Inkjet recording method and inkjet recording apparatus

Abstract

To provide an inkjet recording method that can record a chromatic image having excellent light-emitting and color-developing properties by combinational use of an ink containing a fluorescent colorant and another ink containing a colorant.SOLUTION: By this inkjet recording method, a first ink containing a fluorescent colorant and a second ink containing a fluorescent colorant or a non-fluorescent colorant are discharged from an inkjet recording head onto a recording medium, thereby recording a chromatic image having a hue angle between the hue angle of the first ink and the hue angle of the second ink. The first ink and the second ink are applied onto the recording medium exclusively for each pixel so that they are partly adjacent to each other, thereby recording an image.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method. [Background technology]

[0002] In recent years, in commercial printing fields such as catalogs, brochures, and point-of-purchase (POP) materials, as well as in packaging printing fields such as food and beverage packaging, vividly colored images that attract customers' attention are being recorded using inkjet recording methods. Furthermore, inks for inkjet recording are required to be able to record images with an expanded color gamut, and in recent years, inks other than the basic colors of cyan, magenta, and yellow (so-called spot color inks) have been used in combination. For example, inkjet inks containing fluorescent colorants have been proposed (Patent Document 1).

[0003] Fluorescent colorants absorb short-wavelength light corresponding to the ultraviolet to visible light region and emit light with wavelengths longer than the absorbed light. Therefore, images recorded with inks containing fluorescent colorants exhibit luminescence and have high brightness, resulting in excellent color reproduction. Furthermore, a method has been proposed to express hues that could not be expressed with conventional colored ink combinations alone by combining cyan, magenta, and yellow colored inks with fluorescent inks (Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-303008 [Patent Document 2] Japanese Patent Publication No. 2002-363455 [Overview of the project] [Problems that the invention aims to solve]

[0005] The inventors investigated the use of an ink containing a fluorescent colorant and another ink containing a colorant in combination in order to record a chromatic image with excellent luminescence and color development. Specifically, they applied the ink containing a fluorescent colorant and the other ink containing a colorant to a recording medium so that they partially overlapped, and then recorded an image. As a result, they found that the luminescence of the recorded image was significantly impaired.

[0006] Next, in order to ensure the luminescence of the image, each ink was applied to the recording medium so that the ink containing the fluorescent colorant was placed on the outermost surface of the image, and the image was recorded. As a result, it was found that the luminescence of the resulting image improved, while the color development decreased. In other words, it was found that simply using an ink containing a fluorescent colorant in combination with another ink containing a colorant is not sufficient to sufficiently improve the luminescence and color development of the image.

[0007] Therefore, an object of the present invention is to provide an inkjet recording method that can record a chromatic image with excellent luminescence and color development by using in combination an ink containing a fluorescent colorant and another ink containing a colorant. [Means for solving the problem]

[0008] In other words , book According to the invention, an inkjet recording method is provided for recording a chromatic image having a hue angle between the hue angle of the first ink and the hue angle of the second ink, wherein the first ink and the second ink are applied to the recording medium exclusively on a pixel-by-pixel basis, with a portion adjacent to each other, and the recording area of ​​the first ink and the recording area of ​​the second ink are irregularly combined to record the image. [Effects of the Invention]

[0009] According to the present invention, an inkjet recording method capable of recording a colored image excellent in luminescence and color development can be provided while using an ink containing a fluorescent coloring material and another ink containing a coloring material in combination.

Brief Description of the Drawings

[0010] [Figure 1] It is a schematic diagram showing an example of a combination of a recording area of a first ink and a recording area of a second ink. [Figure 2] It is a schematic diagram showing an example of a combination of a recording area of a first ink and a recording area of a second ink. [Figure 3] It is a schematic diagram showing an example of a combination of a recording area of a first ink and a recording area of a second ink. [Figure 4] It is a schematic diagram showing an example of a combination of a recording area of a first ink and a recording area of a second ink. [Figure 5] It is a schematic diagram showing an example of a combination of a recording area of a first ink and a recording area of a second ink. [Figure 6] It is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, (a) is a perspective view of a main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. [Figure 7] It is a flowchart showing data processing when the first ink and the second ink are exclusively applied to a recording medium in pixel units.

Embodiments for Carrying Out the Invention

[0011] The preferred embodiments of the present invention are described below to explain the present invention in more detail. In the present invention, when the compound is a salt, although the salt dissociates into ions in the ink, for convenience, it is expressed as "containing a salt". Further, the aqueous ink for inkjet may be simply referred to as "ink". Physical property values are values at normal temperature (25 ° C) and normal pressure (1 atm) unless otherwise specified. The "unit" of the resin means a repeating unit derived from one monomer. Further, when "(meth)acrylic acid" and "(meth)acrylate" are described, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

[0012] The "hue angle" in the present invention refers to the hue angle of the ink. The hue angle is the hue angle in the CIE L * , * C * h color system, which is the hue angle (h) on a plane and is calculated based on the following formula. ·a * ≧0, b * ≧0 (first quadrant), h° = tan -1 (b * / a * ) ·a * ≦0, b * ≧0 (second quadrant), h° = 180 + tan -1 (b * / a * ) ·a * ≦0, b * ≦0 (third quadrant), h° = 180 + tan -1 (b * / a * ) ·a * ≧0, b * ≦0 (fourth quadrant), h° = 360 + tan -1 (b * / a * )

[0013] ​​​​Furthermore, "chromatic colors" refer to colors that possess three properties: "lightness," "hue," and "saturation." So-called "achromatic colors," which only possess "lightness," such as white, black, and intermediate grays, are not included in "chromatic colors." The "hue angle," "lightness," "hue," and "saturation" of ink can be measured using a spectrophotometer or similar device. In this case, each physical property can be measured on a sample prepared by appropriately diluting the ink with water (such as deionized water or ionized water).

[0014] The inventors investigated a method for recording chromatic images with excellent luminescence and color development by using a first ink containing a fluorescent colorant and a second ink containing a non-fluorescent colorant such as a fluorescent colorant or pigment in combination. Specifically, a first ink containing a red fluorescent colorant and a second ink containing a yellow non-fluorescent colorant were used in combination, and these inks were partially overlapped and applied to a recording medium to record an orange image, which is an intermediate color. As a result, it was found that the luminescence of the resulting image was insufficient. Furthermore, in order to improve color development, the inks were applied to the recording medium so that the first ink was placed on the outermost surface of the image, and the image was recorded. As a result, it was found that the luminescence of the resulting image improved, but the color development was impaired. Furthermore, when the inks were applied to the recording medium so that the second ink was placed on the outermost surface of the image, it was found that both the color development and luminescence were insufficient.

[0015] Fluorescent pigments absorb short-wavelength light corresponding to the ultraviolet to visible light region, exciting them from the ground state to an excited state, and emit light by releasing long-wavelength light when returning from the excited state to the ground state. For example, a red fluorescent pigment is excited by light with a wavelength of 300-500 nm and emits light with a wavelength of 550-650 nm. On the other hand, a yellow non-fluorescent pigment absorbs light with a wavelength of 400-500 nm. Therefore, when the first and second inks described above are partially overlapped and applied to a recording medium to record an image, some of the light at the wavelength required to excite the red fluorescent pigment is absorbed by the yellow non-fluorescent pigment. As a result, the fluorescent pigment in the first ink is not sufficiently excited, and the amount of light emitted decreases, leading to a reduction in luminescence.

[0016] On the other hand, as mentioned above, the yellow non-fluorescent pigment absorbs light with wavelengths of 400-500 nm and exhibits a yellow color. The yellow light is reflected at two locations: (i) the surface of the non-fluorescent pigment and (ii) the surface of the recording medium that has passed through the non-fluorescent pigment. In an image recorded by overlaying a red first ink on a yellow second ink, some of the reflected light from the yellow pigment is scattered at the interface between the layer formed by the second ink and the layer formed by the first ink. Similarly, in an image recorded by overlaying a yellow second ink on a red first ink, some of the reflected light from the surface of the recording medium is scattered at the interface with the layer formed by the first ink. As a result, the reflected yellow light is reduced, the yellow color is weakened, and the color reproduction of the image is considered to be insufficient.

[0017] Based on the above, it is presumed that the luminescence and color development of the recorded image will decrease due to the non-fluorescent colorant inhibiting the photoexcitation of the fluorescent colorant and the fluorescent colorant reducing the reflected light of the non-fluorescent colorant. In the above explanation, a combination of a red fluorescent colorant and a yellow non-fluorescent colorant was used as an example, but it can be easily inferred from the excitation, fluorescence, and absorption spectra of each colorant that similar phenomena may occur when colorants of other hues are combined. Furthermore, if both the colorants of the first and second inks are fluorescent colorants, combining them may reduce the luminescence and color development of at least one of the fluorescent colorants.

[0018] Based on the above assumption, the inventors further investigated a method for recording a chromatic image that achieves both luminescence and color development by using a first ink containing a fluorescent colorant and a second ink containing either a fluorescent or non-fluorescent colorant in combination. As a result, they discovered that by applying the first and second inks exclusively to the recording medium on a pixel-by-pixel basis, with some adjacent to each other, it becomes possible to record a chromatic image that achieves both luminescence and color development, leading to the present invention. In the present invention, "pixel" refers to an output pixel in an inkjet recording method. For example, if the output pixel is from a recording head with a nozzle resolution (resolution of the ejection port arrangement in the recording head) of 1,200 dpi and a scanning resolution (resolution of relative scanning between the recording head and the recording medium) of 1,200 dpi, the size of one pixel is 21 μm × 21 μm. That is, in the present invention, "pixel" corresponds to the smallest unit that can be recorded, which is one dot of ink droplet.

[0019] By applying droplets of the first ink and the second ink to the recording medium exclusively without substantial overlap, phenomena such as the aforementioned photoexcitation inhibition and reflected light reduction are less likely to occur, and it is believed that a chromatic image with improved luminescence and color development can be recorded. A single dot formed by a single ink droplet on the recording medium may bleed beyond the pixel. However, by applying each ink to the recording medium exclusively on a pixel-by-pixel basis, with a portion adjacent to it, the main parts of the dots of each ink do not overlap, but the parts where one ink bleeds beyond the pixel overlap with the other ink. As a result, it is possible to record an image that appears as an intermediate color with improved luminescence and color development.

[0020] <Inkjet recording method> The present invention relates to an inkjet recording method in which a first ink and a second ink are ejected from an inkjet recording head and applied to a recording medium to record a chromatic image having a hue angle between the hue angle of the first ink and the hue angle of the second ink. The first ink is an inkjet ink containing a fluorescent colorant. The second ink is an inkjet ink containing a fluorescent colorant or a non-fluorescent colorant. In the present invention's inkjet recording method, the first ink and the second ink are applied to the recording medium exclusively on a pixel-by-pixel basis, with a portion of each ink adjacent to the first ink, to record the chromatic image described above. That is, the image is recorded by applying the droplets of the first ink and the second ink to the recording medium without overlapping, and with a portion of each droplet adjacent to the first ink.

[0021] Figures 1-5 are schematic diagrams showing examples of combinations of the recording areas of the first ink and the second ink. In Figures 1-3, the recording area 1 of the first ink, which corresponds to one pixel, and the recording area 2 of the second ink, which corresponds to one pixel, are combined in a regular manner. On the other hand, in Figures 4 and 5, the recording area 1 of the first ink, which corresponds to one pixel, and the recording area 2 of the second ink, which corresponds to one pixel, are combined irregularly (randomly) without any regularity.

[0022] It is preferable to record an image by (i) irregularly combining the recording area of ​​the first ink and the recording area of ​​the second ink, or (ii) by combining them in a staggered pattern. In particular, it is even more preferable to record an image by irregularly combining the recording area of ​​the first ink and the recording area of ​​the second ink.

[0023] As shown in Figures 4 and 5, it is preferable to record an image by irregularly combining the recording area 1 of the first ink and the recording area 2 of the second ink. As shown in Figures 1 to 3, when an image is recorded by regularly combining the recording area 1 of the first ink and the recording area 2 of the second ink, the frequency of use of a predetermined ejection port among the recording heads that eject ink increases. In this case, the liquid resonates in the common ink chamber that communicates with ejection ports that are used at different frequencies, causing the liquid level of the less frequently used ejection ports to fluctuate, making the amount of ink ejected unstable and potentially causing density unevenness in the image. In contrast, when an image is recorded by irregularly combining the recording area 1 of the first ink and the recording area 2 of the second ink, the amount of ink ejected is stable, and density unevenness in the image is less likely to occur.

[0024] As shown in Figure 1, it is preferable to record an image by combining the recording area 1 of the first ink and the recording area 2 of the second ink in a staggered pattern. By arranging the recording areas of each ink alternately in a staggered pattern, the inhibition of photoexcitation of the fluorescent colorant by the colorant of the second ink and the reduction of reflected light of the colorant of the second ink by the fluorescent colorant can be further suppressed. This makes it possible to further improve the luminescence and color development of the resulting image. However, in this case, for the same reasons as when recording an image by regularly combining the recording area 1 of the first ink and the recording area 2 of the second ink, density unevenness is likely to occur in the image, and it may be difficult to achieve a good balance between luminescence, color development and density unevenness.

[0025] Figure 7 is a flowchart illustrating the data processing when applying the first and second inks exclusively to a recording medium on a pixel-by-pixel basis. First, after image data is input to the recording device, the type of ink to be used is determined according to the input image data. Then, it is decided whether or not to use both the first and second inks. If neither ink is used, the image is recorded using the ink that is selected. On the other hand, if both inks are used, the pixels to which the first ink will be applied are determined first. Then, from the pixels other than those to which the first ink will be applied, the pixels to which the second ink will be applied are determined, and the image is recorded. In this way, each ink can be applied exclusively to each pixel to record the image.

[0026] (ink) The inkjet recording method of the present invention uses a first ink and a second ink. The first ink is an ink containing a fluorescent colorant. The second ink is an ink containing either a fluorescent colorant or a non-fluorescent colorant. Hereinafter, when simply referred to as "ink," it means either the "first ink" or the "second ink." The components of the inks used in the inkjet recording method of the present invention will be described in detail below.

[0027] [Fluorescent colorants] The first ink contains a fluorescent colorant. Examples of fluorescent colorants include fluorescent colorants that may be dissolved in the ink, and fluorescent particles that may be dispersed in the ink. In particular, it is preferable to use fluorescent particles as the fluorescent colorant because they can impart excellent lightfastness to the recorded image.

[0028] In this specification, "fluorescent colorant" refers to a colorant that emits fluorescence when excited by ultraviolet or visible light. Whether or not a colorant is a "fluorescent colorant" can be determined, for example, by the following method: A sample obtained by dissolving or dispersing a colorant in a liquid capable of dissolving or dispersing the colorant is irradiated 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 colorant can be determined to be a "fluorescent colorant" that exhibits fluorescence. A commercially available black light (for example, product name "SLUV-4" (manufactured by AS ONE), etc.) can be used.

[0029] Examples of fluorescent particles include resin particles dyed with a fluorescent colorant, and fluorescent colorants dispersed by a dispersant such as a resin or surfactant. Fluorescent dyes and fluorescent pigments can be used as the fluorescent colorant. It is preferable that the fluorescent particles are either resin particles dyed with a fluorescent colorant, or fluorescent colorants dispersed by a resin. Low to poorly water-soluble fluorescent colorants are dispersed in water-based inks by a dispersant such as a resin or surfactant.

[0030] The fluorescent pigment in resin particles stained with a fluorescent pigment 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 pigment 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).

[0031] As fluorescent dyes, fluorescent dyes such as basic dyes, acid dyes, disperse dyes, and oil-soluble dyes, as well as fluorescent pigments, can be used. As for fluorescent colorants, colored fluorescent colorants are preferred over colorless ones such as fluorescent whitening agents. The "CI" attached to the specific examples of colorants below is an abbreviation for "Color Index." The Color Index is a database of colorants compiled by the British Society for Dye and Coloring and other organizations.

[0032] Basic dyes are fluorescent compounds that have an amino group or imino group (which may form a salt) in their molecular structure. Examples of compounds that have an amino group or imino group in their molecular structure include "dyes whose names in the color index include 'basic'." Examples of dye skeletons include xanthenes, azines, azoles, thiazoles, azos, diarylmethanes, triarylmethanes, acridines, coumarins, and methines. Among these, compounds with xanthene or coumarin skeletons are preferred, and compounds with a xanthene skeleton are even more preferred.

[0033] Specific examples of fluorescent basic dyes, indicated by their CI numbers or common names, include CI Basic Red 1, 1:1, 2, 4, 8, 11, 12, 13; CI Basic Violet 1, 3, 10, 11, 11:1, 14; Rhodamine 19, 575; CI Basic Yellow 1, 2, 9, 13, 24, 37, 40, 96; CI Basic Blue 7; CI Basic Green 1; and CI Fluorescent Brightener 363. Among these, CI Basic Red 1, 1:1; CI Basic Violet 11, 11:1; and CI Basic Yellow 40 are preferred due to their excellent color development.

[0034] Acid dyes are fluorescent compounds that contain carboxylic acid groups or sulfonic acid groups (which may form salts) in their molecular structure. Examples of compounds containing carboxylic acid groups or sulfonic acid groups in their molecular structure include "dyes whose names in the color index include 'acid'." Examples of dye skeletons include triphenylmethane, aminoketones, azo, xanthenes, and azines. Specific examples of fluorescent acid dyes, indicated by their CI numbers, include CI Acid Blue 9, CI Acid Yellow 7, CI Acid Yellow 23, CI Acid Red 52, CI Acid Red 87, CI Acid Red 92, and CI Acid Black 2.

[0035] Disperse dyes are fluorescent compounds that have low or no water solubility. Examples of "disperse dyes" include "dyes whose names in the color index include 'disperse'." Examples of dye skeletons include azo, coumarin, and anthraquinone. Among these, compounds with a coumarin or anthraquinone skeleton are preferred, and compounds with a coumarin skeleton are even more preferred. Specific examples of fluorescent disperse dyes, shown by their CI numbers, include CI Disperse Yellow 82, 186; CI Disperse Red 58, 60; and CI Disperse Orange 11. Among these, CI Disperse Yellow 82 is preferred due to its excellent color development.

[0036] Oil-soluble dyes are fluorescent compounds that have low or no water solubility. Examples of oil-soluble dyes include "dyes whose names in the color index include 'solvent'." Examples of dye skeletons include coumarin, xanthene, azo, aminoketone, and anthraquinone. Among these, compounds with a coumarin or xanthene skeleton are preferred, and compounds with a coumarin skeleton are even more preferred. Specific examples of fluorescent oil-soluble dyes, shown by their CI numbers, include CI Solvent Yellow 7, 43, 44, 85, 98, 131, 160:1, 172, 196; CI Solvent Red 43, 44, 45, 49, 149; and CI Solvent Orange 5, 45, 63, 115. Among these, CI Solvent Yellow 160:1 and 196 are preferred due to their excellent color development.

[0037] Among the fluorescent dyes mentioned above, CI Basic Red 1 is preferred due to its excellent color development. Furthermore, it is preferable that the fluorescent colorant contains two or more fluorescent dyes. The presence of multiple fluorescent dyes within the resin particles inhibits crystallization of the fluorescent dyes, allowing the fluorescent dyes to efficiently interact with the resin particles at a molecular level, resulting in a stable dyed state. Examples of fluorescent pigments include CI Pigment Yellow 101 and CI Pigment Red 81:3.

[0038] The content (mass%) of fluorescent particles in the first ink is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. The content (mass%) of fluorescent colorants 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.

[0039] It is preferable to use resin particles having a so-called core-shell structure, which comprises a core portion and a shell portion covering the core portion, as the resin particles constituting the "resin particles dyed with a fluorescent colorant." The core portion preferably contains aromatic group-containing units and cyano group-containing units. The shell portion preferably contains aromatic group-containing units and anionic group-containing units, and may also contain units derived from a crosslinking agent.

[0040] The monomers that become aromatic group-containing units through polymerization are preferably those that have 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.

[0041] As monomers that become cyano group-containing units through polymerization, those having one polymerizable functional group such as an ethylenically unsaturated bond within the molecule are preferred. Among these, acrylonitrile and methacrylonitrile are particularly preferred because they exhibit good reactivity during polymerization and the resulting resin particles have excellent stability.

[0042] In an anionic group-containing unit, the anionic group is preferably one that has one polymerizable functional group, such as an ethylenically unsaturated bond, within its molecule. Specifically, examples include carboxylic acid groups, sulfonic 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. Of these, (meth)acrylic acid is particularly preferred. The anionic group may be in either an acidic or salt form, and in the case of a salt form, it may be in either a partially dissociated or completely 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.

[0043] The core and shell portions of the resin particles may each contain units other than those described above, as long as the effects of the present invention are not impaired. Preferably, the units other than those described above have one polymerizable functional group in their molecule, and specifically, units derived from ethylenically unsaturated monomers can be mentioned.

[0044] The volume-based cumulative 50% particle diameter (D50) of the fluorescent particles is preferably between 10 nm and 300 nm. If the volume-based cumulative 50% particle diameter (D50) of the fluorescent particles is less than 10 nm, the interaction between particles becomes stronger, which may reduce the storage stability of the ink. On the other hand, if the volume-based cumulative 50% particle diameter (D50) of the fluorescent particles is greater than 300 nm, the glossiness of the recorded image may be slightly reduced.

[0045] [Method for manufacturing dyed resin particles] Resin particles can be manufactured by 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 colorant to form resin particles, and adding the fluorescent colorant to the resin particles and heating them. Among these, the method of adding the fluorescent colorant to the resin particles and heating them is preferred because it can be applied to a wider variety of fluorescent colorants.

[0046] [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.

[0047] (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.

[0048] (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 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.

[0049] (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.

[0050] 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.

[0051] [Second ink colorant] The second ink contains a fluorescent colorant or a non-fluorescent colorant. Examples of fluorescent colorants include those listed as usable in the first ink. For the non-fluorescent colorant, a pigment is preferred. For the colorant of the second ink, a non-fluorescent colorant is preferred, and among these, a non-fluorescent pigment is even more preferred. Using a pigment as the colorant allows for the recording of images with excellent lightfastness. Examples of pigment dispersion methods include resin-dispersed pigments dispersed with a resin dispersant, pigments dispersed with a surfactant, and microcapsule pigments in which at least a portion of the surface of the pigment particles is coated with a resin or the like. Furthermore, self-dispersing pigments in which functional groups including hydrophilic groups such as anionic groups are bonded to the surface of the pigment particles, and pigments in which organic groups containing polymers are chemically bonded to the surface of the pigment particles (resin-bonded self-dispersing pigments) can also be used. In addition, pigments with different dispersion methods may be used in combination.

[0052] Inorganic pigments and organic pigments can be used as pigments. Specific examples of pigments include carbon black, azo, phthalocyanine, quinacridone, isoindolinone, imidazolon, diketopyrrolopyrrole, and dioxazine. Among these, azo and quinacridone are preferred. CI Pigment Yellow 74, an azo pigment, is particularly preferred. The colorant content (mass%) in the second ink is preferably 0.1% to 15.0% by mass, and more preferably 1.0% to 10.0% by mass, based on the total mass of the ink. The second ink may further contain water-soluble colorants such as dyes, as needed.

[0053] [Aqueous medium] The ink is preferably 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 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. Any water-soluble organic solvent commonly used in inks can be used. 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 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink.

[0054] [Other additives] In addition to the components mentioned above, the ink may also contain, as necessary, water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols like trimethylolpropane and trimethylolethane, and urea derivatives like urea and ethylene urea. Furthermore, the ink may also contain, as necessary, various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation accelerators, chelating agents, and other resins.

[0055] [Ink properties] Since the ink is used in an inkjet system, it is preferable to appropriately control its physical properties. Specifically, the static surface tension of the ink at 25°C, as measured by the plate method, is preferably 30 mN / m to 50 mN / m. The viscosity of the ink at 25°C is preferably 2.0 mPa·s to 10.0 mPa·s. The pH of the ink at 25°C is preferably 5.0 to 10.0, and more preferably 7.0 to 9.5.

[0056] It is preferable that the hue angle X(°) of the first ink and the hue angle Y(°) of the second ink satisfy the relationship |XY| ≤ 160°. If the value (absolute value) of |XY| is less than 160°, the photoexcitation inhibition of the fluorescent colorant by the colorant of the second ink tends to be stronger, which may reduce the emission intensity of the resulting image. There are no particular restrictions on the hue angle of each ink and it is determined according to the colorant of the ink.

[0057] (Inkjet recording device) Figure 6 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.

[0058] Methods for ejecting ink from an inkjet recording head include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. Among these, the method of imparting thermal energy to the ink to eject it is particularly preferable. [Examples]

[0059] 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.

[0060] <Preparation of a dispersion of dyed resin particles> (Dispersion of resin particles 1-7) A reaction vessel equipped with a stirring device was placed in a warm water chamber. 1,178 parts of water were added to the reaction vessel, and the internal temperature was maintained at 70°C. A solution of 233 parts styrene, 233 parts acrylonitrile, and 18 parts of a reactive surfactant (product name "SR-10", manufactured by ADEKA) was simultaneously added dropwise to the reaction vessel over 60 minutes under stirring. A solution of 1.9 parts potassium persulfate and 659 parts water was added dropwise. After the dropwise addition was complete, stirring was continued for another 30 minutes to form core particles that would become the core of the resin particles.

[0061] A first solution was prepared by mixing 16 parts styrene, 12 parts methacrylic acid, 32 parts ethylene glycol dimethacrylate (crosslinking agent), 20 parts ethylene glycol diglycidyl ether (crosslinking agent), and 2.5 parts reactive surfactant. The reactive surfactant used was trade name "SR-10" (manufactured by ADEKA). A second solution was prepared by mixing 0.1 parts potassium persulfate and 133 parts water. The first and second solutions were simultaneously added dropwise to a reaction vessel over 10 minutes under stirring. After the dropwise addition was complete, the mixture was stirred further at 80°C for 5 hours to form a shell, and resin particles with a core-shell structure having a core and a shell were prepared.

[0062] After adjusting the pH to 8.5 by adding an 8 mol / L potassium hydroxide aqueous solution to the reaction vessel, dye solutions prepared by dissolving the types of dyes shown in Table 1 in water were added to the reaction vessel without adding a surfactant. The temperature was raised to 80°C and stirred for 2 hours to dye the resin particles. The amount of dye was adjusted to 5 parts per 100 parts total of the monomers, crosslinking agents, and dyes constituting the resin particles. The pH was adjusted to 8.5 by adding an 8 mol / L potassium hydroxide aqueous solution to the reaction vessel. Further dilution with water was obtained to obtain dispersions of dyed resin particles (resin particle dispersions 1-7). The content of dyed resin particles in resin particle dispersions 1-7 was 20.0% in all of them.

[0063] TIFF0007844170000001.tif99170

[0064] <Preparation of Pigment Dispersion> (Pigment dispersions 1-6) A water-soluble resin, a styrene / acrylic acid copolymer (styrene:acrylic acid (molar ratio) = 33:67), was dissolved in deionized water using potassium hydroxide to achieve a neutralization equivalent of 1 to prepare an aqueous solution of a resin dispersant with a resin content of 20.0%. The weight-average molecular weight of this water-soluble resin was 8,000, and its acid value was 150 mgKOH / g. A mixture of 15.0 parts of the pigments of the types shown in Table 2, 30.0 parts of the aqueous solution of the resin dispersant, and 55.0 parts of water was placed in a sand grinder and dispersed for 1 hour. After removing coarse particles by centrifugation, the mixture was pressure filtered through a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. An appropriate amount of deionized water was added to obtain pigment dispersions 1 to 6. The pigment content in pigment dispersions 1 to 6 was 10.0% in all of them. The resin content in pigment dispersions 1 to 6 was 3.0% in all of them.

[0065] TIFF0007844170000002.tif57170

[0066] <Preparation of liquid containing dye> (Liquid containing dye 1) Liquid 1 containing dye was obtained by mixing 1 part of CI Basic Red 1, 1 part of CI Basic Violet 11, and 98 parts of deionized water.

[0067] (Liquid containing dye 2) Liquid 2 containing dye was obtained by mixing 0.67 parts of CI Disperse Yellow 82, 0.67 parts of CI Solvent Yellow 160, 0.67 parts of CI Solvent Yellow 196, and 98 parts of deionized water.

[0068] (Liquid containing dye 3) Two parts of CI Acid Red 289 and 98 parts of deionized water were mixed to obtain liquid 3 containing the dye.

[0069] (4 liquids containing dye) Two parts of CI Direct Yellow 132 and 98 parts of deionized water were mixed to obtain a liquid 4 containing the dye.

[0070] <Ink preparation> Each component (in %) shown in Tables 3-1 and 3-2 was mixed and thoroughly stirred. The mixture was then pressure filtered through a 3.0 μm pore size microfilter (manufactured by Fujifilm) to prepare inks F1-F9 containing fluorescent colorants and inks C1-C7 containing non-fluorescent colorants. In Tables 3-1 and 3-2, "Acetylenel E100" is the trade name for a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals. The prepared inks were diluted 1,000 times (by volume) with deionized water. The hue angle of this sample was measured using the M1 light source of a spectrophotometer (trade name "X-Rite eXact", manufactured by X-Rite) to obtain the hue angle values ​​of the inks.

[0071] TIFF0007844170000003.tif168170

[0072] TIFF0007844170000004.tif168170

[0073] <Rating> An inkjet recording device, as shown in Figure 6, equipped with a recording head that ejects ink using thermal energy, was prepared. Each prepared ink was filled into an ink cartridge and mounted in the inkjet recording device in the combinations shown in Table 4. In this example, a unit area of ​​1 / 1,200 inch × 1 / 1,200 inch is defined as "1 pixel". An image recorded under the condition that 4.5 ng ± 10% of ink droplets are applied to the unit area of ​​1 pixel is defined as having a recording duty cycle of 100%. Using the above inkjet recording device, a 2 cm × 2 cm solid image with a recording duty cycle of 100% was recorded by applying each ink to the recording medium in a 1:1 ratio (pixel-based) according to the "recording method" shown in Table 4. When multiple second inks were used, the amount of second ink applied was divided in half to record the solid image. The recorded solid image had a hue intermediate between the first and second inks. As the recording medium, the product name "Canon Photo Paper Premium Matte PM-101" (manufactured by Canon) was used. In this invention, "A" and "B" were defined as acceptable levels, and "C" as an unacceptable level, according to the evaluation criteria for each item below. The evaluation results are shown in Table 4.

[0074] The difference in hue angle between the first and second inks was calculated from the previously measured hue angle values ​​of the inks. Table 4 shows the results, with "○" indicating a hue angle difference of 160° or less, and "×" indicating a difference greater than 160°. When the hue angle difference was around 160°, the calculated value was also included in Table 4. When multiple second inks were used, the average value of the hue angles was used to calculate the difference in hue angle with the first ink.

[0075] The "recording method" used in this embodiment is shown below. • M1: As shown in Figure 4, the recording areas of the first ink and the second ink were irregularly combined and exclusively assigned to record an image. • M2: As shown in Figure 1, the recording areas of the first ink and the second ink were combined in a regular staggered pattern and exclusively assigned to record the image. • M3: As shown in Figure 2, the recording areas of the first ink and the second ink were regularly combined and exclusively assigned to record the image. • M4: The first and second inks were applied to the recording medium in any order to record an image. • M5: After applying only the first ink to the recording area, the second ink was applied over the recording area of ​​the first ink to record the image. • M6: After applying only the second ink to the recording area, the first ink was applied over the recording area of ​​the second ink to record the image.

[0076] (Luminous properties) After leaving the recorded image for one day, the brightness (L) of the image in the Lab color system was measured using the M1 light source of a spectrophotometer (product name "X-Rite eXact," manufactured by X-Rite). * The luminescence of the images was evaluated according to the following evaluation criteria. A: Lightness (L * ) was 80 or higher. B: Brightness (L * ) was between 75 and 80. C: Brightness (L * ) was less than 75.

[0077] (Color development) After leaving the recorded image for one day, the saturation (C) of the image in the Lab color system was measured using the M1 light source of a spectrophotometer (product name "X-Rite eXact," manufactured by X-Rite). * The following measurements were taken, and the color reproduction of the images was evaluated according to the evaluation criteria shown below. A: Saturation (C * ) was 65 or higher. B: Saturation (C * ) was between 60 and 65. C: Saturation (C * ) was less than 60.

[0078] (Lightfastness) After the recorded images were left for one day, the optical density of the images before the lightfastness test was measured using a spectrophotometer (product name "FD-7", manufactured by Konica Minolta). The recorded materials were placed in a xenon test apparatus (product name "Atlas Weathermeter Ci4000", manufactured by Toyo Seiki Seisakusho). Under conditions of an internal temperature of 30°C and relative humidity of 40%, xenon light with a wavelength of 420 nm (irradiation intensity: 1.25 W / m²) was used. 2 After irradiating the image with ) for 12 hours, the optical density of the image was measured. From the optical density values ​​before and after the lightfastness test, the optical density retention rate (= (optical density after lightfastness test / optical density before lightfastness test) × 100 (%)) was calculated, and the lightfastness of the image was evaluated according to the evaluation criteria shown below. A: The optical density retention rate was 80% or higher. B: The remaining optical density was less than 80%.

[0079] (Uneven concentration) After recording 1,000 solid images using the aforementioned inkjet recording device, a separate 2cm x 2cm solid image was recorded using a recording method that equalized the amount of ink ejected from all the ejection ports of the recording head. The reason for equalizing the ejection amount was to minimize density variations caused by the influence of the ejection ports of the recording head. After leaving the recorded images for one day, they were visually observed, and the density variations of the images were evaluated according to the evaluation criteria shown below. A: No concentration variations were observed. B: Concentration variations were observed.

[0080] TIFF0007844170000005.tif214170

[0081] Example 1, Reference example 8, and Reference example Regarding item 9, we compared its luminescence and color development. As a result, reference The luminescence and color development of Example 8 are better than those of Example 1 and Reference example Its luminescence and color development were better than that of sample 9.

Claims

1. An inkjet recording method for recording a chromatic image having a hue angle between the hue angle of the first ink and the hue angle of the second ink, wherein a first ink containing a fluorescent colorant and a second ink containing the fluorescent colorant or a non-fluorescent colorant are ejected from an inkjet recording head and applied to a recording medium, The first ink and the second ink are applied to the recording medium exclusively for each pixel unit, with a portion of them adjacent to each other. An inkjet recording method characterized by recording the image by irregularly combining the recording area of ​​the first ink and the recording area of ​​the second ink.

2. The inkjet recording method according to claim 1, wherein the fluorescent colorant is fluorescent particles.

3. The inkjet recording method according to claim 2, wherein the fluorescent particles are at least one selected from the group consisting of (1) resin particles dyed with the fluorescent colorant, and (2) the fluorescent colorant dispersed by a dispersant.

4. The inkjet recording method according to any one of claims 1 to 3, wherein the second ink contains the non-fluorescent colorant.

5. The inkjet recording method according to claim 4, wherein the non-fluorescent colorant comprises a non-fluorescent pigment.

6. The inkjet recording method according to any one of claims 1 to 5, wherein the hue angle X (°) of the first ink and the hue angle Y (°) of the second ink satisfy the relationship |X - Y| ≤ 160°.

7. The inkjet recording method according to any one of claims 1 to 6, wherein the fluorescent colorant in the first ink contains two or more fluorescent dyes.

8. The inkjet recording method according to any one of claims 3 to 6, wherein the fluorescent colorant is C.I. Basic Red 1.

Images