Dispersion liquid

Abstract

To provide a sheet which is excellent in transparency and suppresses curling.SOLUTION: A dispersion liquid contains a fibrous cellulose that has a fiber width of 1,000 nm or less and has an ionic substituent, in which a content of the fibrous cellulose is 3.0 mass% or more with respect to the total mass of the dispersion liquid, and a TI value of the dispersion liquid calculated by the following condition (a) of 1 or more and 80,000 or less. Condition (a): viscosity (η1) on the condition of a shear rate of the dispersion liquid of 1 sec-1 and viscosity (η2) on the condition of shear rate of the dispersion liquid of 1,000 sec-1 are measured using a rheometer, and the TI value is calculated from the following expression: TI value=η1 / η2.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a dispersion. Specifically, the present invention relates to a dispersion containing microfibrillar cellulose.

Background Art

[0002] Conventionally, cellulose fibers have been widely used in clothing, absorbent articles, paper products, etc. As cellulose fibers, in addition to fibrous cellulose having a fiber diameter of 10 μm or more and 50 μm or less, microfibrillar cellulose having a fiber diameter of 1 μm or less is also known. Microfibrillar cellulose has attracted attention as a new material, and its uses are diverse.

[0003] When producing microfibrillar cellulose, a slurry containing a cellulose raw material is defibrated (mechanically treated). For example, Patent Document 1 discloses a method for producing microfibers including a step of treating a cellulose raw material with an enzyme and a step of defibrating the cellulose raw material after the enzyme treatment. Here, it has been studied to sufficiently refine the cellulose raw material by performing enzyme treatment and increase the yield of microfibers. Further, Patent Document 1 aims to produce microfibers having a long fiber length and a large aspect ratio.

[0004] Further, Patent Document 2 discloses microfibrillar cellulose having an average fiber width of 200 nm or less, a degree of polymerization of 50 or more and 500 or less, and having a predetermined polar group. Here, it has been studied to obtain microfibrillar cellulose that is less likely to form aggregates when mixed with an emulsion resin. In the examples of Patent Document 2, a dispersion having a degree of polymerization of 248 to 454 and a viscosity of 108 to 740 at a concentration of 0.5% was obtained.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The uses of a dispersion containing microfibrillar cellulose are diverse, and various studies have been conducted on its processing methods. For example, it has been studied to form a microfibrillar cellulose-containing sheet by coating or papermaking a microfibrillar cellulose dispersion. However, when trying to form a sheet from a conventional microfibrillar cellulose dispersion, it has become clear from the studies of the present inventors that the transparency of the obtained sheet is poor or curling occurs in the sheet.

[0007] Therefore, in order to solve such problems of the prior art, the present inventors have proceeded with studies aiming to provide a sheet having excellent transparency and suppressed curling.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found that in a dispersion containing fibrillar cellulose having a fiber width of 1000 nm or less and an ionic substituent, by setting the content of the fibrillar cellulose to 3.0% by mass or more based on the total mass of the dispersion and setting the TI value of the dispersion to 1 or more and 80000 or less, a sheet having excellent transparency and suppressed curling can be obtained. Specifically, the present invention has the following configuration.

[0009] [1] A dispersion containing fibrillar cellulose having a fiber width of 1000 nm or less and an ionic substituent, wherein the content of the fibrillar cellulose is 3.0% by mass or more based on the total mass of the dispersion, and the TI value of the dispersion calculated by the following condition (a) is 1 or more and 80000 or less; Condition (a): Using a rheometer, the shear rate of the dispersion is 1 sec -1Measure the viscosity (η1) under the conditions and the viscosity (η2) under the conditions of a shear rate of 1000 sec of the dispersion liquid, and calculate the TI value according to the following formula. -1 Measure the viscosity (η2) under the conditions of -1 , and calculate the TI value according to the following formula. TI value = η1 / η2 [2] The dispersion liquid according to [1], wherein the content of the fibrous cellulose is 4.0% by mass or more based on the total mass of the dispersion liquid. [3] The dispersion liquid according to [1], wherein the content of the fibrous cellulose is 5.0% by mass or more based on the total mass of the dispersion liquid. [4] The dispersion liquid according to [1], wherein the content of the fibrous cellulose is 6.0% by mass or more based on the total mass of the dispersion liquid. [5] The ionic substituent is at least one selected from the group consisting of a phosphooxo acid group, a substituent derived from a phosphooxo acid group, a sulfur oxo acid group, and a substituent derived from a sulfur oxo acid group. The dispersion liquid according to any one of [1] to [4]. [6] The dispersion liquid according to any one of [1] to [5], wherein the haze when the dispersion liquid has a concentration of 0.2% by mass is 95% or less. [7] A sheet formed from the dispersion liquid according to any one of [1] to [6]. [Effects of the Invention]

[0010] According to the present invention, a sheet excellent in transparency and having suppressed curling can be obtained. [Brief Description of the Drawings]

[0011]

Figure 1

Figure 2

Figure 3

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

[0013] (Dispersion liquid) The dispersion liquid containing fibrous cellulose of the present embodiment is a dispersion liquid containing fibrous cellulose having a fiber width of 1000 nm or less and having an ionic substituent, wherein the content of the fibrous cellulose is 3.0% by mass or more based on the total mass of the dispersion liquid, and the TI value of the dispersion liquid calculated by the following condition (a) is 1 or more and 80,000 or less. Condition (a): Using a rheometer, the viscosity (η1) of the dispersion liquid under the condition of a shear rate of 1 sec -1 and the viscosity (η2) of the dispersion liquid under the condition of a shear rate of 1000 sec -1 are measured, and the TI value is calculated by the following formula. TI value = η1 / η2

[0014] In this specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as microfibrillated cellulose. Further, a dispersion liquid containing microfibrillated cellulose is also referred to as a microfibrillated cellulose dispersion liquid, a dispersion liquid containing microfibrillated cellulose, or a slurry containing microfibrillated cellulose.

[0015] Since the dispersion of this embodiment has the above configuration, it has excellent transparency and can form a sheet with suppressed curling. Conventionally, in a dispersion containing 3.0 mass% or more of microfibrillated cellulose, because its viscosity is high, it has not been possible to form a sheet from such a dispersion, or even if a sheet has been formed, the sheet has had a large curl width. Also, in the formed sheet, the transparency may have been poor. However, in this embodiment, by setting the concentration of the microfibrillated cellulose dispersion to a high concentration and controlling the TI value of such a high-concentration dispersion within a predetermined range, we have succeeded in enhancing the transparency and curl resistance of the sheet formed from the dispersion. Thus, when a sheet is formed from the dispersion of this embodiment, a highly transparent sheet with suppressed curling can be obtained.

[0016] In the sheet formed from the dispersion of the present embodiment, the generation of curl is suppressed. That is, the sheet formed from the dispersion of the present embodiment is excellent in curl resistance. When evaluating the curl resistance, first, a sheet for evaluation is formed. Specifically, a coating liquid is prepared by mixing solutions in which each component is dispersed so that the solid content mass of the microfibrillar cellulose is 100 parts by mass and the solid content mass of the polyethylene oxide is 20 parts by mass. Next, the coating liquid is metered so that the finished thickness of the obtained sheet (the layer composed of the solid content of the coating liquid) is 40 μm to form a sheet. Next, the obtained microfibrillar cellulose-containing sheet is cut out into a test piece having a width of 15 mm and a length of 130 mm. As shown in FIG. 1, an end portion including one short side of the test piece 50 is supported by a curl test jig 55 having a width of 30 mm, a length of 30 mm, and a height of 25 mm (a test piece having a length of 100 mm is exposed from the jig), and in an environment of a temperature of 23° C. and a relative humidity of 50%, the test piece is placed on a horizontal table so that the width direction of the test piece is perpendicular to the table (the longitudinal direction of the test piece is parallel to the table). Then, the curl width at the end of the test piece 50 is measured and taken as the curl width C0 (the distance of C0 in FIG. 1). After standing for 24 hours, the curl width is measured again and taken as C1 (the distance of C1 in FIG. 1), and C1 - C0 is taken as the curl amount. When the value of the curl amount C1 - C0 is calculated from the curl width measured in this way, C1 - C0 is preferably 25 mm or less, more preferably 5 mm or less. Note that C1 - C0 may be 0 mm. And when the curl is 25 mm or less, it can be determined that the sheet is excellent in curl resistance.

[0017] Note that the dispersion of the present embodiment is not limited to the use of the sheet. The dispersion of the present embodiment is expected to have further expanded uses as a high-concentration dispersion.

[0018] In addition, since the dispersion of the present embodiment is a dispersion containing microfibrillated cellulose at a high concentration, it is possible to significantly reduce the storage cost and transportation cost. Conventionally, in a dispersion containing microfibrillated cellulose, the concentration of microfibrillated cellulose was about 2% by mass. On the other hand, in the dispersion of the present embodiment, since the content of microfibrillated cellulose can be set to a high concentration of 3.0% by mass or more, it is possible to significantly reduce the storage cost and transportation cost, and furthermore, the production efficiency of the dispersion can be increased.

[0019] The content of microfibrillated cellulose may be 3.0% by mass or more with respect to the total mass of the dispersion, preferably 4.0% by mass or more, more preferably 5.0% by mass or more, and even more preferably 6.0% by mass or more. The upper limit of the content of microfibrillated cellulose in the dispersion is not particularly limited, but can be, for example, 20% by mass. Thus, the dispersion of the present embodiment is a high-concentration microfibrillated cellulose dispersion. By setting the content of microfibrillated cellulose in the dispersion within the above range, when forming a sheet from the dispersion, the curl resistance of the sheet can be more effectively enhanced. This is presumably because by forming a sheet from a high-concentration microfibrillated cellulose dispersion, the amount of water brought into the sheet manufacturing process can be reduced, thereby suppressing the occurrence of thermal shrinkage during heating.

[0020] The TI value of the dispersion may be 1 or more, preferably 10 or more, more preferably 30 or more, still more preferably 50 or more, even more preferably 70 or more, and particularly preferably 100 or more. Also, the TI value of the dispersion may be 80,000 or less, preferably 70,000 or less, more preferably 50,000 or less, still more preferably 30,000 or less, and particularly preferably 20,000 or less. By setting the TI value of the dispersion within the above range, when forming a sheet from the dispersion, the curl resistance of the sheet can be more effectively enhanced. Also, by setting the TI value of the dispersion within the above range, when producing a sheet from the dispersion, while appropriately controlling the spreading condition of the dispersion, an appropriate fluidity can be imparted, so that a uniform sheet can be produced even with a high-concentration dispersion.

[0021] Here, the TI value of the dispersion is a value calculated by the following condition (a). Condition (a): Using a rheometer, the viscosity (η1) under the condition of a shear rate of 1 sec -1 of the dispersion and the viscosity (η2) under the condition of a shear rate of 1000 sec -1 of the dispersion are measured, and the TI value is calculated by the following formula. TI value = η1 / η2 Specifically, the viscosity (η1) and the viscosity (η2) are measured under the following conditions. As the rheometer used for the measurement, for example, RheoStress6000 manufactured by HAAKE can be used. Measurement temperature: 23°C Measurement jig: Cone plate (diameter 40 mm, angle 1°) Shear rate: 0.001 to 1000 sec -1 Number of data points: 100 points Data distribution: Log interval Measurement time: 5 minutes

[0022] The shear rate of the dispersion is 1 sec -1The viscosity (η1) under the conditions is preferably 1 Pa·s or more, more preferably 10 Pa·s or more, and even more preferably 50 Pa·s or more. Shear rate 1 sec -1 The viscosity (η1) under the conditions is preferably 5,000 Pa·s or less, more preferably 4,000 Pa·s or less, and even more preferably 3,000 Pa·s or less. Also, for the shear rate of 1000 sec of the dispersion liquid -1 The viscosity (η2) under the conditions is preferably 0.007 Pa·s or more, more preferably 0.01 Pa·s or more, and even more preferably 0.05 Pa·s or more. Shear rate 1000 sec -1 The viscosity (η2) under the conditions is preferably 100 Pa·s or less, more preferably 50 Pa·s or less, and even more preferably 10 Pa·s or less.

[0023] When the dispersion liquid has a concentration of 0.2 mass%, the haze is preferably 95% or less, more preferably 90% or less, even more preferably 80% or less, still more preferably 70% or less, yet more preferably 50% or less, even yet more preferably 30% or less, particularly preferably 10% or less, and most preferably 5% or less. Note that the haze when the dispersion liquid has a concentration of 0.2 mass% may be 0%. When measuring the haze of the dispersion liquid, the haze is measured after adjusting the concentration of the microfibrillar cellulose to 0.2 mass%. The haze of the dispersion liquid is a value measured by putting the dispersion liquid adjusted to a concentration of 0.2 mass% into a glass cell for liquids with an optical path length of 1 cm (manufactured by Fujiwara Seisakusho, MG-40, reverse optical path) and using a haze meter (manufactured by Murakami Color Technology Laboratory, HM-150) in accordance with JIS K 7136:2000. Note that the dispersion liquid to be measured is left standing for 24 hours in an environment of 23°C and a relative humidity of 50% before measurement. Also, the zero point measurement during haze measurement is performed with ion-exchanged water put into the same glass cell. By setting the haze of the dispersion liquid with a concentration of 0.2 mass% within the above range, it becomes easier to form a sheet with excellent transparency.

[0024] When measuring the viscosity of the dispersion liquid, the viscosity of the fine fibrous cellulose dispersion liquid is measured without dilution. The viscosity of the dispersion liquid is measured using a B-type viscometer at 23°C with a rotational speed of 0.3 rpm, and is the viscosity value 3 minutes after the start of measurement. As the B-type viscometer, for example, the digital viscometer DV2T manufactured by BLOOKFIELD can be used.

[0025] The viscosity when the dispersion liquid has a concentration of 3.0 mass% is preferably 10 million mPa·s or less, more preferably 9 million mPa·s or less, and even more preferably 8 million mPa·s or less. Also, the viscosity when the dispersion liquid has a concentration of 3.0 mass% is preferably 100,000 mPa·s or more, more preferably 200,000 mPa·s or more, and even more preferably 300,000 mPa·s or more. The viscosity when the dispersion liquid has a concentration of 6.0 mass% is preferably 50 million mPa·s or less, more preferably 30 million mPa·s or less, and even more preferably 20 million mPa·s or less. Also, the viscosity when the dispersion liquid has a concentration of 6.0 mass% is preferably 500,000 mPa·s or more, more preferably 700,000 mPa·s or more, and even more preferably 1 million mPa·s or more. The viscosity when the dispersion liquid has a concentration of 13.0 mass% is preferably 100 million mPa·s or less, more preferably 50 million mPa·s or less, and even more preferably 30 million mPa·s or less. Also, the viscosity when the dispersion liquid has a concentration of 13.0 mass% is preferably 1 million mPa·s or more, more preferably 5 million mPa·s or more, and even more preferably 10 million mPa·s or more.

[0026] The dispersion of the present embodiment is preferably a dispersion containing microfibrillar cellulose and a dispersion medium. The dispersion medium is not particularly limited, but preferably contains water, and more preferably is a solvent mainly containing water. That is, the dispersion of the present embodiment is preferably an aqueous dispersion containing microfibrillar cellulose. Note that the dispersion medium may be an organic solvent. Examples of the organic solvent include dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), aniline, pyridine, quinoline, lutidine, acetonitrile, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dioxane, ethanol, isopropanol, and the like. Further, as the dispersion medium, a mixed solvent in which these organic solvents and water are mixed can also be used.

[0027] The dispersion of the present embodiment is a high-concentration dispersion containing 3.0% by mass or more of microfibrillar cellulose, but is a dispersion obtained without passing through a concentration step. Further, the dispersion of the present embodiment is also distinguished from, for example, a dispersion obtained by redispersing a solid of microfibrillar cellulose. That is, the dispersion of the present embodiment is neither a concentrated dispersion nor a concentrated and reduced dispersion. The dispersion of the present embodiment is the dispersion itself obtained through a defibrillation treatment step as described later. Therefore, the dispersion of the present embodiment does not contain components involved in concentration and concentration reduction such as flocculants.

[0028] Here, in the prior art, increasing the concentration of microfibrillar cellulose has been studied by adding a flocculant to the dispersion or by heating and concentrating. However, when a flocculant or heating concentration is performed in this way, the microfibrillar cellulose aggregates unevenly, and in some cases, aggregates are formed. Therefore, it has been clarified by the study of the present embodiment that the TI value of the dispersion exceeds 80,000. Further, even in the dispersion obtained by redispersing aggregates or the like, the microfibrillar cellulose is unevenly dispersed, so that the TI value of the dispersion cannot be set within a desired range.

[0029] In the prior art, it was difficult to obtain a high-concentration aqueous dispersion of 3.0% by mass or more, and it was impossible to obtain a high-concentration aqueous dispersion such as 6.0% by mass or 13.0% by mass. Further, even when the fine fibrous cellulose dispersion obtained in the prior art was concentrated to obtain an aqueous dispersion having a concentration of 6.0% by mass or 13.0% by mass, the aqueous dispersion became gel-like, or particulate matter (aggregates of fibers) etc. occurred in the aqueous dispersion, and a uniform aqueous dispersion could not be obtained. Naturally, it was impossible to measure the viscosity of such a high-concentration aqueous dispersion. For example, when an aqueous dispersion having a concentration of 0.5 to 2.0% by mass was subjected to defibrillation treatment and then concentrated by heat treatment or an evaporator, a film-like substance was generated on the wall surface during the concentration process, and a dispersion having a concentration of 6.0% by mass or more in which fine fibrous cellulose was uniformly dispersed could not be obtained. For this reason, it was impossible to obtain a high-concentration aqueous dispersion such as 6.0% by mass or 13.0% by mass in the first place, and it was impossible to obtain a dispersion having a viscosity within the above range in a high-concentration aqueous dispersion such as 6.0% by mass or 13.0% by mass.

[0030] On the other hand, in the present embodiment, since the dispersion obtained without going through the concentration step is used, a highly uniform dispersion can be obtained. Further, the TI value of the dispersion can be within the range of 1 or more and 80,000 or less. For this reason, when a sheet is formed from the dispersion of the present embodiment, for example, a sheet having high transparency and excellent curl resistance can be obtained. Further, in the present embodiment, the dispersion of phosphorylated pulp to be subjected to defibrillation treatment is made to have a high concentration, the defibrillation treatment is performed on such a high-concentration pulp dispersion, and if necessary, a molecular weight reduction treatment as described later is also performed, whereby it becomes possible to measure the viscosity even in an aqueous dispersion containing 3.0% by mass or more of fine fibrous cellulose (for example, an aqueous dispersion of 6.0% by mass or 13.0% by mass), and a relatively low-viscosity aqueous dispersion has been successfully obtained as a high-concentration dispersion.

[0031] (fibrous cellulose) The dispersion of this embodiment contains fibrous cellulose with 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.

[0032] The fiber width of the fibrous cellulose can be measured, for example, by electron microscope observation. The average fiber width of the fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is preferably, for example, 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 setting the average fiber width of the fibrous cellulose to 2 nm or more, dissolution in water as cellulose molecules can be suppressed, and the effects of improving the strength, rigidity, and dimensional stability by the fibrous cellulose can be more easily manifested. Note that the fibrous cellulose is, for example, single-fiber cellulose.

[0033] The average fiber width of the 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 or more and 0.1% by mass or less is prepared, and this suspension is cast onto a carbon film-coated grid that has been hydrophilized to obtain a sample for TEM observation. When including wide fibers, the SEM image of the surface cast on glass may be observed. Next, observation is performed on the electron microscope image at any one of magnifications of 1000 times, 5000 times, 10000 times, or 50000 times according to the width of the fiber to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.

[0034] (1) Draw a straight line X at an arbitrary position within the observation image, and 20 or more fibers intersect this straight line X. (2) Draw a straight line Y that intersects perpendicularly to this straight line within the same image, and 20 or more fibers intersect this straight line Y.

[0035] For the observation images that satisfy the above conditions, visually read the width of the fibers that intersect the straight line X and the straight line Y. In this way, obtain at least three sets of observation images of surface portions that do not overlap with each other. Next, for each image, read the width of the fibers that intersect the straight line X and the straight line Y. As a result, read at least 20×2×3 = 120 fiber widths. Then, take the average value of the read fiber widths as the average fiber width of the fibrous cellulose.

[0036] The fiber length of the fibrous cellulose is not particularly limited, but for example, it 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 crystal regions of the fibrous cellulose can be suppressed. Also, it becomes possible to set the slurry viscosity of the fibrous cellulose within an appropriate range. The fiber length of the fibrous cellulose can be determined, for example, from image analysis using TEM, SEM, or AFM.

[0037] The fibrous cellulose preferably has a type I crystal structure. Here, the fact that the fibrous cellulose has a type I crystal structure can be identified from the diffraction profile obtained from a wide-angle X-ray diffraction photograph using graphite-monochromatized CuKα (λ = 1.5418 Å). Specifically, it can be identified from the fact that typical peaks are present at two positions near 2θ = 14° or more and 17° or less and near 2θ = 22° or more and 23° or less. The proportion of the type I crystal structure in the microfibrillar cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. Thereby, more excellent performance can be expected in terms of heat resistance and manifestation of a low linear thermal expansion rate. Regarding the crystallinity, an X-ray diffraction profile is measured, and it is determined by a conventional method from the pattern (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0038] The axial ratio (fiber length / fiber width) of the fibrous cellulose is not particularly limited, but is preferably, for example, 30 or more and 10,000 or less, and more preferably 50 or more and 1,000 or less. In the present specification, fibrous cellulose with a fiber width of 1,000 nm or less (microfibrillar cellulose) is cellulose nanofiber (CNF), and fibrous cellulose (microfibrillar cellulose) does not include cellulose nanocrystal (CNC). The axial ratio (fiber length / fiber width) of cellulose nanocrystal (CNC) is usually about 10 or more and 30 or less. Further, by setting the axial ratio of the fibrous cellulose to be equal to or higher than the above lower limit value, for example, when handling the fibrous cellulose as an aqueous dispersion, it is preferable in terms of ease of handling such as dilution.

[0039] The fibrous cellulose in the present embodiment has, for example, both a crystalline region and an amorphous region. The microfibrillar cellulose having both a crystalline region and an amorphous region and an axial ratio within the above range is realized by the method for producing microfibrillar cellulose described later.

[0040] The fibrous cellulose in the present embodiment has an ionic substituent. As the ionic substituent, for example, one or both of an anionic group and a cationic group can be included. In the present embodiment, it is particularly preferable to have an anionic group as the ionic substituent. Further, the ionic substituent is preferably a group that is linked to the fibrous cellulose by breaking an ester bond. In this case, the ester bond is formed by dehydration condensation of the fibrous cellulose and a compound that becomes an ionic substituent.

[0041] Examples of the anionic group as the ionic substituent include at least one selected from a phosphooxo acid group or a substituent derived from a phosphooxo acid group (sometimes simply referred to as a phosphooxo 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). It is preferably at least one selected from a phosphooxo acid group and a carboxy group, more preferably at least one selected from a phosphooxo acid group, and particularly preferably a phosphooxo acid group. By introducing a phosphooxo acid group as an ionic substituent into fibrous cellulose, it becomes easier to obtain a highly transparent dispersion, and as a result, it becomes easier to obtain a sheet having better transparency. Further, by introducing a phosphooxo acid group into fibrous cellulose, the salt resistance of fibrous cellulose can also be improved.

[0042] The phosphooxo acid group or the substituent derived from a phosphooxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the substituents represented by the following formula (1) introduced in plurality may be the same or different from each other.

[0043] [Chemical formula]

[0044] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (provided that a = b × m). At least one of the n αs and α's is O - and the rest are R or OR. Note that all of each α and α' may be O - . The n αs may all be the same or different from each other. β b+ is a cation of one or more valences composed of an organic substance or an inorganic substance.

[0045] Each R is a hydrogen atom, a saturated - straight - chain hydrocarbon group, a saturated - branched - chain hydrocarbon group, a saturated - cyclic hydrocarbon group, an unsaturated - straight - chain hydrocarbon group, an unsaturated - branched - chain hydrocarbon group, an unsaturated - cyclic hydrocarbon group, an aromatic group, or a derivative group thereof. In formula (1), n is preferably 1.

[0046] Examples of the saturated - straight - chain hydrocarbon group include, but are not particularly limited to, a methyl group, an ethyl group, an n - propyl group, or an n - butyl group. Examples of the saturated - branched - chain hydrocarbon group include, but are not particularly limited to, an i - propyl group or a t - butyl group. Examples of the saturated - cyclic hydrocarbon group include, but are not particularly limited to, a cyclopentyl group or a cyclohexyl group. Examples of the unsaturated - straight - chain hydrocarbon group include, but are not particularly limited to, a vinyl group or an allyl group. Examples of the unsaturated - branched - chain hydrocarbon group include, but are not particularly limited to, an i - propenyl group or a 3 - butenyl group. Examples of the unsaturated - cyclic hydrocarbon group include, but are not particularly limited to, a cyclopentenyl group or a cyclohexenyl group. Examples of the aromatic group include, but are not particularly limited to, a phenyl group or a naphthyl group.

[0047] Examples of the derivative group in R include a functional group in which at least one type 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 or substituted to the main chain or side chain of the above - mentioned various hydrocarbon groups, but are not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphonooxy acid group can be within an appropriate range, facilitating penetration into the fiber raw material and increasing the yield of micro - cellulose fibers. When there are a plurality of Rs in formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into fibrous cellulose, the plurality of existing Rs may be the same or different from each other.

[0048] β b+is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include, for example, organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include, for example, aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include, for example, aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, and the like. In the formula (1), when β b+ is present in a plurality or when a plurality of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the plurality of β b+ may be the same or different from each other. As the monovalent or higher cation composed of an organic or inorganic substance, sodium or potassium ions that are less likely to turn yellow when heating a fiber raw material containing β b+ and are easy to use industrially are preferred, but not particularly limited.

[0049] More specifically, examples of the phosphooxo acid group or a substituent derived from the phosphooxo acid group include a phosphate group (-PO 3 H 2 ), a salt of the phosphate group, a phosphite group (phosphonic acid group) (-PO 2 H 2 ), and a salt of the phosphite group (phosphonic acid group). Further, the phosphooxo acid group or a substituent derived from the phosphooxo acid group may be a group in which phosphate groups are condensed (for example, a pyrophosphate group), a group in which phosphonic acids are condensed (for example, a polyphosphonic acid group), a phosphate ester group (for example, a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkylphosphonic acid group (for example, a methylphosphonic acid group), or the like.

[0050] In addition, the sulfur oxoacid group (sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of substituents represented by the following formula (2) introduced may be the same or different from each other.

[0051]

Chemical formula

[0052] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (provided that 1 = b × m). When n is 2 or more, the plurality of p's may be the same number or different numbers. In the above structural formula, β b+ is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ion include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ion include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ion include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, and the like. When a plurality of types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the plurality of βs b+ may be the same or different from each other. As the monovalent or higher cation composed of an organic or inorganic substance, sodium or potassium ions, which are less likely to turn yellow when the fiber raw material containing β b+ is heated and are easy to use industrially, are preferable, but not particularly limited.

[0053] The amount of ionic substituents introduced into fibrous cellulose is preferably, for example, 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, still more preferably 0.40 mmol / g or more, even more preferably 0.60 mmol / g or more, yet even more preferably 0.90 mmol / g or more, and particularly preferably 1.00 mmol / g or more per 1 g (mass) of fibrous cellulose. In particular, when the amount of ionic substituents introduced into fibrous cellulose is 1.00 mmol / g or more, the load during fibrillation can be reduced, and the transparency of the resulting microfibrillated cellulose dispersion or sheet is further enhanced. Also, when the amount of ionic substituents introduced into fibrous cellulose is 1.00 mmol / g or more, the salt resistance of fibrous cellulose can be improved. Further, the amount of ionic substituents introduced into fibrous cellulose is preferably, for example, 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, still more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, yet even more preferably 2.00 mmol / g or less, and particularly preferably 1.50 mmol / g or less per 1 g (mass) of fibrous cellulose. Here, the denominator in mmol / g indicates the mass of fibrous cellulose when the counter ion of the ionic substituent is a hydrogen ion (H + +). By setting the amount of ionic substituents introduced within the above range, the fibrillation of the fiber raw material can be facilitated, and the stability of fibrous cellulose can be enhanced. Also, by setting the amount of ionic substituents introduced within the above range, a dispersion having a haze value within a predetermined range can be easily obtained while containing microfibrillated cellulose at a high concentration.

[0054] The amount of ionic substituents introduced into fibrous cellulose can be measured, for example, by a neutralization titration method. In the measurement by the neutralization titration method, the amount introduced is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing fibrous cellulose.

[0055] Figure 2 is a graph showing the relationship between the amount of NaOH dropped and the pH for a fibrous cellulose-containing slurry having a phosphonooxy group. The amount of phosphonooxy group 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, before the treatment with the strongly acidic ion exchange resin, a defibrillation treatment similar to the defibrillation treatment step described below may be performed on the measurement target. Next, while adding an aqueous sodium hydroxide solution, the change in pH is observed to obtain a titration curve as shown in the upper part of FIG. 2. In the titration curve shown in the upper part of FIG. 2, the pH measured with respect to the amount of alkali added is plotted, and in the titration curve shown in the lower part of FIG. 2, the increment (differential value) (1 / mmol) of the pH with respect to the amount of alkali added is plotted. In this neutralization titration, in the curve obtained by plotting the pH measured with respect to the amount of alkali added, two points where the increment (differential value of the pH with respect to the amount of alkali dropped) becomes maximum are confirmed. Among these, the first maximum point of the increment obtained first after starting to add the alkali is called the first end point, and the next maximum point of the increment is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the first dissociation acid amount of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the first end point to the second end point is equal to the second dissociation acid amount 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 dissociation acid amount of the fibrous cellulose contained in the slurry used for titration. Then, 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 titration target slurry is the amount of phosphonooxy group introduced (mmol / g). When simply referring to the amount of phosphonooxy group introduced (or the amount of phosphonooxy group), it represents the first dissociation acid amount. In FIG. 2, the region from the start of titration to the first end point is referred to as the first region, and the region from the first end point to the second end point is referred to as the second region. For example, when the phosphooxo acid group is a phosphate group and this phosphate group undergoes condensation, apparently, the amount of weak acidic groups (also referred to as the second dissociation acid amount in this specification) in the phosphooxo acid group decreases, and the amount of alkali required in the second region becomes less than the amount of alkali required in the first region. On the other hand, the amount of strong acidic groups (also referred to as the first dissociation acid amount in this specification) in the phosphooxo acid group coincides with the amount of phosphorus atoms regardless of the presence or absence of condensation. Further, when the phosphooxo acid group is a phosphorous acid group, since there are no weak acidic groups in the phosphooxo acid group, the amount of alkali required in the second region may decrease, or the amount of alkali required in the second region may be zero. In this case, in the titration curve, there is only one point where the increment of pH becomes maximum.

[0056] Note that since the denominator in the above-mentioned amount of phosphooxo acid group introduced (mmol / g) indicates the mass of the acid-form fibrous cellulose, it represents the amount of phosphooxo acid groups (hereinafter referred to as the amount of phosphooxo acid groups (acid form)) possessed by the acid-form fibrous cellulose. On the other hand, when the counter ion of the phosphooxo acid group is replaced with an arbitrary cation C so that it becomes charge equivalent, by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion, the amount of phosphooxo acid groups (hereinafter referred to as the amount of phosphooxo acid groups (C form)) possessed by the fibrous cellulose with the cation C as the counter ion can be obtained. That is, it is calculated by the following calculation formula. Amount of phosphooxo acid groups (C form) = Amount of phosphooxo acid groups (acid form) / {1 + (W - 1) × A / 1000} A [mmol / g]: Total amount of anions derived from the phosphooxo acid groups possessed by the fibrous cellulose (total dissociation acid amount of the phosphooxo acid groups) W: Formula weight per monovalent of the cation C (for example, 23 for Na and 9 for Al)

[0057] Figure 3 is a graph showing the relationship between the amount of NaOH dropped and the pH for a dispersion containing fibrous cellulose having a carboxy group as an ionic substituent. The amount of carboxy group introduced into the fibrous cellulose is measured, for example, as follows. First, a dispersion containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, a defibrillation treatment similar to the defibrillation treatment process described later may be performed on the measurement target before the treatment with the strongly acidic ion exchange resin. Next, while adding an aqueous sodium hydroxide solution, the change in pH is observed to obtain a titration curve as shown in the upper part of FIG. 3. In the titration curve shown in the upper part of FIG. 3, the pH measured with respect to the amount of alkali added is plotted, and in the titration curve shown in the lower part of FIG. 3, the increment (differential value) (1 / mmol) of the pH with respect to the amount of alkali added is plotted. In this neutralization titration, in the curve where the pH measured with respect to the amount of alkali added is plotted, one point where the increment (differential value of the pH with respect to the amount of alkali dropped) becomes maximum is confirmed, and this maximum point is called the first end point. Here, the region from the start of titration to the first end point in FIG. 3 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the dispersion used for titration. Then, the amount of carboxy group introduced (mmol / g) is calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solid content (g) in the dispersion containing the fibrous cellulose to be titrated.

[0058] Note that since the denominator of the above-mentioned amount of carboxy group introduced (mmol / g) is the mass of the acid-type fibrous cellulose, it indicates the amount of carboxy groups (hereinafter referred to as the amount of carboxy groups (acid type)) possessed by the acid-type fibrous cellulose. On the other hand, when the counter ion of the carboxy group is replaced with an arbitrary cation C so that the charge equivalent is achieved, the amount of carboxy groups (hereinafter referred to as the amount of carboxy groups (C type)) possessed by the fibrous cellulose having the cation C as the counter ion 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 calculation formula. Amount of carboxyl groups (C type) = Amount of carboxyl groups (acid type) / {1 + (W - 1) × (Amount of carboxyl groups (acid type)) / 1000} W: Formula weight per monovalent cation C (for example, Na is 23, Al is 9)

[0059] In the measurement of the amount of ionic substituents by titration, accurate values may not be obtained, such as when the dropping amount of one drop of aqueous sodium hydroxide solution is too large or the titration interval is too short, resulting in a lower amount of ionic substituents than the original. As appropriate dropping amounts and titration intervals, for example, it is desirable to titrate 0.1 N aqueous sodium hydroxide solution in 10 - 50 μL portions every 5 - 30 seconds. Also, in order to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, for example, it is desirable 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.

[0060] Also, the amount of sulfur oxoacid groups introduced into fibrous cellulose can be calculated by measuring the sulfur amount of a sample obtained by wet ashing a slurry containing fibrous cellulose and then diluting it at an appropriate ratio. Specifically, after wet ashing fibrous cellulose using perchloric acid and concentrated nitric acid, it is diluted at an appropriate ratio and the sulfur amount is measured by ICP emission analysis. The value divided by the absolute dry mass of the tested fibrous cellulose is taken as the amount of sulfur oxoacid groups (unit: mmol / g).

[0061] The degree of polymerization of microfibrillated cellulose is preferably 800 or less, more preferably 700 or less, still more preferably 450 or less, and particularly preferably 300 or less. In addition, the degree of polymerization of fibrous cellulose is preferably 100 or more, and more preferably 150 or more. By setting the degree of polymerization of microfibrillated cellulose within the above range, it becomes easier to obtain a dispersion having a TI value within a predetermined range while containing microfibrillated cellulose at a high concentration.

[0062] The degree of polymerization of the microfibrillar cellulose is a value calculated from the pulp viscosity measured according to Tappi T230. Specifically, the viscosity of the microfibrillar cellulose to be measured dispersed in an aqueous solution of copper ethylenediamine (designated as ηX) and the blank viscosity measured with only the dispersion medium (designated as η0) are measured. Then, the specific viscosity (ηsp) and the intrinsic viscosity ([η]) are measured according to the following formulas. ηsp = (ηX / η0) - 1 [η] = ηsp / (c(1 + 0.28 × ηsp)) Here, c in the formula indicates the concentration of the microfibrillar 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 the average degree of polymerization measured by the viscosity method, it is sometimes referred to as the "viscosity average degree of polymerization".

[0063] As described above, the fibrous cellulose according to the present embodiment and the dispersion containing the fibrous cellulose have been described. In addition, in this specification, as another embodiment, a microfibrillar cellulose-containing dispersion having a fiber width of 1000 nm or less and having an ionic substituent, wherein the content of the microfibrillar 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 degree of polymerization of the microfibrillar cellulose is 165 or more and 290 or less, and the viscosity (η1) of the dispersion measured using a rheometer under the condition of a shear rate of 1 sec -1 is 60 Pa·s or more and 830 Pa·s or less, and the viscosity (η2) of the dispersion measured using a rheometer under the condition of a shear rate of 1000 sec -1 is 0.02 Pa·s or more and 0.56 Pa·s or less, is also disclosed. The ionic substituent is particularly preferably a phosphooxo acid group or a substituent derived from a phosphooxo acid group (among them, a phosphate group). Also, the introduction amount of the ionic substituent with respect to the microfibrillar cellulose is particularly preferably 0.90 mmol / g or more and 2.00 mmol / g or less. Since other explanations are the same as those for the dispersion containing the fibrous cellulose according to the above-described present embodiment, they are omitted here.

[0064] <Method for Producing Microfibrillar Cellulose> <Fiber Raw Material> Microfibrillar cellulose is produced from a fiber raw material (cellulose fiber) containing cellulose. The fiber raw material containing cellulose is not particularly limited, but it is preferable to use pulp in terms of easy availability and low cost. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Wood pulp is not particularly limited, but examples include chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), 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 chemigroundwood pulp (CGP), and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Non-wood pulp is not particularly limited, but examples include cotton-based pulps such as cotton linter and cotton lint, and non-wood-based pulps such as hemp, wheat straw, and bagasse. Deinked pulp is not particularly limited, but examples include deinked pulp made from waste paper. The pulp of this embodiment may be used alone or in combination of two or more. Among the above pulps, from the viewpoint of easy availability, for example, wood pulp and deinked pulp are preferable. Among wood pulps, from the viewpoint of a large cellulose ratio and a high yield of microfibrillar cellulose during fibrillation treatment, and a small decomposition of cellulose in the pulp and obtaining microfibrillar cellulose with long fibers having a large aspect ratio, for example, chemical pulp is more preferable, and kraft pulp and sulfite pulp are even more preferable. Among them, pulp derived from softwood is preferably used because it has good fibrillation properties during the fibrillation treatment described later and the transparency of the dispersion is further improved.

[0065] As the fiber raw material containing cellulose, for example, the cellulose contained in jellyfish or the bacterial cellulose produced by acetic acid bacteria can be used. Further, instead of the fiber raw material containing cellulose, fibers formed of linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

[0066] <Phosphonooxy group introduction step> The production process of microfibrillar cellulose includes an ionic substituent introduction step. Examples of the ionic substituent introduction step include a phosphonooxy group introduction step. The phosphonooxy group introduction step is a step of allowing at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing a phosphonooxy group to act on a fiber raw material containing cellulose by reacting with a hydroxyl group of the fiber raw material containing cellulose. By this step, a phosphonooxy group-introduced fiber is obtained.

[0067] In the phosphonooxy group introduction step according to this embodiment, the reaction between the fiber raw material containing cellulose and compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). On the other hand, the reaction between the fiber raw material containing cellulose and compound A may be carried out in the absence of compound B.

[0068] As an example of a method for allowing Compound A to act on a fiber raw material in the co - presence of Compound B, there is a method of mixing Compound A and Compound B with the fiber raw material in a dry state, a wet state, or a slurry state. Among these, it is preferable to use a fiber raw material in a dry state or a wet state because of the high uniformity of the reaction, and it is particularly preferable to use a fiber raw material in a dry state. The form of the fiber raw material is not particularly limited, but for example, it is preferably in a cotton - like or thin - sheet - like form. For Compound A and Compound B, there are methods of adding them to the fiber raw material in a powdery form, in a solution state dissolved in a solvent, or in a state melted by heating to a temperature above the melting point. Among these, since the uniformity of the reaction is high, it is preferable to add them in a solution state dissolved in a solvent, particularly in an aqueous solution state. Also, 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 state, the fiber raw material may be immersed in the solution to absorb the liquid and then taken out, or the solution may be dropped onto the fiber raw material. Further, the required amounts of Compound A and Compound B may be added to the fiber raw material, or after adding excessive amounts of Compound A and Compound B to the fiber raw material respectively, the excess Compound A and Compound B may be removed by pressing or filtration.

[0069] As the compound A used in this embodiment, any compound having a phosphorus atom and capable of forming an ester bond with cellulose may be used, and examples include phosphoric acid or its salts, phosphorous acid or its salts, dehydrated condensed phosphoric acid or its salts, and phosphoric anhydride (phosphorus pentoxide), but it is not particularly limited. As phosphoric acid, those with various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. As phosphorous acid, 99% phosphorous acid (phosphonic acid) can be mentioned. Dehydrated condensed phosphoric acid is a product obtained by condensing two or more molecules of phosphoric acid by a dehydration reaction, and examples include pyrophosphoric acid and polyphosphoric acid. As phosphates, phosphites, and dehydrated condensed phosphates, lithium salts, sodium salts, potassium salts, ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid can be mentioned, and these can have various degrees of neutralization. Among these, from the viewpoints of high introduction efficiency of the phosphate group, easier improvement of fibrillation efficiency in the fibrillation process described later, low cost, and easy industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferable, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferable.

[0070] The addition amount of compound A to the fiber raw material is not particularly limited. For example, when the addition amount of compound A is converted to the amount of phosphorus atoms, the addition amount of phosphorus atoms to the fiber raw material (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 addition amount of phosphorus atoms to the fiber raw material within the above range, the yield of microfibrillar cellulose can be further improved. On the other hand, by setting the addition amount of phosphorus atoms to the fiber raw material below the above upper limit value, a balance between the effect of improving the yield and the cost can be achieved.

[0071] 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, compound B is preferably used as an aqueous solution. Further, 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.

[0072] The addition amount of compound B with respect to the fiber raw material (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.

[0073] In the reaction between the fiber raw material containing cellulose and 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, dimethylacetamide, etc. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, etc. Among these, triethylamine is particularly known to act as a good reaction catalyst.

[0074] In the step of introducing a phosphooxo acid group, it is preferable to add or mix a compound A or the like to the fiber raw material and then perform a heat treatment on the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature at which the phosphooxo acid group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reactions of the fiber. The heat treatment temperature is preferably, for example, 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower. In addition, for the heat treatment, equipment having various heat media can be used. For example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heating device, a plate-type heating device, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized bed dryer, a pneumatic dryer, a vacuum dryer, an infrared heating device, a far-infrared heating device, a microwave heating device, and a high-frequency dryer can be used.

[0075] In the heat treatment according to this embodiment, for example, after adding compound A to a thin sheet-like fiber raw material by a method such as impregnation, a method of heating or a method of heating while kneading or stirring the fiber raw material and compound A with a kneader or the like can be adopted. Thereby, it becomes possible to suppress the concentration unevenness of compound A in the fiber raw material and to introduce the phosphooxo acid group more uniformly onto the surface of the cellulose fiber contained in the fiber raw material. This is presumably due to the fact that when water molecules move to the surface of the fiber raw material during drying, the dissolved compound A is attracted to the water molecules by surface tension and also moves to the surface of the fiber raw material (that is, the concentration unevenness of compound A is caused), which can be suppressed.

[0076] In addition, the heating device used for the heat treatment is preferably a device that can always discharge moisture held by the slurry and moisture generated during the dehydration condensation (phosphoric acid esterification) reaction between the hydroxyl groups contained in compound A and cellulose in the fiber raw material, etc., to the outside of the device system. Examples of such a heating device include a blower-type oven. By always discharging the moisture in the device system, in addition to suppressing the hydrolysis reaction of the phosphoric acid ester bond, which is the reverse reaction of phosphoric acid esterification, it is also possible to suppress the acid hydrolysis of the sugar chain in the fiber. Therefore, it becomes possible to obtain microfibrillar cellulose with a high aspect ratio.

[0077] The heat treatment time is preferably, for example, 1 second or more and 300 minutes or less after substantially removing moisture from the fiber raw material, more preferably 1 second or more and 1000 seconds or less, and even more preferably 10 seconds or more and 800 seconds or less. In this embodiment, by setting the heating temperature and heating time within an appropriate range, the introduction amount of the phosphonooxy group can be made within a preferable range.

[0078] The phosphonooxy group introduction step may be performed at least once, but can also be repeated two or more times. By performing the phosphonooxy group introduction step two or more times, a large amount of phosphonooxy groups can be introduced into the fiber raw material.

[0079] The introduction amount of the phosphoric acid group to the fiber raw material is preferably, for example, 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, still more preferably 0.40 mmol / g or more, even more preferably 0.60 mmol / g or more, still even more preferably 0.90 mmol / g or more, and particularly preferably 1.00 mmol / g or more per 1 g (mass) of the microfibrillar cellulose. Further, the introduction amount of the phosphoric acid group to the fiber raw material is preferably, for example, 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, still more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, still even more preferably 2.00 mmol / g or less, and particularly preferably 1.50 mmol / g or less per 1 g (mass) of the microfibrillar cellulose. By setting the introduction amount of the phosphoric acid group within the above range, the fibrillation of the fiber raw material can be facilitated, and the stability of the microfibrillar cellulose can be enhanced. Further, by setting the introduction amount of the phosphoric acid group within the above range, a dispersion liquid having a haze value within a predetermined range can be easily obtained while containing the microfibrillar cellulose at a high concentration. Further, by setting the introduction amount of the phosphoric acid group to 1.00 mmol / g or more, the salt resistance of the fibrillar cellulose can also be improved.

[0080] <Carboxy Group Introduction Step> The production process of the microfibrillar cellulose may include, as an ionic substituent introduction step, for example, a carboxy group introduction step. The carboxy group introduction step is carried out by subjecting the fiber raw material containing cellulose to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, or a compound having a group derived from a carboxylic acid or a derivative thereof, or an acid anhydride of a compound having a group derived from a carboxylic acid or a derivative thereof.

[0081] The compounds having a group derived from a carboxylic acid are not particularly limited, and examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Further, the derivatives of the compounds having a group derived from a carboxylic acid are not particularly limited, and examples thereof include imidized products of acid anhydrides of compounds having a carboxy group and derivatives of acid anhydrides of compounds having a carboxy group. The imidized products of acid anhydrides of compounds having a carboxy group are not particularly limited, and examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0082] The acid anhydrides of the compounds having a group derived from a carboxylic acid are not particularly limited, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Further, the derivatives of the acid anhydrides of the compounds having a group derived from a carboxylic acid are not particularly limited, and examples thereof include those in which at least a part of the hydrogen atoms of the acid anhydrides of the compounds having a carboxy group, such as dimethyl maleic anhydride, diethyl maleic anhydride, and diphenyl maleic anhydride, are substituted with substituents such as an alkyl group and a phenyl group.

[0083] In the carboxy group introduction step, when performing TEMPO oxidation treatment, for example, it is preferable to carry out the treatment under the condition that the pH is 6 or more and 8 or less. Such treatment is also referred to as neutral TEMPO oxidation treatment. The neutral TEMPO oxidation treatment can be carried out, for example, by adding pulp as a fiber raw material, a nitroxyl radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Further, by coexisting sodium chlorite, the aldehyde generated in the oxidation process can be efficiently oxidized to a carboxy group. Also, the TEMPO oxidation treatment may be carried out under the condition that the pH is 10 or more and 11 or less. Such treatment is also referred to as alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxyl radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material.

[0084] The amount of carboxyl groups introduced into fibrous cellulose varies depending on the type of substituent. For example, when carboxyl groups are introduced by TEMPO oxidation, it is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, further preferably 0.40 mmol / g or more, still 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 per 1 g (mass) of microfibrillated cellulose. Also, the amount of carboxyl groups introduced into fibrous cellulose is preferably 3.65 mmol / g or less, more preferably 3.00 mmol / g or less, further preferably 2.50 mmol / g or less, still more preferably 2.00 mmol / g or less, and even more preferably 1.50 mmol / g or less. Additionally, when the substituent is a carboxymethyl group, it may be 5.8 mmol / g or less per 1 g (mass) of microfibrillated cellulose. By setting the amount of carboxyl groups introduced within the above range, the fibrillation of the fiber raw material can be facilitated, and the stability of the fibrous cellulose can be enhanced. Also, by setting the amount of carboxyl groups introduced within the above range, it becomes easier to obtain a dispersion having a haze value within a predetermined range while containing microfibrillated cellulose at a high concentration.

[0085] <Sulfurous acid group introduction step> The manufacturing process of microfibrillated cellulose may include, as an ionic substituent introduction step, for example, a sulfurous acid group introduction step. In the sulfurous acid group introduction step, a cellulose fiber having a sulfurous acid group (sulfurous acid group-introduced fiber) can be obtained by reacting the hydroxyl groups of the fiber raw material containing cellulose with sulfurous acid.

[0086] In the step of introducing a sulfur oxo acid group, instead of compound A in the <step of introducing a phosphorus oxo acid group> described above, at least one compound selected from compounds capable of introducing a sulfur oxo acid group by reacting with the hydroxyl groups of a fiber raw material containing cellulose (hereinafter also referred to as "compound C") is used. As compound C, any compound having a sulfur atom and capable of forming an ester bond with cellulose may be used, and examples include sulfuric acid or its salts, sulfurous acid or its salts, sulfamic acid, etc., but it is not particularly limited. As sulfuric acid, those with various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. As sulfurous acid, 5% sulfurous acid aqueous solution can be mentioned. As sulfates or sulfites, lithium salts, sodium salts, potassium salts, ammonium salts, etc. of sulfates or sulfites can be mentioned, and these can have various degrees of neutralization. As sulfamic acid, sulfamic acid, etc. can be used. In the step of introducing a sulfur oxo acid group, it is preferable to use compound B in the <step of introducing a phosphorus oxo acid group> described above in the same manner.

[0087] In the step of introducing a sulfur oxo acid group, it is preferable to mix an aqueous solution containing sulfur oxo acid, and urea and / or a urea derivative with the cellulose raw material, and then subject the cellulose raw material to a heat treatment. As the heat treatment temperature, it is preferable to select a temperature at which the sulfur oxo acid group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reactions of the fiber. The heat treatment temperature is preferably 100 °C or higher, more preferably 120 °C or higher, and even more preferably 150 °C or higher. Also, the heat treatment temperature is preferably 300 °C or lower, more preferably 250 °C or lower, and even more preferably 200 °C or lower.

[0088] In the heat treatment step, it is preferable to heat until substantially no moisture remains. For this reason, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material, sulfur oxoacid, and the addition amount of the aqueous solution containing urea and / or urea derivative, but for example, it is preferably 10 seconds or more and 10000 seconds or less. For heat treatment, equipment having various heat media can be used, for example, a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll type heating device, a plate type heating device, a fluidized bed dryer, a band type dryer, a filtration dryer, a vibration fluidized dryer, a pneumatic dryer, a vacuum dryer, an infrared heating device, a far-infrared heating device, a microwave heating device, a high-frequency dryer can be used.

[0089] The introduction amount of the sulfur oxoacid group with respect to the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, further preferably 0.20 mmol / g or more, still more preferably 0.40 mmol / g or more, even more preferably 0.60 mmol / g or more, still even more preferably 0.90 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Also, the introduction amount of the sulfur oxoacid group with respect to the cellulose raw material is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less, further preferably 2.50 mmol / g or less, still more preferably 2.00 mmol / g or less, and particularly preferably 1.50 mmol / g or less. By setting the introduction amount of the sulfur oxoacid group within the above range, it is possible to facilitate the refinement of the fiber raw material and enhance the stability of the fibrous cellulose. Also, by setting the introduction amount of the sulfur oxoacid group within the above range, it becomes easier to obtain a dispersion liquid having a haze value within a predetermined range while containing microfibrillar cellulose at a high concentration.

[0090] <Washing step> In the method for producing microfibrillar cellulose according to the present embodiment, a washing step can be performed on the fiber with an ionic substituent introduced, if necessary. The washing step is performed, for example, by washing the fiber with an ionic substituent introduced with water or an organic solvent. Further, the washing step may be performed after each step described later, and the number of washing times performed in each washing step is not particularly limited.

[0091] <Alkali treatment step> When producing microfibrillar cellulose, an alkali treatment may be performed on the fiber raw material between the step of introducing an ionic substituent and the defibrillation treatment step described later. The method of alkali treatment is not particularly limited, and examples thereof include a method of immersing the fiber with an ionic substituent introduced in an alkali solution.

[0092] The alkali compound contained in the alkali solution is not particularly limited, and may be an inorganic alkali compound or an organic alkali compound. In the present embodiment, since it has high versatility, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkali compound. Further, the solvent contained in the alkali solution may be either water or an organic solvent. Among them, the solvent contained in the alkali solution is preferably a polar solvent containing water or a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing at least water. As the alkali solution, since it has high versatility, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable.

[0093] The temperature of the alkaline solution in the alkali treatment step is not particularly limited, but is preferably, for example, 5°C or higher and 80°C or lower, and more preferably 10°C or higher and 60°C or lower. The immersion time of the fiber with ionic substituent introduced therein in the alkaline solution in the alkali treatment step is not particularly limited, but is preferably, for example, 5 minutes or longer and 30 minutes or shorter, and more preferably 10 minutes or longer and 20 minutes or shorter. The amount of the alkaline solution used in the alkali treatment is not particularly limited, but is preferably, for example, 100% by mass or more and 100,000% by mass or less, and more preferably 1,000% by mass or more and 10,000% by mass or less, based on the absolute dry mass of the fiber with ionic substituent introduced therein.

[0094] In order to reduce the amount of the alkaline solution used in the alkali treatment step, the fiber with ionic substituent introduced therein may be washed with water or an organic solvent after the step of introducing the ionic substituent and before the alkali treatment step. After the alkali treatment step and before the fibrillation treatment step, from the viewpoint of improving the handleability, it is preferable to wash the fiber with ionic substituent introduced therein that has been subjected to the alkali treatment with water or an organic solvent.

[0095] <Acid treatment step> When producing microfibrillar cellulose, an acid treatment may be performed on the fiber raw material between the step of introducing an ionic substituent and the fibrillation treatment step described later. For example, the step of introducing an ionic substituent, the acid treatment, the alkali treatment, and the fibrillation treatment may be performed in this order.

[0096] The method of acid treatment is not particularly limited. For example, a method of immersing a fiber raw material in an acidic solution containing an acid can be mentioned. The concentration of the acidic solution to be used is not particularly limited, but for example, it is preferably 10% by mass or less, and more preferably 5% by mass or less. Further, the pH of the acidic solution to be used is not particularly limited, but for example, it is preferably 0 or more and 4 or less, and more preferably 1 or more and 3 or less. As the acid contained in the acidic solution, for example, an inorganic acid, a sulfonic acid, a carboxylic acid, etc. can be used. Examples of the inorganic acid include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, boric acid, etc. Examples of the sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, etc. Examples of the carboxylic acid 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.

[0097] The temperature of the acid solution in the acid treatment is not particularly limited, but for example, 5°C or more and 100°C or less is preferable, and 20°C or more and 90°C or less is more preferable. The immersion time in the acid solution in the acid treatment is not particularly limited, but for example, 5 minutes or more and 120 minutes or less is preferable, and 10 minutes or more and 60 minutes or less is more preferable. The amount of the acid solution used in the acid treatment is not particularly limited, but for example, it is preferably 100% by mass or more and 100,000% by mass or less with respect to the absolute dry mass of the fiber raw material, and more preferably 1,000% by mass or more and 10,000% by mass or less.

[0098] <Fibrillation treatment> By subjecting the fiber with an ionic substituent introduced thereto to a defibrillation treatment (mechanical treatment) in a defibrillation treatment step, microfibrous cellulose can be obtained. In the defibrillation treatment step, for example, a defibrillation treatment device can be used. The defibrillation treatment device is not particularly limited, and examples thereof include a high-speed defibrillator, a grinder (stone mill type crusher), a high-pressure homogenizer, an ultra-high pressure homogenizer, a high-pressure impact type crusher, a ball mill, a bead mill, a disk type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater. Among the above defibrillation treatment devices, it is more preferable to use a high-speed defibrillator, a high-pressure homogenizer, or an ultra-high pressure homogenizer, which are less affected by the grinding medium and have less risk of contamination.

[0099] In the defibrillation treatment step, for example, it is preferable to dilute the fiber with an ionic substituent introduced thereto with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, and examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, etc. 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. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), etc.

[0100] The concentration of cellulose fibers during the fibrillation treatment can be set as appropriate. In this embodiment, the concentration of cellulose fibers during the fibrillation treatment 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. Also, the upper limit of the concentration of cellulose fibers during the fibrillation treatment is not particularly limited. For example, it may be 20.0% by mass. In this embodiment, by setting the concentration of cellulose fibers during the fibrillation treatment within the above range, a sheet excellent in transparency and with suppressed curling can be easily obtained. In addition, by setting the concentration of cellulose fibers during the fibrillation treatment within the above range, it becomes possible to obtain a high-concentration dispersion liquid, and it is also possible to reduce costs during transportation and storage.

[0101] In addition, the slurry obtained by dispersing the ionically substituted group-introduced fibers in the dispersion medium may contain solids other than the ionically substituted group-introduced fibers, such as hydrogen-bonding urea.

[0102] <Low-viscosity treatment> The method for producing the microfibrillar cellulose of this embodiment preferably includes a step of further performing a low-viscosity treatment in addition to the steps as described above. Specifically, as described above, it preferably includes a step of subjecting the appropriately treated cellulose fibers to a fibrillation treatment to obtain fibrillar cellulose with a fiber width of 1000 nm or less, and a step of subjecting the fibrillar cellulose to a low-viscosity treatment. That is, the method for producing the microfibrillar cellulose of this embodiment preferably includes, for example, a step of performing a low-viscosity treatment after subjecting the cellulose fibers to a fibrillation treatment. Note that the low-viscosity treatment may be performed before the fibrillation treatment step. For example, the low-viscosity treatment may be performed before the fibrillation treatment, and then the low-viscosity treatment may be further performed after the fibrillation treatment. Also, after performing the low-viscosity treatment, the fibrillation treatment may be performed, and after further performing the low-viscosity treatment, the fibrillation treatment step may be performed again. Among them, in order to more effectively reduce the viscosity, it is preferable to perform the low-viscosity treatment after the fibrillation treatment.

[0103] The concentration of microfibrillar cellulose or cellulose fibers during the low-viscosity treatment can be set as appropriate, but it is preferably the same as the concentration of cellulose fibers during the fibrillation treatment. For example, the concentration of microfibrillar cellulose or cellulose fibers during the low-viscosity treatment is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, still more preferably 5.0% by mass or more, and particularly preferably 6.0% by mass or more. Also, the upper limit of the concentration of microfibrillar cellulose or cellulose fibers during the low-viscosity treatment is not particularly limited, but for example, it may be 20.0% by mass. In the present embodiment, by setting the concentration of cellulose fibers during the low-viscosity treatment within the above range, a sheet excellent in transparency and a sheet with suppressed curling are likely to be obtained.

[0104] Examples of the step of performing the low-viscosity treatment include an ozone treatment step, an enzyme treatment step, an acid treatment step, a subcritical water treatment step, and the like. The step of performing the low-viscosity treatment is preferably at least one selected from the ozone treatment step, the enzyme treatment step, and the acid treatment step, and particularly preferably at least one selected from the ozone treatment step and the enzyme treatment step.

[0105] In the ozone treatment step, ozone is added to the microfibrillar cellulose dispersion (slurry). When adding ozone, it is preferably added as an ozone / oxygen mixed gas, for example. At this time, the ozone addition rate per 1 g of microfibrillar cellulose contained in the microfibrillar cellulose dispersion (slurry) is preferably 1.0×10 -4 g or more, more preferably 1.0×10 -3 g or more, and still more preferably 1.0×10 -2 g or more. Note that the ozone addition rate per 1 g of microfibrillar cellulose is preferably 1.0×10 1 g or less. After adding ozone to the microfibrillar cellulose dispersion (slurry), it is preferably stirred under the conditions of 10°C or higher and 50°C or lower for 10 seconds or more and 10 minutes or less, and then left standing for 1 minute or more and 100 minutes or less.

[0106] In the enzyme treatment step, an enzyme is added to the fine fibrous cellulose dispersion (slurry). The enzyme used at this time is preferably a cellulase-based enzyme. Cellulase-based enzymes are classified into the carbohydrate hydrolase family based on the higher-order structure of the catalytic domain having the cellulose hydrolysis reaction function. Cellulase-based enzymes are roughly classified into endo-glucanase and cellobiohydrolase according to their cellulose decomposition characteristics. Endo-glucanase has high hydrolyzability for the amorphous part of cellulose, soluble cellooligosaccharides, or cellulose derivatives such as carboxymethyl cellulose, randomly cuts their molecular chains from the inside, and reduces the degree of polymerization. In contrast, cellobiohydrolase decomposes the crystalline part of cellulose to give cellobiose. Also, cellobiohydrolase hydrolyzes from the end of the cellulose molecule and is also called an exo-type or processive enzyme. The enzyme used in the enzyme treatment step is not particularly limited, but it is preferable to use endo-glucanase.

[0107] In the enzyme treatment step, it is preferable to add an enzyme so that the enzyme activity is 0.1 nkat or more per 1 g of fine fibrous cellulose, more preferably add an enzyme so that the enzyme activity is 1.0 nkat or more, and even more preferably add an enzyme so that the enzyme activity is 10 nkat or more. Also, it is preferable to add an enzyme so that the enzyme activity is 100000 nkat or less per 1 g of fine fibrous cellulose, more preferably add an enzyme so that the enzyme activity is 50000 nkat or less, and even more preferably add an enzyme so that the enzyme activity is 10000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferably treated under the conditions of 0 °C or more and less than 80 °C for 1 minute or more and 100 hours or less, and then the enzyme is inactivated by placing it under the conditions of 80 °C or more.

[0108] 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 microfibrillar cellulose dispersion (slurry). The addition rate of sodium hypochlorite is preferably 1.0×10 -4 g or more per 1 g of microfibrillar 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. Also, the addition rate of sodium hypochlorite is preferably 1.0×10 2 g or less per 1 g of microfibrillar cellulose. After adding sodium hypochlorite to the microfibrillar cellulose dispersion (slurry), it is preferable to stir under the conditions of 10°C or higher and 50°C or lower for 1 minute or more and 10 hours or less.

[0109] After the low-viscosity treatment step, it is preferable to further provide a defibrillation treatment step. Among them, it is preferable to provide a defibrillation treatment step before and after the low-viscosity treatment step. In this case, as the defibrillation treatment step, the same steps as those described above can be exemplified. Among them, in the defibrillation treatment step after the low-viscosity treatment step, it is preferable to use a high-pressure homogenizer or an ultra-high-pressure homogenizer.

[0110] Note that this embodiment may also relate to a method for producing microfibrillar cellulose, which includes at least one step each of defibrating cellulose fibers having an ionic substituent and reducing the viscosity. By including at least one step each of defibrating cellulose fibers having an ionic substituent and reducing the molecular weight in the method for producing microfibrillar cellulose, the concentration of cellulose fibers during the defibrating process can be increased further. Thereby, a highly concentrated microfibrillar cellulose dispersion can be efficiently obtained. In this case, the method for producing microfibrillar cellulose may include a defibrating step, a viscosity reduction treatment step, and a defibrating step in this order, or may include a viscosity reduction treatment step, a defibrating step, a viscosity reduction treatment step, and a defibrating step in this order. It is preferable that an ionic substituent introduction step, a washing step, an alkali treatment step, etc. as described above are provided before the first defibrating step or viscosity reduction treatment step. In such a method for producing microfibrillar cellulose, the viscosity reduction treatment step is preferably at least one selected from an ozone treatment step, an enzyme treatment step, a hypochlorous acid treatment step, and a subcritical water treatment step, and particularly preferably at least one selected from an ozone treatment step and an enzyme treatment step.

[0111] (Additive) The dispersion of this embodiment may contain other additives in addition to the microfibrillar cellulose and the dispersion medium as described above. Examples of other additives include an antifoaming agent, a lubricant, an ultraviolet absorber, a dye, a pigment, a stabilizer, a surfactant, a preservative (for example, phenoxyethanol), etc. Further, the fibrous cellulose dispersion may contain a hydrophilic polymer, a hydrophilic low molecule, an organic ion, etc. as optional components.

[0112] The hydrophilic polymer is preferably a hydrophilic oxygen-containing organic compound (excluding the above-mentioned cellulose fibers). Examples of the oxygen-containing organic compound include hydrophilic polymers such as polyethylene glycol, polyethylene oxide, casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (such as acetacetyl polyvinyl alcohol), polyethylene oxide, polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylates, acrylic acid alkyl ester copolymer, urethane copolymer, cellulose derivatives (hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose, etc.).

[0113] The hydrophilic low-molecular-weight compound is preferably a hydrophilic oxygen-containing organic compound, and more preferably a polyhydric alcohol. Examples of the polyhydric alcohol include glycerin, sorbitol, ethylene glycol, etc.

[0114] Examples of the organic ion include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of the 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 the tetraalkylphosphonium ions include tetramethylphosphonium ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion, and lauryltrimethylphosphonium ion. Also, as the tetrapropylonium ion and tetrabutylonium ion, tetra n-propylonium ion, tetra n-butylonium ion, etc. can be mentioned respectively.

[0115] (Method for producing dispersion liquid) This embodiment may relate to a method for producing the above-described microfibrillar cellulose dispersion. The method for producing the microfibrillar cellulose dispersion includes a step of defibrating cellulose fibers having ionic substituents (defibrating step) and a step of reducing viscosity (viscosity reduction step). Here, in the defibrating step, the concentration of the cellulose fibers is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, still more preferably 5.0% by mass or more, and particularly preferably 6.0% by mass or more. Further, in the viscosity reduction step, the concentration of the microfibrillar cellulose or cellulose fibers is preferably 3.0% by mass or more, more preferably 4.0% by mass or more, still more preferably 5.0% by mass or more, and particularly preferably 6.0% by mass or more, in the same manner as above.

[0116] The step of reducing viscosity may be provided before the defibrating step, or may be provided after the defibrating step. Further, the step of reducing viscosity may be provided before and after the defibrating step. For example, after performing the viscosity reduction treatment before the defibrating treatment, the viscosity reduction treatment may be further performed after the defibrating treatment. Further, after performing the viscosity reduction treatment, the defibrating treatment may be performed, and after further performing the viscosity reduction treatment, the defibrating step may be performed again. Among them, the step of reducing viscosity is preferably provided after the defibrating step. Note that examples of the viscosity reduction treatment include the treatments as described above.

[0117] In the method for producing the dispersion of this embodiment, by including both the defibrating step and the viscosity reduction step and setting the cellulose fibers in the defibrating step to a high concentration, it has been successful in obtaining a high-concentration dispersion in which the content of fibrous cellulose is 3.0% by mass or more based on the total mass of the dispersion. Further, in the method for producing the dispersion of this embodiment, by providing the viscosity reduction step in addition to such a defibrating step, it becomes possible to set the TI value of the dispersion to 1 or more and 80,000 or less.

[0118] In the method for producing the dispersion of the present embodiment, by setting the concentration of the cellulose fiber in the fibrillation treatment step to 3.0% by mass or more, the concentration of the microfibrillated cellulose dispersion obtained after the fibrillation treatment step can be set to 3.0% by mass or more. Therefore, in the method for producing the dispersion of the present embodiment, there is no need to provide a concentration step. The method for producing the dispersion of the present embodiment preferably does not have a concentration step. Examples of the concentration step include a step of performing concentration using a flocculant, a step of heat concentration, and the like.

[0119] (Use) The dispersion of the present embodiment is a dispersion containing microfibrillated cellulose at a high concentration. Therefore, it is particularly preferably used for applications where microfibrillated cellulose is to be added at a high concentration. For example, the microfibrillated cellulose of the present embodiment can be used as an additive to foods, cosmetics, cement, paints (for vehicle coatings such as automobiles, ships, and airplanes, building materials, daily necessities, etc.), inks, pharmaceuticals, and the like. Further, the microfibrillated cellulose of the present embodiment can be added to resin-based materials and rubber-based materials.

[0120] Further, when a sheet or a coating film is formed from the dispersion of the present embodiment containing microfibrillated cellulose at a high concentration, the mechanical strength of the obtained sheet or coating film can be increased. For example, the tensile strength and tensile modulus of the sheet or coating film can be more effectively increased. Furthermore, since the dispersion of the present embodiment is highly transparent, the transparency of the obtained sheet or coating film can also be increased. Thus, the microfibrillated cellulose dispersion of the present embodiment is preferably a dispersion for sheet formation, and the present embodiment may relate to a sheet containing the above-described microfibrillated cellulose.

[0121] Furthermore, when a sheet or a coating film is formed from the dispersion of the present embodiment containing microfibrillated cellulose at a high concentration, a sheet or a coating film with a high basis weight can be obtained.

[0122] When manufacturing a sheet from the dispersion of the present embodiment, it preferably includes a coating step of coating the dispersion on a substrate or a papermaking step of papermaking the dispersion.

[0123] In the coating step, for example, a slurry (coating liquid) containing fibrous cellulose is coated on a substrate, and the sheet formed by drying this is peeled from the substrate to obtain a sheet. By using a coating apparatus and a long substrate, the sheet can be continuously produced. Further, the papermaking step is performed by papermaking the slurry with a paper machine. The paper machine used in the papermaking step is not particularly limited, and examples include continuous paper machines such as a fourdrinier type, a cylinder type, and an inclined type, or a multi-layer combined papermaking machine combining these. In the papermaking step, a known papermaking method such as hand papermaking may be adopted.

[0124] A resin layer or an inorganic layer may be further laminated on the sheet formed from the dispersion of the present embodiment.

[0125] Further, the present embodiment may have the following configuration. <101>A fine fibrous cellulose-containing dispersion having a fiber width of 1000 nm or less and having an ionic substituent, wherein 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 165 or more and 290 or less, the viscosity (η1) of the dispersion measured using a rheometer under the condition of a shear rate of 1 sec -1 is 60 Pa·s or more and 830 Pa·s or less, the viscosity (η2) of the dispersion measured using a rheometer under the condition of a shear rate of 1000 sec -1 is 0.02 Pa·s or more and 0.56 Pa·s or less, a fine fibrous cellulose-containing dispersion. <102>The fine fibrous cellulose-containing dispersion according to <101>, wherein the ionic substituent is a phosphonooxy group or a substituent derived from a phosphonooxy group. The fine fiber cellulose-containing dispersion liquid according to <101> or <102>, wherein the introduction amount of the ionic substituent to the fine fiber cellulose is 0.90 mmol / g or more and 2.00 mmol / g or less.

[0126] <111> A step of subjecting cellulose fibers having an ionic substituent to a defibrillation treatment to obtain fibrous cellulose having a fiber width of 1000 nm or less; A method for producing a fibrous cellulose-containing dispersion liquid, comprising a step of subjecting the fibrous cellulose to a viscosity reduction treatment, wherein the content of the fibrous cellulose is 3.0% by mass or more based on the total mass of the dispersion liquid, and the TI value of the dispersion liquid calculated by the following condition (a) is 1 or more and 80,000 or less; Condition (a): Using a rheometer, the viscosity (η1) of the dispersion liquid under the condition of a shear rate of 1 sec -1 and the viscosity (η2) of the dispersion liquid under the condition of a shear rate of 1000 sec -1 are measured, and the TI value is calculated by the following formula. TI value = η1 / η2 <112> In the step of subjecting to a defibrillation treatment to obtain fibrous cellulose having a fiber width of 1000 nm or less, the concentration of the cellulose fibers is 3.0% by mass or more. The method for producing a fibrous cellulose-containing dispersion liquid according to <111>. <113> The step of subjecting to a viscosity reduction 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. The method for producing a fibrous cellulose-containing dispersion liquid according to <111> or <112>. <114> After the step of subjecting to a viscosity reduction treatment, further comprising a step of subjecting to a defibrillation treatment. The method for producing a fibrous cellulose-containing dispersion liquid according to any one of <111> to <113>. <115> A dispersion liquid produced by the method for producing a fibrous cellulose-containing dispersion liquid according to any one of <111> to <114>.

Example

[0127] The features of the present invention will be further specifically described below with reference to Examples and Comparative Examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following Examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0128] <Production Example 1> [Production of phosphorylated microfibrous cellulose dispersion] As the raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 208 g / m 2 sheet-like, disintegrated, and having a Canadian Standard Freeness (CSF) measured in accordance with JIS P 8121-2:2012 of 700 ml) was used. The raw material pulp was subjected to a phosphoxylation treatment as follows. First, an aqueous mixed solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (dry mass) of the above raw material pulp, and adjusted to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 200 seconds to introduce phosphate groups into the cellulose in the pulp and obtain a phosphorylated pulp.

[0129] Next, the obtained phosphorylated pulp was subjected to a washing treatment. The washing treatment was performed by repeating the operation of pouring 10 L of ion-exchanged water into 100 g (dry mass) of the phosphorylated pulp to obtain a pulp dispersion, stirring the pulp dispersion so that the pulp was uniformly dispersed, and then filtering and dehydrating. The washing was terminated when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0130] Next, the neutralization treatment of the washed phosphorylated pulp was performed as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1N aqueous sodium hydroxide solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 or more and 13 or less. Next, the phosphorylated pulp slurry was dehydrated to obtain a phosphorylated pulp subjected to the neutralization treatment. Next, the above washing treatment was performed on the phosphorylated pulp after the neutralization treatment.

[0131] The infrared absorption spectrum of the phosphorylated pulp thus obtained was measured using FT-IR. As a result, absorption based on phosphate groups was observed around 1230 cm -1 −1, and it was confirmed that phosphate groups were added to the pulp.

[0132] In addition, when the obtained phosphorylated pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions around 2θ = 14° or more and 17° or less and around 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals.

[0133] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content concentration of 3% by mass. This slurry was treated once with a single disk refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. In addition, the amount of phosphate groups (the amount of the first dissociation acid) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.45 mmol / g. The total amount of dissociation acids was 2.45 mmol / g.

[0134] <Production Example 2> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example 1 to prepare a slurry with a solid content concentration of 6% by mass. This slurry was treated once with a single disk refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. In addition, the amount of phosphate groups (the amount of the first dissociation acid) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.45 mmol / g. The total amount of dissociation acids was 2.45 mmol / g.

[0135] <Production Example 3> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example 1 to prepare a slurry having a solid content concentration of 13% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. The amount of phosphate groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g.

[0136] <Production Example 4> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example 1 to prepare a slurry having a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. The amount of phosphate groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g.

[0137] <Production Example 5> [Production of TEMPO-oxidized microfibrillated cellulose dispersion] As the raw material pulp, softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used. Alkaline TEMPO oxidation treatment was performed on this raw material pulp as follows. First, 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), 10 parts by mass of sodium bromide, and 100 parts by mass of the above raw material pulp equivalent to a dry mass were dispersed in 10,000 parts by mass of water. Next, a 13% by mass sodium hypochlorite solution was added so that the amount of sodium hypochlorite became 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 maintain the pH at 10 or more and 10.5 or less, and the reaction was considered to be complete when no change in pH was observed.

[0138] Next, the obtained TEMPO-oxidized pulp was subjected to a washing treatment. The washing treatment was performed by dehydrating the pulp slurry after TEMPO oxidation to obtain a dehydrated sheet, then pouring 5000 parts by mass of ion-exchanged water, stirring to disperse uniformly, and then repeating the operation of filtration and dehydration. The washing end point was determined when the electric conductivity of the filtrate reached 100 μS / cm or less.

[0139] The following oxidation treatment of the remaining aldehyde groups was performed on this dehydrated sheet. The dehydrated sheet corresponding to 100 parts by mass of dry mass was dispersed in 10000 parts by mass of 0.1 mol / L acetic acid buffer (pH 4.8). Then, 113 parts by mass of 80% sodium chlorite was added, and immediately sealed. Then, the reaction was carried out at room temperature for 48 hours with stirring at 500 rpm using a magnetic stirrer to obtain a pulp slurry.

[0140] Next, the obtained post-oxidized TEMPO-oxidized pulp was subjected to a washing treatment. The washing treatment was performed by dehydrating the pulp slurry after post-oxidation to obtain a dehydrated sheet, then pouring 5000 parts by mass of ion-exchanged water, stirring to disperse uniformly, and then repeating the operation of filtration and dehydration. The washing end point was determined when the electric conductivity of the filtrate reached 100 μS / cm or less.

[0141] In addition, when the obtained TEMPO-oxidized pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions near 2θ = 14° or more and 17° or less and near 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals.

[0142] Ion-exchanged water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solid content concentration of 3% by mass. This slurry was treated once with a single disk refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose. Also, the amount of carboxyl groups measured by the measurement method described later was 1.30 mmol / g.

[0143] <Production Example 6> Ion-exchanged water was added to the TEMPO-oxidized pulp obtained in Production Example 5 to prepare a slurry having a solid content concentration of 6% by mass. This slurry was treated once with a single disk refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose. Also, the amount of carboxyl groups measured by the measurement method described later was 1.30 mmol / g.

[0144] <Production Example 7> Ion-exchanged water was added to the TEMPO-oxidized pulp obtained in Production Example 5 to prepare a slurry having a solid content concentration of 13% by mass. This slurry was treated once with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) at a pressure of 200 MPa to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of carboxyl groups measured by the measurement method described later was 1.30 mmol / g.

[0145] <Production Example 8> Ion-exchanged water was added to the TEMPO-oxidized pulp obtained in Production Example 5 to prepare a slurry having a solid content concentration of 6% by mass. This slurry was treated once with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) at a pressure of 200 MPa to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of carboxyl groups measured by the measurement method described later was 1.30 mmol / g.

[0146] <Production Example 9> [Production of Phosphorous Acid Microfibrillated Cellulose Dispersion] As the raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 245 g / m 2A sheet-like material with a Canadian Standard Freeness (CSF) of 700 ml measured in accordance with JIS P 8121-2:2012 after dissociation was used. The raw pulp was subjected to a phosphorous oxooxidation treatment as follows. First, an aqueous mixed solution of phosphorous acid (phosphonic acid) and urea was added to 100 parts by mass (dry mass) of the above raw pulp to prepare a solution containing 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-impregnated pulp. Next, the obtained chemical-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-acidified pulp.

[0147] Next, the obtained phosphorous-acidified pulp was subjected to a washing treatment. The washing treatment was performed by repeating the operation of pouring 10 L of ion-exchanged water into 100 g (dry mass) of the phosphorous-acidified pulp to obtain a pulp dispersion, stirring the pulp dispersion so that the pulp was uniformly dispersed, and then filtering and dehydrating. The washing was terminated when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0148] Next, the washed phosphorous-acidified pulp was subjected to a neutralization treatment as follows. First, the washed phosphorous-acidified pulp was diluted with 10 L of ion-exchanged water, and then a 1N aqueous sodium hydroxide solution was added little by little while stirring to obtain a phosphorous-acidified pulp slurry with a pH of 12 or more and 13 or less. Next, the phosphorous-acidified pulp slurry was dehydrated to obtain a phosphorous-acidified pulp subjected to the neutralization treatment. Next, the above washing treatment was performed on the phosphorous-acidified pulp after the neutralization treatment.

[0149] The infrared absorption spectrum of the thus obtained phosphorous-acidified pulp was measured using FT-IR. As a result, 1210 cm -1Absorption based on P=O of phosphonic acid groups, which are tautomers of phosphorous acid groups, was observed in the vicinity, and it was confirmed that (phosphorous) phosphoric acid groups were added to the pulp. Further, when the obtained phosphorous-acidified pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions in the vicinity of 2θ = 14° or more and 17° or less and in the vicinity of 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals.

[0150] Ion-exchanged water was added to the obtained phosphorous-acidified pulp to prepare a slurry with a solid content concentration of 3% by mass. This slurry was processed once with a single disk refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose. Further, the amount of phosphorous acid groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphorus oxo acid groups] described later was 1.51 mmol / g. The total dissociation acid amount was 1.54 mmol / g.

[0151] <Production Example 10> Ion-exchanged water was added to the phosphorous-acidified pulp obtained in Production Example 9 to prepare a slurry with a solid content concentration of 6% by mass. This slurry was processed once with a single disk refiner (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose. Further, the amount of phosphorous acid groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphorus oxo acid groups] described later was 1.51 mmol / g. The total dissociation acid amount was 1.54 mmol / g.

[0152] <Production Example 11> Ion-exchanged water was added to the phosphorous-acidified pulp obtained in Production Example 9 to prepare a slurry with a solid content concentration of 13% by mass. This slurry was processed once at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose. Further, the amount of phosphorous acid groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphorus oxo acid groups] described later was 1.51 mmol / g. The total dissociation acid amount was 1.54 mmol / g.

[0153] <Production Example 12> Ion-exchanged water was added to the phosphorous acid pulp obtained in Production Example 9 to prepare a slurry having a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa using a wet atomization apparatus (manufactured by Sugino Machine Ltd., Starburst) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. The amount of phosphorous acid groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphono-oxy acid groups] described later was 1.51 mmol / g. The total dissociation acid amount was 1.54 mmol / g.

[0154] <Production Example 13> The same treatment was carried out except that the pulp of Production Example 1 was used as a hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. to obtain a phosphorylated pulp. Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry having a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa using a wet atomization apparatus (manufactured by Sugino Machine Ltd., Starburst) to obtain a fibrous cellulose dispersion containing fine fibrous cellulose. The amount of phosphoric acid groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphono-oxy acid groups] described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g.

[0155] <Production Example 14> A fibrous cellulose dispersion containing fine fibrous cellulose was obtained in the same manner as in Production Example 13, except that a slurry was prepared so that the solid content concentration of the phosphorylated pulp obtained in Production Example 13 was 13% by mass.

[0156] <Production Example 15> Except that the pulp of Production Example 5 was changed to broadleaf dissolving pulp (undried) manufactured by Oji Paper Co., Ltd., the same treatment was carried out to obtain TEMPO-oxidized pulp. Ion-exchanged water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solid content concentration of 13% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Ltd.) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of carboxyl groups measured by the measurement method described later was 1.30 mmol / g.

[0157] <Production Example 16> Except that the pulp of Production Example 9 was changed to broadleaf dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd., the same treatment was carried out to obtain phosphonated pulp. Ion-exchanged water was added to the obtained phosphonated pulp to prepare a slurry with a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Ltd.) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of phosphite groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.51 mmol / g. The total dissociation acid amount was 1.54 mmol / g.

[0158] <Production Example 17> A fibrous cellulose dispersion containing microfibrillated cellulose was obtained in the same manner as in Production Example 16, except that a slurry was prepared so that the solid content concentration of the phosphonated pulp obtained in Production Example 16 was 13% by mass.

[0159] <Production Example 18> [Pre-hydrolysis] 300 g of softwood chips were collected by absolute dry mass and immersed in 10 liters of tap water overnight. Then, the chips were taken out, put through a 400-mesh sieve, and filtered. The dehydrated chips were placed in an autoclave with a volume of 2.5 liters, tap water was added so that the liquid-to-solid mass ratio (when the mass of the chips after absolute drying was 1) was 3, and then heated at 165 °C for 30 minutes to perform pre-hydrolysis. The P-factor at this time was 380. [Cooking] After pre-hydrolysis, waste gas was extracted from the degassing cock of the autoclave. After confirming that the pressure inside the autoclave had reached 0, the processed chips were passed through a 400-mesh sieve and filtered. The filtered chips were put back into a 2.5-liter autoclave, and cooking liquor was added to achieve a liquor ratio of 5. Kraft cooking was carried out 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 based on the oven-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 the cooked pulp. [Bleaching] 70 g of the cooked pulp was taken in terms of oven-dry mass, 2.0% by mass of caustic soda was added based on the total mass of the oven-dry pulp, and then it was diluted with ion-exchanged water to adjust the pulp concentration to 10% by mass. This slurry was put into an indirectly heated autoclave, 99.9% compressed oxygen gas was injected to set the gauge pressure to 0.5 MPa, and oxygen bleaching was carried out at 100°C for 60 minutes. After the oxygen bleaching was completed, the pressure was reduced until the gauge pressure was 0.05 MPa or less, the pulp was taken out of the autoclave, washed with 7 liters of ion-exchanged water, and then dehydrated. In this way, the pulp after oxygen bleaching was obtained. 60 g of oxygen-delignified pulp was collected in terms of absolute dry mass, put into a plastic bag, and ion-exchanged water was added to adjust the pulp concentration to 10% by mass. Then, 1.8% by mass of chlorine dioxide was added based on the total mass of the absolute dry pulp, and it was immersed in a constant temperature water bath at 70°C for 70 minutes (D0 stage treatment). After the D0 stage treatment, the obtained pulp was diluted to 3% by mass 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, ion-exchanged water was added to adjust the pulp concentration to 10% by mass, and then 1.0% by mass of caustic soda and 0.3% by mass of hydrogen peroxide were added based on the total mass of the absolute dry pulp, and they were mixed well. Then, it was immersed in a constant temperature water bath at 70°C for 100 minutes to perform the E / P stage treatment. The obtained pulp was diluted to 3% by mass with ion-exchanged water, and then dehydrated and washed with a Buchner funnel. The pulp after the E / P stage treatment was put into a plastic bag, and the pulp concentration was adjusted to 10% by mass using ion-exchanged water. Then, 0.3% by mass of chlorine dioxide was added based on the total mass of the absolute dry pulp, and it was immersed in a constant temperature water bath at 70°C for 80 minutes to perform the D1 stage bleaching treatment. The obtained pulp was diluted to 3% by mass with ion-exchanged water, and then dehydrated and washed with a Buchner funnel to obtain bleached pulp. [Phosphorylation] Using this bleached pulp, the same treatment as in Production Example 1 was performed to obtain phosphorylated pulp. [Fibrillation] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of phosphate groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphoacid groups] described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g.

[0160] <Production Example 19> A fibrous cellulose dispersion containing microfibrillated cellulose was obtained in the same manner as in Production Example 18, except that a slurry was prepared so that the solid content concentration of the phosphorylated pulp obtained in Production Example 18 was 13% by mass.

[0161] <Production Example 20> The same procedures as in Production Example 5 were carried out except that the bleached pulp of Production Example 18 was used, to obtain a TEMPO-oxidized pulp. Ion-exchanged water was added to the obtained TEMPO-oxidized pulp to prepare a slurry having a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of carboxyl groups measured by the measurement method described later was 1.30 mmol / g.

[0162] <Production Example 21> A fibrous cellulose dispersion containing microfibrillated cellulose was obtained in the same manner as in Production Example 20 except that a slurry was prepared so that the solid content concentration of the TEMPO-oxidized pulp obtained in Production Example 20 was 13% by mass.

[0163] <Production Example 22> The same procedures as in Production Example 9 were carried out except that the bleached pulp of Production Example 18 was used, to obtain a phosphonated pulp. Ion-exchanged water was added to the obtained phosphonated pulp to prepare a slurry having a solid content concentration of 13% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of phosphite groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.51 mmol / g. The total dissociation acid amount was 1.54 mmol / g.

[0164] <Production Example 23> Except that the pulp of Production Example 1 was changed to hardwood kraft pulp (dry sheet) manufactured by Senibra, the same treatment as in Production Example 1 was carried out to obtain phosphorylated pulp. Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. The amount of phosphate groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g.

[0165] <Production Example 24> A fibrous cellulose dispersion containing microfibrillated cellulose was obtained in the same manner as in Production Example 23, except that a slurry was prepared so that the solid content concentration of the phosphorylated pulp obtained in Production Example 23 was 13% by mass.

[0166] <Production Example 25> The raw material pulp of Production Example 5 was changed to hardwood kraft pulp (dry sheet) manufactured by Senibra, and ion-exchanged water was added thereto to obtain a slurry with a pulp concentration of 2% by mass. After thoroughly stirring at 4000 rpm with a disperser to obtain a pulp slurry, it was thoroughly dehydrated with a mesh bag to obtain wet pulp. The same treatment as in Production Example 5 was carried out on the obtained wet pulp to obtain TEMPO-oxidized pulp. Ion-exchanged water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. The amount of carboxyl groups measured by the measurement method described later was 1.30 mmol / g.

[0167] <Production Example 26> A fibrous cellulose dispersion containing microfibrillated cellulose was obtained in the same manner as in Production Example 25, except that a slurry was prepared so that the solid content concentration of the TEMPO-oxidized pulp obtained in Production Example 25 was 13% by mass.

[0168] <Production Example 27> The same procedures as in Production Example 9 were carried out except that the raw material pulp of Production Example 9 was changed to hardwood kraft pulp (dry sheet) manufactured by Senibra Co., Ltd., to obtain phosphonated pulp. Ion-exchanged water was added to the obtained phosphonated pulp to prepare a slurry having a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. The amount of phosphite groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described below was 1.51 mmol / g. The total dissociation acid amount was 1.54 mmol / g.

[0169] <Production Example 28> A fibrous cellulose dispersion containing microfibrillated cellulose was obtained in the same manner as in Production Example 27, except that a slurry was prepared so that the solid content concentration of the phosphonated pulp obtained in Production Example 27 was 13% by mass.

[0170] <Production Example 29> As the raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 208 g / m 2 sheet-like, and the Canadian standard freeness (CSF) measured in accordance with JIS P 8121 after disintegration was 700 ml) manufactured by Oji Paper Co., Ltd. was used. Sulfation treatment was carried out on this raw material pulp as follows. First, an aqueous mixed solution of amidosulfuric acid and urea was added to 100 parts by mass (dry mass) of the above raw material pulp, and adjusted to 38 parts by mass of amidosulfuric acid, 120 parts by mass of urea, and 150 parts by mass of water to obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165 °C for 20 minutes to introduce sulfate groups into the cellulose in the pulp, and a sulfated pulp was obtained.

[0171] Next, the obtained sulfated pulp was subjected to a washing treatment. The washing treatment was performed by repeating the operation of pouring 10 L of ion-exchanged water into 100 g (dry mass) of the sulfated pulp to obtain a pulp dispersion, stirring it so that the pulp was uniformly dispersed, and then filtering and dehydrating. The washing end point was determined when the electrical conductivity of the filtrate became 100 μS / cm or less. Next, the neutralization treatment of the washed sulfated pulp was carried out as follows. First, the washed sulfated pulp was diluted with 10 L of ion-exchanged water, and then a 1N aqueous sodium hydroxide solution was added little by little while stirring to obtain a sulfated pulp slurry with a pH of 12 or more and 13 or less. Next, the sulfated pulp slurry was dehydrated to obtain a sulfated pulp subjected to the neutralization treatment. Next, the above washing treatment was performed on the sulfated pulp after the neutralization treatment.

[0172] The infrared absorption spectrum of the obtained sulfated pulp was measured using FT-IR. As a result, an absorption based on a sulfate group (sulfone group) was observed in the vicinity of 1220 - 1260 cm -1 −1, and it was confirmed that a sulfate group (sulfone group) was added to the pulp. Also, by X-ray diffraction, it was confirmed that the obtained sulfated pulp maintained the cellulose I type crystal.

[0173] Ion-exchanged water was added to the obtained sulfated pulp to prepare a slurry with a solid content concentration of 6% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of sulfate groups measured by the measurement method described in [Measurement of the amount of sulfur oxoacid groups] described later was 1.47 mmol / g.

[0174] <Example 1> In 1000 g (solid content concentration 3% by mass, solid content 30 g) of the microfibrillated cellulose dispersion obtained in Production Example 1, ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of the microfibrillated cellulose, stirred at 25°C in a sealed container, and then allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion.

[0175] The obtained microfibrillar cellulose dispersion was treated three times at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0176] <Example 2> To 1000 g (solid content concentration 3% by mass, solid content 30 g) of the microfibrillar cellulose dispersion obtained in Production Example 1, an enzyme-containing solution having an activity of 16500 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated three times at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst), and then heated to 100°C to inactivate the enzyme, obtaining a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0177] <Example 3> To 1000 g (solid content concentration 3.5% by mass, solid content 35 g) of the microfibrillar cellulose dispersion obtained in Production Example 1, 145 g of a sodium hypochlorite solution (available chlorine concentration 12% by mass) was added and thoroughly mixed at room temperature. The sodium hypochlorite addition rate at this time was 0.5 part by mass per 1 part by mass of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated three times at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0178] <Example 4> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 5 (solid content concentration: 3% by mass, solid content: 30 g), ozone was added at a ratio of 0.2 part by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Subsequently, the container was opened and the mixture was stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated 3 times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0179] <Example 5> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 5 (solid content concentration: 3% by mass, solid content: 30 g), an enzyme-containing solution having an activity of 16500 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 3 times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heated to 100°C to deactivate the enzyme, thereby obtaining a microfibrillar cellulose dispersion. A microfibrillar cellulose dispersion was obtained. Subsequently, the temperature was set to 100°C to deactivate the enzyme. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0180] <Example 6> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 5 (solid content concentration: 3.5% by mass, solid content: 35 g), 145 g of a sodium hypochlorite solution (available chlorine concentration: 12% by mass) was added, and the mixture was thoroughly mixed at room temperature. The sodium hypochlorite addition rate at this time was 0.5 part by mass per 1 part by mass of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 3 times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0181] <Example 7> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 9 (solid content concentration: 3% by mass, solid content: 30 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Subsequently, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0182] <Example 8> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 9 (solid content concentration: 3% by mass, solid content: 30 g), an enzyme-containing solution having an activity of 16500 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heated to 100°C to inactivate the enzyme, thereby obtaining a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0183] <Example 9> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 9 (solid content concentration: 3.5% by mass, solid content: 35 g), 145 g of a sodium hypochlorite solution (available chlorine concentration: 12% by mass) was added and thoroughly mixed at room temperature. The sodium hypochlorite addition rate at this time was 0.5 parts by mass per 1 part by mass of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 3% by mass.

[0184] <Example 10> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 2 (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0185] <Example 11> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 2 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heated to 100°C to inactivate the enzyme, thereby obtaining a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0186] <Example 12> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 6 (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0187] <Example 13> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 6 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added, and enzyme treatment was performed at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 3 times with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa, then heated to 100°C for heat inactivation to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0188] <Example 14> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 10 (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated 3 times with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0189] <Example 15> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 10 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added, and enzyme treatment was performed at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 3 times with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa, then heated to 100°C for heat inactivation to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0190] <Example 16> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 3 (solid content concentration: 13% by mass, solid content: 130 g), ozone was added at a ratio of 0.2 parts by mass with respect to 1 part by mass of the microfibrillar cellulose. After stirring at 25°C in a sealed container, the mixture was allowed to stand for 30 minutes. Subsequently, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion, thereby obtaining a microfibrillar cellulose dispersion. The obtained microfibrillar cellulose dispersion was further treated 4 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0191] <Example 17> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 3 (solid content concentration: 13% by mass, solid content: 130 g), an enzyme-containing solution having an activity of 71500 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat with respect to 1 g of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was further treated 4 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Ltd., Starburst), and then heated to 100°C to cause thermal deactivation, thereby obtaining a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0192] <Example 18> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 7 (solid content concentration: 13% by mass, solid content: 130 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion, thereby obtaining a microfibrillar cellulose dispersion. The obtained microfibrillar cellulose dispersion was further treated 4 times with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0193] <Example 19> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 7 (solid content concentration: 13% by mass, solid content: 130 g), an enzyme-containing solution having an activity of 71500 nkat was added, and the enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was further treated 4 times with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) at a pressure of 200 MPa, and then heated to 100°C to cause heat inactivation, thereby obtaining a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0194] <Example 20> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 11 (solid content concentration: 13% by mass, solid content: 130 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion, thereby obtaining a microfibrillar cellulose dispersion. The obtained microfibrillar cellulose dispersion was further treated 4 times with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0195] <Example 21> To 1000 g of the fine fibrous cellulose dispersion obtained in Production Example 11 (solid content concentration: 13% by mass, solid content: 130 g), an enzyme-containing solution having an activity of 71500 nkat was added, and enzyme treatment was performed at a temperature of 50°C. At this time, the enzyme addition amount was adjusted to 550 nkat per 1 g of the fine fibrous cellulose. The obtained fine fibrous cellulose dispersion was further treated 4 times with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa, and then heat-inactivated at 100°C to obtain a fine fibrous cellulose dispersion. The concentration of the fine fibrous cellulose in this fine fibrous cellulose dispersion was 13% by mass.

[0196] <Example 22> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example 1 to prepare a slurry having a solid content concentration of 6% by mass. In 1000 g of this slurry (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 part by mass per 1 part by mass of the fine fibrous cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Then, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion, thereby obtaining a fibrous cellulose dispersion. The obtained fibrous cellulose dispersion was treated 4 times with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion. The concentration of the fine fibrous cellulose in this fine fibrous cellulose dispersion was 6% by mass.

[0197] <Example 23> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example 1 to prepare a slurry having a solid content concentration of 6% by mass. An enzyme-containing solution having an activity of 33,000 nkat was added to 1000 g of this slurry (solid content concentration 6% by mass, solid content 60 g), and enzyme treatment was carried out at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 550 nkat per 1 g of microfibrillated cellulose. The obtained slurry was treated once with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) at a pressure of 200 MPa, and then the enzyme treatment was continued. Thereafter, it was treated three times at a pressure of 200 MPa and heated to 100°C to cause thermal deactivation, thereby obtaining a microfibrillated cellulose dispersion. The concentration of microfibrillated cellulose in this microfibrillated cellulose dispersion was 6% by mass.

[0198] <Example 24> Ion-exchanged water was added to the TEMPO-oxidized pulp obtained in Production Example 5 to prepare a slurry having a solid content concentration of 6% by mass. In 1000 g of this slurry (solid content concentration 6% by mass, solid content 60 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of microfibrillated cellulose, and after stirring at 25°C in a sealed container, it was allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion, thereby obtaining a fibrillated cellulose dispersion. The obtained fibrillated cellulose dispersion was treated four times with a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) at a pressure of 200 MPa to obtain a microfibrillated cellulose dispersion. The concentration of microfibrillated cellulose in this microfibrillated cellulose dispersion was 6% by mass.

[0199] <Example 25> Ion-exchanged water was added to the TEMPO-oxidized pulp obtained in Production Example 5 to prepare a slurry having a solid content concentration of 6% by mass. To 1000 g of this slurry (solid content concentration 6% by mass, solid content 60 g), an enzyme-containing solution having an activity of 33000 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 550 nkat per 1 g of microfibrillated cellulose. The obtained slurry was treated once with a wet micronizer (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa, and then the enzyme treatment was continued. Thereafter, it was treated three times at a pressure of 200 MPa and heated to 100°C to cause thermal deactivation, thereby obtaining a microfibrillated cellulose dispersion. The concentration of microfibrillated cellulose in this microfibrillated cellulose dispersion was 6% by mass.

[0200] <Example 26> Ion-exchanged water was added to the phosphonated pulp obtained in Production Example 9 to prepare a slurry having a solid content concentration of 6% by mass. In 1000 g of this slurry (solid content concentration 6% by mass, solid content 60 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of microfibrillated cellulose, and after stirring at 25°C in a sealed container, it was allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion, thereby obtaining a fibrillated cellulose dispersion. The obtained fibrillated cellulose dispersion was treated four times with a wet micronizer (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa to obtain a microfibrillated cellulose dispersion. The concentration of microfibrillated cellulose in this microfibrillated cellulose dispersion was 6% by mass.

[0201] <Example 27> Ion-exchanged water was added to the phosphorous acid pulp obtained in Production Example 9 to prepare a slurry having a solid content concentration of 6% by mass. To 1000 g of this slurry (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained slurry was treated once with a wet micronization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then the enzyme treatment was continued. Thereafter, it was treated three times at a pressure of 200 MPa and heated to 100°C for heat inactivation to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0202] <Example 28> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 4 (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated three times with a wet micronization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0203] <Example 29> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 4 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated three times with a wet micronization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heated to 100°C for heat inactivation to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0204] <Example 30> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example 4 to adjust a slurry having a solid content concentration of 7.5% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Then, 250 g of a sodium hypochlorite solution (effective chlorine concentration: 12% by mass) was added to 1000 g of this dispersion (solid content concentration: 7.5% by mass, solid content: 75 g), and the mixture was thoroughly mixed at room temperature. The addition rate of sodium hypochlorite at this time was 0.4 part by mass with respect to 1 part by mass of the microfibrillated cellulose. The obtained microfibrillated cellulose dispersion was treated three times at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a microfibrillated cellulose dispersion. The concentration of the microfibrillated cellulose in this microfibrillated cellulose dispersion was 6% by mass.

[0205] <Example 31> Ozone was added to 1000 g of the microfibrillated cellulose dispersion obtained in Production Example 8 (solid content concentration: 6% by mass, solid content: 60 g) at a ratio of 0.2 part by mass with respect to 1 part by mass of the microfibrillated cellulose. After stirring at 25°C in a sealed container, the mixture was allowed to stand for 30 minutes. Then, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillated cellulose dispersion was treated three times at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a microfibrillated cellulose dispersion. The concentration of the microfibrillated cellulose in this microfibrillated cellulose dispersion was 6% by mass.

[0206] <Example 32> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 8 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 3 times at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst), and then heated to 100°C for heat inactivation to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0207] <Example 33> Ion-exchanged water was added to the TEMPO-oxidized pulp obtained in Production Example 8 to adjust a slurry having a solid content concentration of 7.5% by mass. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a fibrous cellulose dispersion containing microfibrillar cellulose. Then, 250 g of a sodium hypochlorite solution (available chlorine concentration: 12% by mass) was added to 1000 g of this dispersion (solid content concentration: 7.5% by mass, solid content: 75 g), and the mixture was stirred at room temperature. The sodium hypochlorite addition rate at this time was 0.4 part by mass per 1 part by mass of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 3 times at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0208] <Example 34> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 12 (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 parts by mass with respect to 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Subsequently, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0209] <Example 35> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 12 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat with respect to 1 g of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heated to 100°C to inactivate the enzyme, thereby obtaining a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0210] <Example 36> Ion-exchanged water was added to the phosphorous acid pulp obtained in Production Example 12 to adjust a slurry having a solid content concentration of 7.5 mass%. This slurry was treated once at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a fibrous cellulose dispersion liquid containing microfibrillated cellulose. Then, 250 g of a sodium hypochlorite solution (available chlorine concentration: 12 mass%) was added to 1000 g of the microfibrillated cellulose dispersion liquid (solid content concentration: 7.5 mass%, solid content: 75 g), and the mixture was stirred at room temperature. The addition rate of sodium hypochlorite at this time was 0.4 part by mass with respect to 1 part by mass of the microfibrillated cellulose. The obtained microfibrillated cellulose dispersion liquid was treated three times at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a microfibrillated cellulose dispersion liquid. The concentration of the microfibrillated cellulose in this microfibrillated cellulose dispersion liquid was 6 mass%.

[0211] <Example 37> In 1000 g of the microfibrillated cellulose dispersion liquid obtained in Production Example 13 (solid content concentration: 6 mass%, solid content: 60 g), ozone was added so as to be at a ratio of 0.2 part by mass with respect to 1 part by mass of the microfibrillated cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Subsequently, the container was opened and the mixture was stirred for 5 hours to volatilize the ozone remaining in the dispersion liquid. The obtained microfibrillated cellulose dispersion liquid was treated three times at a pressure of 200 MPa with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) to obtain a microfibrillated cellulose dispersion liquid. The concentration of the microfibrillated cellulose in this microfibrillated cellulose dispersion liquid was 6 mass%.

[0212] <Example 38> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 18 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 3 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Limited, Starburst), then heated to 100°C to deactivate the enzyme, and a microfibrillar cellulose dispersion was obtained. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0213] <Example 39> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 14 (solid content concentration: 13% by mass, solid content: 130 g), an enzyme-containing solution having an activity of 71500 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 4 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0214] <Example 40> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 19 (solid content concentration: 13% by mass, solid content: 130 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated 4 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Limited, Starburst), then heated to 100°C to deactivate the enzyme, and a microfibrillar cellulose dispersion was obtained. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0215] <Example 41> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 20 (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 part by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Subsequently, the container was opened and the mixture was stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0216] <Example 42> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 15 (solid content concentration: 13% by mass, solid content: 130 g), an enzyme-containing solution having an activity of 71500 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated four times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa and then heated to 100°C to cause heat inactivation, thereby obtaining a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0217] <Example 43> In 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 16 (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 part by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Subsequently, the container was opened and the mixture was stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0218] <Example 44> To 1000 g of the microfibrillar cellulose dispersion (solid content concentration: 13% by mass, solid content: 130 g) obtained in Production Example 22, an enzyme-containing solution having an activity of 71500 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 4 times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heated to 100°C to deactivate the enzyme, thereby obtaining a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0219] <Example 45> In 1000 g of the microfibrillar cellulose dispersion (solid content concentration: 6% by mass, solid content: 60 g) obtained in Production Example 23, ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Subsequently, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated 3 times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0220] <Example 46> To 1000 g of the microfibrillar cellulose dispersion (solid content concentration: 13% by mass, solid content: 130 g) obtained in Production Example 24, an enzyme-containing solution having an activity of 104000 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 800 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated 4 times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heated to 100°C to deactivate the enzyme, thereby obtaining a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0221] <Example 47> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 25 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 48000 nkat was added, and enzyme treatment was performed at a temperature of 50°C. At this time, the enzyme addition amount was adjusted to 800 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Ltd.) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0222] <Example 48> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 26 (solid content concentration: 13% by mass, solid content: 130 g), ozone was added at a ratio of 0.2 parts by mass per 1 part by mass of microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Then, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated four times with a wet atomization device (Starburst, manufactured by Sugino Machine Ltd.) at a pressure of 200 MPa and then heat-inactivated at 100°C to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0223] <Example 49> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 27 (solid content concentration: 6% by mass, solid content: 60 g), ozone was added at a ratio of 0.2 part by mass per 1 part by mass of the microfibrillar cellulose, and the mixture was stirred at 25°C in a sealed container and then allowed to stand for 30 minutes. Subsequently, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. The obtained microfibrillar cellulose dispersion was treated three times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heat-inactivated at 100°C to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0224] <Example 50> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 28 (solid content concentration: 13% by mass, solid content: 130 g), an enzyme-containing solution having an activity of 104000 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 800 nkat per 1 g of the microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was treated four times with a wet atomization device (Starburst, manufactured by Sugino Machine Limited) at a pressure of 200 MPa, and then heat-inactivated at 100°C to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0225] <Example 51> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 4 (solid content concentration: 6% by mass, solid content: 60 g), an enzyme-containing solution having an activity of 33000 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of the microfibrillar cellulose. Thereafter, heat inactivation was carried out at 100°C to obtain a microfibrillar cellulose dispersion. The concentration of the microfibrillar cellulose in this microfibrillar cellulose dispersion was 6% by mass.

[0226] <Example 52> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 3 (solid content concentration: 13% by mass, solid content: 130 g), an enzyme-containing solution having an activity of 71500 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 550 nkat per 1 g of microfibrillar cellulose. Thereafter, the temperature was raised to 100°C to cause heat inactivation, thereby obtaining a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0227] <Example 53> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 52, except that the microfibrillar cellulose dispersion obtained in Production Example 7 was used.

[0228] <Example 54> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 52, except that the microfibrillar cellulose dispersion obtained in Production Example 11 was used.

[0229] <Example 55> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 52, except that the microfibrillar cellulose dispersion obtained in Production Example 14 was used.

[0230] <Example 56> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 52, except that the microfibrillar cellulose dispersion obtained in Production Example 15 was used.

[0231] <Example 57> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 52, except that the microfibrillar cellulose dispersion obtained in Production Example 17 was used.

[0232] <Example 58> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 52, except that the microfibrillar cellulose dispersion obtained in Production Example 19 was used.

[0233] <Example 59> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 52, except that the microfibrillar cellulose dispersion obtained in Production Example 21 was used.

[0234] <Example 60> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 52, except that the microfibrillar cellulose dispersion obtained in Production Example 22 was used.

[0235] <Example 61> To 1000 g of the microfibrillar cellulose dispersion obtained in Production Example 24 (solid content concentration: 13% by mass, solid content: 130 g), an enzyme-containing solution having an activity of 104000 nkat was added, and enzyme treatment was carried out at a temperature of 50°C. The amount of enzyme added at this time was adjusted to 800 nkat per 1 g of microfibrillar cellulose. The obtained microfibrillar cellulose dispersion was heated to 100°C for heat inactivation to obtain a microfibrillar cellulose dispersion. The concentration of microfibrillar cellulose in this microfibrillar cellulose dispersion was 13% by mass.

[0236] <Example 62> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 61, except that the microfibrillar cellulose dispersion obtained in Production Example 26 was used.

[0237] <Example 63> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 61, except that the microfibrillar cellulose dispersion obtained in Production Example 28 was used.

[0238] <Example 64> A microfibrillar cellulose dispersion was obtained in the same manner as in Example 29, except that the microfibrillar cellulose dispersion obtained in Production Example 29 was used.

[0239] It was confirmed by X-ray diffraction that the microfibrillar cellulose in Examples 1 to 64 maintained cellulose I-type crystals. Further, when the fiber width of these microfibrillar celluloses was measured using a transmission electron microscope, all of them contained microfibrillar cellulose with a fiber width of 3 to 5 nm.

[0240] <Comparative Example 1> Ion-exchanged water was added to softwood kraft pulp (NBKP) to prepare a slurry with a solid content concentration of 6% by mass. This slurry was treated 6 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) to obtain a microfibrillated cellulose dispersion. The concentration of microfibrillated cellulose in this microfibrillated cellulose dispersion was 6% by mass.

[0241] It was confirmed by X-ray diffraction that this microfibrillated cellulose maintained cellulose I-type crystals. Also, the number-average fiber width of the microfibrillated cellulose contained in this dispersion was 1000 nm or less.

[0242] <Comparative Example 2> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example 1 to prepare a slurry with a solid content concentration of 2% by mass. This slurry was treated 5 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Ltd., Starburst) to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of phosphate groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g.

[0243] <Comparative Example 3> The microfibrillated cellulose dispersion obtained in the same manner as in Comparative Example 2 was concentrated while heating at 50°C until the concentration of microfibrillated cellulose reached 6% by mass to obtain a fibrous cellulose dispersion containing microfibrillated cellulose. Also, the amount of phosphate groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphooxo acid groups] described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g.

[0244] <Comparative Example 4> The dispersion of microfibrillated cellulose obtained in the same manner as Comparative Example 2 was diluted to 0.4% by mass. 1 g of calcium chloride as a gelling agent was added to 100 mL of the diluted solution for gelling, and after filtration, it was squeezed with filter paper. After immersion 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. After dilution with ion-exchanged water so that the concentration of the obtained concentrate became 6%, it was stirred, but a uniform dispersion could not be obtained.

[0245] <Measurement> [Measurement of the amount of phosphonooxy groups] The amount of phosphonooxy groups in the microfibrillated cellulose was measured by performing titration with an alkali after treating a fibrous cellulose-containing slurry prepared by diluting a microfibrillated cellulose dispersion containing the target microfibrillated cellulose with ion-exchanged water so that the content became 0.2% by mass with an ion-exchange resin. The treatment with the ion-exchange resin was carried out by adding a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) having a volume of 1 / 10 to the above fibrous cellulose-containing slurry, performing a shaking treatment for 1 hour, and then pouring it onto a mesh with an opening of 90 μm to separate the resin and the slurry. In addition, the titration using an alkali was carried out by measuring the change in the pH value shown by the fibrous cellulose-containing slurry after treatment with an ion-exchange resin while adding 10 μL of a 0.1 N aqueous sodium hydroxide solution to the slurry every 5 seconds. Note that the titration was carried out while blowing nitrogen gas into the slurry for 15 minutes before the start of the titration. In this neutralization titration, two points where the increment (the differential value of the pH with respect to the amount of alkali dropped) becomes maximum are observed in the curve obtained by plotting the measured pH against the amount of alkali added. Among these, the first maximum point of the increment obtained first after starting to add the alkali is called the first end point, and the next maximum point of the increment is called the second end point (Figure 2). The amount of alkali required from the start of the titration to the first end point is equal to the amount of the first dissociable acid in the slurry used for the titration. Also, the amount of alkali required from the start of the titration to the second end point is equal to the total amount of dissociable acid in the slurry used for the titration. Note that the value obtained by dividing the amount of alkali (mmol) required from the start of the titration to the first end point by the solid content (g) in the titration target slurry was defined as the amount of phospho-oxo acid groups (mmol / g).

[0246] 〔Measurement of the amount of carboxyl groups〕 The amount of carboxyl groups in the microfibrillated cellulose was measured by performing titration using an alkali on the fibrous cellulose-containing slurry prepared by diluting a microfibrillated cellulose dispersion containing the target microfibrillated cellulose with ion-exchanged water so that the content became 0.2% by mass, after treatment with an ion-exchange resin. The treatment with the ion-exchange resin was carried out by adding a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) having a volume of 1 / 10 to the above fibrous cellulose-containing slurry, performing a shaking treatment for 1 hour, and then pouring it onto a mesh with an opening of 90 μm to separate the resin and the slurry. Also, the titration using an alkali was performed by measuring the change in the value of the electrical conductivity exhibited by the fibrous cellulose-containing slurry after treatment with an ion exchange resin while adding 50 μL of a 0.1 N aqueous sodium hydroxide solution once every 30 seconds. 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 FIG. 3 in the measurement results by the solid content (g) in the slurry to be titrated.

[0247] [Measurement of the amount of sulfur oxoacid groups] After wet ashing the obtained fibrous cellulose using perchloric acid and concentrated nitric acid, it was diluted at an appropriate magnification and the amount of sulfur was measured by ICP emission analysis. The value obtained by dividing this amount of sulfur by the absolute dry mass of the tested fibrous cellulose was defined as the amount of sulfur oxoacid groups (unit: mmol / g).

[0248] [Measurement of the viscosity of the microfibrillated cellulose dispersion by a rheometer] The viscosities of the microfibrillated cellulose dispersions obtained in Examples 1 to 64 and Comparative Examples 1 to 3 were measured using a rheometer (RheoStress6000, manufactured by HAAKE). Regarding the shear rate, it was changed under the following conditions. Measurement temperature: 23°C Measurement jig: Cone plate (diameter 40 mm, angle 1°) Shear rate: 0.001 to 1000 sec -1 Number of data points: 100 points Data distribution: Log interval Measurement time: 5 minutes

[0249] [Calculation of the TI value] The viscosity of the microfibrillated cellulose dispersion was measured by the method described above, and the value of the viscosity (η1) measured under the condition of a shear rate of 1 sec -1 was divided by the value of the viscosity (η2) measured under the condition of a shear rate of 1000 sec -1 to obtain a value defined as the thixotropic index value (TI value) of the thickener. That is, the TI value was calculated by the following formula. TI value = η1 / η2 η1: Shear rate 1 sec -1 Viscosity measured under the conditions of η2: Shear rate 1000 sec -1 Viscosity measured under the conditions of

[0250] [Measurement of specific viscosity and degree of polymerization of microfibrillated cellulose] The specific viscosity and degree of polymerization of microfibrillated cellulose were measured according to Tappi T230. That is, after measuring the viscosity (designated as ηX) of the microfibrillated cellulose to be measured dispersed in the dispersion medium and the blank viscosity (designated as η0) measured with only the dispersion medium, the specific viscosity (ηsp) and the intrinsic viscosity ([η]) were measured according to the following formulas. ηsp = (ηX / η0) - 1 [η] = ηsp / (c(1 + 0.28 × ηsp)) Here, c in the formula indicates the concentration of cellulose fibers during viscosity measurement. Furthermore, the degree of polymerization (DP) of microfibrillated cellulose was calculated from the following formula. DP = 1.75 × [η] Since this degree of polymerization is the average degree of polymerization measured by the viscosity method, it is sometimes referred to as the "viscosity average degree of polymerization".

[0251] [Measurement of haze of microfibrillated cellulose dispersion] The haze of the microfibrillated cellulose dispersions obtained in Examples 1 to 64 and Comparative Examples 1 to 3 was measured by diluting the microfibrillated cellulose dispersion to 0.2 mass% with ion-exchanged water, and then using a haze meter (HM-150, manufactured by Murakami Color Technology Laboratory) and a glass cell for liquids with an optical path length of 1 cm (MG-40, reverse optical path, manufactured by Fujiwara Seisakusho), and measuring in accordance with JIS K 7136:2000. The zero point measurement was performed with ion-exchanged water placed in the same glass cell. In addition, the dispersion to be measured was allowed to stand for 24 hours in an environment of 23°C and a relative humidity of 50% before measurement. The liquid temperature of the dispersion during measurement was 23°C.

[0252] [Evaluation] [Visual evaluation of microfibrillated cellulose dispersion] The fine fibrillated cellulose dispersions obtained in Examples 1 to 64 and Comparative Examples 1 to 3 were each diluted with ion-exchanged water so that the solid content concentration became 3% by mass. Subsequently, defoaming treatment was performed using a rotation-revolution type super mixer (manufactured by Shinki Co., Ltd., ARE-250). Then, the transparency of the dispersion was visually evaluated. As the evaluation criteria, the dispersion was placed in a glass cell, and a sheet with 11-point characters described on one side was placed, and the evaluation was performed according to the following criteria. A: When viewed from the opposite side, the characters can be clearly read. B: Slightly blurred, but the characters can be read. C: Blurred, the characters cannot be read, but it is known that there are characters. D: Cannot be decoded at all.

[0253] <Preparation of evaluation sheet> Polyethylene oxide (manufactured by Sumitomo Seika Chemicals Co., Ltd., PEO-3P) was added to ion-exchanged water so as to be 5% by mass, and stirred and dissolved to obtain an aqueous polyethylene oxide solution. Subsequently, the fine fibrillated cellulose dispersions obtained in Examples 1 to 64 and Comparative Examples 1 to 3 and the above-mentioned aqueous polyethylene oxide solution were mixed so that the ratio of fine fibrillated cellulose (solid content): polyethylene oxide (solid content) was 100 parts by mass: 20 parts by mass. In addition, in Examples 1 to 9, the solid content concentration was 2.5% by mass, in Examples 10 to 15, 22 to 38, 41, 43, 45, 47, 49, 51, Comparative Examples 1, 3, 4, the solid content concentration was 5% by mass, in Examples 16 to 21, 39, 40, 42, 44, 46, 48, 50, 52 to 64, the solid content concentration was 10% by mass, and in Comparative Example 2, the solid content concentration was 1.5% by mass, and it was appropriately diluted with ion-exchanged water to obtain a coating liquid. Next, the coating liquid was weighed so that the finished thickness of the obtained sheet (the layer composed of the solid content of the coating liquid) became 40 μm, coated on a commercially available polycarbonate plate, and dried in a dryer at 100 °C for 30 minutes. A metal frame for weir stop (a metal frame with an inner dimension of 180 mm × 180 mm and a height of 5 cm) was arranged on the polycarbonate plate so as to have a predetermined basis weight. Then, the dried sheet was peeled off from the polycarbonate plate to obtain a fine fibrillated cellulose-containing sheet.

[0254] [Evaluation of transparency of sheet] The haze measurement of the obtained microfibrillar cellulose-containing sheet was carried out in accordance with JIS K 7136:2000, using a haze meter (HM-150, manufactured by Murakami Color Technology Laboratory). The haze of the sheet was judged according to the following criteria. When the haze of the sheet was less than 95%, it was determined that the transparency was good. A: 0 or more and less than 5% B: 5% or more and less than 30% C: 30% or more and less than 95% D: 95% or more

[0255] [Evaluation of curl property of sheet] The microfibrillar cellulose-containing sheet obtained by the method described above was cut out into test pieces with a width of 15 mm and a length of 130 mm. As shown in Figure 1, one end including a short side of the test piece 50 was supported by a curl test jig 55 with a width of 30 mm, a length of 30 mm, and a height of 25 mm (a test piece with a length of 100 mm was exposed from the jig), and in an environment of a temperature of 23 °C and a relative humidity of 50%, it was left to stand on a horizontal table so that the width direction of the test piece was perpendicular to the table (so that the longitudinal direction of the test piece was parallel to the table). Then, the curl width at the end of the test piece 50 was measured and taken as the curl width C0 (the distance of C0 in Figure 1). After standing for 24 hours, the curl width was measured again and taken as C1 (the distance of C1 in Figure 1), and C1 - C0 was taken as the curl amount. The curl amount was judged according to the following criteria. When the curl amount was 25 mm or less, it was determined that the curl resistance was good. A: 5 mm or less B: More than 5 mm and 25 mm or less C: More than 25 mm

[0256]

Table 1

[0257]

Table 2

[0258]

Table 3

[0259]

Table 4

[0260]

Table 5

[0261]

Table 6

[0262]

Table 7

[0263]

Table 8

[0264] In the examples, a high-concentration fine fibrous cellulose dispersion was obtained, and a sheet with suppressed curling was formed from such a dispersion. It is considered that by forming a sheet from a high-concentration fine fibrous cellulose dispersion, the amount of incorporated moisture can be reduced and heat shrinkage during drying can be suppressed. In Comparative Example 4, a uniform sample could not be prepared, and measurements such as viscosity could not be performed.

Explanation of Signs

[0265] 50 Test piece 55 Test jig

Claims

1. 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 viscosity-reducing treatment, The content of fibrous cellulose is 3.0% by mass or more based on the total mass of the dispersion, A method for producing a fibrous cellulose-containing dispersion, in which the TI value of the dispersion calculated under the following condition (a) is 1 or more and 80,000 or less, and the viscosity (η1) of the dispersion measured under the following condition (a) is 1 Pa s or more and 5,000 Pa s or less, and the viscosity (η2) of the dispersion measured under the following condition (a) is 0.007 Pa s or more and 100 Pa s or less; Condition (a): Using a rheometer, the shear rate of the dispersion is 1 sec －１ Viscosity (η1) under the condition of and shear rate of the dispersion of 1000 sec －１ The viscosity (η2) under the above conditions is measured, and the TI value is calculated according to the following formula. TI value = η1 / η2

2. The method for producing a fibrous cellulose-containing dispersion according to claim 1 , wherein the concentration of cellulose fibers in the step of obtaining fibrous cellulose having a fiber width of 1000 nm or less by defibration treatment is 3.0% by mass or more.

3. 3. The method for producing a fibrous cellulose-containing dispersion according to claim 1, wherein the concentration of cellulose fibers in the step of obtaining fibrous cellulose having a fiber width of 1000 nm or less by defibration treatment is 4.0% by mass or more.

4. The method for producing a fibrous cellulose-containing dispersion according to any one of claims 1 to 3, wherein the concentration of cellulose fibers in the step of obtaining fibrous cellulose having a fiber width of 1000 nm or less by defibration treatment is 5.0 mass% or more.

5. The method for producing a fibrous cellulose-containing dispersion according to any one of claims 1 to 4, wherein the concentration of cellulose fibers in the step of obtaining fibrous cellulose having a fiber width of 1000 nm or less by defibration treatment is 6.0 mass% or more.

6. The method for producing a fibrous cellulose-containing dispersion according to any one of claims 1 to 5, wherein the step of performing a viscosity reduction 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.

7. The method for producing a fibrous cellulose-containing dispersion according to any one of claims 1 to 6, further comprising a step of carrying out a defibration treatment after the step of carrying out the viscosity reduction treatment.

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