Dispersion

Abstract

The present invention aims to provide a dispersion liquid comprising fine fibrous cellulose dispersed in an organic solvent, which has high thixotropy. [Solution] The present invention relates to a dispersion containing fibrous cellulose with a fiber width of 1000 nm or less and an organic solvent, wherein the fibrous cellulose has anionic groups, the content of anionic groups is 0.50 mmol / g or more, the fibrous cellulose has an organo-onium ion as a counterion to the anionic groups, and the B-type viscosity measured by measurement method (A) is 50 Pa·s or more.

Description

[Technical Field]

[0001] This invention relates to a dispersion. Specifically, this invention relates to a dispersion containing fine fibrous cellulose and an organic solvent. [Background technology]

[0002] Traditionally, cellulose fibers have been widely used in clothing, absorbent materials, paper products, and other applications. In addition to fibrous cellulose with a fiber diameter of 10 μm to 50 μm, fine fibrous cellulose with a fiber diameter of 1 μm or less is also known. Fine fibrous cellulose is attracting attention as a new material, and its applications are diverse. For example, development is underway on sheets, resin composites, and thickeners containing fine fibrous cellulose.

[0003] Generally, fine fibrous cellulose is stably dispersed in aqueous solvents and is therefore often provided in the form of an aqueous dispersion for various applications. On the other hand, when mixing fine fibrous cellulose with resin components to produce composites, there is a demand to use fine fibrous cellulose mixed with an organic solvent. To meet this demand, a technology for producing a fine fibrous cellulose-containing dispersion by dispersing fine fibrous cellulose in a dispersion medium containing an organic solvent is being investigated (Patent Documents 1-4).

[0004] For example, Patent Documents 1 to 3 disclose a microfibrous cellulose composite obtained by adsorbing a surfactant onto microfibrous cellulose having carboxyl groups. These documents disclose a method of obtaining microfibrous cellulose by first micronizing cellulose fibers in an aqueous solvent, then agglomerating the microfibrous cellulose and dispersing it in an organic solvent, or by micronizing cellulose fibers in an organic solvent. Patent Document 4 also discloses a spray composition containing hydrophobic modified cellulose fibers to which one or more modifying groups selected from the anionic and hydroxyl groups of cellulose fibers are bonded, and an organic medium. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2011-140738 [Patent Document 2] Japanese Patent Publication No. 2016-188375 [Patent Document 3] Japanese Patent Publication No. 2019-49091 [Patent Document 4] Japanese Patent Publication No. 2020-76054 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Dispersions of fine fibrous cellulose in an organic solvent have a wide range of applications. For example, in applications such as paints, it is sometimes required that the dispersion has high thixotropy.

[0007] Therefore, in order to solve the problems of the prior art, the present inventors conducted research with the aim of providing a dispersion liquid comprising fine fibrous cellulose dispersed in an organic solvent, which has high thixotropy. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the present inventors have found that by introducing an organic onium ion as a counterion to the anionic group of the fine fibrous cellulose in a dispersion containing a predetermined amount or more of anionic groups and an organic solvent, and by further setting the B-type viscosity measured under predetermined conditions to 50 Pa·s or higher, a dispersion with high thixotropy can be obtained. Specifically, the present invention has the following configuration.

[0009] [1] A dispersion containing fibrous cellulose with a fiber width of 1000 nm or less and an organic solvent, The fibrous cellulose has an anionic group, and the content of the anionic group is 0.50 mmol / g or more. The fibrous cellulose has an organic onium ion as a counter ion of the anionic group. A dispersion having a Brookfield viscosity measured by the following measurement method (A) of 50 Pa·s or more. Measurement method (A): With the fibrous cellulose concentration of the dispersion being 3% by mass (w / w), the rotation speed being 0.6 rpm, and the temperature being 23°C, the Brookfield viscosity is measured in accordance with JIS Z 8803 (2011). [2] The dispersion according to [1], having a light transmittance measured by the following measurement method (B) of 80% or more. Measurement method (B): With the fibrous cellulose concentration of the dispersion being 3% by mass (w / w), it is enclosed in a quartz cell with an optical path length of 10 mm, and the light transmittance at a wavelength of 660 nm is measured using an ultraviolet-visible spectrophotometer. [3] The dispersion according to [1] or [2], wherein the fiber width of the fibrous cellulose is 10 nm or less. [4] The dispersion according to any one of [1] to [3], wherein the anionic group is at least one selected from the group consisting of a phosphoxo acid group, a substituent derived from a phosphoxo acid group, a sulfur oxo acid group, and a substituent derived from a sulfur oxo acid group.

Advantages of the Invention

[0010] According to the present invention, a dispersion obtained by dispersing micro-fibrous cellulose in an organic solvent, which has high thixotropic properties, can be obtained.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a graph showing the relationship between the amount of NaOH dropped and the pH for a slurry containing fibrous cellulose having a phosphoxo acid group. [Figure 2] FIG. 2 is a graph showing the relationship between the amount of NaOH dropped and the pH for a slurry containing fibrous cellulose having a carboxy group. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below. The following descriptions of constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments.

[0013] (dispersion) The present invention relates to a dispersion containing fibrous cellulose with a fiber width of 1000 nm or less and an organic solvent. Here, the fibrous cellulose has anionic groups, and the content of anionic groups is 0.50 mmol / g or more. Furthermore, the fibrous cellulose has an organo-onium ion as a counterion to the anionic groups. The B-type viscosity of the dispersion measured by the following measurement method (A) is 50 Pa·s or more. Measurement method (A): The B-type viscosity of the dispersion is measured in accordance with JIS Z 8803 (2011) when the fibrous cellulose concentration of the dispersion is 3% by mass (w / w), the rotation speed is 0.6 rpm, and the temperature is 23°C. It is preferable that the above B-type viscosity of the dispersion is the viscosity of a dispersion consisting of an organic solvent and fibrous cellulose.

[0014] The B-type viscosity of the dispersion measured by the above measurement method (A) of the dispersion in this embodiment may be 50 Pa·s or more, preferably 55 Pa·s or more, more preferably 60 Pa·s or more, even more preferably 70 Pa·s or more, even more preferably 80 Pa·s or more, even more preferably 90 Pa·s or more, and particularly preferably 100 Pa·s or more. The upper limit of the B-type viscosity of the dispersion measured by the above measurement method (A) of the dispersion is not particularly limited, but for example, it is preferably 500 Pa·s or less.

[0015] The dispersion of the present invention, having the above-described structure, possesses high thixotropy. That is, the dispersion of the present invention has the property of decreasing viscosity when shear is applied. The thixotropy of the dispersion can be evaluated, for example, by the TI value calculated using the following formula. TI value = (viscosity value at 0.6 rpm / viscosity value at 60 rpm) Here, the viscosity value at 0.6 rpm is the B-type viscosity obtained when an organic solvent dispersion with a fibrous cellulose concentration of 3% by mass is allowed to stand at 23°C for 24 hours and then rotated at 0.6 rpm for 3 minutes. Similarly, the viscosity value at 60 rpm is the B-type viscosity obtained when an organic solvent dispersion with a fibrous cellulose concentration of 3% by mass is allowed to stand at 23°C for 24 hours and then rotated at 60 rpm for 3 minutes. The B-type viscosity is measured using a B-type viscometer, and for example, a BLOOKFIELD T-LVT analog viscometer can be used.

[0016] The TI value of the dispersion calculated by the above method is preferably 20.0 or higher, more preferably 30.0 or higher, even more preferably 40.0 or higher, and even more preferably 50.0 or higher. While there is no particular upper limit to the TI value of the dispersion, it is preferably, for example, 500 or less.

[0017] In this embodiment, the light transmittance of the dispersion measured by the following measurement method (B) is preferably 80% or more, more preferably 84% or more, even more preferably 88% or more, and particularly preferably 90% or more. Measurement method (B): The fibrous cellulose concentration of the dispersion is set to 3% by mass (w / w), and it is sealed in a quartz cell with a path length of 10 mm. The light transmittance at a wavelength of 660 nm is measured using an ultraviolet-visible spectrometer. For example, the V-770 manufactured by JASCO Corporation can be used as the ultraviolet-visible spectrometer. Zero point measurement is performed using deionized water placed in the same glass cell.

[0018] (organic solvent) The dispersion of the present invention contains an organic solvent. The dispersion of the present invention is a fine fibrous cellulose-containing dispersion in which the fine fibrous cellulose described later is dispersed in a dispersion medium containing an organic solvent. In addition, the dispersion of the present invention may further contain water in addition to the organic solvent as the dispersion medium, but the water content with respect to the total mass of the dispersion is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. In the present embodiment, it is preferable that the dispersion medium substantially does not contain water, and it is particularly preferable that the water content with respect to the total mass of the dispersion is 0% by mass.

[0019] The relative dielectric constant of the organic solvent of the dispersion at 25°C is preferably 60 or less, and more preferably 50 or less. Since the fibrous cellulose contained in the dispersion can exhibit excellent dispersibility even in an organic solvent with a low relative dielectric constant, the relative dielectric constant of the organic solvent at 25°C may be 45 or less, 40 or less, or 35 or less.

[0020] The δd of the Hansen solubility parameter (HSP) of the organic solvent is 5 MPa 1 / 2 or more and 20 MPa 1 / 2 or less, preferably 10 MPa 1 / 2 or more and 19 MPa 1 / 2 or less. Also, δh is preferably 1 MPa 1 / 2 or more and 40 MPa 1 / 2 or less, more preferably 2 MPa 1 / 2 or more and 30 MPa 1 / 2 or less. It is also preferable to simultaneously satisfy that δp is in the range of 0 MPa 1 / 2 or more and 4 MPa 1 / 2 or less, and δh is in the range of 0 MPa 1 / 2 or more and 6 MPa 1 / 2 or less.

[0021] Examples of organic solvents include methanol (dielectric constant 32.6), ethanol (dielectric constant 24.3), n-propyl alcohol (dielectric constant 20.1), isopropyl alcohol (IPA) (dielectric constant 18.62), 1-butanol (dielectric constant 18), m-cresol (dielectric constant 11.8), glycerin (dielectric constant 42.5), acetic acid (dielectric constant 6.15), pyridine (dielectric constant 12.3), tetrahydrofuran (THF) (dielectric constant 7.5), acetone (dielectric constant 20.7), methyl ethyl ketone (MEK) (dielectric constant 15.45), ethyl acetate ( Examples of suitable organic solvents include toluene (dielectric constant 6.4), aniline (dielectric constant 6.89), N-methyl-2-pyrrolidone (NMP) (dielectric constant 32.2), dimethyl sulfoxide (DMSO) (dielectric constant 45), N,N-dimethylformamide (DMF) (dielectric constant 38), hexane (dielectric constant 1.8), cyclohexane (dielectric constant 2.0), benzene (dielectric constant 2.3), toluene (dielectric constant 2.4), p-xylene (dielectric constant 2.3), styrene (dielectric constant 2.3-3.4), diethyl ether (dielectric constant 4.3), chloroform (dielectric constant 4.8), etc. Among these, it is preferable that the organic solvent be at least one selected from the group consisting of toluene, xylene, and styrene.

[0022] The organic solvent content is preferably 10% by mass or more, and more preferably 50% by mass or more, relative to the total mass of solids contained in the dispersion. Furthermore, the organic solvent content is preferably 99.9% by mass or less, more preferably 99.0% by mass or less, and even more preferably 95.0% by mass or less, relative to the total mass of solids contained in the dispersion.

[0023] (Fine fibrous cellulose) The dispersion of the present invention contains fibrous cellulose with a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 20 nm or less, even more preferably 10 nm or less, and particularly preferably 8 nm or less. In this specification, fibrous cellulose with a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose.

[0024] The average fiber width of fibrous cellulose is, for example, 1000 nm or less. Preferably, the average fiber width of fibrous cellulose is, for example, 2 nm to 1000 nm, more preferably 2 nm to 100 nm, even more preferably 2 nm to 50 nm, and particularly preferably 2 nm to 10 nm. Fibrous cellulose is, for example, monocrystalline cellulose.

[0025] The fiber width of 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 1000x, 5000x, 10000x, or 50000x, depending on the width of the fiber to be observed. However, the sample, observation conditions, and magnification should be adjusted to meet the following conditions.

[0026] (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.

[0027] 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.

[0028] The fiber length of fibrous cellulose is not particularly limited, but is preferably between 0.1 μm and 1000 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 fracture of the crystalline region of the fibrous cellulose can be suppressed. It is also possible to set the viscosity of the fibrous cellulose slurry within an appropriate range. The fiber length of fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0029] It is preferable that the fibrous cellulose has a type I crystalline structure. The presence of a type I crystalline structure in fibrous cellulose can be identified by the diffraction profile obtained from a wide-angle X-ray diffraction photograph 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 structure 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 can be determined by measuring the X-ray diffraction profile and analyzing its pattern using conventional methods (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0030] The axial ratio (fiber length / fiber width) of 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 fine fibrous cellulose. Setting the axial ratio below the upper limit is preferable in that it makes handling easier, such as dilution, when handling fibrous cellulose as a dispersion.

[0031] Fibrous cellulose, for example, has both crystalline and amorphous regions. Fine fibrous cellulose having both crystalline and amorphous regions and having an axial ratio within the above range can be realized by the fine fibrous cellulose manufacturing method described later.

[0032] Fibrous cellulose has anionic groups. Examples of anionic 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), and sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups). In particular, it is preferable that the anionic group is at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, sulfur oxoacid groups, and substituents derived from sulfur oxoacid groups. When the anionic group is at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, sulfur oxoacid groups, and substituents derived from sulfur oxoacid groups, it is easier to obtain a dispersion that is more transparent and has higher viscosity.

[0033] 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.

[0034] [ka]

[0035] 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 - 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.

[0036] 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.

[0037] 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.

[0038] 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 fine cellulose fibers. In addition, when there are multiple Rs in formula (1) or when multiple substituents represented by the above formula (1) are introduced into fibrous cellulose, the multiple Rs may be the same or different.

[0039] 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 onium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic onium 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. 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 more 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 readily available for industrial use, but the material is not particularly limited.

[0040] More specifically, substituents derived from a phosphorus oxoacid group include a phosphate group (-PO3H2), a salt of a phosphate group, a phosphonotic group (phosphonic acid group) (-PO2H2), and a salt of a phosphonotic group (phosphonic acid group). Furthermore, substituents derived from a phosphorus oxoacid group may also be groups formed by condensation of a phosphate group (e.g., a pyrophosphate group), groups formed by condensation of a phosphonic acid (e.g., a polyphosphonic acid group), phosphate ester groups (e.g., monomethyl phosphate group, polyoxyethylene alkyl phosphate group), alkylphosphonic acid groups (e.g., a methylphosphonic acid group), and the like.

[0041] Furthermore, the sulfur oxoacid group (sulfur oxoacid group or substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). Multiple substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the substituents represented by the following formula (2) that are introduced may be the same or different.

[0042] [ka]

[0043] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is any number (where 1 = b × m). Note that if n is 2 or greater, the multiple p values ​​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 onium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic onium 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 more 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 readily available for industrial use, but the material is not particularly limited.

[0044] The anionic group content (amount introduced) may be, for example, 0.50 mmol / g or more per 1 g (mass) of fibrous cellulose, more preferably 0.60 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the anionic group content (amount introduced) may be, for example, 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, and particularly preferably 2.00 mmol / g or less. Here, the denominator in the mmol / g unit is the amount of the counterion of the anionic group being a hydrogen ion (H +This indicates the mass of fibrous cellulose when ). By keeping the amount of anionic groups introduced within the above range, the amount of organic onium ions that fibrous cellulose may contain can be set to an appropriate range, thereby more effectively improving the dispersibility of fibrous cellulose in organic solvents.

[0045] The amount of anionic groups introduced into fibrous cellulose can be measured, for example, by neutralization titration. In neutralization titration, the amount introduced is determined by measuring the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the resulting slurry containing fibrous cellulose.

[0046] Figure 1 is a graph showing the relationship between the amount of NaOH added to a slurry containing fibrous cellulose with phosphorus oxoacid groups and the pH. The amount of phosphorus oxoacid groups introduced into the fibrous cellulose can be measured, for example, as follows. First, the slurry containing fibrous cellulose is treated with a strong acid ion exchange resin. If necessary, a defibration treatment similar to the defibration treatment step described later may be performed on the sample to be measured before treatment with the strong acid 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.

[0047] 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)

[0048] Figure 2 is a graph showing the relationship between the amount of NaOH added to a dispersion containing fibrous cellulose having a carboxyl group as an anionic group and the pH. The amount of carboxyl group introduced into the fibrous cellulose can be measured, for example, as follows. First, a dispersion containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, a defibration treatment similar to the defibration treatment process described later may be performed on the sample before treatment with the 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).

[0049] 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)

[0050] In measuring the amount of anionic 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-true amount of anionic groups. Appropriate titration volumes and intervals include, for example, titrating with 10-50 μL of 0.1N sodium hydroxide aqueous solution every 5-30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, 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 performing the measurement.

[0051] Furthermore, the amount of sulfur oxoacid groups introduced into fibrous cellulose can be calculated by freeze-drying a slurry containing fibrous cellulose and then measuring the sulfur content of the pulverized sample. Specifically, the slurry containing fibrous cellulose is freeze-dried, and the pulverized sample is subjected to pressurized thermal decomposition using nitric acid in a sealed container. After appropriate dilution, the sulfur content is measured by ICP-OES. The value obtained by dividing by the oven-dry mass of the fibrous cellulose used is defined as the amount of sulfur oxoacid groups in the fine fibrous cellulose (unit: mmol / g).

[0052] (Method for producing microfiber cellulose) <Fiber raw materials> Fine fibrous cellulose is produced from cellulose-containing fiber raw materials. While there are no particular limitations on the cellulose-containing fiber raw materials, pulp is preferred due to its availability and low cost. Examples of pulp 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, and bagasse. The deinked pulp is not particularly limited, but examples include deinked pulp made from recycled paper. The pulp in this embodiment may be one of the above types used alone, or two or more types may be used in mixture. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Among wood pulps, chemical pulp is more preferred from the viewpoint of having a high cellulose ratio and a high yield of fine fibrous cellulose during defibration treatment, and from the viewpoint 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 increase viscosity.

[0053] As fiber raw materials containing cellulose, for example, cellulose contained in sea squirts or bacterial cellulose produced by acetic acid bacteria can be used. Alternatively, instead of fiber raw materials containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can be used.

[0054] <Phosphorus oxoacid group introduction process> The manufacturing process for fine fibrous cellulose includes an anionic group introduction step. An anionic group introduction step is, for example, 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-containing fiber raw material is reacted with the cellulose-containing fiber raw material. This step yields phosphorus oxoacid group-introduced fibers.

[0055] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with 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 of the cellulose-containing fiber raw material with compound A may be carried out in the absence of compound B.

[0056] One example of a method for reacting compound A with compound B to a fiber raw material is to mix compound A and compound B with the fiber raw material in a dry, wet, or slurry state. Of these, it is preferable to use a dry or wet fiber raw material, and particularly preferable to use a dry fiber raw material, due to the high uniformity of the reaction. The form of the fiber raw material is not particularly limited, but for example, it is preferably in the form of cotton or a thin sheet. 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 fiber raw material simultaneously, separately, or as a mixture. There are no particular limitations on the method of adding compounds A and B, but if compounds A and B are in solution form, the fiber raw material may be immersed in the solution and then removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by pressing or filtration.

[0057] 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, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid or sodium phosphorous acid are more preferred, as they offer high efficiency in introducing phosphorus oxoacid groups, easier improvement in the defibration process described later, low cost, and ease of industrial application.

[0058] The amount of compound A added to the fiber raw material 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 fiber raw material (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 fiber raw material 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 fiber raw material below the above upper limit, it is possible to balance the effect of improving yield with cost.

[0059] Compound B used in this embodiment is at least one selected from urea and its derivatives, as described above. 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.

[0060] The amount of compound B added to the fiber raw material (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.

[0061] 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.

[0062] In the phosphorus oxoacid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material and then subject the fiber raw material 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 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.

[0063] In the heat treatment according to this embodiment, for example, a method can be employed in which compound A is added to a thin sheet-like fiber raw material by impregnation or other methods, and then heated, or a method can be employed in which the fiber raw material and compound A are kneaded or stirred while heating. This makes it possible to suppress uneven concentration of compound A in the fiber raw material and to introduce phosphorus oxoacid groups more uniformly to the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, as water molecules move to the surface of the fiber raw material during drying, dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the surface of the fiber raw material (i.e., uneven concentration of compound A is produced), and this can be suppressed.

[0064] 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 fiber raw material, 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 the fibers. As a result, it becomes possible to obtain fine fibrous cellulose with a high axial ratio.

[0065] 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 fiber raw material. In this embodiment, the amount of phosphorus oxoacid group introduced can be kept within a preferred range by setting the heating temperature and heating time within an appropriate range.

[0066] 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.

[0067] The amount of phosphorus oxoacid groups introduced into the fiber raw material may be, for example, 0.50 mmol / g or more per 1 g (mass) of fiber raw material, more preferably 0.60 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the phosphorus oxoacid group content (introduced amount) may be, for example, 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, and particularly preferably 2.00 mmol / g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, the content of organic onium ions that fibrous cellulose may contain can be set to an appropriate range, thereby more effectively improving the dispersibility of fibrous cellulose in organic solvents.

[0068] <Carboxyloid introduction process> The manufacturing process for fine fibrous cellulose may include, for example, a carboxyl group introduction step as an anionic group introduction step. The carboxyl group introduction step is carried out by treating the cellulose-containing fiber raw material with an oxidation treatment such as ozono-oxidation, Fenton-type oxidation, or TEMPO oxidation treatment, or with a compound having a carboxylic acid-derived group or a derivative thereof, or with an acid anhydride or a derivative thereof of a compound having a carboxylic acid-derived group.

[0069] 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.

[0070] 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.

[0071] 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 pulp as the fiber raw material, a nitroxyl radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer (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 pulp as the fiber raw material.

[0072] The amount of carboxyl groups introduced into the fiber raw material varies depending on the type of substituent. For example, when introducing carboxyl groups by TEMPO oxidation, it is sufficient to have 0.50 mmol / g or more per gram (mass) of fiber raw material, more preferably 0.60 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the amount of carboxyl groups introduced into fibrous cellulose 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, and even more preferably 2.00 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 fine fibrous cellulose. By keeping the amount of carboxyl groups introduced within the above range, the content of organic onium ions that can be contained in fine fibrous cellulose can be set to an appropriate range, thereby more effectively improving the dispersibility of fibrous cellulose in organic solvents.

[0073] <Sulfur oxoacid group introduction process> The manufacturing process for fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an anionic group introduction step. In the sulfur oxoacid group introduction step, a cellulose fiber having sulfur oxoacid groups can be obtained by the reaction of sulfur oxoacid with hydroxyl groups present in the cellulose-containing fiber raw material.

[0074] In the sulfur oxoacid 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 sulfur oxoacid groups by reacting with hydroxyl groups present in the cellulose-containing fiber raw material 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, sulfurous acid 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 sulfurous acid, 5% sulfurous acid water can be used. As sulfates or sulfurous acid salts, examples include lithium salts, sodium salts, potassium salts, and ammonium salts of sulfates or sulfurous acid salts, and these can be neutralized to various degrees. As sulfuric acid amides, sulfamic acid can be used. In the sulfur oxoacid group introduction step, it is preferable to use compound B in the <phosphorus oxoacid group introduction step> described above in the same manner.

[0075] In the sulfur oxoacid group introduction step, it is preferable to mix the cellulose raw material with an aqueous solution containing sulfur oxoacid and urea and / or a urea derivative, and then heat-treat the cellulose raw material. The heat treatment temperature is preferably selected to efficiently introduce sulfur oxoacid 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.

[0076] 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 raw material, the amount of sulfur oxoacid and aqueous solution containing urea and / or urea derivatives added, but it is preferable to heat for 10 seconds or more and 10,000 seconds or less. 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.

[0077] The amount of sulfur oxoacid groups introduced into the cellulose raw material should be 0.50 mmol / g or more per 1 g (mass) of fibrous cellulose, more preferably 0.60 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the amount of sulfur oxoacid groups introduced should preferably be 5.00 mmol / g or less per 1 g (mass) of fibrous cellulose, and more preferably 3.00 mmol / g or less. By keeping the amount of sulfur oxoacid groups introduced within the above range, the content of organic onium ions that can be contained in the fine fibrous cellulose can be set to an appropriate range, thereby more effectively improving the dispersibility of fibrous cellulose in organic solvents.

[0078] <Washing Process> In the method for producing fine fibrous cellulose according to this embodiment, a washing step can be performed on the anionic group-introduced fibers as needed. The washing step is performed, for example, by washing the anionic group-introduced fibers with water or an organic solvent. Furthermore, the washing step may be performed after each of the steps described later, and the number of washings performed in each washing step is not particularly limited.

[0079] <Alkali treatment process> When producing fine fibrous cellulose, an alkaline treatment may be performed on the fiber raw material between the anionic group introduction step and the defibration treatment step described later. The method of alkaline treatment is not particularly limited, but one example is immersing the anionic group-introduced fibers in an alkaline solution.

[0080] 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. Among these, 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.

[0081] The temperature of the alkaline solution in the alkaline treatment process 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 anionic group-introduced fiber in the alkaline solution in the alkaline treatment process 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 anionic group-introduced fiber.

[0082] To reduce the amount of alkaline solution used in the alkaline treatment process, the anionic group-introduced fibers may be washed with water or an organic solvent after the anionic group introduction process and before the alkaline treatment process. After the alkaline treatment process and before the defibration process, it is preferable to wash the alkaline-treated anionic group-introduced fibers with water or an organic solvent to improve handling.

[0083] <Acid treatment process> When producing fine fibrous cellulose, an acid treatment may be performed on the fiber raw material between the anionic group introduction step and the defibration treatment step described later. For example, the anionic group introduction step, acid treatment, alkali treatment, and defibration treatment may be performed in this order.

[0084] The method of acid treatment is not particularly limited, but one example is immersing the fiber raw material 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.

[0085] 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 fiber raw material.

[0086] <Fibroid Release Process> Fine fibrous cellulose can be obtained by defibrating anionic group-introduced fibers in a defibration process. In the defibration process, for example, a defibration processing device can be used. The defibration processing device is not particularly limited, but for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer or ultra-high-pressure homogenizer, high-pressure impact grinder, ball mill, bead mill, disc type refiner, conical refiner, twin-screw kneader, vibrating mill, homomixer under high-speed rotation, ultrasonic disperser, or beater can be used. Among the above defibration processing devices, it is more preferable to use a high-speed defibrator, high-pressure homogenizer, or ultra-high-pressure homogenizer, which have less influence from the grinding media and less risk of contamination.

[0087] In the defibration process, for example, it is preferable to dilute the anionic group-introduced fibers 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 for example, alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents are preferred. 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).

[0088] The solid content concentration of the fine fibrous cellulose during the defibration process can be set as appropriate. Furthermore, the slurry obtained by dispersing the anionic group-introduced fibers in a dispersion medium may contain solid components other than the anionic group-introduced fibers, such as hydrogen-bonding urea.

[0089] (Organo-onium ions) The fine fibrous cellulose contains organic onium ions as counterions to its anionic groups. In this embodiment, at least some of the organic onium ions are present as counterions to the fibrous cellulose, but free organic onium ions may also be present in the dispersion. Note that the organic onium ions do not form covalent bonds with the fibrous cellulose.

[0090] The organic onium ion is preferably one that satisfies at least one of the following conditions (a) and (b). (a) Contains a hydrocarbon group with 5 or more carbon atoms. (b) The total number of carbon atoms is 17 or more. In other words, it is preferable that the fibrous cellulose contains at least one of an organic onium ion selected from an organic onium ion containing a hydrocarbon group with 5 or more carbon atoms, and an organic onium ion with a total of 17 or more carbon atoms, as a counterion to the anionic group. By making the organic onium ion satisfy at least one of the conditions selected from (a) and (b) above, the dispersibility of the fine fibrous cellulose in organic solvents can be more effectively improved.

[0091] The hydrocarbon group having 5 or more carbon atoms is preferably an alkyl group or alkylene group having 5 or more carbon atoms, more preferably an alkyl group or alkylene group having 6 or more carbon atoms, even more preferably an alkyl group or alkylene group having 7 or more carbon atoms, and particularly preferably an alkyl group or alkylene group having 10 or more carbon atoms. Among these, the organo-onium ion is preferably one having an alkyl group having 5 or more carbon atoms, and more preferably an organo-onium ion containing an alkyl group having 5 or more carbon atoms and having a total of 17 or more carbon atoms.

[0092] The organic onium ion is preferably an organic onium ion represented by the following general formula (A).

[0093] [ka]

[0094] In the above general formula (A), M is referred to as the central element of the organo-onium ion. M is preferably a nitrogen atom or a phosphorus atom. R1 to R4 each independently represent a hydrogen atom or an organic group. However, it is preferable that at least one of R1 to R4 is an organic group with 5 or more carbon atoms, or that the sum of the carbon atoms of R1 to R4 is 17 or more. In particular, M is preferably a nitrogen atom. That is, the organic onium ion is preferably an organic ammonium ion. Furthermore, at least one of R1 to R4 is preferably an alkyl group having 5 or more carbon atoms, and the sum of the carbon atoms of R1 to R4 is preferably 17 or more.

[0095] Examples of organic onium ions include lauryltrimethylammonium, cetyltrimethylammonium, stearyltrimethylammonium, octyldimethylethylammonium, lauryldimethylethylammonium, didecyldimethylammonium, lauryldimethylbenzylammonium, tributylbenzylammonium, methyltri-n-octylammonium, hexylammonium, n-octylammonium, dodecylammonium, tetradecylammonium, hexadecylammonium, stearylammonium, N,N-dimethyldodecylammonium, N,N-dimethyltetradecylammonium, N,N-dimethylhexadecylammonium, N,N-dimethyl-n-octadecylammonium, dihexylammonium, di(2 Examples include ethylhexyl)ammonium, di-n-octylammonium, didecylammonium, didodecylammonium, didecylmethylammonium, N,N-didodecylmethylammonium, polyoxyethylenedodecylammonium, alkyldimethylbenzylammonium, di-n-alkyldimethylammonium, behenyltrimethylammonium, tetraphenylphosphonium, tetraoctylphosphonium, acetonyltriphenylphosphonium, allyltriphenylphosphonium, amyltriphenylphosphonium, benzyltriphenylphosphonium, ethyltriphenylphosphonium, diphenylpropylphosphonium, triphenylphosphonium, tricyclohexylphosphonium, tri-n-octylphosphonium, etc. Note that the alkyl group in alkyldimethylbenzylammonium and di-n-alkyldimethylammonium can be a linear alkyl group with 8 to 18 carbon atoms.

[0096] As shown in general formula (A), the central element of an organo-onium ion is bonded to a total of four groups or hydrogen atoms. In the case of the organo-onium ions mentioned above, if there are fewer than four bonded groups, the remaining group is a hydrogen atom, forming the organo-onium ion. For example, in the case of N,N-didodecylmethylammonium, the name indicates that it is bonded to two dodecyl groups and one methyl group. In this case, the remaining group is bonded to a hydrogen atom, forming the organo-onium ion.

[0097] When organic onium contains oxygen atoms, a higher mass ratio of carbon atoms to oxygen atoms (C / O ratio) is preferable, for example, C / O > 5 is preferable. By making the C / O ratio greater than 5, when organic onium ions or compounds that form organic onium ions by neutralization are added to a fine fibrous cellulose-containing slurry, a fibrous cellulose concentrate is more easily obtained.

[0098] The molecular weight of the organic onium ion is preferably 2000 or less, and more preferably 1800 or less. By keeping the molecular weight of the organic onium ion within the above range, the handling properties of the fibrous cellulose can be improved. Furthermore, by keeping the molecular weight of the organic onium ion within the above range, the decrease in the content of fibrous cellulose in the dispersion can be suppressed.

[0099] The content of organic onium ions is preferably 0.5 to 2 times the molar amount relative to the amount of anionic groups contained in the fine fibrous cellulose, but is not particularly limited. The content of organic onium ions can be measured by tracking the atoms typically contained in organic onium ions. Specifically, if the organic onium ion is an ammonium ion, the amount of nitrogen atoms is measured, and if the organic onium ion is a phosphonium ion, the amount of phosphorus atoms is measured. If the fine fibrous cellulose contains nitrogen atoms or phosphorus atoms in addition to organic onium ions, a method for extracting only the organic onium ions, such as acid extraction, can be used, and then the amount of the target atom can be measured.

[0100] The organic onium ion is preferably an ion that exhibits hydrophobicity. That is, the fine fibrous cellulose in this embodiment exhibits hydrophobicity by having an organic onium ion. As a result, its dispersibility in organic solvents is enhanced, and a dispersion with the desired viscosity and light transmittance can be obtained. Furthermore, such a dispersion can exhibit high thixotropy.

[0101] (optional ingredient) The dispersion in this embodiment may be a dispersion of the fine fibrous cellulose and organic solvent described above, but it may also contain optional components in addition to the fine fibrous cellulose and organic solvent described above. Examples of optional components include resins. The type of resin is not particularly limited, but examples include thermoplastic resins and thermosetting resins.

[0102] Examples of resins include acrylic resins, polycarbonate resins, polyester resins, polyamide resins, silicone resins, fluoropolymer resins, chlorine-based resins, epoxy resins, melamine resins, phenolic resins, polyurethane resins, diallyl phthalate resins, alcohol-based resins, cellulose derivatives, and precursors of these resins. Examples of cellulose derivatives include carboxymethylcellulose, methylcellulose, and hydroxyethylcellulose.

[0103] The dispersion may contain a resin precursor as the resin itself. The type of resin precursor is not particularly limited, but examples include precursors of thermoplastic resins and thermosetting resins. A precursor of a thermoplastic resin refers to monomers or oligomers with a relatively low molecular weight that are used to manufacture thermoplastic resins. A precursor of a thermosetting resin refers to monomers or oligomers with a relatively low molecular weight that can undergo polymerization or crosslinking reactions to form thermosetting resins through the action of light, heat, or a curing agent.

[0104] The dispersion may also contain water-soluble polymers as a resin, in addition to the resin types mentioned above. Examples of water-soluble polymers include synthetic water-soluble polymers (e.g., carboxyvinyl polymer, polyvinyl alcohol, alkyl methacrylate / acrylic acid copolymer, polyvinylpyrrolidone, sodium polyacrylate, polyethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, isoprene glycol, hexylene glycol, 1,3-butylene glycol, polyacrylamide, etc.), thickening polysaccharides (e.g., xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, pullulan, carrageenan, pectin, etc.), starches such as cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, and amylose, glycerin such as glycerin, diglycerin, and polyglycerin, hyaluronic acid, and metal salts of hyaluronic acid.

[0105] In addition, optional components include surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, defoaming agents, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, orientation promoters, plasticizers, dispersants, crosslinking agents, and the like.

[0106] (Method for producing dispersion) The method for producing the dispersion includes the steps of: adding an organic onium ion or a compound that forms an organic onium ion by neutralization to a fine fibrous cellulose-containing slurry obtained through the defibration step described above to obtain a fibrous cellulose aggregate (concentrate); and dispersing the fibrous cellulose aggregate (concentrate) in an organic solvent.

[0107] In the process of obtaining fibrous cellulose aggregates (concentrates), organic onium ions as described above, or compounds that form organic onium ions by neutralization, are added to the fine fibrous cellulose-containing slurry obtained in the defibration process described above. In this case, it is preferable to add the organic onium ions as a solution containing organic onium ions, and more preferable to add them as an aqueous solution containing organic onium ions.

[0108] Aqueous solutions containing organic onium ions typically contain both organic onium ions and their counterions (anions). When preparing an aqueous solution of organic onium ions, if the organic onium ions and their corresponding counterions have already formed a salt, they can simply be dissolved in water. When preparing an aqueous solution of organic onium ions, if the organic onium ions and their corresponding counterions have already formed a salt, it is preferable to dissolve them in water or hot water.

[0109] Furthermore, organic onium ions may only be formed after neutralization with an acid, such as with dodecylamine. In this case, the organic onium ion is obtained by the reaction of a compound that forms an organic onium ion upon neutralization with an acid. Examples of acids used for neutralization in this case include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as lactic acid, acetic acid, formic acid, and oxalic acid. In the coagulation step, the compound that forms an organic onium ion upon neutralization may be directly added to the fibrous cellulose-containing slurry, and the anionic groups contained in the fibrous cellulose may be used as counterions to form the organic onium ion.

[0110] The amount of organic onium ions added is preferably 2% by mass or more, more preferably 10% by mass or more, even more preferably 50% by mass or more, and particularly preferably 100% by mass or more, relative to the total mass of the fibrous cellulose. Furthermore, the amount of organic onium ions added is preferably 1000% by mass or less, relative to the total mass of the fibrous cellulose. Furthermore, the number of moles of organic onium ions to be added is preferably 0.2 times or more the value obtained by multiplying the amount (in moles) of inorganic oxoacid groups contained in fibrous cellulose by its valency, more preferably 0.5 times or more, and even more preferably 1.0 times or more. It is also preferable that the number of moles of organic onium ions to be added is 10 times or less the value obtained by multiplying the amount (in moles) of inorganic oxoacid groups contained in fibrous cellulose by its valency.

[0111] When organic onium ions are added and the mixture is stirred, aggregates form in the fibrous cellulose-containing slurry. These aggregates are formed from fibrous cellulose having organic onium ions as counterions. In this specification, such aggregates are also referred to as fibrous cellulose concentrates. The fibrous cellulose aggregates (concentrates) can be recovered by vacuum filtration of the fibrous cellulose-containing slurry in which the aggregates have formed.

[0112] The resulting fibrous cellulose aggregates may be washed with deionized water. Repeated washing of the fibrous cellulose aggregates with deionized water can remove excess organic onium ions and other substances contained in the fibrous cellulose aggregates.

[0113] The solid content concentration of the obtained fibrous cellulose aggregate is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 25% by mass or more. The solid content concentration of the fibrous cellulose aggregate may also be 100% by mass.

[0114] The moisture content of the fibrous cellulose aggregate may be 0% by mass, 0.5% or more by mass, 1% or more by mass, 3% or more by mass, or 5% or more by mass, relative to the total mass of the fibrous cellulose aggregate. Furthermore, the moisture content of the fibrous cellulose aggregate is preferably 20% or less by mass, and more preferably 15% or less by mass, relative to the total mass of the fibrous cellulose aggregate. The moisture content in the fibrous cellulose aggregate can be measured by placing 200 mg of the fibrous cellulose aggregate on a moisture meter (MS-70, manufactured by A&D Co., Ltd.) and heating it at 140°C. The moisture content in the fibrous cellulose aggregate can be calculated from the measured moisture content.

[0115] The fibrous cellulose aggregates may further undergo processes such as drying, aging, spray drying, granulation, sheeting, heating, wetting, crushing, spraying, immersion, filtration, freezing, sublimation, water extraction, pressurized dehydration, centrifugal dehydration, and surface treatment. In particular, it is preferable that the fibrous cellulose aggregates undergo a drying process, which results in fibrous cellulose aggregates with a low moisture content.

[0116] In the step of dispersing the fibrous cellulose aggregates (concentrates) in an organic solvent, the fibrous cellulose aggregates (concentrates) obtained in the above-mentioned step of obtaining the fibrous cellulose aggregates (concentrates) are dispersed in an organic solvent. This dispersion step is also called a redispersion step because it involves dispersing the fibrous cellulose aggregates (concentrates) again in the solvent.

[0117] When dispersing fibrous cellulose aggregates (concentrates) in an organic solvent, the same type of dispersion apparatus as that described in the defibration treatment above can be used. In particular, when dispersing fibrous cellulose aggregates (concentrates) in an organic solvent, it is preferable to use a high-pressure homogenizer or an ultra-high-pressure homogenizer. By using a high-pressure homogenizer in the redispersion step, the redispersibility of the fibrous cellulose aggregates (concentrates) is improved, making it easier to obtain a highly viscous and highly transparent dispersion.

[0118] Furthermore, it is preferable to include a step of heating a suspension obtained by dispersing fibrous cellulose aggregates (concentrates) in an organic solvent during or before the redispersion step. That is, the method for producing the dispersion preferably includes the steps of: obtaining fibrous cellulose aggregates (concentrates) by adding organic onium ions or compounds that form organic onium ions by neutralization to a fine fibrous cellulose-containing slurry; obtaining a suspension by suspending the fibrous cellulose aggregates (concentrates) in an organic solvent; and obtaining a dispersion by heating the suspension and treating it with a high-pressure homogenizer or an ultra-high-pressure homogenizer. In this case, it is preferable to heat the suspension to 40°C or higher. In the heating step, it is preferable that the temperature of the suspension be 100°C or lower. Conventionally, in the redispersion step, cooling was usually performed for the purpose of suppressing thermal denaturation of the fibrous cellulose aggregates (concentrates). However, in this embodiment, a heating step was deliberately included during or before the redispersion step. By including such a heating step, it was successful to obtain a dispersion with higher viscosity and higher transparency.

[0119] In the redispersion process, or when the suspension is heated before the redispersion process, it is preferable to maintain a liquid temperature of 40°C or higher after passing through the dispersion device. Furthermore, when using a high-pressure homogenizer or an ultra-high-pressure homogenizer as the dispersion device, it is preferable to maintain a liquid temperature of 40°C or higher after passing through the grinding mechanism. To achieve a liquid temperature of 40°C or higher after passing through the dispersion device, for example, one can increase the pressure when passing through the dispersion device, reduce the inner diameter of the internal flow path in the grinding section, increase the pump speed, heat the pump before and / or after passing through the pump and / or the grinding section, or preheat the suspension to be tested.

[0120] In this specification, the step of preheating the suspension to be tested is sometimes referred to as the preheating step. In the preheating step, it is preferable to heat the suspension so that its liquid temperature is between 40°C and 100°C. In this embodiment, it is preferable to include such a preheating step, as preheating the suspension to 40°C or higher before high-pressure homogenizer treatment further improves the dispersibility of the fine fibrous cellulose in organic solvents, making it easier to obtain a dispersion with higher viscosity and higher transparency.

[0121] The manufacturing process for the dispersion may include a step of further dispersing an optional component in the obtained dispersion. Examples of optional components used in this step include those mentioned above.

[0122] (Application) The dispersion of the present invention may be used as a thickening agent in various applications. For example, the dispersion of the present invention can be used as an additive to food, cosmetics, cement, paints (for vehicle coatings such as automobiles, ships, and aircraft, building materials, and daily necessities), inks, pharmaceuticals, packaging materials, coating materials, etc. Furthermore, the dispersion of the present invention can be applied to daily necessities by being added to resin-based materials. Among these, the dispersion of the present invention is preferably used for paints.

[0123] Furthermore, the dispersion of the present invention is preferably used for forming molded articles. The shape of the molded article is not particularly limited, and for example, it can be a sheet-like, granular, or thread-like molded article. Among these, the dispersion of the present invention is preferably used for sheet-like molded articles. For example, the dispersion of the present invention can be used to form a film and used as various types of films.

[0124] Molded articles obtained by coating a substrate with a dispersion are suitable for applications such as reinforcing materials, interior materials, exterior materials, packaging materials, electronic materials, optical materials, acoustic materials, process materials, components for transportation equipment, components for electronic devices, and components for electrochemical elements. [Examples]

[0125] 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.

[0126] <Manufacturing example A> The raw material pulp is softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solids content 93% by mass, basis weight 208 g / m²). 2 A sheet-like material with a Canadian standard filtration efficiency (CSF) of 700 ml (measured according to JIS P 8121) was used. This raw material pulp was subjected to phosphorus oxooxidation 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 raw material pulp 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 200 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining phosphorylated pulp.

[0127] Next, the obtained phosphorylated pulp was subjected to a washing treatment. The washing treatment was carried out by repeatedly adding 10 L of deionized water to 100 g (oven-dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0128] Next, the washed phosphorylated pulp was subjected to a neutralization treatment as follows. First, the washed phosphorylated pulp was diluted with 10 L of deionized water, and then a 1N sodium hydroxide aqueous solution was gradually added while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain phosphorylated pulp that had undergone neutralization treatment. Then, the phosphorylated pulp that had undergone neutralization treatment was subjected to the washing treatment described above.

[0129] The resulting 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.

[0130] Deionized water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content concentration (fibrous cellulose concentration) of 2% by mass. This slurry was processed six times at a pressure of 200 MPa in a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion A containing fine fibrous cellulose.

[0131] X-ray diffraction confirmed that this fine fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2–5 nm. Image analysis using AFM revealed that 100 strands of the fine fibrous cellulose were extracted, and the number-average aspect ratio was calculated to be 300. The amount of phosphate groups (first dissociated acid) measured by the method described later was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mol / g.

[0132] <Manufacturing example B> The procedure was carried out in the same manner as in Production Example A, except that 33 parts by mass of phosphorous acid (phosphonic acid) were used instead of ammonium dihydrogen phosphate to introduce phosphorous acid groups into the cellulose in the pulp, in order to obtain phosphorous pulp.

[0133] The obtained phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that at 1210 cm⁻¹ -1 Absorption based on P=O of the phosphonic acid group, a tautomer of the phosphite group, was observed in the vicinity, confirming that phosphite groups (phosphonic acid groups) were attached to the pulp. Furthermore, when the obtained phosphite-oxidized 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.

[0134] The obtained phosphite pulp was processed in a wet pulverizer in the same manner as in Production Example A to obtain a fine fibrous cellulose dispersion B containing fine fibrous cellulose.

[0135] X-ray diffraction confirmed that this fine fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. Additionally, image analysis using AFM revealed that the number-average aspect ratio of 100 extracted fibrous cellulose strands was 280. The amount of phosphorous acid groups (first dissociated acid) measured using the phosphorus oxoacid group measurement method described later was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0136] <Manufacturing example C> Sulfated pulp was obtained by the same procedure as in Production Example A, except that 38 parts by mass of sulfuric acid amidosulfate were used instead of ammonium dihydrogen phosphate.

[0137] The obtained sulfated pulp was subjected to infrared absorption spectroscopy using FT-IR. The results showed that 1220-1260 cm⁻¹ -1 Absorption based on sulfate groups (sulfonic acid groups) was observed in the vicinity, confirming that sulfate groups (sulfonic acid groups) were attached to the pulp. Furthermore, when the obtained sulfated pulp was tested and analyzed using an X-ray diffractometer, typical peaks were found at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals.

[0138] After adding deionized water to the obtained sulfated pulp, the mixture was stirred to prepare a slurry with a solid content concentration (fibrous cellulose concentration) of 2% by mass. This slurry was processed six times at a pressure of 200 MPa using a wet atomizing device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion C containing fine fibrous cellulose. Furthermore, from image analysis by AFM, 100 strands of fine fibrous cellulose were extracted and the number average of the aspect ratios was calculated, which was 280. The amount of sulfate groups (sulfonic acid groups) measured by the sulfur oxoacid group measurement method described later was 1.30 mmol / g.

[0139] <Manufacturing example D> As the raw material pulp, softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used. This raw material pulp was subjected to alkaline TEMPO oxidation treatment as follows: First, 100 parts by mass of the above raw material pulp (equivalent to 100 parts by mass dry), 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were dispersed in 10,000 parts by mass of water. Next, a 13% by mass sodium hypochlorite aqueous solution was added to a concentration of 10 mmol per 1.0 g of pulp to start the reaction. During the reaction, a 0.5 M sodium hydroxide aqueous solution was added dropwise to maintain the pH between 10 and 10.5, and the reaction was considered complete when no change in pH was observed.

[0140] Next, the obtained TEMPO-oxidized pulp was subjected to a washing treatment. The washing treatment was carried out by dewatering the pulp slurry after TEMPO oxidation to obtain a dewatered sheet, adding 5000 parts by mass of deionized water, stirring to uniformly disperse the sheet, and then repeating the filtration and dewatering process. The washing was terminated when the electrical conductivity of the filtrate became 100 μS / cm or less.

[0141] Furthermore, when the obtained TEMPO-oxidized 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.

[0142] Deionized water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solid content concentration (fibrous cellulose concentration) of 2% by mass. This slurry was processed six times at a pressure of 200 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion D containing fine fibrous cellulose.

[0143] X-ray diffraction confirmed that this fine fibrous cellulose maintained its type I cellulose crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2–5 nm. Additionally, image analysis using AFM revealed that the number-average aspect ratio of 100 extracted fibrous cellulose strands was 250. The carboxyl group content, as measured by the method described later, was 1.80 mmol / g.

[0144] [Measurement of phosphorus oxoacid group content] In measuring the amount of phosphorus oxoacid groups (phosphate groups or phosphite groups) in microfibrous cellulose, first, deionized water was added to the target microfibrous cellulose to prepare a slurry with a solid content concentration of 0.2% by mass. The obtained microfibrous cellulose dispersion was then treated with an ion exchange resin, and the amount was measured by titration using 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 above-mentioned fine fibrous cellulose dispersion, shaking for 1 hour, and then pouring the mixture 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 fine fibrous cellulose dispersion after treatment with ion exchange resin, while measuring the change in the pH value of the slurry. Nitrogen gas was blown into the slurry starting 15 minutes before the start of the titration. 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 increment maximum obtained after starting to add alkali is called the first endpoint, and the next increment maximum 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).

[0145] [Measurement of carboxyl group content] In measuring the carboxyl group content of microfibrous cellulose, first, deionized water was added to the target microfibrous cellulose to prepare a slurry with a solid content concentration of 0.2% by mass. The obtained microfibrous cellulose dispersion was then treated with an ion exchange resin, and the content was measured by titration using 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 above-mentioned fine fibrous cellulose dispersion, shaking for 1 hour, and then pouring the mixture 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 50 μL of 0.1 N sodium hydroxide aqueous solution to the fine fibrous cellulose dispersion after treatment with ion exchange resin, once every 30 seconds, and measuring the change in the pH value of the dispersion. The amount of carboxyl groups (mmol / g) was calculated by dividing the amount of alkali (mmol) required in the region corresponding to the first region shown in Figure 2 of the measurement results by the solid content (g) in the slurry being titrated.

[0146] [Measurement of sulfur oxoacid group content] The amount of sulfur oxoacid groups in the fine fibrous cellulose was measured as follows: The fine fibrous cellulose obtained in Production Example C was frozen in a freezer and then dried for 3 days in a freeze dryer (FreeZone, manufactured by Labconco). The resulting freeze-dried material was pulverized into a powder using a hand mixer (LaboMillser PLUS, manufactured by Osaka Chemical) at a rotation speed of 20,000 rpm for 60 seconds. The freeze-dried and pulverized samples were subjected to pressurized thermal decomposition using nitric acid in a sealed container. Subsequently, the sulfur content was measured by ICP-OES after appropriate dilution. The value calculated by dividing by the oven-dry mass of the fine fibrous cellulose was defined as the amount of sulfur oxoacid groups in the fine fibrous cellulose (unit: mmol / g).

[0147] <Example 1> 100 g of an aqueous solution of 3.86% by mass of di-n-stearyldimethylammonium chloride (hereinafter also referred to as DSDMA) was added to 100 g of fine fibrous cellulose dispersion A and stirred for 5 minutes, resulting in the formation of aggregates in the fine fibrous cellulose dispersion. The fine fibrous cellulose dispersion containing the aggregates was filtered under reduced pressure to obtain fine fibrous cellulose aggregates. The obtained fine fibrous cellulose aggregates were repeatedly washed with deionized water to remove excess di-n-stearyldimethylammonium chloride and eluted ions contained in the fine fibrous cellulose aggregates, thereby obtaining a fine fibrous cellulose concentrate. The obtained fine fibrous cellulose concentrate was air-dried to obtain fine fibrous cellulose concentrate A with a solid content concentration of 90% by mass.

[0148] Toluene was added to fine fibrous cellulose concentrate A to a solid content concentration (fibrous cellulose concentration) of 3% by mass to form a suspension. This suspension was then preheated in a water bath to a temperature of 40°C. The suspension preheated to 40°C was processed five times at a pressure of 100 MPa using a high-pressure homogenizer (Beryu-Mini, manufactured by Biryu Co., Ltd.). The liquid temperature after passing through the grinding section was also measured. Thus, a toluene dispersion of fine fibrous cellulose concentrate A was obtained.

[0149] The toluene dispersion obtained above was allowed to stand at 23°C for 24 hours, and then its viscosity was measured using a B-type viscometer (BLOOKFIELD T-LVT analog viscometer). The measurement conditions were 23°C, and the viscosity was measured when the mixture was rotated at 0.6 rpm or 60 rpm for 3 minutes. In addition, the TI value, an indicator of thixotropy, was calculated according to the following formula. TI value = (viscosity value at 0.6 rpm / viscosity value at 60 rpm)

[0150] The toluene dispersion obtained above was sealed in a 10 mm path length quartz glass cell for liquids, and the light transmittance at a wavelength of 660 nm was measured using a UV-Vis spectrometer (V-770, manufactured by JASCO Corporation). Zero point measurement was performed using deionized water placed in the same glass cell. Furthermore, the light transmittance was measured immediately after redispersion in an organic solvent in each example and comparative example.

[0151] <Example 2> An organic solvent dispersion was obtained in the same manner as in Example 1, except that a fine fibrous cellulose dispersion B was used.

[0152] <Example 3> An organic solvent dispersion was obtained in the same manner as in Example 1, except that a fine fibrous cellulose dispersion C was used.

[0153] <Example 4> An organic solvent dispersion was obtained in the same manner as in Example 1, except that preheating was not performed before treatment with a high-pressure homogenizer.

[0154] <Example 5> An organic solvent dispersion was obtained in the same manner as in Example 1, except that a fine fibrous cellulose dispersion D was used.

[0155] <Example 6> An organic solvent dispersion was obtained in the same manner as in Example 1, except that xylene was used instead of toluene.

[0156] <Example 7> An organic solvent dispersion was obtained in the same manner as in Example 1, except that didecyldimethylammonium chloride (hereinafter also referred to as DDDMA) was used instead of di-n-stearyldimethylammonium chloride.

[0157] <Comparative Example 1> An organic solvent dispersion was obtained in the same manner as in Example 1, except that preheating was not performed and the toluene suspension was treated for 10 minutes using an ultrasonic homogenizer (Hielscher UP400S) instead of a high-pressure homogenizer.

[0158] [Table 1]

[0159] The dispersions obtained in the examples were highly viscous and transparent, and their thixotropic properties were improved. Furthermore, in Examples 1-3, 5, and 6, the viscosity and transparency were further improved by raising the liquid temperature to 40°C or higher immediately after high-pressure homogenizer grinding.

Claims

1. A dispersion containing fibrous cellulose with a fiber width of 1000 nm or less and an organic solvent, The fibrous cellulose has anionic groups, and the content of the anionic groups is 0.50 mmol / g or more. The fibrous cellulose has an organic onium ion as a counterion to the anionic group, A dispersion having a B-type viscosity of 50 Pa·s or more as measured by the following measurement method (A); Measurement method (A): The viscosity of the B-type of the dispersion was measured in accordance with JIS Z 8803 (2011) when the fibrous cellulose concentration of the dispersion was 3% by mass (w / w), the rotation speed was 0.6 rpm, and the temperature was 23°C.

2. The dispersion according to claim 1, wherein the light transmittance measured by the measurement method (B) below is 80% or more; Measurement method (B): The fibrous cellulose concentration of the dispersion is set to 3% by mass (w / w), and it is sealed in a quartz cell with a path length of 10 mm. The light transmittance at a wavelength of 660 nm is then measured using an ultraviolet-visible spectrometer.

3. The dispersion according to claim 1 or 2, wherein the fiber width of the fibrous cellulose is 10 nm or less.

4. The dispersion according to any one of claims 1 to 3, wherein the anionic group is at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group.

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