Method for producing quinacridone solid solution pigment, method for producing pigment dispersion and inkjet recording method

Abstract

To provide a method for producing a quinacridone solid solution pigment having a particle size distribution as uniform as possible and capable of obtaining sufficient color developability (saturation C*) when an image is recorded on plain paper by incorporating it into an ink.SOLUTION: There is provided a method for producing a quinacridone solid solution pigment which comprises a first kneading step of kneading a mixture containing two or more kinds of quinacridone pigments having different structures, a water-soluble inorganic salt and a first organic solvent by a salt milling method to obtain a first kneaded product. In addition, the method for producing a quinacridone solid solution pigment comprises a second kneading step of adding a second organic solvent different from the first organic solvent into the first kneaded product after the first kneading step, followed by kneading with weaker force than that of the first kneading step to obtain a second kneaded product.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a quinacridone solid solution pigment, a method for producing a pigment dispersion, and an inkjet recording method.

Background Art

[0002] In recent years, the inkjet recording method has been used to record business documents using ordinary paper as a recording medium and photographic images using glossy paper as a recording medium, and its frequency of use has been increasing at each stage. When using a pigment as a coloring material used when recording an image by the inkjet recording method, the color development property is lower than when using a dye. Therefore, in recent years, in order to exhibit the same color development property as a dye, a finely divided pigment may be used. There are many methods for making a pigment finer, but salt milling has been proposed, in which a pigment, a salt as an abrasive, and an organic solvent are mixed, and then a load is applied to the mixture and kneaded while compressing (Patent Document 1).

[0003] Furthermore, as a magenta pigment, many proposals have been made to use a solid solution of a quinacridone pigment, which is superior in color development property to conventional quinacridone pigments such as C.I. Pigment Red 122 (Patent Document 2). Along with this, a method for producing a quinacridone solid solution pigment has also been proposed (Patent Document 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present inventors have attempted to prepare a quinacridone solid solution pigment based on past findings. However, when a quinacridone solid solution pigment is produced by the acid cyclization method as disclosed in Patent Document 3, the particle size distribution of the pigment is very large, and it was found that various processes must be carried out after production in order to make the particle size distribution of the pigment uniform. Therefore, the present inventors have attempted various studies with the aim of efficiently producing a quinacridone solid solution pigment with a particle size distribution as uniform as possible. As a result, it was found that the purpose can be achieved by producing a quinacridone solid solution pigment using a salt milling method. However, when an image is recorded on plain paper by an inkjet recording method using an ink containing the obtained quinacridone solid solution pigment, sufficient color development (L * a * b * Saturation C in the color system * Another issue arose in that in some cases, the

[0006] Therefore, an object of the present invention is to provide a quinacridone solid solution pigment having a uniform particle size distribution, and to provide sufficient color development (chroma C) when the pigment is incorporated into an ink and an image is recorded on plain paper. * Another object of the present invention is to provide a method for producing a pigment dispersion using the quinacridone solid solution pigment obtained by the above-mentioned production method, and an ink-jet recording method. [Means for solving the problem]

[0007] That is, according to the present invention, there is provided a method for producing a quinacridone solid solution pigment, which is characterized by comprising a first kneading step in which a mixture containing two or more quinacridone pigments having different structures, a water-soluble inorganic salt, and a first organic solvent is kneaded by a salt milling method to obtain a first kneaded product, and a second kneading step in which, after the first kneading step, a second organic solvent different from the first organic solvent is added to the first kneaded product and kneaded with a force weaker than that used in the first kneading step to obtain a second kneaded product. [Effect of the Invention]

[0008] According to the present invention, there is provided a method for producing a quinacridone solid solution pigment having a particle size distribution as uniform as possible, which can provide sufficient color development (chroma C * ) when it is contained in ink and an image is recorded on plain paper. Further, according to the present invention, there can be provided a method for producing a pigment dispersion using the quinacridone solid solution pigment obtained by the above production method, and an inkjet recording method. [Embodiments for Carrying Out the Invention]

[0009] Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, although the salt dissociates into ions and exists in the ink, for convenience, it is expressed as "containing a salt". In addition, the aqueous ink for inkjet may be simply referred to as "ink". Physical property values are values at room temperature (25°C) unless otherwise specified.

[0010] First, the solid solution pigment will be described. A solid solution is a crystal that exists in a uniform solid phase state in a mixed state in which a plurality of different molecules are dissolved, and is not a simple mixture of a plurality of different compounds. Therefore, the quinacridone solid solution pigment is expected to exhibit excellent color development as compared with a mixture in which two or more kinds of quinacridone pigments as raw materials are simply mixed.

[0011] In addition, the crystal structure of the quinacridone solid solution pigment can be confirmed by an X-ray diffraction method (also referred to as X-ray crystal structure analysis) that utilizes the phenomenon that X-rays are diffracted by a crystal lattice. The peak positions in the X-ray diffraction pattern of the quinacridone solid solution pigment show unique values depending on the type and crystal state of the pigment. Utilizing this, it is possible to identify the pigment type and its state by the X-ray diffraction method. The quinacridone solid solution pigment shows an X-ray diffraction pattern different from the sum of the X-ray diffraction patterns calculated by the individual X-ray diffraction methods of two or more kinds of quinacridone pigments as its raw materials.

[0012] Next, the background to the invention will be described in detail. The inventors have tried various methods that are not limited by past knowledge, with the aim of efficiently producing a quinacridone solid solution pigment having a particle size distribution as uniform as possible. In this disclosure, the term "as uniform as possible" refers to a particle size distribution that is as uniform as possible, based on the cumulative 10% particle size (D 10 ) and cumulative 90% particle size (D 90 ) difference (D 90 -D 10 ) is 65 nm or less.

[0013] As a result of the inventors' investigations, they found that the object can be achieved by carrying out a kneading process by a method of kneading a mixture containing two or more quinacridone pigments having different structures, a water-soluble inorganic salt, and an organic solvent in a kneading device under load, i.e., by carrying out a kneading process by the salt milling method. Next, the water-soluble inorganic salt and the organic solvent are removed from the obtained kneaded product to separate the quinacridone solid solution pigment, and then an ink containing the quinacridone solid solution pigment is prepared, and an image is recorded on plain paper using this inkjet recording device. As a result, it was found that sufficient color development may not be obtained because the pigment penetrates into the inside of the plain paper. In the kneading process by the salt milling method, in order to produce a pigment with a particle size distribution as uniform as possible, the average primary particle diameter of the pigment (cumulative 50% particle diameter in the particle size distribution on a volume basis (D 50 )) is crushed to about 20 nm. As a result, the present inventors speculate that the cause is that the pigment is induced to penetrate into the inside of the plain paper.

[0014] Therefore, the present inventors have attempted to obtain a quinacridone solid solution pigment having an average primary particle diameter (D 50) to grow into crystals. Heating and treating the pigment is a common method for growing the crystals of the pigment. The present inventors therefore attempted to grow the crystals of the pigment by heating the kneaded product (hereinafter sometimes referred to as the "first kneaded product") obtained in the kneading step (hereinafter sometimes referred to as the "first kneading step") using the above-mentioned salt milling method to about 90°C. However, although it was confirmed that the pigments would aggregate when the first kneaded product was simply heat-treated, the average primary particle diameter (D 50 ) was not observed to increase.

[0015] Next, the inventors of the present invention added various organic solvents to the same kneading device used to produce the first kneaded product, and then slowly stirred the solvent to promote the crystal growth of the pigment. As a result, they found that the following two conditions could be used to produce a pigment with a particle size distribution as uniform as possible and an average primary particle diameter (D 50 It has been found that it is possible to produce a quinacridone solid solution pigment having a particle size of 40 nm or more and 65 nm or less. One of the two conditions is to add an organic solvent (hereinafter sometimes referred to as a "second organic solvent") different from the organic solvent (hereinafter sometimes referred to as a "first organic solvent") used in the first kneading step to the first kneaded material and knead it. The other condition is to knead the first kneaded material with a weaker force when the second organic solvent is added and kneaded than in the first kneading step (preferably, "kneading with substantially no load applied" rather than "kneading with a load applied").

[0016] After the first kneading step, a kneading step (hereinafter, sometimes referred to as the "second kneading step") is carried out to obtain a kneaded product (hereinafter, sometimes referred to as the "second kneaded product") by kneading under the above two conditions. This second kneading step makes it possible to obtain a kneaded product having an average primary particle diameter (D 50As a result, when an image is recorded on plain paper using an ink containing the obtained quinacridone solid solution pigment, sufficient color development (chroma C * The present inventors speculate as follows why the desired quinacridone solid solution pigment as described above can be obtained by the production method including the first and second kneading steps.

[0017] First, an important condition is to use a second organic solvent in the second kneading step that is different from the first organic solvent used in obtaining the first kneaded product. By using an organic solvent different from the first organic solvent as the second organic solvent, the compatibility of the organic solvent with the quinacridone pigment changes. As a result, the second kneading step creates an environment in which the quinacridone solid solution pigment is more likely to grow crystals, and the quinacridone solid solution pigment has a larger average primary particle diameter (D 50 ) can be produced. On the other hand, if the same organic solvent as the first organic solvent is used in the second kneading step, the compatibility of the organic solvent with the quinacridone pigment does not change, so it is presumed that the quinacridone solid solution pigment is unlikely to undergo crystal growth. From the above, it is considered that the use of a second organic solvent different from the first organic solvent used in the first kneading step after the first kneading step is a necessary condition for obtaining the desired quinacridone solid solution pigment.

[0018] Next, the reason why it is important to knead with a weaker force than that in the first kneading step in the second kneading step to obtain the second kneaded product (preferably, kneading with substantially no load applied, rather than kneading with a load applied) will be explained. As described above, the second kneading step is intended to grow crystals of the fine quinacridone solid solution pigment obtained in the first kneading step, thereby decreasing the average primary particle diameter (D 50) is increased. Therefore, rather than actively applying a load to apply shear force to the kneaded material as in the salt milling method in the first kneading step, it is considered better to stir the first kneaded material to an extent that the second organic solvent is uniformly mixed with the first kneaded material in the second kneading step. Therefore, in the second kneading step, after the first kneading step, a second organic solvent different from the first organic solvent is added to the first kneaded material, and the first kneaded material is kneaded with a weaker force than in the first kneading step to obtain a second kneaded material. When the second organic solvent is added to the first kneaded material and kneaded with the same force as in the first kneading step, a phenomenon of miniaturization occurs simultaneously in addition to the crystal growth of the quinacridone solid solution pigment. Therefore, the particle size distribution of the obtained quinacridone solid solution pigment becomes wider, and as a result, the average primary particle diameter (D 50 ) does not reach the target of 40 nm, and sufficient color development may not be achieved.

[0019] The fact that the kneading in the second kneading step is performed with a weaker force than that in the first kneading step can also be expressed in terms of "shear rate" or "shear stress". Specifically, in the second kneading step, kneading can be performed at a shear rate lower than that in the first kneading step, or at a shear stress lower than that in the first kneading step. Furthermore, "kneading with substantially no load applied" in the preferred second kneading step means that the shear rate and shear stress in the second kneading step are substantially zero. Specifically, in the second kneading step, the average primary particle diameter (D 50 ) is the average primary particle diameter (D 50 ) and stir with a force equal to or greater than that of the mixture.

[0020] On the other hand, in the first kneading process in the salt milling method, "kneading is performed under load." Therefore, the average primary particle diameter (D 50 ) is the average primary particle diameter (D 50Specifically, in the first kneading step, the average primary particle diameter (D 50 ) is the average primary particle diameter (D 50 It is preferable to knead the mixture under a stress of about 50% or less of the kneading force. The "shear stress" can be adjusted not only by the power of the kneading device, but also by the size of the water-soluble inorganic salt, the type of organic solvent, and the mixing ratio of the quinacridone pigment, the water-soluble inorganic salt, and the organic solvent.

[0021] The "average primary particle size" in the present disclosure is a value measured and calculated according to the following procedure. First, the pigment is sufficiently diluted with water to prepare a dispersion. At this time, the pigment is diluted and dispersed to a concentration such that the primary particles of the pigment do not overlap with each other in an image taken with a scanning electron microscope (SEM). Next, the above dispersion is spread on a mesh with a collodion film, dried, and photographed with an SEM. The photographed SEM image (magnification 30,000 times after stretching) is input into a scanner and digitized, and then computer image analysis is performed. Then, the arithmetic mean diameter (number average value) obtained from the distribution of the diameter of a circle having an area equal to the projected area of ​​each extracted primary particle (equivalent area circle diameter) is converted into a volume and the value obtained is regarded as the particle diameter of the pigment, and the average particle diameter in the volume-based particle size distribution is regarded as the "average primary particle diameter". Note that the above-mentioned average primary particle diameter (D 50 ) represents the cumulative 50% particle size in the volume-based particle size distribution.

[0022] <Method of manufacturing quinacridone solid solution pigment> The method for producing a quinacridone solid solution pigment according to one embodiment of the present invention includes a first kneading step in which a mixture containing two or more quinacridone pigments having different structures, a water-soluble inorganic salt, and a first organic solvent is kneaded by a salt milling method to obtain a first kneaded product. The method for producing a quinacridone solid solution pigment also includes a second kneading step in which, after the first kneading step, a second organic solvent different from the first organic solvent is added to the first kneaded product and kneaded with a force weaker than that in the first kneading step to obtain a second kneaded product. Each step and each material used will be described in detail below.

[0023] [First kneading step] The method for producing a quinacridone solid solution pigment includes a first kneading step. The first kneading step is a step of kneading a mixture containing two or more quinacridone pigments having different structures, a water-soluble inorganic salt, and a first organic solvent by a salt milling method to obtain a first kneaded product. The first kneading step obtains a first kneaded product containing a quinacridone solid solution pigment composed of two or more quinacridone pigments, a water-soluble inorganic salt, and a first organic solvent.

[0024] The salt milling method in the first kneading step is also called the solvent salt milling method because an organic solvent is used in addition to the pigment and the water-soluble inorganic salt. The solvent salt milling method is a method in which a mixture containing two or more quinacridone pigments with different structures, a water-soluble inorganic salt, and a first organic solvent is kneaded using a kneading device while compressing the mixture by applying a load to the mixture.

[0025] As the kneading device, for example, a batch type, a continuous type, a normal pressure type, a pressurized type, and a reduced pressure type can be used, and a device that applies a load to the contents to compress and knead can be preferably used. In addition, a kneading device equipped with a material input section such as a kneading kettle and a hopper, and an agitation section such as an agitation blade, an agitation blade, a blade, a screw, and a roll for agitating the materials can be preferably used. Specific examples of the kneading device include kneading devices such as a kneader, a roll mill, a ball mill, an attritor, a sand mill, a planetary mixer, and a continuous uniaxial kneader. An example of the planetary mixer is Trimix (trade name) manufactured by Inoue Seisakusho. An example of the continuous uniaxial kneader is Miracle KCK (trade name) manufactured by Asada Iron Works. Among the kneading devices listed above, it is preferable to use a planetary mixer.

[0026] The mixing ratio of the pigment, the water-soluble inorganic salt, and the first organic solvent in the first kneading step is preferably the following ratio based on the total amount of the quinacridone pigment used. The amount of the water-soluble inorganic salt used in the first kneading step is preferably 3.0 to 20.0 times, more preferably 5.0 to 10.0 times, in mass ratio to the total amount of the quinacridone pigment used. The amount of the first organic solvent used in the first kneading step is preferably 0.5 to 5.0 times, more preferably 0.8 to 3.0 times, in mass ratio to the total amount of the quinacridone pigment used.

[0027] The temperature of the kneaded material during the first kneading step is also a factor that affects the particle size of the resulting quinacridone solid solution pigment. In order to produce a quinacridone solid solution pigment while minimizing the pigment particle size while keeping it as uniform as possible, the temperature during kneading in the first kneading step when obtaining the first kneaded material is preferably 60°C or less, and more preferably 50°C or less. In addition, the above temperature is preferably 0°C or more. In the present disclosure, even if the temperature during kneading in the first kneading step temporarily exceeds 50°C, if the time during which the temperature exceeds 50°C is within 10% of the total time of the first kneading step, the first kneading step is deemed to be performed at a temperature of 50°C or less during kneading. The kneading time in the first kneading step is preferably 1 hour or more and 10 hours or less, and more preferably 2 hours or more and 8 hours or less.

[0028] (Pigments) In the method for producing a quinacridone solid solution pigment, two or more quinacridone pigments with different structures are used as raw pigments. As the quinacridone pigment, unsubstituted quinacridone (CI Pigment Violet 19), 2,9-dimethylquinacridone (CI Pigment Red 122), 2,9-dichloroquinacridone (CI Pigment Red 202), and 3,10-dichloroquinacridone (CI Pigment Red 209) are preferable. In addition, when mixing each pigment, it is preferable to use at least unsubstituted quinacridone, and more preferably, the ratio of the amount (mass) of unsubstituted quinacridone to the total amount (total mass) of two or more quinacridone pigments is maximized.

[0029] (Water-soluble inorganic salts) The water-soluble inorganic salt used in the first kneading step utilizes its high hardness to crush the pigment in the first kneading step, contributing to the refinement of the primary particles of the pigment. The water-soluble inorganic salt is not particularly limited as long as it is an inorganic salt that dissolves in water. Specific examples of the water-soluble inorganic salt include sodium chloride, potassium chloride, sodium sulfate, zinc chloride, calcium chloride, magnesium chloride, and mixtures of two or more of these. Among these, it is preferable to use sodium chloride from the viewpoint of cost.

[0030] The particle size of water-soluble inorganic salts is the cumulative 50% particle size (median particle size; D 50 ) is 1 μm or more and 50 μm or less, and the cumulative 95% particle size (D 95 ) is preferably 80 μm or less. When a particularly fine pigment is desired, it is preferable that the water-soluble inorganic salt used as the grinding aid is also fine. Specifically, the cumulative 50% particle diameter (D 50 ) is 1 μm or more and 10 μm or less, and the cumulative 95% particle size (D 95 ) is 20 μm or less.

[0031] Water-soluble inorganic salt D 50 and D. 95 The value can be measured using an optical microscope. Specifically, the particle diameters of 500 water-soluble inorganic salts are measured using an optical microscope, and D is calculated from the volume-based particle size distribution. 50 and D. 95 The water-soluble inorganic salts used in the examples described below were also measured by the above-mentioned measurement method. 50 and D. 95 asked for.

[0032] (Organic solvent) The first organic solvent used in the first kneading step is intended to moisten the mixture of quinacridone pigment and water-soluble inorganic salt and make it into a dough (a mass formed by kneading) of appropriate hardness. This makes it easier to apply a strong load to the kneaded mixture, increasing the grinding effect and promoting the fineness of the pigment.

[0033] The first organic solvent is not particularly limited, and is preferably a water-soluble organic solvent such as an alcohol, a glycol, an ether, or an aprotic polar solvent. Specific examples of the water-soluble organic solvent include 2-(methoxymethoxy)ethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy)ethanol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, liquid polyethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, low molecular weight polypropylene glycol, aniline, pyridine, tetrahydrofuran, dioxane, methanol, ethanol, isopropanol, n-propanol, isobutanol, n-butanol, ethylene glycol, propylene glycol, propylene glycol monomethyl ether acetate, ethyl acetate, isopropyl acetate, acetone, methyl ethyl ketone, dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone. The above water-soluble organic solvents may be used alone or in combination of two or more kinds, if necessary.

[0034] As the first organic solvent, it is preferable to use an organic solvent having a lower solubility in the quinacridone pigment than the second organic solvent used in the second kneading step described below. By selecting an organic solvent having a low solubility in the quinacridone pigment as the first organic solvent, the quinacridone pigment can be pulverized while changing its crystal structure, and a quinacridone solid solution pigment with high purity can be produced.

[0035] (Other materials) When producing the first kneaded product, in addition to the mixture containing the quinacridone pigment, the water-soluble inorganic salt, and the first organic solvent, a dye derivative may be added for the purpose of adjusting the crystal growth or crystal rearrangement of the pigment. The dye derivative to be added is preferably a dye derivative having the same structure as the pigment as a base, but may be a dye derivative having a different structure. Examples of the substituent of the dye derivative include a hydroxyl group, a carboxyl group, a carbamoyl group, a sulfonic acid group, a sulfonamide group, and a phthalimidomethyl group. In addition, the organic dye also includes pale yellow aromatic polycyclic compounds such as naphthalenes and anthraquinones that are not generally called dyes. In particular, dye derivatives having a basic group are preferably used because they have a large pigment dispersion effect. These can be used alone or in combination of two or more types.

[0036] [Second kneading step] The method for producing a quinacridone solid solution pigment includes a second kneading step. The second kneading step is a step in which, after the first kneading step, a second organic solvent different from the first organic solvent is added to the first kneaded product, and the mixture is kneaded with a force weaker than that in the first kneading step to obtain a second kneaded product. The second kneading step obtains a second kneaded product containing a quinacridone solid solution pigment composed of two or more quinacridone pigments, a water-soluble inorganic salt, a first organic solvent, and a second organic solvent.

[0037] In the second kneading step, the method of adding the second organic solvent to the first kneaded product is not particularly limited, but from the viewpoint of efficiency, it is preferable to add the second organic solvent directly into the kneading device in which the first kneaded product is obtained. The amount of the second organic solvent used is preferably 1.0 times or more, more preferably 2.0 times or more, and even more preferably 5.0 times or more, in terms of mass ratio to the total amount of the two or more quinacridone pigments used in the first kneading step. By using the second organic solvent in the above amount, it is possible to efficiently obtain a desired quinacridone solid solution pigment. Furthermore, the amount of the second organic solvent used is preferably 1.0 times or more, more preferably 2.0 times or more, and even more preferably 5.0 times or more, in terms of mass ratio to the total amount of the two or more quinacridone pigments used or the amount of the first organic solvent used in the first kneading step. The amount of the second organic solvent used is preferably 10.0 times or less, in terms of mass ratio to the total amount of the two or more quinacridone pigments used or the amount of the first organic solvent used.

[0038] As the second organic solvent, specific examples given in the description of the first organic solvent above can be mentioned. However, the second organic solvent is a different type of organic solvent from the first organic solvent used in the first kneading step. Furthermore, it is preferable to use an organic solvent that has a higher solubility in the quinacridone pigment than the first organic solvent as the second organic solvent. Since the solubility of the second organic solvent in the quinacridone pigment is higher than that of the first organic solvent in the quinacridone pigment, the quinacridone solid solution pigment obtained in the first kneading step can be pulverized while changing the crystal structure. This makes it possible to produce a quinacridone solid solution pigment with high purity.

[0039] The solubility of an organic solvent for a quinacridone pigment can be determined as follows. That is, 0.01 g of a quinacridone pigment is added to 100 g of various organic solvents, and the mixture is stirred for at least 30 minutes. After that, the amount of quinacridone pigment remaining is visually checked, and the organic solvent with no remaining quinacridone pigment can be determined to be the organic solvent with the highest solubility for the quinacridone pigment. On the other hand, for organic solvents in which residual quinacridone pigment is confirmed, the quinacridone pigment and the organic solvent are separated after stirring is completed, and the extinction coefficient of the resulting solution is confirmed. The higher the extinction coefficient of the organic solvent, the higher the organic solvent's solubility for the quinacridone pigment is ranked.

[0040] As a combination of organic solvents in which the solubility of the second organic solvent in the quinacridone pigment is higher than the solubility of the first organic solvent in the quinacridone pigment according to the above-mentioned solubility determination method, the following combination is preferable: That is, it is preferable that the first organic solvent is either one or both of ethylene glycol and diethylene glycol, and the second organic solvent is either one or both of dimethyl sulfoxide and N-methyl-2-pyrrolidone.

[0041] As in the first kneading step, the temperature of the kneaded material during kneading in the second kneading step is also a factor that affects the particle size of the resulting quinacridone solid solution pigment. The main purpose of the second kneading step is to cause crystal growth of the quinacridone solid solution pigment in the first kneaded material obtained in the first kneading step. Therefore, the temperature during kneading in the second kneading step is preferably higher than the temperature during kneading in the first kneading step. Specifically, the temperature during kneading in the second kneading step is preferably 70°C or higher, more preferably 80°C or higher, and preferably 150°C or lower. The kneading time in the second kneading step is preferably 1 hour or more and 8 hours or less, more preferably 2 hours or more and 5 hours or less.

[0042] <Method of manufacturing pigment dispersion> It is possible to produce a pigment dispersion using the quinacridone solid solution pigment obtained by the above-described method for producing a quinacridone solid solution pigment. The method for producing the pigment dispersion includes a dispersion step of dispersing the obtained quinacridone solid solution pigment in a dispersion medium after removing a water-soluble inorganic salt, a first organic solvent, and a second organic solvent from the second kneaded product obtained by the above-described method for producing a quinacridone solid solution pigment.

[0043] To produce a pigment dispersion, first, a water-soluble inorganic salt and organic solvents (the first organic solvent and the second organic solvent) are removed from the second kneaded product. For example, after putting the second kneaded product into water at a predetermined ratio with respect to the second kneaded product to obtain a pigment suspension (slurry), the water-soluble inorganic salt and the organic solvents can be removed from the second kneaded product by filtering and washing this pigment suspension. The method of filtration is not particularly limited, but it is preferable to adopt a method of separating by passing the above-described pigment suspension through an ultrafiltration membrane or a dialysis membrane, or a method of separating with a high-pressure filter press. Through such a filtration step, a wet cake of the quinacridone solid solution pigment from which the water-soluble inorganic salt and the organic solvents have been separated is obtained. The obtained wet cake is preferably adjusted to a water content of 30% by mass or more and 50% by mass or less in consideration of the growth of bacteria, and further dried to a water content of 5% by mass or less. Examples of the drying method include batch-type or continuous drying for dehydrating and / or desolventizing the wet cake by heating at 80°C or higher and 120°C or lower with a heat source installed in a dryer. Examples of the dryer include a box-type dryer, a band dryer, and a spray dryer.

[0044] 〔Dispersion step〕 Next, a dispersion step of dispersing the obtained quinacridone solid solution pigment in a dispersion medium can be performed. As the dispersion medium, it is preferable to use an aqueous medium such as water that can be used in the ink described later, more preferably water, and it is preferable to obtain an aqueous dispersion of the quinacridone solid solution pigment.

[0045] In order to disperse the quinacridone solid solution pigment in the dispersion medium, it is preferable to use a resin (resin dispersant) or a surfactant as a dispersant. Among them, it is more preferable to use a resin (resin having an anionic group) that can stably disperse the quinacridone solid solution pigment in the dispersion medium by the action of the anionic group.

[0046] The resin is preferably a resin having a structural unit derived from a hydrophobic monomer and a structural unit derived from a hydrophilic monomer having an anionic group, which is obtained by copolymerizing a polymerizable hydrophobic monomer and a polymerizable hydrophilic monomer. Examples of the hydrophobic monomer include styrene, α-methylstyrene, n-butyl acrylate, n-hexyl acrylate, and benzyl methacrylate. Examples of the hydrophilic monomer include hydrophilic monomers having a carboxy group such as acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, and fumaric acid; hydrophilic monomers having a sulfonic acid group such as styrene sulfonic acid, sulfonic acid-2-propylacrylamide, acrylic acid-2-ethyl sulfonate, methacrylic acid-2-ethyl sulfonate, and butylacrylamidosulfonic acid; hydrophilic monomers having a phosphonic acid group such as methacrylic acid-2-ethyl phosphonate, and acrylic acid-2-ethyl phosphonate.

[0047] The weight average molecular weight of the resin used as the dispersant is preferably 1,000 to 30,000, more preferably 3,000 to 15,000. The weight average molecular weight of the resin can be a value calculated based on standard polystyrene measured using gel permeation chromatography (GPC). The acid value (mgKOH / g) of the resin can be a value measured by a potentiometric titration device using a potassium hydroxide-methanol titrant. The amount of the resin used is preferably 10% by mass to 50% by mass with respect to the amount of the pigment used.

[0048] When dispersing the quinacridone solid solution pigment in a dispersion medium, a dispersing device can be used. Examples of the dispersing device include an ultrasonic homogenizer, a high-pressure homogenizer, a paint shaker, a ball mill, a sand mill, a sand grinder, a Dyno Mill, a Dispermat, an SC Mill, a Spike Mill, a Nanomizer, an Agitator Mill, and a Planetary Mill.

[0049] The content (mass %) of the quinacridone solid solution pigment in the pigment dispersion is preferably from 1.0 mass % to 50.0 mass %, and more preferably from 5.0 mass % to 30.0 mass %, based on the total mass of the pigment dispersion.

[0050] The quinacridone solid solution pigment and the pigment dispersion containing the same can be suitably used in any application requiring coloring function. Examples of such applications include paints, printing inks, colored molded products, toners for developing electrostatic images, color filters for liquid crystal display devices, and inkjet inks. Among these, water-based inkjet inks are preferred.

[0051] <Inkjet recording method> The pigment dispersion obtained by the above-mentioned method for producing a pigment dispersion is preferably used in an inkjet recording method in which an ink is ejected from an inkjet recording head to record an image on a recording medium. Specifically, in this inkjet recording method, an ink containing the pigment dispersion obtained by the above-mentioned method for producing a pigment dispersion can be used. Examples of the method for ejecting the ink include a method for ejecting the ink by applying mechanical energy to the ink and a method for ejecting the ink by applying thermal energy to the ink.

[0052] <Ink> Next, an ink containing the pigment dispersion obtained by the above-mentioned method for producing the pigment dispersion will be described. When preparing this ink, it is preferable to prepare the ink by blending the above-mentioned pigment dispersion, an aqueous medium, and other additives used as necessary.

[0053] (Colorant) The ink contains the pigment dispersion obtained by the above-mentioned method for producing the pigment dispersion, and therefore contains the quinacridone solid solution pigment obtained by the above-mentioned method for producing the quinacridone solid solution pigment as a coloring material. The content (mass %) of the quinacridone solid solution pigment in the ink is preferably 0.1 mass % or more and 15.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

[0054] (aqueous medium) The ink is preferably an aqueous ink containing at least water as an aqueous medium. For the ink, water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent can be used. As the water, deionized water (ion-exchanged water) is preferably used. The content (mass %) of water in the ink is preferably 40.0 mass % or more and 95.0 mass % or less, and more preferably 50.0 mass % or more and 95.0 mass % or less, based on the total mass of the ink.

[0055] Examples of water-soluble organic solvents that can be contained in the ink include alkyl alcohols having 1 to 4 carbon atoms, amides, ketones, ketoalcohols, ethers, polyalkylene glycols, glycols, alkylene glycols having an alkylene group with 2 to 6 carbon atoms, polyhydric alcohols, alkyl ether acetates, alkyl ethers of polyhydric alcohols, nitrogen-containing compounds, and sulfur-containing compounds. One or more of these water-soluble organic solvents can be used as necessary. The content (mass%) of the water-soluble organic solvent in the liquid composition is preferably 3.0% by mass or more and 50.0% by mass or less, and more preferably 3.0% by mass or more and 40.0% by mass or less, based on the total mass of the liquid composition.

[0056] (Other Ingredients) In order to maintain moisture retention, the ink may contain, in addition to the above-mentioned components, compounds that are solid at room temperature and have moisture retention, such as urea, urea derivatives, trimethylolpropane, and trimethylolethane. The content (mass%) of these compounds in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 3.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. In addition to the above-mentioned components, the ink may contain various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and reduction inhibitors, as necessary.

[0057] <Ink cartridges> When the ink described above is used in an inkjet recording method, an ink cartridge can be used. The ink cartridge includes the ink described above and an ink storage section that stores the ink. Furthermore, the ink cartridge may be configured to include an ink storage section and a recording head. EXAMPLES

[0058] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples without departing from the gist of the invention. "Parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0059] <Production of quinacridone solid solution pigment> (Production of Kneaded Materials 1 to 6) The components (unit: parts) shown in the upper part of Table 1 were mixed and kneaded under the kneading conditions shown in the lower part of Table 1 to produce kneaded products 1 to 6. A planetary mixer (product name "Trimix", manufactured by Inoue Seisakusho) was used as the kneading device during kneading. The meanings of the abbreviations in Table 1 are as follows. PV19: CI Pigment Violet 19 PR122: CI Pigment Red 122 PR202: CI Pigment Red 202 Sodium chloride: D 50 is 10μm, D 95 Sodium chloride with a diameter of 15 μm

[0060] TIFF2025079354000001.tif72170

[0061] (Production of Mixtures 7 to 17) Next, in the planetary mixer, the obtained kneaded materials 1 to 6 (unit: parts) were mixed with the organic solvent (unit: parts) shown in the upper part of Table 2 (Table 2-1 and Table 2-2), and then stirred under the kneading conditions shown in the lower part of Table 2 to produce kneaded materials 7 to 17. The same device used for stirring was used as the device used to produce the kneaded materials 1 to 6.

[0062] TIFF2025079354000002.tif83170

[0063] TIFF2025079354000003.tif85170

[0064] <Measurement of purity and particle size distribution of quinacridone solid solution pigment> The kneaded products 1 to 17 thus produced were thoroughly washed with water and filtered to remove sodium chloride and organic solvent, and the resulting pigments were dried, after which the purity and particle size distribution of the quinacridone pigment solid solutions were measured by the methods described below. The results are shown in Table 3.

[0065] (Confirmation of quinacridone pigment solid solution) Whether or not the obtained pigment formed a quinacridone solid solution was judged by powder X-ray diffraction measurement of the particles using an X-ray diffractometer (trade name "X'Pert Pro", manufactured by PANalytical) using CuKα radiation. As a method of judgment, first, the X-ray peak of the pigment mixture before the start of the manufacturing process was measured. Then, the X-ray peak of the pigment after the completion of the manufacturing process was measured and compared with the X-ray pattern of the pigment mixture before the start of the manufacturing process. If a peak that did not exist in the X-ray peak of the pigment mixture before the start of the manufacturing process was confirmed, it was judged that a quinacridone solid solution pigment had been produced. In the "Purity" column shown in Table 3, "OK" indicates that it was judged that a quinacridone solid solution pigment had been produced, and "No" indicates that it was not judged that a quinacridone solid solution pigment had been produced.

[0066] (particle size distribution) Sodium chloride and organic solvents were removed from the final kneaded product, and the resulting pigment was thoroughly diluted with water to prepare a dispersion, after which images were taken with a scanning electron microscope (SEM). The SEM images taken (magnification 30,000 times after enlargement) were input into a scanner and digitized, after which computer image analysis was performed. The arithmetic mean diameter was calculated from the distribution of the diameter of a circle with an area equal to the projected area of ​​each extracted primary particle (equivalent area circle diameter), and the pigment particle size was calculated by volume conversion. From the obtained pigment particle diameters, the cumulative 10% particle diameter (D 10 ), cumulative 50% particle size in the volume-based particle size distribution (D 50 ), cumulative 90% particle size in the volume-based particle size distribution (D 90 ) was calculated.

[0067] TIFF2025079354000004.tif115170

[0068] <Preparation of pigment dispersion> The obtained kneaded products 7 to 17 were thoroughly washed, filtered, and dried, and then a resin aqueous solution was added to the obtained pigment, and a dispersion treatment was performed at a processing pressure of 200 MPa using a high-pressure homogenizer (trade name "Starburst", manufactured by Sugino Machine). A styrene-acrylic acid copolymer (trade name "Joncryl 690", manufactured by BASF) having a weight average molecular weight of 16,500 and an acid value of 240 mgKOH / g was used as the resin for the resin aqueous solution. To this resin (styrene-acrylic acid copolymer), 0.9 equivalents of potassium hydroxide were added relative to the acid value of the resin, and a resin aqueous solution with a resin content of 20.0% was used. After the dispersion treatment, an appropriate amount of ion-exchanged water was added to obtain pigment dispersions 1 to 11 with a pigment content of 15.0%. Table 4 shows the kneaded products used for each of the pigment dispersions 1 to 11.

[0069] TIFF2025079354000005.tif78170

[0070] <Ink Preparation> As shown in Table 5, using pigment dispersions 1 to 11, inks 1 to 11 with numbers corresponding to the numbers of pigment dispersions 1 to 11 were prepared, respectively. Specifically, the following components were mixed, thoroughly stirred to disperse, and then pressure filtered using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm to prepare each ink. Acetylenol E100 is a surfactant manufactured by Kawaken Fine Chemicals. Pigment dispersion: 33.0 parts Glycerin: 10.0 parts Triethylene glycol: 7.0 parts Acetylenol E100: 0.1 parts Wednesday: 49.9 parts

[0071] <Evaluation> Inks 1 to 11 were filled in ink cartridges, and the ink cartridges were set in an inkjet recording device (product name "PIXUS PRO-10", manufactured by Canon) equipped with a recording head that ejects ink by thermal energy. The resolution of this inkjet recording device was 2400 dpi x 1200 dpi. An image recorded under the condition that one ink droplet of 30.4 ng is applied to a unit area of ​​1 / 600 inch x 1 / 600 inch is defined as having a recording duty of 100%. A solid image was recorded on a recording medium (product name "HP Bright White Inkjet Paper", manufactured by HP) with a recording duty of 140% using the inkjet recording device.

[0072] (Color development) Each solid image was measured using a fluorescence spectrodensitometer (product name "FD-7", manufactured by Konica Minolta) under conditions of a light source of D50 and a viewing angle of 2°, and the saturation (C * ) is the maximum value of max C * The results are shown in Table 5. * The larger the value, the more excellent the color development.

[0073] TIFF2025079354000006.tif78170

[0074] The disclosure of this embodiment includes the following methods. (Method 1) A method for producing a quinacridone solid solution pigment, comprising the steps of: a first kneading step of kneading a mixture containing two or more quinacridone pigments having different structures, a water-soluble inorganic salt, and a first organic solvent by a salt milling method to obtain a first kneaded product; a second kneading step in which, after the first kneading step, a second organic solvent different from the first organic solvent is added to the first kneaded product, and the first kneaded product is kneaded with a force weaker than that in the first kneading step to obtain a second kneaded product; A method for producing a quinacridone solid solution pigment, comprising: (Method 2) A method for producing a quinacridone solid solution pigment according to Method 1, wherein the solubility of the second organic solvent in the quinacridone pigment is higher than the solubility of the first organic solvent in the quinacridone pigment. (Method 3) The first organic solvent is either one or both of ethylene glycol and diethylene glycol, and The method for producing a quinacridone solid solution pigment according to method 1 or 2, wherein the second organic solvent is either or both of dimethyl sulfoxide and N-methyl-2-pyrrolidone. (Method 4) The method for producing a quinacridone solid solution pigment according to any one of Methods 1 to 3, wherein the temperature during kneading in the second kneading step is higher than the temperature during kneading in the first kneading step. (Method 5) The temperature during kneading in the first kneading step is 50° C. or less, and The method for producing a quinacridone solid solution pigment according to any one of Methods 1 to 4, wherein the temperature during kneading in the second kneading step is 80° C. or higher. (Method 6) A method for producing a pigment dispersion, comprising the steps of removing the water-soluble inorganic salt, the first organic solvent, and the second organic solvent from the second kneaded product obtained by the method for producing a quinacridone solid solution pigment described in any one of Methods 1 to 5, and then dispersing the obtained quinacridone solid solution pigment in a dispersion medium. (Method 7) An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, comprising the steps of: The inkjet recording method according to claim 6, wherein the ink contains a pigment dispersion obtained by the method for producing a pigment dispersion according to the method 6.

Claims

1. A method for producing a quinacridone solid solution pigment, comprising the steps of: a first kneading step of kneading a mixture containing two or more quinacridone pigments having different structures, a water-soluble inorganic salt, and a first organic solvent by a salt milling method to obtain a first kneaded product; a second kneading step in which, after the first kneading step, a second organic solvent different from the first organic solvent is added to the first kneaded product, and the first kneaded product is kneaded with a force weaker than that in the first kneading step to obtain a second kneaded product; A method for producing a quinacridone solid solution pigment, comprising:

2. 2. The method for producing a quinacridone solid solution pigment according to claim 1, wherein the solubility of the second organic solvent in the quinacridone pigment is higher than the solubility of the first organic solvent in the quinacridone pigment.

3. The first organic solvent is either one or both of ethylene glycol and diethylene glycol, and 2. The method for producing a quinacridone solid solution pigment according to claim 1, wherein the second organic solvent is either or both of dimethyl sulfoxide and N-methyl-2-pyrrolidone.

4. The method for producing a quinacridone solid solution pigment according to claim 1 , wherein a temperature during kneading in the second kneading step is higher than a temperature during kneading in the first kneading step.

5. The temperature during kneading in the first kneading step is 50° C. or less, and 2. The method for producing a quinacridone solid solution pigment according to claim 1, wherein the temperature during kneading in the second kneading step is 80° C. or higher.

6. A method for producing a pigment dispersion liquid, comprising: removing the water-soluble inorganic salt, the first organic solvent, and the second organic solvent from the second kneaded product obtained by the method for producing a quinacridone solid solution pigment described in any one of claims 1 to 5; and then dispersing the obtained quinacridone solid solution pigment in a dispersion medium.

7. An inkjet recording method for recording an image on a recording medium by ejecting ink from an inkjet recording head, comprising:

7. An ink-jet recording method, comprising the step of: forming an ink containing a pigment dispersion liquid obtained by the method for producing a pigment dispersion liquid according to claim 6.

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