JP7552226B2 - Dispersion - Google Patents

Description

The present invention relates to a dispersion liquid. Specifically, the present invention relates to a dispersion liquid containing fine fibrous cellulose and an organic solvent.

Traditionally, cellulose fibers have been widely used in clothing, absorbent articles, paper products, etc. As cellulose fibers, in addition to fibrous cellulose with a fiber diameter of 10 μm or more and 50 μm or less, fine fibrous cellulose with a fiber diameter of 1 μm or less is also known. Fine fibrous cellulose has attracted attention as a new material and has a wide range of applications. For example, the development of sheets, resin composites, and thickeners containing fine fibrous cellulose is underway.

Generally, fine fibrous cellulose is stably dispersed in aqueous solvents, and is therefore often provided in the form of an aqueous dispersion and used for various purposes. On the other hand, when fine fibrous cellulose is mixed with a resin component to produce a composite or the like, there is also a demand for mixing the fine fibrous cellulose with an organic solvent. As a technology to meet such demands, a technology for producing a fine fibrous cellulose-containing dispersion in which fine fibrous cellulose is dispersed in a dispersion medium containing an organic solvent has been investigated (Patent Documents 1 to 4).

For example, Patent Documents 1 to 3 disclose a fine fibrous cellulose composite in which a surfactant is adsorbed to fine fibrous cellulose having carboxyl groups. These documents disclose a method of finely refining cellulose fibers in an aqueous solvent, then agglomerating the fine fibrous cellulose and dispersing it in an organic solvent, and a method of obtaining fine fibrous cellulose by finely refining cellulose fibers in an organic solvent. Patent Document 4 discloses a spray composition containing hydrophobically modified cellulose fibers in which at least one modifying group selected from anionic groups and hydroxyl groups of cellulose fibers is bonded, and an organic medium.

JP 2011-140738 A JP 2016-188375 A JP 2019-49091 A JP 2020-76054 A

Dispersions of fine fibrous cellulose in organic solvents have a wide range of applications. For example, in applications such as paints, the dispersions may be required to have high thixotropy.

Therefore, in order to solve these problems of the conventional technology, the inventors have carried out research with the aim of providing a dispersion liquid in which fine fibrous cellulose is dispersed in an organic solvent and which has high thixotropy.

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

[1] A dispersion containing fibrous cellulose having 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 B-type viscosity of 50 Pa s or more as measured by the following measurement method (A);
Measurement method (A):
The Brookfield viscosity is measured in accordance with JIS Z 8803 (2011) when the fibrous cellulose concentration of the dispersion is 3 mass % (w/w), the rotation speed is 0.6 rpm, and the temperature is 23°C.
[2] The dispersion according to [1], having a light transmittance of 80% or more as measured by the following measurement method (B);
Measurement method (B):
The fibrous cellulose concentration of the dispersion is set to 3 mass % (w/w) and sealed 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 liquid according to any one of [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.

According to the present invention, a dispersion liquid having high thixotropy can be obtained by dispersing fine fibrous cellulose in an organic solvent.

FIG. 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having phosphorus oxoacid groups and pH. FIG. 2 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and the pH.

The present invention will be described in detail below. The components described below may be explained based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

(Dispersion)
The present invention relates to a dispersion containing fibrous cellulose having a fiber width of 1000 nm or less and an organic solvent. Here, the fibrous cellulose has an anionic group, and the content of the anionic group is 0.50 mmol/g or more. The fibrous cellulose also has an organic onium ion as a counter ion of the anionic group. 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 is measured in accordance with JIS Z 8803 (2011) when the fibrous cellulose concentration in the dispersion is 3 mass % (w/w), the rotation speed is 0.6 rpm, and the temperature is 23° C. The B-type viscosity of the dispersion is preferably the viscosity of a dispersion consisting of an organic solvent and fibrous cellulose.

The B-type viscosity of the dispersion liquid of this embodiment measured by the above-mentioned measurement method (A) 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 liquid measured by the above-mentioned measurement method (A) of the dispersion liquid is not particularly limited, but is preferably, for example, 500 Pa·s or less.

The dispersion of the present invention has the above-mentioned constitution, and therefore has high thixotropy. That is, the dispersion of the present invention has a property that the viscosity decreases when shear is applied. The thixotropy of the dispersion can be evaluated, for example, by the TI value calculated by 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 value when an organic solvent dispersion having a fibrous cellulose concentration of 3% by mass is left to stand for 24 hours at 23° C., and then rotated at 0.6 rpm for 3 minutes. The viscosity value at 60 rpm is the B-type viscosity value when an organic solvent dispersion having a fibrous cellulose concentration of 3% by mass is left to stand for 24 hours at 23° C., and then rotated at 60 rpm for 3 minutes. The B-type viscosity is measured using a B-type viscometer, and as the B-type viscometer, for example, an analog viscometer T-LVT manufactured by BLOOKFIELD can be used.

The TI value of the dispersion calculated by the above method is preferably 20.0 or more, more preferably 30.0 or more, even more preferably 40.0 or more, and even more preferably 50.0 or more. The upper limit of the TI value of the dispersion is not particularly limited, but is preferably, for example, 500 or less.

The light transmittance of the dispersion in this embodiment, as 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 the dispersion is sealed 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 spectrometer. As the ultraviolet-visible spectrometer, for example, V-770 manufactured by JASCO Corporation can be used. The zero point measurement is performed using ion-exchanged water placed in the same glass cell.

(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 below is dispersed in a dispersion medium containing an organic solvent. The dispersion of the present invention may further contain water in addition to the organic solvent as a dispersion medium, but the content of water relative 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 this embodiment, it is preferable that the dispersion medium does not substantially contain water, and it is particularly preferable that the content of water relative to the total mass of the dispersion is 0% by mass.

The 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 dielectric constant, the dielectric constant of the organic solvent at 25°C may be 45 or less, 40 or less, or 35 or less.

The Hansen solubility parameter (HSP) δd of the organic solvent is preferably 5 MPa ^1/2 to 20 MPa ^1/2 , and more preferably 10 MPa ^1/2 to 19 MPa ^1/2 . δh is preferably 1 MPa ^1/2 to 40 MPa ^1/2 , and more preferably 2 MPa ^1/2 to 30 MPa ^1/2 . It is also preferable that δp is in the range of 0 MPa ^1/2 to 4 MPa ^1/2 and δh is in the range of 0 MPa ^1/2 to 6 MPa ^1/2 at the same time.

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 the organic solvent include toluene, toluene (dielectric constant 2.3 to 3.4), diethyl ether (dielectric constant 4.3), chloroform (dielectric constant 4.8), 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 to 3.4), diethyl ether (dielectric constant 4.3), and chloroform (dielectric constant 4.8). Among these, the organic solvent is preferably at least one selected from the group consisting of toluene, xylene, and styrene.

The content of the organic solvent is preferably 10% by mass or more, and more preferably 50% by mass or more, based on the total mass of the solids contained in the dispersion. The content of the organic solvent is preferably 99.9% by mass or less, and more preferably 99.0% by mass or less, and even more preferably 95.0% by mass or less, based on the total mass of the solids contained in the dispersion.

(Fine fibrous cellulose)
The dispersion of the present invention contains fibrous cellulose having 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 having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose.

The average fiber width of the fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. The fibrous cellulose is, for example, monofilament cellulose.

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% by mass to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast onto 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 are adjusted to satisfy the following conditions.

(1) A straight line X is drawn at an arbitrary location within the observed image, and 20 or more fibers intersect with the straight line X.
(2) Within the same image, a straight line Y is drawn that intersects the straight line perpendicularly, and 20 or more fibers intersect the straight line Y.

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

The fiber length of the fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, destruction of the crystalline regions of the fibrous cellulose can be suppressed. It is also possible to set the slurry viscosity of the fibrous cellulose to an appropriate range. The fiber length of the fibrous cellulose can be determined, for example, by image analysis using a TEM, SEM, or AFM.

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

The axial ratio (fiber length/fiber width) of the fibrous cellulose is not particularly limited, but is preferably, for example, 20 to 10,000, and more preferably 50 to 1,000. By setting the axial ratio to the above lower limit or more, it is easy to form a sheet containing fine fibrous cellulose. In addition, by setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when the fibrous cellulose is treated as a dispersion liquid, handling such as dilution is easier.

Fibrous cellulose, for example, has both crystalline and non-crystalline regions. Fine fibrous cellulose that has both crystalline and non-crystalline regions and has an axial ratio within the above range can be realized by the method for producing fine fibrous cellulose described below.

The fibrous cellulose has an anionic group. Examples of the anionic group include a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group (sometimes simply referred to as a phosphorus oxoacid group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), and a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group (sometimes simply referred to as a sulfur oxoacid group). In particular, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group. When 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, a dispersion liquid having higher transparency and higher viscosity is more easily obtained.

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

In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (wherein a=b×m). At least one of the n α and α' is ^O- , and the rest are R or OR. All of the α and α' may be ^O- . The n α may be the same or different. ^{β b+} is a monovalent or higher cation made of an organic or inorganic substance.

Each R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from any of these. In formula (1), n is preferably 1.

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.

In addition, the derivative group in R includes, but is not limited to, a functional group in which at least one selected from functional groups such as a carboxy group, a carboxylate group ( ^-COO- ), a hydroxy group, an amino group, and an ammonium group is added to or substituted for the main chain or side chain of the above-mentioned various hydrocarbon groups. In addition, 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 to an appropriate range, which facilitates penetration into the fiber raw material and increases the yield of fine cellulose fiber. Note that when there are multiple R in formula (1) or when multiple types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the multiple R present may be the same or different.

β ^b+ is a monovalent or higher cation made of an organic or inorganic substance. As the monovalent or higher cation made of an organic substance, an organic onium ion can be mentioned. As the organic onium ion, for example, an organic ammonium ion or an organic onium ion can be mentioned. As the organic ammonium ion, for example, an aliphatic ammonium ion or an aromatic ammonium ion can be mentioned, and as the organic onium ion, for example, an aliphatic phosphonium ion or an aromatic phosphonium ion can be mentioned. As the monovalent or higher cation made of an inorganic substance, an ion of an alkali metal such as sodium, potassium, or lithium, an ion of a divalent metal such as calcium or magnesium, a hydrogen ion, an ammonium ion, etc. can be mentioned. In addition, when there are multiple β ^b+ in the formula (1) or when multiple types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the multiple β ^{b + may be the same or different. As the monovalent or higher cation made of an organic or inorganic substance, sodium or potassium ions are preferable because they are less likely to yellow when a fiber raw material containing β b+} is heated and are easy to use industrially, but are not particularly limited.

More specifically, examples of the phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group include a phosphate group (-PO ₃ H ₂ ), a salt of a phosphate group, a phosphorous acid group (phosphonic acid group) (-PO ₂ H ₂ ), and a salt of a phosphite group (phosphonic acid group). In addition, the phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group may be a group in which a phosphate group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkyl phosphonic acid group (e.g., a methylphosphonic acid group), etc.

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

In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (wherein 1=b×m). When n is 2 or more, the multiple p's may be the same number or different numbers. In the above structural formula, β ^b+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. In addition, when multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple β ^b+ present may be the same or different. As the organic or inorganic cation having a valence of one or more, sodium or potassium ions are preferred, which are less likely to yellow when the fiber raw material containing β ^b+ is heated and are easy to use industrially, but are not particularly limited.

The content (introduction amount) of the anionic group 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. The content (introduction amount) of the anionic group is, for example, preferably 5.20 mmol/g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol/g or less, even more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, and particularly preferably 2.00 mmol/g or less. Here, the denominator in the unit mmol/g indicates the mass of the fibrous cellulose when the counter ion of the anionic group is a hydrogen ion (H ⁺ ). By setting the introduction amount of the anionic group within the above range, the content of the organic onium ion that the fibrous cellulose may contain can be set to an appropriate range, and thus the dispersibility of the fibrous cellulose in an organic solvent can be more effectively improved.

The amount of anionic groups introduced into fibrous cellulose can be measured, for example, by neutralization titration. In the measurement by neutralization titration, an alkali such as an aqueous sodium hydroxide solution is added to the obtained slurry containing fibrous cellulose, and the amount introduced is measured by determining the change in pH.

1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into the fibrous cellulose is measured, for example, as follows.
First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement target may be subjected to a defibration treatment similar to the defibration treatment step described below prior to the treatment with the strongly acidic ion exchange resin.
Next, the change in pH is observed while adding the aqueous sodium hydroxide solution, and a titration curve as 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 added alkali, and in the titration curve shown in the lower part of Figure 1, the increment (differential value) (1/mmol) of pH against the amount of added alkali is plotted. In this neutralization titration, two points are confirmed in the curve plotting the measured pH against the amount of added alkali, where the increment (differential value of pH against the amount of added alkali) is maximum. Of these, the first maximum point of the increment obtained after starting to add the alkali is called the first endpoint, and the second maximum point of the increment obtained next is called the second endpoint. The amount of alkali required from the start of titration to the first end point is equal to the amount of the first dissociated acid of the fibrous cellulose contained in the slurry used for titration, the amount of alkali required from the first end point to the second end point is equal to the amount of the second dissociated acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is equal to the total amount of dissociated acid of the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol/g). Note that when simply referring to the amount of phosphorus oxo acid group introduced (or the amount of phosphorus oxo acid group), it refers to the amount of the first dissociated acid.
In FIG. 1, the region from the start of titration to the first end point is called the first region, and the region from the first end point to the second end point is called the second region. For example, when the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weak acid groups in the phosphorus oxoacid group (also referred to as the second dissociated acid amount in this specification) appears to decrease, and the amount of alkali required in the second region becomes smaller than the amount of alkali required in the first region. On the other hand, the amount of strong acid groups in the phosphorus oxoacid group (also referred to as the first dissociated acid amount in this specification) is equal to the amount of phosphorus atoms regardless of the presence or absence of condensation. In addition, when the phosphorus oxoacid group is a phosphorous acid group, the weak acid groups are no longer present in the phosphorus oxoacid group, so the amount of alkali required in the second region becomes smaller, or the amount of alkali required in the second region may become zero. In this case, there is only one point in the titration curve where the pH increment is maximized.

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

2 is a graph showing the relationship between the amount of NaOH dropped onto a dispersion containing fibrous cellulose having a carboxy group as an anionic group and pH. The amount of carboxy groups introduced into the fibrous cellulose is measured, for example, as follows.
First, a dispersion liquid containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, a defibration treatment similar to the defibration treatment step described below may be performed on the measurement target prior to the treatment with the strongly acidic ion exchange resin.
Next, the change in pH is observed while adding the aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of FIG. 2 is obtained. In the titration curve shown in the upper part of FIG. 2, the measured pH is plotted against the amount of added alkali, and in the titration curve shown in the lower part of FIG. 2, the increment (differential value) (1/mmol) of pH against the amount of added alkali is plotted. In this neutralization titration, in the curve plotting the measured pH against the amount of added alkali, one point where the increment (differential value of pH against the amount of added alkali) is maximum is confirmed, and this maximum point is called the first end point. Here, the region from the start of titration to the first end point in FIG. 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).

The above-mentioned amount of carboxyl groups introduced (mmol/g) indicates the amount of carboxyl groups in the acid-type fibrous cellulose (hereinafter referred to as the amount of carboxyl groups (acid type)) since the denominator is the mass of the acid-type fibrous cellulose. On the other hand, when the counter ion of the carboxyl group is replaced with any cation C so as to be the charge equivalent, the amount of carboxyl groups in the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of carboxyl groups (C type)) can be obtained by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated by the following formula.
Carboxy group amount (C type)=Carboxy group amount (acid type)/{1+(W-1)×(Carboxy group amount (acid type))/1000}
W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

When measuring the amount of anionic groups by titration, if too much sodium hydroxide solution is added or if the titration interval is too short, the amount of anionic groups may be lower than it should be and an accurate value may not be obtained. For example, an appropriate amount of sodium hydroxide and titration interval is preferably 10 to 50 μL of 0.1 N sodium hydroxide solution added every 5 to 30 seconds. In addition, in order to eliminate the effects of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is preferable to measure while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of titration.

The amount of sulfur oxoacid groups introduced into fibrous cellulose can be calculated by freeze-drying a slurry containing fibrous cellulose, pulverizing the slurry, and measuring the amount of sulfur in the resulting pulverized sample. Specifically, a slurry containing fibrous cellulose is freeze-dried, and the resulting pulverized sample is subjected to pressurized heating decomposition using nitric acid in a closed container, and then appropriately diluted and the amount of sulfur is measured using ICP-OES. The value calculated by dividing the value by the bone dry mass of the fibrous cellulose used is taken as the amount of sulfur oxoacid groups in the fine fibrous cellulose (unit: mmol/g).

(Method for producing fine fibrous cellulose)
<Fiber raw materials>
The fine fibrous cellulose is produced from a fiber raw material containing cellulose. The fiber raw material containing cellulose is not particularly limited, but it is preferable to use pulp because it is easily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not particularly limited to, chemical pulp such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP) and oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP), mechanical pulp such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. The non-wood pulp is not particularly limited, but may be, for example, cotton-based pulp such as cotton linters and cotton lint, or non-wood pulp such as hemp, straw, or bagasse. The deinked pulp is not particularly limited, but may be, for example, deinked pulp made from waste paper. The pulp of this embodiment may be used alone or in combination of two or more of the above. Among the above pulps, for example, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Among the wood pulps, for example, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoint of a high cellulose ratio and a high yield of fine fibrous cellulose during defibration treatment, and of small decomposition of cellulose in the pulp and of obtaining long-fiber fine fibrous cellulose with a large axial ratio. Note that the viscosity tends to increase when long-fiber fine fibrous cellulose with a large axial ratio is used.

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

<Phosphorus Oxoacid Group Introduction Step>
The manufacturing process of fine fibrous cellulose includes an anionic group introduction step. An example of the anionic group introduction step is a phosphorus oxo acid group introduction step. The phosphorus oxo acid group introduction step is a step of reacting at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups possessed by a fiber raw material containing cellulose with the fiber raw material containing cellulose. This step results in the production of a fiber into which a phosphorus oxo acid group has been introduced.

In the phosphorus oxoacid group introduction process 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"). On the other hand, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the absence of compound B.

One example of a method for allowing compound A to act on a fiber raw material in the presence of compound B is to mix compound A and compound B with a fiber raw material in a dry, wet, or slurry state. Of these, it is preferable to use a fiber raw material in a dry or wet state, and it is particularly preferable to use a fiber raw material in a dry state, since the reaction is highly uniform. The form of the fiber raw material is not particularly limited, but it is preferable to use a cotton-like or thin sheet-like form, for example. Compound A and compound B are added to the fiber raw material in a powder form, a solution form dissolved in a solvent, or a melted state by heating to a melting point or higher. Of these, it is preferable to add them in a solution form dissolved in a solvent, especially in an aqueous solution form, since the reaction is highly uniform. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method of adding compound A and compound B is not particularly limited, but when compound A and compound B are in a solution form, the fiber raw material may be immersed in the solution to absorb the liquid and then removed, or the solution may be dripped onto 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 squeezing or filtration.

Compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, and may include, but is not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and anhydrous phosphoric acid (diphosphorus pentoxide). Phosphoric acid may be of various purities, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid may be 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is phosphoric acid in which two or more molecules are condensed by a dehydration reaction, and examples of such 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 may be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphorus oxoacid groups, easier improvement of defibration efficiency in the defibration step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, and ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid and sodium phosphite are more preferred.

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, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the effect of improving the yield and costs.

As described above, the compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of the 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 an aqueous solution of compound B. Also, 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.

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

In the reaction of a fiber raw material containing cellulose with compound A, in addition to compound B, for example, 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 in particular is known to act as a good reaction catalyst.

In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material, and then heat-treat the fiber raw material. It is preferable to select a temperature for the heat treatment that can efficiently introduce phosphorus oxo acid groups while suppressing thermal decomposition and hydrolysis of the fiber. 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. In addition, for the heat treatment, equipment having various heat media can be used, such as a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, an airflow dryer, a reduced pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

In the heat treatment according to this embodiment, for example, a method of adding compound A to a thin sheet-like fiber raw material by a method such as impregnation and then heating the material, or a method of heating the fiber raw material and compound A while kneading or stirring the fiber raw material with a kneader or the like can be adopted. This makes it possible to suppress unevenness in the concentration of compound A in the fiber raw material and introduce phosphorus oxoacid groups more uniformly onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be due to the fact that when water molecules move to the surface of the fiber raw material as it dries, the dissolved compound A can be prevented from being attracted to the water molecules by surface tension and moving to the surface of the fiber raw material in the same way (i.e., causing unevenness in the concentration of compound A).

In addition, the heating device used for the heat treatment is preferably a device that can constantly discharge, to the outside of the system, for example, the moisture held by the slurry and the moisture generated by the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. An example of such a heating device is an oven that uses a blowing air system. By constantly discharging the moisture within the system, it is possible to suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, and also to suppress acid hydrolysis of the sugar chains in the fibers. This makes it possible to obtain fine fibrous cellulose with a high axial ratio.

The heat treatment time is preferably from 1 second to 300 minutes after the moisture has been substantially removed from the fiber raw material, more preferably from 1 second to 1000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, the amount of phosphorus oxoacid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within an appropriate range.

The phosphorus oxo acid group introduction process needs to be carried out at least once, but can also be repeated two or more times. By carrying out the phosphorus oxo acid group introduction process two or more times, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material.

The amount of phosphorus oxo acid 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. The content (amount introduced) of phosphorus oxo acid groups is, for example, preferably 5.20 mmol/g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol/g or less, even more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, and particularly preferably 2.00 mmol/g or less. By setting the amount of phosphorus oxo acid groups introduced within the above range, the content of organic onium ions that may be contained in the fibrous cellulose can be set to an appropriate range, and thus the dispersibility of the fibrous cellulose in organic solvents can be more effectively improved.

<Carboxy Group Introduction Step>
The process for producing 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 subjecting a fiber raw material containing cellulose to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or treating the raw material with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.

Examples of compounds having a group derived from a carboxylic acid include, but are not limited to, 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. In addition, examples of derivatives of compounds having a group derived from a carboxylic acid include, but are not limited to, imidized products of acid anhydrides of compounds having a carboxy group, and derivatives of acid anhydrides of compounds having a carboxy group. Examples of imidized products of acid anhydrides of compounds having a carboxy group include, but are not limited to, imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

The acid anhydrides of compounds having a group derived from carboxylic acid include, but are not limited to, acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. In addition, the derivatives of acid anhydrides of compounds having a group derived from carboxylic acid include, but are not limited to, acid anhydrides of compounds having carboxy groups such as dimethylmaleic anhydride, diethylmaleic anhydride, and diphenylmaleic anhydride in which at least some of the hydrogen atoms are substituted with a substituent such as an alkyl group or a phenyl group.

When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of pH 6 or more and 8 or less. Such a treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as a fiber raw material, nitroxy radicals such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to sodium phosphate buffer (pH = 6.8). Furthermore, by allowing sodium chlorite to coexist, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. In addition, the TEMPO oxidation treatment may be performed under conditions of pH 10 or more and 11 or less. Such a treatment is also called alkaline TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be performed, for example, by adding nitroxy radicals such as TEMPO as a catalyst, sodium bromide as a cocatalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material.

The amount of carboxyl groups introduced into the fiber raw material varies depending on the type of the substituent. For example, when carboxyl groups are introduced by TEMPO oxidation, the amount is 0.50 mmol/g or more per 1 g (mass) of the 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. The amount of carboxyl groups introduced into the 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 1 g (mass) of the fine fibrous cellulose. By setting the amount of carboxyl groups introduced within the above range, the content of organic onium ions that the fine fibrous cellulose may contain can be set to an appropriate range, and this makes it possible to more effectively increase the dispersibility of the fibrous cellulose in organic solvents.

<Sulfur oxoacid group introduction step>
The process for producing fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an anionic group introduction step, in which hydroxyl groups in a fiber raw material containing cellulose react with sulfur oxoacid to obtain cellulose fibers having sulfur oxoacid groups (sulfur oxoacid group-introduced fibers).

In the sulfur oxo acid group introduction step, instead of compound A in the above-mentioned <phosphorus oxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfur oxo acid groups by reacting with hydroxyl groups possessed by fiber raw materials containing cellulose is used. Compound C may be any compound that has a sulfur atom and can form an ester bond with cellulose, and examples of such compounds include sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides, but are not limited thereto. As sulfuric acid, those with various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). As sulfurous acid, 5% sulfurous acid water can be used. As sulfates or sulfites, lithium salts, sodium salts, potassium salts, ammonium salts of sulfates or sulfites can be used, and these can be neutralized to various degrees. As sulfuric acid amides, sulfamic acid, etc. can be used. In the sulfur oxo acid group introduction step, it is preferable to use compound B in the above-mentioned <phosphorus oxo acid group introduction step> in the same manner.

In the sulfur oxoacid group introduction process, 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. It is preferable to select a heat-treatment temperature that can 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. The heat-treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

In the heat treatment step, it is preferable to heat until substantially no moisture is present. For this reason, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material and the amount of the aqueous solution containing sulfur oxoacid and urea and/or urea derivative added, but is preferably, for example, 10 seconds to 10,000 seconds. For the heat treatment, equipment having various heat media can be used, such as a hot air dryer, agitator dryer, rotary dryer, disk dryer, roll-type heater, plate-type heater, fluidized bed dryer, band-type dryer, filtration dryer, vibration fluidized dryer, airflow dryer, reduced pressure dryer, infrared heater, far-infrared heater, microwave heater, and high-frequency dryer.

The amount of sulfur oxoacid groups introduced into the cellulose raw material may 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. The amount of sulfur oxoacid groups introduced is preferably 5.00 mmol/g or less per 1 g (mass) of fibrous cellulose, more preferably 3.00 mmol/g or less. By setting the amount of sulfur oxoacid groups introduced within the above range, the content of organic onium ions that may be contained in the fine fibrous cellulose can be set to an appropriate range, and this makes it possible to more effectively increase the dispersibility of the fibrous cellulose in organic solvents.

<Cleaning process>
In the method for producing fine fibrous cellulose in this embodiment, a washing step can be carried out on the anionic group-introduced fiber as necessary. The washing step is carried out, for example, by washing the anionic group-introduced fiber with water or an organic solvent. The washing step may be carried out after each step described below, and the number of washing steps carried out in each washing step is not particularly limited.

<Alkaline treatment step>
When producing fine fibrous cellulose, an alkali treatment may be performed on the fiber raw material between the anionic group introduction step and the defibration step described below. The alkali treatment method is not particularly limited, but may be, for example, a method of immersing the anionic group-introduced fiber in an alkali solution.

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

The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 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 step is not particularly limited, but is preferably 5 minutes to 30 minutes, and more preferably 10 minutes to 20 minutes. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is preferably 100% by mass to 100,000% by mass, and more preferably 1000% by mass to 10,000% by mass, based on the absolute dry mass of the anionic group-introduced fiber.

In order to reduce the amount of alkaline solution used in the alkaline treatment step, the anionic group-introduced fiber may be washed with water or an organic solvent after the anionic group-introducing step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the anionic group-introduced fiber that has been subjected to the alkaline treatment with water or an organic solvent after the alkaline treatment step and before the defibration treatment step.

<Acid treatment step>
When producing fine fibrous cellulose, the fiber raw material may be subjected to an acid treatment between the step of introducing anionic groups and the defibration treatment step described below. For example, the anionic group introduction step, acid treatment, alkali treatment, and defibration treatment may be performed in this order.

The method of acid treatment is not particularly limited, but for example, a method of immersing the fiber raw material in an acidic solution containing an acid can be mentioned. The concentration of the acidic solution used is not particularly limited, but for example, it is preferably 10% by mass or less, more preferably 5% by mass or less. The pH of the acidic solution used is not particularly limited, but for example, it is preferably 0 to 4, more preferably 1 to 3. The acid contained in the acidic solution can be, for example, an inorganic acid, a sulfonic acid, a carboxylic acid, etc. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, boric acid, etc. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, etc. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid, etc. Among these, it is particularly preferable to use hydrochloric acid or sulfuric acid.

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

<Defibrillation process>
The anionic group-introduced fiber is defibrated in a defibration process to obtain fine fibrous cellulose. In the defibration process, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but for example, a high-speed defibrator, a grinder (stone mill type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision type grinder, a ball mill, a bead mill, a disk type refiner, a conical refiner, a biaxial kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater can be used. Among the above defibration treatment devices, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

In the fiber defibration process, for example, the anionic group-introduced fiber is preferably diluted 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 examples of the preferred solvents include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of the alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of the polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of the ketones include acetone and methyl ethyl ketone (MEK). Examples of the 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 the esters include ethyl acetate and butyl acetate. Aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), etc.

The solids concentration of the fine fibrous cellulose during the defibration process can be set as appropriate. In addition, the slurry obtained by dispersing the anionic group-introduced fibers in a dispersion medium may contain solids other than the anionic group-introduced fibers, such as urea with hydrogen bonding properties.

(Organic onium ion)
The fine fibrous cellulose contains organic onium ions as counter ions of the anionic groups. In this embodiment, at least a part of the organic onium ions is present as a counter ion of the fibrous cellulose, but the dispersion may contain free organic onium ions. The organic onium ions do not form covalent bonds with the fibrous cellulose.

The organic onium ion preferably satisfies at least one of the following conditions (a) and (b):
(a) Contains a hydrocarbon group having 5 or more carbon atoms.
(b) The total number of carbon atoms is 17 or more.
That is, the fibrous cellulose preferably contains, as a counter ion of an anionic group, at least one selected from an organic onium ion containing a hydrocarbon group having 5 or more carbon atoms and an organic onium ion having a total carbon number of 17 or more. By using an organic onium ion that satisfies at least one of the conditions (a) and (b) above, the dispersibility of the fine fibrous cellulose in organic solvents can be more effectively improved.

The hydrocarbon group having 5 or more carbon atoms is preferably an alkyl group having 5 or more carbon atoms or an alkylene group having 5 or more carbon atoms, more preferably an alkyl group having 6 or more carbon atoms or an alkylene group having 6 or more carbon atoms, even more preferably an alkyl group having 7 or more carbon atoms or an alkylene group having 7 or more carbon atoms, and particularly preferably an alkyl group having 10 or more carbon atoms or an alkylene group having 10 or more carbon atoms. Among these, the organic onium ion preferably has an alkyl group having 5 or more carbon atoms, and more preferably is an organic onium ion that includes an alkyl group having 5 or more carbon atoms and has a total of 17 or more carbon atoms.

The organic onium ion is preferably an organic onium ion represented by the following general formula (A):

In the above general formula (A), M is referred to as the central element of the organic onium ion. M is preferably a nitrogen atom or a phosphorus atom. R ₁ to R ₄ each independently represent a hydrogen atom or an organic group. However, it is preferable that at least one of R ₁ to R ₄ is an organic group having 5 or more carbon atoms, or the total number of carbon atoms of R ₁ to R ₄ is 17 or more.
Among these, M is preferably a nitrogen atom. That is, the organic onium ion is preferably an organic ammonium ion. Furthermore, it is preferable that at least one of R ₁ to R ₄ is an alkyl group having 5 or more carbon atoms, and the total number of carbon atoms of R ₁ to R ₄ is 17 or more.

Examples of organic onium ions include lauryl trimethyl ammonium, cetyl trimethyl ammonium, stearyl trimethyl ammonium, octyl dimethyl ethyl ammonium, lauryl dimethyl ethyl ammonium, didecyl dimethyl ammonium, lauryl dimethyl benzyl ammonium, tributyl benzyl ammonium, methyl tri-n-octyl ammonium, hexyl ammonium, n-octyl ammonium, dodecyl ammonium, tetradecyl ammonium, hexadecyl ammonium, stearyl ammonium, N,N-dimethyl dodecyl ammonium, N,N-dimethyl tetradecyl ammonium, N,N-dimethyl hexadecyl ammonium, N,N-dimethyl-n-octadecyl ammonium, dihexyl ammonium, di(2 -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. Examples of the alkyl group in alkyldimethylbenzylammonium and di-n-alkyldimethylammonium include linear alkyl groups having 8 to 18 carbon atoms.

As shown in general formula (A), the central element of an organic onium ion is bonded to a total of four groups or hydrogen. In the above-mentioned organic onium ion names, if there are less than four groups bonded, the remaining groups are bonded to hydrogen atoms to form the organic onium ion. For example, in the case of N,N-didodecylmethylammonium, it can be determined from the name that two dodecyl groups and one methyl group are bonded. In this case, hydrogen is bonded to the remaining group to form the organic onium ion.

When the organic onium contains O atoms, the larger the mass ratio of C atoms to O atoms (C/O ratio) the more preferable, and for example, C/O>5. By making the C/O ratio greater than 5, it becomes easier to obtain a fibrous cellulose concentrate when organic onium ions or a compound that forms organic onium ions by neutralization are added to a slurry containing fine fibrous cellulose.

The molecular weight of the organic onium ion is preferably 2000 or less, and more preferably 1800 or less. By setting the molecular weight of the organic onium ion within the above range, the handleability of the fibrous cellulose can be improved. In addition, by setting the molecular weight of the organic onium ion within the above range, a decrease in the content of fibrous cellulose in the dispersion liquid can be suppressed.

The content of organic onium ions is preferably 0.5 to 2 times the molar amount of the 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 the organic onium ions. Specifically, when the organic onium ions are ammonium ions, the amount of nitrogen atoms is measured, and when the organic onium ions are phosphonium ions, the amount of phosphorus atoms is measured. Note that when the fine fibrous cellulose contains nitrogen atoms or phosphorus atoms in addition to the organic onium ions, a method for extracting only the organic onium ions, such as an extraction operation using an acid, can be performed, and then the amount of the target atom can be measured.

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, dispersibility in organic solvents is improved, and a dispersion liquid exhibiting the desired viscosity and light transmittance can be obtained. Furthermore, such a dispersion liquid can exhibit high thixotropy.

(Optional ingredients)
The dispersion of the present embodiment may be a dispersion consisting of the above-mentioned fine fibrous cellulose and organic solvent, but may contain optional components in addition to the above-mentioned fine fibrous cellulose and organic solvent. The optional components may include, for example, resins. The type of resin is not particularly limited, but may include, for example, thermoplastic resins and thermosetting resins.

Examples of resins include acrylic resins, polycarbonate resins, polyester resins, polyamide resins, silicone resins, fluorine resins, chlorine resins, epoxy resins, melamine resins, phenolic resins, polyurethane resins, diallyl phthalate resins, alcohol resins, cellulose derivatives, and precursors of these resins. Examples of cellulose derivatives include carboxymethyl cellulose, methyl cellulose, and hydroxyethyl cellulose.

The dispersion may contain a resin precursor as the resin. 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 a monomer or an oligomer with a relatively low molecular weight that is used to manufacture a thermoplastic resin. A precursor of a thermosetting resin refers to a monomer or an oligomer with a relatively low molecular weight that can form a thermosetting resin by undergoing a polymerization reaction or a crosslinking reaction due to the action of light, heat, or a curing agent.

The dispersion may further contain a water-soluble polymer as a resin in addition to the above-mentioned resin types. Examples of the water-soluble polymer 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 cationic starch, raw starch, oxidized starch, etherified starch, esterified starch, and amylose, glycerins such as glycerin, diglycerin, and polyglycerin, hyaluronic acid, and metal salts of hyaluronic acid.

Optional components include surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, defoamers, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, alignment promoters, plasticizers, dispersants, crosslinking agents, etc.

(Method of Producing Dispersion)
The method for producing the dispersion includes a step of adding an organic onium ion or a compound that forms an organic onium ion upon neutralization to a slurry containing fine fibrous cellulose obtained through the above-mentioned defibration process to obtain a fibrous cellulose agglomerate (concentrate), and a step of dispersing the fibrous cellulose agglomerate (concentrate) in an organic solvent.

In the process of obtaining a fibrous cellulose aggregate (concentrate), the above-mentioned organic onium ions or compounds that form organic onium ions by neutralization are added to the fine fibrous cellulose-containing slurry obtained in the above-mentioned defibration process. In this case, the organic onium ions are preferably added as a solution containing the organic onium ions, and more preferably as an aqueous solution containing the organic onium ions.

An aqueous solution containing an organic onium ion usually contains an organic onium ion and a counter ion (anion). When preparing an aqueous solution of an organic onium ion, if the organic onium ion and the corresponding counter ion have already formed a salt, they can be dissolved in water as is. When preparing an aqueous solution of an organic onium ion, if the organic onium ion and the corresponding counter ion have already formed a salt, they are preferably dissolved in water or hot water.

In some cases, the organic onium ion is generated only after neutralization with an acid, such as dodecylamine. In this case, the organic onium ion is obtained by a reaction between a compound that forms an organic onium ion upon neutralization and the acid. In this case, the acid used for neutralization includes 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 flocculation process, 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 convert the compound into an organic onium ion.

The amount of the organic onium ion 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, based on the total mass of the fibrous cellulose. The amount of the organic onium ion added is preferably 1000% by mass or less, based on the total mass of the fibrous cellulose.
The number of moles of the organic onium ions to be added is preferably 0.2 times or more, more preferably 0.5 times or more, and even more preferably 1.0 times or more, the value obtained by multiplying the amount (number of moles) of inorganic oxo acid groups contained in the fibrous cellulose by the valence. The number of moles of the organic onium ions to be added is preferably 10 times or less the value obtained by multiplying the amount (number of moles) of inorganic oxo acid groups contained in the fibrous cellulose by the valence.

When organic onium ions are added and stirred, aggregates are generated in the fibrous cellulose-containing slurry. These aggregates are formed by agglomeration of fibrous cellulose having organic onium ions as counter ions. In this specification, such aggregates are also referred to as fibrous cellulose concentrates. The fibrous cellulose-containing slurry in which aggregates have formed is filtered under reduced pressure to recover the fibrous cellulose aggregates (concentrates).

The obtained fibrous cellulose aggregate may be washed with ion-exchanged water. By repeatedly washing the fibrous cellulose aggregate with ion-exchanged water, excess organic onium ions and the like contained in the fibrous cellulose aggregate can be removed.

The solids 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 solids concentration of the fibrous cellulose aggregate may be 100% by mass.

The moisture content of the fibrous cellulose aggregate may be 0% by mass, 0.5% by mass or more, 1% by mass or more, 3% by mass or more, or 5% by mass or more, based on the total mass of the fibrous cellulose aggregate. The moisture content of the fibrous cellulose aggregate is preferably 20% by mass or less, more preferably 15% by mass or less, based on 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 at 140°C. The moisture content in the fibrous cellulose aggregate can be calculated from the measured moisture content.

The fibrous cellulose aggregate may be one that has further undergone a drying process, an aging process, a spray drying process, a granulation process, a sheeting process, a heating process, a wetting process, a grinding process, a spraying process, a soaking process, a filtration process, a freezing process, a sublimation process, a water squeezing process, a pressurized dehydration process, a centrifugal dehydration process, a surface treatment process, or the like. Of these, it is preferable that the fibrous cellulose aggregate has undergone a drying process, which results in a fibrous cellulose aggregate with a low moisture content.

In the process of dispersing the fibrous cellulose aggregate (concentrate) in an organic solvent, the fibrous cellulose aggregate (concentrate) obtained in the process of obtaining the fibrous cellulose aggregate (concentrate) described above is dispersed in an organic solvent. This dispersion process is also called a redispersion process, since it is a process in which the fibrous cellulose aggregate (concentrate) is dispersed again in a solvent.

The dispersing device used when dispersing the fibrous cellulose aggregates (concentrate) in an organic solvent can be, for example, the same as the defibration processing device described in the defibration processing described above. In particular, when dispersing the fibrous cellulose aggregates (concentrate) in an organic solvent, it is preferable to disperse the fibrous cellulose aggregates (concentrate) using 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 (concentrate) is improved, making it easier to obtain a highly viscous and transparent dispersion.

In addition, in the redispersion step or before the redispersion step, it is preferable to provide a step of heating the suspension obtained by dispersing the fibrous cellulose aggregates (concentrate) in an organic solvent. That is, the method for producing a dispersion preferably includes a step of adding an organic onium ion or a compound that forms an organic onium ion by neutralization to a fine fibrous cellulose-containing slurry to obtain a fibrous cellulose aggregate (concentrate), a step of suspending the fibrous cellulose aggregate (concentrate) in an organic solvent to obtain a suspension, and a step of heating the suspension and treating it with a high-pressure homogenizer or an ultra-high-pressure homogenizer to obtain a dispersion. In this case, it is preferable to heat the suspension to 40°C or higher. In the heating step, the temperature of the suspension is preferably 100°C or lower. Conventionally, in the redispersion step, cooling was usually performed in order to suppress thermal denaturation of the fibrous cellulose aggregates (concentrate). However, in this embodiment, a heating step is deliberately provided in the redispersion step or before the redispersion step. By implementing this heating process, we were able to successfully obtain a dispersion that was both more viscous and more transparent.

When the suspension is heated during or before the redispersion process, it is preferable that the liquid temperature after passing through the dispersion device is 40°C or higher. When a high-pressure homogenizer or ultra-high-pressure homogenizer is used as the dispersion device, it is preferable that the liquid temperature after passing through the grinding mechanism section is 40°C or higher. In order to make the liquid temperature after passing through the dispersion device 40°C or higher, for example, the pressure during passage through the dispersion device can be increased, the inner diameter of the internal flow path of the grinding processing section can be reduced, the pump speed can be increased, before passing through the pump and/or after passing through the pump and/or the grinding processing section can be heated, the suspension to be tested can be heated in advance, etc.

In this specification, the process of preheating the suspension to be tested is sometimes referred to as a preheating process. In the preheating process, it is preferable to heat the suspension so that the liquid temperature is 40°C or higher and 100°C or lower. In this embodiment, it is preferable to provide such a preheating process, and by preheating the suspension before processing with the high-pressure homogenizer to 40°C or higher, the dispersibility of the fine fibrous cellulose in the organic solvent is further improved, making it easier to obtain a dispersion liquid that is more viscous and highly transparent.

The process for producing the dispersion may further include a step of dispersing optional components in the obtained dispersion. The optional components used in this step include the optional components described above.

(Application)
The dispersion of the present invention may be used as a thickener for various applications. For example, the dispersion of the present invention can be used as an additive to food, cosmetics, cement, paint (for painting vehicles such as automobiles, ships, and aircraft, for building materials, for daily necessities, etc.), ink, medicine, packaging materials, coating materials, etc. In addition, the dispersion of the present invention can be applied to daily necessities by adding it to a resin-based material. Among them, the dispersion of the present invention is preferably used for paint.

The dispersion of the present invention is also preferably used for forming molded bodies. The shape of the molded body is not particularly limited, and it can be, for example, a sheet-like, granular, or thread-like molded body. In particular, the dispersion of the present invention is preferably used for sheet-like molded bodies. For example, the dispersion of the present invention can be formed into a film and used as various films.

The molded articles obtained by coating the dispersion on a substrate are also suitable for use as reinforcing materials, interior and exterior materials, packaging materials, electronic materials, optical materials, acoustic materials, process materials, parts for transport equipment, parts for electronic devices, and parts for electrochemical elements.

The features of the present invention will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed 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 specific examples shown below. In the following, Example 4 shall be read as Reference Example 4.

<Production Example A>
As the raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 208 g/ ^m2 sheet form, Canadian standard freeness (CSF) measured according to JIS P 8121 after disintegration is 700 ml) manufactured by Oji Paper Co., Ltd. was used. This raw material pulp was subjected to phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, to obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 200 seconds to introduce phosphoric acid groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

Then, the obtained phosphorylated pulp was subjected to a washing process. The washing process was carried out by repeatedly pouring 10 L of ion-exchanged water per 100 g (bone dry weight) of phosphorylated pulp to obtain a pulp dispersion, stirring the pulp to uniformly disperse the pulp, and then filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

Next, the washed phosphorylated pulp was subjected to a neutralization treatment as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion exchange water, and then a 1N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain a phosphorylated pulp that had been subjected to a neutralization treatment. Next, the above-mentioned washing treatment was performed on the phosphorylated pulp after the neutralization treatment.

The infrared absorption spectrum of the phosphorylated pulp thus obtained was measured using FT-IR. As a result, absorption due to P=O of the phosphoric acid group was observed around 1230 cm ^-1 , and it was confirmed that the phosphoric acid group was added to the pulp. In addition, when the phosphorylated pulp thus obtained was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, and it was confirmed that the pulp had cellulose type I crystals.

Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solids concentration (fibrous cellulose concentration) of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain fine fibrous cellulose dispersion A containing fine fibrous cellulose.

X-ray diffraction confirmed that this fine fibrous cellulose maintained cellulose type I crystals. 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 an AFM was used to extract 100 pieces of fine fibrous cellulose and calculate the number average aspect ratio, which was found to be 300. The amount of phosphoric acid groups (amount of first dissociated acid) measured using the method for measuring the amount of phosphorus oxoacid groups described below was 1.45 mmol/g. The total amount of dissociated acid was 2.45 mol/g.

<Production Example B>
A phosphite pulp was obtained by the same procedure as in Production Example A, except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate to introduce a phosphite group into the cellulose in the pulp.

The infrared absorption spectrum of the obtained phosphorous-containing pulp was measured using FT-IR. As a result, absorption due to P=O of phosphonic acid group, which is a tautomer of phosphorous acid group, was observed around 1210 cm ^-1 , and it was confirmed that phosphorous acid group (phosphonic acid group) was added to the pulp. In addition, when the obtained phosphorous-containing pulp was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, and it was confirmed that the cellulose had type I crystals.

The obtained hypophosphite pulp was treated in a wet pulp mill in the same manner as in Production Example A to obtain a fine fibrous cellulose dispersion B containing fine fibrous cellulose.

X-ray diffraction confirmed that this fine fibrous cellulose maintained cellulose type I crystals. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm. Image analysis using an AFM revealed that 100 pieces of fine fibrous cellulose were extracted and the number average aspect ratio was calculated to be 280. The amount of phosphorous acid groups (amount of first dissociated acid) measured using the method for measuring the amount of phosphorus oxoacid groups described below was 1.51 mmol/g. The total amount of dissociated acid was 1.54 mmol/g.

<Production Example C>
A sulfated pulp was obtained by the same procedure as in Production Example A, except that 38 parts by mass of amidosulfuric acid was used instead of ammonium dihydrogen phosphate.

The obtained sulfated pulp was subjected to infrared absorption spectroscopy using FT-IR. As a result, absorption due to sulfate groups (sulfonic acid groups) was observed around 1220-1260 cm ^-1 , and it was confirmed that sulfate groups (sulfonic acid groups) were added to the pulp. In addition, when the obtained sulfated pulp was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, and it was confirmed that the pulp had cellulose type I crystals.

Ion-exchanged water was added to the obtained sulfated pulp, and the mixture was stirred to prepare a slurry with a solids concentration (fibrous cellulose concentration) of 2% by mass. This slurry was treated six times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion C containing fine fibrous cellulose. In addition, 100 pieces of fine fibrous cellulose were extracted from the image analysis by AFM, and the number average aspect ratio was calculated, and the number average aspect ratio was 280. The amount of sulfate groups (sulfonic acid groups) measured by the method for measuring the amount of sulfur oxo acid groups described below was 1.30 mmol/g.

<Production 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 an alkaline TEMPO oxidation treatment as follows. First, the raw material pulp equivalent to 100 parts by mass of dry mass, 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 aqueous solution of sodium hypochlorite was added to 10 mmol per 1.0 g of pulp to start the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to keep the pH at 10 to 10.5, and the reaction was deemed to have ended when no change in pH was observed.

Then, the obtained TEMPO oxidized pulp was subjected to a washing process. The washing process was carried out by dehydrating the pulp slurry after TEMPO oxidation to obtain a dehydrated sheet, pouring in 5,000 parts by mass of ion-exchanged water, stirring to disperse uniformly, and then repeatedly filtering and dehydrating the sheet. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

The obtained TEMPO oxidized pulp was also analyzed using an X-ray diffraction device, and typical peaks were confirmed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming that it contains cellulose type I crystals.

Ion-exchanged water was added to the obtained TEMPO oxidized pulp to prepare a slurry with a solids concentration (fibrous cellulose concentration) of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion D containing fine fibrous cellulose.

X-ray diffraction confirmed that this fine fibrous cellulose maintained cellulose type I crystals. 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 an AFM was also used to extract 100 pieces of fine fibrous cellulose and calculate the number average aspect ratio, which was found to be 250. The amount of carboxy groups measured by the method for measuring the amount of carboxy groups described below was 1.80 mmol/g.

[Measurement of phosphorus oxoacid group content]
In measuring the amount of phosphorus oxoacid groups (amount of phosphoric acid groups or amount of phosphorous acid groups) of fine fibrous cellulose, ion-exchanged water was first added to the target fine fibrous cellulose to prepare a slurry with a solid content of 0.2% by mass. The obtained fine fibrous cellulose dispersion was treated with an ion-exchange resin, and then titrated with an alkali to measure the amount of phosphorus oxoacid groups.
The treatment with ion exchange resin was carried out by adding 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose dispersion, shaking the mixture for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the resin from the slurry.
In addition, the titration using alkali was performed by measuring the change in the pH value of the slurry while adding 10 μL of 0.1N sodium hydroxide aqueous solution to the fine fibrous cellulose dispersion after the treatment with ion exchange resin every 5 seconds. The titration was performed while blowing nitrogen gas into the slurry 15 minutes before the start of the titration. In this neutralization titration, two points are observed where the increment (differential value of pH with respect to the amount of alkali dropped) is maximum in the curve plotting the measured pH against the amount of alkali added. Of these, the maximum point of the increment obtained first after the addition of alkali is called the first end point, and the maximum point of the increment obtained next is called the second end point (FIG. 1). The amount of alkali required from the start of the titration to the first end point is equal to the amount of first dissociated acid in the slurry used for the titration. In addition, the amount of alkali required from the start of the titration to the second end point is equal to the total amount of dissociated acid in the slurry used for the titration. The amount of alkali (mmol) required from the start of titration to the first end point was divided by the solid content (g) in the slurry to be titrated, and this value was taken as the amount of phosphorus oxoacid groups (mmol/g).

[Measurement of Carboxy Group Amount]
In measuring the amount of carboxy groups in fine fibrous cellulose, ion-exchanged water was first added to the target fine fibrous cellulose to prepare a slurry with a solid content of 0.2% by mass. The resulting fine fibrous cellulose dispersion was treated with an ion-exchange resin, and then titrated with an alkali to measure the amount of carboxy groups.
The treatment with ion exchange resin was carried out by adding 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose dispersion, shaking the mixture for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the resin from the slurry.
The titration using alkali was carried out by adding 50 μL of 0.1 N aqueous sodium hydroxide solution to the fine fibrous cellulose dispersion after the ion exchange resin treatment once every 30 seconds and measuring the change in 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 by the solid content (g) in the slurry to be titrated.

[Measurement of the amount of sulfur oxoacid groups]
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 freeze-dried product was pulverized into a powder form using a hand mixer (Labo Millser 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 pressure heating decomposition using nitric acid in a closed vessel. The samples were then appropriately diluted and the amount of sulfur was measured by ICP-OES. The value calculated by dividing the amount by the bone dry mass of the fine fibrous cellulose used was taken as the amount of sulfur oxoacid groups (unit: mmol/g) of the fine fibrous cellulose.

Example 1
When 100 g of a 3.86 mass% aqueous solution 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, aggregates were generated in the fine fibrous cellulose dispersion. The fine fibrous cellulose dispersion in which the aggregates were generated was filtered under reduced pressure to obtain a fine fibrous cellulose aggregate. The obtained fine fibrous cellulose aggregate was repeatedly washed with ion-exchanged water to remove excess di-n-stearyldimethylammonium chloride and eluted ions contained in the fine fibrous cellulose aggregate, thereby obtaining a fine fibrous cellulose concentrate. The obtained fine fibrous cellulose concentrate was air-dried to obtain a fine fibrous cellulose concentrate A having a solid content concentration of 90 mass%.

Toluene was added to the fine fibrous cellulose concentrate A so that the solids concentration (fibrous cellulose concentration) was 3% by mass to form a suspension. This suspension was then pre-heated in a hot water bath until the temperature of the suspension reached 40°C. The suspension pre-heated to 40°C was treated five times at a pressure of 100 MPa in a high-pressure homogenizer (Beryu-Mini, manufactured by Biryu Co., Ltd.). The liquid temperature after passing through the grinding treatment section was also measured. In this way, a toluene dispersion of the fine fibrous cellulose concentrate A was obtained.

The toluene dispersion obtained above was allowed to stand at 23° C. for 24 hours, and then the viscosity was measured using a Brookfield viscometer (analog viscometer T-LVT, manufactured by BLOOKFIELD). The measurement conditions were 23° C., and the viscosity was measured when rotated at 0.6 rpm or 60 rpm for 3 minutes. The TI value, which is an index of thixotropy, was calculated according to the following formula.
TI value=(viscosity value at 0.6 rpm/viscosity value at 60 rpm)

The toluene dispersion obtained above was sealed in a quartz glass cell for liquids with an optical path length of 10 mm, and the light transmittance at a wavelength of 660 nm was measured using an ultraviolet-visible spectrophotometer (V-770, manufactured by JASCO Corporation). The zero point measurement was performed using ion-exchanged water placed in the same glass cell. In addition, the light transmittance was measured immediately after redispersion in an organic solvent in each of the examples and comparative examples.

Example 2
An organic solvent dispersion was obtained in the same manner as in Example 1, except that fine fibrous cellulose dispersion B was used.

Example 3
An organic solvent dispersion was obtained in the same manner as in Example 1, except that fine fibrous cellulose dispersion C was used.

Example 4
An organic solvent dispersion was obtained in the same manner as in Example 1, except that pre-heating was not carried out before the treatment with the high-pressure homogenizer.

Example 5
An organic solvent dispersion was obtained in the same manner as in Example 1, except that fine fibrous cellulose dispersion D was used.

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

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.

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

The dispersions obtained in the examples were highly viscous and highly transparent, and had improved thixotropy. In Examples 1 to 3, 5, and 6, the viscosity and transparency were further improved by setting the liquid temperature immediately after the high-pressure homogenizer grinding process to 40°C or higher.

Claims (4)

A dispersion containing fibrous cellulose having 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 B-type viscosity of 80 Pa s or more as measured by the following measurement method (A);
Measurement method (A):
The B-type viscosity of the dispersion liquid is measured in accordance with JIS Z 8803 (2011) when the fibrous cellulose concentration of the dispersion liquid is 3 mass % (w/w), the rotation speed is 0.6 rpm, and the temperature is 23°C. The dispersion according to claim 1, which has a light transmittance of 80% or more as measured by the following measurement method (B);
Measurement method (B):
The dispersion liquid is adjusted to a fibrous cellulose concentration of 3 mass % (w/w) and sealed 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. The dispersion according to claim 1 or 2, wherein the fiber width of the fibrous cellulose is 10 nm or less. 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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