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

Abstract

This invention provides an inkjet water-based ink capable of recording images with excellent scratch resistance and good adhesion recovery, an ink cartridge using this water-based ink, and an inkjet recording method. [Solution] This is an aqueous ink for inkjet use containing a pigment and a resin. The resin is a polyurethane resin having units derived from a polyhydric alcohol and units derived from a polyhydric isocyanate, and the polyhydric alcohol contains a heterocyclic diol. Also, this is an ink cartridge using this aqueous ink and an inkjet recording method.

Description

[Technical Field]

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

[0002] In recent years, inkjet recording methods have been used to record images for printed materials such as posters onto recording media. Because these printed materials are often used as posters both indoors and outdoors, there is a demand for images that possess not only good image quality, including glossiness, but also excellent reliability and robustness to withstand continuous printing.

[0003] To record images with improved properties such as gloss, for example, a dispersion of polyurethane resin having a structure derived from a polyisocyanate having a ring structure, a structure derived from polycarbonate, and a structure derived from an acidic group-containing polyol has been proposed (Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-54938 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present inventors investigated the aqueous ink proposed in Patent Document 1. As a result, they found that it is difficult to record images with the high level of abrasion resistance required in recent years, and that the adhesion recovery properties are not necessarily sufficient. Abrasion resistance refers to the property that even if the back surface of the recording medium or protrusions come into contact with the image, damage or peeling will not easily occur. Furthermore, the adhesion recovery properties of the ink refer to the property that even if the ink dries out in the flow path of the recording head, it can be easily redispersed by supplying new ink.

[0006] Therefore, an object of the present invention is to provide an aqueous inkjet ink with good adhesion recovery properties that can record images with excellent scratch resistance. 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]

[0007] In other words, the present invention provides an aqueous ink for inkjet use containing a pigment and a resin, wherein the resin is a polyurethane resin having units derived from a polyhydric alcohol and units derived from a polyhydric isocyanate, and the polyhydric alcohol contains a heterocyclic diol. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an aqueous inkjet ink with good adhesion recovery properties that can record images with excellent scratch resistance. 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]

[0009] [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]

[0010] 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 printers may be simply referred to as "ink." Unless otherwise specified, the physical properties are given at room temperature (25°C), normal pressure (1 atmosphere = 101,325 Pa), and normal humidity (50% relative humidity). Also, unless otherwise specified, "unit" refers to the unit structure corresponding to one monomer. When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0011] The inventors investigated an aqueous ink containing polyurethane resin in order to record images with excellent scratch resistance. Polyurethane resin is a resin obtained by the reaction of a polyhydric alcohol and a polyhydric isocyanate. More specifically, it is a resin in which units derived from the polyhydric alcohol and units derived from the polyhydric isocyanate are linked by urethane bonds (-CONH-). As a result of the investigation, it was found that when a diol having a ring structure is used as the polyhydric alcohol, the movement of the main chain of the resulting polyurethane resin is suppressed, and the intensity of images recorded with an ink containing such polyurethane resin is increased.

[0012] However, it was found that the adhesion recovery properties of inks containing polyurethane resins obtained using diols with a ring structure sometimes did not improve. As a result of further investigation, the inventors found that by using a polyurethane resin having units derived from polyhydric alcohols containing heterocyclic diols, both the scratch resistance of the image and the adhesion recovery properties of the ink improved, leading to the present invention. It is thought that the heteroelements constituting the heterocycle interact appropriately with water molecules, thereby improving the redispersibility of the dried ink.

[0013] <Water-based ink> The ink of the present invention is an aqueous inkjet ink containing a pigment and a resin. The resin is a polyurethane resin having units derived from polyhydric alcohols and units derived from polyhydric isocyanates. The polyhydric alcohol contains a heterocyclic diol. The components constituting the ink of the present invention and the physical properties of the ink will be described in detail below.

[0014] (resin) The ink contains a resin. As the resin, water-dispersible resins (resin particles) or water-soluble resins can be used. In this invention, "resin particles" refers to a resin that exists in an insoluble state within the aqueous medium constituting the ink. More specifically, it refers to a resin that can exist in the aqueous medium in a state where it forms particles whose particle size can be measured by dynamic light scattering. On the other hand, "water-soluble resin" refers to a resin that exists dissolved within the aqueous medium constituting the ink. More specifically, it refers to a resin that can exist in the aqueous medium without forming particles whose particle size can be measured by dynamic light scattering. When expressing resin particles in contrast to "water-soluble resin," the term becomes "water-dispersible resin (water-insoluble resin)."

[0015] Whether a resin qualifies as "resin particles" can be determined according to the following method. First, the liquid containing the resin to be judged is diluted with pure water to prepare a sample with a resin content of approximately 1.0%. Then, the particle size of the resin in the sample is measured by dynamic light scattering. If particles with a particle size are measured, the resin is determined to be "resin particles" (i.e., "water-dispersible resin"). On the other hand, if particles with a particle size are not measured, the resin is determined not to be "resin particles" (i.e., "water-soluble resin"). The measurement conditions in this case can be, for example, SetZero: 30 seconds, Number of measurements: 10, Measurement time: 120 seconds, Shape: Spherical, Refractive index: 1.5, Density: 1.0. As a particle size distribution analyzer, a particle size analyzer using dynamic light scattering (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 described above.

[0016] The content (mass %) of the resin in the ink is preferably 1 mass % or more and 10 mass % or less, more preferably 3 mass % or more and 8 mass % or less, based on the total mass of the ink. When the content of the resin is less than 1 mass %, the amount of the resin in the image is small, and the effect of improving the abrasion resistance may be reduced. On the other hand, when the content of the resin exceeds 10%, it takes time until an interaction occurs between the hetero element constituting the heterocycle in the resin and the water molecules supplied from the ink, and the effect of improving the fixing recovery property may be reduced.

[0017] The resin is a polyurethane resin having units derived from polyhydric alcohol and units derived from polyvalent isocyanate. Examples of the polyhydric alcohol include dihydric to tetrahydric polyhydric alcohols. The polyhydric alcohol includes heterocyclic diol. The polyhydric alcohol may further contain known polyhydric alcohols (other polyhydric alcohols) other than the heterocyclic diol.

[0018] As the hetero element contained in the heterocycle of the heterocyclic diol, since it easily interacts with water molecules, it is preferably any one of an oxygen atom, a nitrogen atom, and a sulfur atom, and more preferably an oxygen atom. Examples of the heterocyclic diol include isosorbide, furan dimethanol, and pyridine dimethanol. Among them, from the viewpoint that water molecules easily penetrate and interact during drying of the ink, the heterocyclic diol is preferably isosorbide.

[0019] In the resin, the content (mass %) of the unit derived from the heterocyclic diol is preferably 5 mass % or more and 40 mass % or less, based on the total mass of the resin. When the content of the unit derived from the heterocyclic diol is less than 5 mass %, the number of units that interact with water molecules is small, and the effect of improving the fixing recovery property may be reduced. On the other hand, when the content of the unit derived from the heterocyclic diol exceeds 40 mass %, the steric hindrance of the heterocycle may overlap and the image may become brittle, and the effect of improving the abrasion resistance may be insufficient.

[0020] Examples of other polyhydric alcohols include polyhydric alcohols having linear or branched chains; polyhydric alcohols having a cyclic structure such as an aromatic group; sugar alcohols; and the like. Specific examples of other polyhydric alcohols include dihydric alcohols such as ethylene glycol (1,2-ethanediol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzenediol, and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; tetrahydric alcohols such as pentaerythritol; and the like. In addition, as other polyhydric alcohols, oligomers (low molecular weight polymers having a molecular weight of 1,000 or less) can also be used.

[0021] Since the resin is used in the aqueous ink, it preferably has an acid group, and the acid group is preferably a carboxylic acid group. By using a polyhydric alcohol having a carboxylic acid group as a monomer, the carboxylic acid group can be introduced into the resin. Examples of the polyhydric alcohol having a carboxylic acid group include dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, and dimethylolbutyric acid. Among them, dimethylolpropionic acid and dimethylolbutanoic acid are preferred, and dimethylolpropionic acid is more preferred.

[0022] Examples of the polyvalent isocyanate include divalent to tetravalent polyvalent isocyanates. From the viewpoint of enhancing the adhesion to the base material and further improving the abrasion resistance, a polyvalent isocyanate having a linear alkyl chain is preferred, and pentane diisocyanate is more preferred.

[0023] The acid value of the resin is preferably between 4 mg KOH / g and 90 mg KOH / g. If the acid value of the resin is less than 4 mg KOH / g, the hydrophilicity of the resin may decrease, and the effect of improving adhesion recovery may be insufficient. On the other hand, if the acid value of the resin is greater than 90 mg KOH / g, the hydration amount increases, making it difficult to dry, and the film strength may be slightly insufficient, resulting in an insufficient effect of improving abrasion resistance. The acid value of the resin can be controlled by adjusting the ratio of polyhydric alcohols containing acid groups used as part of the polyhydric alcohol during resin synthesis.

[0024] The weight-average molecular weight of the resin, in terms of polystyrene equivalent, is preferably between 10,000 and 40,000. If the weight-average molecular weight of the resin is less than 10,000, entanglement between resin molecules is less likely to occur, which may result in insufficient film strength and an inadequate improvement in abrasion resistance. On the other hand, if the weight-average molecular weight of the resin exceeds 40,000, the molecular motion of the resin decreases, and the time required for water molecules to penetrate into the resin after ink drying tends to increase. This may result in an inadequate improvement in adhesion recovery. The weight-average molecular weight of the resin can be controlled by adjusting the reaction time during resin synthesis.

[0025] The resin is preferably resin particles (water-insoluble resin). Because the resin particles tend to remain on the substrate surface during image formation, the properties of the resin are better exhibited. The cumulative 50% particle size (D) in the volume-based particle size distribution of the resin particles. 50 ) is preferably 50 nm to 200 nm. D of resin particles 50 If the specific surface area is less than 50 nm, the specific surface area increases, which increases the amount of interface during redispersion, and the effect of improving adhesion recovery may be insufficient. On the other hand, the D of the resin particles 50 If the D of the resin particles exceeds 200 nm, stress caused by the particles catching on the surface irregularities of the image becomes more easily transmitted, which may reduce the effect of improving the image's scratch resistance. 50 and D 90This can be measured by dynamic light scattering under the same conditions as the method described above for determining whether or not something qualifies as a "resin particle." The particle size of the resin particles can be controlled by appropriately adjusting the resin manufacturing method and the resin particle manufacturing method.

[0026] Cumulative 50% particle size (D) in the volume-based particle size distribution of resin particles 50 ) is the cumulative 90% particle size (D) in the volume-based particle size distribution of resin particles. 90 The ratio to the material is preferably 0.6 times or more and 0.8 times or less. If the above ratio is less than 0.6 times, the particle size distribution will be wide, and the arrangement of resin particles in the image may become irregular. As a result, the film strength may be somewhat insufficient, and the effect of improving abrasion resistance may be inadequate.

[0027] The resin can be produced according to known methods for synthesizing polyurethane resins. Specifically, polyurethane resin can be obtained by reacting a polyhydric isocyanate with a polyhydric alcohol (urethane reaction). It is preferable to use a catalyst such as dibutyltin dilaurate during the urethane reaction. Alternatively, after neutralizing the acidic groups of the urethane prepolymer with a neutralizing agent, the polyurethane resin can be obtained by reacting it with chain extenders and crosslinking agents.

[0028] Since the resin particles are used as components of aqueous ink, it is preferable that they be in the form of a dispersion in an aqueous liquid medium. The aqueous liquid medium mainly consists of water, such as deionized water, ion-exchanged water, and distilled water, and may contain a water-soluble organic solvent as needed. The water content (mass%) in the aqueous liquid medium is preferably 50% by mass or more, and it is also preferable to use a liquid medium that substantially does not contain a water-soluble organic solvent (i.e., water). Examples of methods for atomizing the resin to form resin particles include dispersion methods and phase inversion (emulsification) methods.

[0029] Distribution methods include the following methods (1) and (2). (1) A method of dispersing a resin by adding a solution obtained by dissolving the resin in an organic solvent to an aqueous liquid medium. (2) A method of adding a resin to an organic solvent, then adding an aqueous liquid medium and mixing to disperse the resin.

[0030] Phase inversion (emulsification) methods include a method in which a resin is dissolved in an organic solvent, and an aqueous liquid medium is added to the resulting solution to invert the resin from a solvent system to an aqueous system, thereby precipitating the resin in the form of particles. In any of these methods, it is preferable to use a known disperser and adjust the particle size of the resulting resin particles by applying appropriate shear force during particle formation. Since the particle size of the resulting resin particles can be precisely adjusted, it is preferable to manufacture resin particles by the phase inversion (emulsification) method. The following describes a method for manufacturing resin particles by the phase inversion (emulsification) method.

[0031] First, the resin is dissolved in an organic solvent to obtain a resin solution. At this time, the separation and dissolution processes of the resin can be omitted by using the same organic solvent that was used in the synthesis reaction of the polyurethane resin. Examples of organic solvents include ethers such as tetrahydrofuran and dibutyl ether; ketones such as acetone and methyl ethyl ketone; and alcohols such as isopropanol. If only organic solvents with low water solubility and poor miscibility with water in any proportion (such as methyl ethyl ketone) are used, it may be difficult to adjust the particle size with high precision. For this reason, it is preferable to use ethers such as tetrahydrofuran, which can be miscible with water in any proportion, as the organic solvent. Ethers such as tetrahydrofuran are also preferable because they have excellent solubility for crystalline polyester resins.

[0032] To ensure uniform dissolution of the resin, it is preferable to dissolve the resin in an organic solvent while heating it. However, it is preferable to heat the solution to a temperature lower than the boiling point of the organic solvent. If the concentration of crystalline polyester resin in the resin solution is dilute, it may be difficult to control the particle size distribution. For this reason, the resin content (mass%) in the resin solution is preferably 10.0% by mass or more and 60.0% by mass or less, and more preferably 30.0% by mass or more and 50.0% by mass or less.

[0033] Next, an aqueous liquid medium is gradually added to the obtained resin solution to precipitate resin particles. It is preferable to add a base before or during the addition of the aqueous liquid medium in order to maintain a stable dispersion state of the resin particles. As the base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, amines and ammonia can be used, and it is preferable to add them in the form of an aqueous solution. The amount of base to be added can be controlled by the neutralization rate (mol%) based on the acid value corresponding to all carboxylic acid groups in the resin. The neutralization rate is preferably 70 mol% or more and 100 mol% or less. As the amount of aqueous liquid medium added increases, the resin solution, which was initially transparent, becomes cloudy and emulsifies, and resin particles are formed. By adjusting the resin content in the resin solution, the neutralization rate, and the shear force applied during dispersion, the particle size and particle size distribution of the obtained resin particles can be controlled.

[0034] The resulting emulsion is subjected to reduced pressure to remove the organic solvent by distillation, and if necessary, it is filtered using a filter of appropriate pore size (stainless steel mesh) to remove coarse particles. Next, water is added to adjust the resin particle content, thereby preparing a liquid containing resin particles (aqueous dispersion of resin particles). The water used to adjust the content is preferably deionized water, ion-exchanged water, or distilled water. From the viewpoint of ink productivity, the resin particle content (mass%) in the liquid containing resin particles is preferably 5.0% by mass or more and 30.0% by mass or less, and more preferably 15.0% by mass or more and 30.0% by mass or less.

[0035] (Pigment) The ink contains a pigment. The pigment can be a resin-dispersed pigment using a resin as a dispersant, or a self-dispersing pigment in which hydrophilic groups are bonded to the surface of the pigment particles. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the surface of the pigment particles, or microcapsule pigments in which the surface of the pigment particles is coated with a resin or the like can be used. Among these, it is preferable to use a resin-dispersed pigment in which the resin used as a dispersant is physically adsorbed onto the surface of the pigment particles. It is preferable to use a resin dispersant having a ring structure as the dispersant.

[0036] The ring structure in the resin dispersant can be introduced by the monomers that make up the resin used as the dispersant. Examples of monomers having a ring structure include styrenes such as styrene; aromatic esters such as benzyl (meth)acrylate; and so on. As the resin dispersant, a copolymer containing units derived from monomers having a ring structure and units derived from other known monomers can be used.

[0037] The resin content (mass%) in the ink is preferably 0.2 to 2.5 times the pigment content (mass%). If the above mass ratio is less than 0.2, the amount of resin in the image will be relatively small, which may result in insufficient improvement in the image's scratch resistance. On the other hand, if the above mass ratio exceeds 2.5, increasing the pigment content above a certain level will also increase the resin content, raising the solid content concentration and making it easier for dry material to form, which may reduce the effect of improving adhesion recovery.

[0038] (aqueous medium) The ink of the present invention 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 outside the above range, the reliability of the inkjet aqueous ink, such as its adhesion resistance, may decrease.

[0039] (Other ingredients) In addition to the above components, the ink may also contain, as necessary, organic compounds that are solid at room temperature, such as trimethylolethane and trimethylolpropane, and nitrogen-containing compounds, such as urea and ethyleneurea. Furthermore, in addition to the above components, the ink may also contain, as necessary, various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation accelerators, and chelating agents. When surfactants are used, the surfactant content (mass%) in the ink is preferably 0.1% to 5.0% by mass, and more preferably 0.1% to 2.0% by mass, based on the total mass of the ink.

[0040] The ink may further contain resins other than those mentioned above (other resins). 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, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred.

[0041] (Ink properties) The ink of the present invention is an aqueous ink for use in inkjet systems. 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.

[0042] <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.

[0043] <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.

[0044] 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.

[0045] Any recording medium may be used. Recording media with ink absorption properties can be used, such as plain paper or other recording media without a coating layer, or glossy paper or matte paper or other recording media with a coating layer. Furthermore, recording media with low or no ink absorption properties, such as printing paper, coated paper, resin sheets, and resin films, can also be used. The ink of the present invention is suitably used for applications in which images are recorded by directly applying ink to such recording media. [Examples]

[0046] 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.

[0047] <Method for measuring physical properties> (Acid value of resin) The resin was precipitated using a 1.0 mol / L hydrochloric acid aqueous solution, thoroughly washed with water, and dried at 60°C to obtain a dried product. The obtained dried product was added to 50 mL of tetrahydrofuran at 50°C and dissolved, then 5 mL of water was added, and the mixture was cooled to room temperature to obtain the measurement sample. The acid value of the resin was measured by neutralization titration of the obtained measurement sample. For neutralization titration, a potentiometric automatic titrator (product name "AT510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a composite glass electrode (product name "C-171", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) was used. A 0.5 mol / L potassium hydroxide ethanol solution was used as the titration reagent.

[0048] (Weight-average molecular weight of resin) The resin was added to tetrahydrofuran and dissolved by stirring at 25°C for 24 hours. The sample was then filtered through a membrane filter. The resin content in the sample was adjusted to approximately 0.3%. The prepared sample was analyzed by gel permeation chromatography according to the measurement conditions shown below, and the weight-average molecular weight (Mw) was calculated using a molecular weight calibration curve created with standard polystyrene resin. The standard polystyrene resin used was "TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500" (manufactured by Tosoh). [Measurement conditions] HPLC system: Product name "2695 Separations Module" (manufactured by Waters) Differential refractive index (RI) detector: Product name "2414 detector" (manufactured by Waters) Column: Four-row column of product name "GPC KF-806M" (manufactured by Showa Denko) Eluent: Tetrahydrofuran Flow rate: 1.0mL / min Oven temperature: 40℃ Sample injection volume: 100 μL

[0049] (Determination of whether the sample is a particle or not, particle size) The liquid containing the sample was diluted with pure water to obtain a measurement sample with a sample content of approximately 1.0%. Then, the particle size (D) of the resin particles in the measurement sample was measured using a particle size analyzer. 50 The particle size was measured. The measurement conditions are as follows. A particle size analyzer using the dynamic light scattering method (product name "NanoTrac WAVE II-Q", manufactured by MicroTrac-Bel) was used as the particle size analyzer. If particles with a particle size were measured, the sample was determined to be "particles" ("aqueous dispersion"), and if particles with a particle size were not measured, the sample was determined not to be "particles" ("aqueous solution"). [Measurement conditions] SetZero: 30 seconds Number of measurements: 10 Measurement time: 120 seconds Shape: true spherical Refractive index: 1.5 Density: 1.0

[0050] <Preparation of resin> (Resin 1-26) A four-necked flask equipped with a thermometer, stirrer, nitrogen inlet tube, and condenser contained the types and amounts (in parts) of polyhydric isocyanates and polyhydric alcohols shown in Tables 1-1 to 1-3, along with 0.01 part of dibutyltin dilaurate. The mixture was then reacted at 80°C for 1 hour under a nitrogen gas atmosphere. Acid-containing diols of the types and amounts (in parts) shown in Tables 1-1 to 1-3 were added, and the mixture was reacted for another 1 hour. After cooling to below 55°C, 4 parts of neopentyl glycol and 150 parts of tetrahydrofuran were added, and the mixture was reacted at 60°C. After reacting for the reaction times shown in Tables 1-1 to 1-3, the mixture was cooled to 30°C. 0.4 parts of ethylenediamine were added, and after stirring for 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. After stirring for 1 hour, the tetrahydrofuran and unreacted methanol were removed by distillation under reduced pressure. Water was added to adjust the concentration, and liquids containing polyurethane resins 1 to 26, each with a resin (solids) content of 30%, were obtained. The acid value and weight-average molecular weight (Mw) of the obtained polyurethane resins are shown in Tables 1-1 to 1-3. The meanings of the abbreviations for each component in Tables 1-1 to 1-3 are shown below. PDI: 1,5-pentamethylene diisocyanate • H6XDI: Bis(isocyanatomethyl)cyclohexane IPDI: Isophorone diisocyanate • IS: Isosorbide FDM: 2.5-Flangeall PDM: 2,6-Pyridinedimethanol • CHDM: 1,4-Cyclohexanedimethanol PPG2000: Polypropylene glycol with a number-average molecular weight of 2,000 PES2000: Polyester polyol with a number-average molecular weight of 2,000 • T6002: Polyhexamethylene carbonate diol with a number-average molecular weight of 2,000 (manufactured by Asahi Kasei Chemicals) • PTMG2000: Polytetramethylene glycol with a number-average molecular weight of 2,000 • PEG2000: Polyethylene glycol with a number-average molecular weight of 2,000 • DMPA: Dimethylolpropionic acid

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[0054] <Manufacturing of resin particles> (Resin particles 1-30) A 2L beaker equipped with a stirrer (product name "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was prepared. Polyurethane resins of the types shown in Tables 2-1 and 2-2 were added to tetrahydrofuran and stirred at 25°C to dissolve them, preparing a resin solution with a polyurethane resin content of 40%. 300 parts of the prepared resin solution were placed in the beaker. A 5% potassium hydroxide aqueous solution in an amount corresponding to the neutralization rate based on the acid value of the polyester resin, as shown in Tables 2-1 and 2-2, was added and stirred for 30 minutes. Under conditions of 25°C, 300 parts of deionized water were added dropwise at a rate of 20 mL / min while stirring at a rotation speed of 150 rpm. After removing the organic solvent and some water by reducing the pressure, the contents of the beaker were filtered using a 150-mesh wire mesh (a filter in which 150 stainless steel wires are woven vertically and horizontally per square inch). By adding an appropriate amount of deionized water to adjust the content, liquids containing resin particles 1 to 30, each with a resin particle content of 25.0%, were obtained. Note that for resin particles 17 to 19, the particle size could not be measured, and water-soluble resin rather than resin particles was obtained; however, for convenience, these were named resin particles 17 to 19. The physical properties of the obtained resin particles 1 to 30 are shown in Tables 2-1 and 2-2.

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[0056] TIFF2026088636000005.tif56170

[0057] <Preparation of Pigment Dispersion> (Pigment dispersions 1-5) A batch-type vertical sand mill (manufactured by AIMEX) filled with 200 parts of 0.3 mm diameter zirconia beads contained a mixture of 10.0 parts of the pigments shown in Table 3, 20.0 parts of a resin-containing liquid, and 70.0 parts of deionized water, which was dispersed for 3 hours. The resin-containing liquid was an aqueous solution with a resin content of 30.0%, obtained by dissolving the dispersants (water-soluble resins) shown in Table 3 in an aqueous potassium hydroxide solution equimolar to the acid value. All of these water-soluble resins had an acid value of 130 mgKOH / g and a weight-average molecular weight of 10,000. After removing coarse particles by centrifugation, the mixture was pressure-filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. The concentration was adjusted by adding an appropriate amount of deionized water to obtain pigment dispersions 1 to 5 with a pigment content of 10.0%. The meaning of the abbreviations for each component in Table 3 is shown below. • NIPex90: Carbon Black (manufactured by Orion Engineered Carbons) • 5GX01: CI Pigment Yellow 74 (Product name "Hansa yellow 5GX 01 LV 3344", manufactured by Clariant) St: Styrene • EA: Ethyl acrylate AA: Acrylic acid BzMA: Benzyl methacrylate BMA: n-butyl methacrylate • CHMA: Cyclohexyl methacrylate • 2EHMA: 2-ethylhexyl methacrylate • MAA: Methacrylic acid

[0058] TIFF2026088636000006.tif49170

[0059] (Pigment dispersion 6) 5.0 g of concentrated hydrochloric acid was dissolved in 5.5 g of water and the solution was cooled to 5°C. 1.6 g of 4-aminophthalic acid was then added to this solution. The container of this solution was placed in an ice bath and stirred to maintain the solution temperature below 10°C. A solution obtained by dissolving 1.8 g of sodium nitrite in 9.0 g of ion-exchanged water at 5°C was then added. After stirring for 15 minutes, 6.0 g of carbon black (product name "NIPex90", manufactured by Orion Engineered Carbons) was added under stirring. The mixture was stirred for another 15 minutes to obtain a slurry. The obtained slurry was filtered through filter paper (product name "Standard Filter Paper No. 2", manufactured by Advantec), the particles were thoroughly washed with water, and the mixture was dried in an oven at 110°C. Subsequently, sodium ions were replaced with potassium ions by ion exchange to obtain pigment dispersion 6, a liquid containing a self-dispersing pigment in which two -C6H3-(COOK) groups are bonded to the surface of the carbon black particles. The content of self-dispersed pigment in the obtained pigment dispersion 6 was 10.0%.

[0060] <Ink preparation> (Examples 1-41, Comparative Examples 1 and 2) The following components were mixed and thoroughly stirred, then pressure filtered through a 2.5 μm pore size microfilter to prepare the ink. Of the components listed below, "Acetylenel E100" is a trade name for a nonionic surfactant (manufactured by Kawaken Fine Chemicals). The physical properties of the ink are shown in Tables 4-1 and 4-2. • Liquid containing resin particles: The amount of resin content R(%) shown in Tables 4-1 and 4-2. • Pigment dispersion: The amount of pigment C (%) shown in Tables 4-1 and 4-2. Glycerin: 5.00% Triethylene glycol: 10.00% • Acetyleneol E100: 0.10% • Ion-exchanged water: Remaining volume (%) where the total amount of components is 100.00%

[0061] (Comparative Example 3) The resin was prepared in accordance with the description in "Example 1" of Japanese Patent Publication No. 2021-54938. The ink was prepared in the same manner as in Example 1, except that the prepared resin was used instead of resin particle 1.

[0062] <Rating> The prepared inks were evaluated as follows. In this invention, "A" and "B" were considered acceptable levels in the evaluation criteria for each item shown below, and "C" was considered an unacceptable level. In cases where a clear difference was observed even within the same evaluation criteria, those that were relatively superior among the "B" grades were designated as "B+". The evaluation results are shown in Tables 4-1 and 4-2.

[0063] (Abrasion resistance) Each prepared ink was filled into an ink cartridge and set in an inkjet recording device (product name "PIXUS iP3100", manufactured by Canon) that ejects ink from the recording head using thermal energy. In this embodiment, the recording duty cycle of a solid image recorded under the condition that one drop of ink with a concentration of 5 pL per drop is applied to a unit area of ​​1 / 1,200 inch × 1 / 1,200 inch is defined as 100%. Using the above inkjet recording device, a 200 mm × 200 mm solid image (recording duty cycle 100%) was recorded on a recording medium (product name "Aurora Coat", manufactured by Nippon Paper Industries). After leaving the recorded solid image for one day, a friction test was performed using a JSPS-type testing machine (product name "Abrasion Resistance Tester", manufactured by Imoto Seisakusho) capable of measurement in accordance with JIS L 0849, under the condition of 10 reciprocating movements with a load of 500 g. The image after the friction test was visually inspected, and the abrasion resistance of the image was evaluated according to the evaluation criteria shown below. A: The image did not have any scratches, or the scratches were at a level that could only be detected by bringing the recording medium close to it. B: From a distance, it was possible to see that there were scratches on the image, but the recording medium was not visible. C: The image had scratches on it, and the recording medium was visible.

[0064] (Adhesion recovery) The following operations were performed using the inkjet recording device described above. After performing a recovery process (cleaning) from the printer driver, a nozzle check pattern was recorded. Then, while the carriage was moving (when the recording head was in a position other than the home position), the power cable was unplugged to leave the recording head uncapped. The inkjet recording device was left in this state for 14 days in an environment with a temperature of 30°C and a relative humidity of 10%. After that, the inkjet recording device was placed in an environment with a temperature of 25°C for 6 hours, and then a nozzle check pattern was recorded while performing a recovery process (cleaning). The recorded nozzle check pattern was examined, and the ink adhesion recovery performance was evaluated according to the evaluation criteria shown below. A: After 3 to 5 recovery attempts, the system was restored to a state where it could record normally. B: After 6 to 10 recovery attempts, the system was able to record normally. C: After performing recovery operations 11 times, the system was not able to record properly.

[0065] TIFF2026088636000007.tif173170

[0066] TIFF2026088636000008.tif178170

[0067] This embodiment includes the following configurations and methods. (Composition 1) A water-based ink for inkjet use containing a pigment and a resin, The resin is a polyurethane resin having units derived from polyhydric alcohols and units derived from polyhydric isocyanates. An aqueous ink characterized in that the polyhydric alcohol contains a heterocyclic diol. (Configuration 2) The aqueous ink according to Configuration 1, wherein the heterocyclic diol is isosorbide. (Configuration 3) The aqueous ink according to Configuration 1 or 2, wherein the content (mass%) of the unit derived from the heterocyclic diol in the resin is 5% by mass or more and 40% by mass or less, based on the total mass of the resin. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the acid value of the resin is 4 mgKOH / g or more and 90 mgKOH / g or less. (Configuration 5) The aqueous ink according to any one of Configurations 1 to 4, wherein the weight average molecular weight of the resin in terms of polystyrene is 10,000 or more and 40,000 or less. (Configuration 6) The resin is resin particles, The cumulative 50% particle size (D 50 ) in the volume-based particle size distribution of the resin particles is 50 nm or more and 200 nm or less. The aqueous ink according to any one of Configurations 1 to 5. (Configuration 7) The aqueous ink according to any one of Configurations 1 to 6, wherein the pigment is dispersed by a resin dispersant having a ring structure. (Configuration 8) The aqueous ink according to any one of Configurations 1 to 7, wherein the content (% by mass) of the resin is 1% by mass or more and 10% by mass or less based on the total mass of the ink. (Configuration 9) The aqueous ink according to any one of Configurations 1 to 8, wherein the content (% by mass) of the resin is 0.2 times or more and 2.5 times or less the mass ratio to the content (% by mass) of the pigment. (Configuration 10) An ink cartridge including ink and an ink storage unit for storing the ink, The ink cartridge, wherein the ink is the aqueous ink according to any one of Configurations 1 to 9. (Method 1) An inkjet recording method of ejecting ink from an inkjet recording head and recording an image on a recording medium, The inkjet recording method, wherein the ink is the aqueous ink according to any one of Configurations 1 to 9.

Claims

1. A water-based ink for inkjet use containing pigments and resins, The resin is a polyurethane resin having units derived from polyhydric alcohols and units derived from polyhydric isocyanates. An aqueous ink characterized in that the polyhydric alcohol contains a heterocyclic diol.

2. The aqueous ink according to claim 1, wherein the heterocyclic diol is isosorbide.

3. The aqueous ink according to claim 1, wherein the content (by mass) of the unit derived from the heterocyclic diol in the resin is 5% by mass or more and 40% by mass or less, based on the total mass of the resin.

4. The aqueous ink according to claim 1, wherein the acid value of the resin is 4 mg KOH / g or more and 90 mg KOH / g or less.

5. The aqueous ink according to claim 1, wherein the weight-average molecular weight of the resin, on a polystyrene basis, is 10,000 or more and 40,000 or less.

6. The aforementioned resin is resin particles, The cumulative 50% particle size (D) in the volume-based particle size distribution of the aforementioned resin particles. ５０ The aqueous ink according to claim 1, wherein the wavelength is 50 nm or more and 200 nm or less.

7. The aqueous ink according to claim 1, wherein the pigment is dispersed in a resin dispersant having a ring structure.

8. The aqueous ink according to claim 1, wherein the resin content (by mass) is 1% by mass or more and 10% by mass or less, based on the total mass of the ink.

9. The aqueous ink according to claim 1, wherein the resin content (mass%) is 0.2 times or more and 2.5 times or less in mass ratio to the pigment content (mass%).

10. 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 any one of claims 1 to 9.

11. 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 an aqueous ink according to any one of claims 1 to 9.

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