Ink composition for inkjet printing

Abstract

The present invention addresses the problem of ensuring low-temperature fluidity, maintaining inkjet discharge stability, and preferably improving long-term stability in a non-aqueous or oil-based inkjet ink, even without using a hydrocarbon solvent. As a solution, provided is an ink composition for solvent-based ink jet printing, which is characterized in that: in the ink composition for solvent-based ink jet printing containing a colorant, a dispersant and a solvent: the colorant is a colorant containing a pigment and / or a dye; the solvent contains a saturated fatty acid diester solvent and an unsaturated fatty acid monoester solvent; the total amount of the saturated fatty acid diester-based solvent and the unsaturated fatty acid monoester-based solvent is 50% by mass or more with respect to the total amount of the solvent-based ink composition for inkjet printing; the mass ratio of the saturated fatty acid diester solvent to the unsaturated fatty acid monoester solvent is (2: 8)-(8: 2).

Description

TECHNICAL FIELD

[0001] The present invention relates to an ink composition for inkjet printing suitable for use in an inkjet recording system, and more particularly to a solvent-based (also referred to as oil-based, non-aqueous, etc.) inkjet ink composition. BACKGROUND

[0002] The inkjet recording method is a method in which an inkjet ink having high fluidity is ejected in the form of ink particles from a fine nozzle of a printing head to record an image on a print medium placed opposite the nozzle. In general, inkjet inks are broadly classified into water-based inks and non-aqueous inks. Non-aqueous inks generally have the advantage of excellent water resistance. Further, non-aqueous inks are broadly classified into inks containing a volatile solvent as a main component and inks not containing a non-volatile solvent as a main component.

[0003] In particular, inks containing a non-volatile solvent as a main component are designed to be capable of delaying drying of the ink nozzle, so that clogging due to drying of the ink on the surface of the nozzle is less likely to occur, and for this reason, the number of times of cleaning of the ink nozzle is small, and thus the inks are suitable for high-speed inkjet printing or industrial inkjet printing.

[0004] As non-aqueous inkjet inks, several proposals have been made (for example, Patent Documents 1 to 7), and most of them contain mineral oil (also referred to as paraffin oil, hydrocarbon solvent) as a solvent. Patent Document 1 discloses a non-aqueous inkjet ink containing di(2-ethylhexyl) sebacate and an aliphatic hydrocarbon solvent; Patent Document 6 discloses a non-aqueous (oil-based) inkjet ink containing a saturated fatty acid ester solvent and a hydrocarbon solvent; and Patent Document 7 discloses a non-aqueous (oil-based) inkjet ink containing a hydrocarbon solvent and a solvent having an ester group and an ether group.

[0005] In addition, Patent Document 2 discloses a non-aqueous ink composition containing an unsaturated fatty acid ester solvent and a non-polar solvent (naphthene solvent); Patent Document 3 discloses a non-aqueous (oil-based) inkjet ink containing an unsaturated fatty acid ester solvent and a hydrocarbon solvent; and Patent Document 4 discloses an inkjet ink containing an unsaturated monoester and a non-polar solvent (petroleum hydrocarbon).

[0006] Further, Patent Document 5 proposes an inkjet ink containing a fatty acid ester from vegetable oil and a non-aqueous polar solvent, which is considered to have less environmental load.

[0007] PATENT DOCUMENTS Patent Document 1: Japanese Patent Application Laid-Open No. 11-279467 Patent Document 2: Japanese Patent Application Laid-Open No. 2003-261808 Patent Document 3: Japanese Patent Application Laid-Open No. 2005-350563 Patent Literature 4: Japanese Patent Application Laid-Open (JP-A) No. 2007-126564 Patent Literature 5: Japanese Patent Application Laid-Open (JP-A) No. 2007-161890 Patent Literature 6: Japanese Patent Application Laid-Open (JP-A) No. 2010-215700 Patent Literature 7: Japanese Patent Application Laid-Open (JP-A) No. 2012-12432 SUMMARY As shown above, non-aqueous (or oily) inkjet inks have been used in combination with fatty acid ester solvents and hydrocarbon solvents as solvents (see Patent Literatures 1 to 4, 6 and 7). Fatty acid ester solvents (especially saturated fatty acid monoester solvents) are high in stability, and are expected to improve the dispersibility of pigments and the like, but on the other hand, they tend to be high in viscosity and poor in low-temperature fluidity (i.e., high in flow point). In contrast, hydrocarbon solvents are high in low-temperature fluidity (i.e., low in flow point), and by combining the two in non-aqueous inkjet inks, it is possible to ensure stability and low-temperature fluidity.

[0008] However, hydrocarbon solvents have been pointed out as being risky to the human body, and the use thereof as ink solvents is sometimes restricted. For example, in France, the use of mineral oil in inks used for printing packaging materials and the like is restricted (see website page: https: / / www.iri-tokyo.jp / site / tiri-news / 202212-02-shien.html). Therefore, the problem of the present application is to ensure low-temperature fluidity while maintaining inkjet ejection stability, and preferably improving long-term stability, in non-aqueous or oily inkjet inks, even if hydrocarbon solvents are not used.

[0009] That is, the present application relates to an ink composition for solvent-based inkjet printing as shown below.

[0010] [1] An ink composition for solvent-based inkjet printing, characterized by containing a color material and a dispersant and a solvent in an ink composition for solvent-based inkjet printing, the color material being a color material containing a pigment and / or a dye, the solvent containing a saturated fatty acid diester solvent and an unsaturated fatty acid monoester solvent, the total amount of the saturated fatty acid diester solvent and the unsaturated fatty acid monoester solvent, the mass ratio of the saturated fatty acid diester solvent to the unsaturated fatty acid monoester solvent being 2:8 to 8:2 with respect to the total amount of the ink composition for solvent-based inkjet printing.

[0011] The present application is further preferably directed to an ink composition for solvent-based inkjet printing as shown below.

[0012] [2] The ink composition for solvent-based inkjet printing according to the above [1], characterized in that the saturated fatty acid diester-based solvent has a flow point of -10°C or lower.

[0013] [3] The ink composition for solvent-based inkjet printing according to the above [1] or [2], characterized in that the unsaturated fatty acid monoester-based solvent has a flow point of 0°C or lower.

[0014] [4] The ink composition for solvent-based inkjet printing according to any one of the above [1] to [3], characterized in that it contains no hydrocarbon-based solvent, or contains 5% by mass or less of a hydrocarbon-based solvent relative to the total amount of the ink composition for solvent-based inkjet printing.

[0015] [5] The ink composition for solvent-based inkjet printing according to any one of the above [1] to [4], characterized in that it further contains a saturated fatty acid monoester.

[0016] [6] The ink composition for solvent-based inkjet printing according to any one of the above [1] to [5], characterized in that the color material is a black pigment and / or a black dye.

[0017] [7] The ink composition for solvent-based inkjet printing according to any one of the above [1] to [6], characterized in that it contains no water, or contains 3% by mass or less of water relative to the total amount of the ink composition for solvent-based inkjet printing.

[0018] [8] The ink composition for solvent-based inkjet printing according to any one of the above [1] to [7], characterized in that the dispersant is a polymeric dispersant.

[0019] The ink composition for solvent-based inkjet printing of the present application has low-temperature fluidity even if it contains no hydrocarbon-based solvent, and has inkjet ejection stability. It is further preferable that the ink composition for solvent-based inkjet printing of the present application also has long-term stability at the time of ink storage. DETAILED DESCRIPTION

[0020] [About 1. Ink composition for solvent-based inkjet printing] The "ink composition for solvent-based inkjet printing (hereinafter also referred to as ink composition)" of the present application contains 1) a color material and 2) a dispersant and 3) a solvent; as the 3) solvent, a specific fatty acid ester-based solvent is contained. Further, the ink composition of the present application can contain 4) an arbitrary other additive.

[0021] [1-1. Color material] The color material contained in the ink composition of the present application is preferably either one of a pigment or a dye, or both.

[0022] Pigments can be either inorganic or organic, without particular limitation. Examples of inorganic pigments include: carbon black, titanium dioxide, iron oxide red, cobalt blue, ultramarine, Prussian blue, kaolin, and silicon dioxide. Examples of organic pigments include: insoluble azo pigments such as toluidine red, toluidine magenta, Hansa yellow, benzidine yellow, and pyrazolone red; oil-soluble azo pigments such as Lithol red, Helio Bordeaux, Pigment Scarlet, and Permanent Red 2B; derivatives of vat dyes such as alizarin red, indigofera tinctoria, and indigofera tinctoria; phthalocyanine organic pigments such as phthalocyanine blue and phthalocyanine green; quinacridone organic pigments such as quinacridone red and quinacridone fuchsin; perylene organic pigments such as perylene red and perylene scarlet; and isoindolinone organic pigments such as isoindolinone yellow and isoindolinone orange. Pyranone-based organic pigments such as pyranone red and pyranone orange; sulfur-indigo organic pigments; condensed azo organic pigments; benzimidazolone organic pigments; quinoline-based organic pigments such as quinoline yellow; isoindoline-based organic pigments such as isoindoline yellow; azo lake pigments; and other pigments such as vat yellow, imide yellow, nickel azo yellow, copper azomethyl yellow, pyrenone orange, anthrone orange, bianthraquinone red, and dioxazine violet. These pigments can be contained individually or in appropriate combinations.

[0023] The pigment particle size can be refined to a level suitable for inkjet printing ink compositions; for example, the average particle size is preferably set to 0.01 to 0.3 μm. Furthermore, the pigment content in the ink composition varies depending on the type of pigment or the printing application of the ink composition, but it is acceptable as long as it is within the range of 0.1 to 20% by mass.

[0024] Dyes can be, for example, oil-soluble dyes such as azo, anthraquinone, and azine dyes, as well as fluorescent dyes.

[0025] Specific examples of oil-soluble dyes include: CI Disperse Yellow 39, 42, 51, 54, 67, 71, 86, 92, 127, 134, 149, 160, 186, 199; CI Solvent Yellow 114, 163, etc. (all yellow dyes); CI Disperse Orange 81, 118, 119, etc. (all orange dyes); CI Disperse Red 53, 55, 55:1, 59, 60, 70, 75, 86, 86:1, 91, 92, 127, 146, 190, 190:1, 191, 20... 7, 283, 302; CI Solvent Red 146, etc. (the above are red dyes); CI Disperse Violet 8, 23, 26, 27, 28, 35, 36, 57; CI Disperse Blue 5, 19, 54, 55, 56, 58, 60, 64, 64:1, 72, 72:1, 73, 73:1, 77, 81, 81:1, 87, 95, 108, 143, 145, 181, 185, 197; CI Solvent Blue 36, 63, 83, 105, 111, etc. (the above are purple to blue dyes).

[0026] Specific examples of fluorescent dyes, listed using color index numbers (C·I), include: BASIC YELLOW 1, BASIC YELLOW 40, BASIC RED 1, BASIC RED 13, BASIC VIOLET 11:1, BASIC VIOLET 7, BASIC VIOLET 10, BASIC ORANGE 22, BASIC BLUE 7, BASIC GREEN 1, ACID YELLOW 3, ACID YELLOW 7, ACID RED 52, ACID RED 77, ACID RED 92, ACID BLUE 9, DISPERSE YELLOW 82, DISPERSE ORANGE 11, DISPERSE RED 58, DISPERSE BLUE 7, DIRECT YELLOW 85, DIRECT ORANGE 8, DIRECT RED 9, DIRECT BLUE 22, DIRECT GREEN 6. Fluorescent Bridging Agent 55, Fluorescent Bridging White XWS 52, Fluorescent Bridging Agent 162, Fluorescent Bridging Agent 112, Solvent Yellow 44, Solvent Yellow 116, Solvent Red 49, Solvent Blue 5, Solvent Pink, Solvent Green 7, Pigment Yellow 1, Pigment Blue 15, Pigment Green 7, Pigment Red 53, Pigment Red 57, FBA 184, etc. These dyes can be used alone or in appropriate combinations of two or more.

[0027] The ink composition of the present invention is a solvent-based (oil-based) inkjet printing ink composition, and its main use is sometimes for marking or numbering. Therefore, the ink composition of the present invention is sometimes preferably a highly visible black ink, preferably containing a black pigment; more preferably containing a black dye or a black pigment such as carbon black that is formulated to be black by combining dyes; and even more preferably containing carbon black.

[0028] [1-2. Dispersant] The dispersant contained in the ink composition of the present invention is mainly used to disperse the components of colorant (e.g., pigment). Examples of dispersants include: hydroxyl-containing carboxylic acid esters, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formaldehyde condensate salts, aromatic sulfonic acid formaldehyde condensate salts, polyoxyethylene alkyl phosphates, polyoxyethylene nonylphenyl ethers, octadecaneamine acetate, etc.

[0029] The dispersant preferably has an affinity for the solvent, and sometimes a polymeric dispersant (polymer-type dispersant) is preferred. Examples of polymeric dispersants include: high molecular weight unsaturated fatty acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formaldehyde condensate salts, aromatic sulfonic acid formaldehyde condensate salts, polyoxyethylene alkyl phosphates, polyoxyethylene nonylphenyl ethers, polyester polyamides, etc.

[0030] In polymer dispersants, polymer dispersants with ester structures are sometimes preferred. Polymer dispersants with ester structures can sometimes impart retention stability and ejection stability to ink compositions. Specific examples of polymer dispersants with ester structures include: Lubrizol's "Solsperse 9000, 13940, 17000, 18000, 28000", Kusunoki Chemicals' "DA-703-50, DA-7300, DA234", BykCemie's "Disperbyk-101", and Kawaken FineChemicals' "KFI-M, HINOACT", etc. The polymer dispersant can be an alkyd resin. Specific examples of alkyd resins include: DIC Corporation's "BECKOSOL OD-E-198-50, ES-5003-50, ES-4505-60X, ES-5103-50X", and Harima Chemicals Group Corporation's "Hariphthal 7250, 915-60L, SB7150X".

[0031] The content of the dispersant (preferably a polymeric dispersant) in the ink composition can be set in a way that allows the colorant (pigment, etc.) to be sufficiently dispersed; typically, it is contained in the ink composition in the range of 0.1 to 10% by mass, and sometimes in the range of 1 to 6% by mass.

[0032] [1-3. Solvents] The ink composition of the present invention contains a fatty acid ester solvent as a solvent; as a fatty acid ester solvent, it contains at least A. a saturated fatty acid diester solvent and B. an unsaturated fatty acid monoester solvent. Furthermore, the fatty acid ester solvent may also contain other fatty acid ester solvents such as C. saturated fatty acid monoesters. In addition, the fatty acid ester solvent may also be a fatty acid ester derived from vegetable oil.

[0033] The solvent contained in the ink composition of the present invention is preferably non-volatile. By using a non-volatile solvent, standby ejection defects (also known as delays) can be suppressed. Standby ejection defects refer to the phenomenon that droplets are ejected abnormally or completely fail to eject when printing resumes after an interruption. Standby ejection defects are usually caused by localized changes in ink concentration near the nozzle opening due to the evaporation of the ink solvent. The ink composition of the present invention, containing a non-volatile solvent, can suppress standby ejection defects.

[0034] The solvent contained in the ink composition of the present invention preferably has at least a portion of a boiling point of 200°C or higher, more preferably 220°C or higher, and even more preferably 240°C or higher. Furthermore, most of the solvents contained in the ink composition of the present invention preferably have a boiling point of 150°C or higher. For example, 60% or more by mass, preferably 70% or more by mass, more preferably 80% or more by mass, and even more preferably 90% or more of the solvents contained in the ink composition preferably have a boiling point of 150°C or higher, and even more preferably 180°C or higher.

[0035] [1-3-1. Saturated fatty acid diester solvents] The ink composition of the present invention contains a saturated fatty acid diester solvent. The saturated fatty acid diester solvent is divalent or higher, preferably a diester of a divalent saturated fatty acid. The ester of the saturated fatty acid diester is preferably an alkyl ester, particularly preferably an ester of an alkyl group having 1 to 12 carbon atoms, and sometimes a branched alkyl ester is also preferred.

[0036] Examples of saturated fatty acids with a valence of 2 or higher include sebacic acid, adipic acid, and azelaic acid. Examples of diesters of sebacic acid include di-2-ethylhexyl sebacic acid, dibutyl octyl sebacic acid, diethyl sebacic acid, dibutyl sebacic acid, and dioctyl sebacic acid. Examples of diesters of adipic acid include di-2-ethylhexyl adipate, diisononyl adipate, diisodecyl adipate, isopropyl adipate, diisooctyl adipate, di(2-propylheptyl) adipate, and diisotridecyl adipate. Examples of diesters of azelaic acid include di-2-ethylhexyl azelaic acid and diisodecyl azelaic acid.

[0037] Compared to saturated fatty acid monoesters, saturated fatty acid diester solvents exhibit better low-temperature fluidity. Specifically, saturated fatty acid diester solvents preferably have a flow point below -10°C, more preferably below -20°C, even more preferably below -30°C, even more preferably below -40°C, particularly preferably below -50°C, and most preferably below -60°C. By using saturated fatty acid diester solvents with good low-temperature fluidity, the low-temperature fluidity of the ink compositions of the present invention can be ensured.

[0038] The term "flow point" in this instruction manual refers to the value obtained by measuring according to the procedures described in Japanese Industrial Standard JIS-K2269. The procedures described in Japanese Industrial Standard JIS-K2269 are briefly explained as follows: Preheat the test tube containing the test sample to 46°C and then cool it. Begin measuring at a temperature 10°C higher than the expected flow point. Remove the test tube from the cooling bath and tilt it horizontally every 2.5°C decrease. If the sample does not flow within 5 seconds, take the previous measurement temperature (i.e., the temperature at which flow disappears) plus 2.5°C as the flow point.

[0039] [1-3-2. Unsaturated fatty acid monoester solvents] The ink composition of the present invention contains an unsaturated fatty acid monoester solvent. The unsaturated fatty acid monoester solvent is monovalent or higher, preferably a monovalent unsaturated fatty acid monoester. The ester of the unsaturated fatty acid monoester is preferably an alkyl ester, more preferably an ester of an alkyl group having 1 to 12 carbon atoms.

[0040] Unsaturated fatty acids are fatty acids having one or more unsaturated bonds (preferably carbon-carbon double bonds), and more preferably fatty acids having one unsaturated bond. Furthermore, unsaturated fatty acids are preferably unsaturated fatty acids with 15 to 25 carbon atoms, typically oleic acid, linoleic acid, and soybean oil fatty acids. Examples of oleic acid monoesters include methyl oleate, ethyl oleate, isopropyl oleate, isobutyl oleate, and 2-ethylhexyl oleate. Examples of linoleic acid monoesters include methyl linoleate, ethyl linoleate, and isobutyl linoleate. Examples of soybean oil fatty acid monoesters include methyl soybean oil and isobutyl soybean oil.

[0041] Unsaturated fatty acid monoester solvents generally exhibit higher fluidity compared to saturated fatty acid monoester solvents. For example, the flow point of unsaturated fatty acid monoester solvents is preferably below 0°C, more preferably below -5°C. Therefore, by using unsaturated fatty acid monoester solvents in conjunction with saturated fatty acid diester solvents, the fluidity of the ink composition of the present invention at low temperatures can be further ensured.

[0042] In addition, most unsaturated fatty acid monoester solvents are low viscosity (for example, isobutyl oleate has a viscosity of 9 cps at 20°C), which can reduce the viscosity of the ink composition of the present invention to a viscosity suitable for inkjet printing.

[0043] [1-3-3. Saturated fatty acid monoester solvents] The ink composition of the present invention may contain a saturated fatty acid monoester solvent. A saturated fatty acid monoester is defined as a monoester of a saturated fatty acid with a valence of 1 or more, preferably a monovalent saturated fatty acid monoester. The ester of the saturated fatty acid monoester is preferably an alkyl ester, more preferably an ester of an alkyl group having 1 to 12 carbon atoms.

[0044] Examples of saturated fatty acids include stearic acid, palmitic acid, myristic acid, lauric acid, isostearic acid, and nonanoic acid. Examples of stearic acid monoesters include 2-ethylhexyl stearate and butyl stearate. Examples of palmitic acid monoesters include isopropyl palmitate, 2-ethylhexyl palmitate, and methyl heptayl palmitate. Examples of myristic acid monoesters include isopropyl myristate and methyl heptayl myristate. Examples of lauric acid monoesters include methyl laurate, butyl laurate, and methyl heptayl laurate. Examples of isostearic acid monoesters include decyl isostearate. Examples of nonanoic acid monoesters include isododecyl nonanoate.

[0045] The saturated fatty acid monoesters preferably have a high boiling point, specifically, preferably 200°C or higher, more preferably 220°C or higher, and even more preferably 240°C or higher. Furthermore, the pour points of saturated fatty acid monoesters are mostly above -10°C, and sometimes above 0°C. By using saturated fatty acid monoesters with higher boiling points, the ink compositions of the present invention can suppress unintended drying (e.g., drying of the ink composition adhering to the ink nozzles of an inkjet printing device).

[0046] Furthermore, saturated fatty acid monoesters can maintain the printing properties of the ink composition of the present invention despite temperature changes (temperature rise of the ink composition), thereby improving the "temperature change tracking" of the ink composition. The ink composition of the present invention is an inkjet printing ink. If inkjet printing is performed continuously for a long time, the printhead in the inkjet printing apparatus will heat up, and the temperature of the ink composition will also rise. When the temperature of the ink composition rises, the quality of the printed matter sometimes deteriorates; for example, sometimes the printed image becomes disordered or pixels are missing. The ink composition of the present invention, by containing saturated fatty acid monoesters, has temperature change tracking properties, preventing such degradation of printed matter quality during continuous printing.

[0047] [1-3-4. Other solvents] The ink composition of the present invention may contain hydrocarbon solvents; however, the amount of hydrocarbon solvents is sometimes preferably small or absent. Hydrocarbon solvents are sometimes also called nonpolar solvents, paraffin oils (mineral oils), etc. Hydrocarbon solvents are nonpolar solvents of various types derived from petroleum, including aliphatic hydrocarbon solvents (paraffin solvents, etc.), cyclic hydrocarbon solvents (cycloalkanes solvents, etc.), and aromatic hydrocarbon solvents.

[0048] Hydrocarbon solvents are widely used as solvents for inkjet printing inks because they impart lubricity, temperature-responsiveness, and low-temperature fluidity to ink compositions. However, the risks of hydrocarbon solvents to living organisms (humans) have been noted, sometimes limiting their use as ink solvents. The ink compositions of this invention exhibit low-temperature fluidity and temperature-responsiveness even without hydrocarbon solvents.

[0049] In addition, the ink composition of the present invention sometimes contains a small amount of hydrocarbon solvent, but its content relative to the whole ink composition is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less; but sometimes it is most preferable to not contain hydrocarbon solvent.

[0050] The ink composition of the present invention may contain organic solvents other than fatty acid ester solvents. Examples of other organic solvents include alcohol solvents, ether solvents, and higher fatty acid solvents. Alcohol solvents may be higher alcohols (e.g., alcohols with 6 or more carbon atoms, preferably 10 or more carbon atoms) such as isomyrrol, isopalmitol, isostearyl alcohol, and oleyl alcohol. Examples of ether solvents include diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, propylene glycol dibutyl ether, triethylene glycol monobutyl ether, and triethylene glycol monomethyl ether. Examples of higher fatty acid solvents include isononanoic acid, isomyrrolidone, hexadecanoic acid, isopalmitic acid, oleic acid, and isostearic acid.

[0051] The ink composition of the present invention is preferably substantially water-free, but may contain less than 3% by mass or less than 1% by mass of water relative to the ink composition.

[0052] [1-3-5. Composition of the solvent] The ink composition of the present invention contains saturated fatty acid diester solvents and unsaturated fatty acid monoester solvents, wherein the total amount of these solvents relative to the ink composition is 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more; on the other hand, it is preferably 93% by mass or less, more preferably 90% by mass or less. Since both saturated fatty acid diester solvents and unsaturated fatty acid monoester solvents have low flow points (e.g., lower than the flow point of saturated fatty acid monoesters), the low-temperature fluidity of the ink composition can be improved by setting the total content of the two solvents to a certain level or more.

[0053] The ink composition of the present invention contains saturated fatty acid diester solvents and unsaturated fatty acid monoester solvents in a relative mass ratio of 2:8 to 8:2, preferably in the range of 3:7 to 7:3. During storage of the ink composition, the unsaturated groups of the unsaturated fatty acid monoester solvents may oxidize, sometimes resulting in a decrease in the storage stability of the ink composition. Therefore, by setting the content ratio of unsaturated fatty acid monoester solvents below a certain level, the long-term stability of the ink composition can be easily improved. Furthermore, since unsaturated fatty acid monoester solvents have a lower viscosity than saturated fatty acid diester solvents, by setting the content ratio of unsaturated fatty acid monoester solvents above a certain level, the viscosity of the ink composition can be reduced, thereby improving the spraying stability.

[0054] The ink composition of the present invention, by combining a specified amount of saturated fatty acid diester solvent and unsaturated fatty acid monoester solvent, can achieve both low-temperature fluidity and spray stability, but sometimes it is more advantageous to further contain saturated fatty acid monoester solvent. For example, by adjusting the saturated fatty acid monoester solvent, the tracking performance to temperature changes can sometimes be further improved. The content of saturated fatty acid monoester solvent only needs to be 0% by mass or more relative to the ink composition, sometimes preferably 5% by mass or more, and may also be 10% by mass or more; on the other hand, it is usually 40% by mass or less, and may also be 30% by mass or less, or may also be 25% by mass or less.

[0055] [1-4. Other additives] The ink composition of the present invention may contain components other than colorants, dispersants, and solvents. Examples of other components include dispersing aids (also known as pigment derivatives), inert resins, leveling agents, preservatives, etc.

[0056] Dispersing agents, together with dispersants, can improve the dispersibility of pigments. Dispersing agents refer to pigment derivatives; examples include sulfonic acid derivatives, sulfonamide derivatives, alkylamino derivatives, and alkyl derivatives of pigments. Examples of dispersing agents include Solsperse 5000, Solsperse 12000, Solsperse 22000 (Lubrizol), EFKA745, and EFKA6750 (EFKACHEMICALS BV). The content of dispersing agents relative to the ink composition can be less than 2% by mass.

[0057] Inert resins can improve the adhesion between the ink composition and the printed material, and can adjust the dot spread of the ink composition on the printed material. Preferably, the inert resin is soluble in the ink composition. Examples of inert resins include: methacrylic resins, styrene-methacrylic resins, styrene-maleic acid resins, rosin resins, rosin ester resins, ethylene-vinyl acetate resins, petroleum resins, coumarone-indene resins, terpene phenolic resins, phenolic resins, polyurethane resins, melamine resins, urea-formaldehyde resins, epoxy resins, cellulose resins, vinyl chloride-vinyl acetate resins, xylene resins, alkyd resins, aliphatic hydrocarbon resins, butyraldehyde resins, maleic acid resins, fumaric acid resins, etc., but are not particularly limited. The content of the inert resin relative to the ink composition can be less than 3% by mass.

[0058] The leveling agent is a surfactant, such as a silicone surfactant, a fluorosurfactant, or a polyoxyethylene adduct that is a nonionic surfactant. Among these, silicone surfactants are preferred from the perspective of improving the wettability of the ink composition while preventing foaming. The content of the leveling agent relative to the ink composition can be 2% by mass or less.

[0059] [1-5. Physical Properties of Ink Compositions] The viscosity of the ink composition of the present invention at 20°C is preferably in the range of 5 to 30 mPa·s, more preferably in the range of 8 to 16 mPa·s. By adjusting the viscosity, printing by inkjet printing can be performed, and the inkjet printing can be stably ejected even if the printhead of the inkjet printer experiences temperature changes. Furthermore, the freezing point of the ink composition of the present invention can be set to below -5°C; more further, it can be set to below -10°C or below -20°C.

[0060] [1-6. Preparation method of ink composition] The ink composition of the present invention can be prepared by referring to conventional methods for preparing solvent-based inkjet printing inks. Specifically, it can be prepared by mixing the components using a disperser (e.g., ball mill, sand mill, vertical ball mill, roller mill, mixer, Henschel mixer, colloid mill, ultrasonic homogenizer, jet mill, annular mill, etc.); furthermore, it can be filtered using a known filter such as a membrane filter, if necessary.

[0061] Alternatively, an ink composition can be prepared by mixing the base ink (a concentrate of colorant (pigment, etc.)) with other components after preparation. The base ink can be obtained by mixing and grinding a portion of the colorant, dispersant, and solvent with any dispersing aid.

[0062] [2. Applications of solvent-based inkjet printing ink compositions] The solvent-based inkjet printing ink composition (ink composition) of the present invention is applied to a substrate for printing via inkjet printing. The inkjet printing method is not particularly limited, and includes: charge-controlled inkjet printing utilizing electrostatic attraction; on-demand inkjet printing utilizing the vibration pressure of piezoelectric elements (pressure pulse method); acoustic inkjet printing converting electrical signals into sound beams and irradiating the ink to eject ink using radial pressure; and thermal foaming inkjet printing heating the ink to form bubbles and utilizing the resulting pressure. Furthermore, inkjet printing can also be continuous inkjet printing; in this case, conductive additives can be added to adjust the conductivity of the ink composition. In addition, the printhead in the inkjet printing apparatus can be either a multi-path mode (serial printhead mode) or a single-path mode (line printhead mode).

[0063] The substrate for printing the ink composition of the present invention is not particularly limited, but absorbent substrates are preferred. Examples of absorbent substrates include paper substrates or fabrics; highly absorbent substrates, such as thick paper or corrugated paper, are particularly preferred as the substrate. Furthermore, since the ink composition of the present invention does not contain hydrocarbon solvents, it further reduces the risk to human health and also promotes the recycling of printed materials. Therefore, it is sometimes advantageous to use it as an ink for widely applied industrial / industrial inkjet printing.

[0064] Example The present invention will be further described in detail below with reference to embodiments. However, the present invention should not be interpreted as limited by the description of these embodiments.

[0065] A. Materials used in the preparation of ink compositions A-1. Color material ·Carbon black: MA7 (Mitsubishi Chemical Corporation) • Magenta pigment: Fastogen Super Magenta RGT (DIC Company) A-2. Dispersant Solsperse 18000 (Lubrizol) A-3. Solvent A-3-1. Unsaturated fatty acid monoesters · Methyl oleate (EXEPARL M-OL, Kao Corporation) Pour point < -5℃, boiling point 218.5℃ Isobutyl oleate (VINYCIZER 30, Kao Corporation) Pour point < -10℃ · 2-Ethylhexyl oleate (UNISTER MB-881, Nippon Oil Company) Pour point -40°C, boiling point 465.8±24.0°C A-3-2. Saturated fatty acid diester • Di-2-ethylhexyl azelate (SANSOCIZER DOZ, Shin Nippon Rikka Co., Ltd.) Pour point < -60℃, boiling point > 282℃ • Di-2-ethylhexyl adipic acid (SANSOCIZER DOA, Shin Nippon Rikka Co., Ltd.) Pour point < -60℃, boiling point 417℃ • Diisononyl adipate (SANSOCIZER DINA, Shin Nippon Rikka Co., Ltd.) Pour point < -60℃, boiling point > 250℃ • Diisodecyl adipic acid (SANSOCIZER DIDA, Shin Nippon Rika Co., Ltd.) Pour point < -60℃, boiling point 282℃ • Di-2-ethylhexyl sebacate (SANSOCIZER DOS, Shin Nippon Rika Co., Ltd.) Pour point < -60℃, boiling point approximately 248℃ A-3-3. Saturated fatty acid monoesters Methyl lauryl ester (EXEPARL ML-85, Kao Corporation) Pour point < 20℃, boiling point approximately 260℃ Isopropyl myristate (EXEPARL IPM, Kao Corporation) Pour point 2~8℃, boiling point approximately 304℃ Isopropyl palmitate (EXEPARL IPP, Kao Corporation) Pour point 8~15℃, boiling point approximately 332℃ · 2-Ethylhexyl stearate (EXEPARL EH-S, Kao Corporation) Possession point -9℃, boiling point approximately 40℃ A-3-4. Other solvents • Saturated hydrocarbon solvents (P-40, MORESCO) A-4. Pigment Derivatives Solsperse 5000 (Lubrizol) A-5. Resin • Methacrylic acid resin (BR-87, Mitsubishi Chemical Corporation) A-6. Leveling agent • Silicon-based surface conditioner (BYK-315N, BYK Corporation) B. Preparation steps of ink composition Prepare ink compositions for the Examples and Comparative Examples (except Comparative Example 9) according to the formulations shown in Tables 1 and 2 (the mixing ratios of each component in Tables 1 and 2 refer to mass %).

[0066] B-1. Manufacturing of base inks for solvent-based inkjet printing Dissolve 10 parts by weight of dispersant (Solsperse 18000) in 59 parts by weight of unsaturated fatty acid monoester (methyl oleate, isobutyl oleate, or 2-ethylhexyl oleate). Stir in 30 parts by weight of colorant (carbon black MA-7 or magenta pigment) and 1 part by weight of desired pigment derivative (Solsperse 5000). Then, grind using a bead mill to obtain a non-aqueous inkjet base ink. In Examples 8 and 11 and Comparative Examples 3 and 8, the unsaturated fatty acid monoester was replaced with a saturated diester (di-2-ethylhexyl azelate) to obtain the non-aqueous inkjet base ink.

[0067] B-2. Preparation of solvent-based inkjet printing ink compositions The base ink and each material were mixed according to the formulation in Table 1 or Table 2 (the mixing ratio of each material is by mass%) to obtain the non-aqueous inkjet ink composition of the examples and comparative examples.

[0068] Preparation of the ink composition of Comparative Example 9 B-1. Manufacturing of base inks for solvent-based inkjet printing Dissolve 10 parts by mass of dispersant (Solsperse 18000) in 59 parts by mass of hydrocarbon solvent, stir and mix 30 parts by mass of colorant (carbon black MA-7) and 1 part by mass of pigment derivative (Solsperse 5000) in the mixture, and then grind the mixture using a bead mill to obtain a non-water-based inkjet base ink.

[0069] B-2. Preparation of solvent-based inkjet printing ink compositions The base ink and each material were mixed according to the formula in Table 2 (the mixing ratio of each material is by mass%) to obtain the non-aqueous inkjet ink compositions of the examples and comparative examples.

[0070] C. Evaluation of ink compositions C-1. Low-temperature fluidity Each ink composition obtained from the examples and comparative examples was placed into a glass bottle, sealed, and stored at -20°C for 24 hours. The state after storage was evaluated according to the following evaluation criteria.

[0071] ○: No freezing or frozen solids were detected; the substance remained fluid. △: Confirm that the frozen or frozen solid can be restored to its original state by gently shaking it. ×: Confirmed solids that cannot be restored to their original state even with strong shaking. C-2. Ejection stability Using the ink compositions obtained in the examples and comparative examples, printing was performed on polyvinyl chloride sheets (trade name: MD5, METAMARK Corporation), and the number of sheets produced by the unprinted portions was evaluated according to the following evaluation criteria.

[0072] 〇: The unprinted portion was produced after the 71st sheet, or the unprinted portion was not produced before the 100th sheet.

[0073] △: The unprinted portions are produced on sheets 30 through 70.

[0074] ×: Unprinted portions are produced before the 30th sheet.

[0075] C-3. Storage stability Each ink composition obtained from the examples and comparative examples was placed into a glass bottle, sealed, and stored at 60°C for 28 days. The condition after storage was evaluated according to the following evaluation criteria.

[0076] ○: No thickening or sediment was detected. △: Confirm that the thickening or sedimentation can be restored to its original state by gently shaking. ×: Confirmed that even strong shaking cannot restore the original level of thickening or sedimentation. [Table 1]

[0077] [Table 2]

[0078] As shown in Example 1 (Table 1), the ink composition containing saturated fatty acid diester (di-2-ethylhexyl azelate) and unsaturated fatty acid monoester (methyl oleate) at a specified mass ratio and totaling 70% by mass exhibits good low-temperature flowability, spray stability, and storage stability. Furthermore, although the ink composition of Example 1 does not contain hydrocarbon solvents, it exhibits the same, or even better, low-temperature flowability, spray stability, and storage stability as the ink composition of Comparative Example 9, which uses hydrocarbon solvents.

[0079] In contrast, as shown in Comparative Examples 1-3 (Table 2), the ink compositions exhibited insufficient properties when the mass ratio of saturated fatty acid diester (di-2-ethylhexyl azelate) to unsaturated fatty acid monoester (methyl oleate) was not within the range of 2:8 to 8:2. This indicates that the ink compositions of Comparative Examples 1 and 2, with their low saturated fatty acid diester content and high relative proportion of unsaturated fatty acid monoester, tended to experience decreased storage stability. This phenomenon suggests that the unsaturated fatty acid monoester may undergo modification during storage, such as oxidation of the unsaturated groups. Furthermore, the ink composition of Comparative Example 3, with an unsaturated fatty acid monoester content of 8.92% by mass and a high relative proportion of saturated fatty acid diester, exhibited insufficient spraying stability. In other words, the ink composition of Comparative Example 3 had a relatively high viscosity.

[0080] Furthermore, as shown in Comparative Examples 4-7 (Table 2), the ink compositions without saturated fatty acid diesters do not exhibit sufficient low-temperature fluidity. In particular, low-temperature fluidity tends to deteriorate when formulated with saturated fatty acid monoester solvents (methyl lauryl ester (flow point < 20°C), isopropyl palmitate (flow point 8-15°C)) that have relatively high flow points.

[0081] The ink composition of Comparative Example 8 (Table 2) has a low total amount of saturated fatty acid diester (di-2-ethylhexyl azelate) and unsaturated fatty acid monoester (methyl oleate) (total 40% by mass), resulting in insufficient low-temperature fluidity.

[0082] As shown in Examples 1-3, even when the type of unsaturated fatty acid monoester is changed (methyl oleate, isobutyl oleate, 2-ethylhexyl oleate), various evaluations are good. Furthermore, as shown in Examples 1 and 4-7, even when the type of saturated fatty acid diester is changed (di-2-ethylhexyl azelate, di-2-ethylhexyl adipate, diisononyl adipate, diisodecyl adipate, di-2-ethylhexyl sebacate), various evaluations are good. Therefore, unsaturated fatty acid monoesters and saturated fatty acid diesters can be appropriately selected and used in ink compositions with reference to the disclosure in this specification.

[0083] As shown in Examples 8 and 9, various evaluations were satisfactory even when the ratio of saturated fatty acid diesters to unsaturated fatty acid monoesters was varied. Furthermore, as shown in Examples 10 and 11, various evaluations were satisfactory even without the formulation of saturated fatty acid monoesters. Thus, the contents of unsaturated fatty acid monoesters and saturated fatty acid diesters can be appropriately set with reference to the disclosure in this specification for use in ink compositions.

[0084] Example 12 is an example of formulating an inert resin (methacrylic resin), Example 13 is an example of formulating a leveling agent (silicone surfactant), Example 14 is an example of not formulating a pigment derivative, and Example 15 is an example of using a magenta pigment instead of carbon black. All of the above ink compositions were evaluated as good.

[0085] Industrial availability The ink composition of the present invention, as a solvent-based inkjet printing ink, is suitable for a wide variety of applications. In particular, the ink composition of the present invention exhibits high low-temperature fluidity and maintains ejection stability even during continuous printing, even without hydrocarbon solvents (containing mineral oil or paraffin oil). Furthermore, since the ink composition of the present invention does not contain hydrocarbon solvents, it further reduces the risk to human health and promotes the recycling of printed materials. Therefore, the ink composition of the present invention is particularly effective as an "industrial inkjet printing ink" for large-volume and continuous use, and can be used as printing ink for various packaging materials or product catalogs, etc.

Claims

1. A solvent-based inkjet printing ink composition, characterized in that, In solvent-based inkjet printing ink compositions containing colorants, dispersants, and solvents The colorant is a colorant containing pigments and / or dyes. The solvent contains saturated fatty acid diester solvents and unsaturated fatty acid monoester solvents. The total amount of the saturated fatty acid diester solvent and the unsaturated fatty acid monoester solvent is 50% by mass or more relative to the total amount of the solvent-based inkjet printing ink composition. The mass ratio of the saturated fatty acid diester solvent to the unsaturated fatty acid monoester solvent is 2:8 to 8:

2.

2. The solvent-based inkjet printing ink composition according to claim 1, characterized in that, The pour point of the saturated fatty acid diester solvent is below -10°C.

3. The solvent-based inkjet printing ink composition according to claim 1 or 2, characterized in that, The unsaturated fatty acid monoester solvent has a flow point below 0°C.

4. The solvent-based inkjet printing ink composition according to claim 1 or 2, characterized in that, It does not contain hydrocarbon solvents, or contains less than 5% by mass of hydrocarbon solvents relative to the total amount of the solvent-based inkjet printing ink composition.

5. The solvent-based inkjet printing ink composition according to claim 1 or 2, characterized in that, It further contains saturated fatty acid monoesters.

6. The solvent-based inkjet printing ink composition according to claim 1 or 2, characterized in that, The colorant is a black pigment and / or a black dye.

7. The solvent-based inkjet printing ink composition according to claim 1 or 2, characterized in that, It contains no water, or contains less than 3% by mass of water relative to the total amount of the solvent-based inkjet printing ink composition.

8. The solvent-based inkjet printing ink composition according to claim 1 or 2, characterized in that, The dispersant is a polymeric dispersant.

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