JP2011219556A - Carbon black dispersion, ink composition, and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous carbon black dispersion excellent in thermal storage stability.SOLUTION: This carbon black dispersion includes at least carbon black, a polymer and an aqueous medium, has viscosity of 4.0 cP or lower, and keeps its pH decremental range within 1.0 when stored at 70°C for one week in a hermetically sealed state. Such the carbon black dispersion possesses better thermal storage stability compared with conventional ones. Preferably, the polymer has an acid value of ≤240 mg-KOH/g, a weight-average molecular weight of ≥15,000 and the content of components having ≤4,000 weight-average molecular weight is ≤20 wt.%.

Description

  The present invention relates to a carbon black dispersion liquid containing at least carbon black, a polymer, and an aqueous medium, and having a specific range of viscosity and a decrease range of pH when stored in a sealed state at 70 ° C. for 1 week. Specifically, the present invention relates to a carbon black dispersion suitable as a recording liquid for an ink jet printer, an ink composition containing the carbon black dispersion, and an ink jet recording method using the ink composition.

  Inkjet printers can easily obtain full-color high-resolution images, have low power consumption, have low introduction costs and low running costs, and have become capable of high-speed printing equivalent to electrophotographic printing. For these reasons, the use of business youth is spreading rapidly. At present, an aqueous recording liquid is mainly used as a recording liquid for an ink jet printer, and an aqueous recording liquid using carbon black which is a pigment as a coloring material is becoming mainstream particularly for a black ink.

  In ink jet recording, in recent years, the amount of ink ejected from an ink ejection nozzle has been remarkably reduced as the resolution of printed matter has improved. Furthermore, when business use is targeted, demands such as a printing speed equivalent to electrophotographic printing, a high printing density, and a high printing durability are increasing. For this reason, higher pigment dispersion stability has been demanded for pigment-dispersed aqueous recording liquids.

  On the other hand, development of a polymer-dispersed pigment dispersion in which a pigment is dispersed with a water-soluble polymer is currently in progress. However, since there is a free water-soluble polymer that does not contribute to the dispersion of the pigment in the aqueous medium, the ink using this dispersion has a high viscosity, and has storage stability and ejection stability. There was a problem that it would be insufficient. In particular, the carbon black dispersion has a strong tendency to agglomerate during storage, and improvement in this respect has been strongly desired.

Therefore, development has been carried out to improve the above points.
For example, in Patent Document 1, an aqueous dispersion ink containing water, a water-soluble organic solvent, a disperse dye or pigment, an alkali-soluble water-soluble polymer and / or a specific surfactant has dispersion stability and ejection stability. It is disclosed that it is excellent.
Further, in Patent Document 2, an ink composition for ink jet recording containing a specific ratio of the weight ratio of a pigment to a resin dispersant and also containing a thermoplastic resin emulsion has no change in physical properties during storage. It is disclosed.

JP-A-8-209048 JP-A-9-176533

  However, in Patent Document 1, there is no example in which carbon black is actually used as a pigment. According to the study by the present inventors, an ink as exemplified in Patent Document 1 is used, and carbon black is used as a pigment. Storage stability when prepared by using was insufficient.

  Further, according to the study by the present inventors, it has been found that a dispersion containing an emulsion as described in Patent Document 2 has a high viscosity and does not provide sufficient storage stability.

  The present invention solves the above-mentioned conventional problems, and is an aqueous pigment dispersion using carbon black as a pigment, which has dispersibility and storage stability, particularly storage stability at a relatively high temperature of about 70 ° C. Carbon black dispersion that can be suitably used for recording liquids such as inkjet printers, an ink composition containing the carbon black dispersion, and the ink composition. It is an object of the present invention to provide an ink jet recording method for obtaining a high quality and highly durable ink jet recorded matter using the above.

  In order to solve the above-mentioned problems, the present inventors have intensively studied an aqueous dispersion of carbon black. As a result, in an aqueous dispersion of carbon black, the pH generally tends to decrease over time due to the influence of impurities and unreacted substances, and this tendency is particularly noticeable when stored under warming conditions, Among such aqueous dispersions of carbon black, it has been found that a carbon black dispersion having a low pH drop and a low viscosity is particularly excellent in storage stability, particularly heat-resistant storage stability. That is, a carbon black dispersion liquid containing at least carbon black, a polymer, and an aqueous medium, having a viscosity of 4.0 cp or less, and having a pH decrease width of 1.0 or less when stored in a sealed state at 70 ° C. for 1 week. The present inventors have found that it has excellent storage stability such as heat-resistant storage stability and discharge durability, and has completed the present invention.

  The gist of the present invention is that it contains at least carbon black, a polymer, and an aqueous medium, has a viscosity of 4.0 cp or less, and has a pH drop of 1.0 or less when stored in a sealed state at 70 ° C. for 1 week. A carbon black dispersion (claim 1).

  Another gist of the present invention resides in an ink composition (Claim 6) containing the carbon black dispersion.

  Still another subject matter of the present invention lies in an ink jet recording method (claim 7), characterized in that a droplet of the ink composition is ejected from an ink jet head and the droplet is adhered to a recording medium.

  Since the carbon black dispersion liquid of the present invention is excellent in dispersibility and storage stability and has a low viscosity, such a carbon black dispersion liquid of the present invention can be suitably used particularly for a recording liquid such as an ink jet printer. Using the ink composition of the present invention containing the carbon black dispersion of the present invention, a high-quality and highly durable ink-jet recorded product can be obtained according to the ink-jet recording method of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of the embodiments of the present invention, and the present invention does not exceed the gist thereof. These contents are not specified.

[Carbon black dispersion]
The carbon black dispersion of the present invention contains at least carbon black, a polymer, and an aqueous medium, has a viscosity of 4.0 cp or less, and has a pH decrease of 1.0 or less when stored in a sealed state at 70 ° C. for 1 week. It is characterized by being.

{Action mechanism}
The details of the mechanism of action of the carbon black dispersion of the present invention that provides the effects of the present invention are not clear, but are considered as follows.
That is, it is the charge amount and steric hindrance of the polymer that plays a role in stably dispersing carbon black in the carbon black dispersion, but the charge amount decreases particularly when the pH of the dispersion is lowered. As a result, the repulsive force between the dispersions is not sufficient to maintain the dispersed state, and the carbon black aggregates. Moreover, when the viscosity of the dispersion liquid is high, the polymer chains are entangled with each other, and the dispersion aggregates tend to cause bridging aggregation. Such a tendency to agglomerate is more remarkable under the heating condition. Therefore, in order to suppress aggregation, it is necessary to suppress the pH drop of the dispersion and to lower the viscosity.
For this reason, in the present invention, by reducing the pH drop when stored in a sealed state at 70 ° C. for 1 week to 1.0 or less, and by setting the viscosity to 4.0 cp or less, high storage stability, It is considered that a carbon black dispersion excellent in discharge durability can be obtained.

{Carbon black}
As the carbon black used in the present invention, various carbon blacks such as acetylene black, channel black and furnace black can be used. Among these, channel black or furnace black is preferable, and furnace black is particularly preferable.

The DBP absorption amount of the carbon black is preferably in the range of 30 ml / 100 g to 250 ml / 100 g from the viewpoint of dispersibility. Among these, from the viewpoint of printing density on plain paper, a range of 80 ml / 100 g to 200 ml / 100 g is more preferable, and a range of 100 ml / 100 g to 150 ml / 100 g is particularly preferable. Carbon black that has too little DBP absorption tends to slip through plain paper, hardly stay on the top surface of the paper, and the print density may be low. Carbon black with too much DBP absorption is difficult to disperse, and storage stability and ejection stability may also deteriorate.
Here, the DBP absorption amount is the amount of dibutyl phthalate (DBP) absorbed by 100 g of carbon black defined by JISK6221.

The average primary particle size of carbon black is preferably 10 nm or more and 50 nm or less, more preferably 15 nm or more and 40 nm or less, and further preferably 15 nm or more and 30 nm or less. If the average primary particle size is too small, the print density tends to be low, and the ejection stability and dispersibility may also deteriorate. On the other hand, if the average primary particle size is too large, the storage stability is deteriorated, and the specific surface area becomes too small, which may lower the printing density.
Here, the primary particle diameter of carbon black is an arithmetic average diameter (number average) measured by an electron microscope.

The pH of the carbon black is preferably 3 or more, more preferably 6 or more from the viewpoint of the storage stability of the dispersion, and further the ink composition, and the upper limit is preferably 11 or less, and more preferably 8 or less. If the pH is too low, the amount of acidic groups on the surface of the carbon black increases, so that the adsorption of the polymer, which will be described later, as a dispersant is hindered, and sufficient storage stability and ejection stability may not be ensured. On the other hand, if it is too high, the charge expression of the polymer is suppressed due to the interaction between the basic functional group on the surface of the carbon black and the anionic group of the polymer, which will be described later. Stability may be insufficient.
The pH of carbon black here is 100 g of distilled water added to 10 g of carbon black, boiled for 10 minutes on a hot plate, cooled to room temperature, the supernatant was separated, and the pH of the muddy material was adjusted to glass. It is the value measured using an electrode pH meter.

  Specific examples of the carbon black include, but are not limited to, the following products (1) to (4).

(1) # 2700B, # 2650, # 2650B, # 2600, # 2600B, 2450B, 2400B, # 2350, # 2300, # 2300B, # 2200B, # 1000, # 1000B, # 990, # 990B, # 980, # 980B, # 970, # 960, # 960B, # 950, # 950B, # 900, # 900B, # 850, # 850B, MCF88, MCF88B, MA600, MA600B, # 750B, # 650B, # 52, # 52B, # 50, # 47, # 47B, # 45, # 45B, # 45L, # 44, # 44B, # 40, # 40B, # 33, # 33B, # 32, # 32B, # 30, # 30B, # 25, # 25B, # 20, # 20B, # 10, # 10B, # 5, # 5B, CF9, CF9B, # 95, # 260, MA77 MA77B, MA7, MA7B, MA8, MA8B, MA11, MA11B, MA100, MA100B, MA100R, MA100RB, MA100S, MA230, MA220, MA200RB, MA14, # 3030B, # 3040B, # 3050B, # 3230B, # 3350B (and above, Mitsubishi Chemical Co., Ltd. product).

(2) Monarch 1400, Black Pearls 1400, Monarch 1300, Black Pearls 1300, Monarch 1100, Black Pearls 1100, Monarch 1000, Black Pearls 1000, Monarch 900, Black Pearl 900 800, Monarch 700, Black Pearls 700, Black Pearls 2000, Vulcan XC72R, Vulcan XC72, Vulcan PA90, Vulcan 9A32, Mogul L, Black Pearls L, Regal 660R, R gal 660, Black Pearls 570, Black Pearls 520, Regal 400R, Regal 400, Regal 330R, Regal 330, Regal 300R, Black Pearls 490, Black Pearls 480, Black Pearls 480, Black Pearls 480, Black Pearls 480, Black Pearls 480, Black Pearls 480, Black Pearls 480, Black Pearls 480 Black Pearls 420, Black Pearls 410, Regal 350R, Regal 350, Regal 250R, Regal 250, Regal 99R, Regal 99I, Elftex Pellets 115, Elftex 8, Elftex 5, Elftex 12, Mftex 12 ch 280, Black Pearls 280, Black Pearls 170, Black Pearls 160, Black Pearls 130, Monarch 120, Black Pearls 120 (above, products of Cabot Corporation).

(3) Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Special Black 4, Special Black 4A, Special Black 4A, Special Black 4A, Special Black 4W, Color Black FW2V, Color Black FW2V, Color Black FW20, Color Black FW200, Special Black Printex V, Printex 150T, Printex 140U, Printex 140V, Printex 95, Printex 90, Printex 85, Printex 80, Printex 75, Printex 55, Printex 45, Printrtex 40, Printex 40 ntex 60, Printex XE, Printex L6, Printex L, Printex 300, Printex 30, Printex 3, Printex 35, Printex 25, Printex 200, Printex A, Printex G, Stex 100 (Degussa product).

(4) Raven 7000, Raven 5750, Raven 5250, Raven 5000 ULTRA, Raven 3500, Raven 2000, Raven 1500, Raven 1250, Raven 1250, Raven 10R, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170, Raven 1170 Raven 1000, Raven 890H, Raven 890, Raven 850, Raven 790 ULTRA, Raven 760 ULTRA, Raven 520, Raven 500, Raven 450, Raven 430, Raven 420, X CULTRA, Raven H2O, Raven CULTRA (or more, Columbia's products).

  Note that the carbon black is not chemically modified, and does not contain impurities other than carbon black, such as a crystallization inhibitor for promoting the reduction in the particle size of carbon black. It is preferable because it does not inhibit the adsorption to carbon black. However, in order to give the carbon black self-dispersibility, carbon black having self-dispersibility which has been subjected to known chemical modification in advance can also be used. That is, as the carbon black used in the carbon black dispersion of the present invention, any carbon black can be used, as described above, whether it is untreated carbon black or carbon black whose surface is chemically modified.

  From the viewpoint of safety, it is preferable to use carbon black in which the polycyclic aromatic component is reduced by baking at 600 to 1500 ° C. or washing with water, warm water, a solvent, or the like. In particular, the baking treatment at a high temperature is more preferable because the functional group on the surface of the carbon black is removed, so that the polymer as a dispersant is more efficiently adsorbed more firmly on the surface of the carbon black.

  As carbon black which concerns on this invention, 1 type of the said carbon black may be used independently, and may be used in combination of 2 or more type. It can also be used in combination with other color materials.

  The shape of carbon black may be any form such as paste, powder, solid solution and the like.

{polymer}
The carbon black dispersion in the present invention contains a polymer. As this polymer, known polymers are used, and among them, a polymer having at least one or more types of hydrophobic monomers and one or more types of hydrophilic monomers as constituent units is preferable from the viewpoint of dispersibility.

The structural unit here is a structural unit of the basic structure of the polymer. In the case of a synthetic polymer, the unit derived from the monomer molecule used for the production of the polymer by polymerization or copolymerization, or a modification thereof. It is a unit modified by In the case of a natural polymer, it is a repeating unit or a unit modified by modification or the like.
In the following, “(meth) acrylate” means “acrylate and / or methacrylate”, and “(meth) acryl” means “acryl and / or methacryl”.

<Hydrophobic monomer>
The hydrophobic monomer that is a structural unit of the polymer is not particularly limited, and a conventionally known hydrophobic monomer can be used. In particular, at least one of the hydrophobic monomers is an aromatic ring-containing monomer as described below. And / or a monomer containing an aliphatic hydrocarbon group.

  The aromatic ring-containing monomer is an aromatic heterocyclic ring-containing monomer or an aromatic hydrocarbon ring-containing monomer. For example, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxyethylene glycol (meth) acrylate, 2-naphthyl ( (Meth) acrylate, 9-anthracenyl (meth) acrylate, 1-pyrenylmethyl (meth) acrylate styrene, vinylnaphthalene, styrene, α-methylstyrene, t-butylstyrene, p-methylstyrene, o-methoxystyrene, m-methoxystyrene , P-methoxystyrene, ot-butoxystyrene, mt-butoxystyrene, pt-butoxystyrene, o-chloromethylstyrene, m-chloromethylstyrene, p-chloromethylstyrene, vinyltoluene, ethyl Nirubenzen, 4-vinyl biphenyl, 1,1-diphenyl ethylene, vinyl phenol, vinyl benzoate, vinyl naphthalene, benzyl vinyl ether.

  Among these, from the viewpoint of affinity with carbon black, a monomer structure having an unsubstituted phenyl group such as benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, styrene, and α-methylstyrene is preferable. Styrene and benzyl methacrylate are more preferred, and styrene is most preferred.

  The aliphatic hydrocarbon group contained in the aliphatic hydrocarbon group-containing monomer may be linear, cyclic, or branched.

Examples of the monomer having a linear or branched aliphatic hydrocarbon group include the following.
Olefins such as ethylene, propylene, 1-butene and isobutene;
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, i-propyl (meth) acrylate, butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, amyl ( (Meth) acrylate, i-amyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, i-octyl (meth) acrylate, decyl (meth) acrylate, i-decyl (meth) acrylate, dodecyl ( (Meth) acrylate esters such as (meth) acrylate, i-dodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, i-stearyl (meth) acrylate, and behenyl (meth) acrylate;
Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether;
Nitriles such as acrylonitrile and methacrylonitrile;
Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride;
Allyl compounds such as allyl acetate and allyl chloride;
Dicarboxylic acid ester derivatives such as maleic acid ester and itaconic acid ester;
Vinylsilyl compounds such as vinyltrimethoxysilane;
Vinyl esters such as vinyl acetate and isopropenyl acetate:

  Examples of the monomer having a cyclic aliphatic hydrocarbon group include cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) ) Acrylate, cyclononyl (meth) acrylate, cyclodecyl (meth) acrylate, etc., isobornyl (meth) acrylate, norbornyl (meth) acrylate, etc., (meth) acrylate esters such as adamantyl (meth) acrylate, cyclopentene, cycloheptene, cyclooctene, Cyclododecene, 1,5-cyclooctadiene, cyclopentadiene, 1,5,9-cyclododecatriene, 1-chloro-1,5-cyclooctadiene, disi Ropentajien, ethylidene norbornene, 5-norbornene-2-carboxylate, and 5-norbornene-2,3-dicarboxylic acid dimethyl and cyclic olefins and the like.

  Among these, (meth) acrylate esters having a linear or branched aliphatic hydrocarbon group are preferable from the viewpoint of affinity with carbon black. Of these, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate are more preferable, and butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and stearyl (meth) acrylate. Is most preferred.

  These hydrophobic monomers may be used alone or in combination of two or more.

<Hydrophilic monomer>
The hydrophilic monomer, which is a constituent unit of the polymer, is not particularly limited, and conventionally known hydrophilic monomers can be used. Among them, anionic monomers, cationic monomers, and nonionic monomers are preferable. Among these, an anionic monomer is most preferable from the viewpoint of dispersibility.

(Anionic monomer)
As the anionic monomer, those exemplified below can be used, but the anionic monomer is not limited thereto, and conventionally known monomers can be used.
Carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, or salts thereof;
Vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, styrene sulfonic acid, 2-acrylamide ethane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-methacrylamide ethane sulfonic acid, 2-methacrylamide-2-methyl Propanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfone Sulfonic acid monomers such as acids or salts thereof;
Vinylphosphonic acid, methacryloxyethyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, Phosphoric monomers such as dioctyl-2- (meth) acryloyloxyethyl phosphate or salts thereof:

  As the anionic monomer, a monomer having a carboxyl group or a salt thereof is preferable from the viewpoint of printing quality such as low print density or bleeding, and methacrylic acid, acrylic acid or a salt thereof, more preferably acrylic acid or a salt thereof.

  The anionic monomer is preferably a salt. Of these, alkali metal salts and alkaline earth metal salts are more preferable, and sodium salts are particularly preferable.

(Cationic monomer)
Although what is illustrated below can be used as a cationic monomer, It is not limited to these, A conventionally well-known thing can be used.
N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-di-t-butylaminoethyl (meth) acrylate N, N-dialkylaminoalkyl (meth) acrylates such as N, N-dimethylaminobutyl (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylamide, N, N-diethylaminoethyl (meth) acrylamide, N Tertiary amino group-containing polymerizable unsaturated monomers such as N, N-dialkylaminoalkyl (meth) acrylamide, such as N, N-dimethylaminopropyl (meth) acrylamide;
(Meth) acryloyloxyethyldimethyloctylammonium chloride, (meth) acryloyloxyethyldimethyloctylammonium bromide, (meth) acryloyloxyethyldimethyldodecylammonium chloride, (meth) acryloyloxyethyldimethyldodecylammonium bromide, (meth) acryloyloxyethyl Dimethyl hexadecyl ammonium chloride, (meth) acryloyloxyethyl dimethyl hexadecyl ammonium bromide, (meth) acryloyloxyethyl diethyl octyl ammonium chloride, (meth) acryloyloxyethyl diethyl octyl ammonium bromide, (meth) acryloyloxyethyl diethyl dodecyl ammonium chloride , (Meta) a Liloyloxyethyl diethyl dodecyl ammonium bromide, (meth) acryloyloxyethyl diethyl hexadecyl ammonium chloride, (meth) acryloyloxyethyl diethyl hexadecyl ammonium bromide, (meth) acryloylaminopropyldimethyloctylammonium chloride, (meth) acryloylamino Propyldimethyloctylammonium bromide, (meth) acryloylaminopropyldimethyldodecylammonium chloride, (meth) acryloylaminopropyldimethyldodecylammonium bromide, (meth) acryloylaminopropyldimethylhexadecylammonium chloride, (meth) acryloylaminopropyl Dimethylhexadecyl ammonium bromide, (meth) ac Royloxyethyltrimethylammonium chloride, (meth) acryloyloxyethyldimethylbenzylammonium chloride, (meth) acryloyloxyethyltrimethylammonium methylsulfate, (meth) acryloyloxyethyldimethylethylammonium ethyl sulfate, (meth) acryloyloxyethyl Trimethylammonium p-toluenesulfonate, (meth) acryloylaminopropyltrimethylammonium chloride, (meth) acryloylaminopropyldimethylbenzylammonium chloride, (meth) acryloylaminopropyltrimethylammonium methyl sulfate, (meth) acryloylaminopropyldimethylethylammonium ethyl Sulfae Pass, (meta) aqua Quaternary ammonium base-containing polymerizable unsaturated monomers such as liloylaminopropyltrimethylammonium p-toluenesulfonate;
In addition, styrenes having a dialkylamino group such as dimethylaminostyrene and dimethylaminomethylstyrene; vinylpyridines such as 4-vinylpyridine and 2-vinylpyridine; or these alkyl halides, benzyl halides, alkyl or aryl sulfones Quaternized with a known quaternizing agent such as acid or dialkyl sulfate, N-vinylformamide and N-vinylacetamide that form an amino group by hydrolysis after polymerization, allylamine hydrochloride, etc .:

  Among them, tertiary amino group-containing polymerizable unsaturated monomers such as N, N-dimethylaminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate, (meth) acryloyloxyethyltrimethylammonium chloride, (meth) Preferred are quaternary ammonium base-containing polymerizable unsaturated monomers such as acryloyloxyethyldimethylbenzylammonium chloride, (meth) acryloyloxyethyltrimethylammonium methylsulfate, (meth) acryloyloxyethyldimethylethylammonium ethylsulfate, among which More preferred are quaternary ammonium base-containing polymerizable unsaturated monomers. Of these, (meth) acryloyloxyethyltrimethylammonium chloride is most preferred.

  A polymer having a quaternary ammonium group-containing polymerizable unsaturated monomer as a constituent unit is obtained by polymerizing a tertiary amino group-containing polymerizable unsaturated monomer, followed by alkyl halide such as methyl chloride, benzyl halide such as benzyl chloride, epichloro It may be synthesized by a quaternization reaction using an alkylating agent such as hydrin, dimethyl sulfate, or diethyl sulfate, or may be synthesized by polymerizing a quaternized product in a monomer state. Among these, a polymer obtained by polymerizing a quaternized monomer is preferable.

(Nonionic monomer)
Nonionic monomers include the following, but are not limited to the following examples, and conventionally known monomers can be used.
Monomers having primary amino groups such as aminoethyl (meth) acrylate and aminopropyl (meth) acrylate;
Secondary such as methylaminoethyl (meth) acrylate, methylaminopropyl (meth) acrylate, ethylaminoethyl (meth) acrylate, ethylaminopropyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine A monomer having an amino group;
(Meth) acrylamide, N-alkyl (meth) acrylamide having 1 to 6 carbon atoms in the alkyl group, N, N-dialkyl (meth) acrylamide, C 1-3 in carbon number in the alkyl group, diacetone (meth) acrylamide, N -Methylol (meth) acrylamide, N-2-hydroxyethyl (meth) acrylamide, N, N-diethanol (meth) acrylamide, N-vinylacetamide, N-methyl-N-vinylacetamide, N-vinylformamide, N-methyl Amide group-containing monomers such as -N-vinylformamide, N- (2- (polyethylene glycol) ethyl) (meth) acrylamide, N, N- (2,2 '-(polyethylene glycol) diethyl) (meth) acrylamide;
2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, N-vinylpyrrolidone, 2-vinyl-2-oxazoline, 5-methyl-2-vinyl-2-oxazoline, N-vinyloxazolidone, 2-N-pyrrolidoneethyl A monomer having a heterocycle such as (meth) acrylate, N-vinylcaprolactam, 9-vinylcarbazole, N-vinylphthalimide, glycidyl (meth) acrylate, aziridine ring-containing monomer;
Monomers containing a hydroxyl group such as 2-hydroxyethyl (meth) acrylic acid ester, 2-hydroxypropyl (meth) acrylic acid ester, 2,3-dihydroxypropyl (meth) acrylate, 2-hydroxyethyl vinyl ether;
Polyethylene glycol (meth) acrylate, methoxy polyethylene glycol (meth) acrylate, ethoxy polyethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, lauroxy polyethylene glycol (meth) acrylate, stearoxy polyethylene glycol (meth) acrylate, nonylphenoxy Polyethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, poly (ethylene glycol-propylene glycol) (meth) acrylate, polyethylene glycol-polypropylene glycol (meth) acrylate, poly (ethylene glycol-) Tetramethylene glycol) (meta Acrylate, poly (propylene glycol-tetramethylene glycol) (meth) acrylate, propylene glycol polybutylene glycol (meth) acrylate, octoxy polyethylene glycol polypropylene glycol (meth) acrylate, stearoxy polyethylene glycol-polypropylene glycol (meth) acrylate, ant Oxyalkylene chain monomers such as loxypolyethylene glycol-polypropylene glycol (meth) acrylate and nonylphenoxypoly (ethylene glycol-propylene glycol) (meth) acrylate;
Glucose, mannose, galactose, glucosamine, mannosamine, galactosamine, etc., hexoses, arabinose, xylose, ribose, etc. Disaccharides such as mannobiose and sophorose, other oligosaccharides such as maltotriose, isomaltotriose, maltotetraose, maltopentaose, mannotriose and manninotriose, polysaccharides such as cellulose and modified cellulose A monomer having a structure as derived and having a glycosyl group, such as a monomer such as glucosylethyl methacrylate;
Macromonomer having a polyvinyl alcohol structure in the side chain:

  Among these nonionic monomers, from the viewpoint of dispersibility and storage stability, an amide group-containing monomer, a monomer having a heterocyclic ring, a monomer containing a hydroxyl group, an oxyalkylene chain monomer, and a polyvinyl alcohol structure as a side chain. In the case of using as a recording liquid for photographic paper, an amide group-containing monomer, a hydroxyl group-containing monomer, and an oxyalkylene chain monomer are preferred from the viewpoint of gloss of printed matter. Oxyalkylene chain monomers are particularly preferred.

  These hydrophilic monomers may be used alone or in combination of two or more.

<Monomer composition>
The polymer is preferably a polymer having at least one or more types of hydrophobic monomers and one or more types of hydrophilic monomers as constituent units, and the monomer composition is preferably as follows.

  The content of the hydrophobic monomer constituent unit is preferably 10 mol% or more, more preferably 20 mol% or more, based on the total constituent units of the polymer. As an upper limit, 90 mol% or less is preferable and 88 mol% or less is still more preferable. If the amount is less than this lower limit, the polymer is difficult to adsorb on the carbon black and the free polymer increases, so the viscosity of the dispersion increases. When this dispersion is used as a recording liquid, the ejection properties are reduced and the storage stability of the recording liquid is increased. May decrease. When the amount is larger than this upper limit, the water dispersibility of the carbon black dispersion may be lowered.

  The content of the hydrophilic monomer structural unit is preferably 10 mol% or more, and more preferably 12 mol% or more with respect to all the structural units of the polymer. As an upper limit, 90 mol% or less is preferable, 80 mol% or less is more preferable, and 70 mol% or less is the most preferable. If the amount is less than this lower limit, the water dispersibility of the carbon black dispersion is extremely reduced. If the amount is more than this upper limit, the polymer is difficult to adsorb on the carbon black and the free polymer increases, so the viscosity of the dispersion increases and this dispersion becomes higher. When used as a recording liquid, the dischargeability may decrease and the storage stability of the recording liquid may decrease.

<Polymer structure>
The polymer structure of the hydrophobic / hydrophilic polymer may be a random copolymer, a diblock copolymer, a triblock or more multi-block copolymer, a gradient copolymer, a graft copolymer, a star copolymer, etc., among which a random copolymer or a block polymer may be used. Random copolymers are preferred and most preferred.

<Acid value>
The acid value of the polymer is preferably 240 mg-KOH / g or less, more preferably 220 mg-KOH / g or less, and even more preferably 200 or less.
The lower limit of the acid value of the polymer is preferably 20 mg-KOH / g or more, more preferably 30 mg-KOH / g or more.
If the acid value of the polymer is less than the above lower limit, the water dispersibility of the carbon black dispersion tends to decrease, and if it exceeds this upper limit, the polymer is difficult to adsorb on the carbon black and the free polymer increases. Viscosity increases, and when this dispersion is used as a recording liquid, there is a tendency that the dischargeability is lowered or the storage stability of the recording liquid is lowered.

<Molecular weight>
The values of the number average molecular weight and the weight average molecular weight here are values in terms of polystyrene measured by GPC (gel permeation chromatography).

  The number average molecular weight (Mn) of the polymer according to the present invention is preferably 150,000 or less, more preferably 100,000 or less, and particularly preferably 50,000 or less as the upper limit. The lower limit is preferably 1,000 or more, more preferably 5,000 or more, and particularly preferably 7,000 or more. If the molecular weight is larger than this range, the viscosity of the dispersion liquid and the recording liquid is increased and the dischargeability is lowered. If the molecular weight is smaller, the polymer may be peeled off from the carbon black when the recording liquid is prepared.

  The upper limit of the weight average molecular weight (Mw) of the polymer is preferably 300,000 or less, more preferably 200,000 or less, and particularly preferably 100,000 or less. The lower limit is preferably 2,000 or more, more preferably 10,000 or more, and particularly preferably 15,000 or more. If the molecular weight is larger than this range, the viscosity of the dispersion liquid and the recording liquid may increase, and the discharge performance may decrease. is there.

Further, the content of the low molecular weight component of the polymer according to the present invention is preferably 20% by weight or less, more preferably 10% by weight or less, for a component having a weight average molecular weight of 4,000 or less. The proportion of the low molecular weight component is considered to be one of the parameters that influence the dispersibility, dispersion stability, and storage stability. However, when the low molecular weight component is larger than the above range, it is easy to ensure the dispersibility. However, it may be difficult to ensure dispersion stability and storage stability. Further, in a thermal type print head, long-term ejection stability tends to deteriorate.
The content of such a low molecular weight component having a weight average molecular weight of 4,000 or less in the polymer is a polystyrene-reduced weight average molecular weight (Mw) 4 in a chromatograph obtained by gel permeation chromatography (GPC) of the polymer. It can be determined by calculating the ratio of the area excluding the peak area of the unreacted monomer and polymerization solvent to the total area from the area of the component of 000 or less.

  These low molecular weight components in the polymer can be reduced by using an ultrafiltration membrane or a dialysis membrane or by reprecipitation of the polymer in a solvent in which the low molecular weight component is dissolved.

<Water-soluble>
As the polymer, a polymer having “water dispersibility” that does not cause precipitation in an aqueous dispersion having a concentration of 2% by weight of the polymer in a state where 90 mol% of ionic groups present in the polymer is neutralized. Among them, a “water-soluble” polymer having a solubility in water at 25 ° C. of 2% by weight or more is particularly preferable. Usually, an aqueous dispersion having a concentration of 20% by weight or less at 25 ° C. that does not precipitate is used. Whether or not precipitation occurs is visually confirmed immediately after the preparation of the polymer aqueous dispersion.

The above-mentioned “ionic group” refers to a group that can dissociate into ions in water, and examples thereof include an amino group, a carboxyl group, a sulfonic acid group, and salts thereof. The above-mentioned "in a state where 90 mol% of the ionic groups present in the polymer are neutralized" means that 90 mol% of the ionic groups contained in the polymer is converted into a salt by the neutralizing agent. Point to. As a procedure for confirming that the polymer is contained in the above definition range, for example, the ratio of the ionic groups in the polymer that are neutralized to form a salt (degree of neutralization of the ionic groups) is measured. The degree of neutralization of the ionic group is adjusted to 90 mol%, and this is dissolved or dispersed in water at 25 ° C. and 2 wt% concentration, and the appearance is visually observed. The degree of neutralization of the ionic group is determined by measuring the composition ratio of the ionic group with respect to the whole polymer by, for example, ¹ H-NMR, and the counter ion of the polymer forming the salt, for example, the carboxyl group forms a salt with Na. , Measure Na ⁺ charge, and divide the amount that is actually Na ⁺ salt by the amount of charge that is calculated from the composition ratio assuming that it is all Na ⁺ salt. Can be sought. As a result of the measurement, when the degree of neutralization is less than 90%, the degree of neutralization is adjusted by adding an alkali. As another method, from the synthesis of the polymer to the preparation of the ink, it is assumed that the addition of alkali neutralizes the ionic groups of the remaining monomers without polymerizing with the ionic groups in the polymer at the same rate. The degree of neutralization of the ionic groups in the polymer can also be estimated by dividing the number of moles of alkali added in the series of steps by the number of moles of the entire ionic groups of the charged monomer at the time of polymer synthesis.

<Polymer synthesis method>
The method for synthesizing the polymer according to the present invention is not particularly limited. For example, a known polymerization method such as radical polymerization, ionic polymerization, polyaddition, polycondensation or the like can be selected, and the polymer is a polymer synthesized by these known methods. Derivatives and modified products may be used. Further, carbon black, a monomer, a polymerization initiator, and, if necessary, a surfactant, a reactive surfactant, and a polymer may be mixed in water or an organic solvent at the same time for polymerization. Furthermore, the monomer may be directly reacted with the carbon black surface for polymerization. Among them, a polymer synthesized using radical polymerization is preferable because the synthesis method is simple.

  Hereinafter, a method for synthesizing a polymer by radical polymerization, which is a preferred method for synthesizing a random copolymer suitable as the polymer according to the present invention, will be described.

(Polymerization reaction solvent)
The polymer according to the invention is particularly preferably a random copolymer. The radical polymerization reaction, which is a preferred synthesis method thereof, can be carried out in the absence of a solvent or in the presence of a solvent, but the polymerization reaction is preferably carried out in the presence of a solvent.

  As a polymerization reaction solvent, ethers such as diethyl ether, tetrahydrofuran, diphenyl ether, anisole and dimethoxybenzene; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; acetonitrile, propionitrile, benzonitrile and the like Nitriles; Carbonyl compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, ethylene carbonate, and propylene carbonate; alcohols such as methanol, ethanol, propanol, isopropanol, n-butyl alcohol, t-butyl alcohol, and isoamyl alcohol Aromatic hydrocarbons such as benzene, toluene, xylene; chlorobenzene, methylene chloride, chloroform, chlorobenzene, carbon tetrachloride And halogenated hydrocarbons. Among these, preferred aqueous solvents as a polymerization reaction solvent.

  The aqueous solvent refers to a solvent obtained by mixing 100% water or water and a polar organic solvent at an arbitrary ratio. The polar organic solvent used here is not particularly limited as long as it can be mixed with water at an arbitrary ratio, and specific examples include methanol, ethanol, isopropanol, acetonitrile, acetone, dimethylformamide, dityl sulfoxide, tetrahydrofuran and the like. Of these, tetrahydrofuran, methyl alcohol, ethyl alcohol, and isopropyl alcohol are particularly preferable.

  Further, the polymerization reaction solvent may be a single solvent composed of only one kind or a mixed solvent composed of two or more kinds.

(Polymerization initiator)
A known radical polymerization initiator can be used for the radical polymerization reaction in the synthesis of the polymer.
As the polymerization initiator, either a water-soluble polymerization initiator or an oil-soluble polymerization initiator can be used.

  Examples of the water-soluble polymerization initiator include 2,2′-azobis (2-amidinopropane) dihydrochloride, 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis [2- (2-Imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2,2′-azobis [ N- (2-carboxyethyl) -2-methylpropionamide], 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl) propane} dihydrochloride, 2, 2′-azobis (1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2′-azobis {2-methyl-N- [2- (1-hydroxybutyl)] propionamide}, 2 , 2'-azobis [2 (5-methyl-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (3,4,5,6, -tetrahydropyrimidin-2-yl) propane] dihydrochloride, etc. Azo compound-based initiators; oxidants such as potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide alone; or these oxidants and sodium sulfite, sodium hyposulfite, ferrous sulfate, ferrous nitrate, sodium Examples thereof include redox initiators combined with water-soluble reducing agents such as formaldehyde sulfoxylate and thiourea.

  These may be used alone or in combination of two or more.

  Examples of oil-soluble polymerization initiators include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobiscyclohexane 1-carbonitrile, , 2′-azobis-4-methoxy-2,4-dimethylvaleronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, dimethyl-2,2′-azobis (2-methylpropionate), Azo compound-based initiators such as 1,1′-azobis (1-acetoxy-1-phenylethane), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile); acetylcyclohexylsulfonyl peroxide; Isobutyryl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, 2,4-dicarbonate Lobenzoyl peroxide, t-butylperoxypivalate, 3,5,5-trimethylhexanonyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, stearoyl peroxide, propionitrile peroxide, saxi Nick acid peroxide, acetyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, parachlorobenzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxymaleic acid, t-butyl peroxylaurate, cyclohexanone peroxide, t-butyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-dibenzoylperoxyhexane, -Butyl peroxyacetate, t-butyl peroxybenzoate, diisobutyl diperoxyphthalate, methyl ethyl ketone peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butyl cumi Ruperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide, pinane hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide and cumene Peroxide polymerization initiators such as peroxides; hydroperoxides (tret-butylhydroxyperoxide, cumenehydroxyperoxides, etc.), dialkyl peroxides (lauroyl peroxide, etc.) ) And oil-soluble peroxides such as diacyl peroxide (benzoyl peroxide, etc.), tertiary amines (triethylamine, tributylamine, etc.), naphthenates, mercaptans (mercaptoethanol, lauryl mercaptan, etc.), organometallic compounds (triethyl) And oil-soluble redox polymerization initiators used in combination with oil-soluble reducing agents such as aluminum, triethylboron and diethylzinc.

  These may be used alone or in combination of two or more.

(Other additives)
In the radical polymerization reaction, in addition to the above polymerization initiator, a known one such as a chain transfer agent, a chain terminator, or a polymerization accelerator can be added and used in order to adjust the resulting polymer to a preferred molecular weight. .

(Polymerization conditions)
When performing the radical polymerization reaction, the order of addition of the monomer, the polymerization reaction solvent, the radical initiator, etc. is arbitrary. For example, after the monomer, the polymerization reaction solvent, the radical polymerization initiator are collectively charged into the reaction vessel, the temperature is increased. The method of raising and performing a polymerization reaction is mentioned. In this case, the monomer or radical polymerization initiator may be added as it is or in a solution. As another method, after a polymerizable monomer and a polymerization reaction solvent are charged into a reaction vessel and the temperature is raised, a monomer solution containing a radical polymerization initiator, a polymerization reaction solvent, or a mixture thereof is continuously added. Or a method in which a polymerization reaction is carried out by adding in portions.
Among these, from the viewpoint of simplicity of operation, a method in which the polymerization reaction is performed by raising the temperature after charging the raw materials all at once is preferable.

  Although the usage-amount of a polymerization reaction solvent is not specifically limited, It is 1 weight part or more normally with respect to 100 weight part of monomers, Usually 2000 weight part or less, Preferably it is 1000 weight part or less.

  The amount of the polymerization initiator used varies depending on the type of the polymerization initiator used and is not particularly limited, but is usually 0.5 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the monomer.

  The polymerization temperature is not particularly limited, but is usually 0 ° C or higher, preferably 20 ° C or higher, and the upper limit is usually 200 ° C or lower, preferably 150 ° C or lower.

  Although there is no particular problem even if the polymer obtained by polymerization is used as it is unpurified, it is preferable to purify it according to a conventional method and use it for the next carbon black dispersion step. Purification methods include dropping the polymer solution into a solvent in which the polymer is insoluble and the monomer and polymerization initiator are soluble, reprecipitation purification by repeating the precipitation and filtration of the polymer, and the polymer and the polymer insoluble in the polymer solution and the polymerization initiator. Add a solvent that is soluble in water, remove the unreacted monomer and reaction solvent by fractional precipitation purification, heating distillation, vacuum distillation, etc. that repeat polymer precipitation and filtration, and then replace the solvent with water and / or aqueous solvent And a method of removing low molecular impurities and low molecular weight oligomer components using an ultrafiltration membrane or a dialysis membrane.

  The polymer contained in the carbon black dispersion may be one type or two or more types. As described above, the polymer is preferably a polymer having at least one or more types of hydrophobic monomers and one or more types of hydrophilic monomers as structural units, but an anionic polymer using an anionic monomer as the hydrophilic monomer or In addition, a cationic polymer using a cationic monomer and a nonionic polymer using a nonionic monomer may be used alone, and a carbon black dispersion liquid in which carbon black is dispersed with a polymer may be produced, or these may be used in combination. . Examples of the combined use include composite polymer capsules in which carbon black is coated with a polymer using electrostatic interaction between an anionic polymer and a cationic polymer.

{Aqueous medium}
Examples of the aqueous medium used for the carbon black dispersion of the present invention include water and / or a water-soluble organic solvent.
Although it will not specifically limit if it is generally used for this use as a water-soluble organic solvent, Specifically, it is a thing with a vapor pressure smaller than water, and the following are mentioned.

Ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, polypropylene glycol, pentamethylene glycol, trimethylene glycol, butylene Glycol, isobutylene glycol, thiodiglycol, 1,2-hexanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, 1,2-pentanediol, 1,5-pentanediol, 2- Methyl-2,4-pentanediol, 1,3-propanediol, 1,4-butanediol, 1,7-heptanediol, 1,8-octanediol, 2 Butene-1,4-diol, polyhydric alcohols such as glycerin;
Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-t-butyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monophenyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl Ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, Lopylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol mono-t-butyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropylene ether, propylene glycol monophenyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether Polyhydric alcohol ethers such as dipropylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether;
Ketones such as acetonylacetone;
Esters such as γ-butyrolactone, diacetin, triethyl phosphate;
Lower alkoxy alcohols such as 2-methoxyethanol and 2-ethoxyethanol;
Amines such as ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, triethylenetetramine, tetraethylenepentamine, pentamethyldiethylenetriamine;
Amides such as formamide, N, N-dimethylformamide, N-methylformamide, N, N-dimethylacetamide;
2-pyrrolidone, N-ethylpyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, morpholine, N-ethylmorpholine, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, imidazole, methylimidazole, hydroxyimidazole , Heterocycles such as dimethylaminopyridine, 1,3-propane sultone, hydroxyethylpiperazine, piperazine;
Sulfoxides such as dimethyl sulfoxide;
Sulfones such as sulfolane:
These may be used alone or in combination of two or more.

  The aqueous medium used in the present invention is preferably water or a mixture of water and a water-soluble organic solvent as described above. Of these, water is particularly preferable.

{Composition of carbon black dispersion}
The carbon black dispersion of the present invention contains at least carbon black as described above, a polymer, and an aqueous medium, and may contain other components as necessary.

  The carbon black concentration in the carbon black dispersion of the present invention is usually 30% by weight or less, preferably 20% by weight or less. Here, if the carbon black concentration is too high, the carbon black becomes poorly dispersed, the viscosity of the dispersion increases, the dispersion becomes gelled, and the dispersion may not be usable due to dispersion failure. If the carbon black concentration is too low, a sufficient print density will not be obtained when an ink composition is prepared. Therefore, it is usually 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more. .

  The weight ratio of carbon black to polymer in the carbon black dispersion of the present invention may be appropriately selected and determined. Generally, however, the polymer (two or more kinds of polymers are added to 1 part by weight of carbon black). In the case where it is included, the total) is preferably 0.001 part by weight or more, more preferably 0.01 part by weight or more, particularly 0.05 part by weight or more, and particularly preferably 0.08% by weight or more, and the upper limit is 2 parts by weight or less. In particular, the amount is preferably 1.5 parts by weight or less. If the amount of polymer is less than this range, the dispersion stability is lowered.

  The carbon black dispersion of the present invention may contain components other than carbon black, polymer, and aqueous medium, and in particular, other additions that can be contained in the ink composition of the present invention as described later. Other components such as emulsion particles and nonionic water-soluble polymers may be included as an agent.

{Physical properties of carbon black dispersion}
<Surface tension>
The surface tension of the carbon black dispersion of the present invention is not particularly limited, but the upper limit is usually +1 dyne / cm as compared with the surface tension of only the aqueous medium, and the lower limit is usually −50 dyne / cm, preferably −40 dyne / cm. That's it. For example, when water is used as the aqueous medium, the surface tension of water is 72.75 dyne / cm, so the upper limit of the surface tension of the carbon black dispersion is usually 73.75 dyne / cm, and the lower limit is usually 22.75 dyne / cm. cm, preferably 32.75 dyne / cm. When the surface tension of the carbon black dispersion is out of the above range, a decrease in printing density, a decrease in ejection stability and a storage stability may be observed.

<Viscosity>
The carbon black dispersion liquid of the present invention has a viscosity of 4.0 cp or less, more preferably 3.5 cp or less, still more preferably 3.0 cp or less, and particularly preferably 2.5 cp or less. The lower limit of the viscosity is preferably 1.0 cp or more, and particularly preferably 1.5 cp or more. If the viscosity of the carbon black dispersion is too low, it may be difficult to control the generation / flying of inkjet droplets, and if it is too high, the inkjet drive frequency may be lowered. Further, as described above, a carbon black dispersion having a high viscosity has a large entanglement between polymers and tends to aggregate, resulting in poor storage stability.

<Average dispersion particle size of carbon black>
The average dispersed particle size of carbon black in the carbon black dispersion of the present invention is usually 300 nm or less, preferably 200 nm or less. Moreover, as a minimum, it is 20 nm or more normally. When the average dispersed particle size of carbon black is too small, it is very difficult to maintain dispersion stability, and the print density may be lowered because it is difficult to remain on the surface of plain paper. Also, when the average dispersed particle size is too large, carbon black tends to settle during storage, and the dispersion stability of the dispersion and the storage stability of the recording liquid may be lowered.
The average dispersed particle size can be measured using an electron microscope such as SEM or TEM, or can be measured using a commercially available dynamic light scattering measurement device.

<PH>
The pH of the carbon black dispersion of the present invention is usually 3 or higher, preferably 5 or higher, more preferably 7 or higher. The upper limit of the pH is usually 12 or less, preferably 11 or less. If the pH of the carbon black dispersion liquid is low, the degree of dissociation of the anionic group is suppressed, and the dispersibility and dispersion stability of the dispersion liquid, the storage stability of the recording liquid, and the discharge performance are deteriorated. May be damaged.

In addition, the pH of the carbon black dispersion of the present invention was prepared separately from the viewpoint of storage stability by using the polymer used for the preparation of the carbon black dispersion, that is, the polymer contained in the carbon black dispersion. The difference from the pH of the 0% by weight polymer aqueous solution is preferably 0.5 or less.
The reason why this pH difference is large is not clear, but it is thought that the coexistence of carbon black greatly changes the conformation of the polymer structure and the dispersion stability is not sufficiently maintained. It means that the storage stability is not good. This pH difference is preferably 0.4 or less and is preferably as small as possible.
When two or more kinds of polymers are contained in the carbon black dispersion liquid, as shown in Comparative Example 2 described later, a 1% by weight aqueous solution of a polymer mixture mixed at a content weight ratio in the carbon black dispersion liquid is prepared. The pH may be evaluated.

<Storage stability>
When the carbon black dispersion of the present invention is stored in a sealed state at 70 ° C. for 1 week, the pH decrease is 1.0 or less, but from the viewpoint of long-term storage stability, this decrease is 0.95 or less. It is preferable that it is 0.90 or less. That is, when the pH before storage of the carbon black of the present invention is “pH ₀ ” and the pH when the carbon black dispersion of the present invention is stored in a sealed state at 70 ° C. for 1 week is “pH ₁ ”, The difference ΔpH = pH ₀ −pH ₁ is 1.0 or less, preferably 0.95 or less, more preferably 0.90 or less. The lower limit of ΔpH is preferably −1.0 or more, more preferably −0.95 or more, and further preferably −0.90 or more.
If this ΔpH is too large or too small, the intended storage stability in the present invention cannot be achieved.

{Production method of carbon black dispersion}
In the method for producing a carbon black dispersion of the present invention, the mixing method and the order of addition of carbon black, polymer, and aqueous medium are arbitrary. For example, carbon black, polymer, and aqueous medium are mixed at one time, and this mixing is performed. What is necessary is just to give a dispersion process with respect to a liquid using a common disperser.

  As the disperser used for the dispersion treatment, various dispersers that are generally used for pigment dispersion can be used.

  The disperser is not particularly limited, but is a kneader, salt milling, roll mill, planetary mixer, paint shaker, ball mill, sand mill, attritor, pearl mill, coball mill, homomixer, homogenizer, wet jet mill, high pressure homogenizer. An ultrasonic homogenizer or the like can be used. Glass beads, zirconia beads, alumina beads, magnetic beads, and styrene beads can be used for those using media as a disperser. Among these, a preferable dispersion treatment method is a method of dispersing with an ultrasonic homogenizer.

  When carrying out dispersion treatment with an ultrasonic homogenizer, carbon black, polymer, and water based on various methods such as kneader, salt milling, roll mill, planetary mixer, homomixer, homogenizer, wet jet mill, high pressure homogenizer, and bead mill in advance. It is preferable to carry out after preliminary dispersion of the medium.

The carbon black concentration during the dispersion treatment with an ultrasonic homogenizer is usually 3 to 30% by weight, preferably 5 to 20% by weight, more preferably 6 to 16% by weight. When the carbon black concentration is lower than this range, the carbon black particles are dilute, so that the dispersion efficiency is poor, and further, the particle size of the carbon black may not be reduced even when the ultrasonic wave is irradiated for a long time. On the other hand, if it is higher than this range, in addition to the concentration of carbon black particles being too high, the dispersion viscosity becomes high, so the stirring efficiency is lowered, so that the ultrasonic waves are less likely to hit the carbon black particles uniformly and the dispersion is reduced. May be non-uniform.
Therefore, when the carbon black concentration of the target carbon black dispersion is different from the carbon black concentration suitable for the dispersion treatment by the ultrasonic homogenizer, it is preferable to dilute with water or concentrate by heating. Adjust to the correct density.

  In addition, during the dispersion treatment using an ultrasonic homogenizer, heat generation is significantly caused by irradiation with ultrasonic waves. Therefore, the dispersion treatment is preferably performed while cooling with ice water or the like. At this time, the dispersion temperature is 60 ° C. or lower, for example, 0 to 50. It is preferable to perform cooling so that the temperature becomes ° C. If the temperature of the dispersion is too high, the carbon blacks are more likely to aggregate than the progress of the dispersion, so the dispersion does not proceed.In addition, the carbon black aggregated on the wall surface is mixed into the dispersion and mixed with coarse particles. This is not good because it deteriorates the discharge performance.

  The output of the ultrasonic homogenizer is not particularly limited as long as the particle size of the carbon black reaches a target size, but is usually 50 W or more and 1200 W or less. If the output is too small, it will not be possible to reduce the particle size to the target particle size, or it will take a long time for dispersion treatment. If the output is too large, the carbon black or polymer structure may be destroyed, or the vibration element (metal tip) Care must be taken because minute metal pieces are peeled off in large quantities and mixed as impurities into the dispersion, resulting in deterioration of dischargeability, storage stability, or filterability.

  The dispersion treatment time is not particularly limited as long as the particle size of the carbon black becomes a target size, but is usually 1 minute / dispersion 1 kg to 800 minutes / dispersion 1 kg, preferably 10 minutes / dispersion. The liquid is 1 kg or more. If the dispersion treatment time is too short, a large amount of coarse particles remain or adsorption of the polymer as a dispersant to the carbon black surface becomes insufficient, and dispersion stability and storage stability are deteriorated. On the other hand, if the dispersion treatment time is too long, a large number of carbon black fine particles of several nanometers to several tens of nanometers are generated, which deteriorates dispersion stability, storage stability, and ejection stability, and further printing. This is not preferable because it causes a decrease in concentration.

[Ink composition]
The ink composition of the present invention containing the carbon black dispersion of the present invention exhibits excellent effects particularly as a recording liquid, particularly an inkjet recording liquid.

  The ink composition of the present invention used as a recording liquid or the like is prepared by adjusting the colorant concentration of the above-described carbon black dispersion of the present invention as necessary, and further adding various additives depending on the application. . Alternatively, it may be prepared by adding various additives depending on the application during the production of the carbon black dispersion.

  As the colorant, in addition to the carbon black in the carbon black dispersion liquid of the present invention described above, self-dispersing pigments surface-treated for purposes such as toning, dyes, surfactants, polymer dispersants, etc. Dispersed pigments or dyes may be additionally included.

  The concentration of the total colorant in the ink composition of the present invention is usually 0.1% by weight or more, preferably 0.5% by weight or more as the total colorant concentration with respect to the total amount of the ink composition. Is usually 25% by weight or less, preferably 20% by weight or less, particularly preferably 15% by weight or less. If the colorant concentration is too high, the viscosity is increased and the discharge properties are deteriorated. If the colorant concentration is too low, the print density may be too low. On the other hand, the amount of the colorant added to the carbon black dispersion is usually 100 parts by weight or less, preferably 75 parts by weight or less, more preferably 50 parts by weight with respect to 100 parts by weight of carbon black in the carbon black dispersion. The amount is particularly preferably 25 parts by weight or less. If the additional amount of the colorant is too large, the effect of the present invention may be reduced.

  The solvent used in the ink composition of the present invention preferably contains water and a water-soluble organic solvent, and may further contain other components as desired.

  The concentration of the water-soluble organic solvent in the ink composition of the present invention may be appropriately selected and determined. Usually, it is 1% by weight to 45% by weight, particularly 40% by weight or less based on the ink composition. preferable. Further, the water content in the ink composition may be an amount that can appropriately set the concentration of the above-described colorant, water-soluble organic solvent, and optional additive components described below.

  As the water-soluble organic solvent, those exemplified as the aqueous medium of the carbon black dispersion liquid of the present invention described above can be used.

  The ink composition of the present invention may contain various additives as necessary within a range not impairing the effects of the present invention.

  Examples of such additives include recording liquids such as penetration enhancers, surface tension modifiers, hydrotropic agents, pH adjusters, chelating agents, preservatives, viscosity modifiers, humectants, antifungal agents, and rust inhibitors. Known additives can be used.

  The content of these additives in the ink composition of the present invention is usually 30% by weight or less, and particularly preferably 15% by weight or less, based on the total amount of the ink composition.

  Examples of penetration enhancers include lower alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol and pentanol, carbitols such as ethylene glycol monobutyl ether and triethylene glycol monobutyl ether glycol ether, and surfactants 1 A seed | species or 2 or more types is mentioned.

  As the surfactant, any one or more of nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, polymer surfactants and the like can be used. Can be used. Of these, nonionic surfactants, anionic surfactants and polymer surfactants are preferred.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, polyoxyethylene derivatives, oxyethylene / oxypropylene block copolymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid Examples thereof include esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, acetylene glycols, and acetylene alcohols.

  Examples of the anionic surfactant include fatty acid salts, alkyl sulfate esters, alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether sulfonates, alkyl phosphates, polyoxyethylene alkyl sulfates. Examples include ester salts, polyoxyethylene alkylaryl sulfate esters, alkane sulfonates, naphthalene sulfonate formalin condensates, polyoxyethylene alkyl phosphates, α-olefin sulfonates, and the like.

  Polymeric surfactants include polyacrylic acid, styrene / acrylic acid copolymer, styrene / acrylic acid / acrylic acid ester copolymer, styrene / maleic acid copolymer, styrene / maleic acid / acrylic acid ester copolymer, styrene / methacrylic acid. Examples thereof include acid copolymers, styrene / methacrylic acid / acrylic acid ester copolymers, styrene / maleic acid half ester copolymers, styrene / styrene sulfonic acid copolymers, vinyl naphthalene / maleic acid copolymers, vinyl naphthalene / acrylic acid copolymers, and salts thereof.

  Examples of the cationic surfactant include, but are not limited to, tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridium salts, imidazolium salts, and the like.

  In addition, silicone surfactants such as polysiloxane oxyethylene adducts, fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, oxyethylene perfluoroalkyl ethers, rhamnolipids, lysolecithins, etc. Surfactants such as biosurfactants can also be used.

  The content of these surfactants may be appropriately selected and determined. Usually, by adding in the range of 0.001 wt% or more and 5 wt% or less with respect to the ink composition, it is possible to further improve the quick drying property and print quality of the printed matter.

  Examples of the surface tension adjusting agent include one or more alcohols such as diethanolamine, triethanolamine, glycerin, and diethylene glycol, nonions, cations, anions, and amphoteric surfactants.

  As the hydrotropic agent, one or more of urea, alkylurea, ethyleneurea, propyleneurea, thiourea, guanidate, halogenated tetraalkylammonium and the like are preferable.

  As a humectant, 1 type (s) or 2 or more types, such as glycerol and diethylene glycol, can also be added as what also serves as a water-soluble organic solvent.

  Furthermore, a solid moisturizing agent (a water-soluble substance having a water retaining function and solid at 25 ° C.) can also be added. Preferred solid humectants include saccharides, sugar alcohols, hyaluronate, trimethylolpropane, 1,2,6-triol and the like. Examples of the saccharide include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides), and polysaccharides. Specifically, glucose, fructose, ribose, xylose, arabinose, galactose, sorbit, maltose, and lactose. , Sucrose, trehalose and the like. Examples of sugar alcohols include maltitol, sorbitol, xylitol, and the like, and one or more of these solid humectants can be added.

  Although it does not specifically limit as a chelating agent, 1 type (s) or 2 or more types, such as a sodium salt of ethylenediaminetetraacetic acid, a diammonium salt of ethylenediaminetetraacetic acid, are used. These are preferably used in the range of 0.005 wt% to 0.5 wt% with respect to the ink composition.

  The antifungal agent is not particularly limited, but sodium dehydroacetate, dichlorophen, sorbic acid, sodium benzoate, p-hydroxybenzoate, 1,2-benzisothiazolin-3-one (product name: Proxel GXL (manufactured by Arch Chemicals) or the like is used. These are preferably contained in the range of 0.05% by weight to 1% by weight with respect to the ink composition.

Further, in order to adjust the pH of the ink composition and obtain the stability of the ink composition, it is not particularly limited, but sodium hydroxide, potassium hydroxide, lithium hydroxide, nitric acid, ammonia, diethanolamine, triethanol A pH adjusting agent such as amine or a buffer solution such as phosphoric acid can be used.
The pH of the ink composition is usually in the neutral to alkaline range, and is preferably adjusted to about pH 6-11.

  When preparing the ink composition of the present invention from the carbon black dispersion of the present invention, polymer components such as emulsion particles and nonionic water-soluble polymers may be additionally added. The amount of the polymer component added at this time is usually 0.05% by weight or more, preferably 0.25% by weight or more, more preferably 0.5% by weight or more based on the ink composition, and the upper limit is 20%. It is preferable that it is 10% by weight or less. Further, the ratio of the polymer component to be added to the polymer contained in the carbon black dispersion is preferably 500% by weight or less.

  The ink composition of the present invention is mixed and dispersed in the same manner by adding a colorant and various additives as necessary to the carbon black dispersion produced by the method described in the method for producing a carbon black dispersion of the present invention. It is prepared by processing. Or you may prepare by adding a coloring agent and various additives as needed at the time of manufacture of a carbon black dispersion liquid, and carrying out a dispersion process.

[Recording method]
As a recording method using the ink composition of the present invention, a method of performing ink jet recording by discharging droplets of the ink composition of the present invention from an ink jet head and adhering the droplets to a recording medium is preferable. Using the composition, a high-quality and high-durability inkjet recording can be obtained according to the inkjet recording method of the present invention.

  Hereinafter, the present invention will be described more specifically with reference to synthesis examples, examples, and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

In the following examples, the number average molecular weight (Mn) and the weight average molecular weight (Mw) of the polymers A to G were measured under the following conditions using gel permeation chromatography (GPC).
Column filler: Styrene-divinylbenzene copolymer Solvent: Tetrahydrofuran (THF)
Flow rate: 0.7 mL / min
Temperature: 40 ° C
Calibration was performed using polystyrene.
In addition, this time, it measured using the following apparatuses, detectors, and columns.
Apparatus: Waters 2690 manufactured by Nippon Waters Co., Ltd.
Detector: Waters 2410 manufactured by Nippon Waters Co., Ltd.
Column: Shodex GPC KF-604, manufactured by Showa Denko KK
KF-603 ・ KF-602.5

  In the following notation, “co” means “co” of copolymer, and “b” means “block” of blockcopolymer.

[Polymer synthesis]
Examples of the synthesis of polymers used as dispersants in Examples and Comparative Examples are shown below. The polymers produced in the following synthesis examples were “water-soluble” in the present invention.

<Synthesis Example 1>
Synthesis of poly (sodium acrylate-co-n-butyl acrylate-co-styrene) (Polymer A) Into a condenser with a nitrogen-substituted interior, a nitrogen introduction tube, a stirrer and a thermometer-equipped flask as a polymerization initiator Charge 30 g of 2'-azobis (2,4-dimethylvaleronitrile), 3500.0 g of tetrahydrofuran (THF) as a solvent, 400.0 g of acrylic acid, 600.0 g of n-butyl acrylate, and 400.0 g of styrene as monomers. It is. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

After completion of the reaction, the reaction solution was cooled to room temperature, and a concentrated solution obtained by distilling off part of THF as a solvent with an evaporator was reprecipitated in acetonitrile. The supernatant was decanted and the solvent was completely removed by vacuum drying, and then neutralized by adding an aqueous sodium hydroxide solution to obtain poly (sodium acrylate-co-n-butyl acrylate-co-styrene): Polymer A An aqueous solution containing was obtained.
This aqueous solution was vacuum-dried to obtain a mixture of poly (sodium acrylate-co-n-butyl acrylate-co-styrene): polymer A and sodium acrylate.
The number average molecular weight (Mn) of this polymer A was 11,000, the weight average molecular weight (Mw) was 15,000, and the molecular weight distribution (Mw / Mn) was 1.4. The low molecular weight component having a weight average molecular weight of 4,000 or less was 8.8% by weight.

After 30.0 g of the mixture of the polymer A and sodium acrylate was dissolved in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer A aqueous solution was concentrated and dried to obtain the polymer A.
When the structure of the polymer A was confirmed by ¹ H-NMR using heavy water as a solvent, the composition ratio of the acrylic acid structural unit, n-butyl acrylate structural unit, and styrene structural unit in the random copolymer A was 40/21. / 39 (molar ratio) = 30/28/42 (weight ratio) (acid value 233 mg-KOH / g).
The pH of a 1.0% by weight aqueous solution of polymer A was 8.88.

<Synthesis Example 2>
Synthesis of poly (sodium acrylate-co-styrene) (Polymer B) 2,2′-Azobis (2,2) as a polymerization initiator was placed in a condenser equipped with nitrogen inside, a nitrogen inlet tube, a stirrer and a flask equipped with a thermometer. 4-dimethylvaleronitrile) 3.15 g was charged, tetrahydrofuran (THF) 384 g as a solvent, acrylic acid 47.35 g and styrene 102.65 g as monomers. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

After completion of the reaction, the reaction solution was cooled to room temperature, and a concentrated solution obtained by distilling off part of THF as a solvent with an evaporator was reprecipitated in acetonitrile. Decant the supernatant, vacuum dry to completely remove the solvent, neutralize by adding aqueous sodium hydroxide, and purify by ultrafiltration membrane, poly (sodium acrylate-co-styrene): polymer An aqueous solution containing B was obtained.
This aqueous solution was vacuum-dried to obtain a mixture of poly (sodium acrylate-co-styrene): polymer B and sodium acrylate.
This polymer B had a number average molecular weight (Mn) of 12,000, a weight average molecular weight (Mw) of 20,000, and a molecular weight distribution (Mw / Mn) of 1.7. The low molecular weight component having a weight average molecular weight of 4,000 or less was 4.2% by weight.

After 30.0 g of the mixture of the polymer B and sodium acrylate was dissolved in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer B aqueous solution was concentrated and dried to obtain the polymer B.
When the structure of the polymer B was confirmed by ¹ H-NMR using heavy water as a solvent, the composition ratio of the acrylic acid structural unit and the styrene structural unit in the random copolymer B was 13/87 (molar ratio) = 9 / 91 (weight ratio) (acid value 73 mg-KOH / g).
The pH of a 1.0% by weight aqueous solution of polymer B was 9.1.

<Synthesis Example 3>
Synthesis of poly (sodium acrylate-co-2-ethylhexyl acrylate) (Polymer C) 2,2'-azobis as a polymerization initiator was placed in a condenser equipped with nitrogen inside, a nitrogen inlet tube, a stirrer and a flask equipped with a thermometer. 2.05 g of (2,4-dimethylvaleronitrile) was charged, 205 g of tetrahydrofuran (THF) as a solvent, 55.46 g of acrylic acid and 94.54 g of 2-ethylhexyl acrylate as monomers. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

After completion of the reaction, the reaction solution was cooled to room temperature, and a concentrated solution obtained by distilling off part of THF as a solvent with an evaporator was reprecipitated in acetonitrile. The supernatant is decanted, and the solvent is completely removed by vacuum drying. Then, an aqueous solution containing poly (sodium acrylate-co-2-ethylhexyl acrylate): polymer C is prepared by adding a sodium hydroxide aqueous solution to neutralize the solution. Obtained.
This aqueous solution was vacuum-dried to obtain a mixture of poly (sodium acrylate-co-2-ethylhexyl acrylate): polymer C and sodium acrylate.
The number average molecular weight (Mn) of this polymer C was 18,000, the weight average molecular weight (Mw) was 22,000, and the molecular weight distribution (Mw / Mn) was 1.2. The low molecular weight component having a weight average molecular weight of 4,000 or less was 7.2% by weight.

After 30.0 g of the mixture of polymer C and sodium acrylate was dissolved in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer C aqueous solution was concentrated and dried to obtain the polymer C.
When the structure of the polymer C was confirmed by ¹ H-NMR using heavy water as a solvent, the composition ratio of the acrylic acid constituent unit and the 2-ethylhexyl acrylate constituent unit in the random copolymer C was 40/60 (molar ratio). = 21/79 (weight ratio) (acid value 161 mg-KOH / g).
Further, the pH of a 1.0 wt% aqueous solution of polymer C was 8.95.

<Synthesis Example 4>
Synthesis of poly (sodium acrylate-co-stearyl acrylate-co-n-butyl acrylate-co-styrene) (Polymer D) Polymerization was carried out in a condenser equipped with nitrogen, nitrogen introduction tube, stirrer and thermometer flask. Charged 37.5 g of 2,2′-azobis (2,4-dimethylvaleronitrile) as an initiator, 4375.0 g of tetrahydrofuran (THF) as a solvent, 600.0 g of acrylic acid as a monomer, 400.0 g of stearyl acrylate, n- 600.0 g of butyl acrylate and 400.0 g of styrene were charged. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

After completion of the reaction, the reaction solution was cooled to room temperature, neutralized with a sodium hydroxide / methanol solution, and precipitated in isopropyl alcohol. The precipitate was filtered and vacuum-dried to obtain a mixture of sodium acrylate-co-stearyl acrylate-co-n-butyl acrylate-co-styrene): polymer D and sodium acrylate.
The number average molecular weight (Mn) of this polymer D was 10,000, the weight average molecular weight (Mw) was 18,000, and the molecular weight distribution (Mw / Mn) was 1.8. The low molecular weight component having a weight average molecular weight of 4,000 or less was 9.5% by weight.

  After dissolving 30.0 g of the polymer D and sodium acrylate mixture in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer D aqueous solution was concentrated and dried to obtain the polymer D.

When the structure of the polymer D was confirmed by ¹ H-NMR using heavy water as a solvent, the composition ratio of the acrylic acid constituent unit, stearyl acrylate constituent unit, n-butyl acrylate constituent unit, and styrene constituent unit in the random copolymer D was as follows. 40/11/14/35 (molar ratio) = 24/30/15/31 (weight ratio) (acid value 188 mg-KOH / g).
The pH of a 1.0 wt% aqueous solution of polymer D was 9.13.

<Synthesis Example 5>
Synthesis of poly (sodium acrylate-co-lauryl acrylate-co-styrene) (Polymer E) 2,2 ′ as a polymerization initiator was placed in a condenser equipped with nitrogen inside, a nitrogen introduction tube, a stirrer and a flask equipped with a thermometer as a polymerization initiator. -30 g of azobis (2,4-dimethylvaleronitrile) was charged, 3500.0 g of tetrahydrofuran (THF) as a solvent, 600.0 g of acrylic acid, 600.0 g of lauryl acrylate, and 400.0 g of styrene as monomers. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

After completion of the reaction, the reaction solution was cooled to room temperature, and a concentrated solution obtained by distilling off part of THF as a solvent with an evaporator was reprecipitated in acetonitrile. Decant the supernatant, vacuum dry to completely remove the solvent, and then neutralize by adding an aqueous sodium hydroxide solution to poly (sodium acrylate-co-lauryl acrylate-co-styrene): aqueous solution of polymer E Got.
This aqueous solution was vacuum-dried to obtain a mixture of poly (sodium acrylate-co-lauryl acrylate-co-styrene): polymer E and sodium acrylate.
The number average molecular weight (Mn) of this polymer E was 12,000, the weight average molecular weight (Mw) was 15,000, and the molecular weight distribution (Mw / Mn) was 1.3. The low molecular weight component having a weight average molecular weight of 4,000 or less was 5.8% by weight.

After dissolving 30.0 g of the polymer E and sodium acrylate mixture in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing sodium acrylate, the polymer E aqueous solution was concentrated and dried to obtain the polymer E.
When the structure of the polymer E was confirmed by ¹ H-NMR using heavy water as a solvent, the composition ratio of the acrylic acid structural unit, lauryl acrylate structural unit, and styrene structural unit in the random copolymer E was 66/7/27. (Molar ratio) = 52/18/30 (weight ratio) (acid value 400 mg-KOH / g).
Further, the pH of a 1.0 wt% aqueous solution of polymer E was 9.19.

<Synthesis Example 6>
Synthesis of poly (sodium acrylate-co-n-butyl acrylate-co-styrene) (Polymer F) Into a flask equipped with a nitrogen-substituted condenser, a nitrogen introducing tube, a stirrer and a thermometer, Charge 30 g of 2'-azobis (2,4-dimethylvaleronitrile), 3500.0 g of tetrahydrofuran (THF) as a solvent, 600.0 g of acrylic acid, 600.0 g of n-butyl acrylate, and 400.0 g of styrene as monomers. It is. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

After completion of the reaction, the reaction solution was cooled to room temperature, neutralized with a sodium hydroxide / methanol solution, and precipitated in isopropyl alcohol. The precipitate was filtered and vacuum-dried to obtain a mixture of poly (sodium acrylate-co-n-butyl acrylate-co-styrene): polymer F and sodium acrylate.
The number average molecular weight (Mn) of this polymer F was 11,000, the weight average molecular weight (Mw) was 18,000, and the molecular weight distribution (Mw / Mn) was 1.6. The low molecular weight component having a weight average molecular weight of 4,000 or less was 5.6% by weight.

After 30.0 g of the mixture of the polymer F and sodium acrylate was dissolved in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing the sodium acrylate, the polymer F aqueous solution was concentrated and dried to obtain the polymer F.
When the structure of the polymer F was confirmed by ¹ H-NMR using heavy water as a solvent, the composition ratio of the acrylic acid structural unit, the n-butyl acrylate structural unit, and the styrene structural unit in the random copolymer F was 43/22. / 35 (molar ratio) = 32/30/38 (weight ratio) (acid value 252 mg-KOH / g).
The pH of a 1.0% by weight aqueous solution of polymer F was 8.66.

<Synthesis Example 7>
Synthesis of polyvinyl alcohol-b-poly (sodium acrylate-co-methyl acrylate-co-sodium methacrylate-co-benzyl methacrylate-co-styrene) (block copolymer G) A flask equipped with an introduction tube, a stirrer, and a thermometer was charged with 3587 g of vinyl acetate, 1907 g of chloroform as a chain transfer agent and a solvent, and heated to 70 ° C. over 1 hour. Next, a polymerization initiator solution in which 0.3 g of azobis (2-methylbutyronitrile) as a polymerization initiator was dissolved in 534 g of chloroform was dropped over 6 hours. Thereafter, a polymerization initiator solution in which 0.5 g of azobis (2-methylbutyronitrile) as a polymerization initiator was dissolved in 444.5 g of chloroform was dropped over 5 hours. After dropwise addition of the catalyst solution, the mixture was heated and polymerized for 10 hours under reflux conditions. After completion of the reaction, 0.01N sodium hydroxide / methanol solution was continuously added dropwise to the reaction solution, and unreacted vinyl acetate and chloroform were distilled off under reduced pressure at an internal temperature of 40 ° C. A vinyl concentration of 74% by weight was obtained. This polyvinyl acetate had a number average molecular weight of 3,500 and a molecular weight distribution (Mw / Mn) of 2.4.

  Next, a condenser, a nitrogen inlet tube, a stirrer, and a thermometer-equipped flask with the inside being replaced with nitrogen were mixed with 17 g of methanol as a solvent and 1048.5 g of isopropyl alcohol as a monomer, 2623 g of methyl acrylate, 2142 g of benzyl methacrylate, and styrene. 63.5 g and the above polyvinyl acetate methanol solution 1353 g as a macroinitiator were charged, and the temperature was raised from room temperature to 60 ° C. over 1 hour. When the internal temperature reached 60 ° C., a catalyst solution in which 0.6 g of cuprous bromide as a catalyst and 12.0 g of tris (2-dimethylamino) ethylamine as a ligand were dissolved in 30 g of methanol was added. After addition of the catalyst solution, the mixture was heated and polymerized for 30 hours under reflux conditions.

  Next, in a reaction vessel equipped with a condenser, a stirrer, and a thermometer, the above polymerized solution 502 g was dissolved in a mixed solvent of 276 g of methanol, 552 g of tetrahydrofuran (THF), and 138 g of water, and then the temperature was raised to 60 ° C. and 5N hydroxylation was performed. Sodium (728 g) was added and the reaction was carried out at 65 ° C. for 7 hours. After completion of the reaction, 550 g of tetrahydrofuran (THF) and 140 g of water were added to the polymer mass obtained by removing the supernatant and suspended, and then 280 g of methanol was added to precipitate the polymer. The supernatant was removed again, 300 g of water was added, neutralized with acetic acid, the solution was heated to 90 ° C., and residual THF and methanol were distilled off to obtain an aqueous polymer solution. Thereafter, impurities were removed from the aqueous polymer solution using an ultrafiltration membrane (ACP-1050, manufactured by Asahi Kasei Corporation). Polyvinyl alcohol-b-poly (sodium acrylate-co-methyl acrylate-co-methacrylic acid) in which the copolymer linked to the polyvinyl alcohol block is a gradient copolymer by concentrating and drying the polymer aqueous solution after ultrafiltration Sodium-co-benzyl methacrylate-co-styrene): Polymer G was obtained.

The structure of the above polymer G was confirmed by ¹ H-NMR using heavy water as a solvent. As a result, the vinyl alcohol constituent unit, the sodium acrylate constituent unit, the methyl acrylate constituent unit, and the sodium methacrylate constituent unit in the block copolymer G were obtained. The composition ratio of benzyl methacrylate structural unit and styrene structural unit is 25/26/21/2/21/5 (molar ratio) = 12/20/20/2/40/6 (weight ratio) (acid value 170 mg -KOH / g).
The number average molecular weight (Mn) of the polymer G was 14,000, the weight average molecular weight (Mw) was 22,000, and the molecular weight distribution (Mw / Mn) was 1.57. The low molecular weight component having a weight average molecular weight of 4,000 or less was 3.0% by weight.

  The pH of the 1.0% by weight aqueous solution of polymer G is 8.01, and the pH of the 1.0% by weight aqueous solution of the polymer mixture in which polymer A and polymer G are mixed at a weight ratio of 5 to 6 is 8. 25.

[Examples and Comparative Examples]
Below, the manufacture example of a carbon black dispersion using the polymers A to G obtained in Synthesis Examples 1 to 7 and the evaluation results using the same are shown.

<Example 1: Carbon black pigment dispersion (1)>
Carbon black (Mitsubishi Chemical Corporation prototype; DBP absorption 102cm ³ / 100g, an average primary particle size 16 nm, pH 7) 36.0 g, polymer A solution (solid content 19.76 wt%) 16.63g, and distilled water 247.37 g was mixed and predispersed for 10 minutes with a homomixer.

Place the above preliminary dispersion in a 500 ml tall beaker, immerse the beaker in ice water, keep the temperature of the dispersion at 0 to 50 ° C., and use an ultrasonic homogenizer (Nippon Seiki Seisakusho; US-600T; chip used 36 mmφ) Was dispersed for 60 minutes to obtain a 12 wt% carbon black dispersion liquid (1).
The pH of this dispersion (1) was 9.13, and the surface tension was 71.1 dyne / cm.

  The average dispersed particle size and viscosity of the carbon black in the carbon black dispersion liquid (1) were measured by the following method to be 123 nm and 2.1 cp.

(Measurement of average dispersed particle size)
The dispersion was diluted 10,000 times with deionized water and measured with an Otsuka Electronics FPAR-1000 using a dilution probe, and the average dispersed particle size was calculated by the Cumulant method.

(Measurement of viscosity)
A rheometer (REOLOGICA AB Instruments; VAR-100; cone 1 ° / 55φ) was used to read the value at a shear rate of 100 / sec.

  The pH of the carbon black dispersion (1) after storage at 70 ° C. for 1 week in a sealed state was 8.17. (PH change = 0.96)

(Evaluation of heat-resistant storage stability of dispersion)
The average dispersion particle size and viscosity of the carbon black after storing the carbon black dispersion (1) at 70 ° C. for 2 weeks were 130 nm and 2.1 cp when measured by the above method.

(Preparation of ink composition)
An ink composition (1) having the following composition was prepared using the carbon black dispersion (1), and the evaluation described below was performed. Here, the ink composition was obtained by mixing the following components and stirring for 15 minutes, followed by ultrasonic dispersion treatment for 30 minutes.

<Ink composition>
Carbon black dispersion (1): 50.0 parts by weight Distilled water: 39.5 parts by weight Diethylene glycol: 5 parts by weight Glycerin: 5 parts by weight Olfine E1010 (surfactant manufactured by Air Products): 0.5 parts by weight

  The average dispersed particle size of carbon black in the ink composition (1) was measured by the same method as described above, and was 120 nm.

(Evaluation of heat-resistant storage stability of ink composition)
The average dispersed particle size of carbon black after holding the ink composition (1) at 70 ° C. for 2 weeks was measured by the same method as described above, and was 121 nm.

<Example 2: Carbon black pigment dispersion (2)>
Carbon black (Mitsubishi Chemical Corporation prototype; DBP absorption 102cm ³ / 100g, an average primary particle size 16 nm, pH 7) 36.0 g, a polymer B solution (solid content 9.28 wt%) 16.63g, and distilled water 227.53 g was mixed and predispersed for 10 minutes with a homomixer.

In the same manner as in Example 1, the preliminary dispersion was subjected to a dispersion treatment using an ultrasonic homogenizer to obtain a 12 wt% carbon black dispersion (2).
The pH of this dispersion (2) was 9.26, and the surface tension was 71.8 dyne / cm.
When the average dispersed particle size and viscosity of carbon black in this carbon black dispersion (2) were measured by the same method as in Example 1, they were 121 nm and 2.2 cp.
The pH of the carbon black dispersion (2) after storage at 70 ° C. for 1 week in a sealed state was 8.63. (PH change = 0.63)

(Evaluation of heat-resistant storage stability of dispersion)
The average dispersion particle size and viscosity of the carbon black after storing the carbon black dispersion (2) at 70 ° C. for 2 weeks were measured to be 116 nm and 1.9 cp.

(Preparation of ink composition)
An ink composition (2) was prepared in the same manner as in Example 1 except that the carbon black dispersion (1) was changed to the carbon black dispersion (2), and the average dispersed particle size was measured in the same manner as described above. However, it was 120 nm.

(Evaluation of heat-resistant storage stability of ink composition)
The average dispersed particle size of carbon black after holding the ink composition (2) at 70 ° C. for 2 weeks was measured by the same method as described above, and was 123 nm.

<Example 3: Carbon black pigment dispersion (3)>
Carbon black (Mitsubishi Chemical Corporation prototype; DBP absorption 102cm ³ / 100g, an average primary particle size 16 nm, pH 7) 36.0 g, polymer C solution (solids 13.84 wt%) 26.53 g, and distilled water 237.47 g was mixed and pre-dispersed with a homomixer for 10 minutes.

In the same manner as in Example 1, the preliminary dispersion was subjected to a dispersion treatment using an ultrasonic homogenizer to obtain a 12 wt% carbon black dispersion (3).
This dispersion (3) had a pH of 9.42 and a surface tension of 68.7 dyne / cm.
The average dispersed particle size and viscosity of carbon black in this carbon black dispersion (3) were measured by the same method as in Example 1, and were 119 nm and 2.0 cp.
The pH of the carbon black dispersion (3) after storage for 1 week at 70 ° C. in a sealed state was 8.76. (PH change = 0.83)

(Evaluation of heat-resistant storage stability of dispersion)
The average dispersion particle size and viscosity of carbon black after storing the carbon black dispersion (3) at 70 ° C. for 2 weeks were 116 nm and 1.9 cp.

(Preparation of ink composition)
An ink composition (3) was prepared in the same manner as in Example 1 except that the carbon black dispersion (1) was changed to the carbon black dispersion (3), and the average dispersed particle size was measured in the same manner as described above. However, it was 122 nm.

(Evaluation of heat-resistant storage stability of ink composition)
The average dispersed particle size of the carbon black after keeping the ink composition (3) at 70 ° C. for 2 weeks was measured by the same method as described above, and it was 123 nm.

<Example 4: Carbon black pigment dispersion (4)>
Carbon black (Mitsubishi Chemical Corporation prototype; DBP absorption 102cm ³ / 100g, an average primary particle size 16 nm, pH 7) 18.0 g, polymer D solution (solids 15.30 wt%) 8.82 g, and distilled water 123.18 g was mixed and predispersed with a homomixer for 10 minutes.

The preliminary dispersion was subjected to a dispersion treatment using an ultrasonic homogenizer in the same manner as in Example 1 to obtain a 12 wt% carbon black dispersion (4).
This dispersion (4) had a pH of 8.94 and a surface tension of 67.4 dyne / cm.
When the average dispersed particle size and viscosity of carbon black in this carbon black dispersion (4) were measured by the same method as in Example 1, they were 121 nm and 2.0 cp.
The pH of the carbon black dispersion (4) after storage at 70 ° C. for 1 week in a sealed state was 8.25. (PH change = 0.69)

(Evaluation of heat-resistant storage stability of dispersion)
The average dispersion particle size and viscosity of the carbon black after storing the carbon black dispersion (4) at 70 ° C. for 2 weeks were 120 nm and 2.0 cp when measured by the above method.

(Preparation of ink composition)
An ink composition (4) was prepared in the same manner as in Example 1 except that the carbon black dispersion (1) was changed to the carbon black dispersion (4), and the average dispersed particle size was measured by the same method as described above. However, it was 119 nm.

(Evaluation of heat-resistant storage stability of ink composition)
The average dispersed particle size of carbon black after the ink composition (4) was held at 70 ° C. for 2 weeks was measured by the same method as described above, and it was 116 nm.

<Example 5: Carbon black pigment dispersion (5)>
Carbon black (Mitsubishi Chemical Corporation prototype; DBP absorption 102cm ³ / 100g, an average primary particle size 16 nm, pH 7) 18.0 g, polymer E solution (solids 19.80 wt%) 5.91 g, and distilled water 126.09 g was mixed and predispersed with a homomixer for 10 minutes.

In the same manner as in Example 1, the preliminary dispersion was subjected to a dispersion treatment using an ultrasonic homogenizer to obtain a 12 wt% carbon black dispersion (5).
The pH of this dispersion (5) was 9.20, and the surface tension was 71.1 dyne / cm.
The average dispersed particle size and viscosity of carbon black in this carbon black dispersion (5) were measured by the same method as in Example 1 and found to be 132 nm and 2.1 cp.
The pH of the carbon black dispersion (5) after storage for 1 week at 70 ° C. in a sealed state was 8.55. (PH change = 0.64)

(Evaluation of heat-resistant storage stability of dispersion)
The average dispersion particle size and viscosity of the carbon black after storing the carbon black dispersion (5) at 70 ° C. for 2 weeks were measured by the above method to be 133 nm and 2.4 cp.

(Preparation of ink composition)
An ink composition (5) was prepared in the same manner as in Example 1 except that the carbon black dispersion (1) was changed to the carbon black dispersion (5), and the average dispersed particle size was measured in the same manner as described above. However, it was 124 nm.

(Evaluation of heat-resistant storage stability of ink composition)
The average dispersed particle size of the carbon black after the ink composition (5) was held at 70 ° C. for 2 weeks was measured by the same method as described above, and was 121 nm.

<Comparative Example 1: Carbon black pigment dispersion (6)>
Carbon black (Mitsubishi Chemical Corporation prototype; DBP absorption 102cm ³ / 100g, an average primary particle size 16 nm, pH 7) 18.0 g, polymer F solution (solids 18.32 wt%) 7.37 g, and distilled water 124.63 g was mixed and predispersed with a homomixer for 10 minutes.

In the same manner as in Example 1, the preliminary dispersion was subjected to a dispersion treatment using an ultrasonic homogenizer to obtain a 12 wt% carbon black dispersion (6).
This dispersion (6) had a pH of 9.47 and a surface tension of 70.3 dyne / cm.
When the average dispersed particle size and viscosity of carbon black in this carbon black dispersion (6) were measured by the same method as in Example 1, they were 122 nm and 2.1 cp.
The pH of the carbon black dispersion (6) after storage at 70 ° C. for 1 week in a sealed state was 8.38. (PH change = 1.09)

(Evaluation of heat-resistant storage stability of dispersion)
The average dispersion particle size and viscosity of the carbon black after storing the carbon black dispersion (6) at 70 ° C. for 2 weeks were measured by the above method to be 240 nm and 13.0 cp.

(Preparation of ink composition)
An ink composition (6) was prepared in the same manner as in Example 1 except that the carbon black dispersion (1) was changed to the carbon black dispersion (6), and the average dispersed particle size was measured by the same method as described above. However, it was 120 nm.

(Evaluation of heat-resistant storage stability of ink composition)
The average dispersed particle size of carbon black after holding the ink composition (6) at 70 ° C. for 2 weeks was measured by the same method as described above, and was 351 nm.

<Comparative Example 2: Carbon black pigment dispersion (7)>
Carbon black (Mitsubishi Chemical Corporation prototype; DBP absorption 102cm ³ / 100g, an average primary particle size 16 nm, pH 7) 18.0 g, polymer A solution (solid content 19.76 wt%) 4.55 g, polymer G solution (Solid content 13.07% by weight) 8.25 g and distilled water 119.2 g were mixed and pre-dispersed with a homomixer for 10 minutes.

The preliminary dispersion was subjected to a dispersion treatment using an ultrasonic homogenizer in the same manner as in Example 1 to obtain a 12 wt% carbon black dispersion (7).
The pH of this dispersion (7) was 9.04, and the surface tension was 70.1 dyne / cm.
The average dispersed particle size and viscosity of carbon black in this carbon black dispersion (7) were measured by the same method as in Example 1, and were 122 nm and 4.1 cp.
The pH of the carbon black dispersion (7) after storage at 70 ° C. for 1 week in a sealed state was 8.28. (PH change = 0.76)

(Evaluation of heat-resistant storage stability of dispersion)
The average dispersion particle size and viscosity of the carbon black after storing the carbon black dispersion (7) at 70 ° C. for 2 weeks were measured by the above method, and were found to be 420 nm and 8.5 cp.

(Preparation of ink composition)
An ink composition (7) was prepared in the same manner as in Example 1 except that the carbon black dispersion (1) was changed to the carbon black dispersion (7), and the average dispersed particle size was measured in the same manner as described above. However, it was 156 nm.

(Evaluation of heat-resistant storage stability of ink composition)
The average dispersed particle size of carbon black after holding the ink composition (7) at 70 ° C. for 2 weeks was measured by the same method as described above, and it was 643 nm.

The results of Examples 1 to 5 and Comparative Examples 1 and 2 are summarized in Tables 1 to 3.
Here, the criteria for the evaluation of heat resistant storage stability of the dispersion (◯ Δ ×) were as follows.
○ The change in average dispersed particle size was 20 nm or less before and after storage at 70 ° C. for 2 weeks,
The change in viscosity is 0.5 cp or less.
Δ: The change in average dispersed particle size is 21 to 100 nm before and after storage at 70 ° C. for 2 weeks.
The change in viscosity is 0.6 to 2.0 cp.
×: The change in average dispersed particle size is 101 nm or more before and after storage at 70 ° C. for 2 weeks,
The change in viscosity is 2.1 cp or more.

  From Tables 1 to 3, the following is clear.

In the dispersion liquid (6) of Comparative Example 1, the viscosity of the carbon black dispersion liquid is as low as 2.1 cp, but the pH drop width ΔpH when stored in a sealed state at 70 ° C. for 1 week is from 1.0. Since it is large, the heat resistant storage stability of the dispersion and the ink composition prepared using the dispersion is poor.
The dispersion (7) of Comparative Example 2 has a pH drop ΔpH of 1.0 or less when stored in a sealed state at 70 ° C. for 1 week, but has a viscosity as high as 4.1 cp. The heat-resistant storage stability of the ink composition prepared using is poor.

  On the other hand, in the dispersions (1) to (5) of Examples 1 to 5, the average dispersed particle size and viscosity of the carbon black are almost the same before and after storage at 70 ° C. for 2 weeks, and good heat-resistant storage stability. The ink composition thus prepared has good heat storage stability.

  From the above results, the carbon black dispersion of the present invention having a pH drop ΔΔ of 1.0 or less and a viscosity of 4.0 cp or less when stored in a sealed state at 70 ° C. for 1 week, and the same are used. It is apparent that the prepared ink composition has good heat-resistant storage stability compared with the conventional ink composition.

Claims (7)

  Carbon black comprising at least carbon black, a polymer, and an aqueous medium, having a viscosity of 4.0 cp or less and having a pH drop of 1.0 or less when stored in a sealed state at 70 ° C. for 1 week. Dispersion.   The carbon black dispersion according to claim 1, wherein the acid value of the polymer is 240 mg-KOH / g or less.   The carbon black dispersion according to claim 1 or 2, wherein the polymer has a weight average molecular weight of 15,000 or more and a content of a component having a weight average molecular weight of 4,000 or less is 20% by weight or less. liquid.   The carbon black dispersion according to any one of claims 1 to 3, wherein the aqueous medium is only water.   5. The difference between the pH of the 1.0 wt% aqueous solution of the polymer and the pH of the carbon black dispersion containing the polymer is 0.5 or less. 6. Carbon black dispersion.   An ink composition comprising the carbon black dispersion according to any one of claims 1 to 5.   An ink jet recording method comprising: ejecting droplets of the ink composition according to claim 6 from an ink jet head and attaching the droplets to a recording medium.