Pigment dispersant, water-based ink, ink cartridge, and inkjet recording method

Abstract

To provide a pigment dispersant or the like capable of stably dispersing a pigment.SOLUTION: The present invention provides a pigment dispersant represented by the general formula (1). (In the general formula (1), Q independently denotes a quinacridone skeleton. L independently denotes a divalent group that connects Q and E. m is an integer of 2 to 4. E is a residue of a polyhydric alcohol forming an ether bond with L).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pigment dispersant, an aqueous ink, an ink cartridge, and an inkjet recording method. [Background technology]

[0002] In recent years, inkjet recording methods using pigment inks have been increasingly used to record images such as business documents clearly onto recording media such as plain paper, and their frequency of use has increased dramatically. For such applications, a higher level of pigment dispersion stability is required than ever before, so that images can be recorded stably even when the inkjet recording device is used for a long period of time. Various technologies to improve inkjet suitability have been investigated so far. For example, non-aqueous inks containing a specific heterocyclic compound as a pigment dispersant have been proposed (see Patent Document 1). Also, aqueous inks containing surface-modified pigments in which a specific functional group has been introduced to the surface of the pigment particles have been proposed (see Patent Document 2). Furthermore, aqueous inks containing a dispersant in which a specific chromophore is suspended from its main chain have been proposed (see Patent Document 3). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2007-023073 [Patent Document 2] Japanese Patent Publication No. 2020-037644 [Patent Document 3] Special Publication No. 2009-501253 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The present inventors investigated the dispersion stability of pigments in aqueous inks using heterocyclic compounds proposed in Patent Document 1, surface-modified pigments proposed in Patent Document 2, and dispersants proposed in Patent Document 3. As a result, it was found that conventional techniques used as pigment dispersion methods can increase the particle size of the pigment, and that improving the dispersion stability of pigments is necessary to meet the high standards required in recent years.

[0005] Therefore, an object of the present invention is to provide a pigment dispersant that can improve the dispersion stability of pigments, an aqueous ink using the pigment dispersant, an ink cartridge using the aqueous ink, and an inkjet recording method. [Means for solving the problem]

[0006] The above objective is achieved by the present invention as described below. That is, the pigment dispersant according to the present invention is characterized by being represented by the following general formula (1).

[0007] [ka]

[0008] (In general formula (1), each Q is independently a structure represented by general formula (2) below. Each L is independently a divalent group linking Q and E. m is an integer from 2 to 4. E is a polyhydric alcohol residue that forms an ether bond with L.)

[0009] [ka]

[0010] (In general formula (2), R1 to R 10 Each of these is independently a hydrogen atom, a halogen atom, or an alkyl group. 11 and R 12 One of them is the bonding site with L, and the other is a hydrogen atom. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a pigment dispersant capable of improving the dispersion stability of a pigment, an aqueous ink using the pigment dispersant, an ink cartridge using the aqueous ink, and an inkjet recording method.

Brief Description of the Drawings

[0012] [Figure 1] It is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. [Figure 2] It is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention. (a) is a perspective view of a main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge.

Modes for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, although the salt dissociates into ions in the ink, for convenience, it is expressed as "containing a salt". In addition, the aqueous ink for inkjet may be simply referred to as "ink". The "unit" of the resin refers to the smallest repeating unit constituting the resin, and means a structure formed by (co)polymerization of one monomer. Physical property values are values at room temperature (25°C) unless otherwise specified.

[0014] The present inventors have variously studied improving the dispersion stability of pigments with a pigment dispersant. As a result, it has been found that by using a pigment dispersant represented by the following general formula (1), an increase in the particle diameter of the pigment can be suppressed and the dispersion stability of the pigment can be improved. The pigment dispersant represented by the general formula (1) is characterized by having a structure in which a plurality of quinacridone skeletons are crosslinked with an alkylene ether.

[0015]

Chemical formula

[0016] (In general formula (1), each Q is independently a structure represented by general formula (2) below. Each L is independently a divalent group linking Q and E. m is an integer from 2 to 4. E is a polyhydric alcohol residue that forms an ether bond with L.)

[0017] [ka]

[0018] (In general formula (2), R1 to R 10 Each of these is independently a hydrogen atom, a halogen atom, or an alkyl group. 11 and R 12 One of them is the bonding site with L, and the other is a hydrogen atom.

[0019] The inventors hypothesize the following mechanism by which the dispersion stability of pigments is improved by using the above-mentioned pigment dispersant. In general formula (1), Q is a quinacridone skeleton. The quinacridone skeleton has a planar structure in which aromatic rings are linked together, and can be adsorbed onto the particle surface of pigments, which are inherently hydrophobic, by the action of at least one of van der Waals forces, π-π interactions, and hydrophobic interactions.

[0020] E is a polyhydric alcohol residue that forms an ether bond with L. In this specification, "polyhydric alcohol residue" refers to structures other than the hydrogen atoms of the hydroxyl group in a linear or branched polyhydric alcohol. Not all hydroxyl groups need to form an ether bond, as long as at least two of the hydroxyl groups of the polyhydric alcohol form an ether bond with L. In other words, the polyhydric alcohol residue may contain unreacted hydroxyl groups that do not form an ether bond with L. The polyhydric alcohol residue contributes to affinity for liquid media. In liquid media such as water or organic solvents, the quinacridone skeleton is adsorbed onto the surface of the pigment particles, and the portion of the polyhydric alcohol residue with high affinity for the liquid media is oriented towards the liquid media. Therefore, the steric hindrance of the portion of the polyhydric alcohol residue can increase the spacing between pigment particles and suppress pigment aggregation.

[0021] L is a linking group between Q and E. In this specification, "linking group" refers to a divalent substructure between the nitrogen atom of the quinacridone skeleton and the oxygen atom of the polyhydric alcohol residue. The pigment dispersant represented by general formula (1) has m = 2 or more, meaning that one molecule contains multiple quinacridone skeletons that act as adsorption sites to the pigment. Therefore, it is difficult for the dispersant to detach after adsorption to the surface of the pigment particles, and the dispersion state of the pigment is stabilized. As a result, it is thought that the aggregation of pigments is suppressed and the increase in particle size is also suppressed, thus improving the dispersion stability of the pigment.

[0022] In the pigment dispersant represented by general formula (1) (hereinafter also simply referred to as pigment dispersant), m, which indicates the number of Q atoms, is between 2 and 4. In other words, the pigment dispersant has 2 to 4 quinacridone skeletons. The 2 to 4 quinacridone skeletons linked by polyhydric alcohol residues are adsorbed at multiple locations on the surface of the pigment particles, forming a loop structure. When m is within the range of 2 to 4, the loop structure formed by the polyhydric alcohol residues maintains an appropriate distance from the surface of the pigment particles, making it difficult for multiple pigment particles to approach each other and suppressing pigment aggregation. When m is 5 or more, part of the loop structure formed by the polyhydric alcohol residues approaches the surface of the pigment particles, making it impossible to suppress pigment aggregation. Also, when m is 1, a loop structure formed by the polyhydric alcohol residues cannot be formed, so the above effect cannot be obtained. Note that because E is a polyhydric alcohol residue, the molecular size of the pigment dispersant is sufficiently small compared to the pigment. Therefore, it is difficult for the multiple quinacridone skeletons of the pigment dispersant to adsorb onto the surfaces of multiple pigment particles and create a state where the pigment particles are linked together.

[0023] <Pigment dispersant> The pigment dispersant of the present invention is a pigment dispersant represented by general formula (1). The pigment dispersant and the pigment dispersed thereby can be suitably used for coloring applications in inks, paints, plastics, rubber, paper, textiles, and the like. The pigment dispersant of the present invention will be described in detail below.

[0024] [ka]

[0025] (In general formula (1), each Q is independently a structure represented by general formula (2) below. Each L is independently a divalent group linking Q and E. m is an integer from 2 to 4. E is a polyhydric alcohol residue that forms an ether bond with L.)

[0026] [ka]

[0027] (In general formula (2), each of R1 to R 10 is independently a hydrogen atom, a halogen atom, or an alkyl group. One of R 11 and R 12 is the bonding site with L, and the other is a hydrogen atom.)

[0028] Q in general formula (1) is a monovalent quinacridone, and one of R 11 or R<00​​​​​​​​​​​​​​​​​​(In structural formula (6), * and ** represent the bonding sites between Q and L, and L and E, respectively.)

[0032] E is a polyhydric alcohol residue that forms an ether bond with L, and is derived from an aliphatic polyol or a polyol having a structure obtained by dehydration condensation of an aliphatic polyol. E may be branched or linear. Not all hydroxyl groups need to form an ether bond, as long as at least two of the hydroxyl groups of the polyhydric alcohol form an ether bond with L. Examples of aliphatic polyols and polyols having a structure obtained by dehydration condensation of an aliphatic polyol include ethylene glycol, propylene glycol, glycerol, and sorbitol. Ethylene glycol, propylene glycol, and glycerol may be polymerized. m is an integer from 2 to 4, that is, the valence of E is between 2 and 4. From the viewpoint of balancing hydrophilicity and hydrophobicity, it is preferable that the valence of E is between 2 and 3, that is, that E has a structure represented by general formula (3) or general formula (4). In general formula (3), n is an integer of 1 or more, and is preferably 25 or less. If the valency of E is 5 or higher, that is, if the pigment dispersant has 5 or more quinacridone skeletons, the quinacridone skeletons within the pigment dispersant tend to associate with each other intramolecularly. As a result, there are insufficient adsorption sites with the pigment, and the dispersion stability of the pigment cannot be obtained.

[0033] [ka]

[0034] (In general formula (3), * represents the bonding site with L. 13 Each of these is independently either a hydrogen atom or a methyl group. n is an integer greater than or equal to 1.

[0035] [ka]

[0036] (In general formula (4), * represents the binding site with L.)

[0037] Furthermore, because the steric hindrance effect is greater, E is preferably a structure represented by general formula (5). Also, q is an integer of 2 or more, and preferably 25 or less. That is, the number of ethylene oxide groups, which are repeating units, is preferably an integer of 2 or more and 25 or less. If the number of ethylene oxide groups in E is within the above range, the dispersion stability of the pigment can be further improved.

[0038] [ka]

[0039] (In general formula (5), * represents the connection site with L. q is an integer greater than or equal to 2.)

[0040] (Specific examples of pigment dispersants) Tables 1 and 2 show specific examples of pigment dispersants (including pigment dispersants represented by general formula (1)). Of course, in the present invention, compounds represented by general formula (1) are not limited to the compounds shown in Tables 1 and 2, as long as they are included in the structure and definition of general formula (1). Compounds 13 and 14 are comparative compounds that do not satisfy general formula (1). In Tables 1 and 2, * and ** represent the binding sites between Q and L, and between L and E, respectively.

[0041] [Table 1]

[0042] [Table 2]

[0043] (Synthesis of pigment dispersants) The pigment dispersant represented by general formula (1) can be synthesized by known synthesis methods. Specifically, one synthesis route involves bonding L to either Q or E, and then bonding the other. It is preferable to use a pigment having a quinacridone skeleton as Q. Examples of pigments having a quinacridone skeleton include CI Pigment Violet 19 (unsubstituted quinacridone), CI Pigment Red 122 (2,9-dimethylquinacridone), and CI Pigment Red 202 (2,9-dichloroquinacridone). In particular, it is preferable to react a glycidyl ether, which is an epoxy compound, with the pigment having a quinacridone skeleton.

[0044] <Water-based ink> The pigment dispersant of the present invention described above, and the pigment dispersed thereby, can be suitably used for various coloring applications. In particular, it can be suitably applied to water-based inkjet inks containing an aqueous medium as the liquid medium. The ink of the present invention is a water-based inkjet ink containing a pigment and the pigment dispersant of the present invention described above. Furthermore, the ink of the present invention does not need to be a so-called "curable ink." Therefore, the ink of the present invention does not need to contain polymerizable monomers or other compounds that can be polymerized by the addition of external energy such as heat or light. The components constituting the ink of the present invention and the physical properties of the ink will be described in detail below.

[0045] (Pigment dispersant) The ink contains a pigment dispersant represented by the general formula (1) described above as a pigment dispersant for dispersing the pigment. The content (mass%) of the pigment dispersant represented by the general formula (1) in the ink is preferably 0.01% by mass or more and 15.0% by mass or less, and more preferably 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0046] (Pigment) The ink contains pigment as a coloring agent. The pigment content (by mass) in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, based on the total mass of the ink, and more preferably 1.0% by mass or more and 10.0% by mass or less.

[0047] Specific examples of pigments include inorganic pigments such as carbon black and titanium dioxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolon, diketopyrrolopyrrole, and dioxazine. Among these, pigments having a quinacridone skeleton or a diketopyrrolopyrrole skeleton are preferred because they have a hue similar to that of the quinacridone skeleton of the pigment dispersant. Pigments with these skeletons have many functional groups in their structure that readily form hydrogen bonds, such as carbonyl groups and imino groups, and form hydrogen bonds with the carbonyl groups and imino groups of the pigment dispersant. As a result, the pigment dispersant is strongly adsorbed to the pigment, further improving the dispersion stability of the pigment. In addition, as mentioned above, polyhydric alcohol residues form a loop structure. Because the pigment dispersant is strongly adsorbed to the above pigments, it is difficult to detach, and the loop structure formed by the polyhydric alcohol residues can be maintained more stably. As a result, it is possible to maintain a state in which interactions between pigment dispersants present on different particle surfaces are less likely to occur, further improving the storage stability of the ink.

[0048] Examples of quinacridone pigments include CI Pigment Violet 19 (unsubstituted quinacridone), CI Pigment Red 122 (2,9-dimethylquinacridone), and CI Pigment Red 202 (2,9-dichloroquinacridone). As quinacridone pigments, quinacridone solid solution pigments formed from two or more quinacridone pigments can also be used. Among these, solid solution pigments of CI Pigment Red 202 and CI Pigment Violet 19, and solid solution pigments of CI Pigment Red 122 and CI Pigment Violet 19 are preferred. Examples of diketopyrrolopyrrole pigments include CI Pigment Orange: 71, 73, etc., and CI Pigment Red: 254, 255, 264, etc. It is particularly preferable to use pigments having a quinacridone skeleton that has a structure common to the quinacridone skeleton of the pigment dispersant. In this case, the pigment dispersant functions as a so-called synergist. A synergist (pigment derivative) is a compound that has the same molecular structure as the pigment, but differs in its substituents and other properties. Because synergists have a similar chemical structure to the pigment molecules, they have an affinity for the pigment and strongly adsorb to the surface of the pigment particles. Furthermore, the presence of a polyhydric alcohol portion, which has an affinity for the liquid medium, effectively suppresses aggregation with other pigment particles. As a result, the dispersion stability of the pigment and the storage stability of the ink can be further improved.

[0049] The content (mass%) of the pigment dispersant represented by general formula (1) in the ink is preferably 0.01 times or more and 0.50 times or less in mass ratio to the pigment content (mass%). If the mass ratio is less than 0.01 times, the dispersion stability of the pigment and the storage stability of the ink may not be sufficiently obtained. If the mass ratio is greater than 0.50 times, the interaction between pigment dispersants bound to the pigment may not be sufficiently suppressed, and the storage stability of the ink may not be sufficiently obtained.

[0050] As for pigment dispersion methods, resin-dispersed pigments using a resin (resin dispersant) as a dispersant, and self-dispersing pigments in which hydrophilic groups are bonded to the surface of the pigment particles can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the surface of the pigment particles, and microcapsule pigments in which the surface of the pigment particles is coated with a resin or the like can be used.

[0051] Among these, resin-dispersed pigments, in which the pigment is dispersed by a resin dispersant, are preferred, and it is even more preferable to use a resin dispersant having an anionic group. By using a resin dispersant in addition to a pigment dispersant, the dispersion stability of the pigment can be further improved. As described above, the pigment dispersant represented by general formula (1) functions as a so-called synergist. Compared to resin dispersants, synergists have a smaller molecular weight and have a chemical structure similar to the pigment to be dispersed, and therefore have particularly high adsorption to pigments. For this reason, by adsorbing onto the surface of pigment particles, the dispersion stability of the pigment can be improved by the structure (E in general formula (1)) that improves the dispersibility of the synergist. On the other hand, resin dispersants have a larger molecular weight, and by coating the surface of the pigment particles with resin, the aggregation of the pigment can be suppressed by electrostatic repulsion and steric repulsion caused by the resin. In this way, by using two components with different mechanisms of pigment dispersion stability in combination, the dispersion stability of the pigment can be further improved.

[0052] (resin) The ink may contain resin. Preferably, the resin content (by mass) in the ink is 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink.

[0053] Resins can be incorporated into inks for purposes such as (i) stabilizing the dispersion state of pigments, i.e., as a resin dispersant or auxiliary for pigments, and (ii) improving various properties of the recorded image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can dissolve in an aqueous medium, or it may be resin particles dispersed in an aqueous medium. The resin particles do not need to contain colorants.

[0054] In this specification, "water-soluble resin" means that when the resin is neutralized with an alkali equivalent to its acid value, it exists in an aqueous medium without forming particles whose particle size can be measured by dynamic light scattering. Whether or not a resin is water-soluble can be determined according to the following method. First, prepare a liquid containing the resin (resin solids content: 10% by mass) neutralized with an alkali equivalent to its acid value (sodium hydroxide, potassium hydroxide, etc.). Next, prepare a sample solution by diluting the prepared liquid 10 times (by volume) with pure water. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if no particles with a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions in this case can be, for example, SetZero: 30 seconds, Number of measurements: 3, Measurement time: 180 seconds. As a particle size distribution analyzer, a particle size analyzer using dynamic light scattering (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution analyzer and measurement conditions used are not limited to those described above.

[0055] The acid value of the resin is preferably 80 mg KOH / g or more and 250 mg KOH / g or less, and more preferably 100 mg KOH / g or more and 200 mg KOH / g or less. The weight-average molecular weight of the resin is preferably 1,000 or more and 30,000 or less, and more preferably 5,000 or more and 15,000 or less. The weight-average molecular weight of the resin is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0056] Examples of resins include acrylic resins, urethane resins, and urea resins. Among these, acrylic resins are preferred. Among acrylic resins, acrylic resins having hydrophilic units and hydrophobic units as constituent units are even more preferred. In particular, acrylic resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from monomers having aliphatic or aromatic groups are preferred. Furthermore, it is preferable to use an acrylic resin having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one monomer of styrene and α-methylstyrene as a resin dispersant. These resin dispersants can be suitably used because they readily interact with pigments.

[0057] A hydrophilic unit is a unit having a hydrophilic group, such as an anionic group. A hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Examples of hydrophilic monomers include acidic monomers having a carboxylic acid group, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. In particular, from the viewpoint of hydrophilicity, it is preferable to use a monomer that imparts anionic groups to the resin, i.e., a hydrophilic monomer having a carboxylic acid group and its salt or anhydride. Examples of cations constituting the salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium, and organic ammonium.

[0058] A hydrophobic unit is a unit that does not have hydrophilic groups such as anionic groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups such as anionic groups. Examples of hydrophobic monomers include monomers having aromatic rings such as styrene, α-methylstyrene, and benzyl (meth)acrylate. Other examples include (meth)acrylic acid ester monomers such as ethyl (meth)acrylate, methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0059] (aqueous medium) The ink is preferably an aqueous ink containing water as an aqueous medium. The ink may contain an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water (ion-exchanged water) is preferably used as the water. The water content (mass%) in the ink is preferably 50.0% by mass or more and 95.0% by mass or less, based on the total mass of the ink.

[0060] There are no particular restrictions on the water-soluble organic solvent, as long as it is water-soluble (preferably, soluble in water at 25°C in any proportion). Specifically, monohydric or polyhydric alcohols, alkylene glycols, glycol ethers, nitrogen-containing polar compounds, sulfur-containing polar compounds, etc., can be used. In particular, the ink does not need to contain 2-pyrrolidone, and it is preferable that it does not contain 2-pyrrolidone. The content (mass%) of the water-soluble organic solvent in the ink is preferably 5.0% by mass or more and 90.0% by mass or less, and more preferably 10.0% by mass or more and 50.0% by mass or less, based on the total mass of the ink.

[0061] (Other additives) Ink may contain various additives as needed, such as surfactants, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, reduction inhibitors, evaporation accelerators, and chelating agents. Among these, it is preferable that the ink contains a surfactant. The surfactant content (mass%) in the ink is preferably 0.1% to 5.0% by mass, and more preferably 0.1% to 2.0% by mass, based on the total mass of the ink. Examples of surfactants include anionic surfactants, cationic surfactants, and nonionic surfactants.

[0062] (Ink properties) Since the ink is for use in an inkjet system, it is preferable to appropriately control its physical properties. The surface tension of the ink at 25°C is preferably 10 mN / m to 60 mN / m, and more preferably 20 mN / m to 40 mN / m. The viscosity of the ink at 25°C is preferably 1.0 mPa·s to 10.0 mPa·s. The pH of the ink at 25°C is preferably 5.0 to 10.0, and more preferably 6.0 to 8.5.

[0063] <Ink Cartridge> The ink cartridge of the present invention comprises ink and an ink storage section for storing this ink. The ink stored in this ink storage section is the aqueous ink of the present invention as described above. Figure 1 is a schematic cross-sectional view showing one embodiment of the ink cartridge of the present invention. As shown in Figure 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section consists of an ink storage chamber 14 and an absorbent storage chamber 16, which are in communication with each other via a communication port 18. The absorbent storage chamber 16 is also in communication with the ink supply port 12. Liquid ink 20 is stored in the ink storage chamber 14, and absorbent materials 22 and 24 that hold the ink in an impregnated state are stored in the absorbent storage chamber 16. The ink storage section may not have an ink storage chamber for storing liquid ink, and the entire amount of ink to be stored may be held by an absorbent. Alternatively, the ink storage section may not have an absorbent, and the entire amount of ink may be stored in a liquid state. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head.

[0064] <Inkjet recording method> The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting the aqueous ink of the present invention described above from an inkjet recording head. Methods for ejecting the ink include methods that impart mechanical energy to the ink and methods that impart thermal energy to the ink. In the present invention, it is particularly preferable to employ a method that imparts thermal energy to the ink to eject it. Aside from using the ink of the present invention, the steps of the inkjet recording method may be those of known origin.

[0065] Figure 2 is a schematic diagram showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, where (a) is a perspective view of the main part of the inkjet recording apparatus and (b) is a perspective view of the head cartridge. The inkjet recording apparatus is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 comprises recording heads 38 and 40 and is configured to hold an ink cartridge 42. While the head cartridge 36 is transported along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is transported in the sub-scanning direction by the transport means (not shown), and an image is recorded on the recording medium 32. [Examples]

[0066] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are by mass. In this specification, "EO" represents an ethylene oxide group.

[0067] <Synthesis of Pigment Dispersants> In a flask equipped with a stirrer, nitrogen inlet tube, reflux condenser, and thermometer, the pigment dispersant raw materials, base (potassium tert-butoxide), and solvent (dimethyl sulfoxide) shown on the left side of Table 3 were added, and the mixture was heated to 80°C and stirred for 1 hour. Then, the types and amounts of epoxy compounds shown in Table 3 were added, and the mixture was heated to 100°C and stirred for 6 hours. After cooling to 25°C, acetic acid was added dropwise until the deep blue reaction solution turned reddish-brown. Next, 100 parts of deionized water and 50 parts of chloroform were added to the reaction solution to extract the product. The chloroform phase was dried over anhydrous magnesium sulfate, then filtered and concentrated to obtain a chloroform solution of the product, which was then purified by gel permeation chromatography (GPC). The isolated compound was measured by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF MS) to confirm its identity as the target product. The structures of the obtained pigment dispersants correspond to the specific examples of pigment dispersants shown in Tables 1 and 2. Details of each component in Table 3 are shown below. n represents the number of repeating units, which are ethylene oxide groups or propylene oxide groups. Pigment dispersants 13 and 14 are comparative compounds, as shown in Table 2.

[0068] • Quinacridone derivative 1: A compound represented by the following structural formula (7), synthesized according to the synthesis method of SYN-1 in International Publication No. 2013 / 087376.

[0069] [ka]

[0070] • Quinacridone derivative 2: A compound represented by the following structural formula (8), synthesized according to the method for synthesizing 2,9-dimethoxyquinacridone described in International Publication No. 2002 / 099432.

[0071] [ka]

[0072] • EX-810: Ethylene glycol diglycidyl ether (product name "Denacol EX-810", manufactured by Nagase ChemteX) • EX-850: Polyethylene glycol (n=2) diglycidyl ether (product name "Denacol EX-850", manufactured by Nagase ChemteX) • EX-821: Polyethylene glycol (n=4) diglycidyl ether (product name "Denacol EX-821", manufactured by Nagase ChemteX) • EX-830: Polyethylene glycol (n=9) diglycidyl ether (product name "Denacol EX-830", manufactured by Nagase ChemteX) • EX-841: Polyethylene glycol (n=13) diglycidyl ether (product name "Denacol EX-841", manufactured by Nagase ChemteX) • EX-861: Polyethylene glycol (n=22) diglycidyl ether (product name "Denacol EX-861", manufactured by Nagase ChemteX) • EX-920: Polypropylene glycol (n=3) diglycidyl ether (product name "Denacol EX-920", manufactured by Nagase ChemteX) • EX-313: Glycerol polyglycidyl ether (product name "Denacol EX-313", manufactured by Nagase ChemteX) • EX-614: Sorbitol polyglycidyl ether (product name "Denacol EX-614", manufactured by Nagase ChemteX) • EX-521: Polyglycerol (n=3) polyglycidyl ether (product name "Denacol EX-521", manufactured by Nagase ChemteX)

[0073] [Table 3]

[0074] <Synthesis of resins> 200.0 parts of solvent (isopropanol) were placed in a flask equipped with a stirrer, nitrogen inlet tube, reflux condenser, and thermometer, and the temperature was raised to 83°C while stirring under a nitrogen atmosphere. Mixtures of monomers of the types and amounts shown in Table 4, and a solution of 2.0 parts polymerization initiator dissolved in 20.0 parts of isopropanol, were added dropwise to the flask over 2 hours while maintaining the system temperature at 83°C. 2,2'-azobis(2-methylbutyronitrile) was used as the polymerization initiator. After stirring for 4 hours while maintaining the system temperature at 83°C, 0.9 equivalents of potassium hydroxide relative to the acid value and an appropriate amount of deionized water were added. The solvent was removed by reducing the pressure to obtain a liquid containing each resin with a resin content of 20.0%. Details of each component in Table 4 are shown below. St: Styrene nBA: n-butyl acrylate MEA: 2-methoxyethyl acrylate AA: Acrylic acid • MAA: Methacrylic acid

[0075] [Table 4]

[0076] <Preparation of Pigment Dispersion> (Pigment dispersions 1-35) 20.0 parts of the pigments of the types shown in Table 5 were mixed with the pigment dispersants, resin dispersants (liquid containing resin, resin content: 20.0%), and deionized water of the types and amounts shown in Table 5. The resulting mixture was placed in a batch-type vertical sand mill (manufactured by AIMEX), filled with 150.0 parts of 0.3 mm diameter zirconia beads, and dispersed for 5 hours while cooling with water. After removing coarse particles by centrifugation, an appropriate amount of deionized water was added as needed to obtain each pigment dispersion. Details of each component in Table 5 are shown below. • Solid solution pigment 1: Solid solution pigment of CI Pigment Red 122 and CI Pigment Violet 19 • Solid solution pigment 2: Solid solution pigment of CI Pigment Red 202 and CI Pigment Violet 19

[0077] • Ratio 1: Compound represented by the following structural formula (9) synthesized according to the synthesis method of compound H-10 in Patent Document 1.

[0078] [ka]

[0079] • Ratio 2: Compound represented by the following structural formula (10) synthesized according to the synthesis method of compound H-21 in Patent Document 1.

[0080] [ka]

[0081] [Table 5]

[0082] (Pigment dispersion 36) A pigment dispersion 36 was obtained in accordance with the preparation example of pigment dispersion 40 in Patent Document 2. Specifically, 20.0 parts of CI pigment red 122, 10.0 parts of a liquid containing resin 1, and 70.0 parts of deionized water were mixed and dispersed. The pigment was then treated with 7.0 parts of phenol (EO) 5 diglycidyl ether (trade name "Denacol EX-145", manufactured by Nagase ChemteX) to obtain a pigment dispersion 36 with a pigment content of 20.0%.

[0083] (Pigment dispersion 37) Pigment dispersion 37 was prepared in the same manner as pigment dispersion 1, except that a compound synthesized according to the synthesis method of polymer dispersant DISP-11 described in Patent Document 3 was used instead of pigment dispersant 5. The compound obtained by synthesis was a compound in which a pigment having a quinacridone skeleton was bonded to the main chain of polyacrylic acid via a linking group containing an ester bond. In other words, a part of the acrylic acid unit had a structure represented by the following structural formula (11). The pigment content was 20.0%, and the pigment dispersant content was 2.0%.

[0084] [ka]

[0085] <Ink preparation> Each of the components shown on the left side of Table 6 was mixed and thoroughly stirred, then pressure filtered through a 2.5 μm pore size microfilter (manufactured by Fujifilm) to prepare each ink. Acetylenel E100 (trade name) is a nonionic surfactant manufactured by Kawaken Fine Chemicals.

[0086] <Rating> Each ink obtained above was evaluated for the following items. In this invention, "AA," "A," and "B" were considered acceptable levels in the evaluation criteria shown below, and "C" was considered an unacceptable level. The evaluation results are shown on the right side of Table 6.

[0087] (dispersion stability) The particle size of the pigment in the prepared inks was measured (referred to as "particle size before storage"). Each ink was placed in a sealed container and stored at 80°C for 4 days. After the inks were returned to 25°C, the particle size of the pigment was measured again (referred to as "particle size after storage"). The particle size of the pigment was measured using a dynamic light scattering particle size analyzer (product name "UPA-EX150", manufactured by Nikkiso), and is the volume-based cumulative 50% particle size (D50). The "percentage change in particle size after storage" (%) was then calculated based on the formula 100 × ("particle size after storage" - "particle size before storage") / ("particle size before storage") to evaluate the dispersion stability of the pigment. The results are shown on the right side of Table 6. AA: The percentage change in particle size after storage was 3% or less. A: The percentage change in particle size after storage was greater than 3% and less than or equal to 5%. B: The percentage change in particle size after storage was greater than 5% and less than or equal to 15%. C: The percentage change in particle size after storage exceeded 15%.

[0088] (Storage stability) The viscosity of the prepared inks was measured (referred to as "viscosity before storage"). Each ink was placed in a sealed container and stored at 80°C. After the inks were allowed to return to 25°C, their viscosity was measured again (referred to as "viscosity after storage"). The viscosity of the inks was measured using an E-type viscometer (product name "RE-80L", manufactured by Toki Sangyo). The storage period at which the change in ink viscosity (mPa·s), calculated based on the formula "viscosity after storage" - "viscosity before storage", reached 0.1 mPa·s was measured. In other words, the period until the viscosity increased by 0.1 mPa·s compared to before storage was investigated. The storage period (in days) of the ink of Comparative Example 1, which contained pigment dispersed only with resin dispersant 1 and without using the pigment dispersant represented by general formula (1), was set as the "standard storage period," and the storage stability of the inks was evaluated according to the evaluation criteria shown below. AA: The storage period was more than 2.0 times the standard storage period. A: The storage period was 1.5 times or more but less than 2.0 times the standard storage period. B: The storage period was 1.1 times or more but less than 1.5 times the standard storage period. C: The storage period was less than 1.1 times the standard storage period.

[0089] [Table 6]

[0090] This embodiment includes the following configurations and methods.

[0091] [Configuration 1] A pigment dispersant represented by the following general formula (1).

[0092] [ka]

[0093] (In general formula (1), each Q is independently a structure represented by general formula (2) below. Each L is independently a divalent group linking Q and E. m is an integer from 2 to 4. E is a polyhydric alcohol residue that forms an ether bond with L.)

[0094] [ka]

[0095] (In general formula (2), R1 to R 10 Each of these is independently a hydrogen atom, a halogen atom, or an alkyl group. 11 and R 12 One of them is the bonding site with L, and the other is a hydrogen atom.

[0096] [Configuration 2] The pigment dispersant according to configuration 1, wherein E has a structure represented by the following general formula (3) or general formula (4).

[0097] [ka]

[0098] (In general formula (3), * represents the bonding site with L. 13 Each of these is independently either a hydrogen atom or a methyl group. n is an integer greater than or equal to 1.

[0099] [ka]

[0100] (In general formula (4), * represents the binding site with L.)

[0101] [Configuration 3] The pigment dispersant according to configuration 1 or 2, wherein E has a structure represented by the following general formula (5).

[0102] [ka]

[0103] (In general formula (5), * represents the connection site with L. q is an integer greater than or equal to 2.)

[0104] [Structure 4] An aqueous inkjet ink comprising a pigment and a pigment dispersant for dispersing the pigment, An aqueous ink characterized in that the pigment dispersant is the pigment dispersant described in any one of the three items of the configuration.

[0105] [Composition 5] The aqueous ink according to configuration 4, wherein the content (mass%) of the pigment dispersant is 0.01 times or more and 0.50 times or less in mass ratio to the content (mass%) of the pigment.

[0106] [Composition 6] The aqueous ink according to composition 4 or 5, wherein the content (by mass) of the pigment dispersant is 0.01% by mass or more and 15.0% by mass or less, based on the total mass of the ink.

[0107] [Composition 7] The aqueous ink according to any one of the constructs 4 to 6, wherein the content (by mass) of the pigment dispersant is 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0108] [Structure 8] The aqueous ink according to any one of claims 4 to 7, wherein the pigment is a pigment having a quinacridone skeleton or a diketopyrrolopyrrole skeleton.

[0109] [Composition 9] The aqueous ink according to any one of claims 4 to 8, wherein the pigment is a pigment having a quinacridone skeleton.

[0110] [Configuration 10] The aqueous ink according to any one of items 4 to 9, wherein the pigment content (by mass) is 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0111] [Composition 11] Furthermore, the aqueous ink according to any one of the configurations 4 to 10, which further contains a resin dispersant for dispersing the pigment.

[0112] [Composition 12] The aqueous ink according to configuration 11, wherein the content (by mass) of the resin dispersant is 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink.

[0113] [Composition 13] An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is an aqueous ink as described in any one of items 4 to 12 of the configuration.

[0114] [Composition 14] An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, An inkjet recording method characterized in that the ink is an aqueous ink according to any one of the items 4 to 12 of the configuration.

Claims

1. A pigment dispersant represented by the following general formula (1). 【Chemistry 1】 (In general formula (1), each Q is independently a structure represented by general formula (2) below. Each L is independently a divalent group linking Q and E. m is an integer from 2 to 4. E is a polyhydric alcohol residue that forms an ether bond with L.) 【Chemistry 2】 (In general formula (2), R １ ~R １０ Each of these is independently a hydrogen atom, a halogen atom, or an alkyl group. １１ and R １２ One of them is the bonding site with L, and the other is a hydrogen atom.

2. The pigment dispersant according to claim 1, wherein E has a structure represented by the following general formula (3) or general formula (4). 【Transformation 3】 (In general formula (3), * represents the bonding site with L. R １３ Each of these is independently either a hydrogen atom or a methyl group. n is an integer greater than or equal to 1. 【Chemistry 4】 (In general formula (4), * represents the bonding site with L.)

3. The pigment dispersant according to claim 1, wherein E has a structure represented by the following general formula (5). 【Transformation 5】 (In general formula (5), * represents the connection site with L. q is an integer greater than or equal to 2.)

4. An aqueous inkjet ink comprising a pigment and a pigment dispersant for dispersing the pigment, An aqueous ink characterized in that the pigment dispersant is the pigment dispersant described in claim 1.

5. The aqueous ink according to claim 4, wherein the content (mass%) of the pigment dispersant is 0.01 times or more and 0.50 times or less in mass ratio to the content (mass%) of the pigment.

6. The aqueous ink according to claim 4, wherein the content (by mass) of the pigment dispersant is 0.01% by mass or more and 15.0% by mass or less, based on the total mass of the ink.

7. The aqueous ink according to claim 4, wherein the content (by mass) of the pigment dispersant is 0.1% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

8. The aqueous ink according to claim 4, wherein the pigment is a pigment having a quinacridone skeleton or a diketopyrrolopyrrole skeleton.

9. The aqueous ink according to claim 4, wherein the pigment is a pigment having a quinacridone skeleton.

10. The aqueous ink according to claim 4, wherein the pigment content (by mass) is 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

11. Furthermore, the aqueous ink according to claim 4 further contains a resin dispersant for dispersing the pigment.

12. The aqueous ink according to claim 11, wherein the content (by mass) of the resin dispersant is 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink.

13. An ink cartridge comprising ink and an ink storage section for storing the ink, An ink cartridge characterized in that the ink is the water-based ink described in any one of claims 4 to 12.

14. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, An inkjet recording method characterized in that the ink is an aqueous ink according to any one of claims 4 to 12.

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