Inkjet ink, ink set, and inkjet recording method

Abstract

To provide a water-based inkjet ink enabling formation of a printed article having superior laminating suitability with use of a solvent-free adhesive in printing onto non-absorptive substrates including OPP film, PET film, and nylon film.SOLUTION: A water-based ink composition for inkjet printing onto non-absorptive media, comprises a colorant, at least one water-soluble organic solvent represented by each of the following general formula (1) and formula (2), a surfactant, and water, wherein the content of the water-soluble organic solvent is from 1% to 13%. A laminate is obtained by bonding a printed material produced using the ink composition with a solvent-free adhesive containing an isocyanate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous inkjet ink (hereinafter simply referred to as "aqueous ink" or "ink"), an aqueous inkjet ink set, a method for producing a printed matter, and a printed matter. [Background technology]

[0002] Digital printing methods are rapidly becoming more popular as printing runs become smaller and needs become more diverse. Because digital printing methods do not require plates, they enable small-lot production, cost reduction, and the miniaturization of printing equipment.

[0003] Inkjet printing, a type of digital printing method, is a method in which tiny droplets of ink are ejected from an inkjet head and landed on a recording medium to form images or characters (hereinafter collectively referred to as "printed matter") on the recording medium. Compared to other digital printing methods, inkjet printing is superior in terms of the size and cost of the printing device, running costs during printing, and ease of full-color printing, and has recently been increasingly used in industrial printing applications.

[0004] The inks used in inkjet printing methods vary widely, including oil-based, solvent-based, active energy ray-curable, and water-based inks. Until now, solvent-based and active energy ray-curable inks have been used for industrial printing applications. However, in recent years, there has been an increasing demand for water-based inks due to concerns about the harmful effects on the environment and people.

[0005] For media with poor ink absorption, such as film, development has progressed on solvent inks primarily composed of organic solvents and UV inks containing polymerizable monomers. However, these inks have many safety issues, such as VOCs and skin sensitization, limiting their applications.

[0006] In recent years, there has been a demand for inkjet printing to be used in a wider range of applications, including packaging applications such as paper containers, labels, and wrapping films, in addition to industrial printing applications. In these cases, it is necessary to produce printed materials with high color reproducibility and image quality, and with properties that can withstand practical use, on low-absorbency substrates such as coated paper and art paper, and non-absorbency substrates such as polypropylene film (e.g., OPP film), polyethylene terephthalate (PET) film, and nylon film.

[0007] Most of the aqueous inks used in inkjet printing methods to date (referred to simply as "aqueous inkjet inks" in this specification) are designed to form images on highly absorbent substrates such as plain paper or specialty paper. When such inks are used on non-absorbent substrates, problems arise such as ink droplets not drying after landing due to penetration and absorption, resulting in a loss of print quality and insufficient adhesion.

[0008] In particular, if the adhesive strength to non-absorbent substrates or the drying time on the substrate are insufficient, when the ink is laminated with another film via an adhesive (lamination), the lack of lamination strength can lead to delamination between the layers. To prevent delamination, it is necessary to improve the drying time on the substrate after printing. However, reducing the amount of organic solvent to improve drying time is known to result in ink instability and lead to pigment separation and sedimentation. On the other hand, increasing the amount of organic solvent or surfactant can ensure ink redispersibility, but this has the drawback of weakening the adhesive strength and making the ink more susceptible to delamination.

[0009] There are two general types of lamination: solvent-based and solventless, both of which are adhesive methods that use a hydroxyl / isocyanate curing system. If the lamination is not dried properly, the remaining organic solvent will deactivate the isocyanate, resulting in insufficient laminate strength.

[0010] To address these issues, the development of water-based inks suitable for lamination has been accelerating. However, these inks contain large amounts of organic solvents, which means that the ink does not dry sufficiently on the substrate, resulting in insufficient laminate strength. Therefore, there is a demand for inks that reduce the organic solvent content, dry quickly, and are suitable for lamination. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent Publication No. 2022-85548 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an aqueous inkjet ink that can produce printed matter with excellent lamination suitability when printed on non-absorbent substrates such as OPP film, PET film, and nylon film. [Means for solving the problem]

[0013] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by an ink composition comprising a colorant, a water-soluble organic solvent represented by general formula (1) and formula (2), a surfactant, and water, wherein the content of the water-soluble organic solvent represented by general formula (1) and formula (2) is 1 to 13%, and have thus completed the present invention.

[0014] That is, the present invention relates to the following 1) to 4). 1) A water-based ink composition for printing on non-absorbent media, comprising a colorant, at least one water-soluble organic solvent represented by the following general formula (1) and at least one water-soluble organic solvent represented by a general formula (2) different from general formula (1), a surfactant (excluding the combined use of an acetylene glycol-based surfactant and a siloxane-based surfactant), and water.

[0015] [ka] (R1 represents a linear or branched hydrocarbon group having from C2 to C6 carbon atoms, R2 represents a methyl group, an ethyl group, a propyl group, or a butyl group, R3 represents a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a benzyl group, or a naphthyl group, and n represents an integer of 1 to 3.) 2) The aqueous ink composition for printing on non-absorbent media according to 1), wherein the total content of the water-soluble organic solvents represented by the general formulas (1) and (2) is 1 to 13% by mass based on the total amount of the ink. 3) An inkjet recording method comprising the step of ejecting droplets of the water-based ink composition according to 1) or 2) onto a printing medium to form an image. 4) A laminated product obtained by laminating a printed matter obtained by the printing method described in 3) together with a laminating substrate using an adhesive containing an isocyanate compound. [Effects of the Invention]

[0016] The present invention provides an inkjet ink with excellent lamination suitability for printing on non-absorbent media, and a printed matter using the inkjet ink. It has been confirmed that the use of the ink obtained by the present invention makes it possible to simultaneously achieve a good balance between lamination strength and ink redispersibility. DETAILED DESCRIPTION OF THE INVENTION

[0017] Specific embodiments to which the present invention is applied will be described in detail below. In this specification, "CI" means "color index." In this specification, including the examples, "%" and "parts" are all based on mass unless otherwise specified. The terms "alkylene," "propylene," and "alkyl" are used to encompass both linear and branched chain structures unless otherwise specified. Inkjet ink may be abbreviated as ink or aqueous ink. The above-mentioned poorly absorbent media, non-absorbent media, and recording media described below may be abbreviated as media.

[0018] <Coloring agent> The colorant may be, for example, a known pigment, disperse dye, solvent dye, etc. Among the pigments, disperse dyes, and solvent dyes, it is preferable to include at least one selected from the group consisting of pigments and disperse dyes, and it is more preferable to include a pigment. Examples of pigments include inorganic pigments, organic pigments, extender pigments, and hollow particles.

[0019] Examples of the inorganic pigment include carbon black, metal oxides, hydroxides, sulfides, ferrocyanides, and metal chlorides.

[0020] When the ink is a black ink and the pigment is an inorganic pigment, the inorganic pigment contained in the black ink is preferably a carbon black such as thermal black, acetylene black, oil furnace black, gas furnace black, lamp black, gas black, or channel black. Specific examples of carbon black include the Raven series manufactured by Columbia Carbon; 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. When the ink is a white ink and the pigment is an inorganic pigment, examples of the inorganic pigment contained in the white ink include oxides, nitrides, and oxynitrides of metals such as zinc, silicon, aluminum, titanium, strontium, and zirconium; and inorganic compounds such as various types of glass and silica, with titanium dioxide and zinc oxide being preferred.

[0021] Examples of the organic pigment include various pigments such as azo, disazo, phthalocyanine, quinacridone, isoindolinone, dioxazine, perylene, perinone, thioindigo, anthraquinone, and quinophthalone.

[0022] 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, 155, 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, 269, 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, 43, 68, 69, 71, and 73; and Green green pigments such as CI Pigment Black 1, CI Pigment Black 2, CI Pigment Blue 3, CI Pigment Blue 4, CI Pigment Blue 5, CI Pigment Blue 6, CI Pigment Blue 7, CI Pigment Blue 8, CI Pigment Blue 9, CI Pigment Blue 10, CI Pigment Blue 11, CI Pigment Blue 12, CI Pigment Blue 13,

[0023] Examples of the extender pigment include silica, calcium carbonate, talc, clay, barium sulfate, white carbon, etc. The extender pigment is often used in combination with other colorants.

[0024] As the hollow particles, known hollow particles described in, for example, U.S. Pat. No. 4,880,465, Japanese Patent No. 3,562,754, Japanese Patent No. 6026234, Japanese Patent No. 5459460, JP-A-2003-268694, Japanese Patent No. 4902216, etc. can be used, and they are particularly preferably used as white pigments.

[0025] The total content of the colorants in the total mass of the ink is preferably 1 to 30%, more preferably 1 to 10%, and particularly preferably 2 to 8%. If the pigment content is within the above range, nozzle clogging of the inkjet recording device is unlikely to occur, and color density can be fully satisfied. The average particle size of the colorant in the ink is preferably 30 nm to 300 nm, and more preferably 50 nm to 250 nm. In this specification, the average particle size refers to the average particle size of particles measured using a laser light scattering method.

[0026] The colorant may further contain other dyes in addition to the pigments and disperse dyes. Examples of other dyes include solvent dyes, direct dyes, acid dyes, and reactive dyes.

[0027] [Water-soluble organic solvent] The water-soluble organic solvent used in the present invention has the property of being soluble in both the water contained in the ink and the organic compounds described below. This property makes it possible to stably dissolve the organic compounds even in inks in which water accounts for the majority of the total mass of the ink, thereby preventing phase separation of the ink. The water-soluble organic solvent represented by general formula (1) or (2) contained in the aqueous ink composition of the present invention refers to an organic solvent that exhibits even a slight solubility in water, and specifically, the solubility in 100 g of water at 25°C is 0.05 g or more. The water-soluble organic solvent includes at least one kind of water-soluble organic solvent represented by the general formula (1) and at least one kind of water-soluble organic solvent represented by the general formula (2). Furthermore, the water-soluble organic solvent represented by the general formula (1) and the water-soluble organic solvent represented by the general formula (2) are not the same water-soluble organic solvent.

[0028] R1 of the water-soluble organic solvent represented by the general formula (1) is preferably a straight-chain or branched-chain hydrocarbon having C2 to C6 carbon atoms, more preferably a straight-chain or branched-chain hydrocarbon having C3 to C6 carbon atoms, and particularly preferably a straight-chain or branched-chain hydrocarbon having C4 to C6 carbon atoms. R2 in the water-soluble organic solvent represented by the general formula (1) is any one of a methyl group, an ethyl group, a propyl group, and a butyl group, and is preferably any one of a methyl group, an ethyl group, and a butyl group. Examples of the water-soluble organic solvent represented by general formula (1) include 3-methoxy-1-butanol, 3-methyl-3-methoxy-1-butanol, 5-methoxy-1-pentanol, 4-methoxy-2-pentanol, and the like. Of these, 3-methoxy-1-butanol and 3-methyl-3-methoxy-1-butanol are preferred, 3-methoxy-1-butanol and 3-methyl-3-methoxy-1-butanol are more preferred, and 3-methoxy-1-butanol is particularly preferred.

[0029] R3 of the water-soluble organic solvent represented by the general formula (2) is any one of a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a benzyl group, and a naphthyl group, and is preferably any one of a methyl group, an ethyl group, a butyl group, a phenyl group, a benzyl group, and a naphthyl group. In the water-soluble organic solvent represented by the general formula (2), n is the number of repetitions of the ethyleneoxy chain, and is preferably an integer of 1 to 3. Examples of the water-soluble organic solvent represented by the general formula (2) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, ethylene glycol-β-naphthyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, diethylene glycol-β-naphthyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, and triethylene glycol-β-naphthyl ether. Preferred are ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, ethylene glycol-β-naphthyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, diethylene glycol-β-naphthyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, and triethylene glycol-β-naphthyl ether, more preferred are ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, ethylene glycol-β-naphthyl ether, diethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, diethylene glycol-β-naphthyl ether, triethylene glycol monophenyl ether, triethylene glycol monobenzyl ether, and triethylene glycol-β-naphthyl ether, and particularly preferred are ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, and triethylene glycol-β-naphthyl ether.

[0030] The total content of the water-soluble organic solvents represented by the formulas (1) and (2) is 1 to 13 mass %, preferably 1 to 10 mass %, and more preferably 3 to 8 mass %, relative to the total mass of the ink according to this embodiment. By setting the amount of water-soluble organic solvent in the ink within the above range, the drying property of the coating film is improved and the laminate strength is improved. In addition, since the organic solvent volatilizes from the printed substrate and is harmful to humans and the environment, it is desirable to reduce the content of the organic solvent. In addition, it makes it easier to redisperse the ink when it dries.

[0031] The water-soluble organic solvents represented by the formulas (1) and (2) can be used in any ratio within the preferred ranges. By changing the combination ratio, the redispersibility, drying property, and lamination suitability can be improved, and the color development of the ink can also be expected. If the content of the water-soluble organic solvent represented by general formula (1) in the ink is A, and the content of the water-soluble organic solvent represented by general formula (2) in the ink is B, and the combination ratio is expressed as the value calculated by "A / B", it is usually 1 or more and 100 or less, preferably 2 or more and 90 or less, more preferably 3 or more and 80 or less, and even more preferably 4 or more and 70 or less.

[0032] [Surfactants] Examples of surfactants include anionic, nonionic, silicone, and fluorine-based surfactants. Among these, surfactants selected from nonionic and silicone surfactants are preferred, and nonionic surfactants are more preferred from the viewpoints of ink storage stability and wettability to poorly absorbent or non-absorbent media (excluding the combined use of acetylene glycol and siloxane surfactants).

[0033] 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-acylmethyl taurines, 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.

[0034] Examples of nonionic surfactants include ether surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ether, and polyoxyethylene distyrenated phenyl ether (for example, Emulgen A-60, A-90, and A-500 manufactured by Kao Corporation); polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, and sorbitan monostearate. ester-based surfactants such as sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate; acetylene glycol (or acetylene alcohol)-based surfactants such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 3,5-dimethyl-1-hexyn-3-ol (for example, Surfynol 104, 104PG50, 82, 420, 440, 465, and 485; Olfine STG; and the like, manufactured by EVONIK Co., Ltd.); and polyglycol ether-based surfactants.

[0035] Examples of silicone surfactants include polyether-modified siloxanes and polyether-modified polydimethylsiloxanes. Examples of such products include Dynol 960 and 980 manufactured by Air Products; Silface SAG001, SAG002, SAG003, SAG005, SAG503A, SAG008, SAG009, and SAG010 manufactured by Nissin Chemical Industry Co., Ltd.; BYK-345, 347, 348, 349, 3450 (also known as BYKLPX 23289), 3451 (also known as BYKLPX 23347), 3455, LP-X23288, and LP G20726 manufactured by BYK; and TEGO Twin 4000, TEGOWet KL 245, 250, 260, 265, 270, and 280 manufactured by Evonic Tego Chemie.

[0036] Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups on the side chains, etc. Commercially available products include Capstone FS-30 and FS-31 manufactured by Chemours.

[0037] [water] The water is preferably water with a low content of impurities such as metal ions, i.e., ion-exchanged water, distilled water, etc. The water content is preferably 60 to 90 mass % of the total mass of the ink according to this embodiment, and more preferably 70 to 90 mass %. By achieving this content, the ink has excellent storage stability, ejection stability, and drying properties on the printing medium.

[0038] Furthermore, the print medium according to this embodiment has at least one selected from the group consisting of the inks or inkjet inks included in the ink set according to this embodiment adhered thereto.

[0039] The ink media set according to this embodiment includes the ink or ink set according to this embodiment described above and a print medium.

[0040] The printing media is preferably non-ink-absorbent, such as PET (polyethylene terephthalate) film, PP (polypropylene) film, nylon film, and PE (polyethylene) film.

[0041] The inkjet recording method according to this embodiment involves ejecting droplets of the ink according to this embodiment from an inkjet head to record on a print medium. There are no particular restrictions on the ink nozzles of the inkjet printer that eject the ink, and they can be selected appropriately depending on the purpose.

[0042] Known inkjet recording methods can be used. Examples include charge control, drop-on-demand (also known as pressure pulse), acoustic inkjet, and thermal inkjet. The inkjet recording method may be either a multi-pass or single-pass (one-pass printing) method. For industrial inkjet printers, single-pass printing using a linehead inkjet printer is also preferred for the purpose of increasing printing speed. Recently, circulation heads have been actively developed, each equipped with a mechanism (i.e., a circulation mechanism) that prevents ink from drying near the nozzles by circulating the ink to the vicinity of the nozzles. The ink according to this embodiment can also be suitably used in such circulation heads.

[0043] When using a printing medium without an ink-receiving layer, it is also preferable to perform a surface modification treatment. Examples of surface modification treatments include corona discharge treatment, plasma treatment, and flame treatment. It is generally known that the effect of surface modification treatment decreases over time. For this reason, it is preferable to perform the surface modification treatment step and the inkjet recording step consecutively, and it is more preferable to perform the surface modification treatment step immediately before the inkjet recording step.

[0044] A printed material printed using the ink described above can be laminated with a known adhesive to form a laminated product, which is obtained by adhering the printed material to a laminating substrate or a sealant substrate with an adhesive.

[0045] The laminating substrate or sealant substrate is selected to be the same as the printing media.

[0046] There are two types of adhesives: solvent-based adhesives that contain organic solvents and solventless adhesives that do not contain organic solvents, and those that contain isocyanate compounds are commonly used. Examples of solvent-based adhesives containing an isocyanate compound include the Takelac® / Takenate® series (A-969V / A-5, A950 / A-4, A-385 / A-50, A-606 / A-10, A310 / A-3) manufactured by Mitsui Chemicals, the Adlock® series (RU-3600 / H689, RU-69 / H-9, etc.) manufactured by Rock Paint, the TM-320 / CAT-13B, TM-569 / CAT-RT37, EA-N373A / B, EA-N6001 / EA-N5510, etc.) manufactured by Toyo-Morton, the DICDRY series (LX-470EL / SP-60, 2K-SF-380A / HA-380B, etc.) manufactured by DIC, and LOCTITE LIOFOL® manufactured by Henkel. Examples include the LA series(R) (7735 / 6159, 7715 / 6099, etc.). Examples of solvent-free adhesives containing an isocyanate compound include Mitsui Chemicals' Takelac® / Takenate® series (A242B / A-242A, A666 / A-65, etc.) and Coim Novacote® series (SF792 / CA336, etc.).

[0047] It is desirable that printed matter to be used for lamination be sufficiently dry. If an excessive amount of water or organic solvent remains in the printed matter, the organic solvent will remain between the printed matter and the substrate to which it is attached, which may cause problems such as film lifting or peeling after lamination or during storage of the processed matter. When the aqueous ink composition according to this embodiment is used, the excellent drying properties make it difficult for water or organic solvent to remain on the printed matter, and it is possible to obtain printed matter with excellent suitability for lamination.

[0048] The ink according to this embodiment may contain, as necessary, ink preparation agents such as dispersants, antifungals, preservatives, pH adjusters, chelating agents, rust inhibitors, antifoaming agents, water-soluble UV absorbers, antioxidants, resin emulsions, etc. The content of each ink preparation agent can be set as desired depending on the intended use of the ink, etc.

[0049] Examples of dispersants include copolymers composed of at least two monomers (preferably at least one of which is a hydrophilic monomer) selected from the following monomers: styrene and its derivatives; vinylnaphthalene and its derivatives; aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids; (meth)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 their derivatives. Examples of hydrophilic monomers include monomers that leave a carboxyl group after polymerization, such as acrylic acid and methacrylic acid.

[0050] 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 copolymers, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers, (meth)acrylic acid ester-(meth)acrylic acid copolymers, and polyethylene glycol (meth)acrylate-(meth)acrylic acid copolymers are preferred, with styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymers, and (meth)acrylic acid ester-(meth)acrylic acid copolymers being more preferred, (meth)acrylic acid ester-(meth)acrylic acid copolymers being even more preferred, and methacrylic acid ester-methacrylic acid copolymers being particularly preferred. Examples of types of copolymers include block copolymers, random copolymers, and graft copolymers. These copolymers may be in the form of a salt. In this specification, the term "(meth)acrylic" is used to mean both "acrylic" and "methacrylic." The same applies to "(meth)acrylate" and the like.

[0051] Dispersants can be synthesized or commercially available. Examples of synthetic dispersants include the AB block polymer disclosed in WO 2013 / 115071. The monomer constituting the A block of the AB block polymer disclosed in WO 2013 / 115071 is at least one monomer selected from (meth)acrylic acid and linear or branched C4 alkyl (meth)acrylates, preferably at least one monomer selected from methacrylic acid and n-butyl methacrylate, and more preferably a combination of these two monomers. Furthermore, the monomer constituting the B block of the AB block polymer disclosed in WO 2013 / 115071 is at least one monomer selected from benzyl methacrylate and benzyl acrylate, preferably benzyl methacrylate. Specific examples of AB block polymers include the block copolymers disclosed in Synthesis Examples 3 to 8 of WO 2013 / 115071.

[0052] Examples of commercially available dispersants include Joncyrl 62, 67, 68, 678, and 687 (styrene-acrylic copolymers manufactured by BASF); Aron AC-10SL (polyacrylic acid manufactured by Toa Gosei Co., Ltd.); and BYKJET 9151, 9152, 9170, and 9171 (wetting dispersants manufactured by BYK).

[0053] The mass average molecular weight (MW) of the dispersant is preferably 3,000 to 50,000, and more preferably 7,000 to 25,000. The mass average molecular weight of the dispersant can be measured by gel permeation chromatography (GPC). Specifically, the measurement can be performed using an HLC-8320GPC (manufactured by Tosoh Corporation) as the GPC device, two TSK gel Super Multipore HZ-H columns (manufactured by Tosoh Corporation, inner diameter 4.6 mm × 15 cm), tetrahydrofuran as the eluent, and TSK Standard (manufactured by Tosoh Corporation) as the standard sample.

[0054] The acid value of the dispersant is preferably from 50 to 300 mgKOH / g, more preferably from 80 to 275 mgKOH / g, and even more preferably from 80 to 250 mgKOH / g.

[0055] The dispersant can be used in a state where it is mixed with the pigment, or in a state where the pigment surface is partially or entirely coated with the dispersant, or both of these states can be used in combination.

[0056] When the ink according to this embodiment contains a dispersant, the ratio of the total mass of the dispersant to the total mass of the pigment is preferably 0.01 to 1.0, more preferably 0.05 to 0.6, and even more preferably 0.1 to 0.5.

[0057] Examples of antifungal agents include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, 1,2-benzisothiazolin-3-one and salts thereof.

[0058] Examples of preservatives include organic sulfur compounds, organic nitrogen sulfur compounds, organic halogen compounds, haloaryl sulfone 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 organic halogen compounds include sodium pentachlorophenol. Specific examples of pyridine oxide compounds include sodium 2-pyridinethiol-1-oxide. Specific examples of isothiazoline compounds include 1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one magnesium chloride, 5-chloro-2-methyl-4-isothiazolin-3-one calcium chloride, 2-methyl-4-isothiazolin-3-one calcium chloride, etc. Specific examples of other antiseptic and antifungal agents include anhydrous sodium acetate, sodium sorbate, sodium benzoate, and Arch Chemical's trade names Proxel GXL(S), Proxel LV, and Proxel XL-2(S).

[0059] Examples of pH adjusters include alkanolamines such as diethanolamine, 2-amino-2-methyl-1-propanol, 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.

[0060] Examples of chelating agents include disodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uracildiacetate.

[0061] Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

[0062] Examples of the defoaming agent include silicone-based, silica mineral oil-based, olefin-based, acetylene-based compounds, etc. Examples of commercially available defoaming agents include Surfynol DF37, DF58, DF110D, DF220, MD-20, and Olfine SK-14, all of which are manufactured by Shin-Etsu Chemical Co., Ltd.

[0063] Examples of the water-soluble ultraviolet absorber include sulfonated benzophenone compounds, benzotriazole compounds, salicylic acid compounds, cinnamic acid compounds, and triazine compounds.

[0064] As the antioxidant, for example, various organic and metal complex anti-fading agents can be used. Examples of organic anti-fading agents include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, and heterocycles.

[0065] The ink according to this embodiment may contain a resin emulsion for the purpose of improving the fixation of the ink to the printing medium. When the ink according to this embodiment contains a resin emulsion, the image fastness, such as water resistance, abrasion resistance, and alcohol resistance, of the image printed on the printing medium tends to be improved. The resin emulsion is preferably at least one selected from a polymer emulsion and a wax emulsion.

[0066] Examples of polymer emulsions include emulsions containing urethane-based, polyester-based, acrylic-based, vinyl acetate-based, vinyl chloride-based, styrene-acrylic-based, acrylic-silicone-based, and styrene-butadiene-based polymers. Among these, emulsions of polymers selected from urethane-based, acrylic-based, and styrene-butadiene-based are preferred.

[0067] Commercially available polymer emulsions include Superflex 420, 470, and 890 (urethane-based resin emulsions manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); Hydran HW-350, HW-178, HW-163, HW-171, AP-20, AP-30, WLS-201, and WLS-210 (urethane-based resin emulsions manufactured by DIC Corporation); 0569, 0850Z, and 2108 (styrene-butadiene-based resin emulsions manufactured by JSR Corporation); AE980, AE981A, AE982, AE986B, and AE104 (acrylic resin emulsions manufactured by E-Tech Co., Ltd.); NeoCryl A-1105, A-1125, and A-1127 (acrylic resin emulsions manufactured by DSM Coating Resin); and NeoCryl A-655 (DSM Coating Resin). styrene-acrylic resin emulsion manufactured by Resin Co., Ltd.);

[0068] The wax emulsion may be an emulsion in which a natural wax or a synthetic wax is dispersed in an aqueous medium.

[0069] Examples of natural wax emulsions include emulsions of various waxes, such as petroleum-based waxes such as paraffin wax and microcrystalline wax; lignite-based waxes such as montan wax; vegetable waxes such as carnauba wax and candelilla wax; and animal and vegetable waxes such as beeswax and lanolin.

[0070] Examples of synthetic wax emulsions include emulsions of polyalkylene wax (preferably poly C2-C4 alkylene wax), oxidized polyalkylene wax (preferably poly C2-C4 alkylene wax), paraffin wax, etc. Among these, emulsions of wax selected from polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and paraffin wax are preferred.

[0071] The average particle size of the wax is preferably 30 nm to 5 μm, and more preferably 30 nm to 1 μm, in order to prevent clogging of the inkjet head.

[0072] Commercially available wax emulsions include, for example, CERAFLOUR 925 (average particle size 6 μm), 929 (average particle size 8 μm), 950 (average particle size 9 μm), and 991 (average particle size 5 μm), AQUACER 498, 515, 526, 531, 537, 539, 552, 1547, and AQUAMAT 208, 263, and 272; MINERPOL 221 (all manufactured by BYK); Mitsui Hiwax NL100, NL200, NL500, 4202E, 1105A, 2203A, NP550, NP055, and NP505 (all manufactured by Mitsui Chemicals, Inc.); KUE-100 and 11 (all manufactured by Sanyo Chemical Industries, Ltd.); and Hitec P-5300 (average particle diameter 30 nm), E-6500 (average particle diameter 60 nm), E-9015 (average particle diameter 50 nm), E-6400 (average particle diameter 55 nm), E-6314 (average particle diameter 100 nm) (all manufactured by Toho Chemical Industry Co., Ltd.);

[0073] When the ink according to this embodiment contains a resin emulsion, the solid content is preferably 1 to 20% by mass, and more preferably 3 to 15% by mass. By setting the solid content of the resin emulsion to 1% by mass or more, the ink tends to exhibit good fixability to the printing medium. Furthermore, by setting the solid content of the resin emulsion to 20% by mass or less, the ink tends to have good jetting properties and storage stability.

[0074] The method for preparing the ink according to this embodiment is not particularly limited, and any known preparation method can be used. One example of such a method is to prepare a dispersion containing a pigment and a dispersant, and then add water and, if necessary, an ink preparation agent to this dispersion and mix them.

[0075] Examples of methods for preparing the dispersion include phase inversion emulsification, acid precipitation, interfacial polymerization, in-situ polymerization, submerged hardening coating, coacervation (phase separation), submerged drying, melt-dispersion cooling, air suspension coating, spray drying, etc. Among these, phase inversion emulsification, acid precipitation, and interfacial polymerization are preferred, and phase inversion emulsification is more preferred.

[0076] When preparing a dispersion by phase inversion emulsification, for example, 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. A pigment is added to the obtained emulsion, and a dispersion treatment is performed. The organic solvent and a portion of the water are distilled off under reduced pressure from the obtained liquid to obtain the desired dispersion.

[0077] Dispersion treatment can be carried out using a sand mill (bead mill), roll mill, ball mill, paint shaker, ultrasonic disperser, microfluidizer, etc. For example, when using a sand mill, beads with a particle diameter of about 0.01 to 1 mm can be used, and the bead packing rate can be appropriately set to carry out dispersion treatment. The particle diameter of the particles contained in the dispersion can be made uniform by subjecting the dispersion obtained as described above to operations such as filtration and centrifugation. If foaming occurs during preparation of the dispersion, a trace amount of a known silicone-based, acetylene glycol-based, or other antifoaming agent can be added.

[0078] The ink according to this embodiment preferably contains a low content of inorganic impurities such as chlorides of metal cations (e.g., sodium chloride) and metal sulfates (e.g., sodium sulfate). Such inorganic impurities are often contained in commercially available pigments. The inorganic impurity content should be approximately 1% by mass or less relative to the total mass of the pigment, with the lower limit being below the detection limit of analytical instruments, i.e., 0% by mass, being ideal. Methods for obtaining pigments with low inorganic impurities include, for example, a method using a reverse osmosis membrane; a method in which a solid pigment is suspended and stirred in a mixed solvent of C1-C4 alcohol, such as methanol, and water, followed by filtering and separating the colored body and drying; and a method in which inorganic impurities are exchanged and adsorbed using an ion exchange resin.

[0079] The ink according to this embodiment is preferably microfiltered in advance. For microfiltration, a membrane filter, glass filter paper, or the like can be used. The pore size of the filter used for microfiltration is usually 0.5 to 20 μm, and preferably 0.5 to 10 μm.

[0080] Examples of ink sets according to this embodiment include a set of the inks according to this embodiment described above, or a set including the ink according to this embodiment described above and another ink different from the ink. The other ink is not particularly limited as long as it has a different structure from the ink according to this embodiment, but it is preferable that the other ink has a different hue from the ink according to this embodiment.

[0081] When recording on a print medium, for example, a container containing ink (ink tank) is loaded into a predetermined position of an inkjet printer, and recording is performed on the print medium using the above-mentioned printing method. Note that full-color printing can also be achieved by loading containers containing ink of each color into a predetermined position of the inkjet printer and recording on the print medium using the above-mentioned printing method.

[0082] The inkjet recording method according to this embodiment also includes a method of improving image quality by ejecting a large number of inks in a small volume, each ink having a low content of colorant; a method of improving image quality by using a plurality of inks having substantially the same hue but different content of colorant; and a method of improving the fixation of a colorant to a printing medium by using a colorless, transparent ink in combination with an ink containing a colorant.

[0083] 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.

[0084] The ink of the present invention has excellent water repellency on a nozzle plate, little erosion of the nozzle plate, excellent storage stability, and excellent ejection reliability. Images recorded with the ink have excellent color development and saturation, as well as excellent fastness properties such as heat abrasion resistance, transferability, water resistance, light resistance, heat resistance, resistance to oxidizing gases (e.g., ozone gas), and abrasion resistance. Furthermore, the ink has excellent drying properties during image formation, little coating unevenness or bleeding, and a large dot diameter, resulting in excellent image formability. [Example]

[0085] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the text, "parts" and "%" are by mass unless otherwise specified. In the examples, when quantitative determination of the pigment solid content in the dispersion was required, it was determined by the dry weight method using an MS-70 manufactured by A&D Co., Ltd. The pigment solid content is a converted value calculated by calculating only the pigment solid content from the total amount of solids.

[0086] [Preparation Example 1] Preparation of DP1 (cyan dispersion) Joncyrl 68 (manufactured by BASF Ltd., mass average molecular weight: 13,000) (9 parts) and triethanolamine (6 parts) were dissolved in ion-exchanged water (75 parts) and stirred for 1 hour. CI Pigment Blue 15:4 (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., Chromofine Blue 4851) (30 parts) was added to the resulting solution, and the mixture was dispersed in a sand grinder at 1,500 rpm for 15 hours. Ion-exchanged water (40 parts) was added dropwise to the resulting solution, and the dispersion beads were removed by filtration, yielding a cyan dispersion with a pigment solids content of 18.7%. The resulting colored dispersion was designated "DP-1." is contained in the above-mentioned inkjet ink. The abbreviations in Tables 1 and 2 below represent the following, and "-" indicates 0 parts. MB: 3-methoxy-1-butanol (Tokyo Chemical Industry Co., Ltd.) DEGPH: Diethylene glycol monophenyl ether (Tokyo Chemical Industry Co., Ltd.) AMP: 2-amino-2-methyl-1-propanol (Tokyo Chemical Industry Co., Ltd.) SF440: Surfynol 440 (EVONIK Co., Ltd., surfactant) SF465: Surfynol 465 (EVONIK Co., Ltd., surfactant) Hitec E-6314: Polyethylene wax (manufactured by Toho Chemical Industry Co., Ltd., solid content 34.9%) MMB: 3-methyl-3-methoxy-1-butanol (Tokyo Chemical Industry Co., Ltd.) EGPH: Ethylene glycol monophenyl ether (Tokyo Chemical Industry Co., Ltd.) Emulgen A60: Polyoxyethylene distyrenated phenyl ether (Kao Corporation)

[0087] [Table 1]

[0088] [Laminate strength evaluation] 20 μL of each of the inks from Examples 1 to 4 and Comparative Example 1 was dropped onto a PET film (E5102, manufactured by Toyobo Co., Ltd.) and coated using a bar coater No. 3 (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) with an automatic coater (PI-1210, manufactured by Tester Sangyo Co., Ltd.). The coated PET film was then left to dry for 2 minutes in a thermo-hygrostat at 70°C. Coim SF792 and CA336 were mixed at a ratio of 100:65 as an adhesive, and the mixture was applied to the ink-coated product using a bar coater No. 00 (manufactured by Yasuda Seiki Seisakusho Co., Ltd.). The film was then laminated to an LDPE film (manufactured by Toyobo Co., Ltd.) and aged at 40°C for 72 hours. The laminate was cut into 15 mm wide pieces, and the strength was measured using a T-peel tester (testing machine: A&D Corporation's Tensilon universal testing machine RTG-1210A), and the "laminate strength" was evaluated based on the following evaluation criteria. A: Adhesive force 3.8N / 15mm or more B: Adhesion strength 3.4N / 15mm or more, less than 3.8N / 15mm C: Adhesion strength 3.0N / 15mm or more, less than 3.4N / 15mm D: Adhesion strength 2.6N / 15mm or more, less than 3.0N / 15mm E: Adhesion strength less than 2.6N / 15mm

[0089] [Redispersibility evaluation] 20 μL of each of the inks from Examples 1 to 4 and Comparative Example 1 was dropped onto a glass petri dish (flat petri dish, diameter 94 mm x height 22 mm, AS ONE Corporation, model number FS-90B) using a micropipette. The ink was then dried in a thermostatic chamber at 60°C for 1 hour to obtain a dried ink product. The cleaning solution described in Example 2 of WO 2020 / 175033 was prepared, and 10 g of this cleaning solution was poured into the petri dish. The petri dish was then shaken horizontally every 5 minutes at an amplitude of 2 cm, 10 times for 5 seconds, and the dissolution of the dried ink product was visually evaluated. A: All dried ink will dissolve within 7 minutes. B: All dried ink is dissolved in more than 7 minutes but not more than 13 minutes. C: All dried ink is dissolved in more than 13 minutes but within 19 minutes. D: All dried ink is dissolved in more than 19 minutes but not more than 25 minutes. E: The dried ink has not dissolved even after 25 minutes.

[0090] [Table 2]

[0091] The results in Table 2 above show that the inks of the examples are superior in lamination strength and redispersibility compared to the inks of the comparative examples. [Industrial Applicability]

[0092] As described above, the water-based ink composition of the present invention can achieve both high lamination strength and good redispersibility, and is extremely suitable as an ink-jet ink. Therefore, the ink of the present invention is also extremely useful as a water-based ink for ink-jet printing.

Claims

1. A water-based ink composition for printing on non-absorbent media, comprising a colorant, at least one water-soluble organic solvent represented by the following general formula (1) and at least one water-soluble organic solvent represented by a general formula (2) different from general formula (1), a surfactant (excluding the combined use of an acetylene glycol-based surfactant and a siloxane-based surfactant), and water: (R １ represents a linear or branched hydrocarbon group having 2 to 6 carbon atoms, and R ２ represents a methyl group, an ethyl group, a propyl group, or a butyl group; R ３ represents any one of a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a benzyl group, and a naphthyl group, and n represents an integer of 1 to 3.

2. 2. The aqueous ink composition for printing on non-absorbent media according to claim 1, wherein the total content of the water-soluble organic solvents represented by general formulas (1) and (2) is 1 to 13% by mass based on the total amount of the ink.

3. An inkjet recording method comprising a step of ejecting droplets of the water-based ink composition according to claim 1 or 2 onto a printing medium to form an image.

4. A laminated product obtained by laminating a printed matter obtained by the printing method according to claim 3 together with a laminating substrate using an adhesive containing an isocyanate compound.

Images