JP7438860B2 - Water-based ink, ink cartridge, and inkjet recording method - Google Patents

Description

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

In recent years, advances in technology have made it possible to easily and inexpensively record high-definition, high-gloss images, such as those achieved by silver halide photography and offset printing, using inkjet recording methods. Coloring materials used in inkjet inks include dyes and pigments, and pigments have been widely used in recent years from the viewpoint of image fastness such as gas resistance, light resistance, and water resistance.

When ink containing a pigment as a coloring material (pigment ink) is applied to a recording medium with a glossy surface such as glossy paper, an image is recorded by fixing the pigment on the surface of the recording medium. For this reason, images recorded with pigment inks are susceptible to scratches on the surface or change in glossiness due to rubbing, so it is a challenge to improve so-called scratch resistance. In particular, when recording media such as glossy paper are used for photo printing, graphic art printing, etc., a high level of scratch resistance is required, with almost no change in gloss even if the surface of the image is rubbed. Ru.

In addition, since pigment inks can record images with good fastness, they are also used when creating recorded materials for bulletin boards, and there are opportunities to record images on non-absorbent recording media such as film. is also increasing. Since recorded materials for outdoor bulletin boards are often rubbed with a squeegee or the like when posted, they need to have strong scratch resistance.

In response to these demands, for example, water-based inks have been proposed that contain copolymers obtained by polymerizing specific monomers and can record images with excellent adhesion to films and scratch resistance. (Patent Document 1). In addition, an ink composition has been proposed that uses a specific water-soluble organic solvent to lower the minimum film-forming temperature and is capable of recording images with improved adhesion and scratch resistance to non-absorbent media ( Patent Document 2).

Japanese Patent Application Publication No. 2008-031276 International Publication No. 2018/143957

The present inventors studied the inks proposed in Patent Documents 1 and 2. As a result, it has been found that while the scratch resistance of images recorded on recording media such as glossy paper using these inks is improved, there is a problem in that image clarity is likely to be impaired. Image clarity refers to a property that is an indicator of the sharpness of an image when it is reflected on an image; when image clarity is low, the image appears blurry, and when image clarity is high, the image appears clear.

Therefore, an object of the present invention is to provide an aqueous ink that can record images with excellent scratch resistance and image clarity. Another object of the present invention is to provide an ink cartridge and an inkjet recording method using this aqueous ink.

That is, according to the present invention, there is provided a water-based inkjet ink containing resin particles and a water-soluble organic solvent, wherein the resin particles have a core portion containing a cyano group-containing unit, an aromatic group-containing unit, and an anionic group-containing unit. A water-based ink comprising a group-containing unit and a shell portion containing a unit derived from a crosslinking agent but not containing a cyano group-containing unit, wherein the water-soluble organic solvent contains a cyclic amide. be done.

According to the present invention, it is possible to provide an aqueous ink that can record images with excellent scratch resistance and image clarity. Further, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method using this aqueous ink.

1 is a cross-sectional view schematically showing an embodiment of an ink cartridge of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge.

Hereinafter, the present invention will be further explained in detail by citing preferred embodiments. In the present invention, when a compound is a salt, the salt is dissociated into ions and exists in the ink, but for convenience, it is expressed as "containing a salt." Furthermore, water-based ink for inkjet is sometimes simply referred to as "ink." Physical property values are values at room temperature (25° C.) unless otherwise specified. In the present invention, the "unit" constituting the resin means a repeating unit derived from one monomer.

In the process of studying the scratch resistance of images recorded with ink containing resin particles, the present inventors investigated the combination of the units contained in the resin forming the resin particles and the water-soluble organic solvent contained in the ink. investigated. As a result, it was found that when resin particles formed of a resin containing a cyano group-containing unit are combined with a cyclic amide water-soluble organic solvent, the scratch resistance of recorded images is improved. A more detailed study revealed that in the case of the above combination, even in cases where the glass transition temperature of the resin particles exceeds 100°C, which would normally require heating to form a film, it is possible to form a film at room temperature. was found to be progressing in a specific manner.

Cyclic amides such as cyclic amide-based water-soluble organic solvents are known to be components that function as film-forming aids. However, when a cyclic amide was combined with resin particles made of a resin that does not contain a cyano group-containing unit, the above phenomenon of improving the scratch resistance of images was not observed. Similarly, when a glycol ether-based water-soluble organic solvent, which is known to function as a film-forming aid, is combined with resin particles made of a resin containing a cyano group-containing unit, the above-mentioned A phenomenon in which the scratch resistance of the image was improved was not observed. The reason why the above-mentioned specific phenomenon occurs only when resin particles made of a resin containing a cyano group-containing unit are combined with a cyclic amide-based water-soluble organic solvent is due to the following reasons. It is assumed that That is, it is thought that the strong interaction between the highly polar cyano group and the similarly highly polar amide group promoted the movement of the resin chains and improved the scratch resistance of the image.

However, when an ink containing resin particles formed from a resin containing a cyano group-containing unit and a cyclic amide is applied to a recording medium such as glossy paper, the image clarity of the recorded image is insufficient. There was found. A detailed study revealed that in the case of the above-mentioned ink in which the resin particles specifically form a film at room temperature, the rapid film formation partially suppresses the penetration of water-soluble organic solvents and water in the ink. A phenomenon such as so-called beading, in which the image is overflowing and unevenness occurs, is likely to occur. As a result, it was found that unevenness was likely to be formed on the image surface, resulting in a decrease in image clarity. Such a phenomenon is not observed when an image is recorded on a non-absorbent recording medium.

As a result of further investigation, it was found that by using resin particles having a core-shell structure containing a cyano group-containing unit only in the core portion, it was possible to record an image with good image clarity while increasing scratch resistance. The shell portion covers the resin particles to prevent the cyano group-containing units, which are the main cause of rapid film formation, from being exposed on the surface of the resin particles. This makes it possible to delay the formation of a film, and it is thought that the formation of a film can proceed while ensuring time for the water-soluble organic solvent and water in the ink to permeate into the recording medium.

The shell portion disposed to cover the core portion includes an anionic group-containing unit that is a hydrophilic unit in order to maintain stable dispersion of the resin particles and thereby ensure ink ejection characteristics. However, if the shell portion contains an anionic group-containing unit, the hydrophilicity of the resin forming the resin particles increases, so that the core portion is likely to be insufficiently covered by the shell portion. For this reason, it was found that the cyano group-containing unit in the core portion is likely to be exposed on the surface of the resin particle, and the effect of improving image clarity becomes insufficient.

The present inventors studied a structure for more firmly covering the core part with the shell part. As a result, it was found that it is important to have a shell portion containing an aromatic group-containing unit and a unit derived from a crosslinking agent. The hydrophobic interaction and π-π interaction between the aromatic group-containing units can prevent the water solubility of the shell portion from increasing excessively. Furthermore, it is believed that by providing the shell portion with a crosslinked structure, the movement of the resin chains forming the shell portion can be suppressed, and the clarity of the recorded image can be improved.

<Water-based ink>
The ink of the present invention is a water-based ink for inkjet use containing resin particles and a cyclic amide-based water-soluble organic solvent. The resin particles have a core portion containing a cyano group-containing unit, and a shell portion containing an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a crosslinking agent, but not containing a cyano group-containing unit. Each component constituting the ink will be explained below. The present invention is not limited by the following description unless it exceeds the gist thereof. Below, "(meth)acrylic acid,""(meth)acrylate," and "(meth)acryloyl" refer to "acrylic acid, methacrylic acid,""acrylate,methacrylate," and "acryloyl, methacryloyl," respectively. shall be taken as a thing. The ink of the present invention does not need to be of an active energy ray-curable type, and therefore does not need to contain a monomer having a polymerizable group. Further, the ink of the present invention does not need to emit light when irradiated with light outside the visible range.

(resin particles)
The term "resin particles" as used herein means a resin that can be dispersed in an aqueous medium and exist in the aqueous medium with a particle size. Therefore, the resin particles exist in a dispersed state in the ink, that is, in a resin emulsion state. Further, the resin particles do not need to contain a coloring material (such as a dye, a pigment, an invisible coloring material that is colored by fluorescence, etc.).

Whether a certain resin is a "resin particle" can be determined according to the method shown below. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali equivalent to an acid value (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by a dynamic light scattering method, if particles having the same particle size are measured, the resin can be determined to be "resin particles." As a particle size distribution measuring device using a dynamic light scattering method, a particle size analyzer (for example, trade name "UPA-EX150", manufactured by Nikkiso Co., Ltd.) or the like can be used. The measurement conditions at this time can be, for example, Set Zero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: spherical, and refractive index: 1.59. Of course, the particle size distribution measuring device and measurement conditions used are not limited to those described above. The reason why the particle size is measured using a neutralized resin is to confirm that particles are being formed even if the resin is sufficiently neutralized and becomes more difficult to form particles. Even under such conditions, the resin having a particle shape exists in the particle state even in the aqueous ink.

As the resin particles, resin particles having a so-called core-shell structure having a core portion and a shell portion covering the core portion are used. The core portion includes a cyano group-containing unit. When the core portion contains a cyano group-containing unit, film formation at room temperature specifically progresses due to the strong interaction that occurs between the cyano group and the cyclic amide described below.

The shell portion includes an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a crosslinking agent. Moreover, the shell part does not substantially contain a cyano group-containing unit. Since the shell part does not contain a cyano group-containing unit, there are substantially no cyano groups on the surface of the resin particles, and image clarity can be improved.

Furthermore, when the shell portion contains an aromatic group-containing unit, hydrophobic interaction occurs with the core portion. This makes it difficult for the shell portion to peel off from the core portion and for the cyano groups in the core portion to be exposed to the surface of the resin particles, thereby improving image clarity.

The monomer that becomes a cyano group-containing unit through polymerization is preferably one having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule. Specific examples include acrylonitrile, methacrylonitrile, chloroacrylonitrile, and 2-cyanoethyl (meth)acrylate. The monomer that becomes a cyano group-containing unit through polymerization is preferably one having no anionic group or aromatic group or having a molecular weight of 300 or less, and more preferably one having a molecular weight of 200 or less. Among these, acrylonitrile and methacrylonitrile are particularly preferred because they have excellent scratch resistance of images, good reactivity during polymerization, and excellent stability of the resulting resin particles.

The monomer that becomes an aromatic group-containing unit through polymerization is preferably one having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule. Specifically, styrene, vinyltoluene, p-fluorostyrene, p-chlorostyrene, α-methylstyrene, 2-vinylnaphthalene, 9-vinylanthracene, 9-vinylcarbazole, phenyl (meth)acrylate, benzyl (meth) Acrylate, 2-phenoxyethyl (meth)acrylate, 2,4-diamino-6-((meth)acryloyloxy)ethyl-1,3,5-triazine, 2-naphthyl (meth)acrylate, 9-anthryl (meth) Examples include acrylate, (1-pyrenyl)methyl (meth)acrylate, and the like. The monomer that becomes an aromatic group-containing unit upon polymerization is preferably one having no anionic group or cyano group or having a molecular weight of 300 or less, more preferably 200 or less. Among these, styrene and its derivatives are more preferred, and styrene and vinyltoluene are particularly preferred, since they have good reactivity during polymerization and the resulting resin particles have excellent stability.

The anionic group in the anionic group-containing unit preferably has one polymerizable functional group such as an ethylenically unsaturated bond in the molecule. Specifically, a carboxylic acid group, a phenolic hydroxy group, a phosphoric acid ester group, etc. can be mentioned. Among these, carboxylic acid groups are preferred because the stability of the resin particles in the ink is good. Monomers that become anionic group-containing units through polymerization include (meth)acrylic acid, p-vinylbenzoic acid, 4-vinylphenol, β-carboxyethyl (meth)acrylate, and phosphoric acid (2-hydroxyethyl methacrylate). Examples include ester, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and the like. The monomer that becomes an anionic group-containing unit upon polymerization is preferably one that does not have an aromatic group or a cyano group, or one that has a molecular weight of 300 or less, and more preferably one that has a molecular weight of 200 or less. Among these, (meth)acrylic acid is particularly preferred. Moreover, it is preferable that the anionic group in the anionic group-containing unit is only a carboxylic acid group. The anionic group may be either an acid type or a salt type, and when it is a salt type, it may be either partially or completely dissociated. When the anionic group is a salt type, examples of the cation serving as a counter ion include an alkali metal cation, ammonium, and organic ammonium.

Examples of the crosslinking agent that becomes a unit derived from the crosslinking agent through polymerization include compounds having two or more polymerizable functional groups such as ethylenically unsaturated bonds in the molecule. Such crosslinking agents include diene compounds such as butadiene and isoprene; 1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, (mono-, di-, tri-, Poly-)ethylene glycol di(meth)acrylate, (mono-, di-, tri-, poly-)propylene glycol di(meth)acrylate, (mono-, di-, tri-, poly-)tetramethylene glycol di( meth)acrylate, ethylene oxide modified bisphenol A di(meth)acrylate, 2-hydroxy-3-(meth)acryloyloxypropyl methacrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate , 9,9-bis(4-(2-(meth)acryloyloxyethoxy)phenyl)fluorene, tricyclodecane dimethanol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,6- Difunctional ( meth)acrylate; tris(2-(meth)acryloyloxyethyl)isocyanurate, trimethylolpropane tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate; ) acrylate, pentaerythritol tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, propoxylated glyceryl tri(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, ε-caprolactone modified tris-(2- Trifunctional (meth)acrylates such as (meth)acryloyloxyethyl) isocyanurate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate; ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, Examples include tetrafunctional (meth)acrylates such as pentaerythritol tetra(meth)acrylate; divinylbenzene, and the like.

The crosslinking agent preferably has a molecular weight of more than 200, more preferably more than 300, and particularly preferably 400 or more. Further, as the crosslinking agent, a compound having two ethylenically unsaturated bonds in the molecule is preferable. By using a compound having two ethylenically unsaturated bonds in the molecule as a crosslinking agent, aggregation of resin particles caused by excessive crosslinking is suppressed, and resin particles having a more uniform particle size can be obtained. Among the compounds having two ethylenically unsaturated bonds in the molecule, divinylbenzene and ethylene glycol di(meth)acrylate are more preferred.

Examples of the crosslinking agent having a glycidyl group include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, sorbitol polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and pentaerythritol polyglycidyl ether. , propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, neopentyl glycol diglycidyl ether, and the like.

A surfactant can be used when producing resin particles. It is preferable to produce resin particles in the presence of a surfactant because the particle size and shape of the resulting resin particles are likely to be stable. However, non-reactive surfactants may easily peel off from resin particles. If the surfactant is peeled off in the ink, it may affect the physical properties of the ink, resulting in a tendency for the ejection characteristics to deteriorate. For this reason, as the surfactant used when producing resin particles, a reactive surfactant is preferable.

Reactive surfactants include compounds in which a polymerizable functional group such as a (meth)acryloyl group, maleyl group, vinyl group, or allyl group is bonded inside or at the end of a molecule consisting of a hydrophilic part and a hydrophobic part. It is preferable to use Examples of the hydrophilic portion include polyoxyalkylene chains such as ethylene oxide chains and propylene oxide chains. Furthermore, examples of the hydrophobic portion include structures such as alkyl, aryl, and combinations thereof. The hydrophilic part and the hydrophobic part may be bonded via a linking group such as an ether group. The reactive surfactant preferably has a molecular weight of more than 200, more preferably more than 300, and particularly preferably 400 or more.

Specific examples of the reactive surfactant include polyoxyethylene nonylpropenylphenyl ether, polyoxyethylene nonylpropenylphenyl ether ammonium sulfate, polyoxyethylene-1-(allyloxymethyl)alkyl ether ammonium sulfate, α-hydro-ω -(1-alkoxymethyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl)), α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl] -ω-Hydroxypolyoxyethylene, α-sulfo-ω-(1-alkoxymethyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl)ammonium salt, 2-sodiumsulfoethyl Methacrylate, bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfate, alkoxypolyethylene glycol methacrylate, alkoxypolyethylene glycol maleate, polyoxyalkylene alkenyl ether, polyoxyalkylene alkenyl ether ammonium sulfate, vinyl ether alkoxylate, alkylaryl sulfosuccinic acid Salts, polyoxyalkylene methacrylate sulfate salts, unsaturated phosphoric acid esters, and the like can be mentioned. Among them, α-sulfo-ω-(1-alkoxymethyl-2-(2-propenyloxy)ethoxy)-poly(oxy-1,2-ethanediyl) ammonium salt (trade name “Adekariasoap” SR manufactured by Adeka) -10S, SR-10, SR-20, SR-3025, SE-10N, SE-20N, etc.) are preferred.

The core portion and shell portion of the resin particles may each contain units other than the above-mentioned units, as long as the effects of the present invention are not impaired. As units other than the above-mentioned units, those having one polymerizable functional group in the molecule are preferable, and specific examples include units derived from ethylenically unsaturated monomers.

Ethylenically unsaturated monomers include alkenes such as ethylene and propylene; alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate, and hexadecyl (meth)acrylate. Acrylates: Monocyclic (meth)acrylates such as cyclopropyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, and cyclodecyl (meth)acrylate; isobornyl (meth)acrylate, norbornyl (meth)acrylate, etc. Bicyclic (meth)acrylates; tricyclic (meth)acrylates such as adamantyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate; methoxy (mono, di- , nonionic hydrophilic group-containing (meth)acrylates such as tri,poly)ethylene glycol (meth)acrylate; As the ethylenically unsaturated monomer, those having no anionic group, cyano group, or aromatic group and those having a molecular weight of 300 or less are preferable, and those having a molecular weight of 200 or less are more preferable. Among these, alkenes having 1 to 22 carbon atoms; alkyl (meth)acrylates having an alkyl group having 1 to 22 carbon atoms are preferred. In addition, since the physical properties of the resin particles can be easily adjusted and resin particles with excellent polymerization stability can be obtained, alkyl (meth)acrylates in which the alkyl group has 1 to 12 carbon atoms are more preferable, and methyl (meth)acrylates are more preferable. Acrylate and ethyl (meth)acrylate are particularly preferred.

As described above, the core portion includes a cyano group-containing unit. The proportion (mass%) of the cyano group-containing unit in the core portion is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 55% by mass or less. If the proportion of the cyano group-containing unit in the core portion is less than 10% by mass, the scratch resistance of the image may be slightly reduced. On the other hand, if the proportion of the cyano group-containing unit in the core portion exceeds 60% by mass, a portion of the cyano group in the core portion is likely to be exposed on the surface of the resin particle, and the image clarity may deteriorate slightly. be. The proportion (mass%) of other units in the core portion is preferably 70% by mass or less. The "other units" in the core section are units other than the cyano group-containing unit. It is preferable that the "other units" of the core portion include an aromatic group-containing unit, an anionic unit, and a unit derived from a reactive surfactant. Further, it is preferable that the core portion is not crosslinked. That is, it is preferable that the "other units" of the core portion do not include units derived from a crosslinking agent.

Further, as described above, the shell portion includes an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a crosslinking agent, and does not substantially contain a cyano group-containing unit. The proportion (mass%) of the aromatic group-containing unit in the shell portion is preferably 1% by mass or more and 60% by mass or less, and more preferably 10% by mass or more and 50% by mass or less.

The proportion (mass%) of the anionic group-containing unit in the shell portion is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 20% by mass or less. If the proportion of the anionic group-containing unit in the shell portion is less than 5% by mass, the ejection characteristics of the ink may deteriorate somewhat. On the other hand, if the proportion of the anionic group-containing unit in the shell portion exceeds 30% by mass, the hydrophilicity of the shell portion may become too high. For this reason, the shell portion may be easily peeled off from the core portion, and the cyano group in the core portion may be easily exposed on the surface of the resin particle, resulting in a slight decrease in image clarity.

The proportion (mass%) of units derived from the crosslinking agent in the shell portion is preferably 30% by mass or more and 80% by mass or less, and more preferably 40% by mass or more and 70% by mass or less. If the proportion of units derived from the crosslinking agent in the shell portion is less than 30% by mass, the cyano group in the core portion may be exposed under conditions where the hydrophilicity of the shell portion is excessively increased due to combined use with a water-soluble resin. This may result in a slight decrease in image clarity. On the other hand, if the proportion of the units derived from the crosslinking agent in the shell portion exceeds 80% by mass, the ejection characteristics of the ink may deteriorate somewhat.

The proportion (mass%) of other units in the shell portion is preferably 10% by mass or less. "Other units" in the shell portion are units other than the aromatic group-containing unit, the anionic group-containing unit, and the unit derived from the crosslinking agent. It is preferable that the "other units" of the shell portion include a unit derived from a reactive surfactant.

The mass ratio of the core part and shell part of the resin particles is a mass ratio where the total is 100, and the core part:shell part is preferably 50:50 to 95:5, and preferably 60:40 to 90:10. It is even more preferable that there be. Further, the volume-based cumulative 50% particle diameter (D50) of the resin particles is preferably 50 nm or more and 120 nm or less. The volume-based cumulative 50% particle diameter (D50) of the resin particles can be measured in the same manner as the above-described method for determining whether or not they are resin particles.

The content (mass%) of resin particles in the ink is preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. If the content of the resin particles is less than 1.0% by mass, the scratch resistance of the image may be slightly reduced. On the other hand, if the content of the resin particles is more than 10.0% by mass, the image clarity may be slightly reduced.

The glass transition temperature of the resin particles is preferably 95°C or higher. If the glass transition temperature of the resin particles is less than 95° C., the resin particles tend to rapidly form a film, and the image clarity may deteriorate somewhat. Further, the ink ejection characteristics may also be slightly degraded. The glass transition temperature of the resin particles is preferably 150°C or lower, more preferably 120°C or lower. The glass transition temperature of the resin particles can be measured using a differential scanning calorimeter (for example, trade name "DSC Q1000", manufactured by TA instruments, etc.).

The minimum film forming temperature of an ink containing resin particles having a glass transition temperature within the above range is preferably 30° C. or lower. If the minimum film forming temperature exceeds 30° C., additional means such as heating may be required to develop the scratch resistance of the image. The minimum film forming temperature of the ink is preferably 0°C or higher, more preferably 15°C or higher. The minimum film-forming temperature of the ink can be measured using a minimum film-forming thermometer (for example, trade name "MFFT-90", manufactured by Rhopoint Instruments) by a method based on ASTM standard D2354.

[Method for manufacturing resin particles]
The resin particles can be produced according to conventionally known methods such as emulsion polymerization, miniemulsion polymerization, seed polymerization, and phase inversion emulsification.

[Resin particle verification method]
The structure of the resin particles can be verified according to the methods shown in (i) to (iii) below. A method for extracting, analyzing and verifying resin particles from ink will be described below, but resin particles extracted from an aqueous dispersion or the like can be similarly analyzed and verified.

(i) Extraction of resin particles Resin particles can be separated and extracted from ink containing resin particles by density gradient centrifugation. Among the density gradient centrifugation methods, the density gradient sedimentation velocity method separates and extracts resin particles based on differences in sedimentation coefficients of components. Furthermore, among the density gradient centrifugation methods, the density gradient sedimentation equilibrium method separates and extracts resin particles based on the difference in density of components.

(ii) Confirmation and separation of layer structure First, resin particles are dyed and fixed with ruthenium tetroxide, and then embedded in epoxy resin and stably maintained. Next, the resin particles embedded in the epoxy resin are cut with an ultramicrotome, and the cross section is observed using a scanning transmission electron microscope (STEM). By observing a cross section cut through the center of gravity of the resin particles, the layered structure of the resin particles can be confirmed. Resin particles embedded in epoxy resin are used as analysis samples, and the elements contained in the layers (core part, shell part) that make up the resin particles are quantitatively analyzed using STEM-EDX, which is equipped with energy dispersive X-ray spectroscopy (EDX). can do.

(iii) Analysis of units (monomers) constituting the resin of each layer The resin particles used as a sample for separating the resin of each layer may be in the form of a dispersion. Alternatively, the sample may be a dried resin particle formed into a film. After dissolving resin particles as a sample in an organic solvent, each layer is separated by gel permeation chromatography (GPC), and the resin constituting each layer is fractionated. Then, the separated resin is subjected to elemental analysis using a combustion method. Separately, after pretreating the resin separated by acid decomposition (hydrofluoric acid addition) method or alkali melting method, inorganic components are quantitatively analyzed by inductively coupled plasma emission spectrometry. By comparing the results of elemental analysis and quantitative analysis of inorganic components with the results of quantitative elemental analysis using STEM-EDX obtained in (ii) above, it was possible to determine the layer of resin particles that the fractionated resin was composed of. You can know.

The fractionated resin is also analyzed by nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). This makes it possible to know the types and proportions of the units (monomers) and crosslinkable components constituting the resin. Furthermore, monomers produced by depolymerization can be directly detected by analyzing the resin separated by pyrolysis gas chromatography.

(cyclic amides)
The water-soluble organic solvent contained in the ink includes cyclic amides. By containing a cyclic amide, film formation at room temperature can specifically proceed due to the strong interaction that occurs between the cyano group in the core part of the resin particle and the cyclic amide.

Examples of cyclic amides include pyrrolidones, imidazolidinones, and hydantoins. Among these, the following compounds are preferred from the viewpoints of high film-forming promoting action, excellent scratch resistance of images, and ease of handling. Namely, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and 1,3-bis(2-hydroxyethyl )-5,5-dimethylhydantoin is preferred.

The content (mass%) of the cyclic amide in the ink is preferably 1.0% by mass or more and 20.0% by mass or less, based on the total mass of the ink. If the content of the cyclic amide is less than 1.0% by mass, the scratch resistance of the image may be slightly reduced. On the other hand, if the content of the cyclic amide exceeds 20.0% by mass, the ejection characteristics of the ink may deteriorate somewhat.

The content (mass %) of the cyclic amide in the ink is preferably 0.5 times or more and 2.5 times or less relative to the content (mass %) of the resin particles. If the above mass ratio is less than 0.5 times, the scratch resistance of the image may be slightly reduced. On the other hand, if the above mass ratio is more than 2.5 times, the image clarity may deteriorate slightly.

(Water-soluble resin)
Preferably, the ink further contains a water-soluble resin. The water-soluble resin is preferably an acrylic resin or a urethane resin, and more preferably an acrylic resin. Moreover, it is preferable that the water-soluble resin contains an aromatic group-containing unit. When a water-soluble resin having an aromatic group-containing unit is present, hydrophobic interactions and π-π interactions occur between the aromatic groups of the water-soluble resin and the aromatic groups of the resin particles. As a result, the strength of the resin film formed on the recording medium is increased, and the scratch resistance of the image is further improved. Further, since the water-soluble resin is adsorbed to the resin particles and the water-soluble resin assists in dispersing the resin particles, the ejection characteristics of the ink are also likely to be improved.

As the aromatic-containing unit in the water-soluble acrylic resin, the above-mentioned aromatic-containing unit can be used. It is preferable that the water-soluble acrylic resin has an anionic group-containing unit in addition to the aromatic group-containing unit. As the anionic group-containing unit in the water-soluble acrylic resin, the anionic group-containing unit described above can be used.

The water-soluble acrylic resin may further have units (other units) other than the aromatic group-containing unit and the anionic group-containing unit. Monomers constituting other units, including those having substituents such as alkoxy groups and hydroxy groups, include 2-hydroxyethyl (meth)acrylate; 3-hydroxypropyl (meth)acrylate; methoxy (mono, di, Tri, poly)ethylene glycol (meth)acrylate; alkenes such as ethylene and propylene; alkyls such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate, and hexadecyl (meth)acrylate (meth)acrylates; monocyclic (meth)acrylates such as cyclopropyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclooctyl (meth)acrylate, and cyclodecyl (meth)acrylate; isobornyl (meth)acrylate, norbornyl (meth)acrylate; ) Acrylate and other bicyclic (meth)acrylates; adamantyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate and other tricyclic (meth)acrylates; etc. can be mentioned. The water-soluble acrylic resin may be a random copolymer, a block copolymer, or a graft copolymer.

As the water-soluble urethane resin, one obtained by reacting polyisocyanate with a component that reacts with it (a polyol having an acid group, a polyol without an acid group, a polyamine, etc.) can be used. Moreover, a product further reacted with a chain extender or a crosslinking agent may be used. At least one of these components has an aromatic group.

The acid value of the water-soluble resin is preferably 100 mgKOH/g or more and 180 mgKOH/g or less. If the acid value of the water-soluble resin is less than 100 mgKOH/g, the scratch resistance of the image may be slightly reduced. On the other hand, when the acid value of the water-soluble resin exceeds 180 mgKOH/g, the anionic groups in the shell portion of the resin particles are neutralized by ions derived from the anionic groups of the water-soluble resin, promoting water solubilization. The state of inclusion in the core becomes loose. As a result, the core portion having a cyano group is likely to be exposed, and image clarity may be slightly reduced.

The content (mass%) of the water-soluble resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink. Further, the content (mass %) of the water-soluble resin is preferably 0.1 times or more and 2.0 times or less relative to the resin particle content (mass %).

Physical properties such as composition, weight average molecular weight, and acid value of the water-soluble resin can be measured according to conventionally known methods. Specifically, the physical property values of the water-soluble resin can be measured by analyzing the sediment and supernatant liquid obtained by centrifuging the ink. Although it is possible to analyze water-soluble resins in the form of ink, it is preferable to analyze water-soluble resins extracted from ink because measurement accuracy can be improved. Specifically, it is preferable to add an excess of acid (such as hydrochloric acid) to a supernatant liquid obtained by centrifuging the ink at 75,000 rpm, and then dry the precipitated resin for analysis.

By analyzing the resin separated from the ink using a high-temperature gas chromatography/mass spectrometer (high-temperature GC/MS), it is possible to confirm the type of unit constituting the water-soluble resin. In addition, the molecular weight and type of monomers that make up each unit can be confirmed by quantitative analysis using nuclear magnetic resonance ( ^13C -NMR) or Fourier transform infrared spectrophotometer (FT-IR). I can do it.

The acid value of the water-soluble resin can be measured by a titration method. Specifically, a water-soluble resin is dissolved in tetrahydrofuran (THF) to prepare a measurement sample. Then, the acid value of the water-soluble resin can be measured by subjecting the prepared measurement sample to potentiometric titration using a potassium hydroxide ethanol titrant using an automatic potentiometric titrator. As the automatic potentiometric titrator, for example, the product name "AT510" (manufactured by Kyoto Electronics Industry Co., Ltd.) can be used.

The weight average molecular weight of the water-soluble resin can be measured by gel permeation chromatography (GPC). The GPC measurement conditions are as shown below.
・Device: Alliance GPC 2695 (manufactured by Waters)
・Column: Shodex KF-806M quadruple column (manufactured by Showa Denko)
・Mobile phase: THF (special grade)
・Flow rate: 1.0mL/min
・Oven temperature: 40.0℃
・Injection volume of sample solution: 0.1mL
・Detector: RI (refractive index)
・Polystyrene standard samples: PS-1 and PS-2 (manufactured by Polymer Laboratories, molecular weight: 7,500,000, 2,560,000, 841,700, 377,400, 320,000, 210,500, 148,000 , 96,000, 59,500, 50,400, 28,500, 20,650, 10,850, 5,460, 2,930, 1,300, 580).

(color material)
Preferably, the ink further contains a coloring material. Note that when the ink does not contain a coloring material, it can be used in combination with another ink containing a coloring material. Pigments and dyes can be used as the coloring material. The content (mass%) of the coloring material in the ink is preferably 0.5% by mass or more and 15.0% by mass or less, and 1.0% by mass or more and 10.0% by mass, based on the total mass of the ink. It is more preferable that it is the following. It is preferable to use a pigment as the coloring material.

Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide; organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine.

Classified by dispersion method, the pigment may be a resin-dispersed pigment using a resin as a dispersant, a self-dispersing pigment in which a hydrophilic group is bonded to the particle surface of the pigment, or the like. Further, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the surface of a pigment particle, a microcapsule pigment in which the surface of a pigment particle is coated with a resin, etc. 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 pigment particle surface, rather than a resin-bonded pigment or a microcapsule pigment.

As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of an anionic group. A water-soluble resin can be used as the resin dispersant. The pigment content (mass %) in the ink is preferably 0.3 times or more and 10.0 times or less relative to the resin dispersant content.

As a self-dispersing pigment, one in which an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group is bonded to the particle surface of the pigment directly or via another atomic group (-R-) is used. be able to. The anionic group may be either an acid type or a salt type, and when it is a salt type, it may be either partially or completely dissociated. When the anionic group is a salt type, examples of the cation serving as a counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of other atomic groups (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene groups and naphthylene groups; carbonyl groups; imino groups; amide groups; sulfonyl groups. Groups; ester groups; ether groups, etc. can be mentioned. Furthermore, a combination of these groups may be used.

As the dye, it is preferable to use one having an anionic group. Specific examples of dyes include dyes such as azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone. The coloring material contained in the ink is preferably a pigment, and more preferably a resin-dispersed pigment.

(aqueous medium)
The ink is an aqueous ink containing at least water as an aqueous medium. The ink can further contain a water-soluble organic solvent as an aqueous medium. As water, it is preferable to use deionized water or ion-exchanged 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. Further, as the water-soluble organic solvent, any one commonly used for ink can be used. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds other than the above-mentioned cyclic amides, and sulfur-containing compounds. The content (mass%) of the water-soluble organic solvent 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. The content of this water-soluble organic solvent is a value including cyclic amides.

(Other additives)
In addition to the above ingredients, the ink may also contain water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethylene urea. You may. Furthermore, the ink may contain surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, and other resins, etc., as necessary. It may contain various additives.

(Physical properties of ink)
Since the ink is a water-based ink applied to the inkjet method, it is preferable to appropriately control its physical property values. Specifically, the surface tension of the ink at 25° C., measured by a plate method, is preferably 20 mN/m or more and 60 mN/m or less, and more preferably 25 mN/m or more and 45 mN/m or less. Further, the viscosity of the ink at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less, and more preferably 1.0 mPa·s or more and 5.0 mPa·s or less. Further, the pH of the ink at 25° C. is preferably 7.0 or more and 10.0 or less.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink storage portion that stores the ink. The ink contained in this ink storage portion is the water-based ink of the present invention described above. FIG. 1 is a cross-sectional view schematically showing an embodiment of an ink cartridge of the present invention. As shown in FIG. 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 serves as an ink storage section for storing ink. The ink storage section includes an ink storage chamber 14 and an absorbent storage chamber 16, which communicate with each other via a communication port 18. Further, the absorbent storage chamber 16 communicates with the ink supply port 12 . The ink storage chamber 14 stores liquid ink 20, and the absorbent storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage section may have a configuration in which the entire amount of ink contained therein is retained by an absorber without having an ink storage chamber that stores liquid ink. Further, the ink accommodating portion may have a form that does not include an absorber and stores the entire amount of ink in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

<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. Examples of methods for ejecting ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of ejecting ink by applying thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be those known in the art.

FIG. 2 is a diagram schematically showing an example of an inkjet recording device used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording device, and (b) is a perspective view of a head cartridge. It is. The inkjet recording apparatus is provided with a conveying means (not shown) for conveying 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 includes recording heads 38 and 40, and is configured such that an ink cartridge 42 is set therein. While the head cartridge 36 is transported in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by a conveying means (not shown). The recording medium 32 is not particularly limited, but it may be a paper-based recording medium (ink It is preferable to use a recording medium having a permeability of This recording medium does not need to be used for transfer purposes.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples in any way unless it exceeds the gist thereof. Regarding component amounts, "parts" and "%" are based on mass unless otherwise specified.

<Preparation of pigment dispersion>
A solution of 100 g of concentrated hydrochloric acid dissolved in 110 g of water was cooled to 5° C., and in this state, 30 g of 4-aminophthalic acid was added. The container containing this solution was placed in an ice bath, and a solution obtained by dissolving sodium nitrite 36 in 180 g of ion-exchanged water at 5° C. was added while stirring to maintain the temperature of the solution at 10° C. or lower. After stirring for 15 minutes, carbon black (trade name "Monak 1000", manufactured by Cabot) was added under stirring, and the mixture was further stirred for 15 minutes to obtain a slurry. The resulting slurry was filtered through a filter paper (trade name "Standard Filter Paper No. 2", manufactured by Advantech), and the particles were thoroughly washed with water and dried in an oven at 110°C to obtain a self-dispersed pigment. The pigment content was adjusted by adding an appropriate amount of water to obtain a pigment dispersion having a pigment content of 15.0%.

<Preparation of aqueous dispersion of resin particles>
(Resin particles 1 to 16)
A reaction vessel equipped with a stirring device was placed in a hot water bath. 1,178 parts of water was placed in the reaction vessel, and the internal temperature was maintained at 70°C. A monomer that becomes a cyano group-containing unit, a monomer that becomes an aromatic group-containing unit (including a monomer as a control example), a monomer that becomes an anionic group-containing unit, and a reactive surfactant that becomes a reactive surfactant unit. Prepared. These components were mixed in the amounts (parts) and breakdown (%) shown in Table 1-1. In this way, a monomer mixture solution for the core portion was prepared. As the reactive surfactant, the trade name "Adekaria Soap SR-10" (manufactured by ADEKA) was used. Further, 1.9 parts of potassium persulfate and 659 parts of water were mixed to prepare an aqueous solution 1 of a polymerization initiator. The monomer mixture for the core portion and the aqueous solution 1 of the polymerization initiator were dropped into the reaction vessel in parallel over 60 minutes. After the dropwise addition was completed, stirring was continued and the reaction was continued for an additional 30 minutes to synthesize particles that would become the core portion of the resin particles. However, for resin particles 10, the core portion was not synthesized.

Next, a monomer that will become an aromatic group-containing unit (including a monomer as a control example), a monomer that will become an anionic group-containing unit, a crosslinking agent that will become a crosslinking agent unit, and a reactive surfactant that will become a reactive surfactant unit. I prepared the medicine. These prepared monomers were mixed in the amount (parts) and breakdown (%) shown in Table 1-2 to prepare a monomer mixture for the shell part. As the reactive surfactant, the trade name "Adekaria Soap SR-10" (manufactured by ADEKA) was used. Further, 0.1 part of potassium persulfate and 133 parts of water were mixed to prepare an aqueous solution 2 of a polymerization initiator. A monomer mixture for the shell part and an aqueous solution of polymerization initiator 2 were dropped in parallel over a period of 10 minutes into the reaction vessel containing the particles to become the core part. After completion of the dropwise addition, the mixture was stirred at 80° C. for 10 minutes to continue the reaction to synthesize a shell portion, thereby synthesizing resin particles having a core-shell structure in which particles serving as a core portion were coated with a resin serving as a shell portion. However, for resin particles 11, no shell portion was synthesized.

Thereafter, an appropriate amount of 8 mol/L potassium hydroxide aqueous solution was added into the reaction vessel to adjust the pH of the liquid to 8.5. An appropriate amount of water was further added to obtain an aqueous dispersion of each resin particle having a resin particle content of 20% and a particle diameter (volume-based cumulative 50% particle diameter) of 80 nm. The particle size of the resin particles was measured using a dynamic light scattering particle size analyzer (trade name "UPA-EX150", manufactured by Nikkiso), Set Zero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape : Measured under the conditions of true spherical shape and refractive index of 1.59. Table 1-2 shows the glass transition temperature of the obtained resin particles. The glass transition temperature of the resin particles was measured according to the following procedure. First, an aqueous dispersion of resin particles was heated to 60° C. to dryness and sealed in an aluminum container to prepare a sample. Next, using a differential scanning calorimeter (trade name "DSC Q1000", manufactured by TA Instruments), the sample was heated to 200°C at a rate of 10°C/min, cooled to -50°C at a rate of 5°C/min, and heated to 200°C. The glass transition temperature (°C) was measured by raising the temperature to 10°C/min.

The meanings of the abbreviations in Tables 1-1 and 1-2 are shown below.
・AN: acrylonitrile ・MAN: methacrylonitrile ・CAN: 2-chloroacrylonitrile ・St: styrene ・EMA: ethyl methacrylate ・MMA: methyl methacrylate ・MAA: methacrylic acid ・EDMA: ethylene glycol dimethacrylate

(Resin particles 17)
67 parts of ethyl acrylate, 30 parts of methacrylonitrile, 3 parts of methacrylic acid, 0.5 parts of anionic surfactant, and 63 parts of ion-exchanged water were mixed and stirred to prepare an emulsion of a monomer mixture. As the anionic surfactant, sodium polyoxyethylene alkyl ether sulfate (trade name "Latemul E-118B", manufactured by Kao, average degree of polymerization 500) was used.

Into another reactor (polymerization vessel) equipped with a stirrer, 82.5 parts of ion-exchanged water, 0.3 parts of anionic surfactant, and 2.0 parts of nonionic surfactant were placed. As the anionic surfactant, sodium polyoxyethylene alkyl ether sulfate (trade name "Latemul E-118B", manufactured by Kao) was used. As the nonionic surfactant, polyoxyethylene cetyl ether (trade name "Emulgen 120", manufactured by Kao) was used. After raising the temperature to 80° C., an aqueous solution obtained by dissolving 0.5 parts of ammonium persulfate in 10.6 parts of water was added. An emulsion of the monomer mixture was continuously added and polymerized over a period of 2 hours. After the addition of the emulsion, the reaction was continued at 80° C. for 90 minutes to obtain an aqueous dispersion of resin particles 17 with a resin particle content of 40%.

(Resin particles 18)
169 g of water was placed in a reaction vessel, and the mixture was stirred and heated to 77°C. Further, an aqueous emulsion was prepared by mixing 13.7 g of water, 0.7 g of polyoxyethylene alkyl ether sulfate, 17.7 g of styrene, and 37.5 g of butyl acrylate. As the polyoxyethylene alkyl ether sulfate, the trade name "Hitenol BC-10" (manufactured by Daiichi Kogyo Seiyaku) was used. After putting 2 g of the prepared aqueous emulsion into a reaction vessel, 0.37 g of potassium persulfate dissolved in the minimum amount of water was added. After 15 minutes, the remainder of the aqueous emulsion was poured into the reaction vessel over 72 minutes to complete the first stage polymerization.

An emulsion was obtained by mixing 34.9 g of water, 1.6 g of polyoxyethylene alkyl ether sulfate, 21.1 g of styrene, 99.0 g of methyl methacrylate, 6.1 g of butyl acrylate, and 2.6 g of methacrylic acid. The obtained emulsion was poured into a reaction vessel over a period of 168 minutes to carry out second stage polymerization. As the polyoxyethylene alkyl ether sulfate, the trade name "Hitenol BC-10" (manufactured by Daiichi Kogyo Seiyaku) was used. The remaining monomer was reduced using ascorbic acid and t-butyl hydroperoxide according to a conventional method, and then the mixture was cooled to 25°C. After adjusting the pH to 8 by adding an aqueous potassium hydroxide solution, an aqueous fungicide suitable for inkjet was added to obtain an aqueous dispersion of resin particles 18 having a resin particle content of 40%.

<Synthesis of water-soluble resin>
A water-soluble acrylic resin, which is a random copolymer having the composition and properties shown in Table 2, was synthesized by polymerizing monomers in a conventional manner. After adding water containing potassium hydroxide in an equimolar amount to the acid value to neutralize the anionic groups, an appropriate amount of water is further added to obtain an aqueous solution of a water-soluble resin with a resin content of 10.0%. I got it. A sample for measurement is prepared by dissolving a water-soluble resin in tetrahydrofuran, and potentiometric titration is carried out using a potassium hydroxide ethanol titrant using an automatic potentiometric titrator (trade name "AT510", manufactured by Kyoto Electronics Industry Co., Ltd.). , the acid value of the water-soluble resin was measured. The weight average molecular weights of the water-soluble resins measured by GPC in terms of polystyrene were all 10,000.

The meanings of the abbreviations in Table 2 are shown below.
・St: Styrene ・BzMA: Benzyl methacrylate ・BA: n-butyl acrylate ・AA: Acrylic acid

<Preparation of ink>
Each component (unit: %) shown in the upper row of Tables 3-1 to 3-4 was mixed, thoroughly stirred, and filtered under pressure using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. was prepared. In Tables 3-1 to 3-4, "Acetylenol E100" is the trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals. The lower rows of Tables 3-1 to 3-4 show the characteristics of the inks. The pH of all the prepared inks was within the range of 8.5 to 9.0.

The minimum film-forming temperature of the ink was measured using a minimum film-forming thermometer (trade name "MFFT-90", manufactured by Low Point Instruments). Since the inks of Example 26, Comparative Example 9, and Comparative Example 10 do not contain coloring material, the inks themselves were used as samples for measurement. For inks other than Example 26, Comparative Example 9, and Comparative Example 10, evaluation inks were prepared in which the pigment dispersion liquid was replaced with water, and these were used as measurement samples. A sample for measurement was applied onto a polyethylene terephthalate film using an applicator, and then set in a minimum film forming thermometer provided with a temperature gradient. The film was observed after 2 hours, and the temperature corresponding to the boundary between the white part and the transparent part was read as the minimum film forming temperature.

<Preparation of pigment ink>
The components shown below were mixed, sufficiently stirred, and filtered under pressure using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare a pigment ink. The prepared pigment ink was used to evaluate the inks of Example 26, Comparative Example 9, and Comparative Example 10, which did not contain a coloring material.
・Pigment dispersion: 20.0%
・Acetylenol E100: 0.5%
・Pure water: 79.5%

<Evaluation>
Each of the prepared inks was filled into an ink cartridge, and the cartridge was set in an inkjet recording device (trade name "PIXUS Pro-10", manufactured by Canon) equipped with a recording head that ejects ink using thermal energy. In this inkjet recording apparatus, an image recorded under conditions in which 8 drops of ink of 3.8 ng±10% are applied to a unit area of 1/600 inch x 1/600 inch is defined as having a recording duty of 100%. The recording environment was a temperature of 25° C. and a relative humidity of 55%. In the present invention, in the evaluation criteria for each item below, "A" and "B" were defined as acceptable levels, and "C" was defined as unacceptable levels. The evaluation results are shown in Table 4. Since the ink of Comparative Example 5 could not be ejected, the following evaluation was not performed.

(Abrasion resistance)
Using the above inkjet recording device, the following image was recorded on a recording medium (glossy paper, product name: "Canon Photo Paper Gloss Pro [Platinum Grade]", manufactured by Canon), and the scratch resistance was evaluated. Ta. Regarding the inks of Example 26, Comparative Example 9, and Comparative Example 10, solid images with a recording duty of 100% were recorded using the previously prepared pigment inks and dried for one day. Thereafter, a solid image with a recording duty of 100% was recorded using each ink so as to overlap the solid image of the pigment ink. Furthermore, for inks other than Example 26, Comparative Example 9, and Comparative Example 10, solid images were recorded with a recording duty of 100%. After drying the recorded image for one day, it was rubbed several times on the surface of the nail. The state of the scratches on the image was visually confirmed, and the scratch resistance of the image was evaluated according to the evaluation criteria shown below.
A: There were no scratches.
B: There were scratches, but the recording medium was not exposed.
C: There were scratches and the recording medium was exposed.

(Image clarity)
Using the above inkjet recording device, the following image was recorded on a recording medium (glossy paper, product name: "Canon Photo Paper Gloss Pro [Platinum Grade]", manufactured by Canon), and the scratch resistance was evaluated. Ta. Regarding the inks of Example 26, Comparative Example 9, and Comparative Example 10, solid images with a recording duty of 100% were recorded using the previously prepared pigment inks and dried for one day. Thereafter, a solid image with a recording duty of 100% was recorded using each ink so as to overlap the solid image of the pigment ink. Furthermore, for inks other than Example 26, Comparative Example 9, and Comparative Example 10, solid images were recorded with a recording duty of 100%. After drying the recorded image for one day, two fluorescent lamps placed 10 cm apart were used as observation light sources, and the fluorescent lamps were projected onto the image from a position 2 m away. The shape of the fluorescent lamp projected onto the image was visually confirmed under conditions of an illumination angle of 45 degrees and an observation angle of 45 degrees, and the image clarity of the image was evaluated according to the evaluation criteria shown below.
A: The boundary between the two projected fluorescent lights was visible, and no blurring was observed at the edges.
B: I could see the boundary between the two projected fluorescent lights, but the edges were slightly blurred.
C: I couldn't see the boundary between the two projected fluorescent lights.

Claims (19)

A water-based ink for inkjet containing resin particles and a water-soluble organic solvent,
The resin particles have a core portion containing a cyano group-containing unit, and a shell portion containing an aromatic group-containing unit, an anionic group-containing unit, and a unit derived from a crosslinking agent, but not containing a cyano group-containing unit. death,
A water-based ink, wherein the water-soluble organic solvent contains a cyclic amide. The glass transition temperature of the resin particles is 95°C or higher,
The aqueous ink according to claim 1, wherein the minimum film forming temperature is 30°C or less. The aqueous ink according to claim 1 or 2, wherein the resin particles have a glass transition temperature of 150°C or less. The water-based ink according to any one of claims 1 to 3, wherein the resin particles have a minimum film-forming temperature of 0°C or higher. The aqueous ink according to any one of claims 1 to 4, wherein the proportion (mass%) of the cyano group-containing unit in the core portion is 10% by mass or more and 60% by mass or less. The aqueous ink according to any one of claims 1 to 5 , wherein the cyano group-containing unit is a unit derived from at least one of acrylonitrile and methacrylonitrile. Any one of claims 1 to 6, wherein the unit derived from the crosslinking agent is a unit derived from at least one selected from the group consisting of a compound having two or more ethylenically unsaturated bonds and a compound having a glycidyl group. The water-based ink according to item 1. The aqueous ink according to any one of claims 1 to 7, wherein the content (mass%) of the resin particles is 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. The cyclic amides include 2-pyrrolidone, N-methyl-2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and 1,3-bis( The aqueous ink according to any one of claims 1 to 8, which is at least one selected from the group consisting of (2-hydroxyethyl)-5,5-dimethylhydantoin. Any one of claims 1 to 9 , wherein the content (mass%) of the cyclic amide is 0.5 times or more and 2.5 times or less as a mass ratio to the content (mass%) of the resin particles. The water-based ink described in . The aqueous ink according to any one of claims 1 to 10, wherein the content (mass%) of the cyclic amide is from 1.0% by mass to 20.0% by mass, based on the total mass of the ink. The water-based ink according to any one of claims 1 to 11 , further comprising a water-soluble resin whose acid value is 100 mgKOH/g or more and 180 mgKOH/g or less. The water-based ink according to claim 12, wherein the water-soluble resin is at least one selected from the group consisting of acrylic resins and urethane resins. The water-based ink according to claim 12 or 13, wherein the content (mass%) of the water-soluble resin is 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink. The aqueous ink according to any one of claims 1 to 14, wherein the resin particles do not include a coloring material. The aqueous ink according to any one of claims 1 to 15 , further comprising a coloring material. The aqueous ink according to claim 16, wherein the content (mass%) of the coloring material is 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink. An ink cartridge comprising ink and an ink accommodating portion accommodating the ink, the ink cartridge comprising:
An ink cartridge, wherein the ink is an aqueous ink according to any one of claims 1 to 17 . An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, the method comprising:
An inkjet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 17 .

Images