Water-based ink, ink cartridge, and ink-jet recording method

Abstract

To provide an aqueous ink for inkjet excellent in storage stability, which hardly increases in viscosity even when stored under a severe environment such as a high-temperature condition.SOLUTION: The aqueous ink for inkjet contains a coloring material and a block copolymer. The block copolymer contains: an A block comprising a segment A having no acid group, and a group represented by the following general formula (1) bonded to one terminal of the segment A; and a B block comprising a segment B having an acid group, and a group represented by the following general formula (2) bonded to one terminal of the segment B. (In the general formula (1), R1 represents an alkylene group; and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. In the general formula (2), R2 and R3 each independently represent an alkyl group or the like.)SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based ink, an ink cartridge, and an ink-jet recording method. [Background technology]

[0002] With the improvement of image quality and recording speed, inkjet recording devices are increasingly being used in the business field. Inkjet inks used in the business field are required to have properties such as being able to record images with excellent fastness, as well as being more reliable than ever before in terms of storage stability, etc. In order to improve these performances, inks to which pigments and block copolymers have been added are being considered.

[0003] For example, an inkjet ink containing a block copolymer having a hydrophobic segment and a hydrophilic segment in which a hydrophobic unit and a hydrophilic unit form a random or gradient copolymer structure has been proposed (Patent Document 1). Also, an inkjet ink containing an ABC triblock copolymer has been proposed (Patent Document 2).

[0004] Meanwhile, as a method for producing block copolymers, living radical polymerization methods have been frequently studied from the viewpoint of compatibility with a wide variety of (meth)acrylic acid esters used as monomers. For example, so-called reversible addition-fragmentation chain transfer polymerization (RAFT polymerization) using a dithioester or trithiocarbonate chain transfer agent has been proposed (Patent Document 3). In addition, an inkjet ink containing an AB block copolymer synthesized by RAFT polymerization has been proposed (Patent Document 4). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-195769 A [Patent Document 2] JP 2012-072357 A [Patent Document 3] Special Publication No. 2000-515181 [Patent Document 4] JP 2018-203802 A Summary of the Invention [Problem to be solved by the invention]

[0006] Inks containing a block copolymer have improved reliability, such as storage stability, to a certain extent, compared to inks not containing a block copolymer. However, the inventors of the present invention have found that the inks proposed in Patent Documents 1 and 2 do not satisfy the level of reliability required for inkjet recording devices for the business field in recent years.

[0007] Therefore, an object of the present invention is to provide a water-based ink for inkjet use that is resistant to an increase in viscosity even when stored under harsh environments such as high temperature conditions and has excellent storage stability. Another object of the present invention is to provide an ink cartridge and an inkjet recording method that use this water-based ink. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided an aqueous ink for inkjet recording containing a colorant and a block copolymer, characterized in that the block copolymer comprises an A block having a segment A that has no acid group and a group represented by the following general formula (1) bonded to one end of the segment A, and a B block having a segment B that has an acid group and a group represented by the following general formula (2) bonded to one end of the segment B.

[0009] TIFF0007631001000001.tif33170 (In the general formula (1), * represents a bonding position with one end of the segment A, R1 represents an alkylene group, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. In the general formula (2), * represents a bonding position with one end of the segment B, R2 and R3 each independently represent a hydrogen atom or an alkyl group, and R2 and R3 may be bonded to each other to form a ring structure.) Effect of the Invention

[0010] According to the present invention, it is possible to provide an aqueous inkjet ink that is resistant to an increase in viscosity even when stored under harsh environments such as high temperature conditions and has excellent storage stability. Furthermore, according to the present invention, it is possible to provide an ink cartridge and an inkjet recording method that use this aqueous ink. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating an embodiment of an ink cartridge of the present invention. [Diagram 2] 1A and 1B are diagrams illustrating an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified. When "(meth)acrylic acid" is written, it means "acrylic acid" or "methacrylic acid," respectively. A "unit" of a copolymer means a repeating unit derived from one monomer, and a "segment" means a unit composed of multiple "units."

[0013] A typical block copolymer contains two or more types of polymer blocks with different properties, and is formed by covalent bonding of these polymer blocks. Block copolymers used in aqueous inkjet inks are used to stably maintain components having hydrophobic sites, such as coloring materials such as dyes and pigments, in an aqueous medium. Block copolymers used for such purposes usually have a block without acid groups (hydrophobic block) and a block having acid groups (hydrophilic block). The hydrophobic block adsorbs to the hydrophobic sites of the components, and the steric repulsion generated by the hydrophilic block acts to stably maintain the presence of the components in the aqueous medium.

[0014] On the other hand, if the hydrophobic block is enlarged to improve the adsorption to the hydrophobic site, the intermolecular association increases due to the hydrophobic interaction between the hydrophobic blocks. When the intermolecular association increases, the movement of the molecular chain is suppressed, and the adsorption to the components decreases, which makes the storage stability of the ink more likely to decrease. Furthermore, the hydrophilic block also self-associates due to hydrogen bonds within the molecule, which makes the steric repulsion more likely to decrease.

[0015] The present inventors have investigated the suppression of intermolecular association of hydrophobic blocks and intramolecular association of hydrophilic blocks by binding a group having a specific structure to the end of each block of a so-called AB block copolymer, which is composed of a hydrophobic block and a hydrophilic block. As a result, they have found a block copolymer in which a specific group is bound to each end of a segment A that does not have an acid group and a segment B that has an acid group. By binding a group represented by the following general formula (1) to one end of a segment A that does not have an acid group, the end of the A block is negatively charged in an aqueous medium. As a result, it has been found that the carboxylic acid group in the general formula (1) pulls and extends the molecular chain, thereby suppressing hydrophobic interactions. In addition, by binding a group represented by the following general formula (2) to one end of a segment B that has an acid group, the end of the B block is also negatively polarized in an aqueous medium due to the electron-withdrawing property of the cyano group in the general formula (2). As a result, it has been found that the molecular chain is pulled and extended, thereby suppressing self-association due to intramolecular hydrogen bonds.

[0016] TIFF0007631001000002.tif33170 (In the general formula (1), * represents a bonding position with one end of the segment A, R1 represents an alkylene group, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. In the general formula (2), * represents a bonding position with one end of the segment B, and R2 and R3 each independently represent a hydrogen atom or an alkyl group. R2 and R3 may be bonded to each other to form a ring structure.)

[0017] It was also found that by incorporating a block copolymer containing the above-mentioned A block and B block into an aqueous ink, the viscosity of the ink is less likely to increase even when stored in harsh environments such as high temperature conditions, and storage stability is improved. It is believed that the steric repulsion between the block copolymers is improved by hydrogen bonding between the acid group in the B block, whose self-association is suppressed by the cyano group in general formula (2), and the carboxylic acid group in general formula (1), thereby improving the storage stability of the ink.

[0018] <Ink> The ink of the present invention is an aqueous inkjet ink containing a block copolymer. The block copolymer contains a hydrophobic block A block and a hydrophilic block B block. The A block is a polymer block having a segment A that does not have an acid group and a group represented by the following general formula (1) bonded to one end of the segment A. The B block is a polymer block having a segment B that has an acid group and a group represented by the following general formula (2) bonded to one end of the segment B. The components constituting the ink of the present invention and the physical properties of the ink are described in detail below.

[0019] TIFF0007631001000003.tif33170 (In the general formula (1), * represents a bonding position with one end of the segment A, R1 represents an alkylene group, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. In the general formula (2), * represents a bonding position with one end of the segment B, and R2 and R3 each independently represent a hydrogen atom or an alkyl group. R2 and R3 may be bonded to each other to form a ring structure.)

[0020] (Block Copolymer) The block copolymer includes an A block, which is a hydrophobic block, and a B block, which is a hydrophilic block. The content (mass%) of the block copolymer in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 2.0% by mass or less, based on the total mass of the ink. The block copolymer may be present in the ink in a dissolved state, or in a dispersed state. In particular, the block copolymer is preferably present in the ink in a dispersed state, that is, in the form of micelles. The state of the block copolymer in the ink can be controlled by adjusting the balance between its hydrophilicity and hydrophobicity. Specifically, the state of the block copolymer in the ink can be controlled by the type and ratio of the units constituting each block, the number average molecular weight and the ratio of each block, and the like.

[0021] The A block is a hydrophobic block in which a group represented by general formula (1) is bonded to one end of a segment A that does not have an acid group. The B block is a hydrophilic block in which a group represented by general formula (2) is bonded to one end of a segment B that has an acid group. Both the segment A and the segment B can be formed from known monomers. Both the segment A and the segment B may be homopolymers formed only from units derived from a single monomer, or may be copolymers containing units derived from multiple monomers.

[0022] The A block and the B block may each contain a plurality of segments A and a plurality of segments B. Specifically, the block copolymer may be a so-called AB block copolymer consisting of only one A block and one B block. Alternatively, the block copolymer may be a block copolymer containing an A block consisting of two segments A and a B block consisting of one segment B. Alternatively, the block copolymer may be a block copolymer containing an A block consisting of one segment A and a B block consisting of two segments B. Of course, the configuration of each block is not limited to these.

[0023] [Block A] The A block is a hydrophobic polymer block comprising a segment A having no acid group and a group represented by general formula (1) bonded to one end of the segment A. The segment A can be formed by (co)polymerizing one or more known monomers having no acid group.

[0024] Examples of monomers for forming segment A include monomers having an aromatic group such as styrene, vinyl toluene, α-methyl styrene, and benzyl (meth)acrylate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; (meth)acrylic acid esters (monomers having an aliphatic group) that may have a substituent such as an amino group, such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dimethylaminoethyl (meth)acrylate; and (meth)acrylic acid derivatives such as (meth)acrylonitrile and (meth)acrylamide. From the viewpoint of increasing the adsorption to coloring materials such as pigments and further improving the storage stability of the ink, it is preferable for the monomers that become units for forming segment A by polymerization to include monomers having an aromatic group such as styrene and benzyl (meth)acrylate.

[0025] A group represented by the following general formula (1) is bonded to one end of segment A.

[0026] TIFF0007631001000004.tif25170

[0027] In the general formula (1), * represents a bonding position with one end of the segment A. R1 represents an alkylene group. The alkylene group may have a substituent and may be either linear or branched. The alkylene group preferably has 1 to 8 carbon atoms, more preferably 2 to 6 carbon atoms. Examples of the alkylene group include a methylene group, an ethylene group, an n-propylene group, an i-propylene group, and a hexylene group. Examples of the substituent include a halogen atom such as a fluorine atom, a chlorine atom, or a bromine atom; a cyano group; a hydroxy group; and an amino group. Among these, an electron-withdrawing group such as a halogen atom or a cyano group is preferable. M represents a hydrogen atom, an alkali metal, an ammonium, or an organic ammonium.

[0028] The group represented by formula (1) is preferably a group that is easily negatively charged in order to more effectively suppress self-association within the molecule of block A. Specifically, the group represented by formula (1) is preferably represented by the following formula (1a) or (1b), and more preferably represented by the following formula (1a) having a cyano group.

[0029] TIFF0007631001000005.tif32170 (In the general formulas (1a) and (1b), * represents a bonding position with one end of the segment A, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.)

[0030] [Block B] The B block is a hydrophilic polymer block comprising a segment B having an acid group and a group represented by general formula (1) bonded to one end of the segment B. The segment B can be formed by (co)polymerizing one or more known monomers including a monomer having an acid group. The segment B is preferably a copolymer containing two or more types of units, and more preferably a random copolymer.

[0031] As the monomer having an acid group, a monomer having a carboxylic acid group is preferable, and (meth)acrylic acid is more preferable. As a monomer for constituting segment B, a monomer having no acid group can be further used. As the monomer having no acid group, the same monomers as those exemplified as the monomer for forming segment A described above can be mentioned. As a monomer that becomes a unit for forming segment B by polymerization, from the viewpoint of effectively suppressing self-association due to intramolecular hydrogen bonds and further improving the storage stability of the ink, it is preferable to include a monomer having no acid group in addition to (meth)acrylic acid. This monomer having no acid group preferably includes a (meth)acrylic acid ester.

[0032] A group represented by the following general formula (2) is bonded to one end of segment B.

[0033] TIFF0007631001000006.tif33170

[0034] In the general formula (2), * represents a bonding position with one end of the segment B. R2 and R3 each independently represent a hydrogen atom or an alkyl group, and R2 and R3 may bond to each other to form a ring structure such as a cycloalkyl group. The alkyl group may have a substituent and may be either linear or branched. The number of carbon atoms in the alkyl group is preferably 1 to 8, and more preferably 1 to 6. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an i-butyl group, and a hexyl group. Examples of the above-mentioned substituent include an acid group such as a carboxylic acid group, a sulfonic acid group, and a phosphonic acid group; an alkoxy group having 1 to 4 carbon atoms such as a methoxy group and an ethoxy group; an amino group; and a group combining at least two of these groups. Examples of the ring structure formed by bonding R2 and R3 to each other include a cycloalkyl group having about 3 to 8 carbon atoms, such as a cyclopropyl group, a cyclobutyl group, and a cyclohexyl group.

[0035] The group represented by general formula (2) is preferably represented by any one of the following formulae (2a), (2b), (2c), (2d), (2e), and (2f), and more preferably represented by the following formula (2a), in terms of more effectively suppressing intramolecular association of the B block.

[0036] TIFF0007631001000007.tif77170 (in the formulas (2a), (2b), (2c), (2d), (2e), and (2f), * indicates the binding position to one end of the segment B)

[0037] It is preferred that the group represented by general formula (1) bonded to one end of segment A is represented by the following general formula (1a), and the group represented by general formula (2) bonded to one end of segment B is represented by the following formula (2f). This makes it easier for the carboxylic acid group present at one end of the A block of the block copolymer to form a hydrogen bond with the B block, further improving storage stability.

[0038] TIFF0007631001000008.tif36170 (In the general formula (1a), * represents a bonding position to one end of the segment A, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. In the formula (2f), * represents a bonding position to one end of the segment B.)

[0039] [Physical properties of block copolymers] The acid value of the block copolymer is preferably 50 mgKOH / g or more and 200 mgKOH / g or less, more preferably 100 mgKOH / g or more and 160 mgKOH / g or less. If the acid value of the block copolymer is less than 100 mgKOH / g, the amount of acid groups in one molecule of the block copolymer is too small, so that the hydrophilicity is reduced and the adhesion recovery is likely to be reduced. On the other hand, if the acid value of the block copolymer is more than 160 mgKOH / g, the amount of acid groups in the block copolymer as a whole is too large, so that the molecules of the block copolymer tend to spread in the ink, the viscosity of the ink increases, and the adhesion recovery is likely to be reduced. If the adhesion recovery is reduced, when the ink is fixed to the ejection port of the recording head and the ink is difficult to eject normally, many recovery operations are required to restore the ink to a normal ejection state. The acid value of the block copolymer can be measured by neutralization titration using a potential difference.

[0040] The number average molecular weight of the block copolymer is preferably 5,000 or more and 20,000 or less. If the number average molecular weight of the block copolymer is less than 5,000, the molecular chain of the block copolymer is short, so the effect of improving the adsorption force and steric repulsion is weak, and the storage stability may be easily reduced. On the other hand, if the number average molecular weight of the block copolymer exceeds 20,000, the viscosity of the ink increases, and the adhesion recovery may be easily reduced. The number average molecular weight (MnA) of the A block is preferably 2,500 or more and 5,000 or less. In addition, the number average molecular weight (MnB) of the B block is preferably 2,500 or more and 5,000 or less. The number average molecular weight of the block copolymer and each block is a value measured by gel permeation chromatography (GPC) in terms of polystyrene.

[0041] The ratio (MnB / MnA (times)) of the number average molecular weight of the B block (MnB) to the number average molecular weight of the A block (MnA) is preferably 0.8 times or more and 1.2 times or less, and more preferably 0.9 times or more and 1.1 times or less. If the value (times) of MnB / MnA is too large, the adsorption force is likely to decrease, and the storage stability of the ink may be easily deteriorated. On the other hand, if the value (times) of MnB / MnA is too small, the steric repulsion force is likely to decrease, and the storage stability of the ink may be easily deteriorated. The value of MnB / MnA can be calculated from the number average molecular weight (MnA and MnB) of each block constituting the block copolymer. The number average molecular weight of each block can be known by a general method such as measuring the chemical shift corresponding to the repetition of the units constituting the block by NMR and calculating using a calibration curve prepared in advance. The calibration curve used in this case can be created using a resin with a known number of repetitions of the units. For example, the "resin 1" synthesized in the examples described later can be analyzed as follows. In order to know the number of repeats of benzyl methacrylate constituting the A block, the chemical shift due to the repeats of the benzene ring is measured. Then, the ratio of the A block in the resin is calculated from the number of repeats of benzyl methacrylate, and MnA and MnB can be calculated from the Mn of the block copolymer measured separately.

[0042] [Method of manufacturing block copolymer] The block copolymer can be produced by various living polymerization methods such as living radical polymerization, living anionic polymerization, and living cationic polymerization. Among them, producing the block copolymer by living radical polymerization is preferred because the copolymer to be contained in the aqueous inkjet ink is easily compatible with monomers having a general aromatic group and monomers such as (meth)acrylic acid esters. Examples of living radical polymerization methods include the NMP method, the ATRP method, the RAFT method, the TERP method, the SBRP method, the BIRP method, the CMRP method, and the RTCP method. Among them, the RAFT method (reversible addition-fragmentation chain transfer polymerization method) is preferred because it is a simple method in which a RAFT agent, which is a chain transfer agent, is added to a normal radical polymerization system using an azo initiator. Furthermore, the RAFT method does not require the use of metals or halogens, and is also preferred from the viewpoint of waste liquid treatment and the like.

[0043] In the living radical polymerization method, the polymerization rate of the first block is calculated from the concentration of the residual monomer measured by dry solid content or gas chromatography, and when the consumption of the monomer is confirmed, the monomer constituting the second block is added to proceed with the polymerization reaction. This makes it possible to obtain a diblock copolymer in which the first block and the second block are bonded. In addition, by repeating the above operation multiple times, it is possible to obtain a block copolymer in which blocks composed of multiple segments are bonded.

[0044] The method of bonding a group represented by general formula (1) to the end of segment A contained in the block copolymer and bonding a group represented by general formula (2) to the end of segment B is not particularly limited. In order to bond a group represented by general formula (1) to the end of segment A, for example, a method of polymerizing a monomer in the presence of a RAFT agent can be mentioned. As the RAFT agent, a general-purpose agent can be used, and a compound having a structure corresponding to the group represented by general formula (1) can be selected. At this time, a polymerization initiator in an amount necessary for starting RAFT polymerization can be used. In addition, in order to bond a group represented by general formula (2) to the end of segment B, for example, following the above procedure, another monomer is further polymerized to synthesize a copolymer having a moiety containing a sulfur atom at the end. Then, a method of reacting a radical polymerization initiator or the like as a terminal treatment agent can be mentioned. As the radical polymerization initiator, a general-purpose azo compound or the like can be used, and a compound having a structure corresponding to the group represented by general formula (2) can be selected. When a copolymer is polymerized by the RAFT method, the site containing a sulfur atom formed at the end of the polymerization reaction site has activity, so that an azo radical polymerization initiator can react efficiently with the end of the polymerization site to introduce a group represented by general formula (2). In addition, by selecting a RAFT agent, it is easy to set the structure of both ends of the copolymer.

[0045] In order to easily increase the efficiency of terminal treatment, the reaction conditions for terminal treatment with a terminal treatment agent are preferably as follows. The amount of the terminal treatment agent used is preferably 2.0 times or more in molar ratio based on the amount of the RAFT agent used. The molar ratio is preferably 10.0 times or less, and more preferably 5.0 times or less. In addition, it is preferable to react the terminal treatment agent within 30 minutes after the polymerization of the monomer in the presence of the RAFT agent is completed. In order to narrow the molecular weight distribution of the copolymer, it is preferable to react at a temperature 20°C or more higher than the 10-hour half-life temperature of the terminal treatment agent (azo-based radical polymerization initiator). The 10-hour half-life temperature is known to be a value in toluene or water, which is a liquid medium commonly used as a polymerization solvent.

[0046] (Colorant) The ink of the present invention contains a coloring material. A pigment or a dye can be used as the coloring material. The coloring material is preferably a pigment, and more preferably a resin-dispersed pigment. The content (mass %) of the coloring material in the ink is preferably 0.1 mass % or more and 15.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

[0047] Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide, and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, perinone, etc. Among these, organic pigments such as azo and quinacridone are preferred.

[0048] As a pigment dispersion method, resin-dispersed pigments using a resin as a dispersant, self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface, etc. can be used. In addition, resin-bonded pigments in which organic groups containing a resin are chemically bonded to the pigment particle surface, and microcapsule pigments in which the pigment particle surface is coated with a resin, etc. can be used. Among them, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the pigment particle surface, rather than resin-bonded pigments or microcapsule pigments.

[0049] As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use a water-soluble resin that can disperse the pigment in the aqueous medium by the action of an acid group. This resin dispersant is preferably different from the above-mentioned block copolymer. The content (mass %) of the pigment in the ink is preferably 0.3 to 10.0 times the mass ratio of the content of the resin dispersant.

[0050] Examples of the resin dispersant include acrylic resins, urethane resins, etc. Among them, acrylic resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylic acid esters are more preferred.

[0051] The acrylic resin preferably has a hydrophilic unit and a hydrophobic unit as a segment. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer is preferred. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of styrene and α-methylstyrene is preferred. These resins are likely to interact with pigments, and therefore can be suitably used as a resin dispersant for dispersing pigments.

[0052] The hydrophilic unit is a unit having a hydrophilic group such as an acid group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit not having a hydrophilic group such as an acid group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer not having a hydrophilic group such as an acid group. Specific examples of the hydrophobic monomer include monomers having an aromatic group such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid esters such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0053] As the self-dispersing pigment, a pigment having an acid group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group bonded directly or via another atomic group (-R-) to the particle surface of the pigment can be used. The acid group may be either an acid type or a salt type, and when it is a salt type, it may be either a partially dissociated state or a completely dissociated state. When the acid group is a salt type, examples of the cation serving as a counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. In addition, it may be a group that is a combination of these groups.

[0054] It is preferable to use a dye having an acid group, and specific examples of the dye include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes.

[0055] (aqueous medium) The ink of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the aqueous ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The content (mass%) of the water-soluble organic solvent in the aqueous ink is preferably 5.0% by mass or more and 90.0% by mass or less, more preferably 10.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used.

[0056] (Other resins) The ink may further contain resins (other resins) other than the block copolymer and resin dispersant described above. The other resins may be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. The other resins may also be added to the ink (ii) to improve various properties of the recorded image. Examples of the form of the resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. The resin particles do not need to contain a coloring material. The content (mass%) of the other resins in the ink is preferably 0.1% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass or more and 5.0% by mass or less, based on the total mass of the ink.

[0057] The other resin is preferably a resin having an acid group. Specific examples of the other resin include acrylic resins, polyester resins, urethane resins, urea resins, polysaccharides, and polypeptides. Among them, acrylic resins and urethane resins are preferred because they are easy to ensure the ejection stability of the ink.

[0058] In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, it exists in an aqueous medium in a state in which it does not form particles whose particle size can be measured by dynamic light scattering. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if particles having a particle size are not measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, as follows. [Measurement conditions] SetZero: 30 seconds Number of measurements: 3 Measurement time: 180 seconds

[0059] As the particle size distribution measuring device, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150" manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution measuring device and the measurement conditions to be used are not limited to those described above.

[0060] The acid value of the other resin is preferably 30 mgKOH / g or more and 350 mgKOH / g or less. The weight average molecular weight of the other resin, measured by gel permeation chromatography (GPC) in terms of polystyrene, is preferably 1,000 or more and 100,000 or less, and more preferably 5,000 or more and 50,000 or less.

[0061] (Compound represented by general formula (3)) The block copolymer used in the ink of the present invention is believed to be present in the ink in a widely spread state because two or more molecules are easily linked by hydrogen bonds while suppressing intramolecular association. If free block copolymers that are not adsorbed to the components in the ink are present in the ink in a widely spread state, the viscosity of the ink may increase. If the viscosity of the ink increases excessively, the adhesion recovery of the ink may be easily reduced.

[0062] The present inventors have investigated ways to suppress excessive viscosity increase of the ink and improve adhesion recovery while containing the above-mentioned block copolymer. As a result, they have found that the ink further contains a compound represented by the following general formula (3), which suppresses the ink viscosity increase and further improves adhesion recovery. That is, it is preferable that the ink of the present invention further contains a compound represented by the following general formula (3). It is believed that the block copolymer that is present in the ink in a free state without being adsorbed to the components in the ink exhibits the effect of suppressing the viscosity increase by forming micelles. It is presumed that the compound represented by the general formula (3) functions as a core for the block copolymer to form micelles, and the formation of micelles is promoted, thereby suppressing the viscosity increase of the ink.

[0063] TIFF0007631001000009.tif32170

[0064] In general formula (3), Z represents an amino group, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, or an arylthio group, and R4 represents a segment having an acid group.

[0065] Z represents an amino group, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, or an arylthio group, which may have a substituent. The alkyl group is preferably a linear or branched alkyl group having 1 to 16 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, a hexyl group, a decyl group, or a dodecyl group. The aryl group is preferably an aryl group having 6 to 10 carbon atoms, such as a phenyl group, or a naphthyl group. The alkoxy group is preferably a linear or branched alkoxy group having 1 to 16 carbon atoms, such as a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, a hexyloxy group, a decyloxy group, or a dodecyloxy group. The aryloxy group is preferably an aryloxy group having 6 to 10 carbon atoms, such as a phenoxy group, or a naphthoxy group. The alkylthio group is preferably a linear or branched alkylthio group having 1 to 16 carbon atoms, such as a methylthio group, an ethylthio group, an n-propylthio group, an i-propylthio group, a hexylthio group, a decylthio group, a dodecylthio group, etc. The arylthio group is preferably an arylthio group having 6 to 10 carbon atoms, such as a phenylthio group, a naphthylthio group, etc. Examples of the above-mentioned substituent include a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, etc.; an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphonic acid group, etc.; a hydroxyl group; an amino group; etc.

[0066] R4 represents a segment having an acid group. Examples of monomers for constituting this segment include the same as those exemplified as the monomer for forming the above-mentioned segment B. In addition to the monomer having an acid group, a monomer not having an acid group can be further used. Examples of monomers not having an acid group include the same as those exemplified as the monomer for forming the above-mentioned segment A. R4 is preferably a copolymer segment of (meth)acrylic acid and a (meth)acrylic acid ester, and more preferably a copolymer segment of methacrylic acid and a methacrylic acid ester.

[0067] From the viewpoint of keeping the viscosity of the ink in an appropriate range, it is preferable that the molecular weight of the compound represented by general formula (3) is 1,000 or less. ppm ) is preferably 10 ppm or more and 1,000 ppm or less, more preferably 10 ppm or more and 100 ppm or less, based on the total mass of the ink. If the content of the compound represented by general formula (3) is less than 10 ppm, the effect of suppressing the increase in the viscosity of the ink is weak, and the fixation recovery property may be easily reduced. On the other hand, if the content of the compound represented by general formula (3) is more than 1,000 ppm, the odor specific to sulfur compounds may be easily noticeable, and the fixation recovery property of the ink may be easily reduced.

[0068] (Other additives) In addition to the above components, the ink may contain various additives, such as surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and reduction inhibitors, if necessary.

[0069] Examples of the surfactant include anionic surfactants, cationic surfactants, nonionic surfactants, etc. The content (mass %) of the surfactant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 2.0% by mass or less, based on the total mass of the ink.

[0070] <Ink cartridges> The ink cartridge of the present invention includes ink and an ink storage section that stores the ink. The ink stored in the ink storage section is the water-based ink of the present invention described above. FIG. 1 is a cross-sectional view that shows a schematic diagram of an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to a recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage section for storing ink. The ink storage section is composed of an ink storage chamber 14 and an absorber storage chamber 16, which are communicated with each other via a communication port 18. The absorber storage chamber 16 is also communicated with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage section may not have an ink storage chamber that stores liquid ink, and may be in a form in which the entire amount of ink stored is held by the absorber. The ink storage section may also be in a form in which the entire amount of ink stored is stored in a liquid state, without having an absorber. Furthermore, the ink cartridge may be configured to have an ink container and a recording head.

[0071] <Inkjet recording method> The inkjet recording method of the present invention is a method of ejecting the above-described aqueous ink of the present invention from an inkjet recording head to record an image on a recording medium. Methods for ejecting the ink include a method of imparting mechanical energy to the ink and a method of imparting thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of ejecting the ink by imparting thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be known.

[0072] FIG. 2 is a diagram showing an example of an inkjet recording device used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording device, and (b) is a perspective view of a head cartridge. The inkjet recording device is provided with a conveying means (not shown) for conveying a recording medium 32, and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 is equipped with recording heads 38 and 40, and is configured so that an ink cartridge 42 is set thereon. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by a conveying means (not shown). Any recording medium may be used as the target recording medium for recording using the ink of the present invention. In particular, it is preferable to use a recording medium having a permeability and a base material such as paper, such as a recording medium without a coating layer such as plain paper, or a recording medium with a coating layer such as glossy paper or matte paper. EXAMPLES

[0073] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples without departing from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0074] <Method of measuring physical properties> (Acid value of resin (block copolymer)) After adding 1.0 mol / L hydrochloric acid to a liquid containing a resin (block copolymer), the resulting precipitate was washed with water to obtain a solid resin. The obtained solid resin was added to 60 mL of a mixed solvent of water and tetrahydrofuran (water:tetrahydrofuran = 1:6 (mass ratio)) and stirred at 25 °C to dissolve the resin, preparing a sample. Neutralization titration was performed on the prepared sample to measure the acid value of the resin. For the neutralization titration, an automatic potentiometric titrator (product name "AT510", Kyoto Electronics Manufacturing Co., Ltd.) equipped with a composite glass electrode (product name "C-171", Kyoto Electronics Manufacturing Co., Ltd.) was used. A 0.5 mol / L potassium hydroxide-ethanol solution was used as the titration reagent.

[0075] (Number average molecular weight of A block and B block) The A block or block copolymer was added to tetrahydrofuran, stirred at 25°C for 24 hours to dissolve, and then filtered through a membrane filter to obtain a sample. The content of the resin (A block or block copolymer) in the sample was adjusted to about 0.3%. Gel permeation chromatography (GPC) was performed on the obtained sample under the conditions shown below. Then, using a molecular weight calibration curve created using standard polystyrene resin, the number average molecular weight converted to polystyrene was calculated. The value obtained by subtracting the number average molecular weight of the A block from the number average molecular weight of the block copolymer was taken as the number average molecular weight of the B block. As the standard polystyrene resin, trade names "TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500" (manufactured by Tosoh) were used. [GPC conditions] HPLC equipment: Product name "2695 Separations Module" (Waters) Refractive index (RI) detector: Product name "2414 detector" (manufactured by Waters) Column: 4 columns of the product name "GPC KF-806M" (manufactured by Showa Denko) Eluent: Tetrahydrofuran ·Flow rate: 1.0mL / min Oven temperature: 40℃ Sample injection volume: 100μL

[0076] <Production of resin (block copolymer)> (Resin 1-45) A four-neck flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube was replaced with nitrogen. Into this flask, 100.0 parts of methyl isobutyl ketone, the types and amounts of "RAFT agent" and "Segment A1" monomers (unit: parts) shown in Table 1-1, and a polymerization initiator (azobisisobutyronitrile) in an amount 0.25 times that of the "RAFT agent" were placed. The amount of this polymerization initiator used is the amount consumed by RAFT polymerization. After replacing with nitrogen at 25°C for 30 minutes, the temperature was raised to 80°C to start the reaction. The reaction solution was extracted at regular intervals, and the dry solid content in the solution was measured to calculate the polymerization rate. In addition, the molecular weight of the product was measured using a portion of the extracted reaction solution.

[0077] After it was confirmed that the polymerization rate was 90% or more, the monomer (unit: parts) shown in "Segment A2" in Table 1-1 was added and further reacted. A part of the sample taken from the flask at regular intervals was dried and the polymerization rate was calculated from the concentration of the solids in the sample. In addition, the number average molecular weight of the resin produced was measured using a part of the taken sample. After it was confirmed that the polymerization rate was 90% or more, the monomer (unit: parts) shown in "Segment B1" and the monomer (unit: parts) shown in "Segment B2" in Table 1-2 were added in sequence and further reacted.

[0078] Next, the type of "terminal treatment agent" shown in Table 1-2 was dissolved in 10.0 parts of tetrahydrofuran at 4.0 times (molar ratio) the amount of the RAFT agent used to prepare a solution. The entire amount of this solution was added to a flask that had been heated to the "terminal treatment temperature" shown in Table 1-2, and reacted for another 30 minutes. The polymerization rate was calculated in the same manner as above, and after confirming that the final polymerization rate was 98%, 50.0 parts of methyl isobutyl ketone was added and the flask was cooled to stop the reaction. The reaction solution was added to a large amount of n-hexane, and the resulting precipitate was vacuum dried at 40°C for 24 hours to obtain a resin (block copolymer). Potassium hydroxide 0.9 times the acid value of the resin in molar ratio and an appropriate amount of ion-exchanged water were added to obtain a liquid containing a resin with a resin (solid content) of 10.0%. Since the water solubility of resin 45 was low, a liquid containing a resin with a resin (solid content) of 8.0% was prepared. The terminal structures of segments A and B of the obtained resin are shown in Table 2-1 as acid type (H type). * indicates the bonding position with the end of each segment. The acid value of the resin (acid value corresponding to all carboxylic acid groups), number average molecular weight (Mn), number average molecular weight of A block (MnA), number average molecular weight of B block (MnB), and number average molecular weight of B block / number average molecular weight of A block (MnB / MnA) are shown in Table 2-2. The meanings of the abbreviations in Tables 1-1 and 1-2 are as follows:

[0079] [monomer] ·BzMA: Benzyl methacrylate St: styrene nBMA: n-butyl methacrylate MMA: Methyl methacrylate HEMA: 2-hydroxyethyl methacrylate ·MAA: Methacrylic acid ·AA: Acrylic acid

[0080] [RAFT Agents] RAFT Agent 1: 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid RAFT Agent 2: 2-[(dodecylsulfanylthiocarbonyl)sulfanyl]propanoic acid RAFT Agent 3: S-(Thiobenzoyl)thioglycolic acid RAFT Agent 4: 2-Cyano-2-propyl dithiobenzoate

[0081] [End treatment agent] End treatment agent 1: 2,2'-azobis(2,4-dimethylvaleronitrile) End treatment agent 2: 4,4'-azobis(4-cyanovaleric acid) End treatment agent 3: 1,1'-azobis(cyclohexane-1-carbonitrile) End treatment agent 4: 2,2'-azobis(isobutyronitrile) End treatment agent 5: 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) Terminal treatment agent 6: 2,2'-azobis(2-methylbutyronitrile)

[0082] TIFF0007631001000010.tif255170

[0083] TIFF0007631001000011.tif239170

[0084] TIFF0007631001000012.tif252170

[0085] TIFF0007631001000013.tif244170

[0086] (End processing efficiency) Resin 25-1 (terminal treatment temperature: 60°C) and resin 25-2 (terminal treatment temperature: 70°C) were obtained in the same manner as resin 25, except that the terminal treatment temperature was changed by using terminal treatment agent 4, which has a 10-hour half-life temperature of about 60°C. The final polymerization rate of resin 25-1 only reached 86%. In addition, the molecular weight distribution (Mw / Mn) of resin 25 obtained at a terminal treatment temperature of 90°C was 1.2, while the molecular weight distribution of resin 25-2 obtained at a terminal treatment temperature of 70°C was 1.3. From these results, it can be seen that it is preferable to carry out the reaction at a temperature 20°C or more higher than the 10-hour half-life temperature.

[0087] (Resin 46) Resin 46 was synthesized according to the description of Synthesis Example 4 in Patent Document 1 (JP Patent Publication 2008-195769 A). 0.5 mmol of copper bromide (I), 1.0 mmol of bipyridine, 1.0 mmol of ethyl 2-bromoisopropionate, 100 mmol of benzyl methacrylate (BzMA), and 15 g of dimethylformamide were mixed under a nitrogen atmosphere to obtain a mixture. After dissolving oxygen in the obtained mixture was replaced with nitrogen, the mixture was reacted and polymerized at 90°C. Polymerization was performed while checking the polymerization rate by analysis by gas chromatography, and the reaction was stopped by quenching with liquid nitrogen. The reaction liquid was passed through an alumina column to remove the copper catalyst, and then added to methanol, and the resulting precipitate was dried under reduced pressure to obtain polybenzyl methacrylate (p(BzMA)) that would become the A block. The number average molecular weight (Mn) of p(BzMA) was 8,800. A bromine atom was bonded to the end of the obtained p(BzMA).

[0088] The obtained p(BzMA) (0.4 mmol), copper(I) chloride (0.2 mmol), pentamethyldiethylenetriamine (0.2 mmol), BzMA (60 mmol), t-butyl acrylate (tBA) (60 mmol), and dimethylformamide (30 mL) were mixed to obtain a mixture. The dissolved oxygen in the obtained mixture was replaced with nitrogen, and then the mixture was reacted and polymerized at 90°C. The polymerization rate was confirmed by analysis using gas chromatography, and the reaction was stopped by quenching with liquid nitrogen.

[0089] The reaction liquid was passed through an alumina column to remove the copper catalyst, and then added to methanol, and the resulting precipitate was dried under reduced pressure to obtain a dried product. The resulting dried product was dissolved in tetrahydrofuran, and then concentrated hydrochloric acid was added under reflux conditions to hydrolyze the product. The reaction liquid was added to methanol, and the resulting precipitate was dried under reduced pressure to obtain a block copolymer containing units in which at least a portion of the ester of the units derived from tBA in the B block was hydrolyzed to become acid-type carboxylic acid groups. The B block thus obtained is composed of units derived from butyl acrylate (BA) and acrylic acid (AA). The number average molecular weight (Mn) of the B block was 6,200. Potassium hydroxide in a molar ratio of 0.9 times the acid value of the resin and an appropriate amount of ion-exchanged water were added to obtain a liquid containing resin 46 with a resin (solid content) content of 10.0%. The acid value of resin 46 was 131 mgKOH / g, the number average molecular weight (Mn) was 15,000, and the number average molecular weight of the B block / the number average molecular weight of the A block (MnB / MnA) was 0.7.

[0090] (Resin 47) Resin 47 was synthesized according to the synthesis method of polymer aqueous solution 73 in Patent Document 2 (JP Patent Publication 2012-072357). In a nitrogen-substituted glove box, 0.650 g of styrene and 0.015 g of (1-methyltellanyl-ethyl)benzene were reacted at 100°C for 30 hours. Then, 0.119 g of 2-hydroxyethyl methacrylate was added and reacted at 100°C for 30 hours. Furthermore, 0.231 g of methacrylic acid was added and reacted at 100°C for 30 hours. The product was dissolved in 5 mL of chloroform to prepare a solution. This solution was poured into 300 mL of a water / methanol mixed solution (water:methanol = 1:4 (mass ratio)) under stirring, and the resulting precipitate was dried by suction filtration to obtain a resin (block copolymer). Potassium hydroxide in an amount 0.8 times the acid value of the resin in terms of molar ratio and an appropriate amount of ion-exchanged water were added and stirred, and then the solvent was removed under reduced pressure, and an appropriate amount of ion-exchanged water was added to obtain a liquid containing resin 47 with a resin (solid content) content of 10.0%. Resin 47 had an acid value of 151 mgKOH / g and a number average molecular weight (Mn) of 10,000.

[0091] (Resin 48) Resin 48 was synthesized according to Example 58 of Patent Document 3 (JP Patent Publication 2000-515181). 2 mL of styrene and 32.8 mg of 4-cyano-4-(thiobenzoylthio)pentanoic acid were mixed to prepare a solution. 1 mL of the prepared solution was placed in an ampoule, degassed, and sealed. The ampoule was heated to 100°C for polymerization to obtain a styrene homopolymer (resin 48). When the bonding position with the polymer end is represented by *, the structure of one end of resin 48 was *-C(CH3)(CN)-C2H4-COOH, and the structure of the other end was *-SC(=S)-C6H5. In addition, the number average molecular weight (Mn) of resin 48 was 8,900. Since the obtained resin C did not dissolve in water, a liquid containing resin 48 could not be prepared.

[0092] (Resin 49) Resin 49 was synthesized according to the fixing resin 1 of Patent Document 4 (JP Patent Publication 2018-203802). A reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer was prepared. Into this reaction vessel, 20.0 parts of toluene, 7.5 parts of methacrylic acid, 7.5 parts of methyl methacrylate, 0.9 parts of 2,2'-azobisisobutyronitrile, and 3.6 parts of 2-(dodecylthiocarbonothioylthio)-isobutyric acid were placed. After replacing with nitrogen gas, the temperature was raised to 75 ° C. and reacted for 3 hours to obtain a copolymer containing units derived from each of methacrylic acid and methyl methacrylate, which becomes the A block. After cooling to 25 ° C., 60.0 parts of toluene, 60.0 parts of methyl methacrylate, and 25.0 parts of butyl methacrylate were placed in the reaction vessel. After replacing with nitrogen gas, the temperature was raised to 75°C and reacted for 3 hours to obtain an AB block copolymer (resin 49) in which a copolymer (B block) containing units derived from each of methyl methacrylate and butyl methacrylate was added to the A block. The mixture was cooled to 25°C, and 9.3 parts of dimethylaminoethanol was added to neutralize the acid group, and then 200.0 parts of water was added. Next, toluene was azeotroped with water to distill off the toluene, and an appropriate amount of ion-exchanged water was added to obtain a liquid containing resin 49 with a resin (solid content) content of 10.0%. The bond position with the end of segment A is represented by *, and the structure of the end of segment A in resin 49 was *-C(CH3)2-COOH. The acid value of resin 49 was 49 mgKOH / g, the number average molecular weight (Mn) was 9,800, and the number average molecular weight of B block / number average molecular weight of A block (MnB / MnA) was 5.5.

[0093] (Resin 50) By copolymerizing the monomers by a standard method, a random copolymer, resin 50 (styrene-ethyl acrylate-acrylic acid copolymer), was obtained. Potassium hydroxide in a molar ratio of 1.0 times the acid value of the resin and an appropriate amount of ion-exchanged water were added and stirred to obtain a liquid containing resin 50 with a resin (solid content) content of 10.0%. The acid value of resin 50 was 167 mgKOH / g, and the weight average molecular weight of resin 50 measured by GPC was 10,000.

[0094] <Preparation of pigment dispersion> (Pigment dispersion 1) A mixture of 10.0 parts of pigment, 60.0 parts of liquid containing 50 parts of resin, and 30.0 parts of ion-exchanged water was placed in a batch-type vertical sand mill (manufactured by Imex) filled with 200 parts of zirconia beads with a diameter of 0.3 mm, and dispersed for 5 hours. A solid solution pigment of CI Pigment Violet 19 and CI Pigment Red 122 was used as the pigment. After removing coarse particles by centrifugation, the mixture was filtered under pressure with a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to obtain Pigment Dispersion Liquid 1. The pigment content in Pigment Dispersion Liquid 1 was 10.0%, and the resin content was 6.0%.

[0095] (Pigment dispersion 2) Pigment dispersion 2 was obtained in the same manner as in the case of pigment dispersion 1 described above, except that CI Pigment Yellow 74 was used instead of the solid solution pigment of CI Pigment Violet 19 and CI Pigment Red 122. The pigment content in pigment dispersion 2 was 10.0%, and the resin content was 6.0%.

[0096] (Pigment dispersion 3) Pigment dispersion 3 was obtained in the same manner as for pigment dispersion 1, except that an aqueous solution of resin 1 was used as the resin-containing liquid. The pigment content in pigment dispersion 3 was 10.0%, and the resin content was 6.0%.

[0097] (Pigment Dispersion 4) A solution of 5.0g of concentrated hydrochloric acid in 5.5g of water was cooled to 5℃, and 1.6g of 4-aminobenzenesulfonic acid was added in this state. The container containing this solution was placed in an ice bath, and while stirring to maintain the temperature of the solution below 10℃, a solution obtained by dissolving 1.8g of sodium nitrite in 9.0g of water was added. After stirring for 15 minutes, 6.0g of a solid solution pigment of CI Pigment Violet 19 and CI Pigment Red 122 was added and mixed. The mixture was stirred for another 15 minutes to obtain a slurry. The obtained slurry was filtered with filter paper (product name "Standard Filter Paper No. 2", Advantec), the particles were thoroughly washed with water, and dried in an oven at 110℃. After treatment with hydrochloric acid, it was neutralized with an aqueous potassium hydroxide solution. An appropriate amount of ion-exchanged water was added to obtain pigment dispersion 4 with a self-dispersing pigment content of 20.0%.

[0098] <Production of Additive A> A four-neck flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a reflux tube was substituted with nitrogen. Into this flask, 84.0 parts of toluene, a mixture of 5.0 parts of methacrylic acid and 5.0 parts of n-butyl methacrylate, 5.0 parts of RAFT agent 1, and 1.0 parts of azobisisobutyronitrile were placed. After 30 minutes of nitrogen substitution at 25°C, the temperature was raised to 90°C under a nitrogen atmosphere to start the reaction. After 4 hours of reaction, 50.0 parts of toluene were added, and the flask was cooled to stop the reaction. The reaction liquid was added to a large amount of n-hexane, and the resulting precipitate was vacuum dried at 40°C for 24 hours to obtain additive A corresponding to the compound represented by general formula (3) (Z: dodecylthio group, R4: copolymerization segment of methacrylic acid and n-butyl methacrylate). The molecular weight of the obtained additive A was 542.

[0099] <Ink Preparation> Each ink was prepared by mixing the components shown below (unit: %), thoroughly stirring, and then filtering under pressure through a microfilter (manufactured by Fujifilm) with a pore size of 2.5 μm. Among the components shown below, "Acetylenol E100" is the trade name of a nonionic surfactant (ethylene oxide adduct of acetylene glycol) manufactured by Kawaken Fine Chemicals. Resins of the types shown in Table 3: Amount that results in a resin content of 0.5% Colorants of the types shown in Table 3: Amount that results in a colorant content of 5.0% Glycerin: 5.0% Triethylene glycol: 10.0% Acetylenol E100: 0.1% Additive A: Amount that results in the concentration (ppm) shown in Table 3 Ion-exchanged water: the amount that makes the total of the ingredients 100.0%

[0100] TIFF0007631001000014.tif199170

[0101] <Evaluation> The prepared inks were evaluated as follows. In the present invention, the evaluation criteria for each item shown below were "AA", "A", and "B" as acceptable levels, and "C" as unacceptable levels. The evaluation results are shown in Table 4.

[0102] (Storage stability) The viscosity of each ink prepared was measured. The prepared ink was placed in a sealed container and stored in an oven at 80°C for 4 days. After returning to room temperature, the ink viscosity was measured. The ink viscosity was measured using an E-type viscometer (product name "RE80-L", manufactured by Toki Sangyo Co., Ltd.) equipped with a rotor (1°34' x R24) in which antifreeze solution was circulated through a tube in a thermostatic bath set at 25°C. The viscosity increase rate was calculated from the viscosity of the ink before and after storage, and the storage stability of the ink was evaluated according to the following evaluation criteria. AA: The increase in viscosity was less than 1%. A: The viscosity increase rate was 1% or more and less than 3%. B: The viscosity increase rate was 3% or more and less than 5%. C: The viscosity increase rate was 5% or more.

[0103] (Adhesion recovery) Each prepared ink was filled into an ink cartridge and mounted on the recording head of an inkjet recording device (product name "PIXUS MX7600", manufactured by Canon). Then, a nozzle check pattern was recorded on a recording medium (plain paper, product name "PPC paper GF-500", manufactured by Canon) by operating a printer driver. Then, the recording head (head cartridge) equipped with the ink cartridge was removed from the inkjet recording device and left for 7 days in an environment with a temperature of 30°C and a relative humidity of 10%. After leaving it, the head cartridge was reattached to the inkjet recording device and a nozzle check pattern was recorded. If clogging occurred and the nozzle check pattern was not recorded normally, the nozzle check pattern was recorded again after cleaning by operating the printer driver. If clogging still occurred at this point, the nozzle check pattern was recorded again after cleaning and further strong cleaning. If clogging still occurred, the strong cleaning and recording of the nozzle check pattern were repeated. Then, the number of strong cleanings required until the nozzle check pattern could be recorded normally was measured, and the adhesion recovery property was evaluated according to the evaluation criteria shown below. A: After two deep cleanings, the nozzle check pattern was printed successfully. B: The nozzle check pattern was recorded successfully after deep cleaning 3 to 10 times. C: The nozzle check pattern was not printed correctly even after performing deep cleaning 11 or more times.

[0104] TIFF0007631001000015.tif204170

Claims

1. A water-based inkjet ink containing a colorant and a block copolymer, The block copolymer comprises a segment A having no acid group, and an A block having a group represented by the following general formula (1) bonded to one end of the segment A:

1. An aqueous ink comprising: a segment B having an acid group; and a block B having a group represented by the following general formula (2) bonded to one end of the segment B: (In the general formula (1), * represents a bonding position with one end of the segment A, and R １ represents an alkylene group, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. In the general formula (2), * represents a bonding position with one end of the segment B, R ２ and R ３ each independently represents a hydrogen atom or an alkyl group; R ２ and R ３ may be bonded to each other to form a ring structure)

2. The aqueous ink according to claim 1 , wherein the group represented by the general formula (1) is represented by the following general formula (1a) or (1b): (In the general formulas (1a) and (1b), * represents a bonding position with one end of the segment A, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium.)

3. The aqueous ink according to claim 1 or 2, wherein the group represented by general formula (2) is represented by any one of the following formulas (2a), (2b), (2c), (2d), (2e), and (2f). (In the formulas (2a), (2b), (2c), (2d), (2e), and (2f), * represents a bonding position with one end of the segment B.)

4. The group represented by the general formula (1) is represented by the following general formula (1a): The aqueous ink according to claim 1 , wherein the group represented by general formula (2) is represented by the following formula (2f): (In the general formula (1a), * represents a bonding position to one end of the segment A, and M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. In the formula (2f), * represents a bonding position to one end of the segment B.)

5. The aqueous ink according to claim 1 , wherein the segment A comprises a unit derived from at least one monomer selected from the group consisting of a monomer having an aromatic group and a (meth)acrylic acid ester.

6. The aqueous ink according to claim 1 , wherein the segment A contains a unit derived from a monomer having an aromatic group.

7. 7. The aqueous ink according to claim 1, wherein the segment B comprises a unit derived from at least one monomer selected from the group consisting of (meth)acrylic acid, a monomer having an aromatic group, and a (meth)acrylic acid ester.

8. The segment A comprises a unit derived from at least one monomer selected from the group consisting of a monomer having an aromatic group and a (meth)acrylic acid ester, 7. The aqueous ink according to claim 1, wherein the segment B comprises a unit derived from at least one monomer selected from the group consisting of (meth)acrylic acid, a monomer having an aromatic group, and a (meth)acrylic acid ester.

9. The aqueous ink according to claim 1 , wherein the segment B comprises a unit derived from (meth)acrylic acid and a unit derived from a (meth)acrylic acid ester.

10. the segment A includes a unit derived from a monomer having an aromatic group, The aqueous ink according to claim 1 , wherein the segment B comprises a unit derived from (meth)acrylic acid and a unit derived from a (meth)acrylic acid ester.

11. 11. The water-based ink according to claim 1, wherein the block copolymer has an acid value of 100 mg KOH / g or more and 160 mg KOH / g or less.

12. 12. The aqueous ink according to claim 1, wherein the block copolymer has a number average molecular weight of 5,000 or more and 20,000 or less.

13. 13. The aqueous ink according to claim 1, wherein the ratio of the number average molecular weight of the B block to the number average molecular weight of the A block is 0.8 to 1.2 times.

14. The aqueous ink according to claim 1 , wherein the content (mass %) of the coloring material is 0.1 mass % or more and 15.0 mass % or less based on the total mass of the ink.

15. The aqueous ink according to claim 1 , wherein the content (mass %) of the block copolymer is 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink.

16. Further, the composition contains a compound represented by the following general formula (3): The aqueous ink according to claim 1 , wherein the content of the compound represented by the following general formula (3) is from 10 ppm to 1,000 ppm based on the total mass of the ink: (In the general formula (3), Z represents an amino group, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, or an arylthio group; R ４ represents a segment having an acid group)

17. 17. The aqueous ink according to claim 16, wherein the content (ppm) of the compound represented by the general formula (3) is 10 ppm or more and 1,000 ppm or less based on the total mass of the ink.

18. The water-based ink according to claim 1 , wherein the coloring material comprises a pigment.

19. 20. The water-based ink of claim 18, wherein the pigment is dispersed by a resin dispersant different from the block copolymer.

20. 20. The aqueous ink according to claim 18 or 19, wherein the pigment is an organic pigment.

21. An ink cartridge including an ink and an ink storage section for storing the ink, 21. An ink cartridge, wherein the ink is a water-based ink according to claim 1.

22. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, comprising:

21. An ink-jet recording method, wherein the ink is a water-based ink according to claim 1.

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