Mixed liquid

Abstract

The mixture contains (1) a dispersant, (2) cellulose nanofibers and (3) a filler.

Description

Technical Field

[0001] This invention relates to a mixture containing cellulose nanofibers and fillers. Background Technology

[0002] Nanotechnology, a technology that allows for the free control of matter at the nanoscale—the atomic and molecular level—is expected to generate a variety of convenient new materials and devices. Cellulose nanofibers, obtained by finely dissecting plant fibers, are one such example. These nanofibers are characterized by very high crystallinity, a low coefficient of thermal expansion, and a high elastic modulus, exhibiting a high aspect ratio. Therefore, they are expected to be effective additives that impart strength and shape stabilization. Furthermore, their pseudoplastic and thixotropic viscosity properties in the dispersion state also suggest their potential as thickeners and other additives.

[0003] Various developments and studies have been carried out on this cellulose nanofiber. For example, Patent Document 1 discloses microcellulose fibers (cellulose nanofibers) with a number-average fiber diameter of 2 nm to 150 nm obtained by introducing carboxyl groups onto a portion of the hydroxyl groups of cellulose.

[0004] In addition to its strength-imparting and shape-stabilizing properties, this cellulose nanofiber also exhibits high viscosity at low shear rates and low viscosity at high shear rates. Therefore, it is used as a high-performance thickener in various fields such as food, pharmaceuticals / cosmetics, daily necessities, civil engineering / building materials, papermaking, coatings / inks, and other industrial materials. It is known that in these fields, mixtures containing fillers are sometimes used, and the addition of cellulose nanofibers as a thickener improves the dispersion stability of the fillers.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-1728 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, mixtures containing cellulose nanofibers require even better dispersion stability of the filler.

[0010] Therefore, the object of the present invention is to provide a mixture containing cellulose nanofibers with excellent dispersion stability of filler.

[0011] means for solving problems

[0012] The present invention provides the following [1] to [8].

[0013] [1] A mixture, wherein the mixture contains the following (1) to (3):

[0014] (1) Dispersant,

[0015] (2) Cellulose nanofibers,

[0016] (3) Packing material.

[0017] [2] The mixture as described in [1], wherein the above dispersant is an anionic polymer compound.

[0018] [3] The mixture as described in [2], wherein the above-mentioned anionic polymer is a polymer with a carboxyl group or a polymer with a phosphate group.

[0019] [4] The mixture as described in any one of [1] to [3], wherein the cellulose nanofibers are anion-modified cellulose nanofibers.

[0020] [5] The mixture as described in [4], wherein the above-mentioned anion-modified cellulose nanofibers are oxidized cellulose nanofibers.

[0021] [6] The mixture as described in [5], wherein the amount of carboxyl groups in the above-mentioned oxidized cellulose nanofibers is 0.4 mmol / g to 1.0 mmol / g.

[0022] [7] The mixture as described in any one of [1] to [6], wherein the amount of the above-mentioned cellulose nanofibers added is 0.1% by mass or more.

[0023] [8] The mixture as described in any one of [1] to [7], wherein the water separation rate of the mixture after standing for 72 hours is less than 1%.

[0024] Invention Effects

[0025] According to the present invention, a mixture containing cellulose nanofibers can be provided with excellent dispersion stability of fillers. Detailed Implementation

[0026] The mixture of the present invention is characterized by containing (1) a dispersant, (2) cellulose nanofibers and (3) a filler.

[0027] (1) Dispersant

[0028] As a dispersant, any compound that achieves the effects of this invention can be used without particular limitation. For example, low-molecular-weight or high-molecular-weight compounds of any of the following can be used: carboxylic acids, carbamates, acrylic resins, polyethers, polyesters, fatty acids, etc. Considering the properties of the filler and cellulose nanofibers incorporated in the mixture of this invention, compounds that can achieve good dispersibility are preferred. It should be noted that since cellulose nanofibers contain a large number of hydroxyl groups, the presence of a large number of hydrophobic groups in the dispersant may hinder dispersibility. Furthermore, any type of dispersant, whether anionic, cationic, or nonionic, can be used. As a dispersant, one type can be used alone, or two or more types can be mixed.

[0029] It should be noted that the cellulose nanofibers described in (2) are not included as dispersants used in this invention.

[0030] As a dispersant, when using anionic polymers, polymers with functional groups such as carboxyl, sulfonic acid, phosphate, and sulfate groups can be used. These polymers become anionic by being used at a pH higher than the pKa (acid dissociation coefficient) of each functional group, allowing the mixture to be adjusted without causing aggregation of the anionic cellulose nanofiber dispersion. The functional groups can be appropriately selected based on the pH of the mixture to be adjusted and the required alkalinity.

[0031] Examples of carboxyl-containing polymers include polycarboxylic acids, carboxymethyl cellulose, and alginate. Examples of polycarboxylic acids include polyacrylic acid, sodium polyacrylate, styrene-maleic anhydride copolymers, and olefin-maleic anhydride copolymers. When using a carboxyl-containing polymer as a dispersant, the carboxyl group can be either a metal salt or an ammonium salt. When using the mixture of the present invention for applications requiring water resistance, an ammonium salt type can be appropriately selected.

[0032] Examples of polymers containing phosphate groups include polyoxyethylene alkyl ether phosphates, polyoxyethylene phenyl ether phosphates, and alkyl phosphate esters.

[0033] Examples of polyether compounds include Pluronic polyether, polyether dialkyl esters, polyether dialkyl ethers, polyether epoxy modifiers, and polyether amines. For instance, the balance of hydrophilicity and hydrophobicity can be adjusted by changing the ratio of polyethylene oxide to polypropylene oxide. Examples of urethane compounds include urethane-associated compounds. For example, compatibility and steric stability can be adjusted by forming polyester or polyether chains as side chains on the polyurethane backbone. Additionally, examples of fatty acid compounds include fatty alcohol sulfates, aliphatic amines, and aliphatic esters.

[0034] Regarding the amount of dispersant added relative to the mixture of the present invention, an amount sufficient to disperse the filler can be added, preferably 0.01 to 25 parts by mass relative to 100 parts by mass of the filler, more preferably 0.1 to 10 parts by mass.

[0035] (2) Cellulose nanofibers

[0036] In this invention, cellulose nanofibers (CNFs) are fibers obtained by micronizing pulp, a cellulose raw material, to the nanoscale, and are microfibers with a diameter of approximately 3 nm to approximately 500 nm. The average fiber diameter and average fiber length of the cellulose nanofibers can be obtained by averaging the fiber diameter and fiber length obtained from observing individual fibers using atomic force microscopy (AFM) or transmission electron microscopy (TEM). Cellulose nanofibers can be obtained by micronizing pulp by applying mechanical force, or by defibrating modified cellulose obtained through chemical modification, such as anionic modified cellulose (carboxylated cellulose (also known as oxidized cellulose), carboxymethylated cellulose, cellulose with introduced phosphate groups, etc.) or cationic modified cellulose. The average fiber length and average fiber diameter of the microfibers can be adjusted by oxidation treatment and defibrating treatment.

[0037] The cellulose nanofibers used in this invention typically have an average aspect ratio of 50 or higher. There is no particular upper limit, but it is typically 1000 or lower, more preferably 700 or lower, and even more preferably 500 or lower. The average aspect ratio can be calculated using the following formula:

[0038] Aspect ratio = average fiber length / average fiber diameter

[0039] <Cellulose raw materials>

[0040] There are no particular restrictions on the source of the cellulose raw material used as the raw material for cellulose nanofibers. Examples include: plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (unbleached coniferous kraft pulp (NUKP), bleached coniferous kraft pulp (NBKP), unbleached broadleaf kraft pulp (LUKP), bleached broadleaf kraft pulp (LBKP), bleached kraft pulp (BKP), unbleached coniferous sulfite pulp (NUSP), bleached coniferous sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., tunicates), algae, microorganisms (e.g., acetic acid bacteria), microbial products, etc. The cellulose raw material can be any of these, or a combination of two or more. Cellulose raw materials from plants or microorganisms (e.g., cellulose fibers) are preferred, and cellulose raw materials from plants (e.g., cellulose fibers) are more preferred.

[0041] There is no particular limitation on the number-average fiber diameter of cellulose raw materials. In the case of softwood kraft pulp, which is used as general pulp, it is approximately 30 μm to approximately 60 μm, and in the case of hardwood kraft pulp, it is approximately 10 μm to approximately 30 μm. In the case of other pulps, the number-average fiber diameter after general refining is approximately 50 μm. For example, in the case of materials obtained by refining wood chips or other materials several centimeters in size, it is preferable to mechanically process them using a refining machine, pulping machine, or other dissociation machine to adjust the fiber diameter to approximately 50 μm.

[0042] <Chemical Modification>

[0043] In this invention, either anionicly modified cellulose or cationicly modified cellulose can be used as the modified cellulose. Preferably, a modified cellulose that, when mixed with the filler and dispersant used in the mixture of this invention, improves the dispersion of the filler. For example, when using anionic polymers as dispersants, anionicly modified cellulose nanofibers are preferred from the viewpoint of easily obtaining a synergistic effect to suppress filler aggregation.

[0044] Examples of functional groups introduced through anionic modification include carboxyl, carboxymethyl, sulfonyl, phosphate ester, and nitro groups. Among these, carboxyl, carboxymethyl, and phosphate ester groups are preferred, with carboxyl being more preferred.

[0045] (Carboxylation)

[0046] In this invention, when using carboxylated (oxidized) cellulose as the modified cellulose, carboxylated cellulose (also known as oxidized cellulose) can be obtained by carboxylating (oxidizing) the aforementioned cellulose raw material using a known method. During carboxylation, it is preferable to adjust the amount of carboxyl groups to 0.2 mmol / g to 1.55 mmol / g relative to the oven-dry mass of the anionic modified cellulose nanofibers, more preferably to 0.4 mmol / g to 1.0 mmol / g. When the amount of carboxyl groups is too small, a large amount of energy is required for defiberization to obtain a highly transparent and uniform nanofiber dispersion. A highly transparent nanofiber dispersion has less residue of coarse materials such as undefibered fibers, thus not impairing the appearance of the mixture. Furthermore, when the amount of carboxyl groups is too large, fiber deterioration due to excessive addition of oxidizing chemicals may occur, resulting in a decrease in the viscosity of the nanofiber dispersion and a decrease in viscosity retention due to stirring. The relationship between carboxyl group content and viscosity retention is not necessarily clear. It is speculated that when the modified pulp with low degree of modification is fully defibrated, the hydroxyl-containing sites that have not undergone chemical surface treatment are exposed. On the basis of the reduction of surface charge of oxidized CNF, oxidized CNF can also easily form hydrogen bonds with each other, thereby maintaining viscosity under low shear.

[0047] The following is an example of a method for determining the amount of carboxyl groups. 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose was prepared, and the pH was adjusted to 2.5 by adding 0.1 M hydrochloric acid aqueous solution. Then, 0.05 N sodium hydroxide aqueous solution was added dropwise, and the conductivity was measured until the pH reached 11. The amount of carboxyl groups can be calculated using the following formula, from the amount of sodium hydroxide consumed (a) during the neutralization phase of the weak acid with a slow change in conductivity.

[0048] Carboxyl group content [millomoles / g oxidized cellulose] = a[mL] × 0.05 / mass of oxidized cellulose [g]

[0049] As an example of a carboxylation (oxidation) method, one can exemplify the oxidation of cellulose raw materials in water using an oxidizing agent in the presence of an N-oxygen compound and a compound selected from the group consisting of bromides, iodides, or mixtures thereof. Through this oxidation reaction, the primary hydroxyl group at the C6 position of the pyranose ring on the cellulose surface is selectively oxidized, yielding cellulose fibers having an aldehyde and a carboxyl group (-COOH) or an aldehyde and a carboxylate group (-COO-) on the surface. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

[0050] N-oxy compounds are compounds capable of generating nitrocellulose radicals. As an N-oxy compound, any compound can be used as long as it promotes the target oxidation reaction. Examples include 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO).

[0051] The amount of N-oxygen compound used can be any amount of catalyst capable of oxidizing cellulose as a raw material, and there is no particular limitation. For example, relative to 1 g of oven-dry cellulose, it is preferably 0.01 mmol to 10 mmol, more preferably 0.01 mmol to 1 mmol, and even more preferably 0.05 mmol to 0.5 mmol. In addition, relative to the reaction system, it is preferably about 0.1 mmol / L to about 4 mmol / L.

[0052] Bromides refer to compounds containing bromine, including alkali metal bromides that can dissociate and ionize in water. Iodides refer to compounds containing iodine, including alkali metal iodides. The amount of bromide or iodide used can be selected from a range that promotes the oxidation reaction. The combined amount of bromide and iodide is preferably 0.1 mmol to 100 mmol relative to 1 g of oven-dried cellulose, more preferably 0.1 mmol to 10 mmol, and even more preferably 0.5 mmol to 5 mmol.

[0053] As the oxidizing agent, known oxidizing agents can be used, such as halogens, hypohalous acids, halogenated acids, perhalic acids or their salts, halogen oxides, peroxides, etc. Sodium hypochlorite, which is inexpensive and has a low environmental impact, is preferred. The amount of oxidizing agent used, for example, relative to 1 g of oven-dried cellulose, is preferably 0.5 mmol to 500 mmol, more preferably 0.5 mmol to 50 mmol, further preferably 1 mmol to 25 mmol, and most preferably 3 mmol to 10 mmol. Additionally, for example, relative to 1 mole of N-oxygen compound, it is preferably 1 mole to 40 moles.

[0054] The oxidation of cellulose can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4°C to 40°C, but room temperature of about 15°C to about 30°C is also acceptable. As the reaction proceeds, carboxyl groups are generated in the cellulose, thus the pH of the reaction solution decreases. To ensure efficient oxidation, an alkaline solution such as an aqueous sodium hydroxide solution is preferably added to maintain the pH of the reaction solution at 8 to 12, preferably about 10 to about 11. Considering ease of handling and the likelihood of side reactions, water is the preferred reaction medium.

[0055] The reaction time in the oxidation reaction can be set appropriately according to the degree of oxidation, usually from 0.5 hours to 6 hours, for example from about 0.5 hours to about 4 hours.

[0056] Furthermore, the oxidation reaction can be carried out in two stages. For example, by oxidizing the cellulose obtained by filtration after the first stage reaction under the same or different reaction conditions, oxidation can be carried out efficiently while avoiding reaction hindrance caused by the salt produced as a byproduct in the first stage reaction.

[0057] As another example of a carboxylation (oxidation) method, an oxidation method can be described by contacting a gas containing ozone with a cellulose raw material. Through this oxidation reaction, at least the hydroxyl groups at positions 2 and 6 of the pyranose ring are oxidized, causing the decomposition of the cellulose chain. The ozone concentration in the ozone-containing gas is preferably 50 g / m³. 3 ~250g / m 3 More preferably 50g / m 3 ~220g / m 3When the solid content of the cellulose raw material is set at 100 parts by weight, the ozone addition amount relative to the cellulose raw material is preferably 0.1 parts by weight to 30 parts by weight, more preferably 5 parts by weight to 30 parts by weight. The ozone treatment temperature is preferably 0°C to 50°C, more preferably 20°C to 50°C. The ozone treatment time is not particularly limited, ranging from about 1 minute to about 360 minutes, preferably about 30 minutes to about 360 minutes. When the ozone treatment conditions are within these ranges, excessive oxidation and decomposition of cellulose can be prevented, and the yield of oxidized cellulose becomes good. After ozone treatment, an additional oxidation treatment can be performed using an oxidant. The oxidant used for the additional oxidation treatment is not particularly limited, and examples include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfate, and peracetic acid. For example, an oxidant solution can be prepared by dissolving these oxidants in a polar organic solvent such as water or alcohol, and the cellulose raw material can be immersed in the solution for additional oxidation treatment.

[0058] The amount of carboxyl groups in oxidized cellulose can be adjusted by controlling the amount of oxidant added, reaction time, and other reaction conditions.

[0059] (Carboxymethylation)

[0060] In this invention, when carboxymethylated cellulose is used as the modified cellulose, the carboxymethylated cellulose can be obtained by carboxylating the above-mentioned cellulose raw material using a known method, or a commercially available product can be used. In either case, the degree of carboxymethyl substitution per glucosyl anhydride unit of cellulose is preferably 0.01 to 0.50. As an example of a method for manufacturing such carboxymethylated cellulose, the following method can be listed. Cellulose is used as the starting material, and as the solvent, 3 to 20 times the mass of water and / or a lower alcohol can be used. Specifically, water, methanol, ethanol, N-propanol, isopropanol, N-butanol, isobutanol, tert-butanol, etc., can be used alone, or a mixture of two or more media can be used. It should be noted that when a lower alcohol is mixed, the mixing ratio of the lower alcohol is 60% to 95% by mass. As a mercerizing agent, 0.5 to 20 moles of an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, is used per glucosyl anhydride residue of the starting material. The starting materials are mixed with a solvent and a mercerizing agent, and mercerized at a reaction temperature of 0°C to 70°C, preferably 10°C to 60°C, and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Then, a carboxymethylating agent is added at a molar ratio of 0.05 to 10.0 times per glucose residue, and an etherification reaction is carried out at a reaction temperature of 30°C to 90°C, preferably 40°C to 80°C, and a reaction time of 30 minutes to 10 hours, preferably 1 hour to 4 hours.

[0061] It should be noted that, in this specification, "carboxymethyl cellulose," as a type of modified cellulose used in the preparation of cellulose nanofibers, refers to a material in which at least a portion of the fibrous shape is retained when dispersed in water. Therefore, it is distinct from carboxymethyl cellulose, which is exemplified as a dispersant and is a type of water-soluble polymer in this specification. When observing an aqueous dispersion of "carboxymethyl cellulose" using an electron microscope, fibrous material can be observed. On the other hand, even when observing an aqueous dispersion of carboxymethyl cellulose, which is a type of water-soluble polymer, no fibrous material is observed. Furthermore, when "carboxymethyl cellulose" is measured using X-ray diffraction, peaks of cellulose type I crystals can be observed, but cellulose type I crystals are not observed in carboxymethyl cellulose, which is a water-soluble polymer.

[0062] (Phosphorylation)

[0063] Phosphorylated cellulose can be used as a chemically modified cellulose. This cellulose can be obtained by mixing powdered phosphate compound A with an aqueous solution of the aforementioned cellulose raw material, or by adding an aqueous solution of phosphate compound A to a slurry of the cellulose raw material.

[0064] Examples of phosphoric acid compounds A include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, or their esters. They can also be in the form of salts. Among these, compounds having phosphoric acid groups are preferred for reasons such as low cost, ease of handling, and the ability to improve defiberization efficiency by introducing phosphoric acid groups into the cellulose of pulp fibers. Examples of compounds having phosphoric acid groups include: phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate, etc. One or more of these can be used together. Among these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are more preferred from the viewpoints of high efficiency in introducing phosphoric acid groups, ease of defiberization in the following defiberization process, and ease of industrial application. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Furthermore, considering the improvement of reaction uniformity and the increased efficiency of introducing phosphate groups, the phosphate compound A is preferably used in the form of an aqueous solution. From the perspective of improving the efficiency of introducing phosphate groups, the pH of the aqueous solution of phosphate compound A is preferably 7 or lower, and from the viewpoint of suppressing the hydrolysis of pulp fibers, pH 3 to 7 is preferred.

[0065] As an example of a method for manufacturing phosphate-esterified cellulose, the following method can be cited. A phosphate compound A is added to a dispersion of cellulose raw material with a solid content concentration of 0.1% to 10% by mass while stirring, thereby introducing phosphate groups into the cellulose. When the cellulose raw material is set to 100 parts by mass, the amount of phosphate compound A added, based on the amount of phosphorus, is preferably 0.2 parts by mass to 500 parts by mass, more preferably 1 part by mass to 400 parts by mass. If the proportion of phosphate compound A is above the lower limit, the yield of fine fibrous cellulose can be further improved. However, when the upper limit is exceeded, the yield improvement effect reaches its peak, and therefore it is not preferred from a cost perspective.

[0066] At this point, in addition to the cellulose raw material and phosphate compound A, a powder or aqueous solution of compound B, other than those compounds, can also be mixed in. Compound B is not particularly limited, but is preferably a nitrogen-containing compound exhibiting alkalinity. Here, "alkalinity" is defined as an aqueous solution appearing pink to red in the presence of phenolphthalein indicator, or an aqueous solution having a pH greater than 7. The nitrogen-containing compound exhibiting alkalinity used in this invention is not particularly limited as long as it achieves the effects of this invention, but is preferably a compound having an amino group. Examples include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, etc., without particular limitation. Urea, which is low-cost and easy to handle, is preferred. The amount of compound B added relative to 100 parts by weight of the solid component of the cellulose raw material is preferably 2 to 1000 parts by weight, more preferably 100 to 700 parts by weight. The reaction temperature is preferably 0°C to 95°C, more preferably 30°C to 90°C. The reaction time is not particularly limited, and is approximately 1 minute to approximately 600 minutes, more preferably 30 minutes to 480 minutes. When the esterification reaction conditions are within these ranges, excessive esterification of cellulose can be prevented, thus preventing it from becoming easily soluble, resulting in a good yield of phosphorylated cellulose. After dehydrating the obtained phosphorylated cellulose suspension, it is preferable to perform heat treatment at 100°C to 170°C from the viewpoint of inhibiting cellulose hydrolysis. Furthermore, it is preferable to perform heating at 130°C or lower, preferably 110°C or lower, while water is present during the heat treatment, and then perform heat treatment at 100°C to 170°C after removing the water.

[0067] The degree of phosphate substitution per glucose unit of the phosphoric acid esterified cellulose is preferably 0.001 to 0.40. By introducing phosphate substituents into cellulose, the cellulose molecules repel each other electrically. Therefore, cellulose with introduced phosphate groups can be easily nanofibrillated. It should be noted that when the degree of phosphate substitution per glucose unit is less than 0.001, nanofibrillation cannot be sufficiently performed. On the other hand, when the degree of phosphate substitution per glucose unit is greater than 0.40, swelling or dissolution occurs, and therefore, nanofibers are sometimes not obtained. For efficient fibrillation, it is preferable to boil the phosphoric acid esterified cellulose raw material obtained above and then wash it with cold water.

[0068] (cationization)

[0069] As a chemically modified cellulose, cellulose obtained by further cationizing the above-mentioned carboxylated cellulose can be used. This cation-modified cellulose can be obtained by reacting the above-mentioned carboxylated cellulose raw material with a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium halide or its haloalcohol form, and an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, etc.) as a catalyst in the presence of water or an alcohol having 1 to 4 carbon atoms.

[0070] The degree of cationic substitution per glucose unit is preferably 0.02 to 0.50. By introducing cationic substituents into cellulose, the cellulose molecules repel each other electrically. Therefore, cellulose with introduced cationic substituents can be readily nanofibrillated. When the degree of cationic substitution per glucose unit is less than 0.02, sufficient nanofibrillation is not possible. On the other hand, when the degree of cationic substitution per glucose unit is greater than 0.50, nanofibers may not be obtained due to swelling or dissolution. For efficient defibrillation, it is preferable to wash the cationically modified cellulose raw material obtained above. This degree of cationic substitution can be adjusted according to the amount of cationizing agent added in the reaction and the composition ratio of water or alcohols with 1 to 4 carbon atoms.

[0071] In this invention, when the anionic modified cellulose obtained by anionic modification of cellulose raw material is a salt type, there is no limitation on the type of salt, but it is preferred to select salts with good defibrillation and dispersibility, such as sodium and ammonium.

[0072] <Deconstruction>

[0073] In this invention, the defiberization apparatus is not particularly limited, but it is preferable to use a high-speed rotary type, colloid mill type, high-pressure type, roller kneader type, ultrasonic type, or similar apparatus to apply a strong shear force to the aqueous dispersion. In particular, for efficient defiberization, it is preferable to use a wet high-pressure or ultra-high-pressure homogenizer capable of applying a pressure of 50 MPa or more and applying a strong shear force to the aqueous dispersion. The pressure is more preferably 100 MPa or more, and even more preferably 140 MPa or more. Alternatively, the CNF may be pretreated using a known mixing, stirring, emulsifying, or dispersing apparatus such as a high-speed shear mixer, as needed, before the defiberization and dispersion treatment in the high-pressure homogenizer. The number of treatments (passes) in the defiberization apparatus may be one or more, preferably two or more.

[0074] In dispersion processing, modified cellulose is typically dispersed in a solvent. There are no particular limitations on the solvent, as long as it can disperse the modified cellulose; examples include water, organic solvents (e.g., hydrophilic organic solvents such as methanol), and mixtures thereof. Since the cellulose raw material is hydrophilic, water is preferred as the solvent.

[0075] The concentration of the solid component of the modified cellulose in the dispersion is typically 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.3% by mass or more. This results in an appropriate liquid volume relative to the amount of cellulose fiber raw material, leading to high efficiency. The upper limit is typically 10% by mass or less, preferably 6% by mass or less. This maintains fluidity.

[0076] Pretreatment can be performed as needed before defiberization or dispersion. Pretreatment can be carried out using mixing, stirring, emulsifying, and dispersing devices such as high-speed shear mixers.

[0077] If the modified cellulose nanofibers obtained after the defibrillation process are in the salt form, they can be used directly, or they can be made into the acid form by acid treatment with inorganic acids or by using cation exchange resins. Alternatively, they can be used to impart hydrophobicity by using cationic additives.

[0078] Modifiers can be added to the cellulose nanofibers used in this invention. For example, for anionic modified cellulose nanofibers, nitrogen-containing compounds, phosphorus-containing compounds, etc., can be added. Ions and other substances bond with anionic groups on the surface of cellulose nanofibers, changing properties such as polarity, and can regulate the affinity for solvents and the dispersibility of fillers.

[0079] In this invention, when the anionic modified cellulose nanofibers obtained by defibrating anionic modified cellulose contain an acidic form, the dispersibility of the filler may become poor. Therefore, alkaline compounds such as sodium hydroxide and ammonium can be added appropriately to prepare a salt form.

[0080] When the mixture of the present invention is used in coatings or the like, and the coating film obtained after coating and drying the mixture requires water resistance, for example, when ammonium salt type fibers are used as anionic modified cellulose nanofibers, ammonia evaporates during drying, becoming acidic, and the coating film becomes water-resistant, which is therefore preferred.

[0081] (-COO - NH4 + +-COOH+NH3↑)

[0082] The addition of cellulose nanofibers to the mixture of the present invention has the advantage that the higher the addition amount, the better the effect of preventing filler sedimentation. However, when there is too much, the mixture becomes significantly thickened and difficult to handle. From this point of view, the concentration of CNF solids in the mixture is preferably 0.01% to 5% by mass, more preferably 0.1% to 0.5% by mass.

[0083] (3) Packing

[0084] The packing material used in this invention can be any type of inorganic or organic packing material. There are no restrictions on its shape, such as granular, flat, or fibrous.

[0085] Inorganic fillers include: calcium carbonate (light calcium carbonate, heavy calcium carbonate), magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay (kaolin, calcined kaolin, delaminated kaolin), talc, mica, zinc oxide, zinc stearate, titanium dioxide, silica (silica, silica / calcium carbonate composite, silica / titanium dioxide composite) made from sodium silicate and inorganic acids, kaolin, bentonite, diatomaceous earth, calcium sulfate, zeolite, and other inorganic compounds; metals or alloys such as aluminum, alumina, copper, zinc, iron, nickel, and tin; inorganic fillers that recycle ash obtained from the deinking process; and inorganic fillers that form composites with silica and calcium carbonate during the regeneration process. As calcium carbonate-silica composites, in addition to calcium carbonate and / or light calcium carbonate-silica composites, amorphous silica such as silica can also be used.

[0086] Examples of organic fillers include urea-formaldehyde resin, polystyrene resin, phenolic resin, micro hollow particles, acrylamide complexes, wood-derived substances (microfibers, microfibers, powdered kenaf), modified insoluble starch, and ungelatinized starch.

[0087] The above-mentioned fillers can be used alone or in combination of two or more.

[0088] As needed, surfactants such as preservatives and surface conditioners, binder resins, water-resistant agents, thickeners, etc., can be added to the mixture of the present invention.

[0089] In this invention, the sedimentation prevention effect of cellulose nanofiber-based fillers is improved by adding a small amount of dispersant to the mixture. In particular, the larger the particle size and the higher the aspect ratio of the filler, the more coarse the aggregates become during coagulation, and the higher the sedimentation rate, thus making the effect of adding dispersant more apparent.

[0090] Example

[0091] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0092] <Water separation rate>

[0093] 50 mL of the mixture obtained in the examples and comparative examples was injected into a 50 mL graduated cylinder according to JIS R3505, allowed to stand for 72 hours, and then the volume of liquid in the transparent portion at the top of the graduated cylinder was visually read. The water separation rate was then calculated according to the following formula. The results are shown in Table 1.

[0094] Water separation rate (%): (volume of liquid in the transparent portion (mL) / total volume of the mixture (mL)) × 100

[0095] <Particle size and uniformity of particle size distribution>

[0096] The remaining 50 mL of the mixture obtained in the examples and comparative examples was allowed to stand for 3 days, and then samples were collected from the bottom of the container. The volume average particle size (D10, D50, D90) of the obtained samples was determined using a laser diffraction particle size distribution analyzer (MASTER SIZER 3000, Malvern). D10 represents the particle size comprising 10% of the total particle size from the minimum value in the volume average particle size distribution, D50 represents the particle size comprising 50% of the total particle size from the minimum value, and D90 represents the particle size comprising 90% of the total particle size from the minimum value. It should be noted that in this determination, deionized water was used as the dispersion solvent, ultrasound was not used, and circulation was performed using a pump.

[0097] In addition, the uniformity of particle size distribution was determined using the same apparatus and the same sample as the particle size determination. The uniformity of particle size distribution is shown in the following formula.

[0098]

[0099] Here, di is the particle size of each grade, d50 is the center value of the particle size distribution, and Vi is the volume of each grade. Uniformity is the scale of the absolute deviation from the center value of the particle size distribution, preferably 1 or less.

[0100] The results of the obtained particle size and uniformity of particle size distribution are shown in Table 1.

[0101] <Transparency>

[0102] In this specification, transparency refers to the transmittance of light at a wavelength of 660 nm when CNF oxide is prepared as an aqueous dispersion with a solid content of 1% (weight / volume). The transparency of the CNF oxide obtained in the manufacturing example was determined as follows: a CNF dispersion (1% solid content (weight / volume), dispersion medium: water) was prepared, and the transmittance of light at 660 nm was measured using a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) with a square cell having an optical path length of 10 mm.

[0103] <Stability Test>

[0104] 210 g of the 1.0 wt% oxidized cellulose nanofiber aqueous dispersion obtained in the manufacturing example was measured into a 600 mL plastic container, and then deionized water was added to bring the concentration to 0.7% and the mixture was stirred (1000 rpm, 5 minutes) to obtain 300 g of the 0.7 wt% oxidized CNF aqueous dispersion. Immediately after adjusting the concentration, the viscosity (before stirring) was measured using a type B viscometer at 6 rpm for 1 minute.

[0105] 300g of the oxidized CNF aqueous dispersion after the B-type viscosity was measured was stirred for 30 minutes (1000 rpm, 23°C) using a disperser. Immediately after stirring for 30 minutes, the B-type viscosity (viscosity after stirring) was measured using a B-type viscometer at 6 rpm for 1 minute.

[0106] The viscosity retention rate is calculated using the following formula.

[0107] Viscosity retention rate (%) = (Viscosity after stirring / Viscosity before stirring) × 100

[0108] <Manufacturing Example 1>

[0109] 5.00 g (octane dry) of bleached, unbeaten kraft pulp (85% brightness) derived from coniferous trees was added to 500 mL of an aqueous solution containing 20 mg (0.025 mmol / g oven-dry cellulose) of TEMPO (Sigma-Aldrich) and 514 mg of sodium bromide (1.0 mmol / g oven-dry cellulose), and stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to bring the sodium hypochlorite concentration to 2.2 mmol / g, initiating the oxidation reaction. During the reaction, the pH of the system decreased, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the pH of the system no longer changed, consuming the sodium hypochlorite. The pulp was separated by filtering the reaction mixture using a glass filter and thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield was 93%, the oxidation reaction time was 60 minutes, and the carboxyl content (hereinafter sometimes referred to as "degree of modification") was 0.75 mmol / g. The mixture was adjusted to 1.0% (w / v) with water, and defibrilation was performed using a high-pressure homogenizer until the transparency was sufficiently high, yielding an oxidized cellulose nanofiber aqueous dispersion with a transparency of 88%. The average fiber diameter was 4 nm, and the aspect ratio was 280. Stability tests were conducted on this oxidized CNF aqueous dispersion, and type B viscosity values ​​were obtained before and after stirring. The viscosity retention rate was 50%.

[0110] <Manufacturing Example 2>

[0111] 5.00 g (octane dry) of bleached, unbeaten kraft pulp (85% brightness) derived from coniferous trees was added to a 500 mL aqueous solution containing 39 mg (0.05 mmol / g oven-dry cellulose) of TEMPO (Sigma-Aldrich) and 514 mg of sodium bromide (1.0 mmol / g oven-dry cellulose), and stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to bring the sodium hypochlorite concentration to 6.0 mmol / g, initiating the oxidation reaction. During the reaction, the pH of the system decreased, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the pH of the system no longer changed, consuming the sodium hypochlorite. The pulp was separated by filtering the reaction mixture through a glass filter and thoroughly washing the pulp with water, thus obtaining oxidized pulp (carboxylated cellulose). The pulp yield was 90%, the oxidation reaction time was 90 minutes, and the carboxyl content was 1.51 mmol / g. The concentration was adjusted to 1.0% (w / v) with water, and defibrilation was performed using a high-pressure homogenizer, resulting in an aqueous dispersion of oxidized cellulose nanofibers with a transparency of 95.0%. The average fiber diameter was 3 nm, and the aspect ratio was 250. Stability tests were conducted on this oxidized CNF aqueous dispersion, and type B viscosity values ​​were obtained before and after stirring. The viscosity retention rate was 39%.

[0112] <Manufacturing Example 3>

[0113] 5.00 g (octane dry) of bleached, unbeaten kraft pulp (85% brightness) derived from coniferous trees was added to 500 mL of an aqueous solution containing 20 mg (0.025 mmol / g oven-dry cellulose) of TEMPO (Sigma-Aldrich) and 514 mg of sodium bromide (1.0 mmol / g oven-dry cellulose), and stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to bring the sodium hypochlorite concentration to 1.3 mmol / g, initiating the oxidation reaction. During the reaction, the pH of the system decreased, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the pH of the system no longer changed, consuming the sodium hypochlorite. The pulp was separated by filtering the reaction mixture through a glass filter and thoroughly washing the pulp with water, thus obtaining oxidized pulp (carboxylated cellulose). The pulp yield was 99%, the oxidation reaction time was 50 minutes, and the carboxyl content was 0.42 mmol / g. The concentration was adjusted to 1.0% (weight / volume) with water, and the mixture was then subjected to defibrillation using a high-pressure homogenizer until the transparency was sufficiently high, resulting in an aqueous dispersion of oxidized cellulose nanofibers with a transparency of 75.2%. The average fiber diameter was 4 nm, and the aspect ratio was 380. Stability tests were conducted on this oxidized CNF aqueous dispersion, and type B viscosity values ​​were obtained before and after stirring. The viscosity retention rate was 88%.

[0114] <Example 1>

[0115] An aqueous dispersion of oxidized cellulose nanofibers obtained in Manufacturing Example 1 above, with a CNF solids content of 0.2% by mass, was prepared. While stirring at 3000 rpm using a high-speed mixer, polycarboxylic acid (trade name: Aron T-50, manufactured by Toa Synthetic Co., Ltd.) as a dispersant was added to bring the CNF content to 0.1% by mass. Then, 10% by mass of kaolin (trade name: BARRISURF HX, manufactured by Imerys Co., Ltd.) as a filler and water were added to prepare 100 mL of the mixture. The water separation rate, particle size, and particle size uniformity of the obtained mixture were measured.

[0116] <Examples 2-6, Examples 8-9, Examples 12-16>

[0117] As shown in Table 1, mixtures were prepared by varying the amount and concentration of carboxyl groups in the oxidized cellulose nanofiber aqueous dispersion, the type and concentration of the dispersant, and the type of filler, following the same procedure as in Example 1. The water separation rate, particle size, and particle size uniformity of the resulting mixtures were measured.

[0118] <Example 7>

[0119] The oxidized pulp obtained in Manufacturing Example 1 was adjusted to pH 2.4 using hydrochloric acid, and then washed twice with deionized water. Then, 3.2 g of polyetheramine (JEFFAMINE M1000) was added relative to the solids content of 4 g of oxidized pulp, and the volume was adjusted to 400 g using deionized water. The pulp was then subjected to defibrillation treatment using a high-pressure homogenizer, similar to Manufacturing Example 1, to obtain an oxidized cellulose nanofiber aqueous dispersion with a transparency of 90%. The average fiber diameter was 4 nm, and the aspect ratio was 275. Stability tests were performed on this oxidized CNF aqueous dispersion, and type B viscosity values ​​were obtained before and after stirring. The viscosity retention rate was 52%. In the same manner as in Example 1, 10% by mass of kaolin (trade name: BARRISURF HX, manufactured by Imerys) as a filler and water were added to this oxidized cellulose nanofiber dispersion to prepare a 100 mL mixture. The water separation rate, particle size, and particle size uniformity of the obtained mixture were measured.

[0120] <Example 10>

[0121] Except for using the oxidized cellulose nanofiber aqueous dispersion obtained in Manufacturing Example 2, 100 mL of the mixture was prepared in the same manner as in Example 1. The water separation rate, particle size, and particle size uniformity of the resulting mixture were measured.

[0122] <Example 11>

[0123] Except for using the oxidized cellulose nanofiber aqueous dispersion obtained in Manufacturing Example 3, 100 mL of the mixture was prepared in the same manner as in Example 1. The water separation rate, particle size, and particle size uniformity of the resulting mixture were measured.

[0124] <Comparative Examples 1-5>

[0125] Without adding a dispersant, the concentration of oxidized cellulose nanofibers and the type and concentration of fillers were varied as shown in Table 1, and a mixture was prepared in the same manner as in Example 1. The water separation rate, particle size, and particle size uniformity of the resulting mixture were measured.

[0126] <Comparative Examples 6-11>

[0127] Without adding cellulose nanofibers, mixtures were prepared in the same manner as in Example 1 by varying the type and concentration of dispersant and filler, as shown in Table 1. The water separation rate, particle size, and particle size uniformity of the resulting mixtures were measured.

[0128] It should be noted that the details of the dispersants and fillers used in the examples and comparative examples are as follows.

[0129] (Dispersant)

[0130] Product Name: Aron T-50, Sodium Polyacrylate, 43% Solids, Manufactured by Toa Sangyo Co., Ltd.

[0131] • Name: Polycarboxylate A, Solid content 36.0%

[0132] Here, polycarboxylic acid A is manufactured by the following method.

[0133] In a glass reaction vessel equipped with a thermometer, stirrer, reflux device, nitrogen inlet tube, and dropper, 148 parts of water and 94 parts (5 mol%) of polyethylene glycol polypropylene glycol monoallyl ether (average addition moles of ethylene oxide 37, average addition moles of propylene oxide 3, random addition of ethylene oxide to propylene oxide) were added. The reaction vessel was purged with nitrogen under stirring, and the temperature was raised to 80°C under a nitrogen atmosphere. Then, a monomer aqueous solution containing 35 parts (40 mol%) of methacrylic acid, 5 parts (7 mol%) of acrylic acid, 63 parts (5 mol%) of methoxy polyethylene glycol methacrylate (average addition moles of ethylene oxide 25), 60 parts (43 mol%) of hydroxypropyl acrylate, 8 parts of 3-mercaptopropionic acid, and 165 parts of water, and a mixture of 3 parts of ammonium persulfate and 47 parts of water were continuously added dropwise over 2 hours to the reaction vessel maintained at 80°C. Furthermore, by reacting at a temperature maintained at 100°C for 1 hour, an aqueous solution of the copolymer (polycarboxylic acid A) was obtained.

[0134] Product Name: Aron A30SL, Ammonium Polyacrylate, 40% Solids, Manufactured by Toa Synthetic Co., Ltd.

[0135] Product Name: Aron A-6114, Carboxylic Acid Copolymer (Ammonium Salt), 40% Solids, Manufactured by Toa Synthetic Co., Ltd.

[0136] Product Name: FS600LC, Carboxymethyl Cellulose, Powder, Manufactured by Nippon Paper Corporation

[0137] Product Name: JEFFAMINE (registered trademark) M1000, polyetheramine, manufactured by Huntsman Corporation.

[0138] Product Name: Disparlon AQ-330, Polyether Phosphate, 100% Active Ingredient, Manufactured by Kusunoki Chemical Co., Ltd.

[0139] Product Name: Demol EP, High Molecular Weight Polycarboxylic Acid, 25% Solid Content, Manufactured by Kao Corporation

[0140] (filler)

[0141] Product Name: BARRISURF HX, Kaolin, Particle Size %: 64 (<2μm), Manufactured by Imerys Minerals Japan Co., Ltd.

[0142] • Product Name: Callite KT, Calcium Carbonate, Primary Particle Size: 300nm (Electron Microscope Observation), Manufactured by Shiraishi Kogyo Co., Ltd.

[0143] Product Name: A-21S, Mica, Volume Average Particle Size: 23μm, Aspect Ratio: 70, Manufactured by Yamaguchi Mica Co., Ltd.

[0144] Product Name: A-11, Mica, Volume Average Particle Size: 3μm, Manufactured by Yamaguchi Mica Co., Ltd.

[0145] Product Name: B-82, Mica, Volume Average Particle Size: 180 μm, Aspect Ratio: 100, Manufactured by Yamaguchi Mica Co., Ltd.

[0146]

[0147] As shown in Table 1, in the mixture containing (1) dispersant, (2) cellulose nanofibers and (3) filler, the results are low water separation rate, excellent dispersion stability of filler and excellent uniformity of particle size distribution (Examples 1-16).

[0148] On the other hand, in the case containing (2) cellulose nanofibers and (3) filler but not (1) dispersant, the result was a large water separation rate and poor dispersion stability of the filler. Differences were observed in the particle size determination results compared to the examples (Comparative Examples 1-5). Specifically, when the filler was kaolin and mica, the uniformity of particle size distribution was high, and the uniformity deteriorated. In Comparative Example 5, which used large-particle-size B-82 as mica, the particle size D10 value was large. When the filler was calcium carbonate, the particle size D10 and D50 values ​​were large.

[0149] In addition, when (2) cellulose nanofibers were not present but (1) dispersant and (3) filler were present, the result was a large water separation rate and poor dispersion stability of the filler (Comparative Examples 6-11).

[0150] Based on the above results, it is believed that the fine cellulose nanofibers entering the filler hinder its sedimentation. It is further suggested that in the case of anionicly modified cellulose nanofibers, not only is this sedimentation prevention effect achieved, but they also function significantly as anionic dispersants.

[0151] However, even in the presence of cellulose nanofibers, when using substances that easily aggregate in water as fillers, the aggregation prevention effect of the filler is insufficient due to the function of cellulose nanofibers as an anionic dispersant alone, and aggregation will occur. It is believed that aggregated fillers become prone to settling, and water separation will occur even in the presence of cellulose nanofibers. By using cellulose nanofibers and dispersants in combination, the aggregation of the filler can be suppressed, and a settling-preventing effect can be achieved.

Claims

1. A mixture, wherein, The mixture contains the following (1) to (4): (1) A dispersant, wherein the dispersant is selected from one or more anionic polymers and polyethers. (2) Oxidized cellulose nanofibers (3) Packing material, wherein the packing material is an inorganic packing material. The inorganic filler is selected from one or more of the following: calcium carbonate, magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay, talc, mica, zinc stearate, calcium carbonate-silica composite, kaolin, bentonite, diatomaceous earth, calcium sulfate, zeolite, inorganic fillers that recycle ash obtained from the deinking process, and inorganic fillers obtained by forming a composite with silica and calcium carbonate during the regeneration process. (4) Water, The amount of dispersant added in (1) is 0.01 to 25 parts by weight relative to 100 parts by weight of filler. The amount of oxidized cellulose nanofibers added in the mixture is 0.01% to 5% by mass. The carboxyl content of the oxidized cellulose nanofibers described in (2) is 0.4 mmol / g to 1.0 mmol / g. The water separation rate of the mixture after standing for 72 hours is less than 1%.

2. The mixture as described in claim 1, wherein, The anionic polymer is a polymer with a carboxyl group or a polymer with a phosphate group.

3. The mixture as described in claim 1 or 2, wherein, The amount of oxidized cellulose nanofibers added to the mixture is 0.1% to 5% by mass.

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