Method for producing fine-processed fibrous cellulose

Abstract

The purpose of the present invention is to provide a method for producing fine-processed fibrous cellulose from which fine fibrous cellulose excellent in uniformity of quality can be continuously obtained.　A method for producing fine-processed fibrous cellulose according to the present invention comprises, in sequence: a step (1) for discharging a fibrous cellulose dispersion introduced into a tank having a stirrer from the lower part of the tank and transferring the fibrous cellulose dispersion to a defibrating device; a step (2) for fine-processing fibrous cellulose in the transferred fibrous cellulose dispersion by using the defibrating device; and a step (3) for transferring the fine-processed fibrous cellulose dispersion to the upper part of the same tank having the stirrer, said steps (1)-(3) being performed repeatedly. At least said steps (1)-(3) are performed while rotating a stirring blade provided in the tank having the stirrer. The stirring blade provided in the tank having the stirrer has at least one stirring blade selected from the group consisting of a stirring blade A and a stirring blade B described below.　Stirring blade A: a stirring blade installed in a substantially horizontal direction near at least a liquid surface Stirring blade B: a stirring blade rotating along a wall surface

Description

Method for producing finely divided fibrous cellulose

[0001] The present invention relates to a method for producing finely divided fibrous cellulose.

[0002] Micronized fibrous cellulose obtained by micronizing fibrous cellulose has excellent strength, elasticity, thermal stability, and the like, and is used industrially as a filler for compounding resins and rubbers. Furthermore, aqueous dispersions of micronized fibrous cellulose are used as viscosity modifiers, stabilizers, and the like. Micronized fibrous cellulose can be obtained by defibrating pulp fibers through mechanical processing. Patent Document 1 discloses a cellulose nanofiber production apparatus that micronizes pulp fibers in a slurry, with the aim of providing a cellulose nanofiber production apparatus that can efficiently produce cellulose nanofibers while suppressing clogging and contamination of the piping. The cellulose nanofiber production apparatus includes a high-pressure homogenizer that micronizes the pulp fibers in the slurry, a tank that stores the slurry in which the pulp fibers have been micronized using the high-pressure homogenizer, and piping connected to the high-pressure homogenizer and the tank, the piping being sanitary piping connected via a joint equipped with a gasket.

[0003] Patent No. 6776111

[0004] In the micronization treatment of fibrous cellulose, micronization is usually performed multiple times, and it is known to perform micronization multiple times using two tanks, as described in Patent Document 1. When two tanks are used, each tank is a batch-type treatment, and therefore piping must be switched, and a method for producing micronized fibrous cellulose with high production efficiency has been desired. Therefore, an object of the present invention is to provide a method for producing micronized fibrous cellulose that can continuously obtain micronized fibrous cellulose with excellent quality uniformity.

[0005] The present inventors have found that the use of a specific tank equipped with an agitator makes it possible to continuously obtain pulverized fibrous cellulose with excellent quality uniformity, and have thus completed the present invention. The present invention relates to the following [1] to [8]. [1] A method for producing pulverized fibrous cellulose, comprising the steps of: step (1): allowing a fibrous cellulose dispersion charged into a tank equipped with an agitator to flow out from the bottom of the tank and transfer to a defibrator; step (2): using the defibrator to pulverize the fibrous cellulose in the transferred fibrous cellulose dispersion; and step (3): transferring the pulverized fibrous cellulose dispersion to the upper part of the same tank equipped with an agitator, in this order, and repeating steps (1) to (3), wherein steps (1) to (3) are performed while rotating an agitator blade provided in the tank equipped with an agitator, and the agitator blade provided in the tank equipped with an agitator has at least one agitator blade selected from the group consisting of agitator blade A and agitator blade B described below. Agitator blade A: an agitator blade installed at least near the liquid surface in a substantially horizontal direction Agitator blade B: an agitator blade that rotates along the wall surface [2] The method for producing fibrous cellulose according to [1], which has at least agitator blade A. [3] The method for producing fibrous cellulose according to [1] or [2], which has agitator blade A and agitator blade B. [4] The method for producing fibrous cellulose according to any one of [1] to [3], wherein the rotation speed of the agitator blade is 1 rpm or more and 100 rpm or less. [5] The method for producing fibrous cellulose according to any one of [1] to [4], wherein the viscosity of the fibrous cellulose dispersion in the agitator-equipped tank is 1 mPa s or more and 5,000,000 mPa s or less. [6] The method for producing fibrous cellulose according to any one of [1] to [5], wherein the agitator blade A and agitator blade B are single blades. [7] The method for producing pulverized fibrous cellulose according to any one of [1] to [6], wherein the defibration device is at least one selected from the group consisting of a macerator, a beater, and an atomizer.[8] The method for producing pulverized fibrous cellulose according to any one of [1] to [7], wherein the fibrous cellulose in the fibrous cellulose dispersion is fibrous cellulose into which an ionic group has been introduced.

[0006] According to the present invention, there is provided a method for producing fibrous cellulose that can continuously produce fibrous cellulose having excellent uniformity in quality.

[0007] Fig. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. Fig. 2 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fibrous cellulose having carboxy groups and pH. Figs. 3(a) to 3(c) are conceptual cross-sectional views of a tank equipped with an agitator used in this embodiment.

[0008] [Method for Producing Microfibrillated Fibrous Cellulose] The method for producing microfibrillated fibrous cellulose of this embodiment comprises the following steps (1) to (3) in this order, and is a method for producing microfibrillated fibrous cellulose by repeatedly performing steps (1) to (3), wherein steps (1) to (3) are performed while rotating an agitator blade provided in a tank equipped with an agitator, and the agitator blade provided in the tank equipped with an agitator has at least one agitator blade selected from the group consisting of agitator blade A and agitator blade B described below. Agitator blade A: an agitator blade installed in a substantially horizontal direction at least near the liquid surface Agitator blade B: an agitator blade that rotates along the wall surface Step (1): A step of allowing a fibrous cellulose dispersion charged into a tank equipped with an agitator to flow out from the bottom of the tank and transfer it to a defibrator Step (2): A step of microfibrillating the fibrous cellulose in the transferred fibrous cellulose dispersion using a defibrator Step (3): A step of transferring the microfibrillated fibrous cellulose dispersion to the upper part of the same tank equipped with an agitator According to the present invention, there is provided a method for producing microfibrillated fibrous cellulose that can continuously produce microfibrillated fibrous cellulose with excellent uniformity in quality.

[0009] In the defibration process (also known as pulverization process) of fibrous cellulose, defibration processes are performed multiple times, and the pulverized cellulose is circulated between a tank and a defibration processing device. As described in Patent Document 1, using two tanks requires switching between piping, making it unsuitable for continuous operation. On the other hand, performing multiple processes using a single tank simplifies the equipment and enables continuous operation, which is expected to improve production efficiency and reduce costs. However, when attempting to perform multiple defibration processes using a single tank, the high viscosity of the fibrous cellulose dispersion results in only a portion of the fibrous cellulose dispersion circulating in the tank, resulting in the presence of a portion of the fibrous cellulose dispersion that is not circulated, resulting in a decrease in the uniformity of the quality of the resulting pulverized fibrous cellulose. The inventors conducted extensive research to solve the above problem and found that the adoption of an agitator-equipped tank with specific agitator blades could solve the problem. Although the exact reason for this is unknown, the high viscosity of fibrous cellulose dispersions makes it difficult to uniformly agitate the fibrous cellulose dispersion inside the tank using a propeller-type agitator blade or other blade installed at the bottom of the tank. It is believed that the fibrous cellulose dispersion inside the tank was efficiently homogenized by at least one agitator blade selected from the group consisting of an agitator blade (agitator blade A) installed approximately horizontally near the liquid surface and an agitator blade (agitator blade B) that rotates along the wall surface, thereby improving the uniformity of quality. Each step will be described in detail below.

[0010] [Step (1)] Step (1) is a step in which a fibrous cellulose dispersion introduced into a tank equipped with an agitator flows out from the bottom of the tank and is transferred to a defibrator. (Fibrous Cellulose Dispersion) The fibrous cellulose dispersion is preferably a dispersion of chemically modified fibrous cellulose (chemically modified fibrous cellulose), and more preferably a dispersion of fibrous cellulose into which ionic groups have been introduced. In the present invention, examples of raw materials for the fibrous cellulose include various forms of materials mainly composed of cellulose, and the raw materials are not particularly limited, but include pulp raw materials such as wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP); semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-groundwood pulp (CGP); and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, bamboo, and bagasse. Examples of deinked pulp include, but are not limited to, deinked pulp made from recycled paper. The pulp raw materials of this embodiment may be used alone or in combination of two or more of the above. Among the above raw materials, for example, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Furthermore, among wood pulp, for example, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoint of having a high cellulose ratio and high defibration efficiency during defibration treatment, and of obtaining finely divided fibrous cellulose of long fibers with a large axial ratio with little decomposition of cellulose in the pulp. Note that finely divided fibrous cellulose of long fibers with a large axial ratio tends to be expensive.

[0011] In the present invention, when a sheet-like raw material is used, it is preferable to roughly crush it to a size of about 0.5 to 5 cm square. By roughly crushing it to this size, the fibrous cellulose can be efficiently and uniformly modified in the subsequent reaction step. The method for roughly crushing is not particularly limited, and a uniaxial rotary shear grinder, a biaxial rotary shear grinder, a multi-shaft screw grinder, a shredder, a guillotine cutter, or the like can be used. Among these, the use of a uniaxial rotary shear grinder or a shredder is preferred from the viewpoint of rough crushing.

[0012] Fibrous cellulose is chemically modified to obtain chemically modified fibrous cellulose. The chemical modification is preferably carried out by introducing an ionic group (ionic substituent). The ionic group may include, for example, either an anionic group or a cationic group, or both. In this embodiment, it is particularly preferable that the ionic group has an anionic group. Furthermore, the ionic group is preferably a group introduced into the fibrous cellulose via an ester bond or an ether bond, and more preferably a group introduced into the fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation between the raw material fibrous cellulose and a compound that becomes the ionic group.

[0013] Examples of anionic groups as ionic groups include phosphorus oxo acid groups or substituents derived from phosphorus oxo acid groups (sometimes simply referred to as phosphorus oxo acid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxo acid groups or substituents derived from sulfur oxo acid groups (sometimes simply referred to as sulfur oxo acid groups), xanthate groups or substituents derived from xanthate groups (sometimes simply referred to as xanthate groups), phosphonic groups or substituents derived from phosphonic groups, phosphine groups or substituents derived from phosphine groups, sulfonic groups or substituents derived from sulfonic groups, and carboxyalkyl groups. Among these, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, a substituent derived from a sulfur oxoacid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group, more preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group, and even more preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as the anionic group, defibration becomes possible with less energy. Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, and sulfonium groups. Of these, the cationic group is preferably an ammonium group.

[0014] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0015]

[0016] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of n α and α′ is O. － and the rest are R or OR. Note that all of α and α' are O－ The n α's may all be the same or may be different. ｂ＋ is a cation of one or more valences consisting of organic or inorganic substances.

[0017] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. In formula (1), n ​​is preferably 1.

[0018] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, or n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl or t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl or cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl or allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl or 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl or cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl or naphthyl groups.

[0019] In addition, the derivative group in R may be a carboxy group, a carboxylate group (-COO －), functional groups to which at least one functional group selected from functional groups such as a hydroxy group, an amino group, and an ammonium group has been added or substituted, but are not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, facilitating penetration into the fiber raw material and increasing the yield of fibrous cellulose. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fibrous cellulose, the multiple Rs may be the same or different.

[0020] β ｂ＋ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. It should be noted that β in formula (1) ｂ＋ When a plurality of β ｂ＋ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β ｂ＋ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0021] More specifically, the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group is a phosphate group (-PO ３ H２ ), salts of phosphate groups, phosphite groups (phosphonic acid groups) (-PO ２ H ２ and salts of a phosphorous acid group (phosphonic acid group). The phosphorus oxo acid group or the substituent derived from a phosphorus oxo acid group may be a group in which a phosphoric acid group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkyl phosphonic acid group (e.g., a methyl phosphonic acid group), or the like.

[0022] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

[0023]

[0024] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b x m). When n is 2 or more, the multiple p's may be the same or different numbers. In the above structural formula, β ｂ＋ is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple βｂ＋ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β ｂ＋ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0025] The amount of ionic groups introduced into the fibrous cellulose is, for example, preferably 0.10 mmol / g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and even more preferably 0.60 mmol / g or more. The amount of ionic groups introduced into the fibrous cellulose is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, even more preferably 1.50 mmol / g or less, and even more preferably 1.00 mmol / g or less. Here, the denominator in the unit mmol / g is the ratio of the counter ions of the ionic groups to hydrogen ions (H ＋ By setting the amount of ionic groups introduced within the above range, it is possible to easily pulverize the fiber raw material and improve the stability of the fibrous cellulose.

[0026] The amount of ionic groups introduced into the fibrous cellulose can be measured, for example, by neutralization titration after the fibrous cellulose has been subjected to a micronization treatment. In the measurement by neutralization titration, the amount introduced is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fibrous cellulose.

[0027] FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a fibrous cellulose dispersion containing phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into fibrous cellulose is measured, for example, as follows. First, ion-exchange water is added to the target fibrous cellulose to prepare a slurry with a solids concentration of 0.2% by mass. This slurry is treated four times in a wet pulverization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fibrous cellulose dispersion (slurry) containing fibrous cellulose. The fibrous cellulose dispersion is then treated with a strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve such as that shown in the upper part of FIG. 1 is obtained. The titration curve shown in the upper part of FIG. 1 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of FIG. 1 plots the pH increment (differential value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points of maximum increment (the differential value of pH with respect to the amount of alkali added) are observed on a curve plotting measured pH against the amount of alkali added. Of these, the first maximum increment obtained after starting alkali addition is called the first endpoint, and the next maximum increment obtained is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid of the fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the start of titration to the second endpoint is equal to the amount of second dissociated acid of the fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid of the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid groups introduced (mmol / g). The introduction amount of phosphorus oxo acid groups (or the amount of phosphorus oxo acid groups) simply refers to the amount of first dissociated acid. In Figure 1, the region from the start of titration to the first endpoint is called the first region, and the region from the first endpoint to the second endpoint is called the second region.For example, when the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weakly acidic groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) appears to decrease, resulting in a smaller amount of alkali required in the second region than in the first region. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the first dissociated acid amount) corresponds to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Furthermore, when the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weakly acidic groups, so the amount of alkali required in the second region is reduced or may even be zero. In this case, there will be only one point on the titration curve where the pH increment is maximized.

[0028] The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)), since the denominator indicates the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with an arbitrary cation C so as to be the charge equivalent, the amount of phosphorus oxoacid groups in the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C-form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of phosphorus oxoacid groups (C type) = Amount of phosphorus oxoacid groups (acid type) / {1 + (W - 1) × A / 1000}, A [mmol / g]: total amount of anions derived from phosphorus oxoacid groups in the fibrous cellulose (total amount of dissociated acid of phosphorus oxoacid groups), W: formula weight per monovalent of cation C (for example, 23 for Na and 9 for Al).

[0029] FIG. 2 is a graph showing the relationship between the amount of NaOH added dropwise to a fibrous cellulose dispersion having carboxy groups as ionic groups and pH. The amount of carboxy groups introduced into the fibrous cellulose is measured, for example, as follows. First, ion-exchange water is added to the target fibrous cellulose to prepare a slurry with a solids concentration of 0.2% by mass. This slurry is treated four times in a wet pulverization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. The fine fibrous cellulose dispersion is then treated with a strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve such as that shown in the upper part of FIG. 2 is obtained. The titration curve shown in the upper part of FIG. 2 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of FIG. 2 plots the pH increment (differential value) (1 / mmol) against the amount of alkali added. In this neutralization titration, a curve plotting the measured pH against the amount of alkali added reveals a maximum point in the increment (the differential value of pH with respect to the amount of alkali added), and this maximum point is referred to as the first endpoint. Here, the region from the start of titration to the first endpoint in Figure 2 is referred to as the first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the dispersion used for titration. The amount of carboxy groups introduced (mmol / g) is calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solids content (g) in the dispersion containing the fibrous cellulose to be titrated.

[0030] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups possessed by the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with any cation C so as to be charge equivalent, the amount of carboxy groups possessed by the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of carboxy groups (C form) = Amount of carboxy groups (acid form) / {1 + (W - 1) × (Amount of carboxy groups (acid form)) / 1000} W: Formula weight per valence of cation C (for example, 23 for Na, 9 for Al)

[0031] When measuring the amount of ionic groups by titration, if the amount of sodium hydroxide solution added is too large or the titration interval is too short, the amount of ionic groups may be lower than expected, and an accurate value may not be obtained. Appropriate amounts and titration intervals, for example, are preferably titrated with 0.1 N sodium hydroxide solution in increments of 10 μL to 50 μL for 5 to 30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fine fibrous cellulose dispersion, it is preferable to measure while blowing an inert gas such as nitrogen gas into the slurry, for example, from 15 minutes before the start of titration until the end of titration.

[0032] The amount of sulfur oxoacid groups and sulfonic acid groups introduced into the fibrous cellulose is determined by wet ashing the obtained fibrous cellulose using perchloric acid and concentrated nitric acid, diluting it at an appropriate ratio, and measuring the amount of sulfur by ICP atomic emission spectrometry. The amount of sulfur oxoacid groups and sulfonic acid groups (unit: mmol / g) is determined by dividing the amount of sulfur by the bone dry mass of the fibrous cellulose tested.

[0033] In order to obtain fibrous cellulose having the above-mentioned ionic groups introduced therein, it is preferable to have an ionic group introduction step in which ionic groups are introduced into the above-mentioned cellulose-containing fiber raw material (cellulose fiber), and examples of the ionic group introduction step include a phosphorus oxo acid group introduction step, a carboxyl group introduction step, a sulfur oxo acid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. Each of these steps will be explained below.

[0034] -Ionic Group Introduction Step- <Phosphorus Oxo Acid Group Introduction Step> When obtaining chemically modified cellulose having ionic groups, it is preferable to provide a reaction step for introducing ionic groups before the defibration step. An example of the reaction step is a phosphorus oxo acid group introduction step. The phosphorus oxo acid group introduction step is a step in which at least one compound selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups possessed by cellulose fibers (hereinafter also referred to as "compound A") is allowed to act on the raw cellulose fibers. This step results in the production of cellulose fibers having phosphorus oxo acid groups (chemically modified cellulose).

[0035] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction between the cellulose fiber and compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the reaction between the cellulose fiber and compound A may be carried out in the absence of compound B.

[0036] An example of a method for reacting compound A with cellulose fibers in the presence of compound B is a method in which compound A and compound B are mixed with cellulose fibers in a dry, wet, or slurry state. Among these methods, using cellulose fibers in a dry or wet state is preferred because of the high uniformity of the reaction, and using cellulose fibers in a dry state is particularly preferred. The form of the cellulose fibers is not particularly limited, but a cotton-like or thin sheet-like form is preferred. Compound A and compound B may be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state obtained by heating to or above their melting point. Among these methods, adding compound A and compound B in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred because of the high uniformity of the reaction. Compound A and compound B may be added to the cellulose fibers simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited. When compound A and compound B are in the form of a solution, the cellulose fibers may be immersed in the solution, absorbed, and then removed, or the solution may be dripped onto the cellulose fibers or sprayed onto them. Alternatively, the required amounts of compound A and compound B may be added to the cellulose fibers, or excess amounts of compound A and compound B may be added to the cellulose fibers, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0037] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, including, but not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acid can be used with various purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid can be 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is formed by the condensation of two or more molecules of phosphoric acid through a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphate groups, ease of further improving defibration efficiency in the defibration step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferred.

[0038] The amount of compound A added to the cellulose fibers is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the cellulose fibers (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the cellulose fibers within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the cellulose fibers to the above upper limit or less, a balance can be achieved between the yield improvement effect and costs.

[0039] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

[0040] The amount of compound B added relative to the cellulose fiber (bone dry mass) is not particularly limited, but is preferably, for example, 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0041] In the reaction of a fiber raw material containing cellulose with compound A, the reaction system may contain, in addition to compound B, for example, amides or amines. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0042] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to cellulose fibers and then heat-treat the cellulose fibers. The heat treatment temperature is preferably selected so that phosphorus oxo acid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fibers. The heat treatment temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C. Various types of equipment having heat media can be used for the heat treatment, including, for example, a stirring dryer, rotary dryer, disk dryer, roll-type heater, plate-type heater, fluidized-bed dryer, band-type dryer, filtration dryer, vibration fluidized dryer, flash dryer, reduced-pressure dryer, infrared heater, far-infrared heater, microwave heater, and high-frequency dryer.

[0043] The heat treatment according to this embodiment can employ, for example, a method in which compound A is added to a thin sheet of cellulose fiber by a method such as impregnation, followed by heating, or a method in which the cellulose fiber and compound A are kneaded or stirred in a kneader or the like while heating. This makes it possible to suppress unevenness in the concentration of compound A in the cellulose fiber and to more uniformly introduce phosphorus oxoacid groups onto the surface of the cellulose fiber. This is thought to be because, when water molecules move to the surface of the cellulose fiber as it dries, the dissolved compound A is attracted to the water molecules by surface tension, preventing it from migrating to the surface of the cellulose fiber (i.e., causing unevenness in the concentration of compound A).

[0044] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the device system, for example, the water retained in the slurry and the water generated in the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in the cellulose, etc., in the cellulose fibers. Examples of such heating devices include an oven using a blower system. Constantly discharging the water from within the device system can suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, and also suppress acid hydrolysis of the sugar chains in the cellulose fibers. This makes it possible to obtain fine fibrous cellulose with a high axial ratio.

[0045] The heat treatment time is, for example, preferably from 1 second to 300 minutes after the water content has been substantially removed from the cellulose fiber, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, by setting the heating temperature and heating time within appropriate ranges, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range.

[0046] The phosphorus oxo acid group introduction step may be carried out at least once, but may also be carried out twice or more times. By carrying out the phosphorus oxo acid group introduction step twice or more, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material.

[0047] The amount of phosphorus oxoacid groups introduced into the cellulose fibers is, for example, preferably 0.10 mmol / g or more per 1 g (mass) of cellulose fiber, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and even more preferably 1.00 mmol / g or more. The amount of phosphorus oxoacid groups introduced into the cellulose fibers is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of cellulose fiber, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, it is possible to facilitate the micronization of cellulose fibers in the micronization treatment step and improve the stability of the fine fibrous cellulose.

[0048] <Carboxy group introduction step> The ionic group introduction step may include a carboxy group introduction step, which is carried out by subjecting the cellulose fiber to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or by treating the cellulose fiber with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.

[0049] The compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Furthermore, the derivative of the compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include imidized products of acid anhydrides of compounds having carboxy groups, and derivatives of acid anhydrides of compounds having carboxy groups. The imidized products of acid anhydrides of compounds having carboxy groups are not particularly limited, but examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0050] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, the derivative of an acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of compounds having carboxy groups such as dimethyl maleic anhydride, diethyl maleic anhydride, diphenyl maleic anhydride, etc., in which at least some of the hydrogen atoms have been substituted with a substituent such as an alkyl group or a phenyl group.

[0051] When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of, for example, a pH of 6 or higher and 8 or lower. This type of treatment is also referred to as neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding cellulose fibers, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. The TEMPO oxidation treatment may also be performed under conditions of a pH of 10 or higher and 11 or lower. This type of treatment is also referred to as alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to cellulose fibers.

[0052] The amount of carboxy groups introduced into cellulose fibers varies depending on the type of substituent. For example, when carboxy groups are introduced by TEMPO oxidation, the amount is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and even more preferably 0.60 mmol / g or more per gram (mass) of cellulose fibers. Furthermore, the amount of carboxy groups introduced into cellulose fibers is preferably 3.65 mmol / g or less, more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, even more preferably 1.50 mmol / g or less, and even more preferably 1.00 mmol / g or less. Furthermore, when the substituent is a carboxymethyl group, the amount of carboxy groups introduced may be 5.8 mmol / g or less per gram (mass) of cellulose fibers. By setting the amount of carboxy groups introduced within the above range, it is possible to facilitate the micronization of cellulose fibers in the micronization treatment step and improve the stability of the fine fibrous cellulose.

[0053] <Sulfonic group introduction step> The ionic group introduction step may include a sulfonic group introduction step, in which hydroxyl groups of cellulose fibers are reacted with sulfur oxoacid to obtain cellulose fibers having sulfonic groups (sulfonic group-introduced fibers).

[0054] In the sulfonic acid group introduction step, instead of compound A in the above-described <Phosphorus Oxo Acid Group Introduction Step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfonic acid groups by reacting with hydroxyl groups in cellulose fibers is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Sulfurous acid can be 5% aqueous sulfurous acid. Sulfates or sulfites can include lithium, sodium, potassium, and ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Sulfamic acid or the like can be used as the sulfuric acid amide. In the sulfonic acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus Oxo Acid Group Introduction Step> in the same manner.

[0055] In the sulfonic acid introduction step, it is preferable to mix cellulose fibers with an aqueous solution containing sulfur oxoacid and urea and / or a urea derivative, and then heat-treat the cellulose fibers. The heat-treating temperature is preferably selected so that sulfonic acid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fibers. The heat-treating temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat-treating temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0056] In the heat treatment step, heating is preferably performed until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose fiber and the amount of aqueous solution containing sulfur oxoacid and urea and / or a urea derivative added, but is preferably, for example, 10 seconds to 10,000 seconds. For the heat treatment, various devices having a heat medium can be used, such as a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, an airflow dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

[0057] The amount of sulfonic groups introduced into the cellulose fibers is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and even more preferably 0.50 mmol / g or more. Furthermore, the amount of sulfonic groups introduced into the cellulose fibers is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less. By setting the amount of sulfonic groups introduced within the above range, it is possible to facilitate the micronization of the cellulose fibers in the micronization treatment step and to increase the stability of the fine fibrous cellulose.

[0058] <Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)> The ionic group introduction step may include an oxidation step using a chlorine-based oxidizing agent. In the oxidation step using a chlorine-based oxidizing agent, a chlorine-based oxidizing agent is added to wet or dry cellulose fibers having hydroxyl groups to cause a reaction, thereby introducing carboxyl groups into the cellulose fibers.

[0059] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or may be dissolved in an appropriate solvent and added.

[0060] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent, for example, converted into an effective chlorine concentration, is preferably 1% by mass to 1,000% by mass, more preferably 5% by mass to 500% by mass, and even more preferably 10% by mass to 100% by mass. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of cellulose fibers is preferably 1 part by mass to 100,000 parts by mass, more preferably 10 parts by mass to 10,000 parts by mass, and even more preferably 100 parts by mass to 5,000 parts by mass.

[0061] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. The pH during the reaction is preferably from 5 to 15, more preferably from 7 to 14, and even more preferably from 9 to 13. At the start of the reaction, the pH during the reaction is preferably maintained constant (for example, pH 11) by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0062] <Xanthate group introduction step> The process for producing fine fibrous cellulose may include a xanthate group introduction step as a reaction step. In the xanthate group introduction step, hydroxyl groups of cellulose fibers are substituted with xanthate groups represented by the following formula (3), thereby obtaining cellulose fibers having xanthate groups (xanthate group-introduced fibers). -OCSS－ M ＋ ... (3) Here, M ＋ is at least one selected from the group consisting of hydrogen ions, monovalent metal ions, ammonium ions, and aliphatic or aromatic ammonium ions.

[0063] In the xanthate group introduction step, the cellulose fiber is first treated with an alkaline solution to obtain alkali cellulose. Examples of alkaline solutions include an aqueous alkali metal hydroxide solution and an aqueous alkaline earth metal hydroxide solution. Among these, the alkaline solution is preferably an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide, and more preferably an aqueous sodium hydroxide solution. When the alkaline solution is an aqueous alkali metal hydroxide solution, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 4% by mass or more, more preferably 5% by mass or more. In addition, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 9% by mass or less. By setting the alkali metal hydroxide concentration at or above the lower limit, the mercerization of cellulose can be sufficiently promoted, the amount of by-products generated during the subsequent xanthation can be reduced, and as a result, the yield of xanthate group-introduced fiber can be increased. This makes it possible to more effectively perform the defibration process described below. Furthermore, by setting the alkali metal hydroxide concentration to the above upper limit or less, it is possible to prevent the aqueous alkali metal hydroxide solution from penetrating into the crystalline regions of cellulose while allowing mercerization to proceed, which makes it easier to maintain the cellulose type I crystal structure and further increases the yield of fine fibrous cellulose.

[0064] The alkali treatment time is preferably 30 minutes or more, more preferably 1 hour or more. The alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less. By setting the alkali treatment time within the above range, the final yield can be increased, and productivity can be improved.

[0065] The alkali cellulose obtained by the above-mentioned alkali treatment is preferably subjected to solid-liquid separation afterwards to remove as much aqueous solution as possible.This can reduce the water content during the subsequent xanthate treatment, and can promote the reaction.As a method of solid-liquid separation, for example, a general dehydration method such as centrifugation or filtration can be used.In addition, the concentration of alkali metal hydroxide contained in the alkali cellulose after solid-liquid separation is preferably 3% by mass or more and 8% by mass or less with respect to the total mass of the alkali cellulose after solid-liquid separation.

[0066] In the xanthate group introduction step, a xanthate formation treatment step is carried out after alkali treatment. In the xanthate formation treatment step, carbon disulfide (CS) is added to alkali cellulose. ２ ) is reacted to form (-O － Na ＋ ) group to (-OCSS － Na ＋ ) group to obtain xanthate group-introduced fibers. In the above, the metal ions introduced into the alkali cellulose are typically Na ＋ However, similar reactions occur with other alkali metal ions.

[0067] In the xanthation treatment, it is preferable to supply 10% by mass or more of carbon disulfide relative to the bone dry mass of cellulose in the alkali cellulose.In addition, in the xanthation treatment, the time for contacting carbon disulfide with alkali cellulose is preferably 30 minutes or more, more preferably 1 hour or more.Although the xanthation proceeds quickly when carbon disulfide contacts alkali cellulose, it takes time for carbon disulfide to penetrate into the inside of alkali cellulose, so it is preferable to set the reaction time within the above range.On the other hand, the time for contacting carbon disulfide with alkali cellulose only needs to be 6 hours or less, which allows sufficient penetration into the alkali cellulose mass after dehydration, and can almost complete the reactive xanthation.

[0068] The reaction temperature in the xanthate treatment is preferably 46 ° C or less. By making the reaction temperature within the above range, it is easy to suppress the decomposition of alkali cellulose. In addition, by making the reaction temperature within the above range, it is easy to react uniformly, so it can suppress the generation of by-products, and furthermore, it can also suppress the removal of the generated xanthate group.

[0069] The amount of xanthate group introduced in the xanthate group introduction step is preferably 0.60 mmol / g or more per 1 g (mass) of cellulose fiber, more preferably 0.70 mmol / g or more, more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, and even more preferably 1.20 mmol / g or more.In addition, the amount of xanthate group introduced is, for example, preferably 5.00 mmol / g or less per 1 g (mass) of cellulose fiber, more preferably 3.00 mmol / g or less.By making the amount of xanthate group introduced within the above range, excellent defibration property and excellent transparency can be obtained.

[0070] <Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step)> The ionic group introduction step may include a phosphonic or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phospho group or a phosphine group (compound E) is used as an essential component. Ａ ), and an optional component, an alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups, and the reaction is carried out to introduce phosphonic or phosphine groups into the cellulose fiber.

[0071] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ａ Examples of the compound E include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphinic acid. In terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, compound E Ａis preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0072] Compound E Ａ When adding the reagent, it may be added to the cellulose fiber as it is (solid or liquid) or may be dissolved in an appropriate solvent and then added. The cellulose fiber is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting the cellulose fiber into alkali cellulose is as described above.

[0073] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0074] Compound E Ａ The amount of the additive per 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0075] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0076] <Sulfone Group Introduction Step (Sulfoalkylation Step) (Second Sulfone Group Introduction Step)> The ionic group introduction step may include a sulfone group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfone group (compound E) is used as an essential component. Ｂ ) and, as an optional component, an alkali compound and a compound B selected from the above-mentioned urea and its derivatives are added to wet or dry cellulose fibers having hydroxyl groups and reacted to introduce sulfonic groups into the cellulose fibers.

[0077] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ｂ Examples of suitable acrylic acid esters include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is particularly preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Ｂ is preferably sodium vinyl sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0078] Compound E Ｂ When adding the reagent, it may be added to the cellulose fiber as it is (solid or liquid) or may be dissolved in an appropriate solvent and then added. The cellulose fiber is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting the cellulose fiber into alkali cellulose is as described above.

[0079] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0080] Compound E Ｂ The amount of the additive per 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0081] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0082] <Carboxyalkylation Step (Third Carboxy Group Introduction Step)> The reaction step may include a carboxyalkylation step. As an essential component, a compound having a reactive group and a carboxy group (compound E Ｃ ), and an optional alkaline compound and compound B selected from the above-mentioned urea and its derivatives are added to wet or dry cellulose fibers having hydroxyl groups and reacted to introduce carboxyl groups into the cellulose fibers.

[0083] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ｃ As the compound, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the viewpoints of the efficiency of introducing the substituent, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferred to use, as an optional component, the compound B in the above-mentioned <Phosphorus oxoacid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0084] Compound E Ｃ When adding the reagent, it may be added to the cellulose fiber as it is (solid or liquid) or may be dissolved in an appropriate solvent and then added. The cellulose fiber is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting the cellulose fiber into alkali cellulose is as described above.

[0085] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0086] Compound E Ｃ The amount of the additive per 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0087] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0088] <Cationic Group Introduction Step (Cationization Step)> As an essential component, a compound having a reactive group and a cationic group (compound E Ｄ ), and an optional component, an alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to wet or dry cellulose fibers having hydroxyl groups and reacted to introduce cationic groups into the cellulose fibers.

[0089] Examples of reactive groups include halogenated alkyl groups, vinyl groups, and epoxy groups (glycidyl groups). Examples of cationic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, the cationic group is preferably an ammonium group. Compound E Ｄ As the compound, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing the substituent, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use, as an optional component, the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner. The amount added is also preferably as described above.

[0090] Compound E Ｄ When adding the reagent, it may be added to the cellulose fiber as it is (solid or liquid) or may be dissolved in an appropriate solvent and then added. The cellulose fiber is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting the cellulose fiber into alkali cellulose is as described above.

[0091] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0092] Compound E Ｄ The amount of the additive per 100 parts by mass of cellulose fibers is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0093] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 5 minutes to 500 minutes, and even more preferably from 10 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0094] After the reaction step described above, it is preferable to have a dehydration / washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order. In addition to the washing step, an acid treatment step may also be included. - Dehydration / Washing Step - The dehydration / washing step is a step in which the obtained dispersion of chemically modified cellulose is washed with water or an organic solvent after dehydration treatment. This step is essential for obtaining fine fibrous cellulose with few impurities. Washing is preferably carried out with water. Furthermore, the dehydration / washing step may be carried out after each step described below, and the number of washes performed in each washing step is not particularly limited. In this step, dehydration devices of the centrifugal, vacuum, or pressure dehydration type can be used. Specific examples include centrifugal separators (e.g., centrifuges manufactured by Tanabe Willtech Co., Ltd. and centrifuges manufactured by Kokusan Co., Ltd.), vacuum separators (drum-type vacuum separators, horizontal belt filters manufactured by Tsukishima Kikai Co., Ltd.), and pressure dehydration devices (filter presses, tube presses, screw presses, belt press horizontal belt filters, polydisc filters, vibrating screens, etc.). Among these, pressure dehydration methods (filter press, tube press), centrifugal separation methods (such as a centrifuge manufactured by Tanabe Willtec Co., Ltd. or a centrifuge manufactured by Kokusan Co., Ltd.), and vacuum dehydration methods (drum-type vacuum dehydrators and horizontal belt filters manufactured by Tsukishima Kikai Co., Ltd.) are preferred because they can dehydrate the raw material without applying a strong shear force to it. A combination of these methods can also be used.

[0095] The viscosity of the fibrous cellulose dispersion, i.e., the viscosity (initial viscosity) of the fibrous cellulose dispersion before treatment, is preferably 1 mPa·s or more, more preferably 5 mPa·s or more, and even more preferably 10 mPa·s or more at 23° C. from the viewpoint of suppressing the amount of liquid sent during transfer, and is preferably 10,000 mPa·s or less, more preferably 5,000 mPa·s or less, and even more preferably 3,000 mPa·s or less at 23° C. from the viewpoint of transfer without using a pump. The viscosity of the fibrous cellulose dispersion before treatment is a value measured at a concentration of 2% by mass using a rotational viscometer at a rotational speed of 0.3 rpm.

[0096] An alkali treatment step or an acid treatment step may be performed between the dehydration / washing step and the preparation step described below, or the dehydration / washing step may be performed before or after the alkali treatment step or the acid treatment step. -Alkali Treatment Step- An alkali treatment step may be performed between the reaction step and the preparation step. The alkali treatment method is not particularly limited, but examples include a method of immersing chemically modified fibrous cellulose, preferably fibrous cellulose into which ionic groups have been introduced (ionic group-introduced fibrous cellulose), in an alkali solution.

[0097] The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of their high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility.

[0098] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, from 5° C. to 80° C., and more preferably from 10° C. to 60° C. The immersion time of the chemically modified cellulose in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the chemically modified cellulose.

[0099] In order to reduce the amount of alkaline solution used in the alkaline treatment step, the chemically modified cellulose may be washed with water or an organic solvent after the reaction step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkaline-treated chemically modified cellulose with water or an organic solvent after the alkaline treatment step and before the defibration step.

[0100] -Acid Treatment Step- In the reaction step, an acid treatment step may be provided between the step of introducing ionic groups and the adjustment step. For example, the reaction step, acid treatment, alkali treatment, and defibration treatment may be performed in this order.

[0101] The acid treatment method is not particularly limited, but examples include a method of immersing chemically modified cellulose in an acidic solution containing an acid. The concentration of the acidic solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of the acid contained in the acidic solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, hydrochloric acid or sulfuric acid is particularly preferred.

[0102] The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably from 5° C. to 100° C., and more preferably from 20° C. to 90° C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably from 5 minutes to 120 minutes, and more preferably from 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the chemically modified cellulose.

[0103] -Adjustment Step- In this embodiment, the fibrous cellulose dispersion is preferably in the form of a slurry diluted with a dispersion medium, and the method for preparing the fibrous cellulose dispersion preferably includes an adjustment step of adjusting the solids concentration of the fibrous cellulose dispersion using the dispersion medium. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), etc. Among these, it is preferable to use water.

[0104] The solids concentration of the fibrous cellulose dispersion can be set as appropriate. The solids concentration of the fibrous cellulose dispersion is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and preferably 10% by mass or less, more preferably 6% by mass or less. If the solids concentration is too low, the amount of liquid becomes too large relative to the amount of fibrous cellulose to be treated, resulting in poor efficiency. On the other hand, if the solids concentration is too high, the viscosity increases and fluidity deteriorates. In addition, the fibrous cellulose dispersion may contain solids other than fibrous cellulose, such as urea, which has hydrogen bonding properties.

[0105] (Tank with Stirrer) In the method for producing pulverized fibrous cellulose of this embodiment, the tank with a stirrer into which the above-mentioned fibrous cellulose dispersion is charged has at least one stirring blade selected from the group consisting of stirring blade A and stirring blade B below. Stirring blade A: a stirring blade installed at least near the liquid surface in a substantially horizontal direction Stirring blade B: a stirring blade that rotates along the wall surface In this embodiment, the "stirring blade" is not limited to one that stirs the entire fibrous cellulose dispersion in the tank, but may be one that is attached to a stirring rod (rotating rod) provided in the center of the tank and rotates. In other words, its function is not limited to one that aims to stir the entire dispersion, and includes, as will be described later, aspects that, for example, prevent the dispersion transferred to the upper part of the tank in step (3) from remaining immediately below the dispersion inlet into the tank, or prevent the dispersion from remaining near the wall surface of the tank when the fibrous cellulose dispersion is discharged from the bottom of the tank. The stirring blades preferably serve to at least promote homogenization of the fibrous cellulose dispersion in the tank and to prevent a portion of the fibrous cellulose dispersion from remaining in the tank, causing variations in the degree of pulverization treatment.

[0106] FIG. 3 is a cross-sectional schematic diagram showing an example of an agitator-equipped tank used in this embodiment. FIG. 3(a) is an example of an agitator-equipped tank having agitator blades A and B, FIG. 3(b) is an example of an agitator-equipped tank having only agitator blade A, and FIG. 3(c) is another example of an agitator-equipped tank having agitator blades A and B. In FIG. 3(a), the agitator-equipped tank 10 has a stirring rod (also called a "rotating rod") 30 in the center of the tank 20, agitator blade A 40 installed approximately horizontally near the liquid surface, and agitator blade B 42 rotating along the wall surface. In FIG. 3(a), agitator blades A and B are single blades. In FIG. 3(b), the agitator-equipped tank 10 has a stirring rod 30 in the center of the tank 20, and agitator blade A 40 installed approximately horizontally near the liquid surface. In FIG. 3(b), agitator blade A is a single blade. In Fig. 3(c), the agitator-equipped tank 10 has a stirring rod 30 in the center of the tank 20, an agitator blade A 40 installed substantially horizontally near the liquid surface, and an agitator blade B 42 that rotates along the wall surface. In Fig. 3(c), the agitator blade A and the agitator blade B each have two blades. In this embodiment, the agitator-equipped tank preferably has at least the agitator blade A, and more preferably has the agitator blade A and the agitator blade B.

[0107] -Agitating blade A- Agitating blade A is an agitating blade installed in a substantially horizontal direction at least near the liquid surface. "Near the liquid surface" means that the agitating blade A is installed at a position between ±30 from the liquid surface, where the distance from the liquid surface to the bottom of the tank is 100, the liquid surface is 0, and the bottom of the tank is 100; the agitating blade A is preferably installed at a position between -10 and 30, more preferably -5 or more, even more preferably 0 or more, more preferably 20 or less, and even more preferably 10 or less. It is preferable that the center position of the agitating blade in the height direction is within the above range. Installing agitating blade A near the liquid surface prevents the pulverized fibrous cellulose dispersion transferred from the defibrator from remaining in part of the tank, and can promote homogenization with the fibrous cellulose dispersion in the tank.

[0108] Furthermore, "substantially horizontal" means that the angle of the agitator blade (the angle of the agitator blade from the agitator shaft (the center of the tank) toward the wall) is 45° or less with respect to the horizontal, preferably 30° or less, more preferably 20° or less, even more preferably 10° or less, and even more preferably 0°, i.e., horizontal. When the agitator blade A is installed in a substantially horizontal direction, the refined fibrous cellulose dispersion transferred from the defibrator is prevented from remaining in part of the tank, and can be homogenized with the fibrous cellulose dispersion in the tank.

[0109] The shape of the agitating blade A is not particularly limited, and may be a paddle blade (plate-shaped (rectangular) or rod-shaped) or a propeller blade, but a plate-shaped agitating blade, a paddle blade, is preferred because it allows for efficient uniformization within the tank. The plate-shaped paddle blade may be arranged at an angle of 90° to the horizontal direction, or may be arranged at an incline.

[0110] In Figures 3(a) and (b), the stirring blade A has one blade, and in Figure 3(c) it has two blades. The stirring blade A preferably has one to six blades, more preferably four or fewer blades, even more preferably three or fewer blades, still more preferably two or fewer blades, and even more preferably one blade. When the number of stirring blades A is large, the stirring force tends to increase, but the power required for stirring also tends to increase. In this embodiment, sufficient stirring is possible with a single blade, and using a single blade allows the fibrous cellulose dispersion that hits the stirring blade to escape in the direction of the rotation axis, reducing the risk of the water surface rising excessively or the fibrous cellulose dispersion leaking out of the tank.

[0111] The length of the agitator blade A, i.e., the length extending from the agitator shaft (rotating shaft) to the wall surface, is preferably 50 to 100, more preferably 70 or more, even more preferably 90 or more, and even more preferably 95 or more, when the distance from the center of the tank to the wall surface is 100, with the agitator shaft being 0 and the wall surface being 100.

[0112] The stirring blade A may have a scraper at its tip. The scraper may be one that comes into contact with the wall surface to scrape the wall surface, or it may be a non-contact type that does not come into contact with the wall surface and prevents accumulation near the wall surface. An example of a scraper is one made of Teflon (registered trademark).

[0113] -Agitating blade B- Agitating blade B is an agitating blade that rotates along the wall surface. The presence of agitating blade B suppresses adhesion of fibrous cellulose to the wall surface of the tank and the fibrous cellulose dispersion from remaining in the tank, thereby obtaining uniformly refined fibrous cellulose. The depth-wise length of the wall surface of agitating blade B, where the length of the wall surface from the liquid surface to the bottom is taken as 100, is preferably 20 to 100, more preferably 30 or more, even more preferably 40 or more, even more preferably 50 or more, and more preferably 90 or less. A depth-wise length of agitating blade B within the above range is preferable because it improves the uniformity of the fibrous cellulose dispersion in the tank. Note that agitating blade B may have a shape that rises from the bottom, like an anchor blade, or may be held horizontally from the agitator shaft, as shown in Figures 3(a) and (c). Having the above shape allows the fibrous cellulose dispersion transferred to the top of the agitator-equipped tank to be spread across the interface of the tank with less energy, thereby improving the uniformity of the fibrous cellulose dispersion in the tank.

[0114] The stirring blade B may have a scraper at its tip. The scraper may be one that comes into contact with the wall surface to scrape the wall surface, or it may be a non-contact type that does not come into contact with the wall surface and prevents accumulation near the wall surface. An example of a scraper is one made of Teflon (registered trademark).

[0115] The material of the agitating blades A and B is not particularly limited, but is preferably SUS (stainless steel) from the viewpoint of corrosion resistance and strength. The material of the tank is not particularly limited, but examples include SUS (stainless steel) and FPR (fiber reinforced plastic), and is preferably SUS.

[0116] The agitator-equipped tank of this embodiment has at least one agitator blade selected from the group consisting of agitator blade A and agitator blade B, and may have agitator blades other than agitator blade A and agitator blade B. Specifically, the agitator-equipped tank may have agitator blades installed in a substantially horizontal direction other than near the liquid surface, and may have turbine blades (pitched turbine, disk turbine, etc.) or anchor blades.

[0117] (Step of flowing out from the bottom of the tank and transferring to the defibration device) In this embodiment, the agitator-equipped tank has an outlet at the bottom of the agitator-equipped tank for transfer to the defibration device. The outlet may be provided at the bottom or on the wall surface near the bottom, and is not particularly limited. From the viewpoint of suppressing the residue of fibrous cellulose dispersion in the tank-equipped agitator, it is preferable that the agitator-equipped tank has a tapered shape and has an outlet at the bottom, as shown in Figures 3(a) to 3(c), but is not limited to this. Furthermore, transfer to the defibration device may be performed appropriately using a conventionally known pump or the like, or transfer may be performed using gravity.

[0118] [Step (2)] Step (2) is a step of using a defibrator to pulverize the fibrous cellulose in the transferred fibrous cellulose dispersion. In step (2), the fibrous cellulose in the fibrous cellulose dispersion is defibrated (pulverized) by applying a mechanical shear force. The defibrator used in step (2) is not particularly limited as long as it is a device capable of pulverizing fibrous cellulose, but is preferably at least one selected from the group consisting of a pulverizer, a beater, and a micronizer. It may be appropriately selected so that the fiber diameter of the resulting micronized fibrous cellulose is the desired value. The defibrator is not particularly limited, but examples of the pulverizer include a high-speed pulverizer and a top finer. Examples of the beater include a disk-type refiner (single disk refiner, double disk refiner, etc.) and a conical-type refiner. Examples of the micronizer include a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision-type grinder, a ball mill, a bead mill, a disk mill, a vibration mill, and an ultrasonic disperser. Among the above-mentioned defibrating devices, it is more preferable to use a disc-type refiner (particularly a single-disc refiner), a high-speed defibrator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

[0119] [Step (3)] Step (3) is a step of transferring the fibrous cellulose dispersion that has been subjected to the micronization treatment to the upper part of the same tank equipped with an agitator. The fibrous cellulose dispersion that has flowed out from the lower part of the tank equipped with an agitator is subjected to micronization treatment using a defibrator and then transferred again to the upper part of the same tank equipped with an agitator. While the fibrous cellulose dispersion that has been subjected to step (2) can be returned from the upper part of the tank equipped with an agitator, it is preferable to provide an inlet to the tank near the wall. Note that "near the wall" means that, when the horizontal length from the center of the tank to the wall is 100, the center of the tank is 0, and the wall is 100, the center of the tank is 50 to 100, and the center is preferably 60 to 99, and more preferably 70 to 98. Having an outlet near the wall of the tank is preferable because it improves the agitation of the fibrous cellulose dispersion inside the tank and results in excellent uniformity.

[0120] In the method for producing pulverized fibrous cellulose of this embodiment, the above steps (1) to (3) are repeatedly performed. Repeating steps (1) to (3) means continuously discharging the fibrous cellulose dispersion from a tank equipped with an agitator and transferring it to a defibrator, and then transferring the fibrous cellulose dispersion pulverized in the defibrator to the tank equipped with an agitator. The number of times the pulverization treatment is performed can be calculated from the amount of fibrous cellulose dispersion charged into the tank and the transfer speed, and the number of times the pulverization treatment is performed (number of passes) is preferably 2 to 50 times. The number of times the pulverization treatment is performed (number of passes) may be appropriately set depending on the type of defibrator, the desired fiber width of the pulverized fibrous cellulose, and the like. When the pulverization treatment is performed using a disc refiner (preferably a single disc refiner), the number of times the pulverization treatment is performed is preferably 2 to 50 times, more preferably 4 or more, even more preferably 10 or more, and more preferably 40 or less, and even more preferably 30 or less. Furthermore, when the micronization treatment is carried out using a homogenizer, the number of times of the micronization treatment is preferably 2 to 10, more preferably 8 or less, even more preferably 7 or less, still more preferably 6 or less, even more preferably 5 or less, and still more preferably 4 or less. The micronization treatment may be carried out using a combination of two different types of defibration devices.

[0121] The above steps (1) to (3) are performed while rotating the stirring blades provided in the tank equipped with the stirrer. The rotational speed (rotational velocity) of the rotor may be any speed that allows uniform pulverization without allowing only a portion of the fibrous cellulose dispersion to flow out of the bottom of the tank. Because the viscosity of the fibrous cellulose dispersion is high, the rotational speed is preferably 1 rpm or more and 100 rpm or less, more preferably 3 rpm or more, even more preferably 5 rpm or more, and even more preferably 10 rpm or more. Taking into consideration the load on the apparatus, the rotational speed is preferably 80 rpm or less, even more preferably 60 rpm or less, even more preferably 40 rpm or less, and even more preferably 30 rpm or less. In the production method of this embodiment, the stirring blades do not stir the entire fibrous cellulose dispersion inside the tank, but rather mix the fibrous cellulose dispersion transferred from the defibration device to the tank with the fibrous cellulose dispersion already present in the tank (promoting homogenization).

[0122] The pulverization process may be carried out in one stage using the above-mentioned defibration device, or in two stages consisting of a rough defibration process and a fine defibration process. When the defibration process is carried out in two stages, it is preferable to use a refiner to perform defibration in the rough defibration process, and the refiner performs preliminary defibration of the fibrous cellulose. A refiner is a device that beats fibrous cellulose, and by beating while applying a load, it applies a shear force to the fibrous cellulose, causing fluffing in the fibrous cellulose and softening the fibers, thereby performing preliminary defibration.

[0123] In this embodiment, the viscosity of the fibrous cellulose dispersion in the tank equipped with a stirrer tends to increase due to the pulverization treatment. That is, the viscosity of the fibrous cellulose dispersion tends to increase due to the pulverization treatment using a defibrator. The viscosity of the fibrous cellulose dispersion in the tank equipped with a stirrer tends to increase with the pulverization treatment as described above, but is, for example, 1 mPa·s or more and 5,000,000 mPa·s or less, preferably 5 mPa·s or more, more preferably 10 mPa·s or more, even more preferably 20 mPa·s or more, and preferably 4,800,000 mPa·s or less, more preferably 4,700,000 mPa·s or less, and even more preferably 4,500,000 mPa·s or less.

[0124] In this embodiment, the viscosity of the pulverized fibrous cellulose dispersion, i.e., the viscosity (final viscosity) of the finally obtained pulverized fibrous cellulose dispersion, is, for example, 100,000 mPa·s or more and 5,000,000 mPa·s or less, preferably 300,000 mPa·s or more, more preferably 500,000 mPa·s or more, even more preferably 1,000,000 mPa·s or more, and preferably 4,800,000 mPa·s or less, more preferably 4,700,000 mPa·s or less, even more preferably 4,500,000 mPa·s or less.

[0125] <Micronized Fibrous Cellulose> Micronized fibrous cellulose is obtained through steps (1) to (3). The micronized fibrous cellulose is obtained in the form of a slurry, and may be dried, as necessary. The micronized fibrous cellulose obtained by the production method of this embodiment only needs to have a reduced fiber width compared to the fiber width of the fibrous cellulose initially charged into the agitator-equipped tank. The type of defibration device used and the number of passes are appropriately set depending on the desired fiber width. The fiber width of the obtained micronized fibrous cellulose is not particularly limited, but is preferably 30 μm or less, more preferably 25 μm or less. The micronized fibrous cellulose may also be fine fibrous cellulose having a fiber width of 1,000 nm or less. The fiber width of the micronized fibrous cellulose can be measured, for example, by observation with an electron microscope.

[0126] The average fiber width of pulverized fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of pulverized fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast on a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast on glass may be observed. Next, electron microscope images are observed at magnifications of 1,000x, 5,000x, 10,000x, or 50,000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions: (1) A line X is drawn at any location within the observed image, and 20 or more fibers intersect with line X. (2) A line Y is drawn within the same image, perpendicular to line X, and 20 or more fibers intersect line Y.

[0127] For observation images that satisfy the above conditions, the widths of fibers intersecting with lines X and Y are visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the widths of fibers intersecting with lines X and Y are read. In this way, the widths of at least 20 fibers x 2 x 3 = 120 fibers are read. The average value of the read fiber widths is then taken as the average fiber width of the fibrous cellulose.

[0128] The pulverized fibrous cellulose preferably has a type I crystal structure. The presence of type I crystal structure in pulverized fibrous cellulose can be identified by a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromatized with graphite. Specifically, it can be identified by the presence of two typical peaks at two positions: 2θ=14° to 17° and 2θ=22° to 23°. The proportion of type I crystal structure in the pulverized fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to provide even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and determining the pattern using a conventional method (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0129] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0130] [Phosphating Treatment] As the raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 208 g / m) manufactured by Oji Paper Co., Ltd. was used. ２A sheet-like pulp (disintegrated, Canadian Standard Freeness (CSF) of 700 mL as measured in accordance with JIS P 8121-2:2012) was used. This raw pulp was subjected to a phosphating treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 200 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

[0131] [Washing Treatment] The resulting phosphorylated pulp was then washed. The washing treatment was carried out by repeatedly adding 10 L of ion-exchanged water to 100 g (bone dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the resulting solution to uniformly disperse the pulp, and then filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0132] [Neutralization Treatment] Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain a neutralized phosphorylated pulp. Next, the neutralized phosphorylated pulp was subjected to the above-mentioned washing treatment.

[0133] The infrared absorption spectrum of the phosphorylated pulp thus obtained was measured using FT-IR. －１Absorption due to the P=O of the phosphate group was observed near the peak, confirming that the phosphate group had been added to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. Furthermore, the amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0134] [Defibrillation Treatment] Example 1: Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solids concentration of 2% by mass. The viscosity of the obtained slurry (viscosity of the fibrous cellulose dispersion before treatment) was 2,800 mPa·s. 150 L of this slurry was poured into a tank with a capacity of 170 L (inner diameter (diameter) 760 mm) equipped with an agitator. The agitator had the shape shown in FIG. 3(a), consisting of two horizontal paddles, one at the top and one at the bottom, and one blade along the tank wall. The longitudinal length of the horizontal paddle was 370 mm, the center of the height of the upper horizontal paddle was ±100 mm above the liquid level, and the blade along the tank wall was 10 mm from the tank wall. The tank's depth (maximum depth) was 760 mm, and the depth-wise length of the blade along the tank wall was 640 mm. While the agitator was rotating at 15 rpm, a mono pump (manufactured by Heishin Soubi Co., Ltd.) installed at the bottom of the tank was used to send the slurry to a single disc refiner (manufactured by Aikawa Iron Works Co., Ltd.) at a flow rate of 150 L / min. The sent slurry was processed in the single disc refiner under conditions of a clearance of 0.6 mm and a blade rotation speed of 3,300 rpm. The slurry processed in the single disc refiner was returned to the tank through piping from near the upper wall of the agitator-equipped tank. While measuring the processing time, the processing was continued until 10 passes were made in the single disc refiner, and a finely divided fibrous cellulose dispersion was obtained. The entire slurry after processing was uniform. Slurry was collected and analyzed from three locations: directly below the inlet, around the rotation axis, and on the opposite side of the rotation axis from the inlet. The haze measured by the measurement method described below was 31.0%, 31.5%, and 32.2%, respectively.

[0135] Example 2 The same procedure as in Example 1 was repeated, except that the agitator had a single horizontal paddle as shown in Figure 3(b), the length of the horizontal paddle in the longitudinal direction was 370 mm, and the center of the height of the horizontal paddle was the height of the liquid surface ±10 mm. Treatment was performed until 10 passes were made through the single-disc refiner, thereby obtaining a refined fibrous cellulose dispersion. The slurry after treatment was uniform throughout. Slurry samples were collected from three locations: directly below the inlet, around the rotation axis, and on the opposite side of the rotation axis from the inlet, and analyzed. The haze, measured by the measurement method described below, was 31.7%, 36.7%, and 42.2%, respectively.

[0136] Example 3 The same processing as in Example 1 was carried out until 10 passes were made through the single-disc refiner, to obtain a refined fibrous cellulose dispersion, except that the shape of the agitator was such that the blades of Example 1 were also installed at positions opposite to the rotation axis. The slurry after processing was uniform throughout. Slurry samples were collected from three locations: directly below the inlet, around the rotation axis, and on the opposite side of the rotation axis from the inlet, and analyzed. The haze values ​​measured by the measurement method described below were 31.6%, 33.0%, and 33.1%, respectively.

[0137] Example 4: Ion-exchanged water was added to the resulting phosphorylated pulp to prepare a slurry with a solids concentration of 3.1% by mass. 150 L of this slurry was poured into a 170 L (760 mm inner diameter) agitator-equipped tank. The agitator had the shape shown in FIG. 3(a), consisting of two horizontal paddles, one at the top and one at the bottom, and one blade along the tank wall. The longitudinal length of the horizontal paddle was 370 mm, the center of the height of the upper horizontal paddle was ±100 mm above the liquid level, and the blade along the tank wall was 10 mm from the tank wall. The tank's depth (maximum depth) was 760 mm, and the depth of the blade along the tank wall was 640 mm. While the agitator was rotating at 15 rpm, the liquid was pumped to a single-disc refiner (Aikawa Iron Works Co., Ltd.) at a flow rate of 100 L / min using a Mono Pump (Heishin Soubi Co., Ltd.) installed at the bottom of the tank. The delivered slurry was processed in a single-disc refiner under conditions of a clearance of 0.6 mm and a blade rotation speed of 2,400 rpm. The slurry processed in the single-disc refiner was returned to the tank from the top of the agitator-equipped tank through piping. Processing was continued until 10 passes were made in the single-disc refiner while measuring the processing time, and a refined fibrous cellulose dispersion was obtained. The entire slurry after processing was uniform. Slurry was collected and analyzed from three locations: directly below the inlet, around the rotation axis, and on the opposite side of the rotation axis from the inlet. The haze, measured by the measurement method described below, was 45.2%, 47.4%, and 49.9%, respectively.

[0138] Example 5 A pulverized fibrous cellulose dispersion was obtained in the same manner as in Example 1, except that the rotation speed of the stirrer was set to 30 rpm and the number of passes was set to 20. The entire slurry after treatment was uniform. Slurry was sampled and analyzed from three locations: directly below the inlet, around the rotation axis, and on the opposite side of the rotation axis from the inlet. The haze measured by the measurement method described below was 19.0%, 20.1%, and 21.6%, respectively.

[0139] Example 6 Finely refined fibrous cellulose was obtained in the same manner as in Example 4, except that the clearance of the single-disc refiner was 0.8 mm, the blade rotation speed was 3,300 rpm, and the number of treatment passes was 6. The entire slurry after treatment was uniform. Slurry was collected and analyzed from three locations: directly below the inlet, around the rotation axis, and on the opposite side of the rotation axis from the inlet. The haze measured by the measurement method described below was 32.8%, 33.7%, and 33.1%, respectively.

[0140] Comparative Example 1 Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solids concentration of 2% by mass. 150 L of this slurry was poured into a tank with a capacity of 170 L (inner diameter 760 mm). Using a Mohno pump (manufactured by Heishin Soubi Co., Ltd.) installed at the bottom of the tank, the slurry was pumped to a single-disc refiner (manufactured by Aikawa Iron Works Co., Ltd.) at a flow rate of 150 L / min. The pumped slurry was processed in the single-disc refiner under conditions of a clearance of 0.6 mm and a blade rotation speed of 3,300 rpm. The slurry processed in the single-disc refiner was returned to the tank from the top of the agitator-equipped tank through piping. The processing time was measured, and the processing was continued until 10 passes were made through the single-disc refiner, yielding a fine fibrous cellulose dispersion. The entire slurry after processing was non-uniform. Slurry was collected from three locations: directly below the inlet, around the rotation axis, and on the opposite side of the rotation axis from the inlet, and analyzed. The haze measured by the measurement method described below was 32.2%, 43.1%, and 71.8%, respectively.

[0141] [Measurement and Evaluation] <Measurement of Phosphorus Oxo Acid Group Amount> Ion-exchanged water was added to the obtained phosphate-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated twice at a pressure of 200 MPa using a wet pulpizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion. The fine fibrous cellulose dispersion was diluted with ion-exchanged water to 0.2% by mass to prepare a fibrous cellulose-containing slurry. The fibrous cellulose content was then measured by treating the slurry with an ion-exchange resin and then titrating it with an alkali. The ion-exchange resin treatment was carried out by adding 1 / 10 by volume of a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring the slurry onto a mesh with a mesh opening of 90 μm to separate the resin and the slurry. In addition, the alkali titration was performed by adding 10 μL of 0.1 N aqueous sodium hydroxide solution to the fine fibrous cellulose-containing slurry after treatment with an ion exchange resin at 5-second intervals, while measuring the change in the pH value of the slurry. Nitrogen gas was introduced into the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the differential pH value with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. Of these, the maximum point of increment obtained first after starting the addition of alkali is called the first endpoint, and the maximum point of increment obtained next is called the second endpoint (FIG. 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used in the titration. Furthermore, the amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used in the titration. The amount of alkali (mmol) required from the start of titration to the first endpoint was divided by the solid content (g) in the slurry to be titrated, and the value was taken as the amount of phosphorus oxo acid groups (mmol / g).

[0142] <Slurry Haze Measurement> The haze of the slurries obtained in the Examples and Comparative Examples was measured by diluting the fine fibrous cellulose dispersion with ion-exchanged water to 0.2% by mass, and then measuring the haze in accordance with JIS K 7136 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) and a glass cell for liquids (MG-40, reverse optical path, manufactured by Fujiwara Seisakusho Co., Ltd.). Zero-point measurement was performed using ion-exchanged water placed in the same glass cell. The liquid temperature of the dispersion during measurement was 23°C.

[0143] <Viscosity of Fibrous Cellulose Dispersion> The viscosity of the fibrous cellulose dispersion was measured by the following method. (1) Viscosity of Fibrous Cellulose Dispersion Before Treatment The fibrous cellulose dispersion (solid content 2% by mass) transferred to a container was allowed to stand at 23°C for 24 hours, and then measured using a Brookfield viscometer (digital viscometer LVDV2T, spindle LV-61, manufactured by BLOOKFIELD). The measurement conditions were a rotation speed of 0.3 rpm, and the viscosity value 3 minutes after the start of measurement was taken as the viscosity of the dispersion. (2) Viscosity of Micronized Fibrous Cellulose The viscosity of the microfibrous cellulose dispersion was measured as follows. First, the microfibrous cellulose dispersion was subjected to a degassing treatment using a rotation-revolution type super mixer (ARE-250, manufactured by Thinky Corporation). The degassed dispersion was allowed to stand at 23°C for 24 hours, and then measured using a Brookfield viscometer (digital viscometer HBDV2T, spindle LV-65, manufactured by BLOOKFIELD). The viscosity of the fibrous cellulose dispersions obtained in Examples 5 and 6 was measured.

[0144] The results are shown in Table 1 below.

[0145]

[0146] The results in Table 1 show that when a mixer tank having at least one mixer blade selected from the group consisting of mixer blade A and mixer blade B was used and the micronization treatment was continuously carried out while the mixer blade was rotating, the difference in haze between the fibrous cellulose dispersion just below the inlet, the haze of the fibrous cellulose around the rotation axis, and the haze of the fibrous cellulose dispersion on the opposite side of the rotation axis from the inlet was reduced, improving the uniformity of the quality of the fibrous cellulose dispersion inside the mixer tank, and the final product, micronized fibrous cellulose, also had excellent uniformity of quality. On the other hand, as shown in Comparative Example 1, when the tank did not have a specific mixer blade, the difference in haze between just below the inlet and the haze on the opposite side of the rotation axis from the inlet was large, resulting in poor uniformity of quality.

[0147] 10 Tank with agitator 20 Tank 30 Stirring rod 40 Stirring blade A 42 Stirring blade B

Claims

1. A method for producing pulverized fibrous cellulose, comprising the steps of: step (1): allowing a fibrous cellulose dispersion introduced into a tank equipped with an agitator to flow out from the bottom of the tank and transfer to a defibrator; step (2): using the defibrator to refine the fibrous cellulose in the transferred fibrous cellulose dispersion; and step (3): transferring the refined fibrous cellulose dispersion to the upper part of the same tank equipped with an agitator, in this order, and repeatedly carrying out steps (1) to (3), wherein steps (1) to (3) are carried out while rotating an agitator blade provided in the tank equipped with an agitator, and the agitator blade provided in the tank equipped with an agitator has at least one agitator blade selected from the group consisting of agitator blade A and agitator blade B described below. Agitator blade A: an agitator blade installed in a substantially horizontal direction at least near the liquid surface, and agitator blade B: an agitator blade that rotates along the wall surface.

2. The method for producing pulverized fibrous cellulose according to claim 1, which comprises at least an agitator blade A.

3. The method for producing pulverized fibrous cellulose according to claim 1, which comprises stirring blade A and stirring blade B.

4. A method for producing pulverized fibrous cellulose according to any one of claims 1 to 3, wherein the rotation speed of the stirring blade is 1 rpm or more and 100 rpm or less.

5. A method for producing pulverized fibrous cellulose according to any one of claims 1 to 3, wherein the viscosity of the fibrous cellulose dispersion in the tank equipped with an agitator is 1 mPa·s or more and 5,000,000 mPa·s or less.

6. The method for producing pulverized fibrous cellulose according to any one of claims 1 to 3, wherein the agitating blade A and the agitating blade B are each a single blade.

7. The method for producing pulverized fibrous cellulose according to any one of claims 1 to 3, wherein the defibrating device is at least one selected from the group consisting of a disintegrator, a beater, and an atomizer.

8. A method for producing finely divided fibrous cellulose according to any one of claims 1 to 3, wherein the fibrous cellulose in the fibrous cellulose dispersion is fibrous cellulose into which an ionic group has been introduced.

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