Yellow ink for inkjet, image recording method, and image recorded material

Abstract

The present invention provides a yellow inkjet ink capable of recording a yellow image with excellent weather resistance, an image recording method, and an image recorded article having a yellow image with excellent weather resistance. The yellow inkjet ink contains a lake yellow pigment, a yellow pigment other than the lake yellow pigment, a resin, a water-soluble organic solvent, and water.

Description

Technical Field

[0001] The present invention relates to a yellow ink for inkjet, an image recording method and an image recorded material. Background Art

[0002] In recent years, research on yellow ink for inkjet has been conducted.

[0003] For example, Patent Document 1 discloses a yellow ink for inkjet recording that has high fastness and is capable of stably recording high-quality images for a long period of time under any conditions. The yellow ink comprises a polymer dispersant, a water-insoluble colorant, a water-soluble organic solvent, and water. The water-insoluble colorant is at least one selected from the group consisting of CI Solvent Yellow 21, CI Solvent Yellow 42, CI Solvent Yellow 79, CI Solvent Yellow 82, CI Solvent Yellow 83:1, CI Solvent Yellow 88, and CI Solvent Yellow 151. The polymer dispersant is a block copolymer composed of a hydrophobic block and a hydrophilic block, and is obtained by polymerizing a vinyl ether as a monomer, wherein the hydrophilic block is composed of an anionic vinyl ether. Furthermore, the water-insoluble colorant is encapsulated using the polymer dispersant, and the average particle size of the dispersion of the water-insoluble colorant dispersed in the polymer dispersant is 80 nm or less.

[0004] In addition, Patent Document 2 discloses an inkjet ink, which is a new inkjet ink that provides images with suppressed bleeding and excellent color development, and contains water, a colorant, and a water-soluble organic solvent. The colorant is characterized in that the colorant is one or more dyes selected from the group consisting of CI Direct Yellow 86, CI Acid Yellow 23, CI Direct Yellow 173, CI Direct Yellow 132, and CI Direct Yellow 59, and CI Pigment Yellow 74, the surface tension of the ink is 34.0 mN / m or higher, the water-soluble organic solvent contains a poor solvent for the CI Pigment Yellow 74, and the ratio (B / A) of the content B (mass %) of the poor solvent in the ink to the content A (mass %) of the CI Pigment Yellow 74 is 0.75 or higher and 4 or lower.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 4522646

[0008] Patent Document 2: Japanese Patent No. 5142487 Summary of the Invention

[0009] Technical issues to be solved by the invention

[0010] Yellow images recorded using yellow inkjet inks are sometimes required to have improved weather resistance (specifically, properties that combine light resistance, color development, and solvent resistance).

[0011] However, yellow images recorded using ink containing a lake yellow pigment have excellent solvent resistance, but sometimes lack excellent light resistance and color development properties, resulting in sometimes insufficient weather resistance.

[0012] On the other hand, yellow images recorded using inks containing yellow pigments other than lake yellow pigments have excellent light resistance and color development properties, but may not have excellent solvent resistance, resulting in insufficient weather resistance.

[0013] An object of one embodiment of the present invention is to provide a yellow inkjet ink capable of recording a yellow image having excellent weather resistance, an image recording method, and an image recorded material having a yellow image having excellent weather resistance.

[0014] Means for solving technical problems

[0015] Specific methods for solving the problem include the following.

[0016] <1> A yellow ink for inkjet, comprising a yellow pigment, a resin, a water-soluble organic solvent, and water, wherein the yellow pigment includes a lake yellow pigment and a yellow pigment other than a lake yellow pigment.

[0017] <2> The yellow inkjet ink according to <1>, wherein the content of the lake yellow pigment is 10% by mass to 90% by mass relative to the total content of the yellow pigment.

[0018] <3> The yellow inkjet ink according to <1> or <2>, wherein the yellow pigment other than the lake yellow pigment is at least one selected from the group consisting of Pigment Yellow 1, Pigment Yellow 2, Pigment Yellow 3, Pigment Yellow 5, Pigment Yellow 6, Pigment Yellow 10, Pigment Yellow 49, Pigment Yellow 60, Pigment Yellow 65, Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 75, Pigment Yellow 97, Pigment Yellow 98, Pigment Yellow 111, Pigment Yellow 116, Pigment Yellow 130, Pigment Yellow 165, Pigment Yellow 167, and Pigment Yellow 203.

[0019] <4> The yellow inkjet ink according to any one of <1> to <3>, wherein the lake yellow pigment is at least one selected from the group consisting of Pigment Yellow 61, Pigment Yellow 62, Pigment Yellow 133, Pigment Yellow 168, Pigment Yellow 169, Pigment Yellow 205, Pigment Yellow 206, Pigment Yellow 209, and Pigment Yellow 212.

[0020] <5> The yellow inkjet ink according to any one of <1> to <4>, wherein the resin includes a pigment-dispersing resin A and a resin B that is a resin other than the pigment-dispersing resin A.

[0021] <6> The yellow inkjet ink according to <5>, wherein the resin B contains a unit X, and the unit X is a structural unit derived from a monomer having a ClogP of 2.80 to 5.00.

[0022] In the resin B, when the structural unit derived from a monomer having a ClogP of 2.30 or higher is defined as unit Y, the ratio of unit X to the total amount of unit Y is 60% by mass to 100% by mass.

[0023] <7> The yellow inkjet ink according to <5> or <6>, wherein the resin B has a Clo gP of 0.90 to 1.50.

[0024] <8> An image recording method comprising applying the yellow inkjet ink according to any one of <1> to <7> to a recording medium by an inkjet method.

[0025] <9> An image record comprising:

[0026] recording medium; and

[0027] A yellow image is arranged on a recording medium and is formed using the yellow inkjet ink described in any one of <1> to <7>.

[0028] Effects of the Invention

[0029] According to one aspect of the present invention, there are provided a yellow inkjet ink capable of recording a yellow image having excellent weather resistance, an image recording method, and an image recorded material having a yellow image having excellent weather resistance. DETAILED DESCRIPTION

[0030] Hereinafter, the contents of the present invention will be described in detail.

[0031] Although the description of the constituent elements described below may be based on representative embodiments of the present invention, the present invention is not limited to such embodiments.

[0032] In the present invention, “to” indicating a numerical range is used to mean that the numerical values ​​described before and after it are included as the lower limit and the upper limit.

[0033] In the numerical ranges described in stages throughout the present invention, the upper limit or lower limit of one numerical range may be replaced by the upper limit or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in the present invention, the upper limit or lower limit of the numerical range may be replaced by the values ​​shown in the Examples.

[0034] In the present invention, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, the amount refers to the total amount of the multiple components present in the composition.

[0035] The term "solid content" in the present invention means components other than the solvent, and liquid components such as low-molecular-weight components other than the solvent are also included in the "solid content" in this specification.

[0036] In the present invention, the term "solvent" is used to include water, organic solvents, and mixed solvents of water and organic solvents.

[0037] In the present invention, both or either of acrylic acid and methacrylic acid may be referred to as “(meth)acrylic acid.” For example, “(meth)acrylic acid” includes both acrylic acid and methacrylic acid.

[0038] In the present invention, both or either of acrylate and methacrylate may be referred to as "(meth)acrylate".

[0039] In the present invention, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process can be achieved.

[0040] In the present invention, compounds not indicating substitution or unsubstituted may have any substituents within a range that does not impair the effects of the present invention.

[0041] In addition, in the present invention, a combination of preferred embodiments becomes a more preferred embodiment.

[0042] The weight average molecular weight (Mw) in the present invention is measured by gel permeation chromatography (GPC).

[0043] GPC used an HLC-8220GPC (manufactured by TOSOH CORPORATION). Three columns, TSKgeL Super HZ2000, TSKgeL Super HZ4000, and TSKgeL Super HZ-H (all manufactured by TOSOH CORPORATION, 4.6 mm × 15 cm), were connected in series. NMP (N-methylpyrrolidone) was used as the eluent. The sample concentration was set to 0.3% by mass, the flow rate was set to 0.35 ml / min, the sample injection volume was set to 10 μL, the measurement temperature was set to 40°C, and an RI (Refractive Index) detector (differential refractive index detector) was used as the detector. A calibration curve was prepared based on six samples of "TSK standard, polystyrene" manufactured by TOSOH CORPORATION: "F-80," "F-20," "F-4," "F-2," "A-5000," and "A-1000."

[0044] In the present invention, "Pigment Yellow" means CI (Color Index) Pigment Yellow.

[0045] In the present invention, “Pigment Yellow” may be referred to as “PY”.

[0046] Yellow ink for inkjet

[0047] Yellow pigments other than lake yellow pigments (other yellow pigments)

[0048] The yellow inkjet ink of the present invention (hereinafter also referred to simply as "ink") contains a yellow pigment, a resin, a water-soluble organic solvent, and water. The yellow pigment includes lake yellow pigments and yellow pigments other than lake yellow pigments.

[0049] According to the ink of the present invention, a yellow image having excellent weather resistance can be recorded.

[0050] Weather resistance, as used herein, is a comprehensive property of light resistance, color development, and solvent resistance. Therefore, if any of these properties deteriorate, weather resistance deteriorates. For the evaluation method of weather resistance, please refer to the Weather Resistance Evaluation in the Examples.

[0051] The ink of the present invention exhibits the above effects because the lake yellow pigment in the ink ensures solvent resistance of the yellow image, and the yellow pigments other than the lake yellow pigment in the ink ensure light resistance and color development of the yellow image.

[0052] It is considered that the water-soluble organic solvent in the ink of the present invention contributes to ensuring the ejectability from the inkjet head (hereinafter also simply referred to as "ink ejectability").

[0053] It is believed that the resin in the ink of the present invention contributes to improving the image quality of a yellow image obtained after the ink droplets applied to the substrate dry.

[0054] As long as the above-mentioned effects can be maintained, the ink of the present invention may contain lake yellow pigments and pigments other than lake yellow pigments as yellow pigments. For example, pigments other than yellow pigments, inorganic pigments, fluorescent pigments, etc. may be added to adjust transparency and hue. From the perspective of effectively improving the quality of yellow images, it is preferred to use only lake yellow pigments and yellow pigments other than lake yellow pigments as yellow pigments.

[0055] Yellow Lake Pigment

[0056] The ink of the present invention contains at least one lake yellow pigment (ie, a yellow pigment that is a lake pigment).

[0057] From the viewpoint of further improving the weather resistance of the yellow image (hereinafter also referred to as “image”), the lake yellow pigment is preferably an azo lake yellow pigment, and more preferably at least one selected from the group consisting of Pigment Yellow 61, Pigment Yellow 62, Pigment Yellow 133, Pigment Yellow 168, Pigment Yellow 169, Pigment Yellow 205, Pigment Yellow 206, Pigment Yellow 209 and Pigment Yellow 212.

[0058] Yellow pigments other than lake yellow pigments

[0059] The ink of the present invention contains at least one yellow pigment other than a lake yellow pigment.

[0060] This improves the light resistance and color development properties of the image.

[0061] From the viewpoint of further improving the weather resistance of the image, the yellow pigment other than the lake yellow pigment is preferably an azo yellow pigment, and more preferably at least one selected from the group consisting of Pigment Yellow 1, Pigment Yellow 2, Pigment Yellow 3, Pigment Yellow 5, Pigment Yellow 6, Pigment Yellow 10, Pigment Yellow 49, Pigment Yellow 60, Pigment Yellow 65, Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 75, Pigment Yellow 97, Pigment Yellow 98, Pigment Yellow 111, Pigment Yellow 116, Pigment Yellow 130, Pigment Yellow 165, Pigment Yellow 167, and Pigment Yellow 203.

[0062] From the viewpoint of weather resistance of yellow images, the proportion of the lake yellow pigment in all yellow pigments contained in the ink of the present invention (the total content of the lake yellow pigment and yellow pigments other than the lake yellow pigment) is preferably 10% by mass to 90% by mass, more preferably 20% by mass to 80% by mass, and even more preferably 30% by mass to 70% by mass.

[0063] The total content of the yellow pigments contained in the ink of the present invention (the total amount of the lake yellow pigment and the yellow pigments other than the lake yellow pigment) is preferably 1% by mass to 20% by mass, more preferably 2% by mass to 15% by mass, and even more preferably 3% by mass to 10% by mass relative to the total amount of the ink.

[0064] <Preferred combination of lake yellow pigment and yellow pigment other than lake yellow pigment>

[0065] From the viewpoint of weather resistance of the recorded yellow image, in the ink of the present invention, as a combination of a lake yellow pigment and a yellow pigment other than a lake yellow pigment,

[0066] Preferably, the lake yellow pigment is at least one selected from the group consisting of Pigment Yellow 168, Pigment Yellow 169, Pigment Yellow 209, and Pigment Yellow 61, and the yellow pigment other than the lake yellow pigment is at least one selected from the group consisting of Pigment Yellow 65, Pigment Yellow 74, Pigment Yellow 10, and Pigment Yellow 203.

[0067] A combination in which the lake yellow pigment is Pigment Yellow 168 or Pigment Yellow 169 and the yellow pigment other than the lake yellow pigment is Pigment Yellow 74 or Pigment Yellow 65 is more preferable.

[0068] <Resin>

[0069] The ink of the present invention contains at least one resin.

[0070] (Pigment Dispersing Resin A)

[0071] The resin in the ink of the present invention preferably includes at least one pigment dispersing resin A. This further improves the dispersion stability of the yellow pigment (hereinafter also simply referred to as "pigment") in the ink.

[0072] As the pigment dispersion resin A, for example, a resin that adheres to a portion of the surface or the entire surface of the pigment and functions as a dispersant for dispersing the pigment is used.

[0073] The pigment dispersion resin A preferably contains at least one acid group selected from the group consisting of a phosphoric acid group, a sulfonic acid group (sulfo group), and a carboxylic acid group (carboxyl group).

[0074] When the pigment dispersion resin A contains an acid group, the dispersibility of the hydrophobic pigment in water can be further improved.

[0075] The pigment dispersion resin A preferably contains a carboxylic acid group as the acid group.

[0076] The acid group can be introduced into the polymer by polymerizing an acid group-containing monomer. The pigment dispersion resin A preferably contains a structural unit derived from an acid group-containing monomer.

[0077] Preferred embodiments of the acid groups and acid group-containing monomer-derived structural units applicable to the pigment dispersion resin A are the same as those applicable to the resin B described below.

[0078] When the pigment-dispersing resin A is a copolymer containing a structural unit derived from a monomer containing an acid group, from the viewpoint of pigment dispersibility, the content ratio of the structural unit derived from the monomer containing an acid group in the pigment-dispersing resin A is preferably 5% by mass to 40% by mass, and more preferably 8% by mass to 20% by mass, relative to the total amount of the pigment-dispersing resin A.

[0079] Pigment-dispersing resin A preferably contains an aromatic ring. Aromatic rings can be incorporated into the polymer as structural units derived from aromatic ring-containing monomers by polymerizing these monomers. When pigment-dispersing resin A contains aromatic rings, the aromatic rings in the resin render the pigment-dispersing resin A hydrophobic, making it easier for the pigment-dispersing resin A to adhere to the pigment. Consequently, pigment-dispersing resin A can improve the stability of the pigment in water.

[0080] The aromatic ring refers to a cyclic unsaturated ring having aromaticity.

[0081] Examples of the aromatic ring include aromatic hydrocarbon rings such as a benzene ring, a naphthalene ring, an anthracene ring, and a pyrene ring; and heteroaromatic rings such as a pyridine ring, a pyrrole ring, a furan ring, a thiophene ring, an imidazolyl ring, and an acridone ring. Among these, aromatic hydrocarbon rings are preferred.

[0082] As the monomer containing an aromatic ring, a monomer containing an aromatic ring and an ethylenically unsaturated double bond is preferred, and a vinyl monomer containing an aromatic ring is more preferred. Examples of the monomer containing an aromatic ring include styrene, methylstyrene, divinylbenzene, vinylpyridine, diallyl phthalate, and aromatic ring-containing (meth)acrylates (e.g., benzyl acrylate, phenoxyethyl acrylate, etc.).

[0083] The aromatic ring-containing monomer may be an unsubstituted monomer or a substituted monomer substituted with a substituent. Examples of the substituent include a halogen atom, an alkyl group, a carboxylic acid group, and a hydroxyl group.

[0084] Examples of the halogen atom include chlorine, bromine, and iodine.

[0085] The alkyl group is preferably an alkyl group having 1 to 12 carbon atoms (preferably 1 to 8 carbon atoms), and examples thereof include methyl, ethyl, propyl, butyl, hexyl, etc. The alkyl group may be unsubstituted or may have the same substituents as described above.

[0086] Specific examples of the structural unit derived from a monomer containing an aromatic ring are shown below.

[0087] The structural unit derived from a monomer containing an aromatic ring is not limited to the following specific examples.

[0088] In each structure, "*" represents a connecting bond, "iBu" represents an isobutyl group, "nBu" represents an n-butyl group, and "tBu" represents a tert-butyl group.

[0089] [Chemical Formula 1]

[0090]

[0091] The content of the structural unit derived from the aromatic ring-containing monomer in the pigment dispersion resin A is preferably 50 to 85 mass %, more preferably 50 to 80 mass %, and even more preferably 60 to 80 mass %, based on the total amount in one molecule of the pigment dispersion resin A.

[0092] The pigment dispersion resin A may contain a structural unit derived from a monomer not containing an aromatic ring in addition to the structural unit derived from the monomer containing an aromatic ring.

[0093] Preferred examples of the structural unit derived from a monomer not containing an aromatic ring include alkyl (meth)acrylates and the like.

[0094] The alkyl (meth)acrylate is preferably one having an alkyl moiety with 1 to 20 carbon atoms. Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and stearyl (meth)acrylate.

[0095] Specific examples of the pigment dispersion resin A include the following copolymers. The mass ratio of the monomers in the copolymer can be appropriately selected within the range that satisfies the weight average molecular weight. The present invention is not limited to the following specific examples.

[0096] Benzyl methacrylate / acrylic acid copolymer

[0097] Benzyl methacrylate / methacrylic acid copolymer

[0098] Styrene / acrylic acid / alkyl acrylate copolymer

[0099] Styrene / acrylic acid / alkyl methacrylate copolymer

[0100] Benzyl methacrylate / methacrylic acid / alkyl methacrylate copolymer

[0101] Phenoxyethyl methacrylate / methacrylic acid / alkyl methacrylate copolymer

[0102] Phenoxyethyl methacrylate / methacrylic acid / alkyl methacrylate / hydroxyethyl methacrylate copolymer

[0103] From the viewpoint of pigment dispersibility and dispersion stability, the acid value of the pigment dispersion resin A is preferably 50 mgKOH / g to 180 mgKOH / g, more preferably 50 mgKOH / g to 150 mgKOH / g, and even more preferably 50 mgKOH / g to 120 mgKOH / g.

[0104] The acid value can be measured by titration with an indicator, and is a value measured by the method described in Japanese Industrial Standards (JIS) K0070:1992.

[0105] The weight average molecular weight (Mw) of the pigment dispersion resin A is preferably 1,000 to 100,000, more preferably 10,000 to 50,000.

[0106] From the viewpoint of improving the dispersibility of the pigment, the content of the pigment dispersing resin A in the ink is preferably 10% to 80% by mass, and more preferably 25% to 70% by mass, relative to the content of the pigment.

[0107] (Resin B)

[0108] The resin in the ink of the present invention preferably includes at least one resin B as a resin other than the pigment-dispersing resin A.

[0109] When the resin in the ink of the present invention includes resin B, the thickening effect of resin B suppresses the movement of ink droplets in the ink applied to the recording medium, thereby further improving image quality. For example, image detail is further improved, and image bleeding is further suppressed.

[0110] From the viewpoint of more effectively exhibiting the above-mentioned effects, the resin B is preferably a water-soluble resin.

[0111] In the present invention, "water-soluble" in a water-soluble resin means that it dissolves 1 g or more in 100 g of water at 25° C. "Water-soluble" preferably means that it dissolves 3 g or more (more preferably 10 g or more) in 100 g of water at 25° C.

[0112] -Unit X-

[0113] From the viewpoint of further improving the blocking resistance of the image and the ejectability of the ink, the resin B preferably contains a unit X which is a structural unit derived from a monomer having a ClogP of 2.80 to 5.00.

[0114] The ClogP of the monomer being 2.80 or greater contributes to suppressing the retention of moisture in the image, and as a result, contributes to improving the blocking resistance of the image.

[0115] The ClogP of the monomer being 5.00 or less contributes to suppressing ink residue on the liquid-repellent film provided on the ink ejection surface of the inkjet head, and as a result, contributes to improving the ejectability of the ink.

[0116] In the present invention, a structural unit derived from a monomer means a structural unit formed by polymerization of the corresponding monomer.

[0117] ClogP is a parameter indicating the hydrophobicity of a compound. A higher ClogP value indicates a more hydrophobic compound.

[0118] In the present invention, as ClogP, ClogP calculated using ChemDraw (registered trademark) Professional (ver. 16.0.1.4) manufactured by PerkinElmer Informatics is used.

[0119] As the monomer for forming the unit X, monomers having a ClogP of 2.80 to 5.00 are exemplified below.

[0120] In the following examples, the values ​​in brackets represent the ClogP of the corresponding monomer.

[0121] Examples of monomers having a ClogP of 2.80 to 5.00 include:

[0122] Decyl methacrylate (5.87);

[0123] Isobornyl methacrylate (4.97);

[0124] 2-Ethylhexyl acrylate (4.37);

[0125] α-Methylstyrene (3.27);

[0126] Styrene (2.87); etc.

[0127] In the resin B, the ratio of the units X to the total amount of the units Y, which are structural units derived from a monomer having a ClogP of 2.30 or higher, is preferably 60 to 100% by mass, more preferably 80 to 100% by mass.

[0128] When the ratio of the unit X is 60% by mass to 100% by mass, the ejectability of the ink is further improved.

[0129] -Unit Y-

[0130] Unit Y is a structural unit derived from a monomer having a ClogP of 2.30 or greater.

[0131] Unit Y includes the concept of unit X and is a broader concept than unit X.

[0132] The monomers for forming the structural units other than the unit X in the unit Y (ie, monomers having a Clog P of 2.30 or more and less than 2.80) are exemplified below.

[0133] In the following examples, the values ​​in brackets represent the ClogP of the corresponding monomer.

[0134] Examples of monomers having a ClogP of 2.30 or more and less than 2.80 include:

[0135] n-Butyl methacrylate (2.69);

[0136] n-Butyl acrylate (2.38); etc.

[0137] In the resin B, the content of the units Y is preferably 3% by mass to 80% by mass, more preferably 3% by mass to 50% by mass, and even more preferably 5% by mass to 50% by mass, based on the total amount of the resin B.

[0138] When the resin B contains the unit Y, the resin B may contain a structural unit other than the unit Y (ie, a structural unit derived from a monomer having a ClogP of less than 2.30).

[0139] Examples of monomers having a ClogP of less than 2.30 include the acid group-containing monomers described below and alkyl (meth)acrylates having 1 to 3 carbon atoms in the alkyl portion.

[0140] -Acid group-

[0141] The resin B preferably contains at least one acid group selected from the group consisting of a phosphoric acid group, a sulfonic acid group (ie, a sulfonic acid group), and a carboxylic acid group (ie, a carboxyl group).

[0142] As a result, the image quality is further improved.

[0143] Among the acid groups, a carboxylic acid group is preferred from the viewpoint of being able to easily exhibit a thickening effect on the ink and further improve the image quality.

[0144] The acid group that may be contained in the resin B may be an acid group neutralized with a base (for example, -COONa) or an acid group that is not neutralized (for example, -COOH).

[0145] Furthermore, the resin B in the ink may contain both acid groups neutralized with a base and acid groups that are not neutralized.

[0146] When the resin B in the ink contains an acid group neutralized with a base, the water solubility of the resin B is further improved, which is preferred.

[0147] The base is not limited as long as it can neutralize the acid group. Examples of the base include inorganic bases such as alkali metal hydroxides and alkaline earth metal hydroxides, and organic bases such as organic amines.

[0148] Examples of the alkali metal include potassium (K) and sodium (Na).

[0149] Examples of the alkaline earth metal include calcium (Ca) and magnesium (Mg).

[0150] Examples of the alkali metal hydroxide include potassium hydroxide and sodium hydroxide.

[0151] Examples of the hydroxide of the alkaline earth metal include calcium hydroxide and magnesium hydroxide.

[0152] Examples of the organic amine include ammonia, primary amines (e.g., ethylamine, monoethanolamine, etc.), secondary amines (e.g., diethylamine, ethylenediamine, etc.), tertiary amines (e.g., triethylamine, triethanolamine, isopropylethylamine, pyrrolidine, piperidine, etc.), and quaternary ammonium salts. Among these, organic amines having a boiling point of 80° C. or higher are preferred from the viewpoint of storage stability.

[0153] From the viewpoint of storage stability, the base is preferably an alkali metal hydroxide or an organic amine, and more preferably an alkali metal hydroxide or an organic amine having a boiling point of 80° C. or higher.

[0154] Examples of organic amines having a boiling point of 80°C or higher include ethylenediamine (117°C), triethylamine (90°C), monoethanolamine (170°C), triethanolamine (208°C), isopropylethylamine (127°C), pyrrolidine (87°C), and piperidine (106°C).

[0155] The content of the acid group in the resin B is preferably 5% by mass to 40% by mass, and more preferably 7% by mass to 25% by mass, from the viewpoint of satisfactorily exhibiting the thickening effect of the ink during recording.

[0156] From the viewpoint of satisfactorily exhibiting the thickening effect of the ink during recording, the resin B preferably contains a carboxylic acid group as the acid group.

[0157] More preferably, the resin B contains a carboxylic acid group as the acid group, and 40 mol % or more of the carboxylic acid group is neutralized with a base.

[0158] In this case, the ratio of neutralized carboxylic acid groups to the total carboxylic acid groups (hereinafter also referred to as "neutralization degree of carboxylic acid groups") is preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 80 mol% or more. In addition, the upper limit of the neutralization degree of carboxylic acid groups (i.e., the ratio of neutralized carboxylic acid groups) can be set to 100 mol%.

[0159] The acid group can be introduced into the resin B by polymerizing an acid group-containing monomer. The resin B preferably contains a structural unit derived from the acid group-containing monomer.

[0160] Specific examples of the structural unit derived from the acid group-containing monomer are shown below.

[0161] Examples of the structural unit derived from a monomer containing an acid group include structural units in which the acid group (eg, -COOH) in the structural units described below is neutralized to form a salt of the acid group (eg, -COONa).

[0162] The structural unit derived from the acid group-containing monomer is not limited to these specific examples.

[0163] [Chemical Formula 2]

[0164]

[0165] When the resin B contains a structural unit derived from an acid group-containing monomer, the content of the structural unit derived from the acid group-containing monomer relative to the total amount of the resin B is preferably 5 to 40% by mass, more preferably 8 to 20% by mass.

[0166] -Structural unit derived from an alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl portion-

[0167] The resin B may contain a structural unit derived from an alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl portion.

[0168] Examples of the alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl portion include methyl (meth)acrylate, ethyl (meth)acrylate, and propyl (meth)acrylate.

[0169] The content of the structural unit derived from an alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl portion is preferably 3 to 80% by mass, more preferably 5 to 75% by mass, and even more preferably 15 to 75% by mass, based on the total amount of resin B.

[0170] The weight average molecular weight of resin B is preferably 5,000 to 100,000. When the weight average molecular weight of resin B is within the above range, image bleeding and blocking can be further suppressed, and the ink jetting properties are further improved.

[0171] The weight average molecular weight of the resin B is more preferably 10,000 to 80,000, and even more preferably 10,000 to 30,000, from the viewpoint of ink jetting properties.

[0172] The acid value of resin B is preferably 28 to 230 mgKOH / g. When the acid value is 230 mgKOH / g or less, even a small amount of the water-soluble polymer can easily achieve an ink thickening effect, thereby reducing image bleeding. Furthermore, from the perspective of ink thickening, the acid value is more preferably 50 mgKOH / g or greater, and can be 100 mgKOH / g or greater, or even 150 mgKOH / g or greater.

[0173] The acid value can be measured by titration with an indicator in the same manner as for the pigment dispersion resin A, and is a value measured by the method described in Japanese Industrial Standards (JIS) K0070:1992.

[0174] The glass transition temperature (Tg) of the resin B is preferably 80° C. or higher. When Tg is 80° C. or higher, image blocking can be further suppressed.

[0175] The Tg of the resin B is more preferably 95° C. or higher, and even more preferably 110° C. or higher. Furthermore, from the viewpoint of synthetic suitability, the upper limit of the Tg of the resin B is preferably 250° C. or lower.

[0176] Tg is measured by preparing a sample of a water-soluble polymer solution dried under reduced pressure at 150°C for 6 hours and using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min. For example, a differential scanning calorimeter (DSC) DSC7000X manufactured by Hitachi High-Tech Science Corporation can be used as the DSC.

[0177] The content of the resin B in the ink is preferably 1% by mass to 10% by mass relative to the total amount of the ink.

[0178] When the content of the resin B is 1% by mass or more, the thickening effect of the ink is easily obtained.

[0179] When the content of the resin B is 10% by mass or less, the jetting properties of the ink are further improved.

[0180] (Preferred ClogP of Pigment Dispersing Resin A and Resin B)

[0181] From the viewpoint of easily adhering to the pigment and improving dispersibility, the pigment dispersing resin A is preferably more hydrophobic than the resin B, that is, preferably a resin having a ClogP greater than that of the resin B. The ClogP of the pigment dispersing resin A is preferably 1.75 or greater, more preferably 1.80 or greater, and even more preferably 1.85 or greater.

[0182] On the other hand, from the viewpoint of dissolving in the ink and effectively thickening the ink applied to the recording medium (i.e., improving the image quality), the resin B is preferably more hydrophilic than the pigment-dispersed resin A, that is, preferably a resin having a ClogP smaller than the ClogP of the pigment-dispersed resin A.

[0183] The ClogP of the resin B is preferably 1.80 or less, more preferably 1.74 or less, further preferably 1.72 or less, and even more preferably 1.70 or less.

[0184] From the viewpoint of further improving the blocking resistance of the image and the jetting properties of the ink, the Clog P of the resin B is more preferably 0.90 to 1.50, more preferably 0.95 to 1.45, and even more preferably 0.97 to 1.43.

[0185] When the ClogP of the resin B is 0.90 or more, the blocking resistance of the image is further improved.

[0186] When the ClogP of the resin B is 1.50 or less, the jetting properties of the ink are further improved.

[0187] From the viewpoint of more effectively exerting the dispersion stability of the pigment and the thickening effect of the ink imparted to the recording medium (i.e., the image quality improvement effect), in the ink of the present invention, the ClogP of the pigment dispersing resin A is preferably 1.75 or greater and the ClogP of the resin B is preferably 1.74 or less.

[0188] The ClogP of each resin is calculated by taking a weighted average of the ClogPs of the monomers used to form the resin. For example, the ClogP of polyacrylic acid is calculated as the ClogP of acrylic acid. Regarding the ClogP of a polyacrylic acid-polymethacrylic acid copolymer (copolymerization ratio = 50:50 [mass ratio]), the sum of the values ​​obtained by multiplying the ClogP of acrylic acid and the ClogP of methacrylic acid by their respective mass ratios (in this case, 0.5) is used as the ClogP value of the polyacrylic acid-polymethacrylic acid copolymer (copolymerization ratio = 50:50 [mass ratio]).

[0189] As the ClogP of each monomer, the ClogP calculated using ChemDraw (registered trademark) Professional (ver. 16.0.1.4) manufactured by PerkinElmer Informatics was used as described above.

[0190] Water

[0191] The ink of the present invention contains water.

[0192] The water content is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more, relative to the total amount of the ink.

[0193] The upper limit of the water content relative to the total amount of ink also depends on the contents of other components, and is, for example, 99 mass %, 90 mass %, 80 mass %, or the like.

[0194] <Water-soluble organic solvent>

[0195] The ink of the present invention contains at least one water-soluble organic solvent, thereby ensuring the jetting properties of the ink.

[0196] In the present invention, the "water-soluble" in the water-soluble organic solvent refers to the property of dissolving 5 g or more in 100 g of water at 20°C.

[0197] Examples of water-soluble organic solvents include glycerol, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol and other alkanediols (polyols); sugar alcohols; alkyl alcohols having 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol, isopropanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-tert-butyl ether, Ethylene glycol ethers such as propylene glycol monomethyl ether, diethylene glycol mono-tert-butyl ether, triethylene glycol monoethyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-tert-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, and tripropylene glycol monomethyl ether; amide compounds such as formamide, N,N-dimethylformamide, N,N-dimethylacetamide, 2-pyrrolidone, and N-methylpyrrolidone; etc.

[0198] The water-soluble organic solvents can be used alone or in combination of two or more.

[0199] The water-soluble organic solvent preferably contains a first organic solvent having a boiling point of 110°C to 240°C. The inclusion of the first organic solvent allows the content of a high-boiling-point solvent (e.g., a second organic solvent having a boiling point of 245°C to 300°C) to be relatively reduced. This improves the drying properties of the ink and reduces image blocking.

[0200] Examples of the first organic solvent having a boiling point of 110°C to 240°C include ethylene glycol (198°C), propylene glycol (188°C), dipropylene glycol (230°C), ethylene glycol monomethyl ether (124°C), ethylene glycol diethyl ether (162°C), propylene glycol monoethyl ether (120°C), dipropylene glycol dimethyl ether (171°C), diethylene glycol monomethyl ether (194°C), diethylene glycol diethyl ether (188°C), and N-methylpyrrolidone (202°C).

[0201] Examples of the second organic solvent having a boiling point of 245° C. to 300° C. include diethylene glycol (245° C.), glycerin (290° C.), 2-pyrrolidone (245° C.), and triethylene glycol monomethyl ether (248° C.).

[0202] From the perspective of printhead maintenance, the first and second organic solvents are preferably alcoholic and etheric organic solvents. Compared to organic solvents such as amide compounds (such as 2-pyrrolidone), which easily interact with polymer components, alcoholic and etheric organic solvents are less likely to adhere to the interior of the printhead, thereby improving printhead maintenance.

[0203] Specific examples of the alcohol-based organic solvent include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and glycerin.

[0204] Examples of the ether-based organic solvent include the above-mentioned alkyl ethers of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and glycerol.

[0205] Specific examples of the ether-based organic solvent include alkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol diethyl ether, propylene glycol monoethyl ether, dipropylene glycol dimethyl ether, diethylene glycol monomethyl ether, and diethylene glycol diethyl ether.

[0206] In the present invention, each of the first organic solvent and the second organic solvent is preferably at least one alcoholic organic solvent selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, dipropylene glycol, glycerol, and alkyl ethers thereof.

[0207] When the water-soluble organic solvent contains the first organic solvent, the content of the second organic solvent (S 2 ) and the content of the first organic solvent (S 1 ) mass ratio (S 2 / S 1) is preferably in the range of 0 to 0.3. 2 / S 1 When the content is within the above range, the amount of the organic solvent having a high boiling point can be kept low, thereby suppressing the stickiness of the image after drying.

[0208] As S 2 / S 1 , for the same reasons as above, it is more preferably in the range of 0 to 0.2.

[0209] The ink of the present invention may contain organic solvents other than the above-mentioned water-soluble organic solvents within a range that does not significantly impair the effects of the present invention.

[0210] The total amount of the first organic solvent and the second organic solvent in the ink is preferably 5% by mass to 30% by mass relative to the total amount of the ink.

[0211] When the total amount of the first and second organic solvents is within the above range, the amount of organic solvents can be kept low, thereby reducing the stickiness of the dried image. Furthermore, when the total amount of the first and second organic solvents is 5% by mass or greater, solidified ink formed at the air interface within the printhead can be prevented from clogging the ejection orifices, thereby improving ink jettability.

[0212] The total amount of the first organic solvent and the second organic solvent is more preferably in the range of 7.5% by mass to 40% by mass, and further preferably in the range of 10% by mass to 30% by mass, for the same reasons as described above.

[0213] -Other ingredients-

[0214] The ink of the present invention may contain other components as needed in addition to the above-mentioned components within a range that does not significantly impair the effects of the present invention.

[0215] Examples of other components include anti-desiccant (swelling agent), coloring inhibitor, penetration enhancer, ultraviolet absorber, preservative, rust preventive, defoaming agent, viscosity adjuster, pH adjuster, chelating agent, and the like.

[0216] -Ink Properties-

[0217] 1. Surface tension

[0218] The surface tension of the ink is not particularly limited, but can be, for example, 20 mN / m or higher. From the viewpoint of coating properties on recording media, it is preferably 25 mN / m to 40 mN / m, and more preferably 27 mN / m to 37 mN / m.

[0219] The surface tension of the ink is a value measured at 25° C. by a flat plate method using an automatic surface tensiometer (Automatic Surface Tensiometer) CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

[0220] The surface tension of the ink can be adjusted by adding a surfactant, for example.

[0221] 2. pH

[0222] The pH (25°C ± 1°C) of the ink is preferably 6-10, more preferably 7-10.

[0223] The pH is a value measured using a pH meter (for example, WM-50EG manufactured by DKK-TOA CORPORATION) in a state where the temperature of the ink is adjusted to 25°C under a 25°C environment.

[0224] 3. Viscosity

[0225] From the perspective of ink jetting properties, the viscosity of the ink is preferably in the range of 1 mPa·s to 30 mPa·s, more preferably in the range of 1 mPa·s to 20 mPa·s, further preferably in the range of 2 mPa·s to 15 mPa·s, and particularly preferably in the range of 2 mPa·s to 10 mPa·s.

[0226] The viscosity represents a value measured at 25° C. The viscosity can be measured using, for example, VISCOMETER TV-22 (manufactured by TOKISANGYO CO., LTD.).

[0227] [Image Recording Method]

[0228] The image recording method of the present invention includes a step of applying the ink of the present invention described above to a recording medium to record an image (dried product of the ink of the present invention) (hereinafter also referred to as an ink applying step).

[0229] The image recording method of the present invention may further include other steps as necessary.

[0230] Since the image recording method of the present invention uses the ink of the present invention to record an image, according to the image recording method of the present invention, the same effects as those obtained by the ink of the present invention can be obtained.

[0231] -Recording Medium-

[0232] As the recording medium in the image recording method of the present invention, printing paper mainly composed of cellulose (for example, high-quality paper, coated paper, and art paper) can be used.

[0233] As the recording medium, a generally commercially available recording medium can be appropriately selected, and examples thereof include high-quality paper (A) such as “OK PRINCE HIGH GRADE” manufactured by Oji Paper Co., Ltd., “SHIRAOI” manufactured by Nippon Paper Industries Co., Ltd., and “NEW NPI HIGH GRADE” manufactured by Nippon Paper Industries Co., Ltd.; high-quality coated paper such as “SILVER DIA” manufactured by Nippon Paper Industries Co., Ltd.; lightly coated paper such as “OKEVER LIGHT COAT” manufactured by Oji Paper Co., Ltd. and “AURORA S” manufactured by Nippon Paper Industries Co., Ltd.; lightly coated paper (A3) such as “OK COAT L” manufactured by Oji Paper Co., Ltd. and “AURORA L” manufactured by Nippon Paper Industries Co., Ltd.; “OK TOP COAT PLUS” manufactured by Oji Paper Co., Ltd. and Nippon Paper Coated papers (A2, B2) such as "AURORA COAT" manufactured by Industries Co., Ltd., coated papers (A1) such as "OK KANAFUJI PLUS" manufactured by Oji Paper Co., Ltd., and "TOKUBISHI ART" manufactured by Mitsubishi Paper Mills Limited, etc. Various photographic papers for inkjet recording can also be used.

[0234] Among recording media, so-called coated paper, which is commonly used for offset printing, is preferred. Coated paper is formed by applying a coating to the surface of a generally untreated high-quality paper or neutral paper, which is primarily composed of cellulose. Among these, coated paper comprising a base paper and a coating containing kaolin and / or calcium bicarbonate is preferred, with coated paper, coated paper, lightweight coated paper, or lightly coated paper being more preferred.

[0235] From the viewpoint of being able to expect the effect of suppressing the migration of the colorant and obtaining a high-quality image with better color density and color than before, the water absorption coefficient Ka of the recording medium is preferably 0.05 mL / m 2 ·ms 1 / 2 ~0.5mL / m 2 ·ms 1 / 2 , more preferably 0.1 mL / m 2 ·ms 1 / 2 ~0.4mL / m 2 ·ms1 / 2 , more preferably 0.2 mL / m 2 ·ms 1 / 2 ~0.3mL / m 2 ·ms 1 / 2 .

[0236] The water absorption coefficient Ka has the same meaning as that described in JAPAN TAPPI Pulp and Paper Test Method No. 51: 2000 (published by Japan Technical Association of the Pulp and Paper Industry). The absorption coefficient Ka is calculated using an automatic scanning absorptometer KM500Win (manufactured by KUMAG AIRIKI KOGYO Co., Ltd.) based on the difference in water transfer between contact times of 100 ms and 900 ms.

[0237] -Ink application process-

[0238] In the ink applying step, the ink of the present invention is applied to a recording medium to record an image.

[0239] The ink application step may be a step of directly applying the ink of the present invention to the recording medium, or a step of applying the ink of the present invention to the surface of the recording medium to which the treatment liquid has been applied. In the latter case, the image recording method further includes a treatment liquid application step of applying the treatment liquid to the recording medium before the ink application step. The treatment liquid application step will be described later.

[0240] The method for applying the ink is not particularly limited as long as it can apply the ink to the recording medium, and any known method such as coating, dipping, or inkjet can be used. Among them, the inkjet method is preferred from the viewpoint of being able to form a film (e.g., an image) on various recording media.

[0241] The image recording is preferably performed by ejecting ink by an inkjet method.

[0242] There is no particular limitation on the ink jetting method in the inkjet method, and it can be any of the well-known methods (for example, a charge control method that utilizes electrostatic attraction to jet ink, a drop-on-demand method (pressure pulse method) that utilizes the vibration pressure of a piezoelectric element, an acoustic inkjet method that converts an electrical signal into a sound beam to irradiate the ink to jet the ink using radiation pressure, and a thermal inkjet method (bubble jet (registered trademark)) that heats the ink to form bubbles and utilizes the pressure generated thereby, etc.).

[0243] As an inkjet method, the method described in Japanese Patent Application Laid-Open No. 54-59936 can be particularly effectively used, in which the ink undergoes a rapid volume change when subjected to thermal energy, and the ink is ejected from the nozzle using the force generated by the state change.

[0244] As the inkjet method, the method described in paragraphs 0093 to 0105 of Japanese Patent Application Laid-Open No. 2003-306623 can also be applied.

[0245] As inkjet head methods, there are a reciprocating method in which a short serial head records while scanning in the width direction of the recording medium, and a line method in which a line head is used in which recording elements are arranged corresponding to the entire area of ​​one side of the recording medium.

[0246] The line method scans the recording medium in a direction intersecting the arrangement of the recording elements, enabling image recording across the entire surface of the medium. The line method eliminates the need for a carriage or other transport system, such as the one used in the reciprocating method to scan short strips of printheads. Furthermore, compared to the reciprocating method, the line method eliminates the need for complex control between carriage movement and scanning the recording medium; only the recording medium is moved. Therefore, the line method achieves faster image recording than the reciprocating method.

[0247] The ink is preferably applied using an inkjet head having a resolution of 300 dpi or higher (more preferably 600 dpi or higher, and even more preferably 800 dpi or higher). Here, dpi is an abbreviation for dots per inch, and 1 inch is 2.54 cm.

[0248] The amount of ink droplets ejected from the nozzles of the inkjet head is preferably 1 pL (picoliter) to 10 pL, and more preferably 1.5 pL to 6 pL, from the viewpoint of obtaining a high-definition image.

[0249] Furthermore, from the viewpoint of improving image unevenness and connection of continuous gradations, ejection of different droplet amounts in combination is also effective.

[0250] -Other processes-

[0251] The image recording method of the present invention may include an ink drying step, a heat fixing step, a treatment liquid applying step, an ink removing step, and the like, as necessary.

[0252] (a) Ink drying process

[0253] After the ink is applied, the applied ink may be dried by heating.

[0254] As a device for performing heating and drying, a known heating device such as a heater, a known air blowing device such as a dryer, and a device combining these are mentioned.

[0255] As methods for performing heat drying, for example, there can be cited a method of heating the recording medium from the side opposite to the side to which ink is applied using a heater, a method of blowing warm air or hot air onto the side to which ink is applied, a method of heating the side to which ink is applied or from the side opposite to the side to which ink is applied using an infrared heater, and a method of combining a plurality of these methods.

[0256] The heating temperature during heat drying is preferably 55° C. or higher, more preferably 60° C. or higher, and particularly preferably 65° C. or higher. The upper limit of the heating temperature is not particularly limited, but is, for example, 150° C., preferably 130° C.

[0257] The heating and drying time of the ink is not particularly limited, but is preferably 3 seconds to 60 seconds, more preferably 5 seconds to 60 seconds, and even more preferably 10 seconds to 30 seconds.

[0258] Furthermore, the recording medium may be heated before applying the ink.

[0259] The heating temperature can be appropriately set, but the temperature of the recording medium is preferably 20°C to 50°C, more preferably 25°C to 40°C.

[0260] (b) Thermal fixing process

[0261] If necessary, a heat fixing step may be performed after the ink drying step.

[0262] By performing a heat fixing process, the image on the recording medium can be fixed, thereby further improving the scratch resistance of the image. As the heat fixing process, for example, the heat fixing process described in paragraphs 0112 to 0120 of Japanese Patent Application Laid-Open No. 2010-221415 can be applied.

[0263] (c) Treatment liquid application step

[0264] The image recording method of the present invention may further include a treatment liquid applying step of applying a treatment liquid to the recording medium before the ink applying step.

[0265] Examples of the treatment liquid include a treatment liquid containing water and a coagulant, wherein the coagulant is at least one selected from the group consisting of a polyvalent metal salt, an acidic compound, and a cationic polymer.

[0266] As the acidic compound, an acid is preferably used, and examples thereof include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, propanetricarboxylic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, sulfonic acid, orthophosphoric acid, metaphosphoric acid, pyrrolidonecarboxylic acid, pyronecarboxylic acid, pyrrolecarboxylic acid, furancarboxylic acid, pyridinecarboxylic acid, coumaric acid, thiophenecarboxylic acid, nicotinic acid, oxalic acid, and benzoic acid.

[0267] Examples of polyvalent metal salts include salts of alkaline earth metals from Group 2 of the periodic table (e.g., magnesium and calcium), salts of transition metals from Group 3 of the periodic table (e.g., lanthanum), salts of cations from Group 13 of the periodic table (e.g., aluminum), and salts of lanthanide elements (e.g., neodymium). Preferred metal salts include carboxylates (formates, acetates, benzoates, etc.), nitrates, chlorides, and thiocyanates.

[0268] Preferred examples of cationic polymers include poly(vinylpyridine) salts, polyalkylaminoethyl acrylates, polyalkylaminoethyl methacrylates, poly(vinylimidazole), polyethyleneimine, polybiguanide, polyguanidine, polyallylamine, and derivatives thereof.

[0269] Regarding the treatment liquid and the treatment liquid applying step, for example, reference can be made appropriately to known documents such as International Publication No. 2019 / 004485 and International Publication No. 2019 / 163581.

[0270] (d) Ink Removal Process

[0271] In the ink removal process, a maintenance fluid is used to remove ink (e.g., solid ink particles that adhere to the inkjet printing head during drying) as needed. Details of the maintenance fluid and ink removal process can be applied to the maintenance fluid and ink removal process described in International Publication No. 2013 / 180074.

[0272] Example

[0273] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0274] Hereinafter, "parts" and "%" are based on mass unless otherwise specified.

[0275] In the following, unless otherwise specified, “water” means deionized water.

[0276] [Example 1]

[0277] <Preparation of Lake Y Pigment Dispersion>

[0278] The following raw materials were mixed and the resulting mixture was placed in a kneading apparatus (DYNO-MILL KDLA model (manufactured by Willy A. Bachofen AG) filled with 0.5 mm zirconia beads) and kneaded at 2000 rpm for 90 minutes. The resulting kneaded product was removed and filtered through a 1 μm filter to obtain a lake Y pigment dispersion.

[0279] -Raw materials for lake Y pigment dispersion-

[0280] · PY168 (lake Y pigment)…15 parts

[0281] Solsperse 43000 (manufactured by The Lubrizol Corporation; ClogP: 1.85) (Pigment Dispersing Resin A) 5 parts

[0282] · Water…80 parts

[0283] <Preparation of a dispersion of a Y pigment other than a lake Y pigment>

[0284] (Synthesis of Water-Insoluble Resin P1 (Pigment Dispersing Resin A))

[0285] 88 g of methyl ethyl ketone was added to a 1000 mL three-necked flask equipped with a stirrer and a cooling tube. The mixture was heated to 72°C under a nitrogen atmosphere, and a solution of 0.85 g of dimethyl 2,2'-azobisisobutyrate, 50 g of phenoxyethyl methacrylate, 13 g of methacrylic acid, and 37 g of methyl methacrylate dissolved in 50 g of methyl ethyl ketone was added dropwise over 3 hours. After the addition was completed, the mixture was allowed to react for a further hour, followed by a solution of 0.42 g of dimethyl 2,2'-azobisisobutyrate dissolved in 2 g of methyl ethyl ketone. The mixture was heated to 78°C and heated for 4 hours. The resulting reaction solution was reprecipitated twice with excess hexane to precipitate a resin. The precipitated resin was dried to obtain 96.5 g of a phenoxyethyl methacrylate / methyl methacrylate / methacrylic acid (copolymerization ratio [mass ratio] = 50 / 37 / 13) copolymer (water-insoluble resin P1; pigment-dispersible resin A).

[0286] The composition of the obtained water-insoluble resin P1 was determined by proton nuclear magnetic resonance ( 1 The weight average molecular weight (Mw) of the water-insoluble resin P1 determined by GPC was 49400. The acid value of the water-insoluble resin P1 was determined by the method specified in JIS standard (JIS K 0070: 1992) and was 84.8 mgKOH / g.

[0287] The ClogP of the water-insoluble resin P1 was 1.93.

[0288] (Preparation of a Dispersion of a Y Pigment Other than a Lake Y Pigment)

[0289] The following raw materials were kneaded using a roll mill for 2 to 8 hours to obtain a kneaded product.

[0290] -Raw materials for dispersions of Y pigments other than lake Y pigments-

[0291] · PY74 (Y pigment other than lake Y pigment) ... 10 parts

[0292] · Water-insoluble resin P1 (pigment dispersing resin A) ... 4.6 parts

[0293] ·Methyl ethyl ketone…18 parts

[0294] 8.0 parts of 1 mol / L sodium hydroxide aqueous solution

[0295] The obtained kneaded product was dispersed in 60 parts of water to obtain a dispersion.

[0296] Methyl ethyl ketone was removed from the resulting dispersion under reduced pressure at 55°C, and a portion of the water was removed. The resulting liquid was cooled to room temperature and then centrifuged at 10,000 rpm for 30 minutes using a high-speed centrifugal chiller 7550 (manufactured by KUBOTA Corporation Co., Ltd.) and a 50 mL centrifuge tube. The supernatant, excluding the precipitate, was recovered.

[0297] The volume average particle diameter of the supernatant was measured by a dynamic light scattering method using a NANOTRAC particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.) and was found to be 91 nm.

[0298] Then, the pigment concentration was determined from the absorption spectrum, and deionized water was added to the supernatant to obtain a Y pigment dispersion (a dispersion of a Y pigment other than a lake Y pigment) having a PY74 concentration of 14% by mass.

[0299] <Preparation of Resin B Solution>

[0300] A 500 ml three-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet was charged with propylene glycol (35 g) and heated to 90°C under a nitrogen flow. A mixed solution of 5.55 g of V-601 (dimethyl 2,2'-azobis(2-methylpropionate), a radical polymerization initiator; manufactured by FUJIFILM Wako Pure Chemical Corporation), 10.7 g of methacrylic acid (MAA, ClogP = -3.44), 69.3 g of methyl methacrylate (MMA, ClogP = 1.11), 20.0 g of isobornyl methacrylate (IBOMA, ClogP = 4.97), 1.63 g of dodecyl mercaptan, and 65.00 g of propylene glycol was added dropwise at a constant rate over 2 hours. After the addition of the mixed solution, the mixture was stirred for 1 hour. Next, a mixed solution of 1.85 g of V-601 and 24.62 g of propylene glycol was added to the resulting reaction mixture, and the mixture was stirred for a further 1.5 hours. After 120.21 g of propylene glycol was added to the resulting reaction mixture, 8.56 g of a 50% by mass aqueous sodium hydroxide solution (alkali metal hydroxide) was added dropwise using a dripper to obtain a solution of Resin B.

[0301] Here, IBOMA corresponds to both the monomer forming unit X (i.e., a structural unit derived from a monomer having a ClogP of 2.80 to 5.00) and the monomer forming unit Y (i.e., a structural unit derived from a monomer having a ClogP of 2.30 or greater). Methacrylic acid is a monomer containing an acid group, and methyl methacrylate is an alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl moiety.

[0302] The composition of the obtained resin B solution is 1 The solid content concentration of the resin B solution was 30.1% by mass as confirmed by H-NMR.

[0303] Resin B contains a carboxyl group as an acid group in the molecule and has an acid value of 60 mgKOH / g. Resin B has a ClogP of 1.40, a weight average molecular weight (Mw) of 15,000, and a glass transition temperature (Tg) of 127°C.

[0304] The acid value and Mw were measured by the same method as that for the water-insoluble resin P1 (pigment-dispersed resin A).

[0305] The Tg of resin B was measured by the following method.

[0306] A sample was prepared by drying a solution of resin B under reduced pressure at 150° C. for 6 hours, and the sample was measured at a heating rate of 10° C. / min using a differential scanning calorimeter (DSC) DSC7000X manufactured by Hitachi High-Tech Science Corporation.

[0307] In Tables 1 to 3 described below, the column "Units Y derived from monomers having a ClogP of 2.30 or greater in resin B (mass % relative to total units Y)" shows the details of units Y (i.e., structural units derived from monomers having a ClogP of 2.30 or greater) in resin B. Here, the total of units Y is taken as 100%.

[0308] In addition to the units Y, the resin B contains a structural unit derived from methacrylic acid (MAA, ClogP=-3.44) and a structural unit derived from methyl methacrylate (MMA, ClogP=1.11).

[0309] The column for unit Y is divided into the "unit X" column and the "other than unit X" column, which are further divided into specific structural units. Specifically, the monomer name (e.g., "IBOMA") used to form the structural unit is indicated.

[0310] "Unit X" represents a structural unit derived from a monomer having a ClogP of 2.80 to 5.00, and "other than unit X" represents structural units other than unit X in unit Y (i.e., structural units having a ClogP of 2.30 or more and less than 2.80 and structural units having a ClogP of more than 5.00).

[0311] The meanings of the abbreviations of the above monomer names in the table are as follows.

[0312] IBOMA: Isobornyl methacrylate

[0313] 2-HEA: 2-ethylhexyl acrylate

[0314] α-Me-St: α-methylstyrene

[0315] DMA: Styrene

[0316] n-DMA: butyl methacrylate

[0317] n-BA: n-butyl acrylate

[0318] <Preparation of yellow ink>

[0319] A mixed solution was prepared by mixing the components to have the following composition using a lake Y pigment dispersion, a Y pigment dispersion other than the lake Y pigment, and a solution of resin B. After the solution was adjusted, coarse particles were removed from the mixed solution using a 5 μm filter to obtain a yellow ink.

[0320] The yellow ink had a viscosity of 4.1 mPa·s (25° C.), a surface tension of 38.4 mN / m (25° C.), and a pH of 8.9 (25° C.).

[0321] - Composition of yellow ink -

[0322] PY168 (lake Y pigment) ... 2.5% by mass

[0323] PY74 (Y pigment other than lake Y pigment) ... 2.5% by mass

[0324] Solsperse 43000 (manufactured by The Lubrizol Corporation; ClogP: 1.85) (Pigment Dispersing Resin A) ... 1.0 mass%

[0325] Water-insoluble resin P1 (pigment dispersion resin A) ... 1.0 mass%

[0326] Resin B…3.0 mass%

[0327] Propylene glycol (PG; manufactured by FUJIFILM Wako Pure Chemical Corporation) ... 20% by mass

[0328] Glycerin…2.5% by mass

[0329] OLFINE E1010 (manufactured by Nissin Chemical Industry Co., Ltd., nonionic surfactant) ... 1.0 mass%

[0330] Water...amounts that make up 100% by mass

[0331] <Image Record>

[0332] As ink, the above-mentioned yellow ink was used,

[0333] As a recording medium, OK TOP COAT (manufactured by Oji Paper Co., Ltd.) was used.

[0334] As the inkjet head, a line head (printer head GELJET GX5000 manufactured by Ricoh Co., Ltd.) was used which was arranged obliquely with respect to the moving direction of the recording medium.

[0335] The image (yellow image) was recorded as follows.

[0336] Under the conditions of a resolution of 1200×1200 dpi (dots per inch), a droplet ejection volume of 2.4 pL (picoliter) and a worktable speed of 635 mm / second, the above-mentioned yellow ink is applied to the above-mentioned recording medium in a solid state of 20 mm×100 mm from the above-mentioned inkjet head.

[0337] After the yellow ink was applied, the surface of the recording medium opposite to the surface applied with yellow ink was placed in contact with a 60°C hot plate. In this state, 120°C hot air was blown for 10 seconds to dry the yellow ink on the recording medium.

[0338] As described above, a yellow solid image having a size of 20 mm×100 mm was recorded on the recording medium, thereby obtaining an image recorded material (ie, an image recorded material including the recording medium and the yellow solid image).

[0339] <Evaluation>

[0340] The image records and the yellow ink were subjected to the following evaluations.

[0341] The results are shown in Table 1.

[0342] (Weather resistance of images)

[0343] The image recorded material was subjected to a 2,000-hour accelerated weathering test using a Weather-Ometer Ci4000 manufactured by Atlas Weathering Services Group in accordance with ISO 4892-2. The yellow solid image on the image recorded material after 2,000 hours was wiped with a cotton swab soaked in isopropyl alcohol.

[0344] CIELAB values ​​(L*, a*, b*) were measured for the yellow solid image after the accelerated weathering test and the wiping operation, and for the yellow solid image initially (i.e., before the accelerated weathering test) using a Konica Minolta, Inc. spectrocolorimeter CM-2600d under the conditions of illuminant D65, a viewing angle of 2°, and SCE (specular reflection eliminated).

[0345] Calculate the color difference ΔE based on the measurement results.

[0346] Based on the obtained ΔE, the weather resistance of the image was evaluated according to the following evaluation criteria.

[0347] In the following evaluation criteria, the image with the most excellent weather resistance was rated 5.

[0348] -Evaluation Criteria for Weather Resistance of Images-

[0349] 5: ΔE is less than 1.0.

[0350] 4: ΔE is 1.0 or more and less than 1.5.

[0351] 3: ΔE is 1.5 or more and less than 2.0.

[0352] 2: ΔE is 2.0 or more and less than 3.0.

[0353] 1: ΔE is 3.0 or more.

[0354] (Image blocking resistance)

[0355] Two of the above-mentioned image records were prepared.

[0356] Two image records were overlapped in such a way that the yellow solid images of the two images were in contact with each other. In this state, an iron plate of the same size as the image records was used at 0.5 kg / cm 2 The two image recorded materials were pressed under conditions of 30° C. for 1 hour to bring the yellow solid images into close contact with each other.

[0357] Next, the two image recorded materials were peeled off, and the blocking resistance of the images was evaluated according to the following evaluation criteria.

[0358] In the following evaluation criteria, the image having the most excellent blocking resistance was rated as 5.

[0359] -Evaluation Criteria for Image Blocking Resistance-

[0360] 5: There is no peeling or transfer of the yellow solid image, and there is no sound during peeling.

[0361] 4: There is no peeling or transfer of the yellow solid image, but there is a sound when peeling.

[0362] 3: There was no peeling of the yellow solid image, but some transfer was observed (20 area % or less with respect to the entire image).

[0363] 2: There was no peeling of the yellow solid image, but transfer was observed (exceeding 20 area % with respect to the entire image).

[0364] 1: Yellow solid image peeling.

[0365] (Ink jetting properties)

[0366] After recording a yellow solid image continuously for 30 minutes at a speed of 2700 sheets per hour, a parallel line pattern (1 cm in length) consisting of a 75 dpi x 2400 dpi line image arranged parallel to the direction of travel of the recording medium was recorded. The center position of the line width of the line images constituting the parallel line pattern was measured using a general-purpose image processing device, DA-6000, and the standard deviation σ of the distance from the theoretical center position (deviation) was calculated. Based on the obtained results, the ink jetting properties (jetting curve) were evaluated according to the following evaluation criteria.

[0367] In the following evaluation criteria, the most excellent ink jetting property was ranked as 5.

[0368] -Evaluation criteria for sprayability-

[0369] 5: Standard deviation σ<2μm.

[0370] 4: The standard deviation σ is 2μm≤σ<3.5μm.

[0371] 3: The standard deviation σ is 3.5μm≤σ<5μm.

[0372] 2: The standard deviation σ is 5μm≤σ<10μm.

[0373] 1: The standard deviation σ is 10μm≤σ.

[0374] [Examples 2 to 14]

[0375] Under the condition that the total content of Y pigment in the ink (the total content of lake Y pigment and Y pigment other than lake Y pigment) is constant, the same operation as in Example 1 was performed except that the type of Y pigment and the mass % relative to the total Y pigment were changed as shown in Table 1.

[0376] The results are shown in Table 1.

[0377] [Examples 15 to 30]

[0378] The same procedures as in Example 1 were performed except that the types and amounts of monomers used to prepare the solution of Resin B were changed, and the types and mass % of Unit Y (i.e., structural units derived from monomers having a ClogP of 2.30 or greater) in Resin B relative to the total Unit Y were changed as shown in Tables 2 and 3. In these examples, the content of Unit Y relative to the total amount of Resin B was maintained at the same value as in Example 1 (i.e., 20 mass % relative to the total amount of the resin).

[0379] The results are shown in Tables 2 and 3.

[0380] [Comparative Examples 1 to 4]

[0381] The same procedures as in Example 1 were performed, except that the total content of the Y pigment in the ink (the total content of the lake Y pigment and the Y pigments other than the lake Y pigment) was kept constant, and the type of Y pigment and the mass % relative to the total Y pigment were changed as shown in Table 3. However, the evaluation of blocking resistance and jetting properties was omitted.

[0382] The results are shown in Table 3.

[0383]

[0384]

[0385]

[0386] As shown in Tables 1 to 3, the inks of the Examples containing a lake yellow pigment, a yellow pigment other than a lake yellow pigment, a resin, a water-soluble organic solvent, and water recorded yellow images with excellent weather resistance.

[0387] In contrast, in Comparative Examples 1 and 3, in which the inks did not contain a yellow pigment other than a lake yellow pigment, and Comparative Examples 2 and 4, in which the inks did not contain a lake yellow pigment, the recorded yellow images had poor weather resistance.

[0388] Among Examples 1 to 14, the yellow images of Examples 1 to 12 in which the ratio of the lake yellow pigment to the total yellow pigment contained in the ink was 10% by mass to 90% by mass had more excellent weather resistance.

[0389] Among Examples 20 to 27, the inks of Examples 20 to 23, in which the inks contained the pigment dispersion resin A and the resin B as resins and the ratio of the units X in the resin B to the total amount of the units Y was 80 to 100% by mass, exhibited better jetting properties.

[0390] Among Examples 1 to 30, the inks of Examples 1 to 29, in which the inks contained the pigment dispersion resin A and the resin B as resins and the ClogP of the resin B was 1.43 or less, exhibited more excellent jetting properties.

[0391] Among Examples 1 to 30, the yellow images of Examples 1 to 17, 20 to 22, 24 to 26, and 28 to 30, in which the ink contained the pigment dispersion resin A and the resin B as resins and the ClogP of the resin B was 0.97 or more, exhibited more excellent blocking resistance.

[0392] [Example 101]

[0393] The components of the following composition were mixed to obtain a treatment liquid.

[0394] -Composition of treatment liquid-

[0395] ·Diethylene glycol monoethyl ether…4% by mass

[0396] ·Tripropylene glycol monomethyl ether…4% by mass

[0397] Malonic acid (organic acid) ... 17.3% by mass

[0398] Propanetricarboxylic acid (organic acid) ... 4.3% by mass

[0399] Phosphoric acid (inorganic acid) ... 4.3% by mass

[0400] Benzotriazole...1% by mass

[0401] Deionized water...amount to make 100% by mass

[0402] The coating was applied to a recording medium, OK TOP COAT (manufactured by Oji Paper Co., Ltd.), using a wire bar coater at a density of about 1.7 g / m 2 After applying the treatment liquid in a manner of , it was dried at 50° C. for 2 seconds.

[0403] Next, a yellow solid image was recorded on the area of ​​the recording medium to which the treatment liquid had been applied in the same manner as in the image recording in Example 1 using the yellow ink in Example 1 to obtain an image recorded material.

[0404] The ink and the yellow solid image were evaluated in the same manner as in Example 1 (i.e., image weather resistance, image blocking resistance, and ink jetting properties). The results were equivalent to those in Example 1 in all three aspects.

Claims

1. A yellow ink for inkjet, comprising a yellow pigment, a resin, a water-soluble organic solvent and water. The yellow pigment includes lake yellow pigment and yellow pigment other than lake yellow pigment, The ratio of the lake yellow pigment to the total content of the lake yellow pigment and yellow pigments other than the lake yellow pigment is 30% by mass to 70% by mass. The resin includes a pigment-dispersing resin A and a resin B which is a resin other than the pigment-dispersing resin A. The resin B contains a structural unit Y, a structural unit derived from a monomer containing an acid group, and a structural unit derived from an alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl portion, wherein the structural unit Y is a structural unit derived from a monomer having a ClogP of 2.30 or greater. The content of the unit Y is 5% to 50% by mass relative to the total amount of the resin B, the content of the structural unit derived from the monomer containing an acid group is 8% to 20% by mass, and the content of the structural unit derived from the alkyl (meth)acrylate having 1 to 3 carbon atoms in the alkyl portion is 15% to 75% by mass. In the structural unit Y, when the structural unit derived from a monomer having a ClogP of 2.80 to 5.00 is defined as unit X, the ratio of the unit X to the total amount of the unit Y is 60% by mass to 100% by mass. The ClogP of the resin B is 0.97 to 1.

43.

2. The yellow ink for inkjet according to claim 1, wherein The yellow pigment other than the lake yellow pigment is at least one selected from the group consisting of pigment yellow 1, pigment yellow 2, pigment yellow 3, pigment yellow 5, pigment yellow 6, pigment yellow 10, pigment yellow 49, pigment yellow 60, pigment yellow 65, pigment yellow 73, pigment yellow 74, pigment yellow 75, pigment yellow 97, pigment yellow 98, pigment yellow 111, pigment yellow 116, pigment yellow 130, pigment yellow 165, pigment yellow 167 and pigment yellow 203.

3. The yellow ink for inkjet according to claim 1 or 2, wherein The lake yellow pigment is at least one selected from the group consisting of Pigment Yellow 61, Pigment Yellow 62, Pigment Yellow 133, Pigment Yellow 168, Pigment Yellow 169, Pigment Yellow 205, Pigment Yellow 206, Pigment Yellow 209, and Pigment Yellow 212. 4 . An image recording method comprising the step of applying the yellow inkjet ink according to claim 1 to a recording medium by an inkjet method.

5. An image record comprising: recording medium; and A yellow image is arranged on a recording medium and is formed using the yellow inkjet ink according to any one of claims 1 to 3.

Images