JP5441830B2 - Water-based ink - Google Patents

Description

  The present invention relates to an aqueous ink, and more particularly, to an aqueous ink suitable for an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus.

  Conventionally, pigments excellent in fastness such as water resistance and light resistance have been widely used as colorants for printing inks. Also in the ink for ink jet recording, the study of adopting a pigment as a coloring material in the ink has been actively conducted with the aim of further improving the fastness of the ink jet recorded image. By the way, in order to use a pigment as a coloring material for an inkjet aqueous ink, it is important to stably disperse the pigment in an aqueous medium. In general, in order to uniformly disperse the pigment in the aqueous medium, a dispersant such as a resin dispersant is used. Such a resin dispersant generally comprises a water-soluble resin having a hydrophilic group for stably dispersing a pigment in an aqueous medium and a hydrophobic part for physically adsorbing to a hydrophobic pigment surface. ing. It can be said that an image obtained with such a pigment ink has relatively good quality in terms of scratch resistance, marker resistance, and the like due to the presence of the resin dispersant.

  By the way, in order to stably form a high-quality inkjet recording image, it is important that the ink is ejected as a stable droplet from a fine nozzle of the inkjet recording head. Specifically, it is important for stable ink jet recording that, for example, the orifice of the ink jet recording head does not solidify due to drying of the orifice of the ink jet recording head. However, the inkjet ink in which the pigment is dispersed in the aqueous medium by the resin dispersant as described above has a problem in this respect. That is, it is considered that there is a considerable amount of a resin dispersant that is not adsorbed on the pigment surface and exists in the ink in a dissolved state in the ink as described above. There is a case where nozzle clogging is caused by adhering to the orifice or the like of the recording head.

  Various methods for improving the reliability of the pigment ink have been proposed for the above-described problems (see, for example, Patent Document 1 and Patent Document 2). Specifically, a pigment (self-dispersing pigment) that can be stably dispersed in an aqueous ink without using a dispersant by introducing a water-soluble group on the surface of the carbon black particles was used as a color material. An ink is disclosed. However, when printing is performed on a recording medium, particularly plain paper, with water-based ink using such a self-dispersing pigment, the printed surface becomes dirty when the printed surface is rubbed strongly even after the ink has sufficiently dried. The scratch resistance of the image may not be sufficient. As described above, not using the resin dispersant in the ink effectively functions to further improve the reliability of the ink jet recording, but may deteriorate a certain quality of the ink jet recorded matter.

  On the other hand, there is also a proposal of an inkjet ink containing a self-dispersible pigment of a type in which a resin is chemically bonded to the pigment surface and an inkjet recording method using the inkjet ink (see, for example, Patent Document 3). Among them, the self-dispersing pigment includes a segment (A) having a reactive group capable of reacting with a functional group on the surface of the pigment, and having substantially no reactive group, and from the segment (A) Further, it is disclosed that a polymer having a segment (B) having a high affinity for a liquid medium is obtained by heating with a pigment.

  However, in this invention, a specific functional group is required as a polymer to be reacted with the pigment surface, and the usable polymer is limited. Also, a functional group capable of reacting with the polymer is essential on the pigment surface. There is a problem that the types of pigments that can be used are limited. Further, according to the study by the present inventors, as a problem in production, it is difficult to impart ionicity to the pigment surface and the segment not having a reactive group, and it has sufficient dispersibility in an aqueous medium. It is considered difficult to obtain a pigment.

  An inkjet ink composition comprising a macromolecular chromophore comprising at least one water-solubilizing functional group and at least one covalently attached polymer, wherein the polymer comprises the macromolecular color development. There is also a proposal for an ink-jet ink composition that is attached to a group by nucleophilic substitution or acylation reaction (see, for example, Patent Document 4). However, in the present invention, amine or hydroxyl termination is essential in the polymer, and the type of polymer that can be used is limited, and although the scratch resistance is improved by the dispersion by the functional group of the terminal-modified homopolymer, Since the group present on the pigment surface is hydrophilic, the hydrophilic polymer on the pigment particle surface is redissolved by the water in the marker pen or the aqueous organic solvent, and the marker resistance is insufficient. There was a problem.

  There is also a proposal for an ink-jet ink composition containing a macromolecular chromophore comprising at least one water-solubilizing functional group and at least one covalently attached polymer (see, for example, Patent Document 5). ). The ink-jet ink composition according to the present invention comprises modified pigment particles (macromolecular chromophores) having both functional groups attached to impart water solubility and covalently attached vinyl polymer chains. However, when producing such a composition, in the step of covalently adding polymer chains to the pigment surface, the polymer is grown by radical polymerization of the pigment in the presence of a monomer and an initiator. However, according to the study by the present inventors, in this method, it is difficult to control the molecular weight of the polymer in the radical polymerization of the monomer, and it is also possible to control the acid value or amine value as an index of solubility of the water-soluble polymer in water. It was difficult, and in addition, it was not certain that these polymers were covalently bonded to the pigment surface. In other words, the terminal radicals of the growing polymer are surely bonded to the pigment surface and the polymerization is not necessarily stopped, and a part is bonded to the pigment surface, but the polymerization reaction is caused by the bonding between the growing polymers. In some cases, the production problem that it was very difficult to efficiently bind the polymer to the pigment surface was observed.

  A resin-bonded self-dispersing pigment using a plurality of molecules is also known (see, for example, Patent Document 6). This resin-bonded self-dispersible pigment can be dispersed in an aqueous pigment having ionic properties. However, according to the study by the present inventors, the reliability of the ink for the recording head can be ensured by using these resin-bonded self-dispersing pigments, but the image after printing has scratch resistance and resistance. There was still room for improvement in terms of marker properties.

JP-A-8-3498 Japanese Patent Laid-Open No. 10-195360 JP-A-9-272831 JP 2000-53902 A JP 2000-95987 A International Publication No. 01/51566 Pamphlet

  Therefore, the object of the present invention is to solve the problem of ejection bending and non-discharge of ink as in the case of the self-dispersing pigment described above, and to prevent printing stains due to rubbing after printing while having the reliability of ink for the recording head. Scratch resistance that can be suppressed (hereinafter referred to as print stain scratch resistance) is improved, and marker resistance against print stains (hereinafter referred to as print stain resistance marker) that occurs when a water-based marker is applied to an image after printing. A water-based ink containing a resin-bonded self-dispersing pigment having improved properties, and an ink jet recording method excellent by applying such an ink, an ink cartridge using the ink, and a recording unit And providing an inkjet recording apparatus.

The above object is achieved by the present invention described below. That is, the aqueous ink according to one embodiment of the present invention includes [1] a modified pigment in which an organic group is chemically bonded to the surface of pigment particles, and an aqueous medium as a dispersion medium for the pigment. A water-based ink containing the organic group, a functional group chemically bonded to the pigment surface directly or via another atomic group, a copolymer of an ionic monomer and a hydrophobic monomer, The ratio of the organic group in the modified pigment to the total mass of the modified pigment is 5% by mass or more and 40% by mass or less, and the weight of the copolymer. average molecular weight (Mw) 1,000 to 20,000, and a polydispersity Mw / Mn (Mw: weight average molecular weight, Mn: number-average molecular weight) state, and are 3 or less, the chemical on the pigment surface The segment containing the unbonded copolymer is the When present in the tank, of the segment, the ratio to the total amount of said reactant and said segments, characterized in der Rukoto less than 35 wt%.

The following are mentioned as a preferable form of the water-based ink concerning the said invention. [2] before Symbol segment, aqueous ink according to the above [1] ratio is less than 20% by weight relative to the total amount of the reactants and the segments. [ 3 ] The water-based ink according to [1] or [ 2], wherein the other atomic group is a phenyl (2-sulfoethyl) group.

[ 4 ] The water-based ink according to any one of [1] to [ 3 ], wherein the pigment is carbon black. [ 5 ] The water-based ink according to any one of [1] to [ 4 ], wherein the copolymer has an acid value or an amine value of 100 or more and 500 or less .

[ 6 ] Any one of the above [1] to [ 5 ], wherein the ratio of the organic group in the modified pigment to the total mass of the modified pigment is 8 % by mass or more and 30% by mass or less. A water-based ink according to claim 1. [ 7 ] The water-based ink according to the above [ 6 ], wherein the ratio of the organic group in the modified pigment to the total mass of the modified pigment is 10 % by mass or more and 25% by mass or less .

[ 8 ] The water-based ink according to any one of [1] to [ 7 ], which is a water-based ink for inkjet.

The following are mentioned as another embodiment concerning the present invention. [ 9 ] An inkjet recording method comprising a step of discharging the water-based ink according to [ 8 ] above by an inkjet method. [ 10 ] An ink cartridge containing the water-based ink according to any one of [1] to [ 8 ]. [ 11 ] A recording unit comprising: an ink containing portion containing the water-based ink according to [ 8 ] above; and an ink jet head for discharging the ink. [ 12 ] An ink jet recording apparatus comprising: an ink containing portion containing the water-based ink according to [ 8 ] above; and an ink jet head for discharging the ink.

  According to the present invention, as a pigment for an aqueous ink, by using a pigment having a copolymer segment composed of an ionic monomer and a hydrophobic monomer in a state of being bonded to a functional group on the surface of the pigment particle, ink jet ink can be used. When used as an ink, the ink is reliable for recording heads that are free from discharge bends and non-discharge, and the print stains due to rubbing after printing and scratches caused by aqueous markers after printing An aqueous ink having improved marker resistance is also provided. Furthermore, according to the present invention, there are provided an ink jet recording method, an ink cartridge, a recording unit and an ink jet recording apparatus which are excellent by using such ink.

It is a thermogravimetric analysis result about the sample after coagulating the pigment of the pigment dispersion liquid 4 used for Example 4. FIG. It is a thermogravimetric analysis result about the sample after coagulating the pigment of the pigment dispersion liquid 4 used for Example 4, and also wash-processing with THF. It is a thermogravimetric analysis result about the sample after coagulating the pigment of the pigment dispersion liquid 13 used for the comparative example 1. FIG. It is a thermogravimetric analysis result about the sample after coagulating the pigment of the pigment dispersion liquid 13 used for the comparative example 1, and also wash-processing with THF. It is a longitudinal cross-sectional view of an inkjet recording device head. It is a vertical and horizontal view of an inkjet recording device head. FIG. 6 is an external perspective view of a head in which the head shown in FIG. It is a perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view of an ink cartridge. It is a perspective view which shows an example of a recording unit. FIG. 3 is a diagram illustrating an example of a configuration of a recording head.

  Next, the present invention will be described in more detail with reference to preferred embodiments. The aqueous pigment ink according to the present invention is an aqueous ink comprising a modified pigment in which organic groups are chemically bonded to the surface of pigment particles, and an aqueous medium as a dispersion medium for the pigment. The organic group includes a functional group on the surface of the pigment particle or a functional group introduced therein, and a copolymer segment that is a reaction product of an ionic monomer and a hydrophobic monomer bonded to the functional group. And Hereinafter, materials constituting the aqueous pigment ink of the present invention will be described.

[Pigment]
The pigment that can be used in the aqueous pigment ink of the present invention is not particularly limited, and those listed below can be used. These pigments are used after being modified by the method described later. In the present invention, the ratio of the modified pigment to the total weight of the water-based ink is 0.1 to 15% by mass, and further 1 to 10% by mass. % Is preferable.

  Carbon black is suitable as the pigment used in the black ink. For example, any carbon black such as furnace black, lamp black, acetylene black, and channel black can be used. Specifically, for example, Raven 7000, Ray Van 5750, Ray Van 5250, Ray Van 5000 ULTRA, Ray Van 3500, Ray Van 2000, Ray Van 1500, Ray Van 1250, Ray Van 1200, Ray Van 1190 ULTRA-II, Ray Van 1170, Ray Van 1255 (above, Colombia), Black Pearls L, Regal 400R, Regal 330R, Legal 660R, Mogul L, Monarch 700, Monak 800, Monak 880, Monak 900, Monak 1000, Monak 1100, Monak 1300, Monak 1400, Monak 2000, Valcan XC-72R (above, Bot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (above, manufactured by Degussa), No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. Commercial products such as 2300, MCF-88, MA600, MA7, MA8, MA100 (above, manufactured by Mitsubishi Chemical Corporation) can be used. Carbon black newly prepared for the present invention can also be used. However, the present invention is not limited to these, and any conventionally known carbon black can be used. Further, the material is not limited to carbon black, and magnetic fine particles such as magnetite and ferrite, titanium black, and the like may be used as a black pigment.

  Specific examples of the organic pigment include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, and pyrazolone red, soluble azo pigments such as ritole red, heliobordeaux, pigment scarlet, and permanent red 2B, Derivatives from vat dyes such as alizarin, indanthrone, thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, perylene pigments such as perylene red and perylene scarlet, Isoindolinone pigments such as isoindolinone yellow and isoindolinone orange, benzimidazolone yellow, benzimidazolone orange and benzimidazolone red Midazolone pigments, pyranthrone pigments such as pyranthrone red, pyranthrone orange, thioindigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo Yellow, copper azomethine yellow, perinone orange, anthrone orange, dianslaquinonyl red, dioxazine violet and the like. Of course, it is not limited to this, Other organic pigments may be used.

  The organic pigment that can be used in the present invention is represented by a color index (CI) number. I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 150, 151, 153, 154, 166, 168, 180, 185, C.I. I. Pigment orange 16, 36, 43, 51, 55, 59, 61, 71, C.I. I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 254, 255, 272, C.I. I. Pigment violet 19, 23, 29, 30, 37, 40, 50, C.I. I. Pigment Blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64, C.I. I. Pigment green 7, 36, C.I. I. Examples thereof include CI Pigment Brown 23, 25, 26, and the like.

[Functional group]
In the pigment in the aqueous ink according to the present invention, the functional group is chemically bonded to the pigment surface directly or via another atomic group. The functional group is for constituting an organic group by reaction with a copolymer described later, and the type of the functional group is selected in relation to the functional group carried by the copolymer. The The reaction between the functional group and the copolymer is a reaction that generates a bond that does not cause hydrolysis, for example, an amide bond, considering that the pigment is dispersed in an aqueous medium. It is preferable that By making the functional group an amino group and supporting the carboxyl group on the copolymer, the copolymer can be introduced to the pigment particle surface via an amide bond. Similarly, the copolymer can be introduced to the pigment particle surface via an amide bond by converting the functional group to a carboxyl group and supporting the amino group on the copolymer.

  Here, the functional group chemically bonded to the pigment surface may be bonded directly to the pigment surface or may be bonded via another atomic group. However, when a copolymer having a relatively large molecular weight is introduced to the pigment surface, it is preferable to introduce a functional group to the pigment surface via another atomic group in order to avoid steric hindrance between the copolymers. Here, the other atomic groups are not particularly limited as long as they are polyvalent elements or organic groups. However, from the viewpoint of controlling the distance of the functional group from the pigment surface, for example, a divalent organic residue is preferably used. Examples of the divalent organic residue include an alkylene group and an arylene group (phenylene group).

  More specifically, for example, in the examples described later, the pigment is reacted with aminophenyl (2-sulfoethyl) sulfone to introduce an aminophenyl (2-sulfoethyl) sulfone group on the pigment surface. An amino group as a functional group is introduced by reacting an amino group of hexamine with an aminophenyl (2-sulfoethyl) sulfone group. In this case, it can be said that the amino group is chemically bonded to the pigment surface via an atomic group containing a phenyl (2-sulfoethyl) group.

[Copolymer]
As the copolymer composed of the ionic monomer and the hydrophobic monomer, for example, an anionic copolymer having an anionic property or a cationic copolymer having a cationic property is preferably used. Examples of the anionic copolymer include a copolymer composed of a hydrophobic monomer and an anionic monomer, or a salt thereof. Typical hydrophobic monomers used at this time include the following monomers, but the present invention is not limited to these. For example, methacrylic acid alkyl esters such as styrene, vinyl naphthalene, methyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate Alkyl acrylates such as methyl acrylate, phenyl acrylate, benzyl acrylate, acrylonitrile, 2-trimethylsiloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate and sorbyl acrylate.

  Examples of the anionic monomer used above include the following monomers, but the present invention is not limited thereto. For example, acrylic acid, methacrylic acid, maleic acid and the like can be mentioned.

  As an embodiment of the copolymer according to the present invention, the anionic copolymer comprising an anionic monomer and a hydrophobic monomer may be any one selected from the hydrophobic monomers listed above. And at least one monomer selected from at least one selected from anionic monomers. The copolymer includes a block copolymer, a random copolymer, a graft copolymer, or a salt thereof.

  The acid value of such an anionic copolymer is preferably in the range of 100 to 500, and it is preferable to use an acid value whose variation in acid value is within 20% of the average acid value. By setting the acid value within this range, the hydrophilicity of the pigment surface is too high, so that the water and solvent in the ink after printing stays on the pigment surface, and the marker resistance of the ink after printing on the recording medium is improved. Slow expression can be effectively suppressed. In addition, it is possible to effectively suppress the fact that the hydrophilicity of the pigment surface is too low and the pigment is difficult to stably disperse in the ink.

  Examples of the salt include alkali metal salts such as sodium, lithium, and potassium, ammonium salts, alkylamine salts, alkanolamine salts, and the like, and these can be used alone or in combination of several kinds.

  The weight average molecular weight (Mw) of the above anionic copolymer segment is preferably in the range of 1,000 to 20,000, more preferably 3,000 to 20,000. It is good to use the thing of the range. Furthermore, the polydispersity Mw / Mn (Mw: weight average molecular weight, Mn: number average molecular weight) indicating the spread of the molecular weight distribution of the copolymer is preferably 3 or less. The content of the anionic copolymer segment is preferably such that the content of the anionic copolymer with respect to the surface-modified pigment is 5% by mass or more and 40% by mass or less. More preferably, it is used in a proportion of 10% by mass or more and 25% by mass or less. By setting the physical properties of the anionic copolymer within the above-described range, it is possible to achieve both high viscosity suppression and dispersion stability at a high level.

  Next, a cationic copolymer comprising a cationic monomer and a hydrophobic monomer as another embodiment of the copolymer according to the present invention will be described. Examples of the cationic copolymer include copolymers composed of the following hydrophobic monomers and cationic monomers, or salts thereof. Typical hydrophobic monomers include the following monomers, but the present invention is not limited to these. For example, methacrylic acid alkyl esters such as styrene, vinyl naphthalene, methyl methacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate Acrylic acid alkyl esters such as methyl acrylate, phenyl acrylate, benzyl acrylate, acrylonitrile, 2-trimethylsiloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate, and sorbyl acrylate can be used.

  Examples of the cationic monomer include the following monomers, but the present invention is not limited thereto. Specifically, for example, allylamine, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 3-butylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, N-vinylcarbazole, methacrylamide, acrylamide And dimethylacrylamide can be used.

  The cationic copolymer is a block copolymer, a random copolymer, a graft copolymer comprising at least two monomers including a hydrophobic monomer selected from the above monomers and a cationic monomer, or these And the like. In particular, the cationic copolymer having an amine value in the range of 100 to 500 is preferable, and the variation of the amine value is preferably within 20% of the average amine value. The amine value is expressed in mg of KOH equivalent to hydrochloric acid required to neutralize 1 g of the sample. The salt includes acetic acid, hydrochloric acid, nitric acid and the like, and these can be used alone or in appropriate combination of several kinds.

  The cationic copolymer having a weight average molecular weight (Mw) in the range of 1,000 to 20,000 can be preferably used, and more preferably in the range of 3,000 to 20,000. It can be preferably used. Further, the polydispersity Mw / Mn (weight average molecular weight Mw, number average molecular weight Mn) of the cationic copolymer segment should be 3 or less as in the case of the anionic copolymer described above. Is preferred. Further, the content of such a cationic copolymer in the ink is preferably 5% by mass or more and 40% by mass or less with respect to the pigment particles whose surface is modified by the copolymer. Is a ratio of 10 mass% or more and 25 mass% or less. By setting the various physical properties of the cationic copolymer within the range as described above, it is possible to achieve both high viscosity suppression and dispersion stability at a high level.

  Next, taking carbon black as an example, a method for modifying the pigment by chemically bonding an organic group to the pigment particle surface will be described. In the present invention, first, a functional group on the surface of the pigment particle or a functional group is introduced on the surface of the pigment particle, and a copolymer composed of an ionic monomer and a hydrophobic monomer is bonded to these functional groups. Any method can be used as long as it is a method of chemically bonding the polymer to the surface of the pigment particles, and there is no particular limitation. As such a method, the following method etc. can be used, for example.

  A method in which polyethyleneimine or the like is introduced on the surface of pigment particles such as carbon black, and a copolymer composed of an ionic monomer and a hydrophobic monomer having an amino group at its terminal functional group is bonded by a diazonium reaction, carbon Methods such as a method of bonding a copolymer having an amino group and a carboxyl group in the molecule to the surface of pigment particles such as black by a diazonium reaction can be used. As the other example, the most typical example is disclosed in WO01 / 51566A1.

In the above-described method, for example, when an anionic copolymer is chemically bonded to the surface of the carbon black particles, the following three steps are included.
1st process; The process of adding an aminophenyl (2-sulfoethyl) sulfone group (APSES) to carbon black by a diazonium reaction.
Second step: A step of adding polyethyleneimine or pentaethylenehexamine (PEHA) to carbon black subjected to APSES treatment.
Third step: A step of attaching a copolymer of a hydrophobic monomer and an ionic monomer having a carboxyl group.

  In the second step, a phenyl (2-sulfoethyl) sulfone group chemically bonded to the carbon black surface in the first step is reacted with an amino group such as polyethyleneimine or pentaethylenehexamine (PEHA). By doing so, an amino group as a functional group chemically bonded to the carbon black surface is introduced. In the third step, for example, by reacting a part of the carboxyl group of the ionic monomer portion of the copolymer with an amino group to form an amide bond, the copolymer is formed on the surface of carbon black, APSES. A copolymer can be introduced through an atomic group containing a phenyl (2-sulfoethyl) group that is a residue of the above and a residue of PEHA.

Further, in the above-described method, for example, when the cationic copolymer is chemically bonded to the surface of the carbon black particles, the following two steps are included.
First step: A step of adding an aminophenyl (2-sulfoethyl) sulfone group (APSES) to carbon black by a diazonium reaction.
2nd process; The process of attaching the copolymer of a hydrophobic monomer and a cationic monomer.
Through the first step, a sulfone group is introduced as a functional group chemically bonded to the carbon black surface. In the second step, for example, a part of the amino group of the ionic monomer portion of the copolymer is reacted with a sulfone group (nucleophilic substitution), the copolymer is placed on the surface of carbon black, and the APSES A copolymer can be introduced through an atomic group containing a phenyl (2-sulfoethyl) group as a residue.

[Presence of free polymer]
By the way, in the present invention, a segment containing the copolymer that is not chemically bonded to the pigment surface (hereinafter referred to as “free polymer”, including a segment that is physically adsorbed on the pigment surface) is an ink. It does not exclude being present. However, the amount of the free polymer is preferably controlled from the viewpoint of further improving the ink jet characteristics of the aqueous ink according to the present invention. Specifically, based on the total mass of the free polymer and the organic group bonded to the pigment surface, the proportion of the free polymer is less than 50% by mass, particularly less than 35% by mass, and even 20% by mass. It is preferable to make it less than.

  When ink containing a large amount of free polymer is used for ink jet recording, free organic groups adhere to the orifices around the ejection openings of the recording head, resulting in uneven wetting around the ejection openings, resulting in poor ink ejection. There is a problem that the ejection direction bends in a regular manner and the landing point of the ink shifts. Furthermore, if continuous printing is continued, ink will adhere to the orifice surface near the nozzle as the ink overflows from the nozzle, and the ink adheres to the large area around the nozzle. An ink reservoir may be formed on the orifice. If printing is continued in this state, there is a problem that the ink to be ejected is drawn into the ink reservoir on the orifice and cannot be ejected.

  An effective range of ink reliability with respect to the recording head is that the ratio of the organic group chemically bonded to the pigment particle surface to the total of the organic group and the free polymer is 50% or more. It is preferably 65% or more, and more preferably 80% or more. This value can be obtained by a thermogravimetric analysis method for the sample using a dried solid sample taken out from the ink by a method as described later.

[Aqueous medium]
The aqueous medium, which is a pigment dispersion medium obtained by chemically bonding an organic group containing the copolymer to the pigment surface, obtained as described above, will be described below. Examples of the aqueous medium that can be used in the present invention include water or a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, those having an ink drying preventing effect are particularly preferable.

  Specifically, for example, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; dimethylformamide, Amides such as dimethylacetamide; Ketones or ketoalcohols such as acetone and diacetone alcohol; Ethers such as tetrahydrofuran and dioxane; Polyalkylene glycols such as polyethylene glycol and polypropylene glycol; Ethylene glycol, propylene glycol, butylene glycol, tri 2 to 6 alkylene groups such as ethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol Alkylene glycols containing carbon atoms; lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether, etc. Lower alkyl ethers of polyhydric alcohols; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. The above water-soluble organic solvents can be used alone or as a mixture. As the water, it is desirable to use deionized water.

  The content of the water-soluble organic solvent as described above contained in the ink according to the present invention is not particularly limited, but is preferably in the range of 3 to 50% by mass with respect to the total mass of the ink. The amount of water contained in the ink is preferably in the range of 50 to 95% by mass with respect to the total mass of the ink.

  In addition, in order to maintain the moisturizing property of the ink, other moisturizing solid components such as urea, urea derivatives, trimethylolpropane, trimethylolethane and the like may be used as the ink component. The content of moisturizing solids such as urea, urea derivatives, and trimethylolpropane in the ink is generally preferably in the range of 0.1 to 20.0% by weight, more preferably 3.0. It is the range of-10.0 mass%.

  Furthermore, in addition to the above components, the ink according to the present invention includes a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, and an evaporation accelerator as necessary. Various additives such as chelating agents may be contained.

[Surfactant]
In the present invention, as the surfactant, for example, those having an alkylene oxide chain (ethylene oxide chain, propylene oxide chain, etc.) in the molecule are preferably used. Further, the HLB (Hydrophile-Liophile Balance) value of the surfactant is preferably 10 or more, particularly preferably 15 or more. The addition amount of the surfactant cannot be generally defined by the ink composition, but is suitably 0.1 to 5% by mass, particularly 0.3 to 1% by mass with respect to the total mass of the ink. By adding such a surfactant, it is possible to further improve the dispersion stability of the pigment in the aqueous ink according to the present invention. Further, as the characteristics of the water-based ink for inkjet, it is possible to further improve the initial ejection stability and the long-term ejection stability. Here, a part of specific examples of the surfactant that can be used in the present invention are shown below.

上記構造式（１）中、Ｒはアルキル基、具体的には少なくとも６個の炭素数を有する直鎖若しくは分岐鎖状のアルキル基である。ｎは、正の整数、好ましくは１０以上の整数である。より具体的には、例えば、ポリオキシエチレンラウリルエーテル、ポリオキシエチレントリデシルエーテル、ポリオキシエチレンセチルエーテル、ポリオキシエチレンステアリルエーテル、ポリオキシエチレンオレイルエーテル等が挙げられる。

In the structural formula (1), R is an alkyl group, specifically, a linear or branched alkyl group having at least 6 carbon atoms. n is a positive integer, preferably an integer of 10 or more. More specifically, for example, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether and the like can be mentioned.

上記構造式（２）中、Ｒはアルキル基、具体的には少なくとも６個の炭素数を有する直鎖若しくは分岐鎖状のアルキル基であり、ｎは、正の整数、好ましくは１０以上の整数である。より具体的には、例えば、ポリオキシエチレンノニルフェニルエーテルや、ポリオキシエチレンオクチルフェニルエーテル等が挙げられる。

In the structural formula (2), R is an alkyl group, specifically, a linear or branched alkyl group having at least 6 carbon atoms, and n is a positive integer, preferably an integer of 10 or more. It is. More specifically, for example, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether and the like can be mentioned.

上記構造式（３）中、Ｒは水素原子又はアルキル基、具体的には少なくとも１〜６個の炭素数を有するアルキル基であり、又、ｍ及びｎは、夫々、正の整数を表し、好ましくはｍ＋ｎが少なくとも１０である。上記構造式（３）にかかる界面活性剤１分子中におけるエチレンオキサイド鎖の含有率としては、１０〜８０ｗｔ％のものが好ましい。

In the structural formula (3), R is a hydrogen atom or an alkyl group, specifically, an alkyl group having at least 1 to 6 carbon atoms, and m and n each represent a positive integer, Preferably m + n is at least 10. As a content rate of the ethylene oxide chain in 1 molecule of surfactant concerning the said Structural formula (3), a thing of 10-80 wt% is preferable.

上記構造式（４）中、ｍ及びｎは、夫々、正の整数を表す。

In the structural formula (4), m and n each represents a positive integer.

上記構造式（５）中、ａ、ｂ、ｃは各々、正の整数であり、好ましくはａ＋ｂ＋ｃは、少なくとも１０である。又、上記構造式（５）にかかる界面活性剤１分子中におけるエチレンオキサイド鎖の含有率としては、１０〜８０ｗｔ％のものが好ましい。

In the structural formula (5), a, b, and c are each a positive integer, and preferably a + b + c is at least 10. Moreover, as a content rate of the ethylene oxide chain in 1 molecule of surfactant concerning the said Structural formula (5), a 10-80 wt% thing is preferable.

  The ink according to the present invention having the above-described configuration can be used for writing instrument ink and inkjet ink. As an ink jet recording method, there are a recording method in which mechanical energy is applied to ink to eject droplets, and a bubble jet (registered trademark) recording method in which thermal energy is applied to ink and ink droplets are ejected by foaming of the ink. However, the ink of the present invention is particularly suitable for these recording methods.

  By the way, when the ink according to the present invention is used for the ink jet recording as described above, it is preferable that the ink has a characteristic that it can be favorably ejected from the ink jet recording head. For this reason, from the viewpoint of ejectability from the ink jet recording head, the ink characteristics are, for example, a viscosity of 1 to 15 mPa · s, a surface tension of 25 mN / m or more, and a viscosity of 1 to 5 mPa · s. The surface tension is preferably 25 to 50 mN / m.

Further, as a scale representing the permeability of ink into a recording medium, there is a Ka value obtained by the Bristow method. That is, when the ink permeability is expressed by the ink amount V per 1 m ² , the ink penetration amount V (mL / m ² = μm) after a predetermined time t has elapsed since the ink droplet was ejected. ) Is shown by the Bristow equation shown below.
V = Vr + Ka (t−tw) ^1/2

  Here, immediately after the ink droplets adhere to the surface of the recording medium, the ink is mostly absorbed in the uneven portion of the surface of the recording medium (the roughness portion of the surface of the recording medium). Almost no penetration. The time between them is the contact time (tw), and the amount of ink absorbed by the uneven portions of the recording medium at the contact time is Vr. Then, when the contact time is exceeded after the ink is deposited, the amount of penetration into the recording medium increases by the time exceeding the contact time, that is, an amount proportional to (1/2) power of (t-tw). Ka is a proportional coefficient of this increase, and indicates a value corresponding to the penetration rate. The Ka value can be measured using a liquid dynamic permeability test apparatus (for example, trade name: dynamic permeability test apparatus S; manufactured by Toyo Seiki Seisakusho Co., Ltd.) by the Bristow method.

In the ink according to each embodiment of the present invention, it is preferable that the Ka value is less than 1.5 (ml / m ² / msec ^1/2 ) in order to further improve the recorded image quality. More preferably, it is 0.2 (ml / m ² / msec ^1/2 ) or more and less than 1.5 (ml / m ² / msec ^1/2 ). That is, when the Ka value is less than 1.5 (ml / m ² / msec ^1/2 ), solid-liquid separation occurs at an early stage of the ink penetration into the recording medium, and the quality is extremely low. An image can be formed.

  The Ka value according to the Bristow method in the present invention is used for plain paper [for example, a copying machine using an electrophotographic method, a page printer (laser beam printer) manufactured by Canon Inc., or a printer using an ink jet recording method. This is a value measured using a PB paper used or a PPC paper that is a copying machine paper using an electrophotographic method as a recording medium. As a measurement environment, a normal office environment, for example, a temperature of 20 to 25 ° C. and a humidity of 40 to 60% is assumed.

  By the way, the effects of the water-based ink according to the present invention include the following. First, as a first effect, the pigment according to the present invention has a functional group chemically bonded to the surface thereof directly or through another atomic group, and a co-weight of an ionic monomer and a hydrophobic monomer. And a reaction product of the polymer, so that the copolymerization ratio of the ionic monomer and the hydrophobic monomer, which is a forming material of the copolymer used when modifying the surface, can be appropriately changed. It is possible to appropriately adjust the hydrophilicity of the modified pigment. Moreover, since the kind of ionic monomer and hydrophobic monomer to be used, and the combination of both can be changed, various characteristics can be imparted to the pigment surface. Further, when an ink is formed, the characteristics as an ink can be controlled by selecting a solvent to be used in combination with such a pigment.

  As a second effect, according to the study by the present inventors, when a hydrophobic monomer is used in the copolymer bonded to the pigment surface, the marker resistance to ink print stains can be improved. all right. Hereinafter, the reason for improving the marker resistance will be described.

  First, when a hydrophilic polymer is used for the surface modification of the pigment, the polymer particles on the surface of the pigment particle are entangled on the paper after fixing to the recording medium, thereby increasing the cohesive strength of the pigment, As a result, the ink smear resistance (scratch resistance) of the ink is improved. However, when the print surface is rubbed with a water-soluble marker pen, the pigment surface is highly hydrophilic due to water in the marker pen or an aqueous organic solvent, because what is present on the pigment surface is hydrophilic. Since the molecules are redissolved, it flows out so that the pigment particles can be dissolved together with the rubbing of the marker pen, and as a result, it is considered that the marker resistance to printing stains is hardly exhibited.

  In contrast, the pigment used in the present invention has an organic group containing a copolymer of an ionic monomer and a hydrophobic monomer chemically bonded to the pigment surface. After printing, the cohesive force of the pigment becomes stronger due to the entanglement of the copolymer on the surface of the pigment particles on the paper surface, and the scratch resistance against printing stains after ink fixing is improved. This is the same as the case of the ink using the surface modified pigment made of the hydrophilic polymer. However, since the organic group has a copolymer of an ionic monomer and a hydrophobic monomer, when the water and the organic solvent in the ink are dried or permeated in the process of fixing the ink, the pigment It is considered that the polymer on the surface is not only entangled but also oriented so that the hydrophobic portion of the copolymer bonded to the pigment surface faces the outside on the outermost surface of the printed matter. For this reason, the hydrophobic part of the copolymer is oriented on the outermost surface of the printed matter, and the surface of the printed matter becomes hydrophobic. As a result, even when the printing surface is rubbed with a water-soluble marker pen, it becomes difficult for the pigment particles to redissolve in water or an organic solvent in the ink of the marker pen, and the pigment particles are prevented from flowing out by rubbing the marker pen. be able to.

[Analysis method]
Hereinafter, an analysis method and an evaluation method used when evaluating the characteristics of the ink according to the present invention will be described by taking an aqueous pigment ink using carbon black as an example. However, the pigment used for the ink according to the present invention is not particularly limited. The method for analyzing the surface modification state of the pigment whose particle surface has been modified for use in the present invention is not particularly limited, and analysis can be performed using a method that can be generally considered. Preferably, a method of analyzing the binding state of organic groups present on the surface of pigment particles such as carbon black by ESCA, TOF-SIMS or the like can be used.

  The method for measuring the amount of the organic group chemically bonded to the surface of the carbon black particles is not particularly limited, and can be performed by, for example, the following method. First, from the ink containing the surface-modified carbon black, a solid content containing carbon black particles modified with an organic group is collected from the ink by salting out or coagulation. In order to fractionate only the surface-modified carbon black (carbon black in which the organic group is chemically bonded to the particle surface) with high purity from the solid content extracted from the ink by this method, A method of washing and drying a solid content taken out from the ink with a good solvent of a copolymer chemically bonded to the surface of the carbon black particles can be used. The following is a more detailed method for separating the surface-modified carbon black from the ink, and the surface-modified carbon black is obtained by using a dried product obtained after the separation and drying as a measurement sample. An analysis method for measuring the amount of organic groups bonded to the surface of the carbon black particles or the amount of the segment containing the copolymer portion that may be present in the ink as a free polymer will be described.

  First, prior to analysis, pretreatment is performed as follows to prepare a measurement sample. From the ink containing the surface-modified carbon black described above, the solid content obtained as a precipitate by salting out or coagulating is dried and then washed with a good solvent for the copolymer. From this, extraction processing is performed only for carbon black in which the organic group is chemically bonded to the particle surface. The method consists of a series of steps: (1) salting out or coagulating, (2) washing the precipitate, (3) drying, (4) extracting only the surface-modified carbon black, and (5) drying. It can be carried out. In the following, description will be given in order.

  (1) The method for salting out or coagulating the solid content containing the surface-modified carbon black from the ink is not particularly limited. For example, (a) salting out with a salt such as sodium chloride or potassium chloride, b) A method of coagulation (acid precipitation) using an acid such as nitric acid or hydrochloric acid can be used. At this time, as necessary, for example, ultrafiltration may be performed as a pre-process such as salting out.

  (2) The solid content obtained by salting out or coagulating is sufficiently washed with pure water. In particular, when the coagulation of (b) described in (1) is performed, it is preferable to perform sufficient washing until the filtrate after washing becomes neutral.

  (3) The solid content after washing obtained above is sufficiently dried in an oven or the like and taken out as a dry solid. The drying conditions and the like at this time are not particularly limited, and for example, they may be dried at 60 ° C. for about 2 hours.

  (4) The dried product obtained in the above (3) includes a free polymer that is not chemically bonded to the surface of the carbon black particles other than carbon black in which the organic group is chemically bonded to the surface of the carbon black particles. (Including those that are physically adsorbed to the pigment). Therefore, the surface-modified carbon black is extracted with higher purity by washing the dried product obtained in (3) with a good solvent of the copolymer. The good solvent for the free polymer used in the above varies depending on the structure of the copolymer and cannot be generally limited. For example, tetrahydrofuran (THF) is a general-purpose good solvent. In this case, it is preferable to wash the dried product repeatedly using such a good solvent and repeat the removal of free polymer that may be mixed in the solid content.

  (5) As described above, the solid content from which the free polymer has been removed by washing the copolymer part with a good solvent is finally subjected to sufficient drying treatment in an oven or the like to volatilize residual moisture and residual solvent. Let it be a dry solid sample. The oven used for drying is not particularly limited, and for example, drying using a commercially available vacuum dryer or the like may be performed. Also, the drying conditions and the like are not particularly limited as long as the residual water and residual solvent can be sufficiently removed from the surface-modified carbon black dried product. For example, what is necessary is just to dry at 60 degreeC x about 3 hours by the vacuum degree of several hundred Pa or less.

  By using the surface-modified carbon black dried product taken out of the ink by the series of methods (1) to (5) described above as a measurement sample, and measuring the weight change of the sample using thermogravimetric analysis, It is possible to quantitatively measure the amount of organic groups that are chemically bonded to the surface of the carbon black particles. As a result, it is possible to measure the content of organic groups chemically bonded to the carbon black on the basis of the mass of the surface-modified carbon black particles.

  Further, the dried product obtained by the series of steps (1) to (3) above is used as a measurement sample, and the weight change of the sample is measured using thermogravimetric analysis. In addition to the bonded organic groups, the amount of solid content excluding pigments in the ink such as free polymer can be known. As a result, the ratio of the organic group to the total of the organic group and free polymer contained in the ink can be obtained. In order to accurately calculate the ratio of the organic group to the sum of the organic group and the free polymer in the ink when the second polymer other than the copolymer is mixed in the ink. It is preferable to measure the amount of the free polymer alone. In that case, the amount of the free polymer alone can be measured by measuring the carbon black cleaning liquid in the procedure (4) using liquid chromatography or the like.

  By the series of procedures described above (1) salting out or coagulating, (2) washing the precipitate, (3) drying, (4) extracting only the surface-modified carbon black, and (5) drying. There is no particular limitation on the method for measuring the content of the bonded organic group in the obtained dried product sample containing only surface-modified carbon black. For example, a sufficiently dried carbon black solid product finally obtained by the above procedure is measured by thermogravimetric analysis, etc., and it is easily obtained from the thermogravimetric weight loss rate obtained as a result. Can do. Hereinafter, the thermogravimetric analysis performed at this time will be described in detail.

The thermogravimetric analysis weight reduction rate measured by the above method is the content of organic groups introduced on the surface of the carbon black particles in the surface-modified carbon black. That is, the weight loss rate of thermogravimetric analysis is given by the following formula, but it is washed with a good solvent of a polymer substance before thermogravimetric analysis and is extracted with respect to the weight of the dry solid sample obtained by extracting only surface modified carbon black. , A ratio of weight loss caused by desorption or combustion of organic groups bonded to the surface of the carbon black particles, which is generated in a thermogravimetric analysis performed by raising the temperature to 100 to 700 ° C.
Thermogravimetric analysis weight loss rate = A / B x 100 (%)
A = weight loss when the temperature is raised to 100-700 ° C. in thermogravimetric analysis B = weight of sample before thermogravimetric analysis

  The analysis conditions and the like in the thermogravimetric analysis performed in the above are not particularly limited, and the measurement may be performed under normal conditions such as pretreatment and temperature increase rate. As the measuring device, for example, a TGA thermogravimetric measuring device manufactured by METTLER TOLEDO, TGA851e / SDTA, or the like can be used.

  Further, if the thermogravimetric analysis weight reduction rate measurement method described above is used, the bonding state between the substance used for the surface modification and the pigment particles in the pigment such as the surface modified carbon black contained in the aqueous pigment ink of the present invention. Can know. That is, an organic group is chemically bonded to, for example, the surface of carbon black particles, which is a pigment used in the present invention. For this reason, the organic groups on the surface of the carbon black particles are not washed away even after washing with a good solvent of the above-mentioned polymer substance, and are stably bonded to the surface of the carbon black particles. Regardless, the thermogravimetric analysis weight loss rate shows almost the same value. On the other hand, in a resin dispersion type pigment that is generally used, the water-soluble resin used in the dispersant is not chemically bonded to carbon black (pigment), so it was used for dispersion. When the resin is washed with a good solvent, the resin is washed away, so that the weight loss rate of thermogravimetric analysis is greatly different between the case where the extraction process is performed and the case where the process is not performed.

  From this, the modified pigment suitably used in the present invention does not change or substantially does not change the weight loss rate by thermogravimetric analysis before and after washing the copolymer with a good solvent. Can be. Here, the fact that the weight reduction rate by thermogravimetric analysis does not change substantially before and after the cleaning indicates that the difference in value of the weight reduction rate before and after the cleaning is within 5%, for example.

  In addition to using the thermogravimetric analysis described above, there is a method for examining the bonding state of the pigment particle surface with the substance used for surface modification. For example, the carbon black dried product obtained by subjecting the surface-modified carbon black used in the present invention to salting-out or coagulation as described above and then dried to dryness is used as a measurement sample, and this sample is used as TG-GC. -MS (thermogravimetric analysis-gas chromatograph-mass spectrometry), TOF-MS (time-of-flight mass spectrometry), TOF-SIMS (time-of-flight secondary ion mass spectrometry) and the like are also suitable. . By these methods, the bonding state (measurement of adsorption energy) of the substance used for the surface modification in the carbon black dry matter sample, and further the composition of the organic group bonded in the carbon black dry matter sample, The molecular weight distribution as well as the binding unit can be known in detail. An example of a specific apparatus that can be used for such an analysis is shown below.

TG-DTA: Thermo Plus TG8120 (manufactured by RIKEN)
-GC: HP6890 (manufactured by Hewlett-Packard Company)
・ MS: JMS-AM II (manufactured by JEOL)
・ TOF-MS: Shimadzu MALDI-TOFMS AXIMA-CFR (manufactured by Shimadzu Corporation)
・ TOF-SIMS: PHI TRFT II (manufactured by ULVAC-PHI)

  The aqueous pigment ink of the present invention having the above configuration is particularly effective when used for inkjet recording. As the ink jet recording method, there are a recording method for ejecting ink by applying mechanical energy to the ink, and an ink jet recording method for ejecting ink by foaming of the ink by applying thermal energy to the ink. In particular, the aqueous pigment ink of the present invention is particularly suitable.

Recording Method, Recording Unit, Cartridge, and Recording Device Next, an example of the ink jet recording device according to the present invention that can be suitably used for recording using the above-described aqueous pigment ink according to the present invention will be described below. To do. First, an example of a head configuration which is a main part of an ink jet recording apparatus using thermal energy is shown in FIGS. 5 is a cross-sectional view of the head 13 along the ink flow path, and FIG. 6 is a cross-sectional view taken along the line AB of FIG. The head 13 is obtained by bonding a heating element substrate 15 to a glass, ceramic, silicon or plastic plate having a flow path (nozzle) 14 through which ink passes. The heating element substrate 15 includes a protective layer 16 formed of silicon oxide, silicon nitride, silicon carbide, etc., electrodes 17-1 and 17-2 formed of aluminum, gold, aluminum-copper alloy, HfB ₂ , TaN, A heating resistor layer 18 formed of a high melting point material such as TaAl, a heat storage layer 19 formed of thermal silicon oxide, aluminum oxide or the like, and a substrate 20 formed of a material with good heat dissipation such as silicon, aluminum, or aluminum nitride. It has become more.

  When a pulsed electric signal is applied to the electrodes 17-1 and 17-2 of the head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and bubbles are generated in the ink 21 in contact with the surface. The pressure causes the meniscus 23 to protrude, and the ink 21 is ejected through the nozzles 14 of the head to form ink droplets 24 from the ejection orifices 22 and fly toward the recording medium 25. FIG. 7 shows an external view of an example of a multi-head in which many heads shown in FIG. 5 are arranged. This multi-head is made by adhering a glass plate 27 having multi-nozzles 26 and a heating head 28 similar to that described in FIG.

  FIG. 8 shows an example of an ink jet recording apparatus incorporating this head. In FIG. 8, reference numeral 61 denotes a blade as a wiping member, one end of which is held and fixed by a blade holding member and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65, and in the illustrated example, is held in a form protruding in the moving path of the recording head 65.

  Reference numeral 62 denotes a cap on the projection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ink ejection port surface, and performs capping. The structure to perform is provided. Further, reference numeral 63 denotes an ink absorber provided adjacent to the blade 61 and, like the blade 61, is held in a form protruding in the moving path of the recording head 65. The blade 61, the cap 62, and the ink absorber 63 constitute an ejection recovery unit 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ejection port surface.

  Reference numeral 65 denotes a recording head which has discharge energy generating means and performs recording by discharging ink onto a recording medium facing the discharge port surface where the discharge port is arranged. Reference numeral 66 denotes a movement of the recording head 65 by mounting the recording head 65. It is a carriage for performing. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area and its adjacent area can be moved by the recording head 65.

  51 is a paper feed section for inserting a recording medium, and 52 is a paper feed roller driven by a motor (not shown). With these configurations, the recording medium is fed to a position facing the ejection port surface of the recording head 65, and discharged to a paper discharge unit provided with a paper discharge roller 53 as recording progresses. In the above configuration, when the recording head 65 finishes recording and returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port of the recording head 65 is wiped.

  When the cap 62 is in contact with the ejection surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the moving path of the recording head. When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as that at the time of wiping described above. As a result, the ejection port surface of the recording head 65 is wiped even during this movement. The above-mentioned movement of the recording head to the home position is not only at the end of recording or at the time of ejection recovery, but also to the home position adjacent to the recording area at a predetermined interval while the recording head moves the recording area for recording. Then, the wiping is performed with this movement.

  FIG. 9 is a diagram illustrating an example of an ink cartridge that stores ink supplied to the recording head via an ink supply member, for example, a tube. Here, reference numeral 40 denotes an ink container, for example, an ink bag, in which supply ink is stored, and a rubber plug 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the head. An ink absorber 44 receives waste ink. The ink container preferably has a liquid contact surface made of polyolefin, particularly polyethylene.

  The ink jet recording apparatus used in the present invention is not limited to the one in which the head and the ink cartridge are separated as described above, and is preferably used in an apparatus in which they are integrated as shown in FIG. It is done. In FIG. 10, reference numeral 70 denotes a recording unit, in which an ink storage portion that stores ink, for example, an ink absorber is stored, and the ink in the ink absorber from the head portion 71 having a plurality of orifices. It is configured to be ejected as ink droplets. It is preferable for the present invention to use polyurethane as the material of the ink absorber. Alternatively, a structure may be used in which the ink container is an ink bag with a spring or the like inside without using an ink absorber. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere. The recording unit 70 is used in place of the recording head 65 shown in FIG. 8, and is detachable from the carriage 66.

  Next, as a preferable example of an ink jet recording apparatus using mechanical energy, a nozzle forming substrate having a plurality of nozzles, a pressure generating element made of a piezoelectric material and a conductive material disposed opposite to the nozzles, and the pressure An on-demand ink jet recording head that includes ink that fills the periphery of the generating element, displaces the pressure generating element by an applied voltage, and discharges a small droplet of ink from a nozzle can be exemplified. An example of the configuration of a recording head, which is a main part of the recording apparatus, is shown in FIG.

  The head includes an ink flow path 80 communicating with an ink chamber (not shown), an orifice plate 81 for ejecting ink droplets of a desired volume, a vibration plate 82 that directly applies pressure to ink, and the vibration plate 82. And a substrate 84 for indicating and fixing the orifice plate 81, the diaphragm 82 and the like.

  In FIG. 11, an ink flow path 80 is formed of a photosensitive resin or the like, an orifice plate 81 is formed with a discharge port 85 formed by electroforming or punching a metal such as stainless steel or nickel, and the vibration plate 82 is The piezoelectric element 83 is formed of a dielectric material such as barium titanate or PZT. The piezoelectric element 83 is formed of a metal film such as stainless steel, nickel, or titanium and a highly elastic resin film. The recording head configured as described above applies a pulsed voltage to the piezoelectric element 83 to generate a distortion stress, and the energy deforms the vibration plate bonded to the piezoelectric element 83, so that the ink in the ink flow path 80 is obtained. Is pressed vertically and ink droplets (not shown) are ejected from the ejection ports 85 of the orifice plate 81 to perform recording. Such a recording head is used by being incorporated in an ink jet recording apparatus similar to that shown in FIG. The detailed operation of the ink jet recording apparatus can be performed in the same manner as described above.

  Next, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited by the following Example, unless the summary is exceeded. In the text, “parts” and “%” are based on mass unless otherwise specified.

(Preparation of pigment dispersion 1)
500 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 112 ml / 100 g, 45 g of aminophenyl (2-sulfoethyl) sulfone (APSES), and 900 g of distilled water are charged into the reactor, kept at 55 ° C., and rotated at 300 RPM. For 20 minutes. Thereafter, 40 g of 25% sodium nitrite was added dropwise for 15 minutes, and 50 g of distilled water was further added. Then, it was made to react for 2 hours, keeping at 60 degreeC. And the obtained reaction material was taken out, diluting with distilled water, and it adjusted to the density | concentration from which solid content will be 15%. Thereafter, a centrifugal separation treatment and a purification treatment for removing impurities were performed. This prepared dispersion was a dispersion in which the above-described APSES functional group was bonded to carbon black. This dispersion is designated as A1.

  Next, in order to determine the number of moles of functional groups bonded to the carbon black in the dispersion A1, Na ions in the dispersion are measured with a probe-type sodium electrode, and the obtained value is calculated per carbon black powder. In conversion, the number of moles of functional groups bonded to carbon black was determined. Next, the previously prepared dispersion A1 having a solid content of 15% was dropped into a pentaethylenehexamine (PEHA) solution. At this time, the PEHA solution was kept at room temperature with vigorous stirring, and the dispersion A1 was added dropwise over 1 hour. The PEHA concentration at this time was 2 to 3 times the molar number of Na ions measured previously, and the solution amount was the same as that of the dispersion A1. Furthermore, this mixture was stirred for 48 hours, and then a purification treatment for removing impurities was performed. Finally, a dispersion having a solid content of 10% to which pentaethylenehexamine (PEHA) was bound was obtained. This dispersion is designated as B1.

Next, a styrene-acrylic acid resin as a copolymer was prepared as follows. First, 190 g of a styrene-acrylic acid resin having a weight average molecular weight of 15,000, an acid value of 140, and a polydispersity Mw / Mn (weight average molecular weight Mw, number average molecular weight Mn) of 1.5 was weighed, and 1,800 g was measured. Of distilled water was added, NaOH necessary for neutralizing the resin was added, and the mixture was stirred and dissolved to prepare a styrene-acrylic acid resin aqueous solution.
Next, 500 g of the previously prepared dispersion B1 having a solid content of 10% was dropped into the styrene-acrylic acid resin aqueous solution while stirring. Next, the mixture of B1 and a styrene-acrylic acid resin aqueous solution was transferred to a Pyrex (registered trademark) evaporating dish, heated at 150 ° C. for 15 hours to evaporate, and then the evaporated and dried product was cooled to room temperature.

  Subsequently, this evaporated and dried product was dispersed in NaOH-added distilled water adjusted to pH = 9.0 using a disperser, and 1.0 M NaOH was further added with stirring to adjust the pH to 10-11. did. Thereafter, desalting, purification for removing impurities, and removal of coarse particles were performed to obtain a pigment dispersion 1. Regarding the physical properties of the obtained pigment dispersion 1, the solid content was 10%, the pH was 10.1, and the average particle size was 130 nm. Below, the synthetic scheme of the modified pigment which is contained in the pigment dispersion 1 in the above and is formed by chemically bonding an organic group to the surface of the carbon black particles is shown.

(Preparation of pigment dispersions 2 to 7)
Pigment dispersions 2 to 7 were prepared in the same manner as the pigment dispersion 1 except that the copolymers shown in Table 1 below were used. The physical properties of the obtained dispersion are also shown in Table 1.

(Preparation of pigment dispersion 8)
Dispersion A1 was prepared in the same manner as described in the preparation of pigment dispersion 1. Next, A1 having a solid content of 15% is reacted with a styrene-allylamine copolymer (amine number 200, molecular weight 10,000, polydispersity Mw / Mn = 1.8), followed by desalting and removing impurities. Purification and coarse particle removal were performed to obtain a pigment dispersion 8. Regarding the physical properties of the obtained pigment dispersion 8, the solid content was 11%, the pH was 5.5, and the average particle size was 120 nm. Below, the synthetic scheme of the modified pigment which the pigment dispersion liquid 8 contains and an organic group chemically couple | bonds with the carbon black surface is shown.

(Preparation of pigment dispersion 9)
The pigment dispersion liquid was the same as that prepared in the pigment dispersion liquid 8 except that a styrene-allylamine copolymer having an amine value of 450, a molecular weight of 4,000, and a polydispersity Mw / Mn = 1.8 was used. 9 was prepared. Regarding the physical property values of the obtained pigment dispersion 9, the solid content was 10%, the pH was 4.5, and the average particle size was 142 nm.

(Preparation of pigment dispersion 10)
The pigment dispersion was the same as the pigment dispersion 1 except that a styrene-acrylic acid resin having a weight average molecular weight of 5,000, an acid value of 140, and a polydispersity of Mw / Mn = 2.5 was used as the copolymer. 10 was prepared. Regarding the physical properties of the obtained pigment dispersion 10, the solid content was 10.0%, the pH was 10, and the average particle size was 130 nm.

(Preparation of pigment dispersion 11)
A pigment was prepared in the same manner as in the pigment dispersion 1 except that a styrene-acrylic acid resin having a weight average molecular weight of 18,000, an acid value of 200, and a polydispersity Mw / Mn = 1.6 was used as a copolymer. Dispersion 11 was obtained. As for the physical properties of the obtained pigment dispersion 11, the solid content was 10.5%, the pH was 10, and the average particle size was 140 nm.

(Preparation of pigment dispersion 12)
In the same manner as that in the preparation of the pigment dispersion 1, the final desalting, purification for removing impurities, and purification for removing coarse particles are not performed in the step of removing the impurities, and the desalting and coarse particles are removed. Only the removal was performed to obtain a pigment dispersion 12. Regarding the physical property values of the obtained pigment dispersion 12, the solid content was 10.5%, the pH was 9.7, and the average particle size was 150 nm.

<Examples 1 to 12>
The components described in Table 2-1 and Table 2-2 including the pigment dispersions 1 to 12 obtained above were mixed, dissolved or dispersed with sufficient stirring, and then a microfilter having a pore size of 3.0 μm ( The ink of Examples 1 to 12 of the present invention was prepared by pressure filtration with Fuji Film. The composition of each ink is shown in Tables 2-1 and 2-2.

  In addition, in Table 2-1 and Table 2-2, the measured value of Ka value obtained by the Bristow method for each ink of Examples 1 to 12 obtained as described above is described. . Furthermore, by thermogravimetric analysis described later, the ratio (%) of the chemically bonded organic group in the surface-modified pigment for each of the inks of Examples 1 to 12 was obtained with two significant figures. Table 2 -1 and Table 2-2.

  Hereinafter, a specific method for measuring the ratio of chemically bonded organic groups in the surface-modified pigments shown in Table 2-1 and Table 2-2 will be described. First, salting out or coagulation with respect to each of the inks of Examples 1 to 12, specifically, when the organic group has an anionic group, an acid such as hydrochloric acid or sulfuric acid is added, and the organic group becomes a cation. In the case of having an organic group, the pigment and organic group in the ink can be precipitated by salting out by adding an alkali such as sodium hydroxide, and in some cases, coagulation may be performed by adding excessive alcohol. It is possible to precipitate the pigment in the ink.

  Further, as a method for precipitating the pigment in the ink, it is possible to effectively take out the pigment in the ink by combining salting out or coagulation or performing centrifugation. The precipitate containing carbon black which is a pigment obtained by the above operation is collected by filtration, the filtered solid content is sufficiently washed with pure water, and the carbon black-containing solid material after washing is subjected to a 60 ° C. oven. And dried overnight. The obtained carbon black-containing dried product was washed with tetrahydrofuran (THF), which is a good solvent for the segment containing the copolymer. After the carbon black-containing dried product was washed with THF three times, in order to volatilize residual moisture and residual solvent, a vacuum dryer was used and a vacuum degree of several hundred Pa or less at 60 ° C. × It was dried for about 3 hours. As described above, a dried solid product in which the segment containing the copolymer as a free polymer was composed only of the surface-modified carbon black removed as a result of washing the copolymer with a good solvent was obtained.

  Next, the weight loss rate of thermogravimetric analysis was measured by thermogravimetric analysis using the dried product obtained above as a measurement sample. As described above, from the value of the weight reduction rate obtained at that time, the amount of organic groups chemically bonded to the carbon black pigment was determined. For thermogravimetric analysis, a TGA thermogravimetric measuring device TGA851e / SDTA manufactured by METTLER TOLEDO was used.

  1 and 2 are measurement data of the thermogravimetric analysis weight reduction rate obtained by thermogravimetric analysis on the dried solid sample prepared by the above-described method for the ink of Example 4 including the pigment dispersion 4. FIG. FIG. 1 shows a thermal analysis result of a dried product sample after the coagulation and not washed with THF. The thermogravimetric weight loss rate shown in FIG. 1 is the total amount of organic groups chemically bonded to the surface-modified pigment in the ink and the segment containing the polymer portion as a free polymer. Is the ratio to the surface-modified pigment. The weight loss rate was 22.87% as shown in FIG.

  FIG. 2 shows measurement data of thermogravimetric analysis of the dried solid sample obtained after the dried solid sample is further washed with THF. That is, since the thermogravimetric analysis weight reduction rate shown in FIG. 2 is for the sample after removing the segment as a free polymer with THF which is a good solvent for the reaction product, the surface modification was performed. It shows the ratio of chemically bonded organic groups in the pigment. The value was 19.89%.

  In the thermogravimetric analysis measurement data for the ink of Example 4, as shown in FIGS. 1 and 2, a significant weight loss was observed at around 350 ° C. in both cases. In FIG. 2, such a result was obtained even when the dried product was washed with a good solvent for the copolymer when preparing the thermogravimetric analysis sample. It means that it was not lost. That is, it is shown that the pigment in the ink of Example 4 is in a state in which organic substances are chemically bonded to the pigment particle surface by the surface modification. Furthermore, from the thermogravimetric analysis weight reduction rate obtained from FIG. 1 and FIG. 2, the chemical bond organic group contained in the ink is represented by the following formula with respect to the sum of the chemically bonded organic group and the free polymer A percentage is required.

  The weight ratio of thermogravimetric analysis obtained from FIGS. 1 and 2 is substituted into the above formula, and the pigment occupies the total amount of the organic group and free polymer chemically bonded to the modified pigment of Example 4. The proportion of organic groups chemically bonded to the particle surface was determined. As a result, the ratio of the organic group chemically bonded to the total amount of the organic group chemically bonded to the modified pigment of Example 4 and the free polymer was (19.9 / 22.9) × 100. = 86.9%.

  In the same manner as in Example 4, the ratio of organic groups chemically bonded to the pigment particle surface with respect to the total amount of organic groups and segments in the pigment dispersion liquid of Example 12 was determined. First, the thermogravimetric analysis weight reduction rate of the dried solid sample after the coagulation was 32.0%, and the thermal weight of the dried solid sample obtained by extracting only the surface-modified pigment obtained by washing with THF. The analytical weight loss rate was 20.0%. As a result of substituting these numerical values into the above formula, the ratio of the organic group chemically bonded to the total amount of the organic group chemically bonded to the modified pigment of Example 12 and the free polymer is (20.0 / 32.0) × 100 = 62.5%.

<Comparative Example 1>
(Preparation of pigment dispersion 13)
10 parts of a 10% sodium hydroxide neutralized aqueous solution of 10 parts of carbon black having a specific surface area of 210 m ² / g and DBP oil absorption of 74 ml / 100 g and a styrene-acrylic acid copolymer having an acid value of 200 and a weight average molecular weight of 10,000. Furthermore, after mixing 70 parts of ion-exchanged water and dispersing for 1 hour using a sand grinder, coarse particles are removed by centrifugation, and pressure filtration is performed with a micro filter (made by Fuji Film) having a pore size of 3.0 μm. Thus, a pigment dispersion 13 used in Comparative Example 1 was obtained. The physical properties of the obtained pigment dispersion 13 were a solid content of 10%, pH = 10.0, and an average particle size of 120 nm.

(Preparation of ink)
The pigment dispersion 13 obtained above was mixed with the ink composition of Comparative Example 1 shown below, dissolved and dispersed with sufficient stirring, and then pressed with a microfilter (made by Fuji Film) having a pore size of 3.0 μm. Filtration was performed to prepare the ink of Comparative Example 1.
Ink composition / pigment dispersion 13 50 parts / glycerin 5 parts / diethylene glycol 5 parts / trimethylolpropane 5 parts / acetylene glycol EO adduct (trade name: acetylenol EH) 0.1 part / pure water 34.9 parts

<Comparative example 2>
(Preparation of pigment dispersion 14)
Dispersion B1 was prepared in the same manner as in the preparation of pigment dispersion 1. Subsequently, a polyacrylic acid resin having a weight average molecular weight of 30,000 was used instead of the styrene-acrylic acid resin having a weight average molecular weight of 15,000, an acid value of 140, and a polydispersity Mw / Mn = 1.5. Was carried out in the same manner as in the preparation of the pigment dispersion 1, and a pigment dispersion 14 was obtained. Regarding the physical properties of the obtained pigment dispersion 14, the solid content was 10%, the pH was 9.0, and the average particle size was 175 nm.

(Preparation of ink)
Using the pigment dispersion 14 obtained above, the mixture was mixed in the ink composition of Comparative Example 2 shown below, dissolved or dispersed with sufficient stirring, and then pressurized with a microfilter (made by Fuji Film) having a pore size of 3.0 μm. Filtration was performed to prepare the ink of Comparative Example 2.
Ink composition / pigment dispersion 14 50 parts / glycerin 7 parts / diethylene glycol 3 parts / pure water 40 parts

  In addition, using the inks obtained in Comparative Examples 1 and 2, the ratio (%) of chemically bonded organic groups in the surface-modified pigment was measured in the same manner as described in Examples above. The results are shown in Table 3 together with the Ka values of the inks of Comparative Examples 1 and 2.

  3 and 4 show the thermogravimetric analysis data of the evaporated and dried product from the ink of Comparative Example 1. FIG. FIG. 3 shows thermal analysis values for the dried solid sample after coagulation. The weight loss rate of thermogravimetric analysis in FIG. 3 was 13.65%. FIG. 4 is thermogravimetric analysis data for a dried solid sample obtained after washing with THF. In any case, the weight loss near 350 ° C. was found to be small. In particular, in FIG. 4 for the dried solid sample obtained after washing with THF, which is a good solvent for the polymer compound, almost no weight loss was observed even with an increase in temperature. This indicates that the polymer compound used in the preparation of the ink of Comparative Example 1 was lost as a result of washing with THF as a good solvent when preparing the thermogravimetric analysis sample. In other words, unlike Comparative Example 1, Comparative Example 1 indicates that most of the copolymer is not chemically bonded to the pigment.

<Evaluation>
An ink jet recording apparatus BJF having an on-demand type multi-recording head that uses each of the inks of Examples 1 to 12 and Comparative Examples 1 and 2 to eject ink by applying thermal energy to the ink according to a recording signal. -660 (manufactured by Canon Inc.) was remodeled and evaluated as follows. The obtained evaluation results are shown in Table 4.

1. Printing durability Using each of the inks of Examples and Comparative Examples and the above-described inkjet recording apparatus, the solid printing in which the nozzle check pattern is initially placed is continuously printed on three A4 sheets, and then for 2 hours thereafter. A cycle in which three sheets of solid printing were continuously performed was repeated 10 times without printing. The presence or absence of print sag and non-ejection at that time was evaluated according to the following criteria.
○: No print sag or non-ejection is observed.
Δ: Printing spilling is slightly observed, but no ejection is observed.
X: Printing dripping and non-ejection are observed.

2. Character Quality Character printing was carried out on the following five types of copy plain papers A to E using each of the inks and the ink jet recording apparatus described above, and the bleeding of the characters generated at that time was evaluated according to the following criteria.
○: There is almost no bleeding on all five papers.
Δ: Paper with some bleeding is observed.
X: All five papers are blurred.

In the image output test, the following copy paper was used.
A: PPC paper NSK manufactured by Canon Inc.
B: PPC paper NDK manufactured by Canon Inc.
C: Xerox Co., Ltd., PPC paper 4024
D: PPC paper prober bond, manufactured by Fox River Co., Ltd. E: PPC paper for Canon, manufactured by Neuzidora Co., Ltd.

3. Marking resistance against printing stains Using the above-described inks and the above-described ink jet recording apparatus, printing is performed on the above-described five types of normal plain papers A to E, and the obtained images are left for one day. The printed part was marked using an aqueous fluorescent marker pen (for example, Zebra fluorescent pen OPTEXOP-100-Y), and the marking part was observed for dirt, and evaluated according to the following criteria.
○: Dirt is not noticeable on all papers.
Δ: Contamination is noticeable on some paper.
X: Dirt is noticeable on all papers.

<Examples 13 to 17>
(Preparation of pigment dispersion 15)
The styrene-acrylic acid resin as a copolymer was the same as the pigment dispersion 1 except that a resin having a weight average molecular weight of 8,000, an acid value of 170, and a polydispersity Mw / Mn of 1.7 was used. A pigment dispersion 15 was prepared.

  Next, inks of Examples 13 to 17 having the compositions shown in Table 5 below were prepared using the pigment dispersion 15 and the pigment dispersion 8 described above. In addition, Table 5 below shows the Ka value of each ink of Examples 13 to 17 and the chemical bonding ratio in the surface-modified pigment in each ink.

  About the printing sustainability, the character quality, and the marker resistance of the printed matter with the ink according to Examples 13 to 17, the same as the method for evaluating the character quality and the marker resistance of the printed matter with the ink according to Examples 1-12. And evaluated. As a result, regarding the character quality, Examples 13 to 15 and 17 were “Δ”, and Example 16 was “◯”. Moreover, regarding marker resistance, all of Examples 13 to 17 were “◯”.

  Further, the ejection stability of the inks according to Examples 13 to 17 was evaluated by the following method. That is, the ink jet recording apparatus BJF-660 (manufactured by Canon Inc.) was installed in a modified machine, and ink tanks filled with ink according to Examples 13 to 17 were sequentially mounted, and the amount of ink discharged was measured. Specifically, five patterns with a known number of print dots were printed, and the amount of ink decrease divided by the number of print dots was used as the average discharge amount, which was used to measure the discharge amount. First, the solid printing in which the nozzle check pattern was initially placed was continuously performed on 10 sheets of A4 paper, and then left without printing for 2 hours, and then the discharge amount was measured by the method described above. Next, three solid prints were continuously printed again, and then the discharge amount was measured. This cycle was repeated 10 times to observe the change in the discharge amount. The obtained results were evaluated as ejection stability according to the following criteria. As a result, all of the inks of Examples 13 to 17 had a variation in ejection amount within a range of ± 10%.

  As described above, according to the present invention, as the pigment of the water-based ink, by using a pigment having a copolymer segment composed of an ionic monomer and a hydrophobic monomer bonded to a functional group on the surface of the pigment particle. In particular, when used as ink-jet ink, it has ink reliability for recording heads that have eliminated discharge bending and non-discharge, and it is also resistant to print stains due to rubbing after printing. There is provided a water-based ink with improved marker stain resistance due to the water-based marker. Furthermore, according to the present invention, there are provided an ink jet recording method, an ink cartridge, a recording unit and an ink jet recording apparatus which are excellent by using such ink.

13: Head 14: Ink groove (nozzle)
15: heating element substrate 16: protective layer 17-1, 17-2: electrode 18: heating resistor layer 19: heat storage layer 20: substrate 21: ink 22: discharge orifice (micropore)
23: Meniscus 24: Ink droplet 25: Recording medium 26: Multi-nozzle 27: Glass plate 28: Heat generating head 40: Ink bag 42: Plug 44: Ink absorber 45: Ink cartridge 51: Paper feed unit 52: Paper feed roller 53: Discharge roller 61: Blade 62: Cap 63: Ink absorber 64: Discharge recovery unit 65: Recording head 66: Carriage 67: Guide shaft 68: Motor 69: Belt 70: Recording unit 71: Head unit 72: Atmospheric communication Port 80: Ink channel 81: Orifice plate 82: Vibration plate 83: Piezoelectric element 84: Substrate 85: Ejection port

Claims (12)

An aqueous ink comprising a modified pigment in which organic groups are chemically bonded to the surface of pigment particles, and an aqueous medium as a dispersion medium for the pigment,
The organic group includes a reaction product of a functional group chemically bonded to the pigment surface directly or via another atomic group and a copolymer of an ionic monomer and a hydrophobic monomer. ,
The ratio of the organic group in the modified pigment to the total mass of the modified pigment is 5% by mass or more and 40% by mass or less,
The co weight average molecular weight (Mw) of the polymer is 1,000 to 20,000, and a polydispersity Mw / Mn (Mw: weight average molecular weight, Mn: number-average molecular weight) state, and are 3 or less ,
When a segment containing the copolymer that is not chemically bonded to the pigment surface is present in the ink, the ratio of the segment to the total amount of the segment and the reactant is less than 35% by mass. A water-based ink characterized by that. The aqueous ink according to claim 1 of the segment, the ratio to the total amount of the reactants and the segment is less than 20 wt%. The water-based ink according to claim 1 or 2 , wherein the other atomic group is a phenyl (2-sulfoethyl) group. Wherein the pigment is an aqueous ink according to any one of claims 1 to 3 is carbon black. The aqueous ink according to claim 1, any one of 4 acid value or amine value of the copolymer is 100 or more and 500 or less. The organic group in modified pigment, wherein the ratio of the total weight of the modified pigment, the aqueous ink according to any one of claims 1 5 is 30 mass% or more and 8 wt% . The water-based ink according to claim 6 , wherein the ratio of the organic group in the modified pigment to the total mass of the modified pigment is 10% by mass or more and 25% by mass or less. The water-based ink according to any one of claims 1 to 7 , which is an ink-jet water-based ink. An inkjet recording method comprising a step of discharging the water-based ink according to claim 8 by an inkjet method. An ink cartridge containing the water-based ink according to any one of claims 1 to 8 . A recording unit comprising: an ink containing portion containing the water-based ink according to claim 8 ; and an ink jet head for discharging the ink. An ink jet recording apparatus comprising: an ink containing portion containing the water-based ink according to claim 8 ; and an ink jet head for discharging the ink.

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