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

Abstract

This invention provides an inkjet-compatible water-based ink capable of recording images with good storage stability and good scratch resistance. [Solution] This is an aqueous inkjet ink containing resin particles. The resin particles are formed from a first resin and a second resin. The first resin is a polyolefin resin having a melting point of 60°C to 130°C. The second resin is a copolymer having units derived from α-olefins with 4 or more carbon atoms and units derived from unsaturated dibasic acids.

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 devices have been increasingly used in commercial and office printing fields. In these fields, there is a demand for water-based inks that offer excellent scratch resistance to the resulting images.

[0003] For example, Patent Document 1 proposes an aqueous ink containing a polyolefin resin dispersion to improve the scratch resistance of images. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-255089 [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, it was found that it is difficult to record images at the high level of scratch resistance required in recent years while maintaining the storage stability of the ink. Scratch resistance refers to the property that the recorded image is less likely to be scratched or peel off when stress is applied to it. Furthermore, storage stability of the ink refers to the property that the ink's physical properties do not change easily under the usage environment and logistics environment of the ink.

[0006] Therefore, an object of the present invention is to provide an aqueous inkjet ink that can record images with excellent scratch resistance while maintaining the storage stability of the ink. Another object of the present invention is to provide an ink cartridge and an inkjet recording method using this aqueous ink. [Means for solving the problem]

[0007] In other words, the present invention provides an aqueous ink for inkjet use containing resin particles, wherein the resin particles are formed of a first resin and a second resin, the first resin being a polyolefin resin having a melting point of 60°C to 130°C, and the second resin being a copolymer having units derived from α-olefins with 4 or more carbon atoms and units derived from unsaturated dibasic acids. [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 while maintaining the storage stability of the ink. 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] Hereinafter, the present invention will be described in further detail with reference to preferred embodiments. In the present invention, when the compound is in the form of a salt, the salt exists dissociated into ions in the ink, but for convenience, it is expressed as "containing a salt". In addition, aqueous ink for inkjet may be simply referred to as "ink". Unless otherwise specified, physical property values are values at normal temperature (25°C), normal pressure (1 atmosphere = 101,325 Pa), and normal humidity (50% relative humidity). In addition, regarding resins, the term "unit" means a unit structure corresponding to one monomer, unless otherwise specified. When the expressions "(meth)acrylic acid" and "(meth)acrylate" are used, they represent "acrylic acid and methacrylic acid" and "acrylate and methacrylate", respectively.

[0011] The present inventors have studied resin-containing inks in order to improve the scratch resistance of images while maintaining the storage stability of the ink. In order to improve the scratch resistance of an image, it is useful to cover the surface of the image with a component having low surface energy when stress is applied to the image. This is because it can suppress direct application of stress to the image and deformation thereof. It has been found that a polyolefin resin having a melting point of 60°C or higher and 130°C or lower is useful as a material providing such an effect. When the polyolefin resin is present on the surface of an image, the polyolefin resin deforms when stress is applied to the image and covers the surface of the image, thereby suppressing deformation of the image itself.

[0012] In the case of a polyolefin resin having a melting point of less than 60°C, if the polyolefin resin is contained in the ink in a dispersed state described later, the polyolefin resin will be in a molten state or a state close to molten under the storage environment of the ink. As a result, precipitates are formed in the ink, and favorable storage stability cannot be obtained. On the other hand, in the case of a polyolefin resin having a melting point of more than 130°C, when stress is applied to an image, the polyolefin resin itself cannot deform, and force is directly applied to the image, causing the image to deform, resulting in failure to obtain favorable scratch resistance.

[0013] However, polyolefin resins having a melting point of 60°C or higher and 130°C or lower have no affinity for water or have low affinity for water, and thus cannot be used alone in an ink. The present inventors have found that when a polyolefin resin having a melting point within the above range is used as a first resin, resin particles are formed using the first resin together with another second resin, and the resin particles are contained in an ink, an image excellent in scratch resistance can be obtained while maintaining the storage stability of the ink. As the second resin, a copolymer having units respectively derived from an α-olefin having 4 or more carbon atoms and an unsaturated dibasic acid is used. If the α-olefin has less than 4 carbon atoms, when forming resin particles together with the polyolefin resin having a melting point within the above range, no interaction occurs between the resins, precipitates are generated in the ink, and good storage stability cannot be obtained.

[0014] As described above, as the first resin, a polyolefin resin having a melting point of 60°C or higher and 130°C or lower is used. Further, as the second resin, a copolymer having a unit derived from an α-olefin having 4 or more carbon atoms and a unit derived from an unsaturated dibasic acid is used. By using an aqueous inkjet ink containing resin particles formed of this specific first resin and second resin, it is possible to record an image excellent in scratch resistance while maintaining the storage stability of the ink.

[0015] <Aqueous Ink> The ink of the present invention is an aqueous inkjet ink containing resin particles. The resin particles are formed of a first resin and a second resin. The first resin is a polyolefin resin having a melting point of 60°C or higher and 130°C or lower. The second resin is a copolymer having a unit derived from an α-olefin having 4 or more carbon atoms and a unit derived from an unsaturated dibasic acid. Hereinafter, the components constituting the ink of the present invention and the physical properties of the ink will be described in detail.

[0016] (First Resin) The ink contains a polyolefin resin (in this disclosure, it may be simply referred to as "first resin" or "polyolefin resin") as the first resin, having a melting point of 60°C or more and 130°C or less. The first resin, together with the second resin, forms resin particles. The resin particles may use one type of the first resin, i.e., a polyolefin resin with a melting point of 60°C or more and 130°C or less, alone, or two or more types may be used in combination.

[0017] Polyolefin resins are compounds formed by the polymerization of unsaturated hydrocarbons (olefins) such as ethylene, propylene, and butadiene. As long as the chemical structure is that of a polyolefin resin, the raw materials do not need to be olefins. For example, paraffin wax and microcrystalline wax, which are extracts from petroleum waxes, and synthetic waxes such as Fischer-Tropsch wax, which is made from natural gas, are also included in the polyolefin resins of this disclosure.

[0018] Polyethylene is preferred as the polyolefin resin because its melting point can be controlled. That is, the first resin preferably contains polyethylene, and more preferably is polyethylene. Commercially available polyolefin resins may be used as the polyolefin resin. Examples of commercially available polyolefin resins, listed by their trade names or series names, include "Novatec LL", "Novatec LD", "Kernel", and "Harmolex" (all manufactured by Nippon Polyethylene); "Petrocene", "Nipolon-L", and "Nipolon-Z" (all manufactured by Tosoh); "Hiwax", and "Excellex" (both manufactured by Mitsui Chemicals); and "Praffin Wax", "Hi-Mic", "FT115", "FNP-0115", "SX105", "FT-0165", and "FT-0070" (all manufactured by Nippon Seiro).

[0019] [Physical properties of the first resin] [Melting point of the first resin] The first resin has a melting point between 60°C and 130°C, preferably between 90°C and 120°C. If the melting point of the polyolefin resin is below 60°C, the polyolefin resin will be in a molten or near-molten state under the ink's storage conditions, resulting in precipitates in the ink and preventing good storage stability. On the other hand, if the melting point of the polyolefin resin is above 130°C, when stress is applied to the image, the polyolefin resin itself cannot deform, and the force is applied directly to the image, causing deformation and preventing good scratch resistance. Polyolefin resins having a melting point between 60°C and 130°C can be obtained by polyolefin polymerization using a Ziegler catalyst or a metallocene catalyst. The melting point can be adjusted depending on the type of catalyst and molecular weight used. The melting point of the resin refers to the melting peak temperature (temperature of the endothermic peak due to melting) measured by differential scanning calorimetry (DSC) in accordance with JIS K 7121. In this disclosure, a melting peak is determined to exist if the amount of endothermic heat obtained from the integral value of the peak is 20 J / g or more.

[0020] As mentioned above, since polyethylene is preferred as the primary resin, the polyolefin resin is more preferably made of polyethylene having a melting point of 90°C to 120°C, and is particularly preferably polyethylene having a melting point of 90°C to 120°C.

[0021] (Second resin) The ink contains a copolymer (sometimes simply referred to as "second resin" in this disclosure) as a second resin, which has units derived from α-olefins having 4 or more carbon atoms and units derived from unsaturated dibasic acids. The second resin forms resin particles together with the first resin. The resin particles may use one of the second resins, i.e., copolymers having units derived from α-olefins having 4 or more carbon atoms and units derived from unsaturated dibasic acids, alone, or two or more may be used in combination. It is preferable that the second resin does not interfere with the effect of the first resin in reducing the surface energy of the image surface. General-purpose resins such as acrylic resins and styrene-acrylic resins increase the surface energy of the image surface. In contrast, copolymers having units derived from α-olefins having 4 or more carbon atoms and unsaturated dibasic acids do not interfere with the above effect of the first resin, and are therefore used as a second resin to form resin particles together with the first resin. The second resin can be synthesized, for example, by a method similar to the "Method for producing α-olefin-maleic anhydride copolymer" disclosed in Japanese Patent Application Publication No. 1-79207.

[0022] [α-olefin] As the α-olefin, any α-olefin having 4 or more carbon atoms can be used. If the α-olefin has fewer than 4 carbon atoms, the interaction with the first resin will be insufficient, leading to separation within the resin particles or precipitation from the resin particles, and thus the stability cannot be maintained. One type of α-olefin having 4 or more carbon atoms may be used alone in the second resin (polymer), or two or more types may be used in combination. That is, the second resin (polymer) may have units derived from one type of α-olefin having 4 or more carbon atoms, or it may have units derived from each of two or more types of α-olefins.

[0023] Examples of α-olefins having 4 or more carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 1-docosene, 1-tetracosene, 1-hexacosene, 1-octacosene, 1-triacontene, 1-dotriacontene, 1-tetratriacontene, 1-hexatriacontene, 1-octatricontene, and 1-tetracontene, as well as mixtures of two or more of these.

[0024] The carbon number of the α-olefin is preferably 40 or less, and more preferably 10 to 30. When the carbon number of the α-olefin is 10 or more, it interacts more easily with the primary resin, making separation within the resin particles and precipitation from the resin particles less likely, and thus further improving the storage stability of the ink. On the other hand, when the carbon number of the α-olefin is 30 or less, steric hindrance within the molecule of the secondary resin is less likely to occur, making it easier for acid groups derived from unsaturated dibasic acids to appear on the surface of the resin particles, thus improving the dispersion stability of the resin particles and further improving the storage stability of the ink.

[0025] [Unsaturated dibasic acid] As the unsaturated dibasic acid, known unsaturated dibasic acids can be used. Examples include maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, methylene succinic acid, allyl malonic acid, isopropylidene succinic acid, 2,4-hexadiene dioic acid, and acetylenedicarboxylic acid. One or more of these can be used. Among these, at least one unsaturated dibasic acid selected from the group consisting of maleic acid, fumaric acid, and itaconic acid is preferred.

[0026] As the unsaturated dibasic acid, maleic acid is even more preferred because its high proportion of acid groups in the unit and the arrangement of acid groups when copolymerized with α-olefin enhance the stability of the resin particles. In other words, the unsaturated dibasic acid in the unit derived from the unsaturated dibasic acid constituting the second resin (polymer) is even more preferably maleic acid, and particularly preferably maleic acid.

[0027] [Physical properties of the second resin] [Acid value of the second resin] The acid value of the second resin is preferably 30 mg KOH / g or more and 250 mg KOH / g or less, and more preferably 30 mg KOH / g or more and 150 mg KOH / g or less. When the acid value of the second resin is 30 mg KOH / g or more, the affinity of the second resin itself to the aqueous medium in the aqueous ink tends to increase, resulting in good stability as resin particles and further improving the storage stability of the ink. On the other hand, when the acid value of the second resin is 250 mg KOH / g or less, the hydrophilicity of the second resin is moderately suppressed, making it easier to interact with the first resin, resulting in good stability as resin particles and further improving the storage stability of the ink. When the acid value of the second resin is 150 mg KOH / g or less, the storage stability of the ink is further improved. The acid value of the second resin can be adjusted by the proportion of units derived from unsaturated dibasic acids in the second resin. The acid value of the second resin can be measured by neutralization titration using a potassium hydroxide-ethanol solution as the titration reagent.

[0028] (Resin particles) The ink contains resin particles formed from a first resin and a second resin. The resin particles are dispersed in the ink, i.e., they exist in the ink in the form of a resin emulsion. Preferably, the resin particles are dispersed by the action of carboxylic acid groups on the resin particles themselves (self-dispersing type), rather than being dispersed by components such as surfactants or resins (emulsified type). Preferably, it is a so-called soap-free type resin emulsion. The resin particles do not need to contain colorants. The total proportion (mass%) of the first resin and the second resin in the resin forming the resin particles is preferably 50.0% by mass or more, and more preferably 100.0% by mass, based on the total mass of the resin. In other words, it is preferable that the resin particles are substantially formed only from the first resin and the second resin.

[0029] The resin particle content (mass%) in the water-based ink is preferably 1.0% by mass or more and 10.0% by mass or less, and more preferably 3.0% by mass or more and 8.0% by mass or less, based on the total mass of the ink.

[0030] In this disclosure, "resin particles" means resin that exists in an insoluble state in the aqueous medium constituting the ink. More specifically, it means resin that can exist in the aqueous medium in a state in which particles whose particle size can be measured by dynamic light scattering are formed. On the other hand, "water-soluble resin" means resin that exists in a dissolved state in the aqueous medium constituting the ink. More specifically, it means resin that can exist in the aqueous medium in a state in which particles whose particle size can not be measured by dynamic light scattering are not formed. If resin particles are expressed in contrast to "water-soluble resin," they would be called "water-dispersible resin (water-insoluble resin)."

[0031] 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: 3, 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.

[0032] [Physical properties of resin particles] [Particle size of resin particles] The cumulative 50% particle size (D) of the volume-based particle size distribution, which indicates the particle size of resin particles. 50a ) is preferably between 100 nm and 300 nm. 50a If the wavelength is 100 nm or more, the surface area per unit mass of the resin particles becomes relatively smaller, and the probability of contact between particles decreases, which suppresses aggregation of resin particles and further improves the storage stability of the ink. On the other hand, D 50a If the wavelength is 300 nm or less, the unevenness caused by resin particles in the image after recording the image with ink is suppressed, making it less likely for localized forces to occur when stress is applied to the image. Therefore, even if cracks or other damage do not occur in the image itself, it is less likely for blemishes to remain in the image, and it is less likely for the image to have the same appearance as when an image with poor scratch resistance is subjected to a scratch resistance evaluation test. D 50a This can be adjusted by the resin particle manufacturing method described later. 50aThis can be measured by dynamic light scattering under the same conditions as the method described above for determining whether or not a particle is a resin particle.

[0033] [Amount of surface acid groups in resin particles] The surface acid group content (μmol / g) of the resin particles is preferably between 200 μmol / g and 500 μmol / g. "Surface acid group content (μmol / g) of resin particles" is expressed as the amount (μmol) of acid groups, such as carboxylic acid groups, present on the surface of the resin particles per unit mass (g) of the resin particles. Therefore, in a state where all acid groups on the surface of the resin particles have dissociated, the surface acid group content of the resin particles can also be expressed as the amount of anionic groups on the surface of the resin particles.

[0034] When the surface acidity of resin particles is 200 μmol / g or more, the affinity of the resin particles to the aqueous medium in the aqueous ink increases, making aggregation between resin particles less likely and further improving the storage stability of the ink. On the other hand, when the surface acidity of resin particles is 500 μmol / g or less, the affinity of the resin particles to water is moderately suppressed, making it easier to dry after image recording. Therefore, when stress is applied to the image, it is easier to avoid scratches that may occur due to insufficient drying, and the scratch resistance of the image is further improved. The surface acidity of resin particles can be adjusted by the ratio of secondary resin in the resin particles, the acid value of the secondary resin, the particle size, and the manufacturing method of the resin particles. The surface acidity of resin particles (μmol / g) can be measured by colloidal titration using a potential difference at pH 12 or higher, using a methyl glycol chitosan solution as the titration reagent.

[0035] [Mass ratio of the first resin to the second resin] The resin particles are formed from a first resin and a second resin. Preferably, the content (mass%) of the first resin in the resin particles is 0.2 to 5.1 times the mass ratio of the content (mass%) of the second resin. When the mass ratio of the first resin to the second resin is 0.2 times or more, the proportion of the first resin that contributes to imparting abrasion resistance becomes sufficient, and abrasion resistance tends to be further enhanced. On the other hand, when the mass ratio of the first resin to the second resin is 5.1 times or less, the proportion of the second resin that imparts acid groups to the resin particles is sufficient, which tends to increase the affinity of the resin particles to the aqueous medium in the ink, and thus tends to further enhance the storage stability of the ink.

[0036] [Compositional analysis of the first and second resins] The composition of the primary and secondary resins constituting the resin particles can be analyzed by the following method. The liquid containing the resin particles is dried to obtain a solid resin, which is then dissolved in a soluble organic solvent. The primary and secondary resins are separated by preparative gel permeation chromatography (GPC). Next, the degree of branching is evaluated using GPC with a multi-angle light scattering detector (MALS) to confirm the presence of olefin chains in the secondary resin in a grafted manner. Furthermore, the types and proportions of the units (monomers) constituting the resin can be determined by nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS), and pyrolysis gas chromatography-mass spectrometry (Py-GC / MS).

[0037] [Method for manufacturing resin particles] The method for producing resin particles is not limited as long as it can produce the resin particles described above. For example, forced emulsification and phase inversion emulsification methods can be used. A forced emulsification method may involve adding the resin to an aqueous liquid medium after it has been dissolved or molten, and then dispersing the resin. A phase inversion emulsification method may involve adding an aqueous liquid medium to a solution obtained by dissolving the resin in an organic solvent, and precipitating the resin in the form of particles during the phase inversion process from a solvent system to an aqueous system. In either method, it is preferable to adjust the particle size obtained by dispersing the resin in an aqueous liquid medium, then performing a dispersion treatment using a dispersion device such as a high-pressure homogenizer, and then particleizing the particles while applying appropriate shear.

[0038] (Pigment) The ink may contain a colorant. Pigments and dyes can be used as colorants. In particular, it is preferable that the ink contains a pigment. The pigment content (mass%) in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0039] Specific examples of pigments include inorganic pigments and organic pigments. Examples of inorganic pigments include carbon black and titanium dioxide. Examples of organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, imidazolon pigments, diketopyrrolopyrrole pigments, dioxazine pigments, and perinone pigments. Pigments may be used individually or in combination of two or more.

[0040] The pigment is preferably used in the form of a pigment dispersion obtained by dispersing the pigment in ink through some treatment. As a dispersion method for the pigment, a resin-dispersed pigment using a resin (resin dispersant) as a dispersant, a self-dispersing pigment having a hydrophilic group bonded to the particle surface of the pigment, and the like can be used. Furthermore, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, a microcapsule pigment in which the surface of pigment particles is coated with a resin or the like, and the like can be used. It is also possible to use a combination of pigments with different dispersion methods among these. Among these, resin-dispersed pigments obtained by physically adsorbing a resin as a dispersant onto the pigment particle surface, and self-dispersing pigments in which an anionic group is bonded to the pigment particle surface directly or via another atomic group are preferred.

[0041] [Mass ratio of resin to pigment] The content (% by mass) of the resin (resin dispersant) in the ink, as a mass ratio relative to the content (% by mass) of the pigment, is preferably 0.2 times or more and 2.5 times or less. When the mass ratio of the resin content to the pigment content is 0.2 times or more, the resin component occupying the film for forming an image becomes a relatively sufficient amount, so that the scratch resistance of the image is more likely to be further improved. On the other hand, when the mass ratio of the resin content to the pigment content is 2.5 times or less, the total solid content in the ink can be suppressed to an appropriate amount, thereby reducing the collision probability of the pigment and resin particles, so that the storage stability of the ink is more likely to be further improved.

[0042] [Particle diameter of pigment dispersion] The cumulative 50% particle diameter (D 50b ) of the volume-based particle size distribution of the pigment is preferably 50 nm or more and 200 nm or less. When D 50b is 50 nm or more, the surface area per unit mass of the pigment becomes relatively small, and the contact probability between particles decreases, whereby aggregation of the pigment is suppressed, and the storage stability of the ink is more likely to be further improved. On the other hand, when D 50b is 200 nm or less, unevenness derived from the pigment in the image is suppressed after an image is recorded with the ink, so that direct stress is less likely to be applied to the pigment when stress is applied to the image, and thus the scratch resistance of the image is more likely to be further improved. D 50bThis can be adjusted by the type of pigment and the method of dispersing the pigment. 50b This can be measured by dynamic light scattering under the same conditions as the method described above for determining whether or not a particle is a resin particle.

[0043] [Difference in particle size between pigment and resin particles] Furthermore, the cumulative 50% particle size (D) of the volume-based particle size distribution of the pigment. 50b ) is the cumulative 50% particle size (D) of the volume-based particle size distribution of resin particles. 50a It is preferable that the particle size of the pigment (D) is less than or equal to ). 50b ) is the particle size (D) of the resin particles 50a If the particle size distribution of the resin particles is below this value, the probability of resin particles appearing on the outermost surface of the image rather than pigment increases, and when stress is applied to the image, the pigment is less likely to be directly subjected to stress, thus further increasing the scratch resistance of the image. From this perspective, the cumulative 50% particle size (D) of the volume-based particle size distribution of resin particles is important. 50a ) cumulative 50% particle size (D) of pigment volume-based particle size distribution 50b The value obtained by subtracting (D 50a -D 50b ) is preferably between 0 nm and 250 nm. 50a -D 50b It is more preferably 1 nm to 240 nm, and even more preferably 5 nm to 230 nm.

[0044] (aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain an aqueous medium which is water, or a mixed solvent of water and a water-soluble organic solvent. It is preferable to use deionized water (ion-exchanged water) 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, and more preferably 50.0% by mass or more and 90.0% by mass or less, based on the total mass of the ink.

[0045] As the water-soluble organic solvent, any of those usable in inkjet inks, such as alcohols, glycols, (poly)alkylene glycols, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 1.0% by mass or more and 46.0% by mass or less, and more preferably 3.0% by mass or more and 40.0% by mass or less, based on the total mass of the ink.

[0046] (Other ingredients) In addition to the components described above, the ink may also contain, as necessary, water-soluble organic compounds that are solid at 25°C, such as polyhydric alcohols like trimethylolethane and trimethylolpropane, and urea derivatives like urea and ethyleneurea. Furthermore, the ink may contain, as necessary, various additives such as surfactants, pH adjusters, defoamers, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, and chelating agents. When surfactants are used, the surfactant content (mass%) in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 2.0% by mass or less, based on the total mass of the ink.

[0047] In addition to the aforementioned resin particles (first resin and second resin) and dispersant, the ink may further contain other resins. These other resins may include resin dispersants for dispersing pigments. It is preferable to use a water-soluble resin as the other resin. Examples of water-soluble resins include block copolymers, random copolymers, graft copolymers, and combinations thereof. Examples of water-soluble resins include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred.

[0048] (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 even more 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 even more preferably 30 mN / m to 50 mN / m. The pH of the ink at 25°C is preferably 5.0 to 10.0, and even more preferably 7.0 to 9.5.

[0049] <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.

[0050] <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.

[0051] 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.

[0052] Any recording medium can be used as the recording medium to be recorded using the ink of the present invention. Recording media with ink absorption properties can be used, such as recording media without a coating layer, such as plain paper, and recording media with a coating layer, such as glossy paper or matte paper. In addition, recording media with low ink absorption or no ink absorption properties, such as printing paper, coated paper, resin sheets, and resin films, can be used. The ink of the present invention can be suitably used for applications in which images are recorded by directly applying ink to such recording media. [Examples]

[0053] 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.

[0054] <Method for measuring physical properties> (Melting point of resin) Solid or powdered resin was prepared as a sample for measurement, and the melting peak temperature measured using a differential scanning calorimeter (product name "Q1000", manufactured by TA instruments) in accordance with JIS K 7121 was defined as the "melting point". A melting peak was determined to have been obtained when the endothermic amount obtained from the integral value of the peak was 20 J / g or more, and this melting peak temperature was defined as the "melting point".

[0055] (Acid value of resin) Resin particles were precipitated using a 1.0 mol / L hydrochloric acid aqueous solution, thoroughly washed with water, and then dried at 60°C. The resulting dried material 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.

[0056] (Determination of whether the sample is a particle or not, particle size) For the resin particle dispersion and pigment dispersion described later, resin particles or pigment were used as samples, and the liquid containing the samples was diluted with pure water to obtain measurement samples with a sample content of approximately 1.0%. Then, using a particle size analyzer, the cumulative 50% particle size (D) of the volume-based particle size distribution of the particles (resin particles or pigment) in the measurement samples was determined. 50The 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 using the above method, 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: 3 Measurement time: 120 seconds Shape: true spherical Refractive index: 1.5 Density: 1.0

[0057] (Amount of surface acid groups in resin particles) A liquid containing resin particles, adjusted to pH 12, was used as the sample, and the amount of acidic groups on the surface of the resin particles (the amount of carboxylic acid groups on the surface of the resin particles) was measured by colloidal titration using potentiometry. For colloidal titration, a potentiometric automatic titrator (product name "AT510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a flow potentiometry titration unit (product name "PCD-500", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) was used. A 0.005 mol / L methyl glycol chitosan solution was used as the titration reagent.

[0058] <First resin P-1~P-8> The resins shown in Table 1 were used as the primary resins. The product names, polyolefin types, and melting points of the primary resins P-1 to P-8 are shown in Table 1.

[0059] TIFF2026148481000001.tif65170

[0060] <Synthesis of secondary resins Q-1 to Q-18> Secondary resins Q-1 to Q-18 were synthesized according to the procedure shown below. Secondary resins Q-1 to Q-18 were obtained by synthesizing them by substituting the olefins and unsaturated acids listed in Table 2, following the copolymerization reaction of α-olefin and maleic anhydride described in Example 1 of Japanese Patent Publication No. 1-79207. Table 2 shows the types and amounts of olefins constituting secondary resins Q-1 to Q-18, the types and amounts of unsaturated acids used, and the acid value of the obtained secondary resins. Of the types of olefins shown in Table 2, all except 2-butene are α-olefins. Also, of the types of unsaturated acids shown in Table 2, all except acrylic acid are unsaturated dibasic acids.

[0061] TIFF2026148481000002.tif130170

[0062] <Preparation of dispersion of resin particles E-1 to E-38> Resin particles E-1 to E-38 were synthesized according to the following procedure. 700 parts of deionized water and the amount of 8 mol / L potassium hydroxide (KOH) aqueous solution shown in Table 3 were added to a pressurized vessel equipped with a stirring device and heated to 120°C. The first and second resins of the types and amounts shown in Table 3 were heated, added to the pressurized vessel in a molten state, and stirred to obtain an emulsion. The obtained emulsion was passed 10 times through a high-pressure homogenizer (product name "NanoVeta", manufactured by Yoshida Machinery Industry Co., Ltd.) heated to 120°C with the heating option. An appropriate amount of deionized water was added to obtain a dispersion of resin particles E-1 to E-38 with a resin (solid content) of 20.0%. In the synthesis of resin particles E-36 and E-37, the dry form of maleic acid-modified polyethylene wax, product name "High Wax 1105A" (manufactured by Mitsui Chemicals, shown as "1105A" in Table 3), was used as the second resin. Furthermore, in the synthesis of resin particles E-38, the "water-insoluble polymer (iii)" described in Japanese Patent Publication No. 2023-6772 (indicated as "(iii)" in Table 3), synthesized according to the method described in said publication, was used as the second resin. This "water-insoluble polymer (iii)" is a styrene-acrylic acid-ethyl acrylate copolymer. The "first resin / second resin [times]" shown in Table 3 is the mass ratio of the content of the first resin (%) to the content of the second resin (%) in the resin particles. Also, Table 3 shows the cumulative 50% particle size (D) of the volume-based particle size distribution of the obtained resin particles. 50a The dimensions (nm) and surface acid group content (μmol / g) are shown.

[0063] TIFF2026148481000003.tif245170

[0064] <Preparation of Pigment Dispersions D-1 to D-3> A batch-type vertical sand mill (manufactured by AIMEX) filled with 200 zirconia beads with a diameter of 0.3 mm was used to disperse a mixture of 10.0 parts of the pigments shown in Table 4, 20.0 parts of a resin-containing liquid, and 70.0 parts of deionized water for a predetermined time. The abbreviations for the pigments shown in Table 4 are as follows: "NIPex90" is the trade name for carbon black manufactured by Orion Engineered Carbons, "PB15:3" is CI Pigment Blue 15:3, and "PR122" is CI Pigment Red 122. As the resin-containing liquid, an aqueous solution with a resin content of 30.0% was used, obtained by dissolving a water-soluble resin in water containing potassium hydroxide equimolar to its acid value. The water-soluble resin used was a styrene-ethyl acrylate-acrylic acid copolymer with an acid value of 167 mgKOH / g and a weight-average molecular weight of 10,000. Subsequently, coarse particles were removed by centrifugation, and the mixture was pressure filtered through a 3.0 μm pore size microfilter (manufactured by Fujifilm). An appropriate amount of deionized water was added to adjust the pigment content, yielding pigment dispersions D-1 to D-3 with a pigment content of 10.0%. The cumulative 50% particle size (D) of the volume-based particle size distribution of the pigment in the obtained pigment dispersions was then measured. 50b Table 4 shows the values ​​(nm).

[0065] <Preparation of Pigment Dispersion D-4> A solution of 5.0 g concentrated hydrochloric acid dissolved in 5.5 g water was cooled to 5°C, and 1.6 g of 4-aminophthalic acid was added to it. The container of this solution was placed in an ice bath and stirred to maintain the solution temperature below 10°C, while 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. Stirring continued 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 D-4 containing a self-dispersing pigment in which two -C6H3-(COOK) groups were bonded to the surface of the carbon black particles. The self-dispersing pigment content in pigment dispersion D-4 was 10.0%. The type of pigment used in the preparation of pigment dispersion D-4 and the cumulative 50% particle size (D) of the volume-based particle size distribution of the pigment in the obtained pigment dispersion D-4 were determined. 50b Table 4 shows the values ​​(nm).

[0066] TIFF2026148481000004.tif45170

[0067] <Ink preparation> (Examples 1-41, Comparative Examples 1-8) 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 the trade name of a nonionic surfactant (manufactured by Kawaken Fine Chemicals). The types of pigment dispersions and resin particles used in the ink, as well as the respective content (%) of pigments and resin particles in the ink, are shown in Table 5 (Tables 5-1 and 5-2). Table 5 shows the particle size (D) of the resin particles. 50a Particle size of pigment (D nm) 50b The values ​​(nm) are also shown. • Pigment dispersion: Amount corresponding to the pigment content (%) shown in Table 5 • Resin particle dispersion: Amount corresponding to the resin particle content (%) shown in Table 5 Glycerin: 5.0% Triethylene glycol: 10.0% • Acetyleneol E100: 0.1% • Ion-exchanged water: Remaining volume (%) when the total amount of components is 100.0%

[0068] (Comparative Example 9) Resin emulsion B1, manufactured according to the method described in Japanese Patent Publication No. 2012-255089, was used to replace resin particles E-1 in Example 1, and the same evaluation was performed. The image abrasion resistance evaluation, described later, was "B," and the ink storage stability evaluation was "C." The above-mentioned resin emulsion B1 is an emulsion containing polyethylene wax (product name "High Wax 210P," manufactured by Mitsui Chemicals) and maleic acid-modified polyethylene wax (product name "High Wax 1105A," manufactured by Mitsui Chemicals) as resin components.

[0069] (Comparative Example 10) The resin particles E-1 in Example 1 were replaced with the "wax dispersion W7" described in Japanese Patent Publication No. 2023-6772, which was manufactured according to the method described in the said publication, and the same evaluation was performed. The image scratch resistance evaluation, described later, was "C", and the ink storage stability evaluation was "B-". The "wax dispersion W7" is an emulsion containing polyethylene wax (product name "High Wax 110P", manufactured by Mitsui Chemicals) and the "water-insoluble polymer (iii)" as resin components.

[0070] <Rating> In this evaluation, "A" and "B" were considered acceptable levels, and "C" was considered unacceptable levels, based on the evaluation criteria for each item shown below. Furthermore, 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+", and those that were relatively inferior were designated as "B-". The evaluation results are shown in Tables 5-1 and 5-2.

[0071] (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 performing measurements 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, scratches were visible on the image, but the recording medium (underlying material) was not visible. C: The image had scratches, and the recording medium (background) was visible.

[0072] (Storage stability) Each prepared ink was placed in a sealed polytetrafluoroethylene container and stored at 40°C for 3 months. The viscosity η1 (mPa·s) of the ink before storage and the viscosity η2 (mPa·s) of the ink after storage were measured. The viscosity of the ink was measured at 25°C using a rotational viscometer (product name "TV-200E viscometer", manufactured by Toki Sangyo). The rate of change of the ink viscosity (P(%)) was calculated using the formula P = {(η2-η1) / η1} × 100(%), and the storage stability of the ink was evaluated according to the evaluation criteria below. A large value for the rate of change indicates that the dispersion state of the resin particles is unstable, and the ink becomes thicker due to an increase in particle size or aggregation of resin particles, thus indicating low storage stability of the ink. A: The rate of change was less than 5%. B: The rate of change was between 5% and less than 10%. C: The rate of change was 10% or more.

[0073] TIFF2026148481000005.tif168170

[0074] TIFF2026148481000006.tif164170

[0075] Furthermore, the disclosure of this embodiment includes the following configurations and methods. (Configuration 1) An aqueous inkjet ink containing resin particles, The resin particles are formed from a first resin and a second resin, The first resin is a polyolefin resin having a melting point of 60°C or higher and 130°C or lower, An aqueous ink characterized in that the second resin is a copolymer having units derived from α-olefins with 4 or more carbon atoms and units derived from unsaturated dibasic acids. (Configuration 2) The aqueous ink according to Configuration 1, wherein the acid value of the second resin is 30 mg KOH / g or more and 250 mg KOH / g or less. (Configuration 3) The aqueous ink according to Configuration 1 or 2, wherein the number of carbon atoms in the α-olefin is 10 or more and 30 or less. (Configuration 4) The aqueous ink according to any one of Configurations 1 to 3, wherein the unsaturated dibasic acid comprises maleic acid. (Configuration 5) The aqueous ink according to any one of Configurations 1 to 4, wherein the polyolefin resin comprises polyethylene. (Configuration 6) The aqueous ink according to any one of Configurations 1 to 5, wherein the polyolefin resin comprises polyethylene having a melting point of 90°C or more and 120°C or less. (Configuration 7) The aqueous ink according to any one of Configurations 1 to 6, wherein the amount of surface acid groups (μmol / g) of the resin particles is 200 μmol / g or more and 500 μmol / g or less. (Configuration 8) Cumulative 50% particle size (D) of the volume-based particle size distribution of the resin particles 50a A water-based ink according to any one of items 1 to 7, wherein the wavelength is between 100 nm and 300 nm. (Configuration 9) The aqueous ink according to any one of Configurations 1 to 8, wherein the content (mass%) of the first resin in the resin particles is 0.2 times or more and 5.1 times or less by mass ratio to the content (mass%) of the second resin. (Configuration 10) The aqueous ink according to any one of Configurations 1 to 9, wherein the aqueous ink further contains a pigment. (Configuration 11) Cumulative 50% particle size (D) of the volume-based particle size distribution of the pigment 50b ) is the cumulative 50% particle size (D) of the volume-based particle size distribution of the resin particles. 50a ) The water-based ink described in composition 10 below. (Configuration 12) The aqueous ink according to any one of Configurations 1 to 11, wherein the content (mass%) of the resin particles in the aqueous ink is 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. (Configuration 13) 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 12. (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 12.

Claims

1. A water-based inkjet ink containing resin particles, The resin particles are formed from a first resin and a second resin, The first resin is a polyolefin resin having a melting point of 60°C or higher and 130°C or lower, The aqueous ink is characterized in that the second resin is a copolymer having units derived from α-olefins with 4 or more carbon atoms and units derived from unsaturated dibasic acids.

2. The aqueous ink according to claim 1, wherein the acid value of the second resin is 30 mg KOH / g or more and 250 mg KOH / g or less.

3. The aqueous ink according to claim 1, wherein the number of carbon atoms in the α-olefin is 10 or more and 30 or less.

4. The aqueous ink according to claim 1, wherein the unsaturated dibasic acid comprises maleic acid.

5. The aqueous ink according to claim 1, wherein the polyolefin resin comprises polyethylene.

6. The aqueous ink according to claim 1, wherein the polyolefin resin comprises polyethylene having a melting point of 90°C or higher and 120°C or lower.

7. The aqueous ink according to claim 1, wherein the amount of surface acid groups (μmol / g) of the resin particles is 200 μmol / g or more and 500 μmol / g or less.

8. The cumulative 50% particle size (D) of the volume-based particle size distribution of the aforementioned resin particles ５０ａ The aqueous ink according to claim 1, wherein the wavelength is 100 nm or more and 300 nm or less.

9. The aqueous ink according to claim 1, wherein the content (mass%) of the first resin in the resin particles is 0.2 times or more and 5.1 times or less by mass ratio to the content (mass%) of the second resin.

10. The aqueous ink according to claim 1, wherein the aqueous ink further contains a pigment.

11. The cumulative 50% particle size (D) of the volume-based particle size distribution of the aforementioned pigment ５０ｂ ) is the cumulative 50% particle size (D) of the volume-based particle size distribution of the resin particles. ５０ａ The aqueous ink according to claim 10, which is as follows:

12. The aqueous ink according to claim 1, wherein the content (by mass) of the resin particles in the aqueous ink is 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

13. 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 12.

14. 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 12.

Images