other words, in one embodiment, the inkjet printing method using the inkjet ink of this embodiment may include, in this order: a step of ejecting the inkjet ink from an inkjet head onto a printing substrate (step I); a step of irradiating the inkjet ink ejected onto the printing substrate with active energy rays to pre-cure the inkjet ink (step II-A); and a step of fully curing the inkjet ink (step II-B).

[0146] When performing step II-A described above, that is, when pre-curing the inkjet ink ejected onto the printing substrate, it is preferable to use an LED light source that emits ultraviolet light. In this case, from the viewpoint of particularly improving the print quality of the printed material, the maximum illuminance of ultraviolet light on the printing substrate during the pre-curing process should be 2 to 20 mW / cm². 2 Preferably, it is 5-15 mW / cm². 2 It is preferable that it be so.

[0147] Generally, when performing the above process II-A, the time from when the ejected inkjet ink lands on the printing substrate until it partially hardens is an extremely short time, about 0.03 to 0.5 seconds. However, the inkjet ink of this embodiment has particularly excellent wetting and spreading properties, so it can be suitably combined with partial hardening.

[0148] Furthermore, when performing step II-B described above, that is, when curing the inkjet ink ejected onto the printing substrate, an LED light source emitting ultraviolet light can also be used. In this case, the aforementioned 1,000 mW / cm² can be used. 2 The above maximum illuminance, and 50 mJ / cm² 2 It is preferable to perform the procedure with the above-mentioned cumulative light intensity.

[0149] On the other hand, in process II-B, ultraviolet light can also be irradiated using a high-pressure mercury lamp or a metal halide lamp. In this case, the maximum irradiance of the ultraviolet light is 80 mW / cm². 2Preferably, it should be 120 mW / cm² or higher. 2 It is more preferable to set it to the above. Also, the integrated light intensity should be 100 mJ / cm 2 Preferably, it should be 150 mJ / cm² or higher. 2 It is more preferable to set it to 200 mJ / cm² or higher. 2 It is even more preferable to do the above.

[0150] <Printing base material> In the printing method using the inkjet ink of this embodiment, the printing substrate used is preferably a resin film substrate or a paper substrate. The resin film substrate may preferably have a thickness of 10 to 90 μm. Furthermore, the resin film substrate is preferably selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, and nylon. On the other hand, the paper substrate is preferably selected from coated paper, art paper, laminated paper, etc. As described above, the inkjet ink of this embodiment can produce printed materials with excellent curability and adhesion even on printing substrates having pores such as coated paper.

[0151] In one embodiment, the inkjet ink of this embodiment is suitably used for printing on packages formed from the printing substrates listed above. Among the printing of such packages, it is particularly suitable for printing on food packaging.

[0152] As mentioned above, the inkjet ink of this embodiment exhibits excellent curability and adhesion even when printed on a printing substrate having pores, such as coated paper. Specifically, the inkjet ink of this embodiment is preferably used on coated paper substrates with a 60° gloss of 15 to 35. The 60° gloss value used is the value measured by BYK Gardner's "Microtrigloss".

[0153] The above-mentioned "substrate containing a material selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, and nylon" is not limited to a single-layer structure, but may also have a multilayer structure. That is, the substrate may be a resin film substrate having one layer made of a material selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon, or it may be a resin film substrate (laminated film substrate) having two or more of the above layers. Furthermore, for the purpose of improving the strength of the package, blocking oxygen, etc., the layers constituting the laminated film substrate may include layers made of AL (aluminum foil) and VM (vacuum deposition) film (aluminum deposition film, transparent deposition film), etc. [Examples]

[0154] The present invention will be described in more detail below, but the following examples do not limit the scope of the present invention in any way. Unless otherwise specified, "parts" refers to parts by mass, and "%" refers to percentage by mass.

[0155] <Manufacturing of carbon black dispersion> First, 150g of "Solsperse 32000," a basic pigment dispersion resin manufactured by Lubrizol, and 3,250g of dipropylene glycol diacrylate were placed in a mixing container (volume 10L) equipped with a stirrer, and Solsperse 32000 varnish A was manufactured by thoroughly stirring until the contents were uniform. Next, while stirring Solsperse 32000 varnish A in the mixing container, 600g of carbon black ("Special Black 350," manufactured by Orion Engineered Carbons Co., Ltd.) was gradually added to the container. After all the carbon black had been added, stirring was continued for another hour (premixing). Subsequently, the mixture was circulated and dispersed using a "DinoMill" (volume 0.6L) manufactured by Synmaru Enterprises, filled with 1,800g of zirconia beads with a diameter of 0.5mm. The average particle size of the mixture was then measured at regular intervals (e.g., every hour) using the apparatus and method described later. The circulation and dispersion was terminated when the average particle size fell below 180nm, thereby producing a carbon black dispersion (pigment concentration 15% by mass).

[0156] In this disclosure, "average particle size" refers to the volume-based median diameter (D50) measured using a dynamic light scattering particle size distribution analyzer (Microtrac-Bell "Nanotrac UPA-EX150"), and, if necessary, using inkjet ink diluted with ethyl acetate to a measurable concentration.

[0157] <Manufacturing of Titanium Dioxide Dispersion> Solsperse 32000 varnish B was prepared by first adding 180g of "Solsperse 32000," a basic pigment dispersion resin manufactured by Lubrizol, and 2,820g of dipropylene glycol diacrylate to a mixing container (volume 10L) equipped with a stirrer, and thoroughly stirring and mixing until the contents were uniform. Next, while stirring the Solspers 32000 varnish B in the mixing container, 3,000g of titanium dioxide (KRONOS 2310, manufactured by KRONOS) was gradually added to the container. After all the titanium dioxide had been added, stirring was continued for another hour (premixing). Subsequently, the mixture was circulated and dispersed using a "DinoMill" (volume 0.6L) manufactured by Synmaru Enterprises, filled with 1,800g of 1mm diameter zirconia beads. The average particle size of the mixture was then measured at regular intervals (e.g., every hour) using the apparatus and method described above. The circulation and dispersion was terminated when the average particle size fell below 270nm, thereby producing a titanium dioxide dispersion (pigment concentration 50% by mass).

[0158] <Manufacturing of inkjet inks> The materials listed in columns 1-1 to 1-7 of the table below were placed in a mixing vessel equipped with a stirrer. After all materials were added, the mixture was heated while stirring until its temperature reached 40°C. Once 40°C was reached, stirring was continued for another hour while maintaining the temperature. Subsequently, the mixture was filtered through a membrane filter with a pore size of 0.8 μm to produce inkjet ink.

[0159] In the manufacture of the above inkjet ink, each material was added while stirring the mixture in the mixing container. The order in which the materials were added was as follows: pigment dispersion, polymerizable compound other than 5-methyl-3-vinyloxazolidine-2-one, 5-methyl-3-vinyloxazolidine-2-one, polymerization inhibitor, photopolymerization initiator, surface modifier, and organic solvent. However, when manufacturing an inkjet ink that does not contain one or more of these components, the component in question was omitted, and the next component was added in the order specified above. Furthermore, for components containing two or more materials, the order of addition within that component was from the material added in the largest amount to the material added in the smallest amount.

[0160] [Table 1-1]

[0161] [Table 1-2]

[0162] [Table 1-3]

[0163] [Table 1-4]

[0164] [Table 1-5]

[0165] [Table 1-6]

[0166] [Table 1-7]

[0167] The details of the abbreviations used in Tables 1-1 to 1-7 are as follows. <Polymerizable compound> • VMOX: 5-methyl-3-vinyloxazolidine-2-one PEA: Phenoxyethyl acrylate IBXA: Isobornyl acrylate BzA: Benzyl acrylate VCL: N-vinylcaprolactam • HDDA: 1,6-Hexanediol diacrylate BDDA: 1,4-butanediol diacrylate MPDDA: 3-methyl-1,5-pentanediol diacrylate • DDDA: 1,10-decanediol diacrylate DPGDA: Dipropylene glycol diacrylate GlyTA: Glycerin triacrylate TMP(EO)3TA: Ethylene oxide-modified trimethylolpropane triacrylate • DiTMPTA: Ditrimethylolpropanetetraacrylate VEEA: 2-(2-vinyloxyethoxy)ethyl acrylate <Polymerization inhibitors> • BHT: 2,6-di-tert-butyl-4-methylphenol <Photopolymerization initiator> • Omn819: Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (IGM RESINS "Omnirad 819") • TPO-L: Ethoxyphenyl (2,4,6-trimethylbenzoyl)phosphine oxide (Omnirad TPO-L, manufactured by IGM RESINS) • OmnTP: A polymer of ethoxyphenyl (2,4,6-trimethylbenzoyl)phosphine oxide ("OMNIPOL TP" manufactured by IGM RESINS). • DETX: 2,4-Diethylthioxanthone (Omnirad DETX, manufactured by IGM Resins) • OmnTX: A polymer of 3-ethoxycarbonylmethoxytioxane ("OMNIPOL TX" manufactured by IGM RESINS) <Surface modifier> • Rad2330: Acrylate-modified siloxane-based surface conditioner (HLB value 5.2) (Evonik "TegoRad 2330") • Rad2100: Acrylate-modified siloxane-based surface conditioner (HLB value 2.7) (Evonik "TegoRad 2100") • UV3530: Acrylate-modified siloxane-based surface conditioner (HLB value 8.5) (BYK-UV3530, manufactured by BYK Chemie Co., Ltd.) • Rad2500: Acrylate-modified siloxane-based surface conditioner (HLB value 1.3) (Evonik "TegoRad 2500") • UV3500: Acrylate-modified siloxane-based surface conditioner (HLB value 9.3) (BYK-UV3530, manufactured by BYK Chemie Co., Ltd.) • Rad2250: Acrylate-modified siloxane-based surface conditioner (HLB value 10.6) (Evonik "TegoRad 2250") • Glide432: Polyether-modified siloxane-based surface modifier (HLB value 8.2) (Evonik's "TegoGlide 432") • Glide440: Polyether-modified siloxane-based surface modifier (HLB value 12.5) (Evonik's "TegoGlide 440") • Rad2600: Acrylate-modified siloxane-based surface conditioner (HLB value 1.1 or less) (Evonik's "TegoRad 2600") • BYK3420: Polyether-modified siloxane-based surface conditioner (HLB value 13.4) (BYK-3420, manufactured by BIC Chemie Co., Ltd.) • SF104: Acetylenediol-based surface conditioner (HLB value 7.9) (Evonik's "Surfinol 104") <Organic solvents> • DEDG: Diethylene glycol diethyl ether

[0168] <Manufacturing of printed materials> Using the inkjet ink produced as described above, printed materials were manufactured using the method shown below. A Kyocera inkjet head (KJ4A, design resolution 600dpi) with temperature control was installed above the conveyor that transports the printing substrate. Additionally, a temporary curing LED light source (Phoseon FireEdge FE300, maximum emission wavelength 395nm, maximum illuminance 3,000mW / cm²) was installed above the conveyor on the downstream side of the transport direction of the printing substrate. 2 Furthermore, the main curing LED light source (Phoseon FirePower FP300, maximum emission wavelength 395nm, maximum illuminance 16,000mW / cm²) is installed above the conveyor downstream from the installation position of the temporary curing LED light source. 2 The following were installed: The distance between the inkjet head and the temporary curing LED light source was 15 cm, and the distance between the temporary curing LED light source and the main curing LED light source was 35 cm. The inkjet head described above was filled with the inkjet ink manufactured above. Next, the temperature of the inkjet head was adjusted so that the viscosity of the inkjet ink at the time of ejection was 6-7 mPa·s. After that, the paper substrate described later was fixed on a conveyor, and the conveyor was driven at a speed of 50 m / min. When the coated paper substrate passed the inkjet head's mounting section, droplets of inkjet ink were ejected from the inkjet head, and printing was performed. Specifically, under printing conditions of ejection droplet volume of 11 pL and print resolution of 600 dpi x 600 dpi, a solid image with 100% print coverage printed on a 10 cm square, and a composite image consisting of character images (an image in which 20 randomly printed hiragana characters each in sizes of 4 points, 6 points, and 8 points using MS Mincho font) were printed. Then, even after printing with inkjet ink, the conveyor was driven at the same speed, and as the coated paper substrate passed through the installation sections for the preliminary curing LED light source and the final curing LED light source, ultraviolet light was irradiated to each, thereby manufacturing the printed material. Furthermore, the illuminance and integrated light amount of ultraviolet light irradiated onto the inkjet ink after printing are 900 mW / cm² using an LED light source for temporary curing. 2 , integrated light intensity 25 mJ / cm 2 This curing LED light source provides an illuminance of 6,000 mW / cm². 2 Total luminous intensity 150 mJ / cm 2 To achieve this, the output of the two types of LED light sources was adjusted in advance before performing the printing described above. Furthermore, for inkjet inks containing carbon black, UPM RAFLATAC's coated paper substrate "Raflacoat" was used, and for inkjet inks containing titanium dioxide, Fuji Kyowa Paper's black cast-coated paper substrate "Fantas" was used, both as the paper substrates.

[0169] [Examples 1-82, Comparative Examples 1-12] Using the inkjet inks and printed materials manufactured by the method described above, various evaluations were conducted according to the methods shown below. The evaluation results are shown in Tables 1-1 to 1-7.

[0170] <Evaluation 1: Evaluation of curing properties> The surface of the solid image area with 100% print coverage of the printed material produced by the above method was rubbed with a cotton swab to check whether uncured ink adhered to the cotton swab. If inkjet ink adhered to the cotton swab, the printed material was fixed to the conveyor of the inkjet printing apparatus, and without printing inkjet ink, only the curing LED light source was irradiated. Then, the presence or absence of inkjet ink adhering to the cotton swab was checked again. This procedure was repeated, and the number of passes required until no more uncured inkjet ink adhered to the cotton swab was investigated to evaluate the curability. The evaluation criteria for the curability were as follows, with an evaluation of "2" or higher being considered practically usable, and an evaluation of "3" or higher being considered practically suitable.

[0171] ≪Evaluation Criteria for Curing Properties≫ 4. After passing the swab through the device once in total (without requiring additional UV irradiation), no uncured inkjet ink adhered to the cotton swab. 3. After passing the swab through it a total of two times (with one additional UV irradiation), no uncured inkjet ink adhered to the cotton swab. 2. After passing the swab through a total of three times (with two additional UV irradiations), no uncured inkjet ink adhered to the cotton swab. 1. It was necessary to irradiate the cotton swab with ultraviolet light a total of four or more times until no uncured inkjet ink adhered to it.

[0172] <Evaluation 2: Evaluation of adhesion> In the printed material produced by the above method (without additional UV irradiation as performed in Evaluation 1), six vertical and six horizontal cuts were made at 2.5 mm intervals in the solid image area with 100% print coverage. Next, cellophane tape was applied over the cuts and rubbed from above with an eraser to ensure the cellophane tape adhered firmly to the solid image area. Then, the cellophane tape was peeled off while maintaining a 90° angle between the printed surface of the solid image area and the cellophane tape, and the adhesion was evaluated by calculating the ratio of the area of ​​the solid print peeled off with the cellophane tape to the area where the cellophane tape was adhered. The evaluation criteria for the curing properties were as follows, with an evaluation of "2" or higher considered practically usable, and an evaluation of "3" or higher considered practically suitable.

[0173] ≪Criteria for evaluating adhesion≫ 4: The area of ​​the solid print that has peeled off is less than 5%. 3: Area of ​​peeled solid print is 5% or more but less than 15% 2: Area of ​​peeled solid print is 15% or more but less than 25% 1: The area of ​​the solid printed material that has been peeled off is 25% or more.

[0174] <Evaluation 3: Evaluation of dispensing stability> An inkjet ink was filled into a jig equipped with a Kyocera inkjet head (KJ4A, design resolution 600 dpi) with adjustable temperature. Next, the temperature of the inkjet head was adjusted so that the ink viscosity at ejection was 6-7 mPa·s. After confirming that there were no nozzles that were not ejecting ink, continuous ejection of inkjet ink was performed from all nozzles at a drive frequency of 20 kHz. After continuous ejection for 5 minutes, a nozzle check pattern was printed, and the number of nozzles that were not ejecting ink (nozzle loss) was counted to evaluate the ejection stability. The evaluation criteria for the above ejection stability were as follows, and a rating of "2" or higher was considered practical.

[0175] ≪Evaluation Criteria for Discharge Stability≫ 4. The number of nozzles lost was 0 to 2. 3: The number of nozzles lost was 3 to 5. 2: The number of nozzles lost was 6 to 9. 1: The number of nozzle losses was 10 or more.

[0176] <Rating 4: Print quality rating 1 (text legibility (sharpness))> The legibility (resolution) of the characters in the image portion of the printed material produced using the method described above was evaluated by visually checking whether the hiragana characters were legible. The evaluation criteria for the legibility (resolution) were as follows, with a rating of "2" or higher considered practically usable, and a rating of "3" or higher considered practically suitable.

[0177] ≪Evaluation Criteria for Text Legibility (Detail)≫ At 4:4 points, 6 points, and 8 points, all 20 hiragana characters could be identified. While all 20 hiragana characters could be distinguished at 3:6 points and 8 points, some hiragana characters printed at 4 points could not be distinguished. While all 20 hiragana characters could be distinguished at 2:8 point resolution, some hiragana characters printed at 6 point resolution could not be distinguished. Among the hiragana characters printed at a 1:8 point scale, some were indistinguishable.

[0178] <Rating 5: Print quality rating 2 (solid color filling)> The solid color coverage of the printed material was evaluated by visually checking whether there were any streaks parallel to the printing direction in the solid image areas with 100% print coverage, which were caused by insufficient wetting and spreading of the inkjet ink. The evaluation criteria for solid color coverage were as follows, with a rating of "2" or higher considered usable, and a rating of "3" or higher considered practically suitable.

[0179] Criteria for evaluating the solid color filling of printed materials 4: No lines were present in the solid color areas. 3: There was a single streak in the solid color area. 2: There were 2-3 lines in the solid color area. 1: There were four or more lines in the solid color area.

[0180] As shown in Tables 1-1 to 1-7 above, the inkjet inks of Examples 1 to 82, having the above-described configuration, exhibited excellent curability, adhesion, ejection stability, and print quality.

[0181] On the other hand, in Comparative Examples 1 and 3, where the content of 5-methyl-3-vinyloxazolidine-2-one was less than 3% by mass, the curability and adhesion when printed on coated paper substrates were significantly poor and did not reach a practical level. Meanwhile, although the ejection stability and print quality were both at a practical level, they did not reach a level suitable for practical use. Comparative Example 3 is a system in which N-vinylcaprolactam, a representative example of a cyclic N-vinyl compound, was used instead of 5-methyl-3-vinyloxazolidine-2-one. However, as described above, the curability and adhesion were inferior, confirming that 5-methyl-3-vinyloxazolidine-2-one is an essential material in the inkjet ink of this embodiment.

[0182] Conversely, in Comparative Example 2, although the content of 5-methyl-3-vinyloxazolidine-2-one was greater than 25% by mass, the curability and adhesion were still significantly poor and did not reach a practical level. From this example, it can be inferred that when 5-methyl-3-vinyloxazolidine-2-one is present in excess in an inkjet ink, the balance with the content of acrylate compounds with two or more functions is disrupted, and the 5-methyl-3-vinyloxazolidine-2-one that could not participate in the polymerization reaction remains in the printed material, resulting in a significant decrease in curability and adhesion.

[0183] In Comparative Examples 4 and 6-9, the content of siloxane-based surface modifiers with HLB values ​​of 1.3-13.0 was less than 1% by mass. As a result of evaluating these inkjet inks, the solid coverage of printed materials did not reach a practical level. Furthermore, in Comparative Example 6, which contained more than 5% by mass of siloxane-based surface modifiers with HLB values ​​of 1.3-13.0, not only the fineness of the printed material but also the curability, adhesion, and ejection stability did not reach a practical level.

[0184] In Comparative Example 10, the content of monofunctional (meth)acrylate compounds, excluding monofunctional (meth)acrylate compounds having siloxane bonds, was greater than the content of acrylate compounds with two or more functions, resulting in poor curability and adhesion. In Comparative Example 11, however, the content of trifunctional or more (meth)acrylate compounds, excluding trifunctional or more (meth)acrylate compounds having siloxane bonds, was 35% by mass of the total inkjet ink, resulting in poor adhesion.

[0185] Furthermore, in Comparative Example 12, when 2-(2-vinyloxyethoxy)ethyl acrylate was used instead of a bifunctional or more acrylate compound, the curability and adhesion deteriorated significantly.

[0186] The above results demonstrate that the inkjet ink configuration of this embodiment described above is essential for obtaining an inkjet ink that excels in curability, adhesion, ejection stability, and print quality.

[0187] The disclosures of this application are related to the subject matter described in Japanese Patent Application No. 2024-184462, filed on 18 October 2024, and all of its disclosures are incorporated herein by reference.

Claims

1. An active energy ray curable inkjet ink comprising a polymerizable compound (excluding polymerizable compounds having siloxane bonds) (A) and a siloxane-based surface modifier, The total amount of polymerizable compound (A) is 45 to 95% by mass of the total amount of inkjet ink. The polymerizable compound (A) comprises 5-methyl-3-vinyloxazolidine-2-one and a bifunctional or more acrylate compound. The content of 5-methyl-3-vinyloxazolidine-2-one is 3 to 25% by mass of the total amount of the inkjet ink. The total amount of the 5-methyl-3-vinyloxazolidine-2-one and the acrylate compound with two or more functionalities is 45 to 85% by mass of the total amount of the inkjet ink. The siloxane-based surface modifier includes a siloxane-based surface modifier having an HLB value of 1.3 to 13.

0. The content of the siloxane-based surface modifier having an HLB value of 1.3 to 13.0 is 1 to 5% by mass of the total amount of the inkjet ink. The content of monofunctional (meth)acrylate compounds (excluding monofunctional (meth)acrylate compounds having siloxane bonds) is 1.0 times or less the content of the bifunctional or more functional acrylate compounds. An active energy ray-curable inkjet ink in which the content of a trifunctional or greater (meth)acrylate compound (excluding a trifunctional or greater (meth)acrylate compound having a siloxane bond) is 25% by mass or less of the total amount of the inkjet ink.

2. The active energy ray curable inkjet ink according to claim 1, wherein the siloxane-based surface modifier having an HLB value of 1.3 to 13.0 contains a (meth)acryloyl group.

3. The active energy ray curable inkjet ink according to claim 1 or 2, wherein the aforementioned bifunctional or more acrylate compound includes an alkanediol diacrylate having 10 to 15 carbon atoms.

4. The active energy ray-curable inkjet ink according to claim 1 or 2, wherein the content of a polymerizable compound having one or more vinyl groups is 3 to 45% by mass of the total amount of the polymerizable compound (A).

5. The aforementioned acrylate compound with two or more functions includes alkanediol diacrylate, The active energy ray-curable inkjet ink according to claim 1 or 2, wherein the difference between the weighted average value of the HLB value of 5-methyl-3-vinyloxazolidine-2-one and the HLB value of the alkanediol diacrylate and the HLB value of a siloxane-based surface modifier having an HLB value of 1.3 to 13.0 is 0 to 3.

5.

6. The active energy ray curable inkjet ink according to claim 1 or 2, wherein when the content of 5-methyl-3-vinyloxazolidine-2-one is set to 1 by mass, the content of the siloxane-based surface modifier having an HLB value of 1.3 to 13.0 is 0.050 to 1.0 by mass.

7. A printed article obtained by printing the active energy ray-curable inkjet ink described in claim 1 or 2 onto a printing substrate.

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