JPWO2017154568A1 - Redispersion method of cellulose nanofiber dispersion - Google Patents

Abstract

Dispersion of cellulose nanofibers produced for the convenience of storage and transportation from a dispersion of cellulose nanofibers, when dispersed again in an aqueous solvent, uniformly dispersed and stably dispersed Provided is a method for redispersing a cellulose nanofiber dispersion which can maintain the state. When re-dispersing cellulose nanofiber particles produced from wood fibers and the like in an aqueous solvent, mechanical shearing force is applied while stirring. [Selection] Figure 1

Description

  The present invention relates to a method for redispersing a cellulose nanofiber dispersion, in which cellulose nanofibers in powder form produced from wood fibers and the like are dispersed again in an aqueous solvent.

  It is expected that various new materials and devices with high convenience will be born from nanotechnology, which is a technology that freely controls substances in the nanometer range, that is, atomic and molecular scales. In particular, when the fiber is made extremely thin, a completely new physical property, which was not found in conventional fibers, is born. Therefore, nano-order fibers, so-called nanofibers, are attracting a great deal of attention. By applying this nanofiber, for example, it is expected to develop a purification device with a high-performance filter that does not allow any fine foreign substances to pass through, increase the strength of chemical fibers and high-performance clothing, and increase the efficiency of fuel cells. ing. Among these types of nanofibers, cellulose nanofibers are derived from plant fibers produced from wood fibers, so they are renewable resources and have a low environmental impact on production and disposal. Has been.

  Cellulose nanofibers are fibers having a nano-level fiber diameter of 1000 nm or less, and can be generally obtained by defibrating chemically modified cellulose fibers with mechanical shearing force (see Patent Document 1). Moreover, regarding the manufacturing method of a cellulose nanofiber, various manufacturing methods including the manufacturing method described in patent document 1 are examined.

JP 2008-1728 A

  By the way, since cellulose nanofibers are derived from plant fibers, paper mills that make paper from pulp made from wood have an environment suitable for the production of cellulose nanofibers. Moreover, since cellulose nanofibers are suitable for stabilizing and dispersing pigments used in coated paper in aqueous solutions, the produced cellulose nanofibers are mixed with pigments and supplied to the coating process, etc. The application of is expected.

  In paper mills, manufactured cellulose nanofibers can be used in the form of a dispersion. However, for customers who manufacture products using the properties of the cellulose nanofibers, supply them in the form of a dispersion. Is inconvenient for delivering large quantities of cellulose nanofibers because of its large capacity and weight during transportation. For this reason, it is required to deliver cellulose nanofibers in the form of granules that are dehydrated and dried from the cellulose nanofiber dispersion. The customer re-disperses the cellulose nanofibers in this granular form in an aqueous solvent and uses them as a cellulose nanofiber dispersion. Also in a paper mill, storage and management are facilitated if it is a granular material.

  However, when cellulose nanofibers in powder form are redispersed in an aqueous solvent and stirred, a lump of cellulose nanofibers, so-called lumps, are formed, and the aqueous solvent does not penetrate into the dams. There is a risk of becoming a state. The cellulose nanofiber dispersion in which such lumps are present is not evenly dispersed, and since the dispersed state is not stable, the cellulose nanofiber dispersion should be fully utilized. I can't.

  Therefore, when the cellulose nanofibers that have been dried and manufactured in the form of powder are redispersed in an aqueous solvent, the present invention does not form lumps or the like and regenerates the cellulose nanofiber dispersion liquid that is uniformly dispersed. It aims at providing the re-dispersion method of the cellulose nanofiber dispersion liquid.

  For the above purpose, the method for redispersing a cellulose nanofiber dispersion according to the present invention comprises dispersing the cellulose nanofiber powder produced by drying the produced cellulose nanofiber dispersion again in an aqueous solvent. The method of redispersing the cellulose nanofiber dispersion is characterized in that, when the cellulose nanofiber particles are redispersed in an aqueous solvent, stirring and mechanical shearing force are applied.

    In the present invention, the aqueous solvent is not particularly limited, and examples thereof include water and poor solvents such as lower alcohols. Among these, water or alcohols having good compatibility with water are exemplified. It is preferable that it is a mixed solvent. In the case of a mixed solvent such as water and alcohol, the mixing ratio of alcohol or the like is preferably less than 20% by weight.

  That is, cellulose nanofiber powder is put into a treatment liquid such as an aqueous solvent and stirred while mechanically applying a shearing force. By applying a mechanical shearing force, lumps to be formed are decomposed and dispersed in the treatment liquid.

  The cellulose nanofiber dispersion redispersion method according to the invention of claim 2 is a high-speed shear type, a collision type, a bead mill type, a high-speed rotation type, a colloid mill type, a high pressure as the device for applying the mechanical shear force. It is characterized by using any one or two or more of a formula, roll mill type, and ultrasonic type in combination.

  As a device for applying a mechanical shearing force, any of a high speed shear type, a collision type, a bead mill type, a high speed rotation type, a colloid mill type, a high pressure type, a roll mill type, and an ultrasonic type can be used. Further, a plurality of devices of these types may be combined. In particular, it is preferable to use a high-speed shearing type, collision type, or high-speed rotation type defibrating device because a stronger shearing force can be applied.

  The cellulose nanofiber dispersion redispersion method according to the invention of claim 3 is characterized in that the cellulose nanofiber is a chemically modified cellulose nanofiber.

  When supplying manufactured cellulose nanofibers to consumers, a large amount of cellulose nanofibers can be transported at a time with a light weight, and easily and reliably supply the amount of cellulose nanofibers as desired by the customer. can do.

  In addition, the customer can adjust the concentration of the cellulose nanofiber dispersion as desired, and the cellulose nanofiber dispersion according to the application can be obtained with certainty.

  In addition, storage and management of the produced cellulose nanofiber is facilitated.

It is a figure explaining the outline | summary of the equipment for enforcing the manufacturing method of a cellulose nanofiber.

  Hereinafter, based on preferable embodiment, the re-dispersion method of the cellulose nanofiber dispersion concerning this invention is demonstrated. Prior to describing this redispersion method, a method for producing cellulose nanofibers carried out in a paper mill will be described.

  FIG. 1 is a diagram for explaining an outline of an example of equipment when a method for producing cellulose nanofiber is carried out. Various chemical tanks 10 store chemical solutions for chemically modifying the cellulose raw material in the reaction step, and are supplied to the raw material cellulose agitator 11 and the reaction tank 12 by a supply device such as a pump (not shown). . Further, the raw material cellulose is supplied from the stirring device 11 to the reaction tank 12. The reaction tank 12 is supplied to the solid-liquid separation device 13 by a supply device such as a pump (not shown), and is supplied from the solid-liquid separation device 13 to the storage tank 14. The solid-liquid separator 13 and the defibrating device 15 are supplied from the storage tank 14 by a supply device such as a pump (not shown).

  Cellulose raw materials are materials in various forms mainly composed of cellulose, such as pulp (bleached or unbleached wood pulp, bleached or unbleached non-wood pulp, refined linter, jute, Manila hemp, kenaf-derived pulp, etc. ), Natural cellulose such as cellulose produced by microorganisms such as acetic acid bacteria, regenerated cellulose spun after dissolving cellulose in some solvent such as copper ammonia solution and morpholine derivative, and hydrolysis to the above cellulose raw material, alkaline hydrolysis Examples thereof include fine cellulose obtained by depolymerizing cellulose by carrying out mechanical treatment such as enzymatic decomposition, blasting treatment, and vibration ball mill.

  In addition, when a sheet-like material is used as the cellulose raw material, it may be subjected to a crushing step before being supplied to the stirring device 11 to be crushed to a size of about 0.5 to 5 cm square. preferable. By roughly crushing to the size, the cellulose raw material can be modified efficiently and uniformly. The method for coarse crushing is not particularly limited, and a uniaxial rotary shear pulverizer, a biaxial rotary shear pulverizer, a multi-screw screw pulverizer, a shredder, a guillotine cutter, or the like can be used. Among these, it is preferable from the viewpoint of coarse crushing to use a uniaxial rotary shearing type pulverizer and a shredder.

  In the present invention, the cellulose raw material may be unmodified or chemically modified, but is more preferably chemically modified. Cellulose nanofibers manufactured using chemically modified cellulose raw materials have a uniform fiber length and fiber diameter compared to cellulose nanofibers manufactured using unmodified cellulose raw materials. It is assumed that it is stable and exhibits a superior effect. Although the method of chemical modification is not particularly limited, for example, oxidation, etherification, phosphorylation, esterification, silane coupling, fluorination, cationization and the like can be performed. Among these, any of oxidation, carboxymethylation, and cationization using an N-oxyl compound is preferable, and carboxymethylation or oxidation is particularly preferable because it is used for food.

(1) Anion-modified (1-1) Carboxymethylation Using the cellulose raw material as a starting material, 3 to 20 times by weight of a lower alcohol, specifically methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N -A mixed medium of water such as butanol, isobutanol, tertiary butanol, etc., alone or in a mixture of two or more. The mixing ratio of the lower alcohol is 60 to 95% by weight. As the mercerizing agent, 0.5 to 20 times moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide is used per glucose residue of the bottoming material. A bottoming raw material, a solvent, and a mercerizing agent are mixed and subjected to mercerization treatment 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 in an amount of 0.05 to 10.0 times mol per glucose residue, a reaction temperature of 30 to 90 ° C., preferably 40 to 80 ° C., and a reaction time of 30 minutes to 10 hours, preferably 1 hour. Perform etherification reaction for ~ 4 hours.

  It is preferable that the degree of carboxymethyl substitution per glucose unit of the anion-modified cellulose is 0.02 to 0.50. By introducing a carboxymethyl substituent into cellulose, the celluloses are electrically repelled. For this reason, the cellulose which introduce | transduced the carboxymethyl substituent can be nano-defibrated easily. In addition, when the carboxymethyl substituent per glucose unit is smaller than 0.02, nano-defibration cannot be sufficiently performed. On the other hand, if the carboxymethyl substituent per glucose unit is larger than 0.50, it may swell or dissolve, and may not be obtained as a nanofiber.

As a measuring method of the carboxymethyl substitution degree per glucose unit, it can obtain by the following method, for example. That is, 1) About 2.0 g of carboxymethylated cellulose fiber (absolutely dry) is precisely weighed and put into a 300 mL conical stoppered Erlenmeyer flask. 2) Add 100 mL of a solution obtained by adding 100 mL of special concentrated nitric acid to 900 mL of methanol, and shake for 3 hours to convert the carboxymethyl cellulose salt (CM-modified cellulose) into hydrogenated CM-converted cellulose. 3) Weigh accurately 1.5 to 2.0 g of hydrogenated CM-modified cellulose (absolutely dry) and put into a 300 mL conical 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 0.1 N H2SO4 using phenolphthalein as indicator. 6) The degree of carboxymethyl substitution (DS) is calculated by the following formula:
A = [(100 × F ′ − (0.1N H 2 SO 4) (mL) × F) × 0.1] / (absolute dry mass of hydrogenated CM-modified cellulose (g))
DS = 0.162 × A / (1−0.058 × A)
A: 1N NaOH amount (mL) required for neutralizing 1 g of hydrogenated CM-modified cellulose
F: Factor of 0.1N H2SO4 F ': Factor of 0.1N NaOH

(1-2) Oxidation Carboxyl is obtained by oxidizing the cellulose raw material in water using an oxidizing agent in the presence of a compound selected from the group consisting of N-oxyl compounds and bromides, iodides or mixtures thereof. Oxidized cellulose having a group introduced into cellulose can be obtained.

  An N-oxyl compound is a compound capable of generating a nitroxy radical. As the N-oxyl compound used in the present invention, any compound can be used as long as it promotes the target oxidation reaction.

  The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of forming cellulose into nanofibers. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.05 to 0.5 mmol is more preferable with respect to 1 g of the absolutely dry cellulose raw material.

  Bromide is a compound containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Further, an iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, preferably from 0.1 to 100 mmol, more preferably from 0.1 to 100 mmol, and even more preferably from 0.5 to 5 mmol, based on 1 g of an absolutely dry cellulose raw material.

  As the oxidizing agent, known ones can be used, and for example, halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide and the like can be used. Among these, from the viewpoint of cost, sodium hypochlorite, which is the most widely used in industrial processes at present and has low environmental impact, is particularly preferable. The appropriate amount of the oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol with respect to 1 g of the absolutely dry cellulose raw material. preferable.

  The cellulose oxidation process allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature may be a room temperature of about 15 to 30 ° C. As the reaction proceeds, a carboxyl group is generated in the cellulose constituting the pulp, so that the pH of the reaction solution is reduced. In order to advance the oxidation reaction 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 9 to 12, preferably about 10 to 11. The pH is adjusted in the storage tank 14, and the reaction medium at that time is preferably water because it is easy to handle and hardly causes side reactions.

  The reaction time in the oxidation reaction can be appropriately set according to the progress of oxidation, and is usually 0.5 to 6 hours, preferably 2 to 6 hours, more preferably about 4 to 6 hours. However, since the oxidation time can be reduced as described above, the reaction time is preferably 30 minutes to 120 minutes, more preferably 30 to 100 minutes, and even more preferably 30 to 70 minutes.

  The oxidation reaction may be performed in two stages. For example, oxidized cellulose obtained by filtration after the completion of the first stage reaction is oxidized again under the same or different reaction conditions, so that the cellulose is not subject to reaction inhibition by the salt produced as a by-product in the first stage reaction. A carboxyl group can be efficiently introduced into the raw material, and oxidation of the cellulose raw material can be promoted.

  The conditions are preferably set so that the amount of carboxyl groups of oxidized cellulose is 0.2 mmol / g or more with respect to the absolute dry mass of cellulose. In this case, the carboxyl group amount is more preferably 0.6 mmol / g to 2.0 mmol / g, and still more preferably 1.0 mmol / g to 1.8 mmol / g. The amount of the carboxyl group can be adjusted by adjusting the oxidation reaction time, adjusting the oxidation reaction rate, adjusting the pH during the oxidation reaction, adjusting the addition amount of the N-oxyl compound, bromide, iodide, or oxidizing agent.

  Another example of the carboxylation (oxidation) method is a method of oxidizing by contacting a gas containing ozone and a cellulose raw material. By this oxidation reaction, at least the hydroxyl groups at the 2nd and 6th positions of the glucopyranose ring are oxidized and the cellulose chain is decomposed. The ozone concentration in the gas containing ozone is preferably 50 to 250 g / m 3, and more preferably 50 to 220 g / m 3. The amount of ozone added to the cellulose raw material is preferably 0.1 to 30% by weight and more preferably 5 to 30% by weight when the solid content of the cellulose raw material is 100% by weight. The ozone treatment temperature is preferably 0 to 50 ° C, and more preferably 20 to 50 ° C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, and preferably about 30 to 360 minutes. When the conditions for the ozone treatment are within these ranges, the cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. After the ozone treatment, an additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, these oxidizing agents can be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and a cellulose raw material can be immersed in the solution for additional oxidation treatment.

  The amount of the carboxyl group, carboxylate group, and aldehyde group of the cellulose fiber can be adjusted by controlling the amount of the oxidizing agent added and the reaction time.

The carboxyl group content is measured, for example, by preparing 60 ml of a 0.5 wt% slurry (aqueous dispersion) of oxidized cellulose, adding 0.1 M hydrochloric acid aqueous solution to pH 2.5, and then adding 0.05 N sodium hydroxide. The electrical conductivity was measured by dropping the aqueous solution until the pH reached 11, and the amount was calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid where the change in electrical conductivity was slow, using the following formula: can do:
Amount of carboxyl group [mmol / g oxidized cellulose or cellulose nanofiber] = a [ml] × 0.05 / oxidized cellulose weight [g].

(1-3) Esterification As chemically modified cellulose, esterified cellulose can be used. The said cellulose is obtained by the method of mixing the powder and aqueous solution of phosphoric acid compound A with the above-mentioned cellulose raw material, and the method of adding the aqueous solution of phosphoric acid compound A to the slurry of a cellulose raw material.

  Examples of the phosphoric acid compound A include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among these, a compound having a phosphate group is preferable because it is low in cost, easy to handle, and can improve the fibrillation efficiency by introducing a phosphate group into cellulose of the pulp fiber. Compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, phosphorus Examples include tripotassium acid, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate, and the like. These can be used alone or in combination of two or more. Among these, phosphoric acid, phosphoric acid sodium salt, phosphoric acid potassium salt, phosphoric acid, from the viewpoint that phosphoric acid group introduction efficiency is high, is easy to be defibrated in the following defibrating process, and is industrially applicable. The ammonium salt is more preferred. In particular, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferred. In addition, the phosphoric acid compound A is preferably used as an aqueous solution because the uniformity of the reaction is enhanced and the efficiency of introduction of phosphate groups is increased. The pH of the aqueous solution of the phosphoric acid compound A is preferably 7 or less because the efficiency of introducing phosphoric acid groups is high, but is preferably pH 3 to 7 from the viewpoint of suppressing hydrolysis of pulp fibers.

  The following method can be mentioned as an example of the manufacturing method of phosphate esterified cellulose. Phosphoric acid compound A is added to a cellulose-based raw material dispersion having a solid content of 0.1 to 10% by weight with stirring to introduce phosphate groups into the cellulose. When the cellulose-based raw material is 100 parts by weight, the addition amount of the phosphoric acid compound A is preferably 0.2 to 500 parts by weight, more preferably 1 to 400 parts by weight as the amount of phosphorus element. . If the ratio of the phosphoric acid type compound A is more than the said lower limit, the yield of a fine fibrous cellulose can be improved more. However, if the upper limit is exceeded, the effect of improving the yield reaches its peak, which is not preferable from the viewpoint of cost.

  At this time, in addition to the cellulose raw material and the phosphoric acid compound A, powders or aqueous solutions of other compounds B may be mixed. Compound B is not particularly limited, but a nitrogen-containing compound showing basicity is preferable. “Basic” as used herein is defined as an aqueous solution exhibiting a pink to red color in the presence of a phenolphthalein indicator, or an aqueous solution having a pH greater than 7. Although the nitrogen-containing compound which shows the basicity used by this invention is not specifically limited as long as there exists an effect of this invention, the compound which has an amino group is preferable. For example, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like can be mentioned, but not particularly limited. Among these, urea which is easy to handle at low cost is preferable. The amount of compound B added is preferably 2 to 1000 parts by weight, more preferably 100 to 700 parts by weight, based on 100 parts by weight of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95 ° C, more preferably 30 to 90 ° C. The reaction time is not particularly limited, but is about 1 to 600 minutes, and more preferably 30 to 480 minutes. When the conditions for the esterification reaction are within these ranges, the cellulose can be prevented from being excessively esterified and easily dissolved, and the yield of phosphorylated esterified cellulose is improved. After dehydrating the obtained phosphate esterified cellulose suspension, it is preferable to heat-treat at 100 to 170 ° C. from the viewpoint of suppressing hydrolysis of cellulose. Furthermore, while water is contained during the heat treatment, it is preferably heated at 130 ° C. or less, preferably 110 ° C. or less, and after removing water, heat treatment is preferably performed at 100 to 170 ° C.

  It is preferable that the phosphate group substitution degree per glucose unit of phosphorylated cellulose is 0.001 to 0.40. By introducing a phosphate group substituent into cellulose, the celluloses are electrically repelled. For this reason, the cellulose which introduce | transduced the phosphate group can be nano-defibrated easily. In addition, when the phosphate group substitution degree per glucose unit is smaller than 0.001, nano-defibration cannot be sufficiently performed. On the other hand, if the degree of phosphate group substitution per glucose unit is greater than 0.40, it may swell or dissolve, and may not be obtained as a nanofiber. In order to perform defibration efficiently, it is preferable that the phosphoric esterified cellulose raw material obtained above is boiled and then washed with cold water.

(2) Cation modification The cellulose raw material is a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2hydroxypropyltrialkylammonium hydride or its halohydrin type and an alkali metal hydroxide (sodium hydroxide, hydroxide). Cation-modified cellulose can be obtained by reacting potassium and the like in the presence of water and / or alcohol having 1 to 4 carbon atoms. In this method, the cation substitution degree per glucose unit of the cation-modified cellulose obtained is controlled by the amount of the cationizing agent to be reacted, the composition ratio of water and / or alcohol having 1 to 4 carbon atoms. Can be prepared.

  It is preferable that the cation substitution degree per glucose unit of the cation-modified cellulose is 0.012 to 0.045. By introducing a cationic substituent into cellulose, the celluloses repel each other electrically. For this reason, the cellulose which introduce | transduced the cation substituent can be nano-defibrated easily. In addition, when the cation substitution degree per glucose unit is smaller than 0.012, nano-fibrosis cannot be sufficiently performed. On the other hand, if the degree of cation substitution per glucose unit is greater than 0.045, it may swell or dissolve, and may not be obtained as a nanofiber. In order to efficiently perform the next defibration, the oxidized cellulose raw material obtained above is preferably washed.

As a method for measuring the degree of cation substitution, the degree of cation substitution per glucose unit was determined by measuring the nitrogen content with a total nitrogen analyzer TN-10 (Mitsubishi Chemical Corporation) after drying the sample (cation-modified cellulose). Can be calculated by the following formula. The degree of substitution referred to here represents the average value of the number of moles of substituents per mole of anhydroglucose unit.
Degree of cation substitution = (162 × N) / (1-116 × N)
N: Nitrogen content

  The solid-liquid separation / washing process following the reaction process is a process in which the modified cellulose dispersion obtained in the reaction process is washed with a dispersion medium after the solid-liquid separation treatment. It is an essential process for obtaining.

  In this step, a centrifugal, vacuum, or pressure type solid-liquid separator 15 can be used. Specifically, as a centrifugal type, such as a Tanabe Wiltec centrifugal separator, a Kokusan centrifugal separator, etc., as a vacuum type drum-type vacuum dehydrator, a Tsukishima machine horizontal belt filter, etc. as a pressurized type A filter press, a tube press, a belt press, a horizontal belt filter, a polydisc filter, a vibrating screen, and the like can be given. Among these, since solid-liquid separation can be performed without applying a strong shearing force to the solid-liquid separation raw material, a pressurized filter press, a tube press, a centrifugal Tanabe Wiltec centrifuge, a Kokusan centrifuge A vacuum drum type vacuum dehydrator such as a separator or a horizontal belt filter manufactured by Tsukishima Kikai is preferred. A plurality of these can be used in combination.

  In order to smoothly perform defibration in the defibrating step subsequent to the solid-liquid separation / washing step, a dispersion of modified cellulose is prepared to a concentration of 0.1 wt% to 10 wt%. When the concentration is less than 0.1% by weight, the presence of the modified pulp is too small to sufficiently defibrate. On the other hand, when the amount exceeds 10% by weight, as the defibration progresses, the viscosity of the modified pulp dispersion increases, and a sufficient force cannot be applied to the modified pulp.

  In the subsequent defibrating process, the dispersion of the modified cellulose whose concentration is adjusted in the preparation process is subjected to the defibrating apparatus 15 for defibrating, which is an essential process. As the defibrating device 15 used in this process, any type of high-speed shear type, collision type, bead mill type, high-speed rotation type, colloid mill type, high-pressure type, roll mill type, and ultrasonic type may be used. Specifically, a stone mill mill Supermass colloider (made by Masuyuki Sangyo) as a high-speed rotary type, an emulsifier (made by Iwaki) as a colloid mill type, a three-roll mill (made by Amex), an ultrasonic type as a roll mill type As an air purge type ultrasonic dispersion machine (manufactured by SMT), as a high-speed shear type as a nano maker (manufactured by Advanced Nano Technology), as a collision type as a wet atomizer Starburst (manufactured by Sugino Machine), as a bead mill type bead mill MSC A mill (manufactured by Nippon Coke Industries) can be mentioned. A plurality of these can also be used in combination. Among these, it is preferable to use a high-speed shearing type, collision type, and high-speed rotation type defibrating device from the viewpoint of processing a stronger shearing force under a condition where the risk of contamination by media is low.

  The solid content contained in the cellulose nanofiber dispersion is 0.1 to 10% by weight, and only a few cellulose nanofibers are obtained. If this is supplied to a consumer, water will almost be conveyed. For this reason, it is necessary to supply a cellulose nanofiber granular material to a consumer. That is, the cellulose nanofiber dispersion is dried to produce cellulose nanofiber particles.

  In the present invention, the form of the cellulose nanofiber is not particularly limited, and may be a dispersion of cellulose nanofiber, a dry solid of cellulose nanofiber, or a wet solid in an intermediate state. In addition, in this invention, the dry solid substance of a cellulose nanofiber means what dehydrated and dried the dispersion liquid containing a cellulose nanofiber to 12% or less of moisture content.

  When cellulose nanofibers are used as a dry solid, examples include those obtained by drying a dispersion of cellulose nanofibers, or those obtained by drying a mixture of cellulose nanofibers and a water-soluble polymer. The latter is preferable in terms of redispersibility. Examples of the water-soluble polymer include cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, pullulan, starch, and hard starch. , Scrap flour, Positive starch, Phosphorylated starch, Corn starch, Arabic gum, Locust bean gum, Gellan gum, Gellan gum, Polydextrose, Pectin, Chitin, Water-soluble chitin, Chitosan, Casein, Albumin, Soy protein lysate, Peptone, Polyvinyl alcohol , Polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acid, polylactic acid, polymalic acid, polyglyce Latex, rosin sizing agent, petroleum resin sizing agent, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide / polyamine resin, polyethyleneimine, polyamine, plant gum, polyethylene oxide, hydrophilic cross-linked polymer, polyacrylic Refers to acid salts, starch polyacrylic acid copolymers, tamarind gum, gellan gum, pectin, guar gum and colloidal silica and mixtures of one or more thereof. Among these, it is preferable from a compatible point to use carboxymethylcellulose and its salt.

  The dry solid of the cellulose nanofiber is dehydrated and dried after adjusting the pH of the cellulose nanofiber aqueous dispersion or the mixture containing the cellulose nanofiber dispersion and the water-soluble polymer to 9-11. It is preferable from the viewpoint of redispersibility. When the water-soluble polymer is blended in the cellulose nanofiber dispersion, the amount of the water-soluble polymer is preferably 5 to 50% by weight based on the absolutely dry solid content of the cellulose nanofiber. If it is less than 5% by weight, the effect of sufficient redispersibility is not exhibited. On the other hand, when it exceeds 50% by weight, problems such as viscosity characteristics and dispersion stability, which are characteristic of cellulose nanofiber, occur.

  As the dehydration / drying method of the cellulose nanofiber dispersion or the mixture containing the cellulose nanofiber dispersion and the water-soluble polymer, any conventionally known method may be used, for example, spray drying, pressing, air drying, hot air drying, And vacuum drying. Examples of the drying apparatus specifically used in the method of the present invention are as follows. That is, continuous tunnel dryer, band dryer, vertical dryer, vertical turbo dryer, multi-stage disk dryer, aeration dryer, rotary dryer, air dryer, spray dryer dryer, spray dryer , Cylindrical dryers, drum dryers, screw conveyor dryers, rotary dryers with heating tubes, vibration transport dryers, batch-type box dryers, aeration dryers, vacuum box dryers, stirring dryers, etc. These drying apparatuses can be used alone or in combination of two or more. Among these, it is preferable to use a drum drying apparatus from the viewpoint of energy efficiency because the heat energy is uniformly supplied directly to an object to be dried. The drum drying apparatus is also preferable in that it can immediately collect a dried product without applying heat more than necessary.

  The dried solid can be pulverized and classified as necessary. In particular, dry pulverization or wet pulverization is preferable because a more refined additive can be obtained. Examples of the apparatus used in the dry pulverization include impact mills such as a hammer mill and a pin mill, medium mills such as a ball mill and a tower mill, and jet mills. Examples of the apparatus used in the wet pulverization include apparatuses such as a homogenizer, a mass collider, and a pearl mill.

  A consumer to whom cellulose nanofibers are supplied in powder form is dispersed in an aqueous solvent to redisperse the cellulose nanofiber dispersion. At this time, a cellulose nanofiber dispersion is produced while adjusting to a desired concentration.

  When the cellulose nanofiber dispersion is regenerated by adding the cellulose nanofiber powder into an aqueous solvent, the shear force is applied using the defibrating device used in the defibrating process during the production of the cellulose nanofiber. The cellulose nanofiber dispersion liquid in which the cellulose nanofibers are uniformly dispersed in the solution can be redispersed from the cellulose nanofibers in a granular form without stirring to produce the mixture. In the defibrating device, as in the defibrating process, any type of high-speed shear type, collision type, bead mill type, high-speed rotation type, colloid mill type, high-pressure type, roll mill type, and ultrasonic type is used. Things can also be used. A plurality of these can also be used in combination. Among these, it is preferable to use a high-speed shearing type, collision type, and high-speed rotation type defibrating device because a stronger shearing force can be applied.

  Through the above-described steps, for example, a cellulose nanofiber dispersion was produced under the following conditions.

  Bleached kraft pulp pulverized to about 20mm square using an oriental pulverizer, which is a uniaxial rotary shearing pulverizer, is mixed and stirred with caustic soda and monochloroacetic acid soda into a ribbon-type mixing device, and gradually heated to 80 ° C for commercialization. After the reaction proceeded, the slurry was diluted to 0.5% by weight in a tank with an agitator to form a 5 m3 slurry. Next, the slurry was dehydrated to a solid content of 15% by weight with a filter press (manufactured by Kurita Kikai Seisakusho) and diluted to 0.5% by weight in a tank with an agitator to give a 5 m3 slurry. The slurry was again dehydrated to 10% by weight with a filter press and diluted to 0.5% by weight in a tank with an agitator, and the washing was repeated three times. Next, the slurry obtained was defibrated with a stone mill grinder Supermass colloider (manufactured by Masuko Sangyo), immediately after cooling by heat exchange, and storing the slurry in a stock tank was repeated 5 times to obtain a solid content of 0 Thus, 4.5 m3 of a 5% by weight CM-modified cellulose nanofiber aqueous dispersion was obtained.

  The obtained CM-converted cellulose nanofiber aqueous dispersion (4.5 m3) having a solid content of 0.5% by weight was dried with a drum drying apparatus D-0303 (manufactured by Katsuragi Industry Co., Ltd.) until the solid content became 95% by weight, and converted to CM 23 kg of cellulose nanofiber dry solid was obtained. By operating this with a high-speed shearing type powder disperser CMS2000 / 4 (manufactured by IKA Japan) at 6000 rpm and 1.6 kW / h, CM-modified cellulose having a solid content of 0.5% by weight with the same quality as before drying. A nanofiber aqueous dispersion 4 m3 could be produced.

  When cellulose nanofiber powder is put into an aqueous solvent and re-dispersed, the re-dispersed viscosity and fiber length are re-dispersed with a homogenizer used in wet pulverization or a mill used in dry pulverization. Is not suitable because it becomes shorter and the quality changes at the time of defibration.

  Since the cellulose nanofibers produced in the dispersion are dried to form a powder, it is easy to transport and store, and even when supplied to the customer, the cellulose dispersion that is uniformly dispersed can be redispersed. Contributes to the improvement of versatility of cellulose nanofibers.

10 Various chemical tanks
11 Stirrer
12 Reaction tank
13 Solid-liquid separator
14 Storage tank
15 Defibration equipment

Claims (3)

In the method of redispersing the cellulose nanofiber dispersion by dispersing the cellulose nanofiber powder produced by drying the produced cellulose nanofiber dispersion again in an aqueous solvent,
A method for redispersing a cellulose nanofiber dispersion, comprising stirring and applying mechanical shear force when redispersing cellulose nanofiber particles in an aqueous solvent.   As a device for applying the mechanical shearing force, a high-speed shear type, a collision type, a bead mill type, a high-speed rotation type, a colloid mill type, a high-pressure type, a roll mill type, or an ultrasonic type is used in combination. The method for redispersing a cellulose nanofiber dispersion according to claim 1, wherein the method is used.   The method for redispersing a cellulose nanofiber dispersion according to claim 1 or 2, wherein the cellulose nanofiber is a chemically modified cellulose nanofiber.

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