Active energy ray-curable inkjet black ink and printed matter

Abstract

To provide an active energy ray-curable inkjet black ink excellent in all of carbon black dispersion stability, ejection stability, curing properties, and print image fineness.SOLUTION: The active energy ray-curable inkjet black ink comprises carbon black, a basic pigment dispersion resin having an acid value of at most 30 mg KOH / g, and 5-methyl-3-vinyloxazolidin-2-one. When the DBP oil absorption amount of the carbon black is AC (mL / 100 g) and the specific surface area of the carbon black is SC (m2 / g), the value represented by AC×SC is 2,000-12,000. The content of a monofunctional polymerizable compound (excluding the 5-methyl-3-vinyloxazolidin-2-one) is at most 15 mass% with respect to the total mass of the active energy ray-curable inkjet black ink.SELECTED DRAWING: None

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an actinic ray-curable inkjet black ink and a printed matter obtained by printing the actinic ray-curable inkjet black ink on a printing substrate. [Background technology]

[0002] In recent years, digital printing methods have been increasingly adopted in printing markets that emphasize productivity, such as the commercial printing market, the office printing market, and the specialty printing market. The reasons for this include the fact that digital printing methods do not require plate making, so printed materials can be produced at low cost and in a short time, the printing devices are smaller and cheaper than those used in plate-based printing methods, and uniform printed materials can be easily produced regardless of the skill level of the printer.

[0003] Among these, inkjet printing, which is one type of digital printing method, is superior to other digital printing methods in many respects, such as low running costs during printing, ease of full color printing, and the fact that print quality is not dependent on the installation environment of the printing device, etc. For this reason, there is a particularly high demand for the adoption of inkjet printing in the printing market.

[0004] The inks used in the inkjet printing method range widely, including water-based, oil-based, solvent-based, active energy ray-curable, etc. Among these, there has been an increasing demand in recent years for active energy ray-curable inks because of their properties such as the ability to print high-quality prints even on non-permeable printing substrates such as resin films and glass, their rapid drying (curing) time, and the strength of printed matter.

[0005] In the production of printed materials, black is an extremely important color because it can improve the visibility and readability of printed characters and barcodes, the clarity of printed photographs, and other images. However, it is known that it is difficult to improve the curability of black in actinic radiation-curable inks used in inkjet printing systems (simply referred to as "actinic radiation-curable inkjet inks" in this application). This is because carbon black, which is commonly used as a black colorant, absorbs actinic radiation. Insufficient curability leads to a decrease in printing speed, so improving the curability of black actinic radiation-curable inkjet inks is a very important issue when considering expansion into the printing market, which places importance on productivity.

[0006] In the past, active energy ray-curable inkjet inks have been investigated that reproduce black by mixing multiple colorants without using carbon black (see, for example, Patent Document 1). However, it is difficult to reproduce a vivid black color with this method, and further improvements are needed from the standpoint of improving the visibility, readability, and clarity mentioned above.

[0007] Furthermore, there has been a growing demand from the market for environmental considerations in recent years. In response to this, LED lamps are increasingly being used as a method for curing actinic radiation-curable inkjet inks. However, LED lamps have the characteristic of emitting actinic radiation with a narrow wavelength range, and when used in combination with actinic radiation-curable inkjet inks, improving curing performance becomes an issue.

[0008] Studies have been conducted to improve the curability of actinic radiation-curable inkjet inks when used in combination with LED lamps. For example, Patent Document 2 discloses a photocurable inkjet printing ink composition containing 4 to 40 mass% vinyloxyethoxyethyl acrylate and 10 to 65 mass% benzyl acrylate, and further containing 50 mass% or more of a monofunctional monomer. However, the examples in Patent Document 2 do not include any actual printing evaluation using an inkjet printer (printing device), and there is no mention of whether printed matter with excellent visibility, readability, etc. can be stably printed. Furthermore, considering the adoption in the printing market described above, it is believed that the curability of the photocurable inkjet printing ink composition disclosed in Patent Document 2 must be further improved.

[0009] Furthermore, Patent Document 3 discloses an ultraviolet-curable ink composition for inkjet printing, which contains an α-aminoalkylphenone initiator, a thioxanthone initiator, and a tertiary amine (photopolymerization initiator aid). However, in the examples of Patent Document 3, the curability is evaluated using an inkjet printer employing a multi-pass printing method in which actinic energy rays are irradiated to the same location multiple times. Furthermore, in the examples, only a yellow ink composition is evaluated. As mentioned above, it is more difficult to improve the curability of a black actinic energy ray-curable inkjet ink than other colors. Therefore, even if the configuration of Patent Document 3 is simply applied to a black actinic energy ray-curable inkjet ink, taking into consideration its adoption in the printing market, there is a high possibility that the actinic energy ray-curable inkjet ink will not have the desired curability.

[0010] When the composition disclosed in Patent Document 3 is applied to a black actinic radiation-curable inkjet ink, it is possible to increase the amount of the α-aminoalkylphenone initiator, the thioxanthone initiator, and the tertiary amine to enhance sensitivity to actinic radiation and improve curability. However, many of the above-mentioned components are solid at room temperature, and incorporating large amounts of these components can deteriorate the ejection stability from the inkjet head and the dispersion state of the colorant (carbon black, etc.). For this reason, simply increasing the amount of the above-mentioned components is not necessarily a good solution.

[0011] As described above, it has been extremely difficult to achieve both dispersion stability and ejection stability of a colorant (carbon black, etc.) and curability and fineness of printed matter, particularly in a black active energy ray-curable inkjet ink (also referred to as an "active energy ray-curable inkjet black ink" in the present application) used in combination with an LED lamp.

[0012] In this application, the term "definition of printed matter" refers to the excellent visibility and readability even for printed matter containing minute characters and barcodes. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-266548 [Patent Document 2] International Publication No. 2014 / 014017 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-136795 Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention has been made to solve the above-mentioned problems, and an object of one embodiment of the present invention is to provide an actinic energy ray-curable inkjet black ink that is excellent in all of the dispersion stability of carbon black, ejection stability, curability, and fineness of printed matter. [Means for solving the problem]

[0015] As a result of extensive research, the present inventors have found that all of the above-mentioned problems can be solved simultaneously and to a high degree by an active energy ray-curable inkjet black ink having the following composition.

[0016] That is, one embodiment of the present invention relates to the actinic ray-curable inkjet black inks described in [1] to [7] below, and to a printed matter obtained using the actinic ray-curable inkjet black ink described in [8] below. [1] An active energy ray-curable inkjet black ink comprising carbon black, a basic pigment dispersion resin, and a polymerizable compound, The DBP oil absorption of the carbon black is defined as AC (mL / 100g), and the specific surface area of ​​the carbon black is defined as SC (m 2 / g), the value expressed by AC × SC is 2,000 to 12,000, the basic pigment dispersing resin has an acid value of 30 mgKOH / g or less, the polymerizable compound comprises 5-methyl-3-vinyloxazolidin-2-one, An actinic ray-curable inkjet black ink, wherein the content of monofunctional polymerizable compounds (excluding the 5-methyl-3-vinyloxazolidin-2-one) is 15 mass % or less based on the total amount of the actinic ray-curable inkjet black ink. [2] The polymerizable compound contains a radical polymerizable bifunctional monomer represented by the general formula (A), The actinic energy ray-curable inkjet black ink according to [1], wherein the content of the radical polymerizable bifunctional monomer represented by general formula (A) is 15 to 55 mass % of the total amount of the actinic energy ray-curable inkjet black ink. General formula (A): CH2=CR 1 -CO-OR 2 -O-CO-CR 1 =CH2 (In general formula (A), R 1 represents a hydrogen atom or a methyl group, and R 2 represents an alkylene group having 3 to 6 carbon atoms, which may have a branched structure. [3] The polymerizable compound contains a radical polymerizable trifunctional monomer represented by the general formula (B), The actinic energy ray-curable inkjet black ink according to [1] or [2], wherein the content of the radical polymerizable trifunctional monomer represented by general formula (B) is 2 to 15 mass % of the total amount of the actinic energy ray-curable inkjet black ink. General formula (B): [ka] (In general formula (B), R 3 represents a hydrogen atom or a methyl group, and R 4 is an ethylene group or a propylene group. Furthermore, l, m, and n each represent an integer of 0 to 9, and l+m+n is an integer of 0 to 9. [4] Further, a photopolymerization initiator is contained, The actinic ray-curable inkjet black ink according to any one of [1] to [3], wherein the photopolymerization initiator contains an acylphosphine oxide compound. [5] The actinic ray-curable inkjet black ink according to [4], wherein the photopolymerization initiator further contains a thioxanthone compound. [6] The acylphosphine oxide compound contains ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and / or a polymer of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, The active energy ray-curable inkjet black ink according to [4] or [5], wherein the total content of the ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and the ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is 45 to 80 mass % of the total amount of the photopolymerization initiator. [7] The actinic ray-curable inkjet black ink according to any one of [1] to [6], wherein the carbon black has a pH of 2 to 5. [8] A printed matter obtained by printing the active energy ray-curable inkjet black ink according to any one of [1] to [7] on a printing substrate. [Effects of the Invention]

[0017] The active energy ray-curable inkjet black ink according to one embodiment of the present invention exhibits the effects of being excellent in all of the dispersion stability of the carbon black, the ejection stability, the curing properties, and the definition of the printed matter. DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0033] The actinic radiation-curable inkjet black ink (hereinafter simply referred to as "inkjet ink of this embodiment") according to one embodiment of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiment, and includes modifications that are implemented within the scope of the present invention. In addition, in this application, the terms "(meth)acrylate," "(meth)acryloyl," and "(meth)acrylic acid" respectively mean "acrylate and / or methacrylate," "acryloyl and / or methacryloyl," and "acrylic acid and / or methacrylic acid."

[0019] First, the mechanism by which the inkjet ink of the present embodiment achieves the above-mentioned effects will be explained. However, the mechanism described below is based on the inference of the inventors and does not limit the present invention in any way.

[0020] First, the inkjet ink of this embodiment contains 5-methyl-3-vinyloxazolidin-2-one as a polymerizable compound. As described above, cyclic N-vinyl compounds are generally known to react faster with radicals derived from photopolymerization initiators than acrylate compounds. Furthermore, the reaction rate of 5-methyl-3-vinyloxazolidin-2-one is particularly faster than that of other compounds. The reason for this is thought to be that, unlike N-vinylcaprolactam and N-vinylpyrrolidone, which are commonly known as cyclic N-vinyl compounds, 5-methyl-3-vinyloxazolidin-2-one contains an oxygen atom in its ring structure. That is, electrons in the ring structure are attracted to this oxygen atom, which likely makes the vinyl group more susceptible to reaction with radicals derived from photopolymerization initiators. As a result, bleeding of fine characters and thin lines can be suppressed, making it easier to obtain high-definition printed materials.

[0021] Furthermore, by adjusting the content of the monofunctional polymerizable compound (excluding 5-methyl-3-vinyloxazolidin-2-one) to 15 mass% or less of the total amount of the inkjet ink of this embodiment, the reaction between 5-methyl-3-vinyloxazolidin-2-one and radicals is not inhibited, and it is possible to further improve the curability and the definition of the printed matter.

[0022] On the other hand, cyclic N-vinyl compounds such as 5-methyl-3-vinyloxazolidin-2-one have the problem of easily impairing the dispersion stability of pigments and the ejection stability of inkjet inks. This is thought to be due to the fact that the cyclic N-vinyl compounds inhibit stable adsorption of pigment dispersants to the pigment surface and that the vinyl groups in the cyclic N-vinyl compounds react with acid groups present in the pigment dispersants, etc. Furthermore, improving the curability of active energy ray-curable inkjet black inks containing carbon black is particularly difficult. This is due to the fact that active energy rays are absorbed by the carbon black, making it difficult for them to penetrate the ink, and that quinone groups present on the surface of the carbon black trap radicals. Therefore, simply blending 5-methyl-3-vinyloxazolidin-2-one into an active energy ray-curable inkjet black ink containing carbon black not only results in insufficient curability, but also potentially impairs the dispersion stability of the carbon black and the ejection stability of the inkjet black ink. Furthermore, the deterioration of dispersion stability may adversely affect the resolution of printed materials.

[0023] Therefore, in the inkjet ink of this embodiment, the DBP oil absorption is expressed as AC (mL / 100g) and the specific surface area is expressed as SC (m 2 The carbon black used is one that has a value of 2,000 to 12,000 expressed as AC x SC when the total surface area is 100% (AC x SC / g). Carbon black that meets this requirement has large primary particles and relatively small aggregates, which are agglomerations of these primary particles. When such carbon black is used, it is thought that the amount of active energy rays absorbed is reduced, and the small external surface area reduces the amount of radicals trapped on the surface, although the details are unknown.

[0024] Furthermore, the inkjet ink of this embodiment uses a basic pigment dispersion resin with an acid value of 30 mgKOH / g or less to disperse the carbon black. As will be described in detail later, the basic pigment dispersion resin has basic groups that serve as adsorption sites for the pigment (carbon black). It is believed that these basic groups strongly interact with functional groups, such as carboxyl groups, hydroxyl groups, and quinone groups, present on the surface of the carbon black, thereby ensuring the dispersion stability of the carbon black and the ejection stability of the inkjet ink, even in the presence of 5-methyl-3-vinyloxazolidin-2-one. Furthermore, by setting the acid value of the basic pigment dispersion resin to 30 mgKOH / g or less (or even 0 mgKOH / g) and limiting the amount of acid groups that can react with the vinyl groups in 5-methyl-3-vinyloxazolidin-2-one, the ejection stability of the inkjet ink can be further improved.

[0025] As described above, in order to improve all of the dispersion stability, ejection stability, curing properties, and fineness of printed matter of carbon black, an active energy ray-curable inkjet black ink having the above-described configuration is required.

[0026] Next, each of the components constituting the inkjet ink of this embodiment will be described in detail below.

[0027] The inkjet ink of this embodiment is black in color. The "black" inkjet ink includes not only inkjet ink that can be used to produce black printed matter, but also inkjet ink that can be used to produce light black (gray) printed matter. However, it goes without saying that in both the former and latter cases, the inkjet ink must have the above-described configuration.

[0028] <Carbon black> The inkjet ink of this embodiment contains carbon black. The DBP oil absorption of the carbon black is AC (mL / 100 g), and the specific surface area is SC (m 2 / g), the value expressed as AC×SC is 2,000 to 12,000.

[0029] ≪DBP oil absorption amount≫ DBP oil absorption is a value that represents the amount of DBP (dibutyl phthalate) absorbed into the particle voids present within aggregates. Generally, the more aggregates developed in carbon black, the higher the DBP oil absorption value. The DBP oil absorption of carbon black that can be used in the inkjet ink of this embodiment is preferably 40 to 100 mL / 100 g, more preferably 40 to 80 mL / 100 g, and particularly preferably 40 to 65 mL / 100 g. Inkjet inks using carbon black with such DBP oil absorptions exhibit excellent curing properties. Furthermore, the basic pigment dispersion resin can be firmly adsorbed, thereby improving the dispersion stability of the carbon black. The DBP oil absorption can be measured using an "Absorbtometer Type C" manufactured by Brabender or the like in accordance with JIS K 6217-4.

[0030] ≪Specific surface area≫ Generally, carbon black with a large specific surface area has small primary particles and / or many pores. The specific surface area of ​​carbon black that can be used in the inkjet ink of this embodiment is 45 to 120 m 2 / g, and 50 to 95m 2 / g is particularly preferred. Carbon black having such a specific surface area is less likely to absorb active energy rays that have penetrated into the inkjet ink, and also less likely to trap radicals on the surface of the carbon black, improving curability. Furthermore, the amount of carbon black with an excessively large primary particle size is reduced, resulting in good ejection stability. In this application, the "specific surface area" is a value measured by the nitrogen BET method (nitrogen BET specific surface area). The method for measuring the specific surface area of ​​carbon black by the nitrogen BET method is specified in JIS K 6217-2, and this method can be applied mutatis mutandis to this application. As a specific example of the measurement method, nitrogen is adsorbed onto degassed carbon black at liquid nitrogen temperature, and the specific surface area (m) is calculated from the amount of adsorbed nitrogen when equilibrium is reached. 2 / g).

[0031] <DBP oil absorption multiplied by specific surface area> As described above, the carbon black contained in the inkjet ink of this embodiment has a DBP oil absorption of AC (mL / 100 g) and a specific surface area of ​​SC (m 2 / g), the value expressed by AC×SC is 2,000 to 12,000. Furthermore, not only is curability improved, but the definition of printed matter is also improved, and strong adsorption to the basic pigment dispersion resin improves the dispersion stability of the carbon black and the discharge stability of the inkjet ink. Therefore, the value is preferably 2,000 to 7,500, and particularly preferably 2,000 to 6,000.

[0032] pH In addition to the above specifications, the carbon black contained in the inkjet ink of this embodiment preferably has a pH of 2 to 5, and particularly preferably 2 to 4. Carbon black having such a pH will firmly adsorb the basic pigment dispersion resin, thereby significantly improving the dispersion stability of the carbon black and the ejection stability of the inkjet ink. The pH of carbon black can be measured by a conventional method. For example, 5 g of carbon black and 50 mL of ion-exchanged water are mixed in a glass container such as a beaker, and the opening of the beaker is covered with a watch glass or the like, and the mixture is heated for 15 minutes. A small amount (approximately 0.1 mL) of ethanol or acetone may be added to facilitate wetting of the carbon black. After boiling, the mixture is cooled to 25°C, and the supernatant liquid is removed to obtain a slurry. A pH electrode is inserted into the slurry, and the pH is measured. For example, a benchtop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "9681S-10D" (manufactured by Horiba, Ltd.) can be used to measure the pH.

[0033] <Primary particle size> For the same reason as in the case of the specific surface area described above, i.e., because curability and ejection stability are improved, the primary particle diameter of the carbon black is preferably 20 to 50 nm, more preferably 25 to 50 nm, and particularly preferably 30 to 50 nm. The primary particle size of carbon black can be measured by a conventional method, for example, by observing the carbon black with a transmission electron microscope (TEM), measuring the sizes (diameters) of 100 primary particles of the carbon black, and then calculating the average value.

[0034] The content of carbon black that satisfies the above-described requirements in the inkjet ink of this embodiment is preferably 0.5 to 3.5 mass %, and particularly preferably 1.0 to 3.0 mass %, of the total amount of the inkjet ink. When the content of carbon black that satisfies the above-described requirements falls within the above range, the amount of carbon black present in the inkjet ink is optimal, resulting in an inkjet ink that is excellent in curability, ejection stability, and fineness of printed matter.

[0035] Furthermore, the particle size (secondary particle size) of the carbon black contained in the inkjet ink of this embodiment that satisfies the above-mentioned requirements is preferably 80 to 250 nm, and particularly preferably 100 to 200 nm. If the secondary particle size of the carbon black that satisfies the above-mentioned requirements is within the above range, the carbon black can be said to be in a favorable dispersed state, resulting in an inkjet ink that is excellent in all of curability, discharge stability, and carbon black dispersion stability.

[0036] For the same reason, namely, because the carbon black is in a favorable dispersed state, the curing property and ejection stability of the inkjet ink, as well as the dispersion stability of the carbon black, are all improved, the secondary particle diameter (unit: nm) is calculated as the specific surface area (unit: m) of the carbon black that satisfies the above-mentioned requirements. 2 The value obtained by dividing by (wt. / g) is preferably from 1.0 to 4.0, and particularly preferably from 1.5 to 3.5.

[0037] The secondary particle size refers to the median size measured on a volume basis. The secondary particle size can be measured using a dynamic light scattering particle size distribution analyzer (e.g., Nanotrac UPA-EX150 manufactured by Microtrac-Bell) and inkjet ink diluted with ethyl acetate to a concentration that allows measurement of the secondary particle size using the particle size distribution analyzer.

[0038] The inkjet ink of this embodiment may contain carbon black other than the carbon black that satisfies the above-mentioned requirements (also referred to as "other carbon black" in the present application). However, when the inkjet ink of this embodiment contains other carbon black, it is preferable that the amount of other carbon black is an amount that does not inhibit the effects of the carbon black that satisfies the above-mentioned requirements. Specifically, the content of other carbon black contained in the inkjet ink of this embodiment is preferably 0 to 35% by mass, more preferably 0 to 20% by mass, and particularly preferably 0 to 10% by mass, of the total amount of carbon black contained in the inkjet ink.

[0039] In the present application, the expression "amount (content) of 0 mass %" means that the target component is not contained.

[0040] <Other pigments> The inkjet ink of this embodiment may also contain pigments other than carbon black (also referred to as "other pigments" in the present application) in order to improve the curing properties and the definition and blackness of printed matter. When the inkjet ink of this embodiment contains other pigments, for the same reasons as in the case of the other carbon black described above, that is, the effects of the carbon black that satisfies the above-mentioned requirements are effectively exerted, and the curing properties, ejection stability, and dispersion stability of the carbon black are improved. For these reasons, the content of the other pigments contained in the inkjet ink of this embodiment is preferably 0 to 50% by mass, more preferably 0 to 35% by mass, and particularly preferably 0 to 20% by mass, relative to the content of the carbon black that satisfies the above-mentioned requirements.

[0041] The other pigments are not particularly limited, but for example, organic pigments or inorganic pigments represented by the following color index names can be used. For example, red pigments include 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, 184, 188, 202, 209, 242, 254, 255, 264, 266, 269, 282, etc. Violet pigments include CI Pigment Violet 19, 23, etc. Orange pigments include CI Pigment Orange 5, 13, 34, 38, 43, 61, 62, 64, etc. Blue pigments include CI Pigment Blue 1, 2, 3, 15:3, 15:4, 15:6, 16, 22, 60, CI Vat Blue 4, 60, etc. Green pigments include CI Pigment Green 7, 26, 36, 50, 58, etc.; Yellow pigments include CI Pigment Yellow 1, 2, 3, 12, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 128, 129, 138, 139, 147, 150, 151, 154, 155, 180, 185, 213, etc. These pigments can be used as desired depending on the desired curing properties, as well as the fineness and blackness of the printed matter. Two or more of the pigments listed above may be used in combination.

[0042] <Basic pigment dispersing resin> The inkjet ink of this embodiment contains a basic pigment dispersion resin. The basic pigment dispersion resin has an acid value of 30 mgKOH / g or less. The acid value may be 0 mgKOH / g, i.e., the basic pigment dispersion resin may have substantially no acid groups.

[0043] In this application, the term "basic pigment dispersing resin" refers to a dispersing resin in which basic groups serve as adsorption points for the pigment (carbon black) surface. Examples of the basic groups include primary amino groups, secondary amino groups, tertiary amino groups, quaternary ammonium groups, and imino groups. The organic groups bonded to the nitrogen atoms in the tertiary amino groups and the quaternary ammonium groups may also be bonded to each other to form a ring structure (a heterocyclic ring containing the nitrogen atom). Examples of such rings include pyridine, pyrrolidine, pyrrolidone, imidazoline, and caprolactam.

[0044] It should be noted that even if a pigment dispersing resin has an acid group in addition to a basic group, the basic group functions as the adsorption site, and so the resin is considered to be included in the "basic pigment dispersing resin" of the present application. However, as mentioned above, it goes without saying that only resins having an acid value of 30 mgKOH / g or less (0 mgKOH / g is acceptable) can be used as the basic pigment dispersing resin of the present application.

[0045] Examples of basic pigment dispersing resins include the above-mentioned acrylic resins having a basic group, the above-mentioned maleic anhydride resins having a basic group, polyethyleneimine, polyallylamine, polydiallylamine, polyvinylimidazoline, and polyvinylpyrrolidone, as well as graft resins having these resins as the main chain. Commercially available examples of basic pigment dispersing resins include "Ajisper PB-821," "Ajisper PB-822," "Ajisper PB-824," and "Ajisper PB-881" manufactured by Ajinomoto Fine-Techno Co., Ltd., and "DISPERBYK-162," "DISPERBYK-163," "DISPERBYK-168," "DISPERBYK-182," "DISPERBYK-184," "DISPERBYK-185," and "DISPERBYK-186" manufactured by BYK-Chemie. Examples include SPERBYK-2013, DISPERBYK-2155, BYKJET-9150, BYKJET-9151, and BYKJET-9152, as well as Lubrizol's Solsperse 24000, Solsperse 32000, Solsperse 33000, Solsperse 35000, Solsperse 39000, Solsperse 86000, Solsperse J200, and Solsperse X300, and BASF's EFKA PX4701, EFKA PX4703, and EFKA PX4733.

[0046] The term "acrylic resin" refers to a resin using one or more monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters as the monomers constituting the resin (a styrene-based monomer may also be used). However, resins using maleic acid (anhydride) (maleic anhydride and / or maleic acid) as the monomer are not included in the term "acrylic resin." The "maleic anhydride resin" refers to a resin containing at least maleic anhydride as a monomer constituting the resin. The maleic anhydride resin may further contain at least one monomer selected from the group consisting of α-olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, and styrene derivatives.

[0047] As described above, from the viewpoint of improving the ejection stability and curability of the inkjet ink of this embodiment, the acid value of the basic pigment dispersion resin is 30 mgKOH / g or less (may be 0 mgKOH / g). Furthermore, from the viewpoint of enabling the basic pigment dispersion resin to be stably present in the inkjet ink, further improving the ejection stability, and further improving the curability of the inkjet ink, it is particularly preferable that the acid value of the basic pigment dispersion resin is 20 mgKOH / g or less (may be 0 mgKOH / g).

[0048] The "acid value" of a basic pigment dispersion resin is 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 made by mixing diethyl ether and ethanol in a 1:1 mass ratio, and then titrated by potentiometric titration using a 0.1 mol / L potassium hydroxide-ethanol solution. The acid value can then be calculated using the titration amount read from the resulting titration curve.

[0049] The amine value of the basic pigment dispersion resin 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, allowing it to firmly adsorb to carbon black that meets the above-mentioned requirements. As a result, the dispersion stability of the carbon black and the ejection stability of the inkjet ink are improved. Furthermore, the adsorption sites (basic groups) do not inhibit the polymerization reaction of the polymerizable compound, thereby improving the curability of the inkjet ink.

[0050] The "amine value" of a basic pigment dispersion resin is the amount of potassium hydroxide (mg) required to neutralize 1 g of resin, equivalent to the amount of acid. To measure the amine value, the target resin is dissolved in a solvent containing ethanol or tetrahydrofuran and acetic acid, and then titrated potentiometrically using a 0.1 mol / L perchloric acid-acetic acid solution. The titration amount is then read from the resulting titration curve, and converted to mg of potassium hydroxide to calculate the amine value.

[0051] The mass-average molecular weight of the basic pigment dispersion resin is preferably 5,000 to 60,000, more preferably 8,000 to 55,000, and particularly preferably 10,000 to 50,000. When the mass-average molecular weight of the basic pigment dispersion resin is within the above range, the compatibility of the basic pigment dispersion resin with the polymerizable compound is improved, resulting in improved ejection stability. Furthermore, since the basic pigment dispersion resin can be firmly adsorbed to carbon black that satisfies the above-mentioned requirements, the dispersion stability of the carbon black is improved.

[0052] The mass-average molecular weight can be measured by gel permeation chromatography (GPC). Specifically, it is a value obtained as a polystyrene-equivalent molecular weight measured using a TSKgel column (manufactured by Tosoh Corporation) and a GPC (for example, "HLC-8320GPC" manufactured by Tosoh Corporation) equipped with an RI detector, using DMF as a developing solvent.

[0053] The blending amount of the basic pigment dispersion resin is preferably 10 to 100% by mass, more preferably 15 to 70% by mass, and particularly preferably 20 to 50% by mass, of the total amount of pigment components contained in the inkjet ink of this embodiment (carbon black satisfying the above-mentioned requirements, and other carbon black and / or other pigments, if included). Using the basic pigment dispersion resin in the above blending amount range improves the dispersion stability of the pigment components, including carbon black that satisfies the above-mentioned requirements, and also improves the ejection stability of the inkjet ink of this embodiment.

[0054] <Polymerizable compound> In the present application, the polymerizable compound refers to a compound that undergoes a polymerization reaction or a crosslinking reaction due to radicals generated from a photopolymerization initiator or the like, which will be described later, and has the function of curing a composition containing the polymerizable compound.

[0055] As described above, the inkjet ink of this embodiment contains 5-methyl-3-vinyloxazolidin-2-one as a polymerizable compound, and the content of monofunctional polymerizable compounds excluding 5-methyl-3-vinyloxazolidin-2-one is 15 mass % or less of the total amount of the inkjet ink.

[0056] 5-Methyl-3-vinyloxazolidin-2-one As described above, 5-methyl-3-vinyloxazolidin-2-one has particularly excellent curing properties compared to N-vinyl compounds other than 5-methyl-3-vinyloxazolidin-2-one. Furthermore, 5-methyl-3-vinyloxazolidin-2-one is also excellent in terms of safety and odor, making it an essential material for the inkjet ink of this embodiment.

[0057] The content of 5-methyl-3-vinyloxazolidin-2-one is preferably 5 to 40% by mass, more preferably 10 to 35% by mass, and particularly preferably 15 to 30% by mass, of the total amount of the inkjet ink of this embodiment. By ensuring that the content of 5-methyl-3-vinyloxazolidin-2-one falls within the above range, an inkjet ink with excellent curability can be obtained. As a result, the resolution of printed matter is also improved. Furthermore, since the inhibition of stable adsorption of the basic pigment dispersion resin to the surface of carbon black that satisfies the above-mentioned requirements and the reaction with the acid groups present in the basic pigment dispersion resin can be suppressed, the dispersion stability of the carbon black and the ejection stability of the inkjet ink are also improved.

[0058] Other polymerizable compounds The inkjet ink of this embodiment may contain a radically polymerizable compound other than the above-mentioned 5-methyl-3-vinyloxazolidin-2-one (also referred to as "other polymerizable compounds" in the present application). There are no limitations on the compounds that can be used as the other polymerizable compounds, and monomers, oligomers, polymers, and the like having one or more polymerizable groups can be used. Both the "oligomer" and "polymer" are polymers in which multiple monomers are bonded together, and are classified by their degree of polymerization. In the present application, those with a degree of polymerization of 2 to 10 are called "oligomers," and those with a degree of polymerization of 11 or more are called "polymers."

[0059] Examples of the polymerizable group possessed by the radically polymerizable polymerizable compound (radical polymerizable compound) include a (meth)acryloyl group, a vinyl ether group, an allyl group, a vinyl group (excluding a vinyl ether group and an allyl group), etc. Among the above polymerizable groups, it is preferable to use a radical polymerizable compound having one or more polymerizable groups selected from the group consisting of an acryloyl group, a vinyl ether group, and a vinyl group (excluding a vinyl ether group and an allyl group) in terms of excellent curability.

[0060] As the other polymerizable compound, a monofunctional polymerizable compound (monofunctional polymerizable compound) or a bifunctional or higher (multifunctional) polymerizable compound (multifunctional polymerizable compound) may be used. Furthermore, only one type of other polymerizable compound may be used, or multiple polymerizable compounds may be mixed and used. The term "monofunctional" refers to a compound having only one polymerizable group in one molecule, while "bifunctional" and "trifunctional" refer to a compound having two polymerizable groups in one molecule and a compound having three polymerizable groups in one molecule, respectively. Bifunctional or higher functional compounds are collectively referred to as "polyfunctional."

[0061] As described above, the inkjet ink of this embodiment may optionally contain other polymerizable compounds. However, the content of monofunctional polymerizable compounds (excluding 5-methyl-3-vinyloxazolidin-2-one) in the inkjet ink of this embodiment is limited to 15% by mass or less of the total amount of the inkjet ink of this embodiment. This is because limiting the content of monofunctional polymerizable compounds (excluding 5-methyl-3-vinyloxazolidin-2-one) further improves the curability and the resolution of printed matter. From this perspective, the lower the content of monofunctional polymerizable compounds (excluding 5-methyl-3-vinyloxazolidin-2-one), the better. Specifically, the content of monofunctional polymerizable compounds (excluding 5-methyl-3-vinyloxazolidin-2-one) in the inkjet ink of this embodiment is preferably 10% by mass or less, more preferably 6% by mass or less, and particularly preferably 3% by mass or less, of the total amount of the inkjet ink of this embodiment.

[0062] Other examples of monofunctional radically polymerizable compounds (radical polymerizable monofunctional monomers) that can be used as polymerizable compounds include compounds having one (meth)acryloyl group. Specific examples of the compound include benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, ethylene oxide-modified 2-phenoxyethyl (meth)acrylate, propylene oxide-modified 2-phenoxyethyl (meth)acrylate, dicyclopentenyl (oxyethyl) (meth)acrylate, 2-methoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl (meth)acrylate, methoxydipropylene glycol (meth)acrylate, dipropylene glycol (meth)acrylate, ethylene oxide-modified nonylphenol acrylate, propylene oxide-modified nonylphenol acrylate, ethylene oxide-modified o-phenylphenol acrylate, and ethylene oxide-modified 2-ethyl Hexyl acrylate, β-carboxylethyl (meth)acrylate, trimethylolpropane formal (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl acrylate, 4-tert-butylcyclohexyl acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isoamyl (meth)acrylate, isononyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, isodecyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, caprolactone (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 1,Examples of the acrylates include 4-cyclohexanedimethanol (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, (meth)acryloylmorpholine, 2-(diethylamino)ethyl (meth)acrylate, 2-(diisopropylamino)ethyl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, morpholinoethyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, and N-(meth)acryloyloxyethyl hexahydrophthalimide.

[0063] Another example of a radically polymerizable monofunctional monomer that can be used as the polymerizable compound is a polyfunctional radically polymerizable compound (specific examples of which will be described later) in which only one polymerizable group remains and a primary or secondary organic amine is added (Michael addition) to the remaining polymerizable group.

[0064] Furthermore, other examples of radically polymerizable monofunctional monomers that can be used as other polymerizable compounds include compounds having one vinyl group (excluding 5-methyl-3-vinyloxazolidin-2-one), such as N-vinylcaprolactam and N-vinylpyrrolidone.

[0065] Other examples of the difunctional radically polymerizable compound (radical polymerizable difunctional monomer) that can be used as the polymerizable compound include compounds having two (meth)acryloyl groups. Specific examples of the compound include 1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,3-butylenediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, ethylene oxide-modified 1,6-hexanediol di(meth)acrylate, propylene oxide-modified 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene oxide-modified neopentyl glycol di(meth)acrylate, propylene oxide-modified neopentyl glycol di(meth)acrylate, 3-methyl-1,5-pentanediol 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, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol 200 di(meth)acrylate, polyethylene glycol 300 di(meth)acrylate, 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 Examples of the di(meth)acrylate include phenol 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, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethylene oxide-modified isocyanuric acid di(meth)acrylate, tricyclodecane di(meth)acrylate, dimethyloltricyclodecane di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, trimethylolpropane di(meth)acrylate, neopentyl glycol-modified trimethylolpropane di(meth)acrylate, and dicyclopentanyl di(meth)acrylate.

[0066] Other examples of radically polymerizable monofunctional monomers that can be used as other polymerizable compounds include compounds in which two polymerizable groups are left in a polyfunctional radically polymerizable compound (specific examples will be described later) having three or more polymerizable groups, and a primary or secondary organic amine is added (Michael addition) to the remaining polymerizable group.

[0067] Further, other examples of radically polymerizable bifunctional monomers that can be used as other polymerizable compounds include compounds having one (meth)acryloyl group and one vinyl ether group, such as 2-(2-vinyloxyethoxy)ethyl (meth)acrylate and 2-[2-(2-vinyloxyethoxy)ethoxy]ethyl (meth)acrylate.

[0068] Other examples of trifunctional radically polymerizable compounds (radical polymerizable trifunctional monomers) that can be used as polymerizable compounds include compounds having three (meth)acryloyl groups. Specific examples of such compounds 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-modified isocyanuric acid tri(meth)acrylate. acrylate, propylene oxide-modified isocyanuric acid tri(meth)acrylate, propylene oxide-modified dipentaerythritol tri(meth)acrylate tetramethylolmethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, tri((meth)acryloyloxyethyl)isocyanurate, hydroxypivalaldehyde-modified dimethylolpropane tri(meth)acrylate, and sorbitol tri(meth)acrylate.

[0069] Other examples of tetrafunctional radically polymerizable compounds (radical polymerizable tetrafunctional monomers) that can be used as polymerizable compounds include compounds having four (meth)acryloyl groups. Specific examples of such 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.

[0070] Other examples of the pentafunctional radically polymerizable compound (radical polymerizable pentafunctional monomer) that can be used as a polymerizable compound include compounds having five (meth)acryloyl groups. Specific examples of such compounds include sorbitol penta(meth)acrylate and dipentaerythritol penta(meth)acrylate.

[0071] Other examples of hexafunctional radically polymerizable compounds (radical polymerizable hexafunctional monomers) that can be used as polymerizable compounds include compounds having six (meth)acryloyl groups. Specific examples of such compounds include dipentaerythritol hexa(meth)acrylate, sorbitol hexa(meth)acrylate, alkylene oxide-modified hexa(meth)acrylate of phosphazene, and ε-caprolactone-modified dipentaerythritol hexa(meth)acrylate.

[0072] Furthermore, as the other polymerizable compound, a radically polymerizable compound (radical polymerizable oligomer) that is an oligomer can also be used. In this case, a compound having a (meth)acryloyl group as the polymerizable group is preferably used. The number of polymerizable groups contained in the radically polymerizable oligomer is preferably 1 to 6 per molecule from the viewpoint of the balance between curability, discharge stability, and dispersion 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 radically polymerizable oligomer is preferably 400 to 6,000, and more preferably 500 to 4,500.

[0073] Examples of the radically polymerizable oligomer having a (meth)acryloyl 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; and epoxy (meth)acrylate oligomers. The oligomers may be modified, for example, by sulfonic acid, phosphoric acid, amino, or mercapto modification.

[0074] When the inkjet ink of this embodiment contains other polymerizable compounds, it is preferable that the inkjet ink contains a radically polymerizable bifunctional monomer and / or a radically polymerizable trifunctional monomer, from the viewpoint of improving all of curability, ejection stability, and the resolution of printed matter. In particular, in the inkjet ink of this embodiment, it is preferable that the other polymerizable compounds used are a radically polymerizable bifunctional monomer represented by the following general formula (A) and / or a radically polymerizable trifunctional monomer represented by the following general formula (B):

[0075] General formula (A): CH2=CR 1 -CO-OR 2 -O-CO-CR 1=CH2

[0076] In the above general formula (A), R 1 represents a hydrogen atom or a methyl group, and R 2 represents an alkylene group having 3 to 6 carbon atoms, which may have a branched structure.

[0077] General formula (B): [ka]

[0078] In the above general formula (B), R 3 represents a hydrogen atom or a methyl group, and R 4 is an ethylene group or a propylene group. Furthermore, l, m, and n each represent an integer of 0 to 9, and l+m+n is an integer of 0 to 9.

[0079] The radically polymerizable bifunctional monomer represented by the general formula (A) has low viscosity and relatively low surface tension. Therefore, inkjet inks containing the radically polymerizable bifunctional monomer represented by the general formula (A) exhibit excellent wetting and spreading properties on printing substrates, resulting in improved curability. Furthermore, the radically polymerizable bifunctional monomer represented by the general formula (A) is also highly compatible with 5-methyl-3-vinyloxazolidin-2-one, allowing the polymerization reaction to proceed rapidly, further improving curability. Furthermore, deterioration of the dispersion stability of carbon black due to 5-methyl-3-vinyloxazolidin-2-one is suppressed, thereby improving the dispersion stability of the carbon black.

[0080] Specific examples of the radically polymerizable bifunctional monomer represented by the general formula (A) include 1,3-propanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,3-butylene diol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and 3-methyl-1,5-pentanediol di(meth)acrylate.

[0081] From the viewpoints of improving both the curability and the dispersion stability of the carbon black, and further improving the definition of printed matter, when the inkjet ink of this embodiment contains the radical polymerizable bifunctional monomer represented by the above general formula (A), the blending amount thereof is preferably 15 to 55 mass % of the total amount of the inkjet ink, and particularly preferably 25 to 45 mass %.

[0082] On the other hand, the radical polymerizable trifunctional monomer represented by the general formula (B) has a low viscosity among radical polymerizable trifunctional monomers, which makes it easy to achieve both ejection stability and curability of the inkjet ink. Furthermore, since it does not inhibit the effects of the above-mentioned 5-methyl-3-vinyloxazolidin-2-one, it can further improve the curability.

[0083] Specific examples of the radically polymerizable trifunctional monomer represented by the general formula (B) include glycerin tri(meth)acrylate, ethylene oxide-modified glycerin tri(meth)acrylate (number of ethylene oxide groups: 3), ethylene oxide-modified glycerin tri(meth)acrylate (number of ethylene oxide groups: 9), and propylene oxide-modified glycerin tri(meth)acrylate (number of propylene oxide groups: 3).

[0084] From the viewpoint of improving both the curability and ejection stability and also improving the definition of printed matter, when the inkjet ink of this embodiment contains the radical polymerizable trifunctional monomer represented by the above general formula (B), the blending amount thereof is preferably 2 to 15 mass % of the total amount of the inkjet ink, and particularly preferably 55 to 12 mass %.

[0085] In one embodiment, the inkjet ink preferably contains both the radical polymerizable bifunctional monomer represented by the general formula (A) and the radical polymerizable trifunctional monomer represented by the general formula (B), which makes it easy to obtain an inkjet ink that is excellent in all of curability, ejection stability, carbon black dispersion stability, and print resolution.

[0086] When the inkjet ink of the present embodiment contains a radical polymerizable bifunctional monomer represented by the general formula (A) above and a radical polymerizable trifunctional monomer represented by the general formula (B) above, the mass content of the radical polymerizable bifunctional monomer represented by the general formula (A) above contained in the inkjet ink is preferably 2 to 20, and particularly preferably 2.5 to 15, relative to the mass content of the radical polymerizable trifunctional monomer represented by the general formula (B) above contained in the inkjet ink, which is taken as 1.

[0087] In order to improve both the curability and the ejection stability, when the inkjet ink of this embodiment contains a radically polymerizable bifunctional monomer and / or a radically polymerizable trifunctional monomer as other polymerizable compounds, the total content of 5-methyl-3-vinyloxazolidin-2-one and the radically polymerizable bifunctional monomer and / or the radically polymerizable trifunctional monomer is preferably 75 to 100 mass %, more preferably 90 to 100 mass %, and particularly preferably 95 to 100 mass %, of the total amount of polymerizable compounds contained in the inkjet ink.

[0088] Furthermore, since the dispersion stability of carbon black and the ejection stability of inkjet ink can be improved without inhibiting the effects of 5-methyl-3-vinyloxazolidin-2-one described above, the mass of the other polymerizable compound contained is preferably 1 to 15, and particularly preferably 1.2 to 5, relative to the mass of 5-methyl-3-vinyloxazolidin-2-one contained as 1.

[0089] As described above, in the inkjet ink of this embodiment, the content of monofunctional polymerizable compounds other than 5-methyl-3-vinyloxazolidin-2-one is limited. Therefore, it is preferable that a radical polymerizable monofunctional monomer is not used as another polymerizable compound, or that the amount of the radical polymerizable monofunctional monomer used is not more than the above-mentioned amount (15% by mass, preferably 10% by mass, more preferably 6% by mass, and particularly preferably 3% by mass).

[0090] On the other hand, when a radically polymerizable monofunctional monomer is used as the other polymerizable compound, a (meth)acrylate having an alicyclic structure is preferably used because it improves the wetting and spreading of the inkjet ink on the printing substrate, resulting in improved curing properties, and it can prevent deterioration of the dispersion stability of carbon black. Specific examples of the (meth)acrylate having an alicyclic structure include cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl acrylate, 4-tert-butylcyclohexyl acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0091] <Photopolymerization initiator> The inkjet ink of this embodiment preferably contains a photopolymerization initiator that serves as a radical generating source. As the photopolymerization initiator, any one or more conventionally known compounds can be used. Specifically, acylphosphine oxide compounds, benzophenone compounds, indan compounds, thioxanthone compounds, hydroxyacetophenone compounds, alkylaminoacetophenone compounds, oxime ester compounds, etc. can be used.

[0092] The term "polymerization initiator" as used herein also includes materials that promote radical generation in other photopolymerization initiators, commonly referred to as sensitizers. Examples of such materials include aminobenzoate-based compounds, ketocoumarin-based compounds, and anthracene-based compounds.

[0093] Among these photopolymerization initiators, it is preferable to use one or more photopolymerization initiators selected from the group consisting of acylphosphine oxide compounds and thioxanthone compounds, and it is particularly preferable to use at least an acylphosphine oxide compound, because this allows the dispersion stability of carbon black to be maintained in a suitable state and the curability to be significantly improved.

[0094] Furthermore, from the viewpoint that an inkjet ink having particularly excellent curability and fineness of printed matter can be obtained, and furthermore, the inkjet ink has good ejection stability and carbon black dispersion stability, it is extremely preferable to use an acylphosphine oxide-based compound and a thioxanthone-based compound in combination as the photopolymerization initiator.

[0095] In one embodiment, from the viewpoint of significantly improving curability, it is preferable to use one or more photopolymerization initiators selected from the group consisting of acylphosphine oxide compounds and thioxanthone compounds in combination with one or more photopolymerization initiators selected from the group consisting of aminobenzoate compounds and ketocoumarin compounds.

[0096] <Acylphosphine oxide compounds> Specific examples of the acylphosphine oxide compound include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, as well as polymers of these compounds. Commercially available examples of acylphosphine oxide compounds include "Omnirad TPO," "Omnirad TPO-L," "Omnirad TPO-H," "Omnirad 819," and "OMNIPOL TP" manufactured by IGM Resins, and "Speedcure TPO," "Speedcure TPO-L," and "Speedcure BPO" manufactured by Lambson. In addition, for example, acylphosphine oxide compounds and lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate described in WO 2017 / 086224 and WO 2020 / 049378 can also be used. In the inkjet ink of this embodiment, the acylphosphine oxide compounds listed above may be used alone or in combination of two or more.

[0097] Among these compounds, ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and / or a polymer of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide can be preferably used because they have high affinity with 5-methyl-3-vinyloxazolidin-2-one and improve curability and ejection stability.

[0098] From the viewpoint of improving the curability and the definition of printed matter without deteriorating the discharge stability and the dispersion stability of carbon black, the content (total amount) of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and / or ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide polymer relative to the total amount of photopolymerization initiator contained in the inkjet ink of this embodiment is preferably 45 to 80 mass%, and particularly preferably 50 to 70 mass%. It should be noted that the expression "content (total amount)" above refers to the total amount of the contents of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and / or ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide polymers in the inkjet ink of the present embodiment when the inkjet ink contains two or more of these compounds, and refers to the content of only one compound in the inkjet ink when the inkjet ink contains only one compound.

[0099] When the inkjet ink of this embodiment contains an acylphosphine oxide compound, the blending amount of the acylphosphine oxide compound is preferably 4 to 15 mass %, and particularly preferably 5 to 12 mass %, of the total amount of the inkjet ink, from the viewpoint of obtaining an inkjet ink that is excellent in all of curability, ejection stability, and carbon black dispersion stability. Furthermore, from the viewpoint of obtaining an inkjet ink that is excellent in curability and ejection stability, the blending amount of the acylphosphine oxide compound is preferably 0.15 to 2, and particularly preferably 0.2 to 0.8, relative to the mass of 5-methyl-3-vinyloxazolidin-2-one.

[0100] <Thioxanthone compounds> Specific examples of the thioxanthone compounds include 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 3-methoxythioxanthone, 2-carboxymethoxythioxanthone, 3-ethoxycarbonylmethoxythioxanthone, 3-butoxycarboxymethoxythioxanthone, 1,3-dimethyl-2-(2-ethylhexyloxy)thioxanthone, 2-[2,2-bis(ethoxycarbonyl)]ethylthioxanthone, 1-chloro-4-propoxythioxanthone, and polymers of these compounds. Examples of commercially available thioxanthone compounds include "Omnirad ITX," "Omnirad DETX," and "OMNIPOL TX" manufactured by IGM Resins, "SPEEDCURE ITX," "SPEEDCURE 2-ITX," "SPEEDCURE DETX," "SPEEDCURE LTX," "SPEEDCURE CPTX," and "SPEEDCURE 7010" manufactured by Lambson, and "Genopol TX-2" manufactured by RAHN. Of these commercially available products, "OMNIPOL TX," "SPEEDCURE 7010," and "Genopol TX-2" are the above-mentioned multimers. In the inkjet ink of this embodiment, the above-listed thioxanthone compounds may be used alone or in combination of two or more.

[0101] When the inkjet ink of the present embodiment contains a thioxanthone compound, the blending amount of the thioxanthone compound is preferably 0.5 to 8 mass %, and particularly preferably 1 to 5 mass %, of the total amount of the inkjet ink, from the viewpoint of obtaining an inkjet ink that is excellent in all of curability, discharge stability, and carbon black dispersion stability.

[0102] As described above, the inkjet ink of this embodiment preferably uses an acylphosphine oxide compound and a thioxanthone compound in combination. In this case, from the viewpoint of achieving excellent curability and print definition, the mass of the acylphosphine oxide compound is preferably 1 to 25, and particularly preferably 2 to 12, relative to the mass of the thioxanthone compound. Furthermore, from the viewpoint of improving ejection stability in addition to curability and the definition of printed matter, when the sum of the mass content of the thioxanthone compound and the mass content of 5-methyl-3-vinyloxazolidin-2-one is taken as 1, the mass content of the acylphosphine oxide compound is preferably 0.1 to 1.0, and particularly preferably 0.2 to 0.85.

[0103] <Aminobenzoate compounds> Specific examples of the aminobenzoate compounds include methyl 2-(dimethylamino)benzoate, ethyl 4-(dimethylamino)benzoate, ethyl 4-(diethylamino)benzoate, 2-ethylhexyl 2-(dimethylamino)benzoate, 2-butoxyethyl 2-(dimethylamino)benzoate, bis-[(4-dimethylaminobenzoyl)oxyethylene-1-yl]-methylamine, and polymers of these compounds (e.g., polyethylene glycol-bis(methyl 4-dimethylaminobenzoate)). Examples of commercially available aminobenzoate compounds include "Omnirad EDB," "Omnirad EHA," "Esacure A198," and "Omnipol ASA" manufactured by IGM Resins; "SPEEDCURE EDB," "SPEEDCURE EHA," "SPEEDCURE BEDB," and "SPEEDCURE 7040" manufactured by Lambson; and "GENOPOL AB-1" and "GENOPOL AB-2" manufactured by Rahn AG. In the inkjet ink of this embodiment, the aminobenzoate compounds listed above may be used alone or in combination of two or more.

[0104] When the inkjet ink of this embodiment contains an aminobenzoate compound, the blending amount thereof is preferably 0.2 to 8 mass %, and particularly preferably 0.5 to 5 mass %, of the total amount of the inkjet ink.

[0105] <Ketocoumarin compounds> Specific examples of the ketocoumarin compound 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.

[0106] From the viewpoint of significantly improving the curability, it is suitable to use the ketocoumarin compounds listed above in combination with the acylphosphine oxide compounds described above (preferably ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and / or a polymer of the ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide).

[0107] When the inkjet ink of this embodiment contains a ketocoumarin compound, the blending amount thereof is preferably 1 to 10 mass %, and particularly preferably 2 to 8 mass %, of the total amount of the inkjet ink.

[0108] <Other photopolymerization initiators> Examples of commercially available photopolymerization initiators other than acylphosphine oxide compounds, thioxanthone compounds, and ketocoumarin compounds (also referred to as "other photopolymerization initiators" in this application) are shown below.

[0109] Examples of commercially available benzophenone compounds include "Omnirad BP," "Omnirad BMS," "Omnirad 4PBZ," "OMNIRAD EMK," and "Esacure 1001M," manufactured by IGM RESINS.

[0110] An example of a commercially available indane compound is "SpeedCure XFs01" manufactured by LAMBSON.

[0111] Examples of commercially available hydroxyacetophenone compounds include "Omnirad 127," "Omnirad 184," "Omnirad 1173," "Omnirad 2959," and "Esacure KIP150," all manufactured by IGM Resins.

[0112] Examples of commercially available alkylaminoacetophenone compounds include "Omnirad 907," "Omnirad 369," and "Omnirad 379," manufactured by IGM Resins.

[0113] Examples of commercially available oxime ester compounds include "IRGACURE OXE01," "IRGACURE OXE02," and "IRGACURE OXE04," manufactured by BASF.

[0114] An example of a commercially available product of the anthracene-based compound is "Anthracure UVS-581" manufactured by Kawasaki Kasei Chemical Industries, Ltd.

[0115] In addition to the above-listed photopolymerization initiators, for example, "Omnirad 651" and "Omnirad MBF" manufactured by IGM RESINS can also be used.

[0116] When the inkjet ink of this embodiment contains a photopolymerization initiator, the total amount of the photopolymerization initiator is preferably 3 to 20 mass %, more preferably 4 to 17 mass %, and particularly preferably 5 to 15 mass %, relative to the total amount of the inkjet ink. By keeping the total amount of the photopolymerization initiator within the above range, it is possible to achieve both curability and ejection stability.

[0117] <Other ingredients> In addition to the components described above, the inkjet ink of this embodiment may contain a surface conditioner, a polymerization inhibitor, an organic solvent, water, an inert resin, and other additives.

[0118] <Surface conditioner> The inkjet ink of this embodiment preferably contains a surface conditioner for the purpose of improving the wetting and spreading properties of the ink on the printing substrate, the print image quality including the definition of the printed matter, the substrate adhesion, and the ejection stability. Examples of usable surface conditioners include siloxane-based surface conditioners, fluorine-based surface conditioners, acetylene glycol-based surface conditioners, and acetylene monool-based surface conditioners. Among these, it is preferable to use a siloxane-based surface conditioner, from the viewpoint of improving the wetting and spreading properties of the ink on the printing substrate, the print image quality including the definition of the printed matter, the substrate adhesion, and the ejection stability without deteriorating the dispersion stability of the carbon black.

[0119] The siloxane-based surface conditioner may be, for example, a compound having a dimethylsiloxane structure and / or a modified product thereof. Among these, polyether-modified siloxane-based surface conditioners are particularly preferred. The use of a polyether-modified siloxane-based surface conditioner allows the ink that has landed on the printing substrate to be sufficiently wetted and spread without impeding the effects of 5-methyl-3-vinyloxazolidin-2-one. This allows for the ink to be cured, have good print quality (including the resolution of the printed matter), and have good substrate adhesion while maintaining favorable discharge stability and carbon black dispersion stability. Specific examples of the polyether group include a polyethylene oxide group and a polypropylene oxide group. Either one of these groups or both of these groups may be contained in the molecule as the polyether group.

[0120] Commercially available polyether-modified siloxane surface conditioners that can be preferably used include, for example, BYK (registered trademark)-378, 348, 349, 3420, 3760, BYK-UV3500, and UV3510 manufactured by BYK-Chemie; and TEGO (registered trademark) Glide 450, 440, 435, 432, 410, 406, 130, 110, and 100 manufactured by EVONIK.

[0121] When a siloxane-based surface conditioner is used, its content is preferably 0.1 to 5.0% by mass based on the total mass of the inkjet ink. By adjusting the content to 0.1% by mass or more, wetting and spreading properties on the printing substrate are improved, and print quality including the definition of the printed matter and adhesion are also improved. On the other hand, by adjusting the content to 5.0% by mass or less, it becomes easy to ensure curability, dispersion stability of carbon black, and ejection stability.

[0122] <Polymerization inhibitor>

[0043] In order to improve the ejection stability of the inkjet ink, and further improve the hue stability of the printed matter and suppress curing wrinkles, the inkjet ink of this embodiment may contain a polymerization inhibitor. Specific examples of the polymerization inhibitor include hindered phenol compounds, phenol compounds, hydroquinone compounds, phenothiazine compounds, phosphorus compounds, and nitrosophenylhydroxylamine compounds, and these can be suitably used.

[0123] More specific 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.

[0124] The content of the polymerization inhibitor is preferably 0.01 to 2 mass %, more preferably 0.05 to 1 mass %, and particularly preferably 0.1 to 0.8 mass %, based on the total mass of the inkjet ink. When the content is adjusted to the above range, it becomes easy to improve the ejection stability of the inkjet ink while maintaining the curability.

[0125] <Organic solvents, water> The inkjet ink of this embodiment may contain an organic solvent and / or water to reduce the viscosity of the inkjet ink, improve its wetting and spreading properties and adhesion to the printing substrate, and ensure ejection stability. When an organic solvent and / or water is contained, the content thereof is preferably 0.01 to 20% by mass, more preferably 0.05 to 10% by mass, and particularly preferably 0.1 to 5% by mass, based on the total mass of the inkjet ink. Furthermore, when an organic solvent is used, it is preferable to use an organic solvent with a boiling point of 140 to 300°C, from the viewpoints of ejection stability, wetting and spreading properties and adhesion to the printing substrate.

[0126] Examples of the organic solvent 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.

[0127] Among these, it is preferable to include at least one selected from the group consisting of alkylene glycol monoalkyl ethers, alkylene glycol dialkyl ethers, and alkylene glycol monoalkyl ether acetates. In particular, tripropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol dialkyl ether, ethylene glycol monobutyl ether acetate, and diethylene glycol diethyl ether are preferred. In one embodiment, the organic solvent preferably includes at least one selected from the group consisting of tetraethylene glycol dialkyl ether, ethylene glycol monobutyl ether acetate, and diethylene glycol diethyl ether.

[0128] <Inert resin> The inkjet ink of this embodiment may contain an inert resin for the purposes of imparting adhesion to various printing substrates and adjusting the viscoelasticity of the ink to improve ejection stability. Examples of inert resins that can be used include (meth)acrylic resins, urethane resins, vinyl chloride-vinyl acetate copolymer resins, and ketone resins. From the viewpoint of improving both adhesion and ejection stability, it is preferable that the inert resin contain a (meth)acrylic resin and / or a ketone resin.

[0129] When the inkjet ink of this embodiment contains an inert resin, the content thereof 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. When the content is adjusted to within the above range, adhesion and ejection stability can be easily improved without impairing curability.

[0130] In the present application, the term "inert resin" refers to a resin that does not participate in the polymerization reaction, contributes to adhesion to the printing substrate, and has solubility in inkjet ink.

[0131] Other additives The inkjet ink of this embodiment may further contain additives such as an ultraviolet absorber, an anti-fading agent, etc., in addition to the components described above, as necessary. Any conventionally known compounds can be used as these components.

[0132] <Physical properties of inkjet ink> From the viewpoint of improving ejection stability, the inkjet ink of this embodiment preferably has a viscosity at 25°C of 5 to 25 mPa·s, and more preferably 8 to 20 mPa·s. A viscosity of 5 mPa·s or higher allows the inkjet ink to be ejected smoothly from the inkjet head. A viscosity of 25 mPa·s or lower allows for continuous, stable ejection without a decrease in ejection accuracy. Furthermore, from the viewpoint of imparting high frequency suitability and enabling stable ejection even in high-speed printing, the viscosity is particularly preferably 8 to 14 mPa·s. The viscosity can be measured using 1.1 mL of inkjet ink and an E-type viscometer (for example, the TVE25L manufactured by Toki Sangyo Co., Ltd.) equipped with a cone (diameter: 48 mm) with a cone angle of 1°34' at 25°C and a rotation speed of 20 rpm.

[0133] From the viewpoint of improving all of the ejection stability, the resolution of printed matter, and the curing properties, the static surface tension of the inkjet ink at 25°C is preferably 20 to 45 mN / m, and particularly preferably 22 to 40 mN / m. The static surface tension is measured by the plate method (Wilhelmy method). Specifically, the static surface tension can be measured, for example, using an automatic surface tensiometer "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. and a platinum plate in an environment of 25°C.

[0134] <Inkjet ink manufacturing method> The inkjet ink of this embodiment can be produced by a conventionally known method, for example, as follows, but the method for producing the inkjet ink of this embodiment is not limited to the method described below.

[0135] First, a basic pigment dispersion resin is dissolved in a polymerizable compound to produce a basic pigment dispersion resin varnish. Next, carbon black satisfying the above-mentioned requirements is gradually added to the stirred basic pigment dispersion resin varnish and mixed. After mixing for a certain period of time, a dispersion treatment is carried out using a dispersing machine such as a paint shaker, sand mill, roll mill, or media-less disperser to produce a carbon black dispersion. To improve the dispersion stability of the carbon black, it is preferable to use a radically polymerizable bifunctional monomer and / or a radically polymerizable trifunctional monomer as the polymerizable compound used to produce the basic pigment dispersion resin varnish. It is particularly preferable to use a radically polymerizable bifunctional monomer represented by the above general formula (A) and / or a radically polymerizable trifunctional monomer represented by the above general formula (B).

[0136] Thereafter, 5-methyl-3-vinyloxazolidin-2-one, and, if necessary, a photopolymerization initiator, a surface conditioner, a polymerization inhibitor, an organic solvent, water, an inert resin, and other additives are added to the carbon black dispersion and thoroughly mixed. The mixture is then filtered using a filter or the like to remove coarse particles, thereby obtaining the inkjet ink of this embodiment.

[0137] The amount of carbon black present in the carbon black dispersion is preferably 10 to 50% by mass, more preferably 12 to 40% by mass, and particularly preferably 15 to 30% by mass.

[0138] <Inkjet printing method> The inkjet ink of the present embodiment is preferably used in an inkjet printing method, which preferably includes, in this order, a step (Step I) of ejecting the inkjet ink of the present embodiment from an inkjet head onto a printing substrate, and a step (Step II) of irradiating the inkjet ink ejected onto the printing substrate with active energy rays to cure the inkjet ink.

[0139] The inkjet printing method may employ a method in which the same inkjet ink is ejected and applied multiple times from the same inkjet head to the same location on the printing substrate, i.e., a method in which step I is performed multiple times to the same location on the printing substrate (multi-pass printing method). However, in the case of the inkjet printing method using the inkjet ink of this embodiment, from the viewpoint of fully utilizing the effects of the inkjet ink, such as excellent curing properties and ejection stability, and of obtaining printed matter quickly and stably, a method in which the same inkjet ink is ejected and applied only once from the same inkjet head to the same location on the printing substrate is preferred. In other words, it is preferred to employ a method in which step I is performed only once to the same location on the printing substrate (one-pass printing method).

[0140] The one-pass printing method can be carried out, for example, by using a line printer, etc. In this case, the printing speed (the conveying speed of the printing substrate) is preferably 35 to 150 m / min, more preferably 50 to 125 m / min, and even more preferably 75 to 100 m / min, from the viewpoints of productivity and obtaining printed matter with good quality.

[0141] The inkjet ink of this embodiment is an ink for inkjet printing, and therefore, as described above, an inkjet head is used as the inkjet ink ejection means in step I.

[0142] Methods of ejecting ink using an inkjet head include an electrostatic attraction method that uses electrostatic force to eject ink, a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink with the radiation pressure generated at that time to eject the ink, and a thermal inkjet method that heats the ink to form bubbles and ejects the ink using the generated pressure, etc. Among these, in one embodiment, from the viewpoint of ejection stability, the drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element can be preferably used.

[0143] From the viewpoint of print resolution and ejection stability, the drop volume of inkjet ink droplets ejected from the inkjet nozzle is preferably 1 to 50 pL (picoliters), more preferably 2 to 30 pL, and even more preferably 3 to 20 pL. The design resolution of the inkjet head is preferably 300 dpi or higher, more preferably 480 dpi or higher, and even more preferably 600 dpi or higher. dpi refers to the number of dots per 2.54 cm (1 inch).

[0144] Examples of inkjet heads that satisfy the above conditions include Kyocera KJ4A-AA, KJ4A-TA, and KJ4A-RH; Fujifilm Samba G3L; Seiko Epson S3200, S1600, S800, I3200, and I1600; Konica Minolta KM1024i and KM1024; and Ricoh MH5320, MH5340, MH5240, and MH5440, all of which can be suitably used.

[0145] In one embodiment, the inkjet ink can be heated by a heater or other heating device provided in the inkjet head so that the inkjet ink has an appropriate viscosity during ejection. From the viewpoint of continuously and stably ejecting the inkjet ink, the inkjet ink is preferably heated so that the viscosity of the inkjet ink during ejection is 15 mPa s or less, and more preferably 12 mPa s or less.

[0146] On the other hand, in the above step II, the inkjet ink ejected onto the printing substrate is cured by being irradiated with active energy rays, and a cured film (printed matter) is formed.

[0147] In the present application, "active energy rays" refers to energy rays that can provide the energy necessary to generate active species such as radicals, cations, anions, etc. in the irradiated object (inkjet ink). Specific examples of active energy rays include ultraviolet rays, electron beams, visible light, and infrared rays. However, it is preferable to select ultraviolet rays because they can easily improve the curability of the inkjet ink and provide a high degree of freedom in designing the inkjet ink and the printing device.

[0148] Furthermore, examples of light sources for the ultraviolet rays include high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, ultraviolet lasers, and LED lamps. Only one of these may be used, or two or more may be used in combination. For example, because the LED lamps are small, it is easy to arrange multiple LED lamps side by side, or to use them in combination with high-pressure mercury lamps or metal halide lamps, which can easily achieve further improvements in curing properties. Furthermore, when arranging multiple LED lamps side by side, multiple types of LED lamps with different peak emission wavelengths may be used in combination.

[0149] Generally, the ultraviolet light emitted from an LED lamp has a narrow wavelength range and is highly directional (i.e., poor diffusibility), making it difficult to cure actinic ray-curable inkjet inks. In particular, inkjet inks containing carbon black are considered difficult to cure with an LED lamp for the reasons mentioned above, namely, the absorption of ultraviolet light by the carbon black and the trapping of radicals by quinone groups on the surface of the carbon black. However, the inkjet ink of this embodiment has particularly excellent curability and can be suitably combined with an LED lamp.

[0150] In the inkjet printing method using the inkjet ink of this embodiment, when ultraviolet light is selected as the active energy ray and an LED lamp is used as the light source of the ultraviolet light, the peak wavelength of the ultraviolet light is preferably 260 to 450 nm, more preferably 280 to 420 nm, and particularly preferably 320 to 410 nm.

[0151] When an LED lamp that emits ultraviolet light is used in Step II, the maximum illuminance of ultraviolet light on the printing substrate is set to 1,000 mW / cm, from the viewpoint that the above-mentioned effects are fully exerted and prints with excellent print quality, including curing properties and print definition, can be obtained. 2 The maximum illuminance is preferably 2,000 mW / cm or more. 2 More preferably, it is 3,000 mW / cm or more. 2 The integrated amount of light irradiated onto the printing substrate varies depending on the type and content of the polymerizable compound and photopolymerization initiator contained in the inkjet ink, but is preferably 50 mJ / cm or more. 2 The integrated light amount is preferably 100 mJ / cm or more. 2 More preferably, it is 150 mJ / cm or more. 2 It is particularly preferable that the above amount is set to 100%.

[0152] In the above step I, after the inkjet ink droplets have adhered to the printing substrate (i.e., after the completion of the above step I), irradiation with active energy rays is initiated (i.e., the above step II is initiated). The time from the completion of step I to the start of step II is preferably adjusted to 0.03 to 3 seconds. The above time is more preferably 0.04 to 2.5 seconds, and even more preferably 0.6 to 2 seconds. By adjusting the above time within the above range, the dot formation properties of the inkjet ink are improved, and printed matter with excellent definition can be obtained.

[0153] In the inkjet printing method, step II can be repeated multiple times. For example, immediately after applying the inkjet ink to the printing substrate, the inkjet ink can be partially cured by irradiating it with active energy rays, and then the inkjet ink can be completely cured by irradiating it with active energy rays again. This makes it easy to obtain printed matter with exceptionally excellent print quality, including the fineness of the printed matter. In this application, the above-mentioned step of partially curing the inkjet ink is referred to as "pre-curing," and the step of completely curing the inkjet ink is referred to as "main curing."

[0154] That is, in one embodiment, an inkjet printing method using the inkjet ink of the present embodiment may include, in this order, a step of ejecting the inkjet ink from an inkjet head onto a printing substrate (step I), a step of irradiating the inkjet ink ejected onto the printing substrate with active energy rays to pre-cure the inkjet ink (step II-A), and a step of fully curing the inkjet ink (step II-B).

[0155] When carrying out the above step II-A, i.e., when provisionally curing the inkjet ink ejected onto the printing substrate, it is preferable to use an LED lamp that emits ultraviolet light. In this case, from the viewpoint of significantly improving the print quality, including the definition of the printed matter, the maximum illuminance of the ultraviolet light on the printing substrate during the provisional curing is 2 to 20 mW / cm. 2It is preferable that the intensity is 5 to 15 mW / cm 2 It is more preferable that:

[0156] Furthermore, when carrying out the above-mentioned step II-B, i.e., when fully curing the inkjet ink ejected onto the printing substrate, an LED lamp emitting ultraviolet light can also be used. In this case, the above-mentioned 1,000 mW / cm 2 Maximum illuminance of 50mJ / cm or more 2 It is preferable to use the above integrated light amount.

[0157] On the other hand, in step II-B, ultraviolet light can be irradiated using a high-pressure mercury lamp or a metal halide lamp. In this case, the maximum irradiance of the ultraviolet light is 80 mW / cm. 2 It is preferable to set the power to 120 mW / cm or more. 2 It is more preferable that the integrated light amount is 100 mJ / cm or more. 2 It is preferable to set the dose to 150 mJ / cm or more. 2 More preferably, it is 200 mJ / cm or more. 2 More preferably, it is set to the above.

[0158] <Printing base material> The printing substrate used in the printing method using the inkjet ink of this embodiment is preferably a resin film substrate or a paper substrate. The resin film substrate may preferably have a thickness of 10 to 90 μm. Furthermore, a substrate containing a material selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, and nylon is preferably selected as the resin film substrate. On the other hand, coated paper, art paper, laminated paper, etc. are preferably selected as the paper substrate. In one embodiment, the inkjet ink of this embodiment is preferably used for printing on packages formed from the above-listed printing substrates. Among the printing on such packages, it is particularly suitable for printing on food packaging.

[0159] The "substrate containing a material selected from the group consisting of polypropylene, polyethylene, polyethylene terephthalate, and nylon" is not limited to a single-layer structure and may 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 a resin film substrate (laminated film substrate) having two or more of the above layers. Furthermore, for the purpose of improving the strength of the package, blocking oxygen, etc., the layers constituting the laminated film substrate may include a layer made of AL (aluminum foil), VM (vacuum vapor deposition) film (aluminum vapor deposition film, transparent vapor deposition film), etc.

[0160] <Printed material> The inkjet ink of this embodiment can be used to produce a printed matter (a printing substrate on which print information is recorded). The above-mentioned inkjet printing method can be used as a method for producing the printed matter. [Example]

[0161] The present invention will be described in more detail below, but the following examples are not intended to limit the scope of the present invention. Unless otherwise specified, "parts" means parts by mass, and "%" means % by mass.

[0162] <Ingredients used> In the examples shown below, the carbon blacks used were those shown in Table 1. In Table 3 described later, the carbon blacks used are listed by abbreviation.

[0163] [Table 1]

[0164] In the examples shown below, the pigment dispersing resins shown in Table 2 below were used. In Table 3 described later, the pigment dispersing resins used are listed by abbreviation. Of the pigment dispersing resins shown in Table 2 below, all except Solsperse 41000 are basic pigment dispersing resins, and Solsperse 41000 is an acidic pigment dispersing resin (a pigment dispersing resin whose adsorption points with the pigment are acid groups).

[0165] [Table 2]

[0166] <Production of Carbon Black Dispersion> Carbon black dispersions 1 to 27 were produced using the raw materials listed in each column of Table 3 below. Specifically, a pigment dispersion resin and a polymerizable compound were first placed in a mixing vessel (volume 8 L) equipped with a stirrer and stirred for 1 hour (premixing) to produce a pigment dispersion resin varnish. Next, carbon black was added little by little to the stirred pigment dispersion resin varnish, and after the addition was completed, stirring was continued for another 1 hour (pre-dispersion). Subsequently, the mixture was circulated and dispersed for 2 hours using a Shinmaru Enterprises "Dynomill" (volume 0.6 L) filled with zirconia beads with a diameter of 0.8 mm to achieve a filling rate of 70%. Thus, a carbon black dispersion was produced.

[0167] [Table 3]

[0168] [Table 3]

[0169] [Table 3]

[0170] Table 3 also lists the secondary particle size and the pigment dispersion resin content relative to the carbon black content for carbon black dispersions 1 to 27 produced by the above-mentioned method. Details of the abbreviations used in Table 3 that are not listed in Tables 1 and 2 are as follows: HDDA: 1,6-hexanediol diacrylate DPGDA: Dipropylene glycol diacrylate NDDA: 1,9-nonanediol diacrylate

[0171] <Inkjet ink manufacturing> The materials listed in each column of Table 4 below were placed in a mixing vessel equipped with a stirrer. After all the materials were placed, the mixture was heated with stirring until the temperature of the mixture reached 40°C. After reaching 40°C, stirring was continued for an additional hour while maintaining the temperature. The mixture was then filtered through a membrane filter with a pore size of 0.8 μm to produce inkjet inks 1 to 96.

[0172] When producing the inkjet ink, each material was added while stirring the mixture in the mixing vessel. The order of adding the materials was carbon black dispersion, polymerizable compound other than 5-methyl-3-vinyloxazolidin-2-one, 5-methyl-3-vinyloxazolidin-2-one, photopolymerization initiator, polymerization initiator, and surface modifier. However, when producing an inkjet ink that did not contain one or more of these components, that component was not added, and the next component was added in the order listed. For components containing two or more materials, the order of adding the components was from largest to smallest.

[0173] [Table 4]

[0174] [Table 4]

[0175] [Table 4]

[0176] [Table 4]

[0177] [Table 4]

[0178] [Table 4]

[0179] [Table 4]

[0180] [Table 4]

[0181] [Table 4]

[0182] [Table 4]

[0183] Among the abbreviations used in Table 4, details of those not listed in Tables 1 to 3 are as follows: PDDA: 1,3-propanediol diacrylate BDDA: 1,4-butanediol diacrylate MPDDA: 3-methyl-1,5-pentanediol diacrylate GlyTA: Glycerin triacrylate Gly(EO)3TA: Ethylene oxide modified glycerin triacrylate (ethylene oxide group number: 3) Gly(EO)9TA: Ethylene oxide modified glycerin triacrylate (ethylene oxide group number: 9) CHA: Cyclohexyl acrylate IBXA: Isobornyl acrylate BzA: Benzyl acrylate VCL: N-vinylcaprolactam PEG400DA: Polyethylene glycol 400 diacrylate TMP(EO)3TA: Ethylene oxide modified trimethylolpropane triacrylate (ethylene oxide group number: 3) TMP(PO)2TA: Propylene oxide modified trimethylolpropane tri(meth)acrylate (number of propylene oxide groups: 2) MVOZ: 5-methyl-3-vinyloxazolidin-2-one TPO-L: Ethoxyphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (IGM Resins "Omnirad TPO-L") OmnTP: Ethoxyphenyl (2,4,6-trimethylbenzoyl) phosphine oxide polymer ("OMNIPOL TP" manufactured by IGM RESINS) Omn819: Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (IGM Resins "Omnirad 819") DETX: 2,4-diethylthioxanthone (IGM Resins "Omnirad DETX") OmnTX: Polymer of 3-ethoxycarbonylmethoxythioxanthone ("OMNIPOL TX" manufactured by IGM RESINS) Omn379: 2-(dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one (IGM Resins "Omnirad 379") ASA: Polyethylene glycol-bis(p-dimethylaminobenzoate) (IGM Resins "Omnipol ASA") BHT: 2,6-di-tert-butyl-4-methylphenol UV3510: Polyether-modified siloxane surface conditioner (BYK-UV3510 manufactured by BYK-Chemie)

[0184] <Production of printed materials> Using the inkjet ink prepared above, printed matter was produced by the method described below. A temperature-adjustable inkjet head (KJ4A, design resolution 600 dpi) manufactured by Kyocera was installed above the conveyor that transports the printing substrate. In addition, a main curing LED lamp (FirePower FP300 manufactured by Phoseon, maximum emission wavelength 395 nm, maximum illuminance 16,000 mW / cm) was installed downstream of the transport direction of the printing substrate. 2 )) was installed. The inkjet head was filled with the inkjet ink prepared above. The inkjet head temperature was then adjusted so that the inkjet ink viscosity during ejection was 6-7 mPa·s. A Lintec PET substrate (K2411) was then fixed onto a conveyor. The conveyor was driven at a speed of 50 m / min. When the PET substrate passed the inkjet head, inkjet ink droplets were ejected from the inkjet head to print. Specifically, a solid image with 100% coverage and a character image (random hiragana characters printed in MS Mincho font at 4-point, 6-point, and 8-point sizes, 20 of each) were printed under printing conditions of 11 pL droplet volume and 600 dpi x 600 dpi. After printing the inkjet ink, the conveyor was continued to run at the same speed. When the PET substrate passed the curing LED lamp, UV light was applied to produce a printed product. The irradiance of ultraviolet light irradiated on the inkjet ink after printing is 6,000mW / cm 2 , and the cumulative light intensity is 150 mJ / cm 2The output of the LED lamp was adjusted in advance so that the above printing was performed.

[0185] [Examples 1 to 87, Comparative Examples 1 to 9] The inkjet inks and printed materials produced by the above-described methods were used to carry out various evaluations according to the methods described below. The evaluation results are shown in Table 4.

[0186] <Evaluation 1: Evaluation of dispersion stability> For each of the above inkjet inks, the secondary particle diameter was measured immediately after production using the measuring device and method described above. Next, each inkjet ink was filled into a 20 mL glass container so that the filling rate was 80% of the container volume. The glass container filled with the inkjet ink was then sealed and shielded from light and left to stand at 60°C for two weeks, after which the secondary particle diameter of the inkjet ink after standing was measured again. The dispersion stability was evaluated by calculating the rate of increase in secondary particle diameter before and after standing. The evaluation criteria for the dispersion stability were as follows: a rating of "2" or higher was considered practical, and a rating of "3" or higher was considered practically suitable.

[0187] <Evaluation criteria for dispersion stability> 4: The increase in secondary particle size was less than 10% 3: The increase in secondary particle size was 10% or more but less than 20% 2: The increase rate of secondary particle size was 20% or more but less than 30% 1: The increase in secondary particle size was 30% or more

[0188] <Evaluation 2: Evaluation of ejection stability> Inkjet ink was filled into a jig equipped with a Kyocera temperature-adjustable inkjet head (KJ4A, design resolution 600 dpi). The temperature of the inkjet head was then adjusted so that the inkjet ink viscosity during ejection was 6-7 mPa·s. After confirming that there were no nozzles from which inkjet ink was not being ejected, inkjet ink was continuously ejected from all nozzles at a drive frequency of 20 kHz. After five minutes of continuous ejection, the number of nozzles from which inkjet ink was not being ejected (nozzle loss number) was counted to evaluate ejection stability. The evaluation criteria for the above ejection stability were as follows, and a rating of "2" or higher was considered to be practical. However, for the inkjet inks that were rated "1" in the dispersion stability evaluation described above, there was a high risk of damaging the inkjet head, so the ejection stability was not evaluated.

[0189] <Evaluation criteria for ejection stability> 4: The number of nozzle losses was 0 to 2 3: The number of nozzle losses was 3 to 5 2: The number of nozzle losses was 6 to 9 1: The number of nozzle losses was 10 or more

[0190] <Evaluation 3: Evaluation of curability> The surface of a printed material with a 100% solid image coverage produced using the above method was rubbed with a cotton swab to check whether any uncured ink adhered to the swab. If inkjet ink adhered to the swab, the printed material was fixed to the conveyor of the inkjet printing device and irradiated with the main curing LED lamp without printing any inkjet ink. The presence or absence of inkjet ink adhered to the cotton swab after rubbing was then checked again. This procedure was repeated, and the number of passes required until no uncured ink adhered to the cotton swab was counted to evaluate curability. The evaluation criteria for curability were as follows: A rating of "2" or higher was considered practical, and a rating of "3" or higher was considered practically suitable.

[0191] <Curability evaluation criteria> 4: After one pass (without requiring additional UV exposure), the swab is free of uncured ink. 3: After passing the swab twice (and irradiating it with UV light once more), the uncured inkjet ink no longer adhered to the swab. 2: After passing the swab three times (and irradiating it with UV rays two more times), the uncured inkjet ink no longer adhered to the swab. 1: It took at least four LED lamp exposures in total until the uncured ink on the cotton swab was no longer attached.

[0192] <Evaluation 4: Evaluation of print definition (character legibility)> The definition (character legibility) of the printed matter was evaluated by visually checking whether the hiragana characters in the character images created by the above method could be read. The definition evaluation criteria were as follows, with a rating of "2" or higher being considered usable, and a rating of "3" or higher being considered suitable for practical use.

[0193] <Evaluation criteria for print definition (text legibility)> 4: All 20 hiragana characters could be distinguished at 4-point, 6-point, and 8-point sizes. 3: All 20 hiragana characters could be distinguished in both 6-point and 8-point fonts, but some hiragana characters printed in 4-point font were indistinguishable. 2: All 20 hiragana characters could be distinguished in all 8-point fonts, but some hiragana characters printed in 6-point fonts could not be distinguished. Among the hiragana characters printed at 1:8 point, some were indistinguishable.

[0194] As shown in Table 4 above, the inkjet inks of Examples 1 to 87 having the above-described configuration were excellent in all of the dispersion stability of carbon black, ejection stability, curing properties, and definition of printed matter.

[0195] On the other hand, the inkjet inks of Comparative Examples 1 to 4, which used carbon black with a product (AC × SC) of DBP oil absorption (AC) and specific surface area (SC) greater than 12,000, did not achieve practically acceptable dispersion stability or ejection stability. Furthermore, the inkjet inks of Comparative Examples 3 and 4, which had particularly large values ​​for this product, achieved practically acceptable levels of curability and print definition, but did not achieve practically acceptable levels. In contrast, the inkjet inks of Examples 1 to 7, which used carbon black with a product value of 2,000 to 12,000, achieved practically acceptable dispersion stability and ejection stability, and also achieved practically acceptable levels of curability and print definition. These results confirm that controlling the value of this product is important for achieving the aforementioned effects.

[0196] Furthermore, the dispersion stability and ejection stability did not reach practical levels in Comparative Example 5, which used the acidic pigment dispersing resin Solsperse 41000, and Comparative Example 6, which used a basic pigment dispersing resin (DISPERBYK-180) with an acid value of more than 30 mgKOH / g. In these examples, the acid values ​​of the pigment dispersing resins used were too high, causing the acid groups in the pigment dispersing resin to react with the vinyl groups in 5-methyl-3-vinyloxazolidin-2-one, presumably resulting in a deterioration in the dispersion stability and ejection stability of the carbon black.

[0197] The inkjet ink of Comparative Example 7 was a system in which the content of monofunctional polymerizable compounds, excluding 5-methyl-3-vinyloxazolidin-2-one, was greater than 15% by mass, and evaluation confirmed that the curability did not reach a practically acceptable level. Furthermore, the resolution of the printed matter was at a practically acceptable level, but not at a level suitable for practical use.

[0198] Furthermore, the inkjet ink of Comparative Example 8, in which N-vinylcaprolactam, a typical example of an N-vinyl compound, was used instead of 5-methyl-3-vinyloxazolidin-2-one, did not achieve a practically acceptable level of dispersion stability, and the curability and print definition, while acceptable, were not at a practically acceptable level. Compared to the inkjet ink of Example 2, in which 5-methyl-3-vinyloxazolidin-2-one was used instead of N-vinylcaprolactam, the inkjet ink of Comparative Example 8 was significantly inferior in quality, confirming that 5-methyl-3-vinyloxazolidin-2-one is an essential ingredient in the inkjet ink of this embodiment.

[0199] Furthermore, the importance of 5-methyl-3-vinyloxazolidin-2-one in the inkjet ink of this embodiment was confirmed by the fact that the inkjet ink of Comparative Example 9, which did not contain 5-methyl-3-vinyloxazolidin-2-one, did not achieve practically acceptable levels of curability and fineness of printed matter.

Claims

1. An active energy ray-curable inkjet black ink comprising carbon black, a basic pigment dispersion resin, and a polymerizable compound, The DBP oil absorption of the carbon black is AC (mL / 100g), and the specific surface area of ​​the carbon black is SC (m 2 / g), the value represented by AC×SC is 2,000 to 12,000, the basic pigment dispersing resin has an acid value of 30 mgKOH / g or less, the polymerizable compound contains 5-methyl-3-vinyloxazolidin-2-one, an active energy ray-curable inkjet black ink, wherein the content of a monofunctional polymerizable compound (excluding the 5-methyl-3-vinyloxazolidin-2-one) is 15 mass % or less based on the total amount of the active energy ray-curable inkjet black ink;

2. the polymerizable compound contains a radically polymerizable bifunctional monomer represented by general formula (A), 2. The active energy ray-curable inkjet black ink according to claim 1, wherein the content of the radical polymerizable bifunctional monomer represented by general formula (A) is 15 to 55 mass % of the total amount of the active energy ray-curable inkjet black ink. General formula (A): CH 2 =CR 1 -CO-O-R 2 -O-CO-CR 1 =CH 2 (In general formula (A), R 1 represents a hydrogen atom or a methyl group, R 2 represents an alkylene group having 3 to 6 carbon atoms, which may have a branched structure.

3. the polymerizable compound contains a radical polymerizable trifunctional monomer represented by general formula (B), 3. The active energy ray-curable inkjet black ink according to claim 1, wherein the content of the radical polymerizable trifunctional monomer represented by general formula (B) is 2 to 15 mass % of the total amount of the active energy ray-curable inkjet black ink. General formula (B): 【Chemical 1】 (In general formula (B), R 3 represents a hydrogen atom or a methyl group, R 4 is an ethylene group or a propylene group. Furthermore, l, m, and n each represent an integer of 0 to 9, and l+m+n is an integer of 0 to 9.

4. Further, it contains a photopolymerization initiator, The actinic ray-curable inkjet black ink according to claim 1 , wherein the photopolymerization initiator comprises an acylphosphine oxide compound.

5. The actinic ray-curable inkjet black ink according to claim 4 , wherein the photopolymerization initiator further comprises a thioxanthone compound.

6. the acylphosphine oxide compound contains ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and / or a polymer of ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 6. The active energy ray-curable inkjet black ink according to claim 4, wherein the total content of the ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and the ethoxyphenyl(2,4,6-trimethylbenzoyl)phosphine oxide is 45 to 80 mass% of the total amount of the photopolymerization initiator.

7. 6. The actinic ray-curable inkjet black ink according to claim 1, wherein the carbon black has a pH of 2 to 5.

8. A printed matter obtained by printing the actinic ray-curable inkjet black ink according to claim 1, 2, 4 or 5 on a printing substrate.

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