Cellulose nanofiber manufacturing apparatus

Abstract

Provided is a cellulose nanofiber manufacturing apparatus that realizes an extended service life of a high-pressure pump of a high-pressure homogenizer. **Solution**: A cellulose nanofiber manufacturing apparatus including a high-pressure homogenizer that performs a fibrillation treatment on pulp fibers, wherein the high-pressure homogenizer includes a high-pressure pump that pressurizes a cellulose raw material which is a raw material of the cellulose nanofibers, and the high-pressure pump includes a cylinder that receives the cellulose raw material and an outer cylinder portion that covers 50% or more of an outer peripheral surface of the cylinder.

Description

Technical Field

[0001] The present invention relates to a cellulose nanofiber manufacturing apparatus equipped with a high-pressure homogenizer.

Background Art

[0002] From nanotechnology, which is a technology for freely controlling substances in the nanometer region, that is, at the atomic or molecular scale, various convenient new materials and devices are expected to be born. In particular, when fibers are made extremely thin, completely new physical properties that conventional fibers do not have are generated. Therefore, nano-order fibers (nanofibers) have attracted great attention. By applying this nanofiber, for example, the realization of a purification device using a high-performance filter that does not allow any fine foreign matter to pass through, the improvement of the strength of chemical fibers and the realization of high-functional clothing, and the development of improving the efficiency of fuel cells are expected.

[0003] Cellulose nanofibers are fibers having a fiber diameter at the nano level of 1000 nm or less, and can be obtained by first increasing the pressure of a chemically modified cellulose raw material with a high-pressure pump of a high-pressure homogenizer and then defibrating it with mechanical shear force by a nozzle of the high-pressure homogenizer (see, for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the above-described high-pressure homogenizer, since extremely high pressure is repeatedly applied to the high-pressure pump, the parts of the high-pressure pump are severely worn due to the long-time fibrillation treatment, and there is a problem that the expensive parts of the high-pressure pump must be replaced frequently.

[0006] An object of the present invention is to provide a cellulose nanofiber manufacturing apparatus that realizes a long life of the high-pressure pump of a high-pressure homogenizer.

Means for Solving the Problems

[0007] The present inventors have completed the present invention in order to solve the above problems. The present invention provides the following. (1) A cellulose nanofiber manufacturing apparatus including a high-pressure homogenizer that performs fibrillation treatment of pulp fibers, wherein the high-pressure homogenizer includes a high-pressure pump that pressurizes a cellulose raw material that is a raw material of the cellulose nanofiber, and the high-pressure pump includes a cylinder that receives the cellulose raw material, and an outer cylinder portion that covers 50% or more of the outer peripheral surface of the cylinder. A cellulose nanofiber manufacturing apparatus characterized by this. (2) The cellulose nanofiber manufacturing apparatus according to (1), wherein the cylinder and the outer cylinder portion are formed of a single member. (3) The cellulose nanofiber manufacturing apparatus according to (1), wherein the outer cylinder portion is press-fitted onto the outer peripheral surface of the cylinder. (4) The cellulose nanofiber manufacturing apparatus according to any one of (1) to (3), wherein an outer diameter of the outer cylinder portion is twice or more as large as an inner diameter of the cylinder. (5) The material of the cylinder is stainless steel containing 15.0% by mass or more and 17.5% by mass or less of Cr, 3.0% by mass or more and 5.0% by mass or less of Ni, and 3.0% by mass or more and 5.0% by mass or less of Cu, chromium molybdenum steel containing 0.9% by mass or more and 1.2% by mass or less of Cr and 0.25% by mass or less of Ni, or titanium. The cellulose nanofiber manufacturing apparatus according to any one of (1) to (3).

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a cellulose nanofiber manufacturing apparatus that realizes an extended service life of the high-pressure pump of a high-pressure homogenizer.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] Hereinafter, with reference to the drawings, a cellulose nanofiber manufacturing apparatus according to an embodiment of the present invention will be described. The cellulose nanofiber manufacturing apparatus according to this embodiment is a cellulose nanofiber manufacturing apparatus including a high-pressure homogenizer that performs a fibrillation treatment on pulp fibers. FIG. 1 is a diagram showing a schematic configuration of a high-pressure homogenizer included in the cellulose nanofiber manufacturing apparatus according to this embodiment. The high-pressure homogenizer 1 includes a high-pressure pump 2, a nozzle section 3, a valve 4, and pipes 5, 6, and 7. The cellulose raw material, which is the raw material for cellulose nanofibers, is conveyed to the high-pressure pump 2 through pipes 5 and 6. Further, the cellulose raw material pressurized in the high-pressure pump 2 is pressure-fed to the nozzle section 3 through pipes 6 and 7. The cellulose raw material is pressure-fed in a state of being pressurized in the nozzle section 3, so that a strong shearing action occurs in the nozzle section 3, and fibrillation is highly performed.

[0011] Figures 2 and 3 are diagrams showing the configuration of the high-pressure pump 2 according to this embodiment. Figure 2 shows a state where the plunger 10 (described later) is located at the stroke end in the downward direction of the paper surface, and Figure 3 shows a state where the plunger 10 is located at the stroke end in the upward direction of the paper surface. The high-pressure pump 2 is a pump for pressurizing the cellulose raw material as described above. As shown in Figures 2 and 3, it includes a cylinder 8, an outer cylinder portion 9, a plunger 10, and a hydraulic cylinder 11. For the convenience of explaining the configuration, the cylinder 8 and the outer cylinder portion 9 shown in Figures 2 and 3 are longitudinal central sectional views, and the other configurations are external views.

[0012] The cylinder 8 receives the cellulose raw material supplied through the pipe 6 shown in Figure 1 inside the cylinder. The material of the cylinder 8 is (1) stainless steel containing 15.0% by mass or more and 17.5% by mass or less of Cr, 3.0% by mass or more and 5.0% by mass or less of Ni, and 3.0% by mass or more and 5.0% by mass or less of Cu, (2) chromium molybdenum steel containing 0.9% by mass or more and 1.2% by mass or less of Cr and 0.25% by mass or less of Ni, or (3) titanium.

[0013] The outer cylinder portion 9 covers the outer peripheral surface of the upper part of the cylinder 8 and covers 50% or more of the outer peripheral area of the cylinder 8. Also, the outer diameter D1 of the outer cylinder portion 9 is 2 times or more and 10 times or less the size of the inner diameter D2 of the cylinder 8. By providing the outer cylinder portion 9, the stress applied radially outward to the cylinder 8 and the strain of the cylinder 8 are reduced. Further, the outer cylinder portion 9 is shrink-fitted to the outer peripheral surface of the cylinder 8 by shrink fitting or cold fitting. In this embodiment, with the outer diameter D1 of the outer cylinder portion 9 being 30 to 400 mm, the inner diameter D2 of the cylinder 8 being 15 to 70 mm, and the outer diameter D3 of the cylinder 8 being 30 to 140 mm, the interference is 80 / 1000 mm or less, and the stress applied radially inward from the inner peripheral surface of the outer cylinder portion 9 due to shrink fitting cancels the stress applied radially outward from the outer peripheral surface of the cylinder 8. Note that the interference may be 20 / 1000 mm or more and 80 / 1000 mm or less.

[0014] In this embodiment, a case where the cylinder 8 and the outer cylinder portion 9 are formed of separate members and are press-fitted is taken as an example, but the cylinder 8 and the outer cylinder portion 9 may be formed of a single member.

[0015] The plunger 10 has a cylindrical shape with its axis in the vertical direction of the paper surface of FIG. 2, and reciprocates axially within the cylinder 8. The hydraulic cylinder 11 is fixed to the hydraulic cylinder head 18. The hydraulic cylinder 11 includes a piston 11a and functions as an actuator for reciprocating the plunger 10. When the piston 11a of the hydraulic cylinder 11 moves from the position shown in FIG. 3 to the position shown in FIG. 2, the plunger 10 moves within the cylinder 8 from the position shown in FIG. 3 to the position shown in FIG. 2, sucking the cellulose raw material pumped by the decompression action inside the cylinder 8 and a supply pump (not shown) into the cylinder 8. Further, when the piston 11a of the hydraulic cylinder 11 moves from the position shown in FIG. 2 to the position shown in FIG. 3, the plunger 10 moves within the cylinder 8 from the position shown in FIG. 2 to the position shown in FIG. 3, discharging the cellulose raw material outside the cylinder 8 by the pressurization inside the cylinder 8. In this embodiment, the hydraulic cylinder 11 is taken as an example of the actuator, but it may also be an air cylinder or a ball screw.

[0016] According to the cellulose nanofiber manufacturing apparatus according to this embodiment, since the high-pressure pump 2 of the high-pressure homogenizer 1 includes the outer cylinder portion 9 that covers 50% or more of the outer peripheral surface of the cylinder 8, the stress applied radially outward to the cylinder 8 and the strain of the cylinder 8 are reduced. Further, since the outer cylinder portion 9 is press-fitted to the outer peripheral surface of the cylinder 8, the stress applied radially inward from the inner peripheral surface of the outer cylinder portion 9 due to the press fit cancels the stress applied radially outward from the outer peripheral surface of the cylinder 8. Therefore, it is possible to prevent the cylinder 8 from suffering fatigue failure, and thus it is possible to achieve a long service life of the cylinder 8.

[0017] (Method for manufacturing cellulose nanofibers) The manufacturing method using the manufacturing apparatus for cellulose nanofibers of the present invention has a fibrillation step of applying mechanical shearing force to a cellulose raw material with a high-pressure homogenizer 1 according to this embodiment to fibrillate it. In the present invention, it is possible to use chemically modified cellulose as the cellulose raw material. In that case, before subjecting it to the fibrillation step, it is preferable to perform a step of dehydrating and washing the dispersion of the chemically modified cellulose and a step of adjusting the dispersion concentration of the chemically modified cellulose.

[0018] (Cellulose nanofibers) Cellulose nanofibers are materials produced by finely unraveling plant fibers to the nanolevel, and are generally fine fibers with an average fiber diameter of about 3 to 500 nm and an average aspect ratio of 50 or more. The average fiber diameter and average fiber length of cellulose nanofibers can be obtained by averaging the fiber diameter and fiber length obtained from the observation results of each fiber using a field emission scanning electron microscope (FE-SEM). Also, the aspect ratio can be calculated by the following formula. Aspect ratio = average fiber length / average fiber diameter

[0019] (Cellulose raw material) In the present invention, the cellulose raw material refers to various forms of materials mainly composed of cellulose, such as pulp (bleached or unbleached wood pulp, bleached or unbleached non-wood pulp, purified lint, jute, Manila hemp, kenaf, etc., pulp derived from herbs), 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 copper ammonia solution or a morpholine derivative, and fine cellulose obtained by depolymerizing cellulose by subjecting the above cellulose raw material to hydrolysis, alkaline hydrolysis, enzymatic hydrolysis, blasting treatment, mechanical treatment such as a vibration ball mill, etc.

[0020] In the present invention, when using a sheet-like cellulose raw material, it is preferably crushed into a size of about 0.5 to 5 cm square. By crushing to the above size, the cellulose raw material can be modified efficiently and uniformly in the next reaction step. The method of crushing is not particularly limited, but a uniaxial rotary shearing crusher, a biaxial rotary shearing crusher, a multi-axis screw crusher, a shredder, a guillotine cutter, etc. can be used. Among these, it is preferable to use a uniaxial rotary shearing crusher from the viewpoint of crushing.

[0021] Cellulose has three hydroxyl groups per glucose unit and can undergo various chemical modifications. In the present invention, a cellulose raw material (chemically modified cellulose) obtained by chemical modification may be used. Examples of chemical modification include oxidation (carboxylation), carboxymethylation, cationization, esterification, etc. Among them, oxidation (carboxylation) and carboxymethylation are more preferable.

[0022] (Chemical modification of cellulose) (Oxidation) In the present invention, the oxidation of the cellulose raw material can be carried out using a known method and is not particularly limited, but it is preferable to adjust the amount of carboxyl groups to be 0.5 mmol / g to 3.0 mmol / g based on the absolute dry mass of the cellulose nanofibers.

[0023] As an example, it can be obtained by oxidizing cellulose in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides, or mixtures thereof. By 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-based fiber having an aldehyde group and a carboxyl group or carboxylate group on the surface can be obtained. The concentration of cellulose during the reaction is not particularly limited, but 5% by mass or less is preferred. The N-oxyl compound refers to a compound capable of generating a nitroxyl radical. As the N-oxyl compound, any compound can be used as long as it promotes the target oxidation reaction.

[0024] The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing the raw material cellulose. For example, for 1 g of absolutely dry cellulose, 0.01 to 10 mmol is preferred, 0.02 to 1 mmol is more preferred, and 0.05 to 0.5 mmol is even more preferred. Also, about 0.1 to 4 mmol / L is suitable for the reaction system.

[0025] The bromide is a compound containing bromine, and examples thereof include alkali metal bromides that can dissociate and ionize in water. The iodide is a compound containing iodine, and examples thereof include alkali metal iodides. The amount of the bromide or iodide used can be selected within a range capable of promoting the oxidation reaction. The total amount of the 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 absolutely dry cellulose.

[0026] As the oxidizing agent, known ones can be used. For example, halogens, hypohalous acids, halous acids, perhalic acids or their salts, halogen oxides, peroxides, etc. can be used. Among them, inexpensive sodium hypochlorite is preferred. 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, still more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol with respect to 1 g of absolutely dry cellulose. Further, for example, 1 to 40 mol is preferred with respect to 1 mol of the N-oxyl compound.

[0027] The oxidation process of cellulose can efficiently proceed even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, and may also be room temperature of about 15 to 30°C. Since carboxyl groups are generated in the cellulose as the reaction proceeds, a decrease in the pH of the reaction solution is observed. In order to efficiently proceed the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at 8 to 12, preferably about 10 to 11. The reaction medium is preferably water in view of ease of handling and difficulty in causing side reactions.

[0028] The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually 0.5 to 6 hours, for example, about 1 to 4 hours. Further, the oxidation reaction may be carried out in two steps. For example, the oxidized cellulose obtained by filtration after the completion of the first-step reaction is oxidized again under the same or different reaction conditions, so that it can be efficiently oxidized without being inhibited by the salt by-produced in the first-step reaction.

[0029] As another example of the carboxylation (oxidation) method, a method of oxidizing by bringing a gas containing ozone into contact with a cellulose raw material can be mentioned. By this oxidation reaction, at least the hydroxyl groups at the 2-position and 6-position of the glucopyranose ring are oxidized, and decomposition of the cellulose chain occurs. The ozone concentration in the gas containing ozone is preferably 50 to 250 g / m 3 and more preferably 70 to 220 g / m 3It is more preferable. When the solid content of the cellulose raw material is 100 parts by mass, the ozone addition amount to the cellulose raw material is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass. 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 300 minutes. When the ozone treatment conditions are within these ranges, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of oxidized cellulose becomes good. After the ozone treatment, a post-oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the post-oxidation treatment is not particularly limited, and examples thereof include chlorine-based compounds such as chlorine dioxide and sodium chlorite, and oxygen, hydrogen peroxide, persulfuric acid, peracetic acid, etc. 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 the post-oxidation treatment can be performed by immersing the cellulose raw material in the solution.

[0030] The amounts of carboxyl groups, carboxylate groups, and aldehyde groups in the cellulose fiber can be adjusted by controlling the addition amount of the above-mentioned oxidizing agent and the reaction time. The measurement method of the carboxyl group amount is, for example, to prepare 60 mL of a 0.5 mass% slurry (aqueous dispersion) of oxidized cellulose, add 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then dropwise add 0.05 N sodium hydroxide aqueous solution until the pH reaches 11, and measure the electrical conductivity. From the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid where the change in electrical conductivity is gentle, it can be calculated using the following formula. Amount of carboxyl groups [mmol / g oxidized cellulose or cellulose nanofiber] = a [mL] × 0.05 / mass of oxidized cellulose [g]

[0031] (Carboxymethylation) In the present invention, the carboxymethylation of the cellulose raw material can be carried out using a known method, and is not particularly limited, but it is preferable to adjust so that the degree of carboxymethyl group substitution per anhydroglucose unit of cellulose is 0.01 to 0.50. As an example, the following production method can be cited, but it may be synthesized by a conventionally known method, or a commercially available product may be used. Using cellulose as the starting material, 3 to 20 times the mass of water and / or a lower alcohol, specifically methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, etc. alone, or a mixed medium of two or more is used. The mixing ratio of the lower alcohol is 60 to 95% by mass. As the mercerizing agent, 0.5 to 20 times the molar amount of an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, per anhydroglucose residue of the starting material is used. The starting material, the solvent, and the mercerizing agent are mixed, and a mercerization treatment is carried out 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 the molar amount per glucose residue, and an etherification reaction is carried out at 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 to 4 hours.

[0032] As a method for measuring the degree of carboxymethyl substitution per glucose unit, it can be obtained, for example, by the following method. That is, 1) Weigh accurately about 2.0 g of carboxymethylated cellulose fiber (bone-dry) and put it into a 300 mL conical flask with a stopper. 2) Add 100 mL of a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of nitric acid methanol, shake for 3 hours to convert carboxymethyl cellulose salt (CM cellulose) into hydrogen-type CM cellulose. 3) Weigh accurately 1.5 - 2.0 g of hydrogen-type CM cellulose (bone-dry) and put it into a 300 mL conical flask with a stopper. 4) Moisten the hydrogen-type CM cellulose with 15 mL of 80% methanol, add 100 mL of 0.1N NaOH, and shake at room temperature for 3 hours. 5) Using phenolphthalein as an indicator, back-titrate the excess NaOH with 0.1N H2SO4. 6) Calculate the degree of carboxymethyl substitution (DS) by the following formula. A = [(100×F’ - (0.1N H2SO4)(mL)×F)×0.1] / (bone-dry mass of hydrogen-type CM cellulose (g)) DS = 0.162×A / (1 - 0.058×A) A: Amount of 1N NaOH (mL) required for neutralizing 1 g of hydrogen-type CM cellulose F’: Factor of 0.1N H2SO4 F: Factor of 0.1N NaOH

[0033] (Cationization) In the present invention, the cationization of the cellulose raw material can be carried out using known methods. Through cationization, for example, ammonium, phosphonium, sulfonium, and groups having these ammonium, phosphonium, or sulfonium can be introduced into the cellulose molecule. Among them, groups having ammonium are preferred, and in particular, groups containing quaternary ammonium are preferred. Specific methods of cationization are not particularly limited. As an example, in the presence of water and / or an alcohol having 1 to 4 carbon atoms, a cellulose raw material is reacted with a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrate or its halohydrin type, and an alkali metal hydroxide (such as sodium hydroxide, potassium hydroxide) as a catalyst, whereby cation-modified cellulose having a group containing quaternary ammonium can be obtained.

[0034] In this method, the degree of cation substitution per glucose unit of the obtained cation-modified cellulose can be adjusted by controlling the addition amount of the cationizing agent to be reacted and the composition ratio of water and / or an alcohol having 1 to 4 carbon atoms. The degree of substitution referred to here indicates the number of introduced substituents 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 the hydroxyl groups of 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 (the minimum value is 0).

[0035] In the present invention, the cation substitution degree per glucose unit of the cationized cellulose is preferably from 0.01 to 0.40. By introducing a cation substitution group into cellulose, the celluloses repel each other electrically. Therefore, the cellulose into which the cation substitution group has been introduced can be easily nanofibrillated. Note that if the cation substitution degree per glucose unit is less than 0.01, it cannot be sufficiently nanofibrillated. On the other hand, if the cation substitution degree per glucose unit is greater than 0.40, it swells or dissolves, so that the fiber form cannot be maintained and it may not be obtained as nanofibers.

[0036] The cation substitution degree 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 Corporation). The substitution degree referred to here represents the average value of the number of moles of the substitution group per mole of anhydroglucose unit. Cation substitution degree = (162 × N) / (1 - 151.6 × N) N: Nitrogen content

[0037] (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, and examples thereof include a method of reacting a compound A with cellulose raw materials or defibrated cellulose fibers. The compound A will be described later.

[0038] Examples of the method of reacting a compound A with cellulose raw materials or defibrated cellulose fibers include a method of mixing the powder or aqueous solution of the compound A with cellulose raw materials or defibrated cellulose fibers, and a method of adding the aqueous solution of the compound A to the slurry of cellulose raw materials or defibrated cellulose fibers. Among these, the method of mixing the aqueous solution of the compound A with cellulose raw materials or defibrated cellulose fibers or their slurry is preferred because the uniformity of the reaction is enhanced and the esterification efficiency is increased.

[0039] Examples of compound A include phosphoric acid compounds (e.g., phosphoric acid, polyphosphoric acid), phosphorous acid, phosphonic acid, polyphosphonic acid, esters thereof, etc. Compound A may be in the form of a salt. Among these, phosphoric acid compounds are preferred because they are low-cost, easy to handle, and can introduce a phosphate group into the cellulose of a cellulose raw material (e.g., pulp fiber) to improve the fibrillation efficiency. The phosphoric acid compound may be any compound having a phosphate group. For example, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate, etc. may be mentioned. The phosphoric acid compound used may be one kind or a combination of two or more kinds. Among these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are preferred from the viewpoints of high efficiency of phosphate group introduction, easy fibrillation in the following fibrillation step, and easy industrial application. Sodium salts of phosphoric acid are more preferred, and sodium dihydrogen phosphate and disodium hydrogen phosphate are even more preferred. Also, in esterification, it is preferable to use an aqueous solution of a phosphoric acid compound because the uniformity of the reaction is enhanced and the efficiency of phosphate group introduction is increased. The pH of the aqueous solution of the phosphoric acid compound is preferably 7 or less because the efficiency of phosphate group introduction is increased. From the viewpoint of suppressing the hydrolysis of pulp fiber, pH 3 to 7 is more preferred.

[0040] Examples of the esterification method include the following methods. Compound A is added to a suspension of a cellulose raw material or defibrated cellulose fibers (for example, a solid content concentration of 0.1 to 10% by mass) while stirring to introduce a phosphate group into the cellulose. When the cellulose raw material or defibrated cellulose fibers are 100 parts by mass, if Compound A is a phosphoric acid-based compound, the addition amount of Compound A is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more in terms of the amount of phosphorus element. Thereby, the yield of the 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. Thereby, a yield commensurate with the amount of Compound A used can be efficiently obtained. Therefore, 0.2 to 500 parts by mass is preferable, and 1 to 400 parts by mass is more preferable.

[0041] When reacting Compound A with a cellulose raw material or defibrated cellulose fibers, Compound B may be further added to the reaction system. Examples of the method of adding Compound B to the reaction system include a method of adding Compound B to a slurry of a cellulose raw material or defibrated cellulose fibers, an aqueous solution of Compound A, or a slurry of a cellulose raw material or defibrated cellulose fibers and Compound A.

[0042] Compound B is not particularly limited, but preferably exhibits basicity, and more preferably a nitrogen-containing compound exhibiting basicity. "Exhibiting basicity" generally means that the aqueous solution of Compound B exhibits a pink to red color in the presence of a phenolphthalein indicator, and / or the pH of the aqueous solution of Compound B is greater than 7. The nitrogen-containing compound exhibiting basicity is not particularly limited as long as the effects of the present invention are achieved, but a compound having an amino group is preferred. Examples of the compound having an amino group include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, and the like. Among these, urea is preferred in terms of low cost and ease of handling. The addition amount of Compound B is preferably 2 to 1000 parts by mass, and more preferably 100 to 700 parts by mass. The reaction temperature is preferably 0 to 95°C, and more preferably 30 to 90°C. The reaction time is not particularly limited, but is usually about 1 to 600 minutes, and preferably 30 to 480 minutes. When the conditions of the esterification reaction are within any of these ranges, it is possible to suppress excessive esterification and easy dissolution of cellulose, and improve the yield of phosphorylated cellulose.

[0043] After reacting Compound A with a cellulose raw material or fibrillated cellulose fibers, usually a suspension of esterified cellulose fibers or esterified cellulose nanofibers is obtained. The suspension of esterified cellulose fibers or esterified cellulose nanofibers is dehydrated as necessary. After dehydration, it is preferable to perform a heat treatment. Thereby, hydrolysis of the cellulose raw material or fibrillated cellulose fibers can be suppressed. The heating temperature is preferably 100 to 170°C, and it is more preferable to heat at 130°C or lower (more preferably 110°C or lower) while water is contained during the heat treatment, and then perform the heat treatment at 100 to 170°C after removing the water.

[0044] In phosphorylated cellulose, a phosphate group substituent is introduced into the cellulose, and the celluloses repel each other electrically. Therefore, phosphorylated cellulose fibers can be easily defibrated into cellulose nanofibers (the defibration process to obtain cellulose nanofibers in this way is also referred to as nanofibrillation). The degree of substitution of phosphate groups per glucose unit of phosphorylated cellulose fibers is preferably 0.001 or more. Thereby, sufficient defibration (for example, nanofibrillation) can be carried out. The upper limit of the degree of substitution of phosphate groups per glucose unit of phosphorylated cellulose fibers is preferably 0.40 or less. Thereby, swelling or dissolution of phosphorylated cellulose fibers can be suppressed, and the occurrence of a situation where cellulose nanofibers cannot be obtained can be suppressed. Therefore, the degree of substitution of phosphate groups per glucose unit of phosphorylated cellulose fibers is preferably 0.001 to 0.40. Also, the degree of substitution of phosphate groups per glucose unit of cellulose nanofibers modified by phosphorylation (phosphorylated cellulose nanofibers) is preferably 0.001 or more. The upper limit is preferably 0.40 or less. Therefore, the degree of substitution of phosphate groups per glucose unit of phosphorylated cellulose nanofibers is preferably 0.001 to 0.40. It is preferable that the phosphorylated cellulose fibers are subjected to a washing treatment such as washing with cold water after boiling. Thereby, defibration can be carried out efficiently.

[0045] In addition, the reaction tank used in the step of chemically modifying this cellulose raw material to obtain modified cellulose is not particularly limited, but examples thereof include a tank provided with stirring blades, a pulper, a kneader, a ribbon type mixing device, and a screw type mixing device. Among these, when the reaction proceeds at a raw material concentration of generally 3% or less, it is preferable to use a tank or a pulper provided with stirring blades capable of stirring a liquid or a liquid slurry. Also, when the reaction proceeds under conditions where the raw material concentration generally exceeds 3%, since the reactants do not take a liquid form but are in a solid state, it is preferable to use a kneader, a ribbon type mixing device, or a screw type mixing device capable of mixing and stirring them.

[0046] (Washing process) In the present invention, this is a process of washing the obtained dispersion of chemically modified cellulose with water after dehydration treatment. By this process, cellulose nanofibers with few impurities can be obtained.

[0047] In this process, a dehydration device of the centrifugal separation type, vacuum dehydration type, or pressure dehydration type can be used. Specifically, centrifugal separation type: (Tanabe Wiltech centrifuge, Kokusan centrifuge, etc.), vacuum dehydration type: drum-type vacuum dehydrator, Tsukishima Machinery horizontal belt filter, pressure dehydration type: filter press, tube press, screw press, belt press horizontal belt filter, poly disc filter, vibrating screen, etc. Among these, since dehydration can be performed without applying a strong shearing force to the dehydration raw material, the pressure dehydration type (filter press, tube press), centrifugal separation type (Tanabe Wiltech centrifuge, Kokusan centrifuge, etc.), and vacuum dehydration type (drum-type vacuum dehydrator) are preferred. Also, a combination of a plurality of these can be used.

[0048] (Concentration adjustment process of chemically modified cellulose) In the present invention, in order to efficiently perform the following fibrillation process, it is preferable to adjust the concentration of the dispersion of chemically modified cellulose to 0.1% by mass to 10% by mass. If it is less than 0.1% by mass, the presence of modified pulp is too small to be fibrillated sufficiently. On the other hand, if it exceeds 10% by mass, as fibrillation progresses, the viscosity of the modified pulp dispersion increases, and sufficient force cannot be applied to the modified pulp, so sufficient fibrillation cannot be achieved.

[0049] (Fibrillation process) In the present invention, the high-pressure homogenizer 1 according to this embodiment is used for defibrating the chemically modified cellulose. The defibrating by the high-pressure homogenizer 1 is performed by applying a pressure of 50 MPa or more and a strong shearing force to the aqueous dispersion. The applied pressure is more preferably 100 MPa or more, and even more preferably 140 MPa or more. Further, prior to the defibrating / dispersing treatment with the high-pressure homogenizer 1, if necessary, it is also possible to perform a pretreatment on the above-mentioned cellulose nanofibers using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shearing mixer.

[0050] When defibrating by the above treatment, the solid content concentration as the cellulose fiber raw material is preferably 0.1% by mass or more, preferably 0.2% by mass or more, particularly 0.3% by mass or more, and 10% by mass or less, particularly preferably 6% by mass or less. If the solid content concentration is too low, the amount of liquid becomes too large with respect to the amount of the cellulose fiber raw material to be treated, resulting in poor efficiency. If the solid content concentration is too high, the fluidity deteriorates.

Explanation of Reference Numerals

[0051] 1... High-pressure homogenizer, 2... High-pressure pump, 3... Nozzle part, 4... Valve, 5, 6, 7... Pipes, 8... Cylinder, 9... Outer cylinder part, 10... Plunger, 11... Hydraulic cylinder, 11a... Piston, 18... Hydraulic cylinder head.

Claims

1. A cellulose nanofiber manufacturing apparatus comprising a high-pressure homogenizer for performing fibrillation treatment of pulp fibers, wherein the high-pressure homogenizer includes a high-pressure pump for pressurizing a cellulose raw material which is a raw material of the cellulose nanofibers, the high-pressure pump, comprises a cylinder for receiving the cellulose raw material, and an outer cylinder portion that covers 50% or more of the outer peripheral surface of the cylinder and has an outer diameter that is at least twice the inner diameter of the cylinder, and the outer cylinder portion is press-fitted onto the outer peripheral surface of the cylinder. A cellulose nanofiber manufacturing apparatus characterized by this.

2. The cellulose nanofiber manufacturing apparatus according to claim 1, wherein the outer cylinder portion is press-fitted onto the outer peripheral surface of the cylinder with an interference of 20 / 1000 mm or more and 80 / 1000 mm or less.

3. The material of the cylinder is stainless steel containing 15.0% by mass or more and 17.5% by mass or less of Cr, 3.0% by mass or more and 5.0% by mass or less of Ni, and 3.0% by mass or more and 5.0% by mass or less of Cu, chrome molybdenum steel containing 0.9% by mass or more and 1.2% by mass or less of Cr and 0.25% by mass or less of Ni, or titanium. The cellulose nanofiber manufacturing apparatus according to claim 1 or claim 2, characterized by this.

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