Method for producing pigment composition, method for producing pigment dispersion, method for producing aqueous ink, and inkjet recording method

Abstract

To provide a method for producing a pigment composition which enables preparation of an aqueous ink with superior antibacterial activity and superior discharge stability, exhibiting effective inhibition of on microorganisms and biofilms even within the maximum concentration of antibacterial agents that can be added to ink.SOLUTION: A method for producing a pigment composition includes a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent by the solvent salt milling technique to provide a kneaded product. The mixture further contains an antibacterial agent. The antibacterial agent includes at least one selected from the group consisting of an isothiazolin-based compound, a gemini-type quaternary ammonium salt-based compound, a gramicidin-based compound, an aldehyde-based compound, a nitrile-based compound, and silver ion-loaded zeolite.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a pigment composition, a method for producing a pigment dispersion, a method for producing an aqueous ink, and an inkjet recording method.

Background Art

[0002] In recent years, the market using pigments has expanded in various fields such as color filters and inks for inkjet. Along with this, pigments are required to have various reliabilities, not only high color characteristics, but also stability, filterability when made into a coloring composition, and suitability when applied to a substrate. For meeting the above requirements for high color characteristics, it is effective to use a pigment with a refined primary particle size. As a method for refining the primary particle size of a pigment, for example, there is a method of mechanically kneading a pigment together with a water-soluble inorganic salt such as sodium chloride and an organic solvent using a kneading device such as a kneader. A method of kneading a mixture containing such a pigment, a water-soluble inorganic salt, and an organic solvent is called salt milling or solvent salt milling. By washing the kneaded product obtained by the kneading step by the salt milling method with water to remove the water-soluble inorganic salt and the organic solvent from the kneaded product, a refined pigment can be obtained (see, for example, Patent Document 1). In this method, since the pulverization and crystal growth of the primary particles of the pigment occur in parallel, finally a pigment with a narrow particle size distribution, a small average particle size, and a small surface area is obtained.

[0003] On the other hand, the inkjet recording method can record a high-definition image with a relatively simple device and has been rapidly developing in various fields. However, since the main component of the aqueous ink for inkjet is water and many other components such as colorants are organic compounds, microorganisms such as fungi are likely to occur. When microorganisms such as fungi occur, the ink deteriorates, physical properties such as viscosity change, or foreign substances are generated due to precipitation or aggregation of the components of the ink, resulting in a decrease in ejection characteristics. To address such problems, components such as antibacterial agents are blended into the ink to suppress the generation of microorganisms.

[0004] Various components are known as antibacterial agents. In aqueous inks for inkjet printers, antibacterial agents such as isothiazoline compounds including 1,2-benzisothiazolin-3-one are widely used because they have a broad antibacterial spectrum and are less likely to degrade the ink ejection performance themselves (see Patent Document 2). In addition, inks containing multiple antibacterial agents have been proposed to enhance the bactericidal action against biofilms produced by spore-forming bacteria and microorganisms (see Patent Document 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the concentration of antibacterial agents that can be added to the ink is limited. Even inks containing multiple antibacterial agents up to the upper limit concentration were insufficient to suppress the growth of microorganisms included in spore-forming bacteria and biofilms. Furthermore, the antibacterial properties against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were also insufficient.

[0007] Therefore, an object of the present invention is to provide a method for producing a pigment composition capable of preparing an aqueous ink having excellent antibacterial properties and excellent ejection stability, which has a good inhibitory effect on microorganisms and biofilms even within the upper limit concentration of antibacterial agents that can be added to the ink. Another object of the present invention is to provide a method for producing a pigment dispersion, a method for producing an aqueous ink, and an inkjet recording method using the pigment composition obtained by the above production method.

Means for Solving the Problems

[0008] That is, according to the present invention, there is provided a method for producing a pigment composition including a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent by a solvent-salt milling method to obtain a kneaded product, wherein the mixture further contains an antibacterial agent, and the antibacterial agent contains at least one selected from the group consisting of isothiazoline-based compounds, gemini-type quaternary ammonium salt-based compounds, gramicidin-based compounds, aldehyde-based compounds, nitrile-based compounds, and silver ion-supported zeolites.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a method for producing a pigment composition capable of preparing an aqueous ink having excellent antibacterial properties and excellent ejection stability, which has a good inhibitory effect on microorganisms and biofilms even within the upper limit concentration of the antibacterial agent that can be added to the ink. Further, according to the present invention, it is possible to provide a method for producing a pigment dispersion, a method for producing an aqueous ink, and an inkjet recording method using the pigment composition obtained by the above production method.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when a compound is a salt, although the salt is dissociated into ions 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.

[0011] Microorganisms and biofilms that can occur in the ink can cause instability in the ejection stability of the ink. Microorganisms and biofilms have a structure that does not bring hydrophobic / hydrophilic substances close to each other. However, since the acquisition of nutrients by microorganisms and biofilms is carried out through a site called "porin" of the protein component, it is important to efficiently contact the antibacterial agent with the "porin" of the microorganisms.

[0012] In addition, since microorganisms exist not only on the surface of pigment aggregates but also inside the pigment aggregates, it is considered that adding an antibacterial agent in the ink form existing as pigment aggregates has little effect.

[0013] In view of the above characteristics of microorganisms, the present inventors examined a method for efficiently allowing an antibacterial agent to act on microorganisms or biofilms. As a result of the examination, the present inventors found that it is effective to add an antibacterial agent during kneading of a pigment by a solvent-salt milling method in order to exhibit a good inhibitory effect on microorganisms and biofilms even within the upper limit concentration of the antibacterial agent that can be added to the ink. And it was clarified that the ink prepared using the pigment composition produced by the following method including the above kneading step is excellent in ejection stability.

[0014] As a method for producing a pigment composition, it is a method including a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, an antibacterial agent, and an organic solvent by a solvent-salt milling method to obtain a kneaded product. In the pigment composition obtained by this production method, it is considered that the antibacterial agent acts efficiently on the protein component "porin" of microorganisms and also acts on the microorganisms inside the pigment aggregates during kneading. Therefore, it is presumed that it is possible to prepare an ink excellent in ejection stability by using this pigment composition.

[0015] <Method for Producing Pigment Composition> The production method according to an embodiment of the present invention is a method for producing a pigment composition including a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent by a solvent-salt milling method to obtain a kneaded product. The above mixture further contains an antibacterial agent. The antibacterial agent contains at least one selected from the group consisting of isothiazoline-based compounds, gemini-type quaternary ammonium salt-based compounds, gramicidin-based compounds, aldehyde-based compounds, nitrile-based compounds, and silver ion-supported zeolites. Hereinafter, the kneading step, each material used, and the like will be described in detail.

[0016] 〔Kneading Step〕 In the kneading step in the method for producing the pigment composition of the present embodiment, a mixture containing a pigment, an antibacterial agent, a water-soluble inorganic salt, and an organic solvent is kneaded by a solvent-salt milling method to obtain a kneaded product. The solvent-salt milling method is a method of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent while applying a load to the mixture to compress it using a kneading device. In the method for producing the pigment composition of the present embodiment, a kneaded product containing a refined pigment, an antibacterial agent, a water-soluble inorganic salt, and an organic solvent can be obtained by the kneading step by the solvent-salt milling method.

[0017] As the kneading device, for example, batch type and continuous type, and kneading devices such as atmospheric pressure type, pressure type, and reduced pressure type can be used, and a device that kneads while applying a load to the contents to compress them can be preferably used. Further, a kneading device provided with a material input section such as a kneading kettle and a hopper, and a stirring section such as a stirring blade, a stirring vane, a blade, a screw, and a roll for stirring the material 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 single-screw kneader. Examples of the planetary mixer include Trimix (trade name) manufactured by Inoue Manufacturing Co., Ltd. Examples of the continuous single-screw kneader include Miracle KCK (trade name) manufactured by Asada Iron Works. Among the kneading devices listed above, it is preferable to use a planetary mixer.

[0018] In the method for producing the pigment composition of the present embodiment, in order to make the antibacterial agent act efficiently on the pigment, it is important to expose the crushing surface of the pigment during kneading. Therefore, kneading is performed by the solvent-salt milling method that applies a strong load to the pigment. When specifically expressing this "applying a load", it can be expressed by the "shear rate". The shear rate during kneading in the kneading step is preferably 10 s -1 or more, and more preferably 15 s -1 or more from the viewpoint of more easily applying a shearing force to the pigment itself. When the shear rate is 15 s-1 By performing kneading as described above, it is possible to further improve the ejection stability and storage stability of the ink when the obtained pigment composition is contained in the ink. From this perspective, the shear rate is 20 s -1 and it is more preferably so.

[0019] The temperature during kneading in the kneading step is preferably 0°C or higher and 130°C or lower, more preferably 10°C or higher and 120°C or lower, and even more preferably 20°C or higher and 90°C or lower. Also, the kneading time in the 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.

[0020] In the kneading step, the total amount of the antibacterial agent used is preferably 0.0009 times or more and 0.025 times or less, and more preferably 0.001 times or more and 0.020 times or less, based on the mass ratio to the amount of the pigment used. When the total amount of the antibacterial agent used is 0.001 times or more based on the mass ratio to the amount of the pigment used, the ejection stability of the ink is more likely to be further improved when preparing the ink using the obtained pigment composition. On the other hand, when the total amount of the antibacterial agent used is 0.020 times or less based on the mass ratio to the amount of the pigment used, the ejection stability and storage stability of the ink are more likely to be further improved when preparing the ink using the obtained pigment composition. From this perspective, it is even more preferably 0.018 times or less based on the mass ratio to the amount of the pigment used.

[0021] Regarding the mixing ratio of the pigment, water-soluble inorganic salt, and organic solvent in the kneading step, it is preferably the following ratio based on the amount of the pigment used. In the kneading step, the amount of the water-soluble inorganic salt used is preferably 3.0 times or more and 20.0 times or less, and more preferably 5.0 times or more and 10.0 times or less, based on the mass ratio to the amount of the pigment used. Also, in the kneading step, the amount of the organic solvent used is preferably 0.5 times or more and 5.0 times or less, and more preferably 0.8 times or more and 3.0 times or less, based on the mass ratio to the amount of the pigment used.

[0022] (Pigment) Examples of the pigments used in the kneading process include carbon black and organic pigments. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Examples of organic pigments include water-insoluble azo pigments such as toluidine red, toluidine maroon, C.I. Pigment Red 150, Hansa yellow, benzidine yellow, C.I. Pigment Yellow 74, and pyrazolone red; water-soluble azo pigments such as lithol red, heliobordo, pigment scarlet, and permanent red 2B; phthalocyanine-based pigments such as copper phthalocyanine blue and copper phthalocyanine green; quinacridone-based pigments such as quinacridone red and quinacridone magenta; perylene-based pigments such as perylene red and perylene scarlet; isoindolinone-based pigments such as isoindolinone yellow and isoindolinone orange; benzimidazolone-based pigments such as benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red; pyranthrone-based pigments such as pyranthrone red and pyranthrone orange; and indigo-based pigments, condensed azo-based pigments, thioindigo-based pigments, diketopyrrolopyrrole-based pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, and dioxazine violet. Of course, it is not limited to these. One of the above pigments may be used alone, or two or more thereof may be used in combination.

[0023] (Antibacterial agent) The antibacterial agent used in the kneading process contains at least one selected from the group consisting of isothiazoline-based compounds, gemini-type quaternary ammonium salt-based compounds, gramicidin-based compounds, aldehyde-based compounds, nitrile-based compounds, and silver ion-supported zeolites. The antibacterial agent used in the kneading process is preferably one or two or more of the above antibacterial agents.

[0024] (Isothiazoline-based compound) Isothiazoline compounds are antibacterial agents that inhibit the growth of microorganisms by inhibiting the metabolism of thiol groups. Examples of isothiazoline compounds include 1,2-benzisothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, and N-(n-butyl)-1,2-benzisothiazolin-3-one. One or more of these isothiazoline compounds can be used. 1,2-benzisothiazolin-3-one is widely used as a preservative for inkjet inks. 1,2-benzisothiazolin-3-one is commercially available, for example, as the Proxel series (manufactured by Avecia, CRL, BDN, GXL, XL.2, TN, LV, etc.).

[0025] (Gemini-type quaternary ammonium salt-based compound) Common quaternary ammonium salt-based compounds used as antibacterial agents exhibit a high bactericidal effect against various fungi, but their bactericidal activity against spore-forming bacteria and fungi is not necessarily high. Also, in a low-temperature environment or in the presence of proteins, the bactericidal effect is likely to decrease. In contrast, among quaternary ammonium salt-based compounds, Gemini-type quaternary ammonium salt-based compounds not only exhibit a high bactericidal effect against spore-forming bacteria and fungi but can also suppress the formation of biofilms.

[0026] Gemini-type quaternary ammonium salt-based compounds are symmetric ammonium salts having two ammonium heads (hydrophilic groups). Among them, bis-type quaternary ammonium salts with different bridge structures are more effective. More specific Gemini-type quaternary ammonium salt-based compounds include amide-type N,N-tetramethylenebis(1-dodecyl-4-carbamoylpyridinium iodide), anti-amide-type (1,4-tetramethylenedicarbonyl diamine) bis(1-decylpyridinium iodide), ester-type (1,6-hexamethylenedioxydicarbonyl) bis(1-decylpyridinium iodide), and thioether-type (1,6-hexamethylenedithio) bis(1-octylpyridinium iodide), etc. One or more of these Gemini-type quaternary ammonium salt-based compounds can be used.

[0027] (Gramicidin-based compound) Gramicidin-based compounds used as antibacterial agents exhibit high bactericidal activity against bacteria and fungi and can also inhibit the formation of biofilms. Gramicidin-based compounds only need to have the backbone of gramicidin. Specific examples of Gramicidin-based compounds include Gramicidin S, Gramicidin A, and Gramicidin B, etc. One or more of these Gramicidin-based compounds can be used. Among them, Gramicidin S having a cyclic peptide structure is preferred.

[0028] (Aldehyde-based compound) Aldehyde-based compounds used as antibacterial agents are mainly widely used in medical applications and have no corrosiveness to metals, rubbers, plastics, etc. Also, aldehyde-based compounds are less likely to have their efficacy reduced by organic substances and exhibit bactericidal activity against fungi and spore-forming bacteria.

[0029] Examples of aldehyde compounds include glutaraldehyde (also known as 1,5-pentanedial), orthophthalaldehyde, benzaldehyde, phenylacetaldehyde, 4-methylbenzaldehyde, 2-phenylpropionaldehyde, 2-ethylbutyraldehyde, hexanal, para-anisaldehyde, cinnamaldehyde, and perillaldehyde. One or more of these aldehyde compounds can be used.

[0030] (Nitrile compounds) Nitrile compounds used as antibacterial agents not only exhibit high bactericidal activity but also excellent immediate efficacy. The bactericidal mechanism of nitrile compounds is the destruction of the cell protoplasm. Therefore, the formation of biofilms can be suppressed.

[0031] Examples of nitrile compounds include 1,2-dibromo-2,4-dicyanobutane, 2,2-dibromo-3-nitrilopropionamide, 2-bromo-2-bromomethylglutaronitrile, etc. One or more of these nitrile compounds can be used.

[0032] (Silver ion-loaded zeolite) Silver-loaded inorganic compounds such as silver-loaded titanium oxide used as antibacterial agents exhibit high bactericidal effects against fungi and spore-forming bacteria due to the action of silver ions and have characteristics such as suppressing the formation of biofilms. However, when a general silver-loaded inorganic compound is contained in an aqueous ink, silver ions are easily released and the coloring material salts out, tending to reduce the storage stability of the ink. In contrast, the silver ions in the silver ion-loaded zeolite are chemically bonded to the crystal framework of the zeolite and are stably held in the state of silver ions. Therefore, when the silver ion-loaded zeolite is contained in the aqueous ink, the silver ions are gradually released into the system, so that the storage stability of the ink can be improved while maintaining a high bactericidal effect.

[0033] Zeolite carrying silver ions is preferably of type A (LTA) because of its high affinity for silver ions. The silver ion-carrying zeolite can be prepared, for example, by adding zeolite having a desired crystal structure to water to form a suspension, and further adding silver nitrate or silver chloride and stirring. By adjusting the amount of silver nitrate or silver chloride, the amount of silver ions carried on the obtained silver ion-carrying zeolite can be controlled. When preparing an ink using a pigment composition obtained by using silver ion-carrying zeolite as an antibacterial agent, the silver ion-carrying zeolite is preferably dispersed in the ink by a dispersant such as a resin. Therefore, the ink obtained by using the pigment composition obtained by the production method of the present embodiment preferably further contains a dispersant such as a resin for dispersing the silver ion-carrying zeolite.

[0034] (Other antibacterial agents) In the kneading step, as an antibacterial agent, an antibacterial agent other than those listed above (other antibacterial agents) may be further used. Examples of other antibacterial agents include phenolic compounds, oxazoline compounds, pyridine compounds, imidazole compounds, and thiazole compounds. One or more of these can be used.

[0035] (Water-soluble inorganic salts) The water-soluble inorganic salt used in the kneading step utilizes its high hardness to crush the pigment in the 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 water-soluble inorganic salts include sodium chloride, potassium chloride, sodium sulfate, zinc chloride, calcium chloride, and magnesium chloride, and mixtures of two or more of them. Among them, it is preferable to use sodium chloride from the perspective of cost.

[0036] The particle size of the water-soluble inorganic salt is such that in the volume-based particle size distribution, the cumulative 50% particle size (median particle size; D 50 ) is 5 μm or more and 500 μm or less, and the cumulative 95% particle size (D 95) is preferably 750 μm or less. Particularly when a fine pigment is desired, it is preferable that the water-soluble inorganic salt used as a grinding aid is also fine. Specifically, in the particle size distribution based on volume, the cumulative 50% particle diameter (D 50 ) is 20 μm or more and 300 μm or less, and the cumulative 95% particle diameter (D 95 ) is more preferably a water-soluble inorganic salt of 500 μm or less.

[0037] For the D of the water-soluble inorganic salt 50 and D 95 , values measured using an optical microscope can be adopted. Specifically, the particle diameters of 500 water-soluble inorganic salt particles are measured using an optical microscope, and a method of calculating D 50 and D 95 from the particle size distribution based on volume can be mentioned. For the water-soluble inorganic salt used in the examples described later, D 50 and D 95 were also determined by the above measurement method.

[0038] (Organic solvent) The organic solvent used in the kneading step is for wetting the mixture containing the pigment, antibacterial agent, and water-soluble inorganic salt to form a dough (a lump formed by kneading) of appropriate firmness. Thereby, in the solvent-salt milling method, a strong load is likely to be applied to the kneaded material, increasing the grinding effect and playing a role in generating the crushed surface of the pigment.

[0039] The organic solvent is not particularly limited, but organic solvents such as alcohols, glycols, ethers, and aprotic polar solvents are preferred. Specifically, for example, 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, N,N-dimethylformamide, dimethyl sulfoxide, 2-pyrrolidone, and N-methylpyrrolidone can be mentioned. One of the above water-soluble organic solvents may be used alone, or two or more thereof may be mixed and used as necessary.

[0040] Among the above organic solvents, glycol-based solvents (glycols) are more preferred. Examples of glycol-based solvents include diethylene glycol, triethylene glycol, liquid polyethylene glycol, dipropylene glycol, low molecular weight polypropylene glycol, ethylene glycol, and propylene glycol. One or more of these glycol-based solvents can be used.

[0041] (Other materials) When producing a kneaded product in the kneading process, in addition to a mixture containing a pigment, an antibacterial agent, a water-soluble inorganic salt, and an organic solvent, a dye derivative may be added for the purpose of adjusting crystal growth and crystal dislocation of the pigment. As the dye derivative to be added, a dye derivative having the same structure as the pigment as a parent body is preferable, but a dye derivative having a different structure may also be used. Examples of the substituent of the dye derivative include a hydroxyl group, a carboxy group, a carbamoyl group, a sulfonic acid group, a sulfonamide group, and a phthalimidomethyl group. In addition, organic dyes generally include light yellow aromatic polycyclic compounds such as naphthalene-based and anthraquinone-based compounds that are not generally called dyes. In particular, a dye derivative having a basic group can be preferably used because it has a large dispersion effect on the pigment. These can be used alone or in combination of two or more.

[0042] 〔Other processes〕 By the above kneading process, a kneaded product containing a pigment, an antibacterial agent, a water-soluble inorganic salt, an organic solvent, etc. can be obtained. In the method for producing the pigment composition of the present embodiment, it is preferable to perform a step of removing the water-soluble inorganic salt and the organic solvent from the kneaded product obtained by the above kneaded process. As the method, for example, after putting the kneaded product into water at a predetermined ratio with respect to the kneaded product to obtain a pigment suspension (slurry), the water-soluble inorganic salt and the organic solvent can be removed from the kneaded product by filtering and washing this pigment suspension. The filtration method is not particularly limited, but it is preferable to adopt a method of separating the above pigment suspension by passing it through an ultrafiltration membrane or a dialysis membrane, or a method of separating it with a high-pressure filter press.

[0043] Through processes including the above-mentioned filtration, etc., a wet cake of a pigment composition from which water-soluble inorganic salts and organic solvents have been separated is obtained. Considering the growth of bacteria, it is preferable to dry the obtained wet cake so that the water content is 5% by mass or less. Examples of the drying method include batch or continuous drying in which dehydration and / or desolvation of the wet cake is performed by heating at 80°C or higher and 120°C or lower using a heat source installed in a dryer. Examples of the dryer include a box dryer, a band dryer, and a spray dryer.

[0044] <Method for producing pigment dispersion> Using the pigment composition obtained by the above-described method for producing a pigment composition, it is possible to produce a pigment dispersion. The method for producing the pigment dispersion includes a dispersion step of mixing the pigment composition obtained by the above-described method for producing a pigment composition, a dispersant, and water, and dispersing the pigment composition in water with the dispersant. As the pigment composition, it is preferable to use a pigment composition containing a pigment and an antibacterial agent obtained by removing water-soluble inorganic salts and organic solvents from the kneaded product obtained in the above-described method for producing a pigment composition. As the water, it is preferable to use deionized water such as ion-exchanged water or pure water.

[0045] 〔Dispersion step〕 As a dispersion method for dispersing a pigment in water as a dispersion medium, for example, a resin-dispersed pigment using a resin as a dispersant, a self-dispersing pigment having a hydrophilic group bonded to the particle surface of the pigment, etc. can be used. Also, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the particle surface of the pigment, a microcapsule pigment in which the particle surface of the pigment is coated with a resin, etc. can be used. In order to disperse the above-described pigment composition in water as a 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) capable of stably dispersing the pigment composition in the dispersion medium by the action of an anionic group.

[0046] As the resin, 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, is preferable. Examples of the hydrophobic monomer include styrene, α-methylstyrene, n-butyl acrylate, n-hexyl acrylate, benzyl methacrylate, and the like. One or more of the hydrophobic monomers can be used. Examples of the hydrophilic monomer include hydrophilic monomers having a carboxy group such as acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propyl acrylic acid, isopropyl acrylic acid, itaconic acid, and fumaric acid; hydrophilic monomers having a sulfonic acid group such as styrene sulfonic acid, sulfonic acid-2-propyl acrylamide, 2-sulfonic acid ethyl acrylate, 2-sulfonic acid ethyl methacrylate, and butyl acrylamide sulfonic acid; hydrophilic monomers having a phosphonic acid group such as 2-phosphonic acid ethyl methacrylate and 2-phosphonic acid ethyl acrylate; and the like. One or more of the hydrophilic monomers can be used.

[0047] The weight average molecular weight of the resin used as the dispersant is preferably 1,000 or more and 30,000 or less, and more preferably 3,000 or more and 15,000 or less. The weight average molecular weight of the resin can be a value in terms of standard polystyrene measured using gel permeation chromatography (GPC). The acid value (mgKOH / g) of the resin is preferably 40 mgKOH / g or more and 300 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 250 mgKOH / g or less. The acid value of the resin can be a value measured by a potentiometric titration apparatus using a potassium hydroxide-methanol titrant. The amount of the resin used is preferably 10% by mass or more and 50% by mass or less based on the amount of the pigment used.

[0048] When dispersing the pigment composition 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, etc.

[0049] The content (mass%) of the pigment in the pigment dispersion is preferably 1.0 mass% or more and 50.0 mass% or less, more preferably 5.0 mass% or more and 30.0 mass% or less, based on the total mass of the pigment dispersion. The total content (mass%) of the antibacterial agent in the pigment dispersion is preferably 0.0009 times or more and 0.025 times or less, more preferably 0.001 times or more and 0.020 times or less, in terms of the mass ratio to the content (mass%) of the pigment in the pigment dispersion. The above mass ratio is more preferably 0.001 times or more and 0.018 times or less.

[0050] The pigment composition and the pigment dispersion containing the same can be suitably used for any application that requires a coloring function. Examples of such applications include paints, printing inks, colored molded articles, toner for electrostatic charge image development, color filters for liquid crystal display devices, and inks for inkjet. Among these, aqueous inks for inkjet are preferred.

[0051] <Method for manufacturing ink> It is possible to manufacture an aqueous ink using the pigment dispersion obtained by the method for manufacturing the pigment dispersion described above. The method for manufacturing the aqueous ink includes a step of mixing the pigment dispersion obtained by the method for manufacturing the pigment dispersion described above and components containing a water-soluble organic solvent. When preparing the ink in this step, in addition to the aforementioned pigment dispersion and water-soluble organic solvent, water and other additives used as needed can be blended as the above components to prepare the ink.

[0052] (Colorant) Since the ink contains the pigment dispersion obtained by the above-described method for producing a pigment dispersion, it contains, as a coloring material, the pigment composition obtained by the above-described method for producing a pigment composition. The content (% by mass) of the pigment in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0053] (Antibacterial agent) Since the ink contains the pigment dispersion obtained by the above-described method for producing a pigment dispersion, it contains the above-described antibacterial agent as a component in the pigment composition obtained by the above-described method for producing a pigment composition. Further, the ink may contain an antibacterial agent separately from the pigment composition. The content (% by mass) of the antibacterial agent in the ink is preferably 0.004% by mass or more and 0.150% by mass or less, more preferably 0.005% by mass or more and 0.120% by mass or less, based on the total mass of the ink.

[0054] (Aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. As the aqueous medium, water or 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 (% by mass) of water in the ink is preferably 40.0% by mass or more and 95.0% by mass or less, more preferably 50.0% by mass or more and 95.0% by mass or less, based on the total mass of the ink.

[0055] As the water-soluble organic solvent, any of those conventionally generally used in inks for inkjet can be used. Examples of the water-soluble organic solvent include alkyl alcohols having 1 to 4 carbon atoms, amides, ketones, keto alcohols, ethers, polyalkylene glycols, glycols, alkylene glycols having 2 to 6 carbon atoms in the alkylene group, polyhydric alcohols, alkyl ether acetates, alkyl ethers of polyhydric alcohols, nitrogen-containing compounds, and sulfur-containing compounds. These water-soluble organic solvents can be used alone or in combination of two or more as necessary. The content (mass %) of the water-soluble organic solvent in the ink is preferably 3.0 mass % or more and 50.0 mass % or less, more preferably 3.0 mass % or more and 40.0 mass % or less based on the total mass of the ink.

[0056] (Other Additives) In the ink, for maintaining moisture retention and the like, in addition to the above-described components, solid compounds having moisture retention at normal temperature such as urea, urea derivatives, trimethylolpropane, and trimethylolethane may be contained. The content (mass %) of such a compound in the ink is preferably 0.1 mass % or more and 20.0 mass % or less, more preferably 3.0 mass % or more and 10.0 mass % or less based on the total mass of the ink. Further, in the ink, various additives such as surfactants, pH adjusters, rust preventives, antiseptics, fungicides, antioxidants, anti-reducing agents, and ultraviolet absorbers may be contained as necessary in addition to the above-described components.

[0057] <Inkjet Recording Method> The ink obtained by the above-described method for producing an ink is preferably used in an inkjet recording method. The inkjet recording method is an inkjet recording method in which the aqueous ink obtained by the above-described method for producing an aqueous ink is ejected from an inkjet recording head and an image is recorded on a recording medium. Examples of the method for ejecting the ink include a method of ejecting the ink by applying mechanical energy to the ink and a method of ejecting the ink by applying thermal energy to the ink.

[0058] <Ink Cartridge> When using the above ink in an inkjet recording method, an ink cartridge can be used. The ink cartridge includes the above ink and an ink storage unit for storing the ink. Furthermore, it may be an ink cartridge configured to have an ink storage unit and a recording head.

Example

[0059] Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Regarding the component amounts, "parts" and "%" are based on mass unless otherwise specified.

[0060] <Manufacture of Pigment Composition> (Pigment) The following pigments were prepared. · C.I. Pigment Blue 15:3 (hereinafter also referred to as "PB15:3"). · C.I. Pigment Yellow 74 (hereinafter also referred to as "PY74").

[0061] (Antibacterial Agent) The following antibacterial agents were prepared. · Isothiazoline-based compound: 1,2-benzisothiazolin-3-one · Gemini-type quaternary ammonium salt: N,N-tetramethylenebis(1-dodecyl-4-carbamoylpyridinium iodide) · Gramicidin-based compound: Gramicidin S · Aldehyde-based compound: Glutaraldehyde · Nitrile-based compound: 1,2-dibromo-2,4-dicyanobutane · Silver ion-loaded zeolite: Trade name "Zeomic" (manufactured by Sinanen Holdings)

[0062] (Water-Soluble Inorganic Salt) The following water-soluble inorganic salts were prepared. · NaCl:D 50 is 200 μm, D 95 is 450 μm sodium chloride

[0063] (organic solvent) The following organic solvents were prepared. · Diethylene glycol (hereinafter also referred to as "DEG"). · 2-Pyrrolidone (hereinafter also referred to as "2Py").

[0064] (Pigment compositions 1 to 17) Mixtures prepared by blending the components (unit: parts) shown in the upper row of Table 1 (Table 1-1 and Table 1-2) were kneaded for 8 hours by the solvent salt milling method under the kneading apparatus and kneading conditions shown in the middle row of Table 1 to obtain kneaded products. The obtained kneaded products were thoroughly washed with water, filtered, and dried to remove water-soluble inorganic salts and organic solvents from the kneaded products, thereby producing pigment compositions 1 to 17. "○" in the kneading apparatus column in the middle row of Table 1 represents the kneading apparatus used. Trimix is the trade name "Trimix TX-15" of a planetary mixer manufactured by Inoue Seisakusho. For the kneader, the trade name "PBV-03" manufactured by Irie Shokai was used. "Antibacterial agent / pigment (times)" shown in the lower row of Table 1 represents the mass ratio (times) of the amount of antibacterial agent used (parts) to the amount of pigment used (parts).

[0065] TIFF2025098317000001.tif104170

[0066] TIFF2025098317000002.tif107170

[0067] <Preparation of resin aqueous solution> Resins 1 and 2, which are water-soluble random copolymers, were synthesized according to the procedure shown below. After putting 200.0 parts of isopropanol into a flask equipped with a stirrer, a nitrogen inlet tube, a reflux condenser, and a thermometer, the temperature was raised to 85°C with stirring under a nitrogen atmosphere. The monomer mixture shown in Table 2 and the polymerization initiator were each added dropwise into the flask over 2 hours while maintaining the temperature at 80°C. The internal temperature was maintained at 80°C and stirred for 4 hours to synthesize each resin. After adding 0.9 equivalents of potassium hydroxide and an appropriate amount of ion-exchanged water to the acid value of the resin, isopropanol was removed under reduced pressure to obtain resin aqueous solutions 1 and 2, which are alkaline aqueous solutions of resins 1 and 2. The content of the resin (solid content) in both resin aqueous solutions 1 and 2 was 20.0%. The meanings of the abbreviations in Table 2 are shown below. St: Styrene nBA: n-Butyl acrylate AA: Acrylic acid Polymerization initiator: A solution prepared by dissolving 5.0 parts of the product name "Perkadox L-W75(LS)" (manufactured by Kayaku Akzo, dibenzoyl peroxide, purity 75%) in 10.0 parts of isopropanol

[0068] TIFF2025098317000003.tif37170

[0069] <Preparation of pigment dispersion> (Pigment dispersions 1 to 17) Each component shown in Table 3 (unit: part) was mixed and subjected to a dispersion treatment at a treatment pressure of 200 MPa using a high-pressure homogenizer (product name "Starburst", manufactured by Sugino Machine). Thereafter, an appropriate amount of ion-exchanged water was added to obtain each pigment dispersion having a pigment content of 20.0%.

[0070] TIFF2025098317000004.tif118170

[0071] <Preparation of ink> Mix the components (unit: %) shown in Table 4 (Table 4-1 and Table 4-2), stir well until dispersed, and then perform pressure filtration using a microfilter with a pore size of 3.0 μm (manufactured by Fujifilm) to prepare each ink. The "remaining amount" in the blending amount (%) of ion-exchanged water shown in Table 4 means the remaining amount when the total of each component is 100%. Also, the "solvent" shown in Table 4 is glycerin, and the "antibacterial agent" is 1,2-benzisothiazolin-3-one.

[0072] TIFF2025098317000005.tif61170

[0073] TIFF2025098317000006.tif61170

[0074] <Evaluation> (Discharge stability) Fill Inks 1 to 18 into ink cartridges respectively, and set them in an inkjet recording apparatus (trade name "PIXUS PRO-10", manufactured by Canon) equipped with a recording head that discharges ink by thermal energy. The resolution of this inkjet recording apparatus is 2400 dpi × 1200 dpi. Then, an image recorded under the condition of applying 8 ink droplets of 3.8 ng to a unit area of 1 / 600 inch × 1 / 600 inch is defined as having a recording duty of 100%. Using the above inkjet recording apparatus, a solid image of A4 size with a recording duty of 50% was continuously recorded on a recording medium (plain paper; trade name "PB PAPER", manufactured by Canon) for 200 sheets. Then, the state of the distortion of the images of the first sheet and the 200th sheet was visually confirmed, and the discharge stability was evaluated according to the evaluation criteria shown below. The evaluation results are shown in Table 5. In this example, "A" and "B" were set as acceptable levels and "C" as unacceptable levels according to the evaluation criteria shown below. Since microorganisms and biofilms generated in the ink cause instability in the discharge stability of the ink, it can be said that the better the discharge stability, the better the antibacterial property in the evaluation of the inks used in this example and the comparative examples. A: It was possible to record 200 sheets, and there was no distortion in the image of the 200th sheet. B: It was possible to record 200 sheets. There was distortion in the 200th image, but there were no white missing parts. C: It was possible to record 200 sheets, but there were distortion and white missing parts in the 200th image.

[0075] (Storage stability) The viscosity of the ink obtained above (the viscosity of the ink before storage) was measured. The ink whose viscosity was measured was put into a sealed container and placed in a constant temperature bath at 70 °C for 2 weeks, and then returned to 25 °C to measure the viscosity (the viscosity of the ink after storage). The viscosity of the ink was measured using an E-type viscometer (trade name "RE-80L type", manufactured by Toki Sangyo Co., Ltd.). Then, the viscosity ratio was calculated according to the formula "viscosity ratio" = "viscosity of the ink after storage" / "viscosity of the ink before storage", and the storage stability of the ink was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 5. In this example, "A" and "B" were set as acceptable levels and "C" as unacceptable level according to the following evaluation criteria. A: The viscosity ratio was 1.1 or less. B: The viscosity ratio exceeded 1.1 and was 1.2 or less. C: The viscosity ratio exceeded 1.2.

[0076] TIFF2025098317000007.tif124170

[0077] Note that the disclosure of this embodiment includes the following methods. (Method 1) A method for producing a pigment composition including a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent by a solvent-salt milling method to obtain a kneaded product, wherein the mixture further contains an antibacterial agent, and the antibacterial agent contains at least one selected from the group consisting of isothiazoline-based compounds, gemini-type quaternary ammonium salt-based compounds, gramicidin-based compounds, aldehyde-based compounds, nitrile-based compounds, and silver ion-supported zeolites. A method for producing a pigment composition characterized by that. (Method 2) The method for producing a pigment composition according to Method 1, wherein the shear rate during kneading in the kneading step is 15 s -1 or more. (Method 3) The method for producing a pigment composition according to Method 1 or 2, wherein the total amount of the antibacterial agent used in the kneading step is 0.001 times or more and 0.020 times or less in terms of the mass ratio to the amount of the pigment used. (Method 4) The method for producing a pigment composition according to any one of Methods 1 to 3, wherein the organic solvent contains a glycol-based solvent. (Method 5) A method for producing a pigment dispersion liquid, comprising a dispersion step of mixing a pigment composition, a dispersant, and water obtained by the method for producing a pigment composition according to any one of Methods 1 to 4, and dispersing the pigment composition in the water with the dispersant. (Method 6) A method for producing an aqueous ink, comprising a step of mixing a pigment dispersion liquid obtained by the method for producing a pigment dispersion liquid according to Method 5 and a component containing a water-soluble organic solvent. (Method 7) An inkjet recording method of ejecting ink from an inkjet recording head to record an image on a recording medium, wherein the ink is an aqueous ink obtained by the method for producing an aqueous ink according to Method 6.

Claims

1. A method for producing a pigment composition, comprising a kneading step of kneading a mixture containing a pigment, a water-soluble inorganic salt, and an organic solvent by a solvent-salt milling method to obtain a kneaded product, wherein the mixture further contains an antibacterial agent, and the antibacterial agent contains at least one selected from the group consisting of isothiazoline-based compounds, gemini-type quaternary ammonium salt-based compounds, gramicidin-based compounds, aldehyde-based compounds, nitrile-based compounds, and silver ion-supported zeolites. A method for producing a pigment composition, characterized by this.

2. The shear rate during kneading in the kneading step is 15 s －１ or more, and the method for producing a pigment composition according to claim 1.

3. The method for producing a pigment composition according to Claim 1, wherein the total amount of the antibacterial agent used in the kneading step is 0.001 times or more and 0.020 times or less in terms of mass ratio to the amount of the pigment used.

4. The method for producing a pigment composition according to Claim 1, wherein the organic solvent contains a glycol-based solvent.

5. A method for producing a pigment dispersion liquid, characterized by including a dispersion step of mixing a pigment composition, a dispersant, and water obtained by the method for producing a pigment composition according to any one of Claims 1 to 4, and dispersing the pigment composition in the water with the dispersant.

6. A method for producing an aqueous ink, characterized by including a step of mixing a pigment dispersion liquid obtained by the method for producing a pigment dispersion liquid according to Claim 5 and a component containing a water-soluble organic solvent.

7. An inkjet recording method of ejecting ink from an inkjet recording head and recording an image on a recording medium, wherein the ink is an aqueous ink obtained by the method for producing an aqueous ink according to Claim 6.

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