Water-based inkjet inks and printed materials

Abstract

To provide an aqueous inkjet ink which can produce printed matter with excellent print density and print quality on various printing substrates regardless of the permeability of the printing substrate, which has good drying properties and abrasion resistance, and which is also excellent in ink storage stability and linear advancement of ink droplets from an inkjet head. [Solution] The aqueous inkjet ink comprises crosslinked polymer particles (A) containing a crosslinking reaction product obtained by crosslinking a polymer (A-1) having an aromatic ring or the like and a specified acid value with a specific amount of a compound (A-2) having multiple glycidyl groups, a binder resin (B) containing a resin (B-1) having an aromatic ring and a specified acid value, and an organic solvent (C) containing a glycol monoalkyl ether solvent (C-1) having a specified boiling point and number of carbon atoms, and the difference in the amount of structural units derived from the aromatic ring-containing polymerizable monomer contained in the polymer (A-1) and the resin (B-1) is specified.

Description

[Technical Field]

[0001] The present invention relates to an aqueous inkjet ink and a printed matter obtained by printing the aqueous inkjet ink on a printing substrate. [Background technology]

[0002] Inkjet printing is a recording method in which droplets are ejected directly from minute nozzles and deposited on a printing substrate to produce characters and / or images. Inkjet printing has become extremely popular due to its many advantages, including low noise and ease of operation, ease of use, low cost, full color printing, and non-contact printing on a variety of printing substrates.

[0003] In recent years, inkjet printing has been increasingly used not only in offices and homes (consumer printing applications), but also in the commercial and industrial printing markets. Demand for water-based inkjet inks is also increasing, with the aim of increasing printing speed, improving print quality, and reducing environmental impact.

[0004] In particular, in the commercial printing market, consumer needs are becoming increasingly diverse, and there is a demand for printing on low-permeability substrates such as coated paper in addition to high-permeability substrates such as fine paper and plain paper. Thus, the commercial printing market is in need of aqueous inkjet inks that can print on a variety of printing substrates with different liquid permeabilities without the need for replacement.

[0005] However, aqueous inkjet inks generally have low viscosity. Therefore, when printed on a highly permeable substrate, the colorant components contained in the aqueous inkjet ink may penetrate into the highly permeable substrate, resulting in a decrease in print density. In particular, when a paper substrate is used as the printing substrate, feathering (a phenomenon in which the aqueous inkjet ink penetrates along the paper fibers, causing characters and images to bleed) may occur, which may lead to a deterioration in print image quality, such as the visibility of characters.

[0006] On the other hand, when printing on low-permeability substrates such as coated paper, aqueous inkjet inks have difficulty penetrating, and colorant components tend to remain on the surface of the printing substrate, making it easier to achieve higher print density than when using highly permeable substrates. However, if the surface of the film (ink film) formed by the dried aqueous inkjet ink after drying the aqueous inkjet ink on the printing substrate is not smooth, it is difficult to achieve high print density. For example, after drying of the aqueous inkjet ink, coarse particle components contained in the aqueous inkjet ink are exposed on the ink film surface, creating unevenness, which can cause light incident on the ink film to be diffusely reflected by the ink film surface, resulting in a decrease in print density. In addition, because aqueous inkjet inks have difficulty penetrating low-permeability substrates such as coated paper, there is also the problem that the ink does not dry during high-speed printing, making it difficult to achieve sufficient abrasion resistance, compared to highly permeable substrates such as fine paper and plain paper.

[0007] Furthermore, some low-permeability substrates, such as coated paper, have low surface free energy. When aqueous inkjet ink is printed on such a substrate, the ink is less likely to spread across the surface of the substrate, resulting in white spots (a phenomenon in which areas of the substrate where the ink is not applied appear as spots and / or streaks). Furthermore, because the ink is less likely to penetrate a substrate with low surface free energy, droplets of the ink in a wet state tend to coalesce, resulting in color bleeding.

[0008] In order to improve print quality when printing on low-permeability substrates, it is effective to reduce the surface tension of the aqueous inkjet ink, and surfactants and organic solvents are generally used for this purpose. For example, Patent Document 1 describes that an aqueous inkjet ink containing a low-boiling-point water-soluble organic solvent, a low-surface-tension organic solvent, and a siloxane-based surfactant can improve the printability and print quality of low-permeability substrates such as coated paper, art paper, and vinyl chloride sheets. However, when printing on high-permeability substrates such as plain paper or high-quality paper using the aqueous inkjet ink described in Patent Document 1, feathering is likely to occur, which may result in deterioration of print quality, such as character visibility. Furthermore, depending on the configuration of the aqueous inkjet ink, there is also the problem that the low surface tension makes it easy for the ink to penetrate into high-permeability substrates, making it difficult to achieve excellent print density.

[0009] Patent Document 2 discloses an aqueous inkjet black ink that uses carbon black having a specific specific surface area, an alkanediol having 5 to 8 carbon atoms, and a resin having a specific acid value, thereby enabling the production of high-density prints on printing substrates that do not have an ink-receiving layer. In the examples of Patent Document 2, coated paper that does not have a receiving layer is used as the printing substrate. However, when printing with the aqueous inkjet black ink on highly permeable substrates such as plain paper or high-quality paper, the carbon black does not sufficiently remain on the printing substrate, making it difficult to obtain excellent print density. Furthermore, when the aqueous inkjet black ink specifically disclosed in the examples of Patent Document 2 is used, depending on the structure of the inkjet head used for printing and the printing conditions, the carbon black may aggregate when the aqueous inkjet black ink dries near the nozzles of the inkjet head. The precipitation of the aggregated carbon black may cause deflection of the ink (a phenomenon in which droplets of the aqueous inkjet ink are ejected in a direction that is not perpendicular to the nozzle surface of the inkjet head). When deflection occurs, that is, when the straightness of droplets of aqueous inkjet ink deteriorates, it can lead to deterioration in print quality, such as the occurrence of streaky unevenness in the printed matter.

[0010] Meanwhile, various methods for improving print density when printed on highly permeable substrates have also been studied. For example, Patent Document 3 discloses an aqueous inkjet ink that uses a self-dispersed pigment with a specific particle size in combination with a resin-dispersed pigment, making it possible to produce printed matter with high print density on plain paper. However, depending on the type of highly permeable substrate, such as plain paper, it may not be possible to prevent the pigment from penetrating into the highly permeable substrate, resulting in insufficient print density. Furthermore, the aqueous inkjet ink specifically disclosed in the examples of Patent Document 3 may not dry sufficiently when printed on a low-permeable substrate, such as coated paper, resulting in color bleeding and poor abrasion resistance.

[0011] Furthermore, Patent Document 4 discloses an ink composition for inkjet recording containing three types of acetylene diol surfactants with different structures. It is also claimed that use of this ink composition enables high-speed recording of images with excellent print quality (color unevenness, aggregation, and bleeding) and fixation (abrasion resistance) on a variety of printing substrates with different absorbencies. However, when this ink composition is used on a highly permeable substrate, the surfactant reduces the surface tension of the ink composition, which can lead to the pigment components penetrating into the printing substrate and reducing print density. Furthermore, the inventors' investigations revealed that the ink composition specifically disclosed in the examples of Patent Document 1 not only has poor drying properties and abrasion resistance of printed matter, but also can cause problems with droplet straightness depending on printing conditions, etc. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-205768 [Patent Document 2] Japanese Patent Publication No. 2020-125452 [Patent Document 3] Japanese Patent Application Publication No. 2018-172502 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-124238 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an aqueous inkjet ink that can produce printed matter with excellent print density and print quality on various printing substrates regardless of the permeability of the printing substrate, that has good drying properties and abrasion resistance, and that further has excellent ink storage stability and straightness of ink droplets traveling from an inkjet head. [Means for solving the problem]

[0014] The present inventors have conducted extensive research to solve the above problems, and have discovered an aqueous inkjet ink having the following composition, thereby completing the present invention.

[0015] That is, the present invention relates to the aqueous inkjet inks described below in [1] to [4], and to the printed matter described below in [5], which is obtained by printing the aqueous inkjet ink on a printing substrate. [1] An aqueous inkjet ink containing pigment-containing crosslinked polymer particles (A), a binder resin (B), an organic solvent (C), and a surfactant (D), the crosslinked polymer particles (A) contain a crosslinked reaction product obtained by crosslinking a polymer (A-1) with a compound (A-2) having a plurality of glycidyl groups in one molecule, the polymer (A-1) has an aromatic ring and a carboxy group and / or a carboxylate group, and has an acid value of more than 50 mgKOH / g and not more than 160 mgKOH / g; The content of the compound (A-2) is an amount such that the content of the glycidyl group represented by the following formula (1) is 50 to 200 mol %, the binder resin (B) contains a resin (B-1) having an aromatic ring and an acid value of 50 mgKOH / g or less, the organic solvent (C) contains a glycol monoalkyl ether solvent (C-1) having a boiling point of 120 to 230°C under 1 atmospheric pressure and having 4 to 10 carbon atoms; An aqueous inkjet ink, wherein the value represented by W1-W2 is 1 to 60, where W1 (mass%) is the content of structural units derived from polymerizable monomers having an aromatic ring relative to the total mass of the polymer (A-1), and W2 (mass%) is the content of structural units derived from polymerizable monomers having an aromatic ring relative to the total mass of the resin (B-1). Formula (1):

number

[0016] The present invention has made it possible to provide an aqueous inkjet ink that can produce printed matter with excellent print density and print quality on a variety of printing substrates, regardless of the permeability of the printing substrate, that has good drying properties and abrasion resistance, and that is also excellent in ink storage stability and the ability of ink droplets to travel in a straight line from an inkjet head. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of the aqueous inkjet ink (hereinafter also referred to simply as "ink") of the present invention are described in detail below. Note that the present invention is not limited to the following embodiments, and includes modifications that are implemented within the scope of the present invention.

[0018] As described above, when printing an aqueous inkjet ink containing a colorant component such as a pigment on a highly permeable substrate such as plain paper or high-quality paper, the components in the aqueous inkjet ink penetrate into the printing substrate together with a portion of the colorant component, which tends to reduce the pigment concentration on the surface of the printing substrate, i.e., the print density. Furthermore, when a paper substrate is used as the highly permeable substrate, feathering tends to occur as described above, which tends to lead to a decrease in print image quality, such as a decrease in the visibility of characters. Therefore, in order to improve the print density on a highly permeable substrate and suppress feathering, it is important to retain the pigment on the surface of the printing substrate and suppress its penetration.

[0019] On the other hand, low-permeability substrates, such as coated paper, tend to retain pigments on the substrate, making it less likely that print density will decrease due to pigment penetration, as it does with high-permeability substrates. However, as mentioned above, unevenness may occur on the ink film surface after drying of the aqueous inkjet ink, potentially resulting in a decrease in print density. Therefore, to improve print density on low-permeability substrates, it is important to increase the smoothness of the ink film surface after printing. In addition, some low-permeability substrates have low surface free energy. Water-based inkjet inks are extremely difficult to wet and spread on the surface of such printing substrates, which can lead to a decrease in print density and deterioration of print quality, such as whiteout. Furthermore, low-permeability substrates also have low penetration of liquid components into the substrate, which can lead to the risk of another ink droplet landing adjacent to a previously landed aqueous inkjet ink droplet before it has fully dried, resulting in beading (a phenomenon in which wet ink droplets coalesce). Beading can cause color bleeding and uneven density, and is therefore undesirable from the perspective of improving print quality. Thus, in order to achieve improved print quality in inkjet printing on low-permeability substrates, it is necessary to ensure sufficient wettability and permeability of the aqueous inkjet ink.

[0020] In general, an effective method for ensuring the wettability and permeability of an ink is to reduce the surface tension of the ink using surfactants and organic solvents. However, while this method can improve the wettability and permeability of the ink on low-permeability substrates, when high-permeability substrates such as plain paper and high-quality paper are used, the aqueous inkjet ink tends to penetrate along the fibers of the paper substrate. As a result, feathering occurs, which can easily lead to deterioration in print image quality, such as reduced character visibility.

[0021] Incidentally, plain paper and fine paper, which are highly permeable substrates, contain cationic components such as salts of polyvalent metals such as calcium and cationic polymers as fillers, pigments, sizing agents, etc. On the other hand, aqueous inkjet inks containing pigments contain carboxyl groups, carboxylate groups (COO - In this case, a resin (pigment dispersion resin) having anionic groups such as methyl methacrylate (MMA), ...

[0022] Generally, pigment dispersion resins used in aqueous inkjet inks have the above-mentioned anionic group and a hydrophobic group such as an aromatic ring structure or a long-chain alkyl group. The anionic group is introduced to improve affinity for water, which is the main component, and to stabilize the dispersed state of the pigment by electric charge repulsion between pigment dispersion resins. On the other hand, the hydrophobic group functions, for example, as an adsorptive group for the pigment.

[0023] However, while improving the reactivity of the pigment dispersion resin with cationic components improves print density on high-permeability substrates, it also makes it difficult to maintain pigment dispersion stability in the aqueous inkjet ink, potentially leading to a decrease in the storage stability of the ink. It has also been found that when printing on low-permeability substrates such as coated paper, the pigment easily aggregates during the drying process, resulting in a loss of ink film surface smoothness and a decrease in print density. Furthermore, when printing on low-permeability substrates, secondary particles consisting of aggregated pigment generated due to poor dispersion in the ink inhibit the orientation of surfactants to the interface within the ink droplets. As a result, it has also been found that the wettability and permeability on the low-permeability substrate are reduced, potentially resulting in a decrease in print density and print image quality. In addition, it has become clear that when water, the main component of the aqueous inkjet ink, partially evaporates near the nozzle of the inkjet head, the aqueous inkjet ink containing the pigment whose dispersion state has been destroyed increases in viscosity, causing the ink droplets ejected from the inkjet head to deflect in flight, resulting in streaky unevenness when they land on the printing substrate, i.e., leading to further deterioration of the print image quality or worsening the straightness of the ink droplets.

[0024] Among the above-mentioned phenomena, high-boiling-point organic solvents are generally used to suppress water evaporation near the nozzles of inkjet heads and prevent ink thickening. However, high-boiling-point organic solvents tend to remain on the printing substrate. On the other hand, because water volatilizes preferentially, when an ink containing a high-boiling-point organic solvent is printed on a highly permeable substrate, the amount of water required in the ink to elute the cationic components is relatively small. As a result, it has been found that the reaction between the pigment dispersion resin and the cationic components is insufficient, resulting in a decrease in print density. Furthermore, it has been found that the residue of high-boiling-point solvents on a highly permeable substrate can cause the ink to penetrate along the paper fibers, resulting in feathering and reduced character visibility, i.e., a deterioration in the print quality of the printed material.

[0025] In order to solve the above-mentioned problems, the present inventors conducted extensive research and discovered an aqueous inkjet ink having the above-mentioned configuration. In other words, by using such an aqueous inkjet ink, it is possible to obtain printed matter with excellent print density, print quality, and drying properties on various printing substrates, regardless of the permeability of the printing substrate, and the ink droplets from the inkjet head also have excellent linearity. Furthermore, the aqueous inkjet ink also has the effect of excellent abrasion resistance. Although the detailed mechanism by which the above-mentioned configuration achieves these effects is unclear, the following may be an example.

[0026] First, the pigment-containing crosslinked polymer particles (A) contained in the aqueous inkjet ink of the present invention contain a crosslinked reaction product obtained by crosslinking a polymer (A-1) having an aromatic ring and a carboxyl group and / or a carboxylate group and an acid value of more than 50 mgKOH / g and not more than 160 mgKOH / g with a compound (A-2) having multiple glycidyl groups per molecule. Furthermore, the compound (A-2) is used so that the glycidyl group content represented by formula (1) is 50 to 200 mol %.

[0027] In general, pigment dispersion resins with higher acid values ​​tend to repel charges more easily in liquid media containing water (aqueous media), enabling stable dispersion of pigments in the aqueous media. On the other hand, on highly permeable substrates, the pigment dispersion state is less likely to be disrupted even when in contact with the cationic component, making it difficult to obtain excellent print quality and print density. Conversely, pigment dispersion resins with lower acid values ​​are more susceptible to the influence of the cationic component, i.e., the reactivity of the pigment dispersion resin with the cationic component is high. However, as described above, in this case, the pigment dispersion state is likely to become unstable in the aqueous media, making it difficult to ensure the straightness of ink droplets from the inkjet head, storage stability, and even print density and print quality of printed matter on low-permeable substrates.

[0028] In contrast, the crosslinked polymer particles (A) of the present invention contain a crosslinked reaction product obtained by crosslinking a polymer (A-1) having an aromatic ring and a carboxyl group and / or a carboxylate group and an acid value of more than 50 mgKOH / g and not more than 160 mgKOH / g with a compound (A-2) having multiple glycidyl groups in one molecule, whereby the acid value of the crosslinked reaction product is smaller than that of the polymer (A-1).

[0029] In polymer (A-1), the aromatic rings function as adsorption groups to the pigment, and the carboxyl and / or carboxylate groups react (crosslink) with compound (A-2). As a result, desorption of polymer (A-1) from the pigment surface is suppressed. Furthermore, even if the crosslinked reaction product has a low acid value, the dispersion stability of the crosslinked polymer particles (A) in the aqueous inkjet ink and the storage stability of the ink can be maintained. Furthermore, since the formation of secondary pigment particles, which can hinder surfactant orientation, is suppressed, the surfactant can be quickly oriented at the ink interface, resulting in prints with excellent print quality and minimal whiteout and color bleeding, even on low-permeability substrates such as coated paper. Furthermore, even if a portion of the water in the ink evaporates near the nozzle of the inkjet head, the dispersion stability of the crosslinked polymer particles (A) is maintained, which is believed to result in an aqueous inkjet ink with excellent ink droplet linearity. Additionally, a crosslinked reaction product that satisfies the acid value requirements of polymer (A-1) and the glycidyl group content requirement described above has a sufficiently low acid value. Therefore, on highly permeable substrates, the crosslinked polymer particles (A) can react quickly with the cationic component, resulting in prints with excellent print density. Furthermore, the increased aggregation rate on highly permeable substrates is thought to suppress bleeding along the paper fibers, leading to improved print quality. On the other hand, when printing on low-permeable substrates, the dispersion state is less likely to be destroyed during the drying process after printing, suppressing aggregation of the crosslinked polymer particles (A). As a result, the smoothness of the ink film is less likely to be impaired, resulting in prints with excellent print density.

[0030] The aqueous inkjet ink of the present invention further comprises, as the binder resin (B), a resin (B-1) having an aromatic ring and an acid value of 50 mgKOH / g or less. Furthermore, when the content of structural units derived from a polymerizable monomer having an aromatic ring contained in 100 g of the polymer (A-1) is W1 (g), and the content of structural units derived from a polymerizable monomer having an aromatic ring contained in 100 g of the resin (B-1) is W2 (g), the value represented by W1 - W2 is 1 to 60.

[0031] Generally, binder resins are used to bond ink films to printing substrates, and the resins form films during the drying process, improving the drying properties and abrasion resistance of the ink film. However, if the compatibility between the binder resin and the dispersing resin is poor, the resin molecules may not be sufficiently entangled during the drying process, which may lead to poor film formation and reduced drying properties and abrasion resistance. Furthermore, if the compatibility between the binder resin and the dispersing resin is poor, localized thickening of the ink present at the nozzle end face of the inkjet head may occur, causing the ink droplets to deflect, i.e., reducing their ability to travel in a straight line.

[0032] As described above, dispersion resins used in aqueous inkjet inks generally contain anionic groups and hydrophobic groups. From the perspective of improving compatibility with such dispersion resins, it is preferable for the binder resin to have a structure similar to that of the dispersion resin. However, while introducing anionic groups into the binder resin improves compatibility with the dispersion resin, when printing on a highly permeable substrate, cationic components may react with the anionic groups in the binder resin on the paper surface, inhibiting the reaction with the dispersion resin and resulting in a decrease in print density. Furthermore, when hydrophobic groups are introduced into the binder resin, the hydrophobic groups in the binder resin adsorb to the pigment, stabilizing the dispersion of the pigment itself. This makes it difficult for the pigment to aggregate when reacting with the cationic components on a highly permeable substrate, and this may also result in a printed product with poor print density.

[0033] Therefore, the ink of the present invention uses a resin (B-1) having an acid value of 50 mgKOH / g or less as the binder resin (B), and the value represented by W1-W2 satisfies 1 to 60. By keeping the difference between the amount of structural units derived from the aromatic ring-containing polymerizable monomer in the resin (B-1) and the amount of structural units derived from the aromatic ring-containing polymerizable monomer in the polymer (A-1) below a certain value, sufficient affinity between the hydrophobic portion of the crosslinked reaction product formed by crosslinking the polymer (A-1) with the compound (A-2) and the hydrophobic portion of the resin (B-1) is achieved, and adsorption of the resin (B-1) to the pigment is also suppressed. As a result, the crosslinked polymer particles (A) and the resin (B-1) are sufficiently compatible even during the drying process, providing excellent drying properties and abrasion resistance on low-permeability substrates and excellent print density and print quality on high-permeability substrates. Furthermore, the ink can be produced with excellent ink droplet linearity from an inkjet head.

[0034] Additionally, the aqueous inkjet ink of the present invention contains, as the organic solvent (C), one or more glycol monoalkyl ether solvents (C-1) having a boiling point of 120 to 230°C at 1 atmospheric pressure and having 4 to 10 carbon atoms.

[0035] This improves the ink's wettability and penetration into low-permeability substrates, as well as the film-forming properties of the resin (B-1), resulting in prints with excellent print quality and minimal color bleeding and whiteout. The drying and scratch resistance of the prints are also improved. Furthermore, the glycol monoalkyl ether solvent (C-1) is less likely to remain on high-permeability substrates, which is believed to facilitate the suppression of the rate at which the water content in the ink decreases as the ink dries. As a result, a sufficient amount of cationic components in the high-permeability substrate are eluted into the ink, allowing the reaction between the cationic components and the crosslinked polymer particles (A) to proceed favorably. This not only suppresses feathering, but also results in prints with excellent print density.

[0036]

[0023] As described above, the above-described configuration is essential for obtaining an aqueous inkjet ink that can produce printed matter with excellent print density and print quality on a variety of printing substrates regardless of the permeability of the printing substrate, and that also has excellent ink storage stability, linearity of ink droplets from an inkjet head, and drying properties and abrasion resistance of the printed matter. Note that the above-described mechanism is merely speculation and does not limit the present invention in any way.

[0037] Next, the main components of the aqueous inkjet ink of the present invention will be described below.

[0038] <Pigment-containing crosslinked polymer particles (A)> The aqueous inkjet ink of the present invention contains pigment-containing crosslinked polymer particles (A). The pigment-containing crosslinked polymer particles (A) contain the pigment and a crosslinking reaction product. The crosslinking reaction product is obtained by crosslinking a polymer (A-1) having an aromatic ring and a carboxyl group and / or a carboxylate group and having a viscosity of more than 50 mgKOH / g and not more than 160 mgKOH / g with a compound (A-2) having multiple glycidyl groups per molecule. The crosslinking treatment crosslinks the polymer (A-1) on the pigment surface, making it possible to suppress detachment of the polymer (A-1) in the aqueous inkjet ink. As a result, it is possible to achieve both print density and print image quality of the printed matter, ejection stability, and storage stability of the aqueous inkjet ink.

[0039] In the present application, "pigment-containing crosslinked polymer particles" refers to particles obtained after a crosslinking treatment is performed on a polymer contained in a pigment-containing crosslinked polymer particle precursor using compound (A-2) as a crosslinking agent (a compound used to chemically bond polymer molecules together). Furthermore, the "pigment-containing crosslinked polymer particle precursor" refers to particles in a stage prior to the crosslinking treatment, such as one or more particles selected from the group consisting of particles of a polymer encapsulating a pigment, particles containing a polymer and a pigment and having a sea-island structure in which part of the pigment may be exposed on the particle surface, and pigment particles having a polymer chemically adsorbed and / or bonded to at least part of their surface.

[0040] As is clear from the above, the polymer (A-1) constituting the "pigment-containing crosslinked polymer particle precursor" has at least the function of a pigment dispersing resin.

[0041] Pigments The pigment contained in the pigment-containing crosslinked polymer particles (A) may be an organic pigment and / or an inorganic pigment. The hue of the pigment used is not particularly limited, and examples thereof include chromatic pigments such as yellow, green, cyan, blue, violet, magenta, red, and orange, and achromatic pigments such as white and black.

[0042] When an inorganic pigment is used as the pigment, examples of the inorganic pigment that can be used include titanium oxide, zinc white, zinc sulfide, white lead, calcium carbonate, precipitated barium sulfate, white carbon, alumina white, kaolin clay, 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, Prussian blue, cobalt blue, cerulean blue, cobalt silica blue, cobalt zinc silica blue, manganese violet, and cobalt violet.

[0043] As the carbon black, carbon black produced by the furnace method or the channel method can be used. Among these carbon blacks, those having a primary particle size of 11 to 40 nm and a specific surface area measured by the BET method of 50 to 400 m 2 / g, a volatile content of 0.5 to 10%, a pH value of 2 to 10, and the like are suitable.

[0044] 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, benzimidazolone pigments, and threne pigments.

[0045] Specific examples of organic pigments that can be used as the pigment include, by color index, CI Pigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, and 64, which are cyan or blue organic pigments.

[0046] Furthermore, examples of organic pigments that exhibit magenta, red, or violet include CI 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, and 282, and CI Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, and 50.

[0047] Further, examples of organic pigments that exhibit a yellow color include CI 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.

[0048] Examples of black pigments include aniline black (CI Pigment Black 1), perylene black (CI Pigment Black 31, 32), and azomethine azo black.

[0049] In addition to the above pigments, CI Pigment Green 7, 10, 36, CI Pigment Brown 3, 5, 25, 26, CI Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, etc. can also be used.

[0050] The pigments listed above may be used alone or in combination of two or more. For example, a black pigment composition may be prepared by using two or more of the pigments listed above. 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, based on the total mass of the aqueous inkjet ink.

[0051] <Polymer (A-1)> As described above, the polymer (A-1) used in the present invention has the function of dispersing pigments, i.e., it is a pigment dispersing resin. The polymer (A-1) also has an aromatic ring and a carboxyl group and / or a carboxylate group in its structure. Furthermore, the acid value of the polymer (A-1) is greater than 50 mgKOH / g and less than 160 mgKOH / g. Any resin can be used as the polymer (A-1) in the ink of the present invention, as long as it satisfies these requirements and has the function of dispersing pigments. Specifically, types of resins that can be used as the polymer (A-1) include acrylic, styrene, maleic acid, urethane, and polyester. Among these, acrylic and / or maleic acid polymers are preferred because they have strong adsorption to pigments and can stably disperse pigments even after crosslinking.

[0052] In this application, the term "acrylic polymer" refers to a polymer using one or more polymerizable monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters (a styrene-based monomer may also be used). However, polymers containing maleic acid (anhydride) (maleic acid and / or maleic anhydride) as a polymerizable monomer are not included in the term "acrylic polymer." In the present application, the term "maleic acid-based polymer" refers to a polymer using at least maleic acid (anhydride) as a polymerizable monomer. The maleic acid-based polymer may further use one or more polymerizable monomers selected from the group consisting of α-olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, and styrene derivatives.

[0053] The polymer (A-1) has a carboxy group and / or a carboxylate group. Preferably, the polymer (A-1) has at least a carboxylate group. This is because the charge of the carboxylate group allows the pigment-containing crosslinked polymer particles (A) to be stably dispersed by charge repulsion even when the acid value after the crosslinking reaction is low, thereby improving the storage stability of the ink.

[0054] The carboxylate groups in the polymer (A-1) may be introduced into the polymer (A-1) by synthesizing a polymer using a polymerizable monomer having a carboxylate group, or may be formed in the polymer (A-1) by neutralizing at least a portion of the carboxy groups present in the polymer with a basic compound (neutralization treatment). Examples of the basic compound include ammonia; alkanolamines such as dimethylaminoethanol, diethanolamine, and triethanolamine; and alkali metal compounds such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, and sodium borate. Among these, alkali metal compounds are preferred as the basic compound, as they improve the dispersion stability of the pigment-containing crosslinked polymer particles (A) and thus the storage stability of the ink, and also suppress pigment aggregation during the ink drying process, resulting in excellent droplet linearity from the inkjet head and excellent print density. The use of hydroxides such as sodium hydroxide and potassium hydroxide is particularly preferred. The basic compounds listed above can be used alone or in combination of two or more.

[0055] As the polymer (A-1), a polymer having only carboxy groups (hereinafter referred to as polymer (A-1-0)) may be used as is, or a polymer obtained by neutralizing at least a portion of the carboxy groups in the polymer (A-1-0) may be used as the polymer (A-1). However, as described above, since the polymer (A-1) preferably has at least carboxylate groups, in the ink of the present invention, it is more preferable to use a polymer obtained by neutralizing the polymer (A-1-0) as the polymer (A-1), rather than using the polymer (A-1) as the polymer (A-1). On the other hand, when neutralization is performed, the amount of basic compound used to neutralize the carboxy groups in the polymer to be neutralized is preferably an amount such that the neutralization ratio, represented by the following formula (2), is 10 to 200 mol %. By performing neutralization so that the neutralization ratio is 10 to 200 mol %, the dispersion stability of the pigment and crosslinked polymer particles (A), and therefore the storage stability of the ink, are improved. The neutralization rate is more preferably 40 to 160 mol %, and particularly preferably 60 to 120 mol %.

[0056] Formula (2):

number

[0057] The "polymer" in formula (2) above may be the polymer (A-1-0) having only carboxy groups, or a polymer having both carboxy and carboxylate groups. The "acid value of the polymer" in formula (2) above can be measured by standard methods. For example, approximately 1 g of sample is precisely weighed into an Erlenmeyer flask and dissolved in 50 mL of a distilled water / dioxane mixture (distilled water / dioxane = 1 / 9 by mass). The sample solution is then titrated with a 0.1 mol / L potassium hydroxide-ethanol solution (potency F) using a potentiometric measurement device (e.g., the "AT-710M Automatic Potentiometric Titrator" manufactured by Kyoto Electronics Manufacturing Co., Ltd.). The amount of potassium hydroxide-ethanol solution (α (mL)) required to reach the titration endpoint is then measured. The acid value of the polymer (mg KOH / g) can then be calculated using formula (3) below.

[0058] Formula (3): Acid value (mgKOH / g)={(5.611×α×F) / S}

[0059] In the above equation (3), S is the amount of sample polymer collected (g), α is the amount of 0.1 mol / L potassium hydroxide ethanol solution used until the titration ends (mL), and F is the titer of the 0.1 mol / L potassium hydroxide ethanol solution.

[0060] The acid value of the polymer (A-1-0) and the acid value of the polymer obtained by neutralizing the polymer (A-1-0) are assumed to be the same.

[0061] The acid value of polymer (A-1) (i.e., the acid value of polymer (A-1-0)), which can be measured by the above-mentioned method, is preferably more than 50 mgKOH / g and not more than 160 mgKOH / g, more preferably 70 to 160 mgKOH / g, and particularly preferably 80 to 150 mgKOH / g, from the viewpoints of favorable reaction with cationic components present in highly permeable substrates such as fine paper, producing printed matter with excellent print density and print quality, maintaining strong adsorption to the pigment even after becoming a crosslinked reaction product and improving the storage stability of the ink, and maintaining excellent ink droplet linearity when some water evaporates on the inkjet head.

[0062] The weight-average molecular weight (Mw) of the polymer (A-1) is preferably 5,000 to 100,000. From the viewpoints of making the dispersion stability of the crosslinked polymer particles (A) and the storage stability of the ink favorable and maintaining the dispersed state even when water evaporates in the inkjet head, and thus improving the straightness of the ink droplets, the weight-average molecular weight (Mw) is more preferably 10,000 to 50,000, and even more preferably 15,000 to 35,000.

[0063] The weight-average molecular weight of the polymer can be measured by a conventional method, for example, a polystyrene-equivalent value measured using a TSKgel column (manufactured by Tosoh Corporation) with a GPC ("HLC-8120GPC" manufactured by Tosoh Corporation) equipped with an RI detector and THF as a developing solvent can be used.

[0064] The content ratio of the pigment to the polymer (A-1) (pigment / polymer (A-1)) is preferably 1 to 100 by mass. By making this ratio 1 or more, the viscosity of the ink can be controlled to a level suitable for an inkjet ink, and by making it 100 or less, the dispersion stability and storage stability can be improved. Furthermore, the content ratio of the pigment to the polymer (A-1) is more preferably 2 to 50.

[0065] ≪Compound (A-2)≫ The compound (A-2) used in the ink of the present invention is preferably a compound having multiple glycidyl groups per molecule. The compound (A-2) may be either water-soluble or water-insoluble, but its solubility in 100 g of water at 25°C is preferably 0.1 to 50 g / 100 g H2O. By controlling the solubility of the compound (A-2) in water within the above range, reaction with components other than the polymer (A-1), such as water, can be suppressed, and the crosslinking reaction of the polymer (A-1) can proceed near the pigment, preventing detachment of the polymer (A-1) associated with the crosslinking reaction. This results in particularly improved linearity of ink droplets from the inkjet head, and allows for prints of excellent print quality, free of white voids, to be obtained on low-permeability substrates such as coated paper. Furthermore, from the viewpoint of more suitably exhibiting these effects, the amount of the compound (A-2) dissolved in 100 g of water at 25° C. is more preferably 0.2 to 40 g / 100 g H2O, and even more preferably 0.5 to 30 g / 100 g H2O.

[0066] It is more preferable to use a compound having a plurality of glycidyl ether groups, i.e., two or more, in one molecule as compound (A-2).Furthermore, it is particularly preferable that compound (A-2) is a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms.

[0067] The epoxy equivalent of the compound (A-2) is preferably 90 to 300 g / eq., and more preferably 100 to 200 g / eq., from the viewpoint of being able to efficiently undergo a crosslinking reaction with the carboxy groups and / or carboxylate groups present in the polymer (A-1) in an aqueous medium.

[0068] Specific examples of compounds having two or more glycidyl ether groups in one 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, bisphenol A diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether.

[0069] The compound (A-2) used in the ink of the present invention is preferably used in an amount such that the glycidyl group content represented by the above formula (1) is 50 to 200 mol %. The glycidyl group content is more preferably 65 to 180 mol %, and even more preferably 80 to 160 mol %. By keeping the glycidyl group content within the above range, it becomes possible to crosslink the polymer (A-1) adsorbed to the pigment at a high density. As a result, the storage stability of the aqueous inkjet ink can be improved, the straightness of the ink droplets from the inkjet head can be improved, and printed matter with excellent print density and print quality can be easily obtained regardless of the permeability of the printing substrate.

[0070] <<Method for producing aqueous dispersion of pigment-containing crosslinked polymer particles (A)>> Examples of methods for producing an aqueous dispersion of pigment-containing crosslinked polymer particles (A) include the following. First, a polymer (A-1-0) having only carboxy groups is mixed with a basic compound in water, and at least a portion of the carboxy groups is neutralized (neutralization treatment) to obtain an aqueous solution of polymer (A-1) having at least carboxylate groups. Next, a pigment is added to the aqueous solution of polymer (A-1), and after thorough mixing, further dispersion treatment is performed to produce an aqueous dispersion of the pigment (pigment-containing crosslinked polymer particle precursor) dispersed by the polymer (A-1). Then, compound (A-2) is added to the aqueous dispersion of the pigment-containing crosslinked polymer particle precursor, and crosslinking treatment is performed to produce an aqueous dispersion of pigment-containing crosslinked polymer particles (A).

[0071] In the present application, the term "aqueous solution" refers to a solution containing an aqueous solvent and components dispersed and / or dissolved in the aqueous solvent.

[0072] Distributed processing In dispersing the pigment, it is preferable to pre-disperse (premix) the pigment and the polymer (A-1) using a commonly used mixing and stirring device such as a stirrer, and then disperse (main dispersion) using a conventionally known disperser. By performing pre-dispersion before main dispersion, a pigment dispersion liquid with a uniform particle size can be obtained. The dispersing machine used for the main dispersion of the pigment can be any commonly used dispersing machine, such as a paint shaker, a ball mill, a roll mill, a bead mill, a kneader, an attritor, or a high-pressure homogenizer. Among these, a bead mill is preferably used because it can disintegrate and refine coarse pigment particles. Examples of bead mills include a super mill, a sand grinder, an agitator mill, a grain mill, a dyno mill, a pearl mill, and a cobol mill (all of which are trade names), and any of these can be suitably used.

[0073] <Cross-linking treatment> In the crosslinking treatment, the polymer (A-1) adsorbed on the pigment is crosslinked by the compound (A-2), thereby obtaining a crosslinked reaction product. In the above-described production method, after the crosslinking treatment is completed, an aqueous dispersion of crosslinked polymer particles (A) containing the pigment can be obtained.

[0074] From the viewpoint of efficient crosslinking reaction, the temperature for the crosslinking treatment is preferably 50 to 95° C., more preferably 70 to 85° C. From the same viewpoint as above, the time for the crosslinking treatment is preferably 0.5 to 10 hours, more preferably 1 to 8 hours, and even more preferably 2 to 5 hours.

[0075] The average particle size of the pigment-containing crosslinked polymer particles (A) is preferably 60 to 200 nm, more preferably 70 to 175 nm, and particularly preferably 80 to 150 nm, from the viewpoints of enabling the ink to be stably ejected from the nozzle and ensuring good straightness of the ink droplets.

[0076] The "average particle size" refers to the median diameter on a volume basis and can be measured by dynamic light scattering. For example, it can be measured using a Microtrac-Bell Nanotrac UPA-EX150 at 25°C.

[0077] The pH of the aqueous dispersion of the pigment-containing crosslinked polymer particles (A) is preferably 8 to 12. If the pH is within this range, the carboxy groups in the polymer (A-1) are likely to become carboxylate groups, and favorable charge repulsion can improve the dispersion stability of the crosslinked polymer particles (A) and the storage stability of the ink. A more preferred pH value is 9 to 11.

[0078] The pH of the aqueous dispersion can be measured by a conventional method, for example, using a tabletop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "6337-10D" (manufactured by Horiba, Ltd.) at 25°C.

[0079] <Binder resin (B)> ≪Resin (B-1)≫ The binder resin (B) used in the present invention is a resin (polymer) used to bind the ink film to the printing substrate. The resin forms a film during drying and / or the resin molecules become entangled, thereby improving the abrasion resistance of the ink film. In the present invention, the binder resin (B) is a resin (B-1) having an aromatic ring and an acid value of 50 mgKOH / g or less. The difference between the amount of structural units derived from the polymerizable monomer having an aromatic ring in the resin (B-1) and the amount of structural units derived from the polymerizable monomer having an aromatic ring in the polymer (A-1), i.e., the value represented by the formula W1-W2, is 1 to 60. By satisfying these requirements, it is believed that the crosslinking reaction product of the polymer (A-1) and the resin (B-1) are not incompatible with each other, and at the same time, it is possible to suppress adsorption of the resin (B-1) to the crosslinked polymer particles (A). As a result, the ink film formation rate can be improved during the ink drying process, which in turn facilitates improved drying and abrasion resistance when printed on low-permeability substrates such as coated paper. Furthermore, when printed on high-permeability substrates such as plain paper and high-quality paper, the resin (B-1) does not inhibit the reaction between the cationic components in the printing substrate and the polymer (A-1), thereby promoting aggregation of the crosslinked polymer particles (A) and improving print density. In addition, permeation along the fibers of the high-permeability substrate is suppressed, resulting in printed matter with minimal bleeding and excellent print quality. As described above, the above-mentioned requirements are essential for obtaining an aqueous inkjet ink that can achieve excellent print density on various printing substrates, regardless of the permeability of the printing substrate, and that also provides excellent drying and abrasion resistance to printed matter. To more effectively demonstrate these effects, the value of W1-W2 is more preferably 5 to 55, and particularly preferably 10 to 50.

[0080] The acid value of the resin (B-1) is preferably 0 to 50 mgKOH / g, more preferably 0 to 40 mgKOH / g. By using a binder resin having such an acid value, it becomes easy to obtain printed matter having excellent abrasion resistance and drying properties. Furthermore, the reactivity between the cationic component and the crosslinked polymer particles (A) is improved on highly permeable substrates such as plain paper and fine paper, allowing for the production of printed matter having excellent print density. Furthermore, controlling the acid value is also effective in improving the linearity of ink droplets ejected from an inkjet head when using aqueous inkjet inks.

[0081] The acid value of the resin (B-1) can be measured using the same method as that for the acid value of the polymer (A-1) described above.

[0082] Generally, water-soluble resins and resin particles are known as binder resins. In the ink of the present invention, either of these may be used alone as the resin (B-1), or both may be used in combination. Here, the "water-soluble resin" refers to a resin having a solubility of 1 g or more in 100 g of water at 25°C. On the other hand, the "resin particles" refers to a form of water-insoluble resin (a resin that is not a water-soluble resin) and has an average particle size in water of 5 to 1,000 nm, which can be measured in the same manner as the pigment-containing crosslinked polymer particles (A) described above.

[0083] In the case of the aqueous inkjet ink of the present invention, it is preferable to use a water-soluble resin as the resin (B-1), from the viewpoint that the aqueous inkjet ink can be quickly thickened on a low-permeability substrate such as coated paper during the drying process of the aqueous inkjet ink, thereby improving both the drying properties and the print image quality.

[0084] The glass transition temperature of the resin (B-1) is preferably 60 to 140°C, more preferably 70 to 135°C, and particularly preferably 80 to 130°C, in order to improve the drying properties and abrasion resistance of printed matter even during high-speed printing.

[0085] The glass transition temperature is a value measured using a DSC (differential scanning calorimeter) and can be measured, for example, as follows, in accordance with JIS K 7121. Approximately 2 mg of a sample obtained by drying the resin is weighed on an aluminum pan, and the aluminum pan is set as a test container in a holder in a DSC measurement device (for example, a "DSC-60Plus" manufactured by Shimadzu Corporation). Measurement is then performed under conditions of a temperature increase of 5°C / min, and the temperature at the intersection of the low-temperature baseline and the tangent to the inflection point, read from the obtained DSC chart, is taken as the glass transition temperature in this application.

[0086] When a water-soluble resin is used as the resin (B-1), the types of resin that can be used as the water-soluble resin include acrylic, urethane, polyamine, maleic acid, polyester, etc. Among these, it is preferable to use one or more resins selected from the group consisting of acrylic and urethane resins, from the viewpoint of obtaining a printed matter with excellent abrasion resistance and print quality, and further obtaining an ink with excellent drying properties and ejection stability.

[0087] The water-soluble resin can be synthesized by a conventionally known method, or a commercially available product can be used. There are no particular limitations on the structure, and resins having, for example, a random structure, a block structure, a graft structure, a comb structure, a star structure, etc. can be used. Among these, it is preferable to use a water-soluble resin having a block structure, a graft structure, or a comb structure, in order to fully utilize the properties of the polymerizable monomers constituting the resin (B-1). Each intermediate unit constituting the block structure, graft structure, or comb structure (e.g., each block in the block structure, the main chain and graft chain in the graft structure, etc.) may be formed from a single polymerizable monomer or may be a random copolymer of multiple types of polymerizable monomers.

[0088] The weight-average molecular weight of the water-soluble resin preferably used as Resin (B-1) is preferably 5,000 to 50,000, from the viewpoints of ensuring the straightness of ink droplets from the inkjet head, obtaining printed matter with excellent drying properties on various printing substrates, and ensuring the storage stability of the aqueous inkjet ink. Furthermore, from the viewpoint of improving the straightness of ink droplets from the inkjet head, the weight-average molecular weight is more preferably 8,000 to 45,000, and particularly preferably 10,000 to 40,000.

[0089] The weight average molecular weight of the water-soluble resin can be measured in the same manner as the weight average molecular weight of the polymer (A-1) described above.

[0090] When a water-soluble resin is used as the resin (B-1), the content of the water-soluble resin relative to the total amount of the aqueous inkjet ink is preferably 0.1 to 10 mass %, more preferably 0.5 to 9 mass %, and even more preferably 1 to 8 mass % in terms of solid content. By setting the amount of the water-soluble resin within the above range, it is possible to obtain a printed matter that is excellent in drying properties and abrasion resistance without reducing storage stability or the ability of ink droplets to travel straight from the inkjet head.

[0091] On the other hand, when resin particles are used as the resin (B-1), types of resins that can be used for the resin particles include acrylic, urethane, styrene butadiene, polyamide, polyester, polyolefin, vinyl chloride, vinyl acetate, etc. Among them, from the viewpoint of being able to improve both the scratch resistance and ejection stability of printed matter, resin particles made of at least one selected from the group consisting of acrylic, urethane, styrene butadiene, and vinyl chloride are preferred, resin particles made of at least one selected from the group consisting of acrylic and urethane are more preferred, and from the viewpoint of improving ejection stability, it is particularly preferred to use acrylic resin particles.

[0092] The resin particles can be synthesized by a conventional method or can be commercially available. There are no particular limitations on the structure of the resin particles, and resins having, for example, a random structure, a block structure, a graft structure, a comb structure, a star structure, etc. can be used.

[0093] When resin particles are used as the resin (B-1), the content of the resin particles relative to the total amount of the aqueous inkjet ink is preferably 1 to 10 mass %, more preferably 2 to 8 mass %, and even more preferably 3 to 7 mass % in terms of solid content. By setting the amount of resin particles within the above range, it is possible to obtain an aqueous inkjet ink that has excellent abrasion resistance and drying properties for printed matter without reducing storage stability or the ability of ink droplets to travel straight from the inkjet head.

[0094] Other binder resins In the ink of the present invention, resins other than the above resin (B-1) can be used as binder resins, as long as they do not impair the effects described above.

[0095] <Organic solvent (C)> The water-based inkjet ink of the present invention contains an organic solvent (C). In this application, the term "organic solvent" refers to an organic compound that is liquid at 45°C.

[0096] From the viewpoint of obtaining printed matter with excellent print quality and print density as well as excellent drying properties and abrasion resistance on various printing substrates regardless of the permeability of the printing substrate, it is preferred that the organic solvent (C) contains at least one glycol monoalkyl ether solvent (C-1) having a boiling point of 120 to 230°C at 1 atmospheric pressure and having 4 to 10 carbon atoms.

[0097] Specific examples of glycol monoalkyl ether solvents having a boiling point of 120 to 230°C under 1 atmosphere and having 4 to 10 carbon atoms include ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl 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, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, 3-methoxybutanol, and 3-methyl-3-methoxybutanol. From the viewpoints of improving the wetting of the ink on low-permeability substrates, producing printed matter having excellent print quality with little white voids, and improving the drying properties and scratch resistance of the printed matter; suppressing the residue of organic solvent on high-permeability substrates, and improving the print density and print quality of the printed matter; and improving the film-forming properties of the resin (B-1), it is preferable that the glycol monoalkyl ether solvent (C-1) contains at least one (poly)propylene glycol monoalkyl ether solvent. The term "(poly)propylene glycol monoalkyl ether" refers to propylene glycol monoalkyl ether and / or polypropylene glycol monoalkyl ether.

[0098] In the ink of the present invention, organic solvents other than the glycol monoalkyl ether solvent (C-1) (hereinafter also referred to as "other organic solvents") can also be used as the organic solvent (C). Examples of organic solvents other than the glycol monoalkyl ether solvent (C-1) include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 3-methyl-1,3-butanediol, 1,2-hexanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2,4-pentanediol, 2,5-pentanediol, 1,6 ... Examples of suitable oleic anhydride include, but are not limited to, hexanediol, 1,2-octanediol, 2-ethylhexane-1,3-diol, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, γ-butyrolactone, glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tetraethylene glycol dimethyl ether, 2-pyrrolidone, N-methyloxazolidinone, and ε-caprolactone.

[0099] In the aqueous inkjet ink of the present invention, the organic solvent (C) preferably contains two or more compounds, and the weighted average boiling point of the organic solvent (C) at 1 atmosphere is preferably 150 to 200°C. Having a weighted average boiling point at 1 atmosphere of 150°C or higher provides favorable drying properties for the ink, preventing the ink droplets from adhering to the inkjet head. Furthermore, when printed on a low-permeability substrate, degradation of print quality such as color bleeding and white spots, as well as deterioration of drying properties, are prevented. Furthermore, when printed on a high-permeability substrate, no organic solvent remains, suppressing occurrence of feathering and improving print quality, such as character visibility. Furthermore, having a weighted average boiling point at 1 atmosphere of 200°C or lower can favorably suppress degradation of drying properties when printed on a low-permeability substrate, and suppress residue of organic solvent and deterioration of print density and print quality when printed on a high-permeability substrate. From the viewpoint of achieving excellent linearity of droplets from an inkjet head and excellent print density in printed matter on highly permeable substrates, the weighted average boiling point of the organic solvent (C) at 1 atmospheric pressure is more preferably 150 to 195°C, and even more preferably 155 to 190°C.

[0100] Furthermore, when the organic solvent (C) contains two or more compounds, it becomes easy to adjust the weighted average boiling point. Furthermore, for example, by combining multiple compounds with different properties such as surface tension and hydrophilicity, it becomes easy to achieve effects such as print quality and drying speed when printed on a low-permeability substrate, print density and print quality when printed on a high-permeability substrate, ink droplet linearity, and storage stability. From this perspective, it is preferable to use a glycol monoalkyl ether solvent (C-1) and another organic solvent in combination as the two or more compounds. In this case, the difference between the surface tension of the glycol monoalkyl ether solvent (C-1) at 25°C and the surface tension of the other organic solvent at 25°C is preferably 4 to 40 mN / m, particularly preferably 8 to 25 mN / m.

[0101] In this disclosure, the surface tension is measured by the Wilhelmy method (plate method). Specifically, the surface tension is measured at 25°C using an automatic surface tensiometer CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. and a platinum plate.

[0102] The total content of the organic solvent (C) in the aqueous inkjet ink is preferably 2 to 40% by mass based on the total amount of the aqueous inkjet ink. If the total content of the organic solvent (C) is 2% by mass or more, the ink will spread better on the printing substrate, regardless of the permeability of the printing substrate, resulting in improved print density and print image quality. In addition, drying of the ink on the inkjet head can be prevented, and the straightness of the ink droplets will not be impaired. On the other hand, if the total content of the organic solvent (C) is 40% by mass or less, the solvent will not remain on the printing substrate, regardless of the permeability of the printing substrate, resulting in improved print density and print image quality. Furthermore, in order to obtain an ink that has properties such as high print density even on a highly permeable substrate and excellent print quality such as good character visibility, as well as excellent drying properties on the printing substrate and straightness of ink droplets from the inkjet head, the total content of the above components is more preferably 5 to 35% by mass, and particularly preferably 10 to 30% by mass, of the total amount of the aqueous inkjet ink.

[0103] <Surfactant (D)> The aqueous inkjet ink of the present invention preferably contains one or more surfactants (D) from the viewpoints that the wettability of ink droplets is improved on low-permeability substrates such as coated paper, forming a smoother ink film and thereby producing printed matter with high print density, and that the improved wettability and permeability suppress color bleeding and white voids, making it easy to produce printed matter with excellent print quality. As the surfactant (D), various surfactants can be used depending on the application, such as acetylene diol-based, acetylene monool-based, siloxane-based, fluorine-based, and polyoxyalkylene ether-based surfactants. In particular, the ink of the present invention preferably contains one or more nonionic surfactants selected from the group consisting of acetylene diol-based surfactants, siloxane-based surfactants, and polyoxyalkylene ether-based surfactants, and it is particularly preferred that the ink contain at least a siloxane-based surfactant.

[0104] Examples of siloxane surfactants that can be suitably used in the ink of the present invention include 8032ADDITIVE, FZ-2104, FZ-2120, FZ-2122, FZ-2162, FZ-2164, FZ-2166, FZ-2404, FZ-7001, FZ-7002, FZ-7006, L-7001, L-7002, SF8427, SF8428, SH3748, SH 3749, SH3771M, SH3772M, SH3773M, SH3775M, SH8400, BYK-331, BYK-333, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-3420, BYK-UV3500, BYK-UV3510, BYK-UV3530, BYK-UV3570 manufactured by BYK Japan, and TEGO manufactured by Evonik. Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, TEGO Wet 280, TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 450, TEGO Twin 4000, TEGO Twin 4100, TEGO Twin 4200, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, KF-643, KF-644, KF-945, KF-6011, KF-6012, KF-6015, KF-6017, KF-6020, KF-6204, X-22-4515 manufactured by Shin-Etsu Chemical Co., Ltd., and the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd. In particular, siloxane-based surfactants in which one or more ethylene oxide groups and / or one or more propylene oxide groups have been introduced into the side chain and / or both ends of the polydimethylsiloxane chain are preferably used.

[0105] In the present invention, the surfactant preferably contains at least one siloxane-based surfactant having a measured HLB value of 1 to 10, from the viewpoints that the surfactant quickly orients at the interface of the ink droplets, suppressing color bleeding on low-permeability substrates such as coated paper, and further suppressing penetration along the paper fibers even when printing on high-permeability substrates, making it easier to obtain printed matter with high print quality and minimal bleeding.

[0106] The "HLB (Hydrophilic-Lipophilic Balance) value" is one of the parameters that indicates the degree of hydrophilicity and hydrophobicity of a material. The smaller the HLB value, the more hydrophobic the material, and the larger the HLB value, the more hydrophilic the material. The HLB value can be calculated by calculation from the molecular structure or by actual measurement through experiments. In this disclosure, the HLB value of a surfactant is calculated by actual measurement using the method described below (actually measured HLB value). (1) Dissolve 0.5 g of the target surfactant in 5 mL of ethanol. (2) At 25°C, the mixture from (1) is titrated with a 2% aqueous phenol solution while stirring. The endpoint is when the mixture becomes cloudy and no longer returns to a transparent state upon dropwise addition of the 2% aqueous phenol solution. (3) When the amount of 2% phenol aqueous solution dropped up to the end point is A [mL], calculate the measured HLB value according to the following formula (4).

[0107] Formula (4): Actual HLB value = 0.89 x A + 1.11

[0108] On the other hand, examples of acetylenic diol surfactants used in the ink of the present invention include, but are not limited to, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, and their ethylene oxide and / or propylene oxide adducts. From the viewpoint of obtaining excellent print quality with few white spots on low-permeability substrates, it is preferable to contain at least one acetylenic diol having a measured HLB value of 6 to 8.5.

[0109] Furthermore, examples of polyoxyalkylene ether surfactants that can be suitably used in the ink of the present invention include compounds represented by the following general formula (5).

[0110] General formula (5): R 1 -O-(EO) p -(PO) q -H

[0111] In the above general formula (5), R 1 represents an alkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, an alkylcarbonyl group having 8 to 22 carbon atoms, or an alkenylcarbonyl group having 8 to 22 carbon atoms. 1 may have a branched structure. EO represents an ethylene oxide group, and PO represents a propylene oxide group. p represents the average number of moles of EO added and is a number from 2 to 100, and q represents the average number of moles of PO added and is a number from 0 to 50. When q is not 0, (EO) p and (PO) q The order of addition does not matter, and the addition may be in blocks or randomly.

[0112] The surfactant used in the present invention preferably has a hydrophobic group and a hydrophilic group separated in the molecule, and therefore, among the surfactants exemplified above, those having a hydrophilic ethylene oxide group are particularly preferably selected.

[0113] The content of the surfactant in the aqueous inkjet ink of the present invention is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, based on the total amount of the ink.

[0114] <Water> The water contained in the aqueous inkjet ink of this embodiment is preferably ion-exchanged water (deionized water) rather than ordinary water containing various ions.

[0115] The content of water contained in the ink of this embodiment is preferably in the range of 20 to 90 mass % of the total mass of the ink.

[0116] <Other ingredients> In addition to the above-mentioned components, the ink of the present invention may contain additives such as a pH adjuster, an infrared absorber, an ultraviolet absorber, a preservative, etc., as needed to provide the ink with desired physical properties. The total amount of these additives is preferably 0.01 to 10% by mass based on the total mass of the ink.

[0117] <Ink set> The ink of this embodiment may be used in a single color, or may be used as an ink set combining multiple colors depending on the application. While the combination is not particularly limited, a full-color image can be obtained by using three colors: cyan, yellow, and magenta. The addition of black ink can also improve the sense of black, thereby increasing the visibility of characters, etc. Color reproducibility can also be improved by adding colors such as orange and green. When printing on a printing substrate other than white, a clear image can be obtained by using white ink in combination.

[0118] <Ink preparation method> The following method is an example of a method for preparing the ink of the present invention containing the components described above, but the method for preparing the ink of the present invention is not limited to the following method.

[0119] First, an aqueous dispersion of pigment-containing crosslinked polymer particles (A) is obtained by the method described above. Next, to the aqueous dispersion of crosslinked polymer particles (A), an aromatic ring-containing resin having an acid value of 50 mgKOH / g or less, a glycol monoalkyl ether solvent (C-1), a surfactant (D), water, and, if necessary, other organic solvents and other components are appropriately added, followed by stirring and mixing. Then, coarse particles are removed by filtration or the like to obtain the ink of the present invention.

[0120] <Printing base material> The ink of the present invention can be particularly suitably used on various printing substrates regardless of the permeability of the printing substrate. For example, it may be used on non-permeable substrates in addition to high-permeability substrates and low-permeability substrates.

[0121] The permeability of the printing substrate can be determined by the amount of water absorption measured by a dynamic scanning absorptivity meter. Specifically, the water absorption coefficient measured by the Bristow method (J. TAPPI Paper Pulp Test Method No. 51-87) is 0.4 ml / m 2 msec 1 / 2 High permeability substrate, 0.1ml / m 2 msec 1 / 2 Ultra 0.4ml / m 2 msec 1 / 2 A low permeability substrate is one that is less than 0.1 ml / m 2 msec 1 / 2 The absorption coefficient was measured using an automatic scanning liquid absorption meter "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd., water, and the target printing substrate under an environment of 23°C and 50% RH, and was calculated as the amount of water absorbed (ml / m) during a contact time of 25 to 500 milliseconds. 2 ) and the square root of the contact time (msec 1 / 2 ) is calculated as the slope of the line obtained by the least squares method.

[0122] Specific examples of highly permeable substrates include uncoated paper such as wood paper, medium-grade paper, fine paper, and recycled paper; fabrics such as cotton, synthetic fiber fabrics, silk, hemp, and nonwoven fabrics; leather; etc. Among these, uncoated paper such as wood paper, medium-grade paper, fine paper, and recycled paper is preferably used because it allows prints to be obtained that are excellent in print density and print quality.

[0123] Specific examples of low permeability substrates include coated paper such as coated paper, art paper, cast paper, lightly coated paper, and synthetic paper.

[0124] Specific examples of impermeable substrates include plastics such as polyvinyl chloride, polystyrene, PMMA (polymethyl methacrylate), PP (polypropylene), PE (polyethylene), PET (polyethylene terephthalate), and polycarbonate; metals such as aluminum, iron, and stainless steel; and glass.

[0125] The printing substrates listed above may have a smooth or uneven surface. The printing substrates may be in the form of rolls or sheets. Two or more of the printing substrates listed above may be bonded together to form the printing substrate. A release adhesive layer or the like may be provided on the side opposite the printed surface, or an adhesive layer or the like may be provided on the printed surface after printing.

[0126] Furthermore, it is also preferable to subject the printing surface of the printing substrates listed above to surface modification such as corona treatment and plasma treatment, since this improves the wetting and spreading of the ink of the present invention and makes it easy to obtain printed matter with excellent print density, print image quality, and drying properties.

[0127] <Printing method> The ink of the present invention is used in a printing method (inkjet printing method) in which ink is ejected from the nozzles of an inkjet head and ink droplets are deposited on a printing substrate. The ink applied to the printing substrate is dried, preferably by the drying method described below, to form a printed product.

[0128] <Drying method> A printing device (inkjet printer) equipped with the ink of the present invention and used in the inkjet printing method preferably includes a mechanism for drying the ink on a printing substrate. The drying method may be any one of the following: direct contact of the ink with a heat source, indirect contact of the ink with a heat source, or electromagnetic wave irradiation. Alternatively, a combination of two or more methods may be used. For example, by using both infrared drying (electromagnetic wave irradiation) and hot air drying (direct contact of the ink with a heat source), the ink can be dried more quickly than by using either method alone. When using a hot air drying method in which the ink is brought into direct contact with a heat source, it is preferable to set the hot air temperature to 50 to 250°C from the viewpoint of preventing bumping of the liquid components contained in the ink and obtaining printed matter with excellent print density, color reproducibility, and print image quality. When using a substrate heating method (a method in which the non-printing surface of a printing substrate is brought into contact with a heat source) in which the ink is brought into indirect contact with a heat source, it is preferable to set the temperature of the heat source to 35 to 100°C from the same viewpoint as in the case of the hot air temperature described above.

[0129] <Printed material> A printed matter according to one embodiment of the present invention comprises a printing substrate and a printed layer formed using the aqueous inkjet ink of the present invention. The printed layer is a layer formed by drying the aqueous inkjet ink printed in the shape of an image and / or characters. The printed matter produced using the ink of the present invention described above exhibits excellent print density and print quality. The inkjet printing method described above is preferably used as a method for forming a printed layer by drying the aqueous inkjet ink after printing in the shape of an image and / or characters. The "image" also includes solid images (images printed at a coverage rate of 100% so as to completely cover the surface of the printing substrate) and seamless images such as checkerboard patterns. In the present disclosure, the expression "ink film" is used to encompass the above-mentioned "printed layer", i.e., the printed layer is an ink film printed in the shape of an image and / or characters. [Example]

[0130] The present disclosure will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" represent "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0131] <Production example of dispersion resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of methyl ethyl ketone and purged with nitrogen gas. After heating the contents of the reaction vessel to 110°C, a mixture of polymerizable monomers (25 parts styrene, 20 parts acrylic acid, 20 parts methyl methacrylate, and 35 parts lauryl methacrylate) and a polymerization initiator (6 parts V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over a two-hour period. After the completion of the dropwise addition, the temperature of the contents of the reaction vessel was maintained at 110°C, and the polymerization reaction was continued for three hours. Subsequently, 0.6 parts of V-601 was added, and the reaction was continued for one hour at 110°C to obtain a dispersion resin 1 precursor containing only carboxyl groups as anionic groups. The resulting dispersion resin 1 precursor had a weight-average molecular weight of 19,500 and an acid value of 158 mgKOH / g. The acid value of the dispersion resin 1 precursor and the above formula (2) were then used to calculate the amount of potassium hydroxide required to achieve a neutralization rate of 100 mol%, and a 48% by mass aqueous potassium hydroxide solution containing an amount of potassium hydroxide equivalent to the calculated amount was added to convert the carboxy groups present in the dispersion resin 1 precursor to carboxylate groups (neutralization treatment). After neutralization, 150 parts of ion-exchanged water was added, and the solution was heated to 50°C. After reaching 50°C, the solution was stirred for 1 hour while maintaining the temperature. Ion-exchanged water was then added to obtain a 20% solids concentration aqueous solution of dispersion resin 1.

[0132] <Production examples of pigment dispersion resins 2 to 20> Aqueous solutions of dispersion resins 2 to 20 (each with a solids concentration of 20%) were obtained using the same raw materials and procedures as for dispersion resin 1, except that the polymerizable monomers listed in Table 1 were used as the polymerizable monomers.

[0133] [Table 1]

[0134] Table 1 also lists the raw materials used in the above-mentioned dispersion resin 1, as well as the weight-average molecular weights and acid values ​​of dispersion resins 1 to 20. The abbreviations listed in Table 1 are as follows: St: Styrene AA: Acrylic acid MMA: Methyl methacrylate LMA: Lauryl methacrylate

[0135] <Production example of dispersion resin 21> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with the polymerizable monomers 26 parts 1-octadecene, 14 parts maleic anhydride, and 60 parts N-phenylmaleimide; and the solvent 100 parts methyl ethyl ketone. After purging with nitrogen gas, the contents of the reaction vessel were heated to 130°C while stirring. Next, while maintaining the temperature and stirring of the contents, 1.0 part of the radical polymerization initiator t-butylperoxy-2-ethylhexanoate was added dropwise over 2 hours. The polymerization reaction was then continued for another 1 hour while maintaining the temperature at 130°C. The solids concentration of the contents was measured at regular intervals after the start of the polymerization reaction, and the ratio of the solids concentration to the assumed solids concentration when all of the charged polymerizable monomers had polymerized (polymerization conversion rate) was calculated. When the polymerization conversion rate reached 95% or higher, the temperature in the reaction vessel was lowered to 60°C, and 33.0 parts of water and 0.01 parts of diazabicycloundecene were added. The contents of the reaction vessel were then heated to 80°C while stirring, and after reaching 80°C, the temperature was maintained at that temperature for 4 hours to open the ring of the maleic anhydride, yielding a dispersion resin 21 precursor having only carboxy groups as anionic groups. The resulting dispersion resin 21 precursor had a weight-average molecular weight of 19,000 and an acid value of 159 mgKOH / g. The acid value of the dispersion resin 9 precursor and the above formula (2) were then used to calculate the amount of potassium hydroxide required to achieve a neutralization rate of 100%, and a 48% by mass aqueous potassium hydroxide solution containing an equal amount of potassium hydroxide was added to convert the carboxy groups present in the dispersion resin 21 precursor to carboxylate groups (neutralization treatment). After the neutralization treatment, 150 parts of ion-exchanged water was added, and the solution was heated to 50°C. After reaching 50°C, the solution was stirred for 1 hour while maintaining the temperature. Ion-exchanged water was then added to obtain a 20% solids concentration aqueous solution of dispersion resin 21.

[0136] <Production Examples of Dispersion Resins 22 to 31> Except for changing the type and amount of polymerizable monomer used as shown in Table 2, synthesis was carried out using the same raw materials and procedures as for dispersion resin 21, to obtain aqueous solutions of dispersion resins 22 to 31 (each with a solids concentration of 20%).

[0137] [Table 2]

[0138] Table 2 also lists the weight average molecular weights and acid values ​​of dispersion resins 21 to 31. Among the abbreviations listed in Table 2, those not used in Table 1 are as follows: OctD: 1-octadecene Manh: Maleic anhydride PMI: N-phenylmaleimide CMI: Cyclohexylmaleimide MI: Maleimide

[0139] <Production Example of Aqueous Dispersion of Cyan Pigment-Containing Crosslinked Polymer Particle Precursor 1 (CB1)> 600 g of LIONOL BLUE FG-7351 (CI Pigment Blue 15:3, manufactured by Toyocolor Co., Ltd.), 750 g of an aqueous dispersion resin 1 solution (20% solids concentration), and 1,650 g of ion-exchange water were added to a mixing vessel. After all ingredients were added and stirred for 1 hour (pre-dispersion), a 0.6 L bead mill (Dyno Mill, manufactured by Shinmaru Enterprises Co., Ltd.) filled with 1,800 g of 0.5 mm diameter zirconia beads was used to initiate circulatory dispersion. The median diameter (volume-based) was then measured at 25°C using a Microtrac-Bell Nanotrac UPA-EX150 at regular intervals (e.g., every hour). The circulatory dispersion was terminated when the median diameter reached 150 nm or less. Thereafter, 800 g of ion-exchanged water was added to the obtained mixture, and further, a part of the ion-exchanged water and methyl ethyl ketone were distilled off under reduced pressure while the mixture was heated at 60° C. Then, the pigment concentration was adjusted to 15% using ion-exchanged water, thereby obtaining an aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1).

[0140] <Production Example of Water Dispersion of Cyan Pigment-Containing Crosslinked Polymer Particles 1 (CP1)> 93.3 parts of the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1) obtained by the method described above, 1.24 parts (an amount such that the glycidyl group content represented by the above formula (1) was 90 mol %) of compound (A-2) (a crosslinking agent, Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140 g / eq.)), and 5.46 parts of ion-exchanged water were placed in a reaction vessel. The contents of the reaction vessel were then heated to 80°C with stirring. After reaching 80°C, the temperature was maintained while stirring was continued for 3 hours to allow a crosslinking reaction to occur. The reaction vessel was then cooled to room temperature (approximately 25°C), and ion-exchanged water was added to adjust the solids concentration. After adjustment, the mixture was filtered through a 5 μm membrane filter to obtain an aqueous dispersion of cyan pigment-containing crosslinked polymer particle 1 (CP1) in which dispersion resin 1 was crosslinked (pigment concentration: 14%).

[0141] <Production Example of Aqueous Dispersions of Cyan Pigment-Containing Crosslinked Polymer Particle Precursors 2 to 31 (CB2 to CB31)> Aqueous dispersions of cyan pigment-containing crosslinked polymer particle precursors 2 to 31 (CB2 to CB31) were obtained using the same materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1), except that the dispersing resin was changed to dispersing resins 2 to 25. The pigment concentration in all aqueous dispersions was 15%.

[0142] <Production Example of Aqueous Dispersion of Cyan Pigment-Containing Crosslinked Polymer Particles 2 to 40 (CP2 to CP40)> Aqueous dispersions of cyan pigment-containing crosslinked polymer particles 2 to 40 (CP2 to CP40) were obtained in the same manner as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that the type of cyan pigment-containing crosslinked polymer particle precursor used and the amounts of compound (A-2) (Denacol EX-321) and ion-exchanged water added were changed as shown in Table 3. The pigment concentration in all aqueous dispersions was 14%.

[0143] [Table 3]

[0144] <Production Example of Magenta Pigment-Containing Crosslinked Polymer Particle Precursor 1> 300 g of TOSHIKI RED 150TR (CI Pigment Red 150, Tokyo Color Materials Co., Ltd.), 300 g of Cinquasia Pink K 4410 (CI Pigment Red 122, BASF), 750 g of an aqueous dispersion resin 1 solution (20% solids), and 1,650 g of ion-exchanged water were added to a mixing vessel. All raw materials were added and pre-dispersed using a mixer. The dispersion was then carried out using a 0.6 L Dyno-Mill filled with 1,800 g of 0.5 mm diameter zirconia beads. After the dispersion, 800 g of ion-exchanged water was added to the resulting mixture, and the mixture was heated at 80°C while a portion of the ion-exchanged water and methyl ethyl ketone were distilled off under atmospheric pressure. The pigment concentration was then adjusted to 15% using ion-exchanged water, and the mixture was filtered through a 5 μm membrane filter to obtain an aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursor 1 (MB1).

[0145] <Production Example of Magenta Pigment-Containing Crosslinked Polymer Particles 1 (MP1)> An aqueous dispersion of magenta pigment-containing crosslinked polymer particles 1 (MP1) was obtained using the same materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that an aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursor 1 (MB1) was used. The pigment concentration of the aqueous dispersion of magenta pigment-containing crosslinked polymer particles 1 (MP1) was 14%.

[0146] <Production Example of Aqueous Dispersions of Magenta Pigment-Containing Crosslinked Polymer Particle Precursors 2 to 31 (MB2 to MB31)> Aqueous dispersions of magenta pigment-containing crosslinked polymer particle precursors 2 to 31 (MB2 to MB31) were obtained using the same materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (MB1), except that the dispersing resin was changed to dispersing resins 2 to 31. The pigment concentration in all aqueous dispersions was 15%.

[0147] <Production Examples of Magenta Pigment-Containing Crosslinked Polymer Particles 2 to 40 (MP2 to MP40)> Aqueous dispersions of magenta pigment-containing crosslinked polymer particles 2 to 40 (MP2 to MP40) were obtained in the same manner as for the aqueous dispersion of magenta pigment-containing crosslinked polymer particles 1 (MP1), except that the type of magenta pigment-containing crosslinked polymer particle precursor and the amounts of compound (A-2) (Denacol EX-321) and ion-exchanged water added were changed as shown in Table 4. The pigment concentration in all aqueous dispersions was 14%.

[0148] [Table 4]

[0149] <Production Examples of Yellow Pigment-Containing Crosslinked Polymer Particle Precursors 1 to 31 (YB1 to YB31)> An aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1) was obtained using the same materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1), except that FAST YELLOW 7413 (CI Pigment Yellow 74, manufactured by Sanyo Dish Co., Ltd.) was used as the pigment. The pigment concentration of the aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1) was 15%. Aqueous dispersions of yellow pigment-containing crosslinked polymer particle precursors 2 to 31 (YB2 to YB31) were obtained using the same materials and method as for the aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1), except that the dispersing resin was changed to dispersing resins 2 to 31. The pigment concentration in all aqueous dispersions was 15%.

[0150] <Production Example of Yellow Pigment-Containing Crosslinked Polymer Particles 1 (YP1)> An aqueous dispersion of yellow pigment-containing crosslinked polymer particles 1 (YP1) was obtained using the same materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that an aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1) was used. The pigment concentration of the aqueous dispersion of yellow pigment-containing crosslinked polymer particles 1 (YP1) was 14%.

[0151] <Production Examples of Yellow Pigment-Containing Crosslinked Polymer Particles 2 to 31 (YP2 to YP31)> Aqueous dispersions of yellow pigment-containing crosslinked polymer particles 2 to 40 (YP2 to YP40) were obtained in the same manner as for the aqueous dispersion of yellow pigment-containing crosslinked polymer particles 1 (YP1), except that the type of yellow pigment-containing crosslinked polymer particle precursor and the amounts of compound (A-2) (Denacol EX-321) and ion-exchanged water added were changed as shown in Table 5. The pigment concentration in all aqueous dispersions was 14%.

[0152] [Table 5]

[0153] <Production Examples of Black Pigment-Containing Crosslinked Polymer Particle Precursors 1 to 31 (KB1 to KB31)> An aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1) was obtained using the same materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1), except that PrinteX80 (carbon black manufactured by Orion Engineered Carbons) was used as the pigment. The pigment concentration of the aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1) was 15%. In addition, aqueous dispersions of black pigment-containing crosslinked polymer particle precursors 2 to 31 (KB2 to KB31) were obtained using the same materials and method as for the aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1), except that the dispersing resin was changed to dispersing resins 2 to 31. The pigment concentration in all aqueous dispersions was 15%.

[0154] <Production Example of Black Pigment-Containing Crosslinked Polymer Particles 1 (KP1)> An aqueous dispersion of black pigment-containing crosslinked polymer particles 1 (KP1) was obtained using the same materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that an aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1) was used. The pigment concentration of the aqueous dispersion of black pigment-containing crosslinked polymer particles 1 (KP1) was 14%.

[0155] <Production Examples of Black Pigment-Containing Crosslinked Polymer Particles 2 to 40 (KP2 to KP40)> Aqueous dispersions of black pigment-containing crosslinked polymer particles 2 to 40 (KP2 to KP40) were obtained in the same manner as for the aqueous dispersion of black pigment-containing crosslinked polymer particles 1 (KP1), except that the type of black pigment-containing crosslinked polymer particle precursor and the amounts of compound (A-2) (Denacol EX-321) and ion-exchanged water added were changed as shown in Table 6. The pigment concentration in all aqueous dispersions was 14%.

[0156] [Table 6]

[0157] <Production example of binder resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of butanol and purged with nitrogen gas. The contents of the reaction vessel were heated to 110°C, and a mixture of polymerizable monomers (6 parts acrylic acid, 64 parts methyl methacrylate, 20 parts 2-ethylhexyl acrylate, 10 parts styrene) and 6 parts of polymerization initiator V-601 (Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After the addition, the contents of the reaction vessel were maintained at 110°C and the polymerization reaction was continued for 3 hours. Then, 0.6 parts of V-601 was added, and the reaction was continued for another 1 hour at 110°C to obtain a solution of binder resin 1. Next, the binder resin 1 solution was cooled to room temperature, and 7.1 parts of dimethylaminoethanol was added to neutralize the carboxyl groups in binder resin 1. 100 parts of ion-exchanged water was then added. The mixture was then heated to above 100°C while stirring. After reaching 100°C, stirring was continued while maintaining the temperature, resulting in an azeotropic distillation of butanol with water, and the butanol was then distilled off. The solids concentration was then adjusted to 40% using ion-exchanged water, yielding an aqueous solution of binder resin 1, a water-soluble resin with a random structure. The weight-average molecular weight of the resulting binder resin 1 was 19,000, and the acid value was 47 mgKOH / g.

[0158] <Production examples of binder resins 2 to 15> Aqueous solutions of binder resins 2 to 14, which are water-soluble resins with a random structure, were obtained using the same raw materials and procedures as for binder resin 1, except that the type and amount of polymerizable monomer used and the amount of dimethylaminoethanol used to neutralize the carboxyl groups were changed as shown in Table 7. All aqueous solutions had a solids concentration of 40%.

[0159] [Table 7]

[0160] Among the abbreviations listed in Table 7, those not used in Tables 1 and 2 are as follows: ·MAA: methacrylic acid 2EHA: 2-Ethylhexyl acrylate STMA: Stearyl methacrylate

[0161] <Production examples of binder resins 16-17> Into a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer, 124 parts of ion-exchanged water and 0.06 parts of an emulsifier, polyoxyethylene lauryl ether sodium sulfate ("Latemul E-150" manufactured by Kao Corporation) were charged. Meanwhile, another mixing vessel equipped with a stirrer was prepared, and polymerizable monomers, 0.5 parts of acrylic acid, 20 parts of styrene, and 79.5 parts of methyl methacrylate; 64 parts of ion-exchanged water; and 0.8 parts of polyoxyethylene lauryl ether sodium sulfate ("Latemul E-150" manufactured by Kao Corporation), were charged, followed by stirring and mixing to form an emulsion. Next, 8 portions of the emulsion were taken and placed in a reaction vessel, the internal temperature was raised to 80°C, and the atmosphere inside the reaction vessel was thoroughly purged with nitrogen gas. Then, 4 parts of a 5% aqueous solution of potassium persulfate and 8 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added to initiate the polymerization reaction. After the polymerization reaction started, the internal temperature of the reaction vessel was maintained at 80°C, and the remaining emulsion, 1.2 parts of a 5% aqueous solution of potassium persulfate, and 2.5 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added dropwise over 1.5 hours, and stirring was continued for another 2 hours. After the reaction vessel was cooled to room temperature, 0.48 parts of dimethylethanolamine was added, and the solid content was adjusted to 40% using ion-exchanged water to obtain an aqueous dispersion (solid content 40%) of binder resin 16, which has a random structure and is made of resin particles. The acid value of the obtained binder resin 16 was 3 mgKOH / g.

[0162] In addition, an aqueous dispersion of binder resin 17 (solid concentration 40%) having a random structure and consisting of resin particles was obtained using the same raw materials and procedures as in the case of binder resin 16, except that the type and amount of polymerizable monomer used and the amount of dimethylaminoethanol added were changed as shown in Table 7 above.

[0163] <Production of water-based inkjet ink> The raw materials listed in each column of Tables 8 and 9 were added to a mixing vessel equipped with a stirrer while stirring the contents of the mixing vessel. After all the raw materials were added, the contents were stirred until sufficiently uniform, and then filtered through a 0.8 μm membrane filter to remove coarse particles that may cause clogging of the inkjet head, thereby preparing an aqueous inkjet ink. In preparing the aqueous inkjet inks, pigment-containing crosslinked polymer particles or pigment-containing crosslinked polymer particle precursors (cyan, magenta, yellow, and black) with the same number but different colors were used to prepare a set of aqueous inkjet inks consisting of four colors: cyan, magenta, yellow, and black. The prepared set of four ink colors (ink set) was then used in the evaluations shown below.

[0164] [Table 8-1]

[0165] [Table 8-2]

[0166] [Table 8-3]

[0167] [Table 8-4]

[0168] [Table 8-5]

[0169] [Table 8-6]

[0170] [Table 8-7]

[0171] [Table 8-8]

[0172] [Table 9-1]

[0173] [Table 9-2]

[0174] The abbreviations listed in Tables 8 and 9 are as follows: PG: Propylene glycol (boiling point: 188°C) 1,2-BuD: 1,2-butanediol (boiling point: 191°C) DEG: Diethylene glycol (boiling point: 245°C) HexG: 2-methyl-2,4-pentanediol (boiling point: 197°C) DPG: Dipropylene glycol (boiling point: 232°C) GLY: Glycerin (boiling point: 290°C) EGM: Ethylene glycol monomethyl ether (boiling point: 124°C) PGM: Propylene glycol monomethyl ether (boiling point: 120°C) EGE: Ethylene glycol monoethyl ether (boiling point: 135°C) i-PDG: Diethylene glycol monoisopropyl ether (boiling point: 207°C) EDG: Diethylene glycol monoethyl ether (boiling point: 193°C) PNP: Propylene glycol monopropyl ether (boiling point: 150°C) DPM: Dipropylene glycol monomethyl ether (boiling point: 190°C) DPNP: Dipropylene glycol monopropyl ether (boiling point: 210°C) DPNB: Dipropylene glycol monobutyl ether (boiling point: 230°C) PNB: Propylene glycol monobutyl ether (boiling point: 170°C) BDG: Diethylene glycol monobutyl ether (boiling point: 235°C) HeDG: Diethylene glycol monohexyl ether (boiling point: 260°C) TEGO Wet 240: Evonik Japan siloxane surfactant (actual HLB value: 9-10) TEGO Wet 270: Evonik Japan siloxane surfactant (measured HLB value: 2.5-3.5) TEGO Twin 4100: Silicone surfactant manufactured by Evonik Japan (measured HLB value: 8-9) BYK348: Siloxane surfactant manufactured by BYK Japan (measured HLB value: 12-13) BYK349: Siloxane surfactant manufactured by BYK Japan (measured HLB value: 10.1-11) Surfynol 104: Evonik Japan acetylene diol surfactant (2,4,7,9-tetramethyl-5-decyne-4,7-diol, measured HLB value: 7.9) Surfynol 440: Acetylene diol surfactant manufactured by Evonik Japan (ethylene oxide adduct of Surfynol 104, ethylene oxide adduct mole number 10.5, measured HLB value: 8.1) Dynol 604: Ethoxy compound of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, average number of moles of ethylene oxide added: 4, actual HLB value: 10.1

[0175] [Examples 1 to 80, Comparative Examples 1 to 20] The prepared aqueous inkjet inks were evaluated as follows, and the evaluation results are shown in Tables 8 and 9 above.

[0176] <Evaluation 1: Evaluation of ink storage stability> The viscosity of each ink constituting the ink set was measured using an E-type viscometer. Next, the ink after viscosity measurement was placed in a container, sealed, and then left to stand in a constant temperature incubator set at 70°C. After a predetermined period of time had passed, the viscosity of the aqueous inkjet black ink in the sealed container was removed from the constant temperature incubator and measured again. The viscosity change rate before and after standing was calculated to evaluate the viscosity stability over time. The evaluation criteria were as follows, with AA, A, and B being considered as practical ranges. Tables 8 and 9 show the evaluation of the color with the worst evaluation results. AA: Viscosity change rate after leaving at 70°C for 6 weeks was within ±5% A: The viscosity change rate after leaving the sample at 70°C for 5 weeks was within ±5%. B: The viscosity change rate after leaving the sample at 70°C for 4 weeks was within ±5%. C: The viscosity change rate after leaving the sample at 70°C for 4 weeks was more than +5% or less than -5%.

[0177] <Evaluation 2: Evaluation of white spots on coated paper> An inkjet ejection device equipped with four Kyocera inkjet heads (KJ4B-1200) was placed in a 25°C environment. Next, each ink constituting the ink set was loaded into the inkjet head so that the printing order was black, cyan, magenta, and yellow. A nozzle check pattern was then printed to confirm that ink was ejecting normally from all nozzles. The device was then left for one minute. After this time, a solid print was performed on Oji Paper OK Topcoat+ (coated paper) using only one of the ink colors at a 100% coverage rate under the following printing conditions: frequency 40 kHz, 1,200 x 1,200 dpi, and drop volume 3 pL. The printed substrate was then immediately placed in a 70°C air oven and dried for one minute to obtain a solid print. The solid print was then visually and under a magnifying glass to evaluate the degree of whiteout. The evaluation criteria were as follows, with AA, A, and B being considered acceptable for practical use. Solid prints were created using inkjet inks of four colors: cyan, magenta, yellow, and black, and whiteout was evaluated for each solid print. Tables 8 and 9 show the results for the color with the worst evaluation. AA: No white spots were observed visually or with a magnifying glass. A: A slight white spot was observed under a magnifying glass, but no white spot was observed visually. B: Slight white spots were observed visually C: White spots were clearly observed by visual inspection

[0178] <Evaluation 3: Evaluation of color bleeding on coated paper> Using the inkjet printing device used in Evaluation 2 above, a nozzle check pattern was used to confirm that ink was being ejected normally from all nozzles. Then, using all inks installed in the inkjet printing device, a layered gradation image was printed on OK Topcoat+ (coated paper) manufactured by Oji Paper Co., Ltd. The "layered gradation image" refers to an image in which the printing rate for one ink color is continuously varied from 10 to 60% within a predetermined area, and these images are layered in the order of black, cyan, magenta, and yellow. Therefore, the total printing rate of the layered gradation image (the sum of the printing rates for each color) is 40 to 240%. However, the printing rate for each color is the same for each total printing rate. For example, if the total printing rate is 40%, the printing rate for each color is 10%, and if the total printing rate is 240%, the printing rate for each color is 60%. After printing, the printed substrate with the inks was immediately placed in a 70°C air oven and dried for 1 minute to obtain a layered gradation print. The degree of color bleeding in the overlapping gradation print was then evaluated by visual inspection and by using a magnifying glass. The evaluation criteria were as follows, with AA, A, and B being considered to be within the range of practical use. AA: No color bleeding was observed in all areas with a total print ratio of 40 to 240%. A: No color bleeding occurred in areas with a total print rate of 200% or less, but color bleeding was observed in areas with a total print rate of over 200% and up to 240%. B: No color bleeding occurred in areas with a total print rate of 160% or less, but color bleeding was observed in areas with a total print rate of over 160% and up to 240%. C: No color bleeding occurred in areas with a total print rate of 120% or less, but color bleeding was observed in areas with a total print rate of over 120% and up to 240%. D: Color mixing and bleeding was observed in areas with a total print ratio of 120% or less.

[0179] <Evaluation 4: Evaluation of print density on coated paper> The density of the solid prints of each color created in Evaluation 2 above was measured using a spectrophotometer (X-rite's "eXact Advance") to evaluate the print density. The measurement conditions were ISO status T as the density standard, a viewing angle of 2°, and a light source D50. The evaluation criteria were as follows, with AA, A, and B ratings being considered as usable ranges. AA: In all solid prints, the print density was 0.3 or more higher than the print density of a solid print of the same color produced using the ink set of Comparative Example 1. A: In the solid print of the color that had the smallest difference in print density compared to the solid print of the same color created using the ink set of Comparative Example 1, the value of the difference was 0.15 or more and less than 0.3. B: In the solid print of the color that had the smallest difference in print density from the solid print of the same color created using the ink set of Comparative Example 1, the value of the difference was greater than 0 and less than 0.15. C: In the solid print of the color that had the smallest difference in print density compared to the solid print of the same color produced using the ink set of Comparative Example 1, the difference value was 0 or less (i.e., there was a solid print with a print density lower than the solid print produced using the ink set of Comparative Example 1).

[0180] <Evaluation 5: Evaluation of bleeding of characters on high-quality paper> Using the inkjet printing device used in Evaluation 2 above, a nozzle check pattern was used to confirm that ink was being ejected normally from all nozzles. Then, using the black ink from the inkjet printing device, a test was carried out on the NPi Form NEXT-IJ α (manufactured by Nippon Paper Industries Co., Ltd.). <70> Character images (20 randomly selected characters from Hiragana and Katakana arranged in a horizontal row for each character size) in MS Mincho font were printed on high-quality paper (wood-free paper). Immediately after printing, the printout was placed in a 60°C air oven and dried for 1 minute to obtain a character print. The degree of bleeding in the resulting printed characters was then evaluated by visual inspection and by using a magnifying glass. The evaluation criteria were as follows, with AA+, AA, A, and B being considered to be in the practical range. AA+: No bleeding was observed with the naked eye or with a magnifying glass on a 3-point character image. AA: In the 3-point character image, slight bleeding was observed under a magnifying glass, but no bleeding was observed visually and the image was legible. In addition, in the 4-point character image, no bleeding was observed visually or under a magnifying glass. A: A 4-point character image. Slight blurring was observed under a magnifying glass, but no blurring was visible to the naked eye and the image was legible. B: A 4-point character image. Slight blurring was visible to the naked eye, but it was still legible. C: In the 4-point text image, the text was clearly blurred and illegible even when viewed visually.

[0181] <Evaluation 6: Evaluation of print density on high-quality paper> Using the inkjet printing device used in Evaluation 2 above, a nozzle check pattern was used to confirm that ink was being ejected normally from all nozzles. Then, using each of the inks installed in the inkjet printing device, a test was carried out on Nippon Paper Industries Co., Ltd.'s NPi Form NEXT-IJ α <70> A solid print was made on high-quality paper with a printing rate of 100%. Immediately after printing, the printed substrate was placed in an air oven at 70°C and dried for 1 minute to obtain a solid print. The density of the solid prints of each color was then measured using a spectrophotometer (X-rite's "eXact Advance") to evaluate the print density. The measurement conditions were ISO status T as the density standard, a viewing angle of 2°, and a light source D50. The evaluation criteria were as follows, with AA, A, and B ratings being considered as usable ranges. Solid prints were created using each of the four inkjet inks: cyan, magenta, yellow, and black, and each solid print was evaluated for whiteout. Tables 8 and 9 show the results for the color with the worst evaluation result. AA: In all solid prints, the print density was 0.2 or more higher than the print density of a solid print of the same color produced using the ink set of Comparative Example 1. A: In the solid print of the color that had the smallest difference in print density compared to the solid print of the same color created using the ink set of Comparative Example 1, the value of the difference was 0.1 or more and less than 0.2. B: In the solid print of the color that had the smallest difference in print density from the solid print of the same color created using the ink set of Comparative Example 1, the value of the difference was greater than 0 and less than 0.1 C: In the solid print of the color that had the smallest difference in print density compared to the solid print of the same color produced using the ink set of Comparative Example 1, the difference value was 0 or less (i.e., there was a solid print with a print density lower than the solid print produced using the ink set of Comparative Example 1).

[0182] <Evaluation 7: Evaluation of droplet straightness from inkjet head> The inkjet head installed in the inkjet printing device used in Evaluation 2 above was filled with each ink constituting the ink set. A nozzle check pattern was printed, and after confirming that ink was being ejected normally from all nozzles, the inkjet printing device was left to stand for a certain period of time in an environment of 25°C. Thereafter, a nozzle check pattern was printed again, and compared with the nozzle check pattern before the stand-by, the ink droplet landing positions were checked using a magnifying glass to check for any deviations, thereby evaluating straightness. The evaluation criteria were as follows, with AA+, AA, A, and B being considered within the practical range. Tables 8 and 9 show the evaluation of the color with the worst evaluation results. AA+: Even when a nozzle check pattern was printed after waiting for 2 hours, no deviation was observed in the ink droplet landing position compared to the nozzle check pattern before leaving the printer still. AA: In the nozzle check pattern printed after waiting for two hours, there were some areas where the ink droplet landing positions were misaligned compared to the nozzle check pattern before leaving it still, but in the nozzle check pattern printed after waiting for one hour, no such misalignment was observed. A: In the nozzle check pattern printed after waiting for one hour, there were some areas where the ink droplet landing positions were misaligned compared to the nozzle check pattern before leaving it still, but in the nozzle check pattern printed after waiting for 30 minutes, no such misalignment was observed. B: In the nozzle check pattern printed after waiting for 30 minutes, there were 1 to 10 locations where the ink droplet landing position was shifted from the nozzle check pattern before leaving it still. C: In the nozzle check pattern printed after waiting for 30 minutes, there were 11 or more locations where the ink droplet landing position was shifted compared to the nozzle check pattern before leaving it still.

[0183] <Evaluation 8: Evaluation of dryness and abrasion resistance> Using the inkjet printing device used in Evaluation 2 above, a nozzle check pattern was used to confirm that ink was being ejected normally from all nozzles. Then, using all inks installed in the inkjet printing device, a half-overlapped solid image was printed on OK Topcoat+ (coated paper) manufactured by Oji Paper Co., Ltd. The "half-overlapped solid image" described above was an image in which each ink was applied to the entire surface of a specified area at a printing rate of 60%, and all inks (black, cyan, magenta, and yellow) installed in the inkjet printing device were applied to the same area in that order. Therefore, the total printing rate of the half-overlapped solid image was 240%. After printing the overlapping half-solid image, the printed substrate with the ink was placed in an air oven at 70°C, and the printed material was removed at regular intervals and evaluated for drying by touching with a finger. Furthermore, abrasion resistance was also evaluated by rubbing the printed material with a cotton swab after drying for 1 minute 30 seconds. The evaluation criteria were as follows, with AA, A, and B being considered practical ranges. AA: After 1 minute of drying, there was no tackiness when touched with the fingers, and the printed matter did not peel off even after rubbing with a cotton swab 10 times. A: After 1 minute of drying, there was no tackiness when touched with the fingers, and the print did not peel off even after rubbing with a cotton swab 5 times, but after rubbing 10 times, the print began to peel off. B: After a drying time of 1 minute 30 seconds, there was no tackiness when touched with the finger, and the printed matter did not peel off even after rubbing with a cotton swab five times. However, after a drying time of 1 minute, there was a tackiness when touched with the finger. C: Drying time was 1 minute 30 seconds and tackiness was observed when touched with the fingers.

[0184] In Examples 1 to 80, which satisfied the elements of the present invention, it was confirmed that prints with excellent print density and print quality were obtained on various printing substrates regardless of the permeability of the printing substrate, and that the prints also had excellent drying properties and abrasion resistance, as well as good ink storage stability and straightness of ink droplets from the inkjet head.

[0185] On the other hand, in Comparative Example 1, because a pigment-containing crosslinked polymer particle precursor was used, the ink droplets exhibited decreased storage stability and deflected flight (deteriorated straightness) on the inkjet head, presumably due to detachment of the dispersion resin from the pigment. The deterioration in straightness also adversely affected print quality. Furthermore, in Comparative Examples 2 and 7, in which the acid value of the polymer (A-1) was higher than 160 mg KOH / g, decreased print density and blurred characters were observed when printing on high-quality paper. These results are believed to be due to the slow aggregation rate of the crosslinked polymer particles (A) when reacting with the cationic components present in the high-quality paper. Conversely, in Comparative Example 3, in which the acid value of the polymer (A-1) was lower than 50 mg KOH / g, the ink storage stability, droplet straightness, and print quality when printed on coated paper did not reach practical levels. All of these results are believed to be due to the insufficient dispersion stability of the crosslinked polymer particles (A). Furthermore, the print quality was also believed to be due to the disruption of landing accuracy caused by the deterioration in the straightness of the ink droplets. Furthermore, in Comparative Examples 4 to 6, in which a polymer (A-1) without an aromatic ring was used, it is believed that the adsorption of the polymer (A-1) to the pigment was insufficient. As a result, it became difficult to maintain the dispersion stability of the crosslinked polymer particles (A) in the ink, resulting in the occurrence of deflected droplets and deterioration of print quality due to disturbances in droplet landing accuracy. On the other hand, in Comparative Example 8, in which the glycidyl group content was less than 50 mol%, the crosslinked structure was not sufficiently formed, making it difficult to maintain the dispersion stability of the crosslinked polymer particles (A), resulting in deterioration of the straightness of the ink droplets from the inkjet head and further deterioration of print quality. Conversely, in Comparative Example 9, in which the glycidyl group content was greater than 200 mol%, the amount of carboxyl groups and carboxylate groups remaining in the crosslinked polymer particles (A) was too low, which is believed to have deteriorated the dispersion stability of the crosslinked polymer particles (A) in the ink. Furthermore, the deterioration of dispersion stability also resulted in deflected droplets and deterioration of print quality.

[0186] In Comparative Example 10, in which the acid value of the resin (B-1) was greater than 50 mgKOH / g, and in Comparative Example 11, in which a binder resin not containing an aromatic ring was used, it was difficult to maintain the dispersion state of the crosslinked polymer particles (A) after the water evaporated on the inkjet head, and this is thought to have resulted in a deterioration in the straightness of the droplets and a degradation in print quality. Furthermore, in Comparative Examples 12 to 14, in which the difference (W1) between the amount of structural units derived from the aromatic ring-containing monomer in the crosslinked polymer particles (A) and the amount (W2) of structural units derived from the aromatic ring-containing monomer in the binder resin (B) (the value represented by W1 - W2) was not within the above-mentioned range, a deterioration in print quality was observed when printing on a highly permeable substrate, and a deterioration in the straightness of the ink droplets from the inkjet head. The possible causes of these results are that the affinity between the crosslinking reaction product in the crosslinked polymer particles (A) and the resin (B-1) is too high, causing the crosslinked polymer particles (A) to be stabilized by the resin (B-1), resulting in reduced reactivity with the cationic components present in the highly permeable substrate; or that the affinity is too low, causing localized thickening in the ink present at the nozzle end face of the inkjet head, resulting in deflection of the ink droplets.

[0187] In Comparative Examples 15 to 17 and 20, which did not contain the solvent (C-1), the drying properties and scratch resistance on the low-permeability substrate were deteriorated, and further, the ink droplets did not travel in a straight line from the inkjet head, and the print quality was deteriorated. Furthermore, Comparative Example 18, which did not contain the surfactant (D), and Comparative Example 19, which did not contain the resin (B-1), did not satisfy the constituent elements of the present invention, and it was revealed that one or more of the items evaluated were at a level that was not suitable for practical use.

Claims

1. An aqueous inkjet ink comprising: pigment-containing crosslinked polymer particles (A); a binder resin (B); an organic solvent (C); and a surfactant (D), the crosslinked polymer particles (A) contain a crosslinked reaction product obtained by crosslinking a polymer (A-1) with a compound (A-2) having a plurality of glycidyl groups in one molecule, the polymer (A-1) has an aromatic ring and a carboxy group and / or a carboxylate group, and has an acid value of more than 50 mgKOH / g and not more than 160 mgKOH / g; The content of the compound (A-2) is an amount such that the glycidyl group content represented by the following formula (1) is 50 to 200 mol %, the binder resin (B) contains a resin (B-1) having an aromatic ring and an acid value of 50 mgKOH / g or less, the organic solvent (C) contains a glycol monoalkyl ether solvent (C-1) having a boiling point of 120 to 230°C under 1 atmospheric pressure and having 4 to 10 carbon atoms; The aqueous inkjet ink has a value of W1-W2, where W1 (mass%) is the content of structural units derived from polymerizable monomers having an aromatic ring relative to the total mass of the polymer (A-1), and W2 (mass%) is the content of structural units derived from polymerizable monomers having an aromatic ring relative to the total mass of the resin (B-1), and W1-W2 is 1 to 60. Formula (1): [Equation 1]

2. 2. The aqueous inkjet ink according to claim 1, wherein the surfactant (D) comprises a siloxane-based surfactant having a measured HLB value of 1 to 10.

3. 3. The aqueous inkjet ink according to claim 1, wherein the glycol monoalkyl ether solvent (C-1) contains at least one (poly)propylene glycol monoalkyl ether solvent.

4. The aqueous inkjet ink contains two or more organic solvents (C), and 3. The aqueous inkjet ink according to claim 1, wherein the organic solvent (C) has a weighted average boiling point at 1 atmospheric pressure of 150 to 200°C.

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

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