Method for producing pigment composition, pigment composition, ink, and printed material

Abstract

A method for producing a pigment composition containing carbon black, a resin having an acid value, and an aqueous medium, the method comprising at least a first dispersion step in which dispersion is performed in a cyclic or pass-through manner, and a second dispersion step in which dispersion is performed in the cyclic or pass-through manner, the second dispersion treatment step is a step using a medium-type dispersion machine, the bead diameter used in the second dispersion treatment step is 0.01-0.5 mm, and the pigment concentration of the pigment composition at the end of the second dispersion treatment step is 16-32 mass% with respect to the total mass of the pigment composition.

Description

Technical Field

[0001] The present invention relates to a method for producing a pigment composition, a pigment composition, ink, and printed matter.

[0002] This application claims priority based on Japanese Patent Application No. 2023-035397 filed in Japan on March 8, 2023, the contents of which are incorporated herein by reference. Background Art

[0003] Pigment compositions are used in various printing inks or inks for printing plates, inkjet printing, etc. As a method for producing a pigment composition, there is known a method of obtaining a pigment composition by treating a raw material composition containing a pigment component and a liquid medium with a disperser.

[0004] Pigment compositions used in inkjet printing inks, in particular, require a low number of coarse particles to prevent nozzle clogging during printing and achieve good ejection stability. While repeated pulverization and / or crushing of a raw material composition containing a pigment component and a liquid medium has been considered to reduce the number of coarse particles, increased processing time can lead to decreased productivity. Therefore, methods for producing pigment compositions are required to efficiently reduce the number of coarse particles.

[0005] Patent Document 1 discloses that the number of coarse particles in a pigment composition can be efficiently reduced by wet dispersion by using an in-line rotor-stator type processor and determining the range of the raw material composition and its solid content concentration.

[0006] In recent years, product designs that reduce CO2 throughout the product lifecycle have been demanded to reduce environmental impact. This has also led to a demand for higher pigment concentrations in pigment compositions to reduce transportation energy consumption. While kneading and dispersion processes, where pigments are dispersed at very high solids concentrations, are being employed, the kneading process tends to be labor-intensive.

[0007] In addition, a centrifugation step is performed as a process to reduce the number of coarse particles. However, this process is not only time-consuming but also produces a large amount of waste, which increases the environmental impact. Therefore, a dispersion method that can reduce the number of coarse particles to a level that eliminates the need for a centrifugation step is desired.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2021 / 075333 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] An object of the present invention is to provide a method for producing a pigment composition, a pigment composition, an ink, and a printed matter, which can reduce the workload and efficiently reduce the number of coarse particles in the pigment composition.

[0013] Methods for solving problems

[0014] The present inventors conducted intensive research on a method for producing a pigment composition based on wet dispersion that can achieve both high pigment concentration and effective reduction in the number of coarse particles. As a result, they discovered that in a method for producing a pigment composition containing carbon black, a resin having an acid value, and an aqueous medium, at least a first wet dispersion treatment step and a second wet dispersion treatment step are sequentially included. The first dispersion treatment step is carried out in a circulation or through-flow process, and the second wet dispersion treatment step is carried out using a media-type disperser. This method reduces the workload and can effectively reduce the number of coarse particles in the pigment composition while maintaining a high pigment concentration, thereby completing the present invention.

[0015] That is, the present invention provides the following configurations.

[0016] [1] A method for producing a pigment composition comprising carbon black, a resin having an acid value, and an aqueous medium, the method comprising at least a first dispersion treatment step and a second dispersion treatment step in sequence, the first dispersion treatment step being a step of dispersing in a circulation or through-dispersion process, the second dispersion treatment step being a step of using a media-type disperser, the beads used in the second dispersion treatment step having a diameter of 0.01 to 0.5 mm, and the pigment concentration of the pigment composition at the end of the second dispersion treatment step being 16 to 32% by mass relative to the total mass of the pigment composition.

[0017] [2] The method for producing a pigment composition according to [1], further comprising a third dispersion step after the second dispersion step, wherein the third dispersion step is performed using a media-type disperser.

[0018] [3] The method for producing a pigment composition according to [1] above, wherein the first dispersion treatment step is a step using a rotor-stator type processor.

[0019] [4] The method for producing a pigment composition according to [1] above, wherein the pigment composition further contains a defoaming agent.

[0020] [5] A pigment composition produced by the production method described in any one of [1] to [4] above.

[0021] [6] An ink comprising the pigment composition described in [5] above.

[0022] [7] A printed matter comprising the ink described in [6] above.

[0023] Effects of the Invention

[0024] According to the present invention, a method for producing a pigment composition, a pigment composition, an ink, and a printed matter can be provided, which can reduce the workload and efficiently reduce the number of coarse particles in the pigment composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 In the drawings, (A) and (B) are a schematic axial cross-sectional view and a schematic radial cross-sectional view showing an example of a rotor-stator type processor used in the method for producing a pigment composition according to an embodiment of the present invention.

[0026] Figure 2 In the equation (A) to (C) Figure 1 Schematic side view of a modified example of the stator in FIG.

[0027] Figure 3 It is used to illustrate the use of Figure 1 A partially enlarged schematic diagram of a comminution or crushing process performed by a rotor-stator type processor. DETAILED DESCRIPTION

[0028] 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 implemented with various modifications within the scope of the gist of the present invention.

[0029] In this specification, the numerical range represented by "~" indicates a range that includes the numerical values ​​recorded before and after "~" as the minimum and maximum values, respectively. In the numerical ranges recorded in stages in this specification, the upper limit or lower limit of the numerical range of a certain stage can be arbitrarily combined with the upper limit or lower limit of the numerical range of other stages. In the numerical ranges recorded in this specification, the upper limit or lower limit of its numerical range can also be replaced by the values ​​shown in the examples. "A or B" only needs to include either A or B, or both. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. When there are multiple substances equivalent to each component in the composition, the content of each component in the composition refers to the total amount of the multiple substances present in the composition unless otherwise specified. The term "process" is not only an independent process, but also includes this term as long as the desired effect of the process can be achieved even if it cannot be clearly distinguished from other processes. "(Meth)acrylic acid" is a general term for acrylic acid and its corresponding methacrylic acid, and the same applies to other similar expressions such as "(meth)acrylate". Crushing, for example, refers to a process of breaking up a mass. Cracking, for example, refers to a process of breaking up an aggregate.

[0030] [Method for producing pigment composition]

[0031] The method for producing a pigment composition according to the present embodiment is a method for producing a pigment composition containing carbon black, a resin having an acid value, and an aqueous medium, and includes at least a first dispersion treatment step and a second dispersion treatment step in this order.

[0032] The pigment composition produced by the production method of this embodiment can be used to obtain ink and can also be used as ink. The pigment composition of this embodiment can be used as a pigment composition for printing ink (for example, inkjet printing ink).

[0033] The pigment composition before the first dispersion treatment process in the present embodiment is sometimes referred to as a raw material composition, and the pigment composition may contain the same type of component as the raw material composition. In addition, the raw material composition through the dispersion treatment process is sometimes referred to as a mixture (pigment composition), and the mixture (pigment composition) through the second dispersion treatment process becomes the pigment composition manufactured by the manufacture method of the present invention. It should be noted that, when including the third dispersion treatment process, the mixture (pigment composition) through the third dispersion treatment process becomes the pigment composition manufactured by the manufacture method of the present invention. In the case of having a solid-liquid mixing process, the raw material composition through the solid-liquid mixing process is sometimes also referred to as a raw material composition. In addition, "pigment composition" sometimes refers to all of the raw material composition, mixture (pigment composition) and pigment composition.

[0034] <First Dispersion Process>

[0035] The first dispersion treatment step is a step of performing dispersion in a circulation method or a flow method.

[0036] This cyclic dispersion process involves circulating the raw material composition slurry between a storage tank and a disperser for dispersion, significantly different from a batch-type dispersion process. This cyclic dispersion process is suitable for difficult-to-crush or difficult-to-disperse slurries, which offer excellent workability and require long processing times. Furthermore, the dispersion process proceeds over time, making particle size control and operation automation easier. Furthermore, it also facilitates ongoing status confirmation and the addition of optional components to the raw material composition.

[0037] This process of dispersing in a continuous manner is a so-called catch-ball method in which a disperser and a plurality of dispersion tanks A and B are used. After the pigment composition in dispersion tank A is dispersed, it is placed in another dispersion tank B. Once the entire pigment composition in dispersion tank A has been treated, the pigment composition is moved from dispersion tank B, which is also being treated, to dispersion tank A, and then from dispersion tank A to dispersion tank B, repeatedly treating the pigment composition.

[0038] The first dispersion treatment step does not include solid-liquid mixing steps that do not significantly contribute to the dispersion of the pigment composition. Specifically, steps that do not cause a change of 5% or more in the pigment particle size of the pigment composition do not constitute the first dispersion treatment step.

[0039] The disperser used in the first dispersion treatment step is not particularly limited as long as it performs dispersion in a circulation type or a through-type manner. Examples thereof include a high-pressure homogenizer, a media-type disperser, a ball mill, an attritor, a sand mill, a sand grinder, a dyno mill, a high-speed disperser (dispermat), an SC mill, a pin crusher, a stirred mill, a rotor-stator type processor, an ultrasonic homogenizer, and a nano homogenizer.

[0040] Among them, as the disperser used in the first dispersion treatment step, a rotor-stator type disperser and a media type disperser are preferably used.

[0041] (Rotor-stator type processor)

[0042] A rotor-stator type processor comprises a rotor having a rotatable blade portion and a stator having a wall portion disposed on the outer circumference of the blade portion. The processor may be any of a pulverizer, a crusher, a disperser, and the like. The rotor and stator may be of any commercially available shape, or a combination of rotors and stators of different or identical shapes may be used. Depending on the shape, the transportability, shear rate (micronization capability), and calorific value of the raw material composition during micronization differ, so a combination can be selected based on the properties of the raw material composition. Generally, a rotor with a large number of teeth facilitates micronization, resulting in a greater calorific value.

[0043] Figure 1 (A) and Figure 1 (B) is a schematic axial cross-sectional view and a schematic radial cross-sectional view showing an example of a rotor-stator type processing machine used in the method for producing the pigment composition of the present embodiment. Figure 1 The rotor-stator type handler 100 shown includes a center shaft 10, a rotor 20, and a stator 30. Examples of the constituent materials of the center shaft 10, the rotor 20, and the stator 30 include metal materials, ceramics, and the like.

[0044] The center shaft 10 is an elongated member, for example, extending in the vertical direction, and supports the rotor 20 and the stator 30 .

[0045] The rotor 20 includes an annular (e.g., circular) blade portion 22 extending along the longitudinal direction of the central axis 10 on the outer periphery of the rotor 20, and a connecting portion 24 connecting the blade portion 22 to the central axis 10. The blade portion 22 is rotatable about the central axis 10. The blade portion 22 includes an opening (through hole) 22a extending therethrough, for example, a plurality of openings 22a spaced apart (e.g., at equal intervals) along the circumferential direction of the blade portion 22. The opening direction of the opening 22a may be inclined relative to the radial direction. The vertically upper end of the opening 22a may be open without being provided with a component constituting the rotor 20. The number, arrangement, and shape of the openings 22a are not particularly limited.

[0046] The arrangement and shape of the blades in the rotor of a rotor-stator type processing machine are not particularly limited. For example, the blades are not limited to being annular members arranged on the outer periphery of the rotor; they may also have a shape extending from the center of the rotor toward the outer periphery. The rotor may also have multiple blades extending from the center of the rotor toward the outer periphery. The blades extending from the center of the rotor toward the outer periphery may have a streamlined shape.

[0047] The stator 30 includes an annular (e.g., circular) wall portion 32 extending along the longitudinal direction of the central shaft 10 on the outer periphery of the stator 30, and a connecting portion 34 connecting the wall portion 32 to the central shaft 10. The wall portion 32 is disposed on the outer periphery of the blade portion 22 in the rotor-stator type processing machine 100. The wall portion 32 includes openings (through holes) 32a extending therethrough. For example, the wall portion 32 includes a plurality of openings 32a spaced apart (e.g., at equal intervals) along the circumference of the wall portion 32. The opening direction of the openings 32a may be inclined relative to the radial direction.

[0048] The number, arrangement, and shape of the openings in the wall portion of the stator are not particularly limited. Figure 2 (A)~ Figure 2 (C) is displayed Figure 1 Schematic side view of a modified example of the stator (stator wall) in FIG. As an example of the stator wall, a wall having openings arranged in an array (for example, rectangular openings such as squares) can be cited. Figure 2 (A)) A wall portion having a plurality of rectangular openings arranged in a row ( Figure 2 (B)) a wall portion having a plurality of circular (for example, true circular) openings arranged in a row ( Figure 2 (C)) etc. Examples of the shape of the opening include a rectangle (square, rectangular, etc.), a circle (perfect circle, ellipse, etc.), and the like.

[0049] The stator may include multiple annular (e.g., circular) wall portions extending along the length of the central axis on the outer periphery of the stator. For example, the stator may include the aforementioned wall portion 32 as a first wall portion, a second wall portion disposed on the outer periphery of the first wall portion in a rotor-stator type processor, and a third wall portion disposed on the outer periphery of the second wall portion in a rotor-stator type processor. The number of wall portions is not particularly limited and may be four or more.

[0050] Figure 3 For illustrative purposes Figure 1 FIG. 1 is a partially enlarged schematic diagram of a pulverization or crushing process performed by a rotor-stator type processor 100, showing a portion of the outer periphery of the rotor-stator type processor 100. In the rotor-stator type processor 100, for example, after a raw material composition containing a pigment component and a liquid medium is supplied to the periphery of the central axis 10, as shown in FIG. Figure 3As shown, the raw material composition passes through the openings 22a of the blades 22 of the rotor 20 (flow path F1 in the figure) and reaches the space between the blades 22 and the wall 32 of the stator 30. Then, in this space, the shear force generated by the rotational motion of the blades 22 is applied to the coarse particles P (solid component), thereby crushing or shattering the coarse particles P. Subsequently, a portion of the composition containing the crushed or shattered particles flows out to the outer periphery of the wall 32 through the openings 32a of the wall 32 (flow path F2 in the figure), while the remaining portion of the composition further travels into the space between the blades 22 and the wall 32, where the particles are further crushed or shattered by the shear force. Thus, the pigment component in the raw material composition containing the pigment component and the liquid medium is crushed or shattered by the crushing or shattering process of the rotor-stator processor 100.

[0051] From the viewpoint of being easy to reduce the number of coarse particles efficiently, being easy to reduce the particle size of the solid content after treatment, being easy to reduce the viscosity of the pigment composition, and being easy to obtain excellent storage stability of the pigment composition, the shear rate (refining ability) applied by the treatment section composed of the rotor and the stator is preferably 50,000 s -1 More than 75000s, more preferably -1 More than 90000s, more preferably -1 Above, particularly preferably 100000s -1 Above, most preferably 120000s -1 Above, preferably 150000s -1 More than 170000s, more preferably -1 The upper limit of the shear rate can be, for example, 400,000 s -1 Below, can also be 250000s -1 From these viewpoints, the shear rate is preferably 50,000 to 400,000 s. -1 . Shear rate (s -1 ) can be obtained by dividing the circumferential speed of the rotor blade portion (m / s) by the distance (m) between the blade portion and the wall portion of the stator.

[0052] The rotor-stator type processing machine can have a plurality of processing parts (crushing parts or crushing parts) consisting of a rotor and a stator. By making the raw material composition flow from the processing part with a low shear rate to the processing part with a high shear rate, it is easy to suppress blockage, and therefore it is easy to efficiently reduce the number of coarse particles. The rotor-stator type processing machine can have a plurality of processing parts (can have a multi-stage processing part) along the central axis extending in the vertical direction. When the rotor-stator type processing machine has a plurality of processing parts along the central axis, from the viewpoint of being easy to efficiently reduce the number of coarse particles, it is preferably more toward the processing part with a higher shear rate configuration below the vertical direction.

[0053] From the perspectives of easily and efficiently reducing the number of coarse particles, easily shortening the time required to obtain a pigment composition having the desired physical properties (number of coarse particles, particle size, etc.) of the solid component in the second treatment step, and easily increasing the resin's adsorption rate to the pigment component by promoting the dissolution of a resin having an acid value when used, thereby easily achieving excellent storage stability, the treatment temperature during the first dispersion treatment step of the present invention in a rotor-stator type processor is preferably within the following range. The temperature is preferably 25°C or higher, more preferably 30°C or higher, even 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, even more preferably 70°C or lower, particularly preferably 65°C or lower, and extremely preferably 60°C or lower. From these perspectives, the temperature is preferably 25-80°C, more preferably 50-80°C, and even more preferably 60-80°C.

[0054] As a rotor-stator type processor, an inline processor can be used. In an inline processor, the raw material composition is continuously supplied. For example, a processor can be installed midway through a processing path (e.g., a pulverization process path and a crushing process path, such as a piping) to continuously process the raw material composition (pulverization or crushing). In an inline processor, since the entire raw material composition is forced to pass through the processor, it is easier to uniformly process the entire raw material composition in a shorter time than when using a batch processor that primarily processes only the rotor periphery. The inline processor can easily and efficiently reduce the number of coarse particles, thereby easily preventing piping clogging in the processor of the second treatment step. In particular, the use of an inline processor as the rotor-stator processor can more effectively reduce the number of coarse particles with a diameter of 0.5 μm or more contained in the final pigment composition than when using a batch processor alone. The inline processor can easily reduce the viscosity of the pigment composition.

[0055] As rotor-stator type processors, there are the device name "magic LAB" manufactured by IKA Corporation (online type, maximum peripheral speed: 41 m / s, maximum rotation speed: 26,000 rpm), the device name "VERSO" manufactured by Silverson Nippon Corporation (high shear online mixer, online type, maximum peripheral speed: 20 m / s, maximum rotation speed: 10,000 rpm), the device name "L5M-A" manufactured by Silverson Nippon Corporation (intermittent type, maximum peripheral speed: 20 m / s, maximum rotation speed: 10,000 rpm), etc. As a processor manufactured by IKA Corporation, a processor 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 sections (stages) consisting of a rotor and a stator, and the shear rate can be adjusted by the combination of the rotor and the stator, so it is easy to efficiently reduce the number of coarse particles. For example, by using a processing unit that is sequentially 2P / 4M / 6F from the vertical direction, it is possible to configure a processing unit with a higher shear rate toward the vertical direction below. The MK module has a 1-stage processing unit (stage) consisting of a rotor and a stator. By rotating the handle provided by the stator periphery at any angle from the initial position, it is possible to adjust the shear rate to any desired shear rate, thereby easily and efficiently reducing the number of coarse particles to a desired value. For example, by rotating the handle at an angle of 275 °, the interval between the blade portion and the wall portion of the stator can be set to 0.1 mm.

[0056] As the rotor-stator type processor, a processor with a rotation speed in the range of 1000 to 30000 rpm is preferably used, and a processor with a rotation speed in the range of 3000 to 25000 rpm is more preferably used. From the viewpoint of facilitating efficient reduction of the number of coarse particles, facilitating reduction of the particle size of the solid content after treatment, facilitating reduction of the viscosity of the pigment composition, and facilitating obtaining excellent storage stability in the pigment composition, a processor with a rotation speed in the range of 8000 to 20000 rpm is particularly preferably used.

[0057] As the rotor-stator type processor, a processor having a maximum peripheral speed in the range of 5 m / s to 50 m / s is preferably used, and a processor having a maximum peripheral speed in the range of 10 m / s to 40 m / s is more preferably used. From the viewpoint of facilitating efficient reduction of the number of coarse particles, facilitating reduction of the particle size of the solid content after treatment, facilitating reduction of the viscosity of the pigment composition, and facilitating excellent storage stability of the pigment composition, a processor having a maximum peripheral speed in the range of 15 m / s to 35 m / s is particularly preferably used.

[0058] (Media type disperser)

[0059] A media-type disperser is a device that continuously pumps a slurry containing particles into a cylindrical container called a vessel, which is filled with beads serving as a grinding medium. A stirrer, acting as a stirring element, rotates to stir the beads, pulverizing and dispersing the particles within the vessel using collision and shear forces. A media-type disperser, also known as a bead mill, is equipped with a separator at the outlet to eject only the slurry.

[0060] The vessel is preferably made of a ceramic such as alumina, alumina zirconium oxide, or silicon nitride, which is a heat-resistant material. Furthermore, the stirrer is preferably made of a ceramic such as zirconium oxide, silicon nitride, or alumina, which is a wear-resistant material. The separator may be a gap separator, a screen separator, a centrifugal separator, or a centrifugal screen separator. However, when using microbeads with a bead diameter of 0.2 mm or less, a centrifugal separator or a centrifugal screen separator is preferred.

[0061] The stirrer preferably has a plurality of stirring discs, and a mechanism for forming a backflow in the space between the stirring disc and the adjacent stirring disc is provided, thereby improving the bead crushing ability and making it difficult for the beads to segregate at the outlet of the vessel.

[0062] The slurry ejected from the outlet of the vessel is returned to the tank by a pump and is again fed into the vessel from the supply port.

[0063] Preferably, a jacket is provided on the outer circumference of the vessel and the tank at a distance from the vessel and the tank. The jacket can pass cooling water or hot water, etc., to adjust the temperature in the vessel.

[0064] The container is filled with beads as a grinding medium, and the beads can be granular beads with a diameter of about 0.01 to 2 mm. The bead diameter is appropriately selected according to the maximum particle size of the pigment particles and the pigment particle size to be obtained as a dispersion result. In addition, when a medium-type disperser is used in the first dispersion treatment process of the present invention, it is preferred to use beads of 0.4 to 3.0 mm, more preferably 0.4 to 1.2 mm, and even more preferably 0.5 to 1.0 mm. By using a medium-type disperser filled with beads of a bead diameter within this range in the first dispersion treatment process, clogging of the powder can be suppressed, and stable operation can be achieved. In addition, in the next process (second dispersion treatment process), the desired dispersed particle size can be obtained in a short time, and the number of coarse particles can be reduced.

[0065] In addition, the material of the beads can be zirconium oxide, aluminum oxide, glass, special glass, silica-based ceramic beads, silicon nitride beads, etc., and the specific gravity and brittleness can be used as indicators to select according to the purpose. In the manufacturing method of the present invention, zirconium oxide beads are preferably used, which can efficiently disperse the carbon black particles and suppress the contamination of the pigment composition caused by bead wear. The bead filling rate in the vessel is preferably about 50 to 90% of the vessel capacity, and can be set by considering the wear and heat of the medium-type disperser components. When using 0.4 to 3.0 mm beads in the first dispersion treatment process, it is preferred to set the bead filling rate to 70 to 88% of the vessel capacity, and more preferably to 80 to 85%. By setting the bead filling rate to this range, the kinetic energy transfer efficiency can be fully maintained, and heat and wear can be suppressed to achieve stable operation.

[0066] The greater the peripheral speed of the stirrer, the faster the crushing and dispersion speed tends to be. When a medium-type disperser is used in the first dispersion treatment step, the peripheral speed of the stirrer is preferably set to 5 to 16 m / s, more preferably 8 to 15 m / s, and even more preferably 11 to 15 m / s. If the peripheral speed of the stirrer is within this range, the desired dispersion result can be obtained in a short time, and therefore it is preferred.

[0067] The liquid feed rate in a media-type disperser depends on the pump capacity and can be adjusted appropriately based on the vessel volume, bead diameter, the amount of pigment composition to be processed, the pigment concentration, and the solids concentration of the pigment composition. It is preferable to adjust the liquid feed rate so that at least 10 times the amount of pigment composition to be processed can be processed within a given dispersion time. For example, if 10 kg of pigment composition is to be produced in 60 minutes, the flow rate can be set to 10 kg x 10 / 60 minutes = 1.7 kg / min. If 100 kg of pigment composition is to be produced in 60 minutes, the flow rate can be set to 100 kg x 10 / 60 minutes = 16.7 kg / min.

[0068] When using 0.4-3.0 mm beads in the first dispersion treatment step, the flow rate is preferably 2-10 kg / min, more preferably 4-8 kg / min. By setting the liquid feed rate within this range, a pigment composition suitable for the next step (second dispersion treatment step) can be obtained in a short time.

[0069] In order to ensure stable operation of the media-type disperser, it is preferable to adjust the liquid feed flow rate so that the pressure gauge installed at the disperser outlet is 0.15 MPa or less.

[0070] From the perspectives of easily and efficiently reducing the number of coarse particles, easily shortening the time required to obtain a pigment composition having desired solids properties (number of coarse particles, particle size, etc.) in the second dispersion treatment step, and easily increasing the resin's adsorption rate to the pigment component by promoting resin dissolution when a resin with an acid value is used, thereby easily achieving excellent storage stability, the treatment temperature during the first dispersion treatment step of the present invention using a media-type disperser is preferably within the following range. The temperature is preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, particularly preferably 25°C or higher, and very preferably 30°C or higher. The temperature is preferably 60°C or lower, more preferably 55°C or lower, even more preferably 50°C or lower, particularly preferably 45°C or lower, and extremely preferably 40°C or lower. From these perspectives, the temperature is preferably 10-60°C, more preferably 25-50°C, even more preferably 25-40°C, and particularly preferably 30-40°C. Temperature adjustment is preferably performed by passing cold or hot water through a jacket around the container or tank.

[0071] The first dispersion treatment process of the present invention is a process for dispersing in a cyclic or through-type manner. When dispersing in a cyclic manner, the particle size decreases continuously over time. When a medium-type disperser is used in the first dispersion treatment process, the dispersion time is not particularly limited, but for the end of the first dispersion treatment process, as long as sampling is performed at a certain interval, the particle size and / or coarse particle number of the sample obtained reaches the target. From the viewpoint of being an effective dispersion process, it is preferred to change and adjust the flow rate, vessel capacity, peripheral speed, etc. in such a way that the dispersion time in the first dispersion treatment process ends within 30 to 180 minutes.

[0072] When dispersion is performed by a pass method in the first dispersion treatment step of the present invention, it is preferable to adjust the conditions so as to complete the process with approximately 10 passes.

[0073] Examples of the media-type disperser include the "Mugen Flow" series and the "Star Mill" series manufactured by Ashizawa Finetech Co., Ltd., the "Neos" series manufactured by NETZSCH Co., Ltd., the "MicroMedia" series manufactured by Bühler Co., Ltd., the "Dyno Mill" series manufactured by Shinmaru Enterprises Co., Ltd., the "Pico Mill" series, the "Eco Mill" series, the "Revo Mill" series, and the "Nano Mill" series manufactured by Asada Iron Works Co., Ltd., and the "SC Mill" series manufactured by Nippon Coking Industry Co., Ltd., but are not limited thereto.

[0074] The pigment concentration of the pigment composition at the completion of the first dispersion treatment step of the present invention is not particularly limited. When the first dispersion treatment step is performed using a rotor-stator type dispersing machine, the pigment concentration is preferably 20-35% by mass relative to the total mass of the pigment composition. Furthermore, when the first dispersion treatment step is performed using a media-type dispersing machine, the pigment concentration is preferably 18-25% by mass. When the pigment concentration falls within this range, the viscosity of the pigment composition is likely to be within an appropriate range for each dispersing machine, maintaining dispersion efficiency.

[0075] The raw material supply unit in the pigment composition production apparatus of this embodiment is not particularly limited as long as it can supply the raw material composition to a disperser such as a rotor-stator type processor or a media type disperser.

[0076] <Second treatment step>

[0077] The second dispersion step of the present invention is a step for pulverizing or crushing the pigment component in the mixture (pigment composition) obtained in the first dispersion step. This second dispersion step is performed using a media disperser. The beads used in this second dispersion step have a diameter of 0.01 to 0.5 mm.

[0078] The media disperser used in the second dispersion treatment step can be the media disperser used in the first dispersion treatment step. The beads are preferably made of zirconia beads, which can efficiently disperse the carbon black particles and suppress contamination of the pigment composition caused by bead wear.

[0079] When the first dispersion treatment step involves dispersion using a rotor-stator processor, the mixture (pigment composition) dispersed using the rotor-stator processor is further dispersed using a media disperser. When the first dispersion treatment step involves dispersion using a media disperser, the second dispersion treatment step involves dispersion using a media disperser under different conditions from those used in the first dispersion treatment step. Specifically, the dispersion is preferably performed using different bead diameters in the first and second dispersion treatment steps. Specifically, the bead diameter used in the second dispersion treatment step is preferably 0.01 to 0.5 mm, and the bead diameter used in the first dispersion treatment step is different from that used in the second dispersion treatment step, and is particularly preferably larger than the bead diameter used in the second dispersion treatment step.

[0080] The relationship between the bead diameter (D1) used in the first dispersion treatment step and the bead diameter (D2) used in the second dispersion treatment step is preferably D2 / D1 = 0.01 to 0.5, more preferably 0.1 to 0.5. When the relationship between D1 and D2 is within this range, coarse particles can be effectively reduced.

[0081] The diameter of the beads used in the second dispersion treatment step must be 0.01 to 0.5 mm, preferably 0.05 to 0.4 mm, and more preferably 0.1 to 0.3 mm. Furthermore, the bead filling rate within the vessel during the second dispersion treatment step is preferably 80 to 95% of the vessel capacity, more preferably 85 to 92%. By maintaining the bead filling rate within this range, kinetic energy transfer efficiency is maintained, while heat generation and wear are suppressed, achieving stable operation.

[0082] The peripheral speed of the stirrer in the second dispersion treatment step is preferably set to 5 to 16 m / s, more preferably 8 to 15 m / s, and even more preferably 11 to 15 m / s. If the peripheral speed of the stirrer is within this range, the desired dispersion result can be obtained in a short time, which is therefore preferred.

[0083] In the second dispersion treatment step, as in the first dispersion treatment step, the liquid feed flow rate may be appropriately adjusted depending on the vessel volume, bead diameter, amount of the pigment composition to be treated, pigment concentration, and solid content concentration of the pigment composition. Preferably, the liquid feed flow rate is adjusted so that 10 times or more of the amount of the pigment composition to be treated can be treated within an arbitrarily set dispersion time.

[0084] The liquid feeding rate in the second dispersion treatment step is preferably in the range of 0.5 to 30 kg / min. In addition, for stable operation of the media type disperser, the liquid feeding rate is preferably adjusted so that the pressure gauge installed at the disperser outlet is 0.15 MPa or less.

[0085] From the perspective of being able to efficiently reduce the number of coarse particles, being able to shorten the time required to obtain a pigment composition having the desired physical properties (number of coarse particles, particle size, etc.) of the solid component, and being able to easily increase the resin's adsorption rate to the pigment component by promoting the dissolution of the resin when using a resin with an acid value, and being able to easily obtain excellent storage stability, the treatment temperature in the second dispersion treatment step is preferably within the following range. The temperature is preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, particularly preferably 25°C or higher, and very preferably 30°C or higher. The temperature is preferably 60°C or lower, more preferably 55°C or lower, even more preferably 50°C or lower, particularly preferably 45°C or lower, and extremely preferably 40°C or lower. From these perspectives, the temperature is preferably 10-60°C, more preferably 25-50°C, and even more preferably 30-40°C. Temperature adjustment is preferably performed by passing cold water or hot water through a pipe around the outer periphery of the vessel and the tank.

[0086] In the second dispersion treatment step, the dispersion time is not particularly limited. The second dispersion treatment step can be terminated by sampling at regular intervals until the particle size and / or number of coarse particles in the sample obtained reach the target. To ensure an efficient dispersion process, it is preferred to modify and adjust the flow rate, vessel capacity, peripheral speed, etc. so that the dispersion time in the second dispersion treatment step is completed within 30 to 180 minutes.

[0087] At the completion of the second dispersion treatment step of the present invention, the pigment concentration of the pigment composition is 16-32% by mass relative to the total mass of the pigment composition. Preferably, the pigment concentration is 18-23% by mass. Within this range, the viscosity of the pigment composition is likely to be within an appropriate range, maintaining dispersion efficiency. Furthermore, within this range, the pigment composition can be dispersed with sufficient collision frequency between the beads and the pigment, effectively crushing or disintegrating coarse particles.

[0088] (Third Dispersion Process)

[0089] The method for producing the pigment composition of the present invention may further include a third dispersion step after the second dispersion step. The third dispersion step is preferably performed using a media disperser.

[0090] The third dispersion step is performed using a media disperser under conditions different from those of the second dispersion step. Specifically, the second and third dispersion steps are preferably performed under conditions with different bead diameters. Specifically, the bead diameter used in the second dispersion step is preferably 0.01 to 0.5 mm, and the bead diameter used in the third dispersion step is different from that used in the second dispersion step, and particularly preferably smaller than that used in the second dispersion step.

[0091] The relationship between the bead diameter (D2) used in the second dispersion treatment step and the bead diameter (D3) used in the third dispersion treatment step is preferably D3 / D2 = 0.01 to 0.8, more preferably 0.1 to 0.5, and even more preferably 0.15 to 0.5. When the relationship between D2 and D3 falls within this range, coarse particles can be effectively reduced.

[0092] The diameter of the beads used in the third dispersion treatment step is preferably 0.01 to 0.3 mm, more preferably 0.05 to 0.2 mm, and even more preferably 0.05 to 0.1 mm. Furthermore, the bead filling rate within the vessel in the third dispersion treatment step is preferably 80 to 95% of the vessel capacity, more preferably 85 to 92%. By setting the bead filling rate within this range, kinetic energy transfer efficiency can be adequately maintained while suppressing heat generation and wear, achieving stable operation.

[0093] The peripheral speed of the stirrer in the third dispersion treatment step is preferably set to 5 to 16 m / s, more preferably 8 to 15 m / s, and even more preferably 11 to 15 m / s. If the peripheral speed of the stirrer is within this range, the desired dispersion result can be obtained in a short time, which is therefore preferred.

[0094] In the third dispersion treatment step, as in the first and second dispersion treatment steps, the liquid feed flow rate may be appropriately adjusted depending on the vessel volume, bead diameter, amount of the pigment composition to be treated, pigment concentration, and solid content concentration of the pigment composition. Preferably, the liquid feed flow rate is adjusted so that at least ten times the amount of the pigment composition to be treated can be treated within an arbitrarily set dispersion time.

[0095] The liquid feeding rate in the third dispersion treatment step is preferably in the range of 0.5 to 25 kg / min. In addition, for stable operation of the media type disperser, the liquid feeding rate is preferably adjusted so that the pressure gauge installed at the disperser outlet is 0.15 MPa or less.

[0096] From the perspectives of easily and efficiently reducing the number of coarse particles, easily shortening the time required to obtain a pigment composition having the desired physical properties (number of coarse particles, particle size, etc.) of the solid component, and easily increasing the resin's adsorption rate to the pigment component by promoting the dissolution of the resin when using a resin with an acid value, thereby easily achieving excellent storage stability, the treatment temperature in the third dispersion treatment step is preferably within the following range. The temperature is preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, particularly preferably 25°C or higher, and very preferably 30°C or higher. The temperature is preferably 60°C or lower, more preferably 55°C or lower, even more preferably 50°C or lower, particularly preferably 45°C or lower, and extremely preferably 40°C or lower. From these perspectives, the temperature is preferably 10-60°C, more preferably 25-50°C, and even more preferably 30-40°C. Temperature adjustment is preferably performed by passing cold water or hot water through a pipe around the outer periphery of the vessel and the tank.

[0097] The dispersion time in the third dispersion treatment step is not particularly limited. The third dispersion treatment step can be terminated by sampling at regular intervals until the particle size and / or number of coarse particles in the sample obtained reach the target. To ensure an efficient dispersion process, it is preferable to modify and adjust the flow rate, vessel capacity, peripheral speed, etc. so that the dispersion time in the third dispersion treatment step is completed within 30 to 180 minutes.

[0098] At the completion of the third dispersion treatment step of the present invention, the pigment concentration of the pigment composition is preferably 12 to 32% by mass relative to the total mass of the pigment composition. Furthermore, the pigment concentration is more preferably 12 to 23% by mass. Within this range, the viscosity of the pigment composition is likely to be within an appropriate range, maintaining dispersion efficiency. Furthermore, within this range, the pigment concentration allows for dispersion with a sufficient frequency of collisions between the beads and the pigment, effectively crushing or disintegrating coarse particles.

[0099] (Solid-liquid mixing process)

[0100] The production method of the present invention may include a solid-liquid mixing step prior to the first dispersion step, in which the carbon black and the resin having an acid value are moistened with an aqueous medium. This solid-liquid mixing step differs from the first dispersion step in that it is not a circulation or through-flow process and is not a dispersion step.

[0101] The mixer used in the solid-liquid mixing process is not particularly limited, and commercially available stirring devices can be used. Examples of the mixer include dispersers, three-in-one motors, homogenizers, magnetic stirrers, inline mixers, and dissolvers.

[0102] Alternatively, a disperser may be used as the mixer. In this case, mixing is preferably performed under conditions such that the carbon black is not dispersed, specifically, under conditions such that the particle size of the carbon black does not change by 5% or more, for example, within a short period of time. In this case, a high-pressure homogenizer, paint shaker, bead mill, roller mill, sand mill, ball mill, attritor, basket mill, sand mill, sand grinder, Dyno mill, high-speed disperser, SC mill, nail crusher, stirred mill, ultrasonic homogenizer, nano homogenizer, dissolver, disperser, high-speed impeller disperser, kneader, planetary mixer, butterfly mixer, etc. may be used.

[0103] <Pigment Composition>

[0104] The pigment composition contains carbon black, a resin having an acid value, and an aqueous medium. Furthermore, it may contain additives other than these. The solid content concentration of the raw material composition used as the pigment composition before the first dispersion treatment step in the present invention, i.e., the total concentration of the carbon black and the resin having an acid value, can be 1-60% by mass, 10-50% by mass, or 15-40% by mass relative to the total mass of the raw material composition.

[0105] Carbon blacks produced by known methods such as contact method, furnace method, and thermal method can be used. These carbon blacks can be suitably used in the production of printing inks (e.g., inkjet printing inks). One type of carbon black can be used alone or in combination of two or more types.

[0106] As carbon black, #2300, #980, #960, #995B, #900, #52, #45L, #45, #40, #33, MA100, MA8, MA7 etc. manufactured by Mitsubishi Chemical Corporation, Regal series, Monarch series, BLACKPEARLS series etc. manufactured by Cabot Corporation, Color Black FW1, Color Black series, Printex series, Special Black series, NIPEX series etc. manufactured by Orion Engineered Carbons Co., Ltd. can be used. In addition, dry pigment (pigment in dry powder state) or wet pigment (pigment in wet cake state) can be used. A mixture or solid solution containing two or more kinds of pigments can also be used.

[0107] From the viewpoint of more effectively suppressing the sedimentation of the pigment component over time, the primary particle size of carbon black is preferably 30 nm or less, more preferably 10 to 20 nm. The primary particle size refers to the value of the number average particle size measured using a transmission electron microscope (TEM).

[0108] The carbon black content is preferably 1 to 50% by mass, more preferably 10 to 30% by mass, and even more preferably 15 to 25% by mass relative to the total mass of the raw material composition, the mixture (pigment composition), and the pigment composition. In these cases, since appropriate fluidity is easily achieved, efficient and uniform handling can be achieved in each process, and excellent storage stability is easily achieved, which prevents the solid components in the pigment composition from settling over time. Sedimentation of the solid components in the ink over time is easily prevented, and clogging of the ink ejection nozzles during the initial ink ejection phase is easily suppressed (excellent initial ejection stability is easily achieved). Clogging of the ink ejection nozzles over time is easily suppressed (excellent ejection stability over time is easily achieved).

[0109] Examples of the aqueous medium include water, organic solvents, and mixtures thereof. Examples of water include pure water and ultrapure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water. From the perspective of preventing the growth of mold or bacteria during long-term storage of the pigment composition or ink, water sterilized by ultraviolet irradiation, addition of hydrogen peroxide, or the like is preferably used.

[0110] The water is preferably used in an amount of 10 to 90% by mass relative to the total mass of the aqueous medium contained in the pigment composition of the present invention, and preferably in an amount of 15 to 80% by mass from the viewpoint of producing the aqueous ink.

[0111] As the organic solvent, a water-soluble organic solvent is preferably used. A water-soluble organic solvent can easily and effectively wet the surface of the pigment component, and a resin dissolved in water (such as a neutralized resin) can be easily adsorbed to the pigment component, which can shorten the time it takes to achieve desired physical properties.

[0112] Examples of the water-soluble organic solvent include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, and polypropylene glycol; glycols such as butanediol, pentanediol, and hexanediol; glycol esters such as propylene glycol laurate; diethylene glycol ethers such as diethylene glycol monoethyl ester, diethylene glycol monobutyl ester, diethylene glycol monohexyl ester, and carbitol; glycol ethers such as cellosolve containing propylene glycol ether, dipropylene glycol ether, or triethylene glycol ether; alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butanol, and pentanol (excluding glycols); sulfolane, esters, ketones, lactones such as γ-butyrolactone; lactams such as N-(2-hydroxyethyl)pyrrolidone and 2-pyrrolidone; glycerol and its polyalkylene oxide adducts; and the like. The water-soluble organic solvents can be used alone or in combination of two or more.

[0113] The content of the water-soluble organic solvent is preferably 10 to 500 parts by mass, more preferably 15 to 200 parts by mass, and even more preferably 15 to 150 parts by mass, relative to 100 parts by mass of the pigment component contained in the pigment composition. Using a water-soluble organic solvent within this range improves the adsorption rate of the resin having an acid value onto the surface of the pigment component, thereby easily achieving excellent storage stability that prevents the solid components in the pigment composition from settling over time. This also helps prevent the solid components in the ink from settling over time, and helps suppress clogging of the ink ejection nozzle during the initial ejection phase (facilitating excellent initial ejection stability). It also helps suppress clogging of the ink ejection nozzle over time (facilitating excellent over-time ejection stability). Examples of water-soluble organic solvents that can improve this adsorption rate include triethylene glycol, glycerin, 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, dipropylene glycol, propylene glycol, and 1,5-pentanediol.

[0114] When an inkjet printing ink obtained using the pigment composition is used in a thermal inkjet printing method described below, a high-boiling-point solvent having a boiling point of 100°C or higher is preferably used as the organic solvent. Furthermore, from the perspectives of promoting wetting of the pigment, thereby facilitating adsorption of the resin to the pigment and improving storage stability, a high-boiling-point solvent having a boiling point of 100°C or higher is preferably used as the organic solvent.

[0115] As the high-boiling-point solvent, for example, glycerin, 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, dipropylene glycol, propylene glycol, 1,5-pentanediol, etc. can be used.

[0116] As the aqueous medium, it is preferred to use an aqueous medium having a dispersion term (δD1), a polar term (δP1), and a hydrogen bonding term (δH1) within the following ranges in order to obtain an ink having better storage stability and easily suppressing clogging of the ink ejection nozzle in the initial stage of ink ejection, and a pigment composition used for its production.

[0117] The dispersion term (δD1) of the aqueous medium (a) is preferably in the range of 12 to 24, more preferably 14 to 21, and particularly preferably 16 to 19.

[0118] The polarity term (δP1) of the aqueous medium (a) is preferably in the range of 4-17, more preferably 6-15, and particularly preferably 8-13.

[0119] The hydrogen bonding term (δH1) of the aqueous medium (a) is preferably in the range of 6 to 43, more preferably 9 to 35, and particularly preferably 9 to 30.

[0120] As an aqueous medium having a dispersion term (δD1), a polar term (δP1) and a hydrogen bonding term (δH1) within the above-mentioned range, for example, triethylene glycol, glycerol, 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, dipropylene glycol, propylene glycol, 1,5-pentanediol, etc. can be used.

[0121] It should be noted that the values ​​of the dispersion term (δD1), polar term (δP1), and hydrogen bonding term (δH1) of the above-mentioned aqueous medium are the values ​​included in "Hansen Solubility Parameters in Practice 4th Edition 4.1.07 (HSPiP)", which is a computer software.

[0122] The aqueous medium having the above-mentioned dispersion term (δD1), polar term (δP1), and hydrogen bonding term (δH1) is preferably used in an amount of 10 to 95% by mass, more preferably 50 to 80% by mass, relative to the total mass of the aqueous medium contained in the pigment composition.

[0123] The aqueous medium contained in the pigment composition of the present invention is preferably used in an amount of 30 to 98% by mass relative to the total mass of the pigment composition, and preferably in an amount of 60 to 95% by mass from the perspective of producing a water-based ink.

[0124] As the aqueous medium used in the pigment composition of the present invention, it is preferred to use water in combination with the high-boiling-point solvent, an aqueous medium having the dispersion term (δD1), polar term (δP1), and hydrogen bonding term (δH1). This facilitates adsorption of a resin having an acid value, such as the pigment dispersing resin, onto the surface of the pigment component. In particular, when a wet dispersing apparatus is used to produce the pigment composition of the present invention, or when an inkjet printing ink obtained using the pigment composition is applied to a thermal inkjet printing method described below, it is preferred to use water in combination with the high-boiling-point solvent, an aqueous medium having the dispersion term (δD1), polar term (δP1), and hydrogen bonding term (δH1), etc., as the aqueous medium, from the perspectives of promoting pigment wetting, thereby facilitating resin adsorption onto the pigment and improving storage stability.

[0125] From the perspective of easily and efficiently reducing the number of coarse particles and easily shortening the time required to obtain a pigment composition having desired solid content properties (number of coarse particles, particle size, etc.) in the second treatment step, the aqueous medium preferably satisfies at least one of the following conditions.

[0126] The aqueous medium preferably contains at least one selected from glycols, lactams, and glycerol.

[0127] The aqueous medium preferably contains at least one selected from triethylene glycol, triethylene glycol, and dipropylene glycol.

[0128] The aqueous medium preferably contains at least one selected from N-(2-hydroxyethyl)pyrrolidone and 2-pyrrolidone.

[0129] In the case where the pigment component contains carbon black, the aqueous medium preferably contains at least one selected from N-(2-hydroxyethyl)pyrrolidone, 2-pyrrolidone, triethylene glycol, and glycerin.

[0130] The aqueous medium is preferably used in an amount of 40 to 90% by mass relative to the total mass of the pigment composition of the present invention, and preferably in an amount of 60 to 85% by mass from the viewpoint of producing an aqueous ink.

[0131] The pigment composition contains a resin having an acid value. Examples of the resin having an acid value include pigment dispersing resins and binder resins. Conventionally known resins can be used as the resin having an acid value, for example, free radical polymers, preferably free radical polymers having an aromatic ring structure or a heterocyclic structure. In this case, the resin having an acid value is easily adsorbed onto the pigment component through the π-π interaction between the resin having an acid value and carbon black, thereby easily achieving excellent storage stability that prevents the solid components in the pigment composition from settling over time. This also easily prevents the solid components in the ink from settling over time, easily suppresses clogging of the ink ejection nozzle during the initial ink ejection phase (easily achieving excellent initial ejection stability), and easily suppresses clogging of the ink ejection nozzle over time (easily achieving excellent ejection stability over time).

[0132] When using a radical polymer with anionic groups as a resin with an acid value (e.g., a pigment-dispersing resin), it is preferable to use a radical polymer in which some or all of the anionic groups have been neutralized with a basic compound (neutralized product). Neutralization makes the resin with an acid value easily soluble in an aqueous medium containing water, promoting adsorption on the surface of the pigment component and facilitating the maintenance of a well-dispersed state. As a result, excellent storage stability is easily achieved, which prevents the solid components in the pigment composition from settling over time. This also easily prevents the solid components in the ink from settling over time, and easily suppresses clogging of the ink ejection nozzle during the initial ink ejection phase (facilitating excellent initial ejection stability). It also easily suppresses clogging of the ink ejection nozzle over time (facilitating excellent ejection stability over time).

[0133] Examples of aromatic or heterocyclic structures include those introduced into free radical polymers using monomers having aromatic or heterocyclic structures. The aromatic cyclic structure is preferably a benzene ring structure, more preferably a structure derived from styrene. Using a resin having an acid value as a free radical polymer having an aromatic or heterocyclic structure improves the adsorption of the resin to the pigment component, thereby easily achieving excellent storage stability that prevents the solid components in the pigment composition from settling over time. This also makes it easier to prevent the solid components in the ink from settling over time, and to suppress clogging of the ink ejection nozzle during the initial ink ejection phase (easily achieving excellent initial ejection stability). This also makes it easier to suppress clogging of the ink ejection nozzle over time (easily achieving excellent ejection stability over time).

[0134] As a radical polymer that can be used as a resin having an acid value, for example, a polymer obtained by radical polymerization of various monomers can be used.

[0135] As the monomer, when an aromatic ring structure is introduced into a resin having an acid value, a monomer having an aromatic ring structure can be used, and when a heterocyclic structure is introduced, a monomer having a heterocyclic structure can be used.

[0136] Examples of the monomer having an aromatic ring structure include styrene, p-tert-butyldimethylsilyloxystyrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, p-tert-butoxystyrene, m-tert-butoxystyrene, p-tert-(1-ethoxymethyl)styrene, m-chlorostyrene, p-chlorostyrene, p-fluorostyrene, α-methylstyrene, p-methyl-α-methylstyrene, vinylnaphthalene, and vinylanthracene.

[0137] Examples of the monomer having a heterocyclic structure include vinyl pyridine-based monomers such as 2-vinyl pyridine and 4-vinyl pyridine.

[0138] When a polymer having both an aromatic ring structure and a heterocyclic structure is used as the radical polymer, a monomer having an aromatic ring structure and a monomer having a heterocyclic structure may be used in combination as monomers.

[0139] As the resin having an acid value, a radical polymer having an aromatic ring structure is preferred. Therefore, as the monomer, a monomer having an aromatic ring structure is preferred, and at least one selected from styrene, α-methylstyrene, and tert-butylstyrene is more preferred.

[0140] From the viewpoint of further improving the adsorption of the pigment component by the resin having an acid value, the content of the monomer having an aromatic ring structure or a heterocyclic structure is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 50 to 95% by mass, relative to the total mass of the monomers.

[0141] As the resin having an acid value, a monomer having an anionic group can be used as a monomer from the viewpoint of producing a radical polymer having an acid value in the range described below.

[0142] Examples of monomers having anionic groups include monomers having anionic groups such as carboxyl groups, sulfonyl groups, and phosphate groups. Monomers having anionic groups are preferably monomers having carboxyl groups, and more preferably at least one selected from acrylic acid and methacrylic acid. In these cases, excellent storage stability is easily achieved, which prevents the solid components in the pigment composition from settling over time. This also helps prevent the solid components in the ink from settling over time, and helps prevent clogging of the ink ejection nozzle during the initial ejection phase (easily achieving excellent initial ejection stability). This also helps prevent clogging of the ink ejection nozzle over time (easily achieving excellent ejection stability over time).

[0143] From the viewpoint of easily obtaining a radical polymer having an acid value in the range described below, the content of the monomer having an anionic group is preferably 5 to 80% by mass, more preferably 5 to 60% by mass, and even more preferably 5 to 50% by mass, relative to the total mass of monomers that can be used when producing a resin having an acid value.

[0144] As monomers that can be used in the manufacture of resins having an acid value, in addition to the above-mentioned monomers, other monomers can be used as needed. Examples of other monomers include methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, 1,3-dimethylbutyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-methylbutyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, nonyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 1,3-dimethylbutyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-methylbutyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, nonyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 1,3-dimethylbutyl (meth)acrylate, acrylate, 3-ethoxybutyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, ethyl (meth)acrylate -α-(hydroxymethyl) ester, dimethylaminoethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, phenylethyl (meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, glycerol (meth)acrylate, bisphenol A (meth)acrylate, dimethyl maleate, diethyl maleate, vinyl acetate, etc. These monomers can be used alone or in combination of two or more. As other monomers, one such acrylate or methacrylate can be used alone, or an acrylate and a methacrylate can be used in combination.

[0145] As the resin having an acid value, a polymer having a linear structure formed by free radical polymerization of monomers, a polymer having a branched (grafted) structure, a polymer having a crosslinked structure, etc. can be used. In each polymer, the monomer arrangement is not particularly limited, and a polymer having a random arrangement or a block arrangement can be used.

[0146] A polymer having a cross-linked structure can be produced by using a monomer having a cross-linking functional group as a monomer. Examples of the monomer having a cross-linking functional group include polyol (meth)acrylates such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, poly(oxyethylene oxypropylene) glycol di(meth)acrylate, and tri(meth)acrylates of alkylene oxide adducts of glycerol, glycidyl (meth)acrylate, and divinylbenzene.

[0147] As the resin having an acid value, a polymer having a structural unit derived from the above-mentioned monomers can be used, but a polymer obtained by polymerizing only a monomer having an anionic group and a monomer having an aromatic ring structure or a heterocyclic structure is preferred.

[0148] The resin having an acid value is preferably a polymer having structural units derived from styrene and structural units derived from (meth)acrylic acid, and more preferably at least one selected from styrene-(meth)acrylic acid copolymers and styrene-(meth)acrylic acid ester-(meth)acrylic acid copolymers. The polymer having structural units derived from styrene and structural units derived from (meth)acrylic acid preferably has an acid value within the range described below. The aromatic ring portion of the structural unit derived from styrene is firmly adsorbed to the surface of the pigment component, and the carboxyl group in the structural unit derived from (meth)acrylic acid has good affinity for water, thereby easily achieving good dispersion stabilization. This makes it easy to obtain excellent storage stability that prevents the solid components in the pigment composition from settling over time, easily prevents the solid components in the ink from settling over time, easily suppresses clogging of the ink ejection nozzle during the initial ink ejection process (easy to obtain excellent initial ejection stability), and easily suppresses clogging of the ink ejection nozzle over time (easy to obtain excellent ejection stability over time).

[0149] As the styrene-(meth)acrylic acid copolymer, any of styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, and styrene-acrylic acid-methacrylic acid copolymers can be used, preferably at least one selected from styrene-acrylic acid copolymers and styrene-acrylic acid-methacrylic acid copolymers. In this case, it is easy to adjust the adsorption capacity with the pigment component and the dispersion capacity in water. As a result, it is easy to achieve excellent storage stability that prevents the solid components in the pigment composition from settling over time, and it is easy to prevent the solid components in the ink from settling over time. It is easy to suppress the occurrence of clogging of the ink ejection nozzle during the initial ink ejection (easy to achieve excellent initial ejection stability), and it is easy to suppress the occurrence of clogging of the ink ejection nozzle over time (easy to achieve excellent ejection stability over time).

[0150] In the styrene-(meth)acrylic acid copolymer, the total amount of the structural units derived from styrene, the structural units derived from acrylic acid, and the structural units derived from methacrylic acid is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, relative to the total mass of the structural units of the styrene-(meth)acrylic acid copolymer.

[0151] It is believed that the radical polymerization rate (reaction rate) of each monomer during radical polymerization is substantially the same, and the ratio of each monomer used (charging ratio) is the same as the ratio of the structural units derived from each monomer constituting the radical polymer.

[0152] The radical polymer can be produced by radical polymerization of the above-mentioned monomers by, for example, bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization or the like.

[0153] When producing the radical polymer, a known and commonly used polymerization initiator, chain transfer agent (polymerization degree regulator), surfactant, defoaming agent, etc. may be used as needed.

[0154] Examples of the polymerization initiator include 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), benzoyl peroxide, dibutyl peroxide, and butyl peroxybenzoate. The content of the polymerization initiator is preferably 0.1 to 10% by mass relative to the total mass of the monomers used in the production of the radical polymer.

[0155] When using a free radical polymer obtained by solution polymerization, the resin having an acid value can be one obtained by removing the solvent contained in the free radical polymer solution obtained by solution polymerization, followed by drying and pulverization to form microparticles. When a water-soluble organic solvent and an alkaline compound are used in combination, the resin having an acid value as the microparticle-formed free radical polymer is neutralized by the alkaline compound in the first step, dissolved in an aqueous medium containing the water-soluble organic solvent, and adsorbed onto the surface of the pigment component moistened by the aqueous medium. This results in excellent storage stability that prevents the solid components in the pigment composition from settling over time, prevents the solid components in the ink from settling over time, and easily suppresses clogging of the ink ejection nozzle during the initial stage of ink ejection (easily achieving excellent initial ejection stability). It also helps suppress clogging of the ink ejection nozzle over time (easily achieving excellent ejection stability over time).

[0156] As the resin having an acid value, one classified with a mesh sieve having an opening size (diameter) of 1 mm or less is preferable.

[0157] The acid value of the resin (e.g., pigment-dispersing resin) is preferably 60 to 300 mgKOH / g, more preferably 80 to 250 mgKOH / g, even more preferably 100 to 200 mgKOH / g, and particularly preferably 120 to 180 mgKOH / g. In these cases, the resin's adsorption of the pigment component can be enhanced, and it is easier to obtain a moderate affinity for aqueous media (e.g., aqueous media containing water and a water-soluble organic solvent), thereby facilitating the maintenance of a well-dispersed state. Consequently, excellent storage stability is easily achieved, preventing the solid components in the pigment composition from settling over time. This also facilitates the prevention of long-term settling of the solid components in the ink, and suppresses clogging of the ink ejection nozzle during the initial ejection phase (facilitating excellent initial ejection stability). This also facilitates the suppression of clogging of the ink ejection nozzle over time (facilitating excellent long-term ejection stability).

[0158] The acid value is preferably an acid value derived from anionic groups such as carboxyl groups, sulfonyl groups, and phosphate groups. The acid value is measured in accordance with Japanese Industrial Standards "K0070:1992. Test methods for acid value, saponification value, ester value, iodine value, hydroxyl value, and unsaponifiable matter of chemicals," except that tetrahydrofuran is used as the solvent instead of diethyl ether. The acid value is the amount (mg) of potassium hydroxide required to completely neutralize 1 g of the resin having the acid value.

[0159] The weight-average molecular weight of a resin having an acid value (e.g., a pigment-dispersing resin) is preferably 2,000 to 40,000, more preferably 5,000 to 30,000, even more preferably 5,000 to 25,000, preferably 6,000 to 20,000, and particularly preferably 8,000 to 12,000. In these cases, aggregation of adjacent pigment components is suppressed, and excellent storage stability is easily achieved by preventing the solid components in the pigment composition from settling over time. Sedimentation of the solid components in the ink over time is easily prevented, and clogging of the ink ejection nozzles during the initial ejection of the ink is easily suppressed (favoring excellent initial ejection stability), and clogging of the ink ejection nozzles over time is easily suppressed (favoring excellent aging ejection stability). The "weight-average molecular weight" is a value measured by GPC (gel permeation chromatography) and is converted to the molecular weight of polystyrene used as a standard substance.

[0160] The content of the resin having an acid value (e.g., a pigment dispersing resin) is preferably 5 to 200 parts by mass, more preferably 10 to 100 parts by mass, per 100 parts by mass of the pigment component. This facilitates maintaining a well-dispersed state due to its sufficient affinity for aqueous media (e.g., water). The acid resin readily adsorbs to the pigment component, thus easily achieving excellent storage stability by preventing the solid components in the pigment composition from settling over time. This prevents the solid components in the ink from settling over time, easily suppresses clogging of the ink ejection nozzles during the initial ejection phase (e.g., achieving excellent initial ejection stability), and easily suppresses clogging of the ink ejection nozzles over time (e.g., achieving excellent over-time ejection stability). Furthermore, the amount of free acid resin not adsorbed to the pigment component is easily reduced, improving the ink's ejection properties. Furthermore, aggregation of the pigment component caused by the free resin is easily suppressed, facilitating ink stabilization.

[0161] The pigment composition may contain a basic compound. If the acidic resin has anionic groups, the basic compound neutralizes these anionic groups. Neutralization of the acidic resin by the basic compound improves the affinity of the pigment component adsorbed by the acidic resin for the aqueous medium. As a result, coarse particles are easily reduced, the dispersion of the solid components in the pigment composition is easily stabilized, the generation of coarse particles over time is effectively prevented, and sedimentation of the solid components over time is easily suppressed.

[0162] As the basic compound, inorganic basic compounds, organic basic compounds etc. can be used. As the inorganic basic compound, the hydroxides of alkali metals such as potassium, sodium, the carbonates of alkali metals such as potassium, sodium, the carbonates of alkaline earth metals such as calcium, barium etc. can be enumerated. As the organic basic compound, the amino alcohols such as triethanolamine, N, N-dimethylolamine, N-ethylethanolamine, dimethylethanolamine, N-butyldiethanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine etc., piperazines such as N-(2-hydroxyethyl) piperazine, piperazine hexahydrate, ammonium hydroxide etc. can be enumerated. Due to the excellent neutralization efficiency to the resin with acid number, the dispersion stability of the pigment component adsorbed by the resin with acid number in the aqueous medium is easy to improve, and the basic compound is preferably an alkali metal hydroxide (potassium hydroxide, sodium hydroxide, lithium hydroxide etc.), more preferably potassium hydroxide.

[0163] When using an anionic group-containing acidic resin, it is preferable to use a basic compound so that the neutralization ratio of the acidic resin is within a range of 80-120%. This increases the affinity of the neutralized acidic resin for the aqueous medium, which in turn tends to improve the dispersion stability of the pigment component adsorbed by the acidic resin in the aqueous medium. The neutralization ratio can be calculated, for example, using the following formula.

[0164] Neutralization rate [%] = ((mass of basic compound [g] × 56 × 1000) / (acid value of resin having acid value × equivalent weight of basic compound × mass of resin having acid value [g])) × 100

[0165] The pigment composition of this embodiment can be prepared into an ink by diluting it to a desired concentration with the aqueous medium and / or adding additives such as a resin having an acid value (a binder such as the acrylic resin or polyurethane resin), a drying inhibitor, a penetrant, a surfactant, a preservative, a viscosity modifier, a pH modifier, a chelating agent, a plasticizer, an antioxidant, and a UV absorber. The ink can also be centrifuged or filtered after it is obtained.

[0166] Examples of the ink include automotive or building material coatings, inkjet inks, offset inks, gravure inks, flexographic inks, screen printing inks, and other printing inks. When the ink is used as an inkjet ink, the content of the pigment component in the ink is preferably 1 to 10% by mass relative to the total mass of the ink.

[0167] As the aqueous medium, a water-soluble organic solvent can be used to prevent the ink from drying out and to adjust the ink viscosity or concentration to an appropriate range. The water-soluble organic solvent can be any of the aforementioned water-soluble organic solvents that are components of the pigment composition. Examples of water-soluble organic solvents that improve the ink's permeability to the recording medium include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.

[0168] Examples of drying inhibitors include glycerol, ethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol mono-n-butyl ether, polyethylene glycols with a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanediol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, erythritol, and pentaerythritol. The drying inhibitor can be the same compound as the water-soluble organic solvent used in the pigment composition. Therefore, if a water-soluble organic solvent is already used in the pigment composition, it can also function as a drying inhibitor.

[0169] Penetrants can be used to improve the permeability to the recording medium or to adjust the spot diameter on the recording medium. Examples of penetrants include lower alcohols such as ethanol and isopropyl alcohol, and glycol monoethers of alkyl alcohols such as ethylene glycol hexyl ether, diethylene glycol butyl ether, and propylene glycol propyl ether.

[0170] Surfactants can be used to adjust ink properties such as surface tension. While not particularly limited, examples of surfactants include various anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Preferably, the surfactant is at least one selected from anionic surfactants and nonionic surfactants. Surfactants may be used alone or in combination of two or more.

[0171] Examples of the anionic surfactant include alkylbenzenesulfonates, alkylphenylsulfonates, alkylnaphthalenesulfonates, higher fatty acid salts, sulfuric acid ester salts of higher fatty acid esters, sulfonic acid salts of higher fatty acid esters, sulfuric acid ester salts and sulfonic acid salts of higher alcohol ethers, higher alkylsulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkylphosphates, polyoxyethylene alkylether phosphates, etc. Specific examples thereof include dodecylbenzenesulfonate, isopropylnaphthalenesulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenylsulfonate, and dibutylphenylphenol disulfonate.

[0172] Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, glycerol fatty acid esters, polyoxyethylene glycerol fatty acid esters, polyglycerol fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkanolamides, alkyl alkanolamides, acetylenic glycols, oxyethylene adducts of acetylenic glycols, and polyethylene glycol-polypropylene glycol block copolymers. Among these, at least one selected from the group consisting of polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid alkanolamides, acetylenic glycols, oxyethylene adducts of acetylenic glycols, and polyethylene glycol-polypropylene glycol block copolymers is preferred.

[0173] As other surfactants, silicone surfactants such as polysiloxane oxyethylene adducts, fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers, and biosurfactants such as echinopsinic acid, rhamnolipids, and lysolecithin can also be used.

[0174] (Defoaming Agent)

[0175] In the manufacture method of the present invention, preferably add defoamer in pigment composition and raw material composition. Pigment composition and raw material composition comprising defoamer are difficult for foaming in the dispersion process, and can realize the stable operation of dispersion machine. As defoamer, surfactant with low hydrophilic-hydrophobic balance (HLB) can be used, particularly surfactant with HLB below 9, metal soap defoamer, polyether defoamer, mineral oil defoamer, silicone defoamer etc. are used. Wherein, preferably use acetylene glycol surfactant, specifically, preferably use Surfynol104 series, Surfynol420, Surfynol440, Surfynol465, Surfynol485, Surfynol2502, SurfynolCT211, SurfynolPSA-336, SurfynolSE-F (all are Nissin Chemical Industry Co., Ltd. system), more preferably use SurfynolSE-F and Surfynol 440.

[0176] In the pigment composition obtained by the above method, when the total mass of the acid-valued resin is set to 100 mass%, preferably 20 to 60 mass% of the acid-valued resin is adsorbed on the pigment component. This reduces the viscosity from increasing significantly over time, and allows for a pigment composition with excellent storage stability. The mass ratio of the acid-valued resin adsorbed on the pigment component relative to the total mass of the acid-valued resin (mass of the acid-valued resin adsorbed on the pigment component / total mass of the acid-valued resin) (hereinafter referred to as the "resin adsorption rate") is a value calculated by the following method.

[0177] Using a particle charge meter (Spectris, trade name: PCD-04), the streaming potential is measured within a ±2500 mV range using the platinum electrode of the sample cell. The pigment composition is placed in the sample cell and titrated with a titrant (0.01N, Poly-DADMAC). The charge is determined based on the potential difference (i.e., the streaming potential) generated by the movement of the sample cell and the piston (the "streaming potential" of the liquid). The titration is terminated when the streaming potential exceeds zero (positive potential). The amount added from the inflection point is divided by the amount added when the streaming potential reaches zero, and the resulting value is multiplied by 100 to represent the resin adsorption rate.

[0178] From the perspective of producing an inkjet printing ink that is less likely to cause a significant increase in viscosity over time and has very excellent storage stability, and further capable of reducing the number of coarse particles having a particle size of 1.0 μm or more that can be contained in the pigment composition, thereby enabling the production of printed materials with high color development, the resin adsorption rate is more preferably in the range of 20 to 50% by mass, and particularly preferably in the range of 25 to 40% by mass.

[0179] The pigment composition obtained by the manufacturing method of the present invention is particularly suitable for use as an ink for inkjet printing because the number of coarse particles is small. The number of coarse particles of the pigment composition manufactured by the manufacturing method of the present invention refers to the number of particles with a diameter of 1.0 μm or more and the number of particles with a diameter of 0.5 μm or more, which can be measured using a particle size distribution meter (Particle Sizing Systems, Accusizer 780APS, number counting method). As a specific measurement method, the pigment composition can be diluted with pure water so that the sensitivity is in the range of 1000 to 4000 particles / mL. The number of particles with a diameter of 1.0 μm or more and the number of particles with a diameter of 0.5 μm or more contained in the diluted pigment composition are measured three times using a particle size distribution meter. The measured values ​​of the number of particles are multiplied by the dilution concentration, and the average value of the obtained values ​​is calculated as the number of coarse particles.

[0180] Regarding the number of coarse particles of the pigment composition produced by the production method of the present invention, the number of particles with a diameter of 1.0 μm or more in 1.0 mL of the pigment composition having a pigment concentration of 13% is preferably 2600×10 6 The number of particles with a diameter of 0.5 μm or less is 14400×10 6 More preferably, the number of particles with a diameter of 1.0 μm or more is 300×10 6 The number of particles with a diameter of 0.5 μm or more is 2000×10 6 When the number of the coarse particles is within this range, the number of steps such as centrifugal separation can be reduced, and clogging of inkjet printing ink nozzles can be suppressed.

[0181] The pigment composition manufactured by the manufacturing method of the present invention has an appropriate particle size, so the optical density (OD) during printing becomes high, and an excellent printed material can be obtained. The particle size can be measured using a Nanotrac particle size distribution meter "UPA150" manufactured by Microtrac BEL Co., Ltd. by detecting the scattered light of the laser at 25°C. The volume average particle size (Mv), number average particle size (Mn), D50, D90 and D95 ​​are measured as the particle size. The volume average particle size (Mv) is preferably 50nm to 170nm, more preferably 80nm to 150nm. The number average particle size (Mn) is preferably 30nm to 120nm, more preferably 50nm to 100nm. In addition, the median particle size D50 is preferably 70nm to 140nm, the median particle size D90 is preferably 120nm to 230nm, and the median particle size D95 is preferably 150nm to 270nnm.

[0182] (Ink)

[0183] The pigment composition obtained by the production method of the present invention can be suitably used as an ink, particularly an ink for inkjet printing. In addition to the pigment composition obtained by the production method of the present invention, the ink may further contain an aqueous medium, a surfactant, a resin, a wax, an additive, and the like.

[0184] The aqueous medium and surfactant to be further added may be the same as those mentioned above.

[0185] Examples of the resin include polyurethane resins, acrylic resins, epoxy resins, polyester resins, and shellac. The resin content is preferably 5.5% by mass or less relative to the total amount of the ink. From the perspective of achieving an ink that exhibits excellent scratch resistance even with a very short drying time after printing and can produce printed materials with high color rendering properties when printed on plain paper, the content is more preferably 3.5% by mass or less.

[0186] Examples of the wax include polyolefin waxes. Specifically, polyethylene, polypropylene, polybutene, polytetrafluoroethylene, and polymers of ethylene and propylene or butene are preferably used as the polyolefin wax. Polyethylene, polypropylene, and polybutene are more preferably used. Polyethylene is particularly preferably used from the perspective of obtaining an ink that can be printed by inkjet printing and can produce a printed material with excellent color development and scratch resistance.

[0187] As the additives, for example, an alkali agent, a pH adjuster, a surfactant, a preservative, a chelating agent, a plasticizer, an antioxidant, an ultraviolet absorber, etc. may be added according to the desired properties.

[0188] The above-mentioned ink can be produced, for example, by mixing an aqueous medium, a wetting agent, a binder resin, wax, an additive, etc., as needed, with the pigment dispersion obtained by the production method of the present invention. Specifically, the ink can be produced, for example, by adding an aqueous medium such as pure water to the above-mentioned pigment dispersion, followed by adding a lubricant as needed, and stirring at room temperature for 30 to 90 minutes. A resin dispersion, etc., is then added to the aqueous medium, and further stirred at room temperature for 30 to 90 minutes. Then, a potassium hydroxide aqueous solution having a potassium hydroxide concentration of 5% by mass is added to adjust the pH of the ink to 8.5 to 9.8, and stirring at room temperature for 30 to 90 minutes. However, the present invention is not limited to this.

[0189] As the ink, for example, it is preferable to use an ink having a viscosity in the range of 1 to 10 mPa·sec. In particular, when the ink is ejected by inkjet printing, it is more preferable to use an ink having a viscosity in the range of 1 to 6 mPa·sec.

[0190] (Printed Materials)

[0191] The ink containing the pigment composition obtained by the production method of the present invention can be used for printing on a recording medium.

[0192] Examples of the recording medium include micro-coated paper and plain paper, the surface of which is thinly coated with an agent that accelerates ink drying, and these paper can produce high-quality printed materials.

[0193] Representative examples of the plain paper include PPC paper used in electrophotographic copiers, etc. Although the usage rate of waste paper pulp, degree of bleaching, etc., and the thickness of the plain paper vary depending on the type, any suitable paper can be used.

[0194] The above-mentioned ink can be applied to various printing methods, but is preferably used when printing primarily using inkjet printing. Examples of such inkjet printing methods include continuous jet printing (charge-controlled printing, spray printing, etc.) and on-demand printing (piezoelectric printing, thermal printing, electrostatic attraction printing, etc.). It is particularly suitable for printing using thermal inkjet printing. Furthermore, this water-based ink for inkjet recording generally enables extremely stable ink ejection when applied to these various inkjet printing methods.

[0195] Example

[0196] Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

[0197] <Preparation of Styrene-Acrylic Acid Copolymer>

[0198] (Styrene-acrylic acid copolymer A)

[0199] After adding 100 parts by mass of methyl ethyl ketone to a reaction vessel equipped with a stirring apparatus, a dropping apparatus, and a reflux apparatus, the atmosphere in the reaction vessel was purged with nitrogen while stirring. The reaction vessel was then heated, and while the methyl ethyl ketone was refluxed, a mixture of 77 parts by mass of styrene, 10 parts by mass of acrylic acid, 13 parts by mass of methacrylic acid, and 8 parts by mass of a polymerization catalyst (Wako Pure Chemical Industries, Ltd., trade name: V-59) was added dropwise over 2 hours from the dropping apparatus. The temperature of the reaction vessel was maintained at 80°C from the beginning of the addition. After the addition was completed, the reaction was continued at the same temperature for a further 25 hours. After the reaction was completed, the reaction vessel was cooled, and methyl ethyl ketone was added to obtain a solution with a solids concentration of 50% by mass. The solution was then dried and pulverized into a powder of less than 1 mm to obtain styrene-acrylic acid copolymer A. Styrene-acrylic acid copolymer A had an acid value of 150 mgKOH / g and a weight-average molecular weight of 8800.

[0200] The weight average molecular weight is a value measured by GPC (gel permeation chromatography) and is a value converted to the molecular weight of polystyrene used as a standard substance. The measurement is performed using the following apparatus and conditions.

[0201] Liquid delivery pump: LC-9A (manufactured by Shimadzu Corporation)

[0202] System controller: SLC-6B (manufactured by Shimadzu Corporation)

[0203] Automatic injector: S1L-6B (Shimadzu Corporation)

[0204] Detector: RID-6A (manufactured by Shimadzu Corporation)

[0205] Data processing software: Sic480 II data station (manufactured by System Instruments)

[0206] Column: GL-R400 (guard column) + GL-R440 + GL-R450 + GL-R400M (made by Hitachi Chemical Co., Ltd.)

[0207] Elution solvent: THF (tetrahydrofuran)

[0208] Elution flow rate: 2mL / min

[0209] Column temperature: 35°C

[0210] <Preparation of Pigment Composition>

[0211] (Black pigment composition)

[0212] [Example 1]

[0213] 5000 g of black pigment (manufactured by Mitsubishi Chemical Corporation, carbon black, #960, dry pigment), 2000 g of the above-mentioned styrene-acrylic copolymer A, 5500 g of triethylene glycol, 250 g of Surfynol SEF, 6616 g of pure water and 634 g of a 48% by mass aqueous potassium hydroxide solution were mixed to prepare 20,000 g of a raw material composition (pigment concentration: 25% by mass, solid content concentration: 35% by mass).

[0214] 20,000 g of the raw material composition was placed in a rotor-stator processor (manufactured by IKA, equipment name: MK2000 / 05, pilot machine, in-line type, lid adjustment 0.1 mm). Next, as a first dispersion treatment step (crushing or crushing), the raw material composition was dispersed at a flow rate of 40 kg / min, while the temperature was raised to 60°C and the circumferential speed was 32 m / s (shear rate: 320,000 s). -1), a rotation speed of 8200 rpm was used for 30 minutes of circulation treatment to prepare a first pigment composition (slurry). By applying the first treatment step to the raw material composition multiple times, the first pigment composition (slurry) required for the next step was prepared. Then, pure water was added to the obtained first pigment composition to make the pigment concentration 20% by mass and the solid content concentration 28% by mass. As a second dispersion treatment step (crushing or crushing treatment), a media type disperser (made by Ashizawa Finetech, equipment name: wet bead mill "Mugen Flow (registered trademark)" MGF2) was used. For 35,000 g of the first pigment composition with a pigment concentration of 20% by mass, a bead diameter of 0.2 mm, a bead filling rate of 90%, a liquid feed rate of 23 kg / min, and a circumferential speed of 14 m / s while heating to above 30°C were used for 150 minutes to obtain a second pigment composition. Furthermore, as a third dispersion treatment step (crushing or crushing treatment), a media-type disperser (manufactured by Ashizawa Finetech Co., Ltd., equipment name: wet bead mill "Mugen Flow (registered trademark)" MGF2) was used to circulate 12850 g of the second pigment composition at a peripheral speed of 14 m / s for 75 minutes while raising the temperature to 30°C or higher, with a bead diameter of 0.1 mm, a bead filling rate of 90%, and a liquid feed rate of 10 kg / min. A third pigment composition was obtained.

[0215] [Example 2]

[0216] Pure water was added to the second pigment composition obtained in Example 1 to adjust the pigment concentration to 17% by mass and the solid content concentration to 24% by mass. A third pigment composition was obtained by performing the third dispersion treatment step (pulverization or crushing) in the same manner as in Example 1, except that the bead diameter and liquid feed flow rate in the third dispersion treatment step were changed to the values ​​shown in Table 1.

[0217] [Example 3]

[0218] A raw material composition was obtained in the same manner as in Example 1. As a first dispersion treatment step, a rotor-stator type processor (manufactured by IKA, equipment name: DR2000 / 05, pilot machine, in-line, 3-stage, with a processing section (rotor and stator) of 2G / 4M / 6F in the vertical direction) was used. 20,000 g of the raw material composition was subjected to a liquid feed rate of 10 kg / min and a peripheral speed of 32 m / s (shear rate: 64,000 s) while the temperature was raised to 60°C. -1), and a rotation speed of 8200 rpm for 30 minutes to produce a first pigment composition (slurry). Subsequently, pure water was added to the obtained first pigment composition to adjust the pigment concentration to 22% by mass and the solid content concentration to 31% by mass. As a second dispersion treatment step, a medium-type disperser (manufactured by Asada Iron Works Co., Ltd., equipment name: Nano Mill (NM-L), Lab machine) was used to circulate 3000 g of the first pigment composition with a pigment concentration of 22% by mass, with a bead diameter of 0.3 mm, a bead filling rate of 80%, and a liquid feed rate of 0.6 kg / min, while heating to above 30°C and at a peripheral speed of 12.5 m / s for 60 minutes to produce a second pigment composition.

[0219] [Example 4]

[0220] Pure water was added to the raw material composition obtained in the same manner as in Example 1 to adjust the pigment concentration to 20% by mass and the solid content concentration to 28% by mass. As the first dispersion treatment step, a rotor-stator type processor (manufactured by IKA, equipment name: magic LAB (DR), Lab machine, in-line, three-stage, with a processing section (rotor and stator) of 2P / 4M / 6F from the vertical direction) was used. 1700 g of the raw material composition having a pigment concentration of 20% by mass was subjected to a liquid feed rate of 0.17 kg / min and a peripheral speed of 32 m / s (shear rate: 170,000 s) while heating to 60° C. -1 ), and 7 passes at a rotation speed of 20000 rpm. By performing the first treatment step multiple times on the raw material composition, the first pigment composition (slurry) of the amount required for the next step is prepared.

[0221] Next, 20,000 g of the obtained first pigment composition was subjected to a second dispersion treatment step using a media-type disperser (manufactured by Ashizawa Finetech Co., Ltd., equipment name: wet bead mill "Mugen Flow (registered trademark)" MGF2) with a bead diameter of 0.1 mm, a bead filling rate of 80%, a liquid feed rate of 2.5 kg / min, and a circulation treatment at a peripheral speed of 8 m / s for 120 minutes while raising the temperature to 30°C or higher. This yielded a second pigment composition.

[0222] [Example 5]

[0223] A second pigment composition was obtained by performing the second dispersion treatment step in the same manner as in Example 4 except that 20,000 g of the first pigment composition obtained in Example 4 was treated at a peripheral speed of 14 m / s while heating to 30° C. or higher.

[0224] [Example 6]

[0225] Pure water was added to the raw material composition obtained in the same manner as in Example 1 to a pigment concentration of 20% by mass and a solids concentration of 28% by mass. In the first dispersion treatment step, 35,000 g of the raw material composition was circulated for 90 minutes using a media-type disperser (manufactured by Ashizawa Finetech Co., Ltd., equipment name: wet bead mill "Mugen Flow (registered trademark)" MGF2) with a bead diameter of 1 mm, a bead filling rate of 85%, a liquid flow rate of 5 kg / min, and a peripheral speed of 13.5 m / s while heating to 30°C or above. This yielded a first pigment composition. The raw material composition was subjected to the first treatment step multiple times to prepare the first pigment composition (slurry) required for the next step. 32,000 g of the resulting first pigment composition was subjected to a second dispersion treatment step (pulverization or crushing) under the same conditions as in Example 1 to yield a second pigment composition. Furthermore, 12500 g of the obtained second pigment composition was subjected to a third dispersion treatment step (crushing or crushing treatment) using a media-type disperser (manufactured by Ashizawa Finetech Co., Ltd., equipment name: wet bead mill "Mugen Flow (registered trademark)" MGF2) with a bead diameter of 0.1 mm, a bead filling rate of 90%, a liquid feed flow rate of 10 kg / min, and a circulation treatment at a peripheral speed of 14 m / s for 75 minutes while heating to 30°C or higher. Thus, a third pigment composition was obtained.

[0226] [Example 7]

[0227] 35000 g of the first pigment composition obtained in Example 6 was subjected to the second and third dispersion treatment steps in the same manner as in Example 6, except that the bead diameter was changed to the value shown in Table 1 in the second dispersion treatment step, thereby obtaining a third pigment composition.

[0228] [Comparative Example 1]

[0229] A raw material composition was obtained in the same manner as in Example 1. As the first dispersion treatment step, a rotor-stator type processor (manufactured by IKA, equipment name: magicLAB (DR), Lab machine, in-line, three-stage, with a processing section (rotor and stator) of 2P / 4M / 6F from the vertical direction) was used. 1500 g of the raw material composition was subjected to a liquid feed rate of 0.17 kg / min, while being heated to 60° C. and at a peripheral speed of 34 m / s (shear rate: 170,000 s -1) and 20,000 rpm, and passed through the mixture five times to produce a first pigment composition (slurry). Next, as a second dispersion treatment step, 1,500 g of the first pigment composition was passed through a high-pressure homogenizer (manufactured by Sugino Machinery Co., Ltd., equipment name: Starburst 10, oblique collision chamber) at 140 MPa once to produce a second pigment composition.

[0230] [Comparative Example 2]

[0231] 250 g of the first pigment composition obtained in Comparative Example 1 was subjected to the second dispersion treatment step in the same manner as in Comparative Example 1, except that the first pigment composition was subjected to one pass treatment at 140 MPa using a high-pressure homogenizer (manufactured by Sugino Machinery Co., Ltd., equipment name: Starburst Mini, ball collision chamber). A second pigment composition was obtained.

[0232] <Evaluation of Pigment Composition>

[0233] The first, second, and third pigment compositions were used to evaluate the number of coarse particles, particle size, and viscosity according to the following procedures. The results are shown in Tables 1 and 2.

[0234] (number of coarse particles)

[0235] Using a particle size distribution meter (Accusizer 780APS, manufactured by Particle Sizing Systems, number counting method), measure the number of particles with a diameter of 1.0 μm or greater and the number of particles with a diameter of 0.5 μm or greater according to the following procedure. Dilute the pigment composition with pure water so that the sensitivity is in the range of 1000 to 4000 particles / mL. Next, use the particle size distribution meter to measure the number of particles with a diameter of 1.0 μm or greater and the number of particles with a diameter of 0.5 μm or greater in the diluted pigment composition three times. Next, calculate the average value of the measured particle number multiplied by the dilution concentration as the number of coarse particles.

[0236] (Particle size)

[0237] The pigment composition was placed in an approximately 4 mL cell. Particle size was measured using a Nanotrac particle size distribution analyzer (UPA150) manufactured by Microtrac BEL Co., Ltd. by detecting scattered laser light at 25°C. Particle sizes included volume average particle size (Mv), number average particle size (Mn), D50, D90, and D95.

[0238] (Viscosity)

[0239] After 1.0 mL of the pigment composition was placed in a sample cup, the viscosity of the pigment composition was measured using a TV-20 viscometer manufactured by Toki Sangyo Co., Ltd. at 25° C. The viscosity of the pigment composition having a pigment concentration of 25% by mass or more was too high to be measured.

[0240] [Table 1]

[0241]

[0242] [Table 2]

[0243]

[0244] As shown in Tables 1 and 2, it can be seen that in Examples 1 to 7, when the first dispersion treatment step in the pigment composition production method is a step using a circulating or through-type rotor-stator type processor or a media-type disperser, and further, when the second dispersion treatment step is a step using a media-type disperser using beads having a diameter of 0.01 to 0.5 mm, the pigment concentration of the pigment composition at the time of completion of the second dispersion treatment step is 20% by mass relative to the total mass of the pigment composition. In addition, after the completion of the second dispersion treatment step, the number of coarse particles of the pigment composition having a particle size of greater than 0.5 μm is 2060×10 6 The coarse particles of the pigment composition with a particle size greater than 1.0 μm were 18×10 6 It can be seen that the number of coarse particles in the pigment composition can be reduced efficiently while reducing the workload.

[0245] On the other hand, in Comparative Example 1, when a high-pressure homogenizer (oblique collision chamber) was used in the second dispersion treatment step, the pigment concentration of the pigment composition at the end of the second dispersion treatment step was 13% by mass relative to the total mass of the pigment composition, which is lower than that of any of Examples 1 to 7. In addition, the number of coarse particles of the pigment composition having a particle size greater than 0.5 μm was 2700×10 6 The coarse particles of the pigment composition with a particle size greater than 1.0 μm are 500×10 6 The number of coarse particles in the pigment composition was greater than that in any of Examples 1 to 7.

[0246] In Comparative Example 2, when a high-pressure homogenizer (ball collision chamber) was used in the second dispersion treatment step, the pigment concentration of the pigment composition at the end of the second dispersion treatment step was 13% by mass relative to the total mass of the pigment composition, which is lower than that of any of Examples 1 to 7. In addition, the number of coarse particles of the pigment composition having a particle size greater than 0.5 μm was 5000×10 6 / mL, and the coarse particles of the pigment composition with a particle size greater than 1.0 μm are 600×10 6 / mL, similarly to Comparative Example 1, the number of coarse particles in the pigment composition was larger than that of any of Examples 1 to 7.

[0247] Explanation of symbols

[0248] 10…Center axis, 20…Rotor, 22…Blade portion, 22a…Opening, 24…Connecting portion, 30…Stator, 32…Wall portion, 32a…Opening, 34…Connecting portion, 100…Rotor-stator type processor, F1, F2…Flow paths.

Claims

1. A method for producing a pigment composition, comprising: producing a pigment composition comprising carbon black, a resin having an acid value, and an aqueous medium; The method for producing the pigment composition comprises at least a first dispersion treatment step and a second dispersion treatment step in sequence. The first dispersion treatment step is a step of dispersing in a circulation or through-flow manner. The second dispersion treatment step is a step using a medium-type disperser. The diameter of the beads used in the second dispersion treatment step is 0.01 to 0.5 mm. The pigment concentration of the pigment composition at the end of the second dispersion treatment step is 16 to 32% by mass relative to the total mass of the pigment composition.

2. The method for producing a pigment composition according to claim 1, wherein After the second dispersion treatment step, a third dispersion treatment step is further included. The third dispersion treatment step is a step using a media-type disperser.

3. The method for producing a pigment composition according to claim 1, wherein The first dispersion treatment step is a step using a rotor-stator type processor.

4. The method for producing a pigment composition according to claim 1, wherein The pigment composition further comprises a defoaming agent. 5 . A pigment composition produced by the production method according to claim 1 . An ink comprising the pigment composition according to claim 5 .

7. A printed matter comprising the ink according to claim 6.

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