JP2016017103A - Aqueous inkjet ink set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous inkjet ink set that has excellent printability on a general print medium, particularly a print medium having low water absorption such as coated paper, art paper and polyvinyl chloride sheet and can give a high-quality image.SOLUTION: The aqueous inkjet ink set includes a deep color ink and a light color ink having at least the same hue but different color densities. Each ink comprises at least a colorant, an organic solvent (A) having a boiling point of 200°C or higher and 280°C or lower and a surface tension of 20 mN/m or more and 30 mN/m or less, and water. The light color ink further contains a water-soluble organic solvent (B) having a boiling point of 50°C or higher and 180°C or lower. A difference in the viscosity at 25°C between the deep color ink and the light color ink is 3.5 mPa s or less.SELECTED DRAWING: None

Description

The present invention relates to a water-based inkjet ink set that is excellent in printability to a general printing medium, particularly a printing medium having low water absorption such as coated paper, art paper, and vinyl chloride sheet, and that can obtain a high-quality image. .

The ink jet recording method is a recording method in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle onto a recording member and attaching them. According to this method, there is an advantage that not only the noise of the apparatus to be used is small and the operability is good, but also colorization is easy and plain paper can be used as a recording member. It is widely used as an output machine in offices and homes.

On the other hand, in industrial applications, it is expected to be used as an output machine for digital printing due to the improvement of inkjet technology. For non-absorbable print media (plastic base materials such as PVC and PET) using solvent ink and UV ink. Printing machines capable of printing have actually been marketed. However, in recent years, the demand for water-based inks has increased from the viewpoint of dealing with the environment.

As water-based inks for ink jets, as described in Patent Documents 1, 2, and 3, the development of inks in which special printing papers such as plain paper and photographic glossy paper have been developed for a long time. On the other hand, in recent years, the application of the ink jet recording system is expected to be expanded, and the need for direct printing on a non-absorbable printing medium used for coated paper such as coated paper or outdoor advertising is increasing. Since conventional ink performs drawing by absorbing droplets on paper, when printing on a printing medium with low water absorption, the image blurs and cannot be used.

Patent Documents 4 and 5 disclose inks for the purpose of printing on a print medium having low water absorption. As disclosed in these documents, it is possible to perform printing on a print medium having low water absorption by using a specific solvent and adjusting the printing conditions in some cases. Furthermore, in the printing ink for such low-absorbing and non-absorbing printing media as well as the printing ink for the absorptive printing medium, in order to reduce the graininess of the highlight portion and improve the image quality. In addition, it has been desired to develop a light color ink having a low density.

In order to lower the color density of the light color ink as compared with the dark color ink, it is necessary to reduce the amount of pigment contained in the ink. As a result, when an ink having the same composition as that of the dark color ink is prepared, the viscosity of the light color ink is lowered, which may adversely affect the discharge property. In addition, if the amount of solvent is increased to increase the viscosity to the same level as that of dark ink, the balance between the drying properties of dark ink and light ink may be lost, and the image quality may deteriorate on print media with low water absorption. there were.

Japanese Patent No. 4764562 Japanese Patent No. 4595281 JP 2008-247951 A JP 2007-211081 A JP 2011-201228 A

An object of the present invention is an aqueous inkjet ink which is excellent in printability on a general printing medium, in particular, a printing medium having low water absorption such as coated paper, art paper and vinyl chloride sheet, and can obtain a high quality image. Is to provide a set.

That is, the present invention is a water-based inkjet ink set including a dark color ink and a light color ink having at least the same hue but different color densities,
Each ink includes at least a colorant, an organic solvent (A) having a boiling point of 200 ° C. or higher and 280 ° C. or lower and a surface tension of 20 mN / m or higher and 30 mN / m or lower, and water,
The light color ink further contains a water-soluble organic solvent (B) having a boiling point of 50 ° C. or higher and 180 ° C. or lower,
The present invention relates to a water-based inkjet ink set characterized in that a difference in viscosity at 25 ° C. between a dark color ink and a light color ink is 3.5 mPa · s or less.

The present invention also includes the content (SA1) of the organic solvent (A) having a boiling point of 200 ° C. to 280 ° C. and a surface tension of 20 mN / m to 30 mN / m, and a boiling point of the light ink. Is a ratio of 6:10 to 10: 6 with the content (SA2) of the organic solvent (A) having a surface tension of 20 mN / m or more and 30 mN / m or less. The present invention relates to the water-based inkjet ink set.

Further, the present invention is characterized in that the total content (ST2) of all organic solvents contained in the light color ink is 5 to 20% by weight larger than the total content (ST1) of all organic solvents contained in the dark color ink. The present invention relates to the water-based inkjet ink set.

Further, in the present invention, the content (SB2) of the water-soluble organic solvent (B) having a boiling point of 50 ° C. or higher and 180 ° C. or lower contained in the light color ink is 5 to 20% by weight. It relates to an ink set.

In the present invention, the ratio of the solid content (W1) contained in the dark color ink to the solid content (W2) contained in the light color ink is 7:10 to 10: 7. The present invention relates to the water-based inkjet ink set.

The present invention is also the above water-based inkjet, characterized in that a dark color ink and a colorant of a light color ink are pigments dispersed by a pigment dispersion resin, and the pigment dispersion resin has an alkyl chain having 10 or more carbon atoms. It relates to an ink set.

Further, the present invention is characterized in that as a combination of dark ink and light ink, cyan ink and light cyan ink, magenta ink and light magenta ink, and a combination of black ink and light black (gray) ink are included. The present invention relates to the water-based inkjet ink set.

According to the present invention, there is provided an aqueous ink jet ink set which is excellent in printability on a general printing medium, particularly a printing medium having low water absorption such as coated paper, art paper and vinyl chloride sheet, and can obtain a high quality image. It became possible to provide.

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

In the present invention, an organic solvent (A) having a boiling point of 200 ° C. or higher and 280 ° C. or lower and a surface tension of 20 mN / m or higher and 30 mN / m or lower is used for the dark ink, and a boiling point of 200 ° C. or higher and 280 ° C. or lower is used for the light color ink. By using an organic solvent (A) having a surface tension of 20 mN / m or more and 30 mN / m or less and a water-soluble organic solvent (B) having a boiling point of 50 ° C. or more and 180 ° C. or less, a print medium having low water absorption can be obtained. Excellent printability and high quality images can be obtained.

Conventionally, in order to make the dark ink and the light ink have the same viscosity, it has been generally performed to increase the amount of the solvent of the light ink as described above. However, when printing on a print medium with low water absorption, the image quality may be deteriorated due to a decrease in drying property due to an increase in the amount of solvent. The present inventors use a water-soluble organic solvent (B) having a boiling point of 50 ° C. or higher and 180 ° C. or lower for light color ink, thereby making the viscosity of the light color ink equal to that of the dark color ink without reducing the drying property. Made it possible to get good quality prints.

The main components of the present invention are described below.

(Organic solvent)
In the present invention, at least two specific organic solvents are used. The first organic solvent is an organic solvent (hereinafter referred to as “solvent A”) having a boiling point of 200 ° C. or more and 280 ° C. or less and a surface tension of 20 mN / m or more and 30 mN / m or less. The second organic solvent is a water-soluble organic solvent (hereinafter referred to as “solvent B”) having a boiling point of 50 ° C. or higher and 180 ° C. or lower. In the present invention, by using the solvent A for the dark ink having a high color density and the solvent A and the solvent B for the light ink having a low color density, the ink can be ejected onto a printing medium having a low water absorption property, and the drying property. It improves printability and makes it possible to obtain high quality images. This is thought to be due to the following principle. First, the solvent amount can be increased while the drying property is kept equal to that of the dark ink by the solvent B which is used for the light-colored ink and has a low boiling point and is quickly dried. As a result, the viscosity of the light color ink can be increased to the same level as that of the dark color ink, and good discharge properties can be obtained. Further, by using the solvent A for both the dark color ink and the light color ink, printing on a print medium having low water absorption is enabled. Since the solvent A has a high boiling point, the ink lands on the print medium and remains in the ink droplets even after water, solvent B, and the like are volatilized. Furthermore, since the solvent A has a low surface tension, it is considered that the solvent A remaining in the ink droplets causes the ink droplets to spread on the printing medium and form a uniform image.

The content of the solvent A in the dark ink and the light ink is preferably 5 to 30% by weight based on the total weight of the ink. When the content is 5% by weight or more, sufficient wettability with respect to the print medium can be ensured, and an image with high print quality can be obtained without being affected by the type of the print medium. Further, when the content is 30% by weight or less, sufficient storage stability of the ink can be ensured. More preferably, it is 7-25 weight%, More preferably, it is 9-22 weight%, Most preferably, it is 11-18 weight%.

Moreover, it is preferable that ratio of the content rate (SA1) of the solvent A contained in the dark color ink and the content rate (SA2) of the solvent B contained in the light color ink is in the range of 6:10 to 10: 6. If this ratio deviates greatly, there may be a difference in wettability between the dark color ink and the light color ink, and the image quality may deteriorate. Within the above range, the same wettability can be secured with each ink, and even when ink droplets come into contact with each other, flow between inks hardly occurs, and a high-quality image without bleeding can be obtained. . More preferably, it is the range of 7: 10-10: 7, More preferably, it is the range of 8: 10-10: 8, Most preferably, it is the range of 9: 10-10: 9.

As the solvent A, any solvent can be used as long as it has an boiling point of 200 ° C. or higher and 280 ° C. or lower and a surface tension of 20 mN / m or higher and 30 mN / m or lower. Here, the “surface tension” means a value measured by the Wilhelmy method (plate method, vertical plate method) under the condition of 25 ° C. Specifically, it can be measured using a device such as a high-precision surface tension meter DY-700 (manufactured by Kyowa Interface Science Co., Ltd.). Although not particularly limited, examples of the solvent A include 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, ethylene glycol monohexyl ether, ethylene glycol-2-ethylhexyl ether, and diethylene glycol. Monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol-2-ethylhexyl ether, triethylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, diethylene glycol methyl butyl ether, Triethylene glycol methyl butyl ether and tripropylene Glycol dimethyl ether, and the like. Among these, an alkanediol solvent and / or a glycol ether solvent having 3 or more carbon atoms in the terminal carbon chain is preferable. More preferred is an alkanediol solvent, and more preferred is 1,2-hexanediol.

The content (SB2) of the solvent B in the light-colored ink is preferably 3 to 30% by weight based on the total weight of the ink. When the content is 3% by weight or more, a sufficient viscosity can be obtained, and the difference in the appropriate amount of the discharge liquid between the dark color ink and the light color ink can be reduced to obtain a good image. In addition, when the content is 30% by weight or less, suitable drying properties are obtained, and non-ejection due to nozzle clogging due to ink drying does not occur at the time of ejection, and a high-quality image with high glossiness is obtained without causing bleeding on the printing medium. be able to. More preferably, it is 5-20 weight%, More preferably, it is 8-18 weight%, Most preferably, it is 10-15 weight%.

As the solvent B, any solvent can be used as long as it is a water-soluble organic solvent having a boiling point of 50 ° C. or higher and 180 ° C. or lower. Although it does not specifically limit, As said solvent B, methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, propylene, for example Examples include glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, methoxybutanol, 3-methyl-3-methoxybutanol, diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl ether acetate, and ethyl lactate. . Among these, at least one selected from the group consisting of ethanol, 2-propanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, methoxybutanol, 3-methyl-3-methoxybutanol, It is preferable from the viewpoint of drying properties and print quality. Moreover, the water-soluble organic solvent whose boiling point is 100 degreeC or more and 180 degrees C or less is preferable from the point of discharge stability. More preferably, it is at least one selected from the group consisting of propylene glycol monomethyl ether, methoxybutanol, and 3-methyl-3-methoxybutanol. More preferred is propylene glycol monomethyl ether and / or methoxybutanol. Most preferred is propylene glycol monomethyl ether.

As the organic solvent in the dark color ink and the light color ink, in addition to the above two types of solvents A and B, other solvents can be used for the purpose of adjusting the viscosity or improving the discharge property. Other solvents that can be used include glycerin, diols at both ends, 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methyloxazolidinone, N-ethyloxazolidinone, γ-butyrolactone, ε-caprolactone, and N, N-dimethyl-β-methoxypropionamide and the like can be mentioned.

The total content of all the organic solvents in the dark ink and the light ink is preferably 10 to 45% by weight. When the total content is too small, the drying property and the wettability to the printing medium are poor, and the printing quality may be lowered depending on the printing medium. When the total content is more than 45% by weight, the storage stability of the ink may be lowered. The total content (ST1) of all the solvents in the dark ink is more preferably 12 to 40% by weight, still more preferably 14 to 35% by weight, and most preferably 17 to 28% by weight. The total content (ST2) of all the solvents of the light-color ink is more preferably 14 to 42% by weight, still more preferably 19 to 39% by weight, and most preferably 24 to 36% by weight.

The total content (ST2) of all the solvents of the light color ink is preferably 5 to 20% by weight higher than the total content (ST1) of all the solvents of the dark ink. Within this range, the difference in viscosity between the dark color ink and the light color ink can be kept small, and the difference in the appropriate amount of the discharge liquid between the dark color ink and the light color ink can be reduced to obtain a good image. Moreover, the drying properties of the dark color ink and the light color ink become uniform, and mottling is less likely to occur. More preferably, it is 6-18 weight%, More preferably, it is 8-16 weight%, Most preferably, it is 9-14 weight%.

(Coloring agent)
In the present invention, a colorant is used for each ink. Examples of the colorant include dyes and pigments. These colorants may be used alone or in combination of two or more. It is preferable to use a pigment in order to improve the resistance of the printed material.

In the case of using a dye, various dyes usually used for ink jet recording, such as a direct dye, an acid dye, a food dye, a basic dye, a reactive dye, a disperse dye, and a vat dye, can be used.

More specifically, cyan dyes include C.I. I. Acid Blue 1, 7, 9, 15, 22, 23, 25, 27, 29, 40, 41, 43, 45, 54, 59, 60, 62, 72, 74, 78, 80, 82, 83, 90, 92, 93, 100, 012, 103, 104, 112, 113, 117, 120, 126, 127, 129, 130, 131, 138, 140, 142, 143, 151, 154, 158, 161, 166, 167, 168, 170, 171, 182, 183, 184, 187, 192, 199, 203, 204, 205, 229, 234, 236, 249, C.I. I. Direct Blue 1, 2, 6, 15, 22, 25, 41, 71, 76, 77, 78, 80, 86, 87, 90, 98, 106, 108, 120, 123, 158, 160, 163, 165, 168, 192, 193, 194, 195, 196, 199, 200, 201, 202, 203, 207, 225, 226, 236, 237, 246, 248, 249, C.I. I. Reactive Blue 1, 2, 3, 4, 5, 7, 8, 9, 13, 14, 15, 17, 18, 19, 20, 21, 25, 26, 27, 28, 29, 31, 32, 33, 34, 37, 38, 39, 40, 41, 43, 44, 46, C.I. I. Food Blue 1, 2, C.I. I. Basic Blue 9, 25, 28, 29, 44 etc. are mentioned. As the magenta dye, C.I. I. Acid Red 1, 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 37, 42, 51, 52, 57, 75, 77, 80, 82, 85, 87, 88, 89, 92, 94, 97, 106, 111, 114, 115, 117, 118, 119, 129, 130, 131, 133, 134, 138, 143, 145, 154, 155, 158, 168, 180, 183, 184, 186, 194, 198, 209, 211, 215, 219, 249, 252, 254, 262, 265, 274, 282, 289, 303, 317, 320, 321, 322, C.I. I. Direct Red 1, 2, 4, 9, 11, 13, 17, 20, 23, 24, 28, 31, 33, 37, 39, 44, 46, 62, 63, 75, 79, 80, 81, 83, 84, 89, 95, 99, 113, 197, 201, 218, 220, 224, 225, 226, 227, 228, 229, 230, 231, C.I. I. Reactive Red 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 15, 16, 17, 19, 20, 21, 22, 23, 24, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 46, 49, 50, 58, 59, 63, 64, C.I. I. Food Red 7, 9, 14 etc. are mentioned. Examples of yellow dyes include C.I. I. Acid Yellow 1, 3, 11, 17, 19, 23, 25, 29, 36, 38, 40, 42, 44, 49, 59, 61, 70, 72, 75, 76, 78, 79, 98, 99, 110, 111, 127, 131, 135, 142, 162, 164, 165, C.I. I. Direct Yellow 1, 8, 11, 12, 24, 26, 27, 33, 39, 44, 50, 58, 85, 86, 87, 88, 89, 98, 110, 132, 142, 144, Reactive Yellow 1, 2, 3, 4, 6, 7, 11, 12, 13, 14, 15, 16, 17, 18, 22, 23, 24, 25, 26, 27, 37, 42, C.I. I. Food Yellow 3, 4 etc. are mentioned. As the black dye, C.I. I. Direct Black 1, 7, 19, 32, 51, 71, 108, 146, 154, 166 etc. are mentioned.

Examples of dyes other than cyan, magenta, yellow and black include C.I. I. Acid Green 7, 12, 25, 27, 35, 36, 40, 43, 44, 65, 79, C.I. I. Direct Green 1, 6, 8, 26, 28, 30, 31, 37, 59, 63, 64, C.I. I. Reactive Green 6, 7, C.I. I. Direct Violet 2, 48, 63, 90, C.I. I. Reactive Violet 1, 5, 9, 10 etc. are mentioned.

When a pigment is used, either an inorganic pigment or an organic pigment can be used. Examples of inorganic pigments include titanium oxide, zinc white, zinc sulfide, lead white, calcium carbonate, precipitated barium sulfate, white carbon, alumina white, kaolin clay, talc, bentonite, black iron oxide, cadmium red, brown rice, molybdenum red, Molybdate orange, chrome vermilion, yellow lead, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, viridian, titanium cobalt green, cobalt green, cobalt chrome green, Victoria green, ultramarine, bituminous, cobalt blue, cerulean blue, Examples thereof include cobalt silica blue, cobalt zinc silica blue, manganese violet, and cobalt violet.

Examples of organic pigments include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, isoindolinone pigments, quinophthalone pigments, dye lake pigments, and fluorescent pigments.

More specifically, examples of cyan pigments include C.I. I. 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.

Examples of the black pigment include carbon black produced by the furnace method and the channel method. For example, these carbon blacks have a primary particle diameter of 11 to 40 nm, a specific surface area by BET method of 50 to 400 m <2> / g, a volatile content of 0.5 to 10%, a pH value of 2 to 10 and the like. What has is suitable. 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.

As pigments other than cyan, magenta, yellow and black, 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.

When these pigments are used, it is preferable to use them dispersed in an ink medium in order to maintain long-term ink stability. As a method for dispersing the pigment, there are a method in which the pigment is surface-modified by oxidation treatment or the like and the pigment is dispersed without a dispersant, and a method in which the pigment is dispersed using a surfactant or resin as a dispersant. In order to obtain a more stable ink, it is preferable to disperse the pigment using a dispersion resin.

The content of the colorant is preferably 0.01% by weight or more and 15% by weight or less based on the total weight of the ink. More preferably, it is 0.05 weight% or more and 10 weight% or less. In the case of dark ink, it is preferably from 0.5% by weight to 9% by weight, more preferably from 1% by weight to 8% by weight, still more preferably from 2% by weight to 7% by weight. In the case of light color ink, it is preferably 0.1% by weight to 5% by weight, more preferably 0.15% by weight to 3% by weight, and further preferably 0.2% by weight to 1% by weight.

By adjusting the ratio of the content ratio of the colorant of the dark color ink and the light color ink, gradation printing or the like can be reproduced smoothly without causing gradation skip. The ratio of the colorant content is preferably 1: 0.01 to 1: 0.4, more preferably 1: 0.05 to 1: 0.3, and 1: 0.08 to 1: 0.25. Is more preferable, and 1: 0.1 to 1: 0.2 is most preferable.

The “same color as each other” defined in the present invention refers to a printed matter obtained by coating a dark color ink and a light color ink on a white print medium so that a wet film thickness is 6 to 10 μm, a D50 light source, ° Hue for chromatic ink with chroma C * (C * = √ (a * ^ 2 + b * ^ 2)) calculated from L * a * b * values measured under visual field conditions The angle h (h = tan-1 (b * / a *)) indicates that the dark ink and the light ink are within 30 °. In the case of an achromatic ink having a chroma C * of less than 10, In order to satisfy this, it is preferable to use the same colorant for the dark color ink and the light color ink.

(Pigment dispersion resin)
When the colorant is a pigment and dispersion is performed with a pigment dispersion 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 is used. be able to. Among these, it is preferable to use an acrylic resin or a styrene acrylic resin.

Here, the “acrylic resin” described in the present specification means a polymer including a structural unit obtained by polymerizing at least one of (meth) acrylic acid and (meth) acrylic acid ester. In one embodiment, the “acrylic resin” may be a polymer having a structural portion obtained by polymerizing a (meth) acrylic acid ester having an alkyl group having 1 or more carbon atoms. In such an embodiment, the polymer preferably has an alkyl group having 8 or more carbon atoms, and more preferably has an alkyl chain having 10 or more carbon atoms. The polymer is a homopolymer of a (meth) acrylic acid ester having an alkyl group having 8 or more carbon atoms, or a copolymer of the ester and another polymerizable monomer compound such as (meth) acrylic acid. May be. In any embodiment, it is easy to improve the dispersion stability of the ink because the polymer has an alkyl group having 8 or more carbon atoms. Further, with the improvement of the dispersion stability, it is possible to further enhance the effect of improving the ejection property, the print quality and the gloss. Therefore, in one embodiment, the pigment dispersion resin preferably has an alkyl group having 8 or more carbon atoms.

The alkyl group having 8 or more carbon atoms may be linear or branched. Specific examples of the alkyl group include octyl group (C8), 2-ethylhexyl group (C8), nonyl group (C9), decyl group (C10), lauryl group (C12), myristyl group (C14), cetyl group (C16). Stearyl group (C18), Aralkyl group (C20), Behenyl group (C22), Lignoceryl group (C24), Serotoyl group (C26), Montanyl group (C28), Melissyl group (C30), Dotria contanoyl group (C32) ), Tetratriacontanoyl group (C34), hexatriacontanoyl group (C36) and the like. Among these, a linear alkyl group is preferable, and a linear alkyl group having 10 or more carbon atoms is more preferable. When the polymer used as the pigment dispersion resin has an alkyl group having 8 or more carbon atoms, it is easy to improve printing quality and gloss of printed matter. Moreover, when it has a C10 or more alkyl group, the further improvement effect of the said characteristic is acquired. On the other hand, if the alkyl group in the polymer is too long, the ink ejection stability may deteriorate. Therefore, the carbon number of the alkyl group is preferably 12-30, and more preferably 18-24.

The acid value of the pigment-dispersed resin is preferably 50 to 400 mgKOH / g. When the acid value is less than 50 mgKOH / g, the pigment-dispersed resin is difficult to dissolve in water, so that the viscosity of the ink is increased and ejection may be affected. Even when the acid value is larger than 400 mgKOH / g, the interaction between the resins may be strengthened and the viscosity of the ink may be increased. From such a viewpoint, the acid value of the pigment-dispersed resin is more preferably 100 to 350 mgKOH / g, and further preferably 150 to 300 mgKOH / g.

The weight average molecular weight of the pigment-dispersed resin is preferably 5,000 to 100,000. By adjusting the molecular weight to 5000 or more, excellent dispersion stability can be easily obtained. Moreover, the influence on discharge can be easily suppressed by making the said molecular weight 100000 or less. More preferably, the molecular weight is 10,000 to 50,000, and still more preferably the molecular weight is 15,000 to 30,000.

The pigment dispersion resin preferably has an aromatic group. By introducing the aromatic group into the polymer, it becomes easy to enhance the pigment dispersibility and improve the dispersion stability and gloss. Examples of the aromatic group include phenyl group, naphthyl group, anthryl group, tolyl group, xylyl group, mesityl group, anisyl group and the like. Especially, it is preferable that the said aromatic group is a phenyl group or a tolyl group. More specifically, the pigment dispersion resin is preferably an acrylic resin having an aromatic group, and is referred to as “styrene acrylic resin” in the present specification. "Styrene acrylic resin" means a polymer containing a structural unit obtained by polymerizing styrene and / or a styrene derivative and (meth) acrylic acid and / or (meth) acrylic ester. Examples of the styrene derivative include methyl styrene and vinyl naphthalene.

Although it does not specifically limit, in preferable embodiment of this invention, pigment dispersion resin is (i) (meth) acrylic acid, (ii) (meth) acrylic acid ester which has a C8 or more alkyl group, Furthermore, if necessary, (iii) a copolymer obtained by polymerizing a polymerizable monomer compound having an aromatic group. In one embodiment, the blending ratio of each monomer component constituting the copolymer is 10 to 50% by weight, preferably 20 to 40% by weight, (ii) based on the total amount of all monomer components. Is 10 to 70% by weight, preferably 20 to 50% by weight, and (iii) is 0 to 50% by weight, preferably 10 to 40% by weight.

In the pigment dispersion resin used in the present invention, it is preferable that acid groups in the dispersion resin are neutralized with a base in order to improve the solubility in water. Examples of the base include organic bases such as dimethylaminoethanol, diethanolamine, and triethanolamine, and inorganic bases such as aqueous ammonia, lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, the use of an organic base is preferable because the base volatilizes when the ink is dried and the water resistance of the printed matter tends to be improved.

The weight ratio of the pigment to the pigment dispersion resin is preferably 2/1 or more and 100/1 or less. When the weight ratio of the pigment dispersion resin is 2/1 or more, it is easy to keep the ink viscosity low. Further, when it is 100/1 or less, the dispersion stability is improved, and it is easy to improve the stability of the ink. The weight ratio of the pigment to the pigment dispersion resin is more preferably 4/1 to 50/1, further preferably 5/1 to 25/1, and most preferably 10/1 to 20/1.

(Binder resin)
The water-based ink of the present invention may further contain a binder resin with respect to the ink in order to increase the resistance of the printed matter. As binder resins for water-based inks, water-soluble resins and resin fine particles are generally classified. In general, the resin fine particles have a higher molecular weight than the water-soluble resin, and can achieve high resistance. Further, the resin fine particles can reduce the viscosity of the ink and can be blended in a large amount in the ink, so that it is suitable for increasing the resistance of the printed matter. Examples of the resin fine particles include acrylic resin, urethane resin, styrene butadiene resin, vinyl chloride resin, and polyolefin resin. In consideration of the stability of the ink and the durability of the printed matter, it is preferable to use resin fine particles of an acrylic resin.

By increasing the glass transition temperature (Tg) of the binder resin, it is easy to improve resistance such as abrasion resistance and chemical resistance. Therefore, Tg of binder resin becomes like this. Preferably it is 50-120 degreeC, More preferably, it is good to set it as the range of 80-100 degreeC. When Tg is higher than 50 ° C., sufficient resistance is obtained, and it is easy to suppress a problem that an ink coating film is peeled off from a printed matter in practical use. Moreover, when Tg is lower than 120 ° C., the coating film is hard to be hard, and it is easy to suppress problems such as cracks and cracks on the printed surface when the printed material is bent.

The content of the binder resin in the ink is in the range of 2% by weight to 30% by weight, preferably in the range of 3% by weight to 20% by weight, based on the total weight of the ink. More preferably, it is in the range of 6 wt% to 15 wt%.

(Solid content)
The solid content in the ink is preferably 5% by weight or more and 20% by weight or less based on the total amount of the ink. When the content is less than 20% by weight, it is possible to suppress irregularities derived from dots due to ink jet printing on the printed matter, and it is easy to improve image quality. The content is preferably 8% by weight or more and 18% by weight or less, more preferably 10% by weight or more and 15% by weight or less.

In the present invention, the ratio of the solid content (W1) of the dark color ink to the solid content (W2) of the light color ink is preferably 7:10 to 10: 7. When there is a large difference in the solid content of the dark color ink and the light color ink, unevenness may occur on the printed matter, resulting in a decrease in gloss. Within the above range, it is easy to obtain high gloss. More preferably, it is 8: 10-10: 8, More preferably, it is 8.5: 10-10: 8.5, Most preferably, it is 9: 10-10: 9.

The solid content in the ink can be measured as follows. About 1 to 3 g of ink is weighed into a glass petri dish and dried in an oven at 180 ° C. for 30 minutes. The weight after drying is measured, and the ratio in the ink is determined from the weight before and after drying, using this as the solid content.

(Surfactant)
In the present invention, it is also possible to add a surfactant to the ink. By using a surfactant, high wettability can be exhibited and a good quality image can be obtained.

As the surfactant, a silicon-based surfactant, an acetylene-based surfactant, a fluorine-based surfactant, a glycol ether-based surfactant, or the like can be used. Of these, silicon surfactants and acetylene surfactants are preferably used, and silicon surfactants are more preferable.

As the silicon surfactant, it is preferable to use compounds represented by general formulas 1 to 3. A compound represented by general formula 2 or 3 is more preferable, and a compound represented by general formula 2 is still more preferable. The content of the surfactant in the ink is preferably from 0.1% by weight to 5% by weight, more preferably from 0.5% by weight to 3% by weight, still more preferably from 0.8% by weight to 2%. % By weight or less, and most preferably 1% by weight or more and 1.5% by weight or less.

（式中ａは１〜５００の整数、ｂは０〜１０の整数。Ｒ１はアルキル基、またはアリール基を示す。Ｒ２は下記（Ａ）、（Ｂ）、（Ｃ）、（Ｄ）の内の何れかの置換基で示され、Ｒ２の内、少なくとも一つは（Ａ）を含む。） [General Formula 1]

(In the formula, a is an integer of 1 to 500, b is an integer of 0 to 10. R1 represents an alkyl group or an aryl group. R2 represents the following (A), (B), (C), (D) And at least one of R2 includes (A).)

（ｃは１〜２０の整数であり、ｄは０〜５０の整数であり、ｅは０〜５０の整数である。Ｒ３は水素原子またはアルキル基を示し、Ｒ４は水素原子、アルキル基、アシル基の何れかを示す。） (A)

(C is an integer of 1-20, d is an integer of 0-50, e is an integer of 0-50. R3 represents a hydrogen atom or an alkyl group, R4 represents a hydrogen atom, an alkyl group, an acyl. Indicates any of the groups.)

（ｆは２〜２０の整数である。Ｒ５は水素原子、アルキル基、アシル基、ジメチルプロピル骨格を有するエーテル基の何れかを示す。） (B)

(F is an integer of 2 to 20. R5 represents any of a hydrogen atom, an alkyl group, an acyl group, and an ether group having a dimethylpropyl skeleton.)

（ｇは２〜６の整数であり、ｈは０〜２０の整数であり、ｉは１〜５０の整数であり、ｊは０〜１０の整数であり、ｋは０〜１０の整数である。Ｒ６は水素原子、アルキル基、アシル基の何れかを示す。） (C)

(G is an integer of 2-6, h is an integer of 0-20, i is an integer of 1-50, j is an integer of 0-10, k is an integer of 0-10. R6 represents a hydrogen atom, an alkyl group, or an acyl group.)

(D)
An alkyl group or an aryl group.

Examples of commercially available compounds represented by the general formula 1 include Tegotwin 4000 and Tegotwin 4100 manufactured by Evonik Degussa.

（式中ｌは１０〜８０の整数を示す。Ｒ７は下記（Ｅ）の置換基で示される。） [General formula 2]

(In the formula, l represents an integer of 10 to 80. R7 is represented by the substituent (E) below.)

（ｍは１〜６の整数、ｎは０〜５０の整数、ｏは０〜５０の整数であり、ｎ＋ｏは１以上の整数で示される。Ｒ８は水素原子または炭素数１〜６のアルキル基、または（メタ）アクリル基である。） (E)

(M is an integer of 1 to 6, n is an integer of 0 to 50, o is an integer of 0 to 50, and n + o is an integer of 1 or more. R8 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Or (meth) acrylic group.)

Examples of commercially available compounds represented by the general formula 2 include BY16-201, SF8427 manufactured by Toray Dow Corning, BYK-331, BYK-333, BYK-UV3500 manufactured by BYK Chemie, and Evonik Degussa Examples include Tegoglide 410, Tegoglide 432, Tegoglide 435, Tegoglide 440, and Tegoglide 450.

（ｐおよびｑは１以上の整数であり、ｐ＋ｑは３〜５０の整数で示される。Ｒ９は下記（Ｅ）の置換基で示され、Ｒ１０は炭素数１〜６のアルキル基で示される。） [General formula 3]

(P and q are integers of 1 or more, and p + q is an integer of 3 to 50. R9 is represented by the substituent (E) below, and R10 is an alkyl group having 1 to 6 carbon atoms. )

（ｒは１〜６の整数、ｓは０〜５０の整数、ｔは０〜５０の整数であり、ｓ＋ｔは１以上の整数で示される。Ｒ１１は水素原子または炭素数１〜６のアルキル基、または（メタ）アクリル基である。） (F)

(R is an integer of 1 to 6, s is an integer of 0 to 50, t is an integer of 0 to 50, and s + t is an integer of 1 or more. R11 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Or (meth) acrylic group.)

Examples of commercially available compounds represented by general formula 3 include SF8428, FZ-2162, 8032ADDITIVE, SH3749, FZ-77, L-7001, L-7002, FZ-2104, FZ manufactured by Toray Dow Corning. -2110, F-2123, SH8400, SH3773M, BYK-345, BYK-346, BYK-347, BYK-348, BYK-349, manufactured by Big Chemie, Tegowet 250, Tegowet 260, Tegowet 270, Tegowet 280, manufactured by Evonik Degussa Examples thereof include KF-351A, KF-352A, KF-353, KF-354L, KF355A, KF-615A, KF-640, KF-642, KF-643 and the like manufactured by Kogyo.

As the acetylene surfactant, it is preferable to use a compound represented by the general formula 4. Examples of commercially available compounds represented by the general formula 4 include Surfinol 104, Surfinol 420, Surfinol 440, Surfinol 465, Surfinol 485 and the like manufactured by Air Products.

（式中ｕおよびｖはそれぞれ独立に０〜５０の整数を示す。） [General formula 4]

(In the formula, u and v each independently represent an integer of 0 to 50.)

(water)
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% by weight to 90% by weight, more preferably in the range of 40% by weight to 85% by weight, and more preferably 60% by weight to 80% by weight. % Or less is more preferable.

(Other ingredients)
In addition to the above components, the ink of the present invention may be appropriately added with additives such as antifoaming agents, thickeners, pH adjusters, preservatives, etc., in order to obtain inks having desired physical properties as required. Can do. The additive amount of these additives 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 weight of the ink. 3% by weight or less.

(Ink viscosity)
The ink of the present invention preferably has a viscosity of 1 to 20 mPa · s. If it is this range, it becomes easy to maintain the favorable discharge property from an inkjet head. More preferably, it is 2-15 mPa * s, More preferably, it is 3-12 mPa * s. Further, the viscosity difference between the dark color ink and the light color ink needs to be within 3.5 mPa · s. When the viscosity between inks is greatly different, a difference occurs in the amount of ejected droplets. Due to the difference in the appropriate amount of liquid, the dot diameter becomes non-uniform, causing problems such as generation of graininess and disturbance of color balance. If the viscosity difference is within 3.5 mPa · s, a good image can be obtained. More preferably, it is 2 mPa * s or less, More preferably, it is 1 mPa * s or less, Most preferably, it is 0.5 mPa * s or less.

(Ink set)
The hue of the ink set of the present invention is not particularly limited as long as it is a dark ink and a light color ink set that have the same hue but different color densities. It is preferable to apply to inks having a hue of magenta and black. That is, it is preferably applied to a set of cyan ink and light cyan ink, a set of magenta ink and light magenta ink, and a set of black ink and light black (gray) ink.

Moreover, it can also be set as the set which combined the ink of several hue. For example, a six-color ink set of cyan ink, light cyan ink, magenta ink, light magenta ink, yellow ink, and black ink. A 7-color ink set with light black (gray) ink added. Further, as a special color, it is possible to make a set in which inks such as red, green, blue, orange, violet, and white are combined.

When the ink set of the present invention is used as an ink set containing a combination of cyan, light cyan, magenta, light magenta and yellow, examples of preferable pigments are as follows. As cyan and light cyan pigments, C.I. I. Pigment Blue 15: 3, 15: 4. As magenta and light magenta pigments, C.I. I. Pigment Red 122, 150, 202, 209, 269, C.I. I. Pigment Violet 19. As a yellow pigment, C.I. I. Pigment Yellow 74, 120, 150, 155, 185. By using a combination of pigments selected from these, high color reproducibility can be easily obtained.

(Printing method)
In the ink set of the present invention, prior to the printing step, a high-quality printed matter can be obtained by directly printing on the printing medium without providing a functional layer such as an ink receiving layer on the printing medium in advance. It is preferable to carry out the printing process while heating the printing medium to room temperature or higher. The heating is preferably in the range of 40 to 80 ° C, more preferably 45 to 70 ° C, and still more preferably 50 to 60 ° C. By performing heating at a temperature of 40 ° C. or higher, the printing surface dries immediately after the ink droplets of the water-based ink land on the print medium, so it is easy to suppress the occurrence of bleeding between ink colors. can do. Furthermore, by suppressing bleeding, it becomes easy to obtain a higher quality printed matter. Further, by performing the heating at a temperature of 80 ° C. or less, the inkjet head is also heated, and it becomes easy to suppress the problem that the ink around the nozzle is dried and cannot be ejected.

The print medium is not particularly limited, and a known print medium representative in the art can be used. Examples thereof include paper media such as high-quality paper, coated paper, art paper, cast paper, synthetic paper, and ink jet dedicated paper. Moreover, plastic media, such as a polyvinyl chloride sheet, PET film, and PP film, are mentioned. The surface of these print media may be smooth or may have irregularities formed thereon. The print medium may be transparent, translucent, or opaque. Furthermore, the shape of the print medium is not particularly limited, and may be a sheet-shaped substrate or a plate-shaped substrate. The print media may be used alone or two or more print media may be bonded to each other. A functional layer such as an adhesive layer whose surface is protected by a release sheet or the like may be provided on the opposite side of the printing surface with respect to the printing medium. Or you may provide functional layers, such as the said adhesion layer, in the printing surface of the said printing medium after printing.

The present invention is particularly suitable for printing on coated paper such as coated paper, art paper, and cast paper, and on plastic media such as polyvinyl chloride sheets, PET films, and PP films. Such a print medium has lower water absorption than a general paper medium. Therefore, when printing is performed using such a conventional water-based ink on a print medium having low water absorption, image bleeding often occurs. However, according to the present invention, it is possible to easily obtain a quality printed matter by suppressing bleeding of the image. That is, according to the present invention, a water-based inkjet ink having excellent printability for various print media is provided. Therefore, a high-quality printed material can be printed on various print media without limiting the print media. Can be easily formed.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In the following description, “parts” and “%” represent “parts by weight” and “% by weight”, respectively, unless otherwise specified.

(Example of production of pigment dispersion resin A)
A reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer was charged with 93.4 parts of butanol and replaced with nitrogen gas. The reaction vessel was heated to 110 ° C., and a mixture of 70 parts of 2-ethylhexyl methacrylate as a polymerization monomer, 30 parts of acrylic acid, and 6 parts of V-601 (manufactured by Wako Pure Chemical Industries) as a polymerization initiator was taken over 2 hours. The solution was added dropwise to carry out a polymerization reaction. After completion of the dropwise addition, the mixture was further reacted at 110 ° C. for 3 hours, and then 0.6 part of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added and the reaction was further continued at 110 ° C. for 1 hour to obtain a dispersion resin A solution. It was. Further, after cooling to room temperature, 37.1 parts of dimethylaminoethanol was added for neutralization, and 100 parts of water was added to make it aqueous. Then, it heated to 100 degreeC or more, butanol was azeotroped with water, butanol was distilled off, and it adjusted so that solid content might be 50%. As a result, an aqueous solution having a solid content of 50% of the pigment dispersion resin A was obtained.

(Example of production of pigment dispersion resins B to D)
A water-soluble solution having a solid content of 50% in the pigment dispersion resins B to D was obtained in the same manner as the pigment dispersion resin A except that the monomers listed in Table 1 were used as the polymerization monomers.

Abbreviations listed in Table 1 are as follows.
2EHMA: 2-ethylhexyl methacrylate LMA: lauryl methacrylate VA: behenyl acrylate St: styrene AA: acrylic acid

(Example of production of pigment dispersion A)
20 parts of Pigment Blue 15: 3 as a pigment, 12 parts of an aqueous solution of Pigment Dispersing Resin A, and 68 parts of water were mixed, predispersed with a disper, and then filled with 1800 g of zirconia beads having a diameter of 0.5 mm. This dispersion was performed for 2 hours using a 6 L dyno mill to obtain pigment dispersion A.

(Examples of production of pigment dispersions B to D)
Pigment dispersions B to D were obtained in the same manner as in the pigment dispersion A except that the pigment dispersion resins B to D were used as the pigment dispersion resins.

(Production example of dark ink 1)
15 parts of pigment dispersion A, 8 parts of 1,2-hexanediol, 20 parts of a dispersion of resin fine particles (solid content 40%, resin Tg 80 ° C.), activator (silicon-based activator TegoGlide 440 manufactured by Evonik Degussa) The remaining ink was adjusted to 5 parts with water as 100 parts, and this was stirred with a disper until it was sufficiently uniform. Thereafter, filtration with a membrane filter was performed to remove coarse particles that would cause clogging of the head, and dark ink 1 was prepared. When the viscosity of the ink prepared was 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, the viscosity of the dark ink 1 was 2.1 mPa · s. there were.

(Production examples of dark inks 2 to 14 and light inks 1 to 16)
Using the raw materials described in Tables 2 and 3, inks were prepared in the same manner as in the dark ink 1 production example.

Abbreviations listed in Tables 2 and 3 are as follows.
HexD: 1,2-hexanediol BDG: diethylene glycol monobutyl ether EtOH: ethanol MP: propylene glycol monomethyl ether MB: methoxybutanol BuD: 1,2-butanediol resin fine particles: acrylic emulsion (solid content 40%, resin Tg 80 ° C.)
Activator: TegoGlide 440 (manufactured by Eponic Degussa, silicon-based activator)

Example 1
The prepared dark color ink 1 and light color ink 2 were filled into a VersaCAMM VS-540 (an ink jet printer manufactured by Roland DG) as an ink set, and printing was performed. Printing was performed using a polyvinyl chloride sheet as a print medium while heating the print medium to 40 ° C. Various characteristics were evaluated as follows with respect to the used ink, printing conditions, and the obtained printed matter. The evaluation results are shown in Table 4.

(Dischargeability)
Solid printing with a printing width of 1 m was performed with the printer, and a nozzle check pattern was printed for each printing length of 1 m for both dark and light inks, and the number of missing nozzles was counted, and the number was evaluated.
A: Printing length 5 m, no nozzle missing B: Printing length 2-4 m, no nozzle missing C: Printing length 1 m, nozzle missing 10 or less D: Printing length 1 m, nozzle missing 11 or more

(Droplet amount)
An appropriate amount of liquid per droplet was calculated by discharging and measuring 100,000 ink drops of each nozzle as dark ink and light ink using the printer. Evaluation was carried out by the difference in the appropriate amount of liquid between the dark color ink and the light color ink.
A: The difference between the appropriate amount of the dark ink and the light ink is less than 0.3 pL. B: The difference between the appropriate amount of the dark ink and the light ink is 0.3 pL or more and less than 0.6 pL. C: The liquid of the dark ink and the light ink. Appropriate amount difference is 0.6 pL or more and less than 1 pL D: Difference in appropriate amount of liquid between dark ink and light color ink is 1 pL or more

(Drying)
The number of printing passes was changed with the printer, and a gradation pattern was printed in 5% increments up to a printing rate of 5 to 100%. The occurrence of mottling in each printed material was observed, and the drying property was evaluated.
A: Mottling does not occur when printing is performed with 4 printing passes B: Mottling does not occur when printing is performed with 8 printing passes C: Motting when printing is performed with 16 printing passes Ring does not occur D: Mottling does not occur when printing with 32 printing passes E: Mottling occurs even when printing with 32 printing passes

(Image reproducibility)
The printer evaluated the image by printing a pattern in which a line with dark ink and a line with light ink intersect, and a gradation pattern in 5% increments up to a printing rate of 5 to 100%. For the intersection pattern, bleeding between colors at the intersection was evaluated, and for the gradation pattern, gradation reproducibility was evaluated.
A: No blur and gradation is reproduced smoothly B: Blot is slightly observed but gradation is reproduced smoothly C: Slight blur is observed and the gradation is slightly crushed D: Bleeding was observed and the gradation was crushed. E: Bleeding was significant and the gradation was brilliant.

(Storage stability)
The evaluation ink was stored in a thermostat at 70 ° C. and accelerated over time, and then the viscosity of the ink was measured. The viscosity change rate was determined by calculation from the viscosity of the ink before and after aging, and evaluation was performed using dark inks and light color inks having a large viscosity change rate.
A: Viscosity change rate after storage for two weeks is less than ± 10% B: Viscosity change rate after storage for one week is less than ± 10% C: Viscosity change rate after storage for one week is ± 10% or more and less than ± 20% D : Viscosity change rate after storage for 1 week ± 20% or more

(Glossy)
Evaluation was made by measuring the 60 ° gloss of the printed material under conditions where mottling did not occur in the drying evaluation. Note that the gloss is not evaluated when mottling occurs even when the number of printing passes is 32 in the dryness evaluation (evaluation E).
A: Glossiness of 70 or more B: Glossiness of 50 or more and less than 70 C: Glossiness of 30 or more and less than 50 D: Glossiness of less than 30

(Examples 2-45, Comparative Examples 1-9)
As in Example 1, as shown in Table 4, a dark color ink and a light color ink were combined and evaluated as a set.

As shown in Table 4, in the examples, the solvent A is used for the dark ink, the solvent A and the solvent B are used for the light ink, and the viscosity difference between the dark ink and the light ink is 3.5 mPa · s or less. The evaluation of also shows a good result. In particular, in Examples where the difference in viscosity was small, the amount of droplets between the inks was equal, and a printed matter without graininess could be obtained. By adjusting the ratio of the content ratio of the solvent A between the inks, the wettability of the dark color ink and the light color ink was made uniform, and an improvement tendency of bleeding when the ink contacted was observed. Furthermore, by adjusting the content of the solvent B of the light-colored ink and the total content of the organic solvent of the light-colored ink and the dark-colored ink and making the drying property between the inks uniform, mottling can be suppressed. Moreover, the unevenness | corrugation on printed matter became small and the improvement in gloss was seen for the thing with a small difference of the solid content of dark color ink and light color ink.

When the dispersant was changed to one having a long alkyl chain, the dispersion stability was improved, whereby the fluidity of the ink was improved and the tendency to improve the ejection property was observed. Furthermore, when an aromatic ring group was further introduced into the dispersant, the gloss of the printed matter was improved.

On the other hand, in the comparative example, an ink set that satisfies all the characteristics is not obtained. In particular, when solvent B is not used in light-colored inks, there is a difference in drying properties between dark-colored inks and light-colored inks, resulting in problems such as mottling, blurring or gradations that cannot be reproduced smoothly. Could not get a good image.

As can be seen from the above results, the solvent A is used for the dark ink, the solvent A and the solvent B are used for the light ink, and the viscosity difference between the dark ink and the light ink is 3.5 mPa · s or less. An ink satisfying the properties at a high level could be obtained.

Claims (7)

A water-based inkjet ink set comprising a dark color ink and a light color ink having at least the same hue but different color densities,
Each ink includes at least a colorant, an organic solvent (A) having a boiling point of 200 ° C. or higher and 280 ° C. or lower and a surface tension of 20 mN / m or higher and 30 mN / m or lower, and water,
The light ink further includes a water-soluble organic solvent (B) having a boiling point of 50 ° C. or higher and 180 ° C. or lower,
An ink set for water-based inkjet, wherein the difference in viscosity at 25 ° C. between the dark color ink and the light color ink is 3.5 mPa · s or less. The content (SA1) of the organic solvent (A) having a boiling point of 200 to 280 ° C. and a surface tension of 20 to 30 mN / m, and a boiling point of 200 to 280 The ratio with respect to the content (SA2) of the organic solvent (A) having a surface tension of 20 mN / m or more and 30 mN / m or less is 6:10 to 10: 6. Water-based inkjet ink set The total content (ST2) of all organic solvents contained in the light-colored ink is 5 to 20% by weight greater than the total content (ST1) of all organic solvents contained in the dark-colored ink. 2. The ink set for water-based inkjet according to 2. The content (SB2) of the water-soluble organic solvent (B) having a boiling point of 50 ° C to 180 ° C contained in the light-colored ink is 5 to 20% by weight. Water-based inkjet ink set. The ratio of the solid content (W1) contained in the dark color ink to the solid content (W2) contained in the light color ink is 7:10 to 10: 7. Any one of the ink sets for water-based inkjets. 6. The dark color ink and the light color ink colorant are pigments dispersed by a pigment dispersion resin, and the pigment dispersion resin has an alkyl chain having 10 or more carbon atoms. Water-based inkjet ink set. The combination of dark ink and light color ink includes any combination of cyan ink and light cyan ink, magenta ink and light magenta ink, and black ink and light black (gray) ink. 6. The water-based inkjet ink set according to any one of 6.