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

Abstract

We provide a water-based ink that complies with regulations for FCM (Food Contact Material) and is capable of recording images with excellent adhesion to recording media. [Solution] An aqueous ink containing a self-dispersing pigment and a resin. The self-dispersing pigment is self-dispersing carbon black in which an aromatic monobasic acid group is bonded to the surface of carbon black particles, the carbon black is gas black containing 0.1% by mass or less of toluene extract, and the aromatic monobasic acid group is represented by the following general formula (1) or (2). TIFF2026057822000010.tif30170 (In general formulas (1) and (2), X independently represents a hydrogen atom, an alkali metal ion, an ammonium ion, or an organic ammonium ion, and * indicates the bonding position with the carbon black particle surface.)

Description

Technical Field

[0001] The present invention relates to an aqueous ink, an ink cartridge, and an inkjet recording method.

Background Art

[0002] In recent years, as an ink used for an inkjet recording method, an ink using particulate colorants such as pigments has attracted attention. An ink containing a pigment as a colorant is advantageous in that it can record an image with better fastness such as light resistance and gas resistance than an ink containing a dye as a colorant.

[0003] As a black pigment, carbon black is usually used. Carbon black is classified according to differences in raw materials, the principle of pyrolysis, and manufacturing processes. Gas black (channel black) is a carbon black with fine particles, a narrow particle size distribution, and excellent blackness. In addition, self-dispersing carbon black has excellent dispersion stability and a high degree of freedom in ink formulation. However, since carbon black tends to remain on the surface of the recording medium, the adhesion of the image to the recording medium tends to decrease, and problems such as defects occurring in the image due to rubbing may occur.

[0004] In addition, there are various restrictions on the concentrations of various materials used for food contact materials (FCM: Food Contact Material). For example, for carbon black used in FCM, it is desirable that both polycyclic aromatic hydrocarbons (PAH: Polycyclic Aromatic Hydrocarbons) and toluene extracts are in low concentrations.

[0005] Furthermore, the raw materials for the inks used in FCMs must comply with legal regulations such as European Commission Regulation 10 / 2011, European Commission Regulation 1272 / 2013, and Swiss Ordinance 817.023.21. For example, a recording solution containing carbon black with a PAH content of 500 ppm or less has been proposed (Patent Document 1). In addition, an aqueous ink containing carbon black from which organic solvent-soluble components have been removed has been proposed (Patent Document 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-354884 [Patent Document 2] Japanese Patent Publication No. 2001-200184 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present inventors investigated the properties of water-based inks and the like proposed in Patent Documents 1 and 2. As a result, it was found that images recorded using these water-based inks did not necessarily adhere well to the recording medium, and there is room for further improvement.

[0008] Therefore, an object of the present invention is to provide an aqueous ink that complies with FCM regulations and is capable of recording images with excellent adhesion to recording media. Another object of the present invention is to provide an ink cartridge using this aqueous ink and an inkjet recording method. [Means for solving the problem]

[0009] In other words, the present invention provides an aqueous ink containing a self-dispersing pigment and a resin, wherein the self-dispersing pigment is a self-dispersing carbon black in which an aromatic monobasic acid group is bonded to the surface of carbon black particles, the carbon black is gas black containing 0.1% by mass or less of toluene extract, and the aromatic monobasic acid group is represented by the following general formula (1) or (2).

[0010] TIFF2026057822000001.tif30170 (In the above general formulas (1) and (2), X independently represents a hydrogen atom, an alkali metal ion, an ammonium ion, or an organic ammonium ion, and * indicates the bonding position with the carbon black particle surface.) [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an aqueous ink that complies with legal regulations for FCM and is capable of recording images with excellent adhesion to recording media. Furthermore, according to the present invention, it is possible to provide an ink cartridge using this aqueous ink and an inkjet recording method. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. [Figure 2] This figure schematically shows 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 part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. [Modes for carrying out the invention]

[0013] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, water-based ink for inkjet applications may be simply referred to as "ink." In the present invention, "average particle size" means the cumulative 50% particle size (D50; median diameter) in the volume-based particle size distribution measured by dynamic light scattering. Unless otherwise specified, physical properties are values ​​at room temperature (25°C), normal pressure (1 atm = 101,325 Pa), and normal humidity (relative humidity 50%).

[0014] The inventors investigated the composition of an ink capable of recording images with excellent adhesion to recording media. Specifically, they investigated the use of pigments and materials that strongly interact with the recording media in order to improve the adhesion of images to the recording media. As a result, they found that using self-dispersing carbon black in which aromatic monobasic acid groups are bonded to the surface of carbon black particles, and using gas black with a toluene extract content of 0.1% by mass or less as carbon black, led to the present invention.

[0015] The inventors speculate that the above configuration improves the adhesion of images to the recording medium as follows: First, using gas black with a toluene extract content of 0.1% by mass or less removes adsorbed PAHs. Also, unlike furnace black and the like, gas black does not contain alkaline earth metals derived from quench water. Furthermore, by surface-modifying the gas black with aromatic monobasic acid groups, it is possible to suppress polarity while ensuring the dispersion stability necessary for a self-dispersing pigment. For these reasons, it is thought that the surface of the gas black particles readily interacts hydrophobically with the resin in the ink and the recording medium, thereby improving the adhesion of images to the recording medium.

[0016] <Water-based ink> The ink of the present invention is an aqueous ink suitable for inkjet printing, containing a self-dispersing pigment and a resin. The self-dispersing pigment is a self-dispersing carbon black in which an aromatic monobasic acid group is bonded to the particle surface of carbon black. The carbon black is a gas black having a toluene extract of 0.1% by mass or less. And the aromatic monobasic acid group is a group represented by the following general formula (1) or (2). Hereinafter, the details of the ink of the present invention will be described.

[0017] TIFF2026057822000002.tif30170(In the general formulas (1) and (2), X independently represents a hydrogen atom, an alkali metal ion, an ammonium ion, or an organic ammonium ion, and * represents the bonding position with the particle surface of carbon black)

[0018] (Self-dispersing pigment) The self-dispersing pigment is a self-dispersing carbon black produced by modifying carbon black by a surface modification method. Examples of the production method of the surface-modified type self-dispersing pigment include a method of chemically treating a pigment using a compound capable of generating a diazonium salt, a diazene compound, a substituted triazine compound, or a compound having an anionic group as a treating agent. However, as a raw material conforming to the FCM-related regulations, it is preferable to chemically treat carbon black using a primary aromatic amine having a monobasic acid group as a treating agent. More specifically, it is preferable to use 4-aminobenzoic acid or 5-aminosalicylic acid as a treating agent.

[0019] An aromatic monobasic acid group is bonded to the particle surface of carbon black. The aromatic monobasic acid group is composed of an aromatic ring and one carboxylic acid group bonded to the aromatic ring. Note that a hydroxyl group may be further bonded to the aromatic ring. The carboxylic acid group and the hydroxyl group may form a salt or an anhydride as much as chemically possible. When the carboxylic acid group or the hydroxyl group forms a salt, at least one proton of each of these groups is substituted with a cation.

[0020] Examples of the cation include alkali metal ions, ammonium ions, and organic ammonium ions. Examples of the alkali metal ions include ions such as lithium, sodium, and potassium. Examples of the organic ammonium ions include aliphatic amines such as mono- to trialkylamines; cations of aliphatic alcohol amines such as mono- to trialkanolamines and salts thereof. The aromatic monobasic acid group bonded to the particle surface of carbon black is a group represented by the following general formula (1) or (2).

[0021] TIFF2026057822000003.tif30170(In the general formulas (1) and (2), X independently represents a hydrogen atom, an alkali metal ion, an ammonium ion, or an organic ammonium ion, and * represents the bonding position with the particle surface of carbon black)

[0022] The amount of the anionic group directly or indirectly bonded via another atomic group to the particle surface of the pigment (carbon black) can be measured as the surface charge amount of the self-dispersing pigment. The surface charge amount can be measured by colloid titration using a potential difference. A larger value of the surface charge amount means more anionic groups, and a smaller value means fewer anionic groups. The surface charge amount of the self-dispersing pigment is the amount per 1 g of the solid content of the self-dispersing pigment. In the examples described later, a potentiometric automatic titrator (trade name "AT-510", manufactured by Kyoto Electronics Industry Co., Ltd.) equipped with a streaming potential titration unit (PCD-500) was used, and the surface charge amount of the self-dispersing pigment in the pigment dispersion was measured by colloid titration using a potential difference. Methyl glycol chitosan was used as the titration reagent. It is also possible to measure the surface charge amount using the self-dispersing pigment extracted from the ink by an appropriate method.

[0023] The surface charge (mmol / g) of the self-dispersing pigment is preferably between 0.025 mmol / g and 1.000 mmol / g. If the surface charge is less than 0.025 mmol / g, there are fewer functional groups bonded to the surface of the pigment (carbon black) particles, resulting in too much of the hydrophobic particle surface being exposed. Therefore, in ink formulations containing a large amount of water-soluble solvent, this can lead to a decrease in charge repulsion due to a decrease in dielectric constant, potentially reducing the dispersion stability of the pigment. On the other hand, if the surface charge is greater than 1.000 mmol / g, there are more functional groups bonded to the surface of the pigment particles, including many anionic groups. This can lead to a decrease in hydrophobic interaction with non-polar or low-polarity recording media, potentially reducing the effect of promoting adhesion between the pigment and the recording media.

[0024] The content (by mass) of the self-dispersing pigment (self-dispersing carbon black) in the ink is preferably 0.10% by mass or more and 15.00% by mass or less, and more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink.

[0025] [Carbon Black] As the carbon black used, gas black that is not quenched with water during manufacturing is used. The toluene extract content (mass%) of the gas black is 0.1% by mass or less.

[0026] The DBP oil absorption rate of carbon black (gas black) is preferably 50 mL / 100g or more and 200 mL / 100g or less, and more preferably 80 mL / 100g or more and 150 mL / 100g or less. The DBP oil absorption rate can be measured by methods in accordance with JIS K6221 or ASTM D 2414. These methods involve adding dibutyl phthalate dropwise to 100 g of carbon black under stirring and measuring the amount of dibutyl phthalate added when the torque is at its maximum.

[0027] The specific surface area of ​​carbon black (gas black) obtained by the BET method is 100m². 2 / g or more 600m 2It is preferable that the amount is less than or equal to / g. The specific surface area can be measured by the BET method using methods compliant with JIS K6217 or ASTM D6556. These methods involve immersing degassed carbon black in liquid nitrogen and measuring the amount of nitrogen adsorbed on the surface of the carbon black particles when equilibrium is reached.

[0028] The primary particle size of carbon black (gas black) is preferably between 10 nm and 40 nm. Carbon black typically exists as multiple primary particles linked together three-dimensionally, like a bunch of grapes. The primary particle size refers to the particle size of the smallest unit of carbon black (primary particle) that forms a single particle. The primary particle size of carbon black can be determined by observing and measuring the particle size of the smallest unit of carbon black forming a particle at approximately 100 points using a transmission or scanning electron microscope, and then calculating the arithmetic mean of these measurements.

[0029] The average particle size of carbon black (gas black) is preferably between 50 nm and 200 nm. The average particle size of carbon black refers to the particle size of carbon black in its usual form. The average particle size of carbon black is the median diameter (D50) measured using a dynamic light scattering particle size distribution analyzer or the like.

[0030] (resin) The ink contains a resin. The resin is added to the ink (i) to stabilize the dispersion state of the self-dispersing pigment, i.e., as a resin dispersant or its auxiliary. It is also added to the ink (ii) to improve various properties such as the scratch resistance of the recorded image. The resin content (mass%) in the ink is preferably 0.10% by mass or more and 15.00% by mass or less, and more preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink.

[0031] The resin content (mass%) in the ink is preferably 1.0 to 4.0 times the self-dispersing carbon black content (mass%), and more preferably 1.5 to 3.0 times. If the above mass ratio is less than 1.0 times, for example, the image adhesion to a non-absorbent recording medium may decrease. On the other hand, if the above mass ratio is greater than 4.0 times, the image adhesion to the recording medium is sufficient, but the color density of the image may decrease because the amount of carbon black is relatively small.

[0032] As the resin, it is preferable to use a resin having anionic groups. Specific examples of resins include acrylic resins, polyester resins, polyurethane resins, polyurea resins, polysaccharides, and polypeptides. Among these, acrylic resins and polyurethane resins are preferred because they easily ensure ink discharge stability. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. Among these, resins that comply with the regulations for FCM, i.e., those listed in the positive list (see Article 18, Paragraph 3 and Notification No. 370 of the revised Food Sanitation Act), can be suitably used.

[0033] The resin preferably has units derived from hydrophobic compounds. Furthermore, it is preferable that these hydrophobic compound-derived units include units derived from aromatic compounds. Examples of aromatic compounds in the case of acrylic resins include monomers having aromatic rings such as styrene, α-methylstyrene, and (meth)acrylate. Examples of hydrophobic compounds other than aromatic compounds that constitute the hydrophobic compound-derived units of the acrylic resin include (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0034] In the case of polyester resins, examples of aromatic compounds include aromatic dicarboxylic acids (aromatic acid components) such as isophthalic acid, terephthalic acid, 4-hydroxybenzoic acid, naphthalenedicarboxylic acid, 6-hydroxy-2-naphthoic acid, biphenyldicarboxylic acid, and tetrahydrophthalic acid.

[0035] In the case of polyurethane resins, examples of aromatic compounds include isocyanate compounds (aromatic-containing isocyanates) such as tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyle diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α',α'-tetramethylxylylene diisocyanate.

[0036] The resin contains units derived from hydrophobic compounds, including units derived from aromatic compounds, and the proportion of units derived from aromatic compounds to the total number of units derived from hydrophobic compounds is preferably 40% by mass or more and 80% by mass or less. It is even more preferably 45% by mass or more and 75% by mass or less. If the proportion of units derived from aromatic compounds to the total number of units derived from hydrophobic compounds constituting the resin is less than 40% by mass, the hydrophobic interaction between the carbon black particle surface and the recording medium (substrate) tends to decrease. This can slightly reduce the effect of improving image adhesion. On the other hand, if the proportion of units derived from aromatic compounds to the total number of units derived from hydrophobic compounds constituting the resin exceeds 80% by mass, the proportion of rigid components in the resin increases. As a result, while the image intensity increases, the flexibility tends to decrease, and the effect of improving image adhesion may slightly decrease.

[0037] The resin in the ink may be dissolved in the aqueous medium, or dispersed in the aqueous medium as resin particles. In particular, it is preferable that the resin be contained in the ink in the form of resin particles. That is, it is preferable that the resin be in the form of resin particles. In this invention, "resin particles" means resin that exists in an insoluble state in the aqueous medium that constitutes the ink. More specifically, it means resin that can exist in the aqueous medium in a state in which particles whose particle size can be measured by dynamic light scattering are formed. On the other hand, "water-soluble resin" means resin that exists in a dissolved state in the aqueous medium that constitutes the ink. More specifically, it means resin that can exist in the aqueous medium in a state in which particles whose particle size can not be measured by dynamic light scattering are not formed. If resin particles are expressed in contrast to "water-soluble resin," they become "water-dispersible resin (water-insoluble resin)."

[0038] Whether a resin qualifies as "resin particles" can be determined according to the following method. First, prepare a liquid containing the resin to be judged (resin content: 10% by mass). Next, prepare a sample by diluting this liquid with pure water to a resin content of approximately 1.0%. Then, measure the particle size of the resin in the sample using dynamic light scattering. If particles with a particle size are measured, the resin is determined to be "resin particles" (i.e., a "water-dispersible resin"). On the other hand, if no particles with a particle size are measured, the resin is determined not to be "resin particles" (i.e., a "water-soluble resin"). The measurement conditions in this case can be, for example, SetZero: 30 seconds, Number of measurements: 10 times, Measurement time: 120 seconds, Shape: Spherical, Refractive index: 1.5, Density: 1.0.

[0039] As a particle size distribution analyzer, a dynamic light scattering particle size analyzer (for example, product name "NanoTrac WAVE II-Q," manufactured by MicroTrac-Bell) can be used. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those mentioned above.

[0040] The acid value of the water-soluble resin is preferably 30 mg KOH / g or more and 350 mg KOH / g or less. Furthermore, the weight-average molecular weight of the resin (weight-average molecular weight in polystyrene terms, determined by gel permeation chromatography) is preferably 1,000 or more and 100,000 or less, and more preferably 5,000 or more and 50,000 or less.

[0041] A liquid containing resin particles can be prepared by adding a resin to an aqueous medium and then dispersing it using a disperser or similar device under conditions that cause the resin to melt. Alternatively, a liquid containing resin particles can also be prepared by dissolving a resin in an organic solvent and then gradually adding an aqueous medium. The resin used may be in solid or resin solution form.

[0042] The average particle size (D50) of the resin particles is preferably 150 nm or less, and more preferably 50 nm to 120 nm. If the average particle size of the resin particles exceeds 150 nm, the difference with the average particle size of the carbon black (gas black) becomes somewhat larger. As a result, the distribution of carbon black in the image formed after drying may become uneven, and the optical density of the image may decrease slightly.

[0043] (aqueous medium) The ink is an aqueous ink containing an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water (ion-exchanged water) is preferably used as the water. The water content (mass%) in the ink is preferably 50.0% by mass or more and 95.0% by mass or less, based on the total mass of the ink. As the water-soluble organic solvent, any solvent usable for inkjet inks, such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The water-soluble organic solvent content (mass%) in the ink is preferably 3.0% by mass or more and 50.0% by mass or less, based on the total mass of the ink. If the water-soluble organic solvent content is less than 3.0% by mass, sufficient reliability, such as adhesion resistance, may not be obtained as an aqueous inkjet ink. On the other hand, if the water-soluble organic solvent content exceeds 50.0% by mass, ink supply problems may occur.

[0044] (Other ingredients) In addition to the components mentioned above, the ink may also contain, as necessary, water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethyleneurea. Furthermore, the ink may contain, as necessary, various additives such as surfactants, pH adjusters, defoamers, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, and chelating agents. When surfactants are used, the surfactant content (mass%) in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 2.0% by mass or less, based on the total mass of the ink.

[0045] The ink may further contain other resins besides those mentioned above. These other resins may include dispersants for dispersing pigments. It is preferable to use a water-soluble resin as the other resin. Examples of water-soluble resins include block copolymers, random copolymers, graft copolymers, and combinations thereof. Examples of water-soluble resins include acrylic resins, polyurethane resins, and olefin resins. Among these, acrylic resins and polyurethane resins are preferred.

[0046] (Ink properties) The ink of the present invention is an aqueous ink suitable for inkjet printing. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. The viscosity of the ink at 25°C is preferably 1.0 mPa·s to 10.0 mPa·s, more preferably 1.0 mPa·s to 5.0 mPa·s, and particularly preferably 1.0 mPa·s to 3.0 mPa·s. The surface tension of the ink at 25°C is preferably 10 mN / m to 60 mN / m, more preferably 20 mN / m to 60 mN / m, and particularly preferably 30 mN / m to 50 mN / m. The pH of the ink at 25°C is preferably 5.0 to 10.0, and more preferably 7.0 to 9.5.

[0047] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0048] <Inkjet recording method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known origin.

[0049] Figure 2 is a schematic diagram showing 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 part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 comprises recording heads 38 and 40 and is configured to hold an ink cartridge 42. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32.

[0050] Examples of recording media include paper, resin films, metals, and glass. Among these, polyethylene terephthalate, polypropylene, nylon, and polystyrene are preferred materials for the recording media. These materials readily interact with the resin in the ink. Furthermore, even after applying ink to the recording media and then heating and drying it, the thermal expansion coefficients of the ink layer (image) and the surface of the recording media (recording surface) are close, so stress is less likely to remain at the interface, allowing for the recording of images with superior adhesion and abrasion resistance. [Examples]

[0051] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0052] <Manufacturing of polyurethane resin> (Liquid containing PU resin 1-5) Polyester polyols of the types shown in Table 1 (PP-1, PP-2) were prepared. In a four-necked flask equipped with a thermometer, stirrer, nitrogen inlet tube, and condenser, the isocyanate and polyester polyols in the amounts (in parts) shown in Table 2 were placed. Furthermore, 0.01 parts of dibutyltin dilaurate were added, and the mixture was reacted at 80°C for 1 hour under a nitrogen atmosphere. The acid polyol and amine in the amounts (in parts) shown in Table 2 were added, and the mixture was reacted for another 1 hour. After cooling to below 55°C, the chain extender in the amounts (in parts) shown in Table 2 and 150 parts of tetrahydrofuran were added, and the mixture was reacted at 60°C. After the reaction time shown in Table 2, the mixture was cooled to 30°C, and the polyamine in the amounts (in parts) shown in Table 2 was added. After 1 hour, 10 parts of methanol were added to stop the reaction. An appropriate amount of deionized water was added while stirring with a homomixer for 1 hour, and then the tetrahydrofuran and unreacted methanol were removed by distillation under reduced pressure. Water was added to adjust the concentration, and liquids containing PU resins 1-5 with a resin (solids) content of 30.0% were obtained. Table 2 shows the acid value, weight-average molecular weight, and the percentage of units derived from aromatic compounds relative to units derived from hydrophobic compounds for the obtained PU resins. Table 2 also shows the average particle size (D50) of the resin particles in the liquids containing the obtained PU resins. The average particle size of the resin particles was controlled by adjusting the stirring speed of the homomixer. The meaning of the abbreviations in Table 2 is shown below. • XDI: Xylylene diisocyanate • EDA: Ethylenediamine • DMPA: Dimethylolpropionic acid TEA: Triethylamine • NPG: Neopentyl glycol

[0053] TIFF2026057822000004.tif41170

[0054] TIFF2026057822000005.tif65170

[0055] <Manufacturing of acrylic resin> (Liquid containing acrylic resin 1) In a reaction vessel equipped with a stirrer, nitrogen gas inlet tube, condenser, and thermometer, 50 parts styrene, 18 parts n-butyl acrylate, 16 parts methyl methacrylate, 16 parts acrylic acid, and 100 parts toluene were added. Under a nitrogen gas atmosphere, 3 parts benzoyl peroxide were added at 100°C and the mixture was reacted for 2 hours. After the reaction, the solvent was removed by distillation at 140°C and 26 Pa. After returning to 25°C and atmospheric pressure, the product was crushed with a crusher to obtain acrylic resin 1. The acid value of the obtained acrylic resin 1 was 120 mg KOH / g, the weight-average molecular weight was 10,000, and the proportion (%) of units derived from aromatic compounds to units derived from hydrophobic compounds was 60.0%. The obtained acrylic resin 1 was neutralized with potassium hydroxide in a molar ratio of 0.9 times the acid value to obtain a liquid containing acrylic resin 1 with a resin (solids) content of 15.0%.

[0056] (Liquid containing acrylic resin 2) Acrylic resin 2 was obtained in the same manner as for acrylic resin 1 described above, except that 30 parts styrene, 20 parts n-butyl acrylate, 34 parts methyl methacrylate, and 16 parts acrylic acid were used as monomers. The acid value of the obtained acrylic resin 2 was 120 mg KOH / g, the weight-average molecular weight was 10,000, and the proportion (%) of units derived from aromatic compounds to units derived from hydrophobic compounds was 35.0%. Furthermore, the obtained acrylic resin 2 was neutralized with potassium hydroxide in a molar ratio of 0.9 times the acid value to obtain a liquid containing acrylic resin 2 with a resin (solids) content of 15.0%.

[0057] <Preparation of Pigment Dispersion> (Method for measuring the surface charge of self-dispersing pigments) The surface charge of self-dispersing pigments in a pigment dispersion was measured by potentiometric titration using a potentiometric titration system (product name "AT-510," manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a flow potentiometric titration unit (PCD-500) and methyl glycol chitosan as the titrator.

[0058] (Pigment dispersion 1) A solution was prepared by dissolving 5.0g of concentrated hydrochloric acid in 5.5g of water and cooled to 5°C. 1.2g of 4-aminobenzoic acid (treatment agent) was then added. The container of this solution was placed in an ice bath and stirred to maintain the solution temperature below 10°C. A solution prepared by dissolving 2.2g of potassium nitrite in 9.0g of ion-exchanged water at 5°C was then added. After stirring for 15 minutes, a pigment (carbon black (gas black), trade name "NIPex1601IQ", manufactured by Orion Engineered Carbon, BET specific surface area 248m²) was added. 2 6.0 g of (DBP oil absorption 128 mL / 100 g) was added under stirring, and the mixture was stirred for another 15 minutes to obtain a slurry. Then, an 8 mol / L potassium hydroxide aqueous solution was added to adjust the pH of the liquid to 10 to obtain a dispersion. The dispersion was purified by removing impurities using an ultrafiltration apparatus (product name "RP-2100" (Aira), filter: pencil-type module "SAP-0013" (Asahi Kasei Chemicals)). Purification was carried out by diafiltration until the electrical conductivity of the filtrate was 500 μS / cm or less. Coarse particles were removed by centrifugation at 5,000 rpm for 30 minutes, and an appropriate amount of deionized water was added to adjust the pigment content to obtain pigment dispersion 1 with a pigment content of 15.0%. The D50 of the self-dispersing pigment in pigment dispersion 1 was 121 nm, and the surface charge was 0.180 mmol / g.

[0059] (Pigment dispersion 2) Pigment dispersion 2, with a pigment content of 15.0%, was obtained in the same manner as for pigment dispersion 1 described above, except that the treatment agent was changed to 1.4 g of 5-aminosalicylic acid. The D50 of the self-dispersing pigment in pigment dispersion 2 was 128 nm, and the surface charge was 0.190 mmol / g.

[0060] (Pigment dispersion 3) A pigment dispersion 3 with a pigment content of 15.0% was obtained in the same manner as for pigment dispersion 1 described above, except that the treatment agent was changed to 3-aminobenzoic acid. The D50 of the self-dispersing pigment in pigment dispersion 3 was 122 nm, and the surface charge was 0.180 mmol / g.

[0061] (Pigment dispersion 4) A mixture was obtained by mixing 20.0 parts of pigment, 30.0 parts of acrylic resin aqueous solution, and 50.0 parts of deionized water. The pigment used was carbon black (gas black) (product name "NIPex1601IQ", manufactured by Orion Engineered Carbon, BET specific surface area 248 m²). 2 A zirconia bead density of 128 mL / g and a DBP oil absorption rate of 128 mL / 100 g were used. The mixture was placed in a media-type disperser (product name "Bead Mill LMZ2", manufactured by Ashizawa Finetech) with a zirconia bead packing rate of 80%, dispersed at a peripheral speed of 12 m / s, and then centrifuged at 5,000 rpm for 30 minutes to remove aggregated components. Next, an appropriate amount of deionized water was added to prepare pigment dispersion 4. The pigment content in pigment dispersion 4 was 15.0%, the resin content was 5.0%, and the D50 of the pigment was 110 nm.

[0062] (Pigment dispersion 5) Carbon black is used with furnace black (product name "#970", manufactured by Mitsubishi Chemical, BET specific surface area 260m²). 2 A pigment dispersion 5 with a pigment content of 15.0% was obtained in the same manner as for pigment dispersion 1 described above, except that the ratio of pigments per gram ( / g) and the DBP oil absorption rate (79 mL / 100 g) were changed. The D50 of the self-dispersing pigment in pigment dispersion 5 was 108 nm, and the surface charge was 0.170 mmol / g.

[0063] (Pigment dispersion 6) A pigment dispersion 6 with a pigment content of 15.0% was obtained in the same manner as for pigment dispersion 1 described above, except that the treatment agent was changed to 2.0 g of 5-amino-1,2,3-benzenetricarboxylic acid. The D50 of the self-dispersing pigment in pigment dispersion 6 was 129 nm, and the surface charge was 0.580 mmol / g.

[0064] <Ink preparation> Each of the components listed below was mixed and thoroughly stirred, then pressure filtered through a cellulose acetate filter with a pore size of 1.2 μm (product name "Minisart", manufactured by Sartorius) to prepare each ink. "Ion-exchanged water: remainder" refers to the amount that makes up 100.0% of all the components constituting the ink. "Acetylenel E100" is the product name of a nonionic surfactant (acetylene glycol type) manufactured by Kawaken Fine Chemicals. • Pigment dispersion: Usage amount (%) as shown in Table 3 • Liquids containing resin: Usage amount (%) shown in Table 3 Glycerin: 5.0% Triethylene glycol: 10.0% Acetyleneol E100: 0.1% • Ion-exchanged water: remaining portion

[0065] TIFF2026057822000006.tif126170

[0066] <Rating> Each of the prepared inks was evaluated as follows. In this invention, in the evaluation criteria for each evaluation item shown below, "AA," "A," and "B" were defined as acceptable levels, and "C" as an unacceptable level. The evaluation results are shown in Table 4.

[0067] (FCM compatibility) We verified whether all the raw materials used in the preparation of the pigment dispersion were listed in the Union List of Annex I of European Commission Regulation 10 / 2011, and evaluated the FCM compliance of the ink according to the evaluation criteria shown below. A: It is listed and conforms to FCM standards. C: Not listed and does not conform to FCM.

[0068] (Adhesion) Each prepared ink was filled into an ink cartridge and set in an inkjet recording device (product name "PIXUS Pro9500", manufactured by Canon) equipped with a recording head that ejects ink by the action of thermal energy. In this example, an image recorded under the condition that eight ink droplets with a mass of 3.5 ng each are applied to a unit area of ​​1 / 600 inch × 1 / 600 inch is defined as having a recording duty cycle of 100%. Using this inkjet recording device, a pattern including a 20 cm × 20 cm solid image with a recording duty cycle of 100% was recorded on a recording medium, and then dried in an 80°C oven for 10 minutes to obtain the recorded material. A biaxially oriented polypropylene film (product name "Pyrene®", manufactured by Toyobo) was used as the recording medium. After storing the obtained recorded material at room temperature for 24 hours, a 50 mm long, 15 mm wide tape "Cellotape® CT15" (manufactured by Nichiban) was applied to the surface of the image for 40 mm, leaving a 10 mm margin. Subsequently, the applied tape was peeled off at an angle of 90° and a speed of 100 mm / sec. The area of ​​the image that was detached by the removal of the tape (detached area) was measured, and the adhesion of the image was evaluated according to the evaluation criteria shown below. AA: No peeling, or peeling area was less than 5%. A: The peeling area was between 5% and less than 10%. B: The peeling area was between 10% and less than 20%. C: The peeling area was 20% or more.

[0069] TIFF2026057822000007.tif122170

[0070] This embodiment includes the following configurations and methods. (Composition 1) A water-based ink containing a self-dispersing pigment and a resin, The self-dispersing pigment is a self-dispersing carbon black in which an aromatic monobasic acid group is bonded to the surface of carbon black particles. The carbon black is a gas black containing 0.1% by mass or less of toluene extract. An aqueous ink characterized in that the aforementioned aromatic monobasic acid group is represented by the following general formula (1) or (2). TIFF2026057822000008.tif30170 (In the above general formulas (1) and (2), X independently represents a hydrogen atom, an alkali metal ion, an ammonium ion, or an organic ammonium ion, and * indicates the bonding position with the carbon black particle surface.) (Configuration 2) The aqueous ink according to Configuration 1, wherein the resin is resin particles. (Configuration 3) The resin has units derived from a hydrophobic compound, which includes units derived from an aromatic compound. The aqueous ink according to configuration 1 or 2, wherein the proportion of units derived from the aromatic compound to units derived from the hydrophobic compound is 40% by mass or more and 80% by mass or less. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the content (mass%) of the resin is 1.0 times or more and 4.0 times or less in mass ratio to the content (mass%) of the self-dispersing carbon black. (Component 5) A water-based ink described in any one of Components 1 to 4, which is for inkjet use. (Configuration 6) An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is the water-based ink described in configuration 5. (Method 1) An inkjet recording method in which ink is ejected from an inkjet recording head to record an image on a recording medium, An inkjet recording method characterized in that the ink is the water-based ink described in configuration 5.

Claims

1. A water-based ink containing a self-dispersing pigment and a resin, The self-dispersing pigment is a self-dispersing carbon black in which an aromatic monobasic acid group is bonded to the surface of carbon black particles. The carbon black is a gas black containing 0.1% by mass or less of toluene extract. An aqueous ink characterized in that the aforementioned aromatic monobasic acid group is represented by the following general formula (1) or (2). (In the general formulas (1) and (2) above, X independently represents a hydrogen atom, an alkali metal ion, an ammonium ion, or an organic ammonium ion, and * indicates the bonding position with the carbon black particle surface.)

2. The aqueous ink according to claim 1, wherein the resin is resin particles.

3. The resin has units derived from a hydrophobic compound, which includes units derived from an aromatic compound. The aqueous ink according to claim 1, wherein the proportion of units derived from the aromatic compound to the units derived from the hydrophobic compound is 40% by mass or more and 80% by mass or less.

4. The aqueous ink according to any one of claims 1 to 3, wherein the content (mass%) of the resin is 1.0 times or more and 4.0 times or less by mass ratio to the content (mass%) of the self-dispersing carbon black.

5. The aqueous ink according to claim 4, which is for inkjet use.

6. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is the water-based ink described in claim 5.

7. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, An inkjet recording method characterized in that the ink is the aqueous ink described in claim 5.

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