JP2005200601A - Aqueous blue ink and aqueous ink set - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new aqueous blue ink that provides bright colorfulness of high level when used for full-color printing of high bright colorfulness and the like, and an aqueous ink set. <P>SOLUTION: This aqueous blue ink comprises a subphthalocyanine pigment, dispersed in an aqueous liquid in an average particle size of 10-500 nm, as a coloring matter represented by general formula (1) (wherein X represents a halogen atom, a hydroxyl group, an alkyl group, an aryl group, an alkoxy group or an aryloxy group, and rings Y<SP>1</SP>, Y<SP>2</SP>and Y<SP>3</SP>are each a benzene ring or a naphthalene ring which may contain a substituent). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a blue water-based ink used for high-brightness full-color printing and the like, and a water-based ink set including the same.

  Conventionally, full-color printing is generally performed by using a four-color ink set composed of indigo, red, yellow, and black. In this method, color reproduction is performed by subtractive or side-by-side color mixing of the three primary colors of indigo, red, and yellow, so that a full-color printed product can be easily produced, while hues between these three primary colors (red, green, blue, etc.) ), It is difficult to express high-brightness colors, and there is a drawback that satisfactory color reproduction cannot be achieved, for example, in printing a specific color such as a corporate color or in art printing such as a photo book or an art book. There is also a method of separately using “spot colors” that have been pre-mixed to express specific colors, but in this case, maintenance of a large number of spot color inks with different color tones is necessary, which reduces productivity. There is.

  Therefore, a method (so-called hi-fi printing method) has been proposed in which one to three primary colors are further added to the conventional three primary colors to improve color reproducibility. Examples of primary colors to be added include red to orange, green to grass, blue to purple. For example, Patent Document 1 discloses seven colors (six primary colors) composed of indigo, red, yellow, orange, green, purple and black. In Japanese Patent Application Laid-Open No. 2004-26853, a printing method using an ink set of 5 to 7 colors using at least one color selected from orange, green and purple in addition to four colors consisting of indigo, red, yellow and black ( A printing method using a 4-6 primary color ink set is disclosed. Since the method using these 4 to 6 primary colors provides high color reproducibility, it is possible to express the high-brightness color, which was difficult to express by the conventional method, by combining the primary colors. It has become a useful method.

Japanese Examined Patent Publication No. 7-75908 JP 2001-260516 A Japanese Patent Laid-Open No. 2002-241661 JP 2002-338858 A JP 2002-178622 A Special table 2003-500510 gazette

  As the coloring material used in these primary color inks, organic pigments are generally used because of their excellent hue vividness and coloring power. However, as the demand for high brightness in printed materials increases, primary color inks or coloring materials are used. The demand for high brightness has become even stronger. For example, a carbazole dioxazine violet pigment is often used as a colorant for blue ink as disclosed in Patent Document 1 and the like, but the transparency and dispersion stability of the pigment are insufficient. It was difficult to improve chroma. Therefore, there has been a demand for a bright blue ink that uses an organic pigment having good transparency and dispersion stability instead of the pigment.

  In consideration of safety, environmental hygiene, and the like, water-based inks containing a coloring material in an aqueous liquid are widely used. Water-based ink sets having 4 to 6 primary colors are also known. For example, Patent Documents 3 and 4 disclose water-based ink sets for inkjet printing, and Patent Document 5 discloses a water-based ink set for gravure printing. However, the blue water-based inks used in these water-based ink sets are still insufficient in terms of lightness, and high-brightness blue water-based inks using organic pigments with good dispersion stability in aqueous liquids are particularly desirable. It was rare.

  On the other hand, Patent Document 6 discloses a proposal regarding an ink composition containing a subphthalocyanine compound. However, Patent Document 6 discloses that a subphthalocyanine compound can be used as a colorant in an ink composition, but does not describe any specific embodiment of the ink composition.

  Accordingly, an object of the present invention is to provide a novel blue water-based ink that gives a high level of brightness when used in high-brightness full-color printing or the like. Another object of the present invention is to provide a water-based ink set that provides a high level of brightness.

  As a result of studies to solve the above problems, the present inventors have found that a specific pigment can be suitably used for blue water-based ink, and have completed the present invention.

（但し、Ｘはハロゲン原子、ヒドロキシル基、アルキル基、アリール基、アルコキシ基又はアリールオキシ基を、環Ｙ¹〜Ｙ³はそれぞれ置換基を有していてもよいベンゼン環又はナフタレン環を示す） That is, the present invention is a blue aqueous ink comprising a subphthalocyanine pigment represented by the following general formula (1) dispersed in an aqueous liquid with an average particle size of 10 to 500 nm.

(However, X represents a halogen atom, a hydroxyl group, an alkyl group, an aryl group, an alkoxy group or an aryloxy group, and the rings Y ^{1 to} Y ³ each represent a benzene ring or a naphthalene ring which may have a substituent)

（但し、Ｘはハロゲン原子又はヒドロキシル基を、Ｚ¹〜Ｚ¹²はそれぞれ水素原子又はハロゲン原子を示す） Here, the subphthalocyanine pigment is more preferably a subphthalocyanine pigment represented by the following general formula (2).

(However, X represents a halogen atom or a hydroxyl group, and Z ^{1 to} Z ¹² represent a hydrogen atom or a halogen atom, respectively)

In the blue aqueous ink of the present invention, the subphthalocyanine pigment is preferably dispersed in an aqueous solvent together with a dispersant, and it is more preferable to contain 0.1 to 15% by weight of the subphthalocyanine pigment in the blue aqueous ink.
Furthermore, the present invention is a water-based ink set having at least six primary colors of indigo, red, yellow, red, green and blue, wherein the blue water-based ink is the above-mentioned blue water-based ink. It is also an ink set.

Hereinafter, the present invention will be described in detail.
The blue aqueous ink of the present invention is obtained by dispersing a subphthalocyanine pigment represented by the general formula (1) or (2) in an aqueous liquid with a predetermined average particle diameter. Other necessary components (additives, etc.) can be blended. In particular, it is preferable to add a dispersant in terms of improving the dispersion stability of the subphthalocyanine pigment and contributing to high brightness.

  The blue aqueous ink of the present invention is obtained by dispersing the subphthalocyanine pigment represented by the general formula (1) or (2) in an aqueous liquid with an average particle diameter of 10 to 500 nm. Here, the range of the average particle diameter is preferably 50 to 400 nm, and more preferably 100 to 300 nm. When the average particle size is smaller than 10 nm, coloring power and weather resistance are insufficient, and a high-bright blue color cannot be obtained. On the other hand, when the average particle size is larger than 500 nm, the vividness and transparency of the hue are insufficient, and a high-bright blue color cannot be obtained.

The subphthalocyanine pigment used in the present invention has a structure represented by the general formula (1) or (2). Here, X is not particularly limited as long as it is a halogen atom, a hydroxyl group, an alkyl group, an aryl group, an alkoxy group or an aryloxy group, but is preferably a halogen atom or a hydroxyl group in view of excellent handling, and a chlorine atom. Or a bromine atom is more preferable. Further, the rings Y ^{1 to} Y ³ are not particularly limited as long as they may each have a substituent and may be a benzene ring or naphthalene ring. A benzene ring substituted with ˜4 halogen atoms is preferred. As Z ^{1 to} Z ¹² in the general formula (2), any of a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom and the like can be preferably used. A combination of the above may also be used. These substituents affect the hue of the subphthalocyanine pigment. For example, as more atoms having a large atomic weight are introduced into Z ^{1 to} Z ¹² , the hue of the subphthalocyanine pigment gradually becomes bluish and becomes purple to reddish blue. Therefore, it is possible to obtain a desired hue by appropriately selecting atoms Z ^{1 to} Z ¹² .

  Specific examples of such subphthalocyanine pigments include fluoroboron subphthalocyanine, chloroboron subphthalocyanine, bromoboron subphthalocyanine, iodoboron subphthalocyanine, hydroxoboron subphthalocyanine, phenylboron subphthalocyanine, methoxyboron subphthalocyanine, phenoxy. Boron subphthalocyanine, chloroboron (dodecafluoro) subphthalocyanine, bromoboron (dodecafluoro) subphthalocyanine, chloroboron (dodecachloro) subphthalocyanine, bromoboron (dodecachloro) subphthalocyanine, chloroboron (hexachloro) subphthalocyanine, bromoboron (hexachloro) subphthalocyanine, chloroboron ( Trichloro) subphthalocyanine, bro Boron (trichloro) subphthalocyanine, chloroboron (trinitro) subphthalocyanine, bromoboron (trinitro) subphthalocyanine, chloroboron (trimethyl) subphthalocyanine, bromoboron (trimethyl) subphthalocyanine, chloroboron (tri-tert-butyl) subphthalocyanine, bromoboron (tri-) tert-butyl) subphthalocyanine, chloroboron subnaphthalocyanine, bromoboron subnaphthalocyanine and the like. These subphthalocyanine pigments may be used alone or in combination of two or more.

  Such a subphthalocyanine pigment is generally produced by synthesizing and purifying a subphthalocyanine compound and converting it into a pigment. Subphthalocyanine compounds are known from the above-mentioned Patent Document 6 or the like, or can be obtained by the synthesis methods described in these documents. Specifically, the synthesis of the subphthalocyanine compound can be performed by, for example, reacting 1 mol of boron trihalide with 3 mol of phthalonitrile having a substituent introduced as necessary. The subphthalocyanine compound thus obtained often contains impurities caused by side reactions or the like, but the impurities can be removed by, for example, Soxhlet extraction. Examples of the impurities include hydrolysis products of raw material boron trihalides, unreacted phthalonitriles, and the like. The solvent used in Soxhlet extraction or the like is not particularly limited as long as it dissolves impurities and does not dissolve the subphthalocyanine compound. For example, a low boiling point solvent such as acetone, methanol, hexane, or the like can be used. However, the synthesis method and the purification method are not limited to the above methods.

  As a method for pigmentizing the subphthalocyanine compound, a known method can be used, and examples thereof include an acid pasting method, an acid slurry method, a dry milling method, a solvent milling method, a salt milling method, and a solvent salt milling method. However, a solvent milling method, a salt milling method, a solvent salt milling method and the like are particularly preferable in that a finely divided subphthalocyanine pigment having a controlled particle size can be obtained. However, the pigmentation method is not particularly limited.

  The blue aqueous ink of the present invention is preferably one obtained by dispersing a subphthalocyanine pigment in an aqueous solvent together with a dispersant. Here, the dispersant is not particularly limited as long as it is commercially available as a dispersant, a dispersion accelerator, a surfactant, or the like, or an equivalent thereof. , Anionic polymer dispersants, nonionic polymer dispersants, cationic surfactants, anionic surfactants, nonionic surfactants, and the like. When these dispersants are blended, the blending amount is not particularly limited, but is preferably 10 to 100% by weight, more preferably 20 to 70% by weight with respect to the subphthalocyanine pigment. High viscosity substances such as resins generally have an action of stabilizing dispersion, but those having no ability to promote dispersion are not treated as dispersants. However, it is not limited to use for the purpose of stabilizing dispersion.

  As the aqueous solvent, water or a mixture of water and a water-soluble organic solvent is used. Here, the water is preferably purified water such as distilled water or ion exchange water. As the water-soluble organic solvent, any known water-soluble organic solvent can be preferably used, for example, alcohols such as methanol, ethanol, isopropyl alcohol, ethylene glycol, propylene glycol, glycerin, cellosolve, methyl cellosolve, Ether alcohols such as carbitol, methyl carbitol, diethylene glycol, triethylene glycol, ethers such as tetrahydrofuran, dioxane, monoglyme, diglyme, triglyme, ketones such as acetone, ethylenediamine, ethanolamine, diethanolamine, 2-pyrrolidone, N -Nitrogen-containing solvents such as methyl-2-pyrrolidone, formamide, N, N-dimethylformamide, acetonitrile, dimethyl sulfoxide, sulfolane, etc. It can be mentioned sulfur-based solvents, and the like. These may be selected according to the use of the blue water-based ink, and may be used alone or in combination of two or more. In the present invention, the aqueous liquid in which the pigment is dispersed preferably contains 50% by weight or more of water.

  The resins are not particularly limited as long as they are known water-based resins, and examples thereof include acrylic-based, urethane-based, polyester-based, polyamide-based, and polyether-based aqueous resins. Can do. When blending these resins, the blending amount is not particularly limited, but is preferably 1 to 1000% by weight with respect to the subphthalocyanine pigment.

  The blue water-based ink of the present invention has a subphthalocyanine pigment as a colorant, and the blending amount thereof is preferably 0.1 to 15% by weight, and 0.5 to 10% by weight in the blue water-based ink. Is more preferable, and it is still more preferable that it is 1 to 5 weight%. When the amount of the subphthalocyanine pigment is less than 0.1% by weight, coloring is insufficient and a bright blue color cannot be obtained. On the other hand, when the amount is more than 15% by weight, not only the coloring becomes too strong, but also the dispersion stability tends to deteriorate, and a high-bright blue color cannot be obtained.

  In addition, another colorant can be used in combination with the above subphthalocyanine pigment for the purpose of adjusting the hue. Here, the other colorant is not particularly limited as long as it is a known pigment, dye or the like, but is preferably a blue or purple organic pigment in terms of hue, for example, Pigment Blue 15 and 15 : 1, 15: 2, 15: 3, 15: 4, 15: 6, 16:22, 60, 65, 66, 80, Pigment Violet 19, 23, 33, 37, etc. When other colorants are used in combination, the blending amount is not particularly limited, but it is preferably 0.1 to 100% by weight based on the subphthalocyanine pigment, and the colorant containing the subphthalocyanine pigment is used. The total amount of is preferably not more than 15% by weight in the blue water-based ink.

  The blue water-based ink of the present invention has a modification called a dispersion aid for the purpose of improving the adsorptivity of the dispersant on the pigment surface, improving the hydrophilicity of the pigment surface, and improving the dispersion stability due to electrostatic repulsion effect. A quality agent can also be blended. Here, as the dispersion aid, a pigment derivative type dispersion aid in which various functional groups are introduced into the pigment skeleton can be preferably used, but a blue to purple pigment derivative is more preferable in terms of hue, for example, Subphthalocyanine derivatives, copper phthalocyanine derivatives, indanthrone derivatives, benzimidazolone dioxazine derivatives, quinacridone derivatives, carbazole dioxazine derivatives, and the like can be given. These pigment derivative type dispersion aids are preferably used in an amount of 0.1 to 20% by weight based on the subphthalocyanine pigment. Further, the pigment derivative type dispersion aid used functions as a dispersion aid and simultaneously functions as a component of the colorant of the blue water-based ink.

The method for producing the blue water-based ink of the present invention is not particularly limited, and a known method can be used. For example, a dispersion in which a subphthalocyanine pigment is dispersed in an aqueous solvent (preferably using a dispersant) is manufactured, and if necessary, a resin, an additive, an additional solvent, and the like are added to obtain a blue aqueous ink. There are methods.
In addition, as a method for producing the dispersion, known methods can be used, and examples thereof include a dispersion treatment using a kneader, an attritor, a roll mill, a bead mill, a paint shaker, a disperser, and the like. The method for producing the dispersion is not particularly limited.

  In addition to the colorant, dispersant, resins, and aqueous solvent, the blue aqueous ink of the present invention includes a surface conditioner, viscosity adjuster, pH adjuster, wetting agent, antifoaming agent, antioxidant, chelate as necessary. An agent, preservative, antifungal agent and the like can be blended.

  The blue water-based ink of the present invention is useful not only as a high-brightness full-color printing ink but also as a paint, writing ink, ink-jet printing ink, special color ink, etc. In this case, a material suitable for each application is blended. Is done. The blue water-based ink of the present invention uses a subphthalocyanine pigment having excellent hue vividness, coloring power, transparency and dispersion stability as a coloring material. When used in ink, it improves transparency, and when used in ink for ink jet printing, it improves ejection properties and reduces the clogging of ink jet nozzles.

  In the present invention, the reason for using the subphthalocyanine pigment as the colorant is due to the excellent spectral characteristics and dispersion stability of the pigment. In order to realize a high-brightness blue water-based ink, it is necessary to use a coloring material having excellent hue vividness, coloring power and transparency, and the subphthalocyanine pigment satisfies all these elements. Further, since the subphthalocyanine pigment is excellent in dispersion stability in an aqueous liquid, the blue aqueous ink obtained by dispersing the subphthalocyanine pigment has extremely high brightness.

  The water-based ink set of the present invention comprises at least six primary colors of water-based inks of indigo, red, yellow, red, green and blue. In order to improve the color reproducibility of the printed matter, other colors can be added to these six primary colors. In particular, it is preferable to add a black color to form a seven-color ink set. Further, if necessary, white, light indigo color, light red, light yellow, or other ink can be added to further improve color reproducibility.

  The blue water-based ink of the present invention is used as the blue ink of the water-based ink set, and any known water-based ink can be preferably used for the other primary color inks. Here, as a coloring material used for other primary color inks, an organic pigment is preferable because of vividness of hue and coloring power. Examples of usable organic pigments include those disclosed in Patent Documents 1, 2, 4, and the like. For example, azo pigments (soluble azo pigments, insoluble azo pigments, condensed azo pigments, etc.), azomethine pigments, Examples thereof include phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, dioxazine pigments, selenium pigments, perylene pigments, perinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, and thioindigo pigments. These may be selected according to the intended hue of each primary color, and one or more of them can be used in combination.

Moreover, it is preferable that the structure of the other primary color ink is the same as that of the blue water-based ink of the present invention. Specifically, it is preferable to disperse the above-mentioned organic pigment or the like in an aqueous liquid with an average particle diameter of 10 to 500 nm, and if necessary, add a dispersant, resins, additives and the like. The content of the coloring material is preferably 0.1 to 15% by weight in the water-based ink.
In addition, a well-known method can be utilized as a method of producing printed matter using the blue water-based ink and water-based ink set of the present invention.

  Since the blue water-based ink and water-based ink set in the present invention have a high level of lightness, they are extremely useful in terms of enabling production of high-brightness full-color prints and the like. In addition to the high-brightness full-color printing ink, the blue water-based ink in the present invention is a paint that requires high gloss, a writing ink that requires high transparency, and an ink jet printing that requires good ejection properties. It is also useful as an ink, special color ink, and the like.

  Hereinafter, the present invention will be described specifically by way of examples. In the following, “part” means part by weight.

Example 1
10 parts of chloroboron (dodecachloro) subphthalocyanine pigment, 4 parts of an anionic polymer-based dispersant and 86 parts of water were blended and subjected to dispersion treatment using a paint shaker (manufactured by Asada Tekko Co., Ltd.) to obtain 100 parts of dispersion A. . Here, 0.4 mmφ zirconia beads were used as the paint shaker media at a filling rate of 20%, and the dispersion time was 3 hours. Next, 20 parts of the above dispersion A is mixed in a mixed solution of 10 parts of ethylene glycol, 10 parts of carbitol, 59.5 parts of water and 0.5 part of a nonionic surfactant, and the mixture is stirred and mixed for 1 hour. 100 parts of a blue aqueous ink A having a concentration of 2% by weight was produced.
For this blue water-based ink A, the average particle diameter of the pigment was measured with a particle size distribution meter (trade name: Concentrated Particle Size Analyzer FPAR-1000, manufactured by Otsuka Electronics Co., Ltd.). The average particle diameter was 199 nm. It was. In addition, the blue water-based ink A showed low viscosity and low thixotropy, and the dispersion stability was good. When this blue water-based ink A was applied to the paper surface, a bright reddish blue color with transparency was obtained.

Example 2
Using 6 parts instead of 4 parts of the anionic polymer dispersant and 84 parts of the water instead of 86 parts of water, the same treatment as in Example 1 was performed to produce 100 parts of a blue aqueous ink B.
With respect to this blue water-based ink B, the average particle diameter of the pigment was measured in the same manner. As a result, the average particle diameter was 147 nm. In addition, the blue water-based ink B showed low viscosity and low thixotropy, and the dispersion stability was good. When this blue water-based ink B was applied to the paper surface, a bright reddish blue color with transparency was obtained.

Example 3
In place of 10 parts of chloroboron (dodecachloro) subphthalocyanine pigment, 10 parts of chloroboron subphthalocyanine pigment was used and the same treatment as in Example 1 was carried out to produce 100 parts of blue water-based ink C.
With respect to this blue water-based ink C, the average particle diameter of the pigment was measured in the same manner. As a result, the average particle diameter was 289 nm. In addition, the blue water-based ink C showed low viscosity and low thixotropy, and the dispersion stability was good. When this blue aqueous ink C was applied to the paper surface, a bright purple color with transparency was obtained.

Example 4
Instead of 10 parts of chloroboron (dodecachloro) subphthalocyanine pigment, 10 parts of bromoboron subphthalocyanine pigment was used and the same treatment as in Example 1 was carried out to produce 100 parts of blue aqueous ink D.
With respect to this blue water-based ink D, the average particle diameter of the pigment was measured in the same manner. As a result, the average particle diameter was 243 nm. In addition, the blue water-based ink D exhibited low viscosity and low thixotropy, and the dispersion stability was good. When this blue water-based ink D was applied to the paper surface, a bright purple color with transparency was obtained.

Comparative Example 1
Instead of 10 parts of chloroboron (dodecachloro) subphthalocyanine pigment, 10 parts of benzimidazolone dioxazine blue pigment (Pigment Blue 80) was used and the same treatment as in Example 1 was carried out to produce 100 parts of blue water-based ink X.
With respect to this blue water-based ink X, the average particle diameter of the pigment was measured in the same manner, and the average particle diameter was 543 nm. The blue water-based ink X showed low viscosity and low thixotropy immediately after production, but gradually became unstable due to dispersion instability, resulting in poor fluidity after 2 weeks storage at room temperature. When this blue water-based ink X was applied to the paper surface, a reddish blue color with poor transparency compared to Examples 1 and 2 was obtained. In addition, bronzing was partially observed on the coated surface.

Comparative Example 2
In place of 10 parts of chloroboron (dodecachloro) subphthalocyanine pigment, 10 parts of carbazole dioxazine violet pigment (Pigment Violet 23) was used and the same treatment as in Example 1 was carried out to produce 100 parts of blue aqueous ink Y.
For this blue water-based ink Y, the average particle diameter of the pigment was measured in the same manner, and the average particle diameter was 656 nm. Further, the blue water-based ink Y showed low viscosity and low thixotropy immediately after production, but gradually became unstable due to dispersion instability, resulting in poor fluidity after one week of storage at room temperature. When this blue water-based ink Y was applied to the paper surface, a purple color with a poor transparency compared to Examples 3 and 4 was obtained. Moreover, generation | occurrence | production of the solid foreign material was seen partially on the application surface.

Comparative Example 3
Instead of 4 parts of the anionic polymer-based dispersant, 4 parts of an aqueous urethane resin was used, and the same treatment as in Example 1 was performed to produce 100 parts of a blue aqueous ink Z.
With respect to this blue water-based ink Z, the average particle diameter of the pigment was measured in the same manner. As a result, the average particle diameter was 720 nm. The blue water-based ink Z exhibited low viscosity and low thixotropy immediately after production, but gradually became unstable due to dispersion instability, resulting in poor fluidity after 3 days of storage at room temperature. When this blue water-based ink Z was applied to the paper surface, a reddish blue color with poor transparency compared to Examples 1 and 2 was obtained. Moreover, generation | occurrence | production of the solid foreign material was seen partially on the application surface.

Claims (5)

A blue aqueous ink obtained by dispersing a subphthalocyanine pigment represented by the following general formula (1) in an aqueous liquid with an average particle diameter of 10 to 500 nm.

(However, X represents a halogen atom, a hydroxyl group, an alkyl group, an aryl group, an alkoxy group or an aryloxy group, and the rings Y ^{1 to} Y ³ each represent a benzene ring or a naphthalene ring which may have a substituent) The blue aqueous ink according to claim 1, wherein the subphthalocyanine pigment is a subphthalocyanine pigment represented by the following general formula (2).

(However, X represents a halogen atom or a hydroxyl group, and Z ^{1 to} Z ¹² represent a hydrogen atom or a halogen atom, respectively)   The blue aqueous ink according to claim 1 or 2, wherein the subphthalocyanine pigment is dispersed in an aqueous solvent together with a dispersant.   The blue water-based ink according to any one of claims 1 to 3, comprising 0.1 to 15% by weight of a subphthalocyanine pigment.   A water-based ink set having at least six primary colors of indigo, red, yellow, red, green, and blue, wherein the blue water-based ink is the blue water-based ink according to any one of claims 1 to 4. A water-based ink set.