JP2024060940A - Oil-based ink and method for producing oil-based ink - Google Patents

Abstract

To provide an oil-based ink that is less prone to degradation in viscosity stability against significant changes in storage temperature and offers superior transparency.SOLUTION: An oil-based ink comprises a colorant (A), a resin (B), an organic solvent (C), a nonionic dehydrant reaction product (D), and water. The moisture content in the oil-based ink is 0.5-15.0 mass%. There is also provided a method for producing the oil-based ink that comprises the colorant (A), the resin (B), the organic solvent (C), the nonionic dehydrant reaction product (D), and the water. This method includes a step of adding a nonionic dehydrant (d) to adjust the moisture content in the oil-based ink to be 0.5-15.0 mass%.SELECTED DRAWING: None

Description

The present invention relates to an oil-based ink and a method for producing the same.

Oil-based inks remain in high demand because they can be applied to a wide variety of resins and additives, and they have a high affinity for substrates that can be coated, including not only paper substrates such as fine paper and coated paper, but also various film substrates such as OPP film, PET film, and NY film, as well as metal substrates such as aluminum.

Patent Document 1 discloses an oil-based inkjet ink that is composed of at least a pigment, a dispersant, and an organic solvent, and contains a chemical dehydrating agent that is compatible with the organic solvent.

JP 2011-46759 A

On the other hand, one of the most recent characteristics required for oil-based inks is viscosity stability in harsh environments with fluctuating temperatures, as a risk hedge in case the ink storage cabinet breaks down. No oil-based ink that meets these latest needs has been considered. Furthermore, while oil-based inkjet inks that use conventional chemical dehydrating agents can capture very small amounts of moisture that get mixed in from the air and suppress the formation of deposits around the inkjet nozzle, the use of chemical dehydrating agents alone is not enough to improve color properties such as transparency.

The present invention aims to provide an oil-based ink that has good transparency and is less likely to lose viscosity stability even when the storage temperature changes significantly.

That is, the present invention includes the following embodiments, but the embodiments of the present invention are not limited to the following.
[1] An oil-based ink comprising a colorant (A), a resin (B), an organic solvent (C), a nonionic dehydrating agent reactant (D), and water, the water content being 0.5 to 15.0 mass% in the oil-based ink.
[2] The oil-based ink according to [1], wherein the nonionic dehydrating agent reactant (D) is a reaction product of water with at least one selected from the group consisting of an alkyl silicate and an alkyl silicate oligomer.
[3] The oil-based ink according to [1] or [2], wherein the content of the nonionic dehydrating agent reaction product (D) in the oil-based ink is 0.01 to 100 parts by mass per 100 parts by mass of the colorant (A).
[4] The oil-based ink according to any one of [1] to [3], which is used for plate printing.
[5] A method for producing an oil-based ink comprising a colorant (A), a resin (B), an organic solvent (C), a nonionic dehydrating agent reactant (D), and water, comprising:
A method for producing an oil-based ink, comprising the step of adding a nonionic dehydrating agent (d) to adjust the water content in the oil-based ink to 0.5 to 15.0 mass %.

The terms used in the present invention are defined below. "C.I." is the Color Index number. "(Meth)acrylate" is an acrylate and/or a methacrylate. A monomer is an ethylenically unsaturated group-containing compound before polymerization, and is also called a monomer. The monomer unit is incorporated into the resin after polymerization.
In this specification, the "nonionic dehydrating agent reactant (D)" and the "nonionic dehydrating agent (d)" may be referred to as the "dehydrating agent reactant (D)" and the "dehydrating agent (d)", respectively.
In addition, in this specification, a numerical range specified using "to" is intended to include the numerical values before and after "to" as the lower and upper limit values of the range.
Unless otherwise noted, the various components appearing in this specification may be used independently as a single type or as a mixture of two or more types.
The numerical values specified in this specification are values determined by the methods disclosed in the embodiments or examples.

<Oil-based ink>
The oil-based ink of the present invention comprises a colorant (A), a resin (B), an organic solvent (C), a nonionic dehydrating agent reactant (D), and water, and the water content in the oil-based ink is 0.5 to 15.0 mass %.
The water content in the oil-based ink is preferably 0.7 to 10% by mass. By setting the water content within the above range, an appropriate polarity is imparted to the oil-based ink, promoting the interaction between the nonionic dehydrating agent reactant (D) and the colorant (A), and the nonionic dehydrating agent reactant (D) is adsorbed onto the colorant particle surface, thereby making it possible to achieve good storage stability even in a harsh environment with fluctuating temperatures.
Because it is such an oil-based ink, the viscosity stability is not easily lost even if the storage temperature changes significantly, and the transparency is good.
It is speculated that the reason for these effects is that the non-ionic dehydrating agent reactant is adsorbed onto the surface of the colorant particles and functions as an anti-aggregation agent, thereby improving storage stability even in harsh environments where the storage temperature changes.

<Colorant (A)>
The colorant (A) is not particularly limited, and various pigments or dyes known in the art can be used. It is considered that the nonionic dehydrating agent reactant (D) is adsorbed on the surface of the colorant (A) to improve storage stability, so a colorant that is insoluble in the organic solvent (C) and forms particles is preferred. As such a colorant, a pigment is more preferred.

Pigments include, for example, C.I. Pigment Red 3, 5, 19, 22, 31, 38, 42, 43, 48:1, 48:2, 48:3, 48:4, 48:5, 49:1, 53:1, 57:1, 57:2, 58:4, 63:1, 81, 81:1, 81:2, 81:3, 81:4, 88, 104, 108, 112, 122, 123, 144, 146, 147, 149, 150, 166, 168, 169, 170, 176, 177, 178, 179, 184, 185, 202, 208, 216, 226, 242, 254, 255, 257, 269, 291;
C.I. Pigment Green 7, 26, 36, 50, 58, 59, 62, 63;
C.I. Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 17, 17:1, 22, 27, 28, 29, 36, 60;
C.I. Pigment Orange 13, 16, 20, 34, 36, 38, 43, 62, 64, 71, 73;
C.I. Pigment Yellow 1,3,12,13,14,17,34,35,37,55,74,81,83,93,94,95,97,108,109,110,120,128,129,137,138,139,150,153,154,155,157,166,167,168,174,180,185,193,213,234;
C.I. Pigment Violet 3,19,23,29,30,37,50,88;
C.I. Pigment Black 7, 28, 26, carbon nanotubes, carbon nanohorns, fullerenes;
C.I. Pigment White 6, 18, 21, etc.

Disperse dyes include, for example, C.I. Disperse Red 11, 50, 53, 54, 55, 55:1, 59, 60, 65, 70, 72, 73, 75, 86, 88, 91, 92, 93, 111, 126, 127, 134, 135, 143, 145, 146, 152, 153, 154, 158, 159, 164, 167:1, 177, 181, 190, 190:1, 204, 206, 207, 221, 239, 240, 258, 277, 278, 283, 311, 323, 343, 348, 356, 362;
C.I. Bat Red 41;
C. I. Disperse Green 6:1,9;
C.I. Disperse Blue 19,26,26:1,35,55,56,58,60,64,64:1,72,72:1,73,81,81:1,87,91,95,108,113,128,131,141,143,145,148,154,158,165,165:1,165:2,176,183,185,197,198,201,214,224,225,257,266,267,287,354,358,359,360,365,368;
C.I. Disperse Orange 1, 1:1, 5, 13, 20, 25, 25:1, 29, 31:1, 33, 49, 54, 55, 56, 66, 73, 76, 118, 119, 163;
C.I. Disperse Yellow 3,5,7,8,23,39,42,51,54,60,64,71,79,82,83,86,93,99,100,119,122,124,126,160,184:1,186,198,199,201,204,224,237;
C.I. Disperse Violet 8,17,23,27,28,29,33,36,57;
C.I. Disperse Brown 2; and the like.

Examples of water-soluble dyes include direct dyes, acid dyes, food dyes, basic dyes, and reactive dyes. For example, C.I. Direct Red 2, 4, 9, 23, 26, 31, 39, 62, 63, 72, 75, 76, 79, 80, 81, 83, 84, 89, 92, 95, 111, 173, 184, 207, 211, 212, 214, 218, 223, 224, 225, 226, 227, 232, 233, 240, 241, 242, 243, 247;
C.I. Direct Violet 7,9,47,48,51,66,90,93,94,95,98,100,101;
C.I. Direct Yellow 8,9,11,12,27,28,29,33,35,39,41,44,50,53,58,59,68,86,87,93,95,96,98,100,106,108,109,110,130,132,142,144,161,163;
C.I. Direct Blue 1,10,15,22,25,55,67,68,71,76,77,78,80,84,86,87,90,98,106,108,109,151,156,158,159,160,168,189,192,193,194,199,200,201,202,203,207,211,213,214,218,225,229,236,237,244,248,249,251,252,264,270,280,288,289,291;
C.I. Direct Black 9, 17, 19, 22, 32, 51, 56, 62, 69, 77, 80, 91, 94, 97, 108, 112, 113, 114, 117, 118, 121, 122, 125, 132, 146, 154, 166, 168, 173, 199
C.I. Acid Red 35, 42, 52, 57, 62, 80, 82, 111, 114, 118, 119, 127, 128, 131, 143, 151, 154, 158, 249, 254, 257, 261, 263, 266, 289, 299, 301, 305, 336, 337, 361, 396, 397;
C.I. Acid Violet 5,34,43,47,48,90,103,126;
C.I. Acid Yellow 17,19,23,25,39,40,42,44,49,50,61,64,76,79,110,127,135,143,151,159,169,174,190,195,196,197,199,218,219,222,227;
C.I. Acid Blue 9, 25, 40, 41, 62, 72, 76, 78, 80, 82, 92, 106, 112, 113, 120, 127: 1, 129, 138, 143, 175, 181, 205, 207, 220, 221, 230, 232, 247, 258, 260, 264, 271, 277, 278, 279, 280, 288, 290, 326
C. I. Acid Black 7, 24, 29, 48, 52: 1, 172;
C.I. Reactive Red 3, 13, 17, 19, 21, 22, 23, 24, 29, 35, 37, 40, 41, 43, 45, 49, 55;
C.I. Reactive Violet 1,3,4,5,6,7,8,9,16,17,22,23,24,26,27,33,34;
C.I. Reactive Yellow 2, 3, 13, 14, 15, 17, 18, 23, 24, 25, 26, 27, 29, 35, 37, 41, 42;
C.I. Reactive Blue 2,3,5,8,10,13,14,15,17,18,19,21,25,26,27,28,29,38;
C.I. Reactive Black 4, 5, 8, 14, 21, 23, 26, 31, 32, 34;
C.I. Basic Red 12,13,14,15,18,22,23,24,25,27,29,35,36,38,39,45,46;
C.I. Basic Violet 1,2,3,7,10,15,16,20,21,25,27,28,35,37,39,40,48;
C.I. Basic Yellow 1,2,4,11,13,14,15,19,21,23,24,25,28,29,32,36,39,40;
C.I. Basic Blue 1,3,5,7,9,22,26,41,45,46,47,54,57,60,62,65,66,69,71;
C.I. Basic Black 8; and the like.

The average primary particle diameter of the colorant (A) is preferably 10 to 1,000 nm, and more preferably 30 to 700 nm. This is preferable because an average primary particle diameter in the above range suppresses light scattering on the particle surface and improves transparency. The average primary particle diameter can be measured by observing 100 primary particles using a transmission electron microscope (TEM) and calculating the arithmetic average of the long diameters.

The content of colorant (A) in the oil-based ink is preferably 0.1 to 70% by mass, more preferably 0.5 to 60% by mass, and even more preferably 1 to 50% by mass, relative to 100% by mass of the oil-based ink. When the content of colorant (A) in the oil-based ink is within the above range, it is preferable because it can be used as a vivid coating film when applied to a substrate.

The colorant (A) may be in the form of a powder with a low moisture content, or in the form of a wet cake with a high moisture content.

<Resin (B)>
The resin (B) is not particularly limited, and various conventionally known resins can be used.
Examples of the resin include acrylic resin, methacrylic resin, urethane resin, urea resin, polyester resin, polyether resin, polyol resin, vinyl chloride resin, vinyl acetate resin, cellulose resin, olefin resin, chlorinated olefin resin, and a composite resin of two or more of these (for example, vinyl chloride-vinyl acetate resin).
Among these, from the viewpoint of transparency, acrylic resins, methacrylic resins, urethane resins, vinyl chloride resins, and composite resins of these are preferred.

The weight average molecular weight (Mw) of the resin (B) is preferably 3,000 to 100,000, and more preferably 10,000 to 70,000. The glass transition temperature (Tg) is preferably −50° C. to 300° C. The content of the resin (B) in the oil-based ink is preferably 0.1 to 50% by mass, more preferably 0.5 to 40% by mass, and even more preferably 1 to 30% by mass, relative to 100% by mass of the oil-based ink.
It is preferable that the weight average molecular weight, glass transition temperature, and content are within the above ranges, since the resistance of a coating film formed by applying the oil-based ink to a substrate is good.

When the resin (B) has an acid value, the acid value is preferably 1 to 300 mgKOH/g, more preferably 2 to 100 mgKOH/g. When the resin (B) has an amine value, the amine value is preferably 1 to 300 mgKOH/g, more preferably 2 to 100 mgKOH/g. When the resin (B) has a hydroxyl value, the hydroxyl value is preferably 1 to 100 mgKOH/g, more preferably 2 to 30 mgKOH/g.
When the acid value, amine value, or hydroxyl value is within these ranges, aggregation of the colorant (A) is suppressed due to charge repulsion, and storage stability is good even in harsh environments where the temperature fluctuates, which is preferable.

<Organic Solvent (C)>
The organic solvent (C) is not particularly limited, and various conventionally known organic solvents can be used.
For example, aromatic organic solvents such as toluene, xylene, naphthalene, and nitrobenzene;
Ketone-based organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone;
Ester-based organic solvents such as ethyl acetate, n-propyl acetate, butyl acetate, hexyl acetate, and propylene glycol monomethyl ether acetate;
Alcohol-based organic solvents such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and 1-hexanol;
Glycol ether solvents such as ethylene glycol monopropyl ether and propylene glycol monomethyl ether;
Aliphatic organic solvents such as methylcyclohexane;
etc.

The content of the organic solvent (C) in the oil-based ink is preferably from 10 to 95% by mass, more preferably from 20 to 90% by mass, and even more preferably from 30 to 80% by mass, relative to 100% by mass of the oil-based ink.
In addition, when there is an organic solvent produced as a by-product by reaction of the dehydrating agent (d) with water, this content is the total content including the organic solvent.

Among the organic solvents (C), organic solvents having a boiling point of 150° C. or less are preferred. By selecting such an organic solvent, it becomes possible to dry the coating on a substrate at a lower temperature, and this is preferable because it is possible to reduce the energy consumed in the drying process and thereby reduce CO ₂ emissions.

Examples of organic solvents with a boiling point of 150°C or less include toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, n-propyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol monopropyl ether, propylene glycol monomethyl ether, and methylcyclohexane.

<Non-ionic dehydrating agent reactant (D)>
The non-ionic dehydrating agent reactant (D) is the reaction product of a non-ionic dehydrating agent (d) with water.
Examples of the non-ionic dehydrating agent reactant (D) include silica compounds such as silicone polymers obtained by reacting alkyl silicates, alkyl silicate oligomers, chlorosilanes, trimethylsilane, or the like with water when the dehydrating agent (d) is used.

The content of the nonionic dehydrating agent reactant (D) in the oil-based ink is preferably 0.01 to 100 parts by mass, more preferably 0.1 to 50 parts by mass, and even more preferably 1 to 30 parts by mass, relative to 100 parts by mass of the colorant (A). Within the above range, the nonionic dehydrating agent reactant (D) can prevent secondary aggregation without impairing the hue of the colorant (A), and transparency is further improved, which is preferable. The content of the nonionic dehydrating agent reactant (D) is a theoretical value when it is assumed that the entire amount of the dehydrating agent (d) has reacted.
In addition, when an organic solvent is by-produced by reaction of the nonionic dehydrating agent (d) with water, the organic solvent is treated as the organic solvent (C) and is not included in the content of the nonionic dehydrating agent reactant (D).

(Dehydrating Agent (d))
The dehydrating agent (d) is a non-ionic dehydrating agent. Examples of the dehydrating agent (d) include compounds having a silicon atom, such as alkyl silicates, alkyl silicate oligomers, chlorosilanes, and trimethylsilane.
The dehydrating agent (d) is a compound that chemically reacts with water, and does not include molecular sieves, activated carbon, or other substances that do not chemically react with water but physically adsorb and remove water.
The dehydrating agent (d) may be used alone or in combination of two or more kinds.

[Alkyl silicate]
The alkyl silicate may be a compound represented by the following general formula (1).

General formula (1)


(In general formula (1), n represents an integer of 1 to 4.)

Examples of such compounds include methyl silicate, ethyl silicate, propyl silicate, and butyl silicate.
An example of such a commercially available product is Ethyl Silicate 28 (Ethyl Silicate) manufactured by Colcoat Co., Ltd.

[Alkyl silicate oligomer]
The alkyl silicate oligomer may be a compound represented by the following general formula (2).

General formula (2)

(In general formula (2), n represents an integer of 1 to 4, and m represents an integer of 2 to 100.)

Examples of such compounds include methyl silicate oligomer, ethyl silicate oligomer, propyl silicate oligomer, and butyl silicate oligomer.
Examples of such commercially available products include methyl silicate 51 (n=1, average m value: 4), methyl silicate 53A (n=1, average m value: 7), ethyl silicate 40 (n=2, average m value: 5), and ethyl silicate 48 (n=2, average m value: 10), all of which are manufactured by Colcoat Co., Ltd.

[Chlorosilanes]
Examples of chlorosilanes include chlorosilane, dichlorosilane, trichlorosilane, chlorodimethylsilane, chlorodiethylsilane, dichloromethylsilane, and dichloroethylsilane.

<Water>
The water may be ordinary tap water, but is preferably ion-exchanged water, distilled water, or purified water. The total amount of metal ions contained in the water is preferably 10 ppm or less, more preferably 1 ppm or less, and even more preferably 100 ppb or less. In particular, when the resin (B) has an acid group such as a carboxy group, divalent metal ions such as calcium and magnesium react with two acid groups to crosslink the resins, so it is preferable to suppress them as much as possible. This improves the storage stability of the oil-based ink.

The water content in the oil-based ink is 0.5 to 15% by mass relative to 100% by mass of the oil-based ink. It is preferably 0.7 to 10% by mass, more preferably 1 to 7% by mass, and most preferably 2 to 5% by mass. By keeping the water content within the above range, the oil-based ink is given an appropriate polarity, promoting the interaction with the non-ionic dehydrating agent reactant (D) and colorant (A), and the non-ionic dehydrating agent reactant (D) is adsorbed to the surface of the colorant particles, thereby achieving good storage stability even in harsh environments with fluctuating temperatures.

<Other additives>
It is preferable to use other additives such as known additives in the oil-based ink of the present invention. Examples of the additives that can be used include dye derivatives, wetting agents, adhesion aids, leveling agents, defoaming agents, antistatic agents, trapping agents, antiblocking agents, wax components, isocyanate-based curing agents, and silane coupling agents.

[Dye derivatives]
The dye derivative is a compound having an acidic group, a basic group, a neutral group, etc. in an organic dye residue. Examples of the dye derivative include compounds having an acidic substituent such as a sulfo group, a carboxy group, or a phosphate group, and amine salts thereof, compounds having a basic substituent such as a sulfonamide group or a tertiary amino group at the terminal, and compounds having a neutral substituent such as a phenyl group or a phthalimidoalkyl group.
Examples of organic pigments include diketopyrrolopyrrole pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, perinone pigments, perylene pigments, thiazine indigo pigments, triazine pigments, benzimidazolone pigments, indole pigments such as benzoisoindole, isoindoline pigments, isoindolinone pigments, quinophthalone pigments, naphthol pigments, threne pigments, metal complex pigments, azo pigments such as azo, disazo, and polyazo, and the like.

<Manufacture of oil-based ink>
The method for producing the oil-based ink is not particularly limited, but in general, the colorant (A), resin (B), organic solvent (C), dehydrating agent (d), and, if necessary, water, etc. are mixed simultaneously or sequentially, and dispersed using a dispersing machine such as a bead mill, to produce an oil-based ink containing the colorant (A), resin (B), organic solvent (C), nonionic dehydrating agent reactant (D), and water, and having a water content of 0.5 to 15.0 mass % in the oil-based ink.

The method for obtaining the nonionic dehydrating agent reactant (D) is not particularly limited, and examples thereof include a method in which a dehydrating agent (d) and water are mixed in advance, the water and the dehydrating agent (d) are reacted to obtain a nonionic dehydrating agent reactant (D), and then the nonionic dehydrating agent reactant (D) is added to an oil-based ink, and a method in which a dehydrating agent (d) is added to an oil-based ink containing water, and the water and the dehydrating agent (d) are reacted to obtain a nonionic dehydrating agent reactant (D).
In particular, the method of adding a dehydrating agent (d) to an oil-based ink containing water is preferred because a nonionic dehydrating agent reactant (D) is easily generated and adsorbed onto the particle surface of the colorant (A), thereby suppressing aggregation of the colorant (A) particles and ensuring good transparency even when stored in a harsh environment where the storage temperature fluctuates.

The method of reacting water with the dehydrating agent (d) is not particularly limited, but can be selected appropriately depending on the dehydrating agent (d) used. For example, alkyl silicates and alkyl silicate oligomers react easily with water, so it is preferable to mix them in the range of -20°C to 50°C.

The dehydrating agent (d) may be added all at once, or may be added in small portions in separate additions, or may be added in small portions intermittently. Because there is a possibility of an explosive reaction between water and the dehydrating agent (d), it is preferable to add the dehydrating agent (d) in small portions in separate additions, or to add the dehydrating agent (d) in small portions intermittently.

The amount of the dehydrating agent (d) added is preferably 0.1 to 500 parts by mass, more preferably 1 to 300 parts by mass, and even more preferably 3 to 200 parts by mass, relative to 100 parts by mass of the colorant (A). By setting the amount of the dehydrating agent (d) added within the above range, the particles of the colorant (A) can be coated with the nonionic dehydrating agent reaction product (d), and the storage stability becomes good even in a harsh environment where the temperature fluctuates, which is preferable.
At this time, in order to react the entire amount of the dehydrating agent (d), the number of moles of the dehydrating agent (d) must be less than the number of moles of water contained in the oil-based ink.

The oil-based ink of the present invention is preferably produced in the following order of steps (I) and (II).
This manufacturing method is preferable because it allows the dehydrating agent (d) to more efficiently cover the particle surfaces of the colorant (A), resulting in good transparency.
Step (I): A step of obtaining a colorant mixture from a colorant (A) and at least one of a resin (B) and an organic solvent (C).
Step (II): adding a dehydrating agent (d) to the colorant mixture obtained in step (I), and reacting the water and the dehydrating agent (d) to form a non-ionic dehydrating agent reactant (D), comprising a colorant (A), a resin (B), an organic solvent (C), the non-ionic dehydrating agent reactant (D), and water;
A process for producing an oil-based ink having a moisture content of 0.5 to 15.0% by mass in the oil-based ink.

[Step (I)]
Step (I) is a step of obtaining a colorant mixture from a colorant (A) and at least one of a resin (B) and an organic solvent (C).

The method for mixing the colorant (A) with the resin (B) or the organic solvent (C) is not particularly limited, and examples thereof include a method in which the colorant (A) and the resin (B) or the organic solvent (C) are added and mixed with a stirring blade, a method in which the colorant (A) and the resin (B) or the organic solvent (C) are mixed with a beads disperser filled with beads such as zirconia beads, water is then added, and the mixture is mixed with a stirring blade or a beads disperser.
Also included is a method in which a resin (B) or an organic solvent (C) is added to a wet cake containing a colorant (A) and water, and the mixture is kneaded using a kneader such as a kneader or a flasher (so-called flushing method).

In particular, in the case of the flushing method, the use of a wet cake containing colorant (A) and water reduces the aggregation between colorant particles, and by adding resin (B) and organic solvent (C) to this, not only can the colorant (A) be transferred from the water phase to the organic solvent phase (oil phase) while reducing the aggregation, but an appropriate amount of water can also be left in the system.

The water content in the colorant mixture is preferably 1 to 20% by mass, and more preferably 3 to 15% by mass. This range is preferable because it increases the polarity of the solvent contained in the mixture, localizes the nonionic dehydrating agent reactant (D) generated in the second step described below on the particle surface of the colorant (A), and provides good storage stability even in harsh environments with fluctuating temperatures.

It is preferable that the water content of the colorant mixture, which is a combination of the components other than the dehydrating agent (d), the colorant (A), the resin (B), the organic solvent (C), and water in the final oil-based ink, is 1 to 20 mass %.
Adding a dehydrating agent (d) to this colorant mixture and adjusting the water content in the final oil-based ink to 0.5 to 15.0 mass % is preferable because it allows the nonionic dehydrating agent (D) to more efficiently cover the particle surfaces of the colorant (A), resulting in good transparency.

[Step (II)]
Step (II) is a step of adding a dehydrating agent (d) to the colorant mixture obtained in step (I) to react the water with the dehydrating agent (d) to form a nonionic dehydrating agent reactant (D), thereby producing an oil-based ink that contains the colorant (A), the resin (B), the organic solvent (C), the nonionic dehydrating agent reactant (D), and water, and has a water content of 0.5 to 15.0 mass % in the oil-based ink.

The colorant mixture obtained in step (I) can be further mixed with resin (B), organic solvent (C) or water to produce an oil-based ink.

The oil-based ink of the present invention can be suitably used in lithographic printing such as offset printing, letterpress printing such as flexographic printing, intaglio printing such as gravure printing, stencil printing such as silk screen printing, on-demand printing such as inkjet printing and toner printing, paints, writing implements, color filters, solid-state imaging devices, sensors such as LiDAR, and the like. Among these, plate printing applications such as lithographic printing, letterpress printing, intaglio printing, and stencil printing are preferred. The inclusion of a nonionic dehydrating agent reactant (D) in the oil-based ink is preferred because it makes it difficult for the oil-based ink to remain on the plate, allowing the formation of a good image.

The oil-based ink of the present invention can be used by printing or coating on various conventionally known substrates.
Examples of the substrate include highly water-absorbent substrates such as plain paper, fabric, and knitted fabric, low water-absorbent substrates such as art paper, coated paper, vinyl chloride, wood, concrete, eggshells, tablets, food, polyethylene film, polypropylene film, and polyethylene terephthalate film, and non-water-absorbent substrates such as metals (aluminum, stainless steel, etc.) and glass. The substrate surface may be smooth or may have irregularities. The substrate shape may be flat or curved.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means parts by mass, and "%" means % by mass. In addition, NV means nonvolatile content.

The abbreviations in the examples have the following meanings.
<Colorant (A)>
PB15:3:C. I. Pigment Blue 15:3
PY14: C. I. Pigment Yellow 14
PR122:C. I. Pigment Red 122
PG7: C. I. Pigment Green 7
PO34: C. I. Pigment Orange 34
<Resin (B)>
Joncryl 693: Styrene acrylic resin manufactured by BASF <Organic solvent (C)>
NPAC: n-propyl acetate IPA: isopropyl alcohol

(Moisture content measurement method)
The amount of water (mg) was measured using a Karl Fischer titrator (volumetric water content measuring device KF-06, manufactured by Mitsubishi Chemical Corporation), and the water content (mass%) in the oil-based ink was calculated using the following formula.
Moisture content (mass%)=[moisture content (mg)/measurement sample weight (mg)]×100

(Hydroxyl value)
It was determined in accordance with JIS K0070.

(Acid value)
It was determined in accordance with JIS K0070.

(Amine value)
The amine value is expressed as the number of milligrams of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize the amino groups contained in 1 g of resin, and was determined according to the following method in accordance with JIS K0070.
0.5 to 2 g of sample was precisely weighed out (non-volatile content of sample: Sg). 50 mL of a mixed solution of methanol/methyl ethyl ketone = 60/40 (mass ratio) was added to the precisely weighed sample to dissolve it. Bromophenol blue was added as an indicator to the resulting solution, and the resulting solution was titrated with 0.2 mol/L ethanolic hydrochloric acid solution (titer: f). The point at which the color of the solution changed from green to yellow was set as the end point, and the titration amount (A mL) at this time was used to calculate the amine value according to the following formula.
Amine value = (A x f x 0.2 x 56.108) / S [mg KOH / g]

(Weight average molecular weight)
The weight average molecular weight was determined by measuring the molecular weight distribution using a GPC (gel permeation chromatography) device (HLC-8220 manufactured by Tosoh Corporation) and calculating the molecular weight converted using polystyrene as a standard substance. The measurement conditions are shown below.
Columns: The following columns were used in series connection:
Tosoh Guard Column HXL-H
Tosoh Corporation TSKgel G5000HXL
Tosoh Corporation TSKgel G4000HXL
Tosoh Corporation TSKgel G3000HXL
Tosoh TSKgel G2000HXL
Detector: RI (differential refractometer)
Measurement conditions: column temperature 40°C
Eluent: tetrahydrofuran Flow rate: 1.0 mL/min

(Glass-transition temperature)
The glass transition temperature (Tg) was determined by DSC (differential scanning calorimetry). The measurement was performed using a Rigaku DSC8231, with a measurement temperature range of −70 to 250° C., a heating rate of 10° C./min, and the midpoint between the endothermic start and end temperatures due to the glass transition in the DSC curve was taken as the glass transition temperature.

(Synthesis Example 1) Polyurethane resin solution [PU1]
54.719 parts of a polyester diol having a number average molecular weight of 2,000 obtained from adipic acid and 3-methyl-1,5-pentanediol, 3.989 parts of isophorone diisocyanate (hereinafter "IPDI"), and 10.0 parts of n-propyl acetate (hereinafter "NPAC") were reacted at 85°C for 3 hours under a nitrogen stream, 10.0 parts of nPAc was added, and the mixture was cooled to obtain 78.708 parts of a solvent solution of a terminal isocyanate prepolymer. Next, 78.708 parts of the obtained solvent solution of the isocyanate-terminated prepolymer was gradually added at room temperature to a mixture of 1.031 parts of isophorone diamine (hereinafter "IPDA"), 0.261 parts of di-n-butylamine, 72.96 parts of nPAc, and 47.04 parts of isopropanol (hereinafter "IPA"), and then the mixture was allowed to react at 50°C for 1 hour to obtain a polyurethane resin solution [PU1] having a nonvolatile content of 30%, a weight average molecular weight of 60,000, and an amine value of 3.0 mgKOH/g.

(Synthesis Example 2) Polyurethane resin solution [PU2]
200 parts of polypropylene glycol (hereinafter "PPG700") having a number average molecular weight of 700, 127 parts of IPDI, and 81.8 parts of ethyl acetate were reacted under a nitrogen stream at 80 ° C. for 4 hours to obtain a resin solution of a terminal isocyanate urethane prepolymer. Next, 49.5 parts of IPDA, 3 parts of 2-ethanolamine, and 803.9 parts of a mixed solvent of ethyl acetate / isopropanol (hereinafter "IPA") = 50 / 50 (mass ratio) were mixed, and the obtained resin solution of the terminal isocyanate urethane prepolymer was gradually added at 40 ° C., and then reacted at 80 ° C. for 1 hour to obtain a polyurethane resin solution [PU2] with a non-volatile content of 30%, an amine value of 3.5 mg KOH / g, a hydroxyl value of 7.3 mg KOH / g, and a weight average molecular weight of 40,000. The glass transition temperature was -32 ° C.

Example 1
Preparation of oil-based ink (1) 100 parts of C.I. Pigment Blue 15:3 (PB15:3), 700 parts of sodium chloride, and 200 parts of diethylene glycol were added and kneaded for 5 hours at 70 ° C. in a 1-gallon kneader manufactured by Inoue Seisakusho Co., Ltd. The kneaded product obtained was added to 5,000 parts of water, stirred and filtered, and this operation was repeated to sufficiently remove sodium chloride and diethylene glycol, and a wet cake was obtained that was adjusted to NV 70% by drying at 40 ° C. under reduced pressure.

Next, 10 parts of the obtained wet cake (containing 7 parts of PB15:3 and 3 parts of water) was mixed with 30 parts of polyurethane resin solution [PU1], 5 parts of polyurethane resin solution [PU2], 20 parts of NPAC, and 5 parts of IPA, and the mixture was ground in a sand mill. Next, 20 parts of polyurethane resin solution [PU2], 9 parts of NPAC, and 4 parts of IPA were added, and the mixture was mixed and stirred to obtain a mixture.

Next, 14.1 parts of Ethyl Silicate 28 (manufactured by Colcoat Co., Ltd.) was added as a dehydrating agent (d) to the obtained mixture, and the mixture was stirred at room temperature for 1 hour to obtain an oil-based ink (1) containing a silicone polymer as a nonionic dehydrating agent reactant (D).
The water content in the oil-based ink (1) was 0.5% by mass. The content of the nonionic dehydrating agent reactant (D) was theoretically 3.4% by mass, and the content was 57 parts by mass relative to 100 parts by mass of the colorant (A).
The composition ratio (content) of the oil-based ink is shown in Table 2.

(Examples (2) to (4))
Preparation of Oil-Based Inks (2) to (4) Oil-based inks (2) to (4) were obtained in the same manner as in Example 1, except that the amount of dehydrating agent (d) added was changed as shown in Table 1.

(Example (5))
Preparation of oil-based ink (5) 100 parts of C.I. Pigment Blue 15:3 (PB15:3), 700 parts of sodium chloride, and 200 parts of diethylene glycol were added and kneaded for 5 hours at 70 ° C. in a 1-gallon kneader manufactured by Inoue Seisakusho Co., Ltd. The kneaded product obtained was added to 5,000 parts of water, stirred and filtered, and this operation was repeated to sufficiently remove sodium chloride and diethylene glycol, and a wet cake was obtained by drying under reduced pressure at 40 ° C. and adjusting the NV to 68%.

Next, 10.3 parts of the obtained wet cake (containing 7 parts of PB15:3 and 3.3 parts of water) was mixed with 30 parts of polyurethane resin solution [PU1], 5 parts of polyurethane resin solution [PU2], 20 parts of NPAC, and 5 parts of IPA, and the mixture was ground in a sand mill. Next, 20 parts of polyurethane resin solution [PU2], 9 parts of NPAC, and 4 parts of IPA were added, and the mixture was mixed and stirred to obtain a mixture.

Next, 1.0 part of Ethyl Silicate 28 (manufactured by Colcoat Co., Ltd.) was added as a dehydrating agent (d) to the obtained mixture, and the mixture was stirred at room temperature for 1 hour to obtain an oil-based ink (5) containing a silicone polymer as a non-ionic dehydrating agent reactant (D).
The water content in the oil-based ink (5) was 3.0% by mass. The theoretical content of the nonionic dehydrating agent reactant (D) was 0.3% by mass, and the content was 4 parts by mass per 100 parts by mass of the colorant (A).

(Example (6))
Preparation of oil-based ink (6) 100 parts of C.I. Pigment Blue 15:3 (PB15:3), 700 parts of sodium chloride, and 200 parts of diethylene glycol were added and kneaded for 5 hours at 70 ° C. in a 1-gallon kneader manufactured by Inoue Seisakusho Co., Ltd. The kneaded product obtained was added to 5,000 parts of water, stirred and filtered, and this operation was repeated to sufficiently remove sodium chloride and diethylene glycol, and a wet cake was obtained by drying under reduced pressure at 40 ° C. and adjusting the NV to 56%.

Next, 12.5 parts of the obtained wet cake (containing 7 parts of PB15:3 and 5.5 parts of water) was mixed with 30 parts of polyurethane resin solution [PU1], 5 parts of polyurethane resin solution [PU2], 20 parts of NPAC, and 5 parts of IPA, and the mixture was ground in a sand mill. Next, 20 parts of polyurethane resin solution [PU2], 9 parts of NPAC, and 4 parts of IPA were added, and the mixture was mixed and stirred to obtain a mixture.

Next, 1.0 part of Ethyl Silicate 28 (manufactured by Colcoat Co., Ltd.) was added as a dehydrating agent (d) to the obtained mixture, and the mixture was stirred at room temperature for 1 hour to obtain an oil-based ink (6) containing a silicone polymer as a non-ionic dehydrating agent reactant (D).
The water content in the oil-based ink (6) was 5.0% by mass. The theoretical content of the nonionic dehydrating agent reactant (D) was 0.3% by mass, and the content was 4 parts by mass per 100 parts by mass of the colorant (A).

(Example (7))
Preparation of oil-based ink (7) 100 parts of C.I. Pigment Blue 15:3 (PB15:3), 700 parts of sodium chloride, and 200 parts of diethylene glycol were added and kneaded for 5 hours at 70 ° C. in a 1-gallon kneader manufactured by Inoue Seisakusho Co., Ltd. The kneaded product obtained was added to 5,000 parts of water, stirred and filtered, and this operation was repeated to sufficiently remove sodium chloride and diethylene glycol, and a wet cake was obtained by drying at 40 ° C. under reduced pressure and adjusted to NV 45%.

Next, 15.6 parts of the obtained wet cake (containing 7 parts of PB15:3 and 8.6 parts of water) was mixed with 30 parts of polyurethane resin solution [PU1], 5 parts of polyurethane resin solution [PU2], 20 parts of NPAC, and 5 parts of IPA, and the mixture was ground in a sand mill. Next, 20 parts of polyurethane resin solution [PU2], 9 parts of NPAC, and 4 parts of IPA were added, and the mixture was mixed and stirred to obtain a mixture.

Next, 4.0 parts of Ethyl Silicate 28 (manufactured by Colcoat Co., Ltd.) as a dehydrating agent (d) was added to the obtained mixture, and the mixture was stirred at room temperature for 1 hour to obtain an oil-based ink (7) containing a silicone polymer as a nonionic dehydrating agent reactant (D).
The water content in the oil-based ink (7) was 7.0% by mass. The theoretical content of the nonionic dehydrating agent reactant (D) was 1.0% by mass, and the content was 16 parts by mass per 100 parts by mass of the colorant (A).

(Example (8))
Preparation of oil-based ink (8) 100 parts of C.I. Pigment Blue 15:3 (PB15:3), 700 parts of sodium chloride, and 200 parts of diethylene glycol were added and kneaded for 5 hours at 70°C in a 1-gallon kneader manufactured by Inoue Seisakusho Co., Ltd. The kneaded product obtained was added to 5,000 parts of water, stirred and filtered, and this operation was repeated to sufficiently remove sodium chloride and diethylene glycol, and a wet cake with an NV of 35% was obtained by adjusting the filtration time.

Next, 20.0 parts of the obtained wet cake (containing 7 parts of PB15:3 and 13.0 parts of water) was mixed with 30 parts of polyurethane resin solution [PU1], 5 parts of polyurethane resin solution [PU2], 20 parts of NPAC, and 5 parts of IPA, and the mixture was ground in a sand mill. Next, 20 parts of polyurethane resin solution [PU2], 9 parts of NPAC, and 4 parts of IPA were added, and the mixture was mixed and stirred to obtain a mixture.

Next, 6.2 parts of Ethyl Silicate 28 (manufactured by Colcoat Co., Ltd.) was added as a dehydrating agent (d) to the obtained mixture, and the mixture was stirred at room temperature for 1 hour to obtain an oil-based ink (8) containing a silicone polymer as a nonionic dehydrating agent reactant (D).
The water content in the oil-based ink (8) was 10.0% by mass. The theoretical content of the nonionic dehydrating agent reactant (D) was 1.5% by mass, and the content was 26 parts by mass per 100 parts by mass of the colorant (A).

(Example (9))
Preparation of oil-based ink (9) 100 parts of C.I. Pigment Blue 15:3 (PB15:3), 700 parts of sodium chloride, and 200 parts of diethylene glycol were added and kneaded for 5 hours at 70°C in a 1-gallon kneader manufactured by Inoue Seisakusho Co., Ltd. The kneaded product obtained was added to 5,000 parts of water, stirred and filtered, and this operation was repeated to sufficiently remove sodium chloride and diethylene glycol, and a wet cake with an NV of 25% was obtained by adjusting the filtration time.

Next, 28.0 parts of the obtained wet cake (containing 7 parts of PB15:3 and 21.0 parts of water) was mixed with 30 parts of polyurethane resin solution [PU1], 5 parts of polyurethane resin solution [PU2], 20 parts of NPAC, and 5 parts of IPA, and the mixture was ground in a sand mill. Next, 20 parts of polyurethane resin solution [PU2], 9 parts of NPAC, and 4 parts of IPA were added, and the mixture was mixed and stirred to obtain a mixture.

Next, 8.7 parts of Ethyl Silicate 28 (manufactured by Colcoat Co., Ltd.) was added as a dehydrating agent (d) to the obtained mixture, and the mixture was stirred at room temperature for 1 hour to obtain an oil-based ink (9) containing a silicone polymer as a nonionic dehydrating agent reactant (D).
The water content in the oil-based ink (9) was 15.0% by mass. The content of the nonionic dehydrating agent reactant (D) was theoretically 2.7% by mass, and the content was 50 parts by mass per 100 parts by mass of the colorant (A).

(Example (10))
Preparation of Oil-Based Ink (10) Oil-based ink (10) was obtained in the same manner as in Example 5, except that the dehydrating agent (d) was changed to methyl silicate 51.

(Example (11))
Preparation of Oil-Based Ink (11) Oil-based ink (11) was obtained in the same manner as in Example 5, except that the dehydrating agent (d) was changed to 1.3 parts of methyl silicate 51.

(Examples (12) to (15))
Preparation of Oil-Based Inks (12) to (15) Oil-based inks (12) to (15) were obtained in the same manner as in Example 5, except that the colorant (A) was changed as shown in Table 1.

(Example (16))
Preparation of oil-based ink (16) 100 parts of C.I. Pigment Blue 15:3 (PB15:3), 700 parts of sodium chloride, and 200 parts of diethylene glycol were added and kneaded for 5 hours at 70 ° C. in a 1-gallon kneader manufactured by Inoue Seisakusho Co., Ltd. The kneaded product obtained was added to 5,000 parts of water, stirred and filtered, and this operation was repeated to sufficiently remove sodium chloride and diethylene glycol, and a wet cake was obtained by drying under reduced pressure at 40 ° C. and adjusting the NV to 68%.

Next, 10.3 parts of the obtained wet cake (containing 7 parts of PB15:3 and 3.3 parts of water) was mixed with 16.5 parts of Joncryl 693, 40 parts of NPAC, and 10 parts of IPA, and ground in a sand mill. Next, 19 parts of NPAC and 7.5 parts of IPA were added, and the mixture was mixed and stirred to obtain a mixture.

Next, 1.0 part of Ethyl Silicate 28 (manufactured by Colcoat Co., Ltd.) was added as a dehydrating agent (d) to the obtained mixture, and the mixture was stirred at room temperature for 1 hour to obtain an oil-based ink (16) containing a silicone polymer as a nonionic dehydrating agent reactant (D).
The water content in the oil-based ink (16) was 3.0% by mass. The theoretical content of the nonionic dehydrating agent reactant (D) was 0.3% by mass, and the content was 4 parts by mass per 100 parts by mass of the colorant (A).

(Example (17))
Preparation of Oil-Based Ink (17) Oil-based ink (17) was obtained in the same manner as in Example 5, except that IPA was changed to toluene as the organic solvent (C) to be added.

(Comparative Example (1))
Preparation of oil-based ink (21) 100 parts of C.I. Pigment Blue 15:3 (PB15:3), 700 parts of sodium chloride, and 200 parts of diethylene glycol were added and kneaded for 5 hours at 70 ° C. in a 1-gallon kneader manufactured by Inoue Seisakusho Co., Ltd. The kneaded product obtained was added to 5,000 parts of water, stirred and filtered, and this operation was repeated to sufficiently remove sodium chloride and diethylene glycol, and a wet cake was obtained by drying under reduced pressure at 40 ° C. and adjusting the NV to 69%.

Next, 10.3 parts of the obtained wet cake (containing 7 parts of PB15:3 and 3.3 parts of water) was mixed with 30 parts of polyurethane resin solution [PU1], 5 parts of polyurethane resin solution [PU2], 20 parts of NPAC, and 5 parts of IPA, and the mixture was ground in a sand mill. Next, 20 parts of polyurethane resin solution [PU2], 9 parts of NPAC, and 4 parts of IPA were added, and the mixture was mixed and stirred to obtain oil-based ink (21).

The water content in the oil-based ink (21) was 3.0% by mass. The theoretical content of the nonionic dehydrating agent reactant (D) was 0% by mass, and the content per 100 parts by mass of the colorant (A) was 0 parts by mass.

(Comparative Examples (2) to (5))
Preparation of Oil-Based Inks (22) to (25) Oil-based inks (22) to (25) were obtained in the same manner as in Comparative Example 1, except that the colorant (A) used was changed.

<Evaluation of oil-based ink>
The storage stability and transparency of the oil-based ink of the present invention were evaluated by the following methods. The results are shown in Table 2. Table 2 also shows the composition ratio (content (mass %)) of the oil-based ink.

<Storage stability evaluation>
The viscosity of the prepared oil-based ink was measured at 25°C using a cone-plate type viscometer TV-22 manufactured by Toki Sangyo Co., Ltd., and was designated as initial viscosity _Vb . This aqueous pigment dispersion was placed in a 20 mL glass sample tube, and a temperature fluctuation cycle test was performed for 90 days in which the dispersion was stored at 5°C for 6 hours, at 25°C for 6 hours, at 50°C for 6 hours, and at 25°C for 6 hours. After that, the oil-based ink was removed from the sealed container and measured at 25°C in the same manner as the initial viscosity, and was designated as aged viscosity _Va . The aged viscosity value was divided by the initial viscosity value to calculate the value _Va / _Vb , and the viscosity stability was evaluated according to the following criteria.
[Evaluation criteria]
◎: Value of _Va / _Vb is less than 105% (excellent)
○: Value of _Va / _Vb is 105% or more and less than 110% (good)
△: The value of V _a /V _b is 110% or more and less than 115% (no problem in practical use)
×: Value of _Va / _Vb is 115% or more (bad)

<Transparency>
The oil-based ink that had been subjected to the temperature fluctuation cycle test in the storage stability evaluation was printed on a biaxially oriented polypropylene (OPP) film (Futamura Chemical Co., Ltd., FOR, thickness 25 μm) that had been corona discharge-treated on one side using a gravure printing machine equipped with a Helio 175 line gradation plate (plate type compressed gradation 100% to 3%) at a printing speed of 80 m/min, to obtain a solid gravure print.
The obtained print (OPP film) was overlaid with a test chart KL-14H manufactured by LENETA (a test paper having a white background and a black background). Using an X-Rite eXact spectrophotometer manufactured by X-Rite, the L ^* of the portion overlapping the black background of the test chart KL-14H was measured from the direction of the obtained print (OPP film). Transparency was evaluated based on the L ^* (STD) of the oil-based ink obtained by the same measurement method using the same colorant type obtained in Comparative Examples 1 to 5.
[Evaluation criteria]
◎: L ^* -L ^* (STD) value is 2 or more (excellent)
○: The value of L ^* -L ^* (STD) is 1 or more and less than 2 (good)
△: The value of L ^* -L ^* (STD) is 0.1 or more and less than 1 (no problem in practical use)
×: The value of L ^* -L ^* (STD) is less than 0.1 (defective)

As described above, the oil-based ink containing the nonionic dehydrating agent reactant (D) and a specified amount of water had good storage stability even in harsh environments with fluctuating temperatures, and the transparency of the printed matter was good.

In addition, as for letterpress printing, the oil-based inks (1) to (17) and (21) to (25) were spread by letterpress printing on one-sided glossy kraft paper using a hand proofer (200 L/inch) to produce flexographic prints with an ink layer (coating amount of approximately 1.7 g/m2). Compared with the oil-based inks (21) to (25) of the comparative examples, the oil-based inks (1) to (17) produced letterpress prints with good transparency.
In addition, for stencil printing, a label film having a polyvinyl chloride layer (Oji Tack Co., Ltd., PVCW80/F93/YW16, 80 μm) was used, and a pattern was stencil-printed on this substrate with oil-based inks (1) to (17) and (21) to (25) using a screen printing plate (NBC Meshtec Co., Ltd., L-SCREEN, 100-035/255PW) to produce a stencil print. Compared with the comparative oil-based inks (21) to (25), the oil-based inks (1) to (17) gave stencil prints with good transparency.

These results confirm that the oil-based ink of the present invention can be suitably used for various printing inks, paints, writing instruments, color filters, solid-state imaging devices, sensors, etc.

Claims (5)

A composition comprising a colorant (A), a resin (B), an organic solvent (C), a non-ionic dehydrating agent reactant (D), and water,
An oil-based ink having a moisture content of 0.5 to 15.0% by mass. The oil-based ink according to claim 1, wherein the nonionic dehydrating agent reactant (D) is a reaction product of water with at least one of an alkyl silicate and an alkyl silicate oligomer. The oil-based ink according to claim 1, wherein the content of the nonionic dehydrating agent reactant (D) in the oil-based ink is 0.01 to 100 parts by mass per 100 parts by mass of the colorant (A). The oil-based ink according to any one of claims 1 to 3, which is used for plate printing. A method for producing an oil-based ink comprising a colorant (A), a resin (B), an organic solvent (C), a nonionic dehydrating agent reactant (D), and water, the method comprising the steps of:
A method for producing an oil-based ink, comprising the step of adding a nonionic dehydrating agent (d) to adjust the water content in the oil-based ink to 0.5 to 15.0 mass %.