Fibrous cellulose, fibrous cellulose aqueous dispersion, rubber composition, and crosslinked rubber product

Abstract

The purpose of the present invention is to provide: a fibrous cellulose which enables the achievement of a crosslinked rubber product having excellent physical properties such as hardness and tensile properties after crosslinking when the fibrous cellulose is added to a rubber component and the resulting rubber component is crosslinked, the crosslinked rubber product being suppressed in decrease of water resistance in comparison to a case where a conventional fibrous cellulose is added to the rubber component; and a fibrous cellulose aqueous dispersion which contains the fibrous cellulose.　A fibrous cellulose according to the present invention has an anionic group and a fiber width of 100 μm or less, and the counter ion of the anionic group is an ammonium ion (NH4 +).

Description

Fibrous cellulose, aqueous dispersion of fibrous cellulose, rubber composition, and crosslinked rubber product

[0001] The present invention relates to a fibrous cellulose, an aqueous dispersion of fibrous cellulose, a rubber composition, and a crosslinked rubber product.

[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] As fibrous cellulose, fine fibrous cellulose with an average fiber width of 1000 nm or less is also known. Fine fibrous cellulose has attracted attention as a new material and has a wide range of applications. For example, the development of sheets, resin composites, and thickeners containing fine fibrous cellulose is underway. Furthermore, composite materials in which fine fibrous cellulose is combined with resin emulsions and / or rubber latex are being considered.

[0004] Cited Document 1 discloses a composition containing a base rubber, a maleic anhydride-modified polymer, and non-chemically modified and unmodified cellulose nanofibers, with the aim of providing a composition in which cellulose nanofibers are defibrated and dispersed and from which crosslinked rubber with excellent tensile properties can be produced. Patent Document 2 also discloses a polymer composition containing (I) a polymer; (II) a nanocellulose dispersion composition (NDC) comprising: (i) a deflocculating agent comprising a carbon black filler, an elastomer latex, a wax, or any combination thereof; and (ii) nanocellulose; and (III) a carbon black additive, with the aim of providing a method for significantly improving the dispersibility of nanocellulose in a polymer blend.

[0005] Japanese Patent Application Publication No. 2021-123639 Japanese Patent Application Publication No. 2022-508946

[0006] Cited Documents 1 and 2 disclose compositions containing cellulose nanofibers, an elastomer, a base rubber, and the like. However, Cited Documents 1 and 2 do not consider the physical properties and kneadability of the compositions, leaving room for improvement. Furthermore, further improvement is desired in the physical properties of the crosslinked rubber after crosslinking. The present invention aims to provide fibrous cellulose and a fibrous cellulose aqueous dispersion containing the fibrous cellulose, which, when added to a rubber component and crosslinked, suppresses a decrease in water resistance compared to when conventional fibrous cellulose is added, and produces a crosslinked rubber product in which deterioration due to water absorption of strength, tensile properties, and the like after crosslinking is suppressed. Another object of the present invention is to provide a rubber composition containing the fibrous cellulose, and a crosslinked rubber product obtained by crosslinking and molding a rubber compound containing the rubber composition and a crosslinking agent.

[0007] The present inventors have found that the anionic group has a counter ion of NH ４ ＋ The present invention relates to the following items <1> to <12>. <1> Fibrous cellulose having anionic groups and a fiber width of 100 μm or less, wherein the counter ions of the anionic groups are ammonium ions (NH ４ ＋). <2> The fibrous cellulose according to <1>, which is fine fibrous cellulose having a fiber width of 1,000 nm or less. <3> The fibrous cellulose according to <1>, which is microfibril cellulose having a fiber width of more than 1 μm and 100 μm or less. <4> The fibrous cellulose according to any one of <1> to <3>, wherein the anionic group is at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group. <5> The fibrous cellulose according to any one of <1> to <4>, which is a rubber modifier. <6> An aqueous fibrous cellulose dispersion containing the fibrous cellulose according to any one of <1> to <5>. <7> A rubber composition obtained by blending the fibrous cellulose according to any one of <1> to <5> with a rubber component. <8> The rubber composition according to <7>, wherein the content of the fibrous cellulose per 100 parts by mass of the rubber component is 0.1 parts by mass or more and 60 parts by mass or less. <9> The rubber composition according to <7> or <8>, wherein the rubber component is a diene rubber. <10> A crosslinked rubber product obtained by crosslinking and molding a rubber compound containing the rubber composition according to any one of <7> to <9> and a crosslinking agent. <11> The crosslinked rubber product according to <10>, wherein the crosslinked rubber product is a tire. <12> A method for producing a rubber composition, comprising the following steps (I) and (II): (I) a mixing step of mixing the aqueous dispersion containing the fibrous cellulose according to any one of <1> to <5> with a rubber latex to obtain a mixture A, and (II) a heating step of heating and drying the mixture A to obtain a rubber composition.

[0008] The present invention aims to provide fibrous cellulose and an aqueous dispersion of fibrous cellulose containing the fibrous cellulose, which, when added to a rubber component and crosslinked, suppresses a decrease in water resistance compared to when conventional fibrous cellulose is added, and gives a crosslinked rubber product in which deterioration due to water absorption of strength, tensile properties, etc. after crosslinking is suppressed. Another object of the present invention is to provide a rubber composition containing the fibrous cellulose, and a crosslinked rubber product obtained by crosslinking and molding a rubber compound containing the rubber composition and a crosslinking agent.

[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 this embodiment (hereinafter also simply referred to as "fibrous cellulose") has an anionic group, has a fiber width of 100 μm or less, and further, the counter ion of the anionic group is an ammonium ion (NH ４ ＋ ). When the fibrous cellulose of this embodiment is added to a rubber component and crosslinked, a decrease in water resistance is suppressed compared to when conventional fibrous cellulose is added, and a crosslinked rubber product is obtained in which deterioration of strength, tensile properties, etc. due to water absorption after crosslinking is suppressed. The detailed reason for obtaining the above effect is unknown, but conventionally, alkali metal ions, particularly sodium ions, have been used as counter ions for fibrous cellulose having anionic groups. The present inventors have found that a crosslinked rubber product obtained by blending fibrous cellulose having sodium ions as counter ions with a rubber component and crosslinking this has excellent mechanical properties such as tensile strength, but has the problem of high water absorption and reduced water resistance. Therefore, as a result of extensive research to suppress the decrease in water resistance, they have found that a crosslinked rubber product obtained by blending fibrous cellulose having sodium ions as counter ions has excellent mechanical properties such as tensile strength, but has the problem of high water absorption and reduced water resistance. ４ ＋ It has been found that the decrease in water resistance is suppressed by fibrous cellulose having anionic groups when compared with conventional fibrous cellulose. This is thought to be because when the counter ion is an alkali metal ion, the degree of ionization is high, and as a result, the fibrous cellulose having anionic groups becomes more hydrophilic. On the other hand, when the counter ion is an ammonium ion (NH ４ ＋), the degree of ionization is low, and it is considered that the decrease in water resistance is suppressed compared to when the counter ion is an alkali metal ion. Furthermore, when producing a rubber composition obtained by compounding the fibrous cellulose of this embodiment with a rubber component, when preparing a rubber compound by adding at least a crosslinking agent to the rubber composition, or when heating to produce a crosslinked rubber product, at least a part of the ammonium ions, which are counter ions of the anionic groups of the fibrous cellulose having anionic groups, dissociates, and the counter ions become protons (H ＋ ) is believed to further suppress the decrease in water resistance and to provide a crosslinked rubber product in which deterioration due to water absorption is suppressed.

[0011] The fiber width (average fiber width) of the fibrous cellulose of this embodiment is 100 μm or less. The fibrous cellulose may be fine fibrous cellulose having a fiber width of 1000 nm or less, or may be microfibril cellulose having a fiber width of more than 1 μm and not more than 100 μm. Furthermore, the fibrous cellulose of this embodiment may contain both fine fibrous cellulose having a fiber width of 1000 nm or less and microfibril cellulose having a fiber width of more than 1 μm and not more than 100 μm. Note that the term "fibrous cellulose" simply includes both "fine fibrous cellulose" and "microfibril cellulose." When the fibrous cellulose of this embodiment is fine fibrous cellulose, the upper limit of the fiber width is 1000 nm or less, 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. In addition, when the fibrous cellulose of this embodiment is fine fibrous cellulose, the rubber composition may contain cellulose fibers having a fiber width exceeding 1 μm (1000 nm) (hereinafter also referred to as "coarse cellulose fibers"), as described below.

[0012] The average fiber width of the fine fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and still more preferably 2 nm or more and 10 nm or less. The fine fibrous cellulose is, for example, monofilament cellulose.

[0013] The fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fine fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast onto glass may be observed. Next, electron microscope images are observed at magnifications of 1000x, 5000x, 10000x, or 50000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions: (1) A line X is drawn at any point within the observed image, and 20 or more fibers intersect with this line X. (2) A line Y is drawn within the same image, intersecting the line X perpendicularly, and 20 or more fibers intersect with this line Y. For observed images that satisfy the above conditions, the widths of the fibers intersecting with line X and line Y are visually determined. In this way, three or more sets of observation images of at least non-overlapping surface portions are obtained. Next, for each image, the widths of the fibers intersecting with lines X and Y are read. This results in reading the widths of at least 20 fibers x 2 x 3 = 120 fibers. The average of the read fiber widths is then taken as the number-average fiber width of the fine fibrous cellulose.

[0014] The fiber length of the fine fibrous cellulose is not particularly limited, but is, for example, preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, destruction of the crystalline regions of the fine fibrous cellulose can be suppressed. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0015] When the fibrous cellulose of this embodiment is microfibril cellulose, the fiber width is more than 1 μm and not more than 100 μm. From the viewpoint of dispersibility in the rubber composition and the physical properties of the resulting crosslinked rubber product, the fiber width of the microfibril cellulose is preferably 3 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and preferably 75 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, and even more preferably 30 μm or less. The fiber width can be adjusted by the defibration treatment conditions in the defibration treatment step, such as the degree of defibration, the defibration treatment time, the number of defibration treatments, etc. For example, when a disc refiner is used as the defibration treatment device, the degree of defibration can be adjusted by changing the clearance or the number of treatments, and when a homogenizer is used, it can be adjusted by the pressure. The fiber width of the microfibril cellulose is measured by the method described in the Examples.

[0016] The fibrous cellulose 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 two typical peaks at two positions: 2θ=14° to 17° and 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 can be determined by measuring the X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0017] The axial ratio (fiber length / fiber width) of the fibrous cellulose is not particularly limited, but is preferably 50 to 10,000, more preferably 100 to 1,000. By setting the axial ratio to the above lower limit or more, a rubber composition containing the fibrous cellulose can be easily formed. By setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when treating the fibrous cellulose as a dispersion, handling such as dilution is facilitated.

[0018] In this embodiment, the fibrous cellulose has, for example, both crystalline regions and amorphous regions. Fibrous cellulose having both crystalline regions and amorphous regions and having an axial ratio within the above range is realized by the method for producing fibrous cellulose described below.

[0019] In this embodiment, the fibrous cellulose has an anionic group. The anionic group is preferably introduced by directly oxidizing a hydroxyl group to be substituted on the cellulose, or is preferably introduced into the fibrous cellulose via an ester bond or an ether bond, and more preferably is introduced into the fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation of the fibrous cellulose and a compound that becomes the anionic group. By introducing the anionic group via an ester bond, the counter ion becomes NH ４ ＋ The anionic group represented by the formula (I) is preferred because it can be easily introduced into cellulose.

[0020] 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 oxo acid group, a substituent derived from a phosphorus oxo acid group, a carboxy group, a sulfur oxo acid group, a substituent derived from a sulfur oxo acid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group, more preferably at least one selected from the group consisting of a phosphorus oxo acid group, a substituent derived from a phosphorus oxo acid group, a carboxy group, a sulfur oxo acid group, and a substituent derived from a sulfur oxo acid group, and from the viewpoint of introduction via an ester bond, a phosphorus oxo acid group, a substituent derived from a phosphorus oxo acid group, a sulfur oxo acid group, and a substituent derived from a sulfur oxo acid group is even more preferred, and a phosphorus oxo acid group is even more preferred. Introducing a phosphorus oxo acid group as the anionic group can further enhance the dispersibility of fibrous cellulose, for example, even under alkaline or acidic conditions, making it easier to obtain crosslinked rubber products excellent in hardness, strength, and elongation.

[0021] 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.

[0022] 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＋ At least ammonium ion (NH ４ ＋ ) is a cation of one or more valences consisting of an organic or inorganic substance.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] β ｂ＋ is the ammonium ion (NH ４ ＋ ) is included. ｂ＋ As, NH ４ ＋ It is not excluded that the compound may have a cation other than β ｂ＋ is NH ４ ＋ The monovalent or higher cations are organic or inorganic cations excluding those mentioned above. Examples of the monovalent or higher cations made of organic substances include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cations made of inorganic substances include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, and hydrogen ions. Note that in formula (1), β ｂ＋ When a plurality of β ｂ＋ may be the same or different. ４ ＋)" means that the main counter ion (50 mol % or more of the counter ions) is an ammonium ion (NH ４ ＋ ) and does not exclude the inclusion of other cations as counter ions. ｂ＋ contains at least ammonium ions (NH ４ ＋ ) and may contain other cations, but from the viewpoint of obtaining a crosslinked rubber product having excellent water resistance, 50 mol % or more of the counter ions are NH ４ ＋ It is preferable that NH is 70 mol % or more, more preferably 90 mol % or more. ４ ＋ The upper limit is not particularly limited, but is 100 mol %. ｂ＋ Ammonium ions (NH ４ ＋ The content of ammonium ions (NH) is the content in fibrous cellulose, and in a fibrous cellulose aqueous dispersion obtained by dispersing the fibrous cellulose in a solvent containing water, a rubber composition obtained by blending the fibrous cellulose in a rubber component, a rubber compound and a crosslinked rubber product described below, ４ ＋ ) dissociates, and the counter ion becomes a proton (H ＋ ) may be substituted.

[0027] 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.

[0028] 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.

[0029]

[0030] 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＋ At least ammonium ion (NH ４ ＋ ) is a monovalent or higher cation consisting of an organic or inorganic substance containing β ｂ＋ is the ammonium ion (NH ４ ＋ ) is included. ｂ＋ As, NH ４ ＋ It is not excluded that the compound may have a cation other than β ｂ＋ is NH ４ ＋ Examples of the monovalent or higher cations composed of organic substances excluding (a) include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cations composed of inorganic substances include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, and hydrogen ions. 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.４ ＋ )" means that the main counter ion (50 mol % or more of the counter ions) is an ammonium ion (NH ４ ＋ ) and does not exclude the inclusion of other cations as counter ions. ｂ＋ contains at least ammonium ions (NH ４ ＋ ) and may contain other cations, but from the viewpoint of obtaining a crosslinked rubber product having excellent water resistance, 50 mol % or more of the counter ions are NH ４ ＋ It is preferable that NH is 70 mol % or more, more preferably 90 mol % or more. ４ ＋ The upper limit is not particularly limited, but is 100 mol %. ｂ＋ Ammonium ions (NH ４ ＋ The content of ammonium ions (NH) is the content in fibrous cellulose, and in a fibrous cellulose aqueous dispersion obtained by dispersing the fibrous cellulose in a solvent containing water, a rubber composition obtained by blending the fibrous cellulose in a rubber component, a rubber compound and a crosslinked rubber product described below, ４ ＋ ) dissociates, and the counter ion becomes a proton (H ＋ ) may be substituted.

[0031] The amount of ionic substituent introduced into the fibrous cellulose is, for example, per 1 g (mass) of the 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 0.60 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, and even more preferably 2.00 mmol / g or less. Here, the denominator in the unit mmol / g is the ratio of the counter ion of the ionic substituent to the hydrogen ion (H ＋By setting the amount of ionic substituents introduced within the above range, it is possible to facilitate defibration of the fiber raw material and to increase the stability of the fibrous cellulose.

[0032] 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.

[0033] 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-exchange water is added to the target cellulose fibers (e.g., fibrous cellulose, which is defibrated cellulose fibers) to prepare a slurry with a solids concentration of 0.2% by mass. The slurry 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. In FIG. 1, the region from the start of titration to the first endpoint is called the first region, and the region from the first endpoint to the second endpoint is called the second region.For example, when the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weakly acidic groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) appears to decrease, resulting in a smaller amount of alkali required in the second region than in the first region. 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) corresponds to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Furthermore, when the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weakly acidic groups, so the amount of alkali required in the second region is reduced or may even be zero. In this case, there will be only one point on the titration curve where the pH increment is maximized.

[0034] 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 fibrous 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).

[0035] 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-exchange water is added to the target cellulose fibers (e.g., fibrous cellulose, which is defibrated cellulose fibers) to prepare a slurry with a solids concentration of 0.2% by mass. The slurry 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 versus 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) versus the amount of alkali added. In this neutralization titration, a single point where the increment (differential value of pH versus the amount of alkali added) is maximized is identified on the curve plotting the measured pH versus 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.

[0036] 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)

[0037] 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.

[0038] 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).

[0039] The degree of polymerization of the fibrous cellulose is preferably 100 or more and 1000 or less. A degree of polymerization of 100 or more is preferable because, for example, when added to a rubber component, a sufficient reinforcing effect can be obtained. On the other hand, a degree of polymerization of 1000 or less is preferable because, for example, when added to a rubber component, more excellent dispersibility can be obtained. The degree of polymerization of the fibrous cellulose is more preferably 150 or more, even more preferably 300 or more, even more preferably 400 or more, and more preferably 900 or less.

[0040] The degree of polymerization of fibrous cellulose is a value calculated from the pulp viscosity measured in accordance with Tappi T230. Specifically, the fibrous cellulose to be measured is dispersed in a copper ethylenediamine aqueous solution to measure the viscosity (referred to as η1), and the blank viscosity (referred to as η0) is measured using only the dispersion medium, and then the specific viscosity (ηsp) and intrinsic viscosity ([η]) are measured according to the following formula: ηsp = (η1 / η0) - 1 [η] = ηsp / (c(1+0.28×ηsp)) where c represents the concentration (g / mL) of the fibrous cellulose at the time of viscosity measurement. Furthermore, the degree of polymerization (DP) is calculated according to the following formula: DP = 1.75×[η] Because this degree of polymerization is the average degree of polymerization measured by the viscosity method, it is sometimes referred to as the "viscosity-average degree of polymerization."

[0041] In order to obtain fibrous cellulose having the above-mentioned anionic groups (anionic substituents) introduced therein, it is preferable to have an anionic substituent introduction step for introducing an anionic substituent into a cellulose-containing fiber raw material, a washing step, and a defibration treatment step in this order, and an acid treatment step may be carried out instead of or in addition to the washing step. ４ ＋ Examples of the anionic 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, and a sulfonic group introduction step. Each of these steps will be described below.

[0042] <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.

[0043] <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.

[0044] In the phosphorus oxoacid 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"). On the other hand, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the absence of compound B, but from the viewpoint of reactivity and the viewpoint of obtaining fibrous cellulose having ammonium ions as counter ions, it is preferable to carry out the reaction in the presence of compound B.

[0045] 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.

[0046] 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 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, or ammonium salt of phosphorous acid are preferred, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite is more preferred, phosphoric acid, ammonium dihydrogen phosphate, or phosphorous acid is even more preferred, and ammonium dihydrogen phosphate or phosphorous acid is even more preferred.

[0047] 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.

[0048] 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 viewpoints of reactivity and availability, urea is preferred as compound B. 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 preferred to use an aqueous solution in which both compound A and compound B are dissolved.

[0049] 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.

[0050] 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 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, and a high-frequency dryer.

[0051] 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).

[0052] 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 moisture retained in the slurry and the moisture 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 moisture 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.

[0053] 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.

[0054] 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.

[0055] 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, defibration of cellulose fiber in the defibration treatment step can be facilitated, and the stability of fibrous cellulose can be improved.

[0056] <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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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 0.40 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. Setting the amount of carboxy groups introduced within the above range facilitates defibration of cellulose fibers in the defibration treatment step and enhances the stability of fibrous cellulose.

[0061] <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).

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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, even more preferably 2.50 mmol / g or less, and still more preferably 2.00 mmol / g or less. By setting the amount of sulfonic groups introduced within the above range, defibration of cellulose fibers in the defibration treatment step can be facilitated, and the stability of fibrous cellulose can be increased.

[0066] <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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] <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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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 setting the amount of xanthate group introduction within the above range, it is possible to facilitate defibration of the fiber raw material and improve the stability of the fibrous cellulose.

[0078] <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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] Compound E Ａ The amount of addition 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.

[0083] 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.

[0084] <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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] Compound E Ｂ The amount of addition 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.

[0089] 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.

[0090] <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.

[0091] 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.

[0092] 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.

[0093] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 70°C or higher and 200°C or lower, and even more preferably 90°C or higher and 150°C or lower.

[0094] Compound E Ｃ The amount of addition 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.

[0095] 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.

[0096] <Washing step> In the step of obtaining cellulose fibers having anionic substituents, a washing step can be carried out on the fibers into which anionic substituents have been introduced, if necessary. The washing step is carried out by washing the fibers into which anionic substituents have been introduced 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 washings carried out in each washing step is not particularly limited.

[0097] In this embodiment, the counter ion of the anionic group of the fibrous cellulose is an ammonium ion (NH ４ ＋ When an anionic group is introduced into cellulose fibers by esterification using the above-mentioned compound B, the counter ion of the introduced anionic group is NH ４ ＋ On the other hand, when an anionic group is introduced by TEMPO oxidation treatment, hypochlorous acid oxidation treatment, carboxymethylation treatment, or the like, the counter ion of the anionic group can be replaced by NH ４ ＋ In this case, the anionic group-introduced cellulose fiber is subjected to an acid treatment process and a counter ion is replaced with NH ４ ＋ It is preferable to carry out a step of replacing the counter ion with NH. ４ ＋ The step of replacing the cellulose with cellulose syrup may be carried out before or after the defibration step described below, but from the viewpoint of ease of production, it is preferably carried out before the defibration step. Since the fibrous cellulose after the defibration step has high water absorption and the slurry has high viscosity, the load on the washing step increases.

[0098] <Acid Treatment Step> In the step of obtaining cellulose fibers having an anionic substituent, an acid treatment step may be provided between the anionic substituent introduction step and the defibration step. ４ ＋ The acid treatment step converts the counter ions of the anionic groups into hydrogen ions.

[0099] 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.

[0100] 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 90 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably from 100 parts by mass to 100,000 parts by mass, more preferably from 1,000 parts by mass to 10,000 parts by mass, per 100 parts by mass of the absolute dry mass of the fiber raw material.

[0101] <Counter ion is NH ４ ＋Step of replacing the counter ion with NH ４ ＋ The method for substitution is not particularly limited, but an example is a method in which the anionic group-introduced fiber that has been subjected to the acid treatment step described above is immersed in aqueous ammonia. The concentration of the aqueous ammonia used is not particularly limited, but is preferably 5N or more, more preferably 10N or more, and even more preferably 14N or more.

[0102] The temperature of the ammonia water 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 ammonia water is not particularly limited, but is, for example, preferably from 5 minutes to 120 minutes, more preferably from 10 minutes to 90 minutes.

[0103] <Defibrillation Treatment Step> Fibrous cellulose is obtained by defibrating anionic group-introduced fibers in a defibration treatment step. Depending on the degree of defibration treatment, the obtained fibrous cellulose may be fine fibrous cellulose having a fiber width of 1000 nm or less, or may be microfibrillated cellulose having a fiber width of more than 1 μm and not more than 100 μm. In the defibration treatment step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include high-speed defibrators, grinders (stone mills), high-pressure homogenizers, ultra-high-pressure homogenizers, high-pressure collision grinders, ball mills, bead mills, disk refiners, conical refiners, twin-screw kneaders, vibration mills, homomixers under high-speed rotation, ultrasonic dispersers, and beaters. To obtain fine fibrous cellulose, it is more preferable to use, among the above-mentioned defibration treatment devices, a high-speed defibrator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination. Furthermore, in order to obtain microfibril cellulose, from the viewpoint of obtaining microfibril cellulose having a desired fiber width, a refiner is preferred, a disk-type refiner is more preferred, and a single-disc refiner is even more preferred. Furthermore, in addition to the disk-type refiner, a high-speed defibrator, a high-pressure homogenizer, an ultra-high-pressure homogenizer, or the like may be used in combination, and in this case, the defibration treatment using one selected from the group consisting of the high-speed defibrator, the high-pressure homogenizer, and the ultra-high-pressure homogenizer may be carried out for one to three passes, preferably one to two passes, and more preferably one pass.

[0104] In the defibration process, for example, the anionic group-introduced fibers are 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).

[0105] The solids concentration of the fibrous cellulose during the defibration treatment can be set as appropriate. In addition, the slurry obtained by dispersing the anionic group-introduced fibers in a dispersion medium may contain solids other than the anionic group-introduced fibers, such as urea having hydrogen bonding properties.

[0106] <Polymerization Degree Reduction Treatment> In addition to the steps described above, the method for producing fibrous cellulose of this embodiment may further include a step of performing a polymerization degree reduction treatment to obtain fibrous cellulose with a desired polymerization degree. Specifically, as described above, the method may include a step of performing a defibration treatment on cellulose fibers into which anionic groups have been introduced to obtain fibrous cellulose with a fiber width of 100 μm or less, and a step of performing a polymerization degree reduction treatment on the fibrous cellulose. Note that the order of the defibration treatment and the polymerization degree reduction treatment may be either first, but it is preferable to perform the polymerization degree reduction treatment after the defibration treatment. That is, the method for producing fibrous cellulose of this embodiment may include, for example, a step of performing a defibration treatment on cellulose fibers into which anionic groups have been introduced, followed by a polymerization degree reduction treatment. In the following explanation, the case where the polymerization reduction treatment step is performed after the defibration treatment step will be mainly described, but when the polymerization reduction treatment step is performed before the defibration treatment step, the dispersion containing fibrous cellulose will be interpreted as a dispersion of cellulose fibers (preferably cellulose fibers into which anionic groups have been introduced) before the defibration treatment step. Note that, because the amount of anionic substituents in the fibrous cellulose hardly changes even after the polymerization reduction treatment, the amount of anionic substituents in the fibrous cellulose before the polymerization reduction treatment can be approximated as the amount of anionic substituents in the fibrous cellulose after the polymerization reduction treatment.

[0107] In this specification, the step of carrying out a polymerization degree reduction treatment is a step of carrying out a treatment to reduce the degree of polymerization of a dispersion containing fibrous cellulose to an appropriate range. Specifically, the step of carrying out a polymerization degree reduction treatment is a step of reducing the degree of polymerization of fibrous cellulose having anionic groups and a fiber width of 100 μm or less to preferably 100 or more and 500 or less. The degree of polymerization of the fibrous cellulose obtained by the polymerization degree reduction treatment step is more preferably 110 or more, even more preferably 130 or more, still more preferably 150 or more, and more preferably 450 or less, even more preferably 400 or less, and still more preferably 350 or less.

[0108] Examples of the process for carrying out the polymerization degree reduction treatment include an ozone treatment process, an enzyme treatment process, a hypochlorous acid treatment process, a subcritical water treatment process, and a radiation irradiation treatment process. The process for carrying out the polymerization degree reduction treatment is preferably at least one selected from an ozone treatment process, an enzyme treatment process, a hypochlorous acid treatment process, a subcritical water treatment process, and a radiation irradiation treatment process, and is particularly preferably an ozone treatment process. Note that what is common to the ozone treatment process, the enzyme treatment process, the hypochlorous acid treatment process, the subcritical water treatment process, and the radiation irradiation treatment process is the reduction of the polymerization degree.

[0109] In the ozone treatment step, ozone is added to the fibrous cellulose dispersion (slurry). When adding ozone, it is preferable to add it as an ozone / oxygen mixed gas, for example. In this case, the ozone addition rate per 1 g of fibrous cellulose contained in the fibrous cellulose dispersion (slurry) is 1.0 × 10 －４ g or more, and 1.0 × 10 －３ The ozone addition rate per 1 g of fibrous cellulose is preferably 1.0 × 10 １ g or less, and 1.0 × 10 ０ g or less, and more preferably 1.0 × 10 －１ g or less, and more preferably 3.0 × 10 －２ g or less, and more preferably 1.5 × 10 －２ g or less, and more preferably 1.0 × 10 －２ g or less, and more preferably 6.0 × 10 －３ After adding ozone to the fibrous cellulose dispersion (slurry), it is preferable to stir the mixture at a temperature of 10°C to 50°C for 10 seconds to 10 minutes, and then leave it to stand for 1 minute to 100 minutes.

[0110] In the enzyme treatment step, an enzyme is added to a fibrous cellulose dispersion (slurry). The enzyme used here is preferably a cellulase enzyme. Cellulase enzymes are classified into the carbohydrate hydrolase family based on the higher-order structure of the catalytic domain that functions to hydrolyze cellulose. Cellulase enzymes are broadly classified into endo-glucanases and cellobiohydrolases based on their cellulose degradation properties. Endo-glucanases have high hydrolytic activity against the amorphous portion of cellulose, soluble cellooligosaccharides, and cellulose derivatives such as carboxymethylcellulose, randomly cleaving their molecular chains from the inside and reducing the degree of polymerization. In contrast, cellobiohydrolases decompose the crystalline portion of cellulose to produce cellobiose. Cellobiohydrolases hydrolyze cellulose from the end of the molecule and are also called exo- or processive enzymes. The enzyme used in the enzyme treatment step is not particularly limited, but it is preferable to use an endo-glucanase.

[0111] In the enzyme treatment step, the enzyme addition rate was 1.0 × 10 per 1 g of fibrous cellulose. －７ g or more, and preferably 1.0 × 10 －６ g or more, and more preferably 5.0 × 10 －６ g or more, and more preferably 1.0 × 10 －５ The enzyme addition rate is more preferably 1.0 × 10 per 1 g of fibrous cellulose. －２ After adding the enzyme to the fibrous cellulose dispersion (slurry), it is preferable to stir the mixture at a temperature of 30°C to 70°C for 1 minute to 10 hours, and then place the mixture at a temperature of 90°C or higher to inactivate the enzyme.

[0112] In the hypochlorite treatment step, sodium hypochlorite is added to the fibrous cellulose dispersion (slurry). The sodium hypochlorite addition rate is 1.0 × 10 per 1 g of fibrous cellulose. －４ g or more, and preferably 1.0 × 10 －３g or more, and more preferably 1.0 × 10 －２ The sodium hypochlorite addition rate is preferably 1.0×10 to 1 g of fibrous cellulose. ２ g or less, and preferably 1.0 × 10 １ g or less, and more preferably 3×10 ０ After adding sodium hypochlorite to the fibrous cellulose dispersion (slurry), the mixture is preferably stirred at a temperature of 10°C or higher and 50°C or lower for 1 minute or longer and 10 hours or shorter.

[0113] In the subcritical water treatment step, a fibrous cellulose dispersion (slurry) is subjected to high-temperature and high-pressure treatment to bring it to a subcritical state. The fibrous cellulose is hydrolyzed in the subcritical state. Specifically, the fibrous cellulose dispersion (slurry) is placed in a reaction vessel, and the temperature is increased to 150°C to 500°C, preferably 150°C to 350°C, and the pressure inside the reaction vessel is increased to 10 MPa to 80 MPa, preferably 10 MPa to 20 MPa. The heating and pressurizing time is preferably 0.1 seconds to 100 seconds, more preferably 0.3 seconds to 50 seconds.

[0114] After the above-described polymerization degree reduction treatment, a second defibration treatment step may be further carried out. The second defibration treatment step may be the same as the above-described defibration treatment step for obtaining fibrous cellulose.

[0115] [Fibrous Cellulose Water Dispersion] This embodiment also relates to a fibrous cellulose water dispersion (also referred to as a fibrous cellulose-containing slurry or slurry) obtained by dispersing the above-mentioned fibrous cellulose in a solvent containing water. The fibrous cellulose water dispersion may be, for example, a rubber modifier used to be added to a rubber component.

[0116] The content of fibrous cellulose in the fibrous cellulose aqueous dispersion is preferably 0.1% by mass or more and 8.0% by mass or less, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, still more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, and more preferably 7.0% by mass or less, even more preferably 6.0% by mass or less, and still more preferably 5.0% by mass or less, relative to the total mass of the fibrous cellulose aqueous dispersion. A fibrous cellulose content of at least the lower limit is preferred because the amount of fibrous cellulose blended in the aqueous dispersion is small and the dispersion is suitable for storage and transportation, while a fibrous cellulose content of at most the upper limit is preferred because the dispersion is easy to manufacture and the viscosity falls within an appropriate range.

[0117] The fibrous cellulose aqueous dispersion may contain, in addition to a water-containing solvent and the fibrous cellulose of the present embodiment, other additives such as antifoaming agents, lubricants, ultraviolet absorbers, dyes, pigments, stabilizers, surfactants, and preservatives (e.g., phenoxyethanol).

[0118] The fibrous cellulose of the present embodiment suppresses the decrease in water resistance when blended with the fibrous cellulose, compared to conventional fibrous cellulose in which the counter ion is an alkali metal ion. Therefore, the fibrous cellulose can be applied to various applications in which the decrease in water resistance when fibrous cellulose is added is a problem. Among these, it is preferably used as a reinforcing material for the purpose of improving mechanical properties such as tensile strength, and is preferably used as a rubber modifier added to a rubber component.

[0119] [Rubber Composition] The rubber composition of this embodiment contains the fibrous cellulose of this embodiment and a rubber component. <Rubber Component> In this embodiment, the rubber composition contains a rubber component in addition to the above-mentioned fibrous cellulose. 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.

[0120] 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.

[0121] In the rubber composition of this embodiment, the content of fibrous cellulose per 100 parts by mass of the rubber component is, from the viewpoint of good kneadability, preferably 0.1 part by mass or more and 200 parts by mass or less, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, still more preferably 15 parts by mass or more, and more preferably 150 parts by mass or less, even more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, and still more preferably 40 parts by mass or less. The content of fibrous cellulose per 100 parts by mass of the rubber component in 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 made into a crosslinked rubber product. Specifically, the content of fibrous cellulose may be increased in the rubber composition, and the content of fibrous cellulose per rubber component may be adjusted by adding a rubber component when preparing a rubber compound.

[0122] The total amount of fibrous cellulose and rubber components in the rubber composition is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and the upper limit is not particularly limited, but is 100% by mass or less.

[0123] In this embodiment, the rubber composition may contain other components in addition to the above-mentioned fibrous cellulose and rubber component. When the fibrous cellulose is fine fibrous cellulose, examples of other components include coarse cellulose fibers having a fiber width of more than 1 μm (1000 nm). The coarse cellulose fibers may be the microfibril cellulose of this embodiment, but may also be other fibers that do not fall under this category, such as coarse cellulose fibers that do not have anionic groups or that have anionic groups and a counter ion of NH ４ ＋ The coarse cellulose fibers contained in the rubber composition of this embodiment may be coarse cellulose fibers other than those mentioned above. The fiber width of the coarse cellulose fibers contained in the rubber composition of this embodiment is not particularly limited, but is, for example, preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more, even more preferably 10 μm or more, and more preferably 50 μm or less, and even more preferably 40 μm or less. The fiber width of the coarse cellulose fibers can be determined using a fiber length distribution measuring device (for example, FS5 manufactured by Valmet or L&W Fiber Tester Plus manufactured by ABB).

[0124] From the viewpoint of improving dispersibility in the rubber composition, the coarse cellulose fibers preferably have an ionic substituent, more preferably an anionic substituent. The preferred anionic substituents are the same as those for the fine fibrous cellulose, and the preferred ranges of the type and amount of the substituent are also the same.

[0125] When the rubber composition contains coarse cellulose fibers, the content of the coarse cellulose fibers per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more and 80 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 50 parts by mass or less, and even more preferably 20 parts by mass or less. Furthermore, when the rubber composition contains coarse cellulose fibers, the content of the coarse cellulose fibers per 100 parts by mass of the total of the fine fibrous cellulose and the coarse cellulose fibers is preferably 1 part by mass or more and 95 parts by mass or less, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and preferably 90 parts by mass or less, and more preferably 85 parts by mass or less. When the content of the coarse cellulose fibers is within the above range, coarse cellulose fibers can be produced more inexpensively than fine fibrous cellulose, and therefore a rubber composition can be produced more inexpensively, and which has excellent kneadability and excellent physical properties after crosslinking, which is preferable.

[0126] 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.

[0127] <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 dispersion containing at least a rubber component and fibrous cellulose and removing the dispersion medium from the dispersion. In the above-mentioned production method, it is preferable to first mix the fibrous cellulose and the rubber component to prepare a dispersion of the mixture in an aqueous medium (hereinafter also simply referred to as a "dispersion of the mixture"). That is, the method for producing the rubber composition of this embodiment preferably includes the following steps (I) and (II): (I) a mixing step of mixing the aqueous dispersion containing the fibrous cellulose of this embodiment with rubber latex to obtain a mixture A; and (II) a heating step of heating and drying the mixture A to obtain a rubber composition.

[0128] Specifically, fibrous cellulose and a rubber component can be mixed and dispersed in an aqueous medium to obtain a dispersion of the mixture. Alternatively, a mixture can be obtained by mixing an aqueous dispersion of fibrous cellulose (e.g., the above-described aqueous fibrous cellulose dispersion) with an aqueous dispersion of a rubber component (rubber latex). Among these, it is preferable to mix a dispersion of fibrous cellulose (aqueous fibrous cellulose dispersion) with an aqueous dispersion of a rubber component (rubber latex) to obtain a dispersion containing fibrous cellulose and a rubber component (mixture 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 a dispersion of the mixture, thorough mixing of the fibrous cellulose and the rubber component tends to improve the physical properties after crosslinking.

[0129] 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.

[0130] The solids concentration (by mass) of the mixture dispersion 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 mixture dispersion is within the above range, the amount of energy required to remove 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 cross-linked product.

[0131] 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)

[0132] The rubber composition is obtained by heating and drying the resulting mixture dispersion (mixture A) as shown in step (II) above. The heating and drying method is not particularly limited, and examples thereof include a method of coating the mixture dispersion on a substrate and a method of drying using a drum dryer. In the coating method, for example, a dispersion of a mixture containing fibrous cellulose and a rubber component 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 mixture dispersion can suppress shrinkage of the sheet during drying, and it is preferable to select a substrate from which the sheet formed after drying can be easily peeled off. Among these, resin films or plates or metal films or 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, as well as those with oxidized surfaces; stainless steel films and plates; and brass films and plates. In coating methods, 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. While the damming frame is not particularly limited, 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 plates whose surfaces have been oxidized, and molded stainless steel plates, brass plates, etc. The coater used to coat the dispersion of the mixture on the substrate is not particularly limited, and examples of applicable machines 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.

[0133] The temperature of the mixture dispersion and the ambient temperature when coating the mixture dispersion onto a substrate (hereinafter, the mixture dispersion temperature and 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 above the lower limit, the mixture dispersion can be more easily coated. If the coating temperature is below the 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 coat the mixture dispersion onto a substrate so that the finished basis weight and thickness of the sheet are within the preferred ranges described above.

[0134] The mixture dispersion 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 medium (generally steam) is introduced into the interior of a rotating cylinder 1 (drum), and the mixture dispersion is introduced into a feed section 2. The introduced mixture dispersion forms a sheet-like mixture 3 and adheres to the surface of the heated cylinder 1, which is then 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.

[0135] 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 mixture. 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, a rubber composition can be obtained that has good production efficiency, excellent kneading properties, and excellent physical properties after crosslinking.

[0136] 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.

[0137] 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.

[0138] 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]. 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.

[0139] 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.

[0140] In the preparation of the rubber composition, it is believed that some or all of the ammonium ions that the fibrous cellulose has as counter ions of the anionic groups are dissociated by heating or the like. Therefore, some or all of the counter ions are converted into protons (H ＋ ) may be substituted.

[0141] [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.

[0142] 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).

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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 2 parts by mass or more and 8 parts by mass or less, per 100 parts by mass of the rubber component.

[0148] [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 and crosslinked rubber product 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 30 parts by mass or less, and even more preferably 20 parts by mass or less, from the viewpoint of improving water resistance and mechanical properties.

[0149] 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.

[0150] 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.

[0151] [Crosslinked Rubber and Crosslinked Rubber Product] The crosslinked rubber of this embodiment is obtained by crosslinking a rubber compound containing a crosslinking agent. Furthermore, by molding during crosslinking, a crosslinked rubber product can be obtained. That is, the crosslinked rubber product is obtained by crosslinking and molding a rubber compound prepared from a rubber composition containing the fibrous cellulose of this embodiment. The method for producing a crosslinked rubber product of the present invention may further include a step of molding the rubber compound obtained in the kneading step into a desired shape (molding step). Molding in this molding step can be performed by various molding methods using an extruder, calendar roll, press, injection molding machine, transfer molding machine, blow molding machine, foam molding machine, etc. 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.

[0152] 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 composition 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.

[0153] In the present embodiment, the water absorption of the crosslinked rubber composition and the crosslinked rubber product is preferably low, specifically, preferably 24.0% or less, more preferably 22.0% or less, even more preferably 20.0% or less, still more preferably 18.0% or less, even more preferably 16.0% or less, and even more preferably 14.0% or less, with no particular lower limit, being 0% or more. The water absorption is measured by the method described in the Examples.

[0154] <Applications> The crosslinked rubber product of the present embodiment can be used for rubber parts such as, but not limited to, automotive rubber members, hose materials, gaskets, rubber rolls, industrial cables, industrial conveyor belts, shoe soles, and vibration-proof rubber. Examples of automotive rubber members include tires, automotive gaskets, automotive oil seals, automotive packing, automotive rubber hoses, V-belts, and automotive vibration-proof rubber.

[0155] 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.

[0156] <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. ２A sheet-form 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 completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0157] The infrared absorption spectrum of the obtained phosphorylated pulp was measured using FT-IR. －１ Absorption 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 was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0158] 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 treated twice with a wet pulverization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion A containing fine fibrous cellulose. The fiber width of the resulting fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm.

[0159] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described below in [Measurement of amount of phosphorus oxo acid group] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0160] <Production Example 2> [TEMPO Oxidation Treatment] Softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to an alkaline TEMPO oxidation treatment as follows. First, 100 parts by mass of the raw material pulp (dry mass equivalent), 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were dispersed in 10,000 parts by mass of water. Next, a 13% by mass aqueous solution of sodium hypochlorite was added to 10 mmol per 1.0 g of pulp to initiate the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to maintain the pH at 10 to 10.5. The reaction was considered to be complete when no further change in pH was observed.

[0161] The resulting TEMPO-oxidized pulp was then washed. The pulp slurry after TEMPO oxidation was dehydrated to obtain a dehydrated sheet, to which 5,000 parts by mass of ion-exchanged water was poured, stirred to uniformly disperse the pulp, and then filtered and dehydrated. This process was repeated. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0162] The remaining aldehyde groups in this dehydrated sheet were further oxidized as follows: 100 parts by weight of the dehydrated sheet (dry mass equivalent) was dispersed in 10,000 parts by weight of 0.1 mol / L acetate buffer (pH 4.8). 113 parts by weight of 80% by weight sodium chlorite was then added. The container was immediately sealed and then stirred at 500 rpm using a magnetic stirrer for 48 hours at room temperature to obtain a pulp slurry.

[0163] The resulting TEMPO-oxidized pulp was then washed. The washing process consisted of dehydrating the pulp slurry after the additional oxidation to obtain a dehydrated sheet, pouring 5,000 parts by mass of ion-exchanged water into the sheet, stirring to uniformly disperse the pulp, and then filtering and dehydrating the sheet. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0164] This TEMPO-oxidized pulp was subjected to the following treatment to replace the counter ions of the carboxyl groups with hydrogen ions. The washed TEMPO-oxidized pulp was impregnated with 12 N hydrochloric acid and reacted at room temperature for 60 minutes. The hydrochloric acid-impregnated pulp was dehydrated to obtain a dehydrated sheet, after which 5,000 parts by mass of 1 N hydrochloric acid was poured into the sheet, which was stirred to disperse uniformly and then filtered and dehydrated.

[0165] The resulting TEMPO-oxidized pulp was then washed. 100 g (bone dry mass) of TEMPO-oxidized pulp was mixed with 10 L of ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then repeatedly filtered and dehydrated. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0166] The resulting hydrogen ion-exchanged TEMPO-oxidized pulp was then subjected to the following treatment to replace the counter ions of the carboxyl groups with ammonium ions. The washed hydrogen ion-exchanged TEMPO-oxidized pulp was immersed in 15N ammonia water and allowed to react at room temperature for 60 minutes. The ammonia water-impregnated pulp was dehydrated to obtain a dehydrated sheet, after which 5,000 parts by mass of ion-exchanged water was poured into the sheet, which was stirred to uniformly disperse the sheet, and the sheet was filtered and dehydrated. This washing process was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less, marking the end point of the washing.

[0167] The carboxyl group content of the resulting TEMPO-oxidized pulp, as measured by the method described below, was 1.80 mmol / g. Furthermore, when the resulting TEMPO-oxidized pulp was 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.

[0168] Ion-exchanged water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated twice in a wet atomizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion B containing fine fibrous cellulose.

[0169] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxy groups in the obtained fine fibrous cellulose, as measured by the method described below, was 1.80 mmol / g.

[0170] <Production Example 3> The same procedure as in Production Example 1 was carried out except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate, thereby obtaining a fine fibrous cellulose dispersion C containing phosphite pulp and fine fibrous cellulose.

[0171] The infrared absorption spectrum of the obtained phosphited pulp was measured using FT-IR. －１ Absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed near the peak, confirming that a phosphorous acid group (phosphonic acid group) had been added to the pulp. Furthermore, when the obtained phosphorous-oxidized pulp was 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 phosphorous acid groups (amount of first dissociated acid) measured by the measurement method described below in [Measurement of phosphorous oxo acid group amount] was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0172] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphorous groups (amount of first dissociated acid) of the obtained fine fibrous cellulose, measured by the measurement method described below in "Measurement of phosphorus oxo acid group amount," was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0173] <Production Example 4> The same operations as in Production Example 1 were carried out, except that 38 parts by mass of amidosulfuric acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate and the heating time was extended to 20 minutes, to obtain a fine fibrous cellulose dispersion D containing sulfated pulp and fine fibrous cellulose.

[0174] The infrared absorption spectrum of the obtained sulfated pulp was measured using FT-IR. －１ Absorption due to S=O of sulfate ester groups was observed around 2θ=14° to 17° and 2θ=22° to 23°, confirming that sulfate ester groups were added to the pulp. Furthermore, when the obtained sulfated pulp was 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 sulfate ester groups measured by the method described below in [Measurement of sulfate ester group amount] was 1.47 mmol / g.

[0175] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of sulfate ester groups in the obtained fine fibrous cellulose, as measured by the method described below, was 1.47 mmol / g.

[0176] <Production Example 5> [Carboxymethylation] As a raw material pulp, softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. was used. ２A sheet-like product having a Canadian Standard Freeness (CSF) of 700 mL when disintegrated according to JIS P 8121-2:2012 was used.

[0177] To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 83 parts by mass of 12N NaOH aqueous solution, 175 parts by mass of sodium monochloroacetate, and 313 parts by mass of ion-exchanged water (571 parts by mass in total) was added, yielding a chemical-impregnated pulp. The resulting chemical-impregnated pulp was then heated in a water bath at 95°C for 60 minutes to introduce carboxymethyl groups (carboxy groups) into the cellulose in the pulp, yielding a carboxymethyl-group-introduced pulp.

[0178] The resulting carboxymethyl-group-introduced pulp was then washed. The resulting carboxymethyl-group-introduced pulp was washed by pouring ion-exchanged water over the resulting carboxymethyl-group-introduced pulp to obtain a pulp dispersion. The resulting pulp was stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0179] This carboxymethyl-group-introduced pulp was treated in the same manner as in Production Example 2, and the counter ions of the carboxy groups were replaced with ammonium ions. The amount of carboxy groups in the resulting carboxymethyl-group-introduced pulp, as measured by the measurement method described below, was 1.21 mmol / g. Furthermore, when the carboxymethyl-group-introduced pulp was 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.

[0180] Ion-exchanged water was added to the obtained carboxymethyl group-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated twice in a wet atomizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion E containing fine fibrous cellulose.

[0181] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxy groups in the obtained fine fibrous cellulose, as measured by the method described below, was 1.21 mmol / g.

[0182] <Production Example 6> [Hypochlorous Acid Oxidation] A sheet (solid content concentration 90% by mass) made from bleached softwood kraft pulp (NBKP) was mixed with a hand mixer (Lab Millser PLUS, manufactured by Osaka Chemical Co., Ltd.) at 20,000 rpm for 15 seconds to produce a fluffy fluffed pulp (solid content concentration 90% by mass). Sodium hypochlorite pentahydrate was then added to ion-exchanged water to prepare an aqueous solution with a sodium hypochlorite solid content concentration of 22% by mass. 9,000 parts by mass of a 22% by mass aqueous sodium hypochlorite solution was added to 100 parts by mass of the fluffy fluffed pulp, and the mixture was allowed to react for 2 hours while adjusting the temperature in a warm bath to 30°C, yielding a carboxyl-introduced pulp. During the reaction, a 1N aqueous sodium hydroxide solution was added as needed to maintain the pH at 11.

[0183] The resulting carboxylated pulp was then washed. The washing was performed by pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, stirring the resulting dispersion to uniformly disperse the pulp, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0184] This carboxyl group-introduced pulp was treated in the same manner as in Production Example 2 to replace the counter ions of the carboxyl groups with ammonium ions.

[0185] The amount of carboxy groups in the resulting carboxy-introduced pulp was 0.70 mmol / g, as measured by the method described below. The resulting carboxy-introduced pulp was analyzed using an X-ray diffractometer, revealing typical peaks at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0186] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated twice in a wet atomizer at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion F containing fine fibrous cellulose.

[0187] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxy groups in the obtained fine fibrous cellulose, as measured by the method described below, was 0.70 mmol / g.

[0188] <Production Example 7> In Production Example 1, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous sodium hydroxide solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated and washed to obtain a neutralized phosphorylated pulp. A fine fibrous cellulose dispersion G was obtained in the same manner as in Production Example 1, except that this phosphorylated pulp was used.

[0189] <Production Example 8> A fine fibrous cellulose dispersion H was obtained in the same manner as in Production Example 2, except that the hydrogen ion substitution treatment and the ammonium ion substitution treatment were omitted.

[0190] <Production Example 9> A fine fibrous cellulose dispersion I was obtained in the same manner as in Production Example 3, except that the same neutralization treatment as in Production Example 7 was carried out.

[0191] <Production Example 10> A fine fibrous cellulose dispersion J was obtained in the same manner as in Production Example 4, except that the same neutralization treatment as in Production Example 7 was carried out.

[0192] <Production Example 11> A fine fibrous cellulose dispersion K was obtained in the same manner as in Production Example 7, except that a tetrabutylammonium hydroxide solution was used instead of the aqueous sodium hydroxide solution.

[0193] <Production Example 12> Ion-exchanged water was added to the washed phosphorylated pulp in Production Example 1 to prepare a slurry with a solids concentration of 2% by mass. This slurry was processed 20 times in a single-disc refiner with a clearance set to 600 μm for defibration treatment, thereby obtaining microfibril cellulose dispersion A. The fiber width of the microfibril cellulose in dispersion A was 25.3 μm.

[0194] <Production Example 13> The microfibril cellulose dispersion A obtained in Production Example 12 was treated once with a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 150 MPa to obtain microfibril cellulose dispersion B. The fiber width of the microfibril cellulose in dispersion B was 20.3 μm.

[0195] Production Example 14 The same treatment as in Production Example 12 was carried out except that the phosphorylated pulp obtained in Production Example 7 was used, to obtain a microfibril cellulose dispersion C. The fiber width of the microfibril cellulose in the dispersion C was 17.4 μm.

[0196] [Measurement] The methods for measuring the content of each ionic group and fiber width are as follows. [Measurement of the amount of phosphorus oxoacid groups] To measure the amount of phosphorus oxoacid groups (amount of phosphate groups or amount of phosphite groups) in fibrous cellulose, ion-exchanged water was first added to the target fibrous cellulose to prepare a slurry with a solids concentration of 0.2% by mass. The resulting fibrous cellulose dispersion was treated with an ion exchange resin, followed by titration with an alkali. The ion exchange resin treatment was performed by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the fibrous cellulose dispersion, shaking for 1 hour, and then pouring the mixture onto a 90 μm mesh to separate the resin from the slurry. The alkali titration was performed by adding 10 μL of 0.1 N aqueous sodium hydroxide solution to the fibrous cellulose-containing slurry after the ion exchange resin treatment, and 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 derivative of pH with respect to the amount of alkali added) were observed on a plot of the measured pH against the amount of alkali added. The first maximum point of increment after starting the addition of alkali is called the first endpoint, and the next maximum point of increment is called the second endpoint (Figure 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 for titration. 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 for titration. The amount of alkali required from the start of the titration to the first endpoint (mmol) divided by the solids content (g) in the slurry to be titrated was used as the amount of phosphorus oxo acid group (amount of first dissociated acid) (mmol / g). The amount of alkali (mmol) required from the start of titration to the second end point was divided by the solid content (g) in the slurry to be titrated, and the resulting value was taken as the total amount of dissociated acid (mmol / g).

[0197] [Measurement of Carboxy Group Amount] The carboxyl group amount of fibrous cellulose was measured by adding ion-exchange water to a fibrous cellulose dispersion containing the target fibrous cellulose to adjust the content to 0.2% by mass, treating with ion exchange resin, and then titrating with alkali. The ion-exchange resin treatment was performed by adding 1 / 10 by volume of a strongly acidic ion-exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a 0.2% by mass fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring the mixture onto a 90 μm mesh to separate the resin and slurry. The alkali titration was performed by adding 0.1 N aqueous sodium hydroxide to the fibrous cellulose-containing slurry after the ion-exchange resin treatment and measuring the change in pH of the slurry. Observing the change in pH while adding aqueous sodium hydroxide resulted in a titration curve as shown in Figure 2. As shown in Figure 2, in this neutralization titration, a single point is observed where the increment (the differential value of pH with respect to the amount of alkali added) is maximum on the curve plotting the measured pH against the amount of alkali added. This maximum increment is called the first end point. Here, the region from the start of titration to the first end point in Figure 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali introduced (mmol / g) was then calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solids content (g) in the fine fibrous cellulose-containing slurry to be titrated.

[0198] [Measurement of the amount of sulfur oxoacid groups or sulfonic groups] The amount of sulfur oxoacid groups or sulfonic groups in fibrous cellulose was measured by wet ashing the fibrous cellulose with 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 was divided by the bone dry mass of the fibrous cellulose tested, and the resulting value was taken as the amount of sulfur oxoacid groups or sulfonic groups (unit: mmol / g).

[0199] (Measurement of fiber width) The fiber width of microfibril cellulose is the number average fiber width measured using a fiber length measuring instrument (FS-5, manufactured by Valmet Co., Ltd.) The fiber width of fine fibrous cellulose is the number average fiber width measured using a transmission electron microscope.

[0200] Example 1 The fine fibrous cellulose dispersion A obtained in Production Example 1 was charged into a vessel so that the solid content of the fine fibrous cellulose was 20 parts by mass, and then ion-exchanged water was charged so that the solid content concentration of the fine fibrous cellulose 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 fine fibrous cellulose dispersion.

[0201] [Mixing Step] An aqueous dispersion of natural rubber latex (ULACOL, manufactured by Resitex Corporation, ammonia amount less than 0.1%) having a solids concentration of 61% by mass was added to the obtained 1.0% by mass fine fibrous cellulose dispersion so that the solids content of the rubber component was 100 parts by mass. A tornado stirrer equipped with a stirring blade having a diameter of 6 inches was used as the stirrer, and stirring was carried out at 1000 rpm for 5 minutes to obtain a mixed solution containing fine fibrous cellulose / natural rubber latex.

[0202] [Drying Step] The obtained mixed liquid containing fine fibrous cellulose / natural rubber latex was spread on a tray whose surface was treated with Teflon (registered trademark) so that the thickness after drying would be 0.05 mm, and the mixture was dried in an explosion-proof dryer at 40°C for 48 hours to obtain a sheet-like rubber composition containing fine fibrous cellulose / natural rubber.

[0203] [Preparation of Rubber Compound] The obtained rubber composition containing fine fibrous cellulose / natural rubber was masticated for 10 minutes using an open roll (6-inch two-roll mill, manufactured by Daihan Co., Ltd.) 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 a vulcanization accelerator (zinc oxide type 2, manufactured by Seido Chemical Industry Co., Ltd.), and 1.5 parts by mass of an antioxidant (ANTAGE MB, ANTAGE RD, manufactured by Kawaguchi Chemical Industry Co., Ltd.) were added to 100 parts by mass of the rubber component, and kneaded for 6 minutes to obtain a rubber compound having a thickness of about 2 mm or more.

[0204] [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.

[0205] Example 2 A sheet-shaped rubber composition containing fine fibrous cellulose and natural rubber was obtained by treating in the same manner as in Example 1. In the [Preparation of Rubber Compound] using the obtained rubber composition, 1.5 parts by mass of sulfur (Mucron OT-20, manufactured by Shikoku Chemical Industry Co., Ltd.), 2 parts by mass of a vulcanization accelerator aid, 2 parts by mass of an antioxidant (ANTAGE RD), 2 parts by mass of stearic acid (Stearic Acid 50S, manufactured by New Japan Chemical Co., Ltd.), and 2 parts by mass of a vulcanization accelerator (Noccela MSA-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added per 100 parts by mass of the rubber component. A rubber compound was obtained in the same manner as in Example 1. In the [Crosslinking Step], a 2 mm-thick sheet of the crosslinked rubber composition was produced by press-heating at 150°C for 10 minutes.

[0206] Example 3 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion B was used instead of the fine fibrous cellulose dispersion A.

[0207] Example 4 The same treatment as in Example 1 was carried out except that the fine fibrous cellulose dispersion C was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0208] Example 5 The same treatment as in Example 1 was carried out except that the fine fibrous cellulose dispersion D was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0209] Example 6 The same treatment as in Example 1 was carried out except that the fine fibrous cellulose dispersion E was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0210] Example 7 The same treatment as in Example 1 was carried out except that the fine fibrous cellulose dispersion F was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0211] Example 8 A sheet of a crosslinked rubber composition was obtained by the same treatment as in Example 1, except that an aqueous dispersion of modified natural rubber latex (MG-10, solid content concentration 54 mass%, manufactured by Resitex Corporation, modified natural rubber latex graft-polymerized with methyl methacrylate) was used instead of the aqueous dispersion of natural rubber latex.

[0212] Example 9 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 1, except that an aqueous dispersion of natural rubber latex (LA-LATEX, solid content concentration 61.5% by mass, manufactured by Resitex Corporation, ammonia amount less than 0.3%) was used.

[0213] Example 10 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 1, except that an aqueous dispersion of natural rubber latex (HA-LATEX, solid content concentration 61.5% by mass, manufactured by Resitex Corporation, ammonia amount approximately 0.7%) was used.

[0214] Example 11 The same treatment as in Example 8 was carried out except that the microfibril cellulose dispersion A was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0215] Example 12 The same treatment as in Example 9 was carried out except that the microfibril cellulose dispersion A was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0216] Example 13 The same treatment as in Example 10 was carried out except that the microfibril cellulose dispersion A was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0217] Example 14 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 13, except that the microfibril cellulose dispersion B was used instead of the microfibril cellulose dispersion A.

[0218] Example 15 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 2, except that an aqueous dispersion of modified natural rubber latex (MG-10, solid content concentration 54 mass%, manufactured by Resitex Co., Ltd.) was used instead of the aqueous dispersion of natural rubber latex.

[0219] Example 16 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 2, except that an aqueous dispersion of natural rubber latex (HA-LATEX, solid content concentration 61.5% by mass, manufactured by Resitex Co., Ltd.) was used.

[0220] Example 17 A sheet of a crosslinked rubber composition was obtained by the same treatment as in Example 15, except that microfibril cellulose dispersion A was used instead of fine fibrous cellulose dispersion A, and an aqueous dispersion of natural rubber latex (LA-LATEX, solid content concentration 61.5% by mass, manufactured by Resitex Co., Ltd.) was used.

[0221] Example 18 The same treatment as in Example 16 was carried out except that the microfibril cellulose dispersion A was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0222] Comparative Example 1 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion G was used instead of the fine fibrous cellulose dispersion A.

[0223] Comparative Example 2 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 2, except that the fine fibrous cellulose dispersion G was used instead of the fine fibrous cellulose dispersion A.

[0224] Comparative Example 3 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion H was used instead of the fine fibrous cellulose dispersion A.

[0225] Comparative Example 4 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion I was used instead of the fine fibrous cellulose dispersion A.

[0226] Comparative Example 5 The same treatment as in Example 1 was carried out except that the fine fibrous cellulose dispersion J was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0227] Comparative Example 6 The same treatment as in Example 1 was carried out except that the fine fibrous cellulose dispersion K was used instead of the fine fibrous cellulose dispersion A, to obtain a sheet of a crosslinked rubber composition.

[0228] Comparative Example 7 A sheet of a crosslinked rubber composition was obtained in the same manner as in Comparative Example 1, except that an aqueous dispersion of natural rubber latex (HA-LATEX, solid content concentration 61.5% by mass, manufactured by Resitex Co., Ltd.) was used.

[0229] Comparative Example 8 The same treatment as in Comparative Example 7 was carried out except that the microfibril cellulose dispersion C was used instead of the fine fibrous cellulose dispersion G, to obtain a sheet of a crosslinked rubber composition.

[0230] Comparative Example 9 A sheet of a crosslinked rubber composition was obtained in the same manner as in Comparative Example 2, except that an aqueous dispersion of natural rubber latex (HA-LATEX, solid content concentration 61.5% by mass, manufactured by Resitex Co., Ltd.) was used.

[0231] Comparative Example 10 The same treatment as in Comparative Example 9 was carried out except that the microfibril cellulose dispersion C was used instead of the fine fibrous cellulose dispersion G, to obtain a sheet of a crosslinked rubber composition.

[0232] Reference Example 1 A sheet of a crosslinked rubber composition was obtained in the same manner as in Example 1, except that natural rubber latex was used instead of the mixed liquid containing fine fibrous cellulose / natural rubber latex.

[0233] Reference Example 2 A sheet-shaped natural rubber composition was obtained in the same manner as in Reference Example 1. Except for using the obtained natural rubber composition, the same treatment as in Example 2 was performed to obtain a sheet of crosslinked rubber composition.

[0234] Reference Example 3 A sheet of a crosslinked rubber composition was obtained by the same treatment as in Example 1, except that in [Preparation of rubber compound] in Example 1, natural rubber (RSS#3, manufactured by Koshigaya Rubber Industry Co., Ltd.) was used instead of the rubber composition containing fine fibrous cellulose / natural rubber.

[0235] [Measurement and Evaluation] <Water Absorption Test> For the sheets of the crosslinked rubber compositions obtained in Examples 1 to 18, Comparative Examples 1 to 10, and Reference Examples 1 to 3, test specimens were punched into the shape of a dumbbell (dumbbell No. 6) as described in JIS K 6251:2017. The mass of each test specimen was measured in a 23°C, 50% RH environment according to JIS K 7209A Method:2000, and then the specimen was immersed in ion-exchanged water at 70°C for 48 hours. The mass was measured after wiping off the surface moisture. The water absorption was calculated according to the following formula: Water absorption (%) = (W - Wo) / Wo × 100 (where Wo is the mass in a 23°C, 50% RH environment, and W is the mass after immersion in ion-exchanged water for 48 hours).

[0236] <Tensile Test Under Humidity-Controlled Conditions> For the sheets of the crosslinked rubber compositions obtained in Examples 1 to 18, Comparative Examples 1 to 10, and Reference Examples 1 to 3, test specimens were punched into dumbbell shapes (dumbbell No. 6) according to JIS K 6251:2017. Tensile tests were performed on the specimens using a universal testing machine (manufactured by Shimadzu Corporation) at 23±2°C, a gauge length of 20 mm, and a tensile speed of 500 mm / min according to JIS K 6251:2017, to measure the 50% modulus (σ50 (MPa)), 100% modulus (σ100 (MPa)), 300% modulus (σ300 (MPa)), strength (tensile strength (MPa)), and fracture E (J). Note that fracture E is the area of ​​the SS curve (stress-strain curve).

[0237] <Water Resistance Test> After measuring the mass of the immersed test piece used in the [Water Absorption Test], a tensile test was immediately performed using a universal testing machine (manufactured by Shimadzu Corporation) at 23±2°C, a gauge length of 20 mm, and a tensile speed of 500 mm / min in accordance with JIS K 6251:2017, to measure the 50% modulus (σ50 (MPa)), 100% modulus (σ100 (MPa)), 300% modulus (σ300 (MPa)), strength (tensile strength (MPa)), and fracture E (J) under water absorption conditions. Water resistance was evaluated based on the ratio of each physical property under water absorption conditions to each physical property under humidity-controlled conditions. It is preferable that the water absorption rate is low, and the ratio of each property under water absorption conditions to each property under humidity control conditions, i.e., 50% modulus (σ50 (MPa)), 100% modulus (σ100 (MPa)), 300% modulus (σ300 (MPa)), strength (tensile strength (MPa)), and fracture E (J), is preferably close to 1.0. The above measurement results are shown in Table 1 below.

[0238]

[0239] In Table 1, "PO" represents dicumyl peroxide as a crosslinking agent, and "S" represents sulfur. Furthermore, in the evaluation of physical properties after crosslinking, "after / before" represents the ratio of each physical property under water absorption conditions to each physical property under humidity-controlled conditions. From the results in Table 1, the crosslinked rubbers (crosslinked rubber products) obtained in the Examples had lower water absorption and better water resistance than the crosslinked rubbers of the Comparative Examples. Furthermore, the ratios of the 50% modulus (σ50 (MPa)), 100% modulus (σ100 (MPa)), 300% modulus (σ300 (MPa)), strength (tensile strength (MPa)), and fracture E (J) before and after water absorption were also greater than those of the Comparative Examples, indicating that deterioration of physical properties was suppressed. The above effects were the same whether the crosslinking was by peroxide crosslinking or sulfur crosslinking. Furthermore, the same effects were observed whether the anionic group was a phosphate group, a carboxy group (TEMPO oxidation, hypochlorous acid oxidation), a phosphite group, a sulfate group, or a carboxymethyl group. Further, in Reference Example 1, the tensile strength under humidified conditions was 5.3 MPa, and in Example 1, it was 15.1 MPa. Similarly, in Reference Example 2, the tensile strength under humidified conditions was 13.8 MPa, and in Example 2, it was 17.5 MPa. Thus, the addition of fibrous cellulose significantly improved the tensile strength. As shown in the comparative example, when the counter ion was a sodium ion (Na ＋ ) the water absorption rate was high and the deterioration of various physical properties was also significant.

[0240] The fibrous cellulose of the present embodiment is effective as a rubber modifier, and is less susceptible to deterioration of physical properties due to water absorption than when conventional fibrous cellulose is added. Therefore, it is expected to be used as an additive for various rubber products.

[0241] 10... double drum dryer, 1... cylinder, 2... feed section, 3... sheet-like mixture, 4... scraper, 5... composite material

Claims

1. Fibrous cellulose having an anionic group and a fiber width of 100 μm or less, wherein the counter ion of the anionic group is an ammonium ion (NH ４ ＋ ) fibrous cellulose.

2. The fibrous cellulose according to claim 1, which is a fine fibrous cellulose having a fiber width of 1000 nm or less.

3. The fibrous cellulose according to claim 1, which is microfibril cellulose having a fiber width of more than 1 μm and not more than 100 μm.

4. The fibrous cellulose according to claim 2 or 3, wherein the anionic group is at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group.

5. A fibrous cellulose aqueous dispersion containing the fibrous cellulose according to claim 2 or 3.

6. A rubber composition comprising a rubber component and the fibrous cellulose according to claim 2 or 3 blended therein.

7. The rubber composition according to claim 6, wherein the content of the fibrous cellulose is 0.1 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the rubber component.

8. The rubber composition according to claim 6, wherein the rubber component is a diene rubber.

9. A crosslinked rubber product obtained by crosslinking and molding a rubber compound containing the rubber composition according to claim 6 and a crosslinking agent.

10. The crosslinked rubber product according to claim 9, which is a tire.

11. A method for producing a rubber composition, comprising the following steps (I) and (II): (I) a mixing step of mixing the aqueous dispersion containing fibrous cellulose according to claim 2 or 3 with rubber latex to obtain a mixture A; and (II) a heating step of heating and drying the mixture A to obtain a rubber composition.

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