Method for supplying rubber composition containing fine cellulose fiber

Abstract

The present invention is a method for supplying a rubber composition containing fine cellulose fibers, the method being characterized by obtaining an intermediate kneaded material in which a mixture of a rubber latex and a fine cellulose fiber having a length-weighted average fiber length of more than 400 nm is molded into a sheet shape at a first kneading place, transferring the intermediate kneaded material to a second kneading place in a packed form in which a plurality of the intermediate kneaded materials are stacked, and then diluting the intermediate kneaded material and further kneading the diluted intermediate kneaded material at the second kneading place.

Description

Method for supplying rubber composition containing fine cellulose fibers

[0001] The present invention relates to a method for supplying a rubber composition containing fine cellulose fibers.

[0002] It is known that rubber compositions produced from a masterbatch containing a rubber component and cellulosic fibers have excellent mechanical strength. For example, Patent Document 1 describes that a rubber / short fiber masterbatch in which the short fibers are uniformly dispersed in rubber can be obtained by fibrillating short fibers having an average fiber diameter of less than 0.5 μm in water, mixing the resulting dispersion with rubber latex, and drying the mixture. It also describes that a rubber composition having an excellent balance between rubber reinforcement and fatigue resistance can be produced from this masterbatch.

[0003] Japanese Patent Application Laid-Open No. 2006-206864

[0004] However, unless fine cellulose fibers such as cellulose nanofibers are uniformly dispersed in a rubber composition, it is difficult for the expected effects to be achieved. Therefore, there has been a demand for a method for supplying a rubber composition containing fine cellulose fibers that can be more easily and uniformly dispersed so that uniform desired effects can be obtained at various rubber processing plants with different working conditions.

[0005] The present invention aims to provide a method for supplying a rubber composition containing fine cellulose fibers that can be easily and uniformly dispersed and that is likely to exhibit the desired effects, and also aims to provide a method for supplying a rubber composition that prevents compression bonding in an unvulcanized state and is easy to work with in rubber processing plants.

[0006] As a result of extensive investigation, the present inventors have found that the problems can be solved by the following (1) to (8). (1) A method for supplying a rubber composition containing fine cellulose fibers, comprising: forming an intermediate kneaded product into a sheet-like shape at a first kneading location from a mixture of fine cellulose fibers having a length-weighted average fiber length of more than 400 nm and rubber latex; transporting the intermediate kneaded product to a second kneading location in a packaged form in which multiple layers are stacked; and diluting and further kneading the intermediate kneaded product at the second kneading location. (2) The method for supplying a rubber composition according to (1), wherein the fine cellulose fibers have a length-weighted average fiber diameter of 1 nm or more and 20 nm or less. (3) The method for supplying a rubber composition according to (1) or (2), wherein the intermediate kneaded product contains the fine cellulose fibers in an amount of 10 to 40% by weight. (4) The method for supplying a rubber composition according to (1) or (2), characterized in that the intermediate kneaded product is laminated and packaged without being subjected to treatments such as coating with a release agent or attaching a protective film. (5) The method for supplying a rubber composition according to (1) or (2), characterized in that the intermediate kneaded product is unvulcanized. (6) The method for supplying a rubber composition according to (1) or (2), characterized in that the intermediate kneaded product is formed into a sheet by a roll kneading method. (7) The method for supplying a rubber composition according to (1) or (2), characterized in that the fine cellulose is anion-modified. (8) The method for supplying a rubber composition according to (1) or (2), characterized in that the fine cellulose has not been subjected to a hydrophobic treatment.

[0007] According to the present invention, a method for supplying a rubber composition containing fine cellulose fibers that can be easily and uniformly dispersed and that is likely to exhibit the desired effects can be provided, and a method for supplying a rubber composition that prevents compression bonding in an unvulcanized state and is excellent in workability in rubber processing plants can be provided.

[0008] (1. Raw Materials for Rubber Composition) The raw materials for the rubber composition contain at least fine cellulose fibers and a rubber component, and may contain additives as needed. Each raw material will be described below.

[0009] (1.1 Microfibrillated Cellulose Fibers) Microfibrillated cellulose fibers are fine fibrous cellulose derived from cellulose raw materials. Microfibrillated cellulose, for example, exhibits a light transmittance of 1 to 99% when a dispersion (1 wt%) of microfibrillated cellulose fibers is measured at an optical path length of 1 cm / 660 nm using a visible spectrophotometer (UV-1800, manufactured by Shimadzu Corporation). Methods for producing microfibrillated cellulose fibers include a method of defibrating pulp and a method of chemically modifying the pulp before or after defibration (usually before defibration) as needed. Microfibrillated cellulose fibers with a fiber diameter on the nano-order are called cellulose nanofibers, and microfibrillated cellulose fibers with a fiber diameter on the micron order are called cellulose microfibrils. The size of the microfibrillated cellulose fibers can be adjusted by the conditions of the microfibrillation treatment and chemical modification treatment, etc.

[0010] Furthermore, powdered cellulose does not disperse even when stirred in a solvent such as water, but rather settles, making it impossible to measure the light transmittance of the dispersion, and therefore is clearly distinguishable from fine cellulose fibers.

[0011] (Example of Fine Cellulose Fiber: Cellulose Nanofiber) In this specification, cellulose nanofiber (CNF) means cellulose fiber having a fiber diameter on the nano-order, which is prepared through a micronization treatment.

[0012] The average fiber diameter (length-weighted average fiber diameter) of the 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. There is no particular lower limit, but it is usually 1 nm or more, preferably 2 nm or more. Therefore, the average fiber diameter (length-weighted average fiber diameter) of the CNF is usually 1 to 500 nm or 2 to 500 nm, preferably 2 to 300 nm or 2 to 100 nm, more preferably 1 to 50 nm, 1 to 30 nm, or 1 to 20 nm.

[0013] It is important that the average fiber length (length-weighted average fiber length) is more than 400 nm, preferably 420 nm or more, and more preferably 440 nm or more. The upper limit is preferably 3000 nm or less, more preferably 2000 nm or less, even more preferably 1500 nm or less, 1000 nm or less, or 800 nm or less.

[0014] The average fiber diameter and average fiber length of the fine cellulose fibers can be obtained by averaging the fiber diameter and fiber length obtained from the observation of each fiber using a fractionator manufactured by Valmet Co., Ltd., a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM) appropriately selected depending on the fiber diameter. When a fractionator is used, the average fiber diameter and average fiber length can be determined as the length-weighted fiber width and the length-weighted average fiber length, respectively.

[0015] (Example of Fine Cellulose Fiber: Cellulose Microfibril) In this specification, cellulose microfibril (microfibrillated cellulose, MFC) means cellulose fiber having a fiber diameter on the order of microns, which is prepared through a pulverization treatment.

[0016] The average fiber diameter of MFC is usually 500 nm or more, preferably 1 μm or more, and more preferably 3 μm or more. This allows it to exhibit higher water retention than undefibrated cellulose fibers, and even a small amount can provide higher strength and yield improvement effects than finely defibrated CNF. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 20 μm or less, but there is no particular limit.

[0017] The average fiber length is usually 10 μm or more, preferably 20 μm or more, more preferably 40 μm or more. The upper limit is not particularly limited, but is usually 3,000 μm or less, preferably 2,500 μm or less, more preferably 2,000 μm or less, even more preferably 1,500 μm or less, 1,000 μm or less, 500 μm or less, 400 μm or less, or 200 μm or less.

[0018] (Modification) The microfibrillated cellulose fibers may be modified or unmodified. Modified microfibrillated cellulose fibers refer to microfibrillated cellulose fibers (e.g., cellulose nanofibers, cellulose microfibrils) in which at least one of the three hydroxyl groups contained in the glucose unit has been chemically modified (hereinafter simply referred to as "modified"). The chemical modification treatment sufficiently refines the cellulose fibers, and cellulose nanofibers with a uniform average fiber diameter can be obtained by defibration. Therefore, when composited with a rubber component, a sufficient reinforcing effect can be exhibited. From this perspective, modified (particularly anionically modified) cellulose fibers are preferred. Furthermore, it is preferable that the microfibrillated cellulose fibers used in the present invention have not been subjected to a hydrophobic treatment.

[0019] Examples of the modification include anionic modification such as oxidation, etherification, esterification such as phosphate esterification, and the like, as well as silane coupling, fluorination, cationization, etc. Among these, oxidation (carboxylation), etherification, cationization, and esterification are preferred, with oxidation (carboxylation) being more preferred.

[0020] - Oxidation (Carboxylation) - Oxidized fine cellulose fibers typically have a structure in which at least one carbon atom bearing a primary hydroxyl group contained in a glucopyranose unit constituting the cellulose molecular chain (e.g., the carbon atom bearing a primary hydroxyl group at the C6 position) is oxidized. The amount of carboxyl groups in oxidized cellulose fibers or 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, based on the bone dry mass. The upper limit of this amount is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, and even more preferably 2.0 mmol / g or less. The amount of carboxyl groups is preferably 0.5 to 3.0 mmol / g, more preferably 0.8 to 2.5 mmol / g, and even more preferably 1.0 to 2.0 mmol / g. The amount of carboxyl groups can be adjusted by controlling the conditions for oxidizing the cellulose fibers (e.g., the amount of oxidizing agent added, the reaction time). Furthermore, by controlling these conditions, the amount of carboxylate groups and aldehyde groups can also be adjusted.

[0021] The amount of carboxy groups can be calculated using the following procedure. 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose is prepared. 0.1 M aqueous hydrochloric acid is added to the prepared slurry to adjust the pH to 2.5. 0.05 N aqueous sodium hydroxide is then added dropwise, and the electrical conductivity is measured until the pH reaches 11. The amount of carboxy groups is calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid, where the change in electrical conductivity is gradual: Amount of carboxy groups [mmol / g oxidized cellulose] = a [mL] × 0.05 / mass of oxidized cellulose [g]

[0022] The oxidation method is not particularly limited, but an example is a method in which a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound, a bromide, an iodide, or a mixture thereof. According to this method, the C6 position of the glucopyranose ring on the surface of cellulose is selectively oxidized to produce an aldehyde group, a carboxy group (—COOH), and a carboxylate group (—COO －The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by mass or less.

[0023] An N-oxyl compound refers to a compound capable of generating a nitroxy radical. Examples of nitroxyl radicals include 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO). Any compound that promotes the target oxidation reaction can be used as the N-oxyl compound. The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing the raw cellulose. For example, per 1 g of bone-dry cellulose raw material, the amount 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 the N-oxyl compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.02 to 0.5 mmol, per 1 g of bone-dry cellulose raw material. The amount of the N-oxyl compound used in the reaction system is typically 0.1 to 4 mmol / L.

[0024] Bromides are compounds containing bromine, such as alkali metal bromides that can dissociate and ionize in water. Iodides are compounds containing iodine, such as alkali metal iodides. The amount of bromide or iodide used can be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol, per 1 g of bone-dry cellulose raw material.

[0025] Known oxidizing agents can be used, such as halogens, hypohalous acids, halous acids, perhalogen acids or their salts, halogen oxides, and peroxides. Among these, hypohalous acids or their salts are preferred because they are inexpensive and have a low environmental impact, hypochlorous acid or its salts are more preferred, and sodium hypochlorite is preferred. The appropriate amount of oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and even more preferably 3 to 10 mmol, per 1 g of bone-dry cellulose raw material. Furthermore, for example, 1 to 40 mol is preferred per 1 mol of the N-oxyl compound.

[0026] The oxidation process of cellulose raw materials proceeds efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, and may also be about 15 to 30°C, i.e., room temperature. As the reaction proceeds, carboxyl groups are generated in the cellulose, resulting in a decrease in the pH of the reaction solution. To efficiently proceed with the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8 to 12, or 10 to 11. Water is preferred as the reaction medium because it is easy to handle and is less likely to cause side reactions.

[0027] The reaction time in the oxidation reaction can be appropriately set depending on the degree of progress of the oxidation, and is usually from 0.5 to 6 hours, for example, from about 0.5 to 4 hours.

[0028] The oxidation reaction may be carried out in two stages. For example, the oxidized cellulose obtained by filtration after the completion of the first-stage reaction can be oxidized again under the same or different reaction conditions, thereby enabling efficient oxidation without reaction inhibition by sodium chloride produced as a by-product in the first-stage reaction.

[0029] Another example of a carboxylation (oxidation) method is a method in which cellulose raw materials are oxidized by contacting them with an ozone-containing gas (ozone oxidation). This oxidation reaction oxidizes at least the hydroxyl groups at positions 2 and 6 of the glucopyranose ring, and decomposes the cellulose chain. The ozone concentration in the ozone-containing gas is 50 to 250 g / m.３ is preferred, and 50 to 220 g / m ３ The amount of ozone added is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass, based on 100 parts by mass of the solids content of the cellulose raw material. The ozone treatment temperature is preferably 0 to 50°C, and more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, and preferably about 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, and a good yield of oxidized cellulose can be achieved.

[0030] After the ozone treatment, a further oxidation treatment may be carried out using an oxidizing agent. The oxidizing agent used in the further oxidation treatment is not particularly limited, but examples include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. The further oxidation treatment may be carried out, for example, by dissolving the oxidizing agent in water or a polar organic solvent such as alcohol to prepare an oxidizing agent solution, and then immersing the oxidized cellulose in the solution.

[0031] An example of a method for measuring the amount of carboxy groups is explained below. 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose is prepared, and a 0.1 M aqueous hydrochloric acid solution is added to adjust the pH to 2.5. A 0.05 N aqueous sodium hydroxide solution is then added dropwise, and the electrical conductivity is measured until the pH reaches 11. The amount of carboxy groups can be calculated using the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid, where the change in electrical conductivity is gradual, using the following (Equation 2): (Equation 2): Amount of carboxy groups [mmol / g (oxidized cellulose or oxidized cellulose nanofiber)] = a [mL] × 0.05 / mass of oxidized cellulose or oxidized cellulose nanofiber [g]

[0032] - Acid-type oxidized cellulose and desalting - Oxidized cellulose contains carboxy groups as a result of oxidation, but the acid-type carboxy groups (-COOH) are converted to salt-type carboxy groups (e.g., -COOH). －, —COONa) or may contain more salt-type carboxy groups than acid-type carboxy groups. The amounts of salt-type carboxy groups and acid-type carboxy groups can be adjusted by desalting treatment. Salt-type carboxy groups can be converted to acid-type carboxy groups by desalting treatment. In this specification, oxidized cellulose (which has undergone desalting) is referred to as acid-type oxidized cellulose, and oxidized cellulose (which has not undergone the desalting treatment described below) is referred to as salt-type oxidized cellulose. Salt-type oxidized cellulose usually contains primarily salt-type carboxy groups. On the other hand, acid-type oxidized cellulose contains many acid-type carboxy groups, and the proportion of acid-type carboxy groups in the carboxy groups is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. Acid-type oxidized cellulose can exhibit a superior reinforcing effect. The proportion of acid-type carboxy groups can be calculated by the following procedure.

[0033] 1) First, 250 mL of an aqueous dispersion of acid-form oxidized cellulose with a solids concentration of 0.1% by mass before desalting is prepared. A 0.1 M aqueous hydrochloric acid solution is added to the prepared aqueous dispersion to adjust the pH to 2.5, and then a 0.1 N aqueous sodium hydroxide solution is added and the electrical conductivity is measured until the pH reaches 11. The amount of acid-form carboxy groups and the amount of salt-form carboxy groups, i.e., the total amount of carboxy groups, is calculated using the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid, where the change in electrical conductivity is gradual, using the following formula: Total amount of carboxy groups (mmol / g oxidized cellulose (salt form)) = a (mL) × 0.1 / mass (g) of oxidized cellulose (salt form) 2) 250 mL of an aqueous dispersion of desalted acid-form oxidized cellulose with a solids concentration of 0.1% by mass is prepared. A 0.1 N aqueous sodium hydroxide solution is added to the prepared aqueous dispersion and the electrical conductivity is measured until the pH reaches 11. The amount of acid-type carboxy groups is calculated using the following formula from the amount of sodium hydroxide (b) consumed in the neutralization stage of a weak acid where the change in electrical conductivity is gradual: Amount of acid-type carboxy groups (mmol / g acid-type oxidized cellulose) = b (mL) × 0.1 / mass of acid-type oxidized cellulose (g) 3) The proportion of acid-type carboxy groups is calculated using the calculated total amount of carboxy groups and the amount of acid-type carboxy groups using the following formula: Proportion of acid-type carboxy groups (%) = (amount of acid-type carboxy groups / total amount of carboxy groups) × 100

[0034] Desalting can be carried out after oxidation, either before or after defibration (before or after step (2)). However, it is usually carried out after oxidation, and preferably before step (2). Desalting is usually carried out by substituting salts (e.g., sodium salts) contained in the salt-form oxidized cellulose with protons. Examples of desalting methods include adjusting the system to an acidic state and contacting the oxidized cellulose with a cation exchange resin. When adjusting the system to an acidic state, the pH of the system is preferably adjusted to 2 to 6, more preferably 2 to 5, and even more preferably 2.3 to 5. To adjust the system to an acidic state, an acid (e.g., inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid, and phosphoric acid; organic acids such as acetic acid, lactic acid, oxalic acid, citric acid, and formic acid) is usually used. After the addition of the acid, a washing treatment may be carried out as appropriate. As the cation exchange resin, either a strongly acidic or a weakly acidic ion exchange resin can be used as long as the counter ion is H+. The ratio of the oxidized cellulose and the cation exchange resin when they are contacted is not particularly limited, and can be appropriately determined by a person skilled in the art from the viewpoint of efficient proton substitution. After contact, the cation exchange resin can be recovered by a conventional method such as suction filtration.

[0035] -Etherification- Examples of etherification include carboxyalkylation, methylation, ethylation, cyanoethylation, hydroxyethylation, hydroxypropylation, ethylhydroxyethylation, and hydroxypropylmethylation. Carboxyalkylation is preferred, and carboxymethylation is more preferred.

[0036] Carboxyalkylated cellulose fibers typically have a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is carboxymethylated.

[0037] The degree of carboxyalkyl substitution (DS, preferably the degree of carboxymethyl substitution) per anhydroglucose unit of the carboxyalkylated cellulose is preferably 0.01 or more, 0.02 or more, or 0.05 or more, more preferably 0.10 or more, even more preferably 0.15 or more, even more preferably 0.20 or more, and particularly preferably 0.25 or more. This ensures a degree of substitution sufficient to obtain the effects of chemical modification. The upper limit of the degree of substitution is preferably 0.50 or less, more preferably 0.45 or less, 0.40 or less, or 0.35 or less. This makes it difficult for the cellulose fibers to dissolve in water, allowing the fiber form to be maintained in water. Therefore, the degree of carboxyalkyl substitution is preferably 0.01 to 0.50, more preferably 0.01 to 0.45, even more preferably 0.02 to 0.40, 0.10 to 0.35, or 0.15 to 0.30.

[0038] The degree of substitution, for example, the degree of carboxymethyl substitution, can be measured by the following method. Approximately 2.0 g of carboxymethylated cellulose (bone dry) is weighed out and placed in a 300 mL Erlenmeyer flask with a ground stopper. 100 mL of a solution of 1,000 mL of methanol and 100 mL of concentrated nitric acid is added, and the mixture is shaken for 3 hours to convert the salt-form carboxymethylated cellulose (hereinafter also referred to as "salt-form carboxymethylated cellulose") to the acid-form carboxymethylated cellulose (hereinafter also referred to as "acid-form carboxymethylated cellulose"). 1.5 to 2.0 g of acid-form carboxymethylated cellulose (bone dry) is weighed out and placed in a 300 mL Erlenmeyer flask with a ground stopper. The acid-form carboxymethylated cellulose is wetted with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH is added, and the mixture is shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, excess NaOH is back-titrated with 0.1N H2SO4, and the degree of carboxymethyl substitution (DS) can be calculated by the following formula: A = [(100 x F - (0.1N H2SO4 (mL)) x F') x 0.1] / (bone-dry mass (g) of acid-type carboxymethylated cellulose) DS = 0.162 x A / (1 - 0.058 x A) A: amount (mL) of 1N NaOH required to neutralize 1 g of acid-type carboxymethylated cellulose F': factor of 0.1N H2SO4 F: factor of 0.1N NaOH

[0039] The degree of carboxyalkyl substitution can be adjusted by controlling the reaction conditions such as the amount of the carboxyalkylating agent to be reacted, the amount of the mercerizing agent, and the composition ratio of water to the organic solvent.

[0040] As a method of carboxyalkylation, for example, a method in which a cellulosic raw material as a starting material (bottom raw material) is mercerized and then etherified can be mentioned. Carboxymethylation will be explained below as an example.

[0041] Carboxymethylated cellulose can be produced by using unmodified cellulose fibers (cellulose raw material: e.g., pulp) as the starting material, subjecting them to a mercerization treatment, followed by an etherification reaction. This reaction is typically carried out in the presence of a solvent. Examples of the solvent include water and lower alcohols (e.g., methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and tertiary butanol), either singly or in combination. When a lower alcohol is mixed, the mixing ratio of the lower alcohol is preferably 60 to 95% by mass. The amount of solvent is approximately three times the amount of the cellulose raw material, in mass terms. The upper limit of this amount is not particularly limited, but is preferably 20 times or less. The amount of solvent is preferably 3 to 20 times the amount of the cellulose raw material, in mass terms.

[0042] Examples of the mercerizing agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.

[0043] The amount of the mercerizing agent used is, in molar terms, preferably 0.5 times or more, more preferably 1.0 times or more, and even more preferably 1.5 times or more per anhydroglucose residue of the starting material. The upper limit of this amount is usually 20 times or less, preferably 10 times or less, and more preferably 5 times or less. The amount of the mercerizing agent used is, in molar terms, preferably 0.5 to 20 times, more preferably 1.0 to 10 times, and even more preferably 1.5 to 5 times.

[0044] The reaction temperature for mercerization is usually 0° C. or higher, preferably 10° C. or higher. The upper limit is usually 70° C. or lower, preferably 60° C. or lower. The reaction temperature is usually 0 to 70° C., preferably 10 to 60° C.

[0045] The reaction time for mercerization is usually 15 minutes or more, preferably 30 minutes or more. The upper limit is usually 8 hours or less, preferably 7 hours or less. The reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

[0046] The etherification reaction is usually carried out by adding a carboxymethylating agent, such as sodium monochloroacetate, to the reaction system after mercerization.

[0047] The amount of the carboxymethylating agent added is, in molar terms, preferably 0.05 times or more, more preferably 0.5 times or more, and even more preferably 0.8 times or more per glucose residue of the cellulose raw material. The upper limit of this amount is usually 10.0 times or less, preferably 5 times or less, and more preferably 3 times or less. The amount of the carboxymethylating agent added is, in molar terms, preferably 0.05 to 10.0 times, more preferably 0.5 to 5 times, and even more preferably 0.8 to 3 times.

[0048] The reaction temperature is usually 30°C or higher, preferably 40°C or higher. The upper limit is usually 90°C or lower, preferably 80°C or lower. The reaction temperature is usually 30 to 90°C, preferably 40 to 80°C. The reaction time is usually 30 minutes or longer, preferably 1 hour or longer. The upper limit is usually 10 hours or shorter, preferably 4 hours or shorter. The reaction time is usually 30 minutes to 10 hours, preferably 1 hour to 4 hours. During the carboxymethylation reaction, the reaction solution may be stirred as needed.

[0049] -Differences from carboxymethyl cellulose- Carboxyalkylated cellulose fibers preferably maintain at least a portion of their fibrous shape when dispersed in water. Carboxyalkylated cellulose fibers are distinguished from carboxymethyl cellulose, a type of water-soluble polymer that dissolves in water and imparts viscosity. When an aqueous dispersion of carboxyalkylated cellulose fibers is observed under an electron microscope, fibrous substances can be observed. On the other hand, when an aqueous dispersion of carboxymethyl cellulose, a type of water-soluble polymer, is observed, fibrous substances are usually not observed. Furthermore, when anion-modified cellulose fibers are measured by X-ray diffraction, peaks of cellulose type I crystals can be observed, but when carboxymethyl cellulose powder, a water-soluble polymer, is similarly measured, cellulose type I crystals are usually not observed.

[0050] - Acid-type carboxyalkylated cellulose and desalting - Carboxyalkylated cellulose may contain more acid-type carboxy groups than salt-type carboxy groups, or may contain more salt-type carboxy groups than acid-type carboxy groups. The amounts of salt-type carboxy groups and acid-type carboxy groups can be adjusted by desalting treatment. By desalting treatment, salt-type carboxy groups can be converted to acid-type carboxy groups. In this specification, carboxyalkylated cellulose (which has been subjected to desalting) is referred to as acid-type carboxyalkylated cellulose, and carboxyalkylated cellulose (which has not been subjected to the desalting treatment described below) is referred to as salt-type carboxyalkylated cellulose. Salt-type carboxyalkylated cellulose usually contains more salt-type carboxy groups (-COO － On the other hand, acid-type carboxyalkylated cellulose has a large number of acid-type carboxy groups, and the ratio of the amount of acid-type carboxy groups to the amount of carboxy groups in the acid-type carboxyalkylated cellulose is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. The method for calculating the proportion of acid-type carboxy groups is as described above.

[0051] The desalting is usually carried out after carboxyalkylation, preferably after etherification and before fibrillation. For example, the desalting method may be a method of contacting the carboxyalkylated cellulose with a cation exchange resin. The cation exchange resin has a counter ion of H ＋ As long as the cation exchange resin is strong acidic or weak acidic, either a strong acidic or a weak acidic ion exchange resin can be used. The ratio of the carboxyalkylated cellulose and the cation exchange resin when contacting them is not particularly limited, and can be appropriately determined by a person skilled in the art from the viewpoint of efficient proton substitution. For example, the ratio can be adjusted so that the pH of the aqueous dispersion after addition of the cation exchange resin to the carboxyalkylated cellulose aqueous dispersion is preferably 2 to 6, more preferably 2 to 5. The cation exchange resin after contact can be recovered by a conventional method such as suction filtration.

[0052] Esterification (Phosphorylation) A first example of an esterified cellulose fiber is a phosphorylated cellulose fiber. Phosphorylated cellulose usually has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is phosphorylated.

[0053] The amount of ionic substituent introduced into the phosphated cellulose fiber (ionic substituent amount, phosphorus oxo acid substituent amount) may be 0.10 mmol / g or more per 1 g (mass) of phosphated CNF, preferably 0.20 mmol / g or more, more preferably 0.30 mmol / g or more, even more preferably 0.40 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably 0.60 mmol / g or more, and particularly preferably 0.70 mmol / g or more. The amount of ionic substituent introduced into the phosphated CNF may be 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. The amount of ionic substituent introduced into the phosphated cellulose fiber is also preferably 1.00 mmol / g or less per 1 g (mass) of phosphated cellulose fiber, more preferably 0.95 mmol / g or less. Here, the denominator in the unit mmol / g is the value obtained when the counter ion of the ionic substituent is a hydrogen ion (H ＋ The amount of phosphorus oxo acid substituents can be measured by the following method.

[0054] (Measurement of phosphorus oxoacid group content) The phosphorus oxoacid group content of fine cellulose fibers can be measured by treating a cellulose fiber-containing slurry prepared by diluting a fine cellulose fiber dispersion containing the target fine cellulose fibers with ion exchange water to a content of 0.2 mass %, followed by titration using an alkali.

[0055] The treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above cellulose fiber-containing slurry, shaking for 1 hour, and then pouring it onto a mesh with 90 μm openings to separate the resin from the slurry.

[0056] In addition, the alkali titration was performed by adding 10 μL of 0.1 N sodium hydroxide aqueous solution every 5 seconds to the cellulose fiber-containing slurry after treatment with the ion exchange resin, while measuring the change in the pH value of the slurry. Nitrogen gas was blown into the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (differential value of pH with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. Of these, the maximum point of increment obtained first after starting the addition of alkali is called the first endpoint, and the maximum point of increment obtained next 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. The amount of alkali (mmol) required from the start of titration to the first endpoint was divided by the solid content (g) in the slurry to be titrated to determine the amount of phosphorus oxoacid groups (mmol / g). The presence or absence of phosphate groups was confirmed by measuring the infrared absorption spectrum, and the absorption due to phosphate groups (1230 cm －１ This may be done by checking the area around the

[0057] The amount of phosphate groups can be adjusted by controlling the reaction conditions such as the amount of the compound having a phosphate group added and the amount of the basic compound added as needed.

[0058] Examples of phosphorylation methods include a method of reacting unmodified cellulose fibers with a compound having a phosphate group (phosphorylation). Examples of phosphate esterification methods include a method of mixing a powder or aqueous solution of a compound having a phosphate group with a cellulosic raw material (e.g., a suspension (solids concentration of about 0.1 to 10% by mass)), and a method of adding an aqueous solution of a compound having a phosphate group to an aqueous dispersion of the cellulosic raw material, with the latter being preferred. This can increase the uniformity of the reaction and the efficiency of esterification. The pH of the aqueous solution of the compound having a phosphate group is preferably 7 or less from the viewpoint of increasing the efficiency of introduction of the phosphate group, and more preferably 3 to 7 from the viewpoint of suppressing hydrolysis.

[0059] Examples of compounds having a phosphate group include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, esters and salts thereof, etc. These compounds are low-cost and easy to handle, and can be used to introduce phosphate groups into cellulose, thereby improving defibration efficiency. Specific examples of compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate. One or more compounds having a phosphate group can be used in combination. The amount of the compound having a phosphate group added to the cellulose raw material is preferably 0.1 to 500 parts by mass, more preferably 1 to 400 parts by mass, and even more preferably 2 to 200 parts by mass, in terms of elemental phosphorus, per 100 parts by mass of the solids content of the cellulose raw material. This allows for efficient yields commensurate with the amount of compound having a phosphate group used. The reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C. The reaction time is not particularly limited, but is usually about 1 to 600 minutes, preferably 30 to 480 minutes. When the esterification reaction conditions are within any of these ranges, it is possible to prevent the cellulose from being excessively esterified and becoming more soluble, thereby improving the yield of phosphated cellulose. When reacting a compound having a phosphate group, a basic compound (e.g., a compound having an amino group that exhibits basicity, such as urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, or hexamethylenediamine) may be further added to the reaction system.

[0060] The suspension obtained after esterification is preferably dehydrated as needed, and then subjected to a heat treatment after dehydration. This can suppress hydrolysis of the cellulose raw material. The heating temperature is preferably 100 to 170°C. During the heat treatment, while water is still present, it is more preferable to heat at 130°C or lower (preferably 110°C or lower), and after removing the water, to heat at 100 to 170°C. After boiling, a washing treatment such as washing with cold water and / or a neutralization treatment is preferably performed. This allows for efficient defibration. Washing can be performed by adding water and then dehydrating (e.g., filtration), and may be repeated two or more times. Washing is preferably performed until the electrical conductivity of the filtrate decreases. For example, it can be performed until the electrical conductivity is preferably 200 or lower, more preferably 150 or lower, and even more preferably 120 or lower. Furthermore, after washing, a neutralization treatment may be performed as needed. The neutralization treatment can be performed by adding an alkali (e.g., sodium hydroxide), for example. Washing may be performed again after neutralization.

[0061] - Esterification (Phosphite Esterification) - A second example of a method for producing an esterified cellulose fiber is a phosphite cellulose fiber. Phosphite cellulose fibers usually have a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is phosphorous-substituted.

[0062] The degree of substitution of phosphite groups per glucose unit in phosphite-esterified cellulose fibers (hereinafter simply referred to as "phosphite group substitution degree") is preferably 0.001 to 0.60. This facilitates electrical repulsion between cellulose molecules, facilitating nanofibrillation. The degree of substitution of phosphite groups can be measured using the same method as for measuring the degree of phosphate group substitution. The degree of substitution of phosphite groups can be adjusted by controlling reaction conditions such as the amount of phosphorous acid or its salt added, and the amount of alkali metal ion-containing material, urea, or its derivative added if necessary.

[0063] As a method for phosphite esterification, for example, a method in which phosphorous acid or a metal salt thereof (preferably sodium hydrogen phosphite) is reacted with unmodified cellulose fibers to introduce a phosphorous acid ester group can be mentioned.

[0064] Examples of phosphorous acid and its metal salts include phosphorous acid compounds such as phosphorous acid, sodium hydrogen phosphite, ammonium hydrogen phosphite, potassium hydrogen phosphite, sodium dihydrogen phosphite, sodium phosphite, lithium phosphite, potassium phosphite, magnesium phosphite, calcium phosphite, triethyl phosphite, triphenyl phosphite, and pyrophosphorous acid, as well as combinations of two or more selected from these, with sodium hydrogen phosphite being preferred. This allows alkali metal ions to be introduced into the cellulose fibers. The amount of phosphorous acid or its metal salts added is preferably 1 to 10,000 g, more preferably 100 to 5,000 g, and even more preferably 300 to 1,500 g per kg of unmodified cellulose fibers. In addition to phosphorous acid and its metal salts, an alkali metal ion-containing substance (e.g., hydroxide, metal sulfate, metal nitrate, metal chloride, metal phosphate, or metal carbonate) may also be added to the reaction system.

[0065] Urea or a derivative thereof may also be added to the reaction system. This allows carbamate groups to be introduced into the cellulose fibers. Examples of urea and urea derivatives include urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, and combinations of two or more selected from these, with urea being preferred. The amount of urea and urea derivative added is preferably 0.01 to 100 mol, more preferably 0.2 to 20 mol, and even more preferably 0.5 to 10 mol per mol of phosphorous acid or its metal salt.

[0066] The reaction temperature is preferably 100 to 200°C, more preferably 100 to 180°C, and even more preferably 100 to 170°C. During the heat treatment, while water is present, it is more preferable to heat at 130°C or lower (preferably 110°C or lower), and after removing the water, to heat treat at 100 to 170°C. The reaction time is usually about 10 to 180 minutes, more preferably 30 to 120 minutes. The phosphite-esterified cellulose fiber is preferably washed prior to defibration. The degree of substitution of phosphite groups per glucose unit is preferably 0.01 or higher but less than 0.23.

[0067] Esterification (sulfate esterification)—A third example of a method for producing an esterified cellulose fiber is a sulfated cellulose fiber. Sulfated cellulose fibers usually have a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing a primary hydroxyl group at C6 constituting the glucopyranose unit) is phosphorylated.

[0068] The amount of sulfate groups per glucose unit in sulfated cellulose fibers (hereinafter simply referred to as "sulfate group amount") is preferably 0.42 to 9.9 mmol / g, more preferably 0.5 mmol / g to 2.0 mmol / g. Introducing sulfate groups into the cellulose raw material causes electrical repulsion between cellulose molecules. Therefore, sulfated cellulose with sulfate groups introduced can be easily defibrated to nanofibers. When the amount of sulfate groups is 0.42 mmol / g or more, sufficient nanofiber defibration can be achieved due to the electrical repulsion between cellulose molecules. On the other hand, when the amount is 9.9 mmol / g or less, swelling or dissolution can be suppressed, preventing a situation in which nanofibers cannot be obtained. For efficient defibration, it is preferable to wash the sulfated cellulose obtained above.

[0069] The amount of sulfate groups per glucose unit can be measured by the following method. An aqueous dispersion of sulfated CNF is solvent-substituted with ethanol and then t-butanol, and then freeze-dried. 15 mL of ethanol and 5 mL of water are added to 200 mg of the obtained sample, and the mixture is stirred for 30 minutes. 10 mL of 0.5 N aqueous sodium hydroxide solution is then added, and the mixture is stirred at 70°C for 30 minutes, and then further stirred at 30°C for 24 hours. Phenolphthalein is then added as an indicator, and the mixture is titrated with hydrochloric acid, and the amount of sulfate groups per glucose unit is calculated using the following formula: Amount of sulfate groups [mmol / g sample] = (5 - (0.1 × titration amount of hydrochloric acid [mL] × 2)) / 0.2

[0070] The amount of sulfate groups can be adjusted by controlling the reaction conditions such as the amount of sulfate compound added to the reaction mixture.

[0071] An example of a method for sulfate esterification is a method in which unmodified cellulose fibers are reacted with a sulfate compound to introduce sulfate groups derived from the sulfate compound into cellulose to produce sulfated cellulose. Examples of sulfate compounds include sulfuric acid, sulfamic acid, chlorosulfonic acid, sulfur trioxide, and esters or salts thereof. Among these, sulfamic acid is preferred because it has low cellulose solubility and low acidity.

[0072] For example, when sulfamic acid is used as the sulfate compound, the amount of sulfamic acid used can be appropriately adjusted taking into consideration the amount of anionic groups introduced into the cellulose chain, and is preferably 0.01 to 50 mol, more preferably 0.1 to 3.0 mol, per mol of glucose unit in the cellulose molecule.

[0073] - Salt type / acid type - Esterified cellulose may contain more acid type carboxy groups than salt type carboxy groups, or may contain more salt type carboxy groups than acid type carboxy groups. Among esterified cellulose, those that have not undergone desalting treatment and those that have undergone desalting treatment are called salt type esterified cellulose and acid type esterified cellulose, respectively. Salt type esterified cellulose mainly contains salt type carboxy groups. Acid type esterified cellulose is presumed to have a superior reinforcing effect. The counter cations of the salt type carboxy groups and the method for preparing them are as explained in the explanation of oxidized cellulose.

[0074] -Cationization- Cationized cellulose usually has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing a primary hydroxyl group at the C6 position constituting a glucopyranose unit) is cationized, and usually contains a cation such as ammonium, phosphonium, or sulfonium, or a group containing such a cation, in the molecule. The degree of cationic substitution per glucose unit in cationized cellulose is preferably 0.02 to 0.50. The degree of cationic substitution per glucose unit can be measured by the following method. After drying the cationized cellulose fiber, the nitrogen content is measured using a total nitrogen analyzer (TN-10 manufactured by Mitsubishi Chemical Corporation), and the degree of cationic substitution (the average number of moles of substituents per mole of anhydroglucose unit) is calculated using the following formula: Degree of cationic substitution=(162×N) / (1−151.6×N), where N is the nitrogen content.

[0075] The degree of cation substitution can be adjusted by adjusting the reaction conditions such as the amount of cationizing agent to be reacted and the composition ratio of water or alcohol having 1 to 4 carbon atoms.

[0076] An example of a cationization method is to react unmodified cellulose fibers with a cationizing agent (e.g., glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydride, or a halohydrin form thereof) and an alkali metal hydroxide catalyst (e.g., sodium hydroxide, potassium hydroxide) in the presence of water and / or an alcohol having 1 to 4 carbon atoms. By using any of the cationizing agents listed above, it is possible to obtain cationized cellulose having a group containing a quaternary ammonium group. The cationization reaction is usually carried out in the presence of water or an alcohol.

[0077] The amount of the cationizing agent is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, relative to 100 parts by mass of the cellulose raw material. The upper limit of the amount is usually 800 parts by mass or less, preferably 500 parts by mass or less.

[0078] Examples of catalysts that may be used as needed during cationization include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of catalyst is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the cellulose raw material. The upper limit of the amount is usually 7 parts by mass or less, preferably 3 parts by mass or less.

[0079] - Base-type cationized cellulose fibers - After cationization, the cationized cellulose fibers are preferably converted into base-type cationized cellulose or base-type cationized cellulose nanofibers by desalting. By desalting, the salt in the cationized cellulose can be converted into a base. In this specification, cationized cellulose (nanofibers) that has undergone desalting is referred to as base-type cationized cellulose (nanofibers) or cationized cellulose (nanofibers) (base type). Furthermore, cationized cellulose and cationized cellulose nanofibers that have not undergone desalting are referred to as salt-type cationized cellulose (nanofibers) or cationized cellulose (nanofibers) (salt type). Desalting may be carried out either before defibration (cationized cellulose) or after defibration (cationized cellulose nanofibers), as described below. Desalting removes salts (for example, Cl) contained in the cationized cellulose (salt type) and cationized cellulose nanofibers (salt type). － ) is replaced with a base to form a base. For example, a method for desalting after cationization includes contacting the cationized cellulose or cationized cellulose nanofiber with an anion exchange resin. Anion exchange resins are used for cations in which the counter ions are OH. － As long as the anion exchange resin is strong-basic or weak-basic, both can be used. The ratio of the two when contacting the modified cellulose with the anion exchange resin is not particularly limited, and a person skilled in the art can appropriately set it from the viewpoint of efficiently carrying out cation substitution. As an example, the ratio can be adjusted so that the pH of the aqueous dispersion after addition of the anion exchange resin to the cationized cellulose nanofiber aqueous dispersion is preferably 8 to 13, more preferably 9 to 13. The anion exchange resin after contact can be recovered by a conventional method such as suction filtration.

[0080] (Refining (defibration, fibrillation)) Refining is usually carried out by a mechanical treatment. The mechanical treatment (preferably beating or defibration) is usually carried out wet (i.e., in the form of an aqueous dispersion of cellulose fibers). Examples of equipment used for the mechanical treatment include refiners (e.g., disc type, conical type, cylinder type), high-speed defibrators, shear-type agitators, colloid mills, high-pressure jet dispersers, beaters, PFI mills, kneaders, dispersers, high-speed defibrators (top finers), high-pressure or ultra-high-pressure homogenizers, grinders (stone-type grinders), ball mills, vibration mills, bead mills, single-screw, twin-screw, or multi-screw kneaders / extruders, homomixers under high-speed rotation, refiners, defibrators, friction grinders, high-shear defibrators, etc. Examples of such a device include a device capable of applying a mechanical defibration force, such as a wet defibrator, a disperger, or a homogenizer (e.g., a microfluidizer), and devices capable of applying a wet defibration force are preferred, with a high-speed disintegrator and a refining device being more preferred, but the device is not particularly limited.

[0081] When defibration is performed by a wet method, an aqueous dispersion of cellulose fibers is usually prepared. The solids concentration of the modified cellulose in the aqueous dispersion is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more. The upper limit of the concentration is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. During the mechanical treatment, pH adjustment (e.g., to 7 or less, 6 or less, or 5 or less) may be performed as necessary.

[0082] Prior to preparation of the aqueous dispersion, a pretreatment such as dry pulverization (e.g., pulverization after drying) may be carried out. Examples of equipment used for dry pulverization include, but are not limited to, impact mills such as hammer mills and pin mills, media mills such as ball mills and tower mills, and jet mills. Furthermore, post-treatment may be carried out after defibration. Examples of post-treatment include, but are not limited to, drying (e.g., freeze drying, spray drying, tray drying, drum drying, belt drying, thin spreading on a glass plate or the like and drying, fluidized bed drying, microwave drying, heated fan-type reduced pressure drying, and reduced pressure (degassing) drying), re-dispersion in water (the dispersion device is not limited), and pulverization (e.g., pulverization using equipment such as a cutter mill, hammer mill, pin mill, or jet mill).

[0083] (Solid) The fine cellulose fibers may be in the form of an aqueous dispersion obtained after production, or may be a dry solid or a wet solid of the dispersion. Methods for preparing the dry solid or the wet solid include, for example, drying (e.g., freeze drying, spray drying, tray drying, drum drying, belt drying, a method of thinly spreading on a glass plate or the like and drying, fluidized bed drying, microwave drying, and heated fan-type reduced pressure drying). The dry solid or the wet solid may contain a water-soluble polymer. This can improve the redispersibility of the fine cellulose fibers and suppress the aggregation of CNF in the solid rubber. Examples of water-soluble polymers include cellulose derivatives (e.g., carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, or ethyl cellulose or salts thereof), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginates, pullulan, starch, potato starch, arrowroot flour, cationic starch, phosphorylated starch, corn starch, gum arabic, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soy protein lysate, and peanut. Examples of suitable sizing agents include but are not limited to, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acids, polylactic acid, polymalic acid, polyglycerin, latex, rosin-based sizing agents, petroleum resin-based sizing agents, urea resins, melamine resins, epoxy resins, polyamide resins, polyamide-polyamine resins, polyethyleneimine, polyamines, vegetable gums, polyethylene oxide, hydrophilic crosslinked polymers, polyacrylates, starch-polyacrylic acid copolymers, tamarind gum, guar gum, and colloidal silica, as well as mixtures of one or more thereof. Among these, carboxymethyl cellulose or a salt thereof is preferred from the viewpoint of compatibility.

[0084] After production, the fine cellulose fibers may be subjected to post-treatment such as re-dispersion in a dispersion medium such as water or alcohol (the dispersion device is not limited), or pulverization (for example, pulverization using equipment such as a cutter mill, hammer mill, pin mill, or jet mill).

[0085] (Physical Properties of Fine Cellulose Fibers) The fine cellulose fibers preferably have the following physical properties.

[0086] -Specific surface area- The BET specific surface area of ​​the fine cellulose fibers is preferably 10 m 2 / g or more, more preferably 50m 2 / g or more, more preferably 100m 2 The BET specific surface area can be measured by substituting t-BuOH for the aqueous dispersion and then freeze-drying the resulting sample according to the nitrogen gas adsorption method (JIS Z 8830) using a BET specific surface area meter.

[0087] -Crystallization degree of cellulose type I- The crystallinity of cellulose type I in fine cellulose fibers is usually 50% or more, preferably 60% or more. There is no particular upper limit, but in reality it is thought to be around 90%. The crystallinity of cellulose can be controlled by the degree of chemical modification. The crystallinity of cellulose type I can be calculated by measuring and comparing the intensities of the (200) peak around 22.6° and the valley between (200) and (110) (around 18.5°) in X-ray diffraction measurement.

[0088] - Viscosity - When microfibrillated cellulose fibers are dispersed in water, it is preferable that the viscosity of the water dispersion is low. This allows the material to be easily handled despite being fibrillated. For example, the Brookfield viscosity (25°C, 60 rpm) of an aqueous dispersion with a solids content of 1% by mass is usually 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, and even more preferably 50 mPa·s or more, 100 mPa or more, 500 mPa or more, 1,000 mPa or more, or 1,500 mPa or more. The Brookfield viscosity can be measured, for example, by the following method. After fibrillation (e.g., defibration), the mixture is left to stand for at least one day, diluted as necessary, and stirred with a homodisper (e.g., at 3000 rpm for 5 minutes), followed by viscosity measurement (measure the viscosity after rotating at 60 rpm for 3 minutes).

[0089] -Water retention capacity- When the fine cellulose fibers are cellulose microfibrils, the water retention capacity is preferably 10 or more, more preferably 15 or more, even more preferably 20 or more, and even more preferably 30 or more. The upper limit is thought to be about 200 or less in practice, but is not particularly limited. The water retention capacity corresponds to the mass of water in the sediment relative to the mass of the solid content of the fibers in the sediment, and is the ratio of the water content to the solid content in the sediment gel, measured and calculated by centrifuging a 0.3 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 x A) / (0.003 x A - C) A: Mass of an aqueous dispersion of cellulose microfibrils with a solid content concentration of 0.3 mass% B: Mass of the sediment separated after centrifuging the aqueous dispersion of mass A at 30°C at 25,000 G for 30 minutes C: Mass of the solid content in the aqueous phase separated after the centrifugation

[0090] The higher the water retention capacity value, the stronger the fiber's ability to retain water. Water retention capacity can be measured or calculated for fibers that have undergone fibrillation, but it is usually not possible to measure it for fibers that have not undergone fibrillation or defibration, or for cellulose nanofibers that have been defibrated to single microfibrils. When cellulose fibers that have not been fibrillated or defibrated are centrifuged under the above-mentioned conditions, a dense sediment cannot be formed, making it difficult to separate the sediment from the aqueous phase. When cellulose nanofibers are centrifuged under the above-mentioned conditions, there is usually very little sedimentation.

[0091] -Fibrillation rate- When the fine cellulose fibers are cellulose microfibrils, the fibrillation rate (Fibrillation %) is preferably 1.0% or more, more preferably 1.2% or more, and even more preferably 1.5% or more. This allows confirmation that fibrillation is sufficient. The fibrillation rate can be adjusted depending on the type of cellulosic raw material used. The fibrillation rate can be determined using an image analysis type fiber analyzer such as a fractionator manufactured by Valmet Co., Ltd.

[0092] -Electrical Conductivity- The electrical conductivity of an aqueous dispersion of fine cellulose fibers (solid content concentration 1.0% by mass) is preferably 500 mS / m or less, more preferably 300 mS / m or less, even more 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 electrical conductivity can be measured by preparing 200 g of an aqueous dispersion of fine cellulose fibers having a solid content concentration of 1.0% by mass and using an electrical conductivity meter (ES-71 model manufactured by HORIBA).

[0093] - Degree of polymerization - The fine cellulose fibers of the present invention preferably have a degree of polymerization in the range of 250 to 1,000, as measured by a viscosity method using a copper ethylenediamine solution. It is more preferably 300 to 900, and even more preferably 350 to 800. Within such a range, the viscosity does not become too high when the fine cellulose fibers are mixed with rubber latex, making them easy to disperse, and as a rubber reinforcing material, the fine cellulose fibers can form a network structure in the rubber, thereby maintaining sufficient strength.

[0094] The degree of polymerization by the viscosity method using a copper ethylenediamine solution can be calculated by the following method: In the case of TEMPO-oxidized fine cellulose fibers, reduction treatment is first carried out. A 1% aqueous dispersion of fine cellulose fibers is added with NaBH ４ The mixture is added at 10 wt % to the fine cellulose fibers, adjusted to pH 10 with NaOH, and then stirred for 4 hours for reduction treatment. Ethanol is then added and the mixture is centrifuged, after which the supernatant is discarded and ethanol is added again, followed by stirring and centrifugation. This process is repeated three times to recover the fine cellulose fibers, and reduced TEMPO-oxidized fine cellulose fibers are obtained.

[0095] The fine cellulose fibers are freeze-dried and dissolved in 0.5 M copper ethylenediamine solution 1 to form solution 2. The viscosities of solutions 1 and 2 are measured using a capillary viscometer (Cannon-Fenske viscometer). The viscosity of solution 2 is defined as η and the viscosity of solution 1 as η0, and the intrinsic viscosity [η] of the anion-modified pulp is calculated using the following formula:

[0096] Intrinsic viscosity [η] = (η / η0) / {c(1 + 0.28 × η / η0)} (where c is the concentration of the fine cellulose fibers (g / dL))

[0097] Furthermore, the degree of polymerization DP is calculated by the following formula: Degree of polymerization DP = intrinsic viscosity [η] / (5.7 × 10-3)

[0098] The fine cellulose fibers may be of one type or a combination of two or more types.

[0099] (1.2 Rubber Component) Examples of the rubber component include, but are not limited to, synthetic rubbers such as 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 rubber (EPDM), chlorosulfonated polyethylene (CSM), acrylic rubber (ACM), fluororubber (FKM), epichlorohydrin rubber (CO, ECO), urethane rubber (U), silicone rubber (Q), halogenated butyl rubber, and polysulfide rubber. Furthermore, thermoplastic elastomers such as polystyrene-based thermoplastic elastomers, polypropylene-based thermoplastic elastomers, polydiene-based thermoplastic elastomers, chlorine-based thermoplastic elastomers, and engineering plastic-based elastomers can also be used. The rubber component is preferably natural rubber (NR) or acrylonitrile butadiene rubber (NBR).

[0100] The rubber component may be one type alone or a combination of two or more types.

[0101] (2. Method for producing intermediate kneaded product) The method for supplying a rubber composition of the present invention is characterized in that an intermediate kneaded product is obtained by molding a mixture of fine cellulose fibers having a length-weighted average fiber length of more than 400 nm and rubber latex into a sheet shape at a first kneading location.

[0102] (2.1 Mixing Step) (Microfine Cellulose Fiber Dispersion) The microfine cellulose fibers to be mixed with the rubber latex are preferably a dispersion obtained by dispersing microfine cellulose fibers in a dispersion medium (e.g., water, alcohol). The Brookfield viscosity (60 rpm) of such a microfine cellulose fiber dispersion is usually 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 usually 100,000 or less, preferably 70,000 or less, more preferably 50,000 mPa·s or less. The solids concentration of the microfibrillated cellulose fiber dispersion (concentration of microfibrillated cellulose fibers) is not particularly limited, but is usually 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 usually 20.0% or less, preferably 15.0% or less, more preferably 10.0% or less or 5.0% or less. The viscosity can be adjusted by the solids concentration, dispersion conditions, the physical properties and size of the microfibrillated cellulose fibers, etc.

[0103] (Rubber Latex) The rubber latex used in the mixing step may be an aqueous dispersion of a rubber component. The rubber latex can be prepared by dispersing a rubber component in water using a conventional method. The viscosity of the rubber latex is not particularly limited, but is usually 5 or more, preferably 10 mPa·s or more, and more preferably 15 mPa·s or more, and the upper limit is usually 400 mPa·s or less or 300 mPa·s or less, preferably 200 mPa·s or less, and more preferably 100 mPa·s or less. The amount of the solvent (water) for the rubber latex is usually 10 to 1000 parts by mass per 100 parts by mass of the rubber component (the total amount when two or more rubber components are used).

[0104] (Other Components) As raw materials for the rubber composition, raw materials other than the fine cellulose fibers and the rubber component may be used, such as a dispersant, a solvent, and a rubber additive.

[0105] (Dispersant) By using a dispersant together with the fine cellulose fibers, for example, when the fine cellulose fibers are in a dried state, the dispersibility can be improved. Examples of the dispersant include water-soluble polymers and surfactants, and water-soluble polymers are preferred. When the fine cellulose fibers are chemically modified cellulose fibers, the water-soluble polymer covers the low charge density areas on the surface, suppresses the formation of hydrogen bonds, and prevents the fine cellulose fibers from aggregating together during drying.

[0106] -Water-soluble polymer- It is believed that water-soluble polymers can penetrate between the fibers of the fine cellulose fibers and increase the distance between the fibers, thereby suppressing the aggregation of the fine cellulose fibers after drying. Examples of water-soluble polymers include cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ethyl cellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginates, pullulan, starch, potato starch, arrowroot flour, modified starch (cationized starch, phosphorylated starch, phosphate cross-linked starch, phosphate monoesterified phosphate cross-linked starch, hydroxypropyl starch, hydroxypropylated phosphate cross-linked starch, acetylated adipate cross-linked starch, acetylated phosphate cross-linked starch, acetylated oxidized starch, octenyl succinate starch sodium, acetate starch, oxidized starch), corn starch, gum arabic, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, and chitosan. Examples of suitable water-soluble polymers include casein, albumin, soy protein lysate, peptone, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acids, polylactic acid, polymalic acid, polyglycerin, rosin-based sizing agents, petroleum resin-based sizing agents, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide-polyamine resin, polyethyleneimine, polyamine, vegetable gum, polyethylene oxide, hydrophilic crosslinked polymers, polyacrylates, starch-polyacrylic acid copolymers, tamarind gum, guar gum, and colloidal silica, as well as mixtures of one or more thereof. Cellulose derivatives are preferred because of their high affinity with chemically modified fine cellulose fibers, and carboxymethylcellulose or a salt thereof is more preferred. The water-soluble polymer may be one type or a combination of two or more types.

[0107] -Surfactant- Examples of surfactants include, but are not limited to, nonionic surfactants such as fatty acid salts, higher alkyl sulfates, alkylbenzene sulfonates, higher alcohols, alkylphenols, and alkylene oxide adducts of fatty acids, anionic surfactants, cationic surfactants, amphoteric surfactants, organic solvents, proteins, enzymes, natural polymers, synthetic polymers, etc. The surfactant may be one type or a combination of two or more types.

[0108] (Solvent) Examples of solvents include aqueous solvents, which can improve the dispersibility of the mixture of fine cellulose fibers and rubber components. Examples of aqueous solvents include water, water-soluble organic solvents, and mixtures thereof. Water is preferred because fine cellulose fibers are hydrophilic. Use of water ensures a good dispersion state during dispersion. The aqueous solvent may contain a non-water-soluble organic solvent to the extent that the effect of the invention is not impaired.

[0109] The water-soluble organic solvent may be any organic solvent that can be dissolved in water, and examples thereof include lower alcohols having 1 to 4 carbon atoms (e.g., methanol, ethanol, 2-propanol, butanol), glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, and combinations thereof. Among these, lower alcohols having 1 to 4 carbon atoms are preferred, with methanol, ethanol, and 2-propanol being more preferred, and from the viewpoints of safety and availability, methanol and ethanol are even more preferred, with ethanol being even more preferred.

[0110] The amount of the 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, and more preferably 90% by mass or less.

[0111] (Rubber additives) Examples of rubber additives include additives used for crosslinking rubber components. Crosslinking is generally carried out using a vulcanization system that combines a crosslinking agent (vulcanizing agent) such as sulfur or a sulfur-donating compound (e.g., sulfur halide) with various general-purpose vulcanization accelerators such as sulfenamide-based and thiuram-based compounds. The crosslinking agent is 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 having methylol groups; compounds containing crosslinking groups such as isocyanate groups, carbodiimide groups, oxazoline groups, aziridine groups, and epoxy groups, polyfunctional cations, and compounds containing polyvalent metals. Examples of organic peroxides that can be used include 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)hexyne-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. In the case of organic peroxide crosslinking, it is preferable to use a polyfunctional unsaturated compound, for example, triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, or N,N'-m-phenylene bismaleimide in combination.

[0112] 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 the present invention, even if a vulcanizing agent or the like is contained, the effect of the present invention can be more effectively exhibited by being unvulcanized without being subjected to vulcanization treatment (heat treatment after addition of the vulcanizing agent).

[0113] The rubber additives are not limited to the above examples, and examples thereof 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, hydrophobizing agents, oils, curing resins, waxes, antioxidants, and colorants. The content of each agent is not particularly limited.

[0114] The weight ratio of the 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, relative to the rubber component (solid content). This allows the effect of improving tensile strength to be fully achieved. The upper limit is preferably 70 phr or less, more preferably 50 phr or less, and even more preferably 30 phr or less. This allows processability to be maintained in the manufacturing process, improves the dispersibility of the fine cellulose fibers in the rubber, and reduces crimping during transport.

[0115] (Method for Producing the Mixture) The method for producing the mixture is not particularly limited, but examples include a method in which fine cellulose fibers, a rubber component, and other raw materials (e.g., a solvent) used as needed are added and stirred. The fine cellulose fibers are preferably used as a dispersion (e.g., an aqueous dispersion), and the dispersion may contain a dispersant as needed. The rubber component is preferably added as a rubber latex. Stirring may be performed using equipment such as a homodisper or a supermixer.

[0116] (2.2 Drying Step) The mixture containing at least fine cellulose fibers and rubber latex may be subjected to a drying step before being formed into a sheet. In the drying step, the mixture can be dried by a known drying method such as drum drying, natural drying, oven drying, freeze drying, spray drying, pulse combustion, etc., but drum drying is particularly preferred.

[0117] (Drum Dryer) A drum dryer is a dryer equipped with a rotatable drum (cylinder) and a doctor blade (knife, scraper knife) that can scrape off the material on the drum to be dried as the drum rotates. The drum can be heated by introducing a heat medium (e.g., steam) into the drum (e.g., made of metal). A sample (liquid) to be treated is continuously supplied to the preheated, rotating drum surface, and the sample is adhered to the drum surface in the form of a thin film. During rotation, the water in the sample evaporates and condenses, drying the sample, which can then be scraped off the drum surface with a doctor blade to obtain a dried material. The drum dryer may further be equipped with a feeder that supplies the sample (liquid) to the drum surface.

[0118] (Drying Temperature) The temperature conditions during drying are usually 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 the drying process to proceed efficiently. The upper limit is usually 160°C or lower, preferably 150°C or lower, 140°C or lower, or 135°C or lower. This can suppress cellulose denaturation due to heat and prevent a decrease in the mechanical properties of the resulting dried product after molding. Therefore, a temperature of usually 70 to 160°C, preferably 80 to 150°C, more preferably 90 to 150°C, 100 to 150°C, or 110 to 150°C allows the drying process to proceed efficiently and prevents a decrease in mechanical properties. In this specification, the temperature during drying refers to the temperature of the drum surface of a drum dryer.

[0119] The mixed liquid may be at room temperature when supplied to the drum dryer, or may be preheated. When 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 particular upper limit, and the temperature may be 70° C. or lower.

[0120] The moisture content of the dried product after the drying step is usually 8% by mass or less, preferably 5% by mass or less. This range improves workability in the subsequent mixing step (e.g., mastication and kneading). The lower limit is not particularly limited, and may be 0% by mass (bone dry) or more.

[0121] (2.3 Step of Obtaining a Sheet-Like Intermediate Kneaded Material) The dried material obtained above can be subjected to roll treatment multiple times using a roll kneading device such as an open roll to obtain an intermediate kneaded material formed into a sheet shape. As the roll kneading device, a two-roll or three-roll device can be used.

[0122] The clearance can be set in the range of 0.1 to 10 mm. Because the volume change of the dried material before and after roll treatment is large and the load is heavy, it is preferable to increase the clearance stepwise within the above range when repeating roll treatment multiple times so as to satisfy the relationship A<B<C, for example, when the clearance during the first roll treatment is A, the clearance during the second roll treatment is B, and the clearance during the third roll treatment is C.

[0123] In the present invention, in order to more effectively exert the effects of the present invention, it is preferable that the intermediate kneaded product contains fine cellulose fibers in an amount of usually 10 to 40 parts by mass per 100 parts by mass of the rubber component (when two or more rubber components are used, the total amount thereof).

[0124] (3. Method for Producing Rubber Composition) The method for supplying a rubber composition of the present invention is characterized in that an intermediate kneaded product molded into a sheet shape is transported to a second kneading location in a packaged form in which multiple layers are stacked, and then the intermediate kneaded product is diluted and further kneaded in the second kneading location to obtain a rubber composition.

[0125] (3.1 Packaging Process) It is important that the intermediate kneaded product molded into a sheet is laminated into two or more layers by folding / cutting / rolling, etc., and packaged. Normally, unvulcanized rubber compositions are prone to pressure bonding, so it is difficult to laminate and package them in sheet form (which significantly reduces work efficiency). Therefore, it is necessary to apply a release agent or attach a protective film, or package them as a mass such as a bale, but these processes are economical and inefficient.

[0126] Since the intermediate kneaded product of the present invention contains fine cellulose fibers having a number average fiber length of 400 nm or more, the surface becomes moderately stiff (uneven), preventing crimping, and making it possible to stack and package the unvulcanized sheet-like intermediate kneaded product without reducing work efficiency. Furthermore, since the intermediate kneaded product of the present invention is in a sheet form but can be prevented from crimping, it is easy to remove from the package at the transport destination, and furthermore, it is excellent in workability, as the required sample can be cut out with a small tool such as scissors.

[0127] Regarding the lamination form, when the sheet-like material is folded or cut, it may be laminated in either the vertical or horizontal direction, and a lamination form suitable for packaging can be appropriately adopted. When laminated in a roll form, for example, the sheet-like intermediate kneaded material can be wound directly around a core so as to form multiple layers. There is no particular upper limit on the number of layers, and it can be appropriately adjusted within the range that allows it to be packed in a packaging material.

[0128] The packaging form should be such that the multiple layers of intermediate kneaded material can be packaged in an outer bag that protects it from impact, and such an outer bag can be appropriately selected from those normally used for packaging, such as cardboard boxes, containers, polystyrene boxes, plastic boxes, and impact-resistant bags.

[0129] In order to prevent the stacked intermediate kneaded products from collapsing, they can be fixed with an inner bag, sheet, band, etc. as needed before being packed in an outer bag.

[0130] (3.2 Transfer Step) In the method for supplying a rubber composition of the present invention, the packaged intermediate kneaded product is transferred from a first kneading location where the above-described mixing step is carried out to a second kneading location where the below-described dilution step is carried out. The form of transfer is not particularly limited and any ordinary distribution method can be selected.

[0131] (3.3 Dilution Step) The intermediate kneaded product transferred to the second kneading location is diluted by mixing with another rubber latex, further kneaded, and molded into a desired shape. The other rubber latex is the same as that described in (1.2 Rubber Component), but is preferably the same rubber component as the rubber latex used in producing the intermediate kneaded product.

[0132] As the method for dilution kneading, any ordinary rubber kneading method can be used without limitation, and examples thereof include open kneading methods such as roll kneading, and closed kneading methods such as a Banbury mixer or kneader.

[0133] It is preferable to dilute the rubber composition after dilution and kneading so that the content of the fine cellulose fibers in the rubber composition is 0.01 to 20 parts by weight, preferably 0.1 to 15 parts by weight, and more preferably 1 to 10 parts by weight, per 100 parts by weight of rubber.

[0134] According to the method for supplying a rubber composition of the present invention, an intermediate mixture in which fine cellulose fibers are dispersed at a high concentration is prepared in a first mixing location, and then a rubber composition in which fine cellulose fibers are adequately dispersed can be obtained by simple dilution mixing in a second mixing location.

[0135] As described above, since the average fiber length of the fine cellulose fibers is 400 nm or more, the laminated sheet-like rubber compositions are prevented from being pressed against each other even during transportation, and therefore the sheets can be easily removed from the packaging at the second kneading location.In addition, even during dilution kneading, the sheet-like intermediate kneaded material can be roll kneaded as is, making it possible to carry out a simple process.

[0136] (Other Additives) The rubber composition may contain additives as needed during kneading. Examples of such additives include additives used to crosslink rubber components when producing rubber products. Crosslinking is generally carried out using a vulcanization system that combines a crosslinking agent (vulcanizing agent) such as sulfur or a sulfur-donating compound (e.g., sulfur halide) with various general-purpose vulcanization accelerators such as sulfenamides and thiuram compounds. The crosslinking agent is 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 having methylol groups; compounds containing crosslinking groups such as isocyanate groups, carbodiimide groups, oxazoline groups, aziridine groups, and epoxy groups, and polyfunctional cations; and compounds containing polyvalent metals. Examples of organic peroxides that can be used include 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)hexyne-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. In the case of organic peroxide crosslinking, it is preferable to use a polyfunctional unsaturated compound, for example, triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, or N,N'-m-phenylene bismaleimide in combination.

[0137] The content of the crosslinking agent is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 1.7 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.

[0138] Examples of vulcanization accelerators include N-t-butyl-2-benzothiazole sulfenamide and N-oxydiethylene-2-benzothiazolylsulfenamide. The content of the vulcanization accelerator is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less.

[0139] The additives are not limited to the above examples, and examples thereof 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, hydrophobizing agents, oils, curable resins, waxes, antioxidants, and colorants. The content of optional components is not particularly limited and may be determined appropriately depending on conditions such as the type of optional component.

[0140] The additives described above can also be used appropriately for the intermediate kneaded product. However, since the intermediate kneaded product is subsequently diluted and kneaded to produce the target rubber composition, it is preferable to keep the intermediate kneaded product unvulcanized even when additives and the like are added.

[0141] Examples of the present invention will be described below, but the present invention is not limited to these.

[0142] TENPO-oxidized CNF was produced as follows: In the following production examples, the amount of carboxyl groups, average fiber length, and average fiber diameter were measured by the methods described above.

[0143] <Production Example 1> 5,000 g (bone dry) of bleached, unbeaten kraft pulp derived from softwood (brightness 85%) was added to 50 L of an aqueous solution containing 7,800 mg of TEMPO (Sigma-Aldrich) and 755 g of sodium bromide, followed by stirring until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to a concentration of 6.0 mmol / g to initiate the oxidation reaction. The pH of the system decreased during the reaction, but was adjusted to pH 10 by sequential addition of 3 M aqueous sodium hydroxide. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. The reaction mixture was filtered through a glass filter to separate the pulp, which was then thoroughly washed with water to obtain oxidized pulp. The pulp yield was 90%, and the oxidation reaction took 90 minutes. The oxidized pulp obtained in the above process was adjusted to 1.0% (w / v) with water and defibrated twice using an ultra-high-pressure homogenizer (20°C, 150 MPa) to obtain a dispersion of oxidized CNF. The resulting TEMPO-oxidized CNF had a carboxyl group 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.

[0144] The concentration of the TEMPO-oxidized CNF prepared above was adjusted to obtain a slurry containing 1% CNF. The Brookfield viscosity of the slurry was measured (25°C, 60 rpm) as follows: After stirring for 5 minutes at 3000 rpm using a homodisper, the viscosity measurement was started (60 rpm). The viscosity after 3 minutes was recorded and was found to be 5180 mPa s.

[0145] <Production Example 2> 40 kg (bone-dry) of bleached, unbeaten kraft pulp derived from coniferous trees (brightness 85%: manufactured by Nippon Paper Industries Co., Ltd.) was added to 4000 L of an aqueous solution containing 312 g (0.05 mmol per 1 g of bone-dry cellulose) of TEMPO (manufactured by Sigma-Aldrich) and 4112 g (1.0 mmol per 1 g of bone-dry cellulose) of sodium bromide, and the mixture was stirred until the pulp was uniformly dispersed. A sodium hypochlorite aqueous solution was added to the reaction system so that the sodium hypochlorite concentration was 5.5 mmol per 1 g of bone-dry cellulose, and the oxidation reaction was initiated at room temperature. During the reaction, the pH of the system decreased, but 3 M aqueous sodium hydroxide solution was gradually added to adjust the pH to 10. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. Hydrochloric acid was added to the reaction mixture to adjust the pH to 2, and the pulp was thoroughly washed by repeated dehydration and dilution with water, and finally dehydrated until the pulp solids concentration reached 20% by weight to obtain a carboxy-modified pulp (TEMPO-oxidized pulp).

[0146] The resulting carboxy-modified pulp was dispersed in ion-exchanged water, and sodium hydroxide was added and stirred to obtain an aqueous dispersion of carboxy-modified pulp with a pH of 8.8 and a solids concentration of 2% by weight. 74 kg of this aqueous dispersion of carboxy-modified pulp was beaten using a single-disk refiner (Aikawa Iron Works Co., Ltd., 14-inch Lab Refiner (RF-14 type), plate: blade width: 0.6 mm, groove width: 1.0 mm) under a clearance of 0.23 to 0.25 mm for 10 minutes. TEMPO-oxidized MFC was obtained. The length-weighted average fiber length was 59 μm, the average fiber diameter was 5.1 μm, and the carboxy group content was 1.42 mmol / g.

[0147] Example 1 In a first kneading area, 325 g of the aqueous dispersion of TEMPO-oxidized CNF with a solids concentration of 1% obtained in Production Example 1 and 100 g of natural rubber latex (product name: HA Latex, Resitex Corporation, solids concentration 65%) were mixed to a mass ratio of the rubber component (solids of natural rubber latex) to the TEMPO-oxidized CNF solids of 100:20, and the mixture was stirred for 10 minutes using a TK Homomixer (8,000 rpm). The resulting mixture was then dried in a heating oven at 70°C for 5 hours.

[0148] The dried product was passed through an open roll (manufactured by Kansai Roll Co., Ltd.) about five times so that it was visually uniform, to obtain a sheet of unvulcanized intermediate kneaded product 1.

[0149] The obtained sheet of intermediate kneaded material 1 was cut to a length of about 20 cm and tightly laminated under pressure to form 5 to 10 layers so as to prevent bulkiness. The laminated cut sheets were placed in a polyethylene bag that would serve as the inner bag and fixed in place to prevent slippage. Two bundles of laminated sheets filled in this inner bag were packed in a cardboard box of appropriate size. The product was then left at room temperature for one week.

[0150] The cardboard boxes packed with the intermediate kneaded material 1 were then transported by truck to a rubber processing factory, which was the second kneading location. At the second kneading location, the presence or absence of crimping when the intermediate kneaded material was removed from the package was visually confirmed, and the workability (ease of removal from the package and ease of subsequent processing) was evaluated according to the following criteria.

[0151] <Presence or absence of crimping> A: No crimping was observed. B: Crimping was observed.

[0152] <Workability> A: The sheets could be easily removed from the packaging, and the stacked sheets were not pressed together, so they could be easily separated one by one, demonstrating excellent workability. B: The sheets were pressed together, so it was difficult to remove them from the packaging, and it was difficult to separate them one by one.

[0153] The intermediate kneaded material 1 was diluted and kneaded with a pure rubber sheet made from natural rubber latex (product name: HA Latex, Resitex Co., Ltd., solid content concentration 65%) by rolling it multiple times with an open roll so that the mass ratio was 20:80, and a rubber composition containing 5 parts by weight of fine cellulose fibers was obtained.

[0154] Example 2 An intermediate kneaded material 2 was obtained in the same manner as in Example 1, except that the mixed solution of TEMPO-oxidized CNF and natural rubber latex was dried in a double-drum drum dryer (surface temperature 130°C / rotation speed 1 rpm). The obtained intermediate kneaded material 2 was packaged in the same manner as in Example 1 and left to stand for one week, after which it was visually inspected for the presence or absence of compression bonding at the transport destination.

[0155] Example 3 An intermediate kneaded material 3 was obtained in the same manner as in Example 1, except that the TEMPO-oxidized MFC obtained in Production Example 2 was used instead of the TEMPO-oxidized CNF. The obtained intermediate kneaded material 3 was packaged in the same manner as in Example 1, and after leaving it for one week, it was visually inspected for the presence or absence of compression bonding at the transport destination.

[0156] Comparative Example 1 An intermediate kneaded material 4 was obtained in the same manner as in Example 1, except that TEMPO-oxidized CNF was not mixed in. The obtained intermediate kneaded material 4 was packaged in the same manner as in Example 1, and after leaving it for one week, it was visually inspected for the presence or absence of compression bonding at the transport destination.

[0157]

[0158] According to the method for supplying a rubber composition of the present invention, by using an intermediate kneaded product in which fine cellulose fibers having an average fiber length of more than 400 nm are dispersed at a high concentration as a master batch, a rubber composition in which fine cellulose is dispersed can be easily obtained even in a rubber processing factory.

Claims

1. A method for supplying a rubber composition containing fine cellulose fibers, comprising the steps of: forming a mixture of fine cellulose fibers having a length-weighted average fiber length of more than 400 nm and rubber latex into a sheet-like intermediate mixture in a first kneading location; transporting the intermediate mixture in a packaged form in which multiple layers are stacked to a second kneading location; and diluting and further kneading the intermediate mixture in the second kneading location.

2. The method for supplying a rubber composition according to claim 1, characterized in that the fine cellulose fibers have a length-weighted average fiber diameter of 1 nm or more and 20 nm or less.

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

4. The method for supplying a rubber composition according to claim 1 or 2, characterized in that the intermediate mixture is laminated and packaged without being subjected to treatments such as coating with a release agent or attaching a protective film.

5. The method for supplying a rubber composition according to claim 1 or 2, wherein the intermediate mixture is unvulcanized.

6. The method for supplying a rubber composition according to claim 1 or 2, wherein the intermediate mixture is formed into a sheet by a roll kneading method.

7. The method for supplying a rubber composition according to claim 1 or 2, characterized in that the fine cellulose is anionically modified.

8. The method for supplying a rubber composition according to claim 1 or 2, characterized in that the fine cellulose has not been subjected to a hydrophobic treatment.

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