JP7402154B2 - Method for producing cellulose nanofiber dispersion - Google Patents

Description

The present invention relates to a method for producing a highly transparent cellulose nanofiber dispersion that is produced with low power consumption.

Cellulose nanofibers obtained by refining cellulose are fibers with nano-level fiber diameters of about 1 to 100 nm, and their dispersion has high transparency. Therefore, it is expected to be applied to applications that require transparency, such as optical films, coating agents for films, and composites for glass. Therefore, various studies have been conducted regarding methods for producing cellulose nanofibers (see Patent Document 1).

Japanese Patent Application Publication No. 2008-1728

However, in conventional methods for producing cellulose nanofibers, the micronization process is generally performed multiple times using a dispersion machine with strong shearing force, such as an ultra-high pressure homogenizer, and therefore a huge amount of electricity is used for production. In addition, ultra-high-pressure homogenizers apply high pressure by forcing the sample into a very narrow gap, so when processing large fibers such as pulp, they can cause clogging, resulting in extremely poor productivity and workability. It was a problem.

An object of the present invention is to provide a method for producing a cellulose nanofiber dispersion that efficiently produces a highly transparent cellulose nanofiber dispersion with low power consumption.

The present invention provides the following (1) to (7).

(1) A method for producing a highly transparent cellulose nanofiber dispersion from chemically modified cellulose, which comprises the following steps (A) and (B).
Step (A): a preliminary defibration step of beating the chemically modified cellulose using a single disc type refiner;
Step (B): Main defibration step in which the cellulose obtained in the preliminary defibration step (A) is defibrated by treatment with a high-pressure disperser at a treatment pressure of 1 MPa to 400 MPa.

(2) In the preliminary defibration step (A), the plates used in the refiner include a viscous defibration plate, a fine bar type plate, a plate having a structure that blocks the raw material flow path, a grindstone plate, and a flat plate without grooves. The method for producing a cellulose nanofiber dispersion according to (1), characterized in that the dispersion is a metal plate.

(3) Production of the cellulose nanofiber dispersion according to (1) or (2), wherein in the preliminary defibration step (A), the processing speed of the chemically modified cellulose is 30 m ³ /hr or less. Method.

(4) In the preliminary defibration step (A), the concentration of the chemically modified cellulose during treatment is 2.5 to 15% by mass, according to any one of (1) to (3). A method for producing a cellulose nanofiber dispersion.

(5) The cellulose nanofiber dispersion according to any one of (2) to (4), wherein in the preliminary defibration step (A), the clearance of the plate is 0.01 to 0.4 mm. manufacturing method.

(6) The cellulose nanofiber dispersion according to any one of (2) to (5), wherein in the preliminary defibration step (A), the peripheral speed of the plate is 24.5 m/s or more. manufacturing method.

(7) The cellulose nano as described in any one of (2) to (6), wherein in the preliminary defibration step (A), the shear rate of rotation of the plate is 100 (1/ms) or more. Method for producing fiber dispersion.

According to the present invention, it is possible to provide a method for efficiently producing a highly transparent cellulose nanofiber dispersion liquid with low power consumption. Further, according to the present invention, in the main defibration step of converting chemically modified cellulose into nanofibers, it is possible to suppress the occurrence of clogging in the defibration machine, which deteriorates productivity.

The method for producing a cellulose nanofiber dispersion of the present invention includes a step (A): a preliminary defibration step of beating chemically modified cellulose using a single-disk type refiner, and a step (B): the preliminary defibration step. It is characterized by having a main defibration step in which the cellulose obtained in (A) is defibrated by treatment with a high-pressure disperser at a treatment pressure of 1 MPa to 400 MPa.

In the present invention, cellulose fibers are defibrated by different mechanisms by combining preliminary defibration by mechanical defibration using a conventional defibration device and main defibration, thereby reducing power consumption and improving transparency. A high cellulose nanofiber dispersion can be produced.

The reason why a highly transparent cellulose nanofiber dispersion liquid can be obtained according to the present invention is surmised as follows. In the preliminary fibrillation, the chemically modified cellulose used as a raw material becomes finer, and the outside of the cellulose fibers becomes loosened. Therefore, in the subsequent main defibration, shearing energy from an ultra-high-pressure homogenizer or the like can easily act on the cellulose, making it possible to efficiently produce a highly transparent cellulose nanofiber dispersion.

(1) Cellulose raw material In the present invention, cellulose raw material refers to various forms of materials mainly composed of cellulose, including pulp (bleached or unbleached wood pulp, bleached or unbleached non-wood pulp, refined linter, jute, Manila hemp). , pulp derived from herbs such as kenaf), natural cellulose such as cellulose produced by microorganisms such as acetic acid bacteria, regenerated cellulose spun after dissolving cellulose in some solvent such as a cupric ammonia solution or a morpholine derivative, and the above. Examples include fine cellulose obtained by depolymerizing cellulose by subjecting a cellulose raw material to hydrolysis, alkaline hydrolysis, enzymatic decomposition, blasting treatment, mechanical treatment such as a vibrating ball mill, and the like.

(2) Chemical modification process of cellulose (oxidation)
In the present invention, the cellulose raw material can be oxidized using a known method, and is not particularly limited. It is preferable to adjust the amount to 3.0 mmol/g.

As an example thereof, it can be obtained by oxidizing cellulose in water with an oxidizing agent in the presence of N-oxyl compounds and compounds selected from the group consisting of bromides, iodides or mixtures thereof. Through this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, and a cellulose fiber having an aldehyde group and a carboxyl group or a carboxylate group on the surface can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less. The N-oxyl compound refers to a compound capable of generating nitroxy radicals. As the N-oxyl compound, any compound can be used as long as it promotes the desired oxidation reaction.

The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount that can oxidize cellulose as a raw material. For example, it is preferably 0.01 to 10 mmol, more preferably 0.02 to 1 mmol, and even more preferably 0.05 to 0.5 mmol, per 1 g of bone dry cellulose. Further, it is preferably about 0.1 to 4 mmol/L to the reaction system.

Bromide is a compound containing bromine, examples of which include alkali metal bromides that can be dissociated and ionized in water. Moreover, iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide to be used can be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol, per 1 g of bone dry cellulose.

As the oxidizing agent, known ones can be used, such as halogen, hypohalous acid, halous acid, perhalogenic acid, salts thereof, halogen oxides, peroxides, and the like. Among these, sodium hypochlorite is preferred because it is inexpensive and has a low environmental impact. The appropriate amount of the oxidizing agent to be used is, for example, preferably 0.5 to 500 mmol, more preferably 0.7 to 50 mmol, even more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol, per 1 g of bone dry cellulose. . Further, for example, it is preferably 1 to 40 mol per 1 mol of the N-oxyl compound.

In the cellulose oxidation process, the reaction can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, and may be room temperature of about 15 to 30°C. As the reaction progresses, carboxyl groups are generated in the cellulose, so a decrease in the pH of the reaction solution is observed. In order for the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. Water is preferred as the reaction medium because of its ease of handling and the fact that side reactions are less likely to occur.

The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually about 0.5 to 6 hours, for example about 1 to 4 hours. Further, the oxidation reaction may be carried out in two stages. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency can be improved without being inhibited by the salt produced as a by-product in the first-stage reaction. Can be oxidized well.

Another example of the carboxylation (oxidation) method is a method of oxidizing a cellulose raw material by bringing it into contact with a gas containing ozone. This oxidation reaction oxidizes the hydroxyl groups at at least the 2- and 6-positions of the glucopyranose ring and causes decomposition of the cellulose chain. The ozone concentration in the ozone-containing gas is preferably 50 to 250 g/m ³ , more preferably 70 to 220 g/m ³ . The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. The ozone treatment temperature is preferably 0 to 50°C, more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, preferably about 30 to 300 minutes. When the ozone treatment conditions are within these ranges, excessive oxidation and decomposition of cellulose can be prevented, resulting in a good yield of oxidized cellulose. After the ozone treatment, additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the additional oxidation treatment is not particularly limited, but examples include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving these oxidizing agents in water or a polar organic solvent such as alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the solution.

The amount of carboxyl groups, carboxylate groups, and aldehyde groups in the cellulose fiber can be adjusted by controlling the amount of the oxidizing agent mentioned above and the reaction time. The method for measuring the amount of carboxyl groups is, for example, by preparing 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose, adding 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then adding 0.05 N sodium hydroxide to the slurry (aqueous dispersion). Measure the electrical conductivity by dropping the aqueous solution until the pH reaches 11, and calculate using the formula below from the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid, where the electrical conductivity changes slowly. can do.
Carboxyl group amount [mmol/g oxidized cellulose or cellulose nanofiber]
=a [mL] x 0.05/mass of oxidized cellulose [g]

(carboxymethylation)
In the present invention, carboxymethylation of the cellulose raw material can be carried out using a known method, and is not particularly limited, but the degree of carboxymethyl group substitution per anhydroglucose unit of cellulose is 0.01 to 0. It is preferable to adjust it so that it becomes 50. As an example, the following manufacturing method can be mentioned, but it may be synthesized by a conventionally known method, or a commercially available product may be used. Cellulose is used as a base material, and the solvent is 3 to 20 times the mass of water and/or lower alcohol, specifically methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc. A single medium or a mixture of two or more of them is used. Note that the mixing ratio of lower alcohol is 60 to 95% by mass. As the mercerization agent, alkali metal hydroxide, specifically sodium hydroxide and potassium hydroxide, is used in an amount of 0.5 to 20 times the mole per anhydroglucose residue in the bottom starting material. The bottom starting material, a solvent, and a mercerization agent are mixed, and mercerization treatment is performed at a reaction temperature of 0 to 70°C, preferably 10 to 60°C, and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added 0.05 to 10.0 times in mole per glucose residue, and the reaction temperature is 30 to 90°C, preferably 40 to 80°C, and the reaction time is 30 minutes to 10 hours, preferably 1 hour. The etherification reaction is carried out for ~4 hours.

As a method for measuring the degree of carboxymethyl substitution per glucose unit, for example, the following method can be used. That is, 1) Accurately weigh about 2.0 g of carboxymethylated cellulose fiber (absolutely dry) and place it in a 300 mL Erlenmeyer flask with a stopper. 2) Add 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol nitric acid, and shake for 3 hours to convert carboxymethylcellulose salt (CM-modified cellulose) into hydrogen-type CM-modified cellulose. 3) Accurately weigh 1.5 to 2.0 g of hydrogenated CM cellulose (absolutely dry) and place it in a 300 mL Erlenmeyer flask with a stopper. 4) Wet the hydrogenated CM cellulose with 15 mL of 80% methanol, add 100 mL of 0.1N NaOH, and shake at room temperature for 3 hours. 5) Back titrate excess NaOH with 0.1N H ₂ SO ₄ using phenolphthalein as indicator. 6) Calculate the degree of carboxymethyl substitution (DS) using the following formula.
A = [(100 x F' - (0.1N H ₂ SO ₄ ) (mL) x F) x 0.1]/(absolute dry mass (g) of hydrogenated CM cellulose)
DS=0.162×A/(1-0.058×A)
A: Amount of 1N NaOH required to neutralize 1g of hydrogenated CM cellulose (mL)
F': 0.1N H ₂ SO ₄ factor F: 0.1N NaOH factor

(cationization)
In the present invention, the cellulose raw material can be cationized using a known method, and by cationization, for example, ammonium, phosphonium, sulfonium, or a group containing these ammonium, phosphonium, or sulfonium can be added to the cellulose molecule. , groups containing ammonium are preferred, and groups containing quaternary ammonium are particularly preferred. The specific cationization method is not particularly limited, but as an example, a cationization agent such as glycidyltrimethylammonium chloride, 3-chloro-2hydroxypropyltrimethylammonium chloride, or a halohydrin type thereof is added to the cellulose raw material. By reacting an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, etc.) as a catalyst in the presence of water and/or an alcohol having 1 to 4 carbon atoms, a cationically modified product having a group containing quaternary ammonium is produced. cellulose can be obtained.

In addition, in this method, the degree of cation substitution per glucose unit of the obtained cation-modified cellulose can be controlled by controlling the amount of the cationizing agent to be reacted and the composition ratio of water and/or alcohol having 1 to 4 carbon atoms. It can be adjusted by. The degree of substitution here refers to the number of substituents introduced per unit structure (glucopyranose ring) constituting cellulose. In other words, it is defined as "the value obtained by dividing the number of moles of the introduced substituent by the total number of moles of hydroxyl groups in the glucopyranose ring." Since pure cellulose has three substitutable hydroxyl groups per unit structure (glucopyranose ring), the theoretical maximum value of the degree of substitution of the cellulose fiber of the present invention is 3 (minimum value is 0).

In the present invention, the degree of cation substitution per glucose unit of the cationized cellulose is preferably 0.01 to 0.40. By introducing cationic substituents into cellulose, the cells electrically repel each other. Therefore, cellulose into which cationic substituents have been introduced can be easily nano-fibrillated. Note that if the degree of cation substitution per glucose unit is less than 0.01, sufficient nanofibrillation cannot be achieved. On the other hand, if the degree of cation substitution per glucose unit is greater than 0.40, the fibers may swell or dissolve, making it impossible to maintain the fiber form and making it impossible to obtain nanofibers.

The degree of cation substitution per glucose unit can be calculated by the following formula after drying the sample (cation-modified cellulose) and measuring the nitrogen content with a total nitrogen analyzer TN-10 (Mitsubishi Chemical). . The degree of substitution herein refers to the average number of moles of substituents per mole of anhydroglucose unit.
Degree of cation substitution = (162×N)/(1-151.6×N)
N: Nitrogen content

(esterification)
The method for obtaining esterified cellulose fibers or esterified cellulose nanofibers by esterifying cellulose raw materials or defibrated cellulose fibers is not particularly limited, but examples include a method of reacting compound A with cellulose raw materials or defibrated cellulose fibers. It will be done. Compound A will be described later.

Methods for reacting compound A with cellulose raw material or defibrated cellulose fibers include, for example, a method of mixing powder or aqueous solution of compound A with cellulose raw material or defibrated cellulose fiber, and a method of reacting compound A with a slurry of cellulose raw material or defibrated cellulose fiber. Examples include a method of adding an aqueous solution of. Among these methods, the method of mixing an aqueous solution of Compound A with the cellulose raw material, defibrated cellulose fibers, or a slurry thereof is preferred because the uniformity of the reaction and the esterification efficiency are increased.

Examples of the compound A include phosphoric acid compounds (eg, phosphoric acid, polyphosphoric acid), phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. Compound A may be in the form of a salt. Among the above, phosphoric acid compounds are preferred because they are low cost, easy to handle, and can improve fibrillation efficiency by introducing phosphoric acid groups into cellulose used as cellulose raw materials (e.g., pulp fibers). . The phosphoric acid compound may be any compound having a phosphoric acid group, such as phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, dihydrogen phosphate, etc. Potassium hydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate, etc. . The phosphoric acid compounds used may be one type or a combination of two or more types. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid Ammonium salts of phosphoric acid are preferred, sodium salts of phosphoric acid are more preferred, and sodium dihydrogen phosphate and disodium hydrogen phosphate are even more preferred. Furthermore, it is preferable to use an aqueous solution of a phosphoric acid compound in the esterification because it increases the uniformity of the reaction and increases the efficiency of introducing a phosphoric acid group. The pH of the aqueous solution of the phosphoric acid compound is preferably 7 or less, since this increases the efficiency of introducing phosphoric acid groups. From the viewpoint of suppressing hydrolysis of pulp fibers, pH 3 to 7 is more preferable.

Examples of the esterification method include the following methods. Compound A is added to a cellulose raw material or a suspension of defibrated cellulose fibers (for example, solid content concentration 0.1 to 10% by mass) with stirring to introduce phosphoric acid groups into the cellulose. When Compound A is a phosphoric acid compound, when the cellulose raw material or defibrated cellulose fiber is 100 parts by mass, the amount of Compound A added is preferably 0.2 parts by mass or more as the amount of phosphorus element, and 1 part by mass or more. is more preferable. Thereby, the yield of esterified cellulose fibers or esterified cellulose nanofibers can be further improved. The upper limit is preferably 500 parts by mass or less, more preferably 400 parts by mass or less. This makes it possible to efficiently obtain a yield commensurate with the amount of compound A used. Therefore, it is preferably 0.2 to 500 parts by weight, more preferably 1 to 400 parts by weight.

When reacting Compound A with cellulose raw material or defibrated cellulose fiber, Compound B may be further added to the reaction system. Examples of methods for adding compound B to the reaction system include a method of adding compound B to a slurry of cellulose raw material or defibrated cellulose fibers, an aqueous solution of compound A, or a slurry of cellulose raw material or defibrated cellulose fibers and compound A. It will be done.

Compound B is not particularly limited, but preferably exhibits basicity, and more preferably a nitrogen-containing compound that exhibits basicity. "Exhibiting basicity" usually means that an aqueous solution of Compound B exhibits a pink to red color in the presence of a phenolphthalein indicator, and/or that the aqueous solution of Compound B has a pH greater than 7. The basic nitrogen-containing compound is not particularly limited as long as it achieves the effects of the present invention, but compounds having an amino group are preferred. Examples of compounds having an amino group include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, and the like. Among these, urea is preferred because it is low cost and easy to handle. The amount of compound B added is preferably 2 to 1000 parts by mass, more preferably 100 to 700 parts by mass. The reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C. The reaction time is not particularly limited, but is usually about 1 to 600 minutes, preferably 30 to 480 minutes. When the conditions for the esterification reaction are within any of these ranges, it is possible to prevent cellulose from being excessively esterified and become easily dissolved, and it is possible to improve the yield of phosphoesterified cellulose. can.

After reacting the cellulose raw material or defibrated cellulose fibers with Compound A, a suspension of esterified cellulose fibers or esterified cellulose nanofibers is usually obtained. The suspension of esterified cellulose fibers or esterified cellulose nanofibers is optionally dehydrated. It is preferable to perform heat treatment after dehydration. Thereby, hydrolysis of the cellulose raw material or defibrated cellulose fibers can be suppressed. The heating temperature is preferably 100 to 170°C, and while water is included during heat treatment, it is heated at 130°C or less (more preferably 110°C or less), and after water is removed, it is heated at 100 to 170°C. More preferably, it is treated.

In phosphoric acid esterified cellulose, a phosphoric acid group substituent is introduced into the cellulose, and the celluloses electrically repel each other. Therefore, phosphoric acid esterified cellulose fibers can be easily defibrated into cellulose nanofibers (this defibration until cellulose nanofibers are obtained is also referred to as nanofibrillation). The degree of phosphoric acid group substitution per glucose unit of the phosphoric acid esterified cellulose fiber is preferably 0.001 or more. Thereby, sufficient defibration (for example, nano-defibration) can be performed. The upper limit of the degree of phosphoric acid group substitution per glucose unit of the phosphoric acid esterified cellulose fiber is preferably 0.40 or less. Thereby, swelling or dissolution of the phosphoric acid esterified cellulose fibers can be suppressed, and the occurrence of a situation in which cellulose nanofibers cannot be obtained can be suppressed. Therefore, the degree of phosphoric acid group substitution per glucose unit of the phosphoric acid esterified cellulose fiber is preferably 0.001 to 0.40. Moreover, the degree of phosphoric acid group substitution per glucose unit of cellulose nanofibers modified by phosphoric acid esterification (phosphoric acid esterified cellulose nanofibers) is preferably 0.001 or more. The upper limit is preferably 0.40 or less. Therefore, the degree of phosphoryl substitution per glucose unit of the phosphoric acid esterified cellulose nanofiber is preferably 0.001 to 0.40. It is preferable that the phosphoric acid esterified cellulose fibers be subjected to a washing treatment such as washing with cold water after boiling. This allows efficient defibration.

The reaction tank used in the process of chemically modifying this cellulose raw material to obtain modified cellulose is not particularly limited, but may include a tank equipped with stirring blades, a pulper, a kneader, a ribbon type mixing device, and a screw type mixing device. Examples include devices and the like. Among these, when proceeding with the reaction at a raw material concentration of approximately 3% or less, it is preferable to use a tank or pulper equipped with stirring blades capable of stirring a liquid or liquid slurry. In addition, when proceeding with the reaction under conditions where the raw material concentration exceeds 3%, the reactants are not in liquid form but in solid form, so a kneader, ribbon type mixer, or screw type mixer that can mix and stir them is used. It is preferable to do so.

(3) Dehydration/washing step In the present invention, the dispersion of chemically modified cellulose obtained in the cellulose chemical modification step is washed with water after dehydration treatment, and by performing this step, cellulose nano A fiber dispersion can be obtained.

In this step, a centrifugal, vacuum dehydrating, or pressure dehydrating type of dehydration device can be used. Specifically, centrifugal separation types include basket-type centrifuges and decanter-type centrifuges, vacuum dehydration types include drum-type vacuum dehydrators and horizontal belt filters, and pressure dehydration types include filter presses, tube presses, and screw presses. , belt press horizontal belt filter, polydisc filter, vibrating screen, etc. Among these, pressure dehydration methods (filter press, tube press, screw press), centrifugal separation methods (basket type, decanter type), and vacuum dehydration methods are used because dehydration can be performed without applying strong shearing force to the dehydrated raw materials. (drum type vacuum dehydrator, horizontal belt filter) is preferred. Moreover, a plurality of these can also be used in combination.

(4) Chemically modified cellulose concentration adjustment step In the present invention, in order to efficiently perform the preliminary fibrillation step, the concentration of the chemically modified cellulose dispersion is 2.5% by mass to 15% by mass, more preferably 3% by mass. Adjust to ~10% by mass. If the amount is less than 0.5% by mass, the presence of modified pulp is too small and it is not possible to defibrate efficiently. On the other hand, if it exceeds 15% by mass, the viscosity of the chemically modified cellulose dispersion becomes too high to be efficiently defibrated.

(5) Preliminary defibration step (A)
In the present invention, the device used in the pre-fibrillation beating process is a single disc type refiner. Single-disc refiners have high plate surface accuracy and can be operated with narrow plate clearances. By performing the preliminary defibration step (A), the outer layer of the cellulose fibers is loosened and the inside is fibrillated, and in the main defibration step (B), cellulose nanofibers are easily obtained and the load is reduced.

In the preliminary defibration step (A), the processing speed of chemically modified cellulose in a single disc type refiner is 30 m ³ /hr or less. By controlling the processing speed to 30 m ³ /hr or less, a highly transparent cellulose nanofiber dispersion can be produced.

In the preliminary defibration step (A), the single-disc refiner includes a papermaking plate (viscous defibration plate, fine bar type plate), a plate with a structure that blocks the raw material flow path (dam plate), and a grindstone plate. , a flat metal plate without grooves is used.

The plate clearance of the refiner used in the preliminary defibration step (A) is 0.01 mm to 0.4 mm, more preferably 0.1 mm to 0.3 mm. If it is less than 0.01 mm, the plate will be severely worn, and if it exceeds 0.4 mm, the clearance will be too wide and it will be difficult to proceed with the process. In addition, in the preliminary defibration step (A), a normal refiner that adjusts the clearance by moving the rotor side plate using a hydraulic or pneumatic jack may be used, but it is more preferable to use a ball screw type clearance adjustment mechanism. Preliminary fibrillation can be carried out more efficiently by using a refiner with a refining mechanism and by strictly controlling the clearance between the plates using a laser position measuring mechanism.

Further, in the preliminary defibration step (A), the peripheral speed of the plate is preferably 24.5 m/s or more, more preferably 30 m/s or more. Preliminary fibrillation can be efficiently performed by setting the peripheral speed of the plate to 24.5 m/s or more. Further, in the preliminary defibration step (A), the rotational shearing speed of the plate of the refiner is 100 (1/ms) or more, more preferably 150 (1/ms) or more.

Here, the rotational shear speed of the plate=(peripheral speed of the plate/plate clearance). If the rotational shearing speed of the plate is less than 100 (1/ms), preliminary defibration cannot be performed efficiently. In addition, in the preliminary defibration step (A), a refiner with a normal head case shape may be used, but in order to prevent heat generation due to agitation of the raw materials staying inside the head case, the space inside the head case should be kept at 10 L or less. It is better to More preferably, a cooling water jacket for cooling the pulp is installed in the head case internal space to suppress the influence of heat on the pulp while processing.

(6) Main defibration process (B)
In the present invention, main fibrillation refers to cellulose obtained by pre-fibrillation by applying strong shearing force using a high-pressure disperser to achieve an average fiber length of 0.5 to 5 μm and an average fiber width of 3 to 5 μm. This means defibrating to 100 nm. In particular, in order to efficiently obtain cellulose nanofibers, it is preferable to use a wet high-pressure or ultra-high-pressure homogenizer that can apply a pressure of 1 MPa to 400 MPa and a strong shear force to the chemically modified cellulose dispersion. More preferably, a wet high-pressure or ultra-high-pressure homogenizer that can apply a pressure of 10 MPa to 400 MPa and a strong shearing force to the chemically modified cellulose dispersion is preferably used. Through this treatment, the chemically modified cellulose is defibrated to form cellulose nanofibers, and the cellulose nanofibers are dispersed in the medium to produce a cellulose nanofiber dispersion. Note that water is preferably used as the medium for ease of handling.
<Method for measuring average fiber length and average fiber width>
The average fiber length and average fiber width of cellulose nanofibers can be measured by observing cellulose nanofibers using an atomic force microscope (AFM).

Next, the present invention will be explained in more detail based on Examples, but the present invention is not limited to the following Examples.

[Example 1]
(Adjustment of pulp raw material: oxidized pulp)
5 g (absolutely dry) of bleached unbeaten pulp derived from coniferous trees (manufactured by Nippon Paper Industries), 78 mg (0.5 mmol) of TEMPO (manufactured by Tokyo Kasei Co., Ltd.) and 756 mg (7.35 mmol) of sodium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) ) was added to 500 mL of an aqueous solution and stirred until the pulp was uniformly dispersed. Add 2.3 mmol of sodium hypochlorite (manufactured by Wako Pure Chemical Industries, Ltd.) in the form of an aqueous solution to this, and then add the sodium hypochlorite using a liquid feed pump at an addition rate of 0.23 mmol/min per 1 g of pulp. was added gradually to oxidize the pulp. Addition was continued until the total amount of sodium hypochlorite added was 22.5 mmol. During the reaction, the pH in the system decreased, but the pH was adjusted to 10 by successively adding 3N aqueous sodium hydroxide solution. From the time when the sodium hydroxide aqueous solution is added (i.e., from the time when the oxidation reaction starts and a decrease in pH is observed) until the end of the addition (i.e., from the time when the oxidation reaction is completed and no decrease in pH is observed). The reaction time was defined as the reaction time. After neutralizing this reaction solution with hydrochloric acid until it became neutral, the reaction solution was filtered through a glass filter and thoroughly washed with water to obtain oxidized pulp.

(Measurement of carboxyl group content of oxidized pulp)
The amount of carboxyl groups in the oxidized pulp was measured by the following method. Prepare 60 mL of 0.5% by mass slurry of oxidized pulp, add 0.1M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then dropwise add 0.05N sodium hydroxide aqueous solution until the pH reaches 11.Electrical conductivity was measured and calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid where the change in electrical conductivity is gradual.
Carboxyl group amount [mmol/g oxidized pulp]
= a [mL] x 0.05/oxidized pulp mass [g]
As a result of this measurement, the amount of carboxyl groups in the obtained oxidized pulp was 1.60 mmol/g.

(Preliminary defibration of oxidized pulp)
The slurry of the oxidized pulp that had undergone the above oxidation treatment was subjected to preliminary defibration treatment using a single disc type refiner manufactured by Aikawa Iron Works. The refiner used a fine bar type plate, and the shape of the plate blade was 0.8 mm in blade width, 1.5 mm in groove width, 90 mm in blade length, 15° in blade angle, and the plate clearance was 0.1 mm. The processing speed of preliminary defibration by the refiner was 1 m ³ /hr, the raw material concentration of the oxidized pulp slurry used for preliminary defibration was 3% (w/v), and the peripheral speed of the refiner plate was 40.2 m/s. , the rotational shear speed of the plate was 402.0 (1/ms), and the number of refiner passes was 1. As a result, the pre-fibrillation process could be operated without any problems. The power consumption for preliminary fibrillation was 0.76 kWh/kg.

(Main defibration of oxidized pulp)
The pulp slurry subjected to preliminary defibration treatment was treated at a concentration of 3% (w/v) using an ultra-high pressure homogenizer at a treatment pressure of 140 MPa. As a result, this defibration process could be operated without any problems. Power consumption at this time was 1.8 kWh/kg. In addition, the obtained cellulose nanofiber dispersion was diluted to 1% (w/v), degassed using an ultrasonic device, and measured at a wavelength of 660 nm using an ultraviolet-visible spectrophotometer (UV-1800, manufactured by Shimadzu Corporation). The transmittance (%), ie, the transparency, was 71.0%.

[Example 2]
Among the experimental conditions of Example 1, the plate was a fine bar type plate with a dam formed on the outer periphery, and the shape of the plate blade was 0.8 mm in width, 1.0 mm in groove width, and 80 mm in length. The experiment was conducted under the same experimental conditions as in Example 1, except that the blade angle was changed to 15° and the processing speed was changed to 3 m ³ /hr. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.17 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. Further, the transparency of the obtained cellulose nanofiber dispersion was 44.5%.

[Example 3]
The experiment was conducted under the same experimental conditions as in Example 1, except that the plate was changed to a grindstone plate (no blade) and the processing speed was changed to 3 m ³ /hr. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.18 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 44.1%.

[Example 4]
Among the experimental conditions of Example 1, the plate was a plate for viscous beating, and the shape of the plate blade was 4.5 mm in blade width, 3.5-4.5 mm in groove width, 95 mm in blade length, and 10° in blade angle. The plate clearance was changed to 0.13 mm, the processing speed was changed to 19.2 m ³ /hr, the plate circumferential speed was 24.6 m/s, the plate rotational shear speed was 189.2 (1/ms), and the refiner was used. The experiment was conducted under the same experimental conditions as in Example 1, except that the number of treatments was 3. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.03 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 52.3%.

[Example 5]
Among the experimental conditions of Example 1, the plate was a dam type (three-stage dam), and the shape of the plate blade was 4.0 mm in blade width, 4.0 mm in groove width, 75-85 mm in blade length, and 0° blade angle. The processing speed was changed to 9.0 m ³ /hr, the plate circumferential speed was 24.6 m/s, the plate rotational shear speed was 246.0 (1/ms), and the number of treatments by the refiner was set to 2. The experiment was conducted under the same conditions as in Example 1 except for this. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.05 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 51.6%.

[Example 6]
The experiment was conducted under the same experimental conditions as in Example 1, except that the raw material concentration was changed to 5%. As a result, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.65 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. Further, the transparency of the obtained cellulose nanofiber dispersion was 69.0%.

[Example 7]
The experiment was conducted under the same experimental conditions as in Example 1, except that the processing speed was changed to 3 m ³ /hr. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.25 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 54.6%.

[Example 8]
The experiment was conducted under the same experimental conditions as in Example 1, except that the processing speed was changed to 3 m ³ /hr and the raw material concentration was changed to 5%. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.28 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. Further, the transparency of the obtained cellulose nanofiber dispersion was 63.3%.

[Example 9]
The experiment was conducted under the same experimental conditions as in Example 1, except that the processing speed was changed to 9 m ³ /hr. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.07 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 52.7%.

[Example 10]
The experiment was conducted under the same experimental conditions as in Example 1, except that the processing speed was changed to 9 m ³ /hr and the raw material concentration was changed to 5%. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.08 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 63.5%.

[Example 11]
Among the experimental conditions of Example 1, the processing speed was 15 m ³ /hr, the plate circumferential speed was 24.6 m/s, the plate rotational shear speed was 246.0 (1/ms), and the number of treatments by the refiner was 3. The experiment was conducted under the same experimental conditions as in Example 1 except for the following. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.03 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 57.3%.

[Example 12]
Among the experimental conditions of Example 1, the plate clearance was 0.08 mm, the processing speed was 23.4 m ³ /hr, the plate peripheral speed was 30.7 m/s, and the plate rotational shear speed was 383.8 (1/ms). The experiment was conducted under the same experimental conditions as in Example 1, except that the number of treatments by the refiner was changed to 8. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.03 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. Further, the transparency of the obtained cellulose nanofiber dispersion was 63.3%.

[Example 13]
The experiment was conducted under the same experimental conditions as in Example 1, except that the raw material concentration was changed to 7%. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.45 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. Moreover, the transparency of the obtained cellulose nanofiber dispersion was 70.0%.

[Example 14]
The experimental conditions of Example 1 were the same as in Example 1 except that the processing speed was changed to 3 m ³ /hr, the plate circumferential speed was changed to 55.8 m/s, and the plate rotational shear speed was changed to 558.0 (1/ms). The experiment was conducted under the same conditions as the experimental conditions. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.57 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 67.3%.

[Example 15]
The experiment was conducted under the same experimental conditions as in Example 1, except that the processing speed was 9 m ³ /hr, the raw material concentration was 10%, and the number of refiner treatments was 3. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.12 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. Further, the transparency of the obtained cellulose nanofiber dispersion was 60.2%.

[Example 16]
Among the experimental conditions of Example 1, the plate clearance was 0.22 mm, the processing speed was 11.6 m ³ /hr, the raw material concentration was 5%, the plate circumferential speed was 30.7 m/s, and the plate rotational shear speed was 139. 5 (1/ms), and the experiment was conducted under the same experimental conditions as in Example 1, except that the number of times of processing by the refiner was changed to 4. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.29 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. The transparency of the obtained cellulose nanofiber dispersion was 68.0%.

The refiner conditions, power consumption, and experimental results of Examples 1 to 16 are shown in Table 1.

[Comparative example 1]
The main defibration process using an ultra-high pressure homogenizer was performed once at a processing pressure of 140 MPa without performing the preliminary defibration process. As a result, in the present defibration process, clogging occurred in the dispersion nozzle. The power consumption of this defibration was 1.8 kWh/kg. Further, the transparency of the obtained cellulose nanofiber dispersion was 30.0%.

[Comparative example 2]
As the refiner plate, use a cut type plate with a blade width of 2.2 mm, groove width of 3.8-4.8 mm, blade length of 95 mm, and blade angle of 0°, and prepare with a plate clearance of 0.1 mm. An attempt was made to defibrate, but metal touch occurred and preliminary defibration could not be performed.

[Comparative example 3]
The experiment was conducted under the same experimental conditions as in Example 1, except that the processing speed was 40 m ³ /hr and the number of refiner treatments was 3. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 0.07 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. Further, the transparency of the obtained cellulose nanofiber dispersion was 33%, which was low.

[Comparative example 4]
Preliminary defibration was performed under the same experimental conditions as in Example 1, except that the raw material concentration was 16% and the number of refiner treatments was 3. However, the viscosity of the sample was high. However, the operability was poor and preliminary defibration could not be performed.

[Comparative example 5]
The experimental conditions of Example 1 were the same as those of Example 1 except that the plate circumferential speed was 15 m/s, the plate rotational shear speed was 150.0 (1/ms), and the number of refiner treatments was 3. The experiment was conducted under the following conditions. In this case, both the preliminary defibration and main defibration processes could be operated without any problems. The power consumption for preliminary defibration was 1.8 kWh/kg, and the power consumption for main defibration was 1.8 kWh/kg. Further, the transparency of the obtained cellulose nanofiber dispersion was 35.2%, which was low.

The refiner conditions, power consumption, and experimental results of Comparative Examples 1 to 5 are shown in Table 2.

In Examples 1 to 16, high-quality cellulose nanofiber dispersions with high transparency were produced with low power consumption. In addition, the operability of preliminary defibration and main defibration was good, and no clogging of the dispersion nozzle occurred. Furthermore, the number of preliminary defibrations and the number of ultra-high-pressure homo passes may be adjusted as appropriate depending on the desired transparency.

On the other hand, in Comparative Example 1, clogging occurred in the dispersion nozzle during the main defibration treatment, resulting in poor operability. Furthermore, the transparency of the obtained cellulose nanofiber dispersion was lower than that of Examples 1 to 16. In Comparative Example 2, metal touch occurred and preliminary defibration could not be performed. In Comparative Example 3, the transparency of the obtained cellulose nanofiber dispersion was lower than that in Examples 1 to 16. In Comparative Example 4, the viscosity of the sample was too high, resulting in poor operability, and preliminary defibration could not be performed. In Comparative Example 5, the transparency of the obtained cellulose nanofiber dispersion was lower than that in Examples 1 to 16.

Claims (2)

A method for producing a highly transparent cellulose nanofiber dispersion from chemically modified cellulose, comprising the following steps (A) and (B).
Step (A): Using a fine bar type plate of a single disc type refiner, the rotational shear rate of the plate of the refiner is 100 (1/ms) or more , and the processing rate of the chemically modified cellulose is 11.6 m ³ /hr. The following, and a preliminary defibration step of beating the chemically modified cellulose with a circumferential speed of the plate of 30.7 m/s or more and a concentration of 5 to 10% during the beating treatment;
Step (B): Main defibration step in which the cellulose obtained in the preliminary defibration step (A) is defibrated by treatment with a high-pressure disperser at a treatment pressure of 1 MPa to 400 MPa. The method for producing a cellulose nanofiber dispersion according to claim 1 , wherein in the preliminary defibration step (A), the clearance of the plate is 0.01 to 0.4 mm.