Aqueous inkjet ink and printed matter

Abstract

Provided is an aqueous inkjet ink that, even when applied to a low-absorbency print substrate, e.g., coated paper, produces printed matter exhibiting no color bleeding due to the coalescence of droplets or white voids, having excellent dot circularity of the droplets, and showing good print density and color reproducibility, and that also has satisfactory ejection stability. The aqueous inkjet ink contains crosslinked-polymer particles (A) including a pigment and a surfactant (B), wherein the crosslinked-polymer particles (A) comprise a product of crosslinking between a compound (A-1) having a plurality of functional groups which react with a carboxy group and / or a carboxylate group and an uncrosslinked polymer (A-2), and the surfactant (B) comprises a polyoxyethylene alkyl ether compound (B-1) having a specific structure, and a nonionic surfactant (B-2) having an HLB value of 1-10, wherein the ratio between the content of the compound (B-1) and the content of the nonionic surfactant (B-2) is defined.

Description

Water-based inkjet inks and printed materials

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to an aqueous inkjet ink and a printed matter produced using the aqueous inkjet ink.

[0002] Inkjet printing is a recording method in which ink droplets are directly ejected from fine nozzles and deposited on a printing substrate to produce characters and / or images. Inkjet printing has numerous advantages, including low noise and ease of operation, ease of full-color printing, inexpensive printing equipment, and the ability to print on a variety of printing substrates without contact, leading to its widespread adoption. In particular, in recent years, inkjet printing has become increasingly popular not only for consumer applications in offices and homes, but also for commercial and industrial printing applications. In this context, there has been an increasing demand for inkjet inks containing water as a primary component (aqueous inkjet inks) with the aim of reducing the burden on the environment and workers.

[0003] The above "image" also includes seamless images such as solid images and checkered pattern images.

[0004] Aqueous inkjet inks have long been developed for use on plain paper and specialty paper as printing substrates. These applications are based on the premise that the liquid components of the aqueous inkjet ink are absorbed into the printing substrate. Therefore, when the aqueous inkjet ink is printed on poorly absorbent printing substrates, such as those used in the commercial and industrial printing applications, the image bleeds, making it difficult to produce printed materials suitable for practical use.

[0005] For example, coated paper, which is a poorly absorbent printing substrate, has low absorbency of liquid components. Therefore, during printing, if a droplet of aqueous inkjet ink lands adjacent to a previously landed droplet before the previous droplet has dried, adjacent droplets are likely to coalesce (a phenomenon known as beading). Beading can cause color bleeding in printed materials. Furthermore, some poorly absorbent printing substrates, including coated paper, have low surface free energy. When printing on such printing substrates, the aqueous inkjet ink has difficulty wetting and spreading on the surface of the printing substrate, which can easily lead to the occurrence of white spots (a phenomenon in which areas on the printing substrate where the aqueous inkjet ink does not adhere appear as spots and / or streaks).

[0006] Furthermore, water, which is the main solvent of aqueous inkjet inks, has a high surface tension and is difficult to wet and spread on the printing substrate, which can easily cause deterioration in print quality, such as white voids and color bleeding. In order to improve print quality, it is effective to reduce the surface tension of aqueous inkjet inks, and highly hydrophobic surfactants or organic solvents are generally used for this purpose.

[0007] For example, Patent Document 1 discloses an ink composition for inkjet recording containing three types of acetylene diol surfactants with different structures. Patent Document 1 claims that the ink composition can record images with excellent print quality (color unevenness, aggregation, bleeding) and fixability (abrasion resistance) at high speed on a variety of printing substrates with different absorbencies. Patent Document 2 also discloses an aqueous ink composition containing a nonionic surfactant with an HLB value of 4 to 14. Patent Document 2 claims that the ink composition can produce printed matter that is free of aggregation and has excellent wetting and spreading properties, fineness, print density, water resistance, and abrasion resistance (abrasion resistance) on offset media that may be printed with offset ink. Furthermore, Patent Document 3 discloses an inkjet recording method in which recording is performed on a printing substrate having low water absorption using a water-based ink for inkjet recording containing one or more acetylene diol surfactants selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 2,5-dimethyl-3-hexyne-2,5-diol, and a nonionic surfactant. According to Patent Document 3, a printed matter can be obtained that is free from turbidity (white turbidity, oil floating, etc.) and has reduced color unevenness.

[0008] JP 2015-124238 A JP 2004-510028 A JP 2014-139004 A

[0009] On the other hand, the aqueous inkjet inks disclosed in the above Patent Documents 1 and 2 have not been evaluated for ejection stability, which is an essential requirement for use in inkjet printing methods. As will be described in detail later, depending on the material used in combination, the effects of the highly hydrophobic material described above may not be fully exhibited, and the ejection stability of the aqueous inkjet ink may also deteriorate.

[0010] Furthermore, the present inventors reproduced and evaluated the aqueous inkjet ink specifically disclosed in the examples of Patent Document 3, and found that problems such as white voids and color bleeding, which were not evaluated in Patent Document 3, worsened, and that the droplet shapes of the aqueous inkjet ink became distorted (poor dot circularity).

[0011]

[0005] As described above, in order to obtain an aqueous inkjet ink that can produce printed matter free from color bleeding and white voids due to droplet coalescence, with excellent droplet dot circularity, and with excellent ejection stability, further improvements have been required. Furthermore, until now, there has not been an aqueous inkjet ink that can produce printed matter with good print density and color reproducibility while solving these problems.

[0012]

[0013] Accordingly, an object of an embodiment of the present invention is to provide an aqueous inkjet ink that is free from color bleeding due to coalescence of droplets and white voids, that produces printed matter with excellent dot circularity, good print density and color reproducibility, and that also has good ejection stability, even on poorly absorbent printing substrates such as coated paper. Another object of an embodiment of the present invention is to provide an aqueous inkjet ink that, in addition to the above-mentioned effects, also has excellent drying properties.

[0013] In this disclosure, the state of a printed matter in which there is no color bleeding due to the coalescence of droplets, no white spots, and the droplet dots have excellent circularity is also referred to as "excellent print quality."

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

[0015] That is, some embodiments of the present invention relate to aqueous inkjet inks as shown in [1] to [5] below, and printed matter produced using the aqueous inkjet ink as shown in [6] below. [1] An aqueous inkjet ink containing pigment-containing crosslinked polymer particles (A) and a surfactant (B), wherein the crosslinked polymer particles (A) comprise a crosslinked reaction product of a compound (A-1) having, in one molecule, a plurality of functional groups reactive with a carboxy group and / or a carboxylate group, and an uncrosslinked polymer (A-2) having a carboxy group and / or a carboxylate group, and the surfactant (B) contains a compound (B-1) represented by the following general formula 1 and a nonionic surfactant (B-2) having an HLB value of 1 to 10, and the ratio of the content of the compound (B-1) to the content of the nonionic surfactant (B-2) is 1:1.2 to 1:20 by mass. １ -(O-CH ２ -CH ２ ) ｎ -OH General formula 1 (In general formula 1, R １ (n) represents a linear or branched alkyl group having 10 to 25 carbon atoms, and n is an integer from 20 to 100. [2] The aqueous inkjet ink according to [1], further comprising an organic solvent, wherein the organic solvent comprises an alkanediol-based solvent having 5 to 8 carbon atoms and / or a (poly)alkylene glycol monoalkyl ether-based solvent having 5 to 9 carbon atoms. [3] The aqueous inkjet ink according to [2], wherein the organic solvent comprises a (poly)propylene glycol monoalkyl ether-based solvent having 5 to 9 carbon atoms. [4] The aqueous inkjet ink according to any one of [1] to [3], wherein the acid value of the uncrosslinked polymer (A-2) is 60 to 180 mgKOH / g. [5] The aqueous inkjet ink according to any one of [1] to [4], wherein the nonionic surfactant (B-2) having an HLB value of 1 to 10 comprises a gemini type silicone-based surfactant and / or a silicone-based surfactant modified at both ends with polyether (excluding the gemini type silicone-based surfactant). [6] A printed matter obtained by printing with the aqueous inkjet ink according to any one of [1] to [5] above.

[0016] The present disclosure has made it possible to provide an aqueous inkjet ink that is free from color bleeding due to droplet coalescence and white voids, produces excellent dot circularity of the droplets, and produces printed matter with good print density and color reproducibility, even on poorly absorbent printing substrates such as coated paper, and also has good ejection stability. Furthermore, the present invention has made it possible to provide an aqueous inkjet ink that, in addition to the above-mentioned effects, also has excellent drying properties.

[0017]

[0023] Several preferred embodiments of the inkjet ink of the present disclosure (hereinafter also simply referred to as "the ink of the present disclosure") are described in detail below. Note that the present disclosure is not limited to the following embodiments, and includes modifications that are implemented within the scope of the present disclosure.

[0018] As described above, poorly absorbent printing substrates, such as coated paper, have low surface energy, making it difficult for aqueous inkjet inks to sufficiently wet and spread on them. Therefore, even in printed materials with high coverage, image defects such as blank spaces are likely to occur. Furthermore, poorly absorbent printing substrates also have low permeability of liquid components into their interiors, which can lead to beading, as droplets of another ink may land adjacent to previously landed droplets of aqueous inkjet ink before they have sufficiently dried. Beading manifests as color bleeding and uneven density, and is therefore undesirable from the perspective of improving print quality. Thus, in order to achieve improved print quality in inkjet printing on poorly absorbent printing substrates, it is necessary to ensure sufficient wettability and permeability of the aqueous inkjet ink.

[0019] In general, reducing the surface tension of an ink is effective in ensuring the wettability and permeability of the ink. Furthermore, adding a highly hydrophobic surfactant to the ink allows the surfactant to quickly orient at the ink interface (air-liquid interface and the interface between the printing substrate and the ink), making it easier to impart wettability and permeability.

[0020] On the other hand, the inventors' investigations revealed that highly hydrophobic surfactants are adsorbed to the free polymer dispersant present in the aqueous inkjet ink. This is thought to be because highly hydrophobic surfactants have a tendency to have an affinity with other hydrophobic materials, and interact with the hydrophobic groups in the free polymer dispersant.

[0021] Generally, polymer dispersants used in aqueous inkjet inks contain hydrophilic groups such as carboxyl groups and carboxylate groups, and hydrophobic groups such as aromatic ring structures and long-chain alkyl groups. The hydrophilic groups are introduced to improve affinity with water, the main component, and to stabilize the dispersed state of the pigment through charge repulsion between polymer dispersants. On the other hand, the hydrophobic groups function, for example, as adsorption groups for the pigment. Therefore, it is extremely difficult to eliminate hydrophobic groups from polymer dispersants used in aqueous inkjet inks.

[0022] In this way, if a highly hydrophobic surfactant is adsorbed to a free polymer dispersant, when ink droplets land on a printing substrate, the orientation of the surfactant at the interface is hindered by the free polymer dispersant, making it difficult to obtain sufficient wettability and penetration. Furthermore, although the detailed mechanism is unknown, the presence of a large amount of polymer dispersant to which a highly hydrophobic surfactant is adsorbed in the ink tends to deteriorate the ejection stability of the ink.

[0023] Therefore, to obtain printed materials with excellent print quality on poorly absorbent printing substrates such as coated paper and to improve ink ejection stability, it is important to reduce the amount of free polymer dispersant so as not to interfere with the orientation of the surfactant. Therefore, in this embodiment, it is more preferable to use a polymer crosslinked with a crosslinking agent (crosslinked polymer) as the polymer dispersant, from the viewpoint of preventing desorption of the polymer dispersant from the pigment, even when the ink's component ratio changes due to, for example, drying. In particular, by using a crosslinking agent having multiple functional groups per molecule that react with carboxyl groups or carboxylate groups, which are commonly present in polymer dispersants, the polymer dispersant can be crosslinked at a high density, preventing desorption from the pigment. This also enables the surfactant to be quickly oriented at the ink interface, improving the wettability and penetration of the ink. Furthermore, by preventing desorption of the polymer dispersant and reducing the amount of free polymer dispersant, the ink ejection stability is improved.

[0024] However, crosslinking the polymer dispersant and reducing the amount of free polymer dispersant can have the adverse effect that the surfactant, which does not have any components to adsorb, may not be able to stably exist in the ink. In this case, the surfactant may be localized unevenly at the ink interface, causing the ink droplets to wet and spread unevenly, resulting in poor print quality with poor circularity.

[0025] Furthermore, when crosslinking a polymer with a crosslinking agent, the crosslinking reaction generally generates hydrophilic functional groups, such as hydroxyl groups, amino groups, and amide bonds, in the polymer dispersant. As a result, the affinity between the polymer dispersant containing these functional groups and a highly hydrophobic surfactant deteriorates, which can lead to localization and / or separation of the surfactant and the crosslinked polymer (including pigment particles) in printed materials, for example. This can result in reduced print density and color reproducibility.

[0026] In order to solve the above problems, the present inventors conducted extensive research and found that by using crosslinked polymer particles containing a pigment in combination with a compound (B-1) represented by general formula 1 and a nonionic surfactant (B-2) having an HLB value of 1 to 10, and further setting the ratio (mass ratio) of the content of the compound (B-1) to the content of the nonionic surfactant (B-2) to be 1:1.2 to 1:20, it is possible to ensure the wettability and permeability of the ink even on a poorly absorbent printing substrate such as coated paper, and further to obtain printed matter that is excellent in dot circularity, print density, and color reproducibility, thereby arriving at the present invention. Although the detailed mechanism by which these effects are achieved by the above configuration is not clear, the following may be considered, for example.

[0027] First, surfactant (B-2) corresponds to the "highly hydrophobic surfactant" described above. The surfactant (B-2) has an HLB value within a suitable range and can impart excellent penetration and wettability to aqueous inkjet inks, even on poorly absorbent printing substrates such as coated paper. However, as described above, surfactant (B-2) has poor affinity with crosslinked polymers containing hydrophilic functional groups. For example, the surfactant (B-2) may spread unevenly on the printing substrate, resulting in printed matter with poor dot roundness. Furthermore, as water evaporates preferentially during the drying process after printing, the compatibility between the surfactant (B-2) and the crosslinked polymer may decrease, resulting in localization and / or separation of the surfactant (B-2) and the crosslinked polymer (pigment particles containing the crosslinked polymer), potentially resulting in an uneven ink film (dried ink film). In this case, light incident on the ink film may be scattered on the surface of the ink film, causing the printed matter to appear whitish (whitening) or impairing color reproducibility.

[0028] Meanwhile, in compound (B-1), a linear or branched alkyl chain having 10 to 25 carbon atoms functions as a hydrophobic moiety, and a polyethylene oxide chain having an added mole number of 20 to 100 functions as a hydrophilic moiety. Furthermore, by using compound (B-1) and surfactant (B-2) in combination at a suitable ratio, the polyethylene oxide chain in compound (B-1) has affinity for water in the ink, while the alkyl chain is suitably compatible with surfactant (B-2). As a result, surfactant (B-2) emulsified in the ink of the present disclosure can be uniformly oriented without localizing at a portion of the interface. This is thought to enable printed matter with excellent dot circularity to be obtained while suppressing whiteout and color bleeding.

[0029] Furthermore, even after the water has evaporated preferentially during the drying process of the ink, the alkyl chain in compound (B-1) has an affinity with the surfactant (B-2), and the polyethylene oxide chain has an affinity with the crosslinked polymer, so that the materials do not separate and a uniform ink film is formed. As a result, it is possible to obtain printed matter with excellent print density and color reproducibility.

[0030] As described above, in order to obtain an ink that is free from color bleeding and white voids, has excellent dot circularity, and exhibits good print density and color reproducibility, and also has excellent ejection stability, it is advisable to use a compound (B-1) represented by general formula 1 and a surfactant (B-2) having an HLB value of 1 to 10 in addition to crosslinked polymer particles containing a pigment, and further specify the content ratio thereof. Note that the above mechanism is speculation and does not limit the present invention in any way. In the present disclosure, the compound (B-1) and the nonionic surfactant (B-2) are different entities. Specifically, the compound (B-1) is a surfactant other than a nonionic surfactant having an HLB value of 1 to 10.

[0031] The aqueous inkjet inks specifically disclosed in the above-mentioned Patent Documents 1 and 2 differ from the present disclosure in that they do not use crosslinked polymer particles containing a pigment. Furthermore, Patent Documents 1 and 2 do not describe or suggest the use of a polymer having a crosslinked structure as a dispersing polymer, or that the polymer having a crosslinked structure can fully exhibit the effects of a highly hydrophobic surfactant and improve the ejection stability of the aqueous inkjet ink. Meanwhile, "acetylene glycol (A)," which is considered an essential component in Patent Document 3, corresponds to the nonionic surfactant (B-2) in the present disclosure, and part of the "nonionic surfactant (B)" corresponds to the compound (B-1) in the present disclosure (see, for example, Claim 3 of Patent Document 3). However, while Patent Document 3 specifies that the ratio of "nonionic surfactant (B) / acetylene glycol (A)" is 1 to 3, the present disclosure specifies that the ratio of the content of compound (B-1) to the content of the nonionic surfactant (B-2) is 1:1.2 to 1:20 by mass (1 / 20 to 1 / 1.2 (5 / 6) when expressed using the method described in Patent Document 3), and this point is where the two disclosures differ. In fact, Comparative Example 3 of Patent Document 3 discloses an example in which the ratio is 0.3 (1:3.3 when expressed using the method described in the present disclosure), and it is stated that the color unevenness and ejection stability are below practical levels. In contrast, the present disclosure further specifies the structure of compound (B-1), thereby making it possible to achieve good quality even in aqueous inkjet inks that were deemed to be unable to achieve good quality in Patent Document 3.

[0032] Next, the main components constituting the inkjet ink of one embodiment will be described below.

[0033] <Pigment-Containing Crosslinked Polymer Particles (A)> The inkjet ink of this embodiment contains pigment-containing crosslinked polymer particles (A). The pigment-containing crosslinked polymer particles (A) contain the pigment and a crosslinked reaction product of a compound (A-1) having, in one molecule, multiple functional groups reactive with carboxy groups and / or carboxylate groups, and an uncrosslinked polymer (A-2). The crosslinking treatment carried out to produce the crosslinked reaction product crosslinks the uncrosslinked polymer (A-2) to a high density, making it possible to suppress desorption of the polymer dispersant in the ink of the present disclosure. This also allows the surfactant (B-2) to function effectively, making it possible to improve the wettability and penetration of the ink.

[0034] In the present disclosure, "pigment-containing crosslinked polymer particles" refer to particles obtained after a crosslinking treatment using a crosslinking agent (a compound used to chemically bond polymer molecules together) has been applied to the polymer contained in a crosslinked polymer particle precursor. Furthermore, the "crosslinked polymer particle precursor" refers to particles at a stage prior to the crosslinking treatment, such as one or more particles selected from the group consisting of uncrosslinked polymer particles encapsulating a pigment, uncrosslinked particles containing a polymer and a pigment and having a sea-island structure with the pigment partially exposed on the surface of the particle, and pigment particles with a polymer chemically adsorbed and / or bonded to at least a portion of the surface.

[0035] <<Pigment>> The pigment contained in the pigment-containing crosslinked polymer particles (A) may be either an organic pigment or an inorganic pigment. Furthermore, an organic pigment and an inorganic pigment may be used in combination. 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.

[0036] When an inorganic pigment is used as the pigment, examples of the inorganic pigment that can be used include titanium oxide, zinc white, zinc sulfide, white lead, calcium carbonate, precipitated barium sulfate, white carbon, alumina white, kaolin clay, talc, bentonite, carbon black, black iron oxide, cadmium red, red iron oxide, molybdenum red, molybdate orange, chrome vermilion, yellow lead, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, viridian, titanium cobalt green, cobalt green, cobalt chrome green, Victoria green, ultramarine, Prussian blue, cobalt blue, cerulean blue, cobalt silica blue, cobalt zinc silica blue, manganese violet, and cobalt violet.

[0037] As the carbon black, carbon black produced by the furnace method or the channel method can be used. Among these carbon blacks, those having a primary particle size of 11 to 40 nm and a specific surface area measured by the BET method of 50 to 400 m are preferred. ２ / g, a volatile content of 0.5 to 10%, and a pH value of 2 to 10 are preferred.

[0038] On the other hand, specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments.

[0039] Specific examples of organic pigments that can be used as the pigment, based on the color index, include C.I. Pigment Blue 1, 2, 3, 15:1, 15:3, 15:4, 15:6, 16, 21, 22, 60, 64, etc., as organic pigments that exhibit cyan or blue colors.

[0040] In addition, examples of organic pigments that exhibit magenta, red, or violet include C.I. Pigment Red 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, C.I. Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, 50, and the like.

[0041] Further, examples of organic pigments that exhibit a yellow color include C.I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, and 213.

[0042] Examples of black pigments include aniline black (C.I. Pigment Black 1), perylene black (C.I. Pigment Black 31, 32), and azomethine azo black.

[0043] In addition to the above pigments, C.I. Pigment Green 7, 10, 36, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, and the like can be used.

[0044] The pigments listed above may be used alone or in combination of two or more. For example, a black pigment composition may be prepared by using two or more of the pigments listed above. The content of the pigment is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 7% by mass, based on the total mass of the aqueous inkjet ink.

[0045] <<Compound (A-1)>> The compound (A-1) is used as the crosslinking agent and has, in one molecule, a plurality of functional groups that react with carboxy groups and / or carboxylate groups present in the uncrosslinked polymer (A-2). Examples of compounds that can be used as the compound (A-1) include aziridine compounds, isocyanate compounds, epoxy compounds, carbodiimide compounds, oxetane compounds, and oxazoline compounds. Among these, it is preferable to use an epoxy compound as the compound (A-1), i.e., to use a compound (A-1) that has a plurality of epoxy groups in one molecule, because this allows the crosslinking reaction of the polymer (A-2) to proceed in the vicinity of the pigment while maintaining the dispersion stability of the pigment, and prevents detachment of the polymer (A-2) associated with the crosslinking reaction. This allows for the production of printed materials without white voids, and also improves the ejection stability of the aqueous inkjet ink. The compound (A-1) may be water-soluble or water-insoluble. However, from the viewpoint of enabling the crosslinking reaction to proceed more efficiently in a liquid medium mainly composed of water, the amount of the compound (A-1) dissolved in 100 g of water at 25° C. is preferably 0.1 to 50 g / 100 gH. ２ 0 is preferable, and 0.2 to 40 g / 100 gH ２ It is more preferable that the concentration is 0.5 to 30 g / 100 gH. ２ It is O.

[0046] As described above, compound (A-1) is preferably a compound having multiple epoxy groups in one molecule. Furthermore, it is more preferable to use a compound having two or more glycidyl ether groups in one molecule as the compound having multiple epoxy groups in one molecule. Furthermore, compound (A-1) is particularly preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms.

[0047] When the compound having a plurality of epoxy groups in one molecule is used as the compound (A-1), the epoxy equivalent thereof is preferably 90 to 300 g / eq., more preferably 100 to 200 g / eq., from the viewpoint of more efficiently carrying out a crosslinking reaction with the carboxy groups and / or carboxylate groups present in the uncrosslinked polymer (A-2) in a liquid medium mainly composed of water.

[0048] Specific examples of the compound having two or more glycidyl ether groups in one molecule include cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether.

[0049] The compound (A-1) is preferably added so that the content (mol %) of the functional group represented by the following formula 2 is 50 to 150 mol %, more preferably 70 to 120 mol %, and particularly preferably 80 to 100 mol %.

[0050]

[0051] For example, when a compound EW (g) having a plurality of epoxy groups in one molecule and an epoxy equivalent EE (g / eq.) (corresponding to compound (A-1)) is mixed with a polymer PW (g) having an acid value AV (mg KOH / g) (corresponding to polymer (A-2)), the functional group content is expressed by the following formula 2-2.

[0052] Functional group content (mol%)=100×(EW / EE) / {PW×AV / (56.1×1000)} Equation 2-2

[0053] In addition, "56.1" in the above formula 2-2 is the molecular weight of potassium hydroxide.

[0054] When the functional group content is within the above range, the crosslinking density of the polymer dispersant increases, and the amount of free polymer dispersant can be significantly reduced. On the other hand, in this case, the nonionic surfactant (B-2) cannot be stably present in the ink, resulting in uneven wetting and spreading of ink droplets, or an increase in the amount of hydrophilic groups in the polymer dispersant can worsen affinity with the nonionic surfactant (B-2), potentially resulting in reduced print density and color reproducibility. However, the inkjet ink of the present disclosure contains compound (B-1) as described above. Furthermore, the nonionic surfactant (B-2) stabilized by compound (B-1) can be quickly and uniformly oriented, thereby improving the circularity of dots in printed materials and further suppressing whiteout and color bleeding. Furthermore, it is possible to prevent a decrease in print density and color reproducibility, and also improve ejection stability.

[0055] <<Polymer (A-2)>> The uncrosslinked polymer (A-2) used in this embodiment has a carboxy group and / or a carboxylate group (COO － ) In addition, any polymer can be used as the polymer (A-2) as long as it has a carboxy group and / or a carboxylate group. For example, the polymer (A-2) may be a resin (dispersion resin) that has the function of dispersing a pigment.

[0056] Examples of the types of polymer that can be used as the polymer (A-2) include acrylic, maleic acid, urethane, polyester, etc. Furthermore, from the viewpoint of strengthening adsorption to the pigment and stabilizing the pigment dispersion even after the crosslinking reaction, it is preferable to use a polymer having an aromatic ring in its structure as the polymer (A-2).

[0057] In the present disclosure, the term "acrylic polymer" refers to a polymer using one or more polymerizable monomers selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters. In addition to the polymerizable monomers listed above, a styrene-based monomer may also be used as a polymerizable monomer constituting the acrylic polymer. However, polymers containing maleic acid (anhydride) (at least one selected from "maleic acid" and "maleic anhydride") as a polymerizable monomer are excluded from the definition of "acrylic polymer" in the present disclosure. Furthermore, the term "maleic acid-based polymer" refers to a polymer using at least maleic acid (anhydride) as a polymerizable monomer. Furthermore, maleic acid-based polymers may also use, as polymerizable monomers, α-olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene-based monomers, and the like.

[0058] The polymer (A-2) preferably contains at least a carboxylate group. This is because the charge repulsion caused by the charge of the carboxylate group allows for stable dispersion of the pigment-containing crosslinked polymer particles. The carboxylate group may be formed by neutralizing at least a portion of the carboxy groups already present in the polymer with a basic compound (neutralization treatment). Examples of the basic compound include ammonia; alkanolamines such as dimethylaminoethanol, diethanolamine, and triethanolamine; and alkali metal compounds such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, disodium carbonate, sodium bicarbonate, dipotassium carbonate, and sodium borate. Among these, alkali metal compounds are preferred, and hydroxides such as sodium hydroxide and potassium hydroxide are particularly preferred, from the viewpoint of improving the dispersion stability of the pigment-containing crosslinked polymer particles and suppressing pigment aggregation even during the ink drying process, thereby enabling the production of printed materials with excellent print density and color reproducibility. The basic compounds listed above may be used alone or in combination of two or more.

[0059] As the polymer (A-2), for example, a polymer having only carboxy groups (hereinafter referred to as polymer (A-2A)) may be used as is, or a polymer obtained by neutralizing at least a portion of the carboxy groups in the polymer (A-2A) (neutralization treatment) may be used. In the latter case, when the amount of the basic compound used to neutralize the carboxy groups in the polymer (A-2A) is expressed as a neutralization rate (described below), from the viewpoint of improving the dispersion stability of the pigment, the neutralization rate is preferably 10 to 200 mol%, more preferably 40 to 160 mol%, and particularly preferably 60 to 120 mol%. The neutralization rate can be calculated using the following formula 3:

[0060]

[0061] The "acid value of the polymer" also present in Equation 3 above can be measured by a standard method. For example, approximately 1 g of sample is precisely weighed into an Erlenmeyer flask, and 50 ml of a distilled water / dioxane mixture (mixture mass ratio: distilled water / dioxane = 1 / 9) is added and dissolved. Next, the sample solution is titrated with a 0.1 mol / L potassium hydroxide-ethanol solution (potency F) using a potentiometric measuring device ("Automatic Potentiometric Titrator AT-710M" manufactured by Kyoto Electronics Manufacturing Co., Ltd.), and the amount (α (mL)) of potassium hydroxide-ethanol solution required to reach the titration endpoint is measured. The acid value (mg KOH / g) of the polymer can then be calculated using Equation 4 below.

[0062] Acid value (mgKOH / g) = {(5.611×α×F) / S} Formula 4

[0063] In the above formula 4, S is the amount (g) of the sample polymer collected, α is the amount (ml) of the 0.1 mol / L potassium hydroxide ethanol solution used until the titration ends, and F is the titer of the 0.1 mol / L potassium hydroxide ethanol solution.

[0064] The acid value of the polymer (A-2), which can be measured by the above-mentioned method, is preferably 60 to 180 mgKOH / g, more preferably 70 to 160 mgKOH / g, and particularly preferably 80 to 150 mgKOH / g, from the viewpoints of improving the dispersion stability of the pigment, improving the drying properties of the aqueous inkjet ink, and suppressing detachment of the polymer from the pigment even during drying after printing, thereby obtaining printed matter with excellent print density and color reproducibility.

[0065] The weight-average molecular weight (Mw) of the polymer (A-2) is preferably 5,000 to 100,000. By setting the weight-average molecular weight to 5,000 or more, dispersion stability can be made favorable, and by setting it to 100,000 or less, ejection stability can be made favorable. The weight-average molecular weight is more preferably 10,000 to 50,000, and even more preferably 15,000 to 35,000.

[0066] The weight-average molecular weight of the polymer can be measured by a conventional method, for example, a value measured as a weight-average molecular weight in terms of polystyrene using a TSKgel column (manufactured by Tosoh Corporation) with a GPC ("HLC-8120GPC" manufactured by Tosoh Corporation) equipped with an RI detector and THF as a developing solvent can be used.

[0067] The ratio of the pigment content to the polymer (A-2) content (pigment / polymer (A-2)) is preferably 1 / 1 to 100 / 1 by mass. By making the ratio 1 / 1 or more, the viscosity of the ink can be kept within a range suitable for inkjet inks, and by making the ratio 100 / 1 or less, the dispersibility, as well as the dispersion stability and ejection stability after dispersion can be improved. The ratio of the pigment content to the polymer (A-2) is more preferably 2 / 1 to 50 / 1.

[0068] <Production of Aqueous Dispersion of Pigment-Containing Crosslinked Polymer Particles (A)> Examples of methods for producing an aqueous dispersion of pigment-containing crosslinked polymer particles (A) include a method in which the following neutralization step, dispersion step, and crosslinking step are carried out in this order. First, a polymer (A-2A) having only carboxy groups and a basic compound are mixed in an aqueous medium (a medium consisting of a liquid containing at least water) to neutralize at least a portion of the carboxy groups (neutralization step). The polymer obtained after the neutralization step is used as polymer (A-2) in subsequent steps. The polymer (polymer (A-2)) obtained after the neutralization step is in the form of an aqueous solution (a solution containing an aqueous medium and components dispersed and / or dissolved in the aqueous medium). Next, a pigment is added to the aqueous solution of polymer (A-2), and the two are mixed, followed by further dispersion treatment (dispersion step). This dispersion step produces an aqueous dispersion of pigment particles (crosslinked polymer particle precursors) having polymer (A-2) chemically adsorbed to at least a portion of their surfaces. Thereafter, the compound (A-1) is added to the aqueous dispersion of the crosslinked polymer particle precursor to carry out a crosslinking treatment (crosslinking treatment step).By this crosslinking treatment step, an aqueous dispersion of crosslinked polymer particles (A) containing a pigment can be produced.

[0069] <<Dispersion Treatment>> In dispersing the pigment, it is preferable to pre-disperse (premix) the pigment and polymer (A-2) using a commonly used mixing and stirring device such as a disperser, and then disperse (main dispersion) using a conventionally known disperser. 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 main dispersion of the pigment, and examples thereof include a ball mill, a roll mill, a kneader, a sand mill, a bead mill, and a high-pressure homogenizer. Among these, a bead mill is preferably used from the viewpoint of being able to disintegrate and refine coarse pigment particles. Furthermore, examples of bead mills include a super mill, a sand grinder, an agitator mill, a grain mill, a dyno mill, a pearl mill, and a cobol mill (all of which are trade names), and any of these can be suitably used.

[0070] <<Crosslinking Treatment>> In the crosslinking treatment, the polymer (A-2) adsorbed to the pigment is crosslinked by the compound (A-1) in an aqueous dispersion of the crosslinked polymer particle precursor, resulting in the formation of a crosslinked polymer, and an aqueous dispersion of crosslinked polymer particles (A) containing the pigment can be obtained.

[0071] The temperature for the crosslinking treatment is preferably 50 to 95° C., more preferably 70 to 85° C., from the viewpoint of efficiently proceeding with the crosslinking reaction. The time for the crosslinking treatment is preferably 0.5 to 10 hours, more preferably 1 to 8 hours, and even more preferably 2 to 5 hours, from the same viewpoint as above.

[0072] 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 the ink to be stably ejected from the nozzle.

[0073] The "average particle size" refers to the median diameter on a volume basis, and can be measured by dynamic light scattering. For example, it can be measured using a "Nanotrac UPA-EX150" manufactured by Microtrac Bell Inc. in an environment of 25°C.

[0074] The pH of the aqueous dispersion of the pigment-containing crosslinked polymer particles (A) is preferably 8 to 12. If the pH is 8 or higher, the carboxy groups in the crosslinked polymer are likely to become carboxylate groups, and favorable charge repulsion can enhance the dispersion stability of the crosslinked polymer particles (A). A more preferred pH value is 9 to 11.

[0075] The pH of the aqueous dispersion can be measured by a conventional method, for example, using a tabletop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "6337-10D" (manufactured by Horiba, Ltd.) in an environment of 25°C.

[0076] <Surfactant (B)> The ink of this embodiment contains, as surfactant (B), a compound (B-1) represented by general formula 1 above and a nonionic surfactant (B-2) having an HLB value of 1 to 10.

[0077] <<Compound (B-1)>> As described above, the compound (B-1) has affinity with the crosslinked polymer and the nonionic surfactant (B-2), and therefore, it is possible to obtain printed matter that is excellent in dot circularity, print density, and color reproducibility while suppressing whiteout and color mixing bleeding. In particular, from the viewpoint of obtaining printed matter that has excellent print density and color reproducibility, n in General Formula 1 is an integer of 20 to 100, more preferably 25 to 65, and particularly preferably 25 to 50. Because the compound (B-1) contains a hydrophobic moiety and a hydrophilic moiety, it can exhibit favorable compatibility in the ink with the highly hydrophobic surfactant (B-2).

[0078] Furthermore, from the viewpoint of improving the affinity with the surfactant (B-2) described below and obtaining printed matter with excellent dot roundness, R １ The group represented by the formula (I) is a linear or branched alkyl group having 10 to 25 carbon atoms, and more preferably a linear or branched alkyl group having 12 to 22 carbon atoms.

[0079] Furthermore, the surfactant (B-2) can be suitably stabilized in the aqueous inkjet ink, and white spots and color bleeding in printed matter can be easily suppressed, printed matter having excellent print density and color reproducibility can be obtained, and the ejection stability of the aqueous inkjet ink can also be improved. Therefore, in the general formula 1, R １ where CE is the number of carbon atoms in the alkyl group represented by the formula (1), the value of n in the general formula 1 is preferably an integer between CE×1.30 and CE×4.60 (however, when CE×1.30 and CE×4.60 are integers, these integers are also included), and particularly preferably an integer between CE×1.60 and CE×3.50 (however, when CE×1.60 and CE×3.50 are integers, these integers are also included).

[0080] The HLB value of compound (B-1) is preferably 14.0 to 19.4, more preferably 15.8 to 19.0, and particularly preferably 16.6 to 18.2. When the HLB value of compound (B-1) is within the above range, it is easy to suppress white voids and color bleeding in printed matter, improve print density and color reproducibility, and further improve the ejection stability of the aqueous inkjet ink. The method for calculating the HLB value of compound (B-1) is the same as that for the nonionic surfactant (B-2) described below.

[0081] The compound (B-1) may be obtained by synthesis by a conventionally known method, or a commercially available product may be used. Examples of commercially available products of the compound (B-1) include the Emulgen series manufactured by Kao Corporation, the Nonion series manufactured by NOF Corporation, the EMALEX series manufactured by Nippon Emulsion Co., Ltd., the NIKKOL series manufactured by Nikko Chemicals Co., Ltd., the Emulmin series and Sannonik series manufactured by Sanyo Chemical Industries, Ltd., and the Brownon series and Finesurf series manufactured by Aoki Oil & Fat Industries Co., Ltd., but are not limited thereto.

[0082] The content of compound (B-1) is preferably 0.01 to 2% by mass, and more preferably 0.1 to 1% by mass, of the total amount of the aqueous inkjet ink. By setting the content to 0.01% by mass or more, the effects of compound (B-1) described above can be exerted, and by setting the content to 2% by mass or less, the drying properties of the ink on a poorly absorbent printing substrate can be made favorable.

[0083] <<Nonionic Surfactant (B-2)>> The surfactant (B-2) used in this embodiment has an HLB value of 1 to 10. The HLB (Hydrophile-Lipophile Balance) value is one of the parameters that represent the hydrophilicity / hydrophobicity of a material. Various methods are known for calculating the HLB value, such as the Griffin method, the Davis method, and the Kawakami method, but in the present disclosure, the HLB value is calculated using the Griffin method.

[0084] The Griffin method is generally used for non-ionic materials. In the Griffin method, the HLB value is calculated using the molecular weight of the material in question according to the following formula 5. The smaller the HLB value, the more hydrophobic the material, and the larger the HLB value, the more hydrophilic the material.

[0085] HLB value = 20 × (sum of molecular weights of hydrophilic portions) ÷ (molecular weight of material) Equation 5

[0086] The nonionic surfactant (B-2) used in this embodiment is not particularly limited as long as it is a surfactant with an HLB value of 1 to 10. For example, any of acetylene diol surfactants, acetylene monool surfactants, silicone surfactants, fluorine-based surfactants, sorbitan fatty acid ester surfactants, glycerin fatty acid ester surfactants, polyoxyalkylene alkyl ether surfactants (excluding compounds corresponding to general formula (1)), polyoxyalkylene alkylamine surfactants, etc. can be used. These surfactants may be used alone or in combination of two or more. On the other hand, from the viewpoint of obtaining printed matter with excellent dot roundness without white voids or color bleeding on a poorly absorbent printing substrate, it is preferable to use an acetylene diol surfactant and / or a silicone surfactant as surfactant (B-2) among the surfactants listed above, and it is more preferable to use an acetylene diol surfactant and a silicone surfactant in combination.

[0087] Acetylene diol surfactants are preferred because they have excellent orientation speed to interfaces, thereby improving the wettability and penetration of the ink and making it easier to obtain printed matter free of white spots and color bleeding. When an acetylene diol surfactant is used as the nonionic surfactant (B-2), the HLB value is preferably 1 to 8, and more preferably 1 to 4, from the viewpoint of being able to produce printed matter with excellent print quality even on poorly absorbent printing substrates. Specific examples of acetylene diol surfactants having an HLB value of 1 to 4 include, for example, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 4,7-dipropyl-dec-5-yne-4,7-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, 3,6-diisopropyl- Examples of the diol include 2,7-dimethyloct-4-yne-3,6-diol, octadec-9-yne-8,11-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, 5,8-dibutyldodec-6-yne-5,8-diol, 4,7-diisobutyl-2,9-dimethyl-dec-5-yne-4,7-diol, and 5,14-diethyl-8,11-dimethyloctadec-9-yne-8,11-diol. Among these, from the viewpoint of being able to impart sufficient wettability and permeability to the ink on a poorly absorbent printing substrate and obtaining printed matter with excellent print quality, it is preferable to use one or more compounds selected from the group consisting of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, and 2,4,7,9-tetramethyl-5-decyne-4,7-diol. The above compounds may be used alone or in combination of two or more. The above compounds may be synthesized by a conventionally known method, or may be commercially available products.

[0088] The blending amount of the acetylene diol surfactant is preferably 0.1 to 3 mass % of the total amount of the aqueous inkjet ink, more preferably 0.5 to 2 mass %, and even more preferably 0.8 to 1.5 mass %.

[0089] On the other hand, compared to acetylene diol surfactants, silicone surfactants have a slower orientation speed at the interface, but have a high ability to reduce surface tension and are uniformly oriented at the interface, so they are preferably used from the viewpoints of preventing color bleeding between dots and improving dot circularity. In this embodiment, the HLB value of the silicone surfactant is also calculated using the Griffin method.

[0090] The amount of the silicone surfactant having an HLB value of 1 to 10 is preferably 0.1 to 5% by mass, more preferably 0.5 to 3% by mass, and even more preferably 0.8 to 2.5% by mass of the total amount of the ink.

[0091] Furthermore, from the viewpoint of improving the compatibility with the crosslinked polymer and achieving uniform wetting and spreading on the printing substrate to obtain excellent print quality with good dot circularity and little color bleeding, it is preferable to use a gemini type silicone surfactant and / or a polyether-modified silicone surfactant (excluding gemini type silicone surfactants) as the silicone surfactant having an HLB value of 1 to 10. More preferably, it is a gemini type silicone surfactant and / or a silicone surfactant modified at both ends with polyether.

[0092] <<Gemini Silicon Surfactant>> Generally, a gemini surfactant has a structure in which surfactants having a hydrophilic structure and a hydrophobic structure are linked by a linking group (spacer) or a covalent bond. In addition, in the case of a gemini silicone surfactant, for example, a siloxane chain (-[SiR １ R ２ -O]n-, where R １ and R ２ are each any organic group, and n is an integer of 2 or more.), and the hydrophilic structure (for example, a polyether chain) has the following structure: A structure in which the bonding points between the siloxane chain and the hydrophilic structure are located in the middle of the siloxane chain and in the middle of the hydrophilic structure, respectively. A structure in which a plurality of siloxane chains are bonded via a linking group or the like (for example, R in the structural formula of the siloxane chain) １ and / or R ２a structure in which at least a part of the above is an organic chain containing a siloxane chain; a structure in which a plurality of silicone surfactants, each having a plurality of hydrophilic structures, share a part of the hydrophilic structures;

[0093] Gemini surfactants have superior surface tension reducing ability compared to general surfactants. Therefore, by using a gemini silicone surfactant, it is possible to achieve a surface tension reduction that is superior to that of general silicone surfactants. As a result, the wettability of aqueous inkjet inks containing gemini silicone surfactants can be significantly improved, and in addition to improving the above-mentioned color bleeding between dots and dot roundness, it is possible to obtain printed materials that are free of white areas and have excellent print density and color reproducibility.

[0094] Examples of commercially available gemini type silicone surfactants include TEGO Twin 4000, TEGO Twin 4100, and TEGO Twin 4200 manufactured by Evonik Degussa, and KF-6100, KF-6104, KF-6105, KF-6106, and KF-6115 manufactured by Shin-Etsu Chemical Co., Ltd.

[0095] <<Polyether-modified silicone surfactants (excluding gemini silicone surfactants)>> Examples of the polyether-modified silicone surfactants (excluding gemini silicone surfactants) that can be used in the aqueous inkjet ink of this embodiment include compounds having a structure represented by the following general formula 6.

[0096] General formula 6

[0097] In general formula 6, p is an integer of 0 to 99, and q is an integer of 1 to 100. However, p+q is an integer of 1 to 100. ３ is a methyl group or a structure represented by the following general formula 7, and R ４ is an alkyl group having 1 to 6 carbon atoms, or a structure represented by the following general formula 7. ３ When R is a methyl group, p is 0. ３ and R ４At least one of the groups has a structure represented by the following general formula 7 (R ３ and R ４ However, both may have a structure represented by the following general formula 7:

[0098] General formula 7

[0099] In General Formula 7, r is an integer of 1 to 6, s is an integer of 1 to 50, and t is an integer of 0 to 50. However, s+t is an integer of 1 to 100. ５ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an acrylic group, or a methacrylic group. The addition of the ethylene oxide groups and propylene oxide groups in the brackets [ ] may be in a block or random manner.

[0100] The polyether-modified silicone surfactant represented by the general formula 6 is preferably used from the viewpoint of preventing color bleeding between dots and improving white spots. ４ is a structure represented by general formula 7, and R ３ Polyether-modified silicone surfactants (also referred to as "double-end polyether-modified silicone surfactants" in the present disclosure) having a structure other than that represented by general formula 7 are particularly preferably used in the present invention because they tend to be uniformly oriented at the interface, and in addition to improving color bleeding and white voids, they also significantly improve dot circularity.

[0101] Examples of commercially available products of the above-mentioned silicone surfactants modified at both ends with polyether include BY16-201 and SF8427 manufactured by Dow Corning Toray Co., Ltd.; BYK-331, BYK-333, BYK-UV3500, and BYK-3420 manufactured by BYK-Chemie; TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, and TEGO Glide 450 manufactured by Evonik Degussa; and Silface SWP-001, Silface SAG003, and Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd.

[0102] In addition, R in the above general formula 6 ３ is a structure represented by general formula 7, and R ４Examples of commercially available polyether-modified silicone surfactants (also referred to as "side-chain polyether-modified silicone surfactants" in the present disclosure) that do not have a structure represented by general formula 7 include SF8428, FZ-2162, 8032 ADDITIVE, SH3749, FZ-77, L-7001, L-7002, FZ-2104, FZ-2110, F-2123, SH8400, and SH3773M manufactured by Dow Corning Toray Co., Ltd.; BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 manufactured by BYK-Chemie; and TEGO Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, and TEGO Wet 280 manufactured by Evonik Degussa. Wet 280, and KF-351A, KF-352A, KF-353, KF-354L, KF355A, KF-615A, KF-640, KF-642, and KF-643 manufactured by Shin-Etsu Chemical Co., Ltd.

[0103] The total content of the gemini silicone surfactants and polyether-modified silicone surfactants (excluding gemini silicone surfactants) is preferably 0.4 to 3 mass %, and more preferably 0.5 to 2 mass %, of the total amount of the aqueous inkjet ink.

[0104] The ratio of the content of the compound (B-1) represented by general formula 1 used in this embodiment to the content of the nonionic surfactant (B-2) having an HLB value of 1 to 10 (compound (B-1):surfactant (B-2)) is 1:1.2 to 1:20 by mass. The above ratio is more preferably 1:2 to 1:15, and even more preferably 1:3 to 1:10. By blending them in the above-mentioned suitable ratio, the nonionic surfactant (B-2) can be emulsified by the compound (B-1). As a result, the nonionic surfactant (B-2) can be uniformly oriented at the ink interface, allowing the ink to wet and spread uniformly even on a poorly absorbent printing substrate, and improving penetration. Furthermore, it is possible to obtain printed matter with excellent dot circularity while suppressing whiteout and color bleeding. In addition, by using the compound (B-1) and the surfactant (B-2) in the above-mentioned blending ratio in combination, the surfactant (B-2) and the crosslinked polymer can maintain a compatible state even during the drying process of the ink after printing, and separation of the respective materials is suppressed, resulting in a printed product having excellent print density and color reproducibility even after drying. Furthermore, by achieving the above-mentioned suitable ratio, it is possible to suppress non-uniform orientation of the surfactant (B-2) at the nozzle end face of the inkjet head, making it possible to obtain stable ejection properties.

[0105] <Organic Solvent> The ink of this embodiment may contain an organic solvent. From the viewpoints of adjusting the wettability and permeability of the ink on the printing substrate, controlling the print image quality and drying property through such adjustments, and ensuring and improving the ejection stability from the inkjet nozzle, the compounds described below are suitably selected as the organic solvent.

[0106] In the present disclosure, the term "organic solvent" refers to an organic compound that is liquid at 45°C.

[0107] From the viewpoint of ensuring wettability and permeability even for poorly absorbent printing substrates and obtaining printed matter with excellent print quality, it is preferable to select, among organic solvents, a compound that is liquid at 25°C and has a surface tension at 25°C of 20 to 30 mN / m.

[0108] In the present disclosure, the term "surface tension at 25°C" refers to the surface tension measured by the Wilhelmy method (plate method, vertical plate method) in an environment of 25°C. Specifically, for example, the surface tension can be measured using a surface tensiometer ("CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd.) with a platinum plate in an environment of 25°C.

[0109] Furthermore, from the viewpoints of having suitable compatibility with the above-mentioned surfactants, being able to impart excellent wettability and penetration to the ink even on a poorly absorbent printing substrate, and being able to obtain printed matter that is free of white voids and color bleeding, it is preferable that the organic solvent contains an alkanediol solvent having 5 to 8 carbon atoms and / or a (poly)alkylene glycol monoalkyl ether solvent having 5 to 9 carbon atoms.

[0110] In the present disclosure, the term "(poly)alkylene glycol monoalkyl ether solvent" refers to at least one solvent selected from the group consisting of alkylene glycol monoalkyl ether solvents and polyalkylene glycol monoalkyl ether solvents.

[0111] Examples of alkanediol solvents having 5 to 8 carbon atoms include, but are not limited to, 1,5-pentanediol, 1,2-pentanediol, 3-methyl-1,5-pentanediol, 3-methyl-1,3-butanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, and 2-ethylhexane-1,3-diol.

[0112] Examples of (poly)alkylene glycol monoalkyl ether solvents having 5 to 9 carbon atoms include, but are not limited to, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, etc. Among these, (poly)propylene glycol monoalkyl ether solvents are preferably used as the (poly)alkylene glycol monoalkyl ether solvents having 5 to 9 carbon atoms, from the viewpoints that they produce aqueous inkjet inks that have excellent drying properties even on poorly absorbent printing substrates and that printed matter with excellent print quality can be obtained.

[0113] The above-mentioned "(poly)propylene glycol monoalkyl ether" refers to "propylene glycol monoalkyl ether" and / or "polypropylene glycol monoalkyl ether".

[0114] In the inkjet ink of this embodiment, organic solvents other than the compounds exemplified above can also be suitably used, such as ethanol, isopropanol, 2-butanol, tert-butanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, ethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, and γ-butyrolactone.

[0115] In the inkjet ink of this embodiment, high-boiling organic solvents can be used as long as the print image quality and drying properties are not impaired. From the viewpoint of obtaining an aqueous inkjet ink that has sufficient drying properties even on a poorly absorbent printing substrate and that can produce printed matter with reduced color bleeding, the content of high-boiling organic solvents with a boiling point of 230°C or higher (and, for example, 400°C or lower) at 1 atmosphere is preferably 15% by mass or less (or may be 0% by mass) of the total amount of the aqueous inkjet ink, and more preferably 10% by mass or less (or may be 0% by mass). In this disclosure, "0% by mass" means that the target organic solvent is not included.

[0116] Furthermore, from the viewpoint of obtaining printed matter that is free from color bleeding, has excellent print density and color reproducibility, and also has good coating film resistance, the content of ultra-high boiling point organic solvents, which have a boiling point of 270°C or higher (and, for example, 400°C or lower) at 1 atmospheric pressure, is preferably 5% by mass or less (or may be 0% by mass) of the total amount of the aqueous inkjet ink, more preferably 2.5% by mass or less (or may be 0% by mass), and particularly preferably 1% by mass or less (or may be 0% by mass).

[0117] Specific examples of the high-boiling organic solvent having a boiling point of 230° C. or higher at 1 atmosphere include glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, 2-pyrrolidone, N-methyloxazolidinone, ε-caprolactone, etc. Among the above-listed organic solvents, examples of ultra-high-boiling organic solvents having a boiling point of 270° C. or higher at 1 atmosphere include glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, triethylene glycol, tetraethylene glycol, tetraethylene glycol dimethyl ether, etc.

[0118] In this embodiment, the boiling point at 1 atmosphere can be measured using, for example, a thermal analyzer.

[0119] The organic solvent used in the ink of this embodiment preferably has a boiling point (weighted average) at 1 atmosphere of 100 to 230°C, more preferably 120 to 220°C, and particularly preferably 150 to 210°C. A boiling point (weighted average) of 100°C or higher can suppress drying of the ink on the inkjet head, improving ejection stability. Furthermore, a boiling point (weighted average) of 230°C or lower prevents poor drying even on poorly absorbent printing substrates, and prevents color bleeding due to residual organic solvent. As a result, printed matter with excellent drying properties and print quality can be obtained. Furthermore, a boiling point (weighted average) of 230°C or lower improves abrasion resistance even on printed matter printed on poorly absorbent printing substrates such as coated paper. Additionally, residual organic solvent does not impair the compatibility between the surfactant and the crosslinked polymer, improving the print density and color reproducibility of the printed matter.

[0120] In the present disclosure, the term "boiling point (weighted average value) of an organic solvent" refers to the boiling point of the organic solvent when only one type of organic solvent is contained in the composition, and refers to the weighted average value of the boiling points of the two or more organic solvents when two or more types of organic solvents are contained. The weighted average value of the boiling points at 1 atmosphere is a value obtained by adding together the product of the boiling points at 1 atmosphere calculated for each organic solvent and the mass proportion of the organic solvent relative to the total content.

[0121] The total content of organic solvents in the aqueous inkjet ink of this embodiment is preferably 5 to 40% by mass, based on the total amount of the aqueous inkjet ink. In particular, from the viewpoints of ensuring sufficient wettability and permeability even on a poorly absorbent printing substrate, obtaining printed matter with excellent print quality, and improving the drying properties of the aqueous inkjet ink, the total content of organic solvents in the aqueous inkjet ink of this embodiment is more preferably 10 to 35% by mass, and particularly preferably 15 to 30% by mass, based on the total amount of the aqueous inkjet ink.

[0122] <Binder Resin> In the aqueous inkjet ink of this embodiment, it is preferable to use a binder resin in order to improve the scratch resistance of the printed matter and the ejection stability of the aqueous inkjet ink.

[0123] The term "binder resin" as used herein refers to a resin used to bond an ink film to a printing substrate, and the resin forms a film during the drying process and / or the resin molecules become entangled, thereby improving the abrasion resistance and drying properties of the ink film. From this perspective, for example, the resin primarily contained in the ink (specifically, a resin that accounts for 50% by mass or more of the total amount of resin contained in the ink, more preferably a resin that accounts for 60% by mass or more, and particularly preferably a resin that accounts for 70% by mass or more) functions as the binder resin. Note that the crosslinked polymer constituting the pigment-containing crosslinked polymer particles (A) described above may also serve as the binder resin.

[0124] Generally, water-soluble resins and resin particles are known as binder resin forms, and in the present disclosure, either one may be used alone or both may be used in combination. Here, the "resin particles" mentioned above refer to a form of water-insoluble resin (a resin that is not a water-soluble resin) and refer to particles having an average particle size of 5 to 1000 nm measured in the same manner as in the case of the pigment-containing crosslinked polymer particles (A) described above.

[0125] When the aqueous inkjet ink of this embodiment contains a binder resin, it is preferable to use a water-soluble resin, from the viewpoints that the compatibility with the surfactant described above can be improved, resulting in printed matter with excellent print density and color reproducibility, and further that the speed at which the ink film is formed during the ink drying process can be improved, resulting in printed matter with excellent drying properties and print quality.

[0126] The acid value of the binder resin is preferably 1 to 50 mgKOH / g, and more preferably 2.5 to 40 mgKOH / g. By using a binder resin with this acid value, it is possible to improve the ink film formation rate even on a poorly absorbent printing substrate, and to obtain printed matter with excellent print quality and drying properties. Controlling the acid value is also effective in improving the ejection stability of the aqueous inkjet ink.

[0127] The acid value of the binder resin can be measured by the same method as that for the acid value of the polymer (A-2) described above.

[0128] Furthermore, from the viewpoint of improving the abrasion resistance and ejection stability of the printed matter, the glass transition temperature of the binder resin is preferably 60 to 140°C, more preferably 70 to 135°C, and particularly preferably 80 to 130°C.

[0129] The glass transition temperature 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 sample obtained by drying the resin is weighed on an aluminum pan, and the aluminum pan is set as a test container in a holder in a DSC measurement device (for example, a "DSC-60Plus" manufactured by Shimadzu Corporation). Measurement is then performed under conditions of a temperature rise of 5°C / min, and the temperature at the intersection of the low-temperature baseline and the tangent line at the inflection point, read from the obtained DSC chart, is taken as the glass transition temperature in the present disclosure.

[0130] <<Resin Particles>> When resin particles are used as the binder resin, types of resins that can be used for the resin particles include acrylic, epoxy, urethane, styrene butadiene, polyether, polyamide, polyester, vinyl chloride, and copolymers thereof (excluding those containing siloxane chains). Among these, from the viewpoint of being able to improve both the scratch resistance and ejection stability of printed matter, resin particles using at least one selected from the group consisting of acrylic, urethane, styrene butadiene, and vinyl chloride are preferred, resin particles using at least one selected from the group consisting of acrylic and urethane are more preferred, and from the viewpoint of improving ejection stability, it is particularly preferred to use acrylic resin particles.

[0131] The resin particles can be synthesized by a conventional method or can be commercially available. There are no particular limitations on the structure of the resin particles, and resins having, for example, a random structure, a block structure, a comb structure, a star structure, etc. can be used.

[0132] In this embodiment, the content of the resin particles relative to the total amount of the ink is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, and even more preferably 3 to 7% by mass, calculated as solid content. By setting the amount of resin particles within this range, it is possible to obtain an aqueous inkjet ink that exhibits excellent abrasion resistance and drying properties for printed matter without reducing storage stability or ejection stability.

[0133] <<Water-Soluble Resin>> On the other hand, when resin particles are used as the binder resin, types of resins that can be used as the water-soluble resin include acrylic, urethane, styrene-butadiene, vinyl chloride, maleic acid, polyester, etc. (However, those containing siloxane chains are excluded.) Among these, from the viewpoint of obtaining a printed matter with excellent abrasion resistance and print image quality, and further obtaining an ink 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.

[0134] The water-soluble resin can be synthesized by a conventionally known method, or a commercially available product can be used. There are no particular limitations on the structure, and resins having, for example, a random structure, a block structure, a comb structure, a star structure, etc. can be used. Among these, resins having a block structure or a comb structure are preferred from the viewpoint of fully utilizing the properties of the polymerizable monomers constituting the binder resin. Each unit constituting the block structure or the comb structure may be formed from a single polymerizable monomer or may be a random copolymer of multiple types of polymerizable monomers.

[0135] The weight-average molecular weight of the water-soluble resin used as the binder resin is preferably 5,000 to 50,000, from the viewpoint of ensuring ejection stability from an inkjet nozzle and obtaining printed matter having excellent abrasion resistance on a variety of printing substrates; and from the viewpoint of improving the compatibility with the surfactant described above and obtaining printed matter having excellent print density and color reproducibility, the weight-average molecular weight is more preferably 8,000 to 45,000, and particularly preferably 10,000 to 40,000.

[0136] The weight average molecular weight of the water-soluble resin can be measured in the same manner as in the weight average molecular weight of the polymer (A-2) described above.

[0137] The content of the water-soluble resin relative to the total amount of ink is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, and even more preferably 1 to 5% by mass, calculated as solid content. By setting the amount of the water-soluble resin within the above range, it is possible to obtain an aqueous inkjet ink that exhibits excellent abrasion resistance and drying properties of printed matter without reducing dispersion stability or ejection stability.

[0138] <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.

[0139] The content of water in the ink of this embodiment is preferably in the range of 20 to 90% by mass of the total mass of the ink.

[0140] <Other Components> In addition to the components described above, the ink of this embodiment may contain additives such as infrared absorbers, ultraviolet absorbers, preservatives, etc., as needed to provide the ink with desired physical properties. The total amount of these additives blended is preferably 0.01 to 10% by mass relative to the total mass of the ink.

[0141] <Ink Set> The inks of this embodiment may be used in a single color, or may be used as an ink set combining multiple colors depending on the application. The combination is not particularly limited, but a full-color image can be obtained by using three colors: cyan, yellow, and magenta. The addition of black ink can also improve the sense of black, thereby increasing the visibility of characters, etc. The addition of colors such as orange and green can also improve color reproducibility. When printing on a printing substrate other than white, a clear image can be obtained by using white ink in combination.

[0142] <Ink Preparation Method> One example of a method for preparing the ink of this embodiment containing the components described above is the method described below, but the method for preparing the ink of this embodiment is not limited to this.

[0143] First, a pigment dispersion is obtained by the method described above, and then, if necessary, a binder resin, an organic solvent, a surfactant, and other components such as those listed above are appropriately added to the pigment dispersion, followed by stirring and, if necessary, filtration to obtain the ink of the present disclosure.

[0144] Since the ink of this embodiment is for inkjet recording, it is preferable to use a pigment having an optimal particle size distribution from the viewpoint of preventing nozzle clogging, etc. Methods for obtaining a pigment having a desired particle size distribution include the above-mentioned methods of reducing the size of the grinding media in the disperser, increasing the packing rate of the grinding media, extending the processing time, classifying the ink after grinding using a filter or centrifuge, etc., and combinations of these methods. The average particle size of the ink can be measured by the same method as for the average particle size of the crosslinked polymer particles (A) containing the pigment.

[0145] <Printing substrate> The ink of this embodiment can be particularly suitably used on a poorly absorbent printing substrate. A poorly absorbent printing substrate is a printing substrate that does not absorb water or absorbs water slowly, specifically a printing substrate that has a water absorption coefficient of 0 to 0.6 ml / m as measured by the Bristow method (J. TAPPI Paper Pulp Test Method No. 51-87). ２ msec １／２ The absorption coefficient can be measured, for example, by using an automatic scanning absorptivity meter manufactured by Kumagai Riki Kogyo Co., Ltd. Specifically, the amount of water absorbed (ml / m) obtained during a contact time of 100 to 1000 milliseconds using the above-mentioned device and water is ２ ) and the square root of the contact time (msec １／２ ) the gradient of the line obtained by the least squares method is the absorption coefficient.

[0146] Specific examples of poorly absorbent printing substrates include, but are not limited to, paper substrates such as coated paper, art paper, cast paper, lightly coated paper, and synthetic paper; plastic substrates such as polycarbonate, hard PVC, soft PVC, polystyrene, expanded polystyrene, PMMA, polypropylene, polyethylene, and PET; metal substrates such as aluminum and stainless steel; and glass. The inkjet ink of this embodiment can also be suitably used on printing substrates that are not poorly absorbent, such as plain paper, fabric, and wood.

[0147] <Printing method> The inkjet ink of this embodiment is used in a printing method (inkjet printing method) in which ink is ejected from the nozzles of an inkjet head and droplets of the ink are deposited on a printing substrate. The ink deposited on the printing substrate is dried, preferably by a drying method described below, to form a printed matter (having at least an ink film layer on the printing substrate).

[0148] <<Drying Method>> A printing apparatus (inkjet printer) equipped with the inkjet ink of this embodiment and used in the inkjet printing method preferably includes a mechanism for drying the ink on a printing substrate. The drying method may be any one of the following: 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. Alternatively, a combination of two or more of these methods may be used. For example, by combining infrared drying (a method of irradiating with electromagnetic waves) and hot air drying (a method of directly contacting the ink with a heat source), the ink can be dried more quickly than by using either method alone. When using the hot air drying method, which is a method of directly contacting the ink with a heat source, it is preferable to set the hot air temperature to 50 to 250°C in order to prevent bumping of the liquid components contained in the ink and to obtain printed matter with excellent print density, color reproducibility, and print image quality. Furthermore, when a substrate heating method (a method in which the non-printing surface of a printing substrate is brought into contact with a heat source), which is a method in which the ink is indirectly brought into contact with a heat source, is employed, it is preferable to set the temperature of the heat source to 35 to 100°C, from the same viewpoint as in the case of the hot air temperature described above.

[0149] <Printed Material> According to some embodiments, it is possible to provide a printed material obtained by printing the aqueous inkjet ink of the present embodiment described above onto a printing substrate. This printed material comprises a printing substrate and an ink film formed by applying the aqueous inkjet ink of the present embodiment to the printing substrate. Because the ink film is formed by the crosslinked polymer particles (A) and the surfactant (B), this printed material can prevent color bleeding and white voids, have excellent dot circularity, and exhibit good print density and color reproducibility.

[0150] The present disclosure will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" represent "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0151] <Production of Dispersion Resin> The "dispersion resins" shown below all correspond to the uncrosslinked polymer (A-2) described above. These dispersion resins were obtained by synthesis using the method shown below.

[0152] <Production Example of Dispersion Resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of methyl ethyl ketone and purged with nitrogen gas. After heating the contents of the reaction vessel to 110 ° C., a mixture of 23 parts of polymerizable monomers, acrylic acid, 47 parts of methyl methacrylate, and 30 parts of lauryl methacrylate; and 6 parts of a polymerization initiator, V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was added dropwise into the reaction vessel over 2 hours. After completion of the dropwise addition, the temperature of the contents of the reaction vessel was maintained at 110 ° C., and the polymerization reaction was continued for 3 hours. Then, 0.6 parts of V-601 was added, and the reaction was continued for another 1 hour at 110 ° C. to obtain a dispersion resin 1 precursor having only carboxy groups as hydrophilic groups. The weight average molecular weight of the obtained dispersion resin 1 precursor was 18,000, and the acid value was 179 mg KOH / g. The amount of potassium hydroxide required to achieve a neutralization rate of 100% was calculated using the acid value of the dispersion resin 1 precursor and Equation 3 above, and a 48% by mass aqueous potassium hydroxide solution containing an amount of potassium hydroxide equivalent to the calculated amount was added to convert the carboxy groups present in the dispersion resin 1 precursor to carboxylate groups (neutralization treatment). Ion-exchange water was then added to the solution to achieve a solids concentration of 20%, and the solution was heated to 50°C and stirred for 1 hour while maintaining the temperature at 50°C, yielding an aqueous solution of dispersion resin 1.

[0153] <Production Example of Pigment Dispersion Resins 2 to 8> Aqueous solutions of dispersion resins 2 to 8 (solids concentration 20% each) were obtained using the same raw materials and procedures as in the case of dispersion resin 1, except that the polymerizable monomers shown in Table 1 were used as the polymerizable monomers.

[0154]

[0155] Table 1 also lists the raw materials used in the above-mentioned Dispersion Resin 1, as well as the weight average molecular weights and acid values ​​of Dispersion Resins 1 to 8. The abbreviations listed in Table 1 are as follows: St: styrene AA: acrylic acid MMA: methyl methacrylate LMA: lauryl methacrylate

[0156] <Production Example of Dispersion Resin 9> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 26 parts of 1-octadecene, 18 parts of maleic anhydride, and 56 parts of N-phenylmaleimide, which are polymerizable monomers; and 100 parts of methyl ethyl ketone, which is a solvent. After purging with nitrogen gas, the contents in the reaction vessel were heated to 130°C while stirring. Next, while maintaining the temperature and stirring of the contents, 1.0 part of t-butylperoxy-2-ethylhexanoate, which is a radical polymerization initiator, was added dropwise over 2 hours. Thereafter, stirring was continued for another 1 hour while maintaining the temperature of the contents at 130°C, to carry out a polymerization reaction. Furthermore, after the start of the polymerization reaction, the solids concentration of the contents was measured at regular intervals, and the ratio of the solids concentration to the concentration assumed when all of the charged 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 (5 equivalents relative to the amount of maleic anhydride charged) and 0.01 parts of diazabicycloundecene catalyst were added. The contents of the reaction vessel were then heated to 80°C while stirring, and after reaching 80°C, the temperature was maintained at that temperature for 4 hours to open the maleic anhydride ring, thereby obtaining a dispersion resin 9 precursor having only carboxy groups as hydrophilic groups. The resulting dispersion resin 9 precursor had a weight average molecular weight of 20,000 and an acid value of 206 mgKOH / g. The acid value of the dispersion resin 9 precursor and Equation 3 above were then used to calculate the amount of potassium hydroxide required to achieve a neutralization rate of 100%, and a 48% by weight aqueous potassium hydroxide solution containing an equal amount of potassium hydroxide was added to convert the carboxy groups present in the dispersion resin 9 precursor to carboxylate groups (neutralization treatment). Then, ion-exchanged water was added so that the solid concentration became 20%, and the solution was then heated to 50°C and stirred for 1 hour while maintaining the temperature at 50°C, thereby obtaining an aqueous solution of dispersion resin 9.

[0157] <Production Example of Dispersion Resins 10 to 25> Synthesis was carried out using the same raw materials and procedures as in the case of Dispersion Resin 9, except that the type and amount of polymerizable monomer used were changed as shown in Table 2, to obtain aqueous solutions of Dispersion Resins 10 to 25 (each with a solids concentration of 20%).

[0158]

[0159] Table 2 also lists the raw materials used in the above-mentioned dispersion resin 9, as well as the weight average molecular weights and acid values ​​of dispersion resins 9 to 25. Among the abbreviations listed in Table 2, those not used in Table 1 are as follows: OctD: 1-octadecene Manh: maleic anhydride PMI: N-phenylmaleimide CMI: cyclohexylmaleimide MI: maleimide

[0160] <Production Example of an Aqueous Dispersion of Cyan Pigment-Containing Crosslinked Polymer Particle Precursor 1 (CB1)> 20 parts of LIONOL BLUE FG-7351 (C.I. Pigment Blue 15:3 manufactured by Toyocolor Co., Ltd.) as a pigment, 25 parts of an aqueous solution of dispersion resin 1 (solids concentration 20%), and 55 parts of ion-exchanged water were charged into a mixing vessel. All raw materials were charged and pre-dispersed using a stirrer. After pre-dispersion, a 0.6 L Dyno-Mill filled with 1,800 g of zirconia beads having a diameter of 0.5 mm was used to carry out the main dispersion. After the main dispersion, 33.3 parts of ion-exchanged water was added to the resulting mixture, and the mixture was heated at 60 ° C. while a portion of the ion-exchanged water and methyl ethyl ketone were distilled off under reduced pressure. Then, the pigment concentration was adjusted to 15% using ion-exchanged water, thereby obtaining an aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1).

[0161] <Production Example of Aqueous Dispersion of Cyan Pigment-Containing Crosslinked Polymer Particles 1 (CP1)> 93.3 parts of the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1) obtained by the method described above, 1.4 parts of Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140 g / eq.) as compound (A-1) (crosslinking agent) (an amount such that the functional group content represented by the above formula 2 is 90 mol%), and 5.3 parts of ion-exchanged water were added to a reaction vessel. Next, the contents in the reaction vessel were heated to 80 ° C. while stirring, and after reaching 80 ° C., the temperature was maintained while stirring was continued for 3 hours to carry out a crosslinking reaction. Thereafter, the internal temperature of the reaction vessel was cooled to room temperature (about 25 ° C.), and then ion-exchanged water was added to adjust the solids concentration, thereby obtaining an aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1) (pigment concentration 14%) in which the dispersion resin 1 was crosslinked.

[0162] <Production Example of Aqueous Dispersions of Cyan Pigment-Containing Crosslinked Polymer Particle Precursors 2 to 25 (CB2 to CB25)> Aqueous dispersions of cyan pigment-containing crosslinked polymer particle precursors 2 to 25 (CB2 to CB25) were 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 the dispersing resin was changed to dispersing resins 2 to 25, respectively. Note that the pigment concentration in all aqueous dispersions was 15%.

[0163] <Production Example of Aqueous Dispersions of Cyan Pigment-Containing Crosslinked Polymer Particles 2 to 46 (CP2 to CP46)> Aqueous dispersions of cyan pigment-containing crosslinked polymer particles 2 to 46 (CP2 to CP46) were obtained in the same manner as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particle 1 (CP1), except that the types and amounts of cyan pigment-containing crosslinked polymer particle precursor and compound (A-1) (crosslinking agent) used, and the amount of ion-exchanged water used were changed as shown in Table 3. Note that the pigment concentration in all aqueous dispersions was 14%.

[0164]

[0165] The abbreviation "V02" in Table 3 and Tables 4 to 6 described below represents Carbodilite V-02 (carbodiimide compound, NCN equivalent: 590 (g / eq.)) manufactured by Nisshinbo Chemical Inc.

[0166] <Production Example of Magenta Pigment-Containing Crosslinked Polymer Particle Precursors 1 to 25 (MB1 to MB25)> An aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursor 1 (MB1) 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 TOSHIKI RED 150TR (C.I. Pigment Red 150, manufactured by Tokyo Shikizai Co., Ltd.) was used as the pigment. The pigment concentration of the aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursor 1 (MB1) was 15%. Furthermore, aqueous dispersions of magenta pigment-containing crosslinked polymer particle precursors 2 to 25 (MB2 to MB25) were obtained using the same raw materials and method as for the aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursor 1 (MB1), except that the dispersing resin was changed to dispersing resins 2 to 25, respectively. The pigment concentration was 15% in all aqueous dispersions.

[0167] <Production Example of Magenta Pigment-Containing Crosslinked Polymer Particles 1 (MP1)> An aqueous dispersion of magenta pigment-containing crosslinked polymer particles 1 (MP1) was obtained using the same raw materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that an aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursor 1 (MB1) was used. The pigment concentration of the aqueous dispersion of magenta pigment-containing crosslinked polymer particles 1 (MP1) was 14%.

[0168] <Production Example of Magenta Pigment-Containing Crosslinked Polymer Particles 2 to 46 (MP2 to MP46)> Aqueous dispersions of magenta pigment-containing crosslinked polymer particles 2 to 46 (MP2 to MP46) were obtained in the same manner as for the aqueous dispersion of magenta pigment-containing crosslinked polymer particle 1 (MP1), except that the amounts of magenta pigment-containing crosslinked polymer particle precursor, crosslinking agent (compound (A-1)), and ion-exchanged water used were changed as shown in Table 4. In all of the aqueous dispersions, the pigment concentration was 14%.

[0169]

[0170] <Production Example of Yellow Pigment-Containing Crosslinked Polymer Particle Precursors 1 to 25 (YB1 to YB25)> 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 (C.I. Pigment Yellow 74, manufactured by Sanyo Pigment 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 to 25 (YB2 to YB25) were obtained using the same raw materials and method as for the aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1), except that the dispersing resin was changed to dispersing resins 2 to 25, respectively. The pigment concentration in all aqueous dispersions was 15%.

[0171] <Production Example of Yellow Pigment-Containing Crosslinked Polymer Particles 1 (YP1)> An aqueous dispersion of yellow pigment-containing crosslinked polymer particles 1 (YP1) was obtained using the same raw materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that an aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1) was used. The pigment concentration of the aqueous dispersion of yellow pigment-containing crosslinked polymer particles 1 (YP1) was 14%.

[0172] <Production Example of Yellow Pigment-Containing Crosslinked Polymer Particles 2 to 46 (YP2 to YP46)> Aqueous dispersions of yellow pigment-containing crosslinked polymer particles 2 to 46 (YP2 to YP46) were obtained in the same manner as for the aqueous dispersion of yellow pigment-containing crosslinked polymer particle 1 (YP1), except that the amounts of yellow pigment-containing crosslinked polymer particle precursor, crosslinking agent (compound (A-1)), and ion-exchanged water used were changed as shown in Table 5. Note that the pigment concentration in all aqueous dispersions was 14%.

[0173]

[0174] <Production Example of Black Pigment-Containing Crosslinked Polymer Particle Precursors 1 to 25 (KB1 to KB25)> 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 PrinteX85 (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 to 25 (KB2 to KB25) were obtained using the same raw materials and method as for the aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1), except that the dispersing resin was changed to dispersing resins 2 to 25, respectively. The pigment concentration in all aqueous dispersions was 15%.

[0175] <Production Example of Black Pigment-Containing Crosslinked Polymer Particles 1 (KP1)> An aqueous dispersion of black pigment-containing crosslinked polymer particles 1 (KP1) was obtained using the same raw materials and method as for the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that an aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1) was used. The pigment concentration of the aqueous dispersion of black pigment-containing crosslinked polymer particles 1 (KP1) was 14%.

[0176] <Production Example of Black Pigment-Containing Crosslinked Polymer Particles 2 to 46 (KP2 to KP46)> Aqueous dispersions of black pigment-containing crosslinked polymer particles 2 to 46 (KP2 to KP46) were obtained in the same manner as for the aqueous dispersion of black pigment-containing crosslinked polymer particle 1 (KP1), except that the amounts of black pigment-containing crosslinked polymer particle precursor, crosslinking agent (compound (A-1)), and ion-exchanged water used were changed as shown in Table 6. In all of the aqueous dispersions, the pigment concentration was 14%.

[0177]

[0178] <Production Example of Binder Resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of butanol and purged with nitrogen gas. After the contents of the reaction vessel were heated to 110°C, a mixture of polymerizable monomers (6 parts acrylic acid, 64 parts methyl methacrylate, 20 parts 2-ethylhexyl acrylate, 10 parts styrene) and 6 parts of a polymerization initiator (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After completion of the addition, the polymerization reaction was continued for 3 hours while the contents of the reaction vessel were maintained at 110°C, and then 0.6 parts of V-601 was added. The reaction was continued for another 1 hour at 110°C to obtain a solution of binder resin 1. Next, the binder resin 1 solution was cooled to room temperature, and 7.1 parts of dimethylaminoethanol was added to neutralize the carboxyl groups in binder resin 1. 100 parts of ion-exchanged water was then added. The mixture was then heated to 100°C or higher, and the temperature was maintained after reaching 100°C, causing azeotropic distillation of butanol with water, and the butanol was then distilled off. The solids concentration was then adjusted to 40% using ion-exchanged water, yielding an aqueous solution of binder resin 1, which is a water-soluble resin with a random structure. The weight-average molecular weight of the resulting binder resin 1 was 19,000, and the acid value was 47 mgKOH / g.

[0179] <Production Examples of Binder Resins 2 to 10> Aqueous solutions of binder resins 2 to 10, which are water-soluble resins having a random structure, were obtained using the same raw materials and procedures as in the case of binder resin 1, except that the types and amounts of the polymerizable monomers used were changed as shown in Table 7. All of the aqueous solutions had a solids concentration of 40%.

[0180]

[0181] Among the abbreviations listed in Table 7, those not used in Tables 1 and 2 are as follows: MAA: methacrylic acid 2EHA: 2-ethylhexyl acrylate STMA: stearyl methacrylate

[0182] <Production Example of Binder Resin 11> Binder resin 11 having an A-B block structure was produced using the method described in Example 21 of WO 2008 / 139980. Specifically, in the polymerization of the first block, acrylic acid was used as the polymerizable monomer, and the reaction was carried out at 80°C for 2 hours, followed by reprecipitation, to obtain an iodine-added first block copolymer. Next, the first block copolymer and polymerizable monomers styrene, methyl methacrylate, and 2-ethylhexyl acrylate were used in a mass ratio of 10:65.5:15, and the reaction was carried out at 80°C for 2.5 hours, followed by reprecipitation, to replace the iodine-added site of the first block with a second block composed of styrene, methyl methacrylate, and 2-ethylhexyl acrylate. Ion-exchanged water was then added to the mixture, and the mixture was thoroughly stirred to completely dissolve the reaction product, thereby obtaining an aqueous solution (solid concentration: 40%) of binder resin 11 having an A-B block structure. The weight-average molecular weight of the obtained binder resin 11 was 19,000, and the acid value was 37 mgKOH / g.

[0183] <Production Example of Binder Resin 12> A reaction vessel equipped with a thermometer, condenser, stirrer, and dropping funnel was charged with 40 parts of ion-exchanged water and 0.2 parts of Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as an emulsifier. Meanwhile, a separate mixing vessel equipped with a stirrer was charged with 15 parts of 2-ethylhexyl acrylate, 69.5 parts of methyl methacrylate, 0.5 parts of acrylic acid, 15 parts of styrene; 53 parts of ion-exchanged water; and 1.8 parts of Aqualon KH-10 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, and the mixture was thoroughly stirred and mixed to form an emulsion. Five portions of the emulsion were taken and added to the reaction vessel. After the addition, the reaction vessel was heated to an internal temperature of 60°C, and the atmosphere inside the reaction vessel was thoroughly purged with nitrogen gas. Then, 3 parts of a 5% aqueous solution of potassium persulfate and 4 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added to initiate the polymerization reaction. After the polymerization reaction began, the internal temperature of the reaction vessel was maintained at 60°C, and the remaining emulsion, 2 parts of a 5% aqueous solution of potassium persulfate, and 6 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added dropwise over 1.5 hours. After the addition was completed, stirring was continued for another 2 hours. The internal temperature of the reaction vessel was then cooled to 30°C, and diethylaminoethanol was added until the pH of the contents reached 8.5. Ion-exchanged water was then added to adjust the solids concentration to 40%, thereby obtaining an aqueous dispersion of binder resin 12, which is resin particles. The acid value of the resulting binder resin 12 was 3 mgKOH / g.

[0184] <Preparation of Water-Based Inkjet Inks> The raw materials listed in each column of Table 8 were added to a mixing vessel equipped with a stirrer while stirring the contents of the mixing vessel. After all raw materials were added, the contents were stirred until sufficiently uniform, and then filtered through a 0.8 μm membrane filter to remove coarse particles that could cause clogging of the inkjet head, thereby preparing the water-based inkjet inks. To prepare the water-based inkjet inks, a set of water-based inkjet inks consisting of four colors (cyan, magenta, yellow, and black) was prepared using pigment-containing crosslinked polymer particles or pigment-containing crosslinked polymer particle precursors (cyan, magenta, yellow, and black) with the same number but different colors. The prepared four-color ink set (ink set) was then used in the evaluations described below.

[0185]

[0186]

[0187]

[0188]

[0189]

[0190]

[0191]

[0192]

[0193]

[0194]

[0195]

[0196]

[0197]

[0198]

[0199]

[0200]

[0201]

[0202]

[0203] Details of the abbreviations and trade names listed in Table 8 are as follows: PG: Propylene glycol (boiling point at 1 atmosphere: 188°C, surface tension at 25°C: 37mN / m) 1,2-BuD: 1,2-butanediol (boiling point at 1 atmosphere: 191°C, surface tension at 25°C: 32mN / m) 1,2-HexD: 1,2-hexanediol (boiling point at 1 atmosphere: 223°C, surface tension at 25°C: 27mN / m) 1,2-PenD: 1,2-pentanediol (boiling point at 1 atmosphere: 206°C, surface tension at 25°C: 28mN / m) 1,5-PenD: 1,5-pentanediol (boiling point at 1 atmosphere: 239°C, surface tension at 25°C: 42mN / m) HexG: 2-methyl-2,4-pentanediol (boiling point at 1 atmosphere: 197°C, surface tension at 25°C: 29mN / m) 1,2-OctD: 1,2-octanediol (boiling point at 1 atmosphere: 295°C, surface tension at 25°C: 20mN / m) PGM: propylene glycol monomethyl ether (boiling point at 1 atmosphere: 120°C, surface tension at 25°C: 27mN / m) PnP: propylene glycol monopropyl ether (boiling point at 1 atmosphere: 150°C, surface tension at 25°C: 26mN / m) PnB: propylene glycol monobutyl ether (boiling point at 1 atmosphere: 170°C, surface tension at 25°C: 26mN / m) DEG: diethylene glycol (boiling point at 1 atmosphere: 245°C, surface tension at 25°C: 45mN / m) DPG: dipropylene glycol (boiling point at 1 atmosphere: 232°C, surface tension at 25°C: 36mN / m) DPM: dipropylene glycol monomethyl ether (boiling point at 1 atmosphere: 190°C, surface tension at 25°C: 29mN / m) DPnP: dipropylene glycol monopropyl ether (boiling point at 1 atmosphere: 212°C, surface tension at 25°C: 26mN / m) BDG: diethylene glycol monobutyl ether (boiling point at 1 atmosphere: 230°C, surface tension at 25°C: 28mN / m) BEG: ethylene glycol monobutyl ether (boiling point at 1 atmosphere: 171°C, surface tension at 25°C:27 mN / m) GLY: glycerin (boiling point at 1 atmosphere: 290°C, surface tension at 25°C: 65 mN / m) Nonion K-220: R in general formula (1); １ is an alkyl group having 12 carbon atoms, and n is 20 (CE×1.67) (manufactured by NOF Corporation, solid content 100%, HLB=16.5) Nonion B-250: a compound in which R １ is an alkyl group having 22 carbon atoms, and n is 50 (CE×2.27) (manufactured by NOF Corporation, solid content 100%, HLB=17.4) Nonion K-230: a compound in which R １ is an alkyl group having 12 carbon atoms, and n is 30 (CE×2.50) (manufactured by NOF Corporation, solid content 100%, HLB=17.5) Emulgen 150: a compound in which R １ is an alkyl group having 12 carbon atoms, and n is 50 (CE×4.17) (manufactured by Kao Corporation, solid content 100%, HLB=18.4) Nonion K-2100W: a compound in which R １ is an alkyl group having 12 carbon atoms, and n is 100 (CE×8.33) (manufactured by NOF Corporation, solid content 50%, HLB=19.2) Emulgen 1150S-60: a compound in which R １ is an alkyl group having 11 carbon atoms and n is 50 (CE×4.55) (manufactured by Kao Corporation, solid content 60%, HLB=18.6) Emalex 630: a compound in which R １ is an alkyl group having 18 carbon atoms and n is 30 (CE×1.67) (manufactured by Nippon Emulsion Co., Ltd., solid content 100%, HLB=16.6) Emalex 640: a compound represented by the general formula (1), １ is an alkyl group having 18 carbon atoms and n is 40 (CE×2.22) (manufactured by Nippon Emulsion Co., Ltd., solid content 100%, HLB=17.3) Emalex 120: a compound represented by the general formula (1), １ is an alkyl group having 16 carbon atoms and n is 20 (CE×1.25) (manufactured by Nippon Emulsion Co., Ltd., solid content 100%, HLB=15.7) Emalex 125: a compound represented by the general formula (1), １is an alkyl group having 16 carbon atoms and n is 25 (CE×1.56) (manufactured by Nippon Emulsion Co., Ltd., solid content 100%, HLB=16.4) Brownon EL-1540P: a compound represented by the general formula (1), １ is an alkyl group having 12 carbon atoms, and n is 40 (CE×3.33) (manufactured by Aoki Oil & Fat Industries Co., Ltd., solid content 100%, HLB=18.1) Emulgen 120: a compound in which R １ is an alkyl group having 12 carbon atoms, and n is 12 (manufactured by Kao Corporation, solid content 100%, HLB = 14.8) Tergitol TMN-10: a compound in which R １ is an alkyl group having 12 carbon atoms and n is 11 (manufactured by The Dow Chemical Company, solid content 90%, HLB = 14.4) Tergitol TMN-6: a compound represented by the general formula (1), １ is an alkyl group having 12 carbon atoms and n is 8 (manufactured by The Dow Chemical Company, solid content 90%, HLB = 13.1) Surfynol 104: an acetylene diol-based surfactant manufactured by Evonik Japan (2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB = 3.0) Surfynol DF110D: an acetylene diol-based surfactant manufactured by Evonik Japan (2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, HLB = 2.7) Surfynol 440: an acetylene diol-based surfactant manufactured by Evonik Japan (ethoxy compound of Surfynol 104, number of moles of ethylene oxide added 3.5, HLB = 8.1) Surfynol 465: an acetylene diol surfactant manufactured by Evonik Japan (an ethoxy compound of Surfynol 104, 10 moles of ethylene oxide added, HLB = 13.2); Dynol 604: an ethoxy compound of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, an average of 4 moles of ethylene oxide added, HLB = 8.0); TEGO Wet 240: a side chain polyether-modified silicone surfactant manufactured by Evonik Japan (HLB: 5 to 7, R in the above general formula 6) ３ is a structure represented by the above general formula 7, and R ４is not a structure represented by general formula 7) TEGO Wet 270: a side chain polyether-modified silicone surfactant manufactured by Evonik Japan (HLB: 2 to 4, R in general formula 6 above is not a structure represented by general formula 7) ３ is a structure represented by the above general formula 7, and R ４ is not the structure represented by general formula 7) TEGO Glide 440: a silicone surfactant modified at both ends with polyether, manufactured by Evonik Japan Co., Ltd. (HLB: 3 to 5, R in general formula 6 above is not the structure represented by general formula 7) ４ is a structure represented by the above general formula 7, and R ３ is not the structure represented by general formula 7) BYK333: a silicone surfactant modified at both ends with polyether, manufactured by BYK-Chemie (HLB: 10.3 to 12, R in general formula 6 above is not the structure represented by general formula 7) ４ is a structure represented by the above general formula 7, and R ３ does not have the structure represented by general formula 7) TEGO Twin 4100: Gemini type silicone surfactant manufactured by Evonik Japan (HLB: 0 to 2)

[0204] [Examples 1 to 161, Comparative Examples 1 to 18] The above aqueous inkjet inks (sets) were used to carry out the following evaluations, and the evaluation results are shown in Table 8 above.

[0205] <Evaluation 1: Evaluation of White Out> An inkjet ejection device equipped with four Kyocera inkjet heads (KJ4B-1200) was placed in a 25°C environment. Next, the inks constituting the ink set were loaded into the inkjet heads so that the printing order in the inkjet printing device was black, cyan, magenta, and yellow. A nozzle check pattern was then printed, and after confirming that ink was being ejected normally from all nozzles, the device was left as is for one minute. After leaving the device as is, a solid print with a coverage of 100% was performed on the printing substrate shown below using only one of the ink colors under printing conditions of a frequency of 40 kHz, 1,200 x 1,200 dpi, and a drop volume of 3 pL. Then, immediately after printing, the printing substrate with the printed ink was placed in an air oven at 70°C and dried for one minute to obtain a solid print. The degree of white out on the solid print was then evaluated visually and with a magnifying glass. Two types of printing substrates were used: OK Topcoat+ paper manufactured by Oji Paper Co., Ltd., and UPM Fine Gloss paper manufactured by UPM Co., Ltd., and evaluation was performed on each. The evaluation criteria were as follows, with AA, A, and B ratings representing the practical range. Solid prints were created using inkjet inks of four colors: cyan, magenta, yellow, and black, and blanking was evaluated for each solid print. Table 8 also lists the evaluation criteria for the color with the worst evaluation result for each printing substrate. AA: No blanking was observed visually or with a magnifying glass. A: Slight blanking was observed with a magnifying glass, but no blanking was observed visually. B: Slight blanking was observed visually. C: Blanking was clearly observed visually.

[0206] <Evaluation 2: Evaluation of Color Bleeding> Using the inkjet printing device used in Evaluation 1 above, a superimposed gradation image was printed under the same printing conditions and using the same type of printing substrate and all of the inks installed in the inkjet printing device. The "superimposed gradation image" is an image in which, for one color of ink, the printing rate is continuously changed from 10 to 60% within a predetermined area, and these images are superimposed in the order of black, cyan, magenta, and yellow. Therefore, the total printing rate of the superimposed gradation image (the sum of the printing rates of each color) is 40 to 240%. However, the printing rate of each color at each total printing rate is the same (for example, when the total printing rate is 40%, the printing rate of each color is 10%, and when the total printing rate is 240%, the printing rate of each color is 60%). After printing the superimposed gradation image, the printing substrate on which the inks were printed was placed in an air oven at 70°C and dried for 1 minute, thereby obtaining a superimposed gradation print. The degree of color bleeding in the overlapping gradation print was then checked visually and with a magnifying glass to evaluate color bleeding. The evaluation criteria were as follows, with AA, A, and B ratings representing usable areas. AA: No color bleeding was observed in all areas with a total print rate of 40 to 240%. A: No color bleeding occurred in areas with a total print rate of 200% or less, but was observed in areas with a total print rate of more than 200% and less than 240%. B: No color bleeding occurred in areas with a total print rate of 160% or less, but was observed in areas with a total print rate of more than 160% and less than 200%. C: No color bleeding occurred in areas with a total print rate of 120% or less, but was observed in areas with a total print rate of more than 120% and less than 160%. D: Color bleeding was observed in areas with a total print rate of 120% or less.

[0207] <Evaluation 3: Evaluation of Dot Circularity> Using the inkjet printing device used in Evaluation 1 above, a monochromatic gradation image was printed using only one ink color mounted on the inkjet printing device under the same printing conditions and using the same type of printing substrate as in Evaluation 1 above. The "monochromatic gradation image" is an image in which the printing rate continuously changes from 5 to 60% within a predetermined area. After printing the monochromatic gradation image, the printing substrate with the printed ink was placed in an air oven at 70°C and dried for 1 minute to obtain a monochromatic gradation print. A portion of the monochromatic gradation print with a printing rate of 10% was then observed using an image quality analyzer ("PIAS-II" manufactured by Quality Engineering Associates, Inc.) to measure dot circularity. The closer the circularity is to 1, the more circular the dot is and the better the dot shape is. The evaluation criteria are as follows, with AA, A, and B being considered to be within the practical range. AA: The circularity was 1 or more and 2 or less. A: The circularity was more than 2 and 3 or less. B: The circularity was more than 3 and 3.5 or less. C: The circularity was greater than 3.5.

[0208] <Evaluation 4: Evaluation of print density> Using OK top coat + paper as the printing substrate, the density of the solid print of each color produced in Evaluation 1 above was measured with a spectrophotometer (X-rite's "eXact Advance") to evaluate the print density. The measurement conditions were ISO status T as the density standard, a viewing angle of 2°, and a light source D50. The evaluation criteria were as follows, with AA, A, and B ratings being in the usable range. AA: For all colors, the print density was 0.3 or more higher than the print density of a solid print of the same color produced using the ink set of Comparative Example 1. A: For the color that showed the smallest difference in print density from a solid print of the same color produced using the ink set of Comparative Example 1, the difference value was 0.15 or more and less than 0.3. B: For the color that showed the smallest difference in print density from a solid print of the same color produced using the ink set of Comparative Example 1, the difference value was 0 or more and less than 0.15. C: For the color with the smallest difference in print density compared to the solid print of the same color produced using the ink set of Comparative Example 1, the difference value was less than 0 (i.e., the print density of the solid print of the same color produced using the ink set of Comparative Example 1 was greater).

[0209] <Evaluation 5: Evaluation of Color Reproduction Range> Using the inkjet printing device used in Evaluation 1 above, a secondary color solid image was printed under the same printing conditions as in Evaluation 1 above using three colors of ink: cyan, magenta, and yellow, among those installed in the inkjet printing device. OK Topcoat + paper manufactured by Oji Paper Co., Ltd. was used as the printing substrate. The "secondary color solid image" refers to an image in which three solid images are arranged: a red solid image (a solid image using magenta ink superimposed on a solid image using yellow ink), a blue solid image (a solid image using cyan ink superimposed on a solid image using magenta ink), and a green solid image (a solid image using yellow ink superimposed on a solid image using cyan ink). After printing the secondary color solid image, the OK Topcoat + paper on which the inks had been printed was placed in an air oven at 70°C and dried for 1 minute, thereby obtaining a secondary color solid print. The hue (a* value and b* value) of the solid portions of each color in the secondary color solid print was measured using a spectrophotometer (X-rite's "eXact Advance"). The conditions for measuring the hue were the same as those for evaluation 4. The color reproduction gamut was evaluated using the saturation (C value) calculated by adding the square of the a* value and the square of the b* value and taking the square root (√(a*2 + b*2)). A larger C value indicates a wider color reproduction gamut. The evaluation criteria were as follows, with AA, A, and B ratings being considered as usable ranges. AA: The C value of red was 95 or more, the C value of blue was 60 or more, and the C value of green was 80 or more. A: Did not meet all of the above evaluation criterion AA, the following evaluation criterion B, and the following evaluation criterion C. B: Does not meet the above evaluation criterion AA or the following evaluation criterion C, and meets one or more of the following requirements: "C value of red is 85 or more and less than 90," "C value of blue is 50 or more and less than 55," and "C value of green is 70 or more and less than 75." C: Does not meet the above evaluation criterion AA, and meets one or more of the following requirements: "C value of red is less than 85," "C value of blue is less than 50," and "C value of green is less than 70."

[0210] <Evaluation 6: Evaluation of Drying Properties> Using the inkjet printing device used in Evaluation 1 above, a stacked half solid image was printed under the same printing conditions as in Evaluation 1 above, using all of the inks installed in the inkjet printing device. The printing substrate was OK Topcoat + paper manufactured by Oji Paper Co., Ltd. The "stacked half solid image" refers to an image in which images printed on one surface with a coverage rate of 60% for one color of ink were superimposed in the order of black, cyan, magenta, and yellow. Therefore, the total coverage rate of the stacked half solid image was 240%. After printing the stacked half solid image, the OK Topcoat + paper on which the inks had been printed was placed in an air oven at 70°C, and the printed material was removed at regular intervals and touched with a finger to evaluate drying properties. The evaluation criteria were as follows, with AA, A, and B being considered to be within the practical range. AA: After 30 seconds of drying, there was no tackiness when touched with the finger, and the print was dry. A: After 1 minute of drying, there was no tackiness when touched with the finger, and the print was dry, but it was not dry at 30 seconds. B: After 1 minute 30 seconds of drying, there was no tackiness when touched with the finger, and the print was dry, but it was not dry at 1 minute. C: After 1 minute 30 seconds of drying, there was a tackiness when touched with the finger, and the print was not dry.

[0211] <Evaluation 7: Discharge Stability> Using the inkjet printing device used in Evaluation 1 above, the inks constituting the ink set were each loaded into an inkjet head, and a nozzle check pattern was printed to confirm that ink was being discharged normally from all nozzles. Subsequently, 100 A4-sized solid images were printed continuously using the inks installed in the inkjet printing device. After printing, a nozzle check pattern was printed again, and the number of clogged nozzles was visually counted to evaluate discharge stability. The above evaluation was performed under two head drive frequency conditions: 40 kHz and 64 kHz. The evaluation criteria were as follows, with AA, A, and B being considered as practical ranges. The evaluation was performed for each of the four inks constituting the ink set. Table 8 lists the evaluation criteria for the color with the worst evaluation result. AA: No clogged nozzles. A: 1 to 3 clogged nozzles. B: 4 to 9 clogged nozzles. C: 10 to 49 clogged nozzles. D: 50 or more clogged nozzles.

[0212] It was confirmed that the aqueous inkjet inks of Examples 1 to 161, which have the configuration of the aqueous inkjet ink of the present disclosure, have a quality level sufficient for practical use in terms of print image quality, print density, color reproducibility, and ejection stability even on poorly absorbent printing substrates.

[0213] Furthermore, a comparison of Examples 2, 3, and 4 confirms that the print density, color reproducibility, and drying properties of printed matter are improved by adjusting the acid value of the dispersion resin (polymer (A-2)) to 180 mgKOH / g or less, preferably 160 mgKOH / g, and more preferably 150 mgKOH / g or less. Similarly, a comparison of Examples 29, 30, and 31 confirms that the combined use of a binder resin having a specific acid value, specifically an acid value of 50 mgKOH / g or less (preferably 40 mgKOH / g or less), improves dot bleeding and drying properties of printed matter, as well as ejection stability. These results confirm that the acid value of the resins (polymer (A-2) and binder resin) contained in the aqueous inkjet ink of the present disclosure affects drying properties, print image quality, color reproducibility, and print image quality.

[0214] Furthermore, the aqueous inkjet inks of Examples 93, 94, 95, 97, 98, 99, 100, 113, 119, 120, 125, 130, 131, 135, 138, 151, 152, 156, 157, 160, and 161 each use a resin (polymer) having a suitable acid value as the polymer (A-2) and binder resin, and further use a gemini type silicone surfactant (TEGO Twin 4100) or a silicone surfactant modified at both ends with polyether (TEGO Glide 440) as the nonionic surfactant (B-2). These aqueous inkjet inks are rated "AA" in all evaluations. These results confirmed that the use of a silicone surfactant having a specific structure as the nonionic surfactant (B-2) is extremely suitable.

[0215] On the other hand, in Comparative Examples 1 and 4, which reproduced the organic solvent and surfactant compositions of the aqueous inkjet inks specifically disclosed in Examples 4 and 8 of Patent Document 3, respectively, the ratio of compound (B-1) to nonionic surfactant (B-2) was 2:1 or 1:1, which did not meet the preferred blending ratios described in the present disclosure. This resulted in a deterioration in print quality, presumably due to an imbalance in the affinity of the nonionic surfactant (B-2). Furthermore, because Comparative Example 1 used a pigment-containing crosslinked polymer particle precursor, the dispersing resin detached from the pigment and released into the ink inhibited the orientation of the surfactant, which is also thought to have contributed to the deterioration in print quality. Furthermore, the presence of a dispersing resin adsorbed with a highly hydrophobic surfactant in the ink prevented practically acceptable ejection stability. A similar trend was also observed in Comparative Examples 3 and 16, which used a non-crosslinked dispersing resin.

[0216] Furthermore, in Comparative Example 4, Surfynol 104, an acetylene diol surfactant, was used as the nonionic surfactant (B-2). However, since the compound (B-1) was not contained, the Surfynol 104 could not be sufficiently emulsified, and the print quality and print density of the printed matter were not suitable for practical use.

[0217] In addition, the aqueous inkjet inks of Comparative Examples 7 to 15, which are systems that do not contain the compound (B-1) or the nonionic surfactant (B-2) as the surfactant (B), also failed to provide print quality or print density suitable for practical use in printed matter, as in Comparative Example 4. Furthermore, Comparative Examples 2, 6, 17, and 18 are systems that contain the compound (B-1) and the nonionic surfactant (B-2) as the surfactant (B), but the ratio of the compound (B-1) to the nonionic surfactant (B-2) is outside the preferred range described above, and again failed to provide print quality suitable for practical use.

[0218] Although the present disclosure has been described with reference to the above several embodiments, the present disclosure is not limited to the above several embodiments. Various changes can be made to the configuration and details of the present disclosure within the scope of the present disclosure. The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-209883, filed on December 13, 2023, the entire disclosure of which is incorporated herein by reference.

Claims

1. An aqueous inkjet ink containing a pigment-containing crosslinked polymer particle (A) and a surfactant (B), wherein the crosslinked polymer particle (A) comprises a crosslinked reaction product between a compound (A-1) having in one molecule a plurality of functional groups reactive with a carboxy group and / or a carboxylate group, and an uncrosslinked polymer (A-2) having a carboxy group and / or a carboxylate group, the surfactant (B) contains a compound (B-1) represented by the following general formula 1, and a nonionic surfactant (B-2) having an HLB value of 1 to 10, and the ratio of the content of the compound (B-1) to the content of the nonionic surfactant (B-2) is 1:1.2 to 1:20 by mass. R １ -(O-CH ２ -CH ２ ) ｎ -OH General formula 1 (In general formula 1, R １ represents a linear or branched alkyl group having 10 to 25 carbon atoms, and n is an integer of 20 to 100.

2. The aqueous inkjet ink according to claim 1, further comprising an organic solvent, the organic solvent comprising an alkanediol solvent having 5 to 8 carbon atoms and / or a (poly)alkylene glycol monoalkyl ether solvent having 5 to 9 carbon atoms.

3. The water-based inkjet ink according to claim 2, wherein the organic solvent comprises a (poly)propylene glycol monoalkyl ether solvent having 5 to 9 carbon atoms.

4. The aqueous inkjet ink according to claim 1 or 2, wherein the acid value of the uncrosslinked polymer (A-2) is 60 to 180 mgKOH / g.

5. The aqueous inkjet ink according to claim 1 or 2, further comprising an organic solvent, the organic solvent comprising a (poly)propylene glycol monoalkyl ether solvent having 5 to 9 carbon atoms, and the acid value of the uncrosslinked polymer (A-2) is 60 to 180 mgKOH / g.

6. The aqueous inkjet ink according to claim 1 or 2, wherein the nonionic surfactant (B-2) having an HLB value of 1 to 10 comprises a gemini type silicone surfactant and / or a silicone surfactant modified at both ends with polyether (excluding the gemini type silicone surfactant).

7. The aqueous inkjet ink according to claim 1 or 2, further comprising an organic solvent, said organic solvent comprising a (poly)propylene glycol monoalkyl ether solvent having 5 to 9 carbon atoms, and said nonionic surfactant (B-2) having an HLB value of 1 to 10 comprising a gemini type silicon surfactant and / or a silicon surfactant modified at both ends with polyether (excluding said gemini type silicon surfactants).

8. The aqueous inkjet ink according to claim 1 or 2, further comprising an organic solvent, the organic solvent comprising a (poly)propylene glycol monoalkyl ether solvent having 5 to 9 carbon atoms, the acid value of the uncrosslinked polymer (A-2) being 60 to 180 mgKOH / g, and the nonionic surfactant (B-2) having an HLB value of 1 to 10 comprising a gemini type silicone surfactant and / or a silicone surfactant modified at both ends with polyether (excluding the gemini type silicone surfactant).

9. A printed matter obtained by printing with the aqueous inkjet ink according to claim 1 or 2.

Images