JP6783078B2 - Cellulose nanofiber manufacturing method and cellulose nanofiber manufacturing equipment - Google Patents

Description

The present invention relates to a method for producing cellulose nanofibers and an apparatus for producing cellulose nanofibers.

In recent years, nanotechnology has been attracting attention for the purpose of refining substances to the nanometer level and obtaining new physical properties different from the conventional properties of substances. Cellulose nanofibers produced from cellulosic raw materials such as pulp fibers have excellent strength, elasticity, thermal stability, etc., and therefore are filled with filter media, filter aids, ion exchanger base materials, and chromatography analysis equipment. It is used for industrial purposes such as a filler for blending materials, resins and rubbers, and as a blending agent for cosmetics such as lipsticks, powder cosmetics and emulsified cosmetics. In addition, since cellulose nanofibers have excellent water-based dispersibility, they are viscosity-retaining agents for foods, cosmetics, paints, etc., fortifiers for food raw material fabrics, water-retaining agents, food stabilizers, low-calorie additives, and emulsification. It is expected to be used in many applications such as stabilizing aids.

Cellulose nanofibers can be obtained by defibrating pulp fibers by mechanical treatment. However, when cellulose nanofibers are produced only by mechanical treatment, a large number of mechanical treatments are required, and energy consumption becomes very large. Therefore, various methods of performing pretreatment such as oxidation treatment and esterification treatment have been studied before the mechanical treatment. Among these pretreatments, a method of oxidizing pulp using 2,2,6,6-tetramethyl-1-piperidin-N-oxyradical (TEMPO) and sodium hypochlorite (Japanese Patent Laid-Open No. 2008-1728). (Refer to Japanese Patent Application Laid-Open No. 2010-235679) states that the mechanical processing in the subsequent process can be effectively reduced. However, even with this method, the number of mechanical processes is not sufficiently reduced, and since TEMPO is expensive, it is possible to reduce the number of mechanical processes while suppressing the cost increase for commercialization. The manufacturing method is required.

Japanese Unexamined Patent Publication No. 2008-1728 JP-A-2010-235679

The present invention has been made based on the above circumstances, and an object of the present invention is a method for producing cellulose nanofibers capable of producing cellulose nanofibers by reducing the number of mechanical micronization treatments and saving energy, and cellulose. It is to provide a nanofiber manufacturing apparatus.

The inventors have used a chemical treatment and a specific mechanical treatment in combination as a pretreatment step of a process of mechanically refining pulp fibers, and beat the pulp fibers as the specific mechanical treatment. It has been found that the number of times of fine processing in the post-process can be reduced by using the refiner, which is the above, and the present invention has been completed.

That is, the invention made to solve the above problems includes a step of pretreating the pulp fibers in the slurry and a step of refining the pretreated pulp fibers in the slurry by mechanical treatment. A method for producing cellulose nanofibers, wherein the pretreatment step is a step of subjecting the pulp fiber to an oxidation treatment, a hydrolysis treatment, or a chemical treatment consisting of a combination thereof, and the pulp fiber is subjected to a refiner. It is characterized by including a process of coarsely defibrating.

In the production method, before the pulp fibers are refined by mechanical (physical) treatment, that is, defibrated, chemical pretreatment such as oxidation treatment and hydrolysis treatment and rough defibration using a refiner are performed. Two types of pretreatment are performed, such as mechanical pretreatment. The combination of these two pretreatments softens the pulp fibers and efficiently causes preliminary defibration. Specifically, a chemical pretreatment can break a part of the chemical bonds in the pulp fiber and swell the pulp fiber, and a pretreatment using a refiner can provide a shearing force to the pulp fiber. Is effectively applied, fluffing occurs in the pulp fibers, the pulp fibers become flexible, and preliminary defibration occurs. As a result, it is possible to reduce the number of processing times in the miniaturization step in the subsequent process and to produce cellulose nanofibers with energy saving. The number of treatments in the miniaturization step (miniaturization treatment) refers to the number of times the slurry containing the pulp fibers to be treated passes through a machine that undergoes the miniaturization treatment such as a high-pressure homogenizer.

It is preferable that the pretreatment step is performed in the order of the chemical treatment step and the coarse defibration step. By performing the pretreatment in this order, the refining force is efficiently applied to the pulp fibers swollen by the chemical pretreatment, so that the efficiency of preliminary defibration can be improved. it can.

It is preferable that the mechanical treatment in the miniaturization step is performed by a high-pressure homogenizer. By going through two types of pretreatment steps, the pulp fibers are in a sufficiently softened state, and by treating such pulp fibers with a high-pressure homogenizer, collisions between the pulp fibers act. However, defibration occurs effectively. As a result, the number of treatments in the miniaturization step can be further reduced, and the productivity of the cellulose nanofibers can be further increased.

The high-pressure homogenizer is a counter-collision type high-pressure homogenizer, and it is preferable that the slurry is opposed to collide in a straight line in the miniaturization step. By doing so, the energy given by the high-pressure homogenizer can be converted to collision energy to the maximum extent, and more efficient pulp fiber defibration occurs.

Another invention made to solve the above problems is a chemical treatment means for subjecting pulp fibers in a slurry to an oxidation treatment, a hydrolysis treatment, or a chemical treatment consisting of a combination thereof, and pulp in the slurry. An apparatus for producing cellulose nanofibers, which comprises a refiner for coarsely hydrolyzing fibers and a high-pressure homogenizer for refining pulp fibers in the above slurry. According to the manufacturing apparatus, the pulp fibers can be effectively pretreated by the chemical pretreatment means and the refiner, and the number of treatments in the miniaturization step using the high-pressure homogenizer can be reduced. .. Therefore, according to the production method, cellulose nanofibers can be efficiently produced with energy saving.

The "cellulose nanofiber" refers to a fine cellulose fiber obtained by defibrating a pulp fiber, and generally refers to a cellulose fiber containing cellulose fine fiber having a fiber width of nano size (1 nm or more and 1000 nm or less). ..

According to the method for producing cellulose nanofibers and the apparatus for producing cellulose nanofibers of the present invention, it is possible to reduce the number of mechanical micronization treatments and produce cellulose nanofibers with energy saving.

It is a flow chart of the manufacturing method of the cellulose nanofiber which concerns on one Embodiment of this invention. It is a partial schematic diagram of the counter-collision type high pressure homogenizer used in the manufacturing method of the cellulose nanofiber of FIG.

Hereinafter, the method for producing cellulose nanofibers and the apparatus for producing cellulose nanofibers according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.

<Manufacturing method of cellulose nanofibers>
As shown in FIG. 1, the method for producing cellulose nanofibers according to an embodiment of the present invention includes a pretreatment step (s1) and a miniaturization step (s2), and the pretreatment step (s1) is a chemical treatment. It includes a step (s1a) and a coarse defibration step (s1b). The order of the chemical treatment step (s1a) and the coarse defibration step (s1b) is not particularly limited, and any step may be performed first. According to the production method, the combination of two types of pretreatments, the chemical treatment step (s1a) and the coarse defibration step (s1b), makes the pulp fibers flexible and preliminary defibration efficiently occurs. , It is possible to shorten the miniaturization process of the post-process, that is, to reduce the number of processes. Each process will be described in detail below.

<Pretreatment step (s1)>
The pretreatment step (s1) is a step of pretreating the pulp fibers in the slurry, and is a step of pretreating the pulp fibers before making them finer by mechanical treatment. .. The pulp fiber which is a raw material of the cellulose nanofiber will be described below.

Examples of the pulp fiber include broad-leaved kraft pulp (LKP) such as broad-leaved bleached kraft pulp (LBKP) and broad-leaved unbleached kraft pulp (LUKP), coniferous bleached kraft pulp (NBKP), coniferous unbleached kraft pulp (NUKP) and the like. Chemical pulp such as kraft pulp (NKP);
Stone Grand Pulp (SGP), Pressurized Stone Grand Pulp (PGW), Refiner Grand Pulp (RGP), Chemi Grand Pulp (CGP), Thermo Grand Pulp (TGP), Grand Pulp (GP), Thermo Mechanical Pulp (TMP), Mechanical pulp such as Chemi-Thermo Mechanical Pulp (CTMP), Bleached Thermo-Mechanical Pulp (BTMP);
Waste paper pulp manufactured from used tea paper, used kraft envelopes, used magazines, used newspapers, used leaflets, used office paper, used corrugated cardboard, used white paper, Kent used paper, imitation used paper, ground ticket used paper, used paper and paper.
Examples thereof include deinked pulp (DIP) obtained by deinking used paper pulp. These may be used alone or in combination of a plurality of types as long as the effects of the present invention are not impaired.

<Chemical treatment step (s1a)>
The chemical treatment step (s1a), which is one of the pretreatment steps (s1), is a step of subjecting the pulp fibers in the slurry to an oxidation treatment, a hydrolysis treatment, or a chemical treatment consisting of a combination thereof. .. By performing such a chemical treatment, a part of the chemical bond in the pulp fiber can be broken and the pulp fiber can be swollen.

The lower limit of the pulp fiber concentration in the pulp slurry to be subjected to the chemical treatment step (s1a) is preferably 3% by mass, more preferably 5% by mass. On the other hand, the upper limit is, for example, 30% by mass. By setting the concentration in the above range, efficient chemical treatment can be performed. When the concentration is less than the above lower limit, the amount of pulp fibers processed in one treatment is small and the efficiency is low. On the other hand, if the concentration exceeds the above upper limit, sufficient stirring cannot be performed and the reactivity and the like are lowered.

The temperature of the pulp slurry to be subjected to the chemical treatment step (s1a) is preferably, for example, 40 ° C. or higher and 90 ° C. or lower. When the enzyme is used, the treatment is preferably about 40 ° C. or higher and 70 ° C. or lower.

Examples of the oxidizing agent used in the oxidation treatment include ozone, hypochlorous acid or a salt thereof, chloric acid or a salt thereof, perchloric acid or a salt thereof, persulfate or a salt thereof, and a perorganic acid. Among these, persulfates (persulfates and salts thereof) are preferable. When performing the oxidation treatment, an oxidation catalyst such as an N-oxyl compound can also be used in combination. Examples of the catalyst used in the hydrolysis treatment include acids and enzymes. Examples of the acid include sulfuric acid, persulfuric acid, hydrochloric acid and the like, but sulfuric acid and persulfuric acid are preferable. When an acid is used, the pH in the reaction vessel is preferably 3 or less, more preferably 0.5 or more and 2 or less. Examples of the enzyme include cellulase-based enzymes and hemicellulase-based enzymes, and cellulase-based enzymes are preferable. For the oxidation treatment and the hydrolysis treatment, a plurality of kinds of treatment agents may be used, or the oxidation treatment and the hydrolysis treatment may be combined. When an acid that also functions as an oxidizing agent, such as persulfuric acid, is used, both an oxidation reaction and a hydrolysis reaction occur.

The chemical treatment step (s1a) can be carried out by storing the slurry in a known reaction vessel and adding a treatment agent such as an oxidizing agent. As the reaction tank, a papermaking tower such as a bleaching tower can be used. The treatment (reaction) time of the chemical treatment step varies depending on the concentration and temperature of the slurry, the amount of the treatment agent added, and the like, and can be, for example, 0.5 hours or more and 12 hours or less.

The slurry that has undergone the chemical treatment step (s1a) is subjected to a neutralization treatment, a cleaning treatment and the like as necessary, and is used for the next step. In the case of chemical treatment using an enzyme, the reaction can be terminated by raising the slurry temperature by injecting hot water (warm water) into the slurry and inactivating the enzyme.

<Rough defibration processing step (s1b)>
The crude defibration treatment step (s1b), which is one of the pretreatment steps (s1), is a step of coarsely defibrating the pulp fibers in the slurry with a refiner. Pretreatment with a refiner that minimizes the gap and beats while applying a load effectively applies shearing force to the pulp fibers, causes fluffing of the pulp fibers, makes the pulp fibers flexible, and is preliminary. Debrisation occurs. The refiner is a device for beating pulp fibers, and a known device can be used. As the refiner, a conical type, a double disc refiner (DDR) and a single disc refiner (SDR) are preferable from the viewpoints that a shearing force can be efficiently applied to the pulp fibers and preliminary defibration can be promoted. .. It should be noted that the use of a refiner in the coarse defibration treatment step is also preferable from the viewpoint that separation and cleaning after the treatment become unnecessary.

The lower limit of the pulp fiber concentration of the pulp slurry to be subjected to the coarse defibration treatment step (s1b) is preferably 1% by mass, more preferably 2% by mass. On the other hand, as the upper limit, 8% by mass is preferable, and 6% by mass is more preferable. By setting the pulp fiber concentration in the above range, the pulp slurry has a suitable viscosity, so that the pulp fibers are efficiently coarsely defibrated by the refiner.

In the coarse defibration treatment step (s1b), for example, a plurality of refiners can be prepared to continuously treat the pulp fibers. It is also possible to circulate the slurry for one refiner and process it for a long time.

<Order of chemical treatment step (s1a) and coarse defibration treatment step (s1b)>
The chemical treatment step (s1a) and the coarse defibration treatment step (s1b) may be performed first, but it is preferable that the chemical treatment step (s1a) is performed first. By performing the chemical treatment step (s1a) and the coarse defibration step (s1b) in this order, the refiner efficiently applies shearing force to the pulp fibers swollen by the chemical pretreatment, so that it is preliminary. It is possible to increase the efficiency of defibration and reduce the amount of energy consumed.

Further, the chemical treatment step (s1a) and the coarse defibration treatment step (s1b) can be performed in an overlapping manner. For example, by subjecting the slurry to which an acid, an enzyme, an oxidizing agent, etc. is added to the crude defibration treatment step (s1b), the chemical treatment and the coarse defibration treatment can be performed at the same time.

<Miniaturization step (s2)>
The miniaturization step (s2) is a step of refining the pulp fibers in the pretreated slurry by mechanical treatment. Cellulose nanofibers can be obtained through this step. According to the method for producing cellulose nanofibers of the present invention, since the above-mentioned two types of pretreatments are performed, the miniaturization step (s2) can be shortened (the number of treatments can be reduced).

Examples of the method for performing the mechanical treatment in the micronization step (s2) include a grinder method for grinding pulp fibers between rotating grindstones, a pulverization method, and the like, and the pulverization method is preferable. Examples of the crushing method include a crushing method using a pressure homogenizer, a ball mill, and the like. Among these, the method using a pressure homogenizer is preferable. The pressure homogenizer is used as a disperser that discharges a slurry or the like from a pore at a high pressure. As the pressure type homogenizer, a high pressure homogenizer is preferable. The high-pressure homogenizer refers to a homogenizer having an ability to discharge a slurry at a pressure of, for example, 10 MPa or more, preferably 100 MPa or more. By treating the pulp fibers with a high-pressure homogenizer, collisions between the pulp fibers, pressure difference, microcavitation, etc. act, and defibration effectively occurs. As a result, the number of processes in the miniaturization process can be reduced (shortened), and the production efficiency of cellulose nanofibers can be further improved.

As the high-pressure homogenizer, a counter-collision type high-pressure homogenizer (microfluidizer, wet jet mill) is preferable, and in the miniaturization step, the slurry is preferably collided in a straight line. Specifically, as partially shown in FIG. 2, in the opposed collision type high pressure homogenizer 10, the upstream side flow path 11 is formed so that the pressurized slurries S1 and S2 collide with each other at the confluence X. Has been done. The slurries S1 and S2 collide at the confluence X, and the collided slurry S3 flows out from the downstream flow path 12. The downstream flow path 12 is provided perpendicular to the upstream side flow path 11, and the upstream side flow path 11 and the downstream side flow path 12 form a T-shaped flow path. By using such a counter-collision type high pressure homogenizer 10, the energy given by the high pressure homogenizer can be converted to the collision energy to the maximum, and more efficient pulp fiber defibration occurs.

The lower limit of the pulp fiber concentration of the pulp slurry to be subjected to the miniaturization step (s2) is preferably 0.5% by mass, more preferably 1% by mass. On the other hand, as the upper limit, 10% by mass is preferable, and 5% by mass is more preferable. By setting the pulp fiber concentration in the above range, the pulp slurry has a suitable viscosity, so that the pulp fibers are efficiently coarsely defibrated by mechanical treatment using a high-pressure homogenizer or the like.

In the miniaturization step (s2), for example, one high-pressure homogenizer can be subjected to a plurality of miniaturization treatments by circulating the slurry. It is also possible to prepare a plurality of high-pressure homogenizers and continuously process pulp fibers.

<Other processes>
The cellulose nanofibers obtained through the miniaturization step (s2) can be subjected to a modification treatment step and a drying step, if necessary.

The cellulose nanofibers thus obtained are filter media, filter aids, base materials for ion exchangers, fillers for chromatographic analysis equipment, fillers for blending resins and rubbers, cosmetic blenders, and viscosity preservatives. It can be widely used as a toughener for food raw material dough, a water retention agent, a food stabilizer, a low-calorie additive, an emulsion stabilization aid, and the like.

The resulting cellulose nanofibers are sufficiently finely divided and have one peak in the pseudo particle size distribution curve measured by laser diffraction in an aqueous dispersion state. The peak particle size (mode) in the pseudo particle size distribution curve is preferably 5 μm or more and 25 μm or less. When the obtained cellulose nanofibers have such a particle size distribution, they can exhibit sufficiently finely divided and good performance. The "pseudo particle size distribution curve" means a curve showing a volume-based particle size distribution measured using a particle size distribution measuring device (for example, a laser diffraction / scattering type particle size distribution measuring device manufactured by Seishin Enterprise Co., Ltd.).

The method for producing cellulose nanofibers can reduce the number of mechanical micronization treatments and obtain cellulose nanofibers with energy saving without using an expensive oxidation catalyst such as TEMPO or other N-oxyl compound. Therefore, the production cost of cellulose nanofibers can be suppressed. Further, when TEMPO or the like is not used, excessive oxidation is suppressed, so that the content of the carboxy group of the obtained cellulose nanofiber is low. When the amount of the carboxy group of the cellulose nanofiber is small, there is an advantage that excessive hydrophilicity and hydrogen bonds are suppressed, and drying property and dispersibility are improved. The content of the carboxy group of the obtained cellulose nanofibers is, for example, 0.1 mmol / g or less, and may be 0.05 mmol / g or less.

<Cellulose nanofiber manufacturing equipment>
The cellulose nanofiber manufacturing apparatus according to the embodiment of the present invention includes a chemical treatment means, a refiner, and a high-pressure homogenizer.

In the above chemical treatment means, the pulp fibers in the slurry are subjected to an oxidation treatment, a hydrolysis treatment, or a chemical treatment including a combination thereof. Examples of the chemical treatment means include a reaction vessel having a means for adding an oxidizing agent, an acid, an enzyme and the like. As the reaction tank, a papermaking tower such as a bleaching tower can be used as described above. As the refiner and the high-pressure homogenizer, those described in "Method for producing cellulose nanofibers" can be used. The apparatus for producing cellulose nanofibers may be provided with a chemical treatment means, a refiner, a high-pressure homogenizer, a dehydration means such as a filter and a screw press, and a drying means. The cellulose nanofiber manufacturing apparatus can be used by the method described above as the "cellulose nanofiber manufacturing method". According to the cellulose nanofiber manufacturing apparatus, the mechanical micronization treatment step can be shortened, that is, the number of treatments can be reduced, and the cellulose nanofibers can be efficiently produced with energy saving.

Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not limitedly interpreted based on the description of this Example.

[Example 1]
(Chemical treatment process)
A cellulase-based enzyme was added to a pulp slurry (temperature 50 ° C.) having a concentration of 20% by mass (pulp type: LBKP) and chemically treated. After 5 hours, the enzyme was inactivated by heating to 100 ° C.
(Rough defibration process)
The pulp slurry subjected to the above chemical treatment was prepared to have a pulp concentration of 4% by mass, and was subjected to rough defibration treatment with a refiner. The processing time by the refiner was 10 minutes.
(Miniaturization process)
The pulp slurry that had undergone the rough defibration step was prepared to a pulp concentration of 2% by mass and subjected to a miniaturization step by mechanical treatment. This treatment was performed using a face-to-collision wet jet mill (high pressure homogenizer). This wet jet mill is configured so that the slurries collide in a straight line.

[Example 2]
As a chemical treatment step, a pulp slurry (temperature 80 ° C.) having a concentration of 20% by mass was chemically treated by adding an oxidizing agent (ammonium persulfate), and after 5 hours, it was neutralized. The same operation as in Example 1 was carried out to obtain cellulose nanofibers.

[Example 3]
Cellulose nanofibers were obtained by performing the same operation as in Example 2 except that a polishing machine (“mass colloider” manufactured by Masuyuki Sangyo Co., Ltd.) was used as the miniaturization step.

[Example 4]
Cellulose nanofibers were obtained by performing the same operation as in Example 1 except that a polishing machine (“mascoroider” manufactured by Masuyuki Sangyo Co., Ltd.) was used as the miniaturization step.

[Example 5]
As a chemical treatment step, an acid (dilute sulfuric acid) was added to a pulp slurry (temperature 80 ° C.) having a concentration of 20% by mass for chemical treatment, and after 5 hours, neutralization treatment with sodium hydroxide was performed. Obtained cellulose nanofibers by performing the same operation as in Example 1.

[Example 6]
Cellulose nanofibers were obtained in the same manner as in Example 5 except that a polishing machine (“mascoroider” manufactured by Masuyuki Sangyo Co., Ltd.) was used as the miniaturization step.

[Comparative Example 1]
Cellulose nanofibers were obtained in the same manner as in Example 1 except that the chemical treatment step and the coarse defibration step were not performed.

[Comparative Example 2]
Cellulose nanofibers were obtained in the same manner as in Example 1 except that the chemical treatment step was not performed.

[Comparative Example 3]
Cellulose nanofibers were obtained in the same manner as in Example 1 except that the diagonal collision type high-pressure homogenizer was used in the miniaturization step without performing the chemical treatment step.

[Comparative Example 4]
Cellulose nanofibers were obtained in the same manner as in Example 1 except that the coarse defibration step was not performed.

[Comparative Example 5]
Cellulose nanofibers were obtained by performing the same operation as in Example 1 except that a polishing machine (“mass colloider” manufactured by Masuyuki Sangyo Co., Ltd.) was used as a miniaturization step without performing a chemical treatment step.

In each Example and Comparative Example, the volume-based particle size distribution of the pulp fibers in the treated slurry was measured for each treatment by a high-pressure homogenizer or a polishing machine in the miniaturization treatment. This measurement was performed using a laser diffraction / scattering type particle size distribution measuring instrument manufactured by Seishin Enterprise Co., Ltd. In the measured pseudo-particle size distribution curve, the treatment with a high-pressure homogenizer or a polishing machine was repeated until the peak became one and the peak was in the range of 5 μm or more and 25 μm or less. In the pseudo particle size distribution curve, it was judged that the cellulose nanofibers were obtained when the peaks became one and the peaks were in the range of 5 μm or more and 25 μm or less, and the miniaturization step was completed. Table 1 shows the number of processing times of the miniaturization step performed in each Example and Comparative Example.

The numerical values shown in parentheses in the column of each treatment step in Table 1 are relative values indicating the amount of energy consumption per treatment step, where 1 is the energy consumption per enzyme treatment. is there. Table 1 shows the energy (relative value) consumed in the production of the cellulose nanofibers of each Example and Comparative Example as an integrated value of the energy consumed in each step.

As shown in Table 1 above, in Examples 1 to 6 in which chemical treatment and rough defibration treatment using a refiner were performed as pretreatment, the number of treatments in the miniaturization step was reduced to 3 times or less. You can see that there is. Further, in Examples 1 to 6, it can be seen that the amount of energy consumed can be significantly reduced by reducing the number of processes in the miniaturization step, which consumes a large amount of energy each time.

According to the method for producing cellulose nanofibers of the present invention, it is possible to reduce the number of mechanical micronization treatments and produce cellulose nanofibers with energy saving.

s1 Pretreatment process s2 Miniaturization process s1a Chemical treatment process s1b Coarse defibration process 10 Opposed collision type high pressure homogenizer 11 Upstream side flow path 12 Downstream side flow path S1, S2, S3 Slurry X confluence

Claims (4)

A method for producing cellulose nanofibers, which comprises a step of pretreating the pulp fibers in the slurry and a step of refining the pretreated pulp fibers in the slurry by mechanical treatment.
As the pretreatment step,
A step of chemically treating the pulp fiber with a cellulase enzyme , and a step of coarsely defibrating the pulp fiber with a refiner.
In this order,
The pulp fiber concentration of the pulp slurry used in the coarse defibration treatment step is 2% by mass or more and 6% by mass or less.
The cellulose nanofibers obtained by the method for producing cellulose nanofibers have one peak in the pseudo particle size distribution curve measured by a laser diffraction method in an aqueous dispersion state, and the particle size that becomes the peak in the pseudo particle size distribution curve is method for producing cellulose nanofibers, characterized in der Rukoto than 25μm below 5 [mu] m. The method for producing cellulose nanofibers according to claim 1 , wherein the mechanical treatment in the miniaturization step is performed by a high-pressure homogenizer. The method for producing cellulose nanofibers according to claim 2 , wherein the high-pressure homogenizer is a counter-collision type high-pressure homogenizer, and in the miniaturization step, the slurry is opposed to collide on a straight line. A chemical treatment means for chemically treating pulp fibers in a slurry with a cellulase enzyme .
A refiner for coarsely defibrating the pulp fibers in the slurry and a high-pressure homogenizer for refining the pulp fibers in the slurry are provided in this order .
The pulp fiber concentration of the pulp slurry used in the coarse defibration treatment step is 2% by mass or more and 6% by mass or less.
The cellulose nanofibers obtained by the method for producing cellulose nanofibers have one peak in the pseudo particle size distribution curve measured by a laser diffraction method in an aqueous dispersion state, and the particle size that becomes the peak in the pseudo particle size distribution curve is 5μm or 25μm or less der Ru cellulose nanofiber production apparatus.

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