Oily inkjet ink

Abstract

To provide an oily inkjet ink that achieves a superior balance between storage stability and the image density of a printed material.SOLUTION: An oily inkjet ink comprising colored resin particles, non-colored resin particles, and a non-aqueous solvent, wherein the average particle diameter of the colored resin particles is in the range of 150 nm to 350 nm, and the average particle diameter of the non-colored resin particles is larger than that of the colored resin particles and not more than 2.0 times the average particle diameter of the colored resin particles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to oil-based inkjet inks. [Background technology]

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

[0003] Oil-based inks dry better on the surface of a substrate than water-based inks, are less likely to curl the printing paper, and are therefore excellent in printability. Patent Document 1 discloses an oil-based ink that contains colored resin particles, a basic dispersant, and a non-aqueous solvent, and the colored resin particles contain a colorant and a (meth)acrylic resin specified by a predetermined unit, and aims to improve the fixability and color development of the ink on the substrate, as well as the storage stability of the ink. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-053069 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, oil-based inks dry mainly due to the penetration of low-volatility or non-volatile non-aqueous solvents into the substrate. Therefore, in oil-based inks, the colorant penetrates into the substrate together with the non-aqueous solvent, reducing the amount of colorant remaining on the substrate surface, which can cause a decrease in image density.

[0006] In Patent Document 1, in colored resin particles, the (meth)acrylic resin has units having phosphate groups and / or phosphate ester groups in addition to units having carboxy groups and units having aromatic rings, thereby improving the releasability of the colored resin particles from the solvent and achieving color development in printed matter. However, the oil-based ink described in Patent Document 1 does not have sufficient performance, particularly in terms of storage stability.

[0007] An object of the present disclosure is to provide an oil-based inkjet ink that has an excellent balance between storage stability and image density of printed matter. More specifically, an object of the present disclosure is to provide an oil-based inkjet ink that has excellent performance in at least one of storage stability and image density without sacrificing either of them. [Means for solving the problem]

[0008] One embodiment of the present disclosure relates to an oil-based inkjet ink comprising colored resin particles, non-colored resin particles, and a non-aqueous solvent, wherein the colored resin particles have an average particle size in the range of 150 nm to 350 nm, and the non-colored resin particles have an average particle size larger than the average particle size of the colored resin particles but not larger than 2.0 times the average particle size of the colored resin particles. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide an oil-based inkjet ink that has an excellent balance between storage stability and image density of printed matter. DETAILED DESCRIPTION OF THE INVENTION

[0010] Several embodiments of the present invention will be described in detail below, but the present disclosure is not limited to these embodiments.

[0011] According to one embodiment, there is provided an oil-based inkjet ink comprising colored resin particles, non-colored resin particles, and a non-aqueous solvent, wherein the colored resin particles have an average particle size in the range of 150 nm to 350 nm, and the non-colored resin particles have an average particle size larger than the average particle size of the colored resin particles but not larger than 2.0 times the average particle size of the colored resin particles.

[0012] This oil-based inkjet ink has an excellent balance between storage stability and image density of printed matter.

[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 and (meth)acrylic acid ester collectively refer to acrylic acid and methacrylic acid, respectively, and acrylic acid esters and methacrylic acid esters. In this disclosure, a dispersant for dispersing pigments will be referred to as a pigment dispersant. In this disclosure, a dispersant for dispersing resin particles will be referred to as a dispersant for resin particles.

[0014] In one embodiment of the present disclosure, the colored resin particles have an average particle diameter of 150 nm or more, thereby exhibiting excellent solvent removal properties on the substrate. As a result, penetration of the colored resin particles into the substrate is suppressed, and the oil-based ink is efficiently concentrated and thickened on the substrate surface, thereby increasing image density. Furthermore, an average particle diameter of 350 nm or less improves the color development efficiency of the colored resin particles, thereby increasing image density on the printed surface. Furthermore, by using non-colored resin particles with an average particle diameter larger than that of the colored resin particles in combination, these act as a filler, retaining the colored resin particles on the substrate surface, thereby increasing image density.

[0015] In one embodiment, an oil-based inkjet ink containing a colorant as colored resin particles composited with a resin exhibits superior storage stability compared to inks containing a colorant not composited with a resin. However, simply converting the colorant into colored resin particles is not sufficient for long-term storage. Specifically, the high specific gravity of the colored resin particles can cause sedimentation, creating a concentration gradient of the colored resin particles. In layers containing high concentrations of colored resin particles, the interaction between the colorants contained in the colored resin particles can cause viscosity changes. Furthermore, the process of creating a concentration gradient can lead to increased aggregation of colored resin particles and non-adherent resin particles, resulting in viscosity changes. In one embodiment, the colored resin particles have an average particle diameter of 350 nm or less, which suppresses sedimentation and prevents viscosity changes. Furthermore, it is believed that using non-colored resin particles in combination with colored resin particles prevents the colored resin particles from approaching each other, suppressing interactions between the colorants and preventing viscosity changes. In this case, by having the average particle diameter of the non-colored resin particles larger than that of the colored resin particles, the colored resin particles are prevented from approaching each other, thereby sufficiently suppressing the interaction between the colorants. Furthermore, since the colored resin particles containing colorants have a higher specific gravity and are more likely to settle than the non-colored resin particles, using non-colored resin particles with an average particle diameter larger than that of the colored resin particles can suppress the settling of the colored resin particles and the generation of a concentration gradient. Similarly, by having the average particle diameter of the non-colored resin particles be 2.0 times or less the average particle diameter of the colored resin particles, the settling of the non-colored resin particles and the generation of a concentration gradient can be suppressed, viscosity changes can be prevented, and excellent storage stability can be achieved.

[0016] The average particle size of the colored resin particles is preferably 160 nm or more, more preferably 200 nm or more, in order to provide an oil-based ink with better image density in printed matter, and is preferably 300 nm or less, more preferably 280 nm or less, in order to provide an oil-based ink with a better balance between image density in printed matter and storage stability.

[0017] In one embodiment, the average particle size of the colored resin particles is more preferably in the range of 200 to 280 nm.

[0018] In one embodiment, the average particle size of the non-colored resin particles is preferably in the range of 1.05 to 1.3 times the average particle size of the colored resin particles, in order to obtain an ink with an even better balance between image density and storage stability of printed matter.

[0019] The average particle size of the non-colored resin particles may be, for example, 180 nm or more, 200 nm or more, or 230 nm or more. It may also be 420 nm or less, 320 nm or less, or 280 nm or less. The average particle size of the non-colored resin particles may be, for example, in the range of 180 to 420 nm.

[0020] In one embodiment, the average particle diameter of the non-colored resin particles is 2.0 times or less the average particle diameter of the colored resin particles. By having the average particle diameter of the non-colored resin particles within this range, it is possible to obtain an excellent balance between the image density and storage stability of the printed matter without incorporating a large amount of non-colored resin particles, and therefore the amount of non-colored resin particles can be reduced, and the viscosity of the oil-based ink can be kept within an appropriate range for an inkjet ink.

[0021] In the present disclosure, the average particle diameters of the colored resin particles and the non-colored resin particles are arithmetic mean diameters on a volume basis measured by a laser diffraction / scattering method, for example, using a laser diffraction / scattering particle size distribution analyzer "Partica LA-950V2" manufactured by Horiba, Ltd.

[0022] The colored resin particles may contain a resin (hereinafter sometimes referred to as "resin A") and a colorant. The proportion of resin A in the colored resin particles may be 1 to 60 mass %, 5 to 50 mass %, or 10 to 40 mass %.

[0023] Specific examples of resin A include conjugated diene resins such as styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, and vinyl chloride-vinyl acetate copolymer; (meth)acrylic resins such as polymers of acrylic acid esters and methacrylic acid esters or copolymers of these with styrene or the like; vinyl resins such as ethylene-vinyl acetate copolymer; functional group-modified resins obtained by modifying these various resins with a monomer having a functional group such as a carboxy group; melamine resins; urea resins; urethane resins; polyester resins; polyolefin resins; silicone resins; polyvinyl butyral resins; and alkyd resins. Resin A may be used alone or in combination of two or more. Among these, urethane resins are preferred because of their low swelling in non-aqueous solvents, their excellent affinity when used as a paper substrate, and the resulting printed surface with high image density.

[0024] 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.

[0025] 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.

[0026] 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. Among them, the acidic urethane resin is preferable. Examples of the acidic group include a carboxy group, a sulfo group, and a phosphate group.

[0027] The glass transition temperature (Tg) of the urethane resin coating may be −60 to 100° C., 0 to 100° C., or 25 to 85° C. In the present disclosure, the glass transition temperature of the urethane resin is a value measured using a differential scanning calorimeter (DSC).

[0028] Resin A is preferably a water-dispersible resin. Being water-dispersible means that it has the property of being able to disperse in particulate form without dissolving in water. Examples of water-dispersible resins include resins having units with hydrophilic groups, resins having hydrophilic groups at their terminals, resins having side chains with hydrophilic groups, and 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 resins tend to be oil-insoluble in nonaqueous solvents contained in oil-based inks, thereby further enhancing the stability of colored resin particles. Furthermore, as described below, a water-dispersible resin is preferably used as resin A even when producing colored resin particles using a method that involves drying a water-in-oil (W / O) emulsion in oil.

[0029] Resin A is preferably oil-insoluble. Resin A being oil-insoluble suppresses elution of resin A from the colored resin particles in the oil-based ink, thereby maintaining the dispersion stability of the colored resin particles for a longer period of time and suppressing an increase in the viscosity of the oil-based ink. Furthermore, resin A exhibiting oil-insolubility enhances solvent releasability when the oil-based ink lands on a substrate, thereby enabling a higher image density. Specifically, resin A being oil-insoluble means that it has very low solubility in the non-aqueous solvent contained in the oil-based ink. Regarding the degree of oil-insolubility, for example, the amount of resin A that can dissolve in 100 g of non-aqueous solvent contained in the oil-based ink at 23°C may be 3 g or less, 1 g or less, or 0.5 g or less.

[0030] Among the urethane resins preferred as Resin A, commercially available water-dispersible urethane resins include, for example, the "Takelac" series manufactured by Mitsui Chemicals, Inc. ("Takelac WS-5984," "Takelac WS-4022," "Takelac W-635," etc., all trade names), the "Superflex" series manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. ("Superflex 740," "Superflex 150," "Superflex 150H," "Superflex 500M," "Superflex 620," "Superflex 870," etc., all trade names), the "U-Coat UWS-145" manufactured by Sanyo Chemical Industries, Ltd. (trade name), and the "DAOTAN" series manufactured by Daicel-Allnex Corporation ("DAOTAN TW-6490," "DAOTAN TW-6493," etc., all trade names).

[0031] The colored resin particles may contain a pigment, a dye, or a combination thereof as a colorant.

[0032] Examples of pigments include 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 diketopyrrolopyrrole (DPP). 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. One type of pigment may be used alone, or two or more types may be used in combination.

[0033] From the viewpoint of storage stability of the oil-based ink and ejection stability by inkjet printing, the average particle size of the pigment is preferably 300 nm or less, and more preferably 200 nm or less. The average particle size of the pigment may be, for example, in the range of 50 to 300 nm, or in the range of 100 to 200 nm.

[0034] When producing colored resin particles by the oil drying method of a water-in-oil (W / O) emulsion described below, the pigment is preferably in the form of an aqueous dispersion. In this case, a self-dispersing pigment may be used, 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, so that the pigment itself disperses in water. Alternatively, the pigment may be dispersed in water using a pigment dispersant described below. The water in the aqueous pigment dispersion is preferably removed during the ink production process.

[0035] Any dye commonly used in the art can be used. Among them, dyes that are insoluble or poorly soluble in the non-aqueous solvent contained in the ink are preferred from the viewpoint of reducing strike-through when the oil-based ink is printed on a substrate. Furthermore, when producing an oil-based ink by a method using a water-in-oil (W / O) emulsion drying method, it is preferred to use a dye that dissolves or disperses in water.

[0036] As the dye, water-soluble dyes and water-soluble dyes made water-soluble by reduction or the like can be preferably used from among basic dyes, acid dyes, direct dyes, soluble vat dyes, acid mordant dyes, mordant dyes, reactive dyes, vat dyes, sulfur dyes, etc. Also preferably used are disperse dyes such as azo-based, anthraquinone-based, azomethine-based, and nitro-based dyes. These may be used alone or in combination.

[0037] The content of the colorant in the colored resin particles may be, for example, in the range of 10 to 90% by mass, 30 to 80% by mass, or 50 to 70% by mass, in order to better maintain the color development and shape stability of the colored resin particles. The content of the colorant in the ink is usually in the range of 0.01 to 20% by mass, and may be in the range of 1 to 15% by mass from the viewpoint of image density.

[0038] The colored resin particles may contain a pigment dispersant in addition to the resin A and the colorant. In one embodiment, the colored resin particles contain a pigment dispersant in addition to the resin A and the pigment. The pigment dispersant may be any of a basic dispersant, an acidic dispersant, an amphoteric dispersant, and a nonionic dispersant. A preferred example of the pigment dispersant is a (meth)acrylic resin-type pigment dispersant.

[0039] The main chain of the (meth)acrylic resin-type pigment dispersant is not particularly limited. For example, the main chain of the (meth)acrylic resin dispersant 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-type pigment dispersant may contain acrylic acid units, methacrylic acid units, acrylate units, and methacrylate units, either alone or in combination of two or more.

[0040] The (meth)acrylic resin-type pigment dispersant preferably contains a nonionic polyoxyalkylene chain and an acidic group. This allows for a more satisfactory balance between the acid value of the (meth)acrylic resin-type pigment dispersant and its stability in the ink. The (meth)acrylic resin-type pigment dispersant preferably further contains a pigment-affinity group. This allows for sufficient miscibility and adhesion with the pigment in the colored resin particles, and more satisfactory dispersion stability and shape stability of the colored resin particles.

[0041] The (meth)acrylic resin type pigment dispersant may contain a unit having a nonionic polyoxyalkylene chain and a unit having an acidic group. The (meth)acrylic resin type pigment dispersant may further contain other units. The (meth)acrylic resin type pigment dispersant may be a polymer of a monomer mixture containing a monomer having a nonionic polyoxyalkylene chain and a monomer having an acidic group, or may be a polymer of a monomer mixture further containing other monomers. Examples of other units include units having a pigment affinity group. Examples of other monomers include monomers having a pigment affinity group. The units that constitute the (meth)acrylic resin type pigment dispersant are described below.

[0042] 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. 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 even more preferably 2 or 3 carbon atoms. Examples of the alkylene oxide group include a methylene oxide group, an ethylene oxide group, a propylene oxide group, and a butylene oxide group. Among these, an ethylene oxide group, a propylene oxide group, or a combination thereof is preferred, with an ethylene oxide group being more preferred. Furthermore, two or more types of alkylene oxide groups may be combined and contained in one polyoxyalkylene chain. Specifically, a polyoxyethylene chain, a polyoxypropylene chain, a polyoxyethylene-polyoxypropylene chain, etc. are preferred, and from the viewpoint of miscibility with resin A, a polyoxyethylene chain is more preferred.

[0043] The polyoxyalkylene chain is preferably nonionic, and specifically, it is preferable 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 hydroxy group at the terminal of the polyoxyalkylene chain. The hydrocarbon group is an alkyl group having 1 to 20 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms. The alkyl group having 1 to 10 carbon atoms is, for example, preferably an alkyl group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms, and is linear or branched. Examples of the alkyl group 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 the like, and a methyl group or an ethyl group is preferred.

[0044] The polyoxyalkylene chain-containing monomer may contain one polyoxyalkylene chain per molecule, or may contain two or more polyoxyalkylene chains. The polyoxyalkylene chain-containing monomer may be a compound in which a polyoxyalkylene chain has been introduced into (meth)acrylic acid, (meth)acrylate, (meth)acrylamide, or a derivative thereof. This makes it possible to provide a copolymer whose main chain is a (meth)acrylic skeleton. Examples of such a copolymer include an ether of (meth)acrylic acid and polyalkylene glycol, and a (meth)acrylate modified with polyalkylene glycol. A polyalkylene glycol-modified (meth)acrylate can be obtained, for example, by reacting a polyalkylene glycol with a (meth)acrylate to which a functional group serving as a starting point for an isocyanate group or the like has been introduced.

[0045] The molecular weight of the monomer having a nonionic polyoxyalkylene chain is preferably from 800 to 3,000, more preferably from 1,000 to 2,000.

[0046] For example, the nonionic polyoxyalkylene chain may have a structure represented by the following general formula: 1 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.

[0047] *-O-(C n H 2n-1 O) m -R 1 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.

[0048] Examples of commercially available products of monomers having a polyoxyalkylene chain include "ADEKA REASOAP ER-20" (trade name) manufactured by ADEKA CORPORATION, the "BLEMMER" series manufactured by NOF CORPORATION ("BLEMMER PME-1000," "BLEMMER PME-4000," "BLEMMER PE-200," "BLEMMER PP-1000," and the like, all of which are trade names), "NK ESTER M-230G" (trade name), "M-90G" (trade name), and "M-130G" (trade name) manufactured by Shin-Nakamura Chemical Co., Ltd., and "LIGHT ESTER 041MA" (trade name) manufactured by Kyoeisha Chemical Co., Ltd.

[0049] In the (meth)acrylic resin-type pigment dispersant, 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-type pigment dispersant, the above-mentioned monomers may be used alone or in combination of two or more.

[0050] The (meth)acrylic resin-type pigment dispersant may have a carboxy group, a sulfo group, a phosphate group, or the like as the acidic group, but preferably has a carboxy group. The acidic group may be contained in the (meth)acrylic resin-type pigment dispersant alone or in combination of two or more types.

[0051] The (meth)acrylic resin-type pigment dispersant may be 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, it is a (meth)acrylic resin containing a unit having an acidic group. In this case, the acid value of the (meth)acrylic resin-type pigment dispersant can be adjusted by changing the proportion of the unit having an acidic group.

[0052] In the (meth)acrylic resin-type pigment dispersant, the acidic group may be bonded directly 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 is preferably (meth)acrylic acid or a derivative thereof. In the polymerization of the (meth)acrylic resin-type pigment dispersant, the monomer may be used alone or in combination of two or more.

[0053] Examples of other units include units having a pigment affinity group and units having an alkyl group. When a unit having a pigment affinity group is contained in the (meth)acrylic resin-type pigment dispersant, the miscibility between the colorant, the (meth)acrylic resin-type pigment dispersant, and the resin A in the colored resin particles is improved, and better component uniformity can be obtained. Examples of the pigment affinity group include an aromatic ring-containing group and a β-dicarbonyl group.

[0054] 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-type pigment dispersant either alone or in combination of two or more.

[0055] 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.

[0056] By including a unit having an alkyl group in the (meth)acrylic resin-type pigment dispersant, the acid value can be adjusted by combining it with a unit having an acidic group. 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.

[0057] When producing oil-based inks using the drying-in-liquid method, a (meth)acrylic resin-type pigment dispersant is used as the resin solution, so it is preferable to use a (meth)acrylic resin-type pigment dispersant 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.

[0058] 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.

[0059] 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-type pigment dispersant.

[0060] The amount of units having a nonionic polyoxyalkylene chain relative to all units of the (meth)acrylic resin-type pigment dispersant may be 1 to 60 mass %, 10 to 40 mass %, or 15 to 30 mass %. Within these ranges, adjustment of the acid value of the (meth)acrylic resin-type pigment dispersant is simpler, while the miscibility of the colored resin particles with resin A is improved, the component uniformity of the colored resin particles is improved, and the storage stability of the ink can be improved.

[0061] The amount of units having an acidic group relative to the total amount of units in the (meth)acrylic resin-type pigment dispersant may be 10 to 60 mass%, 20 to 50 mass%, or 30 to 40 mass%, within these ranges, making it easier to adjust the acid value of the (meth)acrylic resin-type pigment dispersant.

[0062] The amount of units having a pigment affinity group relative to the total amount of units in the (meth)acrylic resin-type pigment dispersant may be 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.

[0063] The amount of units having an alkyl group relative to the total amount of units in the (meth)acrylic resin-type pigment dispersant may be 0 to 30% by mass, or 0 to 20% by mass, and it is particularly preferable that the total amount of units having an alkyl group with 1 to 4 carbon atoms is within this range.

[0064] The (meth)acrylic resin-type pigment dispersant can be produced, for example, by polymerizing a mixture of monomers in the presence of a polymerization initiator. During the polymerization reaction, a chain transfer agent, a polymerization inhibitor, etc. may be used. The polymerization reaction may also be carried out in a solvent.

[0065] Examples of the polymerization initiator include 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. The amount of the polymerization initiator added may be, for example, in the range of 0.5 to 10% by mass relative to the mass of the total amount of monomers.

[0066] The solvent used in the polymerization reaction is not particularly limited, and is preferably one that has excellent solubility for the monomer and the resulting (meth)acrylic resin-type pigment dispersant. The solvent may be used alone or in a mixture of two or more solvents. Examples of the solvent include alcohol solvents such as ethanol, ketone solvents such as methyl ethyl ketone, and ester solvents such as ethyl acetate. The amount of the solvent used is preferably in the range of 50 to 500% by mass relative to the total mass of the monomers.

[0067] The (meth)acrylic resin-type pigment dispersant preferably has an acid value, since this results in an oil-based ink with superior image density. The (meth)acrylic resin-type pigment dispersant having an acid value promotes separation of the colored resin particles from the non-aqueous solvent on the substrate surface, thereby further improving the image density of printed matter. The acid value of the (meth)acrylic resin-type pigment dispersant is preferably 50 mgKOH / g or more, more preferably 120 mgKOH / g or more, and particularly preferably 150 mgKOH / g or more. It may also be 400 mgKOH / g or less, 300 mgKOH / g or less, or 250 mgKOH / g or less. The acid value of the (meth)acrylic resin-type pigment dispersant may be, for example, in the range of 50 to 400 mgKOH / g. In one embodiment, the colored resin particles contain a pigment and a (meth)acrylic resin-type pigment dispersant having an acid value of 120 mgKOH / g or more.

[0068] In this disclosure, 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 a sample. The acid value of a (meth)acrylic resin-type pigment dispersant 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."

[0069] The weight-average molecular weight (Mw) of the (meth)acrylic resin-based pigment dispersant may be in the range of 10,000 to 200,000, or may be in the range of 30,000 to 150,000. In the present disclosure, the weight-average molecular weight of the (meth)acrylic resin-based pigment dispersant is a value determined using a GPC method and converted into standard polystyrene. The same applies to the weight-average molecular weight of the resins and the like described below.

[0070] The (meth)acrylic resin-type pigment dispersant is preferably oil-insoluble. This inhibits the elution of the (meth)acrylic resin-type pigment dispersant from the colored resin particles in the oil-based ink, thereby improving the dispersion stability of the colored resin particles and effectively suppressing an increase in the viscosity of the oil-based ink. Furthermore, the oil-insolubility of the (meth)acrylic resin-type pigment dispersant enhances solvent releasability when the oil-based ink lands on a printing substrate, thereby further improving image density. Specifically, the oil-insolubility of a (meth)acrylic resin-type pigment dispersant refers to an extremely low solubility in the non-aqueous solvent contained in the oil-based ink. The degree of oil-insolubility, for example, may be such that the amount of the (meth)acrylic resin-type pigment dispersant that can dissolve in 100 g of non-aqueous solvent contained in the oil-based ink at 23°C is 3 g or less, 1 g or less, or 0.5 g or less.

[0071] When producing colored resin particles by the oil drying method of a water-in-oil (W / O) emulsion described below, the (meth)acrylic resin-type pigment dispersant is preferably water-soluble. In this case, the (meth)acrylic resin-type pigment dispersant is preferably used as an aqueous solution by solvent substitution of water for the solvent used during the polymerization reaction. Examples of solvent substitution methods include adding an appropriate amount of water to a polymerization solvent solution of the (meth)acrylic resin-type pigment dispersant, optionally adding and mixing a low-boiling polar organic solvent, and then distilling off the polymerization solvent and the added polar organic solvent using an evaporator or the like.

[0072] When the (meth)acrylic resin-type pigment dispersant has acidic groups, a basic compound may be added to the aqueous solution as a neutralizing agent. Examples of 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. The amount of basic compound added may be adjusted so that the degree of neutralization of the acidic groups in the (meth)acrylic resin-type pigment dispersant is 20 to 90 mol%, 40 to 80 mol%, or 50 to 60 mol%. In the present disclosure, the "degree of neutralization of acidic groups" refers to the ratio (mol %) of the molar equivalents of the basic compound to the molar equivalents of the acidic groups before neutralization.

[0073] The proportion of the (meth)acrylic resin-type pigment dispersant relative to the total amount of pigment dispersant contained in the colored resin particles may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or even 100% by mass.

[0074] Examples of pigment dispersants other than the (meth)acrylic resin type pigment dispersants include, for example, ester type nonionic pigment dispersants, ether type nonionic pigment dispersants, ester-ether type nonionic pigment dispersants, polycarboxylic acid polymer type pigment dispersants, and polysiloxane copolymer type pigment dispersants.

[0075] Ester-type 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.

[0076] Ether-type nonionic pigment dispersants have a structure in which ethylene oxide is added to a raw material having a hydroxyl group, such as a higher alcohol, an alkylphenol, an arylphenol, or an arylalkylphenol, and examples thereof include polyglycol ethers (e.g., aryl polyglycol ethers, 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.

[0077] Ester-ether type nonionic pigment dispersants have a structure in which ethylene oxide is added to an ester of a polyhydric alcohol such as glycerin or sorbitol and a fatty acid, and have both ester and ether bonds in the molecule. Specific examples include fatty acid polyethylene glycol ether esters.

[0078] Among these, fatty acid polyethylene glycol ether esters, polyglycol ethers (for example, aryl polyglycol ethers), and the like are more preferred.

[0079] The ratio of pigment to pigment dispersant in the colored resin particles may be 0.1 to 10 parts by mass, 0.1 to 5 parts by mass, or 1 to 3 parts by mass per part by mass of pigment. The ratio of pigment dispersant in the colored resin particles may be 1 to 30% by mass, 5 to 25% by mass, or 10 to 20% by mass.

[0080] The method for producing colored resin particles is not particularly limited, and examples thereof include a method of producing a non-aqueous solvent dispersion of colored resin particles (hereinafter, sometimes referred to as a "colored resin particle dispersion"). Methods for producing colored resin particle dispersions are generally broadly divided into methods using chemical techniques and methods using physicochemical techniques. Examples of chemical techniques include interfacial polycondensation, interfacial reaction (in situ polymerization), and liquid-cured coating (orifice) techniques. Examples of physicochemical techniques include liquid-drying (water-drying, oil-drying), coacervation, and melt-disperse-cooling. Colored resin particle dispersions may be produced by the oil-drying method of a water-in-oil (W / O) emulsion. A method for producing a colored resin particle dispersion by the oil-drying method of a water-in-oil (W / O) emulsion will be described in detail below.

[0081] In the oil drying method of a water-in-oil (W / O) emulsion, for example, a water-in-oil emulsion is produced containing an aqueous phase containing resin A, a colorant, water, etc., and an oil phase containing a non-aqueous solvent, etc., and the water is then removed from the resulting water-in-oil emulsion to produce a colored resin particle dispersion. The colorant may be a pigment, and the aqueous phase may further contain a pigment dispersant. The oil phase may further contain an emulsifier, and the emulsifier may be a resin particle dispersant described below. In this method, as described above, it is preferable to use resin A and the pigment as an aqueous dispersion, and the pigment dispersant as an aqueous solution.

[0082] Water-in-oil emulsions can be produced, for example, by emulsifying a mixture of an aqueous phase and an oil phase using an ultrasonic homogenizer or the like. The aqueous phase and the oil phase may be mixed all at once, or in portions, or by adding the aqueous phase dropwise to the oil phase. The emulsification may be carried out after the entire amounts of the aqueous phase and the oil phase are mixed, or may be carried out after each portion is added, or by adding the aqueous phase dropwise to the oil phase, etc.

[0083] The proportion of components other than water in the aqueous phase is arbitrary, but may be in the range of 1 to 60% by mass from the viewpoint of production efficiency, etc. Furthermore, the content of a dispersant for resin particles optionally contained in the oil phase may be in the range of 0.1 to 10% by mass. The proportion of the aqueous phase to the oil phase is arbitrary, but may be in the range of 10:90 to 90:10 or 40:60 to 60:40 from the viewpoint of emulsification efficiency, etc.

[0084] Water can be removed from a water-in-oil emulsion by, for example, distilling off water under reduced pressure, heating, or reduced pressure and heating conditions, bubbling gas into the water-in-oil emulsion to promote evaporation of water, or a combination of these methods. The heating temperature is adjusted appropriately depending on the type of non-aqueous solvent in the oil phase, and may be, for example, 30°C or higher, 40 to 100°C, or 60 to 90°C. The amount of water removed may be 90% by mass or higher, 95% by mass or higher, or 99% by mass or higher, based on the total amount of water contained in the aqueous phase.

[0085] The non-aqueous solvent may be either a non-polar organic solvent or a polar organic solvent. Among non-aqueous solvents, 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.

[0086] Preferred examples of non-polar organic solvents 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 paraffinic, isoparaffinic, and naphthenic solvents, and examples of commercially available products thereof 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," and "Cactus Normal Paraffin N-14," all manufactured by ENEOS Corporation. 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," "Naphtesol 220"; ExxonMobil's "Isopah G" and "Isopah H" Examples of commercially available aromatic hydrocarbon solvents include "BHT," "Isopar L," "Isopar M," "Exsol D40," "Exsol D60," "Exsol D80," "Exsol D110," and "Exsol D130" manufactured by MORESCO Corporation; and "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." Examples of commercially available aromatic hydrocarbon solvents include "Solvesso 100," "Solvesso 150," "Solvesso 200," and "Solvesso 200ND" manufactured by XonMobil. The initial boiling point of the distillation of the petroleum-based hydrocarbon solvent may be 100°C or higher, 150°C or higher, or 200°C or higher. In the present disclosure, the initial boiling point of distillation is a value measured in accordance with JIS K0066 "Distillation test method for chemical products."

[0087] Preferred examples of polar organic solvents include fatty acid ester solvents, higher alcohol solvents, and higher fatty acid solvents. For example, 2-ethylhexyl isononanoate, 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, and soybean oil fatty acid methyl esters. Examples of suitable polar organic solvents include fatty acid ester solvents having 13 or more carbon atoms per molecule, preferably 16 to 30, such as ethanol, soybean 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 may be 150°C or higher, 200°C or higher, or even 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.

[0088] These non-aqueous solvents may be used alone or in combination with other organic solvents as long as they form a single phase.

[0089] The dispersant for resin particles is an optional component used to disperse colored resin particles in a non-aqueous solvent. The dispersant for resin particles may be a polymer compound. The dispersant for resin particles may be any of a basic dispersant, an acidic dispersant, and a nonionic dispersant, or may be a basic dispersant. Examples of the basic group possessed by the basic dispersant include an amino group, an amide group, an imino group, an imide group; and nitrogen-containing heterocyclic groups such as a pyrrolidone group, a pyridine group, and a morpholino group.

[0090] A preferred example of the dispersant for resin particles is a resin-type dispersant having an alkanolamine structure. Examples of the resin include (meth)acrylic resin, urethane resin, and olefin resin. Among these, a (meth)acrylic resin having an alkanolamine structure is preferred.

[0091] Examples of the alkanolamine structure include a structure represented by the following general formula (1): Among these, a dialkanolamine structure in which the value of p is 2 is preferred.

[0092] [ka]

[0093] [R in general formula (1)] 2 is a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkylene oxide group having 1 to 4 carbon atoms, or a hydroxypolyalkylene oxide group. p is 1 or 2. When p is 2, two R 2 may be the same or different. 3 is any one of 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, and an arylalkyl group having 7 to 10 carbon atoms.]

[0094] R in general formula (1) 2is any one of a hydroxyalkyl group having 1 to 4 carbon atoms, a hydroxyalkylene oxide group having 1 to 4 carbon atoms, and a hydroxypolyalkylene oxide group. The alkylene group of the hydroxypolyalkylene oxide group may be an ethylene group or a propylene group, and the number of repeating alkylene oxide groups may be in the range of 2 to 20. Among these, a hydroxyalkyl group having 1 to 4 carbon atoms is preferred, and specifically any one of a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, and a hydroxybutyl group. 2 may be a hydroxypropyl group or a 2-hydroxy n-propyl group, and p may be 2.

[0095] R in general formula (1) 3 is any one of 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, and an arylalkyl group having 7 to 10 carbon atoms. Examples of the ether bond-containing group having 1 to 10 carbon atoms include a structural moiety in which one or more carbon atoms in an alkyl group are substituted with oxygen atoms.

[0096] Examples of (meth)acrylic resins having an alkanolamine structure include those obtained by reacting an alkanolamine compound with a (meth)acrylic resin intermediate obtained by polymerizing a monomer containing a polymerizable compound having a functional group reactive with an amino group.

[0097] Regarding polymerizable compounds having a functional group reactive with an amino group, examples of the functional group reactive with an amino group include a glycidyl group and a β-dicarbonyl group. Examples of polymerizable compounds having these functional groups include (meth)acrylates having a glycidyl group, such as glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, and 3,4-epoxycyclohexylmethyl (meth)acrylate; and (meth)acrylates having a β-dicarbonyl group, such as acetoacetoxyethyl (meth)acrylate, acetoacetoxypropyl (meth)acrylate, acetoacetoxybutyl (meth)acrylate, ethylene glycol monoacetoacetate mono(meth)acrylate, 2,3-di(acetoacetoxy)propyl (meth)acrylate, and 2,4-hexadione (meth)acrylate. These may be used alone or in combination of two or more.

[0098] The proportion of the polymerizable compound having a functional group capable of reacting with an amino group relative to the total amount of monomers constituting the (meth)acrylic resin intermediate may be in the range of 5 to 70 mass %, may be in the range of 10 to 50 mass %, or may be in the range of 20 to 40 mass %.

[0099] The (meth)acrylic resin having an alkanolamine structure preferably further contains a polymerizable compound having a lipophilic group as a constituent unit. Examples of the lipophilic group include alkyl groups having 6 to 30 carbon atoms. Examples of the polymerizable compound having a lipophilic group 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. These may be used alone or in combination of two or more.

[0100] The proportion of the polymerizable compound having a lipophilic group relative to the total amount of monomers constituting the (meth)acrylic resin intermediate may be in the range of 30 to 95% by mass, 50 to 90% by mass, or 60 to 80% by mass.

[0101] The (meth)acrylic resin intermediate can be produced, for example, by polymerizing a monomer in the same manner as in the case of the (meth)acrylic resin-type pigment dispersant.

[0102] Examples of the alkanolamine compound include compounds in which * in the above general formula (1) is a hydrogen atom, and specific examples include N-methylethanolamine, N-ethylethanolamine, N-propylethanolamine, N-isopropylethanolamine, N-butylethanolamine, N-ethylbutanolamine, diethanolamine, and diisopropanolamine.

[0103] A (meth)acrylic resin having an alkanolamine structure can be produced, for example, by a method in which a (meth)acrylic resin intermediate is reacted with an alkanolamine compound at a temperature in the range of 80 to 130°C.

[0104] The weight average molecular weight (Mw) of the (meth)acrylic resin having an alkanolamine structure may be in the range of 8,000 to 50,000, for example.

[0105] Other commercially available basic dispersants that can be used as dispersants for resin particles 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.; Disperbyk109 (trade name) manufactured by BYK Japan Co., Ltd.; Acetamine 24 and Acetamine 86 (both trade names) manufactured by Kao Corporation; Hypermer KD3 and Hypermer KD11 (both trade names) manufactured by Croda Japan Co., Ltd.; Ajisper PB-821 (trade name) manufactured by Ajinomoto Fine-Techno Co., Inc.; and Antaron (trade name) manufactured by ISP. V-216" and "ANTARON V-220" (both trade names).

[0106] The non-colored resin particles contain a resin (hereinafter, this may be referred to as "resin B").

[0107] Specific examples of resin B include those exemplified as resin A. Resin B may be used alone or in combination of two or more. Among them, urethane resins are preferred because they have excellent affinity when paper is used as the substrate, provide a better sealing effect for the substrate, and provide a printed surface with high image density.

[0108] Examples of the urethane resin include those previously described as resin A. The proportion of the urethane resin relative to the total amount of resin B may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or even 100% by mass.

[0109] The glass transition temperature (Tg) of the urethane resin coating may be −60 to 50° C., −50 to 30° C., or −30 to 20° C. In the present disclosure, the glass transition temperature of the urethane resin is a value measured using a differential scanning calorimeter (DSC).

[0110] Resin B is preferably one having a large difference in polarity from the non-aqueous solvent, and specifically is preferably a water-dispersible resin, since it has excellent solvent removal properties on the substrate. The explanation of water-dispersible resins and the advantages of being a water-dispersible resin are as described in detail in the explanation of Resin A.

[0111] Resin B is preferably oil-insoluble. The oil-insolubility and advantages of being oil-insoluble are as described in detail in the description of Resin A.

[0112] Commercially available water-dispersible urethane resins that can be used as Resin B include, for example, the "Takelac" series manufactured by Mitsui Chemicals, Inc. ("Takelac WS-5984," "Takelac WS-4022," and the like, all trade names), the "Superflex" series manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. ("Superflex 740," "Superflex 150H," "Superflex 500M," "Superflex 620," and the like, all trade names), the "U-Coat UWS-145" manufactured by Sanyo Chemical Industries, Ltd., and the "DAOTAN" series manufactured by Daicel-Allnex Corporation ("DAOTAN TW-6431," "DAOTAN TW-6490," "DAOTAN TW-6491," "DAOTAN TW-6493," and the like, all trade names).

[0113] The method for producing non-colored resin particles is not particularly limited, and examples thereof include a method of producing a non-aqueous solvent dispersion of non-colored resin particles (hereinafter, sometimes referred to as "non-colored resin particle dispersion"). Like colored resin particles, non-colored resin particle dispersions can be produced, for example, by drying a water-in-oil (W / O) emulsion in oil. Specifically, they can be produced by producing a water-in-oil emulsion containing an aqueous phase containing resin B, water, etc., and an oil phase containing a non-aqueous solvent, etc., and then removing water from the resulting water-in-oil emulsion. The oil phase may further contain an emulsifier, and a dispersant for resin particles may be used as the emulsifier. The procedure for drying a water-in-oil (W / O) emulsion in oil is the same as that described in the method for producing colored resin particle dispersions. Examples of non-aqueous solvents include those exemplified as those used in producing colored resin particles. Examples of dispersants for resin particles include those exemplified as those used in producing colored resin particles.

[0114] The oil-based inkjet ink contains colored resin particles, non-colored resin particles, and a non-aqueous solvent.

[0115] The oil-based inkjet ink can be produced, for example, by mixing a colored resin particle dispersion obtained by drying a water-in-oil (W / O) emulsion in oil, a non-colored resin particle dispersion, and other optional components, and further adding a non-aqueous solvent as necessary.

[0116] The amount of colored resin particles relative to the total amount of oil-based ink is preferably 1% by mass or more, more preferably 3% by mass or more, particularly preferably 5% by mass or more, and even more preferably 10% by mass or more, in order to obtain an ink with a higher image density. The oil-based ink of one embodiment has excellent storage stability even when the content of colored resin particles is relatively high.

[0117] The amount of colored resin particles relative to the total amount of oil-based ink is preferably 40% by mass or less, more preferably 30% by mass or less, and particularly preferably 20% by mass or less, in order to achieve an appropriate viscosity for an inkjet ink. Even when the content of colored resin particles in the oil-based ink of one embodiment is relatively low, the image density is sufficiently high and the image quality is excellent.

[0118] The amount of colored resin particles relative to the total amount of oil-based ink may be, for example, in the range of 1 to 40% by mass, 3 to 30% by mass, 5 to 20% by mass, or 10 to 20% by mass.

[0119] The amount of non-colored resin particles relative to the total amount of oil-based ink is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and particularly preferably 0.5% by mass or more, in order to obtain a sufficient sealing effect for the substrate, prevent the colored resin particles from approaching each other, and sufficiently suppress interactions between the colorants. Furthermore, in order to achieve an appropriate viscosity for an inkjet ink, the amount is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less. The amount of non-colored resin particles relative to the total amount of oil-based ink may be, for example, in the range of 0.1 to 20% by mass, 0.3 to 10% by mass, or 0.5 to 5% by mass.

[0120] Examples of non-aqueous solvents contained in oil-based inks include those exemplified as non-aqueous solvents used in the production of colored and non-colored resin particles. The content of non-aqueous solvent in oil-based inks is adjusted appropriately depending on the desired viscosity, etc., and may be, for example, 50% by mass or more, or 70% by mass or more. It may also be 99% by mass or less, or 90% by mass or less.

[0121] 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.

[0122] The amount of water in the oil-based 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 oil-based ink.

[0123] 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.

[0124] 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.

[0125] The substrate to be printed on is not particularly limited, and examples thereof include printing paper such as plain paper, coated paper, and special paper, cloth, inorganic sheets, films, OHP sheets, and adhesive sheets formed by providing an adhesive layer on the back surface of these substrates. Among these, printing paper such as plain paper and coated paper is preferably used from the viewpoint of ink permeability.

[0126] Here, plain paper refers to 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. Plain paper has paper fibers with a thickness of several μm to several tens of μm that form voids of several tens to several hundreds of μm, making it easy for ink to penetrate.

[0127] 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.

[0128] Some embodiments of the present disclosure are set forth below.

[0129] <1> An oil-based inkjet ink comprising colored resin particles, non-colored resin particles, and a non-aqueous solvent, wherein the colored resin particles have an average particle size in the range of 150 nm to 350 nm, and the non-colored resin particles have an average particle size larger than the average particle size of the colored resin particles but not larger than 2.0 times the average particle size of the colored resin particles.

[0130] <2> The colored resin particles contain a pigment and a (meth)acrylic resin-type pigment dispersant having an acid value of 120 mgKOH / g or more. <1> 1. An oil-based inkjet ink according to claim 1.

[0131] <3> The average particle diameter of the colored resin particles is in the range of 200 to 280 nm. <1> or <2> 1. An oil-based inkjet ink according to claim 1.

[0132] <4> the average particle size of the non-colored resin particles is in the range of 1.05 to 1.3 times the average particle size of the colored resin particles; <1> ~ <3> 1. An oil-based inkjet ink according to any one of the preceding items. [Example]

[0133] 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.

[0134] Unless otherwise specified, common components are the same throughout the following Examples and Comparative Examples. Unless otherwise specified, "%" indicates "% by mass."

[0135] [Production of (meth)acrylic resin-type pigment dispersants 1 and 2] A 500 ml four-neck flask was charged with 39.2 parts by mass of methyl ethyl ketone and 19.6 parts by mass of ethanol, and the mixture was heated to 65°C while aerating with nitrogen gas and stirring. A monomer solution was prepared by adding 9.8 parts by mass of methyl ethyl ketone and 4.9 parts by mass of ethanol to 30 parts by mass of the monomer blend shown in Table 1. 1.5 parts by mass of V-65 (2,2'-azobis(2,4-dimethylvaleronitrile)) was added to the flask, and then the monomer solution 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, yielding a solvent solution of (meth)acrylic resin-type pigment dispersants 1 and 2. The solids content of the solution was 30% by mass.

[0136] Next, the solvent solutions of (meth)acrylic resin-type pigment dispersants 1 and 2, methyl ethyl ketone, ethanol, ion-exchanged water, and a 10% aqueous sodium hydroxide solution as a neutralizer were blended in the proportions shown in Table 2 and mixed using an ultrasonic disperser. Thereafter, the methyl ethyl ketone and ethanol were distilled off using an evaporator to obtain aqueous solutions of (meth)acrylic resin-type pigment dispersants 1 and 2. The solid content of the aqueous solution was 20% by mass.

[0137] [Table 1]

[0138] In Table 1, methacrylic acid, methyl methacrylate, and benzyl methacrylate are available from Tokyo Chemical Industry Co., Ltd.

[0139] Polyethylene glycol monomethacrylate (*1): NOF Corporation "Blenmer PP-1000", the number of moles of ethylene oxide added is approximately 4 to 6

[0140] [Table 2]

[0141] [Production of pigment dispersions 1 to 3] The components were blended in the proportions shown in Table 3 and dispersed using a bead mill (Dynomill KDL-A, manufactured by Shinmaru Enterprises Co., Ltd.) for a residence time of 12 minutes, to obtain pigment dispersions 1 to 3.

[0142] [Table 3]

[0143] Pigment (carbon black) (*2): Cabot Specialty Chemicals "MOGUL L" Pigment dispersant 1 (*3): Borchers "Borchi Gen DFN", aryl alkyl biphenylol polyglycol ether

[0144] [Production of dispersants for resin particles] A 300 ml four-neck flask was charged with 87.5 parts by mass of isotridecyl isononanoate (manufactured by Kokyu Alcohol Kogyo Co., Ltd.), and the temperature was raised to 110°C while aerating with nitrogen gas and stirring. Next, while maintaining the temperature at 110°C, a mixture of 40 parts by mass of stearyl methacrylate, 30 parts by mass of 2-ethylhexyl methacrylate, 30 parts by mass of glycidyl methacrylate, 16.5 parts by mass of isotridecyl isononanoate, and 4 parts by mass of t-hexylperoxy 2-ethylhexanoate (manufactured by NOF Corporation, "Perhexyl O") was added dropwise over 3 hours. Stirring was continued for an additional 2 hours while maintaining the temperature at 110°C, yielding a solvent solution of a (meth)acrylic resin intermediate with a solids content of 50% by mass.

[0145] A 500 ml four-neck flask was charged with 200 parts by mass of the solvent solution of the (meth)acrylic resin intermediate obtained above, and the temperature was raised to 110°C while aerating with nitrogen gas and stirring. 12.0 parts by mass of diisopropanolamine (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was allowed to react at 110°C for 2 hours, after which 12.0 parts by mass of isotridecyl isononanoate was added to obtain a solvent solution of a dispersant for resin particles with a solids content of 50% by mass.

[0146] [Production of Non-Aqueous Solvent Dispersions 1 to 9 of Colored Resin Particles] The solvent solution of the resin particle dispersant obtained above, 2-ethylhexyl isononanoate (manufactured by Kokyu Alcohol Kogyo Co., Ltd.), and a petroleum hydrocarbon solvent were mixed in the proportions shown in Table 4 and stirred with a magnetic stirrer. While stirring, a mixture of the pigment dispersion and water-dispersible resin in the proportions shown in Table 4 was added dropwise, and emulsified for 10 minutes using an ultrasonic homogenizer (Sonics Corporation, Ultrasonic Processor VC-750) to obtain a water-in-oil (W / O) emulsion. The emulsion was ice-cooled during ultrasonic irradiation. Water was removed from the emulsion using an evaporator to obtain non-aqueous solvent dispersions of colored resin particles 1 to 9. The content of each component in the non-aqueous solvent dispersions of colored resin particles is also shown in Table 4.

[0147] [Measurement of particle size of colored resin particles] The average particle size in the volumetric particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer "Partica LA-950V2" manufactured by Horiba, Ltd. The measurement was performed by circulation, and hexyl laurate was used as the solvent in the circulation path.

[0148] [Table 4]

[0149] Petroleum-based hydrocarbon solvent (*4): ExxonMobil's petroleum-based hydrocarbon solvent "Isopar M" Water-dispersible resin 1 (*5): "Superflex 870" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., urethane resin water dispersion, glass transition temperature of resin film 78°C, resin solid content 30% by mass Water-dispersible resin 2 (*6): "Superflex 150" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., urethane resin water dispersion, glass transition temperature of resin film: 40°C, resin solid content: 38% by mass

[0150] [Production of Non-Colored Resin Particle Dispersions 1 to 6 in Non-Aqueous Solvents] The solvent solution of the resin particle dispersant obtained above and a non-aqueous solvent were blended in the proportions shown in Table 5 and stirred with a magnetic stirrer. While stirring, a mixture of water-dispersible resin and ion-exchanged water blended in the proportions shown in Table 5 was added dropwise, and emulsified for 10 minutes using an ultrasonic homogenizer (Sonics Corporation, Ultrasonic Processor VC-750) to obtain a water-in-oil (W / O) emulsion. The emulsion was ice-cooled during ultrasonic irradiation. Water was removed from the emulsion using an evaporator to obtain non-aqueous solvent dispersions 1 to 6 of uncolored resin particles. The content of each component in the non-aqueous solvent dispersions of uncolored resin particles is also shown in Table 5.

[0151] [Measurement of particle size of uncolored resin particles] The particle size was measured in the same manner as in the measurement of the particle size of the colored resin particles.

[0152] [Table 5]

[0153] Water-dispersible resin 3 (*7): "DAOTAN TW6431" manufactured by Daicel Allnex Corporation, urethane resin water dispersion, glass transition temperature of resin film -20°C, resin solid content 45% by mass Water-dispersible resin 4 (*8): "DAOTAN TW6491" manufactured by Daicel Allnex Corporation, urethane resin water dispersion, glass transition temperature of resin film 10°C, resin solid content 33% by mass

[0154] [Examples 1 to 11 and Comparative Examples 1 to 7: Production of Oil-Based Inkjet Inks] The non-aqueous solvent dispersion of colored resin particles and the non-aqueous solvent dispersion of non-colored resin particles obtained above were blended in the proportions shown in Tables 6 and 7 and mixed to prepare inks.

[0155] [Evaluation of image density] The ink was loaded into a line-type inkjet printer "Comphis GD9630" (manufactured by Riso Kagaku Corporation), and a solid chart was printed on plain paper "Riso Paper Multi" (manufactured by Riso Kagaku Corporation) to obtain a print. The resulting print was left at room temperature for one day, and then the print density of the printed surface (front surface) of the print was measured using an Xrite eXact (manufactured by X-Rite) and evaluated according to the following criteria. The results are shown in Tables 6 and 7. S:OD value is 1.18 or more A:OD value is 1.14 or more and less than 1.18 B: OD value is 1.10 or more and less than 1.14 C:OD value is less than 1.10

[0156] [Evaluation of storage stability] Each ink was placed in a sealed container and stored in a thermostatic chamber at 70°C for one month. The viscosity of the ink was measured before and after storage and evaluated according to the following criteria. The ink viscosity was measured at 23°C using an Anton Paar MCR102 rheometer. The results are shown in Tables 6 and 7.

[0157] Viscosity change rate: [(viscosity after one month) / (initial viscosity)-1] x 100 (%) absolute value S: Viscosity change rate less than 5% A: Viscosity change rate 5% or more, less than 7.5% B: Viscosity change rate 7.5% or more, less than 15% C: Viscosity change rate 15% or more

[0158] [Table 6]

[0159] [Table 7]

[0160] As shown in the table, the oil-based inks of each example had an excellent balance between storage stability and image density of printed matter.

[0161] In Comparative Example 1, since the ink did not contain non-colored resin particles, neither the effect of excellent image density nor the effect of excellent storage stability was obtained.

[0162] In Comparative Examples 2, 3, and 6, the average particle size of the non-colored resin particles was smaller than that of the colored resin particles, so the non-colored resin particles did not have a sufficient sealing effect, and excellent image density was not obtained. Furthermore, interactions between the colorants contained in the colored resin particles and concentration gradients of the colored resin particles were likely to occur, and excellent storage stability was not obtained.

[0163] In Comparative Example 4, the average particle size of the colored resin particles was smaller than the specified range, which reduced the releasability of the non-aqueous solvent and made it easier for the solvent to penetrate into the paper, resulting in a decrease in image density.

[0164] In Comparative Example 5, the average particle size of the colored resin particles was larger than the specified range, and furthermore the average particle size of the non-colored resin particles was smaller than the average particle size of the colored resin particles, so that the image density and storage stability were reduced.

[0165] In Comparative Example 7, the average particle size of the uncolored resin particles was more than 2.0 times the average particle size of the colored resin particles, so that a concentration gradient of the uncolored resin particles was likely to occur, and the storage stability was reduced.

Claims

1. The ink contains colored resin particles, non-colored resin particles, and a non-aqueous solvent, The average particle diameter of the colored resin particles is in the range of 150 nm to 350 nm, the average particle size of the non-colored resin particles is larger than the average particle size of the colored resin particles and is not more than 2.0 times the average particle size of the colored resin particles; Oil-based inkjet ink.

2. 2. The oil-based inkjet ink according to claim 1, wherein the colored resin particles contain a pigment and a (meth)acrylic resin-type pigment dispersant having an acid value of 120 mgKOH / g or more.

3. 3. The oil-based inkjet ink according to claim 1, wherein the colored resin particles have an average particle size in the range of 200 to 280 nm.

4. 3. The oil-based ink-jet ink according to claim 1, wherein the average particle size of the non-colored resin particles is in the range of 1.05 to 1.3 times the average particle size of the colored resin particles.

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