Inkjet recording method and inkjet recording device

Abstract

To provide an inkjet recording method capable of recording an image which is less likely to cause image irregularity, has strong fluorescence intensity and has excellent color developability even when an aqueous ink containing a fluorescent dye is discharged from a long recording head.SOLUTION: There is provided an inkjet recording method using an inkjet recording device comprising an aqueous ink containing resin particles dyed by a fluorescent dye and a recording head having a plurality of nozzle rows constituted by arranging a plurality of nozzles for discharging an aqueous ink in a predetermined direction. The plurality of nozzle rows include a first nozzle row and a second nozzle row arranged so that end nozzles of the adjacent nozzle rows are mutually displaced in a predetermined direction so as to constitute an overlapping portion in a direction intersecting the predetermined direction, the overlapping nozzles constituting the overlapping portions discharge the aqueous ink allocated to the first nozzle row and the second nozzle row and the difference in the application time of the aqueous ink discharged from the overlapping nozzles is 20 milliseconds or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In recent years, the demand for commercial printed matter such as catalogs, pamphlets, and POP, as well as printed matter such as packaging for food and beverage products, has been increasing. These printed matters are required to have vivid colors that catch the customer's eye, and the color gamut range is expanded by using special colors other than the basic colors of cyan, magenta, and yellow. In addition, inks containing fluorescent coloring materials have been proposed to expand the color gamut range (Patent Document 1).

[0003] In addition, in the commercial printing and packaging fields, there is a demand for faster printing. In order to meet such demands, a long recording head is used in which multiple nozzle rows are arranged with a shift in a predetermined direction. In the case of such a long recording head, a defect called "streaks" may occur in an image recorded at a discontinuous portion of the boundary between adjacent nozzle rows. In order to suppress the occurrence of such streaks, it is necessary to arrange the multiple nozzle rows so that they partially overlap. For example, an inkjet recording device has been proposed that is equipped with a recording head in which multiple nozzle rows are arranged with a shift from each other in order to accommodate high-speed recording (Patent Document 2). In addition, in recent years, there has been a demand for the use of water-based inks from the viewpoint of reducing environmental impact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-303008 A [Patent Document 2] JP 2018-187921 A Summary of the Invention [Problem to be solved by the invention]

[0005] In order to record an image with excellent color development at high speed, the present inventors recorded an image by ejecting an aqueous ink containing a fluorescent dye onto a recording medium from the recording head of the inkjet recording device proposed in Patent Document 2. As a result, it was found that unevenness was likely to occur in the recorded image.

[0006] Therefore, an object of the present invention is to provide an inkjet recording method capable of recording an image with less image unevenness, high fluorescent intensity, and excellent color development even when an aqueous ink containing a fluorescent dye is ejected from an elongated recording head. Another object of the present invention is to provide an inkjet recording apparatus used in the inkjet recording method. [Means for solving the problem]

[0007] That is, according to the present invention, there is provided an inkjet recording method comprising a step of recording an image on a recording medium using an inkjet recording device equipped with an aqueous ink containing resin particles dyed with a fluorescent dye, and a recording head having a plurality of nozzle rows configured by arranging a plurality of nozzles for ejecting the aqueous ink in a predetermined direction, wherein the plurality of nozzle rows include a first nozzle row and a second nozzle row that are arranged offset from each other in a predetermined direction so that end nozzles of adjacent nozzle rows form an overlapping portion in a direction intersecting the predetermined direction, and the aqueous ink is ejected from overlapping nozzles constituting the overlapping portion by allocating them to the first nozzle row and the second nozzle row, and the application time difference of the aqueous ink ejected from the overlapping nozzles is 20 milliseconds or less. Effect of the Invention

[0008] According to the present invention, it is possible to provide an inkjet recording method capable of recording an image with less image unevenness, high fluorescent intensity, and excellent color development even when an aqueous ink containing a fluorescent dye is ejected from an elongated recording head. Also, according to the present invention, it is possible to provide an inkjet recording apparatus used in the inkjet recording method. [Brief description of the drawings]

[0009] [Figure 1] FIG. 13 is a conceptual diagram showing how an image is recorded by a line head. [Diagram 2] FIG. 1 is a schematic diagram illustrating an example of an inkjet recording apparatus. [Diagram 3] 1A and 1B are diagrams illustrating an example of a line head, in which FIG. 1A is a perspective view and FIG. [Figure 4] 1A and 1B are diagrams showing an example of a recovery mechanism, where (a) is a perspective view and (b) is a schematic view. [Diagram 5] FIG. 4 is a schematic diagram illustrating an example of a supply mechanism that supplies ink to a line head. [Figure 6] FIG. 2 is a schematic diagram showing an example of an arrangement of nozzle rows in a line head. [Figure 7] 10A and 10B are schematic diagrams showing other examples of the arrangement of nozzle rows in a line head. [Figure 8] 2 is a schematic diagram showing the arrangement of nozzles in a nozzle row that constitutes a recording head 2. FIG. [Figure 9] 2 is a schematic diagram showing the arrangement of nozzles in a nozzle row that constitutes a recording head 1. FIG. [Figure 10] 2 is a schematic diagram showing the arrangement of nozzles in a nozzle row that constitutes a recording head 10. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0011] The present inventors have conducted a detailed study on the cause of unevenness in an image recorded by discharging ink containing a fluorescent dye from a long recording head in which multiple nozzle rows are arranged with a mutual shift. As a result, it was found that the image unevenness occurs due to the difference in color between the part recorded at the so-called "joint part" where the ends of the nozzle rows overlap and the part recorded at the so-called "non-joint part" where the ends of the nozzle rows do not overlap. In particular, the fluorescent intensity of the part recorded at the joint part is lower than that of the part recorded at the non-joint part. Further study revealed that the fluorescent dye is in a state of aggregation in the part recorded at the joint part where the fluorescent intensity is lower than that of the part where the fluorescent intensity is not lower. It was also found that this image unevenness does not occur when using an aqueous ink that does not contain a fluorescent dye and contains a coloring material other than the fluorescent dye, but is a phenomenon that occurs specifically when using an aqueous ink that contains a fluorescent dye as a coloring material.

[0012] Generally, in the joints of the nozzle rows, multiple nozzle rows are arranged in parallel to form overlapping portions in a direction intersecting the nozzle arrangement direction so that streaks do not occur at discontinuous locations between the nozzle rows. Then, the overlapping nozzles that exist at positions corresponding to the joints of the nozzle rows are usually controlled as follows to print an image. The overlapping nozzles that exist at positions corresponding to the joints exist in both adjacent nozzle rows. For this reason, by controlling the ink to be distributed and ejected to the adjacent nozzle rows, the misalignment of the ink dot application positions between the nozzle rows is made less noticeable.

[0013] The inks ejected from the overlapping nozzles include ink allocated to the preceding nozzles (hereinafter also referred to as "preceding ink") and ink allocated to the following nozzles (hereinafter also referred to as "following ink"). For this reason, the following ink is applied within a short time after the preceding ink adheres to the recording medium. The present inventors focused on the adhesion time difference between the preceding ink and the following ink and further investigated. As a result, it was found that image unevenness is significantly more likely to occur if the following ink is applied within 20 milliseconds after the preceding ink adheres to the recording medium. The present inventors speculate as follows about the reason for this.

[0014] Until 20 milliseconds have passed since the preceding ink was applied to the recording medium, the concentration of the fluorescent dye increases due to penetration and evaporation of volatile components, and the ink fluidity is maintained to a certain extent. When the following ink, which has a relatively low concentration of fluorescent dye, is applied, a concentration gradient is formed between the preceding ink and the following ink, and convection occurs between the preceding ink and the following ink. As a result, the fluorescent dye moves between the preceding ink and the following ink, and the fluorescent dye partially gathers and aggregates. The fluorescent dye has a characteristic that when the intermolecular distance becomes equal to or less than a certain value, the fluorescent intensity decreases (concentration quenching occurs) due to the interaction between photoexcited molecules and unexcited molecules, which causes energy transfer. For this reason, it is considered that the fluorescent intensity of the image recorded at the joint of the nozzle row decreases, causing image unevenness.

[0015] 20 milliseconds after the ink is applied to the recording medium, the fluidity of the leading ink decreases. Even if the trailing ink comes into contact with the leading ink with reduced fluidity, the fluorescent dye is less likely to move, so it is thought that image unevenness is less likely to occur. The time difference between the application of the leading ink and the trailing ink can be increased by increasing the distance between the nozzle rows or slowing down the scanning speed of the recording head. However, increasing the distance between the nozzle rows tends to increase the size of the recording head. Also, slowing down the relative scanning speed between the recording head and the recording medium tends to decrease productivity.

[0016] Based on the above findings, the present inventors have studied the constituent materials of the ink in order to suppress the occurrence of image unevenness caused by the aggregation of the fluorescent dye on the recording medium. As a result, they have found that by using resin particles dyed with a fluorescent dye as a coloring material, the aggregation of the fluorescent dye can be suppressed and the occurrence of image unevenness can be suppressed even when a recording head in which multiple nozzle rows are arranged in a shifted direction and extended is used, and have arrived at the present invention. The present inventors speculate as follows about the reason why such an effect is obtained.

[0017] When resin particles dyed with a fluorescent dye are used as the fluorescent coloring material, even if convection occurs between the preceding ink and the following ink, the movement of the particulate fluorescent coloring material is suppressed compared to the case of a non-particulate fluorescent dye. Furthermore, even if the fluorescent coloring material moves, the resin particles will aggregate, but the aggregation of the fluorescent dye is suppressed. As a result, the molecules of the fluorescent dye that have dyed the resin particles are present on the recording medium at a constant distance from each other, so it is thought that concentration quenching due to aggregation can be suppressed and the occurrence of image unevenness can be suppressed.

[0018] <Inkjet recording apparatus and inkjet recording method> In the inkjet recording method of the present invention, an inkjet recording device is used that includes an aqueous ink and a recording head having a plurality of nozzle rows in which a plurality of nozzles for ejecting the aqueous ink are arranged in a predetermined direction. The aqueous ink contains resin particles dyed with a fluorescent dye. The inkjet recording method of the present invention includes a step of recording an image on a recording medium using the inkjet recording device (hereinafter also referred to as a "recording step"). The plurality of nozzle rows include a first nozzle row and a second nozzle row that are arranged with a mutual shift in a predetermined direction such that end nozzles of adjacent nozzle rows form an overlapping portion in a direction intersecting the predetermined direction (the nozzle arrangement direction). In the recording step, aqueous ink is ejected from the overlapping nozzles that form the overlapping portion by allocating the first nozzle row and the second nozzle row. The application time difference of the aqueous ink ejected from the overlapping nozzles is 20 milliseconds or less.

[0019] The inkjet recording device of the present invention is an apparatus suitable for use in the inkjet recording method described above, and includes an aqueous ink and a recording head. The inkjet recording device of the present invention includes a first nozzle row and a second nozzle row, which are arranged with a mutual shift in a predetermined direction such that end nozzles of adjacent nozzle rows form an overlapping portion in a direction intersecting the predetermined direction (the nozzle arrangement direction). The overlapping nozzles that form the overlapping portion eject aqueous ink by allocating it to the first nozzle row and the second nozzle row, and the application time difference of the aqueous ink ejected from the overlapping nozzles is 20 milliseconds or less.

[0020] As described above, the overlap nozzles constituting the overlapping portion eject water-based ink by allocating it to the first nozzle row and the second nozzle row, and the application time difference of the water-based ink ejected from the overlap nozzles is 20 ms or less. Moreover, the application time difference is preferably 1 ms or more, and more preferably 5 ms or more.

[0021] Examples of the inkjet recording head include a serial head that records an image by transporting the recording medium in the sub-scanning direction while moving back and forth in the main scanning direction, and a line head that records an image by transporting the recording medium without moving itself. The recording head is preferably (i) a line head; or (ii) a serial head that records an image by applying ink to a unit area of ​​the recording medium in one relative scan with the recording medium (single-pass recording). A comparison is made between a case where an image is recorded by a line head or a serial head that performs single-pass recording, and a case where an image is recorded by a serial head that performs multiple relative scans with the recording medium to apply ink to a unit area of ​​the recording medium to record an image (multi-pass recording). In the former case, image unevenness at the joints is somewhat more noticeable than in the latter case, so that the effect of suppressing image unevenness can be more prominent and images can be recorded at a higher speed. In the case of multi-pass recording, the amount of ink applied at one time is smaller than in single-pass recording, so image unevenness is less likely to occur, but since recording takes time, productivity tends to decrease somewhat.

[0022] The amount of ink ejected per droplet is preferably 40.0 ng or less, and more preferably 10.0 ng or less. By setting the amount of ink ejected per droplet within the above range, the ink can be fixed on the recording medium more quickly. This makes it possible to more efficiently suppress the movement of coloring material when the following ink adheres, thereby further improving the effect of suppressing image unevenness. The amount of ink ejected per droplet is preferably 1.0 ng or more.

[0023] The recording head preferably includes a temperature control mechanism for heating the ink. By applying ink heated in the recording head by the temperature control mechanism to the recording medium, it is possible to promote the penetration and evaporation of the preceding ink, and the movement of the fluorescent coloring material when the following ink is attached can be suppressed, and the effect of suppressing image unevenness can be further improved. The temperature control mechanism can include a heater (sub-heater) for adjusting the ink temperature installed in the recording head, a heater for ink ejection, and the like. The location of the sub-heater is not particularly limited. The sub-heater can be arranged around the nozzle row, or one or more sub-heaters can be arranged corresponding to the nozzles that make up the nozzle row. In order to control (heat or warm) the temperature of the ink with the heater for ink ejection, for example, it is sufficient to repeatedly pass a current that does not eject the ink. The temperature of the ink may be controlled by using the sub-heater and the heater for ink ejection in combination. When using the sub-heater and the heater for ink ejection in combination, they may be used separately so that one heater is used to raise the temperature to a certain temperature, and then the other heater is used to keep the temperature near the desired temperature. The temperature of the ink can be read, for example, by a temperature sensor provided on the recording head. The temperature of the ink is preferably higher than the temperature of the recording environment. The temperature of the ink is preferably 25° C. or higher and 80° C. or lower, and more preferably 40° C. or higher and 60° C. or lower.

[0024] The method of ejecting the ink includes a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. Of these, it is preferable to adopt a method of ejecting the ink by applying thermal energy to the ink. Other steps of the inkjet recording method may be the same as those of known inkjet recording methods.

[0025] FIG. 1 is a conceptual diagram of an image recorded by a line head. FIG. 2 is a schematic diagram showing an example of an inkjet recording device. In the recording device M4000 shown in FIG. 2, a line head (recording head H1000) is fixed to the recording device body, and a method of recording by conveying a recording medium 47 in the direction of an arrow 45 is adopted. The recording device M4000 includes, for example, a recording head H1000Y for yellow ink, a recording head H1000M for magenta ink, a recording head H1000C for cyan ink, and a recording head H1000Bk for black ink (FIG. 1). The ink colors are not limited to those mentioned above, and at least one of the ink colors may be a water-based ink, which will be described later.

[0026] The print heads H1000Y to H1000R shown in Fig. 2 are fixed by a print head holder 42 mounted on the printing apparatus M4000. Figs. 1 and 2 show a configuration in which the colors yellow, magenta, cyan, and black, as well as the reaction liquid, are ejected from separate print heads. Of course, a configuration in which a plurality of inks and further reaction liquid are ejected from each of a plurality of nozzle rows provided on one printing element substrate to print an image may also be used.

[0027] The paper feed cassette 46 stores the recording medium 47 therein, and is detachably attached to the device body. The pick-up roller 48 is a member that feeds out the topmost sheet of the recording media 47 stored in the paper feed cassette 46. The transport roller 49 is a member that transports the recording medium 47 sent out by the pick-up roller 48 to the transport path 50. The transport roller 51, disposed on the outlet side of the transport path 50, is a member that transports the recording medium 47, placed on the transport belt 44, toward the recording head H1000.

[0028] Fig. 3 is a diagram showing an example of a line head, where (a) is a perspective view and (b) is an exploded perspective view. As shown in Fig. 3, the line head (print head H1000) includes a printing element unit H1400 and an ink supply unit H1500, which is a liquid supply unit for supplying ink to the printing element unit H1400. The ink supply unit H1500 includes a connection portion H1700 in which a connection port H1710 is formed to connect to the outside in order to supply ink to an ink chamber (not shown) from the outside of a printing apparatus or the like. The printing element unit H1400 includes a printing element substrate H1100, a support substrate H1200, and a wiring member H1300.

[0029] The support substrate H1200 is a member that holds and fixes the recording element substrate H1100 and the wiring member H1300, and has an ink supply hole H1210 that supplies ink supplied from the ink supply unit H1500 to the recording element substrate H1100. The recording element substrates H1100 are arranged and fixed on the main surface of the support substrate H1200 with a predetermined positional accuracy. The recording element substrates H1100 are arranged in a staggered pattern on the support substrate H1200 so that the nozzles are continuously arranged along the direction of the nozzle row between adjacent recording element substrates H1100. In this way, by arranging the recording element substrates H1100 so that the nozzles at the joints of the adjacent recording element substrates H1100 overlap, it is possible to correct the influence on the image caused by the positional deviation of the recording element substrates, and a full-line type recording head with a long recording width is realized.

[0030] The wiring member H1300 is electrically connected to the recording element substrate H1100 in order to transmit electrical signals and power for driving the recording elements provided on the recording element substrate H1100 from the outside of the printhead H1000 (recording device) to the recording element substrate H1100. A flexible printed wiring board such as a flexible wiring board is used as the wiring member H1300. The flexible wiring member H1300 is bent so as to easily electrically connect the recording element substrate H1100 and the recording device, and is fixed to the ink supply unit H1500.

[0031] FIG. 6 is a schematic diagram showing an example of the arrangement of nozzle rows in a line head. As shown in FIG. 6, a line head, which is an example of a recording head constituting an inkjet recording device of the present invention, includes recording element substrates H1100 and H1105. The recording element substrate H1100 has a first nozzle row 100 configured by arranging a plurality of nozzles that eject ink in a predetermined direction. The recording element substrate H1105 has a second nozzle row 105 configured by arranging a plurality of nozzles that eject ink in a predetermined direction. The adjacent first nozzle row 100 and second nozzle row 105 are arranged with a mutual shift in a predetermined direction so that the end nozzles form an overlapping portion in a direction intersecting the predetermined direction (the nozzle arrangement direction). All of the recording element substrates including the recording element substrate H1100 having the first nozzle row 100 and the recording element substrate H1105 having the second nozzle row 105 are held on a support substrate H1200. In the overlapping portion, the water-based ink is ejected separately from both the overlapping nozzles that form part of the overlapping portion in the first nozzle row and the overlapping nozzles that form part of the overlapping portion in the second nozzle row.

[0032] The arrangement of the recording element substrates is not particularly limited. For example, the recording element substrates may be arranged in a staggered pattern as shown in Fig. 6. Furthermore, as shown in Fig. 7, a plurality of recording element substrates including a recording element substrate H1110 having a first nozzle row 110 and a recording element substrate H1115 having a second nozzle row 115 may be arranged in-line.

[0033] The inkjet recording apparatus used in the inkjet recording method of the present invention may further include a recovery mechanism for recovering ink adhesion at the nozzles of the line head and wetness of the nozzle surface. FIG. 4 shows an example of the recovery mechanism, (a) being a perspective view and (b) being a schematic view. As shown in FIG. 4, the wiper W1001 is held by a clip member W1002, and the clip member W1002 is held by a connecting member W1003. The clip member W1002 is attached to a wipe base W1011 that is movable on a slide rail W1006. The wipe base W1011 can move on the slide rail W1006 by driving a timing belt W1007 through the connecting member W1003. The timing belt W1007 is supported by a driven pulley W1004 and a driving pulley W1005, and the shaft of a driving motor W1010 that drives the timing belt W1007 is connected to the driving pulley W1005. Also, photosensors W1008 and W1009 are provided at both ends of the slide rail W1006 to control the position of the wiper W1001 during recovery operation. During recovery operation by wiping, the wiper W1001 slides and moves on the slide rail W1006, and the wiper W1001 wipes the ejection port surface H1001 of the recording head H100 while bending.

[0034] The inkjet recording device used in the inkjet recording method of the present invention may further include a supply mechanism for supplying liquid such as ink to the line head. FIG. 5 is a schematic diagram showing an example of a supply mechanism for supplying ink to the line head. As shown in FIG. 5, ink is supplied from the subtank T2 to the line head H1000 by the pump P1. Ink overflowing from the line head H1000 is returned to the subtank T2. The valve V1 is provided for switching between pressurizing and releasing the pressure in the ink liquid chamber inside the line head during recovery operation. During pressurization recovery, the valve V1 is closed and the pump P1 applies pressure to remove some of the bubbles in the ink supply path and the ink flow path. The ink liquid level in the subtank T2 is configured to maintain a head difference with the ejection port surface of the line head H1000 within a certain range, and the negative pressure at the ejection port surface of the line head H1000 is maintained within an appropriate range. When the ink in the subtank T2 is insufficient, the pump P2 sends ink from the main tank T1 to the subtank T2. The temperature of each tank and the ink contained therein depends on the environmental temperature in which the inkjet recording apparatus is installed, but is preferably in the range of 15 to 45°C, for example.

[0035] Any recording medium may be used as the target for recording an image by the inkjet recording method of the present invention. In particular, it is preferable to use a recording medium having no coating layer, such as plain paper or uncoated paper, and a paper having permeability, such as a recording medium having a coating layer, such as glossy paper or art paper. In particular, it is preferable to use a recording medium having a coating layer, such as glossy paper or art paper.

[0036] (ink) In the ink jet recording method of the present invention, an ink containing resin particles dyed with a fluorescent dye is used. Each component constituting the ink used in the ink jet recording method of the present invention will be described in detail below.

[0037] [Resin particles dyed with fluorescent dye] The ink contains resin particles dyed with a fluorescent dye (fluorescent particles). By using fluorescent particles in which a fluorescent dye is fixed to resin particles, it is possible to improve the coloring efficiency and also improve the properties of the printed image, such as water resistance.

[0038] In this specification, "resin particles dyed with a fluorescent dye (fluorescent particles)" refers to particles that emit fluorescence when excited by ultraviolet or visible light. Whether a certain particle is a "fluorescent particle" that exhibits fluorescence can be determined, for example, according to the method shown below. A sample obtained by dispersing particles in a liquid capable of dispersing the particles is irradiated with ultraviolet light (ultraviolet light) of a long wavelength (about 315 to 400 nm) that is barely visible to the naked eye using a black light or the like. If light of a color different from the ultraviolet light irradiated by the black light can be visually observed, the particle can be determined to be a "fluorescent particle" that exhibits fluorescence. As the black light, a commercially available product (for example, the product name "SLUV-4" (manufactured by AS ONE) or the like) can be used.

[0039] In this specification, the term "resin particles" refers to a resin that can be present in an aqueous medium in a state of being dispersed in the aqueous medium and having a particle size. Therefore, the resin particles are present in a dispersed state in the ink, i.e., in a state of a resin emulsion.

[0040] Whether or not a certain resin is a "resin particle" can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) 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 having a particle size are measured, the resin can be determined to be a "resin particle". A particle size analyzer (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used as a particle size distribution measuring device using the dynamic light scattering method. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. Of course, the particle size distribution measuring device and measurement conditions used are not limited to those described above. The particle size is measured using neutralized resin in order to confirm that particles are formed even when the resin is sufficiently neutralized to make it more difficult to form particles. Even under such conditions, resins that have a particulate shape exist in the form of particles in the water-based ink.

[0041] The fluorescent dye in the resin particles dyed with the fluorescent dye can be analyzed, for example, according to the following procedure. Resin particles extracted from the ink according to 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 by common structural analysis methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS).

[0042] As the fluorescent dye, a basic dye, an acid dye, a disperse dye, an oil-soluble dye, etc. can be used. Among them, a basic dye is preferable. Examples of the skeleton of the dye include xanthene, azine, azole, thiazole, azo, diarylmethane, triarylmethane, acridine, coumarin, methine, etc. Among them, a compound having a skeleton such as xanthene or coumarin is preferable, and a compound having a xanthene skeleton is more preferable.

[0043] Basic dyes are compounds that have an amino group or an imino group (which may form a salt) in their molecular structure and exhibit fluorescence. Compounds that have an amino group or an imino group in their molecular structure include "dyes whose names in the Colour Index include 'basic'". The Colour Index is a database of colour materials compiled by the British Society of Dyes and Colourants and others.

[0044] Specific examples of fluorescent basic dyes, expressed by CI number or general name, 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 because of their excellent color development.

[0045] Acid dyes are fluorescent compounds that have an acidic group (which may form a salt) such as a carboxylic acid group or a sulfonic acid group in their molecular structure. Examples of compounds that have an acidic group in their molecular structure include dyes whose names in the Color Index include "acid." Specific examples of fluorescent acid dyes, listed by CI number, 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.

[0046] Disperse dyes are compounds that are poorly soluble in water or do not dissolve in water and exhibit fluorescence. Examples of "disperse dyes" include "dyes whose names in the Color Index include 'disperse'". Examples of the skeleton of the dye include azo, coumarin, anthraquinone, etc. Among these, compounds having a skeleton such as coumarin or anthraquinone are preferred, and compounds having a skeleton such as coumarin are even more preferred.

[0047] Specific examples of fluorescent disperse dyes, expressed by 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 because of its excellent color development.

[0048] An oil-soluble dye is a compound that has low water solubility or is insoluble in water and exhibits fluorescence. Examples of oil-soluble dyes include "dyes whose names in the Color Index include 'solvent'". Examples of the skeleton of the dye include coumarin, xanthene, azo, aminoketone, anthraquinone, etc. Among them, compounds having a skeleton such as coumarin or xanthene are preferred, and compounds having a skeleton such as coumarin are more preferred.

[0049] Specific examples of fluorescent oil-soluble dyes, expressed by CI numbers, include CI Solvent Yellow 7, 43, 44, 85, 98, 131, 160:1, 172, 196, CI Solvent Red 43, 44, 45, 49, 149, CI Solvent Orange 5, 45, 63, 115, etc. Among these, CI Solvent Yellow 160:1, 196, etc. are preferred due to their excellent color development properties.

[0050] The content (mass%) of the fluorescent dye in the ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink. The proportion (mass%) of the fluorescent dye in the resin particles is preferably 1.0% by mass or more and 15.0% by mass or less, and more preferably 2.0% by mass or more and 8.0% by mass or less. If the proportion of the fluorescent dye in the resin particles is too low, the color development (saturation) of the image may be slightly decreased. On the other hand, if the proportion of the fluorescent dye in the resin particles is too high, the color development (brightness) of the image may be slightly decreased due to concentration quenching.

[0051] As the resin particles constituting the "resin particles dyed with a fluorescent dye", it is preferable to use resin particles having a so-called core-shell structure, which has a core part and a shell part covering the core part. The core part preferably contains an aromatic group-containing unit and a cyano group-containing unit. The shell part preferably contains an aromatic group-containing unit and an anionic group-containing unit, and may further contain a unit derived from a crosslinking agent.

[0052] As the monomer that becomes the aromatic group-containing unit by polymerization, it is preferable to use one having a polymerizable functional group such as an ethylenically unsaturated bond in the molecule. Among them, styrene and its derivatives are more preferable, and styrene and vinyltoluene are particularly preferable, because they have good reactivity during polymerization and the stability of the obtained resin particles is excellent.

[0053] As the monomer that becomes a cyano group-containing unit by coincidence, those having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule are preferable. Among them, acrylonitrile and methacrylonitrile are particularly preferable because they have good reactivity during polymerization and the resulting resin particles have excellent stability.

[0054] As the anionic group in the anionic group-containing unit, those having one polymerizable functional group such as an ethylenically unsaturated bond in the molecule are preferable. Specifically, a carboxylic acid group, a phenolic hydroxy group, a phosphate ester group, etc. can be mentioned. Among them, a carboxylic acid group is preferable because the stability of the resin particles in the ink is good. The anionic group may be either an acid type or a salt type, and in the case of a salt type, it may be either a state where a part is dissociated or a state where all are dissociated. When the anionic group is in a salt type, examples of the cation that becomes a counter ion include an alkali metal cation, ammonium, and organic ammonium.

[0055] The core part and the shell part of the resin particles may each contain units other than the above units as long as the effects of the present invention are not impaired. As the units other than the above units, those having one polymerizable functional group in the molecule are preferable, and specifically, units derived from ethylenically unsaturated monomers can be mentioned.

[0056] It is preferable that the temperature control temperature Th of the recording head and the glass transition temperature Tg of the resin particles satisfy the relationship Th < Tg. By making the glass transition temperature Tg of the resin particles higher than the temperature control temperature Th of the recording head (the temperature of the ink heated by the temperature control mechanism), it becomes difficult for the fluorescent dye to leak from the fluorescent particles in the ink attached to the recording medium, and the effect of suppressing image unevenness can be further improved. The glass transition temperature Tg of the resin particles is a value measured using a differential scanning calorimeter with the dried resin particles as a measurement sample.

[0057] The content (mass%) of the resin particles in the ink is preferably 1.0% by mass or more and 10.0% by mass or less based on the total mass of the ink. If the content of the resin particles is less than 1.0% by mass, the color development of the image may be slightly decreased. On the other hand, if the content of the resin particles is more than 10.0% by mass, the ejection stability of the ink may be slightly decreased.

[0058] [Method for producing dyed resin particles] The resin particles can be produced according to a conventionally known method such as emulsion polymerization, mini-emulsion polymerization, seed polymerization, and phase inversion emulsification. Examples of the dyeing method for the resin particles include a method of polymerizing a monomer mixture in which a fluorescent dye is dissolved to form resin particles; a method of adding a fluorescent dye to resin particles and heating the particles; and the like. Among them, the method of adding a fluorescent dye to resin particles and heating the particles is preferred because it can be applied to a wider variety of fluorescent dyes. It is preferable not to add a dyeing assistant (water-soluble resin, surfactant, etc.) during heating. If a water-soluble resin is used as a dyeing assistant, the water-soluble resin may form a film and inhibit the redispersion of the resin particles, which may slightly reduce the fixation recovery of the ink. In addition, if a surfactant is used as a dyeing assistant, the physical properties of the ink may be affected, and the ejection stability of the ink may slightly decrease.

[0059] [Method of verifying resin particles] The composition of the resin particles can be verified according to the following methods (i) to (iii). Below, a method for extracting resin particles from ink and analyzing and verifying them will be described, but resin particles extracted from an aqueous dispersion or the like can also be analyzed and verified in the same manner.

[0060] (i) Extraction of resin particles Density gradient centrifugation can be used to separate and extract resin particles from ink that contains them. Among density gradient centrifugation methods, density gradient sedimentation velocity separates and extracts resin particles based on the difference in sedimentation coefficient of components. Also, among density gradient centrifugation methods, density gradient sedimentation equilibrium separates and extracts resin particles based on the difference in density of components.

[0061] (ii) Confirmation and separation of layer structure First, the resin particles are stained and fixed with ruthenium tetroxide, then embedded in epoxy resin to hold them in place. 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 layer structure of the resin particles can be confirmed. Resin particles embedded in epoxy resin are used as an analytical sample, and the elements contained in the layers (core and shell) that make up the resin particles can be quantitatively analyzed by STEM-EDX coupled with energy dispersive X-ray spectroscopy (EDX).

[0062] (iii) Analysis of the units (monomers) that make up the resin of each layer The resin particles to be used as a sample for separating the resin of each layer may be in the form of a dispersion liquid. Alternatively, the resin particles may be dried to form a film to be used as a sample. After dissolving the resin particles to be used as a sample in an organic solvent, the layers are separated by gel permeation chromatography (GPC), and the resins constituting each layer are separated. The separated resin is then subjected to elemental analysis by a combustion method. Separately, the separated resin is pretreated by an acid decomposition (addition of hydrofluoric acid) method or an alkali fusion method, and then the inorganic components are quantitatively analyzed by an inductively coupled plasma optical emission spectrometry method. By comparing the results of the elemental analysis and the quantitative analysis of the inorganic components with the results of the quantitative analysis of the elements by STEM-EDX obtained in (ii) above, the layer of the resin particles that constituted the separated resin can be known.

[0063] The fractionated resin is analyzed by nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS). This allows the types and ratios of the units (monomers) and crosslinking components that make up the resin to be known. Furthermore, the monomers generated by depolymerization can be directly detected by analyzing the fractionated resin by pyrolysis gas chromatography.

[0064] [Water-soluble resin] The ink preferably further contains a water-soluble resin having an anionic group (hereinafter, the "water-soluble resin having an anionic group" is also simply referred to as "water-soluble resin"). The water-soluble resin is preferably at least one selected from the group consisting of acrylic resins and urethane resins. The water-soluble resin is likely to exist without gaps between the fluorescent particles. For this reason, by using an ink containing a water-soluble resin together with the fluorescent particles, the color development of the recorded image can be improved. The water-soluble resin is more preferably a urethane resin. The urethane bond in the urethane resin has high hydrogen bonding properties. For this reason, by using an ink containing a water-soluble urethane resin having an anionic group, a uniform image with improved surface energy can be easily formed, and the color development of the image can be further improved. The content (mass%) of the water-soluble resin in the ink is preferably 1.00 mass% or more and 8.00 mass% or less based on the total mass of the ink.

[0065] The acid value of the water-soluble resin is preferably 100 mgKOH / g or less, more preferably 80 mgKOH / g or less. If the acid value of the water-soluble resin exceeds 100 mgKOH / g, the hydrophilicity of the water-soluble resin increases too much, and the adsorption force of the resin particles to the aggregates decreases, and the effect of improving color development may decrease. The acid value of the water-soluble resin is preferably 30 mgKOH / g or more.

[0066] [Acrylic resin] The acrylic resin is a resin having a unit derived from a monomer having a (meth)acrylic structure, such as (meth)acrylic acid or (meth)acrylic ester. Examples of the form of the acrylic resin include a block copolymer, a random copolymer, a graft copolymer, and a combination thereof. The acrylic resin preferably has a hydrophilic unit and a hydrophobic unit. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene is preferred. By using such an acrylic resin, interaction with the resin particles is easily generated, and color development can be further improved.

[0067] The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed by polymerizing a hydrophilic monomer having a hydrophilic group. Examples of the hydrophilic monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of the cations constituting the salts of the acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium.

[0068] The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0069] [Urethane resin] The urethane resin is a resin having a unit derived from a polyisocyanate and a unit derived from a polyol including an anionic group-containing polyol having an anionic group such as an acid group. The urethane resin is synthesized, for example, using a polyisocyanate and a polyol. During the synthesis, a polyamine, a crosslinking agent, a chain extender, and the like may be used as necessary.

[0070] Polyisocyanate is a compound having two or more isocyanate groups in its molecule. In the urethane resin, the content (mol%) of the unit derived from polyisocyanate is preferably 10 mol% or more and 60 mol% or less. Examples of polyisocyanate include aliphatic polyisocyanate and aromatic polyisocyanate.

[0071] Examples of the aliphatic polyisocyanate include polyisocyanates having a chain structure such as tetramethylene diisocyanate, hexamethylene diisocyanate, and dodecamethylene diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. Examples of the aromatic polyisocyanate include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, and 2,4'-diphenylmethane diisocyanate. The polyisocyanate is preferably an aliphatic polyisocyanate, and more preferably at least one selected from the group consisting of isophorone diisocyanate and hexamethylene diisocyanate.

[0072] A polyol is a compound having two or more hydroxyl groups in its molecule. In the urethane resin, the content (mol%) of the unit derived from the polyol is preferably 40 mol% or more and 90 mol% or less. Examples of the polyol include polyols having no acid group, such as polyether polyol, polyester polyol, and polycarbonate polyol; and polyols having an acid group, such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group.

[0073] As the polyol having no acid group, polyester polyol is preferable. The urethane resin having a unit derived from polyester polyol has an ester bond in its molecule. Therefore, the ink containing the urethane resin having a unit derived from polyester polyol does not hold too much water when it lands on the recording medium, and the urethane resin is less likely to sink in the ink receiving layer constituting the recording medium. This makes it easier for the urethane resin to remain efficiently in the image, and the color development of the image can be further improved.

[0074] Also, polyether polyols are preferred as polyols having no acid groups. Examples of polyether polyols include addition polymers of alkylene oxides and polyols; glycols such as (poly)alkylene glycol; and the like. Examples of alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, and the like. Examples of polyols that undergo addition polymerization with alkylene oxides include 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and the like. Examples of glycols include (poly)alkylene glycols such as polyethylene glycol, propylene glycol, and polypropylene glycol; ethylene glycol-propylene glycol copolymers; and the like. The proportion (mol %) of polyols having no acid groups in all polyols is preferably 50 mol % or more and 80 mol % or less.

[0075] The polyol having an acid group is preferably a polyol having a carboxylic acid group. Examples of the polyol having a carboxylic acid group include dimethylol acetic acid, dimethylol propionic acid, and dimethylol butanoic acid. Among them, the polyol having an acid group is preferably dimethylol propionic acid. The acid group of the polyol having an acid group may be in a salt form. Examples of the cation forming the salt include ions of alkali metals such as lithium, sodium, and potassium; cations of organic amines such as ammonium ions and dimethylamine; and the like. The molecular weight of a general-purpose polyol having an acid group is usually about 400 or less. The unit derived from the polyol having an acid group usually becomes a hard segment of a urethane resin. The proportion (mol%) of the polyol having an acid group in all polyols is preferably 20 mol% or more and 50 mol% or less.

[0076] When the water-soluble resin is a urethane resin, the content (mass%) of the urethane resin in the ink is preferably 0.04 to 1.00 times the content (mass%) of the resin particles dyed with a fluorescent dye. If the mass ratio is less than 0.04, the effect of improving color development may decrease. On the other hand, if the mass ratio is more than 1.00, the amount of urethane resin liberated in the ink becomes slightly large. As a result, the urethane resin in the ink that seeps out around the ejection port may easily adhere to the ejection port, which may decrease the ejection stability.

[0077] [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. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. In addition, as the water-soluble organic solvent, any of those generally used in inks can be used. Examples include alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink.

[0078] [Surfactants] The ink preferably further contains a silicone-based surfactant. When an ink containing a silicone-based surfactant is used, the silicone-based surfactant in the preceding ink that has been applied to the recording medium is quickly oriented on the surface of the ink dot. Even if the succeeding ink applied to the recording medium then adheres to the ink dot, the movement of the fluorescent coloring material between the dots is suppressed, and the effect of suppressing image unevenness can be further improved.

[0079] The content (mass %) of the silicone surfactant in the ink is preferably 0.1% by mass or more and 3.0% by mass or less based on the total mass of the ink. If the content of the silicone surfactant is less than 0.1% by mass, the amount of the silicone surfactant oriented on the surface of the ink dots is small, and the effect of suppressing image unevenness may be slightly reduced. On the other hand, if the content of the silicone surfactant is more than 3.0% by mass, the amount of the silicone surfactant present on the surface of the ink dots may be excessive, and the effect of improving the color development of the image may be slightly reduced. The HLB value of the silicone surfactant is preferably 8 to 16.

[0080] It is preferable that the ink further contains a surfactant (other surfactant) other than the silicone surfactant. Examples of the other surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, and fluorine-based surfactants. Among them, nonionic surfactants such as ethylene oxide adducts of acetylene glycol and polyoxyethylene alkyl ether are preferable. The content (mass %) of the other surfactant in the ink is preferably 0.1 mass % or more and 2.0 mass % or less based on the total mass of the ink.

[0081] [Other additives] In addition to the above-mentioned components, the ink may contain, as necessary, water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols, such as trimethylolpropane and trimethylolethane, and urea derivatives, such as urea and ethyleneurea. Furthermore, the ink may contain, as necessary, various additives, such as a pH adjuster, a rust inhibitor, a preservative, an antifungal agent, an antioxidant, an antireducing agent, an evaporation promoter, a chelating agent, and other resins.

[0082] [Ink properties] The dynamic surface tension of the ink at a life time of 10 ms measured by the maximum bubble pressure method is preferably 40 mN / m or less. When the dynamic surface tension of the ink is within the above range, the dots spread easily on the recording medium, and image unevenness caused by the aggregation of the fluorescent dye can be further suppressed. The dynamic surface tension of the ink can be easily controlled by appropriately selecting the amount and type of the highly penetrating water-soluble organic solvent and the surfactant. There is no particular limit to the lower limit of the dynamic surface tension of the ink at a life time of 10 ms, but it is preferably 30 mN / m or more, and more preferably 35 mN / m or more.

[0083] The maximum bubble pressure method measures the maximum pressure required to release bubbles generated at the tip of a probe (capillary tube) immersed in the liquid to be measured, and calculates the surface tension of the liquid from this maximum pressure. The maximum pressure is measured while bubbles are continuously generated at the tip of the probe. In this case, the time from when a new bubble surface appears at the tip of the probe to when the maximum bubble pressure (the point when the radius of curvature of the bubble is equal to the radius of the probe tip) is called the lifetime. The dynamic surface tension of ink is a value measured at 25°C.

[0084] The pH of the ink at 25° C. is preferably 5.0 to 10.0, more preferably 7.0 to 9.5. The static surface tension of the ink at 25° C. is preferably 30 to 45 mN / m, more preferably 35 to 40 mN / m. The viscosity of the ink at 25° C. is preferably 1.0 to 5.0 mPa·s. EXAMPLES

[0085] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples without departing from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0086] <Preparation of Water Dispersion of Resin Particles> (Measurement of glass transition temperature of resin particles) The dyed resin particles (fluorescent resin particles) and 1 mol / L hydrochloric acid were mixed at a ratio of 1:1 (by mass), and the resulting precipitate was collected. The precipitate was washed with water three times and dried in an oven for 24 hours to obtain a dried product. The obtained dried product was dissolved in tetrahydrofuran (THF) to prepare a THF solution, which was then filtered through a filter made of 0.2 μm polytetrafluoroethylene. The collected filtrate was dried at room temperature for 24 hours. The obtained dried product was collected, and the glass transition temperature was measured using a differential scanning calorimeter (product name "DSC2500", manufactured by TA Instruments Japan). The measured glass transition temperatures of the resin particles are shown in Table 1.

[0087] (Aqueous dispersions of resin particles 1 to 3 and 6 to 9) A reaction vessel equipped with a stirrer was set in a hot water bath. 1,178 parts of water was placed in the reaction vessel, and the internal temperature was maintained at 70°C. 100.0 parts of styrene, 100.0 parts of acrylonitrile, and 18.0 parts of a reactive surfactant (trade name "ADEKA REASOAP SR-10", manufactured by ADEKA) were mixed to prepare a monomer mixture for the core part. In addition, 1.9 parts of potassium persulfate and 659 parts of water were mixed to prepare an aqueous solution of polymerization initiator 1. The monomer mixture for the core part and the aqueous solution of polymerization initiator 1 were dropped into the reaction vessel in parallel over 60 minutes. After the dropwise addition was completed, stirring was continued to react for another 30 minutes to synthesize particles that would become the core part of the resin particles.

[0088] Next, 20.0 parts of styrene, 20.0 parts of methacrylic acid, 20.0 parts of ethylene glycol diglycidyl ether, and 0.8 parts of reactive surfactant were mixed to prepare a monomer mixture for the shell part. EX-810 (trade name "Denacol EX-810", manufactured by Nagase Chemtex) was used as the ethylene glycol diglycidyl ether. The reactive surfactant was the same as that used in the synthesis of the core part. In addition, 0.1 parts of potassium persulfate and 133 parts of water were mixed to prepare an aqueous solution of polymerization initiator 2. The monomer mixture for the shell part and the aqueous solution of polymerization initiator 2 were dropped in parallel over 10 minutes into a reaction vessel containing particles that would become the core part. After the dropwise addition was completed, the mixture was stirred at 80°C for 10 minutes to continue the reaction to synthesize the shell part, and resin particles having a core-shell structure in which the particles that would become the core part were coated with the resin that would become the shell part were synthesized.

[0089] After adding 8 mol / L potassium hydroxide aqueous solution to the reaction vessel to adjust the pH to 8.5, the fluorescent dye (powder) of the type shown in Table 1 was added to the reaction vessel. The amount of fluorescent dye added was the amount that corresponds to the "percentage (%) of the resin particles" shown in Table 1. After heating to 80°C, 8 mol / L potassium hydroxide aqueous solution was added to the reaction vessel to adjust the pH of the liquid to 8.5. After that, the mixture was stirred for 2 hours to dye the resin particles with the fluorescent dye. After adding 8 mol / L potassium hydroxide aqueous solution to adjust the pH of the liquid to 8.5, an appropriate amount of water was further added to obtain an aqueous dispersion of each resin particle with a resin particle content of 20.0%.

[0090] (Aqueous dispersion of resin particles 4) A reaction vessel equipped with a stirrer was set in a hot water bath. 1,178 parts of water was placed in the reaction vessel, and the internal temperature was maintained at 70°C. 75.0 parts of styrene, 20.0 parts of n-butyl acrylate, 10.0 parts of acrylic acid, and 2.5 parts of sodium dodecyl sulfate were mixed to prepare a monomer mixture. 0.1 parts of potassium persulfate and 133 parts of water were mixed to prepare an aqueous solution of polymerization initiator 3. The monomer mixture and the aqueous solution of polymerization initiator 3 were dropped into the reaction vessel in parallel over 10 minutes. After the dropwise addition, stirring was continued and the reaction was continued at 80°C for another 5 hours to synthesize particles.

[0091] 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. In addition, the type of fluorescent dye (powder) shown in Table 1 was added to the reaction vessel. The amount of fluorescent dye added was the amount that corresponded to the "proportion (%) of the resin particles" shown in Table 1. The mixture was then stirred for 2 hours to dye the resin particles with the fluorescent dye. After adding 8 mol / L potassium hydroxide aqueous solution to adjust the pH of the liquid to 8.5, an appropriate amount of water was further added to obtain an aqueous dispersion of resin particles 4 with a resin particle content of 20.0%.

[0092] (Resin particles 5 and 10) A reaction vessel equipped with a stirrer was set in a hot water bath. 1,178 parts of water was placed in the reaction vessel, and the internal temperature was maintained at 70°C. 45.0 parts of styrene, 45.0 parts of n-butyl acrylate, 15.0 parts of acrylic acid, and 2.5 parts of sodium dodecyl sulfate were mixed to prepare a monomer mixture. 0.1 parts of potassium persulfate and 133 parts of water were mixed to prepare an aqueous solution of polymerization initiator 4. The monomer mixture and the aqueous solution of polymerization initiator 4 were dropped into the reaction vessel in parallel over 10 minutes. After the dropwise addition, stirring was continued and the reaction was continued at 80°C for another 5 hours to synthesize particles.

[0093] 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. In addition, the type of fluorescent dye (powder) shown in Table 1 was added to the reaction vessel. The amount of fluorescent dye added was the amount that corresponded to the "proportion (%) of the resin particles" shown in Table 1. The mixture was then stirred for 2 hours to dye the resin particles with the fluorescent dye. After adding 8 mol / L potassium hydroxide aqueous solution to adjust the pH of the liquid to 8.5, an appropriate amount of water was further added to obtain an aqueous dispersion of each resin particle with a resin particle content of 20.0%.

[0094] TIFF2024000522000001.tif110170

[0095] <Preparation of aqueous solution of fluorescent dye> 1.0 part of CI Basic Red 1 and 1.0 part of CI Basic Violet 11 were dissolved in 98.0 parts of ion-exchanged water at 80° C. to prepare an aqueous solution of the fluorescent dye with a fluorescent dye content of 2.0%.

[0096] <Preparation of pigment dispersion> (Pigment dispersion 1) A mixture was obtained by mixing 10.0 parts of pigment, 20.0 parts of an aqueous solution of a resin dispersant (resin (solid content) content 20.0%), and 70.0 parts of ion-exchanged water. CI Pigment Red 122 was used as the pigment. In addition, as the aqueous solution of the resin dispersant, a water-soluble resin, styrene-acrylic acid copolymer (weight average molecular weight 10,000, acid value 200 mgKOH / g), was dissolved in ion-exchanged water using sodium hydroxide in an amount equimolar to the acid value. The obtained mixture was dispersed for 3 hours using a batch-type vertical sand mill, and then pressure-filtered with a microfilter (manufactured by Fujifilm) having a pore size of 1.2 μm. Next, ion-exchanged water was added to adjust the pigment content, and pigment dispersion liquid 1 was obtained. Pigment dispersion liquid 1 contained a pigment dispersed by a water-soluble resin (resin dispersant), and the pigment content was 10.0% and the water-soluble resin content was 4.0%.

[0097] (Pigment dispersion 2) Pigment dispersion 2 was obtained in the same manner as for pigment dispersion 1 described above, except that the type of pigment was changed to CI Pigment Yellow 74. Pigment dispersion 2 contained a pigment dispersed with a water-soluble resin (resin dispersant), with a pigment content of 10.0% and a water-soluble resin content of 4.0%.

[0098] <Preparation of liquid containing water-soluble resin> Poly(3-methylpentylene adipate) glycol (PMPAG) in an amount shown in Table 2 was dissolved in methyl ethyl ketone. Next, isophorone diisocyanate (IPDI) and dimethylol propionic acid (DMPA) in an amount shown in Table 2 were added, and the mixture was reacted at 75°C for 1 hour to obtain a urethane prepolymer solution. The obtained urethane prepolymer solution was cooled to 60°C, and an aqueous solution of potassium hydroxide in an amount equimolar to the acid value of the resin was added to neutralize the carboxylic acid group. The mixture was cooled to 40°C, ion-exchanged water was added, and the mixture was emulsified by high-speed stirring with a homomixer. Ethylene diamine (EDA) in an amount shown in Table 2 was added, and a chain extension reaction was carried out at 30°C for 12 hours. After confirming that the isocyanate group was no longer present by FT-IR, the mixture was heated and reduced pressure to distill off methyl ethyl ketone, and a liquid containing urethane resin 1 with a resin content of 20.0% was obtained. The weight average molecular weight of urethane resin 1 in the obtained liquid was 30,000. The acid value of the urethane resin was measured by potentiometric titration using an ethanolic potassium hydroxide titrant. The abbreviations in Table 2 are: PMPAG: poly(3-methylpentylene adipate) glycol (number average molecular weight 2,000), IPDI: isophorone diisocyanate, DMPA: dimethylolpropionic acid, EDA: ethylenediamine.

[0099] TIFF2024000522000002.tif31170

[0100] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in the upper rows of Tables 3-1 to 3-3, thoroughly stirring, and then filtering under pressure with a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm. The properties of the ink are shown in the lower rows of Tables 3-1 to 3-3. The product names of the surfactants used in the preparation of the inks are as follows. BYK348, BYK347, BYK3456, BYK3420 (product names, manufactured by BYK-Chemie): nonionic silicone surfactants Acetylenol E100 (product name, manufactured by Kawaken Fine Chemicals): a nonionic hydrocarbon surfactant

[0101] TIFF2024000522000003.tif163170

[0102] TIFF2024000522000004.tif174170

[0103] TIFF2024000522000005.tif197170

[0104] <Recording head configuration> We prepared thermal inkjet print heads 1 to 10, which eject ink by applying thermal energy. Each of the print heads 1 to 10 is equipped with a sub-heater for temperature control, has 512 nozzles per nozzle row, has a nozzle density of 600 dpi per nozzle row, has an ejection volume of 4 ng per ink droplet, and has two nozzle rows per ink color.

[0105] (recording head 1) As shown in Fig. 7, this is a line head in which multiple recording element substrates H1110 and H1115 are arranged in-line. As shown in Fig. 9, the number of overlapping nozzles 220 per nozzle row is 16, and the ink ejection amount per nozzle is 5.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0106] (Recording head 2) As shown in Fig. 6, this is a serial head in which multiple recording element substrates H1100 and H1105 are arranged in a staggered pattern. As shown in Fig. 8, the number of overlapping nozzles 200 per nozzle row is 64, and the ink ejection amount per nozzle is 5.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0107] (Recording head 3) As shown in Fig. 7, this is a line head in which multiple recording element substrates H1110 and H1115 are arranged in-line. As shown in Fig. 9, the number of overlapping nozzles 220 per nozzle row is 16, and the ink ejection amount per nozzle is 5.0 ng / dot. The distance between the nozzle rows is 0.2 inches.

[0108] (recording head 4) As shown in Fig. 7, this is a line head in which multiple recording element substrates H1110 and H1115 are arranged in-line. As shown in Fig. 9, the number of overlapping nozzles 220 per nozzle row is 16, and the ink ejection amount per nozzle is 10.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0109] (recording head 5) As shown in Fig. 7, this is a line head in which multiple recording element substrates H1110 and H1115 are arranged in-line. As shown in Fig. 9, the number of overlapping nozzles 220 per nozzle row is 16, and the ink ejection amount per nozzle is 11.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0110] (Recording head 6) As shown in Fig. 6, this is a serial head in which multiple recording element substrates H1100 and H1105 are arranged in a staggered pattern. As shown in Fig. 8, the number of overlapping nozzles 200 per nozzle row is 64, and the ink ejection amount per nozzle is 11.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0111] (recording head 7) As shown in Figure 6, this is a line head in which multiple recording element substrates H1100 and H1105 are arranged in a staggered pattern. The number of overlapping nozzles per nozzle row is 0, and the ink ejection amount per nozzle is 5.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0112] (recording head 8) It is a serial head having one printing element substrate H1100 (Fig. 6) which constitutes the print head 2. The number of overlapping nozzles per nozzle row is 0, and the ink ejection amount per nozzle is 5.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0113] (Recording head 9) As shown in Figure 7, this is a serial head in which multiple recording element substrates H1110 and H1115 are arranged in-line. The number of overlapping nozzles per nozzle row is 0, and the ink ejection amount per nozzle is 5.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0114] (recording head 10) As shown in Fig. 10, this is a serial head having one recording element substrate H1120 in which two nozzle rows are arranged with a mutual offset. The number of overlapping nozzles 240 per nozzle row is 64, and the ink ejection amount per nozzle is 5.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0115] (recording head 11) A piezoelectric inkjet type recording head 11 was prepared, which ejects ink by applying mechanical energy. The recording head 11 is a line head equipped with a sub-heater for temperature control, and has a plurality of recording element substrates H1110 and H1115 arranged in-line, as shown in FIG. 7. As shown in FIG. 9, the number of overlapping nozzles 220 per nozzle row is 16, and the ink ejection amount per nozzle is 5.0 ng / dot. The distance between the nozzle rows is 0.1 inches.

[0116] The configurations of recording heads 1 to 11 are shown in Table 4.

[0117] TIFF2024000522000006.tif82170

[0118] <Evaluation> The following evaluations were carried out using the ink prepared above. In this example, an image recorded under conditions in which 8 drops of 3.8 ng±10% ink were applied to a unit area of ​​1 / 600 inch×1 / 600 inch was defined as having a recording duty of 100%. In the present invention, the evaluation criteria for each of the following items were set as "AA", "A", and "B" as acceptable levels, and "C" as an unacceptable level. The evaluation results are shown in Table 5.

[0119] (Image recording) In Examples 1 to 5, 8 to 27, 30 to 32, Comparative Examples 1 to 3, and Reference Examples 1 and 4, images were recorded using an inkjet recording device having the configuration shown in Fig. 2, which is equipped with recording heads 1, 3 to 5, 7, and 11, which are line heads. The recording heads are fixed to the inkjet recording device. In this inkjet recording device, an image is recorded by one relative scan between the recording head and the recording medium.

[0120] In Examples 6, 7, 28, and 29 and Reference Examples 2 and 3, images were recorded using an inkjet recording device in which the line heads of the inkjet recording device having the configuration shown in Fig. 2 were replaced with serial heads, namely recording heads 2, 6, and 8 to 10. In this inkjet recording device, an image is recorded by the main scanning of the recording head and the transport of the recording medium in the sub-scanning direction.

[0121] The temperature control temperature (heating temperature of ink) of the print heads 1 to 10 was controlled by passing electricity through the heaters of the print heads to such an extent that ink was not ejected, and reading the temperature with a diode sensor provided on the print head. The temperature control temperature (heating temperature of ink) of the print head 11 was controlled by heating the sub-heater for temperature control of the print head, and reading the temperature with a diode sensor provided on the print head. In Examples 1 to 32, Comparative Examples 1 to 3, and Reference Example 4, ink was ejected from the overlap nozzles by allocating it to adjacent print element substrates. Table 5 shows the ink, print head, temperature control temperature Th of the print head, and the application time difference of the ink ejected from the overlap nozzles. The application time difference of the ink ejected from the overlap nozzles was calculated from the distance between the nozzle rows, the relative scanning speed of the print head and the print medium, and the scanning speed of the print head.

[0122] (Color development) Using the above inkjet recording device, an image containing the following gradation pattern was recorded on a recording medium (glossy paper, product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT-201", manufactured by Canon). The gradation pattern is composed of a 2 cm x 2 cm solid image in which the amount of ink applied is gradually changed under the condition that a maximum of six drops of ink are applied to a unit area of ​​1 / 600 inch x 1 / 600 inch. After the recorded image was dried for one day, the hue angle (H) and chroma (C) in the Lab color system were measured using a spectrophotometer (product name "X-Rite eXact" (M1 light source), manufactured by X-Rite). * ), and lightness (L * ) was measured. The color development of the image was evaluated according to the following evaluation criteria. Lightness was evaluated as the value at a saturation of 50. However, when the maximum saturation did not reach 50, the data obtained by measuring the color of the gradation pattern was extrapolated, and the evaluation was performed using the calculated lightness value obtained. The evaluation criteria were changed according to the hue angle because the preferred color tone perceived by the eye differs depending on the type of color.

[0123] [When the hue angle (H) is between 0° and 180°] AA: Maximum saturation was 60 or more and brightness was 80 or more, or maximum saturation was 55 or more and brightness was 85 or more. A: Maximum saturation was 55 or more and less than 60 and brightness was 80 or more and less than 85. B: The maximum saturation was 50 or more and less than 55 and the brightness was 80 or more and less than 85. C: The maximum saturation was less than 50 or the brightness was less than 80.

[0124] [When the hue angle (H) is 180° or more and less than 360°] AA: Maximum saturation was 60 or more and brightness was 70 or more, or maximum saturation was 55 or more and brightness was 75 or more. A: The maximum saturation was 55 or more and less than 60 and the brightness was 70 or more and less than 75. B: The maximum saturation was 50 or more and less than 55, and the brightness was 70 or more and less than 75. C: The maximum saturation was less than 50 or the brightness was less than 70.

[0125] (Image unevenness) Using the above inkjet recording device, the following solid image was recorded on a recording medium (glossy paper, product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT-201", manufactured by Canon). This solid image had a length of 18 cm in the longitudinal direction of the line head or the main scanning direction of the serial head, a length of 10 cm in the conveying direction of the recording medium, and a recording duty of 100%. Thirty minutes after recording, the state of unevenness in the solid image (mainly in overlapping areas) was visually confirmed under illumination with a fluorescent lamp and a black light (product name "SLUV-4", manufactured by AS ONE), and the image unevenness was evaluated according to the evaluation criteria shown below. A: No unevenness was observed under either fluorescent light or black light. B: No unevenness was observed under fluorescent light, but unevenness was observed under black light. C: Unevenness was observed under both fluorescent light and black light.

[0126] TIFF2024000522000007.tif255162

Claims

1. An inkjet recording method comprising the step of recording an image on a recording medium using an inkjet recording apparatus comprising: an aqueous ink containing resin particles dyed with a fluorescent dye; and a recording head having a plurality of nozzle rows configured in which a plurality of nozzles for ejecting the aqueous ink are arranged in a predetermined direction, wherein the method includes the step of recording an image on a recording medium, The plurality of nozzle rows include a first nozzle row and a second nozzle row that are offset from each other in the predetermined direction such that the end nozzles of adjacent nozzle rows form an overlapping portion in a direction intersecting the predetermined direction. The overlapping nozzles constituting the overlapping portion dispense the aqueous ink, which is then allocated to the first nozzle row and the second nozzle row. An inkjet recording method wherein the time difference in the application of the aqueous ink discharged from the overlapping nozzle is 20 milliseconds or less.

2. The inkjet recording method according to claim 1, wherein the recording head is a line head.

3. The inkjet recording method according to claim 1, wherein the recording head is a serial head that applies the aqueous ink to a unit area of ​​the recording medium in a single relative scan with the recording medium.

4. The inkjet recording method according to any one of claims 1 to 3, wherein the amount of the aqueous ink dispensed per drop is 10.0 ng or less.

5. The recording head is equipped with a temperature control mechanism. The inkjet recording method according to any one of claims 1 to 3, wherein the aqueous ink heated in the recording head by the temperature control mechanism is ejected.

6. The inkjet recording method according to claim 5, wherein the temperature control temperature Th of the recording head and the glass transition temperature Tg of the resin particles satisfy the relationship Th < Tg.

7. The inkjet recording method according to any one of claims 1 to 3, wherein the proportion (by mass) of the fluorescent dye in the resin particles is 2.0% by mass or more and 8.0% by mass or less.

8. The aforementioned water-based ink further contains a silicone-based surfactant, The inkjet recording method according to any one of claims 1 to 3, wherein the content (by mass) of the silicone-based surfactant in the aqueous ink is 0.1% by mass or more and 3.0% by mass or less, based on the total mass of the ink.

9. The aqueous ink further contains a water-soluble resin having anionic groups, The inkjet recording method according to any one of claims 1 to 3, wherein the water-soluble resin is a urethane resin.

10. The inkjet recording method according to claim 9, wherein the urethane resin has units derived from polyester polyol.

11. The inkjet recording method according to claim 10, wherein the content (mass%) of the urethane resin in the aqueous ink is 0.04 times or more and 1.00 times or less in mass ratio to the content (mass%) of the resin particles.

12. The inkjet recording method according to any one of claims 1 to 3, wherein the time difference in the application of the aqueous ink discharged from the overlapping nozzle is 1 millisecond or more and 20 milliseconds or less.

13. The inkjet recording method according to any one of claims 1 to 3, wherein the time difference in the application of the aqueous ink ejected from the overlapping nozzles is adjusted by at least one selected from the group consisting of the distance between the nozzle rows, the relative scanning speed between the recording head and the recording medium, and the scanning speed of the recording head.

14. An inkjet recording apparatus comprising: an aqueous ink containing resin particles dyed with a fluorescent dye; and a recording head having a plurality of nozzle rows configured in which a plurality of nozzles for ejecting the aqueous ink are arranged in a predetermined direction, The plurality of nozzle rows include a first nozzle row and a second nozzle row that are offset from each other in the predetermined direction such that the end nozzles of adjacent nozzle rows form an overlapping portion in a direction intersecting the predetermined direction. The overlapping nozzles constituting the overlapping portion dispense the aqueous ink, which is then allocated to the first nozzle row and the second nozzle row. An inkjet recording device in which the time difference in the application of the aqueous ink discharged from the overlapping nozzle is 20 milliseconds or less.

Images