Aqueous inkjet ink and printed matter

Abstract

An aqueous inkjet ink according to the present invention comprises: pigment particles including a pigment and a pigment dispersion resin coating at least a portion of the surface of the pigment; an acetylenediol-based surfactant (B-1) having a measured HLB value of 6-9; a siloxane-based surfactant (B-2); an alkanediol having 3 or 4 carbon atoms; an alkanediol having 5-8 carbon atoms; and a glycol ether having 4-10 carbon atoms. The pigment dispersion resin includes a crosslinked product of a polymer (A-1) having an aromatic ring and an acid group and an acid value of 50-160 mg KOH / g, and a compound (A-2) having multiple glycidyl ether groups in one molecule. The blended amount of compound (A-2) is such that glycidyl group content is 50-200 mol%.

Description

Water-based inkjet inks and printed materials

[0001] This disclosure relates to water-based inkjet inks and printed materials produced using said water-based inkjet inks.

[0002] Inkjet printing, a type of digital printing method, involves firing and landing tiny droplets of ink from an inkjet head onto a printing substrate to form images and / or characters. In recent years, the demand for small-lot printing has increased, accelerating the adoption of digital printing methods. Because digital printing does not require printing plates, it enables the miniaturization of printing equipment and the ability to handle small-lot orders. Furthermore, inkjet printing is superior to other digital printing methods in terms of printing equipment size and cost, running costs during printing, and ease of full-color printing.

[0003] In general, inks used in inkjet printing (referred to as "inkjet inks" in this disclosure) are classified into solvent-based, water-based, and ultraviolet (UV) curing types, depending on their composition. In recent years, there has been a movement to regulate the use of raw materials that are harmful to humans and the environment. Accordingly, there is a shift towards water-based inkjet inks (also referred to as "water-based inkjet inks" in this disclosure) rather than solvent-based or ultraviolet (UV) curing inkjet inks, which use raw materials that pose a high risk of pollution and exposure to humans and the environment.

[0004] In recent years, inkjet inks have become increasingly popular not only for office and home use, but also for commercial and industrial printing. When designing water-based inkjet inks for commercial printing, it is preferable to use pigments as colorants to improve print density, lightfastness, and abrasion resistance. However, conventional water-based inkjet inks have faced challenges in stably dispersing pigments. Furthermore, when the liquid component of the ink evaporates near the nozzle of the inkjet head, the dispersion of the pigment is disrupted, and solidified material adheres to the nozzle, resulting in problems such as incorrect ejection perpendicular to the nozzle surface (deterioration of ejection straightness) or inability to continuously eject stably (deterioration of continuous ejection stability). Naturally, inability to eject stably leads to a decrease in print density and print quality of the printed material.

[0005] Furthermore, when printing with water-based inkjet inks on paper substrates, which are primarily used for commercial printing, it is assumed that the liquid component of the water-based inkjet ink will penetrate into the paper substrate. Therefore, when printing with water-based inkjet inks on paper substrates that do not penetrate well, such as coated paper, beading is likely to occur, making it difficult to produce printed materials with practically acceptable print quality. Beading is a phenomenon in which adjacent droplets of water-based inkjet ink merge when they land adjacent to each other on the printing substrate before the ink droplets have penetrated the substrate and dried. When beading occurs, it results in color bleeding and leads to a decrease in print quality.

[0006] One way to improve the beading described above is to increase the drying speed of the water-based inkjet ink. In this case, the first droplet of water-based inkjet ink to land on the printing substrate will need to dry before the next droplet lands. However, highly drying water-based inkjet inks tend to dry easily near the nozzle, increasing the risk of the aforementioned adhesion. As mentioned above, if solidified water-based inkjet ink adheres near the nozzle, it leads to a deterioration in the straightness of the ejection and the stability of continuous ejection. Thus, in designing water-based inkjet inks for printing on poorly absorbent printing substrates, achieving both image quality and straightness of ejection and stability of continuous ejection is an extremely difficult challenge.

[0007] Another possible strategy to increase the drying speed of water-based inkjet ink is to add a certain amount of surfactant, for example, to wet and spread the ink on the printing substrate, thereby increasing the surface area of ​​the ink droplets. However, in this case, depending on the printing conditions and the printing substrate used, the shape of the droplets (dot shape) after drying may become irregular (the roundness of the dots deteriorates). Irregular dot shapes can lead to poor visibility when printing fine characters, for example, and thus to a deterioration in print quality.

[0008] On the other hand, when printing with water-based inkjet ink on highly permeable paper substrates such as fine paper, the components contained in the water-based inkjet ink, mainly the liquid components, penetrate into the paper substrate. In this process, the pigments in the water-based inkjet ink also penetrate, which can lead to a decrease in print density.

[0009] In particular, when printing on both poorly permeable and permeable printing substrates using the same water-based inkjet ink, it is necessary to solve all of the above-mentioned problems simultaneously, which has been extremely difficult with conventional technology.

[0010] Japanese Patent Publication No. 2015-124238, Japanese Patent Publication No. 2014-224248, Japanese Patent Publication No. 2003-268279

[0011] As an example of studies on aqueous inkjet inks that can print on various types of printing substrates, Patent Document 1 discloses an inkjet recording ink composition containing three types of acetylenediol-based surfactants with different structures. It is also stated that by using the above ink composition, images with excellent print quality (color unevenness, aggregation, bleeding) and fixation (scratchy resistance) can be recorded at high speed on various printing substrates with different absorbencies. On the other hand, when the above ink composition is used on a permeable printing substrate, the pigment components may penetrate into the printing substrate due to the effect of the surfactant on the reduction of the surface tension of the ink composition, which may reduce the print density. Furthermore, the present inventors have found that the ink composition specifically disclosed in the examples of Patent Document 1 may have problems with continuous ejection stability depending on the printing conditions, etc.

[0012] Patent Document 2 discloses an aqueous inkjet ink containing a high-acid-value vinyl polymer as a shear-thickening agent. It is also stated that by using a certain amount of the vinyl polymer, printed materials with excellent print quality and abrasion resistance can be produced not only on highly hydrophobic, poorly penetrating substrates but also on highly permeable printing substrates, and that ejection stability is also good. On the other hand, vinyl polymers with high acid values ​​have many acid groups in their molecules. As a result, the intermolecular interactions formed by these acid groups affect viscoelasticity, and depending on the printing conditions, ejection straightness and continuous ejection stability may deteriorate. Furthermore, the aqueous inkjet ink specifically disclosed in the examples of Patent Document 2 does not contain surfactants. Therefore, depending on the poorly penetrating substrate used, the print quality may not necessarily improve.

[0013] Patent Document 3 discloses an aqueous inkjet ink for offset printing, comprising a surfactant and an aprotic polar solvent having a specific molecular weight. In the examples of Patent Document 3, printing is performed on various coated papers as well as recycled paper (paragraphs 0035, 0039). On the other hand, Patent Document 3 does not evaluate the ejection stability, and when the present inventors reproduced the aqueous inkjet ink having the composition of surfactant and organic solvent specifically disclosed in the examples of Patent Document 3, it was confirmed that the continuous ejection stability may deteriorate depending on the printing conditions.

[0014] As described above, until now, there has been no water-based inkjet ink that can produce printed materials with excellent print density and print quality on various ink-printing substrates while maintaining optimal continuous ejection stability and ejection straightness.

[0015] The present invention was made to solve the above-mentioned problems, and its objective is to obtain an aqueous inkjet ink that has excellent continuous ejection stability and ejection straightness, excellent print density and print quality of printed materials on various printing substrates, especially paper substrates, and also good resolubility.

[0016] Based on the above background, the inventors conducted diligent research and discovered an aqueous inkjet ink having the following configuration, thus completing the present invention.

[0017] In other words, one embodiment of the present invention relates to the aqueous inkjet inks shown in [1] to [4] below. Another embodiment of the present invention relates to printed materials using the above aqueous inkjet inks, as shown in [5] below. However, the present invention is not limited to the following embodiments and includes various embodiments that are modified without changing the essential parts of the present invention. [1] An aqueous inkjet ink comprising pigment particles, a surfactant, and an organic solvent, wherein the pigment particles comprise a pigment and a pigment dispersion resin that coats at least a portion of the surface of the pigment, the pigment dispersion resin comprises a crosslinked product of a polymer (A-1) having aromatic rings and acidic groups and an acid value of 50 to 160 mgKOH / g and a compound (A-2) having multiple glycidyl ether groups in one molecule, the surfactant comprises an acetylenediol-based surfactant (B-1) and a siloxane-based surfactant (B-2) with an measured HLB value of 6 to 9, and the organic solvent comprises an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms, and the glycidyl group content represented by the following formula (1) is 50 to 200 mol%. Formula (1): [2] The aqueous inkjet ink according to [1], wherein the siloxane-based surfactant (B-2) comprises a gemini-type siloxane-based surfactant. [3] The aqueous inkjet ink according to [1] or [2], wherein the alkanediol having 5 to 8 carbon atoms comprises an alkanediol that includes a branched alkyl group and is not a 1,2-alkanediol. [4] The aqueous inkjet ink according to any one of [1] to [3], wherein the glycol ether having 4 to 10 carbon atoms comprises at least one selected from the group consisting of propylene glycol monoalkyl ether having 3 to 4 carbon atoms in the alkyl group at the molecular terminus, and dipropylene glycol monoalkyl ether having 3 to 4 carbon atoms in the alkyl group at the molecular terminus. [5] A printed article obtained by printing the aqueous inkjet ink according to any one of [1] to [4] on a printing substrate.

[0018] One embodiment of the present invention, an aqueous inkjet ink, exhibits excellent continuous ejection stability and straight ejection, provides excellent print density and print quality for various printing substrates, particularly paper substrates, and also exhibits good resolubility.

[0019] The following describes an embodiment of the present invention: an aqueous inkjet ink (hereinafter simply referred to as "the aqueous inkjet ink of this embodiment"). It should be noted that the present invention is not limited to the embodiments described below, and includes modified forms that do not alter the essential parts of the present invention.

[0020] The aqueous inkjet ink of this embodiment exhibits excellent resolubility, continuous ejection stability, and ejection straightness, and also provides excellent print density and print quality for various printing substrates, particularly paper substrates. Although the mechanism is not clear, the inventors speculate as follows. However, the present invention is not limited by the following speculation.

[0021] The aqueous inkjet ink of this embodiment contains a crosslinked product of a polymer (A-1) having aromatic rings and acidic groups and an acid value of 50 to 160 mg KOH / g, and a compound (A-2) having multiple glycidyl ether groups in one molecule, as a pigment dispersion resin that coats at least a portion of the surface of the pigment. Since aromatic rings are easily adsorbed to pigments, the crosslinked product effectively stabilizes the dispersion state of the pigment. In addition, the acidic groups present in the polymer cause charge repulsion in the aqueous inkjet ink. Therefore, when the pigment is dispersed using the polymer (A-1) having the above acid value (i.e., before the crosslinking reaction), the dispersion state of the pigment can be stabilized. On the other hand, when the polymer (A-1) is crosslinked using the compound (A-2) having multiple glycidyl ether groups in one molecule, the glycidyl ether groups in the compound (A-2) react with the acidic groups. This would reduce the number of acid groups in the crosslinked product, meaning the acid value of the crosslinked product would decrease, potentially negatively affecting the dispersion of pigment particles. In response to this, the aqueous inkjet ink of this embodiment further utilizes an acetylenediol-based surfactant (B-1) with a measured HLB value of 6 to 9, an alkanediol with 5 to 8 carbon atoms, and a glycol ether with 4 to 10 carbon atoms to stabilize the dispersion of pigment particles and avoid the aforementioned adverse effects (details will be described later).

[0022] Furthermore, in the pigment-dispersed resin after crosslinking, bonds derived from acid groups in polymer (A-1) (for example, ester bonds if the acid group is a carboxyl group), and hydroxyl groups and ether bonds derived from glycidyl ether groups in compound (A-2) are located in close proximity to each other. On the other hand, paper substrates generally contain polyvalent metal salts derived from fillers, pigments, sizing agents, etc. Therefore, when the aqueous inkjet ink of this embodiment is printed on such a paper substrate, it is thought that interactions occur between the polyvalent metal ions derived from the polyvalent metal salts and the above bonds, hydroxyl groups, and ether bonds. As a result, even when printing on a highly permeable paper substrate, for example, the aqueous inkjet ink becomes less likely to penetrate into the interior of the paper substrate, and the print density of the printed material is improved.

[0023] On the other hand, with respect to the polymer (A-1) and compound (A-2) mentioned above, the aqueous inkjet ink of this embodiment satisfies the requirement that the glycidyl group content represented by formula (1) is 50 to 200 mol%. Because the glycidyl group content is within the above range, a sufficient amount of crosslinked structure is formed, which suppresses the desorption of the pigment dispersion resin from the pigment, and maintains dispersion stability even after some of the liquid components in the aqueous inkjet ink have evaporated.

[0024] Here, we will explain resolubility. As mentioned above, one of the factors causing ejection failures in water-based inkjet inks is the adhesion of water-based inkjet ink near the nozzle. To prevent ejection failures, it is important that the water-based inkjet ink has resolubility, meaning that even if some of the water-based inkjet ink adheres, the adhered material can be redissolved. As a result of our research, we have found that resolubility can be improved by designing the water-based inkjet ink so that the pigment dispersion resin does not detach from the pigment even after some of the liquid components in the inkjet ink have evaporated.

[0025] In one embodiment of the aqueous inkjet ink, as described above, a pigment is used in which at least a portion of the surface is coated with a pigment dispersion resin that has been crosslinked using compound (A-2) so that the glycidyl group content is 50 to 200 mol%. This suppresses the desorption of the pigment dispersion resin and leads to improved resolubility.

[0026] Next, we will explain the print quality. Print quality is greatly affected by the surface tension of the water-based inkjet ink. Furthermore, surfactants are a factor that determines the surface tension of water-based inkjet ink. The inventors have investigated and found that in the water-based inkjet ink of this embodiment, the print quality of printed materials using the above water-based inkjet ink is greatly improved by using in combination an acetylenediol-based surfactant (B-1) with a measured HLB value of 6 to 9 and a siloxane-based surfactant (B-2). The acetylenediol-based surfactant (B-1) with a measured HLB value of 6 to 9 has high hydrophobicity and quickly orients at the interface, but with the acetylenediol-based surfactant (B-1) alone, the wettability to the printing substrate and the dot roundness are not sufficiently good, making it difficult to obtain printed materials with high print quality. On the other hand, although the siloxane-based surfactant (B-2) orients at the interface more slowly than the acetylenediol-based surfactant (B-1), it is an effective material for improving the wettability and dot roundness. In contrast to these, the aqueous inkjet ink of this embodiment achieves improved print quality by using both in combination. The presumed mechanism is that the siloxane-based surfactant (B-2) functions to emulsify the acetylenediol-based surfactant (B-1). In other words, it is thought that the siloxane-based surfactant (B-2) rapidly orients at the interface together with the acetylenediol-based surfactant (B-1), resulting in a significant improvement in wettability to the printing substrate and dot roundness.

[0027] Furthermore, as described above, in the aqueous inkjet ink of this embodiment, the desorption of pigment dispersion resin from the pigment is thought to be suppressed. This prevents the phenomenon in which surfactants are adsorbed onto the desorbed pigment dispersion resin, thereby inhibiting the orientation of the surfactants at the interface. As a result, each surfactant can fully exhibit the functions described above, and the print quality of printed materials can be easily improved.

[0028] Incidentally, the measured HLB value of the above siloxane surfactant (B-2) is preferably from 1 to 8. Further, as the above siloxane surfactant (B-2), gemini-type siloxane surfactants, side-chain polyether-modified siloxane surfactants, both-terminal polyether-modified siloxane surfactants and the like can be preferably used.

[0029] On the other hand, in an aqueous inkjet ink simply combining a pigment at least partially coated on the surface with the above pigment dispersion resin having a crosslinked structure, an acetylene diol surfactant (B-1), and a siloxane surfactant (B-2), there is a risk that the ejection straightness deteriorates. Further, when ejection is continued in a state where the ejection straightness has deteriorated, the aqueous inkjet ink may deposit on a part of the nozzle opening portion. When this deposit increases or dries up, the nozzle opening (a part thereof) may be blocked, making stable ejection impossible, that is, there is also a risk that the continuous ejection stability deteriorates.

[0030] Incidentally, "good ejection straightness" means that the aqueous inkjet ink is ejected in a direction perpendicular to the nozzle surface, and "poor ejection straightness" means that the aqueous inkjet ink is ejected in a direction oblique to the above nozzle surface, respectively.

[0031] One of the reasons for the deterioration of ejection straightness is considered to be poor compatibility between constituent materials. Pigment particles at least partially coated with a pigment dispersion resin having a crosslinked structure have low compatibility with highly hydrophobic surfactants such as acetylene diol-based surfactants (B-1). Therefore, it is considered that acetylene diol-based surfactants (B-1) and siloxane-based surfactants (B-2) are unlikely to be uniformly oriented on the interface of the aqueous inkjet ink present near the nozzle opening. In such a state, the aqueous inkjet ink is not ejected stably straight, and it is considered that droplets of the aqueous inkjet ink are less likely to land on the position where they should originally land on the printing substrate (the landing accuracy deteriorates). Also, depending on the siloxane-based surfactant (B-2) used in combination, the above-described emulsification state may also be destabilized, and there is a possibility that sufficient improvement in print quality cannot be achieved. On the other hand, as described above, in order to obtain a printed matter with excellent print quality, it is essential to use a combination of a highly hydrophobic acetylene diol-based surfactant (B-1) and a siloxane-based surfactant (B-2).

[0032] As a result of intensive studies by the present inventors, it has been found that an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms are further used in combination with the above-described components. Although the detailed mechanism is unknown, it is considered that the compatibility between the pigment particles and the highly hydrophobic surfactant is improved by the combined use of an alkanediol having 5 to 8 carbon atoms and a glycol ether having 4 to 10 carbon atoms. And by this, it is considered that the acetylene diol-based surfactant (B-1), and further the siloxane-based surfactant (B-2) are uniformly oriented on the interface, and the ejection straightness, continuous ejection stability, etc. are improved. Also, the improvement of the above compatibility is effective for stabilizing the dispersion state of the pigment particles.

[0033] In addition, as the alkanediol having 5 to 8 carbon atoms, it is preferable to use an alkanediol that contains a branched alkyl group and is not a 1,2-alkanediol. Since it has a structure similar to that of the acetylene diol-based surfactant (B-1) and has a high affinity, it is considered to particularly effectively contribute to the improvement of the above compatibility.

[0034] Furthermore, in the aqueous inkjet ink of this embodiment, in addition to alkanediols having 5 to 8 carbon atoms and glycol ethers having 4 to 10 carbon atoms, alkanediols having 3 to 4 carbon atoms are also used in combination. Since alkanediols having 5 to 8 carbon atoms and glycol ethers having 4 to 10 carbon atoms do not necessarily have high affinity for water, these components may be a factor in the deterioration of continuous ejection stability, or the stabilization of the emulsion state described above may be insufficient, potentially leading to deterioration of ejection straightness, print quality, etc. Therefore, by using alkanediols having 3 to 4 carbon atoms, which have high affinity for water, the components with poor affinity for water are stabilized within the aqueous inkjet ink, thereby improving continuous ejection stability, ejection straightness, print quality, etc.

[0035] As mentioned above, the water-based inkjet ink of this embodiment has excellent resolubility. That is, it is easy to redissolve the dried film that has adhered to the nozzle opening in the water-based inkjet ink. From this viewpoint as well, the water-based inkjet ink of this embodiment has excellent straight-line ejection and continuous ejection stability.

[0036] As described above, the water-based inkjet ink of this embodiment is essential for solving the aforementioned problems simultaneously and at a high level.

[0037] Next, the components that may be included in one embodiment of the water-based inkjet ink will be described in detail below.

[0038] <Pigment Particles> The aqueous inkjet ink of this embodiment contains pigment particles. The pigment particles also contain a pigment and a pigment dispersion resin that coats at least a portion of the surface of the pigment. Furthermore, the pigment dispersion resin contains a crosslinked product of a polymer (A-1) having an aromatic ring and an acid group and an acid value of 50 to 160 mg KOH / g and a compound (A-2) having multiple glycidyl ethers in one molecule.

[0039] In this disclosure, "the pigment dispersion resin comprises a crosslinked product of polymer (A-1) and compound (A-2) having multiple glycidyl ether groups in one molecule" means that a crosslinked structure is formed between the polymer (A-1) molecules. The formation of a crosslinked structure between polymer (A-1) molecules results in the pigment being coated on at least a portion of its surface by the crosslinked pigment dispersion resin, thereby achieving the suppression of desorption of the pigment dispersion resin, improved resolubility, and enhanced print quality described above. Note that polymer (A-1) may have a crosslinked structure within its own molecule.

[0040] In this disclosure, "coating" refers to a state in which the surface of a pigment is covered with a pigment dispersion resin. However, "coating" also includes states in which only a portion of the surface of the pigment is covered, in addition to states in which the surface of the pigment is completely covered. Furthermore, in this disclosure, when the term "acid group" is used, it is used as a general term to refer to both non-anionized acid groups (e.g., carboxyl groups, sulfo groups, etc.) and anionized acid groups (e.g., carboxylate groups, sulfonate groups, etc.).

[0041] <Pigments> The pigment particles contained in the aqueous inkjet ink of this embodiment contain pigments. Printed materials made using the aqueous inkjet ink containing pigments have a high concentration. Furthermore, by coating at least a portion of the pigment surface with the above-mentioned pigment dispersion resin and using it in combination with the above-mentioned surfactant and organic solvent, printed materials with excellent print quality can be obtained.

[0042] In the aqueous inkjet ink of this embodiment, organic pigments or inorganic pigments may be used as the pigments. Both may also be used in combination.

[0043] When using inorganic pigments, titanium dioxide, zinc oxide, zinc sulfide, lead white, calcium carbonate, precipitated barium sulfate, white carbon, alumina white, kaolin gray, talc, bentonite, carbon black, black iron oxide, cadmium red, red iron oxide, molybdenum red, molybdate orange, chrome vermilion, yellow lead, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, viridian, titanium cobalt green, cobalt green, cobalt chrome green, Victoria green, ultramarine, dark blue, cobalt blue, cerulean blue, cobalt silica blue, cobalt zinc silica blue, manganese violet, cobalt violet, etc. can be used.

[0044] For example, when using carbon black as an inorganic pigment, carbon black produced by either the furnace method or the channel method can be suitably used. Furthermore, these carbon blacks have a primary particle size of 11 to 40 nm and a specific surface area of ​​50 to 400 m² as measured by the BET method. ２ Carbon black having characteristics such as a weight per gram, a volatile content of 0.5 to 10%, and a pH value of 2 to 10 can be used particularly suitably.

[0045] On the other hand, specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolon pigments, and slene pigments. Furthermore, the hue is not particularly limited, and chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used.

[0046] Specifically, examples of pigments that can be used as organic pigments, as shown in the color index, include C.I. Pigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, 64, etc., for cyan and blue pigments.

[0047] Furthermore, examples of red and violet pigments include C.I. Pigment Red 2, 5, 7, 9, 12, 31, 48, 49, 52, 53, 57, 97, 112, 120, 122, 146, 147, 149, 150, 168, 170, 177, 178, 179, 184, 188, 202, 206, 207, 209, 238, 242, 254, 255, 264, 269, 282, and C.I. Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, 50, etc.

[0048] In addition, examples of yellow pigments include C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, and 213.

[0049] Examples of black pigments include aniline black (C.I. Pigment Black 1), perylene black (C.I. Pigment Black 31, 32), and azomethine azoblack. Furthermore, multiple chromatic pigments such as the above-mentioned blue, red, violet, and yellow pigments, as well as the brown and orange pigments listed below, can be mixed and used as black pigments.

[0050] Other pigments not listed above include C.I. Pigment Green 7, 10, 36, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, etc.

[0051] The pigments listed above can be used individually or in combination of two or more. The pigment content is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 7% by mass, relative to the total mass of the aqueous inkjet ink.

[0052] <Pigment Dispersion Resin> The above-mentioned pigment dispersion resin is a resin that has the function of dispersing pigments. In the case of the aqueous inkjet ink of this embodiment, a crosslinked product of a polymer (A-1) having aromatic rings and acidic groups and an acid value of 50 to 160 mgKOH / g and a compound (A-2) having multiple glycidyl ether groups in one molecule is used as the pigment dispersion resin. In the aqueous inkjet ink of this embodiment, any resin that has the function of dispersing pigments can be used as the pigment dispersion resin together with the crosslinked product.

[0053] ≪Polymer (A-1)≫ As described above, polymer (A-1) has acid groups in its molecular structure. Furthermore, it is preferable that acid groups remain in the molecular structure of the crosslinked reaction product. Moreover, in both polymer (A-1) and the crosslinked reaction product, the above-mentioned acid groups are carboxyl groups, carboxylate groups (R-COO － ), or a combination thereof is even more preferable.

[0054] The acid value of polymer (A-1) is preferably 50 to 160 mg KOH / g, more preferably 60 to 140 mg KOH / g, and more preferably 80 to 130 mg KOH / g, from the viewpoint of further improving resolubility and print quality by significantly suppressing the detachment of polymer (A-1) from the pigment. Furthermore, it may be 90 to 125 mg KOH / g.

[0055] Furthermore, if acid groups remain in the crosslinked reaction product, the compatibility with acetylenediol-based surfactant (B-1) is enhanced, and from the viewpoint of improving continuous discharge stability and discharge straightness, the acid value of the crosslinked reaction product is preferably 10 to 90 mg KOH / g, and particularly preferably 15 to 70 mg KOH / g.

[0056] The acid value of polymer (A-1) can be measured by a conventional method. For example, approximately 1 g of polymer (A-1) that has been pre-treated with acid precipitation is accurately weighed into an Erlenmeyer flask, and 50 ml of a 1 / 9 (mass ratio) mixture of distilled water / dioxane is added to dissolve the polymer (A-1). This sample solution is titrated with a 0.1 mol / L potassium hydroxide-ethanol solution (titer F). A potentiometric analyzer (for example, the "AT-710M" potentiometric automatic titrator manufactured by Kyoto Electronics Manufacturing Co., Ltd.) is used for the titration. The acid value (mg KOH / g) can then be determined from the following formula (2) using the amount of potassium hydroxide-ethanol solution required to reach the titration endpoint (let's call it α (mL)).

[0057] Formula (2): Acid value (mgKOH / g) = (5.611×α×F) / S

[0058] In formula (2), S is the amount (g) of the sample polymer (A-1), α is the amount (ml) of 0.1 mol / L potassium hydroxide-ethanol solution added dropwise to the titration endpoint, and F is the titer of the 0.1 mol / L potassium hydroxide-ethanol solution.

[0059] On the other hand, as will be described later, water-soluble resins and water-insoluble resins are generally used as resins in water-based inkjet inks. In this embodiment, either a water-soluble resin or a water-insoluble resin may be used as the polymer (A-1). Similarly, the crosslinked reaction product may be either a water-soluble resin or a water-insoluble resin. Therefore, for example, the crosslinked reaction product obtained by crosslinking a water-soluble polymer (A-1) may take the form of a water-insoluble resin. Alternatively, for example, a crosslinked reaction product obtained by crosslinking a water-insoluble polymer (A-1) (which, of course, is in the form of a water-insoluble resin) can be used.

[0060] This document describes a method for determining whether a resin contained in an aqueous inkjet ink functions as a pigment dispersion resin. For example, in an aqueous inkjet ink, a resin that covers at least a portion of the surface of a pigment is a resin that has the function of dispersing the pigment, i.e., a pigment dispersion resin. In this case, if the resin does not have a cross-linking structure between its molecules, the resin is a polymer (A-1), and if it does have a cross-linking structure, the resin is a cross-linked reaction product.

[0061] On the other hand, if, for example, a water-soluble resin is used as the polymer (A-1), and the adsorption and desorption from the pigment surface are in equilibrium, it is possible to confirm whether the water-soluble resin has the function of dispersing the pigment by a method in accordance with JIS K 5101-1-4:2004.

[0062] Specifically, the primary particle size is 15-25 nm, and the nitrogen adsorption specific surface area is 120-260 m². ２ / g, DBP absorption amount (granular) 40-80cm ３ 600g of carbon black (at 100g / g), 200g of the target resin, and 2,200g of water are thoroughly mixed (premixed). Then, the mixture is dispersed for 4 hours using a 0.6L bead mill (e.g., "Dino Mill" manufactured by Shinmaru Enterprises) filled with 1,800g of grinding beads (e.g., zirconia beads with a diameter of 0.5mm). After dispersion, the viscosity of the obtained carbon black dispersion at 25°C is measured using an E-type viscometer (e.g., "TVE25L Viscometer" manufactured by Toki Sangyo Co., Ltd.). The carbon black dispersion is then stored in a forced-air constant-temperature incubator set to 70°C for one week, and the viscosity is measured again. At this time, if the viscosity of the dispersion immediately after dispersion is 100 mPa·s or less, and the absolute value of the viscosity change rate of the carbon black dispersion before and after storage is 10% or less, it is determined that the resin has the function of dispersing pigments.

[0063] Examples of resins that can be used as polymer (A-1) include acrylic, maleic acid, urethane, and polyester resins. Furthermore, any resin listed above can be used as polymer (A-1) as long as it has an aromatic ring and an acid group and an acid value of 50 to 160 mg KOH / g, as described later.

[0064] In this disclosure, "acrylic resin" refers to a resin using one or more polymerizable monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters. In addition to the polymerizable monomers listed above, styrene monomers may also be used as polymerizable monomers to form the acrylic resin. On the other hand, resins containing (maleic anhydride) (at least one selected from "maleic acid" and "maleic anhydride") as a polymerizable monomer are excluded from "acrylic resin" in this disclosure. Furthermore, "maleic acid resin" refers to a resin using at least (maleic anhydride) as a polymerizable monomer. In addition, maleic acid resins may also use α-olefins, styrene monomers, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, etc. as polymerizable monomers.

[0065] As described above, it is preferable that both the polymer (A-1) and the crosslinked reaction product after crosslinking treatment retain acid groups in their molecular structure. In this case, it is preferable that at least a portion of the non-anionized acid groups contained in these resins become anionized acid groups through neutralization with a basic compound. This is because the charge repulsion between the anionized acid groups allows for stable dispersion of pigment particles and improves continuous ejection stability, ejection straightness, and resolubility. Examples of the basic compounds include ammonia; organic amines such as dimethylaminoethanol, diethanolamine, and triethanolamine; and alkali metal compounds such as lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium bicarbonate, dipotassium carbonate, and sodium borate. Among these, it is preferable to use alkali metal compounds because they allow for easy dispersion stability of pigment particles in aqueous inkjet inks and enable further improvement in continuous ejection stability, ejection straightness, and resolubility. The basic compounds listed above can be used individually or in combination of two or more.

[0066] The amount of basic compound added when neutralizing polymer (A-1) and the crosslinked reaction product is preferably such that the pH of the 20% aqueous solution of polymer (A-1) and the crosslinked reaction product, after adding the entire amount of the basic compound, becomes 7 to 12.

[0067] In this disclosure, "aqueous solution" refers to a liquid containing an aqueous solvent and components dispersed and / or dissolved in the aqueous solvent. The pH of the aqueous solution is the value at 25°C and can be measured by conventional methods. For example, it can be measured using a benchtop pH meter "F-71" (manufactured by Horiba, Ltd.) with a pH electrode "6337-10D" (manufactured by Horiba, Ltd.).

[0068] On the other hand, the preferred amount of basic compound to be added to neutralize the polymer (A-1) and the crosslinked reaction product can be specifically shown using the neutralization rate. From the viewpoint of improving the dispersion stability, resolubility, continuous discharge stability, and straight discharge of the pigment particles, the neutralization rate is preferably 10 to 200 mol%, more preferably 40 to 160 mol%, and particularly preferably 60 to 120 mol%. Here, the neutralization rate is the amount of molars of basic groups in the added basic compound divided by the amount of molars of acid groups in the target resin (polymer (A-1) or crosslinked reaction product), and can be calculated by the following formula (3). Note that when using a resin in which at least a portion is neutralized (for example, containing at least carboxylate groups) as the polymer (A-1) and crosslinked reaction product, the neutralization rate shall be calculated assuming that all acid groups in the resin are unneutralized (for example, assuming that all carboxylate groups in the resin molecule are carboxyl groups).

[0069] Formula (3):

[0070] The content of polymer (A-1) relative to the pigment content is preferably 1 to 100% by mass. By setting the content of polymer (A-1) relative to the pigment content to 1% by mass or more, the viscosity of the aqueous inkjet ink can be kept to a level suitable for inkjet printing applications, and the resolubility is also improved. Furthermore, by setting it to 100% by mass or less, dispersion stability, as well as storage stability and continuous dispensing stability after dispersion, can be improved. The content of polymer (A-1) is more preferably 2 to 50% by mass. The content of polymer (A-1) may also be 10 to 45% by mass, or 20 to 40% by mass.

[0071] Compound (A-2) Compound (A-2), which has multiple glycidyl ether groups in one molecule, is used to crosslink polymer (A-1) and is also known as a "crosslinking agent".

[0072] The epoxy equivalent of compound (A-2) is preferably 90 to 300 g / eq., and more preferably 100 to 200 g / eq., from the viewpoint of enabling more efficient reaction with the acid groups in polymer (A-1) in a liquid medium containing water (aqueous medium). Furthermore, if compound (A-2) can be reacted efficiently, the requirements for glycidyl group content, described later, can be easily met. As a result, the dispersion stability, resolubility, print density, print quality, and continuous ejection stability of the pigment particles can be easily improved.

[0073] Furthermore, while compound (A-2) may be water-soluble or water-insoluble, from the viewpoint of being able to react more efficiently with the acid group in polymer (A-1) in an aqueous medium, its solubility in 100g of water at 25°C should be 0.1 to 50g / 100gH. ２ It is preferable that it be 0, and 0.2 to 40 g / 100 gH ２ It is more preferable that it be 0. Even more preferable that it is 0.5 to 30 g / 100 gH ２ It is O.

[0074] Specific examples of compounds having multiple glycidyl ether groups in a single molecule include cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 4,4'-diglycidyloxybiphenol, bisphenol A type diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether, phthalate diglycidyl ester, terephthalate diglycidyl ester, and hydrogenated phthalate diglycidyl ester.

[0075] In the aqueous inkjet ink of this embodiment, compound (A-2) is added so that the glycidyl group content represented by the following formula (1) is 50 to 200 mol%. By incorporating compound (A-2) so that the glycidyl group content is 50 to 200 mol%, the desorption of the crosslinked reaction product from the pigment can be reduced, improving resolubility and continuous ejection stability. Furthermore, the free polymer (A-1) is less likely to inhibit the expression of the surfactant's function, thereby improving the print quality of the aqueous inkjet ink. In addition, since a sufficient amount of hydroxyl groups and ether bonds derived from glycidyl ether groups are formed in the crosslinked reaction product, the print density of the printed material is also improved. From these viewpoints, it is more preferable that compound (A-2) is added so that the glycidyl group content represented by the following formula (1) is 70 to 120 mol%, and particularly preferable that it is added so that it is 80 to 100 mol%. Formula (1):

[0076] <<Other Pigment Dispersing Resins>> As described above, the aqueous inkjet ink of this embodiment may contain pigment dispersion resins other than the crosslinking reaction product (referred to as "other pigment dispersion resins" in this disclosure). For example, the crosslinking reaction product and polymer (A-1) can be used in combination, that is, the crosslinking reaction product and polymer (A-1) can coexist in the aqueous inkjet ink.

[0077] From the viewpoint of ensuring that the effects of the crosslinked reaction product are expressed favorably, the content of other pigment dispersion resins contained in the aqueous inkjet ink of this embodiment is preferably 80% by mass or less (may be 0% by mass), more preferably 50% by mass or less, and particularly preferably 25% by mass or less, relative to the content of the crosslinked reaction product.

[0078] ≪Method for producing pigment particles containing crosslinking reaction products≫ As an example of a method for producing pigment particles (crosslinked pigment particles) containing pigment and crosslinking reaction products, one example is the method shown below, in which the dispersion treatment step and the crosslinking treatment step are carried out in this order. Although optional, the neutralization treatment step shown below may be carried out before the above dispersion treatment step.

[0079] First, the non-anionized acid groups present in polymer (A-1) and a basic compound are mixed in an aqueous medium to neutralize at least a portion of the non-anionized acid groups (neutralization step). As described above, the neutralization converts the non-anionized acid groups present in polymer (A-1) into anionized acid groups. This pigment dispersion resin, having at least anionized acid groups, is used in subsequent steps. The polymer (A-1) obtained after the neutralization step is in the form of an aqueous solution. Next, the pigment is added to the aqueous solution of polymer (A-1), the two are mixed, and then a dispersion treatment is performed (dispersion step). This dispersion step yields an aqueous dispersion of pigment particles (uncrosslinked pigment particles) in which polymer (A-1) is chemically adsorbed on at least a portion of the pigment surface. Subsequently, compound (A-2) is added to the aqueous dispersion of uncrosslinked pigment particles and a crosslinking treatment is performed (crosslinking step). This crosslinking step produces an aqueous dispersion of crosslinked pigment particles.

[0080] ≪Dispersion Processing Process≫ Any commonly used disperser can be used in the dispersion processing process, such as media-type wet dispersers, media-less wet dispersers, and kneaders. Examples of media-type wet dispersers include paint shakers, ball mills, roll mills, bead mills, and attritors. Examples of media-less wet dispersers include high-pressure homogenizers and ultrasonic dispersers. An example of a kneader is a kneader. Among these, a bead mill is preferable from the viewpoint of crushing and refining coarse pigment particles. Examples of bead mills include Super Mill, Sand Grinder, Agitator Mill, Glen Mill, Dyno Mill, Pearl Mill, and Cobol Mill (all are trade names).

[0081] Using the dispersers listed above, the pigment can be refined to the desired particle size by impact force and shear stress with the media. In particular, from the viewpoint of obtaining a pigment dispersion with a uniform particle size, it is preferable to pre-disperse (pre-mix) the pigment and polymer (A-1) and then further disperse (main dispersion) using the dispersers listed above. As the pre-disperser used for pre-mixing, a commonly used mixing and stirring device such as a disperser can be used.

[0082] <Crosslinking Process> As described above, by crosslinking the polymer (A-1) adsorbed on the pigment, the pigment dispersion resin can be crosslinked to obtain pigment particles. Furthermore, a method of forming a crosslinked structure with compound (A-2) can be suitably used as the crosslinking method. Specifically, one method is to hold a mixture containing uncrosslinked pigment particles, compound (A-2), and water under heating while stirring.

[0083] The temperature during the crosslinking treatment is preferably 50°C to 95°C, more preferably 70°C to 85°C, from the viewpoint of efficiently advancing the crosslinking reaction. The duration of the crosslinking treatment is preferably 0.5 to 10 hours, more preferably 1 to 8 hours, and even more preferably 2 to 5 hours, from the same viewpoint as above.

[0084] The average particle size of the crosslinked pigment particles is preferably 60 to 200 nm, more preferably 70 to 175 nm, and particularly preferably 80 to 150 nm, from the viewpoint of stable discharge from the nozzle.

[0085] The average particle diameter mentioned above is the median diameter on a volume basis, which can be measured by dynamic light scattering. For example, it can be measured using Microtrac-Bell's "Nanotrac UPA-EX150" under conditions of 25°C.

[0086] <Pigment Dispersion> The crosslinked pigment particles may be dispersed in an aqueous medium, that is, in the form of an aqueous dispersion of crosslinked pigment particles. To improve continuous ejection stability, the aqueous inkjet ink of this embodiment is preferably manufactured by mixing a pre-made aqueous dispersion of crosslinked pigment particles with other raw materials described later.

[0087] In this disclosure, a composition containing pigment particles and an aqueous medium is referred to as a "pigment dispersion." Therefore, both the aqueous dispersion of uncrosslinked pigment particles and the aqueous dispersion of crosslinked pigment particles described above are included in the "pigment dispersion." As will be described later, the pigment dispersion is used as a raw material for aqueous inkjet ink and is different from the aqueous inkjet ink itself. Specifically, the pigment dispersion and the aqueous inkjet ink differ in their pigment content. For example, the amount of pigment contained in the pigment dispersion is preferably 10 to 60% by mass, more preferably 15 to 55% by mass, and even more preferably 20 to 50% by mass, of the total amount of the pigment dispersion. On the other hand, the preferred amount of pigment contained in the aqueous inkjet ink is as described later. Furthermore, when the amount of pigment (mass%) contained in the pigment dispersion is denoted as PP and the amount of pigment (mass%) contained in the aqueous inkjet ink is denoted as PI, the value expressed as PP / PI is preferably 1.5 to 10, and more preferably 2 to 8.

[0088] The pigment dispersion may be produced by first manufacturing pigment particles in a dry state (solid) and then mixing them with an aqueous medium. Alternatively, it may be produced by the method for producing pigment particles containing the crosslinking reaction product described above.

[0089] The aqueous medium contained in the above pigment dispersion contains at least water. It may also contain an organic solvent that can be used as a raw material for aqueous inkjet inks (details will be described later). For example, the pigment dispersion may contain ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, etc.

[0090] The pH of the above pigment dispersion is preferably 8 to 12. If the pH is 8 or higher, the anionized acid groups present in the pigment dispersion resin can exist stably, and dispersion stability can be enhanced due to charge repulsion. From this viewpoint, a more preferable pH is 9 to 11. The pH of the pigment dispersion can be measured by the same method as the aqueous solution of polymer (A-1) described above.

[0091] <Surfactants> The aqueous inkjet ink of this embodiment contains, as surfactants, an acetylenediol-based surfactant (B-1) with a measured HLB value of 6 to 9 and a siloxane-based surfactant (B-2).

[0092] The HLB (Hydrophilic-Lipophobic Balance) value is one of the parameters that represent the degree of hydrophilicity and hydrophobicity of a material. A smaller HLB value indicates higher hydrophobicity of the material, while a larger HLB value indicates higher hydrophilicity. There are two methods for determining the HLB value: calculation from the molecular structure and experimental measurement. In this disclosure, the HLB value used is the value calculated by experimental measurement using the method shown below (measured HLB value). (1) Dissolve 0.5 g of the target surfactant in 5 mL of ethanol. (2) Titrate the mixture from (1) with a 2% phenol aqueous solution while stirring at 25°C. The endpoint is reached when the mixture becomes cloudy and does not return to clear when the 2% phenol aqueous solution is added dropwise. (3) When the amount of 2% phenol aqueous solution added dropwise up to the endpoint is A [mL], the measured HLB value is calculated according to the following formula (4).

[0093] Equation (4): Measured HLB value = 0.89 × A + 1.11

[0094] ≪Acetylenediol-based surfactant (B-1)≫ The aqueous inkjet ink of this embodiment contains an acetylenediol-based surfactant (B-1) with a measured HLB value of 6 to 9. It is preferable that the measured HLB value of the acetylenediol-based surfactant (B-1) is 6 to 8, as it has low affinity for water and quickly orients at the gas-liquid interface, resulting in excellent wettability to the printing substrate, and also improves print density.

[0095] Examples of the above-mentioned acetylenediol-based surfactant (B-1) include 2,4,7,9-tetramethyl-5-decine-4,7-diol, ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol (provided that the number of moles of ethylene oxide adducted is 1.5 moles or less), 2,5,8,11-tetramethyl-6-dodecine-5,8-diol, etc. Examples of commercially available products that can be used as acetylenediol-based surfactants (B-1) include Surfinol DF-110D, Surfinol 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 420 (manufactured by Evonik Japan), Acetylenel E00, E13T (manufactured by Kawaken Fine Chemicals Co., Ltd.), etc. These compounds may be used individually or in combination of two or more.

[0096] The content of acetylenediol-based surfactant (B-1) in the aqueous inkjet ink is preferably 0.1 to 5% by mass, more preferably 0.3 to 3% by mass, from the viewpoint of ensuring excellent print quality. Particularly preferably it is 0.5 to 2% by mass.

[0097] ≪Siloxane-based surfactant (B-2)≫ As described above, the aqueous inkjet ink of this embodiment contains a siloxane-based surfactant (B-2). The siloxane-based surfactant (B-2) can be oriented to compensate for the non-uniform orientation of the acetylenediol-based surfactant (B-1), and is therefore effective in improving dot roundness and reducing unevenness. In particular, it is preferable that the measured HLB value of the siloxane-based surfactant (B-2) is 1 to 8, as this increases its affinity with the more hydrophobic acetylenediol-based surfactant (B-1), allowing it to quickly orient at the interface together with the acetylenediol-based surfactant (B-1), improving wettability to the printing substrate and dot roundness, and thus improving print quality.

[0098] As described above, as the siloxane surfactant (B-2), gemini-type siloxane surfactants, both-terminal polyether-modified siloxane surfactants, side-chain polyether-modified siloxane surfactants, etc. can be used. Among them, even with a small addition amount, unevenness can be reduced, and a printed matter with good dot roundness and wettability can be obtained. Furthermore, from the viewpoint of improving the discharge stability of the aqueous inkjet ink, the above siloxane surfactant (B-2) preferably contains at least one selected from the group consisting of gemini-type siloxane surfactants and both-terminal polyether-modified siloxane surfactants.

[0099] <<Gemini-Type Siloxane Surfactant>> Generally, a gemini-type surfactant has a structure in which surfactants having a hydrophilic structure and a hydrophobic structure are linked by a linking group (spacer) or a covalent bond. Also, in the case of a gemini-type siloxane surfactant, for example, a siloxane chain (-(O-SiR １ R ２ - ｘ - represents a hydrophobic structure. However, R １ and R ２ are each an arbitrary organic group, and x is an integer of 2 or more).), and a hydrophilic structure (for example, a polyether chain) has the following structure. - The bonding points between the siloxane chain and the hydrophilic structure are present in the middle of the siloxane chain and the middle of the hydrophilic structure, respectively. - A plurality of siloxane chains are bonded via a linking group or the like (for example, at least a part of R １ and / or R ２ in the structural formula of the siloxane chain is an organic chain containing a siloxane chain). - In a plurality of siloxane chains each having a plurality of hydrophilic structures, a part of the hydrophilic structures is shared.

[0100] Gemini-type surfactants exhibit superior surface tension reduction capabilities compared to general surfactants. Therefore, using gemini-type siloxane-based surfactants results in superior surface tension reduction compared to non-gemini-type siloxane-based surfactants. As a result, the wettability and dot roundness of water-based inkjet inks containing gemini-type siloxane-based surfactants can be significantly improved, leading to a substantial improvement in print quality.

[0101] Examples of commercially available gemini-type siloxane surfactants include, but are not limited to, TEGOTwin4000, TEGOTwin4100, and TEGOTwin4200 manufactured by Evonik Japan.

[0102] <<Siloxane-based surfactants with polyethers at both ends (excluding gemini-type siloxane-based surfactants)>> Siloxane-based surfactants with polyethers at both ends have a structure in which polyether chains are bonded to both ends of a polysiloxane skeleton. Water-based inkjet inks containing these surfactants improve print quality by uniformizing the wetting spread on the printing substrate and improving the roundness of the dots, and also improve continuous ejection stability, although the details are unknown. Compounds represented by the following general formula (5) are preferably used as the siloxane-based surfactants with polyethers at both ends.

[0103] General formula (5):

[0104] In general formula (5), l represents an integer from 1 to 100, and R ３ This represents the structure expressed by the following general formula (6). ３ They may be the same or different from each other.

[0105] General formula (6):

[0106] In general formula (5), p is an integer from 1 to 6, q is an integer from 1 to 100, and r is an integer from 0 to 80. However, p + r is an integer greater than or equal to 1. Also, R ４ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a methacryloyl group, or an acryloyl group. However, the ethylene oxide group (OC) in [ ] represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a methacryloyl group, or an acryloyl group.２ H ４ ) and propylene oxide group (OC ３ H ６ The format of the addition can be block or random.

[0107] Examples of commercially available compounds represented by the above general formula (5) include, but are not limited to, BYK-333, BYK-UV3500, and BYK-3420 from BIC Chemie, TEGOGlide100, TEGOGlide432, TEGOGlide440, and TEGOGlide450 from Evonik Japan, and KF-6004, KF-6123, X-22-4952, and X-22-4272 from Shin-Etsu Chemical Co., Ltd.

[0108] <<Side-chain polyether-modified siloxane surfactants (excluding gemini-type siloxane surfactants)>> As the above siloxane surfactant (B-2), side-chain polyether-modified siloxane surfactants (excluding gemini-type siloxane surfactants) can be used. Even if the side-chain polyether-modified siloxane surfactant has a relatively low molecular weight, it exhibits high orientation in aqueous media and can achieve excellent wettability. It is preferable to use a surfactant represented by the following general formula (7) as the side-chain polyether-modified siloxane surfactant.

[0109] General formula (7):

[0110] In general formula (7), m is a non-negative integer, n is a non-negative integer, and m+n is a non-negative integer from 1 to 100. Also, R ５ This is a structure represented by the above general formula (6), and R ６ R represents an alkyl group having 1 to 6 carbon atoms. If n is 2 or more, multiple R ５ They may all be the same, or some or all be different. ６ They may be the same or different from each other.

[0111] Commercial products of the compound represented by the above general formula (7) include BYK-345, BYK-347, BYK-348, BYK-349, BYK-3450, BYK-3451 from BIC Chemie, TEGOWet240, TEGOWet250, TEGOWet260, TEGOWet270, TEGOWet280 from Evonik Japan, and from Shin-Etsu Chemical Co., Ltd. Examples include, but are not limited to, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, LKF-643, KF-644, KF-945, KF-6011, KF-6012, KF-6015, KF-6017, KF-6020, KF-6204, X-22-4515, etc.

[0112] The content of siloxane-based surfactant (B-2) in aqueous inkjet ink is preferably 0.1 to 5% by mass, more preferably 0.3 to 3.5% by mass, from the viewpoint of ensuring excellent print quality. Particularly preferred is 0.5 to 2.5% by mass.

[0113] <<Other Surfactants>> The aqueous inkjet ink of this embodiment may contain surfactants other than the acetylenediol-based surfactant (B-1) and the siloxane-based surfactant (B-2) described above (also referred to as "other surfactants" in this disclosure).

[0114] As the above-mentioned other surfactants, one or more selected from the group consisting of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants (excluding acetylenediol-based surfactants (B-1) and siloxane-based surfactants (B-2)) can be used. In particular, from the viewpoint of excellent compatibility with acetylenediol-based surfactants (B-1) and siloxane-based surfactants (B-2), and improvement of continuous discharge stability, discharge straightness, and print quality of printed materials, it is preferable to use a nonionic surfactant other than acetylenediol-based surfactants (B-1) and siloxane-based surfactants (B-2) (in this disclosure, also simply referred to as "nonionic surfactant (B-3)").

[0115] As the nonionic surfactant (B-3) mentioned above, acetylenediol-based surfactants (excluding acetylenediol-based surfactant (B-1)), acetylene monool-based surfactants, fluorine-based surfactants, polyoxyalkylene monoalkyl ether-based surfactants (specifically, compounds having an ethylene oxide group, a propylene oxide group, or a combination thereof, where the total number of added moles of ethylene oxide and propylene oxide groups is 5 to 100, and the number of carbon atoms of the alkyl or alkenyl group at the molecular terminus is 5 to 22); and the like can be used. These other surfactants may be used individually or in combination of two or more.

[0116] In particular, the polyoxyalkylene monoalkyl ether surfactant is preferred as the nonionic surfactant (B-3) because it exhibits excellent affinity with acetylenediol-based surfactants (B-1), and also provides good continuous discharge stability, discharge straightness, print quality of printed materials, and resolubility.

[0117] When the aqueous inkjet ink of this embodiment contains a polyoxyalkylene monoalkyl ether surfactant as the nonionic surfactant (B-3), its content is preferably 0.1 to 2% by mass, more preferably 0.2 to 1.5% by mass, from the viewpoint of suitably exhibiting the above-mentioned effects. Particularly preferably it is 0.3 to 1.2% by mass.

[0118] <Organic Solvents> <Specific Organic Solvents> The aqueous inkjet ink of this embodiment contains, as organic solvents, an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms. In this disclosure, these organic solvents are collectively referred to as "specific organic solvents." The alkanediol having 5 to 8 carbon atoms and the glycol ether having 4 to 10 carbon atoms have low surface tension and high compatibility with pigment particles, acetylenediol-based surfactants (B-1), and siloxane-based surfactants (B-2). As a result, these surfactants diffuse uniformly as droplets of aqueous inkjet ink printed on the printing substrate wet and spread. Furthermore, with this diffusion, the surfactants described above tend to be uniformly oriented at the interface. As a result, the straightness of ejection, continuous ejection stability, and print quality are improved. Furthermore, because alkanediols with 3 to 4 carbon atoms have high water solubility, they can stabilize alkanediols with 5 to 8 carbon atoms, glycol ethers with 4 to 10 carbon atoms, acetylenediol-based surfactants (B-1), and other materials within water-based inkjet inks. As a result, the meniscus of the water-based inkjet ink within the inkjet head is stabilized. Consequently, ejection straightness, continuous ejection stability, and print quality are also improved.

[0119] Examples of alkanediols having 5 to 8 carbon atoms include, but are not limited to, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,3-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 2,3-hexanediol, 3,4-hexanediol, 1,5-hexanediol, 1,2-octanediol, 1,3-octanediol, 3-methyl-1,3-butanediol, 2-methyl-1,3-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol (hexylene glycol), 2,2-dimethyl-1,3-pentanediol, and 2-ethyl-1,3-hexanediol.

[0120] Although the detailed mechanism is unknown, using any of these other than 1,2-alkanediols improves print quality such as dot roundness, continuous ejection stability, ejection straightness, and print density. Among these, it is preferable to use an alkanediol having a structure containing a branched alkyl group. Alkanediols having a structure containing a branched alkyl group are thought to have a high affinity for acetylenediol-based surfactants (B-1), which promotes uniform orientation of the acetylenediol-based surfactant (B-1) at the interface, improving ejection straightness, continuous ejection stability, and print quality of the printed material. Examples of alkanediols having a structure containing a branched alkyl group but not being 1,2-alkanediols include 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol (hexylene glycol), and 2-ethyl-1,3-hexanediol. Furthermore, among these, it is particularly preferable to select one or more compounds selected from the group consisting of alkanediols having 5 to 6 carbon atoms, specifically 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, and 2-methyl-2,4-pentanediol (hexylene glycol), in order to improve the print density and print quality of printed materials.

[0121] On the other hand, since the above-described mechanism can effectively orient the surfactant in the aqueous inkjet ink uniformly at the interface, improving both the straightness of ejection and the stability of continuous ejection, it is also preferable to use an alkanediol with low surface tension, i.e., a surface tension of 20 to 30 mN / m at 25°C.

[0122] The content of alkanediols having 5 to 8 carbon atoms is preferably 0.5 to 10% by mass, and particularly preferably 1 to 8% by mass, of the total amount of aqueous inkjet ink. By keeping the content of alkanediols having 5 to 8 carbon atoms within the above range, the mechanism described above functions effectively.

[0123] On the other hand, examples of glycol ethers having 4 to 10 carbon atoms include, but are not limited to, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, and triethylene glycol monobutyl ether.

[0124] In particular, it is preferable that the number of carbon atoms in the alkyl group at the molecular terminus is 3 to 4, as this allows for suitable compatibility of the acetylenediol-based surfactant (B-1) and the siloxane-based surfactant (B-2), thereby improving continuous ejection stability and ejection straightness, as well as improving resolubility. Furthermore, it is more preferable to use propylene glycol monoalkyl ether, dipropylene glycol monoalkyl ether, or a combination thereof, as the above-described mechanism functions effectively and allows the surfactant in the aqueous inkjet ink to be uniformly oriented at the interface, thereby improving ejection straightness, continuous ejection stability, and print quality, as well as improving resolubility. The use of dipropylene glycol monoalkyl ether is particularly preferable. Therefore, in the aqueous inkjet ink of this embodiment, it is preferable to include, as the glycol ether having 4 to 10 carbon atoms, dipropylene glycol monoalkyl ether having 3 to 4 carbon atoms in the alkyl group at the molecular terminus, such as dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, or a combination thereof.

[0125] The content of glycol ethers having 4 to 10 carbon atoms is preferably 0.1 to 10% by mass of the total amount of aqueous inkjet ink, and particularly preferably 0.5 to 7% by mass. By keeping the content of alkanediols having 5 to 8 carbon atoms within the above range, the mechanism described above functions effectively.

[0126] Examples of alkanediols having 3 to 4 carbon atoms include 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, and 1,3-butanediol. Among these, 1,2-alkanediol is preferred because it has a high affinity for water, which allows the above-mentioned effects to be expressed favorably.

[0127] The content of alkanediols having 3 to 4 carbon atoms is preferably 5 to 25% by mass of the total amount of aqueous inkjet ink, and particularly preferably 7 to 20% by mass. By keeping the content of alkanediols having 5 to 8 carbon atoms within the above range, the mechanism described above functions effectively.

[0128] <<Other Organic Solvents>> The aqueous inkjet ink of this embodiment may contain organic solvents other than the specified organic solvents described above (referred to as "other organic solvents" in this disclosure).

[0129] Other organic solvents mentioned above include monohydric alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-methoxy-2-butanol, 2-methoxy-1-butanol, 3-methoxy-1-butanol, and 3-methoxy-3-methyl-1-butanol; polyalkylene glycols such as diethylene glycol, triethylene glycol, and dipropylene glycol; glycol diethers such as diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether; and nitrogen-containing heterocyclic solvents such as 2-pyrrolidone, N-methylpyrrolidone, and N-ethylpyrrolidone.

[0130] The total mass of the organic solvent content in the aqueous inkjet ink of this embodiment is preferably 6 to 45% by mass, and particularly preferably 9 to 35% by mass.

[0131] <Binder Resin> The aqueous inkjet ink of this embodiment preferably contains a resin used for binder applications ("binder resin") in order to improve drying properties, provide scratch resistance, and further improve the print density of the printed material.

[0132] As mentioned above, generally, water-soluble resins and resin microparticles are known as resin forms used in water-based inkjet inks. The binder resin contained in the water-based inkjet ink of this embodiment may be a water-soluble resin or resin microparticles. Alternatively, a combination of water-soluble resin and resin microparticles may be used.

[0133] In this disclosure, resins with a solubility of 1 g or more in 100 g of water at 25°C are referred to as "water-soluble resins," and resins with a solubility of less than 1 g are referred to as "non-water-soluble resins." Furthermore, among the non-water-soluble resins, resins dispersed in particulate form in water and having a median diameter (also referred to as "D50" in this disclosure) of 10 to 1,000 nm on a volume basis are referred to as "resin fine particles."

[0134] The D50 of the resin fine particles can be measured using the same apparatus and method as described above for the average particle size of the crosslinked pigment particles.

[0135] Examples of binder resins that can be used in the aqueous inkjet ink of this embodiment include acrylic, styrene, maleic acid, urethane, polyester, vinyl chloride, vinyl chloride-vinyl acetate, polyolefin, and polyvinyl alcohol. These resins may be used individually or in combination of two or more.

[0136] When the aqueous inkjet ink of this embodiment contains a binder resin, it is preferable that the type of resin used as the binder resin is one or more selected from the group consisting of acrylic, urethane, and polyester resins listed above.

[0137] The preferred content of the binder resin in the aqueous inkjet ink of this embodiment is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, and particularly preferably 2 to 10% by mass, based on the total amount of the aqueous inkjet ink.

[0138] <Other Components> In addition to the components described above, the aqueous inkjet ink of this embodiment may also contain pH adjusters and other additives. Examples of these other additives include crosslinking agents, preservatives, ultraviolet absorbers, and infrared absorbers. For each of these components, one or more conventionally known compounds can be used.

[0139] <Water> The water contained in the aqueous inkjet ink of this embodiment is preferably ion-exchanged water, reverse osmosis water, or a combination thereof. Furthermore, the water content in the aqueous inkjet ink is preferably 30 to 90% by mass of the total amount of aqueous inkjet ink.

[0140] <Method for Manufacturing Water-Based Inkjet Ink> The water-based inkjet ink of this embodiment can be manufactured by conventionally known methods. For example, a method may be used in which water, an acetylene-based surfactant (B-1), a siloxane-based surfactant (B-2), an alkanediol with 3 to 4 carbon atoms, an alkanediol with 5 to 8 carbon atoms, a glycol ether with 4 to 10 carbon atoms, etc., are added to an aqueous dispersion of cross-linked pigment particles manufactured by the method described above, and after thorough stirring and mixing, coarse particles are removed by methods such as filtration and centrifugation. However, the method for manufacturing the water-based inkjet ink of this embodiment is not limited to the method described above.

[0141] <Characteristics of Water-Based Inkjet Ink> The water-based inkjet ink of this embodiment preferably has a viscosity of 3 to 15 mPa·s at 25°C. Within this viscosity range, droplets of the water-based inkjet ink can be stably ejected not only from inkjet heads with ejection frequencies of about 4 to 10 kHz, but also from inkjet heads with high ejection frequencies of about 20 to 70 kHz. In particular, when the viscosity of the water-based inkjet ink of this embodiment is 4 to 10 mPa·s at 25°C, the water-based inkjet ink can be stably ejected even when using an inkjet head with a design resolution of 600 dpi or higher. In this disclosure, the viscosity is measured using a cone-plate type rotational viscometer (E-type viscometer, cone angle 1°34') such as the "TVE25L viscometer" manufactured by Toki Sangyo Co., Ltd., under conditions of 25°C.

[0142] Furthermore, in order to obtain an aqueous inkjet ink with excellent ejection stability and print quality of printed materials, the static surface tension of the aqueous inkjet ink of this embodiment is preferably 18 to 35 mN / m at 25°C, and particularly preferably 20 to 30 mN / m. In this disclosure, the static surface tension is the value measured at a 25°C environment using the Wilhelmy method (plate method) with an automatic surface tension meter such as the "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd.

[0143] <Water-based inkjet ink set> The water-based inkjet ink of this embodiment may be used individually, but it can also be used as a set of water-based inkjet inks, combining two or more types of water-based inkjet inks. An example of such a set of water-based inkjet inks is a set of four water-based inkjet inks (process color ink set) consisting of cyan water-based inkjet ink (water-based cyan ink), magenta water-based inkjet ink (water-based magenta ink), yellow water-based inkjet ink (water-based yellow ink), and black water-based inkjet ink (water-based black ink).

[0144] <Inkjet Recording Method> The aqueous inkjet ink of this embodiment is used in an inkjet printing method. That is, the aqueous inkjet ink of this embodiment is ejected onto a printing substrate from an inkjet head having fine nozzles (ejection step). Furthermore, it is preferable that the aqueous inkjet ink ejected onto the printing substrate is dried by a drying mechanism (drying step).

[0145] ≪Ejection Process≫ In the ejection process, there are two operating methods for the inkjet head: the shuttle (scan) method, which ejects and records aqueous inkjet ink while scanning the inkjet head back and forth in a direction perpendicular to the transport direction of the printing substrate, and the single-pass method, which ejects and records aqueous inkjet ink as the printing substrate passes under the fixedly positioned inkjet head. The inkjet head equipped with aqueous inkjet ink in this embodiment may employ either the shuttle method or the single-pass method. Among these, the single-pass method is preferably selected because it is less likely for the droplets of aqueous inkjet ink to land in a misaligned position, improving the print quality of the printed material, and furthermore, it enables high-speed printing and high productivity.

[0146] Regarding the ejection method from the inkjet head, any known method can be arbitrarily selected. Examples of such ejection methods include the piezoelectric method, which utilizes the volume change of a piezoelectric element; the thermal method, which ejects water-based inkjet ink using bubbles generated by heating with a heater; and the valve method, which ejects pressurized water-based inkjet ink while opening and closing the nozzle cover (valve) with a solenoid.

[0147] The amount of aqueous inkjet ink droplets ejected from the inkjet head is preferably 0.5 to 20 picoliters, and particularly preferably 0.5 to 15 picoliters, from the viewpoint of reducing drying load and improving print quality. Furthermore, from the viewpoint of improving print quality, it is preferable to adjust the printing conditions (specifically, the drive frequency and number of inkjet heads, and the printing speed) so that the recording resolution of the printed material is 600 dpi or higher, and particularly preferable to adjust the printing conditions so that the recording resolution is 1200 dpi or higher.

[0148] <<Drying Process>> Drying methods used in the drying mechanism include heating drying, hot air drying, infrared (e.g., infrared with a wavelength of 700 to 2500 nm) drying, microwave drying, and drum drying. One or more of these methods can be arbitrarily selected and used in the above drying process. When two or more of the above drying methods are used, each drying method may be used separately (e.g., consecutively) or simultaneously in combination. For example, by using heating drying and hot air drying in combination, the water-based inkjet ink can be dried more quickly than when each method is used individually.

[0149] <<Printing Substrate>> Any conventionally known substrate can be used as the printing substrate on which the aqueous inkjet ink of this embodiment is printed. In particular, from the viewpoint of obtaining printed materials with excellent print density and print quality, it is preferable to use a paper substrate as the printing substrate.

[0150] Examples of paper substrates include uncoated papers such as newsprint, medium-grade paper, fine paper, plain paper, and recycled paper; packaging papers such as kraft paper; corrugated cardboard base paper such as liners and corrugated cardboard; and coated papers such as coated paper, art paper, and cast paper. Among these, uncoated papers such as fine paper, plain paper, and recycled paper, as well as coated papers such as coated paper, are preferably used because they yield printed materials with excellent print quality. The aqueous inkjet ink of this embodiment can improve dot circularity and wettability on poorly permeable substrates such as coated paper, and can suppress a decrease in print density on permeable substrates such as fine paper.

[0151] The paper substrates listed above may have smooth or uneven surfaces. Furthermore, the paper substrates may be in roll form or sheet form. Additionally, a release adhesive layer may be provided on the side opposite the printed surface, or an adhesive layer may be provided on the printed surface after printing. To improve the wettability of the aqueous inkjet ink of this embodiment to the printing substrate, and to obtain printed materials with excellent print quality and drying properties, surface modification such as corona treatment and plasma treatment can be applied to the printed surface of the listed paper substrates.

[0152] <<Printed Material>> According to this embodiment, it is possible to provide a printed material in which the aqueous inkjet ink of this embodiment described above is printed on a printing substrate. The aqueous inkjet ink and the printing method thereof are as described above.

[0153] The aqueous inkjet ink of this embodiment will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" refer to "parts by mass" and "% by mass," respectively, unless otherwise specified.

[0154] <Production of Dispersion Resins> All "dispersion resins" shown below correspond to the polymer (A-1) described above. These dispersion resins were obtained by synthesis using the method described below.

[0155] <Example of Production of Dispersion Resin 1> 93.4 parts of methyl ethyl ketone were charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the mixture was purged with nitrogen gas. After heating the contents of the reaction vessel to 110°C, a mixture of polymerizable monomers, consisting of 25 parts styrene, 20 parts acrylic acid, 35 parts methyl methacrylate, and 20 parts lauryl methacrylate, and 6 parts of the polymerization initiator V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was added dropwise to the reaction vessel over 2 hours. After the dropwise addition was complete, the polymerization reaction was continued for 3 hours while maintaining the temperature of the contents of the reaction vessel at 110°C. Then, 0.6 parts of V-601 were added, and the reaction was continued for another hour at 110°C to obtain a solution containing the Dispersion Resin 1 precursor. The acid value of the obtained Dispersion Resin 1 precursor was 155 mg KOH / g. Subsequently, the amount of potassium hydroxide required to achieve a neutralization rate of 100 mol% was calculated from the acid value of the dispersion resin 1 precursor. A 48% by mass potassium hydroxide aqueous solution containing an equal amount of potassium hydroxide was added to the solution to convert the carboxyl groups present in the dispersion resin 1 precursor into carboxylate groups (neutralization treatment). After the neutralization treatment, 150 parts of deionized water were added, and the solution was heated to 50°C. After reaching 50°C, the solution was stirred for 1 hour while maintaining the temperature. Then, deionized water was added to obtain an aqueous solution of dispersion resin 1 by reducing the solid content concentration to 20%.

[0156] <Examples of production of disperse resins 2-4> Except for using the polymerizable monomers listed in Table 1-1 as the polymerizable monomers, aqueous solutions of disperse resins 2-4 (each with a solid content of 20%) were obtained using the same raw materials and procedures as for disperse resin 1.

[0157]

[0158] The abbreviations listed in Table 1-1 are as follows. Table 1-1 also includes the acid values ​​of dispersion resins 1-4. • St: Styrene • AA: Acrylic acid • MMA: Methyl methacrylate • LMA: Lauryl methacrylate

[0159] <Example of production of dispersion resin 5> 93.4 parts of methyl ethyl ketone were charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the mixture was purged with nitrogen gas. After heating the contents of the reaction vessel to 110°C, a mixture of polymerizable monomers, namely 25 parts styrene, 20 parts acrylic acid, 35 parts maleic anhydride, and 20 parts lauryl methacrylate, and 6 parts of the polymerization initiator V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was added dropwise to the reaction vessel over 2 hours. After the dropwise addition was complete, the polymerization reaction was continued for 3 hours while maintaining the temperature of the contents of the reaction vessel at 110°C, then 0.6 parts of V-601 were added, and the reaction was continued for another hour at 110°C to obtain a solution containing the dispersion resin 5 precursor. Next, after lowering the temperature of the reaction vessel to 60°C, 10 parts of water and 0.05 parts of diazabicycloundecene were added to the obtained solution. The reaction vessel was heated to 80°C while stirring the solution. After reaching 80°C, the solution was held at that temperature for 5 hours, allowing the maleic anhydride structure in the dispersion resin 5 precursor to hydrolyze (open the ring) with water. The acid value of the dispersion resin 5 precursor after ring opening was 325 mg KOH / g. Subsequently, the amount of potassium hydroxide required to achieve a neutralization rate of 100 mol% was calculated from the acid value of the dispersion resin 5 precursor after ring opening. A 48% by mass potassium hydroxide aqueous solution containing an equal amount of potassium hydroxide was added to the solution to convert the carboxyl groups in the dispersion resin 5 precursor into carboxylate groups (neutralization treatment). After the neutralization treatment, 140 parts of deionized water were added, and the solution was heated to 50°C. After reaching 50°C, the solution was stirred for 1 hour while maintaining the temperature. Then, deionized water was added to obtain an aqueous solution of dispersion resin 5 by reducing the solid content concentration to 20%.

[0160] <Examples of production of disperse resins 6-8> Except for using the polymerizable monomers listed in Table 1-2 as the polymerizable monomers, aqueous solutions of disperse resins 6-8 (each with a solid content of 20%) were obtained using the same raw materials and procedures as for disperse resin 5.

[0161]

[0162] The abbreviation "Manh" in Table 1-2 represents maleic anhydride. The meanings of the other abbreviations are the same as in Table 1-1. Furthermore, Table 1-1 also includes the acid values ​​of dispersion resins 5 to 8.

[0163] <Example of production of aqueous dispersion 1 of uncrosslinked pigment particles> 600 g of the pigment LIONOL BLUE FG-7351 (C.I. Pigment Blue 15:3, manufactured by Toyo Color Co., Ltd.), 750 g of an aqueous solution of dispersion resin 1 (solid content concentration 20%), and 1,650 g of ion-exchanged water were mixed and stirred with a stirrer for 1 hour (pre-dispersion). Then, circulating dispersion was started using a 0.6 L bead mill (DinoMill, manufactured by Shinmaru Enterprises) filled with 1,800 g of zirconia beads with a diameter of 0.5 mm. Subsequently, the median diameter by volume at a 25°C environment was measured at regular intervals (e.g., every hour) using a NanoTrac UPA-EX150, manufactured by MicroTrac-Bell, and circulating dispersion was stopped when the median diameter became 150 nm or less. Then, 1,000 g of ion-exchanged water was added to the obtained pigment dispersion. Furthermore, while heating at 60°C, a portion of the ion-exchanged water and the entire amount of methyl ethyl ketone contained in the aqueous solution of the pigment dispersion resin 1 were removed by reduced pressure distillation. Then, ion-exchanged water was added and the pigment concentration was adjusted to 15%, thereby obtaining an aqueous dispersion of cyan-colored uncrosslinked pigment particles 1 (pigment concentration 15%).

[0164] <Examples of production of aqueous dispersions 2-8 of uncrosslinked pigment particles> Aqueous dispersions 2-8 of cyan colored uncrosslinked pigment particles were obtained using the same raw materials and method as aqueous dispersion 1 of uncrosslinked pigment particles, except that aqueous solutions of dispersion resins 2-8 were used instead of aqueous solutions of dispersion resin 1. The pigment concentration was 15% in all cases.

[0165] <Example of preparation of aqueous dispersion of crosslinked pigment particles 1> 93.3 parts of the aqueous dispersion of uncrosslinked pigment particles 1 obtained above, and Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX, with an epoxy equivalent of 140 g / eq. and a solubility of 27 g / 100 gH at 25°C) corresponding to compound (A-2) ２1.15 parts of O) (an amount such that the glycidyl group content shown in formula (1) above is 85 mol%) and 5.55 parts of deionized water were mixed, and the mixture was heated to 80°C while stirring, and then maintained at 80°C for 3 hours to perform the crosslinking treatment. After that, deionized water was added to adjust the pigment concentration to 14%, thereby obtaining an aqueous dispersion of cyan crosslinked pigment particles 1 (pigment concentration 14%).

[0166] <Production Examples of Aqueous Dispersions of Crosslinked Pigment Particles 2-12> Except for changing the type of aqueous dispersion of uncrosslinked pigment particles used and the amount of each raw material added as shown in Table 2, cyan-colored aqueous dispersions of crosslinked pigment particles 2-12 were obtained by the same method as aqueous dispersion 1 of crosslinked pigment particles. The pigment concentration was 14% in all cases.

[0167]

[0168] In Table 2, "Denacol EX-313" is an epoxy compound manufactured by Nagase ChemteX Corporation (epoxy equivalent 141 g / eq., solubility at 25°C 99 g / 100 gH). ２ O) "Denacol EX-612" is an epoxy compound manufactured by Nagase ChemteX Corporation (epoxy equivalent 166 g / eq., solubility at 25°C 42 g / 100 gH). ２ O) is correct.

[0169] <Example of Binder Resin 1 Production> 93.4 parts of butanol were charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the mixture was purged with nitrogen gas. After heating the contents of the reaction vessel to 110°C, a mixture of polymerizable monomers, consisting of 6 parts acrylic acid, 64 parts methyl methacrylate, 20 parts 2-ethylhexyl acrylate, and 10 parts styrene, and 6 parts of the polymerization initiator V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was added dropwise to the reaction vessel over 2 hours. After the dropwise addition was complete, the polymerization reaction was continued for 3 hours while maintaining the contents of the reaction vessel at 110°C, then 0.6 parts of V-601 were added, and the reaction was continued for another hour at 110°C to obtain a solution of the binder resin 1 precursor. Next, the solution of the binder resin 1 precursor was cooled to room temperature, and then 7.1 parts of dimethylaminoethanol were added to neutralize the carboxyl groups present in the binder resin 1 precursor. Furthermore, 100 parts of deionized water were added. The mixture was then heated to 100°C, and the temperature was maintained thereafter to azeotrope the butanol with water, thereby distilling off the butanol. Finally, the solution was adjusted using deionized water to a solid content concentration of 40% to obtain an aqueous solution of binder resin 1. The weight-average molecular weight of the obtained binder resin 1 was 19,000, and the acid value was 47 mgKOH / g.

[0170] <Manufacturing of Water-Based Inkjet Ink> The raw materials listed in each column of Tables 3-1 to 3-6 were added to a mixing container equipped with a stirrer. Each raw material was added while stirring the contents of the mixing container with the stirrer. After all the raw materials had been added, the mixture was stirred at room temperature until it was sufficiently uniform. Then, the mixture was filtered through a 0.8 μm membrane filter to remove coarse particles that could cause printhead clogging, thereby manufacturing the water-based inkjet ink.

[0171]

[0172]

[0173]

[0174]

[0175]

[0176]

[0177] The abbreviations listed in Tables 3-1 to 3-6 are as follows. In Tables 3-1 to 3-6, "(A-1) Acid Value" refers to the acid value (unit: mgKOH / g) of the dispersion resin (corresponding to polymer (A-1)) used in the production of the cross-linked pigment particles, and "GL Content" refers to the content of glycidyl groups (unit: mol%) in the above cross-linked pigment particles.・Surfinol DF110D (Acetylenediol-based surfactant manufactured by Evonik Japan, measured HLB value = 6.4) ・Surfinol 104 (Acetylenediol-based surfactant manufactured by Evonik Japan, measured HLB value = 7.9) ・Surfinol 420 (Acetylenediol-based surfactant manufactured by Evonik Japan, measured HLB value = 8.3) ・TEGOTwin 4200 (Gemini-type siloxane-based surfactant manufactured by Evonik Japan, measured HLB value = 8.2) ・TEGOTwin 4000 (Gemini-type siloxane-based surfactant manufactured by Evonik Japan, measured HLB value = 2.0) ・TEGOGlide 440 (Both-terminated polyether-modified siloxane-based surfactant manufactured by Evonik Japan, measured HLB value = 12.5)・TEGOGlide100 (a siloxane-based surfactant with polyethers at both ends, manufactured by Evonik Japan; measured HLB value = 7.1) ・BYK348 (a siloxane-based surfactant with polyethers at both ends, manufactured by BIC Chemie Japan; measured HLB value = 13.0) ・TEGOWET270 (a siloxane-based surfactant with polyethers at both ends, manufactured by Evonik Japan; measured HLB value = 3.3) ・Propylene glycol (surface tension: 36.5 mN / m) ・1,2-Butanediol (surface tension: 31.6 mN / m) ・2-Methyl-1,5-pentanediol (surface tension: mN / m) ・3-Methyl-1,3-butanediol (surface tension: 29.9 mN / m) • 2-methyl-2,4-pentanediol (surface tension: 29.1 mN / m) • 1,2-hexanediol (surface tension: 26.0 mN / m) • Dipropylene glycol monopropyl ether (surface tension: 25.6 mN / m) • Propylene glycol monoethyl ether (surface tension: 26.3 mN / m) • Propylene glycol monopropyl ether (surface tension: 25.9 mN / m) • Propylene glycol monobutyl ether (surface tension: 26.3 mN / m) • Diethylene glycol monobutyl ether (surface tension: 27.9 mN / m).

[0178] [Examples 1-48, Comparative Examples 1-5] The following evaluations were performed using the aqueous inkjet inks manufactured as described above. The evaluation results are shown in Tables 3-1 to 3-6 above.

[0179] <Evaluation of Continuous Ejection Stability> An inkjet ejection unit equipped with a Kyocera inkjet head (KJ4B-1200) was installed in a 25°C environment and filled with each type of water-based inkjet ink. After printing a nozzle check pattern to confirm that water-based inkjet ink was being ejected normally from all nozzles, 100 sheets of solid color printing at 100% coverage were performed continuously on Oji Paper's OK Topcoat+ paper under printing conditions of 1200 x 1200 dpi, drive frequency of 40 kHz, and drop volume of 3 pl. After that, the nozzle check pattern was printed again and the number of nozzle failures was visually counted to evaluate the continuous ejection stability. The evaluation criteria were as follows, with D or higher being considered a usable range. A: No nozzle failures B: 1 to 3 nozzle failures C: 4 to 6 nozzle failures D: 7 to 9 nozzle failures E: 10 or more nozzle failures

[0180] <Evaluation of Discharge Straightness> The inkjet dispensing devices used in the continuous dispensing stability evaluation above were filled with each of the water-based inkjet inks. After printing a nozzle check pattern to confirm that water-based inkjet ink was being dispensed normally from all nozzles, five 25 cm long single-dot lines (line images in which dots made of droplets of water-based inkjet ink extend parallel to the transport direction of the printing substrate) were simultaneously printed on Oji Paper's OK Topcoat+ paper under printing conditions of 1200 x 1200 dpi, drive frequency of 40 kHz, and drop volume of 3 pl. The five resulting single-dot lines were then observed, and the number of locations where droplet misalignment occurred (locations where the line was interrupted midway, and locations where droplets landed outside the single-dot line) was counted to evaluate the discharge straightness. The evaluation criteria were as follows, with C or higher being considered the usable range. A: The total number of mis-targeted shots was 25 or less. B: The total number of mis-targeted shots was between 26 and 70. C: The total number of mis-targeted shots was between 71 and 125. D: The total number of mis-targeted shots was 126 or more.

[0181] <Evaluation of Resolubility> One drop of each water-based inkjet ink was placed on a glass plate and dried in a constant temperature and humidity chamber set to 50°C and 40% RH. After a predetermined time, the glass plate was removed from the constant temperature and humidity chamber, and pure water was dropped onto the dried film to visually check whether it returned to the water-based inkjet ink. The resolubility was evaluated by performing the above evaluation while varying the standing time in the constant temperature and humidity chamber. The evaluation criteria were as follows, with C or higher being considered to be in the practically usable range. A: Even after drying for 30 minutes, it returned to a uniform water-based inkjet ink appearance, and no foreign matter such as dried film or pigment aggregates was observed. B: Even after drying for 20 minutes, it returned to a uniform water-based inkjet ink appearance, and no foreign matter such as dried film or pigment aggregates was observed. However, when using a dried film that had been dried for 30 minutes, the above foreign matter was observed visually after dropping pure water onto it. C: Even after drying for 10 minutes, it returned to a uniform water-based inkjet ink appearance, and no foreign matter such as dried film or pigment aggregates was observed. However, when using a dried film that had been dried for 20 minutes, the above foreign matter was observed visually after dropping pure water onto it. D: After drying for 10 minutes, foreign matter such as dried film and pigment aggregates was observed visually.

[0182] <Evaluation of Print Quality 1 (Dot Roundness)> Each water-based inkjet ink was filled into the inkjet ejector used in the continuous ejection stability evaluation above. Next, a gradient image was printed using the same printing conditions and the same type of printing substrate as the solid printing performed in the continuous ejection stability evaluation above. The "gradient image" above is an image in which the print density is continuously changed from 5% to 60% within a predetermined area. After printing the gradient image, the OK Topcoat + paper printed with water-based inkjet ink was placed in a forced-air constant temperature incubator set to 70°C and dried for 1 minute to obtain a gradient print. Then, the portion of the gradient print with a print density of 10% was observed using an image evaluation device (PIAS-II manufactured by Quality Engineering Associates) and the roundness of the dots was measured. The closer the roundness is to 1, the more perfectly round the dot is, indicating a good dot shape. Furthermore, if the dot shape is good, it can be said that the print quality is good. The evaluation criteria were as follows, with C or higher being considered within the practical range: A: Roundness was 1 or greater and 2 or less B: Roundness was greater than 2 and 3 or less C: Roundness was greater than 3 and 3.5 or less D: Roundness was greater than 3.5

[0183] <Evaluation of Print Quality 2 (Wettability)> Each water-based inkjet ink was filled into the inkjet ejector used in the continuous ejection stability evaluation above. Next, a solid image with 100% print coverage was printed using the same printing conditions and the same type of printing substrate as in the solid printing performed in the continuous ejection stability evaluation above. After printing the solid image, the OK Topcoat + paper printed with water-based inkjet ink was placed in a forced-air constant temperature incubator set to 70°C and dried for 1 minute to obtain a solid print. Then, the wettability of the obtained solid print was evaluated by visually checking the degree of white spots and using a magnifying glass. Generally, white spots are considered a type of printing defect, and poor wettability can cause uneven density, etc., so reducing white spots and improving wettability is effective in improving print quality. The evaluation criteria were as follows, and a rating of C or higher was considered to be in the usable range. A: No white spots were observed with the naked eye or under a magnifying glass. B: Slight white spots were observed under a magnifying glass, but no white spots were observed with the naked eye. C: Slight white spots were observed with the naked eye. D: White spots were clearly visible with the naked eye.

[0184] <Evaluation of Print Density on High-Quality Paper> The inkjet printer used in the continuous ejection stability evaluation above was filled with each of the water-based inkjet inks. Next, a solid image with 100% print density was printed on OK Prince high-quality paper (high-quality paper) manufactured by Oji Paper Co., Ltd. under the same printing conditions as the solid print performed in the continuous ejection stability evaluation above. After printing the solid image, the OK Prince high-quality paper printed with water-based inkjet ink was placed in a 60°C constant temperature oven with forced air setting within 10 seconds and dried for 1 minute to obtain a gradient print. The print was placed in a 60°C air oven. After drying for 1 minute, the print was removed from the oven, and the print density (OD value) of the obtained solid print was measured under the same conditions as in Evaluation 1. The evaluation criteria were as follows, with a rating of B or higher being considered the usable range. A: OD value of 1.3 or higher B: OD value of 1.1 or higher and less than 1.3 C: OD value less than 1.1

[0185] As can be seen from Tables 3-1 to 3-6, the aqueous inkjet inks evaluated in Examples 1 to 48 all exhibited a practical level of quality in terms of continuous ejection stability, ejection straightness, resolubility, dot roundness, wettability, and print density. In particular, the aqueous inkjet inks of Examples 24, 27 to 30 all received an "A" level in evaluations of continuous ejection stability, ejection straightness, resolubility, dot roundness, wettability, and print density on fine paper. The results showed that using a combination of a gemini-type siloxane surfactant and a polyether-modified siloxane surfactant as the siloxane surfactant (B-2), and setting the glycidyl group content represented by Formula 1 above to 70 to 120 mol%, is extremely suitable for solving the problems of the present invention described above.

[0186] On the other hand, Comparative Example 1 is a system in which the pigment dispersion resin has not been crosslinked. Due to insufficient adsorption of the pigment dispersion resin to the pigment, the dispersion stability of the pigment is considered to be poor, and as a result, it was confirmed that the product does not have practical quality in all evaluation items, including poor resolubility, print quality, and print density on high-quality paper.

[0187] Furthermore, in Comparative Example 2, which did not contain the acetylenediol-based surfactant (B-1), the absence of a surfactant with high hydrophobicity and interface orientation speed resulted in insufficient dot roundness and wettability to the printing substrate, as well as inferior continuous ejection stability and ejection straightness.

[0188] Conversely, in Comparative Example 3, which contained an acetylenediol-based surfactant (B-1) but not a siloxane-based surfactant (B-2), the acetylenediol-based surfactant (B-1) could not be uniformly oriented at the gas-liquid interface, and the dot circularity was not practical. Furthermore, deterioration in continuous discharge stability and discharge straightness was observed, which is presumed to be due to the non-uniform orientation of the acetylenediol-based surfactant near the nozzle.

[0189] Furthermore, the aqueous inkjet ink of Comparative Example 4 does not contain alkanediols with 5 to 8 carbon atoms, and the aqueous inkjet ink of Comparative Example 5 does not contain glycol ethers with 4 to 10 carbon atoms. As a result of the evaluation, it was found that the surfactant could not be sufficiently miscible, and in both cases, deterioration in continuous ejection stability occurred, as well as deterioration in print quality, which is thought to be due to the non-uniform orientation of the surfactant at the nozzle interface.

[0190] Although the present invention has been described with reference to several embodiments described above, the present invention is not limited to these embodiments. Various modifications can be made to the structure and details of the present invention within the scope of the invention. This disclosure is related to the subject matter described in Japanese Patent Application No. 2024-226410, filed on 23 December 2024, all of which are incorporated herein by reference.

Claims

1. An aqueous inkjet ink comprising pigment particles, a surfactant, and an organic solvent, wherein the pigment particles comprise a pigment and a pigment dispersion resin coating at least a portion of the surface of the pigment, the pigment dispersion resin comprises a crosslinked product of a polymer (A-1) having aromatic rings and acidic groups and an acid value of 50 to 160 mgKOH / g and a compound (A-2) having multiple glycidyl ether groups in one molecule, the surfactant comprises an acetylenediol-based surfactant (B-1) and a siloxane-based surfactant (B-2) with an measured HLB value of 6 to 9, and the organic solvent comprises an alkanediol having 3 to 4 carbon atoms, an alkanediol having 5 to 8 carbon atoms, and a glycol ether having 4 to 10 carbon atoms, and the glycidyl group content represented by the following formula (1) is 50 to 200 mol%. Formula (1):

2. The aqueous inkjet ink according to claim 1, wherein the siloxane-based surfactant (B-2) comprises a gemini-type siloxane-based surfactant.

3. The aqueous inkjet ink according to claim 1 or 2, wherein the alkanediol having 5 to 8 carbon atoms includes a branched alkyl group and is an alkanediol that is not a 1,2-alkanediol.

4. The aqueous inkjet ink according to claim 1 or 2, wherein the glycol ether having 4 to 10 carbon atoms comprises at least one selected from the group consisting of propylene glycol monoalkyl ether having 3 to 4 carbon atoms in the alkyl group at the molecular terminus, and dipropylene glycol monoalkyl ether having 3 to 4 carbon atoms in the alkyl group at the molecular terminus.

5. A printed article obtained by printing the aqueous inkjet ink according to claim 1 or 2 onto a printing substrate.

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