JP4736858B2 - Water-based dispersant and water-based ink - Google Patents

Description

  The present invention relates to an aqueous dispersant excellent in dispersibility and storage stability, and an aqueous ink excellent in image quality characteristics and ejection properties containing the dispersant.

  In order to disperse each dispersoid well and stably for inorganic pigments such as calcium carbonate and titanium oxide, drilling mud, cement or detergent builder, a dispersant made of a polymer is used. In water-based ballpoint pens and water-based inks for ink-jet recording, the following polymers are used as dispersants in order to disperse the dispersoid pigment in the aqueous medium.

  In a dispersant such as an organic pigment, the polymer has a surface active function that combines a hydrophobic region having an affinity for a dispersoid such as a pigment and a hydrophilic region having an affinity for an aqueous medium. is important. Examples of such a dispersant include graft copolymers composed of a hydrophobic macromonomer and a hydrophilic monomer having an aromatic monomer such as styrene or (meth) acrylic acid alkyl ester as a structural unit, and (meth) acrylic. A graft copolymer composed of a hydrophilic macromonomer containing a monomer such as an acid or a hydroxyalkyl ester of (meth) acrylic acid and a hydrophobic monomer is known (see Patent Document 1, etc.).

  Similarly, a pigment dispersant comprising a graft copolymer having a main chain composed of a hydrophobic monomer and a side chain derived from a macromonomer more hydrophilic than the main chain bonded to the main chain (see Patent Document 2) Copolymer having a side chain made of polysiloxane, polyether, polyester or polyamide on the main chain made of functional monomer and aromatic monomer having reactivity such as chelate bond or coordination bond with carbon black A carbon black dispersion composed of coalescence is disclosed (see Patent Documents 3 and 4). In addition, a pigment dispersant having a lactone or oxyacid condensate or polyalkylene glycol in the side chain (see Patent Document 5), a monomer having an aromatic ring such as styrene, and a single amount having a hydroxyl group such as hydroxyethyl methacrylate An anionic polymer obtained by copolymerizing the product and then adding an acid anhydride to the hydroxyl group is disclosed as a pigment dispersion aid for ink for offset printing (see Patent Document 6).

  However, in the case of an aqueous ink prepared using the graft copolymer shown above, sufficient dispersion stability of a colorant such as a pigment cannot be obtained, and the dispersion state collapses due to environmental changes such as temperature. Cheap. In addition, the pigment dispersants described in Patent Documents 1 and 2 introduce a relatively large amount of ionic functional groups into the hydrophobic chain in order to dissolve in an aqueous medium, or reduce the amount of the hydrophobic component. Must-have. In addition, in the graft copolymer having a nonionic hydrophilic side chain described in Patent Documents 2 to 4, since the electric repulsion between the dispersed particles cannot be obtained, the dispersibility immediately after dispersion is long-term. Difficult to keep.

  In order to solve this problem, water-insoluble vinyl polymer particles containing the monomer are used for the purpose of promoting the adsorptivity of the dispersant to the pigment surface as a dispersoid by using a highly hydrophobic alicyclic monomer. An aqueous ink containing an aqueous dispersion is disclosed (see Patent Documents 7 to 9). However, all of these dispersants are water-insoluble resins, and complicated operations are required to prepare an aqueous dispersion of pigment. In addition, since the resin is highly hydrophobic, the ink ejection method in which heat is applied during ejection has a problem that causes kogation (hereinafter referred to as kogation). In addition, an aqueous ink using a self-water dispersible acrylic resin having an aliphatic condensed ring similar to abietic acid as a dispersant (refer to Patent Document 10), and an acid value containing cyclohexyl acrylate and / or benzyl acrylate is 10 to 200 mg KOH / G polymer compositions are disclosed (see Patent Document 11), but these also have a problem that it is difficult to achieve both the bleeding resistance and the dispersion stability required for the ink.

JP-A-6-100810 (page 3-5) Japanese National Patent Publication No. 10-502097 (Claims) JP-A-9-59331 (Claims) JP-A-9-272706 (Claims) JP-A-60-161464 (Claims) JP 11-12528 A (Claims) JP-A-2004-203996 (Claims) Japanese Patent Laying-Open No. 2005-23247 (Claims) Japanese Patent Laying-Open No. 2005-29597 (Claims) JP 2003-155436 A (Claims) Japanese Patent Laying-Open No. 2005-171223 (Claims)

  In the case where a dispersoid such as a pigment is dispersed in an aqueous medium that is a dispersion medium, in order to obtain excellent dispersion performance, it is important to design the structure of a resin (polymer) having a hydrophobic group and a hydrophilic group. . If the hydrophobic region that adsorbs to the dispersoid and the hydrophilic region that provides solubility in the dispersion medium and electrostatic repulsion between the dispersoids exist too close to each other in the structure of the resin, Since the hydrophilic regions in the polymer are easily affected by the surface charge of the dispersoid, good dispersibility cannot be obtained in the dispersion medium. Therefore, it is necessary to make it less susceptible to the respective effects, for example, through a spacer between the adsorption region for the dispersoid and the affinity region for the dispersion medium in the polymer. The inventors have proposed Japanese Patent Application No. 2003-372143 as a solution to this problem.

  In view of the background art, an object of the present invention is to provide an aqueous dispersant comprising a graft copolymer that is excellent in dispersibility of dispersoids such as pigments and that can stably maintain a dispersed state over a long period of time. Another object of the present invention is to provide a water-based ink that has dispersibility in addition to print density, image quality characteristics such as ink unevenness and bleeding resistance, and ejection properties.

As a result of intensive studies to solve the above problems, the present inventors have found that an aqueous dispersant comprising a graft copolymer characterized by a side chain having a specific length and structure can solve the above problems, The present invention has been completed.
That is, the first of the present invention has a structure represented by the following general formula [1] in which the side chain of the graft copolymer has 4 to 50 carbon atoms from the branch point with the main chain to the carboxylic acid terminal. and, the main chain of the vinyl aromatic monomer (a) and alicyclic the (meth) acrylate (B) as essential constituent monomer units,
An aqueous dispersant comprising a graft copolymer, wherein the acid value is in the range of 40 to 150 mg-KOH / g.

〔式中、Ｒ_１ 、Ｒ_２は水素原子または炭素数１〜２０の直鎖または分岐状のアルキル基、Ｘは酸素原子、アルキレンジオキシ基もしくはウレタン基を含む置換基を示す。ｍは１〜２０の整数、ｎは１〜５の整数を表す。但し、ｍ、ｎは上記の側鎖長（炭素数）の範囲を超えずに組み合される整数である。〕

また、主要な第二の発明は、上記水性分散剤を配合し、これに顔料などの着色剤及び水性媒体を含有させた水性インクである。
尚、本明細書においては、アクリル酸又はメタクリル酸を（メタ）アクリル酸と、アクリレート又はメタクリレートを（メタ）アクリレートとして表す。

[Wherein R ₁ and R ₂ represent a hydrogen atom or a linear or branched alkyl group having 1 to 20 carbon atoms, and X represents a substituent containing an oxygen atom, an alkylenedioxy group or a urethane group. m represents an integer of 1 to 20, and n represents an integer of 1 to 5. However, m and n are integers combined without exceeding the range of the side chain length (carbon number). ]

The main second invention is an aqueous ink in which the above aqueous dispersant is blended and a colorant such as a pigment and an aqueous medium are contained therein.
In this specification, acrylic acid or methacrylic acid is represented as (meth) acrylic acid, and acrylate or methacrylate is represented as (meth) acrylate.

  According to the present invention, the dispersant having a charge only at the end of the side chain that is not bonded to the main chain constituting the graft copolymer has a dispersoid such as a pigment even if a low acid value graft polymer is used. A water-based ink (dispersion) that can be stably dispersed and has both dispersion stability and printing density / bleeding resistance is obtained.

1. Aqueous Dispersant The dispersant of the present invention comprises a graft side chain having a specific structure described in detail below, and a main chain comprising a vinyl aromatic monomer (A) and an alicyclic (meth) acrylate (B). A graft copolymer having an acid value of 40 to 150 mg-KOH / g, contained as a monomer unit.

1.1 Side Chain Structure The side chain constituting the graft copolymer has a structure represented by the following general formula [1] having 4 to 50 carbon atoms from the branch point with the main chain to the carboxylic acid terminal.

〔式中、Ｒ₁ 、Ｒ₂は水素原子または炭素数１〜２０の直鎖または分岐状のアルキル基、Ｘは酸素原子、アルキレンジオキシ基もしくはウレタン基を含む置換基を示す。ｍは１〜２０の整数、ｎは１〜５の整数を表す。但し、ｍ、ｎは上記の側鎖長（炭素数）の範囲を超えずに組み合される整数である。〕

[Wherein, R ₁ and R ₂ represent a hydrogen atom or a linear or branched alkyl group having 1 to 20 carbon atoms, and X represents a substituent containing an oxygen atom, an alkylenedioxy group or a urethane group. m represents an integer of 1 to 20, and n represents an integer of 1 to 5. However, m and n are integers combined without exceeding the range of the side chain length (carbon number). ]

The graft side chain has a carbon number from the branching point with the main chain to the carboxylic acid end, that is, a range of 4 to 50 as the carbon number of the backbone not containing branched R ₁ and R ₂ in the general formula [1]. Of these, 10 to 30 carbon atoms are particularly preferred. If the carbon number is outside this range, the effect of the present invention cannot be obtained and the dispersibility may be poor.

R ₁ and R ₂ in the general formula [1] are each independently or simultaneously a hydrogen atom or a linear or branched alkyl group having 1 to 20 carbon atoms. Specific examples of the alkyl group include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n Examples include -decyl group, n-undecyl group, n-dodecyl group, and those having an alkyl group as a side chain in these groups.
X in the general formula [1] is a substituent containing an oxygen atom, an alkylenedioxy group or a urethane group. When X excluding an oxygen atom is specifically shown as a chemical formula, —O—R ₃ —O—, —NHCO—O—, —O—R ₃ —NHCO—O— (R ₃ has 2 to 8 carbon atoms) A linear or branched alkylene group).
Moreover, in the formula, m is an integer of 1 to 20, and n is an integer of 1 to 5, but as described above, the side chain length (carbon number) is 4 to 50, and m does not exceed this range. It is a combination of n.

As X in the general formula [1], a side chain structure having an oxygen atom can be introduced, for example, by reacting a carboxylic acid with a lactone. A side chain structure having an alkylenedioxy group (—O—R ₃ —O—) can be introduced by reacting a carboxylic acid with a ω-halogenocarboxylic acid in the presence of a base. A side chain structure having a substituent containing a urethane group (for example, —NHCO—O—, —O—R ₃ —NHCO—O—) can be introduced by reacting an isocyanate compound with ω-hydroxycarboxylic acid. .
In addition, said side chain may be comprised only by 1 type, or may consist of 2 or more types.

1.2 The main chain constituting the main chain graft copolymer has a copolymer structure having vinyl aromatic monomer (A) and alicyclic (meth) acrylate (B) as essential constituent monomer units. These are also obtained by copolymerizing the above monomer mixtures.

(A) Vinyl aromatic monomer Examples of the vinyl aromatic monomer constituting the main chain of the graft copolymer include styrene monomers, phenyl group-containing (meth) acrylates, and phenyl group-containing maleimides. Can be mentioned. Among these, styrenic monomers are particularly preferable from the viewpoints of affinity for dispersoids such as pigments and copolymerization with other monomers.

Specific examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-tert-butylstyrene, vinyltoluene and the like.
Specific examples of phenyl group-containing (meth) acrylates include benzyl (meth) acrylate, phenyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxypolyethylene glycol (meta ) Acrylate, nonylphenylethylene oxide adduct (meth) and the like.
Specific examples of phenyl group-containing maleimides include N-phenylmaleimide and N- (2-chlorophenyl) maleimide.
In addition, only one type or two or more types of monomers may be used.

  The content of the vinyl aromatic monomer (A) is preferably 3 to 50% by mass, more preferably 5 to 30% by mass, based on the total mass of all monomers constituting the graft copolymer. %. If the amount is less than 3% by mass, the dispersion is poorly stable over time, and if it exceeds 50% by mass, the dispersibility during initial preparation may be inferior.

(B) Alicyclic (meth) acrylate Examples of the alicyclic (meth) acrylate include monocyclic (meth) acrylate, bicyclic (meth) acrylate, and tricyclic or higher polycyclic (meth) acrylate. .

  For example, for monocyclic (meth) acrylate, cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclononyl (meth) acrylate, cyclodecyl Examples include (meth) acrylate. Moreover, these may have a C1-C6 alkyl substituent on a ring.

  Examples of the bicyclic (meth) acrylate include isobornyl (meth) acrylate and norbornyl (meth) acrylate. Examples of these commercially available products include "FA-544A" (isobornyl acrylate) manufactured by Hitachi Chemical Co., Ltd. and "Acryester IBX" (isobornyl methacrylate) manufactured by Mitsubishi Rayon.

Examples of the polycyclic (meth) acrylate include dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyalkyl (meth) acrylate, and adamantyl (meth) acrylate. These commercial products include Hitachi Chemical FA-511A (dicyclopentenyl acrylate), FA-512A (dicyclopentenyloxyethyl acrylate), FA-512MT (dicyclopentenyloxyethyl methacrylate), “ FA-513A "(dicyclopentanyl acrylate)," FA-513M "(dicyclopentanyl methacrylate) and the like.
Among the alicyclic (meth) acrylates, monocyclic (meth) acrylates are preferable from the viewpoint of adsorptivity to pigments, and cyclohexyl (meth) acrylate is particularly preferable from the viewpoint of dispersion stability when used as a dispersant. preferable. Furthermore, cyclohexyl methacrylate is most preferable from the viewpoint of copolymerization with other monomers.
In addition, said alicyclic (meth) acrylate may use only 1 type, or may use 2 or more types.

Other monomers to be described later can be included as a desired component constituting the main chain, as long as the function of the graft copolymer of the present invention is not impaired.
The content of the alicyclic (meth) acrylate (B) is preferably 10 to 75% by mass, more preferably 15 to 75, based on the total mass of all the monomers constituting the graft copolymer. % By mass. If the amount is less than 10% by mass, the stability of the dispersion over time is poor, and if it exceeds 75% by mass, the water solubility may not be maintained.

The main chain of the graft copolymer is composed of the above-mentioned vinyl aromatic monomer (A) and alicyclic (meth) acrylate (B) as essential constituent monomer units. It can be a component.
Examples of other monomers include alkyl (meth) acrylates, hydroxyalkyl (meth) acrylates, (meth) acrylamide, vinyl acetate, N-vinylpyrrolidone, (meth) acrylonitrile, and (meth) acrylic acid. Can be mentioned. In addition, methylene bisacrylamide, methylene bismethacrylamide, butanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol having two or more vinyl groups in one molecule Crosslinkability of di (meth) acrylate, trimethylolpropane tri (meth) acrylate, di (meth) acryloxyethyl phosphate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, diallyl maleate, polyallyl saccharose A monomer etc. may be included.

Specific examples of the alkyl (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. Etc.
Specific examples of hydroxyalkyl (meth) acrylates include 2-ethylhexyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polyalkylene glycol (n = 2 to 30) (meth) acrylate, polycaprolactone (meta ) Acrylate and the like.
The other monomers may be used alone or in combination of two or more.

1.3 About Graft Copolymers Macromonomer method, ionic polymerization method, introduction of side chain by polymer reaction, etc. are known as graft copolymer synthesis methods, but in order to synthesize the graft copolymer of the present invention. The most suitable is a macromonomer method that allows easy introduction of an ionic functional group at the end of the side chain, adjustment of the degree of polymerization of the main chain and side chain, and easy connection of the main chain and side chain.

  For example, as a specific example, the graft copolymer of the present invention is used together with, or further if desired, the vinyl aromatic monomer (A) and the alicyclic (meth) acrylate (B) constituting the main chain. Along with the addition of other monomers, the macromonomer (C) represented by the following general formula [2] can be used for copolymerization.

〔式中、Ｒ₁ 、Ｒ₂は水素原子または炭素数１〜２０の直鎖または分岐状のアルキル基、Ｘは酸素原子、アルキレンジオキシ基もしくはウレタン基を含む置換基を示す。また、Ｒ₄は水素原子またはメチル基である。ｍは１〜２０の整数、ｎは１〜５の整数を表す。但し、ｍ、ｎは前記の側鎖長（炭素数）の範囲を超えずに組み合される整数である。〕

[Wherein, R ₁ and R ₂ represent a hydrogen atom or a linear or branched alkyl group having 1 to 20 carbon atoms, and X represents a substituent containing an oxygen atom, an alkylenedioxy group or a urethane group. R ₄ is a hydrogen atom or a methyl group. m represents an integer of 1 to 20, and n represents an integer of 1 to 5. However, m and n are integers combined without exceeding the range of the side chain length (carbon number). ]

R ₁ , R ₂ and X in the general formula [2] are the same as those in the general formula [1].
The production method of the macromonomer (C) represented by the above general formula [2], which is an ω-carboxyl macromonomer, is not particularly limited, but the macromonomer (C) in which X is an oxygen atom is (meth) acrylic acid and lactone It can be prepared by a method of reacting. The macromonomer (C) having an alkylenedioxy group (—O—R ₃ —O—) can be prepared by a method of reacting hydroxyalkyl (meth) acrylate with ω-halogenocarboxylic acid in the presence of a base. . The macromonomer (C) having a substituent containing a urethane group (for example, —NHCO—O—, —O—R ₃ —NHCO—O—) is (meth) acryloyl isocyanate or 2- (meth) acryloyloxy. It can be prepared by a method of reacting ethyl isocyanate and ω-hydroxyalkylcarboxylic acid. Examples of commercially available isocyanate monomers include 2-methacryloyloxyethyl isocyanate (trade name “Karenz MOI”, Showa Denko) and acryloyl isocyanate (trade name “MAI”, Nippon Paint).
Among these, the method of reacting carboxylic acid and lactone is industrially useful from the viewpoint of easy removal of by-products.
The macromonomer (C) represented by the general formula [2] may be used alone or in combination of two or more.

  The content of the macromonomer (C) represented by the general formula [2] is preferably set so that the acid value of the copolymer is 40 to 150 mg-KOH / g, and preferably 50 to 120 mg-KOH / g. It is more preferable to set so that. When the acid value is less than 40 mg-KOH / g, the dispersion stability over time cannot be obtained, and when the acid value exceeds 150 mg-KOH / g, when the ink is prepared as a water-based ink, bleeding occurs during printing. May be easier.

  The carboxyl group at the end of the side chain must be ionized by neutralizing part or all of it with a base. Examples of the base used for neutralization include inorganic alkali agents such as alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and organic amines such as diethanolamine and triethanolamine.

  The weight average molecular weight of the side chain constituting the graft copolymer is in the range of 300 to 2,000. If it is less than 300, the dispersion viscosity becomes high or dispersion stability over time cannot be obtained, and if it exceeds 2000, dispersion stability over time may deteriorate.

  In the graft copolymer of the present invention, it is preferable that the content of the graft side chains constituting is 10 to 80% by mass, and the total mass of the monomers constituting the main chain correspondingly is 90 to 20% by mass. More preferably, the content ratio of the graft side chain constituting it is 20 to 70% by mass, and the total mass of the monomers constituting the main chain correspondingly is 80 to 30% by mass. When the total mass of the monomers constituting the main chain is outside the above range, the dispersion performance may be greatly deteriorated.

The synthesis of the graft copolymer of the present invention is preferably a method using a radical polymerization initiator because the polymerization operation and the adjustment of the molecular weight are easy, and the hydrophobic monomer is difficult to dissolve in water. A solution polymerization method in which polymerization is performed in the solvent is more preferable.
Preferred solvents for radical polymerization by the solution polymerization method include ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone, acetate solvents such as ethyl acetate and butyl acetate, and aromatic carbonization such as benzene, toluene and xylene. Examples thereof include hydrogen solvents, isopropanol, ethanol, cyclohexane, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoamide, and the like, and ketone solvents, acetate solvents, and alcohol solvents are more preferable.

As the radical polymerization initiator, those generally used can be used, and specifically, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyesters, cyano series Azobisisobutyronitrile, azobis (2-methylbutyronitrile), non-cyano dimethyl-2,2′-azobisisobutyrate, and the like. Organic peroxides and azo compounds that can easily control the molecular weight and have a low decomposition temperature are preferable, and azo compounds are more preferable.
1-15 mass% is preferable with respect to the total mass of a polymerizable monomer, and, as for the usage-amount of a polymerization initiator, More preferably, it is 5-10 mass%.

  In order to adjust the molecular weight of the graft copolymer, an appropriate amount of chain transfer agent such as mercaptoacetic acid, mercaptopropionic acid, 2-propanethiol, 2-mercaptoethanol, thiophenol, dodecyl mercaptan, thioglycerol is added to the polymerization system. May be.

  A preferable polymerization temperature is 50 to 150 ° C, more preferably 60 to 100 ° C. The preferred polymerization time is 3 to 25 hours. The molecular weight of the graft copolymer of the present invention is preferably 1,000 to 100,000 in terms of weight average molecular weight determined by gel permeation chromatography using polystyrene as a reference substance, and can provide appropriate dispersibility and appropriate solution viscosity. The range of 1,000 to 20,000 is more preferable. A polymer having a weight average molecular weight of less than 1,000 cannot provide a sufficient dispersion effect, and if the weight average molecular weight exceeds 20,000, the viscosity increases and becomes insoluble or forms a lump. It will not function as an agent.

1.4 Applications The dispersant of the present invention can be used in various applications. For example, a dispersant for ceramic particles, a dispersant for agricultural chemical granules, a dispersant for mud, a dispersant for cement, a dispersant for scale dispersion, and a detergent. Examples include builder dispersants, inorganic pigment dispersants, and organic pigment dispersants.

  Specific examples of the respective applications include those for the production of ferrite for ceramic particles, and those for agricultural particles such as insecticides, fungicides, herbicides and acaricides for agricultural chemical granules. In addition, for mud, dispersant for drilling mud, dispersant for sewage sludge cake and purified sludge cake, for cement, mortar dispersant and concrete dispersant, for scale dispersion, calcium carbonate, calcium phosphate and silica Examples of scale dispersants for detergents and detergent builders include detergent addition dispersants such as detergents for clothes such as powder detergents for clothes, liquid detergents for clothes, liquid detergents for tableware, bleaching powder detergents and bleaching liquid detergents.

  Examples of inorganic pigments include calcium carbonate wet pulverization, calcium carbonate dry pulverization, light calcium carbonate production process, recycle sludge and caustic light calcium carbonate production process dispersant. Examples thereof include dispersants for ink pigments.

    Hereinafter, the water-based ink using the water-based dispersant of the present invention will be described in detail. The water-based dispersant of the present invention is particularly preferable among water-based inks from the viewpoint of image quality characteristics such as ink bleeding and unevenness and ejection characteristics. Suitable as an ink pigment dispersant for aqueous inkjet. Furthermore, it is particularly suitable for a bubble (thermal) jet system because of stability at high temperatures and the difficulty of kogation.

2. Water-based ink The water-based ink of the present invention has the above 1. In addition to the aqueous dispersant described in 1., a colorant and an aqueous medium are contained as essential components.

2.1 Colorant The colorant used in the aqueous ink of the present invention is either a dye or a pigment insoluble in an aqueous solvent.
Dyes include water-soluble dyes and hydrophobic dyes, but hydrophobic dyes are preferred from the viewpoint of water resistance. Thus, as the colorant, a hydrophobic dye or a pigment insoluble in an aqueous solvent is preferable, but a pigment is more preferable from the viewpoint of weather resistance.

  Examples of the hydrophobic dye include oily dyes and disperse dyes. These can be suitably used for both an aqueous dispersion of polymer particles obtained by being contained in polymer particles and an aqueous dispersion dispersed in water using a dispersant. Specific examples of oil-based dyes include C.I.solvent Black, C.I.solvent Yellow, C.I.solvent Red, C.I.solvent Violet, C.I.solvent Blue, C.I.solvent Green, C.I.solvent Green, and the like. Examples of the disperse dye include C.I.disperson Yellow, C.I.disperson Orange, C.I.disperson Red, C.I.disperson Violet, and C.I.disperson Green. )

  The pigment may be either an inorganic pigment or an organic pigment. These can be used alone or in combination as required.

  The dispersed particle diameter of the pigment is preferably 0.005 μm to 15 μm, more preferably 0.05 to 5 μm, and most preferably 0.01 to 1 μm. If the dispersed particle size is 0.005 μm or less, more dispersant is required to stabilize the dispersion and the performance of the pigment itself cannot be exhibited, and if it is 15 μm or more, it is difficult to keep the dispersion state stable.

Examples of inorganic pigments include metal oxides such as carbon black and titanium oxide, metal sulfides, and metal chlorides.
Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Specifically, No.2300, No.900, MCF88, No.33, No.40, No.45, No.52, MA7, MA8, No.2200B (manufactured by Mitsubishi Chemical), RAVEN1255 (manufactured by Columbia) ), REGAL400R, REGAL330R, REGAL660R, MOGUL L (manufactured by Cabot), Color Black FW1, Color Black FW18, Color Black S160, Color Black S170, Color Black S150, Color Black FW200, Color Black FW2V, Printex35 , Printex75, PrintexL6, Printex95, Printex U (manufactured by Degussa).

  Organic pigments include azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc .; phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinofullerone pigments Other examples include polycyclic pigments such as nitro pigments, nitroso pigments, and aniline black.

Specific examples of the organic pigment are appropriately given according to the type (color) of the aqueous ink to be obtained using the aqueous dispersant of the present invention. For example, yellow pigments such as CIPigment Yellow 1, CIPigment Yellow 2, CIPigment Yellow 3, CIPigment Yellow 13, CIPigment Yellow 16, CIPigment Yellow 74, CIPigment Yellow 83, CIPigment Yellow 128; CIPigment Red 5, CIPigment Red 7, CIPigment Red 12, Magenta pigments such as CIPigment Red 48 (Ca), CIPigment Red 48 (Mn), CIPigment Red 57 (Ca), CIPigment Red 112, CIPigment Red 122; CIPigment Blue 1, CIPigment Blue 2, CIPigment Blue 3, CIPigment Blue 15: 3, cyan pigments such as CIPigment Blue 16, CIPigment Blue 22, CIVat Blue 4, CIVat Blue 6 and the like.
Examples of the black ink pigment include organic pigments such as aniline black (CIPigment Black 1) in addition to inorganic pigments such as carbon black (CIPigment Black 7) and iron oxide pigment.

2.2 Aqueous medium As the aqueous medium, a mixed solvent of water and a water-soluble organic solvent is suitable. The water is preferably ion exchange water (deionized water). Examples of the water-soluble organic solvent include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol and other alkyl alcohols having 1 to 4 carbon atoms, 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, Ethylene glycol, 1,2-hexanediol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethyleneglycol Alkylene glycols having 2 to 6 carbon atoms such as glycerin, ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether And lower alkyl ethers of monohydric alcohols, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. Among these water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or butyl) ether are preferable.
In addition, said water-soluble organic solvent can be used individually or in combination of 2 or more types as needed.

2.3 Other Components To the water-based ink of the present invention, various known and usual additives that are usually added to water-based inks may be added as other components other than the water-based dispersant, the colorant and the water-based medium. Such additives include surfactants, antifoaming agents, preservatives, antisettling agents, chelating agents, thickeners, anticorrosives, antioxidants and the like. Surfactants include anionic surfactants such as fatty acid salts, higher alcohol sulfates, liquid fatty oil sulfates, alkyl allyl sulfonates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, poly Nonionic surfactants such as oxyethylene sorbitan alkyl esters, acetylene alcohol and acetylene glycol, cationic surfactants such as alkylamine salts and quaternary ammonium salts, and amphoteric surfactants such as alkylbetaines and alkylamine oxides Agents.

2.4 Preparation Method of Aqueous Ink The amount of the dispersant contained in the aqueous ink of the present invention is preferably in the range of 0.1 to 30% by mass, more preferably in the range of 1 to 15% by mass, based on the total mass of the ink. preferable. The amount of the colorant contained in the aqueous ink is preferably in the range of 0.1 to 30% by mass, and more preferably in the range of 1 to 15% by mass.
The content ratio of the dispersant and the colorant contained in the aqueous ink of the present invention is preferably in the range of 1: 1 to 1:30 (mass ratio), and preferably in the range of 1: 2 to 1:15. More preferred.

  The amount of the water-soluble organic solvent contained in the aqueous ink is preferably in the range of 3 to 50% by mass and more preferably in the range of 3 to 40% by mass with respect to the total mass of the aqueous ink. The amount of water contained in the aqueous ink of the present invention is preferably in the range of 10 to 90% by mass, and more preferably in the range of 30 to 80% by mass.

  The pH of the water-based ink is preferably in the range of 5-10. By making pH into this range, the solubility of the dispersing agent consisting of the graft copolymer can be improved, and the storage stability can be improved. In addition, corrosion of members of an apparatus (for example, an ink jet recording apparatus) to which the aqueous ink is applied can be suppressed.

  For pH adjustment of water-based ink, inorganic alkali agents such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, organic amines such as dimethylethanolamine, diethanolamine and triethanolamine, and citric acid, tartaric acid and the like Organic acids, mineral acids such as hydrochloric acid, phosphoric acid and the like can be used as the pH adjusting agent.

  The water-based ink of the present invention can be obtained by mixing and dispersing the above components. Each of the above components is used as it is or after adding an anti-drying agent and other additives as necessary, and diluted with an aqueous medium to be used for inkjet recording inks and aqueous inks for writing instruments such as aqueous ballpoint pens and marker pens. can do. In this case, in order to prevent the inkjet nozzle and the nib from being clogged by drying, it is preferable to add a low-volatile or non-volatile solvent among the water-soluble organic solvents. In order to increase the permeability to the recording medium, a volatile solvent may be added. In particular, when used for water-based ink for ink jet recording, it is also preferable to add a surfactant in order to give the ink an appropriate surface tension.

  Examples of the disperser used for dispersing include a ball mill, a bead mill, a roll mill, and a sand mill.

The effects obtained by this embodiment will be described below.
According to the dispersant of this embodiment, the dispersoid can be stably dispersed in an aqueous medium or the like. For example, in the case of water-based ink, a colorant such as a dispersoid pigment can be stably dispersed in an aqueous medium, and a stable dispersion state can be maintained over a long period of time. Furthermore, blurring during printing can be suppressed and high image quality can be achieved.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. In the following examples, “%” and “part” mean “% by mass” and “part by mass”, respectively.

Example 1
<Synthesis of Macromonomer A>
A glass flask equipped with a stirrer, dropping funnel, reflux condenser and thermometer was charged with 180 parts of acrylic acid, 8 parts of p-toluenesulfonic acid monohydrate and 0.08 part of hydroquinone monomethyl ether as a polymerization inhibitor, and reacted. While maintaining the internal temperature at 80 ° C., 114 parts of ε-caprolactone was added dropwise over 4 hours. After completion of the dropwise addition, the reaction was continued at the same temperature for 2 hours to obtain a macromonomer A having a carboxyl group at the ω position and having an α, β-unsaturated double bond whose skeleton is polycaprolactone.
When the molecular weight of the macromonomer A was measured by GPC method using tetrahydrofuran as an eluent, the weight average molecular weight (hereinafter abbreviated as Mw) was 400 in terms of polystyrene.

<Synthesis of copolymer>
A glass flask equipped with a stirrer, dropping funnel, reflux condenser, nitrogen gas inlet tube and thermometer is charged with 10 g of styrene, 53 g of macromonomer A, 37 g of cyclohexyl methacrylate, and 9 g of azobisisobutyronitrile (AIBN). And polymerized for 7 hours to obtain an isopropyl alcohol solution (solid content: 60%) of the copolymer. Subsequently, the isopropyl alcohol solution of the copolymer was neutralized by adding an equivalent amount of potassium hydroxide and ion-exchanged water with respect to the carboxyl group of the copolymer. Then, the solvent was removed under reduced pressure to distill off isopropyl alcohol to obtain an aqueous solution (solid content 25%) of copolymer E1 (Mw: 9000, acid value 100 mg-KOH / g).

<Preparation of water-based ink>
15 parts aqueous solution of copolymer E1 (solid content 25%), 15 parts quinacridone magenta (Clariant Toner Magenta E02) and 70 parts ion-exchanged water were mixed and dispersed under the following conditions after 10 minutes of premixing Processed.
Dispersing machine: Sand grinder (Igarashi Machine)
Grinding media: Zirconium beads (0.3 mm)
Filling rate of grinding media: 50% (volume)
Grinding time: 3 hours After the above dispersion treatment, centrifugal separation (12,000 RPM, 20 minutes) is performed to remove coarse particles, 40 parts of a dispersion is obtained, 5 parts of glycerin, 15 parts of diethylene glycol, 2- 2 parts of pyrrolidone and 38 parts of ion-exchanged water are mixed, adjusted to pH 8 to 10 with diethylethanolamine, and filtered using a membrane filter having a pore size of 5.0 μm to obtain the intended aqueous ink E1. It was.

(Example 2)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 10 g of styrene, 43 g of macromonomer A, and 47 g of cyclohexyl methacrylate, and other operations were carried out in the same manner as in Example 1 to obtain a copolymer E2 (Mw: 9200, an acid value of 80 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink E2.

(Example 3)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 30 g of styrene, 53 g of macromonomer A, and 17 g of cyclohexyl methacrylate, and the other operations were performed in the same manner as in Example 1 to obtain a copolymer E3 (Mw: 9700, an acid value of 100 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink E3.

Example 4
The monomer used for the synthesis of the copolymer of Example 1 was changed to 5 g of styrene, 53 g of macromonomer A, and 42 g of cyclohexyl methacrylate, and other operations were performed in the same manner as in Example 1 to obtain a copolymer E4 (Mw: 9700, an acid value of 100 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink E4.

(Example 5)
The monomer used in the synthesis of the copolymer of Example 1 was changed to 10 g of benzyl methacrylate, 53 g of macromonomer A, and 37 g of cyclohexyl methacrylate, and the other operations were performed in the same manner as in Example 1 to obtain a copolymer E5 (Mw : 9500, an acid value of 100 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink E5.

(Example 6)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 10 g of styrene, 70 g of macromonomer A, and 20 g of cyclohexyl methacrylate, and the others were operated in the same manner as in Example 1 to obtain a copolymer E6 (Mw: 9800, an acid value of 130 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink E6.

(Example 7)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 37 g of styrene 10 g, macromonomer A 53 g, dicyclopentanyl methacrylate (trade name “Fancryl FA-513M”, manufactured by Hitachi Chemical Co., Ltd.), Other operations were the same as in Example 1 to obtain an aqueous solution of a copolymer E7 (Mw: 9200, acid value 100 mg-KOH / g). Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink E7.

(Example 8)
A glass flask equipped with a stirrer, a dropping funnel, a reflux condenser, and a thermometer was charged with 320 parts of 12-hydroxystearic acid, 0.1 g of dibutyltin laurate, and 0.08 parts of hydroquinone monomethyl ether as a polymerization inhibitor. While maintaining the internal temperature at 50 ° C., 155 parts of 2-methacryloyloxyethyl isocyanate (trade name “Karenz MOI”, Showa Denko) was added dropwise over 4 hours. After completion of the dropwise addition, the reaction was continued at the same temperature for 2 hours to obtain a macromonomer B (Mw: 455) having a carboxyl group at the ω position and having an α, β-ethylenically unsaturated double bond.
Subsequently, the monomer used for the synthesis of the copolymer of Example 1 was changed to 10 g of styrene, 65 g of macromonomer B, and 25 g of cyclohexyl methacrylate, and the other operations were performed in the same manner as in Example 1 to obtain copolymer E8 An aqueous solution having an Mw of 10,000 and an acid value of 80 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink E8.

(Comparative Example 1)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 10 g of styrene, 53 g of macromonomer A, and 37 g of butyl methacrylate, and other operations were carried out in the same manner as in Example 1 to obtain copolymer C1 (Mw: 9800, an acid value of 100 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C1.

(Comparative Example 2)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 10 g of styrene, 53 g of macromonomer A, and 37 g of 2-hydroxyethyl methacrylate, and the other operations were performed in the same manner as in Example 1 to obtain copolymer C2. An aqueous solution (Mw: 9500, acid value 100 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C2.

(Comparative Example 3)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 10 g of styrene, 53 g of macromonomer A, and 37 g of stearyl methacrylate, and the other operations were performed in the same manner as in Example 1 to obtain copolymer C3 (Mw: 9600, an acid value of 100 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C3.

(Comparative Example 4)
The monomer used for the synthesis of the copolymer of Example 1 was changed to Macromonomer A 53 g and cyclohexyl methacrylate 47 g, and the other operations were performed in the same manner as in Example 1 to obtain copolymer C4 (Mw: 9800, acid An aqueous solution having a value of 100 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C4.

(Comparative Example 5)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 10 g of styrene, 15 g of methacrylic acid, and 75 g of cyclohexyl methacrylate, and the others were operated in the same manner as in Example 1 to obtain a copolymer C5 (Mw: 9600, an acid value of 100 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C5.

(Comparative Example 6)
In a glass flask equipped with a stirrer, an air introduction tube and a thermometer, 100 g (0.36 molar equivalent, Mw 440, number average molecular weight 300, hereinafter Mn) of polyethylene glycol monomethacrylate (trade name “Blenmer PE200”, manufactured by NOF Corporation) Abbreviation), 36 g (0.36 mol) of succinic anhydride was charged, the reaction vessel was kept at a temperature of 100 ° C. while bubbling air, and reacted for 5 hours, having a carboxyl group at the ω position, and having a skeleton made of polyethylene. Macromonomer C (Mw: 550) having an α, β-ethylenically unsaturated double bond as an oxide was obtained.
Subsequently, the monomer used for the synthesis of the copolymer of Example 1 was changed to 20 g of styrene and 80 g of macromonomer C, and other operations were performed in the same manner as in Example 1 to obtain a copolymer C6 (Mw: 7600, An aqueous solution having an acid value of 80 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C6.

(Comparative Example 7)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 10 g of styrene and 90 g of macromonomer A, and the other operations were performed in the same manner as in Example 1 to obtain copolymer C7 (Mw: 9600, acid value). 170 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C7.

(Comparative Example 8)
Monomers used for the synthesis of the copolymer of Example 1 were 67 g of styrene, 10 g of acrylic acid, 13 g of methacrylic acid, 10 g of dicyclopentanyl methacrylate (trade name “Fancryl FA-513M”, manufactured by Hitachi Chemical Co., Ltd.). The others were operated in the same manner as in Example 1 to obtain an aqueous solution of a copolymer C8 (Mw: 10500, acid value 145 mg-KOH / g). Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C8.

(Comparative Example 9)
The monomer used for the synthesis of the copolymer of Example 1 was changed to 6 g of methacrylic acid, 5 g of acrylic acid, 84 g of cyclohexyl acrylate, and 5 g of 2-hydroxyethyl methacrylate, and the others were operated in the same manner as in Example 1. An aqueous solution of copolymer C9 (Mw: 10000, acid value 80 mg-KOH / g) was obtained. Thereafter, the same operation as in Example 1 was further performed to obtain an aqueous ink C9.

[Evaluation]
Regarding the water-based inks E1 to E8 and C1 to C9 obtained in Examples 1 to 8 and Comparative Examples 1 to 9, the following items a) to c) were evaluated. The results are shown in Tables 1 and 2.

[A] Particle Size of Water-Based Ink Water was added to the obtained water-based ink and diluted 100 times, and then the particle size of the water-based ink was measured using “Microtrack UPA250” (manufactured by Nikkiso).

[B] Dispersion Stability of Aqueous Dispersion The obtained aqueous ink was allowed to stand at 60 ° C. for 6 months in a sealed state, then visually observed and evaluated based on the following criteria.
○: Aggregation and thickening of pigment particles did not occur.
Δ: Slight aggregation and thickening of pigment particles occurred.
X: Aggregation and thickening of pigment particles were greatly generated.

[C] Printing density Solid printing was performed on recycled paper for PPC (manufactured by Nippon Processing Paper Co., Ltd.) using a micro bubble jet printer (model number BJ-10VL manufactured by Canon). The optical density of the prints after being naturally dried at room temperature for 24 hours was measured with a Macbeth densitometer RD918 (manufactured by Macbeth).
Microbubble jet printer is a registered trademark of Canon Inc.

[D] Image quality characteristic The image of the image printed matter prepared in the above [c] was evaluated based on the following criteria.
A: There is no occurrence of unevenness, white streaks, or bleeding.
○: Slight unevenness, white streaks, and bleeding are observed.
Δ: Unevenness, white streaks, and bleeding are observed to some extent.
X: Unevenness, white streaks and bleeding are clearly observed.

[E] Dischargeability After 100 solid prints of the above [c] were continuously performed, the head portion of the ink cartridge ink was visually observed and evaluated based on the following criteria.
A: Clogging at the ink discharge port and ink adhesion to the printer head are hardly observed.
○: Clogging at the ink discharge port and slight adhesion of ink to the printer head are observed.
Δ: Clogging at the ink discharge port and ink adhesion to the printer head are recognized to some extent.
X: Clogging at the ink discharge port and ink adhesion to the printer head are clearly observed.

表中の略号は、以下である。
St：スチレン
BzMA：ベンジルメタクリレート
AA：アクリル酸
MAA：メタクリル酸
CHMA：シクロヘキシルメタクリレート
CHA：シクロヘキシルアクリレート
DCPMA：ジシクロペンタニルメタクリレート
BMA：ブチルメタクリレート
HEMA：２−ヒドロキシエチルメタクリレート
SMA：ステアリルメタクリレート

Abbreviations in the table are as follows.
St: Styrene
BzMA: benzyl methacrylate
AA: Acrylic acid
MAA: Methacrylic acid
CHMA: cyclohexyl methacrylate
CHA: cyclohexyl acrylate
DCPMA: Dicyclopentanyl methacrylate
BMA: Butyl methacrylate
HEMA: 2-hydroxyethyl methacrylate
SMA: Stearyl methacrylate

  As shown in Tables 1 and 2, the water-based ink of the example gave better results than the water-based ink of the comparative example. In other words, good water-based inks having not only dispersibility and dispersion stability but also image quality characteristics such as ink unevenness and bleeding, and also ejection properties have been obtained in the examples. In particular, the ink adhering to the printer head disturbs the discharge direction of the droplets and causes the printed matter to become blurred. Therefore, by introducing the side chain represented by the general formula [1], the discharge performance can be reduced after printing. It was found that ink adhesion to the printer head was suppressed.

The aqueous dispersant comprising the graft copolymer of the present invention has good dispersibility of the pigment in an aqueous medium as an aqueous ink having a pigment as a dispersoid. Also, pigment aggregation and ink thickening are not observed over a long period of time, the image quality of the printed matter is high, and the ink has excellent image quality characteristics, making it extremely useful as an aqueous ink. In addition, the aqueous dispersant of the present invention is useful because it can be expected to have practical long-term stability as a dispersant for inorganic pigments, a drilling mud dispersant for mud, a dispersant for mortar, a scale dispersant, and a dispersant for detergent builders. It is.

Claims (4)

The side chain of the graft copolymer has a structure represented by the following general formula [1] having 4 to 50 carbon atoms from the branch point with the main chain to the carboxylic acid end,
Backbone vinyl aromatic monomer (A) and alicyclic the (meth) acrylate (B) as essential constituent monomer units,
An aqueous dispersant comprising a graft copolymer, wherein the acid value is in the range of 40 to 150 mg-KOH / g.

[Wherein, R ₁ and R ₂ represent a hydrogen atom or a linear or branched alkyl group having 1 to 20 carbon atoms, and X represents a substituent containing an oxygen atom, an alkylenedioxy group or a urethane group. m represents an integer of 1 to 20, and n represents an integer of 1 to 5. However, m and n are integers combined without exceeding the range of the side chain length (carbon number). ] The aqueous dispersion according to claim 1, wherein the graft copolymer is obtained by copolymerization using a macromonomer (C) represented by the following general formula [2].

[Wherein, R ₁ and R ₂ represent a hydrogen atom or a linear or branched alkyl group having 1 to 20 carbon atoms, and X represents a substituent containing an oxygen atom, an alkylenedioxy group or a urethane group. R ₄ is a hydrogen atom or a methyl group. m represents an integer of 1 to 20, and n represents an integer of 1 to 5. However, m and n are integers combined without exceeding the range of the side chain length (carbon number). ]   The aqueous dispersant according to claim 1 or 2, wherein the alicyclic (meth) acrylate (B) constituting the graft copolymer is a monocyclic (meth) acrylate.   An aqueous ink containing the aqueous dispersant, colorant and aqueous medium according to claim 1.