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

Abstract

The present invention provides an inkjet-based water-based ink capable of recording images with excellent scratch resistance and dent resistance, 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 copolymer containing a carboxylic acid group having a unit derived from alkyl(meth)acrylamide, and the alkyl(meth)acrylamide has a linear alkyl group with 4 to 18 carbon atoms. 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 Art

[0002] In recent years, when recording an image of a printed matter such as for poster use on a recording medium, an inkjet recording method has been used. Since printed matters for such applications are often used as posted materials both indoors and outdoors, it is required to record an image having good image quality such as glossiness and excellent reliability and fastness that can withstand continuous printing.

[0003] In order to record an image with improved characteristics such as glossiness, for example, an aqueous ink containing a water-insoluble polymer having an amide group has been proposed (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present inventors examined the aqueous ink proposed in Patent Document 1. As a result, it has been found that it is difficult to record an image having a high level of rub resistance and indentation resistance required in recent years. Rub resistance means a property in which even when the back surface or protrusions of the recording medium come into contact with the image, problems such as damage or peeling are unlikely to occur. Further, indentation resistance means a property in which even when stress is applied and the image is indented, the image quality does not change.

[0006] Therefore, an object of the present invention is to provide an aqueous ink for inkjet printers that can record images with excellent scratch resistance and dent 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 copolymer containing a carboxylic acid group having a unit derived from alkyl(meth)acrylamide, and the alkyl(meth)acrylamide has a linear alkyl group having 4 to 18 carbon atoms. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an aqueous ink for inkjet printers that can record images with excellent scratch resistance and dent 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)acrylamide," "(meth)acrylic acid," and "(meth)acrylate" are written, they mean "acrylamide, methacrylamide," "acrylic acid, methacrylic acid," and "acrylate, methacrylate," respectively.

[0011] The inventors investigated an aqueous ink containing a resin in order to record images with excellent scratch resistance and dent resistance. Specifically, they investigated an ink containing a copolymer (resin) containing a carboxylic acid group, which has units derived from alkyl(meth)acrylamide having linear alkyl groups with 4 to 18 carbon atoms. Resins having carboxylic acid groups and amide bonds derived from alkyl(meth)acrylamide strongly interact with each other through hydrogen bonding. Therefore, it is thought that a stronger film is formed when an image is recorded using an ink containing such a resin. In addition, the linear alkyl groups of alkyl(meth)acrylamide form interaction domains between alkyl groups. Furthermore, domains formed by linear alkyl groups with 4 to 18 carbon atoms can cause slippage when stress is applied. Moreover, the copolymer (resin) having units derived from alkyl(meth)acrylamide has suppressed molecular motion in the main chain, making it difficult to deform even when stress is applied. Therefore, images recorded using an ink containing such a resin are less prone to dents, resulting in improved dent resistance.

[0012] <Water-based ink> The ink of the present invention is an aqueous inkjet ink containing a pigment and a resin. The resin is a copolymer containing a carboxylic acid group, having a unit derived from alkyl(meth)acrylamide. The alkyl(meth)acrylamide has a linear alkyl group with 4 to 18 carbon atoms. The components constituting the ink of the present invention and the physical properties of the ink will be described in detail below.

[0013] (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)."

[0014] 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.

[0015] 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. 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 rub resistance may be reduced. On the other hand, if the content of the resin exceeds 10%, a step may occur at the interface between the printed part and the non-printed part, and the generated step may be easily recognized as a dent.

[0016] The resin is a copolymer having units derived from alkyl (meth) acrylamide. Further, the alkyl (meth) acrylamide has a linear alkyl group having 4 or more and 18 or less carbon atoms. Examples of the alkyl (meth) acrylamide include N-n-butyl (meth) acrylamide, N-n-pentyl (meth) acrylamide, N-n-hexyl (meth) acrylamide, N-n-heptyl (meth) acrylamide, N-n-octyl (meth) acrylamide, N-n-nonyl (meth) acrylamide, N-n-decyl (meth) acrylamide, N-n-undecyl (meth) acrylamide, N-n-dodecyl (meth) acrylamide, N-n-tetradecyl (meth) acrylamide, N-n-hexadecyl (meth) acrylamide, and N-n-octadecyl (meth) acrylamide.

[0017] From the viewpoint of making it easier to form an interaction domain between alkyl groups to further improve the rub resistance and suppressing the molecular motion of the main chain to further improve the dent resistance, the carbon number of the linear alkyl group is preferably 8 or less. Further, the alkyl (meth) acrylamide is more preferably N-n-octyl (meth) acrylamide.

[0018] The resin is usually a copolymer having units derived from monomers other than alkyl (meth) acrylamide (other monomers). As the other monomers, known polymerizable monomers can be used.

[0019] In the resin, the content (% by mass) of the unit derived from alkyl (meth) acryloyl acrylamide is preferably 5% by mass or more and 50% by mass or less based on the total mass of the resin. When the content of the unit derived from alkyl (meth) acryloyl acrylamide is less than 5% by mass, it is difficult to form an interaction domain by the alkyl group, and the effect of improving the abrasion resistance may be insufficient. On the other hand, when the content of the unit derived from alkyl (meth) acryloyl acrylamide exceeds 50% by mass, the ratio of the interaction domain by the alkyl group becomes large and the image may become slightly brittle. As a result, when stress is applied, it may deform and look like a dent easily.

[0020] The resin is a copolymer containing a carboxylic acid group. The carboxylic acid group can be introduced into the resin by methods such as copolymerization using a carboxylic acid group-containing monomer, copolymerization using an initiator containing a carboxylic acid group, and introduction of a carboxylic acid group by a chemical reaction after copolymerization. Since it is possible to uniformly generate hydrogen bonds with the amide bond portion derived from alkyl (meth) acryloyl acrylamide in the image, it is preferable to introduce a carboxylic acid group into the resin by copolymerization using a carboxylic acid group-containing monomer.

[0021] As the carboxylic acid group-containing monomer, known carboxylic acid group-containing monomers such as (meth) acrylic acid, itaconic acid, and maleic acid can be used. Since it is possible to uniformly distribute the carboxylic acid group in the copolymer (resin), the carboxylic acid group-containing monomer is preferably (meth) acrylic acid.

[0022] The resin is preferably a copolymer further containing a sulfonic acid group. The sulfonic acid group can be introduced into the resin by methods such as copolymerization using a sulfonic acid group-containing monomer and introduction of a sulfonic acid group by a chemical reaction after copolymerization. When a copolymer containing a sulfonic acid group is used, rapid aggregation of the resin is suppressed, a uniform film is easily formed, and the abrasion resistance of the image can be further improved.

[0023] As sulfonic acid group-containing monomers, in addition to sodium p-styrenesulfonate, known sulfonic acid group-containing monomers such as emulsifiers having polymerizable functional groups and sulfonic acid groups, generally referred to as reactive emulsifiers, can be used. In order to control the cohesiveness of the resin, it is desirable that the main chain in the resin and the sulfonic acid groups be appropriately separated. For this reason, it is preferable to use a reactive emulsifier having sulfonic acid groups. Examples of reactive emulsifiers having sulfonic acid groups include Aqualon AR-10, AR-20, KH-05, KH-10, BC-10, BC-20 (all manufactured by Daiichi Kogyo Seiyaku); Antox MS-60, SAD, MS-2N (all manufactured by Nippon Emulsifier); Eleminol JS-20, RS-3000 (all manufactured by Sanyo Chemical); Adekarya Soap SR-10, SR-20 (all manufactured by ADEKA); and others.

[0024] The acid value of the resin is preferably between 10 mg KOH / g and 200 mg KOH / g. If the acid value of the resin is less than 10 mg KOH / g, the portion that forms hydrogen bonds with the amide bonds derived from alkyl (meth)acrylamide decreases, which may result in slightly insufficient image intensity and inadequate improvement of scratch resistance. If the acid value of the resin is greater than 200 mg KOH / g, the hydration amount increases, making drying more difficult, which may result in slightly insufficient film strength and inadequate improvement of scratch resistance. The acid value of the resin can be measured by neutralization titration using a potential difference. The acid value of the resin can be controlled by adjusting the usage ratio of carboxylic acid group-containing monomers used during resin synthesis.

[0025] The glass transition temperature (Tg) of the resin is preferably between 40°C and 120°C. If the glass transition temperature of the resin is below 40°C, the image may deform when stress is applied, making it appear as if it has been indented. On the other hand, if the glass transition temperature of the resin is above 120°C, interaction domains by alkyl groups may not form easily, and the effect of improving abrasion resistance may be insufficient. The glass transition temperature of the resin can be measured by differential scanning calorimetry (DSC) in accordance with JIS K 7121:2012. The glass transition temperature of the resin can be controlled by adjusting the type and usage ratio of copolymer monomers used during resin synthesis.

[0026] 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 density is less than 50 nm, when stress is applied to the image, the pigment may migrate due to the small amount of resin present on the outermost surface of the image, making indentations more easily recognizable. On the other hand, the density 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 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.

[0027] The resin can be obtained by addition polymerization of known unsaturated compounds, such as radical polymerization and ionic polymerization. Because alkyl(meth)acrylamide copolymers are easily obtained, methods such as synthesizing the copolymer by a radical polymerization solution polymerization method followed by phase inversion to an aqueous system, or obtaining an aqueous dispersion of resin particles by a radical polymerization emulsion polymerization method, are preferred.

[0028] (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 a hydrophilic group is bonded to the surface of the pigment particles. Alternatively, a resin-bonded pigment in which an organic group containing resin is chemically bonded to the surface of the pigment particles, or a microcapsule pigment in which the surface of the pigment particles is coated with a resin, can be used. Among these, it is preferable to use a resin-dispersed pigment in which a resin, as a dispersant, is physically adsorbed onto the surface of the pigment particles. As the dispersant, it is preferable to use a resin dispersant having an alkyl group with 2 to 12 carbon atoms.

[0029] Alkyl groups having 2 to 12 carbon atoms in a resin dispersant can be introduced by monomers that constitute the resin used as a dispersant. Examples of monomers having alkyl groups having 2 to 12 carbon atoms include ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate. As a resin dispersant, a copolymer containing units derived from monomers having alkyl groups having 2 to 12 carbon atoms and units derived from other known monomers can be used.

[0030] 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 is greater than 2.5, the amount of pigment in the image will be relatively small, which may cause discoloration in stressed areas to become more noticeable due to the effects of light, making them more easily perceived as dents.

[0031] (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.

[0032] (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.

[0033] 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.

[0034] (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.

[0035] <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.

[0036] <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.

[0037] 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.

[0038] 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]

[0039] 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.

[0040] <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.

[0041] (Glass transition temperature 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 the measurement sample. The glass transition temperature (Tg) of the resin was measured using a differential scanning calorimeter (product name "Q1000", manufactured by TA instruments) in accordance with JIS K 7121:2012.

[0042] (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

[0043] <Preparation of resin> (Resin E1~E29) A mixture was obtained by homogenizing the monomers, emulsifiers, and 150.0 parts of deionized water of the types and amounts (in parts) shown in the upper row of Tables 1-1 and 1-2 using a homogenizer (product name "T50D Ultra-Turrax", manufactured by IKA). 50.0 parts of the mixture was placed in a flask equipped with a stirrer, nitrogen inlet tube, reflux condenser, and thermometer, and heated to 70°C under a nitrogen atmosphere while stirring. The remaining mixture and a liquid obtained by dissolving 1.0 part of potassium persulfate in 20.0 parts of deionized water were added dropwise over 2 hours. After raising the temperature to 80°C, stirring was continued for 2 hours to allow the reaction to proceed and obtain a dispersion containing resin. The pH of the obtained dispersion was adjusted to 8.5 using a 1 mol / L potassium hydroxide aqueous solution, and an appropriate amount of deionized water was added to obtain liquids containing resins E1 to E29, each with a resin (solid content) of 20.0%. The acid value of the resin, the glass transition temperature (Tg), and the cumulative 50% particle size (D) in the volume-based particle size distribution of the resin particles. 50 The following shows the abbreviations in Tables 1-1 and 1-2. • nOAm: Nn-octylacrylamide • nHAm: Nn-hexylacrylamide nBAm:Nn-butylacrylamide nDAm: Nn-dodecylacrylamide • nSAm: Nn-Stearylacrylamide nPAm: Nn-propylacrylamide • tBAm:Nt-butylacrylamide St: Styrene nBMA: n-butyl methacrylate • 2EHMA: 2-ethylhexyl methacrylate • CHMA: Cyclohexyl methacrylate IBOMA: Isobornyl methacrylate AN: Acrylonitrile • MAA: Methacrylic acid • JS-20: Sodium alkylallyl sulfosuccinate, trade name "Eleminol JS-20", manufactured by Sanyo Chemical Industries, Ltd. • KH-10: Ammonium polyoxyethylene-1-(allyloxymethyl)alkyl ether sulfate, trade name "Aqualon KH-10", manufactured by Daiichi Kogyo Seiyaku Co., Ltd. • NS-5S: Emulsifier, product name "Eleminol NS-5S", manufactured by Sanyo Chemical Industries.

[0044] TIFF2026088635000001.tif138170

[0045] TIFF2026088635000002.tif146170

[0046] (Resin R1~R8) 200.0 parts of isopropanol were placed in a flask equipped with a stirrer, nitrogen inlet tube, reflux condenser, and thermometer, and the temperature was raised to 85°C under a nitrogen atmosphere while stirring. Mixtures of monomers and initiators of the types and amounts (in parts) shown in the upper part of Table 2 were added dropwise to the flask over 2 hours while maintaining the internal temperature at 80°C. The mixture was stirred for 4 hours while maintaining the internal temperature at 80°C to obtain resins. After adding 0.9 equivalents of potassium hydroxide and an appropriate amount of deionized water relative to the acid value of the resin, the isopropanol was removed under reduced pressure to obtain liquids containing resins R1 to R8, each with a resin (solid content) of 20.0%. The resins in the obtained liquids were all dissolved and did not form resin particles. The acid value and glass transition temperature (Tg) of the resins are shown in the lower part of Table 2. The meaning of the abbreviations in Table 2 is shown below. • MMA: Methyl methacrylate nBMA: n-butyl methacrylate • EA: Ethyl acrylate nBA: n-butyl acrylate LA: Lauryl acrylate • SA: Stearyl acrylate AA: Acrylic acid • V-59: 2,2'-Azobis(2-methylbutyronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries)

[0047] TIFF2026088635000003.tif120170

[0048] <Preparation of Pigment Dispersion> (Pigment dispersions D1~D6) A batch-type vertical sand mill (manufactured by AIMEX) filled with 200 zirconia beads with a diameter of 0.3 mm was filled with 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, and dispersed for 3 hours. 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 D1 to D6 with a pigment content of 10.0%. The meaning of 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", Made by Clariant

[0049] TIFF2026088635000004.tif55170

[0050] (Pigment dispersion D7) 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 D7, 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-dispersing pigment in the obtained pigment dispersion D7 was 10.0%.

[0051] <Ink preparation> (Examples 1-42, Comparative Examples 1-4) 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. • Resin-containing liquid: 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%

[0052] (Comparative Example 5) The resin was prepared in accordance with the description in "Manufacturing Example No. 4" of Japanese Patent Publication No. 2007-45888. The ink was prepared in the same manner as in Example 1, except that the prepared resin was used instead of resin E1.

[0053] (Comparative Example 6) The resin was prepared in accordance with the description in "Manufacturing Example No. 6" of Japanese Patent Publication No. 2007-45888. The ink was prepared in the same manner as in Example 1, except that the prepared resin was used instead of resin E1.

[0054] <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.

[0055] (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.

[0056] (Dent resistance) Using the inkjet recording device described above, a 200mm x 200mm solid image (100% recording duty cycle) was recorded on glossy paper (product name "PR-101", manufactured by Canon). After leaving the recorded solid image for one day, a robustness test was performed using a 5mm acrylic sphere, a load of 500g, and a tensile speed of 10mm / second. The image after the test was visually inspected, and its dent resistance was evaluated according to the evaluation criteria shown below. A: No traces of the acrylic sphere passing through could be seen in the image. B: By holding the image up to the light, we were able to confirm the trace left by the acrylic sphere. C: The image had traces of an acrylic sphere passing through it.

[0057] TIFF2026088635000005.tif188170

[0058] TIFF2026088635000006.tif198170

[0059] 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 copolymer containing a carboxylic acid group, having a unit derived from alkyl(meth)acrylamide. The aqueous ink is characterized in that the alkyl(meth)acrylamide has a linear alkyl group having 4 to 18 carbon atoms. (Configuration 2) The aqueous ink according to Configuration 1, wherein the number of carbon atoms in the linear alkyl group is 8 or less. (Configuration 3) The aqueous ink according to Configuration 1 or 2, wherein the alkyl(meth)acrylamide is n-octylacrylamide. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the content (mass%) of the units derived from the alkyl(meth)acrylamide in the resin is 5% by mass or more and 50% by mass or less, based on the total mass of the resin. (Configuration 5) An aqueous ink according to any one of Configurations 1 to 4, wherein the acid value of the resin is 10 mg KOH / g or more and 200 mg KOH / g or less. (Configuration 6) The aqueous ink according to any one of Configurations 1 to 5, wherein the glass transition temperature of the resin is 40°C or more and 120°C or less. (Configuration 7) 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 6, wherein the wavelength is 50 nm or more and 250 nm or less. (Configuration 8) The aqueous ink according to any one of Configurations 1 to 7, wherein the resin further comprises a sulfonic acid group. (Configuration 9) The aqueous ink according to any one of Configurations 1 to 8, wherein the pigment is dispersed in a resin dispersant having an alkyl group with 2 to 12 carbon atoms. (Configuration 10) An aqueous ink according to any one of Configurations 1 to 9, 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 11) An aqueous ink according to any one of Configurations 1 to 10, 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%). (Configuration 12) 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 the items 1 to 11. (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 11 of the configuration.

Claims

1. A water-based ink for inkjet use containing pigments and resins, The resin is a copolymer containing a carboxylic acid group, having a unit derived from alkyl(meth)acrylamide. The aqueous ink is characterized in that the alkyl (meth)acrylamide has a linear alkyl group having 4 to 18 carbon atoms.

2. The aqueous ink according to claim 1, wherein the number of carbon atoms in the linear alkyl group is 8 or less.

3. The aqueous ink according to claim 1, wherein the alkyl (meth)acrylamide is n-octylacrylamide.

4. The aqueous ink according to claim 1, wherein the content (by mass) of the units derived from the alkyl (meth)acrylamide in the resin is 5% by mass or more and 50% by mass or less, based on the total mass of the resin.

5. The aqueous ink according to claim 1, wherein the acid value of the resin is 10 mg KOH / g or more and 200 mg KOH / g or less.

6. The aqueous ink according to claim 1, wherein the glass transition temperature of the resin is 40°C or higher and 120°C or lower.

7. 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.

8. The aqueous ink according to claim 1, wherein the resin further comprises sulfonic acid groups.

9. The aqueous ink according to claim 1, wherein the pigment is dispersed in a resin dispersant having an alkyl group with 2 to 12 carbon atoms.

10. 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.

11. 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%).

12. 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 11.

13. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, An inkjet recording method characterized in that the ink is the aqueous ink described in any one of claims 1 to 11.

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