JP4672549B2 - Method for producing aqueous carbon black dispersion - Google Patents

Description

  The present invention relates to an aqueous carbon black dispersion, and more particularly to a method for producing an aqueous carbon black dispersion for inkjet recording.

  Dispersion ink jet recording inks are produced mainly by dispersing carbon black and pigments in water and / or organic solvents and then evaporating and removing the water and / or organic solvents.

  When evaporating and removing water and / or organic solvents, non-evaporated components adhere to the inner wall surface of the evaporation device, reducing the heat transfer efficiency, and the evaporation takes a long time. Then, there is a problem that coarse particles are mixed by peeling.

On the other hand, Patent Document 1 discloses using a thin film evaporation apparatus as an evaporation apparatus. Patent Document 2 discloses an improvement method such as performing an evaporation operation at a position where the liquid level at which evaporation starts is higher than the upper end of the heating unit.
JP 2001-152053 A JP 2005-263864 A

  Further, when the water and / or the organic solvent is removed by evaporation, there is a problem that the evaporation operation cannot be stably performed in the case of a dispersion having severe foaming.

  In particular, in the case of a dispersion using carbon black having a large specific surface area and high oil absorption performance as a pigment, foaming is severe and it takes a long time to evaporate and remove the organic solvent.

  This invention makes it a subject to provide the manufacturing method of the water-system carbon black dispersion which suppresses foaming at the time of evaporation removal of an organic solvent.

  The present invention that solves the above-mentioned problems is the following: after heating a dispersion containing carbon black, a dispersant, a neutralizing agent, an organic solvent, and water to a specific temperature below the boiling point of the dispersion, the temperature This is a method for producing an aqueous carbon black dispersion in which the organic solvent is removed by evaporation under reduced pressure until reaching the boiling point of the body.

  According to the present invention, foaming at the time of evaporating and removing the organic solvent can be suppressed by heating the dispersion to a specific temperature below the boiling point and then reducing the pressure until the temperature reaches the boiling point.

  Hereinafter, embodiments will be described in detail.

  In the method for producing an aqueous carbon black dispersion according to the present embodiment, a dispersion containing carbon black, a dispersant, a neutralizing agent, an organic solvent and water is heated to a specific temperature below the boiling point of the dispersion, The organic solvent is removed by evaporation under reduced pressure until the temperature reaches the boiling point.

  According to this method, foaming at the time of evaporative removal of the organic solvent can be suppressed.

(Components of dispersion)
<Carbon black>
As the carbon black of the present embodiment, for example, carbon black for inkjet inks, general paints, resin coloring, reinforcing, UV prevention, conductive and the like can be used. Also, any of furnace black, thermal black, lamp black, acetylene black, channel black, ketjen black, etc., which are classified according to the production method of carbon black, can be used. As carbon black, a mixture of one or more of these is used.

  From the viewpoint of dispersion stability, the primary average particle diameter of carbon black is preferably 10 to 100 nm, more preferably 11 to 50 nm, and further preferably 12 to 40 nm.

  As the carbon black of the present embodiment, a carbon black having a high structure (porous structure) having a large specific surface area and a large DBP (dibutyl phthalate) oil absorption is preferably used.

The specific surface area of carbon black is preferably 100 m ² / g or more, and more preferably 150 m ² / g or more, from the viewpoints of storage stability, ejection properties, and print density when used for inkjet recording. The specific surface area of carbon black is preferably 1500 m ² / g or less, and more preferably 500 m ² / g or less.

DBP oil absorption of the carbon black, storage stability when used in ink-jet recording, discharge properties, from the viewpoint of print density, is preferably 100 cm ^3/100 g or more, more preferably 120 cm ^3/100 g or more . DBP oil absorption of carbon black is preferably not more than 1000 cm ^3/100 g, more preferably not more than 400 cm ^3/100 g.

  The primary particle diameter, specific surface area, and DBP oil absorption of carbon black are measured by a method based on JIS K6217.

<Dispersant>
As the dispersant of this embodiment, for example, a water-insoluble polymer having an acidic group can be used.

  Here, the “water-insoluble polymer having an acidic group” means that an aqueous dispersion obtained by neutralizing the acidic group with lithium hydroxide to a neutralization degree of 100% is dried at 105 ° C. for 2 hours, A polymer having a solubility of 2 g or less when dissolved in 100 g of water.

  Examples of the water-insoluble polymer having an acidic group include (A) an acidic group-containing monomer (hereinafter sometimes referred to as “(A) component”), (B) a macromer (hereinafter referred to as “(B) component”). And a water-insoluble vinyl polymer obtained by copolymerizing a monomer mixture containing a hydrophobic monomer (hereinafter also referred to as “component (C)”).

  Examples of the acidic group-containing monomer as component (A) include anionic monomers described in paragraph 0022 of JP-A-9-286939. Typical examples include unsaturated carboxylic acid monomers, unsaturated sulfonic acid monomers, and unsaturated phosphoric acid monomers.

  Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.

  Examples of unsaturated sulfonic acid monomers include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylic acid ester, bis- (3-sulfopropyl) -itaconic acid ester, and the like. Can be mentioned.

  Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acrylic acid. And leuoxyethyl phosphate.

  Among these anionic monomers, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are more preferable from the viewpoints of dispersion stability and ejection stability when used in ink jet recording.

  The cationic monomer may be contained within a range not impairing the object of the present invention, and examples thereof include an unsaturated amine-containing monomer and an unsaturated ammonium salt-containing monomer. Among these, N, N-dimethylaminoethyl (meth) acrylate, N- (N ′, N′-dimethylaminopropyl) (meth) acrylamide and vinylpyrrolidone are preferable.

  (A) A component is 1 type (s) or 2 or more types among these.

  Examples of the macromer as the component (B) include a macromer which is a monomer having a polymerizable unsaturated group having a number average molecular weight of 500 to 100,000 (preferably 1000 to 10,000). The number average molecular weight of the component (B) is measured using polystyrene as a standard substance by gel chromatography using 1 mmol / L dodecyldimethylamine-containing chloroform as a solvent.

  Specifically, the component (B) includes, for example, a styrenic macromer having a polymerizable functional group at one end, a silicone macromer having a polymerizable functional group at one end, and a macromer having a polymerizable functional group at one end. And preferably an acrylic (meth) acrylate macromer having 1 to 4 carbon atoms (methyl methacrylate macromer having a polymerizable functional group at one end, butyl acrylate macromer having a polymerizable functional group at one end, one end And isobutyl methacrylate-based macromers having a polymerizable functional group. Among these, a styrenic macromer having a polymerizable functional group at one end is preferable from the viewpoint of sufficiently containing a pigment in the obtained water-insoluble polymer.

  Examples of the styrenic macromer having a polymerizable functional group at one end include, for example, a styrene homopolymer having a polymerizable functional group at one end, and a copolymer of styrene having a polymerizable functional group at one end and another monomer. Etc. Among these, those having an acryloyloxy group or a methacryloyloxy group as a polymerizable functional group at one end are preferable. The styrene content in the macromer is preferably 50% by mass or more, and more preferably 70% by mass or more from the viewpoint of increasing the affinity with the colorant.

  In the copolymer of styrene having a polymerizable functional group at one end and another monomer, examples of the other monomer include (1) acrylonitrile, (2) methyl (meth) acrylate, ethyl (meth) acrylate, ( Iso) propyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) Amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (iso) Stearyl (meth) acrelan (Meth) acrylic acid ester (which may have a hydroxy group) whose ester moiety is an alkyl group having 1 to 18 carbon atoms, (3) α-methylstyrene, vinylnaphthalene, vinyltoluene, ethylvinyl Benzene, 4-vinylbiphenyl, 1,1-diphenylethylene, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, Examples thereof include vinyl monomers having an aromatic hydrocarbon group having 6 to 22 carbon atoms other than styrene such as 2-acryloyloxyethylphthalic acid.

  Examples of commercially available styrenic macromers include trade names of Toa Gosei Co., Ltd., AS-6, AS-6S, AN-6, AN-6S, HS-6, HS-6S, and the like.

  Examples of the silicone macromer having a polymerizable functional group at one terminal include a silicone macromer represented by the following formula (I). Silicone macromers are effective in preventing scorching of the heads of inkjet printers.

X (Y) _q Si (R ⁴ ) _3-r (Z) _r (II)
(Wherein X is a polymerizable unsaturated group, Y is a divalent linking group, R ⁴ is independently a hydrogen atom, a lower alkyl group, an aryl group or an alkoxy group, and Z is a number average molecular weight of 500 or more. A monovalent siloxane polymer residue, q is 0 or 1, and r is an integer of 1 to 3).

  (B) A component is 1 type, or 2 or more types among these.

  Examples of the hydrophobic monomer (C) include alkyl (meth) acrylates and aromatic ring-containing monomers. Among these, an aromatic ring-containing monomer is preferable from the viewpoint of water resistance.

  Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, and (iso) amyl (meth). Acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (iso) stearyl (meth) (Meth) acrylic acid ester etc. which have C1-C22 alkyl groups, such as an acrylate, are mentioned.

  Examples of aromatic ring-containing monomers include styrene, vinyl naphthalene, α-methyl styrene, vinyl toluene, ethyl vinyl benzene, 4-vinyl biphenyl, 1,1-diphenyl ethylene, benzyl (meth) acrylate, and phenoxyethyl (meth) acrylate. 2-hydroxy-3-phenoxypropyl acrylate, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, 2-acryloyloxyethyl phthalic acid, neopentyl glycol acrylic acid benzoate, and the like. In these, the vinyl monomer which has a C6-C22 aromatic hydrocarbon group is preferable, and a styrene-type monomer is preferable from a viewpoint of the printing density at the time of using for inkjet recording, and marker-proof improvement. Of the styrenic monomers, styrene and 2-methylstyrene are preferred. The content of the styrene monomer in the component (C) is preferably 10 to 100% by mass, and 40 to 100% by mass from the viewpoint of improving the printing density and marker resistance when used for inkjet recording. Is more preferable.

  (C) A component is 1 type (s) or 2 or more types among these.

  In the above, the expressions “(iso or tertiary)” and “(iso)” mean that these groups are present both in the presence and in the absence of these groups. When is not present, it is “normal”. Further, “(meth) acrylate” is “acrylate” or “methacrylate”.

  The monomer mixture may further contain one or more types of monomers other than the components (A), (B), and (C) as necessary.

  The content of the component (A) in the water-insoluble vinyl polymer is preferably 1 to 50% by mass, and 2 to 40% by mass from the viewpoint of high-temperature stability and long-term storage stability of the resulting dispersion. It is more preferable.

  The content of the component (B) in the water-insoluble vinyl polymer is 1 to 25% by mass from the viewpoint of increasing the affinity of the water-insoluble vinyl polymer for the colorant and improving the printing density when used for inkjet recording. It is preferable that it is 5 to 20% by mass.

  The content of the component (C) in the water-insoluble vinyl polymer is preferably 5 to 98% by mass from the viewpoint of water resistance, scratch resistance, marker resistance and bleed resistance, and is 10 to 60% by mass. More preferably.

  The mass ratio ((A) / [(B) + (C)]) of the content of the component (A) in the water-insoluble vinyl polymer to the total content of the components (B) and (C) is obtained. From the viewpoint of high-temperature stability of the dispersion, long-term storage stability, printing density when used for inkjet recording, etc., 0.01 to 1 is preferable, and 0.02 to 0.67 is more preferable. .

  The water-insoluble vinyl polymer can be produced by copolymerizing the monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.

  The solvent in the solution polymerization method is not particularly limited, but a polar organic solvent is preferable. Moreover, what mixed the polar organic solvent with water may be sufficient. Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms such as methanol, ethanol and propanol; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and the like. Among these, methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solution of these with water is preferable.

  In addition, as a radical polymerization initiator in the polymerization, for example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), dimethyl-2,2′- Azo compounds such as azobisbutyrate, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile), t-butylperoxyoctoate, di-t-butyl Examples thereof include organic peroxides such as peroxide and dibenzoyl oxide. The amount of the radical polymerization initiator is preferably 0.001 to 5 mol%, more preferably 0.01 to 2 mol%, based on the monomer mixture.

  The polymerization conditions of the monomer mixture vary depending on the radical polymerization initiator, the type of monomer and solvent, etc., but usually the polymerization temperature is 30 to 100 ° C. (preferably 50 to 80 ° C.), and the polymerization time is 1 to 20 hours. is there. The polymerization atmosphere is preferably an inert gas atmosphere such as nitrogen gas.

  After completion of the polymerization reaction, the water-insoluble vinyl polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. The obtained water-insoluble vinyl polymer can be purified by repeating reprecipitation or removing unreacted monomers by membrane separation, chromatographic methods, extraction methods, and the like.

  The weight average molecular weight of the water-insoluble vinyl polymer is preferably 3000 to 100,000 from the viewpoints of water resistance, scratch resistance, marker resistance and dispersion stability after printing.

<Neutralizing agent>
Examples of the neutralizing agent in the present embodiment include trimethylamine, ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide and the like. As the neutralizing agent, a mixture of one or more of these is used.

<Organic solvent>
Examples of the organic solvent of the present embodiment include alcohol solvents such as ethanol and tertiary butanol, ketone solvents such as acetone and methyl ethyl ketone, and ether solvents. As the organic solvent, a mixture of one or more of these is used. Among these organic solvents, methyl ethyl ketone is preferable and may be used alone or in combination with other solvents. The organic solvent preferably has a solubility in water of 50% by mass or less at 20 ° C. The organic solvent preferably has a boiling point at atmospheric pressure (101.3 kPa) of 50 ° C. or higher and lower than 100 ° C. below water.

<Other components>
In this embodiment, in addition to carbon black, a dispersing agent, a neutralizing agent, an organic solvent, and water, the dispersion may contain a surfactant, an antifungal agent, and the like.

(Preparation of dispersion)
In this embodiment, a dispersion is prepared from carbon black, a dispersant, a neutralizing agent, an organic solvent, and water.

  Specifically, the dispersion can be prepared by first dissolving the dispersant in an organic solvent, then adding carbon black, a neutralizing agent and water to the organic solvent, mixing them, and subjecting them to a dispersion treatment.

  Examples of the disperser used in the dispersion process include Ultra Disper (Asada Iron Works Co., Ltd., trade name), Ebara Milder (Ebara Manufacturing Co., Ltd., trade name), TK Homomixer, TK Pipeline Mixer, TK Homojetter, and TK Homo. High-speed stirrers such as Mickline Flow and Fillmix (Primix), Ultrasonic Dispersers such as Ultrasonic Homogenizer (Nippon Seiki Seisakusho Co., Ltd., trade name), High Pressure Homogenizer (Izumi Food Machinery Co., Ltd., trade name) , Homovalve type high pressure homogenizer represented by minilab 8.3H type (Rannie, trade name), Microfluidizer (Microfluidics, trade name), Nanomizer (Yoshida Kikai Kogyo Co., Ltd., trade name), Ultimateizer (Sugino) Machine Co., Ltd., trade name), Genus PY (Hakusui Chemical) Co., Ltd., trade name), DeBEE2000 (Nippon BEE Co., Ltd., trade name) and other chamber type high-pressure homogenizers, Star Mill (Ashizawa Finetech Co., Ltd., trade name), Ultra Apex Mill (Koto Kogyo Co., Ltd., Commodity) Name), Picomill (Asada Tekko Co., Ltd., trade name), DCP Super Flow, Cosmo (Nihon Eirich Co., Ltd., trade name), MSC Mill (Mitsui Mining Co., Ltd., trade name), etc. And kneaders such as a roll mill of 3 rolls and a kneader. Moreover, you may perform a dispersion | distribution process combining a some disperser among these.

  As a mass ratio excluding water in the dispersion, the carbon black is preferably 5 to 50% by mass, the dispersant is preferably 2 to 40% by mass, and the organic solvent is 20 to 70% by mass. It is preferable. In addition, the neutralizing agent should just contain the quantity from which the liquid property of a dispersion is neutral to weak antariness, for example, pH becomes the range of 6.5-9.5.

  The amount of water added is preferably 5 to 100% by mass of the organic solvent when using a kneader or the like that performs dispersion treatment at a high concentration, and when a high-pressure disperser or the like that performs dispersion treatment at a low concentration is used. Is preferably 100 to 1000% by mass of the organic solvent.

(Evaporation removal of organic solvent)
In this embodiment, after heating to a specific temperature below the boiling point of the dispersion, the organic solvent is removed by evaporation under reduced pressure until the temperature reaches the boiling point.

<Evaporation device>
For removing the organic solvent by evaporation, for example, a batch evaporator is used. Among the batch type evaporators, it is preferable to use a stirred tank batch type evaporator, and among them, it is more preferable to use a stirred tank thin film type evaporator.

  Here, the “batch evaporator” means that a heating part such as a jacket part or a heat transfer heater that can pass or vent a heat medium such as hot water or steam is disposed on the outer wall surface of the tank, or It means an evaporation apparatus in which a coil capable of passing or venting a heat medium such as hot water or steam is disposed inside the tank and the solvent can be removed by heating.

  The “stirred tank batch type evaporator” refers to an evaporator in which a batch type evaporator is provided with a stirrer and can evaporate and remove the solvent while stirring in the tank.

  The “stirred tank thin film evaporator” refers to an evaporator capable of forming a thin film such as a solution using a heating inner wall surface and evaporating and removing the solvent from the thin film surface in the stirred tank batch evaporator. . As a specific example of this stirring tank thin film type evaporator, for example, trade name: Wall Wetter manufactured by Kansai Chemical Machinery Co., Ltd. can be mentioned.

  Further, “evaporation removal” means a concentration operation for evaporating and distilling the organic solvent to increase the concentration of the non-evaporated component, and water is also removed by evaporation together with the organic solvent.

<Evaporation removal operation>
As an operation for evaporating and removing the organic solvent from the dispersion, starting from a state at room temperature (usually 5 to 30 ° C.) under atmospheric pressure (101.3 kPa), first, the dispersion is subjected to any temperature below its boiling point ( For example, the temperature is raised to 20 to 80 ° C.

  Next, the pressure is reduced from the atmospheric pressure until the arbitrary temperature reaches the boiling point of the dispersion. At this time, the organic solvent is removed by evaporation. Since the solvent composition of the dispersion is sequentially changed by the evaporation removal of the organic solvent, the boiling point of the dispersion also changes, but further, the arbitrary temperature is changed so that the boiling point of the dispersion in the composition that changes from moment to moment. Continue depressurization. Although the pressure at the time of depressurization depends on the kind of the organic solvent and the above-mentioned arbitrary temperature, it is preferably in the range of 1 to 50 kPa from the viewpoint that the load on the apparatus is small and the operability is good.

  By performing the operation as described above, the organic solvent can be efficiently removed while suppressing foaming of the dispersion. The organic solvent is removed by evaporation, and water is also removed by evaporation at the same time as described above.

  As the reverse operation, when the pressure is first reduced to an arbitrary pressure and then the temperature raising operation is performed, foaming occurs at a stretch near the boiling point of the dispersion, and the pressure condition must be changed immediately. This is because, in the temperature raising operation, in the heat transfer from the jacket part or coil heater provided in the batch evaporator, a time delay due to the temperature distribution occurs until the predetermined temperature is detected, or the control response is poor. This is because overshoot occurs and control to a predetermined temperature is not possible. As a result, the required time to the concentration end point may become longer due to foaming, or may suddenly boil. Moreover, even if the operation of changing the temperature and the pressure stepwise is performed as another method, the operation is still complicated and the time required for evaporation is increased.

  The operation of evaporating the organic solvent while suppressing bubbling requires precise temperature control and pressure control, and as the operation, the pressure is less time lag and the responsiveness is fast, so the operation of this embodiment is preferable. Become.

<Amount of organic solvent to be evaporated>
The evaporation removal of the organic solvent is preferably performed so that the organic solvent in the dispersion is substantially removed to 0.1% by mass or less, and more preferably 0.01% by mass or less. .

In addition, when the above-described stirred tank thin film type evaporator is used, from the viewpoint of efficiently performing the evaporation operation without generating coarse particles, the following formula (1)
30 ≦ (B / A) × 100 ≦ 100 (1)
(In the formula, A is the total amount of organic solvent to be removed by evaporation (kg), and B is the amount of organic solvent to be removed by evaporation in the region above the upper end of the heating unit of the batch evaporator).
It is preferable to evaporate and remove the organic solvent within a range satisfying the condition represented by.

  Further, when the vapor-liquid interface is below the upper end of the heating section, that is, when the condition of 30 ≦ (B / A) × 100 <100 is satisfied, the same amount of water as the fraction of the organic solvent removed by evaporation The evaporation operation may be performed so that the concentration of the non-evaporating component in the dispersion is constant and the gas-liquid interface is not changed.

  From the viewpoint of productivity, the concentration of the non-evaporated component in the dispersion before evaporating and removing the organic solvent is preferably 1 to 40% by mass, and more preferably 10 to 30% by mass.

  The concentration of the non-evaporated component in the dispersion after evaporating and removing the organic solvent is preferably 1 to 60% by mass from the viewpoint of the dispersion stability of the ink when used in inkjet recording, More preferably, it is 40 mass%, and it is further more preferable that it is 10-30 mass%. The non-evaporating component is a total concentration of carbon black, a dispersant, and a neutralizing agent.

  The aqueous carbon black dispersion produced through the above operation is a dispersion in which the solid content of a dispersant containing carbon black is dispersed in water as a main solvent. Here, the form of the dispersant containing carbon black is not particularly limited as long as the particles are formed of at least carbon black and the dispersant. Examples thereof include a particle form in which carbon black is encapsulated in a dispersant, a particle form in which carbon black is uniformly dispersed in the dispersant, and a particle form in which carbon black is exposed on the surface of the dispersant.

  The aqueous dispersion of the dispersant containing carbon black may be used as an aqueous ink as it is. However, if necessary, the dispersion is further centrifuged to remove coarse particles and aggregated particles, and then a wetting agent, a penetrating agent, and a dispersing agent. In addition, a water-based ink for inkjet recording may be added by adding a viscosity modifier, an antifoaming agent, a mildewproofing agent, a rustproofing agent, or the like.

  When used as a water-based ink for inkjet recording, the average particle size of the dispersant containing carbon black in the dispersion is 0.01 to 0.50 μm from the viewpoint of prevention of clogging of the nozzles of the printer and dispersion stability. It is preferably 0.03 to 0.30 μm, more preferably 0.05 to 0.20 μm. The average particle diameter can be measured with a laser particle analysis system ELS-8000 manufactured by Otsuka Electronics Co., Ltd.

  Further, the content (solid content) of the dispersant containing carbon black in the dispersion is usually preferably 0.5 to 30% by mass from the viewpoint of printing density and ejection stability, and preferably 1 to 15%. It is more preferable to set it as the mass%.

(Synthesis of dispersant <water-insoluble vinyl polymer>)
First, a dropping funnel, a condenser and a stirrer were attached to the reaction vessel, the inside of the reaction vessel was sufficiently replaced with nitrogen gas, and the hot water bath was heated to 70 ° C.

  Next, 18 parts by weight of methacrylic acid as component (A), 10 parts by weight of styrene macromer as component (B), 53.3 parts by weight of styrene as component (C), and 2-hydroxyethyl methacrylate as the other monomer component 7 parts by mass and 10 parts by mass of monophenoxypolyethylene glycol (n = 6) methacrylate, 0.7 parts by mass of 3-mercapto-1,2-propanediol as a chain transfer agent, and 2.2′-azobis as a polymerization initiator (2,4-dimethylvaleronitrile) 1.2 parts by mass and 10% by mass of a raw material mixture consisting of 35 parts by mass of methyl ethyl ketone as a solvent are placed in a reaction vessel, while the remaining 90% by mass is added to a dropping funnel. Then, it was dropped into the reaction vessel over 5 hours and polymerized at 70 ° C.

  Thereafter, it was aged at 75 ° C. for 10 hours to obtain a water-insoluble vinyl polymer solution. A part of the obtained water-insoluble vinyl polymer solution was heated at 105 ° C. for 2 hours under reduced pressure to remove the solvent, thereby isolating the water-insoluble vinyl polymer.

  The weight average molecular weight of the isolated water-insoluble vinyl polymer measured by gel permeation chromatography using polystyrene as a standard substance and chloroform containing 1 mmol / L dodecyldimethylamine as a solvent was 25,000.

The details of the compounds used in the synthesis are as follows.
(1) Styrene macromer: manufactured by Toa Gosei Co., Ltd., trade name AS-6 (styrene homopolymerized macromer, one terminal polymerizable functional group: methacryloyloxy group, number average molecular weight: 6000)
(2) Monophenoxypolyethylene glycol (n = 6) methacrylate: Shin-Nakamura Chemical Co., Ltd., trade name: NK ester PHG-6G)
(3) 2-hydroxyethyl methacrylate: Reagent grade 1 manufactured by Kishida Chemical Co., Ltd. (4) Styrene monomer: Reagent special grade manufactured by Wako Pure Chemical Industries, Ltd. (5) 3-Mercapto-1,2-propanediol: Wako Pure Chemical Industries Reagent special grade (6) 2.2'-azobis (2,4-dimethylvaleronitrile) manufactured by Wako Pure Chemical Industries, Ltd. V-65
(7) Methyl ethyl ketone: First grade reagent manufactured by Wako Pure Chemical Industries, Ltd. (Example 1)
2.9 kg of a water-insoluble vinyl polymer as a dispersant obtained by the above synthesis, 0.6 kg of a 7 mass% lithium hydroxide aqueous solution as a neutralizer, 1.4 kg of methyl ethyl ketone as an organic solvent, and ion-exchanged water 6.7 kg was added and mixed with a disper blade at a temperature of 20 ° C. for 30 minutes.

Next, carbon black pigment [manufactured by Degussa trade name: FW18, DBP oil absorption amount added 160cm ³ /100G〕3.4Kg thereto, and mixed for an additional 2 hours.

  Next, 15.0 kg of the obtained dispersion was diluted by adding 7.5 kg of ion-exchanged water so that the concentration of non-evaporated components was 20% by mass, and a high-pressure disperser (trade name: Ultimateizer manufactured by Sugino Machine Co., Ltd.). The 15-pass dispersion process was performed at a pressure of 180 MPa.

  Subsequently, 7.5 kg of ion-exchanged water was further added to 22.5 kg of the dispersion to adjust the non-evaporable component concentration to 15% by mass.

  Then, 30.0 kg of this dispersion was charged into a stirring tank thin film evaporator (trade name: Wall Wetter (45 L container) manufactured by Kansai Chemical Machinery Co., Ltd.), and the jacket warm water temperature was set to 60 ° C. while forming a liquid film by stirring. As a constant, the temperature raising operation was performed first. The temperature in the tank after the completion of the temperature increase indicated 58 ° C.

  Subsequently, the pressure is gradually reduced from atmospheric pressure until 58 ° C. reaches the boiling point of the dispersion liquid composition, and the organic solvent and water are removed by evaporation until the non-evaporated component concentration reaches 25%. A dispersion was produced.

  At this time, there was almost no foaming, and the time required to concentrate the non-evaporated component concentration from 15% by mass to 25% by mass was 6.0 hours.

(Comparative Example 1)
26.3 kg of the dispersion was charged into a stirred tank thin film evaporator (trade name: Wall Wetter (45 L container) manufactured by Kansai Chemical Machinery Co., Ltd.), and the pressure in the tank was increased to 13.0 kPa while forming a liquid film by stirring. The pressure was reduced.

  Subsequently, the temperature is gradually raised by heating the jacket portion with hot water from a temperature in the tank of 25 ° C. to the boiling point of the liquid composition, and the organic solvent and water are removed by evaporation until the concentration of the non-evaporated component reaches 25%. An aqueous carbon black dispersion was produced.

  The other points were the same as in Example 1.

  During the evaporation operation, the evaporation operation was repeatedly interrupted due to the occurrence of foaming, and the time required to concentrate the non-evaporated component concentration from 15% by mass to 25% by mass was 10.5 hours.

  The present invention is useful for a method for producing an aqueous carbon black dispersion, more specifically, an aqueous carbon black dispersion for inkjet recording.

Claims (4)

Carbon black, dispersants, neutralizing agents, the dispersion containing the organic solvent and water, was heated to 20 to 80 ° C. is a temperature lower than the boiling point of the dispersion, and the boiling point temperature of said dispersion A method for producing an aqueous carbon black dispersion in which the organic solvent is removed by evaporation under reduced pressure. Method of manufacturing an aqueous carbon black dispersion according to claim 1 DBP (dibutyl phthalate) oil absorption amount of the carbon black is 100 cm ^3/100 g or more.   The method for producing an aqueous carbon black dispersion according to claim 1 or 2, wherein the organic solvent is removed by evaporation using a stirred tank thin film evaporator.   The aqueous carbon black dispersion according to any one of claims 1 to 3, wherein a non-evaporated component contained in the dispersion is adjusted to 1 to 60 mass% by evaporating and removing the organic solvent from the dispersion. Production method.