JP2000017187A - Aqueous carbon black dispersion and aqueous ink using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous pigment-dispersed ink exhibiting excellent dispersion stability, capable of inhibiting the clogging of nozzles and pen tips and useful for ink jet printers, writing tools, etc., by limiting the surface zeta potential of the dispersed pigment below a specific value. SOLUTION: This aqueous ink contains (A) a pigment and (B) an aqueous medium. Therein, the component A dispersed at pH 3 has a surface zeta potential of <0 mV. The aqueous ink preferably has pH 5-10 and a component B content of 0.5-50 wt.%. The component B is preferably subjected to an ozone oxidation treatment in the presence of water, and has total acidic groups of >=3 μequ/m2, an active hydrogen content of <=2 mmol/g, a particle diameter of 10-30 nm and a DBP oil absorption volume of 50-180 cc/100 g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carbon black, which is preferably used as a pigment for inks for ink jet and writing inks, an aqueous dispersion containing carbon black in an aqueous medium, and an aqueous ink.

[0002]

2. Description of the Related Art Ink-jet recording has characteristics such as low noise during recording, color printing, high-speed printing, printing on plain paper and high quality. It is widely used for computer printing, regardless of the type. There are various types of this ink jet printing, a method of discharging ink in thin nozzles in the print head by electrostatic energy, and a method of flowing a current to a tropical zone in the print head and generating bubbles by generating heat. A method of performing printing by ejecting ink from a nozzle.

[0003] As an ink used for such an ink jet recording, an aqueous ink in which a dye is dissolved or dispersed in water has conventionally been used. Such water-based inks are also used for writing instruments such as fountain pens and ballpoint pens. The performance required for the recording ink used in these applications includes the following items.

[0004] (1) No bleeding of printed or written matter (2) No fading of printed or written matter due to light or heat (3) Even if left for a long time, the nozzle or pen tip in the recording head No clogging (4) Good storage stability (5) Low ink viscosity

[0005] As described above, conventionally, inks for these uses have been used in which a dye is dissolved or dispersed in water as a colorant. However, when a dye is used, bleeding tends to appear on printed or written matter. Due to the problem of fading due to light, inks using carbon black as a black pigment have recently attracted attention.

[0006]

However, when this carbon black is used as a pigment for ink, the dispersibility of the carbon black in water is poor because the surface of the carbon black is lipophilic, so that the carbon black cannot be used in a nozzle or a pen tip. The carbon black becomes clogged with eyes and aggregates during storage, making it unusable. For this reason, it is necessary to add various dispersants. Here, as the dispersant, a dispersant containing both a lipophilic group that is familiar with carbon black and a hydrophilic group that is familiar with water in the molecule, specifically, mainly a resin dispersant, It is used to improve dispersibility or dispersion stability.

However, since such a resin dispersant is expected to have its effect by binding to the surface of carbon black, a dispersing effect cannot be obtained unless it is added in an amount larger than the amount capable of binding to the surface of carbon black. For this reason, an extra dispersant remains in the liquid, and when the ink at the nozzle or the pen tip dries, it becomes a solid with poor resolubility and causes clogging. In addition, the addition of the dispersant increases the viscosity of the ink, which causes a problem that stable ink ejection properties cannot be obtained. The present invention solves the above-mentioned problems in the prior art, and provides a pigment and an ink for water-based ink having excellent dispersion stability, suppressing occurrence of clogging at a nozzle or a pen tip, and having excellent ejection stability. With the goal.

[0008]

Means for Solving the Problems The present inventor has proposed that an oxidized carbon black obtained by oxidizing carbon black by a specific method can be used to provide a water dispersion of carbon black having extremely excellent dispersion stability. Heading reached the present invention. It has been surprisingly found that such a simple operation makes it possible to obtain carbon black having extremely good water dispersibility. That is, the present invention

(1) A water-based ink containing at least a pigment and an aqueous medium, wherein at a pH of 3, the zeta potential of the surface of the dispersed pigment is less than 0 mV; An aqueous carbon black dispersion containing black and an aqueous medium, wherein the zeta potential of the carbon black surface at pH 3 is less than 0 mV,
(3) A carbon black aqueous dispersion containing at least carbon black and an aqueous medium, wherein the zeta potential of the carbon black surface at pH 7 is −15 m
(4) an aqueous carbon black dispersion containing at least carbon black and an aqueous medium and containing no dispersant,
When the zeta potential on the surface of carbon black is 3
(5) an aqueous dispersion of carbon black having a zeta potential of −15 mV or less when the pH of the carbon black is less than mV and a pH of 7, and (5) containing no dispersant. An aqueous dispersion of carbon black,

(6) The concentration of carbon black is 5% by weight.
(2) The aqueous dispersion of carbon black according to any one of (2) to (5);
is μequ / m ² or more (2) to any of the carbon black aqueous dispersion of (6), (8) an active hydrogen content of carbon black is not more than 2.0 mmol / g (2) - (7) (9) The carbon black aqueous dispersion according to any of (2) to (8), wherein the carbon black has been oxidized in the presence of water. The carbon black aqueous dispersion according to the above (9), wherein the treatment is performed using ozone;

(11) The above (2) wherein the pH is 5 to 10.
An aqueous dispersion of carbon black according to any one of (1) to (10),
(12) The aqueous dispersion according to any of (2) to (11) above, wherein the carbon black has a particle size of 10 to 30 nm and a DBP oil absorption of 50 to 180 cc / 100 g. 0.5 black content
(2) to (1)
2) The aqueous dispersion of carbon black according to any one of (1)
4) an aqueous ink using the aqueous carbon black dispersion described in any of the above (2) to (13); (15) an aqueous ink according to the above (1) or (14), which is an inkjet ink; Disperse carbon black in water, p
H3, a carbon black having a zeta potential of less than 0 mV as an aqueous dispersion having a carbon black concentration of 5% by weight in the liquid;

(17) Dispersing carbon black in water,
When an aqueous dispersion having a pH of 7 and a carbon black concentration of 5% by weight in the liquid was prepared, carbon black having a zeta potential of −15 mV or less, (18) carbon black was dispersed in water, and the carbon black concentration in the liquid was 5%. When an aqueous dispersion of weight% is used, carbon black having a pH of less than 0 mV at pH 3 and -15 mV or less at pH 7 and (19) carbon black are dispersed in water, and the carbon black concentration in the liquid at pH 3 is 5% by weight. A carbon black having a zeta potential of less than 0 mV when the aqueous dispersion is a dispersion containing no dispersant;

(20) Dispersing carbon black in water,
When an aqueous dispersion having a pH of 7 and a carbon black concentration of 5% by weight in the liquid and containing no dispersant is used, a carbon black having a zeta potential of -15 mV or less, and (21) carbon black in water When an aqueous dispersion containing 5% by weight of carbon black in the dispersion and containing no dispersant was dispersed, the dispersion was adjusted to pH 3
Is less than 0 mV and the pH of the dispersion is 7
A carbon black having a zeta potential of −15 mV or less when

(22) an aqueous dispersion obtained by dispersing the carbon black of any of the above (16) to (21) in an aqueous medium; (23) an aqueous ink using the aqueous dispersion of the above (22); (24) The above (1), (14) or (1)
5) an ink absorber impregnated with the water-based ink, (25)
An ink tank containing the ink absorber of the above (24),
(26) An ink cartridge having the ink tank of (25), (27) for ink jet recording for recording a color image on a recording material using two or more colors of ink including at least black ink and color ink. In the ink set, (1)
6) to (21), wherein the color ink includes at least a colorant and a surfactant, and the color ink includes at least a colorant and a surfactant. An ink set for inkjet recording, wherein the polarity of the color material contained in the at least one color ink is opposite to that of the black ink.

(28) In an ink jet recording method for recording on a recording material by discharging ink droplets from an orifice according to a recording signal, the ink is the ink set described in (27) above. 29. A method according to claim 29, wherein the ink is the ink set according to claim 27, in a recording unit including an ink storage unit storing the ink and a head unit for discharging the ink as ink droplets. Recording unit,
(30) An ink cartridge provided with an ink containing section containing ink, wherein the ink set described in (27) is provided, and (31) the ink cartridge described in (26) or (30) is provided. Inkjet recording method used,

(32) an ink containing section containing the ink,
An ink jet recording apparatus comprising a recording unit having a head unit for discharging the ink as ink droplets, wherein the ink is the ink set of the above (27), (33) the ink cartridge of the above (31) And an inkjet recording device using the same.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION First, carbon black used in the present invention is not particularly limited, and any carbon black can be used, including carbon black conventionally used as an ink pigment. Oxidized carbon black is preferred, in which an acidic functional group is imparted to the surface by a surface treatment, particularly an oxidation treatment, so that the surface can be dispersed in an aqueous medium without the presence of a dispersant.

The particle size of the carbon black is not limited, but is preferably 100 nm or less, more preferably 30 nm or less, because the sedimentation of the particles is particularly suppressed. This means that the particle size of carbon black is generally 10 in the furnace method.
Can be manufactured in the range of
When the oil absorption is 100 cc / 100 g or more, the particle size hardly affects the print density, and a high print density can be obtained.

The particle diameter is preferably 100 nm or less, particularly preferably 30 nm or less, because the sedimentation of particles is particularly suppressed, and the particle diameter is preferably 30 nm or less in terms of storage stability, ejection stability and print density. Preferred particle size is 20 nm
It is as follows. Among them, those having a size of 18 nm or less, particularly 15 nm or less are most suitable. The primary particle diameter is measured by an arithmetic mean diameter calculation method using an electron microscope. Further, although the specific surface area is also varied raw carbon black and slightly usually 20 to 500 m ² / g, inter alia 100~450m ² / g
Becomes

The DBP oil absorption of carbon black is not particularly limited. In particular, carbon black having a specific range of DBP oil absorption and acidic functional groups has a high print density when used as an aqueous dispersion, and has a high dispersibility and a high nozzle density. And can provide a water-based ink with excellent ejection stability, and can be used not only when printing on special paper but also when printing on plain paper. A high-performance carbon black capable of obtaining a print density and an aqueous ink using the same can be obtained.

That is, the DBP oil absorption is 95 cc / 10
Furnace carbon black having 0 g or more and all acidic groups of 500 μequ / g or more. As a method for producing carbon black having a high DBP oil absorption, besides the furnace method, there are a channel method, a roller method, and an acetylene method. In the channel method and the roller method, however, the yield of the product relative to the raw material is low. Impurities are concentrated,
In particular, sulfur is converted to sulfuric acid by oxidation, and only those having poor dispersibility can be obtained. In addition, carbon black obtained by the acetylene method has a high crystallinity of the carbon black, has a small number of active sites where an oxidizing agent reacts, and is not preferable because oxidation does not proceed sufficiently. Therefore, the DBP oil absorption obtained by the furnace method is 95 cc. / 100g or more and all acidic groups are 500μequ
/ G or more of carbon black is particularly preferred for the above purpose.

The higher the DBP oil absorption, the higher the print density when used as an aqueous dispersion and used as an ink. On the other hand, the higher the DBP oil absorption, the higher the viscosity of the resulting aqueous ink. Therefore, the DBP oil absorption is 95 cc /
100 g or more, preferably 100 cc / 100 g or more,
More preferably, 120 to 200 cc / 100 g, especially 120 to 180 cc / 100 g, particularly 140 to 180 c
c / 100 g is optimal. Also, as the oil absorption, the structure formed by weak bonding was removed.
Measurement of 4M4 oil absorption is also commonly used as a characteristic of carbon black, but DBP oil absorption is 120 cc.
/ 100 g or more, 5 to 50 cc /
The value is about 100 g lower. The 24M4 oil absorption is usually 90 cc / g or more, more preferably 1 cc / g or more.
10 cc / g or more.

These DBP oil absorptions and 24M4DBP
The measurement of the oil absorption is based on JIS K-6221.

Further, sulfur and sulfur compounds in carbon black are oxidized by an oxidizing agent to form sulfate ions in a solution. According to the study of the present inventor, sulfate ions cause re-aggregation in a carbon black dispersion. It was found to be involved. For this reason, the sulfur content in carbon black is as low as possible.
It is desired that the amount is small, but it is preferably 0.5% by weight, preferably 0.1% by weight or less in total sulfur analysis value. In order to reduce the sulfur content, it is possible to use an aromatic hydrocarbon used as a raw material for carbon black, a liquid hydrocarbon used as a fuel, or a low hydrocarbon content gaseous hydrocarbon as a gaseous hydrocarbon. The amount of sulfur in carbon black can be determined, for example, by precisely weighing 0.1 g of carbon black and using "SUL"
MHOGRAPH12A ".

It has been strongly inferred by the present inventors that the halogen ions and nitrate ions in the carbon black are also involved in the re-aggregation. Most of the halogen ions are mainly chloride ions, but it is thought to be derived from cooling water that stops the reaction during carbon black production,
By using pure water as water used as cooling water, halogen ions contained in carbon black can be reduced. In addition, nitrate ions are NOx generated in the combustion gas used when producing carbon black.
It is thought to be derived from Extreme reduction of NOx in the combustion gas is difficult with current technology, so it is desirable to appropriately remove it by ion exchange or the like after the preparation of the dispersion. Halogen ions are TOX-1 manufactured by Mitsubishi Chemical Corporation.
It is possible to measure at 50.

The content of these impurities is preferably 25 ppm or less, more preferably 10 ppm, for sulfate ions.
Or less, more preferably 5 ppm or less. Halogen ions are preferably at most 20 ppm, particularly preferably 10 ppm.
ppm or less, more preferably 5 ppm or less. The total amount of sulfate, halogen and nitrate ions is
Preferably 50 ppm or less, particularly preferably 30 ppm
Or less, more preferably 10 ppm or less. The concentration of these ions in the dispersion can be easily measured by an ion chromatogram, and the following conditions can be used. Ion chromatogram apparatus DX-AQ column made by DIONEX AG12A, AS12A Eluent 2.7 mM Na2CO3-0.3 mM NaHCO3 Sample solution volume 200 μl

If both the cation exchange resin and the anion exchange resin are packed and ion exchanged, not only these anions but also cations can be further removed, which is effective for dispersion stability. When such an ion removal treatment is performed, the pH of the dispersion becomes low, and the pH in the liquid usually becomes 1 to 3. Such an aqueous dispersion has good dispersion stability when left at room temperature, but immediately agglomerates when left at 60 ° C., so that an alkali such as NaOH or amines is added to the aqueous dispersion to adjust the pH from 5 to 5. It is desirable to adjust to 10.
Even when the pH is 10 or more, the dispersion stability at 60 ° C. is poor.

The following method is particularly preferable as a method for oxidizing carbon black. That is, after suspending carbon black in water, oxidation is performed by reacting with an oxidizing agent. The amount of water is 95:
5 to 0.5: 99.5 is suitable, more preferably 5
0:50 to 2:98, more preferably 20:80 to
A range of 5:95 is preferred.

The oxidizing agent is not particularly limited as long as it increases the number of acidic functional groups in the carbon black. In general, it is preferable that the oxidizing agent does not remain in water after the oxidizing agent is oxidized. It is preferably used. Specifically, carbon black can be oxidized through ozone and / or an ozone-containing gas. Here, the oxidant, ozone, can be generated by an ozone generator. This ozone generator generally generates ozone by discharging in air or oxygen, but it can also be generated by electrolyzing water. As the generator for generating ozone used in the present invention, any generator can be used irrespective of the system. However, a higher ozone generation concentration is preferable because the reaction efficiency of oxidation of carbon black is higher. Generally, generators for generating an ozone-containing gas having an ozone concentration of 1 to 20% by weight are commercially available, and these are sufficient.

As described above, the carbon black is oxidized with ozone in the presence of water, and the total amount of acidic groups on the surface of the carbon black becomes a specific amount, or the active hydrogen content becomes a specific amount, as described later. By oxidizing to the extent possible, carbon black having particularly good dispersibility in an aqueous medium can be obtained. Most preferably, by oxidizing both the amount of total acidic groups and the content of active hydrogen within the ranges described below, the dispersibility in the aqueous medium becomes very good. The mechanism by which such a simple operation provides oxidized carbon black with excellent properties is not clear, but if water is present on the surface of the carbon black, the ozone does not directly react with the surface of the carbon black. It is also conceivable that, by dissolving in water and reacting with water molecules, the resulting functional groups also have good compatibility with water and exhibit dispersion stability.

For these reasons, even when compared with carbon black which has been oxidized by ozone oxidation in the gas phase to a level having all the same acidic groups, the oxidization treatment which has greatly improved dispersibility in water has been carried out. It is supposed that carbon black exerts an unexpected effect. The carbon black to be subjected to the above-described oxidation treatment with ozone in the presence of water does not need to be oxidized in advance, but prior to oxidation in the presence of water, the carbon black is treated with conventionally known nitric acid or gas-phase ozone. The oxidized carbon black may be subjected to the oxidation treatment by the above method.

By the above-described oxidation treatment with ozone in the presence of water, all the acidic groups of carbon black are reduced to 3 μeq.
It is desirable to carry out the oxidation treatment until it becomes u / m ² or more. The amount of all acidic groups can be determined as the amount reacted with a strong alkali such as NaOH or KOH. The method for obtaining the total acidic group is as follows. The oxidized carbon black is filtered through a 0.1 micron membrane filter to separate it from water. The separated carbon black is dried all day and night with a dryer at 60 ° C., and then pulverized in an agate mortar. The carbon black after drying is used in 0.1 g.
Take 2 to 0.5 g, place in a Erlenmeyer flask containing 60 cc of 0.01 N NaOH, and flush nitrogen into the Erlenmeyer flask.
The mixture is stirred for 6 hours to react. The reaction product is filtered again using a 0.1 micron membrane filter to obtain a filtrate.

Take 40 cc of this filtrate and add 0.025N
Titration with an automatic neutralization titrator using hydrochloric acid
Determine the OH concentration. The total acidic group of carbon black can be determined by the following calculation.

[0034]

(Equation 1)

If the total acidic group content is less than 3 μequ / m ² , dispersion in an aqueous medium may be difficult. If it is more preferably at least 6 μequ / m ² , the dispersibility in an aqueous medium will be very good. It is preferable to use carbon black having an active hydrogen content of 2.0 mmol / g or less, particularly preferably 1.5 mmol / g or less.

It has been surprisingly found that carbon black having an active hydrogen content of not more than a specific amount is particularly excellent in dispersibility in an aqueous medium and can provide an aqueous dispersion of carbon black having excellent dispersion stability. The inventor has found. Conventionally,
For example, as in the method described in JP-A-8-3498, it has been considered that the acid treatment increases the number of acidic functional groups on the surface of carbon black due to the oxidation treatment, which leads to hydrophilicity and simply contributes to stability in an aqueous medium. It seems. On the other hand, the present inventors surprisingly found that the functional group imparted by the oxidation treatment is detected as a total acidic group, but is not necessarily linked to an increase in the functional group detected as the active hydrogen content. Further, carbon black having a high active hydrogen content is not always said to be excellent in dispersion in an aqueous medium, and increasing the active hydrogen content does not lead to improvement in dispersibility, but rather lowers. I found it. And the active hydrogen content is 2.0 mm
It was found that when an aqueous dispersion was prepared using carbon black of ol / g or less, the dispersibility of carbon black in an aqueous medium was particularly excellent.

The active hydrogen content is determined by the following method. The active hydrogen on the carbon black is exchanged for a methyl group by dropping a diethyl ether solution of diazomethane on the carbon black. Hydrogen iodide having a specific gravity of 1 is added to the carbon black thus treated, and heated to vaporize the methyl group as methyl iodide. This gas of methyl iodide is trapped by a silver nitrate solution and precipitated as methyl silver iodide. From the weight of the silver iodide, the amount of the original methyl group, that is, the amount of active hydrogen is measured.

When carbon black has been subjected to a treatment such as an oxidation treatment and contains a large amount of residual ions, for example, by treatment with sodium hypochlorite, desalting is performed.
An accurate active hydrogen content is obtained by performing a neutralization treatment. As a simple method of performing this desalting, a method of passing a carbon black dispersion through a column containing a cation exchange resin and an anion exchange resin can be used. By such a treatment, the cations associated with the functional groups can be removed, and the pH of the dispersion is acidic, so that the amount of active hydrogen contained in the carbon black can be accurately indicated. In such a pretreatment, the amount of cations in the carbon black is 1000 p.
pm or more. More specifically, a carbon black dispersion (if the carbon black is in a dry state, a dispersion obtained by once dispersing it in water)
After removing the cations through a column packed with a mixture of an anion exchange resin and a cation exchange resin, 0.1 g of the mixture was added.
The mixture is filtered through a 1 μm membrane filter to take out carbon black. 100 ° C
After drying all day and night in a dryer, pulverize in a mortar,
Get a sample. Take 1.0 g of this sample, place it in a flask containing an excess amount of hydrogen iodide solution, heat and boil to generate methyl iodide, transport the generated methyl iodide with nitrogen gas, and use a silver nitrate solution Collect and sediment. After the collected liquid is made acidic with nitric acid, the precipitate is collected by filtration through a membrane filter. After drying the precipitate at 50 ° C., the weight is measured to determine the amount of active hydrogen.

The carbon black is oxidized with ozone in the presence of water, and the carbon black is oxidized until the active hydrogen content on the surface of the carbon black becomes a specific amount or less as described later. Carbon black which exhibits excellent print density and high print density can be obtained. It has been found that when such an oxidation method is employed, the number of functional groups detected as active hydrogen content decreases and the number of acidic functional groups detected as total acidic groups increases, surprisingly. Although the mechanism by which the acidic functional groups contributing to the dispersibility in water are imparted in a well-balanced manner by such a simple oxidation treatment operation to obtain carbon black with excellent properties is not clear, it is presumed as follows. Carbon black is composed of particles obtained by subjecting a raw material hydrocarbon to thermal decomposition and carbonizing while dehydrogenating, and hydrogen that has not been dehydrogenated remains in the particles as active hydrogen. When this carbon black is oxidized with ozone in the presence of water, radicals are generated by the reaction of ozone and water, and a functional group that is compatible with water is generated by replacing active hydrogen, which is originally unfamiliar with water. It is considered that carbon black having good dispersibility in water can be obtained.

As described above, carbon black having a specific range of total acidic group content or carbon black having a specific range of active hydrogen content has good dispersion stability even in an aqueous medium containing no dispersant as described above. The mechanism for producing the surface functional group which exerts and contributes to its dispersion stability is presumed as described above. On the other hand, an attempt was made to elucidate the dispersion stabilizing mechanism of the carbon black, and the following facts were found. That is, when these carbon blacks were dispersed in water to form an aqueous dispersion having a pH of 3 and a carbon black concentration of 5% by weight in the liquid, the zeta potential was found to be less than 0 mV. Further, these carbon blacks are dispersed in water to have a pH of 7,
When an aqueous dispersion having a carbon black concentration of 5% by weight in the liquid is used, the zeta potential can be -15 mV or less. Further, when the pH of the dispersion liquid is 3, it can be less than 0 mV, and when the pH is 7, it can be -15 mV or less.

The zeta potential may be measured by using various kinds of zeta potential measuring devices such as, for example, Central Science “AP8000” (sonic attenuation method). As described above, the carbon black of the present invention can have a surface zeta potential within the above range without the presence of a dispersant. Here, the dispersant refers to a compound (including a polymer compound) having a function of reacting or adsorbing with the carbon black surface and dispersing the carbon black in an aqueous medium,
For example, an anionic substance, a cationic surfactant, and a polymer dispersant can be used. A specific example is disclosed in, for example, JP-A-8-14
3803 and the like.

When the carbon black of the present invention is used, the zeta potential of the carbon black aqueous dispersion in the aqueous carbon black dispersion can be reduced to less than 0 mV in a wide pH range without using these dispersants. That is, the zeta potential of the surface of the carbon black when the pH of the liquid is 3 is less than 0 mV. The zeta potential changes depending on the pH of the liquid. However, as the pH increases, the zeta potential decreases, that is, a negative value is obtained at pH 3. Therefore, as the pH increases, the absolute value of the zeta potential increases. . Although the mechanism by which the carbon black of the present invention has such properties is not clear, it probably exhibits a negative zeta potential even at a low PH due to the formation of a functional group having a high degree of dissociation due to oxidation in water. It is considered something.

Regarding the zeta potential on the surface of the pigment in the pigment-dispersed recording liquid, the pH of the recording liquid is unknown in JP-A-10-46076, but the zeta potential is-.
34.8 mV, -35.1 mV, -41.9 mV, -4
6.4 mV, of which -34.8 mV, -3
It is said that a 5.1 mV zeta potential having an absolute value of 38 mV or more is preferable because the pigment has sedimentation when left at 50 ° C. for 100 hours and has poor storage stability. However, the aqueous dispersion of the present invention maintains a stable dispersion state for a long time even if the absolute value of the zeta potential is less than 38 mV. The reason is probably as follows. First, repulsion due to steric hindrance and electrical repulsion are thought to affect the pigment dispersion state (Surface Coatings International 1997 (9) p.414-42).
0). In other words, the total repulsive force between the particles must be considered in the dispersion stability of the particles, and the larger the absolute value of the zeta potential in a specific state is, the better the dispersion stability is. That is not to say. Further, the aqueous carbon black dispersion of the present invention can maintain a negative zeta potential in a wide pH range. Therefore, it is presumed that aggregation due to a change in pH is suppressed and dispersion stability is good.

Further, in the aqueous dispersion of the present invention, the surface of the carbon black, which is a pigment, can be maintained at the zeta potential as described above without the presence of a dispersant. Will be resolved.

By mixing a polar solvent with the aqueous dispersion prepared as described above, an aqueous ink having excellent performance can be obtained. Here, the aqueous carbon black dispersion refers to a dispersion of carbon black in water or a mixture of water and a water-soluble solvent. Specific examples of the polar solvent include lower alcohols such as ethanol and isopropanol; glycol solvents such as glycerin, diethylene glycol and polyethylene glycol;
Representative examples include N-containing solvents such as -methylpyrrolidone and 2-pyrrolidone and urea.

The concentration of the oxidized carbon black in the aqueous dispersion may be appropriately selected according to the application, but is preferably 0.5 to 50% by weight, particularly preferably 0.5 to 20% by weight. Preferably, it is a black aqueous dispersion. In this range, the printing density of the ink is good, and the viscosity of the ink is suppressed, so that an ink having excellent characteristics can be obtained. The aqueous carbon black dispersion thus obtained can be used as an aqueous ink by adding various additives such as adding a dispersant as needed when the concentration of carbon black exceeds 20 wt%, for example. If necessary, concentrate and dry,
Thereafter, it can be separately diluted and used as an ink. In this case, carbon black may be added to water, and a dispersion treatment using a bead mill, a ball mill, an impact disperser or the like may be used.

Examples of additives for forming an ink include a penetrating agent, a fixing agent, a fungicide and the like. Examples of the penetrant include nonionic surfactants such as polyoxyethylene alkylaryl ether, anionic surfactants such as alkylbenzene sulfonate, and fluorine surfactants.
Diethylene glycol monobutyl ether and the like can be used. As the fixing agent, in addition to water-soluble resins (nonionic water-soluble resins such as polyvinyl alcohol and polyacrylamide, anionic water-soluble resins such as polyacrylic acid and styrene / acrylic water-soluble resins), aqueous emulsions can also be used. . In general, when used as an inkjet ink, a carbon black concentration of 1 to 20% by weight, preferably 5 to 10% by weight is used. When used as an inkjet ink, it is desirable to adjust the pH to 7 to 10 before use.

The aqueous ink of the present invention thus obtained is
Droplet stability, ejection stability for a long time, ejection stability after a long pause, storage stability, fixability to recording material, weather resistance of recorded images required for inkjet inks Both sexes are balanced. Therefore, it is possible to impregnate the ink absorber with the aqueous ink of the present invention, store the ink absorber in an ink tank, and obtain an ink cartridge having the ink tank.

Since the aqueous ink of the present invention can be free of a dispersant, problems with the use of the dispersant, such as deterioration of print quality such as reduction in print density and occurrence of bleeding, can be suppressed. Can be Therefore, for example, in an ink jet recording ink set for recording a color image on a recording material using at least two inks of a black ink and a color ink, the black ink contains the carbon black of the present invention. Is, and, in the color ink, at least a colorant and a surfactant are included,
And, if the color ink contains at least a colorant and a surfactant, and the polarity of the colorant contained in at least one color ink is opposite to the black ink, This is preferable because bleeding during multicolor printing can be reduced.

Using such an ink set, ink-jet recording can be performed in which an ink droplet is ejected from an orifice in accordance with a recording signal to perform recording on a recording material.
Further, by using such an ink set, an ink storage section containing ink, and a recording unit including a head section for discharging the ink as ink droplets can be formed. It is possible to form an ink jet recording apparatus having an ink storage section containing ink, and a recording unit having a head section for discharging the ink as ink droplets, comprising an ink storage section containing such an ink set. Ink cartridge can be formed, ink jet recording can be performed using the ink cartridge, and an ink jet recording device can be formed using such an ink cartridge.

The formation of the ink set, the formation of the ink cartridge, and the ink jet recording method are described in, for example, JP-A-10-140063 and JP-A-10-14006.
Known techniques in this technical field, such as those described in Japanese Patent Publication No. 4 (KOKAI) No. 4 can be appropriately adopted.

[0052]

EXAMPLES The present invention will be described more specifically with reference to the following examples. In addition,% represents weight% unless otherwise specified. The zeta potential was measured using the “AP80” manufactured by Central Science.
00 "(sound attenuation method).

Example 1 Commercially available carbon black ("# 47" manufactured by Mitsubishi Chemical Corporation, particle size 23 nm, sulfur content 0.5%, chlorine content 220 ppm)
Was placed in 50 g of water and 500 cc of water, and dispersed with a household mixer for 5 minutes. The obtained liquid was put into a 3 liter glass container equipped with a stirrer. While stirring with an agitator, an ozone-containing gas having an ozone concentration of 10% by weight was supplied at 500 cc / min.
Time introduced. At this time, an ozone generator of an electric discharge generation type manufactured by PCI was used as an ozone generator, and ozone was generated using oxygen as a raw material.

The dispersion after the ozone treatment was taken out, and the pH was measured to be 2.3. (Measurement of pH is based on JIS
K6221. Also, the particle size distribution in this dispersion was measured with a Nikkiso Co., Ltd. Microtrac UPA.
of this solution, and using an optical microscope,
When the magnification was doubled, it was found that the whole was in micro-Brownian motion in a good dispersion state and the dispersibility was good.

Next, the carbon black was filtered through a micropore filter having a diameter of 0.1 μm, and the wet carbon black was dried at 60 ° C., and the total acid groups were measured. g. The nitrogen adsorption specific surface area was 120 m ² / g. Therefore, the total acidic groups per unit area is 4.00 μm.
equ / g. The active hydrogen content of the carbon black was measured and found to be 1.22 mmol / g. At this time, the filtrate obtained at the same time was directly subjected to ion chromatography to determine the amounts of sulfate ions, halogen ions, and nitrate ions in the solution. The sulfate ion concentration was 300 ppm, the chloride ion concentration was 30 ppm, and the nitrate ion concentration was 113 ppm. there were.

The dispersion 100c obtained by the above oxidation treatment
c into a beaker and 20 CC of an anion exchange resin (“SAN UP” manufactured by Mitsubishi Chemical Corporation) into the beaker.
After heating to 50 ° C., the mixture was stirred with a stirrer for 3 hours. Then, it was cooled to room temperature,
Centrifugation was performed for 30 minutes to remove the ion exchange resin and other foreign substances. A 0.1N NaOH solution was gradually added to the supernatant, the pH was adjusted to 3 and 7, and finally, ion-exchanged water was added so that the carbon black concentration became 5 wt%, and the zeta potential was measured. The zeta potential at this time was -15 mV and -23 mV, respectively. A 0.1N NaOH solution was added little by little to the supernatant after ion exchange to adjust the pH to 8. The dispersion diameter at this time is 75 nm
When the dispersion was observed with an optical microscope, it was found that the dispersibility was good. The sulfate ion concentration obtained from the liquid obtained by separating carbon black from the supernatant was 7%.
ppm, halogen ion is 3 ppm, nitrate ion is 10 ppm
ppm.

70 cc of the pH-adjusted dispersion was placed in a 100 cc bottle with a lid, and left in a dryer maintained at 60 ° C. Three months later, the bottle was taken out, and after cooling, the dispersion diameter was measured.
Also, good dispersion was confirmed by an optical microscope. On the other hand, this dispersion is packed into a cartridge manufactured by NEC Corporation
When printing was performed using a printer “PR101” manufactured by K.K., good printed matter without blurring or blurring was obtained.

Example 2 The same treatment was performed as in Example 1 except that the ozone reaction time was changed to 10 hours. The pH of the resulting dispersion is 2.2.
The average 50% dispersion diameter was 73 nm, and the total acidic groups per unit specific surface area was 7.5 μequ / m ² . The zeta potential of this dispersion, determined in the same manner as in Example 1, was pH
3, 7 were -23 mV and -29 mV, respectively. The sulfate ion concentration in this dispersion was 430 ppm. This dispersion was subjected to the same pretreatment as in Example 1 and left at 60 ° C. for 3 months. This dispersion also has a dispersion diameter of 7 as in Example 1.
The change was as small as 8 nm, and printing was performed by filling the ink into a cartridge manufactured by NEC Corporation. As a result, a good printed matter without bleeding or blurring was obtained. After the ion exchange treatment, the dispersion had a sulfate ion concentration of 7 ppm, a halogen ion of 1 ppm, and a nitrate ion of 0 ppm.

Comparative Example 1 Of the conditions in Example 1, only the ozone treatment time was 1 hour. When the zeta potential of this carbon black dispersion was measured in the same manner as in Example 1, it was +5 mV at pH 3 and p
It was -12 mV at H7. Printing was attempted on this dispersion in the same manner as in Example 1, but no ink was produced and printing was not possible.

As is clear from the above Examples and Comparative Examples, if the oxidation treatment is carried out in a state where water and carbon black coexist as described in the present application, the predetermined total acidity defined in the present invention can be obtained. It is possible to obtain a carbon black having a basic or active hydrogen content. If this carbon black is dispersed in an aqueous medium, its surface can be set to a specific zeta potential, and exhibits excellent dispersion stability.
Its industrial value is great.

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Claims (32)

[Claims] 1. An aqueous ink containing at least a pigment and an aqueous medium, wherein the zeta potential of the surface of the dispersed pigment at pH 3 is less than 0 mV. 2. An aqueous carbon black dispersion containing at least carbon black and an aqueous medium, wherein
When the zeta potential on the surface of carbon black is 3
An aqueous carbon black dispersion that is less than mV. 3. An aqueous dispersion of carbon black containing at least carbon black and an aqueous medium, wherein
When the zeta potential of the carbon black surface is set to −7,
An aqueous carbon black dispersion having a viscosity of 15 mV or less. 4. An aqueous carbon black dispersion containing at least carbon black and an aqueous medium, wherein
When the zeta potential on the surface of carbon black is 3
An aqueous carbon black dispersion having a zeta potential of −15 mV or less at a pH of less than 7 mV and a pH of 7. 5. The aqueous carbon black dispersion according to claim 2, which does not contain a dispersant. 6. The carbon black according to claim 1, wherein all the acidic groups are 3 μequ.
/ M ² or more, the aqueous carbon black dispersion according to any one of claims 2 to 5. 7. The carbon black having an active hydrogen content of 2.
The aqueous carbon black dispersion according to any one of claims 2 to 6, which is 0 mmol / g or less. 8. The aqueous carbon black dispersion according to claim 2, wherein the carbon black has been oxidized in the presence of water. 9. The carbon black aqueous dispersion according to claim 8, wherein the oxidation treatment is performed using ozone. 10. The aqueous carbon black dispersion according to claim 2, which has a pH of 5 to 10. 11. The carbon black having a particle size of 10 to 30.
nm and DBP oil absorption of 50-180cc / 100g
The aqueous dispersion according to any one of claims 2 to 10, wherein 12. A carbon black content of 0.5 to 5
The aqueous carbon black dispersion according to any one of claims 2 to 11, wherein the amount is 0% by weight. 13. An aqueous ink using the aqueous carbon black dispersion according to claim 2. Description: 14. An ink jet ink according to claim 1.
Or the aqueous ink according to 13. 15. A method of dispersing carbon black in water,
3. A carbon black having a zeta potential of less than 0 mV when an aqueous dispersion having a carbon black concentration of 5% by weight in the liquid is used. 16. Dispersing carbon black in water and adjusting the pH
7. A carbon black having a zeta potential of −15 mV or less when an aqueous dispersion having a carbon black concentration of 5% by weight in the liquid is used. 17. When carbon black is dispersed in water to form an aqueous dispersion having a carbon black concentration of 5% by weight, the pH is less than 0 mV at pH 3 and -15 mV at pH 7
The following carbon black. 18. A method of dispersing carbon black in water,
3. A carbon black having a zeta potential of less than 0 mV when an aqueous dispersion having a carbon black concentration of 5% by weight in the liquid and containing no dispersant. 19. A method of dispersing carbon black in water,
7. A carbon black having a zeta potential of -15 mV or less as an aqueous dispersion having a carbon black concentration of 5% by weight in the liquid and containing no dispersant. 20. When carbon black is dispersed in water to form an aqueous dispersion having a carbon black concentration of 5% by weight and containing no dispersant, the dispersion is adjusted to pH.
3, the zeta potential is less than 0 mV, and the pH of the dispersion is
A carbon black having a zeta potential of −15 mV or less when 7 is used. 21. An aqueous dispersion obtained by dispersing the carbon black according to any one of claims 16 to 20 in an aqueous medium. 22. An aqueous ink using the aqueous dispersion according to claim 21. 23. An ink absorber impregnated with the aqueous ink according to claim 1, 13 or 14. 24. An ink tank containing the ink absorber according to claim 23. 25. An ink cartridge having the ink tank according to claim 24. 26. An ink jet recording ink set for recording a color image on a recording material using two or more colors of ink including at least a black ink and a color ink, wherein the black ink comprises: 20
The carbon black according to any of the above, and, in the color ink, at least a colorant and a surfactant are included, and, in the color ink, at least a colorant and a surfactant are included, furthermore An ink set for ink-jet recording, wherein the polarity of the color material contained in one color ink is opposite to that of the black ink. 27. An ink jet recording method in which an ink droplet is ejected from an orifice according to a recording signal to perform recording on a recording material, wherein the ink is the ink set according to claim 26. . 28. A recording unit comprising an ink containing section containing ink and a head section for discharging the ink as ink droplets, wherein the ink is the ink set according to claim 26. Recording unit. 29. An ink cartridge provided with an ink storage portion for storing ink, wherein the ink set is the ink set according to claim 26. 30. An ink jet recording method using the ink cartridge according to claim 25. 31. An ink jet recording apparatus, comprising: a recording unit having an ink container containing ink and a head for discharging the ink as ink droplets, wherein the ink is an ink set according to claim 26. Recording device. 32. An apparatus for ink-jet recording using the ink cartridge according to claim 30.