Active energy ray curable inkjet inks and printed materials

Abstract

The present invention provides an active energy ray curable inkjet ink that exhibits excellent curability during printing, ejection stability, and storage stability, as well as good strength of the cured ink film. [Solution] An active energy ray-curable inkjet ink comprising a polymerizable compound and a photopolymerization initiator, wherein the polymerizable compound comprises a monofunctional monomer (A) having a nitrogen-containing heterocyclic structure and a monofunctional or bifunctional acrylate monomer (B) (excluding the monofunctional monomer (A)) having a molecular weight of 140 to 250, the content of the acrylate monomer (B) relative to the content of the polymerizable compound is 50 to 90% by mass, the content of the monofunctional monomer (A) relative to the content of the acrylate monomer (B) is 3 to 100% by mass, and the photopolymerization initiator comprises di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide.

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 platemaking, 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 consistent print quality can be easily obtained regardless of the skill level of the person performing the printing.

[0003] Among these, 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, the demand for inkjet printing is particularly high in the aforementioned printing market.

[0004] The inks used in the inkjet printing methods described above are diverse, including water-based, oil-based, solvent-based, and active energy ray-curing types. Among these, active energy ray-curing inks have seen increasing demand in recent years due to their ability to print high-quality materials on various types of printing substrates, their fast drying (curing) time, and the strength of the printed materials.

[0005] Conventionally, active energy ray-curable inks used in inkjet printing systems (hereinafter simply referred to as "active energy ray-curable inkjet inks") have often used acylphosphine oxide compounds as photopolymerization initiators to improve curability and shorten curing time. Acylphosphine oxide compounds can absorb active energy rays across a wide wavelength range and generate radicals, making them compounds that can easily improve the curability of inkjet inks.

[0006] Until now, the acylphosphine oxide compounds used have almost exclusively been 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (also referred to as "TPO" in this disclosure) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (also referred to as "BTPO" in this disclosure).

[0007] On the other hand, TPO has slightly inferior polymerization initiation ability compared to other acylphosphine oxide compounds. Therefore, in inkjet inks that mainly contain polymerizable compounds with a small number of polymerizable groups, for example, it is necessary to incorporate a large amount of TPO to ensure curability. However, this can lead to problems such as TPO precipitation in the inkjet head, resulting in poor ejection stability, or poor storage stability due to TPO precipitation or radical generation causing polymerization reactions in the inkjet ink during storage. Furthermore, if a large amount of TPO is incorporated into an inkjet ink, the increased number of radical sources can reduce the molecular weight of the film formed when the inkjet ink hardens (cured ink film), potentially lowering the strength of the cured ink film. On the other hand, BTPO has the problem of poor solubility in polymerizable compounds. Therefore, there is a greater concern than with the case of large amounts of TPO being incorporated that BTPO precipitation will worsen ejection stability and storage stability.

[0008] Numerous active energy ray-curable inkjet inks containing acylphosphine oxide compounds as essential components have been reported. For example, Patent Document 1 describes how curability can be improved by using an acylphosphine oxide compound in combination with a sulfone compound and / or a thiobenzoyl compound as a photopolymerizable compound. Patent Document 2 states that by using an acylphosphine oxide compound in combination with 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, and further using a monofunctional polymerizable compound with a specific molecular weight, it is possible to improve storage stability, discharge stability, curability, and substrate adhesion. Furthermore, according to Patent Document 3, it is stated that both curability and lightfastness can be achieved by using an acylphosphine oxide compound in combination with a hydroxyphenyltriazine compound (ultraviolet absorber) having a specific structure and / or a hindered amine compound (light stabilizer) having a specific mass-average molecular weight. On the other hand, Patent Documents 4 and 5 disclose systems that use acylphosphine oxide compounds in combination with fluorescent whitening agents. Patent Document 4 states that an ultraviolet-curable inkjet ink composition using an acylphosphine oxide compound having a phenyl group in the molecule and a fluorescent whitening agent having specific absorbance characteristics exhibits excellent curability and hue. Patent Document 5 states that by using a polymerizable compound having one vinyl group and one acryloyl group, and a monofunctional monomer having an alicyclic hydrocarbon group or a cyclic ether group, in addition to an acylphosphine oxide compound and a fluorescent whitening agent having a specific structure, it is possible to improve curability, adhesion, and coating film flexibility (stretch resistance) while increasing the solubility of the polymerization initiator. Furthermore, Patent Document 6 describes how both curability and ejection stability are achieved by using an acylphosphine oxide compound that is solid at room temperature and by specifying the amount of dissolved oxygen in the composition. Patent Document 7 also states that by using an acylphosphine oxide compound in combination with a polymerizable compound having an amide group and / or an amino group, and further specifying the amount of each component, LED curability, ejection stability, adhesion, and abrasion resistance can be improved. Furthermore, Patent Document 8 describes a photocurable inkjet recording ink composition that contains a bisacylphosphine oxide compound and a thioxanthone compound as photopolymerization initiators, and further contains a polymerizable compound having a specific structure (a polymerizable compound having a vinyl group and an acryloyl group), which has low viscosity while exhibiting excellent curability and solubility of the photopolymerization initiator. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2022-143981 [Patent Document 2] Japanese Patent Publication No. 2002-241647 [Patent Document 3] Japanese Patent Publication No. 2011-148918 [Patent Document 4] Japanese Patent Publication No. 2012-31254 [Patent Document 5] Japanese Patent Publication No. 2020-139023 [Patent Document 6] Japanese Patent Publication No. 2015-199817 [Patent Document 7] Japanese Patent Publication No. 2016-20457 [Patent Document 8] Japanese Patent Publication No. 2013-60484 [Overview of the project] [Problems that the invention aims to solve]

[0010] In the inkjet inks specifically described in the aforementioned Patent Documents 1 to 8, TPO and / or BTPO are all used. However, as mentioned above, TPO has problems with polymerization initiation ability, and BTPO has problems with solubility in polymerizable compounds. Conventionally, to compensate for these problems, measures such as using different types of photopolymerization initiators in combination, limiting the structure of the materials used in combination (polymerizable compounds, surface modifiers, other additives, etc.), and adjusting the specifications of the inkjet ink have been taken. However, in order to ensure sufficient curability while simultaneously achieving good ejection stability, storage stability, and the strength of the ink-cured film, the above measures alone were sometimes insufficient.

[0011] Therefore, one of the objectives of the present invention is to provide an active energy ray curable inkjet ink that exhibits excellent curability during printing, ejection stability, and storage stability, and furthermore, good strength of the ink cured film. [Means for solving the problem]

[0012] Under the circumstances described above, the inventors conducted diligent research and found that all of the above-mentioned problems can be solved simultaneously and at a high level by an active energy ray curable inkjet ink having the following configuration.

[0013] In other words, one embodiment of the present invention relates to an active energy ray curable inkjet ink as shown in [1] to [4] below, and to a printed material made using the above active energy ray curable inkjet ink as shown in [5] below. [1] An active energy ray curable inkjet ink comprising a polymerizable compound and a photopolymerization initiator, The polymerizable compound comprises a monofunctional monomer (A) having a nitrogen-containing heterocyclic structure and a monofunctional or bifunctional acrylate monomer (B) having a molecular weight of 140 to 250 (excluding the monofunctional monomer (A)). The content of acrylate monomer (B) relative to the content of the polymerizable compound is 50 to 90% by mass. The content mass of the monofunctional monomer (A) with respect to the content mass of the acrylate monomer (B) is 3 to 100% by mass, The active energy ray-curable inkjet ink, wherein the photoinitiator contains di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide. [2] The active energy ray-curable inkjet ink according to [1], wherein the content mass of the monofunctional monomer (A) with respect to the content mass of the di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide is 100 to 550% by mass. [3] The active energy ray-curable inkjet ink according to [1] or [2], wherein the photoinitiator further contains one or more compounds selected from the group consisting of acylphosphine oxide compounds (excluding the di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide), alkylaminoacetophenone compounds, and thioxanthone compounds. [4] The active energy ray-curable inkjet ink according to any one of [1] to [3], wherein the water content is 0.03 to 0.8% by mass with respect to the total amount of the inkjet ink. [5] A printed matter obtained by printing the active energy ray-curable inkjet ink according to any one of [1] to [4] on a printing substrate.

Effect of the Invention

[0014] The active energy ray-curable inkjet ink according to one embodiment of the present invention described above has excellent curability, ejection stability, and storage stability during printing, and further has the effect that the strength of the ink cured film is also good.

Mode for Carrying Out the Invention

[0015] Hereinafter, the active energy ray-curable inkjet ink according to one embodiment of the present invention (hereinafter, also simply referred to as "the inkjet ink of the present embodiment") will be described in detail. Note that the present invention is not limited to the following embodiments, and also includes modified examples implemented within the scope not changing the gist of the present invention.

[0016] Furthermore, in this disclosure, the terms "(meth)acrylate" and "(meth)acryloyl" refer to "acrylate and / or methacrylate" and "acryloyl and / or methacryloyl," respectively.

[0017] As described above, the inkjet ink of this embodiment contains a monofunctional or bifunctional acrylate monomer (B) (excluding the monofunctional monomer (A) described later) with a molecular weight of 140 to 250 as a polymerizable compound. By using an acrylate monomer (B) with a small molecular weight and a small number of polymerizable groups as the main component (a component accounting for 50% or more by mass of the total amount of the target component) in an active energy ray curable inkjet ink, the viscosity characteristics of the inkjet ink are optimized, the ejection stability from the inkjet head is improved, and the storage stability of the inkjet ink is also improved.

[0018] However, because the acrylate monomer (B) has a small number of polymerizable groups, the film formed when the inkjet ink hardens, i.e., the ink-cured film, may have reduced strength.

[0019] On the other hand, the inkjet ink of this embodiment contains a photopolymerization initiator. A photopolymerization initiator is a compound that serves as the starting point for the polymerization reaction of polymerizable compounds and is an essential component for curing the inkjet ink by irradiation with active energy rays. As will be described later, various types of compounds are known as photopolymerization initiators. Also, as mentioned above, acylphosphine oxide compounds are known as compounds that can easily improve the curability of inkjet inks.

[0020] Until now, TPO and BTPO have often been used as the acylphosphine oxide compounds mentioned above. However, as stated above, TPO has the problem of being somewhat inferior in polymerization initiation ability compared to other acylphosphine oxide compounds, and BTPO has the problem of being poorly soluble in polymerizable compounds. Therefore, with inkjet inks using TPO and / or BTPO, it has sometimes been difficult to simultaneously improve curability during printing, ejection stability, storage stability, and the strength of the ink-cured film.

[0021] Therefore, in the inkjet ink of this embodiment, a novel acylphosphine oxide compound, di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide (also referred to as "TrTPO" in this disclosure), is used as the photopolymerization initiator. TrTPO has better solubility in polymerizable compounds than BTPO, and therefore exhibits better discharge stability and storage stability than when BTPO is used.

[0022] However, the solubility of TrTPO in polymerizable compounds is inferior to that of TPO. Therefore, depending on the type of polymerizable compound used in combination, it may lead to a deterioration in ejection stability and storage stability. In addition, the localization of TrTPO within the inkjet ink may cause uneven progress of the polymerization reaction within the inkjet ink on the printing substrate, potentially resulting in a deterioration of the strength of the resulting ink-cured film.

[0023] Thus, simply blending acrylate monomer (B) and TrTPO into an inkjet ink makes it difficult to simultaneously achieve good ejection stability, storage stability, curability, and strength of the cured ink film. Therefore, in the inkjet ink of this embodiment, a monofunctional monomer (A) having a nitrogen-containing heterocyclic structure is used as a third component, and the amount of said monofunctional monomer (A) is set to 3 to 100% by mass relative to the content of the acrylate monomer (B).

[0024] The monofunctional monomer (A) having a nitrogen-containing heterocyclic structure exhibits excellent solubility of TrTPO, thus facilitating the prevention of TrTPO precipitation and improving discharge stability. Furthermore, monofunctional monomer (A) also exhibits excellent affinity with acrylate monomer (B), which is thought to enable homogenization of TrTPO within the inkjet ink. As a result, the polymerization reaction proceeds uniformly within the inkjet ink, and the polymerizable groups in acrylate monomer (B) react evenly, which is thought to improve the curability of the inkjet ink and the strength of the resulting ink-cured film.

[0025] However, if there is an excess of monofunctional monomer (A) in the inkjet ink, the ejection stability, storage stability, and curing properties may deteriorate. Therefore, in the inkjet ink of this embodiment, the amount of monofunctional monomer (A) is set to 3 to 100% by mass relative to the content of the acrylate monomer (B), thereby achieving a balance between ejection stability, storage stability, curing properties, and the strength of the cured ink film.

[0026] 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.

[0027] As mentioned above, in the specific examples of inkjet inks shown in Patent Documents 1 to 8, TPO and / or BTPO are used in all cases. Furthermore, with the exception of Patent Document 7, there are no examples in which monofunctional monomer (A) is used. On the other hand, the example in Patent Document 7 discloses a specific example of an inkjet ink containing the monofunctional monomer (A), N-vinyl-2-caprolactam ("VCAP" in Tables 1 to 2), the acrylate monomer (B), 1,6-hexanediol diacrylate ("IBXA" in Tables 1 to 2) and 1,6-hexanediol diacrylate ("HDDA" in Tables 1 to 2), and TPO (Example 5). However, the ratio of the content of the monofunctional monomer (A) to the total content of the acrylate monomer (B) is {1 ÷ (62 + 10.5)} × 100 ≈ 1.4 (mass%), which is outside the "3 to 100 mass%" range in this disclosure. Therefore, even if the above TPO is replaced with TrTPO, there is a risk that characteristics such as discharge stability will deteriorate (see also the example (Comparative Example 5) of this specification, which will be described later). Furthermore, Patent Documents 1 to 8 do not disclose TrTPO. In addition, Patent Documents 1 to 8 do not describe or suggest the combined use of TrTPO with monofunctional monomer (A) and acrylate monomer (B), nor do they describe adjusting the amounts of these elements within the range described above, nor do they describe the effects of these adjustments.

[0028] Next, each of the components constituting the inkjet ink of this embodiment will be described in detail below.

[0029] <Polymerizable compound> The inkjet ink of this embodiment contains a polymerizable compound. The polymerizable compound used is a monofunctional monomer (A) having a nitrogen-containing heterocyclic structure, and a monofunctional or bifunctional acrylate monomer (B) having a molecular weight of 140 to 250 (excluding the monofunctional monomer (A)).

[0030] In this disclosure, a polymerizable compound refers to a compound that undergoes a polymerization reaction by radicals generated from a photopolymerization initiator, etc., and has the function of curing a composition containing the polymerizable compound. Examples of compounds that can be used as the polymerizable compound include monomers, oligomers, polymers, etc., having one or more polymerizable groups. Examples of the polymerizable groups include (meth)acryloyl groups, vinyl ether groups, allyl groups, vinyl groups (excluding vinyl ether groups and allyl groups).

[0031] The term "monomer" above refers to the smallest unit in a polymer obtained by a polymerization reaction. Both "oligomer" and "polymer" are polymers in which multiple monomers are bonded together, and in this disclosure, they are distinguished by their degree of polymerization. Specifically, a compound in which 2 to 20 monomers are polymerized is called an "oligomer," and a compound in which 21 or more monomers are polymerized is called a "polymer." Note that the monomers constituting oligomers and polymers may include compounds that do not have the polymerizable groups described above (except for compounds used to impart polymerizable groups to oligomers and polymers). For example, an oligomer obtained by reacting a pre-oligomer having an isocyanate group at the terminal, which is a reaction product of 1,6-hexanediol and isophorone diisocyanate, with 2-hydroxyethyl acrylate has 1,6-hexanediol and isophorone diisocyanate as monomers.

[0032] In this disclosure, polymerizable compounds having only one polymerizable group in one molecule are referred to as "monofunctional polymerizable compounds," polymerizable compounds having two polymerizable groups in one molecule are referred to as "difunctional polymerizable compounds," polymerizable compounds having three polymerizable groups in one molecule are referred to as "trifunctional polymerizable compounds," and so on. Furthermore, compounds with two or more functionalities are collectively referred to as "polyfunctional."

[0033] From the viewpoint of improving discharge stability, curability, and the strength of the ink-cured film, the polymerizable compound contained in the inkjet ink of this embodiment preferably includes both a monofunctional polymerizable compound and a polyfunctional polymerizable compound. For the same reason, the amount of the monofunctional polymerizable compound is preferably 5 to 80% by mass, more preferably 8 to 75% by mass, and particularly preferably 10 to 72% by mass of the total amount of polymerizable compound. Furthermore, the above-mentioned "monofunctional polymerizable compounds" include monofunctional polymerizable compounds among the monofunctional monomers (A) and acrylate monomers (B) described later. In addition, the above-mentioned "polyfunctional polymerizable compounds" include difunctional polymerizable compounds among the acrylate monomers (B) described later.

[0034] ≪Monofunctional monomer (A) having a nitrogen-containing heterocyclic structure≫ As described above, the monofunctional monomer (A) having a nitrogen-containing heterocyclic structure dissolves TrTPO, thereby improving ejection stability. Furthermore, it is believed that the homogenization of TrTPO in the inkjet ink in the presence of monofunctional monomer (A) improves curability and the strength of the resulting cured ink film.

[0035] Compounds that can be used as monofunctional monomers (A) having a nitrogen-containing heterocyclic structure include N-vinyl-2-pyrrolidone, 3-methyl-N-vinyl-2-pyrrolidone, N-vinyl-2-valerolactam, N-vinyl-2-caprolactam, N-vinylpyrazole, N-vinylimidazole, N-vinyl-2-oxazolidinone, 5-methyl-N-vinyl-2-oxazolidinone, 4-(meth)acryloylmorpholine, N-(meth)acryloyl-2-oxazolidinone, 2-morpholinoethyl (meth)acrylate, N-(2-(meth)acryloyloxyethyl)-2-oxazolidinone, and N-succinimidyl (meth)acrylate.

[0036] Among these compounds, it is preferable to use one or more selected from the group consisting of N-vinyl-2-pyrrolidone, N-vinyl-2-caprolactam, 5-methyl-N-vinyl-2-oxazolidinone, and 4-(meth)acryloylmorpholine, because they significantly improve the curability of the inkjet ink and increase the glass transition temperature (Tg) of the resulting ink-cured film, thereby increasing the strength of the ink-cured film. Furthermore, it is even more preferable to use N-vinyl-2-caprolactam and / or 5-methyl-N-vinyl-2-oxazolidinone because they have excellent solubility and suitably suppress deterioration of discharge stability when used in combination with TrTPO, and it is particularly preferable to use 5-methyl-N-vinyl-2-oxazolidinone because it improves the storage stability of the inkjet ink.

[0037] From the standpoint of simultaneously improving discharge stability, storage stability, curability, and the strength of the ink-cured film, the content of monofunctional monomer (A) is preferably 2 to 40% by mass, more preferably 3 to 30% by mass, and particularly preferably 4 to 25% by mass, of the total mass of the inkjet ink. As mentioned above, when determining the content mass of monofunctional monomer (A), it is also necessary to take into account the content mass of acrylate monomer (B) used in combination.

[0038] Furthermore, since TrTPO dissolves suitably and becomes homogenized within the inkjet ink, improving ejection stability, storage stability, curability, and the strength of the ink-cured film, the content of monofunctional monomer (A) is preferably 100 to 550% by mass, and particularly preferably 150 to 480% by mass, when the content of TrTPO is taken as 100% by mass.

[0039] <<Monofunctional or bifunctional acrylate monomers (B) with a molecular weight of 140-250>> The inkjet ink of this embodiment mainly contains a monofunctional or bifunctional acrylate monomer (B) having a molecular weight of 140 to 250. This results in good ejection stability and storage stability of the inkjet ink. Furthermore, due to its excellent affinity with the monofunctional monomer (A), TrTPO is homogenized within the inkjet ink, resulting in good curability and strength of the ink-cured film.

[0040] Note that the monofunctional monomer (A) mentioned above is not included in the acrylate monomer (B).

[0041] As mentioned above, the molecular weight of the acrylate monomer (B) is preferably 155 to 245, and more preferably 140 to 250, in order to improve the ejection stability and storage stability of the inkjet ink.

[0042] Furthermore, in addition to improving discharge stability and storage stability, curability and the strength of the ink-cured film, the acryloyl group equivalent of the acrylate monomer (B) is preferably 90 to 220, and particularly preferably 95 to 200. The "acryloyl group equivalent of acrylate monomer (B)" is a value calculated by dividing the molecular weight of the acrylate monomer (B) in question by the number of acryloyl groups that the acrylate monomer (B) possesses.

[0043] As acrylate monomer (B), monomers having one or more acryloyl groups as polymerizable groups can be used. Specifically, examples of monomers that can be used as acrylate monomer (B) and have one acryloyl group as a polymerizable group include benzyl acrylate, 2-phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, dicyclopentenyl (oxyethyl) acrylate, diethylene glycol acrylate, triethylene glycol acrylate, tetraethylene glycol acrylate, dipropylene glycol acrylate, tripropylene glycol acrylate, 2-methoxydiethylene glycol acrylate, 2-methoxytriethylene glycol acrylate, 2-methoxypropylene glycol acrylate, 2-methoxydipropylene glycol acrylate, 2-ethoxyethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, β-carboxyethyl acrylate, and trimethylolpropane. Examples include formal acrylate, tetrahydrofurfuryl acrylate, cyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, 4-tert-butylcyclohexyl acrylate, isobornyl acrylate, norbornyl acrylate, 2-norbornylmethyl acrylate, dicyclopentanyl acrylate, isoamyl acrylate, n-octyl acrylate, isooctyl acrylate, isononyl acrylate, isodecyl acrylate, lauryl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 4-hydroxybutyl acrylate, 1,4-cyclohexanedimethanol acrylate, 2-(dimethylamino)ethyl acrylate, 2-(diethylamino)ethyl acrylate, 2-(diisopropylamino)ethyl acrylate, tert-butylaminoethyl acrylate, etc.

[0044] Furthermore, specific examples of monomers having two acryloyl groups as polymerizable groups that can be used as acrylate monomer (B) include 1,3-propanediol diacrylate, 1,4-butanediol diacrylate, 1,3-butylenediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 3-methyl-1,5-pentanediol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, dipropylene glycol diacrylate, trimethylolpropane diacrylate, and the like.

[0045] Furthermore, specific examples of monomers having one acryloyl group and one vinyl ether group that can be used as acrylate monomer (B) include 2-(2-vinyloxyethoxy)ethyl acrylate and 2-[2-(2-vinyloxyethoxy)ethoxy]ethyl acrylate.

[0046] Among those listed above, compounds having an aromatic ring structure and one acryloyl group are preferably used from the viewpoint of improving discharge stability and storage stability.

[0047] From another perspective, by using a monomer having two acryloyl groups, and / or a monomer having one acryloyl group and one vinyl ether group, as the acrylate monomer (B), the curability and strength of the ink-cured film are improved without degrading the ejection stability of the inkjet ink.

[0048] From the above viewpoint, in one embodiment, it is particularly preferable to use a monomer having one acryloyl group and an aromatic ring structure, a monomer having two acryloyl groups, and / or a monomer having one acryloyl group and one vinyl ether group as the acrylate monomer (B). By using these monomers in combination, it is easy to improve all of the following: discharge stability, storage stability, curability, and the strength of the ink-cured film.

[0049] As described above, in order to optimize the ejection stability and storage stability of the inkjet ink, the content of acrylate monomer (B) is 50 to 90% by mass of the total amount of polymerizable compounds contained in the inkjet ink. Furthermore, since acrylate monomer (B) assists in the homogenization of TrTPO within the inkjet ink, improving not only ejection stability but also curability and the strength of the ink-cured film, the content of acrylate monomer (B) is more preferably 55 to 88% by mass, and particularly preferably 60 to 85% by mass, of the total amount of polymerizable compounds contained in the inkjet ink.

[0050] For similar reasons, namely, to obtain an inkjet ink with excellent ejection stability and storage stability, the content of acrylate monomer (B) is preferably 35 to 80% by mass of the total inkjet ink. Furthermore, from the viewpoint of improving ejection stability, storage stability, curability, and the strength of the ink-cured film, the content of acrylate monomer (B) is more preferably 40 to 75% by mass of the total inkjet ink, and particularly preferably 45 to 70% by mass.

[0051] On the other hand, from the viewpoint of preventing deterioration of discharge stability, storage stability, and curability, the content of the monofunctional monomer (A) relative to the content of the acrylate monomer (B) is preferably 3 to 100% by mass, preferably 6 to 80% by mass, and particularly preferably 10 to 60% by mass.

[0052] <<Other polymerizable compounds>> The inkjet ink of this embodiment may contain polymerizable compounds other than the monofunctional monomer (A) and the acrylate monomer (B) described above (also referred to as "other polymerizable compounds" in this disclosure). There are no restrictions on the compounds that can be used as such other polymerizable compounds; monomers, oligomers, polymers, etc., having one or more polymerizable groups can be used.

[0053] Other examples of monomers that can be used as polymerizable compounds and have one (meth)acryloyl group as a polymerizable group include phenoxypolyethylene glycol (meth)acrylate (3 or more ethylene oxide groups), phenoxypolypropylene glycol (meth)acrylate (2 or more propylene oxide groups), 2-methoxyethyl (meth)acrylate, 2-methoxytetraethylene glycol (meth)acrylate, 2-methoxytripropylene glycol (meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, propylene oxide-modified nonylphenol (meth)acrylate, ethylene oxide-modified o-phenylphenol (meth)acrylate, ethylene oxide-modified 2-ethylhexyl (meth)acrylate (2 or more ethylene oxide groups), and the like.

[0054] Furthermore, other examples of monomers having one (meth)acryloyl group as a polymerizable group that can be used as other polymerizable compounds include polyfunctional monomers (specific examples will be described later) in which only one polymerizable group is left, and a primary or secondary organic amine is added to the remaining polymerizable group (Michael addition).

[0055] Furthermore, other examples of monomers having one methacryloyl group as a polymerizable group that can be used as other polymerizable compounds include compounds in which the acryloyl group in the molecule is replaced with a methacryloyl group in a monomer having one acryloyl group as a polymerizable group that can be used as an acrylate monomer (B) (for example, benzyl methacrylate, 2-phenoxyethyl methacrylate, etc.).

[0056] Other examples of monomers that can be used as polymerizable compounds and have two (meth)acryloyl groups as polymerizable groups include 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, ethylene oxide-modified 1,6-hexanediol di(meth)acrylate, propylene oxide-modified 1,6-hexanediol di(meth)acrylate, ethylene oxide-modified neopentyl glycol di(meth)acrylate, and propylene oxide-modified neopentyl Polyethylene glycol di(meth)acrylate, 2,4-dimethyl-1,5-pentanediol di(meth)acrylate, 2-ethyl-2-butylpropanediol di(meth)acrylate, 2-ethyl-2-butylbutanediol di(meth)acrylate, ethylene oxide-modified cyclohexanemethanol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol 200 di(meth)acrylate, polyethylene glycol 300 di(meth)acrylate, Examples include polyethylene glycol 400 di(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, bisphenol A di(meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, propylene oxide-modified bisphenol A di(meth)acrylate, bisphenol F di(meth)acrylate, ethylene oxide-modified bisphenol F di(meth)acrylate, propylene oxide-modified bisphenol F di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethylene oxide-modified isocyanurate di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, dimethylol tricyclodecane di(meth)acrylate, cyclohexane dimethanol di(meth)acrylate, neopentyl glycol-modified trimethylolpropane di(meth)acrylate, and dicyclopentanyl di(meth)acrylate.

[0057] Furthermore, other examples of monomers having two (meth)acryloyl groups as polymerizable groups that can be used as other polymerizable compounds include polyfunctional monomers (specific examples will be described later) with three or more polymerizable groups, in which two polymerizable groups are left intact and primary or secondary organic amines are added to the remaining polymerizable groups (Michael addition).

[0058] Furthermore, other examples of monomers having two methacryloyl groups as polymerizable groups that can be used as other polymerizable compounds include monomers having two acryloyl groups as polymerizable groups that can be used as acrylate monomers (B), in which the acryloyl groups in the molecule are replaced with methacryloyl groups (for example, 1,3-propanediol dimethacrylate, 1,4-butanediol dimethacrylate, etc.).

[0059] Other examples of monomers having two vinyl ether groups as polymerizable groups that can be used as polymerizable compounds include 1,4-butanediol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, and 1,4-cyclohexanedimethanol divinyl ether.

[0060] Other examples of monomers that can be used as polymerizable compounds and have three (meth)acryloyl groups as polymerizable groups include: trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, ethylene oxide-modified glycerin tri(meth)acrylate, propylene oxide-modified glycerin tri(meth)acrylate, and ethylene oxide Examples include isocyanurate tri(meth)acrylate modified with propylene oxide, isocyanurate tri(meth)acrylate modified with propylene oxide, dipentaerythritol tri(meth)acrylate modified with propylene oxide, tetramethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, tri(meth)acryloyloxyethyl) isocyanurate, hydroxypivalaldehyde-modified dimethylolpropane tri(meth)acrylate, sorbitol tri(meth)acrylate, and the like.

[0061] Other examples of monomers having four (meth)acryloyl groups as polymerizable groups that can be used as polymerizable compounds include pentaerythritol tetra(meth)acrylate, sorbitol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethylene oxide-modified pentaerythritol tetra(meth)acrylate, propylene oxide-modified pentaerythritol tetra(meth)acrylate, and tetramethylolmethane tetra(meth)acrylate.

[0062] Other examples of monomers that can be used as polymerizable compounds and have five (meth)acryloyl groups as polymerizable groups include sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate.

[0063] Other examples of monomers having six (meth)acryloyl groups as polymerizable groups that can be used as polymerizable compounds include dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, alkylene oxide-modified phosphazene hexa(meth)acrylate, and ε-captolactone-modified dipentaerythritol hexa(meth)acrylate.

[0064] When using oligomers as the other polymerizable compounds mentioned above, compounds having (meth)acryloyl groups as polymerizable groups are preferably used. Furthermore, the number of polymerizable groups contained in the oligomer is preferably 1 to 6 per molecule, from the viewpoint of balancing curability, discharge stability, and storage stability. The number of polymerizable groups is more preferably 1 to 4, and particularly preferably 1 to 2. The mass-average molecular weight of the oligomer is preferably 400 to 6,000, and more preferably 500 to 4,500. The mass-average molecular weight of the oligomer can be measured, for example, by the method described later.

[0065] Examples of oligomers having a (meth)acryloyl group as a polymerizable group 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.

[0066] The oligomers described above may be modified. Examples of such modification include sulfonic acid modification, phosphate modification, amino acid modification, mercapto modification, and the like.

[0067] When the inkjet ink of this embodiment contains other polymerizable compounds, it is preferable to include monomers having two acryloyl groups as polymerizable groups, and / or monomers having three acryloyl groups as polymerizable groups, in order to achieve a good balance of ejection stability, curability, and strength of the ink-cured film. In particular, it is preferable to include monomers having at least two acryloyl groups as polymerizable groups. In particular, in the inkjet ink of this embodiment, it is especially preferable to use monomers having ethylene oxide groups as the monomers having two acryloyl groups as polymerizable groups. This is because the presence of ethylene oxide groups allows the ink-cured film to adhere closely to the printing substrate and improves the strength of the ink-cured film.

[0068] Specific examples of monomers having an ethylene oxide group and two acryloyl groups as polymerizable groups include ethylene oxide-modified 1,6-hexanediol diacrylate, ethylene oxide-modified neopentyl glycol diacrylate, polyethylene glycol 200 diacrylate, polyethylene glycol 300 diacrylate, polyethylene glycol 400 diacrylate, ethylene oxide-modified bisphenol A diacrylate, ethylene oxide-modified bisphenol F diacrylate, and ethylene oxide-modified isocyanuric acid diacrylate.

[0069] In order to maintain favorable ejection stability of the inkjet ink while improving the strength of the ink-cured film, if the inkjet ink of this embodiment contains a monomer having an ethylene oxide group and two acryloyl groups as polymerizable groups as another polymerizable compound, the amount of this monomer is preferably 2 to 20% by mass of the total amount of the inkjet ink, and particularly preferably 4 to 15% by mass.

[0070] Furthermore, if the inkjet ink of this embodiment contains other polymerizable compounds, the total amount of these compounds is preferably 2 to 25% by mass of the total amount of the inkjet ink, and particularly preferably 4 to 20% by mass, from the viewpoint of not inhibiting the effects of the monofunctional monomer (A) and acrylate monomer (B) and not adversely affecting the ejection stability, curability, and strength of the ink-cured film.

[0071] <Photopolymerization initiator> The inkjet ink of this embodiment contains a photopolymerization initiator. At least di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide (TrTPO) is used as the photopolymerization initiator.

[0072] Photopolymerization initiators are compounds that initiate the polymerization reaction of polymerizable compounds. Specifically, photopolymerization initiators absorb energy from active energy rays, undergo intramolecular cleavage, or become excited and further extract hydrogen atoms from hydrogen donors, thereby generating radicals. In this disclosure, the term "polymerizable initiator" also includes compounds that can function as hydrogen donors, commonly referred to as sensitizers. Examples of such sensitizers include aminobenzoate compounds, ketocoumarin compounds, and anthracene compounds.

[0073] ≪Di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide≫ As mentioned above, TrTPO offers improved ejection stability compared to using BTPO. Furthermore, by using monofunctional monomer (A) and TrTPO together, the polymerization reaction proceeds uniformly within the inkjet ink, which is expected to improve the curability of the inkjet ink and the strength of the resulting cured ink film.

[0074] From the viewpoint of simultaneously improving ejection stability, storage stability, curability, and the strength of the ink-cured film, the amount of TrTPO blended is preferably 1.5 to 8% by mass, and particularly preferably 3 to 6.5% by mass, of the total amount of inkjet ink.

[0075] <<Other photopolymerization initiators>> From the viewpoint of improving curability and the strength of the ink-cured film, the inkjet ink of this embodiment preferably contains a photopolymerization initiator other than the above-mentioned TrTPO (also referred to as "other photopolymerization initiators" in this disclosure).

[0076] Other photopolymerization initiators that can be used include acylphosphine oxide compounds (excluding TrTPO), alkylaminoacetophenone compounds, benzophenone compounds, hydroxyacetophenone compounds, thioxanthone compounds, oxime ester compounds, and the various sensitizers exemplified above.

[0077] Among these, it is preferable to use one or more photopolymerization initiators selected from the group consisting of acylphosphine oxide compounds (excluding TrTPO), alkylaminoacetophenone compounds, and thioxanthone compounds as other photopolymerization initiators, in order to improve curability and the strength of the ink-cured film while maintaining a suitable discharge stability. In particular, it is preferable to use alkylaminoacetophenone compounds and / or thioxanthone compounds.

[0078] <<Alkylaminoacetophenone compounds>> Specific examples of the alkylaminoacetophenone compounds mentioned above include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, 2-(4-methylbenzyl)-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, 2-benzyl-2-dimethylamino-1-(4-piperidinylphenyl)butan-1-one, and polymers of these compounds. Examples of commercially available alkylaminoacetophenone compounds include "Omnirad 264," "Omnirad 369," "Omnirad 379," "Omnirad 389," "Omnirad 907," and "Omnipol 910" from IGM RESINS. Of these commercially available products, "Omnipol 910" is the aforementioned polymer. In the inkjet ink of this embodiment, only one of the alkylaminoacetophenone compounds listed above may be used, or two or more may be used in combination.

[0079] When the inkjet ink of this embodiment contains an alkylaminoacetophenone compound, the amount of the compound is preferably 0.5 to 6% by mass, and particularly preferably 1 to 4% by mass, of the total amount of the inkjet ink, in order to improve the ejection stability, storage stability, curability, and strength of the ink-cured film.

[0080] Furthermore, in order to achieve both discharge stability and storage stability, as well as curability and the strength of the cured ink film, when the mass content of TrTPO in the inkjet ink is set to 100% by mass, the mass content of the alkylaminoacetophenone compound in the inkjet ink is preferably 5 to 85% by mass, and particularly preferably 15 to 80% by mass.

[0081] ≪Thioxanthone compounds≫ Specific examples of the thioxanthone compounds mentioned above 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. Examples of commercially available thioxanthone compounds include "Omnirad ITX," "Omnirad DETX," and "OMNIPOL TX" 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 aforementioned polymers. In the inkjet ink of this embodiment, only one of the thioxanthone compounds listed above may be used, or two or more may be used in combination.

[0082] When the inkjet ink of this embodiment contains a thioxanthone compound, the amount of the compound added is preferably 0.2 to 6% by mass, and particularly preferably 0.5 to 4% by mass, of the total amount of the inkjet ink, in order to improve the ejection stability, storage stability, curability, and strength of the ink-cured film.

[0083] Furthermore, in order to achieve both discharge stability and storage stability, as well as curability and the strength of the cured ink film, when the mass content of TrTPO in the inkjet ink is set to 100% by mass, the mass content of the thioxanthone compound in the inkjet ink is preferably 3 to 100% by mass, and particularly preferably 7.5 to 80% by mass.

[0084] ≪Acylphosphine oxide compounds (excluding TrTPO)≫ Specific examples of acylphosphine oxide compounds other than TrTPO include TPO and BTPO mentioned above, as well as ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate. Furthermore, polymers of these compounds can also be used as the acylphosphine oxide compounds. Additionally, acylphosphine oxide compounds described in International Publication No. 2017 / 086224 and International Publication No. 2020 / 049378 can also be used. Examples of commercially available acylphosphine oxide compounds other than TrTPO 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. Of these commercially available products, "OMNIPOL TP" is the aforementioned polymer. In the inkjet ink of this embodiment, only one of the acylphosphine oxide compounds listed above, excluding TrTPO, may be used, or two or more may be used in combination.

[0085] When the inkjet ink of this embodiment contains an acylphosphine oxide compound other than TrTPO, ethoxyphenyl (2,4,6-trimethylbenzoyl)phosphine oxide and / or a polymer of ethoxyphenyl (2,4,6-trimethylbenzoyl)phosphine oxide can be preferably used in combination with TrTPO because it is easy to achieve both discharge stability and curability and strength of the ink-cured film.

[0086] Furthermore, in terms of improving ejection stability, storage stability, and the strength of the ink-cured film, the amount of acylphosphine oxide compounds other than TrTPO blended into the total amount of the inkjet ink is preferably 1 to 10% by mass, and particularly preferably 2 to 8% by mass.

[0087] Furthermore, for the same reasons as above, namely because it improves both ejection stability, curability, and the strength of the ink-cured film, when the mass content of TrTPO in the inkjet ink is set to 100% by mass, the mass content of acylphosphine oxide compounds other than TrTPO in the inkjet ink is preferably 15 to 300% by mass, and particularly preferably 30 to 200% by mass.

[0088] Other specific examples of benzophenone compounds include benzophenone, 4-methylbenzophenone, 4-phenylbenzophenone, methyl-2-benzoylbenzoate, 4-(4-methylphenylthio)benzophenone, 4,4'-bis(diethylamino)benzophenone, and 1-[4-(4-benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylphenylsulfonyl)propan-1-one. Examples of commercially available benzophenone compounds include "Omnirad BP," "Omnirad BMS," "Omnirad 4PBZ," "OMNIRAD EMK," and "Esacure 1001M" from IGM RESINS, and "Speedcure BP," "Speedcure MBP," "Speedcure PBZ," "Speedcure EMK," "Speedcure MBB," and "Speedcure BMS" from Lambson.

[0089] Examples of commercially available hydroxyacetophenone compounds include "Omnirad 127," "Omnirad 184," "Omnirad 1173," "Omnirad 2959," and "Esacure KIP150" from IGM Resins, and "SpeedCure 73," "SpeedCure 84," "SpeedCure 2959," and "SpeedCure XFs01" from Lambson.

[0090] Furthermore, examples of commercially available oxime ester compounds include BASF's "IRGACURE OXE01," "IRGACURE OXE02," and "IRGACURE OXE04."

[0091] Furthermore, specific examples of aminobenzoate compounds include methyl 2-(dimethylamino)benzoate, ethyl 4-(dimethylamino)benzoate, ethyl 4-(diethylamino)benzoate, ethylhexyl 2-(dimethylamino)benzoate, 2-butoxyethyl 2-(dimethylamino)benzoate, bis-[(4-dimethylaminobenzoyl)oxyethylene-1-yl]methylamine, and polymers of these compounds (for example, polyethylene glycol-bis(methyl 4-dimethylaminobenzoate)). 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.

[0092] Furthermore, specific examples of ketocoumarin compounds include 3-benzoyl-7-methoxycoumarin, 3-benzoyl-5,7-dimethoxycoumarin, 3-(4-tert-butylbenzoyl)-5,7-dimethoxycoumarin, 3-(4-hexylbenzoyl)-5,7-dimethoxycoumarin, 3-[4-(2-ethylhexyl)benzoyl]-5,7-dimethoxycoumarin, 5,7-dimethoxy-3-[4-(3,5,5-trimethylhexyl)benzoyl]coumarin, 7-methoxy-3-(4-methylbenzoyl)coumarin, 7-methoxy-3-(4-tert-butylbenzoyl)coumarin, 7-methoxy-3-(4-hexylbenzoyl)coumarin, and 7-methoxy-3-[4-(2-ethylhexyl)benzoyl]coumarin.

[0093] Furthermore, examples of commercially available anthracene compounds include "Anthracure UVS-581" manufactured by Kawasaki Chemical Industries, Ltd. In addition, anthracene compounds described in Japanese Patent Publication No. 2014-31346, Japanese Patent Publication No. 2019-31471, and Japanese Patent Publication No. 2020-164485 can also be used.

[0094] In addition to those listed above, other photopolymerization initiators such as "Omnirad 651" and "Omnirad MBF" from IGM Resins can also be used.

[0095] When the inkjet ink of this embodiment contains other photopolymerization initiators, the total amount of such other photopolymerization initiators is preferably 1 to 10% by mass, and particularly preferably 2 to 8% by mass, relative to the total amount of the inkjet ink. By keeping the total amount of other photopolymerization initiators within the above range, it is easy to improve the ejection stability, storage stability, curability, and the strength of the ink-cured film.

[0096] <Other ingredients> In addition to the components described above, the inkjet ink of this embodiment may also contain surface modifiers, polymerization inhibitors, colorants, pigment derivatives, pigment dispersion resins, inert resins, organic solvents, water, and other additives.

[0097] Surface conditioning agent The inkjet ink of this embodiment preferably contains a surface modifier for the purpose of improving wetting spread and adhesion to the printing substrate, print quality, ejection stability, and the strength of the ink-cured film. Examples of such surface modifiers include siloxane-based surface modifiers, fluorine-based surface modifiers, acetylene glycol-based surface modifiers, and acetylene monool-based surface modifiers. Among these, a siloxane-based surface modifier is preferred because it functions well even in the presence of a monofunctional monomer (A) and can easily improve the above-mentioned effects, namely, wetting spread and adhesion to the printing substrate, print quality, ejection stability, and the strength of the ink-cured film.

[0098] As the siloxane-based surface modifier mentioned above, for example, compounds having a dimethylsiloxane structure and / or modified versions thereof can be used. Among these, polyether-modified siloxane-based surface modifiers are particularly preferred. By using a polyether-modified siloxane-based surface modifier, it functions effectively even in the presence of acrylate monomer (B) and TrTPO, and in particular, the wettability and adhesion to the printing substrate, as well as the strength of the ink-cured film, are improved. Specific examples of the polyether group mentioned above include polyethylene oxide group and polypropylene oxide group. These polyether groups may be present in the molecule as either one or both.

[0099] Furthermore, in order to suitably exhibit the above-mentioned effects and maintain the ejection stability of the inkjet ink in a favorable state while improving print quality and the strength of the ink-cured film, the mass-average molecular weight of the polyether-modified siloxane-based surface modifier is preferably 2,000 to 25,000, and particularly preferably 3,000 to 20,000.

[0100] As commercially available polyether-modified siloxane-based surface modifiers, for example, BYK(registered trademark)-331, 333, 378, 348, 349, 3420, 3760, BYK-UV3500, UV3510 from BIC Chemie; and TEGO(registered trademark) Glide 450, 440, 435, 432, 410, 406, 130, 110, 100 from EVONIK are preferably used.

[0101] When using a siloxane-based surface modifier (preferably a polyether-modified siloxane-based surface modifier), its content is preferably 0.1 to 3% by mass, based on the total mass of the inkjet ink. Adjusting the content to 0.1% by mass or more improves the wettability and spreadability on the printing substrate, improving the print quality and adhesion of the printed material, as well as improving the strength of the ink-cured film. On the other hand, adjusting the content to 3% by mass or less makes it easier to ensure curability, pigment dispersion stability, and storage stability and ejection stability of the inkjet ink.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] <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.

[0106] 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 the opacity and strength 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 the gloss and strength 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.

[0107] 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.

[0108] 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 pigment, a compound in which substituents are introduced to the quinacridone skeleton can be preferably used.

[0109] 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.

[0110] 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 a hydrogen ion, a primary amine cation, a secondary amine cation, and a quaternary ammonium cation. By using a pigment derivative having such substituents, it becomes easy to obtain an inkjet ink with excellent storage stability and ejection stability, even in the presence of a monofunctional monomer (A), etc.

[0111] 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.

[0112] 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.

[0113] 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. Furthermore, since the pigment is uniformly dispersed by the pigment dispersion resin, the strength of the ink cured film is also improved.

[0114] The mass-average molecular weight in this disclosure 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.

[0115] 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.

[0116] 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.

[0117] 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".

[0118] 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.

[0119] 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, even in the presence of the monofunctional monomer (A), 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 polymerization reactions of polymerizable compounds such as TrTPO, the curability of the inkjet ink is also improved. Moreover, since the pigment is uniformly dispersed by the basic pigment dispersion resin having the above-mentioned amine value, the strength of the ink-cured film is also improved.

[0120] 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).

[0121] 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 in the inkjet ink of this embodiment is uniformly and stably dispersed, thereby improving the dispersion stability of the pigment, the storage stability and ejection stability of the inkjet ink, and the strength of the ink-cured film.

[0122] 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.

[0123] 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 strength of the ink-cured film.

[0124] Inert Resin The inkjet ink of this embodiment may contain an inert resin for the purpose of providing adhesion to various printing substrates, improving the strength of the ink-cured film, and adjusting the viscoelasticity of the inkjet ink to improve ejection stability. As the inert resin, 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 an acrylic resin and / or a ketone resin.

[0125] 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, discharge stability, and the strength of the ink-cured film can be easily improved without worsening the curability.

[0126] In this disclosure, "inert resin" refers to a resin that does not participate in polymerization reactions, contributes to adhesion to a printing substrate and / or strength of the ink-cured film, and has solubility in inkjet inks.

[0127] Organic solvents In the inkjet ink of this embodiment, an organic solvent may be used to reduce the viscosity of the inkjet ink, improve its wettability and adhesion to the printing substrate, and ensure ejection stability. When an organic solvent is used, its content is preferably 0.03 to 5% by mass, and particularly preferably 0.1 to 3% by mass, based on the total mass of the inkjet ink, from the viewpoint of improving storage stability, ejection stability, and the strength of the ink-cured film. Furthermore, from the viewpoint of ensuring and improving ejection stability, curability, and wettability 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 120 to 250°C, and particularly preferable to use an organic solvent with a boiling point of 180 to 230°C. In this disclosure, "boiling point" refers to the boiling point at 1 atmosphere.

[0128] 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.

[0129] In particular, from the viewpoint of improving wettability and adhesion to the printing substrate, and improving discharge stability, it is preferable to include at least one selected from the group consisting of alkylene glycol monoalkyl ether acetates, alkylene glycol monoalkyl ethers, and alkylene glycol dialkyl ethers. In particular, as the organic solvent, at least one compound selected from the group consisting of ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, 3-methoxy-1-butanol, 3-methoxy-3-methyl-1-butanol, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, and diethylene glycol butyl methyl ether can be preferably used. Furthermore, it is particularly preferable to use at least one selected from the group consisting of ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol monomethyl ether, diethylene glycol monoisobutyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, and diethylene glycol butyl methyl ether. When these organic solvents are used, each component is suitably homogenized within the inkjet ink of this embodiment, improving storage stability, ejection stability, and the strength of the ink-cured film.

[0130] ≪Water≫ Similar to the organic solvents described above, water can be added to the inkjet ink of this embodiment. On the other hand, from the viewpoint of homogenizing each component in the inkjet ink and improving ejection stability, storage stability, and the strength of the ink-cured film, it is preferable to adjust the amount of water in the inkjet ink to a certain range. Specifically, the amount of water in the inkjet ink of this embodiment is preferably 0.03 to 0.8% by mass of the total amount of inkjet ink, and particularly preferably 0.05 to 0.6% by mass.

[0131] The water content in inkjet ink can be measured by volumetric titration using a Karl Fischer moisture meter (for example, the "MKV-710" manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0132] <<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.

[0133] <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.

[0134] 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 acrylate monomer (B) 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 discharge stability of the inkjet ink.

[0135] Subsequently, the pigment dispersion is mixed thoroughly with the remaining monofunctional monomer (A), acrylate monomer (B), TrTPO, and, if necessary, other polymerizable compounds, other photopolymerization initiators, surface modifiers, polymerization inhibitors, organic solvents, water, inert resins, and other additives. Then, the mixture is filtered to remove coarse particles, thereby obtaining the inkjet ink of this embodiment.

[0136] 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, the amount of pigment in the pigment dispersion is preferably 10 to 40% by mass, and particularly preferably 12 to 30% by mass.

[0137] <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).

[0138] Specific examples of inkjet printing methods including the above steps I and II include a method in which ink is ejected onto a printing substrate while scanning the inkjet head in a direction perpendicular to the transport direction of the printing substrate (shuttle head type printing method), and a method in which the printing substrate is transported with the inkjet head fixed, and inkjet ink is ejected when the printing substrate passes below the inkjet head (line head type one-pass printing method).

[0139] ≪Process I≫ The inkjet ink in this embodiment is an inkjet printing ink. Therefore, an inkjet head is used as the inkjet ink ejection means in step I described above.

[0140] Methods for ejecting inkjet 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.

[0141] On the other hand, in step I above, methods for ejecting and applying inkjet ink to the same location on the printing substrate include (1) ejecting and applying the same inkjet ink multiple times from the same inkjet head, (2) ejecting and applying the same inkjet ink only once from the same inkjet head, and (3) ejecting and applying the same inkjet ink once each from multiple inkjet heads, and any of these methods may be adopted. In the shuttle head type printing method above, (1) or (2) may be adopted, and in the line head type one-pass printing method above, (2) or (3) may be adopted.

[0142] In order to effectively utilize the excellent ejection stability and curing properties of the inkjet ink of this embodiment, when the above shuttle head type printing method is adopted as the inkjet printing method, the printing speed is 10 to 50 m 2 It is preferable that it be in hours, 15-40m 2It is particularly preferable that the speed is per hour. Furthermore, when a line head type one-pass printing method is adopted as the inkjet printing method, the printing speed, i.e., the transport speed of the printing substrate, is preferably 35 to 150 m / min, and particularly preferably 50 to 125 m / min.

[0143] ≪Process II≫ 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.

[0144] In this disclosure, "active energy ray" refers to an energy ray 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, and visible light, but 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.

[0145] Furthermore, the above ultraviolet light sources include, for example, high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, ultraviolet lasers, and LED lamps. Only one type may be used, or two or more types may be used in combination. For example, because LED lamps are small in size, it is easy to install multiple lamps side by side, or to use them in combination with high-pressure mercury lamps or metal halide lamps, which makes it easy to further improve curing performance. Also, when installing multiple LED lamps side by side, multiple types of LED lamps with different emission peak wavelengths may be used in combination.

[0146] Generally, ultraviolet light emitted from LED lamps has a narrow wavelength range and exhibits excellent directional propagation (i.e., poor diffusion), making it difficult for active energy ray-curable inkjet inks to cure. On the other hand, the inkjet ink of this embodiment contains TrTPO, which can absorb active energy rays across a wide wavelength range, and furthermore, since the TrTPO is uniformly distributed within the inkjet ink, it is easy to achieve excellent curing performance even when used in combination with an LED lamp.

[0147] Furthermore, in the inkjet printing method using the inkjet ink of this embodiment, when an LED lamp that emits ultraviolet light is used, its emission peak wavelength is preferably 260 to 450 nm, more preferably 280 to 420 nm, and particularly preferably 320 to 410 nm.

[0148] When ultraviolet light is selected as the active energy ray, and a high-pressure mercury lamp or metal halide lamp is used as the light source for said ultraviolet light, the unit length wattage of these lamps is preferably 80 to 300 W / cm, more preferably 100 to 260 W / cm, and particularly preferably 120 to 240 W / cm, from the viewpoint of ensuring discharge stability while achieving excellent curing performance.

[0149] On the other hand, when ultraviolet light is selected as the active energy ray and an LED lamp is used as the light source for said ultraviolet light, the above-mentioned effects can be fully realized and excellent curing properties can be achieved. From this viewpoint, the irradiance of ultraviolet light on the printing substrate should be 1,000 mW / cm². 2 It is preferable that the illuminance is 2,000 mW / cm². 2 It is more preferable that the level be greater than or equal to 3,000 mW / cm². 2 It is especially preferable that the above conditions are met.

[0150] Also, regardless of the type of lamp used, the integrated light amount when irradiating the printing substrate varies depending on the types and contents of the polymerizable compound and photoinitiator 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.

[0151] In the above inkjet printing method, the above step II can be repeated multiple times. For example, in a shuttle head type printing method, light sources of active energy rays are mounted at both ends of a carriage on which an inkjet head is mounted, and when the carriage reciprocates in a direction perpendicular to the conveyance direction of the printing substrate, active energy rays can be irradiated from the above light sources. On the other hand, in a line head type one-pass printing method, light sources of active energy rays are mounted at positions adjacent to the inkjet head and on the downstream side of the inkjet head in the conveyance direction of the printing substrate (for example, when using a plurality of inkjet heads, between the inkjet heads and on the downstream side of the inkjet head existing on the most downstream side), and when the printing substrate passes below each light source, active energy rays can be irradiated respectively. Thus, by performing step II multiple times, it becomes easy to obtain a printed matter having excellent strength of the ink cured film.

[0152] <Printing substrate> In the printing method using the inkjet ink of the present embodiment, the printing substrate used is preferably a resin film substrate or a paper substrate. The above resin film substrate preferably has a thickness of 10 to 90 μm. Further, as the above resin film substrate, a substrate containing a material selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, and nylon is preferably selected. On the other hand, as the above paper substrate, coated paper, art paper, laminated paper, etc. are preferably selected.

[0153] Furthermore, 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. In addition, 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.

[0154] <Printed material> A printed material manufactured using the inkjet ink of this embodiment comprises a printing substrate and a printed layer containing an image and / or text formed on the printing substrate. The printed layer is a layer formed by the curing of the inkjet ink of this embodiment printed on the printing substrate, i.e., a layer consisting of an ink-cured film. Therefore, the "printed material" includes an image and / or text, which consists of an ink-cured film, and the printing substrate. The "image" also includes solid images (images printed at 100% density so as to completely cover the surface of the printing substrate) and seamless images such as checkerboard patterns. In one embodiment, the inkjet printing method described above can be used as a method for printing the inkjet ink of this embodiment and manufacturing a printed material. [Examples]

[0155] The inkjet ink of this embodiment will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" refer to "parts by mass" and "% by mass," respectively, unless otherwise specified.

[0156] <Manufacturing of cyanide pigment dispersion A> Solsperse 32000 varnish A was prepared by first adding 200g of "Solsperse 32000," a basic pigment dispersion resin manufactured by Lubrizol, and 3,200g of 2-phenoxyethyl acrylate 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 A in the mixing container, 600g of CI Pigment Blue 15:3 (Toyo Color Co., Ltd. "LIONOL BLUE FG-7330") was gradually added to the container. After adding all of the CI Pigment Blue 15:3, 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 cyanide pigment dispersion A (pigment concentration 15% by mass). 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 Cyanide Pigment Dispersion B> BYKJET varnish was manufactured by first adding 240g of BYKJET-9151, a basic pigment dispersion resin manufactured by BYK Chemie, and 3,144g of 2-phenoxyethyl acrylate to a mixing container (volume 10L) equipped with a stirrer, and thoroughly stirring and mixing until the contents were uniform. Next, while stirring the BYKJET varnish in the mixing container, 16g of "Solsperse 5000" (a compound in which a sulfonate group with a quaternary ammonium cation as a counterion is introduced as a substituent to a copper phthalocyanine skeleton), manufactured by Lubrizol, was added to the mixing container. Stirring was continued for 10 minutes after the addition to homogenize the mixture. Subsequently, 600g of CI Pigment Blue 15:4 ("LIONOL BLUE FG-7400-G" manufactured by Toyo Color) was added little by little, and stirring was continued for 1 hour after the addition was complete (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 above. The circulation and dispersion was terminated when the average particle size fell below 180nm, thereby producing cyanide pigment dispersion B (pigment concentration 15% by mass).

[0158] <Manufacturing of cyanide pigment dispersion C> Cyanide pigment dispersion C (pigment concentration 15% by mass) was prepared using the same materials and methods as described above for cyanide pigment dispersion A, except that a mixture of 2,400 g of 1,6-hexanediol diacrylate and 800 g of polyethylene glycol 200 diacrylate was used instead of 3,200 g of 2-phenoxyethyl acrylate.

[0159] <Manufacturing of additive solutions A, B, and C> Each ingredient was added to a mixing container equipped with a stirrer, according to the formulations shown in each column of Table 1 below. After adding all the ingredients, stirring and mixing were continued until the mixture was visibly homogeneous to produce additive solutions A, B, and C.

[0160] [Table 1]

[0161] The details of the product names listed in Table 1 above are as follows: • BYK-UV3510: Polyether-modified siloxane-based surface conditioner (manufactured by Bic Chemie) • BHT Swanox: 2,6-di-tert-butyl-4-methylphenol (manufactured by Seiko Chemical Co., Ltd.)

[0162] <Manufacturing of inkjet inks 1-63> The materials listed in columns 2-1 to 2-7 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 inks 1 to 63.

[0163] In the manufacturing 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: pigment dispersion, acrylate monomer (B), monofunctional monomer (A), other polymerizable compounds, photopolymerization initiator, and others (additive solution). 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. Furthermore, for components containing two or more materials, the order of addition within that component was from the one with the largest addition amount to the one with the smallest addition amount.

[0164] [Table 2-1]

[0165] [Table 2-2]

[0166] [Table 2-3]

[0167] [Table 2-4]

[0168] [Table 2-5]

[0169] [Table 2-6]

[0170] [Table 2-7]

[0171] The details of the product names and abbreviations listed in Tables 2-1 to 2-7 above are as follows: • EBECRYL 8402: Aliphatic urethane acrylate oligomer (Number of polymerizable groups: 2, Mass-average molecular weight: 1,000) • EBECRYL 8807: Aliphatic urethane acrylate oligomer (Number of polymerizable groups: 2, Mass-average molecular weight: 1,000) • EBECRYL 303: A mixture of 55% by mass of acrylic acrylate oligomer (number of polymerizable groups: 2, mass-average molecular weight: 900) and 45% by mass of 1,6-hexanediol diacrylate. • TrTPO: Di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide • TPO-L: Ethoxyphenyl (2,4,6-trimethylbenzoyl)phosphine oxide (Omnirad TPO-L, manufactured by IGM RESINS) • BTPO: Bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IGM RESINS "Omnirad 819") Omnirad 369: 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one (manufactured by IGM Resins) • Omnirad ITX: 2-Isopropylthioxanthone (manufactured by IGM Resins) • Omnirad BMS: 4-(4-methylphenylthio)benzophenone (manufactured by IGM RESINS)

[0172] Furthermore, when the water content of the above inkjet inks 1 to 63 was measured using the method described above, it was found to be within the range of 0.1 to 0.4% by mass for all inkjet inks.

[0173] [Examples 1-55, Comparative Examples 1-8] Inkjet inks 1-63, manufactured using the method described above, were evaluated according to the following procedures. The evaluation results are shown in Tables 2-1 to 2-7 above.

[0174] <Evaluation of storage stability> The viscosity of the inkjet ink manufactured by the method described above was measured using a Type E viscometer, the "TVE-25L viscometer" manufactured by Toki Sangyo Co., Ltd. The inkjet ink was then filled into 20 mL glass containers to 90% of their capacity. The containers were then sealed and protected from light and left to stand at 60°C for 14 days. The viscosity of the inkjet ink after standing was measured using the same apparatus as before standing, and the storage stability was evaluated by calculating the percentage increase in viscosity before and after standing. The evaluation criteria were as follows, with ◎, ○, and △ ratings indicating practical usability, and ◎ and ○ ratings indicating practical suitability.

[0175] ≪Evaluation Criteria for Storage Stability≫ ◎: The increase in viscosity before and after standing was 5% or less. ○: The increase in viscosity before and after standing was between 5% and 10%. △: The increase in viscosity before and after standing was between 10% and 20%. ×: The increase in viscosity before and after standing was greater than 20%.

[0176] <Evaluation of discharge stability> An evaluation printing apparatus A was prepared, equipped with a carriage containing an inkjet head. Metal halide lamp units (160 W / cm wattage per unit length) manufactured by iGraphics were installed at both ends of the carriage. The inkjet head had an internal heater, a design resolution of 360 x 360 dpi, and a design drop volume of approximately 14 pL. Furthermore, the integrated UV-V light intensity (per pass) of ultraviolet light irradiated onto the inkjet ink on the printing substrate during printing (as described later) was 150 mJ / cm². 2 The output of the metal halide lamp unit was adjusted to achieve this result. Each of the above inkjet heads was filled with inkjet ink manufactured using the method described above, and the temperature of the internal heater was adjusted so that the inkjet ink was ejected from the nozzle without any problems. In addition, the evaluation printing device A was adjusted so that the number of non-ejecting nozzles was zero, and A4-sized coated paper (OK Topcoat+ manufactured by Oji Paper Co., Ltd.) was placed under the carriage. Then, inkjet ink printing was performed while driving the carriage in a direction intersecting the transport direction of the coated paper (main scanning direction) (sub-scanning direction) (shuttle head type printing method, 4 passes). Inkjet ink was ejected during each reciprocating motion of the carriage, and ultraviolet light was irradiated only from the metal halide lamp located behind the carriage in the direction of movement during each of these reciprocating motions. In this manner, a solid image was printed on the coated paper to produce a solid print. After the production of the solid print was completed, another new sheet of coated paper was immediately placed in the evaluation printing device A, and a solid print was produced using the method described above without adjusting the settings to ensure that the number of non-ejecting nozzles was zero. This process was repeated to produce 20 solid prints consecutively. After that, the device was left to stand for 4 hours without printing, and then a nozzle check image was printed. The number of non-ejecting nozzles was counted to evaluate the ejection stability. The evaluation criteria were as follows, with ◎, ○, and △ ratings indicating usable, and ◎ and ○ ratings indicating suitable for practical use.

[0177] ≪Evaluation Criteria for Discharge Stability≫ ◎: The number of non-discharging nozzles was 4 or less. ○: The number of non-discharging nozzles was 5 to 8. △: The number of non-discharging nozzles was between 9 and 15. ×: The number of non-discharging nozzles was 16 or more.

[0178] <Evaluation of the strength of the ink-cured film> The strength of the ink-cured film (printed material) was comprehensively determined by evaluating the stickiness of the surface of the solid print produced in the adhesion evaluation above when touched with a finger, and the degree of inkjet ink adhering to the cotton swab when rubbed with a cotton swab. The evaluation criteria were as follows, with ◎, ○, and △ ratings indicating usable, and ◎ and ○ ratings indicating suitable for practical use.

[0179] ≪Evaluation Criteria for the Strength of Ink-Cured Films≫ ◎: There was no stickiness on the surface of the cured ink film, and no inkjet ink adhered to the cotton swab. ○: The surface of the ink-cured film was slightly sticky, but no inkjet ink adhered to the cotton swab. △: The surface of the ink-cured film was slightly sticky, and a small amount of inkjet ink adhered to the cotton swab. ×: The surface of the ink-cured film was sticky, and inkjet ink also adhered to the cotton swab.

[0180] <Evaluation of curing properties> An inkjet head is installed above a conveyor capable of transporting printing substrates, and an LED lamp unit (manufactured by Phoseon Technology, with an ultraviolet irradiation wavelength of 395 nm and a maximum illuminance of 16,000 mW / cm²) is installed above the conveyor on the downstream side of the conveying direction of the printing substrates. 2 An evaluation printing device B equipped with the above was prepared. The inkjet head mounted on the above evaluation printing device was the same as that used in evaluation printing device A. In addition, the cumulative amount of ultraviolet light irradiated onto the inkjet ink on the printing substrate during printing, as described later, was set to 200 mJ / cm². 2 The output of the LED lamp unit was adjusted to achieve this result. The inkjet heads described above were each filled with the inkjet ink produced by the method described above, and the temperature of the internal heaters was adjusted so that the inkjet ink was ejected from the nozzles without any problems. In addition, the evaluation printing device B was adjusted so that the number of non-ejecting nozzles was zero. Next, an A4-sized PET substrate (Lintec Corporation's "PET50 (K2411)") was fixed on the conveyor, and the conveyor was driven at a speed of 50 m / min. As the PET substrate passed the inkjet head installation area, a solid image was printed with a drop volume of 14 pL (line head type one-pass printing method). After the inkjet ink was ejected, the conveyor was driven at the same speed, and as the PET substrate passed the LED lamp unit installation area, ultraviolet light was irradiated to produce a solid print. The surface of the solid print material prepared in this manner was rubbed with a cotton swab to check whether uncured inkjet ink adhered to the cotton swab. If inkjet ink adhered, the solid print material was fixed to the conveyor of the inkjet printing apparatus, and without printing with inkjet ink, only ultraviolet light from the LED lamp unit was irradiated, and then the presence or absence of ink adhesion was checked again when rubbing with a cotton swab. This procedure was repeated, and the number of passes required until uncured ink no longer adhered to the cotton swab was recorded to evaluate the curing properties. The evaluation criteria were as follows, with ◎, ○, and △ ratings indicating usable, and ◎ and ○ ratings indicating suitable for practical use.

[0181] ≪Evaluation Criteria for Curing Properties≫ ◎: After passing the cotton swab through it once in total (without requiring additional UV irradiation), no uncured ink adhered to the cotton swab. ○: After passing the cotton swab through it a total of two times (with one additional UV irradiation), no uncured ink adhered to the cotton swab. △: After passing the swab through a total of three times (with two additional UV irradiations), no uncured ink adhered to the cotton swab. ×: It was necessary to pass the cotton swab through the UV lamp a total of four or more times (and perform an additional three or more UV irradiations) until no uncured ink adhered to it.

[0182] As is clear from Tables 2-1 to 2-7 above, the inkjet inks having the above-described configuration exhibited practical quality in terms of storage stability, ejection stability, strength of the cured ink film, and curability (Examples 1 to 53).

[0183] In contrast, in inkjet ink 4 (Comparative Example 1), where the content of monofunctional monomer (A) was greater than 100% by mass relative to the content of acrylate monomer (B), the storage stability and ejection stability did not reach a practical level. Conversely, in inkjet ink 17 (Comparative Example 5), where the content of monofunctional monomer (A) was less than 3% by mass relative to the content of acrylate monomer (B), and in inkjet ink 11 (Comparative Example 4), which contained no monofunctional monomer (A), the ejection stability was not practical. From these results, it was confirmed that an appropriate amount of monofunctional monomer (A) is necessary to suitably dissolve and homogenize TrTPO in inkjet ink and suitably exhibit the effects of the present invention.

[0184] Furthermore, inkjet ink 5 (Comparative Example 2) and inkjet ink 10 (Comparative Example 3) were systems in which the acrylate monomer (B) content relative to the total polymerizable compound content was 48% by mass and 91% by mass, respectively. As a result of evaluation, deterioration in ejection stability was confirmed in both cases, and inkjet ink 5 also showed poor storage stability. These results indicate that a certain amount of acrylate monomer (B) is necessary to ensure the ejection stability of inkjet inks.

[0185] Furthermore, when comparing inkjet inks 1 to 11, inkjet inks 1, 2, 7, and 8 (Examples 1, 2, 5, and 6), which use N-vinyl-2-caprolactam or 5-methyl-N-vinyl-2-oxazolidinone as the monofunctional monomer (A), with the content of the monofunctional monomer (A) relative to the content of the acrylate monomer (B) being 10 to 60% by mass, and the content of the acrylate monomer (B) relative to the content of the polymerizable compound being 60 to 85% by mass, all evaluation items were excellent. In other words, satisfying the above requirements is particularly preferable for realizing the effects of the present invention.

[0186] On the other hand, inkjet ink 38 (Comparative Example 6) and inkjet ink 39 (Comparative Example 7) were systems that did not contain acrylate monomer (B), and the evaluation results showed that the ejection stability or curing performance was at the × level, not reaching a practical level. Furthermore, even in other evaluations that were judged to be practically usable, many items did not reach a level that could be considered practically suitable (△ level). In other words, the results indicate that in order to achieve good storage stability, ejection stability, strength of the ink cured film, and curing performance, it is effective to use acrylate monomer (B), which has a small molecular weight and a small number of polymerizable groups, as the main component.

[0187] Furthermore, as can be seen from the comparison of inkjet ink 33 (Example 28) and inkjet ink 34 (Example 29), and the comparison of inkjet ink 36 (Example 31) and inkjet ink 37 (Example 32), the effects of the present invention can be suitably realized by using a monomer having one acryloyl group and an aromatic ring structure, a monomer having two acryloyl groups, and / or a monomer having one acryloyl group and one vinyl ether group as the acrylate monomer (B).

[0188] Furthermore, in systems that used a large amount of BTPO instead of TrTPO, such as inkjet ink 63 (Comparative Example 8), deterioration in storage stability occurred, which is thought to be due to the low solubility of BTPO. In addition, while the ejection stability and the strength of the cured ink film were usable, they were not at a level suitable for practical use.

[0189] <Manufacturing of inkjet ink bases> The following materials were placed in a mixing container equipped with a stirrer. After all materials were added, the mixture was heated while being stirred until its temperature reached 40°C. Once 40°C was reached, stirring was continued for another hour while maintaining the temperature, thereby producing the inkjet ink base. The method and order of adding each material were the same as those used in the production of inkjet inks 1 to 63 described above. • Cyanide pigment dispersion A: 16.7 parts • N-vinyl-2-caprolactam 12.5 parts • Tetrahydrofurfurylacrylate 7.5 parts 2-Phenoxyethyl acrylate 37.3 parts • Dipropylene glycol diacrylate 12.5 parts ·EBECRYL8402 5.0 copies • TrTPO 5.0 ·BTPO 1.0 part ·Omnirad 369 1.0 copy • Omnirad ITX 1.0 ·BYK-UV3510 0.1 part BHT Swanox 0.4 bu

[0190] <Manufacturing of inkjet inks 64-83> The above inkjet ink bases in the amounts shown in Tables 3-1 to 3-2 were mixed with organic solvents and / or water of the types and amounts shown in Tables 3-1 to 3-2. Inkjet inks 64 to 83 were then produced by filtering the mixture through a membrane filter with a pore size of 0.8 μm.

[0191] [Table 3-1]

[0192] [Table 3-2]

[0193] Tables 3-1 to 3-2 above also show the moisture content of inkjet inks 64 to 83, measured using the method described above.

[0194] [Examples 56-75] Using inkjet inks 64-83 manufactured by the method described above, the storage stability, ejection stability, and strength of the cured ink film were evaluated according to the method described above. The evaluation results are shown in Tables 3-1 to 3-2 above.

[0195] The results in Tables 3-1 to 3-2 above show that by using at least one organic solvent selected from the group consisting of alkylene glycol monoalkyl ether acetates, alkylene glycol monoalkyl ethers, and alkylene glycol dialkyl ethers, with a boiling point of 120 to 250°C (preferably 180 to 230°C), and further by keeping the water content of the inkjet ink within the range of 0.03 to 0.8% by mass, storage stability, ejection stability, and the strength of the ink-cured film are all simultaneously and particularly improved.

Claims

1. An active energy ray curable inkjet ink comprising a polymerizable compound and a photopolymerization initiator, The polymerizable compound comprises a monofunctional monomer (A) having a nitrogen-containing heterocyclic structure and a monofunctional or bifunctional acrylate monomer (B) having a molecular weight of 140 to 250 (excluding the monofunctional monomer (A)). The content of acrylate monomer (B) relative to the content of the polymerizable compound is 50 to 90% by mass. The mass content of the monofunctional monomer (A) relative to the mass content of the acrylate monomer (B) is 3 to 100% by mass. An active energy ray curable inkjet ink comprising the aforementioned photopolymerization initiator di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide.

2. The active energy ray curable inkjet ink according to claim 1, wherein the content of the monofunctional monomer (A) relative to the content of the di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide is 100 to 550% by mass.

3. The active energy ray curable inkjet ink according to claim 1 or 2, wherein the photopolymerization initiator further comprises one or more compounds selected from the group consisting of acylphosphine oxide compounds (excluding the di-p-tolyl(2,4,6-trimethylbenzoyl)phosphine oxide), alkylaminoacetophenone compounds, and thioxanthone compounds.

4. The activated energy ray-curable inkjet ink according to claim 1 or 2, wherein the water content is 0.03 to 0.8% by mass relative to the total amount of the inkjet ink.

5. A printed article comprising an active energy ray-curable inkjet ink according to claim 1 or 2, printed on a printing substrate.

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