Rubber composition and method for manufacturing the same

Abstract

The present invention aims to improve the water resistance of a rubber composition containing rubber components and cellulose fibers, and to provide a method for producing such a rubber composition with good strength. [Solution] The present invention provides a rubber composition comprising component A: a rubber component, component B: fine cellulose fibers, and component C: an amphoteric polyacrylamide additive. The present invention also provides a method for producing the rubber composition, comprising the steps of mixing components A to C and drying them.

Description

[Technical Field]

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

[0002] Rubber compositions containing rubber components and cellulose-based materials are known to possess excellent mechanical strength. For example, Patent Document 1 describes a rubber composition containing rubber components, inorganic fillers, plasticizers, and powdered cellulose having predetermined physical properties in a predetermined blending ratio, which exhibits excellent moldability and mechanical properties. Furthermore, Patent Document 2 describes how adding an anionic polyacrylamide dispersant along with rubber components and cellulose nanofibers enhances dispersibility and reinforcement at the interface with the rubber components, thereby improving the rigidity and durability of the rubber composition. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6878787 [Patent Document 2] Japanese Patent Publication No. 2009-191197 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the conventional rubber compositions mentioned above had problems with water resistance.

[0005] Therefore, the present invention aims to improve the water resistance of a rubber composition containing rubber components and cellulose fibers, and to provide a method for producing such a water-resistant rubber composition.

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

[11] . [1] Component A: Rubber component, Component B: Fine cellulose fibers, Component C: Amphoteric polyacrylamide additive, A rubber composition containing the following: [2] The rubber composition according to [1], wherein the amount of component B is 0.1 to 50 parts by mass per 100 parts by mass of component A. [3] The rubber composition according to [1] or [2], wherein the amount of component C is 0.01 to 5 parts by mass per 100 parts by mass of component A. [4] The rubber composition according to any one of [1] to [3], wherein component B comprises chemically modified fine cellulose fibers. [5] The rubber composition according to any one of [1] to [4], wherein component B comprises anionically modified fine cellulose fibers. [6] The rubber composition according to any one of [1] to [5], wherein component B comprises fine cellulose fibers that have been oxidized in the range of 0.5 to 3.0 mmol / g of carboxyl groups. [7] Component C comprises at least one constituent unit derived from a cationic vinyl monomer. A rubber composition as described in any one of items [1] to [6]. [8] The rubber composition according to [7], comprising 0.1 to 15 mol% of constituent units derived from cationic vinyl monomers. [9] The rubber composition according to any one of [1] to [8], wherein component C contains an amphoteric polyacrylamide additive having a weight-average molecular weight of 2,000,000 to 10,000,000.

[10] A step of mixing component A: rubber component, component B: fine cellulose fiber, and component C: amphoteric polyacrylamide additive to obtain a mixture, and The process of drying the resulting mixture. A method for producing the rubber composition described in any one of items [1] to [9], including the method described in item [9].

[11] The manufacturing method according to

[10] , further comprising the step of vulcanizing the dried product after drying. [Effects of the Invention]

[0007] The present invention provides a rubber composition that can exhibit good water resistance, and an efficient method for producing the same. [Modes for carrying out the invention]

[0008] [1. Rubber composition] The rubber composition contains the following components A to C.

[0009] [1.1 Component A: Rubber component] Component A is a rubber component. Examples of rubber components include, but are not limited to, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), hydrogenated nitrile rubber (H-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, polysulfide rubber, and other synthetic rubbers. Furthermore, thermoplastic elastomers such as polystyrene-based thermoplastic elastomers, polypropylene-based thermoplastic elastomers, polydiene-based thermoplastic elastomers, chlorine-based thermoplastic elastomers, and engineering plastics-based elastomers can also be used.

[0010] As component A, natural rubber (NR), acrylonitrile butadiene rubber (NBR), and hydrogenated nitrile rubber (H-NBR) are 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 sulfenamide-based and thiuram-based compounds. Organic peroxide crosslinking is also possible. Examples of commonly used organic peroxides include tertiary butyl peroxide, dicumyl peroxide, tertiary butylcumyl peroxide, 1,1-di(tertiary butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexane, 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexine-3, 1,3-di(tertiary butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tertiary butylperoxybenzoate, tertiary butylperoxyisopropyl carbonate, and n-butyl-4,4-di(tertiary butylperoxy)valerate. When crosslinking organic peroxides, it is preferable to use polyfunctional unsaturated compounds, such as triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, and N,N'-m-phenylene bismaleimide in combination.

[0012] [1.2 Component B: Fine cellulose fiber] Component B is fine cellulose fiber. Fine cellulose fiber refers to cellulose in the form of fine fibers derived from cellulose raw materials. Fine fibrous cellulose is defined as a dispersion of fine cellulose fibers (1 wt%) that exhibits a light transmittance in the range of 1 to 99% when analyzed using a visible light spectrometer (UV-1800, manufactured by Shimadzu Corporation) with a path length of 1 cm / 660 nm.

[0013] [Cellulose raw material] The cellulose raw material is usually wood, and may be any of hardwood, softwood, or a combination of two or more of the foregoing. Examples of hardwoods include plants of the genera Fagus (e.g., Fagus crenata), Tilia (e.g., Tilia japonica), Betula (e.g., Betula platyphylla, Betula kenaica), Populus (e.g., poplars), Eucalyptus (e.g., eucalyptus), Acacia (e.g., acacia), Quercus (e.g., Quercus mongolica, Quercus phillyraeoides, Quercus serrata, Cyclobalanopsis acuta), Acer (e.g., Acer pictum), Kalopanax (e.g., Kalopanax septemlobus), Ulmus (e.g., elms), Paulownia (e.g., Paulownia tomentosa), Magnolia (e.g., Magnolia hypoleuca), Salix (e.g., willows), Aesculus (e.g., Aesculus turbinata), Zelkova (e.g., Zelkova serrata), Cornus (e.g., Cornus controversa), Fraxinus (e.g., Fraxinus japonica), and plants of the genus Eucalyptus are preferred. Examples of softwoods include plants of the genera Cryptomeria (e.g., Cryptomeria japonica), Picea (e.g., Picea jezoensis), Larix (e.g., Larix kaempferi, Western larch, tamarack), Pinus (e.g., Pinus thunbergii, Pinus parviflora, Pinus radiata, Eastern white pine), Abies (e.g., Abies sachalinensis, Abies firma, Western fir), Taxus (e.g., yews), Chamaecyparis (e.g., Thuja standishii, Yellow cedar (Port Orford cedar)), Picea (e.g., Abies homolepis, Abies firma, Picea asperata, Sitka spruce, Eastern spruce), Podocarpus (e.g., Podocarpus macrophyllus), Chamaecyparis (e.g., Chamaecyparis pisifera, Chamaecyparis obtusa, Lawson cypress), Pseudotsuga (e.g., Pseudotsuga japonica, Douglas fir (Oregon pine), Western hemlock), Thujopsis (e.g., Thujopsis dolabrata, Hiba arborvitae), Tsuga (e.g., Tsuga sieboldii, Tsuga diversifolia), Cephalotaxus (e.g., Cephalotaxus harringtonia), and plants of the genera Cryptomeria and Pinus are preferred. Alternatively, the raw material may be non-wood, examples of which include bamboo, hemp, jute, kenaf, and agricultural waste.

[0014] [Classification by Production Method] Examples of the method for producing fine cellulose fibers include a method of defibrating pulp, and optionally a method of performing chemical modification treatment before and after defibration (usually before defibration), with the latter being preferred. Fine cellulose fibers having a nano-order fiber diameter are referred to as cellulose nanofibers, and fine cellulose fibers having a micron-order fiber diameter are referred to as cellulose microfibrils. The size of the fine cellulose fibers can be adjusted by conditions such as the micronization treatment and chemical modification treatment conditions. Note that the powdered cellulose described above does not enter a dispersed state and settles even when stirred in a solvent such as water, so the light transmittance of the dispersion cannot be measured, and it can be clearly distinguished from fine cellulose fibers.

[0015] [Example of Component B (1): Cellulose Nanofiber] In the present specification, cellulose nanofiber (CNF) refers to a cellulose fiber having a nano-order fiber diameter prepared through a micronization treatment.

[0016] The average fiber diameter (length-weighted average fiber diameter) of CNF is 500 nm or less, preferably 300 nm or less, more preferably 100 nm or less, and still more preferably 50 nm or less. The lower limit is not particularly limited, but is usually 1 nm or more, preferably 2 nm or more. Therefore, the average fiber diameter (length-weighted average fiber diameter) of CNF is usually 1 to 500 nm or 2 to 500 nm, preferably 2 to 300 nm or 2 to 100 nm, more preferably 2 to 50 nm or 3 to 30 nm. The average fiber length (length-weighted average fiber length) is usually 50 to 2000 nm, preferably 100 to 1000 nm. The aspect ratio of CNF is usually 10 or more, preferably 50 or more. The upper limit is not particularly limited, but is usually 1000 or less.

[0017] The average fiber diameter and average fiber length of fine cellulose fibers can be determined using a fractionator manufactured by Valmet. When using the fractionator, they can be obtained as length-weighted fiber width and length-weighted average fiber length, respectively. The average aspect ratio of fine cellulose fibers can be calculated by the formula: average aspect ratio = average fiber length / average fiber diameter.

[0018] [Example of Component B (2): Cellulose Microfibril] In this specification, cellulose microfibrils (microfibrillated cellulose, MFCs) refer to cellulose fibers having a micro-order fiber diameter, which are prepared by micronization treatment.

[0019] The average fiber diameter (average fiber width) of MFCs is usually 500 nm or more, preferably 1 μm or more, and more preferably 3 μm or more. This allows for higher water retention compared to unfibrillated cellulose fibers, and even with a small amount, a high strength-imparting effect and yield improvement effect can be obtained compared to finely fibrillated CNF. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 20 μm or less, but there are no particular restrictions. The average fiber length is usually 10 μm or more, 20 μm or more, or 40 μm or more, preferably 200 μm or more, 300 μm or more, or 400 μm or more, more preferably 500 μm or more, or 550 μm or more, and even more preferably 600 μm or more, 700 μm or more, or 800 μm or more. The upper limit is not particularly limited, but is usually 3,000 μm or less, preferably 2,500 μm or less, more preferably 2,000 μm or less, even more preferably 1,500 μm or less, 1,400 μm or less, or 1,300 μm or less. The aspect ratio of the MFC is preferably 3 or more, more preferably 5 or more, even more preferably 7 or more, and may be 10 or more, 20 or more, or 30 or more. The upper limit of the aspect ratio is not particularly limited, but is preferably 1000 or less, more preferably 100 or less, and even more preferably 80 or less.

[0020] [Degenerate] The fine cellulose fibers may be modified or unmodified. Modified fine cellulose fibers refer to fine 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"). Chemical modification treatment sufficiently refines the cellulose fibers, and defibration yields cellulose nanofibers with a uniform average fiber length and average fiber diameter. Therefore, when compounded with rubber components, they can exhibit a sufficient reinforcing effect. From this viewpoint, modified cellulose fibers are preferred.

[0021] Modifications include, for example, oxidation, etherification, esterification such as phosphate esterification, silane coupling, fluorination, and cationization. Among these, oxidation (carboxylation), etherification, cationization, and esterification are preferred, with oxidation (carboxylation) being more preferred.

[0022] -Oxidation (carboxylation)- Oxidized fine cellulose fibers typically have a structure in which at least one carbon atom having a primary hydroxyl group in the glucopyranose unit constituting the cellulose molecular chain (for example, the carbon atom having a primary hydroxyl group at position C6) is oxidized. The amount of carboxyl groups in oxidized cellulose fibers and oxidized cellulose nanofibers is preferably 0.5 mmol / g or more, more preferably 0.8 mmol / g or more, and even more preferably 1.0 mmol / g or more, relative to the oven-dry mass. The upper limit of this amount is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, and even more preferably 2.0 mmol / g or less. The amount of carboxyl groups is preferably 0.5 to 3.0 mmol / g, more preferably 0.8 to 2.5 mmol / g, and even more preferably 1.0 to 2.0 mmol / g. The amount of carboxyl groups can be adjusted by controlling the conditions when oxidizing the cellulose fibers (for example, the amount of oxidizing agent added, the reaction time). Furthermore, by controlling these conditions, the amounts of carboxylate groups and aldehyde groups can also be adjusted.

[0023] The amount of carboxyl groups can be calculated using the following procedure: Prepare 60 ml of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose. Add 0.1 M hydrochloric acid aqueous solution to the prepared slurry to adjust the pH to 2.5. Then, add 0.05 N sodium hydroxide aqueous solution dropwise and measure the electrical conductivity until the pH becomes 11. From the amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual (a), calculate the amount of carboxyl groups using the following formula: Carboxylate group content [mmol / g cellulose oxide] = a [ml] × 0.05 / Mass of cellulose oxide [g]

[0024] The oxidation method is not particularly limited, but one example is the oxidation of a cellulose raw material in water using an oxidizing agent in the presence of an N-oxyl compound and bromide, iodide, or a mixture thereof. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, resulting in the formation of an aldehyde group, a carboxyl group (-COOH), and a carboxylate group (-COOH). - At least one group selected from the group consisting of ) is produced. The concentration of the cellulose raw material during the reaction is not particularly limited, but 5% by mass or less is preferred.

[0025] An N-oxyl compound is a compound capable of generating a nitroxyl radical. Examples of nitroxyl radicals include 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO). Any compound that promotes the desired oxidation reaction can be used as the N-oxyl compound. The amount of N-oxyl compound used is not particularly limited as long as it is a catalytic amount that can oxidize the cellulose raw material. For example, 0.01 mmol or more is preferred, and 0.02 mmol or more is more preferred, per 1 g of oven-dried cellulose raw material. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, and even more preferably 0.5 mmol or less. The amount of N-oxyl compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.02 to 0.5 mmol, per 1 g of oven-dried cellulose raw material. The amount of N-oxyl compound used in the reaction system is usually 0.1 to 4 mmol / L.

[0026] Bromides are compounds containing bromine, such as alkali metal bromides that can dissociate and ionize in water. Iodides are compounds containing iodine, such as alkali metal iodides. The amount of bromide or iodide used can be selected within a range that promotes the oxidation reaction. The total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol per 1 g of oven-dried cellulose raw material.

[0027] As an oxidizing agent, known substances can be used, such as halogens, hypohalous acids, halogenous acids, perhalous acids or their salts, halogen oxides, and peroxides. Among these, hypohalous acids or their salts are preferred because they are inexpensive and have a low environmental impact, hypochlorous acid or its salts are more preferred, and sodium hypochlorite is preferred. The appropriate amount of oxidizing agent to use is, for example, 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and even more preferably 3 to 10 mmol per 1 g of oven-dried cellulose raw material. Also, for example, 1 to 40 mol per 1 mol of N-oxyl compound is preferred.

[0028] The oxidation process of cellulose raw materials proceeds efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, and can also be around 15 to 30°C, i.e., room temperature. As the reaction progresses, carboxyl groups are formed in the cellulose, causing a decrease in the pH of the reaction solution. To ensure the oxidation reaction proceeds efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at around 8 to 12, or 10 to 11. Water is preferred as the reaction medium due to its ease of handling and the low likelihood of side reactions.

[0029] The reaction time in an oxidation reaction can be set appropriately according to the degree of oxidation, and is usually 0.5 to 6 hours, for example, 0.5 to 4 hours.

[0030] The oxidation reaction may be carried out in two stages. For example, by filtering out the oxidized cellulose after the first stage of the reaction and then oxidizing it again under the same or different reaction conditions, the oxidation can be carried out efficiently without being inhibited by the salt produced as a by-product in the first stage of the reaction.

[0031] Another example of a carboxylation (oxidation) method is oxidation by contacting a cellulose raw material with an ozone-containing gas (ozonolysis). This oxidation reaction oxidizes at least the hydroxyl groups at positions 2 and 6 of the glucopyranose ring, and also causes decomposition of the cellulose chain. The ozone concentration in the ozone-containing gas is 50-250 g / m³. 3 Preferably, 50-220 g / m² 3 This is more preferable. The amount of ozone added is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. 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, it is possible to prevent the cellulose raw material from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved.

[0032] After ozone treatment, a follow-up oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the follow-up oxidation treatment is not particularly limited, but examples include chlorine compounds such as chlorine dioxide and sodium chlorite, as well as oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. The procedure for the follow-up oxidation treatment may involve, for example, dissolving these oxidizing agents in water or a polar organic solvent such as alcohol to prepare an oxidizing agent solution, and then immersing the oxidized cellulose in the solution.

[0033] An example of a method for measuring the amount of carboxyl groups is described below. Prepare 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose, add 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, then add 0.05 N sodium hydroxide aqueous solution dropwise until the pH becomes 11 and measure the electrical conductivity. From the amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual (a), the amount can be calculated using the following formula (Equation 2). (Equation 2): Amount of carboxyl groups [mmol / g (oxidized cellulose or oxidized cellulose nanofiber)] = a [mL] × 0.05 / mass of oxidized cellulose or mass of oxidized cellulose nanofiber [g]

[0034] - Acid-type oxidized cellulose and desalting - Oxidized cellulose contains carboxyl groups as a result of oxidation, but it may contain more acidic carboxyl groups (-COOH) than salty carboxyl groups (e.g., -COO-, -COONa), or more salty carboxyl groups than acidic carboxyl groups. The amounts of salty carboxyl groups and acidic carboxyl groups can be adjusted by desalting. Desalting can convert salty carboxyl groups to acidic carboxyl groups. In this specification, oxidized cellulose (after desalting) is called acidic oxidized cellulose, and oxidized cellulose (without undergoing the desalting treatment described later) is called salty oxidized cellulose. Salty oxidized cellulose usually mainly contains salty carboxyl groups. On the other hand, acidy oxidized cellulose has many acidic carboxyl groups, and the proportion of acidic carboxyl groups to carboxyl groups is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. Acidy oxidized cellulose can exhibit a better reinforcing effect together with component C. The proportion of acidic carboxyl groups can be calculated by the following procedure. 1) First, prepare 250 mL of an aqueous dispersion of acid-type oxidized cellulose with a solid content of 0.1% by mass before desalting. Add 0.1 M hydrochloric acid aqueous solution to the prepared aqueous dispersion to adjust the pH to 2.5, then add 0.1 N sodium hydroxide aqueous solution and measure the electrical conductivity until the pH becomes 11. From the amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual (a), calculate the amount of acid-type carboxyl groups and salt-type carboxyl groups, i.e., the total amount of carboxyl groups, using the following formula: Total amount of carboxyl groups (mmol / g cellulose oxide (salt type)) = a (ml) × 0.1 / mass of cellulose oxide (salt type) (g) 2) Prepare 250 mL of a 0.1% by mass aqueous dispersion of desalted acid-type oxidized cellulose. Add a 0.1 N sodium hydroxide aqueous solution to the prepared aqueous dispersion and measure the electrical conductivity until the pH reaches 11. From the amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity is gradual (b), calculate the amount of acid-type carboxyl groups using the following formula: Amount of acidic carboxyl groups (mmol / g acidic oxidized cellulose) = b (ml) × 0.1 / mass of acidic oxidized cellulose (g) 3) From the calculated total amount of carboxyl groups and the amount of acidic carboxyl groups, calculate the proportion of acidic carboxyl groups using the following formula. Percentage of acidic carboxyl groups (%) = (Amount of acidic carboxyl groups / Total amount of carboxyl groups) × 100

[0035] Desalting can be performed after oxidation, either before or after fibrillation, but is usually done after oxidation and before fibrillation. Desalting is usually carried out by replacing the salt (e.g., sodium salt) contained in the salt-type oxidized cellulose with a proton. Methods of desalting include adjusting the system to an acidic state and contacting the oxidized cellulose with a cation exchange resin. In the case of adjusting the system to an acidic state, the pH of the system is preferably adjusted to 2-6, more preferably 2-5, and even more preferably 2.3-5. Acids (e.g., inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrite, and phosphoric acid; organic acids such as acetic acid, lactic acid, oxalic acid, citric acid, and formic acid) are usually used to adjust the system to an acidic state. After adding the acid, washing treatment may be performed as appropriate. The cation exchange resin has a counterion of H + As long as this condition is met, either a strongly acidic ion exchange resin or a weakly acidic ion exchange resin can be used. The ratio of oxidized cellulose to the cation exchange resin when contacting the cellulose is not particularly limited and can be appropriately set by those skilled in the art from the viewpoint of efficiently performing proton substitution. The cation exchange resin after contact can be recovered by conventional methods such as suction filtration.

[0036] -Aetherification- Examples of etherification include carboxyalkylation, methylation, ethylation, cyanoethylation, hydroxyethylation, hydroxypropylation, ethylhydroxyethylation, and hydroxypropylmethylation, with carboxyalkylation being preferred and carboxymethylation being more preferred.

[0037] Carboxyalkylated cellulose fibers typically have a structure in which at least one carbon atom constituting the cellulose molecular chain (for example, a carbon atom with a primary hydroxyl group at the C6 position that constitutes a glucopyranose unit) is carboxymethylated.

[0038] The degree of carboxyalkyl substitution (preferably carboxymethyl substitution (CM-DS)) per anhydrous glucose unit of carboxyalkylated cellulose is preferably 0.01 or higher, 0.02 or higher, or 0.05 or higher, more preferably 0.10 or higher, even more preferably 0.15 or higher, even more preferably 0.20 or higher, and particularly preferably 0.25 or higher. This ensures a degree of substitution necessary to obtain the effects of chemical modification. The upper limit of this degree of substitution is preferably 0.50 or lower, more preferably 0.45 or lower, 0.40 or lower, or 0.35 or lower. This makes it difficult for cellulose fibers to dissolve in water, allowing them to maintain their fibrous form in water. Therefore, the degree of carboxyalkyl substitution is preferably 0.01 to 0.50, more preferably 0.01 to 0.45, and even more preferably 0.02 to 0.40, 0.10 to 0.35, or 0.20 to 0.30.

[0039] The degree of substitution, for example, the degree of carboxymethyl substitution, can be measured by the following method. Approximately 2.0 g of carboxymethylated cellulose (dry) is accurately weighed and placed in a 300 mL stoppered Erlenmeyer flask. 100 mL of a solution of 1,000 mL of methanol and 100 mL of special grade concentrated nitric acid is added, and the mixture is shaken for 3 hours to convert the salt-type carboxymethylated cellulose (hereinafter also referred to as "salt-type CM-cellulose") to the acid-type carboxymethylated cellulose (hereinafter also referred to as "acid-type CM-cellulose"). 1.5 to 2.0 g of the acid-type CM-cellulose (dry) is accurately weighed and placed in a 300 mL stoppered Erlenmeyer flask. The acid-type CM-cellulose is moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH is added, and the mixture is shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, the excess NaOH is back-titrated with 0.1 N H2SO4, and the degree of carboxymethyl substitution (CM-DS) can be calculated by the following formula: A = [(100 × F - (0.1N H₂SO₄ (mL)) × F') × 0.1] / (Oven-dry mass of acid-type CM-modified cellulose (g)) CM - DS = 0.162 × A / (1 - 0.058 × A) A: Amount of 1N NaOH required to neutralize 1g of acid-type C-mercured cellulose (mL) F': Factor of H2SO4 at 0.1N F: Factor of 0.1N NaOH

[0040] The degree of carboxyalkyl substitution can be adjusted by controlling reaction conditions such as the amount of carboxyalkylating agent added, the amount of mercerizing agent, and the composition ratio of water to organic solvent.

[0041] One method of carboxyalkylation is to merce a cellulosic raw material (starting material) and then etherify it. The following explanation will use carboxymethylation as an example.

[0042] Carboxymethylated cellulose can be produced by using unmodified cellulose fibers (cellulose raw material: e.g., pulp) as a starting material, performing a mercerization treatment, and then carrying out an etherification reaction. This reaction is usually carried out in the presence of a solvent. As the solvent, for example, water, lower alcohols (e.g., methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tertiary butanol) can be used individually or as a mixture of two or more solvents. When lower alcohols are mixed, the mixing ratio of the lower alcohols is preferably 60 to 95% by mass. The amount of solvent is approximately 3 times the mass of the cellulose raw material. There is no particular upper limit to this amount, but it is 20 times or less. Preferably, the amount of solvent is 3 to 20 times the mass of the cellulose raw material.

[0043] Examples of mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of mercerizing agent used is preferably 0.5 times or more per anhydrous glucose residue of the starting material, more preferably 1.0 times or more, and even more preferably 1.5 times or more, on a molar basis. The upper limit of this amount is usually 20 times or less, preferably 10 times or less, and more preferably 5 times or less. The amount of mercerizing agent used is preferably 0.5 to 20 times, more preferably 1.0 to 10 times, and even more preferably 1.5 to 5 times, on a molar basis.

[0044] The reaction temperature for mercellation is usually 0°C or higher, preferably 10°C or higher. The upper limit is usually 70°C or lower, preferably 60°C or lower. The reaction temperature is usually 0 to 70°C, preferably 10 to 60°C. The reaction time for mercellation is usually 15 minutes or more, preferably 30 minutes or more. The upper limit is usually 8 hours or less, preferably 7 hours or less. The reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

[0045] Etherification reactions are typically carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of carboxymethylating agents include monochloroacetic acid or its salts (e.g., metal salts such as sodium salts). The amount of carboxymethylating agent added is preferably 0.05 times or more per glucose residue of the cellulose raw material, more preferably 0.5 times or more, and even more preferably 0.8 times or more, on a molar basis. The upper limit of this amount is usually 10.0 times or less, preferably 5 times or less, and more preferably 3 times or less. The amount of carboxymethylating agent added is preferably 0.05 to 10.0 times, more preferably 0.5 to 5 times, and even more preferably 0.8 to 3 times, on a molar basis.

[0046] The reaction temperature is usually 30°C or higher, preferably 40°C or higher. The upper limit is usually 90°C or lower, preferably 80°C or lower. The reaction temperature is usually 30 to 90°C, preferably 40 to 80°C. The reaction time is usually 30 minutes or more, preferably 1 hour or more. The upper limit is usually 10 hours or less, preferably 4 hours or less. The reaction time is usually 30 minutes to 10 hours, preferably 1 hour to 4 hours. During the carboxymethylation reaction, the reaction solution may be stirred as needed.

[0047] -Differences from carboxymethylcellulose- It is preferable that carboxyalkylated cellulose fibers maintain at least a portion of their fibrous shape (are water-insoluble) even when dispersed in water. Carboxyalkylated cellulose fibers are distinguished from carboxymethylcellulose (for example, component C described later), which is a type of water-soluble polymer that dissolves in water and imparts viscosity. When an aqueous dispersion of carboxyalkylated cellulose fibers is observed with an electron microscope, fibrous material can be observed. On the other hand, when an aqueous dispersion of carboxymethylcellulose, a type of water-soluble polymer, is observed, no fibrous material is observed. Furthermore, anionically modified cellulose fibers are crystalline, and when measured by X-ray diffraction, peaks of cellulose type I crystals can be observed, but when carboxymethylcellulose powder, a water-soluble polymer, is measured similarly, cellulose type I crystals are usually not observed.

[0048] - Acid-type carboxyalkylated cellulose and desalting - Carboxylated cellulose may contain more acidic carboxyl groups than saltic carboxyl groups, or vice versa. The amounts of saltic carboxyl groups and acidic carboxyl groups can be adjusted by desalting. Desalting can convert saltic carboxyl groups to acidic carboxyl groups. In this specification, carboxylated cellulose (after desalting) is referred to as acidic carboxylated cellulose, and carboxylated cellulose (without undergoing the desalting treatment described later) is referred to as saltic carboxylated cellulose. Saltic carboxylated cellulose usually mainly contains saltic carboxyl groups (-COO-). On the other hand, acidic carboxylated cellulose has many acidic carboxyl groups, and the ratio of acidic carboxyl groups to the amount of carboxyl groups in acidic carboxylated cellulose is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more. Acidic carboxylated cellulose is presumed to have superior reinforcing effects with component C. The method for calculating the proportion of acidic carboxyl groups is as described above.

[0049] The timing of desalting is usually after carboxyalkylation, preferably after etherification and before fibrillation. One method of desalting is to contact the carboxyalkylated cellulose with a cation exchange resin. The cation exchange resin has H counterions. + As long as this condition is met, either a strongly acidic ion exchange resin or a weakly acidic ion exchange resin can be used. The ratio of carboxyalkylated cellulose to the cation exchange resin when contacting the carboxyalkylated cellulose is not particularly limited and can be appropriately set by those skilled in the art from the viewpoint of efficiently performing proton substitution. For example, the ratio can be adjusted so that the pH of the aqueous dispersion after adding the cation exchange resin to the carboxyalkylated cellulose aqueous dispersion is preferably 2 to 6, more preferably 2 to 5. The cation exchange resin after contact can be recovered by conventional methods such as suction filtration.

[0050] - Esterification (Phosphate esterification) - One example of esterified cellulose fibers is phosphorylated cellulose. Phosphorylated cellulose typically has a structure in which at least one carbon atom constituting the cellulose molecular chain (for example, the carbon atom with a primary hydroxyl group at position C6 that constitutes the glucopyranose unit) is phosphorylated.

[0051] The degree of substitution of phosphate groups per glucose unit in phosphate-esterified CNF (hereinafter simply referred to as "degree of phosphate group substitution") is preferably 0.001 or more and less than 0.40. The degree of phosphate group substitution can be measured by the following method. A slurry of phosphate-esterified CNF with a solid content of 0.2% by mass is prepared. A strongly acidic ion exchange resin is added to the slurry by volume at 1 / 10, and after shaking for 1 hour, the slurry is poured onto a mesh with a mesh opening of 90 μm to separate the resin from the slurry and obtain hydrogen-type phosphate-esterified CNF. Next, 0.1 N sodium hydroxide aqueous solution is added to the slurry after treatment with the ion exchange resin in 50 μL increments once every 30 seconds, and the change in the electrical conductivity value of the slurry is measured. The amount of alkali (mmol) required in the region where the electrical conductivity rapidly decreases is divided by the solid content (g) in the slurry to be titrated to calculate the amount of phosphate groups (mmol / g) per 1 g of hydrogen-type phosphate-esterified CNF. Furthermore, the degree of phosphate group substitution per glucose unit of phosphate-esterified CNF is calculated using the following formula: Degree of phosphate group substitution = 0.162 × A / (1 - 0.079 × A) A: Amount of phosphate groups per gram of hydrogen-type phosphate-esterified CNF (mmol / g).

[0052] The degree of phosphate group substitution can be adjusted by controlling reaction conditions such as the amount of phosphate-containing compound added and, if necessary, the amount of basic compound added.

[0053] One method of phosphorylation is to react a compound having a phosphate group with unmodified cellulose fibers (phosphate esterification). Examples of phosphate esterification methods include mixing a powder or aqueous solution of a compound having a phosphate group with a cellulosic raw material (e.g., a suspension (solid content concentration of about 0.1 to 10% by mass)) or adding an aqueous solution of a compound having a phosphate group to an aqueous dispersion of a cellulosic raw material, with the latter being preferred. This improves the uniformity of the reaction and increases the esterification efficiency. The pH of the aqueous solution of the compound having a phosphate group is preferably 7 or less from the viewpoint of improving the efficiency of phosphate group introduction, and more preferably 3 to 7 from the viewpoint of suppressing hydrolysis.

[0054] Examples of compounds containing a phosphate group include phosphoric acid, polyphosphate, phosphorous acid, phosphonic acid, polyphosphonic acid, esters and salts thereof. These compounds are low-cost, easy to handle, and allow for the introduction of phosphate groups into cellulose, thereby improving the defibrillation efficiency. Specific examples of compounds containing a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate. One or more compounds containing a phosphate group can be used in combination. The amount of compound containing a phosphate group added to the cellulose raw material is preferably 0.1 to 500 parts by mass, more preferably 1 to 400 parts by mass, and even more preferably 2 to 200 parts by mass, in terms of phosphorus element, per 100 parts by mass of solid content of the cellulose raw material. This allows for the efficient acquisition of a yield commensurate with the amount of compound containing a phosphate group used. The reaction temperature is preferably 0 to 95°C, and more preferably 30 to 90°C. The reaction time is not particularly limited, but is usually about 1 to 600 minutes, and preferably 30 to 480 minutes. If the esterification reaction conditions are within any of these ranges, it is possible to suppress excessive esterification of cellulose and its increased solubility, thereby improving the yield of phosphate-esterified cellulose. When reacting compounds having a phosphate group, a basic compound (for example, a basic compound having an amino group such as urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, etc.) may be added to the reaction system.

[0055] The suspension obtained after esterification is preferably dehydrated as needed, and then heat-treated. This suppresses hydrolysis of the cellulose raw material. The heating temperature is preferably 100 to 170°C, and it is more preferable to heat at 130°C or lower (preferably 110°C or lower) while water is present during the heat treatment, and then heat-treat at 100 to 170°C after removing the water. It is preferable to perform a washing treatment, such as boiling followed by washing with cold water. This allows for efficient defibration. Washing can be performed by adding water and then dehydrating (e.g., filtration), and may be repeated two or more times. It is preferable to continue washing until the electrical conductivity of the filtrate decreases. For example, it can be continued until the electrical conductivity is preferably 200 or lower, more preferably 150 or lower, and even more preferably 120 or lower. After washing, neutralization treatment may be performed as needed. Neutralization treatment can be performed, for example, by adding alkali (e.g., sodium hydroxide). Washing may be performed again after neutralization.

[0056] - Esterification (phosphorite esterification) - A second example of a method for producing esterified cellulose fibers is phosphorylated cellulose fibers. Phosphorylated cellulose fibers typically have a structure in which at least one carbon atom constituting the cellulose molecular chain (for example, a carbon atom with a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is phosphorylated.

[0057] The degree of phosphite group substitution per glucose unit in phosphite-esterified cellulose fibers (hereinafter simply referred to as "phosphite group substitution degree") is preferably 0.001 to 0.60. This facilitates electrical repulsion between cellulose cells, making nanofibrillation easier. The degree of phosphite group substitution can be measured using the same method as for measuring phosphate group substitution. The degree of phosphite group substitution can be adjusted by controlling reaction conditions such as the amount of phosphite or its salt added, and, if necessary, the amount of alkali metal ion-containing substances, urea or its derivatives added.

[0058] One method for esterifying phosphorous acid is to react unmodified cellulose fibers with phosphorous acid or its metal salt (preferably sodium hydrogen phosphite) to introduce an ester group of phosphorous acid.

[0059] Examples of phosphorous acid and its metal salts include phosphorous acid compounds such as phosphorous acid, sodium hydrogen phosphite, ammonium hydrogen phosphite, potassium hydrogen phosphite, sodium dihydrogen phosphite, sodium phosphite, lithium phosphite, potassium phosphite, magnesium phosphite, calcium phosphite, triethyl phosphite, triphenyl phosphite, and pyrophosphorous acid, and combinations of two or more selected from these, with sodium hydrogen phosphite being preferred. This also allows alkali metal ions to be introduced into the cellulose fibers. The amount of phosphorous acid or its metal salt added is preferably 1 to 10,000 g, more preferably 100 to 5,000 g, and even more preferably 300 to 1,500 g per 1 kg of unmodified cellulose fiber. In addition to phosphorous acid and its metal salt, alkali metal ion-containing substances (e.g., hydroxides, metal sulfates, metal nitrates, metal chlorides, metal phosphates, metal carbonates) may be further added to the reaction system.

[0060] Furthermore, urea or its derivatives may be added to the reaction system. This allows carbamate groups to be introduced into the cellulose fibers. Examples of urea and urea derivatives include urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, and two or more combinations selected from these, with urea being preferred. The amount of urea and urea derivatives added is preferably 0.01 to 100 mol, more preferably 0.2 to 20 mol, and even more preferably 0.5 to 10 mol per 1 mol of phosphorous acid or its metal salt.

[0061] The reaction temperature is preferably 100-200°C, more preferably 100-180°C, and even more preferably 100-170°C. During the heat treatment, it is preferable to heat at 130°C or below (preferably 110°C or below) while water is present, and then, after removing the water, to heat-treat at 100-170°C. The reaction time is usually about 10-180 minutes, more preferably 30-120 minutes. It is preferable to wash the phosphite-esterified cellulose fibers before defibration. The degree of substitution of phosphite groups per glucose unit is preferably 0.01 or more and less than 0.23.

[0062] - Esterification (Sulfuric acid esterification) - A third example of a method for producing esterified cellulose fibers is sulfated esterified cellulose fibers. Sulfated esterified cellulose typically has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, a carbon atom with a primary hydroxyl group at the C6 position that constitutes a glucopyranose unit) is phosphorylated.

[0063] The amount of sulfate groups per glucose unit in sulfated esterified cellulose fibers (hereinafter simply referred to as "amount of sulfate groups") is preferably 0.1 to 3.0 mmol / g. By introducing cationic substituents into the cellulose raw material, the cellulose molecules repel each other electrically. For this reason, cationized cellulose with introduced cationic substituents can be easily nanofibrillated. If the degree of cationic substitution per glucose unit is 0.02 or higher, sufficient nanofibrillation can be achieved due to the electrical repulsion between the cellulose molecules. On the other hand, if the degree of cationic substitution per glucose unit is 0.50 or lower, swelling or dissolution can be suppressed, preventing situations where nanofibers cannot be obtained. To efficiently perform fibrillation, it is preferable to wash the cationized cellulose obtained above.

[0064] The amount of sulfate groups per glucose unit can be measured by the following method: A aqueous dispersion of sulfated CNF is solvent-substituted with ethanol and then t-butanol, and then freeze-dried. 200 mg of the resulting sample is mixed with 15 ml of ethanol and 5 ml of water, and stirred for 30 minutes. Then, 10 ml of 0.5 N sodium hydroxide aqueous solution is added, and the mixture is stirred at 70°C for 30 minutes, followed by stirring at 30°C for 24 hours. Next, phenolphthalein is added as an indicator, and the mixture is titrated with hydrochloric acid. The amount of sulfate groups is then calculated using the following formula: Sulfate group amount [mmol / g sample] = (5 - (0.1 × hydrochloric acid titration volume [ml] × 2)) / 0.2.

[0065] The amount of sulfate groups can be adjusted by controlling reaction conditions such as the amount of sulfate-based compound added to the reaction.

[0066] One method of sulfuric acid esterification is to react unmodified cellulose fibers with a sulfuric acid compound, thereby introducing sulfuric acid groups derived from the sulfuric acid compound into the cellulose to produce sulfuric acid-esterified cellulose. Examples of sulfuric acid compounds include sulfuric acid, sulfamic acid, chlorosulfonic acid, sulfur trioxide, or esters or salts thereof. Among these, sulfamic acid is preferred because it has low cellulose solubility and low acidity.

[0067] For example, when sulfamic acid is used as the sulfate compound, the amount of sulfamic acid used can be appropriately adjusted considering the amount of anionic group introduced into the cellulose chain. For example, the amount is preferably 0.01 to 50 mol, more preferably 0.1 to 3.0 mol, per mol of glucose units in the cellulose molecule.

[0068] -Salt type / Acid type- Esterified cellulose may contain more acidic carboxyl groups than salt-type carboxyl groups, or vice versa. Esterified cellulose that has not undergone desalting treatment and that has undergone desalting treatment are called salt-type esterified cellulose and acid-type esterified cellulose, respectively. Salt-type esterified cellulose mainly contains salt-type carboxyl groups. Acid-type esterified cellulose is presumed to be superior due to its reinforcing effect with component C. The countercation of the salt-type carboxyl group and its preparation method are as described in the description of oxidized cellulose.

[0069] -Cationization- Cationized cellulose typically has a structure in which at least one carbon atom constituting the cellulose molecular chain (for example, the carbon atom with a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is cationized, and usually contains cations such as ammonium, phosphonium, sulfonium, or groups having such cations in the molecule. The degree of cation substitution per glucose unit in cationized cellulose is preferably 0.02 to 0.50. The degree of cation substitution per glucose unit can be measured by the following method: After drying the cationized cellulose fibers, the nitrogen content is measured using a total nitrogen analyzer (TN-10, manufactured by Mitsubishi Chemical Corporation), and the degree of cation substitution (average number of moles of substituents per mole of anhydrous glucose unit) is calculated using the following formula: Degree of cation substitution = (162 × N) / (1 - 151.6 × N) N: Nitrogen content.

[0070] The degree of cation substitution can be adjusted by reaction conditions such as the amount of cationizing agent added and the composition ratio of water or C1-C4 alcohols.

[0071] One method of cationization involves reacting unmodified cellulose fibers with a cationizing agent (e.g., glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrate, or its halohydrin form) and an alkali metal hydroxide catalyst (e.g., sodium hydroxide, potassium hydroxide) in the presence of water and / or an alcohol having 1 to 4 carbon atoms. By using any of the cationizing agents exemplified above, cationized cellulose having a quaternary ammonium group can be obtained. The cationization reaction is usually carried out in the presence of water or alcohol.

[0072] The amount of cationizing agent is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of cellulose raw material. The upper limit of this amount is usually 800 parts by mass or less, and preferably 500 parts by mass or less.

[0073] Examples of catalysts used as needed during cationization include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of catalyst is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, per 100 parts by mass of cellulose raw material. The upper limit of this amount is usually 7 parts by mass or less, and preferably 3 parts by mass or less.

[0074] -Basic-type cationized cellulose fiber- It is preferable to convert the cationized cellulose fibers, after cationization, into basic-type cationized cellulose or basic-type cationized cellulose nanofibers by desalting. Desalting can convert the salts in the cationized cellulose into bases. In this specification, cationized cellulose (nanofibers) that have undergone desalting are referred to as basic-type cationized cellulose (nanofibers) or cationized cellulose (nanofibers) (basic type). Furthermore, cationized cellulose and cationized cellulose nanofibers that have not undergone desalting are referred to as salt-type cationized cellulose (nanofibers) or cationized cellulose (nanofibers) (salt type). Desalting may be performed at either the pre-fibrillation (cationized cellulose) or post-fibrillation (cationized cellulose nanofibers) stage described later. Desalting is performed on the salts (e.g., Cl) contained in the cationized cellulose (salt type) and cationized cellulose nanofibers (salt type). - This means substituting the ) with a base to make it a basic form. As a method of desalting after cationization, for example, a method of contacting cationized cellulose or cationized cellulose nanofibers with an anion exchange resin is used. The anion exchange resin has counterions that are OH - As long as this condition is met, either a strongly basic ion exchange resin or a weakly basic ion exchange resin can be used. The ratio of modified cellulose to the anion exchange resin when contacting the modified cellulose is not particularly limited and can be appropriately set by those skilled in the art from the viewpoint of efficiently performing cation substitution. For example, the ratio can be adjusted so that the pH of the aqueous dispersion after adding the anion exchange resin to the cationized cellulose nanofiber aqueous dispersion is preferably 8 to 13, more preferably 9 to 13. The anion exchange resin after contact can be recovered by conventional methods such as suction filtration.

[0075] [Fine reduction (fibrillation)] Micronization is usually carried out by mechanical processing. Mechanical processing (preferably beating or disintegration) is usually carried out wet (i.e., in the form of an aqueous dispersion of cellulose fibers). Examples of equipment used for mechanical processing include refiners (e.g., disc type, conical type, cylinder type), high-speed defibrators, shear-type agitators, colloid mills, high-pressure jet dispersers, beaters, PFI mills, kneaders, dispersers, high-speed dissociators (top finers), high-pressure or ultra-high-pressure homogenizers, grinders (stone mill type grinders), ball mills, vibratory mills, bead mills, single-screw, twin-screw or multi-screw kneaders / extruders, homomixers under high-speed rotation, refiners, defibrators, friction grinders, high-shear defibrators, dispersers, homogenizers (e.g., microfluidizers), and other equipment capable of providing mechanical defibration. Equipment capable of providing defibration in a wet manner is preferred, and high-speed dissociators and refiners are more preferred, but are not particularly limited.

[0076] When defibration is performed by a wet process, an aqueous dispersion of cellulose fibers is usually prepared. The solid content concentration of modified cellulose in the aqueous dispersion is preferably 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 mechanical processing, pH adjustment (e.g., 7 or less, 6 or less, 5 or less) may be performed as needed.

[0077] Prior to the preparation of the aqueous dispersion, pretreatment such as dry pulverization (e.g., pulverization after drying) may be performed. Examples of apparatuses used for dry pulverization include, but are not particularly limited to, impact mills such as hammer mills and pin mills, media mills such as ball mills and tower mills, and jet mills. Post-treatment may also be performed after defibration. Examples of the post-treatment include, but are not particularly limited to, drying (e.g., freeze-drying, spray drying, tray drying, drum drying, belt drying, a method of spreading thinly on a glass plate or the like and drying, fluidized bed drying, microwave drying, heating fan-type vacuum drying, vacuum (deaeration) drying), redispersion in water (the dispersion apparatus is not limited), and pulverization (e.g., pulverization using an apparatus such as a cutter mill, hammer mill, pin mill, or jet mill).

[0078] [Optional Post-Treatment] The fine cellulose fibers may be in the state 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 particularly limited to, drying (e.g., freeze-drying, spray drying, tray drying, drum drying, belt drying, a method of spreading thinly on a glass plate or the like and drying, fluidized bed drying, microwave drying, heating fan-type vacuum drying), redispersion in water (the dispersion apparatus is not limited), and pulverization (e.g., pulverization using an apparatus such as a cutter mill, hammer mill, impact mill, airflow mill, roller mill, or vibration mill).

[0079] [Physical Properties of Fine Cellulose Fibers] The fine cellulose fibers preferably have the following physical properties.

[0080] - Specific Surface Area - The BET specific surface area of the fine cellulose fibers is preferably 25 m 2 / g or more, more preferably 50 m 2 / g or more, still more preferably 100 m 2 / g or more. The BET specific surface area can be measured in accordance with the nitrogen gas adsorption method (JIS Z 8830): after replacing the aqueous dispersion with t-BuOH, the freeze-dried sample is measured with a BET specific surface area analyzer.

[0081] -Crystallization of Cellulose Type I- The crystallinity of type I cellulose in fine cellulose fibers is usually 50% or higher, preferably 60% or higher. While there is no particular upper limit, it is realistically considered to be around 90%. The crystallinity of cellulose can be controlled by the degree of chemical modification. The crystallinity of type I cellulose can be calculated by measuring and comparing the intensities of the (200) peak around 22.6° and the valley between (200) and (110) (around 18.5°) using X-ray diffraction. If the fine cellulose fibers contain type II crystals, it is preferable to separate the peaks based on type II crystals (around 12.3°, 20.2°, and 21.9°) before calculating the intensity of the type I crystals.

[0082] -viscosity- When fine cellulose fibers are used as an aqueous dispersion, a low viscosity of the aqueous dispersion is preferable. This allows for a material with good handling properties despite being fibrillated. For example, the B-type viscosity (25°C, 60 rpm) of an aqueous dispersion with 1% solids by mass is usually 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 B-type viscosity (25°C, 6 rpm) of an aqueous dispersion with a solid 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 B-type viscosity can be measured, for example, by the following method: After fibrillation (e.g., defibrillation), let it stand for at least one day, dilute as necessary, stir with a homodisperser (e.g., 3000 rpm, 5 min), and then measure the viscosity (measure the viscosity after 6 or 60 rpm, 3 minutes of rotation).

[0083] -Transparency- The transparency of a CNF aqueous dispersion with a solid content of 1.0 mass is typically 40% or more, preferably 50% or more, and more preferably 60% or more. There is no particular upper limit; it is acceptable as long as it is 100% or less. The transparency of an MFC aqueous dispersion with a solid content of 1.0 mass is typically 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.

[0084] - Anionization level - When the fine cellulose fibers are modified cellulose microfibrils, their 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 result in more uniform chemical modification throughout the cellulose compared to cellulose fibers with a higher degree of anionization, allowing for more stable acquisition 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, and more preferably 0.30 meq / g or more, but is not particularly limited. Therefore, 0.06 meq / g or more and 2.50 meq / g or less is preferred, 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 is more preferred, and 0.10 meq / g or more and 2.00 meq / g or less is even preferred. The degree of anionization is the equivalent amount of anions per unit mass of modified cellulose microfibrils, and can be calculated from the equivalent amount of diallyldimethylammonium chloride (DADMAC) required to neutralize the anionic groups in a unit mass of modified cellulose microfibrils.

[0085] -Water retention capacity- When the fine cellulose fibers are cellulose microfibrils, their 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 practically expected to be around 200 or less, but is not particularly limited. The water retention capacity corresponds to the mass of water in the precipitate relative to the mass of solids in the fibers in the precipitate, and is measured and calculated by centrifuging a 0.3 mass% aqueous dispersion of fibers at 25,000 G, as the ratio of water content to solid content in the precipitated gel. That is, it is calculated using the following formula: Water retention capacity=(B+C-0.003×A) / (0.003×AC) A: Mass of an aqueous dispersion of cellulose microfibrils with a solid content concentration of 0.3% by mass. B: Mass of the precipitate separated after centrifuging an aqueous dispersion of mass A at 25,000 G for 30 minutes at 30°C. C: Mass of solids in the aqueous phase separated after centrifugation.

[0086] A higher water retention capacity value indicates a greater ability of the fiber to retain water. Water retention capacity can be measured or calculated for fibers that have undergone fibrillation, but it is usually not measurable 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 undergone fibrillation or defibration are centrifuged under the above conditions, a dense precipitate cannot be formed, making it difficult to separate the precipitate from the aqueous phase. When cellulose nanofibers are centrifuged under the above conditions, they usually hardly settle at all.

[0087] -Fibrillation rate- When the fine cellulose fibers are cellulose microfibrils, the fibrillation rate (Fibrillation %) is preferably 1.0% or higher, more preferably 1.2% or higher, and even more preferably 1.5% or higher. This confirms that sufficient fibrillation has occurred. 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 Corporation.

[0088] -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 with a solid content concentration of 1.0% by mass and using an electrical conductivity meter (HORIBA ES-71).

[0089] [1.3 Component C: Amphoteric polyacrylamide] Component C is an amphoteric polyacrylamide. In this specification, amphoteric polyacrylamide means a copolymer having constituent units derived from (meth)acrylamide, constituent units having cationic substituents, and constituent units having anionic substituents.

[0090] [Constituent units derived from (meth)acrylamide] (Meth)acrylamide is either acrylamide or methacrylamide. Amphoteric polyacrylamide may have constituent units derived from either acrylamide or methacrylamide, or it may have constituent units derived from both.

[0091] [Constituent units having cationic substituents] Examples of cationic substituents include groups containing tertiary amines or quaternary ammonium salts.

[0092] -Group containing a tertiary amine- Examples of groups containing tertiary amines include dialkylaminoalkyl groups. The number of carbon atoms in an alkyl group is not particularly limited, but for example, it can be 1-6, 1-5, 1-4, or 1-3. The alkyl group may be linear or branched, but linear is preferred. Examples of alkyl groups include methyl, ethyl, propyl, butyl, pentyl, and hexyl groups, with methyl, ethyl, and propyl groups being preferred, and methyl and ethyl groups being more preferred. Examples of groups containing a tertiary amino group include dimethylaminoethyl, diethylaminoethyl, dimethylaminopropyl, and diethylaminopropyl groups.

[0093] -Groups containing quaternary ammonium salts- Groups containing quaternary ammonium salts include vinyl monomers obtained by the reaction of a monomer containing the tertiary amine group (e.g., vinyl monomer) with a quaternizing agent. Examples of quaternizing agents include alkyl halides such as methyl chloride and methyl bromide, aralkyl halides such as benzyl chloride and benzyl bromide, dimethyl sulfate, diethyl sulfate, epichlorohydrin, 3-chloro-2-hydroxypropyltrimethylammonium chloride, and glycidyltrialkylammonium chloride.

[0094] -Monomers having cationic substituents- The constituent units having cationic substituents are preferably derived from monomers having cationic substituents. Examples of monomers having cationic substituents include vinyl monomers having cationic substituents, and (meth)acrylates and (meth)acrylamides substituted with groups containing cationic substituents are preferred. Specifically, examples include dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and diethylaminopropyl (meth)acrylate, and dialkylaminoalkyl (meth)acrylamides such as dimethylaminopropyl (meth)acrylamide, and diethylaminopropyl (meth)acrylamide; and monomers obtained by the reaction of the above dialkylaminoalkyl (meth)acrylates and dialkylaminoalkyl (meth)acrylamides with a quaternizing agent (as described above).

[0095] [Constituent units having anionic substituents] Examples of anionic substituents include groups containing a hydroxyl group. The hydroxyl group may also be in the form of a salt, such as an alkali metal salt or an ammonium salt.

[0096] -Monomers containing anionic substituents- The constituent units having anionic substituents are preferably derived from monomers having anionic substituents (e.g., hydroxyl groups). Examples of monomers having anionic substituents include vinyl monomers having anionic substituents, specifically unsaturated carboxylic acids, unsaturated sulfonic acids, and unsaturated phosphonic acids.

[0097] Examples of unsaturated carboxylic acids include unsaturated monocarboxylic acids such as (meth)acrylic acid, 2-(meth)acrylamide-N-glycolic acid, N-acryloylglycine, 3-acrylamidepropanoic acid, and 4-acrylamidebutanoic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; unsaturated tricarboxylic acids such as aconitic acid, 3-butene-1,2,3-tricarboxylic acid, and 4-pentene-1,2,4-tricarboxylic acid; and unsaturated tetracarboxylic acids such as 1-pentene-1,1,4,4-tetracarboxylic acid, 4-pentene-1,2,3,4-tetracarboxylic acid, and 3-hexene-1,1,6,6-tetracarboxylic acid. Examples of unsaturated sulfonic acids include vinylsulfonic acid, styrenesulfonic acid, and 2-acrylamide-2-methylpropanesulfonic acid. Examples of unsaturated phosphonic acids include vinylphosphonic acid and α-phenylvinylphosphonic acid. Of these, unsaturated carboxylic acids are preferred, unsaturated mono or dicarboxylic acids are more preferred, and (meth)acrylic acid, 2-(meth)acrylamide-N-glycolic acid, maleic acid, and itaconic acid are even more preferred.

[0098] [Other constituent units] Amphoteric polyacrylamide is typically a copolymer containing the three structural units described above, but it may also contain structural units other than the three described above.

[0099] [Molar ratio of constituent units] The molar ratio of constituent units derived from (meth)acrylamide that constitute the amphoteric polyacrylamide is preferably 70 to 99.8 mol%, more preferably 80 to 99.8 mol%. The molar ratio of constituent units having cationic substituents is preferably 0.1 to 15 mol%, more preferably 0.1 to 10 mol%. The molar ratio of constituent units having anionic substituents is preferably 0.1 to 15 mol%, more preferably 0.1 to 10 mol%. The above molar ratios are the molar ratios of the raw material monomers for each constituent unit.

[0100] [Physical properties of amphoteric polyacrylamide] The amphoteric polyacrylamide preferably has the following physical properties.

[0101] -Weight average molecular weight- The weight-average molecular weight of amphoteric polyacrylamide is typically 2,000,000 or more, preferably 3,000,000 or more, and more preferably 4,000,000 or more. This allows for a greater enhancement of the strength-improving effect. The upper limit is 10,000,000 or less, preferably 9,000,000 or less, and more preferably 8,000,000 or less. Therefore, the weight-average molecular weight is typically 2,000,000 to 10,000,000, preferably 3,000,000 to 9,000,000, and more preferably 4,000,000 to 8,000,000. This suppresses aggregation. The weight-average molecular weight can be measured by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0102] -Ion content- The ionic content of amphoteric polyacrylamide can be expressed as the sum of the anionic group content and cationic group content relative to the total amount of amphoteric polyacrylamide. Typically, the anionic group content is 5% by mass or more, preferably 8% by mass or more, and more preferably 10% by mass or more. This further enhances the strength-improving effect. The upper limit is 50% by mass or less, preferably 40% by mass or less. Similarly, the cationic group content is 5% by mass or more, preferably 8% by mass or more, and more preferably 10% by mass or more. This further enhances the strength-improving effect. The upper limit is 50% by mass or less, preferably 40% by mass or less. This suppresses water absorption by cellulose fibers. The content of anionic and cationic groups can be determined, for example, by the mass ratio of monomers during the production of amphoteric polyacrylamide. It can be adjusted as appropriate according to the desired properties, and the present invention is not particularly limited to the above numerical ranges.

[0103] -viscosity- The B-type viscosity (25°C, 30 rpm) of amphoteric polyacrylamide is typically 2,000 mPa·s or higher, preferably 3,000 mPa·s or higher, and more preferably 3,500 mPa·s or higher. The upper limit is typically 30,000 mPa·s or lower, preferably 25,000 mPa·s or lower, and more preferably 20,000 mPa·s or lower. The B-type viscosity (25°C, 30 rpm) can be measured according to the method of JIS-Z-8803.

[0104] [Manufacturing method] The method for producing amphoteric polyacrylamide is not particularly limited, but examples include polymerizing (meth)acrylamide, monomers having cationic substituents, and monomers having anionic substituents. During polymerization, chain transfer agents, crosslinking agents, and reducing agents may be used as needed, and temperature control (e.g., heating during the reaction (e.g., 20-90°C)) and pressure control (e.g., pressurizing during the reaction) may also be performed.

[0105] [1.4 Content of each component] The content (ratio) of each component is as follows, for example:

[0106] [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, per 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, per 100 parts by mass of component A.

[0107] [Content of component C relative to component A] The content of component C is usually 0.01 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.

[0108] [Content of component C relative to component B] The content of component C is usually 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of component B. The upper limit is usually 20 parts by mass or less, preferably 15 parts by mass or less, and more preferably 10 parts by mass or less. Therefore, the content of component C is usually 0.1 to 20 parts by mass, preferably 0.2 to 15 parts by mass, and more preferably 0.5 to 10 parts by mass, per 100 parts by mass of component B. This can lead to better dispersibility of fine cellulose fibers in the latex.

[0109] [Amount of optional ingredients used] The crosslinking agent content 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, per 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.

[0110] 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.

[0111] [2. Manufacturing method] Examples of methods for producing a rubber composition include a step of kneading components A to C to obtain a mixture, and a step of drying the mixture.

[0112] [Mixing process] In the mixing process, components A to C are kneaded (primary kneading without the vulcanizing agent) to obtain a mixture. The amounts of each component are as described above. Components A to C may all be added to the system simultaneously and mixed by hand, or some (for example, components A and B) may be mixed first, and the remaining components (for example, component C) may be added and mixed afterward. Any optional components may be added as needed during, during, or after the mixing of components A to C, but it is preferable that the crosslinking agent and granule accelerator be added after the mixing and kneading of components A to C.

[0113] The form of components A to C used in the mixing is 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 1000 parts by mass per 100 parts by mass of rubber solids (total amount if two or more rubber components are used). The dispersions and solutions may contain dispersants as needed.

[0114] Primary mixing can be carried out using known equipment such as homomixers, homogenizers, propeller stirrers, and high-speed kneaders if the mixture is a solution. The mixing temperature is not limited, but room temperature (20-30°C) is preferred. The mixing time and mixing speed may also be adjusted as appropriate.

[0115] -Solid content concentration of the mixture- The solid content concentration of the mixture obtained in the mixing step is usually 3% by mass or more, preferably 4% by mass or more, and more preferably 5% by mass or more. This allows for the formation of a thick film in the drying step, thereby reducing the heat transferred to components B and C, suppressing the progression of thermal deformation, and also suppressing the decrease in dispersibility after drying. The upper limit is usually 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 suppresses the increase in viscosity of the mixture and allows for a smooth drying process. Therefore, the solid content concentration is usually 3 to 70% by mass, preferably 4 to 60% by mass, and more preferably 5 to 50% by mass. The solid content concentration of the mixture can be adjusted by the solid content concentration of each component A to C and the amount of solvent added as needed. The processing time is preferably 1 to 24 hours. By setting the heating temperature or heating time to the above conditions, damage to the rubber components can be suppressed. The mixture after drying may be completely dry or may contain residual solvent. Furthermore, the drying method is not limited to the above method, and any conventionally known method for removing the solvent may be appropriately selected.

[0116] The form of component B subjected to 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, and 0.1 to 20% (w / v) when the dispersion medium contains water and an organic solvent such as alcohol. In this specification, a wet solid is a solid that is intermediate in form between the aqueous dispersion and the dry solid. The amount of dispersion medium in the wet solid obtained by dehydrating the aqueous dispersion by a conventional method is preferably 5 to 15% by mass relative to the total amount of solid. The amount of dispersion medium in the wet solid can be adjusted as appropriate by adding liquid or further drying.

[0117] Primary mixing can be carried out using a mixer according to known methods. Examples of mixers include open-type mixers such as two-roll or three-roll mixers, interlocking Banbury mixers, tangential Banbury mixers, pressure kneaders, homodispersers, and supermixers. Primary mixing may also be a multi-stage process. For example, a combination of mixing in a closed-type mixer in the first stage and then re-mixing in an open-type mixer can be used.

[0118] The processing time for the first kneading is usually around 3 to 20 minutes, and the time can be appropriately selected to ensure uniform kneading. The temperature for the first kneading can be around room temperature (for example, around 15 to 30°C), but it may also be heated to a certain temperature. For example, the upper limit of the temperature is usually 150°C or less, preferably 140°C or less, and more preferably 130°C or less. 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 first kneading is preferably 15 to 150°C, more preferably 20 to 140°C, and even more preferably 30 to 130°C.

[0119] [Drying process] In the drying process, the mixture obtained in the mixing process is dried. Drying can be carried out using a drying device such as an oven or drum dryer, or a stirring device equipped with a heating means (e.g., a laboplast mill). The temperature conditions during drying are usually 70°C or higher, preferably 80°C or higher, more preferably 90°C or higher, 100°C or higher, or 110°C or higher. This allows for efficient drying. The upper limit is usually 150°C or lower, preferably 140°C or lower, more preferably 135°C or lower. This suppresses thermal degradation of cellulose and avoids a decrease in the mechanical properties of the resulting dried product after molding. Therefore, by using a temperature of 60-180°C, preferably 65-170°C, more preferably 70-160°C, 80-155°C, or 90-150°C, efficient drying can be carried out while avoiding a decrease in mechanical properties. In this specification, the temperature during drying refers to the temperature of the drum surface when drum drying is performed using a drum dryer. Processing time varies depending on conditions such as temperature and drying equipment, but is typically between 0.01 and 24 hours.

[0120] Drying may be carried out in one stage or in two or more stages. If two or more stages are used, it is preferable that the drying temperature of the second and subsequent stages is higher than that of the first stage, with the first stage being less than 100°C and the second stage being 100°C or higher being more preferable. The drying temperature of the first stage is more preferably 95°C or lower, and even more preferably 90°C or lower. The drying temperature of the second stage is more preferably 110°C or higher, and even more preferably 120°C or higher. Different equipment may be used for each stage, or the same equipment may be used. Examples of equipment combinations include oven drying or drum drying for the first stage, and oven drying and / or drying by a stirring device for the second and subsequent stages. For example, in the case of oven drying for the first stage, the drying time is, for example, 8 to 24 hours, 10 to 22 hours, or 11 to 20 hours, and the drying temperature is, for example, 60 to less than 100°C or 65 to 90°C. For drying using a first-stage drum dryer, drying times are, for example, 0.01 to 1 hour, 0.02 to 0.8 hours, or 0.03 to 0.5 hours, and drying temperatures are 70 to 135°C or 80 to 135°C. For oven drying from the second stage onward, drying times are, for example, 0.01 to 1 hour, 0.03 to 0.8 hours, or 0.05 to 0.5 hours, and drying temperatures are, for example, 100 to 180°C or 110 to 170°C. For drying using an agitator from the second stage onward, the maximum temperature is, for example, 100 to 150°C or 110 to 150°C, and drying times are 0.01 to 0.5 hours or 0.03 to 0.5 hours.

[0121] [Post-drying process] The resulting dried product may be used as is, or, if necessary, further kneaded (for example, kneaded using a kneader such as a roll kneader) and used as a masterbatch. Alternatively, optional additives such as rubber components, crosslinking agents, and vulcanization aids may be added to these masterbatches and kneaded again (secondary kneading) to be used as the final product (vulcanized rubber, crosslinked rubber).

[0122] After mixing is complete, molding may be performed as needed. Examples of molding methods include die molding, injection molding, extrusion molding, hollow molding, and foam molding, and the appropriate equipment should be selected according to the shape, application, and molding method of the final product.

[0123] After mixing is complete, and preferably after molding, further heating is preferable. If the rubber composition contains a crosslinking agent (preferably a crosslinking agent and a vulcanization accelerator), the crosslinking (vulcanization) treatment is performed by heating. Even if the rubber composition does not contain a crosslinking agent and a vulcanization accelerator, a similar effect can be obtained by adding them later and heating. The heating temperature is preferably 150°C or higher, with an upper limit of preferably 200°C or lower, and more preferably 180°C or lower. Therefore, a temperature of about 150 to 200°C is preferable, and a temperature of about 150 to 180°C is more preferable. Examples of heating devices include vulcanization devices such as mold vulcanization, can vulcanization, continuous vulcanization, and injection molding vulcanization.

[0124] Before the mixture becomes the final product, finishing treatments may be performed as needed. Examples of finishing treatments include polishing, surface treatment, lip finishing, lip trimming, and chlorine treatment, and one of these treatments may be performed alone or in combination of two or more.

[0125] [3. Uses of rubber compositions] The use of the rubber composition is not particularly limited; it can be any composition used to obtain a rubber product as the final product. That is, it can be an intermediate (masterbatch) for rubber manufacturing, an unvulcanized rubber composition containing a vulcanizing agent, or a rubber product as the final product.

[0126] The applications of the final product are not particularly limited and include, for example, transportation equipment such as automobiles, trains, ships, and airplanes (e.g., tires, vibration-damping rubber); electrical appliances such as personal computers, televisions, telephones, and watches; mobile communication devices such as mobile phones; portable music players, video players, printing equipment, photocopiers, and sporting goods; building materials (e.g., seismic isolation rubber); office equipment such as stationery; containers; and other materials. It can also be applied to components that use rubber or flexible plastics, even if they are not listed above. [Examples]

[0127] The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to these. Unless otherwise specified, parts and % refer to parts by mass and mass%.

[0128] (Manufacturing Example 1) Production of carboxylated (TEMPO-oxidized) CNF 5 g (absolutely dry) bleached, unbeaten kraft pulp (whiteness 85%) derived from coniferous trees 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. During the reaction, the pH of the system decreased, but 3 M aqueous sodium hydroxide solution was added sequentially to adjust the pH to 10. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. The mixture after the reaction 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 took 90 minutes, and the amount of carboxyl groups 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 in an ultra-high pressure homogenizer (20°C, 150 MPa) to obtain a TEMPO-oxidized CNF dispersion. The average fiber diameter of the obtained TEMPO-oxidized CNF was 3 nm, and the aspect ratio was 150. Furthermore, 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 B-type viscosity (60 rpm, 6 rpm) was 2160 mPa·s and 13930 mPa·s, respectively.

[0129] [Measurement conditions for the physical properties of CNF] (Carboxylate group amount) A 60 mL slurry (aqueous dispersion) of TEMPO-oxidized CNF was prepared, and a 0.1 M hydrochloric acid aqueous solution was added to adjust the pH to 2.5. Then, a 0.05 N sodium hydroxide aqueous solution was added dropwise until the pH reached 11, and the electrical conductivity was measured. The amount of sodium hydroxide consumed during the neutralization stage of the weak acid, where the change in electrical conductivity was gradual, was calculated using the following formula (1): Carboxylate group content [mmol / gTEMPO-oxidized cellulose] = a [mL] × 0.05 / TEMPO Oxide Cellulose Mass [g] (1)

[0130] (Average fiber diameter, average fiber length, aspect ratio) The average fiber diameter and average fiber length of CNF were analyzed using atomic force microscopy (AFM) on 200 randomly selected fibers. The aspect ratio was calculated using the following formula: Aspect ratio = average fiber length / average fiber diameter

[0131] (viscosity) A CNF dispersion with a solid content of 1.0% by mass was prepared (after fibrillation (e.g., defibration), it was allowed to stand for at least one day, and then stirred with a homodisperser (e.g., 3000 rpm, 5 min)). Using a B-type viscometer (manufactured by Eiko Seiki Co., Ltd.), the viscosity was measured at 25°C at a rotation speed of 60 rpm for 3 minutes and at a rotation speed of 6 rpm for 3 minutes.

[0132] (transparency) The transparency (transmittance of 660nm light) of a 1.0% solid content CNF dispersion was measured using a visible light photometer ASV11D (manufactured by AS ONE Corporation).

[0133] Examples 1-7, Comparative Examples 1-3 (Masterbatch preparation) The TEMPO-oxidized CNF and natural rubber latex obtained in Production Example 1 were stirred at 1000 rpm for 15 minutes using a high-speed mixer. Subsequently, diluted solutions (10% by mass) of amphoteric, cationic, and anionic polyacrylamides (details of each are in Table 2) shown in Table 1 were added and stirred at 1000 rpm for 5 minutes to obtain a mixture. The mass ratio of CNF to 100 parts by mass of rubber component was 20 phr, and the mass ratio of polyacrylamides (ratio of solid content of each) was as shown in Table 1. The solid content concentration of the mixture was set to 5.5%. The mixture was dried in an oven at approximately 70°C for 15 hours (first drying) and then cooled to 23°C. In Comparative Example 4 and Examples 1-2, the mixture was dried again in an oven under the conditions shown in Table 1 (second drying). The resulting sheet-like dried material was passed through a roll kneader (gap 0.5 mm) several times to prepare a masterbatch.

[0134] (bridge) To a masterbatch (moisture content: approximately 4% or less (some have 0.8% or less)), 0.5 parts stearic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 6.0 parts zinc oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 3.5 parts sulfur (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.7 parts vulcanization accelerator (N-oxydiethylene-2-benzothiazolyl sulfenamide: Noxellar (MSA-G), manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added per 100 parts of rubber solids. The mixture was then kneaded using an open roll (manufactured by Kansai Roll Co., Ltd.) at 40°C for approximately 20 minutes, followed by vulcanization molding (press crosslinking at 150°C for 9 minutes) to obtain a rubber composition.

[0135] Comparative Example 4 (Sodium Carboxymethylcellulose) The procedure was carried out in the same manner as in Example 1, except that sodium carboxymethylcellulose (Sunrose® F04SH, manufactured by Nippon Paper Industries Co., Ltd.) was used instead of amphoteric polyacrylamide.

[0136] Comparative Example 5 (without amphoteric polyacrylamide) The procedure was the same as in Example 1, except that no amphoteric polyacrylamide was added.

[0137] [Table 1]

[0138] [Footnote to Table 1] "70°C overnight" means drying at 70°C for approximately 12 to 16 hours.

[0139] [Table 2]

[0140] [Measurement method] -Weight average molecular weight (molecular weight: Mw)- Measurements were taken using GPC according to the following conditions. Equipment: HLC-8320GPC (manufactured by Tosoh Corporation) Columns: TSK-gel G-6000 HXL, G-5000 HXL, G-4000 HXL, G-3000 HXL, G-2000 HXL (manufactured by Tosoh Corporation) Eluent:THF Flow rate: 1mL / min Temperature: Pump oven, column oven 40℃ Injection volume: 100μL Standard material: Polystyrene EasiCal PS-1 (manufactured by Agilent Technology)

[0141] -Viscosity (B type viscosity)- The sample was measured into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solid content of 1% (w / v). The aqueous dispersion was stirred at 25°C at 600 rpm for 3 hours using a stirrer. Then, in accordance with the method of JIS-Z-8803, the viscosity was measured after 3 minutes using a Type B viscometer (manufactured by Toki Sangyo Co., Ltd.) with rotor No. 1 and rotation speed of 30 rpm.

[0142] [Method for evaluating the physical properties of rubber compositions] The physical properties of each rubber composition were measured, and the results are shown in Tables 3 and 4.

[0143] (Static tensile strength) In accordance with JIS K6251:2017, the breaking strength, elongation, and tensile stress (M50, M100, M300) were measured.

[0144] (hardness) Durometer hardness (3 sec) was measured according to JIS K6253-3:2012.

[0145] (Dynamic viscoelasticity) The dynamic properties were measured in accordance with JIS K6394:2017 "Vulcanized rubber and thermoplastic rubber - Determination of dynamic properties - General guidelines". Specifically, using a dynamic viscoelasticity analyzer (Hitachi High-Tech Science, DMA7100), under normal temperature control (temperature range: 18-110°C), measurement mode: tensile, DMA frequency: 10Hz, the modulus of elasticity at 23°C (E'@23°C) and the loss tangent at 60°C (tanδ@60°C) were measured.

[0146] (Water absorption rate measurement) Six rubber pieces measuring 5 mm x 40 mm x 2 mm were prepared as test specimens. These specimens were immersed in deionized water heated to 70°C, and three specimens were removed after 24 hours or 48 hours. After wiping off any moisture adhering to the surface, the mass was measured. Based on the mass change before and after the test, the water absorption rate of each specimen was calculated using the following formula, and the average water absorption rate obtained for the three specimens was calculated. Formula for calculating water absorption rate: Water absorption rate (%)=(m2-m1) / m1×100(%) Here, m1 is the mass of the rubber piece before the test (g), and m2 is the mass of the rubber piece after the test (g). The average water absorption rate of each test specimen was calculated and evaluated as the final water absorption rate.

[0147] (Bubble formation) In samples (immediately after preparation) following vulcanization molding (press crosslinking at 150°C for 9 minutes), the appearance was visually inspected, and samples showing the formation of bubbles were evaluated as "present," while those not showing bubbles were evaluated as "absent."

[0148] [Table 3]

[0149] [Table 4]

[0150] In Comparative Examples 1 and 2, which used anionic PAM, and Comparative Example 3, which used cationic PAM, the strength, particularly the breaking strength and M300, was low, and the generation of bubbles was also observed. Furthermore, in Comparative Examples 1 to 3 and Comparative Example 4, which used carboxymethylcellulose, the water absorption rate was high, similar to Comparative Example 5, which had no additives. In contrast, in Examples 1 to 7, good strength was exhibited in a well-balanced manner, and the water absorption rate was kept low. This is presumed to be because, by using amphoteric PAM having both anionic and cationic groups in the examples, the anionic groups improved the dispersibility of CNF, and the cationic groups suppressed the water retention of CNF to some extent, resulting in both improved water resistance and improved strength. The results of these examples demonstrate that the present invention can provide a rubber composition that exhibits good water resistance.

Claims

1. Component A: Rubber component, Component B: Fine cellulose fibers, Component C: Amphoteric polyacrylamide additive, A rubber composition containing the following:

2. The rubber composition according to claim 1, wherein the amount of component B is 0.1 to 50 parts by mass per 100 parts by mass of component A.

3. The rubber composition according to claim 1 or 2, wherein the amount of component C is 0.01 to 5 parts by mass per 100 parts by mass of component A.

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

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

6. The rubber composition according to claim 1 or 2, wherein component B comprises fine cellulose fibers that have been oxidized in a carboxyl group content of 0.5 to 3.0 mmol / g.

7. Component C comprises at least one constituent unit derived from a cationic vinyl monomer. The rubber composition according to claim 1 or 2.

8. Component C contains 0.1 to 15 mol% of constituent units derived from cationic vinyl monomers. The rubber composition according to claim 7.

9. The rubber composition according to claim 1 or 2, wherein component C comprises an amphoteric polyacrylamide additive having a weight-average molecular weight of 2,000,000 to 10,000,000.

10. The process involves mixing component A: rubber component, component B: fine cellulose fibers, and component C: amphoteric polyacrylamide additive to obtain a mixture, and The process of drying the resulting mixture. A method for producing the rubber composition according to claim 1 or 2, including the method described above.

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

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