Block polymer, and coloring material dispersion and ink composition using same

Abstract

[Problem] To provide an aqueous inkjet ink composition that has excellent storage stability and redispersibility. [Solution] It is possible to achieve outstanding performance in an aqueous inkjet ink containing a water-insoluble coloring agent by using, as a dispersant, a block polymer having a segment that includes the following at a predetermined ratio: a monomer having a hydrophobic functional group or a constituent unit derived from a monomer having a hydrophobic functional group; and a monomer having a hydrophilic functional group or a constituent unit derived from a hydrophilic functional group.

Description

Block polymer, coloring material dispersion liquid and ink composition using the same

[0001] The present invention relates to a colorant dispersion and an ink composition that contain a specific block polymer and can be suitably used in aqueous inkjet inks, and the block polymer.

[0002] Pigments have traditionally been widely used as colorants in inkjet recording inks, inks for writing instruments, and the like, due to their excellent fastness, such as water resistance and light resistance. In aqueous inks using pigments, since the pigments are not soluble in water, it is important to stably disperse the pigment in water as fine particles when using them in an ink composition. However, aqueous inks using pigments have a problem with storage stability, which is the deterioration of the recording liquid due to aggregation and sedimentation of the pigment. Storage stability is particularly required to maintain viscosity and particle size within suitable ranges even after long-term storage. Other requirements include excellent color properties such as color development and gloss, the ink not clogging nozzles, and rapid recovery from nozzle clogging after long-term use, i.e., excellent ink ejection stability.

[0003] The cause of the decrease in ejection stability is often the evaporation of the ink medium, which causes the solid components of the ink to precipitate or crystallize at the air / liquid interface. In particular, in the case of aqueous colorant inks, the dispersed colorant may aggregate due to changes in the solvent composition caused by evaporation. The precipitated aggregates must be easily redispersed during head cleaning.

[0004] To address these issues, it has been proposed to improve storage stability by using a block polymer, which has better pigment adsorption properties than a random polymer. For example, Patent Document 1 proposes achieving both dispersibility and glossiness by using a block polymer with a gradient copolymer structure that has a hydrophilic / hydrophobic gradient. Specifically, the block polymer uses a monomer having a single aromatic ring, such as styrene or benzyl methacrylate, in the hydrophobic segment.

[0005] Furthermore, Patent Document 2 proposes a method for improving storage stability, ejection stability, and redispersibility by using a block polymer and a pigment derivative. Specifically, a hydrophobic segment made of a monomer having one aromatic ring is used, as in Patent Document 1, but the use of a derivative is intended to improve storage stability, ejection stability, and redispersibility.

[0006] In addition to using block polymers, for example, Patent Document 3 addresses the problem of poor storage stability by using a water-insoluble polymer dispersant to coat (encapsulate) the colorant. Patent Document 4 also proposes a method of achieving excellent storage stability, redispersibility, and color properties by using a monomer containing a biphenyl group in the hydrophobic segment of a block polymer.

[0007] Japanese Patent Application Publication No. 2008-195769 Japanese Patent Application Publication No. 2011-225834 Japanese Patent Application Publication No. 2016-26256 Japanese Patent Application Publication No. 2020-111683

[0008] However, the present inventors have found that even when the block polymer described in Patent Document 1 is used, the redispersibility related to ejection stability is insufficient. Furthermore, when a pigment derivative is used as described in Patent Document 2, it has been found that the problem of color deterioration occurs, and the problem of color characteristics cannot be solved. Furthermore, the method using a water-insoluble polymer as described in Patent Document 3 still has the problem of poor redispersibility during head cleaning operations due to the high hydrophobicity of the dispersant. Furthermore, when the block polymer described in Patent Document 4 is used, storage stability is improved, but redispersibility is insufficient, and there is a risk of ejection stability being reduced depending on the usage environment and ink composition. The present inventors have found that, in particular, sufficient redispersibility tends to be insufficient when the ink composition has a high solvent content.

[0009] The present invention has been made in view of the problems associated with the conventional techniques, and aims to provide a coloring material dispersion that uses a block polymer having a specific structure, and that has excellent storage stability and higher redispersibility, and that can be used to prepare an ink composition that achieves color characteristics.

[0010] As a result of intensive research aimed at achieving the above-mentioned object, the present inventors have found that the above-mentioned object can be solved by using, as a dispersant, a block polymer having segments containing structural units derived from specific monomers in a specific ratio. Furthermore, the present inventors have found that the above-mentioned object can be solved by using, as a dispersant, a block polymer having segments containing specific functional groups in a specific ratio. That is, according to the present invention, the following block polymer and a coloring material dispersion using the block polymer are provided.

[0011] That is, the present invention provides: (1) a block polymer having at least one segment (A) satisfying the following (a1) and (a2) and at least one segment (B) satisfying the following (b1) and (b2), and characterized in that the block polymer has a peak top molecular weight of 3,000 or more and 16,000 or less; (a1): having a structural unit derived from a monomer having a hydrophobic functional group and a structural unit derived from a monomer having a hydrophilic functional group, wherein the mass ratio between the two (total mass of structural units derived from monomers having hydrophobic functional groups / total mass of structural units derived from monomers having hydrophilic functional groups) is 2.3 or more and 19.0 or less; (a2): having a peak top molecular weight of 750 or more; (b1): having a structural unit derived from a monomer having a hydrophobic functional group and a structural unit derived from a monomer having a hydrophilic functional group, wherein the mass ratio between the two (total mass of structural units derived from monomers having hydrophobic functional groups / total mass of structural units derived from monomers having hydrophilic functional groups) is 0.43 or more and 2.Less than 3 (b2): Peak top molecular weight is 750 or more. (2) The block polymer according to (1) above, wherein in the segment (A), the sum of the mass of the structural units derived from the monomer having a hydrophobic functional group and the mass of the structural units derived from the monomer having a hydrophilic functional group accounts for 10% by mass or more, and in the segment (B), the sum of the mass of the structural units derived from the monomer having a hydrophobic functional group and the mass of the structural units derived from the monomer having a hydrophilic functional group accounts for 10% by mass or more. (3) The block polymer according to (2) above, wherein the sum of the mass of the segment (A) and the mass of the segment (B) accounts for 50% by mass or more in the block polymer. (4) The block polymer according to (3) above, wherein the monomer having a hydrophobic functional group is a monomer having a phenyl group and / or a monomer having a biphenyl group, and the monomer having a hydrophilic functional group is a monomer having a carboxy group. (5) A block polymer having at least one segment (A') that satisfies the following (a1') and (a2) and at least one segment (B') that satisfies the following (b1') and (b2), and characterized by a peak top molecular weight of 3,000 or more and 16,000 or less, (a1'): the molar ratio of hydrophobic functional groups to hydrophilic functional groups (total amount of hydrophobic functional groups / total amount of hydrophilic functional groups) is 0.85 or more and 8.50 or less, (a2): the peak top molecular weight is 750 or more, and (b1'): the molar ratio of hydrophobic functional groups to hydrophilic functional groups (total amount of hydrophobic functional groups / total amount of hydrophilic functional groups) is 0.16 or more and 0.(b2): Peak top molecular weight is 750 or more. (6) The block polymer according to (5) above, wherein in the segment (A'), the sum of the mass of the hydrophobic functional group and the mass of the hydrophilic functional group accounts for 10% by mass or more, and in the segment (B'), the sum of the mass of the hydrophobic functional group and the mass of the hydrophilic functional group accounts for 10% by mass or more. (7) The block polymer according to (6) above, wherein the sum of the mass of the segment (A') and the mass of the segment (B') accounts for 50% by mass or more in the block polymer. (8) The block polymer according to (7) above, wherein the hydrophobic functional group is a phenyl group and / or a biphenyl group, and the hydrophilic functional group is a carboxy group. (9) The block polymer according to any one of (1) to (8) above, wherein the acid value is 120 mgKOH / g or more and 190 mgKOH / g or less. (10) (11) A coloring material dispersion comprising the block polymer described in any one of (1) to (9) above, a water-insoluble coloring material, and an aqueous medium; (12) A method for producing a printing ink comprising mixing the coloring material dispersion described in (10) above with an organic solvent, a resin, and a preservative; and (13) A printing ink containing at least the block polymer described in any one of (1) to (9) above, a coloring material, an organic solvent, a resin, and a preservative.

[0012] By incorporating the block polymer of the present invention, it is possible to obtain a coloring material dispersion that has excellent storage stability and redispersibility and that can be used to prepare an ink composition that achieves color characteristics.

[0013] 1 is a photograph of a coating film obtained in Example 6. FIG. 2 is a photograph of a coating film obtained in Example 7. FIG. 3 is a photograph of a coating film obtained in Example 8.

[0014] The present invention will be described in detail below. (Block polymer) The block polymer of the first invention of the present application is characterized by having at least one segment (A) that satisfies the following (a1) and (a2) and at least one segment (B) that satisfies the following (b1) and (b2): (a1): Having a structural unit derived from a monomer having a hydrophobic functional group and a structural unit derived from a monomer having a hydrophilic functional group, wherein the mass ratio between the two (total mass of structural units derived from monomers having hydrophobic functional groups / total mass of structural units derived from monomers having hydrophilic functional groups) is 2.3 or more and 19.0 or less. (a2): Peak top molecular weight is 750 or more. (b1): Having a structural unit derived from a monomer having a hydrophobic functional group and a structural unit derived from a monomer having a hydrophilic functional group, wherein the mass ratio between the two (total mass of structural units derived from monomers having hydrophobic functional groups / total mass of structural units derived from monomers having hydrophilic functional groups) is 0.43 or more and less than 2.3. (b2): Peak top molecular weight is 750 or more. The block polymer of the second invention of the present application is characterized by having at least one segment (A') that satisfies the following (a1') and (a2), and at least one segment (B') that satisfies the following (b1') and (b2). (a1'): The molar ratio of hydrophobic functional groups to hydrophilic functional groups (total amount of hydrophobic functional groups / total amount of hydrophilic functional groups) is 0.85 or more and 8.50 or less. (a2): The peak top molecular weight is 750 or more. (b1'): The molar ratio of hydrophobic functional groups to hydrophilic functional groups (total amount of hydrophobic functional groups / total amount of hydrophilic functional groups) is 0.16 or more and less than 0.85. (b2): The peak top molecular weight is 750 or more.

[0015] [Hydrophobic Functional Group] The hydrophobic functional group means a functional group having hydrophobicity. The hydrophobic functional group in the block polymer of the present invention is not particularly limited, and typical examples include an alkyl group, a phenyl group, a biphenyl group, and a naphthyl group. However, a biphenyl group and a phenyl group, which have a moderately high level of hydrophobicity, are preferred. In particular, a block polymer of the present invention having a phenyl group is most preferred because it has high redispersibility in a pigment dispersion.

[0016] [Monomer Having a Hydrophobic Functional Group] In the present invention, the monomer having a hydrophobic functional group refers to a monomer having at least one of the above-mentioned hydrophobic functional groups. Any monomer having a hydrophobic functional group can be used without any particular limitation, and examples thereof include tert-butyl acrylate, tert-butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, iso-octyl acrylate, iso-octyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, decyl acrylate, decyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, phenyl acrylate, phenyl methacrylate, phenoxyethyl acrylate, isobornyl acrylate, nonylphenyl acrylate, nonylphenyl methacrylate, benzyl acrylate, benzyl methacrylate, dicyclopentenyl acrylate, dicyclopentenyl methacrylate, styrene, methylstyrene, and vinyltoluene.

[0017] Among these monomers having a hydrophobic functional group, those having a phenyl group or a biphenyl group are preferred, and those having one phenyl group and a molecular weight of 140 to 200 are more preferred. Among these, phenyl acrylate, phenyl methacrylate, and phenoxyethyl acrylate are even more preferred, and phenoxyethyl acrylate is most preferred. Block polymers using these preferred monomers have a moderate level of hydrophobicity and are superior in redispersibility and storage stability. Furthermore, because these preferred monomers have an aromatic ring, when the coloring material also has an aromatic ring, π-π interactions are exhibited, which is thought to further work in favor of storage stability, as will be described later.

[0018] Among monomers having a hydrophobic functional group, those having a LogP of 2.0 or more and 5.0 or less are preferred. Within this range, the strength of hydrophobicity is adequate, and redispersibility and storage stability are superior. More preferably, the LogP of the monomer having a hydrophobic functional group is 2.0 or more and 3.0 or less. Here, LogP is measured by the method for measuring the partition coefficient, "OECD GUIDELINE FOR TESTING OF CHEMICALS, "Partition Coefficient (n-octanol / water), High Performance Liquid Chromatography (HPLC) Method," Adopted by the Council on March 30, 1989." Alternatively, other methods that can obtain equivalent values ​​may be used.

[0019] [Hydrophilic Functional Group] The hydrophilic functional group means a functional group having hydrophilicity. The hydrophobic functional group in the block polymer of the present invention is not particularly limited, but is preferably one that ionizes to generate an anion upon neutralization with an alkali compound, and representative examples include a carboxy group, a phosphate group, and a sulfonic acid group. These groups are particularly excellent in wet friction resistance. Among these, a carboxy group is particularly preferred, as it has a moderate hydrophilicity and can achieve a good balance between the redispersibility and solubility in solvents of a pigment dispersion using the resulting block polymer.

[0020] [Monomer Having a Hydrophilic Functional Group] The monomer having a hydrophilic functional group means a monomer having at least one of the above-mentioned hydrophilic functional groups. The monomer having a hydrophilic functional group used in the present invention is not particularly limited, but representative examples include acrylic acid, methacrylic acid, maleic acid, itaconic acid, vinylphosphonic acid, and vinylsulfonic acid.

[0021] Among monomers having hydrophilic functional groups, those having a carboxy group are preferred, and those having one carboxy group and a molecular weight of 50 to 100 are more preferred, with methacrylic acid and acrylic acid being particularly preferred. When these preferred monomers are used, the block polymer has a moderate level of hydrophilicity and excellent storage stability. Furthermore, it is most preferred that the segments (B) and (B') described below contain both methacrylic acid and acrylic acid. By including both acrylic acid and methacrylic acid, copolymerization during polymer synthesis is improved, resulting in improved polymer uniformity. As a result, the coloring material is further microparticulated, allowing for the production of dispersions and inks with better storage stability.

[0022] Among the monomers having a hydrophilic functional group, those having a LogP of -2.0 or more and 1.0 or less are preferred. Within this range, the hydrophilicity is adequate and the storage stability is superior. The LogP of the monomer having a hydrophilic functional group is more preferably 0.0 or more and 1.0 or less. The method for measuring LogP is as described above.

[0023] (Block polymer of the first invention) [Segment A] The block polymer of the first invention has one or more segments (A) described below. In dispersing a coloring material or the like, it is believed that the segment (A) mainly plays a role in adsorbing the block polymer to the coloring material due to its hydrophobicity, thereby imparting dispersibility.

[0024] Segment (A) contains the structural units derived from the monomer having a hydrophobic functional group and the structural units derived from the monomer having a hydrophilic functional group described above, with the mass ratio (total mass of structural units derived from the monomer having a hydrophobic functional group / total mass of structural units derived from the monomer having a hydrophilic functional group) being 2.3 to 19.0. By maintaining the mass ratio of structural units derived from the monomer having a hydrophobic functional group to structural units derived from the monomer having a hydrophilic functional group within the above range, segment (A) exhibits excellent redispersibility and storage stability. This is believed to be because the inclusion of structural units derived from the monomer having a hydrophobic functional group within the above ratio ensures sufficient adsorption to the colorant. Furthermore, the inclusion of structural units derived from the monomer having a hydrophilic functional group within the above ratio results in slight repulsion between segments (A) of different polymers due to hydrophilic-hydrophobic interactions, suppressing adsorption, entanglement, and aggregation between the polymers, allowing many polymers to efficiently adsorb to the colorant and impart dispersibility. The mass ratio of the structural units derived from the monomer having a hydrophobic functional group to the monomer having a hydrophilic functional group is more preferably 4.0 to 19.0, and even more preferably 5.0 to 12.0. Within this range, better redispersibility and storage stability can be exhibited. To adjust the mass ratio of the constituent units derived from the monomer having a hydrophobic functional group to the constituent units derived from the monomer having a hydrophilic functional group within the above range, the monomer having a hydrophobic functional group and the monomer having a hydrophilic functional group may be polymerized in the above ratio during synthesis of the block polymer. Furthermore, when analyzing and confirming the obtained block polymer, H-NMR, GPC, acid value titration, etc. may be used.

[0025] The peak top molecular weight of segment (A) is 750 or more. If the peak top molecular weight is less than 750, the adsorption force to the material may be insufficient, and redispersibility may be impaired. The peak top molecular weight of segment (A) is preferably 1000 or more, more preferably 2000 or more. The method for measuring the peak top molecular weight is as shown in the examples, but is not limited to this as long as similar results are obtained.

[0026] In the block polymer of the first invention of this application, the mass proportion of segment (A) is preferably 25% by mass or more and 75% by mass or less. If the mass proportion of segment (A) is less than 25% by mass, the pigment adsorption performance is insufficient, and redispersibility and storage stability tend to be low. On the other hand, if the mass proportion of segment (A) is more than 75% by mass, the polymer may not dissolve in a solvent. The mass proportion of segment (A) is more preferably 55% by mass or more and 75% by mass or less, and most preferably 55% by mass or more and 65% by mass or less.

[0027] The order of the structural units derived from each monomer in the segment (A) is not particularly limited, but is preferably random. That is, in the present invention, various forms such as a random copolymer, a block copolymer, and an alternating copolymer can be used as the form of the segment (A), and among these, a random copolymer is particularly preferred.

[0028] Segment (A) may contain any structural unit other than the structural unit derived from a monomer having a hydrophobic functional group and the structural unit derived from a monomer having a hydrophilic functional group. When segment (A) is taken as 100% by mass, the total mass of the structural units derived from monomers having a hydrophobic functional group and the structural units derived from monomers having a hydrophilic functional group in segment (A) is preferably 10% by mass or more, more preferably 25% by mass or more, and even more preferably 50% by mass or more. It is most preferable that 100% by mass, i.e., segment (A) is composed only of structural units derived from monomers having a hydrophobic functional group and structural units derived from monomers having a hydrophilic functional group. By keeping this within the above preferred range, the effects of the present invention can be more effectively exhibited.

[0029] [Segment (B)] The block polymer of the first invention of the present application has one or more segments (B) described below. In dispersing a coloring material or the like, it is believed that segment (B) plays a role in dissolving the block polymer in an aqueous solvent mainly due to its hydrophilicity.

[0030] Segment (B) contains a structural unit derived from the monomer having the hydrophobic functional group and a structural unit derived from the monomer having the hydrophilic functional group, with the mass ratio of the two (mass of the structural unit derived from the monomer having the hydrophobic functional group / mass of the structural unit derived from the monomer having the hydrophilic functional group) being 0.43 or more and less than 2.30. By setting the mass ratio of the structural unit derived from the monomer having the hydrophobic functional group to the structural unit derived from the monomer having the hydrophilic functional group in segment (B) within the above range, redispersibility can be improved and the viscosity of the colorant dispersion or ink can be reduced to a suitable range. The improved redispersibility is believed to be due to the fact that the inclusion of the structural unit derived from the monomer having the hydrophilic functional group within the above ratio allows the polymer to dissolve uniformly in an aqueous solvent, allowing a large amount of polymer to be efficiently adsorbed onto the colorant. The viscosity can be reduced because, inclusion of structural units derived from hydrophilic functional groups in the above ratio allows sufficient solubility in a solvent, and inclusion of structural units derived from hydrophobic functional groups in the above ratio causes slight repulsion between the segments (B) of different polymers due to hydrophilic-hydrophobic interactions, making adsorption, aggregation, and entanglement less likely to occur, and the polymer is more likely to loosen. The mass ratio of the two is more preferably 0.50 to 1.50, and even more preferably 0.67 to 1.00. By maintaining the ratio within this range, the viscosity can be reduced and redispersibility can be improved when used in a dispersion or ink. To adjust the ratio of structural units within the above range, monomers can be polymerized in the above ratio during block polymer synthesis. Furthermore, the resulting block polymer can be analyzed and confirmed using H-NMR, GPC, acid value titration, and the like.

[0031] The peak top molecular weight of segment (B) is 750 or more. If the peak top molecular weight is less than 750, the solubility is insufficient, the viscosity increases, and redispersibility may deteriorate. The peak top molecular weight of segment (B) is preferably 1000 or more, more preferably 2000 or more. The method for measuring the peak top molecular weight is as shown in the examples, but is not limited to this as long as similar results are obtained.

[0032] In the block polymer of the first invention of this application, the mass proportion of segment (B) is preferably 25% by mass or more and 75% by mass or less. If the mass proportion of segment (B) is less than 25% by mass, the polymer may not dissolve in a solvent. On the other hand, if the mass proportion of segment (B) is more than 75% by mass, the pigment adsorption performance tends to be insufficient, and redispersibility and storage stability tend to be poor. The mass proportion of segment (B) is more preferably 25% by mass or more and 45% by mass or less, and most preferably 35% by mass or more and 45% by mass or less.

[0033] The order of the structural units composed of each monomer in segment (B) is not particularly limited, but is preferably random. That is, in the present invention, various forms such as a random copolymer, a block copolymer, and an alternating copolymer can be used as the form of segment (B), and among these, a random copolymer is particularly preferred.

[0034] Segment (B) may contain any structural units other than those derived from monomers having hydrophobic functional groups and those derived from monomers having hydrophilic functional groups. When the entire segment (B) is taken as 100% by mass, the total proportion of structural units derived from monomers having hydrophobic functional groups and those derived from monomers having hydrophilic functional groups in segment (B) is preferably 10% by mass or more, more preferably 25% by mass or more, and even more preferably 50% by mass or more. It is most preferable that 100% by mass of segment (B) is composed solely of structural units derived from monomers having hydrophobic functional groups and those derived from monomers having hydrophilic functional groups. By keeping the proportion within the above preferred range, the effects of redispersibility and viscosity reduction can be more effectively exhibited.

[0035] [Segment Configuration] The block polymer of the first invention of the present application may have two or more of the above-described segment (A) and segment (B) in each block polymer. However, in order to more effectively exhibit the effects of the present invention, it is preferable that each block polymer contains one of each of the segments (A) and (B).

[0036] The block polymer of the first invention of the present application may contain a portion other than segment (A) and segment (B) to the extent that the effects of the present invention are not impaired. In the block polymer of the first invention of the present application, the total mass of segment (A) and segment (B) is preferably 50% by mass or more. More preferably, it contains 90% by mass or more, and most preferably, it contains 100% by mass, i.e., the block polymer is composed only of segment (A) and segment (B). Within the above range, the effects of the present invention can be more effectively exhibited.

[0037] In the block polymer of the first invention of this application, the ratio of segment (A) to segment (B) (segment A mass:segment B mass) is preferably 25:75 to 75:25, more preferably 55:45 to 75:25, and particularly preferably 55:45 to 65:35. By maintaining the ratio within these preferred ranges, superior storage stability is achieved. The ratio of segment (A) to segment (B) can be adjusted during synthesis of the block polymer. As described below, the block polymer of the present invention can be synthesized, for example, by polymerizing segment (A) and then adding segment (B). The amount of monomer added during this process can be adjusted to polymerize and synthesize the segments in the above ratio. Furthermore, when analyzing and confirming the obtained block polymer, H-NMR, GPC, acid value titration, and the like can be used.

[0038] (Block polymer of the second invention) [Segment (A')] The block polymer of the second invention has one or more segments (A') described below. In dispersing a coloring material or the like, the segment (A') is mainly hydrophobic and therefore adsorbs to the coloring material, thereby imparting dispersibility.

[0039] Segment (A') contains the hydrophobic and hydrophilic functional groups described above, with the molar ratio (total amount of hydrophobic functional groups in the segment / total amount of hydrophilic functional groups in the segment) being 0.85 to 8.50. By maintaining the molar ratio of hydrophobic and hydrophilic functional groups in segment (A') within the above range, excellent redispersibility and storage stability can be achieved. This is believed to be because the inclusion of hydrophobic functional groups within the above ratio provides sufficient adsorption to coloring materials, while the inclusion of hydrophilic functional groups within the above ratio causes slight repulsion between segments (A') of different polymers due to hydrophilic-hydrophobic interactions, suppressing adsorption, entanglement, and aggregation between the polymers, allowing many polymers to efficiently adsorb to the coloring materials and impart dispersibility. The molar ratio of the two is more preferably 1.50 to 8.50, and even more preferably 1.50 to 5.00. Within this range, even better redispersibility and storage stability can be achieved. To adjust the molar ratio of the hydrophobic functional group to the hydrophilic functional group within the above range, for example, during synthesis of the block polymer, the aforementioned monomer having the hydrophobic functional group and the monomer having the hydrophilic functional group may be polymerized so that the amounts of the functional groups in the block polymer are in the above ratio. When analyzing and confirming the obtained block polymer, H-NMR, GPC, acid value titration, etc. may be used.

[0040] The peak top molecular weight of segment (A') is 750 or more. If the peak top molecular weight is less than 750, the adsorption force to the material may be insufficient, and redispersibility may be impaired. The peak top molecular weight of segment (A') is preferably 1000 or more, more preferably 2000 or more. The method for measuring the peak top molecular weight is as shown in the examples, but is not limited to this as long as similar results are obtained.

[0041] In the block polymer of the second invention of this application, the mass proportion of segment (A') is preferably 25% by mass or more and 75% by mass or less. If the mass proportion of segment (A') is less than 25% by mass, the pigment adsorption performance is insufficient, and redispersibility and storage stability tend to be low. On the other hand, if the mass proportion of segment (A') is more than 75% by mass, the polymer may not dissolve in a solvent. The mass proportion of segment (A') is more preferably 55% by mass or more and 75% by mass or less, and most preferably 55% by mass or more and 65% by mass or less.

[0042] Segment (A') typically contains a structural unit derived from a monomer having a hydrophobic functional group and a structural unit derived from a monomer having a hydrophilic functional group, but is not limited thereto. Segment (A') can contain any structural unit other than the structural unit derived from a monomer having a hydrophobic functional group and the structural unit derived from a monomer having a hydrophilic functional group. When segment (A') is taken as 100% by mass, the total mass of the structural units derived from monomers having a hydrophobic functional group and the structural units derived from monomers having a hydrophilic functional group in segment (A') is preferably 10% by mass or more, more preferably 25% by mass or more, and even more preferably 50% by mass or more. It is most preferable that segment (A') is 100% by mass, i.e., composed solely of structural units derived from monomers having a hydrophobic functional group and structural units derived from monomers having a hydrophilic functional group. By maintaining the above preferred range, the effects of the present invention can be more effectively exhibited. Furthermore, the order of the structural units derived from each monomer in segment (A') is not particularly limited, but random is preferred. That is, in the present invention, various forms of the segment (A') can be used, such as a random copolymer, a block copolymer, an alternating copolymer, etc., but among these, a random copolymer is particularly preferred.

[0043] When segment (A') is taken as 100% by mass, the proportion of the total mass of the hydrophobic functional groups and the hydrophilic functional groups in segment (A') is preferably 5% by mass or more, more preferably 20% by mass or more, and most preferably 35% by mass or more. By keeping it within the above preferred range, the effects of the present invention can be more effectively exhibited.

[0044] [Segment (B')] The block polymer of the second invention of the present application has one or more segments (B') described below. In dispersing a coloring material or the like, the segment (B') mainly plays a role in dissolving the block polymer in a solvent due to its hydrophilicity.

[0045] Segment (B') contains the hydrophobic functional group and the hydrophilic functional group described above, with the molar ratio (total amount of hydrophobic functional groups in the segment / total amount of hydrophilic functional groups in the segment) being 0.16 or more and less than 0.85. By maintaining the molar ratio of hydrophobic functional groups to hydrophilic functional groups in segment (B') within the above range, redispersibility can be improved and the viscosity of the colorant dispersion or ink can be reduced to a suitable range. The improved redispersibility is believed to be due to the inclusion of hydrophilic functional groups within the above ratio, which allows the polymer to dissolve uniformly in the aqueous solvent and efficiently adsorb many polymers to the colorant. The reduced viscosity is believed to be due to the inclusion of hydrophilic functional groups within the above ratio, which allows sufficient solubility in the solvent, and the inclusion of hydrophobic functional groups within the above ratio, which slightly repels segments (B) of different polymers due to hydrophilic-hydrophobic interactions, making adsorption, aggregation, and entanglement less likely to occur and making the polymer more easily loosened. The molar ratio of the two is more preferably 0.25 or more and 0.60 or less, and even more preferably 0.25 or more and 0.45 or less. Within this range, better redispersibility and storage stability can be achieved. To adjust the molar ratio of the hydrophobic functional group to the hydrophilic functional group within the above range, for example, during synthesis of the block polymer, the aforementioned monomer having a hydrophobic functional group and the monomer having a hydrophilic functional group may be polymerized so that the respective functional groups have the above ratio. Furthermore, when analyzing and confirming the obtained block polymer, H-NMR, GPC, acid value titration, etc. may be used.

[0046] The peak top molecular weight of segment (B') is 750 or more. If the peak top molecular weight is less than 750, the solubility will be insufficient, the viscosity will increase, and redispersibility may be impaired. The peak top molecular weight of segment (B') is preferably 1000 or more, more preferably 2000 or more. The method for measuring the peak top molecular weight is as shown in the examples, but is not limited to this as long as similar results are obtained.

[0047] In the block polymer of the second invention of this application, the mass proportion of segment (B') is preferably 25% by mass or more and 75% by mass or less. If the mass proportion of segment (B') is less than 25% by mass, the polymer may not dissolve in a solvent. On the other hand, if the mass proportion of segment (A') is more than 75% by mass, the pigment adsorption performance tends to be insufficient, and redispersibility and storage stability tend to be poor. The mass proportion of segment (B') is more preferably 25% by mass or more and 45% by mass or less, and most preferably 35% by mass or more and 45% by mass or less.

[0048] Segment (B') typically comprises, but is not limited to, a structural unit derived from a monomer having a hydrophobic functional group and a structural unit derived from a monomer having a hydrophilic functional group. Segment (B') may contain any structural unit other than the structural unit derived from a monomer having a hydrophobic functional group and the structural unit derived from a monomer having a hydrophilic functional group. When segment (B') is taken as 100% by mass, the total mass of the structural units derived from a monomer having a hydrophobic functional group and the structural units derived from a monomer having a hydrophilic functional group in segment (B') is preferably 10% by mass or more, more preferably 25% by mass or more, and even more preferably 50% by mass or more. It is most preferable that segment (B') is 100% by mass, i.e., composed solely of structural units derived from a monomer having a hydrophobic functional group and structural units derived from a monomer having a hydrophilic functional group. By maintaining the above preferred range, the effects of the present invention can be more effectively exhibited. Furthermore, the order of the structural units derived from each monomer in segment (B') is not particularly limited, but random is preferred. That is, in the present invention, the segment (B') may be in the form of a random copolymer, a block copolymer, an alternating copolymer, or the like, with the random copolymer being particularly preferred.

[0049] When segment (B') is taken as 100% by mass, the proportion of the total mass of the hydrophobic functional groups and the hydrophilic functional groups in segment (B') is preferably 5% by mass or more, more preferably 20% by mass or more, and most preferably 40% by mass or more. By keeping it within the above preferred range, the effects of the present invention can be more effectively exhibited.

[0050] [Segment Configuration] The block polymer of the second invention of the present application may have two or more of the above-described segment (A') and segment (B') in each block polymer, but in order to more effectively exhibit the effects of the present invention, it is preferable that each block polymer contains one of each.

[0051] The block polymer of the second invention of this application may contain a portion other than segment (A') and segment (B') to the extent that the effects of the present invention are not impaired. In the block polymer of the first invention of this application, the total mass of segment (A') and segment (B') is preferably 50% by mass or more. More preferably, it contains 90% by mass or more, and most preferably, it contains 100% by mass, i.e., the block polymer is composed only of segment (A') and segment (B'). Within the above range, the effects of the present invention can be more effectively exhibited.

[0052] In the block polymer of the second invention of this application, the ratio of segment (A') to segment (B') (segment (A') mass:segment (B') mass) is preferably 25:75 to 75:25, more preferably 55:45 to 75:25, and particularly preferably 55:45 to 65:35. By maintaining the ratio within these preferred ranges, particularly excellent storage stability is achieved. The ratio of segment (A') to segment (B') can be adjusted by the ratio of monomers used in synthesizing the block polymer. Furthermore, when analyzing and confirming the obtained block polymer, H-NMR, GPC, acid value titration, etc. can be used.

[0053] The block structures of the block polymer of the first invention and the block polymer of the second invention are not particularly limited. Examples of selectable block structures include AB block polymers, ABC triblock polymers, ABA triblock polymers, and triblock structures to which other polymer units are bonded. Among these, AB block polymers and ABA triblock polymers are preferred, and AB block polymers are particularly preferred.

[0054] [Regarding Resin Properties of Block Polymers] The peak top molecular weight of the block polymers of the present invention is 3,000 to 16,000. 4,000 to 14,000 is preferred, and 5,000 to 12,000 is particularly preferred. If the peak top molecular weight is less than 3,000, steric hindrance and charge repulsion become small, making it difficult to maintain storage stability. On the other hand, if the peak top molecular weight is 16,000 or more, the ink viscosity increases, the adsorption rate slows, and dispersion does not progress. In addition, the water solubility of the polymer itself may decrease significantly. The conditions for measuring the peak top molecular weight are as described in the Examples.

[0055] The acid value of the block polymer of the present invention is preferably 120 mgKOH / g or more and 190 mgKOH / g or less. If it exceeds 190 mgKOH / g, the affinity for aqueous media becomes too high, resulting in a decrease in pigment adsorption performance and making dispersion difficult. Conversely, if the acid value is reduced to less than 120 mgKOH / g, water solubility decreases, which may result in poor redispersibility. The acid value is the amount of KOH (mg) required to neutralize 1 g of resin. Specifically, it can be measured by titrating a solution of the resin in methoxypropanol with a 1 N aqueous NaOH solution.

[0056] Aqueous inks or colorant dispersions using the block polymers of the present invention exhibit extremely excellent dispersibility and storage stability. After extensive research, the inventors discovered that existing block polymers used for pigment dispersions are difficult to dissolve in solvents because their hydrophobic and hydrophilic portions aggregate together to form micelles. This results in many polymers remaining in a micellar state without adsorbing to the pigment, resulting in insufficient dispersion performance. Through trial and error, the inventors arrived at a novel technical concept: by incorporating hydrophilic functional groups into the hydrophobic portion responsible for pigment adsorption, to the extent that this does not impair pigment adsorption, to form segment (A) (segment (A')), and by incorporating hydrophobic functional groups into the hydrophilic portion responsible for solvent solubility, to the extent that this does not impair solubility, to form segment (B) (segment (B')). This suppresses entanglement and aggregation of polymers due to repulsion caused by hydrophilic-hydrophobic interactions, resulting in excellent effects such as improved storage stability, shorter dispersion time, improved redispersibility, and reduced viscosity. Based on this novel technical concept, the present invention was completed. Furthermore, since the block polymer of the present invention described above has excellent storage stability and redispersibility, its use as a dispersant eliminates the need for a separate pigment derivative, and therefore colorant dispersions and inks using the block polymer of the present invention also have excellent color properties.

[0057] [Production of Block Polymer] The block polymer of the first invention of the present application can be produced by polymerizing the above-described monomer having a hydrophilic functional group and monomer having a hydrophobic functional group in the ratio described above. The block polymer of the second invention of the present application can be produced by polymerizing the above-described monomer having a hydrophilic functional group and monomer having a hydrophobic functional group so that the ratio of the hydrophilic functional group to the hydrophobic functional group is the ratio described above. The method for producing (synthesizing) the block polymer is not particularly limited. Various methods generally known for producing block polymers include, for example, atom transfer radical polymerization, which is carried out by oxidation-reduction using a metal complex such as copper or ruthenium as a catalyst and an organic halide as an initiator, the nitroxide method in which the -N-O radical of nitroxide is transferred, reversible addition-fragmentation chain transfer polymerization using dithiocarboxylic acid esters, and iodine transfer polymerization. The block polymer of the present application can be produced by first forming segment (A) using these well-known living radical polymerization methods, and then adding a monomer to add segment (B). However, the production method is not limited to these methods as long as similar results are obtained.

[0058] [Initiator] Examples of initiators (initiator compounds) that can be used in producing the block polymer of the present invention include, without limitation, common azo initiators such as azobis(isobutyronitrile) (AIBN), azobis(2,4-dimethylvaleronitrile) (V65), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V70), and oxide initiators such as benzoyl peroxide, dicumyl peroxide, t-butyl peroxybenzoate (BPB), di(4-tert-butylcyclohexyl) peroxydicarbonate (PERKADOX16), and potassium peroxydisulfate. AIBN is particularly preferred.

[0059] [Neutralizing Agent] When the block polymer of the present invention is used as a dispersant, it can be neutralized with an alkaline compound. Specific examples of alkaline compounds that can be used as a neutralizing agent include KOH, NaOH, triethylamine, triethanolamine, and ammonia, among others. Tertiary amines with a boiling point of 100°C or less are particularly preferred. The use of a tertiary amine with a boiling point of 100°C or less further improves water resistance and wet rub resistance. In particular, by preparing the block polymer of the present invention using a monomer having a carboxyl group as the hydrophilic functional group described above and neutralizing it with such a tertiary amine, a colorant dispersion containing the block polymer of the present invention and an ink using the same can exhibit particularly excellent water resistance and wet rub resistance. This is thought to be because, after printing with the ink, the amine compound volatilizes, rendering the polymer, which was solubilized by neutralization, insoluble in water, thereby improving the wet rub resistance of the printed material. Triethylamine or triethanolamine is particularly preferred because it is difficult to volatilize at room temperature and therefore does not volatilize in the ink state, allowing it to maintain resolubility (redispersibility) near the nozzle. The amount of alkaline compound added should be sufficient to neutralize 20% to 200% of the resin's acid value. It is preferably 40 to 180%, and even more preferably 50 to 120%. A lower neutralization rate can cause resin precipitation over time, while a higher neutralization rate can increase the pH, potentially damaging printer head components. Furthermore, water resistance and wet friction resistance can be compromised.

[0060] (Colorant Dispersion) The colorant dispersion of the present invention contains the block polymer of the present invention, a water-insoluble colorant, and an aqueous medium, and can be prepared by mixing these components with any additives and dispersing the mixture by the method described below.

[0061] [Water-Insoluble Colorant] In the colorant dispersion of the present invention, a water-insoluble colorant is used. This is typically a pigment or a water-insoluble dye. Note that "water-insoluble" here also includes so-called poorly water-soluble materials, which are difficult to completely dissolve in water. Examples of pigments include pigments for yellow inks such as C.I. Pigment Yellow 1, 2, 3, 12, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 128, 129, 138, 139, 147, 150, 151, 154, 155, 180, and 185. One or more of these pigments may be used.

[0062] Examples of pigments for magenta inks include C.I. Pigment Red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1, 112, 122, 123, 150, 168, 184, 202, and 209; C.I. Pigment Violet 19; and the like, and one or more of these can be used. Examples of pigments for cyan inks include C.I. Pigment Blue 1, 2, 3, 15:3, 15:4, 16, 22, and 60; C.I. Vat Blue 4 and 60; and the like, and one or more of these can be used. Examples of pigments for black inks include carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, and organic pigments such as aniline black (C.I. Pigment Black 1). Inorganic pigments such as titanium oxide and iron oxide can also be used.

[0063] Among the above pigments, pigments having a structure in which aromatic rings are linked, such as anthracene, quinacridone, and biphenyl structures, exhibit particularly excellent storage stability. This is presumably due to the π-π interaction between the aromatic rings of the pigment and the biphenyl or phenyl group of the block polymer of the present invention, which contributes to further stabilization. Examples of such pigments include Pigment Yellow 74, 114, 147, and 150, Pigment Red 5, 7, 12, 48, 57, 112, 122, 123, 168, 184, 202, and 209, Pigment Violet 19, Pigment Blue 1, 2, 22, and 60, and Pigment Black 7.

[0064] The above-mentioned various pigments may be pigments that have been kneaded with a dispersant.

[0065] The dispersion of the present invention may also contain a disperse dye as a water-insoluble coloring material. Disperse dyes are compounds that are poorly soluble or insoluble in water. Specific examples of disperse dyes include the following. Yellow disperse dyes are not particularly limited, but include, for example, C.I. Disperse Yellow 3, 4, 5, 7, 9, 13, 23, 24, 30, 33, 34, 42, 44, 49, 50, 51, 54, 56, 58, 60, 63, 64, 66, 68, 71, 74, 76, 79, 82, 83, 85, 86, 88, 90, 91, 93, 98, 99, 100, 104, 108, 114, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 16 18, 119, 122, 124, 126, 135, 140, 141, 149, 160, 162, 163, 164, 165, 179, 180, 182, 183, 184, 186, 192, 198, 199, 202, 204, 210, 211, 215, 216, 218, 224, 227, 231, and 232.

[0066] Examples of orange disperse dyes include, but are not limited to, C.I. Disperse Orange 1, 3, 5, 7, 11, 13, 17, 20, 21, 25, 29, 30, 31, 32, 33, 37, 38, 42, 43, 44, 45, 46, 47, 48, 49, 50, 53, 54, 55, 56, 57, 58, 59, 61, 66, 71, 73, 76, 78, 80, 89, 90, 91, 93, 96, 97, 119, 127, 130, 139, and 142. Examples of red disperse dyes include, but are not limited to, C.I. Disperse Red 1, 4, 5, 7, 11, 12, 13, 15, 17, 27, 43, 44, 50, 52, 53, 54, 55, 56, 58, 59, 60, 65, 72, 73, 74, 75, 76, 78, 81, 82, 86, 88, 90, 91, 92, 93, 96, 103, 105, 106, 107, 108, 110, 111, 113, 117, 118, 121, 122, 126, 127, 128, 131, 132, 134, 135, 137, 143, 145, 146, 1 51, 152, 153, 154, 157, 159, 164, 167, 169, 177, 179, 181, 183, 184, 185, 188, 189, 190, 191, 192, 200, 201, 202, 203, 205, 206, 207, 210, 221, 224, 225, 227, 229, 239, 240, 257, 258, 277, 278, 279, 281, 288, 298, 302, 303, 310, 311, 312, 320, 324, and 328.

[0067] Examples of violet disperse dyes include, but are not limited to, C.I. Disperse Violet 1, 4, 8, 23, 26, 27, 28, 31, 33, 35, 36, 38, 40, 43, 46, 48, 50, 51, 52, 56, 57, 59, 61, 63, 69, and 77. Examples of green disperse dyes include, but are not limited to, C.I. Disperse Green 9. Examples of blue disperse dyes include, but are not limited to, C.I. Disperse Blue 3, 7, 9, 14, 16, 19, 20, 26, 27, 35, 43, 44, 54, 55, 56, 58, 60, 62, 64, 71, 72, 73, 75, 79, 81, 82, 83, 87, 91, 93, 94, 95, 96, 102, 106, 108, 112, 113, 115, 118, 120, 122, 125, 128, 130, 139, 141, 142, 143, 146, 148, 149, 153, 154, 158, 165, 167, 171, 173, 174, 176, 181, 183, 185, 186, 187, 189, 197, 198, 200, 201, 205, 207, 211, 214, 224, 225, 257, 259, 267, 268, 270, 284, 285, 287, 288, 291, 293, 295, 297, 301, 315, 330, 333, 359, 360. Black disperse dyes are not particularly limited, but examples include C.I. Disperse Black 1, 3, 10, and 24. One or more of the above pigments or water-insoluble dyes can be appropriately selected and used.

[0068] [Aqueous Medium] Water is usually used as the aqueous medium for the coloring material dispersion of the present invention, but a water-soluble organic solvent may also be used if necessary. Examples of water-soluble organic solvents include 1,2-hexanediol, 1,6-hexanediol, 1,5-pentanediol, 2-pyrrolidone, N-methylpyrrolidone, triethylene glycol monobutyl ether, ethylene glycol, propylene glycol, triethylene glycol, and glycerin. Of these, 1,2-hexanediol, 2-pyrrolidone, and triethylene glycol monobutyl ether are particularly preferred.

[0069] [Additives] Acetylene glycol-based or silicone-based activators or preservatives may be added as needed. Commercially available products can be used. For example, acetylene glycol-based compounds include Olfine Y, Surfynol 82, 440, 465, STG, and E1010, and polysiloxane compounds include BYK302 and BYK348 (manufactured by BYK Japan). [Composition of Colorant Dispersion] In the colorant dispersion of the present invention, the blending ratio of the above-mentioned components can be appropriately selected depending on the application. In addition to the above-mentioned components, the colorant dispersion of the present invention may contain other components depending on the application. In the colorant dispersion of the present invention, the content of the colorant is preferably 1 to 60 parts by weight, more preferably 3 to 40 parts by weight, and most preferably 5 to 25 parts by weight, based on 100 parts by weight of the entire dispersion. The content of the block polymer is preferably 0.1 to 30 parts by weight, more preferably 0.3 to 20 parts by weight, and most preferably 1 to 15 parts by weight, based on 100 parts by weight of the entire dispersion.

[0070] [Production of Colorant Dispersion Liquid] The colorant dispersion liquid of the present invention can be produced by dispersing the above-mentioned components by a known method. For example, the colorant dispersion liquid can be produced by dispersing the above-mentioned components in a bead mill or other wet disperser.

[0071] [Crosslinking Treatment] To ensure both stability and redispersibility, the dispersion of the present invention can be subjected to an appropriate crosslinking treatment after dispersion. Examples of crosslinking agents that can be used include epoxy resins with a glycidyl ether skeleton and resins with oxazoline groups. The amount of crosslinking agent is preferably in the range of 0.5% to 60% relative to the resin. If the amount is less than this, the stabilizing effect of crosslinking cannot be achieved, and if the amount is more, redispersibility may deteriorate. Crosslinking can be achieved by adding a crosslinking agent to the colorant dispersion that has undergone the above-mentioned dispersion process and heating to around 80°C.

[0072] [Ultrafiltration] The coloring material dispersion of the present invention can be subjected to an impurity removal process by ion exchange treatment or ultrafiltration. Ion exchange treatment can remove ionic substances such as cations and anions (divalent metal ions, etc.), and ultrafiltration can remove dissolved impurities (residual substances from pigment synthesis, excess components in the dispersion composition, resins not adsorbed to the organic pigment, contaminants, etc.).

[0073] [Physical Properties of Colorant Dispersion Liquid] Because the block polymer of the present invention has excellent dispersibility as described above, the colorant dispersion liquid of the present invention can have a particle size distribution D50 of 135 nm or less, which is a preferred range. By maintaining the particle size distribution D50 within this range, the ink is less likely to clog nozzles, improving ejection stability, and inhibiting sedimentation of the colorant, improving storage stability. The particle size distribution D50 of the colorant dispersion liquid is particularly preferably 110 nm or less, and most preferably 100 nm or less. The particle size distribution D50 of the colorant dispersion liquid can be adjusted to within the above range by appropriately adjusting the dispersion time and intensity when preparing the colorant dispersion liquid, or by removing coarse particles using a filter, etc. Furthermore, the block polymer of the present invention has excellent storage stability and can maintain the preferred particle size for one week or more. The particle size distribution D50 was measured as described in the examples, but this method is not limited to this as long as similar results are obtained.

[0074] As described above, the block polymer of the present invention is less likely to aggregate or entangle polymers, suppressing viscosity increases. Therefore, the viscosity of the coloring material dispersion of the present invention can be adjusted to a preferred range of 25 mPas or less. By adjusting the viscosity within this range, the ejection properties and print quality of the resulting ink can be improved. A viscosity of 10 mPas or less is particularly preferred, and 5 mPas or less is most preferred. The viscosity of the coloring material dispersion can be adjusted to within the above range by appropriately adjusting the neutralization rate of the block polymer to match the solvent when preparing the coloring material dispersion. Furthermore, the block polymer of the present invention has excellent storage stability and can maintain the preferred viscosity for one week or more. The viscosity measurement method is as described in the examples, but is not limited to this as long as similar results are obtained.

[0075] (Ink) In the present invention, the term "dispersion" means that a water-insoluble coloring material is dispersed in an aqueous medium, and includes so-called "ink" as well as a state in which a coloring material is dispersed in an aqueous medium beforehand when producing ink. When the coloring material dispersion of the present invention is used as an ink, it is preferable to prepare a dispersion in advance in which each of the components described above is dispersed, and then add other components depending on the application.

[0076] [Other Ink Components] When preparing an inkjet ink using the coloring material dispersion of the present invention, other components such as organic solvents, resins, and preservatives can be added. The organic solvent is not particularly limited, but examples thereof include polyhydric alcohols and pyrrolidones. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, and glycerin. Polyhydric alcohols have the effect of increasing the wettability of the ink to paper and preventing drying inside the head nozzles, thereby increasing the ink's moisture retention. When polyhydric alcohols are contained, their content can be 2% by mass or more and 30% by mass or less relative to the total mass of the ink.

[0077] Resins have the function of improving fixability, and examples thereof include acrylic resins, fluorene resins, urethane resins, olefin resins, rosin-modified resins, terpene resins, ester resins, amide resins, epoxy resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymers, and ethylene vinyl acetate resins. These resins can be used alone or in combination of two or more. The resin may be an emulsion type or a solution type. When a resin is contained, its content can be 0.1% by mass or more and 6% by mass or less.

[0078] Examples of antiseptics and antifungal agents include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazolin-3-one (Proxel CRL, Proxel BDN, Proxel GXL, Proxel XL.2, Proxel TN, Proxel LV, available from Zeneca), and 4-chloro-3-methylphenol (Preventol CMK, available from Bayer, etc.).

[0079] [Physical Properties of Ink] As described above, the block polymer of the present invention is less likely to aggregate or entangle with other polymers, suppressing viscosity increases. Therefore, inks using the coloring material dispersion of the present invention can have a viscosity of 7 mPas or less, which is a preferred range. By maintaining the ink viscosity within this range, ejection properties and print quality can be improved. When used as an inkjet ink, a viscosity of 6 mPas or less is particularly preferred. Furthermore, for high-chroma inkjet inks, a viscosity of 3.0 mPas to 5.5 mPas is most preferred. To adjust the ink viscosity within this range, the neutralization rate of the block polymer can be appropriately adjusted to match the solvent when preparing the coloring material dispersion. Furthermore, the block polymer of the present invention has excellent storage stability, and can maintain the preferred viscosity for one week or more. The ink viscosity was measured using the methods described in the Examples, but is not limited to these methods as long as similar results are obtained. The ink's uses are not particularly limited, and examples include printing inks for inkjet printing and inks for writing instruments, but it is particularly suitable for use as an inkjet printing ink.

[0080] The present invention will be explained in more detail below with reference to examples, in which "parts" means "parts by weight".

[0081] (Preparation of Block Polymer 1) A SUS304 reactor was charged with 385 parts of phenoxyethyl acrylate (PEA, molecular weight 192.2) as a monomer having a hydrophobic functional group, 35 parts of acrylic acid (AA, molecular weight 72.1) as a monomer having a hydrophilic functional group, 43 parts of S-benzyl-S-dodecyltrithiocarbonate as a polymerization modifier, 9.6 parts of azobisisobutyronitrile as a radical initiator, and 420 parts of isobutyl alcohol as a reaction solvent. The atmosphere in the reactor was replaced with nitrogen, and the internal temperature was raised to 70°C using an oil bath while stirring. After the temperature increase, the internal temperature was maintained for 6 hours to complete the polymerization reaction. The solvent was then distilled off under reduced pressure to obtain Polymer A. GPC analysis of the resulting Polymer A revealed a molecular weight of 3380 and a molecular weight distribution (Mw / Mn) of 1.14. The synthesized polymer A, 119 parts of phenoxyethyl acrylate as a monomer having a hydrophobic functional group, 87.5 parts of methacrylic acid (MAA, molecular weight 86.09) and 73.5 parts of acrylic acid as monomers having a hydrophilic functional group, 1.9 parts of azobisisobutyronitrile as a radical initiator, and 700 parts of isobutyl alcohol as a reaction solvent were charged into a reaction vessel. The atmosphere inside the vessel was replaced with nitrogen, and the internal temperature was raised to 70°C while stirring. After the temperature increase, the reaction was continued for 8 hours to complete the polymerization. The pressure inside the reaction vessel was then reduced, and the solvent was distilled off to obtain block polymer 1. GPC analysis of the resulting block polymer 1 revealed a molecular weight of 6220 and a molecular weight distribution (Mw / Mn) of 1.21. The acid value was 182 mgKOH / g.

[0082] (Preparation of Resin Dissolved Product 1) To the synthesized block polymer 1, KOH was added in an amount sufficient to neutralize the acid value of the resin by 50%, and ion-exchanged water was added so that the resin concentration became 15%, followed by stirring and dissolving with a dissolver at 80°C for 2 hours to obtain Resin Dissolved Product 1 (50% neutralized product). In addition, the amount of KOH added was changed to an amount sufficient to neutralize the acid value of the resin by 120%, and Resin Dissolved Product 1 (120% neutralized product) was obtained in the same manner.

[0083] (Preparation of Block Polymers 2-12 and Resin Dissolved Materials 2-12) Block polymers 2-12 were obtained using the same procedure as for block polymer 1, but with the monomer ratios changed as shown in Table 1. The physical properties (acid value, peak-top molecular weight, Mw / Mn) of block polymers 2-12 are shown in Table 1. Resin dissolved materials were obtained using the resulting block polymers 2-12 using the same procedure as for resin dissolved material 1. Note that only 50% neutralized products were prepared for block polymers 2-5, 11, and 12, and only 120% neutralized products were prepared for block polymers 6, 9, and 10. (Preparation of Resin Dissolved Materials 2(1)-(3)) Triethylamine was added to block polymer 2 in an amount sufficient to neutralize the acid value of the resin by 50%, and ion-exchanged water was added to achieve a resin concentration of 15%. Resin dissolved material 2(1) (50% neutralized product) was obtained by stirring and dissolving the mixture at 80°C for 2 hours using a dissolver. Resin Dissolved Product 2(2) (50% neutralized product) was obtained in the same manner except that triethylamine was replaced with triethanolamine. Resin Dissolved Product 2(3) (50% neutralized product) was obtained in the same manner except that triethylamine was replaced with KOH.

[0084] (Preparation of Block Polymer 13 and Resin Dissolution 13) 420 parts of "A-LEN10" (trade name, manufactured by Shin-Nakamura Chemical Co., Ltd., ethoxylated o-phenylphenol acrylate, specific gravity 1.135 (25°C), viscosity 150 mPa·s (25°C), refractive index: 1.577, molecular weight 268, log P = 3.98) as a monomer having a hydrophobic functional group, 51.6 parts of S-benzyl-S-dodecyltrithiocarbonate as a polymerization modifier, 11.5 parts of azobisisobutyronitrile as a radical initiator, and 280 parts of methoxypropanol as a reaction solvent were charged into a 2-L stainless steel separable flask, and the system was heated to 70°C in an oil bath with nitrogen bubbling and stirring. After the temperature increase was complete, the reaction was carried out for 6 hours to synthesize Polymer A'. A small sample of the contents was sampled and analyzed by GPC, which revealed a peak-top molecular weight of 3,200 and an Mw / Mn ratio of 1.21. Next, 119 parts of ALEN10 as a monomer having a hydrophobic functional group, 87.5 parts of methacrylic acid and 73.5 parts of acrylic acid as monomers having a hydrophilic functional group, and 420 parts of methoxypropanol as a reaction solvent were added to the flask, and the mixture was reacted at 70°C for 8 hours with nitrogen bubbling and stirring. The system temperature was then raised to 170°C, the system pressure was reduced, and the solvent was distilled off to extract block polymer 13. GPC analysis of the resulting block polymer 13 revealed a peak-top molecular weight of 5,000 and an Mw / Mn ratio of 1.30. The acid value was 143 mgKOH / g. The details of block polymer 13 are shown in Table 2. Resin Dissolve 13 was obtained using the resulting block polymer 13 using the same procedure as for Resin Dissolve 1, except that a 50% neutralized product was not prepared.

[0085] The GPC measurements were carried out under the following conditions: Apparatus: HLC-8220GPC (Tosoh Corporation); Detector: RI (differential thermal refractive index detector); Solvent: Degassed THF; Columns: Gelpack GL-R400M, GL-R440, GL-R450, and a guard column were used in conjunction; Measurement concentration: 10 mg / ml; Flow rate: 2.0 ml / min; Injection volume: 150 μL / min; Column temperature: 40°C.

[0086] Example 1: 40 g of resin solution 1, 15 g of PR150, 5 g of 1,2-hexanediol, and 40 g of water were mixed and dispersed using 0.5 mm zirconia beads and a paint shaker for 5 hours. This mixture was further dispersed using 0.1 mm zirconia beads for 20 hours. The zirconia beads were separated and the recovered dispersion was centrifuged at 16,300 rpm for 10 minutes to remove coarse particles, yielding a pigment dispersion. The resulting pigment dispersion, ion-exchanged water, and a clear ink prepared according to the formulation in Table 3 were mixed in the following formulation to obtain an ink for evaluation. Evaluation Ink Blend Ratio (% by mass): Pigment Dispersion (amount to give 5.60% PR150 by mass): Clear Ink: 45.88; Ion-exchanged Water: Remaining: Total: 100.00. The pigment dispersion and the ink for evaluation were evaluated as follows. The results are shown in Table 4.

[0087] (Examples 2 to 5, Comparative Examples 1 to 6) Pigment dispersions and evaluation inks were prepared in the same manner as in Example 1, except that the block polymer was changed as shown in Table 4, and then the following evaluations were carried out. The results are shown in Table 4.

[0088] (Evaluation of Storage Stability) The viscosity and particle size distribution D50 of each pigment dispersion obtained in Examples 1 to 5 and Comparative Examples 1 to 6 were measured immediately after preparation. The dispersions were then left to stand for one week in a thermostatic chamber at 60°C, and the viscosity and particle size distribution D50 were measured. The viscosity of each ink obtained in Examples 1 to 5 and Comparative Examples 1 to 6 was also measured in the same manner. A cone rotor type rotational viscometer ("TV25 Model" manufactured by Toki Sangyo Co., Ltd.) was used to measure the viscosity, and a "Nanotrac Wave II EX-150" (manufactured by Nikkiso Co., Ltd.) was used to measure the particle size distribution D50. For the particle size distribution D50 of the pigment dispersion, a ⊚ was used for a particle size distribution of 110 nm or less, a ◯ was used for a particle size distribution of 135 nm or less, and an × was used for a particle size distribution greater than 135 nm. For the viscosity of the pigment dispersion, a ⊚ was used for a particle size distribution of 10 mPas or less, a ◯ was used for a particle size distribution of 25 mPas or less, and an × was used for a particle size distribution greater than 25 mPas. For the viscosity of the ink, a ⊚ was used for a particle size distribution of 6 mPas or less, a ◯ was used for a particle size distribution of 7 mPas or less, and an × was used for a particle size distribution greater than 7 mPas.

[0089] (Evaluation of redispersibility) 10 μL of each ink from Examples 1 to 5 and Comparative Examples 1 to 6 was dropped onto the bottom of a plastic container at five locations using a micropipette, and the container was dried under reduced pressure at 60° C. for 1 hour. The container was then filled with the liquids of the ink components to be evaluated other than the pigment dispersion, and the redispersibility was visually confirmed. A rating of ○ indicates that the ink was almost completely redispersed, and a rating of × indicates that the ink was redispersed but some aggregates were observed, or that the ink was not redispersed at all.

[0090]

[0091]

[0092]

[0093]

[0094] (Evaluation Results) As shown in Table 4, Comparative Examples 1, 4, 5, and 6, which do not contain a structural unit derived from a monomer having a hydrophilic functional group in segment (A) (or segment (A')), show insufficient redispersibility. Furthermore, Comparative Examples 1, 2, and 3, which do not contain a structural unit derived from a monomer having a hydrophobic functional group in segment (B) (or segment (B')), show that the initial viscosity or particle size distribution D50 falls outside the preferred range. Furthermore, Comparative Examples 1, 2, 3, and 5 show a significant increase in particle size distribution D50 after one week of storage, indicating poor storage stability.

[0095] In contrast, Examples 1 to 5, which use the block polymer of the present invention, in which both segment (A) (or segment (A')) and segment (B) (or segment (B')) contain a structural unit composed of a monomer having a hydrophobic functional group and a structural unit composed of a monomer having a hydrophilic functional group in a ratio within a specified range, exhibit high redispersibility. Furthermore, even after one week of storage, the viscosity and particle size distribution D50 remain within ranges suitable for inkjet inks, demonstrating high storage stability.

[0096] Example 6: 48 g of resin solution 2(1), 18 g of PB-15:3, 5 g of 1,2-hexanediol, and 29 g of water were mixed and dispersed using 0.5 mm zirconia beads in a paint shaker for 5 hours. This was further dispersed using 0.1 mm zirconia beads for 8 hours. The zirconia beads were separated, and the recovered dispersion was centrifuged at 16,300 rpm for 10 minutes to remove coarse particles, yielding a pigment dispersion. Examples 7 and 8: Pigment dispersions were obtained in the same manner, except that resin solution 2(2) and resin solution 2(3) were used instead of resin solution 2(1). (Evaluation of Wet Rub Resistance) The pigment dispersions obtained in Examples 6 to 8 were mixed in the following formulation to obtain evaluation inks. Pigment dispersion: Amount to give 7% by mass of PB-15:3 Binder (urethane resin): 5 parts 1,2-hexanediol: 10 parts Surface conditioner: 1 part Ion-exchanged water Remainder: Total: 100 The surface conditioner used was "BYK-302" (trade name, polyether-modified polydimethylsiloxane manufactured by Byk Chemie). The D50 and viscosity of the pigment dispersion and the viscosity of the evaluation ink were measured using the methods described above. The results are shown in Table 5.

[0097]

[0098] The ink for evaluation was applied to PET film using a #3 bar coater and then dried in an oven at 80°C for 3 minutes to obtain a coating. A dry friction test was performed using a Gakushin-type friction tester (Yasuda Seiki Seisakusho, Type II friction tester) in which a white cotton cloth moistened with 100% ion-exchanged water was attached to the friction element and rubbed back and forth across the surface of the coating 10 times with a 200g load to evaluate wet friction resistance. The appearance of the coating after 10 strokes was photographed with an Olympus Tough TG-5 digital camera, and the results are shown in Figures 1 to 3. In the figures, 1-a, 2-a, and 3-a show the condition of the film coating after the wet friction test, while 1-b, 2-b, and 3-b show the condition of the white cotton cloth used in the wet friction test after the test. It can be seen that Examples 6 and 7, which used Resin Dissolved Product 2(1) or Resin Dissolved Product 2(2) neutralized with triethylamine or triethanolamine as the neutralizing agent, had smaller peeled areas of the coating film and better wet friction resistance than Example 8, which used Resin Dissolved Product 2(3) neutralized with KOH. This is thought to be because the amine compound neutralizing the resin volatilized, making the resin insoluble in water.

[0099] As described above, the present invention provides a block polymer that exhibits extremely excellent performance as a dispersant, a coloring material dispersion that uses the block polymer and has excellent performance, and an inkjet ink that uses the same and has excellent performance.

Claims

1. A block polymer having at least one segment (A) satisfying the following (a1) and (a2) and at least one segment (B) satisfying the following (b1) and (b2), and having a peak top molecular weight of 3,000 or more and 16,000 or less. (a1): Having a constitutional unit derived from a monomer having a hydrophobic functional group and a constitutional unit derived from a monomer having a hydrophilic functional group, the mass ratio of the two (total mass of constitutional units derived from monomers having hydrophobic functional groups / total mass of constitutional units derived from monomers having hydrophilic functional groups) is 2.3 or more and 19.0 or less. (a2): Peak top molecular weight is 750 or more. (b1): Having a constitutional unit derived from a monomer having a hydrophobic functional group and a constitutional unit derived from a monomer having a hydrophilic functional group, the mass ratio of the two (total mass of constitutional units derived from monomers having hydrophobic functional groups / total mass of constitutional units derived from monomers having hydrophilic functional groups) is 0.43 or more and less than 2.

3. (b2): Peak top molecular weight is 750 or more.

2. The block polymer according to claim 1, characterized in that in said segment (A), the proportion of the total mass of the constitutional units derived from the monomer having a hydrophobic functional group and the total mass of the constitutional units derived from the monomer having a hydrophilic functional group is 10 mass% or more, and in said segment (B), the proportion of the total mass of the constitutional units derived from the monomer having a hydrophobic functional group and the total mass of the constitutional units derived from the monomer having a hydrophilic functional group is 10 mass% or more.

3. The block polymer according to claim 2, wherein the total mass of the segment (A) and the segment (B) accounts for 50% by mass or more of the block polymer.

4. The block polymer described in claim 3, characterized in that the monomer having a hydrophobic functional group is a monomer having a phenyl group and / or a monomer having a biphenyl group, and the monomer having a hydrophilic functional group is a monomer having a carboxy group.

5. A block polymer having at least one segment (A') satisfying the following (a1') and (a2) and at least one segment (B') satisfying the following (b1') and (b2), and having a peak top molecular weight of 3000 or more and 16000 or less. (a1'): The molar ratio of hydrophobic functional groups to hydrophilic functional groups (total amount of substance of hydrophobic functional groups / total amount of substance of hydrophilic functional groups) is 0.85 or more and 8.50 or less (a2): The peak top molecular weight is 750 or more (b1'): The molar ratio of hydrophobic functional groups to hydrophilic functional groups (total amount of substance of hydrophobic functional groups / total amount of substance of hydrophilic functional groups) is 0.16 or more and less than 0.85 (b2): The peak top molecular weight is 750 or more 6. The block polymer according to claim 5, characterized in that in said segment (A'), the proportion of the sum of the mass of said hydrophobic functional group and the mass of said hydrophilic functional group is 10 mass% or more, and in said segment (B'), the proportion of the sum of the mass of said hydrophobic functional group and the mass of said hydrophilic functional group is 10 mass% or more.

7. The block polymer according to claim 6, characterized in that the sum of the mass of the segment (A') and the mass of the segment (B') accounts for 50 mass % or more of the block polymer.

8. The block polymer according to claim 7, wherein the hydrophobic functional group is a phenyl group and / or a biphenyl group, and the hydrophilic functional group is a carboxy group.

9. The block polymer according to any one of claims 1 to 8, characterized in that the acid value is 120 mgKOH / g or more and 190 mgKOH / g or less.

10. A coloring material dispersion comprising the block polymer according to any one of claims 1 to 9, a water-insoluble coloring material, and an aqueous medium.

11. The colorant dispersion according to claim 10, wherein the colorant is a pigment and / or a water-insoluble dye.

12. A method for producing a printing ink, comprising mixing the coloring material dispersion according to claim 10 with an organic solvent, a resin and a preservative.

13. A printing ink comprising at least the block polymer according to any one of claims 1 to 9, a coloring material, an organic solvent, a resin and a preservative.