Cellulose microfiber dried product and method for producing same

Abstract

To provide a cellulose microfiber dried product containing a polyacrylate or polyacrylic acid, the cellulose microfiber dried product being capable of suppressing aggregation of cellulose microfibers during drying and maintaining thixotropy upon redispersion.SOLUTION: There are provided a cellulose microfiber dried product containing cellulose microfibers and a polyacrylate or polyacrylic acid having an average molecular weight of 100,000 or more, and a method for producing the cellulose microfiber dried product.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dried cellulose fine fiber material and a method for producing the same. [Background technology]

[0002] The present invention relates to cellulose fine fibers. Cellulose fine fibers have a fiber diameter of approximately 2 to several hundred nanometers and are highly dispersible in aqueous systems. They are expected to be used for maintaining the viscosity of foods, cosmetics, medical products, paints, etc., strengthening food raw material dough, retaining moisture, improving food stability, and as a low-calorie additive or emulsion stabilizing aid. However, when cellulose fine fibers dispersed in water (wet state) are dried to form a dry solid, hydrogen bonds are formed between the cellulose fine fibers. Even if water is added to this dry solid to redisperse it, various properties such as solubility, dispersibility, sedimentation rate, and viscosity do not return to those before drying (wet state). For this reason, cellulose fine fibers are produced in a water-dispersed state (wet state) and are typically used for various purposes in the wet state without drying. However, to stably maintain cellulose fine fibers in this wet state, water is required in an amount several to several hundred times the mass of the cellulose fine fibers, which poses various problems, such as the need for storage space and increased storage and transportation costs. To solve this problem, methods have been proposed for drying and powdering cellulose fine fibers to prevent aggregation during drying, such as freeze-drying, critical point drying, a method of drying after substitution treatment with an organic solvent, a method using a dispersant, etc. Patent Document 1 describes a dried solid of anion-modified cellulose nanofibers, which is characterized by containing 5 to 300% by mass of a water-soluble polymer such as CMC relative to the anion-modified cellulose nanofibers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 107995 Summary of the Invention [Problem to be solved by the invention]

[0004] Various dispersants have been investigated for the dry powdering of cellulose microfibers, but there has been a demand for a dispersant that does not impair the properties of the original cellulose microfibers as much as possible even after drying. In particular, thixotropy, the property of viscosity decreasing when stirred and returning to normal when left standing, is one of the characteristics of cellulose microfibers, which do not dissolve in water and maintain their fibrous shape, and have structural viscosity. However, the problem with existing dispersants such as CMC is that the thixotropy is significantly reduced.

[0005] The present invention relates to a dried cellulose fine fiber body, and in particular, an object of the present invention is to provide a dried cellulose fine fiber body containing cellulose fine fibers and a polyacrylate or polyacrylic acid, which suppresses aggregation of the cellulose fine fibers during drying and does not impair thixotropy even when redispersed. [Means for solving the problem]

[0006] As a result of intensive research into achieving the above object, the present inventors have found that the problem can be solved by providing a dried cellulose fine fiber product containing cellulose fine fibers and a polyacrylate or polyacrylic acid having an average molecular weight of 100,000 or more. The present invention also provides a method for producing a dried cellulose fine fiber product. The present invention also provides a dried cellulose fine fiber product characterized by containing 30 to 100 parts by mass of the polyacrylate or polyacrylic acid per 100 parts by mass of cellulose fine fibers.

[0007] The present invention provides the following: [1] A dried cellulose fine fiber body comprising cellulose fine fibers and a polyacrylate or polyacrylic acid having an average molecular weight of 100,000 or more. [2] The dried cellulose fine fibers according to [1], characterized in that the polyacrylate or polyacrylic acid is contained in an amount of 30 to 100 parts by mass per 100 parts by mass of the cellulose fine fibers. [3] The dried cellulose fine fibers according to [1] to [2], wherein the polyacrylate is a sodium salt. [4] The dried cellulose fine fiber material according to [1] to [2], wherein the cellulose fine fiber is anion-modified cellulose fine fiber. [5] The dried cellulose fine fibers according to [1] to [2], wherein the cellulose fine fibers are oxidized cellulose fine fibers and have a carboxy group content of 1.0 to 2.0 mmol / g. [6] A method for producing dried cellulose fine fibers, characterized by adding 30 to 100 parts by mass of a polyacrylate or polyacrylic acid having an average molecular weight of 100,000 or more to 100 parts by mass of cellulose fine fibers, followed by drying and pulverizing. [Effects of the Invention]

[0008] According to the present invention, the functionality of cellulose fine fibers can be improved by using a dried cellulose fine fiber material containing cellulose fine fibers and a polyacrylate or polyacrylic acid having an average molecular weight of 100,000 or more. Furthermore, this configuration can provide a dried cellulose fine fiber material containing cellulose fine fibers and a polyacrylate or polyacrylic acid that suppresses aggregation of cellulose fine fibers during drying and does not impair thixotropy even when redispersed. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in detail below. In the present invention, "to" includes the extreme values. That is, "X to Y" includes the values ​​X and Y at both ends.

[0010] The present invention includes at least cellulose fine fibers and a polyacrylate or polyacrylic acid having an average molecular weight of 100,000 or more. Each raw material will be described below.

[0011] (cellulose microfibers) Cellulose microfibers are fine fibrous cellulose derived from cellulose raw materials. Examples of fine fibrous cellulose include those whose dispersion (1 wt%) of cellulose microfibers exhibits a light transmittance of 1 to 99% at an optical path length of 1 cm / 660 nm using a visible spectrophotometer (UV-1800, manufactured by Shimadzu Corporation). The average fiber diameter of cellulose microfibers is not particularly limited, but is typically approximately 1 nm to 60 μm. Methods for producing cellulose microfibers include a method of defibrating pulp and, if necessary, a method of chemically modifying the pulp before or after defibration (usually before defibration). Cellulose microfibers with a nanometer-order fiber diameter are called cellulose nanofibers (cellulose microfibers), and cellulose microfibers with a micrometer-order fiber diameter are called cellulose microfibrils (MFC). The size of cellulose microfibers can be adjusted by the conditions of the micronization treatment and chemical modification treatment.

[0012] (Example of cellulose microfiber: cellulose nanofiber (cellulose microfiber)) In this specification, cellulose fine fibers refer to cellulose fibers having a fiber diameter on the nano-order (for example, less than 500 nm) that are prepared through a micronization treatment.

[0013] The average fiber diameter (length-weighted average fiber diameter) of the cellulose fine fibers is 500 nm or less, preferably 300 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. There is no particular lower limit, but it is usually 1 nm or more, preferably 2 nm or more. Therefore, the average fiber diameter (length-weighted average fiber diameter) of the cellulose fine fibers is usually 1 to 500 nm or 2 to 500 nm, preferably 2 to 300 nm or 2 to 100 nm, and more preferably 2 to 50 nm or 3 to 30 nm. The average fiber length (length-weighted average fiber length) is usually 5 μm or less, preferably 3 μm or less, 2 μm or less, or 1 μm or less. The lower limit is usually 50 nm or more, preferably 100 nm or more. The aspect ratio of the cellulose fine fibers is usually 10 or more, preferably 50 or more. There is no particular upper limit, but it is usually 1,000 or less.

[0014] In this specification, the average fiber diameter and average fiber length of cellulose fine fibers can be measured by analyzing 200 randomly selected fibers using an atomic force microscope (AFM) if the average fiber diameter is less than 20 nm, or by analyzing 200 randomly selected fibers using a field emission scanning electron microscope (FE-SEM) if the average fiber diameter is 20 nm or more, and calculating the average. The average aspect ratio of cellulose fine fibers can be calculated using the formula: average aspect ratio = average fiber length / average fiber diameter.

[0015] (Example of cellulose fine fibers: Microfibrillated cellulose (MFC)) As used herein, cellulose microfibrils (microfibrillated cellulose, MFC) refer to cellulose fibers having a fiber diameter on the micron order (for example, 500 nm or greater) that are prepared through a pulverization process.

[0016] The average fiber diameter of MFC is usually 500 nm or more, preferably 1 μm or more, and more preferably 3 μm or more. This allows it to exhibit higher water retention than undefibrated cellulose fibers and improves yield compared to finely defibrated cellulose fine fibers. 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 is no particular limit. The average fiber length is usually 5 μm or more, 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, it is 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 1,000 or less, more preferably 100 or less, and even more preferably 80 or less.

[0017] (cellulose raw material) Cellulose fine fibers can be produced by defibrating a cellulose raw material. The cellulose raw material is not particularly limited as long as it contains cellulose, and examples thereof include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (e.g., unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), bleached kraft pulp (BKP), unbleached softwood sulfite pulp (NUSP), bleached softwood sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., ascidians), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, and the like. The cellulose raw material may be any one of these or a combination of two or more types. However, a cellulose raw material (e.g., cellulose fiber) derived from a plant or a microorganism is preferred, and a cellulose raw material (e.g., cellulose fiber) derived from a plant is more preferred.

[0018] (anion-modified) The cellulose fine fibers may be modified or unmodified. Modified cellulose fine fibers refer to cellulose fine fibers (e.g., cellulose fine fibers, MFC) in which at least one of the three hydroxyl groups contained in the glucose unit has been chemically modified (hereinafter simply referred to as "modified"). Chemical modification treatment generates electronic repulsion between the microfibrils of the cellulose fibers, which allows sufficient pulverization during defibration, resulting in the production of cellulose fine fibers. From this perspective, modified cellulose fibers, especially anion-modified cellulose fibers, are preferred.

[0019] The number average fiber diameter of the cellulose raw material is not particularly limited, but is about 30 to 60 μm for softwood kraft pulp, which is a common pulp, and about 10 to 30 μm for hardwood kraft pulp. Other pulps that have undergone general refinement have a diameter of about 50 μm. For example, when chips or other pulps several centimeters in size are refined, they are preferably mechanically treated with a disintegrator such as a refiner or beater to be adjusted to about 50 μm.

[0020] Examples of anionic modification include oxidation, etherification, esterification such as phosphate esterification, etc. Among these, oxidation (carboxylation), etherification, cationization, and esterification are preferred, and oxidation (carboxylation) is more preferred.

[0021] -Carboxylation (oxidation)- Oxidized cellulose fine fibers usually have a structure in which at least one of the carbon atoms having a primary hydroxyl group contained in the glucopyranose unit constituting the cellulose molecular chain (for example, the carbon atom having a primary hydroxyl group at the C6 position) is oxidized. The amount of carboxyl groups in the oxidized cellulose fibers or oxidized cellulose fine fibers is preferably 1.0 mmol / g or more, more preferably 1.3 mmol / g or more, based on the bone dry mass. The upper limit of this amount is preferably 2.0 mmol / g or less, more preferably 1.8 mmol / g or less. The amount of carboxyl groups can be adjusted by controlling the conditions for oxidizing the cellulose raw material (for example, the amount of oxidizing agent added and the reaction time). Furthermore, the amounts of carboxylate groups and aldehyde groups can also be adjusted by controlling these conditions.

[0022] 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 aqueous hydrochloric acid to the prepared slurry to adjust the pH to 2.5. Next, add 0.05 N aqueous sodium hydroxide solution dropwise and measure the electrical conductivity until the pH reaches 11. Calculate the amount of carboxyl groups using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid, where the change in electrical conductivity is gradual: Amount of carboxyl groups [mmol / g oxidized cellulose] = a [ml] x 0.05 / mass of oxidized cellulose [g]

[0023] The oxidation method is not particularly limited, but one example is a method in which a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a bromide, iodide, or a mixture thereof. This method selectively oxidizes the C6 position of the glucopyranose ring on the cellulose surface, generating at least one group selected from the group consisting of an aldehyde group, a carboxy group (-COOH), and a carboxylate group (-COO-). The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by mass or less.

[0024] The term "N-oxyl compound" refers to a compound capable of generating a nitroxy radical. Examples of nitroxy radicals include 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO). Any compound that promotes the target oxidation reaction can be used as the N-oxyl compound.

[0025] The amount of N-oxyl compound used is not particularly limited as long as it is a catalytic amount that can oxidize the raw cellulose. For example, about 0.001 to 5 mmol, preferably 0.01 to 1 mmol, and more preferably 0.01 to 0.5 mmol can be used per 1 g of bone dry cellulose raw material. Also, about 0.02 to 0.5 mmol / L of the reaction system is preferable.

[0026] 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 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 raw material.

[0027] Known oxidizing agents can be used, such as halogens, hypohalous acids, halous acids, perhalogen acids or their salts, halogen oxides, and peroxides. Among these, hypohalous acids or their salts are preferred due to their low cost and low environmental impact, hypochlorous acid or its salts are more preferred, and sodium hypochlorite is preferred. The appropriate amount of oxidizing agent used is, for example, preferably 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 bone-dry cellulose raw material. Furthermore, for example, 2 to 500 mol is preferred per 1 mol of the N-oxyl compound.

[0028] 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 may also be about 15 to 30°C, i.e., room temperature. As the reaction proceeds, carboxyl groups are generated in the cellulose, causing a decrease in the pH of the reaction solution. To ensure efficient 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, or 10 to 11. Water is preferred as the reaction medium because it is easy to handle and does not easily cause side reactions.

[0029] The reaction time in the oxidation reaction can be appropriately set depending on the degree of progress of the oxidation, and is usually from 0.5 to 6 hours, for example, about 0.5 to 4 hours.

[0030] The oxidation reaction may 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, thereby enabling efficient oxidation without reaction inhibition by sodium chloride, which is a by-product of the first stage reaction.

[0031] Another example of a carboxylation (oxidation) method is ozone oxidation, which involves contacting a cellulose raw material with an ozone-containing gas to oxidize it. 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 preferably 50 to 250 g / m3, more preferably 50 to 220 g / m3. The amount of ozone added is preferably 0.1 to 30 parts by mass, 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, more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is approximately 1 to 360 minutes, preferably approximately 30 to 360 minutes. When the ozone treatment conditions are within these ranges, excessive oxidation and decomposition of the cellulose raw material can be prevented, resulting in a good yield of oxidized cellulose.

[0032] After the ozone treatment, a further oxidation treatment may be carried out using an oxidizing agent. The oxidizing agent used in the further oxidation treatment is not particularly limited, but examples include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. The further oxidation treatment may be carried out, for example, by dissolving the oxidizing agent 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.

[0033] -Etherification- Examples of etherification include carboxyalkylation, methylation, ethylation, cyanoethylation, hydroxyethylation, hydroxypropylation, ethylhydroxyethylation, and hydroxypropylmethylation, with carboxyalkylation being preferred and carboxymethylation being more preferred.

[0034] Carboxyalkylated cellulose fibers usually have a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is carboxymethylated.

[0035] The degree of carboxyalkyl substitution (DS, preferably the degree of carboxymethyl substitution) per anhydroglucose unit of the carboxyalkylated cellulose is preferably 0.01 or more, 0.02 or more, or 0.05 or more, more preferably 0.10 or more, even more preferably 0.15 or more, even more preferably 0.20 or more, and particularly preferably 0.25 or more. This ensures a degree of substitution sufficient to obtain the effects of chemical modification. The upper limit of the degree of substitution is preferably 0.50 or less, more preferably 0.45 or less, 0.40 or less, or 0.35 or less. This makes it difficult for the cellulose fibers to dissolve in water, allowing 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, even more preferably 0.02 to 0.40, 0.10 to 0.35, or 0.15 to 0.30.

[0036] The degree of carboxyalkyl substitution, e.g., the degree of carboxymethyl substitution, can be measured by the following method. Approximately 2.0 g of carboxymethylated cellulose (bone dry) is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution of 1,000 mL of methanol and 100 mL of concentrated nitric acid is added, and the mixture is shaken for 3 hours to convert the salt-form carboxymethylated cellulose (hereinafter also referred to as "salt-form carboxymethylated cellulose") to the acid-form carboxymethylated cellulose (hereinafter also referred to as "acid-form carboxymethylated cellulose"). 1.5 to 2.0 g of acid-form carboxymethylated cellulose (bone dry) is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. The acid-form carboxymethylated 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, excess NaOH is back-titrated with 0.1 N H2SO4, and the degree of carboxymethyl substitution (DS) can be calculated using the following formula: A = [(100 × F - (0.1N H2SO4 (mL)) × F') × 0.1] / (bone-dry mass of acid-form carboxymethyl cellulose (g)) DS=0.162×A / (1-0.058×A) A: The amount of 1N NaOH (mL) required to neutralize 1 g of acid-type carboxymethyl cellulose F': Factor of 0.1N H2SO4 F: Factor of 0.1N NaOH

[0037] The degree of carboxyalkyl substitution can be adjusted by controlling the reaction conditions such as the amount of carboxyalkylating agent to be reacted, the amount of mercerizing agent, and the composition ratio of water to organic solvent.

[0038] An example of a carboxyalkylation method is a method in which a cellulose raw material as a starting material (bottom raw material) is mercerized and then etherified. Carboxymethylation will be explained below as an example.

[0039] Carboxymethylated cellulose can be produced by using unmodified cellulose fibers (cellulose raw material: for example, pulp) as the starting material, subjecting them to a mercerization treatment with a mercerizing agent, followed by an etherification reaction. This reaction is typically carried out in the presence of a solvent. Examples of the solvent include water and lower alcohols (e.g., methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and tertiary butanol), either singly or in combination. When a lower alcohol is added, the mixing ratio of the lower alcohol is preferably 60 to 95% by mass. The amount of the solvent is approximately three times the amount of the cellulose raw material, calculated by mass. The upper limit of this amount is not particularly limited, but is preferably 20 times or less. The amount of the solvent is preferably 3 to 20 times the amount of the cellulose raw material, calculated by mass.

[0040] Examples of mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of mercerizing agent used, in molar terms, is preferably 0.5 times or more, more preferably 1.0 times or more, and even more preferably 1.5 times or more per anhydroglucose residue of the starting material. 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, in molar terms, is preferably 0.5 to 20 times, more preferably 1.0 to 10 times, and even more preferably 1.5 to 5 times.

[0041] The reaction temperature for mercerization 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 mercerization is usually 15 minutes or longer, preferably 30 minutes or longer. The upper limit is usually 8 hours or shorter, preferably 7 hours or shorter. The reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

[0042] The etherification reaction is usually carried out by adding a carboxymethylating agent, such as sodium monochloroacetate, to the reaction system after mercerization.

[0043] The amount of the carboxymethylating agent added is, in molar terms, preferably 0.05 times or more, more preferably 0.5 times or more, and even more preferably 0.8 times or more, per glucose residue of the cellulose raw material. 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 the carboxymethylating agent added is, in molar terms, preferably 0.05 to 10.0 times, more preferably 0.5 to 5 times, and even more preferably 0.8 to 3 times.

[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 longer, preferably 1 hour or longer. The upper limit is usually 10 hours or shorter, preferably 4 hours or shorter. 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 carboxymethyl cellulose- Carboxyalkylated cellulose fibers typically maintain at least a portion of their fibrous shape when dispersed in water. Carboxyalkylated cellulose fibers are distinct from carboxymethyl cellulose, a type of water-soluble polymer that dissolves in water and imparts viscosity. When aqueous dispersions of carboxyalkylated cellulose fibers are observed under an electron microscope, fibrous substances can be observed. On the other hand, when aqueous dispersions of carboxymethyl cellulose, a type of water-soluble polymer, are observed, fibrous substances are usually not observed. Furthermore, when anion-modified cellulose fibers are measured by X-ray diffraction, peaks of cellulose type I crystals can be observed, but when carboxymethyl cellulose powder, a water-soluble polymer, is similarly measured, cellulose type I crystals are usually not observed.

[0046] -Esterification (phosphate esterification)- A first example of an esterified cellulose fiber is phosphorylated cellulose fiber. Phosphorylated cellulose usually has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing the primary hydroxyl group at C6 constituting the glucopyranose unit) is phosphorylated.

[0047] The amount of ionic substituents introduced into the phosphated cellulose fibers (ionic substituent amount, phosphorus oxo acid substituent amount) per gram (mass) of phosphated cellulose fine fiber cellulose fibers should be 0.10 mmol / g or more, preferably 0.20 mmol / g or more, more preferably 0.30 mmol / g or more, even more preferably 0.40 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably 0.60 mmol / g or more, and particularly preferably 0.70 mmol / g or more. The amount of ionic substituents introduced into the phosphated cellulose fine fiber cellulose fibers should be 1.50 mmol / g or less, preferably 1.35 mmol / g or less, more preferably 1.20 mmol / g or less, and even more preferably 1.10 mmol / g or less per gram (mass) of cellulose fibers. The amount of ionic substituents introduced into the phosphated cellulose fiber is preferably 1.00 mmol / g or less, and more preferably 0.95 mmol / g or less, per gram (mass) of phosphated cellulose fiber. Here, the denominator in the unit mmol / g indicates the mass of the cellulose fiber when the counter ion of the ionic substituent is a hydrogen ion (H+). The amount of phosphorus oxo acid substituents can be measured by the following method.

[0048] The amount of phosphorus oxoacid groups in the cellulose fine fibers can be measured by treating a cellulose fiber-containing slurry with an ion exchange resin after diluting a cellulose fine fiber dispersion containing the target cellulose fine fibers with ion exchange water to a content of 0.2 mass% and then titrating the slurry with an alkali.

[0049] Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above cellulose fiber-containing slurry, shaking for 1 hour, and then pouring it onto a mesh with 90 μm openings to separate the resin from the slurry.

[0050] In addition, alkali titration was performed by measuring the change in the pH of the slurry after ion exchange resin treatment while adding 10 μL of 0.1 N sodium hydroxide solution every 5 seconds. Nitrogen gas was bubbled through the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the derivative of pH with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. The first maximum point of increment after starting the alkali addition is called the first endpoint, and the second maximum point is called the second endpoint. The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used for titration. The amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first endpoint was divided by the solid content (g) in the slurry to be titrated to determine the amount of phosphorus oxoacid groups (mmol / g). The introduction of phosphate groups may be confirmed by measuring infrared absorption spectroscopy to confirm absorption due to phosphate groups (near 1230 cm).

[0051] The amount of phosphate groups can be adjusted by controlling the reaction conditions such as the amount of the compound having a phosphate group added and the amount of the basic compound added as needed.

[0052] Examples of phosphorylation methods include reacting unmodified cellulose fibers with a compound having a phosphate group (phosphorylation). 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 (solids 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 the cellulosic raw material, with the latter being preferred. This can improve the uniformity of the reaction and the efficiency of esterification. The pH of the aqueous solution of the compound having a phosphate group is preferably 7 or less to increase the efficiency of introducing the phosphate group, and more preferably 3 to 7 to suppress hydrolysis.

[0053] Examples of compounds having a phosphate group include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters and salts thereof. These compounds are low-cost and easy to handle, and can be used to introduce phosphate groups into cellulose, thereby improving defibration efficiency. Specific examples of compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate. One or more compounds having a phosphate group can be used in combination. The amount of the compound having 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 elemental phosphorus, per 100 parts by mass of the solid content of the cellulose raw material. This allows for efficient production of a yield commensurate with the amount of compound having a phosphate group used. 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. When reacting a compound having a phosphate group, a basic compound (e.g., a compound having a basic amino group such as urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, or hexamethylenediamine) may be further added to the reaction system.

[0054] The suspension obtained after esterification is preferably dehydrated as needed, and then subjected to a heat treatment after dehydration. This can suppress hydrolysis of the cellulose raw material. The heating temperature is preferably 100 to 170°C. During the heat treatment, while water is still present, it is more preferable to heat at 130°C or lower (preferably 110°C or lower), and after removing the water, to perform a heat treatment at 100 to 170°C. After boiling, it is preferable to perform a washing treatment such as washing with cold water and / or a neutralization treatment. This allows for efficient defibration. Washing can be performed by adding water and then dehydrating (for example, filtration), and may be repeated two or more times. Washing is preferably performed until the electrical conductivity of the filtrate decreases. For example, it can be performed until the electrical conductivity is preferably 200 or lower, more preferably 150 or lower, and even more preferably 120 or lower. Furthermore, after washing, a neutralization treatment may be performed as needed. The neutralization treatment can be performed by adding an alkali (e.g., sodium hydroxide), for example. Washing may be performed again after neutralization.

[0055] -Esterification (phosphite 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 of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is phosphorous-substituted.

[0056] The degree of substitution of phosphite groups per glucose unit in phosphite-esterified cellulose fibers (hereinafter simply referred to as "phosphite group substitution degree") is preferably 0.001 to 0.60. This facilitates electrical repulsion between cellulose molecules, 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 substitution of phosphite groups can be adjusted by controlling reaction conditions such as the amount of phosphorous acid or its salt added, and the amount of alkali metal ion-containing material, urea, or its derivative added as needed.

[0057] As a method for phosphite esterification, for example, a method in which phosphorous acid or a metal salt thereof (preferably sodium hydrogen phosphite) is reacted with unmodified cellulose fibers to introduce an ester group of phosphorous acid can be mentioned.

[0058] 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, as well as combinations of two or more selected from these compounds, with sodium hydrogen phosphite being preferred. This allows alkali metal ions to be introduced into the cellulose fibers. The amount of phosphorous acid or its metal salts 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 kg of unmodified cellulose fibers. In addition to phosphorous acid and its metal salts, an alkali metal ion-containing substance (e.g., hydroxide, metal sulfate, metal nitrate, metal chloride, metal phosphate, or metal carbonate) may also be added to the reaction system.

[0059] Urea or a derivative thereof may also 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 combinations of two or more selected from these, with urea being preferred. The amount of urea and urea derivative 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 mol of phosphorous acid or its metal salt.

[0060] The reaction temperature is preferably 100 to 200°C, more preferably 100 to 180°C, and even more preferably 100 to 170°C. During the heat treatment, while water is still present, it is more preferable to heat at 130°C or lower (preferably 110°C or lower), and after removing the water, to heat treat at 100 to 170°C. The reaction time is usually about 10 to 180 minutes, more preferably 30 to 120 minutes. The phosphite-esterified cellulose fiber is preferably washed prior to defibration. The degree of substitution of phosphite groups per glucose unit is preferably 0.01 or higher and less than 0.23.

[0061] -Esterification (sulfuric acid esterification)- A third example of a method for producing an esterified cellulose fiber is a sulfated cellulose fiber. Cellulose sulfate usually has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing the primary hydroxyl group at C6 constituting the glucopyranose unit) is phosphorylated.

[0062] The amount of sulfate groups per glucose unit in sulfated cellulose fibers (hereinafter simply referred to as "sulfate group amount") is preferably 0.42 to 9.9 mmol / g, more preferably 0.5 mmol / g to 2.0 mmol / g. Introducing sulfate groups into the cellulose raw material causes electrical repulsion between cellulose molecules. Therefore, sulfated cellulose with sulfate groups introduced can be easily defibrated to nanometer size. When the amount of sulfate groups is 0.42 mmol / g or more, sufficient nanometer size defibration can be achieved due to electrical repulsion between cellulose molecules. On the other hand, when the amount is 9.9 mmol / g or less, swelling or dissolution can be suppressed, preventing a situation in which nanofiber cellulose fine fibers cannot be obtained. For efficient defibration, it is preferable to wash the sulfated cellulose obtained above.

[0063] The amount of sulfate groups per glucose unit can be measured by the following method. An aqueous dispersion of sulfated cellulose fine fiber cellulose fiber is solvent-substituted with ethanol and then t-butanol, and then freeze-dried. 15 ml of ethanol and 5 ml of water are added to 200 mg of the obtained sample and stirred for 30 minutes. 10 ml of 0.5 N aqueous sodium hydroxide solution is then added, and the mixture is stirred at 70°C for 30 minutes, and then at 30°C for a further 24 hours. Phenolphthalein is then added as an indicator, and the mixture is titrated with hydrochloric acid, and the amount of sulfate groups per glucose unit is calculated using the following formula: Amount of sulfate group [mmol / g sample] = (5 - (0.1 × titration amount of hydrochloric acid [ml] × 2)) / 0.2

[0064] The amount of sulfate groups can be adjusted by controlling the reaction conditions such as the amount of sulfate compound added to the reaction mixture.

[0065] An example of a method for sulfate esterification is a method in which unmodified cellulose fibers are reacted with a sulfate compound to introduce sulfate groups derived from the sulfate compound into cellulose to produce sulfated cellulose. Examples of sulfate compounds include sulfuric acid, sulfamic acid, chlorosulfonic acid, sulfur trioxide, and esters or salts thereof. Among these, sulfamic acid is preferred because it has low cellulose solubility and low acidity.

[0066] For example, when sulfamic acid is used as the sulfate compound, the amount of sulfamic acid used can be appropriately adjusted taking into consideration the amount of anionic groups introduced into the cellulose chain, and is preferably 0.01 to 50 mol, more preferably 0.1 to 3.0 mol per mol of glucose unit in the cellulose molecule.

[0067] [Fineness (defibration, fibrillation)] The defibration process, which is a process for reducing the diameter of cellulose fibers, is carried out by mechanical treatment, which is usually carried out in a wet state (i.e., in the form of an aqueous dispersion of cellulose fibers). Examples of equipment used for mechanical treatment include equipment capable of imparting mechanical defibration force, such as refiners (e.g., disc-type, conical-type, and cylindrical-type), high-speed defibrators, shear-type agitators, colloid mills, high-pressure jet dispersers, beaters, PFI mills, kneaders, dispersers, high-speed disintegrators (top finers), high-pressure or ultra-high-pressure homogenizers, grinders (stone-type grinders), ball mills, vibration mills, bead mills, single-screw, twin-screw, or multi-screw kneaders / extruders, homomixers operating at high speed, refiners, defibrators, friction grinders, high-shear defibrators, dispergers, and homogenizers (e.g., microfluidizers), and are not particularly limited. Equipment capable of imparting defibration force in a wet manner is preferred, and high-speed disintegrators, refiners, and ultra-high-pressure homogenizers are more preferred. For efficient defibration, an apparatus capable of applying a pressure of preferably 50 MPa or more, more preferably 100 MPa or more, and even more preferably 140 MPa or more, and of applying a strong shear force to the aqueous dispersion is preferred. The mechanical treatment may be carried out using two or more apparatuses. For example, prior to the defibration and dispersion treatment using a high-pressure homogenizer, a preliminary treatment may be carried out as necessary using a mixing, stirring, emulsifying, and dispersing apparatus such as a high-speed shear mixer. The number of treatments (passes) through the apparatus may be one or two or more times, with two or more being preferred.

[0068] When defibration is performed by a wet method, a dispersion of cellulose fibers is usually prepared. The solvent in the dispersion may be any solvent capable of dispersing cellulose, such as water, an organic solvent (e.g., a hydrophilic organic solvent such as methanol), or a mixture thereof. Water is preferred because the cellulose raw material is hydrophilic. The solids concentration of the modified cellulose in the dispersion is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and even more preferably 1.0% 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 treatment, pH adjustment may be performed as necessary.

[0069] Prior to preparing a dispersion for defibration, pretreatment such as dry pulverization (e.g., pulverization after drying) or hydrophobicity impartation may be performed. Examples of equipment used for dry pulverization include, but are not limited to, impact mills such as hammer mills and pin mills, media mills such as ball mills and tower mills, and jet mills. Furthermore, post-treatment may be performed after defibration. Examples of post-treatment include, but are not limited to, drying (e.g., freeze drying, spray drying, tray drying, drum drying, belt drying, thin spreading on a glass plate or the like and drying, fluidized bed drying, microwave drying, heated fan-type reduced pressure drying, and reduced pressure (degassing) drying), re-dispersion in water (the dispersion device is not limited), and pulverization (e.g., pulverization using equipment such as a cutter mill, hammer mill, pin mill, or jet mill). Hydrophobicity can be imparted using a cationic additive.

[0070] [Physical properties of fine cellulose fibers] -viscosity- It is preferable that the viscosity of the aqueous dispersion of microfibrillated cellulose fibers is low. This allows the material to be easily handled despite being fibrillated. For example, the Brookfield viscosity (25°C, 60 rpm) of an aqueous dispersion of microfibrillated cellulose fibers with a solids content of 1.0% by mass is usually 6,000 mPa·s or less or 5,000 mPa·s or less, preferably 3,500 mPa·s or less, and more preferably 2,300 mPa·s or less. The lower limit is preferably 10 mPa·s or more, more preferably 20 mPa·s or more, and even more preferably 50 mPa·s or more, 100 mPa or more, 500 mPa or more, 1,000 mPa or more, or 1,500 mPa or more. Furthermore, for example, the Brookfield viscosity (25°C, 6 rpm) of an aqueous dispersion with a solids content of 1% by mass is typically 25,000 mPa·s or less or 20,000 mPa·s or less, preferably 18,000 mPa·s or less, and more preferably 15,000 mPa·s or less. The lower limit is preferably 100 mPa·s or more, more preferably 500 mPa·s or more, and even more preferably 1,000 mPa·s or more, 2,000 mPa or more, 3,000 mPa or more, 4,000 mPa or more, or 5,000 mPa or more. The Brookfield viscosity can be measured using a Brookfield viscometer (for example, manufactured by Eiko Seiki Co., Ltd.).

[0071] -Transparency- The transparency of a cellulose fine fiber aqueous dispersion with a solid content of 1.0% by mass is usually 40% or more, preferably 50% or more, and more preferably 60% or more. There is no particular upper limit, as long as it is 100% or less. The transparency of a MFC aqueous dispersion with a solid content of 1.0% by mass is usually 1% or more, preferably 5% or more. The upper limit is 50% or less. The transparency can be measured as the transmittance of 660 nm light using a visible light photometer.

[0072] -Crystallization of cellulose type I- The crystallinity of cellulose type I in fine cellulose fibers is usually 50% or more, preferably 60% or more. There is no particular upper limit, but in reality it is thought to be around 90%. The crystallinity of cellulose can be controlled by the degree of chemical modification. The crystallinity of cellulose type I 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°) in X-ray diffraction measurements.

[0073] -Degree of polymerization- The degree of polymerization of the fine cellulose fibers, as measured by a viscosity method using a copper ethylenediamine solution, is preferably in the range of 250 to 1000, more preferably 300 to 900, and even more preferably 350 to 800. Within such a range, the viscosity does not become too high when the fine cellulose fibers are mixed with a rubber component, making them easy to disperse, and as a rubber reinforcing material, the fine cellulose fibers can form a network structure in the rubber, thereby maintaining sufficient strength.

[0074] The degree of polymerization according to the viscosity method using a copper ethylenediamine solution can be calculated by the following method: In the case of TEMPO-oxidized fine cellulose fibers, a reduction treatment is first performed. NaBH4 is added to a 1% aqueous dispersion of fine cellulose fibers at 10 wt% relative to the fine cellulose fibers, and the mixture is adjusted to pH 10 with NaOH. The mixture is then stirred for 4 hours for a reduction treatment. Ethanol is then added and centrifuged, after which the supernatant is discarded and ethanol is added again, stirred, and centrifuged. This process is repeated three times to recover the fine cellulose fibers, yielding reduced, TEMPO-oxidized fine cellulose fibers.

[0075] Freeze-dry the fine cellulose fibers and dissolve them in 0.5M copper ethylenediamine solution 1 to form solution 2. Measure the viscosities of solutions 1 and 2 using a capillary viscometer (Cannon-Fenske viscometer). Using the viscosity of solution 2 as η and the viscosity of solution 1 as η0, calculate the intrinsic viscosity [η] of the anion-modified pulp using the following formula:

[0076] Intrinsic viscosity [η]=(η / η0) / {c(1+0.28×η / η0)} (c is the concentration of fine cellulose fiber (g / dL)) Furthermore, the degree of polymerization DP is calculated by the following formula. Degree of polymerization DP=intrinsic viscosity [η] / (5.7×10 -3 )

[0077] The fine cellulose fibers may be of one type, or may be a combination of two or more types of fine cellulose fibers that are different in cellulose raw material, chemically modified or not, and of different types.

[0078] (Polyacrylates, Polyacrylic Acids) In the present invention, the dried cellulose fine fibers contain polyacrylate or polyacrylic acid. The polyacrylate or polyacrylic acid acts as a dispersant. Examples of polyacrylates include sodium salts and potassium salts, with sodium salts being particularly preferred. According to the present invention, since it has the above-mentioned configuration, it is possible to provide a dried cellulose fine fiber product in which the polyacrylate or polyacrylic acid having a molecular weight of 100,000 or more suppresses aggregation of cellulose fine fibers during drying due to steric repulsion and does not impair thixotropy even when redispersed.

[0079] The average molecular weight of the polyacrylate or polyacrylic acid is preferably 100,000 or more, more preferably 500,000 or more. Although there is no upper limit, from the viewpoint of spinnability, it is preferably 5,000,000 or less. The average molecular weight here refers to the weight average molecular weight, and can be measured by a method such as gel permeation chromatography (GPC).

[0080] In the present invention, from the viewpoint of obtaining an effect of improving redispersibility, it is more preferable that the polyacrylate or polyacrylic acid having a molecular weight of 100,000 or more is contained in an amount of 30 to 100 parts by mass, preferably 60 to 80 parts by mass, per 100 parts by mass of cellulose fine fibers. If the blending ratio of the dispersant is too much higher than the upper limit, problems such as a decrease in viscosity characteristics such as thixotropy, which is a characteristic of cellulose fine fibers, and a decrease in dispersion stability may occur. If the blending ratio of the dispersant is too much lower than the lower limit, sufficient redispersibility cannot be obtained.

[0081] In the present invention, other water-soluble polymers may be used in combination. For example, cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginates, pullulan, starch, potato starch, arrowroot flour, modified starch (cationized starch, phosphorylated starch, phosphate cross-linked starch, phosphate monoesterified phosphate cross-linked starch, hydroxypropyl starch, hydroxypropylated phosphate cross-linked starch, acetylated adipate cross-linked starch, acetylated phosphate cross-linked starch, acetylated oxidized starch, starch sodium octenyl succinate, starch acetate, oxidized starch), corn starch, gum arabic, gellan gum, poly Examples of suitable surfactants include dextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soy protein lysate, peptone, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acids, polylactic acid, polymalic acid, polyglycerin, latex, rosin-based sizing agents, petroleum resin-based sizing agents, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide-polyamine resin, polyethyleneimine, polyamine, vegetable gum, polyethylene oxide, hydrophilic crosslinked polymers, starch-polyacrylic acid copolymer, tamarind gum, guar gum, and colloidal silica, as well as mixtures of one or more thereof.

[0082] (Powder manufacturing method) The method for producing the dried cellulose fine fibers of the present invention is not particularly limited, and examples thereof include a method in which an aqueous suspension containing cellulose fine fibers and a polyacrylate or polyacrylic acid is dehydrated and dried to obtain a dry solid, which is then pulverized in a pulverizer or the like, and the pulverized product is classified as necessary and recovered to obtain a powder, and a method in which the aqueous suspension is spray-dried to simultaneously dehydrate, dry, and powderize the resulting product, and the pulverized product is then classified as necessary and recovered to obtain a powder.

[0083] The method for dehydrating and drying the aqueous suspension containing cellulose fine fibers may be any conventional method, such as spray drying, freeze drying, squeezing, air drying, hot air drying, and vacuum drying. Specific examples of drying apparatuses that can be used include the following: continuous tunnel dryers, band dryers, vertical dryers, vertical turbo dryers, multi-stage disk dryers, through-flow dryers, rotary dryers, flash dryers, spray dryers, spray dryers, cylindrical dryers, drum dryers, reduced-pressure belt dryers, screw conveyor dryers, rotary dryers with heating tubes, vibration transport dryers, fluidized bed dryers, etc.; batch-type box dryers, through-flow dryers, vacuum box dryers, agitator dryers, shelf dryers, freeze dryers, etc., can be used alone or in combination. Among these, drum dryers and belt dryers are preferred, and from the viewpoint of energy efficiency, drum dryers, which directly and uniformly supply heat energy to the material to be dried, are even more preferred.

[0084] The method for pulverizing the dried cellulose fine fibers to obtain a pulverized product is not particularly limited. For example, the pulverized product can be obtained by pulverizing the dried cellulose fine fibers with a pulverizer. Examples of pulverizers include cutting mills: mesh mills (manufactured by HORAI Co., Ltd.), Atoms (manufactured by Yamamoto Hyakuma Manufacturing Co., Ltd.), knife mills (manufactured by Parman Co., Ltd.), cutter mills (manufactured by Tokyo Atomizer Manufacturing Co., Ltd.), CS cutters (manufactured by Mitsui Mining Co., Ltd.), rotary cutter mills (manufactured by Nara Machinery Manufacturing Co., Ltd.), turbo cutters (manufactured by Freund Corporation), pulp crushers (manufactured by Zuiko Co., Ltd.), shredders (manufactured by Kobe Steel Pantech Co., Ltd.), hammer mills: jaw crushers (manufactured by Makino Corporation), and the like. (manufactured by Makino Sangyo Co., Ltd.), hammer crusher (manufactured by Makino Sangyo Co., Ltd.), impact mill: Pulverizer (manufactured by Hosokawa Micron Corporation), Fine Impact Mill (manufactured by Hosokawa Micron Corporation), Super Micron Mill (manufactured by Hosokawa Micron Corporation), Inomizer (manufactured by Hosokawa Micron Corporation), Fine Mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), CUM type centrifugal mill (manufactured by Mitsui Mining Co., Ltd.), Exceed Mill (manufactured by Makino Sangyo Co., Ltd.), Ultraplex (manufactured by Makino Sangyo Co., Ltd.), Contraplex (manufactured by Makino Sangyo Co., Ltd.) Co., Ltd.), Coroplex (Makino Sangyo Co., Ltd.), Sample Mill (Seishin Co., Ltd.), Bantam Mill (Seishin Co., Ltd.), Atomizer (Seishin Co., Ltd.), Tornado Mill (Nikkiso Co., Ltd.), Nea Mill (Dalton Co., Ltd.), HT-type Fine Grinding Mill (Horai Co., Ltd.), Free Grinding Mill (Nara Machinery Works, Ltd.), New Cosmomizer (Nara Machinery Works, Ltd.), Turbo Mill (Freund Corporation), Gather Mill (Nishimura Machinery Works, Ltd.), Super Pow Damper mill (manufactured by Nishimura Machinery Works, Ltd.), Blade mill (manufactured by Nisshin Engineering Inc.), Super rotor (manufactured by Nisshin Engineering Inc.), Npa crusher (manufactured by Sansho Industry Co., Ltd.), Wheeley crusher (manufactured by Sanki Manufacturing Co., Ltd.), Pulp crusher (manufactured by Zuiko Co., Ltd.), Jacobson fine grinder (manufactured by Kobe Steel Pantech Co., Ltd.), Universal mill (manufactured by Tokuju Kosakusho Co., Ltd.), Atomizer (manufactured by Tokyo Atomizer Manufacturing Co., Ltd.), Mill Star Dam (manufactured by Tokyo Atomizer Manufacturing Co., Ltd.),Airflow mills: Stream mill (manufactured by Nippon Coke Engineering Co., Ltd.), CGS type jet mill (manufactured by Mitsui Mining Co., Ltd.), Micron Jet (manufactured by Hosokawa Micron Corporation), Counter Jet Mill (manufactured by Hosokawa Micron Corporation), Cross Jet Mill (manufactured by Kurimoto Iron Works Co., Ltd.), Supersonic Jet Mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), Current Jet (manufactured by Nisshin Engineering Inc.), Jet Mill (manufactured by Sansho Industry Co., Ltd.), Ebara Jet Micronizer (manufactured by Ebara Corporation), Ebara Triad Jet (manufactured by Ebara Corporation), Selenium Mirror (manufactured by Masuko Sangyo Co., Ltd.), New Micro Sic Examples include mat (manufactured by Masuno Manufacturing Co., Ltd.), Kryptron (manufactured by Kawasaki Heavy Industries, Ltd.), disc mill: vibrating disc mill (manufactured by Retsch), centri-cutter (manufactured by Nippon Coke & Engineering Co., Ltd.), turbo disc mill (manufactured by Freund-Turbo Corporation), mortar-type high-speed crusher (manufactured by Makino Sangyo Co., Ltd.), vertical roller mill: vertical roller mill (manufactured by Chinon Co., Ltd.), vertical roller mill (manufactured by Schaeffler Japan Co., Ltd.), roller mill (manufactured by Kotobuki Giken Kogyo Co., Ltd.), VX mill (manufactured by Kurimoto Iron Works Co., Ltd.), KVM-type vertical mill (manufactured by Earth Technica Co., Ltd.), IS mill (manufactured by IHI Plant Engineering Co., Ltd.), etc.

[0085] The processing conditions for these mills cannot be uniformly determined because the principles of milling differ. However, a method can be used in which, for example, processing conditions that affect the milling process, such as the screen diameter at the mill outlet and the rotation speed of the classification rotor, are adjusted, a calibration curve showing the relationship between the processing conditions and the particle size is created, and appropriate processing conditions are determined based on the calibration curve so as to obtain the desired average particle size.

[0086] The pulverized dried cellulose fine fiber material may be classified as needed. When classification is performed, it can be performed using a classifier attached to or mounted on a pulverizer.

[0087] The type of device used to recover the pulverized dried cellulose fine fibers and the granulated product obtained by spray drying is not particularly limited. Examples of recovery devices include a cyclone and a bag filter. The recovered product may be classified.

[0088] (particle size) From the viewpoint of ease of handling, the dried cellulose fine fiber material of the present invention has a particle size lower limit of 45 μm or more, preferably 60 μm or more, and an upper limit of 300 μm or less, preferably 150 μm or less. If the particle size is too small, the material will easily scatter and become difficult to handle. Here, the particle size refers to the average particle size (D50), which is the particle size that includes 50% of the particles when calculated from the minimum value in the volume-based particle size distribution. The particle size distribution can be measured using a laser diffraction / scattering particle size distribution analyzer.

[0089] The dried cellulose fine fibers of the present invention can be used in papermaking, civil engineering, paints, inks, coating compositions, agricultural chemicals, construction, automobiles, disease prevention agents, electronic materials, batteries, flame retardants, heat insulating materials, household goods, detergents, water treatment, etc. They can also be used as an additive in the control of spills and / or recovery of shale gas and oil.

[0090] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0091] (Average fiber diameter and average fiber length of cellulose fine fibers) The powder was redispersed in water, the suspension was diluted, and 200 randomly selected fibers were analyzed using an atomic force microscope (AFM), and the average was taken.

[0092] The aspect ratio was calculated using the following formula. Aspect ratio = average fiber length / average fiber diameter

[0093] (carboxyl group amount) The amount of carboxyl groups was calculated using the following formula: 60 mL of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose was prepared, 0.1 M aqueous hydrochloric acid was added to adjust the pH to 2.5, and 0.05 N aqueous sodium hydroxide was added dropwise until the pH reached 11. The amount of carboxyl groups was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid, where the change in electrical conductivity was gradual: Amount of carboxyl groups [mmol / g carboxylated cellulose] = a [mL] × 0.05 / mass of carboxylated cellulose [g].

[0094] (viscosity) To the dried cellulose fine fibers of the Examples and Comparative Examples, ion-exchanged water was added to give a solids content of 1.0% by mass, and the mixture was stirred at 3000 rpm for 30 minutes using a Homo Disper to prepare a cellulose fine fiber dispersion. The resulting aqueous dispersion was left to stand for one day, and then stirred using a Homo Disper (3000 rpm, 1 minute). The viscosity was measured using a B-type viscometer (manufactured by Eiko Seiki Co., Ltd.) at 25°C at a rotation speed of 60 rpm after 3 minutes and at a rotation speed of 6 rpm after 3 minutes.

[0095] (Evaluation of thixotropy) Ion-exchanged water was added to the dried cellulose fine fibers of the Examples and Comparative Examples so that the solid content was 1.0% by mass, and the mixture was stirred at 3,000 rpm for 30 minutes using a Homodisper to prepare a cellulose fine fiber dispersion. The shear viscosity of this cellulose fine fiber dispersion was measured using a rheometer (Anton Paar: MCR102e), and the larger the value (Ti value) obtained by dividing the shear viscosity at a shear rate of 0.01 / s by the shear viscosity at 100 / s, the higher the thixotropy was evaluated to be.

[0096] (transparency) Ion-exchange water was added to the dried cellulose fine fibers of the Examples and Comparative Examples to a solids content of 1.0% by mass, and the mixture was stirred at 3,000 rpm for 30 minutes using a homodisper to prepare a cellulose fine fiber dispersion. The transparency (transmittance of 660 nm light) of this 1.0% solids cellulose fine fiber dispersion was measured using a visible light photometer ASV11D (manufactured by AS ONE Corporation). The transparency restoration rate (%) was calculated using the formula: (transparency after drying and redispersion) / (transparency before drying) × 100.

[0097] (particle size) The average particle size (D50) of the powders used in the examples and comparative examples was determined from the particle size distribution based on the volume average particle size. Measurements were performed using a laser diffraction / scattering particle size distribution analyzer (Mastersizer 3000, manufactured by Spectris Co., Ltd.) under the condition of a particle refractive index of 1.5. The dry powder sample was directly placed in the analyzer.

[0098] (Evaluation of redispersibility) Deionized water was added to the dried cellulose fine fibers of the Examples and Comparative Examples to a solids content of 1.0% by mass, and the mixture was stirred at 3,000 rpm for 30 minutes using a homodisper to prepare a cellulose fine fiber dispersion. Two drops of ink drop (Kuretake Corporation, 10% solids) were added to this 1.0% by mass re-dispersion of cellulose fine fibers, and the mixture was stirred for 1 minute using a vortex mixer (IUCHI Corporation, Automatic Lab-mixer HM-10H) with the rotation speed set to maximum. The stirred solution was sandwiched between two glass plates to a film thickness of 0.15 mm and observed at 100x magnification using an optical microscope (KEYENCE Corporation, Digital Microscope VHX-6000) to confirm the presence or absence of white particles (aggregates of cellulose fine fibers). A: Almost no white particles are visible B: A small amount of white particles can be seen C: A large amount of white particles can be seen

[0099] (Production Example 1) (Production of carboxylated cellulose fine fibers 1) 500 g (bone-dry) of bleached, unbeaten softwood kraft pulp (85% brightness) was added to 20 L of an aqueous solution containing TEMPO (Sigma-Aldrich) (0.025 mmol / g relative to the cellulose raw material) and sodium bromide (1 mmol / g relative to the cellulose raw material) and stirred until the pulp was uniformly dispersed. The oxidation reaction was initiated by adding aqueous sodium hypochlorite to the reaction system to a concentration of 5.2 mmol / g. The pH of the system decreased during the reaction, but was gradually adjusted to pH 10 by the addition of 3 M aqueous sodium hydroxide. The reaction was terminated when the sodium hypochlorite was consumed and the pH no longer changed. The reaction mixture was filtered through a glass filter to separate the pulp, which was then thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield was 90%, the oxidation reaction took 100 minutes, and the carboxyl group content was 1.4 mmol / g.

[0100] The oxidized pulp obtained in the above process was adjusted to 1.0% (w / v) with water and treated three times with an ultra-high pressure homogenizer (20°C, 150 MPa) to obtain a dispersion of carboxylated cellulose fine fibers 1. The obtained fibers had an average fiber diameter of 4 nm and an aspect ratio of 220.

[0101] Example 1 (Production of dried body) The cellulose fine fibers used were carboxylated cellulose fine fibers 1 (carboxyl group content: 1.4 mmol / g, average fiber diameter: 4 nm, aspect ratio: 220) obtained in Production Example 1. To a 1.2% by mass aqueous suspension of carboxylated cellulose fine fibers 1, sodium polyacrylate A (Aron 7100: average molecular weight 500,000, manufactured by Toa Gosei Co., Ltd.) was added as a dispersant in an amount of 67% by mass relative to the cellulose fine fibers (i.e., so that the solid content of sodium polyacrylate was 67 parts by mass per 100 parts by mass of the solid content of the cellulose fine fibers), and the mixture was stirred for 60 minutes with a TK homomixer (12,000 rpm) to prepare an aqueous dispersion containing cellulose fine fibers. The pH of this dispersion was approximately 7 to 8. To this aqueous dispersion, 0.5% aqueous sodium hydroxide solution was added to adjust the pH to 9, and then the mixture was applied to the drum surface of a drum dryer D0405 (manufactured by Katsuragi Kogyo Co., Ltd.) to form a thin film with a thickness of approximately 100 to 200 μm. The mixture was dried at a drum surface temperature of 80°C, an internal pressure of 2 kPa, and a drum rotation speed of 2 rpm to obtain a dried cellulose fine fiber body with a moisture content of 5% by mass. The dried cellulose fine fiber body obtained as described above was pulverized using a hammer mill (Tokyo Atomizer Co., Ltd., Hammer Mill TAP-3) to obtain a pulverized product. The particle size of the pulverized product obtained was adjusted by adjusting the screen diameter at the outlet of the pulverizer. The pulverized product after particle size adjustment was recovered using a cyclone to obtain a powder of dried cellulose fine fiber body.

[0102] Example 2 A powder of dried cellulose fine fibers was obtained in the same manner as in Example 1, except that sodium polyacrylate B (Aron A-20P-X: average molecular weight 5,000,000, manufactured by Toa Gosei Co., Ltd.) was used as a dispersant instead of sodium polyacrylate A in Example 1, in an amount of 43 mass% relative to the cellulose fine fibers (i.e., so that the solid content of sodium polyacrylate was 43 mass parts when the solid content of the cellulose fine fibers was 100 mass parts).

[0103] (Comparative Example 1) A powder of dried cellulose fine fibers was obtained in the same manner as in Example 1, except that sodium polyacrylate C (Aron 10-SL:, average molecular weight 50,000, manufactured by Toa Gosei Co., Ltd.) adjusted to pH 9 with 3M sodium hydroxide solution as a dispersant was used instead of sodium polyacrylate A in Example 1, at 100 mass% relative to the cellulose fine fibers (i.e., so that the solid content of sodium polyacrylate was 100 mass parts when the solid content of the cellulose fine fibers was 100 mass parts).

[0104] (Comparative Example 2) A powder of dried cellulose fine fibers was obtained in the same manner as in Example 1, except that sodium carboxymethylcellulose (CMC-Na, 350HC, manufactured by Nippon Paper Industries Co., Ltd.) was used as a dispersant instead of sodium polyacrylate A in Example 1.

[0105] (Comparative Example 3) A powder of dried cellulose fine fibers was obtained in the same manner as in Example 1, except that sodium polyacrylate A of Example 1 was used.

[0106] [Table 1]

[0107] The results of the Examples and Comparative Examples, and the results of measuring the physical properties of a 1% redispersion of carboxylated cellulose fine fiber 1 from Production Example 1 as a Reference Example, are shown in Table 1. As can be seen from Table 1, in Examples 1 and 2, in which sodium polyacrylate having a molecular weight of 100,000 or more was added to cellulose fine fibers and then dried and pulverized, aggregation of the cellulose fine fibers during drying was suppressed, and dispersibility and transparency recovery rate were good compared to Comparative Example 1, in which sodium polyacrylate having a molecular weight of less than 100,000 was added, Comparative Example 2, in which sodium carboxymethylcellulose was added as a dispersant, and Comparative Example 3, in which no dispersant was added. Furthermore, a cellulose fine fiber dispersion was obtained that was able to maintain thixotropy even when redispersed.

Claims

1. A dried cellulose fine fiber body comprising cellulose fine fibers and a polyacrylate or polyacrylic acid having an average molecular weight of 100,000 or more.

2. The dried cellulose fine fiber material according to claim 1, characterized in that the polyacrylate or polyacrylic acid is contained in an amount of 30 to 100 parts by mass per 100 parts by mass of the cellulose fine fibers.

3. The dried cellulose fine fiber material according to claim 1 or 2, wherein the polyacrylate is a sodium salt.

4. The dried cellulose fine fiber body according to claim 1 or 2, wherein the cellulose fine fibers are anion-modified cellulose fine fibers.

5. The dried cellulose fine fiber material according to claim 1 or 2, wherein the cellulose fine fibers are oxidized cellulose fine fibers having a carboxy group content of 1.0 to 2.0 mmol / g.

6. A method for producing dried cellulose fine fibers, comprising adding 30 to 100 parts by mass of a polyacrylate or polyacrylic acid having an average molecular weight of 100,000 or more to 100 parts by mass of cellulose fine fibers, followed by drying and pulverizing the mixture.

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