JP2016124969A - Production method of pigment dispersion and inkjet ink produced by the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet ink in which, uniform and minute dispersion of a pigment can be achieved, and which has high storage stability.SOLUTION: A production method of a pigment dispersion comprises a first step, a second step, and a third step. The first step is a step for, performing dispersion processing to a mixture containing a pigment, a dispersant, and an organic solvent by using a media-less dispersion machine in which a clearance of a shearing part is 100 μm or more and 1500 μm or less, for preparing a primary dispersion. The second step is a step for removing coarse particles from the primary dispersion using difference of sedimentation velocity of particles. The third step is a step for, performing the dispersion processing to the primary dispersion from which the coarse particles have been removed, using a media dispersion machine using media particles, for preparing a secondary dispersion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a pigment dispersion and an inkjet ink produced by the method.

  The ink jet recording method is a recording method in which printing is performed by ejecting liquid ink from a nozzle toward a recording medium by using pressure, heat, electric field or the like as a driving source. Such a recording method is low in running cost, can achieve high image quality, and can print various inks according to the application, and thus the market has been expanding in recent years.

  Conventionally, aqueous inks containing pigments and aqueous solvents and oil-based inks containing pigments and organic solvents have been used as inks for ink jets applied to the ink jet recording system. In recent years, higher color developability has been demanded for pigments used as color formers in ink jet inks, and in order to achieve this high color developability, it is necessary to make the dispersed particle size of pigment particles smaller. The nature is increasing.

  Conventionally, as a method for dispersing pigment particles, a method of crushing and pulverizing pigment particles using a media disperser by a shearing force, a frictional force due to stirring / mixing, an impact force due to a collision between media particles, and the like is known. ing.

  Generally, pigment agglomerated particles include particles having a high cohesive force (hereinafter also referred to as particle A) and particles having a relatively low cohesive force (hereinafter also referred to as particle B). Forcible crushing with an external force using a media disperser leads to the destruction of the primary particles of the pigment, and the pigment particles whose primary particles are broken easily reaggregate. And increase in viscosity of the pigment dispersion occur.

  In order to solve this problem, in Patent Document 1, before dispersing the pigment with a media disperser, the pigment is pulverized using a high-speed stirring medialess disperser, thereby reducing the dispersed particle size of the pigment particles. In addition, a method for producing a pigment dispersion capable of obtaining a pigment dispersion having a low viscosity has been proposed.

  In the method for producing a pigment dispersion described in Patent Document 1, after agglomerated particles of the pigment are reduced to some extent by using a medialess disperser having a large shearing force, the dispersion of the media is performed by a relatively small force. It seems that the primary particle is prevented from being broken and the viscosity of the pigment dispersion is prevented from increasing.

JP 2014-56079 A

  In the method for producing a pigment dispersion described in Patent Document 1, since a medialess disperser having a large shearing force is used, both the particles A having a high cohesive force and the particles B having a low cohesive force by the medialess dispersion treatment are to some extent. Forced to break up into small particles. Therefore, in the next media dispersion step, the particles B having a weak cohesive force are easily finely dispersed. However, in the media dispersion process performed by a relatively small force, it is difficult to finely disperse the particles A having a strong cohesive force. There has been a problem that it is difficult to uniformly disperse the pigment.

  The present invention has been made in order to solve the above-mentioned problem. By inserting a step of removing particles A having a strong cohesive force between the medialess dispersion treatment step and the media dispersion treatment step, a uniform pigment can be obtained. The present invention provides a method for producing a pigment dispersion that enables fine dispersion.

  The method for producing a pigment dispersion of the present invention is a method for producing a pigment dispersion having a first step, a second step, and a third step, wherein the first step comprises a pigment, a dispersant, The mixed solution containing an organic solvent is a dispersion process using a medialess disperser having a shear clearance of 100 μm or more and 1500 μm or less to produce a primary dispersion, and the second step is particle sedimentation. It is a step of removing coarse particles from the primary dispersion using a difference in speed, and the third step is to disperse the primary dispersion from which coarse particles have been removed using a media disperser using media particles. It is the process of processing and producing a secondary dispersion, It is characterized by the above-mentioned.

  The inkjet ink of the present invention is characterized by including the pigment dispersion produced by the method for producing a pigment dispersion of the present invention.

  According to the present invention, it is possible to provide an ink-jet ink that can uniformly disperse a pigment and has high storage stability.

FIG. 1 is a cross-sectional view of an essential part showing an example of a medialess disperser used in the present invention.

(Method for producing pigment dispersion of the present invention)
The method for producing a pigment dispersion of the present invention includes a first step, a second step, and a third step, and the first step is a mixing process that includes a pigment, a dispersant, and an organic solvent. The liquid is dispersed using a medialess disperser having a shear clearance of 100 μm or more and 1500 μm or less to produce a primary dispersion. The second step utilizes the difference in the sedimentation rate of particles. And removing the coarse particles from the primary dispersion. In the third step, the primary dispersion from which the coarse particles have been removed is subjected to a dispersion treatment using a media disperser using media particles. It is a process for producing a dispersion.

  Since the method for producing a pigment dispersion of the present invention includes a step of removing coarse particles from the primary dispersion using the difference in the sedimentation rate of particles as the second step, in the first step, Pigment particles having strong cohesion that remain as coarse particles without being sufficiently pulverized can be removed from the primary dispersion, and pigment particles contained in the primary dispersion can be limited to particles having relatively weak cohesion. . As a result, in the third step, since it can be finely dispersed with a relatively small force using a media disperser, a pigment dispersion having a uniform dispersed particle diameter, a stable viscosity, etc. without destruction of primary particles. Can be obtained.

<First step>
In the first step, it is preferable to first prepare a dispersion base solution by dissolving a dispersant in an organic solvent, and prepare a mixed solution by adding a pigment to the dispersion base solution. Thereby, dispersion of the pigment can be more easily generated. The pigment, the dispersant, and the organic solvent will be described later.

  The medialess disperser used in the first step is not particularly limited, but preferably includes a rotor and a stator. This is because by providing the rotor and the stator, the shearing force applied to the pigment particles can be easily adjusted by adjusting the clearance between the rotor and the stator and adjusting the rotational speed of the rotor. As the medialess disperser, for example, a disperser “Clearmix” (trade name) manufactured by M Technique Co., Ltd., a disperser “Desper Mill” (trade name) manufactured by Asada Tekko Co., Ltd. can be used.

  Here, the medialess disperser used in the first step will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an essential part showing an example of a medialess disperser used in the first step of the present invention. In FIG. 1, the medialess disperser 10 includes a stator 11 and a rotor 12 that rotates inside the stator 11. A gap 13 is formed between the stator 11 and the rotor 12. In FIG. 1, the minimum size of the gap 13 between the stator 11 and the rotor 12 is defined as the clear tolerance C. The clearance C is set to a size of 100 μm or more and 1500 μm or less, and the clearance C is more preferably 500 μm or more and 1400 μm or less, and further preferably 800 μm or more and 1300 μm or less. If the clearance C is smaller than 100 μm, particles having a larger cohesive force than the clearance C are forcibly crushed, so that particles having a larger cohesive force cannot be removed as coarse particles in the next second step. On the other hand, if the clearance C exceeds 1500 μm, the shearing force becomes small and particles with weak cohesive force cannot be crushed, so that particles with weak cohesive force are also removed as coarse particles in the next second step.

  In FIG. 1, by rotating the rotor 12 and allowing the mixed solution to pass through the gap 13 between the stator 11 and the rotor 12 in the direction of the arrow, a shearing force can be applied to the pigment particles contained in the mixed solution.

The shear rate in the first ^{step, 1 × 10 6 (1 /} sec) or 1 × 10 ⁷ is preferably (1 / sec) or ^{less, 1 × 10 6 (1 /} sec) or 5 × 10 ⁶ ( 1 / sec) or less. When the shear rate is less than 1 × 10 ⁶ (1 / sec), sufficient shear force cannot be obtained, and many pigment particles remain coarse particles and are removed in the next second step. On the other hand, when the shear rate exceeds 1 × 10 ⁷ (1 / sec), the treatment liquid containing the pigment becomes high temperature during the dispersion treatment, and the pigment is exposed to high temperature, which is not preferable. However, when the cooling capacity of the medialess disperser is high, the shear rate may exceed 1 × 10 ⁷ (1 / sec).

The shear rate is represented by the following formula. In the following formula, the rotational speed of the rotor represents the rotational speed of the most distal portion 12a of the rotor.
Shear rate (1 / sec) = rotor speed (m / sec) / clearance C (m)

<Second step>
In the second step, the method is not limited as long as coarse particles can be removed from the primary dispersion using the difference in sedimentation speed of the particles. However, the removal of the coarse particles in the second step is performed by decantation. Is preferred. This is because, in the decantation described above, it is only necessary to leave the primary dispersion, and the coarse particles can be easily removed.

  The standing time of the primary dispersion in the decantation is not particularly limited, and may be, for example, 6 hours or more and 15 hours or less, depending on the type of pigment.

  Further, the particle diameter of the coarse particles removed in the second step is not particularly limited, but for example, coarse particles of 30 μm or more may be removed.

  Centrifugation can also be used as a method for removing coarse particles utilizing the difference in the sedimentation rate of the particles that can be employed in the second step. If it is the said centrifugation method, the processing time of the said 2nd term | claim process can be shortened more.

The reduction ratio of the solid content concentration of the primary dispersion due to the removal of the coarse particles in the second step is preferably 0.5% or more and 6.0% or less, and 0.7% or more and 3% when expressed by the following formula. 0.0% or less is more preferable, and 1.0% or more and 2.0% or less is still more preferable. If the solid content concentration reduction rate is less than 0.5%, coarse particles may not be sufficiently removed, which may adversely affect the storage characteristics of the ink. Further, if the reduction ratio of the solid content concentration exceeds 6.0%, there is a possibility that necessary pigment particles may be removed, and it may be difficult to produce an efficient pigment dispersion.
Reduction ratio of solid content concentration (%) = [(solid content concentration of primary dispersion before start of second step−solid content concentration of primary dispersion after end of second step) / primary dispersion before start of second step Solid content concentration] × 100

<Third step>
The media disperser used in the third step is not particularly limited. For example, a media disperser “Ecomill” (trade name) manufactured by Asada Tekko Co., Ltd. can be used.

  The particle diameter of the media particles used in the media disperser in the third step is preferably 0.05 mm or more and 0.3 mm or less. This is because if the particle diameter of the media particles is within the above range, the dispersed particle diameter of the pigment particles can be reduced.

  The material of the media particles is not particularly limited, and inorganic materials such as alumina, zirconia, and glass can be used, but zirconia is particularly preferable from the viewpoint of preventing impurities from being mixed into the pigment dispersion.

  The amount of the media particles filled is not particularly limited, but may be set to 65% by volume or more and 85% by volume or less with respect to the vessel capacity of the media disperser in order to perform efficient dispersion processing.

  The average dispersed particle diameter of the pigment particles at the end of the third step is preferably 0.5 μm or less and more preferably 0.3 μm or less because the finer the particle, the better the color developability. However, since the dispersibility is inferior when the pigment particles are too fine, the average dispersed particle size of the pigment particles is preferably 0.05 μm or more, and more preferably 0.07 μm or more. The average dispersed particle size of the pigment particles can be measured by a laser diffraction / scattering type particle size distribution analyzer “LA-920” (trade name) manufactured by Horiba.

  The viscosity of the pigment dispersion at the end of the third step is preferably 15 mPa · s to 40 mPa · s. The viscosity of the pigment dispersion can be measured with a “TV-22 viscometer” manufactured by Toki Sangyo Co., Ltd.

(Inkjet ink of the present invention)
The inkjet ink of the present invention is produced by the above-described method for producing a pigment dispersion of the present invention, and includes a pigment dispersion containing a pigment, a dispersant, and an organic solvent.

  The ink-jet ink of the present invention contains the pigment dispersion produced by the method for producing a pigment dispersion of the present invention, and therefore contains a uniformly finely dispersed pigment and has high storage stability characteristics. ing.

  Next, each component of the inkjet ink of the present invention will be described.

<Pigment>
It does not specifically limit as a pigment which comprises the ink for inkjet of this invention, Both an organic pigment and an inorganic pigment can be used. Examples of the inorganic pigment include titanium oxide, zinc oxide, zinc oxide, tripone, iron oxide, aluminum oxide, silicon dioxide, kaolinite, montmorillonite, talc, barium sulfate, calcium carbonate, silica, alumina, cadmium red, and red rose. Molybdenum red, chrome vermilion, molybdate orange, yellow lead, chrome yellow, cadmium yellow, yellow iron oxide, titanium yellow, chromium oxide, pyridian, cobalt green, titanium cobalt green, cobalt chrome green, ultramarine blue, ultramarine blue, bitumen , Cobalt blue, cerulean blue, manganese violet, cobalt violet, mica and the like. Examples of the organic pigment include organic pigments such as azo, azomethine, polyazo, phthalocyanine, quinacridone, anthraquinone, indigo, thioindigo, quinophthalone, benzimidazolone, and isoindoline. . Carbon black made of acidic, neutral or basic carbon may also be used. Further, crosslinked acrylic resin hollow particles and the like may be used as the organic pigment.

  In the inkjet ink of the present invention, black and pigments of three primary colors of cyan, magenta, and yellow are usually used.

  First, a description will be given of a pigment using a primary color (magenta, cyan, yellow) plus black as a basic color. Specific examples of the pigment include compounds classified as pigments in the color index (CI: issued by The Society of Dyers and Colorists), that is, the color index (CI) as shown below. Those with numbers are listed.

  Examples of the pigment exhibiting the magenta color include C.I. I. Monoazo pigments such as CI Pigment Red 3 (Toluidine Red, etc.); I. Disazo pigments such as C.I. Pigment Red 38 (Pyrazolone Red B, etc.); I. Pigment Red 53: 1 (Lake Red C, etc.) and C.I. I. Azo lake pigments such as C.I. Pigment Red 57: 1 (Brilliant Carmine 6B); I. Condensed azo pigments such as C.I. Pigment Red 144 (condensed azo red BR, etc.); I. Perinone pigments such as C.I. Pigment Red 194 (perinone red, etc.); I. Perylene pigments such as C.I. Pigment Red 149 (perylene scarlet, etc.); I. Pigment Violet 19 (unsubstituted quinacridone, “CINQUASIA Magenta RT-355T” manufactured by Ciba Specialty Chemicals), C.I. I. Quinacridone pigments such as CI Pigment Red 122 (quinacridone magenta, etc.); I. Dichloroquinacridone pigments such as C.I. Pigment Red 202 (dichloroquinacridone magenta, etc.); I. Isoindolinone pigments such as CI Pigment Red 180 (isoindolinone red 2BLT, etc.); I. And alizarin lake pigments such as CI Pigment Red 83 (Mada Lake, etc.).

  Examples of the pigment exhibiting the cyan color include C.I. I. Disazo pigments such as C.I. Pigment Blue 25 (Dianisidine Blue, etc.); I. Pigment blue 15, C.I. I. Pigment Blue 15: 3 (“IRGALITE BLUE GLO” manufactured by Ciba Specialty Chemicals), C.I. I. Phthalocyanine pigments such as C.I. Pigment Blue 15: 4 (phthalocyanine blue, etc.); I. Acidic dye lake pigments such as C.I. Pigment Blue 24 (Peacock Blue Lake, etc.); I. And alkali blue pigments such as CI Pigment Blue 18 (Alkali Blue V-5: 1).

  Examples of the yellow pigment include C.I. I. Pigment Yellow 1 (Fast Yellow G, etc.), C.I. I. A monoazo pigment such as C.I. Pigment Yellow 74; I. Pigment Yellow 12 (disaji yellow AAA, etc.), C.I. I. Pigment yellow 17 and C.I. I. Disazo pigments such as C.I. Pigment Yellow 155 (Disazo Yellow 4G); I. Pigment yellow 180, C.I. I. Non-benzidine type azo pigments such as C.I. Pigment Yellow 200 (Novoperm Yellow 2HG); I. Azo lake pigments such as C.I. Pigment Yellow 100 (eg Tartrazine Yellow Lake); I. Condensed azo pigments such as CI Pigment Yellow 95 (Condensed Azo Yellow GR, etc.); I. Acidic dye lake pigments such as C.I. Pigment Yellow 115 (such as quinoline yellow lake); I. Basic dye lake pigments such as CI Pigment Yellow 18 (Thioflavin Lake, etc.), anthraquinone pigments such as Flavantron Yellow (Y-24), isoindolinone pigments such as Isoindolinone Yellow 3RLT (Y-110), and quinophthalone yellow Quinophthalone pigments such as (Y-138), isoindoline pigments such as isoindoline yellow (Y-139), C.I. I. Nitroso pigments such as C.I. Pigment Yellow 153 (nickel nitroso yellow, etc.); I. And metal complex salt azomethine pigments such as CI Pigment Yellow 117 (copper azomethine yellow, etc.).

  Examples of the black pigment include carbon black, titanium black, and aniline black. An example of carbon black is “SPECIAL BLACK 250” manufactured by Degussa.

  The pigments may be used alone or in combination of two or more. In the present invention, two or more kinds of organic pigments or solid solutions of organic pigments can be used in combination. Further, different pigments may be used for each droplet and liquid to be ejected, or the same pigment may be used.

  The content of the pigment is appropriately selected depending on the color and purpose of use, but from the viewpoint of image density and storage stability, the content is preferably 0.3 to 10% by mass with respect to the total amount of the ink-jet ink. More preferably, it is 0.5-5 mass%.

<Dispersant>
The type of the dispersant used in the inkjet ink of the present invention is not particularly limited, but a known polymer dispersant is preferably used. Examples of the polymer dispersant include “DisperBYK-101”, “DisperBYK-102”, “DisperBYK-103”, “DisperBYK-106”, “DisperBYK-111”, “DisperBYK-161”, and “DisperBYK” manufactured by BYK Chemie. -162 "," DisperBYK-163 "," DisperBYK-164 "," DisperBYK-166 "," DisperBYK-167 "," DisperBYK-168 "," DisperBYK-170 "," DisperBYK-171 "," DisperBYK-1 ""DisperBYK-182";"EFKA4010","EFKA4046","EFKA4080","EFKA5010","EfkaAdditives" “FKA5207”, “EFKA5244”, “EFKA6745”, “EFKA6750”, “EFKA7414”, “EFKA7462”, “EFKA7500”, “EFKA7570”, “EFKA7575”, “EFKA7580”; “Disperse Aid 8”, “Disperse Aid 15”, “Disperse Aid 9100”; “Solsperse 3000”, “Solspers 5000”, “Solspers 9000”, “Solspers 12000”, “ Solsparse 13240, Solsparse 13940, Solsparse 17000, Solsparse 24000, Solsparse 26000, Solsparse 28000, Sol “Sparse Spur 36000”, “Sol Sparse 39000”, “Sol Sparse 41000”, “Sol Sparse 71000”; “Adeka Pluronic L31”, “F38”, “L42”, “L44”, “L61” manufactured by Asahi Denka Co., Ltd. , “L64”, “F68”, “L72”, “P95”, “F77”, “P84”, “F87”, “P94”, “L101”, “P103”, “F108”, “L121”, “ “Isonet S-20” manufactured by Sanyo Kasei Co., Ltd .; “Disparon KS-860”, “873SN”, “874” (polymer dispersing agent), “# 2150” (aliphatic) manufactured by Enomoto Kasei Co., Ltd. Polyvalent carboxylic acid), “# 7004” (polyether ester type), and the like.

  The dispersant may be used in combination with pigment derivatives such as phthalocyanine derivative “EFKA-745” manufactured by Efka, “Solsperse 5000”, “Solsperse 12000”, and “Solsperse 22000” manufactured by Lubrizol.

  Although content of the said dispersing agent is suitably selected according to the intended purpose, it can be set with 0.3-10 mass% with respect to the whole quantity of the ink for inkjet, for example.

<Organic solvent>
The organic solvent used in the inkjet ink of the present invention is not particularly limited, but is preferably water-insoluble. If a water-soluble organic solvent is used, the ink tends to contain a large amount of water, and salt may be generated by the water, or the water may become an aggregating factor of the pigment, which may reduce the storage stability of the ink. It is.

  Examples of the water-insoluble organic solvent include ethylene glycol monoalkyl ether monoalkyl ester, diethylene glycol monoalkyl ether monoalkyl ester, triethylene glycol monoalkyl ether monoalkyl ester, propylene glycol monoalkyl ether monoalkyl ester, and dipropylene glycol. Examples include monoalkyl ether monoalkyl esters and tripropylene glycol monoalkyl ether monoalkyl esters.

  Hereinafter, the present invention will be described in detail based on examples. However, the present invention is not limited to the following examples. In addition, unless otherwise indicated, in the following, “part” means “part by mass”.

Example 1
First, in the medialess dispersion step, a primary dispersion was prepared as follows. That is, in a plastic bottle, 20 parts of a pigment (P.Y.155: Pigment Yellow 155, “NOVOPERM YELLOW 4G01” manufactured by Clariant), 15 parts of a dispersant (“SOLPERSE32000” manufactured by Nippon Lubrizol Co., Ltd.), an organic solvent (Ando) 65 parts of parapropylene dipropylene glycol methyl ether acetate “Dawanol DPMA”) was weighed out, and this mixed solution was a medialess disperser (Asada Tekko Co., Ltd., “2-axis despamyl MD-30” with a shear clearance of 1250 μm. -2 ″), and a dispersion was performed at a shear rate of 1 × 10 ⁶ (1 / sec) for 14 hours to obtain a primary dispersion.

  Next, in the decantation step, the primary dispersion was allowed to stand for 12 hours to settle and remove coarse particles in the primary dispersion.

  Subsequently, in the media dispersion step, 49 parts of zirconia beads having a diameter of 0.1 mm are added to the primary dispersion from which coarse particles are removed, and dispersion is performed for 20 minutes using a media dispersion machine (“Dynomill KD20B” manufactured by Asada Tekko Co., Ltd.). The secondary dispersion was obtained by treatment, and the secondary dispersion was used as the pigment dispersion of this example.

(Example 2)
A pigment dispersion was prepared in the same manner as in Example 1 except that the pigment was changed to P.B.15: 4 (Pigment Blue 15: 4, “HOSTAPERM BLUE BT-617-D” manufactured by Clariant).

Example 3
A pigment dispersion was prepared in the same manner as in Example 1 except that the pigment was changed to PR 202 (Pigment Red 202, “QUINDO MAGENTA 228-6843” manufactured by DIC).

Example 4
A pigment dispersion was prepared in the same manner as in Example 1 except that the pigment was changed to carbon black # 970.

(Example 5)
A pigment dispersion was produced in the same manner as in Example 1 except that the shear rate in the medialess dispersion process was changed to 1 × 10 ⁵ (1 / sec).

(Comparative Example 1)
A pigment dispersion was prepared in the same manner as in Example 1 except that the decantation step was not performed.

(Comparative Example 2)
A pigment dispersion was produced in the same manner as in Example 1 except that the media dispersion step was not performed.

(Comparative Example 3)
A pigment dispersion was produced in the same manner as in Example 1 except that the clearance of the shearing portion in the medialess dispersion process was changed to 25 μm.

(Comparative Example 4)
A pigment dispersion was produced in the same manner as in Example 1 except that the medialess dispersion step was not performed.

  Next, the pigment dispersions of Examples 1 to 5 and Comparative Examples 1 to 4 were evaluated as follows.

<Viscosity change rate>
The viscosity at the time of preparation of each pigment dispersion was measured using a “TV-22 viscometer” manufactured by Toki Sangyo Co., Ltd. under the conditions of 25 ° C. and a cone rotation speed of 10 rpm. Next, each pigment dispersion whose initial viscosity was measured was stored at a temperature of 60 ° C. for 28 days, the viscosity after storage was measured in the same manner as described above, and the viscosity was taken as the viscosity over time. Subsequently, the viscosity change rate was calculated by the following formula. A small viscosity change rate means high ink storage stability.
Viscosity change rate (%) = [(viscosity−initial viscosity) / initial viscosity] × 100

<Average pigment dispersed particle size>
The average dispersed particle size of the pigment contained in each pigment dispersion was measured using a concentrated particle size analyzer “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.

<Decrease rate of solid content concentration>
The solid content concentration at the time of producing each primary dispersion was measured by drying each primary dispersion at 180 ° C. for 30 minutes, and the measured concentration was used as the initial concentration. Moreover, the solid content concentration of each pigment dispersion produced in the same manner was measured to obtain the final concentration. Subsequently, the decreasing rate of the solid content concentration was calculated by the following formula. A small reduction rate of the solid content concentration means that only coarse particles having a strong cohesive force can be efficiently removed.
Reduction ratio of solid content concentration (%) = [(initial concentration−final concentration) / initial concentration] × 100

  The results are shown in Table 1.

From Table 1, the pigment dispersions of Examples 1 to 4 of the present invention have a viscosity change rate of 5.7% or less, a solid content concentration decrease rate of 2% or less, a viscosity change rate and a solid content concentration. It can be seen that the decrease rate is small. In addition, it can be seen that the pigment dispersion of Example 5 in which the shear rate in the medialess dispersion step was less than 1 × 10 ⁶ (1 / sec) had a small rate of change in viscosity, although the rate of decrease in the solid content concentration was slightly large. .

  On the other hand, in the pigment dispersion of Comparative Example 1 in which the decantation process was not performed, the viscosity change rate was large, and in the pigment dispersion of Comparative Example 2 in which the media dispersion process was not performed, the pigment dispersion of Example 1 using the same pigment. Comparative Example 4 in which the average dispersion particle diameter of the pigment was larger than that of the body and the clearance in the medialess dispersion process was less than 100 μm, and the viscosity change rate was large in Comparative Example 3, and the medialess dispersion process was not performed. It can be seen that in the pigment dispersion, the reduction rate of the solid content concentration is large.

  According to the present invention, it is possible to provide an ink-jet ink that can uniformly disperse a pigment and has high storage stability.

DESCRIPTION OF SYMBOLS 10 Medialess disperser 11 Stator 12 Rotor 12a The most advanced part of a rotor 13 Clearance

Claims (9)

A method for producing a pigment dispersion having a first step, a second step, and a third step,
In the first step, a mixed liquid containing a pigment, a dispersant, and an organic solvent is subjected to a dispersion treatment using a medialess disperser having a clearance of a shearing portion of 100 μm or more and 1500 μm or less to produce a primary dispersion. Process,
The second step is a step of removing coarse particles from the primary dispersion using a difference in the sedimentation rate of the particles,
The third step is a step of producing a secondary dispersion by dispersing the primary dispersion from which coarse particles have been removed using a media dispersing machine using media particles to produce a secondary dispersion. Body manufacturing method.   The method for producing a pigment dispersion according to claim 1, wherein the coarse particles are removed by decantation in the second step.   The method for producing a pigment dispersion according to claim 2, wherein the standing time of the primary dispersion in the decantation is 6 hours or more and 15 hours or less.   The method for producing a pigment dispersion according to any one of claims 1 to 3, wherein a particle diameter of the coarse particles is 30 µm or more.   The method for producing a pigment dispersion according to any one of claims 1 to 4, wherein the medialess disperser includes a rotor and a stator. The method for producing a pigment dispersion according to any one of claims 1 to 5, wherein the shear rate in the first step is 1 x 10 ⁶ (1 / sec) or more and 1 x 10 ⁷ (1 / sec) or less. .   The method for producing a pigment dispersion according to any one of claims 1 to 6, wherein a particle diameter of the media particles is 0.05 mm or more and 0.3 mm or less.   The method for producing a pigment dispersion according to any one of claims 1 to 7, wherein the organic solvent is water-insoluble.   An ink-jet ink comprising a pigment dispersion produced by the method for producing a pigment dispersion according to any one of claims 1 to 8.

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