Ink, method for improving abrasion resistance, and method for improving print density

Abstract

To provide an aqueous ink composition for inkjet printing that can be used in a poorly-ink-absorbable printing medium, particularly offset coat paper, and suppresses changes in the glare of a coating layer even when nails or the like leave abrasions thereon, and ensures high print density on both of offset coat paper and plain paper, a method for improving scratch resistance, and a method for improving print density.SOLUTION: An ink composition comprises a water-insoluble colorant selected from the group consisting of a pigment, a disperse dye, and a solvent dye, and crosslinked organic fine particles with an average particle size of less than 150 nm and a refractive index of 1.40 or more and less than 1.65.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to ink, a method for improving abrasion resistance, and a method for improving printing density.

Background Art

[0002] Among various color printing methods, a printing method using an inkjet printer (inkjet printing method) is one of the representative methods. In this method, small droplets of ink are generated and adhered to a printing medium such as paper for printing. With the progress of inkjet technology, the inkjet printing method has come to be used even in the field of high-definition printing that has been realized by silver halide photography and offset printing. In such fields, printing media that are difficult to absorb ink, such as coated paper, are frequently used.

[0003] In recent years, the demand for industrial inkjet printing has increased, and characteristics different from those in the past are required. As one of such characteristics, strong improvement in the abrasion resistance of the ink adhered to the printing medium is desired. For example, when printing on coated paper using an inkjet printer and the obtained printed matter is linearly scratched with a nail or the like, only the linearly scratched portion is pressed and the surface becomes smooth. As a result, light is more strongly specularly reflected only at the linearly scratched portion, causing glare. Since only the linearly scratched portion glares, the appearance of the entire printed matter deteriorates, resulting in a decrease in print quality. Therefore, there is a strong demand for ink with little change in the glare of the coating film even if there are scratches such as those made by a nail. As a method for suppressing the glare of the coating film, applying a pretreatment agent to the coated paper before printing or applying an overcoat agent to the coated paper after printing can be mentioned. However, considering cost reduction of printing, improvement of printing speed, and enlargement of the apparatus due to an additional process, it is desirable to obtain the above-described abrasion resistance without using a pretreatment agent or an overcoat agent. Furthermore, a key requirement for industrial inkjet inks is high print density. Commercial printing paper is broadly categorized into plain paper and coated paper. When using inkjet printing on plain paper, text is more commonly used than images or designs, so color reproduction (print density) tends to be particularly important among the quality requirements for the recorded material. Coated paper is used in high-definition printing fields that have been achieved through silver halide photography and offset printing, so image clarity and gloss are required. It is known that glossiness can be improved by increasing surface uniformity in coated paper. Therefore, efforts are being made to improve the dispersibility of colorants and reduce the particle size in order to achieve high image quality. However, in plain paper and other papers where a lot of fiber is exposed on the surface, the miniaturized colorants become embedded between the fibers, causing the fibers to float and preventing sufficient density from being obtained. Increasing the particle size of the colorants to a certain extent improves the print density on plain paper, but for the reasons mentioned above, the glossiness of coated paper is compromised. Thus, since the functions required of the dispersion differ for plain paper and coated paper, conventional methods have involved installing two types of ink sets, one for plain paper and one for coated paper, or enabling printing on multiple media through pre-treatment. However, these methods involve increasing the ink storage space due to the increase in the number of ink types and increasing the size of the equipment due to the addition of pre-treatment steps. Therefore, if it is possible to achieve both the color development of glossy paper and the density of plain paper with the same ink, these problems can be solved. To improve the print density of plain paper, colorant dispersions and inkjet recording inks have been proposed, for example, combinations of specific carbon black and dispersants, or methods of incorporating inorganic fine particles into the carbon black. Patent Document 1 discloses an aqueous pigment dispersion composed of specific carbon black, a styrene-acrylic copolymer, and a basic substance. Patent Document 2 discloses a dispersion composed of a pigment, collidal silica with an average particle size of 110 nm to 400 nm, and a water-soluble polymer. Patent Document 3 discloses an aqueous pigment dispersion composed of a pigment, hydrophilic fumed silica, and an aqueous medium. However, while the carbon species specified in Patent Document 1 is confirmed to be suitable for plain paper, it is not suitable for improving gloss on coated paper. Regarding Patent Documents 2 and 3, the print density on plain paper is insufficient, and the inorganic microparticles used are large in size and have a wide particle size distribution, which is thought to impair gloss on coated paper. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5273434 [Patent Document 2] Patent No. 4679322 [Patent Document 3] WO2016 / 035787 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide an aqueous inkjet ink composition, a method for improving scratch resistance, and a method for improving print density, which, when used on printing media with poor ink absorption, particularly offset coated paper, exhibits minimal change in the glare of the coating even when scratched with fingernails or other marks, and achieves high print density on both offset coated paper and plain paper. [Means for solving the problem]

[0006] The inventors of the present invention have conducted extensive research to solve the above problems and have found that the above problems can be solved by an ink composition comprising a water-insoluble colorant selected from the group consisting of pigments, disperse dyes, and solvent dyes, and crosslinked organic fine particles having an average particle diameter of less than 150 nm and a refractive index of 1.40 or more and less than 1.65, thereby completing the present invention.

[0007] In other words, the present invention relates to the following 1) to 7). 1) An ink composition comprising a water-insoluble colorant selected from the group consisting of pigments, disperse dyes, and solvent dyes, and cross-linked organic fine particles having an average particle size of less than 150 nm and a refractive index of 1.40 or more and less than 1.65. 2) The ink composition according to 1), wherein the above-mentioned crosslinked organic fine particles include polymethyl methacrylate particles. 3) An ink composition set comprising the ink composition described in 1) or 2) and another ink composition. 4) A printed medium printed using the ink composition described in 1) or 2), or the ink composition set described in 3). 5) An ink media set comprising an ink composition according to 1) or 2), or an ink composition set according to 3), and a printing medium. 6) A method for improving abrasion resistance using the ink composition described in 1) or 2), or the ink composition set described in 3). 7) A method for improving print density using the ink composition described in 1) or 2), or the ink composition set described in 3). [Effects of the Invention]

[0008] The present invention provides an aqueous inkjet ink composition that exhibits minimal change in glare even when scratched by fingernails or other marks, without the need to apply pretreatment agents or overcoats to ink-poor ink-absorbing printing media, particularly coated paper such as offset coated paper. Furthermore, it provides an aqueous inkjet ink composition that can achieve high print density on both offset coated paper and plain paper. [Modes for carrying out the invention]

[0009] In this specification, "CI" means "Color Index." Furthermore, in this specification, including in examples, "%" and "parts" are expressed on a mass basis unless otherwise specified. Furthermore, in this specification, the terms "alkylene," "propylene," and "alkyl" are used to encompass both linear and branched structures unless otherwise specified. Also, when values ​​are given as mass percent and include decimal points, the second decimal place is considered valid, and the second decimal place is rounded to one decimal place.

[0010] The above ink composition comprises a water-insoluble colorant selected from the group consisting of pigments, disperse dyes, and solvent dyes, and cross-linked organic fine particles having an average particle diameter of less than 150 nm and a refractive index of 1.40 or more and less than 1.65. In this specification, the ink composition may be abbreviated as "ink."

[0011] [Water-insoluble colorants selected from the group consisting of pigments, disperse dyes, and solvent dyes] The water-insoluble colorant selected from the group consisting of pigments, disperse dyes, and solvent dyes is not particularly limited as long as it is a water-insoluble colorant selected from pigments, disperse dyes, and solvent dyes. For example, known pigments, disperse dyes, and solvent dyes can be used. In this specification, a water-insoluble colorant refers to a colorant whose solubility in 1 liter of water at 25°C is usually 5 g or less, preferably 3 g or less, more preferably 1 g or less, and even more preferably 0.5 g or less, with the lower limit of solubility including 0 g. In this specification, unless otherwise specified, water-insoluble colorants selected from the group consisting of the above-mentioned pigments, disperse dyes, and solvent dyes may be abbreviated as "water-insoluble colorants" or "colorants." One of the above colorants may be used, or two or more may be used in combination. When using multiple colorants, it is preferable to use two or more if the ink is a color ink other than black ink, and to use three to five if the ink is black ink. However, when the black ink contains carbon black as a colorant, the number of types of the colorant is preferably two or one. In this specification, color ink refers to colored ink other than black ink (for example, inks of various colors such as yellow, magenta, cyan, red, orange, brown, violet, blue, and green). Also, among pigments, disperse dyes, and solvent dyes, pigments are preferred. Examples of pigments include inorganic pigments and organic pigments.

[0012] Examples of the inorganic pigments include carbon black, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides.

[0013] Examples of the colorant contained in the black ink include carbon blacks such as thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, and channel black. Specific examples of carbon black include, for example, the Raven series manufactured by Columbian Carbon; the Monarch series, Regal series, and Mogul series manufactured by Cabot; the ColorBlack series, Printex series, SpecialBlack series, and Nerox series manufactured by Orion Engineered Carbons; the MA series, MCF series, No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, and No. 2300 manufactured by Mitsubishi Chemical.

[0014] Examples of the organic pigments include various pigments such as azo, disazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone.

[0015] Examples of the organic pigments include known organic pigments. Examples of the known organic pigments include, for example, yellows such as C.I.Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 24, 55, 73, 74, 75, 83, 93, 94, 95, 97, 98, 108, 114, 128, 129, 138, 139, 150, 151, 154, 180, 185, 193, 199, 202, 213; reds such as C.I.Pigment Red 5, 7, 12, 48, 48:1, 57, 88, 112, 122, 123, 146, 149, 150, 166, 168, 177, 178, 179, 184, 185, 202, 206, 207, 254, 255, 257, 260, 264, 269, 272; blues such as C.I.Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, 80; violets such as C.I.Pigment Violet 19, 23, 29, 37, 38, 50; oranges such as C.I.Pigment Orange 13, 16, 43, 68, 69, 71, 73; greens such as C.I.Pigment Green7, 36, 54; blacks such as C.I.Pigment Black 1 and other pigments of various colors.

[0016] The above-mentioned disperse dyes include known disperse dyes. Among these, dyes selected from CIDispers are preferred. Specific examples include, for instance, CIDispers Yellow 9, 23, 33, 42, 49, 54, 58, 60, 64, 66, 71, 76, 79, 83, 86, 90, 93, 99, 114, 116, 119, 122, 126, 149, 160, 163, 165, 180, 183, 186, 198, 200, 211, 224, 226, 227, 231, 237, etc.; CIDispers Red 60, 73, 88, 91, 92, 111, 127, 131, 143, 145, 146, 152, 153, 154, 167, 179, 191, 192, 206, 221, 258, 283, etc.; CIDispers Orange Disperse dyes in various colors include orange (9, 25, 29, 30, 31, 32, 37, 38, 42, 44, 45, 53, 54, 55, 56, 61, 71, 73, 76, 80, 96, 97, etc.), violet (CIDispers Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, 79:1, etc.), and blue (CIDispers Blue 27, 56, 60, 79:1, 87, 143, 165, 165:1, 165:2, 181, 185, 197, 202, 225, 257, 266, 267, 281, 341, 353, 354, 358, 364, 365, 368, etc.). Furthermore, dyes selected from CISolvent are preferred as the solvent dyes.

[0017] The total content of the colorant in the total mass of the above ink is usually 1 to 30%, preferably 1 to 10%, and more preferably 2 to 7%. Furthermore, the average particle size of the colorant is typically 50 nm to 250 nm, preferably 60 nm to 200 nm. In this specification, average particle size refers to the average particle size measured using the laser light scattering method.

[0018] [Crosslinked organic fine particles] The above ink composition contains cross-linked organic microparticles. Cross-linked organic microparticles are commercially available. Specific examples of commercially available products include, for example, the Eposter series manufactured by Nippon Shokubai Co., Ltd. Note that the above cross-linked organic microparticles are sometimes abbreviated as organic microparticles. The above-mentioned crosslinked organic fine particles are preferably smooth spheres with few irregularities on the particle surface. Crosslinking refers to a state in which multiple molecules or polymers are bonded together by ionic or covalent bonds.

[0019] From the viewpoint of reducing glare in scratch marks, the particle size of the above organic fine particles must be less than 150 nm, preferably between 1 nm and 120 nm, more preferably between 10 nm and 100 nm, and even more preferably between 15 nm and 80 nm. Furthermore, from the viewpoint of reducing glare in scratch marks, the content of the organic fine particles in the ink composition is preferably between 0.5% by mass and 5.0% by mass, more preferably between 0.8% by mass and 4.0% by mass, and even more preferably between 0.9% by mass and 3.5% by mass. Furthermore, the refractive index of the organic fine particles must be between 1.40 and 1.65, and more preferably between 1.45 and 1.55. Since the refractive index of many resin binders is around 1.5, reducing the refractive index difference between the resin binder and the organic fine particles can be expected to avoid the white haze and milky appearance caused by scattering, resulting in high-gloss, high-quality printed materials. In addition, because the organic fine particles are crosslinkable, they are less likely to swell in the ink, resulting in superior ink stability. Organic fine particles include polymethyl methacrylate beads (refractive index 1.54), acrylic beads (refractive index 1.51), acrylic-styrene copolymer beads (refractive index 1.56), melamine beads (refractive index 1.57), polycarbonate beads (refractive index 1.57), styrene beads (refractive index 1.60), crosslinked polystyrene beads (refractive index 1.61), polyvinyl chloride beads (refractive index 1.60), silicone beads (refractive index 1.50), etc. Among these, the organic fine particles are preferably crosslinked polymer fine particles such as polymethyl methacrylate beads, acrylic beads, acrylic-styrene copolymer beads, and melamine beads because they do not swell easily in ink and the resulting ink is highly stable. Crosslinked polymer fine particles are even more preferable because they do not clog nozzles or flow paths during inkjet printing and improve ink discharge stability. In this embodiment, the particles are preferably smooth spheres with no irregularities on the particle surface, and one type of organic fine particle may be used, or two or more types may be used in combination. The above polymethyl methacrylate beads are the same as the above polymethyl methacrylate particles, and the above organic fine particles preferably contain the above polymethyl methacrylate particles, and more preferably consist of the above polymethyl methacrylate particles. The above refractive index value can be determined by known methods, such as using a commercially available refractometer. The above average particle diameter value can also be determined by known methods, such as using a commercially available dynamic light scattering particle size distribution analyzer, for example, LB-500 (manufactured by Horiba, Ltd.).

[0020] The above ink composition may further contain a resin as a dispersant. Examples of the resin as a dispersant include copolymers composed of at least two monomers (preferably at least one of which is a hydrophilic monomer) selected from monomers of the group consisting of styrene and its derivatives; vinylnaphthalene and its derivatives; aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids; acrylic acid and its derivatives; maleic acid and its derivatives; itaconic acid and its derivatives; fahric acid and its derivatives; vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylamide, and their derivatives. Examples of such copolymers include styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, (meth)acrylic acid ester-(meth)acrylic acid copolymer, polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymer, styrene-maleic acid copolymer, and the like. Among these, styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, (meth)acrylic acid ester-(meth)acrylic acid copolymer, and polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymer are preferred; styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer, and (meth)acrylic acid ester-(meth)acrylic acid copolymer are more preferred; (meth)acrylic acid ester-(meth)acrylic acid copolymer is even more preferred; and methacrylic acid ester-methacrylic acid copolymer is particularly preferred. In this specification, the term "(meth)acrylic" is used to include both "acrylic" and "methacrylic." The same applies to "(meth)acrylate," etc. Examples of copolymer types include block copolymers, random copolymers, graft copolymers, and / or salts thereof. Resins used as dispersants can be synthesized or obtained commercially. Specific examples of commercially available products include, for example, styrene-acrylic copolymers such as Johncryl 62, 67, 68, 678, and 687, all manufactured by Johnson Polymers; Movinyl S-100A (modified vinyl acetate copolymer manufactured by Hoechst Synthetic Co., Ltd.); and Julimer AT-210 (polyacrylic acid ester copolymer manufactured by Nippon Junyaku Co., Ltd.). As copolymers obtained by synthesis, the AB block polymer disclosed in International Publication No. 2013 / 115071 is a preferred example. When the above ink composition contains a resin as a dispersant, the content of the resin as a dispersant is usually 0.1 to 1.0, preferably 0.1 to 0.6, and more preferably 0.2 to 0.5, when the total mass of the colorants contained in the above ink composition is taken as 1.

[0021] The weight-average molecular weight (MW) of the resin used as the dispersant is preferably less than 50,000, more preferably 3,000 or more and less than 50,000, and even more preferably 7,000 to 25,000. The acid value of the resin used as the dispersant is preferably 50 to 300 KOH mg / g, even more preferably 80 to 275 KOH mg / g, and particularly preferably 80 to 250 KOH mg / g.

[0022] The resin used as a dispersant can be used either mixed with the colorant, or with part or all of the surface of the colorant coated with the resin as a dispersant. Both of these states can also be used in combination.

[0023] The above ink composition is preferably prepared by first preparing a dispersion containing a water-insoluble colorant and a resin as a dispersant, then mixing it with other components and the above-mentioned cross-linked organic fine particles. For example, it is preferable to prepare a dispersion containing a water-insoluble colorant and a resin as a dispersant, then add and mix other components, and finally mix in the above-mentioned cross-linked organic fine particles. A known method can be used to prepare the dispersion. One example is the phase inversion emulsification method. That is, the resin as a dispersant is dissolved in an organic solvent such as 2-butanone, and an aqueous solution of a neutralizing agent is added to prepare an emulsion. A colorant is added to the obtained emulsion and a dispersion treatment is performed. The desired dispersion can be obtained by removing the organic solvent and some of the water from the liquid obtained in this way under reduced pressure. Dispersion processing can be carried out using, for example, a sand mill (bead mill), roll mill, ball mill, paint shaker, ultrasonic disperser, microfluidizer, etc. For example, when using a sand mill, beads with a particle size of about 0.01 mm to 1 mm can be used, and the dispersion processing can be carried out by appropriately setting the bead packing ratio. The dispersion obtained as described above can be subjected to operations such as filtration and / or centrifugation. This operation can standardize the particle size of the particles contained in the dispersion. If foaming occurs during the preparation of the dispersion, a very small amount of a known defoaming agent, such as a silicone-based or acetylene glycol-based agent, can be added. Other methods for preparing dispersions include acid precipitation, interfacial polymerization, in-situ polymerization, liquid curing coating, coacervation (phase separation), liquid drying, melt-dispersion-cooling, air suspension coating, and spray drying. Among these, phase inversion emulsification, acid precipitation, and interfacial polymerization are preferred.

[0024] The average particle size (D50) of the water-insoluble colorant in the dispersion is typically 300 nm or less, preferably 30 to 280 nm, more preferably 40 to 270 nm, and even more preferably 50 to 250 nm. Similarly, D90 is usually 400 nm or less, preferably 350 nm or less, and more preferably 300 nm or less. The lower limit is preferably 100 nm or more. Similarly, D10 is usually 10 nm or more, preferably 20 nm or more, more preferably 30 nm or more, with an upper limit of 100 nm or less. Particle size can be measured using laser light scattering.

[0025] The above ink composition may further contain a resin emulsion. The resin emulsion preferably has a weight-average molecular weight (MW) of 50,000 or more and preferably contains one or more selected from polymers and waxes. Examples of the polymers include urethane-based, polyester-based, acrylic-based, vinyl acetate-based, vinyl chloride-based, styrene-acrylic-based, acrylic-silicone-based, and styrene-butadiene-based polymers or emulsions containing them. Among these, polymers selected from urethane-based, acrylic-based, and styrene-butadiene-based polymers are preferred, with acrylic-based polymers being more preferred. The aforementioned polymer can be synthesized or purchased commercially. When synthesizing the polymer, polymers disclosed in, for example, International Publication No. 2015 / 147192, are preferred. Examples of commercially available products include Superflex 126, 130, 150, 170, 210, 420, 470, 820, 830, 890 (urethane resin emulsions manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); Hydran HW-350, HW-178, HW-163, HW-171, AP-20, AP-30, WLS-201, WLS-210 (urethane resin emulsions manufactured by DIC Corporation); 0569, 0850Z, 2108 (styrene-butadiene resin emulsions manufactured by JSR Corporation); and AE980, AE981A, AE982, AE986B, AE104 (acrylic resin emulsions manufactured by E-Tech Co., Ltd.).

[0026] As the wax, a wax emulsion is preferred, and a water-based wax emulsion is more preferred. Natural waxes and synthetic waxes can be used as the wax. Examples of natural waxes include petroleum-based waxes such as paraffin wax and microcrystalline wax; lignite-based waxes such as montane wax; plant-based waxes such as carnauba wax and candelilla wax; and emulsions in which waxes such as beeswax and lanolin are dispersed in an aqueous medium.

[0027] Examples of the synthetic waxes mentioned above include polyalkylene wax (preferably poly C2-C4 alkylene wax), oxidized polyalkylene wax (preferably oxidized poly C2-C4 alkylene wax), and paraffin wax. Of these, one or more waxes selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax are preferred, with oxidized polyethylene wax being more preferred. Furthermore, the average particle size of the wax is preferably 50 nm to 5 μm, and more preferably 100 nm to 1 μm, in order to prevent clogging of the inkjet head.

[0028] Examples of commercially available waxes include CERAFLOUR 925, 929, 950, 991; AQUACER 498, 515, 526, 531, 537, 539, 552, 1547; AQUAMAT 208, 263, 272; MINERPOL 221, etc. from Big Chemie; Mitsui High Wax NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, NP505, etc. from Mitsui Chemicals, Inc.; KUE-100, 11 from Sanyo Chemical Corporation; and HYTEC E-6500, 9015, 6400 from Toho Chemical Co., Ltd.

[0029] The total content of the resin emulsion relative to the total mass of the ink composition is usually 0.6% to 6.0%, preferably 1.0% to 5.0%, from the viewpoint of ink fixation to paper, ink discharge performance, and ink storage stability.

[0030] The above ink composition may further contain, as needed, ink preparations such as organic solvents, surfactants, fungicides, preservatives, pH adjusters, rust inhibitors, defoamers, and water. These ink preparations may be used individually or in combination of two or more.

[0031] The above organic solvents are not particularly limited, but examples include: C1-C6 alkanols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, dic-butanol, or tertiary-butanol; carboxylic acid amides such as N,N-dimethylformamide or N,N-dimethylacetamide; lactams such as 2-pyrrolidone, N-methyl-2-pyrrolidone, or N-methylpyrrolidine-2-one; cyclic ureas such as 1,3-dimethylimidazolidine-2-one or 1,3-dimethylhexahydropyrimido-2-one; ketones, keto alcohols, or carbonates such as acetone, 2-methyl-2-hydroxypentan-4-one, and ethylene carbonate; and cyclic ethers such as tetrahydrofuran and dioxane. Polyethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,4-butylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol (preferably with molecular weights of 400, 800, 1540 or higher), polypropylene glycol, thiodiglycol or dithiodiglycol, and other mono, oligo, or polyalkylene glycols or thioglycols having C2-C6 alkylene units; glycerin, diglycerin, hexane-1,2,6-triol, trimethylolpropane, and other C3-C9 polyols (triols);Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoallyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether (butyl carbitol), triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether Examples include glycol ethers such as ethers (preferably selected from the group consisting of C3-C10 mono, di, or triethylene glycol ethers and C4-C13 mono, di, or tripropylene glycol ethers); C5-C9 alkanediols such as 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, 2,4-diethyl-1,5-pentanediol; γ-butyrolactone or dimethyl sulfoxide; and so on.

[0032] Examples of the above-mentioned surfactants include anionic, nonionic, silicone-based, and fluorine-based surfactants. Among these, surfactants selected from silicone-based and fluorine-based surfactants are preferred, and from the viewpoint of safety for living organisms and the environment, silicone-based surfactants are more preferred.

[0033] Examples of anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, N-acyl amino acids or their salts, N-acyl methyl taurates, alkyl sulfates, polyoxyalkyl ether sulfates, alkyl sulfates, polyoxyethylene alkyl ether phosphates, rosinic acid soaps, castor oil sulfates, lauryl alcohol sulfates, alkylphenol type phosphates, alkyl type phosphates, alkylaryl sulfonates, diethyl sulfosaturates, diethylhexyl sulfosaturates, and dioctyl sulfosaturates.

[0034] Examples of nonionic surfactants include ether-based surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ether, and polyoxyethylene distyrenated phenyl ether (e.g., Emulgen A-60, A-90, A-500 manufactured by Kao Corporation); ester-based surfactants such as polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate; acetylene glycol (alcohol)-based surfactants such as 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, and 3,5-dimethyl-1-hexyn-3-ol; and polyglycol ether-based surfactants. Examples of these commercially available products include Surfinol 104, 104PG50, 82, 420, 440, 465, 485, and Olfin STG from Nisshin Chemical Co., Ltd.; and Emulgen A-60, A-90, and A-500 from Kao Corporation.

[0035] Examples of silicone-based surfactants include polyether-modified siloxanes and polyether-modified polydimethylsiloxanes. Examples include Dynol 960 and 980 from Air Products Corporation; Silface SAG001, SAG002, SAG003, SAG005, SAG503A, SAG008, SAG009, and SAG010 from Nisshin Chemical Co., Ltd.; and BYK-345, 347, 348, 349, 3455, LP-X23288, LP-X23289, and LP-X23347 from BYK Additives & Instruments; and TEGO Twin 4000, TEGO Wet KL 245, 250, 260, 265, 270, and 280 from Evonic Tego Chemie.

[0036] Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in their side chains.

[0037] Specific examples of the above-mentioned antifungal agents include, for example, sodium dehydroacetate, sodium benzoate, sodium pyridinethion-1-oxide, p-hydroxybenzoate ethyl ester, 1,2-benzisothiazolin-3-one, and their salts.

[0038] Examples of the above-mentioned preservatives include compounds such as organosulfur, organonitrogen-sulfur, organohalogen, haloarylsulfone, iodopropagyl, haloalkylthio, nitrile, pyridine, 8-oxyquinoline, benzothiazole, isothiazolin, dithiol, pyridine oxide, nitropropane, organotin, phenol, quaternary ammonium salt, triazine, thiazine, anilide, adamantane, dithiocarbamate, brominated indanone, benzylbromoacetate, or inorganic salts. A specific example of an organic halogen compound is, for instance, sodium pentachlorophenol. A specific example of a pyridine oxide compound is sodium 2-pyridinethiol-1-oxide. Examples of isothiazolin compounds include 1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one magnesium chloride, 5-chloro-2-methyl-4-isothiazolin-3-one calcium chloride, and 2-methyl-4-isothiazolin-3-one calcium chloride. Other specific examples of antiseptics and antifungal agents include anhydrous sodium acetate, sodium sorbate, or sodium benzoate, as well as products manufactured by Arch Chemical Co., Ltd., such as Proxel GXL(S), Proxel LV, and Proxel XL-2(S).

[0039] Specific examples of the above-mentioned pH adjusting agents include, for example, alkanolamines such as diethanolamine, triethanolamine, and N-methyldiethanolamine; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonium hydroxide (ammonia water); alkali metal carbonates such as lithium carbonate, sodium carbonate, sodium bicarbonate, and potassium carbonate; alkali metal salts of organic acids such as sodium silicate and potassium acetate; and inorganic bases such as disodium phosphate.

[0040] Specific examples of the above-mentioned rust inhibitors include, for example, acidic sulfites, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitride, pentaerythritol tetranitrate, or dicyclohexylammonium nitride.

[0041] Examples of the above-mentioned defoaming agents include silicone-based, silica mineral oil-based, olefin-based, and acetylene-based agents. Examples of commercially available defoaming agents include Surfinol DF37, DF58, DF110D, DF220, MD-20, and olefin SK-14, all manufactured by Shin-Etsu Chemical Co., Ltd.

[0042] The water mentioned above is preferably water with a low content of impurities such as metal ions, i.e., ion-exchanged water, distilled water, etc. Such water can be prepared by known methods.

[0043] When preparing the above ink, known methods for producing dispersed inks can be used. For example, one method involves preparing an aqueous dispersion from the above water-insoluble colorant, the above cross-linked organic fine particles, and water, and then adding water, various organic solvents, and, if necessary, an ink preparing agent to this dispersion and mixing to prepare the ink.

[0044] When using the above ink as an inkjet ink, it is preferable to use an ink with a low content of inorganic impurities such as metal cation chlorides (e.g., sodium chloride) and sulfates (e.g., sodium sulfate). Such inorganic impurities are often found in commercially available colorants. The guideline for the inorganic impurity content is approximately 1% by mass or less relative to the total mass of the colorant, and the lower limit should ideally be below the detection limit of analytical instruments, i.e., 0%. Methods for obtaining a colorant with few inorganic impurities include, for example, a method using a reverse osmosis membrane; a method in which the solid colorant is suspended and stirred in a mixed solvent of C1-C4 alcohol such as methanol and water, the colorant is filtered and separated, and then dried; or a method of exchanging and adsorbing inorganic impurities with an ion exchange resin; and other desalting treatments. Furthermore, when using the above ink as an inkjet ink, it is preferable to microfiltration the ink. When microfiltration is performed, a membrane filter and / or glass filter paper can be used. The pore size of the filter used for microfiltration is usually 0.5 μm to 20 μm, preferably 0.5 μm to 10 μm.

[0045] The above ink can be used in various printing fields. For example, it is suitable for writing, printing, information printing, and textile printing. It is particularly preferable to use it in inkjet printing.

[0046] The above inkjet printing method involves ejecting droplets of ink in response to a print signal and adhering them to the printing medium to perform printing. There are no particular restrictions on the ink nozzles of the inkjet printer that eject the ink, and they can be appropriately selected according to the purpose. Inkjet printing methods include improving image quality by ejecting a large number of inks with a low colorant content in small volumes; improving image quality by using multiple inks with substantially the same hue but different colorant content; and improving the fixation of colorants to the printing medium by using a colorless, transparent ink in combination with an ink containing a colorant. The above-mentioned inks can also be used as inks containing colorants in these methods.

[0047] Inkjet printing can utilize known methods. Examples include charge control methods, drop-on-demand methods (also known as pressure pulse methods), acoustic inkjet methods, and thermal inkjet methods.

[0048] The recording medium is not particularly limited as long as it is a substance that can be colored by the ink. Examples of recording media include paper, film, fibers and cloth (cellulose, nylon, wool, etc.), leather, and substrates for color filters. These recording media can be broadly classified into those with an ink-receiving layer and those without.

[0049] Examples of recording media having an ink-receiving layer include those using paper, synthetic paper, film, etc., as a base material, with an ink-receiving layer provided thereon. The ink-receiving layer can be provided, for example, by impregnating or coating the base material with a cationic polymer; or by coating the surface of the base material with inorganic fine particles such as porous silica, alumina sol, or special ceramics together with a hydrophilic polymer such as polyvinyl alcohol or polyvinylpyrrolidone. Such recording media are commonly referred to as inkjet-specific paper, inkjet-specific film, or glossy paper. Representative examples of commercially available products include: Canon Inc.'s product names: Professional Photo Paper, Super Photo Paper, Glossy Gold, and Matte Photo Paper; Seiko Epson Corporation's product names: Photo Paper Crispia (High Gloss), Photo Paper (Glossy), and Photo Matte Paper; Hewlett-Packard Japan Ltd.'s product name: Advanced Photo Paper (Glossy); and Fujifilm Corporation's product name: Gakusai Photo Finish Pro.

[0050] Examples of recording media that do not have an ink-receiving layer include various types of paper such as coated paper and art paper used for gravure printing and offset printing; and cast-coated paper used for label printing.

[0051] When printing on a printing medium using the inkjet printing method described above, for example, a container containing the ink (referred to as an ink tank, etc.) is loaded into a designated position in the inkjet printer, and the printing is performed on the printing medium using the printing method described above. The above inkjet printing method allows for full-color printing using an ink set of multiple inks selected from the above color inks. In this case, the containers containing each color ink are loaded into the designated positions in the inkjet printer as described above, and printing is performed on the printing medium using the above printing method.

[0052] Of the ingredients listed above, only one type may be used. Furthermore, multiple types may be selected and used in combination as needed. For all of the above, a combination of desirable elements is more desirable, and a combination of more desirable elements is even more desirable. The same applies to combinations of desirable elements and more desirable elements, and combinations of more desirable elements and even more desirable elements, etc.

[0053] An ink composition set containing two or more of the above-mentioned ink compositions is also included in the present invention. Furthermore, an ink composition set containing the above-mentioned ink composition and other ink compositions other than the above-mentioned ink composition is also included in the present invention. The above-mentioned other ink compositions are not particularly limited as long as their composition differs from that of the above-mentioned ink compositions, but it is preferable that they differ in hue from that of the above-mentioned ink compositions.

[0054] The present invention also includes a method for improving abrasion resistance, improving print density, or improving both, using any of the above ink composition or ink composition set printed on a printing medium, an ink media set comprising the above ink composition or ink composition set and the printing medium, the above ink composition, the ink composition set, the printing medium, or the ink media set.

[0055] The ink composition of the present invention exhibits excellent storage stability, redispersibility, various abrasive properties, color development, and saturation. Furthermore, it exhibits less uneven coating during image formation and superior image formation performance. [Examples]

[0056] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples. Furthermore, all operations such as synthesis reactions were carried out under stirring unless otherwise specified. In the examples, when quantitative determination of the pigment solids content in the dispersion was necessary, it was determined by the dry weight method using an MS-70 manufactured by A&D Company, Limited. The pigment solids content is a converted value calculated from the total amount of solids, with only the pigment solids content being considered. Each ink described in the examples is included in the above ink composition.

[0057] [Synthesis Example 1] Preparation of dispersion 1. The block copolymer of Synthesis Example 3 was prepared by replicating Synthesis Example 3 of International Publication No. 2013 / 115071. The acid value of the obtained block copolymer was 105 mgKOH / g and Mw was 25000. 6.6 parts of the obtained block copolymer were dissolved in 20 parts of 2-butanone, and a solution of 0.36 parts of sodium hydroxide dissolved in 50 parts of deionized water was added. The mixture was stirred for 30 minutes to obtain an emulsion. 20 parts of Nerox 605 from ORION were added to the emulsion, and the mixture was dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a liquid. 120 parts of deionized water were added to the obtained liquid, and the dispersion beads were filtered to obtain a filtrate. From the obtained filtrate, 2-butanone and a portion of the water were removed by vacuum distillation using an evaporator to obtain dispersion 1 with a pigment solid content of 12%. [Synthesis Example 2] Preparation of dispersion 2. 3.75 parts of Joncryl 67 (MW: 12500) and 2.14 parts of triethanolamine were dissolved in 69.11 parts of deionized water and stirred for one hour. To the resulting solution, Mitsubishi Chemical's carbon black MA600 (specific surface area 140 m²) was added. 2 / g)DBP oil absorption 131(cm) 3 25 parts of (100g) pH 7.0 were added, and the mixture was dispersed using a sand grinder at 1500 rpm for 15 hours. After adding 100 parts of deionized water dropwise to the resulting dispersion, the solution was filtered to obtain dispersion 2, which had a pigment solid content of 12.2% and an average particle size of 123 nm. The average particle size was measured using a dynamic light scattering particle size distribution analyzer, LB-500, manufactured by Horiba, Ltd. [Synthesis Example 3] Preparation of acrylic resin emulsion 3. In a glass reaction vessel (capacity 3 liters), 100 parts water, 0.3 parts ammonium persulfate, and 1 part reactive emulsifier were added to obtain a solution. After replacing the air inside the reaction vessel with nitrogen, the temperature of the solution was raised to 70°C. To this solution, a solution consisting of 120 parts water, 0.9 parts reactive emulsifier, 2 parts methacrylic acid, 37 parts methyl methacrylate, 59 parts 2-ethylhexyl acrylate, and 2 parts allyl methacrylate was added dropwise over 3 hours. During the addition of the solution, the solution temperature was maintained at 70°C while introducing nitrogen, and the reaction was carried out. After the addition of the solution was completed, the reaction was continued at 70°C for another 2 hours to obtain a solution, which was then cooled to 40°C to obtain the final solution. By adding 3.1 parts triethanolamine to the obtained solution, acrylic resin emulsion 3 was obtained as a white suspension with a solid content of 25%. The resulting acrylic resin emulsion 3 had an acid value of 13 KOH mg / g and a Tg of -10°C.

[0058] [Examples 1-8]: Ink preparation. After mixing the components listed in Table 1 below, the mixtures were filtered through a 3 μm membrane filter to obtain the inks for Examples 1 to 8 for evaluation testing.

[0059] [Comparative Examples 1-6]: Preparation of comparative inks. After mixing the components listed in Table 2 below, the mixture was filtered through a 3 μm membrane filter to obtain comparative examples 1 to 6.

[0060] The abbreviations in Tables 1 and 2 represent the following. In Tables 1 and 2, each hyphen indicates "0 parts" in the material column and "not applicable" in the organic particulate diameter and organic particulate quantity columns. DP1: Dispersion 1. DP2: Dispersion 2. 12HD: 1,2-Hexanediol. PG: 1,2-Propylene glycol. TEX: Texanol TEA: Triethanolamine. BYK349: Manufactured by BYK, BYK-349. A3: Acrylic resin emulsion 3. (Classifies as a resin emulsion, solids content 25%) AQ515: Manufactured by BYK, AQUACER 515. (Resin emulsion, solids content 35%) MX020W: Manufactured by Nippon Shokubai Co., Ltd., Epostor MX020W. (Classifies as organic fine particles, solid content 7.5%, particle size 20nm, refractive index 1.54) MX030W: Manufactured by Nippon Shokubai Co., Ltd., Epostor MX030W. (Classifies as organic fine particles, solid content 10%, particle size 40nm, refractive index 1.54) MX050W: Manufactured by Nippon Shokubai Co., Ltd., Epostor MX050W. (Classifies as organic fine particles, solid content 10%, particle size 70nm, refractive index 1.54) MX100W: Manufactured by Nippon Shokubai Co., Ltd., using Epostor MX070W. (Comparative example: fine particles, solid content 10%, refractive index 1.54) GXL(s): Proxel GXL(s) manufactured by Lonza. Organic particulate matter diameter: The average particle size of organic particulate matter. (Unit: nm) Organic particulate matter content: The amount of organic particulate matter in the ink. (by mass) Binder content: Total resin emulsion content in the ink. (by mass)

[0061] [Table 1]

[0062] [Table 2]

[0063] [Inkjet printing on offset coated paper] Inkjet printing was performed using a single-pass (1-pass) method with each ink from Examples 1 to 8 and an inkjet printer. The appropriate amount of ink ejected was 12 picoliters, and the head temperature was 32°C. A Kyocera 600dpi head was used as the print head. The media used was "OK Topcoat+", an offset coated paper manufactured by Oji Paper Co., Ltd. Inkjet printing was performed to obtain a 100% duty cycle image. After the obtained image was completely dry, it was used as a test piece, and the following print density measurements and abrasion tests were performed. Furthermore, inkjet printing, print density measurement, and the following abrasion tests were performed in the same manner as described above, except that the inks from Comparative Examples 1 to 6 were used instead of the inks from Examples 1 to 8.

[0064] [Print density measurement] The colorimeter used was the eXact, manufactured by X-rite. The colorimetric conditions were ANSI T for density, a field of view of 2°, and a light source of D50. The evaluation criteria are as follows. In Table 3 below, if the print meets evaluation criterion A, it will be a clear and visually appealing print image. On the other hand, if the print meets evaluation criterion B or lower, it will be a blurry and visually unappealing print image, and in particular, if the print meets evaluation criterion C, it will be even blurrier and visually unappealing, making it unsuitable for practical use. The evaluation results are shown in Table 4 below.

[0065] [Table 3]

[0066] [Abrasion Test] The printed image obtained as described above was scratched with a fingernail, and then the difference in glare between the scratched and unscratched areas was observed when the printed image was held up to a fluorescent light. The evaluation criteria were A to D below, and the evaluation results are shown in Table 4. An A rating is practically important. A: All 10 observers determined that there was no change in shine or gloss on the scratched area. B: 5 to 9 out of 10 observers determined that there was "no change in gloss or shine on the scratched area." C: 1 to 4 out of 10 observers determined that there was "no change in gloss or shine on the scratched area." D: None of the 10 observers determined that there was "no change in gloss or shine on the scratched area."

[0067] [Inkjet printing on plain paper] Inkjet printing was performed using a single-pass (1-pass) method with each ink from Examples 1 to 9 and an inkjet printer. The appropriate amount of ink ejected was 12 picoliters, and the head temperature was 32°C. A Kyocera 600dpi head was used as the print head. The media used was Nippon Paper Industries' "Npi Form 70 NEXT-IJ" plain paper. Inkjet printing was performed to obtain a 100% duty cycle image. After the obtained image was completely dry, it was used as a test piece, and the print density measurement described above was performed. Furthermore, inkjet printing and the above-described print density measurements were performed in the same manner as above, except that the inks from Comparative Examples 1 to 6 were used instead of the ink media sets from Examples 1 to 9. The evaluation results are shown in Table 4 below.

[0068] [Table 4]

[0069] As is clear from the results in Table 4, the inks in each example were confirmed to exhibit less change in the glare of the coating film even when scratched with fingernails or other marks on offset coated paper, compared to the inks in each comparative example. Furthermore, the print density on both coated paper and plain paper was relatively good, confirming that it is possible to achieve printing that combines high print density with scratch resistance. [Industrial applicability]

[0070] The ink of the present invention is extremely useful as an aqueous inkjet ink composition that exhibits minimal change in glare even when scratched by fingernails or other marks, without the need to apply pretreatment agents or overcoats to printing media that do not absorb ink well, particularly coated paper such as offset coated paper. Furthermore, it is extremely useful as an aqueous inkjet ink composition that can achieve high print density on both offset coated paper and plain paper.

Claims

1. An aqueous ink composition for inkjet printing, comprising a water-insoluble colorant selected from the group consisting of pigments, disperse dyes, and solvent dyes, and crosslinked organic fine particles having an average particle size of less than 150 nm and a refractive index of 1.40 or more and less than 1.

65.

2. The ink composition according to claim 1, wherein the above-mentioned crosslinked organic fine particles include polymethyl methacrylate particles.

3. An ink composition set comprising the ink composition according to claim 1 or claim 2 and another ink composition.

4. A printing medium printed using the ink composition according to claim 1 or claim 2, or the ink composition set according to claim 3.

5. An ink media set comprising an ink composition according to claim 1 or claim 2, or an ink composition set according to claim 3, and a printing medium.

6. A method for improving abrasion resistance using the ink composition described in claim 1 or claim 2, or the ink composition set described in claim 3.

7. A method for improving print density using the ink composition described in claim 1 or claim 2, or the ink composition set described in claim 3.

Images