Method for producing fine fibrous cellulose

Abstract

To provide a method for producing microfibrous cellulose in which quality changes are suppressed.SOLUTION: A method for producing microfibrous cellulose includes: a reaction step of performing chemical modification to cellulose fiber to obtain chemically modified cellulose; a dehydrating / cleaning step of performing dehydrating / cleaning of dispersion liquid of the chemically modified cellulose; an adjustment step of adjusting the concentration of the dispersion liquid of the chemically modified cellulose; and a fibrillation step of adding mechanical shearing force to the dispersion liquid of the chemically modified cellulose to fibrillate the liquid, where a sine pump is used for transfer in at least any step of the dispersion liquid of the chemically modified cellulose.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for producing fine fibrous cellulose. [Background technology]

[0002] Fine fibrous cellulose, obtained by defibrating cellulose fibers to a fiber width of 1000 nm or less, exhibits excellent strength, elasticity, and thermal stability, and is used in industrial applications as a filler in resins and rubber compounds. Furthermore, aqueous dispersions of fine fibrous cellulose are used as viscosity modifiers and stabilizers. Fine fibrous cellulose can be obtained by mechanically defibrating pulp fibers. It is believed that introducing ionic groups into the pulp fibers before defibration can efficiently reduce the energy required for the mechanical processing (see Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-1728 [Patent Document 2] Japanese Patent Publication No. 2010-235679 [Overview of the project] [Problems that the invention aims to solve]

[0004] When various methods for producing fine fibrous cellulose, including the manufacturing methods described in Patent Documents 1 and 2, are scaled up, unexpected quality changes can occur, such as changes in the viscosity of chemically modified cellulose or fine fibrous cellulose. Therefore, the present invention aims to provide a method for producing fine fibrous cellulose in which changes in quality are suppressed. [Means for solving the problem]

[0005] The present invention provides the following [1] to [5]. [1] A method for producing microfibrillar cellulose, comprising a reaction step of chemically modifying cellulose fibers to obtain chemically modified cellulose, a dehydration and washing step of dehydrating and washing a dispersion of the chemically modified cellulose, an adjustment step of adjusting the concentration of the dispersion of the chemically modified cellulose, and a fibrillation step of applying mechanical shear force to the dispersion of the chemically modified cellulose to defibrate it, wherein a sine pump is used for the transfer in at least any one of the steps of the dispersion of the chemically modified cellulose. [2] The method for producing microfibrillar cellulose according to [1], wherein the reaction step is a step of introducing an ionic group into cellulose fibers. [3] The method for producing microfibrillar cellulose according to [2], wherein the ionic group is an anionic group. [4] The method for producing microfibrillar cellulose according to [3], wherein the anionic group is at least one selected from the group consisting of a phosphoxo acid group, a sulfur oxo acid group, and a carboxy group. [5] The method for producing microfibrillar cellulose according to [3], wherein the anionic group is a phosphoxo acid group. [Advantages of the Invention]

[0006] According to the present invention, there is provided a method for producing microfibrillar cellulose in which changes in quality are suppressed. [Brief Description of the Drawings]

[0007] [Figure 1] FIG. 1 is a graph showing the relationship between the amount of NaOH dropped and pH for a fibrous cellulose-containing slurry having a phosphoxo acid group. [Figure 2] FIG. 2 is a graph showing the relationship between the amount of NaOH dropped and pH for a fibrous cellulose-containing slurry having a carboxy group. [Embodiments for Carrying Out the Invention]

[0008] [Method for Producing Microfibrillar Cellulose] The method for producing fine fibrous cellulose according to this embodiment includes a reaction step of chemically modifying cellulose fibers to obtain chemically modified cellulose, a dehydration and washing step of dehydrating and washing the dispersion of the chemically modified cellulose, an adjustment step of adjusting the concentration of the dispersion of the chemically modified cellulose, and a defibration step of applying mechanical shear force to the dispersion of the chemically modified cellulose to defibrate it, wherein a sine pump is used to transport the dispersion of the chemically modified cellulose in at least one of the steps.

[0009] [Sine pump] A sine pump is a positive displacement pump that uses a sinusoidal rotor (rotating impeller). As a single sinusoidal rotor rotates, four chambers of equal volume are created. The fluid to be pumped is drawn sequentially into each chamber through the suction port, and the chambers rotate while discharging the fluid to the discharge port. In addition, as fluid is drawn into the next chamber as it is discharged, pulsation is suppressed. The sine pump can be used in the manufacturing process of fine fibrous cellulose for circulation during chemical modification, such as introducing ionic groups into pulp fibers that serve as raw materials, as well as for transporting the modified reaction slurry, transporting the washed reaction slurry, and for handling high-viscosity fine fibrous cellulose slurry obtained by applying high shear to chemically modified pulp and nano-dispersing it.

[0010] Pumps are broadly classified into two main types: turbo pumps (non-positive displacement pumps) and positive displacement pumps. Turbo pumps include centrifugal pumps such as volute pumps and diffuser pumps, as well as mixed-flow pumps and axial-flow pumps. Positive displacement pumps include reciprocating pumps such as piston pumps, plunger pumps and diaphragm pumps, as well as gear pumps, vane pumps and screw pumps. Sine pumps are broadly classified into positive displacement pumps, and as mentioned above, they are pumps that transfer fluid by continuously moving the space created between a rotor and stator, which have a sinusoidal shape. Compared to turbo-type (non-positive displacement) pumps, which impart kinetic energy to the fluid by rapidly rotating an impeller within the casing, this type of pump is characterized by its lower shear force on the fluid and extremely low leakage between the rotor and stator, resulting in a higher head and the ability to pump relatively viscous fluids.

[0011] The flow rate during transfer using a sine pump is largely dependent on the size of the sine pump and is not particularly limited. By selecting the appropriate size of sine pump according to the desired flow rate, it is possible to obtain a flow rate suitable for the manufacturing process while keeping the shear force applied to the fluid low. The following details each step.

[0012] [Reaction process] The reaction process involves chemically modifying cellulose fibers to obtain chemically modified cellulose. In the present invention, the cellulose fiber used as a raw material refers to various forms of materials mainly composed of cellulose, and is not particularly limited to the cellulose fiber used as a raw material, but examples include wood pulp, non-wood pulp, and deinked pulp. Wood pulp is not particularly limited, but examples include chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolved 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 chemigroundwood pulp (CGP), and mechanical pulps such as crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Non-wood pulp is not particularly limited, but examples include cotton pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, bamboo, and bagasse. The deinked pulp is not particularly limited, but examples include deinked pulp made from recycled paper. The pulp raw material in this embodiment may be one of the above types alone, or two or more types may be mixed and used. Among the cellulose fibers used as raw materials mentioned above, wood pulp and deinked pulp are preferred from the standpoint of ease of availability. Furthermore, among wood pulp, chemical pulp is more preferred from the standpoint of having a high cellulose ratio and a high yield of fine fibrous cellulose during defibration, and from the standpoint of obtaining long-fiber fine fibrous cellulose with a large axial ratio due to minimal cellulose decomposition in the pulp. Kraft pulp and sulfite pulp are even more preferred. It should be noted that using long-fiber fine fibrous cellulose with a large axial ratio tends to result in higher viscosity.

[0013] In the present invention, when using sheet-like cellulose raw material, it is preferable to coarsely crush it to a size of approximately 0.5 to 5 cm square. By coarsely crushing to this size, the cellulose raw material can be modified efficiently and uniformly in the subsequent reaction step. The method of coarse crushing is not particularly limited, but a single-screw rotary shredder, a twin-screw rotary shredder, a multi-screw screw shredder, a shredder, a guillotine cutter, etc., can be used. Among these, using a single-screw rotary shredder or a shredder is preferable from the viewpoint of coarse crushing.

[0014] Chemical modification is performed on cellulose fibers to obtain chemically modified cellulose. Chemical modification is preferably carried out by introducing ionic groups (ionic substituents). That is, the reaction step is preferably a step of introducing ionic groups into cellulose fibers. 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 is an anionic group. Furthermore, the ionic group is preferably a group introduced into the cellulose fiber via an ester bond or an ether bond, and more preferably a group introduced into the cellulose fiber via an ester bond. In this case, the ester bond is preferably formed by the dehydration condensation of the cellulose fiber and the compound that will become the ionic group.

[0015] Examples of anionic groups as ionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxyl groups or substituents derived from carboxyl groups (sometimes simply referred to as carboxyl groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xantate groups or substituents derived from xantate groups (sometimes simply referred to as xantate groups), phosphonone groups or substituents derived from phosphonone groups, phosphine groups or substituents derived from phosphine groups, sulfone groups or substituents derived from sulfone groups, carboxyalkyl groups, and the like. In particular, 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 carboxyl 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 carboxyl group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group; and particularly preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as the anionic group, defibrillation is possible with less energy. Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, ammonium groups are preferred as the cationic group.

[0016] A phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group is, for example, a substituent represented by the following formula (1). Multiple substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the multiple substituents represented by the following formula (1) may be the same or different.

[0017] [ka]

[0018] In equation (1), a, b, and n are natural numbers, and m is any number (where a = b × m). Of the n α and α', at least one is O - And the rest are R or OR. Note that all of each α and α' are O - It is acceptable for this to be the case. The n αs may all be the same, or they may all be different. β b+ It is a cation with one or more valencies, composed of organic or inorganic substances.

[0019] 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 derivative thereof. In formula (1), n ​​is preferably 1.

[0020] 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.

[0021] Furthermore, as derivative groups in R, carboxyl groups and carboxylate groups (-COO) are added to the main chain or side chain of the various hydrocarbon groups mentioned above. -Examples of functional groups include, but are not particularly limited to, a functional group in which at least one selected from functional groups such as hydroxyl groups, amino groups, and ammonium groups is added or substituted. Furthermore, 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, which facilitates penetration into the fiber raw material and can also increase the yield of fibrous cellulose. Note that if there are multiple Rs in formula (1) or if multiple substituents represented by formula (1) are introduced into fibrous cellulose, the multiple Rs may be the same or different.

[0022] β b+ β is a cation with one or more valent units, composed of organic or inorganic substances. Examples of organic cations with one or more valent units include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of inorganic cations with one or more valent units include alkali metal ions such as sodium, potassium, or lithium, divalent metal ions such as calcium or magnesium, hydrogen ions, and ammonium ions. Note that β is included in formula (1). b+ If multiple β atoms exist, or if multiple substituents represented by formula (1) above are introduced into fibrous cellulose, then multiple β atoms exist. b+ These may be the same or different. As a monovalent or greater cation consisting of organic or inorganic material, β b+ Sodium or potassium ions are preferred because they do not easily yellow when the fiber raw material containing them is heated, and are also easily usable industrially, but the invention is not particularly limited.

[0023] Examples of the phosphooxo acid group or a substituent derived from the phosphooxo acid group include, more specifically, a phosphoric acid group (-PO3H2), a salt of the phosphoric acid group, a phosphorous acid group (phosphonic acid group) (-PO2H2), and a salt of the phosphorous acid group (phosphonic acid group). Further, the phosphooxo acid group or a substituent derived from the phosphooxo acid group may be a group in which phosphoric acid groups are condensed (for example, a pyrophosphoric acid group), a group in which phosphonic acids are condensed (for example, a polyphosphonic acid group), a phosphoric acid ester group (for example, a monomethylphosphoric acid group, a polyoxyethylene alkylphosphoric acid group), an alkylphosphonic acid group (for example, a methylphosphonic acid group), or the like.

[0024] Further, the sulfur oxo acid group (sulfur oxo acid group or a substituent derived from the sulfur oxo acid group) is, for example, a substituent represented by the following formula (2). A plurality of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of substituents represented by the following formula (2) introduced may be the same or different from each other.

[0025] [Chemical formula]

[0026] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (however, 1 = b × m). When n is 2 or more, the plurality of p's may be the same number or different numbers. In the above structural formula, β b+β is a cation with one or more valencies composed of organic or inorganic substances. Examples of cations with one or more valencies composed of organic substances include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of cations with one or more valencies composed of inorganic substances include alkali metal ions such as sodium, potassium, or lithium, divalent metal ions such as calcium or magnesium, hydrogen ions, and ammonium ions. When multiple substituents represented by the above formula (2) are introduced into fibrous cellulose, multiple β atoms are present. b+ These may be the same or different. As a monovalent or greater cation consisting of organic or inorganic material, β b+ Sodium or potassium ions are preferred because they do not easily yellow when the fiber raw material containing them is heated, and are also easily usable industrially, but the invention is not particularly limited.

[0027] The amount of ionic groups introduced into the cellulose fibers is preferably 0.10 mmol / g or more per gram (mass) of cellulose fiber, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more. Furthermore, the amount of ionic groups introduced into the cellulose fibers is preferably 5.20 mmol / g or less per gram (mass) of cellulose fiber, 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 particularly preferably 1.00 mmol / g or less. Here, the denominator in the unit mmol / g is the amount of the counterion of the ionic group being a hydrogen ion (H +This indicates the mass of the cellulose fiber when ). By keeping the amount of ionic groups introduced within the above range, it is possible to easily refine the fiber raw material and improve the stability of the cellulose fiber.

[0028] The amount of ionic groups introduced into cellulose fibers can be measured after the cellulose fibers have been subjected to micronization treatment, for example, by a neutralization titration method. In the neutralization titration method, the amount of introduced groups is determined by measuring the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the slurry containing the resulting cellulose fibers.

[0029] Figure 1 is a graph showing the relationship between the amount of NaOH added to a dispersion of fine fibrous cellulose containing phosphorus oxoacid groups and the pH. The amount of phosphorus oxoacid groups introduced into the cellulose fibers can be measured, for example, as follows. First, ion-exchanged water is added to the target cellulose fibers to prepare a slurry with a solid content concentration of 0.2% by mass. This slurry is then processed four times at a pressure of 200 MPa using a wet atomization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. Finally, the fine fibrous cellulose dispersion is treated with a strongly acidic ion-exchange resin. Next, the pH change is observed while adding an aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 1 is obtained. In the titration curve shown in the upper part of Figure 1, the measured pH is plotted against the amount of alkali added, and in the titration curve shown in the lower part of Figure 1, the increment (derivative value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, two points are observed in the curve plotting the measured pH against the amount of alkali added where the increment (derivative value of pH with respect to the amount of alkali added) is maximum. Of these, the first maximum increment obtained after starting to add alkali 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 the titration to the first endpoint is equal to the amount of the first dissociated acid from the fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the first endpoint to the second endpoint is equal to the amount of the second dissociated acid from the fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid from the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of the titration to the first endpoint by the solid content (g) of the slurry being titrated is the amount of phosphorus oxoacid groups introduced (mmol / g). Note that when simply referred to as the amount of phosphorus oxoacid groups introduced (or amount of phosphorus oxoacid groups), it refers to the amount of the 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, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weakly acidic group in the phosphorus oxoacid group (also referred to as the amount of the second dissociated acid in this specification) appears to decrease, and the amount of alkali required in the second region becomes less than the amount of alkali required in the first region. On the other hand, the amount of strongly acidic group in the phosphorus oxoacid group (also referred to as the amount of the first dissociated acid in this specification) is equal to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Also, if the phosphorus oxoacid group is a phosphite group, there is no weakly acidic group in the phosphorus oxoacid group, so the amount of alkali required in the second region becomes less, or in some cases, the amount of alkali required in the second region becomes zero. In this case, there is only one point on the titration curve where the pH increment is maximum.

[0030] The amount of phosphorus oxoacid groups introduced (mmol / g) mentioned above represents the amount of phosphorus oxoacid groups present in acid-type fibrous cellulose (hereinafter referred to as phosphorus oxoacid group amount (acid type)), since the denominator represents the mass of acid-type fibrous cellulose. On the other hand, if the counterion of the phosphorus oxoacid group is substituted with an arbitrary cation C such that it is equivalent in charge, the amount of phosphorus oxoacid groups present in fibrous cellulose with cation C as the counterion can be determined by converting the denominator to the mass of fibrous cellulose when cation C is the counterion (hereinafter referred to as phosphorus oxoacid group amount (C type)). In other words, it is calculated using the following formula. Phosphorus oxoacid group amount (C type) = Phosphorus oxoacid group amount (acid type) / {1 + (W - 1) × A / 1000} A [mmol / g]: Total amount of anions derived from the phosphorus oxoacid group in fibrous cellulose (total amount of dissociated acids from the phosphorus oxoacid group) W: Formula weight per unit charge of the cation C (e.g., Na is 23, Al is 9)

[0031] Figure 2 is a graph showing the relationship between the amount of NaOH added to a fine fibrous cellulose dispersion having carboxyl groups as ionic groups and the pH. The amount of carboxyl groups introduced into the cellulose fibers can be measured, for example, as follows. First, ion-exchanged water is added to the target cellulose fibers to prepare a slurry with a solid content concentration of 0.2% by mass. This slurry is then processed four times at a pressure of 200 MPa using a wet atomization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. Finally, the fine fibrous cellulose dispersion is treated with a strongly acidic ion-exchange resin. Next, the pH change is observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in the upper part of Figure 2. In the titration curve shown in the upper part of Figure 2, the measured pH is plotted against the amount of alkali added, and in the titration curve shown in the lower part of Figure 2, the increment (derivative value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, one point is identified in the curve plotting the measured pH against the amount of alkali added where the increment (derivative value of pH with respect to the amount of alkali added) is maximum, and this maximum point is called the first endpoint. Here, the region from the start of titration to the first endpoint in Figure 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the dispersion used for titration. Then, the amount of alkali required in the first region of the titration curve (mmol) is divided by the solid content (g) in the dispersion containing the fibrous cellulose to be titrated to calculate the amount of carboxyl groups introduced (mmol / g).

[0032] The above-mentioned amount of carboxyl groups introduced (mmol / g) represents the amount of carboxyl groups present in acidic fibrous cellulose (hereinafter referred to as carboxyl group amount (acidic type)), since the denominator is the mass of acidic fibrous cellulose. On the other hand, if the counterion of the carboxyl group is substituted with an arbitrary cation C such that it is equivalent in charge, the amount of carboxyl groups present in fibrous cellulose with cation C as the counterion (hereinafter referred to as carboxyl group amount (C type)) can be determined by converting the denominator to the mass of fibrous cellulose when the cation C is the counterion. That is, it is calculated using the following formula. Carboxylate group weight (C type) = Carboxylate group weight (acid type) / {1 + (W - 1) × (Carboxylate group weight (acid type)) / 1000} W: Formula weight per unit charge of the cation C (e.g., Na is 23, Al is 9)

[0033] In measuring the amount of ionic groups by titration, if the amount of sodium hydroxide aqueous solution added is too large or the titration interval is too short, accurate values ​​may not be obtained, resulting in a lower-than-actual amount of ionic groups. For appropriate titration volume and interval, it is desirable to titrate with 10 μL to 50 μL of 0.1N sodium hydroxide aqueous solution for 5 to 30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fine fibrous cellulose dispersion, it is desirable to blow an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of the titration while measuring.

[0034] Furthermore, the amount of sulfur oxoacid groups and sulfone groups introduced into the fibrous cellulose is determined by wet ashing the obtained fibrous cellulose with perchloric acid and concentrated nitric acid, then diluting it to an appropriate ratio and measuring the sulfur content by ICP emission spectrometry. The amount of sulfur obtained by dividing this sulfur content by the oven-dry mass of the fibrous cellulose tested is defined as the amount of sulfur oxoacid groups / sulfone groups (unit: mmol / g).

[0035] To obtain chemically modified cellulose with the ionic groups described above, it is preferable to have an ionic group introduction step in which ionic groups are introduced into the cellulose-containing fiber raw material (cellulose fiber). Examples of ionic group introduction steps include a phosphorus oxo acid group introduction step, a carboxyl group introduction step, a sulfur oxo acid group introduction step, a xantate group introduction step, a phosphone group or phosphine group introduction step, a sulfone group introduction step, and a cationic group introduction step. Each of these will be explained below.

[0036] <Phosphorus oxoacid group introduction process> When obtaining chemically modified cellulose having ionic groups, it is preferable to include a reaction step to introduce ionic groups before the defibration step. An example of such a reaction step is a phosphorus oxoacid group introduction step. The phosphorus oxoacid group introduction step is a step in which at least one compound (hereinafter also referred to as "compound A") selected from compounds that can introduce phosphorus oxoacid groups by reacting with the hydroxyl groups present in the cellulose fibers is reacted with the cellulose fibers, which are the raw material. Through this step, cellulose fibers having phosphorus oxoacid groups (chemically modified cellulose) are obtained.

[0037] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction between cellulose fibers 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 cellulose fibers and compound A may be carried out in the absence of compound B.

[0038] One example of a method for reacting compound A with cellulose fibers in the presence of compound B is to mix compound A and compound B with cellulose fibers in a dry, wet, or slurry state. Of these, it is preferable to use cellulose fibers in a dry or wet state, and particularly preferable to use cellulose fibers in a dry state, due to the high uniformity of the reaction. The form of the cellulose fibers is not particularly limited, but for example, cotton-like or thin sheet-like forms are preferred. Compounds A and B can be added to the fiber raw material in the form of powder, a solution dissolved in a solvent, or after being heated above their melting point and melted. Of these, it is preferable to add them in the form of a solution dissolved in a solvent, particularly an aqueous solution, due to the high uniformity of the reaction. Compounds A and B may be added to the cellulose fibers simultaneously, separately, or as a mixture. The method of adding compounds A and B is not particularly limited, but if compounds A and B are in solution form, the cellulose fibers may be immersed in the solution and then removed, or the solution may be dropped onto the cellulose fibers, or sprayed. 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 pressing or filtration.

[0039] Compound A used in this embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose, and is not particularly limited to, but includes phosphoric acid or its salts, phosphorous acid or its salts, dehydrated condensed phosphoric acid or its salts, and phosphoric anhydride (phosphorus pentoxide). As phosphoric acid, various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. As phosphorous acid, 99% phosphorous acid (phosphonic acid) can be used. Dehydrated condensed phosphoric acid is obtained by condensing two or more molecules of phosphoric acid through a dehydration reaction, and examples 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, and these can be neutralized to various degrees. Of these, phosphoric acid, sodium phosphoric acid, potassium phosphoric acid, ammonium phosphoric acid, or phosphorous acid, sodium phosphorous acid, potassium phosphorous acid, or ammonium phosphorous acid are preferred from the viewpoint of having high efficiency in introducing phosphate groups, easily improving the defibration efficiency in the defibration process described later, being low cost, and being easily applicable industrially. More preferably, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid or sodium phosphorous acid are preferred.

[0040] 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 to the amount of phosphorus atoms, it is preferable that the amount of phosphorus atoms added to the cellulose fibers (oven-dry mass) be 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 keeping 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 keeping the amount of phosphorus atoms added to the cellulose fibers below the above upper limit, it is possible to balance the effect of improving the yield with the cost.

[0041] 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, it is preferable to use compound B 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.

[0042] The amount of compound B added to cellulose fibers (absolute dry weight) is not particularly limited, but is preferably 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.

[0043] In the reaction of cellulose-containing fiber raw materials with compound A, in addition to compound B, other substances such as amides or amines may be included in the reaction system. 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 act as a particularly good reaction catalyst.

[0044] In the phosphorus oxoacid group introduction step, it is preferable to add or mix compound A or the like to the cellulose fibers and then subject the cellulose fibers to heat treatment. The heat treatment temperature is preferably selected to efficiently introduce phosphorus oxoacid groups while suppressing thermal decomposition and hydrolysis reactions 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. Furthermore, various heat transfer devices can be used for the heat treatment, such as stirring dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

[0045] In the heat treatment according to this embodiment, for example, a method can be employed in which compound A is added to thin sheet-like cellulose fibers by impregnation or other methods, and then heated, or a method can be employed in which the cellulose fibers and compound A are kneaded or stirred while heating. This makes it possible to suppress uneven concentration of compound A in the cellulose fibers and to introduce phosphorus oxoacid groups more uniformly to the surface of the cellulose fibers. This is thought to be because, as water molecules move to the surface of the cellulose fibers during drying, dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the surface of the cellulose fibers (i.e., uneven concentration of compound A is produced), and this can be suppressed.

[0046] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge moisture, such as the moisture held in the slurry and the moisture generated by the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose in the cellulose fibers, from the device system. Examples of such heating devices include ovens with a forced-air system. By constantly discharging moisture from the device system, it is possible to suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as the acid hydrolysis of sugar chains in cellulose fibers. As a result, it becomes possible to obtain fine fibrous cellulose with a high axial ratio.

[0047] The heating time is preferably between 1 second and 300 minutes, more preferably between 1 second and 1000 seconds, and even more preferably between 10 seconds and 800 seconds, after substantially all moisture has been removed from the cellulose fibers. In this embodiment, the amount of phosphorus oxoacid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within an appropriate range.

[0048] The phosphorus oxoacid group introduction process only needs to be performed at least once, but it can also be repeated two or more times. By performing the phosphorus oxoacid group introduction process two or more times, a large number of phosphorus oxoacid groups can be introduced into the fiber raw material.

[0049] The amount of phosphorus oxoacid groups introduced into the cellulose fibers is preferably 0.10 mmol / g or more per gram (mass) of cellulose fiber, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the amount of phosphorus oxoacid groups introduced into the cellulose fibers is preferably 5.20 mmol / g or less per gram (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, the micronization of cellulose fibers in the micronization process can be facilitated, and the stability of the fine fibrous cellulose can be enhanced.

[0050] <Carboxyloid introduction process> The ionic group introduction step may include a carboxyl group introduction step. The carboxyl group introduction step is carried out by treating cellulose fibers with oxidation treatments such as ozone oxidation, Fenton oxidation, or TEMPO oxidation, or with compounds or derivatives thereof that have carboxylic acid-derived groups, or with acid anhydrides or derivatives thereof that have carboxylic acid-derived groups.

[0051] Compounds having a carboxylic acid-derived group are not particularly limited, but examples 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, derivatives of compounds having a carboxylic acid-derived group are not particularly limited, but examples include imidides of acid anhydrides of compounds having a carboxyl group, and derivatives of acid anhydrides of compounds having a carboxyl group. Imidides of acid anhydrides of compounds having a carboxyl group are not particularly limited, but examples include imidides of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0052] Acid anhydrides of compounds having a carboxylic acid-derived group are not particularly limited, but examples include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Furthermore, derivatives of acid anhydrides of compounds having a carboxylic acid-derived group are not particularly limited, but examples include acid anhydrides of compounds having a carboxyl group, such as dimethyl maleic anhydride, diethyl maleic anhydride, and diphenyl maleic anhydride, in which at least some of the hydrogen atoms are substituted with substituents such as alkyl groups and phenyl groups.

[0053] In the carboxyl group introduction step, when performing TEMPO oxidation treatment, it is preferable to carry out the treatment under conditions where the pH is between 6 and 8. Such treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be carried out, for example, by adding cellulose fibers, a nitroxyl radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to sodium phosphate buffer (pH=6.8). Furthermore, by including sodium chlorite, the aldehyde generated during the oxidation process can be efficiently oxidized to the carboxyl group. Alternatively, the TEMPO oxidation treatment may be carried out under conditions where the pH is between 10 and 11. Such treatment is also called alkaline TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxyl radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to cellulose fibers.

[0054] The amount of carboxyl groups introduced into cellulose fibers varies depending on the type of substituent. For example, when introducing carboxyl groups by TEMPO oxidation, it is preferable to have 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferable to have 0.60 mmol / g or more per gram (mass) of cellulose fiber. Furthermore, the amount of carboxyl 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 particularly preferable to have 1.00 mmol / g or less. In addition, when the substituent is a carboxymethyl group, the amount of carboxyl groups introduced may be 5.8 mmol / g or less per gram (mass) of cellulose fiber. By keeping the amount of carboxyl groups introduced within the above range, the micronization of cellulose fibers in the micronization process can be facilitated, and the stability of the fine fibrous cellulose can be increased.

[0055] <Sulfone group introduction process> The ionic group introduction step may include a sulfone group introduction step. In the sulfone group introduction step, a cellulose fiber having a sulfone group (sulfone group-introduced fiber) can be obtained by reacting the hydroxyl group present in the cellulose fiber with a sulfur oxoacid.

[0056] In the sulfone group introduction step, instead of compound A in the <phosphorus oxoacid group introduction step> described above, at least one compound (hereinafter also referred to as "compound C") selected from compounds that can introduce sulfone groups by reacting with the hydroxyl groups present in cellulose fibers is used. Compound C can be any compound that has a sulfur atom and can form an ester bond with cellulose, and examples include sulfuric acid or its salts, sulfite or its salts, and sulfuric acid amides, but is not particularly limited. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. As sulfite, 5% sulfurous acid water can be used. As sulfates or sulfites, examples include lithium salts, sodium salts, potassium salts, and ammonium salts of sulfates or sulfites, and these can be neutralized to various degrees. As sulfuric acid amides, sulfamic acid can be used. In the sulfone group introduction step, it is preferable to use compound B in the same manner as in the <phosphorus oxoacid group introduction step> described above.

[0057] In the sulfone group 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 treatment temperature is preferably selected to efficiently introduce sulfone groups while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. Furthermore, the heat treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0058] In the heat treatment process, it is preferable to heat until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose fibers, the amount of sulfur oxoacid and aqueous solution containing urea and / or urea derivatives added, but it is preferable to heat for at least 10 seconds and no more than 10,000 seconds. Various heat transfer devices can be used for the heat treatment, such as hot air dryers, agitation dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

[0059] The amount of sulfone 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 particularly preferably 0.50 mmol / g or more. Furthermore, the amount of sulfone groups introduced into the cellulose fibers is preferably 5.00 mmol / g or less, and more preferably 3.00 mmol / g or less. By keeping the amount of sulfone groups introduced within the above range, the micronization of cellulose fibers in the micronization process can be facilitated, and the stability of the fine fibrous cellulose can be enhanced.

[0060] <Oxidation process using chlorine-based oxidizing agent (second carboxyl group introduction process)> 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 cellulose fibers having hydroxyl groups in a wet or dry state, and the reaction is carried out to introduce carboxyl groups into the cellulose fibers.

[0061] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorite, chlorous acid, chlorite, chloric acid, chlorate, perchloric acid, perchlorate, and chlorine dioxide. From the standpoint of substituent introduction efficiency, and consequently defibration efficiency, cost, and ease of handling, sodium hypochlorite, sodium chlorite, and chlorine dioxide are preferred as chlorine-based oxidizing agents. When adding a chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be dissolved in a suitable solvent before being added.

[0062] In the oxidation process using a chlorine-based oxidizing agent, the concentration of the chlorine-based oxidizing agent in the solution is preferably 1% by mass or more and 1,000% by mass or less, more preferably 5% by mass or more and 500% by mass or less, and even more preferably 10% by mass or more and 100% by mass or less, when converted to an effective chlorine concentration. The amount of chlorine-based oxidizing agent added per 100 parts by mass of cellulose fiber is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 10 parts by mass or more and 10,000 parts by mass or less, and even more preferably 100 parts by mass or more and 5,000 parts by mass or less.

[0063] The reaction time with the chlorine-based oxidizing agent in the oxidation step may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 10 minutes and 500 minutes, and even more preferably between 20 minutes and 400 minutes. The pH during the reaction is preferably between 5 and 15, more preferably between 7 and 14, and even more preferably between 9 and 13. Furthermore, it is preferable to maintain a constant pH (for example, pH 11) at the start of the reaction and during the reaction by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed away with water by filtration or the like.

[0064] <Xantate group introduction process> The manufacturing process for fine fibrous cellulose may include a xantate group introduction step as a reaction step. In the xantate group introduction step, cellulose fibers having xantate groups (xantate group-introduced fibers) can be obtained by substituting the hydroxyl groups of cellulose fibers with xantate groups represented by the following formula (3). -OCSS - M + ...(3) Here, M + is at least one selected from hydrogen ions, monovalent metal ions, ammonium ions, aliphatic or aromatic ammonium ions.

[0065] In the xantate group introduction step, first, the cellulose fibers are treated with an alkaline solution to obtain alkaline cellulose. Examples of alkaline solutions include aqueous alkali metal hydroxide solutions and alkaline earth metal hydroxide solutions. Among these, the alkaline solution is preferably an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide, and particularly 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, and more preferably 5% by mass or more. Furthermore, 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 to above the above lower limit, the mercellation of cellulose can be sufficiently advanced, the amount of by-products generated during the subsequent xantate formation can be reduced, and as a result, the yield of xantate group-introduced fibers can be increased. This allows the defibration treatment described later to be carried out more effectively. Furthermore, by keeping the alkali metal hydroxide concentration below the above upper limit, it is possible to suppress the penetration of the alkali metal hydroxide aqueous solution into the crystalline region of cellulose while still promoting mercerization. This makes it easier to maintain the type I cellulose crystalline structure and further increase the yield of fine fibrous cellulose.

[0066] The alkaline treatment time is preferably 30 minutes or more, and more preferably 1 hour or more. Furthermore, the alkaline treatment time is preferably 6 hours or less, and more preferably 5 hours or less. By keeping the alkaline treatment time within the above range, the final yield can be increased, and productivity can be improved.

[0067] It is preferable to remove as much of the aqueous solution as possible from the alkali cellulose obtained by the above alkali treatment by solid-liquid separation. This reduces the water content during the subsequent xantate treatment and promotes the reaction. As for the solid-liquid separation method, general dehydration methods such as centrifugation or filtration can be used. It is preferable that the concentration of alkali metal hydroxide in the alkali cellulose after solid-liquid separation is 3% by mass or more and 8% by mass or less of the total mass of the alkali cellulose after solid-liquid separation.

[0068] In the xantate group introduction process, an alkali treatment is followed by a xantate treatment process. In the xantate treatment process, alkali cellulose is reacted with carbon disulfide (CS2) to form (-O - Na + )Based on (-OCSS - Na + ) A xantate group-introduced fiber is obtained using this group. In the above, the metal ions introduced into alkali cellulose are, representatively, Na + As described above, similar reactions proceed with other alkali metal ions.

[0069] In the xantate treatment, it is preferable to supply 10% by mass or more of carbon disulfide relative to the oven-dry mass of cellulose in the alkali cellulose. Furthermore, in the xantate treatment, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, and more preferably 1 hour or more. Although xantate treatment proceeds rapidly upon contact of carbon disulfide with alkali cellulose, it takes time for the carbon disulfide to penetrate into the interior of the alkali cellulose, so it is preferable to set the reaction time within the above range. On the other hand, the contact time between carbon disulfide and alkali cellulose can be 6 hours or less, which allows sufficient penetration even into the dehydrated alkali cellulose mass, and almost complete the reactive xantate treatment.

[0070] The reaction temperature in the xantate treatment is preferably 46°C or lower. Keeping the reaction temperature within this range makes it easier to suppress the decomposition of alkali cellulose. Furthermore, keeping the reaction temperature within this range makes it easier to react uniformly, which suppresses the formation of by-products and also helps to suppress the removal of the generated xantate groups.

[0071] In the xantate group introduction step, the amount of xantate groups introduced is preferably 0.60 mmol / g or more per 1 g (mass) of cellulose fiber, more preferably 0.70 mmol / g or more, even more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more. Furthermore, the amount of xantate groups introduced is preferably 5.00 mmol / g or less per 1 g (mass) of cellulose fiber, and more preferably 3.00 mmol / g or less. By keeping the amount of xantate groups introduced within the above range, fine fibrous cellulose with excellent defibrillation properties and transparency can be obtained.

[0072] <Phosphozone group or phosphine group introduction process (phosphoalkylation process)> The ionic group introduction step may include a phosphone group or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phosphone group or phosphine group (compound E) is used as an essential component. A ) Adding an alkaline compound, compound B selected from the aforementioned urea and its derivatives as an optional component, to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out the reaction introduces a phosphone group or phosphine group into the cellulose fiber.

[0073] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E A Examples include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphinic acid. Compound E is chosen from the standpoint of substituent introduction efficiency, and consequently defibrillation efficiency, cost, and ease of handling. A It is preferable that it be vinylphosphonic acid. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0074] Compound E A When adding the reagent, it may be added directly to the cellulose fibers as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the cellulose fibers are alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed reaction is as described above.

[0075] The reaction 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.

[0076] Compound E AThe amount added per 100 parts by mass of cellulose fiber 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.

[0077] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 10 minutes and 500 minutes, and even more preferably between 20 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0078] <Sulfone group introduction process (sulfoalkylation process) (second sulfone group introduction process)> The ionic group introduction step may include a sulfone group introduction step (sulfoalkylation step). In sulfoalkylation, a compound having a reactive group and a sulfone group (compound E) is used as an essential component. B ) and compound B, selected as an optional component from an alkaline compound and the aforementioned urea and its derivatives, are added to cellulose fibers having hydroxyl groups in a wet or dry state, and the reaction is carried out to introduce sulfone groups into the cellulose fibers.

[0079] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E B Examples include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is considered to have the efficiency of substituent introduction, and consequently the efficiency of defibrillation, cost, and ease of handling. B It is preferable that it be sodium vinyl sulfonate. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0080] Compound EB When adding the reagent, it may be added directly to the cellulose fibers as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the cellulose fibers are alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed reaction is as described above.

[0081] The reaction 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.

[0082] Compound E B The amount added per 100 parts by mass of cellulose fiber 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.

[0083] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 10 minutes and 500 minutes, and even more preferably between 15 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0084] <Carboxyalkylation process (third carboxyl group introduction process)> The reaction step may include a carboxyalkylation step. An essential component is a compound having a reactive group and a carboxyl group (compound E C ) Adding an alkaline compound, compound B selected from the aforementioned urea and its derivatives as an optional component, to cellulose fibers having hydroxyl groups in a wet or dry state and carrying out the reaction introduces carboxyl groups into the cellulose fibers.

[0085] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E CFrom the viewpoint of substituent introduction efficiency, and consequently defibration efficiency, cost, and ease of handling, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0086] Compound E C When adding the reagent, it may be added directly to the cellulose fibers as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the cellulose fibers are alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed reaction is as described above.

[0087] The reaction 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.

[0088] Compound E C The amount added per 100 parts by mass of cellulose fiber 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.

[0089] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 3 minutes and 500 minutes, and even more preferably between 5 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0090] <Cationic group introduction process (cationization process)> As an essential component, a compound having a reactive group and a cationic group (compound E D) A cationic group is introduced into the cellulose fiber by adding an alkaline compound, compound B selected from the aforementioned urea and its derivatives as an optional component, to cellulose fibers having hydroxyl groups in a wet or dry state and carrying out the reaction.

[0091] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Examples of cationic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, ammonium groups are preferred as the cationic group. Compound E D As such, glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, etc. are preferred in terms of substituent introduction efficiency, and consequently defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component. The amount added is also preferably as described above.

[0092] Compound E D When adding the reagent, it may be added directly to the cellulose fibers as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the cellulose fibers are alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed reaction is as described above.

[0093] The reaction 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.

[0094] Compound E D The amount added per 100 parts by mass of cellulose fiber 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.

[0095] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 5 minutes and 500 minutes, and even more preferably between 10 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0096] After the reaction steps described above, it is preferable to have a dehydration and washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and an acid treatment step may also be included in addition to the washing step. [Dehydration and washing process] The dehydration and washing process involves washing the resulting chemically modified cellulose dispersion with water or an organic solvent after dehydration. This process is essential for obtaining fine fibrous cellulose with fewer impurities. Washing is preferably performed with water. Furthermore, the dewatering and washing processes may be performed after each of the processes described later, and the number of washes performed in each washing process is not particularly limited. In this process, centrifugal, vacuum, and pressure dewatering equipment can be used. Specifically, examples include centrifugal separators (such as those manufactured by Tanabe Willtec and Kokusan), vacuum dewatering drums and horizontal belt filters manufactured by Tsukishima Kikai, and pressure dewatering filter presses, tube presses, screw presses, belt presses, horizontal belt filters, polydisc filters, and vibrating screens. Among these, pressure dewatering (filter presses, tube presses), centrifugal separators (such as those manufactured by Tanabe Willtec and Kokusan), and vacuum dewatering (drum-type vacuum dewaterers and horizontal belt filters manufactured by Tsukishima Kikai) are preferred because they can perform dewatering without applying strong shear force to the raw material. It is also possible to use a combination of these.

[0097] Furthermore, an alkaline treatment step and an acid treatment step may be included between the above dehydration and washing step and the preparation step described later, and the above dehydration and washing step may be included before or after the alkaline treatment step and the acid treatment step. <Alkali treatment process> An alkali treatment step may be included between the reaction step and the adjustment step. The alkali treatment method is not particularly limited, but one example is immersing chemically modified cellulose, preferably chemically modified cellulose with introduced ionic groups (ionic group-introduced cellulose), in an alkaline solution.

[0098] The alkali compound contained in the alkaline solution is not particularly limited and may be an inorganic alkali compound or an organic alkali compound. In this embodiment, it is preferable to use sodium hydroxide or potassium hydroxide as the alkali compound due to its high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. In particular, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as alcohol, and more preferably an aqueous solvent containing at least water. As the alkaline solution, for example, an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is preferred due to its high versatility.

[0099] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, 5°C to 80°C, and more preferably 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 preferably, for example, 5 minutes to 30 minutes, and more preferably 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is preferably, for example, 100% by mass to 100,000% by mass, and more preferably 1,000% by mass to 10,000% by mass, relative to the absolute dry mass of the chemically modified cellulose.

[0100] To reduce the amount of alkaline solution used in the alkaline treatment process, the chemically modified cellulose may be washed with water or an organic solvent after the reaction process but before the alkaline treatment process. After the alkaline treatment process but before the defibration process, it is preferable to wash the chemically modified cellulose that has undergone alkaline treatment with water or an organic solvent to improve handling.

[0101] <Acid treatment process> In the reaction process, an acid treatment step may be included 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 carried out in this order.

[0102] The method of acid treatment is not particularly limited, but one example is 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 not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of acids that can be included in the acidic solution include inorganic acids, sulfonic acids, carboxylic acids, etc. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric 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, the use of hydrochloric acid or sulfuric acid is particularly preferred.

[0103] The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably 5°C to 100°C, and more preferably 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably 5 minutes to 120 minutes, and more preferably 10 minutes to 60 minutes. The amount of acid solution used in the acid treatment is not particularly limited, but is preferably 100% to 100,000% by mass, and more preferably 1,000% to 10,000% by mass, relative to the absolute dry mass of the chemically modified cellulose.

[0104] [Adjustment process] In this embodiment, the concentration of the chemically modified cellulose dispersion is adjusted in order to efficiently carry out the subsequent defibration step. In the preparation step, it is preferable to dilute chemically modified cellulose, for example, with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but preferred examples 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), and N-methyl-2-pyrrolidinone (NMP). Of these, using water is preferable.

[0105] The solid content concentration of the chemically modified cellulose dispersion during the preparation process can be set as appropriate. The solid content concentration of the dispersion of chemically modified cellulose is preferably 0.1% by mass or more and 10% by mass or less. More preferably, the solid content concentration of the dispersion of chemically modified cellulose is 0.2% by mass or more, even more preferably 0.3% by mass or more, and preferably 10% by mass or less, and more preferably 6% by mass or less. If the solid content concentration is too low, the volume of liquid becomes too large relative to the amount of chemically modified cellulose being processed, resulting in poor efficiency. If the solid content concentration is too high, the fluidity becomes poor. Furthermore, the dispersion of chemically modified cellulose may contain solid components other than pulp with introduced ionic groups, such as urea with hydrogen bonding properties.

[0106] [Defibration process] In this embodiment, the defibration step is a step in which a mechanical shear force is applied to a dispersion of chemically modified cellulose to defibrate the chemically modified cellulose. In the defibration process, for example, a defibration processing device can be used. The defibration processing device is not particularly limited, but examples of devices that can be used include high-speed defibration machines, grinders (stone mill type grinders), high-pressure homogenizers or ultra-high-pressure homogenizers, high-pressure impact grinders, ball mills, bead mills, disc type refiners, conical refiners, twin-screw kneaders, vibrating mills, homomixers under high-speed rotation, ultrasonic dispersers, or beaters. Among the above defibration processing devices, it is more preferable to use high-speed defibration machines, high-pressure homogenizers, or ultra-high-pressure homogenizers, which have less influence from the grinding media and less risk of contamination.

[0107] The defibration process may be carried out in one step using the defibration processing apparatus described above, or it may be carried out in two steps: a coarse defibration process and a fine defibration process. When the defibration process is carried out in two stages, it is preferable to use a refiner in the rough defibration stage, and the refiner performs preliminary defibration on the chemically modified cellulose. The refiner is a device that beats the chemically modified cellulose, and by beating it under load, it applies shear force to the chemically modified cellulose, causing it to become fuzzy and making the fibers flexible, thereby performing preliminary defibration.

[0108] The refiner is not particularly limited as long as it can beat the chemically modified cellulose, and known types can be used. Conical type refiners, double disc refiners (DDR), and single disc refiners (SDR) are preferred as they can efficiently apply shear force to the chemically modified cellulose and promote preliminary defibration.

[0109] In the microfibrillation process, it is preferable to use a high-pressure homogenizer. A high-pressure homogenizer is used to finely pulverize chemically modified cellulose in a slurry and is used as a disperser that discharges slurry and other materials at high pressure from its pores. A high-pressure homogenizer is a homogenizer that has the ability to discharge slurry at a pressure of, for example, 10 MPa or more, preferably 100 MPa or more. By treating ionic group-introduced pulp with a high-pressure homogenizer, collisions between chemically modified cellulose fibers, pressure differences, microcavitation, etc., act to effectively cause fibrillation. This reduces (shortens) the number of processing steps in the fine pulverization process and further increases the efficiency of manufacturing fine fibrous cellulose.

[0110] <Fine fibrous cellulose> The fine fibrous cellulose obtained by the manufacturing method of this embodiment is fibrous cellulose with a fiber width of 1,000 nm or less. The fiber width of the fibrous cellulose can be measured, for example, by electron microscopy observation. The fiber width of the fine fibrous cellulose is 1,000 nm or less. Preferably, the fiber width of the fine fibrous cellulose is, for example, 2 nm to 1,000 nm, more preferably 2 nm to 100 nm, even more preferably 2 nm to 50 nm, and particularly preferably 2 nm to 10 nm. By making the fiber width of the fine fibrous cellulose 2 nm or more, the dissolution of cellulose molecules in water is suppressed, and the effects of improved strength, rigidity, and dimensional stability due to the fine fibrous cellulose can be more easily expressed.

[0111] The average fiber width of fine fibrous cellulose is, for example, 1,000 nm or less. Preferably, the average fiber width of fine fibrous cellulose is 2 nm to 1,000 nm, more preferably 2 nm to 100 nm, even more preferably 2 nm to 50 nm, and particularly preferably 2 nm to 10 nm. By setting the average fiber width of fine fibrous cellulose to 2 nm or more, the dissolution of cellulose molecules in water is suppressed, and the effects of improved strength, rigidity, and dimensional stability due to fine fibrous cellulose can be more easily expressed. Fine fibrous cellulose is, for example, monofilamentous cellulose.

[0112] The average fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows: First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilic carbon film-coated grid to prepare a sample for TEM observation. If wide fibers are present, an SEM image of the surface cast on glass may be observed. Next, observation is performed using an electron microscope image at a magnification 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 should be adjusted to meet the following conditions. (1) A straight line X is drawn at any point in the observed image, and 20 or more fibers intersect with this straight line X. (2) A line Y is drawn perpendicular to the line in the same image, and 20 or more fibers intersect with line Y.

[0113] For observation images that satisfy the above conditions, the width of the fibers intersecting with lines X and Y is visually read. In this way, at least three sets of observation images of surface areas that do not overlap are obtained. Next, for each image, the width of the fibers intersecting with lines X and Y is read. This allows for the reading of at least 20 × 2 × 3 = 120 fiber widths. The average of the read fiber widths is then taken as the average fiber width of the fibrous cellulose.

[0114] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably between 0.1 μm and 1,000 μm, more preferably between 0.1 μm and 800 μm, and even more preferably between 0.1 μm and 600 μm. By keeping the fiber length within the above range, the breakdown of the crystalline region of the fine fibrous cellulose can be suppressed. It is also possible to set the slurry viscosity of the fine fibrous cellulose within an appropriate range. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0115] It is preferable that the fine fibrous cellulose has a type I crystalline structure. Here, the presence of a type I crystalline structure in fine fibrous cellulose can be identified in the diffraction profile obtained from wide-angle X-ray diffraction images using graphite-monochromatized CuKα (λ=1.5418Å). Specifically, it can be identified by the presence of typical peaks at two locations: around 2θ=14° to 17° and around 2θ=22° to 23°. The proportion of type I crystalline structures in the fine fibrous cellulose is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This allows for even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity is determined by measuring the X-ray diffraction profile and analyzing the pattern using a conventional method (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0116] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably 20 to 10,000, and more preferably 50 to 1,000. Setting the axial ratio above the lower limit makes it easier to form sheets containing the fine fibrous cellulose. Also, it is easier to obtain sufficient viscosity when preparing a solvent dispersion. Setting the axial ratio below the upper limit is preferable in that it makes handling easier, such as dilution, when handling the fine fibrous cellulose as an aqueous dispersion.

[0117] In this embodiment, the aforementioned sine pump is used to transfer the dispersion of chemically modified cellulose. The sine pump may be used when transferring the dispersion of chemically modified cellulose in the dehydration and washing process, or it may be used for transfer in the alkali treatment process or acid treatment process described above. Furthermore, in the adjustment step of adjusting the concentration of the chemically modified cellulose dispersion after washing, it may be used to transfer the chemically modified cellulose dispersion to a tank for storage used in the defibration step, or to transfer it from the tank to the defibration machine, or to transfer the chemically modified cellulose dispersion that has been defibrated by the defibration machine, and is not particularly limited. Among these, it is particularly preferable to use it for transfer in the dehydration and washing process, and for transfer in the defibration process. In the transfer in the defibration process, it is particularly preferable to use it when transferring a dispersion of chemically modified cellulose or a dispersion of fine fibrous cellulose to the defibration machine. Note that processing in the defibration machine may be performed multiple times. In the first processing, the dispersion of chemically modified cellulose is transferred to the defibration machine, but in the second and subsequent processing, the dispersion contains defibrated fine fibrous cellulose and undefibrated or partially defibrated chemically modified cellulose. [Examples]

[0118] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples.

[0119] The raw material, cellulose fiber, is softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m²) manufactured by Oji Paper Co., Ltd. 2 A sheet-like material (which, when disintegrated, had a Canadian standard filtration efficiency (CSF) of 700 mL measured according to JIS P 8121-2:2012) was used.

[0120] The cellulose fibers were subjected to phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (oven-dry mass) of the cellulose fibers to adjust the mixture to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain chemically impregnated pulp. Next, the obtained chemically impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose fibers, thereby obtaining phosphorylated pulp, which is chemically modified cellulose.

[0121] Next, the obtained chemically modified cellulose (phosphorylated pulp) was subjected to a washing treatment. The washing treatment was carried out by adding 20 L of deionized water to 400 g (oven-dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the dispersion to ensure uniform pulp distribution, and then repeatedly sending the dispersion to a vacuum dewatering device at a flow rate of 10 L / min using a Watson-Marlow SPS type sine pump for filtration and dewatering.

[0122] Next, the washed phosphorylated pulp was subjected to a neutralization treatment as follows: First, 15 L of a 1.0% by mass sodium hydroxide aqueous solution was poured into the washed phosphorylated pulp, then it was dehydrated, and then 30 L of deionized water was added and dehydrated again to wash away the excess sodium hydroxide and obtain phosphorylated pulp that had undergone neutralization treatment.

[0123] The obtained phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that 1230 cm⁻¹ -1 Absorption based on the P=O of phosphate groups was observed in the vicinity, confirming that phosphate groups were added to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of Phosphorus Oxoacid Group Amount] below was 1.6 mmol / g.

[0124] <Example 1> Deionized water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass (preparation step). The slurry was placed in a 10L hopper, and the flow rate was adjusted using a Watson-Marlow SPS type sine pump to achieve a discharge pressure of 0.4 MPa or higher, and the slurry was sent to a wet atomizer (Sugino Machine Co., Ltd., Starburst). The pressure of the wet atomizer was set to 200 MPa and the mixture was processed twice to obtain a fine fibrous cellulose dispersion 1 containing fine fibrous cellulose. The processing speed of the wet atomizer was 30 L / h. The viscosity measured by the measurement method described later in [Measurement of Viscosity of 0.4% by mass Fine Fibrous Cellulose Dispersion] was 33,000 mPa·s.

[0125] <Comparative Example 1> Deionized water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass (preparation step). The slurry was placed in a 10L hopper, and the flow rate was adjusted using a twin-screw pump (SQ type) manufactured by Fushiko Metal Industry Co., Ltd. to ensure a discharge pressure of 0.4 MPa or higher, and the slurry was sent to a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.). The pressure of the wet atomizer was set to 200 MPa and the mixture was processed twice to obtain a fine fibrous cellulose dispersion 2 containing fine fibrous cellulose. The processing speed of the wet atomizer was 30 L / h. The viscosity measured by the measurement method described later in [Measurement of Viscosity of 0.4% by mass Fine Fibrous Cellulose Dispersion] was 27,000 mPa·s.

[0126] <Measurement> [Measurement of phosphorus oxoacid group content] The amount of phosphorus oxoacid groups in microfibrous cellulose was measured by diluting a microfibrous cellulose dispersion containing the target microfibrous cellulose with ion-exchanged water to a content of 0.2% by mass, preparing a fibrous cellulose-containing slurry, treating it with an ion-exchange resin, and then performing titration with an alkali. The ion exchange resin treatment was performed by adding 1 / 10 the volume of strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring it onto a mesh with a mesh size of 90 μm to separate the resin from the slurry. Furthermore, the alkali titration was performed by adding 10 μL of 0.1 N sodium hydroxide aqueous solution to a fibrous cellulose-containing slurry after treatment with ion exchange resin, while measuring the change in the slurry's pH value. Nitrogen gas was blown into the slurry starting 15 minutes before the titration began. In this neutralization titration, two points were observed where the increment (the derivative of pH with respect to the amount of alkali added) was maximum on the curve plotting the 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 (Figure 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of the first dissociated acid in the slurry used for titration. Also, 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 for titration. Furthermore, the amount of alkali (mmol) required from the start of the titration to the first endpoint was divided by the solid content (g) in the slurry being titrated to obtain the amount of phosphorus oxoacid groups (mmol / g).

[0127] [Measurement of viscosity of 0.4% by mass fine fibrous cellulose dispersion] The viscosity of the fine fibrous cellulose dispersions obtained in Example 1 and Comparative Example 1 was measured as follows. First, the fine fibrous cellulose dispersion was diluted with deionized water to a solid content concentration of 0.4% by mass, and then stirred in a disperser at 4000 rpm for 5 minutes. The resulting dispersion was defoamed using a rotation-and-revolution type super mixer (Sinky Co., Ltd., ARE-250). Next, the viscosity of the resulting dispersion was measured using a B-type viscometer (BLOOKFIELD, analog viscometer T-LVT). The measurement conditions were a rotation speed of 3 rpm, and the viscosity value 3 minutes after the start of measurement was taken as the viscosity of the dispersion.

[0128] From the results of the examples and comparative examples, in Example 1, where a sine pump was used for transfer, the viscosity was 33,000 mPa·s, while in Comparative Example 1, where a twin-screw pump was used for transfer, the viscosity was 27,000 mPa·s. The decrease in viscosity in Comparative Example 1 is thought to have occurred due to unexpected micronization, and therefore, the quality can be said to have changed in Comparative Example 1. In other words, it can be seen that the use of a sine pump suppressed unexpected changes in quality. In Example 1, where a sine pump was used for transfer, quality changes were suppressed compared to Comparative Example 1, where a twin-screw pump was used for transfer, resulting in the production of higher quality fine fibrous cellulose.

Claims

1. A reaction process to obtain chemically modified cellulose by chemically modifying cellulose fibers, A dehydration and washing step is performed to dehydrate and wash the dispersion of the chemically modified cellulose, A step to adjust the concentration of the chemically modified cellulose dispersion, A defibration step is performed by applying mechanical shear force to the dispersion of chemically modified cellulose to defibrate it. In a method for producing fine fibrous cellulose containing, A sine pump is used to transport the fine fibrous cellulose dispersion obtained by the defibration process, or the dispersion of chemically modified cellulose subjected to the defibration process. A method for producing fine fibrous cellulose.

2. The method for producing fine fibrous cellulose according to claim 1, wherein the reaction step is a step of introducing ionic groups into cellulose fibers.

3. The method for producing fine fibrous cellulose according to claim 2, wherein the ionic group is an anionic group.

4. The method for producing fine fibrous cellulose according to claim 3, wherein the anionic group is at least one selected from the group consisting of a phosphorus oxoacid group, a sulfur oxoacid group, and a carboxyl group.

5. The method for producing fine fibrous cellulose according to claim 3, wherein the anionic group is a phosphorus oxoacid group.

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