JP2002348519A - Method for producing aqueous dispersion of pigment and water-based recording liquid produced by using the aqueous dispersion. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pigment dispersion having improved dispersion degree and low viscosity and effective for increasing the printing speed of an aqueous recording liquid for ink jet recording and improving the quality of printed image. SOLUTION: A mixture composed at least of a pigment and an aqueous medium is passed through a dispersion apparatus to obtain an aqueous dispersion of pigment for water-based recording liquid. In the above production process, the ratio of the total dispersion time to the sum of the average retention time of the mixture in the dispersion apparatus is set to >=2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aqueous pigment dispersion, and an aqueous recording liquid using the pigment dispersion produced by the method.

[0002]

2. Description of the Related Art Conventionally, dyes have been used as coloring materials in writing instruments such as felt-tip pens and water-based markers, and aqueous recording liquids such as inks for ink jet printers. Recording liquids using dyes are excellent in coloring power and sharpness, but have problems in light resistance, water resistance and the like.

To solve the problems of light fastness and water fastness,
In recent years, conversion of colorants from dyes to pigments has been actively studied in the application fields described above. The use of pigments as colorants in this field, especially in the field of ink-jet inks, requires very high levels of dispersibility and dispersion stability in solid-liquid two-phase pigment dispersions. As means for achieving such high dispersibility and dispersion stability, JP-A-9-151342 discloses
A microencapsulated pigment dispersion in which a pigment is coated with an anionic group-containing organic polymer compound is disclosed.

Japanese Patent Application Laid-Open No. H11-166145 discloses a dispersing apparatus suitable for obtaining an aqueous recording liquid for an ink jet printer which is hardly caused to increase in viscosity and particle size during storage and has excellent storage stability. Has been described.

[0005]

However, in order to increase the printing speed and the quality of the printed image, a pigment dispersion having higher dispersion and lower viscosity has been demanded.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, a method for producing an aqueous pigment dispersion by passing a mixture comprising at least a pigment and an aqueous medium through a dispersing apparatus. The aqueous pigment dispersion produced by a method characterized in that the ratio of the total dispersion time to the total sum of the average residence time of the mixture in the dispersing device is 2 or more, and has found that such requirements are satisfied. Thus, the present invention has been completed.

That is, the present invention provides a method for producing a specific aqueous pigment dispersion capable of producing a high-dispersion, low-viscosity aqueous pigment dispersion for solving the above-mentioned problems.

[0008]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, an aqueous pigment dispersion is obtained using a mixture comprising at least a pigment and an aqueous medium. Depending on the final use of the aqueous pigment dispersion, the mixture may be composed of only the pigment and the aqueous medium, but the reason is that the dispersion stability of the pigment is improved, and the fixability when used as an aqueous recording liquid is improved. Thus, an organic polymer compound containing an anionic group is preferably used in combination.

The anionic group-containing organic polymer compound used in the aqueous pigment dispersion of the present invention is not particularly limited as long as it has an anionic group. For example, a carboxyl group, a sulfone group, a phospho group, Anionic group-containing organic polymer compounds obtained by copolymerizing anionic group-containing monomers containing a thiocarboxyl group and other monomers that can be copolymerized with these anionic group-containing monomers can be mentioned. Considering availability, price, and the like, an anionic group-containing organic polymer compound containing a carboxyl group or a sulfone group is preferable, and a carboxyl group is preferred in that the coexistence range of an electrically neutral state and an anion state can be broadly controlled. Is particularly preferred.

Examples of the monomer having a carboxyl group include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid and 4-vinylbenzoic acid; vinyl succinate, maleic acid Polybasic acid unsaturated esters such as allyl, vinyl terephthalate, and allyl trimellitate are exemplified. Examples of monomers containing a sulfonic acid group include unsaturated sulfo-substituted alkyl or aryl esters such as 2-sulfoethyl acrylate and 4-sulfophenyl methacrylate; unsaturated sulfocarboxylic acids such as vinyl sulfosuccinate; Sulfostyrenes such as styrene-4-sulfonic acid; Examples of other monomers that can be copolymerized with the anionic group-containing monomer include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, and t-acrylate. Butyl, 2-ethylhexyl acrylate, n-octyl acrylate, dodecyl acrylate, octadecyl acrylate, cyclohexyl acrylate, isobornyl acrylate, benzyl acrylate, 2,3-epoxypropyl acrylate, 2,3-epoxy acrylate Butyl, 2,3-epoxycyclohexyl acrylate, vinyl acrylate,
Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, Octadecyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, benzyl methacrylate, 2,3-epoxypropyl methacrylate, 2,2-methacrylic acid
3-epoxybutyl, 2,3-epoxycyclohexyl methacrylate, vinyl methacrylate, dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl itaconate, benzyl itaconate, 2-hydroxyethyl acrylate, acrylic 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-aminoethyl acrylate, 2-aminopropyl acrylate, 3-aminopropyl acrylate, 2- (methylamino) ethyl acrylate 2- (methylamino) propyl acrylate, 2- (ethylamino) ethyl acrylate, 2- (ethylamino) propyl acrylate, 2- (dimethylamino) ethyl acrylate, 3- (dimethylamino) propyl acrylate , Etc. Sum fatty acid esters: acrylamide, N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide, N-dimethylacrylamide, N-diethylacrylamide, N-dipropylacrylamide, N- (2-aminoethyl) acrylamide, N- (2-aminopropyl) acrylamide, N- (3-aminopropyl) acrylamide, N
-[2- (methylamino) ethyl] acrylamide, N
-[2- (methylamino) propyl] acrylamide,
N- [3- (methylamino) propyl] acrylamide, N- [2- (dimethylamino) ethyl] acrylamide, N- [2- (dimethylamino) propyl] acrylamide, N- [3- (dimethylamino) propyl] Acrylamide, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-propylmethacrylamide, N-dimethylmethacrylamide, N
-Diethyl methacrylamide, N-dipropyl methacrylamide, N- (2-aminoethyl) methacrylamide, N- (2-aminopropyl) methacrylamide, N
-(3-aminopropyl) methacrylamide, N- [2
-(Methylamino) ethyl] methacrylamide, N-
[2- (methylamino) propyl] methacrylamide,
N- [3- (methylamino) propyl] methacrylamide, N- [2- (dimethylamino) ethyl] methacrylamide, N- [2- (dimethylamino) propyl] methacrylamide, N- [3- (dimethylamino) ) Propyl] methacrylamide, maleamide, N, N-dimethylmaleamide, fumamide, N, N-dimethylfumalamide, etc .; unsaturated fatty acid amides; acrylonitrile, methacrylonitrile, etc .; Carboxylic unsaturated esters such as vinyl propionate, vinyl butanoate, vinyl hexanoate, vinyl 2-ethylhexanoate, vinyl octadecanoate, vinyl benzoate, allyl acetate, allyl propionate, allyl hexanoate, allyl decanoate, etc. Non-existence of ethyl vinyl ether, butyl vinyl ether, etc. Sum ethers; styrene, alpha
-Methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, pt-butylstyrene, 4-methoxystyrene, 4-chlorostyrene, and other styrenes; ethylene, propylene, 1-butene, 1- Unsaturated hydrocarbons such as octene, vinylcyclohexane and 4-vinylcyclohexene; unsaturated halogenated hydrocarbons such as vinyl chloride, vinylidene chloride, tetrafluoroethylene and 3-chloropropylene; 4-vinylpyridine, N- Vinyl-substituted heterocyclic compounds such as vinylcarbazole and N-vinylpyrrolidone; monomers having a substituent having an active hydrogen such as a carboxyl group, a hydroxyl group, or an amino group in the above-mentioned exemplified monomers, and ethylene oxide, propylene oxide, and cyclohexene oxide Reaction products with epoxides; Hydroxyl group of the serial exemplified in the monomer,
A monomer containing a substituent having an amino group or the like and acetic acid,
Reaction products with carboxylic acids such as propionic acid, butanoic acid, hexanoic acid, decanoic acid and dodecanoic acid can be mentioned.

The anionic group-containing organic polymer compound can be synthesized by various conventionally known reaction methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization.

The weight average molecular weight of the organic polymer compound having an anionic group used in the present invention is from 2,000 to 100,
5,000, preferably 5,000 to 5
It is particularly preferred that it is in the range of 000. If the weight-average molecular weight is too small, the dispersion stability of the aqueous pigment dispersion itself decreases, and if it is too large, not only the viscosity of the dispersion increases but also the dispersibility tends to decrease. If the weight average molecular weight is too small or too large, for example, when applied to an ink for an ink jet printer, it adversely affects the printing characteristics and makes it difficult to perform stable printing for a long period of time.

Further, the acid value and the glass transition point of the anionic group-containing organic polymer compound used in the present invention are each 3
It is preferably in the range of 0 to 220 mgKOH / g and -20 to 60 ° C. If the acid value is too low, the dispersibility and dispersion stability of the aqueous pigment dispersion will decrease, and the printing stability when applied to inks for inkjet printers will deteriorate. If the acid value is too high, the water resistance of the image will decrease when applied to an ink for an inkjet printer. If the glass transition point is too high, stable printing is difficult to obtain, and if it is too low, image storability such as abrasion resistance and bar-stacking resistance tends to decrease.

The anionic group-containing organic polymer compound in the aqueous pigment dispersion of the present invention has a dispersibility and dispersion stability in which at least a part of the anionic group is ionized by a basic substance. Is necessary for the expression of The optimal ratio of the ionized group among the anionic groups is not uniquely limited because it varies depending on the composition, molecular weight, acid value, etc. of the organic polymer compound containing an anionic group to be used. , As long as the dispersion stability is expressed, usually 30 to 100%, especially 7 to 100%.
Preferably, it is set in the range of 0 to 100%. The ratio of the ionized group does not mean the molar ratio between the anionic group and the basic substance, but takes into account dissociation equilibrium. For example, when the anionic group is a carboxyl group, the ratio of the group ionized by dissociation equilibrium is less than 100% even when a stoichiometrically equivalent amount of a strong basic substance is used, and the ratio of the carboxylate group and the carboxyl group It is a mixed state.

An anionic group-containing organic polymer compound in which at least a part of an anionic group is ionized by a basic substance is stably dispersed in an aqueous medium over time without using an emulsifier or a dispersion stabilizer. The property that can be obtained is called self-water dispersibility. A polymer compound having a high degree of self-water dispersibility greatly contributes not only to its own dispersion stability but also to the dispersion stability of pigment particles.

The pigment that can be used in the aqueous pigment dispersion of the present invention is not particularly limited. However, in order to take advantage of the high dispersibility and dispersion stability that are features of the present invention, small pigments in the primary particles are used. It is preferable to use a hydrophobic pigment,
For example, various organic pigments and carbon black are particularly effectively used.

Examples of organic pigments include C.I. I. Pigment Red 122, Red 202, Red 20
Quinacridone pigments such as Red 209 and Red 209 and Violet 19; I. Pigment Orange 48,
Quinacridone quinone pigments such as Orange 49;
I. Dioxazine pigments such as C.I. Pigment Violet 23 and Violet 37; I. Pigment Blue 15, Blue 15: 1, Blue 15: 2,
Same Blue 15: 3, Same Blue 15: 4, Same Blue 1
5: 6, phthalocyanine pigments such as Blue 16, Blue 68, Green 7, and Green 36;
C. I. Anthrapyrimidine pigments such as CI Pigment Yellow 108; I. Pigments such as C.I. Pigment Orange 77 and Red 168; I. Pigment Blue 60 and other indanthrone-based pigments;
I. Flavanthrone-based pigments such as CI Pigment Yellow 24; I. Anthraquinone pigments such as CI Pigment Yellow 196 and Red 177; I. Pigment Red 123, Red 149, Red 17
8, perylene pigments such as Red 179, Red 190, and Red 224; I. Perinone pigments such as CI Pigment Yellow 196 and Orange 43;
C. I. Quinophthalone pigments such as CI Pigment Yellow 138; I. Pigment Orange 71, Orange 73, Red 254, Red 255,
Diketopyrrolopyrrole pigments such as Red 264 and Red 272; I. Thioindigo pigments such as CI Pigment Red 88, Red 181 and Brown 27; I. Isoindoline pigments such as CI Pigment Yellow 139, Yellow 185, Orange 69, and Red 260; I. Pigment Yellow 1
Isoindolinone-based pigments such as C.09, Yellow 110 and Yellow 173; I. Azomethine pigments such as CI Pigment Yellow 101, Yellow 129 and Orange 65; I. Pigment Yellow 15
1, yellow 154, yellow 175, yellow 180, yellow 181, orange 36,
Red 175, Red 176, Red 185
Benzimidazolone pigments such as C.I. I. Pigment
Yellow 1, Yellow 65, Yellow 73, Yellow 74, Yellow 116, Red 3,
Red 48: 1, Red 48: 2, Red 48: 3, Red 53: 1, Red 57: 1
Monoazo pigments such as Red 115; I. Disazo pigments such as CI Pigment Yellow 12, Yellow 13, Yellow 17, Yellow 81, Yellow 83, Orange 13, Orange 16;
I. Pigment Yellow 93, Yellow 95, Yellow 128, Red 144, Red 16
6, condensed azo pigments such as Red 220, Red 221 and the like. The pigment may be a powdery, granular or massive dry pigment, and a wet cake or slurry may also be used.

In the present invention, the term "aqueous medium" refers to water alone or a liquid medium mainly composed of water and containing a water-soluble organic solvent.
From the viewpoint of non-hazardous materials, it is ideally desirable that the organic solvent is as small as possible, and it is optimal that the organic solvent is not contained. If used, the water-soluble organic solvent has a boiling point of 70 to 100 ° C.
Are preferred in terms of ease of handling.

The preferred range of the ratio of the pigment to the organic polymer compound having an anionic group in the aqueous pigment dispersion of the present invention varies depending on the pigment and is not uniquely determined. About 25 to 200 parts of the group-containing organic polymer compound is preferable. If the ratio of the anionic group-containing organic polymer compound is too low, the friction resistance when used as an aqueous recording liquid decreases, and if it is too high, the viscosity increases when the aqueous recording liquid is adjusted. A tendency is observed.

The aqueous pigment dispersion of the present invention can be produced by a process including a step of dispersing a mixture comprising at least a pigment, an organic polymer compound having an anionic group, a basic substance and water with a dispersing device. Other steps can be incorporated into this manufacturing process as needed. Examples of other steps that can be incorporated include a preliminary dispersion step, a dissolution step, a dilution step, a distillation step, a centrifugation step, an acid precipitation step, a filtration step, a redispersion step, a pH adjustment step, a filling step, and the like.

Examples of the pre-dispersing step include a step of mixing and dispersing a resin and a pigment in a solution state or a molten state to form a slurry, a paste, or a solid state called a masterbatch or a chip. Examples of the dissolving step include a step of dissolving a solid anionic group-containing organic polymer compound in an organic solvent, preferably a water-soluble organic solvent, or an aqueous medium containing a basic substance, or an anionic group-containing organic compound. There is a step of dissolving a water-soluble organic solvent solution of the polymer compound in an aqueous medium containing a basic substance. Examples of the distillation step include a step of removing an organic solvent when the organic solvent is used in the dispersion step, and a step of removing excess water to obtain a desired solid content concentration. Examples of the centrifugation step include a step of removing coarse particles in the dispersion that adversely affect the suitability for use as an aqueous recording liquid. Examples of the acid precipitation step include:
There is a step of adding an acid such as hydrochloric acid, sulfuric acid, acetic acid or the like to the aqueous dispersion obtained in the dispersion step to acidify the aqueous dispersion to precipitate an anionic group-containing organic polymer compound on the surface of the pigment particles. By this step, the interaction between the pigment and the organic polymer compound having an anionic group can be enhanced. Examples of the filtration step include a step of removing coarse particles in the dispersion using a cartridge filter or a membrane filter as in the centrifugation step,
After the above-mentioned acid precipitation step, there is a step of filtering the solid content with a filter press, a Nutsche type filtration device, a pressure filtration device or the like. Examples of the redispersion step include a step of adding a basic substance and, if necessary, water and additives to the solid obtained by the acid precipitation step and the filtration step to obtain a dispersion again. Thereby, the counter ion of the ionized anionic group in the anionic group-containing organic polymer compound can be changed from that used in the dispersion step.

When the acid precipitation step is included in the essential steps in the present invention, the aqueous pigment dispersion comprises an aqueous pigment containing a microencapsulated pigment coated with an anionic group-containing organic polymer compound. It can be a dispersion. In order to achieve a higher degree of dispersion stability, the pigment and the anionic group-containing organic polymer compound are present in an aqueous medium as particles of the microencapsulated pigment, rather than being present as separate particles in the aqueous medium. It is preferred that it be present.

As the dispersing apparatus that can be used in the dispersing step of the present invention, apparatuses according to various well-known methods can be used and are not particularly limited. Examples thereof include steel, stainless steel, zirconia, alumina, and nitride. For example, a diameter of 0.1 to 10 m made of silicon, glass, or the like
A method that uses the kinetic energy of a spherical dispersion medium (media) of about m, a method that uses the shearing force due to mechanical agitation, a change in the pressure of a distributed material bundle supplied at high speed, a change in the flow path, or a collision. A dispersion method such as a method utilizing the force of the force can be adopted.

In particular, a media mill using a dispersion medium is preferable in that it has excellent crushing ability of pigment aggregates, and a so-called high flow type media mill designed to flow at a high flow rate is particularly preferable. The media mill may be vertical or horizontal. Examples of commercially available media mills that can be used in the present invention include a dyno mill, a DCP mill, an LMZ mill, an SC mill, a supervisco mill, a nano mill, a fine mill, and the like.

The above-mentioned SC mill is disclosed in JP-A-11-166.
This is based on the following apparatus configuration and dispersion principle described in JP-A-145-145.

An outer fixed container (I) having a supply port and a discharge port for the suspension and having a separator and having a cylindrical inner wall, and is provided with a predetermined gap therein and rotatable about a rotation axis. And a cylindrical rotor (II).
I) has a hollow liquid chamber inside the cylinder, a slit facing the supply port through which the mixture of the pigment and the aqueous medium can be supplied toward the liquid chamber, and a plurality of cylindrical side walls communicating with the outside of the liquid chamber. A rotor (II) having a liquid discharge hole, wherein the external fixed container (I) is provided with a plurality of holes having a predetermined diameter smaller than the dispersion medium and facing a circumferential outer wall surface of the rotor via a predetermined gap. A separator having an external fixed container (I) provided on a cylindrical inner wall, and a dispersing device filled with a dispersing medium in a gap between the rotor and the separator.
While rotating the rotor (II), the mixture is supplied to the liquid chamber from the supply port of the container (I) toward the slit of the rotor, and the suspension is discharged from the discharge hole by centrifugal force. This is a dispersion apparatus based on a dispersion principle in which a pigment is finely dispersed in an aqueous medium to obtain an aqueous pigment dispersion by allowing the mixture passed through a separator to be taken out from a discharge port of a container (I).

In order to use the above-mentioned dispersing device effectively, at least a dispersing device and a container holding a mixture containing at least a pigment and an aqueous medium or an aqueous pigment dispersion or a pipe having a volume that can be used similarly thereto It is preferable to adopt a system in which one unit is installed and the mixture circulates between them. The container holding the mixture or the aqueous pigment dispersion may be a container or a pipe, and may have any shape (hereinafter, the container and the pipe are abbreviated as a container). In order to do this, usually, a container for holding the mixture is further provided, and the liquid discharge port, the mixture or the aqueous pigment dispersion is held so that the pigment becomes an aqueous pigment dispersion having a predetermined particle size. The container and the liquid supply port are connected in this order, the mixture is circulated, and the mixture is repeatedly processed.

When the dispersing apparatus is of a self-priming type, a circulation pump is not required for circulating the mixture or the aqueous dispersion in the dispersion system. If the body does not circulate as intended, a required number of circulation pumps can be provided in the middle of the piping in the system.

The above dispersing device is, for example, a dispersion medium stirring type dispersing device having a rotor and a separator in a short cylindrical pulverizing section as shown in FIG.

Hereinafter, description will be made with reference to FIG. The dispersion device that can be used in the present invention is an external fixed container (I) [hereinafter, referred to as an external fixed container 1]. ], A cylindrical rotor (II) [hereinafter, referred to as a cylindrical rotor 2] via a predetermined gap. ] Are provided so as to be rotatable about the rotation shaft 3 thereof. The direction of the rotation axis 3 is arbitrary, but it is preferable that the rotation axis 3 is horizontal, that is, parallel to the ground surface, for the reason described later. In FIG. 1, it is shown in a preferred orientation. The container 1 is provided with a supply port 4 for supplying a mixture containing a pigment and an aqueous medium, and a discharge port 9.

A separator 8 having a plurality of holes having a predetermined diameter that allows the particles in the mixture to pass when the particles have a predetermined particle diameter is fixed to the inner wall of the outer fixed container 1.
The gap between the container 1 and the rotor 2 is filled with particles of the dispersion medium 7 having a predetermined diameter for crushing the particles in the mixture.

On the other hand, a hollow liquid chamber 6 is provided inside the cylinder of the rotor 2. The rotating shaft is provided so that the mixture supplied from the supply port 4 can be further supplied to the liquid chamber 6. A slit 5 having a ring-shaped cut having a shape sandwiched between two circles having different radii at the center is provided. The slit 5 faces the supply port 4.

The cylindrical side wall of the rotor 2 is provided with a plurality of liquid discharge holes (without reference numerals) communicating with the outside of the liquid chamber 6 as shown by arrows. Each of the liquid discharge holes of the rotor 2 has a larger diameter than the particles of the dispersion medium 7, and the mixture is discharged from the liquid discharge holes. The diameter of each hole connected to the outlet 9 is smaller than the diameter of the particles of the dispersion medium 7, so that the dispersion medium 7 itself does not flow out to the discharge port 9.

The outer peripheral wall surface of the rotor 2 and the separator 8 face each other, and the mixture is filled with the particles of the dispersion medium 7 from the liquid chamber 6 into the container 1 and the rotor 2.
Is supplied through the liquid discharge hole to the gap.

The mixture is supplied from the supply port 4 to the slit 5
The liquid is supplied to the liquid chamber 6 as shown by an arrow. When the mixture is supplied to the hollow liquid chamber 6 while the rotor 2 is rotated about the rotation shaft 3, the particles are dispersed by the dispersing device.

In the preferred dispersing apparatus used in the present invention, when the rotor 2 is rotated, a centrifugal force is generated, and the medium 7 is pressed in layers on the inner wall of the separator 8. At the same time, a strong shearing force is generated between the media 7 due to the rotational movement of the rotor 2. Further, since the centrifugal force and the flowing direction of the mixture are the same, uniform pulverization / dispersion and discharge of the mixture at a large flow rate from the separator 8 are possible, and the residence time of the sample in the dispersion device can be adjusted.

The dispersion medium (media) can be present in the gap formed between the cylindrical inner wall and the cylindrical rotor in the external fixed container, and in the liquid chamber inside the cylinder of the rotor. The filling rate is expressed as a ratio of the volume of the dispersion medium to the total volume of the gap and the liquid chamber. In the present invention, the filling rate is defined as the ratio of the volume of the dispersion medium to the volume of the gap.

The pigment and the like in the mixture discharged from the liquid discharge hole by the centrifugal force are dispersed in the gap filled with the particles of the dispersion medium 7, and the pigment and the like are smaller than the hole diameter provided in the separator 8. At the stage when it passed, passed through the hole,
It is taken out from the discharge port 9 together with the liquid medium of the mixture. The mixture in which the pigment and the like are finely dispersed in this manner is taken out to the discharge port 9.

The reason why the rotating shaft 3 of the rotor 2 is made horizontal is to make full use of the effect of this centrifugal force.

In the present invention, in the method of producing an aqueous pigment dispersion by passing a mixture comprising at least a pigment and an aqueous medium through a dispersing apparatus, the “total dispersion time” and the “average residence time of the mixture in the dispersing apparatus” And the ratio of “total sum” is as large as possible.

In the present invention, the ratio of the total dispersing time to the total sum of the average staying times of the mixture in the dispersing device is preferably 2 or more, and 4 or more for more clearly exhibiting the effects of the present invention. Is particularly preferred. On the other hand, there is no particular upper limit on the ratio of the total dispersion time and the sum of the average residence times of the mixture in the dispersing apparatus, but if it is excessive, the batch size becomes large, and it takes a long time to complete the product. Therefore, it is preferable to stop at 30. That is, a preferable range is 4 to 30.

Here, defining the ratio of the total dispersion time to the sum of the average stay times of the mixture in the dispersion apparatus within a certain range does not mean that the total dispersion time or the flow rate of the mixture is optimized. . This point is described in JP-A-11-16614.
This is the greatest reason that even a person skilled in the art could not guess the configuration of the present invention from the invention of JP-A-5. For example, when the flow rate of the mixture is increased while keeping the total dispersion time constant, the average residence time of the mixture per pass decreases in inverse proportion to the flow rate, but the number of circulations increases in proportion to the flow rate. Does not change, and the ratio of the total dispersion time to the sum of the average residence times of the mixture in the dispersion device does not change. Conversely, the same applies if the total dispersion time is changed while the flow rate of the mixture is kept constant. More specifically, 100 kg of a mixture containing a pigment and an aqueous medium is manufactured in 10 hours to produce an aqueous pigment dispersion,
g over 50 hours to produce an aqueous pigment dispersion,
The dispersed particle size of the pigment in the aqueous pigment dispersion becomes smaller,
This also means that the viscosity of the aqueous pigment dispersion is lower.

According to the production method of the present invention, 70 to 250
A dispersion particle size of the particles for the aqueous recording liquid of nm can be achieved. According to the present invention, on the premise that the same dispersing device is used, the particles can be made to have a relatively small dispersed particle size of 20 to 50 nm as compared with the case where the conventional dispersing device is operated under the conventional operating conditions. This makes it possible to approach the ideal dispersion particle size of the aqueous dispersion for an aqueous recording liquid of 20 to 200 nm while maintaining the dispersion stability.

The aqueous pigment dispersion obtained by the production method of the present invention may be, for example, a piezo method, a bubble jet (registered trademark).
It can be used for the preparation of an aqueous recording liquid typified by inks for ink jet printers having various ejection nozzle shapes such as an ink jet system and an acoustic system.

In the dispersion step, a water-soluble organic solvent may be used in combination, whereby the viscosity of the mixture containing the pigment and the aqueous medium in the dispersion step may be reduced in some cases. Examples of the water-soluble organic solvent include ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; methanol, ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, 2-methoxyethanol, And the like; ethers such as tetrahydrofuran, 1,4-dioxane, and 1,2-dimethoxyethane; and amides such as dimethylformamide and N-methylpyrrolidone. These water-soluble organic solvents may be used as an anionic group-containing organic polymer compound solution,
It may be separately and independently added to the mixture.

In the present invention, the organic polymer compound having an anionic group is 2,3-epoxypropyl acrylate, 2,3-epoxybutyl acrylate, 2,3-epoxybutyl acrylate.
It is a copolymer comprising at least one unsaturated fatty acid having an epoxy group such as epoxycyclohexyl, 2,3-epoxypropyl methacrylate, 2,3-epoxybutyl methacrylate, and 2,3-epoxycyclohexyl methacrylate. In this case, in the production process of the aqueous pigment dispersion, a ring-opening reaction can be carried out at any stage after the dispersion step to effect crosslinking. Ring opening reaction temperature is 80-1
About 40 ° C. is preferable. When the reaction temperature is too low, the reaction rate is low and a long time is required for completing the reaction, so that the pigment particles are likely to fuse with each other to form an aggregate. If the reaction temperature is too high, fusion of the pigment particles and growth of the pigment particles themselves occur, which is not preferable in any case. When the reaction temperature becomes higher than the boiling point of the dispersion, it is necessary to use a pressurized reactor.

The aqueous recording liquid of the present invention can be prepared by mixing an aqueous pigment dispersion containing at least a pigment and an organic polymer compound having an anionic group with a water-soluble organic solvent, water and the like. Further, if necessary, a surfactant, a water-soluble resin, a preservative, a viscosity adjuster, a pH adjuster, a chelating agent and the like can be added.

Examples of the water-soluble organic solvent that can be used for preparing the aqueous recording liquid include methanol, ethanol,
1-propanol, 2-propanol, 2-methyl-1
-Propanol, 1-butanol, 2-methoxyethanol, 2-butoxyethanol, 2- (2-methoxyethoxy) ethanol, 2- (2-butoxyethoxy) ethanol, 2- [2- (2-methoxyethoxy) ethoxy] Ethanol, 2- [2- (2-butoxyethoxy)
Ethoxy] alcohols such as ethanol; 1,2-ethanediol, 1,2-propanediol, 1,2-butanediol, 2,3-butanediol, 2,2′-oxybisethanol, 2,2′- Ethylenedioxybis (ethanol), thiodiethanol, glycerin, 1,
Polyhydric alcohols such as 2,6-hexanetriol; amides such as dimethylformamide, dimethylacetamide, N-methyl-pyrrolidone, 1,3-dimethyl-2-imidazolidinone; acetone, methyl ethyl ketone, methyl n-butyl ketone; Ketones such as methyl isobutyl ketone; tetrahydrofuran, 1,4-dioxane,
1,2-dimethoxyethane, 1,2-diethoxyethane, 2,2′-oxybis (2-methoxyethane),
2,2′-oxybis (2-ethoxyethane), 2,
2′-ethylenedioxybis (2-methoxyethane),
Ethers such as 2,2′-ethylenedioxybis (2-methoxyethane) are exemplified. The content ratio of the water-soluble organic solvent in the aqueous recording liquid is preferably 50% by weight or less,
A range of 5 to 40% by weight is particularly preferred.

The surfactant which may be added to the aqueous recording liquid of the present invention may be any of anionic, cationic, zwitterionic and nonionic surfactants.

Examples of anionic surfactants include fatty acid salts such as sodium stearate, potassium oleate, and sodium hydrogenated tallow fatty acid; sodium dodecyl sulfate, tri (2-hydroxyethyl) ammonium dodecyl sulfate, sodium octadecyl sulfate. Alkyl sulfates such as sodium nonylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium octadecylbenzenesulfonate, sodium dodecyldiphenyletherdisulfonate; sodium dodecylnaphthalenesulfonate;
Naphthalene sulfonic acid salts such as naphthalene sulfonic acid formalin condensate; sulfosuccinate ester salts such as sodium dododecyl sulfosuccinate and dioctadecyl sodium sulfosuccinate; sodium polyoxyethylene dodecyl ether sulfate, polyoxyethylene dodecyl ether sulfate Ethyl) ammonium, sodium polyoxyethylene octadecyl ether sulfate, sodium polyoxyethylene dodecyl phenyl ether sulfate and the like; and polyoxyethylene sulfate salts such as potassium dodecyl phosphate and sodium octadecyl phosphate.

Examples of the cationic surfactant include alkylamine salts such as octadecyl ammonium acetate and coconut oil amine acetate; dodecyl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, dioctadecyl dimethyl ammonium chloride, dodecyl benzyl dimethyl ammonium chloride and the like. Quaternary ammonium salts.

Examples of zwitterionic activators include alkyl betaines such as dodecyl betaine and octadecyl betaine; and amine oxides such as dodecyl dimethyl amine oxide.

Examples of the nonionic surfactant include polyoxyethylene alkyl ethers such as polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene octadecyl ether and polyoxyethylene (9-octadecenyl) ether. Polyoxyethylene phenyl ethers such as polyoxyethylene octyl phenyl ether and polyoxyethylene nonyl phenyl ether; oxirane polymers such as polyethylene oxide and co-polyethylene oxide propylene oxide; sorbitan dodecanoate and sorbitan hexadecanoate Sorbitan octadecanoate, sorbitan (9-octadecenoate) ester, sorbitan (9-octadecenoate) triester, polyoxyethylene sorbita Dodecanoic acid ester, polyoxyethylene sorbitan hexadecanoic ester, polyoxyethylene sorbitan octadecanoic ester, polyoxyethylene sorbitan octadecanoic acid triester,
Polyoxyethylene sorbitan (9-octadecenoic acid)
Esters, sorbitan fatty acid esters such as polyoxyethylene sorbitan (9-octadecenoic acid) triester; sorbitol fatty acid esters such as polyoxyethylene sorbitol (9-octadecenoic acid) tetraester; glycerin octadecanoate, glycerin (9-octadecene) Glycerin fatty acid esters such as (acid) esters. Among these nonionic surfactants, those having an HLB of 14 or more are particularly preferred.

Examples of the water-soluble resin that may be added to the aqueous recording liquid of the present invention include glue, gelatin, casein,
Albumin, gum arabic, fish gleu, alginic acid, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyethylene oxide,
Polyvinyl alcohol, polyacrylamide, polyacrylic acid, polyvinyl ether, polyvinylpyrrolidone,
Styrene-maleic acid copolymer, styrene-acrylic acid copolymer, acrylate-acrylic acid copolymer and the like can be mentioned.

The water-soluble resin is used as needed for the purpose of improving fixability, adjusting viscosity, and drying quickly.
When used in a recording liquid, the content of the water-soluble resin in the recording liquid is preferably 30% by weight or less, particularly preferably 20% by weight or less.

The aqueous recording liquid of the present invention can be suitably used as an ink for stationery such as a felt-tip pen, a marker, etc. and various printers and plotters. It can be suitably used as an ink for use.

[0057]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. In the following Examples and Comparative Examples,
“Parts” and “%” represent “parts by mass” and “% by mass”.

Example 1 In a mixing vessel equipped with a cooling jacket, 50 parts of n-butyl methacrylate, 10 parts of 2-hydroxyethyl methacrylate, 20 parts of methacrylic acid, 20 parts of styrene Copolymer having a composition of 20 parts (weight average molecular weight 23000)
130 parts of a 30% 2-butanone solution, 13 parts of a 25% aqueous sodium hydroxide solution, 677 parts of water, Fastgen super magenta RTS (CI Pigment Red 12
2, 160 parts of Dainippon Ink and Chemicals, Inc.) and 20 parts of phthalimidomethylated quinacridone were charged, stirred, and mixed.

As the dispersing device, a dispersing medium stirring type dispersing device (SC mill SC10) having an external fixed container and an internal stirring device (rotor) shown in FIG.
0/32 type, manufactured by Mitsui Mining Co., Ltd .;
66 liters. Self-priming. ) Was used.

The common container (holding container) for holding the mixture containing the pigment and the aqueous medium and the aqueous pigment dispersion, the liquid discharge port of the dispersing device, the holding container, and the liquid supply port of the dispersing device are arranged in this order. The mixture was circulated in the dispersion system until the mixture charged in the holding container became an aqueous pigment dispersion containing particles having a predetermined particle diameter.

The dispersion conditions at this time were as follows: the rotation speed of the internal stirring device of the dispersion device was 2700 rpm (rotation / minute), the medium was 0.3 mmφ zirconia beads (YTZ beads manufactured by Nikkato Co., Ltd.), and the filling rate was 115%. The temperature of the mixture was kept at 40 ° C. or lower by passing cold water through the jacket.

Under these conditions, the average residence time of the mixture in the dispersion apparatus per pass is 0.11 minutes and the number of circulations is 1565 times, so that the total sum of the average residence times of the mixture in the dispersion apparatus is 172 minutes. Where the ratio of the total dispersion time to the sum of the average stay times of the mixture in the dispersion device is 20.9.

After the dispersion is completed, the aqueous pigment dispersion produced is taken out of the holding container, and then the holding container and the dispersing device flow path are washed with 25,000 parts of water. Was. The diluted dispersion was placed in a glass distillation apparatus, and the entire amount of methyl ethyl ketone and a part of water were distilled off to obtain a concentrated dispersion.

After allowing to cool to room temperature, 10% hydrochloric acid was added dropwise to the concentrated dispersion while stirring to adjust the pH to 3.5, and the solid content was filtered with a Nutsche filter and washed with water. The cake is placed in a container, and 310 parts of a 20% aqueous potassium hydroxide solution and 200 parts of water are added thereto. A dispersion stirrer (TK homodisper 20) is added.
Mold, manufactured by Tokushu Kika Kogyo Co., Ltd.). After removing coarse particles with a centrifuge (50A-IV, Sakuma Seisakusho), the nonvolatile content was adjusted to 20%.
An aqueous pigment dispersion containing microencapsulated pigment particles coated with a pigment having an organic polymer compound having a carboxyl group neutralized with a base was obtained.

The resulting aqueous pigment dispersion had an average particle diameter of 104 nm and a viscosity of 4.82 mPa · s. The median diameter measured by a laser Doppler particle size analyzer Microtrac (UPA150, manufactured by Leeds & Northrop Co.) was used as the average particle diameter.

<Example 2> An aqueous pigment dispersion having a nonvolatile content of 20% was obtained by dispersing for 1080 minutes in the same manner as in Example 1 except that the total amount of the mixture was changed to 4.14 liters. Also under these conditions, the average residence time of the mixture in the dispersing apparatus per pass is 0.11 minutes and the number of circulations is 1565 times, so that the sum of the average residence times of the mixture in the dispersing apparatus is 172 minutes, The ratio of the dispersion time to the sum of the average residence times of the mixture in the dispersion device was 6.28. The obtained aqueous pigment dispersion had an average particle size of 125 nm and a viscosity of 5.46 mPa · s.

Example 3 An aqueous pigment dispersion having a non-volatile content of 20% was obtained by dispersing for 360 minutes in the same manner as in Example 1 except that the total amount of the mixture was 1.38 liters. Also under these conditions, the average residence time of the mixture in the dispersing apparatus per pass is 0.11 minutes and the number of circulations is 1565 times, so that the sum of the average residence times of the mixture in the dispersing apparatus is 172 minutes, The ratio of the dispersion time to the sum of the average stay times of the mixture in the dispersion device was 2.09. The average particle diameter of the obtained aqueous pigment dispersion was 134 nm, and the viscosity was 5.68 mPa · s.

<Comparative Example 1> Dispersion was conducted for 234 minutes in the same manner as in Example 1 except that the total amount of the mixture was changed to 0.90 liter, and the same treatment was carried out to obtain an aqueous pigment dispersion having a nonvolatile content of 20%. Also under these conditions, the average residence time of the mixture in the dispersing apparatus per pass is 0.11 minutes and the number of circulations is 1565 times, so that the sum of the average residence times of the mixture in the dispersing apparatus is 172 minutes, The ratio of the dispersion time to the sum of the average residence times of the mixture in the dispersion device is 1.36. The average particle size of the obtained aqueous pigment dispersion was 182 nm, and the viscosity was 6.89 mPa · s.

Example 4 (Evaluation of Suitability of Aqueous Recording Liquid for Piezo-Type Inkjet Printer) An ink for a piezo-type inkjet printer was prepared with reference to Example 1 described in JP-A-7-228808. The ink composition is shown below. Aqueous pigment dispersion 25 parts Triethylene glycol monobutyl ether 10 parts Polyethylene glycol 15 parts Surfynol 465 (manufactured by Air Products) 0.8 parts Water 49.2 parts -8000C type, manufactured by Seiko Epson Corporation), enabling continuous printing of 50 sheets.

[0070]

According to the method of the present invention, when a mixture comprising at least a pigment and an aqueous medium is passed through a dispersing apparatus,
Since the ratio of the total dispersion time and the sum of the average residence time of the mixture in the dispersing device is 2 or more, compared to the aqueous pigment dispersion manufactured under the conventional conditions in which the ratio is less than 2, high dispersion and It has a low viscosity, and when used for a recording liquid such as an ink for an ink jet printer, for example, can provide high-speed printing and provide a high-definition recording liquid, and can form a clear image.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a dispersion apparatus used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 External fixed container 2 Cylindrical rotor 3 Rotor rotation axis 4 Supply port 5 Slit 6 Liquid chamber 7 Dispersion media 8 Separator 9 Discharge port

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C09D 11/00 B41J 3/04 101Y (72) Inventor Harumi Sadakuni 2710 Yanagawa, Hazaki-cho, Kashima-gun, Ibaraki Pref. ) Inventor Masao Tanaka 3556-16 Sahara-I, Sahara-shi, Chiba F-term (reference) 2C056 EA01 FC01 2H086 BA53 BA55 BA59 4J037 AA02 AA30 CC13 CC14 CC15 CC16 CC17 4J039 AD02 AD09 AD13 AD14 AD23 BA04 BE01 BE30 CA06 GA21 GA24 GA26

Claims (8)

[Claims] 1. A method for producing an aqueous pigment dispersion for an aqueous recording liquid by passing a mixture comprising at least a pigment and an aqueous medium through a dispersing apparatus, wherein the total dispersion time and the sum of the average residence time of the mixture in the dispersing apparatus are Wherein the ratio is 2 or more. 2. The process for producing an aqueous pigment dispersion according to claim 1, wherein the ratio of the total dispersion time to the total sum of the average stay times of the mixture in the dispersion device is 4 or more and 30 or less. 3. The method for producing an aqueous pigment dispersion according to claim 1, wherein a mixture comprising at least a pigment, an anionic group-containing organic polymer compound, and an aqueous medium is passed through a dispersing apparatus. 4. The method for producing an aqueous pigment dispersion according to claim 3, wherein the organic polymer compound having an anionic group is self-water dispersible. 5. The method for producing an aqueous pigment dispersion according to claim 3, wherein the pigment is coated with an anionic group-containing organic polymer compound. 6. A dispersing apparatus, a mixture containing at least a pigment and an aqueous medium, or a container or a pipe for holding an aqueous pigment dispersion is installed, and the mixture is dispersed by a method of circulating therebetween. A method for producing the aqueous pigment dispersion according to claim 1. 7. The dispersing device according to claim 1, wherein the dispersing device is a media mill.
7. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 6. 8. An aqueous recording liquid comprising the aqueous pigment dispersion produced by the method according to claim 1.