Method for supplying rubber composition containing fine cellulose fibers

Abstract

The present invention is a method for supplying a rubber composition containing fine cellulose fibers, the method being characterized by obtaining, in a first kneading site, an intermediate kneaded product obtained by molding a mixture of fine cellulose fibers having a length-weighted average fiber length of more than 400 nm and a rubber latex into a sheet shape; after the intermediate kneaded material is transferred to a second kneading site in the form of a bundle in which a plurality of layers are stacked, the intermediate kneaded material is diluted at the second kneading site and further kneaded.

Description

Technical Field

[0001] This invention relates to a method for supplying a rubber composition comprising microfiber cellulose. Background Technology

[0002] It is known that rubber compositions made from masterbatches containing rubber components and cellulose fibers have excellent mechanical strength. For example, Patent Document 1 describes a method for obtaining a rubber / short fiber masterbatch by mixing a dispersion obtained by fibrillating short fibers with an average fiber diameter of less than 0.5 μm in water with a rubber latex and then drying it. This masterbatch allows for the production of rubber compositions with an excellent balance between rubber reinforcement and fatigue resistance.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2006-206864 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] However, if fine cellulose fibers such as cellulose nanofibers are not uniformly dispersed in the rubber composition, it is difficult to achieve the desired effect. In order to obtain the desired homogeneous effect in various rubber processing plants with different operating conditions, a method for supplying rubber compositions containing fine cellulose fibers that can be more easily and uniformly dispersed is desired.

[0008] The object of the present invention is to provide a method for supplying a rubber composition containing fine cellulose fibers that can be easily and uniformly dispersed and readily exhibit the desired effect, and to provide a method for supplying a rubber composition that prevents pressing in the unvulcanized state and has excellent workability in rubber processing plants.

[0009] Methods for solving problems

[0010] The inventors of this application conducted in-depth research and found that the problem can be solved by the following (1) to (8).

[0011] (1) A method for supplying a rubber composition, said rubber composition containing fine cellulose fibers, characterized in that, In the first mixing area, an intermediate compound is obtained by forming a mixture of fine cellulose fibers with a length-weighted average fiber length exceeding 400 nm and rubber latex into sheets. After the intermediate compound is transferred to the second mixing area in a multi-layered bundled form, The intermediate mixture is diluted in a second mixing area and further mixed.

[0012] (2) The method of supplying the rubber composition according to (1) is characterized in that the length-weighted average diameter of the fine cellulose fibers is more than 1 nm and less than 20 nm.

[0013] (3) The method of supplying the rubber composition according to (1) or (2) is characterized in that the intermediate compound contains fine cellulose fibers in the range of 10 to 40% by weight.

[0014] (4) The method of supplying the rubber composition according to (1) or (2) is characterized in that the intermediate compound is stacked and bundled without applying a release agent or attaching a protective film.

[0015] (5) The method of supplying the rubber composition according to (1) or (2) is characterized in that the intermediate compound is unvulcanized.

[0016] (6) The method of supplying the rubber composition according to (1) or (2) is characterized in that the intermediate compound is formed into a sheet by a roll mixing method.

[0017] (7) The method of supplying the rubber composition according to (1) or (2), characterized in that the fine cellulose is anionicly modified.

[0018] (8) The method of supplying the rubber composition according to (1) or (2) is characterized in that the fine cellulose is not hydrophobically treated.

[0019] Invention Effects

[0020] According to the present invention, a method for supplying a rubber composition containing fine cellulose fibers that can be easily and uniformly dispersed and readily exhibit the desired effect can be provided, and a method for supplying a rubber composition that prevents pressing in the unvulcanized state and has excellent workability in a rubber processing plant can be provided. Detailed Implementation

[0021] (1. Raw materials for rubber compositions)

[0022] The raw materials of the rubber composition include at least fine cellulose fibers and rubber components, and may include additives as needed. The raw materials are described below.

[0023] (1.1 Fine cellulose fibers)

[0024] Microcellulose fibers refer to finely fibrous cellulose derived from cellulose raw materials. Microcellulose fibers are defined as a dispersion (1% by weight) of microcellulose fibers obtained, for example, using a visible spectrophotometer (UV-1800, manufactured by Shimadzu Corporation) with a path length of 1 cm / 660 nm, showing a light transmittance ranging from 1% to 99%. Methods for manufacturing microcellulose fibers include defibrillation of pulp and chemical modification treatments before and after defibrillation (usually before defibrillation). Microcellulose fibers with nanometer-scale fiber diameters are called cellulose nanofibers, and microcellulose fibers with micrometer-scale fiber diameters are called cellulose microfibers. The size of microcellulose fibers can be adjusted through micronization treatments, chemical modification treatments, etc.

[0025] It should be noted that powdered cellulose will not disperse even when stirred in solvents such as water, but will instead settle. Therefore, the light transmittance of the dispersion cannot be measured, making it distinct from fine cellulose fibers.

[0026] (An example of microfiber cellulose: cellulose nanofibers)

[0027] In this specification, cellulose nanofibers (CNF) refer to cellulose fibers with nanoscale fiber diameters prepared through micronization.

[0028] 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, even more preferably 50 nm or less, and particularly preferably 20 nm or less. The lower limit is not particularly limited, but is generally 1 nm or more, preferably 2 nm or more. Therefore, the average fiber diameter (length-weighted average fiber diameter) of CNF is generally 1–500 nm or 2–500 nm, preferably 2–300 nm or 2–100 nm, more preferably 1–50 nm or 1–30 nm or 1–20 nm.

[0029] It is important that the average fiber length (length-weighted average fiber length) exceeds 400 nm, preferably 420 nm or more, and more preferably 440 nm or more. As an upper limit, it is preferably 3000 nm or less, more preferably 2000 nm or less, and even more preferably 1500 nm or less, 1000 nm or less, or 800 nm or less.

[0030] The average fiber diameter and average fiber length of microcellulose fibers can be obtained by averaging the fiber diameter and fiber length obtained from observing each fiber, using a classifier manufactured by Valmet Corporation, a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM), depending on the fiber diameter. When using a classifier, the length-weighted average fiber width and length-weighted average fiber length can be calculated separately.

[0031] (Example of fine cellulose fibers: cellulose microfibrils)

[0032] In this specification, cellulose microfibrils (microfibrillated cellulose, MFC) refer to cellulose fibers with micron-sized fiber diameters prepared through micronization processing.

[0033] The average fiber diameter of MFC is typically 500 nm or more, preferably 1 μm or more, and more preferably 3 μm or more. Therefore, it exhibits higher water retention compared to unde-fibered cellulose fibers, and even in small quantities, it provides higher strength and yield improvement compared to micro-de-fibered CNF. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, and even more preferably 20 μm or less, but there are no particular limitations.

[0034] The average fiber length is typically 10 μm or more, preferably 20 μm or more, and more preferably 40 μm or more. There is no particular upper limit, but it is typically 3,000 μm or less, preferably 2,500 μm or less, more preferably 2,000 μm or less, and even more preferably 1,500 μm or less, 1,000 μm or less, or 500 μm or less, 400 μm or less, or 200 μm or less.

[0035] (modified)

[0036] The microcellulose fibers can be modified or unmodified. Modified microcellulose fibers refer to microcellulose fibers (e.g., cellulose nanofibers, cellulose microfibers) whose three hydroxyl groups in the glucose units have been chemically modified (hereinafter referred to as "modified") through chemical treatment. Through chemical modification, the microfibers are sufficiently refined, and cellulose nanofibers with a uniform average fiber diameter can be obtained by defibrillation. Therefore, when compounded with rubber components, they can provide a sufficient reinforcing effect. From this perspective, modified (especially anionic modified) cellulose fibers are preferred. Furthermore, the microcellulose fibers used in this invention are preferably not subjected to hydrophobic treatment.

[0037] Examples of modifications include anionic modifications such as oxidation, etherification, and esterification such as phosphorylation. Other examples include silane coupling, fluorination, and cationization. Among these, oxidation (carboxylation), etherification, cationization, and esterification are preferred, with oxidation (carboxylation) being more preferred.

[0038] -Oxidation (Carboxylation)-

[0039] Oxidized microcellulose fibers typically have a structure in which at least one of the carbon atoms containing a primary hydroxyl group (e.g., the carbon atom with a primary hydroxyl group at the C6 position) in the pyranose units constituting the cellulose molecular chain is oxidized. The amount of carboxyl groups in the 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 absolute dry weight. 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 during the oxidation of the cellulose fibers (e.g., the amount of oxidant added, the reaction time). Furthermore, the amount of carboxylate groups and aldehyde groups can also be adjusted by controlling these conditions.

[0040] The amount of carboxyl groups can be calculated using the following steps. 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 and adjust the pH to 2.5. Then, add 0.05 N sodium hydroxide aqueous solution dropwise and measure the conductivity until the pH reaches 11. Calculate the amount of carboxyl groups using the following formula from the amount of sodium hydroxide consumed (a) during the slow-changing weak acid neutralization phase: Carboxyl group content [mmol / g oxidized cellulose] = a[mL] × 0.05 / mass of oxidized cellulose [g] The oxidation method is not particularly limited. As an example, one method involves oxidizing cellulose raw materials in water using an oxidizing agent in the presence of an N-oxygen compound and bromide, iodide, or a mixture thereof. According to this method, the C6 position of the pyranose ring on the cellulose surface is selectively oxidized, producing an aldehyde group, a carboxyl group (-COOH), or a carboxylate group (-COO). - At least one group from the group consisting of ). The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by mass or less.

[0041] N-oxy compounds refer to compounds capable of generating nitroacin radicals. Examples of nitroacin radicals include 2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO). Any N-oxy compound can be used as long as it promotes the target oxidation reaction. The amount of N-oxy compound used is not particularly limited as long as it is a catalyst sufficient to oxidize the cellulose used as a raw material. For example, relative to 1 g of absolutely dry cellulose raw material, it is preferably 0.01 mmol or more, more preferably 0.02 mmol or more. 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-oxy compound used relative to 1 g of absolutely dry cellulose raw material is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.02 to 0.5 mmol. The amount of N-oxy compound used relative to the reaction system is typically 0.1 to 4 mmol / L.

[0042] Bromide refers to a compound containing bromine, such as alkali metal bromides that can dissociate and ionize in water. Iodide refers to a compound 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 combined amount of bromide and iodide is preferably 0.1 to 100 mmol relative to 1 g of absolutely dry cellulose raw material, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol.

[0043] As an oxidizing agent, known oxidizing agents can be used, such as halogens, hypohalous acids, halogenated acids, perhalous acids or their salts, halogen oxides, peroxides, etc. Among these, hypohalous acids or their salts are preferred from the perspective of low cost and low environmental impact, hypochlorous acid or its salts are more preferred, and sodium hypochlorite is more preferred. The appropriate amount of oxidizing agent used is, for example, relative to 1 g of absolutely dry cellulose raw material, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, further preferably 1 to 25 mmol, and even more preferably 3 to 10 mmol. In addition, for example, relative to 1 mol of N-oxygen compound, preferably 1 to 40 mol.

[0044] The oxidation process of cellulose raw materials proceeds efficiently even under relatively mild conditions. Therefore, the preferred reaction temperature is 4–40°C, but room temperature (around 15–30°C) is also acceptable. As the reaction proceeds, carboxyl groups are generated in the cellulose, resulting in a decrease in the pH of the reaction solution. To ensure efficient oxidation, an alkaline solution, such as an aqueous sodium hydroxide solution, is preferably added to maintain the pH of the reaction solution at approximately 8–12 or 10–11. Water is the preferred reaction medium for ease of operation and minimizing the occurrence of side reactions.

[0045] The reaction time in the oxidation reaction can be set appropriately according to the degree of oxidation, usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.

[0046] Oxidation reactions can be carried out in two stages. For example, by oxidizing the cellulose obtained by filtration and separation after the first stage reaction under the same or different reaction conditions, the reaction hindrance caused by the sodium chloride byproduct produced in the first stage reaction can be avoided, thus achieving efficient oxidation.

[0047] Another example of a carboxylation (oxidation) method is oxidation by contacting a gas containing ozone with a cellulose raw material (ozone oxidation). Through this oxidation reaction, at least the hydroxyl groups at positions 2 and 6 of the pyranose ring are oxidized, while the cellulose chain decomposes. The ozone concentration in the ozone-containing gas is preferably 50–250 g / m³. 3 More preferably 50–220 g / m 3 When the solid content of the cellulose raw material is set at 100 parts by weight, the ozone addition amount is preferably 0.1 to 30 parts by weight, more preferably 5 to 30 parts by weight. 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.

[0048] Alternatively, an additional oxidation treatment can be performed after ozone treatment. There are no particular limitations on the oxidant used for this additional oxidation treatment; examples include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfate, and peracetic acid. As a step in the additional oxidation treatment, for example, an oxidant solution can be prepared by dissolving these oxidants in a polar organic solvent such as water or alcohol, and then impregnating the oxidized cellulose in the solution.

[0049] The following is an example of a method for determining the amount of carboxyl groups. Prepare 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose. Add 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, then add 0.05 N sodium hydroxide aqueous solution dropwise. Measure the conductivity until the pH reaches 11. The amount of sodium hydroxide (a) consumed during the neutralization phase of the weak acid, where the conductivity changes slowly, can be calculated using the following formula (2).

[0050] (Equation 2): Amount of carboxyl groups [mmol / g (oxidized cellulose or oxidized cellulose nanofibers)] = a[mL] × 0.05 / mass of oxidized cellulose or mass of oxidized cellulose nanofibers [g]

[0051] -Acidic oxidized cellulose and desalination-

[0052] Oxidized cellulose, being a product of oxidation, contains carboxyl groups and may contain more carboxyl groups than salt-type carboxyl groups (e.g., -COO). - The cellulose oxidized cellulose (-COOH) may contain more acidic carboxyl groups than acidic carboxyl groups. The amounts of salt-type and acidic carboxyl groups can be adjusted by desalting. Desalting converts salt-type carboxyl groups into acidic carboxyl groups. In this specification, oxidized cellulose (the desalted substance) is referred to as acidic oxidized cellulose, and oxidized cellulose (the substance not subjected to the desalting treatment described below) is referred to as salt-type oxidized cellulose. Salt-type oxidized cellulose typically mainly contains salt-type carboxyl groups. On the other hand, acidic oxidized cellulose has a large number of acidic carboxyl groups, and the proportion of acidic carboxyl groups in the total carboxyl group is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. Acidic oxidized cellulose can exert a superior reinforcing effect. The proportion of acidic carboxyl groups can be calculated using the following steps.

[0053] 1) First, prepare 250 mL of an aqueous dispersion of acidic oxidized cellulose with a solid content of 0.1% by mass before desalination. Add 0.1 M hydrochloric acid to the prepared aqueous dispersion to adjust the pH to 2.5, then add 0.1 N sodium hydroxide aqueous solution, and measure the conductivity until the pH reaches 11. Calculate the amount of acidic carboxyl groups and salt-type carboxyl groups, i.e., the total carboxyl group content, using the following formula from the amount of sodium hydroxide consumed (a) during the neutralization phase of the weak acid with a slow change in conductivity: Total carboxyl content (mmol / g oxidized cellulose (salt form)) = a (mL) × 0.1 / mass of oxidized cellulose (salt form) (g) 2) Prepare 250 mL of an aqueous dispersion of desalted acidic oxidized cellulose with a solid content of 0.1% by mass. Add 0.1 N of sodium hydroxide aqueous solution to the prepared aqueous dispersion and measure the conductivity until the pH reaches 11. Calculate the amount of acidic carboxyl groups using the following formula from the amount of sodium hydroxide consumed (b) during the neutralization phase of the weak acid with a slow change in conductivity: Acidic carboxyl group content (mmol / g acidic oxidized cellulose) = b (mL) × 0.1 / mass of acidic oxidized cellulose (g) 3) Calculate the proportion of acidic carboxyl groups using the following formula based on the calculated total carboxyl group amount and acidic carboxyl group amount.

[0054] The percentage of acidic carboxyl groups (%) = (amount of acidic carboxyl groups / total amount of carboxyl groups) × 100

[0055] The desalination can be carried out after oxidation or before and after decellulose dissociation (before and after step (2)), usually after oxidation, preferably before step (2). Desalination is usually carried out by replacing the salt (e.g., sodium salt) contained in the salt-type oxidized cellulose with protons. As a desalination method, for example, methods of adjusting the system to acidity and methods of contacting the oxidized cellulose with a cation exchange resin can be cited. In the case of adjusting the system to acidity, the pH of the system is preferably adjusted to 2 to 6, more preferably to 2 to 5, and even more preferably to 2.3 to 5. In order to adjust to acidity, an acid is usually used (e.g., inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid, phosphoric acid, etc.; organic acids such as acetic acid, lactic acid, oxalic acid, citric acid, formic acid, etc.). After adding the acid, a washing treatment can be performed appropriately. The above-mentioned cation exchange resin is used as long as the counterion is H + Both strongly acidic and weakly acidic ion exchange resins can be used. There is no particular limitation on the ratio of oxidized cellulose to cation exchange resin when they are in contact; those skilled in the art can set it appropriately from the viewpoint of efficiently performing proton exchange. The cation exchange resin can be recovered using conventional methods such as vacuum filtration after contact.

[0056] -Etherification-

[0057] Examples of etherification include carboxyl alkylation, methylation, ethylation, cyanoethylation, hydroxyethylation, hydroxypropylation, ethyl hydroxyethylation, and hydroxypropyl methylation, with carboxyl alkylation being preferred and carboxyl methylation being more preferred.

[0058] Carboxyalkylated cellulose fibers typically have a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (e.g., the carbon atom with a primary hydroxyl group at the C6 position constituting the pyranose unit) is carboxymethylated.

[0059] The degree of carboxyl alkyl substitution (DS, preferably carboxymethyl substitution) of each dehydrated glucose unit of carboxyalkylated cellulose is preferably 0.01 or more, 0.02 or more, or 0.05 or more, more preferably 0.10 or more, further 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 achieve the effects of chemical modification. The upper limit of this 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, maintaining the fiber morphology in water. Therefore, the degree of carboxyl alkyl substitution is preferably 0.01 to 0.50, more preferably 0.01 to 0.45, and further preferably 0.02 to 0.40, 0.10 to 0.35, or 0.15 to 0.30.

[0060] The degree of substitution, such as the degree of carboxymethyl substitution, can be determined by the following method. Accurately weigh approximately 2.0 g of carboxymethylated cellulose (absolutely dry) and place it in a 300 mL stoppered conical flask. Add 100 mL of liquid containing 100 mL of super-concentrated nitric acid to 1000 mL of methanol, shake for 3 hours, and convert the salt-type carboxymethylated cellulose (hereinafter also referred to as "salt-type CM-methylated cellulose") to the acid-type carboxymethylated cellulose (hereinafter also referred to as "acid-type CM-methylated cellulose"). Accurately weigh 1.5–2.0 g of acid-type CM-methylated cellulose (absolutely dry) and place it in a 300 mL stoppered conical flask. Moisten the acid-type CM-methylated cellulose with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake for 3 hours at room temperature. Using phenolphthalein as an indicator, back-titrate the excess NaOH with 0.1 N H₂SO₄. The degree of carboxymethyl substitution (DS) can be calculated using the following formula: A = [(100 × F - (0.1 N H₂SO₄ (mL)) × F') × 0.1] / (absolute dry mass of acid-type CM-modified cellulose (g)) DS = 0.162 × A / (1 - 0.058 × A) A: The amount of 1N NaOH (mL) required to neutralize 1g of acidified CM cellulose. F': Factor for 0.1N H2SO4 F: Factor of 0.1N NaOH The degree of carboxyl alkyl substitution can be adjusted by controlling reaction conditions such as the amount of carboxyl alkylating agent added, the amount of mercerizing agent, and the composition ratio of water to organic solvent.

[0061] One method for carboxyl alkylation is, for example, the mercerization of a cellulose-based raw material as a starting material (initial raw material) followed by etherification. The following explanation uses carboxymethylation as an example.

[0062] Carboxymethylated cellulose can be produced by using unmodified cellulose fibers (cellulose raw materials: such as pulp) as starting material, mercerizing them, and then subjecting them to an etherification reaction. This reaction is typically carried out in the presence of a solvent. The solvent can be, for example, one of water, a lower alcohol (e.g., methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol), or a mixture of two or more solvents. It should be noted that when a lower alcohol is mixed, the mixing ratio of the lower alcohol is preferably 60–95% by mass. The amount of solvent, in mass conversion, is approximately three times that of the cellulose raw material. There is no particular upper limit to this amount, but it is less than 20 times. The amount of solvent, in mass conversion, is preferably 3–20 times that of the cellulose raw material.

[0063] Examples of mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.

[0064] 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, relative to each dehydrated glucose residue of the starting material. The upper limit of this amount is generally 20 times or less, preferably 10 times or less, and even 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.

[0065] The reaction temperature for mercerization is typically above 0°C, preferably above 10°C. The upper limit is typically below 70°C, preferably below 60°C. The reaction temperature is typically between 0 and 70°C, preferably between 10 and 60°C.

[0066] The mercerizing reaction time is typically 15 minutes or more, preferably 30 minutes or more. The upper limit is typically 8 hours or less, preferably 7 hours or less. The reaction time is typically 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

[0067] Etherification reactions are typically carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of carboxymethylating agents include sodium monochloroacetate.

[0068] The amount of carboxymethylating agent added, in molar terms, is preferably 0.05 times or more, more preferably 0.5 times or more, and even more preferably 0.8 times or more relative to each glucose residue of the cellulose raw material. The upper limit of this amount is generally 10.0 times or less, preferably 5 times or less, and even more preferably 3 times or less. The amount of carboxymethylating agent added, in molar terms, is preferably 0.05 to 10.0 times, more preferably 0.5 to 5 times, and even more preferably 0.8 to 3 times.

[0069] The reaction temperature is typically above 30°C, preferably above 40°C. The upper limit is typically below 90°C, preferably below 80°C. The reaction temperature is typically between 30 and 90°C, preferably between 40 and 80°C. The reaction time is typically above 30 minutes, preferably above 1 hour. The upper limit is typically below 10 hours, preferably below 4 hours. The reaction time is typically between 30 minutes and 10 hours, preferably between 1 hour and 4 hours.

[0070] It should be noted that the reaction solution can be stirred as needed during the carboxymethylation reaction.

[0071] -Different from carboxymethyl cellulose-

[0072] Carboxyalkylated cellulose fibers preferably retain at least a portion of their fibrous shape when dispersed in water. Carboxyalkylated cellulose fibers are distinguished from carboxymethyl cellulose, a water-soluble polymer that imparts viscosity when dissolved in water. When observing an aqueous dispersion of carboxyalkylated cellulose fibers using an electron microscope, fibrous material can be observed. On the other hand, carboxymethyl cellulose, as a water-soluble polymer, typically does not exhibit fibrous material even when its aqueous dispersion is observed. Furthermore, when measuring anionic modified cellulose fibers using X-ray diffraction, peaks of cellulose type I crystals can be observed, but similarly, when measuring carboxymethyl cellulose powder, a water-soluble polymer, cellulose type I crystals are generally not visible.

[0073] -Acidic carboxyalkylated cellulose and desalting-

[0074] Carboxyalkylated cellulose can contain more acidic carboxyl groups than salt-type carboxyl groups, or more salt-type carboxyl groups than acid-type carboxyl groups. The amounts of salt-type and acidic carboxyl groups can be adjusted by desalting. Desalting converts salt-type carboxyl groups into acidic carboxyl groups. In this specification, carboxyalkylated cellulose (cellulose that has undergone desalting) is referred to as acidic carboxyalkylated cellulose, and carboxyalkylated cellulose (cellulose that has not undergone the desalting treatment described below) is referred to as salt-type carboxyalkylated cellulose. Salt-type carboxyalkylated cellulose typically mainly contains salt-type carboxyl groups (-COO). - On the other hand, acid-type carboxyalkyl cellulose has a large number of acid-type carboxyl groups, and the ratio of the amount of acid-type carboxyl groups to the amount of carboxyl groups in acid-type carboxyalkyl cellulose is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. The method for calculating the ratio of acid-type carboxyl groups is as described above.

[0075] Desalination typically occurs after carboxylation, preferably after etherification and before fibrillation. One method of desalination is, for example, contacting the carboxylated cellulose with a cation exchange resin. The cation exchange resin only needs to counterionize H+. + Both strongly acidic and weakly acidic ion exchange resins can be used. The ratio of carboxyalkylated cellulose to cation exchange resin during contact is not particularly limited, and can be appropriately set by those skilled in the art from the viewpoint of efficiently performing proton exchange. For example, relative to the carboxyalkylated cellulose aqueous dispersion, the ratio can be adjusted so that the pH of the aqueous dispersion after adding the cation exchange resin is preferably 2 to 6, more preferably 2 to 5. The cation exchange resin can be recovered after contact using conventional methods such as vacuum filtration.

[0076] -Esterification (phosphorylation)-

[0077] As a first example of esterified cellulose fibers, phosphorylated cellulose fibers can be cited. Phosphorylated cellulose typically has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (e.g., the carbon atom with a primary hydroxyl group at the C6 position constituting the pyranose unit) is phosphorylated.

[0078] The amount of ionic substituents introduced relative to the phosphorylated cellulose fiber (amount of ionic substituents and amount of phosphoric oxyacid substituents) is 0.10 mmol / g or more per 1 g (mass) of phosphorylated CNF, preferably 0.20 mmol / g or more, more preferably 0.30 mmol / g or more, further 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. Furthermore, the amount of ionic substituents introduced relative to the phosphorylated CNF is 1.50 mmol / g or less per 1 g (mass) of cellulose fiber, 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. Additionally, the amount of ionic substituents introduced relative to the phosphorylated cellulose fiber is also preferably 1.00 mmol / g or less per 1 g (mass) of phosphorylated cellulose fiber, more preferably 0.95 mmol / g or less. Here, the denominator in the unit mmol / g indicates that the counter ion of the ionic substituent is the hydrogen ion (H+). + The mass of cellulose fibers at that time. The amount of phosphorus oxyacid substituents can be determined by the following methods.

[0079] (Determination of phosphorus oxyacid content)

[0080] The phosphorus oxyacid content of microcellulose fibers can be determined as follows: a microcellulose fiber dispersion containing the target microcellulose fibers is diluted with ion-exchanged water to a content of 0.2% by mass to prepare a cellulose fiber slurry. The slurry is then treated with an ion-exchange resin and titrated with an alkali to determine the content.

[0081] The treatment using ion exchange resin is carried out as follows: 1 / 10 by volume of a strong acid ion exchange resin (Amberjet 1024; Organo Corporation, adjusted) is added to the slurry containing cellulose fibers. After shaking for 1 hour, the resin is injected into a 90μm mesh screen to separate it from the slurry.

[0082] Furthermore, the titration using alkali was performed as follows: In a cellulose fiber-containing slurry treated with ion exchange resin, 10 μL of a 0.1N sodium hydroxide aqueous solution was added every 5 seconds, while the change in pH value of the slurry was measured. It should be noted that nitrogen gas was blown into the slurry 15 minutes before the start of the titration, simultaneously with the titration. In this neutralization titration, in the curve obtained by plotting the measured pH against the amount of alkali added, two points were observed where the increments (the differential values ​​of pH relative to the amount of alkali added) became maximum. The point where the increment first becomes maximum after the start of alkali addition is called the first endpoint, and the point where the increment becomes maximum afterward 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 in the titration. Furthermore, 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 in the titration. It should be noted that the amount of alkali (mmol) required from the start of titration to the first endpoint is divided by the solid content (g) in the slurry being titrated, and the resulting value is taken as the phosphorus oxyacid content (mmol / g). Furthermore, the presence or absence of phosphate groups can be confirmed by measuring infrared absorption spectroscopy, specifically by confirming the absorption based on phosphate groups (1230 cm⁻¹). -1 (Nearby)

[0083] The amount of phosphate group can be controlled by adjusting reaction conditions such as the amount of phosphate-containing compounds added and the amount of basic compounds used as needed.

[0084] As a method of phosphorylation, for example, a method of reacting a compound having a phosphate group with unmodified cellulose fibers (phosphorylation). Examples of phosphorylation methods include: mixing a powder or aqueous solution of a compound having a phosphate group into a cellulose-based raw material (e.g., a suspension (solid component concentration 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 cellulose-based raw material, the latter being preferred. This improves the uniformity of the reaction and increases the esterification efficiency. From the viewpoint of improving the efficiency of introducing phosphate groups, the pH of the aqueous solution of the compound having phosphate groups is preferably 7 or less, and more preferably 3 to 7 from the viewpoint of inhibiting hydrolysis.

[0085] Examples of compounds containing phosphoric acid groups include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, their esters, and salts. These compounds are low in cost, easy to process, and can introduce phosphoric acid groups into cellulose, thereby improving decellulose decomposition efficiency. Specific examples of compounds containing phosphoric acid groups 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 phosphoric acid groups can be used. The amount of the compound containing phosphoric acid group added to the cellulose raw material, calculated in terms of phosphorus content, is preferably 0.1 to 500 parts by mass relative to 100 parts by mass of the solid content of the cellulose raw material, more preferably 1 to 400 parts by mass, and even more preferably 2 to 200 parts by mass. This allows for a yield commensurate with the amount of the compound containing phosphoric acid group used. The reaction temperature is preferably 0–95°C, more preferably 30–90°C. The reaction time is not particularly limited, typically around 1–600 minutes, preferably 30–480 minutes. When the esterification reaction conditions are within any of these ranges, excessive esterification of cellulose, preventing it from becoming easily soluble, can be suppressed, thereby increasing the yield of phosphoric acid-esterified cellulose. When reacting compounds with phosphate groups, a basic compound (e.g., urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, etc., compounds with amino groups exhibiting basicity) can be further added to the reaction system.

[0086] The suspension obtained after esterification is dehydrated as needed, preferably followed by heat treatment. This inhibits the hydrolysis of the cellulose raw material. The heating temperature is preferably 100–170°C, more preferably below 130°C (preferably below 110°C) while still containing water, and then heated to 100–170°C after water removal. After boiling, a washing treatment such as rinsing with cold water and / or a neutralization treatment is preferably performed. This allows for efficient defiberization. Washing can be performed by adding water and then dehydrating (e.g., filtering), and can be repeated two or more times. Washing is preferably performed until the conductivity of the filtrate decreases. For example, it can be performed until the conductivity is preferably below 200, more preferably below 150, and even more preferably below 120. In addition, after washing, a neutralization treatment can be performed as needed. Neutralization treatment can be performed, for example, by adding an alkali (e.g., sodium hydroxide). After neutralization, washing can be performed again.

[0087] -Esterification (phosphite esterification)-

[0088] As a second example of a method for manufacturing esterified cellulose fibers, phosphorylated cellulose fibers can be cited. Phosphorylated cellulose fibers typically have a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (e.g., the carbon atom with a primary hydroxyl group at the C6 position constituting the pyranose unit) is phosphorylated.

[0089] The degree of substitution of the phosphite group per glucose unit in the phosphite-esterified cellulose fiber (hereinafter referred to as "degree of phosphite substitution") is preferably 0.001 to 0.60. This facilitates electrorepulsion between cellulose fibers, making nanofiber dissociation easier. The degree of phosphite substitution can be determined using the same method as the method for determining the degree of phosphate substitution. The degree of phosphite substitution can be adjusted by controlling reaction conditions such as the amount of phosphorous acid or its salt added, the amount of alkali metal ion inclusions used as needed, and the amount of urea or its derivatives added.

[0090] As a method of phosphorous esterification, for example, one can describe a method of reacting phosphorous acid or its metal salt (preferably sodium hydrogen phosphite) with unmodified cellulose fibers to introduce ester groups of phosphorous acid.

[0091] Examples of phosphorous acid and its metal salts include 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 pyrophosphite, etc., selected from combinations of two or more of these, with sodium hydrogen phosphite being preferred. Thus, alkali metal ions can also be introduced into cellulose fibers. The amount of phosphorous acid or its metal salt added relative to 1 kg of unmodified cellulose fiber is preferably 1 to 10,000 g, more preferably 100 to 5,000 g, and even more preferably 300 to 1,500 g. In addition to phosphorous acid and its metal salts, substances containing alkali metal ions (e.g., hydroxides, metal sulfates, metal nitrates, metal chlorides, metal phosphates, and metal carbonates) can be further added to the reaction system.

[0092] Alternatively, urea or its derivatives may be further added to the reaction system. This allows the carbamate group 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 thereof, with urea being preferred. The amount of urea and urea derivatives added relative to 1 mol of phosphorous acid or its metal salt is preferably 0.01 to 100 mol, more preferably 0.2 to 20 mol, and even more preferably 0.5 to 10 mol.

[0093] The reaction temperature is preferably 100–200°C, more preferably 100–180°C, and even more preferably 100–170°C. More preferably, during the heat treatment, heating is performed at 130°C or below (preferably 110°C or below) while the water is present, and then the heat treatment is performed at 100–170°C after the water is removed. The reaction time is typically about 10–180 minutes, more preferably 30–120 minutes. The phosphite-esterified cellulose fibers are preferably washed before defibrillation. The degree of substitution of the phosphite group per glucose unit is preferably 0.01 or more and less than 0.23.

[0094] -Esterification (sulfation)-

[0095] As a third example of a method for manufacturing esterified cellulose fibers, sulfated cellulose fibers can be cited. Sulfated cellulose typically has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (e.g., the carbon atom with a primary hydroxyl group at the C6 position constituting the pyranose unit) is phosphorylated.

[0096] The amount of sulfate groups per glucose unit in the sulfated cellulose fiber (hereinafter 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. By introducing sulfate groups into the cellulose raw material, the cellulose fibers electrorepel each other. Therefore, sulfated cellulose with introduced sulfate groups can be easily nanofibrillated. It should be noted that when the sulfate group amount is 0.42 mmol / g or higher, nanofibrillation can be sufficiently performed due to the electrorepulsion between the cellulose fibers. On the other hand, when it is 9.9 mmol / g or lower, swelling or dissolution can be suppressed, preventing situations where nanofibers cannot be obtained. For efficient fibrillation, it is preferable to wash the sulfated cellulose obtained above.

[0097] The amount of sulfate per glucose unit can be determined by the following method. An aqueous dispersion of sulfated CNF is solvent-displaced in the order of ethanol and tert-butanol, and then freeze-dried. 15 mL of ethanol and 5 mL of water are added to 200 mg of the resulting sample, and the mixture is 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 further stirring at 30 °C for 24 hours. Next, phenolphthalein is added as an indicator, and the mixture is titrated with hydrochloric acid. The sulfate content is calculated using the following formula: Sulfate content [mmol / g sample] = (5 - (0.1 × hydrochloric acid titration amount [mL] × 2)) / 0.2 The amount of sulfate group can be adjusted by controlling reaction conditions such as the amount of sulfate-based compounds added.

[0098] Examples of methods for sulfation include reacting a sulfated compound with unmodified cellulose fibers to introduce sulfated groups from the compound into the cellulose, thereby producing sulfated cellulose. Examples of sulfated compounds include sulfuric acid, aminosulfonic acid, chlorosulfonic acid, sulfur trioxide, or their esters or salts. Among these, aminosulfonic acid is preferred due to its low solubility and low acidity of cellulose.

[0099] For example, when using aminosulfonic acid as a sulfate-based compound, the amount of aminosulfonic acid used can be appropriately adjusted taking into account the amount of anionic groups introduced into the cellulose chain. For example, it is preferably 0.01 to 50 mol of glucose units per mol of cellulose molecule, and more preferably 0.1 to 3.0 mol.

[0100] -Salt form / Acid form-

[0101] Esterified cellulose can contain more acidic carboxyl groups than salt-type carboxyl groups, or more salt-type carboxyl groups than acidic carboxyl groups. The untreated and desalted forms of esterified cellulose are respectively called salt-type esterified cellulose and acid-type esterified cellulose. Salt-type esterified cellulose mainly contains salt-type carboxyl groups. It is speculated that acid-type esterified cellulose has a superior reinforcing effect. The countercations to salt-type carboxyl groups and their preparation methods are explained in the description of oxidized cellulose.

[0102] -Cation-

[0103] Cationic cellulose typically has a structure in which at least one carbon atom constituting the cellulose molecular chain (e.g., the carbon atom with a primary hydroxyl group at the C6 position constituting the pyranose unit) is cationized, and usually contains cations such as ammonium, phosphonium, and sulfonium, or groups having such cations in the molecule. The degree of cation substitution per glucose unit in cationic cellulose is preferably 0.02 to 0.50. The degree of cation substitution per glucose unit can be determined by the following method: After drying the cationic cellulose fiber, the nitrogen content is determined using a total nitrogen analyzer (TN-10 manufactured by Mitsubishi Chemical Corporation), and the degree of cation substitution (the average number of moles of substituents per mole of dehydrated glucose unit) is calculated using the following formula: Degree of cation substitution = (162 × N) / (1 - 151.6 × N) N: Nitrogen content The degree of cationic substitution can be adjusted by reaction conditions such as the amount of cationic agent added, the composition ratio of water or alcohols with 1 to 4 carbon atoms.

[0104] As a method of cationization, examples include reacting an cationizing agent (e.g., glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydroxide or its haloalcohol form) and an alkali metal hydroxide (e.g., sodium hydroxide, potassium hydroxide) as a catalyst with unmodified cellulose fibers 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 typically carried out in the presence of water or an alcohol.

[0105] The amount of cationic agent relative to 100 parts by weight of cellulose raw material is preferably 5 parts by weight or more, more preferably 10 parts by weight or more. The upper limit of this amount is generally 800 parts by weight or less, preferably 500 parts by weight or less.

[0106] As a catalyst to be used as needed during cationization, examples include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of catalyst relative to 100 parts by mass of the cellulose raw material is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more. The upper limit of this amount is typically 7 parts by mass or less, preferably 3 parts by mass or less.

[0107] -Alkaline cationic cellulose fiber-

[0108] The cationized cellulose fibers are preferably converted into basic cationized cellulose or basic cationized cellulose nanofibers by desalting. Desalting converts the salts in the cationized cellulose into alkalis. In this specification, the desalted cationized cellulose (nanofibers) is referred to as basic cationized cellulose (nanofibers) or cationized cellulose (nanofibers) (basic). Conversely, the 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 can be performed at any time before (cationized cellulose) and after (cationized cellulose nanofibers) defibering, as described later. Desalting refers to the process of removing salts (e.g., Cl) contained in the cationized cellulose (salt-type) and cationized cellulose nanofibers (salt-type). - The cation exchange resin is replaced with an alkali to produce an alkaline form. As a desalination method after cationization, one example is contacting cationized cellulose or cationized cellulose nanofibers with an anion exchange resin. The anion exchange resin only needs to counteract the OH- ion. -Both strongly basic and weakly basic ion exchange resins can be used. The ratio of the modified cellulose to the anion exchange resin during contact 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, relative to the cationized cellulose nanofiber aqueous dispersion, the ratio can be adjusted so that the pH of the aqueous dispersion after adding the anion exchange resin is preferably 8-13, more preferably 9-13. The recovery of the anion exchange resin after contact can be carried out by conventional methods such as vacuum filtration.

[0109] (Micronization (fiber disintegration, fiberization))

[0110] Micronization is typically achieved through mechanical processing. Mechanical processing (preferably pulping or dissociation) is usually carried out wet (i.e., in the form of an aqueous dispersion of cellulose fibers). As for the apparatus used in mechanical processing, examples include refining apparatus (refining machines; e.g., disc type, conical type, cylindrical type), high-speed defiberizers, shear mixers, colloid mills, high-pressure jet dispersers, pulpers, PFI mills, kneaders, dispersers, high-speed defiberizers (top refiners), high-pressure or ultra-high-pressure homogenizers, grinding mills (stone mill type pulverizers), ball mills, vibratory mills, bead mills, single-shaft, double-shaft or multi-shaft mixers / extruders operating at high speeds, refiners, defibrators, friction mills, high-shear defbrator, dispersers, homogenizers (e.g., microfluidizers), etc., which can impart mechanical defiber force. Apparatus that can impart defiber force wetly is preferred, and high-speed defiberizers and refining apparatuses are more preferred, but there are no particular limitations.

[0111] In the case of wet defibrillation, an aqueous dispersion of cellulose fibers is typically prepared. The concentration of the modified cellulose solids in the aqueous dispersion is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, further preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more. As an upper limit for the concentration, it 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, the pH can be adjusted as needed (e.g., 7 or less, 6 or less, 5 or less).

[0112] Before preparing the aqueous dispersion, pretreatment such as dry grinding (e.g., grinding after drying) can be performed. Examples of apparatus used in dry grinding include impact mills such as hammer mills and pin mills, media mills such as ball mills and tower mills, and jet mills, but there are no particular limitations. Furthermore, post-treatment can be performed after defiberization. Examples of post-treatment include drying (e.g., freeze drying, spray drying, tray drying, drum drying, belt drying, methods of thinly spreading and drying on glass plates, fluidized bed drying, microwave drying, heat-generating fan-type vacuum drying, vacuum (deaeration) drying), redispersion in water (without limitation on the dispersion apparatus), and grinding (e.g., grinding using equipment such as shredders, hammer mills, pin mills, and jet mills), without particular limitations.

[0113] (solid matter)

[0114] The microcellulose fibers can be in the form of an aqueous dispersion obtained after manufacturing, or as dried solids or wet solids of the dispersion. Methods for preparing the dried solids or wet solids include, for example, drying (e.g., freeze-drying, spray drying, tray drying, drum drying, belt drying, thin spreading and drying on a glass plate, fluidized bed drying, microwave drying, and heat-generating fan-type vacuum drying). The dried solids or wet solids may contain water-soluble polymers. This improves the redispersibility of the microcellulose fibers and inhibits the aggregation of CNFs in solid rubber. As water-soluble polymers, examples include cellulose derivatives (such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, or ethyl cellulose or their salts), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginate, alginate, pullulan, starch, potato starch, kudzu root powder, cationic starch, phosphorylated starch, corn starch, gum arabic, gellan gum, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soy protein solution, and protein. Peptone, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, vinyl acetate, polyamino acids, polylactic acid, polymalic acid, polyglycerol, latex, rosin-based sizing agents, petroleum resin-based sizing agents, urea-formaldehyde resin, melamine resin, epoxy resin, polyamide resin, polyamide-polyamine resin, polyethyleneimine, polyamine, plant gum, polyethylene oxide, hydrophilic crosslinking polymer, polyacrylate, starch-polyacrylic acid copolymer, tamarind gum, guar gum, and colloidal silica, and mixtures of one or more thereof. From a compatibility point of view, carboxymethyl cellulose or its salts are preferred.

[0115] Microcellulose fibers can undergo post-processing after manufacturing, such as redispersing in dispersion media like water or alcohol (the dispersion device is not limited), or pulverizing (e.g., using equipment like shredders, hammer mills, pin mills, jet mills, etc.).

[0116] (Physical properties of microcellulose fibers)

[0117] The microcellulose fibers preferably have the following physical properties.

[0118] -Specific surface area-

[0119] The preferred BET specific surface area of ​​the microfiber cellulose fibers is 10 m². 2 / g or more, preferably 50m 2 / g or more, further preferably 100m 2 / g or above. The BET specific surface area can be determined by nitrogen adsorption (JIS Z 8830), after replacing the aqueous dispersion with t-BuOH, using a BET specific surface area meter to measure the freeze-dried sample.

[0120] -Crystallinity of cellulose type I-

[0121] The crystallinity of cellulose type I in microcellulose fibers is typically above 50%, preferably above 60%. There is no specific upper limit, but in practice it can be considered 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 performing X-ray diffraction measurements, measuring and comparing the intensity of the (200) peak near 22.6° with the valleys of (200) and (110) near 18.5°.

[0122] -Viscosity-

[0123] When preparing a water dispersion from fine cellulose fibers, a low viscosity is preferred. This allows the material to remain readily workable despite fibrillation. For example, the B-type viscosity (25°C, 60 rpm) of a water dispersion with 1% by mass of solids is typically 4,000 mPa·s or less, or 3,000 mPa·s or less, preferably 2,500 mPa·s or less, and more preferably 2,000 mPa·s or less. The lower limit is preferably 10 mPa·s or more, more preferably 20 mPa·s or more, further 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. The B-type viscosity can be determined, for example, by the following method: After fibrillation (e.g., defibrillation), the mixture is allowed to stand for at least one day, diluted as needed, stirred in a homogenizer (e.g., 3000 rpm for 5 minutes), and then the viscosity is measured (60 rpm for 3 minutes).

[0124] -Water retention capacity-

[0125] When the fine cellulose fibers are cellulose microfibers, their water retention capacity is preferably 10 or more, more preferably 15 or more, further preferably 20 or more, and even more preferably 30 or more. The upper limit is considered to be approximately 200 or less in practice, but is not particularly limited. The water retention capacity is equivalent to the ratio of the mass of water in the sediment to the mass of the fibrous solid component in the sediment, and is the ratio of water content to solid component content in the sedimented gel determined by centrifuging a 0.3% by mass aqueous dispersion of the fibers at 25,000 G. That is, it is calculated using the following formula: Water retention capacity = (B + C - 0.003 × A) / (0.003 × AC) A: The mass of an aqueous dispersion containing 0.3% by mass of solids from cellulose microfibrils. B: The mass of the precipitate separated after centrifuging the aqueous dispersion of mass A at 25,000 G for 30 minutes at 30°C. C: Mass of the solid components in the aqueous phase separated after the above centrifugation. A higher water retention capacity value indicates a greater ability of the fiber to hold water. Water retention capacity can be measured or calculated for fibrillated fibers, but it is generally not possible to measure for unfibrillated or unfibrillated fibers, or for cellulose nanofibers unfibrillated to individual microfibrils. When unfibrillated or unfibrillated cellulose fibers are centrifuged under the above conditions, a dense precipitate cannot form, making it difficult to separate the precipitate from the aqueous phase. When cellulose nanofibers are centrifuged under the above conditions, they typically show almost no sedimentation.

[0126] -Fiberization Rate-

[0127] When the microcellulose fibers are cellulose microfibrils, the fibrilation rate (fibrilation %) is preferably 1.0% or more, more preferably 1.2% or more, and even more preferably 1.5% or more. This confirms that fibrilation is sufficient. The fibrilation rate can be adjusted by the type of cellulose-based raw material used. The fibrilation rate can be determined using an image analysis type fiber analysis device such as a classifier manufactured by Valmet Co., Ltd.

[0128] -Conductivity-

[0129] The conductivity of the aqueous dispersion of fine cellulose fibers (solid component concentration 1.0% by mass) is preferably 500 mS / m or less, more preferably 300 mS / m or less, further preferably 200 mS / m or less, even more preferably 100 mS / m or less, and particularly preferably 70 mS / m or less. The lower limit is preferably 5 mS / m or more, more preferably 10 mS / m or more. The conductivity can be measured using a conductivity meter (HORIBA ES-71 type) on 200 g of an aqueous dispersion of fine cellulose fibers with a solid component concentration of 1.0% by mass.

[0130] -Degree of Aggregation-

[0131] The microcellulose fibers of the present invention preferably have a degree of polymerization in the range of 250 to 1000 based on the viscosity method using a copper ethylenediamine solution. More preferably, it is 300 to 900, and even more preferably, it is 350 to 800. Within this range, the viscosity does not become excessively high when the microcellulose fibers are mixed with rubber latex, thus they are easily dispersed. As a rubber reinforcing material, it offers the advantage that the microcellulose fibers can form a network structure in the rubber while maintaining sufficient strength.

[0132] The degree of polymerization based on the viscosity method using a copper ethylenediamine solution can be calculated using the following method: In the case of TEMPO-oxidized microcellulose fibers, a reduction treatment was first performed. 10% by weight of NaBH4 relative to the microcellulose fibers was added to a 1% aqueous dispersion of microcellulose fibers. The pH was adjusted to 10 with NaOH, and the mixture was stirred for 4 hours for reduction. Then, ethanol was added, and the mixture was centrifuged. The supernatant was discarded, and ethanol was added again, followed by stirring and centrifugation. This process was repeated three times to recover the microcellulose fibers, yielding the reduced TEMPO-oxidized microcellulose fibers.

[0133] The fine cellulose fibers were freeze-dried and dissolved in 0.5M copper ethylenediamine solution 1 to form solution 2. The viscosities of solutions 1 and 2 were measured using a capillary viscometer (Cannon-Fensk viscometer). The viscosity of solution 2 is set as η, and the viscosity of solution 1 is set as η0. The intrinsic viscosity [η] of the anionic modified pulp is calculated using the following formula.

[0134] Intrinsic viscosity [η] = (η / η0) / {c(1+0.28×η / η0)}

[0135] (c represents the concentration of fine cellulose fibers (g / dL))

[0136] Then, the degree of aggregation DP is calculated using the following formula.

[0137] Degree of polymerization DP = Intrinsic viscosity [η] / (5.7 × 10⁻³)

[0138] Microcellulose fibers can be one type or a combination of two or more types.

[0139] (1.2 Rubber Composition)

[0140] Examples of rubber components include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), ethylene propylene rubber (EPM), ethylene propylene diene monomer (EPDM), chlorosulfonated polyethylene (CSM), acrylic rubber (ACM), fluororubber (FKM), epichlorohydrin rubber (CO, ECO), polyurethane rubber (U), silicone rubber (Q), halogenated butyl rubber, and polysulfide rubber, among other synthetic rubbers, without particular limitation. Additionally, thermoplastic elastomers such as polystyrene-based thermoplastic elastomers, polypropylene-based thermoplastic elastomers, polydiene-based thermoplastic elastomers, chlorinated thermoplastic elastomers, and engineering plastic elastomers can also be used. Natural rubber (NR) or acrylonitrile-butadiene rubber (NBR) is preferred as the rubber component.

[0141] One type of rubber component can be used alone, or two or more components can be combined.

[0142] (2. Method for manufacturing intermediate compound)

[0143] In the method of supplying the rubber composition of the present invention, the intermediate compound obtained in a first mixing site is formed into a sheet by shaping a mixture of fine cellulose fibers with a length-weighted average fiber length of more than 400 nm and rubber latex.

[0144] (2.1 Mixing process)

[0145] (Micronized cellulose fiber dispersion)

[0146] The fine cellulose fibers mixed with rubber latex are preferably a dispersion obtained by dispersing the fine cellulose fibers in a dispersion medium (e.g., water, alcohol). The B-type viscosity (60 rpm) of such a fine cellulose fiber dispersion is typically 5,000 mPa·s or more, 6,000 mPa·s or more, 7,000 mPa·s or more, or 8,000 mPa·s or more, preferably 9,000 mPa·s or more, 10,000 mPa·s or more, more preferably 11,000 mPa·s or more, or 12,000 mPa·s or more. The upper limit is typically 100,000 or less, preferably 70,000 or less, more preferably 50,000 mPa·s or less. The concentration of solids in the microcellulose fiber dispersion (the concentration of microcellulose fibers) is not particularly limited, but is typically 1.5% or more, preferably 1.7% or more, more preferably 1.9% or more or 2.0% or more, and the upper limit is typically 20.0% or less, preferably 15.0% or less, more preferably 10.0% or less or 5.0% or less. Viscosity can be adjusted by the concentration of solids, dispersion conditions, the physical properties of the microcellulose fibers, their size, etc.

[0147] (Rubber latex)

[0148] The rubber latex used in the mixing process can be an aqueous dispersion of the rubber components. The rubber latex can be prepared by dispersing the rubber components in water using conventional methods. The viscosity of the rubber latex is not particularly limited, but is generally 5 or higher, preferably 10 mPa·s or higher, more preferably 15 mPa·s or higher, and typically 400 mPa·s or lower or 300 mPa·s or lower, preferably 200 mPa·s or lower, more preferably 100 mPa·s or lower. The amount of solvent (water) in the rubber latex is generally 10 to 1000 parts by mass relative to 100 parts by mass of the rubber components (or the total amount when using two or more rubber components).

[0149] (Other ingredients)

[0150] As raw materials for rubber compositions, fine cellulose fibers and raw materials other than rubber components can also be used. Other raw materials include dispersants, solvents, and rubber additives.

[0151] (Dispersant)

[0152] Dispersants, when used in conjunction with fine cellulose fibers, can improve dispersibility, for example, when the fine cellulose fibers are in a dry mass. Examples of dispersants include water-soluble polymers and surfactants, with water-soluble polymers being preferred. When the fine cellulose fibers are chemically modified cellulose fibers, the water-soluble polymer covers the low-charge-density portions of the surface, inhibiting hydrogen bond formation and preventing the fine cellulose fibers from agglomerating during drying.

[0153] -Water-soluble polymer-

[0154] It is believed that water-soluble polymers can penetrate between the fibers of fine cellulose fibers, thereby increasing the distance between the fibers and inhibiting the aggregation of fine cellulose fibers after drying. Examples of water-soluble polymers include cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ethyl cellulose), xanthan gum, xylo-glucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, pullulan, starch, potato starch, kudzu root powder, processed starches (cationized starch, phosphorylated starch, phosphate-crosslinked starch, phosphate monoesterified phosphate-crosslinked starch, hydroxypropyl starch, hydroxypropylated phosphate-crosslinked starch, acetylated adipic acid crosslinked starch, acetylated phosphate-crosslinked starch, acetylated oxidized starch, sodium octenyl succinate starch, acetic acid starch, oxidized starch), corn starch, gum arabic, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, and chitosan. Sugars, casein, albumin, soy protein solution, peptone, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, vinyl acetate, polyamino acids, polylactic acid, polymalic acid, polyglycerol, rosin-based sizing agents, petroleum resin-based sizing agents, urea-formaldehyde resin, melamine resin, epoxy resin, polyamide resin, polyamide-polyamine resin, polyethyleneimine, polyamine, plant gum, polyethylene oxide, hydrophilic crosslinking polymers, polyacrylates, starch-polyacrylic acid copolymers, tamarind gum, guar gum, and colloidal silica, and mixtures of one or more thereof, are preferred for their high affinity with chemically modified microcellulose fibers, with cellulose derivatives being more preferred, and carboxymethyl cellulose or its salts being more preferred. The water-soluble polymer can be one type or a combination of two or more types.

[0155] -surfactant-

[0156] Examples of surfactants include, but are not limited to, nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, as well as organic solvents, proteins, enzymes, natural polymers, and synthetic polymers. A surfactant can be one type or a combination of two or more.

[0157] (solvent)

[0158] As a solvent, examples include aqueous solvents, which can improve the dispersibility of microcellulose fibers and rubber components in a mixture. Examples of aqueous solvents include water, water-soluble organic solvents, or mixtures thereof. Since microcellulose fibers are hydrophilic, water is preferred. By using water, a good dispersion can be achieved during dispersion. Aqueous solvents may contain non-water-soluble organic solvents to a degree that does not impair the effects of the invention.

[0159] Water-soluble organic solvents can be organic solvents that are soluble in water, such as lower alcohols having 1 to 4 carbon atoms (e.g., methanol, ethanol, 2-propanol, butanol), glycerol, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, and combinations thereof. Lower alcohols having 1 to 4 carbon atoms are preferred, methanol, ethanol, and 2-propanol are more preferred, and from the viewpoint of safety and ease of acquisition, methanol and ethanol are further preferred, and ethanol is even more preferred.

[0160] The amount of water-soluble organic solvent in the mixed solvent is not particularly limited, but is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less.

[0161] (Rubber additives)

[0162] Examples of rubber additives include those used for crosslinking rubber components. Crosslinking is generally carried out through a vulcanization system that combines crosslinking agents (vulcanizing agents) such as sulfur or sulfur-donating compounds (e.g., sulfur halides) with a variety of general vulcanization accelerators such as sulfenamide-based and thiuram-based compounds. Crosslinking agents are not limited to sulfur-based vulcanizing agents. Examples of crosslinking agents other than vulcanizing agents include organic peroxides, quinone dioximes, organic polyamine compounds, alkylphenol resins containing hydroxymethyl groups; compounds containing crosslinking groups such as isocyanate groups, carbodiimide groups, oxazoline groups, aziridinyl groups, and epoxy groups, polyfunctional cations, and compounds containing polyvalent metals. As organic peroxides, commonly used compounds such as tert-butyl peroxide, dicumyl peroxide, tert-butylcumyl peroxide, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn-3, 1,3-di(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylperoxybenzoate, tert-butylperoxyisopropyl carbonate, and n-butyl-4,4-di(tert-butylperoxy)valerate can be used. When crosslinking with organic peroxides, it is preferable to use multifunctional unsaturated compounds, such as triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, and N,N'-m-phenylene bismaleimide.

[0163] The content of the crosslinking agent is preferably 0 parts by mass or more per 100 parts by mass of the rubber component. The upper limit is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less. However, in this invention, even if vulcanizing agents are present, the effects of this invention can be further enhanced through unvulcanized conditions (heat treatment after adding vulcanizing agents) without vulcanization treatment.

[0164] Rubber additives are not limited to the examples mentioned above; other examples include vulcanization accelerators (e.g., zinc oxide, stearic acid), surfactants (cationic surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants), reinforcing agents (e.g., carbon black, silica), silane coupling agents, hydrophobic agents, oils, curing resins, waxes, anti-aging agents, and colorants. The content of each reagent is not particularly limited.

[0165] The weight ratio of fine cellulose fibers to the rubber component is preferably 1 phr or more, more preferably 5 phr or more, and even more preferably 10 phr or more. This allows for a substantial increase in tensile strength. The upper limit is preferably 70 phr or less, more preferably 50 phr or less, and even more preferably 30 phr or less. This maintains processability during manufacturing, improves the dispersion of fine cellulose fibers in the rubber, and reduces crimping during transfer.

[0166] (Method for preparing the mixture)

[0167] The method for manufacturing the mixture is not particularly limited; for example, it can be achieved by adding fine cellulose fibers, rubber components, and other raw materials (e.g., solvents) as needed, followed by stirring. The fine cellulose fibers are preferably used as a dispersion (e.g., an aqueous dispersion), which may contain a dispersant as needed. Additionally, the rubber component is preferably added as rubber latex. Stirring can be performed using equipment such as a homogenizer or a supermixer.

[0168] (2.2 Drying process)

[0169] A mixture comprising at least fine cellulose fibers and rubber latex can be supplied to a drying process before being formed into sheets. In the drying process, the mixture can be dried using known drying methods such as drum drying, natural drying, oven drying, freeze drying, spray drying, and pulse combustion, with drum drying being particularly preferred.

[0170] (Drum dryer)

[0171] A drum dryer is a dryer equipped with a rotating drum (cylinder) and scrapers (knives, scraper blades) that scrape the dried material off the drum as it rotates. Heating of the drum is achieved by introducing a heat medium (e.g., steam) into the drum (e.g., made of metal). When a sample (liquid) is continuously supplied to the preheated and rotating drum surface, causing the sample to adhere to the drum surface in a thin film, the moisture in the sample evaporates and concentrates during rotation, thus drying the sample. The dried material can then be scraped off the drum surface using the scrapers. The drum dryer may also include a feeder for supplying the sample (liquid) to the drum surface.

[0172] (Drying temperature)

[0173] The drying temperature is typically 70°C or higher, preferably 80°C or higher, more preferably 90°C or higher, 100°C or higher, or 110°C or higher. This allows for efficient drying. The upper limit is typically 160°C or lower, preferably 150°C or lower, 140°C or lower, or 135°C or lower. This suppresses heat-induced modification of cellulose and prevents a decrease in the mechanical properties of the dried product after shaping. Therefore, by using temperatures typically 70–160°C, preferably 80–150°C, more preferably 90–150°C, 100–150°C, or 110–150°C, the drying process can be effectively advanced, and a decrease in mechanical properties can be avoided. In this specification, the drying temperature refers to the temperature of the drum surface of the drum dryer.

[0174] The mixture can be supplied to the drum dryer at room temperature or preheated. If heated, the heating temperature is, for example, 40°C or higher, 50°C or higher, 60°C or higher, or 65°C or higher. There is no specific upper limit; it can be below 70°C.

[0175] The moisture content of the dried product after the drying process is typically 8% by mass or less, preferably 5% by mass or less. Within this range, workability in subsequent mixing processes (e.g., refining and compounding) becomes good. The lower limit is not particularly limited and can be 0% by mass or more (absolutely dry).

[0176] (2.3 Process for obtaining the flake-shaped intermediate compound)

[0177] The dried material obtained above can be processed multiple times using a roll mixing apparatus such as an open roll to obtain an intermediate mixture shaped into sheets. Two-roll or three-roll mixing apparatuses can be used as the roll mixing apparatus.

[0178] The gap can be set within the range of 0.1 to 10 mm. Since the dried material undergoes significant volume changes and experiences heavy loads before and after roller processing, it is preferable to gradually increase the gap within this range during repeated roller processing, for example, when setting the gap as A for the first roller processing, B for the second, and C for the third, to satisfy A.

[0179] In order to more effectively exert the effects of the invention, the intermediate compound preferably contains fine cellulose fibers in the range of 10 to 40 parts by mass relative to 100 parts by mass of rubber components (the total amount when using two or more rubber components).

[0180] (3. Method for manufacturing rubber composition)

[0181] ​In the method for supplying the rubber composition of the present invention, the intermediate compound, which is formed into a sheet, is transferred to a second mixing site in a multi-layered bundled form, and then the intermediate compound is diluted and further mixed in the second mixing site to obtain the rubber composition.

[0182] (3.1 Bundling process)

[0183] It is important to stack and bundle sheet-shaped intermediate compounds into multiple layers (two or more) by folding, cutting, or rolling. Uncured rubber compositions are typically easy to press together, making direct stacking and bundling of sheets difficult (significantly degrading work efficiency). This necessitates applying release agents, attaching protective films, or bundling into bales, but such processes are uneconomical and inefficient.

[0184] In the case of the intermediate compound of the present invention, by comprising fine cellulose fibers with a number-average fiber length of 400 nm or more, it can moderately exhibit surface stiffness (unevenness), thus preventing creasing and enabling the unvulcanized sheet-like intermediate compound to be stacked and bundled without reducing work efficiency. Furthermore, although the intermediate compound of the present invention is sheet-like, because it prevents creasing, it is easily removed from the bundle at the transport destination, allowing for the cutting of desired samples using small tools such as scissors, resulting in excellent workability.

[0185] As a layered form, when sheet materials are folded or cut, they can be layered in either the longitudinal or transverse direction, allowing for a suitable layering configuration for bundling. When layered into a roll, for example, sheet-like intermediate compound can be directly wound in multiple layers around a core. It should be noted that there is no particular upper limit to the number of layers; it can be adjusted appropriately within the range of materials suitable for bundling.

[0186] As a form of packaging, any layered intermediate compound can be bundled in an outer bag that protects it from impact. Any such outer bag, such as a corrugated cardboard box, container, expanded polystyrene box, plastic box, or impact-resistant bag, can be appropriately selected.

[0187] In addition, to prevent the layered intermediate mixture from collapsing, it can be properly secured using inner bags, sheets, straps, etc., before being bundled into outer bags.

[0188] (3.2 Transfer Process)

[0189] In the method for supplying the rubber composition of the present invention, the intermediate compound, which is bundled, is transferred from the first mixing site where the above-described mixing process is carried out to the second mixing site where the dilution process described later is carried out. There are no particular limitations on the transfer method; a conventional logistics method can be selected.

[0190] (3.3 Dilution process)

[0191] The intermediate compound transferred to the second mixing area is diluted by mixing with other rubber latexes and further mixed to form the desired shape. The other rubber latexes are the same as those described in (1.2 Rubber Composition), but preferably the same rubber composition as the rubber latex used in the manufacture of the intermediate compound.

[0192] As a method of dilution and mixing, any common rubber mixing method can be used without restriction, such as open mixing methods like roller mixing, and closed mixing methods like Banbury mixers and kneaders.

[0193] The content of fine cellulose fibers in the diluted and mixed rubber composition is preferably diluted to 0.01 to 20 parts by weight, more preferably 0.1 to 15 parts by weight, and more preferably 1 to 10 parts by weight relative to 100 parts by weight of rubber.

[0194] According to the method for supplying the rubber composition of the present invention, by preparing an intermediate compound with a high concentration of fine cellulose fibers dispersed in a first mixing site, a rubber composition with moderately dispersed fine cellulose fibers can be obtained in a second mixing site through simple dilution mixing.

[0195] As described above, by making the average fiber length of the fine cellulose fibers 400 nm or more, the pressing of the stacked sheet rubber compositions together is suppressed even after transfer. Therefore, they can be easily removed from the bundle in the second mixing area. During dilution mixing, the sheet intermediate mixture can be directly rolled, for example, and the process can be carried out with a simple procedure.

[0196] (Other additives)

[0197] Additives may be included in rubber compositions during compounding as needed. For example, additives used in the crosslinking of rubber components can be cited as examples of additives used to obtain rubber products. Crosslinking is generally carried out via a vulcanization system that combines crosslinking agents (vulcanizing agents) such as sulfur or sulfur-donating compounds (e.g., sulfur halides) with a variety of general vulcanization accelerators such as sulfenamide-based and thiuram-based compounds. Crosslinking agents are not limited to sulfur-based vulcanizing agents. Examples of crosslinking agents other than vulcanizing agents include, for instance, organic peroxides, quinone dioximes, organic polyamine compounds, alkylphenol resins containing hydroxymethyl groups; compounds containing crosslinking groups such as isocyanate groups, carbodiimide groups, oxazoline groups, aziridinyl groups, and epoxy groups, polyfunctional cations, and compounds containing polyvalent metals. As organic peroxides, commonly used compounds such as tert-butyl peroxide, dicumyl peroxide, tert-butylcumyl peroxide, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn-3, 1,3-di(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylperoxybenzoate, tert-butylperoxyisopropyl carbonate, and n-butyl-4,4-di(tert-butylperoxy)valerate can be used. When crosslinking with organic peroxides, it is preferable to use multifunctional unsaturated compounds, such as triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, and N,N'-m-phenylene bismaleimide.

[0198] Relative to 100 parts by weight of the rubber component, the content of the crosslinking agent is preferably 1.0 parts by weight or more, more preferably 1.5 parts by weight or more, and even more preferably 1.7 parts by weight or more. The upper limit is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, and even more preferably 5 parts by weight or less.

[0199] Examples of vulcanization accelerators include N-tert-butyl-2-benzothiazolium sulfenamide and N-oxoethylene-2-benzothiazolium sulfenamide. The content of the vulcanization accelerator relative to 100 parts by weight of the rubber component is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.4 parts by weight or more. The upper limit is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and even more preferably 2 parts by weight or less.

[0200] Additives are not limited to the examples mentioned above; for example, they may include vulcanization accelerators (e.g., zinc oxide, stearic acid), surfactants (cationic surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants), reinforcing agents (e.g., carbon black, silica), silane coupling agents, hydrophobic agents, oils, curing resins, waxes, anti-aging agents, and colorants. The content of optional ingredients may be appropriately determined based on the type of optional ingredients and other conditions, and is not particularly limited.

[0201] It should be noted that the aforementioned additives may also be used appropriately for intermediate blends. However, since the intermediate blends are subsequently diluted and mixed to generate the target rubber composition, it is preferable to keep them unvulcanized even if additives are added.

[0202] Example

[0203] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0204] TENPO oxidized CNF is manufactured as follows. It should be noted that in the following manufacturing examples, the carboxyl group content, average fiber length, and average fiber diameter are determined using the methods described above.

[0205] <Manufacturing Example 1>

[0206] 5000g (absolutely dry) of bleached, unbeaten kraft pulp (85% brightness) derived from coniferous trees was added to 50L of an aqueous solution containing 7800mg TEMPO (Sigma Aldrich) and 755g sodium bromide, and stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to reach a concentration of 6.0 mmol / g, initiating the oxidation reaction. 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 pH of the system no longer changed, consuming the sodium hypochlorite. The resulting mixture was filtered through a glass filter for pulp separation, and the pulp was thoroughly washed with water to obtain oxidized pulp. The pulp yield at this point was 90%, and the oxidation reaction time was 90 minutes. The oxidized pulp obtained in the above steps was adjusted to 1.0% (w / v) with water and subjected to two defiberization treatments in an ultra-high pressure homogenizer (20°C, 150MPa) to obtain a dispersion of oxidized CNF. The obtained TEMPO-oxidized CNF had a carboxyl content of 1.42 mmol / g, a length-weighted average fiber length of 567 nm, and a length-weighted average fiber diameter of 2.4 nm.

[0207] The concentration of CNF oxidized by TEMPO prepared above was adjusted to obtain a slurry with 1% CNF. The B-type viscosity of the slurry was determined by the following method (25℃, 60rpm): After stirring with a homogenizer for 3000rpm for 5min, the viscosity was measured (60rpm), and the viscosity value was recorded after 3min. The result was 5180mPa·s.

[0208] <Manufacturing Example 2>

[0209] 40 kg (absolutely dry) of bleached, unbeaten kraft pulp (85% brightness: manufactured by Nippon Paper Co., Ltd.) derived from coniferous trees was added to 4000 L of an aqueous solution containing 312 g of TEMPO (manufactured by Sigma Aldrich, equivalent to 0.05 mmol per 1 g of absolutely dry cellulose) and 4112 g of sodium bromide (equivalent to 1.0 mmol per 1 g of absolutely dry cellulose). The mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to achieve a sodium hypochlorite concentration of 5.5 mmol / 1 g of absolutely dry cellulose, and the oxidation reaction was initiated at room temperature. The pH of the system decreased during the reaction, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the pH of the system no longer changed after consuming sodium hypochlorite. Hydrochloric acid was added to the reaction mixture to adjust the pH to 2, and the pulp was repeatedly dehydrated and diluted with water. The pulp was thoroughly washed with water and finally dehydrated until the pulp solids concentration reached 20% by weight, yielding carboxyl-modified pulp (TEMPO oxidized pulp).

[0210] The obtained carboxyl-modified pulp was dispersed in ion-exchange water, and sodium hydroxide was added and stirred to obtain an aqueous dispersion of carboxyl-modified pulp with a pH of 8.8 and a solid content concentration of 2% by weight. 74 kg of this aqueous dispersion of carboxyl-modified pulp was subjected to beating treatment using a single-disc refining machine (manufactured by Aikawa Iron Works Co., Ltd., 14-inch laboratory refining machine (RF-14 type), plate: blade width: 0.6 mm, groove width: 1.0 mm) with a gap of 0.23–0.25 mm for 10 minutes to produce TEMPO oxidized MFC.

[0211] The length-weighted average fiber length was 59 μm, the average fiber diameter was 5.1 μm, and the carboxyl content was 1.42 mmol / g.

[0212] <Example 1>

[0213] In the first mixing area, 325g of an aqueous dispersion of TEMPO oxidized CNF with a solids concentration of 1% obtained in Manufacturing Example 1 was mixed with 100g of natural rubber latex (trade name: HA latex, Regitex, solids concentration 65%), so that the mass ratio of rubber component (solids of natural rubber latex) to solids of TEMPO oxidized CNF was 100:20. The mixture was stirred for 10 minutes using a TK homogenizer (8000 rpm). The resulting mixture was then dried in a heating oven at 70°C for 5 hours.

[0214] The dried material is passed through the gap between the rollers about 5 times using an open roller (manufactured by Kansai Roller Co., Ltd.) to make it visually uniform, resulting in unvulcanized intermediate compound 1 sheets.

[0215] The obtained intermediate compound 1 is cut into sheets approximately 20 cm in length and then firmly stacked under pressure without becoming fluffy, resulting in 5 to 10 layers. The stacked sheets are placed in a polyethylene bag, which serves as the inner bag, and secured to prevent shifting. Two bundles of the stacked sheets filled in the inner bag are then wrapped in corrugated cardboard of appropriate size. The mixture is then left to stand at room temperature for one week.

[0216] Then, the corrugated paper bundled with intermediate compound 1 is transported by truck to the rubber processing plant, which serves as the second mixing site. At the second mixing site, the presence or absence of crimping when removing the intermediate compound from the bundle is visually confirmed, and workability is evaluated according to the following criteria (ease of removal from the bundle and ease of subsequent processing).

[0217] <Presence or absence of crimping>

[0218] A: No crimping was observed.

[0219] B: Crimping was observed.

[0220] <Operational>

[0221] A: It can be easily removed from the bundle without any difficulty, and the stacked sheets are not crimped, so they can be easily separated one by one, making it highly workable.

[0222] B: Due to the crimping of the sheets, they are difficult to remove from the bundle and difficult to separate one sheet at a time.

[0223] In intermediate compound 1, pure rubber sheets made from natural rubber latex (trade name: HA latex, Regitex, solids concentration 65%) are subjected to multiple rolling processes using open rollers at a mass ratio of 20:80, thereby diluting and mixing to obtain a rubber composition with a microcellulose fiber content of 5 parts by weight.

[0224] <Example 2>

[0225] The mixture of TEMPO oxidized CNF and natural rubber latex was dried using a twin-drum dryer (surface temperature 130 degrees Celsius / speed 1 rpm). Otherwise, intermediate compound 2 was obtained in the same manner as in Example 1. The intermediate compound 2 was bundled in the same manner as in Example 1 and left for one week. The presence or absence of pressing at the destination was then visually confirmed.

[0226] <Example 3>

[0227] The intermediate compound 3 was obtained in the same manner as in Example 1, except that the TEMPO oxidized MFC obtained in Manufacturing Example 2 was used instead of the TEMPO oxidized CNF. The intermediate compound 3 was bundled in the same manner as in Example 1 and left for 1 week. The presence or absence of crimping at the destination was then visually confirmed.

[0228] <Comparative Example 1>

[0229] Intermediate compound 4 was obtained in the same manner as in Example 1, except that TEMPO oxidized CNF was not mixed in. The intermediate compound 4 was bundled in the same manner as in Example 1 and left for 1 week. The presence or absence of crimping at the destination was then visually confirmed.

[0230] [Table 1]

[0231] According to the method for supplying the rubber composition of the present invention, by using an intermediate compound containing fine cellulose fibers with an average fiber length of more than 400 nm dispersed in a high concentration as a masterbatch, a rubber composition containing fine cellulose fibers can be easily obtained in a rubber processing plant.

Claims

1. A method for supplying a rubber composition, said rubber composition containing fine cellulose fibers, characterized in that, In the first mixing area, an intermediate compound is obtained by forming a mixture of fine cellulose fibers with a length-weighted average fiber length exceeding 400 nm and rubber latex into sheets. After the intermediate compound is transferred to the second mixing area in a multi-layered bundled form, The intermediate mixture is diluted in a second mixing area and further mixed.

2. The method for supplying the rubber composition according to claim 1, characterized in that, The length-weighted average diameter of the microcellulose fibers is greater than 1 nm and less than 20 nm.

3. The method for supplying the rubber composition according to claim 1 or 2, characterized in that, The intermediate compound contains fine cellulose fibers in the range of 10 to 40% by weight.

4. The method of supplying the rubber composition according to claim 1 or 2, characterized in that, The intermediate mixture is stacked and bundled without applying a release agent or attaching a protective film.

5. The method of supplying the rubber composition according to claim 1 or 2, characterized in that, The intermediate compound is unvulcanized.

6. The method of supplying the rubber composition according to claim 1 or 2, characterized in that, The intermediate compound is formed into sheets by a roll mixing method.

7. The method of supplying the rubber composition according to claim 1 or 2, characterized in that, The fine cellulose is modified with anions.

8. The method of supplying the rubber composition according to claim 1 or 2, characterized in that, The fine cellulose was not hydrophobically treated.

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