Method for producing coloring agent, pigment composition, and aqueous pigment dispersion

Abstract

To provide a method for efficiently producing a coloring agent which is usable for production of a pigment composition and an aqueous pigment dispersion that gives a dispersion having a small volume average particle diameter and a small number of coarse particles.SOLUTION: A method for producing a coloring agent includes a step 1 of kneading a composition containing a pigment having a primary particle diameter of 100 nm or more, a liquid medium and a water-soluble inorganic salt by a treatment machine, and thereby obtaining a kneaded product containing a pigment having a primary particle diameter of 10 nm or more and less than 100 nm, and a step 2-1 of mixing the kneaded product with a resin having an anionic group and a basic compound.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a colorant, a pigment composition, and an aqueous pigment dispersion that can be used, for example, in the production of inkjet printing ink.

Background Art

[0002] Pigment compositions are used in various printing methods such as inkjet printing. As a method for producing a pigment composition, a method of obtaining a pigment composition by treating a raw material composition containing a pigment component and a liquid medium with a disperser is known (see, for example, Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For a pigment composition, from the viewpoint of suppressing clogging of the ejection nozzles during printing and obtaining good ejection stability, it is required that the volume average particle diameter of the dispersion is small and the number of coarse particles is small. As a method for obtaining a pigment composition having a small volume average particle diameter of the dispersion and a small number of coarse particles, for example, a method of repeatedly performing a grinding treatment or a crushing treatment on a raw material composition containing a pigment and a liquid medium can be mentioned. However, even with the above method, there are cases where the volume average particle diameter of the dispersion cannot be further reduced, the number of coarse particles cannot be further reduced, or the productivity of the pigment composition is reduced.

[0005] Therefore, the problem to be solved by the present invention is to provide a method capable of efficiently producing a colorant that can be used in the production of a pigment composition or an aqueous pigment dispersion having a small volume average particle diameter of the dispersion and a small number of coarse particles.

Means for Solving the Problems

[0006] The present inventors have obtained a kneaded product containing a pigment (A2) having a primary particle diameter in the range of 10 nm or more and less than 100 nm, a liquid medium (D), and a water-soluble inorganic salt (E) by kneading a composition containing a pigment (A1) having a primary particle diameter of 100 nm or more, a liquid medium (D), and a water-soluble inorganic salt (E) with a processor (F) in Step 1, and in Step 2-1 of mixing the kneaded product, a resin (B1) having an anionic group, and a basic compound (C), or in Step 2-2 of mixing the kneaded product and a resin (B2) having an anionic group neutralized with a basic compound (C). The above problem has been solved by a method for producing a colorant in which the pigment (A2) is coated with the resin (B1) or the resin (B2).

Advantages of the Invention

[0007] According to the colorant obtained by the production method of the present invention, a pigment composition or an aqueous pigment dispersion having a small volume average particle diameter of the dispersion and a small number of coarse particles can be obtained.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

[0010] In this specification, a numerical range indicated by "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value of a numerical range at a certain step can be arbitrarily combined with the upper limit value or the lower limit value of a numerical range at other steps. In the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. "A or B" means that either one of A and B may be included, or both may be included. The materials exemplified in this specification can be used alone or in combination of two or more without special notice. The content of each component in the composition means the total amount of the plurality of substances corresponding to each component in the composition, unless otherwise specified, when there are a plurality of substances corresponding to each component in the composition. The term "step" includes not only an independent step but also the step even when it cannot be clearly distinguished from other steps as long as the intended action of the step is achieved. "(Meth)acrylic acid" represents a general term for acrylic acid and the corresponding methacrylic acid, and the same applies to other similar expressions such as "(meth)acrylate".

[0011] The method for producing a colorant of the present invention comprises: Step 1 of kneading a composition containing a pigment (A1) having a primary particle diameter of 100 nm or more, a liquid medium (D), and a water-soluble inorganic salt (E) with a processor (F) to obtain a kneaded product containing a pigment (A2) having a primary particle diameter in the range of 10 nm or more and less than 100 nm, a liquid medium (D), and a water-soluble inorganic salt (E); and Step 2-1 of mixing the kneaded product with a resin (B1) having an anionic group and a basic compound (C), or Step 2-2 of mixing the kneaded product with a resin (B2) having an anionic group neutralized by a basic compound (C). The colorant obtained by the above method has a part or all of the pigment (A2) coated with the resin (B1) or the resin (B2), and can be suitably used for producing a pigment composition or an aqueous pigment dispersion having a small volume average particle diameter of the dispersion and a small number of coarse particles.

[0012] First, Step 1 will be described. In Step 1, a composition containing a pigment (A1) having a primary particle diameter of 100 nm or more, a liquid medium (D), and a water-soluble inorganic salt (E) is kneaded with a processor (F) to obtain a kneaded product containing a pigment (A2) having a primary particle diameter in the range of 10 nm or more and less than 100 nm, a liquid medium (D), and a water-soluble inorganic salt (E). Step 1 is a step for refining the pigment (A1) having a primary particle diameter of 100 nm or more, which is generally called a coarse pigment. Therefore, the kneaded product obtained through Step 1 contains the pigment (A2) having a primary particle diameter in the range of 10 nm or more and less than 100 nm, in which the pigment (A1) has been refined. Note that the primary particle diameters of the pigment (A1) and the pigment (A2) refer to the values measured by the method shown below. A mixture of the pigment (A1) or the pigment (A2) and acetone, ultrasonically dispersed and cast on a grid mesh and dried, was used as a sample. The surface of the sample was observed with a transmission electron microscope, and the diameters (maximum values) of 50 pigments were measured. The average value of the diameters was calculated and used as the primary particle diameter.

[0013] As a method of kneading the composition containing the pigment (A1), the liquid medium (D), and the water-soluble inorganic salt (E) with the processor (F), for example, (i) a method of supplying the pigment (A1), the liquid medium (D), and the water-soluble inorganic salt (E) to the processor (F) and kneading them, (ii) a method of supplying the pigment (A1) and the water-soluble inorganic salt (E) to the processor (F), and then supplying the liquid medium (D) and kneading them thereafter, (iii) a method of supplying the pigment (A1) and the water-soluble inorganic salt (E) to the processor (F), kneading them for 5 to 10 minutes, then supplying the liquid medium (D) and kneading them again, (iv) a method of supplying the water-soluble inorganic salt (E) to the processor (F), kneading it for 5 to 10 minutes, then supplying the pigment (A1) and kneading it, and then supplying the liquid medium (D) and kneading it again can be mentioned. Among them, as the kneading method, it is preferable to carry out the method (iii) in order to efficiently refine the pigment (A1) into the pigment (A2) having a primary particle diameter of 10 nm or more and less than 100 nm in a short time.

[0014] As the processor (F), for example, a kneader can be used. Among them, as the processor (F), it is preferable to use a twin-arm kneader, a trimix, or a kneading machine in order to efficiently and in a short time refine the pigment (A1) into a pigment (A2) having a primary particle diameter of 10 nm or more and less than 100 nm, and it is more preferable to use a twin-arm kneader.

[0015] When kneading the composition with the processor (F) in the step 1, the temperature is preferably in the range of 30°C to 120°C, and preferably in the range of 70°C to 110°C in order to efficiently and in a short time refine the pigment (A1) into a pigment (A2) having a primary particle diameter of 10 nm or more and less than 100 nm.

[0016] Also, when kneading the composition with the processor (F) in the step 1, the time is preferably in the range of 2 hours to 24 hours, and preferably in the range of 5 hours to 9 hours in order to efficiently and in a short time refine the pigment (A1) into a pigment (A2) having a primary particle diameter of 10 nm or more and less than 100 nm.

[0017] The kneaded product obtained through the above step 1 contains the pigment (A2) into which the pigment (A1) has been refined. The primary particle diameter of the pigment (A2) is preferably 10 nm or more and less than 100 nm, preferably 10 nm or more and 80 nm or less, and preferably 10 nm or more and 60 nm or less, because the pigment (A2) can be easily and stably dispersed in an aqueous medium in a short time in the steps described later.

[0018] The kneaded product obtained through the above step 1 contains the water-soluble inorganic salt (E) used to grind the pigment (A1) to obtain the pigment (A2). In the present invention, without removing the water-soluble inorganic salt (E) from the kneaded product obtained in the step 1, the kneaded product containing the water-soluble inorganic salt (E) can be directly used in the step 2-1 or step 2-2. Therefore, according to the method of the present invention, the production efficiency of colorants, aqueous pigment dispersions, etc. can be dramatically improved.

[0019] Next, steps 2-1 and 2-2 will be described. In the present invention, using the kneaded product obtained through the above step 1, either step 2-1 or step 2-2 is carried out. By carrying out step 2-1 or step 2-2, a colorant that can be used for manufacturing a pigment composition or an aqueous pigment dispersion with a small volume average particle diameter of the dispersion and a small number of coarse particles can be obtained. Step 2-1 is a step of mixing the kneaded product obtained in step 1, a resin (B1) having an anionic group, and a basic compound (C). Examples of step 2-1 include a method of mixing a mixture of the resin (B1) having an anionic group and the basic compound (C) in advance with the kneaded product, and a method of mixing the kneaded product and the resin (B1) first, and then supplying and mixing the basic compound (C). Also, step 2-2 is a step of mixing the kneaded product and a resin (B2) having an anionic group neutralized by a basic compound (C). Step 2-2 is, for example, a step of mixing a mixture obtained by neutralizing part or all of the anionic groups of the resin (B1) with the basic compound (C) by mixing the resin (B1) having an anionic group and the basic compound (C) in advance and stirring, etc., with the kneaded product.

[0020] The mixing carried out in steps 2-1 and 2-2 is preferably carried out for 0.5 hours to 5 hours, and more preferably for 1 hour to 3 hours in order to produce a colorant capable of reducing the volume average particle diameter of the dispersion contained in the aqueous pigment dispersion.

[0021] Also, the mixing carried out in steps 2-1 and 2-2 is preferably carried out by adjusting the temperature of the contents such as the kneaded product, the resin (B1), the resin (B2), and the basic compound (C) to the range of 30°C to 70°C, and more preferably to the range of 50°C to 70°C in order to produce a colorant capable of reducing the volume average particle diameter of the dispersion contained in the aqueous pigment dispersion. The colorant obtained through the above-described Step 1 and Step 2-1 or Step 2-2 is such that part or all of the surface of the pigment (A2) is coated with the resin (B1) or the resin (B2). Further, since the colorant obtained by the above method is in a wet state (so-called wet cake), the drying step of the colorant is not essential and can be made an optional step. Thereby, the production efficiency of the colorant can be increased.

[0022] Next, the pigment (A1) used in the method for producing the colorant of the present invention will be described. As the pigment (A1), as described above, generally a coarse pigment having a primary particle diameter of 100 nm or more is used. Such a coarse pigment is usually not suitable as a colorant in many cases. In this Step 1, by refining the pigment (A1), a kneaded product containing a pigment (A2) having a primary particle diameter in the range of 10 nm or more and less than 100 nm, which is suitable as a colorant, is produced. As the pigment (A1), for example, general pigments etc. (azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), dye chelates (for example, basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc.) can be used. Among them, as the pigment (A1), it is preferable to use a polycyclic pigment, and it is more preferable to use a phthalocyanine pigment.

[0023] Next, the liquid medium (D) used in the method for producing the colorant of the present invention will be described. The liquid medium (D) is used for the purpose of wetting the pigment (A1) and the water-soluble inorganic salt (E) in Step 1. As the liquid medium (D), for example, a water-soluble organic solvent in which the water-soluble inorganic salt (E) described later is difficult to dissolve can be used. Specifically, triethylene glycol, diethylene glycol, glycerin, ethylene glycol, propylene glycol, liquid polyethylene glycol, liquid polypropylene glycol, 2-(methoxymethoxy)ethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy)ethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol, 1,2-propanediol, 1-methoxy-2-propanol, etc. can be used. Among these, as the liquid medium (D), using diethylene glycol can efficiently reduce the pigment (A1) to a pigment (A2) having a primary particle size of 10 nm or more and less than 100 nm in a short time, and is more preferable for producing a colorant capable of reducing the volume average particle size of the dispersion contained in the aqueous pigment dispersion. The liquid medium (D) is preferably used in the range of 60% by mass to 100% by mass with respect to the pigment (A1) contained in the composition, and more preferably used in the range of 80% by mass to 100% by mass for efficiently reducing the pigment (A1) to a pigment (A2) having a primary particle size of 10 nm or more and less than 100 nm in a short time. Next, the water-soluble inorganic salt (E) used in the method for producing the colorant of the present invention will be described. The water-soluble inorganic salt (E) is used to grind the pigment (A1) to obtain a pigment (A2) having a primary particle size of 10 nm or more and less than 100 nm. As the water-soluble inorganic salt (E), for example, sodium chloride, potassium chloride, sodium nitrate, etc. can be used. Among them, as the water-soluble inorganic salt (E), it is preferable to use sodium chloride in order to efficiently produce a pigment (A2) having a primary particle size of 10 nm or more and less than 100 nm by grinding the pigment (A1). As the water-soluble inorganic salt (E), in order to efficiently produce a pigment (A2) having a primary particle size of 10 nm or more and less than 100 nm by grinding the pigment (A1), it is preferable to use a solid one. Specifically, as the water-soluble inorganic salt (E), it is preferable to use those having a primary particle size of 0.5 μm to 100 μm, and more preferably those having a primary particle size of 0.5 μm to 50 μm. The primary particle size refers to a value measured by the same method as the measurement method of the primary particle sizes of the pigment (A1) and the pigment (A2). The water-soluble inorganic salt (E) is preferably used in the range of 600% by mass to 900% by mass with respect to the pigment (A1), and more preferably used in the range of 700% by mass to 800% by mass in order to efficiently produce a pigment (A2) having a primary particle size of 10 nm or more and less than 100 nm by grinding the pigment (A1).

[0024] Next, the resin (B1) having an anionic group used in Step 2-1 will be described. The resin (B1) is used to impart good water dispersibility to the pigment (A2). Examples of the anionic group of the resin (B1) include a carboxyl group, a sulfonic acid group, or a phosphoric acid group. Examples of the resin (B1) include a polyvinyl resin having an anionic group, a polyester resin having an anionic group, an amino resin having an anionic group, an acrylic resin having an anionic group, an epoxy resin having an anionic group, a polyurethane resin having an anionic group, a polyether resin having an anionic group, a polyamide resin having an anionic group, an unsaturated polyester resin having an anionic group, a phenolic resin having an anionic group, a silicone resin having an anionic group, a fluorine-based polymer compound having an anionic group, a polysaccharide derivative having an anionic group, etc. Using an acrylic resin having an anionic group is more preferable for producing a colorant capable of reducing the volume average particle diameter of the dispersion contained in the aqueous pigment dispersion. Examples of the acrylic resin having an anionic group that can be used as the resin (B1) include styrene-acrylic acid copolymers such as styrene-(meth)acrylic acid copolymer, styrene-(meth)acrylate-(meth)acrylic acid copolymer, and (meth)acrylate-(meth)acrylic acid copolymer. Among them, as the acrylic resin having an anionic group, using a styrene-acrylic acid copolymer is more preferable for producing an aqueous pigment dispersion having excellent water dispersion stability and an inkjet printing ink having excellent ejection stability because the volume average particle diameter of the dispersion is small and the number of coarse particles is small. As the styrene-acrylic acid copolymer, a polymer of a monomer containing styrene and (meth)acrylic acid can be used. As the styrene-acrylic acid copolymer, it is preferable to use one in which the proportion of the structural unit derived from styrene is 50 to 90% by mass based on the total amount of the styrene-acrylic acid copolymer, and it is more preferable to use one in which the proportion is 70 to 90% by mass for producing an aqueous pigment dispersion having excellent water dispersion stability and an inkjet printing ink having excellent ejection stability because the volume average particle diameter of the dispersion is small and the number of coarse particles is small. Moreover, as the resin (B1), it is preferable to use one having a weight average molecular weight of 5,000 to 20,000, and it is more preferable to use one having a weight average molecular weight of 5,500 to 15,000 because the volume average particle diameter of the dispersion is small and the number of coarse particles is small, so as to produce an aqueous pigment dispersion excellent in water dispersion stability and to obtain an inkjet printing ink excellent in ejection stability. Moreover, as the resin (B1), it is preferable to use one having an acid value of 50 to 300, and it is more preferable to use one having an acid value of 60 to 200 because the volume average particle diameter of the dispersion is small and the number of coarse particles is small, so as to produce an aqueous pigment dispersion excellent in water dispersion stability and to obtain an inkjet printing ink excellent in ejection stability. The resin (B1) is preferably used in the range of 5 to 50% by mass, and more preferably used in the range of 20 to 40% by mass, based on the total amount of the pigment (A2) contained in the kneaded product obtained in the step 1, because the volume average particle diameter of the dispersion is small and the number of coarse particles is small, so as to produce an aqueous pigment dispersion excellent in water dispersion stability and to obtain an inkjet printing ink excellent in ejection stability. Moreover, as the basic compound (C) used in the step 2-1, for example, hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide can be used. Among them, as the basic compound (C), it is preferable to use potassium hydroxide because it is excellent in water dispersion stability and can further improve the ejection stability of the inkjet printing ink. The amount of the basic compound (C) used is preferably in the range such that the neutralization rate of the acid groups possessed by the resin (B1) is 50 to 200%. The neutralization rate refers to the value calculated by the following method. Neutralization rate (%) = mass of basic compound (g) × 56.11 × 100 / resin acid value (mgKOH / g) × equivalent of basic compound (C) × mass of resin (B1) (g) × 100 Next, the resin (B2) having an anionic group neutralized by the basic compound (C) used in the step 2-2 will be described. The resin (B2) used in the step 2-2 refers to a resin obtained by premixing the resin (B1) exemplified as being usable in the step 2-1 and a basic compound (C) and neutralizing part or all of the acid groups of the resin (B1) with the basic compound (C). Therefore, as the resin (B1) and the basic compound (C) used for producing the resin (B2), those similar to those exemplified as being usable in the step 2-1 can be used. The resin (B2) is preferably used in the range of 5 to 50% by mass, more preferably in the range of 20 to 40% by mass, based on the total amount of the pigment (A2) contained in the kneaded product obtained in the step 1. This is because when used within this range, the volume average particle diameter of the dispersion is small and the number of coarse particles is small, which is more preferable for producing an aqueous pigment dispersion having excellent water dispersion stability and obtaining an inkjet printing ink having excellent ejection stability. The colorant obtained by the production method having the above step 1 and step 2-1 or step 2-2 can reduce the volume average particle diameter of the dispersion contained in the pigment composition and the aqueous pigment dispersion described later using the colorant, and can significantly reduce the number of coarse particles. The colorant obtained by the production method having the above step 1 and step 2-1 or step 2-2 contains the water-soluble inorganic salt (E) used for grinding the pigment (A1), the liquid medium (D), and the like. If a large amount of the water-soluble inorganic salt (E) remains in the colorant, it may reduce the dispersibility of the colorant in the aqueous medium. Therefore, it is preferably removed as much as possible. As a method for removing the water-soluble inorganic salt (E), for example, the colorant obtained by the production method having the above step 1 and step 2-1 or step 2-2 is mixed with water at 60°C to 80°C to dissolve the water-soluble inorganic salt (E) in water, and then filtered. On one hand, in order to increase the proportion of covering a part or all of the surface of the pigment (A2) with the resin (B1) or resin (B2), and as a result, obtain a colorant that can be used in the production of an aqueous pigment dispersion or the like with even more excellent water dispersion stability, it is preferable to mix the colorant obtained by the production method having the above step 1 and step 2-1 or step 2-2 with an acidic aqueous solution (G) to form a precipitate, and use this precipitate as the colorant. Therefore, in the present invention, in order to perform the filtration step for removing the water-soluble inorganic salt (E) and the step for obtaining the precipitate in one batch, the colorant obtained by the production method having the above step 1 and step 2-1 or step 2-2 is mixed with water at, for example, 60°C to 80°C to dissolve the water-soluble inorganic salt (E) in water. Then, after supplying the acidic aqueous solution (G) to form a precipitate, it is filtered, and the precipitate is washed through step 3 to produce the colorant. As the acidic aqueous solution (G), for example, those in which hydrochloric acid or sulfuric acid is dissolved in water can be used. The pH of the acidic aqueous solution (G) is preferably 3 to 4. It is preferable to use an aqueous solution of hydrochloric acid as the acidic aqueous solution (G) in order to precipitate the resin (B1) or resin (B2) on the surface of the pigment (A2) and obtain a colorant capable of producing a pigment composition or an aqueous pigment dispersion with a small volume average particle diameter of the dispersion and a small number of coarse particles. It is preferable to use the hydrochloric acid aqueous solution containing 0.5 to 5% by mass of hydrochloric acid based on the total amount of the hydrochloric acid aqueous solution, and more preferably use the one containing 1 to 3% by mass, in order to precipitate the resin (B1) or resin (B2) on the surface of the pigment (A2) and obtain a colorant capable of producing a pigment composition or an aqueous pigment dispersion with a small volume average particle diameter of the dispersion and a small number of coarse particles. Examples of the method for mixing the colorant and the acidic aqueous solution (G) include, for example, a method of previously preparing a mixture of the colorant and water, and dropping the acidic aqueous solution (G) into the mixture. The dropping of the acidic aqueous solution (G) is preferably carried out at a rate of, for example, 100 cc to 800 cc per hour in order to deposit the resin (B1) on the surface of the pigment (A2), and to obtain a colorant capable of producing a pigment composition or an aqueous pigment dispersion having a small volume average particle diameter of the dispersion and a small number of coarse particles. When the mixture containing the colorant and water and the acidic aqueous solution (G) are mixed by the above method, a colorant containing the pigment (A2) and the resin (B1) or resin (B2) precipitates. This colorant is in the so-called wet cake form, and most of the liquid medium (D) and the water-soluble inorganic salt (E) contained in the colorant before passing through the step 3 are removed. As a method for sufficiently removing the liquid medium (D) and the water-soluble inorganic salt (E) from the precipitate, a method of washing the precipitate with water at preferably 60°C to 80°C can be mentioned.

[0025] The colorant obtained through the step 3 has the water-soluble inorganic salt (E) and the like removed, and the resin (B1) or resin (B2) is deposited on a part or all of the surface of the pigment (A2), covering a part or all of the surface of the pigment (A2) with the resin (B1), making it easy to disperse in an aqueous medium. By using the colorant, a pigment composition or an aqueous pigment dispersion having a small volume average particle diameter of the dispersion and a small number of coarse particles can be obtained.

[0026] Next, a method for producing a pigment composition using the colorant obtained by the above method will be described. The pigment composition is obtained by passing through a step 4 of treating the colorant obtained through the step 1 and the step 2-1 or step 2-2 and, if necessary, the step 3 with a rotor-stator type processor.

[0027] The manufacturing method of the pigment composition according to this embodiment can be manufactured by passing through a step 4 of mixing the colorant and an aqueous medium or the like using a rotor-stator type processing machine. The step 4 is a step of manufacturing an aqueous dispersion to such an extent that it can be fed into a high-pressure homogenizer in a step 5-1 or step 5-2 described later. At that time, the colorant may be pulverized or crushed in the first treatment step. Crushing means, for example, a treatment of crushing a lump that is integral. Cracking means, for example, a treatment of dissociating and loosening aggregates.

[0028] The pigment composition according to this embodiment may be used to obtain an ink and may also be used as an ink. The pigment composition according to this embodiment can be used, for example, as a pigment composition for printing ink (for example, inkjet printing ink).

[0029] The manufacturing apparatus of the pigment composition according to this embodiment is a manufacturing apparatus for a pigment composition for ink, and includes a rotor-stator type first processing machine that mixes the colorant and an aqueous medium or the like, and a raw material supply unit that supplies the colorant or the like to the first processing machine. Hereinafter, the "rotor-stator type first processing machine" will be simply referred to as the "rotor-stator type processing machine".

[0030] In a rotor-stator type processing machine, as will be described later, a shearing force is applied to the colorant between the rotor and the stator, so that the aggregated coarse particles contained in the colorant are pulverized or crushed. Therefore, according to the manufacturing method and manufacturing apparatus of the pigment composition according to this embodiment, by using a rotor-stator type processing machine, the number of coarse particles in the pigment composition can be more efficiently further reduced, and the number of coarse particles having a particle diameter of 1.0 μm or more can be further reduced. According to the manufacturing method and manufacturing apparatus of the pigment composition according to this embodiment, by suppressing an increase in the processing time for obtaining a pigment composition with a small number of coarse particles, a pigment composition with an even smaller number of coarse particles can be obtained with high productivity. According to the manufacturing method and manufacturing apparatus of the pigment composition according to this embodiment, the number of coarse particles having a particle diameter of 0.5 μm or more can also be further reduced.

[0031] According to the method and apparatus for manufacturing a pigment composition according to this embodiment, the viscosity of the pigment composition can be reduced to such an extent that the pigment composition can be introduced into a high-pressure homogenizer, and the number of coarse particles in the pigment composition can be more efficiently reduced further. According to the method and apparatus for manufacturing a pigment composition according to this embodiment, excellent storage stability (dispersion stability of the solid content) can be obtained in the pigment composition.

[0032] According to the method and apparatus for manufacturing a pigment composition according to this embodiment, by using a rotor-stator type processor, a high printing density can be obtained when compared under the condition that the composition of the resin (B1) or resin (B2) and the mass ratio of the resin (B1) or resin (B2) to the pigment (A2) are the same. Further, according to the method and apparatus for manufacturing a pigment composition according to this embodiment, a high adsorption rate of the resin (B1) or resin (B2) to the pigment (A2) can be obtained.

[0033] From the viewpoints of efficiently reducing the number of coarse particles, easily shortening the time required for steps 5-1 and 5-2, and easily improving the adsorption rate of the resin (B1) or resin (B2) to the pigment (A2) and easily obtaining excellent storage stability due to the promotion of the dissolution of the resin (B1) or resin (B2), the following range is preferable for the temperature in step 4. The temperature is preferably 25°C or higher, more preferably 30°C or higher, still more preferably 40°C or higher, particularly preferably 50°C or higher, extremely preferably 55°C or higher, and very preferably 60°C or higher. The temperature is preferably 80°C or lower, more preferably 75°C or lower, still more preferably 70°C or lower, particularly preferably 65°C or lower, and extremely preferably 60°C or lower. From these viewpoints, the temperature is preferably 25 to 80°C, more preferably 50 to 80°C, and still more preferably 60 to 80°C.

[0034] In the rotor-stator type processor in the manufacturing apparatus of the pigment composition according to this embodiment, a rotor-stator type processor includes a rotor having a rotatable blade portion and a stator having a wall portion disposed on the outer peripheral side of the blade portion. The processor may be any of a grinder, a disintegrator, a disperser, and the like. The rotor and the stator can be of any commercially available shape, and those of different shapes or the same shape can be used in combination. Since there are differences in the transportability of the colorant, the share rate (miniaturization ability), the amount of heat generated during miniaturization, etc. depending on the shape, the combination can be selected according to the properties of the colorant. Usually, it is easier to miniaturize with a rotor having a large number of teeth, and the amount of heat generated increases.

[0035] FIG. 1 (FIGS. 1(a) and 1(b)) is a schematic cross-sectional view showing an example of a rotor-stator type processor. The rotor-stator type processor 100 shown in FIG. 1 includes a central axis 10, a rotor 20, and a stator 30. Examples of the constituent materials of the central axis 10, the rotor 20, and the stator 30 include metal materials and ceramics.

[0036] The central axis 10 is a long member and extends, for example, in the vertical direction. The central axis 10 supports the rotor 20 and the stator 30.

[0037] The rotor 20 has an annular (for example, circular ring-shaped) blade portion 22 extending in the longitudinal direction of the central axis 10 at the outer peripheral portion of the rotor 20, and a connecting portion 24 connecting the blade portion 22 and the central axis 10. The blade portion 22 can rotate about the central axis 10. The blade portion 22 has an opening (through hole) 22a penetrating the blade portion 22, and for example, has a plurality of openings 22a at intervals (for example, equal intervals) along the circumferential direction of the blade portion 22. The opening direction of the opening 22a may be inclined with respect to the radial direction. The upper end portion of the opening 22a in the vertical direction may be open without the members constituting the rotor 20 being disposed. The number, arrangement, and shape of the openings 22a are not particularly limited.

[0038] The arrangement and shape of the blade portions in the rotor of the rotor-stator type processor are not particularly limited. For example, the blade portions are not limited to an annular member disposed on the outer peripheral portion of the rotor, and may have a shape extending from the central portion to the outer peripheral portion of the rotor. The rotor may have a plurality of blade portions having a shape extending from the central portion to the outer peripheral portion of the rotor. The blade portions having a shape extending from the central portion to the outer peripheral portion of the rotor may be in a streamline shape.

[0039] The stator 30 has an annular (e.g., circular-ring-shaped) wall portion 32 extending in the longitudinal direction of the central axis 10 on the outer peripheral portion of the stator 30, and a connecting portion 34 connecting the wall portion 32 and the central axis 10. The wall portion 32 is disposed on the outer peripheral side of the blade portion 22 in the rotor-stator type processor 100. The wall portion 32 has an opening (through hole) 32a penetrating the wall portion 32, and for example, has a plurality of openings 32a spaced apart (e.g., at equal intervals) along the circumferential direction of the wall portion 32. The opening direction of the opening 32a may be inclined with respect to the radial direction.

[0040] The number, arrangement, and shape of the openings in the wall portion of the stator are not particularly limited. FIG. 2 is a schematic side view showing an example of the stator (the wall portion of the stator) in the rotor-stator type processor. Examples of the wall portion of the stator include a wall portion having openings arranged in an array (e.g., rectangular openings such as square shapes) (FIG. 2(a)), a wall portion having a plurality of rectangular openings arranged in a row (FIG. 2(b)), a wall portion having a plurality of circular (e.g., perfect circular) openings arranged in a row (FIG. 2(c)), and the like. Examples of the shape of the openings include rectangular shapes (square shapes, rectangular shapes, etc.), circular shapes (perfect circular shapes, elliptical shapes, etc.), and the like.

[0041] The stator may have a plurality of annular (e.g., circular ring-shaped) wall portions extending in the longitudinal direction of the central axis on the outer peripheral portion of the stator. For example, the stator may include the above-described wall portion 32 as the first wall portion, and may further include a second wall portion disposed on the outer peripheral side of the first wall portion in the rotor-stator type processor, and may further include a third wall portion disposed on the outer peripheral side of the second wall portion in the rotor-stator type processor. The number of wall portions is not particularly limited and may be 4 or more.

[0042] FIG. 3 is a schematic diagram for explaining the processing in the rotor-stator type processor, and is a schematic diagram showing an enlarged part of the outer peripheral portion of the rotor-stator type processor 100 shown in FIG. 1. In the rotor-stator type processor 100, for example, after the colorant of the present invention, a basic compound as necessary, and an aqueous medium as necessary are supplied around the central axis 10, as shown in FIG. 3, the colorant and, if necessary, the basic compound and the aqueous medium pass through the opening 22a of the blade portion 22 of the rotor 20 (flow path F1 in the figure) and reach the space between the blade portion 22 and the wall portion 32 of the stator 30. Then, in this space, the colorant is dispersed in the aqueous medium by the shearing force generated due to the rotational movement of the blade portion 22. Also, at this time, the coarse particles P (solid content) are also pulverized or crushed by the shearing force.

[0043] The shear rate (refinement ability) provided by the processing unit composed of the rotor and the stator is preferably 50000 s -1 or more, more preferably 75000 s -1 or more, still more preferably 90000 s -1 or more, particularly preferably 100000 s -1 or more, extremely preferably 120000 s -1 or more, very preferably 150000 s -1 or more, even more preferably 170000 s -1 or more. The upper limit value of the shear rate is, for example, 400000 s -1May be as follows, 250000 s -1 May be as follows. From these viewpoints, the shear rate is preferably 50000 to 400000 s -1 is preferable. The shear rate [s -1 can be obtained by dividing the peripheral speed [m / s] of the blade portion of the rotor by the distance [m] between the blade portion and the wall portion of the stator.

[0044] The rotor-stator type processor may have a plurality of processing units (grinding units or crushing units) composed of a rotor and a stator. By flowing the colorant from the processing unit with a low shear rate toward the processing unit with a high shear rate, clogging is likely to be suppressed, and thus the number of coarse particles can be efficiently reduced. The rotor-stator type processor may have a plurality of processing units along a central axis extending in the vertical direction (may have multiple stages of processing units). When the rotor-stator type processor has a plurality of processing units along the central axis, from the viewpoint of efficiently reducing the number of coarse particles, it is preferable to arrange the processing unit with a higher shear rate downward in the vertical direction.

[0045] The rotor-stator type processor may be an in-line type processor or a batch type processor. In an in-line type processor, a colorant or the like is continuously supplied. For example, the processor can be installed in the middle of a processing path (e.g., a pipe), and the raw material composition can be continuously processed (ground or crushed). In an in-line type processor, since the entire colorant or the like is forced to pass through the processor, it is easier to uniformly process the entire raw material composition in a short time compared to a batch type processor in which mainly only the periphery of the rotor is processed. According to the in-line type processor, since the number of coarse particles can be efficiently reduced, clogging of the pipes in the processor is likely to be suppressed. According to the in-line type processor, the viscosity of the pigment composition is likely to be reduced. In an in-line type processor, the colorant or the like may circulate. In a batch type processor, the colorant or the like is supplied intermittently, and the colorant or the like is replaced for each process.

[0046] Examples of rotor-stator type processors include the device named "magic LAB" (inline type, maximum peripheral speed: 41 m / s, maximum rotation speed: 26,000 rpm) manufactured by IKA Corporation; the device named "VERSO" (high shear inline mixer, inline type, maximum peripheral speed: 20 m / s, maximum rotation speed: 10,000 rpm) manufactured by Silverstone Nippon Co., Ltd.; the device named "L5M-A" (batch type, maximum peripheral speed: 20 m / s, maximum rotation speed: 10,000 rpm) manufactured by Silverstone Nippon Co., Ltd., and the like. As processors manufactured by IKA Corporation, processors equipped with a UTR module (ULTRA-TURRAX), a DR module (DISPAX-REACTOR), an MK module, an MKO module, and a CMX module can be used. The DR module has three processing units (stages) composed of a rotor and a stator, and since the share rate can be adjusted by the combination of the rotor and the stator, it is easy to efficiently reduce the number of coarse particles. For example, by using processing units of 2P / 4M / 6F in order from the upper vertical direction, processing units with a higher share rate can be arranged as going downward in the vertical direction.

[0047] The raw material supply unit in the manufacturing apparatus for the pigment composition according to the present embodiment is not particularly limited as long as it can supply a colorant or the like to a rotor-stator type processor. The raw material supply unit may be a pipe, a pump, or the like that supplies the raw material supply unit.

[0048] The pigment composition obtained in the step 4 can be used for the production of an aqueous pigment dispersion. The aqueous pigment dispersion is one in which the colorant contained in the pigment composition is dispersed in water. The aqueous pigment dispersion can be produced by passing through a step 5-1 of obliquely colliding the pigment compositions obtained in the step 4 with each other, or a step 5-2 of colliding the pigment composition with a spherical rigid body supported rotatably. The second processor that can be used in the step 5-1 and the step 5-2 can further efficiently reduce the number of coarse particles in the aqueous pigment dispersion, and easily adjust the physical properties (number of coarse particles, particle diameter, etc.) of the solid content to desired physical properties. The manufacturing apparatus of the aqueous pigment dispersion according to the present embodiment may include a supply unit (piping, pump, etc.) for supplying the pigment composition obtained in the step 4 to the second processor.

[0049] Examples of the second processor include a high-pressure homogenizer, a paint shaker, a bead mill, a roll mill, a sand mill, a ball mill, an attritor, a basket mill, a sand mill, a sand grinder, a dyno mill, a dispermat, an SC mill, a spike mill, an agitator mill, a juice mixer, an ultrasonic homogenizer, a nanomizer, a desolver, a disper, a high-speed impeller disperser, a kneader, a planetary mixer, etc. As the high-pressure homogenizer, for example, the equipment named "Starburst" manufactured by Sugino Machine Limited can be used. The pressure in the high-pressure homogenizer is preferably 50 to 245 MPa, more preferably 80 to 200 MPa, still more preferably 100 to 200 MPa, and particularly preferably 130 to 200 MPa. When the pigment component contains carbon black, it can be processed at a low pressure, and it is easy to achieve a longer service life of the apparatus and an improvement in the production amount per unit time.

[0050] The second processor is a processor capable of obtaining an aqueous pigment dispersion in which the colorant is dispersed in water by obliquely colliding the pigment compositions obtained in the step 4 with each other. In this case, for example, the second processor may have an obliquely colliding chamber. By pressurized injection of the pigment composition obtained in the step 4 from a plurality of directions, the pigment compositions obtained in the step 4 can be collided with each other.

[0051] The second processor is a processor capable of obtaining an aqueous pigment dispersion in which a colorant contained in the pigment composition is dispersed in water by causing the pigment composition obtained in the step 4 to collide with a spherical hard body rotatably supported (for example, supported). In this case, for example, the second processor may have a ball collision chamber. By pressurized injection of the pigment composition obtained in the step 4, the pigment composition obtained in the first treatment step can be made to collide with the hard body. The hard body may be rotatably supported eccentrically from the injection axis. Examples of the material of the hard body include ceramics and sintered diamond.

[0052] Examples of the chamber used in the second processor include a separation chamber, a single nozzle chamber, a slit chamber, etc., in addition to an oblique collision chamber and a ball collision chamber. Examples of these chambers include the chamber of the equipment named "Starburst" manufactured by Sugino Machine Limited. When avoiding wear of the hard body during long-term use in the oblique collision chamber and obtaining a shearing force superior to that of a chamber (such as a single nozzle chamber) that does not utilize the collision force, it is preferable to use an oblique collision chamber.

[0053] The aqueous pigment dispersion obtained by the above method can be used in the manufacture of ink. Among others, the aqueous pigment dispersion is preferably used in the manufacture of inkjet printing ink.

Example

[0054] (Styrene-acrylic acid copolymer A) After charging 100 parts by mass of methyl ethyl ketone into a reaction vessel equipped with a stirring device, a dropping device, and a reflux device, the inside of the reaction vessel was purged with nitrogen while stirring. Next, the reaction vessel was heated, and while methyl ethyl ketone was refluxing, a mixed solution of 72 parts by mass of styrene, 12 parts by mass of acrylic acid, 16 parts by mass of methacrylic acid, and 8 parts by mass of a polymerization catalyst (trade name: V-59, manufactured by Wako Pure Chemical Industries, Ltd.) was dropped from the dropping device over 2 hours. From the middle of the dropping, the temperature of the reaction vessel was maintained at 80°C. After the dropping was completed, the reaction was continued at the same temperature for 25 hours. After the reaction was completed, the inside of the reaction vessel was allowed to cool, and then methyl ethyl ketone was added to obtain a solution having a solid content concentration of 50% by mass. Further, after drying this solution, it was pulverized into a powder having a particle size of 1 mm or less to obtain styrene-acrylic acid copolymer A. The acid value of styrene-acrylic acid copolymer A was 180 mgKOH / g, and the weight average molecular weight was 9000.

[0055] The weight average molecular weight is a value measured by the GPC (gel permeation chromatography) method and is a value converted to the molecular weight of polystyrene used as a standard substance. The measurement was carried out under the following apparatus and conditions. Liquid delivery pump: LC-9A (manufactured by Shimadzu Corporation) System controller: SLC-6B (manufactured by Shimadzu Corporation) Autoinjector: S1L-6B (manufactured by Shimadzu Corporation) Detector: RID-6A (manufactured by Shimadzu Corporation) Data processing software: Sic480II data station (manufactured by System Instruments Co., Ltd.) Column: GL-R400 (guard column) + GL-R440 + GL-R450 + GL-R400M (manufactured by Hitachi Chemical Co., Ltd.) Elution solvent: THF (tetrahydrofuran) Elution flow rate: 2 mL / min Column temperature: 35°C

[0056] Example 1 (Step 1) Into a twin-screw kneader with a capacity of 1 L (manufactured by Yoshida Seisakusho Co., Ltd.), 400 g of sodium chloride and 53.25 g of a phthalocyanine pigment (crude pigment, β-crude, Pigment Blue 15:3) with a primary particle diameter of 1000 nm or more were charged. After operating for 5 minutes, it was stopped once. Then, 48.75 g of diethylene glycol, 0.6 g of sodium hydroxide (granules), and 1.2 g of xylene were charged, and the operation was started at a set temperature of 94°C. Seven hours after the start of the operation, the kneaded material in the container was sampled, and it was confirmed that the primary particle diameter of the phthalocyanine pigment was within the range of 10 nm or more and 60 nm or less, so Step 1 was completed. (Step 2-1) After changing the set temperature of the kneader to 60°C, 16 g of the above styrene-acrylic acid copolymer A as a resin having an anionic group, 6 g of a 48 mass% potassium hydroxide aqueous solution, and 29.8 g of diethylene glycol were added to the kneaded material obtained in Step 1, and kneading was performed for 2 hours to obtain a colorant in which the pigment was coated with the resin having an anionic group. (Step 3) After adjusting the colorant obtained in Step 2-1 to a pigment concentration of 2 mass% with hot water at 70°C, hydrochloric acid with a concentration of 2 mass% was dropped with a burette. The dropping was performed at a rate of 200 cc / 0.5 hour. Also, the dropping was stopped when the pH of the colorant reached 3.8. The colorant obtained by the above method was filtered using filter paper (Advantec No. 4) and a Buchner funnel. Next, the colorant in which the pigment was coated with the resin having an anionic group remaining on the surface of the filter paper was washed with pure water. The washing was performed until the conductivity of the water (filtrate) after washing the colorant became 200 μS / cm or less. By washing by the above method, a wet cake-like colorant with a pigment concentration of 24.5 mass% was obtained. (Step 4) By supplying pure water to the colorant obtained by the above method, a colorant with a pigment concentration of 15% by mass was obtained. (Pure water was added to adjust the 24.5% wet cake to 15%). To 100 g of the colorant with a pigment concentration of 15% by mass, 2.4 g of a 34% by mass aqueous potassium hydroxide solution was added, and the mixture was put into a rotor-stator type processor (manufactured by Silver Sonic Nippon Co., Ltd., equipment name: L5M-A, square hole high-shear screen, batch type). Next, while heating to 60 °C, the mixture was processed at a peripheral speed of 16 m / s (shear rate: 87000 s -1 ), and a pigment composition was obtained by treating it at a rotational speed of 8000 rpm for 10 minutes. (Step 5) Next, the pigment composition obtained in Step 4 above was processed using a high-pressure homogenizer (manufactured by Sugino Machine Limited, equipment name: Starburst, ball collision chamber, 240 MPa, 1 pass) to obtain an aqueous pigment dispersion.

[0057] Example 2 In Step 2-1 above, the amount of styrene-acrylic acid copolymer A used was changed from 16 g to 26.6 g, and the amount of 48% by mass aqueous potassium hydroxide solution used was changed from 6 g to 9.98 g. In Step 3, instead of the wet cake-like pigment composition with a pigment concentration of 24.5% by mass, a wet cake-like pigment composition with a pigment concentration of 24.7% by mass was obtained. In Step 4, an aqueous pigment dispersion was obtained in the same manner as in Example 1, except that the amount of 48% by mass aqueous potassium hydroxide solution used was changed from 6 g to 9.98 g.

[0058] Example 3 An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that the following Step 2-2 was performed instead of Step 2-1 above, and in Step 3, instead of the wet cake-like pigment composition with a pigment concentration of 24.5% by mass, a wet cake-like pigment composition with a pigment concentration of 24.1% by mass was obtained. (Step 2-2) After completing the above step 1, the set temperature of the kneader was changed to 60°C. Next, an aqueous solution of a resin having an anionic group neutralized with potassium hydroxide was obtained by stirring and mixing 16 g of the styrene-acrylic acid copolymer A1 used as the resin having an anionic group, 6 g of a 48% by mass aqueous potassium hydroxide solution, and 50 g of pure water. Next, 82 g of the aqueous solution and 29.8 g of diethylene glycol were mixed and kneaded for 2 hours to obtain a colorant coated with the resin having an anionic group neutralized with the pigment.

[0059] Example 4 An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that a 2 L Trimix (manufactured by Inoue Manufacturing Co., Ltd.) was used instead of a 1 L kneader (manufactured by Yoshida Manufacturing Co., Ltd.).

[0060] Comparative Example 1 (Step 1) 53.25 g of a phthalocyanine pigment (coarse pigment, β crude, Pigment Blue 15:3) having a primary particle diameter of 1000 nm or more, 400 g of sodium chloride, 48.75 g of diethylene glycol, 0.6 g of sodium hydroxide (granules), and 1.2 g of xylene were charged into a 1 L kneader (manufactured by Yoshida Manufacturing Co., Ltd.), and the operation was started at a set temperature of 94°C. Seven hours after the start of the operation, the kneaded product in the container was sampled, and since it was confirmed that the primary particle diameter of the phthalocyanine pigment had become 10 nm or more and 60 nm or less, Step 1 was completed. (Other steps) The kneaded product obtained in Step 1 was taken out from the kneader, adjusted to a pigment concentration of 2% by mass with 70°C hot water, and then a colorant was obtained by dropping 2% by mass hydrochloric acid with a burette. The dropping was performed at a rate of 200 cc / 0.5 hour. Also, the dropping was stopped when the pH of the colorant reached 3.8. The colorant obtained by the above method was filtered using filter paper (Advantec No. 4) and a Buchner funnel. Next, the pigments and the like remaining on the surface of the filter paper were washed with pure water. The washing was carried out until the conductivity of the water (filtrate) after washing reached 200 μS / cm or less. By washing by the above method, a wet cake-like colorant with a pigment concentration of 25% by mass was obtained. (Step 4) By supplying pure water to the colorant obtained by the above method, a colorant with a pigment concentration of 15% by mass was obtained. To 100 g of the colorant with a pigment concentration of 15% by mass, 2.4 g of a 34% by mass aqueous potassium hydroxide solution was added, and the mixture was put into a rotor-stator type processor (manufactured by Silver Sonic Japan Co., Ltd., equipment name: L5M-A, square hole high-shear screen, batch type). Next, while heating to 60°C, with a peripheral speed of 16 m / s (shear rate: 87000 s -1 ), and processed at a rotational speed of 8000 rpm for 10 minutes to obtain a pigment composition. (Step 5) Next, the pigment composition obtained in Step 4 was processed using a high-pressure homogenizer (manufactured by Sugino Machine Limited, equipment name: Starburst, ball collision chamber, 240 MPa, 1 pass) to obtain an aqueous pigment dispersion.

[0061] Method for measuring the primary particle diameter of the pigment A mixture with a pigment concentration of 0.1% by mass obtained by mixing the pigment and acetone and ultrasonically dispersed for 10 minutes was cast on a grid mesh and dried to obtain a sample. The surface of the sample was observed with a transmission electron microscope, and the diameters (maximum values) of 50 pigments were measured. The average value of the diameters was calculated and taken as the primary particle diameter.

[0062] Method for measuring the particle diameter of the dispersion contained in the aqueous pigment dispersion The aqueous pigment dispersion was put into a cell of about 4 mL. Using a nanoparticle size distribution analyzer "UPA150" manufactured by Microtrac·Bell Co., Ltd., the particle diameter was measured by detecting the scattered light of laser light in an environment at 25°C. As the particle diameter, the volume average particle diameter (Mv), number average particle diameter (Mn), D50, D90, and D95 were measured.

[0063] Method for measuring the number of coarse particles of the dispersion contained in the aqueous pigment dispersion Using a particle size distribution analyzer (Accusizer 780 APS, manufactured by Particle Sizing Systems, number counting method), the number of particles with a diameter exceeding 1.0 μm and the number of particles with a diameter exceeding 0.5 μm were measured according to the following procedure. The aqueous pigment dispersion was diluted with pure water so that the sensitivity was in the range of 1000 - 4000 particles / mL. Next, using the particle size distribution analyzer, the number of particles with a diameter exceeding 1.0 μm and the number of particles with a diameter exceeding 0.5 μm contained in the diluted aqueous pigment dispersion were measured three times. Subsequently, the average value of the values obtained by multiplying the measured values of the number of particles by the dilution concentration respectively was calculated as the number of coarse particles.

[0064] [Table 1]

Explanation of symbols

[0065] 10... central axis, 20... rotor, 22... blade part, 22a... opening, 24... connection part, 30... stator, 32... wall part, 32a... opening, 34... connection part, 100... rotor-stator type processor, F1, F2... flow paths.

Claims

1. A step 1 of obtaining a kneaded product containing a pigment (A2) having a primary particle diameter in the range of 10 nm or more and less than 100 nm, a liquid medium (D), and a water-soluble inorganic salt (E) by kneading a composition containing a pigment (A1) having a primary particle diameter of 100 nm or more, a liquid medium (D), and a water-soluble inorganic salt (E) with a processor (F); and a step 2-1 of mixing the kneaded product with a resin (B1) having an anionic group and a basic compound (C), or a step 2-2 of mixing the kneaded product with a resin (B2) having an anionic group neutralized by a basic compound (C). A method for producing a colorant in which the pigment (A2) is coated with the resin (B1) or the resin (B2).

2. The method for producing a colorant according to claim 1, wherein the processor (F) is a double-arm kneader or a kneader.

3. A step 3 of washing the precipitate after obtaining the precipitate by mixing the colorant obtained by the production method according to claim 1 or 2 with an acidic aqueous solution (G). A method for producing a colorant in which the pigment (A2) is coated with the resin (B1) or the resin (B2).

4. A method for producing a pigment composition having a step 4 of treating the colorant obtained by the production method according to claim 3 with a rotor-stator type processor.

5. The method for producing a pigment composition according to claim 4, wherein the rotor-stator type processor is an in-line processor to which the colorant is continuously supplied.

6. A method for producing an aqueous pigment dispersion having a step 5-1 of obliquely colliding the pigment compositions obtained by the production method according to claim 4 or 5 with each other, or a step 5-2 of colliding the pigment composition with a spherical hard body rotatably supported.

Images