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

Abstract

The present invention provides a water-based inkjet ink that uses a self-dispersing pigment as a coloring material, and that can record images with excellent color development and can suppress the accumulation of aggregates inside the cap of a recording head. The present invention provides a water-based inkjet ink containing a self-dispersing pigment. The self-dispersing pigment has a group represented by the following general formula (1) bonded to the surface of the pigment particle, and the water-based ink has a dynamic surface tension of 52 mN / m or less at 10 milliseconds. In the following general formula (1), M 1 each independently represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium, and * represents the bonding position with the particle surface of the pigment. TIFF2026042725000018.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 pigment having ionic groups bonded to its particle surface directly or via other atomic groups, and a good solvent and a poor solvent for the pigment. According to this proposal, it is possible to record images with a good area factor and high optical density (color development), even when a small amount of ink is applied. [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. 2006-045514 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 if some aqueous inks using self-dispersing pigments have previously produced images with low color development on recording media, there are aqueous inks using self-dispersing pigments that can record images with sufficient color development on those recording media. However, it has been found that recording images over a long period of time using an inkjet recording device equipped with such aqueous inks can result in a deterioration in image quality. Investigations have revealed that ejected ink accumulates inside the recording head cap, and this deposit adheres to the vicinity of the recording head's ejection orifices, preventing normal ejection.

[0007] Therefore, an object of the present invention is to provide an inkjet water-based ink containing a self-dispersing pigment as a colorant, which is capable of recording images with excellent color development and is capable of suppressing the accumulation of aggregates inside the cap of a recording head. Another object of the present invention is to provide an ink cartridge and an inkjet recording method using this water-based 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 a group represented by the following general formula (1) bonded to the surface of the pigment particles, and the aqueous ink has a dynamic surface tension of 52 mN / m or less at 10 milliseconds:

[0009] TIFF2026042725000001.tif44170 (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. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an aqueous inkjet ink containing a self-dispersing pigment as a colorant, which is capable of recording images with excellent color development and is capable of suppressing the accumulation of aggregates inside the cap of a recording head. 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]

[0011] [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

[0012] 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."

[0013] 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 pigment inks that use conventional self-dispersing pigments, in which organic groups are bonded to the surface of pigment particles, as coloring materials tend to sink into 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 inks described in Patent Documents 2 and 3 have a low level of pigment present on or near the surface of the recording medium, and the pigment sinks into the recording medium, resulting in a decrease in the color development of the image.

[0014] By accelerating the aggregation of self-dispersing pigments after the ink is applied to a recording medium, it is believed that high color development can be achieved even on recording media on which images with low color development, such as those described above, are recorded. Ink using a surface-modified pigment obtained by the diazotization reaction of 5-amino-1,2,3-benzenetricarboxylic acid and carbon black, as described in Patent Documents 1 and 2, aggregation of pigments due to evaporation of the liquid components after application to the recording medium is much faster than that of other self-dispersing pigments. Therefore, the ink applied to the recording medium rapidly thickens due to aggregation of pigments due to evaporation of the liquid components. Due to this characteristic, even on recording media on which images with low color development, such as those described above, thickening of the ink and aggregation of the pigment occur before the pigment sinks into the recording medium, allowing a large amount of pigment to be present on and near the surface of the recording medium, thereby achieving high color development.

[0015] However, because ink containing the above-mentioned surface-modified pigments thickens quickly as the liquid components evaporate, the pigments in the ink discharged into the cap during preliminary ejection or suction operations also rapidly aggregate as the liquid components evaporate. Generally, when an inkjet recording device is used over a long period of time, the ink discharged into the cap mixes with newly discharged ink before solid aggregates form, and is discharged to the outside through the cap's outlet. In contrast, with ink containing a surface-modified pigment using 5-amino-1,2,3-benzenetricarboxylic acid, solid aggregates quickly form inside the cap, making them unable to be discharged and resulting in their accumulation within the cap. It was found that these deposits adhere to the surface of the recording head where the ejection ports are formed, preventing normal ejection.

[0016] As described above, with conventional technology, it has been difficult to achieve both excellent color development and suppression of the accumulation of aggregates inside the recording head cap using ink containing a self-dispersing pigment as a colorant. However, as a result of investigations by the present inventors, it has been found that it is possible to achieve both of these goals by using a self-dispersing pigment in which a group represented by general formula (1) is bonded to the pigment particle surface and by controlling the dynamic surface tension of the ink at 10 milliseconds to 52 mN / m or less. The present inventors speculate as follows about the reason for this.

[0017] First, the inventors investigated the factors behind the improved color development. They found that inks containing self-dispersing pigments with groups represented by general formula (1) bonded to the pigment particle surface exhibited slower aggregation during evaporation of the liquid components after application to a recording medium than other self-dispersing pigments. This suggests that the mechanism behind the high color development is different from the rapid aggregation observed in inks containing surface-modified pigments obtained by the diazotization reaction of 5-amino-1,2,3-benzenetricarboxylic acid and carbon black. Further investigations revealed that self-dispersing pigments with groups represented by general formula (1) bonded to the pigment particle surface exhibited significantly higher adsorption to cellulose, a component of recording media such as plain paper, than other self-dispersing pigments. This characteristic allows self-dispersing pigments with groups represented by general formula (1) bonded to the pigment particle surface to adsorb to the cellulose of the recording medium when the ink is applied to the recording medium, preventing them from sinking into the recording medium and remaining on or near the surface of the recording medium. Furthermore, by controlling the dynamic surface tension at 10 milliseconds of an ink containing a self-dispersing pigment in which a group represented by general formula (1) is bonded to the pigment particle surface to 52 mN / m or less, ink droplets adhere to the recording medium and quickly spread across the surface of the recording medium. As this happens, the self-dispersing pigment in which a group represented by general formula (1) is bonded to the pigment particle surface is adsorbed onto the surface of the recording medium, allowing the recording medium to be efficiently coated with the pigment even with a small amount of ink applied.

[0018] For these reasons, it is believed that it has become possible to record images with excellent color development. The improved color development of images achieved by self-dispersing pigments, in which groups represented by general formula (1) are bonded to the pigment particle surface, can be achieved without taking advantage of the sudden increase in viscosity that occurs when the liquid components of the ink applied to the recording medium evaporate, and it is also possible to suppress the accumulation of aggregates inside the cap. Therefore, it is possible to achieve both the recording of images with excellent color development and the suppression of the accumulation of aggregates inside the recording head cap.

[0019] <Water-based ink> The aqueous ink of the present invention is an inkjet ink containing a self-dispersing pigment and having a dynamic surface tension of 52 mN / m or less at 10 milliseconds. The self-dispersing pigment is a self-dispersing pigment in which a group represented by general formula (1) is bonded to the surface of the pigment particle. 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. The components constituting the ink of the present invention and the physical properties of the ink are described in detail below.

[0020] (self-dispersing pigment) The ink contains, as a colorant, a self-dispersing pigment in which a group represented by general formula (1) is bonded to the surface of the pigment particles. The ink may contain one type of self-dispersing pigment in which a group represented by general formula (1) is bonded to the surface of the pigment particles, or may contain two or more types. The self-dispersing pigment may be one in which one type of group represented by general formula (1) is bonded to the surface of the pigment particles, or may be one in which M in general formula (1) is bonded to the surface of the pigment particles. 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.

[0021] TIFF2026042725000002.tif44170(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.

[0022] [Functional group] In general formula (1), COOM 1The 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.

[0023] [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.

[0024] 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.

[0025] 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 is more preferable. 2 By selecting carbon black with a surface area of ​​1 / g 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] [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 compound capable of generating a diazonium salt, an azo compound, a diazene compound, a triazine compound, or the like as a treating agent. As a method for bonding a group represented by general formula (1) to the surface of pigment particles, it is preferable to use a compound having a group represented by general formula (1) as a treating agent and perform a step of surface treating the pigment with the treating agent.

[0030] [Amount of anionic groups] The amount of anionic groups bonded to the pigment particle surface can be measured as the surface charge of the self-dispersed 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-dispersed pigment is the amount (mmol) per gram of solids of the self-dispersed pigment. In the examples described below, the amount of anionic groups of the self-dispersed 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-dispersed pigment extracted from ink by an appropriate method. To accurately measure the amount of anionic groups by removing impurities, it is preferable to perform preliminary preparations such as washing the self-dispersed pigment and centrifuging the sample (pigment dispersion) before preparing the sample.

[0031] The anionic group amount (mmol / g) of the self-dispersing pigment is preferably 0.09 mmol / g or more and 0.20 mmol / g or less. When the anionic group amount of the self-dispersing pigment is 0.09 mmol / g or more, there are sufficient functional groups bonded to the surface of the pigment particles, resulting in fewer exposed areas on the pigment particle surface. This helps prevent the exposed areas of the pigment from agglomerating together when the ink dries inside the cap, facilitating redispersion and discharge of the pigment inside the cap, further enhancing the effect of suppressing the accumulation of aggregates inside the cap. On the other hand, when the anionic group amount of the self-dispersing pigment is 0.20 mmol / g or less, the anionic group amount of the pigment is kept to an appropriate level. In this case, the hydrophilicity of the pigment is appropriately suppressed, thereby appropriately suppressing its affinity for the 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, further enhancing color development. The amount of anionic groups in a self-dispersing pigment means the amount of anionic groups per unit mass of the self-dispersing pigment, and can be adjusted by the amount of groups represented by general formula (1) bonded to the surface of the pigment particles. Note that, although the pigment before undergoing the treatment to bond the groups represented by general formula (1) may also contain a very small amount of anionic groups, the amount is negligible.

[0032] (Compound represented by general formula (2)) The ink preferably contains a compound represented by the following general formula (2). In this case, the ink may contain one or more of the compounds represented by general formula (2). The content C (mmol / kg) of the compound represented by general formula (2) in the ink is preferably 0.030 mmol / kg or more and 12,800 mmol / kg or less. The content C (mmol / kg) is more preferably 0.040 mmol / kg or more and 12,000 mmol / kg or less, and even more preferably 0.120 mmol / kg or more and 8,000 mmol / kg or less.

[0033] TIFF2026042725000003.tif45170(in general formula (2), R 1represents a hydroxy group or a nitro group. 2 each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0034] 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 2 is particularly preferably in the acid form, an alkali metal salt form such as sodium or potassium, or an ammonium salt form.

[0035] When a compound represented by general formula (2) is added to an aqueous ink containing a self-dispersing pigment having a group represented by general formula (1) bonded to the pigment particle surface, the effect of suppressing the accumulation of aggregates in the recording head cap is further improved. When the ink dries inside the cap, it is thought that the hydrophobic portion of the surface structure of the self-dispersing pigment having a group represented by general formula (1) bonded to the pigment particle surface and the benzene ring moiety of the surface functional group interact in a way that can cause aggregation. It is speculated that the presence of a compound represented by general formula (2) in this ink further enhances the effect of suppressing accumulation by inhibiting aggregation through the interaction of the compound represented by general formula (2) with the hydrophobic portion and benzene ring moiety of the self-dispersing pigment.

[0036] From the viewpoint of the effect of suppressing deposition, it is preferable that the content of the compound represented by general formula (2) in the ink be determined in relation to the content of the pigment. Through investigations by the present inventors, it has been found that, from the viewpoint of color development and suppression of deposition, it is preferable that the content C (mmol / kg) of the compound represented by general formula (2) in the aqueous ink and the content P (mass%) of the self-dispersing pigment described above satisfy the relationship shown in formula (3) below. 0.010≦C(mmol / kg) / P(mass%)≦3.000 (3)

[0037] When the value of C (mmol / kg) / P (mass%) is 0.010 or higher, the amount of the compound represented by general formula (2) relative to the self-dispersible pigment is sufficient, thereby more effectively suppressing the accumulation of aggregates in the cap. On the other hand, when the value of C (mmol / kg) / P (mass%) is 3.000 or lower, images with even better color development are likely to be obtained. In this case, the amount of the compound represented by general formula (2) relative to the self-dispersible pigment is appropriately suppressed, which is thought to prevent the compound represented by general formula (2) from adsorbing to particle surfaces other than those that contribute to strong aggregation in the self-dispersible pigment. Therefore, it is thought that an increase in anionic groups on the particle surfaces of the pigment in the self-dispersible pigment, which would increase affinity for liquid components in the ink, is unlikely to occur. As a result, after the ink is applied to the recording medium, the adsorption due to interaction between the pigment and the cellulose on the surface of the recording medium is unlikely to be relatively weak, which is thought to facilitate the production of images with even better color development.

[0038] From the viewpoint of achieving both good image color development and suppression of deposition, 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 (2) and the content P (mass%) of the self-dispersing pigment in the aqueous ink satisfy the relationship of the following formula (4). 0.030≦C(mmol / kg) / P(mass%)≦2.000 (4)

[0039] In addition, in the aqueous ink, R 1 The content C1 of the compound in which is a hydroxy group is preferably 0.60 to 0.95 times the content C of the compound represented by general formula (2) in terms of molar ratio (times). The units of the contents C1 and C are mmol / kg. When the value of C1 / C is 0.60 to 0.95, the effect of suppressing the accumulation of aggregates in the cap is likely to be further enhanced.

[0040] As mentioned above, it is presumed that the compound represented by general formula (2) inhibits aggregation by interacting with the hydrophobic portion of the pigment particle surface, the benzene ring of the surface functional group, etc., of the surface structure of the self-dispersing pigment particle surface. 1 However, it is thought that the compounds having a hydroxyl group and the compounds having a nitro group have different sites where the interaction is relatively strong or weak depending on the site involved in the aggregation of the self-dispersing pigment due to the difference in the substituents. 1 By setting the ratio of compounds with a hydroxy group to 0.60 or more and 0.95 or less, it is estimated that the two compounds will complement each other in areas where their interactions are relatively weak, thereby efficiently inhibiting aggregation and enhancing the deposition suppression effect.

[0041] In the ink, in general formula (2), R 1 The content C1 (mmol / kg) of the compound in which is a hydroxy group is preferably 0.024 mmol / kg or more and 10.240 mmol / kg or less, more preferably 0.032 mmol / kg or more and 9.600 mmol / kg or less, and even more preferably 0.096 mmol / kg or more and 6.400 mmol / kg or less.

[0042] (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.

[0043] (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.

[0044] 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.

[0045] 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 = Log10 C 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.

[0046] 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.

[0047] 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.

[0048] 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 (29.9), 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.

[0049] 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).

[0050] 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.

[0051] 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.

[0052] 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.

[0053] (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.

[0054] 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.

[0055] (Ink properties) [Dynamic surface tension] The ink has a dynamic surface tension of 52 mN / m or less at 10 milliseconds. As a result, the self-dispersing pigment in the ink droplets adheres to the surface of the recording medium as the ink droplets wet and spread. This allows the recording medium to be efficiently coated with the pigment even with a small droplet volume, resulting in images with excellent color development. When considering high-speed fixation, it is generally effective to design the ink to have a low dynamic surface tension to accelerate the diffusion of the liquid components. However, this also tends to cause the pigment to sink into the recording medium, resulting in a decrease in color development. Self-dispersing pigments, in which groups represented by general formula (1) are bonded to the pigment particle surface, can suppress a decrease in color development even with such a low dynamic surface tension.

[0056] From the viewpoint of achieving both fixability and color development, the dynamic surface tension of the ink at 10 milliseconds is more preferably 50 mN / m or less, and even more preferably 48 mN / m or less. Furthermore, the dynamic surface tension of the ink at 10 milliseconds is preferably 32 mN / m or more. By ensuring that the dynamic surface tension of the ink at 10 milliseconds is 32 mN / m or more, sinking of the pigment into the interior of the recording medium is suppressed, further enhancing color development.

[0057] 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.

[0058] [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.

[0059] <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.

[0060] <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.

[0061] 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).

[0062] 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.

[0063] 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]

[0064] 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.

[0065] <Preparation of pigment dispersion> (Amount of anionic groups) To accurately determine the amount of anionic groups in the self-dispersed pigment, the sample was purified prior to measurement. First, the pigment dispersion was diluted to a pigment content of approximately 5%. The dispersion 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 amount of anionic groups in the self-dispersed pigment in the measurement solution was measured using colloidal titration using potential difference. Measurements were performed 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).

[0066] (Pigment dispersion 1-20) A mixture was prepared by mixing 250.0 g of purified water, 30.0 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, a 10% aqueous solution of potassium nitrite (KNO2) (the amount (g) shown in Table 1) was slowly added. 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 stirring time shown in Table 1. An 8 mol / L aqueous solution of potassium hydroxide was then added to adjust the pH to 10. The filtrate was purified by ultrafiltration until the electrical conductivity reached 50 μS / cm or less. After ultrafiltration, for pigment dispersions whose "counter ions" shown in Table 1 were Na or NH4, the counter ions of the anionic groups were replaced by ion exchange. 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, yielding pigment dispersions 1 to 20 with a pigment content of 10.0% and the anionic group amounts shown in Table 1. The resulting pigment dispersions 1 to 14 contained a group represented by general formula (1) and a counter ion (M in general formula (1)) on the surface of the pigment particles. 1 ) is a pigment dispersion containing a self-dispersing pigment having a group bonded thereto of the type shown in Table 1. The abbreviations for the types of pigments 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

[0067] TIFF2026042725000004.tif152170

[0068] (Pigment Dispersion 21) Carbon black (specific surface area 260m 2 20.0 g of (4-aminobenzoylamino)methane-1,1-diyl)bisphosphonic acid sodium monosalt (4-aminobenzoylamino)methane-1,1-diylbisphosphonate ... Pigment dispersion 21 was obtained in which ((4-aminobenzoylamino)-methane-1,1-diyl)bisphosphonic acid groups with potassium counter ions were introduced onto the particle surfaces of carbon black. The amount of anionic groups was 0.18 mmol / g.

[0069] (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%.

[0070] (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%.

[0071] (Pigment Dispersion 24) Pigment dispersion 24 containing a self-dispersing pigment was prepared using 4-aminophthalic acid as a treatment agent in accordance with the description for preparing pigment dispersion B in Patent Document 3. The pigment content in pigment dispersion 24 was 10.0%.

[0072] <Resin synthesis> (acrylic resin aqueous solution) A random copolymer acrylic resin 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 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%.

[0073] (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%.

[0074] <Preparation of the compound represented by general formula (2)> As specific examples of the compound represented by general formula (2), compounds having the structures shown in Table 2 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 2.

[0075] TIFF2026042725000005.tif49170

[0076] <Ink Preparation> Compounds 1 to 6 were mixed and thoroughly stirred to achieve the respective components (unit: %) and concentrations shown in the middle and bottom rows of Table 3 (Tables 3-1 to 3-7). 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 3 were of the type (number) shown in the top row of Table 3. 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" and "Acetylenol E100" are the trade names of nonionic surfactants (ethylene oxide adducts of acetylene glycol) manufactured by Kawaken Fine Chemicals. "Surfynol 465" is the trade name of a nonionic surfactant (ethylene oxide adduct of acetylene glycol) manufactured by Nissin Chemical Industry Co., Ltd. The amounts of ion-exchanged water used in the middle section of Table 3 include the amounts of compounds 1 to 6 used in preparing the ink. The lower section of Table 3 shows the ink properties. The dynamic surface tension of each ink at 10 milliseconds was measured at 25°C using a dynamic surface tensiometer (trade name "BUBBLE PRESSURE TENSIOMETER BP-2", manufactured by KRUSS) using the maximum bubble pressure method.

[0077] TIFF2026042725000006.tif205170

[0078] TIFF2026042725000007.tif205170

[0079] TIFF2026042725000008.tif207170

[0080] TIFF2026042725000009.tif205170

[0081] TIFF2026042725000010.tif206170

[0082] TIFF2026042725000011.tif205170

[0083] TIFF2026042725000012.tif206170

[0084] <Evaluation> Each ink obtained above was filled into an ink cartridge and installed in the position of the black ink in an inkjet recording device (trade name "Maxify iB4130", manufactured by Canon) that ejects ink from a recording head using thermal energy. 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 is defined as having a "100% recording duty." In this example, the following evaluation criteria were used: AA, A, and B were acceptable levels, and C, D, and E were unacceptable levels. The evaluation results are shown in Table 4.

[0085] (Color development) Using the inkjet recording device described above, solid images (2 cm x 2 cm) were recorded on the following two types of recording media (plain paper) at a recording duty of 75%. One day after recording, the optical density of the solid images 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 images was evaluated based on the average optical density of the recording media obtained, according to the following evaluation criteria. [Recording Media] Product name: "Office 70" (Canon) Product name: "npi wood-free paper" (Nippon Paper Industries) [Black ink] AA: The average optical density was 1.34 or more. A: The average optical density was 1.29 or more and less than 1.34. B: The average optical density was 1.24 or more and less than 1.29. C: The average optical density was 1.14 or more and less than 1.24. D: The average optical density was 1.04 or more and less than 1.14. E: The average optical density was 0.94 or more and less than 1.04. [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.

[0086] (Suppression of deposition) To confirm that the inks were concentrated and maintained sufficient performance even under conditions prone to deposition, 10% by mass of each ink was evaporated to prepare concentrated inks. Using the concentrated inks, a black solid image was printed on an A4-sized print medium at 10% print duty at 5-minute intervals using the same inkjet printing device as above, at a temperature of 30°C and a relative humidity of 10%. Before printing one solid image, approximately 0.20 mg of ink was pre-ejected into the cap. Additionally, approximately 0.1 g of ink was sucked out through the cap covering the print head nozzles as a cleaning operation once every 200 prints. After printing 5,000 prints, the condition of the deposits inside the cap was visually inspected, and a nozzle check pattern was printed on the Maxify iB4130 to confirm proper printing. For those in which no deposits were found inside the caps, 1,000 of the above records were added, and at that point deposits were checked and the deposition suppression was evaluated according to the evaluation criteria shown below. AA: After recording 8,000 discs, no deposits were found inside the cap. A: After recording 7,000 sheets, no deposits were found inside the cap. B: After recording 6,000 sheets, no deposits were found inside the cap. C: After recording 5,000 sheets, no deposits were found inside the cap. D: After printing 5,000 sheets, deposits were found inside the cap and the nozzle check pattern was not printed properly.

[0087] TIFF2026042725000013.tif152170

[0088] The color developability of Examples 1 and 33 to 35 was all ranked AA, but compared to Example 1, the color developability of Examples 33 to 35 was relatively excellent.

[0089] 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 has a group represented by the following general formula (1) bonded to the surface of the pigment particle, The aqueous ink has a dynamic surface tension of 52 mN / m or less at 10 milliseconds.

[0090] TIFF2026042725000014.tif44170 (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.

[0091] (Configuration 2) The aqueous ink according to configuration 1, wherein the pigment is carbon black. (Configuration 3) The carbon black has a specific surface area of ​​200 m2 by the BET method. 2 3. The aqueous ink according to claim 2, wherein the ink has a molecular weight of 1.0 or more. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the amount (mmol / g) of anionic groups in the self-dispersing pigment is 0.09 mmol / g or more and 0.20 mmol / g or less. (Configuration 5) The water-based ink according to any one of Configurations 1 to 4, further comprising a compound represented by the following general formula (2):

[0092] TIFF2026042725000015.tif45170 (in the general formula (2), R 1 represents a hydroxy group or a nitro group. 2each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

[0093] (Configuration 6) The aqueous ink according to Configuration 5, wherein the content C (mmol / kg) of the compound represented by general formula (2) and the content P (mass %) of the self-dispersing pigment in the aqueous ink satisfy the relationship of the following formula (3): 0.010≦C(mmol / kg) / P(mass%)≦3.000 (3) (Configuration 7) The aqueous ink according to Configuration 5 or 6, wherein the content C (mmol / kg) of the compound represented by general formula (2) and the content P (mass%) of the self-dispersing pigment in the aqueous ink satisfy the relationship of the following formula (4): 0.030≦C(mmol / kg) / P(mass%)≦2.000 (4) (Configuration 8) In the water-based ink, the R 1 is a hydroxy group, the molar ratio (times) of the compound represented by general formula (2) to the compound represented by general formula (2) is 0.60 times or more and 0.95 times or less. (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 has a group represented by the following general formula (1) bonded to the surface of the pigment particle, The aqueous ink has a dynamic surface tension of 52 mN / m or less at 10 milliseconds. (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.

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

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

4. 2. The aqueous ink according to claim 1, wherein the amount (mmol / g) of anionic groups in the self-dispersing pigment is 0.09 mmol / g or more and 0.20 mmol / g or less.

5. The aqueous ink according to claim 1, further comprising a compound represented by the following general formula (2): (In the general formula (2), R １ represents a hydroxy group or a nitro group. ２ each independently represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.

6. 6. The aqueous ink according to claim 5, wherein the content C (mmol / kg) of the compound represented by general formula (2) and the content P (mass %) of the self-dispersion pigment in the aqueous ink satisfy the relationship of the following formula (3): 0.010≦C (mmol / kg) / P (mass%)≦3.000 (3)

7. 6. The aqueous ink according to claim 5, wherein the content C (mmol / kg) of the compound represented by general formula (2) and the content P (mass%) of the self-dispersion pigment in the aqueous ink satisfy the relationship of the following formula (4): 0.030≦C (mmol / kg) / P (mass%)≦2.000 (4)

8. In the water-based ink, the R １ is a hydroxy group, the molar ratio (times) of the compound represented by general formula (2) to the compound represented by general formula (2) is 0.60 to 0.95 times.

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, comprising: An ink-jet recording method, wherein the ink is the aqueous ink according to any one of claims 1 to 8.

Images