Oily inkjet ink and method for manufacturing the same

Abstract

To provide an oily inkjet ink capable of inhibiting generation of foreign matter in the ink for long-term storage.SOLUTION: An oily inkjet ink includes colored resin particles and a non-aqueous solvent. The colored resin particles include a pigment and a resin A. The resin A includes a structure a1 derived from (meth)acrylic resin, a structure a2 derived from urethane resin, and a nitrogen-containing cross-linking structure a3 that cross-links the structure a1 derived from (meth)acrylic resin and the structure a2 derived from urethane resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to an oil-based inkjet ink and a method for producing the same. [Background technology]

[0002] Inkjet recording, in which highly fluid inkjet ink is ejected as droplets from minute nozzles to record an image on a substrate placed opposite the nozzle, has rapidly become popular in recent years due to its low-noise, high-speed printing capabilities. Inks used in inkjet recording include aqueous inks containing water as the primary solvent, ultraviolet-curable inks (UV inks) containing a high content of polymerizable monomers as the primary component, and hot-melt inks (solid inks) containing a high content of wax as the primary component, as well as so-called non-aqueous inks containing a non-aqueous solvent as the primary solvent. Non-aqueous inks can be classified into solvent-based inks, which contain a volatile organic solvent as the primary solvent, and oil-based inks, which contain a low-volatility or non-volatile organic solvent as the primary solvent. Solvent inks dry on the substrate primarily through the evaporation of the organic solvent, whereas oil-based inks dry primarily through penetration into the substrate.

[0003] Patent Document 1 describes a colored resin particle dispersion containing colored resin particles, a basic dispersant, and a non-aqueous solvent, and the colored resin particles contain a colorant and a crosslinked solid resin, and an inkjet ink containing the same, and describes that the dispersion has excellent storage stability, and that precipitation after storage is suppressed in the ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-134854 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of an embodiment of the present disclosure is to provide an oil-based inkjet ink that can suppress the generation of foreign matter in the ink during long-term storage. [Means for solving the problem]

[0006] One embodiment of the present disclosure is an oil-based inkjet ink comprising colored resin particles and a non-aqueous solvent, the colored resin particles comprising a pigment and a resin A, the resin A comprising a structure a1 derived from a (meth)acrylic resin, a structure a2 derived from a urethane resin, and a nitrogen-containing crosslinked structure a3 that crosslinks the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin.

[0007] Another embodiment of the present disclosure is a method for producing an oil-based inkjet ink, comprising: preparing a water-in-oil emulsion containing an oil phase and an aqueous phase containing a (meth)acrylic resin, a urethane resin, a pigment, a nitrogen-containing crosslinking agent, and water; crosslinking the (meth)acrylic resin and the urethane resin in the water-in-oil emulsion; and removing water from the water-in-oil emulsion.

[0008] Another embodiment of the present disclosure is a method for producing an oil-based inkjet ink, comprising: dispersing a mixture containing a (meth)acrylic resin, a pigment, and water to prepare a resin composition; preparing an aqueous phase containing the resin composition, a urethane resin, and a nitrogen-containing crosslinking agent; preparing a water-in-oil emulsion containing the aqueous phase and an oil phase; crosslinking the (meth)acrylic resin and the urethane resin in the water-in-oil emulsion; and removing water from the water-in-oil emulsion. [Effects of the Invention]

[0009] According to an embodiment of the present disclosure, it is possible to provide an oil-based inkjet ink that can suppress the generation of foreign matter in the ink during long-term storage. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, several embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments and includes various forms.

[0011] According to one embodiment, there is provided an oil-based inkjet ink comprising colored resin particles and a non-aqueous solvent, wherein the colored resin particles comprise a pigment and a resin A, and the resin A comprises a structure a1 derived from a (meth)acrylic resin, a structure a2 derived from a urethane resin, and a nitrogen-containing bridged structure a3 that bridges the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin.

[0012] This oil-based inkjet ink can prevent the generation of foreign matter in the ink during long-term storage.

[0013] Hereinafter, oil-based inkjet inks will also be referred to as "ink" or "oil-based ink." In this disclosure, (meth)acrylic resin collectively refers to resins obtained by polymerizing acrylic acid, methacrylic acid, and derivatives thereof, either alone or in combination. (Meth)acrylic acid collectively refers to acrylic acid and methacrylic acid, and (meth)acrylic acid ester collectively refers to acrylic acid esters and methacrylic acid esters. In this disclosure, a nitrogen-containing crosslinked structure refers to a crosslinked structure containing a nitrogen atom in its structure, and a nitrogen-containing crosslinking agent refers to a crosslinking agent containing a nitrogen atom in its agent. In this disclosure, a dispersant used to disperse pigments when producing colored resin particles will be referred to as a pigment dispersant. In this disclosure, a dispersant used to disperse colored resin particles when producing oil-based inkjet inks will be referred to as a dispersant.

[0014] (Meth)acrylic resins are generally hard and tend to have poor adhesion to pigments. For this reason, if the resin particles in the ink contain (meth)acrylic resin, foreign matter may be generated in the ink when the ink is stored for a long period of time.

[0015] Without being bound by any particular theory, it is speculated that an ink containing colored resin particles containing a resin A containing a structure a1 derived from a (meth)acrylic resin, a structure a2 derived from a urethane resin, and a nitrogen-containing crosslinked structure a3 (hereinafter simply referred to as "nitrogen-containing crosslinked structure a3") that crosslinks the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin can suppress the generation of foreign matter in the ink even when stored for a long period of time, as described below.

[0016] In Resin A, due to crosslinking, in addition to Structure a1 derived from (meth)acrylic resin, Structure a2 derived from urethane resin is also included in the molecule, which gives Resin A the flexible and stretchy properties of urethane resin, improving the adhesion between the pigment and Resin A and suppressing the generation of foreign matter. Furthermore, Resin A contains a nitrogen-containing crosslinked structure a3 that crosslinks Structure a1 derived from the (meth)acrylic resin with Structure a2 derived from the urethane resin, and the crosslinking increases the molecular weight of Resin A, improving solvent resistance and making Resin A less likely to be removed from the pigment. These factors can also reduce the generation of foreign matter. Furthermore, when the nitrogen-containing crosslinked structure a3 is contained in the resin A, the nitrogen atoms of the nitrogen-containing crosslinked structure a3 form hydrogen bonds with functional groups on the pigment surface, making it easier for the structure to be adsorbed to the pigment, which can reduce the generation of foreign matter.

[0017] "Colored resin particles" The colored resin particles contain a pigment and a resin A.

[0018] "Pigment" Pigments can be used in the present invention, including organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, and dye lake pigments, as well as inorganic pigments such as carbon black and metal oxides. Examples of azo pigments include soluble azo lake pigments, insoluble azo pigments, and condensed azo pigments. Examples of phthalocyanine pigments include metal phthalocyanine pigments and metal-free phthalocyanine pigments. Examples of polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments, and diketopyrrolopyrroles (DPPs). Examples of carbon black include furnace carbon black, lamp black, acetylene black, and channel black. Examples of metal oxides include titanium oxide and zinc oxide. These pigments can be used alone or in combination.

[0019] From the viewpoint of storage stability and ejection stability, the average particle size of the pigment is preferably 300 nm or less, and more preferably 200 nm or less. For example, the average particle size of the pigment may be 50 to 300 nm, or 100 to 200 nm.

[0020] For example, when an oil-based ink is produced using a method that uses a water-in-oil (W / O) emulsion and drying it in oil, the pigment is preferably used in the form of an aqueous dispersion in which it is dispersed in water. The pigment may be a self-dispersing pigment, in which a water-solubilizing group such as a carboxyl group, a carbonyl group, a hydroxyl group, or a sulfo group is bonded to the pigment surface, thereby dispersing the pigment itself in water. For example, an aqueous dispersion of a self-dispersing pigment can be preferably used. Alternatively, it is also preferable to disperse the pigment in water using, for example, a pigment dispersant. Examples of pigment dispersants that are preferably used include (meth)acrylic resins with pigment dispersibility and water-soluble nonionic pigment dispersants, as described below. When an aqueous dispersion is used, the water contained in the aqueous dispersion is preferably removed during the ink production process.

[0021] The pigment may be present in an amount of 10 to 90% by mass, 30 to 80% by mass, or 50 to 70% by mass relative to the total amount of the colored resin particles. Within these ranges, the coloring properties and shape stability of the colored resin particles can be maintained more favorably. The pigment is typically present in an amount of 0.01 to 20% by mass relative to the total amount of the ink, and from the viewpoint of image quality, it is preferably present in an amount of 1 to 15% by mass, and more preferably present in an amount of 5 to 10% by mass.

[0022] "Resin A" Resin A contains a structure a1 derived from a (meth)acrylic resin, a structure a2 derived from a urethane resin, and a nitrogen-containing crosslinked structure a3 that crosslinks the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin.

[0023] Resin A may be a (meth)acrylic resin and a urethane resin crosslinked with a nitrogen-containing crosslinking agent. Resin A may be, for example, a (meth)acrylic resin and a urethane resin crosslinked intermolecularly and intramolecularly.

[0024] In the resin A, the structure a1 derived from the (meth)acrylic resin is crosslinked with the structure a2 derived from the urethane resin via the nitrogen-containing crosslinked structure a3.

[0025] The structure a1 derived from the (meth)acrylic resin preferably contains at least one selected from the group consisting of a nonionic polyoxyalkylene chain, an acidic group, a pigment affinity group, and an alkyl group. The nonionic polyoxyalkylene chain, the acidic group, the pigment affinity group, and the alkyl group will be described in detail in the description of the (meth)acrylic resin below. The structure a1 derived from the (meth)acrylic resin may contain, for example, a nonionic polyoxyalkylene chain.

[0026] The (meth)acrylic resin that forms the structure a1 derived from the (meth)acrylic resin will be described.

[0027] The (meth)acrylic resin is preferably an oil-insoluble (meth)acrylic resin. This suppresses the elution of resin components from the colored resin particles in the oil-based ink, making it possible to more fully maintain the dispersion performance of the colored resin particles. Furthermore, suppressing the elution of resin components makes it possible to further suppress an increase in the viscosity of the oil-based ink. Furthermore, the oil-insolubility of the (meth)acrylic resin enhances solvent releasability when the oil-based ink lands on a substrate, improving image properties such as image density, strike-through, and sharpness.

[0028] Specifically, the (meth)acrylic resin is preferably oil-insoluble in the non-aqueous solvent contained in the oil-based ink. For example, at 23° C., the amount of the (meth)acrylic resin that can be dissolved in 100 g of the non-aqueous solvent contained in the oil-based ink is preferably 3 g / 100 g or less, 1 g / 100 g or less, or 0.5 g / 100 g or less.

[0029] The (meth)acrylic resin is preferably a water-soluble (meth)acrylic resin. As will be described later, when an oil-based ink is produced by a method using a water-in-oil (W / O) emulsion drying method in oil, it is preferable to use a water-soluble (meth)acrylic resin as the (meth)acrylic resin.

[0030] The main chain of the (meth)acrylic resin is not particularly limited. For example, the main chain of the (meth)acrylic resin may be obtained by polymerizing acrylic acid, methacrylic acid, and derivatives thereof, either alone or in combination of two or more. For example, the (meth)acrylic resin may contain acrylic acid units, methacrylic acid units, acrylate units, and methacrylate units, either alone or in combination of two or more.

[0031] The (meth)acrylic resin preferably has a functional group capable of reacting with a crosslinking agent (hereinafter also referred to as a "crosslinking reactive group"). The (meth)acrylic resin preferably contains, for example, the crosslinking reactive group and at least one selected from the group consisting of a nonionic polyoxyalkylene chain, an acidic group, a pigment affinity group, and an alkyl group.

[0032] When the (meth)acrylic resin contains a nonionic polyoxyalkylene chain, the balance between the acid value of the (meth)acrylic resin and its stability in the ink can be improved. When the (meth)acrylic resin contains a pigment affinity group, the miscibility and adhesion between the pigment and resin A in the colored resin particles is improved, and the dispersion stability and shape stability of the colored resin particles can be improved. Furthermore, in the production process of the colored resin particles, the (meth)acrylic resin having the pigment affinity group also functions as a pigment dispersant, improving pigment dispersibility in the aqueous phase and allowing colored resin particles with better miscibility and adhesion to be obtained.

[0033] The (meth)acrylic resin preferably contains a unit having a crosslinking reactive group. The (meth)acrylic resin may contain, for example, a unit having a crosslinking reactive group and at least one selected from the group consisting of a unit having a nonionic polyoxyalkylene chain, a unit having an acidic group, a unit having a pigment affinity group, and a unit having an alkyl group. The (meth)acrylic resin may further contain other units.

[0034] The unit having a crosslinking reactive group may be a unit derived from a monomer having a crosslinking reactive group. The unit having a nonionic polyoxyalkylene group may be a unit derived from a monomer having a nonionic polyoxyalkylene chain. The unit having an acidic group may be a unit derived from a monomer having an acidic group. The unit having a pigment affinity group may be a unit derived from a monomer having a pigment affinity group. The unit having an alkyl group may be a unit derived from a monomer having an alkyl group.

[0035] The (meth)acrylic resin may be, for example, a polymer of a monomer having a crosslinking reactive group, or a polymer of a monomer mixture containing a monomer having a crosslinking reactive group.

[0036] The (meth)acrylic resin may be, for example, a polymer of a monomer mixture containing a monomer having a crosslinking reactive group and at least one selected from the group consisting of a monomer having a nonionic polyoxyalkylene chain, a monomer having an acidic group, a monomer having a pigment affinity group, and a monomer having an alkyl group, or may be a polymer of a monomer mixture further containing other monomers.

[0037] In the (meth)acrylic resin, examples of the crosslinking reactive group include a carboxy group, a hydroxy group, an amino group, a thiol group, a carbonyl group, etc., and the carboxy group is preferred. The (meth)acrylic resin may contain one type of crosslinking reactive group alone or two or more types in combination. For example, a carboxy group is also an acidic group, which will be described later. Units and monomers having these crosslinkable reactive groups that are also acidic groups will be described in detail in the description of units and monomers having an acidic group, which will be described later. The monomer having a crosslinkable reactive group may be, for example, a monomer having a carboxy group. Specific examples of monomers having a carboxy group include, for example, examples of monomers having a carboxy group among the examples of monomers having an acidic group, which will be described later. In the polymerization of the (meth)acrylic resin, the monomer having a crosslinking reactive group may be used alone or in combination of two or more.

[0038] In the (meth)acrylic resin, the nonionic polyoxyalkylene chain may be contained, for example, in a side chain relative to the main chain of the (meth)acrylic resin. In the nonionic polyoxyalkylene chain, the number of moles of alkylene oxide (AO) added is not particularly limited, but is preferably 2 to 50, more preferably 2 to 30, and even more preferably 6 to 30. Within this range, the miscibility of the colored resin particles with the urethane resin is improved, the component uniformity of the colored resin particles is improved, and the storage stability and circulation stability of the ink can be improved. The alkylene oxide group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, even more preferably 2 to 4 carbon atoms, and still more preferably 2 or 3 carbon atoms. Examples of alkylene oxide groups include methylene oxide, ethylene oxide, propylene oxide, and butylene oxide. Among these, ethylene oxide, propylene oxide, and combinations thereof are preferred, with ethylene oxide being more preferred. Furthermore, one polyoxyalkylene chain may contain a combination of two or more alkylene oxide groups. Specifically, it is preferable that the copolymer has a polyoxyethylene chain, a polyoxypropylene chain, a polyoxyethylene polyoxypropylene chain, or the like, and from the viewpoint of miscibility with urethane resins, a polyoxyethylene chain is more preferable.

[0039] The polyoxyalkylene chain is preferably nonionic, and specifically, it is preferred that no ionic group is introduced. For example, the terminal of the polyoxyalkylene chain may be a hydroxy group, or a nonionic functional group may be introduced into the hydroxy group. Specifically, a hydrocarbon group may be introduced into the terminal hydroxy group of the polyoxyalkylene chain. The hydrocarbon group is preferably an alkyl group having 1 to 20 carbon atoms, and more preferably an alkyl group having 1 to 10 carbon atoms. The alkyl group having 1 to 10 carbon atoms is preferably a linear or branched alkyl group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, and more preferably 1 to 4 carbon atoms. Examples thereof include a methyl group, an ethyl group, a trimethyl group, a propyl group, an n-butyl group, a tert-butyl group, and a sec-butyl group, and preferably a methyl group or an ethyl group.

[0040] The monomer having a polyoxyalkylene chain may contain one polyoxyalkylene chain in one molecule, or may contain two or more polyoxyalkylene chains. The monomer having a polyoxyalkylene chain can be (meth)acrylic acid, (meth)acrylate, (meth)acrylamide, or a compound in which a polyoxyalkylene chain has been introduced into a derivative thereof, thereby providing a copolymer whose main chain is a (meth)acrylic skeleton. Examples include ethers of (meth)acrylic acid and polyalkylene glycol, (meth)acrylates modified with polyalkylene glycol, etc. Polyalkylene glycol-modified (meth)acrylates can be obtained, for example, by reacting polyalkylene glycol with (meth)acrylate into which a functional group that serves as a starting point for an isocyanate group or the like has been introduced.

[0041] The molecular weight of the monomer having a nonionic polyoxyalkylene chain is preferably 800 to 3,000, more preferably 1,000 to 2,000.

[0042] For example, the nonionic polyoxyalkylene chain may have a structure represented by the following general formula: 10 is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, n is an integer of 2 to 4, and m is an integer that satisfies the condition 2≦m≦30. * is a bonding position. *-O-(C n H 2n-1 O) m -R 10

[0043] Specific examples of monomers having a polyoxyalkylene chain include polyethylene glycol mono(meth)acrylate, methoxypolyethylene glycol mono(meth)acrylate, ethoxypolyethylene glycol mono(meth)acrylate, octoxypolyethylene glycol mono(meth)acrylate, stearoxypolyethylene glycol mono(meth)acrylate; polyethylene glycol-modified 2-isocyanatoethyl (meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol-propylene glycol-mono(meth)acrylate, polyethylene glycol-trimethylene glycol-mono(meth)acrylate; polyethylene glycol-allyl ether, methoxypolyethylene glycol-allyl ether, polyethylene glycol-polypropylene glycol-allyl ether, polypropylene glycol-allyl ether, polyethylene glycol-diallyl ether, polypropylene glycol-diallyl ether; and methoxypolyethylene glycol acrylamide.

[0044] Examples of commercially available products of monomers having a polyoxyalkylene chain include "ADEKA REASOAP ER-20" manufactured by ADEKA CORPORATION, "BLEMMER PME1000" manufactured by NOF CORPORATION, "NK ESTER M-230G", "M-90G", and "M-130G" manufactured by Shin-Nakamura Chemical Co., Ltd., "BLEMMER PME-4000", "BLEMMER PE-200", "BLEMMER PP-1000", and "BLEMMER PME-1000" manufactured by NOF CORPORATION, and "LIGHT ESTER 041MA" manufactured by Kyoeisha Chemical Co., Ltd. (all trade names).

[0045] In the (meth)acrylic resin, the unit having a polyoxyalkylene chain may be contained alone or in combination of two or more. In the polymerization of the (meth)acrylic resin, the above-mentioned monomers may be used alone or in combination of two or more.

[0046] In the (meth)acrylic resin, examples of the acidic group include a carboxy group, a sulfo group, and a phosphate group, with a carboxy group being preferred. The (meth)acrylic resin may contain one type of acidic group alone or two or more types in combination. For example, a carboxy group or the like may also function as a crosslinking reactive group.

[0047] The (meth)acrylic resin may be, for example, a (meth)acrylic resin containing a unit having an acidic group, a (meth)acrylic resin having an acidic group at its terminal, or a (meth)acrylic resin having a side chain having an acidic group. Preferably, the (meth)acrylic resin contains a unit having an acidic group. In this case, the acid value of the (meth)acrylic resin can be adjusted by adjusting the proportion of the unit having an acidic group.

[0048] In the (meth)acrylic resin, the acidic group may be directly bonded to a carbon atom of the carbon chain, or may be bonded to a carbon atom of the carbon chain via a linking group. Examples of monomers having an acidic group include methacrylic acid, acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid. Other examples include β-carboxyethyl (meth)acrylate, 4-[2-(methacryloyloxy)ethoxy]-4-oxo-2-butenoic acid, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl hexahydrophthalic acid, 2-acryloyloxypropyl phthalic acid, 2-acryloyloxypropyl hexahydrophthalic acid, methacryloyloxymethyl succinic acid, methacryloyloxyethyl succinic acid, methacryloyloxyethyl phthalic acid, methacryloyloxyethyl hexahydrophthalic acid, methacryloyloxypropyl phthalic acid, and methacryloyloxypropyl hexahydrophthalic acid. The monomer having an acidic group is preferably (meth)acrylic acid or a derivative thereof. In the polymerization of the (meth)acrylic resin, the monomer having an acidic group may be used alone or in combination of two or more.

[0049] In the (meth)acrylic resin, examples of the pigment-affinitive group include an aromatic ring-containing group and a β-dicarbonyl group.

[0050] In the aromatic ring-containing group, examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, or a substituted version thereof, with a benzene ring being preferred. Examples of the aromatic ring-containing group include a benzyl group, a phenyl group, and a phenylethyl group, with a benzyl group being preferred. The aromatic ring-containing group may be contained in the (meth)acrylic resin either alone or in combination of two or more.

[0051] The unit having an aromatic ring-containing group may be a unit derived from a monomer having an aromatic ring-containing group, such as benzyl (meth)acrylate, phenyl (meth)acrylate, phenylethyl (meth)acrylate, or phenoxyethyl methacrylate.

[0052] The (meth)acrylic resin may have an alkyl group. The (meth)acrylic resin may contain, for example, a unit having an alkyl group. The unit having an alkyl group may be, for example, a unit derived from a monomer having an alkyl group. When the unit having an alkyl group is contained in the (meth)acrylic resin, for example, in combination with a unit having an acidic group, the level of the acid value can be adjusted. The alkyl group may have 1 to 24 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms.

[0053] When producing oil-based inks using the drying-in-liquid method described below, a (meth)acrylic resin is used as a resin solution, so it is preferable to use a (meth)acrylic resin having an alkyl group with a low carbon number so as to exhibit hydrophilicity. In this case, preferred alkyl groups include, for example, methyl, ethyl, propyl, and trimethyl groups.

[0054] The unit having an alkyl group may be a unit derived from a monomer having an alkyl group. Examples of the monomer having an alkyl group include alkyl(meth)acrylates, and specific examples thereof include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, and trimethyl(meth)acrylate.

[0055] Further, specific examples of other monomers include styrene-based monomers such as styrene and α-methylstyrene, vinyl ether-based monomers such as vinyl acetate, vinyl benzoate, and butyl vinyl ether, maleic acid esters, fumaric acid esters, acrylonitrile, methacrylonitrile, α-olefins, etc. Units derived from these monomers may be contained in the (meth)acrylic resin.

[0056] The proportion of units having a nonionic polyoxyalkylene chain relative to all units of the (meth)acrylic resin may be, for example, 0 to 60 mass%, 1 to 60 mass%, 10 to 40 mass%, or 15 to 30 mass%, and the proportion of units having a nonionic polyoxyalkylene chain relative to all units of the (meth)acrylic resin may be, for example, 0 mass%, more than 0 mass%, 1 mass% or more, 10 mass% or more, or 15 mass% or more.

[0057] The units having an acidic group and / or units having a crosslinking reactive group may be, for example, 1 to 60 mass %, 10 to 60 mass %, 20 to 50 mass %, or 30 to 40 mass % relative to all units of the (meth)acrylic resin. The amount of units having a pigment affinity group relative to all units of the (meth)acrylic resin may be, for example, 10 to 80 mass %, 20 to 60 mass %, or 30 to 50 mass %, and it is particularly preferable that the amount of units having an aromatic ring-containing group is within this range. The amount of units having an alkyl group relative to the total amount of units in the (meth)acrylic resin may be 0 to 60 mass%, 0 to 40 mass%, 0 to 30 mass%, or 0 to 20 mass%, and it is particularly preferable that the total amount of units having an alkyl group having 1 to 4 carbon atoms is within this range.

[0058] The weight-average molecular weight (Mw) of the (meth)acrylic resin is preferably 10,000 to 200,000, more preferably 12,000 to 150,000, and even more preferably 30,000 to 150,000. In the present disclosure, the weight-average molecular weight is a value determined by the GPC method in terms of standard polystyrene. The same applies to the weight-average molecular weight of the resins described below.

[0059] The (meth)acrylic resin can be obtained by polymerizing a monomer mixture containing the above-mentioned monomers. During the polymerization reaction, a polymerization initiator, a chain transfer agent, a polymerization inhibitor, a polymerization accelerator, etc. can be added to the reaction system as appropriate to adjust the reaction rate. Examples of polymerization initiators that can be used include thermal polymerization initiators such as azo compounds such as AIBN (azobisisobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); and peroxides such as t-butylperoxybenzoate and t-butylperoxy-2-ethylhexanoate. Photopolymerization initiators that generate radicals upon irradiation with active energy rays can also be used. In addition, the molecular weight of the resulting (meth)acrylic resin can be adjusted by using a chain transfer agent in the reaction system. Preferred examples of the chain transfer agent include thiols such as n-butyl mercaptan, lauryl mercaptan, stearyl mercaptan, and cyclohexyl mercaptan.

[0060] The polymerization solvent (reaction solvent) used in solution polymerization is not particularly limited, but is preferably one that can dissolve the resin obtained by polymerization. When the proportion of monomers having acidic groups is high, it is preferable to carry out polymerization using a polar organic solvent. As the polar organic solvent, one or a combination of two or more of those described below for oil-based inks can be used. Furthermore, when producing an oil-based ink using the in-liquid drying method, it is preferable to use a low-boiling polar organic solvent as the polymerization solvent to facilitate solvent substitution in order to prepare an aqueous resin composition containing a (meth)acrylic resin. The low-boiling polar organic solvent may be a polar organic solvent with a boiling point of less than 100°C, 95°C or less, 90°C or less, 80°C or less, 70°C or less, or 60°C or less, such as ethanol, methyl ethyl ketone, and ethyl acetate.

[0061] The method for providing an aqueous resin composition containing a (meth)acrylic resin by solvent substitution from a composition containing a polymerization solvent and a (meth)acrylic resin is not particularly limited. For example, an appropriate amount of water is added to a composition containing a polymerization solvent and a (meth)acrylic resin, and a low-boiling polar organic solvent is further added and mixed, and then the low-boiling polar organic solvent is removed from this composition using an evaporator or the like, thereby obtaining an aqueous resin composition containing a (meth)acrylic resin.

[0062] When the (meth)acrylic resin contains acidic groups, the acidic groups may be neutralized to improve electrostatic repulsion. The acidic groups of the (meth)acrylic resin can be neutralized using a water-soluble basic compound as a neutralizing agent. From the viewpoint of the stability of the (meth)acrylic resin, monovalent water-soluble basic compounds are preferred. By neutralizing the acidic groups, monovalent water-soluble basic compounds exhibit an electrostatic repulsion effect and can further suppress pigment aggregation during the production of colored resin particles. Examples of water-soluble basic compounds include inorganic bases such as ammonium hydroxide, sodium hydroxide, and potassium hydroxide; and amines such as aminomethylpropanol, aminoethylpropanol, dimethylethanolamine, triethylamine, diethylethanolamine, dimethylaminopropanol, and triethanolamine. When preparing an aqueous resin composition containing a (meth)acrylic resin, a neutralizing agent may be added in the process of mixing a composition containing a (meth)acrylic resin and a polymerization solvent with water. The polymerization solvent can then be removed to obtain a (meth)acrylic resin with neutralized acidic groups.

[0063] The degree of neutralization of the acidic groups in the (meth)acrylic resin may be 20 to 90 mol%, 40 to 80 mol%, or 50 to 60 mol%. For example, the degree of neutralization of the carboxyl groups derived from the carboxyl group-containing monomer is preferably 40 mol% or more, more preferably 50 mol% or more. In the present disclosure, the "degree of neutralization of the acidic groups" refers to the ratio (mol%) of the molar equivalents of the water-soluble basic compound to the molar equivalents of the acidic groups before neutralization.

[0064] From the viewpoint of reducing changes in ink viscosity during long-term storage, the acid value of the (meth)acrylic resin is preferably 120 mgKOH / g or more, more preferably 150 mgKOH / g or more, even more preferably 160 mgKOH / g or more, and even more preferably 175 mgKOH / g or more. When the acid value of the (meth)acrylic resin is in this range, good image properties such as image density, strike-through, and sharpness can be achieved.

[0065] For example, when the ink is circulated in an ink path such as a tube by a pump in a printing device, from the viewpoint of maintaining the circulation stability of the ink, the acid value of the (meth)acrylic resin is preferably 400 mgKOH / g or less, more preferably 350 mgKOH / g or less, and may be, for example, 300 mgKOH / g or less, 280 mgKOH / g or less, 250 mgKOH / g or less, 200 mgKOH / g or less, or 190 mgKOH / g or less.

[0066] For example, the acid value of the (meth)acrylic resin may be 120 mgKOH / g or more and 400 mgKOH / g or less, 120 mgKOH / g or more and 350 mgKOH / g or less, 150 mgKOH / g or more and 300 mgKOH / g or less, 160 mgKOH / g or more and 280 mgKOH / g or less, 170 mgKOH / g or more and 250 mgKOH / g or less, 180 mgKOH / g or more and 200 mgKOH / g or less, or 180 mgKOH / g or more and 190 mgKOH / g or less.

[0067] Here, the acid value is expressed as the number of milligrams (mg) of potassium hydroxide required to neutralize the acidic components contained in 1 g of sample. The acid value of (meth)acrylic resin can be measured according to JIS K0070:1992 "Testing methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemical products."

[0068] In the resin A, the structure a2 derived from the urethane resin is crosslinked with the structure a1 derived from the (meth)acrylic resin via the nitrogen-containing crosslinked structure a3.

[0069] The urethane resin that forms the structure a2 derived from the urethane resin will be described. Urethane resin is a polymer containing urethane bonds. Generally, urethane resin can be synthesized by polyaddition of polyisocyanate and polyol. Examples of urethane resin include polyether-type urethane resins containing ether bonds in the main chain, polyester-type urethane resins containing ester bonds in the main chain, polycarbonate-type urethane resins containing carbonate bonds in the main chain, and polyester-ether-type urethane resins containing ester and ether bonds in the main chain.

[0070] The urethane resin may be a urethane urea resin having a urea bond in addition to a urethane bond. The urethane urea resin can be obtained, for example, by reacting a urethane prepolymer obtained from a material containing a polyol and a polyisocyanate with water and / or a polyamine compound, whereby the isocyanate groups of the urethane prepolymer react with the water and / or the polyamine compound to generate urea bonds and extend the chain.

[0071] The urethane resin may be any of acidic urethane resin, basic urethane resin, and nonionic urethane resin. The acidic urethane resin is a urethane resin having an acidic group, the basic urethane resin is a urethane resin having a basic group, and the nonionic urethane resin is a urethane resin having neither an acidic group nor a basic group. The acidic urethane resin is preferred. Examples of the acidic group include a carboxy group, a sulfo group, and a phosphate group.

[0072] The urethane resin is preferably an oil-insoluble urethane resin. This suppresses the elution of resin components from the colored resin particles in the oil-based ink, allowing the dispersion performance of the colored resin particles to be more fully maintained. Furthermore, suppressing the elution of resin components further suppresses an increase in the viscosity of the oil-based ink. Furthermore, the oil-insolubility of the urethane resin enhances solvent releasability when the oil-based ink lands on a substrate, thereby improving image quality such as image density, strike-through, and sharpness. Specifically, the urethane resin is preferably oil-insoluble in the non-aqueous solvent contained in the oil-based ink. For example, at 23°C, the amount of urethane resin that can be dissolved in 100 g of non-aqueous solvent contained in the oil-based ink is preferably 3 g / 100 g or less, 1 g / 100 g or less, or 0.5 g / 100 g or less.

[0073] The urethane resin is preferably a water-dispersible urethane resin. Being water-dispersible means that it has the property of being able to disperse in particulate form without dissolving in water. Examples include urethane resins having units with hydrophilic groups, urethane resins having hydrophilic groups at their terminals, urethane resins having side chains with hydrophilic groups, and urethane resins whose surfaces have been hydrophilically treated with surfactants or the like. Examples of hydrophilic groups include acidic groups, basic groups, nonionic groups, and combinations thereof. Water-dispersible urethane resins tend to be oil-insoluble in non-aqueous solvents contained in oil-based inks. When the (meth)acrylic resin has an acid value, it tends to be miscible with the (meth)acrylic resin, thereby improving the stability of the colored resin particles. Furthermore, as described below, when producing oil-based inks using a method that involves drying a water-in-oil (W / O) emulsion in oil, it is preferable to use a water-dispersible urethane resin as the urethane resin.

[0074] The urethane resin preferably has a crosslinkable group. Examples of the crosslinkable group include a carboxy group, a hydroxy group, an amino group, a thiol group, and a carbonyl group. A carboxy group is preferred. For example, a carboxy group can also function as a crosslinkable group.

[0075] The glass transition temperature (Tg) of the urethane resin coating may be −60 to 100° C., −50 to 50° C., or −40 to 10° C. In the present disclosure, the glass transition temperature is a value measured using a differential scanning calorimeter (DSC).

[0076] Examples of commercially available water-dispersible urethane resins include "Takelac WS-5984" (trade name), "Takelac WS-4022" (trade name), and "Takelac W-635" (trade name) manufactured by Mitsui Chemicals, Inc.; "Superflex 740" (trade name), "Superflex 150H" (trade name), "Superflex 620" (trade name), and "Superflex 500M" (trade name) manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; "U-coat UWS-145" (trade name) manufactured by Sanyo Chemical Industries, Ltd.; and "DAOTANTW-6493" (trade name) and "DAOTANTW-6490" (trade name) manufactured by Daicel-Allnex Co., Ltd. In the colored resin particles, the urethane resin may be used alone or in combination of two or more types.

[0077] Resin A contains a nitrogen-containing crosslinked structure a3 that crosslinks a structure a1 derived from a (meth)acrylic resin with a structure a2 derived from a urethane resin. This nitrogen-containing crosslinked structure a3 can be obtained using a nitrogen-containing crosslinking agent. The nitrogen-containing crosslinked structure a3 may be a structure derived from the nitrogen-containing crosslinking agent. The nitrogen-containing crosslinking agent is not particularly limited, but may be a nitrogen-containing crosslinking agent having a functional group reactive with the crosslinking reactive group of the resin. The nitrogen-containing crosslinking agent preferably has two or more of these reactive groups in one molecule.

[0078] Examples of nitrogen-containing crosslinking agents include carbodiimide compounds, aziridine compounds, nitrogen-containing metal chelate compounds, isocyanate compounds, melamine compounds, oxazoline compounds, urea compounds, polyamine compounds, polyethyleneimine compounds, and acrylamide compounds. These may be used alone or in combination of two or more. Preferred examples of nitrogen-containing crosslinking agents include carbodiimide compounds, oxazoline compounds, and combinations thereof.

[0079] It is preferable that the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the (meth)acrylic resin, and that the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the urethane resin to form a nitrogen-containing crosslinked structure a3 that crosslinks the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin. From the viewpoint of suppressing the generation of foreign matter during long-term storage, it is preferable that the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the (meth)acrylic resin or urethane resin to form a bond containing a nitrogen atom, and more preferably, the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the (meth)acrylic resin to form a bond containing a nitrogen atom, and the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the urethane resin to form a bond containing a nitrogen atom. From the viewpoint of suppressing the generation of foreign matter during long-term storage, in Resin A, the number of bonds containing nitrogen is preferably 10% or more, more preferably 20% or more, even more preferably 50% or more, even more preferably 70% or more, even more preferably 90% or more, even more preferably 95% or more, or even 100% of the total number of bonds between the reactive groups of the nitrogen-containing crosslinking agent and the crosslinking reactive groups of the (meth)acrylic resin or urethane resin. From this viewpoint, oxazoline-based compounds are more preferable as the nitrogen-containing crosslinking agent.

[0080] A carbodiimide compound has a carbodiimide group represented by "-N=C=N-" in the molecule. For example, cyclic carbodiimides, isocyanate-terminated carbodiimides, dicyclohexylcarbodiimide, diisopropylcarbodiimide, amino group-containing carbodiimides, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, Nt-butyl-N-ethylcarbodiimide, di-t-butylcarbodiimide, etc. can be used.

[0081] As commercially available carbodiimide compounds, for example, "V-02B," "V-04K," and "E-02" from the Carbodilite series manufactured by Nisshinbo Chemical Inc. can be used.

[0082] The aziridine compound is a compound having an aziridine group in the molecule, and it is preferable to use a polyfunctional aziridine compound having two or more aziridine groups in the molecule. For example, 2,2-bishydroxymethylbutanol-tris[3-(1-azirinidyl)propionate], 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane, etc. can be used. As commercially available aziridine compounds, for example, "PZ-33" and "DZ-22E" of the Chemitite series manufactured by Nippon Shokubai Co., Ltd. can be used.

[0083] As the metal chelate compound containing a nitrogen atom, for example, titanium diisopropoxybis(triethanolaminate) or the like can be used.

[0084] The isocyanate compound is a compound having an isocyanate group in the molecule, It is preferable to use a compound having two or more isocyanate groups in the molecule. For example, ethylene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenyl-methane diisocyanate, etc. can be used.

[0085] As the melamine-based compound, for example, methylated melamine compounds, butylated melamine compounds, etherified methylol melamine, benzoguanamine, methylol benzoguanamine, etherified methylol benzoguanamine, etc. can be used.

[0086] As the oxazoline-based compound, for example, a polymer having an oxazoline group is preferred. As the polymer having an oxazoline group, one obtained by polymerizing a monomer component containing an addition-polymerizable oxazoline as an essential component is preferred. Examples of the addition-polymerizable oxazoline group-containing monomer include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0087] Examples of commercially available oxazoline compounds that can be used include "Epocross WS-300, 500, 700," "Epocross K-1010, 1020, 1030E," "Epocross K-2010, 2020, 2030," and "Epocross K-2035E," all manufactured by Nippon Shokubai Co., Ltd.

[0088] From the viewpoint of suppressing the generation of foreign matter during long-term storage, the nitrogen-containing crosslinked structure a3 is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, based on the total amount of ink. The nitrogen-containing crosslinked structure a3 may be, for example, 2.0% by mass or less, or 1.0% by mass or less, based on the total amount of ink. The nitrogen-containing crosslinked structure a3 may be, for example, 0.05 to 2.0% by mass or 0.1 to 1.0% by mass, based on the total amount of ink. Here, the amount of the nitrogen-containing crosslinked structure a3 refers to the amount of the nitrogen-containing crosslinking agent that forms the nitrogen-containing crosslinked structure a3 by crosslinking the (meth)acrylic resin and the urethane resin. The same applies to the amount of the nitrogen-containing crosslinked structure hereinafter. From the viewpoint of suppressing the generation of foreign matter during long-term storage, the nitrogen-containing crosslinked structure a3 is, for example, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.5% by mass or more, based on the total amount of the colored resin particles. The nitrogen-containing crosslinked structure a3 may be, for example, 5.0% by mass or less, or 2.0% by mass or less, based on the total amount of the colored resin particles. The nitrogen-containing crosslinked structure a3 may be, for example, 0.1 to 5.0% by mass, 0.5 to 5.0% by mass, or 0.5 to 2.0% by mass, based on the total amount of the colored resin particles.

[0089] From the viewpoint of suppressing generation of foreign matter during long-term storage, the structure a1 derived from the (meth)acrylic resin may be, for example, 1% by mass or more, 3% by mass or more, or 10% by mass or more, based on the total amount of the colored resin particles. The structure a1 derived from the (meth)acrylic resin may be, for example, 50% by mass or less, 30% by mass or less, or 20% by mass or less, based on the total amount of the colored resin particles. The structure a1 derived from the (meth)acrylic resin may be, for example, 1 to 50% by mass, 3 to 30% by mass, or 10 to 20% by mass, based on the total amount of the colored resin particles.

[0090] From the viewpoint of suppressing generation of foreign matter during long-term storage, the structure a2 derived from the urethane resin may be, for example, 1% by mass or more, 10% by mass or more, 13% by mass or more, or 15% by mass or more, based on the total amount of the colored resin particles. The structure a2 derived from the urethane resin may be, for example, 70% by mass or less, or 50% by mass or less, based on the total amount of the colored resin particles. The structure a1 derived from the urethane resin may be, for example, 1 to 70% by mass, 10 to 70% by mass, 13 to 50% by mass, or 15 to 50% by mass, based on the total amount of the colored resin particles.

[0091] In the resin A, the amount of the structure a1 derived from the (meth)acrylic resin may be 10 to 90 mass%, 20 to 80 mass%, or 40 to 60 mass% relative to the total amount of the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin.

[0092] In the resin A, the structure a2 derived from the urethane resin may be 10 to 90 mass %, 20 to 80 mass %, or 40 to 60 mass % relative to the total amount of the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin.

[0093] In the resin A, the structure a2 derived from the urethane resin may be 20 to 300 parts by mass, 30 to 250 parts by mass, or 40 to 200 parts by mass per 100 parts by mass of the structure a1 derived from the (meth)acrylic resin.

[0094] In the resin A, the structure a1 derived from a (meth)acrylic resin may account for, for example, 10 to 80 mass %, 20 to 70 mass %, or 30 to 60 mass % relative to the total amount of the resin A. In the resin A, the structure a2 derived from a urethane resin may account for, for example, 10 to 80 mass %, 20 to 70 mass %, or 30 to 60 mass % relative to the total amount of the resin A. In the resin A, the nitrogen-containing crosslinked structure a3 may be present in an amount of, for example, 0.1 to 10 mass %, 0.5 to 5 mass %, or 1 to 3 mass % relative to the total mass of the resin A.

[0095] Resin A may contain other partial structures in addition to structure a1 derived from a (meth)acrylic resin, structure a2 derived from a urethane resin, and nitrogen-containing crosslinked structure a3 that crosslinks structure a1 derived from a (meth)acrylic resin and structure a2 derived from a urethane resin. The other partial structures may account for 1 to 50 mass %, 0.5 to 10 mass %, or 0.1 to 1 mass % of the total amount of resin A. Resin A does not necessarily contain the other partial structures. Resin A is preferably oil-insoluble in the non-aqueous solvent contained in the oil-based ink. For example, at 23°C, the amount of resin A that can dissolve in 100 g of non-aqueous solvent contained in the oil-based ink is preferably 3 g / 100 g or less, 1 g / 100 g or less, or 0.5 g / 100 g or less.

[0096] The colored resin particles may contain other resins in addition to resin A. Examples of other resins include polyester resins, vinyl chloride resins, and polyolefin resins. The amount of the other resins may be 1 to 50 mass %, 0.5 to 10 mass %, or 0.1 to 1 mass % relative to the total amount of resins contained in the colored resin particles. The other resins may not be added to the colored resin particles.

[0097] "Pigment dispersant" The colored resin particles may include a pigment dispersant. The pigment dispersant may be any of a basic dispersant, an acidic dispersant, an amphoteric dispersant, and a nonionic dispersant.

[0098] The pigment dispersant is preferably a water-soluble pigment dispersant. When an oil-based ink is produced by the submerged drying method described below, the use of a water-soluble pigment dispersant can improve dispersion stability of the pigment and resin in water. The pigment dispersant is preferably oil-insoluble in the non-aqueous solvent contained in the oil-based ink. For example, at 23° C., the amount of pigment dispersant that can be dissolved in 100 g of the non-aqueous solvent contained in the oil-based ink is preferably 3 g / 100 g or less, 1 g / 100 g or less, or 0.5 g / 100 g or less.

[0099] In one example, among (meth)acrylic resins, a (meth)acrylic resin exhibiting pigment dispersibility can be used as the pigment dispersant. For example, a (meth)acrylic resin having a pigment affinity group can be used as the pigment dispersant. The (meth)acrylic resin used as the pigment dispersant is preferably a water-soluble pigment dispersant.

[0100] In another example, a water-soluble nonionic pigment dispersant can be used as the pigment dispersant.

[0101] Water-soluble nonionic pigment dispersants are dispersants in which the hydrophilic group does not exhibit ionic dissociation. Examples of water-soluble nonionic pigment dispersants include ester-type water-soluble nonionic pigment dispersants, ether-type water-soluble nonionic pigment dispersants, and ester-ether-type water-soluble nonionic pigment dispersants, depending on the main bond type within the molecule.

[0102] Ester-type water-soluble nonionic pigment dispersants have a structure in which a polyhydric alcohol such as glycerin, sorbitol, or sucrose is ester-bonded to a fatty acid, and examples thereof include glycerin fatty acid esters, sorbitan fatty acid esters, and sucrose fatty acid esters.

[0103] Ether-type water-soluble nonionic pigment dispersants can be produced by adding ethylene oxide to raw materials with hydroxy groups, such as higher alcohols, alkylphenols, arylphenols, and arylalkylphenols, and examples include polyglycol ethers (e.g., aryl polyglycol ethers and alkyl polyglycol ethers). More specific examples include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene aryl phenyl ethers, polyoxyethylene aryl alkyl phenyl ethers, and aryl alkyl biphenylol polyglycol ethers.

[0104] Ester-ether type water-soluble nonionic pigment dispersants are compounds in which ethylene oxide is added to an ester of a polyhydric alcohol, such as glycerin or sorbitol, and a fatty acid. They contain both ester and ether bonds in the molecule. For example, fatty acid polyethylene glycol ether esters can be mentioned. Other water-soluble nonionic pigment dispersants that can be used include polycarboxylic acid polymers and polysiloxane copolymers. These water-soluble nonionic pigment dispersants can be used alone or in combination of two or more.

[0105] As the water-soluble nonionic pigment dispersant, fatty acid polyethylene glycol ether ester, polyglycol ether (for example, aryl polyglycol ether), and the like are more preferred.

[0106] In the colored resin particles, the pigment dispersant can be used alone or in combination of two or more. The amount of pigment dispersant in the colored resin particles can be appropriately set. For example, the pigment dispersant can be blended in a mass ratio of 0.1 to 10 parts by mass of pigment to 1 part by mass of pigment, preferably 0.1 to 5 parts by mass, and more preferably 1 to 3 parts by mass. The pigment dispersant may be, for example, 1 to 30% by mass, 5 to 25% by mass, or 10 to 20% by mass, based on the total amount of the colored resin particles. When a (meth)acrylic resin is used as the pigment dispersant, it is preferable that the total amount of the (meth)acrylic resin and other pigment dispersants satisfy these ranges.

[0107] Oil-based inkjet ink The oil-based inkjet ink may contain colored resin particles and a non-aqueous solvent. The oil-based inkjet ink may further contain a dispersant from the viewpoint of dispersion stability of the colored resin particles.

[0108] The amount of colored resin particles relative to the total amount of oil-based ink is preferably 1% by mass or more, 3% by mass or more, 5% by mass or more, or 10% by mass or more. This allows for more sufficient image density in printed matter. Even when the colored resin particles of the present disclosure are contained in ink, the ink has good storage stability and circulation stability, so it is possible to contain a larger amount of colored resin particles in the ink. The amount of colored resin particles relative to the total amount of oil-based ink is preferably 40% by mass or less, 30% by mass or less, 20% by mass or less, or 18% by mass or less. This allows the solid content of the ink to be within an appropriate range, making it possible to more appropriately maintain the ink viscosity, etc. Since the colored resin particles of the embodiment of the present disclosure can contribute to the image density of printed matter, it is possible to obtain sufficient image density of printed matter even if the amount of colored resin particles is reduced. For example, the amount of colored resin particles relative to the total amount of oil-based ink may be 1 to 40% by mass, 3 to 30% by mass, 5 to 20% by mass, or 10 to 18% by mass.

[0109] From the viewpoint of image quality of printed matter, the average particle diameter of the colored resin particles is preferably 100 nm or more, more preferably 150 nm or more, and even more preferably 200 nm or more. On the other hand, from the viewpoint of storage stability and circulation stability of the ink, the average particle diameter of the colored resin particles is preferably 400 nm or less, more preferably 350 nm or less, and even more preferably 300 nm or less. For example, the average particle diameter of the colored resin particles may be 100 to 400 nm, 150 to 350 nm, or 200 to 300 nm.

[0110] In the present disclosure, the particle diameter (D50) of the colored resin particles is a volume-based median diameter measured by a laser diffraction / scattering method, and can be measured using, for example, a laser diffraction / scattering particle size distribution analyzer "Partica LA-950 (manufactured by Horiba, Ltd.)" manufactured by Horiba, Ltd.

[0111] "Dispersant" The dispersant for dispersing the colored resin particles is not particularly limited as long as it can be blended into the oil-based ink. From the viewpoint of stability in the oil-based ink, the dispersant preferably exhibits solubility in the non-aqueous solvent contained in the oil-based ink, and more preferably dissolves uniformly without separating into two phases with the non-aqueous solvent. From this viewpoint, the dispersant is preferably a polymer compound.

[0112] The dispersant may be any of a basic dispersant, an acidic dispersant, and a nonionic dispersant, but is preferably a basic dispersant. A basic dispersant is a dispersant having a basic group. Since the colored resin particles are obtained using a (meth)acrylic resin having an acid value, the use of a basic dispersant can further contribute to the stability of the oil-based ink.

[0113] Examples of basic groups include amino groups, amido groups, imino groups, imido groups; and nitrogen-containing heterocyclic groups such as pyrrolidone groups, pyridine groups, and morpholino groups. Examples of amino groups include unsubstituted amino groups and substituted amino groups such as monoalkylamino groups or dialkylamino groups (e.g., dimethylamino groups). Substituents such as alkyl groups may be further substituted with hydroxyl groups, aryl groups, and other substituents. Examples of amido groups include unsubstituted amido groups and substituted amido groups such as monoalkylamido groups or dialkylamido groups (e.g., dimethylamido groups). Substituents such as alkyl groups may be further substituted with hydroxyl groups, aryl groups, and other substituents. The basic dispersant may contain one basic group alone or two or more basic groups in combination.

[0114] The basic dispersant may be, for example, a polymer compound having a hydrocarbon group having 6 or more carbon atoms, or a hydrocarbon group having 6 or more carbon atoms and having a substituent such as a hydroxy group or an aryl group, and a basic group.

[0115] The basic dispersant may be, for example, a basic dispersant having an alkanolamine structure. The basic dispersant having an alkanolamine structure provides acid-base interaction at the particle interface with the colored resin particles and also provides hydrogen bonding. This makes the basic dispersant having an alkanolamine structure more easily adsorbed onto the colored resin particles containing resin A, contributing to the dispersion stability of the colored resin particles and improving the storage stability of the oil-based ink.

[0116] The alkanolamine structure may be, for example, a structure represented by the following formula (1): In this case, the alkanolamine structure may be a monoalkanolamine structure or a dialkanolamine structure, but is preferably a dialkanolamine structure.

[0117] [ka]

[0118] In formula (1), R 1 R may be a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkylene oxide group having 1 to 4 carbon atoms, or a hydroxypolyalkylene oxide group having 1 to 4 carbon atoms. 2 may be an alkyl group having 1 to 10 carbon atoms, an ether bond-containing group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an arylalkyl group having 7 to 10 carbon atoms. n is 1 or 2. When n=2, R 1 The groups represented by the following formula may be the same or different. * indicates a bonding site to another structure.

[0119] R 1 is preferably a hydroxyalkyl group having 1 to 4 carbon atoms, and may be, for example, a functional group in which a hydrogen atom of any of a methyl group, an ethyl group, a propyl group, a trimethylene group, an n-butyl group, an iso-butyl group, a tert-butyl group, or a sec-butyl group has been substituted with a hydroxy group. More preferably, it is a hydroxyalkyl group having 1 or 2 carbon atoms, and may be, for example, a hydroxymethyl group, a 1-hydroxyethyl group, or a 2-hydroxyethyl group, and even more preferably a 1-hydroxyethyl group.

[0120] R 2 is preferably an alkyl group having 1 to 10 carbon atoms, such as a methyl group, ethyl group, propyl group, trimethylene group, n-butyl group, iso-butyl group, tert-butyl group, sec-butyl group, pentyl group, isopentyl group, neopentyl group, hexyl group, heptyl group, octyl group, isooctyl group, 2-ethylhexyl group, nonyl group, isononyl group, decyl group, isodecyl group, etc. More preferably, it is an alkyl group having 1 to 8 or 1 to 4 carbon atoms, and even more preferably, it is a methyl group or an ethyl group. R 2 The ether bond-containing group having 1 to 10 carbon atoms may be an alkyloxy group or a polyalkylene oxide group. R 2 The aryl group having 6 to 10 carbon atoms may have a substituent, and examples thereof include a phenyl group, a methylphenyl group, and an ethylphenyl group. R 2 As the arylalkyl group having 7 to 10 carbon atoms, it may have a substituent, and examples thereof include a phenylmethyl group and a phenylethyl group.

[0121] The alkanolamine structure is preferably a structure derived from N-methylethanolamine, N-ethylethanolamine, N-propylethanolamine, N-isopropylethanolamine, N-butylethanolamine, N-ethylbutanolamine, diethanolamine, diisopropanolamine, or the like.

[0122] The basic dispersant having an alkanolamine structure is preferably a polymeric compound, and is preferably a polymeric compound in which an alkanolamine is bonded to the main chain of a polymer such as a (meth)acrylic resin, a urethane resin, or an olefin resin by an addition reaction.

[0123] Specifically, the basic dispersant having an alkanolamine structure is preferably a polymer compound obtained by using a polymer having a unit having a reactive functional group reactive with an amino group and a unit having a lipophilic group, and bonding an amino alcohol to the reactive functional group by an addition reaction.

[0124] The amino alcohol used in the reaction may be a compound represented by the general formula (1) in which the binding site * is a hydrogen atom. More specific examples include N-methylethanolamine, N-ethylethanolamine, N-propylethanolamine, N-isopropylethanolamine, N-butylethanolamine, N-ethylbutanolamine, diethanolamine, and diisopropanolamine.

[0125] Examples of reactive functional groups reactive with amino groups include epoxy groups and β-dicarbonyl groups. The epoxy group may be a glycidyl group. Examples of β-dicarbonyl groups include β-diketone groups and β-keto acid ester groups. Examples of β-diketone groups include acetoacetyl groups and propionacetyl groups, and examples of β-keto acid ester groups include acetoacetoxy groups and propionacetoxy groups.

[0126] Examples of units having a lipophilic group include long-chain alkyl groups having 6 to 30, 8 to 22, or 10 to 20 carbon atoms. The basic dispersant having an alkanolamine structure may have other structural units, such as a unit having an aromatic ring. The aromatic ring exhibits affinity for colored resin particles, and is therefore expected to contribute more to dispersibility.

[0127] From the viewpoint of stability in oil-based inks, the basic dispersant having an alkanolamine structure preferably has a (meth)acrylic resin skeleton. For example, the main carbon chain may have an alkanolamine structure bonded to a reactive functional group via an ester bond. Alternatively, the main carbon chain may have another functional group, such as a lipophilic group, via an ester bond.

[0128] A basic dispersant having an alkanolamine structure can be obtained by polymerizing a monomer mixture. The monomer mixture will be described below. Examples of monomers having a reactive functional group reactive with an amino group include monomers having an epoxy group, a β-dicarbonyl group, etc. Specific examples of monomers having an epoxy group include glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, and 3,4-epoxycyclohexylmethyl (meth)acrylate. Furthermore, examples of monomers having a β-dicarbonyl group include acetoacetoxyalkyl (meth)acrylates such as acetoacetoxyethyl (meth)acrylate, acetoacetoxypropyl (meth)acrylate, and acetoacetoxybutyl (meth)acrylate; ethylene glycol monoacetoacetate mono(meth)acrylate, 2,3-di(acetoacetoxy)propyl (meth)acrylate, and 2,4-hexadione (meth)acrylate; allyl acetoacetate; vinyl acetoacetate; and acetoacetoxyalkyl (meth)acrylamides such as acetoacetoxyethyl (meth)acrylamide.

[0129] Examples of monomers having a lipophilic group include monomers having a long-chain alkyl group having 6 to 30 carbon atoms, and specific examples include hexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, isododecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, behenyl (meth)acrylate, and cyclohexyl (meth)acrylate.

[0130] With respect to all units of the basic dispersant having an alkanolamine structure, the unit having an alkanolamine structure is, for example, preferably from 1 to 50 mass %, more preferably from 2 to 40 mass %, and even more preferably from 2 to 30 mass %. The unit having a lipophilic group preferably accounts for 10 to 95 mass %, more preferably 20 to 90 mass %, and even more preferably 40 to 85 mass %, of all units of the basic dispersant having an alkanolamine structure. The other units are optionally contained in the total units of the basic dispersant having an alkanolamine structure, and are, for example, preferably 1 to 90 mass %, more preferably 5 to 50 mass %, and even more preferably 5 to 30 mass %. Each unit may be of one type alone or in combination of two or more types.

[0131] There is no particular limitation on the weight average molecular weight (Mw) of the basic dispersant having an alkanolamine structure, but from the viewpoint of ink viscosity, it is preferably 8,000 to 50,000.

[0132] Other examples of basic dispersants include basic dispersants that are linear or branched polymers having a basic group at the end of the main chain; basic dispersants that are polymers having a basic group and a plurality of side chains containing polyester moieties (hereinafter sometimes referred to as "basic comb dispersants"); etc. From the viewpoint of dispersion stability, basic comb dispersants are preferred.

[0133] In the basic comb dispersant, the polyester moiety in the side chain may be, for example, a structure derived from a hydroxycarboxylic acid or a mixture of a hydroxycarboxylic acid and a carboxylic acid not containing a hydroxy group, or a polymer containing a carbonyl-C3-C6-alkyleneoxy group unit. An example of a structure derived from a mixture of a hydroxycarboxylic acid and a carboxylic acid not containing a hydroxy group is a carbonyl-C17-alkyleneoxy group derived from a self-condensation product of 12-hydroxystearic acid. An example of the carbonyl-C3-C6-alkyleneoxy group is a carbonyl-C5-alkyleneoxy group, and for example, a polymer containing a carbonyl-C5-alkyleneoxy group unit can be obtained by ring-opening polymerization of ε-caprolactone. The degree of polymerization of the polyester portion is not particularly limited, and may be, for example, about 2 to 80.

[0134] The basic comb dispersant may contain basic groups in the main chain backbone, for example in the form of a polyamine backbone, and / or may contain basic groups attached to the main chain directly or via a linking group. When the basic comb dispersant contains a basic group bonded to the main chain directly or via a linking group, the basic comb dispersant may have one or more basic groups, but preferably has two or more basic groups. The type of basic group bonded to the main chain directly or via a linking group is not particularly limited, and for example, the basic groups described above can be used, with amino groups and morpholino groups being preferred, and amino groups being more preferred. Examples of basic comb-shaped dispersants include basic dispersants that are polymers having a main chain containing a polyamine skeleton and having a plurality of side chains containing polyester moieties, and basic dispersants that are polymers having basic groups bonded to the main chain directly or via a linking group and having a plurality of side chains containing polyester moieties.

[0135] As another example of the basic dispersant, a (meth)acrylic polymer dispersant having a basic group may be used. For example, a (meth)acrylic polymer dispersant having a unit having a basic group, a unit having a pigment affinity group, or a unit having a long-chain alkyl group having 6 to 30 carbon atoms may be used. Each of these units may be partly or entirely derived from a (meth)acrylate.

[0136] Examples of the basic group include an amino group, an amido group, an imino group, an imido group, and nitrogen-containing heterocyclic groups such as a pyrrolidone group, a pyridine group, and a morpholino group. Examples of the pigment-affinitive group include an aromatic ring-containing group and a β-dicarbonyl group. As the long-chain alkyl group having 6 to 30 carbon atoms, one or more of those described above for the basic dispersant having an alkanolamine structure may be selected and used.

[0137] The amount of units having a basic group relative to all units of the (meth)acrylic polymer dispersant having a basic group is preferably from 5 to 30 mass %, more preferably from 10 to 20 mass %. The unit having a pigment-affinitive group preferably accounts for 5 to 30 mass %, more preferably 10 to 20 mass %, of all units of the (meth)acrylic polymer dispersant having a basic group. The unit having a long-chain alkyl group having 6 to 30 carbon atoms is preferably 40 to 90 mass %, more preferably 50 to 90 mass %, and even more preferably 60 to 80 mass % or more of the total units of the (meth)acrylic polymer dispersant having a basic group. Each unit may be of one type alone or in combination of two or more types.

[0138] The weight average molecular weight (Mw) of the basic (meth)acrylic dispersant is not particularly limited, but is preferably 5,000 to 30,000 from the viewpoint of ink stability and ink viscosity.

[0139] Commercially available basic dispersants include, for example, Solsperse 11200, Solsperse 13940, Solsperse 16000, Solsperse 17000, Solsperse 18000, Solsperse 19000, Solsperse 24000, Solsperse 32000, Solsperse 38500, Solsperse 39000, Solsperse 71000, Solsperse 22000, and Solsperse 28000 (all trade names) manufactured by Lubrizol Japan Co., Ltd.; Disperse BYK109 (trade name) manufactured by BYK Japan Co., Ltd.; Acetamine 24 and Acetamine 86 (trade names) manufactured by Kao Corporation; Hypermer KD3 and Hypermer KD11 (trade names) manufactured by Croda Japan Co., Ltd.; Ajinomoto Fine-Techno Co., Ltd.; Antaron V-216 and Antaron V-220" (both trade names).

[0140] The oil-based ink may contain one dispersant alone or two or more dispersants in combination. The amount of dispersant can be adjusted as appropriate. The amount of dispersant is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to the total amount of ink. On the other hand, the amount of dispersant is preferably 10% by mass or less, more preferably 5% by mass or less, relative to the total amount of ink. For example, the amount of dispersant is preferably 0.1 to 10% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 5% by mass, relative to the total amount of ink. The amount of the dispersant may be 1 to 50 parts by mass, 5 to 40 parts by mass, or 10 to 30 parts by mass relative to 100 parts by mass of the colored resin particles.

[0141] "Non-aqueous solvent" As the non-aqueous solvent, either a non-polar organic solvent or a polar organic solvent can be used. These can be used alone or in combination. In the present disclosure, it is preferable to use a water-insoluble organic solvent that is not uniformly mixed with the same volume of water at 20°C under 1 atmosphere as the non-aqueous solvent.

[0142] Preferred examples of the non-polar organic solvent include petroleum hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents. Examples of aliphatic hydrocarbon solvents and alicyclic hydrocarbon solvents include non-aqueous solvents such as paraffins, isoparaffins, and naphthenes. Commercially available products include No. 0 Solvent L, No. 0 Solvent M, No. 0 Solvent H, Cactus normal paraffin N-10, Cactus normal paraffin N-11, Cactus normal paraffin N-12D, Cactus normal paraffin N-13, Cactus normal paraffin N-14, Cactus normal paraffin YHNP, Cactus normal paraffin SHNP, Isozol 300, Isozol 400, Teclain N16, Teclain N20, Teclain N22, AF Solvent No. 4, AF Solvent No. 5, AF Solvent No. 6, AF Solvent No. 7, Naphtesol 160, Naphtesol 200, and Naphtesol 220 (all trade names manufactured by ENEOS Corporation); Isopar G, Isopar H Preferred examples of the solvent include BHT, Isopar L, Isopar M, Exxol D40, Exxol D60, Exxol D80, Exxol D110, and Exxol D130 (all trade names manufactured by ExxonMobil Corporation); Moresco White P-60, Moresco White P-70, Moresco White P-80, Moresco White P-100, Moresco White P-120, Moresco White P-150, Moresco White P-200, Moresco White P-260, and Moresco White P-350P (all trade names manufactured by MORESCO Corporation). Preferred examples of the aromatic hydrocarbon solvent include Solvesso 100, Solvesso 150, Solvesso 200, and Solvesso 200ND (all trade names manufactured by ExxonMobil Corporation). The initial boiling point of the petroleum hydrocarbon solvent is preferably 100°C or higher, more preferably 150°C or higher, and even more preferably 200°C or higher. The initial boiling point of distillation can be measured in accordance with JIS K0066 "Testing method for distillation of chemical products."

[0143] Preferred examples of polar organic solvents include fatty acid ester solvents, higher alcohol solvents, and higher fatty acid solvents. For example, isononyl isononanoate, isodecyl isononanoate, isotridecyl isononanoate, methyl laurate, isopropyl laurate, hexyl laurate, isopropyl myristate, isopropyl palmitate, hexyl palmitate, isooctyl palmitate, isostearyl palmitate, methyl oleate, ethyl oleate, isopropyl oleate, butyl oleate, hexyl oleate, methyl linoleate, ethyl linoleate, isobutyl linoleate, butyl stearate, hexyl stearate, isooctyl stearate, isopropyl isostearate, 2-octyldecyl pivalate, soybean oil fatty acid methyl esters, soybean Examples of such solvents include fatty acid ester solvents having 13 or more carbon atoms per molecule, preferably 16 to 30, such as oil fatty acid isobutyl ester, tall oil fatty acid methyl ester, and tall oil fatty acid isobutyl ester; higher alcohol solvents having 6 or more carbon atoms per molecule, preferably 12 to 20, such as isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, oleyl alcohol, isoeicosyl alcohol, and decyltetradecanol; and higher fatty acid solvents having 12 or more carbon atoms per molecule, preferably 14 to 20, such as lauric acid, isomyristic acid, palmitic acid, isopalmitic acid, α-linolenic acid, linoleic acid, oleic acid, and isostearic acid. The boiling points of polar organic solvents such as fatty acid ester solvents, higher alcohol solvents, and higher fatty acid solvents are preferably 150°C or higher, more preferably 200°C or higher, and even more preferably 250°C or higher. Non-aqueous solvents having a boiling point of 250°C or higher also include non-aqueous solvents that do not exhibit a boiling point.

[0144] These non-aqueous solvents may be used alone or in combination of two or more types as long as they form a single phase. In addition, other organic solvents may be contained within the range that allows the non-aqueous solvent to form a single phase. The non-aqueous solvent may be, for example, 60 to 99 mass %, 65 to 97 mass %, 70 to 95 mass %, or 70 to 90 mass % relative to the total mass of the ink.

[0145] In addition to the above components, the oil-based ink may contain various additives. Examples of additives that can be added include nozzle clogging inhibitors, antioxidants, conductivity modifiers, viscosity modifiers, surface tension modifiers, and oxygen absorbers. The types of these additives are not particularly limited, and any additives commonly used in the relevant fields can be used.

[0146] The amount of water in the ink is preferably 1% by mass or less, more preferably less than 1% by mass, even more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, based on the total amount of the ink.

[0147] The suitable range of viscosity of oil-based inkjet inks varies depending on factors such as the nozzle diameter of the ejection head of the inkjet recording system and the ejection environment, but in general, the viscosity is preferably 5 to 30 mPa·s at 23°C, and more preferably 5 to 15 mPa·s.

[0148] "Method of manufacturing oil-based inkjet ink" Hereinafter, several embodiments of the method for producing an oil-based inkjet ink will be described. The oil-based inkjet ink is characterized by the components described above, regardless of the method for producing the ink.

[0149] Methods for producing oil-based inks containing colored resin particles are generally broadly divided into methods using chemical techniques and methods using physicochemical techniques. For example, chemical techniques include the interfacial polycondensation method, the interfacial reaction method (in situ polymerization method), and the liquid-cured coating method (orifice method). Physicochemical techniques include the liquid-drying method (water-drying method, oil-drying method), the coacervation method, and the melt-dispersion-cooling method. In producing the oil-based ink, the submerged drying method can be preferably used, and the submerged drying method of a water-in-oil (W / O) emulsion can be particularly preferably used.

[0150] An example of a method for producing an oil-based ink using the oil-drying method of a water-in-oil emulsion includes the steps of preparing a water-in-oil emulsion containing an oil phase and an aqueous phase containing a (meth)acrylic resin, a urethane resin, a pigment, a nitrogen-containing crosslinker, and water (hereinafter sometimes referred to as "step 1"); crosslinking the (meth)acrylic resin and the urethane resin in the water-in-oil emulsion (hereinafter sometimes referred to as "step 2"); and removing water from the water-in-oil emulsion (hereinafter sometimes referred to as "step 3"). The oil phase preferably contains a non-aqueous solvent. The oil phase may further contain an emulsifier. The emulsifier contained in the oil phase is preferably a lipophilic emulsifier. In this method, the emulsifier may be a dispersant for dispersing the colored resin particles described above. Step 3 may be performed simultaneously with step 2 by, for example, heating the water-in-oil emulsion under reduced pressure. This method, which uses the in-oil drying method of a water-in-oil emulsion, does not require the use of volatile organic solvents and is therefore safe. Furthermore, this method, which uses the in-oil drying method of a water-in-oil emulsion, makes it possible to produce inks with low viscosity. This is thought to be because this method makes it possible to produce inks containing colored resin particles with a small average particle size and a narrow particle size distribution.

[0151] The aqueous phase contains a pigment, a (meth)acrylic resin, a urethane resin, and a nitrogen-containing crosslinking agent, and while the aqueous phase forms droplets in the oil phase, the (meth)acrylic resin and the urethane resin are crosslinked by the nitrogen-containing crosslinking agent. When the water in the aqueous phase is removed, a resin A is formed, which includes a structure a1 derived from the (meth)acrylic resin, a structure a2 derived from the urethane resin, and a nitrogen-containing crosslinked structure a3 that crosslinks the structure a1 derived from the (meth)acrylic resin with the structure a2 derived from the urethane resin, and a mixture of the pigment and resin A is formed in the colored resin particles. In this way, an oil-based inkjet ink can be produced that can suppress the generation of foreign matter in the ink due to long-term storage.

[0152] From the viewpoint of stably incorporating the (meth)acrylic resin into the aqueous phase, the (meth)acrylic resin is preferably hydrophilic. The (meth)acrylic resin is more preferably a water-soluble (meth)acrylic resin. The (meth)acrylic resin may be added to the aqueous phase as an aqueous solution of the resin. In addition, from the viewpoint of stably incorporating the urethane resin into the aqueous phase, the urethane resin is preferably hydrophilic. The urethane resin is more preferably a water-dispersible urethane resin. The urethane resin may be added to the aqueous phase as a water dispersion of the resin.

[0153] The (meth)acrylic resin and urethane resin may be the same as those described in Structure a1 derived from the (meth)acrylic resin of Resin A, a component of the oil-based ink, and Structure a2 derived from the urethane resin. The non-aqueous solvent, pigment, and crosslinking agent may be those described as components of the oil-based ink. Examples of water that can be used include tap water, ion-exchanged water, and deionized water. The emulsifier that may be optionally included may be the same as those described as dispersants for dispersing colored resin particles.

[0154] The (meth)acrylic resin preferably has a nonionic polyoxyalkylene chain. In the submerged drying method, the miscibility of the (meth)acrylic resin with the urethane resin is improved, and the uniformity of the components in the resulting resin A and colored resin particles containing resin A can be further increased. When the urethane resin is an acidic urethane resin, the miscibility with the (meth)acrylic resin can be further improved.

[0155] When the (meth)acrylic resin has an acid value of 120 mgKOH / g or more, the change in viscosity during long-term storage can be further reduced, and the separation of the colored resin particles from the non-aqueous solvent on the substrate surface can be promoted, resulting in improved image quality of the printed matter.

[0156] A water-in-oil emulsion contains a (meth)acrylic resin in the aqueous phase, and if the (meth)acrylic resin has pigment dispersibility, the (meth)acrylic resin can be used as a pigment dispersant. In this case, it is not necessary to add any other pigment dispersant to the aqueous phase other than the (meth)acrylic resin.

[0157] In another example, the aqueous phase of the water-in-oil emulsion may contain, in addition to the (meth)acrylic resin, another pigment dispersant. The other pigment dispersant may be contained in the resulting colored resin particles. As the other pigment dispersant, those described as pigment dispersants for dispersing pigments can be used. Since the other pigment dispersant preferably contributes to pigment dispersibility in the aqueous phase, it may be a water-soluble nonionic pigment dispersant. Furthermore, the (meth)acrylic resin having pigment dispersibility may be used in combination with the other pigment dispersant.

[0158] The water phase of the water-in-oil emulsion may contain other resins described above as components that may be contained in the colored resin particles in the oil-based ink.

[0159] In a water-in-oil emulsion, the mass ratio of the aqueous phase (dispersed phase) to the oil phase (continuous phase) may be, for example, 10:90 to 90:10, 20:80 to 80:20, or 30:70 to 40:60.

[0160] The total amount of the pigment, (meth)acrylic resin, urethane resin, nitrogen-containing crosslinking agent, and optionally contained pigment dispersant may be 1 to 60 mass %, 10 to 50 mass %, or 20 to 40 mass % of the total aqueous phase. When other components are further contained, the total amount of nonvolatile components in the aqueous phase should preferably fall within this range.

[0161] The amount of emulsifier optionally contained in the oil phase may be 0.1 to 10% by mass, 0.5 to 8% by mass, or 1 to 5% by mass, or even about 3 to 4% by mass, based on the total amount of the water-in-oil emulsion. The amount of emulsifier may be 1 to 20 parts by mass, 5 to 15 parts by mass, or 8 to 12 parts by mass, based on 100 parts by mass of the aqueous phase. Within these ranges, a water-in-oil emulsion is formed, and the stability of the water-in-oil emulsion can be improved. Furthermore, by using the above-mentioned dispersant for dispersing the colored resin particles as the emulsifier in the oil-based ink obtained after removing the water, the amount of dispersant relative to the colored resin particles is appropriate, thereby improving the storage stability of the ink.

[0162] In step 1, the water-in-oil emulsion can be produced, for example, by mixing and emulsifying the above-mentioned water phase and oil phase. It is preferable to prepare the aqueous phase and the oil phase separately in advance. Then, it is preferable to add the aqueous phase to the oil phase and emulsify it. The emulsification may be carried out, for example, using an ultrasonic homogenizer while adding the aqueous phase to the oil phase, or may be carried out after adding the aqueous phase to the oil phase.

[0163] A water-in-oil emulsion can be prepared by, for example, mixing an aqueous solution of a (meth)acrylic resin with an aqueous dispersion of a urethane resin to prepare an aqueous phase, adding this to the oil phase, and then emulsifying. Alternatively, a water-in-oil emulsion can be prepared by adding all the components at once and then emulsifying.

[0164] In step 2, it is preferable that the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the (meth)acrylic resin, and that the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the urethane resin to form a nitrogen-containing crosslinked structure a3 that crosslinks the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin. From the viewpoint of suppressing the generation of foreign matter in the ink during long-term storage, it is preferable that the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the (meth)acrylic resin or the urethane resin to form a bond containing a nitrogen atom, and it is more preferable that the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the (meth)acrylic resin to form a bond containing a nitrogen atom, and that the reactive group of the nitrogen-containing crosslinking agent reacts with the crosslinking reactive group of the urethane resin to form a bond containing a nitrogen atom. The method for crosslinking the (meth)acrylic resin and the urethane resin is not particularly limited. For example, a method of heating the water-in-oil emulsion or a method of irradiating it with light can be mentioned. When heating, step 3 can be carried out while carrying out step 2. The heating temperature may be, for example, the temperature described in step 3. Along with crosslinking between the (meth)acrylic resin and the urethane resin, crosslinking may also occur within the molecules of the (meth)acrylic resin and / or the urethane resin.

[0165] In step 3, the water in the water phase of the water-in-oil emulsion is removed. This is thought to result in colored resin particles containing the water-removed water phase components. Methods for removing water include, for example, reducing pressure and / or heating, or bubbling a gas into the liquid to promote evaporation, or a combination of these. The conditions for reducing pressure and / or heating can be such that water is removed but the non-aqueous solvent in the oil phase remains. For reducing pressure, an evaporator can be used, for example. The heating temperature is preferably 30°C or higher, more preferably 40 to 100°C, and even more preferably 60 to 90°C. When reducing pressure and / or heating, the above-mentioned step 2 can also be carried out while carrying out step 3. In step 3, the amount of water removed from the aqueous phase is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on the amount before removal.

[0166] According to one embodiment of a method for producing an oil-based inkjet ink, it is possible to provide a method including: dispersing a mixture containing a (meth)acrylic resin, a pigment, and water to prepare a resin composition; preparing an aqueous phase containing the resin composition, a urethane resin, and a nitrogen-containing crosslinking agent; preparing a water-in-oil emulsion containing an aqueous phase and an oil phase; crosslinking the (meth)acrylic resin and the urethane resin in the water-in-oil emulsion; and removing water from the water-in-oil emulsion.

[0167] In this manufacturing method, explanation of the parts common to the above explanation will be omitted. This production method includes dispersing a mixture containing a (meth)acrylic resin, a pigment, and water to prepare a resin composition (step 1a), preparing an aqueous phase containing the resin composition, a urethane resin, and a nitrogen-containing crosslinking agent (step 1b), and preparing a water-in-oil emulsion containing an aqueous phase and an oil phase (step 1c). This makes it possible to further increase the emulsion stability of the water-in-oil emulsion and further improve the dispersion stability of the (meth)acrylic resin, urethane resin, and pigment in the aqueous phase.

[0168] In step 1a, a mixture containing a (meth)acrylic resin and a pigment is dispersed in water, so that a resin composition with excellent pigment dispersibility can be obtained in advance. In step 1a, a (meth)acrylic resin having pigment dispersibility may be used, or a pigment dispersant may be additionally used, or these may be used in combination. As the pigment dispersant, the pigment dispersants described above for dispersing pigments may be used. Next, in step 1b, a urethane resin and a nitrogen-containing crosslinking agent are added to this resin composition, and an optional dispersion treatment is performed to obtain an aqueous phase. This allows for the production of an aqueous phase in which the pigment to which the (meth)acrylic resin is adsorbed and the urethane resin are mixed with good dispersibility. In step 1b, the resin composition may be mixed with a composition previously prepared by mixing the urethane resin, the nitrogen-containing crosslinking agent, and, if necessary, other components such as water. Next, in step 1c, the aqueous phase and the oil phase are mixed to obtain a water-in-oil emulsion, thereby obtaining emulsion stability of the oil phase and the aqueous phase, while obtaining dispersion stability of the (meth)acrylic resin, the urethane resin, and the pigment in the droplet-like aqueous phase. In step 1c, an emulsifier may be used. As the emulsifier, the dispersant for dispersing the colored resin particles described above can be used. In the resulting water-in-oil emulsion, the (meth)acrylic resin and the urethane resin are crosslinked by the nitrogen-containing crosslinking agent to form a structure a1 derived from the (meth)acrylic resin, a structure a2 derived from the urethane resin, and a crosslinked structure a3 that crosslinks these. Removal of water from the water-in-oil emulsion can further improve the miscibility and uniformity of the components in the colored resin particles.

[0169] "Printing method" The printing method using the oil-based inkjet ink is not particularly limited, and may be any method such as a piezoelectric method, an electrostatic method, a thermal method, etc. When an inkjet recording device is used, it is preferable to eject the ink according to this embodiment from an inkjet head based on a digital signal, and to cause the ejected ink droplets to adhere to a substrate.

[0170] In the present embodiment, the substrate is not particularly limited, and examples thereof include printing paper such as plain paper, coated paper, and special paper, cloth, inorganic sheet, film, OHP sheet, and adhesive sheet having an adhesive layer on the back surface of the substrate, etc. Among these, printing paper such as plain paper and coated paper can be preferably used from the viewpoint of ink permeability.

[0171] Here, plain paper refers to ordinary paper on which no ink-receiving layer or film layer is formed. Examples of plain paper include fine paper, medium-quality paper, PPC paper, wood paper, recycled paper, etc.

[0172] Furthermore, as the coated paper, inkjet coated paper such as matte paper, glossy paper, and semi-glossy paper, as well as so-called coated printing paper, can be preferably used. Here, coated printing paper refers to printing paper that has traditionally been used in letterpress printing, offset printing, gravure printing, and the like, and is printing paper in which a coating layer is provided on the surface of fine or medium-quality paper using a paint containing an inorganic pigment such as clay or calcium carbonate and a binder such as starch. Coated printing paper is classified into lightly coated paper, fine lightweight coated paper, medium lightweight coated paper, fine coated paper, medium coated paper, art paper, cast coated paper, and the like, depending on the amount of paint applied and the coating method.

[0173] Some embodiments of the present disclosure are set forth below.

[0174] <1> An oil-based inkjet ink comprising colored resin particles and a non-aqueous solvent, wherein the colored resin particles comprise a pigment and a resin A, and the resin A comprises a structure a1 derived from a (meth)acrylic resin, a structure a2 derived from a urethane resin, and a nitrogen-containing crosslinked structure a3 that crosslinks the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin. <2> The structure a1 derived from the (meth)acrylic resin is derived from a (meth)acrylic resin with an acid value of 120 mgKOH / g or more. <1> 1. An oil-based inkjet ink according to claim 1. <3> preparing a water-in-oil emulsion containing an oil phase and an aqueous phase containing a (meth)acrylic resin, a urethane resin, a pigment, a nitrogen-containing crosslinking agent, and water; crosslinking the (meth)acrylic resin and the urethane resin in the water-in-oil emulsion; and removing water from the water-in-oil emulsion. <4> preparing a resin composition by dispersing a mixture containing a (meth)acrylic resin, a pigment, and water; preparing an aqueous phase containing the resin composition, a urethane resin, and a nitrogen-containing crosslinking agent; preparing a water-in-oil emulsion comprising said aqueous phase and an oil phase; crosslinking the (meth)acrylic resin and the urethane resin in the water-in-oil emulsion; and removing water from the water-in-oil emulsion. [Example]

[0175] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. Unless otherwise specified, common components are the same throughout the following Examples and Comparative Examples. Unless otherwise specified, "%" indicates "% by mass."

[0176] <Ink materials> The materials of the inks in the examples and comparative examples are shown below.

[0177] Carbon black: "MOGUL L" (trade name), Cabot Specialty Chemicals. Copper phthalocyanine: "FASTGEN Blue LA5380" (product name), DIC Corporation.

[0178] Aqueous resin composition AC1 / (meth)acrylic resin AC1: Produced according to the following procedure. Aqueous resin composition AC2 / (meth)acrylic resin AC2: Produced according to the following procedure. Aqueous resin composition AC3 / (meth)acrylic resin AC3: Produced according to the following procedure. Aqueous resin composition AC4 / (meth)acrylic resin AC4: Produced according to the following procedure. Aqueous resin composition AC5 / (meth)acrylic resin AC5: Produced according to the following procedure. Aryl polyglycol ether: "Borchi Gen DFN" (trade name), Borchers (water-soluble, aryl alkyl biphenylol polyglycol ether, 100% active ingredient).

[0179] Urethane resin water dispersion PU1 / urethane resin PU1: "Takelac WS-5984" (product name), Mitsui Chemicals, Inc., active ingredient 40%. Urethane resin water dispersion PU2 / urethane resin PU2: "Superflex 740" (trade name), Daiichi Kogyo Seiyaku Co., Ltd., active ingredient 40%.

[0180] Crosslinker 1: "Epocross K-2035E" (trade name), manufactured by Nippon Shokubai Co., Ltd., active ingredient 40%, oxazoline compound. Crosslinker 2: "Epocross WS-700" (trade name), manufactured by Nippon Shokubai Co., Ltd., active ingredient 25%, oxazoline compound. Crosslinker 3: "Carbodilite E-02" (trade name), manufactured by Nisshinbo Chemical Inc., active ingredient 40%, carbodiimide compound. Crosslinker 4: "Denacol EX-512" (trade name), manufactured by Nagase ChemteX Corporation, 100% active ingredient, epoxy compound (does not contain nitrogen atoms).

[0181] Dispersant 1: Resin solution a-1 prepared according to the following procedure, active ingredient 50%, solvent is fatty acid ester solvent. Dispersant 2: "Solsperse 13940" (trade name), Lubrizol Japan Co., Ltd., active ingredient 40%, solvent is petroleum-based solvent. Fatty acid ester solvent: isotridecyl isononanoate, Kokyu Alcohol Kogyo Co., Ltd. Petroleum-based hydrocarbon solvent: "Isopar M" (trade name), ExxonMobil Corporation.

[0182] <Synthesis of resin solution a-1> 87.5 g of isotridecyl isononanoate (manufactured by Kao Corporation) was charged into a 300 ml four-necked flask, and nitrogen gas was bubbled through while stirring, and the temperature was raised to 110°C. Next, while maintaining the temperature at 110°C, a mixture of 16.5 g of isotridecyl isononanoate and 4 g of peroctyl O (t-hexyl peroxy 2-ethylhexanoate (manufactured by NOF Corporation)) was added to 100.0 g of the monomer mixture having the composition shown below, and the resulting mixture was added dropwise over 3 hours. Thereafter, the mixture was stirred for 2 hours while maintaining the temperature at 110°C to obtain a resin solution a having an active ingredient content of 50% by mass.

[0183] (Formulation of monomer mixture) Stearyl methacrylate: 40 parts by mass. 2-Ethylhexyl methacrylate: 30 parts by mass. Glycidyl methacrylate: 30 parts by mass. Total: 100 parts by mass.

[0184] Stearyl methacrylate and 2-ethylhexyl methacrylate are available from Tokyo Chemical Industry Co., Ltd., and glycidyl methacrylate is available from NOF Corporation.

[0185] 200 g of the resin solution a was charged into a 500 ml four-necked flask, nitrogen gas was bubbled through, and the temperature was raised to 110°C while stirring. 12 g of diisopropanolamine (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and after reacting at 110°C for 2 hours, 12 g of isotridecyl isononanoate was added to obtain a resin solution a-1 having a solid content of 50% by mass.

[0186] <Synthesis of AC1 to AC5> Table 1 shows the formulation of the monomer mixture. The amount of each component is shown in parts by mass. 39.2 g of methyl ethyl ketone and 19.6 g of ethanol were placed in a 500 ml four-neck flask and heated to 65°C while aerating with nitrogen gas and stirring. A monomer composition was prepared by adding 9.8 g of methyl ethyl ketone and 4.9 g of ethanol to 30.0 g of the monomer mixture mixed in the proportions shown in Table 1. 1.5 g of V-65 (2,2'-azobis(2,4-dimethylvaleronitrile)) was added to the flask, and then the monomer composition was added dropwise over 3 hours while maintaining the temperature at 65°C. After the dropwise addition, the mixture was aged at 70°C for 3 hours to obtain colorless, transparent resin compositions No. 1 to No. 5 containing 30% active ingredient.

[0187] The upper part of Table 2 shows the formulation of the aqueous resin composition before solvent removal, and the lower part shows the formulation of the aqueous resin composition after solvent removal. The amount of each component is shown in parts by mass. Resin compositions No. 1 to No. 5 obtained above were mixed with methyl ethyl ketone, ethanol, an aqueous sodium hydroxide solution, and ion-exchanged water as shown in the upper part of Table 2. Then, the methyl ethyl ketone and ethanol were evaporated using an evaporator to prepare 20% aqueous resin compositions of AC1 to AC5. The formulations after solvent removal are shown in the lower part of Table 2.

[0188] The ingredients used are as follows: Methacrylic acid (MAA), methyl methacrylate (methyl methacrylate: MMA), and benzyl methacrylate (benzyl methacrylate: BMA) are available from Tokyo Chemical Industry Co., Ltd.

[0189] Polyethylene glycol monomethacrylate: "Blenmer PE-200" (trade name), molar addition number approximately 4.5, manufactured by NOF Corporation. NaOH aqueous solution: 10% aqueous solution of NaOH.

[0190] <Preparation of oil-based ink> Table 3 shows the oil-based ink formulation before dehydration, and Table 4 shows the oil-based ink formulation after dehydration. The amount of each component is shown in parts by mass. The components of the aqueous phase (1) shown in Table 3 were mixed in the amounts shown in the table, and the pigment was thoroughly dispersed using a bead mill "Dyno Mill KDL-A" (manufactured by Shinmaru Enterprises Co., Ltd.) for a residence time of 12 minutes to obtain aqueous phase (1). The components of the aqueous phase (2) shown in Table 3 were mixed in the amounts shown in the table to obtain aqueous phase (2). The aqueous phase (1) was mixed with aqueous phase (2) to obtain an aqueous phase. A dispersant and a non-aqueous solvent were mixed in the amounts shown in the table to obtain an oil phase. While stirring the oil phase with a magnetic stirrer, the aqueous phase was added dropwise while irradiating the mixture with an ultrasonic homogenizer "Ultrasonic Processor VC-750" (manufactured by Sonics Corporation) for 10 minutes to obtain a water-in-oil (W / O) emulsion. The mixture was ice-cooled during ultrasonic irradiation. The resulting water-in-oil emulsion was placed in a water bath at 80°C under reduced pressure using an evaporator to remove water from the aqueous phase, yielding a colored resin particle dispersion. Heating under reduced pressure removed the water from the aqueous phase, and in Examples 1 to 14 and Comparative Examples 2 to 4, where a crosslinking agent was used, a crosslinking reaction occurred. This colored resin particle dispersion was used as an oil-based ink.

[0191] <Evaluation method>

[0192] "Viscosity change" Each ink was placed in a sealed container and stored in a thermostatic chamber at 70°C for 4 weeks. The ink viscosity before storage (initial viscosity value) and the ink viscosity after 4 weeks of storage (viscosity after 4 weeks) were measured, and the viscosity change rate was calculated using the following formula. The viscosity change was evaluated based on the obtained viscosity change rate according to the following criteria. The viscosity of the ink was measured at 23° C. using a rheometer MCR102 (manufactured by Anton Paar). Viscosity change rate = [(viscosity after 4 weeks x 100) / (initial viscosity)] - 100(%) A: Viscosity change rate is less than ±5%. B: Viscosity change rate is between ±5% and 10%.

[0193] "Foreign matter after storage" Each ink was placed in a sealed container and stored in a thermostatic chamber at 70°C for 4 weeks. After 4 weeks of storage, 1 ml of each ink was filtered through a 2 μm polycarbonate membrane filter, and the residue on the filter was observed under an optical microscope and evaluated according to the following criteria. A: No foreign matter. B: Traces of foreign matter present. C: Foreign object present.

[0194] [Table 1]

[0195] [Table 2]

[0196] [Table 3]

[0197] [Table 4]

[0198] As shown in Table 4, the oil-based inks of each Example showed excellent results in the evaluation of foreign matter after storage.

[0199] On the other hand, Comparative Example 1, in which no crosslinking agent was used in preparing the ink, Comparative Example 2, in which a crosslinking agent was used in preparing the ink but was not a nitrogen-containing crosslinking agent, Comparative Example 3, in which no (meth)acrylic resin was used in preparing the ink, and Comparative Example 4, in which no urethane resin was used in preparing the ink, all showed poor results in the evaluation of foreign matter after storage.

Claims

1. an oil-based inkjet ink comprising colored resin particles and a non-aqueous solvent, the colored resin particles comprising a pigment and a resin A, the resin A comprising a structure a1 derived from a (meth)acrylic resin, a structure a2 derived from a urethane resin, and a nitrogen-containing crosslinked structure a3 that crosslinks the structure a1 derived from the (meth)acrylic resin and the structure a2 derived from the urethane resin.

2. The oil-based inkjet ink according to claim 1 , wherein the structure a1 derived from the (meth)acrylic resin is derived from a (meth)acrylic resin having an acid value of 120 mgKOH / g or more.

3. preparing a water-in-oil emulsion containing an oil phase and an aqueous phase containing a (meth)acrylic resin, a urethane resin, a pigment, a nitrogen-containing crosslinking agent, and water; crosslinking the (meth)acrylic resin and the urethane resin in the water-in-oil emulsion; and removing water from the water-in-oil emulsion.

4. preparing a resin composition by dispersing a mixture containing a (meth)acrylic resin, a pigment, and water; preparing an aqueous phase containing the resin composition, a urethane resin, and a nitrogen-containing crosslinking agent; preparing a water-in-oil emulsion comprising said aqueous phase and an oil phase; crosslinking the (meth)acrylic resin and the urethane resin in the water-in-oil emulsion; and removing water from the water-in-oil emulsion.

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