Method for diluting a fine cellulose fiber aqueous dispersion, and the dilution thereof

Abstract

The present invention aims to provide a method for diluting a fine cellulose fiber aqueous dispersion that can efficiently dilute and redisperse the fine cellulose fiber aqueous dispersion using inexpensive, easily implemented equipment commonly used by the user. [Solution] A method for diluting a fine cellulose fiber aqueous dispersion, After preparing a mixed solution B by adding water to an aqueous dispersion A containing fine cellulose fibers at a solid content concentration of 1% by mass or more in the storage area, The mixture B stored in the storage section is taken in through the water intake of a plunger pump, which is part of the high-pressure washer, via the water intake of the high-pressure washer having an excess water discharge mechanism consisting of a pressure regulating valve, and discharged from the discharge port or excess water port of the plunger pump. A method for diluting a fine cellulose fiber aqueous dispersion, which provides an aqueous dispersion C in which the dispersibility of fine cellulose fibers, which are in a non-uniform dispersion state in mixed solution B, is improved.

Description

Technical Field

[0001] The present invention relates to a method for diluting an aqueous dispersion of microcrystalline cellulose fibers and a dilution thereof.

Background Art

[0002] Cellulose nanofibers and cellulose microfibrils (hereinafter collectively referred to as "microcrystalline cellulose fibers") obtained by refining cellulose are fine fibrous substances with a fiber diameter in the nano- to micro-order, and have functions such as high strength, high elasticity, and thixotropy, which are not found in ordinary pulp. It is expected to be used in various fields as a novel material.

[0003] Conventionally, microcrystalline cellulose fibers have been produced in a state of being stably dispersed in water by defibrating chemically modified pulp with a high-pressure homogenizer (see, for example, Patent Document 1). Usually, they are transported as they are to the user's factory or the like in the form of a microcrystalline cellulose dispersion liquid having a predetermined concentration, and are used for various purposes as industrial materials or additive materials for foods and cosmetics.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when the dispersion liquid is transported as it is to the user's factory or the like, there is a problem that a large amount of cost is required for its storage and transportation due to the volume and weight of the solvent. Therefore, it is expected to transport the dispersion liquid at a higher concentration. However, since microcrystalline cellulose fibers have a high thickening property, the workability deteriorates when the concentration is increased. In particular, in user factories without large-scale equipment, it is extremely difficult to perform operations such as dilution and redispersion to make the high-concentration microcrystalline cellulose fiber dispersion liquid suitable for use.

[0006] Therefore, the object of the present invention is to provide a method for diluting a fine cellulose fiber aqueous dispersion that can efficiently dilute and redisperse the fine cellulose aqueous dispersion using inexpensive, easily introduced, and commonly used equipment on the user's side. [Means for solving the problem]

[0007] In other words, the present invention is as follows (1) to (6). (1) A method for diluting an aqueous dispersion of fine cellulose fibers, After preparing a mixed solution B by adding water to an aqueous dispersion A containing fine cellulose fibers at a solid content concentration of 1% by mass or more in the storage area, The mixture B stored in the storage section is taken in through the water intake of a plunger pump, which is part of the high-pressure washer, via the water intake of the high-pressure washer having an excess water discharge mechanism consisting of a pressure regulating valve, and discharged from the discharge port or excess water port of the plunger pump. A method for diluting a fine cellulose fiber aqueous dispersion, which provides an aqueous dispersion C in which the dispersibility of fine cellulose fibers, which are in a non-uniform dispersion state in mixed solution B, is improved. (2) A method for diluting a fine cellulose fiber aqueous dispersion according to (1), characterized in that the outlet pressure of the pressure regulating valve controlled by the pressure regulating valve of the high-pressure washer is 0.5 to 25 MPa. (3) A method for diluting an aqueous dispersion of fine cellulose fibers according to any one of (1) or (2), characterized in that the solid content concentration of fine cellulose fibers in the aqueous dispersion C is 0.1 to 10.0% by weight. (4) A method for diluting an aqueous dispersion of fine cellulose fibers according to any one of (1) to (2), characterized in that the fine cellulose fibers are chemically modified. (5) A method for diluting a fine cellulose fiber aqueous dispersion according to any one of (1) to (2), characterized in that the aqueous dispersion C is further taken in from the water intake port of the high-pressure washer and discharged from the discharge port to obtain an aqueous dispersion D in which the dispersibility of fine cellulose is further improved compared to the aqueous dispersion C. (6) A diluted aqueous dispersion of fine cellulose fibers obtained by diluting using any of the dilution methods (1) to (5). [Effects of the Invention]

[0008] According to the present invention, a method for diluting a fine cellulose fiber aqueous dispersion can be provided that allows for efficient dilution and redispersion of the fine cellulose fiber aqueous dispersion using inexpensive, easily introduced, and commonly used equipment on the user's side. [Modes for carrying out the invention]

[0009] In the following invention, "~" includes the endpoints. That is, "X~Y" includes the values ​​X and Y at both ends.

[0010] The present invention relates to a method for diluting a fine cellulose fiber aqueous dispersion, After preparing a mixed solution B by adding water to an aqueous dispersion A containing fine cellulose fibers at a solid content concentration of 2% by mass or more in the storage area, The mixed liquid B stored in the storage section is taken in through the suction port of a plunger pump, which is part of the high-pressure washer, via the suction port of the high-pressure washer having an excess water discharge mechanism consisting of a pressure regulating valve, and discharged from the discharge port of the plunger pump. This is a method for diluting a fine cellulose fiber aqueous dispersion, which yields an aqueous dispersion C in which the dispersibility of fine cellulose fibers, which are in a non-uniform dispersion state in mixed solution B, is improved.

[0011] <Fine Cellulose Fibers> Fine cellulose fibers are cellulose in the form of fine fibers derived from cellulose raw materials. Fine fibrous cellulose is defined as a dispersion of fine cellulose fibers (1 wt%) that exhibits a light transmittance in the range of 1 to 99% when measured using a visible light spectrometer (UV-1800, Shimadzu Corporation) with a path length of 1 cm / 660 nm. Methods for manufacturing fine cellulose fibers include defibration treatment of pulp, and, if necessary, chemical modification treatment before or after defibration (usually before defibration). Fine cellulose fibers with a fiber diameter on the nano-order are called cellulose nanofibers, and fine cellulose fibers with a fiber diameter on the micron-order are called cellulose microfibrils. The size of fine cellulose fibers can be adjusted by conditions such as micronization treatment and chemical modification treatment.

[0012] (Cellulose nanofiber) In this specification, cellulose nanofiber (CNF) means cellulose fibers having a fiber diameter on the nanoscale, which are prepared through a micronization process.

[0013] The average fiber diameter (length-weighted average fiber diameter) of CNF is 500 nm or less, preferably 300 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. The lower limit is not particularly limited, but is usually 1 nm or more, preferably 2 nm or more. Therefore, the average fiber diameter (length-weighted average fiber diameter) of CNF is usually 1 to 500 nm or 2 to 500 nm, preferably 2 to 300 nm or 2 to 100 nm, more preferably 2 to 50 nm or 3 to 30 nm. The average fiber length (length-weighted average fiber length) is usually 50 to 2000 nm, preferably 100 to 1000 nm. The aspect ratio of CNF is usually 10 or more, preferably 50 or more. The upper limit is not particularly limited, but is usually 1000 or less.

[0014] The average fiber diameter and average fiber length of fine cellulose fibers can be determined using a fractionator manufactured by Valmet Co., Ltd. When using the fractionator, these can be determined as length-weighted fiber width and length-weighted average fiber length, respectively. The average aspect ratio of fine cellulose fibers can be calculated using the formula: Average aspect ratio = Average fiber length / Average fiber diameter.

[0015] (Cellulose microfibrils) In this specification, cellulose microfibrils (microfibrillated cellulose, MFCs) refer to cellulose fibers having a micro-order fiber diameter, which are prepared by micronization treatment.

[0016] The average fiber diameter (average fiber width) of MFCs is usually 500 nm or more, preferably 1 μm or more, and more preferably 3 μm or more. This allows for higher water retention compared to unfibrillated cellulose fibers, and provides a higher strength-imparting effect and yield improvement effect even in small quantities compared to finely fibrillated CNF. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 20 μm or less, but there are no particular restrictions. The average fiber length is usually 10 μm or more, 20 μm or more, or 40 μm or more, preferably 200 μm or more, 300 μm or more, or 400 μm or more. More preferably 500 μm or more or 550 μm or more, and even more preferably 600 μm or more, 700 μm or more, or 800 μm or more. The upper limit is not particularly limited, but is usually 3,000 μm or less, preferably 2,500 μm or less, more preferably 2,000 μm or less, even more preferably 1,500 μm or less, 1,400 μm or less, or 1,300 μm or less. The aspect ratio of the MFC is preferably 3 or more, more preferably 5 or more, even more preferably 7 or more, and may be 10 or more, 20 or more, or 30 or more. The upper limit of the aspect ratio is not particularly limited, but is preferably 1000 or less, more preferably 100 or less, and even more preferably 80 or less.

[0017] [Degenerate] The microcrystalline cellulose fiber may be a modified microcrystalline cellulose fiber or an unmodified microcrystalline cellulose fiber. The modified microcrystalline cellulose fiber means a microcrystalline cellulose fiber (for example, cellulose nanofiber, cellulose microfibril) in which at least any one of the three hydroxyl groups contained in the glucose unit is chemically modified (hereinafter simply referred to as "modified"). By the chemical modification treatment, the fibrillation of the cellulose fiber proceeds sufficiently, and cellulose nanofibers having a uniform average fiber length and average fiber diameter can be obtained by defibrillation. Therefore, when added to a dispersion medium such as water to form a dispersion, it is likely to exhibit stable viscosity, and the distribution of fiber length is also suppressed, so that entanglement between fibers is reduced, clogging during spraying can be suppressed, and the modified cellulose fiber is preferred.

[0018] Examples of the modification include esterification such as oxidation, etherification, and phosphoric esterification, silane coupling, fluorination, cationization, and the like. Among them, oxidation (carboxylation), etherification, cationization, and esterification are preferred, and oxidation (carboxylation) is more preferred.

[0019] - Oxidation (carboxylation)- Oxidized fine cellulose fibers typically have a structure in which at least one carbon atom having a primary hydroxyl group in the glucopyranose unit constituting the cellulose molecular chain (for example, the carbon atom having a primary hydroxyl group at position C6) is oxidized. The amount of carboxyl groups in oxidized cellulose fibers and oxidized cellulose nanofibers is preferably 0.5 mmol / g or more, more preferably 0.8 mmol / g or more, and even more preferably 1.0 mmol / g or more, relative to the oven-dry mass. The upper limit of this amount is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, and even more preferably 2.0 mmol / g or less. The amount of carboxyl groups is preferably 0.5 to 3.0 mmol / g, more preferably 0.8 to 2.5 mmol / g, and even more preferably 1.0 to 2.0 mmol / g. The amount of carboxyl groups can be adjusted by controlling the conditions when oxidizing the cellulose fibers (for example, the amount of oxidizing agent added, the reaction time). Furthermore, the amount of carboxyl groups and aldehyde groups can also be adjusted by controlling these conditions.

[0020] The amount of carboxyl groups can be calculated using the following procedure: Prepare 60 ml of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose. Add 0.1 M hydrochloric acid aqueous solution to the prepared slurry to adjust the pH to 2.5. Then, add 0.05 N sodium hydroxide aqueous solution dropwise and measure the electrical conductivity until the pH becomes 11. From the amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual (a), calculate the amount of carboxyl groups using the following formula: Carboxylate group content [mmol / g cellulose oxide] = a [ml] × 0.05 / Mass of cellulose oxide [g]

[0021] The oxidation method is not particularly limited, but one example is to oxidize the cellulose raw material in water using an oxidizing agent in the presence of an N-oxyl compound and a bromide, iodide, or a mixture thereof. In this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of the cellulose is selectively oxidized, producing at least one group selected from the group consisting of an aldehyde group, a carboxyl group (-COOH), and a carboxylate group (-COO-). The concentration of the cellulose raw material during the reaction is not particularly limited, but 5% by mass or less is preferred.

[0022] An N-oxyl compound is a compound capable of generating a nitroxyl radical. Examples of nitroxyl radicals include 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO). Any compound that promotes the desired oxidation reaction can be used as the N-oxyl compound. The amount of N-oxyl compound used is not particularly limited as long as it is a catalytic amount that can oxidize the cellulose raw material. For example, 0.01 mmol or more is preferred, and 0.02 mmol or more is more preferred, per 1 g of oven-dried cellulose raw material. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, and even more preferably 0.5 mmol or less. The amount of N-oxyl compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.02 to 0.5 mmol, per 1 g of oven-dried cellulose raw material. The amount of N-oxyl compound used in the reaction system is usually 0.1 to 4 mmol / L.

[0023] Bromides are compounds containing bromine, such as alkali metal bromides that can dissociate and ionize in water. Iodides are compounds containing iodine, such as alkali metal iodides. The amount of bromide or iodide used can be selected within a range that promotes the oxidation reaction. The total amount of bromide and iodide is 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 oven-dried cellulose raw material.

[0024] As an oxidizing agent, known substances can be used, such as halogens, hypohalous acids, halogenous acids, perhalous acids or their salts, halogen oxides, and peroxides. Among these, hypohalous acids or their salts are preferred because they are inexpensive and have a low environmental impact, hypochlorous acid or its salts are more preferred, and sodium hypochlorite is preferred. The appropriate amount of oxidizing agent to use is, for example, 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and even more preferably 3 to 10 mmol per 1 g of oven-dried cellulose raw material. Also, for example, 1 to 40 mol per 1 mol of N-oxyl compound is preferred.

[0025] The oxidation process of cellulose raw materials proceeds efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, and can also be around 15 to 30°C, i.e., room temperature. As the reaction progresses, carboxyl groups are formed in the cellulose, causing a decrease in the pH of the reaction solution. To ensure the oxidation reaction proceeds 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 around 8 to 12, or 10 to 11. Water is preferred as the reaction medium due to its ease of handling and the low likelihood of side reactions.

[0026] The reaction time in an oxidation reaction can be set appropriately according to the degree of oxidation, and is usually 0.5 to 6 hours, for example, 0.5 to 4 hours.

[0027] The oxidation reaction may be carried out in two stages. For example, by filtering out the oxidized cellulose after the first stage of the reaction and then oxidizing it again under the same or different reaction conditions, the oxidation can be carried out efficiently without being inhibited by the salt produced as a by-product in the first stage of the reaction.

[0028] Another example of a carboxylation (oxidation) method is oxidation by contacting a cellulose raw material with an ozone-containing gas (ozone oxidation). This oxidation reaction oxidizes at least the hydroxyl groups at positions 2, 3, and 6 of the glucopyranose ring, and also causes decomposition of the cellulose chain. The ozone concentration in the ozone-containing gas is preferably 50 to 250 g / m³, and more preferably 50 to 220 g / m³. The amount of ozone added 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 solid 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 preferably 1 to 360 minutes, and more preferably 30 to 360 minutes. When the ozone treatment conditions are within these ranges, it is possible to prevent excessive oxidation and decomposition of the cellulose raw material, and a good yield of oxidized cellulose can be obtained.

[0029] After ozone treatment, a follow-up oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the follow-up oxidation treatment is not particularly limited, but examples include chlorine compounds such as chlorine dioxide and sodium chlorite, as well as oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. The procedure for the follow-up oxidation treatment may involve, for example, dissolving these oxidizing agents in water or a polar organic solvent such as alcohol to prepare an oxidizing agent solution, and then immersing the oxidized cellulose in the solution.

[0030] The method for measuring the amount of carboxyl groups can be the same as described above.

[0031] - Acid-type oxidized cellulose and desalting - Oxidized cellulose contains carboxyl groups as a result of oxidation, but it may contain more acidic carboxyl groups (-COOH) than salty carboxyl groups (e.g., -COO-, -COONa), or more salty carboxyl groups than acidic carboxyl groups. The amounts of salty carboxyl groups and acidic carboxyl groups can be adjusted by desalting. Desalting can convert salty carboxyl groups to acidic carboxyl groups. In this specification, oxidized cellulose (after desalting) is called acidic oxidized cellulose, and oxidized cellulose (without undergoing the desalting treatment described later) is called salty oxidized cellulose. Salty oxidized cellulose usually mainly contains salty carboxyl groups. On the other hand, acidy oxidized cellulose has many acidic carboxyl groups, and the proportion of acidic carboxyl groups to carboxyl groups is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. Acidy oxidized cellulose can exhibit a better reinforcing effect together with component C. The proportion of acidic carboxyl groups can be calculated by the following procedure.

[0032] 1) First, prepare 250 mL of an aqueous dispersion of acid-type oxidized cellulose with a solid content of 0.1% by mass before desalting. Add 0.1 M hydrochloric acid aqueous solution to the prepared aqueous dispersion to adjust the pH to 2.5, then add 0.1 N sodium hydroxide aqueous solution and measure the electrical conductivity until the pH becomes 11. From the amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual (a), calculate the amount of acid-type carboxyl groups and salt-type carboxyl groups, i.e., the total amount of carboxyl groups, using the following formula: Total amount of carboxyl groups (mmol / g cellulose oxide (salt type)) = a (ml) × 0.1 / mass of cellulose oxide (salt type) (g) 2) Prepare 250 mL of a 0.1% by mass aqueous dispersion of desalted acid-type oxidized cellulose. Add a 0.1 N sodium hydroxide aqueous solution to the prepared aqueous dispersion and measure the electrical conductivity until the pH reaches 11. From the amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual (b), calculate the amount of acid-type carboxyl groups using the following formula: Amount of acid-type carboxyl groups (mmol / g acid-type oxidized cellulose) = b (ml) × 0.1 / Mass of acid-type oxidized cellulose (g) 3) From the calculated total amount of carboxyl groups and the amount of acidic carboxyl groups, calculate the proportion of acidic carboxyl groups using the following formula. Percentage of acidic carboxyl groups (%) = (Amount of acidic carboxyl groups / Total amount of carboxyl groups) × 100

[0033] Desalting can be performed after oxidation, either before or after defibration (before or after step (2)), but is usually done after oxidation, preferably before step (2). Desalting is usually carried out by replacing the salt (e.g., sodium salt) contained in the salt-type oxidized cellulose with a proton. Methods of desalting include adjusting the system to be acidic and contacting the oxidized cellulose with a cation exchange resin. In the case of adjusting the system to be acidic, the pH of the system is preferably adjusted to 2-6, more preferably 2-5, and even more preferably 2.3-5. Acids (e.g., inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrite, and phosphoric acid; organic acids such as acetic acid, lactic acid, oxalic acid, citric acid, and formic acid) are usually used to adjust the pH. After adding the acid, washing treatment may be performed as appropriate. The cation exchange resin can be either a strongly acidic ion exchange resin or a weakly acidic ion exchange resin, as long as the counterion is H+. The ratio of oxidized cellulose to the cation exchange resin when contacting them is not particularly limited and can be appropriately set by those skilled in the art from the viewpoint of efficiently performing proton substitution. The cation exchange resin after contact can be recovered by conventional methods such as suction filtration.

[0034] -Etherification- Examples of etherification include carboxyalkylation, methylation, ethylation, cyanoethylation, hydroxyethylation, hydroxypropylation, ethylhydroxyethylation, and hydroxypropylmethylation, with carboxyalkylation being preferred and carboxymethylation being more preferred.

[0035] Carboxyalkylated cellulose fibers typically have a structure in which at least one carbon atom constituting the cellulose molecular chain (for example, a carbon atom with a primary hydroxyl group at the C6 position that constitutes a glucopyranose unit) is carboxymethylated.

[0036] The degree of carboxyalkyl substitution (DS, preferably carboxymethyl substitution) per anhydrous glucose unit of carboxyalkylated cellulose is preferably 0.01 or higher, 0.02 or higher, or 0.05 or higher, more preferably 0.10 or higher, even more preferably 0.15 or higher, even more preferably 0.20 or higher, and particularly preferably 0.25 or higher. This ensures a degree of substitution necessary to obtain the effects of chemical modification. The upper limit of this degree of substitution is preferably 0.50 or lower, more preferably 0.45 or lower, 0.40 or lower, or 0.35 or lower. This makes it difficult for cellulose fibers to dissolve in water, and allows the fiber form to be maintained in water. Therefore, the degree of carboxyalkyl substitution is preferably 0.01 to 0.50, more preferably 0.01 to 0.45, and even more preferably 0.02 to 0.40, 0.10 to 0.35, or 0.20 to 0.30.

[0037] The degree of substitution, for example, the degree of carboxymethyl substitution, can be measured by the following method. Approximately 2.0 g of carboxymethylated cellulose (dry) is accurately weighed and placed in a 300 mL stoppered Erlenmeyer flask. 100 mL of a solution of 1,000 mL of methanol and 100 mL of special grade concentrated nitric acid is added, and the mixture is shaken for 3 hours to convert the salt-type carboxymethylated cellulose (hereinafter also called "salt-type CM-cellulose") to the acid-type carboxymethylated cellulose (hereinafter also called "acid-type CM-cellulose"). 1.5 to 2.0 g of the acid-type CM-cellulose (dry) is accurately weighed and placed in a 300 mL stoppered Erlenmeyer flask. The acid-type CM-cellulose is moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH is added, and the mixture is shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, the excess NaOH is back-titrated with 0.1 N H2SO4, and the degree of carboxymethyl substitution (DS) can be calculated by the following formula: A = [(100 × F - (0.1N H₂SO₄ (mL)) × F') × 0.1] / (Oven-dry mass of acid-type CM-modified cellulose (g)) DS = 0.162 × A / (1 - 0.058 × A) A: Amount of 1N NaOH required to neutralize 1g of acid-type C-mercured cellulose (mL) F': Factor of 0.1N H2SO4 F: Factor of 0.1N NaOH

[0038] The degree of carboxyalkyl substitution can be adjusted by controlling reaction conditions such as the amount of carboxyalkylating agent added, the amount of mercerizing agent, and the composition ratio of water to organic solvent.

[0039] One method of carboxyalkylation is to merce a cellulosic raw material (starting material) and then etherify it. The following explanation will use carboxymethylation as an example.

[0040] Carboxymethylated cellulose can be produced by using unmodified cellulose fibers (cellulose raw material: e.g., pulp) as a starting material, performing a mercerization treatment, and then carrying out an etherification reaction. This reaction is usually carried out in the presence of a solvent. As the solvent, for example, water, lower alcohols (e.g., methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tertiary butanol) can be used individually or as a mixture of two or more solvents. When lower alcohols are mixed, the mixing ratio of the lower alcohols is preferably 60 to 95% by mass. The amount of solvent is approximately 3 times the mass of the cellulose raw material. There is no particular upper limit to this amount, but it is 20 times or less. Preferably, the amount of solvent is 3 to 20 times the mass of the cellulose raw material.

[0041] Examples of mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of mercerizing agent used is preferably 0.5 times or more per anhydrous glucose residue of the starting material, more preferably 1.0 times or more, and even more preferably 1.5 times or more, on a molar basis. The upper limit of this amount is usually 20 times or less, preferably 10 times or less, and more preferably 5 times or less. The amount of mercerizing agent used is preferably 0.5 to 20 times, more preferably 1.0 to 10 times, and even more preferably 1.5 to 5 times, on a molar basis.

[0042] The reaction temperature for mercellation is usually 0°C or higher, preferably 10°C or higher. The upper limit is usually 70°C or lower, preferably 60°C or lower. The reaction temperature is usually 0 to 70°C, preferably 10 to 60°C. The reaction time for mercellation is usually 15 minutes or more, preferably 30 minutes or more. The upper limit is usually 8 hours or less, preferably 7 hours or less. The reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

[0043] The etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of carboxymethylating agents include sodium monochloroacetate. The amount of carboxymethylating agent added is preferably 0.05 times or more per glucose residue of the cellulose raw material, more preferably 0.5 times or more, and even more preferably 0.8 times or more, on a molar basis. The upper limit of this amount is usually 10.0 times or less, preferably 5 times or less, and more preferably 3 times or less. The amount of carboxymethylating agent added is preferably 0.05 to 10.0 times, more preferably 0.5 to 5 times, and even more preferably 0.8 to 3 times, on a molar basis.

[0044] The reaction temperature is usually 30°C or higher, preferably 40°C or higher. The upper limit is usually 90°C or lower, preferably 80°C or lower. The reaction temperature is usually 30 to 90°C, preferably 40 to 80°C. The reaction time is usually 30 minutes or more, preferably 1 hour or more. The upper limit is usually 10 hours or less, preferably 4 hours or less. The reaction time is usually 30 minutes to 10 hours, preferably 1 hour to 4 hours. During the carboxymethylation reaction, the reaction solution may be stirred as needed.

[0045] -Differences from carboxymethylcellulose- It is preferable that carboxyalkylated cellulose fibers maintain at least a portion of their fibrous shape even when dispersed in water. Carboxyalkylated cellulose fibers are distinct from cellulose powders such as carboxymethylcellulose, which are a type of water-soluble polymer that dissolves in water and imparts viscosity. When an aqueous dispersion of carboxyalkylated cellulose fibers is observed with an electron microscope, fibrous material can be observed. On the other hand, when an aqueous dispersion of carboxymethylcellulose, a type of water-soluble polymer, is observed, no fibrous material is observed. Furthermore, when anionically modified cellulose fibers are measured by X-ray diffraction, peaks of at least one of cellulose type I and type II crystals can be observed, but when carboxymethylcellulose powder, a water-soluble polymer, is measured in the same way, such cellulose type I and type II crystals are usually not observed.

[0046] - Acid-type carboxyalkylated cellulose and desalting - Carboxylated cellulose may contain more acidic carboxyl groups than saltic carboxyl groups, or vice versa. The amounts of saltic carboxyl groups and acidic carboxyl groups can be adjusted by desalting. Desalting can convert saltic carboxyl groups to acidic carboxyl groups. In this specification, carboxylated cellulose (after desalting) is referred to as acidic carboxylated cellulose, and carboxylated cellulose (without undergoing the desalting treatment described later) is referred to as saltic carboxylated cellulose. Saltic carboxylated cellulose usually mainly contains saltic carboxyl groups (-COO-). On the other hand, acidic carboxylated cellulose has many acidic carboxyl groups, and the ratio of acidic carboxyl groups to the amount of carboxyl groups in acidic carboxylated cellulose is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. Acidic carboxylated cellulose is presumed to have superior reinforcing effects with component C. The method for calculating the proportion of acidic carboxyl groups is as described above.

[0047] Desalting is usually performed after carboxyalkylation, preferably after etherification and before fibrillation. One method of desalting is to contact the carboxyalkylated cellulose with a cation exchange resin. Both strongly acidic and weakly acidic cation exchange resins can be used, as long as their counterions are H+. The ratio of carboxyalkylated cellulose to the cation exchange resin when contacting them is not particularly limited and can be appropriately set by those skilled in the art from the viewpoint of efficient proton substitution. For example, the ratio can be adjusted so that the pH of the aqueous dispersion after adding the cation exchange resin to the carboxyalkylated cellulose aqueous dispersion is preferably 2-6, more preferably 2-5. The cation exchange resin after contact can be recovered by conventional methods such as suction filtration.

[0048] - Esterification (Phosphate esterification) - One example of esterified cellulose fibers is phosphorylated cellulose. Phosphorylated cellulose typically has a structure in which at least one carbon atom constituting the cellulose molecular chain (for example, the carbon atom with a primary hydroxyl group at position C6 that constitutes the glucopyranose unit) is phosphorylated.

[0049] The degree of substitution of phosphate groups per glucose unit in phosphate-esterified CNF (hereinafter simply referred to as "degree of phosphate group substitution") is preferably 0.001 or more and less than 0.40. The degree of phosphate group substitution can be measured by the following method. A slurry of phosphate-esterified CNF with a solid content of 0.2% by mass is prepared. A strongly acidic ion exchange resin is added to the slurry by volume at 1 / 10, and after shaking for 1 hour, the slurry is poured onto a mesh with a mesh opening of 90 μm to separate the resin from the slurry and obtain hydrogen-type phosphate-esterified CNF. Next, 0.1 N sodium hydroxide aqueous solution is added to the slurry after treatment with the ion exchange resin in 50 μL increments once every 30 seconds, and the change in the electrical conductivity value of the slurry is measured. The amount of alkali (mmol) required in the region where the electrical conductivity rapidly decreases is divided by the solid content (g) in the slurry to be titrated to calculate the amount of phosphate groups (mmol / g) per 1 g of hydrogen-type phosphate-esterified CNF. Furthermore, the degree of phosphate substitution (DS) per glucose unit of phosphate-esterified CNF is calculated using the following formula: DS = 0.162 × A / (1 - 0.079 × A) where A is the amount of phosphate groups per gram of hydrogen-type phosphate-esterified CNF (mmol / g).

[0050] The degree of phosphate group substitution can be adjusted by controlling reaction conditions such as the amount of phosphate-containing compound added and, if necessary, the amount of basic compound added.

[0051] One method of phosphorylation is to react a compound having a phosphate group with unmodified cellulose fibers (phosphate esterification). Examples of phosphate esterification methods include mixing a powder or aqueous solution of a compound having a phosphate group with a cellulosic raw material (e.g., a suspension (solid content concentration of about 0.1 to 10% by mass)) or adding an aqueous solution of a compound having a phosphate group to an aqueous dispersion of a cellulosic raw material, with the latter being preferred. This improves the uniformity of the reaction and increases the esterification efficiency. The pH of the aqueous solution of the compound having a phosphate group is preferably 7 or less from the viewpoint of improving the efficiency of phosphate group introduction, and more preferably 3 to 7 from the viewpoint of suppressing hydrolysis.

[0052] Examples of compounds containing a phosphate group include phosphoric acid, polyphosphate, phosphorous acid, phosphonic acid, polyphosphonic acid, esters and salts thereof. These compounds are low-cost, easy to handle, and allow for the introduction of phosphate groups into cellulose, thereby improving the defibrillation efficiency. Specific examples of compounds containing a phosphate group 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. One or more compounds containing a phosphate group can be used in combination. The amount of compound containing a phosphate group added to the cellulose raw material is preferably 0.1 to 500 parts by mass, more preferably 1 to 400 parts by mass, and even more preferably 2 to 200 parts by mass, in terms of phosphorus element, per 100 parts by mass of solid content of the cellulose raw material. This allows for the efficient acquisition of a yield commensurate with the amount of compound containing a phosphate group used. 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. If the esterification reaction conditions are within any of these ranges, it is possible to suppress excessive esterification of cellulose and its increased solubility, thereby improving the yield of phosphate-esterified cellulose. When reacting compounds having a phosphate group, basic compounds (for example, compounds having basic amino groups such as urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, etc.) may also be added to the reaction system. The suspension obtained after esterification is preferably dehydrated as needed, and then heat-treated. This suppresses the hydrolysis of the cellulose raw material. The heating temperature is preferably 100 to 170°C. During the heat treatment, it is preferable to heat at 130°C or lower (preferably 110°C or lower) while water is present, and then, after removing the water, to heat-treat at 100 to 170°C.It is preferable to perform a washing treatment, such as boiling followed by washing with cold water. This allows for efficient defibration. Washing can be performed by adding water and then dehydrating (e.g., by filtration), and may be repeated two or more times. It is preferable to continue washing until the electrical conductivity of the filtrate decreases. For example, it can be continued until the electrical conductivity is preferably 200 or less, more preferably 150 or less, and even more preferably 120 or less. After washing, neutralization treatment may be performed as needed. Neutralization treatment can be performed, for example, by adding alkali (e.g., sodium hydroxide). Washing may be performed again after neutralization.

[0053] - Esterification (phosphorite esterification) - A second example of a method for producing esterified cellulose fibers is phosphite-esterified cellulose fibers. Phosphite-esterified cellulose fibers typically have a structure in which at least one carbon atom constituting the cellulose molecular chain (for example, the carbon atom at position C6 that has a primary hydroxyl group constituting the glucopyranose unit) is phosphite-oxidized. The degree of substitution of phosphite groups per glucose unit in phosphite-esterified cellulose fibers (hereinafter simply referred to as "degree of phosphite group substitution") is preferably 0.001 to 0.60. This makes electrical repulsion between cellulose cells easier, facilitating nanofibrillation. The degree of substitution of phosphite groups can be measured using the same method as for measuring the degree of phosphate group substitution. The degree of phosphite group substitution can be adjusted by controlling reaction conditions such as the amount of phosphite or its salt added, and, if necessary, the amount of alkali metal ion-containing substances, urea or its derivatives added.

[0054] One method for esterifying phosphorous acid is to react unmodified cellulose fibers with phosphorous acid or its metal salt (preferably sodium hydrogen phosphite) to introduce an ester group of phosphorous acid.

[0055] Examples of phosphorous acid and its metal salts include phosphorous acid compounds such as phosphorous acid, sodium hydrogen phosphite, ammonium hydrogen phosphite, potassium hydrogen phosphite, sodium dihydrogen phosphite, sodium phosphite, lithium phosphite, potassium phosphite, magnesium phosphite, calcium phosphite, triethyl phosphite, triphenyl phosphite, and pyrophosphorous acid, and combinations of two or more selected from these, with sodium hydrogen phosphite being preferred. This also allows alkali metal ions to be introduced into the cellulose fibers. The amount of phosphorous acid or its metal salt added is preferably 1 to 10,000 g, more preferably 100 to 5,000 g, and even more preferably 300 to 1,500 g per 1 kg of unmodified cellulose fiber. In addition to phosphorous acid and its metal salt, alkali metal ion-containing substances (e.g., hydroxides, metal sulfates, metal nitrates, metal chlorides, metal phosphates, metal carbonates) may be further added to the reaction system.

[0056] Furthermore, urea or its derivatives may be added to the reaction system. This allows carbamate groups to be introduced into the cellulose fibers. Examples of urea and urea derivatives include urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, and two or more combinations selected from these, with urea being preferred. The amount of urea and urea derivatives added is preferably 0.01 to 100 mol, more preferably 0.2 to 20 mol, and even more preferably 0.5 to 10 mol per 1 mol of phosphorous acid or its metal salt.

[0057] The reaction temperature is preferably 100-200°C, more preferably 100-180°C, and even more preferably 100-170°C. During the heat treatment, it is preferable to heat at 130°C or below (preferably 110°C or below) while water is present, and then, after removing the water, to heat-treat at 100-170°C. The reaction time is usually about 10-180 minutes, more preferably 30-120 minutes. It is preferable to wash the phosphite-esterified cellulose fibers before defibration. The degree of substitution of phosphite groups per glucose unit is preferably 0.01 or more and less than 0.23.

[0058] - Esterification (Sulfuric acid esterification) - A third example of a method for producing esterified cellulose fibers is sulfated esterified cellulose fibers. Sulfated esterified cellulose typically has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, a carbon atom with a primary hydroxyl group at the C6 position that constitutes a glucopyranose unit) is phosphorylated.

[0059] The amount of sulfate groups per glucose unit in sulfated esterified cellulose fibers (hereinafter simply referred to as "amount of sulfate groups") is preferably 0.1 to 3.0 mmol / g. By introducing cationic substituents into the cellulose raw material, the cellulose molecules repel each other electrically. For this reason, cationized cellulose with introduced cationic substituents can be easily nanofibrillated. If the degree of cationic substitution per glucose unit is 0.02 or higher, sufficient nanofibrillation can be achieved due to the electrical repulsion between the cellulose molecules. On the other hand, if the degree of cationic substitution per glucose unit is 0.50 or lower, swelling or dissolution can be suppressed, preventing situations where nanofibers cannot be obtained. To efficiently perform fibrillation, it is preferable to wash the cationized cellulose obtained above.

[0060] The amount of sulfate groups per glucose unit can be measured by the following method: A aqueous dispersion of sulfated CNF is solvent-substituted with ethanol and then t-butanol, and then freeze-dried. 200 mg of the resulting sample is mixed with 15 ml of ethanol and 5 ml of water, and stirred for 30 minutes. Then, 10 ml of 0.5 N sodium hydroxide aqueous solution is added, and the mixture is stirred at 70°C for 30 minutes, followed by stirring at 30°C for 24 hours. Next, phenolphthalein is added as an indicator, and the mixture is titrated with hydrochloric acid. The amount of sulfate groups is then calculated using the following formula: Sulfate group amount [mmol / g sample] = (5 - (0.1 × hydrochloric acid titration volume [ml] × 2)) / 0.2.

[0061] The amount of sulfate groups can be adjusted by controlling reaction conditions such as the amount of sulfate-based compound added to the reaction.

[0062] One method of sulfuric acid esterification is to react unmodified cellulose fibers with a sulfuric acid compound, thereby introducing sulfuric acid groups derived from the sulfuric acid compound into the cellulose to produce sulfuric acid-esterified cellulose. Examples of sulfuric acid compounds include sulfuric acid, sulfamic acid, chlorosulfonic acid, sulfur trioxide, or esters or salts thereof. Among these, sulfamic acid is preferred because it has low cellulose solubility and low acidity.

[0063] For example, when sulfamic acid is used as the sulfate compound, the amount of sulfamic acid used can be appropriately adjusted considering the amount of anionic group introduced into the cellulose chain. For example, the amount is preferably 0.01 to 50 mol, more preferably 0.1 to 3.0 mol, per mol of glucose units in the cellulose molecule.

[0064] -Salt type / Acid type- Esterified cellulose may contain more acidic carboxyl groups than salt-type carboxyl groups, or vice versa. Esterified cellulose that has not undergone desalting treatment and that has undergone desalting treatment are called salt-type esterified cellulose and acid-type esterified cellulose, respectively. Salt-type esterified cellulose mainly contains salt-type carboxyl groups. Acid-type esterified cellulose is presumed to be superior due to its reinforcing effect with component C. The countercation of the salt-type carboxyl group and its preparation method are as described in the description of oxidized cellulose.

[0065] -Cationization- Cationized cellulose typically has a structure in which at least one carbon atom constituting the cellulose molecular chain (for example, the carbon atom with a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is cationized, and usually contains cations such as ammonium, phosphonium, sulfonium, or groups having such cations in the molecule. The degree of cation substitution per glucose unit in cationized cellulose is preferably 0.02 to 0.50. The degree of cation substitution per glucose unit can be measured by the following method: After drying the cationized cellulose fibers, the nitrogen content is measured using a total nitrogen analyzer (TN-10, manufactured by Mitsubishi Chemical Corporation), and the degree of cation substitution (average number of moles of substituents per mole of anhydrous glucose unit) is calculated using the following formula: Degree of cation substitution = (162 × N) / (1 - 151.6 × N), where N is the nitrogen content.

[0066] The degree of cation substitution can be adjusted by reaction conditions such as the amount of cationizing agent added and the composition ratio of water or C1-C4 alcohols.

[0067] One method of cationization involves reacting unmodified cellulose fibers with a cationizing agent (e.g., glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrate, or its halohydrin form) and an alkali metal hydroxide catalyst (e.g., sodium hydroxide, potassium hydroxide) in the presence of water and / or an alcohol having 1 to 4 carbon atoms. By using any of the cationizing agents exemplified above, cationized cellulose having a quaternary ammonium group can be obtained. The cationization reaction is usually carried out in the presence of water or alcohol.

[0068] The amount of cationizing agent is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, per 100 parts by mass of cellulose raw material. The upper limit of this amount is usually 800 parts by mass or less, preferably 500 parts by mass or less. Examples of catalysts used as needed during cationization include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of catalyst is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of cellulose raw material. The upper limit of this amount is usually 7 parts by mass or less, preferably 3 parts by mass or less.

[0069] -Basic-type cationized cellulose fiber- It is preferable to convert the cationized cellulose fibers, after cationization, into basic-type cationized cellulose or basic-type cationized cellulose nanofibers by desalting. Desalting allows the salts in the cationized cellulose to be converted into bases. In this specification, cationized cellulose (nanofibers) that have undergone desalting are referred to as basic-type cationized cellulose (nanofibers) or cationized cellulose (nanofibers) (basic type). Furthermore, cationized cellulose and cationized cellulose nanofibers that have not undergone desalting are referred to as salt-type cationized cellulose (nanofibers) or cationized cellulose (nanofibers) (salt type). Desalting may be performed at either the pre-fibrillation (cationized cellulose) or post-fibrillation (cationized cellulose nanofibers) stage described later. Desalting means replacing the salts (e.g., Cl-) contained in cationized cellulose (salt type) and cationized cellulose nanofibers (salt type) with bases to make them basic type. An example of a desalting method after cationization is to contact cationized cellulose or cationized cellulose nanofibers with an anion exchange resin. As long as the counterion is OH-, either a strongly basic ion exchange resin or a weakly basic ion exchange resin can be used. The ratio of modified cellulose to the anion exchange resin when contacting them is not particularly limited and can be appropriately set by those skilled in the art from the viewpoint of efficiently performing cation substitution. For example, the ratio can be adjusted so that the pH of the aqueous dispersion after adding the anion exchange resin to the cationized cellulose nanofiber aqueous dispersion is preferably 8 to 13, more preferably 9 to 13. The anion exchange resin after contact can be recovered by conventional methods such as suction filtration.

[0070] [Miniaturization (fibrillation, fibrillation)] Micronization is usually carried out by mechanical processes. These mechanical processes (preferably beating or disintegration) are usually carried out in a wet manner (i.e., in the form of an aqueous dispersion of cellulose fibers). Examples of equipment used for mechanical processing include refiners (e.g., disc type, conical type, cylinder type), high-speed defibrators, shear-type agitators, colloid mills, high-pressure jet dispersers, beaters, PFI mills, kneaders, dispersers, high-speed dissociators (top finers), high-pressure or ultra-high-pressure homogenizers, grinders (stone mill type grinders), ball mills, vibratory mills, bead mills, single-screw, twin-screw or multi-screw kneaders / extruders, homomixers under high-speed rotation, refiners, defibrators, friction grinders, high-shear defibrators, dispersers, homogenizers (e.g., microfluidizers), and other equipment capable of providing mechanical defibration. Equipment capable of providing defibration in a wet manner is preferred, and high-speed dissociators and refiners are more preferred, but are not particularly limited.

[0071] When defibration is performed by a wet process, an aqueous dispersion of cellulose fibers is usually prepared. The solid content concentration of modified cellulose in the aqueous dispersion is preferably as high as possible for efficiency during transportation, and is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2.0% by mass or more, 3% by mass or more, 4% by mass or more, and 5% by mass or more. The upper limit of the concentration is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. During mechanical processing, pH adjustment (e.g., 7 or less, 6 or less, 5 or less) may be performed as needed.

[0072] Prior to preparing the aqueous dispersion, pretreatment such as dry grinding (e.g., grinding after drying) may be performed. Examples of equipment used for dry grinding include, but are not limited to, hammer mills, pin mills and other impact mills, ball mills, tower mills and other media mills, and jet mills. Posttreatment may also be performed after defibration. Examples of posttreatment include drying (e.g., freeze-drying, spray drying, shelf drying, drum drying, belt drying, drying by spreading thinly on a glass plate, etc., fluidized bed drying, microwave drying, heated fan-type vacuum drying, vacuum (deaeration) drying), redispersion in water (dispersion equipment is not limited), and grinding (e.g., grinding using equipment such as cutter mills, hammer mills, pin mills, and jet mills), but are not particularly limited.

[0073] [Optional action] It is important that the fine cellulose fibers are in an aqueous dispersion with a solid content of 2% by mass or more before the dilution treatment described later, but any intermediate treatment may be performed as needed. Such treatments include, but are not limited to, drying (e.g., freeze-drying, spray drying, shelf drying, drum drying, belt drying, drying by spreading thinly on a glass plate, etc., fluidized bed drying, microwave drying, and vacuum drying with a heated fan) and grinding (e.g., grinding using equipment such as a cutter mill, hammer mill, pin mill, or jet mill).

[0074] [Physical properties of fine cellulose fibers] Fine cellulose fibers preferably have the following physical properties.

[0075] -Specific surface area- The BET specific surface area of ​​the fine cellulose fibers is preferably 25 m². 2 / g or more, comfortably 50m 2 / g or more, more preferably 100m 2 The value is 1 / g or greater. The BET specific surface area can be measured using a BET specific surface area meter after replacing the aqueous dispersion with t-BuOH and then freeze-drying the sample, according to the nitrogen gas adsorption method (JIS Z 8830).

[0076] -Crystallization of Cellulose Type I- The crystallinity of type I cellulose in fine cellulose fibers is usually 10% or more, preferably 30% or more, and 50% or more. There is no particular upper limit, but in reality, it is considered to be around 90%. The crystallinity of cellulose can be controlled by the degree of chemical modification. The crystallinity of type I cellulose can be calculated by measuring and comparing the intensities of the (200) peak around 22.6° and the valley between (200) and (110) (around 18.5°) using X-ray diffraction. If the fine cellulose fibers contain type II crystals, it is preferable to separate the peaks based on type II crystals (around 12.3°, 20.2°, and 21.9°) before calculating the intensity of the type I crystals.

[0077] Because the fine cellulose fibers have the aforementioned degree of crystallinity, they are more likely to exert their abrasive effect when sprayed under high pressure, thereby improving the polishing, crushing, and cutting performance of the object being sprayed.

[0078] -viscosity- When fine cellulose fibers are used as an aqueous dispersion, a low viscosity of the aqueous dispersion is preferable. This allows for a material with good handling properties despite being fibrillated. For example, the B-type viscosity (25°C, 60 rpm) of an aqueous dispersion with 1% solids by mass is usually 5,000 mPa·s or less, preferably 4,500 mPa·s or less, and more preferably 4,000 mPa·s or less. The lower limit is preferably 10 mPa·s or more, more preferably 20 mPa·s or more, even more preferably 50 mPa·s or more, 100 mPa or more, 500 mPa or more, and 1,000 mPa or more. The B-type viscosity can be measured, for example, by the following method: After fibrillation (e.g., defibrillation), let it stand for at least one day, dilute as necessary, stir with a homodisperser (e.g., 3000 rpm, 5 min), and then measure the viscosity (measure the viscosity after 60 rpm, 3 minutes of rotation).

[0079] The fine cellulose fibers exhibit the viscosity described above, making it easier to achieve uniform dispersion using the high-pressure washer described later.

[0080] <Method for diluting aqueous dispersions> The present invention is a method for diluting an aqueous dispersion containing fine cellulose fibers obtained as described above using a high-pressure washer equipped with a plunger pump.

[0081] A plunger pump is a pump that changes the volume of liquid inside the pump by reciprocating a plunger (rod-shaped piston) and pushes it out to the discharge port. In the manufacturing method of the present invention, the plunger pump constitutes part of a high-pressure washer having an excess water discharge mechanism. An example of a high-pressure washer having a plunger pump that can be used in the present invention is exemplified in Japanese Patent No. 7377397. In other words, a high-pressure washer is equipped with an intake port for drawing in the dispersion liquid stored in the reservoir, a plunger pump for pressurizing the drawn-in dispersion liquid, a discharge port for discharging the high-pressure dispersion liquid, a nozzle connected to the discharge port via a discharge hose, a pressure regulating valve for adjusting the discharge pressure, and an overflow port for discharging the dispersion liquid into the reservoir when the pressure exceeds a set level, such as when the nozzle is closed. Here, an intake hose is attached to the intake port so that the dispersion liquid can be drawn in from the bottom of the reservoir. Also, an overflow hose is attached to the overflow port so that excess water from the high-pressure washer can be discharged into the reservoir.

[0082] In this invention, a pre-adjusted aqueous dispersion A of fine cellulose fibers with a solid content of 2% by mass or more, and water are added to the storage section to prepare a mixed solution B as a dispersion. The mixed solution B may be lightly stirred with a hand mixer or the like to ensure smooth intake into the high-pressure washer described later.

[0083] When the plunger pump is driven, the mixed liquid B is drawn into the high-pressure washer via the suction hose. This mixed liquid B is drawn in through the suction port of the plunger pump, pressurized within the pump, and then discharged from the discharge port of the plunger pump, via the pressure regulating valve, through the discharge port or overflow port of the high-pressure washer. When the nozzle is opened, high-pressure mixed liquid B is sprayed from the nozzle, and when the nozzle is closed, the high-pressure water is shut off. When the nozzle is closed, the pressure of mixed liquid B between the plunger pump and the pressure regulating valve increases, so the pressure regulating valve activates, and the entire amount of mixed liquid B in the plunger pump is discharged from the overflow port through the overflow hose to the storage section so that the pressure between the pressure regulating valve and the nozzle is maintained at the set pressure.

[0084] In this way, by discharging the mixed liquid B under pressure through a narrow path, the fine cellulose fibers, which are unevenly dispersed in the mixed liquid B, can be dispersed into an aqueous dispersion C with improved dispersibility without the need for stirring or other mixing.

[0085] Furthermore, for example, the water dispersion C discharged from the overflow outlet into the storage area can be taken back into the high-pressure washer by driving the plunger pump again, thereby obtaining a water dispersion D with improved dispersibility. This circulation process may be performed multiple times.

[0086] The set value for the discharge pressure (outlet pressure of the pressure regulating valve) of a high-pressure washer is not particularly limited, but from the viewpoint of efficiently improving dispersion, it is preferably 0.5 to 25 MPa, more preferably 5 to 25 MPa, and even more preferably 0.5 to 20 MPa. The discharge pressure can be controlled by the excess water discharge mechanism, and specifically, it can be done using the pressure regulating screw of the pressure regulating valve.

[0087] Furthermore, the pressure adjustment of the pressure regulating valve and other conditions can be set in accordance with Patent No. 7377397.

[0088] <Optional additives> Any additives can be used as long as they do not impair the effects of the present invention. Examples of such additives include auxiliary agents such as surfactants, binders, tackifiers, thickeners other than the water-soluble polymers mentioned above, colorants, antifreezes, desiccants, antioxidants, UV absorbers, deodorizers, pH adjusters, preservatives, attractants, emulsifiers, emulsions, film-forming agents, and gelling agents, as well as known functional agents such as pesticides, insecticides / insect repellents, fungicides, antibacterial agents, disinfectants, synergists, repellents, fungicides, antioxidants, fragrances, and herbicides. [Examples]

[0089] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the measurement / calculation methods for each numerical value in each example are those described in the specification.

[0090] (Manufacturing example 1: Carboxymethylated cellulose nanofibers) In a stirrer capable of mixing pulp, 200g of pulp (NBKP (coniferous bleached kraft pulp), manufactured by Nippon Paper Industries Co., Ltd.) by dry weight and 111g of sodium hydroxide by dry weight were added, and water was added to achieve a pulp solid content of 20% (w / v). After stirring at 30°C for 30 minutes, 216g of sodium monochloroacetate (calculated as active ingredient) was added. After stirring for 30 minutes, the temperature was raised to 70°C and stirred for 1 hour. The reaction product was then removed, neutralized, and washed to obtain carboxymethylated pulp with a carboxymethyl substitution degree of 0.25 per glucose unit. The carboxymethylated pulp was then diluted with water to a solid content of 1%, and defibrated by processing it five times in a high-pressure homogenizer at 20°C and a pressure of 150MPa to obtain carboxymethylated cellulose fibers. The obtained fibers had an average fiber diameter of 15 nm and an aspect ratio of 50.

[0091] To a 0.7 wt% aqueous suspension of the above-mentioned carboxymethylated cellulose fibers (cellulose nanofibers), carboxymethylcellulose (product name: F350HC-4, manufactured by Nippon Paper Industries Co., Ltd.) was added at a concentration of 10 wt% relative to the cellulose nanofibers, and the mixture was stirred for 60 minutes using a TK homomixer (12,000 rpm). A 0.5% aqueous sodium hydroxide solution was added to this aqueous suspension to adjust the pH to 9. The mixture was then dried in a drum dryer D0405 (manufactured by Katsuragi Industries Co., Ltd.) at a vapor pressure of 0.5 MPa.G and a drum rotation speed of 2 rpm to obtain a mixed dried solid of cellulose nanofibers and carboxymethylcellulose with a moisture content of 5 wt%. The dried solid was pulverized in a dry mill to obtain cellulose nanofiber powder.

[0092] (Manufacturing example 2: Oxidized cellulose microfibrils) 100.0 g (oven-dry) of bleached, unbeaten kraft pulp derived from coniferous trees (NBKP, manufactured by Nippon Paper Industries Co., Ltd., whiteness 85%) was added to 10,000 ml of an aqueous solution containing 780 mg of TEMPO (Sigma Aldrich) (0.05 mmol per 1 g of oven-dry cellulose) and 1280 mg of sodium bromide (1.0 mmol per 1 g of oven-dry cellulose), and the mixture was stirred until the pulp was uniformly dispersed. Sodium hypochlorite aqueous solution was added to the reaction system until the sodium hypochlorite concentration reached 5.5 mmol / g, and the oxidation reaction was started at room temperature. During the reaction, the pH of the system decreased, but 3M sodium hydroxide aqueous solution was added sequentially to adjust the pH to 10. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. Hydrochloric acid was added to the reaction mixture to adjust the pH to 2, and the mixture was filtered through a glass filter to separate the pulp. The separated pulp was thoroughly washed with water to obtain TEMPO oxidized pulp (oxidized pulp / TOP). The pulp yield at this time was 90%, the oxidation reaction took 90 minutes, the carboxyl group content was 1.37 mmol / g, and the pH was 4.5.

[0093] An aqueous dispersion of the obtained oxidized pulp with a solid content of 3.0% by mass was prepared, and after adjusting the pH to 8.0 by adding a 5% NaOH aqueous solution and sodium bicarbonate, it was treated with a Top Finer (manufactured by Aikawa Iron Works Co., Ltd.) for 10 minutes to prepare an oxidized cellulose microfibril (oxidized microfibril / T-MFC) dispersion. The obtained oxidized cellulose microfibril had a carboxyl group content of 1.37 mmol / g, cellulose type I crystallinity of 80.4%, average fiber width of 17.8 μm, average fiber length of 0.37 mm, aspect ratio of 21, specific surface area of ​​182 m2 / g, and type B viscosity (25℃ / 60 rpm / 1 wt%) of 1710 mPa·s.

[0094] (Example 1) The cellulose nanofiber powder obtained in Production Example 1 was dissolved in water to prepare a 20 L liquid composition with a cellulose nanofiber solid content of 3.0% by weight. The obtained liquid composition was placed in a tank, and 10 L of water was added to make a mixture. After lightly stirring with a hand mixer, the power of a high-pressure washer (manufactured by Arimitsu Kogyo Co., Ltd., product name: TRY high-pressure washer, model number: TRY-10200) was turned on, and the mixture from the tank was drawn into the high-pressure washer through the water intake. With the nozzle open, the mixture was discharged from the outlet into another tank. A single pass was performed at a processing rate of 18 L / min to obtain a diluted and dispersed aqueous dispersion of carboxymethylated cellulose nanofibers. The processing pressure of the high-pressure washer was set to 20 MPa.

[0095] (Example 2) A diluted and dispersed aqueous dispersion of oxidized cellulose microfibrils was obtained in the same manner as in Example 1, except that the aqueous dispersion with a solid content of 3.0% by mass obtained in Production Example 2 was used instead of the liquid composition.

[0096] (Example 3) Except for keeping the nozzle closed and discharging the mixed liquid from the excess water outlet to the first tank, and performing two passes at a processing rate of 18 L / min, a diluted and dispersed aqueous dispersion of oxidized cellulose microfibrils was obtained in the same manner as in Example 2.

[0097] (Comparative Example 1) In Example 2, a mixture of the 3.0% by mass aqueous dispersion and water was lightly stirred using a hand mixer, but no high-pressure washer treatment was performed.

[0098] (Visual evaluation of dispersibility after dilution) When the treated aqueous dispersions obtained in Examples 1-3 and Comparative Example 1 were collected in a transparent 500 ml beaker and visually inspected, the aqueous dispersion in Comparative Example 1 showed that the fine cellulose fibers had formed clumps and were not properly dispersed, while the aqueous dispersions in Examples 1-3 showed no clumps and were uniformly dispersed.

Claims

1. A method for diluting an aqueous dispersion of fine cellulose fibers, After preparing a mixed solution B by adding water to an aqueous dispersion A containing fine cellulose fibers at a solid content concentration of 1% by mass or more in the storage area, The mixture B stored in the storage section is taken in through the water intake of a plunger pump, which is part of the high-pressure washer, via the water intake of the high-pressure washer having an excess water discharge mechanism consisting of a pressure regulating valve, and discharged from the discharge port or excess water port of the plunger pump. A method for diluting a fine cellulose fiber aqueous dispersion, which provides an aqueous dispersion C in which the dispersibility of fine cellulose fibers, which are in a non-uniform dispersion state in mixed solution B, is improved.

2. The method for diluting a fine cellulose fiber aqueous dispersion according to claim 1, characterized in that the outlet pressure of the pressure regulating valve controlled by the pressure regulating valve of the high-pressure washer is 0.5 to 25 MPa.

3. A method for diluting an aqueous dispersion of fine cellulose fibers according to any one of claims 1 to 2, characterized in that the solid content concentration of fine cellulose fibers in the aqueous dispersion C is 0.1 to 10.0% by weight.

4. A method for diluting an aqueous dispersion of fine cellulose fibers according to any one of claims 1 to 2, characterized in that the fine cellulose fibers are chemically modified.

5. A method for diluting a fine cellulose fiber aqueous dispersion according to any one of claims 1 to 2, characterized in that the aqueous dispersion C is further taken in from the water intake port of the high-pressure washer and discharged from the discharge port to obtain an aqueous dispersion D in which the dispersibility of fine cellulose is further improved compared to the aqueous dispersion C.

6. A diluted product of an aqueous dispersion of fine cellulose fibers, obtained by diluting using any of the dilution methods of claims 1 to 5.