Ink composition for ink jet printing

Abstract

To maintain inkjet discharge stability and preferably improve long-term stability while securing low-temperature fluidity even without using a hydrocarbon-based solvent in a nonaqueous or oily inkjet ink.SOLUTION: Provided is a solvent-based inkjet printing ink composition containing a colorant, a dispersant, and a solvent, wherein the colorant is a colorant containing a pigment and / or a dye, the solvent contains a saturated fatty acid diester-based solvent and an unsaturated fatty acid monoester-based 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 relative to the total amount of the solvent-based inkjet printing ink composition, and the weight ratio of the saturated fatty acid diester-based solvent and the unsaturated fatty acid monoester-based solvent is 2:8 to 8:2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink jet printing ink composition suitable for use in an ink jet recording system, and in particular to a solvent-based (also called oil-based, non-aqueous, etc.) ink jet ink composition. [Background technology]

[0002] Inkjet recording involves ejecting highly fluid inkjet ink as ink droplets from fine nozzles in a head to record an image on a substrate placed opposite the nozzles. Inkjet inks are generally broadly classified into aqueous inks and non-aqueous inks. Non-aqueous inks generally have the advantage of being highly water-resistant. Non-aqueous inks are further broadly classified into inks containing primarily a volatile solvent and inks containing primarily a non-volatile solvent.

[0003] In particular, inks containing a non-volatile solvent as a main component are designed to dry slowly in the ink nozzles, making them less likely to clog due to the ink drying on the nozzle surface and reducing the need to clean the ink nozzles frequently, making them suitable for use in high-speed inkjet printers and industrial inkjet printers.

[0004] Several non-aqueous inkjet inks have been proposed (for example, Patent Documents 1 to 7), most of which contain mineral oil (also called hydrocarbon solvent) as the 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] Furthermore, 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] Furthermore, Patent Document 5 proposes a non-aqueous inkjet ink that contains a fatty acid ester derived from vegetable oil and a non-aqueous polar solvent and is considered to have a low environmental impact. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication 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 Document 4] Japanese Patent Application Laid-Open No. 2007-126564 [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-161890 [Patent Document 6] Japanese Patent Application Laid-Open No. 2010-215700 [Patent Document 7] Japanese Patent Application Laid-Open No. 2012-12432 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, non-aqueous (or oil-based) inkjet inks often use a combination of fatty acid ester solvents and hydrocarbon solvents as solvents (see Patent Documents 1 to 4, 6, and 7). Fatty acid ester solvents (particularly saturated fatty acid monoester solvents) are highly stable and are expected to have effects such as improving the dispersibility of pigments, but they also tend to have high viscosity and poor low-temperature fluidity (i.e., high pour point). In contrast, hydrocarbon solvents have high low-temperature fluidity (i.e., low pour point), so combining the two in a non-aqueous inkjet ink can ensure both stability and low-temperature fluidity.

[0009] However, hydrocarbon solvents have been identified as posing risks to the human body, and their use as ink solvents is sometimes restricted. For example, in France, the use of mineral oil in inks for printing on packaging materials, etc., is restricted (see website page: https: / / www.iri-tokyo.jp / site / tiri-news / 202212-02-shien.html). Therefore, an object of the present invention is to provide a non-aqueous or oil-based inkjet ink that maintains inkjet ejection stability and preferably improves long-term stability while ensuring low-temperature fluidity, even without using hydrocarbon solvents. [Means for solving the problem]

[0010] That is, the present invention relates to the following solvent-based ink composition for ink-jet printing. [1] A solvent-based ink composition for inkjet printing comprising a colorant, a dispersant, and a solvent: The colorant comprises a pigment and / or a dye; the solvent comprises 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 is 50% by mass or more based on the total amount of the solvent-based inkjet printing ink composition; A solvent-based ink composition for ink-jet printing, wherein the weight ratio of the saturated fatty acid diester solvent to the unsaturated fatty acid monoester solvent is 2:8 to 8:2.

[0011] More preferably, the present invention relates to the following solvent-based ink-jet printing ink composition. [2] The solvent-based ink composition for ink-jet printing according to [1] above, wherein the saturated fatty acid diester solvent has a pour point of −10° C. or lower. [3] The solvent-based ink composition for ink-jet printing according to [1] or [2] above, wherein the pour point of the unsaturated fatty acid monoester solvent is 0°C or lower.

[0012] [4] The solvent-based ink composition for inkjet printing according to any one of [1] to [3] above, which does not contain a hydrocarbon solvent or contains a hydrocarbon solvent in an amount of 5% by mass or less based on the total amount of the solvent-based ink composition for inkjet printing. [5] The solvent-based ink composition for ink-jet printing according to any one of [1] to [4] above, further comprising a saturated fatty acid monoester. [6] The solvent-based ink composition for ink-jet printing according to any one of [1] to [5] above, wherein the coloring material is a black pigment and / or a black dye. [7] The solvent-based ink composition for ink-jet printing according to any one of [1] to [6], which does not contain water or contains 3 mass % or less of water based on the total amount of the solvent-based ink composition for ink-jet printing. [8] The solvent-based ink composition for ink-jet printing according to any one of [1] to [7] above, wherein the dispersant is a polymer dispersant. [Effects of the Invention]

[0013] The solvent-based ink jet printing ink composition of the present invention has low-temperature fluidity and ink jet ejection stability even without containing a hydrocarbon solvent. More preferably, the solvent-based ink jet printing ink composition of the present invention also has long-term stability during ink storage. DETAILED DESCRIPTION OF THE INVENTION

[0014] [1. Solvent-based inkjet printing ink composition] The "solvent-based ink composition for inkjet printing (hereinafter also referred to as ink composition)" of the present invention contains 1) a colorant, 2) a dispersant, and 3) a solvent, and 3) the solvent contains a specific fatty acid ester-based solvent. Furthermore, the ink composition of the present invention can contain 4) any other additives.

[0015] [1-1. Coloring materials] The coloring material contained in the ink composition of the present invention is preferably either a pigment or a dye, or both.

[0016] The pigment may be either an inorganic pigment or an organic pigment, and is not particularly limited. Examples of inorganic pigments include carbon black, titanium oxide, red iron oxide, cobalt blue, ultramarine, Prussian blue, kaolin, silica, etc. Examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, and pyrazolone red; oil-soluble azo pigments such as litol red, helio bordeaux, pigment scarlet, and permanent red 2B; derivatives of vat dyes such as alizarin, indanthrone, and thioindigo maroon; phthalocyanine organic pigments such as phthalocyanine blue and phthalocyanine green; quinacridone organic pigments such as quinacridone red and quinacridone magenta; perylene organic pigments such as perylene red and perylene scarlet; and isoindolinone ethylenediamine. isoindolinone-based organic pigments such as Pyranthrone Red and Isoindolinone Orange; pyranthrone-based organic pigments such as Pyranthrone Red and Pyranthrone Orange; thioindigo-based organic pigments; condensed azo-based organic pigments; benzimidazolone-based organic pigments; quinophthalone-based organic pigments such as Quinophthalone Yellow; isoindoline-based organic pigments such as Isoindoline Yellow; azo lake pigments; and other pigments such as Flavanthrone Yellow, Acylamide Yellow, Nickel Azo Yellow, Copper Azomethine Yellow, Perinone Orange, Anthrone Orange, Dianthraquinonyl Red, and Dioxazine Violet. These pigments may be contained alone or in appropriate combination.

[0017] The particle size of the pigment may be small enough to enable inkjet printing of the ink composition, and preferably has an average particle size of 0.01 to 0.3 μm. The content of the pigment in the ink composition may vary depending on the type of pigment and the printing application of the ink composition, but may be in the range of 0.1 to 20% by mass.

[0018] The dye may be, for example, a conventionally known oil-soluble dye such as an azo dye, an anthraquinone dye, or an azine dye, or a fluorescent dye.

[0019] 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, 207, 28 3, 302; CI Solvent Red 146, etc. (all 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. (all violet to blue dyes).

[0020] Specific examples of fluorescent dyes, listed by color index number (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, and DIRECT GREEN. Representative examples include SOLVENT YELLOW 6, FLUORESCENT BRIGTHING AGENT 55, FLUORESCENT BRIGTHING WHITE XWS 52, FLUORESCENT 162, FLUORESCENT 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, and FBA 184. These dyes can be used alone or in appropriate combination of two or more.

[0021] The ink composition of the present invention is a solvent-based (oil-based) ink composition for inkjet printing, and its main use may be marking or coding. Therefore, it may be preferable for the ink composition of the present invention to be a black ink with high visibility, and it preferably contains a black colorant; it more preferably contains a black dye obtained by combining dyes to obtain a black color, or a black pigment such as carbon black; and it is even more preferable for the ink composition to contain carbon black.

[0022] [1-2. Dispersants] The dispersant contained in the ink composition of the present invention is a component mainly for dispersing colorants (e.g., pigments). Examples of dispersants include hydroxyl group-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, naphthalenesulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ethers, and stearylamine acetate.

[0023] The dispersant preferably has affinity with the solvent, and may be preferably a polymer dispersant (polymer-type dispersant). Examples of polymer dispersants include high-molecular-weight unsaturated fatty acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ethers, polyester polyamines, etc.

[0024] Among polymer dispersants, it may be preferable to use a polymer dispersant having an ester structure. A polymer dispersant having an ester structure may be able to provide storage stability and ejection stability to the ink composition. Specific examples of pigment dispersants having an ester structure include Lubrizol's "Solsperse 9000, 13940, 17000, 18000, 28000," Kusumoto Chemicals' "DA-703-50, DA-7300, DA234," BykCemie's "Disperbyk-101," and Kawaken Fine Chemicals' "KFI-M, Hinoact." The polymer dispersant may be an alkyd resin. Specific examples of alkyd resins include "BECKOSOL OD-E-198-50, ES-5003-50, ES-4505-60X, ES-5103-50X" from DIC Corporation, and "HARIFTAL 7250, 915-60L, SB7150X" from Harima Chemicals Co., Ltd.

[0025] The content of the dispersant (preferably a polymer dispersant) in the ink composition may be set so as to obtain sufficient dispersibility of the colorant (pigment, etc.); typically, the content of the dispersant in the ink composition is often in the range of 0.1 to 10% by mass, and sometimes in the range of 1 to 6% by mass.

[0026] [1-3. Solvent] The ink composition of the present invention contains a fatty acid ester-based solvent as a solvent, and the fatty acid ester-based solvent contains at least A. a saturated fatty acid diester-based solvent and B. an unsaturated fatty acid monoester-based solvent. Furthermore, the fatty acid ester-based solvent may contain other fatty acid ester-based solvents, such as C. a saturated fatty acid monoester. Furthermore, the fatty acid ester-based solvent may be a fatty acid ester derived from vegetable oil.

[0027] The solvent contained in the ink composition of the present invention is preferably non-volatile. The use of a non-volatile solvent can suppress daycap (also known as latency). Daycap refers to a phenomenon in which droplets are ejected abnormally or not at all when inkjet printing is resumed after an interruption. Daycap usually occurs when the ink solvent evaporates, causing a local change in ink concentration near the nozzle opening. The ink composition of the present invention, which contains a non-volatile solvent, can suppress daycap.

[0028] At least a portion of the solvents contained in the ink composition of the present invention preferably have 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, and for example, 60% by mass or more, preferably 70% by mass or higher, more preferably 80% by mass or higher, and even more preferably 90% by mass or higher of the solvents contained in the ink composition preferably have a boiling point of 150° C. or higher, more preferably 180° C. or higher.

[0029] [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 a diester of a saturated fatty acid having a valence of two or more, preferably a divalent fatty acid. The ester of the saturated fatty acid diester is preferably an alkyl ester, particularly an ester of an alkyl having 1 to 12 carbon atoms, and in some cases an ester of a branched chain alkyl may be preferable.

[0030] Examples of divalent or higher saturated fatty acids include sebacic acid, adipic acid, azelaic acid, etc. Examples of diesters of sebacic acid include di-2-ethylhexyl sebacate, dibutyloctyl sebacate, diethyl sebacate, dibutyl sebacate, dioctyl sebacate, etc. Examples of diesters of adipic acid include di-2-ethylhexyl adipate, diisononyl adipate, diisodecyl adipate, isopropyl adipate, diisooctyl adipate, di(2-propylheptyl) adipate, diisotridecyl adipate, etc. Examples of diesters of azelaic acid include di-2-ethylhexyl azelaate, diisodecyl azelaate, etc.

[0031] Saturated fatty acid diester solvents have better low-temperature fluidity than saturated fatty acid monoesters; specifically, saturated fatty acid diester solvents have a pour point of preferably −10° C. or lower, more preferably −20° C. or lower, even more preferably −30° C. or lower, still more preferably −40° C. or lower, particularly preferably −50° C. or lower, and most preferably −60° C. or lower. By using a saturated fatty acid diester solvent with good low-temperature fluidity, the low-temperature fluidity of the ink composition of the present invention can be ensured.

[0032] In this specification, the "pour point" refers to a value measured according to the procedure described in JIS-K2269. Briefly, the procedure described in JIS-K2269 is as follows: a test tube containing a sample to be measured is preheated to 46°C and then cooled, and measurement is started at a temperature 10°C higher than the predicted pour point; every time the temperature is lowered by 2.5°C, the test tube is removed from the cooling bath and inclined on its side; if the sample does not move for 5 seconds, the pour point is determined to be a temperature 2.5°C higher than the previous measurement temperature (= the temperature at which the sample no longer becomes fluid).

[0033] [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 a monoester of a monovalent or higher unsaturated fatty acid, preferably a monovalent unsaturated fatty acid. The ester of the unsaturated fatty acid monoester is preferably an alkyl ester, and more preferably an ester of an alkyl having 1 to 12 carbon atoms.

[0034] The unsaturated fatty acid is a fatty acid having one or more unsaturated bonds (preferably a carbon-carbon double bond), preferably a fatty acid having one unsaturated bond. Furthermore, the unsaturated fatty acid is preferably an unsaturated fatty acid having 15 to 25 carbon atoms, typically oleic acid, linoleic acid, soybean oil fatty acid, etc. Examples of the monoester of oleic acid include methyl oleate, ethyl oleate, isopropyl oleate, isobutyl oleate, 2-ethylhexyl oleate, etc. Examples of the monoester of linoleic acid include methyl linoleate, ethyl linoleate, isobutyl linoleate, etc. Examples of the monoester of soybean oil fatty acid include methyl soybean oil, isobutyl soybean oil, etc.

[0035] Unsaturated fatty acid monoester solvents often have higher fluidity than saturated fatty acid monoester solvents. For example, the pour point of an unsaturated fatty acid monoester solvent is preferably 0°C or lower, more preferably -5°C or lower. Therefore, by using an unsaturated fatty acid monoester solvent together with a saturated fatty acid diester solvent, the fluidity of the ink composition of the present invention at low temperatures can be further ensured.

[0036] Furthermore, unsaturated fatty acid monoester solvents often have low viscosity (for example, the viscosity of isobutyl oleate at 20°C is 9 cps), and can reduce the viscosity of the ink composition of the present invention to a level suitable for inkjet printing.

[0037] [1-3-3. Saturated fatty acid monoester solvents] The ink composition of the present invention may contain a saturated fatty acid monoester solvent. The saturated fatty acid monoester is a monoester of a saturated fatty acid that is monovalent or higher, preferably monovalent. The saturated fatty acid monoester is preferably an alkyl ester, and more preferably an ester of an alkyl having 1 to 12 carbon atoms.

[0038] Examples of saturated fatty acids include stearic acid, palmitic acid, myristic acid, lauric acid, isostearic acid, pelargonic acid, etc. Examples of monoesters of stearic acid include 2-ethylhexyl stearate, butyl stearate, etc. Examples of monoesters of palmitic acid include isopropyl palmitate, 2-ethylhexyl palmitate, methylheptyl palmitate, etc. Examples of monoesters of myristic acid include isopropyl myristate, methylheptyl myristate, etc. Examples of monoesters of lauric acid include methyl laurate, butyl laurate, methylheptyl laurate, etc. Examples of monoesters of isostearic acid include decyl isostearate, etc. Examples of monoesters of pelargonic acid include isododecyl pelargonate, etc.

[0039] The saturated fatty acid monoester preferably has a relatively high boiling point, specifically, preferably 200°C or higher, more preferably 220°C or higher, and even more preferably 240°C or higher. The saturated fatty acid monoester often has a pour point higher than -10°C, and may also be higher than 0°C. By using a saturated fatty acid monoester with a relatively high boiling point, unintended drying of the ink composition of the present invention (for example, drying of the ink composition that has adhered to the ink nozzle of an inkjet printing device) can be suppressed.

[0040] Furthermore, the saturated fatty acid monoester can maintain the printing properties of the ink composition of the present invention when the temperature of the ink composition changes (when the temperature of the ink composition increases), i.e., it can improve the "temperature change response" of the ink composition. The ink composition of the present invention is an ink for inkjet printing, and when inkjet printing is performed continuously for a long period of time, the printer head in the inkjet printing device generates heat, and the temperature of the ink composition also increases accordingly. When the temperature of the ink composition increases, the quality of the printed matter may deteriorate, and for example, the printed image may become distorted or dots may be missing. By containing the saturated fatty acid monoester, the ink composition of the present invention has temperature change response and can prevent such deterioration in the quality of the printed matter during continuous printing.

[0041] [1-3-4. Other solvents] The ink composition of the present invention may contain a hydrocarbon solvent; however, it may be preferable that the amount of hydrocarbon solvent is small or that no hydrocarbon solvent is contained. Hydrocarbon solvents are also referred to as nonpolar solvents, mineral oils, etc. Hydrocarbon solvents are multi-component nonpolar solvents obtained from petroleum, and include aliphatic hydrocarbon solvents (paraffinic solvents, etc.), cyclic hydrocarbon solvents (naphthenic solvents, etc.), aromatic hydrocarbon solvents, etc.

[0042] Hydrocarbon solvents are widely used as solvents for solvent-based inkjet printing inks because they can impart self-lubrication, temperature tracking, and even low-temperature fluidity to ink compositions. However, hydrocarbon solvents have been identified as posing risks to living organisms (human bodies), and their use as ink solvents is sometimes restricted. The ink composition of the present invention has low-temperature fluidity and temperature tracking ability even without containing a hydrocarbon solvent.

[0043] The ink composition of the present invention may contain a small amount of hydrocarbon solvent, and the amount thereof is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, based on the total mass of the ink composition; however, it may be most preferable that the ink composition does not contain any hydrocarbon solvent.

[0044] The ink composition of the present invention may contain an organic solvent other than the fatty acid ester-based solvent. Examples of other organic solvents include alcohol-based solvents, ether-based solvents, and higher fatty acid-based solvents. The alcohol-based solvent may be a higher alcohol (e.g., an alcohol having 6 or more carbon atoms, preferably 10 or more carbon atoms) such as isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, or oleyl alcohol. Examples of ether-based solvents include diethyl 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-based solvents include isononanoic acid, isomyristic acid, hexadecanoic acid, isopalmitic acid, oleic acid, and isostearic acid.

[0045] The ink composition of the present invention preferably contains substantially no water, but may contain 3% by mass or less, or 1% by mass or less, of water relative to the ink composition.

[0046] [1-3-5. Solvent composition] The ink composition of the present invention contains a saturated fatty acid diester solvent and an unsaturated fatty acid monoester solvent, and the total amount of these solvents 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, based on the ink composition; on the other hand, it is preferably 93% by mass or less, and more preferably 90% by mass or less. Both the saturated fatty acid diester solvent and the unsaturated fatty acid monoester solvent have relatively low pour points (for example, lower than the pour point of the saturated fatty acid monoester); by setting the total content of both solvents at a certain level or more, the low-temperature fluidity of the ink composition can be improved.

[0047] The relative mass ratio of the saturated fatty acid diester solvent and unsaturated fatty acid monoester solvent contained in the ink composition of the present invention (saturated fatty acid diester solvent:unsaturated fatty acid monoester solvent) is in the range of 2:8 to 8:2, preferably 3:7 to 7:3. The unsaturated groups in the unsaturated fatty acid monoester solvent may be oxidized during storage of the ink composition, resulting in a decrease in the storage stability of the ink composition. Therefore, by setting the content ratio of the unsaturated fatty acid monoester solvent below a certain level, the long-term stability of the ink composition can be improved. Furthermore, since unsaturated fatty acid monoester solvents have a lower viscosity than saturated fatty acid diester solvents, setting the content ratio of the unsaturated fatty acid monoester solvent above a certain level can reduce the viscosity of the ink composition and improve its ejection stability.

[0048] The ink composition of the present invention can achieve both low-temperature fluidity and ejection stability by combining a predetermined amount of saturated fatty acid diester solvent and unsaturated fatty acid monoester solvent, but it may be advantageous to further include a saturated fatty acid monoester solvent. For example, blending a saturated fatty acid monoester solvent may further improve the ability to respond to temperature changes. The content of the saturated fatty acid monoester solvent may be 0% by mass or more of the ink composition, preferably 5% by mass, and may be 10% by mass or more; however, it is usually 40% by mass or less, and may be 30% by mass or less, or may be 25% by mass or less.

[0049] [1-4. Other additives] The ink composition of the present invention may contain components other than the colorant, dispersant, and solvent. Examples of the other components include a dispersing aid (also called a pigment derivative), an inactive resin, a leveling agent, a preservative, etc.

[0050] The dispersing aid, together with the dispersant, can improve the dispersibility of the pigment. The dispersing aid refers to a pigment derivative; examples of the dispersing aid include sulfonic acid derivatives, sulfonamide derivatives, alkylamino derivatives, and alkyl derivatives of pigments. Examples of the dispersing aid include Solsperse 5000, Solsperse 12000, Solsperse 22000 (Lubrizol Corporation), EFKA745, and EFKA6750 (EFKA CHEMICALS BV). The content of the dispersing aid may be 2% by mass or less of the ink composition.

[0051] The inactive resin can improve the adhesion of the ink composition to the substrate and adjust the spread of dots of the ink composition on the substrate. The inactive resin is preferably dissolved in the ink composition. Examples of inactive resins include, but are not limited to, (meth)acrylic resins, styrene-(meth)acrylic resins, styrene-maleic acid resins, rosin resins, rosin ester resins, ethylene-vinyl acetate resins, petroleum resins, coumarone-indene resins, terpene phenol resins, phenolic resins, urethane resins, melamine resins, urea resins, epoxy resins, cellulose resins, vinyl chloride-vinyl acetate resins, xylene resins, alkyd resins, aliphatic hydrocarbon resins, butyral resins, maleic acid resins, and fumaric acid resins. The content of the inactive resin may be 3% by mass or less of the ink composition.

[0052] The leveling agent may be a surfactant, such as a silicone surfactant, a fluorosurfactant, or a polyoxyethylene adduct of a nonionic surfactant. Among these, silicone surfactants are preferred because they enhance the wettability of the ink composition while preventing foaming. The content of the leveling agent may be 2% by mass or less of the ink composition.

[0053] [1-5. Physical properties of ink composition] The viscosity of the ink composition of the present invention at 20°C is preferably in the range of 5 to 30 mPa·s, and more preferably in the range of 8 to 16 mPa·s. By adjusting the viscosity, printing by inkjet printing becomes possible, and the ink composition can be ejected stably even if the temperature of the inkjet printer head changes. Furthermore, the freezing point of the ink composition of the present invention can be set to -5°C or below, and can also be set to -10°C or -20°C or below.

[0054] [1-6. Method for preparing ink composition] The ink composition of the present invention can be prepared by referring to the preparation method of conventional solvent-based inkjet printing inks. Specifically, it can be prepared by mixing a mixture of the components using a dispersing machine (e.g., a ball mill, a sand mill, an attritor, a roll mill, an agitator mill, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a jet mill, an Ang Mill, etc.); if necessary, it can be further filtered using a known filtering machine such as a membrane filter.

[0055] Alternatively, a base ink (a concentrate of a colorant (e.g., a pigment)) may be prepared, and then the base ink may be mixed with other components to prepare the ink composition. The base ink can be obtained by mixing and kneading a colorant, a dispersant, a portion of the solvent, and an optional dispersion aid.

[0056] [2. Uses of the solvent-based inkjet printing ink composition] The solvent-based inkjet printing ink composition (ink composition) of the present invention is applied to a substrate by inkjet printing and used for printing. The inkjet printing method is not particularly limited, and includes a charge-controlled method that uses electrostatic attraction to eject ink; a drop-on-demand method (pressure pulse method) that uses the vibration pressure of a piezoelectric element; an acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink with the radiation pressure to eject the ink; and a thermal inkjet method that heats the ink to form bubbles and uses the generated pressure. Furthermore, the inkjet printing may be continuous inkjet printing, in which case the electrical conductivity of the ink composition can be adjusted by adding a conductivity-imparting agent. Furthermore, the printhead in the inkjet printing device may be in either a multi-pass mode (serial head mode) or a single-pass mode (line head mode).

[0057] The substrate to be printed with the ink composition of the present invention is not particularly limited, but is preferably an absorbent substrate. Examples of absorbent substrates include paper substrates and fabrics; in particular, highly absorbent substrates such as cardboard and corrugated cardboard are preferred as substrates. Furthermore, since the ink composition of the present invention does not need to contain a hydrocarbon solvent, the risk to human health is further reduced and recycling of printed materials can be promoted. Therefore, it may be advantageous to use the ink composition as an ink for industrial / industrial inkjet printing, which is used in large quantities. [Example]

[0058] The present invention will be described in more detail below with reference to examples. However, the present invention should not be construed as being limited by the descriptions in these examples.

[0059] A. Materials used in preparing the ink composition A-1. Coloring materials Carbon black: MA7 (Mitsubishi Carbon Black Co., Ltd.) Magenta pigment: Fastogen Super Magenta RGT (DIC) A-2. Dispersant Solsperse 18000 (Lubrizol)

[0060] A-3. Solvent A-3-1. Unsaturated fatty acid monoester Methyl oleate (Excepearl M-OL, Kao Corporation) Pour point <-5℃, boiling point 218.5℃ Isobutyl oleate (Vinicizer 30, Kao Corporation) Pour point <-10℃ 2-Ethylhexyl oleate (Unistar MB-881, NOF Corporation) Pour point -40℃, boiling point 465.8±24.0℃ A-3-2. Saturated fatty acid diesters Di-2-ethylhexyl azelaate (Sanso Cizer DOZ, New Japan Chemical Co., Ltd.) Pour point <-60℃, boiling point > 282℃ Di-2-ethylhexyl adipate (Sanso Cizer DOA, New Japan Chemical Co., Ltd.) Pour point <-60℃, boiling point 417℃ Diisononyl adipate (Sanso Cizer DINA, New Japan Chemical Co., Ltd.) Pour point <-60℃, boiling point > 250℃ Diisodecyl adipate (Sanso Cizer DIDA, New Japan Chemical Co., Ltd.) Pour point <-60℃, boiling point 282℃ Di-2-ethylhexyl sebacate (Sanso Cizer DOS, New Japan Chemical Co., Ltd.) Pour point <-60℃, boiling point approx. 248℃ A-3-3. Saturated fatty acid monoester Methyl laurate (Excepar ML-85, Kao Corporation) Pour point <20℃, boiling point approx. 260℃ Isopropyl myristate (Excepar IPM, Kao Corporation) Pour point 2-8℃, boiling point approx. 304℃ Isopropyl palmitate (Excepal IPP, Kao Corporation) Pour point: 8-15°C, boiling point: approx. 332°C 2-Ethylhexyl stearate (Excepal EH-S, Kao Corporation) Pour point -9℃, boiling point approx. 40℃ A-3-4. Other solvents Saturated hydrocarbon solvent (P-40, MORESCO)

[0061] A-4. Pigment derivatives Solsperse 5000 (Lubrizol) A-5. Resin ·Methacrylic resin (BR-87, Mitsubishi Chemical Corporation) A-6.Leveling agent Silicone surface conditioner (BYK-315N, BYK)

[0062] B. Ink Composition Preparation Procedure Each ink composition of the examples and comparative examples (except Comparative Example 9) was prepared according to the formulations shown in Tables 1 and 2 (the blending ratio of each component in Tables 1 and 2 means mass %). B-1. Manufacturing of solvent-based inkjet printing base ink Ten parts by mass of a dispersant (Solsperse 18000) was dissolved in 59 parts by mass of an unsaturated fatty acid monoester (methyl oleate, isobutyl oleate, or 2-ethylhexyl oleate), and 30 parts by mass of a colorant (carbon black MA-7 or magenta pigment) and, if necessary, 1 part by mass of a pigment derivative (Solsperse 5000) were added thereto with stirring and mixing, followed by grinding using a bead mill to obtain a non-aqueous inkjet base ink. However, in Examples 8 and 111 and Comparative Examples 3 and 8, the unsaturated fatty acid monoester was replaced with a saturated diester (di-2-ethylhexyl azelate) to obtain a non-aqueous inkjet base ink. B-2. Preparation of solvent-based ink composition for inkjet printing The base ink and each material were stirred and mixed to obtain the formulation shown in Table 1 or Table 2 (the blending ratio of each material is in mass %) to obtain non-aqueous inkjet ink compositions of Examples and Comparative Examples.

[0063] Preparation of Ink Composition of Comparative Example 9 B-1. Manufacturing of solvent-based inkjet printing base ink 10 parts by mass of a dispersant (Solsperse 18000) was dissolved in 59 parts by mass of a hydrocarbon solvent, and 30 parts by mass of a colorant (carbon black MA-7) and 1 part by mass of a pigment derivative (Solsperse 5000) were stirred and mixed therewith, and then milled using a bead mill to obtain a non-aqueous inkjet base ink. B-2. Preparation of solvent-based ink composition for inkjet printing The base ink and each material were stirred and mixed to obtain the formulation shown in Table 2 (the blending ratio of each material is in mass %), thereby obtaining non-aqueous inkjet ink compositions of Examples and Comparative Examples.

[0064] C. Evaluation of Ink Compositions C-1. Low temperature fluidity Each of the ink compositions obtained in the examples and comparative examples was placed in a glass bottle, sealed, and stored at −20° C. for 24 hours, after which the condition was evaluated according to the following evaluation criteria. ○: No freezing or solids due to freezing were observed, and fluidity was maintained. △: Frozen to the extent that it returns to normal when shaken lightly or solids due to freezing are observed ×: The product is frozen to the extent that it cannot be restored even after strong shaking, or solids are found due to freezing.

[0065] C-2.Discharge stability Using each of the ink compositions obtained in the Examples and Comparative Examples, printing was carried out on vinyl chloride sheets (product name: MD5, manufactured by METAMARK), and the number of sheets on which unprinted areas occurred was evaluated according to the following evaluation criteria. Yes: Unprinted areas occur from the 71st sheet onwards, or unprinted areas do not occur until the 100th sheet. △: Unprinted areas occur on the 30th to 70th sheets. ×: Unprinted areas occur up to the 30th sheet.

[0066] C-3.Storage stability Each of the ink compositions obtained in the Examples and Comparative Examples was placed in a glass bottle, sealed, and stored at 60° C. for 28 days, after which the condition was evaluated according to the following evaluation criteria. ○: Neither thickening nor sedimentation is observed △: Viscosity increase or sedimentation is observed, but the viscosity returns to normal when shaken lightly. ×: Viscosity increase or sedimentation is observed to an extent that does not return to normal even after vigorously shaking

[0067] [Table 1]

[0068] [Table 2]

[0069] As shown in Example 1 (Table 1), an ink composition containing a saturated fatty acid diester (di-2-ethylhexyl azelate) and an unsaturated fatty acid monoester (methyl oleate) in a specified mass ratio of 70% in total exhibited good low-temperature fluidity, ejection stability, and storage stability. Although the ink composition of Example 1 did not contain a hydrocarbon solvent, it exhibited low-temperature fluidity, ejection stability, and storage stability that were similar to or superior to those of the ink composition of Comparative Example 9, which contained a hydrocarbon solvent.

[0070] In contrast, as shown in Comparative Examples 1 to 3 (Table 2), when the mass ratio of saturated fatty acid diester (di-2-ethylhexyl azelate) to unsaturated fatty acid monoester (methyl oleate) was outside the range of 2:8 to 8:2, the ink composition properties were insufficient. In other words, the ink compositions of Comparative Examples 1 and 2, which have a low content of saturated fatty acid diester and a high relative proportion of unsaturated fatty acid monoester, are prone to poor storage stability. This suggests that the unsaturated fatty acid monoester may be modified during storage, for example, the unsaturated group may be oxidized. Furthermore, the ink composition of Comparative Example 3, which has a content of unsaturated fatty acid monoester of 8.92 mass% and a high relative proportion of saturated fatty acid diester, did not have sufficient ejection stability. In other words, the ink composition of Comparative Example 3 had a relatively high viscosity.

[0071] Furthermore, as shown in Comparative Examples 4 to 7 (Table 2), ink compositions that did not contain saturated fatty acid diesters had insufficient low-temperature fluidity. In particular, when saturated fatty acid monoester solvents with relatively high pour points (methyl laurate (pour point <20°C) and isopropyl palmitate (pour point 8 to 15°C)) were blended, low-temperature fluidity was likely to deteriorate.

[0072] The ink composition of Comparative Example 8 (Table 2) had a small total amount of saturated fatty acid diester (di-2-ethylhexyl azelate) and unsaturated fatty acid monoester (methyl oleate) (40% by mass in total), and therefore had insufficient low-temperature fluidity.

[0073] As shown in Examples 1 to 3, various evaluations were good even when the type of unsaturated fatty acid monoester was changed (methyl oleate, isobutyl oleate, 2-ethylhexyl oleate). Furthermore, as shown in Examples 1 and 4 to 7, various evaluations were good even when the type of saturated fatty acid diester was changed (di-2-ethylhexyl azelate, di-2-ethylhexyl adipate, diisononyl adipate, di-isodecyl adipate, di-2-ethylhexyl sebacate). Thus, unsaturated fatty acid monoesters and saturated fatty acid diesters can be appropriately selected with reference to the disclosures of this specification and used in the ink composition.

[0074] As shown in Examples 8 and 9, various evaluations were good even when the ratio of saturated fatty acid diester to unsaturated fatty acid monoester was changed. Furthermore, as shown in Examples 10 and 11, various evaluations were satisfactory even without blending saturated fatty acid monoester. Thus, the contents of unsaturated fatty acid monoester and saturated fatty acid diester can be appropriately set with reference to the disclosures of this specification and used in the ink composition.

[0075] Example 12 is an example in which an inactive resin (methacrylic resin) was blended, Example 13 is an example in which a leveling agent (silicone surfactant) was blended, Example 14 is an example in which no pigment derivative was blended, and Example 15 is an example in which the colorant was a magenta pigment instead of carbon black, but all of the ink compositions were evaluated as good. [Industrial Applicability]

[0076] The ink composition of the present invention can be used in a variety of applications as a solvent-based inkjet printing ink. In particular, the ink composition of the present invention can be characterized by high low-temperature fluidity and the ability to maintain ejection stability even during continuous printing, even without containing a hydrocarbon-based solvent (including mineral oil). Moreover, because the ink composition of the present invention does not need to contain a hydrocarbon-based solvent, the risks to human health are further reduced and recycling of printed materials can be promoted. Therefore, the ink composition of the present invention can be effectively used, in particular, as an "industrial inkjet printing ink" that is used continuously in large quantities, and can be used as a printing ink for various packaging materials, catalogs, etc.

Claims

1. A solvent-based ink composition for ink-jet printing comprising a colorant, a dispersant, and a solvent, The coloring material contains a pigment and / or a dye, the solvent includes 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 is 50% by mass or more based on the total amount of the solvent-based inkjet printing ink composition, The solvent-based ink composition for ink-jet printing, wherein the weight ratio of the saturated fatty acid diester solvent to the unsaturated fatty acid monoester solvent is 2:8 to 8:

2.

2. 2. The solvent-based ink composition for ink-jet printing according to claim 1, wherein the saturated fatty acid diester solvent has a pour point of −10° C. or lower.

3. The solvent-based ink composition for ink-jet printing according to claim 1 or 2, wherein the pour point of the unsaturated fatty acid monoester solvent is 0°C or lower.

4. The solvent-based ink composition for ink-jet printing according to claim 1 or 2, which does not contain a hydrocarbon solvent or contains a hydrocarbon solvent in an amount of 5 mass % or less based on the total amount of the solvent-based ink composition for ink-jet printing.

5. The solvent-based ink-jet printing ink composition according to claim 1 or 2, further comprising a saturated fatty acid monoester.

6. The solvent-based ink composition for ink-jet printing according to claim 1 or 2, wherein the coloring material is a black pigment and / or a black dye.

7. The solvent-based ink-jet printing ink composition according to claim 1 or 2, which does not contain water or contains 3% by mass or less of water based on the total amount of the solvent-based ink-jet printing ink composition.

8. The solvent-based ink-jet printing ink composition according to claim 1 or 2, wherein the dispersant is a polymer dispersant.

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