JP2015168761A - Aqueous inkjet gray ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous gray ink composition which realizes excellent black color tone reproduction, can provide images without granularity, and has excellent stability not causing pigment aggregation or the like.SOLUTION: An aqueous inkjet gray ink contains at least a pigment, a pigment dispersant (which is not a compound of general formula (1)), an organic solvent, water, and a compound of general formula (1). The pigment contains at least one carbon black and at least one chromatic color organic pigment.

Description

  The present invention relates to a gray ink for water-based inkjet that can produce an image having no graininess and excellent black tone reproducibility and is excellent in stability.

  Conventionally, when an image is formed by an inkjet recording method or the like, an ink set containing a gray ink is sometimes used for the purpose of obtaining a high-quality image without graininess. For example, in addition to cyan ink, magenta ink, yellow ink, black ink, light cyan ink, and light magenta ink, gray ink may be added to obtain seven colors. The term “no graininess” as used herein means that dots are not seen when the printed matter is visually confirmed, and smooth printing is performed. Gray ink has a lower carbon black content than black ink, and is used for the purpose of improving the color reproducibility of materials such as metals and smoothing human skin. .

  Further, in gray ink, the smaller the chroma C value, the better the black tone reproducibility, but generally the gray ink using only carbon black tends to have high chroma C.

  There is known a method of using a gray ink composition containing cyan, magenta, yellow organic pigments and the like to correct the saturation of the gray ink. However, a gray ink with low saturation and good black tone reproducibility cannot be obtained unless the pigment type and content of the organic pigment to be added are optimized.

  When a gray ink is prepared by using a plurality of pigments in combination, if the total amount of the pigments contained is too large, the printed material tends to have a graininess, and the pigment amount needs to be optimized.

  In addition, light-colored inks such as gray inks have less pigment dispersant in the ink than dark inks, so the pigment dispersant adsorbed on the pigment is easily detached due to adsorption equilibrium, and the pigments aggregate together. There is a tendency that the stability of the ink becomes low.

  Furthermore, when a plurality of pigment dispersions are added to the gray ink, the pigment dispersant adsorbed on one of the pigments is preferentially desorbed due to the difference in the adsorption equilibrium of the pigment dispersant of each pigment, and pigment aggregation May occur.

JP 2010-261914 A Japanese Patent No. 3859109

  An object of the present invention is to provide a water-based gray ink composition that is excellent in black tone reproducibility, can obtain an image without graininess, and has excellent stability without causing pigment aggregation.

  The present invention contains at least a pigment, a pigment dispersant (except when it is a compound of the following general formula (1)), an organic solvent, water, and a compound of the following general formula (1). Further, the present invention relates to a gray ink for water-based inkjet which contains at least one each of a chromatic organic pigment.

（式中Ｐはｎ価の有機色素残基であり、ｎは１以上の整数、Ｒ₁は下記一般式（２）で表される有機基を示す。 General formula (1)

(In the formula, P is an n-valent organic dye residue, n is an integer of 1 or more, and R ₁ represents an organic group represented by the following general formula (2).

（式中Ｒ₂は（ｍ＋１）価の
有機残基を示し、Ｒ₃はそれぞれ独立に水素原子、ハロゲン原子、または、炭素数１〜１０のアルキル基を示す。）） General formula (2)

(Wherein R ₂ represents an (m + 1) -valent organic residue, and R ₃ independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms.)

  The present invention also relates to the above gray ink for inkjet, wherein the chromatic organic pigment contains two or more organic pigments.

  The present invention also relates to the above gray ink for water-based inkjet, wherein the chromatic organic pigment is a cyan pigment or / and a magenta pigment.

  The present invention also relates to the above gray ink for water-based inkjet, wherein the cyan pigment is a copper phthalocyanine pigment, and the magenta pigment is a quinacridone pigment.

  The present invention also provides the above gray ink for water-based inkjet, wherein the content of the compound of the general formula (1) is 0.01% by weight to 10% by weight with respect to the total amount of the chromatic organic pigment. About.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the water-based gray ink composition which is excellent in black gradation reproducibility, can obtain an image without a graininess, and has excellent stability without causing pigment aggregation. .

  Hereinafter, the present invention will be described with reference to preferred embodiments.

  In the present invention, a chromatic organic pigment such as cyan or magenta is used for canceling the slight coloration of carbon black, and a combination of a compound having a specific structure provides a gray ink having excellent storage stability. .

  In general, an ink using carbon black as a pigment shows black in a dark color, but an ink with a low pigment concentration such as a gray ink has a yellow color with a high chroma C. In order to obtain an image with excellent black tone reproducibility and no graininess, it is important to produce an achromatic gray having a small C value. C value can be controlled by using chromatic organic pigments such as cyan and magenta together. It is preferable to satisfy C ≦ 8 as the C value in order to realize excellent black tone reproducibility without visual impression by visual evaluation of the printed matter, and preferably to realize better black tone reproducibility. Satisfies C ≦ 5, more preferably C ≦ 2. When 8 <C, red is abundant when the a value is +, greenish when the a value is −, yellowish when the b value is +, and bluish when the b value is −.

  The chromatic organic pigment used in combination with carbon black may be used alone or in combination of two or more, but in order to more completely cancel the saturation of carbon black, two or more It is preferable to use a combination of chromatic organic pigments. Furthermore, it is preferable to use a cyan pigment and / or a magenta pigment in order to further lower the saturation.

  Further, if the amount of carbon black in the ink is too large, the printed matter tends to have a graininess. The amount of carbon black is preferably 0.1 to 1.5% by weight in the ink, more preferably 0. 0.3 to 1.2% by weight, most preferably 0.5 to 1.0% by weight.

  If the content of the chromatic organic pigment used in combination with carbon black is too high, the saturation will increase, so the weight ratio of carbon black to chromatic organic pigment is preferably 1: 0.05 to 1: 1. More preferably, it is 1: 0.2 to 1: 0.8.

  Even if the total content of the pigments is too large, graininess is produced. Therefore, the total sum of the pigments is preferably 1.9% by weight or less, more preferably 1.5% by weight or less of the total amount of the ink.

Examples of the carbon black used in the present invention include carbon black produced by a furnace method or a channel method. For example, these carbon blacks have a primary particle diameter of 11 to 40 nm, a specific surface area by the BET method of 50 to 400 m ² / g, a volatile content of 0.5 to 10% by weight, a pH value of 2 to 10 and the like. Those having characteristics are preferred. The following are mentioned as a commercial item which has such a characteristic. For example, no. 33, 40, 45, 52, 900, 2200B, 2300, MA7, MA8, MCF88 (above, manufactured by Mitsubishi Chemical), RAVEN1255 (made by Colombian Carbon), REGA330R, 400R, 660R, MOGUL L, ELFTEX415 (above, made by Cabot) ), Nipex90, Nipex150T, Nipex160IQ, Nipex170IQ, Nipex75, Printex85, Printex95, Printex90, Printex35, PrintexU (manufactured by Evonik Degussa) and the like, and any of them can be preferably used.

  Examples of chromatic organic pigments include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, isoindolinone pigments, quinophthalone pigments, dye lake pigments, and fluorescent pigments. Here, the pigment referred to in the present invention includes a so-called dye that has become solvent-soluble because it has a substituent.

  More specifically, examples of cyan pigments include CI Pigment Blue 1, 2, 3, 15: 1, 15: 3, 15: 4, 15: 6, 16, 21, 22, 60, 64, and the like. Examples of magenta pigments include C.I. I. Pigment Red 5, 7, 9, 12, 31, 48, 49, 52, 53, 57, 97, 112, 120, 122, 146, 147, 149, 150, 168, 170, 177, 178, 179, 184 188, 202, 206, 207, 209, 238, 242, 254, 255, 264, 269, 282, C.I. I. Pigment Violet 19, 23, 29, 30, 32, 36, 37, 38, 40, 50 and the like. Examples of yellow pigments include C.I. I. Pigment Yellow 1, 2, 3, 12, 13, 14, 16, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, 213 and the like.

  As pigments other than cyan, magenta and yellow, C.I. I. Pigment Green 7, 10, 36, C.I. I. Pigment Brown 3, 5, 25, 26, C.I. I. Pigment Orange 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, 71 and the like.

  Among them, as described above, it is preferable to use a cyan pigment and / or a magenta pigment as the chromatic organic pigment to be added to the gray ink because the chroma can be further lowered. Further, from the viewpoint of weather resistance, stability, and color developability, a copper phthalocyanine pigment (CI Pigment Blue 15: 1, 15: 3, 15: 4, 15: 6) is used as a cyan pigment, and a quinacridone pigment (C is used as a magenta pigment). CI Pigment Red 122, 202, 206, 207, 209, 282, CI Pigment Violet 19) is preferred. More preferably, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Red 122 may be used.

  When using these pigments, in order to maintain long-term ink stability, a pigment dispersion is prepared using a resin as a pigment dispersant, and this is mixed with other materials such as organic solvents. Ink is obtained.

  However, since light inks such as gray ink have a smaller proportion of pigment dispersion contained in the ink than dark inks such as black ink, the pigment dispersant adsorbed to the pigment during ink preparation is Desorption is facilitated by adsorption equilibrium. In addition, when two or more different pigment dispersions are added, the pigment dispersant adsorbed on any of the pigment dispersions may be preferentially desorbed and pigment aggregation may occur due to the difference in adsorption equilibrium between them. .

  In addition, since the surface tension of water, which is the main solvent, is extremely high, the water-based ink has a property that it is difficult to wet and spread compared to the solvent ink, and the surface area of the droplets is small, so that it is difficult to dry. Therefore, it is common to add an organic solvent or a surfactant for the purpose of improving the wettability and drying property of the water-based ink.

  However, organic solvents and surfactants that improve wettability and drying properties are highly hydrophobic, and pigment dispersions can be obtained by detaching the pigment dispersant from the pigment or adsorbing the surfactant to the pigment dispersion. Tend to cause pigment aggregation.

  In order to solve the problem regarding the stability of water-based gray ink using a hydrophobic material using two or more kinds of pigments as described above, as a result of investigations by the present inventors, a compound of the general formula (1) is used. As a result, a gray ink that does not cause pigment aggregation and that can produce an image having no graininess and excellent black tone reproducibility has been obtained.

  As a mechanism for improving stability, the compound of the general formula (1) and the pigment are adsorbed, and the compound of the general formula (1) assists the adsorption of the pigment dispersant, thereby stabilizing the dispersion state of the pigment. It is presumed that

General formula (1)

In the formula, P is an n-valent organic dye residue, n is an integer of 1 or more, and R ₁ represents an organic group represented by the general formula (2). n is preferably 1 to 5, more preferably 1 to 3, further preferably 1 to 2, and most preferably 1.

General formula (2)

In the formula, R ₂ represents an (m + 1) -valent organic residue, and R ₃ each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms. R ₂ is preferably a substituted or unsubstituted aliphatic group, specifically a divalent alkylene group having 1 to 10 carbon atoms, more preferably an alkylene group having 1 to 5 carbon atoms. R ₃ is preferably all hydrogen atoms.

  As organic dye residue (P), azo, benzimidazolone, phthalocyanine, quinacridone, anthraquinone, dioxazine, diketopyrrolopyrrole, quinophthalone, isoindolinone, isoindoline, perylene, Examples include perinone, flavanthrone, pyranthrone, and anthrapyrimidine. The structure of the organic dye residue (P) does not necessarily match the structure of the added organic pigment, but it is preferable to have a structure close to that of the added organic pigment. Thereby, adsorption | suction with a pigment increases and it becomes easy to express the effect of a stability improvement. Moreover, when adding 2 or more types of chromatic organic pigments, it is preferable to use together the compound of General formula (1) which has a structure close | similar to each pigment.

  The compound of the general formula (1) is preferably blended at a ratio of 0.01% by weight to 10% by weight with respect to the chromatic organic pigment in the ink, more preferably 0.5% by weight to 3% by weight. It is as follows. If more than 10% by weight is added, the dispersion stability may decrease.

A known pigment dispersant can be used as the pigment dispersant. However, the case of being a compound of general formula (1) is excluded. The pigment dispersant has both a group having affinity for the pigment and a group having affinity for the solvent.
In the present invention, the group having affinity for a solvent or the like is preferably a resin, for example, an acrylic resin, a styrene acrylic resin, a maleic acid resin, a styrene maleic resin, an α-olefin maleic resin, a urethane resin, an ester resin, or the like. Can be mentioned. From the viewpoint of strengthening the adsorption with the compound of the general formula (1) and stabilizing the pigment dispersion, it is preferable to use an acrylic resin or a styrene acrylic resin.
As the group having affinity for the pigment, a group having a pigment structure or a group close to the pigment structure / polarity is used.

  The acid value of the pigment dispersant is preferably in the range of 50 mgKOH / g to 600 mgKOH / g, and the acid value is preferably in the range of 120 mgKOH / g to 500 mgKOH / g. If the acid value of the pigment dispersant used in the present invention is lower than the above range, the dispersion stability of the ink is lowered, and the ejection stability tends to deteriorate. In addition, when the acid value of the pigment dispersant used in the present invention is higher than the above range, the adhesion of the pigment dispersant to the pigment surface decreases, and the storage stability of the ink tends to decrease.

  The weight average molecular weight of the pigment dispersant is preferably 5,000 to 100,000. When the weight average molecular weight is 5000 or less, the dispersion stability may decrease, and when the weight average molecular weight is 100000 or more, ejection may be affected. More preferably, the weight average molecular weight is 10,000 to 50,000, and still more preferably the weight average molecular weight is 15,000 to 30,000.

  The weight ratio of pigment to pigment dispersant is preferably 1/1 to 100/1. When the ratio of the pigment dispersant is larger than 1/1, the viscosity of the ink tends to increase. Moreover, when smaller than 100/1, a dispersibility may fall and stability may fall. The weight ratio of the pigment and the pigment dispersant is more preferably 2/1 to 50/1, and further preferably 3/1 to 20/1.

  The organic solvent used in the present invention is preferably one having an affinity for water. In particular, alkanediol solvents and glycol ether solvents are preferred.

  These compounds include 1,2-hexanediol, 1,2-pentanediol, 1,2-butanediol, 1,3-butanediol, 3-methyl-1,3-butanediol, 3-methoxy-1 -Butanol, 3-methoxy-3-methylbutanol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, ethylene glycol, glycerin, ethylene glycol-2-ethylhexyl ether, diethylene glycol Monobutyl ether, diethylene glycol monohexyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, diethylene glycol methyl butyl ether, triethylene glycol Butyl ether, tripropylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monopentyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether , Triethylene glycol monopropyl ether, tetraethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether Ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol butyl ether, propylene glycol dimethyl ether. Of these, alkanediol solvents and glycol ether solvents having 3 or more carbon atoms in the terminal carbon chain are preferable, alkanediol solvents are more preferable, and 1,2-hexanediol is more preferable.

  Further, a water-soluble nitrogen-containing solvent can be added for the purpose of improving the penetration and adhesion to the hardly absorbent substrate.

  Nitrogen-containing solvents include 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, 3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone, N, N-dimethyl-β-methoxypropionamide, N , N-dimethyl-β-ethoxypropionamide, N, N-dimethyl-β-butoxypropionamide, N, N-dimethyl-β-pentoxypropionamide, N, N-dimethyl-β-hexoxypropionamide, N , N-dimethyl-β-heptoxypropionamide, N, N-dimethyl-β-2-ethylhexoxypropionamide, N, N-dimethyl-β-octoxypropionamide, N, N-diethyl-β-butoxy Propionamide, N, N-diethyl-β-pentoxypropionamide, N, N-diethyl-β- Examples include hexoxypropionamide, N, N-diethyl-β-heptoxypropionamide, N, N-diethyl-β-octoxypropionamide, and the like.

  The total amount of the organic solvent used in the present invention in the ink composition is preferably 10% by weight or more and 45% by weight or less. In order to obtain excellent printability, it is more preferable that the total amount of the organic solvent is 10% by weight or more and 40% by weight or less from the viewpoint of ensuring sufficient wettability and drying on the hardly absorbent substrate. % To 35% by weight is particularly preferable. When the total amount of the organic solvent is less than 10% by weight, the moisture retention of the ink is insufficient, and the ejection stability may be impaired. Moreover, the wettability on a hardly absorbable base material may fall. When the total content of the organic solvent is more than 45% by weight, the viscosity of the ink becomes high, which may impair the ejection stability. Further, the storage stability and drying property of the ink are not suitable for practical use, and the print quality may be deteriorated.

  In the water-based inkjet ink of the present invention, a binder resin can be used in order to improve the drying property of the ink on the highly hydrophobic hardly-absorbing substrate and the coating film resistance of the printed matter. It is preferable to use water-dispersible resin fine particles as the binder resin. Water-soluble resins and fine resin particles are generally known as binder resins for water-based inks. In general, resin fine particles have a higher molecular weight than water-soluble resins, and can achieve high resistance. In addition, the resin fine particles can reduce the viscosity of the ink and can be blended with a larger amount of resin in the ink, so that it can be said that the resin fine particles are suitable for enhancing the resistance of the ink-jet ink. Examples of the resin fine particles include acrylic, urethane, styrene butadiene, vinyl chloride, and polyolefin.

  By increasing the glass transition temperature (Tg) of the water-dispersible resin fine particles, it is possible to improve resistance such as abrasion resistance and chemical resistance, preferably in the range of 50 to 100 ° C., more preferably Is in the range of 75-90 ° C. When the temperature is lower than 50 ° C., sufficient resistance cannot be obtained, and printing may be peeled off from the printed matter in practice. When the temperature is higher than 100 ° C., the coating film becomes very hard, and cracking and cracking may occur on the printed surface when the printed material is bent.

  In addition, the water-dispersible resin fine particles not only increase the coating film resistance of the printed matter, but also suppress the bleeding between ink droplets by forming a film quickly after the droplets land, and there is no bleeding between colors. Excellent print quality can be obtained.

  The content of the water-dispersible resin fine particles as described above in the ink composition is preferably in the range of 3 to 20% by weight based on the total weight of the ink in terms of nonvolatile content.

  As water contained in the water-based inkjet ink of the present invention, it is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions.

  The content of water in the ink composition that can be used in the present invention is preferably in the range of 20 to 90% by weight, and more preferably in the range of 40 to 80% by weight.

  In addition to the above components, the ink of the present invention may be added with surfactants, antifoaming agents, thickeners, pH adjusters, preservatives, etc. in order to obtain inks having desired physical properties as required. An agent can be added as appropriate. The amount of these additives added is 0.01% by weight or more and 10% by weight or less, preferably 0.05% by weight or more and 5% by weight or less, more preferably 0.1% by weight or more with respect to the total mass of the ink. 3% by weight or less.

  Examples of the method for preparing the ink of the present invention comprising the components described above include the following methods, but the present invention is not limited to these. First, the pigment and the compound of the general formula (1) are added to an aqueous medium in which at least a pigment dispersant and water are mixed, and after mixing and stirring, dispersion treatment is performed using a dispersion means described below, and necessary. The desired pigment dispersion is obtained by centrifuging according to the above. Next, if necessary, a water-soluble organic solvent or an appropriately selected additive component as listed above is added to this pigment dispersion, and the mixture is stirred and filtered as necessary to obtain the ink of the present invention. And

  In the ink preparation method of the present invention, as described above, a pigment dispersion obtained by carrying out a dispersion treatment is used for ink preparation, but before the dispersion treatment carried out during the preparation of the pigment dispersion. It is effective to perform premixing. That is, premixing may be performed by adding a pigment to an aqueous medium in which at least a pigment dispersion resin and water are mixed. Such a premixing operation is preferable because it improves wettability of the pigment surface and promotes adsorption of the dispersant to the pigment surface.

  The disperser used in the above-described pigment dispersion treatment may be any disperser that is generally used, and examples thereof include a ball mill, a roll mill, a sand mill, a bead mill, and a nanomizer. Among these, a bead mill is preferably used. Examples of such include a super mill, a sand grinder, an agitator mill, a glen mill, a dyno mill, a pearl mill, and a cobol mill (all are trade names).

  Further, in the above-described pigment premixing and dispersion treatment, the pigment dispersion resin may be dissolved or dispersed only in water, or may be dissolved or dispersed in a mixed solvent of a water-soluble organic solvent and water. .

  Since the ink of the present invention is for inkjet recording, it is preferable to use a pigment having an optimum particle size distribution. That is, in order to allow ink containing pigment particles to be suitably used in the ink jet recording method, it is preferable to use a pigment having an optimum particle size distribution in view of demands such as nozzle clogging resistance. Examples of a method for obtaining a pigment having a desired particle size distribution include the following methods. Reduce the size of the grinding media of the disperser as mentioned above, increase the filling rate of the grinding media, increase the processing time, classify with a filter or centrifuge after grinding, etc. There are methods such as a combination of these methods.

  When printing is performed with an inkjet printing apparatus using the inkjet ink of the present invention, it is preferable to perform printing while heating the printing medium to 40 to 80 ° C. By printing while heating, the ink droplets are dried immediately after landing on the print medium, so that bleeding is unlikely to occur and a high quality printed matter can be obtained.

  A known print medium for ink-jet ink printing of the present invention can be used. For example, paper media such as high-quality paper, coated paper, art paper, cast paper, synthetic paper, and inkjet paper, and plastic media such as polyvinyl chloride sheets, PET films, and PP films. These may have a smooth print medium surface or an uneven surface, or may be transparent, translucent, or opaque. Further, two or more of these print media may be bonded to each other. Furthermore, a peeling adhesive layer or the like may be provided on the opposite side of the printing surface, or an adhesive layer or the like may be provided on the printing surface after printing.

  Hereinafter, the present invention will be described more specifically with reference to examples. In the examples, “part” represents “part by weight”.

  Hereinafter, the manufacture example of Example 1 is demonstrated concretely.

(Production example of black pigment dispersion)
20 parts of carbon black, 6 parts of styrene acrylic resin (molecular weight 16000, acid value 200 mgKOH / g) as a pigment dispersant, 74 parts of water are mixed and predispersed with a disper, and then zirconia beads having a diameter of 0.5 mm as a dispersion medium This dispersion was carried out for 2 hours using a 0.6 L dyno mill filled with 1800 g to obtain a black pigment dispersion 1.

(Production example of cyan pigment dispersion)
20 parts of pigment blue 15: 3 as a pigment, 0.02 part of compound A in which P is a phthalocyanine skeleton, R ₂ is a methylene group, and R ₃ is all hydrogen atoms as a compound of the general formula (1), pigment dispersant 6 parts of styrene acrylic resin (molecular weight 16000, acid value 200 mgKOH / g) and 73.98 parts of water were mixed, predispersed with a disper, and filled with 1800 g of zirconia beads having a diameter of 0.5 mm and having a capacity of 0.6 L Was used for 2 hours to obtain a cyan pigment dispersion 1.
(Production examples of pigment dispersions other than the above)
The pigment, the compound of the general formula (1), and the ratio thereof are changed as shown in Table 1, and the others are the same as the cyan pigment dispersion 1, and the cyan pigment dispersions 2 to 5, the magenta pigment dispersion 1 ~ 4 were obtained.
Compound B is a compound in which P in the general formula (1) is a quinacridone skeleton, R ₂ is a methylene group, and all R ₃ are hydrogen atoms.

(Example of gray ink production)
Disperse various pigments in 10 parts of 1,2-hexanediol, 10 parts of 1,2-butanediol, and 8 parts of acrylic resin fine particles as a binder resin so that the amount of the pigment dispersion is as shown in Table 2. The liquid, 1,2-hexanediol, 1,2-butanediol, binder resin and water were mixed to prepare gray inks of Examples 1 to 16 and Comparative Examples 1 to 7.

  The evaluation method of the prepared ink is shown below.

(Evaluation 1: Evaluation of viscosity stability)
The viscosities of the inks obtained in Examples 1 to 16 and Comparative Examples 1 to 7 were measured using an E-type viscometer (TVE-20L manufactured by Toki Sangyo Co., Ltd.) at 25 ° C. under the condition of a rotation speed of 50 rpm. This ink was stored in a thermostat at 70 ° C. and accelerated with time, and the change in the viscosity of the ink before and after aging was evaluated. The evaluation criteria are as follows, and A and B evaluations are practical areas.
A: Viscosity change rate after storage for 4 weeks is less than ± 5% B: Viscosity change rate after storage for 2 weeks is less than ± 5% C: Viscosity change rate after storage for 1 week is ± 5% or more

(Evaluation 2: Ink hue evaluation)
About the ink obtained in Examples 1-16 and Comparative Examples 1-7, it filled in the inkjet printer which mounts the inkjet head which has a piezoelectric element in a 25 degreeC environment, and a polyvinyl chloride sheet (PVC) is 50 degreeC. Solid printing with a printing rate of 100% with a wet film thickness of about 12 μm while heating (resolution: 1440 × 1440 dpi, printing speed: 3 m ² / h), spectrocolorimeter (X- The saturation C of arbitrary 5 places was measured using observation light source: D50, observation visual field: 2 °, density: ANSI T, white standard: Abs, measurement mode: Reflectance) manufactured by Rite, and an average value was obtained. The evaluation criteria are as follows, and AA, A, and B evaluations are practical areas.
AA: C <2
A: 2 ≦ C <5
B: 5 ≦ C <8
C: 8 ≦ C

(Evaluation 3: Graininess evaluation)
A gradation pattern having a printing rate of 0 to 100% was printed under the same printing conditions as in Evaluation 2, and the graininess of the printed matter was visually evaluated. Evaluation criteria are as follows, and A and B evaluations are practical areas.
A: No graininess B: Slight graininess C: Graininess

Said evaluation result is shown in Table 1 about Examples 1-16 and Comparative Examples 1-7.

  The gray inks having the compositions of Examples 1 to 16 contained two or more pigment dispersions, but the stability was improved as compared with Comparative Examples 2 to 7. Further, the saturation C was improved as compared with Comparative Example 1 by adding an appropriate amount of cyan or magenta pigment. In Example 6 where the total amount of pigment is larger than the others and Comparative Examples 6 and 7 where the amount of carbon black is large, the B evaluation is below, but other inks have smooth gradation printed matter without graininess. Could get. In particular, in Examples 10 to 14 in which Pigment Blue 15: 3 and Pigment Red 122 are used in combination, gray with low saturation and no graininess is obtained, and among them, the type and amount of the compound of the general formula (1) are optimal. The modified Example 14 had excellent stability.

Claims (5)

It contains at least a pigment, a pigment dispersant (except when it is a compound of the following general formula (1)), an organic solvent, water, and a compound of the following general formula (1). A gray ink for water-based inkjet which contains at least one organic pigment.
General formula (1)

(In the formula, P is an n-valent organic dye residue, n is an integer of 1 or more, and R ₁ represents an organic group represented by the following general formula (2).

General formula (2)

(Wherein R ₂ represents an (m + 1) -valent organic residue, and R ₃ independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms.)
2. The gray ink for water-based inkjet according to claim 1, wherein the chromatic organic pigment contains two or more organic pigments. 3. The gray ink for water-based inkjet according to claim 1, wherein the chromatic organic pigment is a cyan pigment or / and a magenta pigment. The gray ink for water-based inkjet according to claim 3, wherein the cyan pigment is a copper phthalocyanine pigment, and the magenta pigment is a quinacridone pigment. The content of the compound of the general formula (1) is 0.01% by weight to 10% by weight with respect to the total amount of chromatic organic pigments. Gray ink.