Method for producing aqueous pigment dispersion, inkjet ink, and printed matter

Abstract

The present invention provides an aqueous pigment dispersion comprising water, a pigment, and a crosslinked polymer, the crosslinked polymer being a reaction product of a dispersing resin having an anionic group and a crosslinking agent, the dispersing resin having an anionic group being water-soluble and having an acid value of 181 to 220 mgKOH / g, the crosslinking agent being a water-soluble compound having two or more epoxy groups, and the crosslinking rate of the crosslinked polymer being greater than 80%. The composition can be used to produce an ink-jet ink that maintains excellent storage stability even at high temperatures or in environments with large temperature changes and has excellent printability.

Description

[Technical field]

[0001] The present invention relates to an aqueous pigment dispersion, an ink-jet ink, and a method for producing a printed matter. [Background technology]

[0002] Inkjet recording is a method of recording in which ink droplets are ejected from extremely fine nozzles directly onto a recording medium, causing them to adhere to the recording medium, resulting in the production of characters and images. This method has the advantages of low noise and good operability of the equipment used, as well as the ease of production of color recordings. For this reason, inkjet recording is used not only as an output device in offices and homes, but also for industrial purposes.

[0003] Ink used in the inkjet recording method is required to have excellent storage stability and to be less susceptible to an increase in viscosity over time and to sedimentation of pigments, etc., in order to prevent ink ejection defects such as nozzle clogging, deflection of ink flight, and droplet division. Furthermore, when the manufactured ink is transported, it may be stored at high or low temperatures, and it is necessary to make the ink such that sedimentation of the pigment, etc. does not occur even when the temperature changes.

[0004] Known examples of aqueous pigment dispersions with excellent storage stability include crosslinked polymer particles for inkjet recording, which are obtained by dispersing a pigment in a water-soluble polymer having an anionic group and a water-insoluble polymer having an anionic group, and then crosslinking the polymers with a crosslinking agent, and aqueous dispersions using the same (see, for example, Patent Document 1).

[0005] However, even when the dispersion is subjected to a crosslinking treatment as described above, the storage stability is highly dependent on the types of dispersing resin and crosslinking agent, as well as the conditions of the crosslinking reaction. If the combination is not appropriate, sufficient storage stability may not be obtained at high temperatures or when exposed to repeated exposure to high and low temperatures.

[0006] Furthermore, as a result of strengthening the crosslinking treatment to improve storage stability, there is a concern that even the dispersion resins that are not adsorbed to the pigment in the dispersion may crosslink with each other and become high molecular weight. The crosslinked polymers that are not adsorbed to the pigment tend to aggregate, which can cause ink discharge problems such as nozzle clogging.

[0007] As described above, in a dispersion that has been subjected to a crosslinking treatment, there is a trade-off between storage stability and ink ejection properties, and there is a demand for the development of a dispersion that achieves both. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2009-49595 A Summary of the Invention [Problem to be solved by the invention]

[0009] The problem to be solved by the present invention is to provide an aqueous pigment dispersion that can be used for producing an inkjet ink that maintains excellent storage stability even at high temperatures or in environments with large temperature changes, has excellent ink ejection properties, and is also excellent in printability. [Means for solving the problem]

[0010] The present invention provides a composition comprising water, a pigment, and a crosslinked polymer, the crosslinked polymer is a reaction product of a dispersing resin having an anionic group and a crosslinking agent; The dispersion resin having an anionic group is water-soluble and has an acid value of 181 to 220 mgKOH / g; The crosslinking agent is a water-soluble compound having two or more epoxy groups, The above-mentioned problems are solved by the aqueous pigment dispersion in which the crosslinking rate of the crosslinked polymer exceeds 80%. Effect of the Invention

[0011] According to the aqueous pigment dispersion of the present invention, it is possible to obtain an ink-jet ink and a printed matter which maintain excellent storage stability, have excellent ink ejection properties, and are also excellent in printability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The aqueous pigment dispersion of the present invention comprises water, a pigment, and a crosslinked polymer, the crosslinked polymer being a reaction product of a dispersing resin having an anionic group and a crosslinking agent, and the crosslinking rate of the crosslinked polymer is greater than 80%. The dispersing resin having an anionic group is water-soluble and has an acid value of 181 to 220 mgKOH / g. The crosslinking agent is a water-soluble compound having two or more epoxy groups.

[0013] (water) As the water used in the present invention, pure water or ultrapure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, etc. can be used. The water is used in an amount of preferably 25% by mass to 90% by mass, more preferably 35% by mass to 85% by mass, and even more preferably 55% by mass to 75% by mass, based on the total amount of the aqueous pigment dispersion.

[0014] (Pigments) As the pigment, for example, organic pigments and inorganic pigments that are usually used in water-based gravure inks, water-based flexographic inks, water-based offset inks, or water-based ink-jet inks can be used.

[0015] The pigment may include one or both of an organic pigment and an inorganic pigment, and the pigment may be either a non-acid-treated pigment or an acid-treated pigment.

[0016] As the inorganic pigment, for example, iron oxide and carbon black produced by a contact method, a furnace method, a thermal method, or the like can be used.

[0017] Examples of organic pigments that can be used include azo pigments (azo lake, insoluble azo pigment, condensed azo pigment, chelate azo pigment, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), lake pigments (for example, basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc.

[0018] Examples of pigments (black pigments) that can be used in black inks include CI Pigment Black 1, 6, 7, 8, 10, 26, 27, and 28. Of these, CI Pigment Black 7 is preferably used. Specific examples of black pigments include No. 2200, No. 2300, No. 2350, No. 2600, No. 650B, No. 750B, No. 850, No. 900, No. 950, No. 960, No. 970, No. 980, No. 990, No. 995B, No. 1000, No. 3030B, No. 3050B, No. 3230B, No. 3400B, No. 25B, No. 30, No. 33, No. 40, No. 44, No. 45, and No. 650B manufactured by Mitsubishi Chemical Corporation. .45L, No.47, No.52, MA7, MA8, MA77, MA100, MA230, MA600, MCF88, etc.; No.5500, No.4500, No.4400, No.8500, etc. manufactured by Tokai Carbon Co., Ltd.; Raven760UP, Raven780UP, Raven860UP, Raven900P, Raven1000P, Raven1060P, Raven1080UP, Raven1255, Raven2000, Raven2350 manufactured by BILRA. ULTRA, Raven2500 ULTRA, Raven2800 ULTRA, Raven2900 ULTRA, Raven3000 ULTRA, Raven3500, Raven5000 ULTRA II, Raven5000 ULTRA 3, Raven UV ULTRA, Conductex SC ULTRA, Conductex K ULTRA etc;Regal 330R, Regal 400R, Regal 660R, Mogul L, Mogul 700, Monarch700, Monarch717, Monarch800, Monarch880, Monarch900, Monarch1000, Monarch1100, Monarch1300, Monarch1400, BLACK PEARLS 800, BLACK PEARLS 880, BLACK PEARLS 1000, BLACK PEARLS 1300, BLACK PEARLS 2000, BLACK PEARLS 4040, BLACK PEARLS 4350, BLACK PEARLS 4560i, BLACK PEARLS 4750, VULCAN XC72, VULCAN XC72R, VULCAN 9A32, ELFTEX 570, ELFTEX P100, ELFTEX TP, etc. manufactured by Cabot Corporation;Orion Engineered Carbon's Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW171, Color Black FW182, Color Black FW200, Color Black FW285, Color Black S150, Color Black S160, Color Black S170, Printex 30, Printex 35, Printex 40, Printex 45, Printex U, Printex V, Printex 1400U, Printex 150T, Printex 55, Printex 70, Printex 75, Printex 80, Printex F80, Printex F85, Printex 90, Printex 95, Printex 300, Printex P beads, Printex L6, Special Black 6, Special Black 5, Special Black 4, Special Black 4A, Special Black 350, Special Black 550, NIPEX 35, NIPEX 75, NIPEX 90, NIPEX 150, NIPEX 160, NIPEX 160IQ, NIPEX 170, NIPEX 170IQ, NIPEX 180, NIPEX 180IQ, NIPEX 1601IQ, HIBLACK 50L, HIBLACK 600L, HIBLACK F890B, HIBLACK 930L, HIBLACK 970LB, Nerox305, Nerox500, Nerox505, Nerox600, Nerox605, etc.;

[0019] Specific examples of pigments (yellow pigments) that can be used in yellow inks include CI Pigment Yellow 1, 2, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 174, 180, and 185.

[0020] Specific examples of pigments (magenta pigments) that can be used in magenta inks include CI Pigment Red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1, 112, 122, 123, 146, 149, 150, 168, 176, 184, 185, 202, 209, 254, 269, 282, and the like; CI Pigment Violet 19, and the like. Specific examples of magenta pigments include Quindo Magenta 228-2120, Fastogen Super Magenta RGT, Fastogen Super Magenta RTS, Fastgen Super Magenta RY, Cinquasia Magenta D4550J, and Cinquasia Magenta D4500J, all manufactured by DIC Corporation; FUJI FAST CARMINE 520, FUJI FAST CARMINE 522-1D, Fuji Fast Carmine 580S, FUJI FAST CARMINE 590-4, FUJI FAST RED 9800, and FUJI FAST CARMINE 6005, all manufactured by Fuji Pigment Co., Ltd.; and Ink Jet Magenta E5B 02, all manufactured by Heubach.

[0021] Specific examples of pigments (cyan pigments) that can be used in cyan ink include CI Pigment Blue 1, 2, 3, 15, 15:3, 15:4, 15:6, 16, 22, 60, 63, and 66. Of these, CI Pigment Blue 15:3 is preferably used. Specific examples of cyan pigments include FSJ-SD, TGR, TGR-J, TGR-SD, SBG-SD, KET BLUE 111, Heliogen Blue L 7101 F, and the like, manufactured by DIC Corporation; and CYANINE BLUE 3023-A, and the like, manufactured by Sanyo Pigment Co., Ltd.

[0022] Specific examples of pigments (white pigments) that can be used in white ink include alkaline earth metal sulfates, carbonates, finely powdered silicic acid, silicas such as synthetic silicates, calcium silicate, alumina, alumina hydrate, titanium oxide, zinc oxide, talc, clay, and the like.

[0023] The pigment is preferably used in a range of 10% by mass to 25% by mass, based on the total amount of the aqueous pigment dispersion, and is preferably used in a range of 12% by mass to 20% by mass, in order to obtain an aqueous pigment dispersion that can suppress aggregation over time and has excellent storage stability.

[0024] In the present invention, if the pigment is a quinacridone pigment, the effects of the present invention can be suitably exhibited, and this is preferable. The quinacridone pigment includes a compound represented by the following general formula (1). Xn-Q-Ym(1) (In the formula, Q represents a quinacridone residue or a quinacridonequinone residue, X and Y represent a hydrogen atom, a methyl group, a chloro group or a methoxy group, and n and m represent integers of 1 to 4.) Specific examples thereof include dimethylquinacridone pigments such as 2,9-dimethylquinacridone, 3,10-dimethylquinacridone, and 4,11-dimethylquinacridone (CI Pigment Red 122, etc.), dichloroquinacridone pigments such as 2,9-dichloroquinacridone, 3,10-dichloroquinacridone, and 4,11-dichloroquinacridone (CI Pigment Red 202, CI Pigment Red 209, etc.), unsubstituted quinacridone pigments (CI Pigment Violet 19, etc.), dimethoxyquinacridone pigments such as 2,9-dimethoxyquinacridone, 3,10-dimethoxyquinacridone, and 4,11-dimethoxyquinacridone, quinacridonequinone pigments, and mixtures or solid solutions of at least two or more pigments selected from these pigments. The pigment may be a powdery, granular, or lump-shaped dry pigment, or may be a wet cake or a slurry. Among the above quinacridone pigments, CI Pigment Red 122 is preferred.

[0025] A solid solution of quinacridone pigments refers to a mixture of two pigments selected from unsubstituted quinacridone pigments, dimethylquinacridone pigments, and dichloroquinacridone pigments, which form a mixed layer in which one quinacridone pigment is dissolved in the other quinacridone pigment. In other words, the solid solution does not contain single crystals of quinacridone pigments. Whether it is a solid solution or a mixture of single crystals can be easily determined by powder X-ray diffraction. Among these, a solid solution of an unsubstituted quinacridone pigment and a dimethylquinacridone pigment is preferred. In the solid solution of quinacridone pigments, the weight ratios of [unsubstituted quinacridone pigment / dimethylquinacridone pigment], [unsubstituted quinacridone pigment / dichloroquinacridone pigment], and [dimethylquinacridone pigment / dichloroquinacridone pigment] are preferably 5 / 95 to 95 / 5, more preferably 10 / 90 to 90 / 10, from the viewpoints of ejection reliability, print density, saturation, etc. In particular, the weight ratio of [unsubstituted quinacridone pigment / dimethylquinacridone pigment] is preferably 5 / 95 to 40 / 60, more preferably 10 / 90 to 30 / 70. The form of the quinacridone pigment solid solution may be a dry pigment in the form of powder, granules or lumps, or may be a wet cake or a slurry.

[0026] In the present invention, the effects of the present invention can be favorably exhibited by using a quinacridone pigment in particular. The reason for this is unclear, but the inventors speculate as follows. As can be seen from the quinacridone molecular structure, the top and bottom directions of the molecular plane show aromatic properties and are highly hydrophobic, but the sides have extremely weak aromatic properties in some directions due to the presence of carbonyl and amino groups, and as a result, the hydrophobicity is thought to be weaker compared to the top and bottom directions. Therefore, quinacridone pigments tend to be difficult to stabilize with hydrophobic functional groups, which are the adsorption groups of dispersing resins. As a result, dispersing resins are easily detached, and quinacridone pigments tend to have poor storage stability in inks, especially when the ink is repeatedly heated and cooled. In the present invention, the quinacridone pigment is dispersed using a dispersing resin having an anionic group, and then the dispersing resin is crosslinked, thereby increasing the molecular weight of the dispersing resin and preventing the dispersing resin from detaching from the quinacridone pigment. This is believed to result in good storage stability, particularly when the ink is subjected to repeated temperature increases and decreases.

[0027] The aqueous pigment dispersion of the present invention preferably does not contain a pigment derivative. In general, pigment derivatives are added to pigments such as quinacridone pigments that tend to have poor storage stability in order to improve the storage stability. However, pigment derivatives that are not adsorbed to the pigment may aggregate with each other, thereby reducing the ejection performance of an inkjet printer, and may also have a negative effect on the storage stability of the ink when the ink is repeatedly heated and cooled. The aqueous pigment dispersion of the present invention can improve the storage stability without using a pigment derivative, even in the case of a dispersion of a pigment such as quinacridone pigments that has relatively poor storage stability, and can also suppress the negative effect of the pigment derivative on the ink.

[0028] (Crosslinked polymer) The aqueous pigment dispersion of the present invention contains a crosslinked polymer. The crosslinked polymer is the reaction product of a dispersing resin having anionic groups and a crosslinking agent.

[0029] The crosslinked polymer is preferably formed, for example, by producing an aqueous pigment dispersion containing the pigment, the dispersing resin, water, and the like, and then mixing the aqueous pigment dispersion with the crosslinking agent to react a carboxyl group of the dispersing resin having an anionic group with an epoxy group of the crosslinking agent.

[0030] (Crosslinking rate of crosslinked polymer) The crosslinked polymer contained in the aqueous pigment dispersion of the present invention has a crosslinking rate of more than 80%. Here, the crosslinking rate is a value that can be calculated by the following calculation formula (2) from the amount of the crosslinking agent used, the number of moles of the reactive groups, the amount of the polymer used, and the number of moles of the reactive groups of the polymer that can react with the reactive groups of the crosslinking agent. Crosslinking rate (mol%)=100×[molar number of reactive groups in crosslinking agent] / [molar number of carboxyl groups in the dispersion resin] Formula (2) In formula (2), the "molar number of reactive groups in the crosslinking agent" is the value obtained by dividing the weight of the crosslinking agent used by the equivalent weight of the reactive groups, i.e., the mole number of the crosslinking agent used multiplied by the number of reactive groups in one molecule of the crosslinking agent.

[0031] When the crosslinking rate exceeds 80%, the storage stability of the ink and the storage stability when the ink is repeatedly heated and cooled can be improved. In order to maintain good ejection properties of the ink, the crosslinking rate is preferably more than 80% and less than 90%. When the crosslinking rate is less than 90%, the anionic groups remaining in the dispersion resin without undergoing the crosslinking reaction also contribute to dispersion stability, and the storage stability can be improved.

[0032] The crosslinked polymer preferably has an anionic group in the range of 0.2 to 2.5 mmol / g based on the total amount of the crosslinked polymer. By using a crosslinked polymer having an anionic group in the above range, an aqueous pigment dispersion and an ink containing the same having excellent storage stability can be obtained. It is more preferable to use the anionic group in an amount in the range of 0.3 to 2.0 mmol / g based on the total amount of the crosslinked polymer in order to further improve the storage stability of the aqueous pigment dispersion and the ink.

[0033] In addition, when the reaction product of the dispersion resin and the crosslinking agent is used as the crosslinked polymer, a part of the anionic group of the dispersion resin reacts with the epoxy group of the crosslinking agent and is consumed. Therefore, the amount of the anionic group relative to the total amount of the crosslinked polymer refers to the amount of the anionic group remaining in the reaction product of the dispersion resin and the crosslinking agent.

[0034] (Dispersion resin with anionic groups) The dispersing resin having an anionic group used in the present invention is water-soluble and has an acid value of 181 to 220 mgKOH / g. In the present invention, the phrase "the dispersion resin is water-soluble" means that the neutralized dispersion resin neutralized with NaOH dissolves in an amount of 10 g or more in 100 g of water. If the dispersing resin is water-soluble, the pigment can be dispersed without using any organic solvent, particularly an ester-based solvent or a ketone-based solvent, in the pigment dispersion process. This eliminates the need for a process for removing the organic solvent. Furthermore, residual organic solvent that cannot be completely removed does not adversely affect storage stability or storage stability when the temperature is repeatedly raised and lowered.

[0035] The acid value of the dispersion resin having an anionic group used in the present invention is 181 to 220 mgKOH / g. The acid value is preferably 181 to 210 mgKOH / g, and more preferably 185 to 205 mgKOH / g. When the acid value is within the above range, an aqueous pigment dispersion can be obtained that is excellent in storage stability by preventing aggregation or precipitation of the pigment over time, and the ejection property is good, so that the printability is excellent. Furthermore, when the ink composition contains a large amount of surfactant or solvent, the storage stability of the ink tends to be poor when the temperature is repeatedly increased and decreased. However, when the acid value is within the above range, even such an ink has good storage stability when the temperature is repeatedly increased and decreased.

[0036] The weight average molecular weight of the dispersion resin having an anionic group used in the present invention is preferably 10,000 to 50,000, more preferably 13,000 to 50,000, further preferably 13,000 to 30,000, and particularly preferably 13,000 to 25,000. When the weight average molecular weight is within the above range, the dispersion stability is good, and the storage stability and the storage stability when the temperature is repeatedly increased and decreased are also good. Furthermore, free dispersed resins are less likely to form aggregates, and the risk that the aggregates will adversely affect the ejection properties of the inkjet can be reduced.

[0037] The content of the dispersing resin having an anionic group in the aqueous pigment dispersion of the present invention is preferably in the range of 10% by mass to 34% by mass, and more preferably in the range of 15% by mass to 30% by mass, based on the total amount of the pigment. In other words, the ratio of dispersing resin having an anionic group to pigment is preferably 0.10 to 0.40, more preferably 0.12 to 0.40, even more preferably 0.15 to 0.40, and particularly preferably 0.18 to 0.30.

[0038] Examples of the dispersion resin having an anionic group include acrylic resins such as acrylic acid-acrylic acid ester copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymers, styrene-acrylic resins such as styrene-maleic acid copolymers, styrene-maleic anhydride copolymers, vinylnaphthalene-acrylic acid copolymers, and salts of the resins. Examples of the dispersion resin include the Acrydic series of DIC Corporation and the Hi-Loss-X series of Seiko PMC Corporation. In addition, the compounds exemplified as polymer (G) in the pamphlet of WO2018 / 190139 can also be used as the dispersion resin. In addition, the dispersion resin having an anionic group may be simply referred to as a dispersion resin.

[0039] Among these, it is preferable to use a styrene-acrylic acid copolymer or a styrene-methacrylic acid copolymer as the dispersing resin having an anionic group, since the pigment can be stably dispersed in water.

[0040] As the dispersing resin having an anionic group, it is preferable to use one in which a part or all of the anionic groups are neutralized with a neutralizing agent.

[0041] The neutralizing agent may be, for example, an alkali metal hydroxide or an amine compound, and the use of an alkali metal hydroxide is preferred in order to further improve the dispersion stability immediately after the production of the aqueous pigment dispersion of the present invention and the storage stability. In addition, the use of an alkali metal hydroxide can also maintain good dischargeability.

[0042] Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide, with sodium hydroxide and potassium hydroxide being preferred, and potassium hydroxide being more preferred.

[0043] The neutralizing agent is preferably used so that the neutralization rate calculated by the following formula is within 100%, in order to prevent precipitation or aggregation of the pigment over time and obtain an aqueous pigment dispersion with excellent storage stability. The neutralization rate refers to a value calculated based on the formula [100 x (molar equivalents of hydroxyl groups of alkali metal hydroxide / molar equivalents of anionic groups of the dispersing resin)].

[0044] (Crosslinking agent) The crosslinking agent used in the present invention is a water-soluble compound having two or more epoxy groups. Examples of the crosslinking agent include polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin triglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, etc. These crosslinking agents may be used alone or in combination of two or more kinds.

[0045] Among them, it is preferable to use a crosslinking agent having an epoxy group and an oxyethylene structure in order to further improve the storage stability of the aqueous pigment dispersion. Specifically, it is preferable to use ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, or trimethylolpropane polyglycidyl ether as the crosslinking agent, and it is more preferable to use ethylene glycol diglycidyl ether.

[0046] The crosslinking agent may be a compound having two or more epoxy groups. The crosslinking agent preferably has two to four epoxy groups in order to further improve the storage stability of the aqueous pigment dispersion, and more preferably has two epoxy groups in order to achieve both the storage stability of the ink and the storage stability when the ink is repeatedly heated and cooled, as well as the ejectability of the ink.

[0047] In addition, as the crosslinking agent, it is preferable to use a compound having epoxy groups at both ends, and it is more preferable to use a compound having epoxy groups only at both ends. By using a compound having epoxy groups at both ends as a crosslinking agent, the dispersion resin can be crosslinked suitably, and even if the dispersion resin that did not contribute to the pigment dispersion is crosslinked, the ejectability is easily maintained. In addition, by using a compound having epoxy groups only at both ends, the crosslinking density can be suitably controlled, and it is more preferable to achieve both the storage stability of the ink and the ejectability of the ink when the ink is repeatedly heated and cooled.

[0048] The amount of epoxy groups contained in a crosslinking agent is expressed by the epoxy equivalent, which is the value obtained by dividing the molecular weight of an epoxy compound by the number of epoxy groups. The smaller this value, the shorter the distance between crosslinking points. The epoxy equivalent of the crosslinking agent is preferably from 100 to 400, more preferably from 100 to 350, and even more preferably from 100 to 300. If the epoxy equivalent is 100 or less, the distance between crosslinking points is short, making it impossible to crosslink dispersed resins together. On the other hand, if the epoxy equivalent is too large, dispersed resins that are farther apart will be crosslinked to form a crosslinked structure, which will cause the ink to thicken.

[0049] The crosslinking agent is water-soluble. Here, "the crosslinking agent is a water-soluble compound" means that the water solubility of the crosslinking agent is 50% or more. The water solubility is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. The higher the water solubility of the crosslinking agent, the less likely the particle size of the pigment is to increase when the dispersion resin is crosslinked, and the more likely it is that the pigment will aggregate. The water solubility (%) is the solubility (mass%) when 10 parts by mass of an epoxy compound is dissolved in 90 parts by mass of water at room temperature of 25° C. Specifically, it can be measured by the following procedure. At room temperature 25°C, 90 parts of ion-exchanged water and 10 parts of crosslinking agent are added to a glass tube (25 mmφ×250 mmh), and the glass tube is left to stand for 1 hour in a thermostatic bath with the water temperature adjusted to 25°C. Next, the glass tube is vigorously shaken for 1 minute, and then left to stand again in the thermostatic bath for 10 minutes. Next, the undissolved matter is weighed, and the water solubility (mass%) is calculated.

[0050] The crosslinking agent is preferably used in a range of 4.0 mmol / g or less relative to the total amount of the dispersing resin in order to obtain an aqueous pigment dispersion with even better storage stability, more preferably in a range of 3.8 mmol / g or less, and even more preferably in a range of 2.3 mmol / g or more and 3.6 mmol / g or less.

[0051] The aqueous pigment dispersion of the present invention can contain, as necessary, a water-soluble solvent, a preservative, a viscosity adjuster, a pH adjuster, a chelating agent, a plasticizer, an antioxidant, an ultraviolet absorber, etc. The chelating agent can reduce the content of metal ions derived from the pigment contained in the aqueous pigment dispersion.

[0052] Next, a method for producing the aqueous pigment dispersion of the present invention will be described. The present invention also provides a method for producing an aqueous pigment dispersion comprising water, a pigment, and a crosslinked polymer, the crosslinked polymer being obtained by crosslinking a dispersing resin having an anionic group with a crosslinking agent, the dispersing resin having an anionic group being water-soluble and having an acid value of 181 to 220 mgKOH / g, the crosslinking agent being a water-soluble compound having two or more epoxy groups, and the crosslinking rate of the crosslinked polymer being greater than 80%. Specifically, the method for producing an aqueous pigment dispersion includes step 1 of mixing water, a pigment, and a dispersion resin having an anionic group to produce a dispersion in which the pigment is dispersed in the water, and step 2 of reacting an anionic group, such as a carboxyl group, of the dispersion resin contained in the dispersion with a functional group, such as an epoxy group, of the crosslinking agent to form a crosslinked polymer, wherein the dispersion resin having an anionic group is water-soluble and has an acid value of 181 to 220 mgKOH / g, the crosslinking agent is a water-soluble compound having two or more epoxy groups, and the crosslinking rate of the crosslinked polymer exceeds 80%.

[0053] The step 1 is, for example, a step of treating a mixture of a pigment, a dispersing resin, and water using a dispersing machine.

[0054] Examples of the dispersing machine that can be used include kneading dispersing machines with high-speed stirring blades, such as an Intensive Mixer (manufactured by Nippon Eirich Co., Ltd.), a Butterfly Mixer (Inoue Seisakusho Co., Ltd.), and a Planetary Mixer (Inoue Seisakusho Co., Ltd.); media-type wet dispersing machines, such as an SC Mill (Nippon Coke and Engineering Co., Ltd.) and a Nano Mill (Asada Iron Works Co., Ltd.); and media-less wet dispersing machines, such as a Starburst (Sugino Machine Corp.) and an ultrasonic processor (Hielscher Ultrasonics GmbH).

[0055] Among them, it is preferable to use a kneading disperser having the high-speed stirring blade as the disperser in order to prevent the ink jet ejection property of the ink from being deteriorated due to the influence of beads and the like used in a media-type wet disperser. Furthermore, the kneading disperser having the high-speed stirring blade can raise the temperature of the contents of the disperser to near 100°C compared to a wet disperser, and as a result, it is possible to increase the ease with which the dispersing resin is adsorbed to the pigment. If there is a small amount of dispersing resin that is not adsorbed to the pigment, agglomerates of the crosslinked polymer are less likely to occur during crosslinking treatment, and the ejection property of the printer is maintained good.

[0056] On the other hand, when the media-type wet disperser or media-less type wet disperser is used, the step 1 may include a step 1-1 of mixing the pigment, dispersing resin, and water, and pre-dispersing the mixture using a stirrer or the like to produce a mixture containing the pigment and water, and a step 1-2 of treating the mixture obtained in the step 1-1 with the media-type wet disperser or media-less type wet disperser. With this step, the dispersibility of the pigment and the like contained in the aqueous pigment dispersion can be confirmed during the process.

[0057] The neutralization of the dispersed resin is preferably carried out during or after the completion of step 1. Specifically, the neutralization can be carried out by supplying and mixing the neutralizing agent to the mixture during step 1 or the dispersion obtained after the completion of step 1.

[0058] Furthermore, the dispersion obtained in the step 1 may be subjected to centrifugation, pH adjustment, or metal ion removal, if necessary, before the step 2 is carried out.

[0059] Next, step 2 will be described. Step 2 is a step of forming a dispersing resin having an anionic group coated or adsorbed on the surface of the pigment by reacting an anionic group such as a carboxyl group of the dispersing resin with a functional group such as an epoxy group of the crosslinking agent. The reaction is preferably carried out at a temperature in the range of 60 to 70° C. in order to obtain an aqueous pigment dispersion having even better storage stability.

[0060] As described above, the crosslinking agent is preferably supplied to the dispersion obtained after completion of step 1, but it may also be supplied to the mixture of the pigment, the dispersing resin, and the water during step 1.

[0061] The aqueous pigment dispersion obtained through steps 1 and 2 is preferably subjected to centrifugation or filtration as necessary in order to remove coarse particles and reduce the amount of sediment contained in the dispersion obtained in step 1, the aqueous pigment dispersion, and the ink.

[0062] The aqueous pigment dispersion obtained by the above method can be used to produce inks such as inkjet inks, as described below. However, since the aqueous pigment dispersion obtained by the above method tends to have a slightly high pH, ​​if there is a discrepancy with the pH expected for the ink, it is preferable to adjust the pH of the aqueous pigment dispersion to a lower value in advance in order to increase the freedom of ink design. As a method for adjusting the pH of the aqueous pigment dispersion, a method of treating the aqueous pigment dispersion with an ion exchange resin can be mentioned. Specifically, a method of mixing a weakly acidic cation exchange resin such as Amberlite IRC76 manufactured by Organo Corporation with the aqueous pigment dispersion and then removing the cation exchange resin can be mentioned.

[0063] (Inkjet ink) The aqueous pigment dispersion of the present invention obtained by the above method can be used, for example, for the production of inks, particularly for the production of inkjet inks. The inkjet ink can be produced, for example, by supplying and mixing the aqueous pigment dispersion with an aqueous medium, a binder, a surfactant, etc., as necessary. When mixing the aqueous pigment dispersion with an aqueous medium, a binder, a surfactant, etc., as necessary, a dispersing machine or various mixers, such as a bead mill, an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a roll mill, a sand mill, a sand grinder, a Dyno Mill, a Dispermat, an SC Mill, or a Nanomizer, can be used.

[0064] The inkjet ink may contain other additives, such as binders, surfactants, waxes, wetting agents (drying inhibitors), penetrating agents, preservatives, viscosity adjusters, pH adjusters, chelating agents, plasticizers, antioxidants, and ultraviolet absorbers, as necessary.

[0065] As the binder, for example, poly(meth)acrylic resin, polyurethane resin, polyester resin, or acid-modified polypropylene resin can be used. As the acid-modified polypropylene resin, a resin obtained by modifying polypropylene with one or more types of acidic compounds can be used, and it is preferable to use one having a skeleton derived from polypropylene (polypropylene skeleton) and a functional group derived from an acidic compound. If the inkjet ink contains the acid-modified polypropylene resin, it is possible to suppress the occurrence of mottling or streak-like printing defects in the printed matter during one-pass printing, even when the ink is printed on a recording medium that does not absorb or does not easily absorb the solvent in the ink.

[0066] The acid-modified polypropylene resin may be a commercially available product. Preferred commercially available products include Auroren (registered trademark) AE-301 and AE-502 manufactured by Nippon Paper Industries Co., Ltd. The oxidized polyethylene wax may be, for example, a polyethylene wax that has been subjected to an oxidation treatment, and specifically, a wax having a skeleton derived from polyethylene (polyethylene skeleton) may be used.

[0067] As the surfactant, for example, anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc. can be used.

[0068] As the surfactant, it is preferable to use one or more types selected from the group consisting of anionic surfactants and nonionic surfactants, from the viewpoint of easily suppressing the occurrence of streak-like printing defects.

[0069] Examples of the anionic surfactant include alkylbenzenesulfonates, alkylphenylsulfonates, alkylnaphthalenesulfonates, higher fatty acid salts, sulfate salts of higher fatty acid esters, sulfonates of higher fatty acid esters, sulfate salts and sulfonates of higher alcohol ethers, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, and polyoxyethylene alkyl ether phosphates. Specific examples of these include dodecylbenzenesulfonates, isopropylnaphthalenesulfonates, monobutylphenylphenol monosulfonates, monobutylbiphenylsulfonates, and dibutylphenylphenol disulfonates.

[0070] Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkylol amides, alkyl alkanol amides, acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymers. Among these, polyoxyethylene nonylphenyl ethers, polyoxyethylene octylphenyl ethers, polyoxyethylene dodecylphenyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid alkylol amides, acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymers are preferred.

[0071] As the nonionic surfactant, the inkjet ink preferably contains an acetylene-based surfactant from the viewpoint of easily suppressing the occurrence of streaky printing defects. The acetylene-based surfactant is a surfactant having an acetylene structure in the molecule. From the viewpoint of easily suppressing the occurrence of streaky printing defects, the acetylene-based surfactant preferably contains one or more types selected from the group consisting of acetylene glycol and oxyethylene adducts of acetylene glycol.

[0072] From the viewpoint of easily suppressing the occurrence of streak-like printing defects, the content of the acetylene-based surfactant is preferably 80 to 100 mass %, more preferably 85 to 99.9 mass %, and even more preferably 90 to 99.5 mass %, based on the total amount of surfactants.

[0073] Other surfactants that can be used include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers; and biosurfactants such as spiculisporic acid, rhamnolipid, and lysolecithin.

[0074] The content of the surfactant is preferably from 0.1 to 2% by mass, more preferably from 0.5 to 2% by mass, and even more preferably from 0.8 to 1.6% by mass, based on the total amount of the inkjet ink. Ink-jet inks containing surfactants in these amounts have good wettability of the ejected droplets on the surface of a substrate, tend to have sufficient wet spread on the substrate, and tend to be effective in preventing streaky printing defects. Furthermore, if the amount of surfactant in the ink is within this range, the surfactant is less likely to become concentrated when the ink is repeatedly heated and cooled, and therefore good storage stability can be maintained.

[0075] The use of a surfactant makes it easy to prevent the occurrence of streaky printing defects, since the inkjet ink discharged from the discharge port of the inkjet head easily wets and spreads on the surface after landing on the printed material, etc. Furthermore, the use of a surfactant makes it easy to improve the leveling property of the inkjet ink by, for example, lowering the surface tension of the inkjet ink.

[0076] As the wax, for example, oxidized polyethylene wax can be used.

[0077] When the ink-jet ink contains the oxidized polyethylene wax, it is possible to obtain a printed matter having excellent image fastness.

[0078] As the oxidized polyethylene wax, it is preferable to use an oxidized polyethylene wax in a state of being dissolved or dispersed in a solvent in order to obtain a printed matter having excellent image fastness.

[0079] The oxidized polyethylene wax may be a commercially available product, and preferred commercially available products include AQUACER 515 and AQUACER 1547 manufactured by BYK.

[0080] The wetting agent can be used for the purpose of preventing the inkjet ink from drying in the ejection nozzle of the inkjet head. As the wetting agent, it is preferable to use one that is miscible with water and has an effect of preventing the ejection port of the inkjet head from being clogged, and examples of the wetting agent include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol with a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, mesoerythritol, pentaerythritol, and glycerin.

[0081] As the wetting agent, a solid wetting agent can also be used. Examples of such wetting agents include urea and urea derivatives. Examples of urea derivatives include ethylene urea, propylene urea, diethyl urea, thiourea, N,N-dimethyl urea, hydroxyethyl urea, hydroxybutyl urea, ethylene thiourea, and diethyl thiourea. These can be used alone or in combination of two or more. From the viewpoint of easily obtaining a printed matter with excellent setting properties, it is preferable to use at least one selected from the group consisting of urea, ethylene urea, and 2-hydroxyethyl urea.

[0082] The content of the humectant in the inkjet ink is 3 to 50% by mass relative to the total amount of the inkjet ink, which allows the ink to dry easily on the recording medium while preventing the inkjet ink from sticking inside the inkjet head.

[0083] Examples of the penetrating agent include lower alcohols such as ethanol and isopropyl alcohol; and glycol monoethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl butyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, and tripropylene glycol monobutyl ether.

[0084] When the ink is repeatedly heated and cooled, the above-mentioned wetting agent and penetrant may promote the concentration of the surfactant at low temperatures, and the concentrated components at high temperatures may adversely affect the dispersion of the pigment. However, by using the aqueous pigment dispersion of the present invention, this adverse effect can be reduced, and good storage stability can be obtained even when the ink is repeatedly heated and cooled.

[0085] In the inkjet ink obtained by the above method, the pigment is preferably used in the range of 1% by mass to 15% by mass, based on the total amount of printing ink, and using the pigment in the range of 2% by mass to 10% by mass is preferable in order to obtain printed matter having high print density, being less susceptible to streaks, excellent image fastness, and excellent dispersion stability.

[0086] The pH of the inkjet ink is preferably 7.0 or more, more preferably 7.5 or more, and even more preferably 8.0 or more, in order to improve the storage stability and ejection stability of the ink, and to improve the wet spread, print density, and abrasion resistance when printed on a poorly ink-absorbing or non-ink-absorbing recording medium. The upper limit of the pH of the aqueous ink composition is preferably 11.0 or less, more preferably 10.5 or less, and even more preferably 10.0 or less, in order to suppress deterioration of members constituting the ink application or ejection device (e.g., ink ejection port, ink flow path, etc.) and to reduce the effect when the ink adheres to the skin. From these viewpoints, the pH of the inkjet ink is preferably 7.0 to 11.0. The above pH is measured at 25°C.

[0087] The viscosity of the inkjet ink is preferably 2 mPa·s or more and less than 10 mPa·s at 32°C. When the viscosity of the inkjet ink is in this range, when the inkjet ink is used in an inkjet recording method, the deviation of the landing position on the recording medium caused by the flight deflection tends to be reduced, and the occurrence of streaks in the printed matter tends to be effectively prevented. In addition, an inkjet ink having a viscosity in this range tends to have excellent storage stability and ejection stability in an inkjet recording method. The viscosity of the inkjet ink at 32°C is preferably 3 mPa·s or more, more preferably 4 mPa·s or more. The viscosity of the aqueous ink composition at 32°C is preferably 8 mPa·s or less, more preferably 7 mPa·s or less. The above viscosity is, for example, a value measured under the following conditions using a cone-plate type rotational viscometer equivalent to an E-type viscometer.

[0088] Measurement equipment: TVE-25 type viscometer (Toki Sangyo Co., Ltd., TVE-25 L) Calibration standard solution: JS20 Measurement temperature: 32℃ Rotation speed: 10~100rpm Injection volume: 1200μL

[0089] The surface tension of the inkjet ink is preferably, for example, 20 to 40 mN / m at 25°C. When the surface tension of the aqueous ink composition is within this range, when used in an inkjet recording method, the wettability of the discharged droplets on the surface of the recording medium tends to be good, and the ink tends to spread sufficiently after landing. The surface tension of the inkjet ink at 25°C is preferably 25 mN / m or more, more preferably 27 mN / m or more. The surface tension of the aqueous ink composition at 25°C is preferably 35 mN / m or less, more preferably 32 mN / m or less.

[0090] The inkjet ink containing the aqueous pigment dispersion of the present invention has a high crosslinking rate, so that the dispersing resin is more firmly adsorbed to the pigment surface, and the storage stability is good. Here, good storage stability means that the rate of change in the volume average particle diameter measured by the following method is less than 10% after 2 weeks of testing, less than 15% after 4 weeks, and less than 20% after 8 weeks. In addition, the storage by the following method is an accelerated test, and when stored at 60°C for 8 weeks, the same results as when stored at room temperature (25°C) for approximately 2 years can be obtained, and deterioration due to long-term storage can be predicted.

[0091] (Storage stability evaluation method) The volume average particle diameter D0 of the ink-jet ink immediately after production was measured by the particle diameter measurement method described below. Next, 30 mL of the inkjet ink was filled into a polypropylene bottle having a volume of 30 mL and stored in a thermostatic chamber at 60° C. After a certain period of time from the start of the storage, the volume average particle diameter D1 of the inkjet ink was measured by the particle diameter measurement method described below.

[0092] The rate of change in particle diameter of the inkjet ink after storage for a certain period from the start of storage was calculated based on the volume average particle diameters D0 and D1 and the following formula, and the storage stability of the inkjet ink was evaluated based on the rate of change. Particle size change rate = [(D1-D0) / (D0)] x 100

[0093] The particle size of the inkjet ink was measured under the following conditions. Measuring device: Particle size analyzer NANOTRAC WAVE 2 (manufactured by Microtrack Bell Co., Ltd.) Measurement temperature: 25℃ Number of measurements: 1 Measurement time: 180 seconds Particle permeability: transparent Particle refractive index: 1.51 Particle shape: non-spherical Density: 1.00 Solvent refractive index: 1.333 Filter:Stand:Norm

[0094] In addition, the ink-jet ink containing the aqueous pigment dispersion of the present invention can maintain a stable state even when the storage temperature is changed to a low or high temperature due to shipping by ship, etc. The stability under such storage conditions can be evaluated by repeatedly increasing and decreasing the storage temperature. When the storage temperature is high, molecular motion becomes active, so that the adsorption between the pigment and the dispersion resin is easily removed, and the pigment is easily aggregated. On the other hand, when the storage temperature is low (for example, -40°C), some of the components in the inkjet ink (particularly, surfactants) are precipitated or concentrated, and when the ink temperature is subsequently increased, the highly concentrated ink components and the dispersion system may interact with each other, which may easily cause aggregation of the pigment. Due to this mechanism of particle size increase, the storage stability at a constant temperature and the storage stability when the temperature is repeatedly increased and decreased may not be correlated. The inkjet ink containing the aqueous pigment dispersion of the present invention can maintain good storage stability when the temperature is repeatedly increased and decreased. Here, good storage stability when the temperature is repeatedly increased and decreased means that the rate of change in the volume average particle size measured by the following method is less than 10%.

[0095] (Heating / cooling cycle test evaluation method) The volume average particle diameter D0 of the ink-jet ink immediately after production was measured by the particle diameter measurement method described below. Next, 30 mL of the inkjet ink was filled into a 30 mL polypropylene plastic bottle and placed in a thermostatic chamber at room temperature. The temperature inside the chamber was cooled to -40°C and held at -40°C for 4 hours, then raised to 70°C and held at 70°C for 4 hours. This temperature cycle was repeated four times, and the volume average particle diameter D2 of the inkjet ink after the cycle was completed was measured, and the rate of change from MV0 was calculated. Particle size change rate=[(D2-D0) / (D0)]×100

[0096] A printed matter obtained using the inkjet ink of the present invention has, for example, a recording medium and a coating film of the inkjet ink printed on the surface of the recording medium. The ink coating film formed on the surface of the recording medium is, for example, a dried product of the inkjet ink and contains the solid content of the inkjet ink (for example, the pigment and the pigment dispersant (B), etc.).

[0097] The recording medium is, for example, plain paper, inkjet paper, glossy paper, poorly ink-absorbent recording medium, non-ink-absorbent recording medium, etc. This printed matter has sufficient image fastness even if the recording medium is the poorly ink-absorbent or non-ink-absorbent recording medium described above.

[0098] The printed matter can be obtained, for example, by printing the inkjet ink on the surface of a recording medium by an inkjet recording method. Specifically, the printed matter can be obtained by ejecting the inkjet ink and printing on the recording medium by an inkjet recording method in which the distance from a surface (x) having ink ejection ports of an inkjet head to a position (y) where a perpendicular line to the surface (x) intersects with the recording medium is 1 mm or more. EXAMPLES

[0099] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0100] (Dispersion resin A) Dispersion resin A, a radical polymer, is a powder (diameter 1 mm or less) manufactured by solution polymerization and consists of a monomer composition. The composition ratio was styrene / acrylic acid / methacrylic acid / butyl acrylate=72.00 / 12.13 / 15.77 / 0.10 (mass ratio), the weight average molecular weight was 16000, the acid value was 185 mgKOH / g, and the glass transition temperature was 139° C. Furthermore, the dispersion resin A was found to be water-soluble in the water solubility test described below.

[0101] (Dispersion resin B) Dispersion resin B, a radical polymer, is a powder (diameter 1 mm or less) manufactured by solution polymerization and consists of a monomer composition. The composition ratio was styrene / acrylic acid / methacrylic acid / butyl acrylate=69.06 / 13.41 / 17.43 / 0.10 (mass ratio), the weight average molecular weight was 14000, the acid value was 202 mgKOH / g, and the glass transition temperature was 139° C. Furthermore, the dispersion resin B was found to be water-soluble in the water solubility test described below.

[0102] (Dispersion resin C) Dispersion resin C, a radical polymer, is in the form of a powder (diameter 1 mm or less) produced by a solution polymerization method, with a monomer composition ratio of styrene / acrylic acid / methacrylic acid / butyl acrylate = 74.00 / 11.26 / 14.64 / 0.10 (mass ratio), a weight average molecular weight of 11000, an acid value of 173 mgKOH / g, and a glass transition temperature of 115°C. Furthermore, dispersion resin C was found to be water-soluble in the water solubility test described below.

[0103] The weight average molecular weight in the present invention is determined by gel permeation chromatography (GPC). This value is measured by the molecular weight spectrometry (Molecular Weight Graphene) method and is based on the molecular weight of polystyrene used as the standard material. The measurements were carried out using the following equipment and conditions.

[0104] Liquid delivery pump: LC-9A System controller: SLC-6B Autoinjector: S1L-6B Detector: RID-6A The above is manufactured by Shimadzu Corporation. Data processing software: Sic480II Data Station (System Instruments) Made in Japan. Column: GL-R400 (guard column) + GL-R440 + GL-R450 + GL-R 400M (Hitachi Chemical Co., Ltd.) Elution solvent: Tetrahydrofuran (THF) Elution flow rate: 2ml / min Column temperature: 35℃

[0105] The water solubility of the dispersing resin was determined by the following procedure. (1) 10 g of dispersion resin was placed in a beaker. (2) To (1), an aqueous NaOH solution was added so as to achieve 100% neutralization according to the acid value of the dispersion resin. (3) To (2), water was added so that the total amount, including the amount of water in the NaOH aqueous solution, was 100 g, and the mixture was thoroughly stirred while heating to 50 to 60° C. as necessary. (4) The aqueous solution was allowed to stand at 25°C for 24 hours or more, after which it was visually inspected for the presence of any precipitate. Sediment: Water insoluble No sediment: Water soluble

[0106] (Production Example 1) According to the amounts shown in Table 1, dispersion resin A and FASTOGEN SUPER MAGENTA RY (DIC) as a magenta pigment were charged into a planetary mixer (product name: Chemical Mixer ACM04LVTJ-B, Aikosha Seisakusho Co., Ltd.) with a jacket heated to 80°C, and stirred at a rotation speed of 80 rpm and a revolution speed of 25 rpm. After 10 minutes, triethylene glycol as a solvent and a 34% by mass potassium hydroxide aqueous solution as a neutralizing agent were added and stirred again, and kneading was continued until 60 minutes had passed since the current value of the planetary mixer reached its maximum current value, to obtain a kneaded product.

[0107] The obtained kneaded product was gradually mixed with ion-exchanged water to dilute it, and finally, triethylene glycol was added as a diluent to obtain an aqueous pigment dispersion 1 having a pigment concentration of 15.4% by mass.

[0108] (Manufacturing Examples 2 and 3) Aqueous pigment dispersions 2 and 3 were obtained in the same manner as in Production Example 1, except that the raw materials used and their amounts were changed as shown in Table 1.

[0109] [Table 1]

[0110] Example 1 Aqueous pigment dispersion 1 obtained in Production Example 1, a crosslinking agent, and ion-exchanged water were charged in the amounts shown in Table 2 in a plastic container with a lid, and stirred for 5 hours at 70° C. After stirring, the mixture was cooled to obtain crosslinked dispersion 1 having a pigment concentration of 15% by mass. The crosslinking rate of the crosslinked polymer in this crosslinked dispersion was 82%.

[0111] (Examples 2 to 4, Comparative Examples 1 to 6) Crosslinked dispersions 2 to 10 were obtained in the same manner as in Example 1, except that the raw materials used and their amounts were changed as shown in Table 2.

[0112] The crosslinking ratios of the crosslinked polymers of the crosslinked dispersions 1 to 10 of Examples 1 to 4 and Comparative Examples 1 to 6 were calculated as follows. Crosslinking rate (mol%)=100×[molar number of reactive groups in crosslinking agent] / [molar number of carboxyl groups in the dispersion resin] Formula (2) In formula (2), the "molar number of reactive groups in the crosslinking agent" is the value obtained by dividing the weight of the crosslinking agent used by the equivalent weight of the reactive groups, i.e., the mole number of the crosslinking agent used multiplied by the number of reactive groups in one molecule of the crosslinking agent.

[0113] [Table 2]

[0114] Denacol EX313: epoxy equivalent 141, solubility of 10 g of crosslinker in 90 g of ion-exchanged water (water solubility) is 99% by mass (25°C), manufactured by Nagase ChemteX Corporation Denacol EX810: epoxy equivalent 113, solubility of 10 g of crosslinker in 90 g of ion-exchanged water (water solubility) is 100% by mass (25°C), manufactured by Nagase ChemteX Corporation Denacol EX830: epoxy equivalent 268, solubility of 10 g of crosslinker in 90 g of ion-exchanged water (water solubility) is 100% by mass (25°C), manufactured by Nagase ChemteX Corporation

[0115] (Preparation Example 1) In a plastic container, ion-exchanged water, propylene glycol, glycerin, triethanolamine, TegoWET 280 (manufactured by Evonik, silicone-based surfactant), ACTICIDE B20 (manufactured by Thor Japan, preservative), and ethylene urea were charged in the amounts shown in Table 3, and after the ethylene urea was dissolved, propylene glycol and SURFYNOL 420 (manufactured by Evonik, acetylene-based surfactant) were added and stirred to obtain mixture A. Next, Auroren (registered trademark) AE-301 (manufactured by Nippon Paper Industries Co., Ltd., acid-modified polypropylene), ion-exchanged water, AQUACER 515 (manufactured by BYK, high-density oxidized polyethylene wax emulsion), and ion-exchanged water were mixed in the order shown to obtain mixture B. The crosslinked dispersion 1 obtained in Example 1 was mixed in the amount shown in Table 3 to mixture B, and then mixture A was further mixed. The container was washed with ion-exchanged water as washing water, and then stirred to obtain ink 1.

[0116] (Preparation Examples 2 to 10) Inks 2 to 10 were obtained by preparing the inks under the same conditions as in Preparation Example 1, except that the crosslinked dispersion 1 was changed to crosslinked dispersions 2 to 10.

[0117] <Characteristics evaluation> The ink characteristics were evaluated by the methods described below.

[0118] [Storage stability evaluation] Immediately after production, the volume average particle size D0 of each of the inks 1 to 10 was measured using the particle size measurement method described below. Next, 30 mL of each of the inks 1 to 10 was filled into a 30 mL polypropylene bottle and stored in a thermostatic chamber at 60° C. After a certain period of time from the start of the storage, the volume average particle size D1 of each ink after storage was measured using the particle size measurement method described below.

[0119] The rate of change in particle size of each ink after storage for a certain period from the start of storage was calculated based on the volume average particle sizes D0 and D1 and the following formula, and the storage stability of inks 1 to 10 was evaluated based on the rate of change. Particle size change rate = [(D1-D0) / (D0)] x 100 The storage stability of inks 1 to 10 was evaluated as good if the rate of change in volume average particle diameter was less than 10% after 2 weeks of testing, less than 15% after 4 weeks, and less than 20% after 8 weeks.

[0120] [Heating / cooling cycle] Immediately after production, the volume average particle diameter D0 of each of the inks 1 to 10 was measured by the following particle diameter measurement method. Next, 30 mL of the inkjet ink was filled into a 30 mL polypropylene plastic bottle and placed in a thermostatic chamber at room temperature. The temperature inside the chamber was cooled to -40°C, held at -40°C for 4 hours, then raised to 70°C and held at 70°C for 4 hours. This temperature cycle was repeated four times, and the volume average particle diameter D2 of each ink after the cycle was completed was measured by the following method, and the rate of change from D0 was calculated. Particle size change rate=[(D2-D0) / (D0)]×100 The heating and cooling cycles of inks 1 to 10 were rated as "good" if the rate of change in volume average particle diameter was less than 10%.

[0121] The particle size of inks 1 to 10 in the above storage stability and heating / cooling cycle evaluation was expressed as MV (volume average diameter) values ​​measured under the following conditions. Measuring device: Particle size analyzer NANOTRAC WAVE 2 (manufactured by Microtrack Bell Co., Ltd.) Measurement temperature: 25℃ Number of measurements: 1 Measurement time: 180 seconds Particle permeability: transparent Particle refractive index: 1.51 Particle shape: non-spherical Density: 1.00 Solvent refractive index: 1.333 Filter:Stand:Norm

[0122] [Printability test] 50 mL of ink was filtered through a 0.45 μm membrane filter and filled into the black ink cartridge of a Hewlett-Packard printer ENVY4500. The print properties were set to grayscale printing: black ink only, print quality: draft, and solid printing was performed on Sylvamo printing paper HAMMER MILL. The printed area was measured with an X-Rite eXact colorimeter to obtain the saturation. A saturation value of 45 or higher was determined to be suitable for printing.

[0123] The evaluation results are summarized in Table 3.

[0124] [Table 3]

[0125] As shown in Table 3, inks 1 to 4, which are inks using the aqueous pigment dispersion of the present invention, not only had good storage stability but also good results in the heating and cooling cycle evaluation. Furthermore, they were also excellent in printability. On the other hand, inks 5 and 7 to 9 used aqueous pigment dispersions with low crosslinking rates of the crosslinked polymer, and therefore showed poor storage stability and poor heating / cooling cycle evaluation results. In addition, aqueous pigment dispersions 5 and 6 used dispersion resins with low acid values, which resulted in poor printability and low saturation of the printed matter.

[0126] (Production Example 4) According to the amounts listed in Table 4, dispersion resin B and 995B (manufactured by Mitsubishi Chemical Corporation) as a black pigment were charged into a planetary mixer (product name: Chemical Mixer ACM04LVTJ-B, manufactured by Aikosha Seisakusho Co., Ltd.) with a jacket heated to 80°C, and stirred at a rotation speed of 80 rpm and a revolution speed of 25 rpm. After 10 minutes, triethylene glycol was added as a solvent and a 34% by mass potassium hydroxide aqueous solution as a neutralizing agent, and the mixture was stirred again. The mixture was kneaded continuously until 60 minutes had elapsed since the current value of the planetary mixer reached its maximum current value, to obtain a kneaded product.

[0127] The obtained kneaded product was gradually mixed with ion-exchanged water to dilute it, and finally, triethylene glycol was added as a diluent to obtain an aqueous pigment dispersion 4 having a pigment concentration of 13.0% by mass.

[0128] (Production Example 5) Among the raw materials used, the pigment was changed to the cyan pigment SBG-SD (manufactured by DIC Corporation), and the amounts of the other raw materials added were changed as shown in Table 4. Aqueous pigment dispersion 5 was obtained in the same manner as in Production Example 4.

[0129] [Table 4]

[0130] Example 5 Aqueous pigment dispersion 4 obtained in Production Example 4, a crosslinking agent, and ion-exchanged water were charged in the amounts shown in Table 5 in a plastic container with a lid, and stirred for 5 hours at 70°C. After stirring, the mixture was cooled to obtain crosslinked dispersion 11 having a pigment concentration of 12.5% ​​by mass. The crosslinking rate of the crosslinked polymer in this crosslinked dispersion was 82%.

[0131] Example 6 A crosslinked dispersion 12 was obtained in the same manner as in Example 5, except that the raw materials used and their amounts were changed as shown in Table 5.

[0132] [Table 5]

[0133] (Preparation Example 11) In a plastic container, ion-exchanged water, propylene glycol, glycerin, triethanolamine, TegoWET 280 (manufactured by Evonik, silicone-based surfactant), ACTICIDE B20 (manufactured by Thor Japan, preservative), and ethylene urea were charged in the amounts shown in Table 6. After the ethylene urea was dissolved, propylene glycol and SURFYNOL 420 (manufactured by Evonik, acetylene-based surfactant) were added and stirred to obtain a mixture A. Next, Auroren (registered trademark) AE-301 (manufactured by Nippon Paper Industries Co., Ltd., acid-modified polypropylene), ion-exchanged water, AQUACER 515 (manufactured by BYK, high-density oxidized polyethylene wax emulsion), and ion-exchanged water were mixed in the order shown to obtain a mixture B. The crosslinked dispersion 11 obtained in Example 5 was mixed in the amount shown in Table 6 to the mixture B, and then the mixture A was further mixed. The container was washed with ion-exchanged water as washing water, and then stirred to obtain an ink 11.

[0134] (Preparation Example 12) Ink 12 was obtained by preparing the ink under the same conditions as in Preparation Example 11, except that Crosslinked Dispersion 11 was changed to Crosslinked Dispersion 12 in the parts by mass shown.

[0135] [Table 6]

[0136] [Printability test] 50 mL of ink was filtered through a 0.45 μm membrane filter and filled into the black ink cartridge of a Hewlett-Packard printer, ENVY4500. The print properties were set to grayscale printing: black ink only, and print quality: draft, and a solid print was made on Sylvamo printing paper, HAMMER MILL. The printed area was measured with an X-Rite eXact colorimeter to obtain saturation. Inks using black pigments with a saturation value of 5 or less were deemed to be suitable for printing. On the other hand, inks using cyan pigments with a saturation value of 40 or more were deemed to be suitable for printing.

[0137] As shown in Table 6, when black and cyan pigments were used, similar to the magenta pigment, good storage stability and heating / cooling cycle evaluation results were obtained. Furthermore, the printability was also excellent.

Claims

1. Water, a pigment, and a crosslinked polymer; the crosslinked polymer is a reaction product of a dispersing resin having an anionic group and a crosslinking agent; the dispersion resin having an anionic group is water-soluble and has an acid value of 181 to 220 mgKOH / g; the crosslinking agent is a water-soluble compound having two or more epoxy groups, The aqueous pigment dispersion, wherein the crosslinked polymer has a crosslinking rate of more than 80%.

2. 2. The aqueous pigment dispersion according to claim 1, wherein a ratio of the pigment to the dispersing resin having an anionic group (dispersing resin having an anionic group / pigment) is from 0.10 to 0.

40.

3. The aqueous pigment dispersion according to claim 1 , wherein the pigment is a quinacridone pigment.

4. An ink-jet ink comprising the aqueous pigment dispersion according to any one of claims 1 to 3.

5. A printed matter comprising the ink-jet ink according to claim 4 and a recording medium.

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