Pigment dispersant and pigment dispersion liquid

Abstract

To provide an environmentally friendly pigment dispersant capable of preparing a pigment dispersion liquid in which pigments are highly finely dispersed, which can prepare an aqueous inkjet ink having excellent discharge stability and redispersibility, which can record an image having excellent color development, abrasion resistance, alcohol resistance and adhesion to a non-absorbing substrate.SOLUTION: There is provided a pigment dispersant which is a vinyl copolymer containing 5 to 95 mass% of a constitutional unit (1) derived from monomer I such as 4-vinylguaiacol, 5 to 30 mass% of a constitutional unit (2) derived from monomer II such as (meth)acrylic acid and 0 to 90 mass% of a constitutional unit (3) derived from monomer III such as (meth)acrylate and having a number average molecular weight of 5000 to 30000 and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.1 to 2.5 in which a carboxylic group in the molecule is neutralized by alkali and dissolved in water.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pigment dispersant and a pigment dispersion. [Background technology]

[0002] Aqueous pigment dispersions are pigments finely dispersed in an aqueous medium, which is a dispersion medium, and are used as colorants for paints, inks, stationery, and the like. In the pigment dispersions, it is necessary that the finely dispersed pigments do not aggregate for a long period of time and maintain a stable dispersion state. In order to maintain the properties of fine dispersion and long-term dispersion stability of the pigment in the pigment dispersion, a pigment dispersant is usually used. The pigment dispersant is required to have durability such as abrasion resistance, water resistance, solvent resistance, and chemical resistance of the coating film, in addition to adhesion to the substrate of the coating or print. In order to improve the durability of the coating film formed, a binder component, which is a film-forming component, is usually used. However, depending on the type of pigment dispersant used in combination, the performance of the binder component may be reduced, so it is necessary to improve the performance of the pigment dispersant as well.

[0003] Another application of the aqueous pigment dispersion is aqueous inkjet ink. The aqueous pigment dispersion used to prepare the inkjet ink is particularly required to have performance such as pigment dispersibility and durability. The applications of printers and printing machines equipped with inkjet inks are diverse, including personal use, office use, business use, recording, color display, and color photography, as their functions become more sophisticated. In addition, the study of high-speed industrial printing machines is progressing, and in order to meet the demands of higher speeds and higher image quality, the pigment dispersion is further required to have fine pigment dispersibility and dispersion stability.

[0004] In order to increase the durability of the recorded image and improve the dispersibility of the pigment, various inkjet inks and the like have been proposed that utilize innovative compositions of resins and surfactants (Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5403313 [Patent Document 2] JP 2008-45023 A [Patent Document 3] Patent No. 4157868 [Patent Document 4] Special Publication No. 2009-515007 [Patent Document 5] International Publication No. 2013 / 008691 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even with the inks proposed in Patent Documents 1 to 5, it was difficult to record images that were excellent in color development, abrasion resistance, alcohol resistance, and adhesion to non-absorbent substrates. Furthermore, even with the inks proposed in Patent Documents 1 to 5, the ejection stability and redispersibility were not necessarily excellent, and there was room for improvement.

[0007] In recent years, from the viewpoints of reducing carbon dioxide emissions, carbon recycling, and carbon neutrality, there has been an active movement to replace petroleum-derived materials with biomass-derived materials that can be recycled. Specifically, there is a strong demand to actively use biomass-derived materials as materials constituting various compositions such as paints and inks, as well as various molded products such as films. There is also an increasing demand to use biomass-derived materials for water-based inkjet inks for forming images on printed matter.

[0008] The present invention has been made in consideration of the problems associated with the above-mentioned conventional techniques, and an object of the present invention is to provide an environmentally friendly pigment dispersant capable of preparing a pigment dispersion in which a pigment is highly finely dispersed, which can prepare an aqueous inkjet ink having excellent ejection stability and redispersibility and which can record images having excellent color development, abrasion resistance, alcohol resistance, and adhesion to non-absorbent substrates.

[0009] Another object of the present invention is to provide a pigment dispersion liquid in which a pigment is highly finely dispersed and which is environmentally friendly and which can prepare an aqueous inkjet ink having excellent ejection stability and redispersibility and which is capable of recording images having excellent color development, abrasion resistance, alcohol resistance, and adhesion to non-absorbent substrates. [Means for solving the problem]

[0010] That is, according to the present invention, there is provided a pigment dispersant as shown below. [1] A pigment dispersant which comprises 5 to 95 mass% of structural units (1) derived from at least one monomer I selected from the group consisting of 4-vinylguaiacol and 1-acetoxy-2-methoxy-4-vinylbenzene, 5 to 30 mass% of structural units (2) derived from at least one monomer II selected from the group consisting of (meth)acrylic acid, itaconic acid, and an itaconic acid monoester, and 0 to 90 mass% of structural units (3) derived from at least one monomer III selected from the group consisting of (meth)acrylates and an itaconic acid diester, and which has a number average molecular weight of 5,000 to 30,000 and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.1 to 2.5, and which is a vinyl copolymer whose carboxyl groups in the molecule are neutralized with an alkali and which dissolves in water. [2] The pigment dispersant according to [1], wherein the content of the structural unit (1) is 10 to 40 mass%, the content of the structural unit (2) is 5 to 20 mass%, and the content of the structural unit (3) is 50 to 85 mass%, the number average molecular weight is 10,000 to 25,000, and the molecular weight distribution (weight average molecular weight / number average molecular weight) is 1.3 to 2.3. [3] The pigment dispersant according to [1] or [2], wherein the monomer III is at least one selected from the group consisting of ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, diethyl itaconate, and dibutyl itaconate.

[0011] According to the present invention, there is also provided a pigment dispersion liquid as shown below. [4] A pigment dispersion comprising a pigment, a dispersant, a water-soluble organic solvent, and water, wherein the dispersant is the pigment dispersant described in any one of [1] to [3] above. [5] The pigment dispersion liquid according to [4] above, which is used for preparing an aqueous inkjet ink, wherein the pigment content is 5 to 60 mass %, the dispersant content is 0.5 to 20 mass %, the water-soluble organic solvent content is 30 mass % or less, and the water content is 20 to 80 mass %. [6] The pigment dispersion liquid according to [4] or [5], wherein the water-soluble organic solvent is at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide. [7] The pigment dispersion according to any one of [4] to [6], wherein the pigment is at least one selected from the group consisting of a yellow pigment, a red pigment, a blue pigment, a green pigment, an orange pigment, a black pigment, and a white pigment, the yellow pigment is at least one selected from the group consisting of CI Pigment Yellow 74, 150, 155, and 180, the red pigment is at least one selected from the group consisting of CI Pigment Red 122, 202, 254, 269, solid solutions thereof, and CI Pigment Violet 19, 23, and solid solutions thereof, the blue pigment is at least one selected from the group consisting of CI Pigment Blue 15:3, 15:4, and 15:6, the green pigment is at least one selected from the group consisting of CI Pigment Green 7, 36, and 58, the orange pigment is CI Pigment Orange 43, the black pigment is CI Pigment Black 7, and the white pigment is CI Pigment White 6. Effect of the Invention

[0012] According to the present invention, it is possible to provide an environmentally friendly pigment dispersant capable of preparing a pigment dispersion in which the pigment is highly finely dispersed, which can prepare an aqueous inkjet ink having excellent ejection stability and redispersibility and which can record images having excellent color development, abrasion resistance, alcohol resistance, and adhesion to non-absorbent substrates.

[0013] Furthermore, according to the present invention, it is possible to provide a pigment dispersion liquid in which the pigment is highly finely dispersed and which is environmentally friendly and which enables the preparation of an aqueous inkjet ink having excellent ejection stability and redispersibility and which is capable of recording images having excellent color development, abrasion resistance, alcohol resistance, and adhesion to non-absorbent substrates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] <Pigment dispersant> Hereinafter, the embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. One embodiment of the pigment dispersant of the present invention is a vinyl copolymer in which a carboxyl group in the molecule is neutralized with an alkali and dissolved in water, and is a polymer suitable as a material for a pigment dispersion liquid used to prepare an aqueous inkjet ink. The pigment dispersant of this embodiment contains 5 to 95 mass% of a structural unit (1) derived from monomer I, 5 to 30 mass% of a structural unit (2) derived from monomer II, and 0 to 90 mass% of a structural unit (3) derived from monomer III used as needed. Monomer I is at least one selected from the group consisting of 4-vinylguaiacol and 1-acetoxy-2-methoxy-4-vinylbenzene. Monomer II is at least one selected from the group consisting of (meth)acrylic acid, itaconic acid, and itaconic acid monoester. Monomer III is at least one selected from the group consisting of (meth)acrylate and itaconic acid diester. The vinyl copolymer serving as the pigment dispersant of this embodiment has a number average molecular weight of 5,000 to 30,000 and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.1 to 2.5. The pigment dispersant of this embodiment will be described in detail below.

[0015] The pigment dispersant of this embodiment is a pigment dispersant that disperses a pigment in an aqueous medium containing water as a main component and a water-soluble organic solvent used as necessary. By using the pigment dispersant of this embodiment, the pigment can be finely dispersed in the aqueous medium, and the dispersed pigment is less likely to aggregate over time, so that the dispersed state can be maintained for a long period of time. In addition, the adhesion of a coating material or a printed material, such as an ink, to a substrate containing a pigment dispersion liquid prepared using the pigment dispersant can be improved. Furthermore, the pigment dispersant of this embodiment can be composed actively using a material containing a monomer derived from biomass, so that it is an environmentally friendly pigment dispersant that can contribute to carbon dioxide elimination and carbon neutrality.

[0016] The pigment dispersant of this embodiment is a vinyl copolymer (polymer) having structural units derived from vinyl monomers having α,β-unsaturated bonds, such as (meth)acrylic acid monomers and styrene monomers. Since the pigment dispersant of this embodiment is a vinyl copolymer, there are more types of monomers that can be used compared to pigment dispersants that are polyester polymers or polyether polymers. For this reason, it is easy to design the polymer structure in accordance with the physical properties of the pigment, and the dispersibility of the pigment can be easily improved. Furthermore, the pigment dispersant of this embodiment is also excellent in chemical resistance, such as alkali resistance and acid resistance.

[0017] (Structural unit (1)) The structural unit (1) is a structural unit derived from at least one monomer I selected from the group consisting of 4-vinylguaiacol (4VG) and 1-acetoxy-2-methoxy-4-vinylbenzene (4VG-Ac). Hereinafter, "4VG" and "4VG-Ac" are collectively referred to as "4VGs". By using 4VGs, which are compounds in which a methoxy group and a hydroxyl group or a group obtained by acetylating a hydroxyl group are bonded to an aromatic ring, as a monomer, it is possible to introduce an aromatic ring and a phenolic hydroxyl group or an acetyl group into a vinyl copolymer. The aromatic ring introduced into the vinyl copolymer is π-π stacked with the aromatic ring in the pigment, so that the pigment dispersant is adsorbed onto the pigment. In addition, the phenolic hydroxyl group or ester group is hydrogen bonded with the oxygen atom, hydroxyl group, and oxygen atom constituting the carboxyl group in the pigment, so that the pigment dispersant is adsorbed onto the pigment. Furthermore, the phenolic hydroxyl group, which is an acidic group, is neutralized with the basic group in the pigment and ionized, so that the pigment dispersant is adsorbed onto the pigment. Furthermore, a pigment dispersant having an aromatic ring and a phenolic hydroxyl group easily adheres to a substrate such as a film, particularly to a film formed from an aromatic polymer such as polyethylene terephthalate (PET), and therefore can form an image with stronger adhesion to the substrate such as a film.

[0018] In the pigment dispersant, the content of the structural unit (1) is 5 to 95% by mass, preferably 10 to 40% by mass. If the content of the structural unit (1) is less than 5% by mass, the effect of introducing a structural unit derived from 4VG cannot be obtained. On the other hand, if the content of the structural unit (1) is more than 95% by mass, the introduction ratio of the structural unit (2) having a carboxyl group is relatively decreased, so that the pigment dispersant (vinyl copolymer) is difficult to become water-soluble. In addition, since 4VG is a styrene-based monomer having a phenolic hydroxyl group, the phenolic hydroxyl group easily inactivates the growing radical during polymerization, and the molecular weight of the obtained vinyl copolymer may decrease or there may be a remaining monomer that does not polymerize.

[0019] 4VGs can be synthesized using biomass-derived materials. Specifically, γ-oryzanol obtained from rice bran, wheat, and the like is hydrolyzed to obtain ferulic acid. 4VG can be prepared by decarboxylating the obtained ferulic acid with an enzyme or by heating in an organic solvent in the presence of an alkali. In other words, the pigment dispersant of the present embodiment, which is prepared using 4VG, a biomass-derived monomer, is an environmentally friendly polymer material.

[0020] 4VG can be synthesized according to a conventional method. In particular, it is preferable to use 4VG derived from biomass obtained by decarboxylating ferulic acid derived from plants. Ferulic acid (trans-4-hydroxy-3-methoxycinnamic acid) is contained in the cell walls of plants and is extracted from seeds of rice, wheat, and fruits using concentrated alkali. Ferulic acid is also produced using rice bran residue generated in the process of producing rice bran oil from rice bran as a raw material. 4VG-Ac can also be synthesized by acetylating the hydroxyl group of 4VG with acetic anhydride or the like.

[0021] Ferulic acid can be decarboxylated by the action of phenolic acid decarboxylase to prepare 4VG. In addition, it is preferable to heat ferulic acid in an organic solvent in the presence of an alkali and decarboxylate it to prepare 4VG, since this has a good yield. The method of heating ferulic acid in an organic solvent in the presence of an alkali is a conventionally known method. As the organic solvent, polar solvents such as dimethylformamide, N-vinylpyrrolidone, and diethylene glycol dimethyl ether can be used. As the alkali, organic amines such as triethylamine and dimethylaminoethanol; inorganic bases such as potassium acetate and potassium carbonate can be used. The heating temperature may be, for example, 80° C. or higher. After the reaction, the target 4VG can be obtained by extraction, concentration, distillation, etc. according to a conventionally known method.

[0022] The obtained 4VG may be stored as it is, but it is unstable like hydroxyl-substituted styrenes such as hydroxystyrene, and is prone to polymerization and polymerization during storage. For this reason, it is preferable to use it immediately after concentration or distillation, or store it at 0°C or lower, and it is more preferable to dilute it with an organic solvent and store it frozen. It is also preferable to store it by adding phenolic antioxidants such as hydroquinone, methoxyhydroquinone, and trihydroxybenzene; nitroxide radicals such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and 3-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl; or the like. For example, it may be diluted to 50% by mass or less with a solvent used in the subsequent polymerization reaction, and the above-mentioned phenolic antioxidant or TEMPOs may be added to the mixture to less than 0.5% by mass, and then stored at 0°C or lower. The purity of 4VG after synthesis is preferably 99% or more, but may be less than 99% as long as it does not affect the subsequent polymerization reaction. It may also contain a small amount of polymers such as dimers that are by-produced during synthesis.

[0023] The hydroxyl group of 4VG can be acetylated with acetic anhydride, acetic chloride, propenyl acetate, or the like to obtain 4VG-Ac. In the presence of the amine compound used in decarboxylation, acetic anhydride, acetic chloride, or the like may be added dropwise at a temperature below room temperature to cause a reaction, or a base catalyst such as dimethylaminopyridine may be used to heat the resulting product to acetylate. The stability of the monomer is improved by acetylating the unstable hydroxyl group of 4VG. In addition, after polymerizing 4VG-Ac by the method described below, the acetyl group may be eliminated with an acid or alkali to obtain a hydroxyl group, i.e., a structural unit derived from 4VG may be introduced.

[0024] (Constituent unit (2)) The structural unit (2) is a structural unit derived from a monomer II having a carboxy group. The monomer II is at least one selected from the group consisting of (meth)acrylic acid, itaconic acid, and itaconic acid monoesters. Examples of itaconic acid monoesters include itaconic acid monomethyl ester, itaconic acid monoethyl ester, and itaconic acid monobutyl ester. By introducing the structural unit (2) derived from the monomer II, a carboxy group can be introduced into the pigment dispersant (vinyl copolymer). Then, by neutralizing this carboxyl group with an alkali, the pigment dispersant can be dissolved in water.

[0025] The content of the structural unit (2) in the pigment dispersant is 5 to 30% by mass, and preferably 5 to 20% by mass. If the content of the structural unit (2) is less than 5% by mass, it may not be possible to sufficiently dissolve the structural unit (2) in water even after neutralization. On the other hand, if the content of the structural unit (2) is more than 30% by mass, the viscosity of the ink may increase excessively due to too many neutralized portions. In addition, the amount of hydrophilic carboxyl groups is too large, and the water resistance of the resulting image (printed matter) may decrease.

[0026] Itaconic acid is an environmentally friendly monomer produced by fermentation. Therefore, by combining itaconic acid or itaconic acid monoester with the aforementioned 4VG, a more environmentally friendly pigment dispersant can be created.

[0027] (Structural unit (3)) The structural unit (3) is a structural unit derived from monomer III and exhibits adsorptivity to pigments. Monomer III is at least one selected from the group consisting of (meth)acrylates and itaconic acid diesters. By introducing the structural unit (3) derived from monomer III, it is possible to adjust the hydrophobicity (hydrophilicity), softness / hardness, glass transition temperature (Tg), and other physical properties of the pigment dispersant. The content of the structural unit (3) in the pigment dispersant is 0 to 90% by mass, and preferably 50 to 85% by mass.

[0028] Examples of the (meth)acrylate include (meth)acrylates having an alkyl group, a cycloalkyl group, or an aromatic ring, such as methyl (meth)acrylate, butyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, trimethylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, tricyclodecyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and the like. hydroxyl group-containing (meth)acrylates such as (poly)ethylene glycol monomethyl ether (meth)acrylate, (poly)ethylene glycol monoethyl ether (meth)acrylate, and (poly)propylene glycol monomethyl ether (meth)acrylate; amino group-containing (meth)acrylates such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate; tetrahydrofurfuryl (meth)acrylate; and the like.

[0029] Examples of the itaconate diester include dimethyl itaconate, diethyl itaconate, dibutyl itaconate, methylethyl itaconate, and cyclohexyl itaconate.

[0030] The monomer III is preferably at least one monomer (monomer III') selected from the group consisting of ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, diethyl itaconate, and dibutyl itaconate. These monomers III' are compounds that can be prepared using alcohol derived from biomass. For this reason, the use of monomer III' can provide an environmentally friendly pigment dispersant.

[0031] Ethyl (meth)acrylate is produced using ethanol obtained by fermenting sugars, etc. Butyl (meth)acrylate and isobutyl (meth)acrylate are produced using butanol or isobutanol obtained by cracking coconut oil, etc. Dodecyl (meth)acrylate and octadecyl (meth)acrylate are monomers produced using dodecanol or octadecyl alcohol obtained by reducing alkanoic acid such as coconut oil, and since they have a long-chain alkyl group, they adsorb to pigments through hydrophobic interactions. In addition, by using dodecyl (meth)acrylate or octadecyl (meth)acrylate, the Tg of the resulting vinyl copolymer (pigment dispersant) can be lowered. This enhances the film-forming property, and allows the formation of an image with improved adhesion to a substrate such as a film.

[0032] Isobornyl (meth)acrylate is a monomer produced using camphene obtained from pine resin, etc., and has an isobornyl group, which can increase the Tg of the resulting vinyl copolymer (pigment dispersant). In addition, since isobornyl (meth)acrylate has a large number of carbon atoms, it is easy to adsorb to pigments due to hydrophobic interactions, and can form images with further improved adhesion to substrates such as films. Tetrahydrofurfuryl (meth)acrylate is produced using tetrahydrofurfuranol obtained by hydrogenating furanol obtained from corn cobs, etc. Tetrahydrofurfuryl (meth)acrylate has a cyclic ether group, which can increase the hydrophilicity of the resulting pigment dispersant, and can form images with further improved adhesion to substrates such as films by hydrogen bonding with the oxygen atoms of the ether group. As mentioned above, diethyl itaconate and dibutyl itaconate are diesters produced using alcohol derived from biomass, and are environmentally friendly monomers.

[0033] (Physical properties of pigment dispersants, etc.) The number average molecular weight of the pigment dispersant (vinyl copolymer) is 5,000 to 30,000, preferably 10,000 to 25,000. If the number average molecular weight of the pigment dispersant is less than 5,000, it is easily detached from the pigment, and the dispersion stability of the pigment becomes insufficient. On the other hand, if the number average molecular weight of the pigment dispersant is more than 30,000, the viscosity of the pigment dispersion liquid to be prepared may increase excessively, or the pigment may easily aggregate. In addition, by making the number average molecular weight of the pigment dispersant 10,000 or more, an image with further improved adhesion to a substrate such as a film can be formed.

[0034] The molecular weight distribution (PDI=weight average molecular weight (Mw) / number average molecular weight (Mn)) of the pigment dispersant (vinyl copolymer) is 1.1 to 2.5, preferably 1.3 to 2.3. To obtain a pigment dispersant with a PDI of less than 1.1, the synthesis conditions must be controlled very precisely, which is not necessarily suitable for industrial use. In addition, if the PDI of the pigment dispersant exceeds 2.5, it is likely to contain many particles with number average molecular weights outside the above range, and the desired effect may not be achieved.

[0035] In this specification, the number average molecular weight (Mn) and weight average molecular weight (Mw) are values ​​calculated as polystyrene standards measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a developing solvent.

[0036] The pigment dispersant of the present embodiment is a vinyl copolymer whose carboxyl groups in the molecule are neutralized with an alkali and dissolved in water. As the alkali, any conventionally known alkali can be used. Specific examples of the alkali include ammonia; organic amines such as triethylamine and dimethylaminoethanol; and alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. By neutralizing a part or all of the carboxyl groups with these alkalis, the vinyl copolymer, which is the pigment dispersant, can be dissolved in water or an aqueous medium containing water and a water-soluble organic solvent. By dissolving the pigment dispersant in water, the hydroxymethoxybenzene ring in the structural unit (1) and the hydrophobic alkyl group in the structural unit (2) are adsorbed to the pigment, and the pigment can be wetted in water, and the pigment can be finely dispersed by mechanically dispersing it, thereby obtaining a desired pigment dispersion. Furthermore, since the hydroxymethoxybenzene ring and the hydrophobic alkyl group are difficult to be detached from the pigment, the pigment dispersibility can be maintained for a long period of time.

[0037] (Method of manufacturing pigment dispersant) The pigment dispersant (vinyl copolymer) can be produced according to a conventional method. For example, the monomer is polymerized by solution radical polymerization using a water-soluble organic solvent used in the pigment dispersion liquid described later as a polymerization solvent, and then an alkali is added to form an aqueous solution, whereby the pigment dispersant can be produced. An azo-based radical initiator or a peroxide-based radical initiator can be used during polymerization. Among them, it is preferable to use an azo-based radical polymerization initiator. An example of the azo-based radical initiator is azobisisobutyronitrile. An example of the peroxide-based radical initiator is benzoyl peroxide. In addition, the molecular weight of the vinyl copolymer obtained may be adjusted using a chain transfer agent such as a thiol compound. However, since 4VG having a phenolic hydroxyl group is used as a monomer, the generated initiator radical may pull out hydrogen from the phenolic hydroxyl group, and the initiator radical may become inactivated, causing the polymerization to not proceed sufficiently.

[0038] Also, a vinyl copolymer having a relatively uniform molecular weight can be produced by a living radical polymerization method. Examples of living radical polymerization methods include the nitroxide method, the atom transfer radical polymerization method, the reversible addition-fragmentation chain transfer polymerization method (RAFT method), the organotellurium living radical polymerization method (TERP method), the reversible transfer catalyst polymerization method, and the reversible catalyst-mediated polymerization method. The polymer structure of the pigment dispersant (vinyl copolymer) may be a random linear structure, or may be a controlled structure such as a block structure, a graft structure, or a multi-branched structure.

[0039] Examples of the water-soluble organic solvent used as the polymerization solvent include alcohol-based solvents such as methanol, ethanol, isopropanol, propyl alcohol, butanol, and isobutanol; glycol-based solvents such as ethylene glycol, propylene glycol, and glycerin; diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, ethylene glycol monobutyl ether, diethylene glycol, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and propylene glycol monomethyl ether. Examples of the solvent include glycol ethers such as pyrene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, and 3-methoxy-3-methyl-1-butanol; amide solvents such as dimethylformamide, dimethylacetamide, pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide; carbonate solvents such as ethylene carbonate, propylene carbonate, and dimethyl carbonate; dimethyl sulfoxide; tetramethylurea; dimethylimidazolidinone; and the like.

[0040] As the polymerization solvent, it is preferable to use a water-soluble organic solvent used in an aqueous inkjet ink. Specifically, it is preferable to use at least one water-soluble organic solvent selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide.

[0041] The pigment dispersant can also be obtained by taking out the polymer produced as a solid after solution polymerization and dissolving it in water. Specifically, after polymerizing a monomer in an organic solvent, the reaction liquid is added to a poor solvent to precipitate the polymer produced in a solid state. Alternatively, the reaction liquid can be neutralized with an alkali to form an aqueous solution, added to a large amount of water, homogenized, and then an acid is added to precipitate the polymer in a solid state. Next, the carboxyl group is neutralized by reaction with an alkali in water or an aqueous medium containing water and a water-soluble organic solvent, and the polymer is made into an aqueous solution, thereby obtaining the desired pigment dispersant.

[0042] <Pigment dispersion> One embodiment of the pigment dispersion of the present invention is a pigment dispersion that contains a pigment, a dispersant, a water-soluble organic solvent, and water, and is also suitable as a material for preparing an aqueous ink-jet ink. The dispersant used to disperse the pigment in the pigment dispersion is the pigment dispersant described above.

[0043] (Pigments) The pigment dispersion of the present embodiment contains a pigment in a finely dispersed state. As the pigment, conventionally known organic pigments and inorganic pigments used in aqueous inkjet inks and the like can be used. As the organic pigment, chromatic pigments such as phthalocyanine-based, azo-based, azomethine azo-based, azomethine-based, anthraquinone-based, perinone-perylene-based, indigo-thioindigo-based, dioxazine-based, quinacridone-based, isoindoline-based, isoindolinone-based, diketopyrrolopyrrole-based, quinophthalone-based, and indanthrene-based pigments; carbon black pigments such as furnace black, lamp black, acetylene black, and channel black can be given. As the inorganic pigment, extender pigments, titanium oxide-based pigments, iron oxide-based pigments, and spinel pigments can be given.

[0044] Examples of pigments, listed by Color Index (CI) number, are CI Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 97, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 175, 180, 181, 185, 191; solid solutions with C.I. Pigment Red 4, 5, 9, 23, 48, 49, 52, 53, 57, 97, 112, 122, 122, 123, 144, 146, 147, 149, 150, 166, 168, 170, 176, 177, 180, 1 84, 185, 192, 202, 207, 214, 215, 216, 217, 220, 221, 223, 224, 226, 227, 228, 238, 240, 242, 254, 255, 264, 269, 272; CI Pigment Violet 19, 23, 29, 30, 37, 40, 50; CI Pigment Blue 15, 15:1, 15:3, 15:4, 15:6, 22, 60, 64; CI Pigment Green 7, 36, 58; CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63; CI Pigment Black 7; CI Pigment White 6; and the like.

[0045] Among them, from the viewpoints of color development, dispersibility, weather resistance, etc., it is preferable that the pigment is at least one selected from the group consisting of yellow pigments, red pigments, blue pigments, green pigments, orange pigments, black pigments, and white pigments. And, it is preferable that the yellow pigment is at least one selected from the group consisting of CI Pigment Yellow 74, 150, 155, and 180. It is preferable that the red pigment is at least one selected from the group consisting of CI Pigment Red 122, 202, 254, 269, solid solutions thereof, CI Pigment Violet 19, 23, and solid solutions thereof. It is preferable that the blue pigment is at least one selected from the group consisting of CI Pigment Blue 15:3, 15:4, and 15:6. It is preferable that the green pigment is at least one selected from the group consisting of CI Pigment Green 7, 36, and 58. It is preferable that the orange pigment is CI Pigment Orange 43. It is preferable that the black pigment is CI Pigment Black 7. The white pigment is preferably CI Pigment White 6. Of these pigments, as the organic pigment, it is particularly preferable to use an organic pigment formed from a material derived from biomass.

[0046] Except when a printing material (image) requires hiding power, it is preferable to use an organic fine particle pigment. When a printing material showing high definition and transparency is required, it is preferable to use a pigment that has been finely milled by wet grinding such as salt milling or dry grinding. Considering the avoidance of nozzle clogging, it is preferable to use an organic pigment having a number average particle diameter of 0.2 μm or less, from which pigments having a particle diameter of more than 1.0 μm have been removed, or an inorganic pigment having a number average particle diameter of 0.4 μm or less. By using a pigment having a number average particle diameter within the above range, the optical density, saturation, color development, and printing quality of the printed matter recorded can be improved, and the sedimentation of the pigment in the ink can be appropriately suppressed. The number average particle diameter of the pigment can be measured using, for example, an electron microscope or a light scattering particle size distribution meter.

[0047] The pigment may be any of the following: an untreated pigment; a self-dispersing pigment having a functional group introduced on its surface; a treated pigment that has been surface-treated with a surface treatment agent such as a coupling agent or an activator, or a polymer, or that has been encapsulated. The pigment may also be treated with the above-mentioned pigment dispersant. For example, a pigment dispersant may be present when synthesizing the pigment, when pigmenting, or when micronizing the pigment. The pigment dispersant and the pigment may be mixed and stirred in water to disperse the pigment, and then the pigment may be treated by precipitating in a poor solvent or by acid precipitation.

[0048] (dispersion medium) The pigment dispersion of the present embodiment contains a liquid medium containing water and a water-soluble organic solvent as a dispersion medium for the pigment. As the water, it is preferable to use ion-exchanged water, distilled water, purified water, or the like.

[0049] The water-soluble organic solvent not only functions as a moisturizing agent, but also as an anti-drying agent, and when a plastic film is used as the substrate, it also has the effect of improving the wettability of the substrate. Examples of the water-soluble organic solvent include alcohol-based solvents such as methanol, ethanol, and isopropanol; ketone-based solvents such as acetone; alkylene glycol-based solvents such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 3-methoxy-3-methyl-1-butanol, and 1,2-hexanediol; alkylene glycol monoalkyl ether-based solvents such as ethylene glycol methyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; glycerin-based solvents such as glycerin, diglycerin, and ethylene oxide adducts of glycerin; amide-based solvents such as 2-pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; urea-based solvents such as tetramethylurea and dimethylimidazolidinone; and carbonate-based solvents such as ethylene carbonate and dimethyl carbonate.

[0050] As the water-soluble organic solvent, glycol solvents and amide solvents are preferred from the viewpoints of moisture retention and prevention of drying, etc. Among them, it is more preferred to use at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide.

[0051] (Other additives) The pigment dispersion of the present embodiment may contain other additives as necessary, such as a surfactant, a preservative, an organic solvent other than the water-soluble organic solvent described above, a leveling agent, a surface tension adjuster, a pH adjuster, an ultraviolet absorber, a light stabilizer, an antioxidant, a dye, a filler, a wax, a thickener, an antifoaming agent, an antifungal agent, an antistatic agent, metal fine particles, and a magnetic powder.

[0052] By adding a surfactant to the pigment dispersion liquid, the surface tension of the pigment dispersion liquid or the ink can be maintained within a predetermined range. Examples of the surfactant include silicone-based, acetylene glycol-based, fluorine-based, alkylene oxide-based, and hydrocarbon-based surfactants. Among them, silicone-based, acetylene glycol-based, and fluorine-based surfactants are preferable. Generally, surfactants can cause the ink to foam or the ink to be repelled by the film surface. For this reason, it is preferable to appropriately control the amount of surfactant added to the pigment dispersion liquid.

[0053] Preservatives include sodium benzoate, benzimidazole, thiabendazole, potassium sorbitanate, sodium sorbitanate, sodium dehydroacetate, thiazosulfamide, and pyridinethiol oxide.

[0054] (Pigment dispersion) Pigments and pigment dispersants are blended in the pigment dispersion liquid according to the application, such as paint, stationery colorant, water-based gravure ink, and water-based flexographic ink. In the case of a pigment dispersion liquid used for preparing a water-based inkjet ink, the content of the pigment in the pigment dispersion liquid is preferably 5 to 60 mass%. In the case of an organic pigment, the content of the organic pigment in the pigment dispersion liquid is preferably 5 to 30 mass%, and more preferably 10 to 25 mass%. In addition, in the case of an inorganic pigment, the content of the inorganic pigment in the pigment dispersion liquid is preferably 20 to 60 mass%, and more preferably 30 to 50 mass%.

[0055] The content of the dispersant in the pigment dispersion is preferably 0.5 to 20% by mass. If the content of the pigment dispersant is less than 0.5% by mass, it becomes difficult to stably disperse the pigment. On the other hand, if the content of the pigment dispersant is more than 20% by mass, the viscosity becomes too high and the pigment exhibits non-Newtonian viscosity, which may make it impossible to eject the pigment linearly using an inkjet method.

[0056] The content of the dispersant is preferably set according to the type of pigment, surface properties, particle size, etc. Specifically, the content of the pigment dispersant is preferably 5 to 50 parts by mass, more preferably 10 to 30 parts by mass, per 100 parts by mass of the organic pigment. Also, the content of the pigment dispersant is preferably 1 to 20 parts by mass, more preferably 3 to 10 parts by mass, per 100 parts by mass of the inorganic pigment.

[0057] The content of the water-soluble organic solvent in the pigment dispersion is preferably 30% by mass or less, and more preferably 0.5 to 20% by mass. If the content of the water-soluble organic solvent exceeds 30% by mass, the water-soluble organic solvent is likely to remain in the print film, which may cause blocking and decrease the physical properties of the image, such as water resistance and abrasion resistance. In addition, the viscosity of the pigment dispersion may increase, causing the dispersant to detach from the pigment and aggregate.

[0058] The content of water in the pigment dispersion is preferably 20 to 80% by mass. By preparing an aqueous pigment dispersion containing an appropriate amount of water, an aqueous inkjet ink can be easily prepared.

[0059] If the content of the surfactant in the pigment dispersion is too high, the pigment may be easily aggregated. For this reason, it is preferable to appropriately control the content of the surfactant. The content of the surfactant in the pigment dispersion is preferably 0 to 3.5% by mass, more preferably 0.01 to 2% by mass. The content of the preservative in the pigment dispersion is preferably 0.05 to 2% by mass, more preferably 0.1 to 1% by mass.

[0060] (Method of manufacturing pigment dispersion) The pigment dispersion can be produced according to a conventional method. For example, a pigment, a dispersant, water, and a water-soluble organic solvent are mixed, and then stirred and dispersed to obtain a pre-pigment dispersion. When mixing, stirring, and dispersing, a conventional mixer, stirrer, and disperser can be used. Examples of the stirrer include a dissolver and a homogenizer. Examples of the mixer and disperser include a kneader, an attritor, a ball mill, a vertical media disperser and a horizontal media disperser loaded with glass beads or zirconia beads, a colloid mill, a jet mill, a high-pressure homogenizer, and an ultrasonic disperser. In addition, it is preferable to use beads of 1 mm or less as the media to be loaded into the media disperser. By using such beads as the media, the crystals and shape of the pigment are less likely to be destroyed, and so-called soft dispersion can be achieved.

[0061] It is preferable to disperse the pigment into primary particles by the above-mentioned mixing, stirring, and dispersion treatment. However, the pigment may be aggregated to a required particle size. The dispersion state of the pigment can be confirmed by a conventionally known method. For example, it can be confirmed by using an optical microscope or an electron microscope, by measuring with a particle size distribution measuring device such as light scattering, or by measuring absorbance using a spectrophotometer. After the dispersion treatment, coarse particles may be removed by centrifugal filtration, filter filtration, or the like. Thereafter, other additives, etc. can be added as necessary to obtain a pigment dispersion liquid.

[0062] (Physical properties of pigment dispersion) The physical properties of the pigment dispersion are appropriately designed according to the application. For example, the viscosity of the aqueous inkjet ink is adjusted to an appropriate viscosity that allows the ink to be ejected from the nozzles of a recording head by an inkjet method, depending on the type of pigment, etc. For example, the viscosity of an ink containing an organic pigment at 25°C is preferably 2 to 10 mPa·s. Also, the viscosity of an ink containing an inorganic pigment at 25°C is preferably 5 to 30 mPa·s.

[0063] The pH of the pigment dispersion at 25°C is preferably 7.0 to 10.0, and more preferably 7.5 to 9.5. If the pH of the pigment dispersion is less than 7.0, the dispersant may be more likely to precipitate and the pigment may be more likely to aggregate. On the other hand, if the pH of the pigment dispersion is more than 10.0, the pigment dispersion may be more alkaline and difficult to handle. The surface tension of the pigment dispersion at 25°C is preferably 15 to 45 mN / m, and more preferably 20 to 40 mN / m.

[0064] The pigment dispersion of the present embodiment is useful as a pigment dispersion to be incorporated into an aqueous inkjet ink. The inkjet ink can be applied to inkjet printers for consumer use, industrial use, and textile printing. Examples of media (recording media) to be printed include plain paper, glossy paper, matte paper, films made of polyester such as PET or vinyl chloride, fibers such as cotton or polyester, and metals such as aluminum plates. By using an ink prepared using the pigment dispersion of the present embodiment, images with excellent color development can be recorded at high speed even on paper containing a large amount of inorganic filler. In addition, the ink prepared using the pigment dispersion of the present embodiment is suitable for high-speed printing, and is therefore suitable for industrial label printing, packaging printing, and wide-format inkjet printers. EXAMPLES

[0065] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are by mass unless otherwise specified.

[0066] <Synthesis of 4-vinylguaiacol (4VG; 4-methoxyhydroxystyrene)> (Synthesis Example 1) 105 parts of dimethylformamide (DMF), 105 parts of ferulic acid, and 0.5 parts of methoxyphenol (HQ) were placed in a reaction vessel and stirred. A mixed solution of 109 parts of triethylamine (TEA) and 109 parts of DMF was dropped into the reaction vessel over 1 hour. Some heat generation was confirmed. The mixture was heated to 100°C and reacted for 5 hours. Gas generation was confirmed. The reaction solution was placed in a separatory funnel, and 600 parts of water and 250 parts of ethyl acetate were added to extract the product. The ethyl acetate layer was washed twice with 500 parts of 0.1% hydrochloric acid and with 500 parts of saturated saline. The removed ethyl acetate layer was dried over anhydrous magnesium sulfate. 0.5 parts of HQ was added to the dried ethyl acetate layer, and the mixture was concentrated with an evaporator to obtain 73.4 parts of a slightly brown liquid. The liquid obtained was analyzed using a nuclear magnetic resonance (NMR) and an infrared spectrophotometer (IR) to confirm the disappearance of the carboxyl group peak, as well as the presence of a phenolic hydroxyl group, an unsaturated bond, an aromatic ring derived from phenol, and a methyl group of the methoxy group. This confirmed the production of 4VG. The purity measured by gas chromatography was 93.3%. 70 parts of the obtained 4VG and 60.6 parts of diethylene glycol monobutyl ether (BDG) were mixed to obtain a BDG solution of 4VG (4VG solution) with a 4VG content (concentration) of 50%. The obtained 4VG solution was stored at 0°C.

[0067] <Synthesis of 1-acetoxy-2-methoxy-4-vinylbenzene (4VG-Ac)> (Synthesis Example 2) 70 parts of 4VG obtained in Synthesis Example 1 were cooled to 10°C in an ice bath. 55.2 parts of acetic anhydride were added dropwise over 1 hour, and then the mixture was stirred for 2 hours. The mixture was then heated to 50°C and reacted for 1 hour. Thereafter, the mixture was extracted, washed, dried, and concentrated in the same manner as in Synthesis Example 1 described above, to obtain 97.3 parts of a brown liquid. The liquid obtained was analyzed using NMR and IR, and the disappearance of the carboxyl group peak, as well as the presence of unsaturated bonds, aromatic rings derived from phenol, ester groups of acetyl groups, methyl groups of acetyl groups, and methyl groups of methoxy groups, were confirmed. This confirmed that 4VG-Ac had been produced. The purity measured by gas chromatography was 95.6%. The obtained 4VG-Ac was stored at 0°C.

[0068] <Production of pigment dispersants> Example 1 30 parts of BDG, 140 parts of 4VG solution (70 parts of 4VG), 20 parts of tetrahydrofurfuryl acrylate (THFA), and 10 parts of acrylic acid (AA) were placed in a reaction vessel and heated to 80°C while bubbling nitrogen. 3 parts of 2,2'-azobis(isobutyrate)dimethyl (FUJIFILM Corporation, V-601) were added, and polymerized at 80°C for 8 hours to form a polymer, obtaining a polymer solution. A part of the obtained polymer solution was sampled, and the number average molecular weight (Mn) of the polymer measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a developing solvent was 8,100, and the molecular weight distribution (PDI) was 2.39. The obtained polymer solution was heated at 150°C until it reached a constant weight, dried, and the solid content measured was 49.8%, confirming that most of the monomers were polymerized. After cooling the polymer solution to 50°C, 100 parts of an aqueous alkali solution containing 9.2 parts of 28% ammonia water and 91.2 parts of water was added to obtain a solution of pigment dispersant D-1 (solid content: 33.0%), which is a light yellow transparent liquid. The pH of the resulting pigment dispersion D-1 was 8.9. When the resulting pigment dispersant D-1 solution was added to a large amount of water, it dissolved transparently.

[0069] (Examples 2 to 4) Solutions of pigment dispersants D-2 to D-4 were obtained in the same manner as in Example 1 described above, except that the formulations were as shown in Table 1. Details of the obtained solutions of pigment dispersants D-2 to D-4 are shown in Table 1. Details of the abbreviations in Table 1 are as follows. MPG: Propylene glycol monomethyl ether PPG: Propylene glycol monopropyl ether ·THFA: Tetrahydrofurfuryl acrylate THFMA: Tetrahydrofurfuryl methacrylate IBXA: Isobornyl acrylate IBXMA: Isobornyl methacrylate ·MAA: Methacrylic acid IT: Itaconic acid ITE: Diethyl itaconate

[0070] TIFF2025047712000001.tif171170

[0071] Comparative Example 1 Polymerization and neutralization were performed in the same manner as in Example 2, except that the amounts of THFMA, IBXMA, MAA, and 28% aqueous ammonia were 23 parts, 22.5 parts, 4.5 parts, and 4.6 parts, respectively, to obtain a solution of pigment dispersant HD-1. It was confirmed that most of the monomers were polymerized. The Mn of the obtained polymer was 8,400 and the PDI was 2.35. When an aqueous alkali solution was added, the solution became cloudy and emulsified. The solid content of the obtained liquid was 33.2%, and the pH was 8.9. When the obtained solution of pigment dispersant HD-1 was added to water, the solution became cloudy and emulsified.

[0072] Comparative Example 2 100 parts of BDG, 70 parts of styrene (St), 20 parts of THFA, 10 parts of AA, and 0.5 parts of dedocylthiol were placed in a reaction vessel and heated to 80°C while bubbling nitrogen. After adding 1 part of V-601, polymerization was carried out for 8 hours in the same manner as in Example 1 described above to form a polymer, and a polymer solution was obtained. The Mn of the obtained polymer was 7,200, and the PDI was 1.89. It was also confirmed that most of the monomers were polymerized. Next, neutralization was carried out in the same manner as in Example 1 described above to obtain a solution of pigment dispersant HD-2 (solid content: 33.4%). The pH of the obtained pigment dispersion liquid HD-2 solution was 8.8. When the obtained solution of pigment dispersant HD-2 was added to a large amount of water, it was dissolved.

[0073] Example 5 80 parts of BDG were placed in a reaction vessel. 40 parts of 4VG solution (20 parts of 4VG), 15 parts of ethyl methacrylate (EMA), 15 parts of IBXMA, 15 parts of THFMA, 20 parts of dodecyl methacrylate (LMA), 15 parts of MAA, and 3 parts of V-601 were mixed and stirred to obtain a homogenized monomer solution. 1 / 3 of the obtained monomer solution was added to the reaction vessel. Next, 2 / 3 of the monomer solution was dropped into the reaction vessel over 1 hour, and polymerized for 7 hours to form a polymer, obtaining a polymer solution. The Mn of the obtained polymer was 18,000, and the PDI was 2.18. It was also confirmed that most of the monomers were polymerized. 100 parts of an alkaline aqueous solution containing 11.6 parts of 28% ammonia water and 88.4 parts of water was added to obtain a solution of pigment dispersant D-5 (solid content: 33.2%). The pH of the obtained pigment dispersion D-5 solution was 8.9. When the resulting solution of pigment dispersant D-5 was added to a large amount of water, it dissolved.

[0074] (Examples 6 to 10, Comparative Examples 3 and 4) Solutions of pigment dispersants D-6 to 10 and solutions of pigment dispersants HD-3 and 4 were obtained in the same manner as in Example 5 described above, except that the formulations were as shown in Table 2. Details of the obtained solutions of pigment dispersants D-6 to 10 and solutions of pigment dispersants HD-3 and 4 are shown in Table 2. Details of the abbreviations in Table 2 are shown below. BMA: Butyl methacrylate StMA: Octadecyl methacrylate ·DMAE: Dimethylaminoethanol

[0075] TIFF2025047712000002.tif138170

[0076] <Preparation of pigment dispersion (1)> Example 11 A transparent solution was obtained by mixing 350 parts of the pigment dispersant D-1 solution, 70 parts of propylene glycol, and 195 parts of water. 350 parts of phthalocyanine pigment CI Pigment Blue 15:3 (trade name "A-220JC", manufactured by Dainichi Seikagaku Kogyo Co., Ltd.) were added to the obtained solution, and then the solution was stirred for 30 minutes using a disperser to prepare a mill base. The pigment was thoroughly dispersed in the mill base by dispersing at a peripheral speed of 10 m / s using a horizontal media disperser (trade name "Dyno Mill 0.6 liter ECM type", manufactured by Shinmaru Enterprises Co., Ltd., diameter of zirconia beads: 0.5 mm). 316 parts of water were added to adjust the pigment concentration to 18%. The mill base removed from the disperser was centrifuged (7,500 rpm, 20 minutes), and then filtered through a membrane filter with a pore size of 10 μm. The mixture was diluted with water to obtain a pigment dispersion IJ-1 for inkjet ink with a pigment concentration of 14%.

[0077] The number average particle size of the pigment in pigment dispersion IJ-1, measured using a particle size analyzer (product name "NICOMP 380ZLS-S", manufactured by International Business Co., Ltd.), was 101 nm, confirming that the pigment was finely dispersed. In addition, the viscosity of pigment dispersion IJ-1 was 3.8 mPa·s and the pH was 8.3. The number average particle size of the pigment measured after storing pigment dispersion IJ-1 at 70°C for one week was 100 nm and the viscosity was 3.6 mPa·s. This confirmed that the storage stability of pigment dispersion IJ-1 is very good.

[0078] (Examples 12 to 20, Comparative Examples 5 to 8) Pigment dispersions IJ-2 to 10 and pigment dispersions IJ-H1 to 4 were obtained in the same manner as in Example 11, except that solutions of the pigment dispersants shown in Table 3 were used. Details of the obtained pigment dispersions are shown in Table 3.

[0079] (Evaluation of dispersibility) The dispersibility of the pigment was evaluated according to the following evaluation criteria. The results are shown in Table 3. In the evaluation criteria shown below, "○" and "△" were considered to be acceptable, and "×" was considered to be unacceptable. ◯: The pigment was finely dispersed, and the storage stability was also good. Δ: The pigment was finely dispersed, but the storage stability was slightly poor. ×: The pigment could not be finely dispersed, and the storage stability was also poor.

[0080] TIFF2025047712000003.tif78170

[0081] <Preparation of pigment dispersion (2)> (Examples 21 to 23) Pigment dispersions IJ-11 to IJ-13 were obtained in the same manner as in Example 11 above, except that the pigments used were CI Pigment Red 122 (product name "CFR130P, Dainichiseika Color & Chemicals Mfg. Co., Ltd.), which is a quinacridone pigment; CI Pigment Yellow 74 (product name "Seika First Yellow 2016G, Dainichiseika Color & Chemicals Mfg. Co., Ltd.), which is an azo pigment; and CI Pigment Black 7 (product name "S170, Degussa Co., Ltd.), which is a carbon black pigment. Details of the obtained pigment dispersions are shown in Table 4.

[0082] TIFF2025047712000004.tif103170

[0083] <Ink preparation and evaluation (1)> (Evaluation Examples 1 to 13) Using the pigment dispersions IJ-1 to IJ-13, the components were mixed according to the ink formulations shown below to obtain mixtures. The resulting mixtures were thoroughly stirred and then filtered through a membrane filter with a pore size of 10 μm to obtain inks IJI-1 to IJI-13, which are water-based inks for inkjet printing. [Ink formula] Pigment dispersion: 40 parts ·Wednesday: 44.0 copies 1,2-Hexanediol: 5 parts Glycerin: 10 parts Surfactant (product name "Surfinol 465", manufactured by Air Products): 1 part

[0084] The resulting inks were filled into cartridges and then installed in an inkjet printer (product name "EM930C", manufactured by Seiko Epson Corporation). Using this inkjet printer, solid areas on plain paper (product name "ColorLok paper", manufactured by Hewlett-Packard Company) were filled in at maximum print density to obtain a printed matter. It was confirmed that each ink could be ejected from the inkjet nozzle without any problems. The resulting printed matter was visually observed to be of high color density, vivid, and highly colorable.

[0085] <Ink preparation and evaluation (2)> (Evaluation Examples 14-28) Pigment dispersions IJ-1 to 13 and pigment dispersions IJ-H2 and 3 were used, and each component was mixed according to the following recipe to obtain a mixture. As the urethane water dispersion, a urethane emulsion was used, which was obtained by neutralizing a polyurethane with an acid value of 34.2 mg KOH / g formed from isophorone diisocyanate / polyhexamethylene carbonate diol / dimethylol butanoic acid / hydrazine with triethylamine, and had a number average particle size of 42.2 nm measured by a light scattering method and a solid content of 25.0%. The obtained mixture was thoroughly stirred and then filtered through a membrane filter with a pore size of 10 μm to obtain inks IJI-14 to 28, which are water-based inks for inkjet printing. [Ink formula] Pigment dispersion: 20 parts Urethane water dispersion: 20 parts ·Wednesday: 33 parts Propylene glycol: 26 parts Surfactant: Trade name "Surfinol 465" (manufactured by Air Products): 1 part

[0086] The viscosity and number average particle size of the pigment of the obtained inks were measured in the same manner as in Example 11, and a storage stability test was performed by storing the inks at 70° C. for one week. As a result, it was confirmed that the viscosity and number average particle size of the pigment of all the inks hardly changed, and the inks had excellent dispersibility and storage stability.

[0087] An inkjet printer with a plate heater (product name "MMP825H", manufactured by Mastermind) and a substrate (PET (polyethylene terephthalate) film, manufactured by Futamura Chemical Co., Ltd., thickness 50 μm) were prepared. Then, using each of the prepared inks, an image was recorded on the substrate by an inkjet recording method to obtain a printed matter. Specifically, the substrate was heated using a plate heater so that the surface temperature was 55 ° C., and then the ink was applied, and then the substrate was dried for 10 minutes in a thermostatic chamber heated to 90 ° C. to obtain a printed matter. Thereafter, the ejection stability, adhesion, abrasion resistance, and alcohol resistance were evaluated by the following method. In addition, in the evaluation criteria for each evaluation shown below, "◎" and "○" were considered to be acceptable, and "△" and "×" were considered to be unacceptable. The results are shown in Table 5.

[0088] [Discharge stability] The ink ejection state during printing was visually observed, and the ink ejection stability was evaluated according to the following evaluation criteria. ◯: Discharge was possible without any problems, and a good image was printed. △: Scattering of minute droplets was observed. ×: Droplets splashed and scattered during ejection, causing image disturbance.

[0089] [Adhesion] Cellophane tape was pressed thoroughly against the image and then peeled off. The degree of peeling of the image from the substrate was visually observed, and the adhesion of the image was evaluated according to the following evaluation criteria. : No peeling at all. A: Slightly peeled off. Δ: The peeled area was smaller than the area that did not peel. ×: The peeled area was larger than the non-peeled area.

[0090] [Friction resistance (dry friction resistance and wet friction resistance)] A dry rub test was conducted by moving a dry white cloth back and forth over the surface of the image 100 times with a weight of 500g using a Gakushin type rub fastness tester (product name "RT-300", manufactured by Daiei Kagaku Co., Ltd.), and a wet rub test was conducted by moving a water-soaked white cloth back and forth over the surface of the image 100 times with a weight of 200g. After the rub test, the degree of peeling of the image was visually observed, and the rub resistance of the image (dry rub resistance and wet rub resistance) was evaluated according to the following evaluation criteria. : No peeling at all. ○: Slight peeling. Δ: The peeled area was smaller than the area that did not peel. ×: The peeled area was larger than the non-peeled area.

[0091] [Alcohol resistance] A 70% ethanol solution was dropped onto the surface of the image, and after leaving it for 10 seconds, the surface of the image was rubbed back and forth with a cotton swab. The number of times the surface was rubbed back and forth until the coating (image) was peeled off was counted, and the alcohol resistance of the image was evaluated according to the following evaluation criteria. ◎: 20 or more times ○: 10 to less than 20 times △: 5 to less than 10 times ×: Peeled off immediately - less than 5 times

[0092] TIFF2025047712000005.tif69170

[0093] <Preparation of pigment dispersion (3)> Example 24 125 parts of the pigment dispersant D-1 obtained in Example 1, 50 parts of 3-methoxy-3-methyl-1-butanol, and 325 parts of water were mixed. 500 parts of CI Pigment White 6 (trade name "JR-405", manufactured by Teika Co., Ltd.) which is a white pigment was added, and the mixture was stirred using a disperser, and then the pigment was sufficiently dispersed using a horizontal media disperser to obtain a mill base. The mill base taken out of the disperser was filtered through a membrane filter with a pore size of 10 μm. The mixture was diluted with water to obtain a pigment dispersion liquid IJ-14 for inkjet inks with a pigment concentration of 14%.

[0094] The number average particle size of the pigment in pigment dispersion IJ-14 was 201 nm. The viscosity of pigment dispersion IJ-14 was 13.4 mPa·s, and the pH was 9.4. When pigment dispersion IJ-14 was placed in a sample bottle and stored at 70°C for one week, the pigment settled. When the sample bottle was shaken 10 times, the pigment was dispersed again. The number average particle size of the pigment was 206 nm, and no "lumps" were observed on the inner wall of the sample bottle. It is believed that the high acid value polymer, which has a structural unit derived from itaconic acid, has an affinity with water and forms a hydration layer between the pigment particles, preventing the pigments from agglomerating, and that the original dispersion state can be easily restored by stirring. [Industrial Applicability]

[0095] The pigment dispersion of the present invention is useful, for example, as a pigment dispersion used for preparing an aqueous inkjet ink. In addition to the aqueous inkjet ink, the pigment dispersion of the present invention is also useful, for example, as a pigment dispersion used for preparing paints, stationery inks, aqueous flexographic inks, aqueous gravure inks, and the like.

Claims

1. The composition comprises 5 to 95% by mass of structural units (1) derived from at least one monomer I selected from the group consisting of 4-vinylguaiacol and 1-acetoxy-2-methoxy-4-vinylbenzene, 5 to 30% by mass of structural units (2) derived from at least one monomer II selected from the group consisting of (meth)acrylic acid, itaconic acid, and an itaconic acid monoester, and 0 to 90% by mass of structural units (3) derived from at least one monomer III selected from the group consisting of (meth)acrylates and itaconic acid diesters, A pigment dispersant which is a vinyl copolymer having a number average molecular weight of 5,000 to 30,000 and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.1 to 2.5, and in which carboxyl groups in the molecule are neutralized with an alkali and dissolve in water.

2. the content of the structural unit (1) is 10 to 40% by mass, the content of the structural unit (2) is 5 to 20% by mass, and the content of the structural unit (3) is 50 to 85% by mass, 2. The pigment dispersant according to claim 1, which has a number average molecular weight of 10,000 to 25,000 and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.3 to 2.

3.

3. 2. The pigment dispersant according to claim 1, wherein the monomer III is at least one selected from the group consisting of ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, isobornyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, diethyl itaconate, and dibutyl itaconate.

4. A pigment dispersion containing a pigment, a dispersant, a water-soluble organic solvent, and water, A pigment dispersion liquid, wherein the dispersant is the pigment dispersant according to any one of claims 1 to 3.

5. The content of the pigment is 5 to 60% by mass, The content of the dispersant is 0.5 to 20% by mass, The content of the water-soluble organic solvent is 30% by mass or less, The water content is 20 to 80% by mass. The pigment dispersion of claim 4 used to prepare an aqueous ink-jet ink.

6. 6. The pigment dispersion liquid according to claim 5, wherein the water-soluble organic solvent is at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide.

7. the pigment is at least one selected from the group consisting of a yellow pigment, a red pigment, a blue pigment, a green pigment, an orange pigment, a black pigment, and a white pigment; The yellow pigment is at least one selected from the group consisting of C.I. Pigment Yellow 74, 150, 155, and 180; The red pigment is at least one selected from the group consisting of C.I. Pigment Red 122, 202, 254, 269, solid solutions thereof, C.I. Pigment Violet 19, 23, and solid solutions thereof; The blue pigment is at least one selected from the group consisting of C.I. Pigment Blue 15:3, 15:4, and 15:6; The green pigment is at least one selected from the group consisting of C.I. Pigment Green 7, 36, and 58; The orange pigment is C.I. Pigment Orange 43; The black pigment is C.I. Pigment Black 7; 6. The pigment dispersion according to claim 5, wherein the white pigment is C.I. Pigment White 6.

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