Binder component, emulsion, pigment fluid dispersion, and aqueous inkjet ink

Abstract

To provide a binder component capable of preparing an aqueous inkjet ink for printing on a paper medium excellent in dispersibility and storage stability of a pigment, capable of recording an image excellent in fixability, adhesion and water resistance, and excellent in discharge stability and clog recoverability.SOLUTION: A binder component mixed in an aqueous inkjet ink used for printing on a paper medium is a methacrylate polymer satisfying the following (1) to (3). (1) The methacrylate polymer is an AB block copolymer having a ratio of a number average molecular weight of a polymer block A to a number average molecular weight of a polymer block B of 5.0 to 15.0. (2) The polymer block A is a water-insoluble polymethacrylate including a constitutional unit (A-1) derived from alkyl methacrylate. (3) The polymer block B is a polymethacrylate including a constitutional unit (B-1) derived from a methacrylic acid, which turns into water-insoluble by neutralizing with an alkali.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a binder component, an emulsion, a method for producing the emulsion, a pigment dispersion, and an aqueous inkjet ink. [Background technology]

[0002] For writing and printing on paper media, organic solvent-based and water-based pigment inks are used from the viewpoint of water resistance, etc. Among them, water-based inks are often used from the viewpoint of odor and other problems and environmental friendliness. From the viewpoints of fixation to paper media, water resistance, abrasion resistance, gloss, etc., a binder component for forming a film is blended into the ink. As water-based inks for printing images and the like on paper media, water-based inkjet inks are used, which have design properties and can produce colorful and highly appealing printed matter.

[0003] As the functionality of recording devices has increased, the uses of recording devices such as printers equipped with aqueous inkjet inks (hereinafter also referred to simply as "inks") have become more diverse, including personal use, office use, business use, recording, color display, industrial use, packaging, and color photography. Recording devices for personal and office use mainly print on paper media and have traditionally been used as aqueous inkjet recording devices. Currently, printing methods, recording heads, inks, and the like are being actively developed to meet the demands for higher speeds, higher clarity, better color development, and higher fineness.

[0004] Ink contains a polymer as a binder component, which is a film-forming component. By incorporating a polymer as a binder component into ink, it is possible to achieve print (image) properties such as fixation, drying, gloss, high color development, water resistance, chemical resistance, and marker resistance. In addition, low-viscosity ink is required from the standpoints of ejection stability from the recording head, clogging recovery, resolubility, and the like, and there is a demand for the development of a polymer for the binder component that does not hinder the low viscosity of the ink.

[0005] As binder components for inks, various polymers have been developed. For example, emulsions and aqueous dispersions of polymers such as styrene (meth)acrylate-based, (meth)acrylate-based, and urethane-based polymers are known. And as styrene (meth)acrylate-based and (meth)acrylate-based polymers, emulsions using emulsifiers, emulsions using reactive emulsifiers, and emulsions obtained by polymerizing monomers in the presence of water-soluble polymers have been proposed (Patent Documents 1 to 5).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when preparing an emulsion using an emulsifier, problems such as the easy generation of bubbles are likely to occur. Also, in the case of inks prepared using conventional emulsions prepared with emulsifiers, the recording head is likely to become clogged due to drying, and it has been difficult to redissolve the resulting clogging. Furthermore, the ejection stability of the ink is likely to decrease, and unevenness and streaks may easily occur in the obtained image.

[0008] The present invention has been made in view of the problems of such prior art, and the problem to be solved is to provide a binder component capable of preparing an aqueous inkjet ink for paper medium printing that is excellent in pigment dispersibility and storage stability, and capable of recording an image excellent in fixing property, adhesion property, and water resistance, and having excellent ejection stability and clogging recovery property.

[0009] Another problem to be solved by the present invention is to provide an emulsion using this binder component, a method for producing the same, an aqueous inkjet ink, and a pigment dispersion liquid suitably used for this aqueous inkjet ink.

Means for Solving the Problems

[0010] That is, according to the present invention, the following binder component is provided. [1] A binder component to be blended in an aqueous inkjet ink used for printing on a paper medium, which is a methacrylate polymer satisfying the following (1) to (3). (1) Having a polymer block A and a polymer block B, The ratio (MnA / MnB) of the number average molecular weight (MnA) of the polymer block A to the number average molecular weight (MnB) of the polymer block B is 5.0 to 15.0, It is an AB block copolymer having a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.1 to 1.6. (2) The polymer block A contains 40 to 70% by mass of a structural unit (A-1) derived from an alkyl methacrylate having an alkyl group having 8 to 18 carbon atoms, and a structural unit (A-2) derived from at least one selected from the group consisting of an alkyl methacrylate having a linear alkyl group having 1 to 6 carbon atoms, a branched alkyl methacrylate, a cycloalkyl methacrylate having a cycloalkyl group having 6 to 18 carbon atoms, an alkyl cycloalkyl methacrylate having an alkyl cycloalkyl group having 6 to 18 carbon atoms, an aromatic ring-containing methacrylate, and a cyclic ether group-containing methacrylate. The water-insoluble polymethacrylate has a total content of the constitutional unit (A-1) and the constitutional unit (A-2) of 90% by mass or more, a number average molecular weight of 5,000 to 20,000, a molecular weight distribution of 1.05 to 1.5, and a glass transition temperature of 0°C or lower. (3) The polymer block B contains 30 to 60% by mass of a constitutional unit (B-1) derived from methacrylic acid, is a polymethacrylate having a number average molecular weight of 500 to 3,000, a glass transition temperature of 50°C or higher, and being water-soluble after being neutralized with an alkali. [2] The polymer block A contains a constitutional unit (A-1) derived from lauryl methacrylate and a constitutional unit (A-2) derived from at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. The polymer block B further contains a constitutional unit (B-2) derived from at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. The binder component according to [1] above. [3] The alkali is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide. The binder component according to [1] or [2] above.

[0011] Further, according to the present invention, an emulsion shown below and a method for producing the same are provided. [4] An emulsion containing a liquid medium and emulsion particles formed of a polymer dispersed or emulsified in the liquid medium, wherein the polymer is a methacrylate polymer which is the binder component described in any one of [1] to [3], the liquid medium is an aqueous liquid medium containing at least one water-soluble solvent selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether and water, the content of the water-soluble solvent with respect to 100 parts by mass of the methacrylate polymer is 5 to 100 parts by mass, and the number average particle diameter of the emulsion particles measured by the dynamic light scattering method is 20 to 150 nm. [5] The emulsion according to [4] above, which is at 25 °C and has a viscosity of 10 to 100 mPa·s when the content of the methacrylate polymer is 25% by mass. [6] A method for producing the emulsion according to [4] or [5] above, which comprises carrying out living radical polymerization in a reaction system containing 20 to 40% by mass of the water-soluble solvent and 60 to 75% by mass of the monomers constituting the methacrylate polymer, and then adding and neutralizing the aqueous solution containing an alkali to self-emulsify the produced methacrylate polymer to form the emulsion particles.

[0012] Furthermore, according to the present invention, the following pigment dispersion is provided. [7] A pigment dispersion containing a pigment and a pigment dispersant for dispersing the pigment, wherein the pigment dispersant is a polymer satisfying the following (4) to (6). (4) Having a polymer chain A and a polymer chain B, The ratio (MnB / MnA) of the number average molecular weight (MnB) of the polymer chain B to the number average molecular weight (MnA) of the polymer chain A is 1.0 to 3.0, It is an AB block copolymer having a number average molecular weight of 6,000 to 15,000 and a molecular weight distribution of 1.2 to 2.0. (5) The polymer chain A contains 80% by mass or more of a structural unit (a-1) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, a water-insoluble polymethacrylate having a number average molecular weight of 500 to 6,000 and a molecular weight distribution of 1.1 to 1.8. (6) The polymer chain B contains 10 to 40% by mass of a structural unit (b-1) derived from methacrylic acid and a structural unit (b-2) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, methyl methacrylate, ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, and a polymethacrylate in which the total content of the structural unit (b-1) and the structural unit (b-2) is 90% by mass or more, having a number average molecular weight of 3,000 to 10,000, and being water-soluble after being neutralized with an alkali.

[0013] Further, according to the present invention, there is provided an aqueous inkjet ink shown below. [8] An aqueous inkjet ink used for printing on a paper medium, containing a pigment or a pigment dispersion liquid in which the pigment is dispersed with a pigment dispersant, water, a water-soluble organic solvent, and a binder component, wherein the binder component is the binder component according to any one of [1] to [3]. [9] The aqueous inkjet ink according to [8], wherein the pigment dispersion liquid is the pigment dispersion liquid according to [7]. [Advantages of the Invention]

[0014] According to the present invention, it is possible to provide a binder component capable of preparing an aqueous inkjet ink for printing on a paper medium, which is excellent in dispersion stability and storage stability of a pigment, and excellent in ejection stability and clogging recovery property, and capable of recording an image excellent in fixing property, adhesion property, and water resistance.

[0015] Further, according to the present invention, there can be provided an emulsion using this binder component, a method for producing the same, an aqueous inkjet ink, and a pigment dispersion suitably used for this aqueous inkjet ink.

Embodiments for Carrying Out the Invention

[0016] <Binder Component> Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. One embodiment of the binder component of the present invention is a binder component blended in an aqueous inkjet ink used for printing on a paper medium, and is a methacrylate polymer satisfying the following (1) to (3). Hereinafter, the details of the binder component of this embodiment will be described. (1) It has polymer block A and polymer block B, The ratio (MnA / MnB) of the number average molecular weight (MnA) of polymer block A to the number average molecular weight (MnB) of polymer block B is 5.0 to 15.0, It is an AB block copolymer having a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.1 to 1.6. (2) Polymer block A contains 40 to 70% by mass of a structural unit (A-1) derived from an alkyl methacrylate having an alkyl group having 8 to 18 carbon atoms, and a structural unit (A-2) derived from at least one selected from the group consisting of an alkyl methacrylate having a linear alkyl group having 1 to 6 carbon atoms, a branched alkyl methacrylate, a cycloalkyl methacrylate having a cycloalkyl group having 6 to 18 carbon atoms, an alkyl cycloalkyl methacrylate having an alkyl cycloalkyl group having 6 to 18 carbon atoms, an aromatic ring-containing methacrylate, and a cyclic ether group-containing methacrylate, The total content of the structural unit (A-1) and the structural unit (A-2) is 90% by mass or more, the number average molecular weight is 5,000 to 20,000, the molecular weight distribution is 1.05 to 1.5, and the glass transition temperature is 0°C or lower, and it is a water-insoluble polymethacrylate. (3) The polymer block B contains 30 to 60% by mass of structural units (B-1) derived from methacrylic acid, It is a polymethacrylate having a number average molecular weight of 500 to 3,000, a glass transition temperature of 50°C or higher, and being neutralized with an alkali to become water-soluble.

[0017] The methacrylate polymer which is the binder component of this embodiment is an AB block copolymer mainly composed of a structural unit derived from methacrylic acid and a structural unit derived from methacrylate which is an ester of methacrylic acid. By making the polymer block A and the polymer block B constituting the AB block copolymer have different performances, characteristics different from those of conventional binders can be exhibited. The polymer block A is a water-insoluble polymer block having a film-forming ability, and fixability and adhesiveness to a recording medium (paper medium). Further, the polymer block A is a polymer block capable of improving the scratch resistance, marker resistance, and water resistance of an image. The polymer block B is a water-soluble polymer block that functions as a film-forming component and also functions as a component that stably emulsifies and disperses the methacrylate polymer as a binder component in water. Furthermore, the polymer block B is a polymer block capable of improving characteristics such as ink ejection stability, redissolubility, and clogging prevention by stably dispersing particles such as pigments.

[0018] (AB block copolymer) The methacrylate polymer which is the binder component of this embodiment is an AB block copolymer having a polymer block A and a polymer block B. And the ratio (MnA / MnB) of the number average molecular weight (MnA) of the polymer block A to the number average molecular weight (MnB) of the polymer block B is 5.0 to 15.0, preferably 6.0 to 12.0. The number average molecular weight and weight average molecular weight in this specification are values in terms of polystyrene measured by gel permeation chromatography unless otherwise specified.

[0019] The number average molecular weight of polymer block A is larger than that of polymer block B. By increasing the molecular weight of the water-insoluble (hydrophobic) polymer block A, the water resistance of the image can be improved. In addition, polymer block A can be dispersed and emulsified in water in the form of nano-sized particles, and the dispersed particles can be stabilized by polymer block B.

[0020] When the value of MnA / MnB is less than 5.0, the particles become too small, the viscosity of the emulsion increases, and it becomes difficult to lower the viscosity. On the other hand, when the value of MnA / MnB exceeds 10.0, the proportion of the hydrophobic polymer block A becomes excessive, and it becomes difficult to stabilize the dispersed state of the particles.

[0021] The molecular weight distribution (weight average molecular weight / number average molecular weight) of the methacrylate-based polymer (AB block copolymer) is 1.1 to 1.6, preferably 1.15 to 1.3. When the molecular weight distribution of the AB block copolymer exceeds 1.6, the number average molecular weight of polymer block B goes out of the desired range, and it becomes difficult to lower the viscosity.

[0022] (Polymer block A) Polymer block A contains a structural unit (A-1) derived from an alkyl methacrylate having an alkyl group with 8 to 18 carbon atoms. By containing such a structural unit (A-1), polymer block A is soft and has a low glass transition temperature, which contributes to the fixing property and adhesion to the paper medium. In addition, since polymer block A is water-insoluble, the methacrylate-based polymer can be made into particles, emulsified and dispersed in water to form a low-viscosity emulsion.

[0023] Examples of alkyl methacrylates having an alkyl group with 8 to 18 carbon atoms include methacrylate esters of linear and branched hydrocarbon alcohols such as octyl methacrylate, 2-ethyl methacrylate, decyl methacrylate, isodecyl methacrylate, dimethyldecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, hexadecyl methacrylate, and octadecyl methacrylate. Among them, lauryl methacrylate is preferred as the alkyl methacrylate having an alkyl group with 8 to 18 carbon atoms. That is, polymer block A preferably contains a structural unit (A-1) derived from lauryl methacrylate. The glass transition temperature (Tg) of the homopolymer of lauryl methacrylate is -62°C. By including such a structural unit (A-1) derived from lauryl methacrylate, a more softened polymer block A can be obtained. In addition, lauryl methacrylate is a methacrylate of lauryl alcohol obtained from vegetable oils such as coconut oil and is a so-called biomass material. Therefore, by including a structural unit (A-1) derived from lauryl methacrylate, it is environmentally friendly and can contribute to carbon neutrality.

[0024] In polymer block A, the content of the structural unit (A-1) is 40 to 70% by mass, preferably 50 to 66.6% by mass. When the content of the structural unit (A-1) is less than 40% by mass, the softness of polymer block A becomes insufficient, and at the same time, the viscosity of the emulsion increases, making it difficult to lower the viscosity. On the other hand, when the content of the structural unit (A-1) exceeds 70% by mass, polymer block A may become too soft and turn sticky or liquid, and problems such as image stickiness are likely to occur.

[0025] Polymer block A contains a structural unit (A-2) derived from a methacrylate other than the alkyl methacrylate having an alkyl group with 8 to 18 carbon atoms as described above that constitutes the structural unit (A-1) (other methacrylates). The other methacrylates are at least one selected from the group consisting of alkyl methacrylates having a linear alkyl group with 1 to 6 carbon atoms, branched alkyl methacrylates, cycloalkyl methacrylates having a cycloalkyl group with 6 to 18 carbon atoms, alkyl cycloalkyl methacrylates having an alkyl cycloalkyl group with 6 to 18 carbon atoms, aromatic ring-containing methacrylates, and cyclic ether group-containing methacrylates.

[0026] Examples of the alkyl methacrylate having a linear alkyl group with 1 to 6 carbon atoms include methyl methacrylate, ethyl methacrylate, butyl methacrylate, and hexyl methacrylate. Examples of the branched alkyl methacrylate include isopropyl methacrylate, isobutyl methacrylate, and t-butyl methacrylate. Examples of the cycloalkyl methacrylate having a cycloalkyl group with 6 to 18 carbon atoms include cyclohexyl methacrylate, tricyclodecyl methacrylate, and isobornyl methacrylate. Examples of the alkyl cycloalkyl methacrylate having an alkyl cycloalkyl group with 6 to 18 carbon atoms include 4-butylcyclohexyl methacrylate and trimethylcyclohexyl methacrylate. Examples of the aromatic ring-containing methacrylate include phenyl methacrylate, benzyl methacrylate, phenylethyl methacrylate, and phenoxyethyl methacrylate. Examples of the cyclic ether group-containing methacrylate include furfuryl methacrylate, tetrahydrofurfuryl methacrylate, and tetrahydropyranyl methacrylate.

[0027] As other methacrylates, at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate is preferable. That is, the polymer block A preferably contains a structural unit (A-2) derived from at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. By including such a structural unit (A-2), the softening of the polymer block A can be adjusted, and adhesiveness can be exhibited without inhibiting the reduction in the viscosity of the ink.

[0028] Ethyl methacrylate is an esterified product using ethanol as an alcohol. This ethanol is an alcohol obtained by fermenting biomass such as sugarcane, corn, and wood. Tetrahydrofurfuryl methacrylate is an esterified product of tetrahydrofurfuryl alcohol. This tetrahydrofurfuryl alcohol is an alcohol industrially obtained by a hydrogenation reaction of furfural contained in the cob of corn or the bagasse of sugarcane with a catalyst. Isobornyl methacrylate is an esterified product using isoborneol as an alcohol. This isoborneol is a plant-derived alcohol obtained from camphene obtained from rosin or the like. That is, ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate are all so-called biomass materials. Therefore, by including the structural unit (A-2) derived from these methacrylates, it is possible to be environmentally friendly and contribute to carbon neutrality.

[0029] In polymer block A, the total content of structural unit (A-1) and structural unit (A-2) is 90% by mass or more, preferably 100% by mass. That is, polymer block A is preferably substantially composed of only structural unit (A-1) and structural unit (A-2). Note that polymer block A may contain other structural units other than structural unit (A-1) and structural unit (A-2) as necessary, as long as the intended effects are not impaired. As monomers constituting the other structural units, methacrylic acid and methacrylate monomers (excluding the monomers constituting structural unit (A-1) and structural unit (A-2)) can be used. However, if the content of the structural unit derived from methacrylic acid is large, polymer block A is likely to dissolve in water. Therefore, the content of the structural unit derived from methacrylic acid in polymer block A is preferably less than 3% by mass. Examples of the methacrylate monomer include hydroxyl group-containing methacrylates such as hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate; polyalkylene glycol monoalkyl methacrylates such as polyethylene glycol monomethyl ether methacrylate; amino group-containing methacrylates such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; and the like.

[0030] The number average molecular weight of polymer block A is 5,000 to 20,000, preferably 6,000 to 15,000. When the number average molecular weight of polymer block A is less than 5,000, properties such as adhesion and abrasion resistance become insufficient, and since the molecular weight is small, the particle diameter of the emulsion particles becomes too small, making it difficult to reduce the viscosity. On the other hand, when the number average molecular weight of polymer block A exceeds 20,000, emulsification and dispersion become difficult because the molecular weight is large.

[0031] The molecular weight distribution of polymer block A is from 1.05 to 1.5, preferably from 1.1 to 1.3. It is substantially difficult to obtain polymer block A with a molecular weight distribution of less than 1.05. On the other hand, when the molecular weight distribution of polymer block A exceeds 1.5, it cannot be sufficiently reduced in viscosity, and the particle size of the emulsion particles also becomes large.

[0032] The glass transition temperature (Tg) of polymer block A is 0 °C or lower, preferably -5 °C or lower, and more preferably -10 °C or lower. By setting the glass transition temperature to 0 °C or lower, polymer block A becomes soft, and the fixing property and adhesion to the paper medium can be enhanced. Further, because it is soft, even if polymerization is carried out so that the amount of polymer component increases, the solution viscosity does not become excessively high, and stirring during polymerization is easy.

[0033] The glass transition temperature (Tg) in this specification is a value (theoretical value) calculated from the Tg of the homopolymer. For example, in the case of a polymer (copolymer) obtained by copolymerizing x types of monomers, assuming the mass (g) of each monomer as "W1, W2, ··· Wx" and the Tg (°C) of the homopolymer of each monomer as "T1, T2, ··· Tx", the Tg (T (°C)) of this copolymer can be calculated from the following formula (A). 1 / T = W1 / (T1 + 273) + W2 / (T2 + 273) + ··· Wx / (Tx + 273) ··· (A)

[0034] As the value of the Tg of the homopolymer, the value described in "Polymer Handbook, 4th Edition" may be used, or alternatively, the values in various other documents may be used. In this specification, the value described in "Polymer Handbook, 4th Edition" is used.

[0035] (Polymer block B) Polymer block B contains a structural unit (B-1) derived from methacrylic acid. That is, a carboxy group derived from methacrylic acid is present in the structural unit (B-1). Therefore, polymer block B is a polymer block that becomes water-soluble by neutralizing this carboxy group with an alkali. Also, by including polymer block B having many carboxy groups, the emulsion dispersion stability of the methacrylate polymer is improved, and even if it dries, it can be redissolved by using a cleaning agent such as a liquid medium.

[0036] In polymer block B, the content of the structural unit (B-1) is 30 to 60% by mass, preferably 33.3 to 50% by mass. If the content of the structural unit (B-1) is less than 30% by mass, the water solubility of polymer block B is insufficient, making it difficult to emulsify and disperse polymer block A in water and resulting in insufficient redissolubility. Also, since the hydrophilicity of polymer block B is insufficient, the viscosity of the emulsion tends to increase. On the other hand, if the content of the structural unit (B-1) exceeds 60% by mass, the polymerization viscosity may increase due to the presence of a large amount of methacrylic acid during polymerization, making stirring difficult. Also, the hydrophilicity of the AB block copolymer (methacrylate polymer) may increase excessively, causing the viscosity of the emulsion to increase.

[0037] Polymer block B preferably further contains a structural unit (B-2) derived from at least one selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. By including such a structural unit (B-2), it is possible to contribute to being environmentally friendly and carbon-neutral without inhibiting the reduction of the ink viscosity.

[0038] The number average molecular weight of polymer block B is from 500 to 3,000, preferably from 1,000 to 2,500. By setting the number average molecular weight of polymer block B within this range, polymer block A can be sufficiently emulsified and dispersed. If the number average molecular weight of polymer block B is less than 500, polymer block A cannot be emulsified and dispersed, and the particle size of the emulsion particles may become excessively large or may precipitate. On the other hand, if the number average molecular weight of polymer block B exceeds 3,000, the viscosity of the emulsion may become excessively high. The number average molecular weight (MnB) of polymer block B is the value obtained by subtracting the number average molecular weight (MnA) of polymer block A from the overall number average molecular weight (Mn) of the AB block copolymer (MnB = Mn - MnA).

[0039] The glass transition temperature (Tg) of polymer block B is 50°C or higher, preferably 100°C or higher. Since the glass transition temperature of polymer block B is higher than that of polymer block A, even if polymer block A is soft, an image with low tack and suppressed stickiness can be recorded. If the glass transition temperature of polymer block B is less than 50°C, the recorded image may be sticky.

[0040] As the alkali for neutralizing polymer block B, conventionally known alkalis can be used. Examples of the alkali include ammonia; organic amines such as triethylamine and diethanolamine; alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; and the like. Among them, the alkali is preferably at least one selected from the group consisting of sodium hydroxide and potassium hydroxide. Note that all carboxy groups in polymer block B may be neutralized with an alkali, or may be partially neutralized within the range where water solubility is achieved. Further, it may be used in combination with other alkalis such as ammonia. The carboxy groups neutralized with sodium hydroxide or potassium hydroxide become sodium salts or potassium salts. Therefore, even when dried, it is difficult to return to carboxy groups, and it exists as a salt, maintaining water solubility. For this reason, even when the recording head dries and clogging occurs, it can be easily redissolved.

[0041] <Emulsion> Next, the emulsion of the present invention will be described. One embodiment of the emulsion of the present invention contains a liquid medium and emulsion particles formed of a polymer dispersed or emulsified in the liquid medium, and the polymer is a methacrylate-based polymer which is the binder component described above.

[0042] As described above, in the methacrylate-based polymer which is the binder component, polymer block B is neutralized with an alkali and ionized, and water-insoluble polymer block A becomes particles and is dispersed and emulsified in an aqueous liquid medium containing water. In order to disperse and emulsify in a good state, as the liquid medium, an aqueous liquid medium containing a water-soluble solvent and water is used. The water-soluble solvent is at least one selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether. Among them, it is preferable to use diethylene glycol monobutyl ether. Since diethylene glycol monobutyl ether has a relatively small molecular weight, the viscosity of the emulsion can be reduced.

[0043] The content of the water-soluble solvent relative to 100 parts by mass of the methacrylate polymer is 5 to 100 parts by mass, preferably 10 to 50 parts by mass. By setting the content of the water-soluble solvent within the above range relative to 100 parts by mass of the methacrylate polymer, the dispersion and emulsification of the emulsion particles can be promoted, and the emulsion particles can be stabilized. If the content of the water-soluble solvent is less than 5 parts by mass, the stability of the emulsion particles will decrease. On the other hand, if the content of the water-soluble solvent exceeds 100 parts by mass, it will be difficult to reduce the viscosity of the emulsion.

[0044] The emulsion can further contain other water-soluble solvents other than the above-mentioned water-soluble solvent. Examples of other water-soluble solvents include alcohol-based solvents such as methanol, ethanol, and isopropanol; polyhydric glycol-based solvents such as ethylene glycol, propylene glycol, dipropylene glycol, glycerin, and 1,2-hexanediol; glycol ether-based solvents such as propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and propylene glycol monopropyl ether; amide-based solvents such as pyrrolidone and 3-methoxy-N,N-dimethylpropionamide; urea-based solvents such as tetramethylurea; and the like.

[0045] The number average particle diameter of the emulsion particles in the emulsion measured by the dynamic light scattering method is 20 to 150 nm, preferably 30 to 100 nm. If the number average particle diameter of the emulsion particles is less than 20 nm, the particles are too fine, so the viscosity of the emulsion tends to increase. On the other hand, if the number average particle diameter of the emulsion particles exceeds 150 nm, the recording head is likely to be clogged.

[0046] The emulsion can be blended with conventionally known compounding agents. Examples of the compounding agents include surfactants, defoamers, leveling agents, wax components, and organic solvents other than the aforementioned water-soluble solvents.

[0047] When the emulsion of the present embodiment is at 25°C and the content of the methacrylate polymer (binder component) is 25% by mass, the viscosity is preferably 10 to 100 mPa·s, more preferably 15 to 50 mPa·s. It is substantially difficult to prepare an emulsion with a viscosity of less than 10 mPa·s. On the other hand, when the viscosity of the emulsion exceeds 100 mPa, the viscosity of the ink using the emulsion may increase excessively.

[0048] (Method for producing emulsion) The emulsion of the present embodiment can be produced according to the method shown below. That is, one embodiment of the method for producing the emulsion of the present invention is living radical polymerization in a reaction system containing 20 to 40% by mass of the above-mentioned water-soluble solvent and 60 to 75% by mass of the monomers constituting the methacrylate polymer as the binder component, and then adding an aqueous solution containing an alkali to neutralize and self-emulsifying the produced methacrylate polymer to form emulsion particles. One of the characteristics of the method for producing the emulsion of the present embodiment is living polymerization in the presence of a relatively high concentration of monomers.

[0049] The content of the water-soluble solvent in the reaction system is 20 to 40% by mass, preferably 30 to 35% by mass. When the content of the water-soluble solvent in the reaction system is less than 20% by mass, the viscosity of the reaction system (polymerization solution) becomes too high, stirring becomes difficult, and the polymerization rate decreases. On the other hand, when the content of the water-soluble solvent in the reaction system exceeds 40% by mass, the viscosity of the resulting emulsion may increase.

[0050] By synthesizing through living radical polymerization, a methacrylate polymer with a desired molecular weight and molecular weight distribution can be obtained. It is difficult to obtain a polymer with a block structure by ordinary radical polymerization, but by using living radical polymerization, a methacrylate polymer which is an AB block copolymer having a desired block structure can be obtained.

[0051] Examples of this living radical polymerization method include the nitroxide method (NMP method) that utilizes the dissociation and recombination of amine oxide radicals; the atom transfer radical polymerization method (ATRP method) that uses heavy metals such as copper, ruthenium, nickel, and iron, and ligands that form complexes with these heavy metals, and polymerizes using a halogen compound as an initiator compound; the reversible addition-fragmentation chain transfer polymerization method (RAFT method) that uses a dithiocarboxylic acid ester or the like as an initiator compound and uses an addition-polymerizable monomer and a radical initiator for polymerization; the TERP method that uses an organic tellurium compound as an initiator compound and uses ditelluride as a catalyst; the reversible transfer catalysis polymerization method (RTCP method, RCMP method) that uses at least one of iodine and iodine compounds as a polymerization initiator compound and uses a commercially available organic compound that can become a radical as a catalyst; and the like. Among them, the TERP method, the RTCP method, and the RAFT method are suitable for the molecular weight control and block structuring of methacrylate-based polymers, and the RTCP method that uses inexpensive raw materials and uses an organic compound as a catalyst is particularly preferred.

[0052] After forming polymer block A, monomers for forming polymer block B are added to form polymer block B, and the target methacrylate-based polymer can be obtained. Note that polymer block A may be formed after forming polymer block B.

[0053] After forming an AB block copolymer (methacrylate-based polymer), preferably while vigorously stirring, an aqueous solution containing an alkali (alkali aqueous solution) is added for neutralization, and the methacrylate-based polymer is self-emulsified to form emulsion particles. Thereby, a desired emulsion can be obtained. After adding the alkali aqueous solution, it may be heated as necessary while stirring sufficiently. The content of the methacrylate-based polymer in the obtained emulsion is preferably controlled to be 30% by mass or less, and more preferably controlled to be 27.5% by mass or less. By appropriately controlling the content of the methacrylate-based polymer, the viscosity of the obtained emulsion can be lowered, and handling can be facilitated.

[0054] <Water-based inkjet ink> One embodiment of the water-based inkjet ink of the present invention is an ink used for printing on a paper medium, and contains a pigment or a pigment dispersion liquid in which a pigment is dispersed with a pigment dispersant, water, a water-soluble organic solvent, and a binder component. And the binder component is the aforementioned binder component (methacrylate polymer). By using the above-mentioned methacrylate polymer as the binder component, it is possible to obtain an ink for printing on a paper medium that is excellent in ejection stability and clogging recovery property and can record an image excellent in fixing property, adhesion property, and water resistance.

[0055] (Paper medium) Since the methacrylate polymer used as the binder component is relatively soft, the ink of this embodiment has good fixing property and adhesion property to the paper medium. In addition, it can also be printed on non-absorbent media such as plastic films. However, since the binder component is soft and has a polymer block A containing many structural units (A-1) derived from alkyl methacrylates having an alkyl group with 8 to 18 carbon atoms, properties such as abrasion resistance and alcohol resistance may be slightly inferior. On the other hand, when printing on a paper medium, since the soft methacrylate polymer can penetrate and adhere to the fiber surface and inside of the paper medium, properties such as abrasion resistance can be greatly improved.

[0056] As the paper medium, paper mainly composed of cellulose can be used. More specifically, plain paper, neutral paper, acid paper, cardboard, Japanese paper, paperboard, coated paper, matte paper, high-quality paper, kraft paper, and Kent paper can be mentioned. In addition, inkjet paper or glossy paper provided with an ink receiving layer on the paper can also be used. Furthermore, synthetic paper such as Yupo paper can also be used.

[0057] (Colorant: Pigment) The ink contains a colorant. As the colorant, a pigment or a pigment dispersion liquid in which the pigment is dispersed with a pigment dispersant is used. The pigment needs to be dispersed in the ink. For this reason, as the pigment, it is preferable to use a self-dispersing pigment in which hydrophilic groups such as a polyethylene glycol chain, a carboxy group, a phosphoric acid group, and a sulfonic acid group are bonded to the surface and which can be neutralized with an alkali and dispersed in water. A silane coupling agent having a hydrophilic group can be reacted with the pigment, the pigment can be added to sulfuric acid and sulfonated, or an aromatic diazonium salt having these hydrophilic groups bonded thereto can be coupled to an aromatic ring in the structure of the pigment, whereby the hydrophilic group can be introduced onto the surface.

[0058] As the pigment, an organic pigment or an inorganic pigment can be used. Examples of the organic pigment include a soluble azo pigment, an insoluble azo pigment, a phthalocyanine pigment, a quinacridone pigment, an isoindolinone pigment, an isoindoline pigment, a perylene pigment, a perinone pigment, a dioxazine pigment, an anthraquinone pigment, a dianthraquinonyl pigment, an anthrapyrimidine pigment, an ansanthrone pigment, an indanthrone pigment, a flavanthrone pigment, a pyranthrone pigment, a diketopyrrolopyrrole pigment, and a solid solution pigment thereof. Examples of the inorganic pigment include titanium dioxide, iron oxide, antimony pentoxide, zinc oxide, silica, cadmium sulfide, calcium carbonate, barium carbonate, barium sulfate, clay, talc, lead yellow, carbon black, aluminum flake, and mica pigment.

[0059] Examples of the pigments used in common inkjet inks include C.I. Pigment Blue 15:3, 15:4, 15:6; C.I. Pigment Red 122, 176, 254, 269, 291; C.I. Pigment Violet 19, 23; C.I. Pigment Yellow 74, 150, 155, 180; C.I. Pigment Green 36, 58; C.I. Pigment Orange 43, 71; C.I. Pigment Black 7; C.I. Pigment White 6; etc.

[0060] The number average particle diameter (primary particle diameter) of the organic pigment is preferably 150 nm or less. The number average particle diameter (primary particle diameter) of the inorganic pigment is preferably 300 nm or less. By using a pigment with a number average particle diameter within the above range, the optical density, chroma, color development property, and printing quality of the recorded image can be improved, and sedimentation of the pigment in the ink can be moderately suppressed. The number average particle diameter of the pigment can be measured using, for example, an electron microscope, a light scattering particle size distribution meter, or the like.

[0061] The content of the organic pigment in the ink is preferably 1 to 5% by mass. Also, the content of the inorganic pigment in the ink is preferably 1 to 10% by mass.

[0062] (Colorant: Pigment dispersion liquid) Even when using a pigment dispersion liquid as the colorant, the above-mentioned pigments can be used. As the pigment dispersant for dispersing the pigment, conventional dispersants such as surfactants and polymer-type pigment dispersants can be used. As the polymer-type pigment dispersant, polymers having a random structure, block structure, and graft structure such as polystyrene maleic acid and its esterified products, polystyrene acrylic acid type, polystyrene acrylate acrylic acid type, polystyrene methacrylic acid type, polystyrene methacrylate methacrylic acid type, poly(meth)acrylic acid type, poly(meth)acrylate (meth)acrylic acid type, polyvinyl pyrrolidone type, carboxymethyl cellulose type, polyurethane type, and polyether type can be used. When using a pigment dispersion liquid as the colorant, the content of the pigment dispersant in the ink is preferably 0.1 to 5% by mass.

[0063] In the case of an aqueous inkjet ink containing a pigment dispersion using a conventional dispersant, the ejection stability, redissolubility, and viscosity reduction may be somewhat insufficient. And even when the above-mentioned methacrylate polymer is used as a binder component, it may be difficult to sufficiently improve these properties. Therefore, as the pigment dispersion, it is preferable to use the following pigment dispersion containing a specific AB block copolymer as a pigment dispersant. Thereby, the viscosity of the ink can be reduced without inhibiting the properties of the methacrylate polymer as the binder component, and the properties of the aqueous inkjet ink such as ejection stability and redissolubility can be further improved.

[0064] (Liquid medium) The ink contains a liquid medium containing water and a water-soluble organic solvent. The content of the water-soluble organic solvent in the ink is preferably 5 to 30% by mass.

[0065] (Binder component) The ink contains the above-mentioned methacrylate polymer as a binder component. When preparing the ink, it is preferable to blend the binder component in the state of the above-mentioned emulsion. The content of the binder component (methacrylate polymer) in the ink is preferably 1 to 10% by mass.

[0066] If necessary, it may further contain a binder component other than the methacrylate polymer (other binder components). Examples of other binder components include polymers such as acrylic polymers, styrene-acrylic polymers, urethane polymers, polyester polymers, and polyolefin polymers. These polymers can be used in the form of aqueous solutions, aqueous dispersions, and emulsions.

[0067] (Additive) The ink can contain various additives used in general aqueous inkjet inks. Examples of the additives include surfactants, organic solvents, humectants, pigment derivatives, dyes, leveling agents, defoaming agents, ultraviolet absorbers, preservatives, antibacterial agents, and waxes. As the surfactant, ether-based nonionic surfactants such as polyethylene glycol alkyl ethers and acetylene-based surfactants, silicone-based surfactants, and fluorine-based surfactants can be used. The content of the surfactant in the ink is preferably 0.1 to 2% by mass.

[0068] Examples of the wax include polyethylene wax, polyolefin wax, and silicone wax. Among them, it is preferable to use polyethylene wax. Since polyethylene wax has high hydrophobicity, an image with excellent durability can be recorded by using an ink containing polyethylene wax. Polyethylene wax can be used, for example, in the form of a dispersion (polyethylene wax emulsion) dispersed in water. The content of polyethylene wax in the ink is preferably 0.1 to 2.5% by mass, more preferably 0.3 to 1.5% by mass based on the total amount of the ink.

[0069] By blending various components to a predetermined amount, stirring well using a disper or the like, and then removing coarse particles and dust through a filter, the target aqueous inkjet ink can be obtained.

[0070] (Physical properties of the ink) The ink is adjusted to an appropriate viscosity that can be ejected by an inkjet method from the nozzles of the recording head according to the type of pigment and the like. For example, when an organic pigment is used, the viscosity of the ink at 25°C is preferably 2 to 10 mPa·s. When an inorganic pigment is used, the viscosity of the ink at 25°C is preferably 5 to 30 mPa·s. The viscosity of the ink can be controlled, for example, by adjusting the content of the water-soluble organic solvent used. Note that it is preferable to keep the content of the glycol-based solvent in the ink constant. However, when adding a conventional binder component, the viscosity of the ink tends to increase. On the other hand, by using the above-mentioned binder component (methacrylate-based polymer), the viscosity of the ink can be reduced. The viscosity of the ink of this embodiment with reduced viscosity at 25°C is preferably 2.5 to 3.5 mPa·s.

[0071] The pH of the ink at 25°C is preferably 7.0 to 10.0, and more preferably 7.5 to 9.5. When the pH of the ink is less than 7.0, the pigment dispersant is likely to precipitate and the pigment may easily aggregate. On the other hand, when the pH of the ink exceeds 10.0, the alkalinity becomes strong and it may be difficult to handle.

[0072] The surface tension of the ink is appropriately set according to the performance of a recording device such as an inkjet printer. For example, the surface tension of the ink at 25°C is preferably 15 to 45 mN / m, and more preferably 20 to 40 mN / m.

[0073] <Pigment dispersion liquid> One embodiment of the pigment dispersion liquid of the present invention contains a pigment and a pigment dispersant for dispersing the pigment. As the pigment, the above-mentioned organic pigment or inorganic pigment can be used. And the pigment dispersant is a polymer that satisfies the following (4) to (6). (4) It has a polymer chain A and a polymer chain B, The ratio (MnB / MnA) of the number average molecular weight (MnB) of the polymer chain B to the number average molecular weight (MnA) of the polymer chain A is 1.0 to 3.0, It is an AB block copolymer having a number average molecular weight of 6,000 to 15,000 and a molecular weight distribution of 1.2 to 2.0. (5) The polymer chain A contains 80% by mass or more of a structural unit (a-1) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. It is a water-insoluble polymethacrylate having a number average molecular weight of 500 to 6,000 and a molecular weight distribution of 1.1 to 1.8. (6) The polymer chain B contains 10 to 40% by mass of a structural unit (b-1) derived from methacrylic acid and a structural unit (b-2) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, methyl methacrylate, ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, and the total content of the structural unit (b-1) and the structural unit (b-2) is 90% by mass or more. It is a polymethacrylate having a number average molecular weight of 3,000 to 10,000 and becoming water-soluble when neutralized with an alkali.

[0074] (AB block copolymer) The pigment dispersant is an AB block polymer having a polymer chain A and a polymer chain B. The polymer chain A is a water-insoluble polymer block. The polymer chain B is a water-soluble polymer block having a carboxy group derived from methacrylic acid, and at least a part of the carboxy group is neutralized with an alkali. Since the polymer chain A is a water-insoluble polymer block, it has high hydrophobicity and easily undergoes hydrophobic interaction with water-insoluble pigments. Therefore, the polymer chain A adsorbs to the pigment by hydrogen bonding or the like. Also, since the polymer chain A has a high molecular weight, it is difficult to desorb from the adsorbed pigment. Furthermore, since the polymer chain A adsorbs to the pigment and the polymer chain B dissolves in water, the finely dispersed pigments repel each other sterically, and the finely dispersed state of the pigment is maintained over a long period. Also, even when the amount of the dispersant free or dissolved in the liquid medium is small, since the water-insoluble polymer chain A forms particles, the ejection stability of the ink can be improved.

[0075] Also, even when the ink dries in a recording head or the like, the pigment dispersant, which is an AB block copolymer having a polymer chain B that is a water-soluble polymer block, is difficult to desorb from the adsorbed pigment. Therefore, aggregation of the pigment and film formation by the desorbed pigment dispersant can be suppressed, and it has excellent redissolubility and can be easily returned to the original dispersed state by adding an aqueous liquid medium.

[0076] The ratio (MnB / MnA) of the number average molecular weight (MnB) of the polymer chain B to the number average molecular weight (MnA) of the polymer chain A is 1.0 to 3.0, preferably 1.5 to 2.5. When the value of MnB / MnA is less than 1.0, the polymer itself tends to form particles in the aqueous medium, and the adsorptivity to the pigment decreases. On the other hand, when the value of MnB / MnA exceeds 300, even if the polymer chain A adsorbs to the pigment, the polymer chain B is likely to desorb, so the dispersion stability of the pigment decreases.

[0077] The number average molecular weight of the AB block copolymer is 6,000 to 15,000. If the number average molecular weight of the AB block copolymer is less than 6,000, it is likely to desorb from the pigment. On the other hand, if the number average molecular weight of the AB block copolymer exceeds 15,000, the viscosity may increase excessively during polymerization, or the viscosity of the pigment dispersion may increase excessively.

[0078] The molecular weight distribution (weight average molecular weight / number average molecular weight) of the AB block copolymer is 1.2 to 2.0, preferably 1.2 to 1.5. If the molecular weight distribution of the AB block copolymer exceeds 2.0, the dispersibility of the pigment will decrease.

[0079] (Polymer chain A) Polymer chain A contains 80 mass% or more, preferably 85 mass% or more of the structural unit (a-1) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. The structural unit (a-1) adsorbs to the pigment by hydrophobic interaction, π-π stacking, hydrogen bonding, etc. In addition, since both tetrahydrofurfuryl methacrylate and isobornyl methacrylate are biomass materials, including the structural unit (a-1) derived from these methacrylates can be environmentally friendly and contribute to carbon neutrality.

[0080] In polymer chain A, if the content of the structural unit (a-1) is less than 80 mass%, the adsorption to the pigment becomes insufficient and the dispersion stability of the pigment decreases. Note that polymer chain A may contain other structural units other than the structural unit (a-1) as necessary, as long as the intended effect is not impaired.

[0081] The number average molecular weight of polymer chain A is 500 to 6,000, preferably 1,000 to 5,000. If the number average molecular weight of polymer chain A is less than 500, the adsorption to the pigment is insufficient due to the small molecular weight. On the other hand, if the number average molecular weight of polymer chain A exceeds 6,000, the adsorption to the pigment may decrease slightly.

[0082] The molecular weight distribution of polymer chain A is from 1.1 to 1.8, preferably from 1.2 to 1.6. It is substantially difficult to obtain a polymer chain A with a molecular weight distribution of less than 1.1. On the other hand, when the molecular weight distribution of polymer chain A exceeds 1.8, the dispersion stability of the pigment decreases.

[0083] (Polymer chain B) Polymer chain B contains 10 to 40% by mass, preferably 15 to 30% by mass, of a structural unit (b-1) derived from methacrylic acid, and at least one structural unit (b-2) selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, methyl methacrylate, ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate. When the content of the structural unit (b-1) in the polymer chain B is less than 10% by mass, it may not dissolve in water even after neutralizing the carboxy group. On the other hand, when the content of the structural unit (b-1) exceeds 40% by mass, there are too many carboxy groups, so that the viscosity of the pigment dispersion or ink excessively increases and the water resistance of the image decreases.

[0084] By including the structural unit (b-2) in the polymer chain B, the dispersion stability of the pigment can be improved and the adhesion of the image can be enhanced. Also, in the polymer chain B, the total content of the structural unit (b-1) and the structural unit (b-2) is 90% by mass or more, preferably 100% by mass. That is, it is preferable that the polymer chain B is substantially composed only of the structural unit (b-1) and the structural unit (b-2).

[0085] The number average molecular weight of polymer chain B is from 3,000 to 10,000, preferably from 4,000 to 8,000. When the number average molecular weight of polymer chain B is less than 3,000, since the molecular weight of the water-soluble polymer chain is small, the dispersibility of the pigment becomes insufficient. On the other hand, when the number average molecular weight of polymer chain B exceeds 10,000, since the water-soluble polymer chain increases, the viscosity increases or the water resistance decreases. Further, even when polymer chain A is adsorbed on the pigment, since polymer chain B of the water-soluble polymer is too large, the pigment dispersant is likely to desorb from the pigment, and the dispersibility of the pigment decreases. The number average molecular weight (MnB) of polymer chain B is a value obtained by subtracting the number average molecular weight (MnA) of polymer chain A from the overall number average molecular weight (Mn) of the AB block copolymer (MnB = Mn - MnA).

[0086] As the alkali for neutralizing polymer chain B, conventionally known alkalis can be used. As the alkali, the same ones as those for neutralizing polymer block B of the aforementioned binder component (methacrylate polymer) can be preferably used. It is preferable that the alkali for neutralizing polymer chain B is the same as the alkali for neutralizing polymer block B of the aforementioned binder component (methacrylate polymer). When these alkalis are different, the neutralization ion pairs may be exchanged between the polymers, and the dispersibility of the pigment may become unstable or the viscosity may increase.

[0087] (Method for producing AB block copolymer) The above AB block copolymer used as a pigment dispersant can be produced by living radical polymerization, similar to the aforementioned methacrylate-based polymer. Among them, it is preferably produced by the TERP method, RTCP method, or RAFT method. The polymerization method may be any method such as solvent-free, solution polymerization, and emulsion polymerization. Among them, solution polymerization in an organic solvent is preferred, and solution polymerization in the same organic solvent as the water-soluble organic solvent to be blended in the pigment dispersion is more preferred. As the organic solvent, it is preferable to use the water-soluble organic solvent contained in the ink. Among them, glycol-based solvents are preferred, and it is more preferred to use diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, etc. used when polymerizing the methacrylate-based polymer. After solution polymerization, alkaline water is added to make an aqueous solution. Thereby, it can be used directly in the pigment dispersion without taking out the AB block copolymer.

[0088] (Dispersion medium) The pigment dispersion usually contains a dispersion medium (liquid medium). The dispersion medium is preferably an aqueous medium mainly composed of water. The aqueous medium may contain a water-soluble organic solvent for improving wettability and adjusting viscosity. As the water-soluble organic solvent, alcohol-based, polyhydric alcohol-based, glycol-based, amide-based, and urea-based solvents can be used.

[0089] (Other additives) The pigment dispersion may further contain various additives. Examples of the additives include organic solvents other than the above-mentioned water-soluble organic solvents, surfactants, preservatives, leveling agents, surface tension adjusters, pH adjusters, ultraviolet absorbers, light stabilizers, antioxidants, dyes, fillers, waxes, thickeners, defoamers, fungicides, and antistatic agents. Examples of the surfactants include silicone-based, acetylene glycol-based, fluorine-based, alkylene oxide-based, and hydrocarbon-based surfactants. Examples of the preservatives include sodium benzoate, benzimidazole, thiabendazole, potassium sorbate, sodium sorbate, sodium dehydroacetate, thiazosulfamide, and pyridine thione oxide.

[0090] (Composition of the Pigment Dispersion) The content of the pigment in the pigment dispersion is preferably 5 to 60% by mass. When the pigment is an organic pigment, the content of the organic pigment in the pigment dispersion is preferably 5 to 30% by mass, more preferably 10 to 25% by mass. When the pigment is an inorganic pigment, the content of the inorganic pigment in the pigment dispersion is preferably 20 to 60% by mass, more preferably 30 to 50% by mass.

[0091] The content of water in the pigment dispersion is preferably 20 to 80% by mass. By making an aqueous pigment dispersion containing an appropriate amount of water, an aqueous inkjet ink can be easily prepared.

[0092] The content of the water-soluble organic solvent in the pigment dispersion is preferably 30% by mass or less, more preferably 0.5 to 20% by mass. If the content of the water-soluble organic solvent exceeds 30% by mass, the recorded image may be difficult to dry.

[0093] The content of the pigment dispersant in the pigment dispersion is preferably set according to the type, surface properties, particle size, etc. of the pigment. Specifically, it is preferably 5 to 50 parts by mass, more preferably 10 to 30 parts by mass of the pigment dispersant with respect to 100 parts by mass of the organic pigment. Further, with respect to 100 parts by mass of the inorganic pigment, it is preferably 1 to 20 parts by mass, more preferably 3 to 10 parts by mass of the polymer dispersant.

[0094] As other additives, for example, 0.01 to 1% by mass of a surfactant can be added. Further, 0.05 to 2.0% by mass of a preservative can be added.

[0095] (Physical properties of the pigment dispersion) The viscosity of the pigment dispersion can be appropriately set according to the properties of the pigment and the viscosity of the aqueous inkjet ink to be prepared. When an organic pigment is used, the viscosity of the pigment dispersion at 25°C is preferably 3 to 20 mPa·s. When an inorganic pigment is used, the viscosity of the pigment dispersion at 25°C is preferably 5 to 30 mPa·s.

[0096] The surface tension of the pigment dispersion at 25°C is preferably 15 to 45 mN / m, more preferably 20 to 40 mN / m. The surface tension of the pigment dispersion can be adjusted, for example, by the type and amount of the water-soluble organic solvent or by adding a surfactant or the like.

[0097] (Method for preparing the pigment dispersion) The pigment dispersion can be prepared according to a conventionally known method. For example, water and, if necessary, a water-soluble organic solvent are added to prepare a mixture of a pigment, a pigment dispersant, and the like. Then, a paint shaker, a ball mill, an attritor, a sand mill, a horizontal media mill, a colloid mill, a roll mill, etc. are used to finely disperse the pigment to prepare a dispersion. Water and a water-soluble organic solvent are added to the prepared dispersion, and, if necessary, a binder component (emulsion), other additives, etc. are added to adjust to a desired concentration. Further, an alkali or the like may be added to adjust the pH. And by adding various additives such as a surfactant and a preservative as needed, the target pigment dispersion can be obtained. Note that after mixing and dispersing each component, it is preferable to remove coarse particles using a centrifuge or a filter.

[0098] To make the number average particle diameter (particle size distribution) of the pigment fall within a desired range, for example, the following methods are adopted: reducing the size of the grinding media used; increasing the filling rate of the grinding media; lengthening the processing time; slowing down the discharge rate; classifying with a filter or a centrifuge etc. after grinding; etc. Also, it is preferable to use a pigment that has been pre-fined by a conventionally known method such as the salt milling method.

Example

[0099] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. Note that "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

[0100] <Manufacture of Emulsion> (Synthesis Example 1) 82.8 parts of diethylene glycol monobutyl ether (BDG), 58.8 parts of benzyl methacrylate (homopolymer Tg: 54°C, BzMA), 58.8 parts of lauryl methacrylate (homopolymer Tg: -65°C, LMA), 1.4 parts of iodine, 2.5 parts of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (trade name "V-70", manufactured by Fuji Film Co., Ltd., V-70), and 0.015 parts of N-iodosuccinimide (NIS) were placed in a reaction vessel. While bubbling nitrogen, the mixture was heated to 45°C and polymerized for 5 hours to form polymer block A. The solid content measured by heating a sampled portion of the reaction solution in a thermostat at 150°C until a constant weight was reached and the polymerization rate converted from the formulation was approximately 100%. Also, when analyzed by gas chromatography (GC), almost no residual monomer was confirmed. Furthermore, the number average molecular weight (Mn) in terms of polystyrene measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the eluent was 10,100, and the molecular weight distribution (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 1.11. The Tg of the homopolymer of BzMA, the Tg of the homopolymer of LMA, and the Tg of polymer block A calculated from the composition ratio thereof were -18°C.

[0101] 7.1 parts of BzMA, 7.1 parts of cyclohexyl methacrylate (homo-polymer Tg: 83 °C, CHMA), and 14.1 parts of methacrylic acid (homo-polymer Tg: 228 °C, MAA) were placed in a separate container to prepare a mixed solution. The prepared mixed solution was put into a dropping device and added into the reaction vessel. The concentration of the monomers in this reaction system (monomer concentration) could be calculated to be 64.4%. Polymerization was carried out for 5 hours to form polymer block B, and an AB block copolymer was obtained. The polymerization rate calculated by sampling a part of the reaction solution was about 100%. Also, the Mn of the AB block copolymer was 11,600, and the PDI was 1.19. Since Mn was increasing, it was found that polymer block B was formed and the AB block copolymer was generated. The Mn of polymer block B (the value obtained by subtracting the Mn of polymer block A from the Mn of the AB block copolymer) was 1,500. The Tg of polymer block B calculated from the Tg of the homo-polymer and the composition ratio was 132 °C. The ratio of the Mn of polymer block A (MnA) to the Mn of polymer block B (MnB) (MnA / MnB) could be calculated to be "6.7".

[0102] A mixed solution of 4.3 parts of sodium hydroxide and 318.4 parts of water was put into a dropping device and added into the reaction vessel. Initially, it thickened, but it self-emulsified by stirring while adding. It was aged at 70 °C for 1 hour to obtain emulsion E-1, which was a slightly turbid transparent liquid. The solid content of emulsion E-1 was 27.4%, and the pH was 9.4. It was diluted with water to a solid content of 25%, and the viscosity at 25 °C measured using a B-type viscometer was 32.1 mPa·s. The number average particle diameter of the emulsion particles measured using a particle size distribution meter by dynamic light scattering method was 34.0 nm. The BDG content in emulsion E-1 calculated from the formulation was 14.9%.

[0103] (Example Synthesis Examples 2 - 14, Comparative Synthesis Examples 1 - 5) Emulsions E-2 - 14 and CE-1 - 5 were obtained in the same manner as in the above-mentioned Example Synthesis Example 1, except that the formulations shown in Tables 1 - 3 were used. The meanings of the abbreviations in Tables 1 - 3 are shown below. · 2EHMA: 2-Ethylhexyl methacrylate, homopolymer Tg = -10 °C · StMA: Stearyl methacrylate, homopolymer Tg = -100 °C · THFMA: Tetrahydrofurfuryl methacrylate, homopolymer Tg = 60 °C · IBXMA: Isobornyl methacrylate, homopolymer Tg = 155 °C

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[0105] TIFF2025113716000002.tif191170

[0106] TIFF2025113716000003.tif201170

[0107] (Comparative Synthesis Example 6) An attempt was made to produce an emulsion in the same manner as in Synthesis Example 6, except that the amount of BDG used during polymerization was 40 parts. The monomer concentration in the reaction system was 79.0%. As a result, the reaction solution during the polymerization of polymer block A had a high viscosity. Also, the viscosity of the reaction solution during the polymerization of polymer block B became extremely high, making stirring difficult and the polymerization rate reached 80%. For this reason, the reaction solution could not be stirred sufficiently, and the polymerization reaction could not be completed.

[0108] <Production of Pigment Dispersant> (Synthesis Example 15) 100 parts of BDG were placed in a reaction vessel and heated to 78 °C. 20 parts of styrene, 15 parts of methyl methacrylate (MMA), 15 parts of ethyl methacrylate (EMA), 20 parts of 2EHMA, 15 parts of 2-hydroxyethyl methacrylate (HEMA), 15 parts of MAA, and 3 parts of azobisisobutyronitrile (AIBN) were placed in a separate container to prepare a uniform mixed solution. The prepared mixed solution was placed in a dropping device, and after adding 1 / 3 of the amount into the reaction vessel, the remainder was added dropwise over 1 hour. After polymerization at 78 °C for 5 hours to form a polymer, it was cooled to room temperature. The Mn of the polymer sampled and measured was 15,000, and the PDI was 2.1. A mixed solution of 6.9 parts of sodium hydroxide and 93.1 parts of water was placed in a dropping device and added dropwise into the reaction vessel to obtain a pigment dispersant D-1 which is an aqueous solution of a random copolymer. The solid content of the obtained aqueous solution was 33.3%, and the pH was 8.8.

[0109] (Synthesis Example 16) 39 parts of BDG, 39 parts of propylene glycol monomethyl ether (MPG), 29.5 parts of BzMA, 3.3 parts of HEMA, 0.7 part of iodine, 1.4 parts of V-70, and 0.01 part of NIS were placed in a reaction vessel. While bubbling nitrogen, it was heated to 45 °C and polymerized for 5 hours to form polymer chain A. The polymerization rate was about 100%. Also, the Mn of polymer chain A was 3,000, and the PDI was 1.25. 30.1 parts of BzMA and 12.9 parts of MAA were added and polymerized for another 5 hours to form polymer chain B, and an AB block copolymer was obtained. The polymerization rate was about 100%. Also, the Mn of the AB block copolymer was 7,000, and the PDI was 1.25. Since the Mn has increased, it can be seen that polymer chain B was formed and the AB block copolymer was generated. The Mn of polymer chain B (the value obtained by subtracting the Mn of polymer chain A from the Mn of the AB block copolymer) was 4,000. The ratio of the Mn of polymer chain B (MnB) to the Mn of polymer chain A (MnA) (MnB / MnA) can be calculated as "1.33".

[0110] A mixed solution of 6.0 parts of sodium hydroxide and 71.9 parts of water was added to obtain a pigment dispersant D-2, which is an aqueous solution (transparent liquid) of an AB block copolymer. The solid content of the obtained aqueous solution was 33.4%, and the pH was 9.6.

[0111] (Example Synthesis Examples 17 and 18) Pigment dispersants D-3 and D-4 were obtained in the same manner as in Example Synthesis Example 16 except that the formulations shown in Table 4 were used.

[0112] TIFF2025113716000004.tif185170

[0113] (Manufacture of Pigment Dispersion) (Example 1) 93.5 parts of pigment dispersant D-2 and 333.4 parts of ion-exchanged water were mixed and homogenized to obtain a solution. 150 parts of copper phthalocyanine pigment (PB-15:3, trade name "Cyanine Blue A220JC", manufactured by Dainichi Seika Kogyo Co., Ltd.) was added to the obtained solution, and the mixture was stirred with a disper for 30 minutes to obtain a mill base. Using a horizontal medium disperser (trade name "Dynomill 0.6 liter ECM type", manufactured by Shinmaru Enterprises Co., Ltd., zirconia bead diameter: 0.5 mm), the obtained mill base was dispersed under the condition of a peripheral speed of 7 m / s to sufficiently disperse the pigment. After centrifugal separation treatment (7,500 rpm, 20 minutes), the mixture was filtered through a 10 μm membrane filter to remove coarse particles. Ion-exchanged water was added to adjust the concentration, and a blue pigment dispersion liquid B-1 with a pigment concentration of 14% was obtained.

[0114] The number average particle diameter of the pigment in the pigment dispersion liquid measured using a particle size analyzer (trade name "NICOMP 380ZLS-S", manufactured by International Business Co., Ltd.) was 105.9 nm, confirming that the pigment was finely dispersed. Using an E-type viscometer, the viscosity (25 °C) of the pigment dispersion liquid measured under the condition of 60 rotations was 3.58 mPa·s, and the pH was 8.8. The pigment dispersion liquid was stored at 70 °C for 1 week. After storage, the number average particle diameter of the pigment in the pigment dispersion liquid was 106.3 nm, and the viscosity was 3.56 mPa·s.

[0115] (Examples 2 to 6) Except for using the types of pigment dispersants and pigments shown in Table 5, pigment dispersions B-2 to 6 were obtained in the same manner as in Example 1 described above. Table 5 shows the measurement results of the number average particle diameter of the pigment and the viscosity of the pigment dispersion immediately after dispersion and after storage at 70°C for 1 week. The details of the materials in Table 5 are shown below. · PY-155: Azo yellow pigment (trade name "VERSAL YELLOW 4GNY", manufactured by Clariant) · PR-122: Quinacridone pigment (trade name "CFR130P", manufactured by Dainichi Seika Kogyo Co., Ltd.) · PB-7: Carbon black pigment (trade name "S170", manufactured by Degussa)

[0116] (Evaluation) The storage stability of the pigment dispersion was evaluated according to the evaluation criteria shown below. An evaluation of "○" is considered a pass. The results are shown in Table 5. ○: The pigment was finely dispersed, and the number average particle diameter and viscosity of the pigment did not change significantly after storage at 70°C for 1 week. △: The pigment was finely dispersed, but the viscosity was over 4 mPa·s. However, even after storage at 70°C for 1 week, the number average particle diameter and viscosity of the pigment did not change significantly. ×: The pigment was finely dispersed, but when stored at 70°C for 1 week, the number average particle diameter or viscosity of the pigment increased.

[0117] TIFF2025113716000005.tif63170

[0118] (Example 7) 401.2 parts of water and 98.8 parts of pigment dispersant D-2 were mixed and homogenized. 500 parts of C.I. Pigment White 6 (trade name "JR-404", manufactured by Ishihara Sangyo Co., Ltd.) were added, and the mixture was thoroughly stirred and mixed with a dissolver to obtain a mixture containing a pigment and a pigment dispersant. The obtained mixture was sufficiently dispersed in the same manner as in Example 1 above, and then filtered through a 10 μm membrane filter to remove coarse particles, thereby obtaining a white pigment dispersion liquid B-7 with a pigment concentration of 50%. The number average particle diameter of the pigment in the pigment dispersion liquid was 243.6 nm, and the viscosity was 11.9 mPa·s. When the stability after storage at 70°C for one week was confirmed, the number average particle diameter of the pigment was 239.4 nm, and the viscosity was 11.8 mPa·s. Moreover, there was almost no precipitate of titanium oxide at the bottom of the storage container.

[0119] <Production of Aqueous Inkjet Ink> (Examples 8 to 24, Comparative Examples 1 to 4) 13 parts of propylene glycol, 5 parts of 1,2-hexanediol, 0.5 part of a surfactant (trade name Surfynol 465, manufactured by Air Products), and 50 parts of water were mixed to obtain a dilution liquid. 28.7 parts of a pigment dispersion liquid of the type shown in Table 6 were added and stirred uniformly, and then 4 parts (as the polymer content) of an emulsion of the type shown in Table 6 were further added, and water was added to make 100 parts. After thorough stirring, the mixture was filtered through a membrane filter with a pore size of 10 μm to obtain inks I-1 to 17 and CI-1 to 4 which are aqueous inkjets.

[0120] (Evaluation (1)) The number average particle diameter and viscosity of the pigment in the obtained ink were measured immediately after dispersion and after storage at 70°C for one week. Then, the storage stability of the ink was evaluated according to the following evaluation criteria. The evaluations of "○" and "△" are considered qualified. The results are shown in Table 6. ○: The viscosity is 3.0 to 3.4 mPa·s, the pigment is finely dispersed, and the number average particle diameter and viscosity of the pigment do not change significantly even after storage at 70°C for one week. △: The viscosity is more than 3.4 mPa·s and 3.6 mPa·s or less, and the number average particle diameter and viscosity of the pigment hardly change even after storage at 70°C for one week. ×: The viscosity is more than 3.6 mPa·s, or although the pigment is finely dispersed, when stored at 70 °C for one week, the number average particle diameter or viscosity of the pigment increases.

[0121] (Evaluation (2)) One drop of the obtained ink was dropped onto a glass plate and dried at 60 °C for 24 hours. Ion-exchanged water was added thereto. Whether it returned to the original dispersed state was observed, and the redissolubility of the ink was evaluated according to the following evaluation criteria. Evaluations of "◎" and "○" are considered passing. The results are shown in Table 6. ◎: It returned to a state without lumps and film. ○: Fine film-like substances were observed, but it returned to the original liquid state. △: The film-like substance peeled off. ×: It did not dissolve.

[0122] TIFF2025113716000006.tif155170

[0123] (Example 25) 13 parts of propylene glycol, 5 parts of 1,2 - hexanediol, 0.5 part of a surfactant (trade name: Surfynol 465, manufactured by Air Products), and 50 parts of water were mixed to obtain a diluent. 28.7 parts of pigment dispersion liquid B - 7 was added and stirred uniformly. Then, 4 parts of the emulsion E - 3 obtained in Synthesis Example 3 (however, as the polymer component) was further added, and water was added to make 100 parts. After sufficient stirring, it was filtered through a membrane filter with a pore size of 10 μm to obtain Ink I - 18 which is an aqueous inkjet ink. The number average particle diameter of the pigment immediately after dispersion was 226.2 nm, and the viscosity was 3.56 mPa·s. Also, after storing at 70 °C for one week, the average particle diameter of the pigment was 231.7 nm, and the viscosity was 3.49 mPa·s. There was almost no sediment at the bottom of the storage container.

[0124] <Evaluation of Ink> The obtained inks were each filled into cartridges and installed in an inkjet printer (trade name "EM930C", manufactured by Seiko Epson Corporation). Using this inkjet printer, a patch pattern was printed on plain paper (trade name "4024", manufactured by Xerox Corporation) and dedicated glossy photo paper (PGPP).

[0125] (Discharge stability) The discharge state of the ink was observed, and the discharge stability of the ink was evaluated according to the evaluation criteria shown below. An evaluation of "○" is considered a pass. The results are shown in Table 7. ○: It was possible to discharge without problems, and a good image could be printed. △: Splashing of micro droplets was observed. ×: When discharging, the droplets splashed and scattered, and the image was distorted.

[0126] (Fixing property) After drying the image obtained by printing on plain paper at room temperature for 24 hours, the surface of the image was rubbed with a yellow aqueous fluorescent pen (trade name "ZEBRA PEN2, manufactured by Zebra Corporation"). The presence or absence of dirt adhering to the pen tip was visually observed, and the fixing property of the image was evaluated according to the evaluation criteria shown below. An evaluation of "○" is considered a pass. The results are shown in Table 7. ○: No dirt was generated even when rubbing the same part twice. △: No dirt was generated when rubbed once, but dirt was generated when rubbed twice. ×: Dirt was generated when rubbed once.

[0127] (Adhesion) The image obtained by printing on dedicated glossy photo paper was left at room temperature for 1 hour. The image part was gently rubbed with a finger, and the change in the glossiness of the image surface was visually confirmed. The adhesion of the image was evaluated according to the criteria shown below. An evaluation of "○" is considered a pass. The results are shown in Table 7. ○: The trace of rubbing with a finger could not be distinguished, and there was no gloss change. △: The trace of rubbing with a finger could be distinguished, but there was almost no gloss change. ×: The trace of rubbing with a finger could be clearly distinguished, and there was a gloss change.

[0128] Water resistance After drying the image obtained by printing on ordinary paper at room temperature for 24 hours, water was dropped one by one. The occurrence of bleeding was visually confirmed, and the water resistance of the image was evaluated according to the evaluation criteria shown below. An evaluation of "○" is considered a pass. The results are shown in Table 7. ○: No bleeding was observed at all. △: Slight bleeding was observed. ×: Bleeding was observed.

[0129] Clogging recovery After continuously printing for 10 minutes, the ink cartridge was removed, and the recording head was left in a state removed from the head cap in an environment of 50 °C for 1 week. After leaving it, the cleaning operation was repeated until all nozzles ejected equivalently to the initial state, and the clogging recovery was evaluated according to the evaluation criteria shown below. An evaluation of "○" is considered a pass. The results are shown in Table 7. ○: Printing equivalent to the initial state could be achieved within 2 cleanings. △: Printing equivalent to the initial state could be achieved within 3 to 4 cleanings. ×: Printing equivalent to the initial state could not be achieved within 4 cleanings.

[0130] TIFF2025113716000007.tif148170

Industrial applicability

[0131] The ink containing the binder component of the present invention is suitable as an ink for inkjet printing using paper for personal, office, and industrial use, etc. as a recording medium. Further, the ink of the present invention is also useful as a printing ink such as an aqueous paint for automobiles and building materials, aqueous stationery, aqueous gravure ink, and aqueous flexo ink.

Claims

1. A binder component formulated in an aqueous inkjet ink used for printing on paper media, which is a methacrylate polymer satisfying the following (1) to (3). (1) Having polymer block A and polymer block B, The ratio (MnA / MnB) of the number average molecular weight (MnA) of the polymer block A to the number average molecular weight (MnB) of the polymer block B is 5.0 to 15.0, It is an AB block copolymer with a molecular weight distribution (weight average molecular weight / number average molecular weight) of 1.1 to 1.

6. (2) The polymer block A contains 40 to 70% by mass of a structural unit (A-1) derived from an alkyl methacrylate having an alkyl group with 8 to 18 carbon atoms, and at least one selected from the group consisting of alkyl methacrylates having a linear alkyl group with 1 to 6 carbon atoms, branched alkyl methacrylates, cycloalkyl methacrylates having a cycloalkyl group with 6 to 18 carbon atoms, alkyl cycloalkyl methacrylates having an alkyl cycloalkyl group with 6 to 18 carbon atoms, aromatic ring-containing methacrylates, and cyclic ether group-containing methacrylates. A structural unit (A-2) derived from the above, The total content of the structural unit (A-1) and the structural unit (A-2) is 90% by mass or more, the number average molecular weight is 5,000 to 20,000, the molecular weight distribution is 1.05 to 1.5, and the glass transition temperature is 0°C or lower. It is a water-insoluble polymethacrylate. (3) The polymer block B contains 30 to 60% by mass of a structural unit (B-1) derived from methacrylic acid, It is a polymethacrylate having a number average molecular weight of 500 to 3,000, a glass transition temperature of 50°C or higher, and being water-soluble when neutralized with an alkali.

2. The polymer block A contains a structural unit (A-1) derived from lauryl methacrylate and at least one structural unit (A-2) selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, The binder component according to claim 1, wherein the polymer block B further contains at least one structural unit (B-2) selected from the group consisting of ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate.

3. The binder component according to claim 1, wherein the alkali is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide.

4. An emulsion containing a liquid medium and emulsion particles formed of a polymer dispersed or emulsified in the liquid medium, wherein the polymer is a methacrylate polymer which is the binder component according to any one of claims 1 to 3, the liquid medium is an aqueous liquid medium containing at least one water-soluble solvent selected from the group consisting of diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether and water, the content of the water-soluble solvent with respect to 100 parts by mass of the methacrylate polymer is 5 to 100 parts by mass, an emulsion in which the number average particle diameter of the emulsion particles measured by the dynamic light scattering method is 20 to 150 nm.

5. The emulsion according to claim 4, which is at 25 ° C and has a viscosity of 10 to 100 mPa·s when the content of the methacrylate polymer is 25% by mass.

6. A method for producing the emulsion according to claim 4, which comprises carrying out living radical polymerization in a reaction system containing 20 to 40% by mass of the water-soluble solvent and 60 to 75% by mass of the monomers constituting the methacrylate polymer, adding an aqueous solution containing the alkali to neutralize, and self-emulsifying the produced methacrylate polymer to form the emulsion particles.

7. A pigment dispersion liquid containing a pigment and a pigment dispersant for dispersing the pigment, wherein the pigment dispersant is a polymer satisfying the following (4) to (6). (4)Having polymer chain A and polymer chain B, the ratio (MnB / MnA) of the number average molecular weight (MnB) of the polymer chain B to the number average molecular weight (MnA) of the polymer chain A is 1.0 to 3.0, an AB block copolymer having a number average molecular weight of 6,000 to 15,000 and a molecular weight distribution of 1.2 to 2.

0. (5)The polymer chain A contains 80% by mass or more of a structural unit (a-1) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, It is a water-insoluble polymethacrylate having a number-average molecular weight of 500 to 6,000 and a molecular weight distribution of 1.1 to 1.

8. (6) The polymer chain B contains 10 to 40% by mass of a structural unit (b-1) derived from methacrylic acid, and a structural unit (b-2) derived from at least one selected from the group consisting of benzyl methacrylate, cyclohexyl methacrylate, methyl methacrylate, ethyl methacrylate, tetrahydrofurfuryl methacrylate, and isobornyl methacrylate, and the total content of the structural unit (b-1) and the structural unit (b-2) is 90% by mass or more, it is a polymethacrylate having a number-average molecular weight of 3,000 to 10,000 and being water-soluble after being neutralized with an alkali.

8. An aqueous inkjet ink used for printing on a paper medium, containing a pigment or a pigment dispersion liquid in which the pigment is dispersed with a pigment dispersant, water, a water-soluble organic solvent, and a binder component, The aqueous inkjet ink, wherein the binder component is the binder component according to any one of claims 1 to 3.

9. The aqueous inkjet ink according to claim 8, wherein the pigment dispersion liquid is the pigment dispersion liquid according to claim 7.

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