Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B11/00—Preparation of cellulose ethers
  • C08B11/02—Alkyl or cycloalkyl ethers
  • C08B11/04—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals
  • C08B11/10—Alkyl or cycloalkyl ethers with substituted hydrocarbon radicals substituted with acid radicals
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
  • C08B15/08—Fractionation of cellulose, e.g. separation of cellulose crystallites
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/20—Compounding polymers with additives, e.g. colouring
  • C08J3/205—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase
  • C08J3/21—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase the polymer being premixed with a liquid phase
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K7/00—Use of ingredients characterised by shape
  • C08K7/02—Fibres or whiskers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
  • C08L1/02—Cellulose; Modified cellulose
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L21/00—Compositions of unspecified rubbers

Definitions

• the present invention relates to a method for producing a rubber composition.
• Cellulose nanofibers and microfibrillated cellulose obtained by micronizing cellulose are fine fibers with diameters on the nano to micro order, and are expected to be used in a variety of fields as new materials with properties not found in ordinary pulp, such as high strength, high elasticity, and thixotropy.
• the existing method for drying a mixture of rubber latex and filler involves coagulating the mixture with acid, removing most of the water in a dehydrator, and then drying with hot air in a dryer.
• the filler is fine cellulose fiber
• the water retention of the fine cellulose fiber and carboxymethyl cellulose which is used in combination as necessary, inhibits acid coagulation, so a method of directly drying without acid coagulation has been adopted.
• Various drying methods using dryers have been used, but hot air drying using an oven is common (e.g., Reference 1).
• oven drying has some issues, such as the long drying time it takes, the limited amount that can be dried at one time, the fact that drying begins from the surface, and therefore uneven drying of the surface and interior can occur when there is a large amount of material, and drying at high temperatures can result in a deterioration of the physical properties of the resulting rubber composition.
• the present invention aims to provide a method for producing a rubber composition that can efficiently and thoroughly dry fine cellulose fibers and rubber components, while minimizing the effects on the physical properties of the resulting rubber composition and, in fact, enhancing them.
• the present invention provides the following: [1] A method for producing a rubber composition, comprising a drying step of drying a mixture containing fine cellulose fibers and a rubber component and having a solid content concentration of 3 to 70 mass % at a temperature of 70 to 150 ° C. using a drum dryer. [2] The method according to claim 1, wherein the fine cellulose fibers include chemically modified fine cellulose fibers. [3] The method according to [1] or [2], wherein the weight ratio of the content of the fine cellulose fibers in the mixture to the content of the rubber component is 0.1 to 50 phr. [4] The manufacturing method according to [1] or [2], wherein the drum dryer is a double-drum type drum dryer.
• a composition comprising fine cellulose fibers and a rubber component
• a composition wherein the difference ⁇ L between the L1 value, which is the lightness L* defined by the L*a*b* color system of the composition immediately after production and one week after production, and the L2 value, which is the lightness L* of a composition similar to the composition except that it does not contain fine cellulose fibers, is 1 to 15.
• the present invention by carrying out drying using a drum dryer during the process of producing a rubber composition, it is possible to improve the drying efficiency of the mixture of fine cellulose fibers and rubber components, and to obtain a rubber composition that exhibits good physical properties even when a high drying temperature is used.
• ⁇ includes the extreme values.
• X ⁇ Y includes the values X and Y at both ends.
• the raw materials of the rubber composition include at least fine cellulose fibers and a rubber component. Each raw material will be described below.
• the fine cellulose fiber is a fine fibrous cellulose derived from a cellulose raw material.
• the fine fibrous cellulose is one in which the light transmittance obtained by measuring a dispersion (1 wt%) of the fine cellulose fiber at an optical path length of 1 cm/660 nm using a visible spectroscopic analyzer (UV-1800, manufactured by Shimadzu Corporation) is in the range of 1 to 99%.
• the average fiber diameter of the fine cellulose is not particularly limited, but is usually about 1 nm to 60 ⁇ m.
• Examples of a method for producing the fine cellulose fiber include a method of defibrating pulp, and a method of chemically modifying the pulp before or after defibration (usually before defibration) as necessary.
• the fine cellulose fiber having a fiber diameter of the nano-order is called cellulose nanofiber (CNF)
• the fine cellulose fiber having a fiber diameter of the micron order is called cellulose microfibril (MFC).
• the size of the fine cellulose fiber can be adjusted by the conditions of the micronization treatment and the chemical modification treatment.
• CNF cellulose nanofiber
• 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 even more preferably 50 nm or less.
• the lower limit is not particularly limited, but is usually 1 nm or more, preferably 2 nm or more. Therefore, the average fiber diameter (length-weighted average fiber diameter) of 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 is usually 5 ⁇ m or less, preferably 3 ⁇ m or less, 2 ⁇ m or less, or 1 ⁇ m or less.
• the lower limit is usually 50 nm or more, preferably 100 nm or more.
• 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.
• the average fiber diameter of fine cellulose fibers can be obtained from the results of observing each fiber using a fiber tester manufactured by ABB Co., Ltd., a fractionator manufactured by Valmet, a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM) appropriately selected according to the size of the fiber diameter.
• a fiber tester manufactured by ABB Co., Ltd. a fractionator manufactured by Valmet
• SEM scanning electron microscope
• AFM atomic force microscope
• TEM transmission electron microscope
• the value measured by the fiber tester can be determined as the average fiber diameter.
• the value measured by the AFM can be determined as the fiber diameter.
• the average fiber length can be measured using a fiber tester manufactured by ABB Corporation, a fractionator manufactured by Valmet, a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM).
• SEM scanning electron microscope
• AFM atomic force microscope
• TEM transmission electron microscope
• the fiber length can be measured by analyzing 200 randomly selected fibers and calculating the average.
• microfibrillated cellulose [Example of fine cellulose fiber: microfibrillated cellulose (MFC)]
• MFC microfibrillated cellulose
• MFC refer to cellulose fibers having a fiber diameter of the micron order (e.g., 500 nm or more) prepared through a pulverization process. MFC can exhibit higher water retention than undefibrated cellulose fibers and can exhibit a yield improvement effect compared to finely defibrated CNF.
• the lower limit of the average fiber diameter of MFC is not particularly limited, but is usually 500 nm or more, preferably 1 ⁇ m or more, and more preferably 4 ⁇ m or more.
• the average fiber diameter is less than 500 nm, when the average fiber diameter is measured under the following conditions, if 1000 or more unfibrillated fibers (for example, fibers with a fiber diameter of 4 ⁇ m or more) are counted, it is MFC.
• the presence of unfibrillated fibers can be confirmed by dispersing 0.1 g of fine cellulose fiber in 300 mL of water with an ABB fiber tester, circulating it for 5 minutes, and confirming that the number of fibers counted is 1000 or more.
• the upper limit of the average fiber diameter is preferably 60 ⁇ m or less, more preferably 40 ⁇ m or less, even more preferably 30 ⁇ m or less, and even more preferably 20 ⁇ m or less, but there is no particular limit.
• the average fiber length is usually 5 ⁇ m or more, 10 ⁇ m or more, 20 ⁇ m or more, or 40 ⁇ m or more, preferably 200 ⁇ m or more, 300 ⁇ m or more, or 400 ⁇ m or more, more preferably 500 ⁇ m or more, or 550 ⁇ m or more, even more preferably 600 ⁇ m or more, 700 ⁇ m or more, or 800 ⁇ m or more.
• the upper limit is not particularly limited, but is usually 3,000 ⁇ m or less, preferably 2,500 ⁇ m or less, more preferably 2,000 ⁇ m or less, even more preferably 1,500 ⁇ m or less, 1,400 ⁇ m or less, or 1,300 ⁇ m.
• 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.
• the fine cellulose fibers can be produced by defibrating a cellulose raw material.
• the cellulose raw material is not particularly limited as long as it contains cellulose, and examples thereof include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), bleached kraft pulp (BKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., ascidians), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, and the like.
• plants e.g., wood, bamboo, hemp, jute, kenaf, agricultural
• the cellulose raw material may be any one of these or a combination of two or more types, but is preferably a cellulose raw material derived from a plant or a microorganism (e.g., cellulose fiber), and more preferably a cellulose raw material derived from a plant (e.g., cellulose fiber).
• a cellulose raw material derived from a plant or a microorganism e.g., cellulose fiber
• a cellulose raw material derived from a plant e.g., cellulose fiber
• the fine cellulose fibers may be modified fine cellulose fibers or unmodified fine cellulose fibers.
• Modified fine cellulose fibers refer to fine cellulose fibers (e.g., CNF, MFC) in which at least one of the three hydroxyl groups contained in the glucose unit is chemically modified (hereinafter simply referred to as "modified").
• the chemical modification treatment causes electronic repulsion between the microfibrils of the cellulose fibers, which allows sufficient micronization during defibration, resulting in the production of fine cellulose fibers. Therefore, when compounded with a rubber component, a sufficient reinforcing effect can be achieved. From this perspective, modified cellulose fibers are preferred.
• the number average fiber diameter of the cellulose raw material is not particularly limited, but for common softwood kraft pulp, it is about 30 to 60 ⁇ m, and for hardwood kraft pulp, it is about 10 to 30 ⁇ m. For other pulps, those that have undergone general refining are about 50 ⁇ m. For example, when refining chips or other materials several centimeters in size, it is preferable to adjust them to about 50 ⁇ m by mechanical processing using a disintegrator such as a refiner or beater.
• modifications include oxidation, etherification, esterification such as phosphate esterification, silane coupling, fluorination, cationization, etc.
• oxidation carboxylation
• etherification e.g., benzylation
• cationization e.g., benzylation
• esterification e.g., benzylation
• the oxidized fine cellulose fiber usually has a structure in which at least one of the carbon atoms having a primary hydroxyl group contained in the glucopyranose unit constituting the cellulose molecular chain (for example, a carbon atom having a primary hydroxyl group at the C6 position) is oxidized.
• the amount of carboxyl groups in the oxidized cellulose fiber or the oxidized fine cellulose fiber is preferably 0.5 mmol/g or more or 0.6 mmol/g or more, more preferably 0.8 mmol/g or more, and even more preferably 1.0 mmol/g or more, based on the bone dry mass.
• the upper limit of the amount is preferably 3.0 mmol/g or less, more preferably 2.5 mmol/g or less, and even more preferably 2.0 mmol/g or less.
• the amount of carboxyl groups is preferably 0.5 to 3.0 mmol/g, more preferably 0.8 to 2.5 mmol/g, and even more preferably 1.0 to 2.0 mmol/g.
• the amount of carboxyl groups can be adjusted by controlling the conditions (for example, the amount of oxidizing agent added, the reaction time) when oxidizing the cellulose raw material.
• the amount of carboxylate groups and aldehyde groups can also be adjusted by controlling these conditions.
• the oxidation method is not particularly limited, but an example is a method in which a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a bromide, an iodide, or a mixture thereof.
• the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized to generate at least one group selected from the group consisting of an aldehyde group, a carboxy group (-COOH), and a carboxylate group ( -COO- ).
• the concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by mass or less.
• N-oxyl compound is a compound that can generate a nitroxy radical.
• 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 an N-oxyl compound.
• the amount of N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing the raw cellulose.
• 0.001 to 5 mmol, preferably 0.01 to 1 mmol, and more preferably 0.01 to 0.5 mmol can be used.
• the amount is preferably about 0.02 to 0.5 mmol/L for the reaction system.
• Bromides are compounds containing bromine, such as bromides of alkali metals that can dissociate and ionize in water.
• Iodides are compounds containing iodine, such as iodides of alkali metals.
• the amount of bromide or iodide used can be selected within a range that can promote the oxidation reaction.
• the total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol, per 1 g of bone-dry cellulose raw material.
• the oxidizing agent may be any known oxidizing agent, such as halogen, hypohalous acid, hypohalous acid, perhalogen acid or their salts, halogen oxide, or peroxide.
• hypohalous acid or its salt is preferred
• hypochlorous acid or its salt is more preferred
• sodium hypochlorite is preferred, because it is inexpensive and has a low environmental impact.
• the appropriate amount of oxidizing agent to be used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and even more preferably 3 to 10 mmol, per 1 gram of bone-dry cellulose raw material.
• 2 to 500 mol is preferred per mol of N-oxyl compound.
• the reaction temperature is preferably 4 to 40°C, or may be around 15 to 30°C, i.e. room temperature.
• carboxyl groups are generated in the cellulose, causing a decrease in the pH of the reaction solution.
• 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 the preferred reaction medium because it is easy to handle and unlikely to cause side reactions.
• the reaction time for the oxidation reaction can be set appropriately according to the degree of progress of the oxidation, and is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours.
• the oxidation reaction may be carried out in two stages.
• the oxidized cellulose obtained by filtration after the completion of the first stage reaction can be oxidized again under the same or different reaction conditions, allowing efficient oxidation without reaction inhibition by salt produced as a by-product in the first stage reaction.
• Another example of the carboxylation (oxidation) method is a method of oxidizing the cellulose raw material by contacting it with an ozone-containing gas (ozone oxidation).
• This oxidation reaction oxidizes at least the hydroxyl groups at the 2- and 6-positions of the glucopyranose ring, and decomposes the cellulose chain.
• the ozone concentration in the ozone-containing gas is preferably 50 to 250 g/m 3 , more preferably 50 to 220 g/m 3.
• the amount of ozone added is preferably 0.1 to 30 parts by mass, more preferably 5 to 30 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material.
• the ozone treatment temperature is preferably 0 to 50°C, more preferably 20 to 50°C.
• the ozone treatment time is not particularly limited, but is about 1 to 360 minutes, and preferably about 30 to 360 minutes. When the ozone treatment conditions are within these ranges, the cellulose raw material can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is good.
• a further oxidation treatment may be carried out using an oxidizing agent.
• the oxidizing agent used in the further oxidation treatment is not particularly limited, but examples include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid.
• the procedure for the further oxidation treatment may include, for example, dissolving these oxidizing agents in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and immersing the oxidized cellulose in the solution.
• Acid-type oxidized cellulose and desalination - Oxidized cellulose contains carboxy groups as a result of oxidation, but may contain more acid-type carboxy groups (-COOH) than salt-type carboxy groups (e.g., -COO-, -COONa), or may contain more salt-type carboxy groups than acid-type carboxy groups.
• the amount of salt-type carboxy groups and acid-type carboxy groups can be adjusted by desalting treatment. By desalting treatment, salt-type carboxy groups can be converted to acid-type carboxy groups.
• oxidized cellulose (which has been desalted) is called acid-type oxidized cellulose, and oxidized cellulose (which has not been desalted, as described below) is called salt-type oxidized cellulose.
• Salt-type oxidized cellulose usually contains mainly salt-type carboxy groups.
• acid-type oxidized cellulose contains many acid-type carboxy groups, and the proportion of acid-type carboxy groups in the carboxy groups is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more.
• Acid-type oxidized cellulose can exhibit a superior reinforcing effect together with component C.
• the proportion of acid-type carboxy groups can be calculated by the following procedure.
• the timing of desalting may be after oxidation, and may be either before or after defibration (before or after step (2)), but is usually after oxidation, and preferably before step (2).
• Desalting is usually carried out by replacing salts (e.g., sodium salts) contained in the salt-type oxidized cellulose with protons.
• Examples of desalting methods include a method of adjusting the system to be acidic, and a method of contacting oxidized cellulose with a cation exchange resin.
• the pH of the system is preferably adjusted to 2 to 6, more preferably 2 to 5, and even more preferably 2.3 to 5.
• an acid e.g., inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, nitrous acid, and phosphoric acid; organic acids such as acetic acid, lactic acid, oxalic acid, citric acid, and formic acid
• a washing treatment may be carried out as appropriate.
• the cation exchange resin either a strongly acidic ion exchange resin or a weakly acidic ion exchange resin can be used as long as the counter ion is H+.
• the ratio of the oxidized cellulose and the cation exchange resin when they are contacted is not particularly limited, and a person skilled in the art can set it appropriately from the viewpoint of efficient proton replacement.
• the cation exchange resin after contact can be recovered by a conventional method such as suction filtration.
• etherification examples include carboxyalkylation, methylation, ethylation, cyanoethylation, hydroxyethylation, hydroxypropylation, ethylhydroxyethylation, and hydroxypropylmethylation, with carboxyalkylation being preferred and carboxymethylation being more preferred.
• Carboxyalkylated cellulose fibers usually have a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom bearing a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is carboxymethylated.
• the degree of carboxyalkyl substitution (DS, preferably the degree of carboxymethyl substitution) per anhydrous glucose unit of the carboxyalkylated cellulose is preferably 0.01 or more, 0.02 or more, or 0.05 or more, more preferably 0.10 or more, even more preferably 0.15 or more, even more preferably 0.20 or more, and particularly preferably 0.25 or more. This ensures a degree of substitution that can achieve the effects of chemical modification.
• the upper limit of the degree of substitution is preferably 0.50 or less, more preferably 0.45 or less, 0.40 or less, or 0.35 or less. This makes it difficult for the cellulose fiber to dissolve in water, and allows the fiber form to be maintained in water. Therefore, the degree of carboxyalkyl substitution is preferably 0.01 to 0.50, more preferably 0.01 to 0.45, even more preferably 0.02 to 0.40, 0.10 to 0.35, or 0.15 to 0.30.
• the degree of carboxyalkyl substitution for example, the degree of carboxymethyl substitution, can be measured by the following method. Approximately 2.0 g of carboxymethylated cellulose (bone dry) is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution of 1,000 mL of methanol and 100 mL of concentrated nitric acid is added, and the mixture is shaken for 3 hours to convert the salt-type carboxymethylated cellulose (hereinafter also referred to as "salt-type carboxymethylated cellulose") to the acid-type carboxymethylated cellulose (hereinafter also referred to as "acid-type carboxymethylated cellulose").
• salt-type carboxymethylated cellulose hereinafter also referred to as "salt-type carboxymethylated cellulose”
• the degree of carboxyalkyl substitution can be adjusted by controlling the reaction conditions, such as the amount of carboxyalkylating agent added to the reaction, the amount of mercerizing agent, and the composition ratio of water and organic solvent.
• carboxyalkylation method is to mercerize the cellulose raw material as the starting material (bottom raw material) and then etherify it. Carboxymethylation will be explained below as an example.
• Carboxymethylated cellulose can be produced by starting with unmodified cellulose fibers (cellulose raw material: e.g., pulp) and carrying out a mercerization treatment with a mercerizing agent, followed by an etherification reaction. The reaction is usually carried out in the presence of a solvent.
• a solvent for example, water or a lower alcohol (e.g., methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tertiary butanol) can be used alone or in a mixture of two or more.
• a lower alcohol e.g., methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tertiary butanol
• the mixing ratio of the lower alcohol is preferably 60 to 95% by mass.
• the amount of the solvent is about three times the amount of the cellulose raw material, calculated by mass.
• the upper limit of the amount is not particularly limited, but is 20 times or less.
• the amount of the solvent is preferably 3 to 20 times the amount of the cellulose raw material, calculated by mass.
• mercerizing agents include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.
• the amount of mercerizing agent used, in molar terms is preferably 0.5 times or more per anhydrous glucose residue of the starting material, more preferably 1.0 times or more, and even more preferably 1.5 times or more.
• the upper limit of this amount is usually 20 times or less, preferably 10 times or less, and more preferably 5 times or less.
• the amount of mercerizing agent used, in molar terms is preferably 0.5 to 20 times, more preferably 1.0 to 10 times, and even more preferably 1.5 to 5 times.
• the reaction temperature for mercerization is usually 0°C or higher, preferably 10°C or higher.
• the upper limit is usually 70°C or lower, preferably 60°C or lower.
• the reaction temperature is usually 0 to 70°C, preferably 10 to 60°C.
• the reaction time for mercerization is usually 15 minutes or 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.
• the etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization, such as sodium monochloroacetate.
• a carboxymethylating agent such as sodium monochloroacetate.
• the amount of the carboxymethylating agent added is, in molar terms, preferably 0.05 times or more, more preferably 0.5 times or more, and even more preferably 0.8 times or more per glucose residue of the cellulose raw material.
• the upper limit of the amount is usually 10.0 times or less, preferably 5 times or less, and more preferably 3 times or less.
• the amount of the carboxymethylating agent added is, in molar terms, preferably 0.05 to 10.0 times, more preferably 0.5 to 5 times, and even more preferably 0.8 to 3 times.
• 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.
• the reaction liquid may be stirred as necessary.
• Carboxyalkylated cellulose fibers usually maintain at least a part of their fibrous shape even when dispersed in water.
• Carboxyalkylated cellulose fibers are distinguished from carboxymethyl cellulose, a type of water-soluble polymer that dissolves in water and imparts viscosity. When an aqueous dispersion of carboxyalkylated cellulose fibers is observed under an electron microscope, a fibrous substance can be observed. On the other hand, when an aqueous dispersion of carboxymethyl cellulose, a type of water-soluble polymer, is observed, a fibrous substance is usually not observed.
• Carboxyalkylated cellulose may contain more acid-type carboxy groups than salt-type carboxy groups, or may contain more salt-type carboxy groups than acid-type carboxy groups.
• the amount of salt-type carboxy groups and acid-type carboxy groups can be adjusted by desalting treatment. By desalting treatment, salt-type carboxy groups can be converted to acid-type carboxy groups.
• carboxyalkylated cellulose (which has been desalted) is called acid-type carboxyalkylated cellulose
• carboxyalkylated cellulose which has not been desalted, as described below) is called salt-type carboxyalkylated cellulose.
• Salt-type carboxyalkylated cellulose usually has mainly salt-type carboxy groups (-COO-).
• acid-type carboxyalkylated cellulose has many acid-type carboxy groups, and the ratio of the amount of acid-type carboxy groups to the amount of carboxy groups in the acid-type carboxyalkylated cellulose is preferably 40% or more, more preferably 60% or more, and even more preferably 85% or more.
• the method for calculating the ratio of acid-type carboxy groups is as described above.
• the timing of desalting is usually after carboxyalkylation, preferably after etherification and before fibrillation.
• the desalting method may be a method of contacting carboxyalkylated cellulose with a cation exchange resin.
• the cation exchange resin either a strong acid ion exchange resin or a weak acid ion exchange resin can be used as long as the counter ion is H + .
• the ratio of the two when contacting carboxyalkylated cellulose with a cation exchange resin is not particularly limited, and a person skilled in the art can appropriately set it from the viewpoint of efficient proton replacement.
• the ratio can be adjusted so that the pH of the aqueous dispersion after addition of the cation exchange resin is preferably 2 to 6, more preferably 2 to 5, relative to the carboxyalkylated cellulose aqueous dispersion.
• the cation exchange resin after contact may be recovered by a conventional method such as suction filtration.
• a first example of an esterified cellulose fiber is phosphorylated cellulose fiber.
• Phosphorylated cellulose usually has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom having a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is phosphorylated.
• the amount of ionic substituent introduced into the phosphated cellulose fiber may be 0.10 mmol/g or more per 1 g (mass) of phosphated cellulose fiber, preferably 0.20 mmol/g or more, more preferably 0.30 mmol/g or more, even more preferably 0.40 mmol/g or more, even more preferably 0.50 mmol/g or more, even more preferably 0.60 mmol/g or more, and particularly preferably 0.70 mmol/g or more.
• the amount of ionic substituent introduced into the phosphated cellulose fiber may be 1.50 mmol/g or less per 1 g (mass) of cellulose fiber, preferably 1.35 mmol/g or less, more preferably 1.20 mmol/g or less, and even more preferably 1.10 mmol/g or less.
• the amount of ionic substituent introduced into the phosphated cellulose fiber may be 1.00 mmol/g or less per 1 g (mass) of phosphated cellulose fiber, more preferably 0.95 mmol/g or less.
• the denominator in the unit mmol/g indicates the mass of the cellulose fiber when the counter ion of the ionic substituent is a hydrogen ion (H + ).
• the amount of phosphorus oxo acid substituent can be measured by the following method.
• the amount of phosphorus oxoacid groups in fine cellulose fibers can be measured by diluting a fine cellulose fiber dispersion containing the target fine cellulose fibers with ion exchange water to a content of 0.2 mass% to prepare a cellulose fiber-containing slurry, treating it with an ion exchange resin, and then titrating it with an alkali.
• the treatment with ion exchange resin was carried out by adding 1/10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the cellulose fiber-containing slurry, shaking for 1 hour, and then pouring onto a mesh with 90 ⁇ m openings to separate the resin from the slurry.
• a strongly acidic ion exchange resin Amberjet 1024; Organo Corporation, conditioned
• the titration using alkali was performed by measuring the change in the pH value of the slurry while adding 10 ⁇ L of 0.1N sodium hydroxide aqueous solution to the cellulose fiber-containing slurry after the treatment with the ion exchange resin every 5 seconds. The titration was performed while blowing nitrogen gas into the slurry 15 minutes before the start of the titration. In this neutralization titration, two points are observed where the increment (differential value of pH with respect to the amount of alkali dropped) is maximum on a curve plotting the measured pH against the amount of alkali added.
• the maximum point of the increment obtained first after the addition of alkali is called the first end point, and the maximum point of the increment obtained next is called the second end point.
• the amount of alkali required from the start of the titration to the first end point is equal to the amount of first dissociated acid in the slurry used for the titration.
• the amount of alkali required from the start of the titration to the second end point is equal to the total amount of dissociated acid in the slurry used for the titration.
• the amount of the alkali (mmol) required from the start of the titration to the first end point was divided by the solid content (g) in the slurry to be titrated to determine the amount of phosphorus oxoacid groups (mmol/g).
• the introduction of phosphate groups may be confirmed by measuring infrared absorption spectroscopy to confirm absorption due to phosphate groups (near 1230 cm -1 ).
• the amount of phosphate groups can be adjusted by controlling the reaction conditions, such as the amount of compound containing phosphate groups added and the amount of basic compound added if necessary.
• An example of a phosphorylation method is to react a compound having a phosphate group with unmodified cellulose fibers (phosphorylation).
• Examples of the phosphorylation method include mixing a powder or an aqueous solution of a compound having a phosphate group with a cellulosic raw material (e.g., a suspension (solids concentration of about 0.1 to 10% by mass)) and adding an aqueous solution of a compound having a phosphate group to an aqueous dispersion of the cellulosic raw material, with the latter being preferred.
• a cellulosic raw material e.g., a suspension (solids concentration of about 0.1 to 10% by mass)
• an aqueous solution of a compound having a phosphate group to an aqueous dispersion of the cellulosic raw material, with the latter being preferred.
• the pH of the aqueous solution of the compound having a phosphate group is preferably 7 or less from the viewpoint of
• Examples of compounds having a phosphate group include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, esters and salts thereof. These compounds are low cost and easy to handle, and can be introduced into cellulose to improve defibration efficiency.
• compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate.
• Compounds having a phosphate group can be used alone or in combination of two or more.
• the amount of the compound having a phosphate group added to the cellulose raw material is preferably 0.1 to 500 parts by mass, more preferably 1 to 400 parts by mass, and even more preferably 2 to 200 parts by mass, in terms of phosphorus element, per 100 parts by mass of the solid content of the cellulose raw material. This makes it possible to efficiently obtain a yield that corresponds to the amount of the compound having a phosphate group used.
• the reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C.
• the reaction time is not particularly limited, but is usually about 1 to 600 minutes, preferably 30 to 480 minutes.
• a basic compound e.g., a compound having an amino group that shows basicity, such as urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, or hexamethylenediamine
• a basic compound e.g., a compound having an amino group that shows basicity, such as urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, or hexamethylenediamine
• the suspension obtained after esterification is dehydrated as necessary, and preferably subjected to a heat treatment after dehydration.
• This can suppress hydrolysis of the cellulose raw material.
• the heating temperature is preferably 100 to 170°C, and while water is contained during the heating treatment, it is more preferable to heat at 130°C or less (preferably 110°C or less), remove the water, and then heat the mixture at 100 to 170°C.
• After boiling it is preferable to perform a washing treatment such as washing with cold water and/or a neutralization treatment. This allows efficient defibration. Washing can be performed by adding water and then dehydrating (for example, filtration), and may be repeated two or more times. Washing is preferably performed until the electrical conductivity of the filtrate decreases.
• the electrical conductivity is preferably 200 or less, more preferably 150 or less, and even more preferably 120 or less.
• a neutralization treatment may be performed as necessary.
• the neutralization treatment can be performed by adding an alkali (for example, sodium hydroxide). Washing may be performed again after neutralization.
• a second example of a method for producing an esterified cellulose fiber is a phosphite-esterified cellulose fiber.
• Phosphite-esterified cellulose fiber usually has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom having a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is phosphorylated.
• the degree of substitution of phosphite groups per glucose unit in phosphite esterified cellulose fibers is preferably 0.001 to 0.60. This makes it easier for electrical repulsion to occur between cellulose molecules, facilitating nano-fibrillation.
• the degree of substitution of phosphite groups can be measured using the same method as for measuring the degree of phosphate group substitution.
• the degree of phosphite group substitution can be adjusted by controlling reaction conditions such as the amount of phosphorous acid or its salt added, the amount of alkali metal ion-containing material used as necessary, and the amount of urea or its derivative added.
• An example of a method for phosphite esterification is to react unmodified cellulose fibers with phosphorous acid or a metal salt thereof (preferably sodium hydrogen phosphite) to introduce an ester group of phosphorous acid.
• phosphorous acid or a metal salt thereof preferably sodium hydrogen phosphite
• 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 allows alkali metal ions to be introduced into the cellulose fibers.
• 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
• the amount of phosphorous acid or its metal salts added is preferably 1 to 10,000 g, more preferably 100 to 5,000 g, and even more preferably 300 to 1,500 g per kg of unmodified cellulose fibers.
• an alkali metal ion-containing material e.g., hydroxide, metal sulfate, metal nitrate, metal chloride, metal phosphate, metal carbonate
• hydroxide, metal sulfate, metal nitrate, metal chloride, metal phosphate, metal carbonate may be further added to the reaction system.
• Urea or a derivative thereof may also be added to the reaction system. This allows carbamate groups to be introduced into the cellulose fibers.
• urea and urea derivatives include urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, and combinations of two or more selected from these, with urea being preferred.
• the amount of urea and urea 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 mol of phosphorous acid or its metal salt.
• the reaction temperature is preferably 100 to 200°C, more preferably 100 to 180°C, and even more preferably 100 to 170°C.
• the reaction time is usually about 10 to 180 minutes, more preferably 30 to 120 minutes. It is preferable to wash the phosphite esterified cellulose fiber before defibrating it.
• the degree of substitution of phosphite groups per glucose unit is preferably 0.01 or more and less than 0.23.
• a third example of a method for producing an esterified cellulose fiber is a sulfated cellulose fiber.
• Cellulose sulfate usually has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom having a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is phosphorylated.
• the amount of sulfate groups per glucose unit in sulfated cellulose fibers is preferably 0.42 to 9.9 mmol/g, and more preferably 0.5 mmol/g to 2.0 mmol/g.
• the amount is 9.9 mmol/g or less, swelling or dissolution can be suppressed, and a situation in which fine cellulose fibers cannot be obtained can be prevented.
• the amount of sulfate groups per glucose unit can be measured by the following method.
• An aqueous dispersion of sulfated cellulose fibers is subjected to solvent replacement with ethanol and then t-butanol, and then freeze-dried.
• 15 ml of ethanol and 5 ml of water are added to 200 mg of the obtained sample, and the mixture is stirred for 30 minutes.
• 10 ml of a 0.5 N aqueous sodium hydroxide solution is added, and the mixture is stirred at 70°C for 30 minutes and further stirred at 30°C for 24 hours.
• the amount of sulfate groups can be adjusted by controlling the reaction conditions, such as the amount of sulfate compound added to the reaction.
• One example of a method for sulfate esterification is to react unmodified cellulose fibers with a sulfate compound to introduce sulfate groups derived from the sulfate compound into the cellulose to produce sulfated cellulose.
• sulfate compounds include sulfuric acid, sulfamic acid, chlorosulfonic acid, sulfur trioxide, and esters or salts of these. Of these, it is preferable to use sulfamic acid, since it has low solubility in cellulose and low acidity.
• the amount of sulfamic acid used can be adjusted appropriately taking into account the amount of anion groups introduced into the cellulose chain.
• the amount is preferably 0.01 to 50 mol, more preferably 0.1 to 3.0 mol, per 1 mol of glucose units in the cellulose molecule.
• the esterified cellulose may contain more acid-type carboxy groups than salt-type carboxy groups, or may contain more salt-type carboxy groups than acid-type carboxy groups.
• esterified cellulose those that have not been subjected to a desalting treatment and those that have been subjected to a desalting treatment are called salt-type esterified cellulose and acid-type esterified cellulose, respectively.
• Salt-type esterified cellulose mainly has salt-type carboxy groups. It is presumed that acid-type esterified cellulose has a superior reinforcing effect due to the component C.
• the counter cation of the salt-type carboxy group and the preparation method thereof are as explained in the explanation of oxidized cellulose.
• -Cationization- Cationized cellulose usually has a structure in which at least one of the carbon atoms constituting the cellulose molecular chain (for example, the carbon atom having a primary hydroxyl group at the C6 position constituting the glucopyranose unit) is cationized, and usually contains cations such as ammonium, phosphonium, and sulfonium, or groups having such cations, in the molecule.
• cations such as ammonium, phosphonium, and sulfonium, or groups having such cations
• the degree of cationic substitution per glucose unit in cationic cellulose is preferably 0.02 or more. This allows the cellulose fibers to be easily defibrated.
• the upper limit is preferably 0.50 or less. This allows the swelling or dissolution of cellulose to be suppressed.
• the degree of cationic substitution can be adjusted by the reaction conditions, such as the amount of cationizing agent added to be reacted and the composition ratio of water or alcohol with 1 to 4 carbon atoms.
• An example of a cationization method is to react unmodified cellulose fibers or carboxylated cellulose fibers with a cationization agent (e.g., glycidyl trimethylammonium chloride, 3-chloro-2-hydroxypropyl trialkylammonium hydride or a halohydrin type thereof) and an alkali metal hydroxide catalyst (e.g., sodium hydroxide, potassium hydroxide) in the presence of water and/or an alcohol having 1 to 4 carbon atoms.
• a cationization agent e.g., glycidyl trimethylammonium chloride, 3-chloro-2-hydroxypropyl trialkylammonium hydride or a halohydrin type thereof
• an alkali metal hydroxide catalyst e.g., sodium hydroxide, potassium hydroxide
• the amount of the 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 the cellulose raw material.
• the upper limit of the amount is usually 800 parts by mass or less, and preferably 500 parts by mass or less.
• Catalysts that may be used as necessary during cationization include, for example, 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 the 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.
• Base-type cationized cellulose fiber The cationized cellulose fibers after cationization are preferably converted to base-type cationized cellulose or base-type cationized fine cellulose fibers by desalting.
• the salt in the cationized cellulose can be converted to a base by desalting.
• cationized (fine) cellulose fibers that have been desalted are referred to as base-type cationized (fine) cellulose fibers or cationized (fine) cellulose fibers (base type).
• Desalting may be performed at any time before (cationized cellulose) or after (cationized fine cellulose fibers) defibration, which will be described later. Desalting means that the salt (e.g. Cl- ) contained in the cationized cellulose (salt type) and the cationized fine cellulose fibers (salt type) is replaced with a base to make it a base type.
• a method of contacting the cationized cellulose or the cationized fine cellulose fibers with an anion exchange resin can be mentioned.
• the anion exchange resin either a strong basic ion exchange resin or a weak basic ion exchange resin can be used as long as the counter ion is OH- .
• the ratio of the two when the modified cellulose is contacted with the anion exchange resin is not particularly limited, and a person skilled in the art can set it appropriately from the viewpoint of efficient cationic replacement.
• the ratio can be adjusted so that the pH of the aqueous dispersion after addition of the anion exchange resin to the cationized fine cellulose fiber aqueous dispersion is preferably 8 to 13, more preferably 9 to 13.
• the anion exchange resin after contact can be recovered by a conventional method such as suction filtration.
• the pulverization is usually carried out by a mechanical treatment.
• the mechanical treatment is usually carried out in a wet manner (i.e., in the form of an aqueous dispersion of cellulose fibers).
• Examples of the apparatus used for the mechanical treatment include a refiner (e.g., a disk type, a conical type, a cylinder type), a high-speed defibrator, a shear type agitator, a colloid mill, a high-pressure jet disperser, a beater, a PFI mill, a kneader, a disperser, a high-speed disintegrator (top finer), a high-pressure or ultra-high-pressure homogenizer, a grinder (a stone-type grinder), a ball mill, a vibration mill, a bead mill, a single-axis, twin-axis or multi-axis kneader/extruder, a homomixer under high-speed rotation, a refiner, a defibrator, a friction grinder, a high-shear defibrator, and a high-shear defibrator.
• a refiner e.g.,
• the mechanical defibration device examples include a device capable of imparting a mechanical defibration force, such as a defibrator, a disperger, a homogenizer (e.g., a microfluidizer), and a cavitation jet device.
• a device capable of imparting a defibration force in a wet manner is preferred, and a high-speed disintegrator, a refiner, and an ultra-high pressure homogenizer are more preferred, but are not particularly limited.
• a device capable of applying a pressure of preferably 50 MPa or more, more preferably 100 MPa or more, and even more preferably 140 MPa or more to the aqueous dispersion and applying a strong shear force, and a cavitation jet device capable of efficiently defibrating at a pressure of about 7 MPa are preferred.
• the mechanical treatment may be performed using two or more devices.
• a preliminary treatment may be performed using a mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer, as necessary.
• the number of treatments (passes) using the device may be one or more, and is preferably two or more.
• a dispersion of cellulose fibers is usually prepared.
• the solvent in the dispersion may be any solvent capable of dispersing cellulose, such as water, an organic solvent (e.g., a hydrophilic organic solvent such as methanol), or a mixture thereof. Since the cellulose raw material is hydrophilic, water is preferred.
• the solids concentration of the modified cellulose in the dispersion is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and even more preferably 1.0% by mass or more.
• the upper limit of the concentration is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less.
• pH adjustment may be performed as necessary.
• pretreatment such as dry grinding (e.g., grinding after drying) and hydrophobicity may be performed.
• dry grinding e.g., grinding after drying
• hydrophobicity examples of the apparatus used for dry grinding include, but are not limited to, impact mills such as hammer mills and pin mills, media mills such as ball mills and tower mills, and jet mills.
• posttreatment may be performed after defibration.
• posttreatment examples include, but are not limited to, drying (e.g., freeze drying, spray drying, tray drying, drum drying, belt drying, thin spreading on a glass plate or the like and drying, fluidized bed drying, microwave drying, heated fan vacuum drying, and vacuum (degassing) drying), redispersion in water (dispersion apparatus is not limited), and grinding (e.g., grinding using equipment such as a cutter mill, hammer mill, pin mill, or jet mill). Hydrophobicity can be imparted using a cationic additive.
• drying e.g., freeze drying, spray drying, tray drying, drum drying, belt drying, thin spreading on a glass plate or the like and drying, fluidized bed drying, microwave drying, heated fan vacuum drying, and vacuum (degassing) drying
• redispersion in water dispenser apparatus is not limited
• grinding e.g., grinding using equipment such as a cutter mill, hammer mill, pin mill, or jet mill. Hydrophobicity can be imparted using a cationic additive.
• the fine cellulose fibers may be in the form of an aqueous dispersion, or may be a dry solid or a wet solid of the dispersion.
• methods for preparing the dry solid or the wet solid include drying (e.g., freeze drying, spray drying, tray drying, drum drying, belt drying, a method of thinly spreading on a glass plate or the like and drying, fluidized bed drying, microwave drying, and heated fan reduced pressure drying).
• the viscosity of the aqueous dispersion of the fine cellulose fibers is preferably low. This allows the material to have good handleability despite being fibrillated.
• the B-type viscosity (25°C, 60 rpm) of an aqueous dispersion of fine cellulose fibers having a solid content of 1.0% by mass is usually 6,000 mPa ⁇ s or less or 5,000 mPa ⁇ s or less, preferably 3,500 mPa ⁇ s or less, more preferably 2,300 mPa ⁇ s or less.
• the lower limit is preferably 10 mPa ⁇ s or more, more preferably 20 mPa ⁇ s or more, even more preferably 50 mPa ⁇ s or more, 100 mPa or more, 500 mPa or more, 1,000 mPa or more, or 1,500 mPa or more.
• the 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, 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, even more preferably 1,000 mPa ⁇ s or more, 2,00 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 using a B-type viscometer (for example, manufactured by Eiko Seiki Co., Ltd.).
• the transparency of a CNF aqueous dispersion having a solid content of 1.0% by mass is usually 40% or more, preferably 50% or more, and more preferably 60% or more. There is no particular upper limit, and it may be 100% or less.
• the transparency of a MFC aqueous dispersion having a solid content of 1.0% by mass is usually 1% or more, preferably 5% or more.
• the upper limit is 50% or less.
• the transparency can be measured as the transmittance of 660 nm light using a visible light photometer.
• the crystallinity of cellulose type I in fine cellulose fibers is usually 50% or more, preferably 60% or more.
• the upper limit is not particularly limited, but it is practically considered to be about 90%.
• the crystallinity of cellulose can be controlled by the degree of chemical modification.
• the crystallinity of cellulose type I can be calculated by measuring and comparing the intensity of the (200) peak around 22.6° and the valley between (200) and (110) (around 18.5°) by X-ray diffraction measurement.
• the water retention capacity is preferably 10 or more, more preferably 15 or more, even more preferably 20 or more, and even more preferably 30 or more.
• the upper limit is thought to be about 200 or less in reality, but is not particularly limited.
• the water retention capacity corresponds to the mass of water in the sediment relative to the mass of the solid content of the fibers in the sediment, and is the ratio of the water content to the solid content in the precipitated gel, measured and calculated by centrifuging a 0.3 mass% aqueous dispersion of the fibers at 25,000 G.
• Water retention capacity (B+C-0.003 ⁇ A)/(0.003 ⁇ A-C)
• Water retention can be measured or calculated for fibers that have been fibrillated, but cannot usually be measured for fibers that have not been fibrillated or defibrated, or for cellulose nanofibers that have been defibrated down to single microfibrils.
• cellulose fibers that have not been fibrillated or defibrated are centrifuged under the above conditions, a dense sediment cannot be formed, making it difficult to separate the sediment from the aqueous phase.
• cellulose nanofibers are centrifuged under the above conditions, there is usually very little sedimentation.
• the fibrillation rate (Fibrillation %) is preferably 1.0% or more, more preferably 1.2% or more, and even more preferably 1.5% or more. This allows confirmation that fibrillation is sufficient.
• the fibrillation rate can be adjusted depending on the type of cellulose-based raw material used.
• the fibrillation rate can be determined by an image analysis type fiber analyzer such as a fractionator manufactured by Valmet Co., Ltd.
• the electrical conductivity of the aqueous dispersion of fine cellulose fibers (solid content concentration 1.0% by mass) is preferably 500 mS/m or less, more preferably 300 mS/m or less, even more preferably 200 mS/m or less, even more preferably 100 mS/m or less, and particularly preferably 70 mS/m or less.
• the lower limit is preferably 5 mS/m or more, more preferably 10 mS/m or more.
• the electrical conductivity can be measured by preparing 200 g of an aqueous dispersion of fine cellulose fibers having a solid content concentration of 1.0% by mass and using an electrical conductivity meter (HORIBA ES-71 type).
• the degree of polymerization of the fine cellulose fibers is preferably in the range of 250 to 1000. More preferably, it is 300 to 900, and even more preferably, it is 350 to 800. Within such a range, the viscosity of the fine cellulose fibers does not become too high when mixed with a rubber component, making them easy to disperse, and as a rubber reinforcing material, the fine cellulose fibers can form a network structure in the rubber and can maintain sufficient strength.
• the degree of polymerization according to the viscosimetry using a copper ethylenediamine solution can be calculated by the following method:
• a reduction treatment is first performed.
• NaBH4 is added to a 1% aqueous dispersion of fine cellulose fibers at 10 wt% relative to the fine cellulose fibers, and the pH is adjusted to 10 with NaOH, followed by stirring for 4 hours for reduction treatment.
• Ethanol is then added and centrifuged, after which the supernatant is discarded, and ethanol is added again, stirred, and centrifuged.
• the fine cellulose fibers are freeze-dried and dissolved in 0.5M copper ethylenediamine solution 1 to form solution 2.
• the viscosities of solutions 1 and 2 are measured using a capillary viscometer (Cannon-Fenske viscometer).
• the viscosity of solution 2 is ⁇ and the viscosity of solution 1 is ⁇ 0, and the intrinsic viscosity [ ⁇ ] of the anion-modified pulp is calculated using the following formula.
• the fine cellulose fibers may be of one type, or may be a combination of two or more types of fine cellulose fibers with different cellulose raw materials, chemically modified or not, and of different types.
• the rubber component is a component containing natural rubber (NR) or synthetic rubber.
• synthetic rubber include isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR), ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), chlorosulfonated polyethylene (CSM), acrylic rubber (ACM), fluororubber (FKM), epichlorohydrin rubber (CO, ECO), urethane rubber (U), silicone rubber (Q), halogenated butyl rubber, polysulfide rubber, and other synthetic rubbers, but are not particularly limited.
• 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.
• the rubber component is preferably natural rubber (NR) or acrylonitrile butadiene rubber (NBR).
• the rubber component is usually provided in the form of a latex for the production of a rubber composition.
• the solid content of the latex is usually 30% or more, preferably 40% or more, and more preferably 50% or more.
• the upper limit is usually 80% or less, but is not particularly limited.
• the rubber component may be one type alone or a combination of two or more types.
• raw materials for the rubber composition raw materials other than the fine cellulose fibers and the rubber component may be used, such as a dispersant, a solvent, and a rubber additive.
• the dispersant can be used together with the fine cellulose fibers to improve dispersibility, for example, when the fine cellulose fibers are in a dry state.
• the dispersant include water-soluble polymers and surfactants, and water-soluble polymers are preferred.
• the water-soluble polymers cover the low charge density areas on the surface, suppressing the formation of hydrogen bonds and preventing aggregation of the fine cellulose fibers during drying.
• the water-soluble polymer can improve the redispersibility after drying by penetrating between the fibers of the fine cellulose fibers and widening the distance between the fibers.
• the water-soluble polymer include cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginates, pullulan, starch, potato starch, kudzu starch, processed starch (cationized starch, phosphorylated starch, phosphate crosslinked starch, phosphate monoesterified phosphate crosslinked starch, hydroxypropyl starch, hydroxypropylated phosphate crosslinked starch, acetylated adipic acid crosslinked starch, acetylated phosphate crosslinked starch, acetylated oxidized
• chitosan casein, albumin, soy protein lysate, peptone, polyvinyl alcohol, polyacrylamide, polysodium acrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acids, polylactic acid, polymalic acid, polyglycerin, rosin-based sizing agents, petroleum resin-based sizing agents, urea resins, melamine resins, epoxy resins, polyamide resins, polyamide-polyamine resins, polyethyleneimine, polyamines, vegetable gums, polyethylene oxide, hydrophilic crosslinked polymers, polyacrylates, starch-polyacrylic acid copolymers, tamarind gum, guar gum, colloidal silica, and mixtures of one or more thereof.
• Cellulose derivatives are preferred because of their high affinity with chemically modified fine cellulose fibers, and carboxymethylcellulose or a salt thereof is more preferred.
• the water-soluble polymer may be one type or a combination of two or more
• surfactants include, but are not limited to, nonionic surfactants such as fatty acid salts, higher alkyl sulfates, alkylbenzene sulfonates, higher alcohols, alkylphenols, and alkylene oxide adducts of fatty acids, anionic surfactants, cationic surfactants, amphoteric surfactants, organic solvents, proteins, enzymes, natural polymers, synthetic polymers, etc.
• the surfactant may be one type or a combination of two or more types.
• solvent examples include aqueous solvents, which can enhance the dispersibility of the mixture of fine cellulose fibers and rubber components.
• aqueous solvent examples include water, water-soluble organic solvents, and mixtures of these. Water is preferred because fine cellulose fibers are hydrophilic. By using water, a good dispersion state can be achieved during dispersion.
• the aqueous solvent may contain a non-water-soluble organic solvent to the extent that the effect of the invention is not impaired.
• the water-soluble organic solvent may be any organic solvent that can be dissolved in water, and examples thereof include lower alcohols having 1 to 4 carbon atoms (e.g., methanol, ethanol, 2-propanol, butanol), glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, and combinations thereof.
• lower alcohols having 1 to 4 carbon atoms e.g., methanol, ethanol, 2-propanol, butanol
• glycerin e.g., methanol, ethanol, 2-propanol, butanol
• glycerin e.g., 1,4-dioxane, N-methyl-2-pyrrolidone
• lower alcohols having 1 to 4 carbon atoms are preferred, with methanol, ethanol, and 2-propanol being more preferred, and from the standpoint of safety and availability, methanol and ethanol are even more preferred, with ethanol being even more preferred.
• the amount of the water-soluble organic solvent in the mixed solvent is not particularly limited, but is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more.
• the upper limit is preferably 95% by mass or less, and more preferably 90% by mass or less.
• Examples of rubber additives include additives used for crosslinking rubber components.
• Crosslinking is generally performed by a vulcanization system that uses a crosslinking agent (vulcanizing agent) such as sulfur or a sulfur donor compound (e.g., sulfur halide) in combination with various general-purpose vulcanization accelerators such as sulfenamide-based and thiuram-based compounds.
• vulcanizing agent such as sulfur or a sulfur donor compound (e.g., sulfur halide)
• various general-purpose vulcanization accelerators such as sulfenamide-based and thiuram-based compounds.
• the crosslinking agent is not limited to a sulfur-based vulcanizing agent.
• crosslinking agents other than vulcanizing agents include organic peroxides, quinone dioximes, organic polyamine compounds, and alkylphenol resins having methylol groups; compounds containing crosslinking groups such as isocyanate groups, carbodiimide groups, oxazoline groups, aziridine groups, and epoxy groups, polyfunctional cations, and compounds containing polyvalent metals.
• organic peroxides examples include commonly used compounds such as tert-butyl peroxide, dicumyl peroxide, tert-butylcumyl peroxide, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, 1,3-di(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylperoxybenzoate, tert-butylperoxyisopropylcarbonate, and n-butyl-4,4-di(tert-butylperoxy)valerate.
• tert-butyl peroxide dicumyl peroxid
• organic peroxide crosslinking it is preferable to use a polyfunctional unsaturated compound, for example, triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, or N,N'-m-phenylene bismaleimide in combination.
• a polyfunctional unsaturated compound for example, triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, trimethylolpropane trimethacrylate, or N,N'-m-phenylene bismaleimide in combination.
• the content of the crosslinking agent is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 1.7 parts by mass or more, per 100 parts by mass of the rubber component.
• the upper limit is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less.
• vulcanization accelerators examples include N-t-butyl-2-benzothiazole sulfenamide and N-oxydiethylene-2-benzothiazolylsulfenamide.
• the content of the vulcanization accelerator is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more, per 100 parts by mass of the rubber component.
• the upper limit is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less.
• Rubber additives are not limited to the above examples, but include, for example, vulcanization accelerators (e.g., zinc oxide, stearic acid), surfactants (cationic surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants), reinforcing agents (e.g., carbon black, silica), silane coupling agents, hydrophobizing agents, oils, curing resins, waxes, antioxidants, and colorants.
• vulcanization accelerators e.g., zinc oxide, stearic acid
• surfactants cationic surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants
• reinforcing agents e.g., carbon black, silica
• silane coupling agents e.g., silane coupling agents
• hydrophobizing agents oils, curing resins, waxes, antioxidants, and colorants.
• the content of each agent is not particularly limited.
• the rubber composition preferably has a lightness difference ⁇ L value of 1 to 15. This can result in less discoloration and good strength.
• the ⁇ L value is the difference between the L1 value, which is the lightness L* of the rubber composition, and the L2 value, which is the lightness L* of a composition similar to the above composition except that it does not contain fine cellulose fibers (a 100% rubber composition of the same composition except that it contains the same weight of rubber instead of the fine cellulose fibers in the above composition).
• the lightness difference is a value according to the L*a*b* color system.
• the L1 and L2 values are preferably measured in an unvulcanized state between immediately after production and one week later.
• the composition at the time of measurement is a dry product, and its moisture content is preferably 8% by mass or less, and more preferably 5% by mass or less.
• the method for producing the rubber composition includes a drying step in which a mixture containing fine cellulose fibers and a rubber component is dried at a temperature of 70 to 150° C. using a drum dryer. 2.1 Mixtures The mixture to be dried contains fine cellulose fibers and a rubber component. The fine cellulose fibers and the rubber component are as described above.
• the mass ratio of the fine cellulose fibers to 100 parts by mass of the rubber component in the mixture is preferably 0.1 phr or more, more preferably 1 phr or more, and even more preferably 5 phr or more. This allows the effect of improving tensile strength to be fully exhibited.
• the upper limit is preferably 50 phr or less, more preferably 40 phr or less, and even more preferably 30 phr or less. This allows the processability in the manufacturing process to be maintained, and the dispersibility of the fine cellulose fibers in the rubber to be improved.
• the solid content concentration of the mixture is usually 3% by mass or more, preferably 4% by mass or more, more preferably 5% by mass or more, 6% by mass or more, or 7% by mass or more. This allows a film with a large thickness to be formed by the drum dryer, so that the heat transmitted to the fine cellulose fibers can be reduced, thereby suppressing the progress of thermal denaturation and 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 an increase in the viscosity of the mixture, and allows the mixture to be smoothly supplied to the drum dryer.
• the solid content concentration is usually 3 to 70% by mass, preferably 4 to 60% by mass, more preferably 5 to 50% by mass, 6 to 40% by mass, or 7 to 30% by mass.
• the solid content concentration of the mixture can be adjusted by the solid content concentration when the fine cellulose fibers are a dispersion, the solid content concentration when the rubber component is a latex, and the amount of solvent added as necessary.
• the method for producing the mixture is not particularly limited, but examples thereof include a method of adding fine cellulose fibers, a rubber component, and other raw materials (e.g., a solvent) used as needed, and stirring them.
• the fine cellulose fibers are preferably used as a dispersion (e.g., an aqueous dispersion), and the dispersion may contain a dispersant as needed.
• the rubber component is preferably added as a rubber latex. Stirring may be performed using equipment such as a homodisper or a super mixer.
• the mixture is dried using a drum dryer.
• the drum dryer is a dryer equipped with a rotatable drum (cylinder) and a doctor blade (knife, scraper knife) capable of scraping off the material on the drum while the drum is rotating.
• the drum can be heated by introducing a heat medium (e.g., steam) into the drum (e.g., made of metal).
• a heat medium e.g., steam
• the sample to be treated (liquid) is continuously supplied to the preheated and rotating drum surface and the sample is attached to the drum surface in a thin film, the water in the sample evaporates and condenses during rotation, causing the sample to dry, and the sample can be scraped off from the drum surface by the doctor blade to obtain a dried material.
• the drum dryer may further be equipped with a feeder that supplies the sample (liquid) to the drum surface.
• Drum dryers are classified into double drum type (inward rotating type), twin drum type (outward rotating type) and single drum type depending on the number of drums, but drum dryers consisting of multiple (usually two) drums such as double drum type and twin drum type are preferred.
• twin drum type and double drum type two drums are arranged close to each other, parallel and horizontally.
• the sample to be treated is supplied to a liquid reservoir formed above the closest point of the two drums.
• the feeder may be either a pendulum type or a liquid supply pipe equipped with liquid supply nozzles at regular intervals.
• a double drum type dryer is preferred from the viewpoint that the thickness of the thin film can be adjusted by adjusting the drum interval (clearance: the interval at the closest point).
• Single drum type drum dryers are classified into dip type, spray type, splash type, upper roll type (single stage, multistage), side roll type and lower roll type depending on the liquid supply method, and any of these can be used.
• the drum dryer may be of either the normal pressure type (drying process performed under normal pressure) or the vacuum type (drying process performed under vacuum or reduced pressure), with the normal pressure type being preferred for ease of operation and manufacturing.
• the pressure conditions are usually 50 kPa or less, preferably 30 kPa or less, and more preferably 10 kPa or less. There is no particular lower limit, and it is sufficient as long as it is 0 kPa or more.
• the material of the surface of the drum equipped in the drum dryer is not particularly limited, but it is preferable that the drum has a coating.
• the material include metal plating such as chrome plating and ceramic coating, and ceramic coating is preferable.
• a drum having a ceramic coating formed on its surface has excellent peelability of the dried body after drum drying of the mixture containing the fine cellulose fibers and the rubber component, and the dried body can be efficiently scraped off without pressing the doctor blade hard against the drum. Therefore, when a drum having a ceramic coating is used, frictional heat generated between the knife and the drum can be suppressed, and thermal denaturation of the obtained dried fine cellulose fiber body can be suppressed, resulting in good mechanical properties.
• thermal spraying refers to a method of forming a thermal spray coating by heating a thermal spraying material to a molten or softened state and spraying it onto the substrate surface.
• thermal spraying method There are no particular limitations on the thermal spraying method, and examples include flame spraying, arc spraying, and plasma spraying, with plasma spraying being preferred from the viewpoint of workability.
• Thermal spray materials include, for example, metals, alloys, ceramics, plastics, etc., and it is preferable to use those containing ceramics because of their wear resistance and high strength.
• ceramics include tungsten carbide and chromium carbide, and tungsten carbide (WC) is preferable from the viewpoint of peelability of the dried body.
• a thermal spray material containing ceramics it is preferable to use a metal binder in combination.
• a coating formed by a thermal spray material containing ceramic and a metal binder is a so-called cermet coating.
• the metal binder for example, at least one selected from chromium, nickel, and cobalt is preferable, at least one selected from chromium and nickel is more preferable, and one containing both chromium and nickel is even more preferable.
• the diameter ( ⁇ ) of the circle at each end of the drum is usually 100 mm to 2,000 mm, preferably 120 mm to 1,800 mm, more preferably 130 mm to 1,500 mm.
• the drum face length (w) is usually 150 mm to 4,000 mm, preferably 180 mm to 3,500 mm, more preferably 200 mm to 3,000 mm.
• the total drum length (L: length including the shaft) is usually 300 mm to 5,000 mm, preferably 350 mm to 4,500 mm, more preferably 400 mm to 4,000 mm.
• the clearance is usually 0.07 mm or more, preferably 0.1 mm or more, more preferably 0.12 mm or more. This can avoid deterioration of mechanical properties.
• the upper limit is usually 1 mm or less, preferably 0.8 mm or less, more preferably 0.6 mm or less. This can facilitate scraping after drying.
• the rotation speed of the drum is usually 0.5 rpm or more, preferably 0.75 rpm or more.
• the upper limit is usually 3.5 rpm or less, preferably 2.5 rpm or less.
• the peripheral speed is usually 0.25 m/min or more, preferably 0.38 m/min or more.
• the upper limit is usually 1.8 m/min or less, preferably 1.3 m/min or less.
• the thickness of the thin film formed on the drum surface is usually 5 ⁇ m or more, preferably 50 ⁇ m or more. This can prevent deterioration of mechanical properties.
• the upper limit is preferably 500 ⁇ m or less, more preferably 250 ⁇ m or less. This can facilitate scraping after drying.
• the doctor blade may be made of, for example, high carbon steel, stainless steel (SUS), polyether ether ketone (PEEK) resin, carbon, phosphorus bronze, etc., and may be appropriately selected according to the material of the drum surface.
• the peelability of the dried material varies depending on the material of the drum surface, and the force required for scraping may also be affected.
• a doctor blade made of high carbon steel is preferred from the viewpoint of protecting the coating on the drum surface and/or from the viewpoint of the durability of the doctor blade.
• high carbon steel include SK-1 to SK-7 (carbon atom content 0.6 to 1.5%), and among these, SK-4 to SK-6 (carbon atom content 0.7 to 1.0%) are preferred, and SK-5 (0.8 to 0.9%) is more preferred.
• the temperature condition during drying is usually 70°C or higher, preferably 80°C or higher, more preferably 90°C or higher, 100°C or higher, or 110°C or higher. This allows the drying process to proceed efficiently.
• the upper limit is usually 150°C or lower, preferably 140°C or lower, more preferably 135°C or lower. This makes it possible to suppress the denaturation of cellulose due to heat, and to avoid a decrease in the mechanical properties of the resulting dried body after molding. Therefore, by usually setting the temperature at 70 to 150°C, preferably 80 to 140°C, more preferably 90 to 135°C, 100 to 135°C, or 110 to 135°C, the drying process can be efficiently proceeded and a decrease in the mechanical properties can be avoided.
• the temperature during drying means the temperature of the drum surface of the drum dryer.
• the mixed liquid may be at room temperature when supplied to the drum dryer, but may also be preheated. If heated, the heating temperature is, for example, 40°C or higher, 50°C or higher, 60°C or higher, or 65°C or higher. There is no upper limit, and it is sufficient as long as it is 70°C or lower.
• molding After drying by drum drying, molding may be performed as necessary. Molding allows the shape of the rubber composition to be adjusted and improves workability. Molding can be performed using a device such as an open roll.
• the moisture content of the dried product after the drying process is usually 8% by mass or less, and preferably 5% by mass or less. This range ensures good workability in the subsequent mixing process (e.g., kneading and blending). There is no particular lower limit, and it is sufficient to be 0% by mass (absolutely dry) or more.
• the dried product can be used as a masterbatch, which is an intermediate in rubber production. Alternatively, it can be used as a rubber product by immediately carrying out the following treatment.
• the temperature during mixing may be about room temperature (e.g., about 15 to 30°C), or may be heated to a high temperature so long as the rubber components do not undergo a crosslinking reaction.
• room temperature e.g., about 15 to 30°C
• it is 140°C or lower, more preferably 120°C or lower.
• the lower limit is usually 35°C or higher, preferably 40°C or higher. Therefore, the heating temperature is preferably about 35 to 140°C, more preferably about 40 to 120°C.
• Mixing can be carried out using equipment such as a Banbury mixer, kneader, or open roll.
• molding may be performed as necessary.
• molding equipment include metal mold molding, injection molding, extrusion molding, blow molding, and foam molding, and the appropriate type may be selected depending on the shape, application, and molding method of the final product.
• the rubber composition it is preferable to heat the rubber composition after mixing, preferably after molding.
• a crosslinking agent preferably a crosslinking agent and a vulcanization accelerator
• crosslinking is performed by heating. Even if the rubber composition does not contain a crosslinking agent or a vulcanization accelerator, the same effect can be obtained by adding them before heating.
• the heating temperature is preferably 150°C or higher, with an upper limit of 200°C or lower, and more preferably 180°C or lower. Therefore, a temperature of about 150 to 200°C is preferable, and about 150 to 180°C is more preferable.
• Examples of heating devices include vulcanization devices such as mold vulcanization, can vulcanization, and continuous vulcanization.
• finishing treatment Before the coagulated material is made into a final product, it may be subjected to a finishing treatment as necessary.
• finishing treatments include polishing, surface treatment, lip finishing, lip cutting, and chlorine treatment. Only one of these treatments may be performed, or two or more may be combined.
• the reaction was terminated when the sodium hypochlorite was consumed and the pH of the system did not change.
• the mixture after the reaction was acidified using hydrochloric acid, filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain an oxidized pulp (hereinafter sometimes referred to as "carboxylated cellulose", “carboxylated pulp”, or “TEMPO oxidized pulp”).
• the pulp yield was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxy 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 with 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.
• the physical properties of the TEMPO-oxidized CNF dispersion are shown in Table 1.
• the average fiber diameter and average fiber length of the CNFs were analyzed using an atomic force microscope (AFM) for 200 randomly selected fibers.
• the average fiber diameter of MFC was measured as follows. 0.1 g of fine cellulose fibers was dispersed in 300 mL of water using an ABB fiber tester, and the fibers were circulated for 5 minutes. When the number of fibers counted was 10,000 or more (e.g., the above Production Example 4), the value measured by the fiber tester was taken as the average fiber diameter. On the other hand, when the number of fibers counted was less than 10,000 (e.g., the above Production Examples 2 and 3), the value measured by AFM using the above method was taken as the average fiber diameter.
• viscosity A CNF dispersion with a solid content of 1.0 mass% was prepared (after fibrillation (e.g., defibration), the dispersion was left to stand for at least one day, and then stirred with a homodisper (e.g., 3,000 rpm, 5 min)). The viscosity after 3 minutes at a rotation speed of 60 rpm and after 3 minutes at a rotation speed of 6 rpm were measured using a B-type viscometer (manufactured by Eiko Seiki Co., Ltd.) at 25°C.
• a homodisper e.g., 3,000 rpm, 5 min
• the values of the L*a*b* system were obtained by a method conforming to JIS Z 8781-4:2013 "Colorimetry-Part 4: CIE 1976 L*a*b* color space".
• the L value of a rubber sample not containing fine cellulose immediately after passing through the roll was measured in the same manner to obtain the L2 value.
• the ⁇ L of each sample was calculated by calculating the difference between the above-mentioned L1 value and L2 value (the above-mentioned formula (1)).
• Example 3 The TEMPO-oxidized MFC1 produced in Production Example 2 was diluted with pure water to a concentration of 2 wt %, to obtain a 2 wt % MFC dispersion.
• This dispersion and NR latex (NR-Lx: ULACOL, manufactured by Resitex, solid content 60%) were mixed in a super mixer (manufactured by Kawata, SMV-20Ba) so that the solid content of MFC was 20 parts (20 phr) per 100 parts by mass of NR-Lx solid (solid content of the mixture was 10.3%).
• a super mixer manufactured by Kawata, SMV-20Ba
• the drum drying conditions were the same as those in Example 2.
• Example 4 The TEMPO-oxidized MFC1 produced in Production Example 3 was diluted with pure water to a concentration of 1 wt %, to obtain a 1 wt % MMFC dispersion.
• This dispersion and NR latex (NR-Lx: ULACOL, manufactured by Resitex, solid content 60%) were mixed in a super mixer (manufactured by Kawata, SMV-20Ba) so that the solid content of MFC was 5 parts (5 phr) per 100 parts by mass of NR-Lx solid (solid content of the mixture was 15.9%).
• a super mixer manufactured by Kawata, SMV-20Ba
• the drum drying conditions were the same as those in Example 2.
• Example 5 A dried product was obtained in the same manner as in Example 4, except that TEMPO-oxidized MFC2 produced in Production Example 3 was used instead of TEMPO-oxidized MFC1.
• Example 6 A dried product was obtained in the same manner as in Example 4, except that TEMPO-oxidized MFC3 produced in Production Example 4 was used instead of TEMPO-oxidized MFC1.
• the resulting dried product after drying in the dryer was passed through an open roll (Kansai Roll Co., Ltd.) at room temperature 3 to 5 times until it was visually uniform, and then molded to obtain a dried rubber product after passing through the roll.
• moisture content all approximately 4% or less (some were 0.8% or less)
• 0.5 parts of stearic acid (Fuji Film Wako Pure Chemical Industries Co., Ltd.)
• 6.0 parts of zinc oxide Fluji Film Wako Pure Chemical Industries Co., Ltd.
• 3.5 parts of sulfur Fluji Film Wako Pure Chemical Industries Co., Ltd.
• vulcanization accelerator N-oxydiethylene-2-benzothiazolylsulfenamide: Noccela (MSA-G), Ouchi Shinko Chemical Industry Co., Ltd.
• open roll Kansai Roll Co., Ltd.
• DMA Dynamic Viscoelasticity
• drying efficiency The drying efficiency (g/h (solid content)) was calculated using the following formula (2) for the drum drying examples (Examples 1 to 4) and the following formula (3) for the oven drying example (Comparative Example 1).
• the hardness was measured using a manual durometer stand (GS-615, manufactured by Techlock Corporation).
• Tc90 Vulcanization time (Tc90) Tc90 was measured using a rubber vulcanization tester (MDRH2030, manufactured by M&K Co., Ltd.).
• Examples 1 and 2 which were drum-dried, had better drying efficiency and a very high E' (storage modulus) than Comparative Example 1, which was oven-dried.
• the Example and Comparative Example were repeated, and E' of the drum-dried and oven-dried products was measured.
• the difference in E' and hardness is thought to be due to the difference in thermal history between oven drying and drum drying, and it is presumed that drum drying at high temperature for a short time is superior to oven drying at low temperature for a long time.
• the drum-dried product had less discoloration after vulcanization.
• Example 7 Drum drying was carried out under the same conditions as in Example 2, except that the drum rotation speed was changed to the speed shown in Table 5 (Tables 5 and 6).
• the solid content concentration was calculated by regarding the weight of the dried sample when it was dried overnight in an oven at 70° C. as the absolute dry weight and calculating the solid content concentration according to the following formula (4).

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