Water-based ink, ink cartridge, and ink-jet recording method

Abstract

The present invention provides a water-based ink that uses a self-dispersing pigment as a coloring material, which is capable of recording images with good color development and has good storage stability. [Solution] A water-based inkjet ink containing a self-dispersing pigment. The self-dispersing pigment is a self-dispersing pigment having functional groups bonded to the surface of the pigment particles. The functional groups include a first functional group represented by the following general formula (1) and a second functional group containing at least one group represented by the following general formula (2). In the self-dispersing pigment, the amount of anionic groups in the first functional group is 0.20 to 0.97 times the total amount of anionic groups in the first functional group and the second functional group, in terms of molar ratio. TIFF2026042724000024.tif44170

Description

[Technical Field]

[0001] The present invention relates to a water-based ink, an ink cartridge, and an inkjet recording method. [Background technology]

[0002] In recent years, inkjet recording devices have been increasingly used in offices. In such applications, it is necessary to achieve a high level of image quality on a wide variety of recording media, particularly plain paper, and to maintain the ejection characteristics even when the recording device is used for a long period of time.

[0003] In response to these demands, a technology for achieving both image quality and reliability has been proposed: inks using self-dispersing pigments, which are modified by bonding organic groups to the pigment particle surface. For example, Patent Document 1 proposes a modified pigment to which an organic group having a carboxylic acid group is bonded. Patent Document 2 proposes improving the optical density of images by using a self-dispersing pigment in which a functional group highly reactive with calcium is selected based on a calcium index value, which defines an index of reactivity with calcium. Patent Document 3 also proposes an ink containing a self-dispersing pigment bonded with a functional group containing a phosphonic acid group, which is an ionic group that readily reacts with inorganic salts contained in a recording medium, and a functional group containing a carboxylic acid group or a sulfonic acid group, which is an ionic group that readily ionizes. This proposal is said to enable the recording of images with excellent color development and to improve the intermittent ejection stability of the ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2009-506196 [Patent Document 2] Special Publication No. 2009-515007 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-253230 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors, aiming to achieve both high image quality and reliability, used various self-dispersing pigments in which organic groups are bonded to the pigment particle surface, and prepared aqueous inkjet inks corresponding to each of the various self-dispersing pigments. When image quality was evaluated using various plain papers as recording media, some recording media produced images with high color development. However, on the other hand, most of the aqueous inks using various self-dispersing pigments produced images with low color development, and it was found that the quality was insufficient.

[0006] Furthermore, even when an image with low color development has been recorded on a recording medium using some water-based inks that use self-dispersing pigments, there are water-based inks that use self-dispersing pigments that can record an image with sufficient color development on that recording medium. However, it has been found that the particle size of the pigment in the ink after storage increases significantly compared to the particle size of the pigment in the ink before storage, and that some of these inks have an insufficient level of storage stability.

[0007] Therefore, an object of the present invention is to provide an aqueous inkjet ink containing a self-dispersing pigment as a colorant, which is capable of recording images with good color development and has good storage stability. Another object of the present invention is to provide an ink cartridge and an inkjet recording method using this aqueous ink. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided an aqueous inkjet ink containing a self-dispersing pigment, wherein the self-dispersing pigment is a self-dispersing pigment having functional groups bonded to the surface of the pigment particles, the functional groups comprising a first functional group represented by the following general formula (1) and a second functional group containing at least one type of group represented by the following general formula (2), and the amount of anionic groups of the first functional group in the self-dispersing pigment (mmol / g) is 0.20 to 0.97 times the molar ratio of the total amount of anionic groups of the first functional group and the second functional group (mmol / g):

[0009] TIFF2026042724000001.tif45170 (in the general formula (1), M 1 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. * represents the bonding position with the particle surface of the pigment.

[0010] TIFF2026042724000002.tif45170 (in the general formula (2), R 1 ~R 5 Two of them are COOM 2 and three are hydrogen atoms, and the two COOM 2 are adjacent to each other or are separated by one carbon atom that constitutes a benzene ring. 2 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. * represents the bonding position with the particle surface of the pigment. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an aqueous ink containing a self-dispersing pigment as a colorant, which is capable of recording images with good color development and has good storage stability. Furthermore, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method using this aqueous ink. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a cross-sectional view schematically illustrating an embodiment of an ink cartridge of the present invention. [Figure 2] 1A and 1B are diagrams schematically illustrating an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which FIG. 1A is a perspective view of the main part of the inkjet recording apparatus, and FIG. 1B is a perspective view of a head cartridge. [Figure 3] FIG. 2 is a schematic diagram illustrating an example of a cleaning unit of an inkjet recording apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Unless otherwise specified, physical property values ​​are values ​​at room temperature (25°C) and normal pressure (1 atmosphere). Furthermore, the unit "mmol / kg" in the present invention is calculated assuming that the specific gravity of the ink is "1 g / mL."

[0014] When using the same aqueous ink, a recording medium on which an image with low color development is recorded has characteristics such as a faster ink penetration rate and a lower amount of inorganic salts, such as calcium, that cause pigment aggregation, compared to a recording medium on which an image with high color development is recorded. In such recording media, many conventional self-dispersing pigments, in which organic groups are bonded to the surface of pigment particles, such as the ink described in Patent Document 2, tend to sink into the interior of the recording medium after the ink is applied to the recording medium before agglomerating on or near the surface of the recording medium. Therefore, the amount of pigment present on or near the surface of the recording medium is low, and the pigment sinks into the interior of the recording medium, resulting in a decrease in the color development of the image.

[0015] One conventional technique for improving the color development of images on the above-described recording media involves agglomerating the pigment before it sinks into the recording medium, leaving it on or near the surface of the recording medium. This method effectively involves designing an ink formulation that accelerates pigment aggregation as the ink's liquid components evaporate. However, with this type of formulation, when an inkjet recording device is used over a long period of time, interactions between pigment particles can cause the pigment to aggregate, increasing the pigment particle size and reducing storage stability. Therefore, with conventional techniques, it has been difficult to achieve both image color development and ink storage stability.

[0016] Furthermore, as described in Patent Documents 2 and 3, there is a method in which an ink containing a self-dispersing pigment bonded with a functional group containing a specific ionic group is used, and the pigment is aggregated by a reaction between an inorganic salt in the recording medium and the ionic group, and remains on the surface of the recording medium or in its vicinity. However, even when an ink containing such a self-dispersing pigment is used, it has been found that the color development of the recorded image is poor on recording media that are easy to penetrate with the ink and have a low content of inorganic salt.

[0017]

[0003] In order to improve the color development of images without impairing the storage stability of the ink, the present inventors investigated a technique for efficiently retaining the pigment on the surface of a recording medium without using a method that promotes aggregation of the pigment when the liquid components of the ink evaporate. As a result, they concluded that it would be effective to adsorb the pigment to cellulose, a component of the recording medium, by utilizing an interaction that occurs between the pigment and cellulose. Based on this technical concept, the present inventors prepared and investigated self-dispersing pigments in which various surface functional groups are bonded to the pigment particle surface.

[0018] As a result, we found that a self-dispersing pigment in which a functional group represented by general formula (1) is bonded to the surface of the pigment particle has improved adsorption to cellulose, and can improve the color development of images even on recording media on which ink penetrates quickly and images with low color development are recorded. However, even when this self-dispersing pigment is used, storage stability can sometimes be poor when using an inkjet recording device over a long period of time.

[0019] Therefore, the present inventors investigated a self-dispersing pigment in which, in addition to a first functional group represented by general formula (1), a second functional group containing at least one group represented by general formula (2) is bonded to the surface of the pigment particle. They found that both image color development and ink storage stability can be achieved by adjusting the molar ratio of the anionic group content of the first functional group to the total anionic group content of the first and second functional groups to 0.20 to 0.97. The anionic group content (mmol / g) of the first and second functional groups is the number of millimoles (mmol) of anionic groups per unit mass (g) of the pigment. The present inventors speculate as follows about the reason why aqueous inks containing the above specific self-dispersing pigments can achieve both image color development and ink storage stability.

[0020] First, we will explain color development. Self-dispersing pigments with a first functional group represented by general formula (1) bonded to the pigment particle surface have been shown to exhibit improved cellulose adsorption compared to self-dispersing pigments with other surface functional groups, suggesting that they have a specific interaction with cellulose. The interactions involved in the adsorption of self-dispersing pigments to cellulose include the interaction between the pigment particle surface and cellulose, and the interaction between the surface functional group and cellulose, each of which can involve hydrophobic and hydrophilic interactions. Cellulose has a structure in which hydrophilic hydroxyl groups are arranged at both ends of the main chain of the glucopyranose ring. The first functional group represented by general formula (1) has a structure in which two hydrophilic carboxylic acid groups are located para to each other with respect to the benzene ring. Compared to general formula (2), the structure of the functional group represented by general formula (1) has a substituent positional relationship that efficiently generates both hydrophobic interactions between the glucopyranose ring and benzene ring of cellulose and hydrogen bonds between the hydroxyl group and carboxylic acid group of cellulose. It is presumed that this structure allows specific interactions to occur, improving the adsorption of the self-dispersing pigment to cellulose.

[0021] However, inks containing self-dispersing pigments in which only the first functional group, out of the first functional group represented by general formula (1) and the second functional group containing at least one type of group represented by general formula (2), is bonded to the pigment particle surface have the following problem: Specifically, the pigment may aggregate after accelerated testing at high temperatures, simulating the long-term use of an inkjet recording device. To address this issue, it was found that it is sufficient to bond the first functional group and the second functional group to the pigment particle surface and set the molar ratio of the anionic group in the first functional group to the total anionic group amount of the above functional groups at 0.20 to 0.97 times. By achieving this configuration, it was possible to improve storage stability without impairing color development.

[0022] To maintain stable pigment dispersion, it is important to ensure sufficient electrostatic repulsion between particles. In the first functional group represented by general formula (1), two carboxylic acid groups are attached to the benzene ring via two of the carbon atoms that make up the benzene ring, and are positioned para to each other relative to the benzene ring. In contrast, in the group represented by general formula (2), the two carboxylic acid groups attached to the benzene ring are adjacent or are attached to the benzene ring via one of the carbon atoms that make up the benzene ring, and are positioned ortho or meta to each other relative to the benzene ring. Therefore, the group represented by general formula (2) has a closer distance between the carboxylic acid-derived charges than the first functional group represented by general formula (1), resulting in a structure in which the charges are localized. This structural difference is thought to improve storage stability in inks containing self-dispersible pigments in which both the first and second functional groups are attached to the pigment particle surface, as the localized charges effectively act as electrostatic repulsion between pigment particles.

[0023] On the other hand, an ink containing both a self-dispersing pigment having a first functional group but no second functional group and a self-dispersing pigment having a second functional group but no first functional group cannot achieve both image color development and ink storage stability. The reason for this is presumed to be as follows: Self-dispersing pigments without a second functional group have weak interparticle electrostatic repulsion in the ink. Therefore, when an inkjet recording device is used over a long period of time, the pigment aggregates due to interactions between the pigment particles, increasing the pigment particle size and resulting in poor storage stability. Furthermore, as mentioned above, self-dispersing pigments without a first functional group have weak interactions with cellulose in the recording medium and tend to sink into the recording medium before agglomerating, resulting in poor image color development. In other words, it is necessary to use a self-dispersing pigment in which both a first functional group and a second functional group are bonded to the pigment particle surface.

[0024] Additionally, in a self-dispersing pigment having both a first functional group and a second functional group bonded to the surface of the pigment particles, the molar ratio of the anionic group content of the first functional group to the total anionic group content of the first functional group and the second functional group is set to 0.20 or more. This effectively improves the adsorption of the pigment to cellulose, thereby improving the color development of the image. Furthermore, by setting the molar ratio to 0.97 or less, the electrostatic repulsion between pigment particles is effectively exerted, improving the storage stability of the ink.

[0025] As described above, in the present invention, by controlling the ratio of functional groups in the self-dispersing pigment based on the properties of each functional group described above, it is possible to improve the adsorption of the pigment to cellulose and the color development of a recording medium on which an image with low color development is recorded, while also achieving storage stability.

[0026] <Water-based ink> The aqueous ink of the present invention is an aqueous inkjet ink containing a self-dispersing pigment. The self-dispersing pigment is a self-dispersing pigment in which specific functional groups are bonded to the surface of the pigment particles. The ink of the present invention does not need to be a so-called "curable ink." Therefore, the ink of the present invention does not need to contain a compound such as a polymerizable monomer that can be polymerized by the addition of external energy. Below, each component constituting the ink of the present invention and the physical properties of the ink are described in detail.

[0027] (self-dispersing pigment) The ink contains, as a colorant, a self-dispersing pigment in which a functional group is bonded to the surface of the pigment particles. The functional group in the self-dispersing pigment includes a first functional group represented by the following general formula (1) and a second functional group containing at least one type of group represented by the following general formula (2). The ink may contain one type of self-dispersing pigment in which the first functional group and the second functional group are bonded to the surface of the pigment particles, or may contain two or more types. Furthermore, in the self-dispersing pigment, the first functional group bonded to the surface of the pigment particles may be of one type, like the second functional group, or may be of multiple types, such as M in general formula (1). 1 The content (mass %) of the self-dispersing pigment in the ink is preferably from 0.10% to 15.00% by mass, and more preferably from 1.00% to 10.00% by mass, based on the total mass of the ink.

[0028] TIFF2026042724000003.tif45170(in general formula (1), M 1 Each independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. * represents the bonding position with the pigment particle surface.

[0029] TIFF2026042724000004.tif45170(in general formula (2), R 1 ~R 5 Two of them are COOM 2 and three are hydrogen atoms, and the two COOM 2 are adjacent to each other or are separated by one carbon atom that constitutes a benzene ring. 2Each independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. * represents the bonding position with the pigment particle surface.

[0030] [Functional group] In the general formulas (1) and (2), COOM 1 and COOM 2 The carboxylic acid group represented by the formula (I) is a type of anionic group, and at least a portion of it may form a salt. When the carboxylic acid group forms a salt, at least one of the protons of each group is substituted with a cation. Examples of the cation include alkali metal ions, ammonium ions, and organic ammonium ions. Examples of the alkali metal ions include ions of lithium, sodium, potassium, etc. Examples of the organic ammonium ions include cations of aliphatic amines such as mono- to trialkylamines; and aliphatic alkanolamines such as mono- to trialkanolamines, and salts thereof. The anionic group is particularly preferably an alkali metal salt type such as sodium or potassium, or an ammonium salt type.

[0031] In general formula (2), R 1 , R 2 , R 3 , R 4 , and R 5 Two of these are COOM 2 and three are hydrogen atoms. 1 ~R 5 Two of the COOM 2 are adjacent to each other or are separated by one carbon atom that constitutes a benzene ring. 2 are located in the ortho or meta position relative to the benzene ring. 2 The bonding positions of the group (a) can be the 2nd and 3rd positions, the 3rd and 4th positions, the 2nd and 4th positions, or the 3rd and 5th positions, assuming that the bonding position with the pigment particle surface (* in general formula (2)) is the 1st position.

[0032] The second functional group containing at least one type of group represented by general formula (2) preferably contains a group represented by the following general formula (3). By using a self-dispersing pigment in which the first functional group and the group represented by the following general formula (3) are bonded to the surface of the pigment particles, the storage stability of the ink is further improved. In general formula (3), two carboxylic acid groups (COOM) bonded to a benzene ring 2 ) are adjacent to each other, the distance between the charges derived from the carboxylic acid is short, resulting in a structure in which the charges are localized. In addition, because the two carboxylic acid groups are arranged so that they face outward relative to the pigment particle surface, the localized charges are likely to contribute to electrostatic repulsion. As a result, the group represented by general formula (3) is presumed to have excellent storage stability because electrostatic repulsion between pigment particles works more effectively than other groups represented by general formula (2).

[0033] TIFF2026042724000005.tif35170(in general formula (3), M 2 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0034] In a self-dispersing pigment having functional groups containing the first and second functional groups bonded to the particle surface of the pigment, the molar ratio of the anionic group content of the first functional group to the total anionic group content of the first and second functional groups is 0.20 to 0.97. From the viewpoint of more effectively generating an interaction between the first functional group represented by general formula (1) and cellulose, a component of the recording medium, and further improving the color development of the image, the molar ratio is preferably 0.40 to 0.97.

[0035] The anionic group amount (mmol / g) of the first functional group is preferably 0.010 mmol / g or more and 0.200 mmol / g or less. The anionic group amount (mmol / g) of the second functional group is preferably 0.005 mmol / g or more and 0.150 mmol / g or less. The anionic group amount of the functional group of the self-dispersion pigment refers to the amount (mol) of anionic groups contained in the functional group per unit mass of the self-dispersion pigment.

[0036] The anionic group amounts of the first and second functional groups can be measured by analyzing the structure of the atomic groups bonded to the particle surface of the pigment constituting the self-dispersed pigment using pyrolysis gas chromatography / mass spectrometry (pyrolysis GC / MS). Specifically, a self-dispersed pigment having only one of the two functional groups to be quantified is used as a standard, and the anionic group amount of each functional group is calculated. In the examples described below, a thermogravimetric analyzer (trade name "TGA550" manufactured by TA Instruments) was used to heat the sample from 30°C to 600°C at a temperature increase rate of 2°C / min, and the amount of anionic groups was calculated from the mass at 400°C. It is also possible to measure the anionic group amounts of the first and second functional groups using a self-dispersed pigment extracted from ink by an appropriate method. To accurately measure the anionic group amounts of the first and second functional groups by removing impurities, it is preferable to purify the sample by washing the self-dispersed pigment and centrifuging the sample (pigment dispersion) during sample preparation.

[0037] The total anionic group amount (mmol / g) of the first functional group and the second functional group is preferably 0.08 mmol / g or more. When the total anionic group amount (mmol / g) is 0.08 mmol / g or more, the pigment has sufficient functional groups, and the electrostatic repulsion effect between particles derived from the anionic groups in the functional groups is sufficient, which further improves the storage stability of the ink. Furthermore, the total anionic group amount (mmol / g) is more preferably 0.20 mmol / g or less. When the total anionic group amount is 0.20 mmol / g or less, the pigment's anionic groups are kept to an appropriate amount. In this case, the pigment's hydrophilicity is appropriately reduced, which also appropriately reduces its affinity for liquid components in the ink. Therefore, after the ink is applied to a recording medium, adsorption due to interaction between the pigment and cellulose on the surface of the recording medium becomes relatively more likely, which further improves color development. The total amount of anionic groups, including the first and second functional groups, refers to the total amount of anionic groups, including the first and second functional groups, per unit mass of the self-dispersion pigment, and can be adjusted by the amount of the first and second functional groups bonded to the surface of the pigment particles. Note that the pigment before the treatment to bond each functional group may also contain a small amount of anionic groups, but this amount is negligible.

[0038] The total amount of anionic groups, consisting of the first and second functional groups bonded to the pigment particle surface, can be measured as the surface charge of the self-dispersible pigment. The surface charge can be measured by colloid titration using potential difference. A larger surface charge indicates a larger number of anionic groups, while a smaller surface charge indicates a smaller number of anionic groups. The amount of anionic groups (mmol / g) of a self-dispersible pigment is the amount (mmol) per gram of solids in the self-dispersible pigment. In the examples described below, the amount of anionic groups in the self-dispersible pigment in the pigment dispersion was measured by colloid titration using potential difference using an automatic potentiometric titrator (product name "AT-510" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500). Methyl glycol chitosan was used as the titration reagent. It is also possible to measure the amount of anionic groups using a self-dispersible pigment extracted from ink by an appropriate method. In order to accurately measure the amount of anionic groups by removing impurities, it is preferable to perform preliminary preparations such as washing the self-dispersing pigment and centrifuging the sample (pigment dispersion) when preparing the sample. Note that, although the pigment may contain a very small amount of anionic groups before the treatment to attach each functional group is performed, this amount is negligible. The total amount of anionic groups in the first and second functional groups can also be measured by the above-mentioned pyrolysis GC / MS, but colloid titration is preferred because it does not require a standard sample and allows for easy measurement.

[0039] [Pigment types and physical properties] Examples of pigments that can be used to form self-dispersing pigments include inorganic pigments such as carbon black, calcium carbonate, and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine. One or more of these pigments can be used. For purposes such as color matching, dyes can be used in combination with the pigment. Among the pigments, carbon black is preferred. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black, and one or more of these can be used.

[0040] The DBP oil absorption of carbon black is preferably 50 mL / 100 g or more and 200 mL / 100 g or less. Of these, 120 mL / 100 g or more and 170 mL / 100 g or less is more preferable, and 120 mL / 100 g or more and 150 mL / 100 g or less is particularly preferable. The DBP oil absorption of carbon black can be measured by a method conforming to JIS K6221 or ASTM D 2414. These methods involve adding dibutyl phthalate dropwise to 100 g of carbon black while stirring, and measuring the amount of dibutyl phthalate added at the point where the torque reaches its maximum.

[0041] The specific surface area of ​​carbon black by the BET method is 100m 2 / g or more 600m 2 / g or less. The specific surface area of ​​carbon black measured by the BET method can be measured by a method conforming to JIS K6217, ASTM D6556, or the like. These methods involve immersing degassed carbon black in liquid nitrogen and measuring the amount of nitrogen adsorbed on the particle surface of the carbon black when equilibrium is reached. The specific surface area of ​​carbon black measured by the BET method is 200 m 2 / g or more. 2 By selecting carbon black with a surface area of ​​1 / 2 or more, it is possible to ensure that the self-dispersing pigment has a surface area that can effectively adsorb onto cellulose, further improving color development.

[0042] The primary particle diameter of carbon black is preferably 10 nm or more and 40 nm or less. Carbon black usually exists in the form of secondary particles, in which multiple primary particles are connected three-dimensionally like a bunch of grapes. The primary particle diameter refers to the particle diameter of the smallest unit of carbon black (primary particle) that forms one secondary particle. The primary particle diameter of carbon black can be determined by observing and measuring the particle diameters of approximately 100 smallest unit carbon black particles that form a particle using a transmission or scanning electron microscope, and then calculating the arithmetic average value.

[0043] The average particle size of carbon black is preferably 50 nm or more and 200 nm or less. The average particle size of carbon black means the particle size of carbon black in the form in which it normally exists, i.e., the particle size of carbon black as secondary particles. The average particle size of carbon black is the 50% cumulative value [D 50 (nm)] can be measured using a particle size distribution measuring device using a dynamic light scattering method.

[0044] Measurement of the surface charge amount by colloid titration, which will be described later, can be affected if the particle size of the pigment is extremely large or small. In order to improve measurement accuracy while obtaining high-level ejection characteristics as an inkjet ink, it is necessary to determine the average particle size (D 50 ) is preferably 60 nm or more and 180 nm or less. 90 (90% cumulative value of particle size distribution on a volume basis) is preferably 100 nm or more and 320 nm or less.

[0045] [Method for producing self-dispersing pigment] Manufacturing methods for self-dispersing pigments are broadly divided into oxidation type and surface modification type. For self-dispersing pigments used in aqueous inks, a surface modification type manufacturing method is selected, which allows control of the chemical structure and amount of surface functional groups. Examples of surface modification type manufacturing methods include chemically treating the pigment using a treating agent such as a compound capable of generating a diazonium salt, an azo compound, a diazene compound, or a triazine compound.

[0046] Methods for producing self-dispersing pigments include a method for bonding first and second functional groups to the surface of pigment particles in a stepwise manner, and a method for bonding first and second functional groups in parallel. Either method can produce a self-dispersing pigment. The method for bonding first and second functional groups in a stepwise manner preferably involves a step of surface-treating the pigment with a first treatment agent having a first functional group and a step of surface-treating the pigment with a second treatment agent having a second functional group. The method for bonding first and second functional groups in parallel preferably involves a step of surface-treating the pigment using both the first and second treatment agents. In the present invention, it is preferable to produce a self-dispersing pigment by performing the steps for bonding each functional group in a stepwise manner. It is particularly preferable to produce a self-dispersing pigment by performing a step of surface-treating the pigment with a first treatment agent having a first functional group and a step of surface-treating the pigment with a second treatment agent having a second functional group in a stepwise manner.

[0047] (Compound represented by general formula (4)) The ink preferably contains a compound represented by the following general formula (4). In this case, the ink may contain one or more of the compounds represented by general formula (4). The content C (mmol / kg) of the compound represented by general formula (4) in the ink is preferably 0.01 mmol / kg or more and 15.00 mmol / kg or less. The content C (mmol / kg) is more preferably 0.02 mmol / kg or more and 14.00 mmol / kg or less, and even more preferably 0.05 mmol / kg or more and 13.50 mmol / kg or less.

[0048] TIFF2026042724000006.tif44170(in general formula (4), R 6 represents a hydroxy group or a nitro group. 3 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0049] Examples of alkali metals include lithium, sodium, and potassium. Examples of organic ammonium include alkylamines having 1 to 3 carbon atoms, such as methylamine and ethylamine; and mono-, di-, or trialkanolamines having 1 to 4 carbon atoms, such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, and triisopropanolamine. M 3 is particularly preferably in the acid form, an alkali metal salt form such as sodium or potassium, or an ammonium salt form.

[0050] Adding a compound represented by general formula (4) to an ink containing a self-dispersible pigment in which the aforementioned first and second functional groups are bonded to the pigment particle surface makes it possible to record images with even higher color development. The compound represented by general formula (4) has a structure in which the benzene ring and carboxylic acid group are positioned in substituent positions that efficiently generate hydrophobic interactions and hydrogen bonds with the surface functional groups of the self-dispersible pigment and cellulose. Therefore, even when the self-dispersible pigment and cellulose are present in the ink at a distance that prevents direct hydrophobic interaction, the compound represented by general formula (4) is believed to interact with both the self-dispersible pigment and cellulose. It is speculated that this allows the self-dispersible pigment to interact with cellulose and efficiently adsorb.

[0051] From the viewpoint of color development, the content of the compound represented by general formula (4) in the ink is preferably determined in relation to the content of the pigment. Studies by the present inventors have revealed that, from the viewpoint of color development and storage stability, it is preferable for the content C (mmol / kg) of the compound represented by general formula (4) in the aqueous ink and the content P (mass%) of the self-dispersing pigment to satisfy the relationship shown in formula (5) below. 0.010≦C(mmol / kg) / P(mass%)≦3.000 (5)

[0052] When the value of C (mmol / kg) / P (mass%) is 0.010 or more, the amount of the compound represented by general formula (4) relative to the self-dispersible pigment is sufficient, which tends to further enhance the effect of improving color development. On the other hand, when the value of C (mmol / kg) / P (mass%) is 3.000 or less, the storage stability of the ink tends to be further improved. This is presumably because the compound represented by general formula (4) appropriately suppresses the ion concentration, making it difficult for the electric double layer formed by the anionic groups of the self-dispersible pigment to be compressed, making it easier to maintain a stable dispersion state of the pigment.

[0053] From the viewpoint of achieving both good image color development and good ink storage stability, it is more preferable that the value of C (mmol / kg) / P (mass%) be 0.030 or more and 2.000 or less. In other words, it is more preferable that the content C (mmol / kg) of the compound represented by general formula (4) in the ink and the content P (mass%) of the self-dispersing pigment in the ink satisfy the relationship of the following formula (6): 0.030≦C(mmol / kg) / P(mass%)≦2.000 (6)

[0054] (resin) The ink may contain a resin. Examples of the resin include acrylic resins, urethane resins, and olefin resins. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. One type of resin may be used alone, or two or more types may be used in combination. The content (mass %) of the resin in the ink is preferably 0.10% by mass or more and 20.00% by mass or less, and more preferably 0.50% by mass or more and 15.00% by mass or less, based on the total mass of the ink.

[0055] (aqueous medium) The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the ink is preferably 10.00% to 95.00% by mass, and more preferably 50.00% to 95.00% by mass, based on the total mass of the ink. The water-soluble organic solvent content (mass %) in the ink is preferably 3.00% to 50.00% by mass, and more preferably 3.00% to 40.00% by mass, based on the total mass of the ink. Any water-soluble organic solvent that can be used in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used. One of these water-soluble organic solvents may be used alone, or two or more may be used in combination.

[0056] Among water-soluble organic solvents, it is preferable to use a first water-soluble organic solvent that has a LogP value of −0.77 or less at 25° C., a vapor pressure of 1.9 Pa or more at 25° C., and a chain hydrocarbon group having 2 to 4 carbon atoms in its main chain. The use of the first water-soluble organic solvent can further improve the color development of the image. While the term “water-soluble organic solvent” typically refers to a liquid, in the present invention, the term “water-soluble organic solvent” also includes those that are solid at 25° C. Specific examples of water-soluble organic solvents that are solid at 25° C. and are commonly used in inks include 1,6-hexanediol, trimethylolpropane, ethylene urea, urea, and polyethylene glycol with a number-average molecular weight of 1,000.

[0057] First, we will explain the LogP (Log Pow) value, which is an index showing the polarity of a water-soluble organic solvent. The LogP value of a water-soluble organic solvent in the present invention is a value at 25°C. The LogP value refers to the partition coefficient between water and octanol (1-octanol). The LogP value is a physical property value related to the affinity of the target substance with water, and the smaller this value, the higher the polarity. The LogP value is expressed as LogP = Log 10C o / C w (C o represents the concentration of the target substance in the octanol phase, and C w where LogP represents the concentration of the target substance in the aqueous phase. The LogP value can also be determined experimentally using the method described in JIS Z 7260-107. It can also be determined using commercially available calculation software such as "ACD / PhysChem Suite" (manufactured by ACD / Labs). In the examples described below, values ​​determined using "ACD / PhysChem Suite Version 12.00" (manufactured by ACD / Labs) were used. The water-soluble organic solvent contained in the ink is preferably one whose vapor pressure at 25°C is lower than that of water.

[0058] Specific examples of water-soluble organic solvents include those shown below (the numbers in parentheses are LogP values ​​at 25°C): polyethylene glycol with a number average molecular weight of 1,000 (-6.35), polyethylene glycol with a number average molecular weight of 400 (-2.82), polyethylene glycol with a number average molecular weight of 200 (-1.88), tetraethylene glycol (-1.88), bishydroxyethyl sulfone (-1.86), glycerin (-1.85), urea (-1.66), triethylene glycol (-1.65), diethylene glycol (-1.65), ... Ethylene glycol (-1.41), 1,2,6-hexanetriol (-1.39), ethylene glycol (-1.36), ethyleneurea (-1.24), 1,3-propanediol (-1.09), 2-pyrrolidone (-1.09), 1,2-propanediol (-1.01), trimethylolpropane (-0.97), 1,4-butanediol (-0.77), 1,3-butanediol (-0.74), Triethylene glycol dimethyl ether (-0.68), triethylene glycol monoethyl ether (-0.66), N-methyl-2-pyrrolidone (-0.64), γ-butyrolactone (-0.63), δ-valerolactam (-0.57), 1,5-pentanediol (-0.56), 1,2-butanediol (-0.50), 3-methyl-1,5-pentanediol (-0.21), δ-valerolactone (-0.10), 1,6-hexanediol (-0.05), isopropanol (0.18), triethylene glycol monobutyl ether (0.36), 1,2-hexanediol (0.52), ethylene glycol monobutyl ether (0.83), 1-pentanol (1.35), 1,2-octanediol (1.54), tripropylene glycol monobutyl ether (1.66), etc.

[0059] Next, vapor pressure will be described. The vapor pressure of the water-soluble organic solvent in the present invention is the value at 25°C. Values ​​listed in books such as Solvent Pocket Book (Ohmsha) can be used for the vapor pressure value. Alternatively, the temperature-vapor pressure data listed in the Basic Chemistry Handbook, Third Revised Edition (Maruzen) can be converted to vapor pressure at 25°C using the relationship lnP = -ΔHvap / RT + C derived from the Clapeyron-Clausius equation. In the above formula, P is vapor pressure, ΔHvap is the molar heat of vaporization (constant), R is the gas constant, T is temperature, and C is a constant. Vapor pressure can also be calculated using commercially available calculation software such as "Advanced Chemistry Development (ACD / Labs) Software V11.02 (c1994-2023 ACD / Labs)." In the examples described below, values ​​calculated using "Advanced Chemistry Development (ACD / Labs) Software V11.02 (c1994-2023 ACD / Labs)" were used.

[0060] Specific examples of water-soluble organic solvents having a vapor pressure of 1.9 Pa or more at 25° C. include the following (the numbers in parentheses are vapor pressures at 25° C. (units: Pa)): Diethylene glycol ethyl methyl ether (292.0), 3-methoxy-1-butanol (98.4), 3-methoxy-3-methylbutanol (90.0), 1-methyl-2-pyrrolidone (39.9), triethylene glycol dimethyl ether (28.0), 1,2-propanediol (27.2), 1,2-butanediol (19.7), ethylene glycol (12.8), diethylene glycol monoethyl ether (9.8), 1,2-pentanediol (7.7), 1,3-propanediol (4.6), 1,3-butanediol (7.2), 2-pyrrolidone (3.9), 2-methyl-1,3-propanediol (3.0), 1,2-hexanediol (2.6), 1,4-butanediol (1.9), 3-methyl-1,5-pentanediol (1.9), etc.

[0061] Specific examples of water-soluble organic solvents having a vapor pressure of less than 1.9 Pa at 25°C include the following (the numbers in parentheses are vapor pressures at 25°C (units: Pa)): diethylene glycol monobutyl ether (1.7), 1,5-pentanediol (1.0), 1,6-hexanediol (0.9), diethylene glycol (0.6), triethylene glycol (0.04), glycerin (0.03), trimethylolpropane, 1-(2-hydroxyethyl)-2-pyrrolidone, ethylene urea, tetraethylene glycol, polyethylene glycol having a number average molecular weight of 200 to 1000, and an ethylene oxide adduct of glycerin under the trade name "Liponic EG-07" (manufactured by Vantage).

[0062] The first water-soluble organic solvent has a LogP value of -0.77 or less at 25°C and a vapor pressure of 1.9 Pa or more at 25°C, and has a chain hydrocarbon group having 2 to 4 carbon atoms in its main chain. Examples of the chain hydrocarbon in the chain hydrocarbon group having 2 to 4 carbon atoms include ethane, propane, and butane. The chain hydrocarbon group having 2 to 4 carbon atoms is preferably a divalent chain hydrocarbon group. Among these, an ethylene group (-CH2CH2-), a trimethylene group (-CH2CH2CH2-), a propylene group (-CH(CH3)CH2-), or a tetramethylene group (-CH2CH2CH2CH2-) is more preferred. The first water-soluble organic solvent has a structure in which such a chain hydrocarbon group is used as the main chain, and a hydrophilic group such as a hydroxyl group is substituted on a portion of the chain.

[0063] Examples of the first water-soluble organic solvent include ethylene glycol, 1,3-propanediol, 1,2-propanediol, and 1,4-butanediol. Among these, at least one selected from the group consisting of 1,3-propanediol, 1,2-propanediol, and 1,4-butanediol is preferred. The first water-soluble organic solvent may be used alone or in combination of two or more.

[0064] The content (% by mass) of the first water-soluble organic solvent in the ink is preferably 1.00% by mass or more and 50.00% by mass or less, and more preferably 3.00% by mass or more and 40.00% by mass or less, based on the total mass of the ink. Furthermore, the content (% by mass) of the first water-soluble organic solvent in the aqueous ink is preferably 1.5 times or more the mass ratio of the content (% by mass) of the self-dispersing pigment having a group represented by general formula (1) bonded to the surface of the pigment particles. When this mass ratio is 1.5 times or more, the effect of improving color development is enhanced, making it easier to achieve excellent color development. Furthermore, this mass ratio is preferably 10.0 times or less.

[0065] (Other ingredients) In addition to the above components, the ink may contain, as needed, water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethyleneurea. Furthermore, as needed, the ink may contain various additives, such as pH adjusters, antifoaming agents, rust inhibitors, preservatives, mildew inhibitors, antioxidants, reduction inhibitors, and evaporation promoters. It is not necessary to include higher fatty acids or their salts.

[0066] The ink may contain a surfactant. Examples of surfactants include known anionic surfactants, nonionic surfactants, and cationic surfactants. One of these surfactants may be used alone, or two or more may be used in combination. Among these, it is preferable to contain a nonionic surfactant in the ink. Nonionic surfactants having various structures, such as hydrocarbon-based, silicone-based, and fluorine-based, can be used. Among these, it is preferable to use a hydrocarbon-based nonionic surfactant. When a surfactant is contained in the ink, the content (mass %) of the surfactant in the ink is preferably 0.01% by mass or more and 5.00% by mass or less, and more preferably 0.01% by mass or more and 3.00% by mass or less, based on the total mass of the ink.

[0067] (Ink properties) [Dynamic surface tension] From the viewpoint of fixability as an ink for use in inkjet printing, the dynamic surface tension of the ink at 10 milliseconds is preferably set as follows: 52 mN / m or less is preferable, 50 mN / m or less is more preferable, and 48 mN / m or less is even more preferable. By setting the dynamic surface tension of the ink at 10 milliseconds to 52 mN / m or less, the ink penetrates quickly and fixes well. Furthermore, by setting the dynamic surface tension of the ink at 10 milliseconds to 32 mN / m or more, sinking of the pigment into the recording medium is suppressed, thereby improving the color development of the image, which is also preferable.

[0068] The dynamic surface tension of ink is measured using the maximum bubble pressure method at 25°C. The maximum bubble pressure method measures the maximum pressure required to expel a bubble generated at the tip of a probe (capillary tube) immersed in the liquid being measured, and then calculates the liquid's surface tension from the measured maximum pressure. Specifically, the maximum pressure is measured while continuously generating bubbles at the tip of the probe. The time from when a new bubble surface appears at the tip of the probe to when the maximum bubble pressure is reached (when the radius of curvature of the bubble equals the radius of the probe tip) is called the "lifetime." In other words, the maximum bubble pressure method measures the surface tension of a liquid in motion. The dynamic surface tension of ink over a 10-millisecond period can be easily adjusted by adjusting the type and content of water-soluble organic solvents and surfactants.

[0069] [Other physical properties] From the viewpoint of reliability as an ink for use in inkjet printing, it is preferable to appropriately control the physical properties of the ink. Specifically, the viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. Furthermore, the pH of the ink at 25°C is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less. The viscosity of the ink can be measured using a rotational viscometer or the like.

[0070] <Ink cartridges> The ink cartridge of the present invention includes ink and an ink storage section that stores the ink. The ink stored in the ink storage section is the aqueous ink of the present invention described above. FIG. 1 is a cross-sectional view schematically illustrating one embodiment of the ink cartridge of the present invention. As shown in FIG. 1, the bottom of the ink cartridge is provided with an ink supply port 12 for supplying ink to the recording head. The interior of the ink cartridge serves as an ink storage section for storing the ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16, which are connected to each other via a communication port 18. The absorber storage chamber 16 is also connected to the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 contains absorbers 22 and 24 that retain the ink in an impregnated state. The ink storage section may not have an ink storage chamber that stores liquid ink, but may instead use an absorber to hold all of the ink stored therein. Alternatively, the ink storage section may not have an absorber and may store all of the ink in a liquid state. Furthermore, the ink cartridge may be configured to have an ink storage section and a recording head.

[0071] <Inkjet recording method> The inkjet recording method of the present invention is a method of ejecting the above-described aqueous ink of the present invention from an inkjet recording head to record an image on a recording medium. Methods for ejecting the ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to employ a method of ejecting the ink by applying thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be any known method.

[0072] FIG. 2 is a diagram schematically illustrating an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main components of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting a recording medium 32, and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 is equipped with recording heads 38 and 40, and is configured to accommodate an ink cartridge 42. While the head cartridge 36 is transported in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. An image is then recorded on the recording medium 32 by transporting the recording medium 32 in the sub-scanning direction by a transport means (not shown).

[0073] FIG. 3 is a schematic diagram showing an example of a cleaning unit of an inkjet recording device. The cleaning unit covers the nozzles by abutting the cap 51 against the nozzle surface of the recording head, thereby preventing ink evaporation. More specifically, capping is performed by raising the cap holder 56 using a vertically movable mechanism (not shown) and abutting the cap 51 against the nozzle surface of the recording head with an appropriate contact force. When the pump 50 is operated in the capped state, negative pressure is generated between the nozzle surface and the cap 51, sucking ink from the nozzles and cleaning the recording head. Furthermore, ejecting ink (pre-ejection) into the suction chambers 52 and 53 can restore the normal ejection state. Furthermore, by separating the cap 51 from the nozzle surface of the recording head and suctioning ink on the cap 51 through an outlet (not shown), ink adhesion to the recording head and other adverse effects can be prevented. An ink absorbing member or the like may be provided inside the suction chamber.

[0074] 3 shows a configuration in which the suction chamber formed by peripheral wall portion 54 is divided into two suction chambers 52 and 53 having the same volume by partition wall 55, but these suction chambers may have different volumes, or may be formed as a single suction chamber without a partition wall. Furthermore, a configuration may be used in which each of the ejection port arrays that eject multiple types of ink is covered collectively with a single cap, or a cap may be provided for each of the ejection port arrays that eject multiple types of ink. [Example]

[0075] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0076] <Preparation of pigment dispersion> (Total Amount of Anionic Groups in First Functional Groups and Second Functional Groups) To accurately determine the total anionic group content of the primary and secondary functional groups, the sample was purified. First, the pigment dispersion was diluted to approximately 5% pigment content. It was centrifuged at 80,000 rpm for 2 hours using an ultracentrifuge (product name "Optima MAX-XP" manufactured by Beckman Coulter). The settled pigment was redispersed in 30 times the amount (by mass) of pure water to prepare the measurement solution. The total anionic group content of the primary and secondary functional groups of the self-dispersed pigment in the measurement solution was measured using colloid titration using potential difference. For the measurement, an automatic potentiometric titrator (product name "AT-510" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500) was used.

[0077] (Amount of Anionic Groups in First Functional Group and Second Functional Group) The following pretreatment was performed to measure the anionic group content of each functional group. To accurately determine the anionic group content of the first and second functional groups, the sample was purified by acid precipitation using hydrochloric acid. A pigment dispersion containing 10% pigment (mass%) was prepared, and an excess amount of hydrochloric acid (approximately three times the amount of anionic groups on a molar basis) was added and thoroughly stirred. This procedure caused the self-dispersed pigment to aggregate, forming agglomerates. The aggregates were filtered off by suction and washed with water to obtain a solid pigment. The resulting pigment was vacuum-dried at 60°C for 24 hours. Thermogravimetric analysis was performed using 2 mg of pigment as a sample, heating the sample from 30°C to 600°C at a temperature increase rate of 2°C / min using a thermogravimetric analyzer (product name "TGA550" manufactured by TA Instruments).

[0078] As standard samples, pigment dispersions were prepared: self-dispersed pigment X, which had the same amount of anionic groups as the self-dispersed pigment to be measured, but had a first functional group but no second functional group; and self-dispersed pigment Y, which had a second functional group but no first functional group. The percentage of the mass of the sample remaining at 400°C, relative to the mass of the sample at the start of the thermogravimetric analysis, was defined as "mass residual ratio (%)." First, the pigment dispersion of self-dispersed pigment X, which had a first functional group, was subjected to the above-described procedure to measure the mass residual ratio w1 (%) at 400°C. Next, the pigment dispersion of self-dispersed pigment Y, which had a second functional group, was subjected to the same procedure to measure the mass residual ratio w2 (%) at 400°C. Furthermore, the self-dispersed pigment to be measured was subjected to the above-described procedure to measure the mass residual ratio w (%) at 400°C.

[0079] The ratio r1 (times) of the anionic group of the first functional group to the total anionic group amount (mmol / g) of the first functional group and the second functional group, and the ratio r2 (times) of the anionic group amount of the second functional group were calculated based on the following formulas (7) and (8), respectively. r1=(w2-w) / (w2-w1)...Equation (7) r2=(w-w1) / (w2-w1)...Equation (8) The anionic group amounts of the first functional group and the second functional group were calculated from the anionic group amounts using the anionic group ratio r1 (times) of the first functional group and the anionic group ratio r2 (times) of the second functional group obtained in this way. It was confirmed that the anionic group amount of the first functional group calculated by this method roughly coincides with the anionic group amount of the first functional group calculated from the anionic group amount of the pigment dispersion obtained in the first step of the pigment dispersion preparation step described below.

[0080] (average particle size of pigment) Average particle size of pigment (cumulative 50% particle size by volume, D 50 ) was measured using a particle size measuring device (trade name "Nanotrac Wave", manufactured by Microtrack Bell) using the dynamic light scattering method.

[0081] (Pigment dispersions 1-17, 20, 21) As a method for bonding a first functional group and a second functional group to the surface of pigment particles, each pigment dispersion was obtained by a stepwise method in which the pigment was surface-treated with a treatment agent having a first functional group and then with a second treatment agent having a second functional group. This method is explained in detail below.

[0082] [1st process] A mixture was prepared by mixing 440.0 g of purified water, 50.0 g of the pigment shown in Table 1, and the type and amount (g) of treatment agent shown in the first step column of Table 1. This mixture was cooled to 10°C and, while stirring, slowly added the amount (g) of 20% potassium nitrite (KNO2) aqueous solution shown in Table 1. The mixture was stirred for 15 minutes and then further stirred at 10,000 rpm using a precision emulsifier / disperser (product name "Clearmix CLM-0.8S" manufactured by M Technique) for the time shown in Table 1. Next, 8 mol / L potassium hydroxide aqueous solution was added to the mixture to adjust the pH to 10. The filtrate was purified by ultrafiltration until the electrical conductivity was 10 μS / cm or less. After ultrafiltration, the mixture was centrifuged at 10,000 rpm for 30 minutes to remove coarse particles, and an appropriate amount of ion-exchanged water was added to adjust the pigment content, resulting in a pigment dispersion with a pigment content of 12.0%. The abbreviations for the pigment types shown in Table 1 are as follows: CB: Carbon black PB15:3:CI Pigment Blue 15:3 PR122: CI Pigment Red 122 PY74: CI Pigment Yellow 74

[0083] [Second process] 30.0 g of pure water, 170.0 g of the resulting pigment dispersion, and the type and amount (g) of the treatment agent shown in the second step column of Table 1 were mixed to obtain a mixture. While stirring this mixture, the amount (g) of 20% potassium nitrite (KNO2) aqueous solution shown in Table 1 was slowly added to the mixture. The mixture was stirred using a magnetic stirrer for the time shown in Table 1. Next, 8 mol / L potassium hydroxide aqueous solution was added to the mixture to adjust the pH to 10. For pigment dispersions in which the "counter ion" shown in Table 1 was Na or NH4, the counter ions of the anionic groups were replaced by ion exchange. The filtrate was purified by ultrafiltration until the electrical conductivity was 10 μS / cm or less. After ultrafiltration, an appropriate amount of ion-exchanged water was added to adjust the pigment content to 10.0% and the average particle diameter (D 50 A pigment dispersion liquid having the properties shown in Table 2 was obtained.

[0084] By the above-mentioned first and second steps, pigment dispersions 1 to 17, 20, and 21 were prepared, each containing a self-dispersing pigment having a first functional group represented by general formula (1) and a second functional group represented by general formula (2) bonded to the surface of the pigment particles. The prepared pigment dispersions 1 to 17, 20, and 21 have a first functional group and a second functional group (respectively, M in general formula (1), which are counter ions) bonded to the surface of the pigment particles. 1 and M in general formula (2) 2 ) contains a self-dispersing pigment having attached thereto a group of the type shown in Table 1.

[0085] (Pigment dispersions 18, 19) A mixture was prepared by mixing 440.0 g of pure water, 50.0 g of the pigment shown in Table 1, and the type and amount (g) of treatment agent shown in Table 1. This mixture was cooled to 10°C and, while stirring, slowly added the amount (g) of 20% potassium nitrite aqueous solution shown in Table 1. The mixture was stirred for 15 minutes and then further stirred at 10,000 rpm for the time shown in Table 1 using a precision emulsifying disperser (product name "Clearmix CLM-0.8S" manufactured by M Technique). An 8 mol / L potassium hydroxide aqueous solution was then added to the mixture to adjust the pH to 10. The filtrate was purified by ultrafiltration until the electrical conductivity was 10 μS / cm or less. After ultrafiltration, the mixture was centrifuged at 10,000 rpm for 30 minutes to remove coarse particles. An appropriate amount of ion-exchanged water was added to adjust the pigment content to 10.0% and the average particle diameter (D 50 A pigment dispersion liquid having the properties shown in Table 2 was obtained.

[0086] (Pigment Dispersion 22) Pigment dispersion 22 containing a self-dispersing pigment was prepared using 5-aminobenzene-1,2,3-tricarboxylic acid as a treatment agent in accordance with the description in Example 2 of Patent Document 1. The pigment content in Pigment Dispersion 22 was 15.0%.

[0087] (Pigment Dispersion 23) Pigment dispersion 23 containing a self-dispersing pigment was prepared using [(4-aminophenyl)(hydroxyl)methylene]bisphosphonic acid monosodium salt as a treatment agent in accordance with the description in Example 10 of Patent Document 2. The pigment content in Pigment Dispersion 23 was 12.0%.

[0088] (Pigment Dispersion 24) Pigment dispersion 24 containing a self-dispersing pigment was prepared in accordance with the description of the preparation method for self-dispersing pigment 1 in Patent Document 3, using ((4-aminobenzoylamino)-methane-1,1-diyl)bisphosphonic acid and p-aminobenzoic acid as treatment agents. The pigment content in pigment dispersion 24 was 10.0%.

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[0091] <Preparation of the compound represented by general formula (4)> As specific examples of the compound represented by general formula (4), compounds having the structures shown in Table 3 were prepared. These were all salts of 2-hydroxyterephthalic acid or 2-nitroterephthalic acid, which are commercially available as reagents, neutralized at the carboxylic acid group with a neutralizing agent shown in Table 3.

[0092] TIFF2026042724000009.tif37170

[0093] <Resin synthesis> (aqueous solution of acrylic resin 1) Acrylic resin 1, a random copolymer, was synthesized by copolymerizing 60.0 parts of styrene, 21.0 parts of n-butyl acrylate, and 19.0 parts of acrylic acid using a conventional method. Potassium hydroxide was added in an amount equimolar to the acid value. An appropriate amount of pure water was then added to prepare an aqueous solution of acrylic resin 1 with an acid value of 148 mg KOH / g, a weight-average molecular weight of 10,000, and a resin (solids) content of 20.0%.

[0094] (aqueous solution of acrylic resin 2) Acrylic resin 2, a random copolymer, was synthesized by copolymerizing 44.6 parts of styrene, 40.0 parts of α-methylstyrene, and 15.4 parts of acrylic acid using a conventional method. Potassium hydroxide was added in an amount equimolar to the acid value. An appropriate amount of pure water was then added to prepare an aqueous solution of acrylic resin 2 with an acid value of 120 mg KOH / g, a weight-average molecular weight of 10,000, and a resin (solids) content of 20.0%.

[0095] (aqueous solution of urethane resin) A four-neck flask equipped with a thermometer, stirrer, nitrogen inlet, and condenser was charged with 39.3 g of polytetramethylene glycol (number-average molecular weight: 2,000), 44.5 g of isophorone diisocyanate, and 0.007 g of dibutyltin dilaurate. The mixture was reacted at 100°C for 5 hours under a nitrogen gas atmosphere and then cooled to below 65°C. 13.2 g of dimethylolpropionic acid, 3.0 g of neopentyl glycol, and 150.0 g of methyl ethyl ketone were added and reacted at 80°C. The mixture was then cooled to 40°C and 20.0 g of methanol was added to terminate the reaction. An appropriate amount of ion-exchanged water was then added, and while stirring with a homomixer, the potassium hydroxide aqueous solution required to neutralize the resin was added. Thereafter, methyl ethyl ketone and unreacted methanol were distilled off under heating and reduced pressure to prepare an aqueous solution of urethane resin containing a urethane resin with an acid value of 55 mgKOH / g and a weight average molecular weight of 15,000 and a resin (solids) content of 20.0%.

[0096] <Ink Preparation> Compounds 1 to 4 were mixed and thoroughly stirred to achieve the respective components (unit: %) and concentrations shown in the middle and bottom rows of Table 4 (Tables 4-1 to 4-5). Each ink was then prepared by pressure filtration using a 2.5 μm pore-size membrane filter (trade name "HDCII Filter," manufactured by Pall). The pigment dispersions shown in the middle row of Table 4 were the pigment dispersions of the types (numbers) shown in the top row of Table 4. The parenthesized values ​​for water-soluble organic solvents are the LogP values ​​and vapor pressures (units Pa omitted) at 25°C. Note that vapor pressures for solid components at 25°C are indicated as "-." The values ​​attached to polyethylene glycols represent the number-average molecular weight. "Acetylenol E60" is the trade name of a nonionic surfactant (an ethylene oxide adduct of acetylene glycol) manufactured by Kawaken Fine Chemicals. "Surfynol 465" is the trade name of a nonionic surfactant (an ethylene oxide adduct of acetylene glycol) manufactured by Nissin Chemical Industry. The amounts of ion-exchanged water used in the middle section of Table 4 include the amounts of compounds 1 to 4 used in preparing the ink. The lower section of Table 4 shows the ink properties. The "self-dispersing pigments having groups represented by general formulas (1) and (2) at a specific ratio" shown in the lower section of Table 4 refer to self-dispersing pigments in which the molar ratio of the "anionic group amount in the first functional group / the total anionic group amount in the first functional group and the second functional group" is between 0.20 and 0.97. The dynamic surface tension of each ink at 10 ms was in the range of 47 to 48 mN / m. The dynamic surface tension of each ink at 10 ms was measured at 25°C using a dynamic surface tensiometer (product name "BUBBLE PRESSURE TENSIOMETER BP-2" manufactured by KRUSS) using the maximum bubble pressure method.

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[0101] TIFF2026042724000014.tif179170

[0102] <Evaluation> Each ink obtained above was filled into an ink cartridge, and the following evaluations were carried out using an inkjet recording device (trade name "Maxify iB4130", manufactured by Canon) that ejects ink from a recording head using thermal energy. The ink cartridge was set in a position on the recording device corresponding to the color of the prepared ink. In this example, a solid image recorded by applying 23.4 ng of ink to a unit area of ​​1 / 600 inch x 1 / 600 inch was defined as having a "100% recording duty." In this example, according to the following evaluation criteria, A and B were considered acceptable levels, and C and D were considered unacceptable levels. The evaluation results are shown in Table 5.

[0103] (Color development) Using the inkjet recording device described above, solid images (2 cm x 2 cm) were recorded on the following three types of recording media (plain paper). For black ink, which uses carbon black as the colorant, the recording duty for the solid image was 85%. For color ink, which uses organic pigments as the colorant, the recording duty for the solid image was 50%. One day after recording, the optical density of the solid image was measured using a fluorescence spectrodensitometer (product name "FD-7", manufactured by Konica Minolta) under the following conditions: illumination conditions: M1 (D50), observation light source: D50, and field of view: 2°. The color development of the image was evaluated based on the average optical density of the obtained recording media according to the following evaluation criteria. [Recording Media] Product name: "CS-680" (Canon) Product name: "Office 70" (Canon) Product name: "Multi-purpose paper" (Canon) [Black ink] A: The average optical density was 1.28 or more. B: The average optical density was 1.22 or more and less than 1.28. C: The average optical density was 1.16 or more and less than 1.22. D: The average optical density was less than 1.16. [Color ink] A: The average optical density was 1.03 or more. B: The average optical density was 0.98 or more and less than 1.03. C: The average optical density was 0.93 or more and less than 0.98. D: The average optical density was less than 0.93.

[0104] (Storage stability) Each ink obtained above was placed in a polytetrafluoroethylene container and sealed. As an accelerated test assuming long-term use of an inkjet recording device, the sealed ink was placed in a thermostatic chamber set at 80°C and heated for one week. After the ink was returned to 25°C, the average particle diameter of the pigment (cumulative 50% particle diameter on a volume basis, D 50 ) was measured using a particle size measuring device (trade name "Nanotrack Wave", manufactured by Microtrack Bell). 50 was measured under the following conditions: Set zero: 30 seconds, measurement count: 3 times, measurement time: 180 seconds. The particle size ratio of the pigment before and after storage = average particle size of the pigment after storage / average particle size of the pigment before storage was calculated, and the storage stability of the ink was evaluated according to the evaluation criteria shown below. A: The particle size ratio of the pigment before and after storage was less than 1.10. B: The particle size ratio of the pigment before and after storage was 1.10 times or more and less than 1.25 times. C: The particle size ratio of the pigment before and after storage was 1.25 times or more.

[0105] TIFF2026042724000015.tif121170

[0106] The color development properties of Examples 1 and 26 to 28 were all ranked A, but compared to Example 1, the color development properties of Examples 26 to 28 were relatively excellent.

[0107] The disclosure of this embodiment includes the following configurations and methods. (Configuration 1) A water-based inkjet ink containing a self-dispersing pigment, the self-dispersion pigment is a self-dispersion pigment having a functional group bonded to the surface of the pigment particle, The functional group includes a first functional group represented by the following general formula (1) and a second functional group including at least one group represented by the following general formula (2), An aqueous ink, characterized in that the molar ratio of the anionic group amount (mmol / g) of the first functional group in the self-dispersion pigment to the total anionic group amount (mmol / g) of the first functional group and the second functional group is 0.20 to 0.97.

[0108] TIFF2026042724000016.tif45170 (in the general formula (1), M 1 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. * represents the bonding position with the particle surface of the pigment.

[0109] TIFF2026042724000017.tif45170 (in the general formula (2), R 1 ~R 5 Two of them are COOM 2 and three are hydrogen atoms, and the two COOM 2 are adjacent to each other or are separated by one carbon atom that constitutes a benzene ring. 2 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. * represents the bonding position with the particle surface of the pigment.

[0110] (Configuration 2) The aqueous ink according to Configuration 1, wherein the molar ratio of the anionic group amount (mmol / g) of the first functional group in the self-dispersing pigment to the total anionic group amount (mmol / g) of the first functional group and the second functional group is 0.40 times or more and 0.97 times or less. (Configuration 3) The aqueous ink according to Configuration 1 or 2, wherein the pigment is carbon black. (Configuration 4) The carbon black has a specific surface area of ​​200 m2 by the BET method. 2 4. The aqueous ink according to claim 3, wherein the ink has a molecular weight of 1 / g or more. (Configuration 5) The aqueous ink according to any one of Configurations 1 to 4, wherein the second functional group includes a group represented by the following general formula (3):

[0111] TIFF2026042724000018.tif35170 (in the general formula (3), M 2 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. * represents the bonding position with the particle surface of the pigment.

[0112] (Configuration 6) The aqueous ink according to any one of Configurations 1 to 5, wherein the total anionic group amount (mmol / g) of the first functional group and the second functional group is 0.08 mmol / g or more. (Configuration 7) The water-based ink according to any one of Configurations 1 to 6, further comprising a compound represented by the following general formula (4):

[0113] TIFF2026042724000019.tif44170 (in the general formula (4), R 6 represents a hydroxy group or a nitro group. 3 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0114] (Configuration 8) The aqueous ink according to Configuration 7, wherein the content C (mmol / kg) of the compound represented by general formula (4) and the content P (mass%) of the self-dispersing pigment in the aqueous ink satisfy the relationship of the following formula (5): 0.010≦C(mmol / kg) / P(mass%)≦3.000 (5) (Configuration 9) An ink cartridge including ink and an ink storage section for storing the ink, 9. An ink cartridge, wherein the ink is the aqueous ink described in any one of configurations 1 to 8. (Method 1) An inkjet recording method in which ink is ejected from an inkjet recording head to record an image on a recording medium, 9. An inkjet recording method, wherein the ink is the aqueous ink described in any one of Configurations 1 to 8.

Claims

1. 1. A water-based inkjet ink containing a self-dispersed pigment, comprising: the self-dispersion pigment is a self-dispersion pigment having a functional group bonded to the surface of the pigment particle, The functional group includes a first functional group represented by the following general formula (1) and a second functional group including at least one group represented by the following general formula (2), an anionic group amount (mmol / g) of the first functional group in the self-dispersion pigment is 0.20 times or more and 0.97 times or less in terms of a molar ratio relative to a total anionic group amount (mmol / g) of the first functional group and the second functional group. (In the general formula (1), M １ each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. * represents the bonding position with the particle surface of the pigment. (In the general formula (2), R １ ~R ５ Two of them are COOM ２ and three are hydrogen atoms, and the two COOM ２ are adjacent to each other or are separated by one carbon atom constituting a benzene ring. ２ each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. * represents the bonding position with the particle surface of the pigment.

2. 2. The aqueous ink according to claim 1, wherein the molar ratio of the anionic group amount (mmol / g) of the first functional group to the total anionic group amount (mmol / g) of the first functional group and the second functional group in the self-dispersion pigment is 0.40 to 0.

97.

3. 2. The water-based ink of claim 1, wherein the pigment is carbon black.

4. The specific surface area of ​​the carbon black measured by the BET method is 200 m ２ The aqueous ink according to claim 3, wherein the viscosity is 1 / g or more.

5. The aqueous ink according to claim 1 , wherein the second functional group comprises a group represented by the following general formula (3): (In the general formula (3), M ２ each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. * represents the bonding position with the particle surface of the pigment.

6. 2. The aqueous ink according to claim 1, wherein the total amount (mmol / g) of anionic groups in the first functional group and the second functional group is 0.08 mmol / g or more.

7. The aqueous ink according to claim 1, further comprising a compound represented by the following general formula (4): (In the general formula (4), R ６ represents a hydroxy group or a nitro group. ３ each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

8. 8. The aqueous ink according to claim 7, wherein the content C (mmol / kg) of the compound represented by general formula (4) and the content P (mass%) of the self-dispersion pigment in the aqueous ink satisfy the relationship of the following formula (5): 0.010≦C (mmol / kg) / P (mass%)≦3.000 (5)

9. An ink cartridge comprising ink and an ink storage section for storing the ink, 9. An ink cartridge, wherein the ink is the aqueous ink according to claim 1.

10. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, An ink-jet recording method, wherein the ink is the aqueous ink according to any one of claims 1 to 8.

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