Aqueous pigment ink set for inkjet recording apparatus

Abstract

To provide an ink set capable of producing a print image exhibiting markedly improved resistance to mottling and inter-color bleeding, and to provide an inkjet recording method employing the ink set, as well as a printing medium and a printing medium set.SOLUTION: An aqueous pigment ink set for an inkjet recording apparatus comprises an ink 1 and an ink 2, characterized in that, when a dot diameter A on a print with the ink 1 printed earlier is 100, a dot diameter B on a print with the ink 2 printed later is more than 86 and less than 120.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based pigment ink set for an inkjet recording apparatus and an inkjet recording method using the ink set. [Background technology]

[0002] Among various color printing methods, inkjet printing, one of the most representative methods, generates small droplets of ink and deposits them on a printing medium such as paper to print. In recent years, demand for inkjet printers for industrial use has increased, and there is a demand for inks that can be used to print on a variety of printing media.

[0003] Among printing media, inks that wet and spread well on non-ink-absorbent media and poorly ink-absorbent media (hereinafter sometimes referred to as "non-ink-absorbent or poorly ink-absorbent media") are in demand. Good wet and spreadability on media means that a larger area can be colored using the same amount of ink droplets (in other words, the ink dot diameter becomes larger), thereby reducing ink consumption. However, non-ink-absorbent or poorly ink-absorbent media are media that have poor ink absorption. As a result, ink does not soak into the media easily, and compared to ink-absorbent media, the ink wets and spreads poorly, generally resulting in smaller ink dot diameters. For this reason, improvements are needed.

[0004] Furthermore, print quality requires minimal graininess. Inks containing water-insoluble colorants are in a non-uniform state (not in a solution state, but in a dispersion state). When solid printing is performed on print media using such non-uniform ink, the printed image may appear to have scattered grains of varying shades, resulting in an inconsistent appearance. Such printed images are evaluated as having "graininess" and are one of the factors that significantly degrade print quality. For this reason, there is a strong demand for inks that produce printed images with minimal graininess. For example, Patent Documents 1, 2, and 3 disclose ink compositions that combine specific organic solvents and surfactants, and provide inks with good wetting and spreading properties for non- or poorly ink-absorbing media.

[0005] Furthermore, when performing color printing, an ink set consisting of multiple colors is used. It is known that when performing color printing using such an ink set, bleeding between the first and second colors can occur when the landing positions of a first color ink and a second color ink are adjacent to each other on the printing medium. This "inter-color bleeding" is one of the factors that significantly deteriorates print quality. For this reason, there is a demand for eliminating this inter-color bleeding, and ink sets that solve this problem have been proposed.

[0006] Patent Document 4 discloses an ink containing a polyalkoxylate of an acetylene glycol surfactant in order to eliminate this inter-color bleeding, and proposes an ink that can produce high-quality images with little color unevenness and inter-color bleeding for non-ink or poorly ink-absorbing media. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-044188 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-139004 [Patent Document 3] International Publication No. 2011 / 136000 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-136573 Summary of the Invention [Problem to be solved by the invention]

[0008] There is a demand for ink sets that produce high-quality images with minimal intercolor bleeding.

[0009] The present invention has been made in view of the above circumstances, and has an object to provide an ink set that makes it possible to provide printed images with extremely good inter-color bleeding, as well as an inkjet recording method, printing medium, and printing medium set that use the ink set. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that a specific ink set can solve the above-mentioned problems, thereby completing the present invention.

[0011] That is, the present invention relates to the following 1) to 4). 1) A water-based pigment ink set for an inkjet recording device, comprising ink 1 and ink 2, in which, when the print dot diameter A on a printed matter of ink 1, which is printed first, is taken as 100, the print dot diameter B on a printed matter of ink 2, which is printed later, is greater than 86 and less than 120. 2) The water-based pigment ink set for an inkjet recording device according to 1), wherein the ink 2 contains a compound represented by the following formula (1):

[0012] [ka]

[0013] [In formula (1), R1 represents a hydroxy group, an alkoxy group having a hydroxy group, an acyloxy group, or an arylcarbonyloxy group; R2 represents a hydrogen atom or an alkyl group; R3 represents a hydrogen atom or an alkyl group; R4 represents a hydrogen atom, a hydroxy group, or an alkyl group; and R5 represents an alkyl group.] 3) Furthermore, when the ink 1 contains the compound represented by the above formula (1), and the content mass of the compound represented by the above formula (1) in the ink 1 is X, and the content mass of the compound represented by the above formula (1) in the ink 2 is Y, the aqueous pigment ink set for an inkjet recording apparatus according to 2), which satisfies the relationship X < Y. 4) The inkjet recording apparatus is a single-pass type inkjet recording apparatus, and the aqueous pigment ink set for an inkjet recording apparatus according to any one of 1) to 3). [Advantages of the Invention]

[0014] According to the present invention, it is possible to provide an ink set, an inkjet printing method, a printing medium, and a printing medium set that enable a printed image with extremely good bleeding between colors. [Modes for Carrying Out the Invention]

[0015] The present invention will be described in detail below. In this specification, the aqueous pigment ink set for an inkjet recording apparatus may be abbreviated as an ink set. "C.I." means "Color Index". Also, in this specification, unless otherwise specified, "%", "parts", and "amounts" including in Examples and the like are all described on a mass basis.

[0016] The aqueous pigment ink set for an inkjet recording apparatus includes ink 1 and ink 2. When the printing dot diameter A on the printed matter of the ink 1 printed first is set to 100, the printing dot diameter B on the printed matter of the ink 2 printed later exceeds 86 and is less than .....

[0017] [Ink 1] There are no particular limitations on the ink 1 contained in the water-based pigment ink set for inkjet recording devices, as long as it is an ink that is printed on a printed material before ink 2, which is contained in the ink set and will be described later.

[0018] The ink 1 may contain a pigment. Examples of pigments include inorganic pigments, organic pigments, and extender pigments. Examples include:

[0019] Examples of inorganic pigments include titanium oxide, carbon black, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides.

[0020] Examples of organic pigments include various pigments such as azo, diazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone. Specific examples of organic pigments include yellows such as CI 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, and 213; and CI Pigment Red. Reds such as 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, and 272; Blues such as CI Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 25, 60, 66, and 80; Violets such as CI Pigment Violet 19, 23, 29, 37, 38, and 50; Oranges such as CI Pigment Orange 13, 16, 68, 69, 71, and 73; Greens such as CI Pigment Green 7, 36, and 54; and CI Pigment Examples of pigments include various black colors such as Black 1.

[0021] Examples of extender pigments include silica, calcium carbonate, talc, clay, barium sulfate, and white carbon. Extender pigments are often used in combination with other colorants.

[0022] The disperse dye may be any known disperse dye, and among them, dyes selected from CI Disperses are preferred. Specific examples thereof include yellows such as CI Dispers 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, and 237; reds such as CI Dispers Red 60, 73, 88, 91, 92, 111, 127, 131, 143, 145, 146, 152, 153, 154, 167, 179, 191, 192, 206, 221, 258, and 283; and CI Dispers Orange. Examples of disperse dyes include oranges such as 9, 25, 29, 30, 31, 32, 37, 38, 42, 44, 45, 53, 54, 55, 56, 61, 71, 73, 76, 80, 96, and 97; violets such as CI Disperse Violet 25, 27, 28, 54, 57, 60, 73, 77, 79, and 79:1; and blues such as CI Disperse 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, and 368.

[0023] The ink 1 may further contain ink preparation agents in addition to the pigment. Examples of ink preparation agents include dispersants, binders, penetrants, viscosity adjusters, surfactants, preservatives, antifungal agents, pH adjusters, chelating agents, rust inhibitors, water-soluble ultraviolet absorbers, antioxidants, and water.

[0024] (a) Dispersant A dispersant is preferably used to disperse the pigment contained in Ink 1 in the ink. The dispersant is not particularly limited, and known dispersants can be used. Polymer dispersants such as resins are generally used as dispersants. Examples of such resins include polymers derived from polyvinyl alcohol, cellulose derivatives, polyethylene oxide, polypropylene oxide, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid monoesters, maleic acid, maleic acid monoesters, fumaric acid, fumaric acid monoesters, vinyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, ionic monomers such as α,β-unsaturated monomers of sulfonated vinylnaphthalene, styrene, styrene derivatives, vinylnaphthalene, vinylnaphthalene derivatives, aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids, acrylonitrile, vinylidene chloride, vinyl acetate, vinyl chloride, acrylamide, methacrylamide, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate, and N-butoxymethylacrylamide.

[0025] Examples of resins used as dispersants include copolymers composed of at least two monomers (preferably at least one of which is a hydrophilic monomer) selected from 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, faric acid and its derivatives, vinyl acetate, vinyl alcohol, vinylpyrrolidone, acrylamide, and derivatives thereof. Examples of such copolymers include styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers, (meth)acrylic acid ester-(meth)acrylic acid copolymers, polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymers, and styrene-maleic acid copolymers. 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 the specification and claims of this application, the term "(meth)acrylic acid" is used to include both "acrylic acid" and "methacrylic acid." Similarly, "(meth)acrylate" refers to both methacrylate and acrylate. Examples of types of copolymers include block copolymers, random copolymers, and graft copolymers, and / or salts thereof.

[0026] The resin used as the dispersant can be synthesized or commercially available. Specific examples of commercially available resins include styrene-acrylic copolymers such as JONCRYL 62, 67, 68, 678, and 687 (manufactured by BASF), Movinyl S-100A (a modified vinyl acetate copolymer manufactured by Japan Coating Resins), and JURIMER AT-210 (a polyacrylic acid ester copolymer manufactured by Toagosei Co., Ltd.). Preferred synthetic copolymers include the AB block polymer disclosed in WO 2013 / 115071.

[0027] The acid value of the dispersant is usually 90 to 200 mgKOH / g, preferably 100 to 150 mgKOH / g, and more preferably 100 to 120 mgKOH / g. The mass average molecular weight of the dispersant is usually 10,000 to 60,000, preferably 10,000 to 40,000, more preferably 15,000 to 30,000, and even more preferably 20,000 to 25,000. The PDI (mass average molecular weight / number average molecular weight) of the dispersant is about 1.29 to 1.49. By setting the PDI in this range, the dispersibility and storage stability of the ink can be improved.

[0028] Examples of neutralizing agents used to dissolve the pigment dispersion prepared using the block copolymer in water include ammonia, alkali metal hydroxides, alkaline earth metal hydroxides, aliphatic amine compounds, and alkanolamine compounds. Ammonia and alkali metal hydroxides are preferred. The amount of neutralizing agent used is not particularly limited. As a guideline, the degree of neutralization is typically 30 to 300%, more preferably 50 to 200%, with 100% neutralization being defined as neutralization with an amount theoretically equivalent to the acid value of the dispersant.

[0029] The resin as the dispersant can be used either in a state where it is mixed with the pigment or in a state where a part or all of the surface of the colorant is coated with the resin as the dispersant, or both of these states can be used in combination. Ink 1 is preferably prepared by preparing a dispersion containing a pigment and a resin as a dispersant, and then mixing it with other ingredients. A known method can be used to prepare the dispersion. One example is the phase inversion emulsification method. Specifically, a resin as a dispersant is dissolved in an organic solvent such as 2-butanone, and an aqueous solution of a neutralizer is added to prepare an emulsion. The pigment is then added to the resulting emulsion and subjected to a dispersion treatment. The organic solvent and a portion of the water are removed from the resulting solution by vacuum distillation, yielding the desired dispersion. The dispersion treatment can be carried out using, for example, a sand mill (bead mill), a roll mill, a ball mill, a paint shaker, an ultrasonic disperser, a microfluidizer, etc. When using a sand mill, for example, beads with a particle diameter of about 0.01 mm to 1 mm are used, and the dispersion treatment can be carried out by appropriately setting the bead packing rate. The dispersion obtained as described above can be subjected to filtration and / or centrifugation, etc. This operation allows the particle diameter of the particles contained in the dispersion to be uniform. If foaming occurs during the preparation of the dispersion, a very small amount of a known antifoaming agent such as a silicone-based or acetylene glycol-based agent can be added. Other methods for preparing the dispersion liquid include acid precipitation, interfacial polymerization, in-situ polymerization, submerged hardening coating, coacervation (phase separation), submerged drying, melt-dispersion cooling, air suspension coating, and spray drying. Of these, acid precipitation and interfacial polymerization are preferred.

[0030] The average particle size (D50) of the pigment dispersion in the dispersion is usually 300 nm or less, preferably 30 to 280 nm, more preferably 40 to 270 nm, and even more preferably 50 to 250 nm. Furthermore, 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. D10 is usually 10 nm or more, preferably 20 nm or more, and more preferably 30 nm or more, with the upper limit being 100 nm. Having the particle size of the pigment in the dispersion within the above range ensures ink storage stability and allows the ink to be ejected stably without clogging the inkjet head nozzles. Here, the average particle size (D50) is the particle size at which the cumulative particle size distribution from the small particle size side in the particle size distribution obtained by the laser diffraction / scattering method is 50%, D10 is the particle size at which the cumulative particle size distribution from the small particle size side is 10%, and D90 is the particle size at which the cumulative particle size distribution from the small particle size side is 90%.

[0031] (b) Binder The binder is preferably at least one selected from waxes and (meth)acrylic acid-based polymers. By incorporating a binder into the ink, the scratch resistance of the printed image can be improved. The binder is preferably incorporated in the form of an emulsion, and an aqueous emulsion is more preferred. The average particle size of the binder is preferably 50 nm to 5 μm, more preferably 100 nm to 1 μm, in order to prevent clogging of the inkjet head. When ink 1 contains a binder, the content of the binder, calculated as solid content, relative to the total mass of ink 1 is usually 0.1 to 14%, preferably 0.5 to 12%, more preferably 2 to 10%, and even more preferably 3 to 8%. This content can improve the scratch resistance of the printed image.

[0032] As the wax, natural wax and synthetic wax can be used. Examples of natural waxes include petroleum-based waxes such as paraffin wax and microcrystalline wax; lignite-based waxes such as montan wax; plant-based waxes such as carnauba wax and candelilla wax; and emulsions of animal and plant-based waxes such as beeswax and lanolin dispersed in an aqueous medium. Examples of synthetic waxes include polyalkylene waxes (preferably poly C2-C4 alkylene waxes), oxidized polyalkylene waxes (preferably poly C2-C4 alkylene waxes), and paraffin waxes. Among these, one or more waxes selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax are preferred, and oxidized polyethylene wax is more preferred. Commercially available wax emulsions include, for example, CERAFLOUR 925, 929, 950, and 991 manufactured by BYK Japan; AQUACER 498, 515, 526, 531, 537, 539, 552, and 1547; AQUAMAT 208, 263, and 272; and MINERPOL 221, manufactured by Mitsui Chemicals, Inc.; Mitsui Hiwax NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, and NP505, manufactured by Mitsui Chemicals, Inc.; and KUE-100 and 11, manufactured by Sanyo Chemical Co., Ltd. Among these, AQUACER 515, 531, 537, 539, and 1547 are preferred, and AQUACER 515, 531, 537, and 1547 are more preferred.

[0033] The (meth)acrylic acid-based polymer used as the binder is a polymer different from the dispersant described above. The (meth)acrylic acid-based polymer is preferably a (meth)acrylic acid-based polymer composed of four types of monomers: C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate. The C1-C4 alkyl methacrylate preferably has a linear or branched alkyl moiety, more preferably a linear alkyl moiety. The C1-C4 alkyl methacrylate is preferably a C1-C3 alkyl methacrylate, more preferably a C1-C2 alkyl methacrylate, and even more preferably methyl methacrylate. The C6-C10 alkyl acrylate preferably has a linear or branched alkyl moiety, more preferably a branched alkyl moiety. The C6-C10 alkyl acrylate is preferably a C7-C9 alkyl acrylate, more preferably a C8 alkyl acrylate, and even more preferably 2-ethylhexyl acrylate. The contents of the four monomers, C1-C4 alkyl methacrylate, C6-C10 alkyl acrylate, methacrylic acid, and allyl methacrylate, in the (meth)acrylic acid-based polymer are typically 40-60%, 38-58%, 1-10%, and 1-5%, respectively, by mass, and preferably 45-55%, 52-42%, 2-4%, and 1-3%, and it is preferable that the total of these monomer contents be 100%. The acid value (unit: mgKOH / g) of the (meth)acrylic acid-based polymer is usually -10 to 35, preferably -5 to 30, and more preferably 0 to 25. The glass transition temperature (Tg) of the (meth)acrylic acid polymer is usually from -20 to 30°C, preferably from -15 to 25°C, and more preferably from -10 to 20°C.

[0034] (c) Penetrating agent Examples of penetrating agents include 1,2-pentanediol, ethylene glycol monoallyl ether, isopropyl alcohol, isopropyl glycol, diethylene glycol ethyl methyl ether, dipropylene glycol dimethyl ether, 3-methoxy-3-methyl-1-butanol, butyl triglycol, diethylene glycol diethyl ether, 1,2-hexanediol, diethylene glycol monoisobutyl ether, propyl propylene glycol, butyl diglycol, dipropylene glycol n-propyl ether, 2,2-diethyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 1,2-octanediol, and hexyl diglycol. When the ink contains a penetrant, the total content of the penetrant in the total mass of the ink is usually 0.1 to 30%, preferably 0.2 to 20%, more preferably 0.5 to 10%, even more preferably 2 to 8%, and particularly preferably 4 to 6%.

[0035] (d) Viscosity modifier The ink 1 can further contain a viscosity modifier. Industrial inkjet printers usually have a set viscosity range for the ink they can eject, based on the specifications of the printer head (the head that ejects the ink). For this reason, adding a viscosity modifier to the ink can adjust the viscosity to an appropriate range. The viscosity adjuster is not particularly limited as long as it can adjust the viscosity of the ink, and known substances can be used. Specific examples include water-soluble organic solvents (excluding the penetrants). Examples of water-soluble organic solvents include 2-methyl-2,4-pentanediol, tripropylene glycol monomethyl ether, isopropyl diglycol, dipropylene glycol monomethyl ether, ethanol, 3-methyl-1,5-pentanediol, diethylene glycol dimethyl ether, propylene glycol monomethyl ether, 3-methyl-1,3-butanediol, trimethylolpropane, N-methyl-2-pyrrolidone, 1,2-butanediol, 3-ethyl-3-hydroxymethyloxetane, 1,5-pentanediol, 2-methyl-1,3-propanediol, dipropylene glycol, 1,3-butanediol, methyl diglycol, methyl triglycol, 2-pyrrolidone, propylene glycol, 1,4-butanediol, diethylene glycol, ethylene glycol, triethylene glycol, glycerin, diglycerin, and Glycereth-3 and Glycereth-20 manufactured by Aoki Oil & Fat Industries Co., Ltd. When the ink 1 contains a water-soluble organic solvent, the total content of the water-soluble organic solvent is usually about 0% to 55%, preferably about 5% to 40%, and more preferably about 10% to 30%.

[0036] (e) Surfactants Examples of the surfactant include anionic, cationic, amphoteric, fluorine-based, and silicone-based surfactants.

[0037] Examples of anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, N-acylamino acids or salts thereof, N-acylmethyltaurines, alkyl sulfates, polyoxyalkyl ether sulfates, alkyl sulfates, polyoxyethylene alkyl ether phosphates, rosin acid soaps, castor oil sulfates, lauryl alcohol sulfates, alkylphenol phosphates, alkyl phosphates, alkylaryl sulfonates, diethyl sulfosuccinates, diethylhexyl sulfosuccinates, and dioctyl sulfosuccinates.

[0038] Examples of cationic surfactants include 2-vinylpyridine derivatives and poly(4-vinylpyridine) derivatives.

[0039] Examples of amphoteric surfactants include lauryl dimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine, polyoctyl polyaminoethyl glycine, and imidazoline derivatives.

[0040] 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 on the side chains.

[0041] Examples of silicone surfactants include polyether-modified polysiloxanes, polyether-modified polydimethylsiloxanes, etc. Specific examples of polyether-modified siloxanes include BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 (manufactured by BYK Japan). Specific examples of polyether-modified polydimethylsiloxanes include BYK-306, BYK-307, BYK-333, BYK-342, BYK-3420, BYK-3455 (manufactured by BYK Japan), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, and KF-6017 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0042] (f) Preservatives Examples of preservatives include organic sulfur compounds, organic nitrogen sulfur compounds, organic halogen compounds, haloarylsulfone compounds, iodopropargyl compounds, haloalkylthio compounds, nitrile compounds, pyridine compounds, 8-oxyquinolines, benzothiazole compounds, isothiazolinone compounds, dithiols, pyridine oxide compounds, nitropropane compounds, organic tin compounds, phenol compounds, quaternary ammonium salt compounds, triazine compounds, thiazine compounds, anilides, adamantane compounds, dithiocarbamates, brominated indanone compounds, benzyl bromoacetate compounds, and inorganic salt compounds. Specific examples of commercially available preservatives include Proxel GXL(S) and XL-2(S) manufactured by Arch Chemicals.

[0043] (g) Antifungal agents Examples of antifungal agents include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, and 1,2-benzisothiazolin-3-one and salts thereof.

[0044] (h) pH adjuster Any substance can be used as the pH adjuster as long as it does not adversely affect the prepared ink and can adjust the pH to 5 to 11. Specific examples include alkanolamines such as diethanolamine, triethanolamine, and N-methyldiethanolamine; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonium hydroxide (aqueous ammonia); 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.

[0045] (i) Chelating agents Examples of chelating agents include disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uracildiacetate.

[0046] (j) Rust inhibitors Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0047] (k) Water-soluble ultraviolet absorber Examples of the water-soluble ultraviolet absorber include sulfonated benzophenone compounds, benzotriazole compounds, salicylic acid compounds, cinnamic acid compounds, and triazine compounds.

[0048] (m) antioxidants Examples of the antioxidant include various organic and metal complex anti-fading agents, such as hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, and heterocycles.

[0049] (n) water The ink composition contains the above-mentioned components and, if necessary, ink preparation agents, with the remainder being water. The water used in the ink is preferably ion-exchanged water, distilled water, or the like, which has a low content of impurities such as metal ions.

[0050] The ink 1 may contain a compound represented by the formula (1). In formula (1), R1 represents a hydroxy group, an alkoxy group having a hydroxy group, an acyloxy group, or an arylcarbonyloxy group, R2 represents a hydrogen atom or an alkyl group, R3 represents a hydrogen atom or an alkyl group, R4 represents a hydrogen atom, a hydroxy group, or an alkyl group, and R5 represents an alkyl group. Formula (1) and R1 to R5 in formula (1), including preferred examples thereof, may be the same as those disclosed in patent document (WO2014 / 136569), with Texanol being preferred.

[0051] The pH of the ink 1 is usually 7 to 11, and preferably 8 to 10. The surface tension of the ink composition is usually 10 to 50 mN / m, and preferably 20 to 40 mN / m. The viscosity of the ink composition is usually 2 to 30 mPa·s, and preferably 3 to 20 mPa·s. The pH and surface tension of ink 1 can be adjusted by using a pH adjuster, a surfactant, a water-soluble organic solvent, and the like.

[0052] Known manufacturing methods can be used to prepare the ink 1. One example of such a method is to prepare the ink by adding ink preparation agents, if necessary, to an aqueous dispersion prepared from a pigment and a dispersant and mixing them.

[0053] The ink 1 can be prepared using a conventionally known device such as a ball mill, sand mill, attritor, basket mill, roll mill, etc. During preparation, it is preferable to remove coarse particles using a membrane filter, mesh filter, etc.

[0054] Furthermore, the ink 1 is preferably microfiltered. When microfiltering, 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, and preferably 0.5 μm to 10 μm.

[0055] [Ink 2] There are no particular limitations on the ink 2 contained in the water-based pigment ink set for inkjet recording devices, as long as it is an ink that is printed on a printed material after the above-mentioned ink 1 contained in the ink set.

[0056] The ink 2 may contain a pigment, which may be the same as that described for the ink 1.

[0057] The ink 2 may further contain ink preparation agents in addition to the pigment. The ink preparation agents may be the same as those described for ink 1 above.

[0058] The ink 2 may contain a compound represented by the formula (1). The formula (1) and R1 to R5 in the formula (1), including preferred examples thereof, may be the same as those disclosed in patent document (WO2014 / 136569), with texanol being preferred.

[0059] The pH of the ink 2 is usually 7 to 11, and preferably 8 to 10. The surface tension of the ink composition is usually 10 to 50 mN / m, and preferably 20 to 40 mN / m. The viscosity of the ink composition is usually 2 to 30 mPa·s, and preferably 3 to 20 mPa·s. The pH and surface tension of the ink 2 can be adjusted by using a pH adjuster, a surfactant, a water-soluble organic solvent, and the like.

[0060] Known manufacturing methods can be used to prepare the ink 2. One example of such a method is to prepare the ink by adding ink preparation agents, if necessary, to an aqueous dispersion prepared from a pigment and a dispersant and mixing them.

[0061] The ink 2 can be prepared using a conventionally known device such as a ball mill, sand mill, attritor, basket mill, roll mill, etc. During preparation, it is preferable to remove coarse particles using a membrane filter, mesh filter, etc.

[0062] Furthermore, the ink 2 is preferably microfiltered. When microfiltering, 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.

[0063] [Printing dot diameter on printed matter] The print dot diameter on an ink print refers to the average diameter of the "dots" formed by ink droplets ejected from each nozzle of an inkjet recording device in an image recorded on a print medium by inkjet recording, in an image that can be observed independently, and this diameter can be determined by measurement using an optical microscope, etc. In this specification, the print dot diameter on an ink print may be abbreviated to "dot diameter."

[0064] In the inks 1 and 2 contained in the ink set, when the dot diameter A of ink 1 is taken as 100, the dot diameter B of ink 2 is preferably greater than 86 and less than 120, more preferably 95 or greater and 110 or less, even more preferably 100 or greater and 110 or less, and particularly preferably greater than 100 and 107 or less. In order to achieve the effect of reducing intercolor bleeding, which will be described later, it is preferable that the relationship of dot diameter A<dot diameter B be satisfied.

[0065] The ink 2 preferably contains a compound represented by the formula (1) above. The compound represented by the formula (1) may be the same as above, with texanol being preferred.

[0066] The above Ink 1 and Ink 2 may each independently contain a compound represented by the above formula (1). When the content mass of the compound represented by the above formula (1) in Ink 1 is X and the content mass of the compound represented by the above formula (1) in Ink 2 is Y, it is preferable to satisfy the relationship X < Y, more preferably to satisfy the relationship 1.1X ≤ Y ≤ 10X, even more preferably to satisfy the relationship 1.4X ≤ Y ≤ 5X, and particularly preferably to satisfy the relationship 1.8X ≤ Y ≤ 2.2X.

[0067] The above ink set may independently contain one or more of the above Ink 1 and Ink 2. In the above ink set, at least one type of Ink 1 may be printed before at least one type of Ink 2. When there are multiple types of Ink 1, it is preferable that the last printed Ink 1 is printed before Ink 2. Also, when there are multiple types of Ink 2, Ink 1 may be printed before the last printed Ink 2, and it is preferable that Ink 1 is printed before the first printed Ink 2.

[0068] The above ink set may further contain other inks in addition to the above Ink 1 and Ink 2. The above other inks are not particularly limited as long as they are different from both the above Ink 1 and Ink 2. The printing order in the above ink set is not particularly limited as long as the printing order of Ink 1 and Ink 2 is included in the printing order. For example, it may be in the order of other Ink 1, Ink 1, Ink 2, the order of Ink 1, Ink 2, other Ink 1, the order of Ink 1, other Ink 1, Ink 2, the order of other Ink 1, Ink 1, Ink 2, other Ink 2, the order of other Ink 1, Ink 1, other Ink 2, Ink 2, other Ink 3, etc.

[0069] Regarding all the above matters, combinations of preferable ones are more preferable, and combinations of more preferable ones are even more preferable. The same applies to combinations of a preferable one and a more preferable one, combinations of a more preferable one and an even more preferable one, etc. Unless otherwise specified, all of the above-mentioned components can be used singly or in combination of two or more.

[0070] The ink set can provide printed images that exhibit little intercolor bleeding, low mottling, and excellent wettability to print media, lightfastness, humidity resistance, dry abrasion resistance, wet abrasion resistance, heat resistance, etc. The ink set is extremely useful for various printing applications, particularly inkjet printing applications.

[0071] [Inkjet recording method] The present invention also includes an inkjet recording method using the ink set. The inkjet recording method uses the ink set and includes the steps of ejecting droplets of ink 1 onto a printing medium to form a first image, and ejecting droplets of ink 2 onto the printing medium on which the first image has been formed to form a second image. The steps of forming the first image and forming the second image can be carried out using an inkjet system.

[0072] Known inkjet methods can be used, including, for example, a charge control method, a drop-on-demand (pressure pulse) method, an acoustic inkjet method, and a thermal inkjet method. Inkjet methods also include a method of improving image quality by ejecting a large number of small volumes of ink containing a small amount of pigment or other colorant, a method of improving image quality by using multiple inks that are essentially the same hue but have different concentrations of pigment or other colorant, and a method of improving the fixability of pigment or other colorant by using colorless, transparent ink.

[0073] [Inkjet recording device] It is preferable to print the ink set using an inkjet recording device. Examples of the inkjet recording device include: Examples of inkjet printing methods include charge control, drop-on-demand (pressure pulse), acoustic inkjet, and thermal inkjet. Inkjet printing methods also include methods that improve image quality by ejecting a large number of inks with a small colorant content in a small volume, methods that improve image quality by using multiple inks with substantially the same hue but different colorant concentrations, and methods that improve colorant fixation by using colorless, transparent ink. Industrial inkjet printers are preferably configured as linehead inkjet printers for the purpose of achieving high printing speeds, and single-pass printing is also preferred. The inks described above can produce high-quality prints, particularly under single-pass printing conditions.

[0074] [Print Media] The print medium refers to a material to which the inks of the ink set can adhere. Examples of print media include paper, film, fibers and cloth (cellulose, nylon, wool, etc.), leather, and color filter substrates. Print media can be broadly divided into those with and without an ink-receiving layer. The ink set described above can be applied to either type of print media, but is particularly suitable for use with print media that do not have an ink-receiving layer. Printing media having an ink-receiving layer are usually called inkjet paper, inkjet film, glossy paper, etc. Representative commercially available examples include Professional Photo Paper, Super Photo Paper, Gloss Gold, and Matte Photo Paper manufactured by Canon Inc.; Crispia (high gloss) photo paper, glossy photo paper, and matte photo paper manufactured by Seiko Epson Corporation; Advanced Photo Paper (glossy) manufactured by Hewlett-Packard Japan; and Gasai Photo Finishing Pro manufactured by Fujifilm Corporation. Examples of printing media that do not have an ink-receiving layer include various types of paper, such as coated paper and art paper, used in applications such as gravure printing and offset printing; and cast-coated paper used in label printing. When using printing media that do not have an ink-receiving layer, it is preferable to subject the printing media to a surface modification treatment in order to improve the fixation of the colorant, etc. Examples of surface modification treatments include known methods such as corona discharge treatment, plasma treatment, and flame treatment. The printing media printed with the above ink set are also included in the present invention.

[0075] [Ink Media Set] The ink-media set is a set that includes the ink set and the printing media, and is included in the present invention. [Example]

[0076] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. Unless otherwise specified, all operations such as synthesis reactions in the examples were carried out under stirring. The temperatures of the reactions and the like are those inside the reaction solutions. Furthermore, the "water" used in the examples is "ion-exchanged water" unless otherwise specified.

[0077] [Preparation Example 1]: Preparation of cyan dispersion A block copolymer was prepared as described in Synthesis Example 3 of WO 2013 / 115071. The resulting block copolymer (6 parts) was dissolved in 20 parts of methyl ethyl ketone to obtain a homogeneous solution. A mixture of sodium hydroxide (0.45 parts) and water (53.55 parts) was added to the resulting solution, followed by 20 parts of CI Pigment Blue 15:4 (Chromofine Blue 4851, manufactured by Dainichi Seika Color & Chemicals Co., Ltd.). The mixture was dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a liquid. Water (100 parts) was added to the resulting solution, and the resulting solution was filtered through a GA-100 glass filter to remove aggregates and obtain a filtrate. The resulting filtrate was subjected to vacuum distillation of the methyl ethyl ketone and a portion of the water in the filtrate, resulting in a pigment content of 12.0%. This yielded a cyan dispersion.

[0078] [Preparation Example 2]: Preparation of magenta dispersion A magenta dispersion with a pigment content of 12.0% was obtained in the same manner as in Preparation Example 1, except that CI Pigment Red 122 (Clariant Inkjet Magenta E02VP2621) was used instead of CI Pigment Blue 15:4 used in Preparation Example 1 above.

[0079] [Preparation Example 3]: Preparation of resin emulsion. By following Preparation Example 4 of WO 2015 / 147192, a resin emulsion with an acid value of 6 KOHmg / g and a solids content of 25% was prepared. This is designated Resin 1.

[0080] Each ink composition for evaluation testing was obtained by mixing the components shown in Table 1 below and then filtering through a 3 μm membrane filter, and each ink set shown in Table 1 below was then prepared. In Table 1 below, blank spaces indicate 0 parts.

[0081] The abbreviations in Table 1 below represent the following: PG: Propylene glycol. 1,2HD: 1,2-hexanediol. TEA: Triethanolamine. BYK-349: Silicone surfactant (manufactured by BYK Japan) TEX: Texanol (manufactured by Eastman Chemical Co.) Resin 1: Resin emulsion obtained in Preparation Example 7. AQ515: AQUACER 515 (manufactured by BYK Japan; solid content 35%) DW: Ion-exchanged water.

[0082] [Table 1]

[0083] [Evaluation of printing dot diameter] (1) Preparation of test piece 1 A 5% solid image was printed for each of the inks of Example 1 and Comparative Examples 1 and 2, to obtain a printed image. Printing was performed using a printing tool equipped with a KJ4B inkjet head manufactured by Kyocera Corporation, with a frequency of 10 kHz and fine droplets, and using "OK Topcoat+" manufactured by Oji Paper Co., Ltd. as the printing medium. The obtained printed image was left to dry in a thermostatic chamber set at 70°C for 2 minutes, to obtain test piece 1. (2) Evaluation When test piece 1 is magnified with an optical microscope, individual printed dots can be observed. The diameter of these printed dots was measured, and the diameter of the magenta dot was calculated by setting the actual measured dot diameter of the cyan ink in the same ink set to 100. This is called the printed dot diameter. For example, if the actual measured dot diameter of the cyan ink is 50 μm and the actual measured dot diameter of the magenta ink is 60 μm, the printed dot diameter of the cyan ink in this ink set is 100, and the printed dot diameter of the magenta ink is 120. The printed dot diameter was measured using the PIAS-II print image evaluation device manufactured by QEA. The printing speed was 25.4 m / min.

[0084] [Evaluation of intercolor bleeding] (1) Preparation of test piece 2 Using the ink sets of Example 1 and Comparative Examples 1 and 2, a single linear image (magenta image) was printed with magenta ink at 100% coverage and a line width of 1.0 mm, so as to overlap a 100% solid image (cyan image) printed with cyan ink, resulting in a printed image. Printing was performed using a printing tool equipped with two KJ4B inkjet heads manufactured by Kyocera Corporation, in the order of cyan ink and magenta ink, at a frequency of 10 kHz and three-level printing (combined fine and medium droplets), using "OK Topcoat+" manufactured by Oji Paper Co., Ltd. as the printing medium. The two inkjet heads were installed in the printing evaluation device, in the order of cyan ink and magenta ink, from the upstream side in the feed direction of the printing medium. The spacing between the inkjet heads filled with cyan ink and magenta ink was set to 90 mm. The resulting printed image was placed in a thermostatic chamber set to 70°C and dried for 2 minutes to obtain test piece 2. (2) Evaluation The line width of test piece 2 was measured, and the expansion coefficient was calculated according to the following expansion coefficient calculation formula. This expansion coefficient is called bleeding. The line width was measured using a print image evaluation device PIAS-II manufactured by QEA. The printing speed was 25.4 m / min. (Expansion rate calculation formula) Expansion rate (%) = Line width of magenta image on cyan image ÷ Line width of magenta image not overlapping on cyan image × 100 The expansion rate was evaluated based on the following criteria: The smaller the expansion rate, the better the performance in preventing intercolor bleeding. [Evaluation criteria] A: Expansion rate is 50% or less B: Expansion rate is 51% or more and 70% or less C: Expansion rate is 71% or more

[0085] From Table 1 above, it is clear that the ink sets of the examples have extremely little intercolor bleeding and can provide good printed images, and it is also clear that these ink sets have the ability to suppress both intercolor bleeding and mottling.

[0086] The present invention provides an ink set that can provide printed images with extremely good intercolor bleeding, an inkjet printing method that uses the ink set, a print medium, and a print medium set. The ink set of the present invention is extremely useful for various printing applications, particularly inkjet printing applications.

Claims

1. A water-based pigment ink set for an inkjet recording device, comprising ink 1 and ink 2, wherein when the print dot diameter A on a printed matter of ink 1, which is printed first, is taken as 100, the print dot diameter B on a printed matter of ink 2, which is printed later, is greater than 86 and less than 120.

2. 2. The water-based pigment ink set for an inkjet recording device according to claim 1, wherein the ink 2 contains a compound represented by the following formula (1): 【Chemical 1】 [In formula (1), R １ represents a hydroxy group, an alkoxy group having a hydroxy group, an acyloxy group, or an arylcarbonyloxy group; R ２ represents a hydrogen atom or an alkyl group, R ３ represents a hydrogen atom or an alkyl group, R ４ represents a hydrogen atom, a hydroxy group, or an alkyl group; R ５ represents an alkyl group.

3. 3. The water-based pigment ink set for an inkjet recording device according to claim 2, wherein ink 1 further contains a compound represented by formula (1), and when the mass content of the compound represented by formula (1) in ink 1 is X and the mass content of the compound represented by formula (1) in ink 2 is Y, the relationship X<Y is satisfied.

4. 3. The water-based pigment ink set for an ink-jet recording apparatus according to claim 1, wherein the ink-jet recording apparatus is a single-pass ink-jet recording apparatus.

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