Oil-based inkjet ink

Abstract

To provide an oil-based inkjet ink that exhibits excellent surface density and abrasion resistance of a printed matter.SOLUTION: An oil-based inkjet ink comprising colored resin particles containing a colorant, a resin, and a betaine compound, and a nonaqueous solvent.SELECTED DRAWING: None

Description

[Technical Field]

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

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

[0003] As a technology relating to oil-based inkjet inks, Patent Document 1 describes an oil-based inkjet ink that contains a colorant, an oil-soluble resin that is an acrylic polymer having a side chain containing a polydimethylsiloxane structure, and a non-aqueous solvent, and that has improved ink ejection properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-172956 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 the surface density of the printed material.

[0006] An object of the present disclosure is to provide an oil-based inkjet ink that provides excellent surface density and abrasion resistance in printed matter. [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 colorant, a resin, and a betaine compound, and a non-aqueous solvent. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide an oil-based inkjet ink that exhibits excellent surface density and abrasion resistance in printed matter. 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] In this disclosure, oil-based inkjet inks are also referred to as "ink" or "oil-based ink." Acrylic resin is a general term for resins obtained by polymerizing acrylic acid, methacrylic acid, and derivatives thereof, either alone or in combination. (Meth)acrylic acid is a general term for acrylic acid and methacrylic acid, and (meth)acrylic acid ester is a general term for acrylic acid ester and methacrylic acid ester.

[0011] An oil-based inkjet ink according to one embodiment includes colored resin particles containing a colorant, a resin, and a betaine compound, and a non-aqueous solvent. In one embodiment, the ink contains the colorant as colored resin particles, which allows the colorant to remain on the substrate surface more efficiently, resulting in a printed matter with high surface density. On the other hand, if the colorant is simply colored resin particles, the adhesion between the colored resin particles remaining on the substrate surface and the substrate may be insufficient, resulting in poor abrasion resistance. In one embodiment, the ink contains a betaine compound, which improves the adhesion between the colored resin particles and the substrate, resulting in a printed matter with excellent surface density and abrasion resistance.

[0012] Generally, betaine compounds are not soluble in non-aqueous solvents, and adding a betaine compound directly to ink is difficult and not only is it unrealistic in terms of the storage stability of the ink, but in one embodiment of the ink, by incorporating a betaine compound into colored resin particles, it is possible to create an oil-based ink that is highly stable even when it contains a betaine compound.

[0013] An oil-based inkjet ink according to one embodiment will now be described. The colored resin particles contained in the oil-based inkjet ink contain a colorant, a resin, and a betaine compound.

[0014] One type of colorant may be used alone, or two or more types may be used in combination. The colorant is preferably oil-insoluble, and in particular, it is preferable that the colorant has very low solubility in the non-aqueous solvent contained in the oil-based ink. In terms of the degree of oil-insolubility, for example, the amount of colorant that can be dissolved 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. When multiple types of colorants are used, the above-mentioned dissolution amount refers to the dissolution amount of each colorant.

[0015] Various pigments can be used as colorants. Examples of pigments include organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, and dye lake pigments; and 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.

[0016] From the viewpoint of storage stability and ejection stability of the ink, the average particle diameter of the pigment is preferably 300 nm or less, and more preferably 200 nm or less. The average particle diameter of the pigment may be, for example, in the range of 50 to 300 nm, or may be 100 to 200 nm.

[0017] From the viewpoint of ink color development, the content of the colorant in the colored resin particles is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more. It may also be 80% by mass or less, 70% by mass or less, or 65% by mass or less. The content of the colorant in the colored resin particles may be in the range of 30 to 80% by mass.

[0018] From the viewpoints of the surface density of the printed matter and the viscosity of the ink, the content of the colorant in the oil-based inkjet ink is preferably 0.1% by mass or more, more preferably 1% by mass or more, and particularly preferably 5% by mass or more. Also, it is preferably 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. The content of the colorant in the ink may be in the range of 0.1 to 25% by mass.

[0019] One type of resin may be used alone, or two or more types may be used in combination. The resin is preferably oil-insoluble, and in particular, it is preferable that the resin has very low solubility in the non-aqueous solvent contained in the oil-based ink. In terms of the degree of oil-insolubility, for example, the amount of resin 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. Note that when multiple types of resins are used, the above-mentioned dissolution amount refers to the dissolution amount of each resin.

[0020] The type of resin is not particularly limited, and examples thereof include acrylic resin, urethane resin, polyester resin, alkyd resin, silicone resin, etc. Among these, urethane resin is preferred in that it results in resin particles with low swelling properties in non-aqueous solvents.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] As will be described later, in one example of a method for producing colored resin particles, the urethane resin is preferably in the form of an aqueous solution or aqueous dispersion. Examples of commercially available urethane resin aqueous dispersions include the "Takelac" series manufactured by Mitsui Chemicals, Inc. ("Takelac WS-5984", "Takelac WS-4022", "Takelac W-635", etc.), the "Superflex" series manufactured by Daiichi Kogyo Seiyaku Co., Ltd. ("Superflex 150", "Superflex 150H", "Superflex 500M", "Superflex 420", "Superflex 470", "Superflex 620", "Superflex 740", "Superflex 870", etc.), the "U-Coat UWS-145" manufactured by Sanyo Chemical Industries, Ltd., and the "DAOTAN" series manufactured by Daicel-Allnex Co., Ltd. ("DAOTAN TW-6490", "DAOTAN TW-6493", etc.).

[0025] From the viewpoint of the stability of the resin particles, the resin content in the colored resin particles is preferably 10% by mass or more, more preferably 15% by mass or more, and particularly preferably 20% by mass or more. It may also be 50% by mass or less, 40% by mass or less, or 30% by mass or less. The resin content in the colored resin particles may be in the range of 10 to 50% by mass.

[0026] The resin content in the oil-based inkjet ink may be 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or more. It may also be 15% by mass or less, 10% by mass or less, or 8% by mass or less. The resin content in the ink may be in the range of 0.1 to 15% by mass.

[0027] A betaine compound has a positive charge and a negative charge on atoms that are not adjacent to each other in the same molecule, and the positively charged atom has no dissociable hydrogen bonded to it, so the molecule as a whole has no charge. One type of betaine compound may be used alone, or two or more types may be used in combination.

[0028] The betaine compound preferably has a molecular weight of 200 or less, since this further improves the effect of excellent abrasion resistance of printed matter and increases the shape stability of colored resin particles. The molecular weight of the betaine compound may be 80 or more and 200 or less.

[0029] Specific examples of betaine compounds having a molecular weight of 200 or less include trimethylglycine, α-alanine betaine, β-alanine betaine, γ-butyrobetaine, lysine betaine, carnitine, stachydrine, homarine, trigonelline, and valine betaine. Among these, it is preferable that the betaine compound contains trimethylglycine, as this further improves the effect of providing excellent abrasion resistance to printed matter. In this case, the proportion of trimethylglycine relative to the total amount of the betaine compound may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or even 100% by mass.

[0030] The content of the betaine compound in the colored resin particles is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more, because this further improves the effect of excellent abrasion resistance of printed matter and increases the shape stability of the colored resin particles. It may also be 10% by mass or less, 5% by mass or less, or 3% by mass or less. The content of the betaine compound in the colored resin particles may be in the range of 0.1 to 10% by mass.

[0031] The content of the betaine compound in the oil-based inkjet ink may be 0.01% by mass or more, 0.1% by mass or more, or 0.2% by mass or more. It may also be 5% by mass or less, 3% by mass or less, or 2% by mass or less. The content of the betaine compound in the ink may be in the range of 0.01 to 5% by mass.

[0032] The colored resin particles may be produced by any method, and the method for producing the colored resin particles is not particularly limited. 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 colorant, a resin, and a betaine compound and an oil phase containing a non-aqueous solvent (hereinafter, this may be referred to as "step 1"), and a step of removing water from the water-in-oil emulsion (hereinafter, this may be referred to as "step 2"). This method can produce a non-aqueous solvent dispersion of colored resin particles (hereinafter, this may be referred to as "colored resin particle dispersion"). When producing colored resin particles using this method, it is preferable that the resin is in the form of an aqueous solution or aqueous dispersion in advance.

[0033] In step 1, the aqueous phase may contain all of the colorant, resin, and betaine compound in one liquid, or may be prepared in multiple liquid phases. For example, the aqueous phase may be prepared in two liquid phases: aqueous phase 1 containing at least one of the colorant, resin, and betaine compound, and aqueous phase 2 containing other components; or aqueous phase 1 containing the colorant, aqueous phase 2 containing the resin, and aqueous phase 3 containing the betaine compound.

[0034] When a pigment is used as a colorant, a water-based pigment dispersant may be used to disperse the pigment in water. One type of pigment dispersant may be used alone, or two or more types may be used in combination. Examples of pigment dispersants include polymer dispersants and surfactant-type dispersants.

[0035] Examples of commercially available polymer dispersants include the TEGO Disperse series manufactured by EVONIK (such as "TEGO Disperse 740W," "TEGO Disperse 750W," "TEGO Disperse 755W," "TEGO Disperse 757W," and "TEGO Disperse 760W"), and the Solsperse series manufactured by Lubrizol Japan Co., Ltd. (such as "Solsperse 20000," "Solsperse 27000," "Solsperse 41000," "Solsperse 41090," "Solsperse 43000," "Solsperse 44000," and "Solsperse 46000"). 000), the JONCRYL series manufactured by BASF Japan Ltd. (JONCRYL 57, JONCRYL 60, JONCRYL 62, JONCRYL 63, JONCRYL 71, JONCRYL 501, etc.), BYK-Chemie Japan Co., Ltd.'s DISPERBYK-102, DISPERBYK-185, DISPERBYK-190, DISPERBYK-193, DISPERBYK-199, etc., and Dai-ichi Kogyo Seiyaku Co., Ltd.'s Polyvinylpyrrolidone K-30 and Polyvinylpyrrolidone K-90, etc.

[0036] Examples of surfactant-type dispersants include commercially available anionic surfactants such as the Demol series manufactured by Kao Corporation ("Demol P," "Demol EP," "Demol N," "Demol RN," "Demol NL," "Demol RNL," "Demol T-45," etc.), and nonionic surfactants such as the Emulgen series manufactured by Kao Corporation ("Emulgen A-60," "Emulgen A-90," "Emulgen A-500," "Emulgen B-40," "Emulgen L-40," "Emulgen 420," etc.).

[0037] The amount of the water-based pigment dispersant used may be, for example, in the range of 0.1 to 3 parts by mass per 1 part by mass of the pigment, and the proportion of the water-based pigment dispersant in the colored resin particles may be in the range of 1 to 20% by mass.

[0038] Furthermore, when producing colored resin particles using the above method, hydrophilic self-dispersing pigments may be used. Self-dispersing pigments are pigments in which hydrophilic functional groups have been introduced onto their surfaces by chemical or physical treatment. The hydrophilic functional groups introduced into self-dispersing pigments are preferably ionic. By charging the pigment surface anionic or cationic, electrostatic repulsion can be utilized to stably disperse the pigment particles in water. Examples of anionic functional groups include carboxyl groups, sulfo groups, sulfino groups, sulfate ester groups, phosphate groups, phosphate ester groups, phosphite groups, and phosphite ester groups. Examples of cationic functional groups include quaternary ammonium groups and quaternary phosphonium groups. These hydrophilic functional groups may be bonded directly to the pigment surface or via other atomic groups. Examples of other atomic groups include alkylene groups, phenylene groups, and naphthylene groups. Examples of pigment surface treatment methods include diazotization, sulfonation, hypochlorite treatment, humic acid treatment, and vacuum plasma treatment.

[0039] Examples of self-dispersing pigments include the "CAB-O-JET" series manufactured by Cabot Corporation ("CAB-O-JET200 Black Colorant," "CAB-O-JET300 Black Colorant," "CAB-O-JET400 Black Colorant," "CAB-O-JET250C," "CAB-O-JET260M," "CAB-O-JET270Y," "CAB-O-JET450C," and "CAB-O-JET465M," etc.), and the "BONJET" series manufactured by Orient Chemical Industries Co., Ltd. ("BONJET BLACK CW-1," "BONJET BLACK CW-1S," "BONJET BLACK CW-2," "BONJET BLACK CW-3," "BONJET BLACK CW-4," etc.).

[0040] In the aqueous phase used in step 1, when the aqueous phase contains a pigment as a coloring material, the pigment, an optional aqueous pigment dispersant, and water may be mixed together, and then dispersed using a bead mill or the like.

[0041] Examples of water used in the aqueous phase include ion-exchanged water, distilled water, ultrapure water, etc. The proportion of water in the aqueous phase is arbitrary, but from the viewpoint of production efficiency, etc., the proportion of water in the entire aqueous phase may be in the range of 40 to 90 mass %.

[0042] The non-aqueous solvent contained in the oil phase can be either a non-polar organic solvent or a polar organic solvent. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination. Other organic solvents may also be included to the extent that they can form a single phase with the non-aqueous solvent used. It is preferable to use a water-insoluble organic solvent that is not uniformly miscible with the same volume of water at 20°C under 1 atmosphere as the non-aqueous solvent.

[0043] Examples of non-polar organic solvents include petroleum-based 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 paraffin-based, isoparaffin-based, and naphthenic solvents. 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," manufactured by ENEOS Corporation; and "Isozol G" and "Isozol H" manufactured by ExxonMobil Corporation. Examples of suitable solvents include "BHT," "Isopar L," "Isopar M," "Exsor D40," "Exsor D60," "Exsor D80," "Exsor D110," and "Exsor 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" manufactured by MORESCO Corporation. Examples of suitable aromatic hydrocarbon solvents include "Solvesso 100," "Solvesso 150," "Solvesso 200," and "Solvesso 200ND" manufactured by ExxonMobil Corporation. The initial boiling point of petroleum-based hydrocarbon solvents is preferably 100°C or higher, more preferably 150°C or higher, and particularly preferably 200°C or higher. The initial boiling point of distillation can be measured according to JIS K0066, "Test Method for Distillation of Chemical Products."

[0044] 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.

[0045] The oil phase may contain other components in addition to the non-aqueous solvent. Examples of other components include a non-aqueous dispersant for dispersing the colored resin particles in the non-aqueous solvent. One type of non-aqueous dispersant may be used alone, or two or more types may be used in combination.

[0046] From the viewpoint of the shape stability of the colored resin particles, the non-aqueous dispersant preferably has a basic group. An example of a non-aqueous dispersant having a basic group is a resin-type dispersant having a basic group. Examples of the resin include acrylic resin, urethane resin, and olefin resin. Among them, acrylic resin is preferred because it has better dispersibility for the colored resin particles.

[0047] The basic group possessed by the non-aqueous dispersant is not particularly limited, but specific examples include an amino group, an alkanolamine structure, etc. 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.

[0048] [ka]

[0049] [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.]

[0050] R in general formula (1) 2 is 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.

[0051] 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.

[0052] Examples of acrylic resins having at least one of an amino group or an alkanolamine structure include acrylic resins obtained by polymerizing a monomer containing a polymerizable compound having an amino group or an alkanolamine structure (hereinafter, this may be referred to as "acrylic resin (1)"), and acrylic resins obtained by reacting an alkanolamine compound with an acrylic resin intermediate obtained by polymerizing a monomer containing a polymerizable compound having a functional group reactive with an amino group (hereinafter, this may be referred to as "acrylic resin (2)").

[0053] Regarding the acrylic resin (1), examples of polymerizable compounds having an amino group include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, morpholinoethyl (meth)acrylate, and N,N-dimethylacrylamide. Examples of polymerizable compounds having an alkanolamine structure include N-methylolacrylamide. These may be used alone or in combination of two or more.

[0054] The acrylic resin (1) preferably further contains, as a constituent unit, a polymerizable compound having a lipophilic group. 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.

[0055] The proportion of the polymerizable compound having an amino group or an alkanolamine structure relative to the total amount of monomers constituting the acrylic resin (1) may be, for example, 5% by mass or more, 10% by mass or more, or 20% by mass or more. It may also be 60% by mass or less, 50% by mass or less, or 40% by mass or less. The proportion of the polymerizable compound having an amino group or an alkanolamine structure relative to the total amount of monomers constituting the acrylic resin (1) may be in the range of 5 to 60% by mass.

[0056] The ratio of the polymerizable compound having a lipophilic group to the total amount of monomers constituting the acrylic resin (1) may be, for example, 30% by mass or more, 40% by mass or more, or 50% by mass or more. It may also be 90% by mass or less, 85% by mass or less, or 80% by mass or less. The ratio of the polymerizable compound having a lipophilic group to the total amount of monomers constituting the acrylic resin (1) may be in the range of 30 to 90% by mass.

[0057] The acrylic resin (1) can be produced, for example, by polymerizing a mixture of monomers in the presence of a polymerization initiator. A chain transfer agent, a polymerization inhibitor, etc. may be used during the polymerization reaction. The polymerization reaction may also be carried out in a solvent.

[0058] 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.

[0059] The solvent used in the polymerization reaction is not particularly limited, and may be, for example, the non-aqueous solvent contained in the oil phase. The amount of the solvent used may be in the range of 50 to 500% by mass based on the mass of the total amount of monomers.

[0060] Regarding the acrylic resin (2), the polymerizable compound having a functional group reactive with an amino group includes, for example, a glycidyl group and a β-dicarbonyl group. Examples of the polymerizable compound having such a functional group 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 compounds may be used alone or in combination.

[0061] The acrylic resin intermediate preferably further contains a polymerizable compound having a lipophilic group as a constituent unit. Examples of the polymerizable compound having a lipophilic group include the compounds exemplified as constituent units of the acrylic resin (1), and these may be used alone or in combination of two or more.

[0062] The acrylic resin intermediate can be produced, for example, by the same method as that for the acrylic resin (1).

[0063] 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.

[0064] The acrylic resin (2) can be produced, for example, by a method in which an acrylic resin intermediate is reacted with an alkanolamine compound at a temperature in the range of 80 to 130°C.

[0065] The weight average molecular weight (Mw) of the acrylic resin (1) and the acrylic resin (2) may be, for example, in the range of 8,000 to 50,000.

[0066] Other commercially available examples of non-aqueous dispersants 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 manufactured by Lubrizol Japan Co., Ltd.; Disperbyk 109 manufactured by BYK Japan Co., Ltd.; Acetamine 24 and Acetamine 86 manufactured by Kao Corporation; Hypermer KD3 and Hypermer KD11 manufactured by Croda Japan Co., Ltd.; Ajisper PB-821 manufactured by Ajinomoto Fine-Techno Co., Inc.; Antaron V-216 and Antaron 216 manufactured by ISP Co., Ltd. V-220"; and "Disparlon KS-860" and "Disparlon KS-873N4" manufactured by Kusumoto Chemicals Co., Ltd.

[0067] When the oil phase contains a non-aqueous dispersant, its content may be in the range of 0.1 to 10% by mass, and the ratio of the non-aqueous dispersant in the ink may be in the range of 0.1 to 10% by mass.

[0068] In step 1, a method for preparing a water-in-oil emulsion from an aqueous phase and an oil phase 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 non-aqueous dispersant, the non-aqueous dispersant 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.

[0069] 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.

[0070] 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 appropriately adjusted 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 under reduced pressure conditions. 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.

[0071] In the colored resin particle dispersion, the average particle diameter of the colored resin particles is preferably 150 nm or more, more preferably 170 nm or more, in order to obtain an ink with a higher surface density of printed matter. Furthermore, in order to obtain an ink with superior abrasion resistance of the printed surface, the average particle diameter is preferably 400 nm or less, more preferably 300 nm or less. The particle diameter of the colored resin particles can be adjusted, for example, by the amount of non-aqueous dispersant used, as described above. Specifically, the greater the amount of non-aqueous dispersant used, the smaller the particle diameter of the colored resin particles, and the smaller the amount of non-aqueous dispersant used, the larger the particle diameter of the colored resin particles.

[0072] In the present disclosure, the average particle size of the colored resin particles is the average particle size of the particle size distribution on a volume basis 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.

[0073] 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.

[0074] The amount of colored resin particles relative to the total amount of oil-based ink is not particularly limited, but may be, for example, 1% by mass or more, 5% by mass or more, or 10% by mass or more. It may also be 40% by mass or less, 30% by mass or less, or 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.

[0075] 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, 60% by mass or more, or 70% by mass or more. It may also be 99% by mass or less, 95% by mass or less, or 90% by mass or less. The content of non-aqueous solvent in oil-based inks may be in the range of 50 to 99% by mass.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] The substrate 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 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 permeability of the non-aqueous solvent.

[0081] 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.

[0082] 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.

[0083] Some embodiments of the present disclosure are set forth below. <1> An oil-based inkjet ink comprising colored resin particles containing a colorant, a resin, and a betaine compound, and a non-aqueous solvent.

[0084] <2> The betaine compound includes trimethylglycine. <1> The oil-based inkjet ink described herein.

[0085] <3> The average particle diameter of the colored resin particles is in the range of 170 to 300 nm. <1> or <2> The oil-based inkjet ink described herein. [Example]

[0086] 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."

[0087] [Production of non-aqueous dispersant 1] 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 N,N-diethylaminoethyl methacrylate, 16.5 parts by mass of isotridecyl isononanoate, and 4 parts by mass of t-butylperoxy 2-ethylhexanoate (manufactured by NOF Corporation, "Perbutyl O") was added dropwise over 3 hours. Stirring was continued for another 2 hours while maintaining the temperature at 110 ° C., yielding a solvent solution of nonaqueous dispersant 1 (solids content 50% by mass).

[0088] [Examples 1 to 7 and Comparative Example 1: Production of oil-based inkjet inks] The pigment, aqueous pigment dispersant, and water were mixed in the proportions shown in Table 1 and dispersed using a bead mill to obtain an aqueous pigment dispersion. The pigment aqueous dispersion was then blended with a resin and a betaine compound to obtain an aqueous phase. A non-aqueous solvent and a non-aqueous dispersant were mixed to obtain an oil phase. While the aqueous phase was being stirred with a magnetic stirrer, the mixture was irradiated with ultrasonic waves 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. This colored resin particle dispersion was used as an oil-based inkjet ink. The content of each component in the ink is shown in Table 2.

[0089] Comparative Example 2: Production of oil-based inkjet ink The pigment, betaine compound, and non-aqueous dispersant were mixed in the proportions shown in Table 1 and dispersed in a bead mill to obtain a colored resin particle dispersion. This colored resin particle dispersion was used as an oil-based inkjet ink. The content of each component in the ink is shown in Table 2.

[0090] [Measurement of the average 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.

[0091] [Evaluation of surface density of printed matter] The ink was loaded into a line-type inkjet printer "Comphis GD9630" (manufactured by Riso Kagaku Corporation), and a solid image 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 24 hours, after which the OD value of the surface of the print was measured using a spectrodensitometer ("Xrite eXact" manufactured by X-Rite) and evaluated according to the following criteria. The results are shown in Table 2. A:OD value is 1.20 or more B:OD value is 1.10 or more and less than 1.20 C:OD value is less than 1.10

[0092] [Evaluation of abrasion resistance of printed matter] A print was obtained in the same manner as in the evaluation of surface density. The print was left at room temperature for 24 hours, and then the solid image area was rubbed with a white cotton cloth five times in five seconds using a crock meter ("CM-1" manufactured by Atlas Electric Devices Co., Ltd.) to evaluate the abrasion resistance based on the degree of staining around the image. The evaluation criteria were as follows. The results are shown in Table 2. A: Almost no contamination is visible around the image. B: Contamination around the image is visible. C: Contamination around the image is noticeable.

[0093] [Table 1]

[0094] [Table 2]

[0095] Pigment 1: Carbon black, "MOGUL L" manufactured by Cabot Specialty Chemicals Pigment 2: Phthalocyanine blue pigment, "Lionol BGFJ" manufactured by Toyo Ink Co., Ltd. Water-based pigment dispersant: Lubrizol "Solsperse 27000" Resin 1 emulsion: "Takelac WS-5984" manufactured by Mitsui Chemicals, Inc., urethane resin emulsion, resin solid content 40% by mass Resin 2 emulsion: "Superflex 740" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., urethane resin emulsion, resin solid content 40% by mass Betaine compound: Trimethylglycine, "Betaine" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Non-aqueous solvent 1: isotridecyl isononanoate, manufactured by Kokyu Alcohol Kogyo Co., Ltd. Non-aqueous solvent 2: Exxon Mobil "Isopar M" Non-aqueous dispersant 1 solution: the one prepared above, solid content 50% by mass Non-aqueous dispersant 2 solution: Lubrizol's "Solsperse 13940," solid content 40% by mass

[0096] As shown in Table 2, the oil-based inkjet inks of each Example contained colorants as colored resin particles and further contained a betaine compound, resulting in printed matter with an excellent balance between surface density and abrasion resistance. On the other hand, Comparative Example 1, which did not contain a betaine compound, contained colorants as colored resin particles, resulting in excellent surface density, but insufficient adhesion to the substrate and poor abrasion resistance. Furthermore, Comparative Example 2, in which the colorants were not converted into colored resin particles, resulted in printed matter with low surface density.

Claims

1. An oil-based inkjet ink comprising colored resin particles containing a colorant, a resin, and a betaine compound, and a non-aqueous solvent.

2. The oil-based ink-jet ink of claim 1 , wherein the betaine compound comprises trimethylglycine.

3. 2. The oil-based inkjet ink according to claim 1, wherein the average particle size of the colored resin particles is in the range of 170 to 300 nm.

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