Ink set, printing device, and printing method

Abstract

To provide an ink that offers excellent gloss uniformity and fixation on glossy paper. [Solution] An ink set comprising black, cyan, magenta, and yellow inks, wherein each ink comprises a colorant, a water-soluble organic solvent, resin particles, and water, and each ink comprises the following (A), or (A) and (B): (A) a compound represented by general formula (1) or general formula (2); (B) a colorant whose surface is partially coated with a water-insoluble resin. TIFF2026061258000029.tif59159 TIFF2026061258000030.tif38153

Description

Technical Field

[0001] The present invention relates to an ink set, a printing apparatus, and a printing method.

Background Art

[0002] Patent Document 1 describes an ink in which the content ratio of a resin emulsion to a coloring material is 1 / 5 or more and 15 / 1 or less, and the content ratio of a silicon acrylic resin emulsion to a coloring material is 1 / 20 or more and 5 / 1 or less. Patent Document 2 describes a recording method in which the ratio of a urethane resin to a coloring material is 0.10 or more, the ratio of cyan is larger than that of yellow, the ratio of magenta is larger than that of yellow, and the acrylic resin content in yellow is larger than the urethane resin content in yellow. Patent Document 3 describes an ink in which the value of the product of the surface tension σ at a bubble life time of 150 ms by the maximum bubble pressure method at 25°C is 100 or more and 130 or less.

Summary of the Invention

Problems to be Solved by the Invention

[0003] An object of the present invention is to provide an ink excellent in gloss uniformity and fixing property with respect to glossy paper.

Means for Solving the Problems

[0004] The present invention for solving the above problems is as described below. An ink set including black ink, cyan ink, magenta ink, and yellow ink, wherein the black ink, the cyan ink, the magenta ink, and the yellow ink contain a coloring material, a water-soluble organic solvent, resin particles, and water,​​​​​When the concentration of the colorant in the ink is denoted as P by mass%, and the concentration of the resin particles is denoted as R by mass%, the R / P value is highest for the magenta ink among the inks included in the ink set. Among the cyan ink, magenta ink, and yellow ink, the difference between the largest and smallest R / P values ​​is 0.10 or more and 0.40 or less. An ink set characterized by the following features. (A) Compounds represented by the following general formula (1) or general formula (2) (B) Colorants whose surface is coated with a water-insoluble resin in at least a portion of it. [ka] (In general formula (1), m represents an integer between 1 and 4.) [ka] (In general formula (2), R 1 (where l represents an alkyl group with 1 to 20 carbon atoms, an aralkyl group with 7 to 8 carbon atoms, or an allyl group; l represents an integer from 0 to 7; and n represents an integer from 20 to 200.) [Effects of the Invention]

[0005] According to the present invention, it is possible to provide an ink that exhibits excellent gloss uniformity and fixation on glossy paper. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a perspective view showing an example of the inkjet printing apparatus of the present invention. [Figure 2] Figure 2 is a cross-sectional view showing an example of the overall configuration of the inkjet printing apparatus of the present invention. [Figure 3] Figure 3 is a plan view illustrating an example of a nozzle plate in the inkjet printing apparatus of the present invention. [Figure 4] Figure 4 is an enlarged cross-sectional diagram illustrating the nozzle portion of the nozzle plate in the inkjet printing apparatus of the present invention. [Figure 5]Figure 5 shows the state in which a silicone resin is applied using a dispenser to form an ink-repellent layer. [Modes for carrying out the invention]

[0007] <ink> The following describes the organic solvents, water, colorants, resins, additives, etc., used in the ink.

[0008] <Organic solvents> The organic solvent used in the present invention is not particularly limited, and water-soluble organic solvents can be used. Examples include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Specific examples of water-soluble organic solvents include, for example, ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, and 1,5-pentanediol. Polyhydric alcohols such as pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, petriol, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether. Examples include polyhydric alcohol alkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate; and ethylene carbonate. It is preferable to use an organic solvent with a boiling point of 250°C or lower, as it not only functions as a wetting agent but also provides good drying properties.

[0009] Polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used. Specific examples of the polyol compound having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, and the like. Specific examples of the glycol ether compound include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, etc.; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, and the like.

[0010] The polyol compound having 8 or more carbon atoms and the glycol ether compound can improve the ink penetration when paper is used as the recording medium.

[0011] The content of the organic solvent in the ink is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of the drying property and ejection reliability of the ink, it is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 60% by mass or less.

[0012] <Water> The content of water in the ink is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of the drying property and ejection reliability of the ink, it is preferably 10% by mass or more and 90% by mass or less, and more preferably 20% by mass to 60% by mass.

[0013] <Colorant> The colorant is not particularly limited, and pigments and dyes can be used. As the pigment, an inorganic pigment or an organic pigment can be used. These can be used alone or in combination of two or more. Also, mixed crystals can be used. Examples of pigments that can be used include black pigment, yellow pigment, magenta pigment, cyan pigment, white pigment, green pigment, orange pigment, and glossy or metallic pigments such as gold and silver. As inorganic pigments, titanium dioxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chromium yellow can be used, as well as carbon black produced by known methods such as the contact method, furnace method, and thermal method. In addition, organic pigments such as azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (e.g., basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, and aniline black can be used. Of these pigments, those with good affinity for the solvent are preferred. Other uses such as resin hollow particles and inorganic hollow particles are also possible. Specific examples of pigments include carbon blacks (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, or metals such as copper, iron (CI Pigment Black 11), and titanium dioxide, as well as organic pigments such as aniline black (CI Pigment Black 1). Furthermore, for color applications, we have CI Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213, and CI Pigment O Range 5, 13, 16, 17, 36, 43, 51, CI Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B(Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88 , 101 (Bengara), 104, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, CI Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, 38; CI Pigment Blue 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3, 15:4 (Phthalocyanine Blue), 16, 17:1, 56, 60, 63; CI Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc. are available. The dyes used are not particularly limited and include acid dyes, direct dyes, reactive dyes, and basic dyes. They may be used individually or in combination of two or more types. Examples of the aforementioned dyes include CI Acid Yellow 17, 23, 42, 44, 79, 142; CI Acid Red 52, 80, 82, 249, 254, 289; CI Acid Blue 9, 45, 249; CI Acid Black 1, 2, 24, 94; CI Food Black 1, 2; CI Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173; CI Direct Red 1, 4, 9, 80, 81, 225, 227; CI Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202; CI Direct Black 19, 38, 51, 71, 154, 168, 171, 195; and CI Reactive Red. Examples include 14, 32, 55, 79, 249, and CI Reactive Black 3, 4, 35.

[0014] It is preferable that the black ink colorant is carbon black, the cyan ink colorant is Pigment Blue 15:3, the magenta ink colorant is Pigment Red 122 or 269, and the yellow ink colorant is Pigment Yellow 74, as this provides storage stability and expands the color gamut.

[0015] Methods for obtaining ink by dispersing pigments include introducing hydrophilic functional groups into the pigment to create a self-dispersible pigment, coating the surface of the pigment with a resin and dispersing it, and using a dispersant to disperse it. One method for creating self-dispersible pigments by introducing hydrophilic functional groups into pigments is to add functional groups such as sulfone groups or carboxyl groups to a pigment (e.g., carbon) to make it dispersible in water. One method for coating and dispersing pigments with a resin is to encapsulate the pigments in microcapsules, making them dispersible in water. This can be rephrased as resin-coated pigments. In this case, it is not necessary for all pigments incorporated into the ink to be coated with resin; as long as the effects of the present invention are not impaired, uncoated pigments or partially coated pigments may be dispersed in the ink. Methods of dispersion using dispersants include using well-known low-molecular-weight dispersants, such as surfactants, and high-molecular-weight dispersants.

[0016] As a dispersant, a compound represented by the following general formula (1) or a compound represented by the following general formula (2) is used. By using this dispersant, an aqueous pigment dispersion and aqueous ink with a small average particle size and excellent storage stability can be obtained. The content of the compound represented by the following general formula (1) or the compound represented by the following general formula (2) is preferably 0.01 to 0.5 by mass ratio per 1 unit of pigment in the ink, and more preferably 0.1 to 0.4. A content within this range is preferable because it allows for the acquisition of an ink with a small volume-average particle size, good pigment dispersibility, and appropriate ink viscosity. [ka] (In general formula (1), m represents an integer between 1 and 4.) [ka] (In general formula (2), R 1 (where l represents an alkyl group with 1 to 20 carbon atoms, an aralkyl group with 7 to 8 carbon atoms, or an allyl group; l represents an integer from 0 to 7; and n represents an integer from 20 to 200.) It is preferable to use naphthalene sulfonic acid formalin condensate as the compound described in general formula (1) and polyoxyethylene-β-naphthyl ether as the compound described in general formula (2) to obtain good dispersibility.

[0017] In the ink set of the present invention, the black ink, cyan ink, and yellow ink each contain the following component (A). In contrast, if the magenta ink contains (A) below, the dot surface will not be smooth, resulting in a decrease in gloss. If the magenta ink does not contain the compound represented by the above general formula (1) or (2), and uses a colorant encapsulated in a water-insoluble resin, the gloss will improve due to the effect of the water-insoluble resin. Therefore, the magenta ink in the ink set of the present invention does not contain (A) below, but contains (B). In addition, the black ink, cyan ink, and yellow ink may contain (B) below as components. (A) Compounds represented by the following general formula (1) or general formula (2) (B) Colorants whose surface is coated with a water-insoluble resin in at least a portion of it.

[0018] <Fluorescent whitening agent> Fluorescent whitening agents are substances that absorb invisible short-wavelength ultraviolet light and convert it into visible violet to blue light. They are also called fluorescent dyes, and may be used to increase the perceived concentration of a substance beyond what is visible to the naked eye. Examples of fluorescent whitening agents used include those having a structural unit represented by the following structural formula (1) or the following structural formula (2). [ka] [ka]

[0019] The material having the structural unit represented by structural formula (1) is a benzoxazole or a derivative thereof, and the material having the structural unit represented by structural formula (2) is a coumarin or a derivative thereof, which may be hydrophilic or hydrophobic.

[0020] The content of the fluorescent whitening agent in the ink is preferably 0.001% by mass or more and 1% by mass or less, and more preferably 0.005% by mass or more and 0.2% by mass or less. By setting the content of the fluorescent whitening agent to 0.001% by mass or more, a visually high concentration can be achieved. On the other hand, by setting the content of the fluorescent whitening agent to 1% by mass or less, the concentration quenching phenomenon, in which the fluorescence intensity decreases due to the immediate absorption of incident light or collisions between molecules, can be suppressed.

[0021] Examples of fluorescent whitening agents include commercially available products such as TINOPAL OB (manufactured by BASF), Nikkafluor OB, Nikkabright PAW-L, and Nikkafluor MCT (manufactured by Nippon Chemical Industries, Ltd.).

[0022] <Fluorescent whitening enhancer> In this invention, a fluorescent whitening enhancer may be used to improve the effect of the fluorescent whitening agent. The fluorescent whitening enhancer improves the effect of the fluorescent whitening agent by improving its dispersibility and causing it to migrate to the surface, and specifically, it is a polyether polyol. The content of the fluorescent whitening enhancer in the ink is preferably 0.2% to 2% by mass relative to the colorant content, and more preferably 0.5% to 2% by mass. By setting the fluorescent whitening enhancer content to 0.2% by mass or more relative to the colorant content, a visually high concentration can be achieved. On the other hand, by setting the fluorescent whitening enhancer content to 2% by mass or less relative to the colorant content, it is possible to improve the ejection stability. Examples of fluorescent whitening enhancers include commercially available products such as OptiAct I-10 manufactured by Sanopco.

[0023] <Pigment dispersion> It is possible to obtain ink by mixing pigments with materials such as water and organic solvents. Alternatively, ink can be manufactured by mixing pigments with other materials such as water and dispersants to create a pigment dispersion, and then mixing this dispersion with water and organic solvents. The aforementioned pigment dispersion is obtained by mixing and dispersing water, pigment, pigment dispersant, and other components as needed, and adjusting the particle size. Dispersion is preferably performed using a disperser. While there are no particular restrictions on the particle size of the pigment in the pigment dispersion, it is preferable that the maximum frequency, calculated in terms of maximum number, be between 20 nm and 500 nm, and more preferably between 20 nm and 150 nm, as this improves the dispersion stability of the pigment and enhances image quality such as ejection stability and image density. The particle size of the pigment can be measured using a particle size analyzer (NanoTrac Wave-UT151, manufactured by MicroTrac-Bell Co., Ltd.). In the aforementioned pigment dispersion, from the viewpoint of gloss uniformity on glossy paper, the difference between the highest and lowest pigment concentrations is preferably 2% by mass or less for cyan ink, magenta ink, and yellow ink, and more preferably 1% by mass or less. The pigment dispersion is preferably filtered to remove coarse particles and degassed using a filter, centrifuge, or other means, as needed.

[0024] <Resin> In the present invention, the ink may contain a polyether-based urethane resin represented by the following general formula (7). Including the polyether-based urethane resin represented by general formula (7) stabilizes the dispersion of the pigment, and in particular, provides excellent storage stability. The resin represented by general formula (7) can be identified, for example, by using GC-MS and NMR. [ka] The acid value of the polyether-based urethane resin is preferably between 48 KOH mg / g and 80 KOH mg / g. An acid value between 48 KOH mg / g and 80 KOH mg / g ensures stable pigment dispersion and good storage stability. The acid value can be measured by dissolving the sample in an ethanol / ether mixture, adding a phenolphthalein indicator solution, then adding a 0.1 mol / L potassium hydroxide solution dropwise, and calculating the acid value from the 0.1 mol / L potassium hydroxide solution required for titration. Polyether-based urethane resin particles may also be used. The aforementioned resin particles may be synthesized as appropriate, or commercially available products may be used. Examples of commercially available products include Takelac W5661 and W932 manufactured by Mitsui Chemicals, Inc. Furthermore, these may be used individually or in combination of two or more types of resin particles. The ink may also contain other resins. There are no particular restrictions on the type of resin contained in the ink, and it can be appropriately selected depending on the purpose. Examples include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, and acrylic silicone resin. Resin particles made from these resins may also be used. Ink can be obtained by mixing the resin particles, dispersed in water as a dispersion medium in a resin emulsion, with materials such as colorants and organic solvents. The resin particles may be synthesized as appropriate, or commercially available products may be used. Furthermore, these may be used individually or in combination of two or more types of resin particles.

[0025] There are no particular restrictions on the volume-average particle size of the resin particles, and they can be appropriately selected depending on the purpose. However, from the standpoint of obtaining good adhesion and high image hardness, a size of 10 nm to 1,000 nm is preferred, 10 nm to 200 nm is more preferred, and 10 nm to 100 nm is particularly preferred. The volume-average particle size can be measured, for example, using a particle size analyzer (NanoTrac Wave-UT151, manufactured by MicroTrac-Bell Co., Ltd.).

[0026] There are no particular restrictions on the resin content, and it can be appropriately selected depending on the purpose. However, from the viewpoint of fixation and storage stability of the ink, it is preferable that the resin content be 1% to 30% by mass, and more preferably 5% to 20% by mass, relative to the total amount of ink.

[0027] There are no particular restrictions on the particle size of the solids in the ink, and they can be appropriately selected depending on the purpose. However, from the standpoint of improving ejection stability and image quality such as image density, it is preferable that the maximum frequency in terms of maximum number is between 20 nm and 1000 nm, and more preferably between 20 nm and 150 nm. The solids include resin particles, pigment particles, etc. The particle size can be measured using a particle size analyzer (NanoTrac Wave-UT151, manufactured by MicroTrac-Bell Co., Ltd.).

[0028] Furthermore, in order to improve gloss uniformity and fixation on glossy paper, when the colorant concentration in the ink is P by mass% and the resin concentration is R by mass%, it is preferable that the R / P value is highest for magenta ink among black ink, cyan ink, magenta ink, and yellow ink, and that the difference between the largest and smallest R / P values ​​among cyan ink, magenta ink, and yellow ink is 0.1 or more and 0.4 or less. Furthermore, it is preferable that the average of the R / P values ​​for cyan ink, magenta ink, and yellow ink is between 0.25 and 0.35. Note that "total resin content" refers to all resins contained in the ink, including resins used to coat the colorants and binder resins. Resin refers to organic substances with a weight-average molecular weight of 5,000 or more.

[0029] <Additives> The ink may contain surfactants, defoamers, preservatives, antifungal agents, rust inhibitors, pH adjusters, etc., as needed.

[0030] <Surfactants> Silicone compounds, acetylene compounds, and polyoxyethylene alkyl ether compounds can be suitably used in the inks of the present invention. Surfactants are added to improve penetration or wettability into the substrate, and generally, surfactants with a low HLB (Hydrophilic Lipophilic Balance) are used. However, surfactants with a low HLB generally have poor solubility in water-containing vehicles, which can lead to problems such as poor storage stability and separation. To solve the above problems, the present invention includes one of the following: a silicon-based compound represented by general formulas (3) and (4), an acetylene-based compound represented by general formula (5), or a polyoxyethylene alkyl ether-based compound represented by general formula (6). The compounds of general formulas (3) to (6) can be identified, for example, by using GC-MS and NMR. [ka] (In general formula (3), a is an integer from 0 to 23, b is an integer from 1 to 10, c is an integer from 1 to 23, d is an integer from 0 to 23, and R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.) [ka] (In general formula (4), a is an integer from 1 to 8, and R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.) [ka] (In general formula (5), R1 to R4 are alkyl groups, m+n are integers from 1 to 20, and Y represents an acetylene group.) [ka] (In general formula (6), n represents an integer between 8 and 12.)

[0031] In the present invention, it is preferable to use a polysiloxane compound represented by general formula (3) with a low HLB and a polysiloxane compound represented by general formula (4) with a high HLB, and these may be used individually or in combination. In particular, when used in combination, the polysiloxane compound with a low HLB can be made compatible with the polysiloxane compound with a high HLB, so that separation over time can be suppressed while maintaining wettability to the substrate.

[0032] The content of the silicon-based compound is preferably 0.001% by mass or more and 3% by mass or less, and more preferably 0.01% by mass or more and 1% by mass or less, relative to the total amount of ink. As for the silicon-based compound, a synthesized one may be used as appropriate, or a commercially available product may be used. Examples of commercially available products include KF-6028, KF-6038 (manufactured by Shin-Etsu Chemical Co., Ltd.), SAG002, and SAG503A (manufactured by Nisshin Chemical Industry Co., Ltd.). Among these, KF6028 and SAG503A are particularly preferred from the viewpoint of storage stability.

[0033] In the present invention, it is preferable to use an acetylene compound represented by the general formula (5) with an HLB of 8 to 13. A HLB of 8 or higher ensures that the product does not become difficult to dissolve in water-containing vehicles, resulting in better storage stability. Furthermore, an HLB of 13 or lower prevents deterioration of defoaming properties. The acetylene compound content is preferably 0.1% to 3.0% by mass relative to the total amount of ink, and more preferably 0.5% to 2.0% by mass.

[0034] As for the acetylene compound, a synthesized one may be used as appropriate, or a commercially available product may be used. Examples of commercially available products include Surfinol 104 series, Surfinol 420, 440, 465, 485, Orphine PD-002W, EXP.4001, EXP.4200, EXP.4123 (manufactured by Nisshin Chemical Industry Co., Ltd.), and Acetinol E60, E100, E200 (manufactured by Kawaken Fine Chemical Co., Ltd.). Among these, Surfinol 440, 465, Orphine PD-002W, EXP.4001, EXP.4200, and EXP.4123 from Nisshin Chemical Industry Co., Ltd. are particularly preferred from the viewpoint of antifoaming properties and storage stability. These may be used individually or in combination of two or more.

[0035] In the present invention, it is preferable to use a polyoxyethylene alkyl ether compound represented by the general formula (6) described above. The content of the polyoxyethylene alkyl ether compound is preferably 0.1% by mass or more and 2.0% by mass or less relative to the total amount of ink, and more preferably 0.5% by mass or more and 1.0% by mass or less. When the compound represented by the general formula (6) is 0.1% by mass or more relative to the total amount of ink, the desired image density can be obtained without the dots spreading after the ink lands on the recording medium. On the other hand, when it is 2.0% by mass or less, the surface tension does not decrease, and the time it takes for the ink that overflows from the nozzle after being ejected from an ink ejection means such as an inkjet head to return into the nozzle does not increase, so there is no risk of frequent misalignment of the ejected ink.

[0036] As the polyoxyethylene alkyl ether compound, a compound that has been synthesized as appropriate may be used, or a commercially available product may be used. Examples of commercially available products include TRITON® HW-1000, TMN-3, TMN-6, TMN-100X, and TMN-10 (manufactured by Dow Chemical), among which TRITON® HW-1000 and TMN-6 are particularly preferred. These may be used individually or in combination of two or more.

[0037] Furthermore, the above-mentioned surfactants may be used in combination with other surfactants; for example, fluorinated surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can all be used. There are no particular restrictions on silicone-based surfactants, and they can be appropriately selected according to the purpose. Among them, those that do not decompose even at high pH are preferred, and examples include side-chain modified polydimethylsiloxane, both-end modified polydimethylsiloxane, one-end modified polydimethylsiloxane, and both-end modified polydimethylsiloxane. Those having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group as a modifying group are particularly preferred because they exhibit good properties as aqueous surfactants. In addition, polyether-modified silicone-based surfactants can also be used as the silicone-based surfactant, and examples include compounds in which a polyalkylene oxide structure is introduced into the Si side chain of dimethylsiloxane. Examples of fluorinated surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains, as they exhibit low foaming properties. Examples of the perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acid and perfluoroalkyl sulfonate salts. Examples of the perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acid and perfluoroalkyl carboxylic acid salts. Examples of polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains include sulfate ester salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in their side chains and salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in their side chains. Examples of counterions for the salts of these fluorinated surfactants include Li, Na, K, NH4, NH3CH2CH2OH, NH2(CH2CH2OH)2, and NH(CH2CH2OH)3. Examples of amphoteric surfactants include laurylaminopropionate, lauryldimethylbetaine, stearyldimethylbetaine, and lauryldihydroxyethylbetaine. Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol. Examples of anionic surfactants include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, lauryl salt, and salts of polyoxyethylene alkyl ether sulfate. These can be used individually or in combination of two or more types.

[0038] <Defoaming agent> There are no particular restrictions on the defoaming agent. For example, silicone-based defoaming agents, polyether-based defoaming agents, fatty acid ester-based defoaming agents, etc. can be mentioned. These can be used alone or in combination of two or more. Among these, silicone-based defoaming agents are preferred because of their excellent defoaming effect.

[0039] <Antiseptic and mold inhibitor> There are no particular restrictions on the antiseptic and mold inhibitor. For example, 1,2-benzisothiazolin-3-one, etc. can be mentioned.

[0040] <Rust inhibitor> There are no particular restrictions on the rust inhibitor. For example, acid sulfite, sodium thiosulfate, etc. can be mentioned.

[0041] <pH adjuster> There are no particular restrictions on the pH adjuster as long as it can adjust the pH to 7 or higher. Amines such as diethanolamine and triethanolamine can be mentioned.

[0042] There are no particular restrictions on the physical properties of the ink, and they can be appropriately selected according to the purpose. For example, it is preferable that the viscosity, surface tension, pH, etc. are in the following ranges. The viscosity of the ink at 25°C is preferably 5 mPa·s or more and 30 mPa·s or less, and more preferably 5 mPa·s or more and 25 mPa·s or less, from the points that the printing density and character quality are improved and good ejection performance can be obtained. Here, for example, a rotational viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) can be used to measure the viscosity. As the measurement conditions, it can be measured at 25°C, with a standard cone rotor (1°34’×R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and for 3 minutes. The surface tension of the ink is preferably 35 mN / m or less, and more preferably 32 mN / m or less, at 25°C, in order to ensure proper ink leveling on the recording medium and shorten the ink drying time. Furthermore, in order to suppress color mixing (bleeding) between ink colors, the surface tension of cyan, magenta, and yellow inks is lower than that of black ink, and the difference is preferably 3.0 mN / m or more, and preferably between 3.0 mN / m and 7.0 mN / m. From the viewpoint of preventing corrosion of metal components in contact with the ink, the pH of the ink is preferably 7 to 12, and more preferably 8 to 11.

[0043] <Silicone oil> Silicone oil may be added to prevent ink from sticking to the nozzle surface of the inkjet head. Silicone oil is a non-aqueous compound, and because the silicone oil, a non-aqueous component, covers the surface of the ink, even if ink adheres to the nozzle surface, the ink does not solidify on the nozzle surface, and the ink can be removed by the cleaning operation of the main unit. The silicone pill content is preferably 0.01% by mass or more and 1% by mass or less relative to the total amount of ink. More preferably 0.01% by mass or more and 0.5% by mass or less.

[0044] <wax> The liquid composition used in this invention may contain wax for the purpose of providing slipperiness to the image area. Among the aforementioned waxes, polyethylene wax or carnauba wax is particularly preferred from the viewpoint of film-forming properties and slipperiness when the liquid composition is applied to the image area. The melting point of the wax is preferably 80°C to 140°C, and more preferably 100°C to 140°C. By setting the melting point to 80°C or higher, the wax is less likely to melt or solidify excessively even at room temperature, thus maintaining the storage stability of the liquid composition. On the other hand, by setting the melting point to 140°C or lower, the wax melts sufficiently even at room temperature, making it possible to impart slipperiness to the liquid composition. The particle size of the wax is preferably 0.01 μm or larger, and more preferably 0.01 μm or larger and 0.1 μm or smaller. By setting the particle size to 0.01 μm or larger, the wax particles are more likely to orient themselves on the surface of the liquid composition, making it possible to impart slipperiness to the liquid composition. Examples of the polyethylene wax mentioned above include the Hi-Tech series manufactured by Toho Chemical Industry Co., Ltd. and the AQUACER series manufactured by BYK Corporation, which are commercially available products. Examples of the aforementioned carnauba wax include commercially available products such as Cellosol 524 and Trasol CN manufactured by Chukyo Oils Co., Ltd. The wax content is preferably 0.1% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 1% by mass or less.

[0045] <Recording medium> Recording media used for recording are not particularly limited, but examples include plain paper, glossy paper, specialty paper, cloth, film, OHP sheets, and general-purpose printing paper.

[0046] <Records> The ink recording material of the present invention has an image formed on a recording medium using the ink of the present invention. The data can be recorded and produced as a record using an inkjet recording device and an inkjet recording method.

[0047] <Recording device> As shown in Figure 1, the inkjet recording device used in the present invention comprises a device body 101, a paper feed tray 102 for loading paper attached to the device body 101, and a paper output tray 103 for storing paper attached to the device body 101 on which images have been recorded. The upper surface of the upper cover 111 of the device body 101 is a flat surface, and the front surface 112 of the front cover of the device body 101 is inclined diagonally downward and backward relative to the upper surface. Below this inclined front surface 112 of the front cover, there are a paper output tray 103 and a paper feed tray 102 that protrude forward (towards the front).

[0048] Furthermore, one end of the front surface 112 has an ink cartridge loading section 104 that protrudes forward from the front surface 112 and is lower than the upper cover 111. This ink cartridge loading section 104 has an openable and closable front cover 115 for inserting and removing ink cartridges. As shown in Figure 2, within the main body 101 of the device, the carriage 133 is held slidably in the main scanning direction by guide rods 131 and stays 132, which are guide members horizontally mounted on the left and right side plates, and is moved and scanned by a main scanning motor (not shown). This carriage 133 is equipped with a recording head 134 consisting of four inkjet heads that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (K). The recording head 134 has multiple ink ejection ports arranged in a direction intersecting the main scanning direction, and the ink droplet ejection direction is facing downwards.

[0049] The inkjet head constituting the recording head 134 can be equipped with an energy generating means for ejecting ink, such as a piezoelectric actuator like a piezoelectric element, a thermal actuator that utilizes a phase change due to the boiling of a liquid film using an electrothermal conversion element like a heating resistor, a shape memory alloy actuator that uses a metal phase change due to temperature changes, or an electrostatic actuator that uses static electricity.

[0050] Furthermore, the carriage 133 is equipped with sub-tanks 135 for each color to supply ink of each color to the recording head 134. Ink is supplied to these sub-tanks 135 via ink supply tubes (not shown) from the ink cartridges according to the present invention, which are loaded in the ink cartridge loading section 104.

[0051] On the other hand, the paper feeding section for feeding the paper 142 stacked on the paper stacking section 141 of the paper feed tray 103 includes a crescent roller (paper feeding roller) 143 that separates and feeds the paper 142 one sheet at a time from the paper stacking section 141, and a separation pad 144 made of a material with a high coefficient of friction that faces the paper feeding roller 143, and this separation pad 144 is biased toward the paper feeding roller 143.

[0052] On the other hand, the transport unit for transporting the paper 142 fed from the paper feed unit below the recording head 134 includes a transport belt 151 for electrostatically attracting and transporting the paper 142, a counter roller 152 for sandwiching and transporting the paper 142 sent from the paper feed unit via a guide 145 between itself and the transport belt 151, a transport guide 153 for changing the direction of the vertically upward-feeding paper 142 by 90° to make it conform to the transport belt 151, and a tip pressure roller 155 biased toward the transport belt 151 by a pressing member 154. In addition, a charging roller 156 is provided as a means for charging the surface of the transport belt 151.

[0053] Here, the conveyor belt 151 is an endless belt, stretched between the conveyor roller 157 and the tension roller 158, and configured to circulate in the belt conveying direction. This conveyor belt 151 has, for example, a surface layer that serves as the paper adsorption surface, formed from a pure resin material with a thickness of about 40 μm and no resistance control, such as ETFE pure material, and a back layer (earth layer) made of the same material as the surface layer but with resistance control using carbon. Furthermore, a guide member 161 is positioned on the back side of the transport belt 151, corresponding to the printing area by the recording head 134.

[0054] Furthermore, as a paper discharge section for ejecting the paper 142 recorded by the recording head 134, it is equipped with a separation claw 171 for separating the paper 142 from the transport belt 151, a paper discharge roller 172 and a paper discharge roller 173, and a paper discharge tray 103 is provided below the paper discharge roller 172.

[0055] The recording paper, held in place by the transport belt, is ejected from above by the ejection rollers. Essentially, the paper is transported by the transport belt and rollers, with the ejection rollers in the printer playing a supplementary role, such as preventing the paper from lifting. Therefore, compared to conventional inkjet printers, the number of rollers can be significantly reduced, minimizing smudges and scratches on recorded images.

[0056] Furthermore, a double-sided paper feed unit 181 is detachably attached to the rear of the main body 101 of the device. This double-sided paper feed unit 181 takes in the paper 142 that is returned by the reverse rotation of the transport belt 151, flips it over, and feeds it again between the counter roller 152 and the transport belt 151. In addition, a manual feed section 182 is provided on the top surface of this double-sided paper feed unit 181. When performing double-sided printing, the paper is immediately transported to the double-sided paper feed unit and flipped over without any waiting time after the printing of the front side is completed. The ink of this invention has high penetration into the paper and low moisture content, so it evaporates quickly, and the printed image can be flipped over without smudging, without requiring drying time or drying means such as heaters.

[0057] In this configured inkjet recording device, sheets of paper 142 are fed one by one from the paper feed section. The paper 142 fed vertically upward is guided by a guide 145 and transported between a transport belt 151 and a counter roller 152. Its leading edge is then guided by a transport guide 153 and pressed against the transport belt 151 by a leading pressure roller 155, thereby changing the transport direction by 90°. At this time, the transport belt 157 is charged by the charging roller 156, and the paper 142 is electrostatically attracted to the transport belt 151 and transported. Then, by moving the carriage 133 and driving the recording head 134 in accordance with the image signal, ink droplets are ejected onto the stationary paper 142 to record one line, and after transporting a predetermined amount of paper 142, the next line is recorded. Upon receiving a recording completion signal or a signal that the rear end of the paper 142 has reached the recording area, the recording operation is terminated and the paper 142 is ejected into the output tray 103.

[0058] An AC bias is applied to the charging belt, and positive and negative charges are alternately charged onto the transport belt at a constant pitch. The recording paper is attracted to the transport belt by the electrostatic force generated by the intermittently occurring minute electric field. The preferred range for the applied AC bias is ±1.2kV to ±2.6kV, and more preferably ±1.6kV to ±2.4kV. If the AC bias value is below the lower limit, sufficient attraction force cannot be obtained, and if it exceeds the upper limit, the minute droplets generated when ink is ejected from the nozzle are affected by the charge and, instead of landing on the paper, float back to the head and contaminate the area around the head. The effect of the charge on the minute droplets is related to the electrical properties of the ink. That is, the higher the electrical conductivity of the ink, the more susceptible the ejected droplets are to the effect of the charge, so it is necessary to suppress the electrical conductivity of the ink. Then, when the ink level in the sub-tank 135 is detected to be near the end, a predetermined amount of ink is supplied from the ink cartridge to the sub-tank 135.

[0059] Figure 3 is a plan view illustrating an example of a nozzle plate in the inkjet printing apparatus of the present invention. The nozzle plate used in this invention will be described with reference to Figures 3 and 4. Figure 4 is an enlarged cross-sectional diagram illustrating one nozzle section.

[0060] The nozzle plate 10 has a nozzle base material 20 in which holes (hereinafter sometimes referred to as "nozzles") 21 that become nozzles 11 for discharging liquid are formed, an intermediate layer 30 formed on the surface of the nozzle base material 20, and an ink-repellent layer 40 formed on the liquid discharge surface side. The nozzle base material 20 is, for example, a flat metal plate. A stainless steel flat metal plate is used as the nozzle base material 20, but it is not limited to this. The nozzle 11 has a cylindrical portion 21a on the liquid discharge side and a frustoconical portion 21b on the side opposite the liquid discharge side.

[0061] The intermediate layer 30 is composed of one or more layers, such as an underlying SiO2 layer or a silane coupling agent layer. This intermediate layer 30 is optional. The ink-repellent layer 40 is a layer containing silicone resin. The ink-repellent layer 40 has a sloped region 41 on the outer circumference of the nozzle 11, where the sloped surface 41a is formed in a direction that causes the film thickness to decrease toward the edge 11a side of the nozzle 11. The area 42 of the ink-repellent layer 40 other than the sloped region 41 has a nearly constant film thickness and is flat. The sloped surface 41a of the sloped region 41 may be straight in cross-sectional shape or curved in cross-sectional shape. The average film thickness of the ink-repellent layer 40 on the ink ejection surface side is preferably 1 μm or more and 3 μm or less. Furthermore, it is preferable that the intermediate layer 30 is a silane coupling agent layer having amino groups, which serves as the base layer for the ink-repellent layer 40. This allows for high adhesion through the interaction between the amino groups and the liquid-repellent film material.

[0062] (Manufacturing method for nozzle components of inkjet heads) Figure 5 shows a configuration in which a silicone resin is applied using the dispenser 34 according to this embodiment to form an ink-repellent layer 31 on the surface of the nozzle plate 32. A dispenser 34 for applying a silicone solution to the ink discharge surface of a nozzle plate 32 made of Ni electroformed material is positioned, and by scanning the dispenser 34 while dispensing silicone resin from the tip of the needle 35, while maintaining a predetermined constant distance between the nozzle plate 32 and the tip of the needle 35, a silicone resin film is selectively formed on the ink discharge surface of the nozzle plate 32.

[0063] In this embodiment, room-temperature curing silicone resin SR2411 (manufactured by Toray Dow Corning) was used as the silicone resin. However, some silicone leakage was observed around the nozzle holes and on the back surface of the nozzle plate. The thickness of the silicone resin film selectively formed in this way was 1.2 μm, and the surface roughness (Ra) was 0.18 μm. Any material that repels ink can be used for the ink-repellent layer, but specifically, a silicone-based water-repellent material can be mentioned.

[0064] The aforementioned silicone-based water-repellent material may be a room-temperature curing liquid silicone resin or elastomer, which is preferably applied to the surface of a substrate and polymerized and cured by being left in the atmosphere at room temperature to form an ink-repellent film. The silicone-based water-repellent material described above may be a heat-curing liquid silicone resin or elastomer, which may be applied to the surface of a substrate and cured by heat treatment to form an ink-repellent film. The aforementioned silicone-based water-repellent material may be an ultraviolet-curable liquid silicone resin or elastomer, which is applied to the surface of a substrate and hardened by irradiation with ultraviolet light to form an ink-repellent film. The viscosity of the silicone-based water-repellent material is preferably 1000 cp or less.

[0065] The critical surface tension of the ink-repellent layer is preferably 5 mN / m to 40 mN / m, and more preferably 5 mN / m to 30 mN / m. If the critical surface tension exceeds 30 mN / m, the nozzle plate may become too wet with ink during long-term use, which can lead to ink ejection deviations and particle abnormalities with repeated printing. If it exceeds 40 mN / m, the nozzle plate may become too wet with ink from the start, which can lead to ink ejection deviations and particle abnormalities from the start.

[0066] Furthermore, in the terminology of this invention, image formation, recording, printing, and the like are all synonymous. Recording media, media, and printed materials are all considered synonyms. [Examples]

[0067] 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 these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass" and respectively, unless otherwise specified. Unless otherwise specified, preparation and evaluation were carried out under conditions of 23°C and 50% humidity.

[0068] (Preparation of pigment dispersions) <Preparation of black pigment dispersion> A mixed slurry was obtained by premixing 250 parts of carbon black (manufactured by Degussa), 50 parts of the compound represented by the general formula (1) (Takesurf A-45-K, manufactured by Takemoto Oil Co., Ltd.), and 700 parts of distilled water. Next, the mixture was circulated and dispersed using 0.015 mm zirconia beads (70% packing rate) in a disc-type media mill (UMA type, manufactured by Kotobuki Kogyo Co., Ltd.) at a peripheral speed of 6 m / s and a liquid temperature of 10°C until the volume average particle size was approximately 100 nm. Then, coarse particles were separated using a centrifuge (Model-7700, manufactured by Kubota Shoji Co., Ltd.), and after filtration through a pore size of 1.2 μm, the water content was adjusted so that the solid content concentration was 15% to obtain a black pigment dispersion with a pigment concentration of 15%.

[0069] <Preparation of blue pigment dispersion> A mixed slurry was obtained by premixing 250 parts of Pigment Blue 15:3 (manufactured by Dainichi Seika Kogyo Co., Ltd.), 50 parts of the compound represented by the general formula (2) (Pionin D-7240, manufactured by Takemoto Yushi Co., Ltd.), and 700 parts of distilled water. Next, the mixture was circulated and dispersed using 0.015 mm zirconia beads (70% packing rate) in a disc-type media mill (UMA type, manufactured by Kotobuki Kogyo Co., Ltd.) at a peripheral speed of 6 m / s and a liquid temperature of 10°C until the volume average particle size was approximately 100 nm. Then, coarse particles were separated using a centrifuge (Model-7700, manufactured by Kubota Shoji Co., Ltd.), and after filtration through a pore size of 1.2 μm, the water content was adjusted so that the solid content concentration was 15% to obtain a blue pigment dispersion with a pigment concentration of 15%.

[0070] <Preparation of red pigment dispersion> In the preparation of the blue pigment dispersion described above, a red pigment dispersion with a pigment concentration of 15% was obtained in the same manner as the preparation of the blue pigment dispersion, except that Pigment Blue 15:3 was replaced with Pigment Red 122 (manufactured by Dainichi Seika Kogyo Co., Ltd.).

[0071] <Preparation of yellow pigment dispersion> In the preparation of the blue pigment dispersion described above, a yellow pigment dispersion with a pigment concentration of 15% was obtained in the same manner as the preparation of the blue pigment dispersion, except that Pigment Blue 15:3 was replaced with Pigment Yellow 74 (manufactured by Dainichi Seika Kogyo Co., Ltd.).

[0072] (Preparation of styrene-acrylic resin coated pigment dispersions) <Preparation of resin-coated black pigment dispersion> 11.2g of styrene, 2.8g of acrylic acid, 12g of lauryl methacrylate, 4g of polyethylene glycol methacrylate, 4g of styrene macromer, and 0.4g of mercaptoethanol were mixed and heated to 65°C. Next, a mixed solution of 100.8g of styrene, 25.2g of acrylic acid, 108g of lauryl methacrylate, 36.2g of polyethylene glycol methacrylate, 60g of hydroxyethyl methacrylate, 36g of styrene macromer, 3.6g of mercaptoethanol, 2.4g of azobismethylvaleronitrile, and 18g of methyl ethyl ketone was added dropwise to the flask over 2.5 hours. After the dropwise addition, a mixed solution of 0.8g of azobismethylvaleronitrile and 18g of methyl ethyl ketone was added dropwise to the flask over 0.5 hours. After aging at 65°C for 1 hour, 0.8g of azobismethylvaleronitrile was added and the mixture was aged for another hour. After the reaction was complete, 364 g of methyl ethyl ketone was added to the flask to obtain 800 g of a polymer solution with a solid content of 50%.

[0073] Next, 25 g of polymer solution, 50 g of carbon black (Cabot Corporation), 13.6 g of 1 mol / L potassium hydroxide aqueous solution, 20 g of methyl ethyl ketone, and 13.6 g of water were thoroughly mixed and then kneaded in a roll mill. The resulting paste was added to 200 g of pure water and thoroughly mixed, then the methyl ethyl ketone was removed using an evaporator. After pressure filtration through a polyvinylidene fluoride membrane filter with an average pore size of 5 μm, the water content was adjusted to achieve a solid content concentration of 20%, yielding a styrene-acrylic resin-coated black pigment dispersion with a solid content concentration of 20% (pigment concentration 15%, coating resin concentration 5%).

[0074] <Preparation of resin-coated blue pigment dispersion> In the preparation of the above-mentioned resin-coated black pigment dispersion, a styrene-acrylic resin-coated blue pigment dispersion with a solid content of 20% (pigment concentration 15%, coating resin concentration 5%) was obtained in the same manner as the preparation of the resin-coated black pigment dispersion, except that carbon black was replaced with Pigment Blue 15:3 (manufactured by Dainichi Seika Kogyo Co., Ltd.).

[0075] <Preparation of resin-coated red pigment dispersion> In the preparation of the above-mentioned resin-coated black pigment dispersion, a styrene-acrylic resin-coated red pigment dispersion with a solid content of 20% (pigment concentration 15%, coating resin concentration 5%) was obtained in the same manner as the preparation of the resin-coated black pigment dispersion, except that carbon black was replaced with Pigment Red 122 (manufactured by Dainichi Seika Kogyo Co., Ltd.).

[0076] <Preparation of resin-coated yellow pigment dispersion> In the preparation of the resin-coated black pigment dispersion described above, a styrene-acrylic resin-coated yellow pigment dispersion with a solid content of 20% (pigment concentration 15%, coating resin concentration 5%) was obtained in the same manner as the preparation of the resin-coated black pigment dispersion, except that carbon black was replaced with Pigment Yellow 74 (manufactured by Dainichi Seika Kogyo Co., Ltd.).

[0077] <Synthesis of aqueous dispersion of aqueous polyurethane resin> In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 119.70 g of 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate was added as the polyisocyanate component, 60.90 g of dimethylolpropionic acid, 60.40 g of bisphenoxyethanol fluorene (manufactured by Osaka Gas Chemical Co., Ltd.), and 13.37 g of polytetramethylene glycol with a number average molecular weight of 2,000 were added as the active hydrogen component, and 300.00 g of methyl ethyl ketone was added as the solvent. The mixture was then heated to 80°C under a nitrogen atmosphere and stirred for 12 hours. After confirming the disappearance of the isocyanate absorption band by infrared absorption spectroscopy, the mixture was cooled to 40°C, neutralized with 45.99 g of triethylamine, and then dispersed using a homodisperser with 700.00 g of water. Subsequently, methyl ethyl ketone was removed by distillation at 50°C under reduced pressure of 6.66 kPa to obtain an aqueous dispersion of polyurethane resin that was substantially solvent-free, with a fluorene skeleton content of 20% by mass, an acid value of 85 KOH mg / g, a solids content of 30% by mass, and a viscosity of 200 mPa·s.

[0078] (Ink preparation) First, the organic solvents, surfactants, other additives (such as defoamers, pH adjusters, and antibacterial agents) shown in Tables 1 and 2, along with deionized water, were mixed and stirred for 1 hour. Next, resin particles were added and the mixture was stirred for another hour to ensure uniform mixing. Then, various pigment dispersions were added and the mixture was stirred for another hour to ensure uniform mixing. This mixture was pressure filtered through a polyvinylidene fluoride membrane filter with an average pore size of 0.8 μm to remove coarse particles and debris, thereby obtaining the ink.

[0079] <Resin particles> Polyether-based urethane resin particles A (manufactured by Mitsui Chemicals, Inc. - Takelac W5661: Acid value = 48 KOH mg / g) * Compounds of general formula (7) Polyether-based urethane resin particles B (manufactured by Mitsui Chemicals, Inc. - Takelac W932: Acid value = 80 KOH mg / g) * Compounds of general formula (7) Polyether urethane resin particles C (synthetic product: acid value = 85 KOH mg / g)

[0080] <Surfactants> Silicone-based surfactant A (Shin-Etsu Chemical Co., Ltd., KF-6028) * Compounds of general formula (3) Silicone-based surfactant B (manufactured by Nisshin Chemical Industry Co., Ltd., SAG503A) * Compounds of general formula (4) Acetylene-based surfactant (Surfinol 440, manufactured by Nisshin Chemical Industry Co., Ltd.) * Compounds of general formula (5) Polyoxyethylene alkyl ether surfactant (Dow Chemical Company, TRITON® HW-1000) * Compounds of general formula (6) Fluorine-based surfactant (OMNOVA PF656)

[0081] <Organic solvents> Organic solvent A (Glycerin, manufactured by Sakamoto Pharmaceutical Co., Ltd.) Organic solvent B (1,3-butylene glycol, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0082] <Silicone oil> Polyether-modified silicone oil (Shin-Etsu Chemical Co., Ltd., KF353)

[0083] <wax> Polyethylene-based wax emulsion (BYK AQUACER-539)

[0084] <Printing method> Tables 1 and 2 show black (Example K-1), cyan (Example C-1), yellow (Example Y-1), and various magenta inks (Examples M-1 to M-16, Comparative Examples M-1 to M-4). The image was printed at a resolution of 1200 x 1200 dpi onto a recording medium (Sakurai Star Glossy Photo 3) using an image forming apparatus (Ricoh SG5200) equipped with a nozzle plate having an ink-repellent layer made of silicone resin (Toray Dow Corning's room-temperature curing silicone resin SR2411). The printed sample was dried at room temperature for 24 hours. The print chart used a 2cm square solid black image and a solid color image. For the solid black image, two versions were created: one printed with black ink alone, and another with a composite black image created using each color ink.

[0085] <60° gloss evaluation> The gloss level of solid images in printed samples was measured using a gloss meter (BYK Microgloss 60), and the following evaluation criteria were used for judgment. A judgment of △, ○, or ◎ indicates a level suitable for practical use. (Evaluation Criteria) ◎: 70 or higher ○: 60 or more and less than 70 △: 50 or more but less than 60 ×: Less than 50

[0086] <Uniform gloss> In this invention, gloss uniformity is evaluated by the gloss difference between the composite black, cyan, magenta, and yellow solid areas formed with cyan / magenta / yellow. The evaluation method is as follows. The gloss level within the composite black, cyan, magenta, and yellow solid images was measured using a gloss meter (BYK MicroGloss 60). The gloss difference between each color (maximum gloss - minimum gloss) was calculated, and the results were evaluated according to the following criteria. Furthermore, the glossiness of each color was determined by measuring the glossiness at multiple locations (5 locations) within the solid color image and taking the average. If the rating is △ or ○, it is at a level where it can be used in practice. (Evaluation Criteria) Less than 0:30 △: 30 or more but less than 50 ×: 50 or more

[0087] <Evaluation of retention> A solid image in a printed sample was rubbed five times back and forth using a scratching device (Clockmeter, manufactured by Daiei Kagaku Seiki Co., Ltd.) with a cotton cloth attached. The ink density transferred to the cotton cloth was measured using an image measuring device (Exact, manufactured by X-Rite Co., Ltd.), and the result was judged according to the evaluation criteria below. A result of △, ○, or ◎ indicates a level that is actually usable. (Evaluation Criteria) ◎: Less than 0.05 ○: 0.05 or more and less than 0.10 △: 0.10 or more and less than 0.20 ×: 0.20 or higher

[0088] <Image density evaluation> The image density within the solid-color images of the printed samples was measured using an image measuring device (X-Rite Exact), and the results were evaluated according to the following criteria. A rating of △, ○, or ◎ indicates a level suitable for practical use. (Evaluation Criteria) ◎: 2.0 or higher ○: 1.8 or higher and less than 2.0 △: 1.6 or higher and less than 1.8 ×: Less than 1.6

[0089] <Ink surface tension measurement> The surface tension of the ink was measured using an automatic surface tension meter (DY-300, manufactured by Kyowa Interface Science Co., Ltd.). [Table 1] [Table 2]

[0090] Examples of the present invention are as follows: (1) An ink set including black ink, cyan ink, magenta ink, and yellow ink, The black ink, the cyan ink, the magenta ink, and the yellow ink each contain a colorant, a water-soluble organic solvent, resin particles, and water. The black ink, the cyan ink, and the yellow ink each contain the following components (A), or (A) and (B). The magenta ink includes the following (B): When the concentration of the colorant in the ink is denoted as P by mass%, and the concentration of the resin particles is denoted as R by mass%, the R / P value is highest for the magenta ink among the inks included in the ink set. Among the cyan ink, magenta ink, and yellow ink, the difference between the largest and smallest R / P values ​​is 0.10 or more and 0.40 or less. An ink set characterized by the following features. (A) Compounds represented by the following general formula (1) or general formula (2) (B) Colorants whose surface is coated with a water-insoluble resin in at least a portion of it. [ka] (In general formula (1), m represents an integer between 1 and 4.) [ka] (In general formula (2), R 1 (where l represents an alkyl group with 1 to 20 carbon atoms, an aralkyl group with 7 to 8 carbon atoms, or an allyl group; l represents an integer from 0 to 7; and n represents an integer from 20 to 200.) (2) The ink set according to (1) above, wherein the difference between the highest and lowest colorant concentration among the cyan ink, magenta ink, and yellow ink is 2% by mass or less. (3) The ink set according to (1) or (2) above, wherein the average value of the R / P values ​​of the cyan ink, the magenta ink, and the yellow ink is 0.25 or more and 0.35 or less. (4) The ink set according to any one of items (1) to (3) above, wherein the ink constituting the ink set further comprises one of the following: a silicon-based compound represented by the following general formula (3) or the following general formula (4), an acetylene-based compound represented by the following general formula (5), or a polyoxyethylene alkyl ether-based compound represented by the following general formula (6). [ka] (In general formula (3), a is an integer from 0 to 23, b is an integer from 1 to 10, c is an integer from 1 to 23, d is an integer from 0 to 23, and R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.) [ka] (In general formula (4), a is an integer from 1 to 8, and R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.) [ka] (In general formula (5), R1 to R4 are alkyl groups, m+n are integers from 1 to 20, and Y represents an acetylene group.) [ka] (In general formula (6), n represents an integer between 8 and 12.) (5) The ink set according to any one of items (1) to (4) above, wherein the ink constituting the ink set further includes a polyether-based urethane resin represented by the following general formula (7). [ka] (6) The ink set according to (5) above, wherein the acid value of the polyether-based urethane resin is 48 KOH mg / g or more and 80 KOH mg / g or less. (7) The ink set according to any one of items (1) to (6) above, wherein the ink constituting the ink set further includes silicone oil. (8) The ink set according to any one of items (1) to (7) above, wherein the ink constituting the ink set further comprises polyethylene wax. (9) The ink set according to any one of items (1) to (8) above, wherein the water-insoluble resin is styrene-acrylic resin. (10) The ink set according to any one of items (1) to (9) above, wherein the surface tension values ​​of the cyan ink, the magenta ink, and the yellow ink are 3 mN / m or more lower than the surface tension value of the black ink. (11) An ink set according to any one of (1) to (10) above, wherein the ink is ejected by an inkjet head having an ink ejection nozzle and further comprising a nozzle plate having an ink-repellent layer containing a silicone resin or fluororesin on at least the surface on the ink ejection side. (12) A printing apparatus having an inkjet head, an ink set including black ink, cyan ink, magenta ink, and yellow ink, the nozzle plate having an ink-repellent layer containing a silicone resin or fluororesin on the ink ejection surface side surface, and a nozzle plate having an ink-repellent layer containing a silicone resin or fluororesin on the ink ejection surface side surface, A printing apparatus characterized in that the ink set is the ink set described in any one of the above items (1) to (10). (13) A printing method in which ink is ejected using an inkjet head equipped with a nozzle plate having an ink ejection nozzle and further having an ink-repellent layer containing a silicone resin on the ink ejection surface side, A printing method characterized by using an ink set described in any one of the above items (1) to (10) as the ink. (14) The printing method described in (13) above, wherein when printing a black image, the black ink is not used, and the cyan ink, magenta ink, and yellow ink are ejected to print the black image. [Explanation of symbols]

[0091] 10, 32 Nozzle Plate 11 nozzles 11a Edge 20 Nozzle base material 21 holes, nozzle 21a Cylindrical portion 21b frustum-shaped portion 30 Middle Class 31, 40 Ink-repellent layer 34 Dispensers 35 Needles 41 Slope area 41a Slope 101 Main unit of the device 102 Paper feed tray 103 Paper Output Tray 104 Ink cartridge loading section 105 Operation section 111 Top cover 112 Front of the front cover 115 Front Cover 131 Guide Rod 132 Stay 133 Carriage 134 Recording head 135 Sub-tank 141 Paper loading section 142 sheets 143 Paper feed roller 144 Separation Pad 145 Guide 151 Conveyor belt 152 Counter Roller 153 Conveyor Guide 154 Retaining member 155 Pressure roller at the tip 156 Electrostatic Roller 157 Conveyor Rollers 158 Tension Roller 161 Guide member 171 Separation claw 172 Paper output roller 173 Paper output roller 181 Duplex Paper Feed Unit 182 Manual feed section [Prior art documents] [Patent Documents]

[0092] [Patent Document 1] Patent No. 6814199 [Patent Document 2] Japanese Patent Publication No. 2018-149691 [Patent Document 3] Japanese Patent Publication No. 2023-101323

Claims

1. An ink set including black ink, cyan ink, magenta ink, and yellow ink, The black ink, the cyan ink, the magenta ink, and the yellow ink each contain a colorant, a water-soluble organic solvent, resin particles, and water. The black ink, the cyan ink, and the yellow ink each contain the following components (A), or (A) and (B): The magenta ink includes the following (B): When the concentration of the colorant in the ink is denoted as P by mass%, and the concentration of the resin particles is denoted as R by mass%, the R / P value is highest for the magenta ink among the inks included in the ink set. Among the cyan ink, magenta ink, and yellow ink, the difference between the largest and smallest R / P values ​​is 0.10 or more and 0.40 or less. An ink set characterized by the following features. (A) Compounds represented by the following general formula (1) or general formula (2) (B) A colorant whose surface is coated with a water-insoluble resin in at least a portion of it. 【Chemistry 1】 (In general formula (1), m represents an integer from 1 to 4.) 【Chemistry 2】 (In general formula (2), R １ (where l represents an alkyl group with 1 to 20 carbon atoms, an aralkyl group with 7 to 8 carbon atoms, or an allyl group; l represents an integer from 0 to 7; and n represents an integer from 20 to 200.)

2. The ink set according to claim 1, wherein the difference between the highest and lowest colorant concentrations among the cyan ink, magenta ink, and yellow ink is 2% by mass or less.

3. The ink set according to claim 1, wherein the average value of the R / P values ​​of the cyan ink, the magenta ink, and the yellow ink is 0.25 or more and 0.35 or less.

4. The ink set according to claim 1, wherein the ink constituting the ink set further comprises one of the following: a silicon-based compound represented by the following general formula (3) or the following general formula (4); an acetylene-based compound represented by the following general formula (5); or a polyoxyethylene alkyl ether-based compound represented by the following general formula (6). 【Transformation 3】 (In general formula (3), a is an integer from 0 to 23, b is an integer from 1 to 10, c is an integer from 1 to 23, d is an integer from 0 to 23, and R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.) 【Chemistry 4】 (In general formula (4), a is an integer from 1 to 8, and R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.) 【Transformation 5】 (In general formula (5), R １ ~R ４ (where m+n represents an alkyl group, m+n is an integer from 1 to 20, and Y represents an acetylene group.) 【Transformation 6】 (In general formula (6), n represents an integer between 8 and 12.)

5. The ink set according to claim 1, wherein the ink constituting the ink set further comprises a polyether-based urethane resin represented by the following general formula (7). 【Transformation 7】

6. The ink set according to claim 5, wherein the acid value of the polyether-based urethane resin is 48 KOH mg / g or more and 80 KOH mg / g or less.

7. The ink set according to claim 1, wherein the ink constituting the ink set further includes silicone oil.

8. The ink set according to claim 1, wherein the ink constituting the ink set further comprises polyethylene wax.

9. The ink set according to claim 1, wherein the water-insoluble resin is styrene-acrylic resin.

10. The ink set according to claim 1, wherein the surface tension values ​​of the cyan ink, the magenta ink, and the yellow ink are each 3 mN / m or more lower than the surface tension value of the black ink.

11. An ink set according to any one of claims 1 to 10, wherein the ink is ejected by an inkjet head having an ink ejection nozzle and a nozzle plate further having an ink-repellent layer containing a silicone resin or fluororesin on at least the ink ejection surface side surface.

12. A printing apparatus having an inkjet head equipped with a nozzle plate having an ink-discharging nozzle and further having an ink-repellent layer containing silicone resin or fluororesin on the ink-discharging surface, and an ink set including black ink, cyan ink, magenta ink, and yellow ink, A printing apparatus characterized in that the ink set is the ink set described in any one of claims 1 to 10.

13. A printing method for ejecting ink using an inkjet head that has an ink ejection nozzle and a nozzle plate further having an ink-repellent layer containing silicone resin on the ink ejection surface side, A printing method characterized by using an ink set described in any one of claims 1 to 10 as the ink.

14. The printing method according to claim 13, wherein when printing a black image, the black ink is not used, and the cyan ink, magenta ink, and yellow ink are ejected to print the black image.

Images