Water-based ink for inkjet printing

Abstract

One embodiment of the present invention is a water-based ink for inkjet printing on lowly liquid-absorbing printing substrates, the ink comprising a pigment, an organic solvent (A), an organic solvent (B), and water, wherein the organic solvent (A) is a glycol ether having an octanol / water partition coefficient logP of 0.75 or higher, the organic solvent (B) is a glycol ether or alkylene glycol having an octanol / water partition coefficient logP less than 0.75, the Hansen solubility parameter (HSP) distance Ra between the organic solvent (A) and the organic solvent (B) is 5.5 or less, and the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.4-2.5.

Description

Water-based ink for inkjet printing

[0001] The present invention relates to a water-based ink for ink-jet printing.

[0002] Inkjet printing involves ejecting ink droplets from minute nozzles and depositing them directly onto a printing substrate to produce printed matter bearing characters and images. This printing method has become extremely popular due to its numerous advantages, including the ease and cost-effectiveness of producing full-color prints, the ability to use a variety of printing substrates, including plain paper, label paper, and plastic film, and the fact that it is non-contact with the printing substrate. In particular, inks that use pigments as colorants are becoming mainstream, due to their superior weather resistance and water resistance.

[0003] For example, Japanese Patent Laid-Open No. 2023-056263 (Patent Document 1) discloses an inkjet ink that has excellent ejection stability and is capable of forming an image with excellent adhesion while suppressing bleeding and ink repellency when forming an image on a non-permeable recording medium, and the inkjet ink contains a pigment, a polysaccharide, a water-soluble organic solvent, and self-emulsifying polyolefin resin particles, the content of the polysaccharide being 0.01% by mass or more and 0.20% by mass or less, the water-soluble organic solvent contains a specific glycol ether compound, the content of the specific glycol ether compound being 3.0% by mass or more and 24.0% by mass or less, and the mass M of the self-emulsifying polyolefin resin particles is 0.01% by mass or more and 0.20% by mass or less, the water-soluble organic solvent contains a specific glycol ether compound, and the content of the specific glycol ether compound is ...0.01% by mass or more and 0.20% by mass or less, the water-soluble organic solvent contains a specific glycol ether compound, and the content of the specific glycol ether compound is 0.01% by mass or more and 0.20% by mass or less, the mass M of the self-emulsifying polyolefin resin particles is 0.01% by mass or more and 0.20% by mass or less, the water-soluble organic solvent contains a specific glycol ether compound, and the content of the specific glycol ether compound is 0.01% by mass or more and 0.20% by mass or less, the water-soluble organic solvent contains a specific glycol ether compound, and the content of the specific glycol ether Ｘ The mass M of the pigment Ｙ The ratio (M Ｙ / M Ｘ) is 0.24 or more and 3.10 or less. Furthermore, Japanese Patent Laid-Open No. 2021-133555 (Patent Document 2) discloses an inkjet ink that uses an aqueous ink composition to form a recording medium, with the aim of providing an inkjet recording method that improves image quality on both low-ink-absorbency or non-ink-absorbency recording media and ink-absorbency recording media, and that has good ink ejection stability. The inkjet recording method includes an ink deposition step of ejecting the aqueous ink composition from an inkjet head and depositing it on the recording medium, the aqueous ink composition containing organic solvent A, which is a 1,2-alkanediol having a surface tension of 30 mN / m or less at 25°C, and organic solvent B, which is an alkanediol having a normal boiling point of 250°C or less and has 3 or more carbon atoms at both ends, and the inkjet head is equipped with a circulation mechanism for circulating the aqueous ink composition.

[0004] The present inventors have discovered that the above-mentioned problems can be solved by providing a water-based ink for inkjet printing on a low-liquid-absorbent printing substrate, the ink comprising a pigment, an organic solvent (A), an organic solvent (B), and water, wherein the organic solvent (A) is a glycol ether having an octanol-water partition coefficient log P (hereinafter also simply referred to as "log P") of 0.75 or more, the organic solvent (B) is a glycol ether or an alkylene glycol having an octanol-water partition coefficient log P of less than 0.75, the Hansen solubility parameter (HSP) distance Ra between the organic solvents (A) and (B) being 5.5 or less, and the mass ratio (A) / (B) of the organic solvents (A) to (B) being 0.4 or more and 2.5 or less. That is, the present invention provides the following [1] and [2]. [1] A water-based ink for inkjet printing on a low-liquid-absorbent printing substrate, the ink containing a pigment, an organic solvent (A), an organic solvent (B), and water, wherein the organic solvent (A) is a glycol ether having an octanol-water partition coefficient log P of 0.75 or more, and the organic solvent (B) is a glycol ether or an alkylene glycol having an octanol-water partition coefficient log P of less than 0.75, the HSP distance Ra between the organic solvents (A) and (B) is 5.5 or less, and the mass ratio (A) / (B) of the organic solvents (A) to (B) is 0.4 or more and 2.5 or less. [2] A method of inkjet printing, comprising printing on a low-liquid-absorbent printing substrate using the water-based ink for inkjet printing according to item [1] above. Detailed Description of the Invention

[0005] In recent years, with the spread of digital printing, inkjet printing has been increasingly used not only in consumer and commercial printing but also in industrial printing using low-absorbency coated paper and non-absorbent resin films. In particular, because resin film substrates are hydrophobic, the use of aqueous inks results in poor wetting and substrate adhesion, leading to problems such as poor ink coverage during inkjet printing, resulting in reduced image quality, and poor ink adhesion to the substrate, resulting in reduced print quality. Therefore, hydrophobic organic solvents or surfactants are sometimes incorporated into inks to improve ink wetting and substrate adhesion. However, when printing on non-absorbent resin film substrates, convection can occur within the ink coating, resulting in unevenness and reduced print density due to unevenness in the ink coating. Therefore, to improve the quality of printed materials, it is necessary to suppress convection and thereby improve print density. However, the inkjet ink described in Patent Document 1 leaves room for improvement in the print density of the ink on low-absorbency printing substrates. Furthermore, the water-based ink composition described in Patent Document 2 leaves room for improvement in the adhesion of the ink to a low-liquid-absorbent printing substrate and the wetting and spreading properties of the ink.

[0006] An object of the present invention is to provide a water-based ink for inkjet printing that exhibits excellent substrate adhesion, wetting and spreading properties, and print density when applied to low-liquid-absorbent printing substrates, and an inkjet printing method that uses the water-based ink for inkjet printing.

[0007] [Water-based ink for inkjet printing] The water-based ink for inkjet printing of the present invention (hereinafter also simply referred to as "water-based ink") is a water-based ink for inkjet printing on a low-liquid-absorbent printing substrate, the ink containing a pigment, an organic solvent (A), an organic solvent (B), and water, wherein the organic solvent (A) is a glycol ether having an octanol-water partition coefficient log P of 0.75 or more, the organic solvent (B) is a glycol ether or an alkylene glycol having an octanol-water partition coefficient log P of less than 0.75, the HSP distance Ra between the organic solvent (A) and the organic solvent (B) is 5.5 or less, and the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.4 or more and 2.5 or less.

[0008] According to the present invention, it is possible to provide an aqueous ink containing a pigment, an organic solvent, and water, which exhibits excellent substrate adhesion, wetting and spreading properties, and print density for low-absorbency printing substrates. The reasons for this are not entirely clear, but are thought to be as follows. It is believed that the organic solvent (A) contained in the aqueous ink of the present invention has a hydrophobic log P, which allows the aqueous ink of the present invention to sufficiently wet and spread even on low-absorbency printing substrates that are hydrophobic and have low surface free energy. It is also believed that the organic solvent (A) having a hydrophobic log P plasticizes the resin component in the ink until the later drying stage of the ink, thereby promoting resin film formation and improving substrate adhesion. On the other hand, because the log P of the organic solvent (A) is high, at 0.75 or more, the organic solvent (A) has low solubility in water and is prone to phase separation in the aqueous ink. Therefore, the aqueous ink of the present invention contains an organic solvent (B) having a log P of less than 0.75, the HSP distance Ra between the organic solvents (A) and (B) is 5.5 or less, and the mass ratio (A) / (B) of the organic solvents (A) to (B) is 0.4 or more and 2.5 or less, so that the organic solvents (A) and (B) are easily soluble in the aqueous ink and phase separation of the hydrophobic organic solvent (A) in the aqueous ink can be suppressed. This is thought to suppress the occurrence of convection within the ink coating film, improve print density, and also to suppress destabilization of the pigment dispersion in the ink, thereby improving the storage stability of the ink.

[0009] According to the present invention, it is possible to provide a water-based ink for inkjet printing that exhibits excellent substrate adhesion, wetting and spreading properties, and print density when applied to low-liquid-absorbent printing substrates, and an inkjet printing method that uses the water-based ink.

[0010] Definitions of various terms used in this specification are provided below. "Containing component X" also means "composed of component X." "Water-based" means that water accounts for the largest proportion by mass of the medium. "Water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 5 mL or more. The "low liquid absorption" of a low liquid-absorbent printing substrate is a concept that encompasses both low liquid absorption and non-absorption, and refers to a printing substrate with a water absorption of 0 g / m2 when the printing substrate is in contact with pure water for 100 ms. 2 10g / m or more 2 The water absorption amount can be measured as the amount transferred in a contact time of 100 ms with pure water using an automatic scanning absorption meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.) under conditions of 23°C and 50% relative humidity. "Printing" is a concept that includes printing and printed letters that record characters and images, and "printed matter" is a concept that includes printed matter and printed matter on which characters and images are recorded. The boiling point means the boiling point at normal pressure (101.33 kPa).

[0011] <Pigments> The pigments used in the present invention may be either inorganic or organic, and lake pigments and fluorescent pigments may also be used. If necessary, these pigments may be used in combination with extender pigments. Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, and pearlescent pigments. Carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments. Achromatic pigments such as white, black, and gray can be used in achromatic inks, while chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used in chromatic inks. Specific examples of preferred organic pigments include one or more product numbers selected from C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green. Examples of extender pigments include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination.

[0012] From the viewpoint of print density, the content of the pigment in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less.

[0013] (Pigment Dispersant) In the aqueous ink of the present invention, the pigment is dispersed in the medium by a pigment dispersant. Examples of the form of the pigment in the aqueous ink of the present invention include a form in which the pigment is dispersed using a resin (hereinafter also referred to as a "pigment dispersing resin") or a surfactant as the pigment dispersant. Among these, the form of the pigment in the aqueous ink of the present invention is preferably a form in which the pigment is dispersed using a pigment dispersing resin, and more preferably a form in which the pigment is contained in resin particles (hereinafter also referred to as "pigment-containing resin particles"). The form of the pigment-containing resin particles is not particularly limited, as long as they are formed from at least a pigment and a pigment dispersing resin, and are particles in which the pigment dispersing resin is adsorbed onto the pigment in the aqueous ink. Examples of the form of the pigment-containing resin particles include a form in which the pigment is encapsulated in the pigment dispersing resin, a form in which the pigment is uniformly dispersed in the pigment dispersing resin, a form in which the pigment is exposed on the surface of the pigment dispersing resin particles, and mixtures thereof.

[0014] (Pigment Dispersion Resin) The pigment dispersion resin may be either a water-soluble resin or a water-insoluble resin. Regarding the "water-soluble" and "water-insoluble" of a resin, when a resin is dried at 105°C for 2 hours and allowed to reach a constant weight, and the resin is dissolved in 100 g of water at 25°C until saturation is reached, the resin is judged to be "water-soluble" if the dissolved amount exceeds 10 g, and "water-insoluble" if the dissolved amount is 10 g or less. Furthermore, as described below, when the pigment dispersion resin has anionic groups and the anionic groups are neutralized with a neutralizer, the pigment dispersion resin is judged to be water-soluble by measuring the dissolved amount in the presence of the neutralizer under conditions where the mass ratio of the pigment dispersion resin to the neutralizer is the same as that in the aqueous ink of the present invention.

[0015] Examples of pigment dispersion resins include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); and condensation resins such as polyester resins and polyurethane resins. The pigment dispersion resin may be an appropriately synthesized product, or a commercially available product. Among these, the pigment dispersion resin is preferably a single vinyl resin or a mixture of two or more vinyl resins, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density.

[0016] The pigment dispersion resin may have a crosslinked structure. In this case, the pigment dispersion resin preferably has a structure including a resin having a linear two-dimensional structure that may have a branched chain and a component derived from a crosslinking agent. It is believed that such a crosslinked structure is formed by a resin having a linear two-dimensional structure that may have a branched chain being converted into a three-dimensional structure by a component derived from a crosslinking agent. Examples of resins having a linear two-dimensional structure that may have a branched chain include vinyl resins obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds); condensation resins such as polyester resins and polyurethane resins; and the vinyl resins described below are preferred. The crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms, even more preferably one or more selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and even more preferably trimethylolpropane polyglycidyl ether. When the crosslinking agent is a polyfunctional epoxy compound, the epoxy group equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, even more preferably 150 or less.

[0017] [Vinyl Resin] From the viewpoint of improving the dispersion stability of the pigment, the vinyl resin used as the pigment dispersing resin preferably contains a structural unit derived from an anionic group-containing monomer. In this specification, the term "anionic group" refers to an anionic group or a group that can be ionized to become an anionic group. Examples of the anionic group include a carboxy group (-COOM), a sulfonic acid group (-SO ３ M), phosphate group (-OPO ３ M ２) are included. In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Examples of vinyl resins include homopolymers of anionic group-containing monomers, copolymers of anionic group-containing monomers and hydrophobic monomers, and copolymers of anionic group-containing monomers, hydrophobic monomers, and nonionic monomers. Here, the "hydrophobic" of hydrophobic monomers means that when the monomer is dissolved in 100 g of ion-exchanged water at 25°C until saturated, the amount dissolved is less than 10 g. Furthermore, nonionic monomers are monomers that have a high affinity for water, such as monomers containing a hydroxy group or a polyalkylene glycol chain. When the vinyl resin is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer.

[0018] Examples of anionic group-containing monomers include carboxyl group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Among these, carboxyl group-containing monomers are preferred, and (meth)acrylic acid is more preferred. Examples of hydrophobic monomers include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms; aromatic group-containing monomers such as styrene-based monomers and aromatic group-containing (meth)acrylates; and styrene-based macromonomers. The molecular weight of the aromatic group-containing monomer, preferably the styrene-based monomer, is preferably less than 500. The styrene-based macromonomer is a compound having a polymerizable functional group at one end and a number average molecular weight of 500 to 100,000. Among these, the hydrophobic monomer is preferably a (meth)acrylate or styrene-based monomer having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, more preferably at least one selected from the group consisting of alkyl(meth)acrylates having from 3 to 8 carbon atoms, styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, and even more preferably at least one selected from the group consisting of butyl acrylate, cyclohexyl acrylate, and styrene. Examples of nonionic monomers include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate. The term "(meth)acrylic acid" refers to at least one selected from the group consisting of acrylic acid and methacrylic acid. The term "(meth)acrylate" refers to at least one selected from the group consisting of acrylates and methacrylates. Each of the vinyl resin monomers may be used alone or in combination of two or more.

[0019] When the vinyl resin is a copolymer, the vinyl resin preferably contains one or more structural units derived from anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, one or more structural units derived from hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, and one or more structural units derived from nonionic monomers selected from the group consisting of polyalkylene glycol mono(meth)acrylates and alkoxypolyalkylene glycol mono(meth)acrylates, and more preferably one or more structural units derived from anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid. and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers; and structural units derived from one or more nonionic monomers selected from the group consisting of polyalkylene glycol mono(meth)acrylates and alkoxypolyalkylene glycol mono(meth)acrylates, and more preferably structural units derived from one or more anionic group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers.

[0020] When the vinyl resin is a copolymer of an anionic group-containing monomer and a hydrophobic monomer, the content of the constituent units derived from each monomer component in all the constituent units of the vinyl resin is as follows: From the viewpoint of improving the dispersion stability of the pigment and obtaining an ink excellent in substrate adhesion, wet spreadability, and print density, the content of the constituent units derived from the anionic group-containing monomer in all the constituent units of the vinyl resin is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more; and from the same viewpoints as above, it is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. From the viewpoints as above, the content of the constituent units derived from the hydrophobic monomer in all the constituent units of the vinyl resin is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more; and from the same viewpoints as above, it is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. The vinyl resin can be obtained, for example, by addition polymerization of raw material monomers including an anionic group-containing monomer, a hydrophobic monomer, or a nonionic monomer by a known method.

[0021] From the viewpoint of improving the dispersion stability of the pigment, the acid value of the vinyl resin is preferably 40 mgKOH / g or more, more preferably 50 mgKOH / g or more, even more preferably 60 mgKOH / g or more, even more preferably 80 mgKOH / g or more, even more preferably 100 mgKOH / g or more, and even more preferably 150 mgKOH / g or more. From the same viewpoint as above, the acid value is preferably 800 mgKOH / g or less, more preferably 500 mgKOH / g or less, even more preferably 400 mgKOH / g or less, and even more preferably 300 mgKOH / g or less. The acid value of the vinyl resin can be determined by the method described in the Examples, but it can also be calculated from the mass ratio of the constituent monomers. Furthermore, the acid value of a vinyl resin having a crosslinked structure can also be calculated using the following formula: Acid value of vinyl resin having a crosslinked structure (mgKOH / g) = [Acid value of vinyl resin before crosslinking (mgKOH / g) × [(100 - crosslinking rate (mol %)) / 100]

[0022] The weight-average molecular weight of the vinyl resin is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more, from the viewpoints of pigment dispersion stability and obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, and from the same viewpoints as above, is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The weight-average molecular weight of the vinyl resin can be measured by the method described in the examples.

[0023] Commercially available vinyl resins include, for example, polyacrylic acids such as "Aron AC-10SL" (manufactured by Toagosei Co., Ltd.); and styrene / acrylic resins such as "Joncryl 67," "Joncryl 611," "Joncryl 678," "Joncryl 680," "Joncryl 690," and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

[0024] When the pigment in the aqueous ink of the present invention is in the form of pigment-containing resin particles, the pigment-containing resin particles are preferably blended into the aqueous ink as an aqueous dispersion (hereinafter also referred to as "pigment aqueous dispersion") by dispersing the pigment, pigment dispersing resin, and optionally a neutralizing agent, surfactant, etc., using a known method. A preferred method for producing a pigment aqueous dispersion is to disperse a pigment mixture containing a pigment, pigment dispersing resin, an organic solvent, and water to obtain a dispersion, and then remove the organic solvent from the obtained dispersion. If necessary, a crosslinking agent may be further added to the obtained pigment aqueous dispersion to crosslink the pigment dispersing resin. Specific examples of such methods include the method described in paragraphs

[0022] to

[0026] of JP-A 2022-104084. When the pigment is blended in the aqueous ink as a pigment aqueous dispersion, the average particle size of the pigment-containing resin particles in the pigment aqueous dispersion is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, from the viewpoints of dispersion stability of the pigment and of obtaining an ink that is excellent in substrate adhesion, wetting spreadability, and print density, and from the same viewpoints as above, is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less. The average particle size of the pigment-containing resin particles in the pigment aqueous dispersion can be measured by the method described in the Examples.

[0025] When the pigment is in the form of pigment-containing resin particles, the mass ratio of the pigment content to the total content of the pigment and pigment dispersant [pigment / (pigment+pigment dispersant)] is preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more, from the viewpoint of improving the dispersion stability of the pigment, and is preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.75 or less, from the same viewpoint as above. When the pigment dispersant is a pigment dispersant resin that has been crosslinked with a crosslinking agent, the content of the pigment dispersant in the ink of the present invention is the total content of the pigment dispersant resin and the crosslinking agent before crosslinking.

[0026] <Organic Solvent> The water-based ink of the present invention contains organic solvent (A) and organic solvent (B). The distance Ra of the Hansen solubility parameters (HSP) between organic solvent (A) and organic solvent (B) (hereinafter also referred to as "HSP distance Ra") is 5.5 or less, preferably 5.0 or less, and more preferably 4.0 or less. The Hansen solubility parameter (HSP) is a value (unit: MPa) expressed by δ according to the following calculation formula: １／２ ) δ = (δD ２ +δP ２ +δH ２ ) １／２ In the above formula, δD represents the dispersion term, δP represents the polar term, and δH represents the hydrogen bond term (all in units of MPa). １／２ ). The dispersion term δD, polarity term δP, and hydrogen bond term δH are values ​​calculated using HSPiP (Hansen Solubility Parameter in Practice). When the HSPs of organic solvent (A) and organic solvent (B) are plotted as coordinates (δD, δP, δH) in Hansen space, the closer the coordinates of organic solvent (A) and organic solvent (B) are, the more easily organic solvent (A) and organic solvent (B) dissolve in each other. The HSP distance Ra is an index of whether the coordinates of organic solvent (A) and organic solvent (B) are close to each other, and is calculated by the method described in the examples.

[0027] (Organic Solvent (A)) The organic solvent (A) is a glycol ether having an octanol-water partition coefficient log P of 0.75 or more. From the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, the octanol-water partition coefficient log P of the organic solvent (A) is preferably 0.80 or more, more preferably 0.85 or more, and from the same viewpoint, it is preferably 2.50 or less, more preferably 2.20 or less, and even more preferably 2.00 or less. From the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, the boiling point of the organic solvent (A) is preferably 200°C or more, more preferably 205°C or more, even more preferably 210°C or more, and from the same viewpoint, it is preferably 280°C or less, more preferably 278°C or less, and even more preferably 276°C or less. Thus, it is believed that when the boiling point of the organic solvent (A) is high, it remains on the printing substrate until the later drying stage of the ink, thereby further expanding the dot diameter of the aqueous ink.

[0028] Examples of the organic solvent (A) include monoaliphatic ethers of alkylene glycols, dialiphatic ethers of alkylene glycols, and monoaromatic ethers of alkylene glycols.

[0029] Examples of the organic solvent (A) include dipropylene glycol monopropyl ether (boiling point: 212°C, log P: 0.88, δD: 15.6, δP: 6.1, δH: 11.0), dipropylene glycol monobutyl ether (boiling point: 231°C, log P: 1.29, δD: 15.7, δP: 6.5, δH: 10.0), ethylene glycol monobenzyl ether (boiling point: 253°C, log P: 1.30, δD: 17.7, δP: 5.8, δH: 10.2), diethylene glycol monohexyl ether (boiling point: 259°C, log P: 1.49, δD: 16.2, δP: 5.6, δH: 9.4), and ethylene glycol monohexyl ether (boiling point: 258°C, log P: 1.65, δD: 16.2, δP: monoaliphatic ethers of alkylene glycols such as tripropylene glycol monobutyl ether (boiling point: 274°C, log P: 1.90, δD: 16.0, δP: 6.7, δH: 7.0), diethylene glycol mono-2-ethylhexyl ether (boiling point: 272°C, log P: 2.31, δD: 16.2, δP: 5.6, δH: 9.4), ethylene glycol mono-2-ethylhexyl ether (boiling point: 229°C, log P: 2.46, δD: 16.0, δP: 4.1, δH: 10.5); dialiphatic ethers of alkylene glycols such as diethylene glycol dibutyl ether (boiling point: 255°C, log P: 2.26, δD: 15.8, δP: 4.3, δH: 4.8);Examples of suitable organic solvents include monoaromatic ethers of alkylene glycols such as propylene glycol monophenyl ether (boiling point: 243°C, logP: 1.71, δD: 18.3, δP: 6.3, δH: 11.1). From the viewpoint of obtaining an ink that exhibits excellent substrate adhesion, wetting and spreading properties, and print density, preferred organic solvents are one or more selected from dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, ethylene glycol monohexyl ether, and diethylene glycol monohexyl ether, more preferred are one or more selected from dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, and ethylene glycol monohexyl ether, and even more preferred is dipropylene glycol monopropyl ether. The organic solvent (A) may be used singly or in combination of two or more.

[0030] The content of the organic solvent (A) in the water-based ink of the present invention is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of obtaining an ink that is excellent in substrate adhesion, wetting and spreading properties, and print density; and from the same viewpoints, it is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 13% by mass or less, still more preferably 10% by mass or less, and still more preferably 7% by mass or less.

[0031] (Organic Solvent (B)) The organic solvent (B) is a glycol ether or alkylene glycol having an octanol-water partition coefficient log P of less than 0.75. From the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, the octanol-water partition coefficient log P of the organic solvent (B) is preferably 0.70 or less, more preferably 0.60 or less, and from the same viewpoint, it is preferably −2.00 or more, more preferably −1.50 or more, and even more preferably −1.00 or more. From the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, the boiling point of the organic solvent (B) is preferably 200° C. or more, more preferably 205° C. or more, and even more preferably 210° C. or more, and from the same viewpoint, it is preferably 280° C. or less, more preferably 278° C. or less, and even more preferably 276° C. or less. Thus, when the boiling point of the organic solvent (B) is high, it is believed that the organic solvent (B) remains on the printing substrate until the later stage of drying of the ink, thereby further improving the wetting and spreading properties of the ink and the adhesion to the substrate.

[0032] Examples of the organic solvent (B) include monoaliphatic ethers of alkylene glycols, dialiphatic ethers of alkylene glycols, and alkylene glycols.

[0033] Examples of the organic solvent (B) include diethylene glycol monoisopropyl ether (boiling point: 207°C, log P: 0.09, δD: 16.1, δP: 6.5, δH: 10.3), tripropylene glycol monomethyl ether (boiling point: 242°C, log P: 0.08, δD: 16.3, δP: 5.9, δH: 8.3), triethylene glycol monobutyl ether (boiling point: 271°C, log P: 0.51, δD: 16.2, δP: 6.1, δH: 9.1), diethylene glycol monoisobutyl ether (boiling point: 220°C, log P: 0.50, δD: 16.1, δP: 6.0, δH: 9.9), and diethylene glycol monoisopropyl ether (boiling point: 220°C, log P: 0.50, δD: 16.1, δP: 6.0, δH: 9.9). monoaliphatic ethers of alkylene glycols such as butyl ether (boiling point: 231°C, log P: 0.67, δD: 16.3, δP: 6.2, δH: 10.5), triethylene glycol monomethyl ether (boiling point: 249°C, log P: -1.12, δD: 16.2, δP: 7.6, δH: 12.5), triethylene glycol dimethyl ether (boiling point: 216°C, log P Examples of the organic solvent (B) include dialiphatic ethers of alkylene glycols such as dipropylene glycol (boiling point: 230°C, log P: -0.82, δD: 16.7, δP: 8.2, δH: 15.5) and tripropylene glycol (boiling point: 273°C, log P: -0.38, δD 16.6, δP: 9.1, δH: 14.1), and from the viewpoint of obtaining an ink that exhibits excellent substrate adhesion, wetting and spreading properties, and print density, preferred are one or more organic solvents selected from diethylene glycol monoisopropyl ether, tripropylene glycol monomethyl ether, dipropylene glycol, and tripropylene glycol, and more preferred is tripropylene glycol monomethyl ether. The organic solvent (B) may be used singly or in combination of two or more organic solvents.

[0034] The content of the organic solvent (B) in the water-based ink of the present invention is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of obtaining an ink that is excellent in substrate adhesion, wetting and spreading properties, and print density; and from the same viewpoints, it is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 13% by mass or less, still more preferably 10% by mass or less, and still more preferably 7% by mass or less.

[0035] The mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.4 or more, preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading property, and print density, and from the same viewpoint, is 2.5 or less, preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.3 or less.

[0036] A preferred embodiment of the water-based ink of the present invention is a water-based ink for inkjet printing on a low-absorbency printing substrate, the ink comprising a pigment, an organic solvent (A), an organic solvent (B), and water, the organic solvent (A) being a glycol ether having a boiling point of 200°C or higher and 280°C or lower and an octanol-water partition coefficient log P of 0.75 or higher, the organic solvent (B) being a glycol ether or an alkylene glycol having a boiling point of 200°C or higher and 280°C or lower and an octanol-water partition coefficient log P of less than 0.75, the distance Ra of the Hansen solubility parameters (HSP) between the organic solvent (A) and the organic solvent (B) being 5.5 or lower, and the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) being 0.5 or higher and 2 or lower.

[0037] (Organic Solvent (C)) The water-based ink of the present invention preferably contains an organic solvent (C) other than the organic solvent (A) and the organic solvent (B). The organic solvent (C) can be appropriately selected depending on the purpose. Examples of the organic solvent (C) include water-soluble organic solvents such as polyhydric alcohols, glycol ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, from the viewpoint of obtaining an ink that is excellent in substrate adhesion, wetting and spreading properties, and print density, the water-based ink preferably contains one or more organic solvents selected from polyhydric alcohols and glycol ethers as the organic solvent (C).

[0038] Examples of polyhydric alcohols include ethylene glycol (boiling point: 197°C), propylene glycol (boiling point: 188°C), 1,2-butanediol (boiling point: 207°C, δD: 17.1, δP: 9.1, δH: 19.8), 1,3-butanediol (boiling point: 207°C, δD: 16.5, δP: 8.1, δH: 19.8), and H: 20.9), 1,2-pentanediol (boiling point: 206 ° C, δD: 16.8, δP: 7.8, δH: 17.7), 1,5-pentanediol (boiling point: 242 ° C, δD: 17.0, δP: 8.9, δH: 18.9), 1,2-hexanediol (boiling point: 224 ° C, δD: 16.7, δP: 7.1, δH: 17.5), 1,6-hexanediol (boiling point: 250 ° C, δD: 15.7, δP: 8.4, δH: 17.8), Examples of the glycol ether include alkanediols such as 2-methyl-1,3-propanediol (boiling point: 214°C, δD: 17.2, δP: 8.6, δH: 21.2), 3-methyl-1,3-butanediol (boiling point: 204°C, δD: 16.8, δP: 8.1, δH: 16.8), and 2-methyl-2,4-pentanediol (boiling point: 197°C), and diethylene glycol (boiling point: 245°C, δD: 16.6, δP: 12.0, δH: 19.0). Examples of the glycol ether include ethylene glycol dimethyl ether (boiling point: 82°C), propylene glycol monopropyl ether (boiling point: 150°C), diethylene glycol dimethyl ether (boiling point: 162°C), and dipropylene glycol monomethyl ether (boiling point: 187°C). Among these, the organic solvent (C) is preferably a polyhydric alcohol, more preferably an alkanediol, and even more preferably propylene glycol.

[0039] From the viewpoint of obtaining an ink that is excellent in substrate adhesion, wetting and spreading properties, and print density, the content of the organic solvent (C) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and from the same viewpoints, the content is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less.

[0040] The mass ratio (A) / (C) of the organic solvent (A) to the organic solvent (C) is preferably 0.1 or more, more preferably 0.2 or more, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading property, and print density, and from the same viewpoint, is 1.0 or less, more preferably 0.7 or less, even more preferably 0.5 or less, and still more preferably 0.4 or less.

[0041] The mass ratio (B) / (C) of the organic solvent (B) to the organic solvent (C) is preferably 0.1 or more, more preferably 0.2 or more, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading property, and print density, and from the same viewpoint, is 1.0 or less, more preferably 0.7 or less, even more preferably 0.5 or less, and still more preferably 0.4 or less.

[0042] <Surfactant> The water-based ink of the present invention may contain one or more surfactants (X) selected from acetylene-based surfactants and polyether-modified silicone-based surfactants, each having an HLB value (Griffin method) of 1.0 or more and 10.0 or less.

[0043] From the viewpoint of suppressing solubility in water and obtaining an ink that is excellent in substrate adhesion, wetting and spreading properties, and print density, the HLB value of the surfactant (X) is preferably 2.0 or more, more preferably 2.5 or more, even more preferably 3.0 or more, and is preferably 9.5 or less, more preferably 9.0 or less, even more preferably 8.5 or less, still more preferably 7.0 or less, still more preferably 6.0 or less, and still more preferably 5.0 or less.

[0044] (Acetylene-Based Surfactants Having an HLB Value of 1.0 or More and 10.0 or Less) Examples of acetylene-based surfactants having an HLB value of 1.0 or more and 10.0 or less include acetylene glycols having 8 to 22 carbon atoms and ethylene oxide adducts of the acetylene glycols, preferably one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol, 2,4-dimethyl-5-hexyn-3-ol, and ethylene oxide adducts thereof, more preferably one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol and ethylene oxide adducts thereof, and even more preferably an ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol. Commercially available products of ethylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol include Surfynol 104-PG50 (HLB value 4.0), Surfynol SE (HLB value 6.0), Surfynol 440 (HLB value 8.0), Surfynol 2502 (HLB value 8.0), Dynol 604 (HLB value 8.0), and Dynol 607 (HLB value 8.0), all of which are manufactured by Nissin Chemical Industry Co., Ltd.

[0045] (Polyether-modified silicone surfactants with an HLB value of 1.0 or more and 10.0 or less) Examples of polyether-modified silicone surfactants with an HLB value of 1.0 or more and 10.0 or less include compounds in which polyether groups are grafted onto a silicone main chain, and compounds in which polyether groups are bonded in block form to both ends of a silicone main chain. Examples of the polyether group include polyethyleneoxy groups, polypropyleneoxy groups, and polyalkyleneoxy groups in which ethyleneoxy groups and propyleneoxy groups (trimethyleneoxy groups or propane-1,2-diyloxy groups) are added in block form or randomly.

[0046] Specific examples of polyether-modified silicone surfactants having an HLB value of 1.0 or more and 10.0 or less include PEG-3 dimethicone (HLB value 4.5), PEG-9 methyl ether dimethicone (HLB value 4.5), PEG-10 dimethicone (HLB value 4.5), PEG / PPG-20 / 22 butyl ether dimethicone (HLB value 7.0), PEG-9 polydimethylsiloxyethyl dimethicone (HLB value 4.0), cetyl PEG / PPG-10 / 1 dimethicone (HLB value 3.5), lauryl PEG-9 polydimethylsiloxyethyl dimethicone (HLB value 3.0), and PEG-9 dimethicone (HLB value 10.0). Examples of commercially available polyether-modified silicone surfactants with an HLB value of 1.0 to 10.0 include KF-6012 (HLB value 7.0), KF-6015 (HLB value 4.5), KF-6017 (HLB value 4.5), KF-6017P (HLB value 4.5), KF-6028 (HLB value 4.0), KF-6028P (HLB value 4.0), KF-6048 (HLB value 3.5), and KF-6004 (HLB value 9.0) manufactured by Shin-Etsu Chemical Co., Ltd.; Silface (registered trademark) SAG005 (HLB value 7.0) and Silface (registered trademark) SAG008 (HLB value 7.0) manufactured by Nissin Chemical Industry Co., Ltd.; and TEGO (registered trademark) Wet 270 (HLB value 3.0), TEGO (registered trademark) Wet 280 (HLB value 3.5), and BYK345 (HLB value 3.5) and BYK349 ​​(HLB value 4.0) manufactured by BYK Japan Co., Ltd.

[0047] The content of the surfactant (X) having an HLB value of 1.0 or more and 10.0 or less is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and still more preferably 0.25% by mass or more, from the viewpoint of obtaining an ink that is excellent in substrate adhesion, wetting and spreadability, and print density, and from the same viewpoint, is preferably 1.5% by mass or less, more preferably 1.2% by mass or less, even more preferably 1.0% by mass or less, and still more preferably 0.7% by mass or less.

[0048] The mass ratio (A) / (X) of the organic solvent (A) to the surfactant (X) is preferably 1 or more, more preferably 4 or more, and even more preferably 7 or more, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, and from the same viewpoint, is preferably 25 or less, more preferably 20 or less, and even more preferably 15 or less.

[0049] The mass ratio (B) / (X) of the organic solvent (B) to the surfactant (X) is preferably 1 or more, more preferably 4 or more, and even more preferably 7 or more, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, and from the same viewpoint, is preferably 25 or less, more preferably 20 or less, and even more preferably 15 or less.

[0050] The water-based ink of the present invention may further contain, in addition to the surfactant (X) having an HLB value of 1.0 or more and 10.0 or less, one or more surfactants (Y) having an HLB value of more than 10.0 and selected from acetylene-based surfactants and polyether-modified silicone-based surfactants.

[0051] From the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, the HLB value of the surfactant (Y) is preferably more than 10, more preferably 12 or more, even more preferably 13 or more, and is preferably 20 or less, more preferably 18 or less, even more preferably 16 or less.

[0052] Examples of acetylene surfactants having an HLB value of more than 10.0 include ethylene oxide adducts of acetylene glycols having 8 to 22 carbon atoms, which have a different number of moles of ethylene oxide added than the ethylene oxide adducts of acetylene glycols having 8 to 22 carbon atoms listed above as acetylene surfactants having an HLB value of 1.0 or more and 10.0 or less. Commercially available acetylene surfactants having an HLB value of more than 10.0 include Surfynol 465 (HLB value 13.0) and Surfynol 485 (HLB value 17.0) manufactured by Nissin Chemical Industry Co., Ltd.; Acetylenol E81 (HLB value 13.9) and Acetylenol E200 (HLB value 16.4) manufactured by Kawaken Fine Chemicals Co., Ltd.

[0053] Examples of polyether-modified silicone surfactants having an HLB value of greater than 10.0 include PEG-11 methyl ether dimethicone (HLB value 14.5). Commercially available polyether-modified silicone surfactants having an HLB value of greater than 10.0 include KF-6011 (HLB value 14.5), KF-6011P (HLB value 14.5), and KF-6043 (HLB value 14.5) manufactured by Shin-Etsu Chemical Co., Ltd., Silface (registered trademark) SAG002 (HLB value 12.0) and Silface (registered trademark) SAG503A (HLB value 11.0) manufactured by Nissin Chemical Industry Co., Ltd., and ABIL (registered trademark) Care XL 80 MB (HLB value 11.0) manufactured by EVONIK.

[0054] The content of the surfactant (Y) having an HLB value of more than 10.0 is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, from the viewpoint of obtaining an ink that is excellent in substrate adhesion, wetting and spreading properties, and print density, and from the same viewpoint, is preferably 3.0% by mass or less, more preferably 2.0% by mass or less, and even more preferably 1.5% by mass or less.

[0055] The mass ratio (A) / (Y) of the organic solvent (A) to the surfactant (Y) is preferably 1 or more, more preferably 2 or more, and even more preferably 4 or more, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, and from the same viewpoint, is preferably 25 or less, more preferably 20 or less, even more preferably 15 or less, still more preferably 10 or less, and still more preferably 8 or less.

[0056] The mass ratio (B) / (Y) of the organic solvent (B) to the surfactant (Y) is preferably 1 or more, more preferably 2 or more, and even more preferably 4 or more, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, and from the same viewpoint, is preferably 25 or less, more preferably 20 or less, even more preferably 15 or less, still more preferably 10 or less, and still more preferably 8 or less.

[0057] The mass ratio (Y) / (X) of the surfactant (Y) to the surfactant (X) is preferably 0.7 or more, more preferably 1.0 or more, and even more preferably 1.3 or more, from the viewpoint of obtaining an ink that is excellent in intermittent ejection stability, wetting and spreading properties, and suppressing the occurrence of white spots on printed matter; and from the same viewpoint, it is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less.

[0058] <Fixing Resin> The water-based ink of the present invention may further contain a fixing resin. From the viewpoint of improving the scratch resistance and water resistance of the printed matter, the fixing resin preferably has a carboxy group (-COOM). The carboxy group is a group that exhibits acidity by dissociating and releasing a hydrogen ion, or a group in the dissociated ionic form (-COOM). － In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium, as in the anionic group described above.

[0059] From the viewpoint of improving abrasion resistance and water resistance, the acid value of the fixing resin is preferably 3 mgKOH / g or more, more preferably 5 mgKOH / g or more, and even more preferably 10 mgKOH / g or more, and from the same viewpoint as above, it is preferably 30 mgKOH / g or less, more preferably 25 mgKOH / g or less, and even more preferably 20 mgKOH / g or less. The acid value of the fixing resin can be determined by the method described in the examples, but it can also be determined by calculation from the mass ratio of the constituent monomers.

[0060] Examples of fixing resins include vinyl resins such as (meth)acrylic resins, styrene resins, styrene / (meth)acrylic resins, butadiene resins, styrene / butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins; polyurethane resins; and polyester resins. Note that "(meth)acrylic" refers to acrylic or methacrylic. Furthermore, when the fixing resin is a copolymer, it may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer. Among these, from the viewpoint of improving abrasion resistance and water resistance, the fixing resin is preferably one or more selected from the group consisting of vinyl resins having a carboxy group, polyurethane resins having a carboxy group, and polyester resins having a carboxy group, and more preferably a vinyl resin having a carboxy group.

[0061] In the present invention, the vinyl resin having a carboxy group used as the fixing resin preferably contains a structural unit derived from a carboxy group-containing monomer and a structural unit derived from a hydrophobic monomer. The carboxy group-containing monomer is preferably (meth)acrylic acid. Preferred examples of the hydrophobic monomer include those exemplified above for the vinyl resin as a pigment dispersant. The hydrophobic monomer is preferably at least one selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, more preferably at least one selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms and aromatic group-containing monomers, even more preferably (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms, even more preferably (meth)acrylates having an alkyl group having 1 to 12 carbon atoms, and even more preferably (meth)acrylates having an alkyl group having 1 to 8 carbon atoms. Each of the monomers of the vinyl resin having a carboxy group can be used alone or in combination of two or more.

[0062] The vinyl resin having a carboxy group preferably contains structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, aromatic group-containing monomers, and styrene-based macromers, more preferably structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms and aromatic group-containing monomers, and even more preferably structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid. The (meth)acrylic resin is a (meth)acrylic resin containing structural units derived from a carboxy group-containing monomer and structural units derived from a (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol having from 1 to 22 carbon atoms, and even more preferably a (meth)acrylic resin containing structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid and structural units derived from a (meth)acrylate having an alkyl group having from 1 to 12 carbon atoms, and even more preferably a (meth)acrylic resin containing structural units derived from one or more carboxy group-containing monomers selected from the group consisting of acrylic acid and methacrylic acid and structural units derived from a (meth)acrylate having an alkyl group having from 1 to 8 carbon atoms, and even more preferably a copolymer of methacrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate.

[0063] When the vinyl resin having a carboxy group is a copolymer of a carboxy group-containing monomer and a hydrophobic monomer, the content of the structural units derived from each monomer component in the vinyl resin is as follows. From the viewpoint of improving abrasion resistance and water resistance, the content of the structural units derived from the carboxy group-containing monomer in the vinyl resin having a carboxy group is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more. From the same viewpoints as above, it is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less. From the viewpoint of improving abrasion resistance and water resistance, the content of the structural units derived from the hydrophobic monomer in the vinyl resin having a carboxy group is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more. From the same viewpoints as above, it is preferably 99.5% by mass or less, more preferably 99% by mass or less, even more preferably 98% by mass or less.

[0064] From the viewpoint of improving abrasion resistance and water resistance, the weight-average molecular weight of the vinyl resin having a carboxy group is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 30,000 or more, even more preferably 50,000 or more, even more preferably 100,000 or more, even more preferably 300,000 or more, even more preferably 500,000 or more. From the same viewpoint as above, it is preferably 1,500,000 or less, more preferably 1,000,000 or less, even more preferably 800,000 or less. The weight-average molecular weight can be measured by the method described in the Examples. The vinyl resin having a carboxy group is produced by polymerizing raw material monomers by a known polymerization method. Preferred polymerization methods include, for example, emulsion polymerization and suspension polymerization, with emulsion polymerization being more preferred.

[0065] In the present invention, the polyurethane resin having a carboxy group used as the fixing resin is preferably a polyaddition product of an organic compound (polyol) component having two or more alcoholic hydroxyl groups in the molecule, including a dialkanolcarboxylic acid, and a polyisocyanate component. Examples of dialkanolcarboxylic acids include dimethylolbutanoic acid, dimethylolpropionic acid, and salts thereof. Among these, dimethylolpropionic acid is preferred.

[0066] The polyol component is not particularly limited as long as it is a compound having two or more alcoholic hydroxyl groups in the molecule, and examples thereof include polycarbonate polyols, polyester polyols, and polyether polyols. Examples of the polyisocyanate component include chain aliphatic diisocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; aliphatic diisocyanates having a cyclic structure such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate and tetramethylxylylene diisocyanate; aromatic diisocyanates such as tolylene diisocyanate and diphenylmethane diisocyanate; and modified products of these diisocyanates (carbodiimide-, uretdione-, and uretoimine-containing modified products, etc.).

[0067] From the viewpoint of improving abrasion resistance and water resistance, the polyurethane resin having a carboxy group is more preferably a polyaddition product of dimethylolpropionic acid and a polycarbonate polyol as the polyol component and dicyclohexylmethane 4,4'-diisocyanate as the polyisocyanate component.

[0068] Examples of solvents used in the polyaddition reaction include acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, ethyl acetate, toluene, and xylene. In the polyaddition reaction, a chain extender or a reaction terminator may be used in combination, if necessary. The use of a chain extender can further increase the molecular weight. Examples of chain extenders include polyols and polyamines, and examples of reaction terminators include monoalcohols and monoamines.

[0069] From the viewpoint of dispersion stability in aqueous inks, it is preferable that at least a portion of the carboxy groups of the vinyl resin having a carboxy group, the polyurethane resin having a carboxy group, and the polyester resin having a carboxy group be neutralized with a neutralizing agent, such as alkylamines such as butylamine and triethylamine; alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine; and inorganic bases such as morpholine, ammonia, and sodium hydroxide.

[0070] Commercially available aqueous dispersions of pigment-free vinyl resin particles (fixing resin particles) having carboxy groups include acrylic resins such as "Neocryl A-1127" (trade name, anionic self-crosslinking aqueous acrylic resin, manufactured by DSM Coating Resins), "Joncryl 390", "Joncryl 7100", "Joncryl 7600", "Joncryl 537J", "Joncryl PDX-7164", "Joncryl 538J", and "Joncryl 780" (trade names, manufactured by BASF Japan Ltd.); styrene / butadiene resins such as "SR-100" and "SR102" (all trade names, manufactured by Nippon A&L Inc.); and vinyl chloride resins such as "Vinyblan 700" and "Vinyblan 701" (trade names, manufactured by Nissin Chemical Industry Co., Ltd.). Commercially available aqueous dispersions of pigment-free polyurethane resin particles (fixing resin particles) having carboxy groups include, for example, "NeoRez R-9603" (trade name, manufactured by DSM Coating Resins) and "WBR-2018" and "WBR-2000U" (trade names, manufactured by Taisei Fine Chemical Co., Ltd.). Commercially available aqueous dispersions of pigment-free polyester resin particles (fixing resin particles) having carboxy groups include, for example, "ELITEL KA-5034," "ELITEL KA-5071S," "ELITEL KZA-1734," "ELITEL KZA-6034," "ELITEL KZA-1449," "ELITEL KZA-0134," and "ELITEL KZA-3556" (all trade names, manufactured by Unitika Ltd.).

[0071] The fixer resin is preferably used as pigment-free resin particles, and from the viewpoint of improving the productivity of the water-based ink, it is preferably blended into the water-based ink as an aqueous dispersion of pigment-free resin particles. The fixer resin may be appropriately synthesized or a commercially available product. When the fixer resin is blended as an aqueous dispersion of pigment-free resin particles, the average particle size of the pigment-free resin particles in the aqueous dispersion is preferably 30 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, from the viewpoint of ink storage stability, and is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less, from the same viewpoint as above. The average particle size of the pigment-free resin particles in the aqueous dispersion is measured by the method described in the examples.

[0072]

[0033] When the water-based ink of the present invention contains a fixing resin, the content of the fixing resin in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of obtaining an ink excellent in substrate adhesion, wetting and spreading properties, and print density, and from the same viewpoints as above, is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less. When the pigment in the water-based ink of the present invention is in a form dispersed by a pigment dispersing resin, the mass ratio of the content of the fixing resin to the total content of the pigment dispersing resin and the fixing resin in the water-based ink of the present invention [fixing resin / (pigment dispersing resin+fixing resin)] is preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.30 or more, and preferably 1.0 or less, more preferably 0.7 or less, and even more preferably 0.5 or less.

[0073] <Water> The water-based ink of the present invention contains water. The water used in the water-based ink of the present invention is preferably pure water or ion-exchanged water from the viewpoint of preventing the inclusion of unintended substances.

[0074] The water content in the water-based ink is preferably 40% by mass or more, more preferably 45% by mass or more, and even more preferably 50% by mass or more, from the viewpoint of obtaining an ink that is excellent in substrate adhesion, wetting and spreading properties, and print density, and from the same viewpoint as above, is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less.

[0075] The water-based ink of the present invention may further contain various additives, such as a humectant, wetting agent, wetting / penetrating agent, viscosity adjuster, antifoaming agent, preservative, antifungal agent, and antirust agent, if necessary.

[0076] The water-based ink of the present invention can be obtained by mixing and stirring a pigment, organic solvent (A), organic solvent (B), and water, and, if necessary, a fixing resin, a surfactant, a neutralizing agent, additives, etc. When the pigment is in the form of pigment-containing resin particles, as described above, the pigment-containing resin particles are preferably prepared by dispersing the pigment, pigment dispersing resin, and, if necessary, a neutralizing agent, a surfactant, etc., by a known method to obtain an aqueous dispersion of the pigment-containing resin particles, and then blending this with the remaining components of the water-based ink.

[0077] (Physical Properties of Water-Based Ink for Inkjet Printing) The viscosity of the water-based ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 3.5 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, even more preferably 7 mPa·s or less. The viscosity of the water-based ink can be measured using an E-type viscometer. The pH of the water-based ink of the present invention at 25°C is preferably 7.0 or more, more preferably 7.2 or more, even more preferably 7.5 or more. Furthermore, from the viewpoints of component resistance of the printing device and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, even more preferably 9.5 or less. The pH of the water-based ink can be measured by a conventional method.

[0078] [Inkjet printing method] The inkjet printing method of the present invention includes printing on a low-liquid-absorbent printing substrate using the above-mentioned water-based ink of the present invention. In the inkjet printing method of the present invention, a piezo system is preferred as a system for ejecting the water-based ink from the viewpoint of ejection performance.

[0079] (Low-liquid-absorbent printing substrate) Examples of low-liquid-absorbent printing substrates used in the inkjet printing method of the present invention include low-liquid-absorbent coated paper and resin films. Examples of low-liquid-absorbent coated paper include general-purpose glossy paper and multicolor foam gloss paper. Examples of resin films include films made of synthetic resins. Examples of such synthetic resins include polyolefin resins such as polyethylene resins and polypropylene resins; polyester resins such as polyethylene terephthalate resins; and polyvinyl chloride resins. The resin film may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film. Among these, the low-liquid-absorbent printing substrate is preferably a printing substrate made of a synthetic resin, and more preferably a low-liquid-absorbent printing substrate made of one or more synthetic resins selected from the group consisting of polyethylene resins, polypropylene resins, and polyethylene terephthalate resins.

[0080] The present invention also includes the following aspects: <1> A water-based ink for inkjet printing on a low-liquid-absorbency printing substrate, the ink comprising a pigment, an organic solvent (A), an organic solvent (B), and water, the organic solvent (A) is a glycol ether having an octanol-water partition coefficient log P of 0.75 or more, the organic solvent (B) is a glycol ether or an alkylene glycol having an octanol-water partition coefficient log P of less than 0.75, the distance Ra of the Hansen solubility parameters (HSP) between the organic solvent (A) and the organic solvent (B) is 5.5 or less, and the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.4 or more and 2.5 or less. <2> The water-based ink for inkjet printing according to <1>, wherein the organic solvent (A) is one or more selected from dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, ethylene glycol monohexyl ether, and diethylene glycol monohexyl ether. <3> The water-based ink for inkjet printing according to <1> or <2>, wherein the content of the organic solvent (A) is 0.1% by mass or more and 20% by mass or less. <4> The water-based ink for inkjet printing according to any one of <1> to <3>, wherein the organic solvent (B) is one or more selected from diethylene glycol monoisopropyl ether, dipropylene glycol, tripropylene glycol monomethyl ether, and tripropylene glycol. <5> The water-based ink for inkjet printing according to any one of <1> to <4>, wherein the content of the organic solvent (B) is 0.1% by mass or more and 20% by mass or less. <6> The water-based ink for ink-jet printing according to any one of <1> to <5>, wherein the organic solvent (A) is dipropylene glycol monopropyl ether and the content of the organic solvent (A) is 3% by mass or more and 7% by mass or less, the organic solvent (B) is tripropylene glycol monomethyl ether and the content of the organic solvent (B) is 3% by mass or more and 7% by mass or less, and the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.5 or more and 1.5 or less. <7>The water-based ink for inkjet printing according to any one of <1> to <6>, further comprising an organic solvent (C) other than the organic solvent (A) and the organic solvent (B). <8> The water-based ink for inkjet printing according to <7>, further comprising one or more organic solvents selected from the group consisting of polyhydric alcohols and glycol ethers. <9> The water-based ink for inkjet printing according to any one of <1> to <8>, further comprising one or more surfactants (X) having an HLB value of 1.0 or more and 10.0 or less, selected from the group consisting of acetylene-based surfactants and polyether-modified silicone-based surfactants. <10> The water-based ink for inkjet printing according to any one of <1> to <9>, further comprising one or more surfactants (Y) having an HLB value of more than 10.0, selected from the group consisting of acetylene-based surfactants and polyether-modified silicone-based surfactants. <11> The water-based ink for inkjet printing according to item 2 above in <10>, wherein the mass ratio (Y) / (X) of the surfactant (Y) to the surfactant (X) is 0.7 or more and 5.0 or less. <12> The water-based ink for inkjet printing according to any one of items <1> to <11>, further comprising a fixing resin, the fixing resin being at least one resin selected from the group consisting of vinyl resins having a carboxy group, polyurethane resins having a carboxy group, and polyester resins having a carboxy group. <13> The water-based ink for inkjet printing according to any one of items <1> to <12>, wherein the pigment is in the form of pigment-containing resin particles. <14> The water-based ink for inkjet printing according to item <7> or <8>, wherein the content of the organic solvent (C) is 5% by mass or more and 30% by mass or less. <15> The water-based ink for inkjet printing according to item <9>, wherein the content of the surfactant (X) is 0.01% by mass or more and 1.5% by mass or less. <16> The water-based ink for ink-jet printing according to <10> or <11>, wherein the content of the surfactant (Y) is 0.1% by mass or more and 3.0% by mass or less. <17> The water-based ink for ink-jet printing according to <7> or <8>, wherein the mass ratio (A) / (C) of the organic solvent (A) to the organic solvent (C) is 0.1 or more and 1.0 or less. <18>The water-based ink for inkjet printing according to <7> or <8>, wherein the mass ratio (B) / (C) between the organic solvent (B) and the organic solvent (C) is 0.1 or more and 1.0 or less. <19> The water-based ink for inkjet printing according to <9>, wherein the mass ratio (A) / (X) between the organic solvent (A) and the surfactant (X) is 1 or more and 25 or less. <20> The water-based ink for inkjet printing according to <10>, wherein the mass ratio (A) / (Y) between the organic solvent (A) and the surfactant (Y) is 1 or more and 25 or less. <21> The water-based ink for inkjet printing according to <9>, wherein the mass ratio (B) / (X) between the organic solvent (B) and the surfactant (X) is 1 or more and 25 or less. <22> The water-based ink for inkjet printing according to <10>, wherein the mass ratio (B) / (Y) between the organic solvent (B) and the surfactant (Y) is 1 or more and 25 or less. <23> The organic solvent (A) is dipropylene glycol monopropyl ether, and the content of the organic solvent (A) is 3% by mass or more and 7% by mass or less; The organic solvent (B) is tripropylene glycol monomethyl ether, and the content of the organic solvent (B) is 3% by mass or more and 7% by mass or less; The mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.5 or more and 1.5 or less; The organic solvent (C) is propylene glycol, and the content of the organic solvent (C) is 15% by mass or more and 25% by mass or less; The surfactant (X) is an acetylene-based surfactant having an HLB value of 2.0 or more and 6.0 or less, and the content of the surfactant (X) is 0.25% by mass or more and 0.7% by mass or less; The surfactant (Y) is a polyether-modified silicone-based surfactant having an HLB value of 13 or more and 16 or less, and the content of the surfactant (Y) is 0.5% by mass or more and 1.5% by mass or less; the fixing resin is a vinyl resin having a carboxy group, which contains a structural unit of methacrylic acid, a structural unit of methyl methacrylate, and a structural unit of 2-ethylhexyl acrylate, the weight average molecular weight of the fixing resin is 500,000 or more and 1,000,000 or less, the acid value of the fixing resin is 10 mgKOH / g or more and 25 mgKOH / g or less, and the content of the fixing resin is 2% by mass or more and 6% by mass or less,the pigment is in the form of pigment-containing resin particles, a resin of the resin particles contains acrylic acid structural units and styrene structural units, the weight average molecular weight of the resin is 10,000 or more and 20,000 or less, and the acid value of the resin is 150 mgKOH / g or more and 400 mgKOH / g or less, the mass ratio (Y) / (X) of the surfactant (Y) to the surfactant (X) is 1.0 or more and 3.0 or less, the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.5 or more and 2.0 or less, the mass ratio (A) / (C) of the organic solvent (A) to the organic solvent (C) is 0.1 or more and 0.5 or less, the mass ratio (B) / (C) of the organic solvent (B) to the organic solvent (C) is 0.1 or more and 0.5 or less, the mass ratio (A) / (X) of the organic solvent (A) to the surfactant (X) is 7 or more and 15 or less, The water-based ink for inkjet printing according to <10> or <11>, wherein the mass ratio (A) / (Y) of the organic solvent (A) to the surfactant (Y) is 2 or more and 8 or less, the mass ratio (B) / (X) of the organic solvent (B) to the surfactant (X) is 7 or more and 15 or less, and the mass ratio (B) / (Y) of the organic solvent (B) to the surfactant (Y) is 2 or more and 8 or less. <24> An inkjet printing method, comprising printing on a low-liquid-absorbent printing substrate using the water-based ink for inkjet printing according to any one of <1> to <23>. <25> Use of a composition as a water-based ink for inkjet printing, comprising a pigment, an organic solvent (A), an organic solvent (B), and water, wherein the organic solvent (A) is dipropylene glycol monopropyl ether and the content of the organic solvent (A) is 3% by mass or more and 7% by mass or less, the organic solvent (B) is tripropylene glycol monomethyl ether and the content of the organic solvent (B) is 3% by mass or more and 7% by mass or less, and the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.5 or more and 1.5 or less. <26> Use of a composition as a water-based ink for inkjet printing, comprising a pigment, an organic solvent (A), an organic solvent (B), and water, wherein the organic solvent (A) is dipropylene glycol monopropyl ether and the content of the organic solvent (A) is 3% by mass or more and 7% by mass or less,Use of a water-based ink for inkjet printing for printing on a resin film, wherein the organic solvent (B) is tripropylene glycol monomethyl ether, the content of the organic solvent (B) is 3% by mass or more and 7% by mass or less, and the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.5 or more and 1.5 or less. <27> A toner image forming apparatus comprising a pigment, organic solvents (A), (B), (C), surfactants (X), (Y), a fixing resin, and water, wherein the organic solvent (A) is dipropylene glycol monopropyl ether, and the content of the organic solvent (A) is 3% by mass or more and 7% by mass or less, the organic solvent (B) is tripropylene glycol monomethyl ether, and the content of the organic solvent (B) is 3% by mass or more and 7% by mass or less, the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.5 or more and 1.5 or less, the organic solvent (C) is propylene glycol, and the content of the organic solvent (C) is 15% by mass or more and 25% by mass or less, the surfactant (X) is an acetylene-based surfactant having an HLB value of 2.0 or more and 6.0 or less, and the content of the surfactant (X) is 0.25% by mass or more and 0.7% by mass or less, the surfactant (Y) is a polyether-modified silicone surfactant having an HLB value of 13 or more and 16 or less, and the content of the surfactant (Y) is 0.5% by mass or more and 1.5% by mass or less; the fixer resin is a vinyl resin having a carboxy group containing methacrylic acid structural units, methyl methacrylate structural units, and 2-ethylhexyl acrylate structural units, and the weight average molecular weight of the fixer resin is 500,000 or more and 1,000,000 or less, and the acid value of the fixer resin is 10 mgKOH / g or more and 25 mgKOH / g or less, and the content of the fixer resin is 2% by mass or more and 6 mass% or less; the pigment is in the form of pigment-containing resin particles, and the resin of the resin particles contains acrylic acid structural units and styrene structural units, and the weight average molecular weight of the resin is 10,000 or more and 20,000 or less, and the acid value of the resin is 150 mgKOH / g or more and 400 mgKOH / g or less; the mass ratio (Y) / (X) of the surfactant (Y) to the surfactant (X) is 1.0 or more and 3.0 or less;a mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) being 0.5 or more and 2.0 or less; a mass ratio (A) / (C) of the organic solvent (A) to the organic solvent (C) being 0.1 or more and 0.5 or less; a mass ratio (B) / (C) of the organic solvent (B) to the organic solvent (C) being 0.1 or more and 0.5 or less; a mass ratio (A) / (X) of the organic solvent (A) to the surfactant (X) being 7 or more and 15 or less; a mass ratio (A) / (Y) of the organic solvent (A) to the surfactant (Y) being 2 or more and 8 or less; a mass ratio (B) / (X) of the organic solvent (B) to the surfactant (X) being 7 or more and 15 or less; and a mass ratio (B) / (Y) of the organic solvent (B) to the surfactant (Y) being 2 or more and 8 or less. Use of a composition as a water-based ink for ink-jet printing. <28> A toner image forming apparatus comprising a pigment, organic solvents (A), (B), (C), surfactants (X), (Y), a fixing resin, and water, wherein the organic solvent (A) is dipropylene glycol monopropyl ether, and the content of the organic solvent (A) is 3% by mass or more and 7% by mass or less, the organic solvent (B) is tripropylene glycol monomethyl ether, and the content of the organic solvent (B) is 3% by mass or more and 7% by mass or less, the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.5 or more and 1.5 or less, the organic solvent (C) is propylene glycol, and the content of the organic solvent (C) is 15% by mass or more and 25% by mass or less, the surfactant (X) is an acetylene-based surfactant having an HLB value of 2.0 or more and 6.0 or less, and the content of the surfactant (X) is 0.25% by mass or more and 0.7% by mass or less, the surfactant (Y) is a polyether-modified silicone surfactant having an HLB value of 13 to 16, and the content of the surfactant (Y) is 0.5% by mass to 1.5% by mass, the fixing resin is a vinyl resin having a carboxy group containing methacrylic acid structural units, methyl methacrylate structural units, and 2-ethylhexyl acrylate structural units, the weight average molecular weight of the fixing resin is 500,000 to 1,000,000, the acid value of the fixing resin is 10 mgKOH / g to 25 mgKOH / g, and the content of the fixing resin is 2% by mass to 6% by mass,the pigment is in the form of pigment-containing resin particles, a resin of the resin particles contains acrylic acid structural units and styrene structural units, the weight average molecular weight of the resin is 10,000 or more and 20,000 or less, and the acid value of the resin is 150 mgKOH / g or more and 400 mgKOH / g or less, the mass ratio (Y) / (X) of the surfactant (Y) to the surfactant (X) is 1.0 or more and 3.0 or less, the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.5 or more and 2.0 or less, the mass ratio (A) / (C) of the organic solvent (A) to the organic solvent (C) is 0.1 or more and 0.5 or less, the mass ratio (B) / (C) of the organic solvent (B) to the organic solvent (C) is 0.1 or more and 0.5 or less, the mass ratio (A) / (X) of the organic solvent (A) to the surfactant (X) is 7 or more and 15 or less, Use of a water-based ink for inkjet printing, wherein a mass ratio (A) / (Y) of the organic solvent (A) to the surfactant (Y) is 2 or more and 8 or less, a mass ratio (B) / (X) of the organic solvent (B) to the surfactant (X) is 7 or more and 15 or less, and a mass ratio (B) / (Y) of the organic solvent (B) to the surfactant (Y) is 2 or more and 8 or less, for printing on a resin film.

[0081] In the following Production Examples, Examples, and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows. Pressure is expressed as absolute pressure.

[0082] (1) Measurement of Resin Acid Value An automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610) was used to measure the acid value of the resin. Specifically, the resin was dissolved in a titration solvent containing a mixture of toluene and acetone (toluene:acetone=2:1 (volume ratio)), and this was titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve being the endpoint. The acid value (mg KOH / g) was calculated from the titration amount of the potassium hydroxide solution up to the endpoint.

[0083] (2) Measurement of Resin Weight-Average Molecular Weight The resin weight-average molecular weight was determined by gel permeation chromatography. The measurement sample was prepared by mixing 0.1 g of resin with 10 mL of the following eluent in a glass vial, stirring the mixture with a magnetic stirrer at 25°C for 10 hours, and then filtering the mixture through a syringe filter (Advantec Co., Ltd.'s "DISMIC-13HP," pore size: 0.2 μm, material: PTFE). The measurement conditions were as follows: GPC apparatus: "HLC-8320GPC" manufactured by Tosoh Corporation Column: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", "TSKgel guard column Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide to concentrations of 60 mmol / L and 50 mmol / L, respectively Flow rate: 0.5 mL / min Standard substance: monodisperse polystyrene kit with known molecular weight, manufactured by Tosoh Corporation "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)"

[0084] (3) Measurement of solids concentration of aqueous pigment dispersion and aqueous dispersion of fixative resin particles Approximately 10 g of sodium sulfate, adjusted to a constant weight in a desiccator, was weighed into a 30 mL ointment container, and approximately 1 g of sample was added thereto and mixed, and then weighed. The mixture was then kept at 105°C for 2 hours to remove volatiles, and then left in the desiccator for another 15 minutes, after which the mass was precisely weighed. The mass of the sample after volatiles removal was taken as the solids content and divided by the mass of the sample added to the ointment container to obtain the solids concentration (%).

[0085] (4) Calculation of the octanol-water partition coefficient log P of organic solvents The log P of each organic solvent was calculated using ChemDraw Professional ver. 22.2.0.3300 (manufactured by PerkinElmer).

[0086] (5) Calculation of HSP distance Ra between organic solvent (A) and organic solvent (B) The HSP distance Ra was calculated using the following formula: (Ra) ２ = 4 (δD Ｂ -δDＡ ) ２ + (δP Ｂ -δP Ａ ) ２ + (δH Ｂ -δH Ａ ) ２ In the above formula, δD Ａ , δP Ａ , and δH Ａ respectively represent δD, δP, and δH of the organic solvent (A), and δD Ｂ , δP Ｂ , and δH Ｂ respectively indicate δD, δP, and δH of the organic solvent (B).

[0087] (6) Measurement of the average particle size of particles in the water-based ink The water-based ink was subjected to cumulant analysis using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle size was measured as the average particle size of the particles in the water-based ink. The measurement sample had a particle concentration of 5 × 10 -３ The water-based ink was diluted with water to a concentration of 1.333% (solids concentration equivalent). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The particles in the water-based ink included both pigment-containing resin particles and fixing resin particles.

[0088] (7) Measurement of the average particle size of fixing resin particles A water dispersion of fixing resin particles was subjected to cumulant analysis using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle size was measured as the average particle size of the fixing resin particles. The measurement sample contained fixing resin particles having a concentration of 5 × 10 -３ % (solid content equivalent) was used. The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent.

[0089] (8) Calculation of HLB Value of Surfactant The HLB value indicates the affinity of a surfactant to water and oil, and was calculated using the Griffin method according to the following formula. In the following formula, examples of the "hydrophilic group contained in the surfactant" include a hydroxyl group and an ethyleneoxy group. HLB = 20 × [(molecular weight of the hydrophilic group contained in the surfactant) / (molecular weight of the surfactant)]

[0090] (9) Measurement of Viscosity of Water-Based Ink The viscosity of the water-based ink at 32° C. was measured using an E-type viscometer ("TV-25" manufactured by Toki Sangyo Co., Ltd., standard cone rotor 1°34'×R24, rotation speed 50 rpm).

[0091] (10) Measurement of pH of Water-Based Ink The pH of the water-based ink at 25° C. was measured using a tabletop pH meter ("F-71" manufactured by Horiba, Ltd.) equipped with a pH electrode ("6337-10D" manufactured by Horiba, Ltd.).

[0092] [Production Example 1 (Production of Pigment Aqueous Dispersion 1)] (1) Synthesis of Pigment Dispersion Resin D1: A monomer mixture was prepared by mixing 31 parts of acrylic acid and 69 parts of styrene. A reaction vessel was charged with 10 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.2 parts of 2-mercaptoethanol (a polymerization chain transfer agent), and 10% of the monomer mixture, and the mixture was thoroughly purged with nitrogen gas. Meanwhile, a dropping funnel was charged with a mixture of the remaining 90% of the monomer mixture, 0.2 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of an azo-based radical polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-65). Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 65°C while being stirred, and the mixture in the dropping funnel was added dropwise to the reaction vessel over 3 hours. The resulting reaction solution was maintained at 65°C for 2 hours after the completion of the dropwise addition of the mixed solution, and then a solution of 0.1 parts of the polymerization initiator dissolved in 2 parts of MEK was added. The mixture was further aged at 65°C for 2 hours and then at 70°C for 2 hours, followed by drying under reduced pressure to partially distill off the MEK, yielding an MEK solution (solids concentration 45%) of pigment dispersion resin D1 (acid value: 240 mg KOH / g, weight average molecular weight: 13,900). To 17.0 parts of the resulting MEK solution of pigment dispersion resin D1, 4.9 parts of MEK was added to dilute the solution to a solids concentration of 35%. Next, 3.1 parts of a 5N aqueous NaOH solution (water was ion-exchanged water) was added so that the degree of neutralization of the carboxy groups in pigment dispersion resin D1 was 40 mol%, and the mixture was stirred at 25°C. Subsequently, 75.0 parts of ion-exchanged water was added over 1 hour, and the pigment dispersion resin D1 was subjected to phase inversion emulsification. After the addition of the ion-exchanged water was completed, the MEK was distilled off using an evaporator to obtain an aqueous dispersion of pigment dispersing resin D1 (solid concentration: 25%).

[0093] (2) Production of Pigment Aqueous Dispersion 1 To 32.97 parts of an aqueous dispersion of pigment dispersion resin D1 (solids concentration 25%), 2.10 parts of MEK and 17.25 parts of ion-exchanged water were added, and 18.77 parts of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 Pigment Blue 15:3) were further added to obtain a pigment mixture. The obtained pigment mixture was mixed for 1 hour under conditions of 7000 rpm and 20°C using a disper blade, and then further dispersed using a Microfluidizer (manufactured by Microfluidics, high-pressure homogenizer, trade name: M-140K) at a pressure of 180 MPa for 10 passes to obtain a pigment dispersion. From the obtained pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the ion-exchanged water was removed. The mixture was then centrifuged, and the liquid phase portion was filtered through a membrane filter (manufactured by Sartorius GmbH, trade name: Minisart Syringe Filter, pore size: 5 µm, material: cellulose acetate) to remove coarse particles, thereby obtaining Pigment Aqueous Dispersion 1 (solid concentration 22%, pigment: 15.4%, resin: 6.6%). The average particle size of the pigment-containing resin particles in Pigment Aqueous Dispersion 1 was 105.3 nm.

[0094] [Production Example 2 (Production of Pigment Water Dispersion 2)] (1) Synthesis of Pigment Dispersion Resin D2: A monomer mixture was prepared by mixing 26 parts of acrylic acid, 19 parts of butyl acrylate, and 55 parts of cyclohexyl acrylate. A reaction vessel was charged with 10 parts of MEK, 0.2 parts of 2-mercaptoethanol (a polymerization chain transfer agent), and 10% of the monomer mixture, and the mixture was thoroughly purged with nitrogen gas. Meanwhile, a dropping funnel was charged with a mixture of the remaining 90% of the monomer mixture, 0.2 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of an azo-based radical polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-65). Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 65°C while being stirred, and the mixture in the dropping funnel was added dropwise to the reaction vessel over 3 hours. The resulting reaction solution was maintained at 65°C for 2 hours after the completion of the dropwise addition of the mixed solution, and then a solution of 0.1 parts of the polymerization initiator dissolved in 2 parts of MEK was added. The mixture was further aged at 65°C for 2 hours and then at 70°C for 2 hours, followed by drying under reduced pressure to partially distill off the MEK, yielding an MEK solution (solids concentration 45%) of pigment dispersion resin D2 (acid value: 200 mg KOH / g, weight average molecular weight: 16,100). To 17.0 parts of the resulting MEK solution of pigment dispersion resin D2, 4.9 parts of MEK was added to dilute the solution to a solids concentration of 35%. Next, 3.1 parts of a 5N aqueous NaOH solution (water was ion-exchanged water) was added so that the degree of neutralization of the carboxy groups in pigment dispersion resin D2 was 40 mol%, and the mixture was stirred at 25°C. Subsequently, 75.0 parts of ion-exchanged water was added over 1 hour, and the pigment dispersion resin D2 was subjected to phase inversion emulsification. After the addition of the ion-exchanged water was completed, the MEK was distilled off using an evaporator to obtain an aqueous dispersion of pigment dispersing resin D2 (solid concentration: 25%).

[0095] (2) Production of Pigment Aqueous Dispersion 2 To 32.97 parts of an aqueous dispersion of pigment dispersion resin D2 (solids concentration 25%), 2.10 parts of MEK and 17.25 parts of ion-exchanged water were added, and 18.77 parts of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 Pigment Blue 15:3) were further added to obtain a pigment mixture. The obtained pigment mixture was mixed for 1 hour under conditions of 7000 rpm and 20°C using a disper blade, and then further dispersed using a Microfluidizer (manufactured by Microfluidics, high-pressure homogenizer, trade name: M-140K) at a pressure of 180 MPa for 10 passes to obtain a pigment dispersion. From the obtained pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the ion-exchanged water was removed. The mixture was then centrifuged, and the liquid phase portion was filtered through a membrane filter (manufactured by Sartorius GmbH, trade name: Minisart Syringe Filter, pore size: 5 µm, material: cellulose acetate) to remove coarse particles, thereby obtaining Pigment Aqueous Dispersion 2 (solids concentration 22%, pigment: 15.4%, resin: 6.6%). The average particle size of the pigment-containing resin particles in Pigment Aqueous Dispersion 2 was 103.7 nm.

[0096] [Production Example 3 (Production of Aqueous Dispersion of Fixing Resin Particles)] In a reaction vessel equipped with a dropping funnel, the monomers shown in the "Initially Charged Monomer Emulsion" column of Table 1, LATEMULL E-118B (polyoxyethylene alkyl ether sodium sulfate, manufactured by Kao Corporation) as a surfactant, potassium persulfate (FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, and ion-exchanged water were mixed and purged with nitrogen gas to obtain an initially charged monomer emulsion. Furthermore, the monomers, surfactants, polymerization initiators, and ion-exchanged water shown in the "Dropped Monomer Emulsion" column of Table 1 were mixed to obtain a dropped monomer emulsion, and the dropped monomer emulsion was then placed in a dropping funnel and purged with nitrogen gas. Under a nitrogen atmosphere, the temperature of the initially charged monomer emulsion in the reaction vessel was raised from room temperature to 80°C over 30 minutes while stirring, and while maintaining the temperature at 80°C, the dropped monomer emulsion in the dropping funnel was gradually added dropwise into the reaction vessel over 3 hours. After completion of the dropwise addition, the mixture was stirred for 1 hour while maintaining the temperature in the reaction vessel. The resulting solution was filtered through a 200 mesh filter to obtain an aqueous dispersion of fixing resin particles (acid value: 16 mg KOH / g, weight average molecular weight: 750,000, solid content: 44.1%). The average particle size of the fixing resin particles in the aqueous dispersion of fixing resin particles was 95 nm.

[0097]

[0098] Example 1 (Preparation of Water-Based Ink I1) To obtain the ink composition (total 100 parts) shown in Table 2, 7.1 parts (solids content equivalent) of Pigment Water-Based Dispersion 1 (solids content concentration: 22%, pigment: 15.4%, polymer: 6.6%, acid value of pigment dispersing resin: 240 mgKOH / g) obtained in Production Example 1, 4.0 parts (solids content equivalent) of an aqueous dispersion of fixing resin particles (solids content concentration: 44.1%), 20.0 parts of propylene glycol (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 5.0 parts of dipropylene glycol monopropyl ether (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and tripropylene glycol were mixed. A water-based ink I1 was obtained by mixing 5.0 parts of monomethyl ether (reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 0.5 parts of an acetylene glycol surfactant ("Surfynol 104PG50" manufactured by Nissin Chemical Industry Co., Ltd., active content 50%), 1.0 part of a polyether-modified silicone surfactant ("KF-6011" manufactured by Shin-Etsu Chemical Co., Ltd., active content 100%), and ion-exchanged water, thoroughly stirring the mixture, and filtering it through a membrane filter ("Minisart Syringe Filter" manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate). The amount of ion-exchanged water in Table 2-1 (57.4 parts) is the total amount of ion-exchanged water contained in the water-based ink I1, and includes the ion-exchanged water contained in the pigment aqueous dispersion, the ion-exchanged water contained in the aqueous dispersion of fixer resin particles, the ion-exchanged water contained in the 5N-NaOH aqueous solution, etc.

[0099] Examples 2 to 12 and Comparative Examples 1 to 3 Water-based inks I2 to I12 and IC1 to IC3 were obtained in the same manner as in Example 1, except that the ink compositions in Example 1 were changed to those shown in Table 2.

[0100] The symbols in Table 2 have the following meanings: PFDG: dipropylene glycol monopropyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 212°C, logP: 0.88, δD: 15.6, δP: 6.1, δH: 11.0) BFDG: dipropylene glycol monobutyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 231°C, logP: 1.29, δD: 15.7, δP: 6.5, δH: 10.0) HeDG: diethylene glycol monohexyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 259°C, logP: 1.49, δD: 16.2, δP: 5.6, δH: 9.4) BFTG: tripropylene glycol monobutyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 274°C, logP: 1.90, δD: 16.0, δP: 6.7, δH: 7.0) BDG: diethylene glycol monobutyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 231°C, logP: 0.67, δD: 16.3, δP: 6.2, δH: 10.5) iPDG: diethylene glycol monoisopropyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 207°C, logP: 0.09, δD: 16.1, δP: 6.5, δH: 10.3) DPG: dipropylene glycol (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 230°C, log P: -0.82, δD: 16.7, δP: 8.2, δH: 15.5) MFTG: tripropylene glycol monomethyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 242°C, log P: 0.08, δD: 16.3, δP: 5.9, δH: 8.3) TPG: tripropylene glycol (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 273°C, log P: -0.38, δD: 16.6, δP: 9.1, δH: 14.1) MFDG: dipropylene glycol monomethyl ether (reagent, Fujifilm Wako Pure Chemical Industries, Ltd., boiling point: 187°C, log P: 0.22) 1,2-HD: 1,2-Hexanediol (reagent, Fujifilm Wako Pure Chemical Industries, boiling point: 224°C, δD: 16.7, δP: 7.1, δH: 17.5, logP: 0.85) PG: Propylene glycol (reagent, Fujifilm Wako Pure Chemical Industries, boiling point: 188°C) TEGO WET 280: Polyether-modified silicone surfactant (EVONIK Corporation, "TEGO (registered trademark) Wet 280", HLB value 3.5) 104PG50: Acetylene glycol surfactant (Nissin Chemical Industry Co., Ltd., "Surfynol 104-PG50", HLB value 4.0) 440: Acetylene glycol surfactant (Nissin Chemical Industry Co., Ltd., "Surfynol 440", HLB value 8.0) KF-6011: Polyether-modified silicone surfactant (manufactured by Shin-Etsu Chemical Co., Ltd., HLB value 14.5),

[0101] The inks obtained in the examples and comparative examples were evaluated according to the following (1) to (4).

[0102] (1) In an environment with a substrate adhesion temperature of 32°C, an inkjet printing evaluation device (manufactured by Tritec Corporation) equipped with a print head (manufactured by Kyocera Corporation, product name: KJ4B-1200, piezo type) was filled with the water-based inks of the examples and comparative examples. The print head voltage was set to 26 V, drive frequency: 30 kHz, ejected droplet volume: 3 pL, print head temperature: 32°C, and print head resolution: 1200 dpi. A 20 mm x 20 mm solid image was printed at 100% duty on a polyethylene terephthalate film (manufactured by Toray Industries, Inc., "Lumirror #25-T60") (hereinafter referred to as "PET") as a low-liquid-absorbency printing substrate heated to 40°C. Tape (manufactured by Nichiban Co., Ltd., "Cellotape (registered trademark)", 18 mm wide, model number: CT-18S) was attached to the solid image portion of the obtained print, and the edge of the tape was quickly peeled off at a 90° angle. The solid image area after tape peeling was binarized using a print density value that was half the print density value of the solid image area before tape peeling as a threshold value, and the area percentage of the non-peeled area was determined by image analysis. The area percentage of the non-peeled area was calculated as the coating film remaining rate (%) after the tape peeling test. The higher the coating film remaining rate (%), the better the tape peel resistance, and a value of 70% or more is practically acceptable. The results are shown in Table 2. (Evaluation criteria) A: The coating film remaining rate after the tape peeling test is 90% or more. B: The coating film remaining rate after the tape peeling test is 80% or more but less than 90%. C: The coating film remaining rate after the tape peeling test is 70% or more but less than 80%. D: The coating film remaining rate after the tape peeling test is 60% or more but less than 70%. E: The coating film remaining rate after the tape peeling test is less than 60%.

[0103] (2) Wetting and Spreading Properties: A 20 mm x 20 mm solid image was printed on PET at a duty of 10% under the printing conditions described above in "(1) Adhesion to Substrate." The resulting print was observed under an optical microscope, and the diameter of the ink dots was measured. This value was recorded as the dot diameter. To print evenly on a PET surface at a resolution of 1200 dpi and with an appropriate amount of ink ejected of 3 pL, a dot diameter of 30 μm is theoretically required. However, due to impact accuracy and ejection errors inherent in the inkjet head, a dot diameter of 30 μm may result in streaks (white spaces). Therefore, taking into account an ejection error of 20%, it was determined that the dot wetting and spreading properties were practically usable if the dot diameter was 36 μm or greater. The results are shown in Table 2. (Evaluation criteria) A: Dot diameter is 42 μm or more B: Dot diameter is 39 μm or more and less than 42 μm C: Dot diameter is 36 μm or more and less than 39 μm D: Dot diameter is 33 μm or more and less than 36 μm E: Dot diameter is less than 33 μm

[0104] (3) Print Density: Under the printing conditions described in "(1) Adhesion to Substrate" above, a 20 mm x 20 mm solid image was printed on PET at 100% duty. After leaving it at 25°C for 24 hours, the print density was measured at five points, the center and four corners of the resulting print (20 mm x 20 mm), using a Macbeth densitometer (manufactured by GretagMacbeth, product number: Spectroeye), and the average value was calculated. The higher the value, the better the print density, and a print density of 1.7 or higher is practically acceptable. The results are shown in Table 2.

[0105] (4) Ink Storage Stability The average particle size of particles contained in the aqueous inks of the Examples and Comparative Examples was measured as the "average particle size of particles in the aqueous ink before storage" based on the above "(6) Measurement of the average particle size of particles in the aqueous ink." Each aqueous ink was placed in a screw tube (manufactured by Maruemu Co., Ltd.), sealed, and allowed to stand for four weeks in a thermostatic chamber set at 70°C. The "average particle size of particles in the aqueous ink after storage" was then determined using the same method as for measuring the "average particle size of particles in the aqueous ink before storage." The average particle size increase rate was then calculated using the following formula: Average particle size increase rate (%) = [(average particle size of particles in the aqueous ink after storage - average particle size of particles in the aqueous ink before storage) / average particle size of particles in the aqueous ink before storage] × 100. The smaller the average particle size increase rate, the better the storage stability of the aqueous ink. An average particle size increase rate of less than 15% is practically acceptable. The results are shown in Table 2. <Evaluation criteria> A: The average particle size increase rate is less than 5% B: The average particle size increase rate is 5% or more and less than 10% C: The average particle size increase rate is 10% or more and less than 15% D: The average particle size increase rate is 15% or more E: Aggregation occurs and measurement is impossible

[0106]

[0107]

[0108] Table 2 shows that the water-based inks of the Examples are superior to the water-based inks of the Comparative Examples in substrate adhesion to low-absorbency printing substrates, ink wetting and spreading, print density, and ink storage stability. On the other hand, the evaluation results for the water-based ink of Comparative Example 1 show that when diethylene glycol monobutyl ether, an organic solvent with a log P of less than 0.75, was used instead of the organic solvent (A) in the water-based ink, substrate adhesion and wetting and spreading were inferior to the water-based inks of the Examples. The evaluation results for the water-based ink of Comparative Example 2 show that when dipropylene glycol monomethyl ether, an organic solvent with a boiling point of less than 200°C, was used instead of the organic solvent (B) in the water-based ink, wetting and spreading and print density were inferior to the water-based inks of the Examples. The evaluation results for the water-based ink of Comparative Example 3 show that when 1,2-hexanediol, an organic solvent with an HSP distance Ra greater than 5.5, was used instead of the organic solvent (B) in the water-based ink, print density and ink storage stability were inferior to the water-based inks of the Examples. Furthermore, if the boiling point of the organic solvent (A) or the organic solvent (B) exceeds 280° C., the solvent will not dry, causing the printed ink to mix colors, which is thought to prevent normal printing.

[0109] According to the present invention, it is possible to provide an ink-jet printing water-based ink that is excellent in substrate adhesion to low-liquid-absorbent printing substrates, ink wetting and spreading properties, and print density. Therefore, the ink-jet printing water-based ink of the present invention can be suitably used for printing on low-liquid-absorbent printing substrates for which water-based inks for ink-jet printing have conventionally been used.

Claims

1. A water-based ink for inkjet printing on a low-absorbency printing substrate, the ink comprising a pigment, an organic solvent (A), an organic solvent (B), and water, wherein the organic solvent (A) is a glycol ether having an octanol-water partition coefficient log P of 0.75 or more, and the organic solvent (B) is a glycol ether or an alkylene glycol having an octanol-water partition coefficient log P of less than 0.75, the distance Ra of the Hansen solubility parameters (HSP) between the organic solvent (A) and the organic solvent (B) is 5.5 or less, and the mass ratio (A) / (B) of the organic solvent (A) to the organic solvent (B) is 0.4 or more and 2.5 or less.

2. The water-based ink for ink-jet printing according to claim 1, wherein the organic solvent (A) is at least one selected from the group consisting of dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, ethylene glycol monohexyl ether, and diethylene glycol monohexyl ether.

3. The water-based ink for ink-jet printing according to claim 1 or 2, wherein the content of the organic solvent (A) is 0.1% by mass or more and 20% by mass or less.

4. The water-based ink for ink-jet printing according to any one of claims 1 to 3, wherein the organic solvent (B) is at least one selected from the group consisting of diethylene glycol monoisopropyl ether, dipropylene glycol, tripropylene glycol monomethyl ether, and tripropylene glycol.

5. The water-based ink for ink-jet printing according to any one of claims 1 to 4, wherein the content of the organic solvent (B) is 0.1% by mass or more and 20% by mass or less.

6. The water-based ink for ink-jet printing according to any one of claims 1 to 5, further comprising an organic solvent (C) other than the organic solvent (A) and the organic solvent (B).

7. The water-based ink for ink-jet printing according to claim 6, wherein the organic solvent (C) is at least one selected from the group consisting of polyhydric alcohols and glycol ethers.

8. The water-based ink for ink-jet printing according to any one of claims 1 to 7, further comprising one or more surfactants (X) selected from the group consisting of acetylene-based surfactants and polyether-modified silicone-based surfactants, each having an HLB value of 1.0 or more and 10.0 or less.

9. The water-based ink for ink-jet printing according to any one of claims 1 to 8, further comprising one or more surfactants (Y) having an HLB value of more than 10.0 and selected from the group consisting of acetylene-based surfactants and polyether-modified silicone-based surfactants.

10. The water-based ink for ink-jet printing according to claim 9, wherein the mass ratio (Y) / (X) of the surfactant (Y) to the surfactant (X) is 0.7 or more and 5.0 or less.

11. The water-based ink for ink-jet printing according to any one of claims 1 to 10, further comprising a fixing resin, the fixing resin being at least one resin selected from the group consisting of vinyl resins having a carboxy group, polyurethane resins having a carboxy group, and polyester resins having a carboxy group.

12. The water-based ink for ink-jet printing according to any one of claims 1 to 11, wherein the pigment is in the form of pigment-containing resin particles.

13. The water-based ink for ink-jet printing according to claim 6, wherein the content of the organic solvent (C) is 5% by mass or more and 30% by mass or less.

14. The water-based ink for ink-jet printing according to claim 8, wherein the content of the surfactant (X) is 0.01% by mass or more and 1.5% by mass or less.

15. The water-based ink for ink-jet printing according to claim 9, wherein the content of the surfactant (Y) is 0.1% by mass or more and 3.0% by mass or less.

16. The water-based ink for ink-jet printing according to claim 6, wherein the mass ratio (A) / (C) of the organic solvent (A) to the organic solvent (C) is 0.1 or more and 1.0 or less.

17. The water-based ink for ink-jet printing according to claim 6, wherein the mass ratio (B) / (C) of the organic solvent (B) to the organic solvent (C) is 0.1 or more and 1.0 or less.

18. The water-based ink for ink-jet printing according to claim 8, wherein the mass ratio (A) / (X) of the organic solvent (A) to the surfactant (X) is 1 or more and 25 or less.

19. The water-based ink for ink-jet printing according to claim 9, wherein the mass ratio (A) / (Y) of the organic solvent (A) to the surfactant (Y) is 1 or more and 25 or less.

20. The water-based ink for ink-jet printing according to claim 8, wherein the mass ratio (B) / (X) of the organic solvent (B) to the surfactant (X) is 1 or more and 25 or less.

21. The water-based ink for ink-jet printing according to claim 9, wherein the mass ratio (B) / (Y) of the organic solvent (B) to the surfactant (Y) is 1 or more and 25 or less.

22. An inkjet printing method, comprising printing on a low-liquid-absorbent printing substrate using the water-based ink for inkjet printing according to any one of claims 1 to 21.

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