Aqueous black inkjet ink and printed matter

Abstract

Provided is an aqueous black inkjet ink which comprises crosslinked-polymer particles (A) comprising carbon black and a crosslinked polymer (A-2) and an organic solvent (B). The carbon black has a pH of 6.0-10.0 and satisfies requirements concerning DBP oil absorption and specific surface area, and the crosslinked polymer (A-2) is one obtained by crosslinking an uncrosslinked polymer (A-1) having a carboxy group and / or a carboxylate group and having an acid value of 50-180 mgKOH / g. The aqueous black inkjet ink further has a specified content of a high-boiling-point organic solvent.

Description

Water-based inkjet black ink and printed materials

[0001] An embodiment of the present invention relates to a water-based inkjet black ink and a printed matter formed by printing the water-based inkjet black ink on a printing substrate.

[0002] Inkjet printing is a recording method in which droplets are directly ejected from fine nozzles and deposited on a printing substrate to obtain characters and / or images. Here, the term "image" includes solid images (images printed at 100% coverage so as to completely cover the surface of the printing substrate) and seamless images such as checkerboard images. Inkjet printing has become extremely popular due to its many advantages. Advantages of inkjet printing include low noise and easy operability of the device, easy and inexpensive full-color printing, and the ability to print on a variety of printing substrates without contact.

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

[0004] In particular, in the commercial printing market, consumer needs are becoming increasingly diverse, and there is a demand for printing on low-permeability substrates such as coated paper in addition to high-permeability substrates such as fine paper and plain paper. Thus, there is a demand for aqueous inkjet inks that can print on a variety of printing substrates with different liquid permeabilities.

[0005] However, aqueous inkjet inks generally have low viscosity. Therefore, when a substrate has high permeability, the aqueous inkjet ink penetrates the substrate, resulting in a decrease in print density. Furthermore, when a paper substrate is used as the printing substrate, the aqueous inkjet ink penetrates along the paper fibers, causing feathering. Feathering leads to a deterioration in print quality, such as the visibility of characters.

[0006] On the other hand, in the case of low-permeability substrates such as coated paper, aqueous inkjet inks have difficulty penetrating, and the pigments tend to remain on the surface of the printing substrate, making it easy to obtain high print density. However, in reality, if the surface of the aqueous inkjet ink film (ink film) is not smooth after the aqueous inkjet ink on the printing substrate is dried, it is difficult to obtain high print density. For example, after the aqueous inkjet ink is dried, the pigment contained in the aqueous inkjet ink is exposed on the ink film surface, causing unevenness, which causes light incident on the ink film to be diffused on the ink film surface, resulting in a decrease in print density.

[0007] Furthermore, some low-permeability substrates, such as coated paper, have low surface free energy. When an aqueous inkjet ink is printed on such a substrate, the ink is less likely to spread across the surface of the substrate, which can lead to white spots. Here, white spots refer to the phenomenon in which spots (spots and / or streaks) appear on the substrate where the ink is not applied.

[0008] In particular, water, the main solvent of aqueous inkjet inks, has a high surface tension. Therefore, water has the property of being difficult to wet and spread on printing substrates with low surface free energy, and aqueous inkjet inks are prone to deterioration in print quality, such as white voids. In order to improve print quality, it is effective to reduce the surface tension of aqueous inkjet inks, and surfactants and organic solvents are generally used to achieve this.

[0009] For example, Patent Literature 1 discloses an aqueous inkjet pigment ink containing a specific poorly water-soluble solvent and a surfactant. It also describes that this ink can produce printed matter with excellent print quality, free of white streaks, color unevenness, and inter-color bleeding, on low-permeability substrates such as coated paper. However, when printing on high-permeability substrates such as plain paper or high-quality paper, the ink penetrates along the paper fibers, causing bleeding and deteriorating print quality, such as character visibility. Furthermore, the pigment ink penetrates into high-permeability substrates, making it impossible to achieve excellent print density.

[0010] On the other hand, various methods for improving print density when printed on highly permeable substrates have also been studied. For example, Patent Document 2 discloses a black pigment dispersion for inkjet recording for preparing an aqueous pigment ink for inkjet recording that can provide high print density on plain paper, which uses, as constituent materials, carbon black having a specific primary particle size, specific surface area, and DBP oil absorption, and a resin having a specific composition and acid value. However, simply using the above-mentioned pigment and dispersion resin cannot prevent the pigment from penetrating highly permeable substrates such as plain paper and fine paper, and there are cases in which sufficient print density cannot be obtained.

[0011] Furthermore, Patent Document 3 discloses a water-based ink for inkjet recording that contains water-insoluble polymer particles containing carbon black having a specific DBP oil absorption, other water-insoluble polymer particles, an organic solvent, and a nonionic surfactant, as an ink that has good print density, fixation, and ejection stability not only on plain paper but also on low-water-absorbency printing substrates. However, with the water-based ink, depending on the highly permeable substrate used, the pigment may not be sufficiently retained on the printing substrate, making it difficult to obtain excellent print density. Furthermore, many of the organic solvents actually used in the examples of Patent Document 3 have high boiling points, and on highly permeable substrates, the water-insoluble polymer particles containing carbon black permeate along the paper fibers, reducing the visibility of characters.

[0012] Furthermore, Patent Document 4 discloses an aqueous dispersion for inkjet printing containing a self-dispersing pigment and metal oxide particles, and an aqueous ink for inkjet printing containing the aqueous dispersion, and describes that the aqueous ink has excellent print density on plain paper. However, Patent Document 4 uses a self-dispersing pigment in which a carboxyl group or the like is bound to the surface of the pigment directly or via another atomic group. When an aqueous ink containing such a self-dispersing pigment is printed on a low-permeability substrate such as coated paper, unevenness is likely to occur on the surface of the printed matter, and light is diffusely reflected, which results in a problem that excellent print density cannot be obtained.

[0013] As described above, with the conventional techniques, it has been difficult to provide a water-based inkjet black ink that can produce printed matter with excellent print density and print quality regardless of the permeability of the printing substrate, and that also has excellent ejection stability from an inkjet head.

[0014] JP 2012-136573 A JP 2009-144060 A JP 2016-44188 A JP 2008-31356 A

[0015] The present invention has been made to solve the above-mentioned problems, and in one embodiment of the present invention, there is provided an aqueous inkjet black ink that can produce printed matter with excellent print density and print quality regardless of the permeability of the printing substrate, and that also has excellent ejection stability from an inkjet head and storage stability. In another embodiment, there is provided an aqueous inkjet black ink that, in addition to the above-mentioned effects, also has excellent drying properties.

[0016] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by an aqueous inkjet black ink that contains crosslinked polymer particles containing carbon black having specific specifications and that further contains a limited amount of high-boiling organic solvent, and have thus completed the present invention.

[0017] One embodiment of the present invention is an aqueous inkjet black ink containing crosslinked polymer particles (A) containing carbon black and a crosslinked polymer (A-2), and an organic solvent (B), wherein the pH of the carbon black is 6.0 to 10.0, and the DBP oil absorption of the carbon black is AC (mL / 100 g), and the specific surface area of ​​the carbon black is SC (m ２ / g), the AC is 60 to 130, and the value expressed by AC x SC is 20,000 to 35,000, the crosslinked polymer (A-2) is a crosslinked polymer obtained by crosslinking an uncrosslinked polymer (A-1) having a carboxy group and / or a carboxylate group and an acid value of 50 to 180 mgKOH / g with a crosslinking agent, the crosslinking agent containing a compound having multiple functional groups in one molecule that react with a carboxy group and / or a carboxylate group, and the content of an organic solvent having a boiling point of 230°C or higher at 1 atmosphere is 10% by mass or less of the total amount of the aqueous inkjet black ink. Another embodiment of the present invention relates to a printed matter having a printing substrate and an ink film formed on the printing substrate using the aqueous inkjet black ink of the above embodiment.

[0018] According to one embodiment of the present invention, it is possible to provide an aqueous inkjet black ink that can produce printed matter with excellent print density and print quality regardless of the permeability of the printing substrate, and that also has excellent ejection stability from an inkjet head and storage stability. Furthermore, according to another embodiment of the present invention, it is possible to provide an aqueous inkjet black ink that, in addition to the above-mentioned effects, also has excellent drying properties.

[0019] An inkjet black ink (hereinafter also simply referred to as "ink") will be described in detail below as one embodiment of the present invention. However, the present invention is not limited to the following embodiment, and the present invention also includes modifications that are implemented within the scope of the present invention.

[0020] As described above, when printing a pigment-containing aqueous inkjet ink on a highly permeable substrate such as plain paper or high-quality paper, the components of the aqueous inkjet ink penetrate into the printing substrate along with a portion of the pigment, which tends to reduce the pigment concentration on the surface of the printing substrate, i.e., the print density. Furthermore, when a paper substrate is used as the highly permeable substrate, feathering tends to occur as described above, which tends to lead to a decrease in print quality, such as a decrease in the visibility of characters. Therefore, in order to improve the print density on a highly permeable substrate and suppress feathering, it is important to retain the pigment on the surface of the printing substrate and suppress penetration into the interior of the printing substrate.

[0021] On the other hand, low-permeability substrates, such as coated paper, tend to retain pigments on the substrate, making it difficult for the print density to decrease due to pigment penetration, as occurs with high-permeability substrates. However, as mentioned above, unevenness may occur on the ink film surface after the aqueous inkjet ink dries, potentially resulting in a decrease in print density. Therefore, to improve print density on low-permeability substrates, it is important to increase the smoothness of the ink film surface after printing. Furthermore, some low-permeability substrates have low surface free energy. Water-based inkjet inks are extremely difficult to wet and spread on the surface of such printing substrates, which not only reduces print density but also tends to lead to deterioration in print quality, such as whiteouts.

[0022]

[0003] Generally, it is known that a method of reducing the surface tension of an aqueous inkjet ink using a surfactant or organic solvent is effective in improving the wetting and spreading of the aqueous inkjet ink and increasing the smoothness of the ink film surface. While this method can improve the wetting and spreading of the aqueous inkjet ink on a low-permeability substrate and the smoothness of the ink film surface, when a highly permeable substrate such as plain paper or high-quality paper is used, the aqueous inkjet ink tends to penetrate along the fibers of the paper substrate, which can easily lead to deterioration in print image quality, such as a decrease in the visibility of characters.

[0023] Plain paper and fine paper, which are highly permeable substrates, contain cationic components such as salts of polyvalent metals such as calcium and cationic polymers as fillers, pigments, sizing agents, etc. On the other hand, aqueous inkjet inks containing pigments contain carboxyl groups, carboxylate groups (COO), etc. in order to stably disperse the pigments. － In such a typical aqueous inkjet ink, a resin (pigment dispersion resin) having an anionic group such as methyl methyl acrylate (methyl acrylate), methyl methacrylate (methyl meth ...

[0024] In general, pigment dispersion resins used in aqueous inkjet inks have the above-mentioned anionic group and a hydrophobic group such as an aromatic ring structure or a long-chain alkyl group. The anionic group is introduced to improve affinity for water, which is the main component of the ink, and to stabilize the dispersed state of the pigment by electric charge repulsion between pigment dispersion resins. On the other hand, the hydrophobic group functions, for example, as an adsorptive group for the pigment.

[0025] However, although improving the reactivity of the pigment dispersion resin with cationic components improves print density on highly permeable substrates, it becomes difficult to maintain the dispersion stability of the pigment in the aqueous inkjet ink. In particular, it has been revealed that when water, the main component of the aqueous inkjet ink, evaporates near the nozzle of the inkjet head, the dispersion state is destroyed, the aqueous inkjet ink thickens, and it becomes difficult to ensure ejection stability. The above-mentioned deterioration in ejection stability can occur even when the aqueous inkjet ink is continuously ejected, but it tends to occur more easily when ejection is resumed after a temporary stop (standby).

[0026] Generally, high-boiling-point organic solvents are used to suppress water evaporation near the nozzles of inkjet heads and improve ejection stability. However, high-boiling-point organic solvents tend to remain on the printing substrate. On the other hand, because water evaporates preferentially, the amount of water into which cationic components dissolve is relatively small when printing on a highly permeable substrate. As a result, it has been found that the reaction between the pigment dispersion resin and the cationic components becomes insufficient, resulting in a decrease in print density. Furthermore, it has been found that the residue of high-boiling-point solvents on highly permeable substrates can cause the ink to penetrate along the paper fibers, reducing the visibility of characters and deteriorating the print quality of printed materials.

[0027] In order to solve the above problems, the present inventors conducted extensive research and found that a carbon black pigment dispersion containing carbon black having specific specifications and a specific crosslinked polymer as a pigment dispersing resin can be suitably used to prepare an aqueous inkjet black ink. From this perspective, one embodiment of the present invention relates to a carbon black pigment dispersion containing carbon black having specific specifications and a specific crosslinked polymer. Details of the carbon black and the crosslinked polymer are described below. In some embodiments, the carbon black pigment dispersion preferably contains water as a dispersion medium. That is, in some embodiments, the carbon black pigment dispersion may be an aqueous dispersion containing carbon black.

[0028] Another embodiment of the present invention relates to an aqueous inkjet black ink containing the above-mentioned carbon black pigment dispersion. More specifically, the aqueous inkjet black ink of this embodiment may be an aqueous inkjet black ink containing crosslinked polymer particles (A) containing carbon black and having a pH of 6.0 to 10.0, and an organic solvent (B). In the above ink, the crosslinked polymer particles (A) are a pigment dispersion containing carbon black and a crosslinked polymer (A-2) described below, and are preferably prepared separately prior to preparation of the ink. The carbon black has a DBP oil absorption of the carbon black, AC (mL / 100 g), and a specific surface area of ​​the carbon black, SC (m ２ / g), AC is 60 to 130, and the value expressed by AC x SC is 20,000 to 35,000. The crosslinked polymer particles (A) contain a crosslinked polymer (A-2) obtained by crosslinking an uncrosslinked polymer (A-1) having a carboxy group and an acid value of 50 to 180 mgKOH / g with a crosslinking agent. The crosslinking agent contains a compound having multiple functional groups per molecule that react with carboxy groups and / or carboxylate groups. In some embodiments, the aqueous inkjet black ink preferably contains an organic solvent with a boiling point of 230°C or higher at 1 atmosphere in an amount of 10% by mass or less based on the total amount of the aqueous inkjet black ink. When the aqueous inkjet black ink configured as described above is used, printed matter with excellent print density and print quality can be obtained regardless of the permeability of the printing substrate. The aqueous inkjet black ink also exhibits excellent ejection stability from an inkjet head and storage stability. While the detailed mechanism by which these effects are achieved by the above configuration is not clear, it is thought that the following may be the case.

[0029] First, the water-based inkjet black ink of this embodiment has a DBP oil absorption of AC (mL / 100g) and a specific surface area of ​​SC (m ２ / g), the carbon black has an AC of 60 to 130, a value expressed by AC x SC of 20,000 to 35,000, and a pH of 6.0 to 10.0. This carbon black is composed of a large number of carbon black particles with small primary particle sizes, which aggregate to form relatively large aggregates. The small primary particle size of each carbon black particle enhances the blackness of the aqueous inkjet black ink. Furthermore, the large aggregates (large structure) facilitate the formation of larger aggregates when printed on the highly permeable substrate and the cationic component contained in the highly permeable substrate reacts with the crosslinked polymer particles (A) containing the carbon black, thereby allowing the carbon black to remain on the highly permeable substrate. As a result, it is believed that it is possible to achieve both high print density, storage stability, and ejection stability.

[0030] Carbon black is broadly classified as acidic, neutral, or basic depending on its pH. The inventors of the present invention have investigated the relationship between the pH of carbon black, i.e., the surface polarity of the carbon black, and the dispersion stability of the carbon black, and have found that it is difficult to ensure dispersion stability when acidic carbon black is used. This is thought to be due to the fact that the hydrophobic groups present in the pigment dispersion resin are difficult to adsorb to the surface of the anionic, acidic carbon black; and, further, the protons generated from the acidic carbon black react with the anionic groups in the pigment dispersion resin, making dispersion stabilization difficult due to charge repulsion between the anionic groups. For these reasons, the ink of this embodiment uses carbon black with a pH of 6.0 to 10.0. This allows the hydrophobic groups in the pigment dispersion resin to be favorably adsorbed to the carbon black surface, and furthermore, the charge repulsion caused by the anionic groups in the pigment dispersion resin is not inhibited. This allows the carbon black to be stably dispersed in the aqueous inkjet black ink, leading to further improvements in storage stability and ejection stability.

[0031] In the aqueous inkjet black ink of this embodiment, the carbon black described above is present in crosslinked polymer particles (A) (i.e., in the pigment dispersion). The crosslinked polymer particles (A) also contain a crosslinked polymer (A-2) as a pigment dispersing resin. The crosslinked polymer (A-2) is a crosslinked polymer obtained by crosslinking an uncrosslinked polymer (A-1) having a carboxy group and / or a carboxylate group and an acid value of 50 to 180 mgKOH / g with a crosslinking agent. The crosslinking agent further contains a compound having, in one molecule, a plurality of functional groups reactive with carboxy groups and / or carboxylate groups.

[0032] In general, pigment dispersion resins with a higher acid value tend to repel charges more easily in a liquid medium (aqueous medium) containing water as a main component, enabling stable dispersion of the pigment. On the other hand, on a highly permeable substrate, the pigment dispersion state is less likely to be destroyed even when it comes into contact with a cationic component, making it difficult to obtain high print density. Conversely, pigment dispersion resins with a low acid value are more susceptible to the influence of cationic components on a highly permeable substrate, but the pigment dispersion state is more likely to become unstable in an aqueous medium, making it difficult to ensure ejection stability and storage stability.

[0033] In contrast, the crosslinked polymer particles (A) of the present invention contain a crosslinked polymer (A-2) obtained by crosslinking an uncrosslinked polymer (A-1) having carboxy groups and / or carboxylate groups and an acid value of 50 to 180 mgKOH / g with a crosslinking agent. Furthermore, the crosslinking agent used is a compound having multiple functional groups per molecule that react with the carboxy groups and / or carboxylate groups also present in the uncrosslinked polymer (A-1). This results in the acid value of the crosslinked polymer (A-2) being smaller than that of the uncrosslinked polymer (A-1).

[0034] Such crosslinking treatment with a crosslinking agent inhibits the detachment of the crosslinked polymer (A-2), which is a pigment dispersion resin, from the carbon black surface, and also enables the dispersion stability and storage stability of the carbon black to be maintained in the aqueous inkjet black ink, even with a low acid value. Furthermore, even if water, the main component of the aqueous inkjet ink, volatilizes near the nozzle of the inkjet head, the dispersion stability of the crosslinked polymer particles (A) can be maintained, and it is believed that an aqueous inkjet ink with excellent ejection stability can be obtained. Furthermore, since the acid value of the crosslinked polymer (A-2) after the crosslinking treatment is sufficiently small, it can react quickly with the cationic component on a highly permeable substrate, resulting in a printed matter with excellent print density. Furthermore, the increased aggregation rate on a highly permeable substrate can also inhibit bleeding along the paper fibers, which is believed to lead to improved print quality. Additionally, when printing on a low-permeability substrate, the dispersion state is less likely to be destroyed during the drying process after printing, thereby inhibiting carbon black aggregation associated with dispersion destruction. As a result, the smoothness of the ink film is not impaired, and printed matter with excellent print density can be obtained even on low-permeability substrates.

[0035] Furthermore, in the aqueous inkjet black ink of this embodiment, the content of organic solvents having a boiling point of 230°C or higher at 1 atmosphere is 10% by mass or less. In some embodiments, the ink does not need to contain organic solvents having a boiling point of 230°C or higher at 1 atmosphere. By adjusting the content of the organic solvent in the ink in this manner, it is possible to reduce the amount of organic solvent remaining, particularly on highly permeable substrates, and to suppress inhibition of the reaction between the cationic component and the crosslinked polymer particles (A). This not only reduces feathering but also allows the crosslinked polymer particles (A) to react favorably with the cationic component, promoting aggregation. As a result, printed matter with excellent print density and print quality can be obtained.

[0036] As described above, when the carbon black-containing crosslinked polymer particles (A) and the organic solvent have the above-described configurations, it is possible to obtain a printed matter with excellent print density and print quality, regardless of the permeability of the printing substrate, and it is also possible to easily obtain an aqueous inkjet black ink with excellent ejection stability from an inkjet head and storage stability. Note that the above mechanism is merely speculation and does not limit the present invention in any way.

[0037] Next, the main components of the water-based inkjet black ink of this embodiment will be described below.

[0038] <Crosslinked Polymer Particles (A) Containing Carbon Black> The aqueous inkjet black ink of this embodiment contains crosslinked polymer particles (A) containing carbon black. The carbon black-containing crosslinked polymer particles (A) contain the above-described carbon black and a crosslinked polymer (A-2). The crosslinked polymer (A-2) is obtained by crosslinking an uncrosslinked polymer (A-1) having a carboxy group and / or a carboxylate group and an acid value of 50 to 180 mgKOH / g with a crosslinking agent. The crosslinking agent is a compound having multiple functional groups per molecule that react with carboxy groups and / or carboxylate groups. By crosslinking the uncrosslinked polymer (A-1), the uncrosslinked polymer (A-1) is crosslinked on the surface of the carbon black, making it possible to suppress detachment of the uncrosslinked polymer (A-1) in the aqueous inkjet black ink. As a result, it is possible to achieve both print density, ejection stability, carbon black dispersion stability, and storage stability of the aqueous inkjet black ink.

[0039] In this specification, "crosslinked polymer particles containing carbon black" refers to particles obtained after a crosslinking treatment using a crosslinking agent has been applied to an uncrosslinked polymer contained in a carbon black-containing crosslinked polymer particle precursor. Furthermore, the "crosslinked polymer particle precursor containing carbon black" refers to particles (dispersion) at a stage prior to the crosslinking treatment, such as one or more particles selected from the group consisting of particles of an uncrosslinked polymer encapsulating carbon black, particles containing an uncrosslinked polymer and carbon black and having a sea-island structure in which part of the carbon black may be exposed on the particle surface, and carbon black particles having an uncrosslinked polymer chemically adsorbed and / or bonded to at least part of the surface.

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

[0041] <Carbon Black> There is no particular limitation on the type of carbon black used in this embodiment, and furnace black, channel black, acetylene black, thermal black, etc. may be used. In addition, among these carbon blacks, the DBP oil absorption of the carbon black is AC (mL / 100 g), and the specific surface area is SC (m ２ / g), carbon black having an AC of 60 to 130, a value expressed by AC×SC of 20,000 to 35,000, and a pH of 6.0 to 10.0 can be preferably used.

[0042] (DBP Oil Absorption) DBP oil absorption (DBP absorption) is a value that represents the amount of DBP (dibutyl phthalate) absorbed (absorbed) into the voids between carbon black aggregates. Generally, the more developed the aggregates (structure) of carbon black, the higher the DBP oil absorption value. DBP oil absorption can be measured, for example, using an "Absorbtometer Type C" manufactured by Brabender. The DBP oil absorption of the carbon black used in this embodiment is preferably 60 to 130 mL / 100 g, and more preferably 80 to 130 mL / 100 g.

[0043] (Specific Surface Area) The specific surface area of ​​carbon black is the surface area per unit mass. The larger the specific surface area, the smaller the carbon black particles and / or the more pores there are in the carbon black. In this specification, the value measured by the nitrogen BET method is used as the specific surface area. Specifically, nitrogen is adsorbed onto degassed carbon black at liquid nitrogen temperature, and the specific surface area (m) is calculated from the amount of adsorbed nitrogen when equilibrium is reached. ２ The specific surface area of ​​the carbon black used in this embodiment is 200 to 400 m ２ / g, and 200 to 350m ２ It is more preferable that the SiO2 content is 1 / g.

[0044] The DBP oil absorption of carbon black is AC (mL / 100g), and the specific surface area is SC (m ２ / g), the value expressed by AC×SC is preferably 20,000 to 35,000, more preferably 22,000 to 35,000, and even more preferably 22,000 to 30,000. As described above, such carbon black not only has high blackness, but also enables storage stability, ejection stability, and print density on highly permeable substrates. Furthermore, when the value expressed by AC×SC is 20,000 or more, large aggregates are rapidly formed when the cationic components contained in highly permeable substrates such as plain paper or fine paper react with the crosslinked polymer particles (A) containing the carbon black. Therefore, the crosslinked polymer particles (A) are more likely to remain on the highly permeable substrate, making it easy to obtain excellent print density. Furthermore, when the value expressed by AC×SC is 35,000 or less, the dispersion stability of the crosslinked polymer particles (A) in the ink can be ensured. Furthermore, even when water evaporates near the nozzles of an inkjet head, the crosslinked polymer particles (A) do not aggregate, and favorable ejection stability is maintained. On the other hand, when printing on a low-permeability substrate such as coated paper, the pigment is less likely to aggregate during the drying process, making it less likely that unevenness will form, making it easier to achieve excellent print density.

[0045] (pH) The pH of carbon black can be measured by a conventional method. For example, 5 g of carbon black and 50 mL of ion-exchanged water are mixed in a glass container such as a beaker, and the opening of the beaker is covered with a watch glass or the like, and the mixture is heated for 15 minutes. A small amount (approximately 0.1 mL) of ethanol or acetone may be added to facilitate wetting of the carbon black. After boiling, the mixture is cooled to 25°C, and the supernatant liquid is removed to obtain a muddy substance. A pH electrode is inserted into this muddy substance, and the pH is measured. For example, a benchtop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "9681S-10D" (manufactured by Horiba, Ltd.) can be used to measure the pH. The pH of carbon black is preferably 6.0 to 10.0, more preferably 7.0 to 9.0, from the viewpoint of ensuring storage stability and dispersion stability in the ink.

[0046] (Primary Particle Size) The primary particle size of carbon black is preferably 10 to 20 nm, particularly from the viewpoint of obtaining excellent print density on a low-permeability substrate such as coated paper. The primary particle size can be measured by a conventional method. For example, carbon black is observed using a transmission electron microscope (TEM). The size of carbon black particles within a certain observation area can then be directly measured to determine the primary particle size.

[0047] From the viewpoint of obtaining excellent print density, storage stability, and ejection stability regardless of the permeability of the printing substrate, the content of carbon black is preferably 0.1 to 20 mass %, more preferably 1 to 10 mass %, and particularly preferably 3 to 8 mass %, relative to the total mass of the ink.

[0048] <Crosslinking Agent> A crosslinking agent is a compound used to chemically bond polymer molecules together. In this embodiment, the crosslinking agent used is a compound having, in one molecule, multiple functional groups that react with carboxy groups and / or carboxylate groups present in the uncrosslinked polymer (A-1) having an acid value of 50 to 180 mgKOH / g. Examples of the crosslinking agent that can be used include aziridine compounds, isocyanate compounds, epoxy compounds, carbodiimide compounds, oxetane compounds, and oxazoline compounds. Of these, it is preferable to use an epoxy compound as the crosslinking agent, because it can promote a crosslinking reaction with the uncrosslinked polymer (A-1) in the vicinity of the carbon black particles while maintaining the dispersion stability of the carbon black, and further, it can prevent detachment of the crosslinked polymer (A-2) after the crosslinking reaction, thereby improving the ejection stability and storage stability of the ink.

[0049] The crosslinking agent may be water-soluble or water-insoluble, but from the viewpoint of being able to more efficiently proceed with the crosslinking reaction in a liquid medium mainly composed of water and improving both the ejection stability and the storage stability, it is preferable that the amount of the crosslinking agent dissolved in 100 g of water at 25° C. is 0.1 to 50 g / 100 gH ２ It is preferable to use a crosslinking agent in which the crosslinking agent is O. The dissolution amount is 0.2 to 40 g / 100 gH ２ It is more preferable to use a crosslinking agent containing 0.0, and even more preferable to use a crosslinking agent containing 0.5 to 30 g / 100 gH２ It is O.

[0050] As described above, the crosslinking agent is preferably a compound having multiple epoxy groups in one molecule. Furthermore, as the 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, and it is even more preferable to use a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms. The epoxy equivalent of the compound having multiple epoxy groups in one molecule 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 carboxy groups and / or carboxylate groups present in the uncrosslinked polymer (A-1) in a liquid medium mainly composed of water.

[0051] Specific examples of the compound having two or more glycidyl ether groups in one molecule include cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether.

[0052] The crosslinking agent is preferably blended so that the functional group content (mol %) represented by the following formula 2 is 50 to 150 mol %. From the viewpoints of suppressing desorption of the uncrosslinked polymer (A-1), maintaining dispersion stability even during drying, obtaining printed matter having excellent print density on low-permeability substrates such as coated paper, and further ensuring ejection stability, the functional group content is more preferably 70 to 120 mol %, and particularly preferably 80 to 100 mol %.

[0053]

[0054] <Uncrosslinked Polymer (A-1)> As described above, the uncrosslinked polymer (A-1) used in this embodiment has the function of dispersing carbon black (it is a pigment dispersing resin). Furthermore, any resin can be used as the uncrosslinked polymer (A-1), as long as it has a carboxy group and / or a carboxylate group in its structure, an acid value of 50 to 180 mgKOH / g, and the function of dispersing carbon black. Examples of polymers that can be used as the uncrosslinked polymer (A-1) include acrylic, maleic acid, urethane, and polyester polymers. Furthermore, it is preferable to use a polymer having an aromatic ring in its structure, as this polymer has strong adsorption to carbon black and can stably disperse carbon black even after the crosslinking reaction.

[0055] As used herein, 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. The term may also refer to a polymer using a styrene-based monomer in addition to the above-mentioned polymerizable monomers. However, polymers containing maleic acid (anhydride) (maleic acid and / or maleic acid anhydride) as a polymerizable monomer are not included in the term "acrylic polymer." Furthermore, as used herein, the term "maleic acid-based polymer" refers to a polymer using at least maleic acid (anhydride) as a polymerizable monomer. Furthermore, the maleic acid-based polymer may also use one or more polymerizable monomers selected from the group consisting of α-olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, and styrene derivatives.

[0056] The uncrosslinked polymer (A-1) has a carboxy group and / or a carboxylate group. The uncrosslinked polymer (A-1) preferably has at least a carboxylate group. This is because the charge of the carboxylate group allows the crosslinked polymer particles (A) containing carbon black to be stably dispersed by charge repulsion, even after the crosslinking reaction. The carboxylate group in the uncrosslinked polymer (A-1) may be introduced into the uncrosslinked polymer (A-1) by synthesizing a polymer using a polymerizable monomer having a carboxylate group, or may be formed in the uncrosslinked polymer (A-1) by neutralizing at least a portion of the carboxy groups present in a polymer having a carboxy group with a basic compound (neutralization treatment). Examples of the basic compound that can be used include ammonia; alkanolamines such as dimethylaminoethanol, diethanolamine, and triethanolamine; and alkali metal compounds such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, and sodium borate. Among these, it is preferable to use an alkali metal compound as the basic compound, and hydroxides such as sodium hydroxide and potassium hydroxide are particularly preferred, from the viewpoint that the dispersion stability of the crosslinked polymer particles (A) containing carbon black is improved and aggregation of the carbon black can be suppressed even during the drying process of the ink, thereby obtaining printed matter with excellent print density. The basic compounds listed above can be used alone or in combination of two or more.

[0057] The uncrosslinked polymer (A-1) may be produced, for example, by neutralizing the carboxy groups in an uncrosslinked polymer having only carboxy groups (hereinafter referred to as polymer (A-0)). In this case, when the amount of the basic compound used to neutralize the carboxy groups in polymer (A-0) is expressed as a neutralization rate represented by the following formula 3, from the viewpoint of improving the dispersion stability of carbon black, the neutralization rate is preferably 10 to 200 mol%, more preferably 40 to 160 mol%, and particularly preferably 60 to 120 mol%.

[0058]

[0059] The "acid value of the polymer" described in Equation 3 above and elsewhere can be measured by conventional methods. For example, approximately 1 g of sample is precisely weighed into an Erlenmeyer flask, and 50 mL of a distilled water / dioxane mixture (distilled water / dioxane mixed at a mass ratio of 1 / 9) is added and dissolved. Next, the sample solution is titrated with a 0.1 mol / L potassium hydroxide-ethanol solution (potency F) using a potentiometric measuring device (e.g., the "AT-710M Automatic Potentiometric Titrator" manufactured by Kyoto Electronics Manufacturing Co., Ltd.), and the amount (α (mL)) of potassium hydroxide-ethanol solution required to reach the titration endpoint is measured. The acid value (mg KOH / g) of the polymer can then be calculated using Equation 4 below.

[0060] Acid value (mgKOH / g) = {(5.611×α×F) / S} Formula 4

[0061] In the above formula 4, S is the amount (g) of the sample polymer collected, α is the amount (mL) of the 0.1 mol / L potassium hydroxide ethanol solution used until the titration ends, and F is the titer of the 0.1 mol / L potassium hydroxide ethanol solution.

[0062] The acid value of the uncrosslinked polymer (A-1), which can be measured by the above-mentioned method, is preferably 60 to 180 mgKOH / g, more preferably 70 to 160 mgKOH / g, and particularly preferably 80 to 150 mgKOH / g, from the viewpoints of favorable reaction with cationic components in highly permeable substrates such as fine paper, obtaining printed matter with excellent print density and print quality, and strengthening adsorption to carbon black and improving discharge stability.

[0063] The weight-average molecular weight (Mw) of the uncrosslinked polymer (A-1) is preferably 5,000 to 100,000. By setting the weight-average molecular weight to 5,000 or more, dispersion stability can be made favorable, and by setting it to 100,000 or less, ejection stability can be made favorable. The weight-average molecular weight is more preferably 10,000 to 50,000, and even more preferably 15,000 to 35,000.

[0064] The weight-average molecular weight of the polymer can be measured by a conventional method, for example, a polystyrene-equivalent value measured using a TSKgel column (manufactured by Tosoh Corporation) with a GPC ("HLC-8120GPC" manufactured by Tosoh Corporation) equipped with an RI detector and THF as a developing solvent can be used.

[0065] The content ratio of carbon black to uncrosslinked polymer (A-1) (carbon black / uncrosslinked polymer (A-1)) is preferably 1 / 1 to 100 / 1 by mass. By making the ratio 1 / 1 or more, the viscosity of the ink can be controlled to a level suitable for an inkjet ink, and by making the ratio 100 / 1 or less, the dispersion stability, storage stability, and ejection stability can be improved. Furthermore, the content ratio of carbon black to uncrosslinked polymer (A-1) is more preferably 2 / 1 to 50 / 1.

[0066] <Method for Producing an Aqueous Dispersion of Crosslinked Polymer Particles (A) Containing Carbon Black> Examples of methods for producing an aqueous dispersion of crosslinked polymer particles (A) containing carbon black include the following. First, a polymer (A-0) having only carboxy groups is mixed with a basic compound in water, and at least a portion of the carboxy groups is neutralized (neutralization treatment) to obtain an aqueous solution of an uncrosslinked polymer (A-1). Next, carbon black is added to the aqueous solution of the uncrosslinked polymer (A-1), and after thorough mixing, further dispersion treatment is performed to produce an aqueous dispersion of carbon black dispersed by the uncrosslinked polymer (A-1) (a crosslinked polymer particle precursor containing carbon black). Thereafter, a crosslinking agent is added to the aqueous dispersion of the crosslinked polymer particle precursor containing carbon black, and a crosslinking treatment is performed to produce an aqueous dispersion of crosslinked polymer particles (A) containing carbon black. This aqueous dispersion of crosslinked polymer particles (A) containing carbon black corresponds to one example of the carbon black pigment dispersion described above.

[0067] In this specification, the term "aqueous solution" refers to a solution containing an aqueous solvent and components dispersed and / or dissolved in the aqueous solvent.

[0068] (Dispersion Treatment) In dispersing carbon black, it is preferable to pre-disperse (premix) the carbon black and the uncrosslinked polymer (A-1) using a commonly used mixing and stirring device such as a stirrer, and then disperse (main dispersion) using a conventionally known disperser. By performing pre-dispersion before main dispersion, a carbon black dispersion with uniform particle size can be obtained. Furthermore, any commonly used disperser can be used for the main dispersion of carbon black, and examples thereof include a ball mill, a roll mill, a kneader, a sand mill, a bead mill, and a high-pressure homogenizer. Among these, a bead mill is preferred from the viewpoint of its ability to disintegrate and refine coarse carbon black 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.

[0069] In the crosslinking treatment, the uncrosslinked polymer (A-1) adsorbed on the carbon black is crosslinked by a crosslinking agent, resulting in the formation of a crosslinked polymer (A-2), and an aqueous dispersion of crosslinked polymer particles (A) containing carbon black can be obtained.

[0070] From the viewpoint of efficiently promoting the crosslinking reaction, the temperature of the crosslinking treatment is preferably 50 to 95° C., more preferably 70 to 85° C. From the same viewpoint as above, the time of the crosslinking treatment is preferably 0.5 to 10 hours, more preferably 1 to 8 hours, and even more preferably 2 to 5 hours.

[0071] The average particle size of the carbon black-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.

[0072] The "average particle size" refers to the median diameter on a volume basis, and can be measured by dynamic light scattering. For example, it can be measured using a "Nanotrac UPA-EX150" manufactured by Microtrac Bell Inc. in an environment of 25°C.

[0073] The pH of the aqueous dispersion of the carbon black-containing crosslinked polymer particles (A) is preferably 8 to 12. If the pH is 8 or higher, the carboxy groups in the crosslinked polymer (A-2) tend to become carboxylate groups, and favorable charge repulsion can enhance the dispersion stability of the crosslinked polymer particles (A). A more preferred pH value is 9 to 11.

[0074] The pH of the aqueous dispersion can be measured by a conventional method, for example, using a tabletop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "6337-10D" (manufactured by Horiba, Ltd.) in an environment of 25°C.

[0075] <Organic Solvent (B)> The aqueous inkjet black ink of this embodiment contains an organic solvent (B). The organic solvent (B) is suitably selected from the compounds described below from the viewpoints of adjusting the wettability and penetrability of the aqueous inkjet black ink on a printing substrate, controlling print image quality, print density, and drying properties through such adjustments, and ensuring and improving ejection stability from inkjet nozzles, etc.

[0076] In this specification, the term "organic solvent" refers to an organic compound that is liquid at 45°C.

[0077] In this embodiment, the content of the organic solvent having a boiling point of 230°C or higher at 1 atmosphere is preferably 10% by mass or less based on the total amount of the aqueous inkjet black ink. In some embodiments, the content of the organic solvent in the ink may be 0% by mass. In this specification, "0% by mass" means that the target organic solvent is not contained. When the content of the organic solvent having a boiling point of 230°C or higher at 1 atmosphere is 10% by mass or less, the organic solvent does not remain on a highly permeable substrate such as plain paper or fine paper, thereby suppressing the occurrence of feathering and improving the visibility of characters. Furthermore, since the organic solvent remaining on the highly permeable substrate does not prevent the elution of cationic components in the highly permeable substrate, the reaction with the carbonyl group and / or carboxylate group in the crosslinked polymer (A-2) proceeds favorably, making it easier to obtain excellent print density. From the perspective of obtaining excellent print density, the content of the organic solvent having a boiling point of 230°C or higher at 1 atmosphere is more preferably 5% by mass or less based on the total amount of the aqueous inkjet black ink. In some embodiments, the content of the organic solvent in the ink may be 0% by mass.

[0078] Specific examples of the high-boiling organic solvent having a boiling point of 230°C or higher under 1 atmosphere include glycerin, 1,2,4-butanetriol, 1,2,6-hexanetriol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, 2-pyrrolidone, N-methyloxazolidinone, ε-caprolactone, 1,2-octanediol, 2-ethylhexane-1,3-diol, diethylene glycol monobutyl ether, triethylene glycol monoethyl ether, and dipropylene glycol monobutyl ether.

[0079] On the other hand, the ink of this embodiment preferably contains a compound represented by the following general formula 1 as the organic solvent (B). When the following compound is used as the organic solvent (B), the ink has suitable wettability on a low-permeability substrate such as coated paper, and a smooth ink film can be formed after drying, thereby improving the print density of the printed matter. Furthermore, even on such a low-permeability substrate, a printed matter with good print quality can be obtained. Furthermore, when a binder resin described below is used in combination, the film-forming properties of the binder resin can be improved, and improved drying properties can be achieved.

[0080] R １ -(O-CH(CH ３ )-CH ２ ) ｎ -OH General formula 1

[0081] In the above general formula 1, R １ is an alkyl group having 1 to 4 carbon atoms, and n is 1 or 2. In particular, from the viewpoint of achieving both excellent print density and drying properties on a low-permeability substrate, R １ is particularly preferably an alkyl group having 2 to 4 carbon atoms. In some embodiments, n in the above general formula 1 is preferably 2. In this case, the aqueous inkjet black ink will wet and spread well on a low-permeability substrate, making it easy to achieve both excellent print image quality and high print density. In addition, it will be easy to improve ejection stability while maintaining drying properties.

[0082] Examples of the compound represented by the general formula 1 include propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether. In some embodiments, among the above compounds, at least one selected from the group consisting of dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether can be preferably used. These compounds are represented by the general formula 1 R １is an alkyl group having 2 to 4 carbon atoms, and n is 2.

[0083] The content of the compound represented by the general formula 1 is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 8.5% by mass, based on the total amount of the aqueous inkjet black ink.

[0084] In the aqueous inkjet black ink of this embodiment, the above-mentioned organic solvents having a boiling point of 230°C or higher at 1 atmosphere, and organic solvents other than the compounds represented by General Formula 1 above can also be suitably used as the organic solvent (B). Organic solvents other than those described above that can be used in the present embodiment are not particularly limited, and examples thereof include ethanol, isopropanol, 2-butanol, t-butanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-pentanediol, 3-methyl-1,3-butanediol, 1,2-hexanediol, 2-methyl-2,4-pentanediol, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, and γ-butyrolactone.

[0085] The total content of the organic solvent (B) contained in the aqueous inkjet black ink of this embodiment is preferably 5 to 40% by mass, based on the total amount of the aqueous inkjet black ink. In particular, in some embodiments, this total content is more preferably 10 to 35% by mass, and particularly preferably 15 to 30% by mass, based on the total amount of the aqueous inkjet black ink. When the content of the organic solvent (B) is adjusted within the above range, printed matter with high print density and excellent character visibility can be easily obtained, even on highly permeable substrates such as plain paper or high-quality paper. Furthermore, drying properties on the printed substrate are easily improved. Furthermore, ejection stability from the inkjet head is easily improved. When the total content of the organic solvent (B) is 5% by mass or more, wetting and spreading on the printed substrate is improved, regardless of the permeability of the printed substrate, resulting in good print density and print image quality. Furthermore, ejection stability is not significantly impaired. On the other hand, when the total content of the organic solvent (B) is 40% or less, no solvent remains on the printed substrate, regardless of the permeability of the printed substrate, and print density and print image quality are improved.

[0086] The aqueous inkjet black ink of this embodiment contains the above-described carbon black-containing crosslinked polymer particles (A) and an organic solvent (B), and may further contain additional components as necessary. In some embodiments, the ink preferably further contains a binder resin to improve the print density and drying properties of the printed matter.

[0087] <Binder Resin> In this specification, the term "binder resin" refers to a resin (polymer) used to bind the ink film to the printing substrate. When the ink further contains a binder resin, the resin forms a film during the drying process and / or the resin molecules become entangled, thereby improving the abrasion resistance and drying properties of the ink film. From this perspective, for example, the resin primarily contained in the aqueous inkjet black ink (specifically, a resin that accounts for 50% by mass or more of the total amount of resin contained in the ink, more preferably a resin that accounts for 60% by mass or more, and particularly preferably a resin that accounts for 70% by mass or more) functions as the binder resin. In some embodiments, the crosslinked polymer (A-2) constituting the above-described carbon black-containing crosslinked polymer particles (A) may also serve as the binder resin.

[0088] Generally, water-soluble resins and resin particles are known as binder resin forms. In this embodiment, either of the above may be used alone, or both may be used in combination. Here, the "water-soluble resin" refers to a resin that dissolves in an amount of 1 g or more in 100 g of water at 25°C. On the other hand, the "resin particles" refer to a form of water-insoluble resin (a resin that is not a water-soluble resin) and has an average particle size in water of 5 to 1,000 nm, which can be measured in the same manner as in the case of the crosslinked polymer particles (A) containing carbon black described above.

[0089] When the aqueous inkjet black ink of this embodiment contains a binder resin, the ink film formation rate can be increased during the drying process of the aqueous inkjet black ink, resulting in improved drying properties on low-permeability substrates such as coated paper. Furthermore, when printing on plain paper or high-quality paper, the binder resin itself reacts with a cationic component, rendering the binder resin insoluble on the printing substrate and suppressing penetration along the fibers of the printing substrate. As a result, printed matter with excellent print quality and minimal bleeding can be obtained. From the perspective of rapidly thickening the ink on the printing substrate and improving both drying properties and print quality, it is preferable to use a water-soluble resin as the binder resin.

[0090] The acid value of the binder resin is preferably 1 to 50 mgKOH / g, and more preferably 2 to 40 mgKOH / g. By using a binder resin having this acid value, it is possible to improve the ink film formation rate even on low-permeability substrates, and to obtain printed matter with excellent drying properties. Furthermore, it is possible to obtain excellent print quality even on high-permeability substrates such as fine paper. Furthermore, controlling the acid value is effective in improving the ejection stability of the aqueous inkjet black ink.

[0091] The acid value of the binder resin can be measured using the same method as that for the acid value of the uncrosslinked polymer (A-1) described above.

[0092] Furthermore, from the viewpoint of improving the abrasion resistance and ejection stability of the printed matter, the glass transition temperature of the binder resin is preferably 60 to 140°C, more preferably 70 to 135°C, and particularly preferably 80 to 130°C.

[0093] The glass transition temperature is a value measured using a DSC (differential scanning calorimeter) and can be measured in accordance with JIS K 7121, for example, as follows. Approximately 2 mg of a sample obtained by drying the resin is weighed on an aluminum pan, and the aluminum pan is set as a test container in a holder in a DSC measurement device (for example, a "DSC-60Plus" manufactured by Shimadzu Corporation). Measurement is then carried out under conditions of a temperature rise of 5°C / min, and the temperature at the intersection of the low-temperature baseline and the tangent line at the inflection point, read from the obtained DSC chart, is taken as the glass transition temperature in this specification.

[0094] (Resin Particles) When resin particles are used as the binder resin, examples of the types of resin that can be used as the resin particles include acrylic, epoxy, urethane, styrene butadiene, polyamide, polyester, polyolefin, vinyl chloride, vinyl acetate, etc. Among these, from the viewpoint of being able to improve both the scratch resistance and ejection stability of printed matter, resin particles made of at least one selected from the group consisting of acrylic, urethane, styrene butadiene, and vinyl chloride are preferred, resin particles made of at least one selected from the group consisting of acrylic and urethane are more preferred, and from the viewpoint of improving ejection stability, it is particularly preferred to use acrylic resin particles.

[0095] The resin particles can be synthesized by a conventional method or can be commercially available. There are no particular limitations on the structure of the resin particles, and resins having, for example, a random structure, a block structure, a comb structure, a star structure, etc. can be used.

[0096] The content of the resin particles relative to the total amount of the aqueous inkjet black ink is preferably 1 to 10% by mass, more preferably 2 to 8% by mass, and even more preferably 3 to 7% by mass, calculated as solid content. By setting the amount of resin particles within the above range, it is possible to obtain an aqueous inkjet black ink that exhibits excellent abrasion resistance and drying properties of printed matter without reducing storage stability or ejection stability.

[0097] (Water-soluble resin) On the other hand, when a water-soluble resin is used as the binder resin, examples of the type of resin that can be used as the water-soluble resin include acrylic, urethane, styrene butadiene, vinyl chloride, maleic acid, polyester, etc. Among these, it is preferable to use one or more resins selected from the group consisting of acrylic and urethane resins, from the viewpoint of obtaining a printed matter having excellent abrasion resistance and print image quality, and further obtaining an ink having excellent drying properties and ejection stability.

[0098] The water-soluble resin can be synthesized by a conventionally known method, or a commercially available product can be used. There are no particular limitations on the structure, and resins having, for example, a random structure, a block structure, a comb structure, a star structure, etc. can be used. Among these, it is preferable to use a water-soluble resin having a block structure or a comb structure, from the viewpoint of fully utilizing the properties of the polymerizable monomers constituting the binder resin. Each unit constituting the block structure or the comb structure may be formed from a single polymerizable monomer or may be a random copolymer of multiple types of polymerizable monomers.

[0099] The weight-average molecular weight of the water-soluble resin used as the binder resin is preferably 5,000 to 50,000, from the viewpoints of ensuring ejection stability from an inkjet nozzle, obtaining printed matter with excellent drying properties on a variety of printing substrates, and ensuring the storage stability of the aqueous inkjet black ink. Furthermore, from the viewpoints of improving ejection stability and storage stability, the weight-average molecular weight is more preferably 8,000 to 45,000, and particularly preferably 10,000 to 40,000.

[0100] The weight average molecular weight of the water-soluble resin can be measured in the same manner as in the weight average molecular weight of the uncrosslinked polymer (A-1) described above.

[0101] The content of the water-soluble resin relative to the total amount of the aqueous inkjet black ink is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, and even more preferably 1 to 5% by mass, calculated as solid content. By setting the amount of the water-soluble resin within the above range, it is possible to obtain printed matter that is excellent in drying properties and abrasion resistance without reducing storage stability and ejection stability.

[0102] <Surfactant> The aqueous inkjet black ink of this embodiment preferably further contains one or more surfactants, from the viewpoint of improving the wettability of ink droplets on a low-permeability substrate and forming a smoother ink film, thereby obtaining a printed matter with high print density.

[0103] As the surfactant, various surfactants can be used depending on the application, such as acetylenic diol-based, acetylene monool-based, siloxane-based, fluorine-based, polyoxyalkylene ether-based, etc. Among them, it is preferable to contain one or more nonionic surfactants selected from the group consisting of acetylenic diol-based surfactants, siloxane-based surfactants, and polyoxyalkylene ether-based surfactants, and it is more preferable to contain one or more surfactants selected from the group consisting of acetylenic diol-based surfactants and siloxane-based surfactants.

[0104] Examples of the acetylene diol surfactant used in the present embodiment include, but are not limited to, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, hexadec-8-yne-7,10-diol, 6,9-dimethyl-tetradec-7-yne-6,9-diol, 7,10-dimethylhexadec-8-yne-7,10-diol, and ethylene oxide and / or propylene oxide adducts thereof.

[0105] Examples of siloxane-based surfactants that can be suitably used in this embodiment include the following: 8032 ADDITIVE, FZ-2104, FZ-2120, FZ-2122, FZ-2162, FZ-2164, FZ-2166, FZ-2404, FZ-7001, FZ-7002, FZ-7006, L-7001, L-7002, SF8427, SF8428, SH3748, SH3749, SH3771M, SH3772M, SH3773M, SH3775M, and SH8400, all manufactured by Dow Corning Toray Co., Ltd. BYK-331, BYK-333, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, BYK-UV3500, BYK-UV3510, BYK-UV3530, BYK-UV3570 manufactured by BYK Japan, and TEGO Wet 240, TEGO Wet 250, TEGO Wet 260, TEGO Wet 270, TEGO Wet 280, TEGO Glide 410, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide manufactured by Evonik 450, TEGO Twin 4000, TEGO Twin 4100, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-640, KF-642, KF-643, KF-644, KF-945, KF-6011, KF-6012, KF-6015, KF-6017, KF-6020, KF-6204, X-22-4515 manufactured by Shin-Etsu Chemical Co., Ltd., and the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd. Particularly suitable siloxane surfactants include compounds in which one or more ethylene oxide groups and / or one or more propylene oxide groups are introduced into the side chains and / or both ends of a polydimethylsiloxane chain.

[0106] Furthermore, examples of polyoxyalkylene ether surfactants that can be suitably used include compounds represented by the following general formula 5.

[0107] R ２ -O-(EO) ｐ - (PO) ｑ -H General formula 5

[0108] In the above general formula 5, R ２ represents an alkyl group having 8 to 22 carbon atoms, an alkenyl group having 8 to 22 carbon atoms, an alkylcarbonyl group having 8 to 22 carbon atoms, or an alkenylcarbonyl group having 8 to 22 carbon atoms. ２ may have a branched structure. EO represents an ethylene oxide group, and PO represents a propylene oxide group. p represents the average number of moles of EO added and is a number from 2 to 100, and q represents the average number of moles of PO added and is a number from 0 to 50. When q is not 0, (EO) ｐ and (PO) ｑ The order of addition does not matter, and the addition may be in blocks or randomly.

[0109] The surfactant used in this embodiment preferably has a hydrophobic group and a hydrophilic group separated in the molecule, and therefore, among the surfactants exemplified above, those having a hydrophilic ethylene oxide group are particularly preferably selected.

[0110] In this embodiment, the HLB value of the surfactant is preferably 12 or less, more preferably 0 to 8, and even more preferably 0 to 4. When a surfactant having an HLB value within the above range is used, the surfactant quickly orients at the air-liquid interface and the interface between the printing substrate and the droplets, improving the wettability of the ink droplets on the low-permeability substrate and forming a smoother ink film, making it possible to easily obtain a high print density.

[0111] The HLB (Hydrophile-Lipophile Balance) value is one of the parameters that indicate the hydrophilicity and 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. In this embodiment, the HLB value is calculated using the Griffin method.

[0112] The Griffin method is generally used for nonionic materials. In the Griffin method, the HLB value is calculated using the molecular weight of the material in question using the following formula 6. The smaller the HLB value, the more hydrophobic the material is, and the larger the HLB value, the more hydrophilic the material is.

[0113] HLB value = 20 × (sum of molecular weights of hydrophilic portions) ÷ (molecular weight of material) Equation 6

[0114] When the aqueous inkjet black ink of this embodiment contains a surfactant having an HLB value of 12 or less (the HLB value is preferably 0 to 8, and more preferably 0 to 4), the surfactant having an HLB value of 12 or less is preferably an acetylenic diol surfactant. An acetylenic diol surfactant has two hydroxyl groups per molecule. Meanwhile, the crosslinked polymer particles (A) contained in the aqueous inkjet ink of this embodiment contain structures (e.g., ester bonds, amide bonds) formed upon crosslinking reaction between the crosslinking agent and the carboxyl groups and / or carboxylate groups in the uncrosslinked polymer (A-1). Because these structures can form hydrogen bonds with hydroxyl groups, it is believed that the crosslinked polymer particles (A) and the acetylenic diol surfactant having an HLB value of 12 or less have a high affinity. Generally, surfactants with a low HLB value have a high rate of orientation to interfaces, which may adversely affect ejection stability and storage stability. However, when the surfactant and the crosslinked polymer particles (A) are used in combination, the high affinity between them prevents deterioration of the ejection stability and storage stability, and also makes it easier to obtain printed matter with high print density and excellent wettability.

[0115] When the aqueous inkjet ink of this embodiment contains an acetylenic diol surfactant having an HLB value of 12 or less, it is preferable to appropriately adjust the contents of both surfactants from the viewpoint described above, i.e., from the viewpoint that improved affinity between the acetylenic diol surfactant having an HLB value of 12 or less and the crosslinked polymer particles (A) results in prints with excellent print density and wettability, and further improves ejection stability and storage stability. In some embodiments, when the content of the crosslinking agent contained in the aqueous inkjet ink is WC (mass %) and the content of the acetylenic diol surfactant having an HLB value of 12 or less is WA (mass %), the value (ratio of the two) represented by "WA / WC" is preferably 75 to 250. The value of "WA / WC" is more preferably 90 to 215, and particularly preferably 100 to 195. Note that the crosslinking agent content WC includes crosslinking agent molecules incorporated in the crosslinked polymer particles (A). In other words, the content of the crosslinking agent added for the crosslinking reaction is entirely included in WC.

[0116] The content of the surfactant in the aqueous inkjet black ink of this embodiment is preferably 0.1 to 5 mass % relative to the total amount of the ink, and more preferably 0.5 to 3.5 mass %.

[0117] <Water> The water contained in the aqueous inkjet black ink of this embodiment is preferably ion-exchanged water (deionized water) rather than ordinary water containing various ions.

[0118] The content of water in the aqueous inkjet black ink is preferably adjusted taking into account the content of liquid media other than water, such as organic solvent (B). In some embodiments, the content of water in the aqueous inkjet black ink may be in the range of 10 to 90% by mass, and preferably in the range of 20 to 90% by mass, of the total mass of the aqueous inkjet black ink. In some embodiments, the content of the aqueous medium containing water and organic solvent (B) may be in the range of 25 to 95% by mass, of the total mass of the aqueous inkjet black ink. The content of the aqueous medium may preferably be 35 to 92% by mass, and more preferably 50 to 88% by mass. Here, the aqueous medium may further contain an organic solvent having a boiling point of 230°C or higher at 1 atmosphere, but its content in the ink is preferably 10% by mass or less. In some embodiments, the content of the organic solvent in the ink is preferably 0% by mass. In some embodiments, the ratio (mass ratio) of water to the organic solvent (B) in the aqueous medium may be preferably 50 / 50 to 95 / 5, more preferably 55 / 45 to 90 / 10, and even more preferably 60 / 40 to 85 / 15.

[0119] <Other Components> In addition to the components described above, the aqueous inkjet black ink of this embodiment may contain other components as necessary to provide the ink with desired physical properties. For example, additives such as infrared absorbers, ultraviolet absorbers, and preservatives may be added as appropriate. The total amount of these additives is preferably 0.01 to 10% by mass relative to the total mass of the ink.

[0120] <Ink Manufacturing Method> The water-based inkjet black ink of this embodiment can be manufactured according to the method described below. However, the ink manufacturing method is not limited to the method described below, and known methods can also be used.

[0121] The method for producing an aqueous inkjet black ink of this embodiment includes (i) preparing an aqueous dispersion of carbon black-containing crosslinked polymer particles (A) (carbon black pigment dispersion), and (ii) adding an organic solvent (B) and, if necessary, additional components to the aqueous dispersion of carbon black-containing crosslinked polymer particles (A), followed by stirring and mixing. In step (i), the aqueous dispersion of carbon black-containing crosslinked polymer particles (A) can be obtained according to the method described above. In step (ii), the desired ink can be obtained by adding, if necessary, additional components such as a binder resin, a surfactant, and the other components described above, followed by stirring and mixing. After step (ii), filtration may be performed as needed.

[0122] <Ink Set> The aqueous inkjet black ink of this embodiment may be used in a single black color, or may be combined with aqueous inkjet inks of other colors to form an ink set depending on the application. The combination is not particularly limited, but examples include a cyan aqueous inkjet ink, a yellow aqueous inkjet ink, and a magenta aqueous inkjet ink. One embodiment of the present invention is an ink set that combines the three inks of cyan, yellow, and magenta with the aqueous inkjet black ink of this embodiment. Such an ink set can easily produce a full-color image with high clarity. The color reproducibility of printed materials can also be improved by adding an aqueous inkjet ink of an orange or green color to the ink set. Furthermore, when printing on a printing substrate other than white, a clear image can be obtained by using a white aqueous inkjet ink in combination.

[0123] <Printed Material and Manufacturing Method Thereof> One embodiment of the present invention relates to a printed material, which has a printing substrate and an ink film formed on the printing substrate using the aqueous inkjet black ink or ink set of the above-described embodiment. The ink film is formed by printing the ink onto the printing substrate according to the inkjet printing method described below. (Printed Material) The printing substrate onto which the aqueous inkjet black ink of this embodiment or an ink set containing the aqueous inkjet black ink is printed is not particularly limited, and the high-permeability substrates and low-permeability substrates described above can be suitably used. A non-permeable substrate may also be used as the printing substrate. As described above, the aqueous inkjet black ink of this embodiment can produce printed materials with excellent print density and print quality regardless of the permeability of the printing substrate.

[0124] In this specification, the permeability of a printing substrate is determined by the amount of water absorption measured by a dynamic scanning absorptivity meter. Specifically, the amount of pure water absorption measured by the following method for a contact time of 100 msec is 10 g / m ２ A printing substrate having a permeability of 1 g / m or more is called a "high permeability substrate." ２ 10g / m or more ２ A printing substrate with a permeability of less than 1 g / m is called a "low permeability substrate," and a printing substrate with a permeability of less than 1 g / m is called a "low permeability substrate." ２ A printing substrate that is less than this is considered an "impermeable substrate."

[0125] The amount of water absorption of a printing substrate can be measured under the following conditions. A dynamic scanning absorptivity meter, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd., is used to measure the amount of transferred pure water under the following conditions at 23°C and 50% RH using a printing substrate approximately 15 to 20 cm square: - Measurement method: Spiral scanning - Measurement start radius: 20 mm - Measurement end radius: 60 mm - Contact time: 10 to 1,000 msec - Number of sampling points: 19 (measured at approximately equal intervals relative to the square root of the contact time) - Scanning interval: 7 mm - Rotating table speed switching angle: 86.3 degrees - Headbox conditions: width 5 mm, slit width 1 mm

[0126] Examples of highly permeable substrates include uncoated paper such as sawdust paper, medium-grade paper, fine paper, and recycled paper, cotton, synthetic fiber fabrics, silk, hemp, and fabrics such as nonwoven fabrics, leather, etc. Among these, uncoated paper such as sawdust paper, medium-grade paper, fine paper, and recycled paper is preferably used because it allows prints to be obtained that are excellent in print density, color development, and print image quality.

[0127] Examples of low-permeability substrates include coated paper substrates such as coated paper, art paper, and cast paper. Examples of impermeable substrates include plastic substrates such as polyvinyl chloride, polyethylene terephthalate (PET), polypropylene, polyethylene, nylon, polystyrene, and polyvinyl alcohol, metal substrates such as aluminum, iron, stainless steel, and titanium, and glass substrates.

[0128] The printing substrates listed above may have a smooth or textured surface, and may be transparent, translucent, or opaque. Two or more of these printing substrates may be laminated together. A release adhesive layer or the like may be provided on the side opposite the printing surface, or an adhesive layer or the like may be provided on the printing surface after printing. The printing substrate used in the inkjet recording method described above may be in the form of a roll or a sheet.

[0129] (Printing method) The aqueous inkjet black ink of this embodiment is used in a printing method (inkjet printing method) in which the 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 then dried, preferably by a drying method described below, to form a printed matter (having at least an ink film layer on the printing substrate).

[0130] (Drying Method) A printing apparatus (inkjet printer) equipped with an aqueous inkjet black ink and used in the inkjet printing method preferably includes a mechanism for drying the aqueous inkjet black ink on a printing substrate. The drying method may be any one of the following: direct contact of the aqueous inkjet black ink with a heat source; indirect contact of the aqueous inkjet black ink with a heat source; and electromagnetic wave irradiation. Alternatively, a combination of these methods may be used. For example, by combining infrared drying (a method involving electromagnetic wave irradiation) and hot air drying (a method involving direct contact with a heat source), the aqueous inkjet black ink can be dried more quickly than by using either method alone. When using the hot air drying method, which involves direct contact of the aqueous inkjet black ink with a heat source, it is preferable to set the hot air temperature to 50 to 250°C in order to prevent bumping of the liquid components contained in the aqueous inkjet black ink and to obtain printed matter with excellent print density and print image quality. Furthermore, when a substrate heating method (a method in which the non-printing surface of a printing substrate is brought into contact with a heat source), which is a method indirectly bringing the water-based inkjet black ink into contact with a heat source, is employed, it is preferable to set the temperature of the heat source to 35 to 100°C, from the same viewpoint as in the case of the hot air temperature described above.

[0131] Representative embodiments of the present invention are described below. <1> An aqueous inkjet black ink containing crosslinked polymer particles (A) containing carbon black and an organic solvent (B), wherein the pH of the carbon black is 6.0 to 10.0, and the DBP oil absorption of the carbon black is AC (mL / 100 g), and the specific surface area of ​​the carbon black is SC (m ２ / g), the AC is 60 to 130, and the value expressed by AC x SC is 20,000 to 35,000, the crosslinked polymer particles (A) contain a crosslinked polymer (A-2) obtained by crosslinking an uncrosslinked polymer (A-1) having a carboxy group and / or a carboxylate group and an acid value of 50 to 180 mgKOH / g with a crosslinking agent, the crosslinking agent contains a compound having a plurality of functional groups in one molecule that react with a carboxy group and / or a carboxylate group, and the content of an organic solvent having a boiling point of 230°C or higher at 1 atmosphere is 10% by mass or less of the total amount of the aqueous inkjet black ink. <2> The aqueous inkjet black ink according to the above item <1>, wherein the organic solvent (B) contains a compound represented by the following general formula 1: １ -(O-CH(CH ３ )-CH ２ ) ｎ -OH General formula 1 (In general formula 1, R １ is an alkyl group having 1 to 4 carbon atoms, and n is 1 or 2. <3> The aqueous inkjet black ink according to <1> or <2> above, further comprising a surfactant having an HLB value of 12 or less. <4> The aqueous inkjet black ink according to any one of <1> to <3> above, further comprising a binder resin having an acid value of 1 to 50 mgKOH / g. <5> A printed material obtained by printing a printing substrate with the aqueous inkjet black ink according to any one of <1> to <4> above. The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2024-022493, filed on February 19, 2024, the entire disclosure of which is incorporated herein by reference.

[0132] The present invention will be described in more detail below with reference to examples and comparative examples. In the following description, "parts" and "%" represent "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0133] <Production of Pigment Dispersion Resin> The "pigment dispersion resins (also referred to as dispersion resins)" shown below all correspond to the uncrosslinked polymer (A-1) described above. These dispersion resins were obtained by synthesis using the method shown below.

[0134] <Production Example of Dispersion Resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of methyl ethyl ketone and purged with nitrogen gas. After heating the contents of the reaction vessel to 110 ° C, a mixture of 23 parts of polymerizable monomers, acrylic acid, 47 parts of methyl methacrylate, and 30 parts of lauryl methacrylate; and 6 parts of a polymerization initiator, V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was added dropwise to the reaction vessel over 2 hours. After completion of the dropwise addition, the temperature of the contents of the reaction vessel was maintained at 110 ° C, and the polymerization reaction was continued for 3 hours. After 3 hours, 0.6 parts of V-601 was added, and the reaction was continued for another 1 hour at 110 ° C, yielding a dispersion resin 1 precursor having only carboxy groups as hydrophilic groups. The weight average molecular weight of the resulting dispersion resin 1 precursor was 18,000 and the acid value was 179 mg KOH / g. The amount of potassium hydroxide required to achieve a neutralization rate of 100% was calculated using the acid value of the dispersion resin 1 precursor and Equation 3 above, and a 48% by mass aqueous potassium hydroxide solution containing an amount of potassium hydroxide equivalent to the calculated amount was added to convert the carboxy groups present in the dispersion resin 1 precursor to carboxylate groups (neutralization treatment). Ion-exchange water was then added to the solution to achieve a solids concentration of 20%, and the solution was heated to 50°C and stirred for 1 hour while maintaining the temperature at 50°C, yielding an aqueous solution of dispersion resin 1.

[0135] <Production Example of Dispersion Resins 2 to 8> Aqueous solutions of dispersion resins 2 to 8 (solid concentration 20% each) were obtained using the same raw materials and procedures as in the case of dispersion resin 1, except that the polymerizable monomers shown in Table 1 were used as the polymerizable monomers.

[0136]

[0137] 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

[0138] <Production Example of Dispersion Resin 9> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 26 parts of 1-octadecene, 18 parts of maleic anhydride, and 56 parts of N-phenylmaleimide, which are polymerizable monomers; and 100 parts of methyl ethyl ketone, which is a solvent. After purging with nitrogen gas, the contents in the reaction vessel were heated to 130°C while stirring. Next, while maintaining the temperature and stirring of the contents, 1.0 part of t-butylperoxy-2-ethylhexanoate, which is a radical polymerization initiator, was added dropwise over 2 hours. Thereafter, stirring was continued for another 1 hour while maintaining the temperature of the contents at 130°C, to carry out a polymerization reaction. After the start of the polymerization reaction, the solids concentration of the contents was measured at regular intervals, and the ratio of the solids concentration to the solids concentration assuming that all of the charged polymerizable monomers had polymerized (polymerization conversion rate) was calculated. When the polymerization conversion rate reached 95% or higher, the temperature in the reaction vessel was lowered to 60°C, and 33.0 parts of water and 0.01 parts of diazabicycloundecene catalyst were added. The contents of the reaction vessel were then heated to 80°C while stirring, and after reaching 80°C, the temperature was maintained at that temperature for 4 hours to open the maleic anhydride ring, resulting in a dispersion resin 9 precursor having only carboxy groups as hydrophilic groups. The resulting dispersion resin 9 precursor had a weight-average molecular weight of 20,000 and an acid value of 206 mgKOH / g. The acid value of the dispersion resin 9 precursor and Equation 3 above were then used to calculate the amount of potassium hydroxide required to achieve a neutralization rate of 100%, and a 48% by weight aqueous potassium hydroxide solution containing an equal amount of potassium hydroxide was added to convert the carboxy groups present in the dispersion resin 9 precursor into carboxylate groups (neutralization treatment). Then, ion-exchanged water was added so that the solid concentration became 20%, and the solution was then heated to 50°C and stirred for 1 hour while maintaining the temperature at 50°C, thereby obtaining an aqueous solution of dispersion resin 9.

[0139] <Production Example of Dispersion Resins 10 to 26> Synthesis was carried out using the same raw materials and procedures as in the case of Dispersion Resin 9, except that the type and amount of polymerizable monomer used were changed as shown in Table 2, to obtain aqueous solutions of Dispersion Resins 10 to 26 (solids concentration of 20% each).

[0140]

[0141] Table 2 also lists the raw materials used in the above-mentioned dispersion resin 9, as well as the weight average molecular weights and acid values ​​of dispersion resins 9 to 26. 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

[0142] <Example of Production of Aqueous Dispersion of Carbon Black-Containing Crosslinked Polymer Particle Precursor 1 (KB1)> 20 parts of PrinteX 90 (carbon black manufactured by Orion Engineered Carbons, physical properties will be described later), 25 parts of an aqueous solution of Dispersion Resin 1 (solids concentration 20%), and 55 parts of ion-exchanged water were charged into a mixing vessel. All raw materials were charged and pre-dispersed using a stirrer. After pre-dispersion, the main dispersion was carried out using a 0.6 L Dyno-Mill filled with 1,800 g of zirconia beads with a diameter of 0.5 mm. After the main dispersion, 33.3 parts of ion-exchanged water was added to the resulting mixture, and the mixture was heated at 60 ° C. while a portion of the ion-exchanged water and methyl ethyl ketone were distilled off under reduced pressure. Then, the pigment concentration was adjusted to 15% using ion-exchanged water to obtain an aqueous dispersion of carbon black-containing crosslinked polymer particle precursor 1 (KB1).

[0143] <Production Example of Aqueous Dispersions of Carbon Black-Containing Crosslinked Polymer Particle Precursors 2 to 39 (KB2 to KB39)> Aqueous dispersions of carbon black-containing crosslinked polymer particle precursors 2 to 39 (KB2 to KB39) were obtained in the same manner as for the aqueous dispersion of carbon black-containing crosslinked polymer particle precursor 1 (KB1), except that the carbon black and aqueous dispersion resin solutions shown in Table 3 were used. The pigment concentration in all aqueous dispersions was 15%. The physical properties of the carbon black used are shown in Table 4.

[0144]

[0145]

[0146] <Production Example of Aqueous Dispersion of Carbon Black-Containing Crosslinked Polymer Particles 1 (KP1)> 93.3 parts of the aqueous dispersion of carbon black-containing crosslinked polymer particle precursor 1 (KB1) obtained by the method described above, 1.4 parts (an amount such that the functional group content represented by the above formula 1 is 90 mol%) of Denacol EX-321 (an epoxy compound manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140 (g / eq.)) as a 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, stirring was continued for 3 hours while maintaining the temperature, thereby allowing a crosslinking reaction to occur. Thereafter, the internal temperature of the reaction vessel was cooled to room temperature (approximately 25°C), and ion-exchanged water was added to adjust the solids concentration, thereby obtaining an aqueous dispersion of carbon black-containing crosslinked polymer particles 1 (KP1) (pigment concentration 14%) in which the dispersion resin 1 was crosslinked.

[0147] <Production Example of Aqueous Dispersions of Carbon Black-Containing Crosslinked Polymer Particles 2 to 54 (KP2 to KP54)> Aqueous dispersions of carbon black-containing crosslinked polymer particles 2 to 54 (KP2 to KP54) were obtained in the same manner as for the aqueous dispersion of carbon black-containing crosslinked polymer particle 1 (KP1), except that the type of carbon black-containing crosslinked polymer particle precursor, the type and amount of crosslinking agent, and the amount of ion-exchanged water were changed as shown in Table 5. In all aqueous dispersions, the pigment concentration was 14%.

[0148]

[0149]

[0150] The abbreviation "V02" in Table 5 represents Carbodilite V-02 (carbodiimide compound, NCN equivalent: 590 (g / eq.)) manufactured by Nisshinbo Chemical Inc.

[0151] <Production Example of Binder Resin 1> A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 93.4 parts of butanol and purged with nitrogen gas. After heating the contents of the reaction vessel to 110°C, a mixture of polymerizable monomers (6 parts acrylic acid, 64 parts methyl methacrylate, 20 parts 2-ethylhexyl acrylate, 10 parts styrene) and 6 parts of a polymerization initiator (V-601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to the reaction vessel over 2 hours. After the addition was completed, the polymerization reaction was continued for 3 hours while the contents of the reaction vessel were maintained at 110°C. After 3 hours, 0.6 parts of V-601 was added, and the reaction was continued for another 1 hour at 110°C to obtain a solution of binder resin 1. Next, the binder resin 1 solution was cooled to room temperature, and 7.1 parts of dimethylaminoethanol was added to neutralize the carboxyl groups in binder resin 1. 100 parts of ion-exchanged water was then added. The mixture was then heated to 100°C or higher, and the temperature was maintained after reaching 100°C, causing azeotropic distillation of butanol with water, and the butanol was then distilled off. The solids concentration was then adjusted to 40% using ion-exchanged water, yielding an aqueous solution of binder resin 1, which is a water-soluble resin with a random structure. The weight-average molecular weight of the resulting binder resin 1 was 19,000, and the acid value was 47 mgKOH / g.

[0152] <Production Examples of Binder Resins 2 to 10> Aqueous solutions of binder resins 2 to 10, which are water-soluble resins having a random structure, were obtained using the same raw materials and procedures as for binder resin 1, except that the type and amount of polymerizable monomer used and the amount of dimethylaminoethanol used to neutralize the carboxyl groups were changed as shown in Table 6. The solids concentration of all of the aqueous solutions produced was 40%.

[0153]

[0154] Among the abbreviations listed in Table 6, those not used in Tables 1 and 2 are as follows: MAA: methacrylic acid 2EHA: 2-ethylhexyl acrylate STMA: stearyl methacrylate

[0155] <Production Example of Binder Resins 11 to 13> 124 parts of ion-exchanged water and 0.06 parts of an emulsifier, polyoxyethylene lauryl ether sodium sulfate ("Latemul E-150" manufactured by Kao Corporation), were charged into a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer. Meanwhile, a separate mixing vessel equipped with a stirrer was prepared, and polymerizable monomers, 0.5 parts of acrylic acid, 20 parts of styrene, and 79.5 parts of methyl methacrylate; 64 parts of ion-exchanged water; and 0.8 parts of an emulsifier, polyoxyethylene lauryl ether sodium sulfate ("Latemul E-150" manufactured by Kao Corporation), were charged, followed by stirring and mixing to form an emulsion. Next, 8 portions of the emulsion were taken and charged into a reaction vessel, the internal temperature was raised to 80°C, and the atmosphere inside the reaction vessel was thoroughly purged with nitrogen gas. Then, 4 parts of a 5% aqueous solution of potassium persulfate and 8 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added to initiate the polymerization reaction. After the polymerization reaction began, the internal temperature of the reaction vessel was maintained at 80°C, and the remaining emulsion, 1.2 parts of a 5% aqueous solution of potassium persulfate, and 2.5 parts of a 1% aqueous solution of anhydrous sodium bisulfite were added dropwise over 1.5 hours, followed by stirring for another 2 hours. After the reaction vessel was cooled to room temperature, 0.48 parts of dimethylethanolamine was added, and the solids concentration was adjusted to 40% using ion-exchanged water to obtain an aqueous dispersion of binder resin 11 (solids concentration 40%), which has a random structure and is made of resin particles. The acid value of the obtained binder resin 11 was 3 mgKOH / g.

[0156] Aqueous dispersions of binder resins 12 and 13, which have a random structure and are resin particles, were obtained using the same raw materials and procedures as for binder resin 11, except that the type and amount of polymerizable monomer used and the amount of dimethylaminoethanol added were changed as shown in Table 6. All of the aqueous dispersions had a solids concentration of 40%.

[0157] <Production of aqueous inkjet black ink> The raw materials listed in each column of Tables 7 and 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 black ink.

[0158]

[0159]

[0160]

[0161]

[0162]

[0163]

[0164]

[0165]

[0166]

[0167]

[0168]

[0169]

[0170]

[0171]

[0172]

[0173] The abbreviations listed in Tables 7 and 8 are as follows: PG: Propylene glycol (boiling point: 188°C) 1,2-BuD: 1,2-butanediol (boiling point: 191°C) 2m-2,4-PeD: 2-methyl-2,4-pentanediol (boiling point: 196°C) DPG: Dipropylene glycol (boiling point: 232°C) PGM: Propylene glycol monomethyl ether (boiling point: 120°C) DPM: Dipropylene glycol monomethyl ether (boiling point: 190°C) PNP: Propylene glycol monopropyl ether (boiling point: 150°C) DPNP: Dipropylene glycol monopropyl ether (boiling point: 210°C) PNB: Propylene glycol monobutyl ether (boiling point: 170°C) HeDG: Diethylene glycol monohexyl ether (boiling point: 260°C) DEG: Diethylene glycol (boiling point: 245°C) GLY: Glycerin (boiling point: 290°C)

[0174] TEGO Wet 240: siloxane-based surfactant manufactured by Evonik Japan (HLB value: 5 to 7) TEGO Wet 270: siloxane-based surfactant manufactured by Evonik Japan (HLB value: 2.5 to 4) BYK333: siloxane-based surfactant manufactured by BYK Japan (HLB value: 10 to 11) KF-6011: siloxane-based surfactant manufactured by Shin-Etsu Chemical Co., Ltd. (HLB value: 11 to 12) KF-640: siloxane-based surfactant manufactured by Shin-Etsu Chemical Co., Ltd. (HLB value: 13 to 14) Surfynol 104: acetylene diol-based surfactant manufactured by Evonik Japan (2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB value: 3.1) Surfynol 440: an acetylene diol surfactant manufactured by Evonik Japan (an ethylene oxide adduct of Surfynol 104, 3.5 moles of ethylene oxide added, HLB value: 8.1); Surfynol 465: an acetylene diol surfactant manufactured by Evonik Japan (an ethylene oxide adduct of Surfynol 104, 10 moles of ethylene oxide added, HLB value: 13.2);

[0175] Acetylenol E40: an acetylenic diol surfactant manufactured by Kawaken Fine Chemicals Co., Ltd. (ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, number of moles of ethylene oxide added: 4, HLB value: 8.8) Acetylenol E60: an acetylenic diol surfactant manufactured by Kawaken Fine Chemicals Co., Ltd. (ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, number of moles of ethylene oxide added: 6, HLB value: 10.8) Surfynol DF110D: an acetylenic diol surfactant manufactured by Evonik Japan Co., Ltd. (2,5,8,11-tetramethyldodeca-6-yne-5,8-diol, solids concentration: 32% by mass, HLB value: 2.7) Nonionic S-215: Polyoxyethylene stearyl ether (HLB value: 14.2) manufactured by NOF Corporation. NeoCryl A633: Acrylic resin particles (acid value: 33 (mgKOH / g)) manufactured by DSM.

[0176] [Examples 1 to 125, Comparative Examples 1 to 15] The aqueous inkjet black inks prepared above were evaluated as follows. The evaluation results are shown in Tables 7 and 8.

[0177] <Evaluation 1: Print density on coated paper> An inkjet ejection device equipped with an inkjet head (KJ4B-1200) manufactured by Kyocera Corporation was placed in a 25°C environment. Next, the water-based inkjet black ink produced above was filled into the inkjet head. After that, a nozzle check pattern was printed, and after confirming that ink was being ejected normally from all nozzles, the ink was left as is for 1 minute. After leaving it as is, a print density was also measured using OK Topcoat+ (coated paper, basis weight 104.7 g / m) manufactured by Oji Paper Co., Ltd. under printing conditions of a frequency of 40 kHz, 1,200 x 1,200 dpi, and a drop volume of 3 pL. ２A solid image (printing rate 100%, ink film thickness equivalent to approximately 6 μm) was printed on a sheet of paper, and the print was placed in a 60°C air oven within 10 seconds. After drying for 1 minute, the print was removed from the oven and the optical density (OD value) of the resulting solid print was measured using a spectrodensitometer (eXact manufactured by X-RITE). The optical density measurements were performed using a D50 light source, a 2° viewing angle, an ISO Status T density status, and an absolute value density white standard. The evaluation criteria were as follows, with "AA", "A", and "B" ratings being considered as usable ranges. (Evaluation Criteria) AA: OD value 2.1 or more A: OD value 2.0 or more but less than 2.1 B: OD value 1.90 or more but less than 2.0 C: OD value less than 1.90

[0178] <Evaluation 2: Print Density on Fine Paper> Using the inkjet printing device and under the same printing conditions as in Evaluation 1 above, a solid image (equivalent to 100% printing rate and ink film thickness of approximately 6 μm) was printed on OK Prince fine paper (fine paper) manufactured by Oji Paper Co., Ltd., and the print was placed in an air oven at 60°C within 10 seconds. After drying for 1 minute, the print was removed from the oven and the optical density (OD value) of the resulting solid print was measured under the same conditions as in Evaluation 1. The evaluation criteria were as follows, with "AA", "A", and "B" being considered as practical ranges. (Evaluation Criteria) AA: OD value 1.3 or more A: OD value 1.2 or more but less than 1.3 B: OD value 1.1 or more but less than 1.2 C: OD value less than 1.1

[0179] <Evaluation 3: Evaluation of white spots on coated paper> Using the inkjet printing device used in the above evaluation 1 and under the same printing conditions, white spots were printed on OK Topcoat + paper (coated paper, basis weight 104.7 g / m) manufactured by Oji Paper Co., Ltd. ２A solid image (printing rate 100%, ink film thickness equivalent to approximately 6 μm) was printed on a sheet of paper, and the print was placed in an air oven at 60°C within 10 seconds. After drying for 1 minute, the print was removed from the oven, and the degree of white bleed on the resulting solid print was checked visually and with a magnifying glass to evaluate white bleed. The evaluation criteria were as follows, with "AA", "A", and "B" being considered to be in the usable range. (Evaluation criteria) AA: No white bleed was observed visually or with a magnifying glass. A: Slight white bleed was observed with a magnifying glass, but no white bleed was observed visually. B: Slight white bleed was observed visually. C: White bleed was clearly observed visually.

[0180] <Evaluation 4: Evaluation of letter bleeding on fine paper> Using the inkjet printing device and under the same printing conditions as in Evaluation 1 above, a letter image was printed in 4-point MS Mincho font on OK Prince fine paper (fine paper) manufactured by Oji Paper Co., Ltd., and the printout was placed in an air oven at 60°C within 10 seconds. After drying for 1 minute, the printout was removed from the oven, and the degree of bleeding of the resulting letter image was evaluated visually and with a magnifying glass to evaluate bleeding. The evaluation criteria were as follows, with "AA", "A", and "B" being considered as practical ranges. (Evaluation criteria) AA: No letter bleeding was observed visually or with a magnifying glass. A: Slight letter bleeding was observed with a magnifying glass, but no bleeding was observed visually. B: Slight letter bleeding was observed visually. C: Letter bleeding was clearly observed visually.

[0181] <Evaluation 5: Evaluation of Ink Storage Stability> The viscosity of the aqueous inkjet black ink produced above was measured using an E-type viscometer. Next, the aqueous inkjet ink after viscosity measurement was placed in a container, sealed, and then left to stand in an air-blowing constant temperature incubator set at 70°C. After a predetermined period of time had passed, the viscosity of the aqueous inkjet black ink in the sealed container was removed from the air-blowing constant temperature incubator and measured again. The viscosity stability over time was evaluated by calculating the rate of change in viscosity before and after standing. The evaluation criteria were as follows, with "AA," "A," and "B" being considered as practical ranges. (Evaluation Criteria) AA: Viscosity change rate of 5% or less after storage at 70°C for 6 weeks A: Viscosity change rate of 5% or less after storage at 70°C for 5 weeks B: Viscosity change rate of 5% or less after storage at 70°C for 4 weeks C: Viscosity change rate of more than 5% after storage at 70°C for 4 weeks

[0182] <Evaluation 6: Evaluation of ejection stability> Using the inkjet printing device used in the above evaluation 1 and under the same printing conditions, an ink jet print was printed on OK Topcoat+ (coated paper, basis weight 104.7 g / m) manufactured by Oji Paper Co., Ltd. ２ ) and a nozzle check pattern was printed on the inkjet printer. After confirming that ink was being ejected normally from all nozzles, 100 A4-sized solid images were printed continuously using the ink loaded in the inkjet printing device as is. After printing, a nozzle check pattern was printed again and the number of clogged nozzles was visually counted to evaluate ejection stability. The evaluation criteria were as follows, with "AA", "A", and "B" being considered as practical ranges. (Evaluation criteria) AA: No clogged nozzles at all A: 1 to 3 clogged nozzles B: 4 to 9 clogged nozzles C: 10 to 49 clogged nozzles D: 50 or more clogged nozzles

[0183] <Evaluation 7: Evaluation of Drying Property> Using the inkjet printing device used in Evaluation 1 above and under the same printing conditions, a dryability test was carried out on OK Topcoat+ (coated paper, basis weight 104.7 g / m) manufactured by Oji Paper Co., Ltd. ２A solid image (printing rate 100%, ink film thickness equivalent to approximately 6 μm) was printed on a sheet of paper. After printing, the resulting printed substrate was placed in an air oven at 60°C, and the printed matter was removed at regular intervals and touched with the fingers to evaluate drying properties. The evaluation criteria were as follows, with "AA", "A", and "B" being considered as practically acceptable ranges. (Evaluation criteria) AA: The printed matter was dry with no tackiness when touched with the finger after 30 seconds of drying. A: The printed matter was dry with no tackiness when touched with the finger after 1 minute of drying, but was not dry at 30 seconds. B: The printed matter was dry with no tackiness when touched with the finger after 1 minute 30 seconds of drying, but was not dry at 1 minute. C: The printed matter was tackiness when touched with the finger after 1 minute 30 seconds of drying, and was not dry.

[0184] It was confirmed that the aqueous inkjet black inks of Examples 1 to 125, which had the constitution of the aqueous inkjet black ink of the present invention, had quality at a level suitable for practical use in all aspects of print density, print image quality, storage stability, ejection stability, and drying properties, regardless of the permeability of the printing substrate.

[0185] Furthermore, a comparison of Examples 2, 3, and 4 confirmed that by adjusting the acid value of the dispersion resin (uncrosslinked polymer (A-1)) to 180 mgKOH / g or less (preferably 160 mgKOH / g, and more preferably 150 mgKOH / g or less), print density and ejection stability on highly permeable substrates such as fine paper were improved. Furthermore, a comparison of Examples 24, 38, 39, and 99 to 106 confirmed that the use of a binder resin having an acid value of 50 mgKOH / g or less (preferably 40 mgKOH / g or less) improved the drying properties of printed matter, print image quality on highly permeable substrates, and ejection stability. These results confirmed that the acid values ​​of the uncrosslinked polymer (A-1) used in the production of the aqueous inkjet ink of this embodiment and the binder resin contained in the aqueous inkjet ink affected drying properties as well as print image quality and print density.

[0186] Furthermore, the aqueous inkjet black inks of Examples 75, 79, 81 to 83, 85, 86, 89, 93, 98, 102 to 104, 110, 111, 116, 121, and 122 used resins (polymers) having suitable acid values ​​as the uncrosslinked polymer (A-1) and binder resin, respectively, a compound represented by general formula 1 as the organic solvent (B), a surfactant having an HLB value of 0 to 4 (Surfynol 104, Surfynol DF110D, or TEGO WET270) as the surfactant, and furthermore, the amount of carbon black contained in the aqueous inkjet black ink was 3 to 8 mass%. All of these aqueous inkjet black inks were evaluated as "AA." These results confirmed that using a resin having the above-mentioned acid value, an organic solvent having a specific structure, and a surfactant having a specific HLB value, and further specifying the carbon black content, is extremely suitable for achieving the above-mentioned effects.

[0187] On the other hand, in Comparative Examples 1, 14, and 15, which used a carbon black-containing crosslinked polymer particle precursor, it is believed that the dispersion resin did not firmly adsorb to the carbon black, and as a result, the resulting aqueous inkjet black ink did not have storage stability and ejection stability at a practical level. In addition, a decrease in print density on coated paper was observed, which is believed to be due to the aggregation of the carbon black.

[0188] The aqueous inkjet black inks of Comparative Examples 2 to 4 had acid values ​​of the uncrosslinked polymer (A-1) outside the range specified by the present invention, and it was found that none of them had ejection stability that met practical quality. In particular, in Comparative Examples 2 and 3, which used an uncrosslinked polymer (A-1) with an acid value higher than 180 mg KOH / g, deterioration in print density and print image quality on fine paper was also observed, which is thought to be due to the uncrosslinked polymer (A-1) being less likely to react with cationic components. On the other hand, the aqueous inkjet black ink of Comparative Example 4, which used an uncrosslinked polymer (A-1) with an acid value lower than 50 mg KOH / g, exhibited deterioration in storage stability and a decrease in print density on coated paper.

[0189] Furthermore, the aqueous inkjet black ink of Comparative Example 5, which did not contain the organic solvent (B), did not have suitable wettability on coated paper, resulting in the occurrence of white voids, making it difficult to obtain printed matter with excellent print density and print quality.

[0190] In contrast, the aqueous inkjet black ink of Comparative Example 7 used carbon black (PrinteX 60) having specifications similar to those of the carbon black disclosed in the examples of Patent Document 2. The value of PrinteX 60, expressed as AC×SC, was below 20,000, and as a result, the print density and print quality of the printed matter on high-quality paper deteriorated.

[0191] On the other hand, in Comparative Examples 11 and 12, which used carbon black with an AC×SC value exceeding 35,000, it was difficult to ensure dispersion stability in the ink, and the ejection stability did not reach a practical level. Furthermore, when printing on a low-permeability printing substrate such as coated paper, a deterioration in print density was observed, which is thought to be due to aggregation of the pigment during the drying process.

[0192] Furthermore, in Comparative Examples 9 and 10, which used carbon black with a pH below 6.0, it was difficult to ensure excellent storage stability and ejection stability, and a decrease in print density on coated paper was also observed.

[0193] In Comparative Examples 13 and 14, which contained more than 10% by mass of an organic solvent with a boiling point of 230°C or higher, a decrease in print density and print image quality was observed, which was thought to be due to the organic solvent remaining on the fine paper. Furthermore, poor drying occurred on coated paper, making the ink unsuitable for practical use. The deterioration in print density on the fine paper is thought to be due to the large amount of organic solvent with a boiling point of 230°C or higher at 1 atmosphere, which made it difficult for the cationic components present in the fine paper to elute into the aqueous inkjet black ink. Furthermore, the organic solvent remaining on the fine paper is thought to have caused the aqueous inkjet black ink to penetrate along the fibers of the fine paper, resulting in a deterioration in print image quality.

[0194] The aqueous inkjet black ink of Comparative Example 14 reproduces the organic solvent composition of the aqueous inkjet ink specifically disclosed in the examples of Patent Document 3. As a result of the evaluation, as described above, the content of the organic solvent having a boiling point of 230°C or higher at 1 atmosphere was greater than 10% by mass, resulting in deterioration of print density and print image quality on fine paper. Furthermore, since Comparative Example 14 uses a carbon black-containing crosslinked polymer particle precursor, the pigment dispersion resin does not firmly adsorb to the carbon black, which is thought to have led to deterioration of storage stability and ejection stability, as well as a decrease in print density on coated paper.

[0195] The deterioration in storage stability and ejection stability, as well as the decrease in print density on coated paper, observed in Comparative Example 14 were also confirmed in Comparative Example 15, which used a carbon black-containing crosslinked polymer particle precursor. The aqueous inkjet black ink of Comparative Example 15 also exhibited deterioration in print density and print image quality on fine paper, which is thought to be due to an inability to react quickly with the cationic component. The aqueous inkjet black ink of Comparative Example 15 reproduces the organic solvent and surfactant composition of the aqueous inkjet ink disclosed in the examples of Patent Document 1.

[0196] [Examples 88B to 125B] On the other hand, the aqueous inkjet black inks 88 to 125 prepared by the method described above were subjected to the following evaluations 1B, 4B, and 8. The evaluation results are shown in Table 9.

[0197] <Evaluation 1B: Print density B on coated paper (infrared drying)> Using the inkjet printing device used in the above evaluation 1 and under the same printing conditions, a print density was measured using OK Topcoat+ (coated paper, basis weight 104.7 g / m) manufactured by Oji Paper Co., Ltd. 2A solid image (equivalent to a 100% printing rate and an ink film thickness of approximately 6 μm) was printed on the recording medium. Within 5 seconds, the resulting print was passed through an infrared dryer at a speed of 50 m / min. The infrared dryer used had an infrared lamp with a peak wavelength of 1.5 μm positioned parallel to the transport direction of the recording medium, irradiating the print substrate with infrared light over a length of 12 cm. In other words, the infrared light was irradiated onto the same location on the print substrate for approximately 0.14 seconds. The infrared output power was also adjusted in advance so that the surface temperature of the solid print was 90°C immediately after infrared irradiation. The print was then passed through the infrared dryer and the optical density (OD value) of the resulting solid print was measured using a spectrodensitometer (eXact, manufactured by X-RITE). The optical density measurements were performed using a D50 light source, a 2° viewing angle, an ISO Status T density status, and an absolute density white standard. The evaluation criteria were as follows, with "AA", "A", "B", "C", and "D" being considered as practical ranges. (Evaluation criteria) AA: OD value 2.25 or more A: OD value 2.2 or more and less than 2.25 B: OD value 2.1 or more and less than 2.2 C: OD value 2.0 or more and less than 2.1 D: OD value 1.9 or more and less than 2.0 E: OD value less than 1.9

[0198] <Evaluation 4B: Evaluation of Character Bleeding on Plain Paper> Using the inkjet printing device and under the same printing conditions as in Evaluation 1 above, character images were printed in 3-point and 4-point MS Mincho fonts on J Paper (plain paper) manufactured by Konica Minolta, and the prints were placed in an air oven at 60°C within 10 seconds. After drying for 1 minute, the prints were removed from the oven, and the degree of bleeding of the resulting character images was evaluated visually and with a magnifying glass. The evaluation criteria were as follows, with "AA", "A", "B", and "C" being considered as practical ranges. (Evaluation criteria) AA: No bleeding was observed with the naked eye or with a magnifying glass in the 3-point character image. A: Slight bleeding was observed with a magnifying glass in the 3-point character image, but no bleeding was observed with the naked eye. B: Slight bleeding was observed with a magnifying glass in the 4-point character image, but no bleeding was observed with the naked eye. C: Slight bleeding was observed with the naked eye in the 4-point character image. D: Clear bleeding of the characters was observed with the naked eye in the 4-point character image.

[0199] <Evaluation 8: Evaluation of ejection stability after standby for printing> A solid image was printed with a coverage rate of 100% using the inkjet printing device and under the same printing conditions as in Evaluation 1 above. After that, the inkjet printing device was left to stand by for a certain period of time in an environment of 25°C without printing, and then a nozzle check pattern was printed. The nozzle check pattern was then observed, and the number of missing nozzles (nozzles that were not ejecting) was visually confirmed to evaluate the ejection stability after standby for printing. The evaluation criteria were as follows, with ratings of "AA," "A," "B," "C," and "D" being considered to be within the range of practical use. (Evaluation criteria) AA: No missing nozzles occurred when printing after waiting for 3 hours. A: No missing nozzles occurred when printing after waiting for 2 hours, but missing nozzles occurred when printing after waiting for 3 hours. B: No missing nozzles occurred when printing after waiting for 1 hour, but missing nozzles occurred when printing after waiting for 2 hours. C: 1 to 3 missing nozzles occurred when printing after waiting for 1 hour. D: 4 to 9 missing nozzles occurred when printing after waiting for 1 hour. E: 10 or more missing nozzles occurred when printing after waiting for 1 hour.

[0200]

[0201] Aqueous inkjet black inks 88-125 contain higher carbon black content than aqueous inkjet black inks 1-87. Examples 88B-125B provide a detailed evaluation of the quality differences in such systems.

[0202] In Examples 88B to 98B, the effects of surfactants contained in aqueous inkjet black inks on print density, bleeding, and ejection stability of printed materials were evaluated. The evaluation results showed that the use of surfactants with an HLB value of 12 or less (preferably 8 or less, and particularly preferably 4 or less) significantly improved print density on coated paper. In particular, when a surfactant with an HLB value of 4 or less was used, the aqueous inkjet black ink quickly spread on low-permeability substrates, resulting in a smooth ink film surface and excellent print density, even when rapidly heated and dried using infrared irradiation or the like. Furthermore, Examples 93B and 98B contain an acetylene-based surfactant with an HLB value of 4 or less, and the ratio of the content of the acetylene-based surfactant to the content of the crosslinker (0.0054% by mass) contained in the aqueous inkjet black ink was approximately 185. These systems were confirmed to not only achieve excellent print density on coated paper, but also excellent ejection stability after waiting for printing.

[0203] Furthermore, from a comparison of Examples 99B to 106B, it was confirmed that by controlling the acid value of the binder resin, specifically, by setting the acid value to 1 to 50 mgKOH / g (preferably 2 to 40 mgKOH), bleeding of characters is suppressed and print image quality is improved, not only when printing on high-permeability substrates such as not only fine paper but also plain paper, and ejection stability is also improved.

[0204] Furthermore, a comparison of Examples 118B to 125B confirmed that by incorporating a crosslinking agent such that the functional group content calculated by the above formula 2 is 50 to 150 mol%, dispersion stability can be ensured even after water has evaporated, the print density is improved on a low-permeability substrate, and further, excellent ejection stability is maintained even after waiting for printing.

Claims

1. An aqueous inkjet black ink containing crosslinked polymer particles (A) containing carbon black and a crosslinked polymer (A-2), and an organic solvent (B), wherein the pH of the carbon black is 6.0 to 10.0, and the DBP oil absorption of the carbon black is AC (mL / 100g), and the specific surface area of ​​the carbon black is SC (m ２ / g), the AC is 60 to 130, and the value expressed by AC x SC is 20,000 to 35,000, the crosslinked polymer (A-2) is a crosslinked polymer obtained by crosslinking an uncrosslinked polymer (A-1) having a carboxy group and / or a carboxylate group and an acid value of 50 to 180 mgKOH / g with a crosslinking agent, the crosslinking agent containing a compound having a plurality of functional groups in one molecule that react with a carboxy group and / or a carboxylate group, and the content of an organic solvent having a boiling point of 230°C or higher at 1 atmospheric pressure is 10% by mass or less of the total amount of the aqueous inkjet black ink.

2. The water-based inkjet black ink according to claim 1, wherein the organic solvent (B) contains a compound represented by the following general formula 1: １ -(O-CH(CH ３ )-CH ２ ) ｎ -OH General formula 1 (In general formula 1, R １ is an alkyl group having 1 to 4 carbon atoms, and n is 1 or 2.

3. The water-based inkjet black ink according to claim 1 or 2, further comprising a surfactant having an HLB value of 12 or less.

4. The water-based inkjet black ink according to claim 1 or 2, further comprising a binder resin having an acid value of 1 to 50 mgKOH / g.

5. A printed matter having a printing substrate and an ink film formed on the printing substrate using the water-based inkjet black ink according to claim 1 or 2.

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