Fibrous cellulose, method for producing same, rubber composition, and crosslinked rubber composition

Abstract

The purpose of the present invention is to provide a fibrous cellulose which, when added to a rubber component to form a rubber composition and then crosslinked to form a crosslinked rubber composition, yields a crosslinked rubber composition that has excellent anisotropy of modulus and excellent strength and elastic modulus. Also provided are: a method for producing the fibrous cellulose; a rubber composition obtained by mixing the fibrous cellulose with a rubber component; and a crosslinked rubber composition obtained by crosslinking the rubber composition.　The fibrous cellulose has a viscosity change represented by formula (1) of −190 to −30 mPaꞏs (inclusive).　Formula (1): Viscosity change (mPaꞏs) = η1000 − η100. In formula (1), η1000 is the viscosity (mPaꞏs) at a shear rate of 1000 s−1 of a 0.4 mass% aqueous dispersion, and η100 is the viscosity (mPaꞏs) at a shear rate of 100 s−1 of a 0.4 mass% aqueous dispersion.

Description

Fibrous cellulose and its manufacturing method, rubber composition, and crosslinked rubber composition

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

[0002] In recent years, materials using renewable natural fibers have been attracting attention due to the need to replace petroleum resources and growing environmental awareness. Among natural fibers, fibrous cellulose with a fiber diameter of 10 μm to 50 μm, particularly wood-derived fibrous cellulose (pulp), has been widely used mainly for paper products.

[0003] Cited Document 1 discloses a method for producing a rubber composition, the method comprising: (a) treating pulp with an acid; (b) mechanically defibrating the acid-treated pulp to prepare microfibrillated plant fibers having an average fiber length of 1 to 20 μm, an average fiber diameter of 10 μm or less, and an aspect ratio of 2 to 1000; (c) mixing the microfibrillated plant fibers obtained in step (b) with rubber latex to disperse the microfibrillated plant fibers in the rubber latex; and (d) drying the dispersion obtained in step (c), with the aim of providing a rubber composition in which microfibrillated plant fibers are well dispersed in the rubber component and have improved breaking properties.

[0004] Furthermore, Patent Document 2 discloses a method and apparatus for manufacturing a pneumatic tire that can make the anisotropy of the modulus of the tread rubber more pronounced than before without using a reinforcing material such as short fibers, and that can simultaneously improve ride comfort and handling stability. The method and apparatus disclose a method in which an unvulcanized base tire is placed on the outer peripheral surface of a metal rigid inner mold, and this base tire is placed in a vulcanization mold together with the rigid inner mold, and then the unvulcanized base tire is vulcanized while unvulcanized rubber is injected into a cylindrical cavity formed between the inner peripheral surface of the vulcanization mold and the outer peripheral surface of the base tire, and a tread portion is formed on the outer peripheral surface of the base tire by vulcanizing the unvulcanized rubber, and this tread portion is integrally attached to the outer peripheral surface of the base tire. the tire width direction dimension w of the circumferential injection ports is made larger than the tire circumferential direction dimension d; side injection ports for the unvulcanized rubber are arranged circumferentially spaced apart on the inner peripheral surface of the vulcanizing mold, which forms the outer peripheral surface of the cavity; the unvulcanized rubber supplied by a circumferential side injector is injected from the wider circumferential injection port toward the radially inward direction of the tire; and the unvulcanized rubber supplied by a side side injector is injected from the circumferential injection port toward the other side surface of the vulcanizing mold.

[0005] JP 2015-025141 A JP 2016-155308 A

[0006] Patent Document 1 discloses a method for producing a rubber composition containing microfibrillated plant fibers and a rubber component. Patent Document 2 describes a method for producing a pneumatic tire using a specific method to enhance modulus anisotropy. However, fibrous cellulose that, when added to a rubber component, has a high effect of improving strength and elastic modulus and provides excellent modulus anisotropy has not been fully investigated. The present invention aims to provide fibrous cellulose that, when added to a rubber component to form a rubber composition and then crosslinked to form a crosslinked rubber composition, provides a crosslinked rubber composition with excellent modulus anisotropy and excellent strength and elastic modulus. Furthermore, the present invention aims to provide a method for producing the fibrous cellulose, a rubber composition in which the fibrous cellulose is mixed with a rubber component, and a crosslinked rubber composition obtained by crosslinking the rubber composition.

[0007] The present inventors have found that the above-mentioned problems can be solved by using fibrous cellulose having a specific viscosity change rate. The present invention relates to the following items <1> to <8>. <1> Fibrous cellulose having a viscosity change expressed by the following formula (1) of -190 mPa·s or more and -30 mPa·s or less. Viscosity change (mPa·s) = η １０００ -η １００ (1) In equation (1), η １０００ is the shear rate of 1000 s for a 0.4 mass% aqueous dispersion －１ is the viscosity (mPa s) at １００ is the shear rate of a 0.4 mass% aqueous dispersion at 100 s －１ <2> The viscosity (mPa·s) at the η １００<1> The fibrous cellulose according to <1>, wherein the viscosity of the fibrous cellulose is 240 mPa·s or less. <3> The fibrous cellulose according to <1> or <2>, wherein the fibrous cellulose is chemically modified fibrous cellulose. <4> A rubber composition containing 1 part by mass or more and 200 parts by mass or less of the fibrous cellulose according to any one of <1> to <3> per 100 parts by mass of a rubber component. <5> A crosslinked rubber composition obtained by crosslinking a rubber compound containing the rubber composition according to <4> and a crosslinking agent. <6> A method for producing fibrous cellulose, comprising a beating step of beating pulp fibers with a single-disc refiner, wherein the clearance of the single-disc refiner in the beating step is 0.4 mm or more. <7> A method for producing fibrous cellulose according to <6>, wherein the pulp fibers are chemically modified pulp fibers. <8> A method for producing fibrous cellulose according to <6> or <7>, further comprising a micronization step of defibrating the pulp fibers with a wet micronization device after the beating step.

[0008] According to the present invention, there is provided fibrous cellulose which, when added to a rubber component to form a rubber composition and then crosslinked to form a crosslinked rubber composition, can provide a crosslinked rubber composition that has excellent anisotropy of modulus and excellent strength and elastic modulus. Furthermore, according to the present invention, there are provided a method for producing the fibrous cellulose, a rubber composition in which the fibrous cellulose is mixed with a rubber component, and a crosslinked rubber composition obtained by crosslinking the rubber composition.

[0009] 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a phosphorus oxo acid group and pH. 2 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and pH. 3 is a side cross-sectional schematic diagram of a double drum dryer, which is an example of a heated cylindrical dryer. 4 is a side cross-sectional schematic diagram of a double drum dryer, which is an example of a heated cylindrical dryer.

[0010] [Fibrous Cellulose] The fibrous cellulose of the present embodiment has a viscosity change expressed by the following formula (1) of −190 mPa·s or more and −30 mPa·s or less: Viscosity change (mPa·s)=η １０００ -η １００ (1) In equation (1), η１０００ is the shear rate of 1000 s for a 0.4 mass% aqueous dispersion －１ is the viscosity (mPa s) at １００ is the shear rate of a 0.4 mass% aqueous dispersion at 100 s －１ The viscosity (mPa·s) at a shear rate of 1000 s is the viscosity (mPa·s) at a shear rate of 1000 s. When the fibrous cellulose of this embodiment is added to a rubber component to form a rubber composition, and then crosslinked to form a crosslinked rubber composition, a crosslinked rubber composition having excellent anisotropy of modulus, strength, and elastic modulus can be obtained. The detailed mechanism by which the above effect is obtained is unknown, but is thought to be as follows. －１ Viscosity (mPa·s) and shear rate at 100 s －１ A small difference in viscosity (mPa·s) between the two curves, i.e., a small slope, is thought to suggest that the entangled fiber network has collapsed and a structure in which the fibers are well oriented has been formed. On the other hand, if the slope is too small, it means that there is no thixotropy, and the time-dependent structural destruction recovers quickly, making it difficult for the fibers to be oriented in one direction. From the above, it is presumed that anisotropy is expressed when the viscosity change in the high shear region is within a specific range. Furthermore, it is presumed that the use of fibrous cellulose with a fiber length long enough to express anisotropy will result in a composite with excellent strength and elastic modulus. Note that the mechanism by which the effects of the present invention are obtained is not limited to the above. In the following description, a crosslinked rubber composition with excellent physical properties means a crosslinked rubber composition with high modulus anisotropy and high tensile strength and tensile modulus.

[0011] Hereinafter, embodiments of the present invention will be described in detail. The following description of the constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. When a numerical range is written in stages, the upper and lower limits of each numerical range can be combined in any way.

[0012] The fibrous cellulose of this embodiment has a viscosity change represented by the following formula (1) of -190 mPa·s or more and -30 mPa·s or less. From the viewpoint of obtaining a crosslinked rubber composition with excellent physical properties, the viscosity change is preferably -170 mPa·s or more, more preferably -150 mPa·s or more, and preferably -40 mPa·s or less, more preferably -50 mPa·s or less, and even more preferably -60 mPa·s or less. Viscosity change (mPa·s) = η １０００ -η １００ (1) In equation (1), η １０００ is the shear rate of 1000 s for a 0.4 mass% aqueous dispersion －１ is the viscosity (mPa s) at １００ is the shear rate of a 0.4 mass% aqueous dispersion at 100 s －１ Here, the viscosity (mPa·s) at １０００ and η １００ is a value measured at 23°C, specifically measured by the method in the Examples.

[0013] Fibrous cellulose having a viscosity change represented by formula (1) within the above-mentioned range can be appropriately adjusted by selecting the degree of defibration of the fibrous cellulose and the defibration method. Among these, it is preferable to have a beating step in which pulp fibers are beaten with a single-disc refiner, and to perform the beating under conditions in which the clearance of the single-disc refiner is 0.4 mm or more. The clearance is more preferably 0.45 mm or more, even more preferably 0.50 mm or more, still more preferably 0.55 mm or more, and preferably 1.0 mm or less, more preferably 0.80 mm or less, even more preferably 0.70 mm or less, and still more preferably 0.65 mm or less. Beating with a single-disc refiner having a relatively wider clearance than conventional ones produces fibrous cellulose having a viscosity change in the high shear region within the above-mentioned range, although the reason for this is not fully understood. The number of passes through the single-disc refiner is preferably 3 to 100 passes, more preferably 5 or more, even more preferably 8 or more, and more preferably 80 or less, even more preferably 60 or less, still more preferably 40 or less, and even more preferably 35 or less. After beating with the single-disc refiner, it is preferable to have a micronization step in which the material is defibrated with a wet micronization device. Examples of wet micronization devices include high-pressure homogenizers, ultra-high-pressure homogenizers, high-pressure collision crushers, ball mills, bead mills, disc mills, vibration mills, and ultrasonic dispersers. Among these, high-pressure homogenizers and ultra-high-pressure homogenizers are preferred. When defibration treatment is performed using a high-pressure homogenizer or an ultra-high-pressure homogenizer, the pressure is preferably 30 MPa or more and 500 MPa or less, more preferably 50 MPa or more, even more preferably 80 MPa or more, still more preferably 100 MPa or more, and preferably 400 MPa or less, more preferably 300 MPa or less, even more preferably 280 MPa or less, and still more preferably 250 MPa or less.The number of passes in the defibration treatment with a homogenizer is preferably 1 to 5 passes, more preferably 4 passes or less, even more preferably 3 passes or less, still more preferably 2 passes or less, and most preferably 1 pass. As will be described later, the fibrous cellulose is preferably chemically modified fibrous cellulose.

[0014] The fibrous cellulose of this embodiment is 0.4 mass% aqueous dispersion at a shear rate of 100 s －１ Viscosity at (η １００ ) is preferably 45 mPa·s or more and 240 mPa·s or less, more preferably 50 mPa·s or more, even more preferably 60 mPa·s or more, still more preferably 70 mPa·s or more, still more preferably 80 mPa·s or more, even more preferably 85 mPa·s or more, and is preferably 230 mPa·s or less, more preferably 220 mPa·s or less, even more preferably 210 mPa·s or less, and still more preferably 205 mPa·s or less. １００ is within the above range, η １０００ -η １００ This is preferred because it is easy to adjust the viscosity to between -190 mPa·s and -30 mPa·s, and a crosslinked rubber composition with excellent physical properties can be obtained.

[0015] The fibrous cellulose of this embodiment is 0.4 mass% aqueous dispersion at a shear rate of 1000 s －１ Viscosity at (η １０００ ) is preferably 18 mPa·s or more and 60 mPa·s or less, more preferably 20 mPa·s or more, even more preferably 22 mPa·s or more, and is preferably 58 mPa·s or less, more preferably 56 mPa·s or less, even more preferably 54 mPa·s or less. １０００ is within the above range, η １０００ -η １００ This is preferred because it is easy to adjust the viscosity to between -190 mPa·s and -30 mPa·s, and a crosslinked rubber composition with excellent physical properties can be obtained.

[0016] The fibrous cellulose of this embodiment may be a cellulose nanofiber having a fiber width of less than 1000 nm, or may be microfibril cellulose having a fiber width of 1 μm (1000 nm) or more, or may further comprise a combination of cellulose nanofibers and microfibril cellulose. When the fibrous cellulose is a cellulose nanofiber, the average fiber width is preferably 3 nm or more and less than 1000 nm, preferably 100 nm or less, more preferably 50 nm or less, even more preferably 20 nm or less, and even more preferably 10 nm or less. When the fibrous cellulose is microfibril cellulose, the average fiber width is preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more, even more preferably 10 μm or more, still more preferably 15 μm or more, and more preferably 80 μm or less, even more preferably 60 μm or less, even more preferably 40 μm or less, and even more preferably 35 μm or less. When fibrous cellulose is produced by beating it with a single-disc refiner, the resulting fibrous cellulose is microfibril cellulose, and when this is further subjected to defibration treatment with a homogenizer, the resulting fibrous cellulose is cellulose nanofiber. The fiber width can be adjusted by the treatment conditions in the beating or defibration treatment, such as the equipment used, the degree of beating or defibration, the treatment time, the number of treatments, etc. The degree of beating or defibration can be adjusted, for example, when a disc refiner is used, by changing the clearance or the number of treatments, and when a homogenizer is used, by changing the pressure.

[0017] The fibrous cellulose of this embodiment preferably has a type I crystal structure. The presence of type I crystal structure in fibrous cellulose can be identified by a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified by the presence of typical peaks at two positions: approximately 2θ=14° to 17° and approximately 2θ=22° to 23°. The proportion of type I crystal structure in the fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. The degree of crystallinity is determined by measuring an X-ray diffraction profile and using a conventional method from the pattern (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959). In this embodiment, the fibrous cellulose has, for example, both crystalline and amorphous regions. The fibrous cellulose of this embodiment is realized by the method for producing fibrous cellulose described below.

[0018] In this embodiment, the fibrous cellulose is preferably chemically modified fibrous cellulose. The chemical modification is preferably carried out by introducing an ionic group (ionic substituent). That is, the chemically modified fibrous cellulose is preferably fibrous cellulose into which an ionic substituent has been introduced. The ionic substituent may include, for example, either an anionic group or a cationic group, or both. In this embodiment, it is particularly preferable that the ionic group has an anionic group. Furthermore, the ionic group is preferably a group introduced into the cellulose fiber via an ester bond or an ether bond, and more preferably a group introduced into the cellulose fiber via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation between the cellulose fiber and a compound that becomes the ionic group.

[0019] Examples of anionic groups as ionic groups include phosphorus oxo acid groups or substituents derived from phosphorus oxo acid groups (sometimes simply referred to as phosphorus oxo acid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxo acid groups or substituents derived from sulfur oxo acid groups (sometimes simply referred to as sulfur oxo acid groups), xanthate groups or substituents derived from xanthate groups (sometimes simply referred to as xanthate groups), phosphonic groups or substituents derived from phosphonic groups, phosphine groups or substituents derived from phosphine groups, sulfonic groups or substituents derived from sulfonic groups, and carboxyalkyl groups. Among these, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, a substituent derived from a sulfur oxoacid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group, more preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group, and even more preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as the anionic group, the dispersibility of fibrous cellulose can be further improved, for example, even under alkaline or acidic conditions, making it easier to obtain a crosslinked rubber composition with excellent strength and elastic modulus. Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, the cationic group is preferably an ammonium group.

[0020] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0021] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of n α and α′ is O. －and the rest are R or OR. Note that all of α and α' are O － The n α's may all be the same or may be different. ｂ＋ is a cation of one or more valences consisting of organic or inorganic substances.

[0022] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. In formula (1), n ​​is preferably 1.

[0023] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, or n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl or t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl or cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl or allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl or 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl or cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl or naphthyl groups.

[0024] In addition, the derivative group in R may be a carboxy group, a carboxylate group (-COO －), functional groups to which at least one functional group selected from functional groups such as a hydroxy group, an amino group, and an ammonium group has been added or substituted, but are not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, which facilitates penetration into the fiber raw material and increases the yield of fibrous cellulose. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fibrous cellulose, the multiple Rs may be the same or different.

[0025] β ｂ＋ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. It should be noted that in formula (1), β ｂ＋ When a plurality of β ｂ＋ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β ｂ＋ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0026] More specifically, the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group is a phosphate group (-PO ３ H ２), salts of phosphate groups, phosphite groups (phosphonic acid groups) (-PO ２ H ２ and salts of a phosphorous acid group (phosphonic acid group). The phosphorus oxo acid group or the substituent derived from a phosphorus oxo acid group may be a group in which a phosphoric acid group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkyl phosphonic acid group (e.g., a methyl phosphonic acid group), or the like.

[0027] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

[0028]

[0029] In formula (2), b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, multiple p's may be the same number or different numbers. In formula (2), β ｂ＋ is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by formula (2) are introduced into the fibrous cellulose, the multiple β ｂ＋may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β ｂ＋ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0030] The amount of ionic substituents, preferably anionic groups, introduced into the fibrous cellulose is, for example, per 1 g (mass) of fibrous cellulose, preferably 0.10 mmol / g or more and 5.20 mmol / g or less, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, still more preferably 0.50 mmol / g or more, even more preferably 0.60 mmol / g or more, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, still more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, and even more preferably 1.50 mmol / g or less. Here, the denominator in the unit mmol / g is calculated based on the number of counter ions of the ionic substituents being hydrogen ions (H ＋ By setting the amount of ionic substituents introduced within the above range, it is possible to easily pulverize the fiber raw material and improve the stability of the fibrous cellulose.

[0031] The amount of ionic substituents introduced into fibrous cellulose can be measured, for example, by neutralization titration after defibrating the cellulose fibers. In measurement by neutralization titration, the amount introduced is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fibrous cellulose. Note that, since the change in the amount of ionic substituents introduced by defibrating is slight, the amount of ionic substituents introduced into cellulose fibers before defibrating can also be determined by measuring the amount of ionic substituents introduced into the fibrous cellulose.

[0032] FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into fibrous cellulose is measured, for example, as follows. First, ion-exchanged water is added to the target fibrous cellulose (cellulose fiber) to prepare a slurry with a solids concentration of 0.2% by mass. The fibrous cellulose dispersion is then treated with a strongly acidic ion-exchange resin. Next, the pH change is observed while adding aqueous sodium hydroxide solution, and a titration curve such as that shown in the upper part of FIG. 1 is obtained. The titration curve shown in the upper part of FIG. 1 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of FIG. 1 plots the pH increment (differential value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points at which the increment (differential value of pH with respect to the amount of alkali added) is maximized are confirmed on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum point of the increment obtained after starting the addition of alkali is called the first endpoint, and the next maximum point of the increment is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid of the fibrous cellulose contained in the slurry used for titration, the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid of the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol / g). Note that when simply referring to the amount of phosphorus oxo acid group introduced (or amount of phosphorus oxo acid group), it refers to the amount of first dissociated acid. 1, the region from the start of titration to the first endpoint is referred to as Region 1, and the region from the first endpoint to the second endpoint is referred to as Region 2. For example, when the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weak acid groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) appears to decrease, and the amount of alkali required in Region 2 becomes smaller than the amount of alkali required in Region 1.On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the first dissociated acid amount) is equal to the amount of phosphorus atoms, regardless of whether condensation occurs. Furthermore, when the phosphorus oxoacid group is a phosphorous acid group, the phosphorus oxoacid group does not contain any weakly acidic groups, so the amount of alkali required in the second region may be reduced or even zero. In this case, the titration curve will have only one point at which the pH increment is maximized.

[0033] The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)), since the denominator indicates the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with an arbitrary cation C so as to be the charge equivalent, the amount of phosphorus oxoacid groups in the cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of phosphorus oxoacid groups (C type) = Amount of phosphorus oxoacid groups (acid type) / {1 + (W - 1) × P / 1000}, P [mmol / g]: total amount of anions derived from phosphorus oxoacid groups in the fibrous cellulose (total amount of dissociated acid of phosphorus oxoacid groups), W: formula weight per monovalent of cation C (for example, 23 for Na and 9 for Al).

[0034] FIG. 2 is a graph showing the relationship between the amount of NaOH added dropwise to a fibrous cellulose dispersion having carboxy groups as ionic substituents and pH. The amount of carboxy groups introduced into the fibrous cellulose is measured, for example, as follows: First, ion-exchanged water is added to the target fibrous cellulose (cellulose fiber) to prepare a slurry with a solids concentration of 0.2% by mass. The fibrous cellulose dispersion is then treated with a strongly acidic ion-exchange resin. Next, the pH change is observed while adding aqueous sodium hydroxide solution, and a titration curve such as that shown in the upper part of FIG. 2 is obtained. The titration curve shown in the upper part of FIG. 2 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of FIG. 2 plots the pH increment (differential value) (1 / mmol) against the amount of alkali added. In this neutralization titration, a single point where the increment (differential value of pH with respect to the amount of alkali added) is maximized is identified on the curve plotting the measured pH against the amount of alkali added. This maximum point is referred to as the first endpoint. Here, the region from the start of titration to the first endpoint in Figure 2 is referred to as the first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the dispersion used for titration. The amount of carboxy groups introduced (mmol / g) is calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solid content (g) in the dispersion containing the fibrous cellulose to be titrated.

[0035] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups possessed by the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with any cation C so as to be charge equivalent, the amount of carboxy groups possessed by the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of carboxy groups (C form) = Amount of carboxy groups (acid form) / {1 + (W - 1) × (Amount of carboxy groups (acid form)) / 1000} W: Formula weight per valence of cation C (for example, 23 for Na, 9 for Al)

[0036] When measuring the amount of ionic substituents by titration, if too much sodium hydroxide aqueous solution is added or if the titration interval is too short, the amount of ionic substituents may be lower than expected, and an accurate value may not be obtained. An appropriate amount of addition and titration interval, for example, is preferably a 0.1 N sodium hydroxide aqueous solution titrated at 10 to 50 μL intervals over 5 to 30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose dispersion, it is preferable to perform the measurement while blowing an inert gas such as nitrogen gas into the slurry, for example, from 15 minutes before the start of titration until the end of titration.

[0037] The amount of sulfate ester groups and sulfonic acid groups introduced into the fibrous cellulose is determined by wet ashing the obtained fibrous cellulose using perchloric acid and concentrated nitric acid, diluting the cellulose at an appropriate ratio, and measuring the amount of sulfur by ICP atomic emission spectrometry. The amount of sulfur is divided by the bone dry mass of the fibrous cellulose used, and this value is taken as the amount of sulfur oxoacid groups and sulfonic acid groups (unit: mmol / g).

[0038] To obtain fibrous cellulose having an ionic substituent introduced therein, it is preferable to have an ionic substituent introduction step for introducing an ionic substituent into a cellulose-containing fiber raw material, a washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and an acid treatment step may be included instead of or in addition to the washing step. Examples of the ionic substituent introduction step include a phosphorus oxo acid group introduction step, a carboxy group introduction step, a sulfur oxo acid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. Each of these steps will be explained below.

[0039] <Fiber Raw Materials> The fiber raw materials are fiber raw materials containing cellulose. Examples of the fiber raw materials include, but are not limited to, wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP), semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP), and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, bamboo, and bagasse. The deinked pulp is not particularly limited, but examples thereof include deinked pulp made from waste paper. The pulp raw material of this embodiment may be one of the above, or a mixture of two or more. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Furthermore, among wood pulps, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoints of a high cellulose ratio, a high yield of fibrous cellulose during defibration treatment, and the fact that decomposition of cellulose in the pulp is small and long fiber fibrous cellulose with a large axial ratio can be obtained. Note that the viscosity tends to increase when long fiber fibrous cellulose with a large axial ratio is used.

[0040] <Phosphorus Oxo Acid Group Introduction Step> When obtaining cellulose fibers having ionic substituents, it is preferable to provide an ionic substituent introduction step before the defibration treatment step. Examples of the ionic substituent introduction step include a phosphorus oxo acid group introduction step. The phosphorus oxo acid group introduction step is a step of reacting a cellulose-containing fiber raw material with at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups possessed by the cellulose-containing fiber raw material. This step results in the production of cellulose fibers having phosphorus oxo acid groups.

[0041] In the phosphorus oxo acid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material may be reacted with compound A in the absence of compound B.

[0042] An example of a method for reacting compound A with a fiber raw material in the presence of compound B is a method in which compound A and compound B are mixed with a fiber raw material in a dry, wet, or slurry state. Among these, using a fiber raw material in a dry or wet state is preferred because of the high uniformity of the reaction, and using a fiber raw material in a dry state is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably, for example, in a cotton-like or thin sheet form. Examples include methods in which compound A and compound B are added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state obtained by heating to or above their melting point. Among these, adding compound A and compound B in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred because of the high uniformity of the reaction. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited. When compound A and compound B are in the form of a solution, the fiber raw material may be immersed in the solution to absorb the liquid and then removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0043] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, including, but not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acid can be used with various purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid can be 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is formed by the condensation of two or more molecules of phosphoric acid through a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphate groups, ease of further improving defibration efficiency in the defibration treatment step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferred.

[0044] The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the yield improvement effect and costs.

[0045] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

[0046] The amount of compound B added relative to the fiber raw material (bone dry mass) is not particularly limited, but is, for example, preferably 1 mass% or more and 500 mass% or less, more preferably 10 mass% or more and 400 mass% or less, and even more preferably 100 mass% or more and 350 mass% or less.

[0047] In the reaction of a fiber raw material containing cellulose with compound A, the reaction system may contain, in addition to compound B, for example, amides or amines. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0048] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like with the fiber raw material and then heat-treat the fiber raw material. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower. Various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized-bed dryer, a band-type dryer (hot-air heating dryer), a filtration dryer, a vibration fluidized-bed dryer, an airflow dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, and a high-frequency dryer.

[0049] In this embodiment, the heat treatment can be carried out by, for example, adding compound A to a thin sheet-like fiber raw material by a method such as impregnation, followed by heating, or by heating while kneading or stirring the fiber raw material and compound A in a kneader or the like. This can suppress unevenness in the concentration of compound A in the fiber raw material, making it possible to more uniformly introduce phosphorus oxoacid groups onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be due to the fact that, when water molecules move to the surface of the fiber raw material as it is dried, dissolved compound A can be prevented from being attracted to the water molecules by surface tension and similarly moving to the surface of the fiber raw material (i.e., causing unevenness in the concentration of compound A).

[0050] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the device system, for example, the water retained in the slurry and the water generated in the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include an oven using a blower system. Constantly discharging the water from the device system can suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as the acid hydrolysis of sugar chains in the fiber. This makes it possible to obtain fibrous cellulose with a high axial ratio.

[0051] The heat treatment time is, for example, from when moisture is substantially removed from the fiber raw material, preferably from 1 second to 300 minutes, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, by setting the heating temperature and heating time within appropriate ranges, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range.

[0052] The phosphorus oxo acid group introduction step may be carried out at least once, but may also be carried out twice or more times. By carrying out the phosphorus oxo acid group introduction step twice or more, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material.

[0053] The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 0.10 mmol / g or more and 5.20 mmol / g or less, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, still more preferably 1.00 mmol / g or more, and more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, still more preferably 2.50 mmol / g or less, and even more preferably 2.00 mmol / g or less, per gram (mass) of cellulose fiber. By keeping the amount of phosphorus oxoacid groups introduced within the above ranges, it is possible to facilitate the fine pulverization of cellulose fibers in the defibration treatment step and to increase the stability of fibrous cellulose.

[0054] <Carboxy group introduction step> The ionic substituent introduction step may include a carboxy group introduction step, which is carried out by subjecting a fiber raw material containing cellulose to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or by treating the fiber raw material with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.

[0055] The compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Furthermore, the derivative of the compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include imidized products of acid anhydrides of compounds having carboxy groups, and derivatives of acid anhydrides of compounds having carboxy groups. The imidized products of acid anhydrides of compounds having carboxy groups are not particularly limited, but examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0056] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, the derivative of an acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of compounds having carboxy groups such as dimethyl maleic anhydride, diethyl maleic anhydride, diphenyl maleic anhydride, etc., in which at least some of the hydrogen atoms have been substituted with a substituent such as an alkyl group or a phenyl group.

[0057] When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of, for example, a pH of 6 or higher and 8 or lower. This type of treatment is also referred to as neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as the fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxy groups. The TEMPO oxidation treatment may also be performed under conditions of a pH of 10 or higher and 11 or lower. This type of treatment is also referred to as alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as the fiber raw material.

[0058] The amount of carboxy groups introduced into cellulose fibers varies depending on the type of substituent. For example, when carboxy groups are introduced by TEMPO oxidation, the amount per 1 g (mass) of cellulose fibers is preferably 0.10 mmol / g or more and 3.65 mmol / g or less, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, still more preferably 0.60 mmol / g or more, and more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, and still more preferably 2.00 mmol / g or less. Alternatively, when the substituent is a carboxymethyl group, the amount of carboxy groups introduced may be 5.8 mmol / g or less per 1 g (mass) of cellulose fibers. By setting the amount of carboxy groups introduced within the above range, it is possible to facilitate the fine pulverization of cellulose fibers in the defibration treatment step and improve the stability of fibrous cellulose.

[0059] <Sulfonic acid group introduction step> The ionic substituent introduction step may include a sulfonic acid group introduction step, in which a hydroxyl group in a fiber raw material containing cellulose reacts with a sulfur oxoacid to obtain a cellulose fiber having a sulfonic acid group (a sulfonic acid group-introduced fiber).

[0060] In the sulfonic acid group introduction step, instead of compound A in the above-described <Phosphorus Oxo Acid Group Introduction Step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfonic acid groups by reacting with hydroxyl groups in cellulose-containing fiber raw materials is used. Compound C may be any compound having a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Examples of sulfurous acid include 5% aqueous sulfurous acid. Examples of sulfates or sulfites include lithium, sodium, potassium, and ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Examples of sulfuric acid amides include sulfamic acid. In the sulfonic acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus Oxo Acid Group Introduction Step> in the same manner.

[0061] In the sulfonic acid introduction step, the cellulose raw material is preferably mixed with an aqueous solution containing a sulfur oxoacid and urea and / or a urea derivative, and then the cellulose raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that sulfonic acid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably 100°C or higher and 300°C or lower, more preferably 120°C or higher, even more preferably 150°C or higher, and more preferably 250°C or lower, even more preferably 200°C or lower.

[0062] In the heat treatment step, heating is preferably performed until substantially no moisture is present. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material and the amount of aqueous solution containing sulfur oxoacid and urea and / or a urea derivative added, but is preferably 10 seconds or more and 10,000 seconds or less. For the heat treatment, various devices having a heat medium can be used, such as a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, a flash dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

[0063] The amount of sulfonic groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more and 5.00 mmol / g or less, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, still more preferably 0.40 mmol / g or more, even more preferably 0.50 mmol / g or more, and more preferably 3.00 mmol / g or less, and even more preferably 2.50 mmol / g or less. By setting the amount of sulfonic groups introduced within the above range, it is possible to facilitate the fine pulverization of cellulose fibers in the defibration treatment step and to increase the stability of fibrous cellulose.

[0064] <Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)> The ionic substituent introduction step may include an oxidation step using a chlorine-based oxidizing agent. In the oxidation step using a chlorine-based oxidizing agent, a chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0065] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or may be dissolved in an appropriate solvent and added.

[0066] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent is, for example, converted into an effective chlorine concentration, preferably from 1 to 1,000% by mass, more preferably from 5 to 500% by mass, and even more preferably from 10 to 100% by mass. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably from 1 to 100,000 parts by mass, more preferably from 10 to 10,000 parts by mass, and even more preferably from 100 to 5,000 parts by mass.

[0067] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent may vary depending on the reaction temperature, but is, for example, preferably 1 minute to 1,000 minutes, more preferably 10 minutes to 500 minutes, and even more preferably 20 minutes to 400 minutes. The pH during the reaction is preferably 5 to 15, more preferably 7 to 14, and even more preferably 9 to 13. At the start of the reaction, the pH during the reaction is preferably maintained constant (for example, pH 11) by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0068] <Xanthate group introduction step> The process for producing fibrous cellulose may include a xanthate group introduction step as an ionic substituent introduction step. In the xanthate group introduction step, hydroxyl groups in a fiber raw material containing cellulose are substituted with xanthate groups represented by the following formula (3), thereby obtaining cellulose fibers having xanthate groups (xanthate group-introduced fibers). -OCSS － M ＋ ... (3) Here, M＋ is at least one selected from the group consisting of hydrogen ions, monovalent metal ions, ammonium ions, and aliphatic or aromatic ammonium ions.

[0069] In the xanthate group introduction process, first, the cellulose-containing fiber raw material is treated with an alkaline solution to obtain alkali cellulose. Examples of alkaline solutions include an aqueous alkali metal hydroxide solution and an aqueous alkaline earth metal hydroxide solution. Among these, the alkaline solution is preferably an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide, and more preferably an aqueous sodium hydroxide solution. When the alkaline solution is an aqueous alkali metal hydroxide solution, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 4% by mass or more to 9% by mass or less, more preferably 5% by mass or more. By setting the alkali metal hydroxide concentration at or above the lower limit, the cellulose mercerization can be sufficiently promoted, the amount of by-products generated during the subsequent xanthation can be reduced, and as a result, the yield of xanthate group-introduced fiber can be increased. This allows the defibration process described below to be performed more effectively. Furthermore, by setting the alkali metal hydroxide concentration to the above upper limit or less, it is possible to prevent the aqueous alkali metal hydroxide solution from penetrating into the crystalline regions of cellulose while allowing mercerization to proceed, which makes it easier to maintain the cellulose type I crystal structure and further increases the yield of fibrous cellulose.

[0070] The alkali treatment time is preferably 30 minutes to 6 hours, more preferably 1 hour to 5 hours. By setting the alkali treatment time within the above range, the final yield can be increased, and productivity can be improved.

[0071] The alkali cellulose obtained by the above-mentioned alkali treatment is preferably subjected to solid-liquid separation afterwards to remove as much aqueous solution as possible.This can reduce the water content during the subsequent xanthate treatment, and can promote the reaction.As a method of solid-liquid separation, for example, a general dehydration method such as centrifugation or filtration can be used.In addition, the concentration of alkali metal hydroxide contained in the alkali cellulose after solid-liquid separation is preferably 3% by mass or more and 8% by mass or less with respect to the total mass of the alkali cellulose after solid-liquid separation.

[0072] In the xanthate group introduction step, a xanthate formation treatment step is carried out after alkali treatment. In the xanthate formation treatment step, carbon disulfide (CS) is added to alkali cellulose. ２ ) is reacted to form (-O － Na ＋ ) group to (-OCSS － Na ＋ ) group to obtain xanthate group-introduced fibers. In the above, the metal ions introduced into the alkali cellulose are typically Na ＋ However, similar reactions occur with other alkali metal ions.

[0073] In the xanthation treatment, it is preferable to supply 10% by mass or more of carbon disulfide relative to the bone dry mass of cellulose in the alkali cellulose.In addition, in the xanthation treatment, the time for which carbon disulfide and alkali cellulose are in contact is preferably 30 minutes or more, more preferably 1 hour or more.Although the xanthation proceeds quickly when carbon disulfide contacts alkali cellulose, it takes time for carbon disulfide to penetrate into the inside of the alkali cellulose, so it is preferable to set the reaction time within the above range.On the other hand, the time for which carbon disulfide and alkali cellulose are in contact can be 6 hours or less, which allows sufficient penetration into the alkali cellulose mass after dehydration, and can almost complete the reactive xanthation.

[0074] The reaction temperature in the xanthate treatment is preferably 46 ° C or less. By making the reaction temperature within the above range, it is easy to suppress the decomposition of alkali cellulose. In addition, by making the reaction temperature within the above range, it is easy to react uniformly, so it can suppress the generation of by-products, and furthermore, it can also suppress the removal of the generated xanthate group.

[0075] The amount of xanthate group introduced in the xanthate group introduction step is preferably 0.60 mmol / g or more and 5.00 mmol / g or less per 1 g (mass) of fiber raw material, more preferably 0.70 mmol / g or more, even more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, even more preferably 1.20 mmol / g or more, and more preferably 3.00 mmol / g or less. By making the amount of xanthate group introduced within the above range, it is possible to facilitate the pulverization of the fiber raw material and improve the stability of the fibrous cellulose.

[0076] <Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step)> The ionic substituent introduction step may include a phosphonic or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phospho group or a phosphine group (compound E) is used as an essential component. Ａ ), and an optional component, an alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group, and the reaction is carried out to introduce a phosphonic group or a phosphine group into the fiber raw material.

[0077] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ａ Examples of the compound E include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphinic acid. In terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, compound E Ａis preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0078] Compound E Ａ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0079] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0080] Compound E Ａ The amount of the additive per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0081] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0082] <Sulfone Group Introduction Step (Sulfoalkylation Step) (Second Sulfone Group Introduction Step)> The ionic substituent introduction step may include a sulfone group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfone group (compound E) is used as an essential component. Ｂ ) and, as an optional component, an alkali compound and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a sulfonic acid group into the fiber raw material.

[0083] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ｂ Examples of suitable acrylic acid esters include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is particularly preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Ｂ is preferably sodium vinyl sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0084] Compound E Ｂ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0085] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0086] Compound E Ｂ The amount of the additive per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0087] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0088] <Carboxyalkylation Step (Third Carboxy Group Introduction Step)> The ionic substituent introduction step may include a carboxyalkylation step. As an essential component, a compound having a reactive group and a carboxy group (compound E Ｃ ), and an optional component, an alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

[0089] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ｃ As the compound, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the viewpoints of the efficiency of introducing the substituent, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferred to use, as an optional component, the compound B in the above-mentioned <Phosphorus oxoacid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0090] Compound E Ｃ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0091] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0092] Compound E Ｃ The amount of the additive per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0093] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0094] <Cationic Group Introduction Step (Cationization Step)> As an essential component, a compound having a reactive group and a cationic group (compound E Ｄ ), and an optional component, an alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a cationic group into the fiber raw material.

[0095] Examples of reactive groups include halogenated alkyl groups, vinyl groups, and epoxy groups (glycidyl groups). Examples of cationic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, the cationic group is preferably an ammonium group. Compound E Ｄ As the compound, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use, as an optional component, the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner. The amount added is also preferably as described above.

[0096] Compound E Ｄ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0097] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0098] Compound E ＤThe amount of the additive per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0099] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 5 minutes to 500 minutes, and even more preferably from 10 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0100] <Washing step> In the step of obtaining cellulose fibers having ionic substituents, a washing step can be carried out on the fibers having ionic substituents introduced therein, if necessary. The washing step is carried out by washing the fibers having ionic substituents introduced therein with, for example, water or an organic solvent. Furthermore, the washing step may be carried out after each step described below, and the number of washing steps carried out in each washing step is not particularly limited.

[0101] <Alkali Treatment Step> In the step of obtaining cellulose fibers having ionic substituents, an alkali treatment step may be provided between the ionic substituent introduction step and the defibration treatment step. The alkali treatment method is not particularly limited, but examples thereof include a method of immersing the ionic substituent-introduced fibers in an alkali solution.

[0102] The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of their high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility.

[0103] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5° C. to 80° C., more preferably from 10° C. to 60° C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5 minutes to 30 minutes, more preferably from 10 minutes to 20 minutes. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the ionic substituent-introduced fiber.

[0104] In order to reduce the amount of alkaline solution used in the alkali treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkali treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkali-treated ionic substituent-introduced fiber with water or an organic solvent after the alkali treatment step and before the defibrating step.

[0105] <Acid Treatment Step> In the step of obtaining cellulose fibers having an ionic substituent, an acid treatment step may be provided between the ionic substituent introduction step and the defibration treatment step. For example, the ionic substituent introduction step, acid treatment, alkali treatment, and defibration treatment may be performed in this order.

[0106] The acid treatment method is not particularly limited, but examples include a method of immersing the fiber raw material in an acid-containing acid solution. The concentration of the acid solution used is not particularly limited, but is preferably 10% by mass or less, more preferably 5% by mass or less. The pH of the acid solution used is also not particularly limited, but is preferably 0 to 4, more preferably 1 to 3. Examples of the acid contained in the acid solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, hydrochloric acid or sulfuric acid is particularly preferred.

[0107] The temperature of the acid solution in the acid treatment is not particularly limited, but is, for example, preferably from 5° C. to 100° C., more preferably from 20° C. to 90° C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is, for example, preferably from 5 minutes to 120 minutes, more preferably from 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably from 100 mass % to 100,000 mass %, more preferably from 1,000 mass % to 10,000 mass %, based on the absolute dry mass of the fiber raw material.

[0108] <Defibrillation Treatment Step> Fibrous cellulose is obtained by defibrating raw fiber material or fibers having ionic substituents introduced therein in a defibration treatment step. In the defibration treatment step, for example, a defibration device can be used. The defibration device is not particularly limited, but examples of defibrators include high-speed defibrators and top finers, examples of beating machines include disc-type refiners (single disc refiners, double disc refiners, etc.) and conical refiners, and examples of micronization devices include high-pressure homogenizers, ultra-high-pressure homogenizers, high-pressure collision grinders, ball mills, bead mills, disc mills, vibration mills, and ultrasonic dispersers. Among the above defibration treatment devices, from the viewpoint of obtaining fibrous cellulose having the desired viscosity change, refiners are preferred, disc-type refiners are more preferred, and single disc refiners are even more preferred. In addition to the above refiners, high-pressure homogenizers and ultra-high-pressure homogenizers may also be used. As described above, when obtaining fibrous cellulose as the fibrous cellulose, it is preferable to use only a refiner (preferably a disk-type refiner, more preferably a single-disc refiner). Furthermore, when obtaining cellulose nanofibers as the fibrous cellulose, it is preferable to further include a defibration step using a homogenizer after the defibration step using a refiner. The preferred treatment conditions (clearance and number of passes) for the beating treatment using a single-disc refiner are as described above, and the preferred treatment conditions (pressure and number of passes) for the atomization treatment using a high-pressure homogenizer or ultra-high-pressure homogenizer are as described above.

[0109] In the defibration process, for example, the fiber raw material or the fiber having an ionic substituent introduced therein is preferably diluted with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0110] The solids concentration of the fibrous cellulose during the defibration treatment can be appropriately set. In addition, the slurry obtained by dispersing the ionic substituent-introduced fibers in a dispersion medium may contain solids other than the ionic substituent-introduced fibers, such as urea having hydrogen bonding properties.

[0111] [Rubber Composition] The rubber composition of this embodiment contains the fibrous cellulose of this embodiment and a rubber component. [Rubber Component] The rubber composition of this embodiment contains a rubber component. As the rubber component, for example, natural rubber (NR) or synthetic rubber can be used. Examples of synthetic rubber include styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene propylene rubber (EPDM), butyl rubber (IIR), chlorobutyl rubber (CIIR), acrylic rubber (ACM), silicone rubber (Q), fluororubber (FKM), butadiene rubber (BR), epoxidized butadiene rubber (EBR), epichlorohydrin rubber (CO, CEO), urethane rubber (U), and polysulfide rubber (T). Nitrile rubbers include modified nitrile rubbers such as hydrogenated nitrile rubber, carboxyl-modified nitrile rubber, silicone-modified nitrile rubber, maleic acid-modified nitrile rubber, and hydroxyl-modified nitrile rubber, as well as hydrogenated versions of these; and acrylonitrile-butadiene-isoprene copolymers in which part of the butadiene is replaced with isoprene. Hydrogenated nitrile rubber (H-NBR) is sometimes called hydrogenated nitrile rubber or hydrogenated acrylonitrile-butadiene rubber. Hydrogenated nitrile rubber can be obtained by hydrogenating the double bonds contained in nitrile rubber. In addition to natural rubber (NR), natural rubbers include modified natural rubbers such as epoxidized natural rubber (ENR) and methyl methacrylate (MMA) graft-polymerized natural rubber, hydrogenated natural rubber, and deproteinized natural rubber. These rubber components may be used alone or in combination. These rubber components may be pre-crosslinked raw materials that do not have a crosslinked structure, or they may have a crosslinked structure.

[0112] Among these, the rubber component is preferably a diene rubber, and is preferably at least one selected from natural rubber, nitrile rubber, butadiene rubber, and styrene-butadiene rubber, more preferably at least one selected from natural rubber, nitrile rubber, and styrene-butadiene rubber, and even more preferably at least one selected from natural rubber, carboxylated nitrile rubber, and styrene-butadiene rubber. The rubber component may also be a pre-crosslinking raw material. The rubber component is preferably a latex of these rubber components. Use of a rubber component latex improves the dispersibility of fibrous cellulose, making it easier to obtain a composite material with excellent tensile properties. When using a rubber component latex, a solid rubber component may also be mixed in. The solid rubber component may be added when masticating the rubber composition or when preparing a rubber compound, but is preferably added when preparing a rubber compound.

[0113] In the rubber composition of this embodiment, from the viewpoint of ease of production of the rubber composition and obtaining a crosslinked rubber composition with superior physical properties, the content of fibrous cellulose per 100 parts by mass of the rubber component is preferably 1 part by mass or more and 200 parts by mass or less, more preferably 2 parts by mass or more, even more preferably 5 parts by mass or more, still more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and preferably 150 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, still more preferably 60 parts by mass or less, even more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. Note that the content of fibrous cellulose per 100 parts by mass of the rubber composition of this embodiment may be different from the content of fibrous cellulose per 100 parts by mass of the rubber component when the crosslinked rubber composition is obtained. Specifically, the content of fibrous cellulose may be increased in the rubber composition, and a rubber component may be added when preparing a rubber compound described below to adjust the content of fibrous cellulose per rubber component.

[0114] The rubber composition of the present embodiment may contain other components such as zinc oxide, a vulcanization accelerator, an antioxidant, and a reinforcing agent, which may be added at any stage in the production process.

[0115] <Method for Producing Rubber Composition> The method for producing the rubber composition is not particularly limited, but it is preferable to produce the rubber composition by preparing a mixed liquid containing at least a rubber component and fibrous cellulose and removing the solvent from the mixed liquid. In the above-mentioned production method, it is preferable to first prepare a mixed liquid containing the rubber component and fibrous cellulose. That is, the method for producing the rubber composition of this embodiment preferably includes the following steps (I) and (II): (I) a step of preparing a mixed liquid containing the rubber component and fibrous cellulose; and (II) a step of drying the mixed liquid to obtain the rubber composition.

[0116] Specifically, in step (I), the rubber component and fibrous cellulose are mixed and dispersed in an aqueous medium to obtain a dispersion of the mixture. Alternatively, a mixed liquid can be obtained by mixing an aqueous dispersion of the rubber component (rubber latex) with an aqueous dispersion of fibrous cellulose. Among these, it is preferable to mix an aqueous dispersion of the rubber component (rubber latex) with a dispersion of fibrous cellulose to obtain a dispersion containing the rubber component and fibrous cellulose (mixed liquid A). Mixing can be performed using known devices such as a disperser, a three-one motor, a clearmix, a homomixer, a homogenizer, or a propeller agitator (e.g., a tornado agitator). The mixing temperature is not limited, but room temperature (20 to 30°C) is preferred. The mixing time can also be adjusted as appropriate. When preparing the dispersion of the mixture, thorough mixing of the rubber component and fibrous cellulose tends to improve the physical properties after crosslinking.

[0117] The rubber latex is preferably a dispersion of a rubber component in an aqueous medium. The aqueous medium contains water as a main component, and the water content relative to the entire aqueous medium is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. The upper limit is not particularly limited, but is 100% by mass or less. In addition to water, the aqueous medium may contain a known organic solvent or the like to the extent that the effects of the present disclosure are not impaired.

[0118] The solids concentration (by mass) of the mixed liquid is preferably 0.5% by mass or more and 50% by mass or less, more preferably 1% by mass or more, even more preferably 3% by mass or more, and more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the solids concentration of the mixed liquid is within the above range, the amount of energy required to remove solvents such as water can be reduced, and further, aggregation of fibrous cellulose particles in the resulting rubber composition is less likely to occur, resulting in excellent kneadability of the resulting rubber composition and excellent properties of the crosslinked rubber composition.

[0119] The solid content concentration of the mixture dispersion can be calculated by the following formula (I) from the mass of the dried product obtained by drying a predetermined amount of the dispersion in a dryer at 105°C until it reaches a constant weight and the mass of the mixture dispersion subjected to drying: solid content concentration (mass %) of the mixture dispersion = mass of dried product [g] / mass of the mixture dispersion subjected to drying [g] × 100 (I)

[0120] The rubber composition is obtained by heating and drying the resulting mixed liquid, as shown in step (II) above. The heating and drying method is not particularly limited, and examples include a method of coating the mixed liquid on a substrate and a method of drying using a drum dryer. In the coating method, for example, a mixed liquid containing a rubber component and fibrous cellulose is coated on a substrate. Furthermore, sheets can be continuously produced by using a coating device and a long substrate. The material of the substrate used in the coating method is not particularly limited, but a substrate with high wettability with the mixed liquid can suppress shrinkage of the sheet during drying, and it is preferable to select a substrate that allows easy peeling of the formed sheet after drying. Among these, resin films and plates or metal films and plates are preferred, but are not particularly limited. For example, resin films and plates such as acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polypropylene, polycarbonate, and polyvinylidene chloride, metal films and plates such as aluminum, zinc, copper, and iron plates, and their surfaces with oxidation treatment, stainless steel films and plates, brass films and plates, etc. can be used. In the coating method, if the viscosity of the mixture dispersion is low and it spreads on the substrate, a damming frame may be fixed to the substrate to obtain a sheet of the desired thickness and basis weight. Alternatively, a substrate with a batt-shaped damming frame may be used. The damming frame is not particularly limited, but it is preferable to select one that allows the edge of the sheet to be easily peeled off after drying. From this perspective, molded resin or metal plates are more preferable. In this embodiment, for example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polypropylene plates, polycarbonate plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and metal plates with their surfaces oxidized, stainless steel plates, brass plates, etc., can be used. The coating machine used to coat the mixture onto the substrate is not particularly limited, but examples include roll coaters, gravure coaters, die coaters, curtain coaters, and air doctor coaters.A die coater, curtain coater, or spray coater is particularly preferred since it can make the thickness of the sheet more uniform.

[0121] The temperature of the mixed liquid and the ambient temperature when applying the mixed liquid to the substrate (hereinafter, the temperature of the mixed liquid and the ambient temperature are collectively referred to as the "coating temperature") are not particularly limited, but are preferably, for example, 5°C or higher and 80°C or lower, more preferably 10°C or higher and 60°C or lower, even more preferably 15°C or higher and 50°C or lower, and particularly preferably 20°C or higher and 50°C or lower. If the coating temperature is higher than the above lower limit, the dispersion of the mixture can be applied more easily. If the coating temperature is lower than the above upper limit, evaporation of the dispersion medium during coating can be suppressed. The drying device used is not particularly limited, but examples include explosion-proof dryers. In the coating process, it is preferable to apply the dispersion of the mixture to the substrate so that the finished basis weight and thickness of the sheet are within the above-mentioned preferred ranges.

[0122] The mixed liquid may be heated and dried in a heated cylindrical dryer to obtain a rubber composition. FIG. 3 is a schematic side cross-sectional view of a double drum dryer 10, which is an example of a heated cylindrical dryer, and FIG. 4 is a schematic side view of the double drum dryer 10. First, a heat transfer medium (generally steam) is introduced into the interior of a rotating cylinder 1 (drum), and the mixed liquid is introduced into a feed section 2. The introduced mixed liquid adheres to the surface of the heated cylinder 1 as a sheet-like mixture 3, and is quickly heated and dried. As the cylinder 1 rotates, the sheet-like mixture 3 is scraped off by a fixed scraper 4, and a rubber composition 5 (heat-dried product) can be obtained.

[0123] The lower limit of the surface temperature of the heated cylindrical dryer is preferably 80°C or higher, more preferably 90°C or higher. The upper limit of the surface temperature is preferably 250°C or lower, more preferably 200°C or lower. The surface temperature of the heated cylindrical dryer refers to the temperature of the cylinder surface that comes into contact with the mixed liquid. The surface temperature of the heated cylindrical dryer may be, for example, 80 to 250°C, 90 to 200°C, or 95 to 180°C. When the surface temperature of the heated cylindrical dryer is within the above range, production efficiency is good and a rubber composition that has excellent physical properties after crosslinking can be obtained.

[0124] The lower limit of the heat-drying time in a heated cylindrical dryer is preferably 2 seconds or more, more preferably 4 seconds or more. The upper limit of the heat-drying time is preferably 1800 seconds or less, more preferably 600 seconds or less. The heat-drying time [sec] in a heated cylindrical dryer refers to the time [sec] during which the mixture is in contact with the surface of the cylinder, and the heat-drying time may be, for example, 2 to 1800 seconds, 4 to 600 seconds, or 6 to 400 seconds. By keeping the heat-drying time within the above range, a dried product that is neither underdried nor overdried can be obtained, and the product has excellent releasability from the drum.

[0125] The lower limit of the cylinder width w of the heating cylinder dryer is preferably 0.1 m or more, more preferably 0.2 m or more. The upper limit of the cylinder width w is not particularly limited, but is usually 7 m or less. The cylinder width w may be, for example, 0.1 to 7 m, or 0.2 to 5 m. By keeping the cylinder width w within the above range, a dried product with a uniform thickness can be obtained.

[0126] The lower limit of the cylinder rotation speed v of the heated cylinder dryer is preferably 0.001 [m / sec] or more, more preferably 0.002 [m / sec] or more. The upper limit of the cylinder rotation speed v is not particularly limited, but is usually 35 [m / sec] or less. The cylinder rotation speed v may be, for example, 0.001 to 3.5 [m / sec], or 0.002 to 0.2 [m / sec]. By keeping the cylinder rotation speed v within the above range, the time the mixture is in contact with the heated drum can be kept within an appropriate range, and a dried product with excellent kneading properties and post-crosslinking physical properties can be obtained.

[0127] The heated cylindrical dryer used in the method for producing a rubber composition may be a conduction heating dryer in which a heat medium is introduced into the interior of a cylinder and the mixture is brought into contact with the surface of the heated cylinder to heat and dry. For example, a drum dryer such as a double drum dryer, a single drum dryer, or a twin drum dryer may be used, and a cylinder dryer, Yankee dryer, etc. may also be used. Among these, from the viewpoint of heat and drying efficiency, the heated cylindrical dryer is preferably a double drum dryer or a cylinder dryer.

[0128] [Rubber Compound] In this embodiment, the rubber compound refers to a composition obtained by kneading a rubber composition and before crosslinking. The rubber compound preferably contains at least a crosslinking agent, and may contain, in addition to the crosslinking agent, additives usable in the rubber field, such as zinc oxide, a vulcanization accelerator, a filler, a softener, a fatty acid, an antioxidant, a peptizer, a colorant, a pH adjuster, and a cured resin. Furthermore, a new solid rubber may be added in addition to the rubber components used in preparing the rubber composition. When a new solid rubber is added, the solid rubber may be the same as those exemplified as the rubber component, but it may be added in a solid state (solid rubber) rather than in a latex form. Examples of the crosslinking agent include sulfur-based crosslinking agents (e.g., powdered sulfur, sulfur flowers, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, and other sulfur; sulfur-containing compounds such as amine disulfide, polymer polysulfide, sulfur olefin adducts, sulfur chloride, and sulfur dichloride; and insoluble polymeric sulfur), peroxide-based crosslinking agents (e.g., dicumyl peroxide, dichlorobenzoyl peroxide, benzoyl peroxide, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, di-t-butylperoxy-di-isopropylbenzene, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane), and quinoid-based crosslinking agents (e.g., p-quinonedioxime and p,p'-dibenzoylquinonedioxime), and among these, sulfur-based crosslinking agents or peroxide-based crosslinking agents are preferred. The amount of the crosslinking agent added is not particularly limited, but is preferably 0.1 part by mass or more and 10 parts by mass or less, more preferably 0.5 part by mass or more, even more preferably 1.0 part by mass or less, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, per 100 parts by mass of the rubber component.

[0129] Furthermore, a crosslinking accelerator having the effect of accelerating crosslinking by a crosslinking agent may be contained, and when a sulfur-based crosslinking agent is used, it is preferable to contain a crosslinking accelerator (vulcanization accelerator). When a sulfur-based crosslinking agent (vulcanizing agent) is used as the crosslinking agent, it is preferable to use a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a thiuram-based vulcanization accelerator, a dithiocarbamate-based vulcanization accelerator, or the like as the crosslinking accelerator (vulcanization accelerator).

[0130] Examples of the filler include carbon black and silica. These fillers may be used alone or in combination of two or more. The content of the filler is not particularly limited and is preferably 10 parts by mass or more and 150 parts by mass or less, more preferably 20 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the rubber component.

[0131] Examples of the softener include aromatic oils, paraffin oils, naphthenic oils, vegetable oils other than castor oil, low PCA oils such as MES, TDAE, and SRAE, and heavy naphthenic oils. Suitable low PCA oils include various plant-derived oils harvested from vegetables, nuts, and seeds. Examples of plant-derived oils include soybean oil, sunflower oil, safflower oil, corn oil, linseed oil, cottonseed oil, rapeseed oil, cashew oil, sesame oil, camellia oil, jojoba oil, macadamia nut oil, coconut oil, and palm oil. The content of the softener is preferably 1 part by mass or more and 35 parts by mass or less, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less, per 100 parts by mass of the rubber component.

[0132] Examples of the fatty acid include stearic acid, palmitic acid, arachidic acid, oleic acid, linoleic acid, and arachidonic acid. Among these, stearic acid is preferred. The content of the fatty acid is not particularly limited, and is preferably 0.1 parts by mass or more and 5 parts by mass or less, more preferably 1 part by mass or more and 4 parts by mass or less, per 100 parts by mass of the rubber component.

[0133] Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), N,N'-diphenyl-p-phenylenediamine (DPPD), and 2-mercaptobenzimidazole (MBI). One type of antioxidant may be used alone, or two or more types may be used in combination. The content of the antioxidant is not particularly limited, and is preferably 0.1 parts by mass or more and 5 parts by mass or less, more preferably 1 part by mass or more and 3 parts by mass or less, per 100 parts by mass of the rubber component. The total content of the antioxidants is preferably 0.2 parts by mass or more and 10 parts by mass or less, more preferably 1 part by mass or more and 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0134] The amount of zinc oxide (zinc white) is not particularly limited and is preferably 1 part by mass or more and 10 parts by mass or less, and more preferably 1.5 parts by mass or more and 8 parts by mass or less, per 100 parts by mass of the rubber component.

[0135] [Method for Producing Rubber Compound] The method for producing the rubber compound is not particularly limited, but preferably includes at least a kneading step of kneading the rubber composition of the present embodiment. In the kneading step, it is preferable to masticate the rubber composition of the present embodiment, and then add at least a crosslinking agent and knead the mixture. In addition to the crosslinking agent, the additives described above may be compounded. Furthermore, in the kneading step, a solid rubber may be compounded in addition to the rubber component contained in the rubber composition. In the present embodiment, in the rubber compound and the crosslinked rubber composition described below, the content of fibrous cellulose per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more and 50 parts by mass or less, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, and more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, from the viewpoint of improving the physical properties of the crosslinked rubber composition.

[0136] The method for producing the rubber compound is not particularly limited, but preferably includes a step of masticating the rubber composition of this embodiment. Mastication improves the dispersibility of the crosslinking agent and other components to be subsequently blended. Mastication may be performed by a conventional method, but may be low-temperature kneading using a roll machine such as an open roll, or high-temperature kneading using a Banbury mixer or the like. Among these, low-temperature kneading is preferred from the viewpoint of the dispersibility of fibrous cellulose in the rubber composition. The temperature for low-temperature kneading is preferably 15°C or higher and 70°C or lower, more preferably 20°C or higher and 65°C or lower, and even more preferably 25°C or higher and 60°C or lower. The temperature for high-temperature kneading is preferably 80°C or higher and 200°C or lower. Furthermore, a rubber compound is produced by adding additives such as a crosslinking agent to the masticated rubber composition and kneading them.

[0137] Kneading is a process of uniformly dispersing a crosslinking agent and other compounding ingredients in a rubber composition (preferably a masticated rubber composition). Kneading may be carried out in a known manner, for example, using a Banbury mixer, kneader, open roll, or the like. Examples of crosslinking agents include sulfur and peroxides. Examples of other compounding ingredients include the above-mentioned additives and solid rubbers.

[0138] [Crosslinked Rubber Composition and Manufacturing Method Thereof] The crosslinked rubber composition of this embodiment is obtained by crosslinking a rubber compound containing a crosslinking agent. Molding may also be performed during crosslinking. That is, the manufacturing method of the crosslinked rubber composition preferably includes a step of crosslinking the rubber composition and the rubber compound containing the crosslinking agent, and a crosslinking and molding step. The manufacturing method of the crosslinked rubber composition of the present invention may further include a step of molding the rubber compound obtained by the kneading step into an intended shape (molding step). Molding in this molding step can be performed by various molding methods using an extruder, a calendar roll, a press, an injection molding machine, a transfer molding machine, a blow molding machine, a foam molding machine, or the like. The molding method may be appropriately selected depending on the shape, application, and molding method of the final product. The kneading step and the molding step may be performed separately or consecutively.

[0139] Regarding crosslinking, there are no particular limitations on the temperature as long as the conditions are such that the crosslinking reaction proceeds, but generally, a crosslinked rubber composition is obtained by heating an uncrosslinked rubber compound obtained by kneading to crosslink (also called vulcanization when sulfur is contained). The heating temperature is preferably 140°C or higher, and preferably 200°C or lower, and more preferably 180°C or lower. Therefore, the heating temperature is preferably about 140 to 200°C, and more preferably about 140 to 180°C. For crosslinking, for example, a vulcanization device that performs mold vulcanization, can vulcanization, continuous vulcanization, etc. can be used.

[0140] In this embodiment, the 50% modulus (σ50 (MPa)) of the crosslinked rubber composition when subjected to a tensile test based on JIS K 6251:2017 at 23±2°C, a gauge length of 20 mm, and a tensile speed of 500 mm / min is σ50 in the MD direction (σ50 ＭＤ ) and σ50 in the CD direction (σ50 ＣＤ ) and the ratio (σ50 ＭＤ / σ50 ＣＤ ) is preferably large. ＭＤ / σ50 ＣＤ A larger σ50 means better anisotropy. ＭＤ / σ50 ＣＤ is preferably 1.5 or more, and although there is no particular upper limit, from the viewpoint of ease of production, it is preferably 3.0 or less, more preferably 2.6 or less, and even more preferably 2.2 or less. ＭＤ and σ ＣＤ is measured by the method described in the Examples.

[0141] In this embodiment, when a tensile test is performed on the crosslinked rubber composition having the formulation described in the Examples according to JIS K 6251:2017 at 23±2°C, a gauge length of 20 mm, and a tensile speed of 500 mm / min, the sum of the tensile strength in the MD direction and the tensile strength in the CD direction is preferably 29 MPa or more, more preferably 29.5 MPa or more, and even more preferably 30 MPa or more. The upper limit is not particularly limited, but from the viewpoint of ease of production, it is preferably 50 MPa or less, more preferably 45 MPa or less, and even more preferably 40 MPa or less. The tensile strength in the MD direction and the tensile strength in the CD direction of the crosslinked rubber composition are measured by the method described in the Examples. Note that when the sum of the tensile strength in the MD direction and the tensile strength in the CD direction obtained by crosslinking a rubber compound without adding a reinforcing material is C (MPa), and the sum of the tensile strength in the MD direction and the tensile strength in the CD direction of the crosslinked rubber composition obtained by crosslinking a rubber compound with adding a reinforcing material is D (MPa), the increase rate of tensile strength can be obtained by the following formula. Increase rate of tensile strength (%) = (D - C) ÷ C × 100 The increase rate of tensile strength is preferably 30% or more, more preferably 35% or more, and although there is no particular upper limit, from the viewpoint of ease of production, it is preferably 200% or less, more preferably 100% or less, and even more preferably 80% or less.

[0142] In this embodiment, when a tensile test is performed on the crosslinked rubber composition having the formulation described in the Examples according to JIS K 6251:2017 at 23±2°C, a gauge length of 20 mm, and a tensile speed of 500 mm / min, the sum of the tensile modulus in the MD direction and the tensile modulus in the CD direction is preferably 9.0 MPa or more, more preferably 9.5 MPa or more. The upper limit is not particularly limited, but from the viewpoint of ease of manufacture, it is preferably 20.0 MPa or less, more preferably 18.0 MPa or less, and even more preferably 15.0 MPa or less. The tensile modulus in the MD direction and the tensile modulus in the CD direction of the crosslinked rubber composition are measured by the method described in the Examples. The sum of the tensile modulus in the MD direction and the tensile modulus in the CD direction obtained by crosslinking a rubber compound without adding a reinforcing material is E (MPa), and the sum of the tensile modulus in the MD direction and the tensile modulus in the CD direction of the crosslinked rubber composition obtained by crosslinking a rubber compound with adding a reinforcing material is F (MPa). The increase rate of the tensile modulus is obtained by the following formula: Increase rate of tensile modulus (%) = (F - E) ÷ E × 100 The increase rate of tensile modulus is preferably 100% or more, more preferably 200% or more, even more preferably 250% or more, and still more preferably 280% or more. There is no particular upper limit, but from the viewpoint of ease of production, it is preferably 800% or less, more preferably 600% or less, and even more preferably 400% or less.

[0143] <Applications> The crosslinked rubber composition of the present embodiment can be used for various applications, and is not particularly limited. For example, it is preferably used for sealing materials, hoses, shoe soles, tire components, anti-vibration rubber, etc. Among these, the crosslinked rubber composition is preferably used for tires.

[0144] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0145] <Production Example 1> [Phosphorus oxo-oxidation treatment] As raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. was used. ２ A sheet-like pulp (disintegrated, with a Canadian Standard Freeness (CSF) of 700 mL as measured in accordance with JIS P 8121-2:2012) was used. This raw pulp was subjected to a phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw pulp to adjust the total weight to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, to obtain a chemical-impregnated pulp. The resulting chemical-impregnated pulp was then heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp. The resulting phosphorylated pulp was then subjected to a washing treatment. The washing treatment was carried out by repeatedly adding 10 L of ion-exchanged water to 100 g (bone dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the resulting dispersion to uniformly disperse the pulp, followed by filtration and dewatering. The washing was terminated when the electrical conductivity of the filtrate reached 100 μS / cm or less. The washed phosphorylated pulp was then neutralized as follows: First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 to 13. The phosphorylated pulp slurry was then dehydrated and washed to obtain a neutralized phosphorylated pulp.

[0146] The obtained phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. －１Absorption due to the P=O of the phosphate group was observed near the peak, confirming that the phosphate group had been added to the pulp. Furthermore, when the obtained phosphorylated pulp was tested and analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described below in [Measurement of phosphorus oxo acid group amount] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0147] Ion-exchanged water was added to the resulting phosphorylated pulp to prepare a slurry with a solids concentration of 2.2% by mass. This slurry was processed 30 times using a single-disc refiner with a clearance set to 600 μm to obtain a phosphorylated microfibril cellulose fiber dispersion. The resulting phosphorylated microfibril cellulose fiber dispersion was then processed once using a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 150 MPa to obtain a fibrous cellulose dispersion containing phosphorylated cellulose nanofibers. The fiber width of the phosphorylated cellulose nanofibers was measured using a transmission electron microscope and found to be 3 to 5 nm.

[0148] X-ray diffraction confirmed that the phosphorylated cellulose nanofibers maintained cellulose type I crystals. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η １００ The difference between (η １０００ -η １００ ) was −93 mPa·s.

[0149] <Production Example 2> A fibrous cellulose dispersion containing phosphorylated cellulose nanofibers was obtained by carrying out the same process as in Production Example 1, except that the treatment was carried out 28 times with the single-disc refiner instead of 30 times in Production Example 1. Furthermore, the fiber width of the phosphorylated cellulose nanofibers was measured using a transmission electron microscope and was found to be 3 to 5 nm.

[0150] X-ray diffraction confirmed that the phosphorylated cellulose nanofibers maintained cellulose type I crystals. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η １００ The difference between (η １０００ -η １００ ) was −67 mPa·s.

[0151] <Production Example 3> A fibrous cellulose dispersion containing phosphorylated cellulose nanofibers was obtained by carrying out the same process as in Production Example 1, except that the treatment was carried out 10 times with the single-disc refiner instead of 30 times in Production Example 1. Furthermore, the fiber width of the phosphorylated cellulose nanofibers was measured using a transmission electron microscope and was found to be 3 to 5 nm.

[0152] X-ray diffraction confirmed that the phosphorylated cellulose nanofibers maintained cellulose type I crystals. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η １００ The difference between (η １０００ -η １００ ) was −93 mPa·s.

[0153] <Production Example 4> A fibrous cellulose dispersion containing phosphorylated microfibril cellulose fibers was obtained by the same procedures as in Production Example 1, except that the treatment using a wet atomization apparatus was omitted. The fiber width of the phosphorylated microfibril cellulose fibers was measured using an FS5 manufactured by Valmet and found to be 21 μm.

[0154] X-ray diffraction confirmed that this phosphorylated microfibril cellulose maintained cellulose type I crystallinity. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η１００ The difference between (η １０００ -η １００ ) was −125 mPa·s.

[0155] <Production Example 5> The same treatment as in Production Example 4 was carried out, except that treatment with the single disc refiner was carried out 28 times instead of 30 times in Production Example 4, to obtain a fibrous cellulose dispersion containing phosphorylated microfibril cellulose fibers. The fiber width of the phosphorylated microfibril cellulose fibers was measured using an FS5 manufactured by Valmet and was found to be 22 μm.

[0156] X-ray diffraction confirmed that this phosphorylated microfibril cellulose maintained cellulose type I crystallinity. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η １００ The difference between (η １０００ -η １００ ) was −133 mPa·s.

[0157] <Production Example 6> The same treatment as in Production Example 4 was carried out, except that treatment with the single disc refiner was carried out 20 times instead of 30 times in Production Example 4, to obtain a fibrous cellulose dispersion containing phosphorylated microfibril cellulose fibers. The fiber width of the phosphorylated microfibril cellulose fibers was measured using an FS5 manufactured by Valmet and was found to be 22 μm.

[0158] X-ray diffraction confirmed that this phosphorylated microfibril cellulose maintained cellulose type I crystallinity. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η １００ The difference between (η １０００ -η １００ ) was −147 mPa·s.

[0159] <Production Example 7> The same treatment as in Production Example 4 was carried out, except that treatment with the single disc refiner was carried out 12 times instead of 30 times in Production Example 4, to obtain a fibrous cellulose dispersion containing phosphorylated microfibril cellulose fibers. The fiber width of the phosphorylated microfibril cellulose fibers was measured using an FS5 manufactured by Valmet and was found to be 22 μm.

[0160] X-ray diffraction confirmed that this phosphorylated microfibril cellulose maintained cellulose type I crystallinity. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η １００ The difference between (η １０００ -η １００ ) was −66 mPa·s.

[0161] <Production Example 8> The same treatment as in Production Example 4 was carried out, except that the treatment conditions in the single-disc refiner in Production Example 4 were changed to a clearance of 75 μm and the treatment was carried out five times, to obtain a fibrous cellulose dispersion containing phosphorylated microfibril cellulose fibers. The fiber width of the phosphorylated microfibril cellulose fibers was measured using an FS5 manufactured by Valmet and was found to be 20 μm.

[0162] X-ray diffraction confirmed that this phosphorylated microfibril cellulose maintained cellulose type I crystallinity. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η １００ The difference between (η １０００ -η １００ ) was −26 mPa·s.

[0163] Production Example 9: Ion-exchanged water was added to phosphorylated pulp obtained in the same manner as in Production Example 1 to prepare a slurry with a solids concentration of 2.2% by mass. This slurry was treated twice with a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 150 MPa to obtain a fibrous cellulose dispersion containing phosphorylated cellulose nanofibers. The fiber width of the phosphorylated cellulose nanofibers was measured using a transmission electron microscope and found to be 3 to 5 nm.

[0164] X-ray diffraction confirmed that the phosphorylated cellulose nanofibers maintained cellulose type I crystals. －１ Viscosity at time η １０００ And, 100 seconds －１ Viscosity at time η １００ The difference between (η １０００ -η １００ ) was −198 mPa·s.

[0165] Example 1 The fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1 was placed in a container so that the solid content of the cellulose nanofibers was 100 parts by mass, and then ion-exchanged water was added so that the solid content concentration of the cellulose nanofibers was diluted to 1.0% by mass. A tornado agitator (general-purpose constrained agitator, PM-202, manufactured by AS ONE Corporation) was used as the agitator, and a stirring blade with a diameter of 6 inches was attached. The mixture was stirred at 1,000 rpm for 5 minutes to obtain a diluted fibrous cellulose dispersion.

[0166] [Mixing Step] An aqueous dispersion of natural rubber latex (ULACOL, manufactured by Resitex Co., Ltd.) with a solids concentration of 61% by mass was added to the obtained 1.0% by mass fibrous cellulose dispersion so that the solids content of the rubber component was 500 parts by mass. Using a tornado stirrer equipped with a stirring blade having a diameter of 6 inches, stirring was carried out at 1000 rpm for 5 minutes to obtain a cellulose nanofiber (fibrous cellulose) / natural rubber latex mixture.

[0167] [Drying Step] The obtained cellulose nanofiber / natural rubber latex mixture was spread on a tray with a Teflon (registered trademark) surface and dried in an explosion-proof dryer at 40°C for 48 hours to obtain a sheet-like cellulose nanofiber / natural rubber composition.

[0168] [Preparation of Rubber Compound] The resulting cellulose nanofiber / natural rubber composition was masticated for 10 minutes using an open roll (6-inch two-roll mill, manufactured by Daihan) at a rotation speed of 26 / 30 rpm without heating. Next, 2 parts by mass of a crosslinking agent (Percumyl D (dicumyl peroxide), manufactured by NOF Corporation), 3 parts by mass of zinc oxide (zinc oxide type 2, manufactured by Seido Chemical Industry Co., Ltd.), and 1.5 parts by mass each of antioxidants (ANTAGE MB (2-mercaptobenzimidazole) and ANTAGE RD (2,2,4-trimethyl-1,2-dihydroquinoline polymer), manufactured by Kawaguchi Chemical Industry Co., Ltd.) were added to 100 parts by mass of the rubber component, and the mixture was kneaded for 6 minutes to obtain a rubber compound with a thickness of approximately 2 mm or more. During the kneading process, the flow direction of the rubber charged into the two-roll mill was defined as the MD direction, and the direction perpendicular to the flow direction was defined as the CD direction.

[0169] [Crosslinking Step] The obtained rubber compound was placed in a mold and press-heated at 165°C for 20 minutes to prepare a 2 mm thick sheet of the crosslinked rubber composition.

[0170] Example 2 A sheet of a crosslinked rubber composition was obtained by carrying out the same treatment as in Example 1, except that the fibrous cellulose dispersion obtained in Production Example 2 was used instead of the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1.

[0171] Example 3 A sheet of a crosslinked rubber composition was obtained by carrying out the same treatment as in Example 1, except that the fibrous cellulose dispersion obtained in Production Example 3 was used instead of the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1.

[0172] Example 4 A sheet of a crosslinked rubber composition was obtained by carrying out the same treatment as in Example 1, except that the fibrous cellulose dispersion containing microfibril cellulose obtained in Production Example 4 was used instead of the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1.

[0173] Example 5 A sheet of a crosslinked rubber composition was obtained by carrying out the same treatment as in Example 1, except that the fibrous cellulose dispersion containing microfibril cellulose obtained in Production Example 5 was used instead of the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1.

[0174] Example 6 A sheet of a crosslinked rubber composition was obtained by carrying out the same treatment as in Example 1, except that the fibrous cellulose dispersion containing microfibril cellulose obtained in Production Example 6 was used instead of the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1.

[0175] Example 7 A sheet of a crosslinked rubber composition was obtained by carrying out the same treatment as in Example 1, except that the fibrous cellulose dispersion containing microfibril cellulose obtained in Production Example 7 was used instead of the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1.

[0176] Comparative Example 1 A sheet of a crosslinked rubber composition was obtained by carrying out the same treatment as in Example 1, except that the fibrous cellulose dispersion containing microfibril cellulose obtained in Production Example 8 was used instead of the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1.

[0177] Comparative Example 2 A sheet of a crosslinked rubber composition was obtained by carrying out the same treatment as in Example 1, except that the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 9 was used instead of the fibrous cellulose dispersion containing cellulose nanofibers obtained in Production Example 1.

[0178] Reference Example 1 Natural rubber latex was spread on a tray with a Teflon (registered trademark) surface and dried in an explosion-proof dryer at 40°C for 48 hours to obtain a sheet of natural rubber composition. Except for using this natural rubber composition, the same treatment as in Example 1 was carried out to obtain a sheet of crosslinked rubber composition.

[0179] [Measurement of phosphorus oxoacid group content] Ion-exchanged water was added to the phosphate-introduced pulp obtained in Production Example 1 to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated twice at a pressure of 150 MPa using a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion. The fine fibrous cellulose dispersion was diluted with ion-exchanged water to 0.2% by mass to prepare a fibrous cellulose-containing slurry. The cellulose content was then measured by treating the slurry with an ion-exchange resin and then titrating it with an alkali. The ion-exchange resin treatment was carried out by adding 1 / 10 by volume of a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring the slurry onto a mesh with a mesh opening of 90 μm to separate the resin and the slurry. In addition, the alkali titration was performed by adding 10 μL of 0.1 N aqueous sodium hydroxide solution to the fine fibrous cellulose-containing slurry after treatment with an ion exchange resin at 5-second intervals, while measuring the change in the pH value of the slurry. Nitrogen gas was introduced into the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the differential pH value with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. Of these, the maximum point of increment obtained first after starting the addition of alkali is called the first endpoint, and the maximum point of increment obtained next is called the second endpoint (FIG. 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used in the titration. Furthermore, the amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used in the titration. The amount of alkali (mmol) required from the start of titration to the first endpoint was divided by the solid content (g) in the slurry to be titrated, and the value was taken as the amount of phosphorus oxo acid groups (mmol / g).

[0180] [Rheometer Measurement] Ion-exchanged water was added to the fibrous cellulose dispersions containing cellulose nanofibers or microfibril cellulose obtained in Production Examples 1 to 9 so as to give a slurry with a solid content of 0.4% by mass. －１ Viscosity value at (η １０００ ) mPa·s and 100 sec －１ Viscosity value at (η １００ ) mPa·s was measured. The dispersion to be measured was left to stand for 24 hours in an environment of 23°C and relative humidity 50% before measurement. The temperature of the dispersion during measurement was 23°C. The measurement conditions were as follows: Measurement jig: cone plate (diameter 35 mm, angle 2°) Shear rate: 0.01 to 1000 sec －１ Number of data points: 31 points Measurement time: 5 minutes

[0181] [Tensile Test] In the MD and CD directions of the sheets of the crosslinked rubber compositions obtained in Examples 1 to 7, Comparative Examples 1 and 2, and Reference Example 1, test pieces were punched into the shape of a dumbbell (dumbbell No. 6) as defined in JIS K 6251:2017. Tensile tests were carried out in accordance with JIS K 6251:2017 using a tensile tester Tensilon (manufactured by A&D Corporation) at 23±2°C, a gauge length of 20 mm, and a pulling speed of 500 mm / min, to measure the tensile strength (MPa), tensile modulus (MPa), and 50% modulus (σ50 (MPa)).

[0182]

[0183] 10... double drum dryer, 1... cylinder, 2... feed section, 3... sheet-like mixture, 4... scraper, 5... composite material

Claims

1. Fibrous cellulose having a viscosity change expressed by the following formula (1) of -190 mPa·s or more and -30 mPa·s or less: Viscosity change (mPa·s) = η １０００ -η １００ (1) In equation (1), η １０００ is the shear rate of 1000 s for a 0.4 mass% aqueous dispersion －１ is the viscosity (mPa s) at １００ is the shear rate of a 0.4 mass% aqueous dispersion at 100 s －１ is the viscosity (mPa·s) at 2. The aforementioned η １００ 2. The fibrous cellulose according to claim 1, wherein the viscosity is 240 mPa·s or less.

3. The fibrous cellulose of claim 1, wherein the fibrous cellulose is chemically modified fibrous cellulose.

4. A rubber composition containing 1 part by mass or more and 200 parts by mass or less of the fibrous cellulose according to any one of claims 1 to 3 per 100 parts by mass of the rubber component.

5. A crosslinked rubber composition obtained by crosslinking a rubber compound containing the rubber composition according to claim 4 and a crosslinking agent.

6. A method for producing fibrous cellulose, comprising a beating step of beating pulp fibers with a single-disc refiner, wherein the clearance of the single-disc refiner in the beating step is 0.4 mm or more.

7. The method for producing fibrous cellulose according to claim 6, wherein the pulp fibers are chemically modified pulp fibers.

8. The method for producing fibrous cellulose according to claim 6 or 7, further comprising a micronization step of defibrating the cellulose in a wet micronization device after the beating step.

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