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

Abstract

To provide aqueous fluorescent ink capable of recording an image of a fluorescent color excellent in color development property and light resistance, an ink cartridge using the aqueous fluorescent ink, and an inkjet recording method.SOLUTION: There is provided an aqueous fluorescent ink for inkjet containing resin particles dyed with a fluorescent dye, and a quinacridone pigment. The fluorescent dye contains a basic dye having a xanthene skeleton. The resin particles contain a cyano group-containing unit. A mass ratio of a content (mass%) of the quinacridone pigment to a content (mass%) of the fluorescent dye is 1.0 time or less. There are also provided an ink cartridge having an ink storage part for storing the aqueous fluorescent ink, and an inkjet recording method for discharging the aqueous fluorescent ink from an inkjet type recording head, and recording an image on a recording medium.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous fluorescent ink, an ink cartridge, and an inkjet recording method.

Background Art

[0002] In the printing industry, an expansion of the expressible color gamut is demanded. Examples of color gamut standards include PANTONE certification (X-rite), Japan Color certification (Japan Printing Machinery Industry Association), DIC Color Guide certification (DIC), Kaleido certification (Toyobo Ink), and the like. In recent years, for color gamut expansion, inkjet recording apparatuses that employ special inks other than the basic colors of cyan, magenta, and yellow, and high-brightness special color inks have come to be used.

[0003] Another need in the printing industry is the production of recorded matter with a vivid color tone that attracts attention. For example, posters and POP displays, and packaging of food and beverage products are required to be recorded in vivid colors in order to attract the customer's line of sight. And it can be said that fluorescent colors are effective in meeting such needs. So far, fluorescent materials suitable for paints and inks have been proposed (Patent Document 1). However, at present, fluorescent materials having sufficient inkjet suitability have not yet been established.

[0004] On the other hand, inks added with fluorescent dyes have been proposed in order to improve the color development property in an image in the magenta region recorded with pigment ink (Patent Documents 2 and 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

[0006] Currently, offset printing is the dominant method for recording fluorescent images. However, when recording fluorescent images with a single offset print, it is difficult to achieve vivid colors, so it has been common practice to perform two or more overprints. Therefore, recording fluorescent images with excellent color reproduction through overprinting has presented challenges in terms of productivity and cost.

[0007] Furthermore, in the case of digital recording using electrophotography, it is possible to record highly vibrant fluorescent images using liquid toner. However, electrophotography has limitations in terms of recording media, making it difficult to apply to, for example, textile recording, large format printing, and thick materials.

[0008] In contrast, digital recording using the inkjet method can be applied to various recording media by taking advantage of the fact that the recording head that ejects the ink does not come into contact with the recording medium (it is contactless). However, because ink is ejected from a micron-order minute nozzle by applying mechanical or thermal energy, it is susceptible to constraints on the physical properties of the ink, such as viscosity. In particular, many of the materials that affect the performance of the ink, such as colorants and resins, are solids, and in order to add these materials to the ink they need to be dissolved or dispersed in a liquid medium such as water or organic solvents, which limits the amount that can be added to the ink. The same applies to fluorescent colorants such as fluorescent dyes; even if one tries to add a sufficient amount of fluorescent colorant to the ink in order to record an image with excellent color development, constraints arise in terms of the physical properties of the ink.

[0009] Furthermore, fluorescent dyes decompose in a chain reaction when their molecules react with radicals generated by light (ultraviolet light) or ozone. This has been found to cause problems with the lightfastness of images. Using the inks proposed in Patent Documents 2 and 3, it is possible to improve the color reproduction (saturation) of images in the magenta region that are recorded. However, the color reproduction required for fluorescent images, such as high saturation and brightness as well as excellent fluorescence intensity, is still not sufficient, and there is room for further improvement.

[0010] Therefore, an object of the present invention is to provide an aqueous fluorescent ink capable of recording fluorescent images with excellent color development and lightfastness. Another object of the present invention is to provide an ink cartridge using this aqueous fluorescent ink and an inkjet recording method. [Means for solving the problem]

[0011] In other words, according to the present invention, an aqueous fluorescent ink for inkjet use containing resin particles dyed with a fluorescent dye and a quinacridone pigment, wherein the fluorescent dye includes a basic dye having a xanthene skeleton, the resin particles include a cyano group containing unit, and the content (mass%) of the quinacridone pigment is 1.0 times or less by mass ratio to the content (mass%) of the fluorescent dye. The basic dye is at least one selected from the group consisting of CI Basic Red 1, CI Basic Red 1:1, CI Basic Violet 11, and CI Basic Violet 11:1; the quinacridone pigment is at least one selected from the group consisting of CI Pigment Red 122, CI Pigment Red 202, and CI Pigment Violet 19, and solid solution pigments comprising at least one of these; and the cyano group-containing unit is a unit derived from at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile. A water-based fluorescent ink is provided that has the following characteristics. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an aqueous fluorescent ink capable of recording fluorescent images with excellent color development and lightfastness. Furthermore, according to the present invention, it is possible to provide an ink cartridge using this aqueous fluorescent ink and an inkjet recording method. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. [Figure 2]This figure schematically shows an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. [Modes for carrying out the invention]

[0014] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, water-based fluorescent ink for inkjet printing may be simply referred to as "ink." Unless otherwise specified, the physical properties are values ​​at room temperature (25°C). In the present invention, the "unit" constituting the resin means a repeating unit derived from one monomer.

[0015] The inventors of this invention have investigated the composition of an ink capable of recording fluorescent images with excellent color development and lightfastness. In particular, in order to improve the color development of images, they focused on expanding the color gamut in the high-brightness region, which is difficult to express with basic colors. To expand the color gamut in the high-brightness region, it is preferable to use a fluorescent dye as a colorant.

[0016] Among fluorescent dyes, basic dyes with a xanthene skeleton are effective in expanding the color gamut. However, it has been found that fluorescent dyes decompose through a chain reaction with radicals generated when their molecules are exposed to light (ultraviolet light) or ozone, resulting in reduced image lightfastness. Therefore, the inventors investigated means that can expand the color gamut and suppress the decrease in lightfastness in the high-brightness region, and found that using quinacridone pigment in addition to basic dyes with a xanthene skeleton that exhibit fluorescence is effective. Hereinafter, "basic dyes with a xanthene skeleton that exhibit fluorescence" may simply be referred to as "fluorescent dyes."

[0017] The inventors attempted to add a fluorescent dye itself to the ink. However, it was found that when the addition amount of the fluorescent dye was increased to achieve the desired level of color development, although the chroma of the image improved, the brightness significantly decreased. This is considered to be due to concentration quenching peculiar to fluorescent materials. From the above, it was found that it is essential to dye the fluorescent dye onto resin particles and then add them to the ink. When the fluorescent dye is dyed onto the resin particles, the fluorescent dye is fixed to the resin particles, so that a decrease in the color development property (brightness) of the image can be suppressed.

[0018] As general methods for dyeing a fluorescent dye onto resin particles, there are: (i) a method called the addition-condensation bulk resin pulverization method, in which a bulk resin is condensed and dyed and then pulverized to obtain particles; and (ii) a method of producing resin particles by emulsion polymerization in an aqueous system and then dyeing them. The resin particles obtained by the method (i) have a size on the micron order and low water dispersibility, so it is difficult to apply them to inks used in inkjet recording methods. On the other hand, the resin particles obtained by the method (ii) have applicability to an aqueous system and their size can be controlled to the nano order, so they are excellent in inkjet suitability. However, when the color development property was examined using an ink containing conventional resin particles produced by the method (ii), it was found that several problems occurred.

[0019] Therefore, the inventors examined the color development property of an image recorded with an ink containing resin particles dyed with a fluorescent dye. To enhance the color development property of the image, it is important to dye the resin with the fluorescent dye by a strong interaction. For this reason, the inventors examined the composition of the resin particles for efficiently dyeing the fluorescent dye according to the characteristics of the fluorescent dye.

[0020] First, the inventors used a basic fluorescent dye having a positively polarized portion and a resin having a cyano group-containing unit as a negatively polarized group, and by dyeing the resin with the fluorescent dye using an electrostatic action, it was found that high color development property can be achieved.

[0021] Furthermore, fluorescent dyes have low lightfastness, and when using fluorescent dyes alone, radicals generated from the fluorescent dye attack nearby fluorescent dyes, leading to a chain reaction and decomposition, which was a problem. Therefore, the inventors conducted further investigations and found that using a fluorescent dye (a basic dye having a xanthene skeleton and exhibiting fluorescence) in combination with a quinacridone pigment can improve the lightfastness of images. In particular, it was found that using quinacridone pigment in combination with the aforementioned fluorescent dye can specifically improve lightfastness among various pigments. However, it was also found that even when using these pigments and dyes, depending on the ratio of quinacridone pigment to fluorescent dye, the balance between the color development and lightfastness required for fluorescent images may be insufficient. Specifically, the content (mass%) of quinacridone pigment in the ink should be 1.0 times or less by mass ratio to the content (mass%) of the fluorescent dye.

[0022] The inventors hypothesize the following reason why the above configuration allows for the recording of fluorescent images with excellent color development and lightfastness: Strong interactions occur due to the heterocycle of the xanthene skeleton, the π-π bond of the heterocycle of the quinacridone pigment, the hydrogen bond between the oxygen atom of the xanthene skeleton and the hydrogen atom of the quinacridone pigment, and the π-π bond of each aromatic group. Furthermore, when the mass ratio of quinacridone pigment to fluorescent dye (pigment / fluorescent dye) is 1.0 or less, the fluorescent dye is present around the quinacridone pigment on the recording medium to which the ink is applied. As a result, the quinacridone pigment receives radicals generated when light (ultraviolet light) or ozone strikes the fluorescent dye, suppressing the chain reaction of attack on the fluorescent dye by radicals. For these reasons, it is believed that color development and lightfastness can be improved in a balanced manner.

[0023] <Water-based fluorescent ink> The present invention is an aqueous fluorescent ink for inkjet use containing resin particles dyed with a fluorescent dye and a pigment. "Fluorescent ink" refers to an ink capable of recording fluorescent images. A fluorescent image refers to an image that emits fluorescence when excited by ultraviolet or visible light. The fluorescent dye is a basic dye having a xanthene skeleton. The pigment is a quinacridone pigment. The resin particles contain cyano group-containing units. The quinacridone pigment content (mass%) is 1.0 times or less by mass ratio to the fluorescent dye content (mass%).

[0024] The following describes each component that makes up the ink. The present invention is not limited by the following description unless it exceeds the gist of the invention. Hereinafter, when "(meth)acrylic acid," "(meth)acrylate," and "(meth)acryloyl" are written, they refer to "acrylic acid, methacrylic acid," "acrylate, methacrylate," and "acryloyl, methacryloyl," respectively. The ink of the present invention does not need to be curable by active energy rays, and therefore does not need to contain monomers having polymerizable groups.

[0025] (Fluorescent dyes) The ink contains resin particles dyed with a fluorescent dye. This fluorescent dye includes a basic dye having a xanthene skeleton, and preferably the fluorescent dye is a basic dye having a xanthene skeleton. The xanthene skeleton is represented by the following formula (1).

[0026] TIFF0007830174000001.tif22170

[0027] In this specification, "fluorescent dye" refers to a dye that emits fluorescence when excited by ultraviolet or visible light. Whether or not a dye is a "fluorescent dye" can be determined, for example, by the following method: Dissolve the dye in a liquid that can dissolve the dye to obtain a sample, and irradiate the sample with ultraviolet light (UV light) of a slightly visible long wavelength (approximately 315-400 nm) using a black light or the like. If light of a different color from the UV light irradiated by the black light can be observed with the naked eye, the dye can be determined to be a "fluorescent dye" that exhibits fluorescence. A commercially available black light (for example, product name "SLUV-4" (manufactured by AS ONE), etc.) can be used.

[0028] Fluorescent dyes in resin particles stained with fluorescent dyes can be analyzed, for example, by following the procedure shown below. Resin particles extracted from the ink by a conventional method are dissolved in an organic solvent such as chloroform to prepare a sample. The fluorescent dye is isolated from the prepared sample using HPLC (high-performance liquid chromatography). The isolated dye is analyzed using common structural analysis techniques such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS).

[0029] Basic dyes are fluorescent compounds that contain amino groups or imino groups (which may form salts) in their molecular structure. Examples of compounds containing amino groups or imino groups in their molecular structure include "dyes whose names in the Color Index include 'basic'." The Color Index is a database of colorants compiled by the British Dye and Color Society and other organizations.

[0030] Specific examples of basic dyes that exhibit fluorescence and have a xanthene skeleton, indicated by their CI numbers or common names, include CI Basic Red 1, 1:1, 4, 8, 11; CI Basic Violet 10, 11, 11:1; and Rhodamine 19, 575. Among these, CI Basic Red 1, 1:1 and CI Basic Violet 11, 11:1 are preferred due to their excellent color development.

[0031] The amount of fluorescent dye in the ink (mass%) is preferably 0.01% to 5.00% by mass, and more preferably 0.05% to 1.00% by mass, based on the total mass of the ink. The proportion of fluorescent dye in the resin particles (mass%) is preferably 1.0% to 15.0% by mass, and more preferably 1.0% to 8.0% by mass. If the proportion of fluorescent dye in the resin particles is less than 1.0% by mass, the color reproduction (saturation) of the image may be slightly reduced. On the other hand, if the proportion of fluorescent dye in the resin particles is greater than 15.0% by mass, the color reproduction (brightness) of the image may be slightly reduced due to density quenching.

[0032] (Quinacridone pigment) The ink contains quinacridone pigment. Quinacridone pigment is a pigment composed of compounds having a skeleton (quinacridone skeleton) represented by the following formula (2).

[0033] TIFF0007830174000002.tif36170

[0034] Specific examples of quinacridone pigments include CI Pigment Orange: 48, 49; CI Pigment Red: 122, 192, 202, 206, 207, 209; and CI Pigment Violet 19. Alternatively, solid solution pigments composed of two or more quinacridone pigments may be used. Solid solution pigments, also known as mixed crystals, are formed when two or more pigments dissolve together to create a uniform solid phase, and differ from simply mixing two or more pigments. As for quinacridone pigments, solid solution pigments composed of two or more quinacridone pigments are preferred. The crystal lattice of a solid solution pigment has a more complex structure than a crystal lattice composed of a single pigment. Using solid solution pigments facilitates multifaceted interactions with fluorescent dyes, making it easier for the fluorescent dye to be more reliably present around the quinacridone pigment, thus further improving the lightfastness of the image.

[0035] The pigment dispersion method may be a resin dispersion method using a resin dispersant, or a self-dispersion method in which anionic groups, etc., are bonded to the surface of the pigment particles. Among these, the resin dispersion method using a resin dispersant (resin-dispersed pigment) is preferred. Examples of resin-dispersed pigments include those in which resin is physically adsorbed and dispersed on the surface of the pigment particles, and microcapsule pigments in which at least a part of the surface of the pigment particles is coated with resin or the like.

[0036] The quinacridone pigment content (by mass) in the ink is preferably between 0.01% by mass and 0.70% by mass, based on the total mass of the ink. If the quinacridone pigment content is less than 0.01% by mass, the lightfastness of the image may be slightly reduced. On the other hand, if the quinacridone pigment content exceeds 0.70% by mass, the color reproduction (brightness) of the image may be slightly reduced.

[0037] The quinacridone pigment content (mass%) in the ink is 1.0 times or less in mass ratio to the fluorescent dye content (mass%). In other words, unlike conventional techniques that use fluorescent dyes as an aid to improve the color development of pigment inks, the fluorescent dye content in the ink is greater than or equal to the quinacridone pigment content in order to create an ink that can record fluorescent images. If the above mass ratio exceeds 1.0 times, there will be too much quinacridone pigment compared to the fluorescent dye, reducing the vividness of the fluorescent color and resulting in insufficient color development (brightness) of the image. Furthermore, it is preferable that the quinacridone pigment content (mass%) is 0.1 times or more in mass ratio to the fluorescent dye content (mass%). If the above mass ratio is less than 0.1 times, there will be too little quinacridone pigment compared to the fluorescent dye, weakening the interaction and potentially reducing the effect of improving lightfastness.

[0038] The total content of fluorescent dye (by mass) and quinacridone pigment (by mass) in the ink is preferably 0.10% by mass or more and 1.50% by mass or less, based on the total mass of the ink. If the total content of fluorescent dye and quinacridone pigment is less than 0.10% by mass, the total amount of colorants is small, which may reduce the color reproduction of the image. On the other hand, if the total content of fluorescent dye and quinacridone pigment exceeds 1.50% by mass, if there is too much fluorescent dye, density quenching is likely to occur, and if there is too much pigment, the brightness-enhancing effect unique to fluorescent dyes is weakened, which may reduce the color reproduction (brightness) of the image.

[0039] (Resin particles) In this specification, "resin particles" means resin that is dispersed in an aqueous medium and can exist in the aqueous medium in a state having particle size. Therefore, the resin particles exist in a dispersed state in the ink, that is, in the state of a resin emulsion.

[0040] Whether a resin is "resin particles" or not can be determined by the following method. First, a liquid containing resin (resin solids content: 10% by mass) is prepared, neutralized with an alkali (such as sodium hydroxide or potassium hydroxide) with an acid value equivalent to the resin's value. 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 dynamic light scattering, if particles with a defined particle size are measured, the resin can be determined to be "resin particles." A particle size analyzer (for example, product name "UPA-EX150," manufactured by Nikkiso) can be used as the particle size distribution analyzer for dynamic light scattering. The measurement conditions in this case can be, for example, SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: perfectly spherical, refractive index: 1.59. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those described above. Measuring particle size using neutralized resin is done to confirm that particles are still formed even when the resin is sufficiently neutralized and less likely to form particles. Even under these conditions, resin with a granular structure exists in a granular state within water-based ink.

[0041] The resin particles contain cyano group-containing units. Preferably, the resin particles further contain anionic group-containing units. Furthermore, it is preferable that the resin particles have a so-called core-shell structure, having a core portion and a shell portion covering the core portion. And preferably, the shell portion contains anionic group-containing units. By using such resin particles, the ink ejection stability can be improved. Furthermore, it is preferable that the shell portion does not contain cyano group-containing units.

[0042] The monomers that become cyano group-containing units through polymerization are preferably those that have one polymerizable functional group, such as an ethylenically unsaturated bond, within the molecule. Specifically, examples include acrylonitrile, methacrylonitrile, chloroacrylonitrile, and 2-cyanoethyl (meth)acrylate. The monomers that become cyano group-containing units through polymerization are preferably those that do not have anionic or aromatic groups, and have a molecular weight of 300 or less, and more preferably those with a molecular weight of 200 or less. Among these, acrylonitrile and methacrylonitrile are particularly preferred because they exhibit good reactivity during polymerization and the resulting resin particles have excellent stability.

[0043] Examples of anionic groups in anionic group-containing units include carboxylic acid groups, phenolic hydroxyl groups, and phosphate ester groups. Among these, carboxylic acid groups are preferred because they provide good stability for resin particles in the ink. Monomers that become anionic group-containing units through polymerization are preferably those having one polymerizable functional group, such as an ethylenically unsaturated bond, within the molecule. Specifically, examples include (meth)acrylic acid, p-vinylbenzoic acid, 4-vinylphenol, β-carboxyethyl (meth)acrylate, phosphoric acid (methacrylate-2-hydroxyethyl) ester, 2-hydroxyethyl (meth)acrylate, and 3-hydroxypropyl (meth)acrylate. Monomers that become anionic group-containing units through polymerization are preferably those without a cyano group, or with a molecular weight of 300 or less, and even more preferably with a molecular weight of 200 or less. Among these, (meth)acrylic acid is particularly preferred. Furthermore, it is preferable that the anionic group in the anionic group-containing unit consists solely of a carboxylic acid group. The anionic group may be in either an acidic or salt form, and if it is in the salt form, it may be in either a partially dissociated or fully dissociated state. When the anionic group is in the salt form, examples of cations that become counterions include alkali metal cations, ammonium, and organic ammonium.

[0044] The resin particles may further contain other units, such as aliphatic group-containing units and aromatic group-containing units. The monomers that form the aliphatic group-containing units are preferably those having one polymerizable functional group, such as an ethylenically unsaturated bond, within the molecule. Among these, alkyl (meth)acrylates with 1 to 12 carbon atoms in the alkyl group portion are preferred. The monomers that form the aromatic group-containing units are also preferably those having one polymerizable functional group, such as an ethylenically unsaturated bond, within the molecule. Among these, styrene and its derivatives are even more preferred, and styrene and vinyltoluene are particularly preferred, due to their good reactivity during polymerization and the excellent stability of the resulting resin particles.

[0045] A crosslinking agent can be used when manufacturing resin particles. That is, resin particles having units derived from the crosslinking agent can be used. By using a crosslinking agent, it is possible to obtain resin particles having a core-shell structure that can suppress excessive hydrophilicity of the shell portion and improve ink adhesion recovery. Furthermore, by using two or more types of crosslinking agents, a dense crosslinked structure can be formed that can more efficiently suppress excessive hydrophilicity of the shell portion.

[0046] Surfactants can be used when manufacturing resin particles. Manufacturing resin particles in the presence of a surfactant is preferable because it tends to stabilize the particle size and shape of the resulting resin particles. However, non-reactive surfactants may easily detach from the resin particles. If surfactants detach from resin particles in ink, it can affect the physical properties of the ink, potentially reducing discharge stability. For this reason, reactive surfactants are preferred as surfactants used when manufacturing resin particles, as they are incorporated into the resin. In other words, resin particles having units derived from reactive surfactants can be used.

[0047] As the reactive surfactant, it is preferable to use a compound in which polymerizable functional groups such as (meth)acryloyl groups, maleyl groups, vinyl groups, and allyl groups are bonded to the interior or terminal of a molecule composed of a hydrophilic part and a hydrophobic part. Examples of the hydrophilic part include polyoxyalkylene chains such as ethylene oxide chains and propylene oxide chains. Examples of the hydrophobic part include alkyl, aryl, and combinations thereof. The hydrophilic and hydrophobic parts may be bonded via linking groups such as ether groups. The molecular weight of the reactive surfactant is preferably greater than 200, more preferably greater than 300, and particularly preferably 400 or more.

[0048] The mass ratio of the core portion to the shell portion of resin particles having a core-shell structure is preferably 50:50 to 95:5, and more preferably 60:40 to 90:10, with the total mass ratio being 100.

[0049] The resin particle content (mass%) in the ink is preferably 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink. If the resin particle content is less than 1.00% by mass, the color reproduction of the image may be slightly reduced. On the other hand, if the resin particle content exceeds 10.00% by mass, the ink ejection stability may be slightly reduced.

[0050] The content (mass%) of resin particles in the ink is preferably 9 to 100 times the mass ratio of the content (mass%) of quinacridone pigment. If the above mass ratio is less than 9 times, the resin particles stained with fluorescent dye will be less likely to be present around the quinacridone pigment on the recording medium to which the ink is applied, which may reduce the lightfastness of the image. On the other hand, if the above mass ratio exceeds 100 times, the amount of resin particles and stained fluorescent dye will be too large compared to the quinacridone pigment, resulting in a relatively small amount of quinacridone pigment, which may reduce the lightfastness of the image.

[0051] The cumulative 50% particle size (D50) of the volume-based particle size distribution of resin particles is preferably between 140 nm and 300 nm. If the cumulative 50% particle size of the volume-based particle size distribution of resin particles is less than 140 nm, some of the resin particles tend to sink in the thickness direction of the recording medium, which can reduce the amount of fluorescent dye present around the quinacridone pigment and decrease the lightfastness of the image. On the other hand, if the cumulative 50% particle size of the volume-based particle size distribution of resin particles exceeds 300 nm, the ink ejection stability may decrease.

[0052] [Method for manufacturing dyed resin particles] Resin particles can be manufactured according to conventionally known methods such as emulsion polymerization, miniemulsion polymerization, seed polymerization, and phase inversion emulsification. Methods for dyeing the resin particles include polymerizing a monomer mixture containing a dissolved fluorescent dye to form resin particles, and adding the fluorescent dye to the resin particles and heating them. Among these, the method of adding the fluorescent dye to the resin particles and heating them is preferred because it can be applied to a wider variety of fluorescent dyes.

[0053] [Method for verifying resin particles] The composition of the resin particles can be verified according to the methods shown in (i) to (iii) below. The following describes a method for extracting, analyzing, and verifying resin particles from ink, but resin particles extracted from aqueous dispersions, etc., can be similarly analyzed and verified.

[0054] (i) Extraction of resin particles Density gradient centrifugation allows for the separation and extraction of resin particles from ink containing them. Within density gradient centrifugation, the density gradient sedimentation velocity method separates and extracts resin particles based on the difference in the sedimentation coefficients of the components. Furthermore, the density gradient sedimentation equilibrium method separates and extracts resin particles based on the difference in density of the components.

[0055] (ii) Confirmation and separation of the layered structure First, the resin particles are stained and immobilized with ruthenium tetroxide, and then embedded in epoxy resin for stable retention. 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 the cross-section cut through the center of gravity of the resin particles, the layered structure of the resin particles can be confirmed. Using the resin particles embedded in epoxy resin as the analytical sample, STEM-EDX, which combines energy-dispersive X-ray spectroscopy (EDX), allows for quantitative analysis of the elements contained in the layers (core and shell) that make up the resin particles.

[0056] (iii) Analysis of the units (monomers) that make up each layer of resin The resin particles used as a sample for separating the resins of each layer may be in the form of a dispersion. Alternatively, the resin particles may be dried and formed into a film, which can then be used as the sample. After dissolving the resin particles to be used as a sample in an organic solvent, each layer is separated by gel permeation chromatography (GPC), and the resin constituting each layer is isolated. The isolated resin is then subjected to elemental analysis by combustion. Separately, the isolated resin is pretreated by acid decomposition (addition of hydrofluoric acid) or alkali fusion, and then the inorganic components are quantitatively analyzed by inductively coupled plasma atomic emission spectroscopy. By comparing the results of the elemental analysis and quantitative analysis of inorganic components with the results of the elemental quantitative analysis by STEM-EDX obtained in (ii) above, the layers of resin particles that constituted the isolated resin can be determined.

[0057] Furthermore, the separated resins are analyzed using nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS). This allows us to determine the types and proportions of the units (monomers) and crosslinking components that make up the resin. In addition, by analyzing the separated resins using pyrolysis gas chromatography, it is possible to directly detect the monomers produced by depolymerization.

[0058] (aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. The ink may further contain a water-soluble organic solvent as an aqueous medium. Deionized water or ion-exchanged water is preferred as the water. The water content (mass%) in the ink is preferably 50.00% by mass or more and 95.00% by mass or less based on the total mass of the ink. Any of the water-soluble organic solvents commonly used in inks can be used as the water-soluble organic solvent. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. The water-soluble organic solvent content (mass%) in the ink is preferably 3.00% by mass or more and 50.00% by mass or less based on the total mass of the ink.

[0059] (Other additives) In addition to the components mentioned above, the ink may also contain, as necessary, polyhydric alcohols such as trimethylolpropane and trimethylolethane, and water-soluble organic compounds that are solid at room temperature, such as urea and urea derivatives such as ethylene urea. Furthermore, the ink may also contain, as necessary, various additives such as water-soluble resins, undyed resin particles, surfactants, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, and other resins. The ink may also contain colorants such as dyes (including dyes that do not exhibit fluorescence and dyes that exhibit fluorescence other than basic dyes) and pigments other than quinacridone pigments, but usually, such colorants do not need to be included. When resins (water-soluble resins, resin particles) are used, acrylic resins are preferred, and urethane resins are not preferred.

[0060] (Physical properties of ink) Since the ink is an aqueous ink used in an inkjet system, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the ink at 25°C, as measured by the plate method, is preferably 20 mN / m to 60 mN / m, and more preferably 25 mN / m to 45 mN / m. The viscosity of the ink at 25°C is preferably 1.0 mPa·s to 10.0 mPa·s, and more preferably 1.0 mPa·s to 5.0 mPa·s. The pH of the ink at 25°C is preferably 7.0 to 10.0.

[0061] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0062] <Inkjet recording method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known origin.

[0063] Figure 2 is a schematic diagram showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 comprises recording heads 38 and 40 and is configured to hold an ink cartridge 42. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32. There are no particular restrictions on the recording medium 32, but it is preferable to use a recording medium with a paper base, such as a recording medium without a coating layer, such as plain paper, or a recording medium with a coating layer, such as glossy paper or matte paper. This recording medium does not need to be for transfer purposes. [Examples]

[0064] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0065] <Preparation of an aqueous dispersion of resin particles> A reaction vessel equipped with a stirring device was placed in a hot water bath. 1,178 parts of water were added to the reaction vessel, and the internal temperature was maintained at 70°C. The monomers shown in Table 1-1 were mixed in the amounts (parts) and percentages (%) shown in Table 1-1. This prepared the monomer mixture for the core. In addition, 1.9 parts of potassium persulfate and 659 parts of water were mixed to prepare aqueous polymerization initiator solution 1. The monomer mixture for the core and aqueous polymerization initiator solution 1 were added dropwise to the reaction vessel in parallel over 60 minutes. After the dropwise addition was complete, stirring was continued and the reaction was allowed to proceed for another 30 minutes to synthesize the particles that would form the core of the resin particles.

[0066] Next, the monomers shown in Table 1-1 were mixed in the amounts (parts) and percentages (%) shown in Table 1-1 to prepare a monomer mixture for the shell portion. In addition, 0.1 parts potassium persulfate and 133 parts water were mixed to prepare aqueous solution 2 of the polymerization initiator. The internal temperature of the reaction vessel containing the particles that would become the core portion was maintained at 80°C, and the monomer mixture for the shell portion and aqueous solution 2 of the polymerization initiator were added dropwise in parallel over 10 minutes. After the addition was complete, the reaction was continued by stirring for 120 minutes to synthesize the shell portion, and resin particles having a core-shell structure were synthesized in which the particles that would become the core portion were coated with the resin that would become the shell portion. However, a shell portion was not synthesized for resin particle 5. In addition, a crosslinking agent that would become a crosslinking agent unit was added to resin particle 6.

[0067] Subsequently, an appropriate amount of 8 mol / L potassium hydroxide aqueous solution was added to the reaction vessel to adjust the pH of the liquid to 8.5. Furthermore, the amount of fluorescent dye powder shown in Table 1-2 was added, and the temperature was raised to 80°C. After that, the mixture was stirred for 2 hours to allow the fluorescent dye to adhere to the resin particles. Next, an appropriate amount of 8 mol / L potassium hydroxide aqueous solution was added to the reaction vessel to adjust the pH of the liquid to 8.5. An appropriate amount of water was further added to obtain aqueous dispersions of each resin particle with a resin particle content of 20%. However, resin particle 19 was not dyed. The particle size of the resin particles (cumulative 50% particle size of the volume-based particle size distribution) is shown in Table 1-2. The particle size of the resin particles was measured using a dynamic light scattering particle size analyzer (product name "UPA-EX150", manufactured by Nikkiso) under the following conditions: SetZero: 30 seconds, Number of measurements: 3, Measurement time: 180 seconds, Shape: Spherical, Refractive index: 1.59.

[0068] The meanings of the abbreviations in Tables 1-1 and 1-2 are shown below. St: Styrene AN: Acrylonitrile • MAN: Methacrylonitrile • EMA: Ethyl methacrylate AA: Acrylic acid • MAA: Methacrylic acid • EDMA: Ethylene glycol dimethacrylate • EX-810: Ethylene glycol diglycidyl ether (product name "Denacol EX-810", manufactured by Nagase ChemteX) BR1: CI Basic Red 1 BR1:1:CI Basic Red 1:1 BV11: CI Basic Violet 11 · BV11:1:CI Basic Violet 11:1 SR49: CI Solvent Red 49

[0069] TIFF0007830174000003.tif165170

[0070] TIFF0007830174000004.tif164170

[0071] <Preparation of Pigment Dispersion> Pigment dispersions 1 to 6 were prepared. As the resin dispersant, a resin aqueous solution was used, which was obtained by neutralizing a styrene-acrylic acid random copolymer with an acid value of 120 mg KOH / g and a weight-average molecular weight of 10,000 with an equimolar amount of 10% potassium hydroxide aqueous solution. The pigment content in each pigment dispersion was 20.0%, and the resin content was 6.0%.

[0072] (Pigment dispersion 1) 20.0 parts pigment, 30.0 parts resin dispersant, and 50.0 parts water were mixed and dispersed in a sand grinder for 1 hour, after which undispersed material containing coarse particles was removed by centrifugation. As the pigment, a solid solution of CI Pigment Red 202 and CI Pigment Violet 19 (product name "Cromophtal Jet Magenta 2BC", manufactured by BASF) was used. Next, the mixture was pressure filtered through a 3.0 μm pore size microfilter (manufactured by Fujifilm) to prepare pigment dispersion 1.

[0073] (Pigment dispersion 2) Pigment dispersion 2 was obtained in the same manner as the preparation of pigment dispersion 1, except that the pigment was changed to a solid solution of CI Pigment Red 122 and CI Pigment Violet 19 (product name "FASTGEN SUPER MAGENTA RY", manufactured by DIC).

[0074] (Pigment dispersion 3) Pigment dispersion 3 was obtained in the same manner as the preparation of pigment dispersion 1, except that the pigment was changed to CI Pigment Red 122 (product name "PV Fast Pink E", manufactured by Clariant).

[0075] (Pigment dispersion 4) Pigment dispersion 4 was obtained in the same manner as the preparation of pigment dispersion 1, except that the pigment was changed to CI Pigment Violet 19 (product name "Ink Jet Magenta E5B02", manufactured by Clariant).

[0076] (Pigment dispersion 5) Pigment dispersion 5 was obtained in the same manner as the preparation of pigment dispersion 1, except that the pigment was changed to the azo pigment CI Pigment Red 41 (trade name "SUIMEI Dianisidine Red R", manufactured by Sansui Shikko).

[0077] (Pigment dispersion 6) Pigment dispersion 6 was obtained in the same manner as the preparation of pigment dispersion 1, except that the pigment was changed to CI Pigment Red 254 (trade name "Cromophtal DPP Red BP", manufactured by BASF), which is a diketopyrrolopyrrole pigment.

[0078] <Ink preparation> (Examples 1-29 and Comparative Examples 1-7) Each ink was prepared by mixing the components (in %) shown in the upper section of Tables 2-1 to 2-4, stirring thoroughly, and then pressure filtering through a 3.0 μm pore size microfilter (manufactured by Fujifilm). In Tables 2-1 to 2-4, "Acetylenel E100" is the trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals. The lower section of Tables 2-1 to 2-4 shows the properties of the inks, including Comparative Example 8, which will be described later. The pH of all prepared inks was within the range of 8.5 to 9.0.

[0079] TIFF0007830174000005.tif112170

[0080] TIFF0007830174000006.tif113170

[0081] TIFF0007830174000007.tif121170

[0082] TIFF0007830174000008.tif124170

[0083] (Comparative Example 8) In accordance with the description in "Example 1" of Patent Document 1, an ink for Comparative Example 8 containing the resin particles and pigment (CI Pigment Red 122) described later was prepared. These resin particles are single-layer resin particles composed of units derived from acrylonitrile, styrene, and acrylic acid, respectively, and are dyed with basic dyes (two types of fluorescent dyes) having a xanthene skeleton. The two types of fluorescent dyes are CI Basic Violet 11:1 and CI Basic Red 1 (0.3:2.0 (mass ratio)).

[0084] <Rating> Each prepared ink was filled into an ink cartridge and set in an inkjet recording device (product name "PIXUS Pro-10", manufactured by Canon) equipped with a recording head that ejects ink using thermal energy. In this inkjet recording device, an image recorded under the condition of applying 8 drops of 3.8 ng ± 10% ink to a unit area of ​​1 / 600 inch × 1 / 600 inch is defined as having a 100% recording duty cycle. The recording environment was set to a temperature of 25°C and a relative humidity of 55%. In this invention, "A" and "B" were defined as acceptable levels and "C" as unacceptable levels in the evaluation criteria for each item below. The evaluation results are shown in Table 3.

[0085] (Color development) Using the inkjet recording device described above, an image containing a tonal pattern with multiple solid images with different ink application amounts was recorded on a recording medium (glossy paper, product name "Photo Paper - Fine-grained Glossy Luster", manufactured by Canon). The tonal pattern consists of multiple 2cm x 2cm solid images, each recorded by gradually changing the ink application amount under the condition that a maximum of 6 drops of ink are applied to a 1 / 600 inch x 1 / 600 inch unit area. After drying the recorded image for one day, the hue angle (H(°)) and saturation (C) in the Lab color system were determined. * ), and brightness (L * ), and fluorescence intensity (maximum reflected light intensity in the wavelength range of 400-700 nm) were measured. For color measurement, the M1 light source of a spectrophotometer (product name "X-Rite eXact", manufactured by X-Rite) was used. The color reproduction of the image was then evaluated according to the evaluation criteria shown below. Brightness was evaluated using the value at a saturation of 50. However, if the maximum saturation did not reach 50, the data obtained by measuring the color of multiple solid images constituting the gradation pattern was extrapolated, and the calculated value of brightness obtained was used for evaluation. The reason why the evaluation criteria differ depending on the hue angle is that the preferred color tone perceived by the eye differs depending on the type of color. In fluorescent images, the intensity of reflected light is higher than that of incident light. Therefore, whether or not a recorded image exhibits fluorescence can be determined by whether or not the maximum reflected light intensity is 100% or more.

[0086] [When the hue angle is between 0° and less than 180°] A: The maximum reflected light intensity was 100% or more, and the maximum saturation was 70 or more and the lightness was 80 or more, or the maximum saturation was 65 or more and the lightness was 85 or more. B: The maximum reflected light intensity was 100% or more, the maximum saturation was 65 or more but less than 70, and the brightness was 80 or more but less than 85. C: The maximum reflected light intensity was less than 100%, the maximum saturation was less than 65, and the brightness was less than 80.

[0087] [When the hue angle is between 180° and less than 360°] A: The maximum reflected light intensity was 100% or more, and the maximum saturation was 70 or more and the brightness was 70 or more, or the maximum saturation was 65 or more and the brightness was 75 or more. B: The maximum reflected light intensity was 100% or more, the maximum saturation was 65 or more but less than 70, and the brightness was 70 or more but less than 75. C: The maximum reflected light intensity was less than 100%, the maximum saturation was less than 65, and the brightness was less than 70.

[0088] (Lightfastness) Using the inkjet recording device described above, a 2cm x 2cm solid image with a 100% recording duty cycle was recorded onto two recording media (glossy paper, product name "Photo Paper - Fine-grained Glossy Luster", manufactured by Canon). One of the recorded solid images was placed in a xenon test apparatus (product name "Atlas Weatherometer Ci4000", manufactured by Toyo Seiki Seisakusho) at a temperature of 30°C, relative humidity of 40%, and irradiation intensity of 1.25 W / m². 2 The solid color image was irradiated with xenon light for 18 hours under the specified conditions. Subsequently, the optical density (OD) of the solid color image irradiated with xenon light and the optical density (OD) of the solid color image not irradiated with xenon light were measured. Ini The optical density was measured using the same spectrophotometer as above. Then, the remaining optical density (%) = (OD / OD Ini The optical density retention rate was calculated based on the formula ) × 100 (%), and the lightfastness of the image was evaluated according to the evaluation criteria shown below. A: The optical density retention rate was 90% or higher. B: The remaining optical density was between 80% and 90%. C: The remaining optical density was less than 80%.

[0089] TIFF0007830174000009.tif152170

[0090] In Example 21, the ink ejection was unstable, resulting in some areas of the solid image used to evaluate color development and lightfastness showing areas where the ink was not ejected.

Claims

1. An aqueous fluorescent ink for inkjet use containing resin particles dyed with a fluorescent dye and a quinacridone pigment, The fluorescent dye comprises a basic dye having a xanthene skeleton, The resin particles include cyano group-containing units, The content (mass%) of the quinacridone pigment is 1.0 times or less in mass ratio to the content (mass%) of the fluorescent dye. The basic dye is at least one selected from the group consisting of C.I. Basic Red 1, C.I. Basic Red 1:1, C.I. Basic Violet 11, and C.I. Basic Violet 11:

1. The quinacridone pigment is at least one selected from the group consisting of C.I. Pigment Red 122, C.I. Pigment Red 202, and C.I. Pigment Violet 19, and solid solution pigments comprising at least one of these pigments. An aqueous fluorescent ink characterized in that the cyano group-containing unit is derived from at least one monomer selected from the group consisting of acrylonitrile and methacrylonitrile.

2. The aqueous fluorescent ink according to claim 1, wherein the sum of the content (by mass) of the fluorescent dye and the content (by mass) of the quinacridone pigment is 0.10% by mass or more and 1.50% by mass or less, based on the total mass of the ink.

3. The aqueous fluorescent ink according to claim 1 or 2, wherein the content (mass%) of the resin particles is 9 times or more and 100 times or less in mass ratio to the content (mass%) of the quinacridone pigment.

4. The aqueous fluorescent ink according to any one of claims 1 to 3, wherein the cumulative 50% particle diameter of the volume-based particle size distribution of the resin particles is 140 nm or more and 300 nm or less.

5. The aqueous fluorescent ink according to any one of claims 1 to 4, wherein the quinacridone pigment is a solid solution pigment composed of two or more quinacridone pigments.

6. The aqueous fluorescent ink according to any one of claims 1 to 5, wherein the content (by mass) of the quinacridone pigment is 0.1 times or more by mass relative to the content (by mass) of the fluorescent dye.

7. The aqueous fluorescent ink according to any one of claims 1 to 6, wherein the content (by mass) of the quinacridone pigment is 0.01% by mass or more and 0.70% by mass or less, based on the total mass of the ink.

8. The aqueous fluorescent ink according to any one of claims 1 to 7, wherein the content (mass%) of the resin particles is 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink.

9. The aqueous fluorescent ink according to any one of claims 1 to 8, wherein the content (by mass) of the fluorescent dye is 0.01% by mass or more and 5.00% by mass or less, based on the total mass of the ink.

10. The aqueous fluorescent ink according to any one of claims 1 to 9, wherein the proportion (by mass) of the fluorescent dye in the resin particles is 1.0% by mass or more and 15.0% by mass or less.

11. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is the aqueous fluorescent ink described in any one of claims 1 to 10.

12. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, An inkjet recording method characterized in that the ink is an aqueous fluorescent ink according to any one of claims 1 to 10.

Images