Water-based inkjet inks and printed materials

Abstract

This invention provides a water-based inkjet ink that yields printed materials with excellent print density and print quality on various printing substrates, regardless of the penetration properties of the printing substrate, and also exhibits good drying properties and abrasion resistance, as well as excellent storage stability of the ink and straight-line propagation of ink droplets from the inkjet head. [Solution] A water-based inkjet ink comprising: crosslinked polymer particles (A) containing a crosslinked reaction product obtained by crosslinking a polymer (A-1) having aromatic rings and a defined acid value using a specific amount of a compound (A-2) having multiple glycidyl groups; a binder resin (B) containing a resin (B-1) having aromatic rings and a defined acid value; and an organic solvent (C) containing a glycol monoalkyl ether solvent (C-1) with a defined boiling point and carbon number, wherein the difference in the amount of structural units derived from aromatic ring-containing polymerizable monomers contained in the polymer (A-1) and the resin (B-1) is defined.

Description

[Technical Field]

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

[0002] Inkjet printing is a recording method that obtains characters and / or images by directly ejecting droplets of liquid from a fine nozzle and adhering them to a printing substrate. Inkjet printing has become extremely popular due to its numerous advantages, including low noise levels, ease of operation, the ability to easily and inexpensively produce full-color prints, and the ability to print on various printing substrates without contact.

[0003] In recent years, inkjet printing methods have expanded beyond office and home use (consumer printing applications) to include the commercial and industrial printing markets. Furthermore, demand for water-based inkjet inks is increasing due to the need for faster printing speeds, higher print quality, and reduced environmental impact.

[0004] In particular, the commercial printing market is seeing increasing diversification of consumer needs, with demands for printing on low-permeability substrates such as coated paper, in addition to high-permeability substrates like fine paper and plain paper. Thus, the commercial printing market is looking for water-based inkjet inks that can print on various printing substrates with different liquid permeability without the need for replacement.

[0005] However, water-based inkjet inks generally have low viscosity. Therefore, when printing on highly permeable substrates, the coloring agents contained in the water-based inkjet ink may penetrate into the interior of the substrate, potentially reducing print density. In particular, when paper substrates are used as the printing substrate, feathering (a phenomenon in which water-based inkjet ink penetrates along the paper fibers, causing blurring of text and images) may occur, leading to a deterioration in print quality, such as the legibility of text.

[0006] On the other hand, when printing on low-permeability substrates such as coated paper, water-based inkjet inks do not penetrate easily, and the coloring agents tend to remain on the surface of the printing substrate. Therefore, it is easier to obtain a higher print density compared to when using high-permeability substrates. However, if the surface of the film (ink film) formed after the water-based inkjet ink dries on the printing substrate is not smooth, it is difficult to obtain a high print density. For example, after the water-based inkjet ink dries, coarse particulate components contained in the water-based inkjet ink may be exposed on the surface of the ink film, creating irregularities. This can cause light incident on the ink film to be diffusely reflected, potentially leading to a decrease in print density. Furthermore, on low-permeability substrates such as coated paper, water-based inkjet inks do not penetrate easily. Compared to high-permeability substrates such as fine paper and plain paper, the ink may not dry properly during high-speed printing, resulting in insufficient abrasion resistance.

[0007] Furthermore, some low-permeability substrates, such as coated paper, have low surface free energy. When water-based inkjet ink is printed on such substrates, the ink does not spread easily on the surface of the substrate, which can easily lead to white spots (a phenomenon in which areas where the water-based inkjet ink does not adhere to the substrate appear as spots and / or streaks). In addition, because water-based ink does not penetrate easily on substrates with low surface free energy, undried water-based inkjet ink droplets tend to coalesce, leading to color bleeding and mixing.

[0008] To improve print quality when printing on low-permeability substrates, it is effective to lower the surface tension of the water-based inkjet ink, and generally, surfactants and organic solvents are used. For example, Patent Document 1 states that a water-based inkjet ink containing a low-boiling point water-soluble organic solvent, a low-surface-tension organic solvent, and a siloxane-based surfactant can improve printability and print quality on low-permeability substrates such as coated paper, art paper, and vinyl chloride sheets. However, when printing on high-permeability substrates such as plain paper and fine paper using the water-based inkjet ink described in Patent Document 1, feathering is likely to occur, potentially degrading print quality such as the legibility of characters. Furthermore, depending on the composition of the above-mentioned water-based inkjet ink, the low surface tension makes it easy to penetrate into the interior of high-permeability substrates, resulting in the problem of difficulty in achieving excellent print density.

[0009] Furthermore, Patent Document 2 discloses an aqueous inkjet black ink that can produce high-density prints on a printing substrate without an ink-receiving layer by using carbon black having a specific specific surface area, an alkanediol having 5 to 8 carbon atoms, and a resin having a specific acid value. In the examples of Patent Document 2, coated paper without an ink-receiving layer is used as the printing substrate. However, when printing on highly permeable substrates such as plain paper or fine paper using the aqueous inkjet black ink, the carbon black sometimes does not remain sufficiently on the printing substrate, making it difficult to obtain excellent print density. In addition, when using the aqueous inkjet black ink specifically disclosed in the examples of Patent Document 2, 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 nozzle of the inkjet head, and the deposition of the aggregated carbon black may cause flight curvature (a phenomenon in which droplets of aqueous inkjet ink are ejected in a direction other than perpendicular to the nozzle surface of the inkjet head). When ink droplets deviate from their flight path, meaning the straight-line flight of water-based inkjet ink droplets deteriorates, it can lead to a decrease in print quality, such as the appearance of streaks or unevenness in printed materials.

[0010] On the other hand, various studies have been conducted on methods to improve print density when printing on highly permeable substrates. For example, Patent Document 3 discloses an aqueous inkjet ink that can produce printed materials with high print density on plain paper by using a self-dispersing pigment and a resin-dispersing pigment having a specific particle size in combination. However, depending on the type of highly permeable substrate such as plain paper, it may not be possible to prevent the aforementioned pigments from penetrating into the substrate, and sufficient print density may not be obtained. In addition, with the aqueous inkjet ink specifically disclosed in the examples of Patent Document 3, when printed on a low-permeability substrate such as coated paper, it may not dry sufficiently, resulting in poor color bleeding and scratch resistance.

[0011] Furthermore, Patent Document 4 discloses an inkjet recording ink composition containing three types of acetylenediol-based surfactants with different structures. It is also stated that by using the above ink composition, images with excellent print quality (color unevenness, aggregation, bleeding) and fixation (scratchy resistance) can be recorded at high speed on various printing substrates with different absorbencies. On the other hand, when the above ink composition is used on a highly permeable substrate, the pigment components may penetrate into the printing substrate due to the effect of the surfactant on the reduction of the surface tension of the ink composition, which may reduce the print density. In addition, the present inventors have investigated and found that the ink composition specifically disclosed in the example of Patent Document 1 has poor drying properties and scratch resistance of printed materials, and that problems with the straightness of droplets may occur depending on the printing conditions. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2014-205768 [Patent Document 2] Japanese Patent Publication No. 2020-125452 [Patent Document 3] Japanese Patent Publication No. 2018-172502 [Patent Document 4] Japanese Patent Publication No. 2015-124238 [Overview of the project] [Problems that the invention aims to solve]

[0013] Therefore, the present invention has been made to solve the above problems, and its objective is to provide an aqueous inkjet ink that can produce printed materials with excellent print density and print quality on various printing substrates, regardless of the penetration of the printing substrate, and that also has good drying properties and abrasion resistance, as well as excellent storage stability of the ink and straightness of ink droplets from the inkjet head. [Means for solving the problem]

[0014] The inventors of the present invention have conducted intensive studies to solve the above problems, and have found an aqueous inkjet ink having the following composition, thereby completing the present invention.

[0015] That is, the present invention relates to an aqueous inkjet ink shown in the following [1] to [4], and a printed matter obtained by printing the above aqueous inkjet ink on a printing substrate shown in the following [5]. [1] An aqueous inkjet ink containing crosslinked polymer particles (A) containing a pigment, a binder resin (B), an organic solvent (C), and a surfactant (D), where the crosslinked polymer particles (A) include 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, a carboxy group and / or a carboxylate group, and an acid value greater than 50 mgKOH / g and 160 mgKOH / g or less, 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) includes a resin (B-1) having an aromatic ring and an acid value of 50 mgKOH / g or less, the organic solvent (C) includes a glycol monoalkyl ether solvent (C-1) having a boiling point of 120 to 230°C under 1 atm and a carbon number of 4 to 10, when the content of the structural unit derived from the polymerizable monomer having an aromatic ring with respect to the total mass of the polymer (A-1) is W1 (mass%), and the content of the structural unit derived from the polymerizable monomer having an aromatic ring with respect to the total mass of the resin (B-1) is W2 (mass%), the value represented by W1 - W2 is 1 to 60, the aqueous inkjet ink. Formula (1):

Number

[0016] The present invention makes it possible to provide an aqueous inkjet ink that yields printed materials with excellent print density and print quality on various printing substrates, regardless of the penetration properties of the printing substrate, and that also exhibits good drying properties and abrasion resistance, as well as excellent storage stability of the ink and straight-line propagation of ink droplets from the inkjet head. [Modes for carrying out the invention]

[0017] Preferred embodiments of the aqueous inkjet ink of the present invention (hereinafter also simply referred to as "ink") will be described in detail below. However, the present invention is not limited to the following embodiments, and includes modifications that do not alter the essence of the invention.

[0018] As described above, when printing with water-based inkjet inks containing coloring agents such as pigments onto highly permeable substrates such as plain paper and fine paper, the components in the water-based inkjet ink penetrate into the printing substrate along with some of the coloring agents, which tends to result in a low pigment concentration on the surface of the printing substrate, i.e., a low print density. Furthermore, when using paper substrates as highly permeable substrates, feathering occurs as described above, which can lead to a decrease in print quality, such as reduced legibility of characters. Therefore, in order to improve print density on highly permeable substrates 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, with low-permeability substrates such as coated paper, pigments tend to remain on the substrate surface, and the decrease in print density due to pigment penetration is less likely to occur as with high-permeability substrates. However, as mentioned above, after water-based inkjet ink dries, irregularities may form on the ink film surface, potentially leading to a decrease in print density. Therefore, to improve print density on low-permeability substrates, it is important to improve the smoothness of the ink film surface after printing. Furthermore, some low-permeability substrates have low surface free energy. On the surface of such printing substrates, water-based inkjet ink does not wet and spread very easily, which can lead to a decrease in print density as well as deterioration of print quality such as white spots. In addition, because low-permeability substrates have low penetration into the interior of liquid components, there is a risk that droplets of water-based ink that have landed earlier may land adjacent to droplets of other ink before the previously landed droplets have sufficiently dried, potentially causing beading (a phenomenon in which droplets of undried ink merge together). Beading is a cause of color bleeding and density unevenness, and is therefore undesirable from the standpoint of improving print quality. Thus, in inkjet printing on low-penetration substrates, it is necessary to ensure sufficient wettability and penetration of water-based inkjet inks in order to improve print quality.

[0020] Generally, an effective method for ensuring the wettability and penetration of ink is to lower the surface tension of the ink using surfactants and organic solvents. However, while this method can improve wettability and penetration to low-permeability substrates, when using high-permeability substrates such as plain paper and fine paper, water-based inkjet inks tend to soak into the fibers of the paper substrate more easily. As a result, feathering occurs, which can easily lead to a deterioration of print quality, such as a decrease in the legibility of characters.

[0021] Incidentally, ordinary paper and fine paper, which are highly permeable substrates, contain cationic components such as salts of polyvalent metals like calcium and cationic polymers as fillers, pigments, and sizing agents. On the other hand, in water-based inkjet inks containing pigments, carboxyl groups and carboxylate groups (COO) are used to stably disperse the pigments. - A resin having anionic groups such as ) (pigment dispersion resin) is used. The inventors investigated and found that when such an aqueous inkjet ink comes into contact with the above-mentioned highly permeable substrate, the cationic components present on the contact surface dissolve into water, which is the main component of the aqueous inkjet ink, and react with the anionic groups in the pigment dispersion resin. Further investigation revealed that by improving the reactivity of the pigment dispersion resin to the cationic components, the dispersion state of the pigment on the highly permeable substrate is destroyed, the pigment aggregates, and penetration is suppressed, thereby improving the print density.

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

[0023] However, while improving the reactivity of the pigment dispersion resin to cationic components increases print density on highly permeable substrates, it becomes difficult to maintain the dispersion stability of the pigment in water-based inkjet inks, which can easily lead to a decrease in the storage stability of the ink. Furthermore, it has been found that when printing on low-permeability substrates such as coated paper, the pigment easily aggregates during the drying process, causing a loss of smoothness on the ink film surface and resulting in a decrease in print density. In addition, when printing on low-permeability substrates, secondary particles consisting of aggregated pigment, generated due to the deterioration of the dispersion state in the ink, inhibit the orientation of surfactants at the interface within the ink droplet. As a result, it has been found that wettability and permeability on the aforementioned low-permeability substrates decrease, potentially leading to a deterioration in print density and print quality. In addition, it has become clear that when some of the water, the main component of water-based inkjet ink, evaporates near the nozzle of the inkjet head, the water-based inkjet ink containing pigments whose dispersion state has been disrupted becomes thicker. This causes the ink droplets ejected from the inkjet head to bend in flight, resulting in streaky unevenness upon landing on the printing substrate, which leads to further deterioration of print quality, or worsens the straightness of the ink droplets.

[0024] In order to suppress the evaporation of water near the nozzles of the inkjet head and thus suppress ink viscosity, high-boiling-point organic solvents are generally used. However, high-boiling-point organic solvents tend to remain on the printing substrate. On the other hand, water evaporates preferentially, so when ink containing high-boiling-point organic solvents is printed on a highly permeable substrate, the amount of water in the ink necessary for the cationic components to dissolve becomes relatively small. As a result, the reaction between the pigment dispersion resin and the cationic components becomes insufficient, and it has been found that the print density decreases. Furthermore, it has become clear that the residue of high-boiling-point solvents on highly permeable substrates can cause the ink to seep along the paper fibers, resulting in feathering and reduced legibility of the text, that is, the print quality of the printed material may deteriorate.

[0025] To solve the aforementioned problems, the inventors conducted extensive research and discovered an aqueous inkjet ink having the above-described configuration. That is, by using such an aqueous inkjet ink, it becomes possible to obtain printed materials with excellent print density, print quality, and drying properties on various printing substrates, regardless of the substrate's permeability, and the ink droplets from the inkjet head also exhibit excellent straight-line propagation. Furthermore, the aqueous inkjet ink also exhibits excellent abrasion resistance. Although the detailed mechanism by which these effects are achieved by the above configuration is not yet clear, the following are possible explanations.

[0026] First, the crosslinked polymer particles (A) containing pigment in the aqueous inkjet ink of the present invention include a crosslinked reaction product obtained by crosslinking a polymer (A-1) having an aromatic ring and a carboxyl group and / or carboxylate group, and having an acid value greater than 50 mgKOH / g and 160 mgKOH / g or less, with a compound (A-2) having multiple glycidyl groups in one molecule. Furthermore, the above compound (A-2) is used such that the glycidyl group content represented by formula (1) is 50 to 200 mol%.

[0027] Generally, pigment dispersion resins with a high acid value exhibit greater charge repulsion in water-containing liquid media (aqueous media), allowing for stable dispersion of pigments in such media. On the other hand, on highly permeable substrates, the dispersion state of the pigment is less likely to be destroyed even when in contact with the cationic components, making it difficult to obtain excellent print quality and print density. Conversely, pigment dispersion resins with a low acid value are more susceptible to the effects of the cationic components; that is, they have high reactivity to the cationic components. However, in this case, as mentioned above, the dispersion state of the pigment tends to become unstable in aqueous media, making it difficult to ensure the straightness of ink droplets from the inkjet head, storage stability, and print density and print quality of printed materials on low-permeability substrates.

[0028] In contrast, the crosslinked polymer particles (A) in the present invention contain a crosslinked reaction product obtained by crosslinking a polymer (A-1), which has an aromatic ring and a carboxyl group and / or carboxylate group and has an acid value greater than 50 mgKOH / g and 160 mgKOH / g or less, with a compound (A-2) that has multiple glycidyl groups in one molecule. As a result, the acid value of the crosslinked reaction product is lower than that of the polymer (A-1).

[0029] In polymer (A-1), the aromatic ring acts as an adsorption group to the pigment, while the carboxyl group and / or carboxylate group react with compound (A-2) (crosslinking reaction). As a result, the desorption of polymer (A-1) from the pigment surface is suppressed, and even with a low acid value of the crosslinked reaction product, the dispersion stability of the crosslinked polymer particles (A) in the aqueous inkjet ink and the storage stability of the ink can be maintained. In addition, since secondary pigment particles that can inhibit the orientation of surfactants are less likely to form, the surfactant can quickly orient itself at the ink interface, and even on low-permeability substrates such as coated paper, it is possible to obtain printed materials with excellent print quality with less whiteout and color bleeding. Furthermore, even if some 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, so it is thought that an aqueous inkjet ink with excellent straight-line propagation of ink droplets can be made. In addition, the crosslinked reaction product that satisfies the acid value requirements of polymer (A-1) and the glycidyl group content requirements will have a sufficiently low acid value. Therefore, on a highly permeable substrate, the cross-linked polymer particles (A) can react quickly with cationic components, resulting in printed materials with excellent print density. Furthermore, the increased aggregation rate on the highly permeable substrate suppresses bleeding along the paper fibers, which is expected to lead to improved print quality. On the other hand, when printing on a low-permeability substrate, the dispersion state is less likely to be destroyed during the drying process after printing, and aggregation of the cross-linked polymer particles (A) can be suppressed. As a result, the smoothness of the ink film is less likely to be impaired, and printed materials with excellent print density can be obtained.

[0030] Furthermore, the aqueous inkjet ink of the present invention contains a resin (B-1) as the binder resin (B), which has an aromatic ring and an acid value of 50 mgKOH / g or less. Moreover, when W1 (g) is the content of structural units derived from polymerizable monomers having an aromatic ring contained in 100 g of the above polymer (A-1), and W2 (g) is the content of structural units derived from polymerizable monomers having an aromatic ring contained in 100 g of resin (B-1), the value expressed as W1-W2 is between 1 and 60.

[0031] Generally, binder resins are used to bond ink films to printing substrates, and the film formation of the resin during the drying process can improve the drying properties and abrasion resistance of the ink film. However, if the compatibility between the binder resin and the dispersion resin is poor, the resin molecules may not intertwine sufficiently during the drying process, which can lead to poor film formation and a decrease in drying properties and abrasion resistance. Furthermore, poor compatibility between the binder resin and the dispersion resin can also cause localized viscosity increase in the ink present on the nozzle end face of the inkjet head, resulting in deflection of ink droplets and, in other words, a decrease in straight-line flight.

[0032] As mentioned above, the dispersion resins used in water-based inkjet inks generally have anionic and hydrophobic groups. From the viewpoint of improving compatibility with such dispersion resins, it is preferable that the binder resin has a structure similar to that of the dispersion resin. However, when anionic groups are introduced into the binder resin, while compatibility with the dispersion resin improves, when printed on a highly permeable substrate, the cationic components react with the anionic groups in the binder resin on the paper surface, inhibiting the reaction with the dispersion resin and potentially reducing the print density. Furthermore, when hydrophobic groups are introduced into the binder resin, these hydrophobic groups adsorb to the pigment, stabilizing the dispersion of the pigment itself. This makes it difficult for the pigment to aggregate when reacting with cationic components on a highly permeable substrate, potentially resulting in a print that does not have excellent print density.

[0033] Therefore, in the ink of the present invention, a resin (B-1) having an acid value of 50 mgKOH / g or less is used as the binder resin (B), and the values ​​represented by W1-W2 above satisfy 1 to 60. By keeping the difference between the amount of structural units derived from polymerizable monomers having aromatic rings in resin (B-1) and the amount of structural units derived from polymerizable monomers having aromatic rings in polymer (A-1) below a certain value, the hydrophobic portion of the crosslinked reaction product formed by crosslinking polymer (A-1) with compound (A-2) and the hydrophobic portion of resin (B-1) become sufficiently compatible, and the adsorption of resin (B-1) to the pigment is also suppressed. As a result, the crosslinked polymer particles (A) and resin (B-1) are sufficiently compatible even during the drying process, and excellent drying properties and abrasion resistance are obtained on low-permeability substrates, while excellent print density and print quality are obtained on high-permeability substrates. Furthermore, it becomes possible to create an ink with excellent straight-line propagation of ink droplets from the inkjet head.

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

[0035] This method improves the wettability and penetration of the ink to low-permeability substrates, as well as the film-forming properties of the resin (B-1), resulting in printed materials with excellent print quality, less color bleeding and white spots, and improved drying properties and abrasion resistance. Furthermore, on high-permeability substrates, the glycol monoalkyl ether solvent (C-1) is less likely to remain, making it easier to suppress the rate of decrease in the water content of the ink during drying. As a result, a sufficient amount of cationic components in the high-permeability substrate are dissolved into the ink, allowing the reaction between these cationic components and the cross-linked polymer particles (A) to proceed favorably. This not only suppresses feathering but also results in printed materials with excellent print density.

[0036] As described above, in order to obtain an aqueous inkjet ink that yields printed materials with excellent print density and print quality on various printing substrates, regardless of the penetration of the printing substrate, and furthermore, an aqueous inkjet ink that also has excellent storage stability of the ink, straightness of ink droplets from the inkjet head, and excellent drying properties and abrasion resistance of the printed material, the above-described configuration is essential. However, the above mechanism is a hypothesis 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 cross-linked polymer particles (A)> The aqueous inkjet ink of the present invention contains crosslinked polymer particles (A) containing a pigment. The crosslinked polymer particles (A) containing the pigment contain a 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 carboxylate group, and having a KOH content greater than 50 mg / g and less than or equal to 160 mg / g, with a compound (A-2) having multiple glycidyl groups in one molecule. By performing the crosslinking treatment, the polymer (A-1) is crosslinked on the pigment surface, making it possible to suppress the desorption of the polymer (A-1) in the aqueous inkjet ink. As a result, it is possible to achieve a balance between print density and print quality of printed materials, ejection stability, and storage stability of the aqueous inkjet ink.

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

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

[0042] When using inorganic pigments as pigments, the following can be used: titanium dioxide, zinc oxide, zinc sulfide, lead white, calcium carbonate, precipitated barium sulfate, white carbon, alumina white, kaolin gray, talc, bentonite, carbon black, black iron oxide, cadmium red, red iron oxide, molybdenum red, molybdate orange, chrome vermilion, lead yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, viridian, titanium cobalt green, cobalt green, cobalt chrome green, Victoria green, ultramarine, dark blue, cobalt blue, cerulean blue, cobalt silica blue, cobalt zinc silica blue, manganese violet, cobalt violet, etc.

[0043] The carbon black used above can be carbon black produced by the furnace method or the channel method. In particular, carbon black with a primary particle size of 11-40 nm and a specific surface area of ​​50-400 m² as measured by the BET method is suitable. 2 Preferably, the product has characteristics such as a volume of 0.5-10% volatile matter and a pH value of 2-10.

[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 slene pigments.

[0045] Specifically, examples of organic pigments that can be used as the above pigments, as shown in the color index, include CIPigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, and 64, which are organic pigments that exhibit cyan or blue colors.

[0046] In addition, examples of organic pigments exhibiting magenta, red, or violet colors include CIPigment Red 2, 5, 7, 9, 12, 31, 48, 49, 52, 53, 57, 97, 112, 120, 122, 146, 147, 149, 150, 168, 170, 177, 178, 179, 184, 188, 202, 206, 207, 209, 238, 242, 254, 255, 264, 269, 282, and CIPigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, 50, etc.

[0047] In addition, examples of organic pigments that exhibit a yellow color include CIPigment 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] Other examples of black pigments include aniline black (CIPigment Black 1), perylene black (CIPigment Black 31, 32), and azomethine azoblack.

[0049] In addition, other pigments that can be used include CIPigment Green 7, 10, 36, CIPigment Brown 3, 5, 25, 26, CIPigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, etc.

[0050] The pigments listed above may be used individually or in combination of two or more. For example, multiple pigments listed above can be used to create a black pigment composition. The preferred pigment content is 0.1 to 20% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 7% by mass, relative to the total mass of the aqueous inkjet ink.

[0051] ≪Polymer (A-1)≫ As described above, the polymer (A-1) used in the present invention has the function of dispersing pigments, that is, it is a pigment-dispersing resin. Furthermore, the polymer (A-1) has an aromatic ring and a carboxyl group and / or a carboxylate group in its structure. In addition, the acid value of polymer (A-1) is greater than 50 mgKOH / g and 160 mgKOH / g or less. Any resin can be used as 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, examples of resins that can be used as polymer (A-1) include acrylic, styrene, maleic acid, urethane, and polyester resins. Among these, it is preferable to use an acrylic and / or maleic acid polymer from the viewpoint that it has strong adsorption to pigments and can stably disperse pigments even after the crosslinking reaction.

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

[0053] Polymer (A-1) has carboxyl groups and / or carboxylate groups. Preferably, polymer (A-1) has at least carboxylate groups. This is because the charge of the carboxylate groups allows for stable dispersion of the crosslinked polymer particles (A) containing pigment through charge repulsion, even when the acid value is low after the crosslinking reaction, thereby improving the storage stability of the ink.

[0054] The carboxylate groups in polymer (A-1) may be introduced into polymer (A-1) by synthesizing a polymer using a polymerizable monomer having carboxylate groups, or they may be formed in polymer (A-1) by neutralizing at least a portion of the carboxylate groups present in the polymer having carboxylate groups 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. In particular, alkali metal compounds are preferred as the basic compound because they provide good dispersion stability of the crosslinked polymer particles (A) containing pigment, and consequently, good storage stability of the ink, and also suppress pigment aggregation during the ink drying process, resulting in excellent straight-line movement of droplets from the inkjet head and high print density of printed materials. In particular, hydroxides such as sodium hydroxide and potassium hydroxide are preferred. The basic compounds listed above can be used individually or in combination of two or more.

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

[0056] Formula (2):

number

[0057] The "polymer" described in formula (2) above may be a polymer having only carboxyl groups (A-1-0) as described above, or a polymer having both carboxyl groups and carboxylate groups. Furthermore, the "acid value of the polymer" in formula (2) above can be measured by a conventional method. For example, approximately 1 g of the sample is accurately weighed into an Erlenmeyer flask, and 50 mL of a distilled water / dioxane mixture (distilled water / dioxane mixed in a mass ratio of 1 / 9) is added to dissolve it. Next, the sample solution is titrated with a 0.1 mol / L potassium hydroxide-ethanol solution (titer F) using a potentiometric analyzer (for example, the "AT-710M" potentiometric automatic titrator manufactured by Kyoto Electronics Manufacturing Co., Ltd.), and the amount of potassium hydroxide-ethanol solution required to reach the titration endpoint (α (mL)) is measured. Then, the acid value of the polymer (mgKOH / g) can be calculated using formula (3) below.

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

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

[0060] Furthermore, the acid value of polymer (A-1-0) and the acid value of the polymer obtained by neutralizing 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 method described above, is preferably greater than 50 mg KOH / g and less than or equal to 160 mg KOH / g, and more preferably between 70 and 160 mg KOH / g. Particularly preferably between 80 and 150 mg KOH / g.

[0062] The weight-average molecular weight (Mw) of polymer (A-1) is preferably 5,000 to 100,000. Furthermore, from the viewpoint of ensuring good dispersion stability of the crosslinked polymer particles (A) and storage stability of the ink, and maintaining the dispersion state even when water evaporates in the inkjet head, resulting in good straight-line movement of ink droplets, the above 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 a polymer can be measured by conventional methods. For example, the polystyrene-equivalent value obtained by measuring with a TSKgel column (Tosoh Corporation) and a GPC (Tosoh Corporation "HLC-8120GPC") equipped with an RI detector, using THF as the developing solvent, can be used.

[0064] The ratio of pigment to polymer (A-1) (pigment / polymer (A-1)) is preferably 1 to 100 by mass. By setting the above ratio to 1 or more, the viscosity of the ink can be kept to a level suitable for inkjet ink, and by setting it to 100 or less, dispersion stability and storage stability can be improved. Furthermore, the ratio of pigment to 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 in one molecule. Furthermore, compound (A-2) may be water-soluble or water-insoluble, but its solubility in 100g of water at 25°C is preferably 0.1 to 50g / 100gH2O. By keeping the solubility of compound (A-2) in water within the above range, reactions with components other than polymer (A-1), such as water, can be suppressed, and the crosslinking reaction of polymer (A-1) can proceed near the pigment, preventing the desorption of polymer (A-1) associated with this crosslinking reaction. As a result, the straightness of ink droplets from the inkjet head is particularly improved, and printed materials with excellent print quality and no white spots can be obtained on low-permeability substrates such as coated paper. Furthermore, from the viewpoint of more favorably exhibiting these effects, the solubility of the above compound (A-2) in 100g of water at 25°C is more preferably 0.2 to 40g / 100gH2O, and even more preferably 0.5 to 30g / 100gH2O.

[0066] It is more preferable to use a compound (A-2) that has multiple glycidyl ether groups, i.e., two or more, within a single molecule. Furthermore, it is particularly preferable that compound (A-2) is a polyglycidyl ether compound of a polyhydric alcohol having hydrocarbon groups with 3 to 8 carbon atoms.

[0067] The epoxy equivalent of compound (A-2) is preferably 90 to 300 g / eq., and more preferably 100 to 200 g / eq., from the viewpoint of efficiently crosslinking with carboxyl groups and / or carboxylate groups present in 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 type diglycidyl ether, and hydrogenated bisphenol A type 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 formula (1) above 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 setting the glycidyl group content within the above range, it becomes possible to crosslink the polymer (A-1) adsorbed on the pigment at high density. As a result, the storage stability of the aqueous inkjet ink can be improved, the straightness of ink droplets from the inkjet head can be improved, and it becomes easier to obtain printed materials with excellent print density and print quality regardless of the permeability of the printing substrate.

[0070] ≪Method for producing an aqueous dispersion of cross-linked polymer particles (A) containing pigment≫ One example of a method for producing an aqueous dispersion of crosslinked polymer particles (A) containing a pigment is as follows: First, a polymer (A-1-0) having only carboxyl groups is mixed with a basic compound in water to neutralize at least a portion of the carboxyl groups (neutralization treatment) to obtain an aqueous solution of polymer (A-1) having at least carboxylate groups. Next, a pigment is added to this aqueous solution of polymer (A-1), mixed thoroughly, and then subjected to a dispersion treatment to produce an aqueous dispersion of the pigment dispersed by polymer (A-1) (a precursor of crosslinked polymer particles containing a pigment). Subsequently, compound (A-2) is added to the aqueous dispersion of the precursor of crosslinked polymer particles containing a pigment and subjected to a crosslinking treatment to produce an aqueous dispersion of crosslinked polymer particles (A) containing a pigment.

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

[0072] Distributed Processing In the pigment dispersion process, it is preferable to pre-disperse (premix) the pigment and polymer (A-1) using a commonly used mixing and stirring device such as a stirrer, and then disperse (main dispersion) using a conventionally known dispersion device. By performing pre-dispersion before main dispersion, a pigment dispersion with uniform particle size can be obtained. Furthermore, any commonly used disperser can be used for the final dispersion of the pigment, such as a paint shaker, ball mill, roll mill, bead mill, kneader, attritor, and high-pressure homogenizer. Among these, a bead mill is preferred because it can crush and refine coarse pigment particles. Examples of bead mills include Super Mill, Sand Grinder, Agitator Mill, Glen Mill, Dyno Mill, Pearl Mill, and Cobol Mill (all trade names), all of which can be suitably used.

[0073] ≪Cross-linking treatment≫ In the crosslinking process, the polymer (A-1) adsorbed on the pigment is crosslinked by compound (A-2), yielding a crosslinked reaction product. In the manufacturing method described above, after the completion of the crosslinking process, an aqueous dispersion of crosslinked polymer particles (A) containing the pigment can be obtained.

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

[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 viewpoint of enabling stable ejection of the ink from the nozzle and ensuring good straight-line propagation of the ink droplets.

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

[0077] The pH of the aqueous dispersion of the pigment-containing crosslinked polymer particles (A) is preferably 8 to 12. When the pH is within this range, the carboxyl groups in the polymer (A-1) are more likely to become carboxylate groups, and due to suitable charge repulsion, the dispersion stability of the crosslinked polymer particles (A) and the storage stability of the ink can be improved. A more preferable pH value is 9 to 11.

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

[0079] <Binder resin (B)> ≪Resin (B-1)≫ The binder resin (B) used in the present invention is a resin (polymer) used to bond the ink film to the printing substrate. During the drying process, the resin forms a film and / or the resin molecules intertwine, thereby improving the abrasion resistance of the ink film. In the present invention, the binder resin (B) used is a resin (B-1) having an aromatic ring and an acid value of 50 mgKOH / g or less. Furthermore, the difference between the amount of structural units derived from polymerizable monomers having aromatic rings in resin (B-1) and the amount of structural units derived from polymerizable monomers having aromatic rings in polymer (A-1), i.e., the value represented by W1-W2 above, is between 1 and 60. By satisfying these requirements, it is believed that the crosslinked reaction product consisting of polymer (A-1) and the resin (B-1) will not be incompatible with each other, while at the same time suppressing the adsorption of the resin (B-1) to the crosslinked polymer particles (A). As a result, the film formation rate of the ink film can be improved during the ink drying process, which in turn makes it easier to improve the drying properties and abrasion resistance when printing on low-permeability substrates such as coated paper. Furthermore, when printing on high-permeability substrates such as plain paper and fine paper, the resin (B-1) does not inhibit the reaction between the cationic components in the printing substrate and the polymer (A-1), thus promoting the aggregation of cross-linked polymer particles (A) and improving the print density. In addition, as penetration along the fibers of the high-permeability substrate is suppressed, printed materials with less bleeding and superior print quality can be obtained. As described above, the above requirements are essential to obtain an aqueous inkjet ink that provides excellent print density on various printing substrates regardless of the permeability of the printing substrate, and also exhibits excellent drying properties and abrasion resistance of printed materials. In order to more favorably exhibit these effects, the values ​​of W1-W2 are more preferably 5 to 55, and particularly preferably 10 to 50.

[0080] The acid value of the above resin (B-1) is preferably 0 to 50 mg KOH / g, and more preferably 0 to 40 mg KOH / g. By using a binder resin having the above acid value, it becomes easy to obtain printed materials with excellent abrasion resistance and drying properties. In addition, on highly permeable substrates such as plain paper and fine paper, the reactivity between the cationic component and the crosslinked polymer particles (A) is improved, resulting in printed materials with excellent print density. Furthermore, controlling the above acid value is also effective in improving the straightness of ink droplets from the inkjet head of water-based inkjet inks.

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

[0082] Generally, binder resins are known in the form of water-soluble resins and resin particles. 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 whose solubility in 100g of water at 25°C is 1g or more. On the other hand, the "resin particles" refer to a form of non-water-soluble resin (a resin that is not a water-soluble resin), which has an average particle size in water of 5 to 1000 nm, and can be measured in the same manner as in the case of the cross-linked polymer particles (A) containing pigment described above.

[0083] In the case of the aqueous inkjet ink of the present invention, it is preferable to use a water-soluble resin (B-1) as the resin (B-1) because, in the drying process of the aqueous inkjet ink, it can rapidly thicken on a low-permeability substrate such as coated paper, thereby improving both drying properties and print quality.

[0084] Furthermore, 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 the printed material, even during high-speed printing.

[0085] The glass transition temperature described above is a value measured using a DSC (Differential Scanning Calorimeter), and can be measured in accordance with JIS K 7121, for example, as follows: Approximately 2 mg of a dried resin sample is weighed onto an aluminum pan, and this aluminum pan is set as a test container in a holder within a DSC measuring device (for example, Shimadzu Corporation's "DSC-60Plus"). The measurement is then performed under a heating condition of 5°C / min, and the temperature at the intersection of the low-temperature baseline and the tangent at the inflection point, read from the obtained DSC chart, is taken as the glass transition temperature in this application.

[0086] When using a water-soluble resin as the above-mentioned resin (B-1), the types of resins that can be used as the water-soluble resin include acrylic, urethane, polyamine, maleic acid, and polyester resins. In particular, from the viewpoint of obtaining printed materials with excellent abrasion resistance and print quality, and furthermore, inks with excellent drying properties and ejection stability, it is preferable to use one or more resins selected from the group consisting of acrylic and urethane resins.

[0087] The above-mentioned water-soluble resin can be synthesized by conventionally known methods or a commercially available product can be used. Furthermore, there are no particular restrictions on its structure; for example, resins having random structures, block structures, graft structures, comb structures, star structures, etc., can be used. Among these, from the viewpoint of fully exhibiting the properties of the polymerizable monomers constituting resin (B-1), it is preferable to use a water-soluble resin having a block structure, graft structure, or comb structure. Note that each intermediate unit constituting the block structure, graft structure, or comb structure (for example, each block in a block structure, the main chain and graft chain in a graft structure, etc.) may be formed from a single polymerizable monomer or may be a random copolymer of multiple polymerizable monomers.

[0088] The weight-average molecular weight of the water-soluble resin (B-1) that is suitably used is preferably 5,000 to 50,000, from the viewpoint of ensuring the straightness of ink droplets from the inkjet head, obtaining printed materials with excellent drying properties on various printing substrates, and further, ensuring the storage stability of the water-based inkjet ink. Moreover, 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 using the same method as the weight-average molecular weight of polymer (A-1) described above.

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

[0091] On the other hand, when resin particles are used as the resin (B-1) mentioned above, the types of resins that can be used as such resin particles include acrylic, urethane, styrene-butadiene, polyamide, polyester, polyolefin, vinyl chloride, vinyl acetate, and the like. Among these, from the viewpoint of improving both the abrasion resistance and discharge stability of printed materials, resin particles consisting of at least one selected from the group consisting of acrylic, urethane, styrene-butadiene, and vinyl chloride are preferred, resin particles consisting of at least one selected from the group consisting of acrylic and urethane are even more preferred, and from the viewpoint of improving discharge stability, the use of acrylic resin particles is particularly preferred.

[0092] The above-mentioned resin particles can be synthesized using conventionally known methods or commercially available products can be used. Furthermore, there are no particular restrictions on their structure; for example, resins having random structures, block structures, graft structures, comb-shaped structures, star-shaped structures, 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 aqueous inkjet ink is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, and even more preferably 3 to 7% by mass, in terms of solid content. By keeping the amount of resin particles within the above range, an aqueous inkjet ink with excellent abrasion resistance and drying properties for printed materials can be obtained without reducing storage stability or the straightness of ink droplets from the inkjet head.

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

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

[0096] Regardless of the permeability of the printing substrate, it is preferable to include at least one glycol monoalkyl ether solvent (C-1) as the organic solvent (C), which has a boiling point of 120 to 230°C at 1 atmosphere and has 4 to 10 carbon atoms, in order to obtain printed materials with excellent print quality, print density, drying properties, and abrasion resistance on various printing substrates.

[0097] Specific examples of glycol monoalkyl ether solvents having a boiling point of 120-230°C at 1 atmosphere and having 4-10 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 wettability of ink on low-penetration substrates, producing printed materials with excellent print quality and minimal white spots, and improving the drying properties and abrasion resistance of said printed materials; suppressing the residue of organic solvents on high-penetration substrates, and improving the print density and print quality of printed materials; and improving the film-forming properties of resin (B-1), it is preferable that the glycol monoalkyl ether solvent (C-1) contains at least one (poly)propylene glycol monoalkyl ether solvent. Note that "(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, other organic solvents besides the glycol monoalkyl ether solvent (C-1) described above (hereinafter also referred to as "other organic solvents") can be used as the organic solvent (C). Examples of organic solvents other than the glycol monoalkyl ether solvent (C-1) described above 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, and 2-methyl-2,4-pentanediol. Examples include, but are not limited to, tandiol, 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, ε-caprolactone, etc.

[0099] In the aqueous inkjet ink of the present invention, the organic solvent (C) preferably contains two or more compounds, and the weighted average value of the boiling points of the organic solvent (C) at 1 atmosphere is preferably 150 to 200°C. A weighted average value of the boiling points at 1 atmosphere of 150°C or higher results in favorable ink drying properties, preventing loss of straightness of ink droplets from the inkjet head, and preventing deterioration of print quality such as color bleeding and white spots, as well as poor drying properties, when printing on low-permeability substrates. Furthermore, when printing on high-permeability substrates, no organic solvent remains, suppressing feathering and improving print quality, such as the legibility of characters. Additionally, if the weighted average value of the boiling points at 1 atmosphere is 200°C or lower, the decrease in drying properties when printing on low-permeability substrates, the residue of organic solvents, and the deterioration of print density and print quality when printing on high-permeability substrates can be effectively suppressed. From the viewpoint of obtaining excellent straight-line propagation of droplets from the inkjet head and excellent print density in printed materials on highly permeable substrates, the weighted average value of the boiling points of the above organic solvent (C) at 1 atmosphere is more preferably 150 to 195°C, and even more preferably 155 to 190°C.

[0100] Furthermore, by including two or more compounds in the organic solvent (C), it becomes easier to adjust the weighted average value of the boiling points mentioned above. Moreover, by combining multiple compounds with different properties such as surface tension and hydrophilicity, it becomes easier to achieve effects such as print quality and drying properties when printing on low-permeability substrates, print density and print quality when printing on high-permeability substrates, the straightness of ink droplets, and storage stability. From this viewpoint, it is preferable to use a glycol monoalkyl ether solvent (C-1) and other organic solvents in combination as the two or more compounds mentioned above. In that case, it is preferable that 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 be 4 to 40 mN / m, and particularly preferable that be 8 to 25 mN / m.

[0101] In this disclosure, the surface tension used is the value measured by the Wilhelmy method (plate method). Specifically, the value measured using the Kyowa Interface Science Co., Ltd. "Automatic Surface Tension Meter CBVP-Z" and a platinum plate at a temperature of 25°C can be used.

[0102] The total content of organic solvent (C) in the water-based inkjet ink is preferably 2 to 40% by mass relative to the total amount of the water-based inkjet ink. If the total content of organic solvent (C) is 2% by mass or more, the wetting and spreading of the ink on the printing substrate is improved regardless of the penetration of the printing substrate, and the print density and print quality are improved. In addition, drying of the ink on the inkjet head is prevented, and the straightness of the ink droplets is not impaired. On the other hand, if the total content of organic solvent (C) is 40% by mass or less, no solvent remains on the printing substrate regardless of the penetration of the printing substrate, and the print density and print quality are improved. Furthermore, in order to produce an ink that has characteristics such as high print density even on a highly permeable substrate, excellent print quality including legibility of characters, and excellent drying properties on the printing substrate and straight movement of ink droplets from the inkjet head, the total amount of the above-mentioned components is more preferably 5 to 35% by mass, and particularly preferably 10 to 30% by mass, based on the total amount of aqueous inkjet ink.

[0103] <Surfactant (D)> The aqueous inkjet ink of the present invention preferably contains one or more surfactants (D) from the viewpoint that, on low-permeability substrates such as coated paper, the wettability of ink droplets is improved, a smoother ink film is formed, and printed materials with high print density can be obtained. Furthermore, by improving wettability and permeability, color bleeding and white spots are suppressed, and printed materials with excellent print quality can be easily obtained. Various surfactants (D) can be used as the surfactant (D) depending on the application, such as acetylenediol-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 acetylenediol-based surfactants, siloxane-based surfactants, and polyoxyalkylene ether-based surfactants, and it is especially preferable that it contains at least one siloxane-based surfactant.

[0104] Examples of siloxane-based surfactants that can be suitably used in the ink of the present invention include 8032 ADDITIVE, 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, manufactured by Toray Dow Corning Corporation. 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 Bic Chemie 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 Examples include 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 from Shin-Etsu Chemical Co., Ltd., and the Silface SAG series from Nisshin Chemical Co., Ltd. In particular, siloxane-based surfactants in which one or more ethylene oxide groups and / or one or more propylene oxide groups are introduced into the side chains and / or both ends of a polydimethylsiloxane chain can be suitably used.

[0105] In the present invention, it is preferable that the surfactant contains at least one siloxane-based surfactant having a measured HLB value of 1 to 10, from the viewpoint that it can quickly orient itself at the interface of ink droplets, suppress color bleeding on low-permeability substrates such as coated paper, and furthermore, even when printing on high-permeability substrates, it can easily obtain printed materials with low bleeding quality by suppressing penetration along paper fibers, etc.

[0106] The HLB (Hydrophilic-Lipophilic Balance) value is one of the parameters that represent the degree of hydrophilicity and hydrophobicity of a material. A smaller HLB value indicates higher hydrophobicity of the material, while a larger HLB value indicates higher hydrophilicity. There are two methods for determining the HLB value: calculation from the molecular structure and experimental measurement. In this disclosure, the HLB value of the surfactant is calculated by the method described below (measured HLB value). (1) Dissolve 0.5 g of the target surfactant in 5 mL of ethanol. (2) At 25°C, titrate the mixture from (1) with a 2% phenol aqueous solution while stirring. The endpoint is reached when the mixture becomes cloudy and does not return to clear when the 2% phenol aqueous solution is added dropwise. (3) When the amount of 2% phenol aqueous solution added dropwise to the endpoint is A [mL], the measured HLB value is calculated according to the following formula (4).

[0107] Formula (4): Measured HLB value = 0.89 × A + 1.11

[0108] On the one hand, examples of the acetylene diol-based surfactant 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, hexadeca-8-yne-7,10-diol, 6,9-dimethyl-tetradeca-7-yne-6,9-diol, 7,10-dimethylhexadeca-8-yne-7,10-diol, and their ethylene oxide and / or propylene oxide adducts. From the perspective of obtaining excellent printing image quality with less white spots on a low-permeability substrate, it is preferable to contain at least one kind of acetylene diol having a measured HLB value of 6 to 8.5.

[0109] In addition, examples of the polyoxyalkylene ether-based surfactant that can be preferably 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. Note that the above R 1 may have a branched structure. Also, EO represents an ethylene oxide group and PO represents a propylene oxide group. p represents the average number of added moles of EO and is a number from 2 to 100, and q represents the average number of added moles of PO and is a number from 0 to 50. When q is not 0, the addition order of (EO) p and (PO) q is not limited, and the addition may be in blocks or randomly.

[0112] The surfactant used in this invention preferably has hydrophobic and hydrophilic groups separated within the molecule. Therefore, among the surfactants exemplified above, those having hydrophilic ethylene oxide groups are particularly preferred.

[0113] The surfactant content in the aqueous inkjet ink of the present invention is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, relative to the total amount of 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 water content in the ink of this embodiment is preferably in the range of 20 to 90% by mass of the total mass of the ink.

[0116] <Other ingredients> In addition to the components described above, the ink of the present invention may contain additives such as pH adjusters, infrared absorbers, ultraviolet absorbers, and preservatives as needed to obtain an ink with desired physical properties. The total amount of these additives is preferably 0.01 to 10% by mass of the total mass of the ink.

[0117] <Ink Set> The inks of this embodiment may be used as single colors, but they can also be used as an ink set combining multiple colors depending on the application. While the combinations are not particularly limited, a full-color image can be obtained by using cyan, yellow, and magenta. Adding black ink can improve the blackness and enhance the visibility of text and other elements. Further additions such as orange and green can improve color reproduction. When printing on non-white printing substrates, using white ink in combination can produce a sharper image.

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

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

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

[0121] The permeability of the printing substrate can be determined by the amount of water absorbed, measured by a dynamic scanning liquid absorber. Specifically, the absorption coefficient for water, measured by the Bristow method (J. TAPPI Paper Pulp Test Method No. 51-87), is 0.4 ml / m². 2 msec 1 / 2 The ultra-high permeability substrate is 0.1 ml / m². 2 msec 1 / 2 Ultra 0.4ml / m 2 msec 1 / 2 The following are low-penetration substrates, 0.1 ml / m² 2 msec 1 / 2 The following are defined as non-permeable substrates. The above absorption coefficient was measured using a Kumagai Riki Kogyo Co., Ltd. automatic scanning liquid absorption meter "KM500win", water, and the target printing substrate, under conditions of 23°C and 50% RH, and obtained during a contact time of 25 to 500 milliseconds, based on the amount of water absorbed (ml / m²). 2 ) and the square root of the contact time (msec 1 / 2 In the relationship diagram between ( ), it is obtained as the gradient of a straight line determined by the least squares method.

[0122] Specific examples of highly permeable substrates include uncoated papers such as newsprint, medium-grade paper, fine-grade paper, and recycled paper; fabrics such as cotton, synthetic fibers, silk, hemp, and nonwoven fabrics; and leather. Among these, uncoated papers such as newsprint, medium-grade paper, fine-grade paper, and recycled paper are preferred because they yield printed materials with excellent print density and print quality.

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

[0124] Furthermore, specific examples of non-permeable 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 smooth or uneven surfaces. Furthermore, the printing substrates may be in roll form or sheet form. Additionally, two or more of the listed printing substrates may be laminated together and used as a printing substrate. A release adhesive layer may be provided on the opposite side of the printed surface, or an adhesive layer may be provided on the printed surface after printing.

[0126] Furthermore, since the wetting spread of the ink of the present invention is improved, and printed materials with excellent print density, print quality, and drying properties can be easily obtained, it is also preferable to apply surface modification such as corona treatment and plasma treatment to the printed surface of the printing substrates listed above.

[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 onto a printing substrate. Furthermore, the ink applied to the printing substrate is preferably dried by a drying method described later, after which it becomes a printed product.

[0128] <Drying method> A printing apparatus (inkjet printer) equipped with the ink of the present invention and used in the above-described inkjet printing method preferably includes a mechanism for drying the ink on the printing substrate. As the drying method, only one of the following may be used: a method of directly contacting the ink with a heat source, a method of indirectly contacting the ink with a heat source, and a method of irradiating with electromagnetic waves, or multiple methods may be used in combination. For example, by using infrared drying (a method of irradiating with electromagnetic waves) and hot air drying (a method of directly contacting the ink with a heat source) in combination, the ink can be dried more quickly than when each method is used alone. Furthermore, when employing the hot air drying method, which involves direct contact between the ink and the heat source, it is preferable to set the hot air temperature to 50-250°C from the viewpoint of preventing sudden boiling of the liquid components contained in the ink and obtaining printed materials with excellent print density, color reproducibility, and print quality. Also, when employing the substrate heating method (a method in which the non-printing surface of the printing substrate is in contact with the heat source), which involves indirect contact between the ink and the heat source, it is preferable to set the temperature of the heat source to 35-100°C, from the same viewpoint as described above for the hot air temperature.

[0129] <Printed material> A printed material 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 aqueous inkjet ink printed in the shape of an image and / or characters. A printed material produced using the ink of the present invention as described above will have excellent print density and print quality. The inkjet printing method described above can be suitably used as a method for the aqueous inkjet ink to be printed in the shape of an image and / or characters and then dried to form a printed layer. The "image" also includes solid images (images printed at 100% print density so as to completely cover the surface of the printing substrate) and seamless images such as checkerboard patterns. In this disclosure, the term "ink film" is used to encompass the "printed layer" described above. That is, the printed layer is an ink film printed in the shape of an image and / or characters. [Examples]

[0130] The present disclosure will be further explained below with reference to examples and comparative examples. In the following description, unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0131] <Example of dispersion resin 1 production> 93.4 parts of methyl ethyl ketone were charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the vessel was purged with nitrogen gas. After heating the contents of the reaction vessel to 110°C, a mixture of polymerizable monomers, consisting of 25 parts styrene, 20 parts acrylic acid, 20 parts methyl methacrylate, and 35 parts lauryl methacrylate, and 6 parts of the polymerization initiator V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was added dropwise to the reaction vessel over 2 hours. After the dropwise addition was complete, the polymerization reaction was continued for 3 hours while maintaining the temperature of the contents of the reaction vessel at 110°C. Subsequently, 0.6 parts of V-601 were added, and the reaction was continued at 110°C for 1 hour to obtain a dispersion resin 1 precursor having only carboxyl groups as anionic groups. The weight-average molecular weight of the obtained dispersion resin 1 precursor was 19,500, and the acid value was 158 mgKOH / g. Subsequently, the amount of potassium hydroxide required to achieve a neutralization rate of 100 mol% was calculated using the acid value of the dispersion resin 1 precursor and equation (2) above. A 48% by mass aqueous potassium hydroxide solution containing an equivalent amount of potassium hydroxide was added to convert the carboxyl groups present in the dispersion resin 1 precursor into carboxylate groups (neutralization treatment). After the neutralization treatment, 150 parts of deionized water were added, and the solution was heated to 50°C. After reaching 50°C, the solution was stirred for 1 hour while maintaining the temperature. Then, deionized water was added to bring the solid content concentration to 20% to obtain an aqueous solution of dispersion resin 1.

[0132] <Manufacturing examples of pigment-dispersed resins 2-20> Aqueous solutions of dispersion resins 2 to 20 (each with a solid content 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 Dispersion Resin 1, as well as the weight-average molecular weight and acid value 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] <Example of dispersion resin 21 production> In a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, 26 parts of polymerizable monomers, 14 parts of maleic anhydride, and 60 parts of N-phenylmaleimide, along with 100 parts of the solvent, methyl ethyl ketone, were charged. After purging with nitrogen gas, the contents of the reaction vessel were heated to 130°C while being stirred. Next, while maintaining the temperature and stirring of the contents, 1.0 part of t-butylperoxy-2-ethylhexanoate, a radical polymerization initiator, was added dropwise over 2 hours. Subsequently, stirring was continued for another hour while maintaining the temperature of the contents at 130°C to carry out the polymerization reaction. Furthermore, the solid content concentration of the contents was measured at regular intervals after the start of the polymerization reaction, and the ratio to the solid content concentration assuming that all of the polymerizable monomers had polymerized (polymerization conversion rate) was calculated. Then, when the polymerization conversion rate reached 95% or more, 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. Subsequently, the contents of the reaction vessel were heated while stirring until the temperature reached 80°C, and after reaching 80°C, the temperature was maintained at that temperature for 4 hours to open the ring of maleic anhydride, thereby obtaining a dispersion resin 21 precursor having only carboxyl groups as anionic groups. The weight-average molecular weight of the obtained dispersion resin 21 precursor was 19,000, and the acid value was 159 mgKOH / g. Subsequently, the amount of potassium hydroxide required to achieve a 100% neutralization rate was calculated using the acid value of the dispersion resin 9 precursor and equation (2) above. A 48% by mass potassium hydroxide aqueous solution containing an equal amount of potassium hydroxide was added to convert the carboxyl groups present in the dispersion resin 21 precursor into carboxylate groups (neutralization treatment). After the neutralization treatment, 150 parts of deionized water were added, and the solution was heated to 50°C. After reaching 50°C, the solution was stirred for 1 hour while maintaining the temperature. Then, deionized water was added to bring the solid content concentration to 20% to obtain an aqueous solution of dispersion resin 21.

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

[0137] [Table 2]

[0138] Table 2 also includes the weight-average molecular weight and acid value of dispersion resins 21-31. Furthermore, the abbreviations listed in Table 2 that were not used in Table 1 are as follows: • OctD:1-Octadecene Manh: Maleic anhydride • PMI: N-phenylmaleimide • CMI: Cyclohexylmaleimide • MI: Maleimide

[0139] <Example of preparation of aqueous dispersion of cyanide pigment-containing crosslinked polymer particle precursor 1 (CB1)> 600g of LIONOL BLUE FG-7351 (CIPigment Blue 15:3, manufactured by Toyo Color Co., Ltd.) as a pigment, 750g of an aqueous solution of dispersion resin 1 (solid content concentration 20%), and 1,650g of deionized water were added to a mixing container. After adding all the raw materials, the mixture was stirred with a stirrer for 1 hour (pre-dispersion), and then circulating dispersion was started using a 0.6L bead mill (DinoMill, manufactured by Shinmaru Enterprises) filled with 1,800g of 0.5mm diameter zirconia beads. Subsequently, the median diameter by volume at a 25°C environment was measured at regular intervals (e.g., every hour) using a NanoTrac UPA-EX150, manufactured by MicroTrac-Bell, and circulating dispersion was terminated when the median diameter fell to 150nm or less. Subsequently, 800 g of deionized water was added to the resulting mixture, and while the mixture was heated at 60°C, some of the deionized water and methyl ethyl ketone were removed by reduced-pressure distillation. Then, using deionized water, the pigment concentration was adjusted to 15% to obtain an aqueous dispersion of cyanide pigment-containing crosslinked polymer particle precursor 1 (CB1).

[0140] <Example of preparation of an aqueous dispersion of cyanide pigment-containing crosslinked polymer particles 1 (CP1)> 93.3 parts of the aqueous dispersion of cyanide pigment-containing crosslinked polymer particle precursor 1 (CB1) obtained by the method described above, 1.24 parts of compound (A-2) (Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX, epoxy equivalent: 140 g / eq.), which is the crosslinking agent (an amount that results in a glycidyl group content of 90 mol% as shown in formula (1) above), and 5.46 parts of deionized water were added to the reaction vessel. Next, the contents of the reaction vessel were heated to 80°C while stirring, and after reaching 80°C, stirring was continued for 3 hours while maintaining the temperature to carry out the crosslinking reaction. After that, the internal temperature of the reaction vessel was cooled to room temperature (approximately 25°C), and then deionized water was added to adjust the solid content concentration. After adjustment, the mixture was filtered through a 5 μm membrane filter to obtain an aqueous dispersion of cyanide pigment-containing crosslinked polymer particles 1 (CP1) (pigment concentration 14%) in which the dispersion resin 1 was crosslinked.

[0141] <Example of preparation of aqueous dispersion of cyanide pigment-containing crosslinked polymer particle precursors 2-31 (CB2-CB31)> Aqueous dispersions of cyanide pigment-containing crosslinked polymer particle precursors 2-31 (CB2-CB31) were obtained using the same raw materials and methods as the aqueous dispersion of cyanide pigment-containing crosslinked polymer particle precursor 1 (CB1), except that the dispersion resin was changed to dispersion resin 2-25. The pigment concentration in all aqueous dispersions was 15%.

[0142] <Example of manufacturing an aqueous dispersion of cyanide pigment-containing crosslinked polymer particles 2-40 (CP2-CP40)> Aqueous dispersions of cyanide pigment-containing crosslinked polymer particles 2-40 (CP2-CP40) were obtained using the same method as for the aqueous dispersion of cyanide pigment-containing crosslinked polymer particles 1 (CP1), except that the type of cyanide pigment-containing crosslinked polymer particle precursor used, and the amounts of added compound (A-2) (Denacol EX-321) and deionized water were changed as shown in Table 3. The pigment concentration in all aqueous dispersions was 14%.

[0143] [Table 3]

[0144] <Example of production of magenta pigment-containing crosslinked polymer particle precursor 1> 300g of TOSHIKI RED 150TR (CIPigment Red 150, manufactured by Tokyo Shikizai Co., Ltd.) and 300g of Cinquasia Pink K 4410 (CIPigment Red 122, manufactured by BASF) were added to a mixing container. 750g of an aqueous solution of dispersion resin 1 (solid content 20%) and 1,650g of deionized water were added. After adding all the raw materials and performing preliminary dispersion with a stirrer, the final dispersion was carried out using a 0.6L Dynomiil container filled with 1,800g of 0.5mm diameter zirconia beads. After the final dispersion, 800g of deionized water was added to the resulting mixture, and then, while heating the mixture at 80°C, some of the deionized water and methyl ethyl ketone were removed by distillation at atmospheric pressure. Then, using deionized water, the pigment concentration was adjusted to 15%, and further filtered through a 5 μm membrane filter to obtain an aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursor 1 (MB1).

[0145] <Example of manufacturing 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 raw materials and method as the aqueous dispersion of cyanide 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] <Example of preparation of aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursors 2-31 (MB2-MB31)> Aqueous dispersions of magenta pigment-containing crosslinked polymer particle precursors 2-31 (MB2-MB31) were obtained using the same raw materials and methods as the aqueous dispersion of cyanide pigment-containing crosslinked polymer particle precursor 1 (MB1), except that the dispersion resin was changed to dispersion resin 2-31. The pigment concentration in all aqueous dispersions was 15%.

[0147] <Example of manufacturing magenta pigment-containing crosslinked polymer particles 2-40 (MP2-MP40)> Aqueous dispersions of magenta pigment-containing crosslinked polymer particles 2-40 (MP2-MP40) were obtained using the same method 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 amount of added compound (A-2) (Denacol EX-321) and ion-exchanged water were changed as shown in Table 4. The pigment concentration in all aqueous dispersions was 14%.

[0148] [Table 4]

[0149] <Examples of manufacturing yellow pigment-containing crosslinked polymer particle precursors 1-31 (YB1-YB31)> An aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1) was obtained using the same raw materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1), except that FAST YELLOW 7413 (CIPigment Yellow 74, manufactured by Sanyo Shikiso 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%. Furthermore, aqueous dispersions of yellow pigment-containing crosslinked polymer particle precursors 2-31 (YB2-YB31) were obtained using the same raw materials and methods as the aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1), except that the dispersion resin was changed to dispersion resin 2-31. The pigment concentration in all aqueous dispersions was 15%.

[0150] <Example of manufacturing 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 raw materials and method as the aqueous dispersion of cyanide 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] <Example of manufacturing yellow pigment-containing crosslinked polymer particles 2-31 (YP2-YP31)> Aqueous dispersions of yellow pigment-containing crosslinked polymer particles 2-40 (YP2-YP40) were obtained using the same method 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 amount of added compound (A-2) (Denacol EX-321) and ion-exchanged water were changed as shown in Table 5. The pigment concentration in all aqueous dispersions was 14%.

[0152] [Table 5]

[0153] <Examples of manufacturing black pigment-containing crosslinked polymer particle precursors 1-31 (KB1-KB31)> An aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1) was obtained using the same raw 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%. Furthermore, aqueous dispersions of black pigment-containing crosslinked polymer particle precursors 2-31 (KB2-KB31) were obtained using the same raw materials and methods as the aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1), except that the dispersion resin was changed to dispersion resins 2-31. The pigment concentration in all aqueous dispersions was 15%.

[0154] <Example of manufacturing 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 raw materials and method as the aqueous dispersion of cyanide 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] <Example of manufacturing black pigment-containing cross-linked polymer particles 2-40 (KP2-KP40)> Aqueous dispersions of black pigment-containing crosslinked polymer particles 2-40 (KP2-KP40) were obtained using the same method 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 added compound (A-2) (Denacol EX-321) and ion-exchanged water were changed as shown in Table 6. The pigment concentration in all aqueous dispersions was 14%.

[0156] [Table 6]

[0157] <Example of Binder Resin 1 Production> 93.4 parts of butanol were charged into a reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer, and the mixture was purged with nitrogen gas. After heating the contents of the reaction vessel to 110°C, a mixture of polymerizable monomers, consisting of 6 parts acrylic acid, 64 parts methyl methacrylate, 20 parts 2-ethylhexyl acrylate, and 10 parts styrene, and 6 parts of the polymerization initiator V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was added dropwise to the reaction vessel over 2 hours. After the dropwise addition was complete, the polymerization reaction was continued for 3 hours while maintaining the contents of the reaction vessel at 110°C, then 0.6 parts of V-601 were added, and the reaction was continued for another hour at 110°C to obtain a solution of binder resin 1. Next, after cooling the binder resin 1 solution to room temperature, 7.1 parts of dimethylaminoethanol were added to neutralize the carboxyl groups in binder resin 1, and then 100 parts of deionized water were added. The mixture was then heated to over 100°C while stirring, and after reaching 100°C, stirring was continued while maintaining the temperature to azeotrope the butanol with water and distill off the butanol. Finally, by adjusting the solid content concentration to 40% using deionized water, an aqueous solution of binder resin 1, which has a random structure and is a water-soluble resin, was obtained. The weight-average molecular weight of the obtained binder resin 1 was 19,000, and the acid value was 47 mgKOH / g.

[0158] <Manufacturing examples of binder resins 2-15> Aqueous solutions of binder resins 2-14, which have a random structure and are water-soluble resins, 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 for neutralizing the carboxyl group, were changed as shown in Table 7. The solid content concentration of all aqueous solutions was 40%.

[0159] [Table 7]

[0160] Of 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] <Manufacturing examples of binder resins 16-17> In a reaction vessel equipped with a gas inlet pipe, thermometer, condenser, and stirrer, 124 parts of deionized water and 0.06 parts of polyoxyethylene lauryl ether sodium sulfate (Kao Corporation's "Latemul E-150"), an emulsifier, were added. Meanwhile, in a separate mixing container equipped with a stirrer, 0.5 parts of polymerizable monomers, 20 parts of styrene, and 79.5 parts of methyl methacrylate; 64 parts of deionized water; and 0.8 parts of polyoxyethylene lauryl ether sodium sulfate (Kao Corporation's "Latemul E-150") were added, and the mixture was stirred to form an emulsion. Next, eight parts of the emulsion were taken and added to the reaction vessel. The internal temperature was then raised to 80°C, and the inside of the reaction vessel was thoroughly purged with nitrogen gas. Subsequently, four parts of a 5% aqueous solution of potassium persulfate and eight parts of a 1% aqueous solution of anhydrous sodium bisulfite were added to start the polymerization reaction. After the start of the polymerization reaction, while maintaining the internal temperature of the reaction vessel at 80°C, the remaining emulsion, along with 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 a further 2 hours. After cooling the reaction vessel to room temperature, 0.48 parts of dimethylethanolamine were added, and the solid content was adjusted to 40% using deionized water to obtain an aqueous dispersion of binder resin 16 (solid content 40%) having a random structure and being resin particles. The acid value of the obtained binder resin 16 was 3 mg KOH / g.

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

[0163] <Manufacturing of water-based inkjet inks> The raw materials listed in each column of Tables 8 and 9 were added to a mixing container equipped with a stirrer, while stirring the contents of the container. After adding all the raw materials, the contents were stirred until they were sufficiently uniform, and then filtered through a 0.8 μm membrane filter to remove coarse particles that could clog the inkjet head, thereby preparing the aqueous inkjet ink. In preparing the water-based inkjet inks, a set of four water-based inkjet inks consisting of cyan, magenta, yellow, and black was prepared by using pigment-containing crosslinked polymer particles or pigment-containing crosslinked polymer particle precursors (cyan, magenta, yellow, and black) that had the same number but differed only in color. The prepared set of four inks (ink set) was then used in the evaluation described 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℃) • 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: Siloxane-based surfactant manufactured by Evonik Japan (measured HLB value: 9-10) • TEGO Wet 270: Siloxane-based surfactant manufactured by Evonik Japan (Measured HLB value: 2.5~3.5) • TEGO Twin 4100: Silicone-based surfactant manufactured by Evonik Japan (measured HLB value: 8-9) • BYK348: Siloxane-based surfactant manufactured by Big Chemie Japan (Measured HLB value: 12-13) • BYK349: Siloxane-based surfactant manufactured by Big Chemie Japan (Measured HLB value: 10.1~11) • Surfinol 104: Acetylenediol-based surfactant manufactured by Evonik Japan (2,4,7,9-tetramethyl-5-decine-4,7-diol, measured HLB value: 7.9) • Surfinol 440: Acetylenediol-based surfactant manufactured by Evonik Japan (ethylene oxide adduct of Surfinol 104, ethylene oxide addition moles: 10.5, measured HLB value: 8.1) • Dynol 604: Ethoxy compound of 2,5,8,11-tetramethyl-6-dodecine-5,8-diol, average number of moles of ethylene oxide added: 4, measured HLB = 10.1)

[0175] [Examples 1-80, Comparative Examples 1-20] The following evaluations were performed using the adjusted water-based inkjet inks described above. The evaluation results are shown in Tables 8 and 9 above.

[0176] <Evaluation 1: Evaluation of the storage stability of the ink> The viscosity of each ink constituting the ink set was measured using an E-type viscometer. Next, the inks, after viscosity measurement, were placed in containers, sealed, and then left to stand in a forced-air constant-temperature incubator set to 70°C. After a predetermined period, the viscosity of the water-based inkjet black ink in the sealed containers removed from the incubator was measured again, and the viscosity stability over time was evaluated by calculating the viscosity change rate before and after standing. The evaluation criteria were as follows, with AA, A, and B ratings considered to be within the usable range. Tables 8-9 show the evaluation for the color with the worst evaluation result. AA: The viscosity change rate after standing at 70°C for 6 weeks was within ±5%. A: The viscosity change rate after standing at 70°C for 5 weeks was within ±5%. B: The viscosity change rate after standing at 70°C for 4 weeks was within ±5%. C: The viscosity change rate after standing at 70°C for 4 weeks was greater than +5% or less than -5%.

[0177] <Evaluation 2: Evaluation of white spots on coated paper> An inkjet ejection unit equipped with four Kyocera inkjet heads (KJ4B-1200) was installed in a 25°C environment. Next, the inks constituting the ink set were filled into the inkjet heads in the order of black, cyan, magenta, and yellow for printing. After that, a nozzle check pattern was printed to confirm that ink was being ejected normally from all nozzles, and then the unit was left to stand for 1 minute. After this period, a solid print with 100% coverage was performed on Oji Paper's OK Topcoat+ (coated paper) using only one of the inks, under printing conditions of frequency 40kHz, 1,200 x 1,200 dpi, and drop volume 3 pL. Immediately after printing, the printed substrate was placed in a 70°C air oven and dried for 1 minute to obtain a solid print. Subsequently, the degree of white gaps in the solid print materials was evaluated by visual inspection and using a magnifying glass. The evaluation criteria were as follows, with AA, A, and B ratings considered to be within the usable range. Solid print materials were created using four inkjet inks: cyan, magenta, yellow, and black, and white gap evaluations were performed for each solid print material. 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 visible under magnification, but no white spots were visible to the naked eye. B: A slight white patch was visible to the naked eye. C: Clearly visible white areas were observed.

[0178] <Evaluation 3: Evaluation of color bleeding on coated paper> Using the inkjet printer used in Evaluation 2 above, after confirming that ink was being ejected normally from all nozzles using a nozzle check pattern, a superimposed gradient image was printed on OK Topcoat+ (coated paper) manufactured by Oji Paper Co., Ltd. using all the inks installed in the inkjet printer. The "superimposed gradient image" is an image created by superimposing images in the order of black, cyan, magenta, and yellow, where the print density of one color of ink is continuously changed from 10% to 60% within a predetermined area. Therefore, the total print density of the superimposed gradient image (sum of the print density of each color) is 40% to 240%. However, the print density of each color is the same at each total print density. For example, if the total print density is 40%, the print density of each color is 10%, and if the total print density is 240%, the print density of each color is 60%. Immediately after printing, the printed substrate with the ink was placed in a 70°C air oven and dried for 1 minute to obtain the superimposed gradient print. The degree of color bleeding in the superimposed gradient print was then evaluated by visual inspection and using a magnifying glass. The evaluation criteria were as follows, with AA, A, and B ratings considered to be within the usable range. AA: No color bleeding was observed in any area between 40% and 240% total print coverage. A: No color bleeding occurred in areas with a total print density of 200% or less, but color bleeding was observed in areas with a total print density between 200% and 240%. B: No color bleeding occurred in areas with a total print density of 160% or less, but color bleeding was observed in areas with a total print density between 160% and 240%. C: No color bleeding occurred in areas with a total print density of 120% or less, but color bleeding was observed in areas with a total print density between 120% and 240%. D: In areas with a total print density of 120% or less, color bleeding was observed.

[0179] <Evaluation 4: Evaluation of print density on coated paper> The density of the solid color prints created in Evaluation 2 above was measured using a spectrophotometer (X-rite "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 of D50. The evaluation criteria were as follows, with AA, A, and B ratings considered to be in the usable range. AA: In all solid print samples, the print density was 0.3 or more higher than that of the solid print samples of the same color produced using the ink set of Comparative Example 1. A: In the solid print of the same color produced using the ink set of Comparative Example 1, the difference in print density was smallest, and the value of that difference was 0.15 or more and less than 0.3. B: In the solid print of the same color created using the ink set of Comparative Example 1, the difference in print density was smallest, and the value of that difference was greater than 0 and less than 0.15. C: In the solid print of the same color produced using the ink set of Comparative Example 1, the difference in print density was smallest for the solid print of the same color, and the value of that difference was 0 or less (i.e., there was a solid print with a print density lower than that of the solid print produced using the ink set of Comparative Example 1).

[0180] <Rating 5: Evaluation of ink bleeding on high-quality paper> Using the inkjet printer used in Evaluation 2 above, after confirming that ink was being ejected normally from all nozzles using a nozzle check pattern, the black ink from the inks installed in the inkjet printer was used to print Nippon Paper Industries' NPi Form NEXT-IJ α. <70> A character image consisting of MS Mincho font in 3-point and 4-point font sizes (20 randomly selected hiragana and katakana characters arranged in a horizontal row according to their respective font sizes) was printed on high-quality paper. Immediately after printing, the printed material was placed in a 60°C air oven and dried for 1 minute to obtain the character print. The degree of ink bleeding in the resulting printed text was then evaluated by visual inspection and using a magnifying glass. The evaluation criteria were as follows, with AA+, AA, A, and B ratings considered to be within the usable range. AA+: No blurring was observed in the 3-point text image, both visually and with a magnifying glass. In the AA:3-point text image, slight blurring was observed with a magnifying glass, but no blurring was visible to the naked eye, and the text was legible. Furthermore, no blurring was observed in the 4-point text image, neither to the naked eye nor with a magnifying glass. A: In the 4-point text image, slight blurring was observed with a magnifying glass, but no blurring was visible to the naked eye, and it was legible. B: The text image was 4-point, and while slight blurring was visible to the naked eye, it was still legible. In the C:4 point text image, there was noticeable blurring of the characters, making some characters illegible.

[0181] <Evaluation 6: Evaluation of print density on high-quality paper> Using the inkjet printer used in Evaluation 2 above, after confirming that ink was being ejected normally from all nozzles using a nozzle check pattern, each of the inks installed in the inkjet printer was used to print Nippon Paper Industries' NPi Foam NEXT-IJ α. <70> A solid print with 100% ink density was performed on (high-quality paper). Immediately after printing, the printed substrate was placed in a 70°C air oven and dried for 1 minute to obtain a solid print. The density of solid prints of each color was measured using a spectrophotometer (X-rite "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 of D50. The evaluation criteria were as follows, with AA, A, and B ratings considered to be in the usable range. Solid prints were created using four inkjet inks: cyan, magenta, yellow, and black, and the white gaps were evaluated for each solid print. Tables 8 and 9 show the results for the color with the worst evaluation. AA: In all solid print samples, the print density was 0.2 or more higher than that of the solid print samples of the same color produced using the ink set of Comparative Example 1. A: In the solid print of the same color produced using the ink set of Comparative Example 1, the difference in print density was smallest, and the value of that difference was 0.1 or greater and less than 0.2. B: In the solid print of the same color produced using the ink set of Comparative Example 1, the difference in print density was smallest, and the value of that difference was greater than 0 and less than 0.1. C: In the solid print of the same color produced using the ink set of Comparative Example 1, the difference in print density was smallest for the solid print of the same color, and the value of that difference was 0 or less (i.e., there was a solid print with a print density lower than that of the solid print produced using the ink set of Comparative Example 1).

[0182] <Evaluation 7: Evaluation of the straightness of droplet propagation from the inkjet head> The inkjet heads installed in the inkjet printer used in Evaluation 2 above were filled with each of the inks that make up the ink set. After printing a nozzle check pattern and confirming that ink was being ejected normally from all nozzles, the inkjet printer was left idle for a certain period of time in an environment of 25°C. Then, the nozzle check pattern was printed again, and the straightness of the ink droplets was evaluated by checking with a magnifying glass whether there was any deviation in the landing position of the ink droplets compared to the nozzle check pattern before the idle period. The evaluation criteria were as follows, with AA+, AA, A, and B ratings being considered to be in the usable range. Tables 8-9 show the evaluation for the color with the worst evaluation result. AA+: Even after waiting for 2 hours, no deviation was observed in the ink droplet placement relative to the nozzle check pattern before standing. AA: In the nozzle check pattern printed after a 2-hour waiting period, there were some areas where the ink droplet placement was shifted compared to the nozzle check pattern before standing. However, in the nozzle check pattern printed after a 1-hour waiting period, the above shift was not observed. A: In the nozzle check pattern printed after waiting for 1 hour, there were some areas where the ink droplet placement was shifted compared to the nozzle check pattern before standing. However, in the nozzle check pattern printed after waiting for 30 minutes, the above shift was not observed. B: In the nozzle check pattern printed after a 30-minute waiting period, there were 1 to 10 locations where the ink droplet placement was shifted compared to the nozzle check pattern before the waiting period. C: In the nozzle check pattern printed after a 30-minute waiting period, there were 11 or more locations where the ink droplet placement was shifted compared to the nozzle check pattern before the waiting period.

[0183] <Evaluation 8: Evaluation of drying properties and abrasion resistance> Using the inkjet printer used in Evaluation 2 above, after confirming that ink was being ejected normally from all nozzles using a nozzle check pattern, a superimposed half-solid image was printed on Oji Paper's OK Topcoat+ (coated paper) using all the inks installed in the inkjet printer. The "superimposed half-solid image" is an image created by applying each ink to the entire surface of a predetermined area under the condition of a print density of 60%, and then superimposing all the inks installed in the inkjet printer (black, cyan, magenta, yellow) in this order onto the same area. Therefore, the total print density of the superimposed half-solid image is 240%. After printing the above overlapping half-solid color image, the ink-printed substrate was placed in a 70°C air oven, and the drying properties were evaluated by removing the printed material at regular intervals and touching it with a finger. Furthermore, the abrasion resistance was evaluated by rubbing the printed material, which had been dried for 1 minute and 30 seconds, with a cotton swab. The evaluation criteria were as follows, with AA, A, and B ratings considered to be in the practical application range. AA: After a drying time of 1 minute, there was no tackiness when touched, and the print did not peel off even after rubbing it 10 times with a cotton swab. A: After a drying time of 1 minute, there was no tackiness when touched, and the print did not peel off even after rubbing it 5 times with a cotton swab. However, after rubbing it 10 times, the print began to peel off. B: After a drying time of 1 minute and 30 seconds, there was no tackiness when touched with a finger, and the print did not peel off even after rubbing it five times with a cotton swab. However, tackiness was observed when touched with a finger after a drying time of 1 minute. C: After a drying time of 1 minute and 30 seconds, a tucked texture was still visible to the touch.

[0184] In Examples 1 to 80, which satisfy the constituent elements of the present invention, it was confirmed that printed materials with excellent print density and print quality were obtained on various printing substrates regardless of the permeability of the printing substrate, and that the printed materials also exhibited excellent drying properties and abrasion resistance, as well as good ink storage stability and straight-line propagation of ink droplets from the inkjet head.

[0185] On the other hand, in Comparative Example 1, a pigment-containing crosslinked polymer particle precursor was used, resulting in decreased storage stability and deviation of ink droplet flight (deterioration of straightness) on the inkjet head, which is thought to be due to the desorption of the dispersion resin from the pigment. Furthermore, the deterioration of straightness negatively affected print quality. In Comparative Examples 2 and 7, where the acid value of polymer (A-1) was higher than 160 mgKOH / g, decreased print density and blurring of characters were observed when printing on high-quality paper. These results are thought to be due to the slow aggregation rate of the crosslinked polymer particles (A) when reacting with cationic components present in the high-quality paper. Conversely, in Comparative Example 3, where the acid value of polymer (A-1) was lower than 50 mgKOH / g, the storage stability of the ink, the straightness of the droplets, and the print quality when printing on coated paper did not reach a practical level. In all cases, it is thought that the dispersion stability of the crosslinked polymer particles (A) could not be sufficiently ensured. Regarding print quality, it is thought that the deterioration of the straightness of the ink droplets disrupted the accuracy of the droplet placement. Furthermore, in Comparative Examples 4-6, which used polymers (A-1) without aromatic rings, it is thought that the adsorption of polymers (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, leading to flight deviations and deterioration of print quality due to irregularities in droplet placement accuracy. On the other hand, in Comparative Example 8, where the glycidyl group content was less than 50 mol%, it was difficult to maintain the dispersion stability of the crosslinked polymer particles (A) because the crosslinked structure was not sufficiently formed, resulting in poor straightness of ink droplets from the inkjet head and deterioration of print quality. Conversely, in Comparative Example 9, where the glycidyl group content was greater than 200 mol%, it is thought that the amount of carboxyl groups and carboxylate groups remaining in the crosslinked polymer particles (A) was too reduced, leading to deterioration of the dispersion stability of the crosslinked polymer particles (A) in the ink. In addition, flight deviations and deterioration of print quality were observed along with this deterioration of dispersion stability.

[0186] Furthermore, in Comparative Example 10, where the acid value of resin (B-1) was greater than 50 mgKOH / g, and in Comparative Example 11, which used a binder resin that did not contain aromatic rings, it was difficult to maintain the dispersion state of the crosslinked polymer particles (A) after the water evaporated on the inkjet head, resulting in deterioration of droplet straightness and a decrease in print quality. Moreover, in Comparative Examples 12 to 14, where the difference (value expressed as W1-W2) between the amount of structural units derived from aromatic ring-containing monomers in the crosslinked polymer particles (A) (W1) and the amount of structural units derived from aromatic ring-containing monomers in the binder resin (B) was not within the range described above, deterioration of print quality and deterioration of ink droplet straightness from the inkjet head were observed when printing on highly permeable substrates. Possible causes of these results include: either the affinity between the crosslinked polymer particles (A) and the resin (B-1) was too high, causing the crosslinked polymer particles (A) to be stabilized by the resin (B-1), reducing their reactivity with the cationic components present in the highly permeable substrate; or, the affinity was too low, causing localized thickening in the ink at the nozzle end face of the inkjet head, resulting in deflection of ink droplet flight.

[0187] In Comparative Examples 15-17 and 20, which did not contain solvent (C-1), deterioration in drying properties and abrasion resistance on low-penetration substrates was observed, as well as a decrease in the straightness of ink droplets from the inkjet head and a deterioration in print quality. Furthermore, Comparative Example 18, which did not contain surfactant (D), and Comparative Example 19, which did not contain resin (B-1), both failed to satisfy the components of the present invention, and it became clear that they were at a level unsuitable for practical use in one or more of the evaluated items.

Claims

1. A water-based inkjet ink containing crosslinked polymer particles (A) containing pigment, a binder resin (B), an organic solvent (C), and a surfactant (D), The crosslinked polymer particles (A) include a crosslinked reaction product obtained by crosslinking a polymer (A-1) with a compound (A-2) having multiple glycidyl groups in one molecule. The polymer (A-1) has an aromatic ring and a carboxyl group and / or a carboxylate group, and its acid value is greater than 50 mgKOH / g and 160 mgKOH / g or less. The content of the compound (A-2) is such that the glycidyl group content represented by the following formula (1) is 50 to 200 mol%, The binder resin (B) comprises a resin (B-1) having an aromatic ring and an acid value of 50 mg KOH / g or less. The organic solvent (C) comprises a glycol monoalkyl ether solvent (C-1) having a boiling point of 120 to 230°C at 1 atmosphere and having 4 to 10 carbon atoms. A water-based inkjet ink in which, when W1 (mass%) is the content of structural units derived from polymerizable monomers having aromatic rings relative to the total mass of the polymer (A-1), and W2 (mass%) is the content of structural units derived from polymerizable monomers having aromatic rings relative to the total mass of the resin (B-1), the value expressed as W1 - W2 is between 1 and 60. Formula (1): [Math 1]

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

3. The aqueous inkjet ink according to claim 1 or 2, characterized in that 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 The aqueous inkjet ink according to claim 1 or 2, wherein the weighted average value of the boiling points of the organic solvent (C) at 1 atmosphere is 150 to 200°C.

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

Images