Aqueous ink set for inkjet recording

Abstract

Disclosed is an aqueous ink set for inkjet recording, which includes at least one black inkjet ink and one color inkjet ink. The aqueous ink set for inkjet recording is characterized in that: each inkjet ink contains a pigment, a poorly water-soluble resin, a nonionic surfactant, an organic solvent, and water; in each inkjet ink, the content of the organic solvent having a boiling point of more than 250°C under 1 atmospheric pressure with respect to the total amount of the inkjet ink is 5 mass% or less; if X mass% is the total solid content in each black ink and Y mass% is the total solid content in each color ink, the value of X-Y is 0.1 to 5.0 inclusive; and the total content (mass%) of the nonionic surfactant in each black ink is less than the total content (mass%) of the nonionic surfactant in each color ink. An aqueous ink set for inkjet recording according to the present invention is suitable for use in inkjet printing.

Description

Water-based ink set for inkjet recording.

[0001] The present invention relates to an aqueous ink set for inkjet recording, a method for manufacturing the same, and a printing method using the aqueous ink set for inkjet recording.

[0002] Inkjet printing is a recording method that directly ejects ink droplets from fine nozzles and adheres them to a recording medium to obtain characters and images. This method has become widespread due to its numerous advantages, including ease of full-color printing, low cost, the ability to use plain paper as a recording medium, and non-contact printing. In recent years, with the spread of digital printing, its use has expanded beyond consumer printing to commercial and industrial printing using low-absorbent coated paper, etc. The demand for inkjet ink is increasing further, with the aim of increasing printing speed, improving image quality, and reducing environmental impact. To meet these demands, various inkjet inks are being proposed, provided that they meet basic performance requirements such as ejection stability and storage stability.

[0003] For example, Patent Document 1 aims to provide an inkjet recording method that can obtain a good image without unevenness or color mixing without thermally deforming the medium when used for printing on a low-liquid-absorbent recording medium, and discloses an ink set used in this recording method that ejects inks in order from those with the highest static surface tension. Patent Document 2 also aims to provide an inkjet recording ink set that does not cause color bleeding even on coated paper for low-liquid-absorbent printing, and discloses an ink set in which the solid content concentration of the black ink is 2.5% by weight or more higher than the solid content concentration of each color ink.

[0004] Japanese Patent Publication No. 2017-222146 Japanese Patent Publication No. 2010-111752

[0005] The present invention relates to the following [1]. [1] An inkjet water-based ink set for inkjet recording comprising at least one black ink and one color ink, wherein each inkjet ink contains a pigment, a water-insoluble resin, a nonionic surfactant, an organic solvent, and water, and in each inkjet ink, the content of the organic solvent, which has a boiling point of more than 250°C at 1 atmosphere, relative to the total amount of inkjet ink is 5% by mass or less, and the value of X-Y, where the total solid content in each black ink is X% by mass and the total solid content in each color ink is Y% by mass, is 0.1 or more and 5.0 or less, and the total content (by mass) of the nonionic surfactant in each black ink is less than the total content (by mass) of the nonionic surfactant in each color ink. Detailed description of the invention

[0006] In inkjet recording methods, characters are sometimes printed with black ink, and then a solid color ink is printed over them. The reason for this overlapping printing is to make it difficult to detect printing defects caused by misalignment of the landing positions of each color due to improper adjustment of the recording head or uneven transport caused by bending of the mechanically transported recording media. However, to the inventor's knowledge, there is no inkjet ink set that can print characters without bleeding and with an even background color regardless of the printing order of black and color inks. For example, it has been found that the ink set described in Patent Document 1 has the problem that if the black ink is printed after the color ink, the characters printed with black ink will bleed. Also, it has been found that the inkjet recording ink set described in Patent Document 2 has the problem that the characters printed with black ink will bleed regardless of the printing order.

[0007] The present invention relates to an inkjet water-based ink set for recording, a method for manufacturing the same, and a printing method using the inkjet water-based ink set, which can produce a record in which bleeding of characters is suppressed even when characters printed with black ink and backgrounds printed with color ink overlap, regardless of the printing order of black ink and color ink, and in which solid color areas are uniformly wetted and spread, resulting in good solid coverage.

[0008] According to the present invention, regardless of the printing order of black ink and color ink, even when characters printed with black ink and backgrounds printed with color ink overlap, bleeding of characters is suppressed, and the solid color areas are uniformly wetted and spread, resulting in a record that provides good solid coverage. The present invention also provides an inkjet water-based ink set for recording, a method for manufacturing the same, and a printing method using the inkjet water-based ink set for recording.

[0009] As a result of the inventors' diligent investigation into the above problems, they have newly discovered that the above problems can be solved by setting the content of a specific organic solvent to below a specific amount, setting the total solid content (mass%) in each black ink to a specific amount greater than the total solid content (mass%) in each color ink, and setting the total content (mass%) of nonionic surfactants in each black ink to less than the total content (mass%) of nonionic surfactants in each color ink. The mechanism is not clear, but the following reasons are considered. When printing black ink first and then color ink, the amount of highly wettable nonionic surfactant is small, so wetting does not spread easily. Furthermore, because the black ink printed first has a large solid content, before the color ink is ejected and lands on the recording medium, the viscosity increases due to drying and it is fixed on the recording medium, so it does not bleed easily. In addition, water-insoluble resins and pigments dispersed in resins are hydrophobic, so they adsorb hydrophobic nonionic surfactants that easily contribute to wetting. Therefore, the surfactants in the later-printed color ink are adsorbed by the resin abundant in the black ink that forms the previously printed characters, minimizing the wetting and spreading of the color ink on the black ink and thus preventing bleeding of the characters. On the other hand, since the color ink contains many nonionic surfactants, it is thought that it enables uniform wetting and good solid filling in the background areas where the black ink is not printed. Next, when printing color ink followed by black ink, the color ink printed first contains many nonionic surfactants, enabling uniform wetting and good solid filling. On the other hand, since the color ink contains more nonionic surfactants than the black ink, its dynamic surface tension decreases rapidly, creating a surface tension difference between it and the black ink, which has fewer nonionic surfactants and is printed later. Therefore, there is a risk that the color ink with low surface tension will erode the black ink with high surface tension.However, in this ink set, the total solid content of the black ink is high, so the hydrophobic particulate components in the black ink adsorb the nonionic surfactants in areas where the ink is printed multiple times or at the boundary between the text and background color, minimizing the erosion of the color inks. Furthermore, the increased viscosity of the concentrated black ink causes it to quickly fix onto the recording medium. It is believed that these combined factors suppress bleeding of the text. In addition, by limiting the content of organic solvents with a boiling point of over 250°C at 1 atmosphere to 5% by mass or less relative to the total amount of ink, it is possible to prevent a significant decrease in the drying properties of the ink, and it is believed that the above effects are more easily achieved even in recording methods with high printing speeds such as one-pass printing.

[0010] [Water-based ink set for inkjet recording] The water-based ink set for inkjet recording of the present invention (hereinafter also simply referred to as "ink set") comprises two or more types of inkjet ink, comprising at least one type of black ink and one type of color ink. Examples of the color ink include one or more known color inks such as yellow ink, magenta ink, cyan ink, green ink, orange ink, violet ink, and white ink. Preferred embodiments include an ink set comprising black ink, yellow ink, magenta ink, and cyan ink, and further embodiments comprising green ink, orange ink, violet ink, and / or white ink. In addition, the ink set may also include a pre-treatment agent effective for improving image quality and a post-treatment agent effective for protecting the ink coating, in addition to the black ink and color ink.

[0011] [Inkjet Ink] The inkjet ink of the present invention (hereinafter also simply referred to as "ink") contains a pigment, a water-insoluble resin, a nonionic surfactant, an organic solvent, and water. Inkjet ink is an ink used for inkjet printing, and the inkjet ink of the present invention is an aqueous inkjet ink in which water accounts for the largest proportion by mass in the medium it contains.

[0012] The definitions of various terms used in this specification are as follows: "Printing" is a concept that includes printing and printing that records characters and images, and "Printed material" is a concept that includes printed material and printed material on which characters and images are recorded. "(Meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. "(Meth)acrylate" means at least one selected from the group consisting of acrylate and methacrylate.

[0013] <Pigments> The pigments contained in the inkjet ink of the present invention may be either inorganic pigments or organic pigments. Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferred for black ink. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Examples of white ink include metal oxides such as titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. The pigments can be used individually or in combination of two or more. In this patent, "black ink" refers to ink containing carbon black as a pigment, and "color ink" refers to ink containing pigments other than carbon black.

[0014] Preferred forms of pigments include pigments that can maintain a dispersed state without a dispersant, i.e., self-dispersing pigments; pigment particles in which the pigment is dispersed with a low-molecular-weight or high-molecular-weight surfactant; and resin particles containing the pigment. Of these, the form of resin particles containing the pigment is preferred from the viewpoint of dispersion stability and fixation of the pigment. Furthermore, the resin in the resin particles containing the pigment may be an uncrosslinked resin or a crosslinked resin. Here, "resin particles containing pigment" (hereinafter also referred to as "pigment-containing resin particles") means particles in which the resin encapsulates the pigment, particles in which a part of the pigment is exposed on the surface of particles consisting of resin and pigment, particles in which the resin is adsorbed onto a part of the pigment, or mixtures thereof. Of these, particles in which the resin encapsulates the pigment are more preferred.

[0015] [Pigment-containing resin particles] The pigment-dispersing resin constituting the pigment-containing resin particles must be a resin that has the ability to disperse pigments in an aqueous medium, and may be water-soluble or sparingly water-soluble. Here, "sparingly water-soluble" means that when a resin that has been dried at 105°C for 2 hours and reached a constant weight is dissolved in 100g of water at 25°C until saturation is reached, the amount dissolved is 10g or less. If the sparingly water-soluble resin is an anionic resin, the amount dissolved is the amount dissolved when the anionic groups of the resin are 100% neutralized with sodium hydroxide. If the pigment-dispersing resin constituting the pigment-containing resin particles is sparingly water-soluble, it may be a resin with the same constituent units and physical properties as the sparingly water-soluble resin described later, or it may be a resin with different constituent units or physical properties.

[0016] [Resin for Pigment Dispersion] Examples of resins for pigment dispersion include vinyl resins, polyester resins, and polyurethane resins. Among these, vinyl resins obtained by addition polymerization of vinyl monomers are preferred from the viewpoint of storage stability and ejection stability of inkjet inks. Such vinyl resins preferably contain (a-1) constituent units derived from hydrophilic ionic monomers and (a-2) constituent units derived from hydrophobic monomers, and may further contain (a-3) constituent units derived from hydrophilic nonionic monomers. "Hydrophobic" in hydrophobic monomers refers to the property of excluding water molecules and being poorly compatible with water. "Hydrophilic" in hydrophilic ionic monomers and hydrophilic nonionic monomers refers to the property of forming weak bonds with water molecules through electrostatic interactions or hydrogen bonding, and being easily compatible with water.

[0017] [(a-1) Hydrophilic Ionic Monomers] (a-1) As hydrophilic ionic monomers, anionic monomers are preferred, and examples include carboxylic acid monomers and sulfonic acid monomers, with carboxylic acid monomers being more preferred. Examples of carboxylic acid monomers include one or more selected from acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, but one or more selected from acrylic acid and methacrylic acid are more preferred.

[0018] [(a-2) Hydrophobic monomers] Specific examples of (a-2) hydrophobic monomers include those described in paragraphs

[0020] to

[0022] of Japanese Patent Application Publication No. 2018-83938. Among these, alkyl (meth)acrylates having an alkyl group with 1 to 18 carbon atoms, particularly 1 to 10 carbon atoms, aromatic group-containing monomers having an aromatic group with 6 to 22 carbon atoms, macromonomers having a polymerizable functional group at one end are preferred, and one or more selected from styrene, α-methylstyrene, and benzyl (meth)acrylate are more preferred.

[0019] Macromonomers having a polymerizable functional group at one end are compounds with a number-average molecular weight of 500 to 100,000, preferably 1,000 to 10,000, and examples of polymerizable functional groups include acryloyloxy groups and methacryloyloxy groups. As macromonomers, aromatic group-containing monomer-based macromonomers are preferred, and examples of aromatic group-containing monomers that constitute them include the aforementioned aromatic group-containing monomers. Specific examples of commercially available styrene-based macromonomers include AS-6(S), AN-6(S), and HS-6(S) manufactured by Toagosei Co., Ltd.

[0020] [(a-3) Hydrophilic Nonionic Monomers] (a-3) Hydrophilic nonionic monomers are monomers that have a high affinity for water and water-soluble organic solvents, and are monomers that include hydroxyl groups or polyalkylene glycol chains, for example. Specific examples of component (a-3) include those described in paragraph

[0018] of Japanese Patent Application Publication No. 2018-83938. Among these, one or more selected from methoxypolyethylene glycol (n=1 to 30) (meth)acrylate and polypropylene glycol (n=2 to 30) (meth)acrylate are preferred. Components (a-1) to (a-3) can each be used by using the monomer components contained in each component individually or by mixing two or more of them.

[0021] (Content of each constituent unit in the pigment dispersion resin) The content of constituent units derived from components (a-1) to (a-3) in the pigment dispersion resin is as follows, from the viewpoint of the dispersion stability of the pigment and the storage stability and ejection stability of the inkjet ink. The content of component (a-1) is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. The content of component (a-2) is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. If component (a-3) is included, the content of component (a-3) is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0022] The mass ratio of [component (a-1) / component (a-2)] is preferably 0.4 or more, more preferably 0.5 or more, even more preferably 0.6 or more, and preferably 2 or less, more preferably 1.5 or less, and even more preferably 1 or less. In the present invention, the content of constituent units derived from components (a-1) to (a-3) in the pigment dispersion resin can be determined by measurement, or it can be substituted by the charging ratio of raw material monomers containing components (a-1) to (a-3) during the production of the pigment dispersion resin.

[0023] (Production of Pigment Dispersion Resin) The pigment dispersion resin can be produced by copolymerizing the above-mentioned monomer mixture by a known polymerization method. Solution polymerization is preferred as the polymerization method. There are no restrictions on the solvent used in solution polymerization, but polar solvents such as water, lower aliphatic alcohols, ketones such as methyl ethyl ketone, ethers, and esters are preferred. Polymerization initiators such as azo compounds and persulfates, and polymerization chain transfer agents such as mercaptans can be used during polymerization. The polymerization temperature varies depending on the type of polymerization initiator, monomer, and solvent used, but is preferably 30°C or higher, more preferably 50°C or higher, and preferably 95°C or lower, more preferably 80°C or lower. The pigment dispersion resin is preferably neutralized with an alkali metal compound as described later.

[0024] The weight-average molecular weight of the pigment dispersion resin is preferably 4,000 or more, more preferably 6,000 or more, even more preferably 8,000 or more, even more preferably 10,000 or more, and preferably 150,000 or less, more preferably 100,000 or less, even more preferably 80,000 or less, even more preferably 50,000 or less, even more preferably 30,000 or less, and even more preferably 20,000 or less, from the viewpoint of pigment dispersion stability. From the same viewpoint as above, the acid value of the pigment dispersion resin is preferably 50 mg KOH / g or more, more preferably 90 mg KOH / g or more, even more preferably 100 mg KOH / g or more, even more preferably 180 mg KOH / g or more, even more preferably 200 mg KOH / g or more, even more preferably 220 mg KOH / g or more, and preferably 400 mg KOH / g or less, more preferably 320 mg KOH / g or less, even more preferably 300 mg KOH / g or less, and even more preferably 280 mg KOH / g or less. The weight-average molecular weight and acid value of the pigment dispersion resin can be measured by the method described in the examples.

[0025] <Manufacturing of Pigment-Containing Resin Particles> Resin particles containing pigments can be efficiently manufactured by a method comprising the following steps I and II. Step I: A step of neutralizing at least a portion of the carboxyl groups of a pigment dispersion resin with an alkali metal compound to obtain an aqueous dispersion of the pigment dispersion resin. Step II: A step of dispersing the aqueous dispersion of the pigment dispersion resin obtained in Step I with a pigment to obtain an aqueous dispersion of pigment containing resin particles dispersed in the pigment dispersion resin.

[0026] Furthermore, in the production of pigment-containing resin particles, the process may optionally include a step III in which the aqueous pigment dispersion obtained in step II is crosslinked with a crosslinking agent.

[0027] (Step I) Preferably, at least a portion of the carboxyl groups of the pigment dispersion resin are neutralized using an alkali metal compound. This is thought to increase the charge repulsion force that develops after neutralization, suppressing the aggregation of pigment particles in inkjet ink and improving the dispersion stability of the pigment. The neutralization in Step I is preferably carried out so that the pH is between 7 and 11. Examples of alkali metal compounds include one or more selected from alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; alkali metal salts of carbonic acid such as disodium carbonate, sodium bicarbonate, and dipotassium carbonate; and alkali metal salts of boric acid such as sodium borate. Among these, from the viewpoint of availability and economy, alkali metal hydroxides are preferred, more preferably one or more selected from sodium hydroxide and potassium hydroxide, and even more preferably sodium hydroxide.

[0028] The degree of neutralization of the pigment dispersion resin is preferably 20 mol% or more, more preferably 25 mol% or more, and even more preferably 30 mol% or more, from the viewpoint of ensuring the dispersion stability of the pigment, and preferably 60 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less, from the viewpoint of crosslinking the pigment dispersion resin with a crosslinking agent. Here, the degree of neutralization (mol%) is calculated by the following formula: Degree of neutralization (mol%) = [Number of moles of alkali metal compound / Number of moles of carboxyl groups in the pigment dispersion resin] × 100 In the present invention, if an excess of alkali metal compound is used compared to the number of moles of carboxyl groups in the pigment dispersion resin, the degree of neutralization may exceed 100 mol%.

[0029] (Step II) In Step II, the dispersion treatment can be performed by main dispersion using shear stress alone to finely atomize the pigment particles to the desired particle size. However, from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture before further main dispersion. As a disperser used for pre-dispersion, commonly used mixing and stirring devices such as anchor blades and disperser blades can be used. As a disperser used for main dispersion, kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersers such as paint shakers and bead mills can be used. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment. When performing dispersion treatment using a high-pressure homogenizer, the average particle size of the pigment-containing resin particles in the aqueous pigment dispersion can be adjusted by controlling the processing pressure and the number of passes. From the viewpoint of productivity and economy, the processing pressure is preferably 60 MPa to 300 MPa, and the number of passes is preferably 3 to 30.

[0030] (Step III) In Step III, the pigment dispersion resin in which the pigment is dispersed is crosslinked with a crosslinking agent to form a crosslinked resin, and a pigment aqueous dispersion can be obtained in which particles of the crosslinked resin containing the pigment are dispersed in an aqueous medium.

[0031] As the crosslinking agent used in Step III, an epoxy compound is preferred, and a compound having two or more epoxy groups in the molecule is more preferred. A compound having two or more epoxy groups in the molecule is the same as the polyfunctional epoxy compound described later. Also, the preferred range of the epoxy equivalent of the compound having two or more epoxy groups in the molecule is the same as that of the polyfunctional epoxy compound described later.

[0032] When the resin for pigment dispersion is crosslinked by a crosslinking agent, the degree of crosslinking of the particles of the crosslinked resin for pigment dispersion is preferably 35 mol% or more, more preferably 40 mol% or more, still more preferably 45 mol% or more, from the viewpoints of storage stability and ejection stability of the inkjet ink, and, from the same viewpoints as above, is preferably 65 mol% or less, more preferably 60 mol% or less, still more preferably 55 mol% or less.

[0033] Here, in Step III, the degree of crosslinking (mol%) of the particles of the crosslinked resin for pigment dispersion may be the theoretically calculated degree of crosslinking by the following formula. However, when the theoretically calculated degree of crosslinking exceeds 100 mol%, the degree of crosslinking is taken as 100 mol%. Degree of crosslinking (mol%) of the particles of the crosslinked resin for pigment dispersion = [amount of crosslinking agent added / {equivalent of functional group of crosslinking agent (g / eq.) × number of moles of carboxylic acid of the resin for pigment dispersion contained in the pigment-containing resin particles}] × 100

[0034] The nonvolatile component concentration (solid content concentration) of the aqueous dispersion of the obtained pigment-containing resin particles is preferably 10% by mass or more, more preferably 15% by mass or more, from the viewpoint of dispersion stability, and is preferably 30% by mass or less, more preferably 25% by mass or less.

[0035] The content of the pigment in the aqueous dispersion of the pigment-containing resin particles is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 12% by mass or more, from the viewpoint of dispersion stability, and is preferably 25% by mass or less, more preferably 20% by mass or less, still more preferably 18% by mass or less.

[0036] The average particle diameter of the pigment-containing resin particles in the aqueous dispersion of the pigment-containing resin particles is preferably 50 nm or more, more preferably 70 nm or more, still more preferably 80 nm or more, and preferably 350 nm or less, more preferably 250 nm or less, still more preferably 150 nm or less, from the viewpoint of reducing coarse particles and improving the ejection stability of the inkjet ink.

[0037] The average particle diameter of the pigment-containing resin particles in the inkjet ink is substantially the same as the average particle diameter in the aqueous dispersion of the pigment-containing resin particles. The solid content concentration and the average particle diameter of the aqueous dispersion of the pigment-containing resin particles are measured by the method described in the examples.

[0038] The content of the pigment in the inkjet ink is preferably 2% by mass or more, more preferably 3% by mass or more, still more preferably 3.5% by mass or more, and preferably 8% by mass or less, more preferably 6% by mass or less, still more preferably 5% by mass or less, from the viewpoints of the storage stability and the ejection stability of the inkjet ink.

[0039] When the pigment is in the form of resin particles containing the pigment, the content of the resin particles containing the pigment in the inkjet ink is preferably 3% by mass or more, more preferably 4% by mass or more, still more preferably 4.5% by mass or more, even more preferably 5% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 7% by mass or less, even more preferably 6% by mass or less, from the viewpoints of the storage stability and the ejection stability of the inkjet ink.

[0040] <Water-Insoluble Resins> As for water-insoluble resins, the form of water-insoluble resin particles is preferred. Examples of water-insoluble resins include vinyl resins, polyester resins, polyurethane resins, etc. Among these, from the viewpoint of storage stability and ejection stability of inkjet inks, vinyl resins obtained by addition polymerization of vinyl monomers are preferred, and acrylic resins are more preferred. The water-insoluble resin preferably contains 0.5% by mass or less of pigment, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and even more preferably substantially free of pigment, i.e., 0% by mass. Such vinyl resins preferably contain (b-1) constituent units derived from hydrophilic ionic monomers and (b-2) constituent units derived from hydrophobic monomers, and may further contain (b-3) constituent units derived from hydrophilic nonionic monomers.

[0041] [(b-1) Hydrophilic Ionic Monomers] (b-1) Hydrophilic ionic monomers are preferably anionic monomers, such as carboxylic acid monomers and sulfonic acid monomers, with carboxylic acid monomers being more preferred. Carboxylic acid monomers include one or more selected from acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, with one or more selected from acrylic acid and methacrylic acid being more preferred.

[0042] [(b-2) Hydrophobic Monomers] The water-insoluble resin preferably contains one or more hydrophobic monomers selected from the group consisting of alkyl (meth)acrylates, cycloalkyl (meth)acrylates, aromatic group-containing (meth)acrylates, and aromatic group-containing monomers. As alkyl (meth)acrylates, alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms are preferred, as cycloalkyl (meth)acrylates having a cycloalkyl group with preferably 4 to 12 carbon atoms, more preferably 5 to 8 carbon atoms are preferred, and as aromatic group-containing (meth)acrylates, aromatic group-containing (meth)acrylates having 6 to 22 carbon atoms are preferred. As aromatic group-containing monomers, aromatic group-containing monomers having an aromatic group with 6 to 22 carbon atoms are preferred. Among these, one or more selected from cycloalkyl (meth)acrylates, styrene, α-methylstyrene, and benzyl (meth)acrylates are more preferred, and cycloalkyl (meth)acrylates are even more preferred. Preferred examples of cycloalkyl (meth)acrylates include one or more selected from cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and cycloheptyl (meth)acrylate. Among these, one or more selected from cyclopentyl acrylate, cyclohexyl acrylate, and cycloheptyl acrylate are preferred, with cyclohexyl acrylate being more preferred. The content of constituent units derived from cycloalkyl (meth)acrylate in the water-insoluble resin is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, even more preferably 45% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0043] [(b-3) Hydrophilic Nonionic Monomers] (b-3) Hydrophilic nonionic monomers are monomers that have a high affinity for water and water-soluble organic solvents, and are monomers that include hydroxyl groups or polyalkylene glycol chains, for example. Specific examples of component (b-3) include those described in paragraph

[0018] of Japanese Patent Application Publication No. 2018-83938. Among these, one or more selected from methoxypolyethylene glycol (n=1 to 30) (meth)acrylate and polypropylene glycol (n=2 to 30) (meth)acrylate are preferred. Components (b-1) to (b-3) above can be used individually or by mixing two or more monomer components contained in each component.

[0044] (Production of water-poorly soluble resin particles) Water-poorly soluble resin particles may be synthesized as appropriate or commercially available. A preferred embodiment of water-poorly soluble resin particles is described below, in which the water-poorly soluble resin is acrylic resin. Acrylic resin can be produced by copolymerizing raw material monomers containing the above monomers (b-1) to (b-3), etc., by a known polymerization method. Solution polymerization is preferred as the polymerization method. There are no restrictions on the solvent used in solution polymerization, but polar solvents such as aliphatic alcohols, ketones, ethers, and esters are preferred, and methanol, ethanol, acetone, methyl ethyl ketone, etc., are more preferred. Polymerization initiators and polymerization chain transfer agents can be used during polymerization. Examples of polymerization initiators include persulfates such as ammonium persulfate and potassium persulfate; and azo compounds such as water-soluble azo polymerization initiators and polymer azo polymerization initiators. Examples of polymerization chain transfer agents include thiols and mercaptans. The polymerization temperature varies depending on the type of polymerization initiator, monomer, and solvent used, but is preferably 30°C or higher, more preferably 50°C or higher, and more preferably 95°C or lower, and more preferably 80°C or lower.

[0045] The water-insoluble resin particles are preferably used as an aqueous dispersion in an aqueous medium, and may contain a dispersant such as a surfactant if necessary.

[0046] (Physical properties of acrylic resin) The acid value of the acrylic resin relating to the water-poorly soluble resin particles is preferably 100 mg KOH / g or more, more preferably 110 mg KOH / g or more, even more preferably 120 mg KOH / g or more, even more preferably 150 mg KOH / g or more, and even more preferably 190 mg KOH / g or more, and from the same viewpoint as above, preferably 350 mg KOH / g or less, more preferably 330 mg KOH / g or less, even more preferably 310 mg KOH / g or less, and even more preferably 290 mg KOH / g or less.

[0047] The weight-average molecular weight of the acrylic resin relating to the water-poorly soluble resin particles is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more, from the viewpoint of obtaining high-quality recordings in low-liquid-absorbent recording media, and also preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less, from the same viewpoint as above.

[0048] The acid value of the acrylic resin relating to the poorly water-soluble resin particles is calculated from the mass ratio of the constituent monomers. Furthermore, the weight-average molecular weight of the acrylic resin is measured by the method described in the examples.

[0049] Furthermore, in the production of water-insoluble resin particles, the obtained aqueous dispersion may be treated with a crosslinking agent to produce crosslinked resin particles. The crosslinking agent used is preferably an epoxy compound, and more preferably a compound having two or more epoxy groups in its molecule. The compounds having two or more epoxy groups in their molecule are the same as those described later for polyfunctional epoxy compounds. The preferred range of epoxy equivalents for compounds having two or more epoxy groups in their molecule is also the same as that for polyfunctional epoxy compounds described later.

[0050] (Polyfunctional epoxy compound) The polyfunctional epoxy compound is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having hydrocarbon groups with 3 to 8 carbon atoms, even more preferably one or more selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether. The epoxy group equivalent of the polyfunctional epoxy compound is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, and even more preferably 170 or less.

[0051] (Manufacturing of Crosslinked Resin Particles) Crosslinked resin particles can be efficiently manufactured by a method comprising the following steps 1 and 2. Crosslinked resin particles manufactured by the method comprising steps 1 and 2 have a crosslinked structure on the surface of the crosslinked resin particles, consisting of a structure derived from carboxyl groups in the water-insoluble resin particles and a structure derived from a polyfunctional epoxy compound. Step 1: A step to obtain an aqueous dispersion of water-insoluble resin particles by neutralizing at least a portion of the carboxyl groups of the water-insoluble resin particles with an alkali metal compound. Step 2: A step to obtain an aqueous dispersion of crosslinked resin particles by adding a polyfunctional epoxy compound to the aqueous dispersion of water-insoluble resin particles obtained in step 1 and reacting the carboxyl groups in the water-insoluble resin particles with the epoxy groups in the polyfunctional epoxy compound.

[0052] (Step 1) Preferably, at least a portion of the carboxyl groups of the water-insoluble resin particles are neutralized using an alkali metal compound. This is thought to increase the charge repulsion force that emerges after neutralization, suppressing aggregation of crosslinked resin particles in the ink and improving the dispersion stability of the crosslinked resin particles. The neutralization in Step 1 is preferably carried out so that the pH is between 7 and 11. Examples of alkali metal compounds include one or more selected from alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; alkali metal salts of carbonic acid such as disodium carbonate, sodium bicarbonate, and dipotassium carbonate; and alkali metal salts of boric acid such as sodium borate. Among these, from the viewpoint of availability and economic efficiency, alkali metal hydroxides are preferred, more preferably one or more selected from sodium hydroxide and potassium hydroxide, and even more preferably sodium hydroxide.

[0053] The degree of neutralization of the water-insoluble resin particles is preferably 15 mol% or more, more preferably 20 mol% or more, and even more preferably 25 mol% or more, from the viewpoint of ensuring the dispersion stability of the water-insoluble resin particles, and preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 35 mol% or less, from the viewpoint of the productivity of the crosslinked resin particles. Here, the degree of neutralization (mol%) is calculated by the following formula: Degree of neutralization (mol%) = [Number of moles of alkali metal compound / Number of moles of carboxyl groups of water-insoluble resin particles] × 100 In the present invention, if an excess of alkali metal compound is used compared to the number of moles of carboxyl groups of water-insoluble resin particles, the degree of neutralization may exceed 100 mol%.

[0054] (Step 2) In Step 2, the temperature at which the carboxyl groups in the water-insoluble resin particles react with the epoxy groups in the polyfunctional epoxy compound is preferably 50°C or higher, more preferably 70°C or higher, and preferably 95°C or lower, and more preferably 90°C or lower, from the viewpoint of completing the crosslinking reaction and economic efficiency. Also, from the same viewpoint as above, the time for the crosslinking treatment is preferably 1 hour or more, more preferably 3 hours or more, and preferably 10 hours or less, and more preferably 8 hours or less.

[0055] The amount of polyfunctional epoxy compound used is such that, from the viewpoint of obtaining high-quality recordings on low-liquid-absorption recording media, the degree of crosslinking of the resulting crosslinked resin particles is preferably 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, and even more preferably 30 mol% or more. Furthermore, from the same viewpoint as above, the amount is such that the degree of crosslinking of the resulting crosslinked resin particles is preferably 80 mol% or less, more preferably 75 mol% or less, even more preferably 70 mol% or less, and even more preferably 65 mol% or less. Here, in step 2, the degree of crosslinking (mol%) of the crosslinked resin particles may be the theoretical degree of crosslinking calculated by the following formula, which may be used as the degree of crosslinking of the pigment-containing polymer. However, if the theoretical degree of crosslinking exceeds 100 mol%, the degree of crosslinking shall be 100 mol%. Degree of crosslinking of crosslinked resin particles (mol%) = [Amount of polyfunctional epoxy compound added / {Equivalent amount of functional groups of the polyfunctional epoxy compound (g / eq.) × Number of moles of carboxylic acid in the water-poorly soluble resin particles contained in the crosslinked resin particles}] × 100

[0056] From the viewpoint of obtaining high-quality recordings on low-liquid-absorption recording media, the acid value of the crosslinked resin particles is preferably 35 mg KOH / g or more, more preferably 40 mg KOH / g or more, and even more preferably 50 mg KOH / g or more. From the same viewpoint, it is preferably 220 mg KOH / g or less, more preferably 190 mg KOH / g or less, even more preferably 155 mg KOH / g or less, even more preferably 130 mg KOH / g or less, even more preferably 110 mg KOH / g or less, even more preferably 100 mg KOH / g or less, even more preferably 80 mg KOH / g or less, and even more preferably 70 mg KOH / g or less. In the present invention, the acid value of the crosslinked resin particles is the acid value of the resin constituting the crosslinked resin particles, and is calculated from the acid value of the water-insoluble resin particles before crosslinking, the degree of crosslinking, and the amount of polyfunctional epoxy compound added.

[0057] The content of water-insoluble resin particles in the inkjet ink is preferably 2.5% by mass or more, more preferably 3.0% by mass or more, even more preferably 3.5% by mass or more, and even more preferably 4.0% by mass or more, from the viewpoint of obtaining high-quality recordings on low-liquid-absorbent recording media, and also preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. When the inkjet ink is black, the content is preferably 2.5% by mass or more, more preferably 3.0% by mass or more, even more preferably 3.5% by mass or more, even more preferably 4.0% by mass or more, and even more preferably 5% by mass or more, and also preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 7% by mass or less, from the viewpoint of obtaining high-quality recordings on low-liquid-absorbent recording media. When the inkjet ink is color, from the viewpoint of obtaining high-quality recordings on a low-liquid-absorbent recording medium, the amount is preferably 2.5% by mass or more, more preferably 3.0% by mass or more, even more preferably 3.5% by mass or more, and even more preferably 4.0% by mass or more. Furthermore, from the same viewpoint as above, it is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 7% by mass or less, even more preferably 6% by mass or less, and even more preferably 5% by mass or less.

[0058] The total solid content in the inkjet ink is not limited as long as it satisfies the following relationship, but from the viewpoint of obtaining high-quality recordings on a low-liquid-absorbent recording medium, it is preferably 8% by mass or more, more preferably 9% by mass or more, and even more preferably 10% by mass or more, and from the same viewpoint as above, it is preferably 16% by mass or less, more preferably 15% by mass or less, and even more preferably 14% by mass or less.

[0059] From the viewpoint of suppressing ink bleeding and enabling good solid filling, the total solid content in the inkjet ink is such that the X-Y value, where X is the total solid content in each black ink and Y is the total solid content in each color ink, is 0.1 or more and 5.0 or less, preferably 0.2 or more, more preferably 0.5 or more, even more preferably 1.0 or more, and even more preferably 1.5 or more, and from the same viewpoint as above, preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and even more preferably 2.5 or less. In embodiments using multiple black inks and color inks, the above relationship is satisfied between each inkjet. For example, if the total solid content in the black ink is X by mass and the total solid content in the yellow ink is Y １ Y is defined as the total solid content in magenta ink in mass percent. ２ Y represents the total solid content in the cyan ink, expressed in mass %, ３ In an embodiment of an ink set comprising mass %, X-Y １ X-Y ２ X-Y ３ The values ​​satisfy the relationship that all fall within the above range.

[0060] <Nonionic Surfactants> Nonionic surfactants contained in the inkjet ink of the present invention include acetylene glycol-based surfactants, ether-based surfactants, silicone-based surfactants, and fluorine-based surfactants. Among these, one or more selected from acetylene glycol-based surfactants, ether-based surfactants, and silicone-based surfactants are preferred, with acetylene glycol-based surfactants being the most preferred. Nonionic surfactants can be used individually or in combination of two or more.

[0061] Examples of acetylene glycol-based surfactants include acetylene diols such as 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, and 2,4-dimethyl-5-hexyn-3-ol, as well as ethylene oxide adducts of these acetylene diols, from the viewpoint of wettability to recording media and defoaming properties. Examples of commercially available acetylene glycol-based surfactants include the "Surfinol" series and "Orfin" series manufactured by Nisshin Chemical Industry Co., Ltd.

[0062] As for ether-based surfactants, polyoxyalkylene alkyl ether type surfactants are preferred. Examples of commercially available ether-based surfactants include the "Emulgen®" series manufactured by Kao Corporation.

[0063] As a silicone-based surfactant, polyether-modified silicone is preferred. Examples of commercially available silicone-based surfactants include the KF series from Shin-Etsu Chemical Co., Ltd. (KF-353, KF-355A, KF-642, KF-6011, etc.), the Silface SAG series from Nisshin Chemical Industry Co., Ltd. (SAG-005, SAG-008, etc.), the DOWSIL series from Dow Toray Industries, Inc. (FZ-2123, etc.), and the BYK series from BIC Chemie Japan Co., Ltd.

[0064] The total content of nonionic surfactants in inkjet ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, from the viewpoint of improving the continuous ejection of ink and obtaining a good image without unevenness or color mixing, and from the same viewpoint as above, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and even more preferably 2.5% by mass or less. When the inkjet ink is black, the total content of nonionic surfactants in inkjet ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and even more preferably 1.0% by mass or more, from the viewpoint of improving the continuous ejection of ink and obtaining a good image without unevenness or color mixing, and from the same viewpoint as above, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, even more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less. When the inkjet ink is colored, the total content of nonionic surfactants in the inkjet ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, even more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, and from the same viewpoint as above, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, even more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less.

[0065] In the aqueous ink set for inkjet recording of the present invention, as described above, the total content (% by mass) of the nonionic surfactant in each black ink is less than the total content (% by mass) of the nonionic surfactant in each color ink. For example, when the total content of the nonionic surfactant in each black ink is x% by mass and the total content of the nonionic surfactant in each color ink is y% by mass, the value of y - x is preferably 0.01 or more, more preferably 0.05 or more, still more preferably 0.10 or more, still more preferably 0.15 or more, still more preferably 0.20 or more, still more preferably 0.25 or more, still more preferably 0.30 or more from the viewpoint of suppressing bleeding of characters and enabling good solid filling, and from the same viewpoint as above, it is preferably 1.00 or less, more preferably 0.80 or less, still more preferably 0.50 or less. In an embodiment using a plurality of black inks and color inks, the above relationship is satisfied between each inkjet. For example, in an ink set comprising a total content of x% by mass of a nonionic surfactant in a black ink, a total content of y １ % by mass of a nonionic surfactant in a yellow ink, a total content of y ２ % by mass of a nonionic surfactant in a magenta ink, and a total content of y ３ % by mass of a nonionic surfactant in a cyan ink, the relationships of y １ - x, y ２ - x, y ３ - x all satisfy the relationship within the above range.

[0066] <Organic solvent> The organic solvents contained in the inkjet ink of the present invention include glycol ethers, polyhydric alcohols, nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, and alkanolamines. Among these, from the viewpoints of the spreading property, penetrability, storage stability, and ejection stability of the inkjet ink onto the recording medium, one or more selected from the group consisting of glycol ethers and polyhydric alcohols are preferable. The water-soluble organic solvent can be used alone or in combination of two or more.

[0067] Examples of glycol ethers include alkylene glycol monoalkyl ethers such as monoalkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers; and alkylene glycol dialkyl ethers such as monoalkylene glycol dialkyl ethers and dialkylene glycol dialkyl ethers. The alkylene oxide group of the glycol ether can be one or more selected from the group consisting of ethylene oxide group and propylene oxide group, with the ethylene oxide group being more preferred. The glycol ether preferably has at least one hydrocarbon group having 2 to 8 carbon atoms.

[0068] From the viewpoint of storage stability and ejection stability of inkjet inks, glycol ethers with an octanol-water partition coefficient logP value (hereinafter also simply referred to as "logP") of 0 or more are preferred. Examples of glycol ethers with an octanol-water partition coefficient logP value of 0 or more include alkylene glycol monoalkyl ethers. Among these, ethylene glycol monoisopropyl ether (logP: 0.23) and diethylene glycol monoisopropyl ether are preferred. Preferably, one or more selected from the group consisting of (logP: 0.07), ethylene glycol monoallyl ether (logP: 0.26), ethylene glycol monobutyl ether (logP: 0.81), diethylene glycol monoisobutyl ether (logP: 0.64), diethylene glycol mono-n-butyl ether (logP: 0.67), diethylene glycol ethyl methyl ether (logP: 0.12), diethylene glycol diethyl ether (logP: 0.45), dipropylene glycol monomethyl ether (logP: 0.05), propylene glycol monopropyl ether (logP: 0.71), propylene glycol monobutyl ether (logP: 1.13), dipropylene glycol monopropyl ether (logP: 0.88), and dipropylene glycol monobutyl ether (logP: 1.29) is preferred, with dipropylene glycol monomethyl ether being more preferred.

[0069] The glycol ether content in the inkjet ink of the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, even more preferably 5% by mass or more, and even more preferably 7% by mass or more, and from the same viewpoint as above, preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 10% by mass or less.

[0070] From the viewpoint of storage stability and ejection stability of inkjet inks, one or more polyhydric alcohols selected from the group consisting of propylene glycol (1,2-propanediol), 1,2-hexanediol, and other alkanediols having 2 to 6 carbon atoms, and diethylene glycol are preferred, with propylene glycol being more preferred.

[0071] The polyhydric alcohol content in the inkjet ink of the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, even more preferably 5% by mass or more, and even more preferably 7% by mass or more, and from the same viewpoint as above, preferably 15% by mass or less, more preferably 13% by mass or less, and even more preferably 10% by mass or less.

[0072] The content of the water-soluble organic solvent in the inkjet ink of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, from the viewpoint of storage stability and ejection stability of the inkjet ink, and, from the same viewpoint as above, preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

[0073] Furthermore, from the viewpoint of suppressing ink bleeding and enabling good filling, it is preferable that the content of organic solvents with a boiling point of more than 250°C at 1 atmosphere is low. The content of organic solvents with a boiling point of more than 250°C at 1 atmosphere relative to the total amount of inkjet ink is 5% by mass or less, preferably 4% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, even more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, and may be 0% by mass. Examples of organic solvents with a boiling point of more than 250°C at 1 atmosphere include glycerin, triethanolamine, triethylene glycol monobutyl ether, tripropylene glycol monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol mono-2-ethylhexyl ether, diethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monobenzyl ether, polyethylene glycol monomethyl ether, and the like.

[0074] <Water> The inkjet ink of the present invention contains water. From the viewpoint of preventing the contamination of unintended substances, pure water or ion-exchanged water is preferred as the water used in the inkjet ink of the present invention.

[0075] The water content in the inkjet ink is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of storage stability and ejection stability of the inkjet ink, and from the same viewpoint as above, preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0076] The inkjet ink of the present invention may contain various additives commonly used in inkjet inks, such as humectants, wetting agents, viscosity modifiers, defoamers, preservatives, fungicides, rust inhibitors, and neutralizing agents.

[0077] [Method for Manufacturing Inkjet Ink] The inkjet ink of the present invention can be efficiently manufactured by blending the above-mentioned pigment, water-insoluble resin, nonionic surfactant, organic solvent, and water, and optionally other surfactants, other additives, etc., and mixing the mixture. There are no particular restrictions on the method of mixing, but stirring is preferred. The amount of each component blended in the method for manufacturing the inkjet ink of the present invention can be considered as the content of each component in the inkjet ink of the present invention.

[0078] (Physical properties of inkjet ink) The viscosity of the inkjet ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, and even more preferably 3.5 mPa·s or more, from the viewpoint of obtaining high-quality recordings on low-liquid-absorbent recording media, and also preferably 10 mPa·s or less, more preferably 8 mPa·s or less, and even more preferably 6 mPa·s or less, from the same viewpoint as above.

[0079] The pH of the inkjet ink of the present invention is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher. Furthermore, from the viewpoint of material resistance and skin irritation, the pH is preferably 11.0 or lower, more preferably 10.0 or lower, and even more preferably 9.0 or lower. The viscosity and pH of the inkjet ink at 32°C can be measured by conventional methods.

[0080] [Method for manufacturing the ink set] The ink set of the present invention can be prepared by loading the above-mentioned inkjet ink into a known inkjet printing apparatus.

[0081] [Ink Set Printing Method] The ink set of the present invention can be loaded into a known inkjet printing device and ejected as ink droplets onto a recording medium such as coated paper or film to print images, etc. Piezoelectric, thermal, or electrostatic methods can all be used for ejecting the ink droplets. The ink set of the present invention is preferably used in an inkjet recording device that records by performing a single scan of the recording medium relative to the recording head.

[0082] As recording media used in printing with the ink set of the present invention, low-water-absorbent coated paper, particularly gloss coated paper, matte coated paper, and low-water-absorbent resin films can also be used as low-water-absorbent printing substrates. In printing substrates, "low-water-absorbent" is a concept that includes both low-water-absorbent and non-water-absorbent properties, and the amount of water absorbed by the resin film substrate at a contact time of 100 milliseconds with pure water is 0 g / m². ２ 10g / m or more ２ This means the following: Examples of resin films include transparent synthetic resin films, such as polyester films like polyethylene terephthalate film; vinyl chloride film; polyolefin films like polypropylene film and polyethylene film; and polyamide films like nylon film. These resin films may be stretched films such as biaxially oriented films and uniaxially oriented films, or unstretched films. Among these, the ink set of the present invention can produce high-quality recordings on gloss-coated paper and matte-coated paper, so it is preferable that the printing substrate be one or more selected from gloss-coated paper and matte-coated paper.

[0083] With regard to the embodiments described above, the present invention further discloses the following water-based ink set for inkjet recording, etc.

[0084] <1> An inkjet water-based ink set for inkjet recording, comprising at least one black ink and one color ink, wherein each inkjet ink contains a pigment, a water-insoluble resin, a nonionic surfactant, an organic solvent, and water, and in each inkjet ink, the content of the organic solvent, which has a boiling point of more than 250°C at 1 atmosphere, relative to the total amount of inkjet ink is 5% by mass or less, and the value of X-Y, where the total solid content in each black ink is X% by mass and the total solid content in each color ink is Y% by mass, is 0.1 or more and 5.0 or less, and the total content (by mass) of the nonionic surfactant in each black ink is less than the total content (by mass) of the nonionic surfactant in each color ink. <2> The inkjet water-based ink set for inkjet recording according to <1>, wherein the form of the pigment is in the form of resin particles containing the pigment, and the acid value of the pigment-dispersing resin constituting the resin particles is 100 mg KOH / g or more and 400 mg KOH / g or less. <3> The water-based inkjet recording ink set according to <1> or <2> above, wherein the water-insoluble resin is an acrylic resin. <4> The water-based inkjet recording ink set according to any one of <1> to <3> above, wherein the water-insoluble resin contains one or more hydrophobic monomers selected from the group consisting of cycloalkyl (meth)acrylates. <5> The water-based inkjet recording ink set according to any one of <1> to <4> above, wherein the nonionic surfactant contains an acetylene glycol-based surfactant. <6> The water-based inkjet recording ink set according to any one of <1> to <5> above, wherein the value of y-x is 0.01 or more and 1.00 or less when the total content of nonionic surfactant in each black ink is x by mass% and the total content of nonionic surfactant in each color ink is y by mass%. <7> The water-based inkjet recording ink set according to any one of <1> to <6> above, wherein the organic solvent contains a glycol ether. <8> An inkjet water-based ink set for use in an inkjet recording device that records by performing a single scan of the recording medium relative to the recording head, as described in any of <1> to <7> above. <9>A water-based inkjet recording ink set according to any of <1> to <8> above, used for printing on low-absorbent coated paper or non-absorbent film. <10> The black ink contains a pigment-containing resin, the pigment-containing resin contains components derived from acrylic acid and components derived from styrene, the weight-average molecular weight of the pigment-containing resin is 10,000 or more and 20,000 or less, the acid value of the pigment-containing resin is 200 mg KOH / g or more and 300 mg KOH / g or less, and the content of the pigment-containing resin in the black ink is 5% by mass or more and 7% by mass or less, the water-insoluble resin contains components derived from acrylic acid, components derived from butyl acrylate, components derived from cyclohexyl acrylate and components derived from a crosslinking agent, the pigment content in the water-insoluble resin is 0.01% by mass or less, the acid value is 50 mg KOH / g or more and 70 mg KOH / g or less, and the content in the black ink is 5% by mass or more and 7% by mass or less, the nonionic surfactant contains an acetylene glycol-based surfactant, a polyoxyethylene alkyl ether-based surfactant, or a silicone-based surfactant, The nonionic surfactant is contained in the black ink in a total amount of 1% to 2% by mass, the organic solvent is propylene glycol and dipropylene glycol monomethyl ether, the content of propylene glycol in the black ink is 7% to 13% by mass, the content of dipropylene glycol monomethyl ether in the black ink is 7% to 13% by mass, the content of the organic solvent having a boiling point of more than 250°C at 1 atmosphere is 0.1% by mass or less, the color ink contains a pigment-containing resin, the pigment-containing resin contains components derived from acrylic acid and components derived from styrene, the weight-average molecular weight of the pigment-containing resin is 10,000 to 20,000, the acid value of the pigment-containing resin is 200 mg KOH / g to 300 mg KOH / g, the content of the pigment-containing resin is 5% to 7% by mass in the color ink, the water-poorly soluble resin isIt contains components derived from acrylic acid, components derived from butyl acrylate, components derived from cyclohexyl acrylate, and components derived from a crosslinking agent, the pigment content in the water-poorly soluble resin is 0.01% by mass or less, the acid value is 50 mg KOH / g or more and 70 mg KOH / g or less, and it is contained in the color ink at a concentration of 3% by mass or more and 5% by mass or less, the nonionic surfactant includes an acetylene glycol-based surfactant, a polyoxyethylene alkyl ether-based surfactant, or a silicone-based surfactant, the nonionic surfactant is contained in the color ink in a total concentration of 1.5% by mass or more and 2.5% by mass or less, the organic solvent is propylene glycol and dipropylene glycol monomethyl ether, the propylene glycol content in the color ink is 7% by mass or more and 13% by mass or less, the dipropylene glycol monomethyl ether content in the color ink is 7% by mass or more and 13% by mass or less, and the organic solvent content having a boiling point greater than 250°C at 1 atmosphere is 0.1% by mass or less. A water-based inkjet ink set for inkjet recording according to any of <1> to <9>, wherein the X-Y value is 1.5 or more and 2.5 or less when the total solid content in each of the black inks is X by mass and the total solid content in each of the color inks is Y by mass, and the y-x value is 0.3 or more and 0.5 or less when the total content of nonionic surfactant in each of the black inks is x by mass and the total content of nonionic surfactant in each of the color inks is y by mass. <11> An ink set comprising at least one black ink and one color ink, wherein each ink contains a pigment, a water-insoluble resin, a nonionic surfactant, an organic solvent, and water, and the content of the organic solvent, whose boiling point at 1 atmosphere is greater than 250°C, in each ink is 5% by mass or less relative to the total amount of ink, and the value of X-Y, where X is the total solid content in each black ink and Y is the total solid content in each color ink, is 0.1 or more and 5.0 or less, and the total content (by mass) of the nonionic surfactant in each black ink is less than the total content (by mass) of the nonionic surfactant in each color ink, for use as an inkjet recording. <12>The use described in <11>, wherein the form of the pigment is in the form of resin particles containing the pigment, and the acid value of the pigment-dispersing resin constituting the resin particles is 100 mg KOH / g or more and 400 mg KOH / g or less. <13> The use described in <11> or <12>, which is used in an inkjet recording device that records by scanning the recording head relative to the recording medium once. <14> The use described in any of <11> to <13>, which is used for printing on low-water-absorbent coated paper or non-water-absorbent film. <15> The black ink contains a pigment-containing resin, the pigment-containing resin contains components derived from acrylic acid and components derived from styrene, the weight-average molecular weight of the pigment-containing resin is 10,000 or more and 20,000 or less, the acid value of the pigment-containing resin is 200 mg KOH / g or more and 300 mg KOH / g or less, and the content of the pigment-containing resin in the black ink is 5% by mass or more and 7% by mass or less, the water-poorly soluble resin contains components derived from acrylic acid, components derived from butyl acrylate, components derived from cyclohexyl acrylate and components derived from a crosslinking agent, the pigment content in the water-poorly soluble resin is 0.01% by mass or less, the acid value is 50 mg KOH / g or more and 70 mg KOH / g or less, and the black ink contains 5% by mass or more and 7% by mass or less, the nonionic surfactant contains an acetylene glycol-based surfactant, a polyoxyethylene alkyl ether-based surfactant, or a silicone-based surfactant, The nonionic surfactant is contained in the black ink in a total amount of 1% to 2% by mass, the organic solvent is propylene glycol and dipropylene glycol monomethyl ether, the content of propylene glycol in the black ink is 7% to 13% by mass, the content of dipropylene glycol monomethyl ether in the black ink is 7% to 13% by mass, the content of the organic solvent having a boiling point of more than 250°C at 1 atmosphere is 0.1% by mass or less, the color ink contains a resin containing a pigment, the resin containing a pigment contains components derived from acrylic acid and components derived from styrene,The weight-average molecular weight of the pigment-containing resin is 10,000 or more and 20,000 or less, the acid value of the pigment-containing resin is 200 mg KOH / g or more and 300 mg KOH / g or less, the content of the pigment-containing resin is 5% by mass or more and 7% by mass or less in the color ink, the water-poorly soluble resin contains components derived from acrylic acid, components derived from butyl acrylate, components derived from cyclohexyl acrylate and components derived from a crosslinking agent, the pigment content in the water-poorly soluble resin is 0.01% by mass or less, the acid value is 50 mg KOH / g or more and 70 mg KOH / g or less, and it is contained in the color ink at 3% by mass or more and 5% by mass or less, the nonionic surfactant contains an acetylene glycol-based surfactant, a polyoxyethylene alkyl ether-based surfactant, or a silicone-based surfactant, the nonionic surfactant is contained in the color ink in total at 1.5% by mass or more and 2.5% by mass or less, and the organic solvent is propylene glycol and dipropylene glycol monomethyl ether. The content of propylene glycol in the color ink is 7% by mass or more and 13% by mass or less; the content of dipropylene glycol monomethyl ether in the color ink is 7% by mass or more and 13% by mass or less; the content of the organic solvent having a boiling point greater than 250°C at 1 atmosphere is 0.1% by mass or less; the value of X-Y is 1.5 or more and 2.5 or less when the total solid content in each black ink is X% by mass and the total solid content in each color ink is Y% by mass; the value of y-x is 0.3 or more and 0.5 or less when the total content of nonionic surfactant in each black ink is x% by mass and the total content of nonionic surfactant in each color ink is y% by mass or less; the use according to any one of <11> to <14> above. <16> A printing method using the ink set described in any one of <1> to <10> above. <17> A printing apparatus using the ink set described in any one of <1> to <10> above.

[0085] The present invention will be specifically described below with reference to examples. The following examples are merely illustrative of the present invention and do not imply any limitations. "Normal pressure" refers to a state without pressurization or depressurization, and "room temperature" refers to 25°C. In the manufacturing examples, examples, and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%" unless otherwise specified. The measurement and calculation methods for each physical property are as follows.

[0086] (1) Measurement of the weight-average molecular weight of the resin was determined by gel permeation chromatography. The measurement conditions are as follows: GPC instrument: HLC-8320GPC manufactured by Tosoh Corporation Column: TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide in which phosphoric acid and lithium bromide were dissolved at concentrations of 60 mmol / L and 50 mmol / L, respectively Flow rate: 0.5 mL / min Standard substance: Monodisperse polystyrene kit with known molecular weight [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500)] (all manufactured by Tosoh Corporation) Measurement sample: 0.1 g of resin was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and filtered through a syringe filter "DISMIC-13HP" (made of PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.).

[0087] (2) Measurement of the average particle size of pigment-containing resin particles and crosslinked resin particles Cumulant analysis was performed using the laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle size was taken as the average particle size of the pigment-containing acrylic resin particles. The measurement sample had a particle concentration of 5 × 10 -３A dispersion solution diluted with water to a concentration of % (converted to solid content) was used. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent, and the resulting cumulant average particle size was taken as the average particle size of the pigment-containing polymer particles.

[0088] (3) Measurement of the acid value of acrylic resin and pigment dispersion resin The resin was dissolved in a titration solvent of toluene and acetone (2:1) in a potentiometric automatic titrator (manufactured by Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve as the endpoint. The acid value (mgKOH / g) was calculated from the amount of potassium hydroxide solution titrated to the endpoint.

[0089] (4) Calculation of the degree of crosslinking of crosslinked resin particles The degree of crosslinking of crosslinked resin particles was calculated from the mass and epoxy equivalent of the crosslinking agent, and the mass and acid value of the acrylic resin, assuming that all epoxy groups in the crosslinking agent reacted with the carboxyl groups of the acrylic resin.

[0090] (5) Calculation of the acid value of crosslinked resin particles The acid value of the crosslinked resin particles was determined from the acid value of the acrylic resin or acrylic resin vinyl resin before crosslinking, and the degree of crosslinking and mass of the crosslinked resin particles.

[0091] (6) Measurement of solid content concentration of aqueous dispersion of crosslinked resin particles and aqueous dispersion of pigment-containing resin particles 10.0 g of sodium sulfate, which had been stabilized in a desiccator, was accurately weighed into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm). Approximately 1.0 g of the sample was added thereto, mixed, and then accurately weighed. The mixture was maintained at 105°C for 2 hours to remove volatile matter, and then left in the desiccator for another 15 minutes. The mass was then accurately weighed. The mass of the sample after removal of volatile matter was taken as the solid content, and the solid content concentration was obtained by dividing it by the mass of the added sample.

[0092] (7) Measurement of the pH of inkjet ink The pH of the inkjet ink at 25°C was measured using a benchtop pH meter (F-71, manufactured by Horiba, Ltd.) with a pH electrode (6337-10D, manufactured by Horiba, Ltd.).

[0093] (8) Measurement of the melting point of the wax The melting point of the wax was determined using a measuring device in accordance with JIS K 0064. Specifically, a differential scanning calorimeter (Q20, manufactured by T.A. Instruments) was used to heat the sample to 200°C, and then to 0°C at a cooling rate of 10°C / min. Next, the sample was heated at a heating rate of 10°C / min, and the amount of heat was measured up to 200°C. Among the observed heat of fusion peaks, the temperature of the peak with the largest peak area was defined as the maximum peak temperature of melting, and this peak temperature was defined as the melting point.

[0094] (9) Measurement of the average particle size of wax particles in wax emulsion The average particle size of wax particles in wax emulsion was measured using a Microtrac particle size analyzer UPA manufactured by Nikkiso Co., Ltd., with a laser wavelength of 780 nm, laser output of 3 mW, and a sample concentration of 5 × 10⁻¹⁶. －３ The median of the volume-average particle size distribution obtained by taking mass percent, injecting approximately 5 mL of the sample into a cell, inputting the refractive index of water (1.333), and inputting 1 as the refractive index of the resin, is D. ５０ The average particle size of the wax particles in the wax emulsion was defined as ).

[0095] <Production of water-insoluble resin particles (aqueous dispersion of crosslinked resin particles)> (Production of acrylic resin (A)) Production example I-1: Production of acrylic resin A1 A monomer mixture was prepared by mixing 25.7 parts of acrylic acid, 55.0 parts of cyclohexyl acrylate, 55.0 parts of butyl acrylate, and 100 parts of methyl ethyl ketone (hereinafter referred to as "MEK"). In addition, a polymerization initiator solution was prepared by mixing 1.1 parts of 2,2'-azobis-(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) and 12.7 parts of MEK as a polymerization initiator. In a reaction vessel equipped with a stirrer, reflux condenser, and two dropping funnels, 10% of the monomer mixture was added as an initial charge, and the vessel was thoroughly purged with nitrogen gas. In one dropping funnel, a mixture of the remaining 90% of the monomer mixture and 1.2 parts of 2-mercaptoethanol as a polymerization chain transfer agent was prepared. In the other dropping funnel, 80% of the polymerization initiator solution was added. Under a nitrogen atmosphere, the contents of the reaction vessel were stirred while the temperature was raised to 65°C, and the mixtures and polymerization initiator solutions from the two dropping funnels were continuously added to the reaction vessel over 3 hours. After the addition was complete, the reaction was carried out at 65°C for 2 hours. Then, the remaining 20% ​​of the polymerization initiator solution was added, and the reaction was carried out for another 2 hours at 65°C, and then the temperature was raised to 70°C and the reaction was carried out for another 2 hours. After cooling to room temperature, MEK was removed by vacuum drying to obtain acrylic resin A1 (acid value: 200 mg KOH / g, weight-average molecular weight: 21,000).

[0096] Production Example I-2: Acrylic resin A2 was produced in the same manner as in Production Example I-1, except that the monomer mixture for production of acrylic resin A2 consisted of 25.7 parts acrylic acid, 74.3 parts styrene, and 100 parts methyl ethyl ketone (hereinafter referred to as "MEK"). The acid value of the obtained acrylic resin A2 was 200 mgKOH / g, and the weight-average molecular weight was 20,000.

[0097] (Production of aqueous dispersion of cross-linked resin particles) Production example I-3: Production of aqueous dispersion of cross-linked resin particles 1 (Step 1) 40.0 parts of acrylic resin A1 were dissolved in 60.0 parts of MEK, and 10.1 parts of 5N sodium hydroxide aqueous solution (sodium hydroxide solid content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of acrylic resin A1 was 30 mol%. Then, 200.0 parts of water were added over 1 hour, and after the addition was completed, MEK was removed with an evaporator, and ion-exchanged water was added so that the solid content concentration was 20% by mass to obtain an aqueous dispersion of acrylic resin A1. (Step 2) 200.0 parts of the aqueous dispersion of acrylic resin A1 obtained in Step 1 were mixed with 12.0 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-321LT, epoxy equivalent: 140) as a crosslinking agent. The mixture was then heated at 80°C for 5 hours with stirring to react the carboxyl groups in acrylic resin A1 with the epoxy groups in trimethylolpropane polyglycidyl ether. The mixture was then cooled to 25°C and filtered through a 5 μm pore size filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Ion-exchanged water was added to achieve a solid content concentration of 20% by mass to obtain aqueous dispersion of crosslinked resin particles 1. The degree of crosslinking of the crosslinked resin particles in aqueous dispersion of crosslinked resin particles 1 was 60 mol%, the acid value was 60.4 mg KOH / g, and the average particle size was 99 nm.

[0098] Production Example I-4: Production of Aqueous Dispersion 2 of Crosslinked Resin Particles Aqueous dispersion 2 of crosslinked resin particles was produced in the same manner as in Production Example I-3, except that acrylic resin A1 was replaced with acrylic resin A2. The degree of crosslinking of the obtained aqueous dispersion 2 was 60 mol%, the acid value was 61.5 mg KOH / g, and the average particle size was 105 nm.

[0099] <Production of aqueous dispersion of pigment-containing resin particles> (Production of acrylic resin B1) Acrylic resin B1 was produced in the same manner as in Production Example I-1, except that the monomer mixed solution for production of acrylic resin B1 was 30.8 parts of acrylic acid, 69.2 parts of styrene, and 100 parts of methyl ethyl ketone (hereinafter referred to as "MEK"). The acid value of the obtained acrylic resin B1 was 240 mgKOH / g, and the weight-average molecular weight was 14,000.

[0100] (Production of aqueous dispersion of pigment-containing resin particles) Production Example II-1: Production of aqueous dispersion of pigment-containing resin particles 1 (Step I) 25 parts of the obtained acrylic resin B1 were dissolved in 78.6 parts of MEK, and 10.1 parts of a 5N sodium hydroxide aqueous solution (sodium hydroxide solids content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added thereto so that the degree of neutralization of acrylic resin B1 was 40 mol%, thereby obtaining an aqueous dispersion of neutralized acrylic resin B1.

[0101] (Step II) To the aqueous dispersion of acrylic resin B1 obtained in Step I, 400.0 parts of deionized water and 100.0 parts of carbon black pigment (C.I. Pigment Black 7, manufactured by Cabot, trade name: Monarch 717) were added and stirred for 60 minutes at 20°C with the disperser blades rotating at 7000 rpm using a disperser (manufactured by Asada Iron Works Co., Ltd., trade name: Ultra Disperser). Next, the mixture was subjected to a 15-pass dispersion treatment at a pressure of 150 MPa using a microfluidizer (manufactured by Microfluidics, high-pressure homogenizer, trade name: M-140K) to obtain a dispersion. 250.0 parts of deionized water were added to the obtained dispersion and stirred, after which MEK was completely removed at 60°C under reduced pressure, and some water was further removed. The obtained dispersion was collected using a centrifuge to recover the liquid phase, and then filtered through a cellulose acetate membrane filter with a pore size of 5 μm to obtain an aqueous dispersion (solid content concentration 25% by mass) in which the pigment was dispersed in acrylic resin B1.

[0102] (Step III) 100.0 parts of the aqueous dispersion in which the pigment obtained in Step II was dispersed in acrylic resin B1 were placed in a screw-top glass bottle, 31.0 parts of deionized water were added, and 1.5 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-321LT, epoxy equivalent: 140) was added as a crosslinking agent to achieve a degree of crosslinking of 50 mol%, the bottle was sealed tightly, and heated at 70°C for 5 hours while stirring with a stirrer. After that, the dispersion was cooled to room temperature (25°C), filtered through a cellulose acetate membrane filter with a pore size of 5 μm, and an aqueous dispersion of pigment-containing resin particles 1 (solid content concentration 20% by mass, carbon black 15.7%, pigment dispersion resin 4.3%, average particle size of pigment-containing resin particles 107 nm) was obtained.

[0103] Manufacturing Example II-2: Except that the pigment used in Manufacturing Step II of the aqueous dispersion of pigment-containing resin particles 2 was changed to a cyan pigment (manufactured by DIC Corporation, product name: Fastogen Blue FA5380, Pigment Blue 15:3), the same procedure as in Manufacturing Example II-1 was used to obtain an aqueous dispersion of pigment-containing resin particles 2 (solid content concentration 20% by mass, cyan pigment 15.7%, pigment dispersion resin 4.3%, average particle size of pigment-containing resin particles 110 nm).

[0104] [Manufacturing of Ink Set] Example 1 (Manufacturing of Black Ink) Aqueous dispersion of crosslinked resin particles 1 (solid content concentration 20% by mass) 30.0 parts (breakdown: resin 6.0 parts, water 24.0 parts), Aqueous dispersion of pigment-containing resin particles 1 (solid content concentration 20% by mass) 30.0 parts (breakdown: carbon black 4.7 parts, pigment-dispersed resin B1 1.3 parts (1.3 parts, 24.1 parts water), 10.0 parts propylene glycol (manufactured by AGC Inc.), 10.0 parts dipropylene glycol monomethyl ether (manufactured by Nippon Emulsifier Co., Ltd.), 1.0 part Surfinol 104PG-50 (manufactured by Nisshin Chemical Industry Co., Ltd., 50% propylene glycol solution of 2,4,7,9-tetramethyl-5-decine-4,7-diol), 0.8 parts Emulgen (registered trademark) 120 (manufactured by Kao Corporation, 100% active ingredient of ethylene oxide adduct of lauryl alcohol), 0.2 parts KF-6011 (manufactured by Shin-Etsu Chemical Co., Ltd., 100% active ingredient of polyether-modified silicone), and 2-dimethylaminoethanol (reagent manufactured by Fujifilm Wako Pure Chemical Industries Ltd.) were blended to achieve an ink pH of 8.5. Deionized water was then added to bring the total volume to 100 parts, and the mixture was filtered through a cellulose acetate membrane filter with a pore size of 5 μm to obtain inkjet ink 1.

[0105] (Manufacturing of Cyan Ink (Color Ink)) Inkjet ink 2 was obtained in the same manner as the manufacturing of black ink, except that the aqueous dispersion of pigment-containing resin particles 1 was changed to an aqueous dispersion of pigment-containing resin particles 2. Furthermore, inkjet ink 1 (black ink) and inkjet ink 2 (cyan ink) were evaluated as an ink set for printing.

[0106] Examples 2-15, Comparative Examples 1-4 (Manufacturing of Inkjet Inks 3-34) In the same manner as in Example 1, water-based inkjet inks 3-34 were prepared according to the formulations shown in Tables 1 and 2, and ink sets for each example and comparative example were obtained. The amounts of each component in Tables 1 and 2 are the actual formulation amounts.

[0107] The waxes listed in Tables 1 and 2 are as follows: • Polyethylene wax: Manufactured by Toho Chemical Industry Co., Ltd., product name: Hi-Tec E-6500, nonionic polyethylene wax emulsion, melting point: 140°C, average particle size: 60 nm, solid content: 35% by mass

[0108] [Ink Set Evaluation] <Measurement of Black Ink Line Width in Overprinted Areas> In an environment of 25±1°C and 30±5% relative humidity, inkjet ink 1 and inkjet ink 2 were filled into different inkjet recording heads in a printing evaluation device (manufactured by Trytech Co., Ltd.) equipped with an inkjet recording head (Kyocera Corporation, "KJ4B-HD06MHG-STDV", piezo line head). The head voltage was set to 26V, the drive frequency to 20kHz, the head temperature to 32°C, the ejected droplet volume to 7pl, the resolution to 600×600dpi, the number of pre-ejection flashes to 200, and the negative pressure to -4.0kPa. Matte coated paper (GRAFICAS Y FORMULARIOS, product name: Fitnes Matt) was used, and the print medium was fixed to the transport table under reduced pressure with the longitudinal direction of the print medium and the transport direction being the same. A print command was transferred to the print evaluation device, and a print pattern with a 3 cm square area and 100% duty cycle using cyan ink was printed in a single pass, overlapping a line of 20 dots of black ink, to obtain a printed material. The width of the black lines in the overlapping areas of the print was measured using the "PIAS-II" handheld image evaluation system manufactured by Quality Engineering Associates Inc. The smaller the line width, the less bleeding there is, resulting in a more readable printed material. Since the line width in the areas without overlapping was 950 μm, a line width of 950 μm to 1010 μm is acceptable for practical use, preferably 990 μm or less, and more preferably 970 μm or less.

[0109] <Measurement of OD Value of Color Ink in Solid Print Areas> The optical density (hereinafter referred to as "OD value") of the solid color ink areas of the printed material obtained in <Measurement of Line Width of Black Ink in Overprint Areas> above was measured using an X-Rite eXact Standard small spectrophotometer under the conditions of light source D65, field of view 2°, and STATUS E. If the ink does not spread evenly on the paper surface, streaks and uneven coloring occur during solid printing, resulting in a decrease in the OD value. Streaks and uneven coloring result in an uneven appearance, which is considered poor appearance and low image quality, so a high OD value is desirable. An OD value of 1.55 or higher is acceptable for practical use, preferably 1.65 or higher, and more preferably 1.80 or higher.

[0110] The ink sets for Examples 2-15 and Comparative Examples 1-4, shown in Tables 1 and 2, were evaluated in the same manner. For each example, the ink on the left side of the ink set was set in the printer to be printed first. The results are shown in Tables 1 and 2.

[0111]

[0112]

[0113] As shown in Tables 1 and 2, the ink sets of Examples 1 to 15 all suppressed character bleeding and provided good solid coverage. Furthermore, a comparison between Example 1 and Example 14 shows that the results were good regardless of the printing order of the black and color inks.

[0114] The water-based ink set for inkjet recording of the present invention can be suitably used for inkjet printing.

Claims

1. An inkjet water-based ink set for inkjet recording comprising at least one black ink and one color ink, wherein each inkjet ink contains a pigment, a water-insoluble resin, a nonionic surfactant, an organic solvent, and water, and the content of the organic solvent, which has a boiling point of more than 250°C at 1 atmosphere, in each inkjet ink is 5% by mass or less relative to the total amount of inkjet ink, and the value of X-Y, where the total solid content in each black ink is X% by mass and the total solid content in each color ink is Y% by mass, is 0.1 or more and 5.0 or less, and the total content (by mass) of the nonionic surfactant in each black ink is less than the total content (by mass) of the nonionic surfactant in each color ink.

2. The water-based inkjet recording ink set according to claim 1, wherein the form of the pigment is in the form of resin particles containing the pigment, and the acid value of the pigment-dispersing resin constituting the resin particles is 100 mg KOH / g or more and 400 mg KOH / g or less.

3. The water-based ink set for inkjet recording according to claim 1 or 2, wherein the water-poorly soluble resin is an acrylic resin.

4. The water-soluble resin comprises one or more hydrophobic monomers selected from the group consisting of cycloalkyl (meth)acrylates, according to any one of claims 1 to 3.

5. An inkjet recording water-based ink set according to any one of claims 1 to 4, wherein the nonionic surfactant includes an acetylene glycol-based surfactant.

6. An inkjet water-based ink set for recording according to any one of claims 1 to 5, wherein the total content of nonionic surfactants in each black ink is x by mass%, and the total content of nonionic surfactants in each color ink is y by mass%, and the value of y-x is 0.01 or more and 1.00 or less in both cases.

7. An aqueous ink set for inkjet recording according to any one of claims 1 to 6, wherein the organic solvent contains a glycol ether.

8. An inkjet water-based ink set for use in an inkjet recording device that records by performing a single scan of the recording head relative to the recording medium.

9. An inkjet recording water-based ink set according to any one of claims 1 to 8, used for printing on low-absorbent coated paper or non-absorbent film.

10. An ink set comprising at least one black ink and one color ink, wherein each ink contains a pigment, a water-insoluble resin, a nonionic surfactant, an organic solvent, and water, and the content of the organic solvent, which has a boiling point of more than 250°C at 1 atmosphere, in each ink is 5% by mass or less relative to the total amount of ink, and the value of X-Y, where X is the total solid content in each black ink and Y is the total solid content in each color ink, is 0.1 or more and 5.0 or less, and the total content (by mass) of the nonionic surfactant in each black ink is less than the total content (by mass) of the nonionic surfactant in each color ink, for use as an inkjet recording.

11. The use according to claim 10, wherein the form of the pigment is in the form of resin particles containing the pigment, and the acid value of the pigment dispersion resin constituting the resin particles is 100 mg KOH / g or more and 400 mg KOH / g or less.

12. The use according to claim 10 or 11, wherein the recording head is used in an inkjet recording device that performs recording by scanning the recording medium once relative to it.

13. The use according to any one of claims 10 to 12, used for printing on low-absorbent coated paper or non-absorbent film.

14. A printing method using an ink set described in any one of claims 1 to 9.

15. A printing apparatus that prints using an ink set according to any one of claims 1 to 9.

Images