Oily inkjet ink

Abstract

To provide oily inkjet ink which can reduce roller contamination of a printer, and hardly causes contamination of a recording medium.SOLUTION: Oily inkjet ink contains colored resin particles containing a pigment (A) and a resin (B), and a non-aqueous solvent, wherein the resin (B) contains a resin (b1) having a hydroxyl value of 80 mgKOH / g or more, and an urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Inkjet recording, which ejects highly fluid inkjet ink droplets from minute nozzles to record images on a recording medium placed opposite the nozzles, has rapidly gained popularity 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 use volatile organic solvents as the primary solvent, and oil-based inks, which use low-volatility or non-volatile organic solvents as the primary solvent. Solvent inks dry on the recording medium primarily through the evaporation of the organic solvent, while oil-based inks dry primarily through penetration into the recording medium.

[0003] As a technology relating to oil-based inkjet inks, Patent Document 1 discloses a technology that improves the fixability and color development of ink by using a colored resin particle dispersion 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 an inkjet ink that contains the same. [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] Oil-based ink dries primarily due to the penetration of organic solvents into the recording medium. However, as printers have become faster, the drying process has not kept up with the printing speed, and the ink in the image formed on the recording medium has sometimes adhered to the roller surface of the printer's transport roller. This has caused the problem of subsequent recording media being contaminated with this adhered ink. This phenomenon of recording media contamination is called roller transfer contamination. When printing many sheets in succession, roller contamination tends to accumulate, worsening the condition of roller transfer contamination.

[0006] An object of the present disclosure is to provide an oil-based inkjet ink that can reduce printer roller contamination and is less likely to contaminate recording media. [Means for solving the problem]

[0007] One embodiment of the present disclosure relates to an oil-based inkjet ink comprising colored resin particles including a pigment (A) and a resin (B), and a non-aqueous solvent, wherein the resin (B) comprises a resin (b1) having a hydroxyl value of 80 mgKOH / g or more and a urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide an oil-based inkjet ink that can reduce printer roller contamination and is less likely to contaminate recording media. DETAILED DESCRIPTION OF THE INVENTION

[0009] Several embodiments of the present invention will be described in detail below, but the present disclosure is not limited to these embodiments.

[0010] 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 colored resin particles will be referred to as a resin particle dispersant.

[0011] According to the present disclosure, an oil-based inkjet ink is provided, which includes colored resin particles containing a pigment (A) and a resin (B), and a non-aqueous solvent, wherein the resin (B) includes a resin (b1) having a hydroxyl value of 80 mgKOH / g or more and a urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less. Because the colored resin particles contain two types of resins as resin (B), namely, a resin (b1) having a hydroxyl value of 80 mgKOH / g or more and a urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less, an oil-based inkjet ink containing the same can reduce printer roller contamination and is less likely to contaminate the recording medium. The reason for this effect is considered as follows.

[0012] Resin (b1) has a hydroxyl value of 80 mg KOH / g or more, which increases the polarity difference between the colored resin particles and the non-aqueous solvent, thereby improving solvent releasability when the oil-based inkjet ink lands on a recording medium. Meanwhile, urethane resin (b2) has urethane bonding sites with high pigment affinity, resulting in a high pigment coating effect and reduced wetting of the pigment by the non-aqueous solvent. Furthermore, this effect is further enhanced by urethane resin (b2) having a hydroxyl value of 60 mg KOH / g or less. These actions reduce the inhibition of ink fixation by the non-aqueous solvent, improving the fixability of the ink to the recording medium and reducing ink adhesion to the printer roller, i.e., roller contamination, making it less likely for the recording medium to become contaminated.

[0013] The colored resin particles contain a pigment (A) and a resin (B). From the viewpoint of stability and color development of the colored resin particles, the mass ratio of the two components in the colored resin particles is preferably in the range of 20 to 150 parts by mass, more preferably 30 to 100 parts by mass, and particularly preferably 40 to 80 parts by mass of the resin (B) per 100 parts by mass of the pigment (A).

[0014] Examples of pigment (A) that can be used 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 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 may be used alone or in combination.

[0015] 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.

[0016] From the viewpoints of image density and ink viscosity, the content of pigment (A) in the oil-based inkjet ink is preferably 0.1 to 20 mass % relative to the total amount of ink, more preferably 1 to 15 mass %, and even more preferably 5 to 10 mass %.

[0017] The resin (B) contains a resin (b1) having a hydroxyl value of 80 mgKOH / g or more and a urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less. The resin (B) may contain a resin other than the resin (b1) and the urethane resin (b2) as long as the effects of the present invention are not impaired. The total proportion of the resin (b1) and the urethane resin (b2) in the entire resin (B) is preferably 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The total proportion of the resin (b1) and the urethane resin (b2) in the entire resin (B) may be 100% by mass.

[0018] In the colored resin particles, the ratio of resin (b1) to urethane resin (b2) is preferably in the range of 20 to 85 mass %, more preferably in the range of 30 to 75 mass %, and particularly preferably in the range of 35 to 70 mass %, relative to the total mass of both resins, because this more significantly reduces printer roller contamination and makes it less likely for contamination of recording media to occur.

[0019] The resin (b1) is not particularly limited in its specific resin structure, and various resins can be used as long as it has a hydroxyl value of 80 mgKOH / g or more. In one embodiment, the hydroxyl value of the resin (b1) is preferably 100 mgKOH / g or more, and more preferably 120 mgKOH / g or more. The upper limit of the hydroxyl value of the resin (b1) is not particularly limited, but may be, for example, 250 mgKOH / g or less, or 200 mgKOH / g or less.

[0020] In this disclosure, the hydroxyl value of a resin is expressed as the number of milligrams (mg) of potassium hydroxide required to neutralize the acetic acid bonded to the hydroxyl groups when 1 g of a sample is acetylated. Specifically, it 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."

[0021] Resin (b1) is preferably oil-insoluble, and particularly preferably has very low solubility in the non-aqueous solvent contained in the oil-based ink. For example, the degree of oil-insolubility is such that the amount of resin (b1) that can dissolve in 100 g of the non-aqueous solvent contained in the oil-based ink at 23°C is preferably 3 g or less, more preferably 1 g or less, and particularly preferably 0.5 g or less.

[0022] Specific examples of the resin (b1) include (meth)acrylic resins, urethane resins, polyester resins, alkyd resins, and silicone resins. Resin (b1) may be used singly or in combination of two or more. In one embodiment, the resin (b1) preferably includes at least one of (meth)acrylic resin (b1-1) and urethane resin (b1-2). (Meth)acrylic resin (b1-1) is preferred in that it offers high flexibility in resin design and can function as a pigment dispersant depending on the design. Furthermore, urethane resin (b1-2) is preferred in that it has high affinity with pigments and forms resin particles with low swelling in non-aqueous solvents.

[0023] The main chain of the (meth)acrylic resin (b1-1) is not particularly limited. For example, the main chain of the (meth)acrylic resin (b1-1) 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 (b1-1) may contain acrylic acid units, methacrylic acid units, acrylate units, and methacrylate units, either alone or in combination of two or more.

[0024] The (meth)acrylic resin (b1-1) 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 (b1-1) and its stability in the ink. The (meth)acrylic resin (b1-1) preferably further contains a pigment-affinitive 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.

[0025] The (meth)acrylic resin (b1-1) may contain a unit having a nonionic polyoxyalkylene chain and a unit having an acidic group. The (meth)acrylic resin (b1-1) may further contain other units. The (meth)acrylic resin (b1-1) 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 containing further 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 constituting the (meth)acrylic resin (b1-1) are described below.

[0026] 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, and an ethylene oxide group is more preferred. Furthermore, two or more types of alkylene oxide groups may be combined and contained in one polyoxyalkylene chain. Specifically, it is preferred to have a polyoxyethylene chain, a polyoxypropylene chain, a polyoxyethylene polyoxypropylene chain, etc., and from the viewpoint of miscibility with the urethane resin (b2), a polyoxyethylene chain is more preferred.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] For example, the nonionic polyoxyalkylene chain may have a structure represented by the following general formula: 1is 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 1

[0031] 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.

[0032] 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.

[0033] In the (meth)acrylic resin (b1-1), 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 (b1-1), the above-mentioned monomers may be used alone or in combination of two or more.

[0034] The (meth)acrylic resin (b1-1) may have, as the acidic group, a carboxy group, a sulfo group, a phosphate group, or the like, but preferably has a carboxy group. The acidic group may be contained in the (meth)acrylic resin (b1-1) either alone or in combination of two or more.

[0035] The (meth)acrylic resin (b1-1) 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 (b1-1) can be adjusted by adjusting the proportion of the unit having an acidic group.

[0036] In the (meth)acrylic resin (b1-1), 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 is preferably (meth)acrylic acid or a derivative thereof. In the polymerization of the (meth)acrylic resin (b1-1), the monomer may be used alone or in combination of two or more.

[0037] Examples of other units include units having a pigment affinity group and units having an alkyl group. When the unit having a pigment affinity group is contained in the (meth)acrylic resin (b1-1), the miscibility between the colorant, the (meth)acrylic resin (b1-1), and the urethane resin (b2) 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.

[0038] 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 (b1-1) either alone or in combination of two or more.

[0039] 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.

[0040] By including a unit having an alkyl group in the (meth)acrylic resin (b1-1), the acid value can be adjusted in combination 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.

[0041] When producing an oil-based ink using the drying-in-liquid method, the (meth)acrylic resin (b1-1) is used as a resin solution, and therefore, it is preferable to use a (meth)acrylic resin (b1-1) having an alkyl group with a low carbon number so as to exhibit hydrophilicity. In this case, the alkyl group is preferably, for example, a methyl group, an ethyl group, a propyl group, or a trimethyl group.

[0042] 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.

[0043] 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 (b1-1).

[0044] The amount of units having a nonionic polyoxyalkylene chain relative to all units of the (meth)acrylic resin (b1-1) 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 (b1-1) is simpler, while the miscibility of the colored resin particles with the urethane resin (b2) is improved, the component uniformity of the colored resin particles is improved, and the storage stability of the ink can be improved.

[0045] The amount of units having an acidic group relative to all units in the (meth)acrylic resin (b1-1) 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 (b1-1). The amount of units having a pigment affinity group relative to all units in the (meth)acrylic resin (b1-1) 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. The amount of units having an alkyl group relative to all units in the (meth)acrylic resin (b1-1) 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 having 1 to 4 carbon atoms falls within this range.

[0046] The (meth)acrylic resin (b1-1) 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.

[0047] 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.

[0048] 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 (b1-1). One solvent may be used alone, or two or more solvents may be used in combination. 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.

[0049] The (meth)acrylic resin (b1-1) preferably has an acid value, since this results in an oil-based ink with superior image density. When the (meth)acrylic resin (b1-1) has an acid value, separation of the colored resin particles from the non-aqueous solvent on the recording medium is promoted, thereby further improving the image density of the printed matter. The acid value of the (meth)acrylic resin (b1-1) may be 50 mgKOH / g or more. In one embodiment, the acid value of the (meth)acrylic resin (b1-1) is preferably 100 mgKOH / g or more. It is 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 (b1-1) may be, for example, in the range of 50 to 400 mgKOH / g.

[0050] In the present 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 the (meth)acrylic resin (b1-1) 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."

[0051] The weight-average molecular weight (Mw) of the (meth)acrylic resin (b1-1) 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 (b1-1) 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 described below.

[0052] The (meth)acrylic resin (b1-1) is preferably oil-insoluble. This prevents the (meth)acrylic resin (b1-1) from leaching out from the colored resin particles in the oil-based ink, 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 (b1-1) enhances solvent releasability when the oil-based ink lands on a recording medium, further improving image density. Specifically, the oil-insolubility of the (meth)acrylic resin (b1-1) refers to 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 (b1-1) that can dissolve in 100 g of the 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.

[0053] When the colored resin particles are produced by the method of drying a water-in-oil (W / O) emulsion in oil described below, the (meth)acrylic resin (b1-1) is preferably water-soluble. In this case, the (meth)acrylic resin (b1-1) is preferably used as an aqueous solution by replacing the solvent used in the polymerization reaction with water. Examples of solvent replacement methods include adding an appropriate amount of water to a polymerization solvent solution of the (meth)acrylic resin (b1-1), 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.

[0054] When the (meth)acrylic resin (b1-1) has acidic groups, a basic compound may be added to the aqueous solution as a neutralizing agent. Examples of the basic compound 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 the basic compound added may be adjusted so that the degree of neutralization of the acidic groups in the (meth)acrylic resin (b1-1) 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.

[0055] Urethane resins are polymers containing urethane bonds and can generally be synthesized by polyaddition of polyisocyanate and polyol. In addition to urethane bonds, urethane resins may also contain (poly)oxyalkylene structures, (poly)ester structures, (poly)carbonate structures, urea bonds, etc.

[0056] Examples of polyisocyanates include aliphatic diisocyanates such as butane diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate; alicyclic diisocyanates such as norbornane diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, and hydrogenated diphenylmethane diisocyanate; aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, diphenylmethane diisocyanate, and 1,5-naphthalene diisocyanate; and isocyanurate-modified, biuret-modified, and allophanate-modified versions of these.

[0057] Examples of polyol compounds include aliphatic polyols such as ethylene glycol, propylene glycol, butanediol, hexanediol, glycerin, trimethylolpropane, ditrimethylolpropane, pentaerythritol, and dipentaerythritol; aromatic polyols such as biphenol and bisphenol; polyols having a polyoxyalkylene structure; polyols having a polyester structure; and polyols having a polycarbonate structure.

[0058] The urethane resin used as resin (b1) (hereinafter, this may be referred to as "urethane resin (b1-2)") may have an acidic group. The acid value of the urethane resin (b1-2) may be in the range of 20 to 100 mgKOH / g.

[0059] As will be described later, in one example of a method for producing colored resin particles, the urethane resin (b1-2) is preferably in the form of an aqueous solution or aqueous dispersion. Examples of commercially available urethane resin aqueous dispersions that can be used as the urethane resin (b1-2) include the "DAOTAN" series (such as "DAOTAN TW-7000 / 40WA") manufactured by Daicel-Allnex Corporation.

[0060] Regarding the urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less, as mentioned above, the urethane resin is a polymer having a urethane bond, and can generally be synthesized by polyaddition of a polyisocyanate and a polyol. In addition to the urethane bond, the urethane resin may contain a (poly)oxyalkylene structure, a (poly)ester structure, a (poly)carbonate structure, a urea bond, or the like. Specific examples of polyisocyanates and polyols are as mentioned above.

[0061] The hydroxyl value of the urethane resin (b2) may be 60 mgKOH / g or less, and the lower limit is not particularly limited, but may be, for example, 5 mgKOH / g or more. The urethane resin (b2) may have an acidic group. The acid value of the urethane resin (b2) may be in the range of 10 to 50 mgKOH / g.

[0062] The urethane resin (b2) is preferably oil-insoluble, and particularly preferably has very low solubility in the non-aqueous solvent contained in the oil-based ink. For example, the degree of oil-insolubility is such that the amount of urethane resin (b2) that can dissolve in 100 g of the non-aqueous solvent contained in the oil-based ink at 23°C is preferably 3 g or less, more preferably 1 g or less, and particularly preferably 0.5 g or less.

[0063] As will be described later, in one example of a method for producing colored resin particles, the urethane resin (b2) is preferably in the form of an aqueous solution or aqueous dispersion. Examples of commercially available urethane resin aqueous dispersions that can be used as the urethane resin (b2) include the "DAOTAN" series manufactured by Daicel-Allnex Corporation ("DAOTAN TW1225 / 40WANEP," "DAOTAN TW6425 / 40WA," "DAOTAN TW6450 / 30WA," "DAOTAN VTW6460 / 35WA," "DAOTAN VTW6462 / 36WA," "DAOTAN VTW6463 / 36WA," "DAOTAN TW6464 / 36WA," "DAOTAN TW6466 / 36WA," "DAOTAN TW6473 / 37WA," and "DAOTAN TW6493 / 35WA").

[0064] The method for producing the colored resin particles is not particularly limited, and any method may be used. One example of a method for producing colored resin particles includes a step of preparing a water-in-oil emulsion from an aqueous phase containing a pigment (A) and a resin (B) and an oil phase containing a non-aqueous solvent (hereinafter referred to as "step 1"), and a step of removing water from the water-in-oil emulsion (hereinafter referred to as "step 2"). The colored resin particles can be produced as a non-aqueous solvent dispersion of colored resin particles (hereinafter referred to as "colored resin particle dispersion"). When producing colored resin particles using this method, it is preferable that the resin (B) is in the form of an aqueous solution or aqueous dispersion in advance.

[0065] In step 1, when preparing the aqueous phase, a pigment dispersant may be used to disperse the pigment (A) if necessary. When the resin (B) contains a resin with pigment dispersibility, such as a (meth)acrylic resin (b1-1) with pigment dispersibility, a highly stable colored resin particle dispersion can be obtained without using a separate pigment dispersant. On the other hand, when the resin (B) does not contain a resin with pigment dispersibility, it is preferable to use a separate pigment dispersant. Note that the resin (B) may contain both resins with and without pigment dispersibility, and even when the resin (B) contains a resin with pigment dispersibility, a pigment dispersant may be used if necessary.

[0066] Examples of pigment dispersants include ester-type nonionic pigment dispersants, ether-type nonionic pigment dispersants, ester-ether-type nonionic pigment dispersants, polycarboxylic acid polymer-type pigment dispersants, polysiloxane copolymer-type pigment dispersants, etc. Among these, ether-type nonionic pigment dispersants are preferred.

[0067] 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.

[0068] The amount of pigment dispersant used may be, for example, in the range of 0.1 to 3 parts by mass per 1 part by mass of pigment, and the proportion of pigment dispersant in the colored resin particles may be in the range of 0.5 to 5% by mass.

[0069] The aqueous phase can be prepared by separately preparing an aqueous phase 1, which is a pigment dispersion, and an aqueous phase 2, which contains a resin, and then mixing them to obtain a more stable colored resin particle dispersion. The aqueous phase 1 can be obtained, for example, by dispersing a pigment in water using a pigment dispersant. When the resin (B) contains a resin with pigment dispersibility, such as a (meth)acrylic resin (b1-1) with pigment dispersibility, the resin with pigment dispersibility can be included in the aqueous phase 1 to form a pigment dispersion. As mentioned above, in this case, the pigment dispersant is an optional component. Other resins, specifically, acrylic resins (b1-1) that do not have pigment dispersibility, urethane resins (b1-2), urethane resins (b2), etc., are preferably included in the aqueous phase 2 as an aqueous solution or aqueous dispersion.

[0070] The proportion of water in the aqueous phase is optional, but may be in the range of 40 to 90% by mass from the viewpoint of production efficiency and the like.

[0071] The non-aqueous solvent contained in the oil phase may be either a non-polar organic solvent or a polar organic solvent. These may be used alone or in combination. In the present invention, 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.

[0072] 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."

[0073] 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.

[0074] 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.

[0075] The oil phase may contain other components in addition to the non-aqueous solvent, such as a dispersant for resin particles for dispersing the colored resin particles in the non-aqueous solvent.

[0076] An example of a 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, (meth)acrylic resin having an alkanolamine structure is preferred.

[0077] 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.

[0078] [ka]

[0079] [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.]

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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 %.

[0085] 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.

[0086] 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.

[0087] The (meth)acrylic resin intermediate can be produced, for example, by polymerizing a monomer in the same manner as in the (meth)acrylic resin (b1-1).

[0088] Examples of the alkanolamine compound include compounds in which * in the above general formula (2) is a hydrogen atom, and specific examples include N-methylethanolamine, N-ethylethanolamine, N-propylethanolamine, N-isopropylethanolamine, N-butylethanolamine, N-ethylbutanolamine, diethanolamine, and diisopropanolamine.

[0089] 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.

[0090] 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.

[0091] Other commercially available examples of dispersants for resin particles include "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.; "ANTARON V-216" and "ANTARON" manufactured by ISP Co., Ltd. V-220" (both product names).

[0092] When the oil phase contains a dispersant for resin particles, the content thereof may be in the range of 0.1 to 10% by mass.

[0093] In step 1, a method for preparing a water-in-oil emulsion from an aqueous phase and an oil phase containing a non-aqueous solvent includes, for example, emulsifying a blend of the aqueous phase and the oil phase using an ultrasonic homogenizer or the like. When the oil phase contains a dispersant for resin particles, the dispersant for resin particles may function as an emulsifier in step 1. The aqueous phase and the oil phase may be blended all at once, in portions, or by adding the aqueous phase dropwise to the oil phase. Furthermore, the emulsification may be performed after blending the entire amounts of the aqueous phase and the oil phase, or may be performed after each portion addition, or by adding the aqueous phase dropwise to the oil phase, for example.

[0094] The ratio of the aqueous phase to the oil phase is arbitrary, but from the viewpoint of emulsification efficiency and the like, the mass ratio between the two may be in the range of 10:90 to 90:10, or may be in the range of 40:60 to 60:40.

[0095] In step 2, water is removed from the obtained water-in-oil emulsion. Water removal can be carried out, for example, by distilling off water under reduced pressure, heating, or reduced pressure and heating conditions, by bubbling gas into the water-in-oil emulsion to promote water evaporation, or by a combination of these methods. The heating temperature is adjusted appropriately depending on the type of non-aqueous solvent, 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.

[0096] In the colored resin particle dispersion, the average particle size of the colored resin particles is preferably 150 nm or more, more preferably 200 nm or more, in order to provide an ink that is effective in reducing printer roller contamination and also has excellent image quality, and is preferably 400 nm or less, more preferably 300 nm or less, in order to provide an ink that has excellent storage stability.

[0097] In the present disclosure, the average particle size of the colored resin particles is a volume-based particle size measured by a laser diffraction / scattering method, and can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device "Partica LA-950" manufactured by Horiba, Ltd.

[0098] The oil-based inkjet ink contains colored resin particles. The oil-based inkjet ink may contain other optional components in addition to the colored resin particles and non-aqueous solvent. The oil-based inkjet ink can be produced, for example, by adding other optional components to the non-aqueous solvent dispersion of colored resin particles obtained by the method described above.

[0099] The amount of colored resin particles relative to the total amount of oil-based ink is not particularly limited, but in order to obtain an ink that not only reduces printer roller contamination but also has excellent image quality, it 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. Furthermore, in order to obtain an ink with an appropriate viscosity for an inkjet ink, it is preferably 40% by mass or less, more preferably 30% by mass or less, and particularly preferably 20% by mass or less. 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.

[0100] Examples of non-aqueous solvents contained in oil-based inks include those exemplified as non-aqueous solvents used in the production of 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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 recording medium.

[0105] The recording medium may be any substrate that is permeable to the non-aqueous solvent, and examples thereof include printing paper such as plain paper, coated paper, and special paper, cloth, porous sheets, and adhesive sheets having an adhesive layer on the back surface of the substrate. Among these, printing paper such as plain paper and coated paper is preferably used from the viewpoint of permeability to the non-aqueous solvent.

[0106] 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 non-aqueous solvents to penetrate.

[0107] 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.

[0108] Some embodiments of the present disclosure are set forth below. <1> An oil-based inkjet ink comprising colored resin particles containing a pigment (A) and a resin (B), and a non-aqueous solvent, wherein the resin (B) comprises a resin (b1) having a hydroxyl value of 80 mgKOH / g or more and a urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less.

[0109] <2> The hydroxyl value of the resin (b1) is 100 mgKOH / g or more. <1> The oil-based inkjet ink described herein.

[0110] <3> The resin (b1) contains at least one of a (meth)acrylic resin (b1-1) and a urethane resin (b1-2). <1> or <2> The oil-based inkjet ink described herein.

[0111] <4> the resin (b1) contains a (meth)acrylic resin (b1-1), and the acid value of the (meth)acrylic resin (b1-1) is 100 mgKOH / g or more; <3> The oil-based inkjet ink described herein. [Example]

[0112] 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."

[0113] [Production of Resins (b1-1a) to (b1-1f) and (Meth)acrylic Resins (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 each resin. The solids content of the solution was 30% by mass.

[0114] Next, the solvent solutions of each resin, methyl ethyl ketone, ethanol, ion-exchanged water, and 10% aqueous sodium hydroxide solution as a neutralizer were blended in the proportions shown in Table 2 and mixed using an ultrasonic disperser. The methyl ethyl ketone and ethanol were then removed using an evaporator to obtain aqueous solutions of each resin, namely resins (b1-1a) to (b1-1f) and (meth)acrylic resins (1) and (2). The solid content of the aqueous solutions was 20% by mass.

[0115] [Table 1]

[0116] In Table 1, methacrylic acid, methyl methacrylate, benzyl methacrylate, and hydroxyethyl methacrylate are available from Tokyo Chemical Industry Co., Ltd.

[0117] Polyethylene glycol monomethacrylate (*1): NOF Corporation "Blenmer PE-200", the average number of moles of ethylene oxide added is 4.5

[0118] [Table 2]

[0119] [Production of Dispersant 1 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.

[0120] A 500 ml four-neck flask was charged with 200 parts by mass of the (meth)acrylic resin intermediate solution obtained above, and the mixture was aerated with nitrogen gas and heated to 110°C while stirring. 12.0 parts by mass of diisopropanolamine (Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was allowed to react at 110°C for 2 hours. After that, 12.0 parts by mass of isotridecyl isononanoate was added to obtain a dispersant 1 for resin particles with a solids content of 50% by mass.

[0121] Examples 1 to 10 and Comparative Examples 1 to 4 [Production of colored resin particle dispersion] The components shown in the "W1" column of Tables 3 and 4 were blended in the amounts shown in the tables. The blend was dispersed using a bead mill ("Dyno Mill KDL-A" manufactured by Shinmaru Enterprises Co., Ltd.) for a residence time of 12 minutes to obtain a pigment dispersion.

[0122] To the resulting pigment dispersion, each component shown in the "W2" column of Tables 3 and 4 was blended in the amounts shown in the table to obtain an aqueous phase.

[0123] The components shown in the "Oil Phase" column of Tables 3 and 4 were mixed according to the amounts shown in the tables. While stirring the oil phase with a magnetic stirrer, the aqueous phase obtained above was added dropwise, and the mixture was emulsified for 10 minutes using an ultrasonic homogenizer (Sonics Corporation, Ultrasonic Processor VC-750) to obtain a water-in-oil (W / O) emulsion. The mixture was ice-cooled during ultrasonic irradiation. Water was removed from the emulsion using an evaporator to obtain a colored resin particle dispersion. The content of each component in the colored resin particle dispersion is shown in Tables 5 and 6.

[0124] [Evaluation of roller transfer stains] The colored resin particle dispersion obtained above was used as an oil-based inkjet ink. Using an inkjet printer "Comphis GD9630" (Riso Kagaku Corporation), 100 solid images were printed on plain paper "Riso Paper Multi" (Riso Kagaku Corporation), yielding 100 prints. The 100th print was visually observed and evaluated according to the following criteria. The results are shown in Tables 5 and 6. A: Almost no contamination is visible around the image. B: Slight contamination around the image. C: Contamination around the image is observed.

[0125] [Table 3]

[0126] [Table 4]

[0127] Pigment 1 (*2): Carbon black, "MOGUL L" manufactured by Cabot Specialty Chemicals Pigment 2 (*3): Copper phthalocyanine, DIC Corporation "FASTGEN Blue LA5380" Pigment dispersant (*4): Borchers "Borchi Gen DFN", aryl alkyl biphenylol polyglycol ether Resin (b1-2) (*5): "DAOTAN TW7000 / 40WA" manufactured by Daicel Allnex Corporation, urethane resin emulsion, hydroxyl value of resin 170 mg KOH / g, acid value of resin 28 mg KOH / g, resin solid content 40 mass% Urethane resin (b2-1) (*6): "DAOTAN VTW6460 / 35WA" manufactured by Daicel-Allnex Corporation, urethane resin emulsion, hydroxyl value of resin 30 mg KOH / g, acid value of resin 18 mg KOH / g, resin solid content 35% by mass Urethane resin (b2-2) (*7): "DAOTAN VTW6425 / 40WA" manufactured by Daicel Allnex Corporation, urethane resin emulsion, hydroxyl value of resin 55 mg KOH / g, acid value of resin 29 mg KOH / g, resin solid content 40 mass% Dispersant for resin particles 2 (*8): Lubrizol's "Solsperse 13940", solid content 40% by mass Non-aqueous solvent (*9): Isotridecyl isononanoate, manufactured by Kokyu Alcohol Kogyo Co., Ltd. Non-aqueous solvent (*10): Exxon Mobil's "Isopar M"

[0128] [Table 5]

[0129] [Table 6]

[0130] As shown in the table, the oil-based inks of each example reduced roller contamination during printing, and as a result, contamination of the recording medium was less likely to occur even when printing was performed continuously.

[0131] In Comparative Examples 1 to 3, the ink did not contain a resin (b1) with a hydroxyl value of 80 mgKOH / g or more, and therefore the ink was prone to adhere to the roller, resulting in contamination of the recording medium. In Comparative Example 4, since the ink did not contain the urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less, the ink was prone to adhere to the roller, resulting in contamination of the recording medium.

Claims

1. A colored resin particle containing a pigment (A) and a resin (B), and a non-aqueous solvent, The oil-based inkjet ink, wherein the resin (B) comprises a resin (b1) having a hydroxyl value of 80 mgKOH / g or more and a urethane resin (b2) having a hydroxyl value of 60 mgKOH / g or less.

2. 2. The oil-based inkjet ink according to claim 1, wherein the resin (b1) has a hydroxyl value of 100 mgKOH / g or more.

3. 3. The oil-based inkjet ink according to claim 1, wherein the resin (b1) comprises at least one of a (meth)acrylic resin (b1-1) and a urethane resin (b1-2).

4. 4. The oil-based inkjet ink according to claim 3, wherein the resin (b1) comprises a (meth)acrylic resin (b1-1), and the acid value of the (meth)acrylic resin (b1-1) is 100 mgKOH / g or more.

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