Ink composition

Abstract

One embodiment of the present invention provides an ink composition containing (A) C.I. Pigment Yellow 180, (B) an aluminum salt of C.I. Pigment Yellow 180 having a sulfonic acid group, (C) a dispersant, and (D) a solvent, wherein the Hansen solubility parameters of the solvent are a dispersion (dD) of 16.0-18.0, a polarity (dP) of 6.0-11.5, and hydrogen bonding (dH) of 9.0-17.0 or 18.0-27.0.

Description

Ink composition

[0001] This invention relates to an ink composition containing C.I. Pigment Yellow 180.

[0002] Traditionally, pigments have been used primarily in inks, paints, toners, coloring of rubber and plastics, coloring of synthetic fiber stocks, pigment printing, and cosmetics. Among these, printing applications, such as inks, play a particularly important industrial role. For example, gravure inks and flexographic inks are widely used to impart aesthetic appeal and functionality to the printed substrates of flexible packaging films. Furthermore, with the recent proliferation of inkjet printers, expectations for the development of inkjet inks with superior performance are increasing.

[0003] Inkjet printers are widely used not only in homes but also in industrial applications, driven by the trend towards smaller print runs. In recent years, the business has expanded to include textile and flexible packaging applications. Among these, yellow ink, along with cyan, magenta, and black, is a crucial and central ink.

[0004] Currently, water-based inks are becoming the mainstream for inkjet printers, and the pigments used in these inks are required to have properties such as coloring power, lightfastness, and easy dispersibility. Conventionally, yellow pigments used in inkjet printer inks have often included C.I. Pigment Yellow 74 (hereinafter also referred to as "PY74"), which has high coloring power, and C.I. Pigment Yellow 155 (hereinafter also referred to as "PY155"), which has high lightfastness (for example, Patent Documents 1 and 2). However, PY74 has poor lightfastness and PY155 has low coloring power, and C.I. Pigment Yellow 180 (hereinafter also referred to as "PY180"), which has an excellent balance of coloring power and lightfastness, is attracting attention as a new yellow pigment (for example, Patent Documents 3 and 4).

[0005] Japanese Patent Publication No. 2009-179722, Japanese Patent Publication No. 2009-67866, Japanese Patent No. 6984791, Japanese Patent No. 7622908

[0006] The inventors investigated conventional pigment compositions containing PY180 and found that there is room for improvement in storage stability when used in inks and the like.

[0007] The present inventors have diligently researched to solve the above problems and have found that by using a predetermined PY180 derivative, a predetermined solvent, and a dispersant in combination with PY180, an ink composition with excellent properties such as storage stability can be obtained. The present invention is, for example, as follows: [1] An ink composition comprising (A) C.I. Pigment Yellow 180, (B) an aluminum salt of C.I. Pigment Yellow 180 having a sulfonic acid group, (C) a dispersant, and (D) a solvent, wherein the dispersion force term (dD) of the solvent in the Hansen solubility parameter is 16.0 to 18.0, the polarity term (dP) is 6.0 to 11.5, and the hydrogen bonding term (dH) is 9.0 to 17.0 or 18.0 to 27.0. [2] The solvent satisfies one or more of the following (a) to (d) in the ink composition according to [1]: (a) a compound containing one or more hydroxyl groups; (b) a compound having two or more carbon atoms; (c) a compound having an oxygen atom / carbon atom ratio of 0.25 to 1.00; (d) a compound not containing nitrogen atoms. [3] The solvent is selected from the group consisting of 1,2-butanediol, propylene glycol, 1,3-butanediol diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, 1,4-butanediol, ethylene glycol, 1,2,4-butanetriol, 1,2,6-hexanetriol and 1,5-pentanediol, and the ink composition according to [1] or [2]. [4] The solvent is (B) C.I. having a sulfonic acid group. The aluminum salt of Pigment Yellow 180 is an ink composition according to any one of [1] to [3], comprising a cation portion containing aluminum ions and an anion portion represented by the following general formula (I): [In the formula, X １ ~X ６ and Y １ ~Y ８ Each of these independently represents a hydrogen atom or a sulfonic acid group (however, X １ ~X ６ and Y１ to Y ８ at least one of which is a sulfonic acid group)]. [5] The cationic moiety containing the aluminum ion is Al ３＋ , [Al(OH)] ２＋ and [Al(OH) ２ ＋ selected from the group consisting of, the ink composition according to [4]. [6] The anionic moiety represented by the general formula (I) is X １ to X ６ and Y １ to Y ８ a monosubstituted product in which one of is a sulfonic acid group, X １ to X ６ and Y １ to Y ８ ​The ink composition according to [4] or [5], comprising a disubstituted product in which two of the groups are sulfonic acid groups, or a mixture thereof. [7] The ink composition according to [6], wherein the molar ratio (SN ratio (disubstituted product / monosubstituted product)) of the monosubstituted product to the disubstituted product in the aluminum salt of C.I. Pigment Yellow 180 having the (B) sulfonic acid group is 0.1 to 30.0. [8] The ink composition according to any one of [1] to [7], wherein the dispersant is a styrene-(meth)acrylic acid resin. [9] The ink composition according to any one of [1] to [8], wherein the content of the solvent is 0.1 to 30.0% by mass with respect to 100% by mass of the ink composition.

[10] The aluminum salt of C.I. Pigment Yellow 180 having the sulfonic acid group comprises the steps of (1) introducing a sulfonic acid group into C.I. Pigment Yellow 180 and C.I. Pigment Yellow 180 into which the sulfonic acid group has been introduced. A pigment dispersion according to any one of [1] to [9], manufactured by a method comprising the step (2) of reacting pigment yellow 180 with an aluminum salt.

[11] A pigment dispersion according to any one of [1] to

[10] , wherein the average aspect ratio of the C.I. pigment yellow 180 is 1.0 to 4.0 or greater than 2.0 to 4.0.

[12] An inkjet ink comprising the ink composition according to any one of [1] to

[11] .

[13] A method comprising preparing C.I. pigment yellow 180 (A), a dispersant (C), and a solvent (D); introducing sulfonic acid groups into C.I. pigment yellow 180, and reacting the C.I. pigment yellow 180 with the introduced sulfonic acid groups with an aluminum salt to produce C.I. A method for producing an ink composition according to any one of [1] to [9], comprising: obtaining an aluminum salt (B) of pigment yellow 180; and simultaneously or sequentially mixing (A), (B), (C), and (D) [wherein the Hansen solubility parameter of the solvent, the dispersion force term (dD) is 16.0 to 18.0, the polarity term (dP) is 6.0 to 11.5, and the hydrogen bonding term (dH) is 9.0 to 17.0 or 18.0 to 27.0].

[0008] According to the present invention, it is possible to provide an ink composition with excellent properties such as storage stability.

[0009] Embodiments of the present invention will be described in detail below. According to one embodiment, the ink composition comprises the following components (A) to (D): (A) C.I. Pigment Yellow 180, (B) an aluminum salt of C.I. Pigment Yellow 180 having a sulfonic acid group, (C) a dispersant, and (D) a solvent. The dispersion force term (dD) of the solvent in the Hansen solubility parameter is 16.0 to 18.0, the polarity term (dP) is 6.0 to 11.5, and the hydrogen bonding term (dH) is 9.0 to 17.0 or 18.0 to 27.0.

[0010] As a result of diligent research, the present inventors have found that by combining PY180 (hereinafter also referred to as "component (A)") with an aluminum salt of PY180 having a sulfonic acid group (hereinafter also referred to as "component (B)" or "PY180 derivative"), a dispersant (hereinafter also referred to as "component (C)"), and a solvent having specific properties (hereinafter also referred to as "component (D)" or "specific solvent"), an ink composition with improved storage stability can be obtained. In the ink composition according to the embodiment, when stored, the increase in the size of dispersed particles of the pigment component in the ink composition over time is suppressed, and as a result, the increase in viscosity of the ink composition is also suppressed. Therefore, the quality of the ink composition according to the embodiment is maintained even when stored. Using such an ink composition as an inkjet ink also has the advantage of preventing clogging of the nozzle head of an inkjet printer.

[0011] Although the reason why such effects are obtained is not clear, it is speculated as follows. When a pigment is used as a colorant for inks and the like, it is used after being dispersed in a dispersion medium such as a solvent. A mechanical force is applied to the pigment in the dispersion medium to disintegrate the pigment particles and disperse them into the dispersion medium. However, if dispersion is performed only with the pigment and the dispersion medium, there is a concern that the pigment particles will reaggregate. To prevent this, it is effective to further use a dispersant in combination to stabilize the dispersion system. When a dispersant is used in combination, in order to obtain the above effects, it is important that the dispersant adsorbs well to the pigment particles. Adsorption between pigment particles and a dispersant is mediated by intermolecular interactions; for example, hydrogen bonding that produces relatively strong intermolecular interactions is preferable. Since PY180 molecules have amide bonds and benzimidazolone moieties, intermolecular hydrogen bonding can potentially occur.

[0012] However, PY180 adopts a crystal structure in which molecules are arranged in an orderly manner, and hydrogen bonds are used for interactions between PY180 molecules to maintain this crystal structure. As a result, hydrogen bonding is unlikely to occur between the surface of PY180 particles and the dispersant. Therefore, an aluminum salt of PY180 having a sulfonic acid group (a PY180 derivative) is used. In this way, the PY180 derivative is adsorbed on the surface of PY180 particles, and the aluminum in the PY180 derivative is, for example, [Al(OH) ２ ＋ Due to this form, hydroxyl groups exist on the surface of the PY180 particles. Hydrogen bonding occurs between these hydroxyl groups and groups contained in the dispersant (for example, urethane bonds in urethane resins, and carboxyl groups in styrene-(meth)acrylic acid copolymers or styrene-maleic acid copolymers). Therefore, the dispersant adsorbs to PY180 and improves the stability of the dispersion system. As a result, it is considered that the storage stability of the ink is improved.

[0013] ​The Hansen solubility parameter (hereinafter also referred to as "HSP") is a parameter devised to predict the solubility of substances, which evaluates intermolecular interactions by dividing them into three components, namely the dispersion term (dD), the polarity term (dP), and the hydrogen bonding term (dH). For common compounds, each compound has one set of the above three parameters, and compounds with similar parameters can be considered to have strong interactions with each other. In the present invention, it is considered that the appropriate balance of the HSP of the aforementioned components (A) to (D) also contributes to improving the storage stability of the ink.

[0014] Hereinafter, each component, manufacturing method, physical properties, uses, and the like of the ink composition according to the embodiment will be described in detail. In the present application, PY180 does not merely mean a compound having the structure shown below, but also means a pigment composed of the compound. The pigment is a concept that not only is characterized by its crystal structure, but also includes substances characterized by the physical properties as primary particles formed by aggregation and / or assembly thereof, and further aggregates and / or assemblies derived from the surface state thereof and the like.

[0015] [A] C. I. Pigment Yellow 180 (PY180) PY180 is specified by CAS No. 77804-81-0, and is represented, for example, by the following structural formula. The ink composition according to the embodiment only needs to contain at least PY180 as a colorant, and may contain pigments and dyes other than PY180 within a range that does not impair the effects of the present invention.

[0016] PY180 can be obtained, for example, by coupling a bisdiazonium salt solution obtained by adding an aqueous sodium nitrite solution to 1,2-bis(2-aminophenoxy)-ethane in the presence of a strong acid under ice-cold conditions, and reacting it with 5-acetoacetylamino-benzimidazolone. As for PY180, commercially available products may be used as is, and examples of commercially available products that can be used include "SYMULER FAST YELLOW BY 2000GT" (manufactured by DIC Corporation). The ink composition according to the embodiment may contain one or more types of PY180. Since PY180 is an azo-hydrazo tautomer, it may contain both the azo form (-N=N-) and the hydrazo form (>N-NH-).

[0017] The average aspect ratio (major diameter / minor diameter) of PY180 is preferably 1.00 to 4.00, for example, 1.50 to 3.80, 1.60 to 2.20, 2.0 to 4.0, or greater than 2.0 to 4.0, from the viewpoint of suppressing aggregation of pigments. The average particle diameter (minor diameter) of PY180 is preferably 30 to 150 nm, more preferably 35 to 100 nm, and particularly preferably 40 to 65 nm, from the viewpoint of increasing the print density (OD). Furthermore, the average particle diameter (major diameter) of PY180 is preferably a value such that the average value of the average aspect ratio and minor diameter falls within the above range, but is preferably 30 to 250 nm, more preferably 50 to 150 nm. The average particle diameter (major diameter, minor diameter) can be measured by image analysis using an electron microscope as described in the examples below, and the average aspect ratio can be calculated by the formula "average particle diameter (major diameter) / average particle diameter (minor diameter)".

[0018] The specific surface area of ​​PY180 is preferably 40 to 90 m² from the viewpoint of ink fluidity and coloring power. ２ / g, more preferably 45 to 80m ２The value is / g. The specific surface area is calculated based on the amount of gas (nitrogen) adsorbed by the one-point method, as described in the examples below. PY180 is preferably included in a proportion of 0.10 to 10.0% by mass, more preferably 0.50 to 7.0% by mass, and particularly preferably 1.0 to 5.0% by mass, based on 100% by mass of the ink composition. The above range of PY180 content results in superior coloring power, storage stability, etc.

[0019] Furthermore, the proportion of PY180 with an aspect ratio of 1.00 to 4.00 in the ink composition is preferably 50% by mass or more (for example, 50 to 100% by mass), more preferably 70% by mass or more (for example, 70 to 100% by mass), and particularly preferably 80% by mass or more (for example, 80 to 100% by mass) or 95% by mass or more (for example, 95 to 100% by mass). Having the proportion of PY180 with an aspect ratio of 1.00 to 4.00 within the above range results in superior coloring power, storage stability, and other properties.

[0020] As described above, PY180 may be a conventionally synthesized product obtained by coupling a bisdiazonium salt solution, obtained by adding an aqueous sodium nitrite solution to 1,2-bis(2-aminophenoxy)-ethane in the presence of a strong acid under ice-cold conditions, with 5-acetoacetylamino-benzimidazolone, or a commercially available product such as "SYMULER FAST YELLOW BY 2000GT" (manufactured by DIC Corporation), but it is preferable to manufacture it by further applying specific treatments.

[0021] The specific treatment described above involves, for example, grinding (solvent salt milling) 100 parts by mass of pigment (crude pigment) with 200 to 1000 parts by mass of inorganic salt while heating in the presence of a solvent. By grinding while heating in the presence of a solvent, the crystallinity of the pigment can be improved while the primary particle size can be set to a specific range.

[0022] As the inorganic salt mentioned above, water-soluble inorganic salts can be suitably used, and it is preferable to use inorganic salts such as sodium chloride, potassium chloride, and sodium sulfate. It is even more preferable to use inorganic salts with an average particle size of 0.5 to 50 μm. Such inorganic salts can be easily obtained by finely grinding ordinary inorganic salts. The amount of inorganic salt used is, for example, 200 to 1000 parts by mass, preferably 300 to 800 parts by mass, per 100 parts by mass of pigment. From the viewpoint of finely grinding the pigment particles, a larger amount of inorganic salt is preferable, but in the present invention, the above range is preferred from the viewpoint of balancing with the degree of crystallinity.

[0023] As the solvent, it is preferable to use an organic solvent that can suppress crystal growth. Suitable organic solvents include water-soluble organic solvents, such as diethylene glycol (DEG), glycerin, ethylene glycol, propylene glycol, liquid polyethylene glycol, liquid polypropylene glycol, 2-(methoxymethoxy)ethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy)ethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, and dipropylene glycol monomethyl ether. Among these, diethylene glycol (DEG) is particularly preferred because it can be heated to an appropriate temperature and has excellent wettability with the pigment. The amount of solvent used is, for example, 10 to 500 parts by mass, preferably 50 to 300 parts by mass, per 100 parts by mass of pigment, in order to achieve an appropriate viscosity during grinding.

[0024] The above-mentioned grinding (solvent salt milling) is carried out by placing the pigment, inorganic salt, and a solvent that does not dissolve it into a kneader and mixing them in the kneader. For example, a kneader, trimix, or mix maller can be used as the kneader. The heating temperature during grinding (solvent salt milling) is, for example, 50 to 100°C, preferably 60 to 90°C. The heating temperature can be changed as appropriate using the temperature control device provided in the kneader. The time for grinding (solvent salt milling) is, for example, 2 to 10 hours, preferably 3 to 8 hours.

[0025] [B] Aluminum salt of PY180 having a sulfonic acid group (PY180 derivative) The ink composition according to the embodiment contains one or more aluminum salts of PY180 having a sulfonic acid group (PY180 derivative). Here, a sulfonic acid group is -SO ３ Not only the H group, but also its ionized state, -SO ３ － It is a concept that also includes the base. -SO ３ The H group is ionized during the mixing stage with other components, resulting in -SO ３ － It can serve as a base. Since the PY180 derivative is an azo-hydrazo tautomer, it may include both the azo (-N=N-) and hydrazo (>N-NH-) forms. According to one embodiment, the PY180 derivative includes an anionic portion which is PY180 having a sulfonic acid group and a cationic portion which contains an aluminum ion.

[0026] More specifically, the anionic portion of the PY180 derivative preferably has a structure represented by the following formula (I). [In the formula, X １ ~X ６ and Y １ ~Y ８ Each of these is independently a hydrogen atom or a sulfonic acid group (-SO ３ H or -SO ３ － ) represents (however, X １ ~X ６ and Y １ ~Y ８ (At least one of them is a sulfonic acid group.)

[0027] X １ ~X ６ and Y １ ~Y ８ Preferably, 1 to 4 of the groups are sulfonic acid groups, more preferably 1 to 3, and particularly preferably 1 to 2. Since the number of sulfonic acid groups in the anionic part represented by formula (I) varies depending on the degree of reaction of each molecule, the number of sulfonic acid groups in anionic parts within the same system is not constant, and anionic parts with different numbers of sulfonic acid groups will exist. Therefore, in other words, the number of sulfonic acid groups (average number of substituents) in the anionic part represented by formula (I) is preferably 1 to 4, more preferably 1 to 3, and particularly preferably 1 to 2. Having the number of sulfonic acid groups within the above range is preferable from the viewpoint of improving dispersion stability and storage stability. Furthermore, the position where the sulfonic acid groups are introduced is not limited, and compounds or salts having sulfonic acid groups at different positions will exist within the same system. １ ~Y ８ A sulfonic acid group is easily introduced into either of the following, and especially in the case of monosubstituted compounds, Y ２ In the case of a disubstituted compound, Y ２ and Y ７ Sulfonic acid groups tend to be easily introduced into these compounds.

[0028] According to a preferred embodiment, the anion portion represented by the general formula (I) is X １ ~X ６ and Y １ ~Y ８ One of them is a monosubstituted compound (a structure in which one sulfonic acid group is introduced into the same molecule), X １ ~X ６ and Y １ ~Y ８It is preferable to include a disubstituted product (a structure in which two sulfonic acid groups are introduced into the same molecule) in which both are sulfonic acid groups, or a mixture thereof. Furthermore, from the viewpoint of dispersion stability, the molar ratio of the monosubstituted product to the disubstituted product (SN ratio (disubstituted product / monosubstituted product)) is preferably 0.1 to 30.0, more preferably 0.5 to 5.0, and particularly preferably 0.75 to 2.5. The average number of substituents on the sulfonic acid groups and the SN ratio can be calculated from the area ratio of each compound in liquid chromatography.

[0029] The cation moiety of the PY180 derivative is not limited as long as it contains aluminum ions, but for example, Al ３＋ [Al(OH)] ２＋ and [Al(OH) ２ ] ＋ Preferably selected from the group consisting of [Al(OH) ２ ] ＋ That is the case.

[0030] Here, if the aluminum ion in the cation is a polyvalent ion, the bonding state between it and the anionic part is uncertain, and the structure of the PY180 derivative cannot be clearly shown. It is speculated that, for example, the aluminum ion bonds with heteroatoms (oxygen atom, nitrogen atom) in the anionic part, and that these bonds are either intramolecular or intermolecular.

[0031] As mentioned above, it is currently impossible and impractical to show the specific structure of PY180 derivatives. However, PY180 derivatives can be produced, for example, by introducing sulfonic acid groups into PY180 and then reacting it with an aluminum salt (e.g., aluminum sulfate, aluminum chloride, aluminum phosphate, etc.). To introduce sulfonic acid groups into PY180, for example, PY180 can be treated with a sulfonating agent such as fuming sulfuric acid, concentrated sulfuric acid, or chlorosulfuric acid. The number of sulfonic acid groups introduced can be adjusted by controlling reaction conditions such as sulfuric acid concentration, pigment content, reaction temperature, and reaction time. Here, pigment content refers to the weight ratio of PY180 to sulfuric acid (amount of pigment charged / amount of sulfuric acid charged).

[0032] In the sulfonic acid group introduction step, the sulfuric acid concentration is, for example, 92 to 100% by weight, preferably 92 to 98% by weight, and more preferably 95 to 98% by weight. The pigment content is, for example, 0.04 to 0.08, preferably 0.04 to 0.07, and more preferably 0.05 to 0.07. The reaction temperature is, for example, 5 to 30°C, preferably 5 to 20°C, and more preferably 10 to 20°C. The reaction time is, for example, 0.5 to 5 hours, preferably 0.5 to 4 hours, and more preferably 1 to 4 hours.

[0033] According to one embodiment, the PY180 derivative is produced by a method comprising the steps of (1) introducing a sulfonic acid group into PY180 and (2) reacting the PY180 with the introduced sulfonic acid group with an aluminum salt. Preferably, the method further includes the steps of dispersing the PY180 with the introduced sulfonic acid group in water and adjusting the resulting dispersion to an alkaline state between steps (1) and (2).

[0034] The PY180 derivative is preferably included in an amount of 0.01 to 1.0% by mass, more preferably 0.03 to 0.50% by mass, and particularly preferably 0.05 to 0.20% by mass, based on 100% by mass of the ink composition. By including the PY180 derivative in such amounts, the desired effects (dispersibility, storage stability, etc.) can be successfully obtained.

[0035] Furthermore, from the viewpoint of dispersion stability, the content of the PY180 derivative per 100 parts by mass of PY180 (component (A)) is preferably 0.5 to 15.0 parts by mass, more preferably 1.0 to 10.0 parts by mass, and particularly preferably 1.5 to 5.0 parts by mass.

[0036] [C] Dispersant The ink composition according to the embodiment further comprises a dispersant. Any material capable of dispersing PY180 can be used as the dispersant, such as a dispersion resin. More specifically, examples include copolymers (e.g., block copolymers, random copolymers, and graft copolymers) consisting of at least two monomers selected from the group consisting of monomers such as styrene and its derivatives, vinylnaphthalene and its derivatives, aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylic acids, (meth)acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, fumaric acid and its derivatives, vinyl acetate, vinyl alcohol, vinylpyrrolidone, and acrylamide.

[0037] The dispersant is preferably one that has pigment adsorption sites and steric hindrance sites. The pigment adsorption sites of the dispersant strongly adsorb to the surface of the pigment particles, thereby covering the pigment particles with the dispersant and preventing direct contact between the particles. In addition, the steric hindrance sites create steric obstruction around the pigment particles, physically preventing the pigment particles from approaching each other and preventing aggregation. Due to these two effects, the pigment particles are stably dispersed by the dispersant, preventing aggregation and sedimentation. Dispersants with such a structure are thought to have three types of HSPs (dD, dP, dH), with two sets each originating from the pigment adsorption sites and the steric hindrance sites. Correspondingly, there may be multiple preferred numerical ranges for the solvent's HSPs as well.

[0038] As the dispersion resin, from the viewpoint of dispersion stability, a polymer having constituent units derived from a styrene compound or its derivative and constituent units derived from a (meth)acrylic acid compound or its derivative (hereinafter also referred to as "styrene-(meth)acrylic acid resin") is preferred. Examples of styrene compounds or their derivatives include styrene, vinyl benzoic acid, methylstyrene, etc. Examples of (meth)acrylic acid compounds or their derivatives include (meth)acrylic acid; alkyl (meth)acrylate esters having alkyl groups such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, iso-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate; methoxytriethylene glycol (meth)acrylate, methoxypolyethylene glycol #400 (meth)acrylate, methoxydi (meth)acrylic acid esters containing ether groups such as propylene glycol (meth)acrylate, methoxytripropylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, ethyl carbitol (meth)acrylate, 2-ethylhexyl carbitol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, p-nonylphenoxyethyl (meth)acrylate, and p-nonylphenoxypolyethylene glycol (meth)acrylate; (meth)acrylic acid esters containing aromatic rings such as benzyl (meth)acrylate;Alicyclic hydrocarbon monomers such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, dicyclopentanyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, ethylcyclohexyl (meth)acrylate, isopropylcyclohexyl (meth)acrylate, isobutylcyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, cyclononyl (meth)acrylate, cyclodecyl (meth)acrylate, etc.; amino groups such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate. Monomers having hydroxyl groups include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, N-(2-hydroxyethyl)(meth)acrylamide, glycerin mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and monomers having hydroxyl groups such as lactone-modified (meth)acrylates with hydroxyl groups at the terminals.

[0039] The weight-average molecular weight (Mw) of the dispersed resin is preferably 1,000 to 30,000, more preferably 2,500 to 28,000, and particularly preferably 5,000 to 26,000, from the viewpoint of storage stability and discharge stability. Mw can be measured by the method described in the examples below.

[0040] From the viewpoint of storage stability, the acid value of the dispersion resin is preferably 50 to 250 mg KOH / g, more preferably 80 to 200 mg KOH / g, and particularly preferably 100 to 180 mg KOH / g. The acid value can be measured and calculated in accordance with JIS K 0070. From the viewpoint of dispersion stability, the amine value of the dispersion resin is preferably 20 mg KOH / g or less, and more preferably 5 mg KOH / g or less. The amine value can be measured and calculated in accordance with ASTM D2074.

[0041] The amount of dispersant per 100% by mass of the ink composition is preferably 0.1 to 5.0% by mass, more preferably 0.3 to 3.0% by mass, and particularly preferably 0.5 to 1.5% by mass, in terms of solid content, from the viewpoint of dispersion stability and discharge performance. When multiple types of dispersants are included, it is preferable to use them so that their total amount is within the above range.

[0042] [D] Solvent The ink composition according to the solvent embodiment further comprises a solvent. The dispersion force term (dD) in the Hansen solubility parameter of the solvent is 16.0 to 18.0, preferably 16.0 to 17.5, more preferably 16.0 to 17.0. The polarity term (dP) in the Hansen solubility parameter of the solvent is 6.0 to 11.5, preferably 6.0 to 11.0, more preferably 6.0 to 10.5. The hydrogen bonding term (dH) in the Hansen solubility parameter of the solvent is 9.0 to 17.0, preferably 10.0 to 16.0, more preferably 10.0 to 15.0 or 9.0 to 12.0. Alternatively, the hydrogen bonding term (dH) is 18.0 to 27.0, preferably 19.0 to 26.0, more preferably 19.5 to 25.5. The ink composition contains one or more solvents having the predetermined Hansen solubility parameters described above (hereinafter also referred to as "specific solvents").

[0043] The solvent is preferably an organic compound, i.e., an organic solvent. Furthermore, the solvent is preferably one or more of the following (a) to (d): (a) a compound containing one or more hydroxyl groups; (b) a compound having two or more carbon atoms; (c) a compound having an oxygen atom / carbon atom ratio of 0.25 to 1.00; (d) a compound that does not contain nitrogen atoms.

[0044] The solvent only needs to satisfy one of (a) to (d), and may satisfy two or more of (a) to (d). That is, the following are possible forms of the solvent: - Satisfying one of (a) to (d); - Satisfying two of (a) to (d) [(a)(b) / (a)(c) / (a)(d) / (b)(c) / (b)(d) / (c)(d)]; - Satisfying three of (a) to (d) [(a)(b)(c) / (a)(b)(d) / (a)(c)(d) / (b)(c)(d)]; - Satisfying all of (a) to (d). Of these, a solvent that satisfies all of (a) to (d) above is preferred.

[0045] The number of hydroxyl groups in (a) above is more preferably 1 to 3. The number of carbon atoms in (b) above is more preferably 2 to 10, particularly preferably 3 to 8, and even more preferably 4 to 6. The ratio of oxygen atoms to carbon atoms in (c) above is more preferably 0.35 to 1.00.

[0046] Solvents that satisfy the Hansen solubility parameters described above include 1,2-butanediol, propylene glycol, 1,3-butanediol, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, 1,4-butanediol, ethylene glycol, 1,2,4-butanetriol, 1,2,6-hexanetriol, and 1,5-pentanediol, with 1,2-butanediol and propylene glycol being particularly preferred. Therefore, the ink composition according to the embodiment preferably contains one or more of the solvents listed herein.

[0047] The content of component (D) (a solvent having a predetermined Hansen solubility parameter; a specific solvent) per 100% by mass of the ink composition is preferably 0.1 to 30.0% by mass, more preferably 0.5 to 25.0% by mass, and particularly preferably 1.0 to 20.0% by mass or 2.0 to 10.0% by mass, from the viewpoint of storage stability and discharge performance. If multiple types of specific solvents are included, it is preferable that their total amount be within the above range. The Hansen solubility parameter of the solvent can be calculated by (1) using physical properties such as heat of vaporization, surface tension, and refractive index, (2) calculating it from the chemical structure of the solvent by the group contribution method, or (3) obtaining the value from an existing database, and commercially available software can be used for all of these methods.

[0048] [E] Other Components The ink composition according to the embodiment may contain, in addition to PY180, yellow pigments or dyes as pigment components. Examples of yellow pigments include azo, disazo, azomethine, anthraquinone, quinophthalone, benzimidazolon, isoindoline, quinacridone, and perinone pigments, and more specifically, C.I. Examples of pigment yellows include Pigment Yellows 1, 2, 3, 12, 13, 14, 16, 17, 20, 23, 24, 34, 35, 37, 53, 55, 73, 74, 75, 81, 83, 86, 93, 95, 97, 98, 100, 101, 104, 108, 109, 110, 114, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 185, 213, etc. In addition, dyes and pigments other than these yellow pigments may be included. In the ink composition according to the embodiment, the proportion of PY180 in the total pigments contained in the ink composition is preferably 60% by mass or more, more preferably 70% by mass or more.

[0049] The ink composition may contain one or more solvents other than the specific solvent as component (D). Examples of other solvents include isopropanol, glycerin, triethylene glycol, 2-pyrrolidone, 1,2-hexanediol, triethanolamine, and pure water. Of these, the embodiment containing isopropanol and water together with the specific solvent is particularly preferred from the viewpoint of storage stability. The content of other solvents per 100% by mass of the ink composition is preferably 52.0 to 99.68% by mass, more preferably 63.0 to 97.35% by mass, and particularly preferably 72.3 to 97.35% by mass, from the viewpoint of storage stability and discharge performance. Furthermore, the content of other solvents (excluding pure water) per 100% by mass of the ink composition is preferably 1.0 to 30.0% by mass, more preferably 2.0 to 20.0% by mass, and particularly preferably 2.0 to 10.0% by mass, from the viewpoint of storage stability and discharge performance.

[0050] The ink composition may further contain additives, such as preservatives, pH adjusters, water-soluble polymer compounds, water-dispersible resins, surfactants, and neutralizing agents.

[0051] Any of the following surfactants can be used: anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants. However, nonionic surfactants are preferred. Examples of nonionic surfactants include silicone-based surfactants, fluorine-based surfactants, and acetylene-based surfactants. From the viewpoint of storage stability and wettability to the substrate, acetylene-based surfactants are preferred.

[0052] More specifically, suitable acetylene-based surfactants include, for example, Surfinol 61, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 420, 440, 465, 485, SE, SE-F, Dynol 604, 607 (manufactured by Evonik), Olfin E1004, E1010, E1020, PD-001, PD-002W, PD-004, PD-005, EXP. 4001, EXP. 4200, EXP. 4123, EXP. 4300 (manufactured by Nisshin Chemical Industry Co., Ltd.). Only one surfactant may be used, or two or more may be used in combination. Furthermore, the surfactant may be synthesized using conventionally known synthesis methods, or a commercially available product may be used.

[0053] The surfactant content per 100% by mass of the ink composition is preferably 0.01 to 2.0% by mass, more preferably 0.05 to 1.5% by mass, and particularly preferably 0.1 to 1.0% by mass, from the viewpoint of storage stability, discharge performance, and wettability to the substrate.

[0054] As a neutralizing agent, known basic compounds can be used, such as sodium hydroxide, potassium hydroxide, ammonia, triethylamine, and methyldiethanolamine. Including an ink composition neutralizing agent moderately promotes the dissociation of anionic groups such as sulfonic acid groups in the ink composition, thereby improving dispersibility.

[0055] The ink composition according to the embodiment is manufactured by mixing the above-described components. The mixing method is not particularly limited and can be done by methods commonly used in the art, such as a mixing method using a dispensing machine. All the materials of the ink composition may be mixed almost simultaneously, or only a portion of the materials may be mixed first to prepare a pigment dispersion, and the remaining materials may be added thereto to make the ink composition. For example, the ink composition can be prepared by pre-mixing materials containing PY180, PY180 derivatives, dispersants and other materials (e.g., neutralizing agents, solvents, etc.) to make a pigment dispersion, and then adding the remaining materials (e.g., solvents, further additives, etc.) thereto. Thus, according to one embodiment, C.I. Pigment Yellow 180 (A), a dispersant (C), and a solvent (D) are prepared; a sulfonic acid group is introduced into C.I. Pigment Yellow 180, and the C.I. Pigment Yellow 180 with the introduced sulfonic acid group is reacted with an aluminum salt to produce C.I. Pigment Yellow 180 having a sulfonic acid group. A method for producing an ink composition is provided, comprising: obtaining an aluminum salt (B) of pigment yellow 180; and simultaneously or sequentially mixing (A), (B), (C), and (D) above [wherein the Hansen solubility parameters of the solvent, the dispersion force term (dD) is 16.0 to 18.0, the polarity term (dP) is 6.0 to 11.5, and the hydrogen bonding term (dH) is 9.0 to 17.0 or 18.0 to 27.0].

[0056] The ink composition according to the embodiment may be used as is, or it may be used after mixing with further components. The type of ink is not particularly limited, but examples include gravure ink, flexographic ink, and inkjet ink. Among these, inkjet ink is preferred from the viewpoint of producing less waste liquid and not requiring a printing plate. From the viewpoint of environmental impact and odor, water-based inkjet ink is preferred.

[0057] The viscosity of the ink according to the embodiment (at 20°C) is preferably 1.0 to 20.0 mPa·s, more preferably 1.5 to 10.0 mPa·s, and especially preferably 2.0 to 5.0 mPa·s, particularly in the case of inkjet inks, from the viewpoint of stabilizing dispersibility and ejection. The viscosity of the ink can be measured by the method described in the examples later. The viscosity change rate before and after the storage stability test described in the examples later is preferably 1.40 or less, more preferably 1.20 or less, and especially preferably 1.10 or less or 1.00 or less.

[0058] The pH of the ink according to this embodiment is, for example, 7.0 or higher, preferably 7.5 or higher, from the viewpoint of further improving the storage stability of the ink. Also, from the viewpoint of material resistance and skin irritation, the pH is, for example, 11.0 or lower, preferably 10.0 or lower.

[0059] The ink according to the embodiment has a volume-average dispersed particle diameter (Mv) value, which is an indicator of dispersion stability, preferably 80 to 280 nm, more preferably 90 to 230 nm, and particularly preferably 100 to 190 nm or 110 to 150 nm. The volume-average dispersed particle diameter (Mv) can be measured by the method described in the examples below. The percentage change in Mv before and after the storage stability test described in the examples below is preferably 1.70 or less, more preferably 1.60 or less, and particularly preferably 1.35 or less or 1.10 or less.

[0060] If the ink according to the embodiment is an inkjet ink, it can be loaded into a known inkjet recording device and ejected as ink droplets onto a recording medium to record images, etc. Inkjet recording devices include continuous ejection type (charge control type, spray type, etc.) and on-demand type (piezo type, thermal type, electrostatic attraction type, etc.), but the ink according to the embodiment can be used in any of these types.

[0061] The present invention will be described in detail below with reference to examples, but the content of the present invention is not limited thereto. The raw materials used in the examples are as follows: [A] C.I. Pigment Yellow 180 The C.I. Pigment Yellow 180 (PY180) listed in Table 1 was synthesized as follows.

[0062] [Synthesis Example A: Synthesis of PY180 Crude] 225 parts by mass of 1,2-bis(2-aminophenoxy)-ethane was dispersed in 3300 parts by mass of water, and then 538.5 parts by mass of 35% hydrochloric acid was added. While maintaining the temperature below 5°C by adding ice, 337 parts by mass of 40% sodium nitrite aqueous solution was added dropwise to prepare the diazo component. Separately, 455 parts by mass of 5-acetoacetylamino-benzimidazolone was dispersed in 3400 parts by mass of water, and then dissolved in 595 parts by mass of 25% sodium hydroxide aqueous solution to obtain the coupler component. The diazo component and coupler component obtained above were then adjusted to 6500 parts by mass and 4500 parts by mass, respectively, by adding water and ice.

[0063] 30.6 parts by mass of 90% acetic acid were added to 6500 parts by mass of water, and the temperature of this solution was adjusted to 20°C. The coupler component was added dropwise to adjust the pH to 6.0, and then the diazo component was added dropwise at a constant rate. To prevent the presence of excess diazonium salt in the acetic acid solution, the addition of the coupler component was started simultaneously with the addition of the diazo solution, and the coupling was performed while adjusting the dropping rate of the coupler component to match the pH of the acetic acid solution to 6.0. During coupling, ice or 5% by mass sodium hydroxide solution was added as needed to maintain the temperature of 20°C and pH of 6.0. After the coupling was completed in about 3 hours, the mixture was heated to 90°C and held for 1 hour. Next, the wet cake obtained by filtration and washing with water was dried at 90°C. The obtained solid was crushed in a juicer mixer to obtain PY180 crude.

[0064] [Synthesis Example B: Synthesis of PY180-1] 500 parts by mass of PY180 crude obtained in Synthesis Example A, 2500 parts by mass of sodium chloride, and 500 parts by mass of diethylene glycol were placed in a 15 L Trimix™ (manufactured by Inoue Seisakusho Co., Ltd.) container, and the mixture was ground for 5 hours while the temperature was controlled to maintain an internal temperature of 80°C to 100°C. The ground material was then added to 50°C warm water, stirred, and thoroughly reslurred. After filtration and washing with water, the resulting wet cake was dried at 90°C. The resulting solid was crushed in a juicer mixer to obtain PY180-1.

[0065] [Synthesis Example C: Synthesis of PY180-2] 700 parts by mass of PY180 crude obtained in Synthesis Example A, 1400 parts by mass of sodium chloride, and 360 parts by mass of diethylene glycol were placed in an 8 L double-arm kneader (manufactured by Inoue Seisakusho Co., Ltd.). The temperature was controlled to maintain an internal temperature of 120°C to 130°C, and the mixture was ground for 5 hours. The ground material was then added to 50°C warm water, stirred, and thoroughly reslurred. After filtration and washing with water, the resulting wet cake was dried at 90°C. The resulting solid was crushed in a juicer mixer to obtain PY180-2.

[0066] The measurement methods for each item in Table 1 are as follows: (Average particle size) 5 mg of C.I. Pigment Yellow 180 was added to 4 mL of cyclohexanone and dispersed for 10 minutes by subjecting it to an ultrasonic cleaner (product name "Bransonic M2800-J", manufactured by Yamato Scientific Co., Ltd.). The obtained dispersion was dropped onto a mesh (collodion membrane attached 200 mesh, manufactured by Nisshin EM Co., Ltd.) to prepare a measurement sample. The measurement sample was photographed using an electron microscope (product name "JEM-1400Flash", manufactured by JEOL Ltd.), and the major and minor axes of 100 primary pigment particles in the obtained photograph were measured using ImageJ (image processing software), and the average value (arithmetic mean) was calculated.

[0067] (Average Aspect Ratio) The average aspect ratio was calculated as "average value of major axis / average value of minor axis". (Specific Surface Area) For 200 mg of C.I. Pigment Yellow 180, the specific surface area was calculated by measuring the amount of gas (nitrogen) adsorbed using the single-point method with a fully automatic specific surface area measuring device Macsorb HM model-1208 (manufactured by Mountec Co., Ltd.).

[0068] [B] Aluminum salt of C.I. Pigment Yellow 180 having sulfonic acid groups (PY180 derivative) Synthesis of PY180 derivative 1 (PY180SA-Al-1) (Synthesis of PY180SA) First, 50 parts by mass of PY180 crude obtained in Synthesis Example A was added to 750 parts by mass of 96.5% by mass sulfuric acid (manufactured by Kanto Chemical Co., Ltd.) at a temperature of 10°C or below. Next, the temperature was raised to 15°C and stirred for 3 hours, and then the resulting mixture was added to 1000 parts by mass of ice water to precipitate the sulfonate. After stirring for another 30 minutes, it was filtered. Then, by washing with 5% by mass saline solution, a wet cake of C.I. Pigment Yellow 180 (PY180SA-1) having sulfonic acid groups was obtained. The signal-to-noise ratio of the product was measured as described later.

[0069] (Synthesis of Aluminum Salt) 237.1 parts by mass of the wet cake of PY180SA-1 obtained above (solid content 20.1% by mass) was added to 716 parts by mass of water and heated to 60°C while stirring. After the wet cake clumps disappeared, the pH was adjusted to 12.0-12.5 with a 25% by mass sodium hydroxide aqueous solution. After stirring for 30 minutes, 13.5 parts by mass of aluminum sulfate 14-18 hydrate (manufactured by Kanto Chemical Co., Ltd.) was added and stirred for 60 minutes. After that, the mixture was filtered and washed with water to obtain a wet cake of aluminum salt of C.I. Pigment Yellow 180 having sulfonic acid groups (PY180SA-Al). The obtained wet cake was dried at 90°C for 14 hours, and the obtained solid was pulverized in a juicer mixer (manufactured by Osaka Chemical Co., Ltd., LAB MILL) to obtain PY180 derivative 1 (PY180SA-Al-1).

[0070] - Synthesis of PY180 derivative 2 (PY180SA-Al-2) (Synthesis of PY180SA) A sulfonate was prepared in the same manner as above, except that 750 parts by mass of 96.5% by mass sulfuric acid (manufactured by Kanto Chemical Co., Ltd.) was diluted with water to 95.0% by mass as sulfuric acid (PY180SA-2). (Synthesis of aluminum salt) PY180 derivative 2 (PY180SA-Al-2) was obtained in the same manner as above, except that in the first step, 202.8 parts by mass of PY180SA-2 wet cake (solid content 23.5% by mass) and 750 parts of water were used.

[0071] The signal-to-noise ratio (SNR) of PY180 derivative 1 and PY180 derivative 2 obtained above was measured. The measurement method is as follows: (SNR measurement) The SNR of the PY180 derivatives was calculated using liquid chromatography (product name "Agilent 1100", manufactured by Agilent Technologies, Inc.). First, 5 mg of the sample to be measured and 10 mL of dimethyl sulfoxide (manufactured by Kanto Chemical Co., Ltd.) were weighed into a 30 mL sample bottle and mixed for 10 seconds using a shaker (product name "VORTEX-GENIE2", manufactured by Scientific Industries, Inc.). Subsequently, the mixture was mixed for 1 hour at 130 rpm while maintaining a temperature of 25°C using a constant temperature shaker (product name "PERSONAL-11", manufactured by Taitec Co., Ltd.). Subsequently, the sample was filtered through a 0.45 μm filter (manufactured by ADVANTECH) and transferred to a 2 mL sample bottle, which was then placed in the Agilent 1100 for measurement.

[0072] Peaks detected within the retention time range of 11.4–12.4 min correspond to disubstituted compounds (structures with two sulfonic acid groups introduced within the same molecule), and peaks detected within the retention time range of 14.7–14.9 min correspond to monosubstituted compounds (structures with one sulfonic acid group introduced within the same molecule). The signal-to-noise ratio (S / N ratio) was calculated from these HPLC peak area values ​​according to the following formula. The HPLC measurement conditions were as described below, and the measurement was repeated twice, with the average value used as the measurement value for that sample.

[0073] [Calculation formula] S / N ratio = Peak area value of disubstituted compound / Peak area value of monosubstituted compound [HPLC measurement conditions] Column: C18 U120 S3 (Φ4.6 mm × 100 mm, 3 μm) Eluent 1: 30 mM Ammonium acetate eluent 2: Methanol gradient (1 / 2): 90 / 10 (~3 min) 0 / 100 (~20 min) Flow rate: 0.1 mL / min Oven: 50°C Wavelength: 400 nm Injection volume: 1.0 μL

[0074] Table 2 shows the peak area values ​​(calculated so that the sum of the disubstituted, monosubstituted, and unsubstituted derivatives equals 100) and signal-to-noise ratios for each PY180 derivative. Note that "unsubstituted derivative" refers to PY180 that does not contain a sulfonic acid group.

[0075] [C] Dispersant: The dispersion resins listed in Table 3 below were used (IPA: isopropanol).

[0076] The weight-average molecular weight (Mw) of the dispersed resin was measured using a gel permeation chromatography (GPC) instrument under the following conditions, and then calculated by converting the results using polystyrene as a standard substance. Instrument: HLC-8320GPC (Tosoh Corporation) Columns: The following columns connected in series: "TSKgel G1000HXL" (7.8 mm I.D. × 30 cm) × 1 "TSKgel G2000HXL" (7.8 mm I.D. × 30 cm) × 1 "TSKgel G3000HXL" (7.8 mm I.D. × 30 cm) × 1 "TSKgel G4000HXL" (7.8 mm I.D. × 30 cm) × 1 Detector: RI (Differential Refractometer) Column temperature: 40°C Eluent: Tetrahydrofuran (THF) Flow rate: 1.0 mL / min Injection volume: 100 μL (THF solution with a sample concentration of 0.1% by mass) Standard sample: Monodisperse polystyrene (TSKgel, Tosoh Corporation) The acid values ​​for "A-500", "A-1000", "A-2500", "A-5000", "F-1", "F-2", "F-4", "F-10", "F-20", "F-40", "F-80", "F-128", and "F-288" were measured and calculated according to JIS K 0070.

[0077] <Preparation Example 1: Preparation of Pigment Dispersion> C.I. Pigment Yellow 180, PY180 derivative, dispersion resin, isopropanol, 25% by mass potassium hydroxide aqueous solution, and ion-exchanged water were mixed according to the formulations shown in Table 4 below to obtain a mixture with a pigment content (total of PY180 and PY180 derivative) of 13.3% by mass. 0.5 mm zirconia beads were added to this mixture and dispersed using paint conditioner for 90 minutes. Then, ion-exchanged water was added to adjust the pigment content to 12.5% ​​by mass to prepare pigment dispersions 1 to 4.

[0078] <Examples 1-13, Comparative Example 1: Ink Preparation> The pigment dispersion obtained in Preparation Example 1, Surfinol 465 (manufactured by Nisshin Chemical Industry Co., Ltd., an acetylene-based surfactant), a specific solvent, and other solvents were mixed in the formulations shown in Table 5 to prepare an inkjet ink with a total volume of 30.0 g.

[0079] The properties of the specific solvents and other solvents used in the examples and comparative examples are summarized in Table 6 below.

[0080] In Table 6, the Hansen solubility parameters are the values ​​recorded in the database of the Hansen Solubility Parameter in Practice (HSPiP) software.

[0081] The obtained inkjet ink was subjected to storage stability tests (volume-average dispersed particle size (Mv) and viscosity). The test method was as follows: (Viscosity) The viscosity of the inkjet ink prepared above was measured before the storage stability test (Day 0). The measurement was performed using an E-type viscometer TV-25 (manufactured by Toki Sangyo Co., Ltd.) under conditions of 20°C and 30 rpm.

[0082] (Volume-average dispersed particle size: Mv) The volume-average dispersed particle size (Mv) of the inkjet ink prepared above was measured before the storage stability test (Day 0). The measurement was performed using a particle size distribution analyzer (Nanotrac WAVE II, Microtrac-Bell). The ink was diluted with pure water so that the loading index was in the range of 8 to 12 before measurement.

[0083] (Storage Stability Test) Inkjet ink was placed in a 30 mL glass bottle (SV-30, manufactured by Nichiden Rika Glass Co., Ltd.), sealed with sealing tape (Tape Seal, manufactured by Valqua Corporation), and then capped. After further securing with vinyl tape (manufactured by Yamato Corporation) over the cap, the bottle was left standing in a 70°C dryer (EOP-450B, manufactured by AS ONE Corporation) for one week. After removing from the dryer, the bottle was left standing at room temperature for one hour and then shaken by hand for 5 seconds. The viscosity and volume-average dispersed particle size (Mv) after the storage stability test were measured using the same method as above (on the 7th day). The viscosity change rate was calculated using [viscosity after test / viscosity before test], and the Mv change rate was calculated using [Mv after test / Mv before test]. The results are shown in Table 7.

[0084] The inks in the examples, by containing a specific solvent, exhibited excellent storage stability, with small changes in viscosity and Mv before and after the storage stability test. Using such inks enables cleaner printing and, because the particle size remains small, can prevent clogging of the nozzle heads of inkjet printers.

[0085] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

Claims

1. An ink composition comprising (A) C.I. Pigment Yellow 180, (B) an aluminum salt of C.I. Pigment Yellow 180 having a sulfonic acid group, (C) a dispersant, and (D) a solvent, wherein the dispersion force term (dD) of the solvent in the Hansen solubility parameter is 16.0 to 18.0, the polarity term (dP) is 6.0 to 11.5, and the hydrogen bonding term (dH) is 9.0 to 17.0 or 18.0 to 27.

0.

2. The ink composition according to claim 1, wherein the solvent satisfies one or more of the following (a) to (d): (a) a compound containing one or more hydroxyl groups; (b) a compound having two or more carbon atoms; (c) a compound having an oxygen atom / carbon atom ratio of 0.25 to 1.00; (d) a compound that does not contain nitrogen atoms.

3. The ink composition according to claim 1 or 2, wherein the solvent is selected from the group consisting of 1,2-butanediol, propylene glycol, 1,3-butanediol diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, 1,4-butanediol, ethylene glycol, 1,2,4-butanetriol, 1,2,6-hexanetriol, and 1,5-pentanediol.

4. The aluminum salt of C.I. Pigment Yellow 180 having the (B) sulfonic acid group comprises a cation portion containing aluminum ions and an anion portion represented by the following general formula (I), according to any one of claims 1 to 3: [In the formula, X １ ~X ６ and Y １ ~Y ８ Each of these independently represents a hydrogen atom or a sulfonic acid group (however, X １ ~X ６ and Y １ ~Y ８ (At least one of them is a sulfonic acid group.) 5. The cation moiety containing the aluminum ion is Al ３＋ , [Al(OH)] ２＋ and [Al(OH) ２ ＋ The ink composition according to claim 4, which is selected from the group consisting of:​ 6. The anion portion represented by the general formula (I) is X １ ~X ６ and Y １ ~Y ８ One of them is a monosubstituted compound with a sulfonic acid group, X １ ~X ６ and Y １ ~Y ８ The ink composition according to claim 4 or 5, comprising a disubstituted product in which two of the groups are sulfonic acid groups, or a mixture thereof.

7. The ink composition according to claim 6, wherein the aluminum salt of C.I. Pigment Yellow 180 having (B) sulfonic acid groups is such that the molar ratio (SN ratio (disubstituted / monosubstituted)) of the monosubstituted product to the disubstituted product is 0.1 to 30.

0.

8. The ink composition according to any one of claims 1 to 7, wherein the dispersant is a styrene-(meth)acrylic acid resin.

9. The ink composition according to any one of claims 1 to 8, wherein the content of the solvent is 0.1 to 30.0% by mass based on 100% by mass of the ink composition.

10. An inkjet ink comprising the ink composition according to any one of claims 1 to 9.

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