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 inkjet ink containing a pigment and a resin. The resin is a polyester resin having units derived from a polyhydric alcohol and units derived from a polyhydric carboxylic acid, and the polyhydric carboxylic acid includes a heterocyclic dicarboxylic acid. Also, this invention relates to 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 glossiness, ink compositions containing copolyesters obtained using, for example, aromatic dicarboxylic acids or cyclic aliphatic dicarboxylic acids have been proposed (Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2014-514382 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The present inventors investigated the ink composition 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, ink adhesion recovery refers 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 polyester resin having units derived from a polyhydric alcohol and units derived from a polyhydric carboxylic acid, and the polyhydric carboxylic acid contains a heterocyclic dicarboxylic acid. [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 polyester resin in order to record images with excellent scratch resistance. Polyester resin is a resin obtained by the reaction of a polyhydric alcohol and a polyhydric carboxylic acid. More specifically, it is a resin in which units derived from a polyhydric alcohol and units derived from a polyhydric carboxylic acid are linked by an ester bond (-COO-). As a result of the investigation, it was found that when a dicarboxylic acid having a ring structure is used as the polyhydric carboxylic acid, the movement of the main chain of the resulting polyester resin is suppressed, and the intensity of images recorded with an ink containing such a polyester resin is increased.

[0012] However, it was found that the adhesion recovery properties of inks containing polyester resins obtained using dicarboxylic acids having a ring structure sometimes did not improve. As a result of further investigation, the inventors found that by using a polyester resin having units derived from polycarboxylic acids including heterocyclic dicarboxylic acids, 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 polyester resin having units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. The polyhydric carboxylic acids include heterocyclic dicarboxylic acids. 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, and more preferably 3 mass % or more and 8 mass % or less, based on the total mass of the ink. If 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, if the content of the resin exceeds 10%, when the ink dries, it takes time until the interaction between the hetero element constituting the heterocycle in the resin and the water molecules supplied from the ink occurs, and the effect of improving the fixing recovery may be reduced.

[0017] The resin is a polyester resin having units derived from polyhydric alcohols and units derived from polyvalent carboxylic acids. Examples of the polyhydric alcohol include dihydric to tetrahydric polyhydric alcohols. Examples of the polyhydric alcohol include straight-chain and branched polyhydric alcohols; polyhydric alcohols having a cyclic structure such as an aromatic group; sugar alcohols; and the like. Specific examples of the polyhydric alcohol 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, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), and isosorbide; trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; tetrahydric alcohols such as pentaerythritol; and the like. Further, an oligomer (a low molecular weight polymer having a molecular weight of 1,000 or less) can also be used as the polyhydric alcohol.

[0018] As the polyhydric alcohol, it is preferable to use a polyhydric alcohol having a cyclic structure from the viewpoint of reducing the mobility of the main chain of the polyester resin and further improving the abrasion resistance of the image. Further, from the viewpoint of further improving the fixing recovery by the interaction with water molecules, the polyhydric alcohol is preferably a heterocyclic diol. And the heterocyclic diol is preferably isosorbide.

[0019] The polyvalent carboxylic acid includes heterocyclic dicarboxylic acids. The polyvalent carboxylic acid may further contain known polyvalent carboxylic acids other than heterocyclic dicarboxylic acids (other polyvalent carboxylic acids). As the hetero element contained in the heterocyclic ring of the heterocyclic dicarboxylic acid, 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 dicarboxylic acid include five-membered aromatic heterocyclic dicarboxylic acids such as furandicarboxylic acid, pyrroledicarboxylic acid, thiophenedicarboxylic acid, imidazoledicarboxylic acid, and pyrazoledicarboxylic acid; six-membered aromatic heterocyclic dicarboxylic acids such as pyridinedicarboxylic acid; five-membered aliphatic heterocyclic dicarboxylic acids such as pyrrolidinedicarboxylic acid; and the like. Among them, from the viewpoint that water molecules easily penetrate and interact during drying of the ink, the heterocyclic dicarboxylic acid is preferably a dicarboxylic acid having a five-membered aromatic heterocyclic ring, and more preferably furandicarboxylic acid.

[0020] In the resin, the content (mass%) of the unit derived from the heterocyclic dicarboxylic acid is preferably 10 mass% or more and 50 mass% or less. When the content of the unit derived from the heterocyclic dicarboxylic acid is less than 10 mass%, since there are few units that interact with water molecules, the effect of improving the fixing recovery may be reduced. On the other hand, when the content of the unit derived from the heterocyclic dicarboxylic acid exceeds 50 mass%, the steric hindrance of the heterocyclic ring may overlap and the image may become brittle, and the effect of improving the abrasion resistance may be insufficient.

[0021] Examples of the other polyvalent carboxylic acids include conventionally known divalent to tetravalent polyvalent carboxylic acids.

[0022] The polyester resin is preferably a resin having units derived from heterocyclic diols and units derived from heterocyclic dicarboxylic acids. Furthermore, the total content (mass%) of units derived from heterocyclic diols and units derived from heterocyclic dicarboxylic acids in the polyester resin is preferably 15% by mass or more and 90% by mass or less, based on the total mass of the resin.

[0023] The acid value of the resin is preferably between 4 mg KOH / g and 60 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 60 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 alcohol and polyhydric carboxylic acid used during resin synthesis.

[0024] 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 250 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 250 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 90 This 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.

[0025] Cumulative 50% particle size (D) in the volume-based particle size distribution of resin particles50 ) 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.

[0026] The resin can be produced according to known methods for synthesizing polyester resins. Specifically, polyester resin can be obtained by reacting a polyhydric alcohol with a polycarboxylic acid (esterification reaction). It is preferable to use an esterification catalyst during the esterification reaction. Examples of esterification catalysts include metal compounds such as tin compounds, titanium compounds, antimony compounds, and germanium compounds. The amount of esterification catalyst is preferably 100 ppm to 5000 ppm based on the total amount of the polyhydric alcohol and polycarboxylic acid. If necessary, the molecular weight of the resulting resin can be adjusted by adding either the polyhydric alcohol or the polycarboxylic acid to the reaction system and performing a transesterification reaction to cleave some of the ester bonds.

[0027] By adjusting the amount of raw materials used in the esterification reaction so that the number of carboxylic acid groups of the polycarboxylic acid exceeds the number of hydroxyl groups of the polyhydric alcohol, a crystalline polyester resin containing carboxylic acid groups can be obtained. Alternatively, a crystalline polyester resin containing carboxylic acid groups can also be obtained by using a polyhydric carboxylic acid in the transesterification reaction.

[0028] The esterification reaction is preferably carried out under an inert gas atmosphere such as nitrogen gas. The reaction temperature during the esterification reaction is preferably between 180°C and 260°C. The reaction time during the esterification reaction is preferably between 1 hour and 5 hours.

[0029] During the esterification reaction, the reaction system may be depressurized to expel the water produced by the reaction, thereby accelerating the esterification (dehydration condensation) reaction. Under reduced pressure, the reaction is carried out under an inert gas atmosphere such as nitrogen gas, following the esterification reaction. The reaction temperature under reduced pressure is preferably 220°C to 280°C. The reaction time under reduced pressure is preferably 0.5 hours to 5 hours, and more preferably 1 hour to 3 hours. The degree of reduced pressure (vacuum) is preferably 1 Pa to 130 Pa, and more preferably 1 Pa to 50 Pa. However, if the degree of reduced pressure is too low, the reaction efficiency will decrease or the weight-average molecular weight of the resulting polyester resin will be small, so it is preferable to adjust it according to the reaction conditions. It is preferable to gradually reduce the pressure from atmospheric pressure (101,325 Pa) to 130 Pa or less over a period of about 0.1 to 3 hours.

[0030] Transesterification reactions are carried out by adding either a polyhydric alcohol or a polyhydric carboxylic acid to the reaction system to cleave some of the ester bonds, thereby adjusting the molecular weight of the resulting resin or, more importantly, to introduce carboxylic acid groups mainly at the ends of the molecular chains. From the viewpoint of efficiently obtaining polyester resins containing carboxylic acid groups, it is preferable to carry out the transesterification reaction using a polyhydric carboxylic acid.

[0031] It is preferable to use the synthesized resin in the next step of particle formation after it has been processed into an appropriate form by means of pressure and pulverization.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] (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.

[0040] 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.

[0041] 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.

[0042] (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.

[0043] (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.

[0044] 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.

[0045] (Physical properties of ink) 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.

[0046] <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.

[0047] <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.

[0048] 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.

[0049] 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]

[0050] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. Regarding the amounts of components, “parts” and “%” are based on mass unless otherwise specified.

[0051] <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 then 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 solution was cooled to room temperature to obtain a measurement sample. The obtained measurement sample was subjected to neutral titration to measure the acid value of the resin. For the neutral titration, an automatic potentiometric titrator (trade name “AT510”, manufactured by Kyoto Electronics Industry Co., Ltd.) equipped with a combined glass electrode (trade name “C-171”, manufactured by Kyoto Electronics Industry Co., Ltd.) was used. As the titration reagent, a 0.5 mol / L potassium hydroxide ethanol solution was used.

[0052] (Judgment Whether Sample is a Particle, Particle Size) A liquid containing the sample was diluted with pure water to obtain a measurement sample in which the content of the sample was adjusted to approximately 1.0%. Then, the particle size (D 50 , D 90 ) of the resin particles in the measurement sample was measured using a particle size measuring device. The measurement conditions are shown below. As the particle size measuring device, a particle size distribution meter based on the dynamic light scattering method (trade name “NanoTrack WAVEII-Q”, manufactured by Microtrac Bell Co., Ltd.) was used. When particles having a particle size were measured, the sample was judged to be “particles” (a “water dispersion”), and when particles having a particle size were not measured, the sample was judged not to be “particles” (an “aqueous solution”). [Measurement Conditions] SetZero: 30 seconds Number of measurements: 10 times Measurement time: 120 seconds Shape: True spherical Refractive index: 1.5 Density: 1.0

[0053] <Preparation of Resin> (Polyester resin 1-35) A reaction vessel equipped with a stirrer, condenser, and thermometer was prepared. A mixture of polyhydric alcohols and polyhydric carboxylic acids of the types and amounts (in parts) shown in Tables 1-1 and 1-2 was placed in this reaction vessel. Furthermore, tetra-n-butyl titanate was added as a catalyst in an amount equal to 200 ppm based on the total amount of polyhydric alcohols and polyhydric carboxylic acids, and the temperature was raised to 240°C over 4 hours to carry out the esterification reaction. After reducing the pressure in the system to 26 Pa over 20 minutes, the reduced pressure state of 240°C and 26 Pa was maintained for 90 minutes to polymerize a resin with a weight-average molecular weight of 25,000. After returning to 25°C and atmospheric pressure, the contents were crushed with a crusher to obtain polyester resins 1 to 35. The physical properties of the obtained polyester resins 1 to 35 are shown in Tables 1-1 and 1-2. The meaning of the abbreviations for each component in Tables 1-1 and 1-2 is shown below. • IS: Isosorbide FDM: 2.5-Flangeall • EG: Ethylene glycol BD: 1,4-butanediol • NPG: Neopentyl glycol BPA: Bisphenol A • FDA: 2,5-Franzicarboxylic acid PDA: 2,5-pyrroledicarboxylic acid • TDA: 2,5-thiophenedicarboxylic acid IDA: 4,5-imidazole dicarboxylic acid PyDA:3,5-pyrazoledicarboxylic acid • PrDA: 2,4-pyrrolidinedicarboxylic acid • PiDA: 2,6-pyridinedicarboxylic acid • CDA: 1,4-cyclohexanedicarboxylic acid • ADA: Adipic acid SUA: succinic acid tPA: Terephthalic acid iPA: Isophthalic acid • TMA: Trimellitus acid

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[0055] TIFF2026091607000002.tif140170

[0056] <Manufacturing of resin particles> (Resin particles 1-43) A 2L beaker equipped with a stirrer (product name "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was prepared. Polyester resins of the types shown in Tables 2-1 to 2-3 were dissolved in tetrahydrofuran at 20°C, and 300 parts of resin solutions of the concentrations shown in Tables 2-1 to 2-3 were prepared and placed in the beaker. An amount of 5% potassium hydroxide aqueous solution corresponding to the neutralization rate shown in Tables 2-1 to 2-3, based on the acid value of the polyester resin, was added, and the mixture was stirred for 30 minutes. Under conditions of 20°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 of the 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). An appropriate amount of deionized water was added to adjust the content, and liquids containing resin particles 1 to 43, each with a resin particle content of 25.0%, were obtained. Regarding resin particle 28, the particle size could not be measured, and a water-soluble resin, not a resin particle, was obtained. However, for convenience, it was named resin particle 28. The physical properties of the obtained resin particles 1 to 43 are shown in Tables 2-1 to 2-3.

[0057] TIFF2026091607000003.tif64170

[0058] TIFF2026091607000004.tif67170

[0059] TIFF2026091607000005.tif68170

[0060] <Preparation of Pigment Dispersion> (Pigment dispersion 1) A batch-type vertical sand mill (manufactured by AIMEX) filled with 200 parts of 0.3 mm diameter zirconia beads was used to disperse a mixture of 10.0 parts pigment, 20.0 parts resin-containing liquid, and 70.0 parts ion-exchanged water for 3 hours. Carbon black (product name "NIPex90", manufactured by Orion Engineered Carbons) was used as the pigment. The resin-containing liquid was an aqueous solution with a resin content of 30.0%, obtained by dissolving a water-soluble resin in an aqueous potassium hydroxide solution equimolar to its acid value. This water-soluble resin is a styrene-ethyl acrylate-acrylic acid copolymer with an acid value of 167 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 dispersion 1 with a pigment content of 10.0%.

[0061] (Pigment dispersion 2) Pigment dispersion 2 was obtained in the same manner as pigment dispersion 1 described above, except that CI Pigment Yellow 74 (5GX01, trade name "Hansa yellow 5GX 01 LV 3344", manufactured by Clariant) was used as the pigment.

[0062] (Pigment dispersion 3) 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 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 3, 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 3 was 10.0%.

[0063] <Ink preparation> (Examples 1-50, Comparative Examples 1-3) 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 3-1 and 3-2. • Liquid containing resin particles: The amount of resin content R(%) shown in Tables 3-1 and 3-2. • Liquid containing pigment: The amount of pigment content C(%) shown in Tables 3-1 and 3-2. 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%

[0064] (Comparative Example 4) A resin was prepared in accordance with the method described in "Entry Number 1" of Japanese Patent Publication No. 2014-514382. The ink was prepared in the same manner as in Example 1, except that the prepared resin was used instead of resin particle 1.

[0065] <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 3-1 and 3-2.

[0066] (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.

[0067] (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.

[0068] TIFF2026091607000006.tif207170

[0069] TIFF2026091607000007.tif211170

[0070] 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 polyester resin having units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. An aqueous ink characterized in that the polycarboxylic acid includes a heterocyclic dicarboxylic acid. (Configuration 2) The aqueous ink according to Configuration 1, wherein the content (mass%) of the unit derived from the heterocyclic dicarboxylic acid in the resin is 10% by mass or more and 50% by mass or less. (Configuration 3) The aqueous ink according to Configuration 1 or 2, wherein the heterocyclic dicarboxylic acid is a dicarboxylic acid having a five-membered aromatic heterocyclic ring. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the heterocyclic dicarboxylic acid is a frangic acid. (Configuration 5) The aqueous ink according to any one of Configurations 1 to 4, wherein the polyhydric alcohol is a heterocyclic diol. (Composition 6) The aqueous ink according to any one of Compositions 1 to 5, wherein the polyhydric alcohol is isosorbide. (Configuration 7) An aqueous ink according to any one of Configurations 1 to 6, wherein the acid value of the resin is 4 mg KOH / g or more and 60 mg KOH / g or less. (Configuration 8) The resin is resin particles, The cumulative 50% particle size (D) in the volume-based particle size distribution of the aforementioned resin particles. 50 A water-based ink according to any one of items 1 to 7, wherein the wavelength is 50 nm or more and 250 nm or less. (Composition 9) An aqueous ink according to any one of Compositions 1 to 8, wherein the resin content (mass%) is 1% by mass or more and 10% by mass or less, based on the total mass of the ink. (Configuration 10) An aqueous ink according to any one of Configurations 1 to 9, wherein the resin content (mass%) is 0.2 times or more and 2.5 times or less by mass ratio to the pigment content (mass%). (Configuration 11) An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is an aqueous ink according to any one of the items 1 to 10 of the configuration. (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 an aqueous ink according to any one of the items 1 to 10.

Claims

1. A water-based ink for inkjet use containing pigments and resins, The resin is a polyester resin having units derived from polyhydric alcohols and units derived from polyhydric carboxylic acids. An aqueous ink characterized in that the polycarboxylic acid includes a heterocyclic dicarboxylic acid.

2. The aqueous ink according to claim 1, wherein the content (by mass) of the unit derived from the heterocyclic dicarboxylic acid in the resin is 10% by mass or more and 50% by mass or less.

3. The aqueous ink according to claim 1, wherein the heterocyclic dicarboxylic acid is a dicarboxylic acid having a five-membered aromatic heterocyclic ring.

4. The aqueous ink according to claim 1, wherein the heterocyclic dicarboxylic acid is a flangic acid.

5. The aqueous ink according to claim 1, wherein the polyhydric alcohol is a heterocyclic diol.

6. The aqueous ink according to claim 1, wherein the polyhydric alcohol is isosorbide.

7. The aqueous ink according to claim 1, wherein the acid value of the resin is 4 mg KOH / g or more and 60 mg KOH / g or less.

8. 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 250 nm or less.

9. 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.

10. 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%).

11. 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 10.

12. 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 10.

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