Method for producing powder containing anion-modified cellulose nanofibers

Abstract

To provide a method for producing a powder containing anion-modified cellulose nanofibers, which, when made into a dispersion, exhibits excellent redispersibility and suspension stability, suppresses a decrease in viscosity compared with a dispersion obtained from a dried raw material prior to pulverization, and further enables excellent operability when used on-site.SOLUTION: The method includes a step of pulverizing a dried raw material containing anion-modified cellulose nanofibers at or below 65°C, The powder has a moisture content of 20 mass% or less, and the powder has an average particle diameter of 40 to 500 μm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing an anion-modified cellulose nanofiber-containing powder.

Background Art

[0002] Cellulose nanofibers and microfibrillated cellulose obtained by refining cellulose (hereinafter collectively referred to as "fine cellulose fibers") are fine fibers with a fiber diameter in the nano- to micro-order, and are expected to be used in various fields as novel materials having functions such as high strength, high elasticity, and thixotropy, which are not present in ordinary pulp.

[0003] Generally, cellulose nanofibers are produced in a state of being stably dispersed in water, and are usually used in various applications as industrial materials or additive materials for foods and cosmetics in the state of a cellulose nanofiber dispersion liquid having a predetermined concentration. In order to stably maintain the state of cellulose nanofibers, about several tens of times the amount of water of cellulose nanofibers is required, and this large amount of water leads to an increase in costs such as packaging, storage, and transportation of cellulose nanofibers. Therefore, it is dried to form a dried product, and water is added and redispersed when used, and it is used as a redispersion liquid.

[0004] The dried product of fine cellulose fibers is commercialized through processes such as drying, pulverization, classification, and recovery for fine cellulose fibers in a state of being dispersed in water (wet state). However, during these processes, due to the formation of hydrogen bonds between the fibers of fine cellulose fibers, even when water is added again to the commercialized dry pulverized product for redispersion, the viscosity characteristics and the like cannot be restored to the same level as before drying, and there is a problem that the excellent characteristics of fine cellulose fibers cannot be exhibited.

[0005] As a technique for obtaining a dried product of fine cellulose fibers that is easily redispersible, a method of drying a mixture of fine cellulose fibers and a solvent using a vacuum drum dryer (Patent Document 1) has been proposed.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The dried fine cellulose fibers obtained in Patent Document 1 have uneven shapes and sizes. When used on-site, they often clog joints and the like of the device frequently, and it may be necessary to stop the operation of the device for cleaning, so they are not excellent in operability.

[0008] In order to suppress the occurrence of clogging of the device, it is necessary to make the dried product obtained in Patent Document 1 into relatively small powder with a particle diameter of about 500 μm or less. However, depending on the pulverization method, the quality of the obtained powder may deteriorate, and it may lack redispersibility and suspension stability.

[0009] Therefore, an object of the present invention is to provide a method for producing an anionic-modified cellulose nanofiber-containing powder that is excellent in redispersibility and suspension stability when used as a dispersion liquid, has a suppressed decrease in viscosity when compared with a dispersion liquid using a dry raw material before pulverization, and can obtain a powder with excellent operability when used on-site.

Means for Solving the Problems

[0010] As a result of intensive studies to achieve such an object, the present inventors have found that it is extremely effective to carry out the step of pulverizing the dry raw material under specific conditions so that the characteristics of the obtained powder are included in a certain range, and have completed the present invention.

[0011] The present invention provides the following. (1) A method for producing an anion-modified cellulose nanofiber-containing powder, comprising a step of pulverizing a dry raw material containing anion-modified cellulose nanofibers at 65°C or lower, wherein the powder has a moisture content of 20% by mass or less and an average particle diameter of 40 to 500 μm. A method for producing an anion-modified cellulose nanofiber-containing powder, characterized by the above. (2) The method for producing an anion-modified cellulose nanofiber-containing powder according to (1), characterized in that the pulverization treatment is carried out using an impact mill. [Advantages of the Invention]

[0012] According to the present invention, a dispersion obtained by dispersing the resulting powder in a solvent such as water is excellent in redispersibility and suspension stability, and the decrease in viscosity is suppressed when compared with a dispersion using the dry raw material before pulverization. Furthermore, it is possible to provide a method for producing an anion-modified cellulose nanofiber-containing powder capable of obtaining a powder excellent in operability when used on-site. [Embodiments for Carrying Out the Invention]

[0013] Hereinafter, the present invention will be described in detail. In the present invention, "~" includes the end values. That is, "X~Y" includes the values X and Y at both ends.

[0014] (Method for Producing Anion-Modified Cellulose Nanofiber-Containing Powder) The present invention relates to a method for producing an anion-modified cellulose nanofiber-containing powder, comprising a step of pulverizing a dry raw material containing anion-modified cellulose nanofibers at 65°C or lower, wherein the powder has a moisture content of 20% by mass or less and an average particle diameter of 40 to 500 μm.

[0015] (Step of Pulverization Treatment) The manufacturing method of the present invention includes a step of pulverizing a dry raw material containing anionic modified cellulose nanofibers at a temperature of 65°C or lower, preferably 60°C or lower, more preferably 50°C or lower, from the viewpoint of maintaining the quality after pulverization. If the temperature during the pulverization process is too high, there is a risk of reduced redispersibility, reduced viscosity, and reduced physical properties. The lower limit of the temperature in the step of performing the pulverization treatment is not particularly limited, but it is preferably 30°C or higher because there is a concern that condensation may occur inside the apparatus, the sample may adhere to the inside of the apparatus, and the operation may become difficult. The temperature in the step of performing the pulverization treatment can be measured by a thermometer attached to the apparatus, a thermometer attached to the surface of the apparatus, or the like.

[0016] (Anionic modified cellulose nanofibers) The anionic modified cellulose nanofibers (anionic modified CNF) used in the present invention can be obtained by defibrating anionic modified cellulose.

[0017] (Cellulose nanofibers (CNF)) The average fiber diameter of the CNF that can be used in the present invention is preferably 100 nm or less, more preferably 2 nm or more and 50 nm or less. The average fiber length is preferably 5 μm or less, more preferably 3 μm or less. The lower limit of the average fiber length is about 0.1 μm or more. The average fiber length can be measured by analyzing 200 randomly selected fibers using an atomic force microscope (AFM) when the diameter is less than 20 nm, and a field emission scanning electron microscope (FE-SEM) when the diameter is 20 nm or more, and calculating the average. The average aspect ratio of the CNF that can be used in the present invention is preferably 40 or more. The upper limit is not particularly limited, but is usually 1000 or less. The average aspect ratio can be calculated by the following formula: Aspect ratio = average fiber length / average fiber diameter

[0018] (Cellulose raw material) Examples of cellulose raw materials for producing anionic modified cellulose include those derived from plant materials (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animal materials (e.g., jellyfish), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc., and any of them can be used. Preferably, they are cellulose fibers derived from plants or microorganisms, and more preferably cellulose fibers derived from plants.

[0019] (Anionic modification) In the present invention, anionic modification means introducing an anionic group into cellulose, specifically, introducing an anionic group into the pyranose ring of cellulose by oxidation (carboxylation) or a substitution reaction. In the present invention, the oxidation (carboxylation) reaction means a reaction of directly oxidizing the hydroxyl group of the pyranose ring to a carboxyl group. Further, in the present invention, the substitution reaction means a reaction of introducing an anionic group into the pyranose ring by a substitution reaction other than the oxidation (carboxylation).

[0020] Examples of anionic modification include oxidation (carboxylation), carboxymethylation, esterification, etc. Among them, oxidation (carboxylation), carboxymethylation, and phosphoric acid esterification are more preferable, and oxidation (carboxylation) is particularly preferable.

[0021] (Oxidation) In the present invention, when using oxidized (carboxylated) cellulose as the anionic modified cellulose, the oxidized cellulose (also referred to as carboxylated cellulose) can be obtained by oxidizing (carboxylating) the above-mentioned cellulose raw material by a known method. Although not particularly limited, during the oxidation (carboxylation), it is preferably adjusted so that the amount of carboxyl groups is 0.6 to 2.0 mmol / g, and more preferably 1.0 mmol / g to 2.0 mmol / g, based on the absolute dry mass of the anionic modified cellulose nanofibers.

[0022] As an example of the oxidation (carboxylation) method, a method can be mentioned in which the cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides or mixtures thereof. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized to obtain cellulose fibers having an aldehyde group, a carboxyl group (-COOH) or 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.

[0023] The N-oxyl compound refers to a compound capable of generating a nitroxyl radical. As the N-oxyl compound, any compound can be used as long as it promotes the target oxidation reaction. For example, 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and its derivatives (for example, 4-hydroxy TEMPO) can be mentioned.

[0024] The amount of the N-oxyl compound used only needs to be a catalytic amount capable of oxidizing the cellulose as the raw material, and is not particularly limited. For example, for 1 g of absolutely dry cellulose, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.05 to 0.5 mmol is even more preferable. Also, about 0.1 to 4 mmol / L is good for the reaction system.

[0025] A bromide is a compound containing bromine, and examples thereof include alkali metal bromides that can dissociate and ionize in water. An iodide is a compound containing iodine, and examples thereof include alkali metal iodides. The usage amount of the bromide or iodide can be selected within a range that can promote the oxidation reaction. The total amount of the bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol, for example, per 1 g of absolutely dry cellulose.

[0026] As the oxidizing agent, known ones can be used. For example, halogens, hypohalous acids, halous acids, perhalic acids or their salts, halogen oxides, peroxides, etc. can be used. Among them, sodium hypochlorite, which is inexpensive and has a low environmental impact, is preferable. The appropriate usage amount of the oxidizing agent is preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol, for example, per 1 g of absolutely dry cellulose. Also, for example, 1 to 40 mol is preferable per 1 mol of the N-oxyl compound.

[0027] The oxidation process of cellulose can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40 °C, and it may also be at room temperature of about 15 to 30 °C. Since carboxyl groups are generated in the cellulose as the reaction progresses, a decrease in the pH of the reaction solution is observed. In order to make the oxidation reaction proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at 8 to 12, preferably about 10 to 11. The reaction medium is preferably water in view of ease of handling and difficulty in causing side reactions.

[0028] The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.

[0029] Also, the oxidation reaction may be carried out in two steps. For example, the oxidized cellulose obtained by filtration after the completion of the first-step reaction is oxidized again under the same or different reaction conditions, so that it can be efficiently oxidized without being inhibited by the sodium chloride by-produced in the first-step reaction.

[0030] As another example of the oxidation (carboxylation) method, a method of oxidizing by bringing a gas containing ozone into contact with a cellulose raw material can be cited. By this oxidation reaction, the hydroxyl groups at least at the 2-position and 6-position of the glucopyranose ring are oxidized, and the decomposition of the cellulose chain occurs. The ozone concentration in the gas containing ozone is preferably 3 50 to 250 g / m 3 and more preferably 50 to 220 g / m. The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass when the solid content of the cellulose raw material is 100 parts by mass. The ozone treatment temperature is preferably 0 to 50°C, and more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, preferably about 30 to 360 minutes. When the ozone treatment conditions are within these ranges, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of oxidized cellulose is good. After the ozone treatment, a post-oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the post-oxidation treatment is not particularly limited, and examples include chlorine-based compounds such as chlorine dioxide and sodium chlorite, and oxygen, hydrogen peroxide, persulfuric acid, peracetic acid, etc. For example, these oxidizing agents are dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the post-oxidation treatment can be performed by immersing the cellulose raw material in the solution.

[0031] The amount of carboxyl groups in the oxidized cellulose can be adjusted by controlling the reaction conditions such as the addition amount of the above-mentioned oxidizing agent and the reaction time.

[0032] (Carboxymethylation) In the present invention, when carboxymethylated cellulose is used as the anionic modified cellulose, the carboxymethylated cellulose may be obtained by carboxymethylating the above-mentioned cellulose raw material by a known method, or a commercially available product may be used. In any case, those having a degree of substitution of carboxymethyl groups per anhydroglucose unit of cellulose of 0.01 to 0.50 are preferred. An example of a method for producing such carboxymethylated cellulose can be the following method. Using cellulose as the starting material, 3 to 20 times by mass of water and / or lower alcohol as the solvent, specifically, water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butyl alcohol, isobutyl alcohol, tertiary butanol, etc. alone, or a mixed medium of two or more kinds is used. In addition, when mixing a lower alcohol, the mixing ratio of the lower alcohol is 60 to 95% by mass. As the mercerizing agent, 0.5 to 20 times the molar amount of an alkali metal hydroxide per anhydroglucose residue of the starting material, specifically, sodium hydroxide or potassium hydroxide is used. The starting material, the solvent, and the mercerizing agent are mixed, and a mercerization treatment is carried out at a reaction temperature of 0 to 70 ° C, preferably 10 to 60 ° C, and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times the molar amount per glucose residue, and an etherification reaction is carried out at a reaction temperature of 30 to 90 ° C, preferably 40 to 80 ° C, and a reaction time of 30 minutes to 10 hours, preferably 1 hour to 4 hours.

[0033] (Crystallinity of Cellulose I) The crystallinity of type I cellulose in carboxymethylated cellulose is preferably 50% or more, more preferably 60% or more. The crystallinity of type I cellulose in carboxymethylated cellulose can be controlled by the concentration of the mercerizing agent during production, the temperature during treatment, and the degree of carboxymethylation. Since a high concentration of alkali is used in mercerization and carboxymethylation, the type I crystals of cellulose are likely to be converted to type II. However, for example, by adjusting the amount of alkali (mercerizing agent) used to adjust the degree of conversion, the desired crystallinity can be maintained. The upper limit of the crystallinity of type I cellulose is not particularly limited. Realistically, it is considered that about 90% is the upper limit. The crystallinity of type I cellulose in carboxymethylated cellulose and the crystallinity of type I cellulose in carboxymethylated CNF obtained by defibrating it are usually the same.

[0034] In this specification, "carboxymethylated cellulose", which is a type of anionic-modified cellulose used for the preparation of anionic-modified CNF, refers to a substance in which at least a part of the fibrous shape is maintained even when dispersed in water. Therefore, it is distinguished from carboxymethyl cellulose, which is a type of water-soluble polymer described later. When the aqueous dispersion of "carboxymethylated cellulose" is observed with an electron microscope, fibrous substances can be observed. On the other hand, even when the aqueous dispersion of carboxymethyl cellulose, which is a type of water-soluble polymer, is observed, fibrous substances are not observed. Also, "carboxymethylated cellulose" can observe the peak of type I cellulose crystals when measured by X-ray diffraction, but type I cellulose crystals are not seen in carboxymethyl cellulose, which is a water-soluble polymer.

[0035] (Esterification) In the present invention, when esterified cellulose is used as the anionic-modified cellulose, the esterified cellulose can be obtained by a method of mixing a powder or aqueous solution of a phosphoric acid-based compound A with the aforementioned cellulose raw material, or a method of adding an aqueous solution of a phosphoric acid-based compound A to a slurry of the cellulose raw material.

[0036] Examples of the phosphoric acid compound A include phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, polyphosphonic acid, or esters thereof. These may be in the form of salts. Among these, compounds having a phosphate group are preferred because they are low in cost, easy to handle, and can introduce a phosphate group into the cellulose of pulp fibers to improve the defibrillation efficiency. Examples of the compound having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, 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, and the like. These can be used alone or in combination of two or more. 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 of phosphate group introduction, easy defibrillation in the following defibrillation step, and easy industrial application. Particularly preferred are sodium dihydrogen phosphate and disodium hydrogen phosphate. Further, since the uniformity of the reaction is enhanced and the efficiency of phosphate group introduction is increased, the phosphoric acid compound A is preferably used as an aqueous solution. The pH of the aqueous solution of the phosphoric acid compound A is preferably 7 or less because the efficiency of phosphate group introduction is increased, but pH 3 to 7 is preferred from the viewpoint of suppressing hydrolysis of pulp fibers.

[0037] As an example of a method for producing a phosphoric acid esterified cellulose, the following method can be cited. To a dispersion of a cellulose raw material having a solid content concentration of 0.1 to 10% by mass, a phosphoric acid-based compound A is added while stirring to introduce a phosphate group into the cellulose. When the cellulose raw material is 100 parts by mass, the addition amount of the phosphoric acid-based compound A is preferably 0.2 to 500 parts by mass, more preferably 1 to 400 parts by mass, in terms of the amount of phosphorus element. If the ratio of the phosphoric acid-based compound A is equal to or higher than the lower limit value, the yield of the fine cellulose fibers can be further improved. However, if it exceeds the upper limit value, the effect of improving the yield reaches a plateau, which is not preferable from the cost aspect.

[0038] At this time, in addition to the cellulose raw material and the phosphoric acid-based compound A, a powder or an aqueous solution of another compound B may be mixed. Compound B is not particularly limited, but a nitrogen-containing compound showing basicity is preferable. Here, "basicity" is defined as that the aqueous solution exhibits a peach to red color in the presence of a phenolphthalein indicator, or the pH of the aqueous solution is greater than 7. The nitrogen-containing compound showing basicity used in the present invention is not particularly limited as long as the effects of the present invention are achieved, but a compound having an amino group is preferable. For example, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, etc. can be mentioned, but it is not particularly limited. Among these, urea which is low-cost and easy to handle is preferable. The addition amount of compound B is preferably 2 to 1000 parts by mass, more preferably 100 to 700 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C. The reaction time is not particularly limited, but is about 1 to 600 minutes, more preferably 30 to 480 minutes. When the conditions of the esterification reaction are within these ranges, it is possible to prevent the cellulose from being excessively esterified and becoming easily soluble, and the yield of the phosphoric acid esterified cellulose becomes good. After dehydrating the obtained phosphoric acid esterified cellulose suspension, from the viewpoint of suppressing the hydrolysis of cellulose, it is preferable to perform heat treatment at 100 to 170°C. Further, while water is contained during the heat treatment, it is preferable to heat at 130°C or lower, preferably 110°C or lower, and after removing the water, perform heat treatment at 100 to 170°C.

[0039] The degree of substitution of phosphate groups per glucose unit of the phosphorylated cellulose is preferably from 0.001 to 0.40. By introducing phosphate group substituents into cellulose, the celluloses repel each other electrically. Therefore, the cellulose into which phosphate groups are introduced can be easily defibrated. Note that if the degree of substitution of phosphate groups per glucose unit is less than 0.001, it cannot be sufficiently defibrated. On the other hand, if the degree of substitution of phosphate groups per glucose unit is greater than 0.40, it may swell or dissolve, and thus may not be obtained as fine cellulose fibers. In order to perform defibration efficiently, the phosphorylated cellulose raw material obtained above is preferably washed by boiling and then washing with cold water. These modifications by esterification are modifications by substitution reaction. The degree of substitution in the esterified cellulose and the degree of substitution when the esterified cellulose is refined are usually the same.

[0040] The phosphorylated cellulose can also be rephrased as cellulose into which a phosphooxo acid group, which is an anionic group, or a substituent derived from a phosphooxo acid group (sometimes simply referred to as a "phosphooxo acid group") is introduced. Here, the phosphooxo acid group is, for example, a divalent functional group corresponding to the one obtained by removing a hydroxy group from phosphoric acid, and specifically, it is a group represented by -PO 3 H 2 Substituents derived from the phosphooxo acid group include substituents such as salts of the phosphooxo acid group and phosphooxo acid ester groups. Note that the substituent derived from the phosphooxo acid group may be included in the cellulose nanofiber as a group in which phosphate groups are condensed (for example, a pyrophosphate group). Further, the phosphooxo acid group may be, for example, a phosphite group (phosphonic acid group), and the substituent derived from the phosphooxo acid group may be a salt of the phosphite group or the like.

[0041] The amount of phosphorus oxoacid groups such as phosphate groups or phosphite groups introduced into the phosphoric acid esterified cellulose is not particularly limited. During the phosphoric acid esterification, it is preferably adjusted so that the amount of the phosphorus oxoacid groups is 0.5 to 5 mmol / g, more preferably 0.5 to 2.5 mmol / g, based on the absolute dry mass of the anionic modified cellulose nanofiber.

[0042] (Defibration) The apparatus used for defibrating the anionic modified cellulose is not particularly limited, and apparatuses such as a high-speed rotation type, a colloid mill type, a high-pressure type, a roll mill type, and an ultrasonic type can be used. It is preferable to apply a strong shearing force to the aqueous dispersion of the anionic modified cellulose during defibration. In particular, for efficient defibration, it is preferable to use a wet high-pressure or ultra-high pressure homogenizer that can apply a pressure of 50 MPa or more and a strong shearing force to the aqueous dispersion. The pressure is more preferably 100 MPa or more, and even more preferably 140 MPa or more. Further, prior to the defibration and dispersion treatment with the high-pressure homogenizer, the aqueous dispersion may be pretreated using a known mixing, stirring, emulsifying, and dispersing apparatus such as a high-speed shearing mixer, if necessary.

[0043] (Dispersant) The anionic modified cellulose nanofiber-containing powder of the present invention preferably contains a dispersant from the viewpoint of improving redispersibility. Examples of the dispersant include water-soluble polymers and surfactants. When a water-soluble polymer is used, it is preferable to use a water-soluble polymer to cover the portion with a low charge density on the surface of the anionic modified cellulose nanofiber and suppress the formation of hydrogen bonds to prevent aggregation of the cellulose nanofibers during drying.

[0044] (Water-soluble polymer) In the present invention, examples of the water-soluble polymer include cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ethyl cellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, pullulan, starch, katakuri starch, kudzu starch, modified starch (cationized starch, phosphorylated starch, phosphorous cross-linked starch, phosphoric monoesterified phosphorous cross-linked starch, hydroxypropyl starch, hydroxypropylated phosphorous cross-linked starch, acetylated adipic acid cross-linked starch, acetylated phosphorous cross-linked starch, acetylated oxidized starch, sodium octenyl succinate starch, acetic acid starch, oxidized starch), corn starch, gum arabic, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soy protein hydrolyzate, peptone, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyvinyl pyrrolidone, polyvinyl acetate, polyamino acid, polylactic acid, poly(lactic acid), polyglycerol, latex, rosin sizing agent, petroleum resin sizing agent, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide-polyamine resin, polyethyleneimine, polyamine, plant gum, polyethylene oxide, hydrophilic cross-linked polymer, polyacrylate, starch polyacrylate copolymer, tamarind gum, guar gum, and colloidal silica, and mixtures of one or more thereof. Among these, cellulose derivatives are preferable from the viewpoint of compatibility with anionic modified cellulose nanofibers, and carboxymethyl cellulose and its salts are particularly preferable. Water-soluble polymers such as carboxymethyl cellulose and its salts are considered to improve redispersibility by entering between anionic modified cellulose nanofibers and increasing the distance between CNFs.

[0045] When using carboxymethyl cellulose or its salt as the water-soluble polymer, it is preferable to use carboxymethyl cellulose having a degree of carboxymethyl group substitution of 0.55 to 1.6 per anhydroglucose unit, more preferably 0.55 to 1.1, and even more preferably 0.65 to 1.1. Also, those with longer molecules (higher viscosity) are preferred because they have a higher effect of widening the distance between CNFs. The B-type viscosity at 25 °C and 600 rpm in a 1% by mass aqueous solution of carboxymethyl cellulose is preferably 3 to 14000 mPa·s, more preferably 7 to 14000 mPa·s, and even more preferably 1000 to 8000 mPa·s. Here, the "carboxymethyl cellulose or its salt" as the water-soluble polymer is completely soluble in water, so it is distinguished from the carboxymethylated cellulose whose fiber shape can be confirmed in the above-mentioned water.

[0046] In the present invention, when the powder containing anionic modified cellulose nanofibers contains a dispersant, the mixing ratio of anionic modified CNF (absolute dry solid content) and the dispersant is preferably 2:8 to 8:2, more preferably 5:5 to 7:3, from the viewpoint of obtaining an improved redispersibility effect. If the mixing ratio of the dispersant is too much higher than the above upper limit value, problems such as viscosity characteristics such as thixotropy, which are characteristics of anionic modified CNF, and a decrease in dispersion stability may occur. If the mixing ratio of the dispersant is too much lower than the above lower limit value, sufficient redispersibility cannot be obtained.

[0047] The dry raw material containing anionic modified cellulose nanofibers used in the present invention can be obtained by dehydrating and drying an aqueous suspension containing anionic modified cellulose nanofibers and a dispersant such as a water-soluble polymer used as necessary. Further, by adjusting the pH of the aqueous suspension to 9 to 11, a powder containing anionic modified cellulose nanofibers with even better redispersibility can be obtained.

[0048] In the present invention, the dehydration and drying method may be any conventionally known method, and examples thereof include spray drying, freeze drying, pressing, air drying, hot air drying, and vacuum drying. Examples of the drying apparatus specifically used may include the following. That is, continuous tunnel drying apparatus, band drying apparatus, vertical drying apparatus, vertical turbo drying apparatus, multi-stage disk drying apparatus, ventilation drying apparatus, rotary drying apparatus, pneumatic drying apparatus, spray dryer drying apparatus, spray drying apparatus, cylindrical drying apparatus, drum drying apparatus, reduced pressure belt drying apparatus, screw conveyor drying apparatus, rotary drying apparatus with heating tubes, vibration transport drying apparatus, fluidized bed drying apparatus, etc., batch box type drying apparatus, ventilation drying apparatus, vacuum box type drying apparatus, stirring drying apparatus, shelf drying apparatus, freeze drying apparatus, etc. These drying apparatuses can be used alone or in combination of two or more. Among these, it is preferable to use a drum drying apparatus or a belt drying apparatus, and from the viewpoint of energy efficiency, it is more preferable to use a drum drying apparatus that directly supplies thermal energy to the object to be dried uniformly.

[0049] In the present invention, from the viewpoint of reducing the load on the pulverizer, the dried raw material is preferably dried so that the moisture content becomes 20% by mass or less. The moisture content is more preferably 0 to 15% by mass, and even more preferably 0 to 10% by mass. It may also be dried to a moisture content of 0% (absolute dry).

[0050] (Pulverizer) The type of pulverizer that can be used in the pulverization process of the present invention is not particularly limited as long as the treatment temperature can be set to 65°C or lower when obtaining particles with an average particle diameter of 40 to 500 μm. Examples thereof include impact pulverizers and disk pulverizers. From the viewpoints of low increase in the body temperature during pulverization and high pulverization efficiency, it is preferable to use an impact pulverizer.

[0051] Examples of impact crushers include Pulverizer (manufactured by Hosokawa Micron Corporation), Fine Impact Mill (manufactured by Hosokawa Micron Corporation), Super Micron Mill (manufactured by Hosokawa Micron Corporation), Inomizer (manufactured by Hosokawa Micron Corporation), Fine Mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), CUM Type Centrifugal Mill (manufactured by Mitsui Mining Co., Ltd.), IXeed Mill (manufactured by Mino Industries Co., Ltd.), Ultra Plex (manufactured by Mino Industries Co., Ltd.), Contra Plex (manufactured by Mino Industries Co., Ltd.), Colo Plex (manufactured by Mino Industries Co., Ltd.), Sample Mill (manufactured by Seishin Co., Ltd.), Bantam Mill (manufactured by Seishin Co., Ltd.), Atomizer (manufactured by Seishin Co., Ltd.), Tornado Mill (manufactured by Nikkiso Co., Ltd.), Near Mill (manufactured by Dalton Co., Ltd.), HT Type Fine Crusher (manufactured by Horai Co., Ltd.), Free Crusher (manufactured by Nara Machinery Co., Ltd.), New Cosmomizer (manufactured by Nara Machinery Co., Ltd.), Turbo Mill (manufactured by Freund Industries Co., Ltd.), Gather Mill (manufactured by Nishimura Machinery Co., Ltd.), Spar Powder Mill (manufactured by Nishimura Machinery Co., Ltd.), Blade Mill (manufactured by Nisshin Engineering Co., Ltd.), Super Rotor (manufactured by Nisshin Engineering Co., Ltd.), Npa Crusher (manufactured by Sanjo Industry Co., Ltd.), Wire Mill (manufactured by Mitsuki Manufacturing Co., Ltd.), Pulp Crusher (manufactured by Zuiho Co., Ltd.), Jacobson Fine Crusher (manufactured by Kobe Steel Pantech Co., Ltd.), Universal Mill (manufactured by Tokuju Kousakusho Co., Ltd.), Atomizer (manufactured by Tokyo Atomizer Manufacturing Co., Ltd.), Mill Stardom (manufactured by Tokyo Atomizer Manufacturing Co., Ltd.), etc. From the viewpoint of obtaining good crushed products due to the low rise in the body temperature during crushing, it is preferable to use a Pulverizer, Mill Stardom, and Sample Mill.

[0052] Examples of disk crushers include Vibration Disk Mill (manufactured by Retch), Centricutter (manufactured by Nippon Coke & Engineering Co., Ltd.), Turbo Disk Mill (manufactured by Freund Turbo Co., Ltd.), Mortar Type High-Speed Crusher (manufactured by Mino Industries Co., Ltd.), etc.

[0053] The temperature of the pulverization process can be adjusted by cooling the body or the airflow that conveys the raw material. Introducing a cooling device into the body is not preferable because the cost will increase significantly. Also, when using a powerful cooler to lower the temperature, there is a concern of moisture mixing into the powder product due to condensation, so it is not preferable.

[0054] In the pulverization process, the pulverization conditions can be appropriately adjusted by creating a calibration curve in advance from the pulverization conditions (for example, processing time, input amount, etc.) and the desired physical properties of the pulverized material and referring to it.

[0055] (Powder containing anionic modified cellulose nanofibers) (Moisture content) The powder containing anionic modified cellulose nanofibers obtained by the production method of the present invention has a moisture content of 20% by mass or less, more preferably 15% by mass or less. It may be dried to 0% (absolutely dry) moisture content. If the moisture content is too high, the efficiency during product transportation may decrease.

[0056] (Average particle diameter) The powder containing anionic modified cellulose nanofibers obtained by the production method of the present invention has an average particle diameter of 40 to 500 μm, more preferably 45 to 450 μm, and even more preferably 45 to 420 μm from the viewpoints of quality and operability. If the average particle diameter is too large, there are problems such as poor fluidity, easy clogging at the joints of the device, etc., resulting in poor operability due to the need for frequent cleaning, and bulkiness and a decrease in transfer efficiency. If the average particle diameter is too small, there is a problem that it becomes ultrafine powder and is prone to dusting. The average particle diameter can be adjusted according to the moisture content of the sample and the conditions of the pulverizer. Here, the average particle diameter (D50) is the particle diameter at which 50% is included when integrated from the minimum value in the particle diameter distribution based on volume. The particle diameter distribution can be measured using a laser diffraction / scattering particle size distribution analyzer.

[0057] According to the method for producing an anion-modified cellulose nanofiber-containing powder of the present invention, since it has a step of pulverizing a dry raw material containing anion-modified cellulose nanofibers at 65°C or lower, the influence of heat on the anion-modified cellulose nanofibers can be reduced. As a result, when the powder obtained by the production method of the present invention is used, it is excellent in redispersibility and suspension stability when made into a dispersion, and the decrease in viscosity is suppressed when compared with a dispersion using the dry raw material before pulverization. In addition, since the powder obtained by the production method of the present invention has an average particle size within a specific range, it is less likely to clog devices and the like during on-site use, and has excellent operability. In order to perform the pulverization treatment under the above conditions, an impact pulverizer can be preferably used.

Examples

[0058] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. When the measurement / calculation method of each numerical value in each example is not particularly described, it is measured / calculated by the method described in the specification.

[0059] (Average fiber diameter and average fiber length of CNF) The suspension obtained by redispersing the powder in water was diluted, and 200 randomly selected fibers were analyzed using an atomic force microscope (AFM), and the average was taken. The aspect ratio was calculated by the following formula. Aspect ratio = average fiber length / average fiber diameter

[0060] (Amount of carboxyl groups) The amount of carboxyl groups was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid with a gentle change in electrical conductivity. After preparing 60 mL of a 0.5 mass% slurry (aqueous dispersion) of oxidized cellulose (carboxymethylated cellulose), adding 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then dropping 0.05 N sodium hydroxide aqueous solution until the pH reached 11 and measuring the electrical conductivity. Amount of carboxyl groups [mmol / g of oxidized cellulose] = a [mL] × 0.05 / mass of oxidized cellulose [g].

[0061] (Degree of carboxymethyl substitution) The degree of carboxymethyl substitution was measured by the following method. Approximately 2.0 g of the sample was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of nitric acid methanol was added, and the mixture was shaken for 3 hours to convert the salt (CMC) of carboxymethylated cellulose CNF to H-CMC (hydrogen-type carboxymethylated CNF). Approximately 1.5 - 2.0 g of the absolute dry H-CMC was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. The H-CMC was moistened with 15 mL of 80% methanol, 100 mL of 0.1 N-NaOH was added, and the mixture was shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, excess NaOH was back-titrated with 0.1 N-H 2 SO 4 and the degree of carboxymethyl substitution (DS value) was calculated by the following formula. A = [(100 × F’ - 0.1 N-H 2 SO 4 (mL) × F) × 0.1] / (absolute dry mass of H-CMC (g)) Degree of carboxymethyl substitution = 0.162 × A / (1 - 0.058 × A) F’: Factor of 0.1 N-H 2 SO 4 F: Factor of 0.1 N-NaOH.

[0062] The degree of carboxymethyl substitution in the CNF of carboxymethylated cellulose is usually the same as that in the carboxymethylated cellulose before it becomes CNF. ​

[0063] (Degree of crystallinity of cellulose I) The degree of crystallinity of cellulose I in the carboxymethylated cellulose nanofiber was measured by the following method. The sample was placed in a glass cell and measured using an X-ray diffractometer (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity was calculated using the method of Segal et al. Based on the diffraction intensity in the range of 2θ = 10° to 50° in the X-ray diffraction pattern, the degree of crystallinity was calculated from the diffraction intensity of the 002 plane at 2θ = 22.6° and the diffraction intensity of the amorphous part at 2θ = 18.5° by the following equation.

[0064] Xc = (I002c - Ia) / I002c × 100 Xc = Degree of crystallinity of cellulose I (%) I002c: Diffraction intensity of the 002 plane at 2θ = 22.6° Ia: Diffraction intensity of the amorphous part at 2θ = 18.5°

[0065] The ratio of type I crystals in the carboxymethylated cellulose nanofiber is usually the same as that in the carboxymethylated cellulose before being made into CNF.

[0066] (Amount of phosphono acid groups) The amount of phosphono acid groups (amount of phosphate groups or phosphite groups) was measured by the following method. First, ion-exchanged water was added to the target CNF to prepare a slurry with a solid content concentration of 0.2% by mass. After treating the obtained slurry with an ion-exchange resin, titration with an alkali was performed for measurement.

[0067] The treatment with the ion-exchange resin was carried out by adding a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) with a volume of 1 / 10 to the above CNF-containing slurry, performing a shaking treatment for 1 hour, and then pouring it onto a mesh with an opening of 90 μm to separate the resin and the slurry.

[0068] Also, the titration using an alkali was performed by measuring the change in the pH value shown by the CNF-containing slurry after treatment with an ion-exchange resin while adding 10 μL of a 0.1 N aqueous sodium hydroxide solution to the slurry every 5 seconds. Note that the titration was performed while blowing nitrogen gas into the slurry for 15 minutes before the start of the titration. In this neutralization titration, two points where the increment (the differential value with respect to the amount of alkali dropped in terms of pH) becomes maximum are observed in the curve plotting the pH measured against the amount of alkali added. Among these, the first maximum point of the increment obtained first after starting to add the alkali is called the first end point, and the next maximum point of the increment is called the second end point. The amount of alkali required from the start of the titration to the first end point is equal to the amount of the first dissociable acid in the slurry used for the titration. Also, the amount of alkali required from the start of the titration to the second end point is equal to the total amount of dissociable acids in the slurry used for the titration. Note that the value obtained by dividing the amount of alkali (mmol) required from the start of the titration to the first end point by the solid content (g) in the slurry to be titrated was defined as the amount of phosphooxo acid groups (mmol / g).

[0069] (Measurement of moisture content) The moisture content in the powders obtained in the examples and comparative examples was calculated as the difference using the mass (absolute dry mass) of the obtained powder after drying at 105 °C for 3 hours or more and the mass before drying.

[0070] (Average particle diameter) The average particle diameter (D50) of the powders obtained in the examples and comparative examples was determined from the particle size distribution by volume average particle diameter. The particle size distribution was measured under the condition of a particle refractive index of 1.5 using a laser diffraction / scattering particle size distribution analyzer (MasterSizer 3000, manufactured by Spectris Co., Ltd.). In the measurement, the dry powder sample was directly put into the apparatus for measurement.

[0071] (Viscosity) The viscosity of the powders obtained in the examples and comparative examples was determined by adding the powder product to water, stirring it at 3000 rpm for 30 minutes using a homodisper to prepare a 1% by mass CNF redispersion, and measuring the viscosity of the obtained CNF redispersion after 3 minutes at 25°C and a rotation speed of 60 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.). The results are shown in Tables 1 and 2.

[0072] (Operability) For the powders obtained in the examples and comparative examples, the operability was evaluated as follows. Specifically, first, the powder product was put into a conical tank. The product was taken out from the rotary valve at the bottom of the tank and discharged to the next process using a screw conveyor. The clogging situation of the powder at each location was checked at each time point after about 10 hours, about 24 hours, and about 48 hours, and the necessity of cleaning was evaluated according to the following criteria. The results are shown in Tables 1 and 2. ○: No cleaning is required even after operating for about 48 hours or more. △: Clogging occurs at joints of the device etc. during operation for about 24 hours, so cleaning is required. ×: Cleaning is required after operating for about 10 hours.

[0073] (Redispersibility) For the powders obtained in the examples and comparative examples, the redispersibility was evaluated as follows. Specifically, the powder product was added to water, stirred at 3000 rpm for 30 minutes using a homodisper to prepare a 0.1% by mass CNF redispersion. A colorant (ink) was added to this CNF redispersion and then observed with an optical microscope, and the presence or absence of CNF aggregates that could not be visually distinguished was evaluated according to the following criteria. The results are shown in Tables 1 and 2. ○: Aggregates are generally not visible. △: Aggregates are sporadically seen, but the aggregate area ratio to the whole is less than 5%. ×: Aggregates are sporadically seen throughout, and the aggregate area ratio to the whole is 5% or more.

[0074] (Suspension stability) For the powders obtained in the examples and comparative examples, the suspension stability was evaluated as follows. Specifically, the powder product was added to water and stirred at 3000 rpm for 30 minutes using a homodisper to prepare a 0.2 mass% CNF redispersion solution. Calcium carbonate powder was added thereto to a concentration of 1 mass%, and the mixture was further stirred at 3000 rpm for 5 minutes. The resulting solution was placed in a colorimetric tube. The dispersion state of calcium carbonate after allowing the colorimetric tube to stand for one month was visually observed and evaluated according to the following criteria. The results are shown in Tables 1 and 2. ○: No sedimentation of calcium carbonate is observed, and the dispersed state is maintained. △: Although calcium carbonate is generally not sedimented, partial water separation has occurred. ×: Sedimentation of calcium carbonate is observed.

[0075] (Production Example 1) (Production of TEMPO-oxidized CNF) 500 g (dry weight) of bleached unbeaten kraft pulp (whiteness 85%) derived from softwood was added to 20 L of an aqueous solution in which TEMPO (Sigma Aldrich, 0.025 mmol / g based on the cellulose raw material) and sodium bromide (1 mmol / g based on the cellulose raw material) were dissolved, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system to a concentration of 5.2 mmol / g to initiate the oxidation reaction. During the reaction, the pH of the system decreased, but a 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain TEMPO-oxidized pulp (carboxylated cellulose). The pulp yield at this time was 90%, the time required for the oxidation reaction was 100 minutes, and the amount of carboxyl groups was 1.4 mmol / g.

[0076] The TEMPO-oxidized pulp obtained in the above process was adjusted to 1.0% (w / v) with water and treated three times with an ultrahigh-pressure homogenizer (20°C, 150 Mpa) to obtain a dispersion of TEMPO-oxidized CNF. The resulting fibers had an average fiber diameter of 4 nm and an aspect ratio of 220.

[0077] (Production Example 2) (Production of Carboxymethylated CNF) To a 5 L twin-screw kneader with the rotation speed adjusted to 100 rpm, 1089 parts of isopropanol (IPA) and a solution prepared by dissolving 31 parts of sodium hydroxide in 121 parts of water were added, and 200 parts were charged based on the dry mass when broadleaf pulp (manufactured by Nippon Paper Industries Co., Ltd., LBKP) was dried at 100 °C for 60 minutes. Stirring and mixing were carried out at 30 °C for 60 minutes to prepare mercerized cellulose. While further stirring, 117 parts of sodium monochloroacetate were added, and after stirring at 30 °C for 30 minutes, the temperature was raised to 70 °C over 30 minutes, and a carboxymethylation reaction was carried out at 70 °C for 60 minutes. The proportion of water in the reaction medium during the mercerization reaction and the carboxymethylation reaction was 10% by mass. After completion of the reaction, it was neutralized, washed with 65% hydrous methanol, de-liquefied, dried, and pulverized to obtain a sodium salt of carboxymethylated cellulose with a carboxymethyl substitution degree of 0.27 and a crystallinity of cellulose I type of 64%. The measurement methods for the carboxymethyl substitution degree and the crystallinity of cellulose I type are as described above.

[0078] The sodium salt of carboxymethylated cellulose obtained in the above process was adjusted to 1.0% (w / v) with water and treated 3 times with an ultra-high pressure homogenizer (20 °C, 150 Mpa) to obtain a dispersion of carboxymethylated CNF. The obtained carboxymethylated CNF had an average fiber diameter of 3.2 nm and an aspect ratio of 40.

[0079] (Production Example 3) (Production of Phosphorylated CNF) Bleached unbeaten kraft pulp derived from softwood (brightness 85%, basis weight 245 g / m 2The following phosphorus oxo-oxidation treatment was carried out on the sheet-like material. First, an aqueous mixed solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (dry basis) of the above raw material pulp, and adjusted to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165 °C for 250 seconds to introduce phosphate groups into the cellulose in the pulp and obtain phosphorylated pulp. 10 L of ion-exchanged water was poured into 100 g (dry basis) of the obtained phosphorylated pulp, and the pulp dispersion obtained was stirred so that the pulp was uniformly dispersed, and then the operation of filtration and dehydration was repeated for washing. When the electrical conductivity of the filtrate became 100 μS / cm or less, it was taken as the end point of washing. Next, after diluting the washed phosphorylated pulp with 10 L of ion-exchanged water, a 1N aqueous sodium hydroxide solution was added little by little while stirring to obtain a phosphorylated pulp slurry with a pH of 12 or more and 13 or less. The phosphorylated pulp slurry was dehydrated and washed to obtain phosphorylated pulp subjected to neutralization treatment.

[0080] FT-IR was used to measure the infrared absorption spectrum of the obtained phosphorylated pulp. As a result, absorption based on P=O of phosphate groups was observed near 1230 cm -1 −1, and it was confirmed that phosphate groups were added to the pulp. In addition, when the obtained phosphorylated pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions near 2θ = 14° or more and 17° or less and near 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals.

[0081] The phosphorylated pulp obtained in the above process was adjusted to 1.0% (w / v) with water and treated 3 times with an ultra-high pressure homogenizer (20 °C, 150 Mpa) to obtain a dispersion of phosphorylated CNF. The obtained fibers had an average fiber diameter of 4 nm and an aspect ratio of 200.

[0082] It was confirmed by X-ray diffraction that the obtained CNF maintained cellulose type I crystals. The amount of phosphate groups (the amount of the first dissociation acid) was 1.45 mmol / g. The total amount of dissociation acid was 2.45 mmol / g.

[0083] (Example 1) (Production of dry raw material) As the anionic modified CNF, TEMPO-oxidized CNF obtained in Production Example 1 (carboxy group amount: 1.4 mmol / g, average fiber diameter: 4 nm, aspect ratio: 220) was used. Carboxymethyl cellulose (trade name: F350HC-4, viscosity (1%, 25 °C) about 3000 mPa·s, degree of carboxymethyl substitution about 0.9) was added to a 0.7 mass% aqueous suspension of TEMPO-oxidized CNF at 40 mass% with respect to the anionic modified CNF (that is, so that the solid content of carboxymethyl cellulose was 40 mass parts when the solid content of the anionic modified CNF was 100 mass parts), and the mixture was stirred with a TK homomixer (12,000 rpm) for 60 minutes to prepare an aqueous dispersion containing anionic modified CNF. The pH of this dispersion was about 7 to 8. An aqueous solution of 0.5% sodium hydroxide was added to this aqueous dispersion, and after adjusting the pH to 9, it was applied to the drum surface of a drum dryer D0405 (manufactured by Katsuragi Kogyo Co., Ltd.) to form a thin film with a thickness of about 100 to 200 μm, and dried at a drum surface temperature of 80 °C, a dryer internal pressure of 2 kPa, and a drum rotation speed of 2 rpm to obtain a dry raw material containing anionic modified CNF with a solid content concentration of 80 mass%. The viscosity of this dry raw material was 1600 mPa·s. The measurement conditions for viscosity and the like were in accordance with the measurement conditions for the above-mentioned powder products.

[0084] (Production of powder) The dry raw material containing CNF obtained as described above was pulverized using an impact pulverizer (Pulverizer, manufactured by Hosokawa Micron Corporation) as a pulverizer. The temperature during pulverization was 60 °C. The obtained pulverized product had its particle size adjusted by the pulverization strength and the adjustment of the pulverizer outlet. The pulverized product after particle size adjustment was collected using a cyclone to obtain an anionic modified CNF-containing powder. The obtained powder had a solid content concentration of 81 mass%, a water content of 19 mass%, and an average particle size of 45 μm.

[0085] (Examples 2 and 3) Except that the raw material solid content concentration was adjusted to 90% in Example 2 and 95% in Example 3, in the same manner as in Example 1, a dry raw material containing anionic modified CNF was obtained. Using the dry raw material thus obtained, except that the particle size was adjusted by the crushing strength and the crushing outlet adjustment of the pulper, in the same manner as in Example 1, an anionic modified CNF-containing powder was obtained. The solid content concentration of the dry raw material, the temperature during crushing, the solid content concentration, the moisture content, and the average particle size of the obtained powder are shown in Table 1.

[0086] (Examples 4 and 5) Except that the raw material solid content concentration was adjusted to 85% in Example 4 and 91% in Example 5, in the same manner as in Example 1, a dry raw material containing anionic modified CNF was obtained. Except for using the dry raw material thus obtained and replacing the impact crusher used as the crusher with a Millstardam (manufactured by Tokyo Atomizer Co., Ltd.) instead of the pulper, in the same manner as in Example 1, an anionic modified CNF-containing powder was obtained. The solid content concentration of the dry raw material, the temperature during crushing, the solid content concentration, the moisture content, and the average particle size of the obtained powder are shown in Table 1.

[0087] (Example 6) Except that the raw material solid content concentration was adjusted to 82%, in the same manner as in Example 1, a dry raw material containing anionic modified CNF was obtained. Except for using the dry raw material thus obtained and replacing the impact crusher used as the crusher with a sample mill (manufactured by Seishin Co., Ltd.) instead of the pulper, in the same manner as in Example 1, an anionic modified CNF-containing powder was obtained. The solid content concentration of the dry raw material, the temperature during crushing, the solid content concentration, the moisture content, and the average particle size of the obtained powder are shown in Table 1.

[0088] (Example 7) (Manufacture of dry raw material) As the anionic modified CNF, carboxymethylated CNF (carboxymethyl substitution degree: 0.27, average fiber diameter: 3.2 nm, aspect ratio: 40) obtained in Production Example 2 was used. To a 0.7 mass% aqueous suspension of carboxymethylated CNF, carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., trade name: F350HC-4, viscosity (1 mass%, 25 °C, 60 rpm) about 3000 mPa·s, carboxymethyl substitution degree about 0.90) was added at 40 mass% with respect to the carboxymethylated CNF (that is, so that the solid content of carboxymethyl cellulose was 40 mass parts when the solid content of carboxymethylated CNF was 100 mass parts), and the mixture was stirred with a TK homomixer (12,000 rpm) for 60 minutes to prepare an aqueous dispersion containing carboxymethylated CNF as an anionic modified CNF. To this aqueous dispersion, 0.5 mass% of an aqueous sodium hydroxide solution was added to adjust the pH to 9, and then it was applied to the drum surface of a drum dryer D0405 (manufactured by Katsuragi Kogyo Co., Ltd.) and dried at 140 °C for 1 minute. The obtained dried product was scraped off to obtain a dried raw material containing anionic modified CNF with a solid content concentration of 90 mass%. The viscosity of this dried raw material was 1200 mPa·s. The measurement conditions for viscosity, etc. were in accordance with the measurement conditions for the above powder products.

[0089] (Production of powder) The dried raw material containing CNF obtained as described above was pulverized using an impact pulverizer (Pulverizer, manufactured by Hosokawa Micron Corporation) as a pulverizer. The temperature during pulverization was 55 °C. The obtained pulverized product had its particle size adjusted by adjusting the outlet screen diameter of the pulverizer. The pulverized product after particle size adjustment was recovered using a cyclone to obtain an anionic modified CNF-containing powder. The obtained powder had a solid content concentration of 92 mass%, a water content of 8 mass%, and an average particle size of 60 μm.

[0090] (Example 8) Except for adjusting the solid content concentration of the raw material to 95%, a dry raw material containing anionic modified CNF was obtained in the same manner as in Example 7. Except for using the dry raw material thus obtained, an anionic modified CNF-containing powder was obtained in the same manner as in Example 7. The solid content concentration of the dry raw material, the temperature during pulverization, the solid content concentration, the moisture content, and the average particle diameter of the obtained powder are shown in Table 1.

[0091] (Example 9) (Manufacture of dry raw material) As the anionic modified CNF, the phosphorylated CNF obtained in Production Example 3 (phosphoric acid group amount: 1.45 mmol / g, average fiber diameter: 4 nm, aspect ratio: 200) was used. This aqueous dispersion was applied to the drum surface of a drum dryer D0405 (manufactured by Katsuragi Kogyo Co., Ltd.) and dried at 140°C for 1 minute to obtain a dry raw material containing anionic modified CNF with a solid content concentration of 80% by mass. The viscosity of this dry raw material was 1700 mPa·s. The measurement conditions for viscosity, etc. were in accordance with the measurement conditions for the above powder products.

[0092] (Manufacture of powder) The dry raw material containing CNF obtained as described above was pulverized using an impact pulverizer (Pulverizer, manufactured by Hosokawa Micron Corporation) as a pulverizer. The temperature during pulverization was 50°C. The particle size of the obtained pulverized product was adjusted by adjusting the outlet screen diameter of the pulverizer. The pulverized product after particle size adjustment was collected using a cyclone to obtain an anionic modified CNF-containing powder. The solid content concentration of the obtained powder was 81% by mass, the moisture content was 19% by mass, and the average particle diameter was 80 μm.

[0093] (Example 10) Except for adjusting the solid content concentration of the raw material to 90%, a dry raw material containing anionic modified CNF was obtained in the same manner as in Example 9. Except for using the dry raw material thus obtained, an anionic modified CNF-containing powder was obtained in the same manner as in Example 9. The solid content concentration of the dry raw material, the temperature during pulverization, the solid content concentration, the moisture content, and the average particle diameter of the obtained powder are shown in Table 1.

[0094] (Comparative Examples 1 to 4) Except that the raw material solid content concentration was adjusted to 75% in Comparative Example 1, 93% in Comparative Example 2, 90% in Comparative Example 3, and 85% in Comparative Example 4, the same procedure as in Example 1 was followed to obtain a dry raw material containing anionic modified CNF. Using the dry raw material thus obtained, an anionic modified CNF-containing powder was obtained in the same manner as in Example 1, except that the particle size was adjusted by the crushing strength and the adjustment of the crushing outlet of the pulper. The solid content concentration of the dry raw material, the temperature during crushing, the solid content concentration, the moisture content, and the average particle size of the obtained powder are shown in Table 2.

[0095] (Comparative Example 5) Except that the raw material solid content concentration was adjusted to 90%, the same procedure as in Example 1 was followed to obtain a dry raw material containing anionic modified CNF. An anionic modified CNF-containing powder was obtained in the same manner as in Example 1, except that the dry raw material thus obtained was used and the impact crusher used as the crusher was replaced with a Millstardam (manufactured by Tokyo Atomizer Co., Ltd.). The solid content concentration of the dry raw material, the temperature during crushing, the solid content concentration, the moisture content, and the average particle size of the obtained powder are shown in Table 2.

[0096] (Comparative Example 6) Except that the raw material solid content concentration was adjusted to 77%, the same procedure as in Example 1 was followed to obtain a dry raw material containing anionic modified CNF. An anionic modified CNF-containing powder was obtained in the same manner as in Example 1, except that the dry raw material thus obtained was used and the impact crusher used as the crusher was replaced with a sample mill (manufactured by Seishin Co., Ltd.). The solid content concentration of the dry raw material, the temperature during crushing, the solid content concentration, the moisture content, and the average particle size of the obtained powder are shown in Table 2.

[0097] (Comparative Example 7) Except that the raw material solid content concentration was adjusted to 85%, the same procedure as in Example 7 was followed to obtain a dry raw material containing anionic modified CNF. An anionic modified CNF-containing powder was obtained in the same manner as in Example 7, except that the dry raw material thus obtained was used. The solid content concentration of the dry raw material, the temperature during crushing, the solid content concentration, the moisture content, and the average particle size of the obtained powder are shown in Table 2.

[0098] (Comparative Example 8) A dry raw material containing anionic modified CNF was obtained in the same manner as in Example 1, except that the solid content concentration of the raw material was adjusted to 85%. An anionic modified CNF-containing powder was obtained in the same manner as in Example 1, except that the thus obtained dry raw material was used and the pulverizer was changed to a pneumatic pulverizer instead of an impact pulverizer. The solid content concentration of the dry raw material, the temperature during pulverization, the solid content concentration, the water content, and the average particle size of the obtained powder are shown in Table 2.

[0099] [Table 1]

[0100] [Table 2]

[0101] As can be seen from Table 1, Examples 1 to 10 employ the production method of the present invention, have a step of pulverizing a dry raw material containing anionic modified cellulose nanofibers at 65°C or lower, the water content of the obtained powder is 20% by mass or less, and the average particle size of the obtained powder is 40 to 500 μm. The powders containing anionic modified cellulose nanofibers of Examples 1 to 10 obtained by the production method of the present invention were excellent in operability, redispersibility, and suspension stability. Further, the dispersion obtained using this powder had a suppressed decrease in viscosity as compared with the case where the dry raw material was used as the dispersion as it was.

[0102] Comparative Example 1 has a lower solid content concentration of the dry raw material compared to Examples 1 to 3. When attempting to pulverize so that the average particle size is included in a predetermined range, it becomes difficult to pulverize, and as a result, the temperature during pulverization rises. The obtained powder is inferior in redispersibility and suspension stability, and the dispersion obtained using this powder has a large decrease in viscosity as compared with the case where the dry raw material is used as the dispersion as it is.

[0103] In Comparative Example 2, as a result of pulverization such that the average particle diameter became smaller than the lower limit of the predetermined range, the temperature during pulverization increased compared to Examples 1 to 3, and the obtained powder was inferior in redispersibility and suspension stability. The dispersion obtained using this powder had a large decrease in viscosity compared to the case where the dry raw material was used as the dispersion as it was.

[0104] In Comparative Example 3, as a result of pulverization such that the average particle diameter became larger than the upper limit of the predetermined range, the obtained powder had low fluidity compared to Examples 1 to 3, and was inferior in workability when using this powder on-site and was difficult to handle within the process.

[0105] In Comparative Example 4, since the temperature during pulverization was too high compared to Examples 1 to 3, the obtained powder was inferior in redispersibility and suspension stability. The dispersion obtained using this powder had a large decrease in viscosity compared to the case where the dry raw material was used as the dispersion as it was.

[0106] In Comparative Example 8, as a result of pulverization using an air jet mill such that the average particle diameter was within the predetermined range, the temperature during pulverization increased compared to Examples 1 to 3, and the obtained powder was inferior in redispersibility and suspension stability. The dispersion obtained using this powder had a large decrease in viscosity compared to the case where the dry raw material was used as the dispersion as it was.

Claims

1. A method for producing an anion-modified cellulose nanofiber-containing powder, comprising: a step of pulverizing a dry raw material containing anion-modified cellulose nanofibers at 65°C or lower; the powder having a moisture content of 20% by mass or less; the powder having an average particle diameter of 40 to 500 μm, characterized in that it is a method for producing an anion-modified cellulose nanofiber-containing powder.

2. The method for producing an anion-modified cellulose nanofiber-containing powder according to claim 1, wherein the pulverization treatment is carried out using an impact mill.