Rubber composition and method for manufacturing same

Abstract

The purpose of the present invention is to improve a rubber composition containing a rubber component and cellulose fibers, and to provide a method for manufacturing such a rubber composition having excellent strength. Specifically, the present invention provides a rubber composition containing: component A which is a rubber component; component B which is a cellulose-based filler; component C which is a water-soluble polymer, preferably, a carboxymethyl cellulose having a B-type viscosity of 20 mPa·s or more when made into a 1 mass%-aqueous solution (25°C, 30 rpm), or a salt of the carboxymethyl cellulose; and, preferably, component D which is a crosslinkable compound having an amino group, and a thiosulfate group or an α,β-unsaturated carbonyl group. Also provided is a method for manufacturing the rubber composition, the method comprising a step for mixing and drying components A-C, preferably components A-D.

Description

Rubber composition and method for producing the same

[0001] The present invention relates to a rubber composition and a method for producing the same.

[0002] It is known that rubber compositions containing a rubber component and cellulosic fibers have excellent mechanical strength. For example, Patent Document 1 describes that a rubber composition containing a rubber component, an inorganic filler, a plasticizer, and powdered cellulose having predetermined physical properties in a predetermined blending ratio has excellent moldability, mechanical properties, etc.

[0003] Patent No. 6878787

[0004] Rubber compositions containing a rubber component and cellulosic fibers are expected to be applied in a variety of fields, and further improvements in strength are required.

[0005] Therefore, an object of the present invention is to improve a rubber composition containing a rubber component and cellulose fibers, and to provide a method for producing such a rubber composition having good strength.

[0006] The present invention provides the following items [1] to

[11] . [1] A rubber composition comprising: Component A: a rubber component; Component B: a cellulose-based filler; and Component C: a water-soluble polymer. [2] The rubber composition according to [1], wherein Component B comprises fine cellulose fibers. [3] The rubber composition according to [1], wherein Component B comprises cellulose nanofibers or cellulose microfibrils. [4] The rubber composition according to any one of [1] to [3], wherein the amount of Component C is 0.05 to 5 parts by mass per 100 parts by mass of Component A. [5] The rubber composition according to any one of [1] to [4], further comprising Component D: a crosslinkable compound having a thiosulfate group or an α,β-unsaturated carbonyl group and an amino group. [6] The rubber composition according to [5], wherein the amino group is an —NH2 group. [7] The rubber composition according to [5] or [6], wherein Component D contains at least one of a compound in which a thiosulfate group and an amino group are linked by an alkyl group, or a compound in which an α,β-unsaturated carbonyl group and an amino group are linked by a divalent group containing an aromatic ring and an amide bond. [8] The rubber composition according to [7], wherein the alkyl group is an alkyl group having 1 to 6 carbon atoms. [9] The rubber composition according to any one of [5] to [8], wherein Component D contains at least S-(3-aminopropyl)thiosulfate.

[10] A method for producing the rubber composition according to any one of [1] to [9], comprising the steps of: mixing Component A: a rubber component; Component B: a cellulose-based filler; and Component C: a water-soluble polymer to obtain a mixture; and drying the obtained mixture.

[11] The method according to

[10] , further comprising the step of vulcanizing the dried product.

[0007] According to the present invention, there are provided a rubber composition containing a rubber component and cellulose fibers, which is capable of exhibiting strength, particularly good dynamic viscoelasticity, and an efficient method for producing the same.

[0008] [1. Rubber Composition] The rubber composition contains the following components A to C, and preferably further contains component D.

[0009] [1.1 Component A: Rubber Component] Component A is a 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.

[0010] As component A, natural rubber (NR) is more preferred.

[0011] The vulcanization of rubber components is generally carried out using a vulcanization system that combines sulfur or a sulfur-donating compound with various general-purpose vulcanization accelerators, such as sulfenamides and thiuram compounds. Organic peroxide crosslinking is also possible. Examples of commonly used organic peroxides include 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-butylperoxyisopropylcarbonate, 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.

[0012] [1.2 Component B: Cellulosic Filler] Component B is a cellulose-based filler. The cellulose-based filler may be any filler derived from a cellulose raw material, and examples thereof include pulp fiber, powdered cellulose, and fine cellulose fiber.

[0013] [Cellulose Raw Material] The cellulose raw material is usually wood, and may be any of broad-leaved trees, soft-leaved trees, or a combination of two or more of these. Examples of broad-leaved trees include plants of the genus Beech (e.g., Fagus crenata), linden (e.g., Tilia japonica), birch (e.g., birch, beetle), poplar (e.g., poplar), Eucalyptus (e.g., eucalyptus), Acacia (e.g., acacia), Quercus (e.g., oak, phillyraeoides phillyraeoides, oak, sawtooth oak), maple (e.g., maple), Kalopanax (e.g., Asiatic maple), Ulmus (e.g., Ulmus repens), Paulownia (e.g., Paulownia serrata), Magnolia (e.g., Magnolia obovata), Salix (e.g., Salix salicina), Aesculus (e.g., horse chestnut), Zelkova (e.g., Zelkova), Cornus (e.g., Cornus controversa), and Ash (e.g., Fraxinus japonica), with Eucalyptus plants being preferred. Examples of conifers include cedars (e.g., Japanese cedar), spruce (e.g., Picea japonicus), larch (e.g., Japanese larch, western larch, tamarack), pine (e.g., Japanese black pine, Japanese white pine, radiata pine, eastern white pine), fir (e.g., Abies sachalinensis, fir, western fir), yew (e.g., Taxus acuta), arborvitae (e.g., Japanese cedar, yellow cedar), spruce (e.g., Abies abies, Abies japonica, Examples of suitable wood include plants of the genus Picea (e.g., Picea abies, Sitka spruce (Sitka spruce), Eastern spruce), Picea (e.g., Picea japonica), Chamaecyparis obtusa (Chamaecyparis japonica), Chamaecyparis japonica (Chamaecyparis obtusa), Chamaecyparis lawsoni (Chamaecyparis japonica), Douglas-fir (Douglas-fir), Western hemlock, Thujopsis dolabrata (e.g., Thujopsis dolabrata, Thuja japonica), Tsuga (e.g., Tsuga sieboldii, Tsuga diversifolia), and Carpinus (e.g., Carpinus carpinus), with plants of the genus Cryptomeria japonica and pine being preferred. On the other hand, non-wood materials may also be used as raw materials, such as bamboo, hemp, jute, kenaf, and agricultural waste.

[0014] [Examples of Component B: (1) Pulp Fibers] Examples of pulp fibers include, but are not limited to, unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), unbleached softwood sulfite pulp (NUSP), bleached softwood sulfite pulp (NBSP), thermomechanical pulp (TMP), linter pulp, recycled pulp, waste paper, etc., non-wood pulp, and combinations of two or more selected from these.

[0015] The average fiber diameter of pulp fibers is not particularly limited, but is usually 60 μm or less, preferably 50 μm or less, more preferably 30 μm or less, or 20 μm or less, and even more preferably 10 μm or less. The average fiber diameter of softwood kraft pulp is about 30 to 60 μm, that of hardwood kraft pulp is about 10 to 30 μm, and that of other pulps (those that have undergone general refinement) is about 50 μm (e.g., 40 to 60 μm). For example, when using raw materials that have been refined from chips or other materials several centimeters in size, treatment to adjust the average fiber diameter (e.g., adjustment to 50 μm or less) may be performed, such as mechanical treatment using a disintegrator such as a refiner or beater.

[0016] [Example of Component B: (2) Powdered Cellulose] Powdered cellulose is powdered cellulose derived from a cellulose raw material. Examples of methods for producing it include Method 1: a method in which pulp is subjected to acid hydrolysis with an acid (e.g., an inorganic acid (specifically, a mineral acid such as hydrochloric acid, sulfuric acid, or nitric acid) followed by treatment such as pulverization; and Method 2: a method in which pulp is subjected to treatment such as mechanical pulverization without acid hydrolysis, with Method 1 being preferred. Method 1 allows for the production of powdered cellulose with few impurities.

[0017] The average particle size of the powdered cellulose is preferably 1 μm or more, more preferably 3 μm or more. The average particle size is preferably 70 μm or less, more preferably 50 μm or less, even more preferably 25 μm or less or less than 15 μm, and even more preferably 11 μm or less. Therefore, the average particle size of the powdered cellulose is preferably 1 to 70 μm, more preferably 1 to 50 μm, 1 to 25 μm, or 1 to 15 μm, and even more preferably 1 to 11 μm. In this specification, the average particle size is defined as the value at which the volume accumulation distribution is 50% when the particle size distribution is expressed as an accumulation distribution using a laser scattering method as the measurement principle.

[0018] The degree of polymerization (average degree of polymerization) of the powdered cellulose is preferably 100 or more, more preferably 200 or more. The upper limit is preferably 1,400 or less, more preferably 1,000 or less, even more preferably 500 or less, and even more preferably 400 or less. Therefore, the degree of polymerization of the powdered cellulose is preferably 100 to 1,400, more preferably 100 to 1,000 or 100 to 500, even more preferably 100 to 500, 100 to 400 or 200 to 500, and even more preferably 100 to 400 or 200 to 400. The degree of polymerization can be determined by a viscosity measurement method using copper ethylenediamine described in the 16th Edition Japanese Pharmacopoeia Commentary, Crystalline Cellulose Verification Test (2). For the range that cannot be measured by the method described in the verification test (2) for crystalline cellulose, the intrinsic viscosity can be measured using, for example, a fully automatic viscosity measurement system for pulp and polymers RPV-1 (manufactured by RHEOTEK), and the intrinsic viscosity can be calculated from the formula [η] = 0.909 × DP0.85 (formula (2) in the document) described in "VISCOSITY MEASUREMENTS OF CELLULOSE / SO-AMINE DIMETHYLSULFOXIDE SOLUTION" (Isogai et al., 1998).

[0019] The apparent specific gravity of the powdered cellulose is preferably 0.1 to 0.6 g / ml, more preferably 0.1 to 0.45 g / ml, even more preferably 0.15 to 0.45 g / ml, and particularly preferably 0.2 to 0.4 g / ml. The apparent specific gravity can be calculated by placing 10 g of a sample in a 100 ml measuring cylinder, tapping the bottom of the cylinder manually for approximately 10 minutes until the height of the sample no longer decreases, reading the scale on the flattened surface, and dividing the reading by the mass of the sample.

[0020] The cellulose type I crystallinity of powdered cellulose is preferably 70 to 90%, more preferably 80 to 90%. The cellulose type I crystallinity can be calculated by subjecting a sample to X-ray diffraction measurement, measuring and comparing the intensities of the (200) peak near 22.6° and the valley between (200) and (110) (near 18.5°). The crystallinity can be adjusted by the type of cellulose raw material and the production method. Powdered cellulose produced through acid hydrolysis treatment (for example, by method (1)) tends to have a high degree of crystallinity, while powdered cellulose produced without such treatment (for example, by method (2)) tends to have a low degree of crystallinity.

[0021] [Example of Component B (3): Microfibrillated Cellulose Fibers] Microfibrillated cellulose fibers are cellulose in the form of fine fibers derived from cellulose raw materials. For example, microfibrillated cellulose 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 cellulose fibers before or after defibration (usually before defibration) as needed. Microfibrillated cellulose fibers with nanometer-order fiber diameters are called cellulose nanofibers, and microfibrillated cellulose fibers with micrometer-order fiber diameters are called cellulose microfibrils. The size of microfibrillated cellulose fibers can be adjusted by the conditions of the microfibrillation and chemical modification treatments. The powdered cellulose described above does not disperse even when stirred in a solvent such as water, but rather sediments, making it impossible to measure the light transmittance of the dispersion, and therefore can be clearly distinguished from microfibrillated cellulose fibers.

[0022] [Example (3-1) of Component B: Cellulose Nanofiber] In this specification, cellulose nanofiber (CNF) refers to cellulose fiber having a fiber diameter on the nano-order, which is prepared through a micronization treatment.

[0023] 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, and even more preferably 50 nm or less. The lower limit is not particularly limited, but is usually 1 nm or more, preferably 2 nm or more. Therefore, the average fiber diameter (length-weighted average fiber diameter) of 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 2 to 50 nm or 3 to 30 nm. The average fiber length (length-weighted average fiber length) is usually 50 to 2,000 nm, preferably 100 to 1,000 nm. The aspect ratio of the CNF is usually 10 or more, preferably 50 or more. The upper limit is not particularly limited, but is usually 1,000 or less.

[0024] The average fiber diameter and average fiber length of the fibrous cellulose fibers can be determined using a fractionator manufactured by Valmet Co., Ltd. When a fractionator is used, they can be determined as the length-weighted fiber width and the length-weighted average fiber length, respectively. The average aspect ratio of the fibrous cellulose fibers can be calculated using the formula: average aspect ratio = average fiber length / average fiber diameter.

[0025] [Example of Component B (3-2): Cellulose Microfibril] In this specification, cellulose microfibril (microfibrillated cellulose, MFC) means cellulose fibers having a fiber diameter on the order of microns, which are prepared through a pulverization treatment.

[0026] The average fiber diameter (average fiber width) 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-imparting effects and yield-improving effects compared to 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 is not particularly limited. The average fiber length is usually 10 μm or more, 20 μm or more, or 40 μm or more, preferably 200 μm or more, 300 μm or more, or 400 μm or more, more preferably 500 μm or more, or 550 μm or more, and even more preferably 600 μm or more, 700 μm or more, or 800 μm or more. The upper limit is not particularly limited, but is usually 3,000 μm or less, preferably 2,500 μm or less, more preferably 2,000 μm or less, even more preferably 1,500 μm or less, 1,400 μm or less, or 1,300 μm or less. The aspect ratio of the MFC is preferably 3 or more, more preferably 5 or more, even more preferably 7 or more, and may be 10 or more, 20 or more, or 30 or more. The upper limit of the aspect ratio is not particularly limited, but is preferably 1,000 or less, more preferably 100 or less, and even more preferably 80 or less.

[0027] [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 uniform average fiber length and 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 cellulose fibers are preferred.

[0028] Examples of the modification include oxidation, etherification, esterification such as phosphate esterification, silane coupling, fluorination, cationization, etc. Among these, oxidation (carboxylation), etherification, cationization, and esterification are preferred, and oxidation (carboxylation) is more preferred.

[0029] - 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.

[0030] 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]

[0031] 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 primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of the cellulose is selectively oxidized to form an aldehyde group, a carboxyl group (—COOH), and a carboxylate group (—COO - The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by mass or less.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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]

[0041] -Acid-Form Oxidized Cellulose and Desalting- Oxidized cellulose contains carboxy groups as a result of oxidation, but it may contain more acid-form carboxy groups (-COOH) than salt-form carboxy groups (e.g., -COO-, -COONa), or it may contain more salt-form carboxy groups than acid-form carboxy groups. The amounts of salt-form carboxy groups and acid-form carboxy groups can be adjusted by desalting treatment. Salt-form carboxy groups can be converted to acid-form carboxy groups by desalting treatment. In this specification, oxidized cellulose (which has been desalted) is referred to as acid-form oxidized cellulose, and oxidized cellulose (which has not been subjected to the desalting treatment described below) is referred to as salt-form oxidized cellulose. Salt-form oxidized cellulose usually contains primarily salt-form carboxy groups. On the other hand, acid-form oxidized cellulose contains many acid-form carboxy groups, and the proportion of acid-form carboxy groups in the carboxy groups is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. Acid-form oxidized cellulose, together with component C, can exhibit a superior reinforcing effect. The proportion of acid-type carboxy groups can be calculated by the following procedure. 1) First, 250 mL of an aqueous dispersion of acid-type oxidized cellulose before desalting is prepared, with a solids concentration of 0.1% by mass. 0.1 M aqueous hydrochloric acid is added to the prepared aqueous dispersion to adjust the pH to 2.5, and then 0.1 N aqueous sodium hydroxide is added and the electrical conductivity is measured until the pH reaches 11. The amount of acid-type carboxy groups and the amount of salt-type 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 type)) = a (ml) × 0.1 / mass (g) of oxidized cellulose (salt type) 2) 250 mL of an aqueous dispersion of desalted acid-type oxidized cellulose with a solids concentration of 0.1% by mass is prepared. 0.1 N aqueous sodium hydroxide 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: Proportion of acid-type carboxy groups (%) = (amount of acid-type carboxy groups / total amount of carboxy groups) × 100.

[0042] The timing of desalting may be after oxidation, and may be either before or after defibration, but is usually after oxidation and before defibration. Desalting is usually carried out by substituting salts (e.g., sodium salts) contained in salt-form oxidized cellulose with protons. Desalting methods include, for example, a method of adjusting the system to an acidic state, and a method of contacting oxidized cellulose with a cation exchange resin. In the method of 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. The cation exchange resin is a cation exchange resin having a counter ion of H + As long as the cation exchange resin satisfies the above condition, either a strongly acidic ion exchange resin or a weakly acidic ion exchange resin can be used. The ratio of the oxidized 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. The cation exchange resin after contact can be recovered by a conventional method such as suction filtration.

[0043] -Etherification- Examples of etherification include carboxyalkylation, methylation, ethylation, cyanoethylation, hydroxyethylation, hydroxypropylation, ethylhydroxyethylation, and hydroxypropylmethylation. Carboxyalkylation is preferred, and carboxymethylation is more preferred.

[0044] 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.

[0045] The degree of carboxyalkyl substitution (preferably the degree of carboxymethyl substitution (CM-DS)) 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 0.20 to 0.30.

[0046] 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 (CM-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-form carboxymethylated cellulose) CM-DS = 0.162 x A / (1 - 0.058 x A) A: amount (mL) of 1N NaOH required to neutralize 1 g of acid-form carboxymethylated cellulose F': factor of 0.1N H2SO4 F: factor of 0.1N NaOH

[0047] 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.

[0048] 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.

[0049] 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.

[0050] Examples of mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of 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 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.

[0051] The reaction temperature for mercerization is usually 0°C or higher, preferably 10°C or higher. The upper limit is usually 70°C or lower, preferably 60°C or lower. The reaction temperature is usually 0 to 70°C, preferably 10 to 60°C. The reaction time for mercerization is usually 15 minutes or longer, preferably 30 minutes or longer. The upper limit is usually 8 hours or shorter, preferably 7 hours or shorter. The reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

[0052] The etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of the carboxymethylating agent include monochloroacetic acid or a salt thereof (e.g., a metal salt such as a sodium salt). 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.

[0053] 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.

[0054] -Differences from Carboxymethyl Cellulose- Carboxyalkylated cellulose fibers preferably maintain at least a portion of their fibrous shape when dispersed in water (are water-insoluble). Carboxyalkylated cellulose fibers are distinguished from carboxymethyl cellulose (e.g., component C, described below), 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, no fibrous substances are observed. Furthermore, anion-modified cellulose fibers are crystalline, and when measured by X-ray diffraction, peaks of cellulose type I crystals can be observed. However, when carboxymethyl cellulose powder, a water-soluble polymer, is similarly measured, cellulose type I crystals are usually not observed.

[0055] -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 amount of salt-type carboxy groups and acid-type carboxy groups can be adjusted by desalting treatment. Desalting treatment can convert salt-type carboxy groups to acid-type carboxy groups. In this specification, carboxyalkylated cellulose (which has undergone desalting) is referred to as acid-type carboxyalkylated cellulose, and carboxyalkylated cellulose (which has not undergone the desalting treatment described below) is referred to as salt-type carboxyalkylated cellulose. Salt-type carboxyalkylated cellulose typically contains primarily salt-type carboxy groups (—COO−). On the other hand, acid-type carboxyalkylated cellulose contains many 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. It is presumed that acid-type carboxyalkylated cellulose has an excellent reinforcing effect when combined with component C. The method for calculating the proportion of acid type carboxy groups is as described above.

[0056] 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.

[0057] Esterification (Phosphorylation) A first example of an esterified cellulose fiber is phosphorylated cellulose. Phosphorylated cellulose typically 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 C6 constituting the glucopyranose unit) is phosphorylated.

[0058] The degree of substitution of phosphate-based groups per glucose unit in phosphated CNF (hereinafter simply referred to as "phosphate group substitution degree") is preferably 0.001 or more and less than 0.40. The degree of phosphate group substitution can be measured by the following method. A slurry of phosphated CNF with a solid content of 0.2% by mass is prepared. A strongly acidic ion exchange resin is added to the slurry in an amount of 1 / 10 by volume, and the slurry is shaken for 1 hour. The resin and the slurry are then separated by pouring the mixture onto a 90 μm mesh to obtain hydrogen-phosphated CNF. Next, 50 μL of 0.1 N aqueous sodium hydroxide is added to the slurry after treatment with the ion exchange resin every 30 seconds, while measuring the change in the electrical conductivity of the slurry. The amount of alkali (mmol) required in the region where the electrical conductivity drops sharply is divided by the solid content (g) of the slurry to be titrated to calculate the amount of phosphate groups (mmol / g) per 1 g of hydrogen-phosphated CNF. Furthermore, the degree of phosphate group substitution per glucose unit of the phosphated CNF is calculated using the following formula: Phosphate group substitution degree = 0.162 × A / (1 - 0.079 × A) A: amount of phosphate groups per 1 g of hydrogen-type phosphated CNF (mmol / g).

[0059] The degree of substitution with 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.

[0060] 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.

[0061] 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 typically about 1 to 600 minutes, preferably 30 to 480 minutes. When the esterification reaction conditions are within any of these ranges, excessive esterification of cellulose, which would otherwise lead to increased solubility, can be prevented, thereby improving the yield of phosphated cellulose. When reacting a compound having a phosphate group, a basic compound (e.g., a compound having a basic amino group, such as urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, or hexamethylenediamine) may be added to the reaction system. The suspension obtained after esterification is preferably dehydrated as needed, and heat-treated after dehydration. This can suppress hydrolysis of the cellulose raw material. The heating temperature is preferably 100 to 170°C, and more preferably, the mixture is heated at 130°C or lower (preferably 110°C or lower) while water is contained during the heat treatment, and then the mixture is heated at 100 to 170°C after removing the water.After boiling, it is preferable to carry out a washing treatment such as washing with cold water. This allows for efficient defibration. Washing can be carried out by adding water and then dehydrating (for example, filtration), and may be repeated two or more times. Washing is preferably carried out until the electrical conductivity of the filtrate decreases. For example, it can be carried out until the electrical conductivity is preferably 200 or less, more preferably 150 or less, and even more preferably 120 or less. Furthermore, after washing, a neutralization treatment may be carried out as necessary. The neutralization treatment can be carried out by adding, for example, an alkali (e.g., sodium hydroxide). Washing may be carried out again after neutralization.

[0062] Esterification (Phosphite Esterification) A second example of a method for producing esterified cellulose fibers is phosphite-esterified cellulose fibers. Phosphite-esterified cellulose fibers typically have a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (e.g., the carbon atom bearing a primary hydroxyl group at the C6 position constituting a glucopyranose unit) is phosphoritized. The degree of substitution of phosphite groups per glucose unit in phosphite-esterified cellulose fibers (hereinafter simply referred to as the "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 phosphate group substitution degree. 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, the amount of alkali metal ion-containing material added as needed, and the amount of urea or its derivative added.

[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 0.1 to 3.0 mmol / g. Introducing cationic substituents into the cellulose raw material causes electrical repulsion between cellulose molecules. Therefore, cationized cellulose with cationic substituents introduced can be easily nano-fibrillated. When the degree of cationic substitution per glucose unit is 0.02 or more, sufficient nano-fibrillation can be achieved due to the electrical repulsion between cellulose molecules. On the other hand, when the degree of cationic substitution per glucose unit is 0.50 or less, swelling or dissolution can be suppressed, preventing the failure to obtain nanofibers. For efficient fibrillation, it is preferable to wash the cationized 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 at 30°C for a further 24 hours. Phenolphthalein is then added as an indicator, and the mixture is titrated with hydrochloric acid, and the amount of sulfate groups per glucose unit is calculated using the following formula: Amount of sulfate 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 celluloses, those that have not been subjected to desalting treatment and those that have been subjected to 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 due to the combination with component C. 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 typically 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 typically 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 fibers, 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 this amount is usually 800 parts by mass or less, preferably 500 parts by mass or less. 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 the catalyst is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the cellulose raw material. The upper limit of this amount is usually 7 parts by mass or less, preferably 3 parts by mass or less.

[0078] - 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.

[0079] [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., disk 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.

[0080] 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.

[0081] 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).

[0082] [Optional Post-Treatment] The fine cellulose fibers may be in the form of an aqueous dispersion obtained after production, or may be subjected to post-treatment as necessary. Examples of the post-treatment include, but are not limited to, drying (e.g., freeze drying, spray drying, tray drying, drum drying, belt drying, a method of thinly spreading the cellulose fibers on a glass plate or the like and drying, fluidized bed drying, microwave drying, and heated fan-type reduced pressure 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, impact mill, airflow mill, roller mill, or vibration mill).

[0083] [Physical Properties of Fine Cellulose Fibers] The fine cellulose fibers preferably have the following physical properties.

[0084] -Specific surface area- The BET specific surface area of ​​the fine cellulose fibers is preferably 25 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.

[0085] -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 X-ray diffraction measurement, measuring and comparing the intensities of the (200) peak around 22.6° and the valley between (200) and (110) (around 18.5°). When fine cellulose fibers contain type II crystals, it is preferable to separate the peaks due to type II crystals (around 12.3°, 20.2°, and 21.9°) and then calculate the intensity of type I crystals.

[0086] - 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 6,000 mPa·s or less or 5,000 mPa·s or less, preferably 4,500 mPa·s or less, and more preferably 4,000 mPa·s or less. The lower limit is preferably 10 mPa·s or more, more preferably 20 mPa·s or more, and even more preferably 50 mPa·s or more, 100 mPa or more, 500 mPa or more, 1,000 mPa or more, or 2,000 mPa or more. Furthermore, for example, the Brookfield viscosity (25°C, 6 rpm) of an aqueous dispersion with a solids content of 1% by mass is usually 25,000 mPa s or less or 20,000 mPa s or less, preferably 18,000 mPa s or less, and more preferably 15,000 mPa s or less. The lower limit is preferably 100 mPa s or more, more preferably 500 mPa s or more, and even more preferably 1,000 mPa s or more, 2,000 mPa or more, 3,000 mPa or more, 4,000 mPa or more, or 5,000 mPa or more. The Brookfield viscosity can be measured, for example, by the following method. After fibrillation (e.g., defibration), the mixture is left to stand for one day or more, diluted as necessary, and stirred with a homodisper (e.g., 3,000 rpm, 5 min), followed by viscosity measurement (the viscosity is measured after 3 minutes of rotation at 6 or 60 rpm).

[0087] -Transparency- The transparency of a CNF aqueous dispersion with a solid content of 1.0 mass% is usually 40% or more, preferably 50% or more, and more preferably 60% or more. There is no particular upper limit, as long as it is 100% or less. The transparency of an MFC aqueous dispersion with a solid content of 1.0 mass% is usually 1% or more, preferably 5% or more. The upper limit is 50% or less. Transparency can be measured as the transmittance of 660 nm light using a visible light photometer.

[0088] - Anionization degree - When the fine cellulose fibers are modified cellulose microfibrils, the degree of anionization (anion charge density) is usually 2.50 meq / g or less, preferably 2.30 meq / g or less, more preferably 2.0 meq / g or less, and even more preferably 1.50 meq / g or less. This is thought to ensure that the chemical modification is more uniform throughout the cellulose than cellulose fibers with a higher degree of anionization, and to enable more stable achievement of effects specific to chemically modified cellulose fibers, such as water retention. The lower limit is usually 0.06 meq / g or more, preferably 0.10 meq / g or more, more preferably 0.30 meq / g or more, but is not particularly limited. Therefore, it is preferably 0.06 meq / g or more and 2.50 meq / g or less, more preferably 0.08 meq / g or more and 2.50 meq / g or less, or 0.10 meq / g or more and 2.30 meq / g or less, and even more preferably 0.10 meq / g or more and 2.00 meq / g or less. The degree of anionization is the equivalent of anions per unit mass of modified cellulose microfibrils, and can be calculated from the equivalent of diallyldimethylammonium chloride (DADMAC) required to neutralize the anionic groups in unit mass of modified cellulose microfibrils.

[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- When the fine cellulose fibers are cellulose microfibrils, the electrical conductivity of their aqueous dispersion (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 cellulose microfibrils having a solid content concentration of 1.0% by mass and using an electrical conductivity meter (ES-71 model manufactured by HORIBA).

[0093] [Component C: Water-Soluble Polymer] Component C is a water-soluble polymer. Examples of the water-soluble polymer include cellulose derivatives (e.g., carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, or ethyl cellulose, or salts thereof (e.g., sodium salts)), 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, locust bean gum, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, and soy protein. These include dissolved substances, peptone, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acids, polylactic acid, polymalic acid, polyglycerin, latex, rosin-based sizing agents, petroleum resin-based sizing agents, urea 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, gellan gum, pectin, guar gum, and colloidal silica, as well as mixtures of one or more thereof. Among these, cellulose derivatives are preferred, cellulose derivatives containing anionic electrolytes are more preferred, and carboxymethylcellulose or its salts (hereinafter referred to as CMC) are even more preferred. The use of CMC can improve compatibility. Component C may be a single water-soluble polymer or a combination of two or more water-soluble polymers.

[0094] CMC refers to a compound having a structure in which the hydroxyl groups in the glucose residues constituting cellulose are substituted with carboxymethyl ether groups. When CMC is in the form of a salt, examples of the salt include metal salts such as sodium salts.

[0095] [Physical Properties of CMC] The CMC may have the following physical properties and shape, and among these, it is preferable that the CMC satisfies a predetermined viscosity.

[0096] Viscosity: The Brookfield viscosity (25°C, 30 rpm) of a 1% by mass aqueous solution of CMC (aqueous solution containing 1% by mass of solids) is typically 20 mPa·s or more, preferably 25 mPa·s or more, and more preferably 30 mPa·s or more. The upper limit is typically 500 or less, preferably 400 or less, more preferably 300 or less, and even more preferably 250 or less. For measuring the Brookfield viscosity, when the water-soluble polymer is CMC, CMC was weighed into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solids content of 1% (w / v). The aqueous dispersion was stirred at 600 rpm for 3 hours at 25°C using a stirrer. Thereafter, the viscosity after 3 minutes was measured using a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd.) with a No. 1 rotor at a rotation speed of 30 rpm in accordance with the method of JIS-Z-8803.

[0097] - Degree of carboxymethyl substitution - The degree of carboxymethyl substitution per anhydroglucose unit of CMC is usually 0.45 or more, preferably 0.6 or more. This allows for sufficient water solubility. The upper limit is usually 2.0 or less, preferably 1.5 or less, and more preferably 1.0 or less. The degree of carboxymethyl substitution can be calculated by the same measurement method as for the degree of substitution of carboxymethylated cellulose described above. The degree of carboxymethyl substitution can be adjusted by controlling reaction conditions, such as the amounts of etherifying agent and mercerizing agent reacted during production.

[0098] -Amount of Acid Carboxy Groups- CMC may have acid carboxy groups, and the amount of acid carboxy groups is usually 20.00 mmol / g or less, preferably 15.00 mmol / g or less, and more preferably 3.00 mmol / g or less. The lower limit may be 0, or may be, for example, 1.15 mmol / g or more. The amount of acid carboxy groups can be adjusted by adjusting the pH of a 1% by mass aqueous solution of CMC to the acidic range.

[0099] The amount of acid carboxy groups in CMC can be calculated using formula (A) by measuring the electrical conductivity of an aqueous solution of CMCx (g) while adding dropwise a sodium hydroxide solution of a predetermined concentration y (N), which is a weak acid that shows a gradual change in electrical conductivity, i.e., the amount of sodium hydroxide solution a (mL) consumed in the neutralization step of the acid carboxy groups. Amount of acid carboxy groups [mmol / g] = a [mL] × y [N] / mass x [g] of CMC (A)

[0100] Specifically, the amount of acid carboxyl groups in CMC can be measured by the following method. 100 mL of ion-exchanged water is added to 0.1 g of CMC to prepare an aqueous solution, to which a 0.1 N sodium hydroxide solution is added dropwise at a rate of 0.5 mL / min while measuring the electrical conductivity. A titration curve is then created by plotting the electrical conductivity against the amount of sodium hydroxide solution added. A first asymptote is then created by the least squares method from points in the range where the electrical conductivity changes gradually on the titration curve, and a second asymptote is created by the least squares method from points in the range where the electrical conductivity changes rapidly. The amount of sodium hydroxide solution added at the intersection of the first and second asymptote is taken as the amount a (mL) of sodium hydroxide solution consumed in the neutralization step of the acid carboxyl groups. The amount of acid carboxyl groups is calculated using formula (A) from the mass (g) of CMC used in the titration, the concentration (N) of sodium hydroxide, and the amount a (mL) of sodium hydroxide solution. The value obtained from the conductivity meter may be used as is for the electrical conductivity, but a corrected electrical conductivity may be obtained by multiplying the value obtained from the conductivity meter by a coefficient calculated from the following formula (B), and the first and second asymptote may be obtained using this corrected electrical conductivity: (Coefficient) = (V ０ (mL)+v(mL)) / V ０ (mL) ... (B) In the above formula, V ０ represents the amount of the aqueous solution of carboxymethyl cellulose or a salt thereof before the addition of the aqueous sodium hydroxide solution, and v represents the amount of the aqueous sodium hydroxide solution added at each electrical conductivity value.

[0101] - pH - The pH (25°C) of a 1 mass % aqueous solution of CMC may be in the neutral range (eg, pH 6.8 to 7.2) or in the acidic range (eg, pH 4.0 or higher and lower than 6.8).

[0102] - Particle size - The maximum particle size of CMC is usually less than 50 μm, preferably less than 45 μm. This can suppress the generation of undissolved matter in an aqueous CMC solution. The lower limit is not particularly limited as long as it is greater than 0. In the case of a granulated product, it is preferable that the maximum particle size of CMC before granulation is within the above range. In this specification, the maximum particle size is the cumulative 100% volume particle size measured with a laser diffraction / scattering particle size distribution analyzer using methanol as a dispersant.

[0103] The average particle size of CMC is usually 30 μm or less, preferably 20 μm or less, more preferably 15 μm or less. The lower limit is usually 12 μm or more. In this specification, the average particle size is the cumulative 50% volume particle size measured with a laser diffraction / scattering particle size distribution analyzer using methanol as a dispersion medium.

[0104] [Method for Producing CMC] The method for producing CMC may be any method that includes carboxymethylation of a cellulose raw material, and an example is as follows.

[0105] Carboxymethylation can be performed on a cellulose raw material (e.g., pulp such as dissolving pulp, linter, regenerated cellulose, crystalline cellulose) as a starting material (starting raw material). For example, the cellulose raw material can be mercerized and then etherified. The molar ratio of the mercerizing agent to the etherifying agent (mercerizing agent / etherifying agent) is preferably 2.00 or more. This allows for sufficient etherification after mercerization and suppresses the residual etherifying agent (e.g., monochloroacetic acid). The upper limit is preferably 2.45 or less. This prevents the generation of by-products (e.g., glycolic acid alkali metal salts) due to the progression of side reactions caused by excess mercerizing agent and etherifying agent (e.g., monochloroacetic acid), allowing the reaction to proceed efficiently. Other conditions (e.g., solvent, type of mercerizing agent and etherifying agent, reaction temperature, reaction time) are as described above. In the production of CMC, the degree of carboxymethyl substitution and crystallinity can be appropriately set to achieve the desired effect. CMC is a water-soluble polymer, and preferably exhibits water solubility by developing an appropriate viscosity, and therefore does not have a fibrous shape in water, which is different from the method for producing carboxymethylated fine cellulose fibers as component B, which maintain a fibrous shape in water after being defibrated.

[0106] - pH Adjustment - The pH of a 1% by mass aqueous solution of CMC obtained through carboxylation is usually in the neutral range, but the pH may be adjusted to the acidic range as needed. An example of a method for adjusting to the acidic range is adding an acid (e.g., acetic acid). The adjustment may be performed in the presence of a solvent (dispersion medium). Examples of the solvent include alcohols such as methanol, water, and mixtures thereof, and preferably methanol or a mixture of methanol and water. After the addition of the acid, the solvent can be removed by dehydration treatment such as filtration or drying.

[0107] To convert carboxymethyl cellulose or a salt thereof having a pH in the neutral range (pH 6.8 to 7.2) when made into an aqueous solution with a solid content of 1% by mass into the carboxymethyl cellulose or a salt thereof of the present embodiment having a pH in the acidic range (pH 4.0 or more and less than 6.8) when made into an aqueous solution with a solid content of 1% by mass, for example, a method of adding an acid can be mentioned.

[0108] - Pulverization - In producing CMC, pulverization or further granulation may be performed as necessary (pulverized product, granulated product). The pulverization is usually a mechanical pulverization performed using a machine. Methods for pulverizing carboxymethyl cellulose or a salt thereof include, for example, a dry pulverization method in which the carboxymethyl cellulose or a salt thereof is treated in a powder state, and a wet pulverization method in which the carboxymethyl cellulose or a salt thereof is treated in a dispersed or dissolved state in a liquid, and either of these is preferred. Examples of pulverization devices that can be used for mechanical pulverization include a cutter mill, a hammer mill, an impact mill, an airflow mill, a roller mill, and a vibration mill, and either a dry pulverizer or a wet pulverizer may be used.

[0109] - Classification Treatment - In the production of CMC, classification treatment may be performed as necessary. In this specification, classification refers to a process of sieving particles to be classified into those having a particle diameter equal to or larger than a certain size and those having a particle diameter smaller than that size, and can be performed based on the particle diameter (preferably the maximum particle diameter). Classification means.

[0110] The classification is preferably carried out based on whether the maximum particle size is less than 50 μm or 50 μm or more, thereby making it possible to selectively collect carboxymethyl cellulose or a salt thereof having a maximum particle size of less than 50 μm.

[0111] When a pulverized product of carboxymethyl cellulose or a salt thereof is used as the carboxymethyl cellulose or a salt thereof, the timing of the classification is not particularly limited, and the classification may be carried out during the pulverization treatment or after the completion of the pulverization treatment.

[0112] As a classification method, known methods can be used, such as methods using a dry classifier or a wet classifier. Examples of dry classifiers include a cyclone classifier, a DS separator, a turbo classifier, a microseparator, and an air separator. On the other hand, examples of wet classifiers include a liquid cyclone classifier, a centrifugal settler, and a hydrosilator. Of these, a dry classifier is preferred, and a cyclone classifier is more preferred.

[0113] [1.3 Component D: Crosslinkable Compound] Component D is a crosslinkable compound. By further including component D, the storage modulus (E') of the rubber composition can be further improved.

[0114] The crosslinkable compound has a thiosulfate group or an α,β-unsaturated carbonyl group and an amino group.

[0115] [Thiosulfate group] The thiosulfate group may be in the acid form (-SSO3H) or the salt form (-SSO3 - In the case of a salt type, the counter cation may be, for example, an alkali metal such as sodium, lithium, calcium, or cesium; 6 ) 4 - Quaternary ammonium salts such as (R 6 may be the same or different and are a hydrogen atom or an organic group such as an alkyl group or an ammonium group. The same applies hereinafter.

[0116] [α,β-Unsaturated Carbonyl Group] Examples of the α,β-unsaturated carbonyl group include those represented by the formula (1): In the formula, R 1 and R 2 each independently represents a hydrogen atom, a halogen atom, a hydroxyl group, an alkoxy group, or a hydrocarbon group; R 1 and R 2 may be linked together. Preferably, R 1 and R 2 Either one of R is a hydrogen atom, and more preferably both are hydrogen atoms. 3 is a counter ion, for example, an alkali metal such as sodium, lithium, calcium, or cesium, N(R 6 ) 4- and the like quaternary ammonium salts.

[0117] [Amino Group] The amino group is a group represented by the following formula (2): In the formula, R 4 and R 5 R each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. 4 and R 5 It is preferable that at least one of them is a hydrogen atom, and it is more preferable that both of them are hydrogen atoms (-NH2).

[0118] [Spacer] Examples of the spacer linking the thiosulfate group or α,β-unsaturated carbonyl group with the amino group include an alkyl group and a divalent group containing an aromatic ring and an amide bond. The spacer linking the thiosulfate group with the amino group is preferably an alkyl group, more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably an alkyl group having 2 to 5 carbon atoms. The spacer linking the α,β-unsaturated carbonyl group with the amino group is preferably a divalent group containing an aromatic ring and an amide bond.

[0119] [Preferred Examples of Crosslinkable Compounds] Preferred crosslinkable compounds are S-(3-aminopropyl)thiosulfuric acid and (2Z)-4-[(4-aminophenyl)amino]-4-oxo-2-butenoic acid (e.g., sodium salt), whose structural formulas are shown in the following formulas (3) and (4), respectively.

[0120] Component D may be a single crosslinkable compound or a combination of two or more crosslinkable compounds. It is preferable to include a crosslinkable compound containing a thiosulfate group, and it is more preferable to include a compound of formula (3) in order to further increase the strength of the resulting rubber composition. The reason why the compound of formula (3) is more preferable is unclear, but is as follows: Since the crosslinkable compound of component D mainly reacts with OH groups in the cellulose structure of component B as crosslinking points, it is presumed that the compound of formula (3), which has relatively little steric hindrance, can accommodate component B having a variety of structures and is more likely to react with the above crosslinking points.

[0121] [1.4 Optional Components] The rubber composition may further contain one or more optional components depending on the requirements of the intended use of the rubber composition. Examples of optional components include compounding agents that can be used in the rubber industry, such as reinforcing agents (e.g., silica, carbon black), fillers other than cellulose fillers (e.g., calcium carbonate, clay), silane coupling agents, crosslinking agents, vulcanization accelerators, vulcanization accelerator aids (e.g., zinc oxide, stearic acid), oils, curing resins, waxes, antioxidants, colorants, and foaming agents. Of these, vulcanization accelerators and vulcanization accelerator aids are preferred. The content of the optional components is not particularly limited and may be determined appropriately depending on conditions such as the type of optional component.

[0122] When the rubber composition is an unvulcanized rubber composition or a final product, it preferably contains at least a crosslinking agent as an optional component. Examples of crosslinking agents include sulfur compounds such as sulfur halides, peroxides (peroxides, for example, organic peroxides such as dicumyl peroxide, bis(α,α-dimethylbenzyl) peroxide, cumene peroxide, cumyl peroxide, and dicumyl peroxide), quinone dioximes, organic polyamine compounds, and alkylphenol resins having methylol groups. Among these, sulfur and peroxides are preferred, and sulfur is more preferred.

[0123] Examples of the vulcanization accelerator include guanidine-based accelerators such as diphenylguanidine (DPG), thiazole-based accelerators such as di-2-benzothiazolyl disulfide (MBTS) and 2-mercaptobenzothiazole (MBT), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide (BBS), N-oxydiethylene-2-benzothiazolylsulfenamide (OBS), and N,N-dicyclohexyl-2-benzothiazolylsulfenamide ( Examples of vulcanization accelerators include sulfenamide-based accelerators such as ethylenethiourea (EU), diethylthiourea (EUR), and trimethylthiourea (TMU), thiourea-based accelerators such as tetramethylthiuram monosulfide (TMTM) and tetramethylthiuram disulfide (TMTD), thiocarbamic acid-based accelerators such as zinc dimethyldithiocarbamate (ZnMDC) and zinc di-n-butyldithiocarbamate (ZnBDC), and xanthogenate-based accelerators such as zinc isopropylxanthogenate (ZIX). These may be used alone or in combination of two or more.

[0124] [1.5 Content of Each Component] An example of the content (ratio) of each component is as follows.

[0125] [Content of Component B Relative to Component A] The content of Component B is usually 0.5 parts by mass or more, preferably 1 part by mass or more, and more preferably 1.5 parts by mass or more, relative to 100 parts by mass of Component A. The upper limit is usually 50 parts by mass or less or 40 parts by mass or less, preferably 35 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. Therefore, the content of Component B is usually 0.5 to 50 parts by mass, 0.5 to 50 parts by mass, preferably 1 to 50 parts by mass or 1 to 30 parts by mass, and more preferably 1.5 to 30 parts by mass or 1.5 to 25 parts by mass, relative to 100 parts by mass of Component A.

[0126] [Content of Component C Relative to Component A] The content of Component C is usually 0.05 parts by mass or more, preferably 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of Component A. The upper limit is usually 5 parts by mass or less, preferably 4 parts by mass or less, and more preferably 3 parts by mass or less. Therefore, the content of Component C is usually 0.05 to 5 parts by mass, preferably 0.1 to 4 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of Component A.

[0127] [Content of Component C Relative to Component B] The content of Component C is usually 0.5 parts by mass or more, preferably 2.5 parts by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of Component B. The upper limit is usually 25 parts by mass or less, preferably 20 parts by mass or less, and more preferably 10 parts by mass or less. Therefore, the content of Component C is usually 0.5 to 25 parts by mass, preferably 2.5 to 20 parts by mass, and more preferably 5 to 10 parts by mass, per 100 parts by mass of Component B. This improves the dispersibility of the fine cellulose fibers in the latex.

[0128] [Content of Component D Relative to Component A] The content of Component D is usually 0.05 parts by mass or more, preferably 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of Component A. The upper limit is usually 10 parts by mass or less, preferably 8 parts by mass or less, and more preferably 5 parts by mass or less. Therefore, the content of Component C is usually 0.05 to 10 parts by mass, preferably 0.1 to 8 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of Component A.

[0129] [Amount of Optional Component Used] The content of the crosslinking agent is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of Component A. 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.

[0130] 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 Component A. The upper limit is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

[0131] [2. Production Method] Examples of methods for producing the rubber composition include a method including a step of kneading components A to C to obtain a mixture, and a step of drying the mixture.

[0132] [Mixing Step] In the mixing step, components A to C are kneaded (primary kneading without a vulcanizing agent system) to obtain a mixture. The amounts of each component are as described above. Component D and optional components may be added as needed when, simultaneously with, during, or after mixing of components A to C, but the crosslinking agent and granulation accelerator are preferably added after mixing and kneading of components A to C.

[0133] The forms of components A to C to be mixed are not particularly limited. Examples include solids of each component, dispersions dispersed in a dispersion medium (latex in the case of component A), and solutions dissolved in a solvent. Examples of dispersion mediums and solvents (hereinafter collectively referred to as "liquids") include water and organic solvents, with water being preferred. The amount of liquid is preferably 10 to 1,000 parts by mass per 100 parts by mass of rubber solids (the total amount when two or more rubber components are used). The dispersions and solutions may contain a dispersant as needed.

[0134] The primary kneading can be carried out using a known device such as a homomixer, homogenizer, or propeller stirrer if the solution is being used. The mixing temperature is not limited, but room temperature (20 to 30°C) is preferred. The mixing time may also be adjusted appropriately.

[0135] -Solids Concentration of Mixture- The solids concentration of the mixture obtained in the mixing step is typically 3% by mass or more, preferably 4% by mass or more, more preferably 5% by mass or more, 6% by mass or more, or 7% by mass or more. This allows for the formation of a thick film during the drying step, thereby reducing the heat transferred to components B and C, thereby inhibiting the progression of thermal denaturation and preventing a decrease in dispersibility after drying. The upper limit is typically 70% by mass or more, preferably 60% by mass or less, more preferably 50% by mass or less, 40% by mass or less, or 30% by mass or less. This inhibits an increase in the viscosity of the mixture and allows for a smooth drying process. Therefore, the solids concentration is typically 3 to 70% by mass, preferably 4 to 60% by mass, more preferably 5 to 50% by mass, 6 to 40% by mass, or 7 to 30% by mass. The solids concentration of the mixture can be adjusted by the solids concentrations of components A to C (and optionally, component D) and the amount of solvent added, if necessary. The treatment time is preferably 1 to 24 hours. By setting the heating temperature or heating time under the above conditions, damage to the rubber component can be suppressed. The mixture after drying may be in an absolutely dry state or may contain residual solvent. The drying method is not limited to the above methods, and any conventionally known method for removing the solvent may be appropriately selected.

[0136] The form of component B subjected to the primary kneading is not particularly limited. Examples include an aqueous dispersion of a cellulose-based filler, a dry solid of the aqueous dispersion, and a wet solid of the aqueous dispersion. The concentration of the cellulose-based filler in the aqueous dispersion may be 0.1 to 5% (w / v) when the dispersion medium is water, or 0.1 to 20% (w / v) when the dispersion medium contains water and an organic solvent such as alcohol. In this specification, the wet solid refers to a solid intermediate between the aqueous dispersion and the dry solid. The amount of the dispersion medium in the wet solid obtained by dehydrating the aqueous dispersion using a conventional method is preferably 5 to 15% by mass relative to the total amount of solids. The amount of the dispersion medium in the wet solid can be appropriately adjusted by adding a liquid or further drying.

[0137] The primary kneading may be carried out using a kneader according to a known method. Examples of the kneader include open kneaders such as two-roll and three-roll kneaders, intermeshing Banbury mixers, tangential Banbury mixers, pressure kneaders, homodispersers, and supermixers. The primary kneading may be a multi-stage process. For example, a combination of kneading in an internal kneader in the first stage and subsequent re-kneading in an open kneader may be used.

[0138] The processing time for the primary kneading is usually about 3 to 20 minutes, and the time can be appropriately selected to ensure uniform kneading. The temperature for the primary kneading may be about room temperature (for example, about 15 to 30°C), but may also be heated to a somewhat higher temperature. For example, the upper limit of the temperature is usually 150°C or lower, preferably 140°C or lower, and more preferably 130°C or lower. The lower limit of the temperature is 15°C or higher, preferably 20°C or higher, and more preferably 30°C or higher. The temperature for the primary kneading is preferably 15 to 150°C, more preferably 20 to 140°C, and even more preferably 30 to 130°C.

[0139] [Drying Step] In the drying step, the mixture obtained in the mixing step is dried. Drying can be carried out using a drying device such as an oven or a drum dryer, with a drum dryer being preferred. The temperature conditions during drying are typically 70°C or higher, preferably 80°C or higher, more preferably 90°C or higher, 100°C or higher, or 110°C or higher. This allows the drying process to proceed efficiently. The upper limit is typically 150°C or lower, preferably 140°C or lower, and more preferably 135°C or lower. This can suppress heat-induced cellulose denaturation and prevent a decrease in the mechanical properties of the resulting dried product after molding. Therefore, a temperature of typically 70 to 150°C, preferably 80 to 140°C, more preferably 90 to 135°C, 100 to 135°C, or 110 to 135°C allows the drying process to proceed efficiently and prevents a decrease in mechanical properties. In this specification, the drying temperature refers to the temperature of the drum surface when drum drying is performed using a drum dryer. The treatment time varies depending on the conditions such as temperature and drying equipment, but is usually 0.01 to 24 hours.

[0140] [Treatment after drying step] The obtained dried product may be used as a masterbatch as it is, or after further kneading (for example, kneading with a kneader such as a roll kneader) as necessary. Furthermore, optional additives such as a rubber component, a crosslinking agent, and a vulcanization aid may be further added to these masterbatches, and the resulting mixture may be kneaded again (secondary kneading) to be used as a final product (vulcanized rubber, crosslinked rubber).

[0141] After kneading, the mixture may be molded as needed by, for example, mold molding, injection molding, extrusion molding, blow molding, or foam molding, and an appropriate molding device may be selected depending on the shape, application, and molding method of the final product.

[0142] After kneading is completed, preferably after molding, it is preferable to further heat the composition. When the rubber composition contains a crosslinking agent (preferably a crosslinking agent and a vulcanization accelerator), a crosslinking (vulcanization) treatment is performed by heating. Also, when the rubber composition does not contain a crosslinking agent or a vulcanization accelerator, the same effect can be obtained by adding these later and heating. The heating temperature is preferably 150°C or higher, with the upper limit being preferably 200°C or lower, and more preferably 180°C or lower. Therefore, a temperature of about 150 to 200°C is preferable, and about 150 to 180°C is more preferable. Examples of heating devices include vulcanization devices such as mold vulcanizers, can vulcanizers, continuous vulcanizers, and injection molding vulcanizers.

[0143] Before the kneaded material is made into a final product, it may be subjected to a finishing treatment as necessary. Examples of the finishing treatment include polishing, surface treatment, lip finishing, lip cutting, and chlorine treatment. Only one of these treatments may be performed, or two or more of them may be combined.

[0144] [3. Use of Rubber Composition] The use of the rubber composition is not particularly limited as long as it is a composition for obtaining a rubber product as a final product. That is, it may be an intermediate (masterbatch) for rubber production, an unvulcanized rubber composition containing a vulcanizing agent, or a rubber product as a final product.

[0145] The uses of the final products are not particularly limited and include, for example, transportation equipment such as automobiles, trains, ships, and airplanes (e.g., tires, vibration-proof rubber); electrical appliances such as personal computers, televisions, telephones, and watches; mobile communication devices such as mobile phones; portable music players, video players, printing machines, copying machines, and sporting goods; building materials (e.g., seismic isolation rubber); office equipment such as stationery; vessels; and containers. The material can also be applied to components that use rubber or flexible plastics.

[0146] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these. Unless otherwise specified, parts and % represent parts by mass and % by mass.

[0147] (Production Example 1) Production of Carboxylated (TEMPO-oxidized) CNF 5 g (bone dry) of bleached, unbeaten kraft pulp derived from softwood (brightness 85%) was added to 500 mL of an aqueous solution containing 39 mg of TEMPO (Sigma-Aldrich) and 514 mg of sodium bromide, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to a concentration of 5.5 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 acidified with hydrochloric acid, filtered through a glass filter to separate the pulp, and thoroughly washed with water to obtain oxidized pulp (hereinafter sometimes referred to as "carboxylated cellulose," "carboxylated pulp," or "TEMPO-oxidized pulp"). The pulp yield was 90%, the oxidation reaction time was 90 minutes, and the carboxyl group content was 1.45 mmol / g. The oxidized pulp (solid content 3.1%) obtained in the above process was adjusted to 3.0% (w / v) with water and treated three times with an ultra-high-pressure homogenizer (20°C, 150 MPa) to obtain a TEMPO-oxidized CNF dispersion. The resulting TEMPO-oxidized CNF had an average fiber diameter of 3 nm and an aspect ratio of 150. The carboxyl group content was 1.45 mmol / g, the solid content during production was 3.12%, the concentration at the time of analysis was 1.0%, the pH was 7.22, the transparency was 93.4%, and the Brookfield viscosity (60 rpm, 6 rpm) was 2160 mPa·s and 13930 mPa·s, respectively.

[0148] [Conditions for Measuring Physical Properties of CNF] (Carboxy Group Amount) 60 mL of a 0.5 mass% slurry (aqueous dispersion) of TEMPO-oxidized CNF was prepared, and 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. After that, 0.05 N aqueous sodium hydroxide solution was added dropwise, and the electrical conductivity was measured until the pH reached 11. The amount of carboxy group was calculated using the following formula (1) from the amount of sodium hydroxide (a) consumed in the neutralization stage of weak acid, where the change in electrical conductivity was gradual: Carboxy group amount [mmol / g TEMPO-oxidized cellulose] = a [mL] × 0.05 / mass of TEMPO-oxidized cellulose [g] (1)

[0149] (Average fiber diameter, average fiber length, aspect ratio) The average fiber diameter and average fiber length of CNF were analyzed using an atomic force microscope (AFM) for 200 randomly selected fibers. The aspect ratio was calculated using the following formula: Aspect ratio = average fiber length / average fiber diameter

[0150] (Viscosity) A CNF dispersion with a solid content of 1.0 mass% was prepared (after fibrillation (e.g., defibration), the dispersion was left to stand for at least one day, and then stirred with a homodisper (e.g., 3000 rpm, 5 min)). Using a B-type viscometer (manufactured by Eiko Seiki Co., Ltd.), the viscosity after 3 minutes at a rotation speed of 60 rpm and after 3 minutes at a rotation speed of 6 rpm was measured at 25°C.

[0151] (Transparency) The transparency (transmittance of 660 nm light) of a CNF dispersion liquid having a solid content concentration of 1.0% was measured using a visible light photometer ASV11D (manufactured by AS ONE Corporation).

[0152] (Production Example 2) Preparation of CMC1 A solution of 688 parts isopropyl alcohol and 36 parts sodium hydroxide in 100 parts water was added to a twin-screw kneader adjusted to 100 rpm, and 100 parts of commercially available dissolving pulp was charged in an oven-dried state. The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. 42 parts of monochloroacetic acid was added with further stirring, and the mixture was heated to 70°C and subjected to an etherification reaction for 90 minutes. After completion of the reaction, the mixture was neutralized, deliquored, dried, and pulverized to obtain sodium carboxymethylcellulose having a carboxymethyl substitution degree per anhydroglucose unit (CM-DS) of 0.63 and a viscosity of a 1% by weight aqueous solution (measured with a Brookfield viscometer at 25°C and 30 rpm) of 205 mPa s.

[0153] (Production Example 3) Preparation of CMC2 A solution of 700 parts isopropyl alcohol and 50 parts sodium hydroxide in 110 parts water was added to a twin-screw kneader adjusted to 100 rpm, and 100 parts of commercially available dissolving pulp was charged in an oven-dried state. The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. With further stirring, 59 parts of monochloroacetic acid was added, and the mixture was heated to 70°C and subjected to an etherification reaction for 90 minutes. After completion of the reaction, the mixture was neutralized, deliquored, dried, and pulverized to obtain sodium carboxymethylcellulose with a carboxymethyl substitution degree per anhydroglucose unit (CM-DS) of 0.88 and a viscosity of a 1% by weight aqueous solution (measured with a Brookfield viscometer at 25°C and 30 rpm) of 205 mPa s.

[0154] (Production Example 4) Preparation of CMC3 A solution of 680 parts isopropyl alcohol and 34 parts sodium hydroxide in 100 parts water was added to a twin-screw kneader adjusted to 100 rpm, and 100 parts of commercially available dissolving pulp was charged in an oven-dried state. The mixture was stirred and mixed at 35°C for 90 minutes to prepare mercerized cellulose. 40 parts of monochloroacetic acid was added with further stirring, and the mixture was heated to 70°C and subjected to an etherification reaction for 90 minutes. After completion of the reaction, the mixture was neutralized, deliquored, dried, and pulverized to obtain sodium carboxymethylcellulose having a carboxymethyl substitution degree per anhydroglucose unit (CM-DS) of 0.60 and a viscosity of a 1% by mass aqueous solution measured with a Brookfield viscometer (25°C, 30 rpm) of 115 mPa s.

[0155] (Production Example 5) Preparation of CMC4 A solution of 700 parts isopropyl alcohol and 51 parts sodium hydroxide in 110 parts water was added to a twin-screw kneader adjusted to 100 rpm, and 100 parts of commercially available dissolving pulp was charged in an oven-dried state. The mixture was stirred and mixed at 40°C for 90 minutes to prepare mercerized cellulose. With further stirring, 60 parts of monochloroacetic acid was added, and the mixture was heated to 70°C and subjected to an etherification reaction for 90 minutes. After completion of the reaction, the mixture was neutralized, deliquored, dried, and pulverized to obtain sodium carboxymethylcellulose having a carboxymethyl substitution degree per anhydroglucose unit (CM-DS) of 0.89 and a viscosity of a 1% by weight aqueous solution (measured with a Brookfield viscometer at 25°C and 30 rpm) of 52 mPa s.

[0156] (Production Example 6) Preparation of CMC5 A solution of 1,100 parts of isopropyl alcohol and 82 parts of sodium hydroxide dissolved in 165 parts of water was added to a twin-screw kneader with the rotation speed adjusted to 100 rpm, and 100 parts of commercially available dissolving pulp was charged in an oven-dried state. The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. With further stirring, 97 parts of monochloroacetic acid was added, and the mixture was heated to 70°C and subjected to an etherification reaction for 90 minutes. After completion of the reaction, the mixture was neutralized, deliquored, dried, and pulverized to obtain sodium carboxymethylcellulose having a carboxymethyl substitution degree per anhydroglucose unit (CM-DS) of 1.42 and a viscosity of a 1% by weight aqueous solution (measured with a Brookfield viscometer at 25°C and 30 rpm) of 31 mPa s.

[0157] Comparative Production Example 1: Preparation of CMC6 A solution of 550 parts isopropyl alcohol and 40 parts sodium hydroxide in 80 parts water was added to a twin-screw kneader adjusted to 100 rpm, and 100 parts of commercially available dissolving pulp was charged in an oven-dried state. The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. With further stirring, 50 parts of monochloroacetic acid was added, and the mixture was heated to 70°C and subjected to an etherification reaction for 90 minutes. After completion of the reaction, the mixture was neutralized, deliquored, dried, and pulverized to obtain sodium carboxymethylcellulose having a carboxymethyl substitution degree per anhydroglucose unit (CM-DS) of 0.75 and a viscosity of a 1% by weight aqueous solution of 12 mPa·s (25°C, 30 rpm) measured with a Brookfield viscometer.

[0158] Table 1 shows the viscosity and CM-DS of each CMC.

[0159]

[0160] [Conditions for Measuring Physical Properties of CMC] - Measurement of Brookfield Viscosity (25°C, 30 rpm) - CMC was weighed into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solids content of 1% (w / v). The aqueous dispersion was stirred at 600 rpm for 3 hours at 25°C using a stirrer. Thereafter, the viscosity after 3 minutes was measured using a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd.) with a No. 1 rotor at a rotation speed of 30 rpm in accordance with the method of JIS-Z-8803.

[0161] -CM-DS (Carboxymethyl Substitution Degree)- Approximately 2.0 g of carboxymethylated cellulose (bone dry) was weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution of 1,000 mL of methanol and 100 mL of concentrated nitric acid was added, and the mixture was 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) was weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. The acid-form carboxymethylated cellulose was wetted with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added, and the mixture was shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, excess NaOH was back-titrated with 0.1N H2SO4, and the degree of carboxymethyl substitution (CM-DS) was calculated by the following formula: A = [(100 x F - (0.1N H2SO4 (mL)) x F') x 0.1] / (bone-dry mass (g) of acid-form carboxymethylated cellulose) CM-DS = 0.162 x A / (1 - 0.058 x A) A: amount (mL) of 1N NaOH required to neutralize 1 g of acid-form carboxymethylated cellulose F': factor of 0.1N H2SO4 F: factor of 0.1N NaOH

[0162] Examples 1 to 10, Comparative Examples 1 and 3 (Preparation of Masterbatches) The TEMPO-oxidized CNF obtained in Production Example 1, the CMC obtained in Production Examples 2 to 5, or Comparative Production Example 1, and natural rubber latex were stirred using a super mixer (SMV-Ba series, manufactured by Kawata Corporation) to obtain a mixture. The mass ratios of CNF and CMC (ratio of solid content) per 100 parts by mass of the rubber component were 20 phr and 1 phr, respectively. The solid content concentration of the mixture was adjusted to 10%. The mixture was dried using a drum dryer at 130°C, and the resulting sheet-like dried product was passed through a roll kneader (gap 0.5 mm) several times to prepare a masterbatch.

[0163] (Crosslinking with sulfur: Examples 1 to 5, Comparative Example 1) To a masterbatch (water content: about 4% or less (some are 0.8% or less)), 0.5 parts of stearic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 6.0 parts of zinc oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 3.5 parts of sulfur (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.7 parts of a vulcanization accelerator (N-oxydiethylene-2-benzothiazolylsulfenamide: Noccela (MSA-G), manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added per 100 parts of rubber solids, and the mixture was kneaded (open roll: manufactured by Kansai Roll Co., Ltd.) at 40°C for about 20 minutes) and vulcanization molded (press crosslinking at 150°C for 9 minutes) to obtain a rubber composition.

[0164] (Crosslinking with peroxide: Examples 6 to 10, Comparative Example 3) To a masterbatch (water content: about 4% or less (some are 0.8% or less)), 3.0 parts of zinc oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 2.0 parts of dicumyl peroxide (Percumyl D (registered trademark); manufactured by NOF Corporation) were added per 100 parts of rubber solids, and the mixture was kneaded (open roll: manufactured by Kansai Roll Co., Ltd.) at 40°C for about 20 minutes) and vulcanized and molded (press crosslinked at 150°C for 9 minutes) to obtain a rubber composition.

[0165] Comparative Examples 2 and 4 (Blank: Rubber and CNF Only) The same treatment as in Examples 1 and 6 was carried out, except that CMC was not added, to obtain rubber compositions.

[0166] The physical properties of each rubber composition were measured, and the relative values, with the measured values ​​of Comparative Example 2 for the sulfur crosslinked example (comparative example) and Comparative Example 4 for the peroxide crosslinked example (comparative example), set to 100, are shown in Table 2.

[0167] [Method for Evaluating Physical Properties of Rubber Composition] (Hardness) Durometer hardness was measured in accordance with JIS K6253-3:2012.

[0168] Dynamic properties were measured in accordance with JIS K6394:2017 "Vulcanized rubber and thermoplastic rubber - Determination of dynamic properties - General guidelines." That is, using a dynamic viscoelasticity measuring device (Hitachi High-Tech Science, DMA7100), the elastic modulus (E') at 23°C and the loss tangent (tanδ) at 60°C were measured under normal temperature control (temperature range: 18-110°C), measurement mode: tension, and DMA frequency: 10 Hz.

[0169] (Static tensile strength) Tensile strength, elongation, and 100% tensile stress (M100) were measured according to JIS K6251:2017.

[0170]

[0171] The storage modulus E' (23°C) and tan δ (60°C) of Comparative Examples 2 and 4 (blank) were 7.0 MPa·s, 0.060, and 7.6 MPa·s, 0.040, respectively.

[0172] The rubber compositions of Comparative Examples 1 and 3 (using the CMC of Comparative Production Example 1) had no difference in dynamic viscoelasticity from Comparative Examples 2 and 4 (no CMC added). In contrast, the rubber compositions of Examples 1 to 10 had better dynamic viscoelasticity than the comparative examples, and their static tensile strength was equal to or greater than that of the comparative examples without any decrease. Focusing on the 100% intermediate stress (M100) of the static tensile strength, Examples 1 to 5 (sulfur crosslinked) tended to show a higher M100 when low-viscosity and / or high-CM-DS CMC was used (Table 2).

[0173] Examples 11 and 12 Rubber compositions were obtained in the same manner as in Examples 5 and 10 (in both cases, CMC5 of Production Example 6 was used), except that the amount of CMC was changed to 4 phr.

[0174] Examples 13 to 15 The same procedure as in Example 5 was carried out, except that S-(3-aminopropyl)thiosulfuric acid (Sumilink (registered trademark) 100, manufactured by Sumitomo Chemical Co., Ltd., abbreviated as SL100) was added in the amount shown in Table 3 during rubber kneading, and the amount of CMC added was changed to the amount shown in Table 3, to obtain rubber compositions.

[0175] Comparative Examples 5 to 10 Comparative Examples 2 and 4 (blank) were conducted in the same manner as in Comparative Examples 2 and 4 (blank), except that S-(3-aminopropyl)thiosulfuric acid (Sumilink (registered trademark) 100, manufactured by Sumitomo Chemical Co., Ltd.) or (2Z)-4-[(4-aminophenyl)amino]-4-oxo-2-butenoic acid (Sumilink (registered trademark) 200, manufactured by Sumitomo Chemical Co., Ltd., abbreviated as SL200) was added in the amounts shown in Table 3 during rubber kneading.

[0176] The physical properties of each rubber composition were measured, and the relative values, with the measured values ​​of Comparative Example 2 for the sulfur crosslinked example (comparative example) and Comparative Example 4 for the peroxide crosslinked example (comparative example), set to 100, are shown in Table 3.

[0177]

[0178] All of the rubber compositions of the Examples exhibited good storage modulus E' (23°C). Among them, Examples 13 to 15 exhibited even better storage modulus E' (23°C), and the storage modulus E' (23°C) was significantly improved to the extent that it could be said to have a synergistic effect compared to Examples 4 and 11, in which CMC was added, and Comparative Examples 5 to 8, in which Sumilink 100 or 200 was added instead of CMC (Table 3).

[0179] The results of the above examples demonstrate that the present invention provides a rubber composition with good dynamic viscoelasticity and a method for producing the same.

Claims

1. A rubber composition comprising: component A: a rubber component; component B: a cellulosic filler; and component C: a water-soluble polymer.

2. The rubber composition according to claim 1, wherein component B comprises fine cellulose fibers.

3. The rubber composition according to claim 1, wherein component B comprises cellulose nanofibers or cellulose microfibrils.

4. The rubber composition according to any one of claims 1 to 3, wherein the amount of component C is 0.05 to 5 parts by mass per 100 parts by mass of component A.

5. The rubber composition according to any one of claims 1 to 4, further comprising: Component D: a crosslinkable compound having a thiosulfate group or an α,β-unsaturated carbonyl group, and an amino group.

6. The rubber composition according to claim 5, wherein the amino group is an --NH2 group.

7. The rubber composition according to claim 5 or 6, wherein component D contains at least one of a compound in which a thiosulfate group and an amino group are linked via an alkyl group, or a compound in which an α,β-unsaturated carbonyl group and an amino group are linked via a divalent group containing an aromatic ring and an amide bond.

8. The rubber composition according to claim 7, wherein the alkyl group is an alkyl group having 1 to 6 carbon atoms.

9. The rubber composition according to claim 5, wherein component D comprises at least S-(3-aminopropyl)thiosulfuric acid.

10. A method for producing a rubber composition according to any one of claims 1 to 9, comprising the steps of: mixing component A: a rubber component; component B: a cellulose-based filler; and component C: a water-soluble polymer to obtain a mixture; and drying the mixture obtained.

11. The method according to claim 10, further comprising a step of vulcanizing the dried product after drying.

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