JP7593329B2 - Fibrous cellulose, fibrous cellulose dispersion and sheet - Google Patents

Description

The present invention relates to fibrous cellulose, a fibrous cellulose dispersion and a sheet.

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 uses.

When producing fine fibrous cellulose, a slurry containing cellulose raw material is subjected to a defibration process (mechanical treatment). For example, Patent Document 1 discloses a method for producing fine fibers that includes a process of treating the cellulose raw material with an enzyme and a process of defibrating the cellulose raw material after the enzyme treatment. Here, it is considered that the cellulose raw material can be sufficiently finely divided by performing the enzyme treatment, thereby increasing the yield of fine fibers. Furthermore, Patent Document 1 aims to produce fine fibers that are long in fiber length and have a large aspect ratio.

Furthermore, Patent Document 2 discloses fine fibrous cellulose having an average fiber width of 200 nm or less, a degree of polymerization of 50 to 500, and a specified polar group. Here, the study is aimed at obtaining fine fibrous cellulose that is less likely to form aggregates when mixed with an emulsion resin. In the examples of Patent Document 2, a dispersion with a degree of polymerization of 248 to 454 and a viscosity of 108 to 740 at a concentration of 0.5% is obtained.

International Publication No. 2013/176033 JP 2014-34673 A

Because fine fibrous cellulose exhibits an excellent thickening effect in a dispersion, it is sometimes used in paints and cosmetics. However, because fine fibrous cellulose exhibits an excellent thickening effect, it has been difficult to produce a fine fibrous cellulose dispersion of high concentration (e.g., 3% by mass or more). Furthermore, the inventors' investigations have revealed that when attempting to obtain a high-concentration dispersion of fine fibrous cellulose, the fine fibrous cellulose does not disperse uniformly in the dispersion, and in some cases aggregates (lumps) of the fine fibrous cellulose are generated.

Thus, in the prior art, it was difficult to obtain a high-concentration fine fibrous cellulose dispersion, and even more difficult to obtain a fine fibrous cellulose dispersion with excellent uniformity when the concentration was high. Therefore, in order to solve such problems of the prior art, the present inventors have conducted research with the aim of providing a high-concentration fine fibrous cellulose dispersion in which fine fibrous cellulose is uniformly dispersed.

As a result of intensive research to solve the above problems, the present inventors have found that by adjusting the degree of polymerization of fine fibrous cellulose having ionic substituents within a predetermined range and further obtaining fine fibrous cellulose having a viscosity within a predetermined range in an aqueous dispersion at a concentration of 0.5% by mass, it is possible to obtain a high-concentration fine fibrous cellulose dispersion in which the fine fibrous cellulose is uniformly dispersed.
Specifically, the present invention has the following configuration.

[1] A fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent,
The degree of polymerization of the fibrous cellulose is 230 or less,
A fibrous cellulose having a viscosity of less than 108 mPa·s at 23° C. when the fibrous cellulose is dispersed in water at a concentration of 0.5% by mass.
[2] The fibrous cellulose according to [1], wherein when the fibrous cellulose is dispersed in water at a concentration of 6.0% by mass, the viscosity of the aqueous dispersion at 23° C. is 500,000 mPa·s or more and 10,000,000 mPa·s or less.
[3] The fibrous cellulose according to [1] or [2], wherein when the fibrous cellulose is dispersed in water at a concentration of 13.0% by mass, the viscosity of the aqueous dispersion at 23° C. is 1,000,000 mPa·s or more and 50,000,000 mPa·s or less.
[4] The fibrous cellulose according to any one of [1] to [3], wherein the ionic substituent 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.
[5] A fibrous cellulose dispersion comprising the fibrous cellulose according to any one of [1] to [4].
[6] The fibrous cellulose dispersion according to [5], wherein the concentration of the fibrous cellulose is 3.0% by mass or more.
[7] A sheet comprising the fibrous cellulose according to any one of [1] to [4].

According to the present invention, it is possible to obtain a high-concentration fine fibrous cellulose dispersion in which the fine fibrous cellulose is uniformly dispersed.

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 following description of the components may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments.

(fibrous cellulose)
The fibrous cellulose of this embodiment is a fibrous cellulose having a fiber width of 1000 nm or less, an ionic substituent, a degree of polymerization of the fibrous cellulose of 230 or less, and a viscosity of the aqueous dispersion of the fibrous cellulose at 23° C. in a concentration of 0.5% by mass is less than 108 mPa·s. When the fibrous cellulose is dispersed in water at a concentration of 0.5% by mass, the viscosity of the aqueous dispersion at 23° C. is preferably 107 mPa·s or less, more preferably 100 mPa·s or less, and even more preferably 95 mPa·s 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 viscosity of the fine fibrous cellulose dispersion (aqueous dispersion) is measured using a Brookfield viscometer at 23°C with a rotation speed of 3 rpm, and is the viscosity value 3 minutes after the start of measurement. As a Brookfield viscometer, for example, an analog viscometer T-LVT manufactured by BLOOKFIELD can be used. When the fine fibrous cellulose is diluted to a 0.5% by mass aqueous dispersion, it is stirred in a disperser at 4000 rpm for 3 minutes, and then the fine fibrous cellulose dispersion is degassed using a rotation-revolution type super mixer (ARE-250 manufactured by Thinky Corporation).

Furthermore, when the fine fibrous cellulose is made into an aqueous dispersion having a concentration of 6.0% by mass, the viscosity of the aqueous dispersion at 23°C is preferably 500,000 mPa·s or more, more preferably 700,000 mPa·s or more, even more preferably 1,000,000 mPa·s or more, even more preferably 1,500,000 mPa·s or more, and particularly preferably 1,800,000 mPa·s or more. When the fine fibrous cellulose is dispersed in water at a concentration of 6.0% by mass, the viscosity of the aqueous dispersion at 23° C. is preferably 10,000,000 mPa·s or less, more preferably 7,500,000 mPa·s or less, even more preferably 4,000,000 mPa·s or less, even more preferably 3,500,000 mPa·s or less, even more preferably 3,100,000 mPa·s or less, and particularly preferably 3,000,000 mPa·s or less. When the fine fibrous cellulose is dispersed in water at a concentration of 13.0% by mass, the viscosity of the aqueous dispersion at 23° C. is preferably 1,000,000 mPa·s or more, more preferably 3,000,000 mPa·s or more, and particularly preferably 5,000,000 mPa·s or more. In addition, when the fine fibrous cellulose is dispersed in water at a concentration of 13.0% by mass, the viscosity of the aqueous dispersion at 23° C. is preferably 50,000,000 mPa·s or less, more preferably 30,000,000 mPa·s or less, and particularly preferably less than 18,000,000 mPa·s. The viscosity of the aqueous dispersion at a concentration of 6.0% by mass or the aqueous dispersion at a concentration of 13.0% by mass is measured using a Brookfield viscometer at 23° C. with a rotation speed of 0.3 rpm, and is the viscosity value 3 minutes after the start of measurement. As the Brookfield viscometer, for example, an analog viscometer T-LVT or a digital viscometer DV2T manufactured by Brookfield can be used. When fine fibrous cellulose is prepared into an aqueous dispersion of 6.0% by mass or 13.0% by mass, the mixture is stirred for 3 minutes at 4000 rpm in a disperser, and then the fine fibrous cellulose dispersion is defoamed in a planetary centrifugal super mixer (ARE-250, manufactured by Thinky Corporation). When preparing an aqueous dispersion of 6.0% by mass or 13.0% by mass, an aqueous dispersion of 6.0% by mass or 13.0% by mass may be obtained by obtaining an aqueous dispersion having a concentration higher than 6.0% by mass or 13.0% by mass, and diluting the aqueous dispersion with water to obtain an aqueous dispersion of 6.0% by mass or 13.0% by mass.

In the prior art, it was difficult to obtain an aqueous dispersion with a high concentration of 3.0% by mass or more, and it was impossible to obtain an aqueous dispersion with a high concentration of 6.0% by mass or 13.0% by mass. Even when the fine fibrous cellulose dispersion obtained in the prior art was concentrated to obtain an aqueous dispersion with a concentration of 6.0% by mass or 13.0% by mass, the aqueous dispersion became gel-like or granular matter (fiber aggregates) was generated in the aqueous dispersion, making it impossible to obtain a uniform aqueous dispersion. Naturally, it was impossible to measure the viscosity of such a high-concentration aqueous dispersion. For example, when an aqueous dispersion with a concentration of 0.5 to 2.0% by mass is subjected to a defibration process and then concentrated with a heat treatment or an evaporator, a film-like matter is generated on the wall surface during the concentration process, making it impossible to obtain a dispersion with a uniform dispersion of 6.0% by mass or more in which fine fibrous cellulose is dispersed. For this reason, even if the viscosity of an aqueous dispersion with a concentration of 0.5 to 2.0 mass % is equivalent to the viscosity of the aqueous dispersion with the same concentration in this embodiment, it is impossible to obtain an aqueous dispersion with a high concentration such as 6.0 mass % or 13.0 mass %, and it is not possible to obtain a dispersion having a viscosity within the above range in an aqueous dispersion with a high concentration such as 6.0 mass % or 13.0 mass %.

On the other hand, in this embodiment, the degree of polymerization of the fine fibrous cellulose is set within the above range, and further, the viscosity of the aqueous dispersion at 23°C when the aqueous dispersion is made into a 0.5% by mass concentration is set within the above range, thereby successfully obtaining a dispersion of fine fibrous cellulose with high concentration and uniform dispersion of fine fibrous cellulose. In addition, in this embodiment, the dispersion of phosphorylated pulp to be subjected to the defibration treatment is made high concentration, and the defibration treatment is performed on such a high concentration pulp dispersion, and if necessary, a low molecular weight treatment is also performed in combination as described below. This makes it possible to measure the viscosity of an aqueous dispersion containing 3.0% or more by mass of fine fibrous cellulose (for example, an aqueous dispersion of 6.0% by mass or 13.0% by mass), and thus it is possible to successfully obtain an aqueous dispersion with a relatively low viscosity for a high concentration dispersion.

In this manner, in this embodiment, a dispersion liquid containing a high concentration of fine fibrous cellulose can be obtained. This allows for a significant reduction in the storage and transportation costs of the dispersion liquid. Furthermore, in this embodiment, the production efficiency of the fine fibrous cellulose dispersion liquid can also be increased.

In this embodiment, the degree of polymerization of the fibrous cellulose may be 230 or less, preferably 225 or less, more preferably 220 or less, even more preferably 215 or less, and particularly preferably 210 or less. The degree of polymerization of the fibrous cellulose is preferably 100 or more, more preferably 150 or more, even more preferably 160 or more, and particularly preferably 170 or more.

The degree of polymerization of the fine fibrous cellulose is a value calculated from the pulp viscosity measured according to Tappi T 230. Specifically, the fine fibrous cellulose to be measured is dispersed in an aqueous copper ethylenediamine solution to measure the viscosity (referred to as η1), and the blank viscosity (referred to as η0) is measured using only the dispersion medium, and then the specific viscosity (ηsp) and intrinsic viscosity ([η]) are measured according to the following formulas.
ηsp=(η1/η0)-1
[η]=ηsp/(c(1+0.28×ηsp))
Here, c in the formula represents the concentration of the fine fibrous cellulose at the time of viscosity measurement.
Furthermore, the degree of polymerization (DP) is calculated from the following formula.
DP=1.75×[η]
Since this degree of polymerization is an average degree of polymerization measured by a viscosity method, it is sometimes called the "viscosity average degree of polymerization."

In this embodiment, the degree of polymerization of the fine fibrous cellulose is set within the above range, and further, by obtaining fine fibrous cellulose having a viscosity of 0.5% by mass in aqueous dispersion at 23°C within the above range, it is possible to obtain a high-concentration fine fibrous cellulose dispersion in which the fine fibrous cellulose is uniformly dispersed. Such a high-concentration fine fibrous cellulose dispersion is preferably used for various applications. For example, it is preferably used for sheet formation, reinforcing material, and coating applications, and is particularly preferably used for applications requiring transparency.

In this embodiment, a high concentration of fine fibrous cellulose dispersion can be obtained. For example, the concentration of the fine fibrous cellulose dispersion is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, even more preferably 5.0% by mass or more, even more preferably 6.0% by mass or more, and particularly preferably 10.0% by mass or more. In this specification, the concentration of the fine fibrous cellulose dispersion refers to the content of fine fibrous cellulose relative to the total mass of the fine fibrous cellulose dispersion. In addition, in this specification, a dispersion containing 3.0% by mass or more of fine fibrous cellulose relative to the total mass of the dispersion (i.e., a dispersion having a fine fibrous cellulose dispersion concentration of 3.0% by mass or more) is referred to as a high concentration fine fibrous cellulose dispersion.

In the high-concentration fine fibrous cellulose dispersion obtained by dispersing the fine fibrous cellulose of this embodiment in a solvent such as water, the fine fibrous cellulose is uniformly dispersed. Therefore, the high-concentration fine fibrous cellulose dispersion is highly transparent. For example, when fine fibrous cellulose is dispersed in a solvent such as water to obtain a high-concentration dispersion of 6.0 mass%, the fine fibrous cellulose is dispersed in the dispersion, so that the fine fibrous cellulose cannot be visually confirmed. In such a case, it can be evaluated that the fine fibrous cellulose is uniformly dispersed in the high-concentration fine fibrous cellulose dispersion. In addition, in such a case, the high-concentration fine fibrous cellulose dispersion is not clouded, but is translucent or transparent.

The fibrous cellulose of this embodiment is fine fibrous cellulose having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose is more preferably 100 nm or less, and even more preferably 8 nm or less.

The fiber width of fibrous cellulose can be measured, for example, by observation under an electron microscope. The average fiber width of fibrous cellulose is, for example, 1000 nm or less. The average fiber width of 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. By making the average fiber width of fibrous cellulose 2 nm or more, it is possible to suppress dissolution of cellulose molecules in water, and to more easily realize the effect of improving strength, rigidity, and dimensional stability due to fibrous cellulose. In addition, the fibrous cellulose is, for example, monofilament cellulose.

The average 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. If the sample contains wide fibers, an SEM image of the surface cast onto glass may be observed. Next, the electron microscope image is observed 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 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 region 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 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 is 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 fibrous cellulose is not particularly limited, but is preferably 20 to 10,000, more preferably 50 to 1,000. In this specification, fibrous cellulose (fine fibrous cellulose) with a fiber width of 1,000 nm or less is cellulose nanofiber (CNF), and fibrous cellulose (fine fibrous cellulose) does not include cellulose nanocrystal (CNC). The axial ratio (fiber length/fiber width) of cellulose nanocrystal (CNC) is usually about 10 to 30. In addition, by setting the axial ratio of fibrous cellulose to the above lower limit or more, it is preferable in that, for example, when handling fibrous cellulose as an aqueous dispersion, dilution and other handling are made easier.

The fibrous cellulose in this embodiment has, for example, both crystalline and non-crystalline regions. Fine fibrous cellulose having both crystalline and non-crystalline regions and an axial ratio within the above range is realized by the method for producing fine fibrous cellulose described below.

The fibrous cellulose of this embodiment has an ionic substituent. The ionic substituent may include, for example, either one or both of an anionic group and a cationic group. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. In addition, it is preferable that the ionic substituent is a group that is linked to the fibrous cellulose through an ester bond. In this case, the ester bond is formed by dehydration condensation of the fibrous cellulose and the compound that becomes the ionic substituent.

The anionic group as the ionic substituent is preferably at least one selected from, for example, a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group (sometimes simply referred to as a phosphorus oxo acid group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), and a sulfur oxo acid group or a substituent derived from a sulfur oxo acid group (sometimes simply referred to as a sulfur oxo acid group), more preferably at least one selected from a phosphorus oxo acid group and a carboxy group, and particularly preferably a phosphorus oxo acid group. By introducing a phosphorus oxo acid group into fibrous cellulose, the transparency of the dispersion can be more effectively increased when a high-concentration dispersion is prepared. In addition, by introducing a phosphorus oxo acid group into fibrous cellulose, the salt resistance of the fibrous cellulose can also be improved.

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 derivative thereof. 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, examples of the derivative group in R include, but are not limited to, functional groups 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 phosphonium 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 phosphonium 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 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 phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. 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 amount of ionic substituent introduced into fibrous cellulose is, for example, preferably 0.10 mmol/g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.40 mmol/g or more, even more preferably 0.60 mmol/g or more, even more preferably 0.90 mmol/g or more, and particularly preferably 1.00 mmol/g or more. In particular, when the amount of ionic substituent introduced into fibrous cellulose is 1.00 mmol/g or more, the load during defibration can be reduced, and the transparency of the resulting fine fibrous cellulose dispersion or sheet is further increased. In addition, when the amount of ionic substituent introduced into fibrous cellulose is 1.00 mmol/g or more, the salt resistance of fibrous cellulose can also be improved. In addition, the amount of ionic substituent introduced into the fibrous cellulose is preferably 5.20 mmol/g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol/g or less, even more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, even more preferably 2.00 mmol/g or less, and particularly preferably 1.50 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 ionic substituent is a hydrogen ion (H ⁺ ). By setting the amount of ionic substituent introduced within the above range, it is possible to easily fine the fiber raw material and to increase the stability of the fibrous cellulose. In addition, by setting the amount of ionic substituent introduced within the above range, it is easy to obtain a highly concentrated and highly transparent fine fibrous cellulose dispersion.

The amount of ionic substituents 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 a slurry containing the obtained 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 alkali added, 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 alkali added is plotted. In this neutralization titration, two points are confirmed in the curve plotting the measured pH against the amount of alkali added, where the increment (differential value of pH against the amount of alkali added) 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 ionic substituent and the pH. The amount of carboxy group 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, one point where the increment (differential value of pH against the amount of added alkali) is maximum is confirmed in the curve plotting the measured pH against the amount of added alkali, 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 ionic substituents by titration, if too much sodium hydroxide solution is added or if the titration interval is too short, the amount of ionic substituents 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 influence 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 wet ashing a slurry containing fibrous cellulose, diluting the sample at an appropriate ratio, and measuring the amount of sulfur. Specifically, fibrous cellulose is wet ashed using perchloric acid and concentrated nitric acid, then diluted at an appropriate ratio and the amount of sulfur is measured by ICP emission spectrometry. The value divided by the bone dry mass of the fibrous cellulose tested is taken as the amount of sulfur oxoacid groups (unit: mmol/g).

The above describes the fibrous cellulose and the dispersion containing the fibrous cellulose according to the present embodiment. In addition, as another embodiment, the present specification also discloses a fine fibrous cellulose-containing dispersion having a fiber width of 1000 nm or less and an ionic substituent, in which the content of the fine fibrous cellulose is 5.0% by mass or more and 14.0% by mass or less with respect to the total mass of the dispersion, and the polymerization degree of the fine fibrous cellulose is 160 to 205. The viscosity of the fine fibrous cellulose-containing dispersion measured using a B-type viscometer is particularly preferably 1800 x 10 ³ mPa·s or more and 13000 x 10 ³ mPa·s or less. The ionic substituent of the fine fibrous cellulose is particularly preferably a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group (especially a phosphoric acid group). In addition, the amount of the ionic substituent introduced into the fine fibrous cellulose is particularly preferably 0.90 mmol/g or more and 2.00 mmol/g or less. The rest of the description is the same as that of the fibrous cellulose and the dispersion liquid containing the fibrous cellulose according to the present embodiment described above, and therefore will not be repeated here.

(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, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), hardwood dissolving pulp (LDKP, LDSP), softwood dissolving pulp (NDKP, NDSP), soda pulp (AP), unbleached kraft pulp (UKP) and oxygen bleached kraft pulp (OKP), semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP), mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. Examples of non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, and bagasse. Examples of deinked pulps include, but are not limited to, deinked pulp made from waste paper. The pulps of this embodiment may be used alone or in combination of two or more. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of availability. Among wood pulps, chemical pulps are 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 from the viewpoint of obtaining long-fiber fine fibrous cellulose with a large axial ratio due to a small decomposition of cellulose in the pulp. Among them, pulps derived from coniferous trees are preferably used because they have good defibration properties during defibration treatment described below and have improved transparency when made into a dispersion.

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 Oxo Acid Group Introduction Step>
The manufacturing process of fine fibrous cellulose includes an ionic substituent introduction step. An example of the ionic substituent 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, because 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. Compound A and compound B can be 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, because 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. In addition, 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, respectively, 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 its salt, phosphorous acid or its salt, dehydrated condensed phosphoric acid or its salt, 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 phosphate 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, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, or 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.

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

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, various devices having heat media can be used for the heat treatment, such as 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, and 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 material while kneading or stirring the fiber raw material and compound A in 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 is attracted to the water molecules by surface tension and is prevented from 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, moisture held by the slurry and moisture generated in the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose, etc., in the fiber raw material. Examples of such heating devices include ovens that use a blowing system. By constantly discharging moisture from 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 time for the heat treatment is preferably from 1 second to 300 minutes after the moisture is 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 is preferably 0.10 mmol/g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.50 mmol/g or more, even more preferably 0.60 mmol/g or more, even more preferably 0.90 mmol/g or more, and particularly preferably 1.00 mmol/g or more. The amount of phosphorus oxo acid groups introduced into the fiber raw material is preferably 5.20 mmol/g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol/g or less, even more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, even more preferably 2.00 mmol/g or less, and particularly preferably 1.50 mmol/g or less. By setting the amount of phosphorus oxo acid groups introduced within the above range, it is possible to easily fine the fiber raw material and increase the stability of the fine fibrous cellulose. In addition, by setting the amount of phosphorus oxoacid groups introduced within the above range, a highly concentrated and highly transparent fine fibrous cellulose dispersion liquid can be easily obtained. In addition, by setting the amount of phosphorus oxoacid groups introduced to 1.00 mmol/g or more, the salt tolerance of the fibrous cellulose can be improved.

<Carboxy Group Introduction Step>
The process for producing fine fibrous cellulose may include, for example, a carboxyl group introduction step as an ionic substituent 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. 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, the 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 the acid anhydrides of compounds having a group derived from carboxylic acid include, but are not limited to, the 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 a sodium phosphate buffer solution (pH = 6.8). By further adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. TEMPO oxidation treatment may also 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 co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material.

The amount of carboxyl groups introduced into the fibrous cellulose varies depending on the type of the substituent. For example, when the carboxyl groups are introduced by TEMPO oxidation, the amount is preferably 0.10 mmol/g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.40 mmol/g or more, even more preferably 0.60 mmol/g or more, even more preferably 0.90 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, even more preferably 2.00 mmol/g or less, and particularly preferably 1.50 mmol/g or less. In addition, when the substituent is a carboxymethyl group, the amount may be 5.8 mmol/g or less per 1 g (mass) of fine fibrous cellulose. By setting the amount of carboxyl groups introduced within the above range, it is possible to easily refine the fiber raw material and increase the stability of the fibrous cellulose. Furthermore, by adjusting the amount of carboxyl groups introduced to fall within the above range, a highly concentrated and highly transparent fine fibrous cellulose dispersion liquid can be easily obtained.

<Sulfur oxoacid group introduction step>
The process for producing fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step, in which a hydroxyl group in a fiber raw material containing cellulose reacts with a 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 of 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-treating temperature that can efficiently introduce sulfur oxoacid groups while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat-treating temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat-treating temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

In the heat treatment process, 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 sulfur oxoacid and the aqueous solution containing urea and/or urea derivatives added, but is preferably, for example, 10 seconds or more and 10,000 seconds or less. 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.

The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 0.05 mmol/g or more, more preferably 0.10 mmol/g or more, even more preferably 0.20 mmol/g or more, even more preferably 0.40 mmol/g or more, even more preferably 0.60 mmol/g or more, even more preferably 0.90 mmol/g or more, and particularly preferably 1.00 mmol/g or more. The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 5.00 mmol/g or less, more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, even more preferably 2.00 mmol/g or less, and particularly preferably 1.50 mmol/g or less. By setting the amount of sulfur oxoacid groups introduced within the above range, it is possible to easily refine the fiber raw material and increase the stability of the fibrous cellulose. In addition, by setting the amount of sulfur oxoacid groups introduced within the above range, it is easy to obtain a highly concentrated and highly transparent fine fibrous cellulose dispersion.

<Cleaning process>
In the method for producing fine fibrous cellulose in this embodiment, a washing step can be carried out on the ionic substituent-introduced fiber as necessary. The washing step is carried out, for example, by washing the ionic substituent-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 carried out on the fiber raw material between the step of introducing an ionic substituent and the step of defibrating the fiber, which will be described later. The method of the alkali treatment is not particularly limited, but may be, for example, a method of immersing the fiber having an ionic substituent introduced therein 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 exemplified by 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 ionic substituent-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 ionic substituent-introduced fiber.

In order to reduce the amount of alkaline solution used in the alkaline treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkaline-treated ionic substituent-introduced fiber 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 an ionic substituent and the defibration treatment step described later. For example, the step of introducing an ionic substituent, the acid treatment, the alkali treatment, and the 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 treatment>
The ionic substituent-introduced fibers are defibrated (mechanically) in the 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, it is preferable to dilute the ionic substituent-introduced fiber with a dispersion medium to make it into a slurry state. As the dispersion medium, one or more types selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but for example, alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, etc. are preferable. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol, etc. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, glycerin, etc. Examples of ketones include acetone, methyl ethyl ketone (MEK), etc. Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n-butyl ether, propylene glycol monomethyl ether, etc. Examples of esters include ethyl acetate, butyl acetate, etc. Aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

The concentration of the cellulose fibers during the defibration process can be set appropriately, but in this embodiment, the concentration of the cellulose fibers during the defibration process is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, even more preferably 5.0% by mass or more, and particularly preferably 6.0% by mass or more. The upper limit of the concentration of the cellulose fibers during the defibration process is not particularly limited, but may be, for example, 20.0% by mass. In this embodiment, by setting the concentration of the cellulose fibers during the defibration process within the above range, it is possible to uniformly disperse the fine fibrous cellulose and obtain a highly transparent high-concentration dispersion. In addition, by setting the concentration of the cellulose fibers during the defibration process within the above range, it is possible to increase the production efficiency of the fine fibrous cellulose, and as a result, it is possible to efficiently produce processed products such as dispersions and sheets containing fine fibrous cellulose. In addition, by setting the concentration of the cellulose fibers during the defibration process within the above range, it is possible to obtain a high-concentration dispersion, and it is also possible to reduce costs during transportation and storage.

In addition, the slurry obtained by dispersing the ionic substituent-introduced fiber in a dispersion medium may contain solid matters other than the ionic substituent-introduced fiber, such as urea having hydrogen bonding properties.

<Low molecular weight processing>
The method for producing fine fibrous cellulose of the present embodiment preferably includes a step of performing a low molecular weight treatment in addition to the steps described above. Specifically, as described above, it is preferable to include a step of performing a defibration treatment on cellulose fibers that have been appropriately treated to obtain fibrous cellulose having a fiber width of 1000 nm or less, and a step of performing a low molecular weight treatment on the fibrous cellulose. That is, the method for producing fine fibrous cellulose of the present embodiment preferably includes, for example, a step of performing a low molecular weight treatment on cellulose fibers after performing a defibration treatment. Note that the low molecular weight treatment may be performed before the defibration treatment step, and for example, the low molecular weight treatment may be performed before the defibration treatment, and then the low molecular weight treatment may be performed after the defibration treatment. In addition, the low molecular weight treatment may be performed after the defibration treatment, and then the low molecular weight treatment may be performed again after the defibration treatment. Among these, it is preferable to perform a low molecular weight treatment after the defibration treatment in order to perform the low molecular weight treatment more effectively.

In this specification, the process of performing the low molecular weight treatment is, for example, a process of reducing the degree of polymerization of fine fibrous cellulose so that the viscosity of an aqueous dispersion at 23°C becomes 100 mPa·s or less when the fine fibrous cellulose is made into an aqueous dispersion with a concentration of 0.5% by mass. Specifically, the process of performing the low molecular weight treatment is preferably a process of reducing the degree of polymerization of fibrous cellulose having a fiber width of 1000 nm or less to 230 or less.

Examples of processes for carrying out low molecular weight treatment include an ozone treatment process, an enzyme treatment process, an acid treatment process, and a subcritical water treatment process. The process for carrying out low molecular weight treatment is preferably at least one selected from an ozone treatment process, an enzyme treatment process, an acid treatment process, and a subcritical water treatment process, and is particularly preferably at least one selected from an ozone treatment process and an enzyme treatment process.

In the ozone treatment step, ozone is added to the fine fibrous cellulose dispersion (slurry). When adding ozone, it is preferable to add it as an ozone/oxygen mixed gas, for example. In this case, the ozone addition rate per 1 g of fine fibrous cellulose contained in the fine fibrous cellulose dispersion (slurry) is preferably 1.0×10 ⁻⁴ g or more, more preferably 1.0×10 ⁻³ g or more, and even more preferably 1.0×10 ⁻² g or more. It is preferable that the ozone addition rate per 1 g of fine fibrous cellulose is 1.0×10 ¹ g or less. After adding ozone to the fine fibrous cellulose dispersion (slurry), stirring is performed under conditions of 10° C. to 50° C. for 10 seconds to 10 minutes, and then it is preferably left to stand for 1 minute to 100 minutes.

In the enzyme treatment process, an enzyme is added to the fine fibrous cellulose dispersion (slurry). The enzyme used in this process is preferably a cellulase enzyme. Cellulase enzymes are classified into the carbohydrate hydrolase family based on the higher-order structure of the catalytic domain that has the function of hydrolyzing cellulose. Cellulase enzymes are broadly classified into endo-glucanases and cellobiohydrolases based on their cellulose decomposition properties. Endo-glucanases have high hydrolysis properties for the amorphous part of cellulose, soluble cellooligosaccharides, and cellulose derivatives such as carboxymethylcellulose, and randomly cut the molecular chains from the inside to reduce the degree of polymerization. In contrast, cellobiohydrolases decompose the crystalline part of cellulose to give cellobiose. Cellobiohydrolases also hydrolyze the ends of cellulose molecules and are also called exo- or processive enzymes. The enzyme used in the enzyme treatment step is not particularly limited, but it is preferable to use an endo-glucanase.

In the enzyme treatment step, it is preferable to add the enzyme so that the enzyme activity is 0.1 nkat or more per 1 g of fine fibrous cellulose, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. It is also preferable to add the enzyme so that the enzyme activity is 100,000 nkat or less per 1 g of fine fibrous cellulose, more preferably 50,000 nkat or less, and even more preferably 10,000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to treat it under conditions of 0°C or more and less than 80°C for 1 minute to 100 hours, and then to inactivate the enzyme by placing it under conditions of 80°C or more.

The acid treatment step is, for example, a step of mixing with sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, boric acid, sulfonic acid (e.g., methanesulfonic acid), etc. Among them, the acid treatment step is preferably a step of mixing with hypochlorous acid (hypochlorous acid treatment step). In the hypochlorous acid treatment step, sodium hypochlorite can also be used in the fine fibrous cellulose dispersion (slurry). The addition rate of sodium hypochlorite is preferably 1.0×10 ⁻⁴ g or more per 1 g of fine fibrous cellulose, more preferably 1.0×10 ⁻³ g or more, even more preferably 1.0×10 ⁻² g or more, and particularly preferably 1.0×10 ⁻¹ g or more. In addition, the addition rate of sodium hypochlorite is preferably 1.0×10 ² g or less per 1 g of fine fibrous cellulose. After sodium hypochlorite is added to the fine fibrous cellulose dispersion (slurry), it is preferable to carry out stirring under conditions of 10° C. or higher and 50° C. or lower for 1 minute or longer and 10 hours or shorter.

In the subcritical water treatment process, the fine fibrous cellulose dispersion (slurry) is subjected to high temperature and high pressure treatment to bring it into a subcritical state. The fine fibrous cellulose is hydrolyzed in the subcritical state. Specifically, after the fine fibrous cellulose dispersion (slurry) is placed in a reaction vessel, the temperature is raised to 150°C to 500°C, preferably 150°C to 350°C, and the pressure in the reaction vessel is increased to 10 MPa to 80 MPa, preferably 10 MPa to 20 MPa. The heating and pressurizing time in this case is preferably 0.1 seconds to 100 seconds, more preferably 3 seconds to 50 seconds.

It is preferable to further provide a defibration process after the low molecular weight processing step. In particular, it is preferable to provide a defibration process before and after the low molecular weight processing step. In this case, the defibration process can be exemplified by the same processes as those described above, and in particular, it is preferable to use a high pressure homogenizer or ultra-high pressure homogenizer in the defibration process after the low molecular weight processing step.

The present embodiment may relate to a method for producing fine fibrous cellulose, which includes at least one step each of a step of defibrating cellulose fibers having an ionic substituent and a step of low molecular weight processing. The method for producing fine fibrous cellulose includes at least one step each of a step of defibrating cellulose fibers having an ionic substituent and a step of low molecular weight processing, so that the concentration of cellulose fibers during defibration processing can be further increased. This makes it possible to efficiently obtain a high concentration fine fibrous cellulose dispersion. In this case, the method for producing fine fibrous cellulose may include a defibration processing step, a low molecular weight processing step, and a defibration processing step in this order, or may include a low molecular weight processing step, a defibration processing step, a low molecular weight processing step, and a defibration processing step in this order. It is preferable that an ionic substituent introduction step, a washing step, an alkali treatment step, or the like, as described above, be provided before the first defibration processing step or the low molecular weight processing step. In such a method for producing fine fibrous cellulose, the molecular weight reduction treatment step is preferably at least one selected from an ozone treatment step, an enzyme treatment step, an acid treatment step, and a subcritical water treatment step, and is particularly preferably at least one selected from an ozone treatment step and an enzyme treatment step.

(Fibrous Cellulose Dispersion)
This embodiment may be an invention related to a fibrous cellulose dispersion containing the above-mentioned fine fibrous cellulose. The fibrous cellulose dispersion is preferably a fibrous cellulose dispersion (also called a fine fibrous cellulose-containing dispersion, a fine fibrous cellulose-containing slurry, or a slurry) obtained by dispersing fine fibrous cellulose in a solvent containing water, and more preferably an aqueous fibrous cellulose dispersion obtained by dispersing fine fibrous cellulose in a solvent mainly composed of water.

The content of fine fibrous cellulose in the fibrous cellulose dispersion (concentration of fine fibrous cellulose) is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, even more preferably 5.0% by mass or more, and particularly preferably 6.0% by mass or more, based on the total mass of the fibrous cellulose dispersion. The content of fine fibrous cellulose (concentration of fine fibrous cellulose) is preferably 30.0% by mass or less, more preferably 20.0% by mass or less, based on the total mass of the fibrous cellulose dispersion.

When the fibrous cellulose dispersion is a fibrous cellulose dispersion having a fine fibrous cellulose concentration of 0.5% by mass, the viscosity of the dispersion at 23°C may be less than 108 mPa·s, preferably 100 mPa·s or less, and more preferably 95 mPa·s or less. The viscosity of the fine fibrous cellulose dispersion is measured using a Brookfield viscometer at 23°C and a rotation speed of 3 rpm, and is the viscosity value 3 minutes after the start of measurement. As the Brookfield viscometer, for example, an analog viscometer T-LVT manufactured by BLOOKFIELD can be used. When preparing a fibrous cellulose dispersion having a concentration of 0.5% by mass of fine fibrous cellulose, the dispersion is stirred at 4000 rpm for 3 minutes in a disperser, and then degassed using a revolution-type super mixer (ARE-250 manufactured by Thinky Corporation).

When the fine fibrous cellulose is dispersed in water at a concentration of 6.0% by mass, the viscosity of the aqueous dispersion at 23°C is preferably 500,000 mPa·s or more, more preferably 700,000 mPa·s or more, and particularly preferably 1,000,000 mPa·s or more. When the fine fibrous cellulose is dispersed in water at a concentration of 6.0% by mass, the viscosity of the aqueous dispersion at 23°C is preferably 10,000,000 mPa·s or less, more preferably 7,500,000 mPa·s or less, and particularly preferably 4,000,000 mPa·s or less. In addition, when the fine fibrous cellulose is made into an aqueous dispersion of 13.0% by mass, the viscosity of the aqueous dispersion at 23° C. is preferably 1,000,000 mPa·s or more, more preferably 3,000,000 mPa·s or more, and particularly preferably 5,000,000 mPa·s or more. In addition, when the fine fibrous cellulose is made into an aqueous dispersion of 13.0% by mass, the viscosity of the aqueous dispersion at 23° C. is preferably 50,000,000 mPa·s or less, more preferably 30,000,000 mPa·s or less, and particularly preferably less than 18,000,000 mPa·s. The viscosity of the aqueous dispersion of 6.0% by mass or the aqueous dispersion of 13.0% by mass is measured using a B-type viscometer at 23° C. with a rotation speed of 0.3 rpm, and is the viscosity value 3 minutes after the start of measurement. As the B-type viscometer, for example, an analog viscometer T-LVT or a digital viscometer DV2T manufactured by BLOOKFIELD Co., Ltd. can be used. When fine fibrous cellulose is prepared into an aqueous dispersion of 6.0% by mass or 13.0% by mass, the mixture is stirred for 3 minutes at 4000 rpm in a disperser, and then the fine fibrous cellulose dispersion is degassed with a rotation-revolution type super mixer (ARE-250 manufactured by Thinky Corporation). When preparing an aqueous dispersion of 6.0% by mass or 13.0% by mass, an aqueous dispersion of 6.0% by mass or 13.0% by mass may be obtained by obtaining an aqueous dispersion of a concentration higher than 6.0% by mass or 13.0% by mass, and diluting the aqueous dispersion with water to obtain an aqueous dispersion of 6.0% by mass or 13.0% by mass.

When the fibrous cellulose dispersion is a fibrous cellulose dispersion having a fine fibrous cellulose concentration of 0.2% by mass, the haze of the dispersion is preferably 80% or less, more preferably 60% or less, even more preferably 40% or less, even more preferably 30% or less, even more preferably 15% or less, and particularly preferably 5% or less. The haze of the dispersion in the above range means that the transparency of the fibrous cellulose dispersion is high and the dispersibility of the fine fibrous cellulose is good. Here, the haze of the fine fibrous cellulose dispersion (fine fibrous cellulose concentration 0.2% by mass) is measured by putting the fibrous cellulose dispersion in a liquid glass cell (manufactured by Fujiwara Seisakusho, MG-40, reverse light path) with an optical path length of 1 cm and using a haze meter (manufactured by Murakami Color Research Laboratory, HM-150) in accordance with JIS K 7136:2000. The dispersion to be measured is allowed to stand for 24 hours in an environment of 23° C. and a relative humidity of 50% prior to the measurement. The zero point measurement for haze measurement is performed using ion-exchanged water placed in the same glass cell.

The fibrous cellulose dispersion may contain other additives in addition to the solvent containing water and the fine fibrous cellulose. Examples of other additives include defoamers, lubricants, UV absorbers, dyes, pigments, stabilizers, surfactants, and preservatives (e.g., phenoxyethanol). The fibrous cellulose dispersion may also contain optional components such as hydrophilic polymers, hydrophilic low-molecular weight compounds, and organic ions.

The hydrophilic polymer is preferably a hydrophilic oxygen-containing organic compound (excluding the above-mentioned cellulose fibers), and examples of the oxygen-containing organic compound include polyethylene glycol, polyethylene oxide, casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (acetoacetylated polyvinyl alcohol, etc.), polyethylene oxide, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates, acrylic acid alkyl ester copolymers, urethane copolymers, cellulose derivatives (hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose, etc.), etc.

The hydrophilic low molecular weight compound is preferably a hydrophilic oxygen-containing organic compound, more preferably a polyhydric alcohol. Examples of polyhydric alcohols include glycerin, sorbitol, and ethylene glycol.

Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of tetraalkylammonium ions include tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, tetrahexylammonium ion, tetraheptylammonium ion, tributylmethylammonium ion, lauryltrimethylammonium ion, cetyltrimethylammonium ion, stearyltrimethylammonium ion, octyldimethylethylammonium ion, lauryldimethylethylammonium ion, didecyldimethylammonium ion, lauryldimethylbenzylammonium ion, and tributylbenzylammonium ion. Examples of tetraalkylphosphonium ions include tetramethylphosphonium ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion, and lauryltrimethylphosphonium ion. Examples of tetrapropylonium ion and tetrabutylonium ion include tetra n-propylonium ion and tetra n-butylonium ion, respectively.

(Application)
The fine fibrous cellulose of this embodiment can be made into a high-concentration dispersion. Therefore, it is particularly preferably used in applications where it is desired to add fine fibrous cellulose at a high concentration. For example, the fine fibrous cellulose of this embodiment 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, medicines, etc. In addition, the fine fibrous cellulose of this embodiment can be applied to daily necessities by adding it to resin-based materials or rubber-based materials.

In addition, when a sheet or coating is formed from a dispersion containing a high concentration of the fine fibrous cellulose of this embodiment, the content of fine fibrous cellulose in the sheet or coating can be increased. This can increase the mechanical strength of the resulting sheet or coating. For example, the tensile strength and tensile modulus of the sheet or coating can be more effectively increased. In this way, the fine fibrous cellulose dispersion of this embodiment is preferably a dispersion for forming a sheet, and this embodiment may relate to a sheet containing the above-mentioned fine fibrous cellulose.

When forming a sheet or coating from a dispersion containing a high concentration of the fine fibrous cellulose of this embodiment, it is preferable to include a coating step of coating the fine fibrous cellulose dispersion onto a substrate, or a papermaking step of making the sheet-forming composition. The sheet thus obtained may further include a resin layer or an inorganic layer laminated thereon.

This embodiment may also have the following configuration.
<101> A dispersion containing fine fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent,
The content of the fine fibrous cellulose is 5.0% by mass or more and 14.0% by mass or less based on the total mass of the dispersion,
The degree of polymerization of the fine fibrous cellulose is 160 or more and 205 or less.
A dispersion containing fine fibrous cellulose.
<102> The fine fibrous cellulose-containing dispersion according to <101>, having a viscosity measured using a B-type viscometer of 1,800×10 ³ mPa·s or more and 13,000×10 ³ mPa·s or less.
<103> The fine fibrous cellulose-containing dispersion according to <101> or <102>, wherein the ionic substituent is a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group.
<104> The fine fibrous cellulose-containing dispersion according to any one of <101> to <103>, wherein the amount of ionic substituents introduced into the fine fibrous cellulose is 0.90 mmol/g or more and 2.00 mmol/g or less.

<111> A step of subjecting cellulose fibers having ionic substituents to a defibration treatment to obtain fibrous cellulose having a fiber width of 1000 nm or less;
and subjecting the fibrous cellulose to a molecular weight reduction treatment,
A method for producing fibrous cellulose, in which, when the fibrous cellulose is dispersed in water at a concentration of 0.5% by mass, the aqueous dispersion has a viscosity of less than 108 mPa·s at 23°C.
<112> The method for producing fibrous cellulose according to <111>, wherein the concentration of cellulose fibers in the step of obtaining fibrous cellulose having a fiber width of 1,000 nm or less by defibration treatment is 3.0 mass% or more.
<113> The method for producing fibrous cellulose according to <111> or <112>, wherein the step of carrying out a molecular weight reduction treatment is a step of reducing the degree of polymerization of the fibrous cellulose to 230 or less.
<114> The method for producing fibrous cellulose according to any one of <111> to <113>, wherein the step of performing the low molecular weight treatment is at least one selected from an ozone treatment step, an enzyme treatment step, an acid treatment step, and a subcritical water treatment step.
<115> The method for producing fibrous cellulose according to any one of <111> to <114>, further comprising a step of carrying out defibration treatment after the step of carrying out the low-molecular-weight treatment.
<116> Fibrous cellulose produced by the method for producing fibrous cellulose according to any one of <111> to <115>.

The features of the present invention are explained 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 changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

<Production Example 1>
[Production of phosphorylated pulp]
As the raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 245 g/ ^m2 sheet form, Canadian standard freeness (CSF) measured according to JIS P 8121-2:2012 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, thereby obtaining a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphoric acid groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

The phosphorylated pulp obtained was then 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 phosphorylated pulp that had been subjected to a neutralization treatment. Next, the neutralized phosphorylated pulp was subjected to the above-mentioned washing treatment to obtain phosphorylated pulp A.

The infrared absorption spectrum of the phosphorylated pulp A thus obtained was measured using FT-IR, and as a result, absorption due to the phosphate group was observed around 1230 cm ⁻¹ , confirming that the phosphate group had been added to the pulp.

In addition, the obtained phosphorylated pulp A was used as a test sample and analyzed using an X-ray diffraction device. 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.

<Production Example 2>
Phosphated pulp B was obtained by carrying out the same treatment as in Production Example 1, except that the heating time in the hot air dryer was changed to 150 seconds.

<Production Example 3>
The washed phosphorylated pulp obtained in Production Example 1 was subjected to the phosphorylation treatment and washing treatment of Production Example 1 once each to obtain phosphorylated pulp C.

<Production Example 4>
Phosphated pulp D was obtained by carrying out the same treatment as in Production Example 1, except that the raw material pulp used in Production Example 1 was changed to hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd.

<Production Example 5>
Phosphated pulp E was obtained by carrying out the same treatment as in Production Example 1, except that the raw material pulp used in Production Example 1 was changed to hardwood kraft pulp (dry sheet) manufactured by Cenibra.

<Production Example 6>
[Prehydrolysis]
300g of softwood chips were collected by bone dry weight and soaked in 10L of tap water overnight. Then, the chips were taken out and sieved through a 400 mesh sieve, and filtered. The dehydrated chips were placed in a 2.5L autoclave, tap water was added so that the liquid mass ratio (when the mass of the bone dry chips is taken as 1) was 3, and the chips were heated at 165°C for 30 minutes to perform prehydrolysis. The P factor at this time was 380.
[Digestion]
After prehydrolysis, the waste gas was extracted from the degassing cock of the autoclave, and after confirming that the pressure inside the autoclave had become 0, the treated chips were emptied into a 400-mesh sieve and filtered. The filtered chips were again placed in a 2.5-liter autoclave, and cooking liquor was added so that the liquor ratio was 5, and kraft cooking was performed under the conditions of a cooking temperature of 165°C and a cooking time of 120 minutes. The cooking liquor contained 21% by mass of active alkali relative to the bone dry mass of the chips, and the sulfidity was 28%. After cooking, the black liquor and pulp were separated, and the pulp was refined using a flat screen equipped with an 8-cut screen plate to obtain a cooked pulp.
[bleaching]
After cooking, 70 g of pulp was collected in bone dry mass, and 2.0% by mass of caustic soda was added to the total mass of the bone dry pulp, and then the pulp concentration was adjusted to 10% by mass by diluting with ion-exchanged water. The slurry was placed in an indirect heating autoclave, and 99.9% compressed oxygen gas was injected to set the gauge pressure to 0.5 MPa, and oxygen exposure was performed at 100°C for 60 minutes. After oxygen exposure was completed, the pressure was reduced until the gauge pressure was 0.05 MPa or less, and the pulp was removed from the autoclave, washed with 7 liters of ion-exchanged water, and then dehydrated. In this way, oxygen-exposed pulp was obtained.
After the oxygen exposure, 60 g of the pulp was collected by bone dry weight, put into a plastic bag, and ion-exchanged water was added to adjust the pulp concentration to 10% by weight. Then, 1.8% by weight of chlorine dioxide was added to the total weight of the bone dry pulp, and the mixture was immersed in a thermostatic water bath at a temperature of 70° C. for 70 minutes (D0 stage treatment). The pulp obtained after the D0 stage treatment was diluted to 3% by weight with ion-exchanged water, and then dehydrated and washed with a Buchner funnel. The pulp after the D0 stage treatment was put into a plastic bag, and ion-exchanged water was added to adjust the pulp concentration to 10% by weight, and then caustic soda was added to 1.0% by weight and hydrogen peroxide was added to 0.3% by weight with respect to the total weight of the bone dry pulp, and mixed well. Then, the mixture was immersed in a thermostatic water bath at a temperature of 70° C. for 100 minutes to perform E/P stage treatment. The pulp obtained was diluted to 3% by weight with ion-exchanged water, and then dehydrated and washed with a Buchner funnel. The pulp after the E/P stage treatment was placed in a plastic bag and adjusted to a pulp concentration of 10% by mass using ion-exchanged water, after which chlorine dioxide was added in an amount of 0.3% by mass based on the total mass of the bone-dry pulp, and the pulp was immersed in a thermostatic water bath at 70° C. for 80 minutes to perform a D1 stage bleaching treatment. The resulting pulp was diluted to 3% by mass with ion-exchanged water, and then dehydrated and washed using a Buchner funnel to obtain bleached pulp.
[Phosphorylation]
The bleached pulp was mixed with 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. The chemical-impregnated pulp was then heated in a hot air dryer at 165° C. for 250 seconds to introduce phosphoric acid groups into the cellulose in the pulp, thereby obtaining phosphorylated pulp F.

<Production Example 7>
[Production of TEMPO oxidized pulp]
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 sodium hypochlorite solution was added so that the amount was 3.8 mmol per 1.0 g of pulp to start the reaction. During the reaction, a 0.5 M aqueous sodium hydroxide solution 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.

The resulting TEMPO oxidized pulp was then 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 remaining aldehyde groups in this dehydrated sheet were subjected to a post-oxidation treatment as follows. 100 parts of the above dehydrated sheet equivalent to the dry mass were dispersed in 10,000 parts of 0.1 mol/L acetate buffer (pH 4.8). Next, 113 parts of 80% sodium chlorite were added, and the container was immediately sealed. The mixture was stirred at 500 rpm using a magnetic stirrer and reacted at room temperature for 48 hours to obtain a pulp slurry.

The resulting TEMPO oxidized pulp was then subjected to a washing process. The washing process was carried out by dehydrating the pulp slurry after the additional 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, and TEMPO oxidized pulp A was obtained.

In addition, the obtained TEMPO oxidized pulp A was tested and 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.

<Production Example 8>
The same treatment as in Production Example 7 was carried out, except that the raw material pulp used in Production Example 7 was changed to hardwood dissolving pulp (undried) manufactured by Oji Paper Co., Ltd., to obtain TEMPO oxidized pulp B.

<Production Example 9>
TEMPO oxidized pulp C was obtained in the same manner as in Production Example 7, except that the raw material pulp used in Production Example 7 was hardwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd.

<Production Example 10>
[Production of Phosphosphite Pulp]
As the raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 245 g/ ^m2 sheet form, Canadian standard freeness (CSF) measured according to JIS P 8121-2:2012 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 phosphorous acid (phosphonic acid) and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to prepare 33 parts by mass of phosphorous acid (phosphonic acid), 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical solution-impregnated pulp. Next, the obtained chemical solution-impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphorous acid groups into the cellulose in the pulp, thereby obtaining a phosphorous-sulphated pulp.

The resulting phosphorus-substituted pulp was then 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 phosphorus-substituted pulp to obtain a pulp dispersion, stirring the resulting solution so that the pulp was uniformly dispersed, and then filtering and dehydrating the resulting solution. The washing was completed when the electrical conductivity of the filtrate reached 100 μS/cm or less.

The washed phosphited pulp was then subjected to a neutralization treatment as follows. First, the washed phosphited 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 phosphited pulp slurry with a pH of 12 to 13. The phosphited pulp slurry was then dehydrated to obtain a phosphited pulp that had been subjected to a neutralization treatment. The neutralized phosphited pulp was then subjected to the above-mentioned washing treatment to obtain phosphited pulp A.

The infrared absorption spectrum of the phosphorous pulp A thus obtained was measured using FT-IR. As a result, absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed around 1210 cm ^-1 , confirming that a phosphorous acid group (phosphonic acid group) was added to the pulp. In addition, when the phosphorous 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°, confirming that the pulp had cellulose type I crystals.

<Production Example 11>
The same treatment as in Production Example 10 was carried out, except that the raw material pulp used in Production Example 10 was changed to hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd., to obtain phosphorous-subtilized pulp B.

<Production Example 12>
The same treatment as in Production Example 10 was carried out, except that the raw material pulp used in Production Example 10 was hardwood kraft pulp (dry sheet) manufactured by Cenibra, to obtain phosphorous-subtilized pulp C.

<Production Example 13>
[Production of sulfur oxo-oxidized pulp]
The same procedure as in Production Example 1 was repeated to produce a sulfated pulp, except that 38 parts by mass of amidosulfuric acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate and the heating time was extended to 20 minutes.

The infrared absorption spectrum of the sulfated pulp thus obtained was measured using FT-IR. As a result, absorption due to sulfate groups (sulfonic groups) was observed around 1220-1260 cm ^-1 , confirming that sulfate groups (sulfonic groups) were added to the pulp. Furthermore, it was confirmed by X-ray diffraction that the sulfated pulp thus obtained maintained cellulose type I crystals.

Example 1
Ion exchange water was added to the phosphorylated pulp A obtained in Production Example 1 to prepare a slurry with a solid content concentration of 6.0% by mass. This slurry was treated once with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fibrous cellulose dispersion containing fine fibrous cellulose. An enzyme-containing solution having an activity of 33,000 nkat was added to 1000 g of this dispersion (solid content concentration 6.0% by mass, solid content 60 g) and subjected to enzyme treatment at a temperature of 50 ° C. The amount of enzyme added at this time was 550 nkat per 1 g of fine fibrous cellulose. Then, the high-pressure homogenizer was used to treat three times at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion. The temperature of the obtained dispersion was set to 100 ° C., and the enzyme was thermally inactivated. The amount of phosphoric acid groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of the amount of phosphorus oxo acid groups] described later was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

Example 2
Ion exchange water was added to the phosphorylated pulp A obtained in Production Example 1 to prepare a slurry with a solid content of 7.5% by mass. This slurry was treated once with a high-pressure homogenizer at a pressure of 200 MPa, and 250 g of sodium hypochlorite solution (effective chlorine concentration 12% by mass) was added to 1000 g (solid content concentration 7.5% by mass, solid content 75 g) and mixed well at room temperature. Then, it was treated three times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion.

Example 3
In 1000 g of the fibrous cellulose dispersion of Example 1 (solid content concentration 6.0 mass%, solid content 60 g), ozone was added at a ratio of 0.2 mass parts per mass part of fine fibrous cellulose, and the mixture was stirred at 25°C in a sealed container and allowed to stand for 30 minutes. The container was then opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The mixture was then treated three times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion.

Example 4
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 1, except for using the TEMPO oxidized pulp A obtained in Production Example 7. The amount of carboxy groups measured by the measurement method described below was 1.30 mmolg.

Example 5
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 2, except that the TEMPO oxidized pulp A obtained in Production Example 7 was used.

Example 6
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 3, except that the TEMPO oxidized pulp A obtained in Production Example 7 was used.

Example 7
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 1, except that the phosphorous pulp obtained in Production Example 10 was used. The amount of phosphorous groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of amount of phosphorous oxo acid group] below was 1.51 mmol/g. The total amount of dissociated acid was 1.54 mmol/g.

Example 8
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 2, except that the phosphited pulp obtained in Production Example 10 was used.

<Example 9>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 3, except that the phosphited pulp obtained in Production Example 10 was used.

Example 10
The phosphorylated pulp A obtained in Production Example 1 was treated once with a single disc refiner to obtain a fibrous cellulose dispersion containing fine fibrous cellulose. The other treatments were the same as in Example 1 to obtain a fine fibrous cellulose dispersion.

Example 11
The TEMPO oxidized pulp A obtained in Production Example 7 was treated once with a single disc refiner to obtain a fibrous cellulose dispersion E containing fine fibrous cellulose. The other treatments were the same as in Example 3 to obtain a fine fibrous cellulose dispersion.

Example 12
The phosphorous-subtilized pulp obtained in Production Example 10 was treated once with a single disc refiner to obtain a fibrous cellulose dispersion containing fine fibrous cellulose. The other treatments were the same as in Example 3 to obtain a fine fibrous cellulose dispersion.

<Example 13>
Ion exchange water was added to the phosphorylated pulp A obtained in Production Example 1 to prepare a pulp slurry with a solid content concentration of 6.0% by mass. An enzyme-containing solution having an activity of 33,000 nkat was added to 1000 g of this slurry (solid content 60 g) and subjected to enzyme treatment at a temperature of 50 ° C. The amount of enzyme added at this time was 550 nkat per 1 g of fine fibrous cellulose. The obtained slurry was treated once at a pressure of 200 MPa with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.), and then the enzyme treatment was carried out. Thereafter, the slurry was treated three times at a pressure of 200 MPa, and the obtained dispersion was heat-inactivated at 100 ° C. to obtain a fine fibrous cellulose dispersion.

<Example 14>
Ion-exchanged water was added to the phosphorylated pulp A obtained in Production Example 1 to prepare a pulp slurry with a solid content of 6.0% by mass. Ozone was added to the pulp in an amount of 0.2 parts by mass per part by mass of pulp, and the mixture was stirred at 25°C in a sealed container and allowed to stand for 30 minutes. The container was then opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The mixture was then treated four times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion.

Example 15
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 14, except that the TEMPO oxidized pulp A obtained in Production Example 7 was used.

<Example 16>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 13, except that the phosphite pulp A obtained in Production Example 10 was used.

<Example 17>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 1, except that the phosphorylated pulp D obtained in Production Example 4 was used.

<Example 18>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 3, except that the phosphorylated pulp E obtained in Production Example 5 was used.

<Example 19>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 1, except that the phosphorylated pulp F obtained in Production Example 6 was used.

<Example 20>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 3, except that the TEMPO oxidized pulp B obtained in Production Example 8 was used.

<Example 21>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 3, except that the phosphite pulp B obtained in Production Example 11 was used.

<Example 22>
Ion exchange water was added to the hypophosphite pulp C obtained in Production Example 12 to prepare a slurry with a solid content concentration of 6.0% by mass. This slurry was treated once with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fibrous cellulose dispersion containing fine fibrous cellulose. An enzyme-containing solution having an activity of 48,000 nkat was added to 1000 g of this dispersion (solid content concentration 6.0% by mass, solid content 60 g) and subjected to enzyme treatment at a temperature of 50 ° C. The amount of enzyme added at this time was 800 nkat per 1 g of fine fibrous cellulose. Then, the mixture was treated three times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion. The temperature of the obtained dispersion was set to 100 ° C., and the enzyme was thermally inactivated.

<Example 23>
Ion exchange water was added to the phosphorylated pulp A obtained in Production Example 1 to prepare a slurry with a solid content concentration of 13.0% by mass. This slurry was treated once with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fibrous cellulose dispersion containing fine fibrous cellulose. An enzyme-containing solution having an activity of 71,500 nkat was added to 1,000 g of this dispersion (solid content concentration 13.0% by mass, solid content 130 g) and subjected to enzyme treatment at a temperature of 50 ° C. The amount of enzyme added at this time was 550 nkat per 1 g of fine fibrous cellulose. Then, the high-pressure homogenizer was used to treat four times at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion. The temperature of the obtained dispersion was set to 100 ° C., and the enzyme was thermally inactivated. The amount of phosphoric acid groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of the amount of phosphorus oxo acid groups] described later was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol/g.

<Example 24>
Ozone was added to the fibrous cellulose dispersion obtained in Example 23 at a ratio of 0.2 parts by mass per part by mass of pulp, and the mixture was stirred at 25°C in a sealed container and allowed to stand for 30 minutes. The container was then opened and the mixture was stirred for 5 hours to volatilize the ozone remaining in the dispersion. The mixture was then treated four times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion.

<Example 25>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 23, except that the TEMPO oxidized pulp A obtained in Production Example 7 was used.

<Example 26>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 24, except that the TEMPO oxidized pulp A obtained in Production Example 7 was used.

<Example 27>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 23, except that the phosphite pulp A obtained in Production Example 10 was used.

<Example 28>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 24, except that the phosphite pulp A obtained in Production Example 10 was used.

<Example 29>
Ion exchange water was added to the phosphorylated pulp A obtained in Production Example 1 to prepare a pulp slurry with a solid content concentration of 13.0% by mass. An enzyme-containing solution having an enzyme activity of 71500 nkat was added to 1000 g of this pulp slurry (solid content concentration 13.0% by mass, solid content 130 g) and subjected to enzyme treatment at a temperature of 50 ° C. The amount of enzyme added at this time was 550 nkat per 1 g of fine fibrous cellulose. The obtained slurry was treated once at a pressure of 200 MPa with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.), and then the enzyme treatment was carried out. Thereafter, the slurry was treated four times at a pressure of 200 MPa, and the obtained dispersion was heat-inactivated at 100 ° C. to obtain a fine fibrous cellulose dispersion. The amount of phosphoric acid groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of the amount of phosphorus oxo acid groups] described later was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol/g.

<Example 30>
Ion-exchanged water was added to the TEMPO oxidized pulp A obtained in Production Example 7 to prepare a pulp slurry with a solid content of 13.0% by mass. Ozone was added to the pulp in an amount of 0.2 parts by mass per part by mass of pulp, and the mixture was stirred at 25°C in a sealed container and allowed to stand for 30 minutes. The container was then opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The mixture was then treated five times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion.

<Example 31>
Ion exchange water was added to the phosphorus-subtilized pulp A obtained in Production Example 10 to prepare a pulp slurry with a solid content of 13.0% by mass. Ozone was added to the mixture in an amount of 0.2 parts by mass per part by mass of pulp, and the mixture was stirred at 25°C in a sealed container and allowed to stand for 30 minutes. The container was then opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The mixture was then treated five times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion.

<Example 32>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 23, except that the phosphorylated pulp D obtained in Production Example 4 was used.

<Example 33>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 24, except that the phosphorylated pulp E obtained in Production Example 5 was used.

<Example 34>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 23, except that the phosphorylated pulp F obtained in Production Example 6 was used.

<Example 35>
Ion-exchanged water was added to the TEMPO oxidized pulp C obtained in Production Example 9 to prepare a slurry with a solid content concentration of 13.0% by mass. This slurry was treated once with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fibrous cellulose dispersion containing fine fibrous cellulose. An enzyme-containing solution having an activity of 104,000 nkat was added to 1,000 g of this dispersion (solid content concentration 13.0% by mass, solid content 130 g) and subjected to enzyme treatment at a temperature of 50 ° C. The amount of enzyme added at this time was 800 nkat per 1 g of fine fibrous cellulose. Then, the mixture was treated four times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion. The temperature of the obtained dispersion was set to 100 ° C., and the enzyme was thermally inactivated.

<Example 36>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 24, except that the TEMPO oxidized pulp B obtained in Production Example 8 was used.

<Example 37>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 35, except that the phosphite pulp C obtained in Production Example 12 was used.

<Example 38>
A fine fibrous cellulose dispersion was obtained in the same manner as in Example 24, except that the phosphite pulp B obtained in Production Example 11 was used.

<Example 39>
Ion exchange water was added to the phosphorylated pulp B obtained in Production Example 2 to prepare a pulp slurry with a solid content concentration of 6.0% by mass. Ozone was added to 1 part by mass of pulp at a ratio of 0.2 parts by mass, and the mixture was stirred at 25°C in a sealed container and allowed to stand for 30 minutes. The container was then opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. After that, the mixture was treated four times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion. The amount of phosphoric acid groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of phosphorus oxo acid group amount] described later was 0.90 mmol/g. The total amount of dissociated acid was 1.60 mmol/g.

<Example 40>
Ion exchange water was added to the phosphorylated pulp C obtained in Production Example 3 to prepare a pulp slurry with a solid content concentration of 6.0% by mass. Ozone was added to 1 part by mass of pulp at a ratio of 0.2 parts by mass, and the mixture was stirred at 25°C in a sealed container and allowed to stand for 30 minutes. The container was then opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. After that, the mixture was treated four times at a pressure of 200 MPa with a high-pressure homogenizer to obtain a fine fibrous cellulose dispersion. The amount of phosphoric acid groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of phosphorus oxo acid group amount] described later was 2.00 mmol/g. The total amount of dissociated acid was 3.35 mmol/g.

<Example 41>
Ion exchange water was added to the sulfated pulp obtained in Production Example 13 to prepare a slurry with a solid content concentration of 6% by mass. This slurry was treated once with a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fibrous cellulose dispersion containing fine fibrous cellulose. An enzyme-containing solution having an activity of 33,000 nkat was added to 1000 g of the obtained fine fibrous cellulose dispersion (solid content concentration 6% by mass, solid content 60 g) and subjected to enzyme treatment at a temperature of 50 ° C. The amount of enzyme added at this time was 550 nkat per 1 g of fine fibrous cellulose. The obtained fine fibrous cellulose dispersion was treated three times with a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa, and then heat-inactivated at 100 ° C. to obtain a fine fibrous cellulose dispersion. The concentration of fine fibrous cellulose in this fine fibrous cellulose dispersion was 6% by mass. The amount of sulfate groups measured by the method described later in [Measurement of amount of sulfur oxoacid groups] was 1.47 mmol/g.

X-ray diffraction confirmed that the fine fibrous cellulose of Examples 1 to 41 maintained cellulose type I crystals. In addition, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and was 3 to 5 nm in all cases.

Using the fine fibrous cellulose dispersions of Examples 1 to 41, sheets were prepared by the following procedure. Polyethylene oxide (PEO-3P, manufactured by Sumitomo Seika Chemicals) was added to ion-exchanged water to a concentration of 5% by mass, and dissolved by stirring to obtain an aqueous polyethylene oxide solution. Next, the obtained fine fibrous cellulose dispersion and the above-mentioned aqueous polyethylene oxide solution were mixed in a ratio of fine fibrous cellulose (solid content):polyethylene oxide (solid content) = 100 parts by mass:20 parts by mass to obtain a coating liquid. At that time, the coating liquid was appropriately diluted with ion-exchanged water to obtain a solid content concentration of 5% by mass in Examples 1 to 22, 39, 40, and 41, and a solid content concentration of 10% by mass in Examples 23 to 38. Next, the coating liquid was weighed so that the finished thickness of the obtained sheet (a layer composed of the solid content of the above-mentioned coating liquid) would be 40 μm, and the coating liquid was applied to a commercially available polycarbonate plate and dried for 30 minutes in a dryer at 100 ° C. In addition, a metal frame for damming (metal frame with inner dimensions of 180 mm × 180 mm and height of 5 cm) was placed on the polycarbonate plate so as to obtain a predetermined basis weight. Next, the dried sheet was peeled off from the polycarbonate plate to obtain a fine fibrous cellulose-containing sheet.

<Comparative Example 1>
Ion-exchanged water was added to the phosphorylated pulp A obtained in Production Example 1 to prepare a pulp slurry having a solid content of 2% by mass. The prepared pulp slurry was treated six times with a high-pressure homogenizer to obtain a fine fibrous cellulose dispersion. The obtained fine fibrous cellulose dispersion was concentrated in a 100°C air blower until the solid content became 6.0% by mass, to obtain a fine fibrous cellulose dispersion.

<Comparative Example 2>
A fine fibrous cellulose dispersion was obtained by concentrating in the same manner as in Comparative Example 1, except that the TEMPO oxidized pulp A obtained in Production Example 7 was used.

<Comparative Example 3>
A fine fibrous cellulose dispersion was obtained by concentrating in the same manner as in Comparative Example 1, except that the phosphited pulp A obtained in Production Example 10 was used.

<Comparative Example 4>
Ion-exchanged water was added to softwood pulp (undried) manufactured by Oji Paper Co., Ltd. to prepare a slurry having a solid content concentration of 6.0% by mass. This slurry was treated six times with a high-pressure homogenizer at a pressure of 200 MPa to obtain a fibrous cellulose dispersion.

<Comparative Example 5>
Ion-exchanged water was added to the phosphorylated pulp A obtained in Production Example 1 to prepare a pulp slurry with a solid content concentration of 2% by mass. The prepared pulp slurry was treated six times with a high-pressure homogenizer to obtain a fine fibrous cellulose dispersion. Then, this fine fibrous cellulose dispersion was diluted to 0.4% by mass. 1 g of calcium chloride was added as a thickening agent to 100 mL of the diluted solution to gel it, and after filtration, it was squeezed with filter paper. After immersing in 100 mL of 0.1N hydrochloric acid aqueous solution for 30 minutes, it was filtered to obtain a concentrate with a solid content concentration of 20% by mass. The obtained concentrate was diluted with ion-exchanged water so that the concentration was 6.0% by mass, and then stirred, but a uniform dispersion was not obtained.

<Measurement>
[Measurement of phosphorus oxoacid group content]
The amount of phosphorus oxoacid groups in the fine fibrous cellulose was measured by treating a fibrous cellulose-containing slurry with an ion exchange resin after diluting a fine fibrous cellulose dispersion containing the target fine fibrous cellulose with ion exchange water to a content of 0.2 mass%, and then titrating the slurry with an alkali.
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 fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring onto a mesh with 90 μm openings to separate the resin and 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 fibrous cellulose-containing slurry after the treatment with the 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 added) 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]
The amount of carboxy groups in the fine fibrous cellulose was measured by treating a fibrous cellulose-containing slurry with an ion exchange resin after diluting a fine fibrous cellulose dispersion containing the target fine fibrous cellulose with ion exchange water to a content of 0.2 mass%, and then titrating the slurry with an alkali.
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 fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring onto a mesh with 90 μm openings to separate the resin and the slurry.
The titration using alkali was carried out by adding 50 μL of 0.1 N aqueous sodium hydroxide solution to the fibrous cellulose-containing slurry after the ion exchange resin treatment once every 30 seconds and measuring the change in the electrical conductivity value of the slurry. 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 obtained fibrous cellulose was wet-ashed using perchloric acid and concentrated nitric acid, then appropriately diluted and the amount of sulfur was measured by ICP emission spectrometry. The amount of sulfur was divided by the bone dry mass of the fibrous cellulose to be tested, and the amount of sulfur oxoacid groups (unit: mmol/g) was determined.

[Measurement of Viscosity of 0.5% by Mass Fine Fibrous Cellulose Dispersion]
The viscosity of the fine fibrous cellulose dispersion obtained in Examples 1 to 41 and Comparative Examples 1 to 5 was measured as follows. First, the fine fibrous cellulose dispersion was diluted with ion-exchanged water so that the solid content concentration was 0.5% by mass, and then stirred in a disperser at 4000 rpm for 3 minutes. The obtained dispersion was subjected to a degassing treatment using a rotation-revolution type super mixer (ARE-250, manufactured by Thinky Corporation). Next, the viscosity of the dispersion thus obtained was measured using a B-type viscometer (analog viscometer T-LVT, manufactured by BLOOKFIELD Corporation). The measurement conditions were a rotation speed of 3 rpm, and the viscosity value 3 minutes after the start of the measurement was taken as the viscosity of the dispersion.

[Measurement of Viscosity of 6.0% by Mass Fine Fibrous Cellulose Dispersion]
The viscosity of the fine fibrous cellulose dispersions obtained in Examples 1 to 22, 39, 40, and 41 and Comparative Examples 1 to 4 was measured as follows. First, the fine fibrous cellulose dispersions were degassed using a rotation-revolution type super mixer (ARE-250, manufactured by Thinky Corporation). Next, the viscosity of the obtained dispersions was measured using a Brookfield type viscometer (analog viscometer T-LVT, manufactured by BLOOKFIELD). The measurement conditions were a rotation speed of 0.3 rpm, and the viscosity value 3 minutes after the start of the measurement was taken as the viscosity of the dispersion.

[Measurement of Viscosity of 13.0% by Mass Fine Fibrous Cellulose Dispersion]
The viscosity of the fine fibrous cellulose dispersions obtained in Examples 23 to 38 was measured as follows. First, the fine fibrous cellulose dispersions were degassed using a rotation-revolution type super mixer (ARE-250, manufactured by Thinky Corporation). Next, the viscosity of the obtained dispersions was measured using a Brookfield type viscometer (DV2T digital viscometer, manufactured by BLOOKFIELD). The measurement conditions were a rotation speed of 0.3 rpm, and the viscosity value 3 minutes after the start of the measurement was taken as the viscosity of the dispersion.

[Measurement of specific viscosity and polymerization degree of fine fibrous cellulose]
The specific viscosity and degree of polymerization of the fine fibrous cellulose were measured according to Tappi T230. That is, the fine fibrous cellulose to be measured was dispersed in a dispersion medium to measure the viscosity (referred to as η1), and the blank viscosity (referred to as η0) was measured using only the dispersion medium, and then the specific viscosity (ηsp) and intrinsic viscosity ([η]) were measured according to the following formulas.
ηsp=(η1/η0)-1
[η]=ηsp/(c(1+0.28×ηsp))
Here, c in the formula represents the concentration of cellulose fibers at the time of viscosity measurement.
Furthermore, the degree of polymerization (DP) of the fine fibrous cellulose was calculated from the following formula.
DP=1.75×[η]
Since this degree of polymerization is an average degree of polymerization measured by a viscosity method, it is sometimes called the “viscosity average degree of polymerization.” In Comparative Examples 1 to 3 and 5, the measurement was performed on the fine fibrous cellulose before concentration.

[Measurement of haze of fine fibrous cellulose dispersion]
The haze of the fine fibrous cellulose dispersions obtained in Examples 1 to 41 and Comparative Examples 1 to 5 was measured by diluting the fine fibrous cellulose dispersions with ion-exchanged water to 0.2% by mass, and then degassing the dispersions with a rotation-revolution type super mixer (ARE-250, manufactured by Thinky Corporation). The haze was measured in accordance with JIS K 7136:2000 using a glass cell for liquids with an optical path length of 1 cm (MG-40, manufactured by Fujiwara Seisakusho, reverse optical path) with a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.). The zero point measurement was performed with ion-exchanged water placed in the same glass cell.

[Appearance evaluation of fine fibrous cellulose dispersion]
The fine fibrous cellulose dispersions obtained in Examples 1 to 41 and Comparative Examples 1 to 5 were subjected to a defoaming treatment using a planetary centrifugal super mixer (ARE-250, manufactured by Thinky Corporation). Thereafter, the appearance was visually evaluated according to the following criteria.
A: Almost no fibers are visible to the naked eye, and the dispersion is transparent.
B: Fibers are visually observed and the dispersion is translucent.
C: The fibers are not uniformly dispersed and the dispersion is cloudy, or particulate matter (fiber agglomerates) can be seen.

In the examples, a high-concentration, uniform dispersion of fine fibrous cellulose was obtained, and the high-concentration dispersion of fine fibrous cellulose had high transparency. In Comparative Examples 1 to 3 and 5, particulate matter (fiber aggregates) was present in the dispersion, and viscosity at a concentration of 6.0% by mass could not be measured.

Claims (6)

A fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent,
The degree of polymerization of the fibrous cellulose is 230 or less,
When the fibrous cellulose is dispersed in water at a concentration of 0.5% by mass, the viscosity of the aqueous dispersion at 23° C. is less than 108 mPa s,
The fibrous cellulose has a viscosity of 500,000 mPa·s or more and 10,000,000 mPa·s or less at 23° C. when the fibrous cellulose is dispersed in water at a concentration of 6.0% by mass. 2. The fibrous cellulose according to claim 1 , wherein when the fibrous cellulose is dispersed in water at a concentration of 13.0% by mass, the aqueous dispersion has a viscosity of 1,000,000 mPa·s or more and 50,000,000 mPa·s or less at 23°C. The fibrous cellulose according to claim 1 or 2 , wherein the ionic substituent 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 fibrous cellulose dispersion comprising the fibrous cellulose according to any one of claims 1 to 3 . The fibrous cellulose dispersion according to claim 4 , wherein the concentration of the fibrous cellulose is 3.0% by mass or more. A sheet comprising the fibrous cellulose according to any one of claims 1 to 3 .

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