Water-based ink composition

Abstract

To provide an aqueous ink composition which, while showing very good wettability for a non- or low-ink-absorbing medium, shows reduced granularity even in a portion printed with a secondary or more color and, further, provides printed images in which blending between colors do not worsen irrespective of storage time.SOLUTION: An aqueous ink composition comprises: water; pigment; a terminal-modified polysiloxane surfactant represented by the following formula (1); and a C3 or more linear monoalcohol. (In formula (1), a is an integer of 1 or more and less than 32; x and y are each independently an integer of 1 to 4; m and n are each independently are an integer of 1 to 50; o and p are each independently are an integer of 0 to 40; m+n is 2 to 100; o+p is 0 to 80; and R1 and R2 are each independently selected from the group consisting of a hydrogen atom, a hydroxyl group, a C1-6 alkyl group, and a (meth)acryl group.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink composition. [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 that graininess be as minimal as possible. 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 ink in such a non-uniform state, the printed image may appear to have scattered "grains" of varying density, making it appear less uniform. Such printed images are evaluated as having "noticeable graininess," which is one of the factors that significantly deteriorates print quality. For this reason, there is a strong demand for inks that can produce printed images with as little graininess as possible.

[0005] Furthermore, when performing color printing, an ink set consisting of multiple colors is used. When performing color printing using such an ink set, it is known that bleeding between the first and second colors may 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. Therefore, there is a need to eliminate this inter-color bleeding, and ink sets that solve this problem have been proposed. Furthermore, with regard to graininess, there is a demand for reducing graininess not only in single colors but also in secondary and higher colors in order to improve print quality. [Prior art documents] [Patent documents]

[0006] [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

[0007] Furthermore, when printing is continued, the consumption of each ink composition varies depending on the type of ink composition. Therefore, when an ink composition with a high consumption rate runs out, it is replaced with a new ink composition. On the other hand, an ink composition with a low consumption rate continues to be used until the ink composition initially used runs out. As a result, new and old ink compositions are used in combination. There may be a difference of several months to a year in the shelf life before use between an ink composition with a high consumption rate and an ink composition with a low consumption rate. When ink compositions with different shelf lives are used in combination for printing, bleeding between colors may worsen, resulting in a deterioration in print quality, even though there is no significant change in the storage stability of each ink composition itself (various physical properties such as ejection performance, average particle size, viscosity, and pH). In addition to the above demands, there is also a strong demand for a solution to this issue. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and has an object to provide a water-based ink composition that exhibits extremely good wettability to non-ink-absorbent or poorly ink-absorbent media, reduces graininess even in printed areas of secondary or higher colors, and enables the provision of printed images that do not suffer from inter-color bleeding regardless of storage period. [Means for solving the problem]

[0009] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by the inventions described in 1) to 5) below, and have completed the present invention.

[0010] That is, the present invention relates to the following 1) to 5). 1) The water-based ink composition includes water, a pigment, a terminal-modified polysiloxane surfactant represented by the following formula (1), and a linear monoalcohol having 3 or more carbon atoms:

[0011] [ka]

[0012] (In formula (1), a is an integer of 1 or more and less than 32; x and y are each independently an integer of 1 to 4; m and n are each independently an integer of 1 to 50; o and p are each independently an integer of 0 to 40; m+n is 2 to 100; o+p is 0 to 80; R 1 and R 2 are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkyl ether group having 1 to 6 carbon atoms, and a (meth)acrylic group. 2) 1), wherein the linear monoalcohol having 3 or more carbon atoms includes at least one selected from the group consisting of 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and 1-nonanol. 3) The water-based ink composition according to 1) or 2), wherein the amount of the linear monoalcohol having 3 or more carbon atoms added is 0.1% to 3% of the total amount of the water-based ink composition, and 1.5% to 40% of the total amount of the pigment contained in the water-based ink composition. 4) The water-based ink composition according to any one of 1) to 3), wherein in formula (1), a is an integer of 1 or more and less than 18. 5) An ink set comprising at least the water-based ink composition according to any one of 1) to 4). DETAILED DESCRIPTION OF THE INVENTION

[0013] The water-based ink composition contains water, a pigment, a terminal-modified polysiloxane surfactant represented by formula (1), and a linear monoalcohol having 3 or more carbon atoms. In this specification, the water-based ink composition may be abbreviated as "ink composition" or "ink."

[0014] [water] The ink is a water-based ink containing water. The water contained in the ink 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 a known method.

[0015] [Pigment] The ink contains a pigment. Examples of pigments include inorganic pigments, organic pigments, and extender pigments. These pigments can be used alone or in combination of two or more. Examples of inorganic pigments include carbon black, titanium oxide, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides. When the ink is a black ink, preferred examples of the carbon black contained in the ink include thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, and channel black. Specific examples of carbon black include the Raven series manufactured by Columbia Carbon Corporation; the Monarch series, Regal series, and Mogul series manufactured by Cabot Corporation; the HIBLACK series, ColorBlack series, Printex series, SPECIALBLACK series, and Nerox series manufactured by Orion Engineered Carbons; and the MA series, MCF series, No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, and No. 2300 manufactured by Mitsubishi Chemical Corporation.

[0016] Examples of the organic pigment include various pigments such as azo, disazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone. Specific examples of the organic pigment 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 organic pigments include black pigments of various colors such as Black 1.

[0017] Examples of the extender pigment include silica, calcium carbonate, talc, clay, barium sulfate, white carbon, etc. The extender pigment is preferably used in combination with other pigments.

[0018] The total content of the pigments relative to the total amount of the ink is usually 1 to 20%, preferably 1.5 to 10%, and more preferably 2 to 8%. Herein, in the specification and claims of the present application, "%" and "parts" are written on a mass basis unless otherwise specified. The average particle size of the pigment is usually 50 nm to 250 nm, and preferably 60 nm to 200 nm. In the specification and claims of the present application, the average particle size refers to the particle size at 50% of the integrated value (D50) in the particle size distribution determined by a laser diffraction / scattering method.

[0019] [Terminally modified polysiloxane surfactant represented by formula (1)] The ink contains a terminal-modified polysiloxane surfactant represented by the formula (1). In this specification, the terminal-modified polysiloxane surfactant represented by the formula (1) may be abbreviated as the surfactant represented by formula (1).

[0020] In the surfactant represented by the above formula (1), a is an integer of 1 or more and less than 32, preferably 1 or more and less than 25, and more preferably 1 or more and less than 18. x and y are each independently an integer of 1 to 4, preferably 1 to 3. m and n are each independently an integer of 1 to 50, preferably 2 to 40, more preferably 4 to 20, and even more preferably 5 to 12. o and p are each independently an integer of 0 to 40, preferably 0 to 20, more preferably 0 to 10, and even more preferably 0 to 5. m+n is 2 to 100, preferably 4 to 80, more preferably 8 to 40, and even more preferably 10 to 25. o+p is 0 to 80, preferably 0 to 40, more preferably 0 to 20, and even more preferably 0 to 10. R 1 and R 2 are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkyl ether group having 1 to 6 carbon atoms, and a (meth)acrylic group, and are preferably a hydroxy group, a methyl ether group, or an ethyl ether group. The surfactant represented by the above formula (1) is a surfactant in which a is 1 or more and less than 25, x is 1 to 4, y is 1 to 4, o is 0 to 10, p is 0 to 10, R 1 is any group selected from the group consisting of a hydrogen atom, a hydroxy group, a methyl ether group, an ethyl ether group, a propyl ether group, and an n-butyl ether group; R 2is preferably a combination of any one group selected from the group consisting of a hydrogen atom, a hydroxy group, a methyl ether group, an ethyl ether group, a propyl ether group, and an n-butyl ether group, a is 1 to 18, x is 1 to 3, y is 1 to 3, o is 0 to 5, p is 0 to 5, R 1 is any group selected from the group consisting of a hydroxy group, a methyl ether group, and an ethyl ether group; R 2 and any group selected from the group consisting of a hydroxy group, a methyl ether group, and an ethyl ether group are more preferred.

[0021] The content of the surfactant represented by the formula (1) in the ink is usually 0.01 to 3%, preferably 0.05 to 2%, and more preferably 0.1 to 1%.

[0022] Specific examples of commercially available surfactants represented by the above formula (1) include Silwet CoatOSil 2812, Silwet CoatOSil 2816, Silwet CoatOSil 3500, and Silwet CoatOSil 3505 manufactured by Momentive Performance Materials, Inc.; BYK-331, BYK-333, BYK-UV3500, and BYK-LPG20726 manufactured by BYK-Chemie; and Tegoglide 410, Tegoglide 432, Tegoglide 435, Tegoglide 440, and Tegoglide 450 manufactured by Evonik Degussa.

[0023] The surfactant represented by the above formula (1) can be synthesized, for example, by a hydrosilylation reaction using a platinum catalyst, using polyethylene glycol having an allyl group at one end and polydimethylsiloxane having hydrogen groups at both ends.

[0024] [Straight-chain monoalcohols with 3 or more carbon atoms] The ink contains a linear monoalcohol having three or more carbon atoms. Specific examples of linear monoalcohols having three or more carbon atoms include 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, and 1-dodecanol. Preferably, the ink contains at least one selected from the group consisting of 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and 1-nonanol. By including the linear monoalcohol having three or more carbon atoms, the ink can have good wettability with respect to media that do not or poorly absorb ink.

[0025] The amount of the linear monoalcohol having 3 or more carbon atoms added to the ink is 0.1% to 3%, and preferably 0.2% to 2%, based on the total amount of the ink. Furthermore, the amount of the linear monoalcohol having 3 or more carbon atoms added to the ink is 0.5% to 50%, preferably 1.5% to 40%, and more preferably 2% to 30% of the total amount of the pigment contained in the ink. By setting the amount of the linear monoalcohol having 3 or more carbon atoms added to the ink as described above, it is possible to ensure good wetting of the ink with respect to non- or poorly absorbent media, while also ensuring the storage stability of the ink. Furthermore, it is more preferable that the amount of the linear monoalcohol having 3 or more carbon atoms added is 0.1% to 3% of the total amount of the ink, and 1.5% to 40% of the total amount of the pigment contained in the ink.

[0026] The ink preferably uses a dispersant to disperse the pigment in the ink composition. 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.

[0027] 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.

[0028] 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" means both methacrylate and acrylate.

[0029] Examples of the copolymer include block copolymers, random copolymers, and graft copolymers, and / or salts thereof.

[0030] Resins used as dispersants 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 polymers disclosed in International Publication No. 2013 / 115071.

[0031] The acid value of the dispersant is usually 70 to 200 mgKOH / g, preferably 80 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 adjusting the acid value within the above range, the dispersibility and storage stability of the ink composition can be improved.

[0032] Examples of neutralizing agents used to disperse pigment dispersions prepared using block copolymers in water include ammonia, alkali metal hydroxides, alkaline earth metal hydroxides, aliphatic amine compounds, and alkanolamine compounds. Ammonia and alkali metal hydroxides are preferred, with ammonia being particularly 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 150%, with 100% neutralization being defined as neutralization with an amount theoretically equivalent to the acid value of the dispersant.

[0033] The resin as a 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 pigment is coated with the resin as a dispersant, or both of these states can be used in combination.

[0034] The ink composition is preferably prepared by preparing a dispersion containing a pigment and a resin as a dispersant, and then mixing it with other components. 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.

[0035] 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, or the like. For example, when using a sand mill, beads with a particle diameter of about 0.01 mm to 1 mm can be used, and the bead packing rate can be appropriately set to carry out the dispersion treatment. The resulting dispersion can be subjected to filtration and / or centrifugation, among other procedures. This procedure allows the particle diameters of the particles contained in the dispersion to be uniform.

[0036] 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.

[0037] The above-described method for preparing a dispersion can also be applied to dispersions using surfactants. Examples of surfactants suitable as dispersants include anionic surfactants such as fatty acid salts, higher alkyl dicarboxylate salts, higher alcohol sulfate salts, higher alkyl sulfonates, condensates of higher fatty acids and amino acids, sulfosuccinate salts, naphthenate salts, liquid fatty oil sulfate salts, and alkylarylsulfonates; cationic surfactants such as fatty acid amine salts, quaternary ammonium salts, sulfonium salts, and phosphonium salts; and nonionic surfactants such as polyoxyethylene phenyl ethers, polyoxyethylene naphthyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, and polyoxyethylene sorbitan alkyl esters. When added to an ink composition, the above-described surfactants function not only as dispersants but also as surfactants.

[0038] From the viewpoint of ensuring dispersion stability, the amount of dispersant added is 5% to 120%, preferably 10% to 100%, and more preferably 20% to 80% of the total amount of pigment.

[0039] In addition to the above, 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.

[0040] 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 has the effect of stably ejecting the ink without clogging the inkjet head nozzles.

[0041] 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%.

[0042] The ink may further contain ink preparation agents in addition to the above components. Examples of ink preparation agents include binders, organic solvents other than linear monoalcohols having 3 or more carbon atoms, viscosity modifiers, surfactants other than the terminally modified polysiloxane surfactant represented by formula (1) above, preservatives, antifungal agents, pH adjusters, chelating agents, rust inhibitors, water-soluble UV absorbers, and antioxidants. The total content of the "other ink preparation agents" excluding the binders, organic solvents, and viscosity modifiers is typically 0 to 30%, preferably 0.1 to 20%, and more preferably 0.5 to 10% of the total mass of the ink.

[0043] The binder is preferably at least one selected from waxes and (meth)acrylic acid-based polymers. By including a binder in the ink composition, the scratch resistance of the printed image can be improved. The binder is preferably included in the form of an emulsion, and an aqueous emulsion is more preferred.

[0044] The binder may be in a particulate form, and when the binder is in a particulate form, the average particle size of the binder is preferably 10 nm to 1 μm, more preferably 20 nm to 500 nm, in order to prevent clogging of the inkjet head.

[0045] When the ink contains the binder, the content of the binder relative to the total amount of ink is usually 0.1 to 14%, preferably 0.5 to 12%, more preferably 1 to 10%, calculated as solid content. By setting the content of the binder relative to the total amount of ink to usually 0.1 to 14%, calculated as solid content, the scratch resistance of the printed image can be improved.

[0046] The wax may be, for example, a natural wax or a synthetic wax. Examples of natural waxes include petroleum-based waxes such as paraffin wax and microcrystalline wax, brown coal-based waxes such as montan wax, plant-based waxes such as carnauba wax and candelilla wax, and emulsions of plant-based waxes such as beeswax and lanolin dispersed in an aqueous medium.

[0047] 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.

[0048] Examples of commercially available waxes include 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.; KUE-100 and 11 manufactured by Sanyo Chemical Co., Ltd.; and HYTEC E-6500, 9015, and 6400 manufactured by Toho Chemical Co., Ltd. Among these, AQUACER 515, 531, 537, 539, and 1547 are preferred, and AQUACER 515, 531, 537, and 1547 are more preferred.

[0049] The (meth)acrylic acid-based polymer used as the binder 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.

[0050] 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.

[0051] 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.

[0052] 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%. It is preferable that the total content of these monomers be 100%. The acid value (unit: mgKOH / g) of the (meth)acrylic acid-based polymer is typically 0-35, preferably 0-30, and more preferably 0-25. The glass transition temperature (Tg) of the (meth)acrylic acid-based polymer is typically -20-30°C, preferably -15-25°C, and more preferably -10-20°C.

[0053] The ink may further contain an organic solvent other than a linear monoalcohol having 3 or more carbon atoms in order to adjust the ink's penetration into the medium, viscosity, drying property, defoaming property, etc. The organic solvent other than a linear monoalcohol having 3 or more carbon atoms is not particularly limited as long as it is different from the linear monoalcohol having 3 or more carbon atoms. Examples of the organic solvent other than a linear monoalcohol having 3 or more carbon atoms include carboxylic acid amides such as N,N-dimethylformamide and N,N-dimethylacetamide; lactams such as 2-pyrrolidone, N-methyl-2-pyrrolidone, and N-methylpyrrolidin-2-one; cyclic ureas such as 1,3-dimethylimidazolidin-2-one and 1,3-dimethylhexahydropyrimid-2-one; ketones, ketoalcohols, or carbonates such as acetone, 2-methyl-2-hydroxypentan-4-one, and ethylene carbonate; tetrahydrofuran, dioxane, etc. cyclic ethers such as ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butylene glycol, 1,4-butylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, thiodiglycol, or dithiodiglycol, and other oligo- or polyalkylene glycols or thioglycols having C2-C6 alkylene units; C3-C9 polyols (triols) such as glycerin, diglycerin, hexane-1,2,6-triol, and trimethylolpropane;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 glycol ethers such as diol ethers (preferably glycol ethers selected from the group consisting of C3-C10 mono-, di-, or triethylene glycol ethers and C4-C13 mono-, di-, or tripropylene glycol ethers); C3-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, and 2,4-diethyl-1,5-pentanediol; γ-butyrolactone or dimethyl sulfoxide; and the like.

[0054] The total amount of the organic solvents in the total amount of the ink is preferably 0.1 to 40%, more preferably 0.2 to 30%, even more preferably 0.5 to 20%, and particularly preferably 2 to 15%.

[0055] The ink may contain a viscosity modifier. In particular, the viscosity range of ink that can be ejected from industrial inkjet printers is usually determined based on the specifications of the printer head (the head that ejects the ink) installed in the printer. Therefore, a viscosity modifier can be added to the ink to adjust the viscosity to an appropriate range. The viscosity modifier is not particularly limited as long as it is a substance that can adjust the viscosity of the ink, and known substances can be used. Specific examples of viscosity modifiers include sugars and hydrophilic resins, in addition to the organic solvents listed above.

[0056] The surfactant other than the terminal-modified polysiloxane surfactant represented by formula (1) above that may be contained in the ink is not particularly limited as long as it is a surfactant other than the terminal-modified polysiloxane surfactant represented by formula (1) above, and examples thereof include anionic, cationic, amphoteric, and fluorine-based surfactants.

[0057] 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.

[0058] Examples of cationic surfactants include 2-vinylpyridine derivatives and poly(4-vinylpyridine) derivatives.

[0059] 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.

[0060] 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. The content of surfactants other than the terminally modified polysiloxane surfactant in the ink composition is preferably 0.1 to 2.0%.

[0061] Examples of the 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.

[0062] Examples of the antifungal agent include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, and 1,2-benzisothiazolin-3-one, as well as salts thereof.

[0063] Examples of the pH adjuster 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.

[0064] Examples of the chelating agent include disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uracildiacetate.

[0065] Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0066] Examples of the water-soluble ultraviolet absorber include sulfonated benzophenone compounds, benzotriazole compounds, salicylic acid compounds, cinnamic acid compounds, and triazine compounds.

[0067] 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.

[0068] The pH of the ink is usually 7 to 11, and preferably 8 to 10. The surface tension of the ink is usually 10 to 50 mN / m, and preferably 20 to 40 mN / m. The viscosity of the ink is usually 2 to 30 mPa s, and preferably 3 to 20 mPa s. The pH and surface tension of the ink can be adjusted by using a pH adjuster, a surfactant, an organic solvent, etc.

[0069] Examples of the defoaming agent include surfactants such as silicone-based, silica mineral oil-based, olefin-based, and acetylene-based surfactants. Examples of commercially available defoaming agents include Surfynol DF37, DF58, DF110D, DF220, MD-20, and Olefin SK-14, all manufactured by Shin-Etsu Chemical Co., Ltd.

[0070] The ink can be used in various printing applications, such as writing instruments, various printing applications, information printing, and textile printing, and is particularly preferably used in inkjet printing.

[0071] The ink can be prepared by any known method, including, for example, a method of preparing the ink by adding water, various organic solvents, and, if necessary, ink preparation agents to an aqueous dispersion prepared from a pigment and a dispersant, and mixing the mixture.

[0072] The ink can be prepared using a conventionally known apparatus, such as a ball mill, a sand mill, an attritor, a basket mill, a roll mill, etc. During preparation, it is preferable to remove coarse particles using a membrane filter, a mesh filter, etc.

[0073] The ink 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.

[0074] The present invention also includes an ink set containing at least the above ink. Examples of the ink set include an ink set containing two or more of the above inks, an ink set containing one or more of the above inks and one or more of other inks other than the above inks, etc. The other inks other than the above inks are not particularly limited as long as they have a different composition from the above inks, but it is preferable that they have a different hue from the above inks.

[0075] The ink and ink set are preferably used in inkjet printing.

[0076] Known inkjet methods can be used. Specific examples of inkjet methods include 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 for improving image quality by ejecting a large number of inks with a small amount of colorant in a small volume, a method for improving image quality by using multiple inks with substantially the same hue but different concentrations of colorant, and a method for improving colorant fixation by using colorless, transparent ink.

[0077] (Print Media) The print medium refers to a material to which the ink or the inks contained in the ink set can adhere. Examples of print media include paper, film, fibers and cloth (cellulose, nylon, wool, etc.), leather, and color filter substrates.

[0078] 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.

[0079] 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.

[0080] 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 colorants, etc. Examples of surface modification treatments include known methods such as corona discharge treatment, plasma treatment, and flame treatment.

[0081] For all of the above items, combinations of preferred items are more preferred, and combinations of more preferred items are even more preferred. The same applies to combinations of preferred items and more preferred items, and combinations of more preferred items and even more preferred items. Unless otherwise specified, all of the above-mentioned components can be used singly or in combination of two or more.

[0082] The ink of the present invention is excellent in storage stability, redispersibility, various abrasion resistance, color development, and saturation. Furthermore, images recorded with the ink of the present invention are excellent in various fastness properties, such as dot diameter, granularity, gloss, hue, dot shape (e.g., suppression of coffee stain), color development, water resistance, light resistance, heat resistance, and oxidation gas (e.g., ozone gas) resistance. Furthermore, there is little coating unevenness during image formation, and the image forming properties are also excellent. Furthermore, images recorded with an ink set containing the ink of the present invention are excellent in suppression of intercolor bleeding, stability of intercolor bleeding, graininess in printed areas of secondary or higher colors, and solid uniformity in printed areas of secondary or higher colors. [Example]

[0083] The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples. In the examples, when it was necessary to measure the pigment content (solid content) of various liquids, the content was calculated as a value calculated based on the pigment alone using an MS-70 (manufactured by A&D Co., Ltd.) by the dry weight method.

[0084] [Preparation Example 1 of Pigment Dispersion Liquid (Dp1)] A block copolymer (block copolymer A) was obtained by reproducing Synthesis Example 3 of WO 2013 / 115071. The obtained block copolymer A (4.8 parts) was dissolved in 20 parts of 2-butanone to obtain a homogeneous solution. A solution prepared by dissolving sodium hydroxide (0.35 parts) in water (58.8 parts) was added to this solution and stirred for 1 hour to obtain a solution. CI Pigment Blue 15:4 (hereinafter referred to as "PB15:4", 16 parts) was added to this solution, and the solution was dispersed in a sand grinder at 1500 rpm for 15 hours to obtain a solution. Water (100 parts) was added dropwise to the obtained solution, and the solution was filtered to obtain a filtrate. The 2-butanone and a portion of the water were distilled off from the obtained filtrate using an evaporator under reduced pressure to obtain a cyan dispersion with a pigment content of 12.0% and particle sizes D10 / D50 / D90 = 70 nm / 120 nm / 220 nm. The resulting dispersion is designated as "Dp1."

[0085] [Preparation Example 2 of Pigment Dispersion Liquid (Dp2)] A yellow dispersion with a pigment content of 12.0% and particle sizes D10 / D50 / D90 = 65 nm / 140 nm / 230 nm was obtained in the same manner as in Preparation Example 1, except that the PB15:4 in Dp1 was replaced with CI Pigment Yellow 74 (hereinafter referred to as "PY74", 16 parts). The obtained dispersion is designated "Dp2".

[0086] [Examples 1 to 16 and Comparative Examples 1 to 6: Preparation Examples of Ink Compositions] Dispersions Dp1 and Dp2 were mixed with the components listed in Tables 1 and 2 below, and then filtered through a 3 μm membrane filter (a cellulose mixed ester type membrane filter manufactured by Advantec Co., Ltd.) to obtain ink compositions C1 to 11 and Y1 to 11 for evaluation tests. The pigment content relative to the total mass of the ink composition was adjusted to 5% as solids for all inks. Ink compositions C1 to 11 listed in Table 1 are all cyan inks. Ink compositions Y1 to 11 listed in Table 2 are all yellow inks.

[0087] [Table 1]

[0088] [Table 2]

[0089] Details of the ingredients in Tables 1 and 2 are as follows: (dispersion) Dp1: Dispersion 1 obtained in Preparation Example 1 Dp2: Dispersion 2 obtained in Preparation Example 1 (organic solvent) PG: Propylene glycol 1,2-HD: 1,2-hexanediol (Terminally modified polysiloxane surfactant) TG450: TEGO Glide 450 BYK20726:BYL-LPG-20726 (Side-chain modified polysiloxane surfactant) BYK-349 (alcohol) C4OH: 1-butanol C6OH: 1-hexanol C7OH: 1-heptanol C8OH:1-octanol 1,2-OD: 1,2-octanediol (wax) Aquacer515 (purified water) Ultrapure water made by further purifying ion-exchanged water using Merck's MillQ water production system

[0090] 1. Monochrome print quality evaluation 1-1. Preparation of test piece 1 For each of the inks of Examples 1 to 16 and Comparative Examples 1 to 6, a step chart with a concentration of 0% to 100% in 5% increments was printed. Printing was performed using a printing tool equipped with two KJ4B inkjet heads manufactured by Kyocera Corporation, at a frequency of 10 kHz and multi-drop (5 pL, 12 pL) on Oji Paper's "OK Topcoat+" printing medium. The resulting printed image was dried for 3 seconds under an IR heater set at 100°C, yielding test piece 1. 1-2. Evaluation of wettability For the inks of Examples 1 to 16 and Comparative Examples 1 to 6, and the comparative inks, the dot diameter was measured at a 5% concentration portion (5 pL) of test piece 1. A print image evaluation device PIAS-II manufactured by QEA was used for the measurements. The results are shown in Tables 1 and 2. Note that the hyphens in Tables 1 and 2 indicate that the dot diameter could not be measured due to distortion of the dot shape. [Evaluation criteria] ◎: Dot diameter is 52 μm or more ○: Dot diameter is 48 μm or more and less than 52 μm △: Dot diameter is 45 μm or more and less than 48 μm ×: Dot diameter is less than 45 μm -: Measurement not possible due to poor dot shape 1-3.Granularity evaluation For the cyan inks of Examples 1 to 8 and Comparative Examples 1 to 3 and the comparative cyan ink, the graininess of test piece 1 at a concentration of 80% was measured to two decimal places with a tile size set to 42.3 μm, and evaluated using the following four-level evaluation criteria. A smaller graininess value indicates less graininess and better print quality. The measurements were performed using a print image evaluation device, PIAS-II, manufactured by QEA. The results are shown in Table 1. [Evaluation criteria] ◎: Less than 2.0 〇: 2.0 or more and less than 2.5 △: 2.5 or more and less than 3.0 ×: 3.0 or higher

[0091] The dot diameter results shown in Tables 1 and 2 demonstrate that the water-based ink composition of the present invention has good wettability. Comparative Examples 2 and 5, which do not contain a polysiloxane surfactant, had excessive wettability, and the dot shape was distorted, making measurement impossible.

[0092] The results of graininess in single colors shown in Tables 1 and 2 demonstrate that the water-based ink composition of the present invention suppresses graininess in single colors and provides excellent print quality.

[0093] [Examples 17 to 21 and Comparative Examples 7 to 9] C4 to 11 and Y4 to 11 shown in Tables 1 and 2 were combined as shown in Table 3 below to form the ink sets of Examples 17 to 21 and Comparative Examples 7 to 9 and the comparative ink set.

[0094] [Table 3]

[0095] 2. Secondary color graininess 2-1. Preparation of test piece 2 For the ink sets of Examples 17 to 21 and Comparative Examples 7 to 9, a step chart was printed in which the secondary color concentration varied in 5% increments from 0% to 100%. The printing device, conditions, and printing media used were the same as those for Test Piece 1. The resulting printed image was dried for 3 seconds under an IR heater set to 100°C, yielding Test Piece 2. 2-2. Evaluation of secondary color granularity The graininess of the 80% density portion obtained with test piece 2 was evaluated in the same manner as in the evaluation of graininess of a single color. The evaluation results are shown in Table 3. [Evaluation criteria] ◎: Less than 2.0 〇: 2.0 or more and less than 2.5 △: 2.5 or more and less than 3.0 ×: 3.0 or higher

[0096] [Examples 22 to 26 and Comparative Example 10] Of the ink sets and comparative ink sets shown in Table 3 above, Examples 17 to 21 and Comparative Example 8 were stored in a constant temperature bath at 60°C for one week to obtain the ink sets and comparative ink sets of Examples 22 to 26 and Comparative Example 10 after the accelerated test shown in Table 4 below. The lowercase letters c and y indicate the ink compositions after the accelerated test; for example, C4 and c4 have the same ink composition.

[0097] [Table 4]

[0098] 3. Evaluation of inter-color bleeding stability 3-1. Preparation of test piece 3 For the ink sets of Examples 17 to 21 and Comparative Example 8, a thick line (second image) of the second ink composition at 100% concentration and 10 mm width was printed on top of one thin line (first image) of the first ink composition at 100% concentration and 1.0 mm width, so that the thick line intersected perpendicularly with the first image, thereby obtaining a printed image. The printing apparatus, conditions, and printing media used were the same as those for Test Piece 1. The obtained printed image was dried for 3 seconds under an IR heater set to 100°C, obtaining Test Piece 3. 3-2. Preparation of test piece 4 For the ink sets of Examples 22 to 26 and Comparative Example 10, an image similar to that of Test Piece 3 was printed. The printing device, conditions, and printing media used were the same as those for Test Piece 1. The resulting printed image was dried for 3 seconds under an IR heater set at 100°C, to obtain Test Piece 4. 3-3. Measurement of intercolor bleeding stability For test pieces 3 and 4, the line width of the first image formed under the second image was measured. The stability of intercolor bleeding was evaluated by calculating the ratio of the line width of test piece 3 to that of test piece 4. The evaluation criteria were three-level, with smaller changes in line width indicating better intercolor bleeding performance. The evaluation results are shown in Table 5 below. [Evaluation criteria] ○: Line width change is less than 5% △: Line width change is 5% or more but less than 10% ×: Line width change is 10% or more

[0099] [Table 5]

[0100] As is clear from Tables 3 and 5, the water-based ink composition of the present invention was shown to improve the graininess of the secondary color and also stabilize inter-color bleeding. [Industrial Applicability]

[0101] The present invention can provide an aqueous ink composition that exhibits excellent wettability to non-ink-absorbent or poorly ink-absorbent media, reduces graininess even in printed areas of secondary or higher colors, and prevents intercolor bleeding from worsening regardless of storage period. The aqueous ink composition of the present invention is extremely useful for various printing applications, particularly inkjet printing applications.

Claims

1. The aqueous ink composition includes water, a pigment, a terminal-modified polysiloxane surfactant represented by the following formula (1), and a linear monoalcohol having 3 or more carbon atoms, the linear monoalcohol including at least one selected from the group consisting of 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, and 1-nonanol: 【Chemistry 1】 (In formula (1), a is an integer of 1 or more and less than 32; x and y are each independently an integer of 1 to 4; m and n are each independently an integer of 1 to 50; o and p are each independently an integer of 0 to 40; m+n is 2 to 100; o+p is 0 to 80; R １ and R ２ are each independently selected from the group consisting of a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, and a (meth)acrylic group.

2. 2. The water-based ink composition according to claim 1, wherein the amount of the linear monoalcohol having 3 or more carbon atoms added is 0.1% to 3% of the total amount of the water-based ink composition, and is 1.5% to 40% of the total amount of the pigment contained in the water-based ink composition.

3. The water-based ink composition according to claim 1 or 2, wherein a in formula (1) is an integer of 1 or more and less than 18.

4. An ink set comprising at least the water-based ink composition according to any one of claims 1 to 3.

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