JP2024011845A - Inkjet recording method and inkjet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording method which can record an image of a fluorescent color that is excellent in scratch resistance and glossiness.

SOLUTION: There is provided an inkjet recording method for discharging aqueous ink from an inkjet type recording head, and recording an image on a recording medium. The aqueous ink contains resin particles dyed by a basic dye exhibiting fluorescence, a water-soluble resin having an anionic group, and a nonionic surface active agent, dynamic surface tension at 10 milliseconds of life time of the aqueous ink measured by a maximum bubble pressure method is 40 mN/m or less, and a contact angle of the recording medium to the aqueous ink measured after 50 milliseconds after the aqueous ink comes in contact therewith is 10° or more.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an inkjet recording method and an inkjet recording apparatus.

BACKGROUND ART In recent years, in the field of commercial printing such as catalogs, pamphlets, and POP, and in the field of package printing typified by the packaging of food and beverage products, printed matter with bright colors that catch the attention of customers has been actively produced. In order to cope with the expansion of the color gamut of printed matter, various inkjet recording apparatuses equipped with inks of special colors other than the basic colors of cyan, magenta, and yellow have been studied.

Additionally, ink containing a fluorescent coloring material has been proposed in order to expand the color gamut (Patent Document 1). Furthermore, an ink containing resin particles dyed with a basic dye has been proposed in order to record fluorescent images with excellent color development (Patent Document 2).

In the above-mentioned commercial printing field and package printing field, inks that can record not only color development but also high scratch resistance to maintain solidity and high gloss to express clarity are needed. is required. However, while the inks proposed in Patent Documents 1 and 2 can record images with improved color development, the scratch resistance and gloss of the images do not reach the required level, and further improvements are required. It was said that

The fluorescent particles attached to the recording medium are fixed in a state in which adjacent fluorescent particles are in close contact with each other. However, if a physical external force is applied to the fixed fluorescent particles, a phenomenon may occur in which the fluorescent particles collapse and the fluorescent coloring material inside is transferred. Furthermore, when the fluorescent particles are in close contact with each other, the smoothness of the image surface is low and incident light is likely to be diffusely reflected, resulting in a lack of gloss.

In order to record images with improved scratch resistance, for example, an inkjet ink containing a self-dispersing pigment and a polyurethane resin having an acidic group has been proposed (Patent Document 3). Furthermore, in order to record images with improved gloss, an ink whose dynamic surface tension at a lifetime of 10 milliseconds is controlled to 40 mN/m or less has been proposed (Patent Document 4).

Japanese Patent Application Publication No. 2000-303008 JP 2021-008598 Publication JP2012-214713A JP 2018-150518 Publication

The present inventors added a urethane resin having an acidic group to an ink containing a fluorescent coloring material, and investigated the scratch resistance of recorded images. As a result, it was found that the scratch resistance of images recorded on some recording media was only slightly improved. In addition, the present inventors controlled the dynamic surface tension of the ink containing the fluorescent coloring material at a lifetime of 10 milliseconds to 40 mN/m or less, and examined the glossiness of the recorded image. As a result, it was found that the glossiness of the recorded images was not necessarily at a sufficient level, and there was room for further improvement.

Therefore, an object of the present invention is to provide an inkjet recording method capable of recording fluorescent color images with excellent scratch resistance and gloss. Another object of the present invention is to provide an inkjet recording apparatus for use in this inkjet recording method.

That is, according to the present invention, there is provided an inkjet recording method in which an image is recorded on a recording medium by discharging aqueous ink from an inkjet recording head, the aqueous ink being dyed with a basic dye that exhibits fluorescence. The water-based ink containing resin particles, a water-soluble resin having an anionic group, and a nonionic surfactant has a dynamic surface tension of 40 mN/m or less at a lifetime of 10 milliseconds as measured by the maximum bubble pressure method. There is provided an inkjet recording method, characterized in that a contact angle of the recording medium with the aqueous ink measured 50 milliseconds after contact with the aqueous ink is 10° or more.

According to the present invention, it is possible to provide an inkjet recording method capable of recording fluorescent color images with excellent scratch resistance and gloss. Further, according to the present invention, it is possible to provide an inkjet recording apparatus for use in this inkjet recording method.

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.

The present inventors have studied a method for recording images with excellent scratch resistance and gloss using an ink containing resin particles (fluorescent particles) dyed with a fluorescent coloring material. First, an image recorded with an ink containing fluorescent particles and a urethane resin having an acidic group was observed. As a result, it was found that almost no resin component remained in the pigment layer of the image in which the scratch resistance was hardly improved.

Next, the behavior of ink droplets was observed using a recording medium on which an image with slightly improved scratch resistance was recorded and a recording medium on which an image with almost no improvement in scratch resistance was recorded. Specifically, 30 to 40 pL of ink was ejected and applied to the recording medium, and changes over time in the contact angle between the ink attached to the recording medium and the recording medium were tracked. As a result, the rate of change in the contact angle with the ink was found to be higher on recording media on which images with little improvement in scratch resistance were recorded than on recording media on which images with slightly improved scratch resistance were recorded. It turned out to be extremely fast. In other words, it was found that the ink penetrated relatively quickly in a recording medium on which an image with little improvement in scratch resistance was recorded. From the above results, the reason why it is difficult to improve the scratch resistance of images even when resin is added is that the resin penetrates into the recording medium and does not remain effectively on the surface of the fluorescent particles or between fluorescent particles. This is presumably because the physical strength of the image could not be increased.

Next, the present inventors investigated ways to increase the surface tension of the ink and reduce the rate of ink penetration into the recording medium. As a result, it was confirmed that as the surface tension of the ink increases, more resin remains on the recording medium and the scratch resistance of the image improves. However, it has been found that the ink droplets become difficult to wet and spread on the recording medium, resulting in a decrease in the surface smoothness of the image and loss of gloss.

When the ink droplets adhere to the recording medium, the ink immediately begins to permeate into the recording medium, and the cation components present on the surface layer of the recording medium also begin to agglomerate the coloring material. When ink droplets form bulky dots on a recording medium, the surface of the image becomes more uneven, impairing its smoothness. For this reason, it is presumed that it is important to control the surface tension of the ink so that the ink droplets immediately after adhering to the recording medium quickly wet and spread, in order to improve the glossiness of the image. As a result of the study, the present inventors found that in order to impart sufficient wetting and spreading properties to ink droplets, the dynamic surface tension of the ink at a lifetime of 10 milliseconds measured by the maximum bubble pressure method should be 40 mN/m or less. I found that it is effective to do so. However, simply setting the dynamic surface tension of the ink to 40 mN/m or less does not allow the resin to remain effectively on the recording medium, making it difficult to improve the scratch resistance of images. Furthermore, since the fluorescent particles tend to aggregate into particles, the smoothness of the image surface decreases, making it difficult to improve the glossiness of the image.

Based on the above study results, the present inventors further studied a method for recording a fluorescent color image that achieves both high levels of scratch resistance and gloss. As a result, the inventors discovered that by satisfying the requirements (i) to (iii) below, it is possible to record fluorescent images with excellent scratch resistance and gloss, leading to the present invention. .
(i) The water-based ink contains resin particles dyed with a fluorescent basic dye, a water-soluble resin having an anionic group, and a nonionic surfactant.
(ii) The dynamic surface tension of the aqueous ink at a lifetime of 10 milliseconds, as measured by the maximum bubble pressure method, is 40 mN/m or less.
(iii) The contact angle of the recording medium with the water-based ink measured 50 milliseconds after contact with the water-based ink is 10° or more.

In order to produce resin particles (fluorescent particles) dyed with a fluorescent coloring material, it is important to firmly bind the fluorescent coloring material and the resin. Among these, it is effective to use a basic dye, which is a dye having a cationic group, in combination with a water-soluble resin having an anionic group, in that good inkjet suitability can be imparted. It is presumed that a portion of the basic dye is arranged in the outermost layer of the resin particles dyed with the basic dye. As water evaporates from the ink adhering to the recording medium, the basic dye arranged on the outermost layer of the resin particles interacts with the anionic water-soluble resin, causing water-soluble dyes to form on the surface of the resin particles and between the resin particles. This binds the adhesive resin and improves the scratch resistance of the image. Furthermore, since the water-soluble resin forms a film on the surface of the resin particles and between the resin particles, unevenness on the image surface is reduced, smoothness is increased, and glossiness is improved.

However, it is difficult to obtain sufficient effects as described above only by using together resin particles dyed with a basic dye and a water-soluble resin having an anionic group. When a water-soluble resin containing anionic groups loses its anionic properties due to interaction with resin particles or reaction with cationic components present on the surface of the recording medium, the hydrophobic parts of the water-soluble resin interact with each other, causing the water-soluble It is assumed that the plastic resin aggregates. It is considered that the aggregated water-soluble resin has insufficient hydrophobic interaction with the resin particles and cannot remain around the resin particles, making it difficult to sufficiently obtain the above effects.

When the ink further contains a nonionic surfactant, the hydrophobic portion of the nonionic surfactant interacts with the hydrophobic portion of the water-soluble resin having an anionic group. It is thought that this causes the nonionic surfactant to be adsorbed to the water-soluble resin having an anionic group, thereby increasing the water solubility of the water-soluble resin. Even when the water-soluble resin has lost its anionic nature, the adsorbed nonionic surfactant suppresses aggregation of the water-soluble resin, and the water-soluble resin can interact with the resin particles. However, even if an anionic surfactant is used in place of a nonionic surfactant, sufficient effects cannot be obtained. This is thought to be because the anionic group of the anionic surfactant interacts with the basic dye, resulting in insufficient interaction with the water-soluble resin having the anionic group.

In order to record fluorescent color images with excellent scratch resistance and gloss, it is important to use a recording medium that is suitably penetrated by ink. Specifically, it is necessary to use a recording medium whose contact angle with the ink measured 50 milliseconds after contact with the ink is 10° or more. The present inventors observed images recorded on a recording medium having the above contact angle of less than 10°. As a result, while the shape of the resin particles could be confirmed, almost no anionic water-soluble resin could be confirmed. In order to record a fluorescent color image with excellent scratch resistance and gloss, it is necessary for some amount of ink to remain on the recording medium. When ink is applied to a recording medium having the above contact angle of less than 10°, it is thought that the water-soluble resin will be absorbed into the recording medium before the resin particles and the water-soluble resin can sufficiently interact with each other.

<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. 1 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 parts 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 contact angle of the recording medium with the ink measured 50 milliseconds after contact with the ink is 10° or more. Further, from the viewpoint of recording an image with better scratch resistance, it is preferable that the contact angle of the recording medium with the ink measured 100 milliseconds after the ink contacts the recording medium is 10° or more.

Preferably, the recording medium has an ink-receiving layer. Further, it is preferable that the recording medium has a glossy surface or a semi-glossy surface. Specifically, it is preferable to use a recording medium having a support and an ink receiving layer provided on at least one surface of the support. The ink-receiving layer preferably contains pigments such as silica, alumina, and hydrates thereof as main components, and further contains additives such as a binder and cationic resin as necessary. The ink receiving layer constituting such a recording medium has a porous structure formed of pigment particles, and the liquid component of the ink is absorbed into the voids of the porous structure. Therefore, by applying ink to a recording medium having such an ink receiving layer, a higher quality image can be recorded.

The support is preferably one that can provide an ink-receiving layer and that can provide the recording medium with rigidity that allows it to be transported by the transport mechanism of an inkjet recording apparatus. Examples of such a support include paper containing pulp and filler. It is also possible to use a recording medium in which a resin layer such as polyolefin is provided on at least one surface of a support and an ink receiving layer is provided on this resin layer. Furthermore, it is also possible to use a recording medium in which ink-receiving layers are provided on both sides of the support. The recording medium can be one that has been cut in advance to a desired size. Alternatively, an image may be recorded on a sheet-like recording medium wound into a roll and then cut into a desired size.

<Water-based ink>
The ink contains resin particles dyed with a fluorescent basic dye, a water-soluble resin having an anionic group, and a nonionic surfactant. Each component constituting the ink will be described in detail below. Hereinafter, when "(meth)acrylic acid", "(meth)acrylate", and "(meth)acryloyl" are written, "acrylic acid, methacrylic acid", "acrylate, methacrylate", "acryloyl, methacryloyl" are respectively used. means.

(fluorescent dye)
The term "fluorescent dye" as used herein refers to a dye that emits fluorescence when exposed to excitation light in the ultraviolet or visible region. Whether a certain dye is a "fluorescent dye" that exhibits fluorescence can be determined, for example, according to the method described below. A sample obtained by dissolving a dye in a liquid capable of dissolving the dye is irradiated with ultraviolet light (ultraviolet light) having a long wavelength (about 315 to 400 nm) that is barely visible to the naked eye using a black light or the like. If light of a different color from the ultraviolet light emitted by the black light can be visually observed, it can be determined that the dye is a "fluorescent dye" that exhibits fluorescence. As the black light, a commercially available product (eg, product name "SLUV-4" (manufactured by As One), etc.) can be used.

The fluorescent dye in the resin particles dyed with the fluorescent dye can be analyzed, for example, according to the procedure shown below. A sample is prepared by dissolving resin particles taken out from the ink in an organic solvent such as chloroform according to a conventional method. Fluorescent dyes are isolated from prepared samples using HPLC (high performance liquid chromatography). The isolated dye is analyzed by common structural analysis techniques such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS).

A basic dye is a compound that exhibits fluorescence and has an amino group or an imino group (which may form a salt) in its molecular structure. Examples of compounds having an amino group or imino group in their molecular structure include "dyes whose names include 'basic' as shown in the color index". The Color Index is a database of coloring materials constructed by the British Society of Dyeing and Dyeing and others. Examples of the dye skeleton include xanthene, azine, azole, thiazole, azo, diarylmethane, triarylmethane, acridine, coumarin, and methine. Among these, compounds having a skeleton such as xanthene or coumarin are preferred, and compounds having a xanthene skeleton are more preferred.

A specific example of a basic dye exhibiting fluorescence is C. I. Indicated by number or common name, C. I. Basic Red 1, 1:1, 2, 4, 8, 11, 12, 13; C. I. Basic Violet 1, 3, 10, 11, 11:1, 14; Rhodamine 19, 575; C.I. I. Basic Yellow 1, 2, 9, 13, 24, 37, 40, 96; C. I. Basic Blue 7;C. I. Basic Green 1;C. I. Examples include Fluorescent Brightener 363. Among them, C. I. Basic Red 1, 1:1; C. I. Basic Violet 11, 11:1; C.I. I. Basic Yellow 40 and the like are preferred.

It is preferable that the fluorescent dye contains two or more kinds of basic dyes. That is, the resin particles are preferably resin particles dyed with two or more types of basic dyes. The presence of multiple basic dyes in the resin particles inhibits the crystallization of the basic dyes, so the fluorescent dyes efficiently interact with the resin particles at the molecular level, resulting in a stable dyed state. be able to.

The content (% by mass) of the fluorescent dye 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. The proportion (mass%) of the fluorescent dye in the resin particles is preferably 1.0% by mass or more and 15.0% by mass or less, and more preferably 4.0% by mass or more and 8.0% by mass or less. preferable. If the proportion of the fluorescent dye in the resin particles is too small, the color development (saturation) of the image may be slightly reduced. On the other hand, if the proportion of the fluorescent dye in the resin particles is too large, the color development (brightness) of the image may be slightly reduced due to concentration quenching.

(resin particles)
The term "resin particles" as used herein means a resin that is dispersed in an aqueous medium and can 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.

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 made of acrylic resin are preferred. The acrylic resin is a resin containing a unit derived from a monomer having a (meth)acryloyl group such as acrylic acid or methacrylic acid, or an alkyl (meth)acrylate. Examples of monomers constituting the acrylic resin include monomers having a hydrophilic group and monomers having a hydrophobic group.

Examples of monomers having a hydrophilic group include acidic monomers having a carboxy group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; anionic monomers such as anhydrides and salts of these acidic monomers; ) Monomers having a hydroxy group such as 2-hydroxyethyl acrylate and 3-hydroxypropyl (meth)acrylate; Monomers having an ethylene oxide group such as methoxy (mono, di, tri, poly)ethylene glycol (meth)acrylate ; and so on.

Monomers with hydrophobic groups include monomers with aromatic rings such as styrene, α-methylstyrene, and benzyl (meth)acrylate; ethyl (meth)acrylate, methyl (meth)acrylate, (iso)propyl (meth)acrylate , (n-, iso-, t-)butyl (meth)acrylate, and monomers having aliphatic groups such as 2-ethylhexyl (meth)acrylate.

The volume-based cumulative 50% particle diameter (D50) of the resin particles is preferably 100 nm or less. When the volume-based cumulative 50% particle diameter (D50) of the resin particles exceeds 100 nm, light scattering by the resin particles tends to occur, and the color development of the image may deteriorate somewhat. The volume-based cumulative 50% particle diameter (D50) of the resin particles is preferably 50 nm or more. 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 color development 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 ejection stability of the ink may be slightly reduced.

[Method for producing dyed 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. Examples of methods for dyeing the resin particles include a method in which a monomer mixture in which a fluorescent dye is dissolved is polymerized to form resin particles; a method in which a fluorescent dye is added to resin particles and heated; and the like. Among these, the method of adding a fluorescent dye to resin particles and heating is preferred because it can be applied to a wider variety of fluorescent dyes. Note that during heating, it is preferable not to add dyeing aids (water-soluble resin, surfactant, etc.). When a water-soluble resin is used as a dyeing aid, the water-soluble resin may form a film and inhibit the redispersion of resin particles, and the fixation recovery property of the ink may be slightly reduced. Furthermore, when a surfactant is used as a dyeing aid, the physical properties of the ink may be affected, and the ejection stability of the ink may be slightly reduced.

[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.

(Water-soluble resin)
The ink contains a water-soluble resin having an anionic group. The water-soluble resin may be any resin having an anionic group, and examples thereof include acrylic resin, urethane resin, polyester resin, and polyolefin resin. Among these, at least one of acrylic resin and urethane resin is preferred from the viewpoint of ink ejection properties. Furthermore, from the viewpoint of recording images with better scratch resistance, urethane resins are preferred.

As the acrylic resin, it is preferable to use a copolymer having a hydrophilic unit and a hydrophobic unit having an anionic group.

Specific examples of monomers that become hydrophilic units through polymerization include (meth)acrylic acid, crotonic acid, ethacrylic acid, propyl acrylic acid, isopropylacrylic acid, itaconic acid, maleic acid, fumaric acid, etc. having a carboxylic acid group. Acid monomers; acid monomers having sulfonic acid groups such as styrene sulfonic acid, sulfonic acid-2-propylacrylamide, butylacrylamide sulfonic acid; ethyl (meth)acrylic acid-2-phosphonate, ethyl acrylic acid-2-phosphonate, etc. Acid monomers having a phosphonic acid group; examples include anhydrides and salts of these acid monomers. The cations constituting the acid monomer salt include cations of alkali metals such as lithium, sodium, and potassium; ammonium ions (NH ₄ ⁺ ); and cations of organic ammoniums such as dimethylamine and triethanolamine. can. Among these, it is preferable to use a water-soluble resin having a hydrophilic unit derived from (meth)acrylic acid.

Specific examples of monomers that become hydrophobic units through polymerization include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, and 2-(meth)acrylate. (Meth)acrylate esters of aliphatic alcohols such as ethylhexyl, nonyl (meth)acrylate, lauryl (meth)acrylate; styrene, α-methylstyrene, pt-butylstyrene, phenyl (meth)acrylate, ( Examples include monomers having an aromatic ring such as benzyl meth)acrylate. Among these, it is preferable to use a water-soluble resin having a hydrophobic unit derived from a (meth)acrylic acid ester of an aliphatic alcohol or a monomer having an aromatic ring.

The anionic group may form a salt. Examples of cations that form salts include cations of alkali metals such as lithium, sodium, and potassium; ammonium ions (NH ₄ ⁺ ); and cations of organic ammoniums such as dimethylamine and triethanolamine.

As the urethane resin, for example, one obtained by reacting a polyol and a polyisocyanate can be suitably used. In addition to these, components that serve as chain extenders and crosslinking agents may be further reacted.

Examples of the polyol include polyols having anionic groups; polyols having no acid groups such as polyether polyols, polyester polyols, and polycarbonate polyols. A polyol having an anionic group becomes a hard segment of a urethane resin, and a unit derived from a polyol having an anionic group can be particularly preferably used to adjust the acid value of the urethane resin. Further, since a polyol having no anionic group becomes a soft segment of the urethane resin, it can be suitably used to increase the flexibility of the urethane resin and improve the marker resistance of images.

Examples of polyols having anionic groups include polyols containing anionic groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups. As the polyol having an anionic group, polyols having a carboxylic acid group such as dimethylol acetic acid, dimethylol propionic acid, dimethylol butanoic acid, and dimethylol butyric acid are preferable. More preferred are dimethylolpropionic acid and dimethylolbutanoic acid.

Examples of polyols without anionic groups include polyester polyols, polyether polyols, polycarbonate polyols, and the like. Among these, it is preferable to use a urethane resin having a unit derived from a polyether polyol.

Examples of polyester polyols include acid esters. Acid components (anionic components) constituting the acid ester include aromatic dicarboxylic acids such as phthalic acid, naphthalene dicarboxylic acid, biphenyl dicarboxylic acid, and tetrahydrophthalic acid; alicyclic acids such as hydrogenated products of the above aromatic dicarboxylic acids; Dicarboxylic acids; malonic acid, succinic acid, tartaric acid, oxalic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, alkylsuccinic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid , aliphatic dicarboxylic acids such as itaconic acid, and the like. Furthermore, anhydrides and derivatives (alkyl esters and acid halides) of these anionic components can also be used as anionic components.

In addition, examples of the component that forms an ester with the anionic component include glycols such as (poly)alkylene glycol; polyhydric alcohols such as diols and triols; and the like. Examples of the (poly)alkylene glycol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly(1,2-butylene glycol), poly(1,3-butylene glycol), ethylene glycol-propylene glycol copolymer, etc. be able to. Examples of diols include hexamethylene glycol, tetramethylene glycol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 4,4'-dihydroxyphenylpropane, 4,4 Examples include '-dihydroxyphenylmethane. Examples of the trivalent or higher polyhydric alcohol include glycerin, trimethylolpropane, 1,2,5-hexanetriol, 1,2,6-hexanetriol, and pentaerythritol.

Examples of the polyether polyol include addition polymers of alkylene oxide and polyhydric alcohols; glycols such as (poly)alkylene glycol; and the like. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, and α-olefin oxide. Examples of polyhydric alcohols and glycols include those exemplified as components constituting the polyester polyol described above.

As the polycarbonate polyol, a polycarbonate polyol manufactured by a known method can be used. Specific examples include alkanediol-based polycarbonate diols such as polyhexamethylene carbonate diol. Other examples include polycarbonate diols obtained by reacting carbonate components such as alkylene carbonate, diaryl carbonate, dialkyl carbonate, and phosgene with aliphatic diol components.

Examples of the polyisocyanate that forms the hard segment of the urethane resin and serves as a hydrophobic unit include aliphatic and aromatic polyisocyanates.

Examples of aliphatic polyisocyanates include tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and 2-methylpentane-1. , 5-diisocyanate, 3-methylpentane-1,5-diisocyanate, and other polyisocyanates having a chain structure; isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, Examples include polyisocyanates having a cyclic structure such as methylcyclohexylene diisocyanate and 1,3-bis(isocyanatomethyl)cyclohexane.

Examples of aromatic polyisocyanates include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, and 1,5-naphthylene diisocyanate. Examples include isocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α,α,α,α-tetramethylxylylene diisocyanate.

A chain extender or a crosslinking agent may be used in the urethane resin. Generally, a crosslinking agent is used during the synthesis of a prepolymer, and a chain extender is used when performing a chain extension reaction after the synthesis of the prepolymer. Basically, chain extenders and crosslinking agents should be appropriately selected from polyisocyanates, polyols, polyamines, etc., including those listed above, depending on the desired use such as chain extension and crosslinking. Can be done. As a chain extender, one that can crosslink the urethane resin can also be used.

The chain extender is a compound that reacts with the remaining isocyanate groups that have not formed urethane bonds in the polyisocyanate units of the urethane prepolymer. In addition to those listed above, chain extenders that can be suitably used include trimethylolmelamine and its derivatives, dimethylolurea and its derivatives, dimethylolethylamine, diethanolmethylamine, dipropanolethylamine, dibutanolmethylamine. , ethylenediamine, propylenediamine, diethylenetriamine, hexylenediamine, triethylenetetramine, tetraethylenepentamine, isophoronediamine, xylylenediamine, diphenylmethanediamine, hydrogenated diphenylmethanediamine, polyvalent amine compounds such as hydrazine, polyamide polyamine, polyethylene polyimine etc. can be mentioned.

In order to give the urethane resin a crosslinked structure, a trifunctional or more functional chain extender can be used. In addition to those listed above, trimethylolmelamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and the like can be used as chain extenders capable of forming a crosslinked structure in a urethane resin. Among these, it is preferable to use trifunctional or higher functional polyamines because they have excellent reactivity with isocyanate groups. Among the trifunctional or higher functional polyamines, it is preferable to use diethylenetriamine and triethylenetetramine. This is because diethylenetriamine and triethylenetetramine have three or four amino groups, respectively, so that they can efficiently react with residual isocyanate groups to form a crosslinked structure, and they also have an appropriately flexible molecular structure.

The acid value of the water-soluble resin having an anionic group is preferably 40 mgKOH/g or more and 300 mgKOH/g or less. In the case of acrylic resin, the acid value is preferably 250 mgKOH/g or less, more preferably 240 mgKOH/g or less. In the case of urethane resin, the acid value is preferably 200 mgKOH/g or less, more preferably 160 mgKOH/g or less.

The content (mass%) of the water-soluble resin having an anionic group in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, and 0.3% by mass, based on the total mass of the ink. More preferably, the content is 5.0% by mass or less. One type or two or more types of water-soluble resins can be used as necessary. The combination of water-soluble resins that can be used together is not limited. For example, multiple types of acrylic resins with different compositions may be used, multiple types of urethane resins with different compositions may be used, or multiple types of acrylic resins and urethane resins may be used.

(Nonionic surfactant)
The ink contains a nonionic surfactant. As the nonionic surfactant, a hydrocarbon nonionic surfactant is preferred. Examples of the hydrocarbon-based nonionic surfactant include polyoxyethylene alkyl ether, ethylene oxide adduct of acetylene glycol, polyethylene glycol polypropylene glycol block copolymer, and the like.

The ink may further contain a surfactant other than the nonionic surfactant. Other surfactants include hydrocarbon surfactants, fluorine surfactants, silicone surfactants, and the like. Other surfactants may be any of anionic surfactants, cationic surfactants, and amphoteric surfactants. The content (mass%) of the surfactant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and 0.2% by mass or more and 1.5% by mass, based on the total mass of the ink. % or less is more preferable.

(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, 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.

(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. In addition, the ink may contain various additives such as pH adjusters, rust preventives, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, and other resins, as necessary. It may also contain an agent.

(Physical properties of ink)
The dynamic surface tension of the ink at a lifetime of 10 milliseconds measured by the maximum bubble pressure method is 40 mN/m or less. Further, it is preferable that the dynamic surface tension of the ink at a lifetime of 10 milliseconds, as measured by the maximum bubble pressure method, be 35 mN/m or less, since an image with better gloss can be recorded.

The maximum bubble pressure method is a method that measures the maximum pressure required to release a bubble generated at the tip of a probe (tube) immersed in the liquid to be measured, and calculates the surface tension of the liquid from the measured maximum pressure. be. Specifically, the maximum pressure is measured while continuously generating bubbles at the tip of the probe. The time from when a new bubble surface is generated at the tip of the probe until reaching the maximum bubble pressure (the point when the radius of curvature of the bubble becomes equal to the radius of the tip of the probe) is called "lifetime." That is, the maximum bubble pressure method is a method of measuring the surface tension of a liquid in a moving state. The surface tension of the ink at 10 milliseconds measured by the maximum bubble pressure method is preferably 25 mN/m or more.

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 (static surface tension) of the ink at 25°C measured by the plate method is preferably 20 mN/m or more and 60 mN/m or less, and 25 mN/m or more and 45 mN/m or less. It is even more preferable that there be. 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.

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 aqueous dispersion of resin particles>
(Resin particle 1)
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 mixture for the core part was prepared by mixing 219.0 parts of styrene, 233.0 parts of acrylonitrile, and 14.0 parts of a reactive surfactant (trade name "Adekaria Soap SR-10", manufactured by ADEKA). did. 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.

Next, 15.2 parts of styrene, 12.0 parts of methacrylic acid, 32.0 parts of ethylene glycol dimethacrylate, 20.0 parts of ethylene glycol diglycidyl ether, and 0.8 parts of a reactive surfactant were mixed to form a shell part. A monomer mixture was prepared. As the ethylene glycol diglycidyl ether, the trade name "Denacol EX-810" (manufactured by Nagase ChemteX) was used. Moreover, the reactive surfactant is the same as that used in the synthesis of the core part. Aqueous solution 2 of polymerization initiator was prepared by mixing 0.1 part of potassium persulfate and 133 parts of water. 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.

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. Furthermore, C. I. 23.2 parts of Basic Red 1 (powder), and C.I. I. 5.8 parts of Basic Violet 11 (powder) was added, the temperature was raised to 80°C, and the mixture was stirred for 2 hours to dye the resin particles with the fluorescent dye. Next, 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 resin particles 1 having a resin particle content of 20.0%. The particle diameter (volume-based cumulative 50% particle diameter) of the obtained resin particles 1 was 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.

(Resin particles 2)
C. I. An aqueous dispersion of resin particles 2 having a resin particle content of 20.0% was obtained in the same manner as the resin particles 1 described above except that 29.0 parts of Basic Red 1 was used as the fluorescent dye.

(Resin particles 3)
C. I. An aqueous dispersion of resin particles 3 having a resin particle content of 20.0% was obtained in the same manner as the resin particles 1 described above except that 29.0 parts of Basic Violet 11 was used as the fluorescent dye.

(Resin particles 4)
C. I. An aqueous dispersion of resin particles 4 having a resin particle content of 20.0% was obtained in the same manner as the resin particles 1 described above except that 29.0 parts of Basic Yellow 40 was used as the fluorescent dye.

<Synthesis of water-soluble resin>
(Acrylic resin 1)
200.0 parts of ethylene glycol monobutyl ether was placed in a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas introduction tube, nitrogen gas was introduced, and the temperature was raised to 130° C. while stirring. A mixture of 63 parts of styrene, 15 parts of n-butyl acrylate, 22 parts of acrylic acid, and 4.0 parts of a polymerization initiator (t-butyl peroxide) was dropped into the flask over 3 hours. After completion of the dropwise addition, the mixture was aged for 2 hours, and ethylene glycol monobutyl ether was removed under reduced pressure to obtain a solid resin. The obtained resin was added to ion-exchanged water containing potassium hydroxide in an equimolar amount to its acid value, and stirred at 80°C, so that the content of acrylic resin 1, which is a water-soluble resin, was 20.0%. An aqueous solution of acrylic resin 1 having an anionic group was obtained. The acid value of acrylic resin 1 was 120 mgKOH/g. The acid value of the resin is determined by using a potassium hydroxide ethanol titration solution using a potentiometric automatic titrator (trade name "AT510", manufactured by Kyoto Denshi Kogyo) using a resin solution prepared by dissolving the resin in tetrahydrofuran as the sample to be measured. It was determined by potentiometric titration.

(Acrylic resin 2)
The content of acrylic resin 2, which is a water-soluble resin, was 20.0 in the same manner as in the above-mentioned acrylic resin 1, except that 72 parts of styrene, 20 parts of n-butyl acrylate, and 8 parts of acrylic acid were used as monomers. % of anionic group-containing acrylic resin 2 was obtained. The acid value of acrylic resin 2 was 40 mgKOH/g.

(Urethane resin 1)
A four-necked flask equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux tube was prepared. Into this flask were placed 30.3 parts of isophorone diisocyanate, 22.9 parts of hexamethylene diisocyanate, 118.1 parts of polypropylene glycol having a number average molecular weight of 2,000, 28.7 parts of dimethylolpropionic acid, and 300 parts of methyl ethyl ketone. After reacting at 80° C. for 6 hours in a nitrogen gas atmosphere, 3.8 parts of ethylenediamine was added and reacting at 80° C. After cooling to 40° C., ion-exchanged water was added, and while stirring at high speed with a homomixer, water containing potassium hydroxide in an equimolar amount to the acid value of the resin was added. After distilling off methyl ethyl ketone under heating and reduced pressure, an appropriate amount of water was added to obtain an aqueous solution of urethane resin 1 having an anionic group in which the content of urethane resin 1, which is a water-soluble resin, was 20.0%. Ta. The acid value of urethane resin 1 was 60 mgKOH/g.

(Urethane resin 2)
Polycarbonate diol having a number average molecular weight of 2,000 was used in place of polypropylene glycol. Except for this, an aqueous solution of urethane resin 2 having an anionic group was obtained in the same manner as urethane resin 1 described above, in which the content of urethane resin 2, which is a water-soluble resin, was 20.0%. The acid value of urethane resin 2 was 60 mgKOH/g.

(Urethane resin 3)
In place of polypropylene glycol, 146.8 parts of polycarbonate diol having a number average molecular weight of 2,000 was used, and dimethylolpropionic acid was not used. Except for this, an aqueous solution of urethane resin 3 having no anionic group was obtained in the same manner as urethane resin 1 described above, in which the content of urethane resin 3, which is a water-soluble resin, was 20.0%. The acid value of urethane resin 3 was 0 mgKOH/g.

<Preparation of surfactant>
Surfactants of the types shown in Table 1 were prepared.

<Preparation of ink>
After mixing each component (unit: %) shown in the upper row of Tables 2-1 and 2-2 and stirring thoroughly, pressure filtration was performed using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. An ink was prepared. The dynamic surface tension of the ink at a lifetime of 10 milliseconds measured by the maximum bubble pressure method is shown in the lower rows of Tables 2-1 and 2-2.

<Preparation of recording medium>
Recording media of the types shown in Table 3 were prepared.

<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.

(Method of measuring contact angle)
The contact angle between the recording medium and the ink was measured using a dynamic contact angle measuring device equipped with a recording head that discharges ink and a camera for observing droplets. Specifically, first, ink droplets each having a volume of 40 pL±10% were ejected from the recording head. The state of the ink droplets was photographed using a droplet observation camera from immediately after the ink droplets adhered to the recording medium until a predetermined period of time had elapsed. After a predetermined period of time had elapsed, the contact angle between the recording medium and the ink was measured from the photographed image. The measurement results are shown in Table 4.

(Abrasion resistance)
Using the above inkjet recording apparatus and the combinations of inks and recording media shown in Table 4, a solid image of 3 cm in length x 10 cm in width was recorded with a recording duty of 100%. Thirty minutes after recording, Silbon paper and a weight with a surface pressure of 222 g/cm ² were placed on top of the solid image, and the solid image and Silbon paper were rubbed together. Thereafter, the Silbon paper and the weight were removed, the state of dirt on the Silbon paper was visually confirmed, and the scratch resistance of the image was evaluated according to the evaluation criteria shown below.
A: Silbon paper was not soiled.
B: Silbon paper was dirty, but no white background was visible in the solid image area.
C: A white background was visible in the solid image.

(Glossiness)
Using the above inkjet recording apparatus and the combinations of inks and recording media shown in Table 4, a solid image of 3 cm in length x 10 cm in width was recorded with a recording duty of 100%. One day after recording, two fluorescent lamps placed 10 cm apart were used as observation light sources, and a fluorescent lamp was projected onto the solid 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 glossiness of the image was evaluated according to the evaluation criteria shown below.
A: Two fluorescent lights were clearly projected on the image.
B: The edges of the two projected fluorescent lights were slightly blurred.
C: I couldn't see the boundary between the two projected fluorescent lights.

Note that the disclosure of this embodiment includes the following methods and configurations.
(Method 1) An inkjet recording method in which an image is recorded on a recording medium by discharging water-based ink from an inkjet recording head, the method comprising:
The water-based ink contains resin particles dyed with a fluorescent basic dye, a water-soluble resin having an anionic group, and a nonionic surfactant,
The dynamic surface tension of the aqueous ink at a lifetime of 10 milliseconds measured by a maximum bubble pressure method is 40 mN/m or less,
An inkjet recording method characterized in that a contact angle of the recording medium with the aqueous ink measured 50 milliseconds after contact with the aqueous ink is 10° or more.
(Method 2) The inkjet recording method according to Method 1, wherein the contact angle of the recording medium with the aqueous ink measured 100 milliseconds after contact with the aqueous ink is 10° or more.
(Method 3) The inkjet recording method according to Method 1 or 2, wherein the aqueous ink has a dynamic surface tension of 35 mN/m or less at a lifetime of 10 milliseconds, as measured by a maximum bubble pressure method.
(Method 4) The inkjet recording method according to any one of Methods 1 to 3, wherein the water-soluble resin is at least one of an acrylic resin and a urethane resin.
(Method 5) The inkjet recording method according to any one of Methods 1 to 3, wherein the water-soluble resin is a urethane resin.
(Method 6) The inkjet recording method according to any one of Methods 1 to 5, wherein the resin particles are resin particles dyed with two or more types of the basic dyes.
(Structure 1) An inkjet recording apparatus comprising aqueous ink and an inkjet recording head that discharges the aqueous ink onto a recording medium,
The water-based ink contains resin particles dyed with a fluorescent basic dye, a water-soluble resin having an anionic group, and a nonionic surfactant,
The dynamic surface tension of the aqueous ink at a lifetime of 10 milliseconds measured by a maximum bubble pressure method is 40 mN/m or less,
An inkjet recording apparatus characterized in that a contact angle of the recording medium with the aqueous ink measured 50 milliseconds after contact with the aqueous ink is 10° or more.

Claims (7)

An inkjet recording method that records an image on a recording medium by discharging water-based ink from an inkjet recording head, the method comprising:
The water-based ink contains resin particles dyed with a fluorescent basic dye, a water-soluble resin having an anionic group, and a nonionic surfactant,
The dynamic surface tension of the aqueous ink at a lifetime of 10 milliseconds measured by a maximum bubble pressure method is 40 mN/m or less,
An inkjet recording method characterized in that a contact angle of the recording medium with the aqueous ink measured 50 milliseconds after contact with the aqueous ink is 10° or more. The inkjet recording method according to claim 1, wherein the contact angle of the recording medium with the aqueous ink measured 100 milliseconds after contact with the aqueous ink is 10° or more. 2. The inkjet recording method according to claim 1, wherein the aqueous ink has a dynamic surface tension of 35 mN/m or less at a lifetime of 10 milliseconds, as measured by a maximum bubble pressure method. The inkjet recording method according to any one of claims 1 to 3, wherein the water-soluble resin is at least one of an acrylic resin and a urethane resin. The inkjet recording method according to any one of claims 1 to 3, wherein the water-soluble resin is a urethane resin. 4. The inkjet recording method according to claim 1, wherein the resin particles are resin particles dyed with two or more kinds of the basic dyes. An inkjet recording apparatus comprising an aqueous ink and an inkjet recording head that ejects the aqueous ink onto a recording medium,
The water-based ink contains resin particles dyed with a fluorescent basic dye, a water-soluble resin having an anionic group, and a nonionic surfactant,
The dynamic surface tension of the aqueous ink at a lifetime of 10 milliseconds measured by a maximum bubble pressure method is 40 mN/m or less,
An inkjet recording apparatus characterized in that a contact angle of the recording medium with the aqueous ink measured 50 milliseconds after contact with the aqueous ink is 10° or more.

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