JP2024035153A - Pigment particle manufacturing method, ink manufacturing method, inkjet recording method - Google Patents

Abstract

[Problem] To obtain pigment particles having a particle size suitable for achieving both high levels of image color development and light fastness even when used as a coloring material for inkjet ink, and having high organic purity. To provide a method for producing pigment particles, etc. [Solution] C. I. This is a method for producing pigment particles in which Pigment Yellow 74 is treated with a pigment derivative. (1) C.I. as a raw material. I. A first step of kneading Pigment Yellow 74 and a specific pigment derivative in the presence of a water-soluble inorganic salt and an organic solvent, and (2) removing a tert-butoxycarbonyl group from the specific pigment derivative, C. I. A second step for obtaining pigment particles of Pigment Yellow 74 is included in this order. [Selection diagram] None

Description

The present invention relates to a method for producing pigment particles, a method for producing ink, and an inkjet recording method.

2. Description of the Related Art In recent years, inkjet recording methods have been used to record business documents using plain paper as a recording medium and photographic images using glossy paper as a recording medium, and the frequency of its use has increased significantly. Pigments have become widely used as coloring materials when recording images using inkjet recording methods from the viewpoint of fastness, but they have the characteristic of being inferior in color development compared to dyes. When the surface area per unit mass of the pigment is increased by making the pigment finer, color development tends to increase. As a method for making pigments finer, for example, a method called solvent salt milling method is known. In this method, the pigment is mechanically kneaded with a water-soluble inorganic salt such as sodium chloride and a hydrophilic organic solvent using a kneader or the like, and then washed with water to remove the water-soluble inorganic salt and the hydrophilic organic solvent. method (see Patent Documents 1 and 2).

In inkjet recording, as pigments with a yellow hue, monoazo pigments, especially C.I. I. Pigment Yellow 74 is widely used. However, C. I. Pigment Yellow 74 has low stability against heat and light, and this tendency becomes more pronounced when the pigment is made finer. As a result, C. I. An image recorded using an ink containing a finely divided pigment of Pigment Yellow 74 may have low color development and light fastness.

Until now, miniaturized C. I. Methods for suppressing the deterioration of color development and light fastness of Pigment Yellow 74 have been studied. A method for producing finely divided pigments has been proposed in which a compound having a similar structure is added during solvent salt milling (see Patent Document 3). In addition, in order to record images with excellent color saturation and light resistance, C.I. I. It has been proposed to use Pigment Yellow 74 (see Patent Document 4).

Japanese Patent Application Publication No. 2020-094173 International Publication No. 2014/185471 JP2013-139488A International Publication No. 2013/099730

As described in Patent Documents 1 and 2, the present inventors used a solvent salt milling method to produce fine C.I. I. A study was conducted to obtain Pigment Yellow 74. As a result, C. I. It was found that Pigment Yellow 74 is a pigment that easily crystallizes and requires milling at low temperatures for a long time in order to make it fine. The present inventors have also developed a method for producing a finely divided pigment by adding a compound (pigment derivative) with a similar structure as proposed in Patent Document 3, and a method for producing a finely divided pigment by adding a compound (pigment derivative) with a similar structure as proposed in Patent Document 4, and a highly crystalline C.I. I. Pigment Yellow 74 was used to examine various properties. As a result, when a pigment derivative is added as in Patent Document 3, the balance between crystal growth and crushing can be controlled, so a finely divided pigment can be obtained in a short time. On the other hand, it has been found that the addition of pigment derivatives may lower the organic purity and reduce the light fastness of images recorded with inks containing the above pigments. Furthermore, as in Patent Document 4, it has been found that images recorded with ink containing highly crystalline pigments may also have reduced light resistance.

Therefore, it is an object of the present invention to have a particle size suitable for achieving both a high level of image color development and light fastness even when used as a coloring material for inkjet ink, and a material with high organic purity. It is an object of the present invention to provide a method for producing pigment particles, which makes it possible to obtain pigment particles. Another object of the present invention is to provide a method for producing an ink using the pigment particles obtained by the above production method, and an inkjet recording method using the ink obtained by this production method.

The above object is achieved by the present invention as follows. That is, the method for producing pigment particles according to the present invention uses C.I. I. A method for producing pigment particles in which Pigment Yellow 74 is treated with a pigment derivative, comprising: (1) C.I. I. Pigment Yellow 74 and a pigment derivative represented by the following general formula (1) are kneaded in the presence of a water-soluble inorganic salt and an organic solvent, and (2) a pigment derivative represented by the general formula (1) shown below. A compound represented by the following general formula (2) is produced by removing the tert-butoxycarbonyl group from the pigment derivative of C. I. A second step for obtaining pigment particles of Pigment Yellow 74 is included in this order.

(In general formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or a tert-butoxycarbonyl group. However, R ₁ and R ₂ are not hydrogen atoms at the same time.)

According to the present invention, even when used as a coloring material for inkjet ink, pigment particles have a particle size suitable for achieving both high levels of image color development and light fastness, and have high organic purity. It is possible to provide a method for producing pigment particles that can obtain pigment particles. Further, according to the present invention, it is possible to provide a method for producing an ink using pigment particles obtained by the above production method, and an inkjet recording method using the ink obtained by this production method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically showing an example of an inkjet recording apparatus used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge.

Hereinafter, the present invention will be further explained in detail by citing preferred embodiments. In the present invention, when a compound is a salt, the salt is dissociated into ions and exists in the ink, but for convenience, it is expressed as "containing a salt." Inkjet ink is sometimes simply referred to as "ink." Also, C. I. Pigment Yellow 74 is sometimes simply referred to as "pigment". Physical property values are values at room temperature (25° C.) unless otherwise specified. The compounds represented by general formula (1) and general formula (2) each have tautomers, but in the present invention, for convenience, they are collectively represented by general formula (1) or general formula (2). .

The present inventors first discovered that C. I. Pigment Yellow 74, a pigment derivative, a water-soluble inorganic salt, and an organic solvent were mixed and then kneaded to obtain pigment particles. Then, the reason why the light fastness of images recorded using the ink containing the pigment particles thus obtained is reduced was investigated.

C. I. When a pigment derivative is added to Pigment Yellow 74 and kneaded, C. I. Pigment derivatives are incorporated into the crystals of Pigment Yellow 74. As a result, pigment particles having a distorted crystal lattice are likely to be formed. Since the crystallinity of such pigment particles is disturbed, crystal growth of the pigment particles is appropriately suppressed. As a result, high color development of the image can be obtained. On the other hand, it is presumed that the pigment particles contain a pigment derivative that increases the surface activity of the pigment particles, which lowers the resistance to light and reduces the light resistance of the image.

Therefore, C. I. In order to improve the light resistance of images recorded with ink containing Pigment Yellow 74, by removing pigment derivatives added during kneading, C. I. An attempt was made to improve the organic purity of pigment particles of Pigment Yellow 74. At this time, the present inventors focused on a cleaning process that reduces unnecessary components (metal atoms, ions, water-soluble inorganic salts, organic solvents) mixed in during the kneading process, which is commonly performed in the solvent salt milling method. did. Acidic liquids are often used in this cleaning step. In other words, we thought that if we could use a pigment derivative whose amount could be reduced in the washing process, we could efficiently improve the organic purity of pigment particles.

Therefore, the present inventors investigated pigment derivatives having the above characteristics. As a result, along with certain compounds (derivatives of pigment derivatives), C. I. We have found a configuration in which after kneading Pigment Yellow 74, a washing step is performed to generate a desired pigment derivative. The pigment particles obtained by such a configuration have a C.I. I. It was found that the proportion of Pigment Yellow 74 was high (high organic purity).

That is, the method for producing pigment particles of the present invention uses C.I. I. This is a method for producing pigment particles in which Pigment Yellow 74 is treated with a pigment derivative, and has the following characteristics. First, C.I. I. A first step is performed in which Pigment Yellow 74 and the pigment derivative represented by general formula (1) are kneaded in the presence of a water-soluble inorganic salt and an organic solvent. Next, a compound represented by the following general formula (2) is produced by removing the tert-butoxycarbonyl group from the pigment derivative represented by the general formula (1), and C. I. A second step is performed to obtain pigment particles of Pigment Yellow 74.

By the above method for producing pigment particles, C. I. The present inventors speculate that the mechanism by which the proportion of Pigment Yellow 74, that is, the organic purity is improved, is as follows. In the present invention, pigment particles are produced by a solvent salt milling method. In the first step, C.I. I. This is a step of kneading Pigment Yellow 74 and a pigment derivative represented by the following general formula (1) in the presence of a water-soluble inorganic salt and an organic solvent.

(In general formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or a tert-butoxycarbonyl group. However, R ₁ and R ₂ are not hydrogen atoms at the same time.)

C. I. The molecule forming Pigment Yellow 74 is a compound represented by the following general formula (2).

The pigment derivative represented by general formula (1) has C.I. I. Pigment Yellow 74 is a compound in which at least one of the nitrogen atoms in the two imino groups is substituted with a tert-butoxycarbonyl group (Boc group). Together with the pigment derivative represented by general formula (1), C.I. I. When Pigment Yellow 74 is kneaded, C. I. The hydrogen bond between the hydrogen atom on the nitrogen atom and the oxygen of the methoxy group or carbonyl group, which would have been formed if only Pigment Yellow 74 was used, becomes difficult to form. As a result, the planarity of the compound collapses, causing C.I. I. While maintaining the adsorption effect of Pigment Yellow 74 on the crystal surface, C. I. It is difficult to be incorporated into the crystals of Pigment Yellow 74.

The second step is a step in which the Boc group of the pigment derivative represented by general formula (1) is eliminated. When the Boc group of the pigment derivative is removed by the action of acid or heat, the pigment derivative becomes a compound represented by the general formula (2), that is, C.I. I. This is the molecule itself that makes up Pigment Yellow 74. The eliminated Boc group is decomposed into carbon dioxide and isobutene, so C. I. It is not incorporated into the crystals of Pigment Yellow 74. In other words, by going through the above steps, C.I. I. Pigment yellow 74 pigment particles can be obtained. Then, C. I. Images recorded with ink containing pigment particles of Pigment Yellow 74 exhibit high color development and light fastness.

<Method for manufacturing pigment particles>
The pigment particles produced according to the present invention can be suitably used as a pigment dispersion and a coloring material for inkjet ink. The method for producing pigment particles of the present invention includes the following steps (1) and (2) in this order. Each step will be explained in detail below.
(1) C.I. as a raw material. I. Pigment Yellow 74 and a pigment derivative represented by the following general formula (1) are kneaded in the presence of a water-soluble inorganic salt and an organic solvent (2) Pigment represented by the above general formula (1) By removing the tert-butoxycarbonyl group from the derivative, a compound represented by the following general formula (2) is produced, and C. I. Second step to obtain pigment particles of Pigment Yellow 74

(In general formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or a tert-butoxycarbonyl group. However, R ₁ and R ₂ are not hydrogen atoms at the same time.)

(1st step)
In the first step, C.I. I. This is a step of kneading Pigment Yellow 74 and a pigment derivative represented by general formula (1) in the presence of a water-soluble inorganic salt and an organic solvent. The method for producing pigment particles of the present invention is carried out by a solvent salt milling method. The solvent salt milling method is a method of mechanically grinding pigment particles using a kneader or the like in the presence of water-soluble inorganic salts (salts) and organic solvents (solvents), and is an efficient way to refine the pigment particles used as raw materials. This is a method that can be done well. Examples of devices used in the first step include a kneader, roll mill, ball mill, attritor, sand mill, and planetary mixer. Among these, it is preferable to use a kneader.

The temperature during the first step is preferably 60°C or lower. If the temperature during the first step exceeds 60°C, C. I. As the crystal growth rate of Pigment Yellow 74 increases, the tert-butoxycarbonyl group is detached from a part of the pigment derivative. As a result, C. I. In some cases, the effect of suppressing the crystal growth of Pigment Yellow 74 cannot be sufficiently obtained, and it is difficult to adjust the average particle size of the pigment particles as desired. The temperature during the first step is preferably 10° C. or higher.

[C. I. Pigment Yellow 74]
In the production method of the present invention, C.I. I. Pigment Yellow 74 is used. C. as a raw material I. Pigment Yellow 74 may be a commercially available one. In particular, from the viewpoint of lightfastness of images when used as pigments in ink, raw materials that have been reduced in impurities such as residues of synthetic raw materials and unintended by-products through operations such as washing and recrystallization are used as raw materials. It is preferable to use

[Pigment derivative]
In the production method of the present invention, a pigment derivative represented by the following general formula (1) is used.

(In general formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or a tert-butoxycarbonyl group. However, R ₁ and R ₂ are not hydrogen atoms at the same time.)

The compound represented by the general formula (1) can be synthesized according to the conditions of the Boc formation reaction, which is widely used as a means for protecting amino groups. This reaction is described, for example, in Japanese Patent Publication No. 2002-533549. Specifically, in an organic solvent in the presence of a base as a catalyst, C.I. I. It can be synthesized by reacting Pigment Yellow 74 with di-tert-butyl dicarbonate. Examples of the organic solvent include benzene, toluene, xylene, anisole, chlorobenzene, N,N-dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran. Furthermore, examples of the base as a catalyst include pyridine and triethylamine.

In the first step, the amount (mass%) of the pigment derivative represented by general formula (1) is determined by the amount of C.I. I. Based on the usage amount (mass%) of Pigment Yellow 74, it is preferably 0.5% by mass or more and 5.0% by mass or less. If the amount used is less than 0.5% by mass, the content of the pigment derivative will be too small and the amount adsorbed onto the surface of the pigment particles will be insufficient. As a result, C. I. In some cases, the effect of suppressing the crystal growth of Pigment Yellow 74 cannot be sufficiently obtained, and it is difficult to adjust the average particle size of the pigment particles as desired. On the other hand, if the amount used is more than 5.0% by mass, the pigment derivative will be excessively adsorbed on the surface of the pigment particles. As a result, the crystal growth of the pigment particles is excessively suppressed, resulting in excessively fine particles, and it may be difficult to adjust the average particle diameter of the pigment particles as desired.

[Water-soluble inorganic salt]
Utilizing its high hardness, inorganic salts are used to crush pigments and make them fine during kneading. As the inorganic salt, it is preferable to use a water-soluble inorganic salt in consideration of handling during removal. The water-soluble inorganic salt is not particularly limited as long as it dissolves in water. Specific examples include alkali metal chlorides such as sodium chloride and potassium chloride, and polyvalent metal chlorides such as zinc chloride and magnesium chloride. You may use these in combination.

The volume-based cumulative 50% particle diameter (D ₅₀ ) of the water-soluble inorganic salt is preferably 1 μm or more and 300 μm or less. Further, the volume-based cumulative 95% particle diameter (D ₉₅ ) of the water-soluble inorganic salt is preferably 400 μm or less. D ₅₀ and D ₉₅ of the water-soluble inorganic salt are the diameters of particles that are 50% and 95%, respectively, of the cumulative particle size curve from the small particle size side, based on the total volume of the measured particles. It is. The D ₅₀ and D ₉₅ of the water-soluble inorganic salt can be measured, for example, using a particle size analyzer using dynamic light scattering.

The amount (mass%) of the water-soluble inorganic salt used is the amount of C. I. It is preferable that the mass ratio is 3.0 times or more and 20.0 times or less relative to the total usage amount (mass%) of Pigment Yellow 74 and the pigment derivative represented by general formula (1). Among these, it is more preferable that the mass ratio is 5.0 times or more and 10.0 times or less.

[Organic solvent]
The organic solvent is used to increase the grinding effect and promote fineness of the pigment by wetting the pigment particles, pigment derivative, and water-soluble inorganic salt during kneading. The organic solvent is not particularly limited as long as it can achieve the above, but water-soluble organic solvents such as alcohols, glycols, and ethers are preferred. Among these, highly viscous water-soluble organic solvents such as ethylene glycol, diethylene glycol, and polyethylene glycol are more preferred from the viewpoint of improving the grinding effect.

The amount (mass%) of the organic solvent used is based on C.I. I. It is preferable that the mass ratio is 0.5 times or more and 5.0 times or less with respect to the total usage amount (mass%) of Pigment Yellow 74 and the pigment derivative represented by general formula (1). Among these, it is more preferably 0.8 times or more and 3.0 times or less. When the mass ratio of the organic solvent is within the above range, C. I. Appropriate shearing force can be applied to Pigment Yellow 74 and the pigment derivative represented by general formula (1). Therefore, the average particle diameter of the pigment particles can be easily adjusted to an appropriate range.

(Second process)
The second step is a step of eliminating the tert-butoxycarbonyl group of the pigment derivative in the kneaded material obtained in the first step. Examples of methods for eliminating the tert-butoxycarbonyl group include acidic conditions, basic conditions, thermal decomposition, and microwave irradiation. Furthermore, as described in JP-A No. 2009-143918, the tert-butoxycarbonyl group can also be removed by heating in a fluorinated alcohol solution. Among these, it is preferable to eliminate the tert-butoxycarbonyl group in the presence of an acid, ie, under acidic conditions, since the elimination efficiency is good even at low temperatures. The temperature during the second step is preferably 60° C. or lower. If the temperature during the second step exceeds 60°C, C. I. The crystal growth of Pigment Yellow 74 progresses, and it may be difficult to adjust the average particle size of the pigment particles as desired. The temperature during the second step is preferably 10° C. or higher.

Moreover, it is preferable to carry out the second step in the presence of an acid, that is, under acidic conditions. This is because the water-soluble inorganic salts, pigment particles, and metal atoms originating from the kneading equipment contained in the kneaded material are ionized, and the water-soluble inorganic salts can be efficiently removed in the post-treatment described below. . When the second step is performed in the presence of an acid, that is, under acidic conditions, for example, the acidic solution is added to the kneaded material transferred to an acid-resistant container, and the mixture is stirred for 1 to 3 hours. Can be done. Examples of the acidic solution include hydrochloric acid, a hydrochloric acid/methanol solution, a hydrochloric acid/ethyl acetate solution, a hydrochloric acid/dioxane solution, a trifluoroacetic acid/dichloromethane solution, and sulfuric acid. Among these, it is preferable to use hydrochloric acid or a hydrochloric acid/methanol solution in order to treat waste liquid and suppress unintended dissolution and crystal growth of pigment particles.

(Post-process)
The post-step is a step of removing water-soluble inorganic salts and organic solvents from the kneaded material obtained in the first step and the second step. Specifically, a method can be mentioned in which water is added to the kneaded material at a predetermined ratio, and then the slurry is filtered and washed. As water, it is preferable to use ion exchange water or pure water. Examples of the filtration method include a method in which a suspension obtained by adding water to a kneaded material is separated by passing through an ultrafiltration membrane or a dialysis membrane, and a method in which separation is performed using a high-pressure filter press. By performing the post-process, a wet cake of pigment particles in which the contents of organic solvent and inorganic salt are reduced or removed can be obtained.

The obtained wet cake is preferably dried so that the water content (moisture content) is approximately 5% or less in order to suppress the proliferation of bacteria. Among these, in order to prepare a pigment dispersion for oil-based ink, it is preferable to remove water so that the water content becomes 0%. Examples of methods for removing water include batch or continuous drying in which dehydration is performed by heating at 80 to 120° C. using a heat source installed in a dryer, drying under reduced pressure, and the like. Specific examples of the dryer include a box dryer, a band dryer, a spray dryer, and the like.

<Pigment particles>
The pigment particles produced by the production method of the present invention have C.I. I. Pigment Yellow 74 pigment particles. The average particle diameter (nm) of the pigment particles is preferably 30 nm or more and 150 nm or less. In this specification, the average particle diameter of a pigment means the number average diameter determined from the distribution of equal area circular diameters of pigment particles. The equal area circular diameter of the pigment particles can be calculated, for example, as the average value of particle sizes of 100 or more points arbitrarily selected and measured from images taken with a scanning electron microscope (SEM). When the average particle diameter of the pigment particles is less than 30 nm, the surface area of the pigment particles is small, so that the influence when the surface of the pigment particles is modified is large, and discoloration is likely to occur. Therefore, when used as a coloring material for ink, the recorded image may not have sufficient light resistance. On the other hand, if the average particle diameter of the pigment particles exceeds 150 nm, the number of pigment molecules inside the pigment particles that are difficult to contribute to color development will increase, so when used as a coloring material in ink, the color development of the recorded image will decrease. You may not be able to get enough sex.

C. in pigment particles. I. The organic purity (%) of the pigment particles, defined by the mass percentage of Pigment Yellow 74, is preferably 97.0% or more and 99.5% or less. The organic purity of the pigment particles is determined by the C.I. I. It can be calculated as a ratio (%) of the area value of the peak of Pigment Yellow 74. If the organic purity of the pigment particles is less than 97.0%, the crystals of the pigment particles are likely to be distorted, resulting in decreased resistance to light and discoloration. Therefore, when used as a coloring material in ink, the recorded image may deteriorate. In some cases, sufficient light resistance may not be obtained. On the other hand, if the organic purity of the pigment particles exceeds 99.5%, fusion and crystal growth at the interface of the pigment particles will easily progress, so when used as a coloring material in ink, the recorded image will be affected. In some cases, sufficient color development may not be obtained.

<Ink>
The pigment particles described above can be suitably used for various coloring purposes. Among these, it can be suitably used for inkjet inks. When used in an inkjet ink, the recorded image exhibits high color development and light fastness as described above. The ink of the present invention is an inkjet ink containing pigment particles produced by the above production method. The components constituting the ink and the physical properties of the ink will be described in detail below.

(color material)
The ink contains, as a coloring material, C.I. I. Contains pigment particles of Pigment Yellow 74. The content (mass%) of the coloring material in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and 1.0% by mass or more and 10.0% by mass, based on the total mass of the ink. It is more preferable that it is the following.

The above pigment derivative can be obtained by removing the tert-butoxycarbonyl group to obtain C.I. I. Since the structure is the molecule itself of Pigment Yellow 74, the pigment particles must be stably dispersed in the ink by the action of a resin or the like. As a dispersion method for coloring materials (pigments), resin-dispersed pigments using a resin (resin dispersant) as a dispersant, self-dispersing pigments in which hydrophilic groups are bonded to the pigment particle surface, etc. can be used. . Further, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the surface of pigment particles, a microcapsule pigment in which the surface of pigment particles is coated with a resin, etc. can be used. It is also possible to use a combination of pigments with different dispersion methods among these. Among these, it is preferable to use a resin-dispersed pigment in which a resin as a dispersant is physically adsorbed onto the pigment particle surface, rather than a resin-bonded pigment or a microcapsule pigment.

As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of an anionic group. As the resin dispersant, a resin having an anionic group can be used, and resins such as those described below can be used. The pigment content (mass %) in the ink is preferably 0.3 times or more and 10.0 times or less relative to the resin dispersant content.

(resin)
The ink can contain a resin. The content (mass%) of the resin in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink. It is more preferable that

Resins are used to (i) stabilize the dispersion state of coloring materials (pigments), that is, serve as resin dispersants for coloring materials (pigments) and their auxiliaries, and (ii) improve various characteristics of recorded images. It can be included in ink depending on the intended use. Examples of the form of the resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. Further, the resin may be a soluble resin that can be dissolved in a liquid medium, or may be resin particles that are dispersed in a liquid medium. The resin particles do not need to contain coloring material.

In this specification, "the resin is soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, it does not form particles whose particle size can be measured by dynamic light scattering. means existing in a liquid medium. Whether or not a resin is soluble can be determined according to the method shown below. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali equivalent to an acid value (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10 times (by volume) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering and no particles having the same particle size are measured, it can be determined that the resin is soluble. The measurement conditions at this time can be, for example, Set Zero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. As the particle size distribution measuring device, a particle size analyzer using a dynamic light scattering method (for example, trade name "UPA-EX150", manufactured by Nikkiso Co., Ltd.) or the like can be used. Of course, the particle size distribution measuring device and measurement conditions used are not limited to those described above.

The acid value of the resin is preferably 80 mgKOH/g or more and 250 mgKOH/g or less, more preferably 100 mgKOH/g or more and 200 mgKOH/g or less. The weight average molecular weight of the resin is preferably 1,000 or more and 30,000 or less, more preferably 5,000 or more and 15,000 or less. The weight average molecular weight of the resin is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

Examples of the resin include acrylic resin, urethane resin, and urea resin. Among these, acrylic resins are preferred. As the acrylic resin, an acrylic resin having a hydrophilic unit and a hydrophobic unit as constituent units is more preferable. Among these, acrylic resins having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from a monomer having an aliphatic group or an aromatic group are preferred. Further, it is preferable to use an acrylic resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer of styrene and α-methylstyrene as the resin dispersant. These resin dispersants are particularly likely to interact with coloring materials (pigments) and can therefore be suitably used.

The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Hydrophilic monomers include acidic monomers with carboxylic acid groups such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples include mercury. Among these, from the viewpoint of hydrophilicity, it is preferable to use a monomer that imparts an anionic group to the resin, that is, a hydrophilic monomer having a carboxylic acid group and a salt or anhydride thereof. Examples of cations constituting the acidic monomer salt include ions such as lithium, sodium, potassium, ammonium, and organic ammonium.

A hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate. Other examples include (meth)acrylic acid ester monomers such as ethyl (meth)acrylate, methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

(liquid medium)
Ink contains a liquid medium. As the liquid medium for the oil-based ink, it is preferable to use water-insoluble organic solvents such as hydrocarbon compounds, ketones, ethers, acetic acid esters, and aromatic compounds. Furthermore, a water-soluble organic solvent, which will be described later, may also be used. These organic solvents can be used alone or in combination as long as they form a single phase. The content (mass%) of the organic solvent in the oil-based ink is preferably 60.0% by mass or more and 95.0% by mass or less, and 80.0% by mass or more and 95.0% by mass, based on the total mass of the ink. % or less is more preferable.

As the liquid medium for the aqueous ink, it is preferable to use an aqueous medium that is water or a mixed solvent of water and a water-soluble organic solvent. As water, it is preferable to use deionized water (ion-exchanged water). The water content (mass%) in the ink is preferably 50.0% by mass or more and 95.0% by mass or less, based on the total mass of the ink. There are no particular limitations on the water-soluble organic solvent that can be used to form the water-based ink, as long as it is water-soluble (preferably one that dissolves in water at an arbitrary ratio at 25°C). Specifically, monohydric or polyhydric alcohols, alkylene glycols, glycol ethers, nitrogen-containing polar compounds, sulfur-containing polar compounds, etc. can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 5.0% by mass or more and 90.0% by mass or less, and 10.0% by mass or more and 50.0% by mass, based on the total mass of the ink. It is more preferable that it is less than % by mass.

(Other additives)
The ink contains various additives such as surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, reduction inhibitors, evaporation accelerators, and chelating agents, as necessary. can be contained. Among these, it is preferable that the ink contains a surfactant. The content (mass%) of the surfactant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and 0.1% by mass or more and 2.0% by mass, based on the total mass of the ink. % or less is more preferable. Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants. The coloring material (pigment) may be dispersed with a surfactant.

(Physical properties of ink)
Since the ink is an ink to be applied to an inkjet method, it is preferable to appropriately control its physical properties. The surface tension of the ink at 25° C. is preferably 10 mN/m or more and 60 mN/m or less, more preferably 20 mN/m or more and 40 mN/m or less. Further, the viscosity of the ink at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 5.0 or more and 10.0 or less, more preferably 6.0 or more and 8.5 or less.

<Inkjet recording method>
The inkjet recording method of the present invention is a method of recording an image on a recording medium by ejecting ink produced by the above-described manufacturing method of the present invention from an inkjet recording head. Examples of methods for ejecting ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to adopt a method of ejecting ink by applying thermal energy to the ink. Other than using the ink of the present invention, the steps of the inkjet recording method may be those known in the art.

FIG. 1 is a diagram schematically showing an example of an inkjet recording device used in the inkjet recording method of the present invention, in which (a) is a perspective view of the main parts of the inkjet recording device, and (b) is a perspective view of a head cartridge. It is. The inkjet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured such that an ink cartridge 42 is set therein. While the head cartridge 36 is transported in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, an image is recorded on the recording medium 32 by conveying the recording medium 32 in the sub-scanning direction by a conveying means (not shown).

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples in any way unless it exceeds the gist thereof. Regarding component amounts, "parts" and "%" are based on mass unless otherwise specified.

<Analysis method of pigment particles>
( ^1H -NMR analysis conditions)
Measuring device: Nuclear magnetic resonance spectrometry device (NMR) (trade name “AVANCE III 500MHz”, manufactured by Bruker Biospin)
Solvent used: heavy dimethyl sulfoxide (DMSO-d ₆ )

(Measurement conditions for average particle diameter)
The average particle diameter of the pigment particles was measured as follows. First, 1 μL of an aqueous dispersion containing 0.0005% pigment particles was dropped onto a platinum-deposited silicon wafer, and a field emission scanning electron microscope (FE-SEM) (product name "SU-70") was used. Images were taken at a magnification of 50,000 times using a camera (manufactured by Hitachi High-Tech). After the photographed image was binarized, the projected area of the pigment particles was measured, and the diameter of a circle with an area equal to the projected area (equal area circle diameter) was calculated. The number average diameter determined from the distribution of equal area circular diameters of 100 particles was defined as the average particle diameter of the pigment particles.

(Measurement conditions for organic purity)
The organic purity of pigment particles was measured as follows. A dimethyl sulfoxide solution containing 0.005% pigment particles was prepared as a sample. Using high performance liquid chromatography (HPLC), C. I. The ratio (%) of the area value of the peak of Pigment Yellow 74 was defined as the organic purity of the pigment particles. The HPLC analysis conditions are as shown below.
・Device: Alliance 2695 (manufactured by Waters)
・Column: SunFire C18 2.1mm x 150mm (manufactured by Waters)
・Column temperature: 40℃
・Detector: Photo Diode Array 2998 (manufactured by Waters)
・Sample injection volume: 1 μL
・Flow rate of mobile phase: 0.2 mL/min
・Mobile phase gradient conditions: Table 1 below

(Mass spectrometry conditions)
Mass spectra were measured under the following conditions for the peaks obtained in the HPLC analysis performed under the above conditions. The most strongly detected m/z was measured with posi(ES+).
Ionization method: Electrospray ionization method (ESI method)
Capillary voltage: 3.5kV
Desolvation gas: 350℃
Ion source temperature: 120℃
Detector: 40V, 200-1500amu/0.9sec (for posi(ES+))

<Preparation of raw materials>
C.I. as a raw material (crude pigment) I. Pigment Yellow 74 was synthesized as follows. A suspension was prepared by adding 25.2 parts of 2-methoxy-4-nitroaniline as a diazo component to 191.0 parts of ion-exchanged water and stirring. 105 parts of 35% hydrochloric acid was added, and the mixture was stirred for 1 hour while maintaining the inside of the system at 5° C. or lower in an ice bath. Thereafter, an aqueous solution prepared by adding 10.5 parts of solid sodium nitrite to 26.9 parts of water was added, and diazotization was carried out by stirring for 1 hour while maintaining the system at 5°C or lower in an ice bath. I did it. Excess nitrous acid was removed by adding 0.15 parts of sulfamic acid to the reaction mixture to prepare an aqueous diazonium solution.

As coupler components, 30.5 parts of o-acetoacetanisidide, 15.4 parts of sodium hydroxide, and 98.6 parts of ion-exchanged water were mixed and completely dissolved by stirring. A coupler slurry was prepared by adding the liquid obtained above to an aqueous solution containing 24.5 parts of acetic acid and 163.6 parts of ion-exchanged water and stirring.

The slurry of the coupler was heated to 40° C. using a hot stirrer, and the diazonium aqueous solution was added dropwise over 1 hour while the inside of the system was maintained at 40° C. Thereafter, after stirring at 40°C for 1 hour, the system was heated to 70°C and stirred for 30 minutes to complete the reaction, and the resulting reaction liquid was filtered to obtain a wet cake of the reaction product. The wet cake of the reaction product was washed twice by stirring with 2 L of ion-exchanged water for 1 hour and filtering, and then dried at 60°C to obtain 53.4 parts of a crude product (yield: 94 %). Next, 48.6 parts of the obtained crude product was dispersed in 900 mL of N-methylpyrrolidone, heated and stirred at 120° C. for 2 hours, and then purified by filtration and drying, which was repeated twice. I. 43.4 parts of yellow-orange crystals of Pigment Yellow 74 were obtained. The organic purity measured by the above method was 99.7%.

<Synthesis of pigment derivative>
(Pigment derivative 1)
A flask equipped with a stirrer, a nitrogen inlet tube, and a thermometer was charged with C. I. 10.0 parts of Pigment Yellow 74, 0.79 parts of 4-dimethylaminopyridine, and 200 parts of tetrahydrofuran were added, and the mixture was stirred at 25°C for 5 minutes. 7.06 parts of di-tert-butyl dicarbonate was added dropwise to this flask, and the mixture was stirred at 25° C. for 12 hours in a nitrogen environment. Unreacted pigment was removed from the reaction mixture by filtration, and the filtrate was distilled under reduced pressure to obtain a viscous crude product. The crude product was washed by two-phase chloroform/water extraction, and the chloroform phase was separated and dried over magnesium sulfate. Thereafter, magnesium sulfate was removed by filtration, and the filtrate was distilled under reduced pressure, and the resulting viscous material was purified by silica gel chromatography (ethyl acetate:heptane = 1:2). As a result, a yellow powder of C. I. 2.90 parts of Pigment Yellow 74-Boc1 substituted product (PY74-Boc1) were obtained. Pigment derivative 1 is C.I. I. Pigment Yellow 74-Boc 1-substituted compound, and in the general formula (1), one of R ₁ and R ₂ is a hydrogen atom and the other is a Boc group.

The results of identifying pigment derivative 1 by ¹ H-NMR and HPLC/MS under the above conditions are shown below.

[ ^1H -NMR]
δ (ppm): 10.23 (1H, bs), 7.99 (1H, dd), 7.87 (1H, d), 7.74 (1H, d), 7.42 (1H, m), 7.22-7.17 (2H, m), 7.04 (1H, m), 3.99 (3H, s), 3.80 (3H, s), 2.48 (3H, s), 1 .26 (9H, s).
[HPLC/MS]
Actual value: MS (ES+) m/z 487.23 ([M+H] ⁺ )
Calculated value: 487.18

(Pigment derivative 2)
A flask equipped with a stirrer, a nitrogen inlet, a reflux condenser, and a thermometer was charged with C. I. 10.0 parts of Pigment Yellow 74, 0.79 parts of 4-dimethylaminopyridine, 5.24 parts of triethylamine, and 200 parts of tetrahydrofuran were added, and the mixture was stirred at room temperature for 5 minutes. After 33.6 parts of di-tert-butyl dicarbonate was added dropwise to the resulting pigment suspension, the mixture was stirred at 60° C. for 3 hours in a nitrogen environment. After cooling to 25° C., the reaction solution was distilled under reduced pressure to obtain a viscous crude product. The crude product was washed by two-phase chloroform/water extraction, and the chloroform phase was separated and dried over magnesium sulfate. Thereafter, magnesium sulfate was removed by filtration, and the filtrate was distilled under reduced pressure, and the resulting viscous material was purified by silica gel chromatography (ethyl acetate:heptane = 1:2). As a result, 11.7 parts of Pigment Derivative 2 (PY74-Boc2), which was a pale yellow powder, was obtained. Pigment derivative 2 is C.I. I. Pigment Yellow 74-Boc disubstituted compound, in which R ₁ and R ₂ are Boc groups in general formula (1).

The results of identifying pigment derivative 2 by ¹ H-NMR and HPLC/MS under the above conditions are shown below.

[ ^1H -NMR]
δ (ppm): 8.05-7.63 (3H, m), 7.41 (1H, m), 7.24 (1H, m), 7.00-6.80 (2H, m), 3 .86 (3H, s), 3.69 (3H, s), 2.44 (3H, s), 1.40 (9H, s), 1.27 (9H, s).
[HPLC/MS]
Actual value: MS (ES+) m/z 87.28 ([M+H] ⁺ )
Calculated value: 587.23

<Manufacture of pigment particles>
Mix each component (part) shown in Tables 2 to 4, and use a table-top kneader (product name "PBV-0.3", manufactured by Irie Shokai) for 8 hours at the temperatures shown in Tables 2 to 4. The first step was carried out by processing. Next, each treatment liquid shown in Tables 2 to 4 was added to the obtained kneaded product, and the mixture was stirred for 3 hours at the temperatures shown in Tables 2 to 4 to carry out the second step. Filtration and water washing were repeated to remove water-soluble inorganic salts and organic solvents, and each pigment particle was obtained by drying at 25°C. In Tables 2 to 4, C. I. Pigment Yellow 74 is a crude pigment, and the one synthesized above was used. Further, the usage amount of the pigment derivative represented by the general formula (1) is listed in the column of "Usage amount S (%) of specific pigment derivative". Pigment derivative 3 (comparison) is monoazo pigment derivative A of Patent Document 3, which is represented by the following structural formula.

<Evaluation>
Each of the pigment particles obtained above was evaluated for each of the following items. In the present invention, "A" and "B" were defined as acceptable levels, and "C" was defined as unacceptable levels based on the evaluation criteria for each item below. The evaluation results are shown in Table 5.

(Average particle size)
The average particle diameter was measured by the method described above, and the average particle diameter of the pigment particles was evaluated according to the evaluation criteria shown below. Pigment particles having a suitable average particle size can also be suitably used for preparing inkjet inks.
A: The average particle diameter of the pigment particles was 30 nm or more and 150 nm or less.
B: The average particle diameter of the pigment particles was 20 nm or more and less than 30 nm, or more than 150 nm and 160 nm or less.
C: The average particle diameter of the pigment particles was less than 20 nm or more than 160 nm.

(organic purity)
The organic purity was measured by the method described above, and the organic purity of the pigment particles was evaluated according to the evaluation criteria shown below. Pigment particles having appropriate organic purity can be suitably used for preparing inkjet inks, and can record images with good color development and light fastness.
A: The organic purity of the pigment particles was 97.0% or more and 99.5% or less.
B: The organic purity of the pigment particles was 96.0% or more and less than 97.0%, or more than 99.5%.
C: The organic purity of the pigment particles was less than 96.0%.

<Manufacture of ink>
(synthesis of resin)
After putting 200.0 parts of isopropanol into a flask equipped with a stirring device, a nitrogen inlet tube, a reflux condenser, and a thermometer, the temperature was raised to 85° C. with stirring under a nitrogen atmosphere. A mixture of 60.0 parts of styrene, 20.0 parts of n-butyl acrylate, 20.0 parts of acrylic acid, and 5.0 parts of polymerization initiator was added to the flask while maintaining the system at 85°C for 2 hours. dripped into. As the polymerization initiator, a solution in which 5.0 parts of the trade name "Perkadox L-W75 (LS)" (dibenzoyl peroxide, manufactured by Kayaku Nuorin, purity 75%) was dissolved in 10.0 parts of isopropanol was used. The inside of the system was maintained at 85° C. and stirred for 4 hours to synthesize resin 1. After adding potassium hydroxide in an amount 0.9 times the acid value of the resin (on a molar basis) and an appropriate amount of ion-exchanged water, isopropanol was removed under reduced pressure to reduce the content of the resin (resin 1) to 20%. A liquid with a concentration of .0% was obtained.

(Preparation of pigment dispersion)
Pigment particles of the type and amount listed in Table 6, 30.0 parts of a liquid containing Resin 1, and 55.0 parts of ion-exchanged water were mixed, and the mixture was mixed using a homogenizer (trade name "Starburst", manufactured by Sugino Machine). Dispersion treatment was performed at a treatment pressure of 200 MPa. Thereafter, an appropriate amount of ion-exchanged water was added to obtain pigment dispersions 1 to 8 having a pigment content of 15.0%.

(Preparation of ink)
Each component shown in Table 7 was mixed, sufficiently stirred, and filtered under pressure using a microfilter (manufactured by Fuji Film) with a pore size of 2.5 μm to prepare each ink. Acetylenol E100 (trade name) is a nonionic surfactant manufactured by Kawaken Fine Chemicals.

<Evaluation using ink>
Each of the prepared inks was filled into an ink cartridge and set in an inkjet recording device (trade name: "PIXUS PRO-10S", manufactured by Canon) equipped with a recording head that ejects ink using thermal energy. The recording environment was a temperature of 25° C. and a relative humidity of 50%. In this example, an image was recorded with a resolution of 600 dpi x 600 dpi and 8 ink droplets of 3.8 ng applied to a unit area of 1/600 inch x 1/600 inch at a recording duty of 100%. Define that there is. A 14-tone solid image was recorded on glossy paper (trade name: "Canon Photo Paper Glossy Gold GL-101", manufactured by Canon) with a recording duty varying in 10% increments from 10 to 140%. After each solid image was recorded, it was placed in a 25° C. environment for 24 hours to dry. The evaluation results are shown in Table 8.

(color development)
The brightness (L ^* ) and chroma (C ^* ) of each solid image were measured using a fluorescence spectrodensitometer (trade name "FD-7", manufactured by Konica Minolta). L ^* and C ^* are based on the color difference display method defined by CIE. Then, the color development of the image was evaluated according to the evaluation criteria shown below. The higher the saturation, the more vivid the image, and the better the color development.
A: The maximum C ^* value was 110 or more.
B: The maximum C ^* value was 100 or more and less than 110.
C: Maximum C ^* value was less than 100.

(light resistance)
Using the fluorescence spectrodensitometer described above, the spectral sensitivity characteristics of each solid image were measured, and the image with the optical density closest to 1.0 was identified. The above spectral sensitivity characteristic is the optical density of the yellow component defined by "ISO Status A". The identified image was placed in a light resistance tester (trade name: "Xenon Weather Meter The irradiation conditions were an irradiation intensity of 0.39 W/(m ² ·nm), a black panel temperature of 63° C., and a relative humidity of 70%. After measuring the optical density of the image after irradiation again, the "optical density residual rate (%)" was calculated from the following formula, and the light resistance of the image was evaluated according to the evaluation criteria shown below.
Optical density residual rate (%) = {(optical density after irradiation)/(optical density before irradiation)}×100
A: The optical density residual rate was 85% or more.
B: The residual optical density was 70% or more and less than 85%.
C: The optical density residual rate was less than 70%.

Claims (10)

C. I. A method for producing pigment particles in which Pigment Yellow 74 is treated with a pigment derivative, the method comprising:
(1) C.I. as a raw material. I. A first step of kneading Pigment Yellow 74 and a pigment derivative represented by the following general formula (1) in the presence of a water-soluble inorganic salt and an organic solvent, and
(2) A compound represented by the following general formula (2) is produced by removing the tert-butoxycarbonyl group from the pigment derivative represented by the general formula (1), and C. I. A second step of obtaining pigment particles of Pigment Yellow 74,
1. A method for producing pigment particles characterized by having the following in this order:

(In general formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or a tert-butoxycarbonyl group. However, R ₁ and R ₂ are not hydrogen atoms at the same time.) The amount (mass%) of the pigment derivative represented by the general formula (1) in the first step is the same as that of the C.I. I. The method for producing pigment particles according to claim 1, wherein the amount is 0.5% by mass or more and 5.0% by mass or less, based on the amount (mass%) of Pigment Yellow 74 used. The method for producing pigment particles according to claim 1, wherein the tert-butoxycarbonyl group is removed from the pigment derivative represented by the general formula (1) by performing the second step in the presence of an acid. The method for producing pigment particles according to claim 1, wherein the pigment particles have an average particle diameter (nm) of 30 nm or more and 150 nm. The C.I. I. The method for producing pigment particles according to claim 1, wherein the organic purity (%), which is a mass proportion of Pigment Yellow 74, is 97.0% or more and 99.5% or less. The amount (mass%) of the water-soluble inorganic salt used is the same as that of the C.I. I. The pigment according to claim 1, which is 3.0 times or more and 20.0 times or less in mass ratio to the total usage amount (mass%) of Pigment Yellow 74 and the pigment derivative represented by the general formula (1). Method of manufacturing particles. The method for producing pigment particles according to claim 1, wherein the temperature in the first step is 60°C or less. The method for producing pigment particles according to claim 1, wherein the temperature in the second step is 60°C or less. A method for producing an inkjet ink containing a coloring material, the method comprising:
A method for manufacturing an ink, characterized in that pigment particles manufactured by the method for manufacturing pigment particles according to any one of claims 1 to 8 are used as the coloring material. An inkjet recording method that records an image on a recording medium by ejecting ink from an inkjet recording head, the method comprising:
An inkjet recording method, characterized in that the ink manufactured by the manufacturing method according to claim 9 is used as the ink.

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