WO2025126526A1 - Aqueous inkjet ink and printed matter - Google Patents

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 matter

Embodiments of the present invention relate to aqueous inkjet inks and printed matter produced using the aqueous inkjet inks.

Inkjet printing is a recording method in which ink droplets are ejected directly from fine nozzles and deposited on a printing substrate to produce characters and/or images. Inkjet printing has many advantages, including low equipment noise and good operability, ease of full color printing, inexpensive printing equipment, and the ability to print on a variety of printing substrates without contact, making it extremely popular. In particular, in recent years, inkjet printing has come to be used not only for consumer purposes in offices and homes, but also for commercial and industrial printing purposes. In this context, there is an ever-increasing demand for inkjet inks that contain water as their main component (aqueous inkjet inks) in order to reduce the burden on the environment and workers.

Note that the above "images" also include seamless images such as solid images and checkered images.

Water-based inkjet inks have long been developed for use on plain paper and specialty paper as printing substrates. In these applications, it is assumed that the liquid components of the water-based inkjet ink are absorbed into the printing substrate. Therefore, when the water-based inkjet ink is printed on poorly absorbent printing substrates such as those used in the commercial and industrial printing applications mentioned above, the image bleeds, making it difficult to produce printed matter that can withstand practical use.

For example, coated paper, which is a poorly absorbent printing substrate, has low absorbency of liquid components, so when a droplet of water-based inkjet ink lands adjacent to the previous droplet before it has dried during printing, adjacent droplets are likely to merge (beading). Beading causes color mixing and bleeding in printed matter. In addition, some poorly absorbent printing substrates, including coated paper, have low surface free energy, and printing on such substrates makes it difficult for the water-based inkjet ink to wet and spread across the surface of the substrate, which can easily lead to the occurrence of white spots (a phenomenon in which spots on the substrate where the water-based inkjet ink is not applied appear as spots and/or streaks).

Furthermore, water, the main solvent in water-based inkjet ink, has high surface tension and is difficult to wet and spread on the printing substrate, which can easily cause poor print quality, such as whiteouts and color bleeding. In order to improve print quality, it is effective to reduce the surface tension of water-based inkjet ink, and highly hydrophobic surfactants and organic solvents are generally used for this purpose.

For example, Patent Document 1 discloses an ink composition for inkjet recording that contains three types of acetylene diol surfactants with different structures. According to Patent Document 1, it is possible to record images with excellent print quality (color unevenness, aggregation, bleeding) and fixability (abrasion resistance) at high speed on various printing substrates with different absorbencies.
Furthermore, Patent Document 2 discloses an aqueous ink composition containing a nonionic surfactant having an HLB value of 4 to 14. According to Patent Document 2, it is said that the ink composition can provide a printed matter that is excellent in wettability, fineness, print density, water resistance, rub resistance (abrasion resistance), etc. and does not aggregate 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, it is said that a printed matter free from turbidity (white turbidity, oil floating, etc.) and with suppressed color unevenness can be obtained.

JP 2015-124238 A Special Publication No. 2004-510028 JP 2014-139004 A

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 effect of the highly hydrophobic material described above may not be fully realized, and the ejection stability of the aqueous inkjet ink may also deteriorate.

The inventors also reproduced and evaluated the aqueous inkjet ink specifically disclosed in the examples of Patent Document 3, and found that problems not evaluated in Patent Document 3, such as whiteout and color mixing, worsened, and that the droplets of the aqueous inkjet ink became distorted (poor dot circularity).

As described above, in the past, further improvements were needed to obtain an aqueous inkjet ink that produces prints that are free of color bleeding and white space caused by droplets coalescing, have excellent dot circularity, and also have excellent ejection stability. Furthermore, until now, there has been no aqueous inkjet ink that can produce prints with good print density and color reproducibility while solving these issues.

In view of this, one of the objects of the present invention is to provide an aqueous inkjet ink that is free of color bleeding and white voids caused by droplets coalescing, has excellent dot circularity, 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. In addition to the above-mentioned effects, another object of the present invention is to provide an aqueous inkjet ink that also has excellent drying properties.

In this disclosure, the state of a print that is free of color bleeding caused by the merging of droplets, free of blank spaces, and has excellent dot circularity of the droplets, is also referred to as having "excellent print quality."

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

That is, some embodiments of the present invention relate to aqueous inkjet inks as shown in [1] to [5] below, and to printed matter produced using the aqueous inkjet ink as shown in [6] below.
[1] An aqueous inkjet ink comprising pigment-containing crosslinked polymer particles (A) and a surfactant (B),
the crosslinked polymer particles (A) contain a crosslinked reaction product between a compound (A-1) having a plurality of functional groups in one molecule that react 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:
The ratio of the content of the compound (B-1) to the content of the nonionic surfactant (B-2) is from 1:1.2 to 1:20 in terms of mass ratio.
R ¹ -(O-CH ₂ -CH ₂ ) _n -OH General formula 1
(In the general formula 1, ^R1 represents a linear or branched alkyl group having 10 to 25 carbon atoms, and n is an integer of 20 to 100.)
[2] Further containing an organic solvent,
The aqueous inkjet ink according to [1], 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 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 includes a gemini type silicon-based surfactant and/or a silicon-based surfactant modified at both ends with polyether (excluding the gemini type silicon-based surfactant).
[6] A printed matter obtained by printing with the aqueous inkjet ink according to any one of [1] to [5] above.

The present disclosure makes it possible to provide an aqueous inkjet ink that is free of color bleeding and white voids caused by droplets coalescing, has excellent dot circularity, 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 makes it possible to provide an aqueous inkjet ink that has excellent drying properties in addition to the effects described above.

Below, 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. Note that the present disclosure is not limited to the following embodiments, and includes modified examples that are implemented within the scope that does not change the gist of the present disclosure.

As mentioned above, poorly absorbent printing substrates such as coated paper have a low surface energy, and it is not easy to make aqueous inkjet ink wet and spread sufficiently. Therefore, even in printed matter with a high printing rate, image defects such as blank spots are likely to occur. In addition, poorly absorbent printing substrates have low permeability of liquid components into the substrate, so there is a risk that droplets of another ink will land adjacent to the previously landed droplets of aqueous inkjet ink before they have sufficiently dried, resulting in beading. Beading appears as color mixing and uneven density, and is therefore undesirable from the perspective of improving print quality. Thus, in order to improve print quality in inkjet printing on poorly absorbent printing substrates, it is necessary to ensure sufficient wettability and permeability of the aqueous inkjet ink.

In general, lowering the surface tension of an ink is effective in ensuring the wettability and permeability of the ink. In addition, by adding a highly hydrophobic surfactant to the ink, the surfactant quickly orients at the interfaces of the ink (air-liquid interface and the interface between the printing substrate and the ink), making it easier to impart wettability and permeability.

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 the property of having an affinity for other hydrophobic materials, and interact with the hydrophobic groups in the free polymer dispersant.

In general, polymer dispersants used in aqueous inkjet inks have hydrophilic groups such as carboxy 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, which is the main component, and to stabilize the dispersed state of the pigment by the 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 exclude hydrophobic groups from polymer dispersants used in aqueous inkjet inks.

In this way, if a highly hydrophobic surfactant is adsorbed to a free polymer dispersant, when the ink droplets land on the 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 permeability. In addition, while the detailed mechanism is unknown, if there is a large amount of polymer dispersant to which a highly hydrophobic surfactant has been adsorbed in the ink, the ejection stability of the ink also tends to deteriorate.

Therefore, in order to obtain a printed matter having excellent print quality on a poorly absorbent printing substrate such as coated paper, and further to improve the ejection stability of the ink, it is important to reduce the amount of the free polymer dispersant so as not to interfere with the orientation of the surfactant. Therefore, in this embodiment, from the viewpoint of being able to suppress the detachment of the polymer dispersant from the pigment even if the component ratio of the ink changes due to drying, for example, it is more preferable to use a polymer crosslinked by a crosslinking agent (crosslinked polymer) as the polymer dispersant. In particular, by using a crosslinking agent having multiple functional groups in one molecule that react with carboxy groups or carboxylate groups, which are generally present in polymer dispersants, the polymer dispersant can be crosslinked at a high density, and detachment from the pigment can be prevented. As a result, it is possible to quickly align the surfactant at the interface of the ink, and it is possible to improve the wettability and permeability of the ink. Furthermore, by preventing the detachment of the polymer dispersant and reducing the amount of the free polymer dispersant, the ejection stability of the ink is also improved.

However, as a drawback of cross-linking the polymer dispersant and reducing the amount of free polymer dispersant, the above-mentioned surfactant, which has no components to adsorb, may not be able to exist stably in the ink. In this case, the above-mentioned surfactant may become unevenly localized at the ink interface, causing the ink droplets to wet and spread unevenly, which may result in print image quality with poor circularity.

Generally, when a polymer is crosslinked with a crosslinking agent, hydrophilic functional groups such as hydroxyl groups, amino groups, and amide bonds are generated in the polymer dispersant by the crosslinking reaction. As a result, the affinity between the polymer dispersant having the functional groups and a highly hydrophobic surfactant deteriorates, and there is a concern that the surfactant and crosslinked polymer (including pigment particles) may localize and/or separate in printed matter, for example. In this case, there is a risk of a decrease in print density and color reproducibility.

In order to solve the above problems, the 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 printing substrate with poor absorption such as coated paper, and further to obtain a printed matter with excellent dot circularity, print density, and color reproducibility, thus leading to the present invention. Although the detailed mechanism by which the above configuration achieves these effects is unclear, the following may be considered, for example.

First, the surfactant (B-2) corresponds to the above-mentioned "highly hydrophobic surfactant". The surfactant (B-2) has an HLB value in a suitable range, and can impart excellent permeability and wettability to the aqueous inkjet ink even on a printing substrate with poor absorption, such as coated paper. On the other hand, as described above, the surfactant (B-2) has poor affinity with crosslinked polymers that have hydrophilic functional groups, and may wet and spread unevenly on the printing substrate, resulting in a printed matter with poor dot roundness. In addition, as water is preferentially evaporated during the drying process after printing, the compatibility between the surfactant (B-2) and the crosslinked polymer decreases, and the surfactant (B-2) and the crosslinked polymer (pigment particles containing the surfactant) may localize and/or separate, resulting in an uneven ink film (dried ink film). In that case, the light incident on the ink film is scattered on the surface of the ink film, causing the printed matter to look whitish (whitening) or the color reproducibility to be impaired.

On the other hand, in compound (B-1), the linear or branched alkyl chain having 10 to 25 carbon atoms functions as a hydrophobic portion, and the polyethylene oxide chain having an added mole number of 20 to 100 functions as a hydrophilic portion. Furthermore, by using compound (B-1) and surfactant (B-2) in combination in a suitable ratio, the polyethylene oxide chain in compound (B-1) has an 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 being localized at a part of the interface. It is believed that this makes it possible to obtain printed matter with excellent dot circularity while suppressing whiteout and color mixing bleeding.

In addition, even after the water has evaporated preferentially during the ink drying process, the alkyl chains in compound (B-1) have affinity with the surfactant (B-2), and the polyethylene oxide chains have affinity with the crosslinked polymer, so that a uniform ink film is formed without the materials separating. As a result, it is possible to obtain printed matter with excellent print density and color reproducibility.

As described above, in order to obtain a printed matter that is free of color bleeding and white voids, has excellent dot circularity, and has 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 to specify the content ratio. Note that the above mechanism is an inference and does not limit the present invention in any way. In this disclosure, the compound (B-1) and the nonionic surfactant (B-2) are different. Specifically, the compound (B-1) is a surfactant other than a nonionic surfactant having an HLB value of 1 to 10.

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 state 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 exert the effect of a highly hydrophobic surfactant and improve the ejection stability of the aqueous inkjet ink.
On the other hand, "acetylene glycol (A)", which is an essential component in Patent Document 3, corresponds to the nonionic surfactant (B-2) in the present disclosure, and a part of "nonionic surfactant (B)" corresponds to the compound (B-1) in the present disclosure (see claim 3 of Patent Document 3, etc.). However, Patent Document 3 specifies that the ratio represented by "nonionic surfactant (B)/acetylene glycol (A)" is 1 to 3, whereas the present disclosure specifies that the ratio between the content of the compound (B-1) and the content of the nonionic surfactant (B-2) is 1:1.2 to 1:20 by mass (when expressed by the method described in Patent Document 3, "1/20 to 1/1.2 (5/6)"), and this point is different between the two. In fact, Comparative Example 3 of Patent Document 3 discloses an example in which the above ratio is "0.3" (when expressed by the method described in the present disclosure, 1:3.3), and it is said that the color unevenness and ejection stability do not meet practical levels. In contrast, in the present disclosure, by further defining the structure of compound (B-1), it is possible to achieve good quality even for aqueous inkjet inks that were not considered to have good quality in Patent Document 3.

Next, the main components that make up one embodiment of the inkjet ink will be described.

<Pigment-containing crosslinked polymer particles (A)>
The inkjet ink of this embodiment contains crosslinked polymer particles (A) containing a pigment. The crosslinked polymer particles (A) containing the pigment contain the pigment, and a crosslinked reaction product between a compound (A-1) having a plurality of functional groups in one molecule that react with a carboxy group and/or a carboxylate group, and an uncrosslinked polymer (A-2). The crosslinking treatment carried out for producing the crosslinked reaction product crosslinks the uncrosslinked polymer (A-2) to a high density, making it possible to suppress the detachment of the polymer dispersant in the ink of the present disclosure. As a result, it becomes possible to allow the surfactant (B-2) to function effectively, and to improve the wettability and penetrability of the ink.

In this disclosure, "crosslinked polymer particles containing a pigment" refers to particles after a crosslinking treatment is performed on the polymer contained in the crosslinked polymer particle precursor using a crosslinking agent (a compound used to chemically bond polymer molecules together). The "crosslinked polymer particle precursor" refers to particles at a stage before the crosslinking treatment, and refers to one or more particles selected from the group consisting of uncrosslinked polymer particles containing a pigment, uncrosslinked particles containing a polymer and a pigment and having an island-in-sea structure with part of the pigment exposed on the surface of the particle, and pigment particles with a polymer chemically adsorbed and/or bonded to at least part of the surface.

＜＜Pigments＞＞
The pigment contained in the pigment-containing crosslinked polymer particles (A) may be either an organic pigment or an inorganic pigment. In addition, organic pigments and inorganic pigments 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, orange, and achromatic pigments such as white and black can be used.

When inorganic pigments are used as pigments, the following can be used as the inorganic pigments: titanium oxide, zinc oxide, 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, cobalt violet, etc.

The carbon black may be produced by the furnace method or the channel method, and among these, carbon black having properties such as a primary particle size of 11 to 40 nm, a specific surface area measured by the BET method of 50 to 400 m ² /g, a volatile content of 0.5 to 10%, and a pH value of 2 to 10 is preferred.

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; 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; and the like.

Specific examples of organic pigments that can be used as the above pigments, 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 a cyan or blue color.

Also, examples of organic pigments that exhibit magenta, red, or violet colors 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, and C.I. Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, and 50.

Also, 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.

Black pigments include aniline black (C.I. Pigment Black 1), perylene black (C.I. Pigment Black 31, 32), azomethine azo black, etc.

Other pigments that can be used include C.I. Pigment Green 7, 10, 36, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71, etc.

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

<<Compound (A-1)>>
The compound (A-1) is a compound used as the crosslinking agent, and has a plurality of functional groups in one molecule that react with the carboxyl group and/or carboxylate group present in the uncrosslinked polymer (A-2). As the compound (A-1), an aziridine compound, an isocyanate compound, an epoxy compound, a carbodiimide compound, an oxetane compound, an oxazoline compound, and the like can be used. Among them, it is preferable to use an epoxy compound as the compound (A-1), that is, the compound (A-1) is a compound having a plurality of epoxy groups in one molecule, from the viewpoints that the crosslinking reaction of the polymer (A-2) can proceed in the vicinity of the pigment while maintaining the dispersion stability of the pigment, and the detachment of the polymer (A-2) accompanying the crosslinking reaction can be prevented, thereby obtaining a printed matter without blank spaces, and the ejection stability of the aqueous inkjet ink can also be improved. In addition, the compound (A-1) may be either water-soluble or water-insoluble, but from the viewpoint of allowing the crosslinking reaction to proceed more efficiently in a liquid medium mainly composed of water, the solubility of the compound (A-1) in 100 g of water at 25° C. is preferably 0.1 to 50 g/100 g H ₂ O, more preferably 0.2 to 40 g/100 g H ₂ O, and even more preferably 0.5 to 30 g/100 g H ₂ O.

As mentioned above, it is preferable that compound (A-1) is a compound having multiple epoxy groups in one molecule. 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, it is particularly preferable that compound (A-1) is a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group with 3 to 8 carbon atoms.

When the compound (A-1) is a compound having multiple epoxy groups in one molecule, the epoxy equivalent is preferably 90 to 300 g/eq., more preferably 100 to 200 g/eq., from the viewpoint of being able to more efficiently crosslink with the carboxyl groups and/or carboxylate groups present in the uncrosslinked polymer (A-2) in a liquid medium mainly composed of water.

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

Compound (A-1) is preferably added so that the functional group content (mol%) shown in the following formula 2 is 50 to 150 mol%. The functional group content is more preferably 70 to 120 mol%, and particularly preferably 80 to 100 mol%.

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

Functional group content (mol%) = 100 x (EW/EE)/{PW x AV/(56.1 x 1000)} Formula 2-2

Note that "56.1" in the above formula 2-2 is the molecular weight of potassium hydroxide.

When the functional group content is within the above range, the crosslinking of the polymer dispersant becomes denser, and the amount of free polymer dispersant can be significantly reduced. On the other hand, in this case, the nonionic surfactant (B-2) cannot exist stably in the ink, and the ink droplets may become unevenly wetted and spread, or the amount of hydrophilic groups in the polymer dispersant may increase, which may deteriorate the affinity with the nonionic surfactant (B-2), resulting in a decrease in print density and color reproducibility. However, the inkjet ink of the present disclosure contains the compound (B-1) as described above. The nonionic surfactant (B-2) stabilized by the compound (B-1) can be quickly and uniformly oriented, which can improve the circularity of dots in the printed matter and further suppress whiteout and color mixing. In addition, it is possible to prevent a decrease in print density and color reproducibility, and also improve ejection stability.

<<Polymer (A-2)>>
The uncrosslinked polymer (A-2) used in this embodiment has a carboxy group and/or a carboxylate group (COO ^- ) in its structure. 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) having a function of dispersing a pigment.

Types of polymers that can be used as polymer (A-2) include acrylic, maleic acid, urethane, and polyester. In addition, from the viewpoint of strengthening the 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 the structure as polymer (A-2).

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 be further used as the polymerizable monomer constituting the acrylic polymer. However, a polymer containing maleic acid (anhydride) (at least one selected from "maleic acid" and "maleic anhydride") as a polymerizable monomer is excluded from the "acrylic polymer" in the present disclosure.
The term "maleic acid-based polymer" refers to a polymer that uses at least maleic acid (anhydride) as a polymerizable monomer. The maleic acid-based polymer may further use, as a polymerizable monomer, an α-olefin, acrylic acid, methacrylic acid, an acrylic acid ester, a methacrylic acid ester, a styrene-based monomer, or the like.

The polymer (A-2) preferably has at least a carboxylate group. This is because the crosslinked polymer particles containing the pigment can be stably dispersed due to the charge repulsion caused by the charge of the carboxylate group. The carboxylate group may be formed by neutralizing at least a part of the carboxyl 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 hydrogen carbonate, dipotassium carbonate, and sodium borate. Among these, alkali metal compounds are preferably used from the viewpoint that the dispersion stability of the crosslinked polymer particles containing the pigment is good and pigment aggregation can be suppressed even during the drying process of the ink, thereby obtaining printed matter with excellent print density and color reproducibility, and hydroxides such as sodium hydroxide and potassium hydroxide are particularly preferably used. The basic compounds listed above may be used alone or in combination of two or more types.

As the polymer (A-2), for example, a polymer having only carboxy groups (hereinafter referred to as polymer (A-2A)) may be used as it 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, the neutralization rate is preferably 10 to 200 mol%, more preferably 40 to 160 mol%, from the viewpoint of improving the dispersion stability of the pigment. It is particularly preferably 60 to 120 mol%. The neutralization rate can be calculated by the following formula 3.

The "acid value of the polymer" also found in formula 3 above can be measured by standard methods. For example, about 1 g of sample is precisely weighed and placed in an Erlenmeyer flask, and 50 ml of a distilled water/dioxane mixture (mixture mass ratio: distilled water/dioxane = 1/9) is added and dissolved. The sample solution is then titrated with a 0.1 mol/L potassium hydroxide-ethanol solution (titer F) using a potentiometer (Kyoto Electronics Manufacturing Co., Ltd.'s "potentiometric automatic titrator AT-710M"), and the amount of potassium hydroxide-ethanol solution (α (mL)) required to reach the titration endpoint is measured. The acid value of the polymer (mg KOH/g) can then be calculated using formula 4 below.

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

In the above formula 4, S is the amount (g) of sample polymer collected, α is the amount (ml) of 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.

The acid value of polymer (A-2), which can be measured by the method described above, is preferably 60 to 180 mgKOH/g, more preferably 70 to 160 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 a printed matter with excellent print density and color reproducibility. The acid value is particularly preferably 80 to 150 mgKOH/g.

The weight average molecular weight (Mw) of the polymer (A-2) is preferably 5,000 to 100,000. By making the weight average molecular weight 5,000 or more, it is possible to obtain favorable dispersion stability, and by making it 100,000 or less, it is possible to obtain good ejection stability. The weight average molecular weight is more preferably 10,000 to 50,000, and even more preferably 15,000 to 35,000.

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

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 suitable range for an inkjet ink, 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.

<Preparation of Aqueous Dispersion of Pigment-Containing Crosslinked Polymer Particles (A)>
As a method for producing an aqueous dispersion of the pigment-containing crosslinked polymer particles (A), for example, there can be mentioned a method in which a neutralization treatment step, a dispersion treatment step, and a crosslinking treatment step are carried out in this order as shown below.
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 part of the carboxy groups (neutralization step). The polymer obtained after the neutralization step is used as polymer (A-2) in the subsequent steps. The polymer (polymer (A-2)) obtained after the neutralization step is in the state of an aqueous solution (a solution containing an aqueous medium and components dispersed and/or dissolved in the aqueous medium).
Next, the pigment is added to the aqueous solution of the polymer (A-2), and the two are mixed, and then a dispersion treatment is further performed (dispersion treatment step). The dispersion treatment step produces an aqueous dispersion of pigment particles (crosslinked polymer particle precursor) having the polymer (A-2) chemically adsorbed on at least a part of the surface thereof.
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 the crosslinking treatment step, an aqueous dispersion of the crosslinked polymer particles (A) containing the pigment can be produced.

<<Distributed Processing>>
In dispersing the pigment, it is preferable to pre-disperse (premix) the pigment and the polymer (A-2) using a commonly used mixing and stirring device such as a disperser, and then disperse (main dispersion) using a conventionally known dispersing device. By performing pre-dispersion before main dispersion, a pigment dispersion liquid with a uniform particle size can be obtained.
The dispersing machine used for the main dispersion of the pigment may be any commonly used dispersing machine, such as 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 crushing and pulverizing coarse pigment particles. Examples of bead mills include a super mill, a sand grinder, an agitator mill, a grain mill, a dyno mill, a pearl mill, and a cobol mill (all trade names), and any of these can be suitably used.

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

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.

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.

The "average particle size" mentioned above refers to the median diameter based on volume, and can be measured by dynamic light scattering. For example, it can be measured using Microtrac Bell's "Nanotrac UPA-EX150" in a 25°C environment.

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 tend to become carboxylate groups, and favorable charge repulsion can enhance the dispersion stability of the crosslinked polymer particles (A). A more preferable pH value is 9 to 11.

The pH of the aqueous dispersion can be measured by standard methods. For example, it can be measured in a 25°C environment using a tabletop pH meter "F-71" (manufactured by Horiba, Ltd.) that uses a pH electrode "6337-10D" (manufactured by Horiba, Ltd.).

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

<<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 a printed matter excellent in dot circularity, print density, and color reproducibility while suppressing whiteout and color mixing bleeding. In particular, from the viewpoint of obtaining a printed matter having excellent print density and color reproducibility, n in the general formula 1 is an integer of 20 to 100, more preferably 25 to 65, and particularly preferably 25 to 50. Since the compound (B-1) contains a hydrophobic portion and a hydrophilic portion, it can exhibit suitable compatibility in the ink with the highly hydrophobic surfactant (B-2).

From the viewpoint of improving the affinity with the surfactant (B-2) described later and obtaining a printed matter with excellent dot circularity, the group represented by R ¹ in general formula 1 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.

Furthermore, in terms of being able to suitably stabilize the surfactant (B-2) in the aqueous inkjet ink, making it easy to suppress white voids and color mixing in printed matter, obtaining printed matter having excellent print density and color reproducibility, and further improving the ejection stability of the aqueous inkjet ink, when the number of carbon atoms in the alkyl group represented by R ¹ in General Formula 1 is CE, the value of n in General Formula 1 is preferably an integer included 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 included between CE×1.60 and CE×3.50 (however, when CE×1.60 and CE×3.50 are integers, these integers are also included).

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 mixing 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 nonionic surfactant (B-2) described below.

The compound (B-1) may be obtained by synthesis using a conventional method, or a commercially available product may be used. Examples of commercially available products of 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 Sanonic series manufactured by Sanyo Chemical Industries Co., Ltd., and the Brownon series and Finesurf series manufactured by Aoki Oil Industries Co., Ltd., but are not limited to these.

The content of compound (B-1) is preferably 0.01 to 2 mass % of the total amount of the aqueous inkjet ink, and more preferably 0.1 to 1 mass %. By making the content 0.01 mass % or more, the above-mentioned effects of compound (B-1) can be exerted, and by making the content 2 mass % or less, the drying properties of the ink on poorly absorbent printing substrates can be made suitable.

<<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 indicate 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.

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 target material according to the following formula 5. Note that the smaller the HLB value, the more hydrophobic the material is, and the larger the HLB value, the more hydrophilic the material is.

HLB value = 20 x (sum of molecular weights of hydrophilic parts) ÷ (molecular weight of material) Formula 5

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

Acetylene diol surfactants are preferably used because they have excellent orientation speed to the interface, which improves the wettability and penetration of the ink and makes it easier to obtain printed matter without whiteout or color mixing. When using an acetylene diol surfactant 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 with 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, hexadeca-8-yne-7,10-diol, 4,7-dipropyl-deca-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 a printed matter having 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, hexadeca-8-yn-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.

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

On the other hand, silicone-based surfactants have a slower orientation speed to the interface than acetylene diol-based surfactants, but have a high ability to reduce surface tension and are evenly oriented to the interface, so they can be used preferably from the perspective of preventing color bleeding between dots and improving dot circularity. In this embodiment, the HLB value of the silicone-based surfactant is also calculated using the Griffin method.

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

In addition, 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 mixing and 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.

<<Gemini type silicone surfactants>>
In general, gemini surfactants have a structure in which surfactants having hydrophilic and hydrophobic structures are linked by a linking group (spacer) or a covalent bond. In the case of gemini silicon-based surfactants, for example, a siloxane chain (hydrophobic structure represented by -[SiR ¹ R ² -O]n-, where R ¹ and R ² are each an arbitrary organic group, and n is an integer of 2 or more) and a hydrophilic structure (for example, a polyether chain) have 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 linking groups or the like (for example, at least a portion of ^R1 and/or ^R2 in the structural formula of the siloxane chain 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 portion of the hydrophilic structures.

Gemini type surfactants have superior surface tension reducing ability compared to general surfactants. Therefore, by using a gemini type silicone surfactant, it is possible to achieve a better reduction in surface tension than with general silicone surfactants. As a result, it is possible to significantly improve the wettability of aqueous inkjet inks containing gemini type silicone surfactants, and in addition to improving the above-mentioned color mixing and bleeding between dots and dot roundness, it is possible to obtain printed matter with no blank spaces, excellent print density, and color reproducibility.

Commercially available examples of Gemini 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.

<<Polyether-modified silicone surfactants (excluding Gemini type silicone surfactants)>>
[0043] Examples of the polyether-modified silicone surfactant (excluding gemini type 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.

General formula 6

In general formula 6, p is an integer from 0 to 99, and q is an integer from 1 to 100. However, p+q is an integer from 1 to 100. Furthermore, R 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. However, when R ³ is a methyl group, p is 0. Furthermore, at least one of R ³ and R ⁴ has a structure represented by the following general formula 7 (R ³ and R ⁴ may both have a structure represented by the following general formula 7).

General formula 7

In general formula 7, r is an integer from 1 to 6, s is an integer from 1 to 50, and t is an integer from 0 to 50, where s+t is an integer from 1 to 100. ^R5 is either a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an acrylic group, or a methacrylic group. The addition pattern of the ethylene oxide groups and propylene oxide groups in [ ] may be block or random.

The polyether-modified silicone surfactant represented by the above general formula 6 can be preferably used from the viewpoint of improving color mixing and bleeding between dots and white spots. In addition, a polyether-modified silicone surfactant in which R ⁴ in the above general formula 6 is a structure represented by general formula 7 and R ³ is not a structure represented by general formula 7 (also referred to as a "double-end polyether-modified silicone surfactant" in the present disclosure) is easily uniformly oriented at the interface, and in addition to improving color mixing and bleeding and white spots, the dot roundness is particularly improved, and therefore it can be particularly preferably used in the present invention.

Commercially available examples of the above-mentioned silicone surfactants modified with polyether at both ends 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 Co., Ltd., TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, and TEGO Glide 450 manufactured by Evonik Degussa Co., Ltd., and Silface SWP-001, Silface SAG003, and Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd.

In addition, examples of commercially available polyether-modified silicone surfactants in which R ³ in the above general formula 6 has a structure represented by general formula 7 and R ⁴ does not have a structure represented by general formula 7 (also referred to as "side chain polyether-modified silicone surfactants" in the present disclosure) 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 Co., Ltd., and TEGO Wet 240, TEGO Wet 250, and TEGO Wet 260 manufactured by Evonik Degussa. Wet 260, TEGO Wet 270, TEGO 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.

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

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 at 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, and the ink can be uniformly wetted and spread even on a poorly absorbent printing substrate, and the penetration is also improved. In addition, a printed matter with excellent dot circularity can be obtained while suppressing whiteout and color mixing bleeding. In addition, by using the compound (B-1) and the surfactant (B-2) in the above-mentioned ratio, 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, so that a printed matter having excellent print density and color reproducibility can be obtained even after drying. Furthermore, by setting the above-mentioned suitable ratio, it is possible to suppress non-uniform orientation of the surfactant (B-2) on the nozzle end surface of the inkjet head, making it possible to obtain stable ejection properties.

<Organic Solvent>
The ink of the present 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 said adjustments, and ensuring and improving the ejection stability from the inkjet nozzle, the compounds described below are suitably selected as the organic solvent.

In this disclosure, "organic solvent" refers to an organic compound that is liquid at 45°C.

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 of 20 to 30 mN/m at 25°C.

In this disclosure, "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, it can be measured using, for example, a surface tensiometer (Kyowa Interface Science Co., Ltd.'s "CBVP-Z") using a platinum plate in an environment of 25°C.

In addition, from the viewpoint of having suitable compatibility with the above-mentioned surfactants, being able to impart excellent wettability and permeability to the ink even on poorly absorbent printing substrates, and being able to obtain printed matter free of white spots 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.

In addition, in this disclosure, "(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.

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.

Furthermore, 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 (poly)alkylene glycol monoalkyl ether solvents having 5 to 9 carbon atoms, from the viewpoint that they provide aqueous inkjet inks with excellent drying properties even on poorly absorbent printing substrates and also provide printed matter with excellent print quality.

The above "(poly)propylene glycol monoalkyl ether" refers to "propylene glycol monoalkyl ether" and/or "polypropylene glycol monoalkyl ether."

In the inkjet ink of this embodiment, organic solvents other than the compounds exemplified above can also be suitably used. Examples include 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.

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

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

Specific examples of the high-boiling organic solvents having a boiling point of 230°C or higher at 1 atmosphere as mentioned above 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, those that also fall under the category 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.

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

The organic solvent used in the ink of this embodiment preferably has a boiling point (weighted average value) at 1 atmosphere of 100 to 230°C, more preferably 120 to 220°C, and particularly preferably 150 to 210°C. If the boiling point (weighted average value) is 100°C or higher, the ink can be prevented from drying on the inkjet head, improving the ejection stability. If the boiling point (weighted average value) is 230°C or lower, poor drying does not occur even on a poorly absorbent printing substrate, and color mixing and bleeding does not occur due to the remaining organic solvent. As a result, it is possible to obtain a printed matter with excellent drying properties and print quality. Furthermore, if the boiling point (weighted average value) is 230°C or lower, the abrasion resistance is improved even in printed matter on a poorly absorbent printing substrate such as coated paper. In addition, the compatibility between the above-mentioned surfactant and the crosslinked polymer is not deteriorated by the remaining organic solvent, and the print density and color reproducibility of the printed matter are improved.

In this disclosure, the term "boiling point (weighted average value) of organic solvents" refers to the boiling point of the organic solvent when only one type of organic solvent is contained in the target 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 ratio of the organic solvent to the total content.

The total content of organic solvents contained 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 contained in the aqueous inkjet ink of this embodiment is more preferably 10 to 35% by mass based on the total amount of the aqueous inkjet ink, and particularly preferably 15 to 30% by mass.

<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.

The "binder resin" in this disclosure refers to a resin used to bond the ink film to the printing substrate, and the resin forms a film during the drying process and/or the resin molecules become entangled with each other, thereby improving the scratch resistance and drying properties of the ink film. From this perspective, for example, the resin that is primarily contained in the ink (specifically, a resin that occupies 50% by mass or more of the total amount of resin contained in the ink, more preferably a resin that occupies 60% by mass or more, and particularly preferably a resin that occupies 70% by mass or more) functions as the binder resin. Note that the crosslinked polymer that constitutes the above-mentioned pigment-containing crosslinked polymer particles (A) may also serve as the binder resin.

Water-soluble resins and resin particles are generally known forms of binder resins, and in this disclosure, either one may be used alone or both may be used in combination. Here, the above-mentioned "resin particles" refers to a form of water-insoluble resin (a resin that is not water-soluble), and refers to particles with 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.

When the aqueous inkjet ink of this embodiment contains a binder resin, it is preferable to use a water-soluble resin from the viewpoints of improving the compatibility with the above-mentioned surfactant, thereby obtaining a printed matter with excellent print density and color reproducibility, and further, improving the speed at which the ink film is formed during the ink drying process, thereby obtaining a printed matter with excellent drying properties and print quality.

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 the above acid value, it is possible to improve the ink film formation speed even on a poorly absorbent printing substrate, and to obtain a printed matter with excellent print quality and drying properties. Controlling the acid value as described above is also effective in improving the ejection stability of the aqueous inkjet ink.

The acid value of the binder resin can be measured using the same method as the acid value of the polymer (A-2) described above.

In addition, 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, from the viewpoint of improving the abrasion resistance and ejection stability of the printed matter.

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 of the dried resin is weighed on an aluminum pan, and the aluminum pan is set in a holder in a DSC measurement device (for example, Shimadzu Corporation's "DSC-60Plus") as a test container. Measurements are then performed under conditions of a temperature rise of 5°C/min, and the temperature of the intersection between the low-temperature baseline and the tangent at the inflection point, as read from the resulting DSC chart, is taken as the glass transition temperature in this disclosure.

<<Resin particles>>
When resin particles are used as the binder resin, the types of resins that can be used as the resin particles include acrylic, epoxy, urethane, styrene butadiene, polyether, polyamide, polyester, vinyl chloride, or copolymers thereof (excluding those containing siloxane chains). Among them, from the viewpoint of improving 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.

The resin particles can be synthesized by a conventional 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.

In this embodiment, the content of the resin particles relative to the total amount of 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 keeping the amount of resin particles within the above range, it is possible to obtain an aqueous inkjet ink that has excellent abrasion resistance and drying properties for printed matter without reducing storage stability or ejection stability.

<<Water-soluble resin>>
On the other hand, when resin particles are used as the binder resin, the types of resins that can be used as the water-soluble resin include acrylic, urethane, styrene butadiene, vinyl chloride, maleic acid, polyester, etc. (excluding those containing siloxane chains). Among them, from the viewpoint of obtaining a printed matter with excellent abrasion resistance and print quality, and further obtaining an ink with excellent drying properties and ejection stability, it is preferable to use one or more resins selected from the group consisting of acrylic and urethane resins.

The water-soluble resin can be synthesized by a conventional method, or a commercially available product can be used. There are no particular limitations on the structure, and resins having a random structure, block structure, comb structure, star structure, etc. can be used. Among them, resins having a block structure or comb structure are preferable from the viewpoint of fully exerting the properties of the polymerizable monomers that make up the binder resin. Each unit that makes up the block structure and comb structure may be formed from a single polymerizable monomer, or may be a random copolymer of multiple types of polymerizable monomers.

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 the inkjet nozzle and obtaining printed matter with excellent abrasion resistance for a variety of printing substrates, and is more preferably 8,000 to 45,000, and particularly preferably 10,000 to 40,000, from the viewpoint of improving compatibility with the above-mentioned surfactants and obtaining printed matter with excellent print density and color reproducibility.

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

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 keeping the amount of water-soluble resin within the above range, it is possible to obtain a water-based inkjet ink that has excellent abrasion resistance and drying properties for printed matter without reducing dispersion stability or ejection stability.

<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.

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

<Other ingredients>
In addition to the above-mentioned components, the ink of this embodiment may contain additives such as infrared absorbing agents, ultraviolet absorbing agents, preservatives, etc., as necessary to provide the ink with desired physical properties. The total amount of these additives is preferably 0.01 to 10% by mass based on the total mass of the ink.

<Ink set>
The ink of this embodiment may be used in a single color, but may also be used as an ink set combining multiple colors according to the application. Although the combination is not particularly limited, a full-color image can be obtained by using three colors, cyan, yellow, and magenta. In addition, the blackness can be improved by adding black ink, and the visibility of characters, etc. Furthermore, it is possible to improve color reproducibility by adding colors such as orange and green. When printing on a printing substrate other than white, a clear image can be obtained by using white ink in combination.

<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.

First, a pigment dispersion is obtained by the method described above. Next, 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, and the mixture is stirred and, if necessary, filtered to produce the ink of the present disclosure.

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 the desired particle size distribution include the above-mentioned method of reducing the size of the grinding media of the disperser, the method of increasing the packing rate of the grinding media, the method of extending the processing time, the method of classifying the ink after grinding using a filter or centrifuge, and combinations of these methods. The average particle size of the ink can be measured by the same method as that for the average particle size of the crosslinked polymer particles (A) containing the pigment.

<Printing base material>
The ink of this embodiment is particularly suitable for use with poorly absorbent printing substrates. A poorly absorbent printing substrate is a printing substrate that does not absorb water or absorbs water slowly, specifically, a substrate having an absorption coefficient for water of 0 to 0.6 ml/m ² msec ^1/2 measured by the Bristow method (J. TAPPI Paper Pulp Test Method No. 51-87). The absorption coefficient can be measured, for example, by using an automatic scanning absorptiometer manufactured by Kumagai Riki Kogyo Co., Ltd. Specifically, the absorption coefficient is determined by the gradient of a straight line obtained by the least squares method using the above device and water from a relationship diagram between the amount of water absorbed (ml/m ² ) and the square root of the contact time (msec ^1/2 ) obtained during a contact time of 100 to 1000 milliseconds.

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, rigid PVC, flexible 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.

<Printing method>
The inkjet ink of the present 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 preferably dried by a drying method described below, and then becomes a printed matter (having at least an ink film layer on the printing substrate).

<<Drying method>>
A printing device (inkjet printer) equipped with the inkjet ink of this embodiment and used in the inkjet printing method is preferably equipped with a mechanism for drying the ink on the printing substrate. As the drying method, only one of the following may be adopted: 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 electromagnetic waves. Alternatively, a combination of two or more of these may be used. For example, by using an infrared drying method (a method of irradiating electromagnetic waves) and a hot air drying method (a method of directly contacting the ink with a heat source) in combination, the ink can be dried more quickly than when each method is used alone.
When using a hot air drying method in which the ink is brought into direct contact with a heat source, from the viewpoint of preventing bumping of the liquid components contained in the ink and obtaining a printed matter having excellent print density, color reproducibility, and print image quality, the hot air temperature is preferably set to 50 to 250° C. When using a substrate heating method (a method in which the non-printed surface of a printing substrate is brought into contact with a heat source), in which the ink is brought into indirect contact with a heat source, from the same viewpoint as in the case of the hot air temperature described above, the temperature of the heat source is preferably set to 35 to 100° C.

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

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

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

<Production Example of Dispersion Resin 1>
A gas inlet tube, a thermometer, a condenser, and a reaction vessel equipped with a stirrer were charged with 93.4 parts of methyl ethyl ketone and replaced with nitrogen gas. After heating the contents in the reaction vessel to 110 ° C., a mixture of 23 parts of acrylic acid, 47 parts of methyl methacrylate, and 30 parts of lauryl methacrylate, which are polymerizable monomers; and 6 parts of V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dropped into the reaction vessel over 2 hours. After the dropwise addition was completed, the temperature of the contents in the reaction vessel was maintained at 110 ° C., and the polymerization reaction was continued for 3 hours, after which 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.
Then, 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 the above formula 3, and an aqueous potassium hydroxide solution with a concentration of 48% by mass 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 into carboxylate groups (neutralization treatment). Then, ion-exchanged water was added so that the solid content concentration became 20%, and the solution was heated to 50° C. and stirred for 1 hour while maintaining the temperature at 50° C., thereby obtaining an aqueous solution of dispersion resin 1.

<Production Examples of Pigment Dispersion Resins 2 to 8>
Except for using the polymerizable monomers shown in Table 1 as the polymerizable monomers, aqueous solutions of dispersion resins 2 to 8 (solid concentration 20% each) were obtained using the same raw materials and operations as in the case of dispersion resin 1.

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

<Production Example of Dispersion Resin 9>
In a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer, 26 parts of 1-octadecene, 18 parts of maleic anhydride, 56 parts of N-phenylmaleimide, and 100 parts of methyl ethyl ketone, which are polymerizable monomers, were charged, and the contents in the reaction vessel were replaced with nitrogen gas, and the contents 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 dropped over 2 hours. Thereafter, the temperature of the contents was kept at 130°C, and stirring was continued for another 1 hour to carry out a polymerization reaction. In addition, after the start of the polymerization reaction, the solid content concentration of the contents was measured at regular intervals, and the ratio (polymerization conversion rate) to the solid content concentration when it was assumed that all the charged polymerizable monomers had been polymerized 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 as a catalyst were added. After that, the contents in the reaction vessel were heated to 80°C while stirring, and after reaching 80°C, the temperature was maintained for 4 hours to open the maleic anhydride ring, thereby obtaining a dispersion resin 9 precursor having only carboxyl groups as hydrophilic groups. The weight average molecular weight of the obtained dispersion resin 9 precursor was 20,000, and the acid value was 206 mgKOH/g.
Then, the amount of potassium hydroxide required to achieve a neutralization rate of 100% was calculated using the acid value of the dispersion resin 9 precursor and the above formula 3, and an aqueous potassium hydroxide solution with a concentration of 48% by mass containing an amount of potassium hydroxide equal to the calculated amount was added to convert the carboxy groups present in the dispersion resin 9 precursor into carboxylate groups (neutralization treatment). Then, ion-exchanged water was added so that the solid content concentration became 20%, and the solution was 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.

<Production Examples of Dispersion Resins 10 to 25>
Except for changing the type and amount of the polymerizable monomer used as shown in Table 2, the synthesis was carried out using the same raw materials and operations as in the case of dispersion resin 9, and aqueous solutions of dispersion resins 10 to 25 (each with a solid content of 20%) were obtained.

Table 2 also lists the raw materials used in the above-mentioned Dispersion Resin 9, and 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

<Production Example of Water 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 Toyo Color Co., Ltd.) as a pigment, 25 parts of an aqueous solution of dispersion resin 1 (solid concentration 20%), and 55 parts of ion-exchanged water were charged into a mixing vessel. After all the raw materials were charged and preliminary dispersion was performed with a stirrer, the main dispersion was performed using a 0.6 L volume Dyno Mill filled with 1,800 g of zirconia beads having a diameter of 0.5 mm. After the main dispersion, 33.3 parts of ion-exchanged water was added to the obtained mixture, and further, while heating the mixture at 60 ° C., a part of the ion-exchanged water and methyl ethyl ketone were distilled off under reduced pressure. Then, by using ion-exchanged water, the pigment concentration was adjusted to 15%, and an aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1) was obtained.

<Production Example of Aqueous Dispersion of Cyan Pigment-Containing Crosslinked Polymer Particle 1 (CP1)>
93.3 parts of the aqueous dispersion of the cyan pigment-containing crosslinked polymer particle precursor 1 (CB1) obtained by the above-mentioned method, 1.4 parts (amount that the functional group content represented by the above formula 2 is 90 mol%) of Denacol EX-321 (epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140 g / eq.) which is the compound (A-1) (crosslinking agent), and 5.3 parts of ion-exchanged water were charged into 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 continuing to stir for 3 hours to carry out a crosslinking reaction. Thereafter, the reaction vessel was cooled until the internal temperature was room temperature (about 25 ° C.), and then ion-exchanged water was added to adjust the solid content concentration, and an aqueous dispersion of the cyan pigment-containing crosslinked polymer particle 1 (CP1) in which the dispersion resin 1 was crosslinked (pigment concentration 14%) was obtained.

<Production Example of Aqueous Dispersion 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 methods as those for the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1), except that the dispersing resin was changed to each of dispersing resins 2 to 25. Note that the pigment concentration in all aqueous dispersions was 15%.

<Production Examples 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 the 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%.

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.

<Production Examples 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 in 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 Color Materials 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%.
Further, aqueous dispersions of magenta pigment-containing crosslinked polymer particle precursors 2 to 25 (MB2 to MB25) were obtained using the same raw materials and methods as those for the aqueous dispersion of magenta pigment-containing crosslinked polymer particle precursor 1 (MB1), except that the dispersing resin was changed to each of dispersing resins 2 to 25. Note that the pigment concentration in all aqueous dispersions was 15%.

<Production Example of Magenta Pigment-Containing Crosslinked Polymer Particle 1 (MP1)>
An aqueous dispersion of magenta pigment-containing crosslinked polymer particles 1 (MP1) was obtained using the same raw materials and method as the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that the 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%.

<Production Examples 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 the magenta pigment-containing crosslinked polymer particle precursor, the crosslinking agent (compound (A-1)), and the ion-exchanged water used were changed as shown in Table 4. Note that the pigment concentration in all aqueous dispersions was 14%.

<Production Examples 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 in 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%.
Further, aqueous dispersions of yellow pigment-containing crosslinked polymer particle precursors 2 to 25 (YB2 to YB25) were obtained using the same raw materials and methods as those for the aqueous dispersion of yellow pigment-containing crosslinked polymer particle precursor 1 (YB1), except that the dispersing resin was changed to each of dispersing resins 2 to 25. Note that the pigment concentration in all aqueous dispersions was 15%.

<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 the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that the 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%.

<Production Examples 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 the yellow pigment-containing crosslinked polymer particle precursor, the crosslinking agent (compound (A-1)), and the ion-exchanged water used were changed as shown in Table 5. Note that the pigment concentration in all aqueous dispersions was 14%.

<Production Examples of Black Pigment-Containing Crosslinked Polymer Particle Precursors 1 to 25 (KB1 to KB25)>
Except for using PrinteX85 (carbon black manufactured by Orion Engineered Carbons) as the pigment, an aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1) was obtained using the same raw materials and method as in the aqueous dispersion of cyan pigment-containing crosslinked polymer particle precursor 1 (CB1). The pigment concentration of the aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1) was 15%.
In addition, aqueous dispersions of black pigment-containing crosslinked polymer particle precursors 2 to 25 (KB2 to KB25) were obtained using the same raw materials and methods as those for the aqueous dispersion of black pigment-containing crosslinked polymer particle precursor 1 (KB1), except that the dispersing resin was changed to each of dispersing resins 2 to 25. The pigment concentration in all aqueous dispersions was 15%.

<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 the aqueous dispersion of cyan pigment-containing crosslinked polymer particles 1 (CP1), except that the 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%.

<Production Examples 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 the black pigment-containing crosslinked polymer particle precursor, the crosslinking agent (compound (A-1)), and the ion-exchanged water used were changed as shown in Table 6. Note that the pigment concentration in all aqueous dispersions was 14%.

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

<Production Examples of Binder Resins 2 to 10>
Except for changing the type and amount of the polymerizable monomer used as shown in Table 7, aqueous solutions of binder resins 2 to 10, which have a random structure and are water-soluble resins, were obtained using the same raw materials and operations as in the case of binder resin 1.
In all of the aqueous solutions, the solids concentration was 40%.

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

<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 a polymerizable monomer, and the mixture was reacted at 80° C. for 2 hours and reprecipitated to obtain a first block copolymer to which iodine was added. 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 mixture was reacted at 80° C. for 2.5 hours and reprecipitated to replace the iodine-added site of the first block with a second block consisting of styrene, methyl methacrylate, and 2-ethylhexyl acrylate. Then, ion-exchanged water was added to the mixture and 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.

<Production Example of Binder Resin 12>
A reaction vessel equipped with a thermometer, a condenser, a stirrer, and a 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 prepare an emulsion.
Five portions of the emulsion were taken and added to the reaction vessel. After the addition, the reaction vessel was heated until the internal temperature reached 60° C., and the inside of the reaction vessel was fully replaced with nitrogen gas, and 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 start the polymerization reaction. After the polymerization reaction started, 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 dropped over 1.5 hours while maintaining the internal temperature of the reaction vessel at 60° C. After the dropwise addition was completed, stirring was continued for another 2 hours. After that, the internal temperature of the reaction vessel was cooled to 30° C., and diethylaminoethanol was added until the pH of the contents reached 8.5. Then, ion-exchanged water was added to adjust the solid content concentration to 40%, thereby obtaining an aqueous dispersion of binder resin 12, which is resin particles. The acid value of the obtained binder resin 12 was 3 mgKOH/g.

<Production of Water-Based Inkjet Inks>
The raw materials shown 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 the raw materials were added, the contents were stirred until sufficiently uniform, and then filtered through a 0.8 μm membrane filter to remove coarse particles that may cause clogging of the inkjet head, thereby preparing an aqueous inkjet ink.
In preparing the aqueous inkjet inks, pigment-containing crosslinked polymer particles or pigment-containing crosslinked polymer particle precursors (cyan, magenta, yellow, black) having the same numbers but different colors were used to prepare a set of aqueous inkjet inks of four colors, cyan, magenta, yellow, and black. The prepared set of four ink colors (ink set) was used in the evaluations shown below.

Details of the abbreviations and product 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: 27 mN/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: 27 mN/m)
PnP: Propylene glycol monopropyl ether (boiling point 150° C. at 1 atmosphere, surface tension at 25° C.: 26 mN/m)
PnB: Propylene glycol monobutyl ether (boiling point at 1 atmosphere: 170° C., surface tension at 25° C.: 26 mN/m)
DEG: Diethylene glycol (boiling point at 1 atmosphere: 245°C, surface tension at 25°C: 45 mN/m)
DPG: Dipropylene glycol (boiling point at 1 atmosphere: 232°C, surface tension at 25°C: 36 mN/m)
DPM: Dipropylene glycol monomethyl ether (boiling point at 1 atmosphere: 190°C, surface tension at 25°C: 29 mN/m)
DPnP: dipropylene glycol monopropyl ether (boiling point at 1 atmosphere: 212°C, surface tension at 25°C: 26 mN/m)
BDG: Diethylene glycol monobutyl ether (boiling point at 1 atmosphere: 230°C, surface tension at 25°C: 28 mN/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: A compound in which R ¹ in the general formula (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 in the general formula (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 in the general formula (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 represented by the general formula (1) 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 represented by the general formula (1) 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 represented by the general formula (1) 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 represented by the general formula (1) 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) in which R 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) in which R 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) in which R ¹ is 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) in which R ¹ is an alkyl group having 12 carbon atoms and n is 40 (CE×3.33) (manufactured by Aoki Oil 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 in the general formula (1) (manufactured by Kao Corporation, solid content 100%, HLB = 14.8)
Tergitol TMN-10: a compound represented by the general formula (1) 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) in which R 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: Acetylene diol surfactant (2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB=3.0) manufactured by Evonik Japan
Surfynol DF110D: Acetylene diol surfactant manufactured by Evonik Japan (2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, HLB=2.7)
Surfynol 440: acetylene diol surfactant manufactured by Evonik Japan (ethoxy compound of Surfynol 104, ethylene oxide addition mole number 3.5, HLB = 8.1)
Surfynol 465: acetylene diol surfactant manufactured by Evonik Japan (ethoxy compound of Surfynol 104, ethylene oxide added mole number 10, HLB = 13.2)
Dynol 604: ethoxy compound of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, average number of moles of ethylene oxide added: 4, HLB = 8.0)
TEGO Wet 240: Side chain polyether modified silicone surfactant manufactured by Evonik Japan (HLB: 5 to 7, R ³ in the above general formula 6 is the structure represented by the above general formula 7, and R ⁴ is not the structure represented by the above general formula 7)
TEGO Wet 270: Side chain polyether modified silicone surfactant manufactured by Evonik Japan (HLB: 2 to 4, R ³ in the above general formula 6 is the structure represented by the above general formula 7, and R ⁴ is not the structure represented by the above general formula 7)
TEGO Glide 440: Silicone surfactant modified with polyether at both ends, manufactured by Evonik Japan (HLB: 3 to 5, R ⁴ in the above general formula 6 is a structure represented by the above general formula 7, and R ³ is not a structure represented by the above general formula 7)
BYK333: Silicone surfactant modified with polyether at both ends, manufactured by BYK-Chemie (HLB: 10.3 to 12, R ⁴ in the above general formula 6 is a structure represented by the above general formula 7, and R ³ is not a structure represented by the above general formula 7)
TEGO Twin 4100: Gemini type silicone surfactant (HLB: 0 to 2) manufactured by Evonik Japan

[Examples 1 to 161, Comparative Examples 1 to 18]
The above water-based inkjet ink (set) was used to carry out the following evaluations. The evaluation results are shown in Table 8 above.

<Evaluation 1: Evaluation of white spots>
An inkjet ejection device equipped with four Kyocera inkjet heads (KJ4B-1200) was placed in a 25°C environment. Next, the inkjet heads were filled with the inks constituting the ink set so that the printing order in the inkjet printing device was black, cyan, magenta, and yellow. After that, a nozzle check pattern was printed, and after confirming that the inks were normally ejected from all the nozzles, the device was left as it was for one minute. After that, solid printing was performed with a printing rate of 100% on the printing substrate shown below using only one of the inks 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 on which the ink was printed was placed in an air oven at 70°C and dried for one minute to obtain a solid print. Then, the degree of whiteout of the solid print was evaluated by visually checking and using a magnifying glass. Two types of printing substrates were used: OK Topcoat+ paper manufactured by Oji Paper Co., Ltd. and UPM Finesse Gloss paper manufactured by UPM Co., Ltd., and evaluation was performed for each of them. The evaluation criteria were as follows, with AA, A, and B ratings being in the practical range. Solid prints were created using inkjet inks of four colors, cyan, magenta, yellow, and black, and blank areas were 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 white spots were observed with the naked eye or with a magnifying glass. A: A slight white spot was observed with a magnifying glass, but no white spots were observed with the naked eye. B: A slight white spot was observed with the naked eye. C: A clear white spot was observed with the naked eye.

<Evaluation 2: Evaluation of color mixing and bleeding>
Using the inkjet printing device used in the above evaluation 1, a superimposed gradation image was printed under the same printing conditions and using the same type of printing substrate as in the above evaluation 1, and using all the inks installed in the inkjet printing device. The "superimposed gradation image" is an image in which the printing rate of one color of ink 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 overlapping gradation image, the printing substrate on which the ink was printed was placed in an air oven at 70° C. and dried for 1 minute to obtain an overlapping gradation print. The degree of color bleeding in the overlapping gradation print was then evaluated by visual inspection and a magnifying glass. The evaluation criteria were as follows, with AA, A, and B ratings being in the range of practical use.
AA: No mixed color bleeding was observed in any area with a total print rate of 40 to 240%. A: No mixed color bleeding occurred in areas with a total print rate of 200% or less, but mixed color bleeding was observed in areas with a total print rate of more than 200% and less than 240%. B: No mixed color bleeding occurred in areas with a total print rate of 160% or less, but mixed color bleeding was observed in areas with a total print rate of more than 160% and less than 200%. C: No mixed color bleeding occurred in areas with a total print rate of 120% or less, but mixed color bleeding was observed in areas with a total print rate of more than 120% and less than 160%. D: Mixed color bleeding was observed in areas with a total print rate of 120% or less.

<Evaluation 3: Evaluation of dot circularity>
Using the inkjet printing device used in the above evaluation 1, a monochromatic gradation image was printed using only one of the ink colors mounted on the inkjet printing device under the same printing conditions and using the same type of printing substrate as in the above evaluation 1. The above "monochromatic gradation image" is an image in which the printing rate is continuously changed from 5 to 60% within a specified area.
After printing the monochromatic gradation image, the printing substrate on which the ink was printed 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 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, indicating a good dot shape. The evaluation criteria were as follows, with AA, A, and B ratings being in the practical range.
AA: Circularity was 1 or more and 2 or less. A: Circularity was more than 2 and 3 or less. B: Circularity was more than 3 and 3.5 or less. C: Circularity was greater than 3.5.

<Evaluation 4: Evaluation of Print Density>
Using OK topcoat + paper as the printing substrate, the density of the solid print of each color created in the above evaluation 1 was measured with a spectrophotometer ("eXact Advance" manufactured by X-rite Corporation) 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 practical 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 created using the ink set of Comparative Example 1. A: For the color that showed the smallest difference from the print density of a solid print of the same color created 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 from the print density of a solid print of the same color created using the ink set of Comparative Example 1, the difference value was 0 or more and less than 0.15. C: For the color that showed the smallest difference from the print density of a solid print of the same color created 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 created using the ink set of Comparative Example 1 was greater).

<Evaluation 5: Evaluation of color reproduction range>
Using the inkjet printing device used in the above evaluation 1, and using the three ink colors cyan, magenta, and yellow installed in the inkjet printing device, a secondary color solid image was printed under the same printing conditions as in the above evaluation 1. Note that OK Topcoat + paper manufactured by Oji Paper Co., Ltd. was used as the printing substrate. The "secondary color solid image" is an image in which three solid images of red solid image (a solid image using magenta ink superimposed on a solid image using yellow ink), blue solid image (a solid image using cyan ink superimposed on a solid image using magenta ink), and green solid image (a solid image using cyan ink superimposed on a solid image using yellow ink).
After printing the secondary color solid image, the ink-printed OK topcoat + paper was placed in a 70°C air oven and dried for 1 minute to obtain a secondary color solid print. The hue (a* value and b* value) of each solid color of the secondary color solid print was measured using a spectrophotometer (X-rite's "eXact Advance"). The hue measurement conditions were the same as those in Evaluation 4. The color reproduction range was evaluated using the saturation (C value) calculated by adding the squared value of the a* value and the squared value of the b* value and taking the square root (√(a*2+b*2)). The larger the C value, the wider the color reproduction range. The evaluation criteria were as follows, with AA, A, and B ratings being practical 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 any of the above evaluation criterion AA, the following evaluation criterion B, and the following evaluation criterion C. B: Did not meet the above evaluation criterion AA or the following evaluation criterion C, and met one or more of the following requirements: "The C value of red was 85 or more and less than 90,""The C value of blue was 50 or more and less than 55," and "The C value of green was 70 or more and less than 75." C: Did not meet the above evaluation criterion AA, and met one or more of the following requirements: "The C value of red was less than 85,""The C value of blue was less than 50," and "The C value of green was less than 70."

<Evaluation 6: Evaluation of drying property>
Using the inkjet printing device used in Evaluation 1, a half-overlapped solid image was printed under the same printing conditions as in Evaluation 1, using all the inks installed in the inkjet printing device. Oji Paper OK Topcoat+paper was used as the printing substrate. The "half-overlapped solid image" refers to an image in which an image printed on one side with a printing rate of 60% for one color of ink is overlaid in the order of black, cyan, magenta, and yellow. Therefore, the total printing rate of the half-overlapped solid image is 240%.
After printing the overlapping half solid image, the OK topcoat + paper on which the ink was printed was placed in an air oven at 70°C, and the print was taken out at regular intervals and touched with fingers to evaluate drying properties. The evaluation criteria were as follows, with AA, A, and B being practical ranges.
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 the 30 second mark. 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 the 1 minute mark. C: After 1 minute 30 seconds of drying, there was a tackiness when touched with the finger, and the print was not dry.

<Evaluation 7: Discharge Stability>
Using the inkjet printing device used in the above evaluation 1, the inks constituting the ink set were filled into the inkjet head, and then a nozzle check pattern was printed to confirm that the ink was ejected normally from all the nozzles. Then, 100 A4 size solid images were printed continuously using the inks mounted in the above inkjet printing device. After printing, a nozzle check pattern was printed again, and the number of nozzles missing was visually counted to evaluate the ejection stability. The above evaluation was performed under two head driving frequency conditions of 40 kHz and 64 kHz. The evaluation criteria were as follows, and AA, A, and B were considered to be in the practical range. The evaluation was performed for each of the four inks constituting the ink set. Table 8 also shows the evaluation criteria for the color with the worst evaluation result.
AA: No missing nozzles at all A: 1 to 3 missing nozzles B: 4 to 9 missing nozzles C: 10 to 49 missing nozzles D: 50 or more missing nozzles

The aqueous inkjet inks of Examples 1 to 161, which have the aqueous inkjet ink configuration of the present disclosure, were confirmed to have a practically usable level of quality in terms of print image quality, print density, color reproducibility, and ejection stability on poorly absorbent printing substrates.

Furthermore, by comparing Examples 2, 3, and 4, it can be confirmed that the print density, color reproducibility, and drying properties of the printed matter are improved by setting 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, by comparing Examples 29, 30, and 31, it can be confirmed that the dot bleeding and drying properties of the printed matter, as well as the ejection stability, are improved by using it in combination with a binder resin having a specific acid value, specifically an acid value of 50 mgKOH/g or less (preferably 40 mgKOH/g or less). From these results, it can be confirmed that the acid value of the resin (polymer (A-2) and binder resin) contained in the aqueous inkjet ink of the present disclosure affects the drying properties as well as the print image quality, color reproducibility, and print image quality.

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 use resins (polymers) having suitable acid values as the polymer (A-2) and binder resin, and further use a gemini type silicon-based surfactant (TEGO Twin 4100) or a silicon-based surfactant modified at both ends with polyether (TEGO Glide 440) as the nonionic surfactant (B-2). All of these aqueous inkjet inks are rated at the "AA" level. From these results, it was confirmed that the use of a silicon-based surfactant having a specific structure as the nonionic surfactant (B-2) is extremely suitable.

On the other hand, in Comparative Examples 1 and 4, which reproduce 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 is not the preferred blending ratio in this disclosure, and deterioration of print image quality was observed, which is presumed to be due to the imbalance of the affinity of the nonionic surfactant (B-2). In addition, since a pigment-containing crosslinked polymer particle precursor was used in Comparative Example 1, the dispersion resin that was detached from the pigment and liberated in the ink inhibited the orientation of the surfactant, which is also thought to have influenced the deterioration of print image quality. Furthermore, the presence of a dispersion resin to which a highly hydrophobic surfactant was adsorbed in the ink prevented practical ejection stability from being obtained. The same tendency was also observed in Comparative Examples 3 and 16, which used a non-crosslinked dispersion resin.

In addition, in Comparative Example 4, the acetylene diol surfactant Surfynol 104 was used as the nonionic surfactant (B-2), but since it did not contain compound (B-1), 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.

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, as in Comparative Example 4 above. In Comparative Examples 2, 6, 17, and 18, although they contain the compound (B-1) and the nonionic surfactant (B-2) as the surfactant (B), the ratio of the compound (B-1) to the nonionic surfactant (B-2) is outside the preferred range described above, and so again, print quality suitable for practical use was not obtained.

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 (9)

An aqueous inkjet ink comprising (A) pigment-containing crosslinked polymer particles and (B) a surfactant,
the crosslinked polymer particles (A) contain a crosslinked reaction product between a compound (A-1) having a plurality of functional groups in one molecule that react 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:
The ratio of the content of the compound (B-1) to the content of the nonionic surfactant (B-2) is from 1:1.2 to 1:20 in terms of mass ratio.
R ¹ -(O-CH ₂ -CH ₂ ) _n -OH General formula 1
(In the general formula 1, ^R1 represents a linear or branched alkyl group having 10 to 25 carbon atoms, and n is an integer of 20 to 100.) Further containing an organic solvent,
2. The water-based inkjet ink according to claim 1, 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. The aqueous inkjet ink according to claim 2, wherein the organic solvent comprises a (poly)propylene glycol monoalkyl ether solvent having 5 to 9 carbon atoms. The aqueous inkjet ink according to claim 1 or 2, wherein the acid value of the uncrosslinked polymer (A-2) is 60 to 180 mg KOH/g. 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) being 60 to 180 mgKOH/g. The aqueous inkjet ink according to claim 1 or 2, wherein the nonionic surfactant (B-2) having an HLB value of 1 to 10 includes a gemini type silicone surfactant and/or a silicone surfactant modified at both ends with polyether (excluding the gemini type silicone surfactant). The aqueous inkjet ink according to claim 1 or 2, further comprising an organic solvent, the organic solvent including a (poly)propylene glycol monoalkyl ether solvent having 5 to 9 carbon atoms, and the nonionic surfactant (B-2) having an HLB value of 1 to 10 including a gemini type silicon surfactant and/or a silicon surfactant modified at both ends with polyether (excluding the gemini type silicon surfactant). 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 silicon-based surfactant and/or a silicon-based surfactant modified at both ends with polyether (excluding the gemini type silicon-based surfactant). 　A printed matter printed with the aqueous inkjet ink according to claim 1 or 2.