Cellulose nanofiber manufacturing apparatus

Abstract

To provide an apparatus for producing cellulose nanofibers, which achieves a long 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 refining 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 nanofibers, and the high-pressure pump includes a cylinder that receives the cellulose raw material, a plunger that the cellulose raw material into the cylinder and discharges the cellulose raw material to the outside of the cylinder by depressurization and pressurization of the inside of the cylinder, an actuator that reciprocates the plunger, and a positioning member that positions relative positions of the actuator and the cylinder, A pump holder fixed to the cylinder is provided, and a spigot structure in which the cylinder and the pump holder are fitted is provided on a surface where the cylinder and the pump holder face each other.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Nanotechnology, a technology that allows for the free control of matter at the nanometer scale, that is, on the atomic and molecular scale, is expected to lead to the creation of a variety of convenient new materials and devices. In particular, nano-order fibers (nanofibers) are attracting a great deal of attention because, when fibers are made extremely thin, they develop completely new physical properties not found in conventional fibers. Applications of nanofibers are expected to lead to the realization of purification devices with high-performance filters that do not allow even the smallest foreign particles to pass through, increased strength of synthetic fibers, high-performance clothing, and increased efficiency of fuel cells.

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

[0004] [Non-Patent Document 1] POWREX Corporation Product information https: / / www.powrex.co.jp / microfluidizer Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-mentioned high-pressure homogenizer, extremely high pressure is repeatedly applied to the high-pressure pump, which causes severe wear on the high-pressure pump parts due to long-term defibration treatment, resulting in the problem that expensive high-pressure pump parts must be replaced frequently.

[0006] An object of the present invention is to provide a cellulose nanofiber production device that achieves a long life for the high-pressure pump of the high-pressure homogenizer. [Means for solving the problem]

[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 production device equipped with a high-pressure homogenizer that performs a pulp fiber refining process, wherein the high-pressure homogenizer is equipped with a high-pressure pump that pressurizes the cellulose raw material that is the raw material for the cellulose nanofibers, and the high-pressure pump is equipped with a cylinder that receives the cellulose raw material, a plunger that sucks the cellulose raw material into the cylinder and expels it out of the cylinder by reducing and increasing the pressure inside the cylinder, an actuator that moves the plunger back and forth, and a pump holder that is a positioning member for positioning the actuator and the cylinder relative to each other and is fixed to the cylinder, and wherein the cellulose nanofiber production device is characterized in that a countersunk structure into which the cylinder and the pump holder fit is provided on the surfaces where the cylinder and the pump holder face each other. (2) The cellulose nanofiber production apparatus according to (1), characterized in that the gap between the side surfaces of the cylinder and the pump holder when the cylinder and the pump holder are fitted together is 1 mm or less. (3) The cellulose nanofiber production apparatus according to (1) or (2), characterized in that the high-pressure pump further comprises a pump base fixed to the pump holder, and a countersunk structure is provided on the surfaces where the pump holder and the pump base face each other. (4) The cellulose nanofiber production apparatus according to (3), characterized in that the gap between the side surfaces of the pump holder and the pump base when the pump holder and the pump base are fitted together is 1 mm or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a cellulose nanofiber production device that achieves a long life for the high-pressure pump of the high-pressure homogenizer. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing a schematic configuration of a high-pressure homogenizer according to an embodiment. [Figure 2] 1 is a diagram showing a schematic configuration of a high-pressure pump according to an embodiment; [Figure 3] 1 is a diagram showing a schematic configuration of a high-pressure pump according to an embodiment; [Figure 4] 10A and 10B are diagrams for explaining a counter mechanism for fitting the cylinder and the pump holder in the embodiment. [Figure 5] 10A and 10B are diagrams for explaining a counter mechanism for fitting together a pump holder and a pump base according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] A cellulose nanofiber production apparatus according to an embodiment of the present invention will now be described with reference to the drawings. The cellulose nanofiber production apparatus according to this embodiment is a cellulose nanofiber production apparatus equipped with a high-pressure homogenizer that performs a micronization process on pulp fibers. FIG. 1 is a diagram showing the schematic configuration of the high-pressure homogenizer equipped in the cellulose nanofiber production apparatus according to this embodiment. High-pressure homogenizer 1 comprises a high-pressure pump 2, a nozzle unit 3, a valve 4, and pipes 5, 6, and 7. The cellulose raw material, which is the source of cellulose nanofibers, is transported to the high-pressure pump 2 via pipes 5 and 6. The cellulose raw material is pressurized by the high-pressure pump 2 and then pressure-fed to the nozzle unit 3 via pipes 6 and 7. The cellulose raw material is pressure-fed to the nozzle unit 3 under increased pressure, generating a strong shearing action within the nozzle unit 3, resulting in a high degree of fiberization.

[0011] 2 and 3 are diagrams showing the configuration of the high-pressure pump 2 according to this embodiment, with Fig. 2 showing a state in which a plunger 10 (described later) is positioned at the stroke end in the downward direction of the page, and Fig. 3 showing a state in which the plunger 10 is positioned at the stroke end in the upward direction of the page. As described above, the high-pressure pump 2 is a pump for pressurizing the cellulose raw material, and as shown in Figs. 2 and 3, it is equipped with a cylinder 8, an outer tubular portion 9, the plunger 10, a hydraulic cylinder 11, a pump holder 14, and a pump base 15. For ease of explanation of the configuration, the cylinder 8, outer tubular portion 9, pump holder 14, and pump base 15 shown in Figs. 2 and 3 are shown as vertical central cross-sectional views, and the other components are shown as external views.

[0012] The cylinder 8 receives the cellulose raw material supplied via the pipe 6 shown in FIG. 1 . The plunger 10 is cylindrical, with its axis extending vertically in the plane of FIG. 2 , and moves back and forth within the cylinder 8 in the axial direction. The hydraulic cylinder 11 includes a piston 11a and functions as an actuator for moving the plunger 10 back and forth. 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 . This reduces the pressure inside the cylinder 8 and draws the cellulose raw material pumped by a supply pump (not shown) into the cylinder 8. 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 . This pressurizes the cylinder 8, discharging the cellulose raw material out of the cylinder 8. Note that although the hydraulic cylinder 11 is used as an example of an actuator in this embodiment, an air cylinder or a ball screw may also be used.

[0013] Pump holder 14 is cylindrical and has a through-hole 14d in the center through which plunger 10 is inserted. It functions as a positioning member for determining the relative positions of hydraulic cylinder 11 and cylinder 8, and is secured to cylinder 8 by a securing member (not shown). Fig. 4 is an enlarged view of the area within circle C1 shown in Fig. 2. As shown in Fig. 4, an annular facing surface 8a of cylinder 8 that faces pump holder 14 has an annular convex portion, and an annular facing surface 14a of pump holder 14 that faces cylinder 8 has an annular concave portion, and the surfaces where cylinder 8 and pump holder 14 fit together (facing surfaces 8a and 14a) are provided with a countersunk structure in which the convex portion of facing surface 8a and the concave portion of facing surface 14a fit together.

[0014] When the cylinder 8 and the pump holder 14 are fitted together, the gap G1 between the side surfaces of the cylinder 8 and the pump holder 14 (between the outer surface of the convex portion of the opposing surface 8a and the inner surface of the concave portion of the opposing surface 14a) is desirably 0.015 mm to 1 mm, more desirably 0.015 mm to 0.5 mm, and the average gap G1 in this embodiment is 0.02 mm. By providing a spigot structure on the surfaces where the cylinder 8 and the pump holder 14 are fitted together (the opposing surfaces 8a and 14a), misalignment due to play between the cylinder 8 and the pump holder 14 when the cylinder 8 and the pump holder 14 are fitted together during assembly of the high-pressure pump 2 can be prevented, and the high-pressure pump 2 can be assembled with the gap between the plunger 10 and the inner diameter of the cylinder 8 kept within the allowable range. In this embodiment, a spigot structure is given as an example in which the opposing surface 8a of the cylinder 8 is a convex portion and the opposing surface 14a of the pump holder 14 is a concave portion, but it may also be a spigot structure in which the opposing surface 8a of the cylinder 8 is a concave portion and the opposing surface 14a of the pump holder 14 is a convex portion.

[0015] The pump base 15 has a through-hole 15c in its center through which the plunger 10 is inserted. The pump base 15 is positioned relative to the pump holder 14 and fixed to the pump holder 14. The pump base 15 is also fixed to the hydraulic cylinder 11 via a fixing member (not shown) and a hydraulic cylinder head 18. FIG. 5 is an enlarged view of the area within circle C2 shown in FIG. 2. As shown in FIG. 5, the annular opposing surface 14f of the pump holder 14 facing the pump base 15 has a convex portion, and the annular opposing surface 15a of the pump base 15 facing the pump holder 14 has a concave portion. The surfaces (opposing surfaces 14f and 15a) where the pump holder 14 and the pump base 15 fit together have a countersunk structure in which the convex portion of the opposing surface 14f fits into the concave portion of the opposing surface 15a. This prevents the pump base 15 from becoming misaligned with the pump holder 14 during assembly of the high-pressure pump 2.

[0016] When the pump holder 14 and the pump base 15 are fitted together, the gap G2 between the side surfaces of the pump holder 14 and the pump base 15 (between the outer surface of the convex portion of the opposing surface 14f and the inner surface of the concave portion of the opposing surface 15a) is desirably 0.015 mm to 1 mm, more preferably 0.015 mm to 0.5 mm, and the average gap G2 in this embodiment is 0.02 mm. By providing a spigot structure on the surfaces where the pump holder 14 and the pump base 15 are fitted together (the opposing surfaces 14f and 15a), misalignment due to play between the pump holder 14 and the pump base 15 when the pump holder 14 and the pump base 15 are fitted together during assembly of the high-pressure pump 2 can be prevented, and the gap between the plunger 10 and the inner diameter of the cylinder 8 can be kept within the allowable range, allowing the high-pressure pump 2 to be assembled. In this embodiment, an inverted lock structure is used as an example in which the opposing surface 14f of the pump holder 14 is a convex portion and the opposing surface 15a of the pump base 15 is a concave portion, but it may also be a inverted lock structure in which the opposing surface 14f of the pump holder 14 is a concave portion and the opposing surface 15a of the pump base 15 is a convex portion.

[0017] Furthermore, the pump base 15 is fixed to the pump holder 14 by a fixing member (not shown) with the opposing surface 14f of the pump holder 14 and the opposing surface 15a of the pump base 15 facing each other. In this embodiment, the pump holder 14 and the pump base 15 are formed from separate members, but the pump holder 14 and the pump base 15 may also be formed from a single member.

[0018] In the cellulose nanofiber production apparatus according to this embodiment, a spigot structure is provided on the mating surfaces of the cylinder 8 and pump holder 14 that constitute the high-pressure pump 2 of the high-pressure homogenizer 1. This prevents misalignment due to play between the cylinder 8 and pump holder 14 when the cylinder 8 and pump holder 14 are fitted together during assembly of the high-pressure pump 2, and keeps the gap between the plunger 10 and the inner diameter of the cylinder 8 within an allowable range, allowing the high-pressure pump 2 to be assembled. Furthermore, a spigot structure is provided on the mating surfaces of the pump holder 14 and pump base 15 that constitute the high-pressure pump 2 of the high-pressure homogenizer 1. This prevents misalignment due to play between the pump holder 14 and pump base 15 when the pump holder 14 and pump base 15 are fitted together during assembly of the high-pressure pump 2, and keeps the gap between the plunger 10 and the inner diameter of the cylinder 8 within an allowable range, allowing the high-pressure pump 2 to be assembled. This prevents the side of the plunger 10 from making uneven contact with the inner surface of the cylinder 8 and the high-pressure seal attached to the inner surface of the cylinder 8 on the −Z direction side, thereby extending the life of the cylinder 8 and the high-pressure seal.

[0019] (Method of manufacturing cellulose nanofibers) The production method using the cellulose nanofiber production apparatus of the present invention includes a defibration step in which a cellulose raw material is defibrated by applying mechanical shear force using the high-pressure homogenizer 1 according to this embodiment. In the present invention, chemically modified cellulose can be used as the cellulose raw material, and in that case, it is preferable to carry out a step of dehydrating and washing the dispersion of chemically modified cellulose and a step of adjusting the concentration of the dispersion of chemically modified cellulose before subjecting it to the defibration step.

[0020] (Cellulose nanofiber) Cellulose nanofibers are materials produced by finely breaking down plant fibers to the nano level. They are typically fine fibers with an average fiber diameter of approximately 3 to 500 nm and an average aspect ratio of 50 or more. The average fiber diameter and length of cellulose nanofibers can be determined by averaging the fiber diameters and lengths obtained from observations of individual fibers using a field emission scanning electron microscope (FE-SEM). The aspect ratio can be calculated using the following formula: Aspect ratio = average fiber length / average fiber diameter

[0021] (cellulose raw material) In the present invention, the cellulose raw material refers to various forms of materials primarily composed of cellulose, and examples thereof include pulp (bleached or unbleached wood pulp, bleached or unbleached non-wood pulp, refined linter, pulp derived from herbs such as jute, Manila hemp, and kenaf), natural cellulose such as cellulose produced by microorganisms such as acetic acid bacteria, regenerated cellulose obtained by dissolving cellulose in a solvent such as a cuprammonium solution or a morpholine derivative and then spinning it, and fine cellulose obtained by depolymerizing the cellulose raw material by subjecting the above-mentioned cellulose raw material to mechanical treatment such as hydrolysis, alkaline hydrolysis, enzymatic decomposition, explosion treatment, or a vibration ball mill.

[0022] In the present invention, when a sheet-like cellulose raw material is used, it is preferable to roughly crush it to a size of about 0.5 to 5 cm square. By roughly crushing it to this size, the cellulose raw material can be efficiently and uniformly modified in the subsequent reaction step. The method of roughly crushing is not particularly limited, and a single-shaft rotary shear grinder, a double-shaft rotary shear grinder, a multi-shaft screw grinder, a shredder, a guillotine cutter, or the like can be used. Among these, the use of a single-shaft rotary shear grinder is preferred from the viewpoint of rough crushing.

[0023] Cellulose has three hydroxyl groups per glucose unit and can be chemically modified in various ways. In the present invention, a cellulose raw material obtained by chemical modification (chemically modified cellulose) may be used. Examples of chemical modifications include oxidation (carboxylation), carboxymethylation, cationization, and esterification. Of these, oxidation (carboxylation) and carboxymethylation are more preferred.

[0024] (Chemical modification of cellulose) (oxidation) In the present invention, oxidation of the cellulose raw material can be carried out using known methods and is not particularly limited, but it is preferable to adjust the amount of carboxyl groups to 0.5 mmol / g to 3.0 mmol / g relative to the bone dry mass of the cellulose nanofibers.

[0025] For example, cellulose can be obtained by oxidizing it 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. This oxidation reaction selectively oxidizes the primary hydroxyl group at C6 of the glucopyranose ring on the cellulose surface, resulting in cellulosic fibers bearing aldehyde groups and carboxyl or carboxylate groups on the surface. The cellulose concentration during the reaction is not particularly limited, but is preferably 5% by mass or less. An N-oxyl compound is a compound capable of generating nitroxy radicals. Any compound that promotes the desired oxidation reaction can be used as the N-oxyl compound.

[0026] The amount of N-oxyl compound used is not particularly limited as long as it is a catalytic amount that can oxidize the raw material cellulose. For example, the amount 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. Furthermore, the amount is preferably about 0.1 to 4 mmol / L relative to the reaction system.

[0027] Bromides are compounds containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Iodides are compounds containing iodine, examples of which include alkali metal iodides. The amount of bromide or iodide 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.

[0028] Known oxidizing agents can be used, such as halogens, hypohalous acids, halous acids, perhalogen acids or their salts, halogen oxides, and peroxides. Among these, inexpensive sodium hypochlorite is preferred. The appropriate amount of oxidizing agent 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. Furthermore, for example, 1 to 40 mol is preferred per 1 mol of the N-oxyl compound.

[0029] The cellulose oxidation process can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, or may be room temperature, about 15 to 30°C. As the reaction proceeds, carboxyl groups are generated in the cellulose, causing a decrease in the pH of the reaction solution. To efficiently proceed with 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 about 8 to 12, preferably about 10 to 11. Water is preferred as the reaction medium because it is easy to handle and does not easily cause side reactions.

[0030] The reaction time for the oxidation reaction can be set appropriately depending on the degree of progress of the oxidation, and is usually 0.5 to 6 hours, for example, about 1 to 4 hours. The oxidation reaction may also be carried out in two stages. For example, the oxidized cellulose obtained by filtration after the completion of the first-stage reaction can be oxidized again under the same or different reaction conditions, allowing for efficient oxidation without reaction inhibition by sodium chloride, a by-product of the first-stage reaction.

[0031] Another example of a carboxylation (oxidation) method is a method in which cellulose raw material is oxidized by contacting it with an ozone-containing gas. This oxidation reaction oxidizes at least the hydroxyl groups at positions 2 and 6 of the glucopyranose ring, and decomposes the cellulose chain. The ozone concentration in the ozone-containing gas is 50 to 250 g / m 3 It is preferable that the thickness is 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, and more preferably 5 to 30 parts by mass, based on 100 parts by mass of the solids content of the cellulose raw material. 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 approximately 1 to 360 minutes, and preferably approximately 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, a post-oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the post-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 post-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 then immersing the cellulose raw material in the solution.

[0032] The amounts of carboxyl groups, carboxylate groups, and aldehyde groups in cellulosic fibers can be adjusted by controlling the amount of oxidizing agent added and the reaction time. For example, the amount of carboxyl groups can be measured by preparing 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose, adjusting the pH to 2.5 with 0.1 M aqueous hydrochloric acid, and then measuring the electrical conductivity by adding 0.05 N aqueous sodium hydroxide dropwise until the pH reaches 11. The amount of carboxyl groups can be calculated using the following formula from the amount of sodium hydroxide (a) consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual: Carboxyl group content [mmol / g oxidized cellulose or cellulose nanofiber] = a (mL) x 0.05 / mass of oxidized cellulose (g)

[0033] (carboxymethylation) In the present invention, carboxymethylation of cellulose raw materials can be carried out using known methods and is not particularly limited. However, it is preferable to adjust the degree of carboxymethyl group substitution per anhydroglucose unit of cellulose to 0.01 to 0.50. One example of such a method is the following production method, but synthesis may be performed using a conventionally known method or a commercially available product. Cellulose is used as the raw material, and 3 to 20 times by mass of water and / or a lower alcohol, specifically methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc., is used as the solvent, either alone or in a mixture of two or more of these. The lower alcohol is used in an amount of 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, is used per anhydroglucose residue of the raw material. The starting material, solvent, and mercerizing agent are mixed and subjected to mercerization treatment at a reaction temperature of 0 to 70°C, preferably 10 to 60°C, for a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added at 0.05 to 10.0 times the moles per glucose residue, and an etherification reaction is carried out at a reaction temperature of 30 to 90°C, preferably 40 to 80°C, for a reaction time of 30 minutes to 10 hours, preferably 1 hour to 4 hours.

[0034] The degree of carboxymethyl substitution per glucose unit can be measured, for example, by the following method: 1) Accurately weigh approximately 2.0 g of carboxymethylated cellulose fiber (bone dry) and place it in a 300 mL Erlenmeyer flask with a stopper. 2) Add 100 mL of a solution of 1000 mL of nitric acid / methanol and 100 mL of concentrated nitric acid, and shake for 3 hours to convert the carboxymethyl cellulose salt (carboxymethylated cellulose) into hydrogenated carboxymethylated cellulose. 3) Accurately weigh 1.5 to 2.0 g of hydrogenated carboxymethylated cellulose (bone dry) and place it in a 300 mL Erlenmeyer flask with a stopper. 4) Wet the hydrogenated carboxymethylated cellulose with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake for 3 hours at room temperature. 5) Using phenolphthalein as an indicator, back-titrate the excess NaOH with 0.1 N H2SO4. 6) Calculate the degree of carboxymethyl substitution (DS) using the following formula: A = [(100 × F' - (0.1N H2SO4) (mL) × F) × 0.1] / (bone-dry mass of hydrogenated carboxymethyl cellulose (g)) DS=0.162×A / (1-0.058×A) A: Amount of 1N NaOH (mL) required to neutralize 1 g of hydrogenated carboxymethyl cellulose F': Factor of 0.1N H2SO4 F: Factor of 0.1N NaOH

[0035] (cationization) In the present invention, cationization of cellulose raw materials can be carried out using known methods. For example, cationization can result in the incorporation of ammonium, phosphonium, or sulfonium groups, or groups containing these ammonium, phosphonium, or sulfonium groups into cellulose molecules. Ammonium groups are preferred, and groups containing quaternary ammonium are particularly preferred. Specific cationization methods are not particularly limited. For example, cationized cellulose containing quaternary ammonium groups can be obtained by reacting the cellulose raw material with a cationizing agent such as glycidyl trimethylammonium chloride, 3-chloro-2-hydroxypropyl trialkylammonium hydride, or a halohydrin form thereof, and an alkali metal hydroxide catalyst (such as sodium hydroxide or potassium hydroxide) in the presence of water and / or an alcohol having 1 to 4 carbon atoms.

[0036] In this method, the degree of cationic substitution per glucose unit of the resulting cationically modified cellulose can be adjusted by controlling the amount of cationizing agent added to the reaction and the composition ratio of water and / or alcohols having 1 to 4 carbon atoms. 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 introduced substituents by the total number of moles of hydroxyl groups on the glucopyranose rings." Since pure cellulose has three substitutable hydroxyl groups per unit structure (glucopyranose ring), the theoretical maximum degree of substitution of the cellulose fiber of the present invention is 3 (minimum is 0).

[0037] In the present invention, the degree of cationic substitution per glucose unit of the cationized cellulose is preferably 0.01 to 0.40. Introducing cationic substituents into cellulose causes electrical repulsion between cellulose molecules. Therefore, cellulose with cationic substituents introduced therein can be easily nanofibrillated. If the degree of cationic substitution per glucose unit is less than 0.01, sufficient nanofibrillation cannot be achieved. On the other hand, if the degree of cationic substitution per glucose unit is greater than 0.40, the cellulose will swell or dissolve, making it impossible to maintain its fiber form, and nanofibers may not be obtained.

[0038] The degree of cationic substitution per glucose unit can be calculated by measuring the nitrogen content of a sample (cationically modified cellulose) using a total nitrogen analyzer TN-10 (Mitsubishi Chemical) after drying, and then using the following formula: The degree of substitution here refers to the average number of moles of substituents per mole of anhydroglucose unit. Degree of cation substitution = (162 x N) / (1-151.6 x N) N: Nitrogen content

[0039] (esterification) The method for esterifying a cellulose raw material or defibrated cellulose fibers to obtain esterified cellulose fibers or esterified cellulose nanofibers is not particularly limited, but examples include a method in which the cellulose raw material or defibrated cellulose fibers are reacted with compound A. Compound A will be described later.

[0040] Examples of methods for reacting compound A with cellulose raw materials or defibrated cellulose fibers include a method of mixing a powder or aqueous solution of compound A with the cellulose raw materials or defibrated cellulose fibers, a method of adding an aqueous solution of compound A to a slurry of the cellulose raw materials or defibrated cellulose fibers, etc. Of these, the method of mixing an aqueous solution of compound A with the cellulose raw materials or defibrated cellulose fibers or a slurry thereof is preferred because it increases the uniformity of the reaction and the esterification efficiency.

[0041] Examples of compound A include phosphoric acid compounds (e.g., 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 be used to improve defibration efficiency by introducing a phosphoric acid group into the cellulose of the cellulose raw material (e.g., pulp fiber). The phosphoric acid compound may be any compound having a phosphoric acid group, and examples thereof include 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, and ammonium metaphosphate. 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, and ammonium salt of phosphoric acid are preferred from the viewpoints of high efficiency of introduction of phosphate groups, ease of defibration in the defibration step described below, and ease of industrial application, with sodium salt of phosphoric acid being more preferred, and sodium dihydrogen phosphate and disodium hydrogen phosphate being even more preferred. Furthermore, it is preferred to use an aqueous solution of a phosphoric acid compound in the esterification, as this increases the uniformity of the reaction and the efficiency of introduction of phosphate groups. The pH of the aqueous solution of the phosphoric acid compound is preferably 7 or less, as this increases the efficiency of introduction of phosphate groups. A pH of 3 to 7 is more preferred from the viewpoint of suppressing hydrolysis of pulp fibers.

[0042] Examples of esterification methods include the following. Compound A is added to a suspension of cellulose raw material or defibrated cellulose fibers (e.g., solids concentration 0.1 to 10% by mass) with stirring to introduce phosphate groups into the cellulose. When compound A is a phosphoric acid compound, the amount of compound A added is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more, in terms of phosphorus element, per 100 parts by mass of cellulose raw material or defibrated cellulose fibers. This can further improve the yield of esterified cellulose fibers or esterified cellulose nanofibers. The upper limit is preferably 500 parts by mass or less, more preferably 400 parts by mass or less. This can efficiently obtain a yield commensurate with the amount of compound A used. Therefore, the amount is preferably 0.2 to 500 parts by mass, more preferably 1 to 400 parts by mass.

[0043] When compound A is reacted with the cellulose raw material or defibrated cellulose fibers, compound B may also be added to the reaction system. Methods for adding compound B to the reaction system include, for example, adding compound B to a slurry of the cellulose raw material or defibrated cellulose fibers, an aqueous solution of compound A, or a slurry of the cellulose raw material or defibrated cellulose fibers and compound A.

[0044] Although the compound B is not particularly limited, it is preferably basic, and a nitrogen-containing compound that exhibits basicity is more preferred. "Basicity" generally 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 pH of the aqueous solution of compound B is greater than 7. The nitrogen-containing compound that exhibits basicity is not particularly limited as long as it exhibits the effects of the present invention, but a compound having an amino group is preferred. Examples of compounds having an amino group include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, urea is preferred because of its low cost and ease of handling. The amount of compound B added is preferably 2 to 1,000 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 esterification reaction conditions are within any of these ranges, it is possible to prevent the cellulose from being excessively esterified and becoming more soluble, thereby improving the yield of phosphated cellulose.

[0045] After reacting compound A with the cellulose raw material or defibrated cellulose fibers, a suspension of esterified cellulose fibers or esterified cellulose nanofibers is usually obtained. The suspension of esterified cellulose fibers or esterified cellulose nanofibers is dehydrated as needed. After dehydration, it is preferable to carry out a heat treatment. This can suppress hydrolysis of the cellulose raw material or defibrated cellulose fibers. The heating temperature is preferably 100 to 170°C, and it is more preferable to heat the mixture at 130°C or below (more preferably 110°C or below) while water is still present during the heat treatment, and then to heat the mixture at 100 to 170°C after removing the water.

[0046] In phosphated cellulose, phosphate group substituents are introduced into the cellulose, causing electrical repulsion between cellulose molecules. Therefore, phosphated cellulose fibers can be easily defibrated down to cellulose nanofibers (defibration performed to produce cellulose nanofibers is also called nanodefibration). The degree of phosphate substitution per glucose unit of phosphated cellulose fibers is preferably 0.001 or more. This allows for sufficient defibration (e.g., nanodefibration). The upper limit of the degree of phosphate substitution per glucose unit of phosphated cellulose fibers is preferably 0.40 or less. This can suppress swelling or dissolution of the phosphated cellulose fibers and prevent the occurrence of situations where cellulose nanofibers cannot be obtained. Therefore, the degree of phosphate substitution per glucose unit of phosphated cellulose fibers is preferably 0.001 to 0.40. Furthermore, the degree of phosphate substitution per glucose unit of cellulose nanofibers modified by phosphate esterification (phosphated cellulose nanofibers) is preferably 0.001 or more. The upper limit is preferably 0.40 or less. Therefore, the degree of phosphate group substitution per glucose unit of the phosphated cellulose nanofiber is preferably 0.001 to 0.40. The phosphated cellulose fiber is preferably subjected to a washing treatment, such as boiling and then washing with cold water, which allows for efficient defibration.

[0047] The reaction tank used in the process of chemically modifying this cellulose raw material to obtain modified cellulose is not particularly limited, and examples include a tank equipped with stirring blades, a pulper, a kneader, a ribbon mixer, a screw mixer, etc. Among these, when the reaction is carried out at a raw material concentration of approximately 3% or less, it is preferable to use a tank or pulper equipped with stirring blades that can stir liquids or liquid slurries. Furthermore, when the reaction is carried out under conditions where the raw material concentration exceeds approximately 3%, the reactants are not in a liquid form but are solid, so it is preferable to use a kneader, ribbon mixer, or screw mixer that can mix and stir them.

[0048] (Cleaning process) In the present invention, the obtained dispersion of chemically modified cellulose is subjected to a dehydration treatment and then washed with water, and this step makes it possible to obtain cellulose nanofibers with few impurities.

[0049] In this process, dehydration equipment of the centrifugal, vacuum, or pressure dehydration type can be used. Specific examples include centrifugal (e.g., Tanabe Willtec centrifuges, Kokusan centrifuges), vacuum (drum-type vacuum dehydrators), and horizontal belt filters manufactured by Tsukishima Kikai, and pressure dehydration (filter presses, tube presses, screw presses, belt press horizontal belt filters, polydisc filters, and vibrating screens). Among these, pressure dehydration (filter presses, tube presses), centrifugal (e.g., Tanabe Willtec centrifuges, Kokusan centrifuges), and vacuum (drum-type vacuum dehydrators) are preferred because they can dehydrate the dehydrated raw material without applying strong shear forces. Furthermore, a combination of these can also be used.

[0050] (Concentration adjustment process for chemically modified cellulose) In the present invention, in order to efficiently carry out the subsequent defibration step, it is preferable to adjust the concentration of the chemically modified cellulose dispersion to 0.1% to 10% by mass. If the concentration is less than 0.1% by mass, the presence of too little modified pulp will result in insufficient defibration. On the other hand, if the concentration exceeds 10% by mass, the viscosity of the modified pulp dispersion will increase as defibration progresses, making it impossible to apply sufficient force to the modified pulp, resulting in insufficient defibration.

[0051] (defibration process) In the present invention, the high-pressure homogenizer 1 according to this embodiment is used to defibrate chemically modified cellulose. Defibration using the high-pressure homogenizer 1 is carried out by applying a pressure of 50 MPa or more and a strong shear force to the aqueous dispersion. The applied pressure is more preferably 100 MPa or more, and even more preferably 140 MPa or more. Furthermore, prior to defibration and dispersion treatment using the high-pressure homogenizer 1, the cellulose nanofibers can be subjected to pre-treatment, if necessary, using a known mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer.

[0052] When defibrating by the above treatment, the solids concentration of the cellulose fiber raw material is 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 6% by mass or less. If the solids concentration is too low, the amount of liquid will be too large relative to the amount of cellulose fiber raw material to be treated, resulting in poor efficiency, and if the solids concentration is too high, the fluidity will be poor. [Explanation of symbols]

[0053] 1...high-pressure homogenizer, 2...high-pressure pump, 3...nozzle section, 4...valve, 5, 6, 7...piping, 8...cylinder, 10...plunger, 11...hydraulic cylinder, 11a...piston, 14...pump holder, 15...pump base, 18...hydraulic cylinder head

Claims

1. A cellulose nanofiber production apparatus equipped with a high-pressure homogenizer that performs a pulp fiber refining process, The high-pressure homogenizer is equipped with a high-pressure pump that pressurizes the cellulose raw material that is the raw material for the cellulose nanofibers, The high-pressure pump a cylinder for receiving the cellulose feedstock; a plunger that draws the cellulose raw material into the cylinder and expels it out of the cylinder by reducing and increasing the pressure inside the cylinder; an actuator that reciprocates the plunger; a pump holder that is a positioning member for positioning the actuator and the cylinder relative to each other and is fixed to the cylinder; A cellulose nanofiber production apparatus characterized in that a countersunk structure into which the cylinder and the pump holder fit is provided on the surfaces where the cylinder and the pump holder face each other.

2. The cellulose nanofiber production apparatus according to claim 1, characterized in that the gap between the side surfaces of the cylinder and the pump holder when the cylinder and the pump holder are fitted together is 1 mm or less.

3. The high-pressure pump a pump base fixed to the pump holder; The cellulose nanofiber production device according to claim 1 or 2, characterized in that a countersunk structure is provided on the surfaces of the pump holder and the pump base facing each other.

4. The cellulose nanofiber production apparatus according to claim 3, characterized in that the gap between the side surfaces of the pump holder and the pump base when the pump holder and the pump base are fitted together is 1 mm or less.

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