JP2000248194A - Aqueous dispersion of carbon black - Google Patents

Abstract

(57) Abstract: Provided is an aqueous carbon black dispersion having excellent dispersibility and dispersion stability. An aqueous carbon black dispersion comprising carbon black, an aqueous medium, and a dispersant represented by the following general formula (1). General formula (1) [Wherein, R ¹ and R ² each represent a hydrogen atom or a carbon atom 1
Represents an alkyl group of ¹ to 4 (R ¹ and R ² may form a ring together), M represents a hydrogen atom, an alkali metal atom, ammonium or an amine, and m and n represent 0 to 3
And 1 ≦ m + n ≦ 3. ]

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aqueous dispersion of carbon black.

[0002]

2. Description of the Related Art Carbon black is used in a wide range of fields such as printing inks, paints, and plastic forming materials as coloring pigments and light-shielding materials. Conventionally, in these applications, carbon black was generally used by dispersing it in an organic medium. Recently, however, the conversion to water-based has been rapidly progressing from the viewpoint of environmental problems and impact on the human body. is there. However, many carbon blacks are inherently lipophilic, and their suitability such as pigment dispersibility in an aqueous vehicle is significantly inferior. Therefore, a satisfactory dispersion cannot be obtained by a usual dispersion method. Therefore, conventionally, a method of modifying the surface of carbon black with various additives, for example, a dispersant such as a surfactant or an aqueous pigment-dispersed resin to impart dispersibility in water has been studied. However, when the surface of the carbon black particles is insufficiently modified, the particles easily re-aggregate and the dispersion stability is impaired, and when the compatibility between the dispersant and the dispersing resin is poor, inks and paints are used. However, there is a problem that the performance is deteriorated. In addition, if the dispersing resin is changed according to the application, a dispersing agent must be selected accordingly, and there is a problem that versatility is lacking.

[0003] On the other hand, various attempts have been made to impart dispersibility in water to carbon black, and one of them is a hydrophilic treatment by oxidizing carbon black. As the oxidation treatment method, a gas phase oxidation method such as ozone treatment and plasma treatment, and a liquid phase oxidation method using nitric acid, hydrogen peroxide solution, sodium perchlorate, and the like have been devised. Comparing general oxidation treatment conditions, liquid-phase oxidation is more effective than gas-phase oxidation, and among liquid-phase oxidations, nitric acid has a greater degree of increase in surface acidity than hydrogen peroxide solution, It is known that the hydrophilicity is further improved. However, liquid phase oxidation has the disadvantage that purification after treatment is difficult. In particular, the problem of mutagenicity has been pointed out for carbon black obtained by nitric acid oxidation. On the other hand, gas phase oxidation has the advantage of not requiring a purification step, but has the drawback that sufficient hydrophilicity cannot be obtained due to low acidity as described above.

[0004] As another method, a hydrophilization treatment method using fluorine gas has been devised, but has a problem in performance stability during storage.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous dispersion of carbon black which does not have these disadvantages and has excellent dispersibility and dispersion stability.

[0006]

That is, the present invention is an aqueous carbon black dispersion comprising a carbon black, an aqueous medium and a dispersant represented by the following general formula (1). General formula (1)

[0007]

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[In the formula, R ¹ and R ² each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms (R ¹ and R ² may be combined to form a ring), and M is Represents a hydrogen atom, an alkali metal atom, ammonium or an amine,
m and n represent an integer of 0 to 3, and 1 ≦ m + n ≦ 3. Further, the present invention is the aqueous carbon black dispersion described above, wherein the total surface functional group content of the carbon black is 0.2 meq / g or more.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The carbon black used in the present invention is not particularly limited by the type and production history, and various types such as commercially available oil furnace black, gas furnace black, thermal black, acetylene black, and channel black can be used. In addition, carbon black subjected to ordinary ozone treatment, plasma treatment, and liquid phase oxidation treatment can also be used. Now, in the process of producing carbon black, surface functional groups such as a carboxyl group (—COOH), a phenolic hydroxyl group (—OH), and a quinone group (> C ＝ O) are generally generated on the particle surface. The quantification of these functional groups is based on the carboxyl group (-C
OOH) and phenolic hydroxyl group (-OH) can be determined by a titration method, and quinone group (> C = O) can be determined by a hydrogen absorption method of sodium borohydride.

The total amount of the above-mentioned surface functional groups in the carbon black used in the present invention, that is, the total amount of the surface functional groups is preferably from 0.2 to 8.0 meq / g, more preferably from 1.0 to 6.0.
0 meq / g is particularly preferred. The total surface functional group content is 0.
If the amount is less than 2 meq / g, a sufficient dispersing effect cannot be obtained because the adsorption of the dispersant or the number of reaction sites is small. On the other hand, when carbon black having a total surface functional group content of more than 8.0 meq / g is used, a remarkable effect on the dispersing effect is hardly exhibited. Further, the ratio of each functional group to the total surface functional group amount is not particularly limited, but it is preferable that the content of the carboxyl group is large.

The particle size of the carbon black used in the present invention is preferably 0.01 to 10 μm, as in the range of the particle size of the carbon black used for ordinary inks and coatings.
1 to 0.5 μm is particularly preferred. However, the particle size referred to here indicates an average primary particle size measured by an electron microscope or the like, and the physical property values are generally used to represent physical properties of carbon black. The dispersant according to the present invention is represented by the general formula (1), in which α-naphthol-mono to tri-sulfonic acid (α-naphthol-mono to tri-sulfonic acid in which the amino group is substituted at the peri-position to the hydroxyl group of α-naphtholsulfonic acid (salt) Salt).
General formula (1)

[0012]

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[Wherein, R ¹ and R ² each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms (R ¹ and R ² may form a ring together), and M is Represents a hydrogen atom, an alkali metal atom, ammonium or an amine,
m and n represent an integer of 0 to 3, and 1 ≦ m + n ≦ 3. The amino group of the dispersant represented by the general formula (1) includes a primary amino group (—NH ₂ ), a methylamino group,
Secondary amino groups such as ethylamino group and butylamino group,
Examples include tertiary amino groups such as dimethylamino, diethylamino, dibutylamino, and piperidino. These amino groups are adsorbed to the carboxyl group (—COOH) and the phenolic hydroxyl group (—OH), which are acidic among the surface functional groups of carbon black, by an acid-base interaction. For NH ₂ ), not only acid-base interaction but also quinone group (> C =
It is considered that a large dispersion effect can be obtained by forming an azomethine bond (> C = N-) with O).

The sulfonic acid (salt) group contained in the dispersant represented by the general formula (1) is a sulfonic acid when M is hydrogen, and a sulfonic acid when M is an alkali metal, ammonium or amine. Represents a sulfonate. M in the general formula (1)
Is a hydrogen atom, that is, sulfonic acid, interacts with the amino group contained in the dispersant, the dispersant causes intermolecular association, thereby inhibiting the adsorption or reaction of the amino group to the surface functional group of carbon black, In some cases, a sufficient dispersion effect cannot be obtained. In such a case, the target aqueous carbon black dispersion can be obtained by neutralizing the sulfonic acid with an alkali metal, ammonia or an amine before or during the dispersion step. The sulfonic acid (salt) group in the general formula (1) is anionic and imparts hydrophilicity to carbon black.

Specific examples of the dispersant used in the present invention include:
1-amino-8-hydroxynaphthalene-2,4-disulfonic acid, 1-amino-8-hydroxynaphthalene-
Examples thereof include 3,6-disulfonic acid, 1-amino-8-hydroxynaphthalene-4-sulfonic acid, and alkali metal salts, ammonium salts, and amine salts thereof. These dispersants may be used alone or in combination of two or more. The amount of the dispersant added in the invention is preferably 0.01 to 10 mmol, particularly preferably 0.1 to 5 mmol, per 1 g of carbon black. If the amount is less than 0.01 mmol, a satisfactory dispersing effect cannot be obtained because the amount of the dispersant adsorbed or reacted on the surface of the carbon black particles is small. On the other hand, if the addition amount is 1
If the amount is more than 0 mmol, a remarkable dispersing effect is difficult to appear.

As the aqueous medium used in the present invention, media containing various aqueous solvents and resins can be used. Here, the aqueous medium refers to water or a mixed solution of an organic solvent compatible with water. Such organic solvents include, for example, lower alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, N, N-dimethylformamide,
Examples thereof include, but are not limited to, amides such as dimethylacetamide, ketones such as acetone and diacetone alcohol, ethers such as tetrahydrofuran and dioxane, and N-methyl-2-pyrrolidone. These aqueous solvents may be used alone or in combination of two or more.

Examples of the resin include acrylic resins, urethane resins, polyoxyalkylene resins, vinyl resins, epoxy resins, amino resins, polyvinyl acetal resins, polyvinyl butyral resins, styrene resins, and phenoxy resins commonly used for water-based paints. Water-soluble or water-dispersible resins such as resins and polyester resins can be mentioned, and these can be used alone or as a mixture of two or more. These resins are not particularly limited in form such as an aqueous solution type and an emulsion type. Further, a dispersant such as a surfactant for the purpose of improving dispersibility or dispersion stability,
Various additives such as an antifoaming agent and a preservative may be used.

The aqueous carbon black dispersion of the present invention comprises:
It is obtained by mixing and stirring carbon black, a dispersant represented by the general formula (1), and an aqueous medium. The method of mixing and stirring is not particularly limited, but it is preferable to finely disperse carbon black in an aqueous medium containing a dispersant by using a pulverizer or a disperser by shearing stress or impact force of the medium. As such a crusher or disperser,
A three-roll mill or two-roll mill for finely dispersing carbon black particles by shear stress, a ball mill, an attritor for finely dispersing carbon black particles by impact force of media such as glass beads and zirconia beads,
Disperser, homogenizer, CLEARMIX (registered by M Technic Co., Ltd.) Trademark), kneaders, extruders, jet mills, etc., which disperse finely by the collision force or shear force between carbon black particles or between carbon black particles and the vehicle or disperser, and ultrasonic dispersers, which disperse finely by ultrasonic waves Can be mentioned. Heat treatment may be performed during or before and after the step of mixing and stirring the carbon black, the dispersant, and the aqueous medium. The temperature of the heat treatment is not particularly limited.
C. is preferred.

The aqueous carbon black dispersion of the present invention comprises:
The amino group of the dispersant adsorbs to the functional group on the surface of the carbon black particle by an acid-base interaction. In particular, regarding the primary amino group (—NH ₂ ), in addition to the acid-base interaction, a quinone group (> C ＝ O) and an azomethine bond (> C ＝ N—)
To form In any case, it is considered that the dispersibility in the aqueous medium is improved by the coordination of the sulfonic acid (salt) group portion of the dispersant on the surface of the carbon black particles. The mechanism of action of the dispersant in the present invention is estimated as follows. The amino group of the dispersant forms a salt with a functional group on the surface of the carbon black particles or forms an azomethine bond. The sulfonic acid (salt) group portion of the dispersant contributes to dispersibility in an aqueous medium. As shown in the following general formulas (2) and (3), the hydroxyl group forms a hydrogen bond with the nitrogen atom of the amino group to thermodynamically stabilize the carbon black and the salt-forming product of the surface treating agent or the azomethine bond. This is considered to have a function of firmly binding the carbon black and the dispersant.

General formula (2)

[0021]

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Wherein R ¹ , R ² , M, m and n have the same meaning as described above. General formula (3)

[0023]

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[Wherein, M, m and n represent the same meaning as described above. That is, the most important point in the molecular structure of the dispersant in the present invention is that an amino group and a hydroxyl group are substituted at the peri-position of the naphthalene ring. Thereby, it is considered that the dispersant can be strongly adsorbed or chemically bonded to the carbon black particle surface. Therefore, α-naphthol in which an amino group is substituted at the peri position of the hydroxyl group of α-naphthol
-Mono- to tri-sulfonic acids (salts) have an excellent dispersing effect, even if there are other substituents at other positions on the naphthalene ring. It does not go beyond the category of forming a six-membered ring structure. That is, although the hydrogen bonding force on the six-membered ring may be somewhat enhanced electronically, this is not an essential point and is included on the same line.

By the action mechanism described above, the aqueous carbon black dispersion of the present invention has excellent dispersion stability,
A highly jet-black, high-gloss, high-density coating film can be obtained. The aqueous carbon black dispersion of the present invention can be used in a wide range of fields such as printing inks, paints, cosmetics, writing inks, toners, electrophotographic materials, recording materials such as ink jets, and colorants such as plastics. .

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to embodiments. In the example,
“Parts” and “%” are “parts by weight” and “% by weight”, respectively. The amount of each surface functional group of the carbon black used in the examples was measured by the following method, and they were summed to obtain the total amount of surface functional groups. The results are shown in Table 1. (1) Measurement of Carboxyl Group (—COOH) Amount 1 g of dry carbon black was weighed in units of 1 mg, and 0.1 g was measured.
The reaction was carried out by shaking for 4 hours in 50 ml of a 1N aqueous sodium hydrogen carbonate solution, followed by filtration, and the supernatant of the filtrate was 20 m
1 is collected and titrated with a 0.01 N hydrochloric acid aqueous solution. The amount of carboxyl group was determined as a milliequivalent (meq./g) in 1 g of carbon black according to the following formula. Carboxyl group amount = (50/20 × 0.01 × (titration−empty titration)) / carbon black sample weight (2) Measurement of hydroxyl group (—OH) amount
The reaction was carried out by shaking for 4 hours in 50 ml of a 1N aqueous sodium hydroxide solution, followed by filtration, and 20 ml of the supernatant of the filtrate.
And titrated with a 0.01 N aqueous hydrochloric acid solution. From this, the total amount of the hydroxyl group amount and the carboxyl group amount was determined as the milliequivalent (meq./g) in 1 g of carbon black according to the following equation. (Carboxyl group + hydroxyl group) amount = (50/20 × 0.01 × (titration-empty titration)) / carbon black sample weight The amount of carboxyl groups previously determined was subtracted from the total amount to determine the amount of hydroxyl groups. (3) Quinone group (> C = O) amount 3 g of dry carbon black was weighed in 1 mg unit, and 100 mg of sodium borohydride dissolved in 0.1N aqueous sodium hydroxide solution was reacted for 2 hours in 50 ml. Thereafter, the amount of hydrogen gas generated when a 6N aqueous sulfuric acid solution is added is measured. A blank test is also performed to determine the amount of hydrogen gas generated. The quinone group content was determined as the milliequivalent (meq./g) in 1 g of carbon black according to the following formula. Quinone group content = reacted sodium borohydride content / carbon black sample weight

[0027]

[Table 1]

The carbon black aqueous dispersions obtained in the examples were evaluated by the following methods.
The viscosity of the dispersion was measured with an ultrasonic viscometer (VM-1A-L, manufactured by Yamaichi Electric Co., Ltd.). The particle size distribution was measured with a laser particle size analyzer (MICROTRAC UPA, manufactured by Nikkiso Co., Ltd.) to determine the average particle size. Further, the state of the sediment in the dispersion when the dispersion was aged at 50 ° C. for one week was examined and evaluated by ○ × △. ○ indicates no precipitate. △ indicates slight precipitation. X indicates that there is a large amount of precipitate. The evaluation results are shown in Table 2.

Example 1 Zirconia beads were added to a composition comprising 20.0 parts of carbon black A, 6.0 parts of ammonium 1-amino-8-hydroxynaphthalene-4-sulfonate, and 74.0 parts of purified water. The mixture was dispersed for 90 minutes using a paint shaker (manufactured by Red Devil Co.) and heat-treated at 70 ° C. for 2 hours to obtain an aqueous carbon black dispersion. Example 2 Zirconia beads were added to a composition consisting of 20.0 parts of carbon black A, 4.0 parts of 1-amino-8-hydroxynaphthalene-3, 6-disulfonate disodium salt and 76.0 parts of purified water, The mixture was dispersed for 90 minutes using a paint shaker (manufactured by Red Devil Co.) to obtain an aqueous carbon black dispersion.

EXAMPLE 3 Zirconia beads were added to a composition comprising 20.0 parts of carbon black A, 4.0 parts of 1-amino-8-hydroxynaphthalene-2,4-disulfonate disodium salt and 76.0 parts of purified water. Was added, and the mixture was dispersed in a paint shaker (manufactured by Red Devil Co.) for 90 minutes, and heat-treated at 50 ° C. for 4 hours to obtain an aqueous carbon black dispersion. Example 4 20.0 parts of carbon black B, 1-amino-8-hydroxynaphthalene-4-sulfonic acid potassium salt 6.5
Zirconia beads were added to a composition composed of 94.4 parts of purified water and 94.4 parts of purified water, and dispersed with a paint shaker for 90 minutes to obtain an aqueous carbon black dispersion.

Example 5 Zirconia beads were added to a composition comprising 20.0 parts of carbon black C, 5.6 parts of ammonium 1-amino-8-hydroxynaphthalene-4-sulfonate, and 74.4 parts of purified water. Disperse with a paint shaker for 90 minutes,
Heat treatment was performed at 50 ° C. for 4 hours to obtain an aqueous carbon black dispersion. Comparative Example 1 Zirconia beads were added to a composition consisting of 20.0 parts of carbon black A and 80.0 parts of purified water, and dispersed with a paint shaker for 90 minutes to obtain an aqueous carbon black dispersion.

Comparative Example 2 Zirconia beads were added to a composition consisting of 20.0 parts of carbon black B and 80.0 parts of purified water, and dispersed with a paint shaker for 90 minutes to obtain an aqueous carbon black dispersion. Comparative Example 3 Zirconia beads were added to a composition consisting of 20.0 parts of carbon black C and 80.0 parts of purified water, and dispersed with a paint shaker for 90 minutes to obtain an aqueous carbon black dispersion.

Comparing Examples 1 and 2 with Comparative Example 1, it can be seen that Examples using the dispersant of the present invention have significantly improved dispersibility and dispersion stability of carbon black. Similar effects can be confirmed by comparing Examples 3 and 4 with Comparative Example 2, or comparing Example 5 with Comparative Example 3.

[0034]

[Table 2]

[0035]

According to the aqueous carbon black dispersion of the present invention, the amino group in the dispersant is adsorbed or chemically bonded to the functional group on the surface of the carbon black particles, and the carbon black and the dispersant are further acted on by the action of the hydroxyl group in the dispersant. The carbon black and the dispersant are firmly bonded by thermodynamically stabilizing the salt form or azomethine bond of
The coordination of the sulfonic acid (salt) group portion on the surface of the carbon black particles could provide excellent dispersibility in an aqueous medium.

 ──────────────────────────────────────────────────続 き Continued on front page F-term (reference) 4J002 BC001 BE061 BF001 BG001 BG021 CC131 CD001 CF001 CH001 CH071 CK021 DA036 EV237 EV257 FD016 HA06 HA07 4J037 AA02 CB04 CB07 CB08 CB16 CB17 CB19 CB21 CC00 DD05 EE28 DD24 DD30

Claims (2)

[Claims] 1. An aqueous carbon black dispersion comprising: carbon black; an aqueous medium; and a dispersant represented by the following general formula (1). General formula (1) [Wherein, R ¹ and R ² each represent a hydrogen atom or a carbon atom 1
Represents an alkyl group of ¹ to 4 (R ¹ and R ² may form a ring together), M represents a hydrogen atom, an alkali metal atom, ammonium or an amine, and m and n represent 0 to 3
And 1 ≦ m + n ≦ 3. ] 2. The aqueous dispersion of carbon black according to claim 1, wherein the total surface functional group content of the carbon black is 0.2 meq / g or more.