JP7497658B2 - Fibrous cellulose, fibrous cellulose dispersion and method for producing fibrous cellulose - Google Patents

Description

The present invention relates to fibrous cellulose, a fibrous cellulose dispersion, and a method for producing fibrous cellulose.

Traditionally, cellulose fibers have been widely used in clothing, absorbent articles, paper products, etc. As cellulose fibers, in addition to fibrous cellulose with a fiber diameter of 10 μm or more and 50 μm or less, fine fibrous cellulose with a fiber diameter of 1 μm or less is also known. Fine fibrous cellulose has attracted attention as a new material, and its applications are diverse.

For example, fine fibrous cellulose may be used as an additive to paint. In this case, the fine fibrous cellulose may function as a viscosity modifier in the paint. For example, Patent Document 1 discloses a glittering pigment dispersion containing water, a viscosity modifier (A), and a scaly glittering pigment (B). Patent Document 2 discloses a glittering pigment dispersion containing water, a scaly aluminum pigment, and a cellulose-based viscosity modifier. Patent Documents 1 and 2 discuss the use of cellulose nanofibers as a viscosity modifier.

International Publication No. 2018/012014 International Publication No. WO 2017/175468

Conventionally, cellulose nanofibers have been used in paints to improve the dispersibility of pigments, etc. However, no attention has been paid to the problem of reduced coatability of such paints due to viscosity changes (thixotropy) caused by applying shear before coating, and there has been room for improvement in terms of coatability.

Therefore, in order to solve these problems of the conventional technology, the inventors have carried out research with the aim of providing fine fibrous cellulose that can exhibit excellent coating suitability when added to paint.

As a result of intensive research to solve the above problems, the present inventors have found that, when fine fibrous cellulose is dispersed in water to form a dispersion and stirred under specified conditions, fine fibrous cellulose can be obtained that can bring the viscosity change rate (%) before and after stirring within a specified range, and that by adding this fine fibrous cellulose to a paint, the coating suitability of the paint can be improved.
Specifically, the present invention has the following configuration.

[1] A fibrous cellulose having a fiber width of 1000 nm or less and having a phosphorous acid group or a substituent derived from a phosphorous acid group,
Fibrous cellulose, which, when dispersed in water to give a dispersion having a viscosity of 2,500 mPa s at 23° C., exhibits a viscosity change rate calculated by the following formula within ±50% when the dispersion is stirred under the following stirring conditions:
Viscosity change rate (%)=(viscosity after stirring−viscosity before stirring)/viscosity before stirring×100
(Mixing conditions)
A dispersion liquid having a viscosity of 2,500 mPa s at 23°C is poured into a cylindrical container having a diameter of 10 cm to a height of 5 cm, and stirred at 23°C for 24 hours using an elliptical stirrer having a length of 5 cm, a width of 2 cm at the center and a width of 1 cm at the end, while maintaining a state in which the center of the liquid surface is recessed by 2 cm.
[2] The fibrous cellulose according to [1], wherein the degree of polymerization of the fibrous cellulose is 300 or more and 500 or less.
[3] The fibrous cellulose according to [1] or [2], in which, when the fibrous cellulose is dispersed in water to a concentration of 0.4% by mass to form a dispersion, the viscosity of the dispersion at 23° C. is 200 mPa·s or more and 3000 mPa·s or less.
[4] The fibrous cellulose according to any one of [1] to [3], which is for use in a paint.
[5] A fibrous cellulose dispersion obtained by dispersing the fibrous cellulose according to any one of [1] to [4] in water.
[6] A step of subjecting cellulose fibers having a phosphorous acid group or a substituent derived from a phosphorous acid group to a defibration treatment to obtain a fibrous cellulose having a fiber width of 1000 nm or less and having a phosphorous acid group or a substituent derived from a phosphorous acid group;
and a step of subjecting the fibrous cellulose to a low thixotropy treatment.
[7] The method for producing fibrous cellulose according to [6], wherein the step of subjecting the fibrous cellulose to a low thixotropy treatment is a step of reducing the degree of polymerization of the fibrous cellulose to 300 or more and 500 or less.
[8] The method for producing fibrous cellulose according to [6] or [7], wherein the step of subjecting the thixotropic reduction treatment is an ozone treatment step.

According to the present invention, it is possible to obtain fine fibrous cellulose that exhibits excellent coating suitability when added to paint.

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

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

(Fine fibrous cellulose)
The present invention relates to a fibrous cellulose having a fiber width of 1000 nm or less and having a phosphorous acid group or a substituent derived from a phosphorous acid group. In this specification, the fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose. Here, when the fibrous cellulose of the present invention is dispersed in water to obtain a dispersion having a viscosity of 2500 mPa·s at 23°C, and the dispersion is stirred under the following stirring conditions, the viscosity change rate calculated by the following formula is within ±50%.
Viscosity change rate (%)=(viscosity after stirring−viscosity before stirring)/viscosity before stirring×100
(Mixing conditions)
A dispersion liquid having a viscosity of 2,500 mPa s at 23°C is poured into a cylindrical container having a diameter of 10 cm to a height of 5 cm, and stirred at 23°C for 24 hours using an elliptical stirrer having a length of 5 cm, a width of 2 cm at the center and a width of 1 cm at the end, while maintaining a state in which the center of the liquid surface is recessed by 2 cm.

In the present invention, fine fibrous cellulose is used as a dispersion, and the viscosity change rate when stirred under the above conditions is within ±50%, so that fine fibrous cellulose that can exhibit excellent coating suitability when added to a paint can be obtained. The dispersion in which the fine fibrous cellulose of the present invention is dispersed has low thixotropy, so it can exhibit excellent coating suitability. For example, even when a paint containing the fine fibrous cellulose of the present invention is stored or transported, the viscosity change of the paint is suppressed, so dripping during coating is suppressed and sedimentation of additives such as pigments can be suppressed. In addition, even when a paint containing the fine fibrous cellulose of the present invention is stirred for a long time and a relatively strong shear is applied to the paint, dripping caused by a decrease in the viscosity of the paint and sedimentation of additives such as pigments can be effectively suppressed.

The fine fibrous cellulose of the present invention is preferably used for paint, and as described above, can improve the coating suitability of the paint. In addition, when the fine fibrous cellulose of the present invention is used as an additive for paint, it can also improve the design and strength after coating. Therefore, the coating layer formed by applying the paint can exhibit excellent design and scratch resistance.

The viscosity change rate of the dispersion calculated by the above formula may be within ±50%, preferably within ±40%, more preferably within ±30%, even more preferably within ±25%, and particularly preferably within ±20%. The viscosity change rate of the dispersion calculated by the above formula may be 0%. Usually, the viscosity of the dispersion is often reduced by applying shear to the dispersion, so the viscosity change rate calculated by the above formula is often a negative value. That is, the viscosity change rate of the dispersion is preferably -50% or more and 0% or less, more preferably -40% or more and 0% or less, even more preferably -30% or more and 0% or less, even more preferably -25% or more and 0% or less, and particularly preferably -20% or more and 0% or less. The viscosity change rate of the dispersion calculated by the above formula can be achieved by controlling, for example, the type and conditions of the treatment for the fine fibrous cellulose, the degree of polymerization of the fine fibrous cellulose, and the amount of phosphorous acid groups introduced, each within an appropriate range.

In this specification, the viscosity before and after stirring used to calculate the viscosity change rate of the dispersion is the viscosity value measured one minute after the start of measurement using a Brookfield viscometer at 23°C and a rotation speed of 6 rpm. As the Brookfield viscometer, for example, an analog viscometer T-LVT manufactured by BLOOKFIELD can be used. The viscosity before stirring is the viscosity of the dispersion adjusted to have a viscosity of about 2500 mPa·s, so the actual viscosity value of the dispersion is preferably 2500 mPa·s, but an error of about ±15% may occur. That is, in the calculation formula for the viscosity change rate, the viscosity before stirring is the actual viscosity of the dispersion adjusted to have a viscosity of about 2500 mPa·s, and is the actual viscosity value measured one minute after the start of measurement using a Brookfield viscometer at 23°C and a rotation speed of 6 rpm. However, when measuring the viscosity before stirring, the fine fibrous cellulose dispersion is poured into a cylindrical container with a diameter of 10 cm to a height of 5 cm, stirred with a disperser at 1500 rpm for 5 minutes, and the measurement is performed 1 minute after the end of stirring. In addition, when adjusting the viscosity of the dispersion before stirring to about 2500 mPa·s, the amount of fine fibrous cellulose used is appropriately adjusted. For example, the viscosity of the dispersion before stirring can be adjusted to about 2500 mPa·s by adjusting the content of fine fibrous cellulose to 0.3 to 3.0 mass% relative to the total mass of the dispersion.

When measuring the viscosity after stirring in the formula for calculating the rate of change in viscosity, first, the dispersion liquid used for the viscosity measurement before stirring is further stirred with a stirrer. In this case, the dispersion liquid before stirring is placed in a cylindrical container with a diameter of 10 cm to a height of 5 cm of fine fibrous cellulose dispersion, and stirred for 24 hours using an elliptical stirrer with a length of 5 cm, width of the center of 2 cm, and width of 1 cm at the end, while maintaining a state in which the center of the liquid surface is depressed by 2 cm. The liquid temperature during stirring is maintained at 23°C. Then, one minute after the end of stirring, the viscosity is measured using a B-type viscometer, and the viscosity value one minute after the start of measurement at 23°C and a rotation speed of 6 rpm is taken as the viscosity after stirring.

When the fine fibrous cellulose of the present invention is dispersed in water to a concentration of 0.4% by mass to form a dispersion, the viscosity of the dispersion at 23°C is preferably 200 mPa·s or more, more preferably 300 mPa·s or more, even more preferably 350 mPa·s or more, and particularly preferably 400 mPa·s or more. The viscosity of the dispersion at 23°C is preferably 3000 mPa·s or less, and more preferably 2500 mPa·s or less. The viscosity of a dispersion having a fine fibrous cellulose concentration of 0.4% by mass can be measured using a B-type viscometer (analog viscometer T-LVT manufactured by BLOOKFIELD). The measurement conditions are 23°C, a rotation speed of 3 rpm, and the viscosity is measured 3 minutes after the start of the measurement.

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

The fiber width of fibrous cellulose can be measured, for example, by observation under an electron microscope. The average fiber width of fibrous cellulose is, for example, 1000 nm or less. The average fiber width of fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. By making the average fiber width of fibrous cellulose 2 nm or more, it is possible to suppress dissolution of cellulose molecules in water, and to more easily realize the effect of improving strength, rigidity, and dimensional stability due to fibrous cellulose. The fibrous cellulose is, for example, monofilament cellulose.

The average fiber width of fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% by mass to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast onto glass may be observed. Next, observation is performed using an electron microscope image at a magnification of 1000x, 5000x, 10000x, or 50000x depending on the width of the fiber to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.

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

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

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

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

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

The fibrous cellulose in this embodiment has, for example, both crystalline and non-crystalline regions. In particular, fine fibrous cellulose having both crystalline and non-crystalline regions and a high axial ratio can be realized by the method for producing fine fibrous cellulose described below.

In this embodiment, the fibrous cellulose has a phosphorous acid group or a substituent derived from a phosphorous acid group (also simply referred to as a phosphorous acid group). From the viewpoint of improving the dispersibility of the fibers in the dispersion medium and increasing the defibration efficiency in the defibration process, it is more preferable that the fibrous cellulose has a phosphorous acid group or a substituent derived from a phosphorous acid group. In addition, fine fibrous cellulose having a phosphorous acid group or a substituent derived from a phosphorous acid group can exhibit better coating suitability when added to a paint.

In the present invention, the phosphite group or the substituent derived from the phosphite group is, for example, a substituent represented by the following formula (2).

In formula (2), b is a natural number, m is an arbitrary number, and b×m=1. α is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from any of these. Of these, it is particularly preferable that α is a hydrogen atom. Note that α in formula (2) does not include groups derived from cellulose molecular chains.

Examples of the saturated linear hydrocarbon group represented by α in formula (2) include, but are not limited to, a methyl group, an ethyl group, an n-propyl group, or an n-butyl group. Examples of the saturated branched hydrocarbon group include, but are not limited to, an i-propyl group or a t-butyl group. Examples of the saturated cyclic hydrocarbon group include, but are not limited to, a cyclopentyl group or a cyclohexyl group. Examples of the unsaturated linear hydrocarbon group include, but are not limited to, a vinyl group or an allyl group. Examples of the unsaturated branched hydrocarbon group include, but are not limited to, an i-propenyl group or a 3-butenyl group. Examples of the unsaturated cyclic hydrocarbon group include, but are not limited to, a cyclopentenyl group or a cyclohexenyl group. Examples of the aromatic group include, but are not limited to, a phenyl group or a naphthyl group.

In addition, the derivative group in α may be, but is not limited to, a functional group in which at least one of functional groups such as a carboxy group, a hydroxy group, or an amino group is added to or substituted for the main chain or side chain of the various hydrocarbon groups described above. In addition, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorous group can be set to an appropriate range, which facilitates penetration into the fiber raw material and increases the yield of fine cellulose fibers.

In formula (2), β ^b+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include aliphatic ammonium or aromatic ammonium, and examples of the monovalent or higher cation made of an inorganic substance include, but are not limited to, ions of alkali metals such as sodium, potassium, or lithium, cations of divalent metals such as calcium or magnesium, or hydrogen ions. These can be used alone or in combination of two or more. Examples of the monovalent or higher cation made of an organic or inorganic substance include, but are not limited to, sodium or potassium ions, which are less likely to yellow when a fiber raw material containing β is heated and are easy to use industrially.

In addition to the phosphorous acid group or a substituent derived from the phosphorous acid group, the fine fibrous cellulose may further have a phosphorous acid group or a group derived from the phosphorous acid group. The phosphorous acid group or a group derived from the phosphorous acid group may be, for example, a substituent represented by the following formula (1) or (3). In addition, the phosphorous acid group or a group derived from the phosphorous acid group may be a condensed phosphorus oxo acid group as represented by the following formula (3).

In formula (1), a and b are natural numbers, and m is an arbitrary number (wherein a=b×m). Of α and α', a are ^O- , and the rest are OR. Here, R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from these. In addition, α in formula (1) may be a group derived from a cellulose molecular chain.

In formula (3), a and b are natural numbers, m is an arbitrary number, and n is a natural number of 2 or more (wherein a=b×m). Of α ¹ , α ² , ..., α ⁿ and α', a number of them are ^O- , and the rest are either R or OR. Here, R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from these. In addition, α in formula (3) may be a group derived from a cellulose molecular chain.

Specific examples of each group in formulas (1) and (3) are the same as the specific examples of each group in formula (2). Specific examples of β ^b+ in formulas (1) and (3) are the same as the specific examples of β ^b+ in formula (2).

The fact that the fine fibrous cellulose has a phosphorous acid group as a substituent can be confirmed by measuring the infrared absorption spectrum of a dispersion containing the fine fibrous cellulose and observing the absorption due to P=O of a phosphonic acid group, which is a tautomer of a phosphorous acid group, at around 1210 cm ^-1 . The fact that the fibrous cellulose has a phosphorous acid group as a substituent can be confirmed by measuring the infrared absorption spectrum of a dispersion containing the fibrous cellulose and observing the absorption due to P=O of a phosphorous acid group at around 1230 cm ^-1 . The fact that the fibrous cellulose has a phosphorous acid group or a phosphorous acid group as a substituent can also be confirmed by a method of confirming a chemical shift using NMR or a method of combining titration with elemental analysis.

The amount of phosphorous acid group introduced into the fibrous cellulose (the amount of phosphorous acid group or the substituent derived from phosphorous acid group) is preferably 0.10 mmol/g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.40 mmol/g or more, and particularly preferably 0.60 mmol/g or more. The amount of phosphorous acid group introduced into the fibrous cellulose is preferably 5.20 mmol/g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol/g or less, even more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, even more preferably 2.00 mmol/g or less, even more preferably 1.50 mmol/g or less, and particularly preferably 1.00 mmol/g or less. Here, the denominator in the unit mmol/g indicates the mass of the fibrous cellulose when the counter ion of the phosphorous acid group is a hydrogen ion (H ⁺ ). By controlling the amount of phosphorous acid group introduced within the above range, it is possible to easily micronize the fiber raw material and to increase the stability of the fibrous cellulose. Also, by controlling the amount of phosphorous acid group introduced within the above range, it is possible to reduce the thixotropy of the paint when the fine fibrous cellulose is added to the paint, thereby more effectively improving the coatability.

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

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

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

When measuring the amount of phosphorus oxoacid groups by titration, if too much sodium hydroxide solution is added or if the titration interval is too short, the amount of phosphorus oxoacid groups may be lower than expected and an accurate value may not be obtained. For example, an appropriate amount of sodium hydroxide solution and titration interval may be 10 to 50 μL of 0.1 N sodium hydroxide solution added every 5 to 30 seconds. In addition, in order to eliminate the effects of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is 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.

In addition, in cases where a phosphorus oxoacid contains either a phosphorus group or a condensed phosphorus group or both in addition to a phosphorus acid group, methods for distinguishing whether the detected phosphorus oxoacid is derived from phosphorus acid, phosphorus, or condensed phosphorus include, for example, a method of performing a process to cleave the condensed structure, such as acid hydrolysis, followed by the titration operation described above, and a method of performing a process to convert the phosphorus acid group to a phosphate group, such as oxidation, followed by the titration operation described above.

The degree of polymerization of the fine fibrous cellulose is preferably 300 or more, more preferably 320 or more, and even more preferably 340 or more. The degree of polymerization of the fine fibrous cellulose is preferably 500 or less, more preferably 490 or less, and even more preferably 460 or less. By setting the degree of polymerization of the fine fibrous cellulose within the above range, the thixotropy of the paint when the fine fibrous cellulose is added to the paint can be reduced (reduced thixotropy), thereby more effectively improving the coating suitability.

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

In the present invention, in particular, by setting the degree of polymerization of the fine fibrous cellulose to 300 or more and 500 or less, and setting the amount of phosphorous acid groups or substituents derived from phosphorous acid groups in the fine fibrous cellulose to 0.4 mmol/g or more and 1.0 mmol/g or less, the thixotropy of the paint when the fine fibrous cellulose is added to the paint can be further reduced, and the coatability of the paint can be more effectively improved. Setting the degree of polymerization of the fine fibrous cellulose and the amount of phosphorous acid groups or substituents derived from phosphorous acid groups within an appropriate range contributes to the dispersion in which the fine fibrous cellulose is dispersed exhibiting low thixotropy, which is thought to improve the coatability of the paint.

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

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

<Phosphite group introduction step>
When the fine fibrous cellulose has a phosphite group, the production process of the fine fibrous cellulose includes a phosphite group introduction step. The phosphite group introduction step is a step of reacting at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing a phosphite group by reacting with a hydroxyl group possessed by a cellulose-containing fiber raw material with the cellulose-containing fiber raw material. This step results in the production of a fiber having a phosphite group introduced therein.

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

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

Compound A used in this embodiment is at least one selected from compounds having a phosphite group and salts thereof. Examples of compounds having a phosphite group include phosphorous acid, and examples of phosphorous acid include 99% phosphorous acid (phosphonic acid). Examples of salts of compounds having a phosphite group include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphorous acid, which can be neutralized to various degrees. Among these, phosphorous acid, sodium salts of phosphorous acid, potassium salts of phosphorous acid, and ammonium salts of phosphorous acid are preferably used from the viewpoints of high efficiency of introduction of phosphorus oxoacid groups, easier improvement of defibration efficiency in the defibration process described below, low cost, and ease of industrial application.

The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted to the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the effect of improving the yield and costs.

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

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

In the reaction of a fiber raw material containing cellulose with compound A, in addition to compound B, for example, amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine in particular is known to act as a good reaction catalyst.

In the phosphorous acid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material, and then heat-treat the fiber raw material. It is preferable to select a temperature for the heat treatment that can efficiently introduce the phosphorous acid group while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C. In addition, various devices having heat media can be used for the heat treatment, such as a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, an airflow dryer, a reduced pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, and a high-frequency dryer.

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

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

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

The phosphite group introduction step needs to be carried out at least once, but can also be repeated two or more times. By carrying out the phosphite group introduction step two or more times, a large number of phosphite groups can be introduced into the fiber raw material. In this embodiment, one preferred embodiment is where the phosphite group introduction step is carried out two times.

The amount of phosphorous acid groups introduced into the fibrous cellulose is preferably 0.10 mmol/g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.20 mmol/g or more, even more preferably 0.40 mmol/g or more, and particularly preferably 0.60 mmol/g or more. The amount of phosphorous acid groups introduced into the fibrous cellulose is preferably 5.20 mmol/g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol/g or less, even more preferably 3.00 mmol/g or less, even more preferably 2.50 mmol/g or less, even more preferably 2.00 mmol/g or less, even more preferably 1.50 mmol/g or less, and particularly preferably 1.00 mmol/g or less. By setting the amount of phosphorous acid groups introduced within the above range, it is possible to easily refine the fiber raw material and increase the stability of the fine fibrous cellulose. Furthermore, by introducing an amount of phosphorous acid group within the above range, the thixotropy of the paint when fine fibrous cellulose is added to the paint can be reduced, thereby more effectively improving the coating suitability.

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

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

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

The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5°C to 80°C, and more preferably 10°C to 60°C. The immersion time of the phosphite-group-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5 minutes to 30 minutes, and more preferably 10 minutes to 20 minutes. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is preferably 100% by mass to 100,000% by mass, and more preferably 1000% by mass to 10,000% by mass, based on the absolute dry mass of the phosphite-group-introduced fiber.

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

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

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

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

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

In the fiber defibration process, for example, the phosphorous group-introduced fiber is preferably diluted with a dispersion medium to form a slurry. As the dispersion medium, one or more types selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but is preferably, for example, alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, etc. Examples of alcohols include, for example, methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol, etc. Examples of polyhydric alcohols include, for example, ethylene glycol, propylene glycol, glycerin, etc. Examples of ketones include, for example, acetone, methyl ethyl ketone (MEK), etc. Examples of ethers include, for example, 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, for example, ethyl acetate, butyl acetate, etc. Aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), etc.

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

<Low thixotropy treatment>
The method for producing fine fibrous cellulose of the present invention preferably includes a step of performing a thixotropy reduction treatment in addition to the steps described above. Specifically, as described above, it preferably includes a step of performing a defibration treatment on appropriately treated cellulose fibers to obtain fibrous cellulose having a fiber width of 1000 nm or less, and a step of performing a thixotropy reduction treatment on the fibrous cellulose. That is, the method for producing fine fibrous cellulose of the present invention preferably includes, for example, a step of performing a thixotropy reduction treatment after performing a defibration treatment on cellulose fibers. Note that, as described above, it is preferable to further include a step of introducing a phosphite group into the cellulose fibers before the defibration treatment step, and it is also preferable to further include a washing step or an alkali treatment step in addition to the step of introducing a phosphite group.

In this specification, the step of performing the low thixotropy treatment is a step of performing a treatment to reduce the thixotropy of a dispersion liquid containing fine fibrous cellulose. Specifically, the step of performing the low thixotropy treatment is preferably a step of reducing the degree of polymerization of fibrous cellulose having a fiber width of 1000 nm or less to 300 or more and 500 or less. The degree of polymerization of the fine fibrous cellulose obtained in the step of performing the low thixotropy treatment is more preferably 320 or more, and even more preferably 340 or more. The degree of polymerization of the fine fibrous cellulose obtained in the step of performing the low thixotropy treatment is more preferably 490 or less, and even more preferably 460 or less.

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

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

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

In the enzyme treatment step, the enzyme addition rate is preferably 1.0×10 ⁻⁷ g or more per 1 g of fine fibrous cellulose, more preferably 1.0×10 ⁻⁶ g or more, and even more preferably 1.0×10 ⁻⁵ g or more. The enzyme addition rate is preferably 1.0×10 ⁻² g or less per 1 g of fine fibrous cellulose. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to stir the mixture at 30° C. or more and 70° C. or less for 1 minute to 10 hours, and then to inactivate the enzyme by placing the mixture at 90° C. or more.

In the hypochlorite treatment step, sodium hypochlorite is added to the fine fibrous cellulose dispersion (slurry). The sodium hypochlorite addition rate is preferably 1.0×10 ⁻⁴ g or more per 1 g of fine fibrous cellulose, more preferably 1.0×10 ⁻³ g or more, even more preferably 1.0×10 ⁻² g or more, and particularly preferably 1.0×10 ⁻¹ g or more. The sodium hypochlorite addition rate is preferably 1.0×10 ² g or less per 1 g of fine fibrous cellulose. After adding sodium hypochlorite to the fine fibrous cellulose dispersion (slurry), it is preferable to stir the mixture for 1 minute to 10 hours under conditions of 10° C. to 50° C.

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

(Fibrous Cellulose Dispersion)
The present invention also relates to a fibrous cellulose dispersion (also called a fine fibrous cellulose-containing slurry or slurry) obtained by dispersing the above-mentioned fine fibrous cellulose in water. The fibrous cellulose dispersion may be, for example, a paint dispersion used for adding to paint.

The content of fine fibrous cellulose in the fibrous cellulose dispersion is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, based on the total mass of the fibrous cellulose dispersion. The content of fine fibrous cellulose is preferably 8.0% by mass or less, more preferably 7.0% by mass or less, and even more preferably 6.0% by mass or less, based on the total mass of the fibrous cellulose dispersion.

When the fibrous cellulose dispersion is a fibrous cellulose dispersion having a fine fibrous cellulose concentration of 0.4% by mass, the viscosity of the dispersion at 23°C is preferably 200 mPa·s or more, more preferably 300 mPa·s or more, even more preferably 350 mPa·s or more, and particularly preferably 400 mPa·s or more. The viscosity of the dispersion at 23°C is preferably 3000 mPa·s or less, and more preferably 2500 mPa·s or less. The viscosity of a dispersion having a fine fibrous cellulose concentration of 0.4% by mass can be measured using a B-type viscometer (analog viscometer T-LVT manufactured by BLOOKFIELD). The measurement conditions are 23°C, a rotation speed of 3 rpm, and the viscosity is measured 3 minutes after the start of the measurement.

When the fibrous cellulose dispersion is a fibrous cellulose dispersion having a fine fibrous cellulose concentration of 0.2% by mass, the haze of the dispersion is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less. The haze of the dispersion in the above range means that the transparency of the fibrous cellulose dispersion is high and the fine fibrous cellulose is well refined. When such a fibrous cellulose dispersion is added to a paint, the paint can exhibit excellent coating suitability. Here, the haze of the fibrous cellulose dispersion (fine fibrous cellulose concentration 0.2% by mass) is a value measured by putting the fibrous cellulose dispersion in a liquid glass cell (manufactured by Fujiwara Seisakusho, MG-40, reverse light path) with an optical path length of 1 cm and using a haze meter (manufactured by Murakami Color Research Laboratory, HM-150) in accordance with JIS K 7136. The zero point measurement is performed with ion-exchanged water placed in the same glass cell.

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

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

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

(Application)
The fine fibrous cellulose of the present invention is preferably used as a thickener for various applications. For example, the fine fibrous cellulose of the present invention can be used as an additive to food, cosmetics, cement, paint (for painting vehicles such as automobiles, ships, and aircraft, for building materials, for daily necessities, etc.), ink, medicines, etc. In addition, the fine fibrous cellulose of the present invention can be added to resin-based materials or rubber-based materials, and can also be applied to daily necessities. Among them, the fine fibrous cellulose of the present invention is particularly preferably fine fibrous cellulose for paints.

The features of the present invention are explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

<Production Example 1>
[Production of Phosphorous Fine Fibrous 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/ ^m2 sheet form, Canadian standard freeness (CSF) measured according to JIS P 8121 after disintegration is 700 ml) was used.

This raw pulp was subjected to phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of phosphorous acid (phosphonic acid) and urea was added to 100 parts by mass (bone dry mass) of the raw pulp to prepare 33 parts by mass of phosphorous acid (phosphonic acid), 120 parts by mass of urea, and 150 parts by mass of water, to obtain chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated for 150 seconds in a hot air dryer at 165°C to introduce phosphorous groups into the cellulose in the pulp, and a phosphorous-oxidized pulp was obtained.

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

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

The infrared absorption spectrum of the phosphorous pulp thus obtained was measured using FT-IR. As a result, absorption based on P=O of the phosphonic acid group, which is a tautomer of the phosphorous group, was observed near 1210 cm ^-1 , and it was confirmed that a phosphorous group (phosphonic acid group) was added to the pulp. In addition, when the obtained phosphorous pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions, near 2θ=14° to 17° and near 2θ=22° to 23°, and it was confirmed that the cellulose had type I crystals. The phosphorous pulp thus obtained had a phosphorous group amount (amount of first dissociated acid) of 0.74 mmol/g measured by the measurement method described in [Measurement of phosphorous oxo acid group amount] described later. The total dissociated acid amount was 0.78 mmol/g.

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

X-ray diffraction confirmed that this fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm. The amount of phosphorous acid groups (amount of first dissociated acid) measured by the measurement method described below was 0.74 mmol/g.

<Production Example 2>
A fine fibrous cellulose dispersion was obtained in the same manner as in Production Example 1, except that the heating time of the chemical-impregnated pulp during the phosphorous oxidation was changed to 250 seconds. The amount of phosphorous groups (amount of first dissociated acid) measured by the measurement method described below was 1.51 mmol/g.

<Production Example 3>
A fine fibrous cellulose dispersion was obtained in the same manner as in Production Example 1, except that the heating time of the chemical-impregnated pulp during the phosphorous oxidation was changed to 400 seconds. The amount of phosphorous groups (amount of first dissociated acid) measured by the measurement method described below was 1.86 mmol/g.

<Production Example 4>
[Preparation of TEMPO-oxidized fine fibrous cellulose dispersion]
As the raw material pulp, softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used. This raw material pulp was subjected to an alkaline TEMPO oxidation treatment as follows. First, the raw material pulp equivalent to 100 parts by mass of dry mass, 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were dispersed in 10,000 parts by mass of water. Next, a 13% by mass aqueous solution of sodium hypochlorite was added to 1.3 mmol per 1.0 g of pulp to start the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to keep the pH at 10 to 10.5, and the reaction was deemed to have ended when no change in pH was observed.

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

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

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

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

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

X-ray diffraction confirmed that this fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxy groups measured using the method described below was 0.70 mmol/g.

<Production Example 5>
A fine fibrous cellulose dispersion was obtained in the same manner as in Production Example 4, except that the amount of sodium hypochlorite solution during the oxidation reaction was 3.8 mmol per 1.0 g of pulp. The amount of carboxyl groups measured by the measurement method described below was 1.30 mmol/g.

<Production Example 6>
A fine fibrous cellulose dispersion was obtained in the same manner as in Production Example 4, except that the amount of sodium hypochlorite solution during the oxidation reaction was 10 mmol per 1.0 g of pulp. The amount of carboxyl groups measured by the measurement method described below was 1.80 mmol/g.

Example 1
(Reduced thixotropy through ozone treatment)
To 1000 g of the fine fibrous cellulose dispersion obtained in Production Example 1 (solid content concentration 2% by mass, solid content 20 g), 1 L of ozone/oxygen mixed gas with an ozone concentration of 200 g/m ³ was added, and the mixture was stirred for 2 minutes at 25°C in a sealed container, and then allowed to stand for 30 minutes. The ozone addition rate at this time was 1.0 × 10 ^-2 g per 1 g of fine fibrous cellulose. Next, the container was opened and stirred for 5 hours to volatilize the ozone remaining in the dispersion. In this way, the fine fibrous cellulose was made low in thixotropy, and the viscosity, polymerization degree, and viscosity change rate of the obtained low thixotropy fine fibrous cellulose dispersion were measured by the method described below.

Example 2
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 1, except for using the fine fibrous cellulose dispersion obtained in Production Example 2. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 3
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 1, except for using the fine fibrous cellulose dispersion obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 4
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 1, except that an ozone/oxygen mixed gas with an ozone concentration of 40 g/ ^m3 was used. The ozone addition rate at this time was 2.0× ^10-3 g per 1 g of fine fibrous cellulose. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 5
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 4, except for using the fine fibrous cellulose dispersion obtained in Production Example 2. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 6
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 4, except for using the fine fibrous cellulose dispersion obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 7
(Reducing thixotropy through enzyme treatment)
To 1000 g of the fine fibrous cellulose dispersion obtained in Production Example 1 (solid content concentration 2% by mass, solid content 20 g), 20 g of an enzyme-containing liquid (manufactured by AB Enzymes, ECOPULP R, enzyme content about 5% by mass) diluted 1000 times was added and stirred at a temperature of 50° C. for 1 hour. The enzyme addition rate at this time was about 5.0×10 ⁻⁵ g per 1 g of fine fibrous cellulose. Next, the mixture was stirred at a temperature of 100° C. for 1 hour to inactivate the enzyme. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 8
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 7, except for using the fine fibrous cellulose dispersion obtained in Production Example 2. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 9>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 7, except for using the fine fibrous cellulose dispersion obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 10
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 7, except that an enzyme-containing liquid (ECOPULP R, manufactured by AB Enzymes, enzyme content: approximately 5% by mass) was diluted 1000 times and 4 g was added to 1000 g of a fine fibrous cellulose dispersion (solid content concentration 2% by mass, solid content 20 g). The enzyme addition rate at this time was approximately 1.0×10 ^-5 g per 1 g of fine fibrous cellulose. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 11
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 10, except for using the fine fibrous cellulose dispersion obtained in Production Example 2. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 12
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 10, except for using the fine fibrous cellulose dispersion obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 13
(Reduced thixotropy by sodium hypochlorite treatment)
170g of sodium hypochlorite solution (effective chlorine concentration 12% by mass) was added to 1000g of the fine fibrous cellulose dispersion obtained in Production Example 1 (solid content concentration 2% by mass, solid content 20g), and stirred at room temperature for 1 hour. The sodium hypochlorite addition rate at this time was 1.02g per 1g of fine fibrous cellulose. The viscosity, polymerization degree and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the method described below.

<Example 14>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 13, except for using the fine fibrous cellulose dispersion obtained in Production Example 2. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

Example 15
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 13, except for using the fine fibrous cellulose dispersion obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 16>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 13, except that 1.70 g of sodium hypochlorite solution (effective chlorine concentration 12% by mass) was added to 1000 g of fine fibrous cellulose dispersion (solid content concentration 2% by mass, solid content 20 g). The sodium hypochlorite addition rate at this time was 1.02×10 ⁻² parts by mass per part by mass of fine fibrous cellulose. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 17>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 16, except for using the fine fibrous cellulose dispersion obtained in Production Example 2. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 18>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 16, except for using the fine fibrous cellulose dispersion obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 19>
(Reducing thixotropy through subcritical water treatment)
The fine fibrous cellulose dispersion obtained in Production Example 1 was placed in a reactor, heated to 200°C, and heated for 10 seconds. The pressure in the reactor at this time was 20 MPa. After heating, the reactor was cooled with water, and the low thixotropic fine fibrous cellulose dispersion in the reactor was recovered. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 20>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 19, except for using the fine fibrous cellulose dispersion obtained in Production Example 2. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 21>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 19, except for using the fine fibrous cellulose dispersion obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 22>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 19, except that the heating time was set to 1 second. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 23>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 22, except for using the fine fibrous cellulose dispersion obtained in Production Example 2. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

<Example 24>
A low thixotropic fine fibrous cellulose dispersion was obtained in the same manner as in Example 22, except for using the fine fibrous cellulose dispersion obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained low thixotropic fine fibrous cellulose dispersion were measured by the methods described below.

In addition, when the sheets obtained by dehydrating and drying the fine fibrous cellulose obtained through the viscosity reduction treatment in Examples 1 to 24 and Comparative Examples 1 to 3 were analyzed by FT-IR, absorption due to P=O of a phosphonic acid group, which is a tautomer of a phosphorous acid group, was observed around 1,210 cm ^-1 .

<Comparative Example 1>
To 100 g of the hypophosphite pulp obtained in Production Example 1 (solid content concentration 20% by mass, solid content 20 g), 1 L of an ozone/oxygen mixed gas with an ozone concentration of 200 g/m ³ was added, and the mixture was stirred in a sealed container at 25° C. for 2 minutes and then allowed to stand for 30 minutes. The ozone addition rate at this time was 1.0×10 ⁻² g per 1 g of fine fibrous cellulose. The hypophosphite pulp was then washed to remove the remaining ozone. Next, a slurry with a solid content concentration of 2% by mass was prepared using the obtained pulp. This slurry was treated six times with a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. The obtained fine fibrous cellulose dispersion was used as it was to measure the viscosity, polymerization degree, and viscosity change rate by the method described below.

<Comparative Example 2>
A fine fibrous cellulose dispersion containing fine fibrous cellulose was obtained in the same manner as in Comparative Example 1, except for using the phosphorous pulp obtained in Production Example 2. The viscosity, degree of polymerization, and rate of viscosity change of the obtained fine fibrous cellulose dispersion were measured by the methods described below.

<Comparative Example 3>
A fine fibrous cellulose dispersion containing fine fibrous cellulose was obtained in the same manner as in Comparative Example 1, except for using the phosphorous pulp obtained in Production Example 3. The viscosity, degree of polymerization, and viscosity change rate of the obtained fine fibrous cellulose dispersion were measured as they were by the methods described below.

<Comparative Example 4>
The fine fibrous cellulose dispersion obtained in Production Example 1 was used as it was to measure the viscosity, degree of polymerization and rate of change in viscosity by the methods described later.

<Comparative Example 5>
The fine fibrous cellulose dispersion obtained in Production Example 2 was used as it was to measure the viscosity, degree of polymerization and rate of change in viscosity by the methods described later.

<Comparative Example 6>
The fine fibrous cellulose dispersion obtained in Production Example 3 was used as it was to measure the viscosity, degree of polymerization and rate of change in viscosity by the methods described later.

<Comparative Example 7>
The fine fibrous cellulose dispersion obtained in Production Example 4 was used as it was to measure the viscosity, degree of polymerization and rate of change in viscosity by the methods described later.

<Comparative Example 8>
The fine fibrous cellulose dispersion obtained in Production Example 5 was used as it was to measure the viscosity, degree of polymerization and rate of change in viscosity by the methods described later.

<Comparative Example 9>
The fine fibrous cellulose dispersion obtained in Production Example 6 was used as it was to measure the viscosity, degree of polymerization and rate of change in viscosity by the methods described later.

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

[Measurement of Carboxy Group Amount]
The amount of carboxy groups in the fine fibrous cellulose was measured by adding ion exchange water to a fine fibrous cellulose-containing slurry containing the target fine fibrous cellulose to adjust the content to 0.2 mass%, treating the slurry with ion exchange resin, and then titrating the slurry with an alkali.
The treatment with ion exchange resin was carried out by adding 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a 0.2% by mass slurry containing fine fibrous cellulose, shaking for 1 hour, and then pouring onto a mesh with 90 μm openings to separate the resin and the slurry.
In addition, the titration using an alkali was performed by measuring the change in the pH value of the slurry while adding 10 μL of 0.1N aqueous sodium hydroxide solution to the fibrous cellulose-containing slurry after the treatment with the ion exchange resin. When the change in pH is observed while adding the aqueous sodium hydroxide solution, a titration curve as shown in FIG. 2 is obtained. As shown in FIG. 2, in this neutralization titration, a point is observed in which the increment (differential value of pH with respect to the amount of alkali added) is maximum in the curve plotting the measured pH against the amount of alkali added. This maximum point of the increment is called the first end point. Here, the region from the start of the titration to the first end point in FIG. 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali required in the first region of the titration curve (mmol) was divided by the solid content (g) in the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxyl groups introduced (mmol/g).
The above-mentioned amount of carboxyl groups introduced (mmol/g) indicates the amount of substituents per 1 g of fibrous cellulose mass when the counter ion of the carboxyl group is a hydrogen ion (H ⁺ ) (hereinafter referred to as the amount of carboxyl groups (acid type)).

[Measurement of Viscosity of Fine Fibrous Cellulose Dispersion]
The viscosity of the fine fibrous cellulose dispersion was measured as follows. First, the fine fibrous cellulose dispersion was diluted with ion-exchanged water so that the solid content concentration was 0.4% by mass, and then stirred in a disperser at 1500 rpm for 5 minutes. Next, the viscosity of the dispersion thus obtained was measured using a B-type viscometer (manufactured by BLOOKFIELD, analog viscometer T-LVT). The measurement conditions were a rotation speed of 3 rpm, and the viscosity value 3 minutes after the start of the measurement was taken as the viscosity of the dispersion. In addition, the dispersion to be measured was left to stand for 24 hours in an environment of 23 ° C. and relative humidity 50% before the measurement. The liquid temperature of the dispersion during the measurement was 23 ° C.

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

[Measurement of Viscosity Change Rate of Fine Fibrous Cellulose Dispersion]
The viscosity change rate of the fine fibrous cellulose dispersion was measured as follows.
(Measurement of viscosity before stirring)
First, the fine fibrous cellulose dispersion was diluted with ion-exchanged water so that the viscosity measured by the method described below was about 2500 mPa·s, and the fine fibrous cellulose dispersion was placed in a cylindrical container with a diameter of 10 cm to a height of 5 cm, and stirred with a disperser at 1500 rpm for 5 minutes. One minute after the end of stirring, the viscosity of the obtained fine fibrous cellulose dispersion was measured using a B-type viscometer (manufactured by BLOOKFIELD, analog viscometer T-LVT). The measurement conditions were a rotation speed of 6 rpm, and the viscosity value one minute after the start of measurement was taken as the viscosity of the dispersion. The liquid temperature of the dispersion during measurement was 23°C.
(Stirring with a stirrer)
The resulting fine fibrous cellulose dispersion having a viscosity of about 2500 mPa s was then poured into a cylindrical container having a diameter of 10 cm to a height of 5 cm, and stirred for 24 hours using an elliptical stirrer having a length of 5 cm, a width of 2 cm at the center, and a width of 1 cm at the end, while maintaining a 2 cm depression in the center of the liquid surface. The temperature of the dispersion during stirring was 23°C.
(Measurement of viscosity after stirring)
One minute after the end of stirring with the stirrer, the viscosity of the fine fibrous cellulose dispersion was immediately measured using a Brookfield viscometer (analog viscometer T-LVT, manufactured by BLOOKFIELD). The measurement conditions were a rotation speed of 6 rpm, and the viscosity value one minute after the start of measurement was taken as the viscosity of the dispersion. The temperature of the dispersion during the measurement was 23°C.
(Calculation of viscosity change rate)
The rate of change in viscosity before and after stirring with a stirrer was calculated using the following formula.
Viscosity change rate (%)=(viscosity after stirring−viscosity before stirring)/viscosity before stirring×100

<Evaluation>
[Evaluation of paint application suitability]
The coating suitability of the coating material using the fine fibrous cellulose dispersion obtained according to the present invention was evaluated as follows.
(Preparation of Fine Fibrous Cellulose-Containing Paint)
To 100 parts by mass of a fine fibrous cellulose dispersion having a viscosity of approximately 2500 mPa·s obtained by the same method as above, 1 part by mass of a lustrous material (aluminum paste WXM7640, manufactured by Toyo Aluminum Co., Ltd., aluminum concentration 58 to 61% by mass) was added, and the mixture was stirred in a disperser at 1500 rpm for 5 minutes to obtain a coating material containing fine fibrous cellulose.
(Paint circulation and spray coating)
Then, the obtained fine fibrous cellulose-containing paint is circulated in the pipe for 24 hours by a pump-type circulation device. Immediately after the end of circulation, the fine cellulose-containing paint is applied to the wall surface with a spray gun, and the presence or absence of dripping is confirmed. In addition, the presence or absence of precipitation of the glittering material in the fine cellulose-containing paint during coating is visually confirmed. Based on the results of dripping of the paint and the precipitation of the glittering material, the coating suitability of the fine fibrous cellulose-containing paint is evaluated in four stages.
A: No dripping or settling of the luster material was observed during coating after the paint was circulated, and the coating suitability was very good.
B: Either dripping or settling of the luster material was observed during coating after the paint was circulated, but it was minor and the coating suitability was good.
C: Dripping and settling of the luster material were observed during coating after the paint was circulated, and the coating suitability was somewhat poor, but no problem was encountered in practical use.
D: There was a lot of dripping and settling of the luster material during coating after the paint was circulated, and the coating suitability was poor, making it problematic for practical use.

The paint using the fine fibrous cellulose obtained in the examples demonstrated excellent coating suitability.

Claims (5)

A fibrous cellulose having a fiber width of 1000 nm or less and having a phosphorous acid group or a substituent derived from a phosphorous acid group,
The phosphite group or a substituent derived from a phosphite group is represented by the following formula (2):

(In formula (2), b is a natural number, m is an arbitrary number, and b×m=1. α is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a derivative group in which at least one functional group selected from the group consisting of a carboxy group, a hydroxy group, and an amino group is added to or substituted on the main chain or side chain of these hydrocarbon groups. ^{β b+} is a monovalent or higher cation consisting of an organic or inorganic substance.)
an introduction amount of a phosphorous acid group or a substituent derived from a phosphorous acid group into the fibrous cellulose is 0.40 mmol/g or more and 1.00 mmol/g or less;
The degree of polymerization of the fibrous cellulose is 320 or more and 500 or less,
When the fibrous cellulose is dispersed in water to a concentration of 0.4% by mass to prepare a dispersion, the viscosity of the dispersion at 23° C. is 200 mPa·s or more and 3000 mPa·s or less,
A fibrous cellulose in which, when the fibrous cellulose is dispersed in water to give a dispersion having a viscosity of 2,500 mPa s at 23° C. and the dispersion is stirred under the following stirring conditions, a viscosity change rate calculated by the following formula is within ±30%;
Viscosity change rate (%)=(viscosity after stirring−viscosity before stirring)/viscosity before stirring×100
(Mixing conditions)
A dispersion liquid having a viscosity of 2,500 mPa s at 23°C is poured into a cylindrical container having a diameter of 10 cm to a height of 5 cm, and stirred at 23°C for 24 hours using an elliptical stirrer having a length of 5 cm, a width of 2 cm at the center and a width of 1 cm at the end, while maintaining a state in which the center of the liquid surface is recessed by 2 cm. The fibrous cellulose according to claim 1, wherein the viscosity change rate is between -30% and 0%. The fibrous cellulose according to claim 1 or 2, wherein the degree of polymerization of the fibrous cellulose is 340 or more and 500 or less. The fibrous cellulose according to any one of claims 1 to 3 , which is for use in paints. A fibrous cellulose dispersion obtained by dispersing the fibrous cellulose according to any one of claims 1 to 4 in water.

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