JP2023018805A - inkjet ink - Google Patents

Abstract

Kind Code: A1 To provide an inkjet ink which is excellent in ejection stability, storage stability and dispersion stability, can form an image having a desired image density, and can suppress the occurrence of nozzle clogging and curling. An inkjet ink contains a pigment, a first dispersant, a second dispersant, and an aqueous medium. The aqueous medium includes water, a first organic solvent, a second organic solvent and a third organic solvent. The content ratio of the first organic solvent, the content ratio of the second organic solvent, and the content ratio of the third organic solvent are each 5.0% by mass or more and 15.0% by mass or less. The acid value of the second dispersant is 25 mgKOH/g or more and 120 mgKOH/g or less. The content of the second dispersant is 0.7% by mass or more and 5.0% by mass or less. [Selection figure] None

Description

The present invention relates to inkjet inks.

An inkjet ink used in an inkjet recording apparatus is required to be excellent in ejection stability, storage stability and dispersion stability, capable of forming an image having a desired image density, and capable of suppressing nozzle clogging. Ink jet inks are also required to be able to suppress the occurrence of a phenomenon (curling) in which recording paper on which an image has been formed bends in a bow shape after image formation.

In response to such demands, for example, an image forming apparatus using an inkjet ink containing a self-dispersing pigment and an organic solvent having a Hansen solubility parameter value within a predetermined range has been proposed (Patent Document 1). . It is said that the inkjet ink described above has excellent dispersion stability and can suppress the occurrence of nozzle clogging.

JP 2014-221533 A

However, the inkjet ink described in Patent Document 1 does not satisfy all of the requirements of ejection stability, storage stability and dispersion stability, image density of formed images, and suppression of nozzle clogging and curling. do not have.

The present invention has been made in view of the above problems, and aims to achieve excellent ejection stability, storage stability, and dispersion stability, to form an image having a desired image density, and to prevent nozzle clogging and curling. An object of the present invention is to provide an inkjet ink capable of suppressing the

The inkjet ink according to the present invention contains a pigment, a first dispersant, a second dispersant, and an aqueous medium. The aqueous medium includes water, a first organic solvent, a second organic solvent and a third organic solvent. The content ratio of the first organic solvent, the content ratio of the second organic solvent, and the content ratio of the third organic solvent are each 5.0% by mass or more and 15.0% by mass or less. In the dispersion term (dD), the polarization term (dP) and the hydrogen bonding term (dH) of the Hansen solubility parameters, the first dispersant has a dD of 15.0 or more and 18.5 or less and a dP of 10.0 or more and 15.5. 0 or less, and dH is 18.0 or more and 30.0 or less. The second dispersant has a dD of 16.0 or more and 20.0 or less, a dP of 5.0 or more and 9.0 or less, and a dH of 12.0 or more and 23.0 or less. The first organic solvent has a dD of 15.0 or more and 18.0 or less, a dP of 10.0 or more and 14.0 or less, and a dH of 23.0 or more and 30.0 or less. The second organic solvent has a dD of 15.0 to 17.5, a dP of 5.0 to 7.5, and a dH of 8.0 to 16.0. The third organic solvent has a dD of 15.0 or more and 18.0 or less, a dP of 7.5 or more and 10.5 or less, and a dH of 17.0 or more and 23.0 or less. The first dispersant and the first organic solvent have an absolute value of dD difference (ΔdD) of 2.5 or less, an absolute value of dP difference (ΔdP) of 3.5 or less, and an absolute value of dH difference ( ΔdH) is 14.0 or less. The acid value of the second dispersant is 25 mgKOH/g or more and 120 mgKOH/g or less. The content of the second dispersant is 0.7% by mass or more and 5.0% by mass or less.

The inkjet ink according to the present invention is excellent in ejection stability, storage stability, and dispersion stability, can form an image having a desired image density, and can suppress the occurrence of nozzle clogging and curling.

Embodiments of the present invention will be described below. As used herein, the term “solvent” refers to components contained in the inkjet ink, excluding pigments, resins and additives.

In this specification, the units of the dispersion term (dD), the polarization term (dP) and the hydrogen bonding term (dH) of the Hansen solubility parameters are all [MPa ^0.5 ]. The acid value can be determined according to the method described in JIS (Japanese Industrial Standard) K0070-1992.

In this specification, acryl and methacryl may be collectively referred to as "(meth)acryl". Each component described in this specification may be used alone or in combination of two or more.

<Inkjet ink>
An inkjet ink (hereinafter sometimes simply referred to as ink) according to an embodiment of the present invention will be described below. The ink of the present invention contains a pigment, a first dispersant, a second dispersant and an aqueous medium. The aqueous medium includes water, first organic solvent, second organic solvent and third organic solvent. The content ratio of the first organic solvent, the content ratio of the second organic solvent, and the content ratio of the third organic solvent are each 5.0% by mass or more and 15.0% by mass or less. In the dispersion term (dD), the polarization term (dP) and the hydrogen bonding term (dH) of the Hansen solubility parameter, the first dispersant has a dD of 15.0 or more and 18.5 or less and a dP of 10.0 or more and 15.0 Below, dH is 18.0 or more and 30.0 or less. The second dispersant has a dD of 16.0 or more and 20.0 or less, a dP of 5.0 or more and 9.0 or less, and a dH of 12.0 or more and 23.0 or less. The first organic solvent has a dD of 15.0 or more and 18.0 or less, a dP of 10.0 or more and 14.0 or less, and a dH of 23.0 or more and 30.0 or less. The second organic solvent has a dD of 15.0 to 17.5, a dP of 5.0 to 7.5, and a dH of 8.0 to 16.0. The third organic solvent has a dD of 15.0 or more and 18.0 or less, a dP of 7.5 or more and 10.5 or less, and a dH of 17.0 or more and 23.0 or less. The first dispersant and the first organic solvent have an absolute value of dD difference (ΔdD) of 2.5 or less, an absolute value of dP difference (ΔdP) of 3.5 or less, and an absolute value of dH difference (ΔdH). is 14.0 or less. The acid value of the second dispersant is 25 mgKOH/g or more and 120 mgKOH/g or less. The content of the second dispersant is 0.7% by mass or more and 5.0% by mass or less.

First, the Hansen solubility parameter (HSP) will be explained. HSP is a value used to predict the solubility of a substance. HSP consists of the following three parameters (unit: MPa ^0.5 ).
Dispersion term (dD): Energy due to intermolecular dispersion force Polarization term (dP): Energy due to intermolecular dipole interaction Hydrogen bond term (dH): Energy due to intermolecular hydrogen bond

The three parameters that make up the HSP can be regarded as coordinates in a three-dimensional space (Hansen space). When two specific substances are arranged in the Hansen space, the closer the distance between the coordinates of the two substances, the closer the properties of the two substances tend to be.

A substance with unknown HSP can be measured for HSP by the following method. First, in a sealable container, 1 part by mass of a substance whose HSP is to be measured (hereinafter sometimes referred to as a target substance) and 49 masses of a solvent in which HSP is known (for example, a solvent with a literature value) Part and The substance of interest and solvent are then thoroughly mixed by handshaking the container. Next, the container is allowed to stand for 12 hours under normal temperature environment (23° C.). Next, the container is turned upside down and the bottom surface of the container is observed. If neither precipitates nor aggregates are present on the bottom of the container, the solvent is considered to have dissolved the target substance. This test is repeated with appropriate changes in solvent type. As a result, a combination of 10 types of solvents composed of a solvent that dissolves the target substance and a solvent that does not dissolve the target substance is determined. As for the combination of 10 kinds of solvents, it is desirable that approximately half (for example, 4 to 6 kinds) of the solvents are solvents that dissolve the target substance, and the remaining solvents are solvents that do not dissolve the target substance. A sphere called the Hansen sphere is drawn in the Hansen space based on the test results for the ten solvents.

In this specification, the combination of 10 kinds of solvents includes the solvents shown in Table 1 below.

Describes how to draw a Hansen sphere. A sphere (Hansen sphere) that includes the coordinates of the solvent in which the target substance is dissolved and does not include the coordinates of the solvent in which the target substance is not dissolved is drawn in the Hansen space. The center coordinates of the drawn Hansen sphere indicate the HSP of the target substance. The size of the Hansen sphere varies depending on the type of target substance. Specifically, a target substance that dissolves in various solvents having different properties has a large Hansen sphere radius R ₀ . Conversely, the radius R ₀ of the Hansen sphere is small for a target substance that dissolves only in solvents with limited specific properties.

A specific method for predicting the solubility of two substances (for example, solvent X and solute Y) using HSP is described. First, two substances are each placed in the Hansen space based on the HSP. Then, the distance R _a between the coordinates of the two substances is calculated. The closer the distance R _a is, the easier it is for the two substances to dissolve in each other. The distance R _a between two substances can be calculated by the following formula (R).

In equation (R), dDx, dPx and dHx represent the dispersion term (dD), polarization term (dP) and hydrogen bonding term (dH) of solvent X, respectively. dDy, dPy and dHy denote the dispersion term (dD), polarization term (dP) and hydrogen bonding term (dH) of solute Y, respectively.

Applying this to the ink of the present invention, the distance R _a between the solvent and the pigment particles in the Hansen space is calculated by the following formula (R-1).

In formula (R-1), dDs, dPs and dHs represent the solvent dispersion term (dD), polarization term (dP) and hydrogen bonding term (dH), respectively. dDp, dPp and dHp indicate the dispersion term (dD), polarization term (dP) and hydrogen bonding term (dH) of the pigment particles, respectively.

Whether or not the solute Y dissolves in the solvent X is determined by whether or not the Hansen sphere of the solute Y includes the coordinates of the HSP of the solvent X in the Hansen space. Specifically, whether or not the solute Y dissolves in the solvent X is determined by the ratio (R _a /R ₀ ) of the distance R _a between the two substances to the radius R ₀ of the Hansen sphere of the solute Y. be. Hereinafter, the ratio (R _a /R ₀ ) is referred to as a relative energy difference (RED) (formula (r) below). When RED is less than 1, solute Y dissolves in solvent X because the coordinates of the HSPs of solvent X lie inside the Hansen sphere of solute Y. On the other hand, when RED is greater than 1, solute Y does not dissolve in solvent X because the HSP coordinates of solvent X lie outside the Hansen sphere of solute Y. Note that solute Y partially dissolves in solvent X when RED is exactly 1.
RED=R _a /R ₀ (r)

When solvent X is a mixed solvent, HSP of solvent X can be calculated by the following method. First, for each solvent constituting the solvent X, the product A of the dispersion term (dD) of the solvent and the mass ratio of the solvent (the ratio of the mass of the solvent to the mass of the solvent X) is calculated. Next, the sum B is calculated by summing the products A of each solvent. This sum B is defined as the dispersion term (dD) of the mixed solvent. The polarization term (dP) and the hydrogen bond term (dH) of the solvent X can also be calculated by the same method as the method of calculating the dispersion term (dD) of the solvent X. As a result, the HSP of solvent X, which is a mixed solvent, is calculated.

The ink of the present invention, which has the above-described structure, is excellent in ejection stability, storage stability, and dispersion stability, can form an image having a desired image density, and can suppress the occurrence of nozzle clogging and curling. The reason is explained below. The ink of the present invention contains a pigment, a first dispersant, a second dispersant and an aqueous medium. In the ink of the present invention, the pigment, first dispersant and second dispersant form, for example, pigment particles. A pigment particle is a particle comprising a core containing a pigment and dispersing agents (first dispersing agent and second dispersing agent) covering the surface of the pigment. In the ink of the present invention, the HSP difference between the first dispersant and the first organic solvent is a certain value or less. That is, the ink of the present invention has excellent compatibility between the first organic solvent and the first dispersant. Additionally, the secondary dispersant has a moderately high acid number. In the ink of the present invention, the pigment particles are stably dispersed by electrostatic repulsion by including the second dispersant. As a result, the ink of the present invention can highly disperse the pigment particles in the aqueous medium, and thus has excellent storage stability and dispersion stability. In addition, the ink of the present invention contains specific amounts of the first organic solvent, the second organic solvent, and the third organic solvent, so that the ink has appropriate viscosity and surface tension, and is excellent in ejection stability.

Here, the first organic solvent is moderately hydrophilic and has a moisturizing effect. Also, the second organic solvent has relatively high hydrophobicity. Furthermore, the second organic solvent collects on the surface of the ink of the present invention when the ink of the present invention stays in the recording head for a long period of time and the moisture in the ink of the present invention evaporates in the vicinity of the ejection nozzles of the recording head. Prevent further drying. Hereinafter, the above effect of the second organic solvent may be referred to as "cap effect". Further, in the ink of the present invention, ΔdD, ΔdP and ΔdH are less than a certain level, and the pigment particles are highly dispersed in the aqueous medium, so that the solid content is difficult to deposit. Furthermore, the third organic solvent improves the compatibility of each of the first organic solvent, the second organic solvent and the first dispersant. The ink of the present invention contains a first organic solvent having a moisturizing action, a second organic solvent having a capping effect, and a third organic solvent, and the compatibility between the first dispersant and the first organic solvent is and the second dispersant stably disperses the pigment particles, it is possible to suppress the precipitation of solid content due to drying of water in the vicinity of the ejection nozzles of the recording head. As a result, the ink of the present invention can suppress the occurrence of nozzle clogging.

Furthermore, it is believed that ink containing water causes curling for the following reasons. First, when the water in the ink permeates the recording paper, the water cuts the hydrogen bonds between the cellulose fibers of the recording paper. The broken hydrogen bonds are rebonded when the recording paper dries and water is removed. However, between cellulose fibers, the positions of hydrogen bonds after recombination are not necessarily the same as the positions of initial hydrogen bonds. Therefore, the cellulose fiber expands and contracts due to a series of hydrogen bond breaking and recombination, resulting in curling. In contrast, the ink of the present invention contains a certain amount of the third organic solvent. The third organic solvent has a hydroxyl group and bonds with the cellulose fibers. When the third organic solvent binds to the cellulose fibers, contact between water and the cellulose fibers becomes difficult. As a result, the ink of the present invention can prevent water from breaking hydrogen bonds between cellulose fibers, thereby suppressing the occurrence of curling. Furthermore, in the ink of the present invention, the pigment particles contain a second dispersant having a moderately high acid value, and thus have anionic properties. On the other hand, a recording medium used for image formation is generally coated with a cationic agent in many cases. Therefore, after the ink of the present invention is ejected onto the surface of the recording medium, electrostatic attraction acts between the pigment particles and the recording medium. As a result, the ink of the present invention can retain the pigment particles on the surface of the recording medium, thereby forming an image having a desired image density. Each component of the ink of the present invention is described below.

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

The content of the pigment in the ink of the present invention is preferably 2.0% by mass or more and 15.0% by mass or less, and preferably 4.0% by mass or more and 8.0% by mass or less. By setting the pigment content to 2.0% by mass or more, the ink of the present invention can more easily form an image having a desired image density. By setting the content of the pigment to 15.0% by mass or less, the ejection stability of the ink of the present invention can be further improved.

[First Dispersant]
Examples of the first dispersant include (meth)acrylic resins, styrene-(meth)acrylic resins, urethane resins and polyester resins. Styrene-(meth)acrylic resin is preferred as the first dispersant.

The first dispersant and the aqueous medium have an absolute value of dD difference (ΔdD) of 3.0 or less, an absolute value of dP difference (ΔdP) of 4.5 or less, and an absolute value of dH difference (ΔdH) of 6. 0.5 or less. ΔdD is more preferably 1.5 or less, even more preferably 1.0 or less. ΔdP is more preferably 3.5 or less, and even more preferably 2.0 or less. ΔdH is more preferably 5.0 or less, and even more preferably 3.5 or less. By setting ΔdD, ΔdP, and ΔdH of the first dispersant and the aqueous medium within the numerical ranges described above, the dispersion stability and storage stability of the ink of the present invention can be further improved.

In the Hansen solubility parameters, the dD of the first dispersant is 15.0 or more and 18.5 or less, preferably 16.0 or more and 17.8 or less. The dP of the first dispersant is 10.0 or more and 15.0 or less, preferably 11.0 or more and 13.0 or less. The dH of the first dispersant is 18.0 or more and 30.0 or less, preferably 20.0 or more and 26.5 or less. By setting dD, dP and dH of the first dispersant within the numerical ranges described above, the dispersion stability and storage stability of the ink of the present invention can be improved.

The first dispersant and the first organic solvent have an absolute value of dD difference (ΔdD) of 2.5 or less, an absolute value of dP difference (ΔdP) of 3.5 or less, and an absolute value of dH difference (ΔdH). is 14.0 or less. ΔdD is preferably 1.0 or less, more preferably 0.5 or less. ΔdP is preferably 2.0 or less, more preferably 1.5 or less. ΔdH is preferably 8.0 or less, more preferably 4.0 or less. By setting ΔdD, ΔdP, and ΔdH of the first dispersant and the first organic solvent within the numerical ranges described above, the dispersion stability and storage stability of the ink of the present invention can be improved.

When the ink of the present invention contains two or more first dispersants, the dD, dP and dH of the first dispersant are the above HSP measurements for the mixture of two or more first dispersants. It is a value that is measured by performing a method.

(Styrene-(meth)acrylic resin)
A styrene-(meth)acrylic resin is a resin having styrene units and repeating units derived from (meth)acrylic acid alkyl esters. The styrene-(meth)acrylic resin may further have repeating units derived from (meth)acrylic acid. (Meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate and butyl (meth)acrylate.

In the styrene-(meth)acrylic resin used for the first dispersant, the content ratio of styrene units to all repeating units is preferably 15.0% by mass or more and 50.0% by mass or less, and 25.0% by mass or more and 45.0% by mass. 0% by mass or less is more preferable.

In the styrene-(meth)acrylic resin used for the first dispersant, the content ratio of repeating units derived from (meth)acrylic acid to all repeating units is preferably 10.0% by mass or more and 60.0% by mass or less, 25.0 mass % or more and 35.0 mass % or less are more preferable.

In the styrene-(meth)acrylic resin used for the first dispersant, the content of repeating units derived from (meth)acrylic acid alkyl ester relative to all repeating units is 10.0% by mass or more and 60.0% by mass or less. It is preferably 25.0% by mass or more and 45.0% by mass or less.

As raw material monomers for the styrene-(meth)acrylic resin used for the first dispersant, the following combination (I) is preferred, and combinations (Ia) to (Ib) are more preferred.
Combination (I): styrene, (meth)acrylic acid, methyl (meth)acrylate, and ethyl (meth)acrylate Combination (Ia): styrene, acrylic acid, methacrylic acid, methyl methacrylate and ethyl acrylate Combination (Ib ): styrene, methacrylic acid, methyl methacrylate and ethyl acrylate

The content of the first dispersant in the ink of the present invention is preferably 0.1% by mass or more and 10.0% by mass or less, more preferably 1.0% by mass or more and 5.0% by mass or less. By setting the content of the first dispersant to 0.1% by mass or more and 10.0% by mass or less, the dispersibility of the pigment particles can be improved.

In the ink of the present invention, the ratio of the mass of the first dispersant to the mass of the pigment (mass of first dispersant/mass of pigment) is preferably 0.1 or more and 1.0 or less, and 0.2 or more and 0.2 or more. 7 or less is more preferable.

[Second dispersant]
Examples of the second dispersant include (meth)acrylic resins, styrene-(meth)acrylic resins, urethane resins and polyester resins. Styrene-(meth)acrylic resin is preferred as the second dispersant.

In the Hansen solubility parameters, the dD of the second dispersant is 16.0 or more and 20.0 or less, preferably 17.0 or more and 18.5 or less. The dP of the second dispersant is 5.0 or more and 9.0 or less, preferably 6.5 or more and 8.0 or less. The dH of the second dispersant is 12.0 or more and 23.0 or less, preferably 13.0 or more and 21.5 or less. By setting dD, dP and dH of the second dispersant within the numerical ranges described above, the dispersion stability and storage stability of the ink of the present invention can be improved.

The acid value of the second dispersant is 25 mgKOH/g or more and 120 mgKOH/g or less, preferably 50 mgKOH/g or more and 100 mgKOH/g or less. By setting the acid value of the second dispersant to 25 mgKOH/g or more and 120 mgKOH/g or less, the dispersion stability and storage stability of the ink of the present invention can be improved. Further, the ink of the present invention can form an image having a desired image density.

When the ink of the present invention contains two or more second dispersants, the dD, dP, dH and acid value of the second dispersant are as described above for the mixture of two or more second dispersants. It is a value measured by carrying out the HSP measurement method and the acid value measurement method.

(Styrene-(meth)acrylic resin)
Examples of the styrene-(meth)acrylic resin used for the second dispersant include those similar to the styrene-(meth)acrylic resins exemplified for the first dispersant.

In the styrene-(meth)acrylic resin used for the second dispersant, the content ratio of the styrene unit to all repeating units is preferably 30.0% by mass or more and 85.0% by mass or less, and 45.0% by mass or more and 75.0% by mass. 0% by mass or less is more preferable.

In the styrene-(meth)acrylic resin used for the second dispersant, the content ratio of repeating units derived from (meth)acrylic acid to all repeating units is preferably 5.0% by mass or more and 45.0% by mass or less, 10.0% by mass or more and 35.0% by mass or less is more preferable.

In the styrene-(meth)acrylic resin used for the second dispersant, the content of repeating units derived from (meth)acrylic acid alkyl ester relative to all repeating units is 10.0% by mass or more and 60.0% by mass or less. It is preferably 15.0% by mass or more and 45.0% by mass or less.

As raw material monomers for the styrene-(meth)acrylic resin used for the second dispersant, the following combination (II) is preferred, and combinations (IIa) and (IIb) are more preferred.
Combination (II): Styrene, (meth)acrylic acid and butyl (meth)acrylate Combination (IIa): Styrene, acrylic acid and butyl acrylate Combination (IIb): Styrene, methacrylic acid and butyl acrylate

The content of the second dispersant in the ink of the present invention is preferably 0.7% by mass or more and 5.0% by mass or less, more preferably 1.0% by mass or more and 2.5% by mass or less. By setting the content of the second dispersant to 0.7% by mass or more and 5.0% by mass or less, the dispersion stability and storage stability of the ink of the present invention can be improved.

In the ink of the present invention, the ratio of the mass of the second dispersant to the mass of the pigment (the mass of the second dispersant/the mass of the pigment) is preferably 0.1 to 1.0, more preferably 0.2 to 0.2. 6 or less is more preferable.

[Aqueous medium]
The aqueous medium includes water, first organic solvent, second organic solvent and third organic solvent. The aqueous medium may further contain components other than water, the first organic solvent, the second organic solvent, and the third organic solvent, if the amount is small. In the aqueous medium, the total proportion of water, the first organic solvent, the second organic solvent and the third organic solvent is preferably 90% by mass or more, more preferably 100% by mass.

The dD of the aqueous medium is preferably 15.0 or more and 19.0 or less, more preferably 16.0 or more and 17.5 or less. The dP of the aqueous medium is preferably 8.0 or more and 12.0 or less, more preferably 9.0 or more and 10.5 or less. The dH of the aqueous medium is preferably 17.0 or more and 25.0 or less, more preferably 19.0 or more and 21.0 or less. By setting the dD, dP and dH of the aqueous medium within the above numerical ranges, the dispersion stability and storage stability of the ink of the present invention can be further improved.

(First organic solvent)
The first organic solvent has a dD of 15.0 or more and 18.0 or less, a dP of 10.0 or more and 14.0 or less, and a dH of 23.0 or more and 30.0 or less. By setting the dD of the first organic solvent to 15.0 or more and 18.0 or less, the difference in dD between the aqueous medium and the first dispersant and the second dispersant is reduced, and the aqueous medium and the first dispersant and the second dispersant are 2 compatibility with the dispersant can be improved. As a result, the dispersion stability and storage stability of the ink of the invention can be improved. Further, by setting dP of the first organic solvent to 10.0 or more and dH of 23.0 or more, it is possible to impart appropriate hydrophilicity to the first organic solvent and exhibit a moisturizing effect. Furthermore, by setting the dP of the first organic solvent to 14.0 or less and the dH to 30.0 or less, the hydrophilicity of the first organic solvent is suppressed from becoming excessively high, and the first organic solvent and the pigment and the compatibility between the first organic solvent and the first dispersant and the second dispersant can be improved.

Examples of the first organic solvent include glycerin, 1,3-propanediol, sorbitol (e.g., "Sorbitol F" manufactured by Bussan Food Science Co., Ltd., an aqueous solution with a concentration of 70% by mass), ethylene glycol, 1,2,3- butanetriol, 1,2,4-butanetriol, 1,2,3,4-butanetetrol, 2-methylamino-1-phenyl-propan-1-ol, xylitol and d-mannitol. Preferred first organic solvents are glycerin, sorbitol, 1,3-propanediol, 1,2,3-butanetriol, or ethylene glycol.

In the ink of the present invention, the content of the first organic solvent is 5.0% by mass or more and 15.0% by mass or less, preferably 6.0% by mass or more and 10.0% by mass or less.

(Second organic solvent)
The second organic solvent has a dD of 15.0 to 17.5, a dP of 5.0 to 7.5, and a dH of 8.0 to 16.0. By setting the dD of the second organic solvent to 15.0 or more and 17.5 or less, the difference in dD between the aqueous medium and the first dispersant and the second dispersant is reduced, and the aqueous medium and the first dispersant and the second dispersant are 2 compatibility with the dispersant can be improved. As a result, the dispersion stability and storage stability of the ink of the invention can be improved. Moreover, by setting the dP of the second organic solvent to 5.0 or more and the dH of 8.0 or more, it is possible to prevent the second organic solvent from becoming excessively hydrophobic. As a result, it is possible to prevent the second organic solvent from inhibiting the adsorption of the first dispersant and the second dispersant to the pigment. By setting the dP of the second organic solvent to 7.5 or less and the dH to 16.0 or less, it is possible to impart appropriate hydrophobicity to the second organic solvent. As a result, the second organic solvent can exhibit the capping effect described above.

Examples of the second organic solvent include 1,2-octanediol, triethylene glycol monobutyl ether, 2-ethyl-1,3-hexanediol, 2-ethyl-1,2-hexanediol, and ethylene glycol methyl t-butyl ether. , ethylene glycol monobutyl ether, 2-methyl-1-butanol, 2,2-diethyl-1,3-propanediol, 3-methoxybutanol, and dipropylene glycol monomethyl ether. The second organic solvent is preferably triethylene glycol monobutyl ether, 1,2-octanediol, 2-ethyl-1,2-hexanediol, or ethylene glycol monobutyl ether.

In the ink of the present invention, the content of the second organic solvent is 5.0% by mass or more and 15.0% by mass or less, preferably 6.0% by mass or more and 10.0% by mass or less.

(Third organic solvent)
The third organic solvent has a dD of 15.0 or more and 18.0 or less, a dP of 7.5 or more and 10.5 or less, and a dH of 17.0 or more and 23.0 or less. By setting the dD of the third organic solvent to 15.0 or more and 18.0 or less, the difference in dD between the aqueous medium and the first dispersant and the second dispersant is reduced, and the aqueous medium and the first dispersant and the second dispersant are 2 compatibility with the dispersant can be improved. As a result, the dispersion stability and storage stability of the ink of the invention can be improved. Moreover, by setting the dH of the third organic solvent to 17.0 or more, it is possible to suppress an excessive increase in the hydrophobicity of the aqueous medium. As a result, the dispersion stability of the ink of the invention can be improved. By setting the dP of the third organic solvent to 10.5 or less and the dH to 23.0 or less, it is possible to suppress an excessive increase in the hydrophilicity of the aqueous medium. As a result, the ink of the present invention can suppress curling. By setting dP of the third organic solvent to 7.5 or more and 10.5 or less and dH of 17.0 or more and 23.0 or less, the first organic solvent, the second organic solvent, the first dispersant and the second The compatibility of each of the dispersants can be improved.

Examples of the third organic solvent include 1,5-pentanediol, propylene glycol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 1,2-butylene glycol, 1, 3-butylene glycol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,2-propanediol, 2-methyl-1,3-propanediol, 1-methyl-1,3-propanediol , 1,2-cyclohexanediol, and 1,2,6-hexanetriol. As the third organic solvent, 3-methyl-1,5-pentanediol, 1,5-pentanediol, propylene glycol, 2-methyl-1,3-propanediol, or 1-methyl-1,3-propanediol is preferred.

In the ink of the present invention, the content of the third organic solvent is 5.0% by mass or more and 15.0% by mass or less, preferably 6.0% by mass or more and 10.0% by mass or less.

(water)
The content of water in the ink of the present invention is preferably 15.0% by mass or more and 50.0% by mass or less, more preferably 25.0% by mass or more and 40.0% by mass or less. By setting the water content to 15.0% by mass or more and 50.0% by mass or less, it becomes easier to adjust the dD, dP and dH of the aqueous medium to the ranges described above.

[Other ingredients]
The ink of the present invention may optionally contain known additives (more specifically, for example, surfactants, antifoaming agents, humectants, dissolution stabilizers, drying inhibitors, antioxidants, viscosity modifiers). , a pH adjuster and an antifungal agent).

(Surfactant)
A surfactant improves the compatibility and dispersion stability of each component contained in the ink of the present invention. Surfactants include, for example, anionic surfactants, cationic surfactants and nonionic surfactants. A nonionic surfactant is preferred as the surfactant.

Examples of nonionic surfactants include polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan monooleate ether, monodecanoyl sucrose, and ethylene oxide addition of acetylene glycol. things are mentioned. As the nonionic surfactant, an ethylene oxide adduct of acetylene glycol is preferred.

When the ink of the present invention contains a surfactant, the content of the surfactant in the ink of the present invention is preferably 0.1% by mass or more and 3.0% by mass or less, and 0.2% by mass or more and 1.5% by mass. 0% by mass or less is more preferable.

(Antifoaming agent)
The antifoaming agent suppresses the generation of air bubbles from the ink of the present invention. Antifoaming agents include, for example, metal soap antifoaming agents, polyether antifoaming agents, silicone antifoaming agents and mineral oil antifoaming agents.

When the ink of the present invention contains an antifoaming agent, the content of the antifoaming agent in the ink of the present invention is preferably 0.01% by mass or more and 1.00% by mass or less, and 0.02% by mass or more and 0.02% by mass or less. 10% by mass or less is more preferable.

[Ink preparation method]
The ink of the present invention comprises, for example, a pigment dispersion containing pigment particles, water, a first organic solvent, a second organic solvent and a third organic solvent, and optionally other components (e.g., surfactant agent) with a stirrer. In the preparation of the ink of the present invention, foreign matters and coarse particles may be removed by uniformly mixing each component and filtering the mixture with a filter (for example, a filter with a pore size of 5 μm or less).

A pigment dispersion can be prepared by dispersing a pigment, a first dispersant and a second dispersant in a dispersion medium (eg, water). Dispersion treatment includes, for example, treatment using a bead mill.

Examples of the present invention will be described below. However, the present invention is not limited to the following examples. In the examples, first, the components used for preparing each ink were prepared.

(Preparation of dispersant (I-1))
A four-necked flask was equipped with a stirrer, a nitrogen inlet tube, a condenser, a stirrer, and a dropping funnel. This four-necked flask was used as a reaction vessel. The reaction vessel was then charged with 100.0 g of isopropyl alcohol and 300.0 g of methyl ethyl ketone. Next, while nitrogen gas was bubbled through the contents of the reaction vessel, the contents of the reaction vessel were heated to 70° C. (reflux state). Separately, 35.0 g of styrene, 10.0 g of acrylic acid, 20.0 g of methyl methacrylate, 15.0 g of ethyl acrylate, 20.0 g of methacrylic acid, and 0.400 g of azobisiso Butyronitrile (AIBN, polymerization initiator) was mixed to obtain a monomer solution. Next, while maintaining the temperature of the contents of the reaction vessel at 70° C. (reflux state), the above monomer solution was added dropwise to the reaction vessel over about 2 hours. After dropping, the temperature of the contents of the reaction vessel was maintained at 70° C. (reflux state) for 6 hours.

Next, 150 g of a methyl ethyl ketone solution containing 0.200 g of AIBN was added dropwise to the reaction vessel over 15 minutes while maintaining the temperature of the contents of the reaction vessel at 70° C. (reflux state). After dropping, the temperature of the contents of the reaction vessel was kept at 70° C. (reflux state) for 5 hours. The contents of the reaction vessel were then evacuated to remove the solvent. As a result, a dispersant (I-1), which is a styrene-(meth)acrylic resin, was obtained.

Dispersants (I-2) to (II-5) were prepared in the same manner as dispersant (I-1) except that the types and amounts of monomers used were changed as shown in Table 2 below. bottom.

(HSP of dispersant)
The HSP of dispersants (I-1) to (II-5) and the acid values of dispersants (II-1) to (II-5) were measured by the method described in the embodiment. The measurement results are shown in Table 3 below.

(Preparation of pigment dispersion (PI-1))
Carbon black (CB-1) as a pigment (“Printex (registered trademark) 80” manufactured by Orion Engineered Carbons Co., Ltd.) 15.0 parts by weight, dispersant (I-1) 10.0 parts by weight, and 0.1 part by mass of a foaming agent (“SN Deformer 1340” manufactured by San Nopco Co., Ltd.) and 74.9 parts by mass of ion-exchanged water were mixed. The resulting mixture was subjected to dispersion treatment for 4 hours using a bead mill (“Dyno Mill” manufactured by Willie & E. Bakkofen). In the dispersion treatment, zirconia beads (0.5 mm in diameter) were used as media. In the dispersion treatment, the filling rate of the media in the vessel of the bead mill was 60% by volume. Furthermore, in the dispersion treatment, the treatment temperature (chiller temperature) was set at 10°C. After the dispersion treatment, after removing the media, the resulting mixture was filtered through a filter with a pore size of 5 μm to remove foreign matter and coarse particles. As a result, a pigment dispersion (PI-1) was obtained.

(Preparation of pigment dispersions (PI-2) to (PII-5))
Pigment dispersions (PI-2) to (PII-5) were prepared in the same manner as the pigment dispersion (PI-1) except that the types and amounts of the raw materials used were changed as shown in Table 4 below. was prepared.

Details of the carbon blacks listed in Table 4 below are shown below.
Carbon black (CB-1): "MOGUL (registered trademark) L" manufactured by Cabot Corporation
Carbon black (CB-2): "#960" manufactured by Mitsubishi Chemical Corporation
Carbon black (CB-3): "Printex (registered trademark) 80" manufactured by Orion Engineered Carbons Co., Ltd.
Carbon black (CB-4): "Monarch (registered trademark) 700" manufactured by Cabot Corporation
Carbon black (CB-5): "HIBLACK (registered trademark) 890" manufactured by Orion Engineered Carbons Co., Ltd.

The Hansen solubility parameters of organic solvents and water used in this example are shown in Table 5 below. In Table 5 below, "Classification" indicates which of the first organic solvent, the second organic solvent, and the third organic solvent. "-" in "Classification" indicates that it does not correspond to any of the first organic solvent, the second organic solvent and the third organic solvent.

<Ink preparation>
After mixing the raw materials shown in Tables 6 and 7 below, they were dispersed for 20 minutes at a temperature of 25° C. and a rotation speed of 3000 rpm using a dispersing machine (“Homo Mixer MARK II 2.5” manufactured by Primix Co., Ltd.). After the dispersion treatment, the resulting mixture was filtered through a filter with a pore size of 5 μm to remove foreign matter and coarse particles. In this way, inks (I-1) to (I-10) of Examples 1 to 10 and inks (I-11) to (I-20) of Comparative Examples 1 to 10 were prepared (pigment concentration: 6.0 mass %). In Tables 6 and 7 below, "surfactant" indicates a surfactant containing an ethylene oxide adduct of acetylene diol ("Olfine (registered trademark) E1010" manufactured by Nissin Chemical Industry Co., Ltd.). "MPD", "TGME", "EHD" and "EGME" are 3-methyl-1,5-pentanediol, triethylene glycol monobutyl ether, 2-ethyl-1,2-hexanediol, ethylene glycol monobutyl ether, respectively. Indicates butyl ether.

(HSP of ink)
The HSP of the aqueous medium (mixture of water and organic solvent) contained in the inks (I-1) to (I-20) was calculated by the method described in the embodiment. The calculation results are shown in Table 8 below.

Ink (I-1) will be described below as a specific example of the method for calculating the HSP of the aqueous medium. The dD of the aqueous medium of the ink of Example 1 was calculated. In the ink of Example 1, the content of water was 63.2% by mass. The ratio of the mass of water to the mass of total aqueous medium is 0.706. The dD of water is 15.1. From the above, the product A of dD of water and the mass ratio (0.706) is 10.7. In a similar manner, in ink (I-1), the product A asked for Then, the sum B obtained by summing the products A of dD of each aqueous medium was taken as the dD of the aqueous medium of ink (I-1). The dD of ink (I-1) in an aqueous medium was 17.1.

By the same method, dP and dH of the aqueous medium of ink (I-1) and dD, dP and dH of the aqueous medium of inks (I-2) to (I-20) were calculated. Table 8 below shows the calculated HSP of the aqueous medium of each ink.

<Evaluation>
By the following methods, the inks (I-1) to (I-20) were tested for nozzle clogging, curling, ejection stability (ejection distortion), storage stability, Dispersion stability (presence or absence of occurrence of ink transparency) and image density of the formed image were evaluated. Volatility was also measured for the inks (I-1) to (I-20). The evaluation was performed under an environment of 1 atmospheric pressure (1013 hPa), no wind, a temperature of 25° C., and a humidity of 60% RH (hereinafter referred to as standard environment), unless otherwise specified. Further, for inks (I-1) to (I-20), the difference between the HSP of the first dispersant and the HSP of the aqueous medium and the difference between the HSP of the first dispersant and the HSP of the first organic solvent were calculated. . The results are shown in Tables 9-12 below. In Tables 9 to 12 below, "aqueous medium/first dispersant" indicates the difference between the HSP of the aqueous medium and the HSP of the first dispersant. "First organic solvent/first dispersant" indicates the difference between the HSP of the first organic solvent and the HSP of the first dispersant. "Determination" indicates whether the HSP difference satisfies the requirements described in the embodiment. Specifically, "Y" indicates that the HSP difference satisfies the requirements described in the embodiment. "N" indicates that the HSP difference does not meet the requirements described in the embodiment.

[Storage stability]
Using a vibrating viscometer ("VM-200T" manufactured by Nittetsu Hokkaido Control System Co., Ltd.), the viscosity (initial viscosity V ₁ ) was measured. Next, about 30 g of the object to be evaluated was placed in a container with a volume of 50 mL and sealed. The container described above was placed in a thermostat set at an internal temperature of 60° C. and kept warm for one month. After that, the above-mentioned container was taken out from the thermostat, and then the above-mentioned container was allowed to stand at room temperature for 3 hours. After that, the object to be measured was taken out from the container described above, and the viscosity (viscosity V ₂ after treatment) was measured using the vibration viscometer described above. Based on the measured initial viscosity _V1 and post-treatment viscosity _V2 , the viscosity change rate [%] was calculated (the following formula). The calculated viscosity change rate was used as an evaluation value for the storage stability of the ink to be measured. The storage stability of ink was evaluated according to the following criteria.
Viscosity change rate [%] = 100 x ( _V1 - _V2 )/ _V1

(Criteria for storage stability)
A (good): the absolute value of the viscosity change rate is 5% or less B (poor): the absolute value of the viscosity change rate is more than 5%

[volatility]
10 g (initial mass) of an object to be evaluated (specifically, any one of inks (I-1) to (I-20)) was put into a container. The container described above was placed under the standard environment described above. At this time, the container was not covered with a lid so that the object to be evaluated and the atmosphere were in contact (contact area: 16 cm ² ). After 60 minutes from the start of standing, the mass of the object to be measured (mass after drying) was measured. The mass change rate of the object to be measured was calculated by the following formula. The calculated mass change rate was used as the volatility evaluation value of the ink to be measured. The volatility of the evaluation target was evaluated according to the following criteria.
Mass change rate = 100 × (initial mass - mass after drying) / initial mass

(volatility criteria)
A (good): mass change rate is less than 10 mass% B (poor): mass change rate is 10 mass% or more

[Evaluation machine]
In the following evaluations, an inkjet recording apparatus (prototype manufactured by Kyocera Document Solutions Co., Ltd.) equipped with a piezo line type recording head was used as an evaluation apparatus. The ink tank of the evaluation machine was filled with an evaluation object (any of inks (I-1) to (I-20)).

[Nozzle clogging]
In the evaluation of nozzle clogging, A4 size inkjet matte paper ("Super Fine Paper" manufactured by Seiko Epson Corporation) was used as evaluation paper. A solid image of 150 mm×200 mm was continuously printed on 100 sheets of evaluation paper using an evaluation machine. Next, the evaluation target was purged from the recording head of the evaluation machine. Next, the ink ejection surface of the recording head of the evaluation machine was wiped to clean the recording head. Hereinafter, the operation of cleaning the print head by purging and wiping may be referred to as cleaning processing. Next, an evaluation machine was used to form a nozzle check pattern image on the evaluation paper. As a result, regardless of which evaluation target was used, the evaluation target was ejected from all nozzles (the number of non-ejection nozzles was 0). Next, the recording head was subjected to cleaning processing again. Next, the evaluation machine was allowed to stand for 7 days without attaching the cap to the recording head. Next, the recording head was subjected to cleaning processing again. Next, an evaluation machine was used to form a nozzle check pattern image (evaluation image) on an evaluation sheet. The evaluation image was checked, and the ratio of the number of ejection failure nozzles to all nozzles (7968 nozzles) was calculated. The calculated ratio of the number of non-ejection nozzles was used as an evaluation value for nozzle clogging. Whether or not the object to be evaluated causes nozzle clogging was evaluated according to the following criteria.

(Criteria for nozzle clogging)
A (Good): Evaluation value less than 10% B (Poor): Evaluation value 10% or more

[Ejection stability]
In the evaluation of ejection stability, A4 size inkjet matte paper ("Super Fine Paper" manufactured by Seiko Epson Corporation) was used as evaluation paper. A solid image of 150 mm×200 mm (100% coverage) was continuously printed on 5,000 sheets of evaluation paper using the evaluation machine. Next, cleaning processing was performed on the recording head of the evaluation machine.

Next, using an evaluation machine, a stripe image formed by a plurality of parallel fine lines was formed on the recording medium. In forming the stripe image, the line width of the fine lines was set to 1 pixel, and the interval between adjacent fine lines (interline pitch) was set to 3 pixels. Next, the stripe image formed on the evaluation paper was read with a microscope. Specifically, the distance A between a specific fine line a and a fine line b located 16 pixels away from the fine line a was measured at 204 points. In addition, there were three separate thin lines between the thin line a and the thin line b. Variation (3σ) of the measured distance A was calculated using image processing software (manufactured by Kyocera Document Solutions Co., Ltd.). The calculated variation (3σ) of the interval A was used as the ejection stability evaluation value. Ejection stability was determined according to the following criteria.

A (good): 3σ is less than 15 B (bad): 3σ is 15 or more

[curl]
In the curl evaluation, A4 size plain paper (“C ² ” manufactured by FUJIFILM Business Innovation Co., Ltd.) was used as evaluation paper. Using the evaluation machine, a solid image of 10 cm×10 cm was formed in the center of one side of the evaluation paper. Immediately after the formation of the solid image, the evaluation paper was placed on a horizontal table. At this time, the evaluation paper was left still so that the surface on which the solid image was formed faced downward. After 10 seconds had passed since the formation of the solid image, the distance between the evaluation paper and the table (the distance the four corners of the evaluation paper were lifted by the evaluation paper being warped) was measured at the four corners of the evaluation paper. The average value of the above distances measured at the four corners was used as the primary curl evaluation value.

Next, 30 seconds after the formation of the solid image, the distance between the evaluation paper and the table (the distance that the four corners of the evaluation paper were lifted due to the warpage of the evaluation paper) was measured at the four corners of the evaluation paper. The average value of the above distances measured at the four corners was used as the secondary curl evaluation value. Whether or not the object to be evaluated can suppress the occurrence of curling was evaluated according to the following criteria.

(Curl standard)
A (good): primary curl evaluation value of 20 mm or less and secondary curl evaluation value of 7 mm or less B (bad): primary curl evaluation value of more than 20 mm or secondary curl evaluation value of more than 7 mm

[Dispersion stability]
In the evaluation of the dispersion stability, A4 size inkjet matte paper ("Super Fine Paper" manufactured by Seiko Epson Corporation) was used as evaluation paper. Next, cleaning processing was performed on the recording head of the evaluation machine. Next, an evaluation machine was used to form a nozzle check pattern image on the evaluation paper. As a result, regardless of which evaluation target was used, the evaluation target was ejected from all nozzles (the number of non-ejection nozzles was 0). The evaluator was then allowed to sit for 1 minute. Next, in the line head of the evaluation machine, a pressure strong enough to prevent the evaluation target (ink) from being ejected was intermittently applied to the evaluation target, and the meniscus on the evaluation target surface was oscillated 800 times at a vibration period of 18 kHz. (Oscillation processing). Next, the evaluation machine was used to form a 1-dot line image (an image including a fine line with a line width of 1 pixel) on the evaluation paper using all the nozzles of the line head. Next, a one-dot line image was observed, and the number of nozzles with missing dots was calculated. The calculated number of nozzles that caused missing dots was used as an evaluation value for dispersion stability. Missing dots occur when the dispersion stability of the evaluation target is low, the aqueous medium and the pigment in the evaluation target are separated by the above-described oscillating process, and only the aqueous medium is ejected. The dispersion stability of the evaluation target was evaluated according to the following criteria.

(Criteria for dispersion stability)
A (Good): Evaluation value is 0 B (Bad): Evaluation value is 1 or more

[Image Density]
In the evaluation of image density, A4 size PPC paper (“C ² ” manufactured by FUJIFILM Business Innovation Co., Ltd.) was used as evaluation paper. Using the evaluation machine, a solid image of 150 mm×200 mm (100% coverage) was formed on each of five evaluation sheets. In forming a solid image, the volume of one droplet of ink ejected from the recording head by the evaluation machine was set to 11 pL. Next, the five sheets of evaluation paper on which solid images were formed were allowed to stand for 24 hours. Next, the reflection density (ID: image density) of the solid image was measured using a portable reflection densitometer ("RD-19" manufactured by X-Rite). Specifically, for each of the five sheets of evaluation paper, the reflection density was measured at ten locations randomly selected from within the solid image. Then, the average value of the reflection density measurement values (50 in total) obtained from the five sheets of evaluation paper was used as the evaluation value (ID) of the image density. Image density was evaluated according to the following criteria.

(Standard of image density)
A (good): ID is 1.15 or more B (bad): ID is less than 1.15

As shown in Tables 5 to 12, inks (I-1) to (I-10) of Examples 1 to 10 contained a pigment, a first dispersant, a second dispersant, and an aqueous medium. rice field. The aqueous medium included water, a first organic solvent, a second organic solvent and a third organic solvent. The content ratio of the first organic solvent, the content ratio of the second organic solvent, and the content ratio of the third organic solvent were each 5.0% by mass or more and 15.0% by mass or less. In the dispersion term (dD), the polarization term (dP) and the hydrogen bonding term (dH) of the Hansen solubility parameter, the first dispersant has a dD of 15.0 or more and 18.5 or less and a dP of 10.0 or more and 15.0 Below, dH was 18.0 or more and 30.0 or less. The second dispersant had a dD of 16.0 or more and 20.0 or less, a dP of 5.0 or more and 9.0 or less, and a dH of 12.0 or more and 23.0 or less. The first organic solvent had a dD of 15.0 to 18.0, a dP of 10.0 to 14.0, and a dH of 23.0 to 30.0. The second organic solvent had a dD of 15.0 to 17.5, a dP of 5.0 to 7.5, and a dH of 8.0 to 16.0. The third organic solvent had a dD of 15.0 to 18.0, a dP of 7.5 to 10.5, and a dH of 17.0 to 23.0. The first dispersant and the first organic solvent have an absolute value of dD difference (ΔdD) of 2.5 or less, an absolute value of dP difference (ΔdP) of 3.5 or less, and an absolute value of dH difference (ΔdH). was 14.0 or less. The acid value of the second dispersant was 25 mgKOH/g or more and 120 mgKOH/g or less. The content of the second dispersant was 0.7% by mass or more and 5.0% by mass or less. The inks (I-1) to (I-10) have excellent ejection stability, storage stability, and dispersion stability, and can form an image having a desired image density by having the above-described constitution, and can prevent nozzle clogging. And the occurrence of curling could be suppressed. Inks (I-1) to (I-10) also had low volatility.

On the other hand, in the ink (I-11) of Comparative Example 1, the content of the first organic solvent is less than 5.0% by mass, the acid value of the second dispersant is less than 25 mgKOH/g, and the second dispersant The HSP of the agent did not meet the requirements described in the embodiment. The ink (I-11) of Comparative Example 1 was insufficient in the image density of the formed image and could not suppress the occurrence of nozzle clogging.

Ink (I-12) of Comparative Example 2 has a first organic solvent content of more than 15.0% by mass, a second organic solvent content of less than 5.0% by mass, and a third organic solvent and the acid value of the second dispersant was greater than 120 mgKOH/g. The ink (I-12) of Comparative Example 2 was insufficient in dispersion stability, the image density of the formed image was insufficient, and curling could not be suppressed.

Ink (I-13) of Comparative Example 3 contained less than 0.7% by mass of the second dispersant and contained no first organic solvent. The ink (I-13) of Comparative Example 3 was insufficient in ejection stability and storage stability, the image density of the formed image was insufficient, and the occurrence of nozzle clogging could not be suppressed.

Ink (I-14) of Comparative Example 4 contained more than 15.0% by mass of the first organic solvent, did not contain the second organic solvent and the third organic solvent, and had an acid value of the second dispersant of was less than 25 mg KOH/g, and the HSP of the second dispersant did not meet the requirements described in the embodiments. The ink (I-14) of Comparative Example 4 was insufficient in dispersion stability, the image density of the formed image was insufficient, and curling could not be suppressed.

Ink (I-15) of Comparative Example 5 did not contain a second dispersant and a first organic solvent. The ink (I-15) of Comparative Example 5 was insufficient in ejection stability, storage stability and dispersion stability, the image density of the formed image was insufficient, and nozzle clogging and curling occurred. I couldn't control it.

Ink (I-16) of Comparative Example 6 did not contain the first dispersant, the acid value of the second dispersant was more than 120 mgKOH/g, and the content of the second organic solvent was 5.0% by mass. was less than The ink (I-16) of Comparative Example 6 was insufficient in ejection stability, storage stability and dispersion stability, and the image density of the formed image was insufficient.

Ink (I-17) of Comparative Example 7 contained less than 5.0% by mass of the second dispersant and had a large difference in HSP between the first dispersant and the first organic solvent. The ink (I-17) of Comparative Example 7 was insufficient in ejection stability, storage stability and dispersion stability.

Ink (I-18) of Comparative Example 8 does not contain a third organic solvent, the acid value of the second dispersant is less than 25 mgKOH/g, and the HSP of the second dispersant satisfies the requirements described in the embodiment. did not meet The ink (I-18) of Comparative Example 8 was insufficient in the image density of the formed image and could not suppress curling.

Ink (I-19) of Comparative Example 9 did not contain a third organic solvent, and the HSP of the second dispersant did not satisfy the requirements described in the embodiment. The ink (I-19) of Comparative Example 9 was insufficient in the image density of the formed image and could not suppress curling.

The ink (I-20) of Comparative Example 10 has a first organic solvent content of less than 5.0% by mass, does not contain a third organic solvent, and contains HSP as a second dispersant as described in the embodiment. The requirements were not met, and the HSP difference between the first dispersant and the first organic solvent was large. The ink (I-20) of Comparative Example 10 was insufficient in ejection stability, storage stability and dispersion stability, the image density of the formed image was insufficient, and nozzle clogging and curling occurred. I couldn't control it.

The inks of the invention can be used to form images.

Claims (3)

containing a pigment, a first dispersant, a second dispersant, and an aqueous medium;
The aqueous medium includes water, a first organic solvent, a second organic solvent and a third organic solvent,
The content ratio of the first organic solvent, the content ratio of the second organic solvent, and the content ratio of the third organic solvent are each 5.0% by mass or more and 15.0% by mass or less,
In the dispersion term (dD), the polarization term (dP) and the hydrogen bonding term (dH) of the Hansen solubility parameter,
The first dispersant has a dD of 15.0 or more and 18.5 or less, a dP of 10.0 or more and 15.0 or less, and a dH of 18.0 or more and 30.0 or less,
The second dispersant has a dD of 16.0 or more and 20.0 or less, a dP of 5.0 or more and 9.0 or less, and a dH of 12.0 or more and 23.0 or less,
The first organic solvent has a dD of 15.0 or more and 18.0 or less, a dP of 10.0 or more and 14.0 or less, and a dH of 23.0 or more and 30.0 or less,
The second organic solvent has a dD of 15.0 or more and 17.5 or less, a dP of 5.0 or more and 7.5 or less, and a dH of 8.0 or more and 16.0 or less,
The third organic solvent has a dD of 15.0 or more and 18.0 or less, a dP of 7.5 or more and 10.5 or less, and a dH of 17.0 or more and 23.0 or less,
The first dispersant and the first organic solvent have an absolute value of dD difference (ΔdD) of 2.5 or less, an absolute value of dP difference (ΔdP) of 3.5 or less, and an absolute value of dH difference ( ΔdH) is 14.0 or less,
The acid value of the second dispersant is 25 mgKOH/g or more and 120 mgKOH/g or less,
The inkjet ink, wherein the content of the second dispersant is 0.7% by mass or more and 5.0% by mass or less. 2. The inkjet ink of claim 1, wherein the first dispersant and the second dispersant each comprise a styrene-(meth)acrylic resin. the first organic solvent comprises glycerin, sorbitol, 1,3-propanediol, 1,2,3-butanetriol, or ethylene glycol;
The second organic solvent contains triethylene glycol monobutyl ether, 1,2-octanediol, 2-ethyl-1,2-hexanediol, or ethylene glycol monobutyl ether,
The third organic solvent is 3-methyl-1,5-pentanediol, 1,5-pentanediol, propylene glycol, 2-methyl-1,3-propanediol, or 1-methyl-1,3-propanediol. The inkjet ink according to claim 1 or 2, comprising: