Inkjet ink and method for producing inkjet ink

Abstract

To provide an inkjet ink capable of forming an image having excellent abrasion resistance and a desired image density while suppressing the occurrence of nozzle clogging.SOLUTION: There is provided an inkjet ink which contains an aqueous medium and pigment particles dispersed in the aqueous medium. The pigment particles contain a pigment and a cross-linked resin. The cross-linked resin is a crosslinked product of a specific resin, a first crosslinking agent and a second crosslinking agent. The first crosslinking agent has an ethylene oxide structure having an addition molar number of 1 or more and 4 or less or a propylene oxide structure having an addition molar number of 1 or more and 4 or less and 2 or more epoxy groups in the molecule. The second crosslinking agent has an ethylene oxide structure having an addition molar number of 5 or more and 15 or less and 2 or more epoxy groups in the molecule. In the cross-linked resin, the ratio (C2 / C1) of the crosslinking rate C2 by the second crosslinking agent to the crosslinking rate C1 by the first crosslinking agent is 18 / 82 or more and 82 / 18 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an ink-jet ink and a method for making an ink-jet ink. [Background technology]

[0002] Inkjet recording devices may use aqueous inkjet inks containing a pigment and an aqueous medium. Inkjet inks are required to be able to impart excellent abrasion resistance and a desired image density to images formed while suppressing nozzle clogging in the recording head of the inkjet recording device. In response to such requirements, for example, inkjet inks have been proposed that include a pigment particle dispersion that contains an azomethine metal complex pigment and a polymer dispersant (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-116600 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, even with the inkjet ink described in Patent Document 1, it is not possible to reliably form an image having excellent abrasion resistance and a desired image density while sufficiently suppressing the occurrence of nozzle clogging.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide an inkjet ink that can form an image having excellent abrasion resistance and a desired image density while suppressing the occurrence of nozzle clogging. [Means for solving the problem]

[0006] The inkjet ink according to the present invention contains an aqueous medium and pigment particles dispersed in the aqueous medium. The pigment particles contain a pigment and a crosslinked resin. The crosslinked resin is a crosslinked product of a specific resin, a first crosslinking agent, and a second crosslinking agent. The specific resin is a neutralized product of a specific copolymer having a first repeating unit derived from α-methylstyrene, a second repeating unit derived from styrene, a third repeating unit derived from (meth)acrylic acid, and a fourth repeating unit derived from an alkylene glycol (meth)acrylate or a dialkylene glycol (meth)acrylate. With respect to 100% by mass of all repeating units contained in the specific copolymer, the content ratio of the first repeating unit is 1% by mass or more and 65% by mass or less, the content ratio of the second repeating unit is 1% by mass or more and 60% by mass or less, the content ratio of the third repeating unit is 10% by mass or more and 40% by mass or less, and the content ratio of the fourth repeating unit is 1% by mass or more and 12% by mass or less. The acid value of the specific copolymer is 50 mgKOH / g or more and 300 mgKOH / g or less. The mass average molecular weight of the specific copolymer is 3000 or more and 18000 or less. The neutralization rate of the specific resin is 20% or more and 100% or less. The first crosslinking agent has an ethylene oxide structure with an added mole number of 1 to 4 or a propylene oxide structure with an added mole number of 1 to 4 and two or more epoxy groups in the molecule. The water solubility rate of the first crosslinking agent is 80% or more. The second crosslinking agent has an ethylene oxide structure with an added mole number of 5 to 15 and two or more epoxy groups in the molecule. The water solubility rate of the second crosslinking agent is 80% or more. In the crosslinked resin, the crosslinking rate C by the first crosslinking agent is 1 Crosslinking rate C by the second crosslinking agent 2 Ratio of (C 2 / C 1 In the crosslinked resin, the total crosslinking rate (C 1 +C 2 ) is greater than or equal to 25% and less than or equal to 95%.

[0007] The method for producing an inkjet ink according to the present invention is a method for producing an inkjet ink containing an aqueous medium and pigment particles dispersed in the aqueous medium. The pigment particles include a pigment and a crosslinked resin. The method for producing an inkjet ink according to the present invention includes a neutralization step of neutralizing a specific copolymer to obtain a specific resin, a dispersion step of dispersing the specific resin and the pigment in water to obtain a pigment particle dispersion, and a crosslinking step of crosslinking the specific resin in the pigment particle dispersion with a first crosslinking agent and a second crosslinking agent to obtain the crosslinked resin. The specific copolymer has a first repeating unit derived from α-methylstyrene, a second repeating unit derived from styrene, a third repeating unit derived from (meth)acrylic acid, and a fourth repeating unit derived from an alkylene glycol (meth)acrylate or a dialkylene glycol (meth)acrylate. The content of the first repeating unit is 1% by mass or more and 65% by mass or less, the content of the second repeating unit is 1% by mass or more and 60% by mass or less, the content of the third repeating unit is 10% by mass or more and 40% by mass or less, and the content of the fourth repeating unit is 1% by mass or more and 12% by mass or less, based on 100% by mass of all repeating units in the specific copolymer. The acid value of the specific copolymer is 50 mgKOH / g or more and 300 mgKOH / g or less. The mass average molecular weight of the specific copolymer is 3000 or more and 18000 or less. The neutralization rate of the specific resin in the neutralization step is 20% or more and 100% or less. The first crosslinking agent has an ethylene oxide structure with an added mole number of 1 to 4 or a propylene oxide structure with an added mole number of 1 to 4 and two or more epoxy groups in the molecule. The water solubility of the first crosslinking agent is 80% or more. The second crosslinking agent has an ethylene oxide structure with an addition mole number of 5 to 15 in a molecule, and two or more epoxy groups. The water solubility of the second crosslinking agent is 80% or more. In the crosslinking step, the crosslinking rate C 1 Crosslinking rate C by the second crosslinking agent 2 Ratio of (C 2 / C 1 The total crosslinking rate (C 1 +C2 ) is greater than or equal to 25% and less than or equal to 95%. Effect of the Invention

[0008] The inkjet ink and the method for producing the inkjet ink according to the present invention can provide an inkjet ink that can form an image having excellent abrasion resistance and a desired image density while suppressing the occurrence of nozzle clogging. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described. In the following, the volume median diameter (D 50 ) is a value measured using a dynamic light scattering particle size distribution analyzer ("Zetasizer Nano ZS" manufactured by Malvern Instruments, unless otherwise specified.

[0010] In this specification, the acid value can be determined according to the method described in JIS (Japanese Industrial Standards) K0070:1992.

[0011] The measured weight average molecular weight (Mw), unless otherwise specified, is a value measured using gel permeation chromatography.

[0012] In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic". In this specification, acrylate and methacrylate may be collectively referred to as "(meth)acrylate". Each component described in this specification may be used alone or in combination of two or more.

[0013] <First embodiment: Inkjet ink> The first embodiment of the present invention relates to an inkjet ink (hereinafter, sometimes simply referred to as ink). The ink of this embodiment contains an aqueous medium and pigment particles dispersed in the aqueous medium. The pigment particles include a pigment and a crosslinked resin. The crosslinked resin is a crosslinked product of a specific resin, a first crosslinking agent, and a second crosslinking agent. The specific resin is a neutralized product of a specific copolymer having a first repeating unit derived from α-methylstyrene, a second repeating unit derived from styrene, a third repeating unit derived from (meth)acrylic acid, and a fourth repeating unit derived from an alkylene glycol (meth)acrylate or a dialkylene glycol (meth)acrylate. With respect to 100% by mass of all repeating units contained in the specific copolymer, the content ratio of the first repeating unit is 1% by mass or more and 65% by mass or less, the content ratio of the second repeating unit is 1% by mass or more and 60% by mass or less, the content ratio of the third repeating unit is 10% by mass or more and 40% by mass or less, and the content ratio of the fourth repeating unit is 1% by mass or more and 12% by mass or less. The acid value of the specific copolymer is 50 mgKOH / g or more and 300 mgKOH / g or less. The mass average molecular weight of the specific copolymer is 3000 or more and 18000 or less. The neutralization rate of the specific resin is 20% or more and 100% or less. The first crosslinking agent has an ethylene oxide structure with an added mole number of 1 to 4 or a propylene oxide structure with an added mole number of 1 to 4 and two or more epoxy groups in the molecule. The water solubility rate of the first crosslinking agent is 80% or more. The second crosslinking agent has an ethylene oxide structure with an added mole number of 5 to 15 and two or more epoxy groups in the molecule. The water solubility rate of the second crosslinking agent is 80% or more. In the crosslinked resin, the crosslinking rate C by the first crosslinking agent is 1 Crosslinking rate C by the second crosslinking agent 2 Ratio of (C 2 / C 1 In the crosslinked resin, the total crosslinking rate (C 1 +C 2 ) is greater than or equal to 25% and less than or equal to 95%.

[0014] In this specification, the crosslinking rate refers to the ratio of the number of functional groups that actually form a crosslinked structure in the crosslinked product formed when the total number of functional groups (groups that can react with a crosslinking agent) contained in the raw material used for crosslinking is taken as 100%. The crosslinking agents (first and second crosslinking agents) used in the ink of this embodiment mainly react with acid groups (particularly -COOH). Therefore, in the ink of this embodiment, the "total number of functional groups contained in the raw material used for crosslinking" corresponds to the number of moles of carboxy groups contained in the specific resin. In addition, the first and second crosslinking agents used in the ink of this embodiment have excellent reactivity with the specific resin. Therefore, the carboxy groups contained in the specific resin react with the epoxy groups contained in the first and second crosslinking agents at an extremely high reaction rate. In other words, the "number of functional groups that actually form a crosslinked structure in the crosslinked product formed" is approximately the same as the total number of moles of epoxy groups contained in the first and second crosslinking agents. From the above, in the ink of this embodiment, the crosslinking rate of the crosslinked resin is approximately the same as the ratio of the total number of moles of epoxy groups contained in the first crosslinking agent and the second crosslinking agent to the number of moles Y of carboxy groups contained in the specific resin (100%).

[0015] The number of moles of epoxy groups contained in the crosslinking agent (first crosslinking agent or second crosslinking agent) is calculated, for example, by dividing the amount [g] of the crosslinking agent used for crosslinking the specific resin by the epoxy equivalent [g / eq.] of the crosslinking agent. The number of moles Y of carboxy groups contained in the specific resin is calculated by multiplying the amount of the specific resin used and the number of moles of carboxy groups per gram of the specific resin. The number of moles of carboxy groups per gram of the specific resin is calculated by dividing the acid value [mgKOH / g] of the specific copolymer that is the raw material of the specific resin by the molecular weight of KOH (56.1).

[0016] The crosslinked resin is crosslinked by the first crosslinking agent and the second crosslinking agent. In other words, in the molecule of the crosslinked resin, there are sites crosslinked by the first crosslinking agent and sites crosslinked by the second crosslinking agent. Therefore, the crosslinking rate of the crosslinked resin is calculated by multiplying the crosslinking rate C by the first crosslinking agent by 1 / C. 1 and the crosslinking rate C by the second crosslinking agent 2 The total crosslinking rate (C 1+C 2 ) The crosslinking rate by the first crosslinking agent C 1 is the mole number X of epoxy groups contained in the first crosslinking agent 1 The crosslinking rate C by the number of moles of carboxyl groups contained in the specific resin is calculated. 2 is the mole number X of epoxy groups contained in the second crosslinking agent 2 It can be calculated by dividing by the number of moles Y of carboxy groups contained in the specific resin.

[0017] To summarize, in a specific resin, the crosslinking rate C 1 , the crosslinking rate by the second crosslinking agent C 2 and the total crosslinking rate (C 1 +C 2 ) is calculated using the following formula: Crosslinking rate C 1 [%] = 100 × moles of epoxy groups contained in the first crosslinking agent X 1 / Y is the mole number of carboxyl groups contained in a specific resin Crosslinking rate C 2 [%] = 100 x moles of epoxy groups contained in the second crosslinking agent x 2 / Y is the mole number of carboxyl groups contained in a specific resin Total crosslinking rate (C 1 +C 2 )[%]=C 1 +C 2

[0018] The application of the ink of the present embodiment is not particularly limited, and can be used, for example, for forming an image on a permeable recording medium or a non-permeable recording medium. The ink of the present embodiment is suitable for forming an image on a permeable recording medium. Permeable recording media have excellent ink permeability. Examples of permeable recording media include printing paper and media made of fibers (e.g., fabric). Examples of printing paper include plain paper, copy paper, recycled paper, thin paper, thick paper, and glossy paper.

[0019] The ink of the present embodiment, by being provided with the above-mentioned configuration, can form an image having excellent abrasion resistance and a desired image density while suppressing the occurrence of nozzle clogging. The reason for this is presumed to be as follows. In a known ink, it is possible to suppress the occurrence of nozzle clogging, form an image having a desired image density, and impart excellent abrasion resistance to the formed image, if each of these is satisfied individually, but it is difficult to satisfy all of them. For example, in order to suppress the occurrence of nozzle clogging in a known ink, it is effective to impart high dispersion stability to the pigment particles. However, an image formed with a known ink containing pigment particles with high dispersion stability often does not have sufficient image density because the pigment particles penetrate deep into the recording medium together with the aqueous medium. In addition, in order to impart a desired image density to an image formed with a known ink, it is effective to increase the hydrophobicity of the pigment particles. Pigment particles with high hydrophobicity are difficult to penetrate deep into the recording medium. Therefore, an image formed with a known ink containing pigment particles with high hydrophobicity can show a desired image density because a large amount of pigment particles remain on the surface of the recording medium. However, an image in which a large amount of pigment particles remain on the recording medium tends to have low abrasion resistance. This is because some of the pigment particles do not adhere directly to the recording medium, but remain on the surface of the recording medium on top of other pigment particles that are adhered to the recording medium. Such pigment particles are easily detached from the recording medium when an external force is applied.

[0020] In contrast, the pigment particles contained in the ink of this embodiment include a pigment and a crosslinked resin. The crosslinked resin is a crosslinked product of a specific resin, a first crosslinking agent, and a second crosslinking agent. The specific resin is a neutralized product of a specific copolymer. Here, the crosslinked resin has a relatively large number of acid groups because the acid value of the specific copolymer that is the raw material is relatively high. In addition, the acid groups of the crosslinked resin are moderately neutralized. The acid groups (especially the neutralized acid groups) are highly hydrophilic. Therefore, the crosslinked resin has a moderately high hydrophilicity. In addition, the first crosslinking agent and the second crosslinking agent each have an ethylene oxide structure or a propylene oxide structure, which are structures with relatively high hydrophilicity. Among them, the ethylene oxide structure with a relatively large number of added moles of the second crosslinking agent has a particularly high hydrophilicity. On the other hand, the propylene oxide structure or the ethylene oxide structure with a relatively small number of added moles of the first crosslinking agent does not have such high hydrophilicity. The specific resin is crosslinked at a predetermined ratio by the first crosslinking agent and the second crosslinking agent having different hydrophilicity, and thus the hydrophilicity is adjusted to an appropriate range. Furthermore, the first crosslinking agent and the second crosslinking agent have high water solubility, and therefore can react efficiently with the specific resin during the crosslinking reaction. Furthermore, the crosslinked resin can efficiently coat the pigment particles because the molecular size of the specific copolymer, which is the raw material, is appropriate. Furthermore, the crosslinked resin has a crosslinked structure, and therefore is difficult to detach from the pigment particles.

[0021] In addition, the specific copolymer that is the raw material of the crosslinked resin has the first repeating unit to the fourth repeating unit in a predetermined content ratio. The first repeating unit derived from α-methylstyrene moderately increases the affinity between the crosslinked resin and the pigment particles. The second repeating unit derived from styrene imparts moderate hydrophobicity to the crosslinked resin and adjusts the dispersion stability of the pigment particles. The third repeating unit derived from (meth)acrylic acid and the fourth repeating unit derived from alkylene glycol (meth)acrylate or dialkylene glycol (meth)acrylate impart moderate hydrophilicity to the crosslinked resin and impart dispersion stability to the pigment particles. As a result, the pigment particles contained in the ink of this embodiment are imparted with a good balance of hydrophilicity and dispersion stability. Therefore, the ink of this embodiment can form an image having excellent abrasion resistance and a desired image density while suppressing the occurrence of nozzle clogging.

[0022] The ink of this embodiment will be described in more detail below. Each of the components described below may be used alone or in combination of two or more.

[0023] [Solid content in the supernatant] Among the crosslinked resins contained in the ink of this embodiment, some of the crosslinked resins may be detached from the pigment particles during the production or storage of the ink of this embodiment and may be free in the aqueous medium. Such crosslinked resins free in the aqueous medium are referred to as free resins. The solid content contained in the supernatant obtained by centrifuging the ink of this embodiment at 1,050,000 G for 3 hours can be regarded as free resin. Free resins may cause nozzle clogging. Therefore, in the ink of this embodiment, it is preferable that the content of free resin is low. However, in the ink of this embodiment, free resins are inevitably generated and are difficult to completely remove. In addition, the free resins also have the function of optimizing the abrasion resistance of the image formed by the ink of this embodiment, so they do not necessarily need to be completely removed.

[0024] From the above, in the ink of this embodiment, the solid content in the supernatant obtained by centrifuging at 1,050,000G for 3 hours is preferably 2.0% by mass or less, more preferably 0.1% by mass to 1.5% by mass or less, and even more preferably 0.5% by mass to 1.0% by mass or less. By making the solid content in the above-mentioned supernatant 0.1% by mass or more, it is possible to impart even more excellent abrasion resistance to the image formed by the ink of this embodiment. By making the solid content in the above-mentioned supernatant 2.0% by mass or less, the ink of this embodiment can more effectively suppress the occurrence of nozzle clogging. The above-mentioned solid content can be measured by the method described in the examples or a method based thereon.

[0025] [Pigment particles] The pigment particles contain a pigment and a crosslinked resin. The pigment particles are composed of, for example, a core containing a pigment and a crosslinked resin that coats the core. The total content of the pigment and the crosslinked resin in the pigment particles is preferably 90% by mass or more, and more preferably 100% by mass.

[0026] From the viewpoint of optimizing the color density, hue, or stability of the ink of this embodiment, the volume median diameter of the pigment particles is preferably 30 nm or more and 200 nm or less, and more preferably 80 nm or more and 130 nm or less.

[0027] In the ink of this embodiment, the content of pigment particles is preferably 6.0% by mass or more and 20.0% by mass or less, and more preferably 10.0% by mass or more and 15.0% by mass or less. By making the content of pigment particles 6.0% by mass or more, the ink of this embodiment can more easily form an image having a desired image density. In addition, by making the content of pigment particles 20.0% by mass or less, the fluidity of the ink of this embodiment can be optimized.

[0028] (Pigments) Examples of pigments include yellow pigments, orange pigments, red pigments, blue pigments, purple pigments, and black pigments. Examples of yellow pigments include CI Pigment Yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of orange pigments include CI Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of red pigments include CI Pigment Red (122 and 202). Examples of blue pigments include CI Pigment Blue (15, more specifically 15:3). Examples of purple pigments include CI Pigment Violet (19, 23, and 33). Examples of black pigments include CI Pigment Black (7).

[0029] In the ink of this embodiment, the pigment content is preferably 3.0 parts by mass to 15.0 parts by mass, and more preferably 7.0 parts by mass to 12.0 parts by mass. The pigment content in the pigment particles is preferably 45% by mass to 80% by mass, and more preferably 55% by mass to 70% by mass.

[0030] (Crosslinked resin) The crosslinked resin coats the pigment, for example, in the case of pigment particles. The crosslinked resin is a crosslinked product of a specific resin with a first crosslinking agent and a second crosslinking agent. The total crosslinking rate of the crosslinked resin by the first crosslinking agent and the second crosslinking agent (C 1 +C 2 ) is 25% or more and 90% or less, preferably 35% or more and 65% or less, and more preferably 35% or more and 45% or less. By making the crosslinking rate of the crosslinking resin 25% or more, it is possible to suppress the crosslinking resin from being detached from the pigment particles. The total crosslinking rate of the crosslinking resin (C 1 +C 2 By making the ratio of the crosslinked resin to 90% or less, the hydrophilicity and dispersion stability of the pigment particles can be optimized. The crosslinking ratio of the crosslinked resin can be calculated by the method described in the Examples or a method based thereon.

[0031] In the ink of this embodiment, the content of the crosslinked resin is preferably 0.5% by mass or more and 10.0% by mass or less, and more preferably 2.0% by mass or more and 4.5% by mass or less. By making the content of the crosslinked resin 0.5% by mass or more, the hydrophilicity and dispersion stability of the pigment particles can be further optimized. By making the content of the crosslinked resin 10.0% by mass or more, the generation of free resin can be suppressed.

[0032] In the pigment particles, the content of the crosslinked resin relative to 100 parts by mass of the pigment is preferably from 25 to 60 parts by mass, and more preferably from 30 to 45 parts by mass. By setting the content of the crosslinked resin relative to 100 parts by mass of the pigment to be from 25 to 60 parts by mass, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0033] (Specific resin) The specific resin is a neutralized product of a specific copolymer. The neutralization rate of the specific resin is 20% or more and 100% or less, preferably 40% or more and 95% or less, and more preferably 50% or more and 70% or less. By setting the neutralization rate of the specific resin to 20% or more and 100% or less, it is possible to impart a moderately high hydrophilicity to the crosslinked resin and optimize the hydrophilicity and dispersion stability of the pigment particles.

[0034] The specific resin preferably contains an alkali metal atom. That is, the specific resin is preferably a neutralized product obtained by neutralizing a specific copolymer with a neutralizing agent containing an alkali metal atom. The alkali metal atom does not volatilize from the ink of the present embodiment even when the ink of the present embodiment is exposed to a dry state. Therefore, by neutralizing the specific copolymer with a neutralizing agent containing an alkali metal atom, the neutralized state (hydrophilicity) of the crosslinked resin is maintained even when the ink of the present embodiment is exposed to a dry state. The alkali metal atom is preferably a potassium atom or a sodium atom. The neutralizing agent is preferably a hydroxide containing an alkali metal atom, and more preferably NaOH or KOH.

[0035] (Specific copolymer) The mass average molecular weight of the specific copolymer is preferably from 3000 to 18000, more preferably from 5000 to 12000, and even more preferably from 8000 to 10000. By setting the mass average molecular weight of the specific resin to be from 3000 to 18000, the crosslinked resin can efficiently cover the pigment particles, thereby preventing the crosslinked resin from being detached from the pigment particles.

[0036] The acid value of the specific copolymer is 50 mgKOH / g or more and 300 mgKOH / g or less, preferably 100 mgKOH / g or more and 200 mgKOH / g or less, and more preferably 150 mgKOH / g or more and 200 mgKOH / g or less. By setting the acid value of the specific copolymer to 50 mgKOH / g or more and 300 mgKOH / g or less, it becomes easy to sufficiently introduce a crosslinked structure into the crosslinked resin, and the hydrophilicity and dispersion stability of the pigment particles can be optimized. By setting the acid value of the specific copolymer to 300 mgKOH / g or less, it is possible to prevent the hydrophilicity and dispersion stability of the pigment particles from becoming excessively high. As a result, it is possible to impart excellent abrasion resistance and desired image density to the image formed by the ink of this embodiment.

[0037] The specific copolymer has a first repeating unit derived from α-methylstyrene, a second repeating unit derived from styrene, a third repeating unit derived from (meth)acrylic acid, and a fourth repeating unit derived from an alkylene glycol (meth)acrylate or a dialkylene glycol (meth)acrylate.

[0038] Examples of the alkylene glycol (meth)acrylate include ethylene glycol (meth)acrylate, propylene glycol (meth)acrylate, and butylene glycol (meth)acrylate, with ethylene glycol (meth)acrylate being preferred.

[0039] Examples of dialkylene glycol (meth)acrylates include diethylene glycol (meth)acrylate, dipropylene glycol (meth)acrylate, and dibutylene glycol (meth)acrylate, with dipropylene glycol (meth)acrylate being preferred.

[0040] The content of the first repeating unit derived from α-methylstyrene is 1% by mass to 65% by mass, preferably 15% by mass to 55% by mass, more preferably 25% by mass to 50% by mass, and even more preferably 40% by mass to 48% by mass, based on 100% by mass of all repeating units in the specific copolymer. By setting the content of the first repeating unit to 1% by mass to 65% by mass, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0041] The content of the second repeating unit derived from styrene is from 1 to 60% by mass, preferably from 10 to 40% by mass, and more preferably from 15 to 27% by mass, based on 100% by mass of all repeating units in the specific copolymer. By setting the content of the second repeating unit to be from 1 to 60% by mass, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0042] The content of the third repeating unit derived from (meth)acrylic acid is 10% by mass to 40% by mass, preferably 20% by mass to 35% by mass, and more preferably 25% by mass to 32% by mass, based on 100% by mass of all repeating units in the specific copolymer. By setting the content of the third repeating unit to 10% by mass to 40% by mass, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0043] The content of the fourth repeating unit derived from an alkylene glycol (meth)acrylate or a dialkylene glycol (meth)acrylate is from 1 to 12% by mass, preferably from 4 to 11% by mass, and more preferably from 4 to 8% by mass, relative to 100% by mass of all repeating units in the specific copolymer. By setting the content of the fourth repeating unit to be from 1 to 12% by mass, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0044] It is preferable that, relative to 100% by mass of all repeating units in the specific copolymer, the content of the first repeating unit is from 15% by mass to 55% by mass, the content of the second repeating unit is from 10% by mass to 40% by mass, the content of the third repeating unit is from 20% by mass to 35% by mass, and the content of the fourth repeating unit is from 4% by mass to 11% by mass.

[0045] The specific copolymer may be a random polymer or a block polymer, and is preferably a random polymer.

[0046] The composition of the monomers that are the raw materials for the specific copolymer is preferably any one of compositions 1 to 3 shown in Table 1 below. The numerical ranges shown in Table 1 below indicate the numerical range of the content ratio [mass %] of each monomer. For example, composition 1 indicates that it contains 20 mass % or more and 24 mass % or less of styrene, 42 mass % or more and 46 mass % or less of α-methylstyrene, 4 mass % or more and 8 mass % or more of ethylene glycol acrylate, and 25 mass % or more and 30 mass % or less of methacrylic acid.

[0047] [Table 1]

[0048] (First Crosslinking Agent) The first crosslinking agent has, in its molecule, an ethylene oxide structure with an added mole number of 1 to 4 or a propylene oxide structure with an added mole number of 1 to 4, and two or more epoxy groups. The water solubility of the first crosslinking agent is 80% or more.

[0049] The water solubility of the first crosslinking agent is preferably 90% or more, and more preferably 98% or more. By making the water solubility of the first crosslinking agent 90% or more, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0050] The water solubility of the first crosslinking agent is the ratio (100×A / 10g) of the mass A of the first crosslinking agent dissolved in water to the total amount (10g) of the first crosslinking agent when 10g of the first crosslinking agent and 90g of water are mixed at 25° C. For example, when 10g of the first crosslinking agent and 90g of water are mixed at 25° C., if 9g of the first crosslinking agent is dissolved in water and 1g of the first crosslinking agent is precipitated without dissolving in water (mass A: 9g), the water solubility is 90%. The water solubility of the second crosslinking agent is also measured by the same method.

[0051] In the first crosslinking agent, the number of epoxy groups in the molecule is preferably from 2 to 8, and more preferably from 2 to 3. In the first crosslinking agent, the number of moles of added ethylene oxide structure or propylene oxide structure in the molecule is preferably from 1 to 3, and more preferably from 2 to 3.

[0052] Examples of the first crosslinking agent include propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether.

[0053] The first crosslinking agent is preferably a compound represented by general formula (1-A) to (1-B), and more preferably a compound represented by chemical formula (1-A1), (1-B1), (1-B2) or (1-B3). In general formula (1-A), n represents an integer of 1 or more and 4 or less. In general formula (1-B), m represents an integer of 1 or more and 4 or less.

[0054] [ka]

[0055] [ka]

[0056] The epoxy equivalent of the first crosslinking agent is preferably 100 g / eq. or more and 230 g / eq. or less, more preferably 120 g / eq. or more and 190 g / eq. or less, and even more preferably 150 g / eq. or more and 170 g / eq. or less. The epoxy equivalent can be determined, for example, according to the method described in JIS (Japanese Industrial Standards) K7236:2009.

[0057] Crosslinking rate of the crosslinked resin by the first crosslinking agent C 1 The crosslinking rate C is preferably 5% or more and 75% or less, more preferably 10% or more and 45% or less, and even more preferably 14% or more and 25% or less. 1 By setting the content of the pigment particles to 5% or more and 75% or less, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0058] (Second Crosslinking Agent) The second crosslinking agent has, in its molecule, an ethylene oxide structure with an added mole number of 5 to 15 and two or more epoxy groups. The water solubility of the second crosslinking agent is 80% or more.

[0059] The water solubility of the second crosslinking agent is preferably 90% or more, and more preferably 98% or more. By making the water solubility of the second crosslinking agent 90% or more, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0060] In the second crosslinking agent, the number of epoxy groups in the molecule is preferably 2 or more and 8 or less, and more preferably 2 or more and 3 or less. In the second crosslinking agent, the number of moles of added ethylene oxide structures in the molecule is preferably 7 or more and 14 or less, and more preferably 9 or 13.

[0061] The second crosslinking agent may, for example, be polyethylene glycol diglycidyl ether.

[0062] The second crosslinking agent is preferably a compound represented by general formula (2-A), more preferably a compound represented by chemical formula (2-A1) or (2-A2): In general formula (2-A), s represents an integer of 5 or more and 15 or less.

[0063] [ka]

[0064] [ka]

[0065] The epoxy equivalent of the second crosslinking agent is preferably from 250 g / eq. to 450 g / eq., more preferably from 250 g / eq. to 400 g / eq., and even more preferably from 250 g / eq. to 300 g / eq.

[0066] Crosslinking rate of the crosslinked resin by the second crosslinking agent C 2 The crosslinking rate C is preferably 5% or more and 75% or less, more preferably 10% or more and 45% or less, and even more preferably 14% or more and 25% or less. 2 By setting the content of the pigment particles to 5% or more and 75% or less, the hydrophilicity and dispersion stability of the pigment particles can be further optimized.

[0067] In crosslinked resins, the crosslinking rate C of the first crosslinking agent 1 Crosslinking rate C by the second crosslinking agent 2 Ratio of (C 2 / C 1 The ratio (C) is 18 / 82 or more and 82 / 18 or less, preferably 30 / 70 or more and 70 / 30 or less, and more preferably 45 / 55 or more and 55 / 45 or less. 2 / C 1 By adjusting the ratio of the water content to 18 / 82 or more and 82 / 18 or less, the hydrophilicity and dispersion stability of the pigment particles can be optimized.

[0068] The crosslinked resin may have a crosslinked structure derived from a crosslinked resin other than the first crosslinking agent and the second crosslinking agent, if the amount is small. In the crosslinked resin, the total crosslinking rate C due to all crosslinking agents (the first crosslinking agent, the second crosslinking agent and other crosslinking agents) is ALL The total crosslinking rate (C 1 +C 2 ) ratio (100 × (C 1 +C 2 ) / CALL ) is preferably 90% or more, more preferably 99% or more, and even more preferably 100%.

[0069] [Aqueous medium] The aqueous medium contained in the ink of this embodiment is a medium containing water. The aqueous medium may function as a solvent or as a dispersion medium. Specific examples of the aqueous medium include aqueous media containing water and a water-soluble organic solvent.

[0070] (water) In the ink of this embodiment, the water content is preferably from 25.0% to 80.0% by mass, and more preferably from 35.0% to 60.0% by mass.

[0071] (Water-soluble organic solvent) Examples of the water-soluble organic solvent include glycol compounds, triol compounds, glycol ether compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, and dimethylsulfoxide.

[0072] Examples of the glycol compound include ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, and 2-ethyl-1,2-hexanediol. Examples of the glycol compound include ethylene glycol, diethylene glycol, 2-ethyl-1,2-hexanediol, 3-methyl-1,5-pentanediol, 1,3-propanediol, 1,5-pentanediol, and propylene glycol.

[0073] Triol compounds include, for example, glycerin and 1,2,3-butanetriol.

[0074] Examples of glycol ether compounds include diethyl diglycol, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether (diethyl diglycol), triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether and propylene glycol monomethyl ether. As the glycol ether compound, triethylene glycol monobutyl ether is preferred.

[0075] Examples of lactam compounds include 2-pyrrolidone and N-methyl-2-pyrrolidone. Of the lactam compounds, 2-pyrrolidone is preferred.

[0076] Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

[0077] An example of the acetate compound is diethylene glycol monoethyl ether acetate.

[0078] The water-soluble organic solvent is preferably glycerin, a glycol compound, a glycol ether compound or a lactam compound, and more preferably glycerin, 1,3-propanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, ethylene glycol, triethylene glycol monobutyl ether, diethyl diglycol or 2-pyrrolidone.

[0079] As the water-soluble organic solvent, the following mixed organic solvents 1 to 3 are preferred. In the following, the numerical range shown in parentheses after each component indicates the preferred content ratio of each component in the ink of this embodiment. Mixed organic solvent 1: ethylene glycol (18.0% by mass or more and 22.0% by mass or less), and diethyl diglycol (13.0% by mass or more and 17.0% by mass or less) Mixed organic solvent 2: glycerin (8.0% by mass or more and 11.0% by mass or less), triethylene glycol monobutyl ether (10.0% by mass or more and 14.0% by mass or less), 3-methyl-1,5-pentanediol (10.0% by mass or more and 14.0% by mass or less), and 2-pyrrolidone (0.5% by mass or more and 3.0% by mass or less) Mixed organic solvent 3: triethylene glycol monobutyl ether (7.0% by mass or more and 9.0% by mass or less), 2-pyrrolidone (1.0% by mass or more and 3.0% by mass or less), 1,3-propanediol (11.0% by mass or more and 14.0% by mass or less), and 1,5-pentanediol (11.0% by mass or more and 14.0% by mass or less)

[0080] The content of the water-soluble organic solvent in the ink of this embodiment is preferably from 10.0% to 50.0% by mass, and more preferably from 30.0% to 40.0% by mass.

[0081] [Surfactants] The ink of the present embodiment preferably further contains a surfactant. The surfactant can optimize the permeability (wettability) of the ink of the present embodiment to the recording medium. Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. The surfactant is preferably a nonionic surfactant.

[0082] Examples of the nonionic surfactant include polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan monooleate ether, monodecanoyl sucrose, and ethylene oxide adducts of acetylene glycol. As the nonionic surfactant, ethylene oxide adducts of acetylene glycol are preferred.

[0083] The content of the surfactant in the ink of this embodiment is preferably from 0.05% by mass to 3.0% by mass, and more preferably from 0.1% by mass to 0.5% by mass.

[0084] [Other ingredients] The ink of this embodiment may further contain known additives (for example, a dissolution stabilizer, a drying inhibitor, an antioxidant, a viscosity adjuster, a pH adjuster, and an anti-mold agent) as necessary.

[0085] Second embodiment: Ink manufacturing method The second embodiment of the present invention relates to a method for producing an ink. The method for producing an ink of this embodiment is a method for producing an ink containing pigment particles dispersed in an aqueous medium. The pigment particles include a pigment and a crosslinked resin. The method for producing an ink of this embodiment includes a neutralization step of neutralizing a specific copolymer to obtain a specific resin, a dispersion step of dispersing the specific resin and the pigment in water to obtain a pigment particle dispersion, and a crosslinking step of crosslinking the specific resin in the pigment particle dispersion with a first crosslinking agent and a second crosslinking agent to obtain a crosslinked resin. The specific copolymer has a first repeating unit derived from α-methylstyrene, a second repeating unit derived from styrene, a third repeating unit derived from (meth)acrylic acid, and a fourth repeating unit derived from an alkylene glycol (meth)acrylate or a dialkylene glycol (meth)acrylate. The content of the first repeating unit is 1% by mass or more and 65% by mass or less, the content of the second repeating unit is 1% by mass or more and 60% by mass or less, the content of the third repeating unit is 10% by mass or more and 40% by mass or less, and the content of the fourth repeating unit is 1% by mass or more and 12% by mass or less, relative to 100% by mass of all repeating units in the specific copolymer. The acid value of the specific copolymer is 50 mgKOH / g or more and 300 mgKOH / g or less. The mass average molecular weight of the specific copolymer is 3000 or more and 18000 or less. The neutralization rate of the specific resin in the neutralization step is 20% or more and 100% or less. The first crosslinking agent has an ethylene oxide structure with an added mole number of 1 to 4 or a propylene oxide structure with an added mole number of 1 to 4 and two or more epoxy groups in the molecule. The water solubility of the first crosslinking agent is 80% or more. The second crosslinking agent has an ethylene oxide structure with an addition mole number of 5 to 15 and two or more epoxy groups in the molecule. The water solubility of the second crosslinking agent is 80% or more. In the crosslinking step, the crosslinking rate C by the first crosslinking agent is 1Crosslinking rate C by the second crosslinking agent 2 Ratio of (C 2 / C 1 The total crosslinking rate of the crosslinked resin by the first crosslinking agent and the second crosslinking agent (C 1 +C 2 ) is greater than or equal to 25% and less than or equal to 95%.

[0086] The ink manufacturing method of this embodiment is suitable as the ink manufacturing method of the first embodiment. In the ink manufacturing method of this embodiment, the aqueous medium, pigment particles, pigment, crosslinked resin, specific copolymer, first crosslinking agent and second crosslinking agent are the same as those in the first embodiment, and therefore description thereof will be omitted. The ink manufacturing method of this embodiment preferably further includes a centrifugation step of centrifuging the pigment particle dispersion liquid after the crosslinking step to obtain a precipitate, and a redispersion step of redispersing the precipitate in water. Each step will be described below.

[0087] (neutralization process) In this step, the specific copolymer is neutralized to obtain the specific resin. For example, the specific copolymer is mixed with a neutralizing agent (e.g., an aqueous alkali solution). For example, an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution are used as the aqueous alkali solution.

[0088] (Dispersion process) In this process, the specific resin and the pigment are dispersed in water to obtain a pigment particle dispersion. More specifically, the specific resin, the pigment, and water are first mixed to prepare a mixed liquid. Then, the mixed liquid is subjected to a dispersion treatment. Examples of the dispersion device used in the dispersion treatment include a wet dispersion device such as a media type disperser.

[0089] The content of the specific resin in the mixed liquid is, for example, 5.0% by mass or more and 25.0% by mass or less. The content of the pigment in the mixed liquid is, for example, 1.0% by mass or more and 10.0% by mass or less. In this process, it is preferable to add an antifoaming agent to the mixed liquid. The content of the antifoaming agent in the mixed liquid is, for example, 0.01% by mass or more and 0.1% by mass or less.

[0090] In this step, it is preferable to filter the obtained pigment particle dispersion using a filter (for example, with a pore size of 5 μm) to remove coarse particles.

[0091] (Crosslinking process) In this process, the specific resin in the pigment particle dispersion is crosslinked with the first crosslinking agent and the second crosslinking agent to obtain a crosslinked resin. Specifically, a carboxy group contained in the specific resin is crosslinked with an epoxy group contained in the first crosslinking agent and the second crosslinking agent. As a result, a crosslinked resin is generated as a reaction product of the first crosslinking agent, the second crosslinking agent, and the specific resin. In this process, for example, the first crosslinking agent and the second crosslinking agent are added to the pigment particle dispersion, and then the pigment particle dispersion is heated while being stirred. The heating temperature can be, for example, 70°C or more and 95°C or less. The heating time can be, for example, 2 hours or more and 6 hours or less.

[0092] In this process, the amount of the first crosslinking agent added relative to 100.0 parts by mass of the specific resin is preferably 3.0 parts by mass or more and 40.0 parts by mass or less, more preferably 5.0 parts by mass or more and 20.0 parts by mass or less, and even more preferably 10.0 parts by mass or more and 16.0 parts by mass or less.

[0093] In this step, the amount of the second crosslinking agent added relative to 100.0 parts by mass of the specific resin is preferably 5.0 parts by mass or more and 80.0 parts by mass or less, more preferably 10.0 parts by mass or more and 40.0 parts by mass or less, and even more preferably 15.0 parts by mass or more and 25.0 parts by mass or less.

[0094] The pigment particle dispersion liquid after this process may be subjected to a centrifugation process described below, and may be used as an ink after adding other components (more specifically, at least one of water, an organic solvent, a surfactant, a dissolution stabilizer, a moisturizer, a penetrating agent, and a viscosity adjuster) as necessary.

[0095] (Centrifugation process) In this step, the pigment particle dispersion liquid after the crosslinking step is centrifuged to obtain a precipitate. The precipitate contains pigment particles. The supernatant contains free resin. The centrifugation conditions can be, for example, a rotation speed of 10,000 rpm or more and 100,000 rpm or less, and a centrifugation time of 12 hours or more and 48 hours or less.

[0096] (Redispersion process) In this step, the precipitate is redispersed in water. In this way, ink can be obtained. In this step, other components (more specifically, at least one of an organic solvent, a surfactant, a dissolution stabilizer, a moisturizer, a penetrating agent, and a viscosity modifier) ​​may be further added to the dispersion of the precipitate as necessary.

[0097] The ink production method of the present embodiment further includes a centrifugation step and a redispersion step, thereby making it possible to reduce the amount of free resin in the produced ink.

[0098] In the ink production method of this embodiment, the ink obtained in the crosslinking step or the redispersion step may be treated with a filter (for example, a filter with a pore size of 5 μm or less), which makes it possible to remove foreign matter and coarse particles in the ink. EXAMPLES

[0099] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0100] In the examples, the crosslinking ratios of the crosslinked resins were calculated by the following method. First, the molar number X of the epoxy groups contained in the first crosslinking agent 1 The mole number X of the epoxy group contained in the first crosslinking agent was calculated. 1 was calculated by dividing the amount [g] of the first crosslinking agent used by the epoxy equivalent [g / eq.] of the first crosslinking agent. Similarly, the number of moles of epoxy groups contained in the second crosslinking agent, X, was calculated by dividing the amount [g] of the second crosslinking agent used by the epoxy equivalent [g / eq.] of the second crosslinking agent. 2was calculated. Next, the number of moles Y of the carboxyl groups contained in the specific resin was calculated. The number of moles Y of the carboxyl groups contained in the specific resin was calculated by multiplying the amount of the specific resin used and the number of moles of the carboxyl groups per gram of the specific resin. The number of moles of the carboxyl groups per gram of the specific resin was calculated by dividing the acid value of the specific resin by the molecular weight of KOH (56.1). Next, the various crosslinking rates of the crosslinked resin were calculated by applying the values ​​obtained above to the following formula. Crosslinking rate C 1 [%] = 100 × moles of epoxy groups contained in the first crosslinking agent X 1 / Y is the mole number of carboxyl groups contained in a specific resin Crosslinking rate C 2 [%] = 100 x moles of epoxy groups contained in the second crosslinking agent x 2 / Y is the mole number of carboxyl groups contained in a specific resin Total crosslinking rate (C 1 +C 2 )[%]=C 1 +C 2

[0101] (Preparation of Copolymer (r-1)) In a four-neck flask equipped with a stirrer, a nitrogen inlet tube, a condenser, and a dropping funnel, 100.0 parts by mass of isopropyl alcohol and 250.0 parts by mass of methyl ethyl ketone were added. Separately, 20.0 parts by mass of styrene, 40.0 parts by mass of α-methylstyrene, 5.0 parts by mass of ethylene glycol acrylate, 25.0 parts by mass of methacrylic acid, and 0.3 parts by mass of azobisisobutyronitrile (AIBN, polymerization initiator) were mixed to prepare a monomer solution. In addition, 150.0 parts by mass of methyl ethyl ketone and 0.1 parts by mass of AIBN were mixed to prepare a methyl ethyl ketone solution.

[0102] Next, nitrogen gas was introduced into the four-neck flask to create a nitrogen atmosphere. Next, while the contents of the four-neck flask were heated to reflux at 70°C, the entire amount of the monomer solution was supplied to the four-neck flask over 2 hours using a dropping funnel. After the monomer solution was supplied, the contents of the four-neck flask were heated to reflux at 70°C for another 6 hours. Next, while the contents of the four-neck flask were heated to reflux at 70°C, the entire amount of the methyl ethyl ketone solution was supplied to the four-neck flask over 15 minutes using a dropping funnel. After the methyl ethyl ketone solution was supplied, the contents of the four-neck flask were heated to reflux at 70°C for another 5 hours. This resulted in a copolymer aqueous solution containing the specific copolymer (r-1). The copolymer (r-1) was isolated by distilling off methyl ethyl ketone and isopropyl alcohol from the copolymer aqueous solution.

[0103] (Acid value measurement) The acid value of the copolymer (r-1) was measured according to the method described in JIS (Japanese Industrial Standards) K0070:1992 (Testing methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemical products). The measurement results are shown in Table 2 below.

[0104] (Measurement of mass average molecular weight) The mass average molecular weight (Mw) of the copolymer (r-1) was measured by gel permeation chromatography (GPC) under the following conditions. The measurement results are shown in Table 2 below.

[0105] (GPC conditions) Measuring device: Tosoh Corporation "HLC-8020GPC" Column: Ultra-high performance semi-micro SEC column ("TSKgel SuperMultipore HZ-H" manufactured by Tosoh Corporation, packing material: styrene-divinylbenzene resin, column size: inner diameter 4.6 mm x length 15 cm, packing material particle size: 6 μm) Number of columns: 3 Eluent: Tetrahydrofuran Eluent flow rate: 0.35mL / min Sample solution volume: 10μL Column temperature: 40℃ Detector: RI (refractive index) detector Calibration curve: A calibration curve created using monodisperse polystyrene standard samples ("F-40", "F-20", "F-4", "F-1", "A-5000", "A-2500" and "A-1000") manufactured by Tosoh Corporation and n-propylbenzene.

[0106] (Preparation of Copolymers (r-2) to (r-14)) Copolymers (r-2) to (r-14) were prepared in the same manner as in the preparation of copolymer (r-1), except that the types and amounts of monomers used in the preparation of the monomer solutions were changed as shown in Table 2 below. In Table 2 below, "EG acrylate" refers to ethylene glycol acrylate. "DPGA" refers to dipropylene glycol acrylate.

[0107] (Preparation of resin aqueous solutions (R-1) to (R-14)) A copolymer (specifically, any of the copolymers (r-1) to (r-14)) as shown in Table 2 below, potassium hydroxide, and water were mixed to obtain specific resin aqueous solutions (R-1) to (R-14). The specific resin aqueous solutions (R-1) to (R-14) contained neutralized resins (corresponding to specific resins). The amount of potassium hydroxide added was such that the neutralization rate of the neutralized resin was as shown in Table 2 below. The amount of water added was such that the solid concentration (content of neutralized resin) of the specific resin aqueous solutions (R-1) to (R-14) was 30 mass%.

[0108] [Table 2]

[0109] For the copolymers (r-1) to (r-14), the respective contents [mass %] of the first to fourth repeating units are shown in Table 3 below.

[0110] [Table 3]

[0111] <Ink Preparation> Inks of Examples 1 to 8 and Comparative Examples 1 to 22 were prepared by the following method. First, the chemical names, chemical formulas, epoxy equivalents, and water solubility of the crosslinking agents (EX-920), (EX-810), (EX-850), (EX-821), (EX-830), (EX-841), (EX-612), (EX-313), and (EX-145) (all "Denacol (registered trademark) series" manufactured by Nagase ChemteX Corporation) used in the examples are shown in Table 4 below. In addition, in Table 4 below, the chemical formula "(4-1) + (4-2)" of the crosslinking agent (EX-313) indicates a mixture of a compound represented by the chemical formula (4-1) and a compound represented by the chemical formula (4-2).

[0112] [Table 4]

[0113] [ka]

[0114] [ka]

[0115] [ka]

[0116] [ka]

[0117] Among the crosslinkers, the crosslinkers (EX-920), (EX-810), (EX-850) and (EX-821) were the first crosslinkers, and the crosslinkers (EX-830) and (EX-841) were the second crosslinkers.

[0118] [Preparation of Ink in Example 1] (Distributed Processing) A mixture was obtained by mixing 15.0 parts by mass of a pigment (Orion Engineered Carbons "Printex (registered trademark) 80", carbon black), 15.0 parts by mass of the above-mentioned specific resin aqueous solution (R-1) (containing 4.5 parts by mass of the neutralized copolymer (r-1)), 0.1 parts by mass of a defoamer (San Nopco Ltd. "SN DEFOAMER 1340", an amide wax surfactant), and ion-exchanged water. The amount of ion-exchanged water added was an amount that would make the mixture 100.0 parts by mass.

[0119] The mixture was subjected to a dispersion treatment for 4 hours using a media-type disperser (Dynomill, manufactured by Willy & Bachofen (WAB)). Zirconia beads with a diameter of 0.5 mm were used as media in the dispersion treatment. The media filling rate was 60 volume % relative to the capacity of the vessel. The treatment temperature (chiller temperature) in the dispersion treatment was set to 10°C. After the dispersion treatment, the media was removed from the contents of the media-type disperser to obtain a pigment particle dispersion. Next, the pigment particle dispersion was filtered through a filter with a pore size of 5 μm to remove foreign matter and coarse particles.

[0120] (Cross-linking treatment) A three-neck flask equipped with a thermometer and a stirring blade was used as a reaction vessel. 100.0 parts by mass of the pigment particle dispersion after filtration was put into the reaction vessel. The temperature of the contents of the reaction vessel was maintained at 30°C using a water bath. Next, 0.51 parts by mass of a crosslinking agent (EX-920) as a first crosslinking agent and 0.78 parts by mass of a crosslinking agent (EX-830) as a second crosslinking agent were put into the reaction vessel. Next, the contents of the reaction vessel were stirred at 250 rpm for 1 hour. Next, while stirring the contents of the reaction vessel at 250 rpm, the temperature of the contents of the reaction vessel was increased to 80°C at a temperature increase rate of 0.5°C / min. Next, while maintaining the temperature of the contents of the reaction vessel at 80°C, the contents of the reaction vessel were stirred at 250 rpm for 4 hours. This allowed the contents of the reaction vessel to react. Next, the temperature of the contents of the reaction vessel was allowed to cool to room temperature. This resulted in the pigment particle dispersion after crosslinking treatment.

[0121] In the pigment particle dispersion of Example 1, the crosslinking rate C of the crosslinked resin by the first crosslinking agent 1 , the crosslinking rate of the crosslinked resin by the second crosslinking agent C 2 , the total crosslinking rate of the crosslinked resin by the first crosslinking agent and the second crosslinking agent (C 1 +C 2 ) was calculated by the following method. For the sake of convenience, the calculation was performed assuming that 1 part by mass = 1 g.

[0122] The number of moles of epoxy groups contained in the first crosslinking agent, X 1 was calculated by dividing the amount of the first crosslinking agent used (0.51 g) by the epoxy equivalent of the first crosslinking agent (176 g / eq). 1 The mole number X of the epoxy group contained in the second crosslinking agent was 2.90 mmol. 2 was calculated by dividing the amount of the second crosslinking agent used (0.78 g) by the epoxy equivalent of the second crosslinking agent (268 g / eq). 2 was 2.91 mmol.

[0123] Next, the number of moles Y of the carboxyl group contained in the copolymer (r-1) after neutralization (i.e., the specific resin) was calculated. First, the acid value (181 mg KOH / g) of the copolymer (r-1) was divided by the molecular weight (56.1) of KOH to calculate the number of moles of the carboxyl group per 1 g of the copolymer (r-1) after neutralization. The number of moles of the carboxyl group per 1 g of the copolymer (r-1) after neutralization was 3.23 mmol / g. Next, the number of moles Y of the carboxyl group contained in the copolymer (r-1) after neutralization was calculated by integrating the amount of the copolymer (r-1) used (4.5 g) after neutralization and the number of moles of the carboxyl group per 1 g of the copolymer (r-1) after neutralization. The number of moles Y of the carboxyl group contained in the copolymer (r-1) after neutralization was 14.54 mmol.

[0124] Next, the crosslinking rate C of the crosslinked resin by the first crosslinking agent is calculated by applying the value obtained above to the following formula: 1 , the crosslinking rate C of the crosslinked resin by the second crosslinking agent2 , the total crosslinking rate of the crosslinked resin by the first crosslinking agent and the second crosslinking agent (C 1 +C 2 ) was calculated. Crosslinking rate C 1 [%] = 100 × moles of epoxy groups contained in the first crosslinking agent X 1 / moles of carboxyl groups Y Crosslinking rate C 2 [%] = 100 x moles of epoxy groups contained in the second crosslinking agent x 2 / moles of carboxyl groups Y Total crosslinking rate [%]=C 1 +C 2

[0125] (Centrifugation and redispersion) The pigment particle dispersion after the crosslinking treatment was transferred to a container, and the container was placed in a centrifugal adhesion measuring device ("NS-C100" manufactured by Nano Seeds Co., Ltd.). Using the centrifugal adhesion measuring device described above, the pigment particle dispersion after the crosslinking treatment was centrifuged for 24 hours at a rotation speed of 50,000 rpm. After the centrifugation, the supernatant was removed from the container, and then ion-exchanged water of the same volume as the removed supernatant was added to the container. The precipitate in the container was then redispersed in the ion-exchanged water. In this way, free components were removed from the aqueous medium of the pigment particle dispersion after the crosslinking treatment.

[0126] (Additive treatment) Each component was added to a container so as to obtain composition 1 shown in Table 5 below. Specifically, in Example 1, 60.0 parts by mass of the pigment particle dispersion after redispersion (about 9 parts by mass of pigment, about 3 parts by mass of crosslinked resin), 20.0 parts by mass of ethylene glycol, 15.0 parts by mass of diethyl diglycol, 0.3 parts by mass of a nonionic surfactant ("Olfine (registered trademark) E1004" manufactured by Nissin Chemical Industry Co., Ltd.), and 4.7 parts by mass of ion-exchanged water were added. The contents of the above-mentioned container were stirred at a rotation speed of 400 rpm using a stirrer ("Three-one Motor BL-600" manufactured by Shinto Scientific Co., Ltd.) to obtain a mixture. The obtained mixture was filtered using a filter (pore size: 5 μm). In this way, the ink of Example 1 was obtained.

[0127] [Preparation of inks in Examples 2 to 8 and Comparative Examples 1 to 22] The inks of Examples 2 to 8 and Comparative Examples 1 to 22 were prepared in the same manner as in the preparation of the ink of Example 1, except that the type of specific resin aqueous solution used in the dispersion treatment, the types and amounts of the first crosslinking agent and the second crosslinking agent used in the crosslinking treatment, and the composition of the components put into the container in the addition treatment (any of compositions 1 to 3 in Table 5 below) were changed as shown in Table 6 below.

[0128] [Table 5]

[0129] [Table 6]

[0130] [Measurement of supernatant solids] The inks of Examples 1 to 8 and Comparative Examples 1 to 22 were centrifuged by the following method. The solid content ratio in the resulting supernatant was then measured. Specifically, the measurement target (any of the inks of Examples 1 to 8 and Comparative Examples 1 to 22) was first centrifuged at a rotation speed of 140,000 rpm (1,050,000 G) for 3 hours using an ultracentrifuge ("himac (registered trademark) CS150FNX" manufactured by Eppendorf-Himac Technologies, Ltd., rotor: S140AT). This allowed the pigment particles contained in the measurement target to settle.

[0131] Next, 30 μL of the supernatant liquid contained in the measurement object after the centrifugation process was transferred to an aluminum container for thermogravimetric measurement. Next, the mass (A) of 30 μL of the supernatant liquid was measured. Next, using a thermogravimetric analyzer ("TG / DTA7200" manufactured by Hitachi High-Tech Science Corporation), thermogravimetric analysis was performed according to the scheme shown in Table 7 below. Then, the mass loss (B) of the measurement object between temperatures of 200°C and 500°C was measured. The mass loss (B) was regarded as the mass of solids (mainly free resin) in the supernatant liquid. The content ratio of solids in the supernatant liquid was calculated according to the following formula. The measurement results are shown in Table 8 below. Solid content in the supernatant [mass%] = 100 × B / A

[0132] [Table 7]

[0133] The solid content in the supernatant was rated as "A (preferable)" when it was 2.0% by mass or less, and "B (unfavorable)" when it exceeded 2.0% by mass.

[0134] <Evaluation> The inks of Examples 1 to 8 and Comparative Examples 1 to 22 were evaluated for nozzle clogging, image density of formed images, and abrasion resistance by the following methods. The evaluation results are shown in Table 8 below.

[0135] [Evaluation machine] The evaluation machine used was a line head-equipped inkjet recording device (a test machine manufactured by Kyocera Document Solutions, Inc.) The inks to be evaluated of Examples 1 to 8 and Comparative Examples 1 to 22 were each filled into a black ink tank of the evaluation machine.

[0136] [Nozzle clogging] The nozzle clogging evaluation was performed under an environment of 25°C temperature and 60% RH humidity. Inkjet matte paper (Seiko Epson Corporation's "Super Fine Paper") was used as the recording medium. Using the evaluation machine, solid images (150 mm x 200 mm) were continuously formed on 100 sheets of recording medium. Next, a purge process was performed to purge ink from the recording head of the evaluation machine. Next, a wipe process was performed to wipe the ink ejection surface of the recording head of the evaluation machine with a cleaning wiper (hereinafter, the process of performing the wipe process after the purge process may be described as a cleaning process). Next, a nozzle check pattern was formed on the above-mentioned matte paper using the evaluation machine. As a result, it was confirmed that ink was ejected from all nozzles (7968 nozzles) in all evaluation subjects. That is, the number of nozzles in which nozzle clogging occurred was 0. Next, a cleaning process was performed on the recording head of the evaluation machine. Next, the evaluation machine was left stationary for 7 days without a cap on the recording head of the evaluation machine. Next, a cleaning process was performed on the recording head of the evaluation machine. Next, a nozzle check pattern was formed on the above-mentioned matte paper using the evaluation machine. The formed nozzle check pattern was then observed to confirm the number of nozzles where nozzle clogging had occurred. The ratio of the number of nozzles where nozzle clogging had occurred to the total number of nozzles in the recording head of the evaluation machine was taken as the evaluation value for nozzle clogging. Nozzle clogging was judged according to the following criteria.

[0137] (Nozzle clogging criteria) A (Good): The evaluation value is less than 10%. B (Poor): Evaluation value is 10% or more.

[0138] [Image Density] The image density was evaluated under an environment of a temperature of 25° C. and a humidity of 50% RH. The recording medium was PPC paper ("C" manufactured by FUJIFILM Business Innovation Co., Ltd.). 2") was used. A 10 cm x 10 cm solid image was formed on the recording medium using the evaluation machine. In forming the solid image, the evaluation machine was set so that the volume of each drop of ink ejected from the recording head was 11 pL (11 pL of ink per pixel). The image density of the formed solid image was measured using a reflection densitometer (X-Rite Corp., "RD-19") In measuring the image density, the image density was measured at each of 10 randomly selected points in the solid image, and the arithmetic mean value of the image densities at the 10 points was adopted as the evaluation value (ID) of the image density. The image density was judged according to the following criteria.

[0139] (Image density standard) A (Good): ID is 1.15 or higher. B (bad): ID is less than 1.15.

[0140] [Abrasion resistance] In the evaluation of scratch resistance, A4 size PPC paper ("C" manufactured by Fujifilm Business Innovation Co., Ltd.) was used as the evaluation paper. 2 ") was used. First, a cleaning process was performed on the recording head of the evaluation machine. Next, a solid image (printing rate 100%) of 100 mm x 100 mm was formed on the evaluation paper using the evaluation machine. An unused evaluation paper (paper A) was placed on top of the evaluation paper on which the solid image was formed. Next, a rectangular parallelepiped weight of 1 kg was placed on the paper A. At this time, the weight was placed so that the center of gravity of the weight was located directly above the center of the solid image. Next, the solid image was rubbed with the paper A by moving the paper A back and forth five times in a certain direction with the weight placed on it (load 1 kg). The image density of the stain image transferred from the solid image to the paper A was measured with a reflection densitometer ("FD-9" manufactured by Konica Minolta, Inc.). In detail, the image density of 10 randomly selected points in the stain image was measured with the reflection densitometer described above, and the maximum value of the image density of the 10 points was used as the evaluation value of the abrasion resistance. The abrasion resistance was evaluated according to the following criteria.

[0141] (Abrasion resistance standard) A (Good): Evaluation value is less than 0.020. B (poor): Evaluation value is 0.020 or more.

[0142] [Table 8]

[0143] The inks of Examples 1 to 8 contained an aqueous medium and pigment particles dispersed in the aqueous medium. The pigment particles contained a pigment and a crosslinked resin. The crosslinked resin was a crosslinked product of a specific resin, a first crosslinking agent, and a second crosslinking agent. The specific resin was a neutralized product of a specific copolymer having a specific repeating unit at a specific content ratio. The acid value of the specific copolymer was 50 mgKOH / g or more and 300 mgKOH / g or less. The mass average molecular weight of the specific copolymer was 3000 or more and 18000 or less. The neutralization rate of the specific resin was 20% or more and 100% or less. The first crosslinking agent had an ethylene oxide structure with an added mole number of 1 to 4 or a propylene oxide structure with an added mole number of 1 to 4 and two or more epoxy groups in the molecule. The water solubility rate of the first crosslinking agent was 80% or more. The second crosslinking agent had an ethylene oxide structure with an added mole number of 5 to 15 and two or more epoxy groups in the molecule. The water solubility of the second crosslinking agent was 80% or more. 2 / C 1 ) was 18 / 82 or more and 82 / 18 or less. 1 +C 2 ) was 25% or more and 95% or less. The inks of Examples 1 to 8 were able to form images having the desired image density and excellent abrasion resistance while suppressing the occurrence of nozzle clogging.

[0144] On the other hand, in the ink of Comparative Example 1, the water solubility rate of the first crosslinking agent was less than 80%, so it was determined that the crosslinking of the crosslinked resin by the first crosslinking agent did not proceed sufficiently. As a result, in the ink of Comparative Example 1, the crosslinked resin constituting the pigment particles was not crosslinked sufficiently, and the content ratio of free resin increased. As a result, the ink of Comparative Example 1 caused nozzle clogging. Furthermore, in the ink of Comparative Example 1, the crosslinked resin was mainly crosslinked by the second crosslinking agent, so the hydrophilicity of the crosslinked resin was excessively high. As a result, the image density of the image formed by the ink of Comparative Example 1 was poor.

[0145] In the ink of Comparative Example 2, a crosslinking agent having no ethylene oxide structure in the molecule and an added mole number of 5 to 15 was used as the second crosslinking agent. It is considered that the crosslinking agent was unable to impart sufficient hydrophilicity to the crosslinked resin. As a result, the ink of Comparative Example 2 had an excessively low hydrophilicity of the crosslinked resin, and the abrasion resistance of the formed image was poor.

[0146] In the ink of Comparative Example 3, a crosslinking agent having only one epoxy group in the molecule was used as the second crosslinking agent. In the ink of Comparative Example 3, the second crosslinking agent is a type of crosslinking agent that cannot form an intermolecular crosslinked structure, so the crosslinked resin is not crosslinked sufficiently, and the content of free resin increases. As a result, the ink of Comparative Example 3 caused nozzle clogging. In addition, the ink of Comparative Example 3 also had poor abrasion resistance of the formed image.

[0147] The ink of Comparative Example 4 did not use a second crosslinking agent. In the ink of Comparative Example 4, the crosslinked resin was crosslinked only by the first crosslinking agent, and therefore the hydrophilicity of the crosslinked resin was excessively low. As a result, the ink of Comparative Example 4 formed images with poor abrasion resistance. The inks of Comparative Examples 8 and 21 had a ratio (C 2 / C 1 ) was excessively small, and the crosslinked resin was mainly crosslinked by the first crosslinking agent. As a result, it was confirmed that the inks of Comparative Examples 8 and 21 had the same results as the ink of Comparative Example 4.

[0148] The ink of Comparative Example 5 did not use the first crosslinking agent. In the ink of Comparative Example 5, the crosslinked resin was crosslinked only by the second crosslinking agent, and therefore the crosslinked resin had excessively high hydrophilicity. As a result, the ink of Comparative Example 5 formed an image with poor image density. The inks of Comparative Examples 9 and 22 had a ratio (C 2 / C 1 ) was excessively large, and the crosslinked resin was mainly crosslinked by the second crosslinking agent. As a result, the inks of Comparative Examples 9 and 22 showed the same results as the ink of Comparative Example 5.

[0149] The cross-linking rate of the cross-linked resin in the ink of Comparative Example 6 was too high. As a result, it is determined that the hydrophilicity of the cross-linked resin in the ink of Comparative Example 6 was low, and the dispersion stability of the pigment particles was insufficient. As a result, the ink of Comparative Example 6 could not suppress the occurrence of nozzle clogging.

[0150] The ink of Comparative Example 7 had an excessively low crosslinking rate of the crosslinked resin. The ink of Comparative Example 7 had an increased content of free resin because the crosslinked resin was not sufficiently crosslinked. As a result, the ink of Comparative Example 7 caused nozzle clogging. Furthermore, the ink of Comparative Example 7 also produced images with poor abrasion resistance.

[0151] In the inks of Comparative Examples 10 to 17, the repeating units contained in the copolymer did not satisfy the prescribed structure. In addition, in the inks of Comparative Examples 16 and 17, the acid value of the specific copolymer was either excessively low or excessively high. For these reasons, it is determined that the inks of Comparative Examples 10 to 17 had low dispersion stability of the pigment particles and were unable to suppress the occurrence of nozzle clogging. In addition, the inks of Comparative Examples 14 and 15 were poor in either the image density or the abrasion resistance of the formed images.

[0152] The neutralization rate of the specific resin was excessively low in the ink of Comparative Example 18. As a result, it is determined that the ink of Comparative Example 18 had low dispersion stability of the pigment particles and was unable to suppress the occurrence of nozzle clogging.

[0153] In the inks of Comparative Examples 19 and 20, the mass average molecular weight of the specific copolymer was either too small or too large. It is considered that the inks of Comparative Examples 19 and 20 could not efficiently coat the pigment with the specific copolymer because the molecular size of the specific copolymer was not appropriate. As a result, the inks of Comparative Examples 19 and 20 could not suppress the occurrence of nozzle clogging. [Industrial Applicability]

[0154] The ink and method of making the ink of the present embodiment can provide ink for use in forming an image.

Claims

1. The ink contains an aqueous medium and pigment particles dispersed in the aqueous medium, The pigment particles include a pigment and a crosslinked resin, the crosslinked resin is a crosslinked product of a specific resin, a first crosslinking agent, and a second crosslinking agent, the specific resin is a neutralized product of a specific copolymer having a first repeating unit derived from α-methylstyrene, a second repeating unit derived from styrene, a third repeating unit derived from (meth)acrylic acid, and a fourth repeating unit derived from an alkylene glycol (meth)acrylate or a dialkylene glycol (meth)acrylate; With respect to 100% by mass of all repeating units contained in the specific copolymer, The content of the first repeating unit is 1% by mass or more and 65% by mass or less, The content of the second repeating unit is 1% by mass or more and 60% by mass or less, The content of the third repeating unit is 10% by mass or more and 40% by mass or less, The content of the fourth repeating unit is 1% by mass or more and 12% by mass or less, The specific copolymer has an acid value of 50 mgKOH / g or more and 300 mgKOH / g or less, The specific copolymer has a mass average molecular weight of 3,000 or more and 18,000 or less, The neutralization rate of the specific resin is 20% or more and 100% or less, the first crosslinking agent has an ethylene oxide structure having an added mole number of 1 to 4 or a propylene oxide structure having an added mole number of 1 to 4, and two or more epoxy groups in a molecule; The water solubility of the first crosslinking agent is 80% or more, the second crosslinking agent has an ethylene oxide structure with an addition mole number of 5 to 15 in a molecule and two or more epoxy groups, The water solubility of the second crosslinking agent is 80% or more, In the crosslinked resin, the crosslinking rate C 1 Crosslinking rate C by the second crosslinking agent 2 The ratio (C 2 / C 1 ) is 18 / 82 or more and 82 / 18 or less, In the crosslinked resin, the total crosslinking rate (C 1 +C 2 ) is 25% or more and 95% or less.

2. 2. The ink-jet ink according to claim 1, wherein the solid content in a supernatant obtained by centrifuging at 1,050,000 G for 3 hours is 2.0% by mass or less.

3. 3. The ink-jet ink according to claim 1, wherein the first crosslinking agent comprises at least one of compounds represented by the following general formulas (1-A) to (1-B): 【Chemistry 1】 (In the general formula (1-A), n represents an integer of 1 or more and 4 or less, In the general formula (1-B), m represents an integer of 1 or more and 4 or less.

4. The ink-jet ink according to claim 3, wherein the first crosslinking agent comprises at least one of compounds represented by the following chemical formulas (1-A1), (1-B1), (1-B2), and (1-B3): 【Chemistry 2】

5. 3. The ink-jet ink according to claim 1, wherein the second crosslinking agent comprises a compound represented by the following general formula (2-A): 【Chemistry 3】 (In the general formula (2-A), s represents an integer of 5 or more and 15 or less.)

6. 6. The ink-jet ink according to claim 5, wherein the second crosslinking agent contains at least one of compounds represented by the following general formulas (2-A1) to (2-A2): 【Chemistry 4】

7. With respect to 100% by mass of all repeating units contained in the specific copolymer, The content of the first repeating unit is 15% by mass or more and 55% by mass or less, The content of the second repeating unit is 10% by mass or more and 40% by mass or less, The content of the third repeating unit is 20% by mass or more and 35% by mass or less, The ink-jet ink according to claim 1 or 2, wherein a content ratio of the fourth repeating unit is 4% by mass or more and 11% by mass or less.

8. 3. The ink-jet ink according to claim 1, wherein the epoxy equivalent of the first crosslinking agent is 100 g / eq. or more and 230 g / eq. or less.

9. 3. The ink-jet ink according to claim 1, wherein the epoxy equivalent of the second crosslinking agent is 250 g / eq. or more and 450 g / eq. or less.

10. 1. A method for producing an inkjet ink containing an aqueous medium and pigment particles dispersed in the aqueous medium, comprising the steps of: The pigment particles include a pigment and a crosslinked resin, a neutralization step of neutralizing the specific copolymer to obtain a specific resin; a dispersing step of dispersing the specific resin and the pigment in water to obtain a pigment particle dispersion; a crosslinking step of crosslinking the specific resin in the pigment particle dispersion with a first crosslinking agent and a second crosslinking agent to obtain the crosslinked resin, The specific copolymer has a first repeating unit derived from α-methylstyrene, a second repeating unit derived from styrene, a third repeating unit derived from (meth)acrylic acid, and a fourth repeating unit derived from an alkylene glycol (meth)acrylate or a dialkylene glycol (meth)acrylate, With respect to 100% by mass of all repeating units contained in the specific copolymer, The content of the first repeating unit is 1% by mass or more and 65% by mass or less, The content of the second repeating unit is 1% by mass or more and 60% by mass or less, The content of the third repeating unit is 10% by mass or more and 40% by mass or less, The content of the fourth repeating unit is 1% by mass or more and 12% by mass or less, The specific copolymer has an acid value of 50 mgKOH / g or more and 300 mgKOH / g or less, The specific copolymer has a mass average molecular weight of 3,000 or more and 18,000 or less, The neutralization rate of the specific resin in the neutralization step is 20% or more and 100% or less, the first crosslinking agent has an ethylene oxide structure having an added mole number of 1 to 4 or a propylene oxide structure having an added mole number of 1 to 4, and two or more epoxy groups in a molecule; The water solubility of the first crosslinking agent is 80% or more, the second crosslinking agent has an ethylene oxide structure with an addition mole number of 5 to 15 in a molecule and two or more epoxy groups, The water solubility of the second crosslinking agent is 80% or more, In the crosslinking step, the crosslinking rate C 1 Crosslinking rate C by the second crosslinking agent 2 The ratio (C 2 / C 1 ) is 18 / 82 or more and 82 / 18 or less, The total crosslinking rate of the crosslinked resin by the first crosslinking agent and the second crosslinking agent (C 1 +C 2 ) is 25% or more and 95% or less.

11. a centrifugation step of centrifuging the pigment particle dispersion liquid after the crosslinking step to obtain a precipitate; The method for producing an ink-jet ink according to claim 10, further comprising a redispersion step of redispersing the precipitate in water.

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