Aqueous ink composition, method for producing the same, and recording method.

Abstract

The present invention addresses the problem of providing: an aqueous ink composition which is capable of achieving a good balance among fastness, adhesion and optical density of a coating film; and the like. The problem is able to be solved by means of an aqueous ink composition which contains nanocellulose, wherein the nanocellulose contains an oxide of a cellulose starting material obtained by means of hypochlorous acid or a salt thereof, but does not substantially contain an N-oxyl compound.

Description

[Technical Field]

[0001] The present invention relates to an aqueous ink composition, a method for producing the same, and a recording method. [Background technology]

[0002] In recent years, water-based ink compositions (hereinafter sometimes referred to as "water-based inks") have been replacing organic solvent-based inks in a wide range of fields. This is because, in addition to their safety and reduced environmental impact, they are used to avoid contamination of food products with organic solvents derived from the ink composition when used in laminates for flexible packaging, and because there is a demand for water-based inks with reduced odor that can be used in enclosed spaces such as offices.

[0003] In recent years, research has been progressing on using plant fibers as compositional materials for water-based inks. Since plant fibers leave almost no ash residue when burned, problems such as ash treatment in incinerators and landfill disposal do not arise. In particular, the use of nanocellulose, which is plant fibers defibrated to the nanoscale, is being researched. Nanocellulose is cellulose that has been uniformly micronized (nanofiberized) to the nanoscale, and it is known to be added to pigment compositions with the aim of imparting good rheological properties (see, for example, Patent Document 1).

[0004] Aqueous ink composition is known that ensures excellent dispersion stability even with colorants of high specific gravity by incorporating nanocellulose into aqueous ink (see, for example, Patent Document 2). The cellulose fibers contained in the aqueous ink composition of Patent Document 2 are cellulose fibers with a number average fiber diameter of 2 to 150 nm, and the cellulose has a cellulose type I crystalline structure, and the hydroxyl group at the C6 position of each glucose unit in the cellulose molecule is selectively oxidized and modified to become one of an aldehyde group, a ketone group, or a carboxyl group, with a carboxyl group content of 0.6 to 2.0 mmol / g and a total content of aldehyde and ketone groups of 0.3 mmol / g or less as measured by the semicarbazide method. The aqueous ink composition of Patent Document 2 is said to have excellent dispersion stability over a long period of time.

[0005] Patent Document 3 discloses an aqueous pigment dispersion characterized by comprising at least a pigment, an anionic group-containing organic polymer compound, and bio-nanofibers having an average diameter of 1 nm to 100 nm and an aspect ratio of 100 or more. The aqueous pigment dispersion of Patent Document 3 is said to have excellent optical density and scratch resistance of the resulting image. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2013-527876 [Patent Document 2] Japanese Patent Publication No. 2013-181167 [Patent Document 3] International Publication No. 2015 / 166808 [Overview of the project] [Problems that the invention aims to solve]

[0007] The microfibrillated cellulose used in the pigment-containing composition of Patent Document 1 is produced by enzymatic treatment of cellulosic fibers. Because enzymes are used, there are challenges in efficiently and stably supplying microfibrillated cellulose.

[0008] The cellulose fibers contained in the aqueous ink composition of Patent Document 2 are obtained by oxidation using a co-oxidizing agent in the presence of an N-oxyl compound such as TEMPO, and after this oxidation, the fibers obtained through reduction, purification, and micronization treatment are used. The cellulose fibers obtained in this way have low manufacturing efficiency, which presents a problem in that aqueous ink compositions using them cannot be efficiently obtained.

[0009] The bio-nanofibers contained in the aqueous pigment dispersion described in Patent Document 3 are specifically nanocellulose obtained by mechanical defibrillation. However, since the production of nanocellulose requires energy, there is a problem in that an aqueous ink composition cannot be efficiently obtained.

[0010] Furthermore, the ink composition is required to possess functional properties such as the durability, adhesion, and optical density of the coating film obtained from the composition.

[0011] This invention has been made in view of the above circumstances, and its main objective is to provide an aqueous ink composition that can achieve both robustness, adhesion, and optical density of the coating film, and an efficient method for producing the same. [Means for solving the problem]

[0012] As a result of diligent research to solve the above problems, we discovered that by using a specific type of nanocellulose, it is possible to efficiently obtain an aqueous ink composition that can achieve both robustness, adhesion, and optical density of the coating film, thus completing the present invention. Specifically, the present invention provides the following means.

[0013] [1] An aqueous ink composition containing nanocellulose, The nanocellulose contains an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, and substantially does not contain an N-oxyl compound. An aqueous ink composition. [2] Further comprising an anionic group-containing organic polymer compound. The aqueous ink composition according to [1]. [3] At least a part of the carboxy groups of the nanocellulose is modified with at least one selected from the group consisting of a metal, ammonia, an amine and a quaternary ammonium. The aqueous ink composition according to [1] or [2]. [4] For inkjet recording. The aqueous ink composition according to any one of [1] to [3]. [5] A recording method including a step of discharging the aqueous ink composition according to any one of [1] to [3] onto a recording member by an inkjet method. [6] A method for producing an aqueous ink composition containing nanocellulose, including a step of obtaining an aqueous ink composition containing nanocellulose by defibrating the oxidized cellulose by stirring a mixture containing the oxidized cellulose and a material other than the nanocellulose of the aqueous ink composition. The oxidized cellulose contains an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, and substantially does not contain an N-oxyl compound. Production method. [7] A method for producing an aqueous ink composition containing nanocellulose, including a step of obtaining an aqueous ink composition containing nanocellulose by defibrating the oxidized cellulose by stirring the oxidized cellulose and continuously mixing a material other than the nanocellulose of the aqueous ink composition. The oxidized cellulose contains an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof, and substantially does not contain an N-oxyl compound. Production method. [8] The material further comprises an anionic group-containing organic polymer compound. The manufacturing method described in [6] or [7]. [9] At least a portion of the carboxyl groups of the oxidized cellulose are modified with at least one selected from the group consisting of metals, ammonia, amines, and quaternary ammonium compounds. The manufacturing method described in any of [6] to [8]. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an aqueous ink composition that can achieve both robustness, adhesion, and optical density of the coating film, as well as an efficient method for producing the same. [Modes for carrying out the invention]

[0015] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and they do not limit the present invention.

[0016] [Water-based ink composition] The aqueous ink composition of the present invention contains nanocellulose. The nanocellulose contained in the aqueous ink composition of the present invention contains an oxide (oxidized nanocellulose) of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds. The aqueous ink composition of the present invention has color development (optical density) and scratch resistance in the image formed by the aqueous ink composition. The mechanism is presumed to be as follows, but is not limited to the above. Because the glucose units that make up cellulose adopt a chair conformation, the hydroxyl group is positioned horizontally to the glucopyranose ring, and only C and H are positioned vertically. Therefore, the vertical direction of cellulose is hydrophobic, and the horizontal direction is hydrophilic. Nano-sizing increases the surface area, further reinforcing this tendency. For this reason, in aqueous ink compositions, the complex formed by nanocellulose with pigment particles and the anionic group-containing organic polymer compounds described later is thought to have achieved a high level of balance essential for stable dispersion of pigments by lowering the interfacial tension between components such as pigment particles and anionic group-containing organic polymer compounds, controlling the charge on the surface of the pigment particles, and providing a repulsive force that can overcome the van der Waals forces between pigment particles. As a result, the pigment particles can be fixed without unnecessarily penetrating the substrate, resulting in high optical density, and in multi-color printing, adjacent color inks do not mix. Furthermore, the nanocellulose included in this invention has excellent binder properties and superior abrasion resistance, including the robustness and adhesion of the coating film. Furthermore, the nanocellulose of the present invention can be obtained by easily defibrating oxidized cellulose oxidized with hypochlorous acid or a salt thereof. This eliminates the need for high-pressure homogenizers or other energy loads to achieve nano-density, allowing for efficient nanocellulose production. Therefore, the aqueous ink composition of the present invention can also be efficiently obtained.

[0017] <Nanocellulose> In this invention, nanocellulose is obtained by nano-sizing oxidized cellulose, which is obtained by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof. Here, the above-mentioned oxidized cellulose can also be called an oxide of the cellulosic raw material. Therefore, nanocellulose in this invention includes oxides of cellulosic raw materials obtained with hypochlorous acid or a salt thereof. The main component of plants is cellulose, and bundles of cellulose molecules are called cellulose microfibrils. Cellulose in cellulosic raw materials is also contained in the form of cellulose microfibrils. In this invention, nanocellulose is a general term for nano-sized cellulose, and includes fine cellulose fibers and cellulose nanocrystals, and also includes modified versions thereof (details of modified versions will be described later). Fine cellulose fibers are also called cellulose nanofibers (also written as CNF).

[0018] The aqueous ink composition of the present invention contains nanocellulose, but it can also be manufactured by incorporating nanocellulose that has been defibrated and nano-sized from oxidized cellulose, or by using oxidized cellulose as a raw material during the preparation of the aqueous ink composition and nano-scaling the oxidized cellulose during the preparation. Therefore, the nanocellulose in the aqueous ink composition is nano-sized at an appropriate point in time.

[0019] In the production of nanocellulose according to the present invention, N-oxyl compounds such as TEMPO are not used in the treatment of oxidizing the cellulosic raw material with hypochlorous acid or its salt. Therefore, the nanocellulose according to the present invention is substantially free of N-oxyl compounds. Consequently, nanocellulose has a high level of safety due to the sufficiently reduced impact of N-oxyl compounds on the environment and the human body, and can be applied to cosmetics, foods, medical products, etc. Here, in this specification, "substantially free of N-oxyl compounds" of nanocellulose (or oxidized cellulose) means that the nanocellulose contains no N-oxyl compounds at all, or that the content of N-oxyl compounds is 2.0 ppm by mass or less, preferably 1.0 ppm by mass or less, relative to the total amount of nanocellulose. Furthermore, if the content of N-oxyl compounds is an increase from the cellulosic raw material, preferably 2.0 ppm by mass or less, more preferably 1.0 ppm by mass or less, it also means "substantially free of N-oxyl compounds." The content of N-oxyl compounds can be measured by known means. Known methods include using a trace total nitrogen analyzer (for example, Nitto Seikou Analytech Co., Ltd., instrument name: TN-2100H).

[0020] The above-mentioned oxidized cellulose exhibits excellent defibrillation properties. In particular, it can be uniformly pulverized even when defibrillated under mild conditions, demonstrating excellent ease of defibrillation. Furthermore, when mixed with the above-mentioned nanocellulose to form a slurry, the slurry viscosity remains stable over time, and it exhibits excellent handling properties.

[0021] (Carboxylate group amount) The amount of carboxyl groups in nanocellulose and oxidized cellulose is preferably 0.20 to 2.0 mmol / g. When the amount of carboxyl groups is 0.20 mmol / g or more, sufficient defibrillability can be imparted to the oxidized cellulose. As a result, even when defibrillation is performed under mild conditions, a nanocellulose-containing slurry with uniform quality can be obtained, improving the viscosity stability and handling properties of the slurry. On the other hand, when the amount of carboxyl groups is 2.0 mmol / g or less, excessive decomposition of cellulose during defibrillation can be suppressed, and nanocellulose with a lower proportion of particulate cellulose and uniform quality can be obtained. This is thought to improve dispersibility and enhance the strength and water resistance of the coating film containing nanocellulose. From this perspective, the amount of carboxyl groups in nanocellulose and oxidized cellulose is more preferably 0.30 mmol / g or more, even more preferably 0.35 mmol / g or more, even more preferably 0.40 mmol / g or more, even more preferably 0.42 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably more than 0.50 mmol / g, and even more preferably 0.55 mmol / g or more. The upper limit of the amount of carboxyl groups may be less than 2.0 mmol / g, 1.5 mmol / g or less, 1.2 mmol / g or less, 1.0 mmol / g or less, or 0.9 mmol / g or less. The preferred range for the amount of carboxyl groups can be determined by appropriately combining the upper and lower limits described above. The amount of carboxyl groups in nanocellulose is more preferably 0.30 mmol / g or more and less than 2.0 mmol / g, even more preferably 0.35 to 2.0 mmol / g, even more preferably 0.35 to 1.5 mmol / g, even more preferably 0.40 to 1.5 mmol / g, even more preferably 0.50 to 1.2 mmol / g, even more preferably more than 0.50 to 1.2 mmol / g, and even more preferably 0.55 to 1.0 mmol / g.

[0022] The amount of carboxyl groups (mmol / g) is calculated using the following formula from the amount of sodium hydroxide consumed during the neutralization stage of a weak acid, where the change in electrical conductivity is gradual. This was done by adding a 0.1 M hydrochloric acid solution to an aqueous solution of oxidized cellulose mixed with water to adjust the pH to 2.5, then adding a 0.05 N sodium hydroxide solution dropwise until the pH reached 11.0. Details are provided in the examples described later. The amount of carboxyl groups can be adjusted by changing the reaction time, reaction temperature, pH of the reaction solution, etc. Carboxylate group amount = a (ml) × 0.05 / Oxidized cellulose mass (g)

[0023] The above-mentioned oxidized cellulose can be obtained, for example, by oxidizing a cellulosic raw material under conditions where the effective chlorine concentration of hypochlorous acid or its salt in the reaction system is relatively high (e.g., 6% to 43% by mass). Alternatively, the oxidized cellulose in this invention can also be produced by appropriately controlling reaction conditions such as the effective chlorine concentration, pH during the reaction, and reaction temperature. The oxidized cellulose thus obtained preferably has a structure in which at least two of the hydroxyl groups of the glucopyranose ring constituting the cellulose are oxidized, and more specifically, it is preferable that the hydroxyl groups at positions 2 and 3 of the glucopyranose ring are oxidized and a dicarboxyl group is introduced. Furthermore, it is preferable that the hydroxyl group at position 6 of the glucopyranose ring in the oxidized cellulose remains unoxidized and as a hydroxyl group. Note that the position of the carboxyl group in the glucopyranose ring of the oxidized cellulose is solid. 13 This can be analyzed using 1C-NMR spectroscopy.

[0024] Rayon has the same chemical structure as cellulose, and its oxide (rayon oxide) is water-soluble. When rayon oxide is dissolved in heavy water, a one-dimensional solution is formed. 13¹¹C-NMR measurement reveals a peak at 165-185 ppm attributed to carbon atoms in the carboxyl group. In one embodiment of oxidized cellulose or nanocellulose obtained by oxidizing a cellulosic raw material with hypochlorous acid or its salt, two signals appear within this chemical shift range. Furthermore, two-dimensional solution NMR measurement can determine that the carboxyl groups are introduced at positions 2 and 3.

[0025] Solid oxidized cellulose or nanocellulose obtained by oxidizing cellulose-based raw materials with hypochlorous acid or its salts. 13 In 1C-NMR, when a large amount of carboxyl groups are introduced, two signals appear at 165-185 ppm, while when a small amount of carboxyl groups are introduced, a very broad signal may appear. As can be seen from the results for rayon oxide, the signals of carboxyl group carbons introduced at positions 2 and 3 are close together, and the solid has low resolution. 13 In 1C-NMR, the separation of the two signals is insufficient. Therefore, when the amount of carboxyl group introduced is small, it is observed as a broad signal. In other words, solid 13 In the 1C-NMR spectrum, the introduction of carboxyl groups at positions 2 and 3 can be confirmed by evaluating the broadening of the peak appearing at 165–185 ppm. In other words, solid 13 A baseline is drawn over the peaks in the 165 ppm to 185 ppm range in the 1C-NMR spectrum to determine the total area value. Then, the area value is vertically divided at the peak top to obtain the ratio of the two resulting peak area values ​​(larger area value / smaller area value). If this ratio is 1.2 or greater, the peak can be considered broad. Furthermore, the presence or absence of the broad peak can be determined by the ratio of the baseline length L in the range of 165 ppm to 185 ppm to the length L' of the perpendicular from the peak top to the baseline. That is, if the ratio L' / L is 0.1 or greater, it can be determined that a broad peak exists. The ratio L' / L may also be 0.2 or greater, 0.3 or greater, 0.4 or greater, or 0.5 or greater. There is no particular upper limit to the ratio L' / L, but it is usually sufficient if it is 3.0 or less, 2.0 or less, or 1.0 or less. Furthermore, the structure of the glucopyranose ring can also be determined by analysis according to the method described in Sustainable Chem. Eng. 2020, 8, 48, 17800-17806.

[0026] In the present invention, nanocellulose is an aggregate of individual fibers. When the nanocellulose in the present invention includes carboxylated nanocellulose, it is sufficient that it contains at least one carboxylated nanocellulose fiber, and it is preferable that carboxylated nanocellulose is the main component. Here, carboxylated nanocellulose being the main component means that the proportion of carboxylated nanocellulose in the total amount of nanocellulose is greater than 50% by mass, preferably greater than 70% by mass, and more preferably greater than 80% by mass. The upper limit of the above proportion is 100% by mass, but it may also be 98% by mass or 95% by mass.

[0027] The average fiber length of nanocellulose is preferably 50 to 2000 nm, more preferably 100 to 1000 nm, even more preferably 100 to 700 nm, even more preferably 100 to 500 nm, and even more preferably 100 to 400 nm. If the average fiber length exceeds 2000 nm, the slurry thickens drastically, making it difficult to handle. Also, if the average fiber length is less than 50 nm, the viscosity characteristic of CNF becomes difficult to achieve.

[0028] The average fiber width of the nanocellulose is preferably 1 to 200 nm, more preferably 1 to 15.0 nm, still more preferably 1 to 10 nm, and even more preferably 1 to 5 nm. When the average fiber width is less than 1 nm, it becomes difficult to improve the strength of the resin containing nanocellulose. Further, when the average fiber width is greater than 200 nm, the ejection stability in inkjet printing may decrease when an ink composition is formed. In addition, the average fiber width and the average fiber length are obtained by mixing nanocellulose and water so that the concentration of nanocellulose is approximately 1 to 10 ppm, naturally drying the sufficiently diluted cellulose aqueous dispersion on a mica substrate, observing the shape of the nanocellulose using a scanning probe microscope, randomly selecting an arbitrary number of fibers from the obtained image, setting the cross-sectional height of the shape image = fiber width, and the perimeter length ÷ 2 = fiber length. For calculating such average fiber width and average fiber length, image processing software can be used. At this time, the conditions for image processing are arbitrary, but even for the same image, the calculated values may differ depending on the conditions. The range of the difference in values depending on the conditions is preferably within ±100 nm for the average fiber length. The range of the difference in values depending on the conditions is preferably within ±10 nm for the average fiber width.

[0029] The nanocellulose in the present invention contains a carboxy group, and the carboxy group may be in the H form (-COOH), may be in the salt form (-COO - X + :X + :X is a cation forming a salt form), or may be in a modified form in which the carboxy group is reacted with another compound to form a covalent bond. Therefore, the aqueous ink composition of the present invention includes an embodiment containing nanocellulose in which at least a part of the carboxy group of the nanocellulose is modified with a metal, ammonia, an amine, or a quaternary ammonium. In the production process of the aqueous ink composition of the present invention, a metal, ammonia, an amine, or a quaternary ammonium may be added as necessary. Thereby, at least a part of the carboxy group of the nanocellulose is modified with a metal, ammonia, an amine, or a quaternary ammonium. Furthermore, when manufacturing the aqueous ink composition of the present invention, nanocellulose that has been pre-modified with a metal, ammonia, amine, or quaternary ammonium may be used.

[0030] In this specification, "modified nanocellulose" refers to nanocellulose in which the carboxyl groups form interactions with metals, ammonia, amines, or quaternary ammonium compounds. Here, the interaction is not limited to any chemical bond that forms an interaction with the carboxyl groups, such as ionic bonds or covalent bonds. It is believed that the nanocellulose is modified when metals, ammonia, amines, or quaternary ammonium salt compounds interact with the carboxyl groups on the surface of the nanocellulose, thereby improving its affinity for components in aqueous ink compositions (e.g., pigments or anionic group-containing organic polymer compounds). Furthermore, nanocellulose modified with metals, ammonia, amines, or quaternary ammonium salt compounds also functions as a surfactant. This eliminates the need to use surfactants in the process of dispersing anionic group-containing organic polymer compounds. The absence of surfactants is advantageous in terms of workability because it prevents foaming during the drying of the resulting aqueous ink composition.

[0031] The metal used to modify the nanocellulose is not particularly limited, and examples include sodium, potassium, magnesium, lithium, silver, gold, copper, and zinc. When used in aqueous inkjet recording inks, potassium salts are preferred because they improve ejection stability.

[0032] The amine used to modify the nanocellulose is not particularly limited and may be primary, secondary, or tertiary. The number of carbon atoms in the hydrocarbon or aromatic group bonded to the nitrogen atom of the amine or quaternary ammonium salt compound (or the total number of carbon atoms if two or more hydrocarbon or aromatic groups are bonded to the nitrogen atom) is not particularly limited and may be selected from between 1 and 100 carbon atoms. From the viewpoint of imparting sufficient hydrophobicity to the nanocellulose and ensuring good miscibility with resin components, the number of carbon atoms is preferably 3 or more, and more preferably 5 or more.

[0033] In addition to hydrocarbon groups and aromatic groups, organic groups such as prolene oxide / ethylene oxide (PO / EO) copolymers can also be used in amines. These may be introduced into nanocellulose individually or in combination of two or more. From the viewpoint of improving pigment dispersibility, amines having PO / EO copolymers are preferred. Amines having a PO / EO copolymer can be prepared according to known methods, and the manufacturing method can be found in Japanese Patent Publication No. 3-181448, etc. Commercially available amines having a PO / EO copolymer can also be suitably used, and specific examples include Jeffamine M-600, Jeffamine M-1000, Jeffamine M-2005, and Jeffamine M-2070 from Huntsman. These may be used individually or in combination of two or more.

[0034] The quaternary ammonium salt compounds that modify nanocellulose are not particularly limited. Specific examples of quaternary ammonium salt compounds include quaternary ammonium hydroxides such as tetrabutylammonium hydroxide, quaternary ammonium chlorides such as tetrabutylammonium chloride, quaternary ammonium bromides such as tetrabutylammonium bromide, and quaternary ammonium iodides such as tetrabutylammonium iodide.

[0035] <Method for producing nanocellulose> The nanocellulose in the present invention can be produced, for example, by a method comprising step A, which involves oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof to obtain oxidized cellulose, and step B, which involves defibrating the oxidized cellulose as needed.

[0036] (Process A: Production of oxidized cellulose) Cellulosic raw materials are not particularly limited as long as they are primarily composed of cellulose. Examples include pulp, natural cellulose, regenerated cellulose, and fine cellulose obtained by depolymerizing cellulose through mechanical treatment. Commercially available cellulose-based raw materials such as crystalline cellulose made from pulp can be used as is. In addition, unused biomass containing a large amount of cellulose, such as okara (soy pulp) or soybean hulls, may also be used as raw materials. Furthermore, the cellulose-based raw materials may be pre-treated with an appropriate concentration of alkali to facilitate the penetration of the oxidizing agent into the pulp.

[0037] Examples of hypochlorous acid or its salts used for the oxidation of cellulosic raw materials include hypochlorous acid water, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite. Among these, sodium hypochlorite is preferred due to its ease of handling.

[0038] One method for producing oxidized cellulose by oxidation of cellulosic raw materials is to mix the cellulosic raw materials with a reaction solution containing hypochlorous acid or a salt thereof. Water is preferred as the solvent in the reaction solution because it is easy to handle and less likely to cause side reactions. In oxidation, the amount of hypochlorous acid or its salt used is not particularly limited, but it is preferable to use hypochlorous acid or its salt with an effective chlorine concentration of 6% by mass or more and 43% by mass or less. By using hypochlorous acid or its salt with an effective chlorine concentration of 6% by mass or more and 43% by mass or less, the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased, finer pulverization can proceed sufficiently, and the mechanical defibrillation treatment after the oxidation reaction can be omitted. Furthermore, the effective chlorine concentration of hypochlorous acid or its salt in the reaction solution (reaction system) is preferably in the range of 6 to 43% by mass.

[0039] From the viewpoint of ensuring a sufficiently high amount of carboxyl groups in oxidized cellulose, the effective chlorine concentration of the reaction solution is more preferably 14% by mass or more, even more preferably 18% by mass or more, and even more preferably 20% by mass or more. Furthermore, from the viewpoint of suppressing excessive decomposition of cellulose during defibration, the effective chlorine concentration of the reaction solution is more preferably 40% by mass or less, and even more preferably 38% by mass or less. The range of the effective chlorine concentration of the reaction solution can be appropriately combined from the lower and upper limits described above. The range of the effective chlorine concentration is more preferably 16 to 43% by mass, and even more preferably 18 to 40% by mass.

[0040] From the viewpoint of reducing the cost of producing oxidized cellulose and improving productivity by making hypochlorous acid or its salts easier to obtain and handle, it is preferable to keep the effective chlorine concentration low. From this viewpoint, the upper limit of the effective chlorine concentration is preferably less than 14% by mass, more preferably 13% by mass or less, even more preferably 12% by mass or less, and even more preferably 11% by mass or less. From the viewpoint of making the micronization of oxidized cellulose proceed more smoothly and improving productivity, the range of the effective chlorine concentration is preferably 6% by mass or more and less than 14% by mass, more preferably 7% by mass or more and less than 14% by mass, even more preferably 7% by mass or more and 13% by mass or less, and even more preferably 8% by mass or more and 13% by mass or less.

[0041] The effective chlorine concentration of hypochlorous acid or its salts is defined as follows. Hypochlorous acid is a weak acid that exists as an aqueous solution, and hypochlorites are compounds in which the hydrogen of hypochlorous acid is replaced by other cations. For example, sodium hypochlorite, which is a hypochlorite, exists in a solvent (preferably in an aqueous solution), so its concentration is measured as the amount of effective chlorine in the solution, not as the concentration of sodium hypochlorite. Here, regarding the effective chlorine of sodium hypochlorite, the oxidizing power of the divalent oxygen atoms produced by the decomposition of sodium hypochlorite is equivalent to two atomic equivalents of monovalent chlorine. Therefore, the bound chlorine atoms of sodium hypochlorite (NaClO) have the same oxidizing power as two unbound chlorine atoms (Cl2), and effective chlorine = 2 × (chlorine in NaClO). The specific measurement procedure is as follows: First, the sample is accurately weighed, water, potassium iodide, and acetic acid are added and left to stand, and the liberated iodine is titrated with sodium thiosulfate solution using starch aqueous solution as an indicator to measure the effective chlorine concentration.

[0042] The oxidation reaction of cellulosic raw materials with hypochlorous acid or its salt is preferably carried out while adjusting the pH within the range of 5.0 to 14.0. Within this range, the oxidation reaction of cellulosic raw materials can proceed sufficiently, and the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased. This makes it easy to defibrillate the oxidized cellulose. The pH of the reaction system is more preferably 7.0 or higher, even more preferably 8.0 or higher, even more preferably 8.5 or higher, even more preferably 9.0 or higher, and even more preferably 9.5 or higher. There is no particular upper limit to the pH of the reaction system, but it is preferably 14.5 or lower, more preferably 14.0 or lower, even more preferably 13.0 or lower, even more preferably 12.5 or lower, even more preferably 12.0 or lower, and even more preferably 11.5 or lower. The pH range of the reaction system is more preferably 7.0 to 14.0, even more preferably 8.0 to 13.5, and even more preferably 8.5 to 13.0.

[0043] During the reaction, the pH of the reaction system decreases as carboxyl groups are generated in the cellulosic raw materials due to the oxidation reaction. Therefore, from the viewpoint of efficiently carrying out the oxidation reaction, it is preferable to add an alkaline agent (e.g., sodium hydroxide) or an acid (e.g., hydrochloric acid) to the reaction system to adjust the pH of the reaction system while carrying out the oxidation reaction.

[0044] The following will further explain the method for producing oxidized cellulose, using sodium hypochlorite as an example, where hypochlorous acid or its salt is used.

[0045] When oxidizing cellulosic raw materials using sodium hypochlorite, the reaction solution is preferably an aqueous sodium hypochlorite solution. Methods for adjusting the effective chlorine concentration of the aqueous sodium hypochlorite solution to the desired concentration (for example, target concentration: in the range of 6% to 43% by mass) include concentrating an aqueous sodium hypochlorite solution with an effective chlorine concentration lower than the target concentration, diluting an aqueous sodium hypochlorite solution with an effective chlorine concentration higher than the target concentration, and dissolving sodium hypochlorite crystals (for example, sodium hypochlorite pentahydrate) in a solvent. Among these, adjusting the effective chlorine concentration as an oxidizing agent by diluting the aqueous sodium hypochlorite solution or dissolving sodium hypochlorite crystals in a solvent is preferred because it results in less self-decomposition (i.e., less decrease in effective chlorine concentration) and is simpler to adjust.

[0046] The method for mixing the cellulose-based raw material and the sodium hypochlorite aqueous solution is not particularly limited, but from the viewpoint of ease of operation, it is preferable to add the cellulose-based raw material to the sodium hypochlorite aqueous solution and mix them.

[0047] To efficiently carry out the oxidation reaction of the cellulosic raw material, it is preferable to stir the mixture of the cellulosic raw material and the sodium hypochlorite aqueous solution during the oxidation reaction. Examples of stirring methods include a stirrer with stirring blades, a homomixer, a disperser-type mixer, a homogenizer, and external circulation stirring. Of these, it is preferable to use one or more types of shear-type stirrers such as homomixers and homogenizers, a stirrer with stirring blades, and a disperser-type mixer, as these allow the oxidation reaction of the cellulosic raw material to proceed smoothly and make it easy to adjust the degree of polymerization of the oxidized cellulose to a predetermined value or less. The method of using a stirrer with stirring blades is particularly preferable. When using a stirrer with stirring blades, devices equipped with known stirring blades such as propeller blades, paddle blades, turbine blades, swept blades, anchor blades, gate blades, Maxblend blades, Fullzone blades, helical ribbon blades, and screw blades (with draft tubes, etc.) can be used as the stirrer. Furthermore, when using a stirrer with stirring blades, it is preferable to stir at a rotational speed of 50 to 300 rpm. In addition, multi-screw mixers such as single-screw mixers and twin-screw mixers can also be used.

[0048] The reaction temperature in the oxidation reaction is preferably 15°C to 100°C, and more preferably 20°C to 90°C. The reaction time for the oxidation reaction can be set according to the degree of oxidation, but it is preferably 15 minutes to 50 hours. If the pH of the reaction system is 10 or higher, it is preferable to set the reaction temperature to 30°C or higher and / or the reaction time to 30 minutes or higher.

[0049] The pressure used during the reaction is not particularly limited, but is usually in the range of atmospheric pressure or higher and 1.0 MPaG or lower (gauge pressure, the same applies hereafter). Here, atmospheric pressure is the pressure equal to atmospheric pressure. By performing oxidation under pressure, the amount of hypochlorous acid or its salt used can be reduced, and oxidized cellulose tends to be produced more efficiently. From the viewpoint of efficiency, the pressure is preferably 0.1 MPaG or more and 1.0 MPaG or less. At this time, the effective chlorine concentration of hypochlorous acid or its salt should be greater than 0% by mass and 43% by mass or less, and from the viewpoint of increasing efficiency, it is preferably 0.1% by mass or more and 20% by mass or less, more preferably 1.0% by mass or more and 15% by mass or less, and even more preferably 1.0% by mass or more and 10% by mass or less.

[0050] In the production of oxidized cellulose, after oxidizing the cellulosic raw material, a treatment may be performed to stop the oxidation reaction. The treatment to stop the oxidation reaction is not particularly limited, but examples include adding an acid or a metal catalyst. Alternatively, a method of reducing hypochlorous acid or its salt is preferred. Specifically, a method of stopping the oxidation reaction includes adding a reducing agent such as sodium sulfite. The amount of reducing agent added should be appropriately adjusted according to the amount of hypochlorous acid or its salt (effective chlorine concentration).

[0051] By using the solution containing oxidized cellulose obtained by the above reaction, known isolation treatments such as centrifugation and filtration can be performed, and further purification may be necessary to obtain oxidized cellulose as an oxide of the cellulosic raw material with hypochlorous acid or its salt. In the isolation treatment, the pH of the solution containing oxidized cellulose may be adjusted to 4 or less to convert some or all of the carboxyl groups in the oxidized cellulose to the H-type (-COOH). Alternatively, the solution containing oxidized cellulose obtained by the above reaction may be used as is and may be subjected to the following defibration step, for example.

[0052] (Reduction process) The cellulose fibers after the above oxidation treatment may be reduced with a reducing agent as needed. This reduces at least some of the aldehyde and ketone groups back to hydroxyl groups. The carboxyl groups are not reduced. The total content of carbonyl groups (aldehyde and ketone groups) in the oxidized cellulose obtained by this reduction, as calculated by the semicarbazide method described later, is not particularly limited and may be 0.3 mmol / g or less, or 0.1 mmol / g or less.

[0053] The total content of carbonyl groups (aldehyde and ketone groups) using the semicarbazide method is measured, for example, as follows: First, 50 ml of a 3 g / l aqueous solution of semicarbazide hydrochloride, adjusted to pH=5 with phosphate buffer, is added to a dried sample, the container is sealed, and shaken for two days. Next, 10 ml of this solution is taken into a 100 ml beaker, 25 ml of 5 N sulfuric acid and 5 ml of 0.05 N potassium iodate aqueous solution are added, and the mixture is stirred for 10 minutes. Then, 10 ml of 5% potassium iodide aqueous solution is added, and the mixture is immediately titrated with 0.1 N sodium thiosulfate solution using an automatic titrator. From the titration volume, the amount of carbonyl groups in the sample can be determined according to the following formula. Note that semicarbazide reacts with aldehyde and ketone groups to form Schiff bases (imines), but does not react with carboxyl groups, so it is considered that only the amount of carbonyl groups can be quantified by the above measurement.

[0054] Common reducing agents can be used in the above reduction reaction, such as borates and sulfites. Using these reducing agents can prevent discoloration.

[0055] The above-mentioned borates are a general term for borates and boronic acid salts. In this invention, borates refer to salts composed of an anion derived from boric acid (B(OH)3) and a monovalent metal ion. In this invention, borates are salts represented as M3[BO3], M2[HBO3], M[H2BO3], M2[R-BO2], or M[R-BO2H] (where M is a monovalent metal ion and R is a monovalent hydrocarbon group). These borates may exist in the composition of this invention as a solid, ionized, or in a state reacted with the functional groups of nanocellulose.

[0056] Examples of the above-mentioned borates include sodium borate, lithium borate, potassium borate, rubidium borate, cesium borate, sodium boronate, potassium boronate, rubidium boronate, and cesium boronate. The amount of the above borates should be in the range of 1 to 30% by mass relative to the oven-dry mass of cellulose oxide.

[0057] The above-mentioned sulfites refer to sulfites (M2SO3: M is a monovalent cation), bisulfites (MHSO3: M is a monovalent cation), pyrosulfites (M2S2O5 or M'S2O5: M is a monovalent cation, M' is a divalent cation), hyposulfites (M2S2O4 or M'S2O4: M is a monovalent cation, M' is a divalent cation), or hydrates thereof. Examples of M include alkali metal ions and ammonium ions, and examples of M' include alkaline earth metal ions. Examples of sulfites include sodium bisulfite, potassium bisulfite, ammonium bisulfite, sodium sulfite, potassium sulfite, ammonium sulfite, sodium hyposulfite, potassium hyposulfite, calcium hyposulfite, sodium pyrosulfite, potassium pyrosulfite, magnesium pyrosulfite, and calcium pyrosulfite. The amount of the above-mentioned sulfites is preferably 0.1 to 15% by mass, more preferably 1 to 15% by mass, even more preferably 1.0 to 12% by mass, and still more preferably 3.0 to 10% by mass, relative to the oven-dry mass of oxidized cellulose.

[0058] The reduction treatment temperature should be around 10-90°C, considering the efficiency of the reduction treatment and the suppression of fiber deterioration. The pH during the reduction treatment should be adjusted as appropriate depending on the reducing agent used, and is usually within the range of pH 2-12. The reaction time in the reduction reaction can be set as appropriate according to the degree of reduction progress and is not particularly limited, but is usually within the range of 0.5-6 hours.

[0059] Oxidized cellulose is preferably in the form of a dispersion. This dispersion refers to a suspension containing oxidized cellulose. The dispersion may contain the solvent used during oxidation. Alternatively, a dispersion medium may be added as appropriate to form the dispersion. The dispersion of oxidized cellulose makes it easier to handle and facilitates micronization. In the present invention, when the oxidized cellulose is a dispersion, the amount of oxidized cellulose is usually in the range of 0.1% by mass or more and 95% by mass or less, preferably 1% by mass or more and 50% by mass or less, and more preferably 1% by mass or more and 30% by mass or less, when the total amount of the dispersion is 100% by mass.

[0060] Oxidized cellulose includes fibrous cellulose obtained by oxidizing cellulosic raw materials with hypochlorous acid or its salts. Oxidized cellulose is also called oxidized cellulose fiber. In other words, oxidized cellulose includes oxides of cellulosic raw materials due to hypochlorous acid or its salts. The main component of plants is cellulose, and bundles of cellulose molecules are called cellulose microfibrils. Cellulose in cellulosic raw materials is also contained in the form of cellulose microfibrils.

[0061] (Process B: Fiber removal treatment) Nanocellulose can be obtained by defibrating the oxidized cellulose obtained above and then nano-fibrillating it as needed. Methods for defibrating oxidized cellulose include methods using weak stirring with a magnetic stirrer, and mechanical defibration.

[0062] Examples of mechanical defibration methods include methods using various mixing and stirring devices such as screw mixers, paddle mixers, disperser mixers, turbine mixers, homomixers under high-speed rotation, high-pressure homogenizers, ultra-high-pressure homogenizers, double-cylinder homogenizers, ultrasonic homogenizers, water flow opposing impact type dispersers, beaters, disc type refiners, conical type refiners, double-disc type refiners, grinders, single-screw or multi-screw kneaders, rotational and revolving stirrers, and vibrating stirrers. By using these devices individually or in combination of two or more types, and preferably treating oxidized cellulose in a dispersion medium, oxidized cellulose can be nano-sized to produce nanocellulose.

[0063] For defibration of oxidized cellulose, a method using an ultra-high pressure homogenizer is preferable because it can produce nanocellulose with more advanced defibration. When applying defibration treatment with an ultra-high pressure homogenizer, the pressure during defibration treatment is preferably 100 MPa or higher, more preferably 120 MPa or higher, and even more preferably 150 MPa or higher. The number of defibration treatments is not particularly limited, but from the viewpoint of sufficiently advancing defibration, it is preferably 2 or more times, more preferably 3 or more times. Furthermore, the above-mentioned oxidized cellulose can also be sufficiently defibrated by mild stirring using a rotational agitator or a vibrating agitator. An example of a vibrating agitator is a vortex mixer (touch mixer). In other words, with the above-mentioned oxidized cellulose, homogenized nanocellulose can be obtained even when defibration treatment is carried out under mild defibration conditions.

[0064] The defibration treatment is preferably carried out with the oxidized cellulose mixed with a dispersion medium. There are no particular restrictions on the dispersion medium, and it can be appropriately selected depending on the purpose. Specific examples of dispersion media include water, alcohols, ethers, ketones, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. One of these may be used alone as the solvent, or two or more may be used in combination.

[0065] Examples of alcohols among the above dispersion media include methanol, ethanol, isopropanol, isobutanol, sec-butyl alcohol, tert-butyl alcohol, methyl cellosolve, ethylene glycol, and glycerin. Examples of ethers include ethylene glycol dimethyl ether, 1,4-dioxane, and tetrahydrofuran. Examples of ketones include acetone and methyl ethyl ketone.

[0066] In the present invention, the nanocellulose preferably satisfies the following zeta potential and light transmittance.

[0067] (Zeta potential) In this invention, the zeta potential of nanocellulose is preferably -30mV or less. When the zeta potential is -30mV or less (i.e., the absolute value is 30mV or more), sufficient repulsion between microfibrils is obtained, making it easier to generate nanocellulose with a high surface charge density during mechanical defibrillation. This improves the dispersion stability of nanocellulose, resulting in a slurry with excellent viscosity stability and handling properties. There is no particular upper limit to the zeta potential, but it is usually sufficient if it is -100mV or less. When the zeta potential is -100mV or higher (i.e., the absolute value is 100mV or lower), oxidative severance in the fiber direction associated with oxidation tends to be suppressed, allowing for the acquisition of nanocellulose of uniform size. This results in stable and highly dispersible nanocellulose in water, and the resulting aqueous ink composition contains nanocellulose uniformly.

[0068] From the above viewpoint, the zeta potential of nanocellulose is preferably -35mV or less, more preferably -40mV or less, and even more preferably -50mV or less. Furthermore, the lower limit of the zeta potential is preferably -90mV or more, more preferably -85mV or more, even more preferably -80mV or more, even more preferably -77mV or more, even more preferably -70mV or more, and even more preferably -65mV or more. The range of the zeta potential can be appropriately combined from the lower and upper limits described above. The zeta potential is preferably -90mV or more and -30mV or less, more preferably -85mV or more and -30mV or less, even more preferably -80mV or more and -30mV or less, even more preferably -77mV or more and -30mV or less, even more preferably -70mV or more and -30mV or less, even more preferably -65mV or more and -30mV or less, and even more preferably -65mV or more and -35mV or less. In this specification, the zeta potential is the value measured for a cellulose aqueous dispersion prepared by mixing nanocellulose and water to a nanocellulose concentration of 0.1% by mass, under conditions of pH 8.0 and 20°C. Specifically, it can be measured according to the conditions described below. [Zeta potential measurement] A dispersion containing nanocellulose is diluted with pure water to a nanocellulose concentration of 0.1%. A 0.05 mol / L sodium hydroxide aqueous solution is added to the diluted nanocellulose aqueous dispersion to adjust the pH to 8.0, and the zeta potential is measured at 20°C using an Otsuka Electronics zeta potential meter (ELSZ-1000).

[0069] (light transmittance) The nanocellulose dispersion in which nanocellulose is dispersed in a dispersion medium according to the present invention exhibits high light transmittance due to reduced light scattering from cellulose fibers. Specifically, it is preferable that the nanocellulose in the present invention has a light transmittance of 95% or more in a mixture obtained by mixing with water to a solid content concentration of 0.1% by mass. More preferably, this light transmittance is 96% or more, even more preferably 97% or more, and even more preferably 99% or more. The light transmittance is the value at a wavelength of 660 nm measured by a spectrophotometer. Furthermore, the light transmittance can be measured using an aqueous dispersion containing nanocellulose. Specifically, measurements can be taken according to the conditions described in the examples below.

[0070] Zeta potential and light transmittance can be controlled by oxidation using hypochlorous acid or its salts, and in particular by adjusting the reaction time, reaction temperature, stirring conditions, etc. of the oxidation reaction. Specifically, as the reaction time is increased and / or the reaction temperature is increased, oxidation of the cellulose microfibrils on the surface of the cellulosic raw material progresses, and the average fiber width tends to decrease due to increased repulsion between fibrils caused by electrostatic repulsion and osmotic pressure. Furthermore, the zeta potential tends to be increased by setting one or more of the oxidation reaction time, reaction temperature, and stirring conditions to the side that promotes oxidation further (i.e., the side that increases the degree of oxidation) (for example, by increasing the reaction time).

[0071] As described above, the nanocellulose in the present invention is obtained by obtaining oxidized cellulose using hypochlorous acid or a salt thereof, and then dissolving it. In this invention, the degree of polymerization of the cellulose oxide used is preferably 600 or less. If the degree of polymerization of the cellulose oxide exceeds 600, it tends to require a large amount of energy for defibration, making it difficult to achieve sufficient defibration properties, which tends to lead to a decrease in pigment dispersibility and, consequently, a decrease in optical density. Furthermore, if the degree of polymerization of the cellulose oxide exceeds 600, there will be a large amount of cellulose oxide that has not been sufficiently defibrated, and when this is dispersed as finely milled nanocellulose in a dispersion medium, light scattering and other effects will increase, which may reduce transparency. In addition, there will be variations in the size of the resulting nanocellulose, which tends to result in non-uniform quality. As a result, the viscosity of the ink composition containing nanocellulose will increase, and the ejection stability in inkjet printing may decrease. From the viewpoint of easy defibration, there is no particular lower limit set for the degree of polymerization of the cellulose oxide. However, if the degree of polymerization of the cellulose oxide is less than 50, the proportion of particulate cellulose rather than fibrous cellulose will increase, which may reduce the scratch resistance of the resulting coating film. From the above viewpoint, the degree of polymerization of the cellulose oxide is preferably in the range of 50 to 600.

[0072] The degree of polymerization of oxidized cellulose is more preferably 580 or less, even more preferably 560 or less, even more preferably 550 or less, even more preferably 500 or less, even more preferably 450 or less, and even more preferably 400 or less. Regarding the lower limit of the degree of polymerization, from the viewpoint of improving the viscosity stability and coating properties of the slurry, it is more preferably 60 or more, even more preferably 70 or more, even more preferably 80 or more, even more preferably 90 or more, even more preferably 100 or more, even more preferably 110 or more, and particularly preferably 120 or more. The preferred range for the degree of polymerization can be determined by appropriately combining the upper and lower limits described above. The degree of polymerization of chemically modified cellulose is more preferably 60 to 600, even more preferably 70 to 600, even more preferably 80 to 600, even more preferably 80 to 550, even more preferably 80 to 500, even more preferably 80 to 450, and particularly preferably 80 to 400.

[0073] The degree of polymerization of oxidized cellulose can be adjusted by changing the reaction time, reaction temperature, pH, and the effective chlorine concentration of hypochlorous acid or its salt during the oxidation reaction. Specifically, since increasing the degree of oxidation tends to decrease the degree of polymerization, methods to reduce the degree of polymerization include, for example, increasing the oxidation reaction time and / or reaction temperature. Alternatively, the degree of polymerization of oxidized cellulose can be adjusted by the stirring conditions of the reaction system during the oxidation reaction. For example, under conditions where the reaction system is sufficiently homogenized using a stirring blade or the like, the oxidation reaction proceeds smoothly and the degree of polymerization tends to decrease. On the other hand, under conditions where stirring of the reaction system is likely to be insufficient, such as stirring with a stirrer, the reaction tends to become non-uniform, making it difficult to sufficiently reduce the degree of polymerization of oxidized cellulose. Furthermore, the degree of polymerization of oxidized cellulose also tends to fluctuate depending on the selection of the raw material cellulose. For this reason, the degree of polymerization of oxidized cellulose can also be adjusted by selecting the cellulosic raw material. In this specification, the degree of polymerization of oxidized cellulose is the average degree of polymerization (viscosity-average degree of polymerization) measured by the viscosity method. Details are described in the examples below.

[0074] <Solvent> The aqueous ink composition of the present invention comprises a water-soluble solvent and / or an aqueous medium such as water as a solvent. These may be water alone or a mixed solvent consisting of water and a water-soluble solvent. Examples of water-soluble solvents include ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; alcohols such as methanol, ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and 1,2-dimethoxyethane; and amides such as 2-pyrrolidone, dimethylformamide, and N-methylpyrrolidone. These may be used individually or in combination of two or more. Among these, ketones with 3 to 6 carbon atoms and alcohols with 1 to 5 carbon atoms are preferred. In addition to the water-soluble solvents mentioned above, other materials such as glycols including ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; diols including butanediol, pentanediol, hexanediol, and other diols of the same group; glycol esters such as propylene glycol laurate; glycol ethers such as cellosolve containing diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl ethers, propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether; sulfolanes; lactones such as γ-butyrolactone; lactams such as N-(2-hydroxyethyl)pyrrolidone; glycerin and its derivatives, polyoxyethylene benzyl alcohol ether, etc., can also be used. Among these, polyhydric alcohols such as glycols and diols with high boiling points, low volatility, and high surface tension are preferred, and glycols such as diethylene glycol and triethylene glycol are more preferred. These water-soluble organic solvents can be used individually or in combination of two or more.

[0075] <Pigments> The ink composition of the present invention contains at least one pigment selected from known and conventional organic or inorganic pigments. Furthermore, the pigment in the present invention can be either an untreated pigment or a treated pigment. The treated pigments include so-called self-dispersing pigments. Self-dispersing pigments are produced, for example, by physically or chemically treating the pigment to bond (graft) hydrophilic groups onto the surface of the pigment.

[0076] In printing on plain paper, yellow ink, cyan ink, magenta ink, black ink, etc., are used individually or in combination as an ink set. The pigments used are not particularly limited, and those commonly used for water-based inks can be used. Specifically, known inorganic and organic pigments that are dispersible in water or water-soluble organic solvents can be used. Examples of inorganic pigments include iron oxide and carbon black produced by known methods such as the contact method, furnace method, and thermal method. Examples of organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinoflarone pigments, etc.), dye chelates (e.g., basic dye type chelates, acid dye type chelates, etc.), nitro pigments, nitroso pigments, and aniline black.

[0077] Pigments used in black ink include, for example, carbon black such as Mitsubishi Chemical's No. 2300, No. 2200B, No. 900, No. 960, No. 980, No. 33, No. 40, No. 45, No. 45L, No. 52, HCF88, MA7, MA8, MA100, etc.; Columbia's Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc.; Cabot's Regal 400R, Regal 330R, Regal 660R, Mogul L, Mogul 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc.; and Degussa's Color Black. Examples include FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex 35, U, V, 1400U, Special Black 6, 5, 4, 4A, NIPEX150, NIPEX160, NIPEX170, NIPEX180, etc.

[0078] Examples of pigments used in yellow ink include CI Pigment Yellow 1, 2, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 174, 180, and 185.

[0079] Examples of pigments used in magenta ink include CI Pigment Red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1, 112, 122, 123, 146, 168, 176, 184, 185, 202, and 209.

[0080] Examples of pigments used in cyan ink include CI Pigment Blue 1, 2, 3, 15, 15:3, 15:4, 16, 22, 60, 63, and 66.

[0081] The self-dispersing pigments mentioned above may be commercially available products, for example. Examples of commercially available products include "CAB-O-JET200", "CAB-O-JET250C", "CAB-O-JET260M", "CAB-O-JET270Y", "CAB-O-JET300", "CAB-O-JET400", "CAB-O-JET450C", "CAB-O-JET465M", and "CAB-O-JET470Y" from Cabot Specialty Chemicals; "BONJET BLACK CW-2" and "BONJET BLACK CW-3" from Orient Chemical Industries, Ltd.; and "LIOJET WD BLACK 002C" from Toyo Ink Manufacturing Co., Ltd. In addition, commercially available pigment dispersions, in which self-dispersing pigments are dispersed in an aqueous medium, can also be used. Examples include "SENSIJJET Black SDP100," "SENSIJJET Black SDP1000," "SENSIJJET Black SDP2000," "Sensijet Ultra Yellow PY74," "Sensijet Ultra Magenta PR122," "Sensijet Ultra Cyan PB15:4," and "Sensijet Ultra K" from Sensient Colors, Inc. These self-dispersing pigments may be used individually or in combination of multiple types.

[0082] For water-based inks, especially those intended for inkjet printing, the pigment content (by mass) should be within the range of 0.5 to 30% of the total water-based ink volume. Furthermore, the particle size of the pigment is preferably 1 μm or less, more preferably the pigment consists of particles of 10 nm to 150 nm, and even more preferably the pigment consists of particles of 50 nm to 120 nm.

[0083] The nanocellulose content used in this invention is preferably in the range of 1 / 100 to 50 / 100 by mass, more preferably in the range of 1 / 100 to 30 / 100, and even more preferably in the range of 3 / 100 to 30 / 100, when used as an aqueous ink. Within this range, the resulting image tends to exhibit good color development and scratch resistance without compromising suitability for various printing methods.

[0084] When an aqueous ink composition is intended for inkjet printing, the nanocellulose content is preferably in the range of 0.001 to 3% by mass, more preferably 0.01 to 2% by mass, and even more preferably 0.1 to 1.8% by mass, relative to the total mass of the ink composition. A content of 0.001% or more makes it easier to ensure optical density and abrasion resistance, while a content of 3% or less tends to suppress the increase in ink viscosity and improve printability.

[0085] <Dispersant> The ink composition of the present invention contains at least the nanocellulose described above, but may also contain other dispersants. Suitable dispersants include anionic group-containing organic polymer compounds. While these anionic group-containing organic polymer compounds are primarily used to disperse pigments, they also function as binders due to their polymeric properties. The inclusion of a binder component further enhances the functionality of the coating film obtained from the ink composition, such as its robustness, adhesion, and optical density. Known anionic group-containing organic polymer compounds can be used. For detailed embodiments of anionic group-containing organic polymer compounds, please refer to International Publication No. 2015 / 166808.

[0086] Examples of anionic group-containing organic polymer compounds include organic polymer compounds containing carboxyl groups, sulfonic acid groups, or phosphate groups. Examples of such anionic group-containing organic polymer compounds include polyvinyl resins having anionic groups, polyester resins having anionic groups, amino resins having anionic groups, acrylic resins having anionic groups, epoxy resins having anionic groups, polyurethane resins having anionic groups, polyether resins having anionic groups, polyamide resins having anionic groups, unsaturated polyester resins having anionic groups, phenolic resins having anionic groups, silicone resins having anionic groups, fluorine polymer compounds having anionic groups, and polysaccharide derivatives having anionic groups. Furthermore, acrylic resins and polyurethane resins having anionic groups are preferred because they are readily available as raw materials, easy to design, and have excellent pigment dispersion properties. The anionic group-containing organic polymer compounds used in this invention can be used individually or in mixtures of two or more types. Combining two or more types may allow for a balance of various properties of the aqueous ink.

[0087] (Acrylic resin having anionic groups) Acrylic resins having anionic groups specifically include resins composed of copolymers of monomers having anionic groups, such as (meth)acrylic acid, and other anionic group-containing organic polymer compounds copolymerizable therewith. In this invention, (meth)acrylic acid refers to both acrylic acid and methacrylic acid. The same interpretation applies to various esters of (meth)acrylic acid.

[0088] As monomers of anionic group-containing organic polymer compounds, it is preferable to use alkylstyrenes such as styrene, α-methylstyrene, β-methylstyrene, 2,4-dimethylstyrene, α-ethylstyrene, α-butylstyrene, and α-hexylstyrene; halogenated styrenes such as 4-chlorostyrene, 3-chlorostyrene, and 3-bromostyrene; and styrene monomers such as 3-nitrostyrene, 4-methoxystyrene, and vinyltoluene; as well as (meth)acrylic acid ester monomers having a benzene ring, such as benzyl (meth)acrylate, phenyl (meth)acrylate, phenylethyl (meth)acrylate, phenylpropyl (meth)acrylate, and phenoxyethyl (meth)acrylate. Among these, it is particularly preferable to use styrene monomers such as styrene, α-methylstyrene, and tert-butylstyrene.

[0089] The copolymer of the acrylic resin having anionic groups in the present invention preferably contains (meth)acrylic acid as a polymerization unit and other copolymerizable polymerization units as essential polymerization units, and may be a binary copolymer thereof or a ternary or more polypolymer with further copolymerizable polymerization units.

[0090] Monomers of anionic group-containing organic polymer compounds include acrylic acid esters and methacrylic acid esters such as methyl acrylate, methyl methacrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, tert-butyl acrylate, 2-ethylbutyl acrylate, 1,3-dimethylbutyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, ethyl methacrylate, n-butyl methacrylate, 2-methylbutyl methacrylate, pentyl methacrylate, heptyl methacrylate, nonyl methacrylate, etc.; 3-ethoxypropyl acrylate, 3-ethoxybutyl acrylate, dimethylaminoethyl acrylate, 2-hydroxyethyl acrylate, Examples include acrylic acid ester derivatives and methacrylic acid ester derivatives such as 2-hydroxybutyl acrylate, ethyl-α-(hydroxymethyl) acrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate; aryl acrylates and aralkyl acrylates such as phenyl acrylate, benzyl acrylate, phenylethyl acrylate, and phenylethyl methacrylate; monoacrylic acid esters or monomethacrylic acid esters of polyhydric alcohols such as diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, and bisphenol A; dialkyl maleate esters such as dimethyl maleate and diethyl maleate, and vinyl acetate. One or more of these monomers can be used.

[0091] The copolymer of an acrylic resin having anionic groups used in the present invention may be a linear copolymer consisting only of polymerization units of a monoanionic group-containing organic polymer compound, or it may be a copolymer containing a portion that is partially crosslinked by copolymerizing a very small amount of various crosslinkable anionic group-containing organic polymer compounds.

[0092] Examples of monomers of anionic group-containing organic polymer compounds having such crosslinking properties include poly(meth)acrylates of polyhydric alcohols such as glycidyl(meth)acrylate, divinylbenzene, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, poly(oxyethyleneoxypropylene) glycol di(meth)acrylate, and tri(meth)acrylate of alkylene oxide adducts of glycerin.

[0093] In this invention, the reaction rates of each monomer used are assumed to be substantially the same, and the proportion of each monomer used is considered to be the mass-converted content of each monomer's polymerization units. The copolymer of acrylic resin having anionic groups in this invention can be synthesized by various known reaction methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In this case, known and conventional polymerization initiators, chain transfer agents (polymerization degree adjusters), surfactants, and defoaming agents can also be used in combination.

[0094] In the present invention, the weight-average molecular weight of the acrylic resin having anionic groups is preferably in the range of 5,000 to 20,000. For example, when using the styrene-acrylic acid copolymer, its weight-average molecular weight is preferably in the range of 5,000 to 20,000, and more preferably in the range of 5,000 to 18,000. In particular, it is especially preferable that it be in the range of 5,500 to 15,000. Here, the weight-average molecular weight is a value measured by GPC (gel permeation chromatography) and is a value converted to the molecular weight of polystyrene used as a standard substance.

[0095] When the anionic group-containing organic polymer compound used in the present invention is a styrene-acrylic acid copolymer, it has carboxyl groups derived from acrylic acid monomer and methacrylic acid monomer, and its acid value is preferably 50 to 220 (mgKOH / g), and more preferably 60 to 200 (mgKOH / g). When the acid value is 220 (mgKOH / g) or less, pigment aggregation tends to occur less easily. The acid value used herein is a value measured according to the Japanese Industrial Standard "K0070:1992. Test methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemical products," and is the amount of potassium hydroxide (mg) required to completely neutralize 1 g of resin.

[0096] (Polyurethane resin having anionic groups) The polyurethane resin having anionic groups used in the present invention specifically includes urethane resins obtained by reacting a polyol having anionic groups such as carboxyl groups or sulfonic acid groups with a polyisocyanate, and, if necessary, a general-purpose polyol without anionic groups or a chain extender.

[0097] Examples of polyols having a carboxyl group used in the present invention include esters obtained by the reaction of a polyhydric alcohol with a polybasic acid anhydride, and dihydroxyalkanoic acids such as 2,2-dimethylol lactic acid, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, and 2,2-dimethylolvaleric acid. Preferred compounds include 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid. Furthermore, examples of polyols having sulfonic acid groups include polyester polyols obtained by reacting dicarboxylic acids such as 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfophthalic acid, and 5[4-sulfophenoxy]isophthalic acid, and their salts, with the low molecular weight polyols.

[0098] Examples of diisocyanates used in the present invention include aliphatic diisocyanate compounds such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; alicyclic diisocyanate compounds such as isophorone diisocyanate, hydrogenated xylylene diisocyanate, and 4,4-cyclohexylmethane diisocyanate; aromatic aliphatic diisocyanate compounds such as xylylene diisocyanate and tetramethylxylylene diisocyanate; and aromatic diisocyanates such as toluene diisocyanate and phenylmethane diisocyanate.

[0099] Furthermore, examples of polyols that do not have a general anionic group include polyester polyols, polyether polyols, polyhydroxy polycarbonates, polyhydroxy polyacetals, polyhydroxy polyacrylates, polyhydroxy polyester amides, and polyhydroxy polythioethers. Among these, polyester polyols, polyether polyols, and polyhydroxy polycarbonates are preferred. These polyols may be reacted individually or in mixtures. In addition to the polyols mentioned above, low molecular weight diols may be used in combination as appropriate for purposes such as adjusting the hardness of the coating on printed materials. Examples include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol.

[0100] The chain extension agent used in the present invention may be one or more diols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol, 1,4-bis(β-hydroxyethoxy)benzene, 1,4-cyclohexanediol, xylylene glycol, or one or more diamines such as ethylenediamine, propylenediamine, xylylenediamine, isophoronediamine, 4,4'-diaminodiphenylmethane, tolylenediamine, and 4,4'-diaminodicyclohexylmethane.

[0101] The polyurethane resin can be produced by, for example, reacting the polyol and the polyisocyanate in the absence of a solvent or in the presence of an organic solvent. Then, the urethane resin having anionic groups formed by neutralization with a basic compound, etc., as described later, can be mixed into an aqueous medium and reacted with a chain extender as needed.

[0102] The reaction between the polyol and the polyisocyanate is preferably carried out in a range of 0.8 to 2.5 for the equivalent ratio of isocyanate groups in the polyisocyanate to hydroxyl groups in the polyol, and more preferably in a range of 0.9 to 1.5.

[0103] In the present invention, the weight-average molecular weight of the polyurethane resin having anionic groups is preferably in the range of 5,000 to 500,000, more preferably in the range of 10,000 to 200,000, and particularly preferably in the range of 15,000 to 100,000. Here, the weight-average molecular weight is a value measured by GPC (gel permeation chromatography) and is a value converted to the molecular weight of polystyrene used as a standard substance.

[0104] Furthermore, it is preferable to use a polyurethane resin having an acid value in the range of 2 to 200 (mgKOH / g), and a range of 2 to 100 (mgKOH / g) is preferable for improving the good water dispersion stability of the polyurethane resin.

[0105] (Neutralizing agent for acrylic resins having anionic groups and polyurethane resins having anionic groups) In the present invention, it is preferable to neutralize the acrylic resin having anionic groups and the polyurethane resin having anionic groups with a basic compound before use. Known basic compounds can be used, such as alkali metal hydroxides such as potassium and sodium; alkali metal carbonates such as potassium and sodium; alkaline earth metal carbonates such as calcium and barium; inorganic basic compounds such as ammonium hydroxide, and amine or quaternary ammonium salt compounds used when modifying nanocellulose. Among these, alkali metal hydroxides, represented by potassium hydroxide, sodium hydroxide, and lithium hydroxide, contribute to lowering the viscosity of aqueous pigment dispersions and are preferred in terms of ejection stability when used as aqueous inkjet recording inks, with potassium hydroxide being particularly preferred. Furthermore, using the same basic compound as that used to modify nanocellulose may improve storage stability.

[0106] (Polysaccharide derivatives having anionic groups) The ink composition of the present invention may contain a polysaccharide derivative having an anionic group. The polysaccharide derivative having an anionic group is not particularly limited as long as it is a polyanionic polysaccharide. Specifically, examples include natural polysaccharides such as hyaluronic acid, alginic acid, pectin, and polygalacturonic acid; carboxyalkyl polysaccharides such as carboxymethyl pullulan, carboxymethyl chitin, carboxymethyl chitosan, carboxymethyl mannan, carboxymethyl starch, carboxymethyl dextran, carboxymethyl cellulose, carboxyethyl cellulose, and carboxymethyl pullulan; oxidized polysaccharides such as oxidized cellulose and oxidized starch; and polysaccharides containing sulfate groups such as chondroitin sulfate, dermatan sulfate, heparin, and heparan sulfate. Among these, carboxymethyl cellulose and hyaluronic acid are preferred, and carboxymethyl cellulose is particularly preferred. The weight-average molecular weight of the raw material polysaccharide is not particularly limited, but is usually in the range of 50,000 to 1,000,000, or it may be in the range of 50,000 to 500,000.

[0107] In the present invention, polysaccharide derivatives having anionic groups are preferably those that form a salt with a cation. While there are no particular limitations on the cations that form a salt with the polysaccharide derivative having anionic groups, examples include protons, metal ions (specifically, metal ions such as sodium, potassium, lithium, calcium, and magnesium), and organic cations such as organic ammonium compounds. Among these, sodium carboxymethylcellulose salt and ammonium carboxymethylcellulose salt are preferred because they are readily available and easily produce the desired effect, with ammonium carboxymethylcellulose salt being particularly preferred due to its significant viscosity-reducing effect. These polysaccharide derivatives having anionic groups can be used individually or in combination of two or more.

[0108] The degree of etherification (also called the degree of substitution (DS)) and neutralization of polysaccharide derivatives having anionic groups used in the present invention, particularly sodium salts and ammonium salts of carboxymethylcellulose, are not particularly limited. However, the viscosity of a 1% by mass aqueous solution measured by a B-type viscometer at a rotor speed of 60 rpm and 25°C should generally be in the range of 300 to 7000 mPa·s, and may also be in the range of 500 to 5000 mPa·s. Here, "degree of etherification" is a numerical value that represents the average number of hydroxyl groups to which the carboxymethyl group is ether-bonded, out of the three hydroxyl groups contained in anhydrous glucose, which is a constituent unit of cellulose, in carboxymethylcellulose. Therefore, theoretically, its value is between 0 and 3.

[0109] The amount of polysaccharide derivative having anionic groups is not particularly limited and is added in an appropriate amount depending on the purpose described above. For example, if the purpose is to improve the color development (optical density) or scratch resistance of the formed image, the amount of parts by mass of the polysaccharide derivative having anionic groups per part by mass of nanocellulose may be 5 or less, 3 or less, or 2 or less.

[0110] Sodium carboxymethylcellulose and ammonium carboxymethylcellulose can be commercially available. For example, the Celogen series sold by Daiichi Kogyo Seiyaku Co., Ltd., the CMC Daicel series sold by Daicel Finechem Co., Ltd., and the Sunrose F series sold by Nippon Paper Chemical Co., Ltd. can be used. As for ammonium carboxymethylcellulose, the DN series sold by Daicel Finechem Co., Ltd. can be mentioned.

[0111] The content (by mass) of the anionic group-containing organic polymer compound used in the present invention is preferably in the range of 0.1 to 10% by mass, more preferably 0.3 to 5%, and even more preferably 0.5 to 2%, relative to the total mass of the ink in an aqueous pigment dispersion, especially for inkjet applications. A content of 0.1% or more makes it easier to ensure abrasion resistance, while a content of 10% or less tends to suppress the increase in ink viscosity and improve printability.

[0112] Furthermore, commercially available organic polymer compounds containing anionic groups can, of course, be used. Examples of commercially available products include the Azisper PB series from Ajinomoto Fine Techno Co., Ltd., the DISPERBYK series and BYK- series from BYK, and the Efka series from BASF.

[0113] <Other ingredients> The aqueous ink composition of the present invention may be diluted with a water-soluble solvent at any time as needed, or may contain wetting agents (drying inhibitors), penetrating agents, surfactants, and other additives, so-called known and conventional additives. With such additions, it can be used in a variety of applications, such as in the automotive and building materials coatings, in the printing ink fields such as offset inks, gravure inks, flexographic inks, and silkscreen inks, or in the inkjet recording ink fields. After the ink is prepared, a centrifugation or filtration process may be added to remove coarse particles.

[0114] (Humectant) A wetting agent is added to prevent the ink from drying out. The wetting agent content in the ink for this purpose is preferably 3 to 50% by mass. The wetting agent used in the present invention is not particularly limited, but examples include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol with a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, mesoerythritol, pentaerythritol, etc. Among these, the inclusion of propylene glycol and 1,3-butyl glycol provides safety and exhibits excellent ink drying and ejection performance in inkjet recording applications.

[0115] (Penetrating agent) Penetrating agents are added to improve penetration into the recording medium and to adjust the dot size on the recording medium. Examples of penetrating agents include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.

[0116] (Surfactants) Surfactants are added to adjust ink properties such as surface tension. The surfactants that can be added for this purpose are not particularly limited and include various anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, among which anionic surfactants and nonionic surfactants are preferred.

[0117] Examples of anionic surfactants include alkylbenzene sulfonates, alkylphenyl sulfonates, alkylnaphthalene sulfonates, higher fatty acid salts, sulfate salts of higher fatty acid esters, sulfonates of higher fatty acid esters, sulfate salts and sulfonates of higher alcohol ethers, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, and polyoxyethylene alkyl ether phosphates. Specific examples of these include dodecylbenzene sulfonate, isopropylnaphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenyl sulfonate, and dibutylphenylphenol disulfonate.

[0118] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, fatty acid alkylolamides, alkyl alkanolamides, acetylene glycols, oxyethylene adducts of acetylene glycols, polyethylene glycol polypropylene glycol block copolymers, etc. Among these, polyoxyethylene nonylphenyl ethers, polyoxyethylene octylphenyl ethers, polyoxyethylene dodecylphenyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid alkylolamides, acetylene glycols, oxyethylene adducts of acetylene glycols, and polyethylene glycol polypropylene glycol block copolymers are preferred.

[0119] Other surfactants that can be used include silicone-based surfactants such as polysiloxane oxyethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers; and biosurfactants such as spicrispolic acid, rhamnolipid, and lysolecithin.

[0120] These surfactants can be used individually or in combination of two or more. When adding surfactants, the amount added is arbitrary, but it is usually sufficient if it is in the range of 0.001 to 2% by mass relative to the total mass of the ink.

[0121] Furthermore, if necessary, other additives such as preservatives, viscosity modifiers, pH adjusters, chelating agents, plasticizers, antioxidants, and UV absorbers may be added.

[0122] (Recording material) The aqueous ink composition of the present invention exhibits high optical density and abrasion resistance, particularly on plain paper. It can also be used on other absorbent recording materials. Examples of recording materials include, but are not limited to, plain paper, (lightly)coated paper, fabric, inkjet-specific paper, inkjet glossy paper, cardboard, and wood.

[0123] [Recording method] The recording method of the present invention includes the step of ejecting the above-mentioned aqueous ink composition onto a recording member by an inkjet method. The details of the inkjet method are not particularly limited, and any known method may be used.

[0124] [Method for manufacturing aqueous ink composition] The method for producing the aqueous ink composition of the present invention can be obtained by known methods without particular limitations. The addition of nanocellulose and the like can be done at any time, before or after the medialess dispersion described later. Furthermore, in the production of the ink composition of the present invention, not only nanocellulose but also oxidized cellulose before nano-processing can be used. For example, (1) a method of preparing an aqueous pigment dispersion comprising at least the pigment of the present invention and nanocerose, etc., by medialess dispersion with the addition of other additives as needed; (2) a method of preparing a high-concentration aqueous dispersion of pigment (pigment paste) in advance, and then diluting it with an aqueous medium while simultaneously adding nanocerose, etc., and other additives as needed.

[0125] (1) Media-less dispersion of aqueous pigment dispersion In this specification, (1) media-less dispersion specifically refers to dispersion methods such as ultrasonic dispersion, high-speed disk impeller, colloid mill, roll mill, high-pressure homogenizer, nanomizer, ultimateizer, etc. However, ultrasonic dispersion is preferred when considering productivity and contamination (inclusion or contamination of foreign matter) due to media wear. In the present invention, the following will be described in detail using an example of ultrasonic dispersion.

[0126] Prior to ultrasonic dispersion, the pigment and aqueous medium may be mixed and stirred as needed. The viscosity range at this stage should generally be between 0.1 and 100 mPa·s to ensure fluidity. The pigment concentration is not particularly limited, but can be between 1 and 30% by mass. The ultrasonic irradiation conditions are not particularly limited and can be performed at an output of 100 to 3000 W and a frequency of 15 to 40 kHz.

[0127] The duration of ultrasonic irradiation should be sufficient to ensure that the pigment particles, nanoceroses, etc., are substantially uniformly dispersed in the aqueous pigment dispersion. Typically, an electrical energy of 5 to 100 W / g is applied relative to the mass of pigment contained in the dispersion.

[0128] After ultrasonic irradiation of the aqueous pigment dispersion, further dispersion may be performed as needed. Alternatively, the dispersion and ultrasonic irradiation may be repeated. Various types of dispersion devices already known can be used in this dispersion process, and are not particularly limited. Examples include media dispersion devices such as sand mills, bead mills, pebble mills, ball mills, pearl mills, basket mills, attritors, dyno mills, bore mills, visco mills, motor mills, SC mills, dry mills, and paint conditioners, as well as media-less dispersion devices such as high-speed disc impellers, colloid mills, high-pressure homogenizers, nanomizers, and ultimateizers.

[0129] The temperature of the aqueous pigment dispersion subjected to ultrasonic irradiation is not particularly limited, but it is preferable to irradiate the aqueous pigment dispersion with ultrasound while controlling the temperature so that it is at its freezing point of ~70°C.

[0130] (2) Method via a high-concentration aqueous pigment dispersion (pigment paste) There are no particular limitations on the method for preparing the pigment paste in advance; known dispersion methods can be used.

[0131] Furthermore, the following (i) to (iii) are examples of methods for preparing this pigment paste. (i) A method for preparing a pigment paste by adding a pigment to an aqueous medium containing a pigment dispersant and water, and then dispersing the pigment in the aqueous medium using a stirring and dispersion device. (ii) A method for preparing a pigment paste by kneading a pigment and a pigment dispersant using a kneader such as a two-roll kneader or mixer, adding the resulting kneaded mixture to an aqueous medium containing water, and using a stirring and dispersion device. (iii) A method of preparing a pigment paste by dissolving a pigment dispersant in an organic solvent that is compatible with water, such as methyl ethyl ketone or tetrahydrofuran, adding a pigment to the solution obtained, dispersing the pigment in the organic solution using a stirring and dispersion device, then emulsifying it using an aqueous medium, and finally removing the organic solvent by distillation.

[0132] The mixing machine is not particularly limited and examples include Henschel mixers, pressure kneaders, Banbury mixers, and planetary mixers. Furthermore, the stirring and dispersion devices are not particularly limited and include, for example, ultrasonic homogenizers, high-pressure homogenizers, paint shakers, ball mills, roll mills, sand mills, sand grinders, Dino mills, Dispermats, SC mills, nanomizers, etc. One of these may be used alone, or two or more types of devices may be used in combination.

[0133] The amount of pigment in the aforementioned pigment paste may be 5 to 60% by mass.

[0134] Since the remaining coarse particles can degrade various image characteristics, it is preferable to remove coarse particles as appropriate before and after ink preparation by centrifugation or filtration.

[0135] After the dispersion process, the mixture may undergo impurity removal processes such as ion exchange treatment or ultratreatment, followed by post-treatment. Ion exchange treatment can remove ionic substances such as cations and anions (e.g., divalent metal ions), and ultratreatment can remove impurity-dissolved substances (e.g., residual substances from pigment synthesis, excess components in the dispersion composition, resins not adsorbed on organic pigments, and foreign contaminants). For ion exchange treatment, known ion exchange resins are used.

[0136] The nanocellulose contained in the present invention is derived from oxidized cellulose, which is easily defibrillated. The aqueous ink composition of the present invention can also be made into an aqueous ink composition containing nanocellulose by blending the above-mentioned oxidized cellulose with other materials of the aqueous ink composition and appropriately defibrillating and nano-sizing it.

[0137] As described above, oxidized cellulose can be used in the manufacture of aqueous ink compositions. During the manufacturing process, the oxidized cellulose is defibrated in the composition through dispersion or mixing operations to become nanocellulose. Specifically, nanocellulose can be obtained by blending the oxidized cellulose with other materials of the aqueous ink composition, stirring such as dispersion or mixing operations to defibrate the mixture, or by the user of the oxidized cellulose defibrating it themselves to make it nano-sized. The stirring can be carried out by the (Step B: Defibration Treatment) described above.

[0138] One aspect of the present invention is a method for producing a binder composition using oxidized cellulose as a material, which contains an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof and substantially does not contain an N-oxyl compound. Specifically, it is a method for producing an aqueous ink composition containing nanocellulose, comprising the step of stirring a mixture containing oxidized cellulose and materials other than nanocellulose of the aqueous ink composition to defibrate the oxidized cellulose and obtain the aqueous ink composition. Furthermore, one aspect of the present invention is a method for producing an aqueous ink composition containing nanocellulose, the method comprising the step of stirring oxidized cellulose and continuously mixing it with materials other than nanocellulose of the aqueous ink composition to defibrate the oxidized cellulose and obtain the aqueous ink composition. Here, the embodiments of nanocellulose, oxidized cellulose, and aqueous ink composition are as described above. The materials other than nanocellulose in the aqueous ink composition are any materials other than nanocellulose that may be included in the aqueous ink composition, and include, but are not limited to, the pigments, dispersants, and solvents mentioned above. Furthermore, in this specification, "continuously mixing materials" means performing the micronization of oxidized cellulose by stirring and the addition of materials in a single process. Specific embodiments of performing stirring and addition in a single process include, but are not limited to, an embodiment in which the micronization of oxidized cellulose and the addition of the materials are performed in a single pot; an embodiment in which the materials are added simultaneously while stirring the oxidized cellulose; and so on.

[0139] In the manufacturing method of the present invention, when stirring oxidized cellulose to micronize at least a portion of it, the operation is not particularly limited as long as it disperses the components constituting the nanocellulose-containing composition, and for example, a velocity field and velocity fluctuation of any strength; collision with inclusions or obstacles; ultrasound; pressure loading; etc. can be used. A liquid-based disperser can be suitably used for such dispersion operations. Therefore, in one embodiment of the manufacturing method of the present invention, stirring is performed by a liquid-based disperser. The liquid dispersion device is not particularly limited and can include, for example, a homomixer, magnetic stirrer, stirring rod, stirrer with stirring blades, disperser-type mixer, homogenizer, external circulation stirring, rotational stirring, vibrating stirring, ultrasonic dispersion device, etc. In addition to the above-mentioned devices, other liquid dispersion devices that can be used include rotary shear stirring devices, colloidal mills, roll mills, pressure homogenizers, container-driven mills, media stirring mills, etc. Furthermore, a kneader can be used as a liquid dispersion device. A rotary shear agitator is a device that disperses a material by passing it through the gap between the rotating blades and the outer cylinder. Dispersion occurs due to the shear flow in the gap and the strong velocity fluctuations before and after the gap. A colloidal mill is a device that disperses material through shear flow in the gap between a rotating disk and a stationary disk. A roll mill disperses material through shear and compressive forces utilizing the gaps between multiple rotating rolls. A pressure homogenizer is a disperser used to discharge slurries and the like from pores at high pressure, and is also called a pressure jet disperser. A high-pressure homogenizer is preferred among the pressure homogenizers mentioned above. A high-pressure homogenizer is a homogenizer capable of discharging slurries at a pressure of, for example, 10 MPa or more, preferably 100 MPa or more. Examples of high-pressure homogenizers include opposing impact type high-pressure homogenizers such as microfluidizers and wet jet mills. Container-driven mills are devices that disperse materials through collision and friction of a medium such as balls inside a container. Specific examples include rotary mills, vibratory mills, and planetary mills. Medium-agitated mills use a medium such as balls or beads and disperse materials through the impact and shear forces of the medium. Specific examples include attritors and bead mills (sand mills). A kneader is a device that performs the operation of wetting powders or other materials with liquid (also called kneading or mixing). Specifically, there are dual-arm kneaders (devices that disperse materials in two semi-cylindrical containers using two mixing blades); Banbury mixers (closed systems that disperse materials under pressure); and extrusion-type kneaders such as screw extruders, con-kneaders, and extruders. These devices may be used individually or in combination of two or more types. While stirring using such a device can promote the micronization of oxidized cellulose, stirring may be continued until the components of the nanocellulose-containing composition are homogenized or emulsified. This allows for the uniform dispersion of nanocellulose within the nanocellulose-containing composition, and also allows for the acquisition of the nanocellulose-containing composition as an emulsion.

[0140] The aqueous ink composition containing nanocellulose obtained by a manufacturing method using oxidized cellulose can be recovered by appropriate post-treatment to obtain an aqueous ink composition. The solvent used in the polymerization reaction of the anionic group-containing organic polymer compound may or may not be removed. The obtained product may also be filtered and washed to obtain an aqueous ink composition.

[0141] The inclusion of nanocellulose in the aqueous ink composition of the present invention can be used as an indicator of the physical properties of the aqueous ink composition. That is, it can be determined that the composition has a function resulting from the nanocellulose, for example, from the fact that the aqueous ink composition has become a slurry or has a viscosity. Specifically, when compared with a composition that does not contain nanocellulose, the composition obtained by the manufacturing method of the present invention can be determined to contain nanocellulose from the fact that it is in a slurry-like state, thickens, and does not cause precipitation of the compounded material. Furthermore, when compared, for example, with a composition containing nanocellulose manufactured in accordance with International Publication No. 2018 / 230354, the composition obtained by the manufacturing method of the present invention has a slurry-like consistency and viscosity equivalent to the above composition, thus indicating that it contains nanocellulose.

[0142] Whether a nanocellulose-containing composition obtained by the manufacturing method of the present invention contains nanocellulose can also be determined by observing the transmission phase contrast with an optical microscope to see if the oxidized cellulose used remains coarse (i.e., whether the original oxidized cellulose is preserved) or not. [Examples]

[0143] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0144] The various physical properties of oxidized cellulose or nanocellulose were measured by the following method.

[0145] [Measurement of average fiber length and average fiber width] Pure water was added to a dispersion containing nanocellulose to adjust the nanocellulose concentration in the nanocellulose aqueous dispersion to 5 ppm. The nanocellulose aqueous dispersion after concentration adjustment was air-dried on a mica substrate, and the shape of the nanocellulose was observed in AC mode using an Oxford Asylum scanning probe microscope "MFP-3D infinity". Regarding fiber length, the obtained images were binarized and analyzed using the image processing software "ImageJ". For more than 100 fibers, the number-average fiber length was calculated using the formula: Fiber length = "Circumference" ÷ 2. For the average fiber width, the number-average fiber width [nm] was calculated for 50 or more fibers using the software included with "MFP-3D infinity," with the cross-sectional height of the shape image equaling the fiber width.

[0146] [Light transmittance measurement] A dispersion containing nanocellulose was placed in a 10 mm thick quartz cell, and the light transmittance at a wavelength of 660 nm was measured using a spectrophotometer (JASCO V-550).

[0147] [Measurement of viscosity-average degree of polymerization] Oxidized cellulose was added to an aqueous sodium borohydride solution adjusted to pH 10, and a reduction treatment was carried out at 25°C for 5 hours. The amount of sodium borohydride was 0.1 g per 1 g of oxidized cellulose. After the reduction treatment, solid-liquid separation was performed by suction filtration, and the obtained oxidized cellulose was washed with water and freeze-dried. 0.04 g of dried oxidized cellulose was added to 10 ml of pure water and stirred for 2 minutes, then 10 ml of 1 M copper ethylenediamine solution was added to dissolve it. Subsequently, the flow time of the blank solution and the flow time of the cellulose solution were measured at 25°C using a capillary viscometer. From the flow time of the blank solution (t0), the flow time of the cellulose solution (t), and the concentration of oxidized cellulose (c [g / ml]), the relative viscosity (ηr), specific viscosity (ηsp), and intrinsic viscosity ([η]) were sequentially determined using the following formula, and the degree of polymerization (DP) of oxidized cellulose was calculated from the viscometer formula. ηr = η / η0 = t / t0 ηsp = ηr - 1 [η]=ηsp / (100×c(1+0.28ηsp)) DP = 175 × [η]

[0148] [Measurement of carboxyl group content in oxidized cellulose] To 60 ml of an aqueous dispersion of oxidized cellulose, adjusted to a concentration of 0.5% by mass, a 0.1 M hydrochloric acid solution was added to bring the pH to 2.5. Then, a 0.05 N sodium hydroxide solution was added dropwise, and the electrical conductivity was measured until the pH reached 11.0. The amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity was gradual (a), was used to calculate the amount of carboxyl groups (mmol / g) using the following formula. Amount of carboxyl groups = a (ml) × 0.05 / Mass of oxidized cellulose (g)

[0149] [Manufacturing Example 1: Production of Oxide Cellulose A] 350 g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass was placed in a beaker, and pure water was added and stirred to reduce the effective chlorine concentration to 21% by mass. Then, 35% by mass hydrochloric acid was added and stirred to obtain an aqueous solution with a pH of 11. The aforementioned sodium hypochlorite aqueous solution was heated to 30°C in a constant temperature water bath while being stirred at 200 rpm using a propeller-type stirring blade with a stirrer (Three One Motor, BL600) manufactured by Shinto Kagaku Co., Ltd. Then, 50 g of TDI's powdered pulp (VP-1), a cellulose-based raw material, was added. After supplying the cellulose-based raw materials, the reaction was carried out in the same constant-temperature water bath, maintaining a temperature of 30°C, while adding 48% by mass sodium hydroxide to adjust the pH to 11. The reaction was then stirred for 30 minutes under the same conditions using a stirrer. Subsequently, the solution was diluted twice with pure water, and sodium hydroxide was added to bring the pH to 13, thereby slowing down the oxidation reaction and obtaining cellulose-based oxides dispersed in water. Subsequently, hydrochloric acid is added to convert the carboxyl group of the cellulose oxide into a salt form (-COO - Na + ) to proton type (-COO - H +A pH 2.5 aqueous dispersion was obtained by ) . In this example, pH control was performed using a pH controller (Tokyo Glass Instruments Co., Ltd., FD-02). The resulting aqueous dispersion with a pH of 2.5 was subjected to solid-liquid separation and washing. Specifically, the supernatant was removed by centrifugation (1000G, 10 minutes) and decantation, and an equivalent amount of pure water was added and the mixture was thoroughly stirred with a spoon until homogenized. This process was repeated six times, and finally, the above centrifugation and decantation were performed to obtain oxidized cellulose. Subsequently, sodium hydroxide in an amount approximately equal to the amount of carboxyl groups introduced is added to convert the carboxylic acid group into a protonated (-COO) form. - H + ) from salt type (-COO - Na + The pH was adjusted to 7.5. The resulting aqueous dispersion slurry was heated to 30°C, and 0.2 mmol / g of sodium borohydride was added to the cellulosic raw material. The mixture was then reduced by reacting for 2 hours to obtain oxidized cellulose A. The concentration of this oxidized cellulose was 10% by mass, the degree of polymerization (viscosity-average degree of polymerization) of oxidized cellulose A was 90, and the amount of carboxyl groups was 0.65 mmol / g.

[0150] The effective chlorine concentration in the sodium hypochlorite aqueous solution was measured by the following method. (Measurement of available chlorine concentration in sodium hypochlorite aqueous solution) 0.582 g of an aqueous solution of sodium hypochlorite pentahydrate crystals added to pure water was precisely weighed, 50 ml of pure water was added, 2 g of potassium iodide and 10 ml of acetic acid were added, and the container was immediately sealed and left in the dark for 15 minutes. After 15 minutes, the liberated iodine was titrated with a 0.1 mol / L sodium thiosulfate solution (indicator: starch solution), and the titration volume was 34.55 ml. A blank test was performed separately and corrected, and since 1 ml of 0.1 mol / L sodium thiosulfate solution corresponds to 3.545 mg Cl, the effective chlorine concentration in the sodium hypochlorite aqueous solution is 21% by mass.

[0151] [Manufacturing Example 2: Production of Oxidized Cellulose B] By replacing sodium hydroxide with potassium hydroxide, the carboxylic acid group is converted to a protonated (-COO) type. - H + ) from salt type (-COO - K + Oxidized cellulose B was obtained by performing the same process as in Production Example 1, except that the other factor was ). The content concentration of this oxidized cellulose was 10% by mass.

[0152] [Manufacturing Example 3: Production of Cellulose Oxide C] Sodium hydroxide is replaced with JEFFAMINE2070 (PO / EO modified amine, Mw2000, PO / EO = 29 / 6 mol ratio), and the carboxylic acid group is converted to a protonated type (-COO - H + Oxidized cellulose C was obtained by performing the same treatment as in Production Example 1, except that it was converted to an amine-modified type. The content concentration of this oxidized cellulose was 10% by mass.

[0153] The nanocellulose I-2SX used in Comparative Examples 1 and 2 is nanocellulose obtained by micronization via TEMPO oxidation. The degree of polymerization (viscosity-average degree of polymerization) of I-2SX was 461, and the carboxyl group content was 2.0 mmol / g.

[0154] <Anionic group-containing organic polymer compounds> The following organic polymer compounds containing anionic groups were used. (Acrylic resin having anionic groups) Resin A was prepared with a monomer composition ratio of styrene / methacrylic acid / acrylic acid = 77 / 13 / 10 (mass ratio), a weight-average molecular weight of 8800, an acid value of 150 mgKOH / g, and a glass transition temperature of 107°C. 50 parts of methyl ethyl ketone (hereinafter abbreviated as MEK), 50 parts of the aforementioned resin A, 87.4 parts of deionized water, and 22 g of a 34% by mass potassium hydroxide (KOH) aqueous solution were added and thoroughly stirred to obtain a resin solution. MEK was removed from this resin solution under reduced pressure conditions of 40 hPa and a water bath temperature of 45°C to obtain a resin solid content of 20%, which was then used as a solution of an anionic acrylic resin (SA-1).

[0155] (Polyurethane resin having anionic groups) 64.2 parts by mass of methyl ethyl ketone were added to a nitrogen-purged container equipped with a thermometer, a nitrogen gas introduction tube, and a stirrer. 18.4 parts by mass of 2,2-dimethylolpropionic acid and 33.9 parts by mass of isophorone diisocyanate were mixed in the methyl ethyl ketone and the mixture was reacted at 80°C for 4 hours. After 4 hours, a further 38.2 parts by mass of methyl ethyl ketone was supplied, and after cooling to below 60°C, 140.1 parts by mass of polyether polyol ("PTMG2000," polytetramethylene glycol manufactured by Mitsubishi Chemical Corporation, number average molecular weight 1000) and 0.01 parts by mass of dibutyltin dilaurine (hereinafter DBTDL) were added, and the reaction was continued at 80°C. After confirming that the weight-average molecular weight of the reactants reached a range of 20,000 to 50,000, the reaction was terminated by adding 1.3 parts by mass of methanol. Subsequently, an organic solvent solution of urethane resin was obtained by adding 41.6 parts by mass of methyl ethyl ketone. By adding 15.1 parts by mass of a 50% by mass potassium hydroxide aqueous solution to the above-mentioned organic solvent solution of urethane resin, some or all of the carboxyl groups of the urethane resin are neutralized. Then, by adding 848.5 parts by mass of water and stirring thoroughly, a mixture is obtained in which the urethane resin, methyl ethyl ketone, and water are dispersed or dissolved in the water. Next, the mixture was aged for about 2 hours, then 0.07 parts by mass of Surfinol 440 (manufactured by Air Products, an ethylene oxide adduct of acetylene glycol, 100% by mass of nonvolatile content) was added to the mixture and stirred for about 20 minutes to obtain the mixture, which was then distilled under reduced pressure of about 1 to 50 kPa. After confirming that 144 parts by mass of methyl ethyl ketone contained in the mixture had been removed, 0.03 parts by mass of Surfinol 440 (manufactured by Air Products Co., Ltd.) was added under reduced pressure, and vacuum distillation was continued. Subsequently, after confirming that 147 parts by mass of water contained in the mixture had been dehydrated, the vacuum distillation was terminated. Next, the non-volatile content was adjusted by adding water to obtain a resin solid content of 20% by mass, which was then used as a solution of polyurethane resin having anionic groups (UR-1).

[0156] (Polysaccharide derivatives having anionic groups) Commercially available DN-800H (manufactured by Daicel Finechem Co., Ltd.): Carboxymethylcellulose ammonium was used.

[0157] <Pigments, etc.> The following commercially available products were used as pigments, etc. #960 (manufactured by Mitsubishi Chemical Corporation): Carbon Black FASTOGEN Blue TGR (manufactured by DIC Corporation): CIPigment Blue 15:3 FASTOGEN Super Magenta RY (manufactured by DIC Corporation): CIPigment Red 122 Fast Yellow 7413 (manufactured by Sanyo Pigment Co., Ltd.): CIPigment Yellow 74

[0158] <Example 1: Preparation of an aqueous ink composition> In a metal beaker, 60 parts of "#960" (carbon black manufactured by Mitsubishi Chemical Corporation), 14 parts of a solution of an anionic group-containing organic polymer compound (SA-1), 20 parts of triethylene glycol, and 20 parts of 2-pyrrolidone were added. The pH was adjusted to between 9 and 10.5 with 34% potassium hydroxide, and pure water was added to bring the total volume to 300 parts. The mixture was then stirred and mixed for 3 minutes at 120 RPM using a three-one motor. Subsequently, the mixture was ultrasonically dispersed for 10 minutes using an ultrasonic disperser (Hielscher UP200St, operating frequency: 26KHz, operating output: 160W). After weighing 30 parts of oxidized cellulose A (10% by mass) in a separate container and adding pure water to adjust the oxidized cellulose concentration to 1% by mass, the material was defibrated using a homomixer (10,000 rpm, 10 minutes) to obtain nanocellulose A with an average fiber length of 200 nm and an average fiber width of 3 nm. When a portion of the obtained nanocellulose A aqueous dispersion was taken out and pure water was added to prepare an aqueous dispersion with a solid content of 0.1% by mass, the light transmittance (660 nm) was 97%, confirming that the oxidized cellulose had been nano-sized. To the mixture after ultrasonic dispersion described above, an aqueous dispersion of nanocellulose A was added. To this mixture, 200 parts (2 parts in terms of solid content of nanocellulose A) were added, and 2 parts of Surfinol 440 were added. After manual stirring, pure water was added to bring the total volume to 1000 parts, and the mixture was ultrasonically dispersed for 25 minutes using an ultrasonic disperser. The resulting liquid was filtered through a 1.2 μm membrane filter to obtain the aqueous ink composition of Example 1.

[0159] <Examples 2-10> An aqueous ink composition was obtained in the same manner as in Example 1, except that the type of pigment used, the type and amount of anionic group-containing organic polymer compound added, and the type and amount of nanocerose added were changed to those listed in Table 1. Note that in Table 1, nanocellulose A to C are derived from oxidized cellulose A to C, respectively.

[0160] <Example 11> In a metal beaker, 20 parts of 10% by mass cellulose A, 60 parts of #960 (carbon black manufactured by Mitsubishi Chemical Corporation), 14 parts of a solution of an anionic group-containing organic polymer compound (SA-1), 20 parts of triethylene glycol, and 20 parts of 2-pyrrolidone were added. The pH was adjusted to between 9 and 10.5 with 34% potassium hydroxide, and pure water was added to a total volume of 300 parts to obtain the mixture. This mixture was stirred and mixed for 3 minutes at 120 RPM using a three-one motor. Subsequently, it was ultrasonically dispersed for 10 minutes using an ultrasonic disperser (Hielscher UP200St, operating frequency: 26KHz, operating output: 160W). Two parts of Surfinol 440 were added to the mixture after ultrasonic dispersion as described above, and after manual stirring, pure water was added to bring the total volume to 1000 parts, and the mixture was ultrasonically dispersed for 25 minutes using an ultrasonic disperser. The resulting liquid was filtered through a 1.2 μm membrane filter to obtain the aqueous ink composition of Example 11. The nano-sized oxidized cellulose was confirmed by the following procedure. A water dispersion was prepared using 20 parts of oxidized cellulose A (10% by mass) and pure water to a total volume of 300 parts. That is, the concentration of oxidized cellulose A in this water dispersion was made the same as the concentration of oxidized cellulose A in the above mixture. The mixture was stirred and mixed for 3 minutes at a rotation speed of 120 RPM using a three-one motor. Then, ultrasonic dispersion was performed for 10 minutes using an ultrasonic disperser (Hielscher UP200St, operating frequency: 26KHz, operating output: 160W). From the dispersion after dispersion, it was confirmed that the nano-cellulose A had an average fiber length of 200 nm and an average fiber width of 3 nm. Furthermore, when a portion of the water dispersion of nano-cellulose A was taken out and pure water was added to prepare a water dispersion with a solid content concentration of 0.1% by mass, the light transmittance (660 nm) was 97%, confirming that the oxidized cellulose was nano-sized.

[0161] <Comparative Example 1> In a metal beaker, 60 parts of "#960" (carbon black manufactured by Mitsubishi Chemical Corporation), 14 parts of a solution of an anionic group-containing organic polymer compound (SA-1), 20 parts of triethylene glycol, and 20 parts of 2-pyrrolidone were added. The pH was adjusted to between 9 and 10.5 with 34% potassium hydroxide, and pure water was added to bring the total volume to 300 parts. The mixture was then stirred and mixed for 3 minutes at 120 RPM using a three-one motor. Subsequently, the mixture was ultrasonically dispersed for 10 minutes using an ultrasonic disperser (Hielscher UP200St, operating frequency: 26KHz, operating output: 160W). 30 parts of I-2SX, weighed in a separate container, were added to pure water to adjust the concentration to 1% by mass. To the mixture after ultrasonic dispersion described above, an aqueous dispersion of I-2SX was added. To this mixture, 200 parts (2 parts in terms of solid content of I-2SX) were added, and 2 parts of Surfinol 440 were added. After manual stirring, pure water was added to bring the total volume to 1000 parts, and the mixture was ultrasonically dispersed for 25 minutes using an ultrasonic disperser. The resulting liquid was filtered through a 1.2 μm membrane filter to obtain the aqueous ink composition of Comparative Example 1.

[0162] <Comparative Example 2> An aqueous ink composition was obtained in the same manner as in Comparative Example 1, except that the amounts of the anionic group-containing organic polymer compound and I-2SX added were changed to the formulations shown in Table 1.

[0163] Table 1 shows the evaluation results of the amount of aqueous ink composition used and its physical properties.

[0164] [Table 1]

[0165] The method for evaluating the physical properties of an aqueous ink composition is as follows:

[0166] <Ink pH measurement> Measurements were taken using an MM-60R (manufactured by Toa DKK Corporation) at an ink temperature of 25°C.

[0167] <Suitable for inkjet (IJ) printing> Regarding ejection performance and printing performance, the aqueous inks of the examples and comparative examples were loaded into an inkjet recording device (Hewlett-Packard ENVY4500) equipped with a thermal inkjet nozzle in a constant temperature and humidity chamber (room temperature 25°C, humidity 50%). Subsequently, a test print pattern (with text, ruled lines, and solid areas) was printed continuously for 10 minutes on PPC paper as the recording material. After 10 minutes of continuous printing, the paper surface was visually observed by three panelists, and the defects and blurring of the printed pattern were evaluated according to the following criteria. A: All three panelists did not notice any defects or smudges in the printed pattern. B: Only one panelist noticed any defects or smudges in the printed pattern (the other two panelists did not notice any defects or smudges in the printed pattern). C: Two or more panelists noticed defects or smudges in the printed pattern.

[0168] <Measurement of Optical Density (OD) Value> Using an inkjet recording device equipped with the thermal inkjet nozzle described above, test print patterns (solid areas) were printed on PPC paper as the recording material using the aqueous inks of the examples and comparative examples to prepare evaluation samples. The optical density (OD value) at three locations in the aforementioned evaluation sample was measured using an X-Rite SpectroEye spectrophotometer (light source: D50, field of view: 2°, ANSI-T), the average value was calculated, and the optical density (OD value) was evaluated according to the evaluation criteria below. Optical Density (OD value) Evaluation Criteria A: The optical density (OD value) was 1.40 or higher. B: The optical density (OD value) was 1.35 or higher and less than 1.40. C: The optical density (OD value) was 1.30 or higher and less than 1.35. D: The optical density (OD value) was less than 1.30.

[0169] (Abrasion resistance test) To investigate the fastness and adhesion of the ink, the prepared ink was applied to glossy paper using a wire bar #3. After 24 hours of natural drying, the applied surface was rubbed with a 45R friction bar wrapped in friction PPC paper using a JSPS friction tester (manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.) under conditions of a load of 200g or 500g and 10 friction cycles. Subsequently, the condition of the applied surface was visually evaluated by five panelists and evaluated according to the following criteria. 5: At both the 200g and 500g load conditions, there were absolutely no scratches, and the condition was extremely good. 4: No damage was observed at all under a load of 200g, but slight scratches were observed under a load of 500g. 3: Minor scratches were observed under a load of 200g, but there were no practical problems. 2: Noticeable damage was observed at a load of 200g. 1: Peeling of the coating was observed at a load of 200g. [Industrial applicability]

[0170] According to the present invention, it is possible to provide an aqueous pigment dispersion and an aqueous ink composition that can easily and inexpensively form a coating film with excellent pigment dispersibility, as well as excellent film durability, adhesion, color density, etc.

Claims

1. An aqueous ink composition containing nanocellulose, The nanocellulose is obtained by defibrating oxidized cellulose that contains an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof, and substantially does not contain an N-oxyl compound. The amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more and less than 2.0 mmol / g. The degree of polymerization of the oxidized cellulose is 400 or less. Water-based ink composition.

2. An aqueous ink composition containing nanocellulose, The nanocellulose is obtained by defibrating oxidized cellulose having a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and carboxyl groups are introduced. The amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more and less than 2.0 mmol / g. The degree of polymerization of the oxidized cellulose is 400 or less. Water-based ink composition.

3. Further comprising an anionic group-containing organic polymer compound, The aqueous ink composition according to claim 1 or 2.

4. At least a portion of the carboxyl groups of the nanocellulose are modified with at least one selected from the group consisting of metals, ammonia, amines, and quaternary ammonium. The aqueous ink composition according to any one of claims 1 to 3.

5. For inkjet recording, The aqueous ink composition according to any one of claims 1 to 4.

6. A recording method comprising the step of ejecting an aqueous ink composition according to any one of claims 1 to 4 onto a recording member by an inkjet method.

7. A method for producing an aqueous ink composition containing nanocellulose, The process includes stirring a mixture containing oxidized cellulose and materials other than nanocellulose of the aqueous ink composition to defibrate the oxidized cellulose and obtain an aqueous ink composition containing nanocellulose, The oxidized cellulose contains an oxide of a cellulosic raw material due to hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds. The amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more and less than 2.0 mmol / g. The degree of polymerization of the oxidized cellulose is 400 or less. Manufacturing method.

8. A method for producing an aqueous ink composition containing nanocellulose, The process includes stirring a mixture containing oxidized cellulose and materials other than nanocellulose of the aqueous ink composition to defibrate the oxidized cellulose and obtain an aqueous ink composition containing nanocellulose, The oxidized cellulose has a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and carboxyl groups are introduced. The amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more and less than 2.0 mmol / g. The degree of polymerization of the oxidized cellulose is 400 or less. Manufacturing method.

9. A method for producing an aqueous ink composition containing nanocellulose, The process includes stirring oxidized cellulose and continuously mixing it with materials other than nanocellulose of the aqueous ink composition to defibrate the oxidized cellulose and obtain an aqueous ink composition containing nanocellulose, The oxidized cellulose contains an oxide of a cellulosic raw material due to hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds. The amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more and less than 2.0 mmol / g. The degree of polymerization of the oxidized cellulose is 400 or less. Manufacturing method.

10. A method for producing an aqueous ink composition containing nanocellulose, The process includes stirring oxidized cellulose and continuously mixing it with materials other than nanocellulose of the aqueous ink composition to defibrate the oxidized cellulose and obtain an aqueous ink composition containing nanocellulose, The oxidized cellulose has a structure in which the hydroxyl groups at the 2nd and 3rd positions of the glucopyranose ring are oxidized and carboxyl groups are introduced. The amount of carboxyl groups in the oxidized cellulose is 0.30 mmol / g or more and less than 2.0 mmol / g. The degree of polymerization of the oxidized cellulose is 400 or less. Manufacturing method.

11. The material further comprises an anionic group-containing organic polymer compound. The manufacturing method according to any one of claims 7 to 10.

12. At least a portion of the carboxyl groups of the oxidized cellulose are modified with at least one selected from the group consisting of metals, ammonia, amines, and quaternary ammonium compounds. The manufacturing method according to any one of claims 7 to 11.

Images