Rubber composite material, rubber compound, crosslinked rubber composition, and method for manufacturing rubber composite material, rubber compound, and crosslinked rubber composition

Abstract

The present invention pertains to providing: a rubber composite material from which a crosslinked rubber composition having excellent water resistance can be obtained; a rubber compound obtained by using the rubber composite material; a crosslinked rubber composition obtained by crosslinking the rubber compound; and a method for manufacturing a rubber composite material, a rubber compound, and a crosslinked rubber composition.　The rubber composite material according to the present invention contains the following components (A), (B), and (Cm), component (A) being a rubber component, component (B) being a fibrous cellulose having an anionic group, and component (Cm) being a metal element belonging to any of groups 2 to 14 of the periodic table, wherein the content of the component (Cm) in the rubber composite material is from 0.02 mol / kg to 1 mol / kg, and the content of a sodium element in the rubber composite material is 0.20 mol / kg or less.

Description

Rubber composite material, rubber compound, and crosslinked rubber composition, and method for producing rubber composite material, rubber compound, and crosslinked rubber composition

[0001] The present invention relates to a rubber composite material, a rubber compound, and a crosslinked rubber composition, and a method for producing a rubber composite material, a rubber compound, and a crosslinked rubber composition.

[0002] In recent years, due to the replacement of petroleum resources and the increasing environmental awareness, materials using renewable natural fibers have attracted attention. Among natural fibers, fibrous cellulose having a fiber diameter of 10 μm or more and 50 μm or less, particularly fibrous cellulose (pulp) derived from wood, has been widely used mainly as paper products.

[0003] As fibrous cellulose, microfibrillar cellulose having an average fiber width of 1,000 nm or less is also known. Microfibrillar 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 microfibrillar cellulose has been promoted. Further, it has also been studied to use a composite material in which microfibrillar cellulose is combined with a resin emulsion and / or a rubber latex.

[0004] Patent Document 1 aims to provide a nanocellulose masterbatch capable of obtaining a rubber composition in which nanocellulose is homogeneously dispersed, viscosity increase is suppressed, and both tensile stress and elongation are excellent, and describes a nanocellulose masterbatch containing a rubber component, nanocellulose surface-treated with a resol-type and / or novolac-type resorcinol-formaldehyde initial condensate and formaldehyde, and a dispersant, wherein the rubber component mainly contains natural rubber or styrene-butadiene copolymer rubber, and A nanocellulose masterbatch is disclosed, wherein the dispersant is a mixture of fatty acid derivatives mainly comprising a metal soap, or a mixture of fatty acid derivatives containing a fatty acid amide or fatty acid ester, and the masterbatch contains 0.3 to 60 parts by mass of the nanocellulose and 0.5 to 10 parts by mass of the dispersant per 100 parts by mass of the rubber component, and contains 0.008 to 1.2 parts by mass of the resol-type and / or novolac-type resorcinol-formaldehyde initial condensate and 0.002 to 0.8 parts by mass of the formaldehyde per 1 part by mass of the nanocellulose.

[0005] Furthermore, Patent Document 2 discloses a rubber composition comprising the following components (A) to (D) for the purpose of providing a rubber composition with good strength that includes a rubber component and cellulose fibers: (A) component: modified cellulose nanofiber; (B) component: surfactant; (C) component: polyvalent metal; and (D) component: rubber component.

[0006] Furthermore, Patent Document 3 discloses a rubber composition for golf balls that does not require the use of expensive fibrous materials or other compounding agents and can further improve durability, characterized by containing (I) a base rubber, (II) an unsaturated carboxylic acid and / or its metal salt, (III) a crosslinking initiator, and (IV) cellulose nanofibers.

[0007] Furthermore, Patent Document 4 discloses a method for manufacturing a fiber material with excellent processability for compounding cellulose nanofibers, comprising: a mixing step of mixing oxidized cellulose nanofibers, a sodium-free metal salt, and an aqueous solvent to obtain a CNF dispersion; a drying step of reducing the aqueous solvent from the CNF dispersion obtained in the mixing step to obtain a fiber precursor; and a washing step of washing the fiber precursor obtained in the drying step with water to obtain a fiber material in which the amount of sodium element derived from the cellulose nanofibers is reduced compared to the fiber precursor, wherein the metal used in the metal salt is a metal with a lower ionization tendency than sodium.

[0008] Japanese Patent No. 7255625, International Publication No. 2018 / 147342, Japanese Unexamined Patent Publication No. 2018-086175, Japanese Patent No. 6989823

[0009] Patent documents 1 to 4 disclose compositions containing fibrous cellulose and rubber or elastomers. The present inventors have found that crosslinked rubber compositions obtained by crosslinking a rubber composition containing fibrous cellulose having anionic groups have low water resistance and tend to have reduced mechanical properties due to water absorption. Improvements are desired in the compositions described in Patent documents 1 to 4 to suppress such reduction in physical properties. The present invention aims to provide a rubber composite material that yields a crosslinked rubber composition with excellent water resistance, a rubber compound containing the rubber composite material, and a crosslinked rubber composition obtained by crosslinking the rubber compound. Furthermore, the present invention aims to provide a method for producing the rubber composite material, the rubber compound, and the crosslinked rubber composition.

[0010] The present inventors have found that the above problem can be solved by a rubber composite material containing fibrous cellulose having anionic groups, further containing a specific amount of a metal element belonging to any of groups 2 to 14 of the periodic table, and having a sodium element content in the rubber composite material below a specific value. The present invention relates to the following <1> to <25>. <1> A rubber composite material containing the following components (A), (B), and (Cm): Component (A): Rubber component Component (B): Fibrous cellulose having anionic groups Component (Cm): Metal element belonging to any of groups 2 to 14 of the periodic table The content of component (Cm) in the rubber composite material is 0.02 mol / kg or more and 1 mol / kg or less, and the content of sodium element in the rubber composite material is 0.20 mol / kg or less. <2> The rubber composite material according to <1>, wherein component (B) contains fine fibrous cellulose with a fiber width of 1 nm or more and 1,000 nm or less. <3> A rubber composite material according to <1> or <2>, wherein the degree of polymerization of component (B) is 100 or more and 800 or less. <4> A rubber composite material according to any one of <1> to <3>, wherein the content of component (B) in the rubber composite material is 0.1% by mass or more and 60% by mass or less. <5> A rubber composite material according to any one of <1> to <4>, wherein component (A) contains diene rubber. <6> A rubber compound containing the rubber composite material according to any one of <1> to <5> and a crosslinking agent. <7> A crosslinked rubber composition obtained by crosslinking the rubber compound according to <6>. <8> A crosslinked rubber composition according to <7>, wherein the water absorption rate of the crosslinked rubber composition, as measured in accordance with JIS K 7209A method:2000, is 15% by mass or less. <9> The cross-linked rubber composition according to <7> or <8>, wherein the ratio of the 50% modulus of the cross-linked rubber composition after the water absorption test (50% modulus after water absorption test / 50% modulus before water absorption test), measured according to JIS K 6251:2017, to the 50% modulus of the cross-linked rubber composition before the water absorption test, measured according to JIS K 6251:2017, is 0.8 or more and 1.2 or less.Water absorption test: A test piece of the crosslinked rubber composition (Type 6 dumbbell as described in JIS K 6251:2017) is immersed in ion-exchanged water at 70°C for 48 hours. <10> The ratio of the 100% modulus of the crosslinked rubber composition after the water absorption test (measured in accordance with JIS K 6251:2017) to the 100% modulus of the crosslinked rubber composition before the water absorption test (measured in accordance with JIS K 6251:2017) is 0.5 or more and 1.1 or less, as described in any one of <7> to <9>. Water absorption test: A test piece of the crosslinked rubber composition (a No. 6 dumbbell as described in JIS K 6251:2017) is immersed in ion-exchanged water at 70°C for 48 hours. <11> The ratio of the 300% modulus of the crosslinked rubber composition after the water absorption test (measured in accordance with JIS K 6251:2017) to the 300% modulus of the crosslinked rubber composition before the water absorption test (measured in accordance with JIS K 6251:2017) is 0.5 or more and 1.0 or less, as described in any one of <7> to <10>. Water absorption test: A test piece of the crosslinked rubber composition (a No. 6 dumbbell as described in JIS K 6251:2017) is immersed in ion-exchanged water at 70°C for 48 hours. <12> A method for producing a rubber composite material, comprising the following mixing step, solidification step and washing step, Mixing step: A step to obtain a mixed solution containing the following components (A), (B), (Cs), (D) and water. Component (A): Rubber component. Component (B): Fibrous cellulose having anionic groups. Component (Cs): Inorganic salt of a metal belonging to any of groups 2 to 14 of the periodic table, and / or organic acid salt of a metal belonging to any of groups 2 to 14 of the periodic table, provided that the number of carbon atoms in the organic acid is 15 or less. Component (D): Sodium ion. Solidification step: A step to obtain a dried product by removing water from the mixed solution. Washing step: A step to obtain a rubber composite material by washing the dried product with water. In the mixed solution, the mol ratio of component (D) to metal ions belonging to any of groups 2 to 14 of the periodic table derived from component (Cs) (component (D) / metal ions of component (Cs)) is 1 / 1 or more and 10 / 1 or less. <13> A method for producing a rubber composite material according to <12>, wherein component (B) contains fine fibrous cellulose with a fiber width of 1 nm or more and 1,000 nm or less.<14> A method for producing a rubber composite material according to <12> or <13>, wherein the degree of polymerization of component (B) is 100 or more and 800 or less. <15> A method for producing a rubber composite material according to any one of <12> to <14>, wherein the content of component (D) in the total solid components contained in the mixed liquid is greater than 0.20 mol / kg. <16> A method for producing a rubber composite material according to any one of <12> to <15>, wherein the content of sodium element in the rubber composite material is 0.20 mol / kg or less. <17> A method for producing a rubber composite material according to any one of <12> to <16>, wherein the content of component (B) in the total solid components contained in the mixed liquid is 0.1% by mass or more and 60% by mass or less. <18> A method for producing a rubber composite material according to any one of <12> to <17>, wherein the content of component (Cs) in the total solid components contained in the mixed liquid is 0.03 mol / kg or more and 0.5 mol / kg or less. <19> A method for producing a rubber composite material according to any one of <12> to <18>, wherein component (A) contains a diene rubber. <20> A method for producing a rubber compound, comprising a kneading step of kneading the rubber composite material and a crosslinking agent obtained by the method for producing a rubber composite material according to any one of <12> to <19>. <21> A method for producing a crosslinked rubber composition, comprising a step of crosslinking the rubber compound obtained by the method for producing a rubber compound according to <20>. <22> A method for producing a crosslinked rubber composition according to <21>, wherein the water absorption rate of the crosslinked rubber composition, as measured in accordance with JIS K 7209A method:2000, is 1% by mass or more and 15% by mass or less. <23> A method for producing a crosslinked rubber composition according to <21> or <22>, wherein the ratio of the 50% modulus of the crosslinked rubber composition after the water absorption test (measured according to JIS K 6251:2017) to the 50% modulus of the crosslinked rubber composition before the water absorption test (measured according to JIS K 6251:2017) is 0.8 or more and 1.2 or less.Water absorption test: A test piece of the crosslinked rubber composition (Type 6 dumbbell as described in JIS K 6251:2017) is immersed in ion-exchanged water at 70°C for 48 hours. <24> The ratio of the 100% modulus of the crosslinked rubber composition after the water absorption test (measured in accordance with JIS K 6251:2017) to the 100% modulus of the crosslinked rubber composition before the water absorption test (measured in accordance with JIS K 6251:2017) is 0.5 or more and 1.1 or less, a method for producing a crosslinked rubber composition according to any one of <21> to <23>. A method for producing a cross-linked rubber composition according to any one of <21> to <24>, wherein the ratio of the 300% modulus of the cross-linked rubber composition after the water absorption test (measured according to JIS K 6251:2017) to the 300% modulus of the cross-linked rubber composition before the water absorption test (measured according to JIS K 6251:2017) is 0.5 or more and 1.0 or less.

[0011] According to the present invention, a rubber composite material is provided that yields a crosslinked rubber composition with excellent water resistance, a rubber compound containing the rubber composite material is provided, and a crosslinked rubber composition is provided that is obtained by crosslinking the rubber compound. Furthermore, according to the present invention, a method for producing the rubber composite material, the rubber compound and the crosslinked rubber composition is provided.

[0012] [Rubber Composite Material] The rubber composite material of this embodiment contains component (A): rubber component, component (B): fibrous cellulose having anionic groups, and component (Cm): a metal element belonging to any of groups 2 to 14 of the periodic table, with a content of component (Cm) of 0.02 mol / kg or more and 1 mol / kg or less in the rubber composite material, and a sodium element content of 0.20 mol / kg or less in the rubber composite material. According to the rubber composite material of this embodiment, the counterions of the anionic groups of the fibrous cellulose are mainly metal elements belonging to any of groups 2 to 14 of the periodic table, and the sodium element content in the rubber composite material is low. Therefore, it is considered that the water absorption rate of the crosslinked rubber composition obtained by crosslinking the rubber composite material can be reduced. The embodiment will be described in detail below. In this specification, the numerical range represented by "X to Y" means a numerical range that includes X as the lower limit and Y as the upper limit. When the numerical range is described in steps, the upper and lower limits of each numerical range can be arbitrarily combined. The components contained in the rubber composite material of this embodiment and the raw materials for said components may be used individually or in combination of two or more. The same applies to the rubber compound and crosslinked rubber composition of this embodiment, which will be described later.

[0013] [Component (A): Rubber Component] The rubber composite material of this embodiment contains a rubber component. As the rubber component, for example, natural rubber (NR) or synthetic rubber can be used. Examples of synthetic rubbers 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), polysulfide rubber (T), etc. Examples of nitrile rubbers include modified nitrile rubbers such as hydrogenated nitrile rubber, carboxyl group modified nitrile rubber, silicone modified nitrile rubber, maleic acid modified nitrile rubber, and hydroxyl group modified nitrile rubber, or hydrogenated versions thereof; and acrylonitrile-butadiene-isoprene copolymers in which a portion of 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. Examples of natural rubber include natural rubber (NR), modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber, and deproteinized natural rubber. These rubber components may be pre-crosslinked raw materials without a crosslinked structure, or they may have a crosslinked structure.

[0014] Among these, the rubber component preferably contains diene rubber, more preferably contains at least one selected from natural rubber, nitrile rubber, butadiene rubber, and styrene-butadiene rubber, and even more preferably contains natural rubber. The rubber component may also be a pre-crosslinking raw material. The rubber component is preferably the latex of these rubber components. By using the latex of the rubber component, the dispersibility of fibrous cellulose is improved, making it easier to obtain a composite material with excellent mechanical strength. When using the latex of the rubber component, a solid rubber component may be further mixed in. The solid rubber component may be added when mixing the rubber composite material.

[0015] [Component (B): Fibrous Cellulose Having Anionic Groups] The rubber composite of this embodiment contains fibrous cellulose having anionic groups (hereinafter also simply referred to as "fibrous cellulose") in order to improve the mechanical strength of the crosslinked rubber composition. The fibrous cellulose is not particularly limited and known types can be used. The fiber width of the fibrous cellulose is preferably 1 nm or more and 1,000 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, even more preferably 20 nm or less, even more preferably 10 nm or less, and more preferably 2 nm or more. Hereinafter, fibrous cellulose with a fiber width of 1,000 nm or less may be referred to as "fine fibrous cellulose". The rubber composite may also contain cellulose fibers with a fiber width exceeding 1 μm (1,000 nm) (hereinafter also referred to as "coarse cellulose fibers"), as will be described later. The fiber width of the coarse cellulose fiber is not particularly limited, but is preferably 1 μm to 100 μm, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 50 μm or less, and even more preferably 40 μm or less. The fiber width of the coarse cellulose fiber can be determined using a fiber length distribution measuring device (for example, the FS5 manufactured by Valmet, or the L&W Fiber Tester Plus manufactured by ABB).

[0016] The average fiber width of fine fibrous cellulose is, for example, 1,000 nm or less. The average fiber width of fibrous cellulose is, for example, preferably 2 nm to 1,000 nm, more preferably 2 nm to 100 nm, even more preferably 2 nm to 50 nm, and even more preferably 2 nm to 10 nm. Fibrous cellulose is, for example, monofibrous cellulose.

[0017] The fiber width of fibrous cellulose is measured, for example, using an electron microscope as follows: First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilic carbon film-coated grid to prepare a sample for transmission electron microscopy (TEM) observation. If wide fibers are present, a scanning electron microscope (SEM) image of the surface cast on glass may be observed. Next, observation of the electron microscope image is performed at a magnification of 1,000x, 5,000x, 10,000x, or 50,000x depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification should be adjusted to satisfy the following conditions: (1) A straight line X is drawn at any point in the observation image, and 20 or more fibers intersect with this line X. (2) A straight line Y is drawn perpendicular to the line X in the same image, and 20 or more fibers intersect with this line Y. For observation images that satisfy the above conditions, the width of the fibers intersecting with lines X and Y is visually read. In this way, at least three sets of observation images of surface areas that do not overlap are obtained. Next, for each image, the width of the fibers intersecting with lines X and Y is read. This allows for the reading of at least 20 × 2 × 3 = 120 fiber widths. The average of the read fiber widths is then taken as the number-average fiber width of the fibrous cellulose.

[0018] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm to 1,000 μm, more preferably 0.1 μm to 800 μm, and even more preferably 0.1 μm to 600 μm. By keeping the fiber length within the above range, the destruction of the crystalline region of the fibrous cellulose can be suppressed. The fiber length of the fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or atomic force microscopy (AFM).

[0019] It is preferable that the fibrous cellulose has a type I crystalline structure. Here, the presence of a type I crystalline structure in fibrous cellulose can be identified in the diffraction profile obtained from a wide-angle X-ray diffraction photograph using graphite-monochromatized CuKα (λ = 1.5418 Å). Specifically, it can be identified by the presence of typical peaks at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°. The proportion of type I crystalline 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 analyzing its pattern using a conventional method (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0020] The axial ratio (fiber length / fiber width) of fibrous cellulose is not particularly limited, but is preferably 50 to 10,000, more preferably 100 to 1,000. Setting the axial ratio above the lower limit makes it easier to form rubber composite materials containing fine fibrous cellulose. Setting the axial ratio below the upper limit is preferable in that it makes handling, such as dilution, easier when handling fine fibrous cellulose as a dispersion.

[0021] The degree of polymerization of fibrous cellulose is preferably 100 or more, more preferably 300 or more, and even more preferably 500 or more, from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, and from the viewpoint of ease of manufacture, it is preferably 800 or less, more preferably 750 or less, and even more preferably 700 or less. Fibrous cellulose can be reduced in degree of polymerization by a low-polymerization treatment such as an ozone treatment process, an enzyme treatment process, a hypochlorous acid treatment process, a subcritical water treatment process, or an irradiation treatment process.

[0022] The degree of polymerization of fibrous cellulose is calculated from the viscosity measured according to Tappi T230. Specifically, the viscosity (η1) measured by dissolving the fibrous cellulose to be measured in an aqueous copper ethylenediamine solution, and the blank viscosity (η0) measured using only the aqueous copper ethylenediamine solution, are measured. Then, the specific viscosity (ηsp) and intrinsic viscosity ([η]) are measured according to the following formulas: ηsp = (η1 / η0) - 1 [η] = ηsp / (c(1 + 0.28 × ηsp)) Here, c in the formula represents the concentration of fibrous cellulose (g / mL) at the time of viscosity measurement. Furthermore, the degree of polymerization (DP) is calculated from the following formula: DP = 1.75 × [η] This degree of polymerization is the average degree of polymerization measured by the viscosity method, and is sometimes called the "viscosity-average degree of polymerization".

[0023] In this embodiment, the fibrous cellulose has both crystalline and amorphous regions. Fibrous cellulose having both crystalline and amorphous regions and having an axial ratio within the above range can be realized by the method for producing fibrous cellulose described later.

[0024] The anionic group present in fibrous cellulose is preferably a group introduced into the fibrous cellulose via an ester bond or an ether bond, and more preferably a group introduced into the fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by the dehydration condensation of the fibrous cellulose and the compound that will become the anionic group.

[0025] Examples of anionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxyl groups or substituents derived from carboxyl groups (sometimes simply referred to as carboxyl groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xantate groups or substituents derived from xantate groups (sometimes simply referred to as xantate groups), phosphonone groups or substituents derived from phosphonone groups, phosphine groups or substituents derived from phosphine groups, sulfone groups or substituents derived from sulfone groups, carboxyalkyl groups, and the like. In particular, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxyl group, a sulfur oxoacid group, a substituent derived from a sulfur oxoacid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group; more preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxyl group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group; and even more preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as the anionic group, for example, the dispersibility of fibrous cellulose can be further improved even under alkaline or acidic conditions, and as a result, sheets with excellent mechanical strength can be easily obtained.

[0026] The anionic group may have a counterion of one or more cations, either organic or inorganic. Examples of organic cations with one or more cations include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of inorganic cations with one or more cations include alkali metal ions such as sodium, potassium, or lithium, divalent metal ions such as calcium or magnesium, hydrogen ions, and ammonium ions, but are not particularly limited. These can be applied individually or in combination of two or more types.

[0027] More specifically, a phosphate group (-PO) is a substituent derived from a phosphate group. ３ H ２ ), phosphate group salt, phosphite group (phosphonic acid group) (-PO ２ H ２ Examples include phosphate groups and salts of phosphite groups. Furthermore, the substituents derived from the phosphate oxoacid group or the phosphate oxoacid group may be groups formed by condensation of a phosphate group (e.g., pyrophosphate group), groups formed by condensation of a phosphonic acid (e.g., polyphosphonic acid group), phosphate ester groups (e.g., monomethyl phosphate group, polyoxyethylene alkyl phosphate group), alkylphosphonic acid groups (e.g., methylphosphonic acid group), etc. Among these, the phosphate group is preferred.

[0028] The amount of anionic groups introduced into fibrous cellulose is preferably 0.10 mmol / g to 5.20 mmol / g per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably 1.00 mmol / g or more, and more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. Here, the denominator in the unit mmol / g is the amount of the counterion of the anionic group which is a hydrogen ion (H ＋ This indicates the mass of fibrous cellulose when ). By keeping the amount of anionic groups introduced within the above range, it is possible to facilitate the refinement of the fiber raw material and improve the stability of fibrous cellulose.

[0029] The amount of anionic groups introduced into fibrous cellulose can be measured, for example, by neutralization titration after the cellulose fibers have been subjected to micronization treatment. In the neutralization titration method, the amount introduced is determined by measuring the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the slurry containing the obtained fibrous cellulose.

[0030] In the case of fibrous cellulose containing phosphorus oxoacid groups, the amount of phosphorus oxoacid groups introduced into the fibrous cellulose is measured, for example, as follows: First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, a defibration treatment similar to the defibration treatment step described later may be performed on the sample before treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding an aqueous sodium hydroxide solution to obtain the relationship between the amount of alkali added (molecules) and pH (titration curve). In this titration curve, the point where the increment (derivative value) of pH with respect to the amount of alkali added is maximum is identified as the endpoint. In the case of phosphorus oxoacid groups, usually two endpoints are identified; the endpoint obtained first after starting to add alkali is called the first endpoint, and the endpoint obtained next is called the second endpoint.

[0031] The amount of alkali added from the start of the titration to the first endpoint is equal to the amount of the first dissociated acid from the fibrous cellulose contained in the slurry used for titration. The amount of alkali added from the first endpoint to the second endpoint is equal to the amount of the second dissociated acid from the fibrous cellulose contained in the slurry used for titration, and the amount of alkali added from the start of the titration to the second endpoint is equal to the total amount of dissociated acid from the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali added from the start of the titration to the first endpoint by the solid content (g) of the slurry being titrated is the amount of phosphorus oxoacid group introduced (mol / g). Note that when simply referred to as the amount of phosphorus oxoacid group introduced (or amount of phosphorus oxoacid group), it refers to the amount of the first dissociated acid. For example, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of the second dissociated acid at the phosphorus oxoacid group appears to decrease, and the amount of the second dissociated acid becomes less than the amount of the first dissociated acid. On the other hand, the amount of the first dissociated acid is equal to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Also, if the phosphorus oxoacid group is a phosphorous acid group, the amount of the second dissociated acid will be small or zero because there is no weak acid group in the phosphorus oxoacid group.

[0032] The amount of phosphorus oxoacid groups introduced as described above indicates the amount of phosphorus oxoacid groups present in acid-type fibrous cellulose, since the denominator represents the mass of acid-type fibrous cellulose (hereinafter referred to as phosphorus oxoacid group amount (acid-type)). On the other hand, if the counterion of the phosphorus oxoacid group is substituted with an arbitrary cation C such that it is equivalent in charge, the amount of phosphorus oxoacid groups present in fibrous cellulose with cation C as the counterion can be determined by converting the denominator to the mass of fibrous cellulose when cation C is the counterion (hereinafter referred to as phosphorus oxoacid group amount (C-type)). That is, it is calculated using the following formula. Phosphorus oxoacid group amount (C type) = Phosphorus oxoacid group amount (acid type) / {1 + (W - 1) × A / 1000} A [mol / g]: Total amount of anions derived from phosphorus oxoacid groups in fibrous cellulose (sum of the amount of first and second dissociated acids of the phosphorus oxoacid group) W: Formula weight per unit of cation C (for example, Na is 23, Al is 9)

[0033] The amount of carboxyl groups (mol / g), sulfur oxoacid groups (mol / g), and sulfone groups (mol / g) introduced into fibrous cellulose can be determined, for example, by the methods described in Japanese Patent Publication No. 2022-90648 and Japanese Patent Publication No. 2024-145179.

[0034] To obtain fibrous cellulose with anionic groups introduced as described above, it is preferable to have an anionic group introduction step, a washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and an acid treatment step may be included instead of the washing step, or in addition to the washing step. Examples of anionic group introduction steps include a phosphorus oxo acid group introduction step, a carboxyl group introduction step, a sulfur oxo acid group introduction step, a xantate group introduction step, a phosphone group or phosphine group introduction step, and a sulfone group introduction step. Each of these will be described below.

[0035] <Fiber Raw Materials> Fiber raw materials are fiber raw materials containing cellulose, and are not particularly limited, but examples include wood pulp, non-wood pulp, and deinked pulp. Wood pulp is not particularly limited, but examples include chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolved 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 chemical groundwood pulp (CGP); and mechanical pulps such as crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Non-wood pulp is not particularly limited, but examples include cotton 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 include deinked pulp made from recycled paper. The pulp raw material in this embodiment may be one of the above types alone or a mixture of two or more types. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Among wood pulps, chemical pulp is more preferred from the viewpoint of having a high cellulose ratio and a high yield of fibrous cellulose during defibration treatment, and from the viewpoint of obtaining long-fiber fibrous cellulose with a large axial ratio due to minimal cellulose decomposition in the pulp. Kraft pulp and sulfite pulp are even more preferred, and softwood kraft pulp is even more preferred. Note that using long-fiber fibrous cellulose with a large axial ratio tends to increase viscosity.

[0036] <Phosphorus Oxoate Group Introduction Process> The phosphorus oxoate group introduction process involves reacting a cellulose-containing fiber raw material with at least one compound selected from compounds capable of introducing phosphorus oxoate groups by reacting with hydroxyl groups present in the cellulose-containing fiber raw material (hereinafter also referred to as the "phosphorus oxoate group introduction component"). This process yields cellulose fibers having phosphorus oxoate groups.

[0037] In the step of introducing a phosphono-oxo acid group according to this embodiment, the reaction between the fiber raw material containing cellulose and the component for introducing a phosphono-oxo acid group may be carried out in the presence of at least one selected from urea and its derivatives. On the other hand, the reaction between the fiber raw material containing cellulose and the component for introducing a phosphono-oxo acid group may be carried out in a state where at least one selected from urea and its derivatives is not present.

[0038] The amount of the phosphono-oxo acid group 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, still more preferably 0.50 mmol / g or more, even more preferably 1.00 mmol / g or more, per 1 g (mass) of cellulose fiber, and is more preferably 3.65 mmol / g or less, still more preferably 3.00 mmol / g or less. By setting the amount of the phosphono-oxo acid group introduced within the above range, the fibrillation of cellulose fibers in the defibrillation treatment step can be facilitated, and the stability of fibrous cellulose can be enhanced.

[0039] The step of introducing a phosphono-oxo acid group, the step of introducing a carboxy group, the step of introducing a sulfur oxo acid group, the step of introducing a xanthate group, the step of introducing a phosphon group or a phosphine group, and the step of introducing a sulfone group can be carried out, for example, by referring to the methods described in JP-A-2022-90648 and JP-A-2024-145179.

[0040] <Washing Step> In the step of obtaining cellulose fibers having an anionic group, a washing step can be carried out on the fibers with an introduced anionic group as necessary. The washing step is carried out, for example, by washing the fibers with an introduced anionic group with water or an organic solvent. Further, the washing step may be carried out after each of the steps described later, and the number of washing times carried out in each washing step is not particularly limited.

[0041] <Alkali Treatment Step> In the step of obtaining cellulose fibers having an anionic group, an alkali treatment step may be provided between the step of introducing an anionic group and the defibrillation treatment step. The method of alkali treatment is not particularly limited, and examples thereof include a method of immersing the fibers with an introduced anionic group in an alkali solution.

[0042] The alkali compound contained in the alkali solution is not particularly limited and may be an inorganic alkali compound or an organic alkali compound. In the present embodiment, since it has high versatility, for example, sodium hydroxide or potassium hydroxide is preferably used as the alkali compound, and sodium hydroxide is more preferably used. Further, the solvent contained in the alkali solution may be either water or an organic solvent. Among them, the solvent contained in the alkali solution is preferably a polar solvent including water or a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing at least water. As the alkali solution, since it has high versatility, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable, and an aqueous sodium hydroxide solution is more preferable.

[0043] The temperature of the alkali solution in the alkali treatment step is not particularly limited. For example, it is preferably 5°C or higher and 80°C or lower, and more preferably 10°C or higher and 60°C or lower. The immersion time of the anionic group-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited. For example, it is preferably 5 minutes or longer and 30 minutes or shorter, and more preferably 10 minutes or longer and 20 minutes or shorter. The amount of the alkali solution used in the alkali treatment is not particularly limited. For example, it is preferably 100 parts by mass or more and 100,000 parts by mass or less, and more preferably 1,000 parts by mass or more and 10,000 parts by mass or less with respect to 100 parts by mass of the absolute dry mass of the anionic group-introduced fiber.

[0044] In order to reduce the amount of the alkali solution used in the alkali treatment step, after the anionic group introduction step and before the alkali treatment step, the anionic group-introduced fiber may be washed with water or an organic solvent. After the alkali treatment step and before the fiber disintegration treatment step, from the viewpoint of improving the handleability, it is preferable to wash the anionic group-introduced fiber subjected to the alkali treatment with water or an organic solvent.

[0045] <Fibration Process> By defibrating the fiber raw material or anionic group-introduced fiber in the defibration process, fibrous cellulose is obtained. Defibration is also called micronization. In the defibration process, for example, a defibration processing device can be used. The defibration processing device is not particularly limited, but for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer or ultra-high-pressure homogenizer, high-pressure impact grinder, ball mill, bead mill, disc type refiner, conical refiner, twin-screw kneader, vibrating mill, homomixer under high-speed rotation, ultrasonic disperser, or beater can be used. Among the above defibration processing devices, it is more preferable to use a high-speed defibrator, high-pressure homogenizer, or ultra-high-pressure homogenizer, which have less influence from the grinding media and less risk of contamination.

[0046] In the defibration process, it is preferable to dilute, for example, the fiber raw material or the anionic group-introduced fiber with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but examples of preferred materials include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents.

[0047] The solid content concentration of fibrous cellulose during the defibration process can be set as appropriate. Furthermore, the slurry obtained by dispersing the anionic group-introduced fibers in a dispersion medium may contain solid components other than the anionic group-introduced fibers, such as hydrogen-bonding urea.

[0048] [Component (Cm): Metal element belonging to any of Groups 2 to 14 of the Periodic Table] The rubber composite material of this embodiment contains a metal element belonging to any of Groups 2 to 14 of the Periodic Table. Among the metal elements belonging to any of Groups 2 to 14 of the Periodic Table, from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, metal elements of the third or fourth period are preferred, Al, Mg, Ca, Ti, Fe, Cu, and Zn are more preferred, and Al, Mg, and Ca are even more preferred.

[0049] <Content> The content of component (Cm) in the rubber composite of this embodiment is 0.02 mol / kg or more and 1 mol / kg or less from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, and 1 mol / kg or less from the viewpoint of ease of manufacturing the rubber composite. The content of component (Cm) in the rubber composite of this embodiment is preferably 0.05 mol / kg or more, more preferably 0.08 mol / kg or more, even more preferably 0.10 mol / kg or more, and even more preferably 0.11 mol / kg or more from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, and preferably 0.75 mol / kg or less, more preferably 0.5 mol / kg or less, and even more preferably 0.3 mol / kg or less from the viewpoint of ease of manufacturing the rubber composite. For example, when aluminum sulfate is used in the rubber composite of this embodiment, the content of component (Cm) in the rubber composite is the total number of moles of aluminum element in 1 kg of rubber composite. The content of component (Cm) in the rubber composite material of this embodiment is preferably 0.05% by mass or more and 6.60% by mass or less, more preferably 0.10% by mass or more, even more preferably 0.15% by mass or more, and even more preferably 5.00% by mass or less, and even more preferably 3.30% by mass or less. From the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, the content of component (Cm) in the rubber composite material of this embodiment is preferably above the lower limit, and from the viewpoint of ease of manufacturing the rubber composite material, it is preferably below the upper limit.

[0050] The upper limit of the sodium element content in the rubber composite of this embodiment is 0.20 mol / kg or less, preferably 0.17 mol / kg or less, more preferably 0.14 mol / kg or less, even more preferably 0.11 mol / kg or less, and even more preferably 0.08 mol / kg or less, from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption. The lower limit is, for example, 0.01 mol / kg or more, from the viewpoint of ease of manufacturing the rubber composite. The upper limit of the sodium element content in the rubber composite of this embodiment is preferably 0.46% by mass or less, more preferably 0.40% by mass or less, and even more preferably 0.20% by mass or less, from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, and the lower limit is, for example, 0.03% by mass or more, from the viewpoint of ease of manufacturing the rubber composite. In the rubber composite material of this embodiment, the upper limit of the ratio of the sodium element content (mol) to the content (mol) of component (Cm) (sodium element / component (Cm)) is preferably 2.00 / 1 or less, more preferably 1.00 / 1 or less, even more preferably 0.60 / 1 or less, even more preferably 0.45 / 1 or less, and even more preferably 0.40 / 1 or less, from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption. The lower limit is, for example, 0.01 / 1 or more, from the viewpoint of ease of manufacturing the rubber composite material.

[0051] The content of component (B) in the rubber composite material of this embodiment is preferably 0.1% by mass or more and 60% by mass or less, more preferably 4% by mass or more, even more preferably 8% by mass or more, even more preferably 12% by mass or more, even more preferably 15% by mass or more, and more preferably 50% by mass or less, even more preferably 40% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, and even more preferably 20% by mass or less. From the viewpoint of improving the mechanical strength of the crosslinked rubber composition, the content of component (B) in the rubber composite material of this embodiment is preferably above the lower limit value, and from the viewpoint of water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, it is preferably below the upper limit value. The rubber composite material of this embodiment may also contain coarse cellulose fibers, and if it contains coarse cellulose fibers, the content of coarse cellulose fibers in component (B) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and 0% by mass or more.

[0052] In the rubber composite material of this embodiment, the content of component (B) per 100 parts by mass of component (A) is preferably 5 parts by mass or more and 35 parts by mass or less, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. In the rubber composite material of this embodiment, the content of component (B) per 100 parts by mass of component (A) is above the lower limit from the viewpoint of improving the mechanical strength of the crosslinked rubber composition, and below the upper limit from the viewpoint of water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption. Note that the content of component (B) per 100 parts by mass of component (A) in the rubber composite material of this embodiment may differ from the content of component (B) per 100 parts by mass of component (A) when making a crosslinked rubber composition. Specifically, the content of component (B) may be increased in the rubber composite material, and the content of component (B) relative to the rubber component may be adjusted by adding rubber components when preparing the rubber compound described later.

[0053] The total amount of component (A), component (B), and component (Cm) in the rubber composite material is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more, and the upper limit is not particularly limited, but is less than 100% by mass.

[0054] The rubber composite material of this embodiment may contain components other than components (A), (B), and (Cm), such as zinc oxide, surfactants, vulcanization accelerators, antioxidants, and reinforcing agents, and may be added at any stage of the manufacturing process.

[0055] From the viewpoint of uniformly dispersing each component in the resulting mixture and improving the water resistance of the crosslinked rubber composition, the surfactant is preferably a 0.1% by mass aqueous solution of the surfactant, with a static surface tension (hereinafter also simply referred to as "static surface tension") measured at 25°C by the Wilhelmy method, which is preferably 20.0 mN / m to 65.0 mN / m, more preferably 24.0 mN / m or more, more preferably 55.0 mN / m or less, even more preferably 45.0 mN / m or less, and even more preferably 40.0 mN / m or less. The static surface tension of the surfactant is measured by the Wilhelmy method using a Wilhelmy surface tension tester (manufactured by Kyowa Interface Science Co., Ltd.) based on JIS K 2241:2017, with a 0.1% by mass aqueous solution as a sample, at 25°C.

[0056] From the viewpoint of uniformly dispersing each component in the resulting mixture and improving the water resistance of the crosslinked rubber composition, the surfactant preferably contains at least one selected from the group consisting of cationic surfactants and nonionic surfactants, and more preferably contains a nonionic surfactant. The total content of cationic surfactants and nonionic surfactants in the surfactant is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and 100% by mass or less, from the viewpoint of uniformly dispersing each component in the resulting mixture and improving the water resistance of the crosslinked rubber composition during the mixing process.

[0057] Cationic surfactants are preferably those having an alkyl group with 8 or more carbon atoms, from the viewpoint of uniformly dispersing each component in the resulting mixture during the mixing process and improving the water resistance of the crosslinked rubber composition. The upper limit of the number of carbon atoms in the alkyl group is, for example, 14 or less. Quaternary ammonium salts are preferred as cationic surfactants, and tetraalkylammonium salts are more preferred. Specific examples of cationic surfactants include octyldimethylethylammonium ethyl sulfate, dodecyltrimethylammonium chloride, octyltrimethylammonium chloride, and lauryltrimethylammonium chloride. Specific examples of nonionic surfactants include polyoxyalkylene alkyl ethers, sucrose fatty acid esters, polyoxyethylene sorbitan monolaurate, and fatty acid alkanolamides. Among these, polyoxyalkylene alkyl ethers are preferred because they exhibit excellent dispersion stability of each component in the mixture obtained during the mixing process. The number of carbon atoms in the alkylene group of the polyoxyalkylene alkyl ether is preferably 2 to 4, and more preferably 2 or 3. The number of carbon atoms in the alkyl group of the polyoxyalkylene alkyl ether is preferably 8 to 14, and more preferably 10 to 12. The surfactant may be used as an aqueous solution from the viewpoint of uniformly dispersing each component in the resulting mixture and improving the water resistance of the crosslinked rubber composition. The solid content concentration of the surfactant aqueous solution is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0058] [Method for Manufacturing Rubber Composite Material] The method for manufacturing the rubber composite material of this embodiment comprises the following mixing step, solidification step, and washing step. Mixing step: A step to obtain a mixed solution containing the following components (A), (B), (Cs), (D) and water. Component (A): Rubber component. Component (B): Fibrous cellulose having anionic groups. Component (Cs): Inorganic salt of a metal belonging to any of groups 2 to 14 of the periodic table, and / or organic acid salt of a metal belonging to any of groups 2 to 14 of the periodic table, provided that the number of carbon atoms in the organic acid is 15 or less. Component (D): Sodium ion. Solidification step: A step to obtain a dried product by removing water from the mixed solution. Washing step: A step to obtain a rubber composite material by washing the dried product with water. In the mixed solution, the mol ratio of component (D) to metal ions belonging to any of groups 2 to 14 of the periodic table derived from component (Cs) (component (D) / metal ions of component (Cs)) is 1 / 1 or more and 10 / 1 or less.

[0059] [Mixing Process] The mixing process is a process of obtaining a mixture containing components (A), (B), (Cs), (D), and water. Components (A) and (B) are the same as components (A) and (B) of the rubber composite material of this embodiment, respectively.

[0060] <Component (Cs): Inorganic salt of a metal belonging to any of Groups 2 to 14 of the Periodic Table, and / or organic acid salt of a metal belonging to any of Groups 2 to 14 of the Periodic Table, provided that the number of carbon atoms in the organic acid is 15 or less> As the metal ion (cation) belonging to any of Groups 2 to 14 of the Periodic Table that forms the inorganic salt of a metal belonging to any of Groups 2 to 14 of the Periodic Table and the organic acid salt of a metal belonging to any of Groups 2 to 14 of the Periodic Table, the ion of component (Cm) contained in the composite material of this embodiment as described above is preferred. As the cation that forms the inorganic acid, from the viewpoint of increasing the water solubility of the inorganic salt, Al, Mg, Zn, Fe, and Cu are preferred, Al, Mg, and Zn are more preferred, and Al and Mg are even more preferred. As the cation that forms the organic acid, from the viewpoint of forming an organic acid salt that can be used as a rubber additive, Ca, Mg, and Zn are preferred, and from the viewpoint of increasing the water solubility of the organic acid salt, Ca and Mg are more preferred, and Ca is even more preferred. The anions that form the inorganic salt are preferably sulfate ions, chloride ions, bromide ions, hydroxide ions, and oxide ions, more preferably sulfate ions and chloride ions, and even more preferably sulfate ions. Specific examples of inorganic salts include aluminum sulfate, magnesium sulfate, aluminum chloride, and magnesium chloride. The organic acids that form the organic salts are preferably carboxylic acids, more preferably aliphatic carboxylic acids, and even more preferably alkyl carboxylic acids. The number of carbon atoms in the organic acid, i.e., the number of carbon atoms in the anions that form the organic salts, is 15 or less, preferably 12 or less. Specific examples of organic salts include calcium 2-ethylhexanoate, calcium neodecanoate, calcium octanoate, and calcium laurate.

[0061] <Component (D): Sodium ion> Component (D) may exist in the mixture as a counterion of the anionic group of component (B), or it may exist dissociated.

[0062] In the mixing step, components (A), (B), and (Cs) are mixed and dispersed in an aqueous medium to obtain a mixed solution. Alternatively, a mixed solution can be obtained by mixing an aqueous dispersion of component (A) (rubber latex), an aqueous dispersion of component (B), and an aqueous solution of component (Cs). Among these, it is preferable to mix an aqueous dispersion of component (A) (rubber latex), an aqueous dispersion of component (B), and an aqueous solution of component (Cs) to obtain a dispersion (mixed solution) containing components (A), (B), (Cs), and (D). Component (D) is, for example, a counterion of the anionic group of component (B). The mixing order of components (A), (B), and (Cs) is not particularly limited, but examples include the following mixing order A and mixing order B. Mixing order A: Mix the aqueous dispersion of component (A) and the aqueous dispersion of component (B) to obtain a dispersion, and then mix the resulting dispersion with an aqueous solution of component (Cs). Mixing order B: Mix the aqueous dispersion of component (B) and the aqueous solution of component (Cs) to obtain a dispersion, and then mix the resulting dispersion with the aqueous dispersion of component (A). Mixing order A is preferable because it allows for more uniform mixing of each component than mixing order B, which tends to improve the mechanical strength after crosslinking. When a surfactant is added, from the viewpoint of uniformly dispersing each component in the resulting mixture and improving the water resistance of the crosslinked rubber composition, it is preferable in mixing order A to mix the aqueous dispersion of component (A) and the aqueous dispersion of component (B) to obtain a dispersion, and then mix this dispersion with an aqueous solution of component (Cs).

[0063] Mixing can be carried out using known devices such as dispersers, three-one motors, Creamix, homomixers, homogenizers, and propeller agitators (e.g., tornado agitators). The mixing temperature is not limited, but room temperature (20-30°C) is preferred. The mixing time can also be adjusted as appropriate.

[0064] The rubber latex is preferably a dispersion of rubber components in an aqueous medium. The aqueous medium mainly consists of water, and the water content relative to the total 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, with no particular upper limit, but not exceeding 100% by mass. In addition to water, known organic solvents and the like may be included to an extent that does not impair the effects of this disclosure.

[0065] In the mixture, the molar ratio of component (D) to metal ions belonging to any of groups 2 to 14 of the periodic table derived from component (Cs) (component (D) / metal ions of component (Cs)) is 1 / 1 or more from the viewpoint of ease of manufacturing the composite material, and 10 / 1 or less from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption. The above "molar ratio (component (D) / metal ions of component (Cs))" is preferably 1.5 / 1 or more from the viewpoint of ease of manufacturing the composite material, and preferably 8 / 1 or less, more preferably 6 / 1 or less, even more preferably 4 / 1 or less, and even more preferably 3.5 / 1 or less from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption.

[0066] The content of component (D) in the total solid components contained in the mixed liquid is preferably greater than 0.20 mol / kg and 0.75 mol / kg or less, more preferably 0.30 mol / kg or more, even more preferably 0.35 mol / kg or more, and even more preferably 0.65 mol / kg or less, and even more preferably 0.55 mol / kg or less. From the viewpoint of ease of manufacturing the rubber composite material, the content of component (D) in the total solid components contained in the mixed liquid is preferably greater than or equal to the above upper limit, and from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, it is preferably less than or equal to the above upper limit.

[0067] The content of component (B) in the total solid components contained in the mixed liquid is preferably 1% by mass or more and 60% by mass or less, more preferably 4% by mass or more, even more preferably 8% by mass or more, even more preferably 12% by mass or more, and more preferably 50% by mass or less, even more preferably 40% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, and even more preferably 20% by mass or less. From the viewpoint of improving the mechanical strength of the crosslinked rubber composition, the content of component (B) in the total solid components contained in the mixed liquid is preferably above the lower limit, and from the viewpoint of the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, it is preferably below the upper limit. In the mixing step, the amount of component (B) added per 100 parts by mass of component (A) is preferably 5 parts by mass or more and 35 parts by mass or less, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and even more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. In the mixing process, the amount of component (B) added per 100 parts by mass of component (A) is preferably above the lower limit from the viewpoint of improving the mechanical strength of the crosslinked rubber composition, and preferably below the lower limit from the viewpoint of water resistance of the crosslinked rubber composition and suppressing a decrease in mechanical strength due to water absorption.

[0068] The content of component (Cs) in the mixed liquid is preferably 0.03 mol / kg or more from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, and preferably 0.5 mol / kg or less, more preferably 0.4 mol / kg or less, and even more preferably 0.3 mol / kg or less from the viewpoint of ease of manufacturing the rubber composite material. The content of component (Cs) in the total solid components contained in the mixed liquid is preferably 0.5% by mass or more and 10% by mass or less, more preferably 0.8% by mass or more, even more preferably 1.1% by mass or more, and even more preferably 9% by mass or less, and even more preferably 8% by mass or less. The content of component (Cs) in the total solid components contained in the mixed liquid is preferably above the lower limit from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, and preferably below the upper limit from the viewpoint of ease of manufacturing the rubber composite material. In the mixing process, the amount of component (Cs) used per 100 parts by mass of component (A) is preferably 0.5 parts by mass or more and 18 parts by mass or less, more preferably 1 part by mass or more, even more preferably 1.5 parts by mass or more, and even more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less. In the mixing process, the amount of component (Cs) used per 100 parts by mass of component (A) is preferably above the lower limit from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, and preferably below the lower limit from the viewpoint of ease of manufacturing the rubber composite material.

[0069] When a surfactant is used, from the viewpoint of uniformly dispersing each component in the resulting mixture, improving the water resistance of the crosslinked rubber composition, and suppressing aggregation when transporting the mixture by pump or the like, the amount of surfactant used per 100 parts by mass of component (A) in the mixing step is preferably 0.2 parts by mass or more and 5 parts by mass or less, more preferably 1.5 parts by mass or more, even more preferably 3 parts by mass or more, and more preferably 4.5 parts by mass or less, and even more preferably 4 parts by mass or less.

[0070] The solid content concentration (by mass) of the mixture 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, even more preferably 40% by mass or less, even more preferably 30% by mass or less, even more preferably 20% by mass or less, and even more preferably 10% by mass or less. By having the solid content concentration of the mixture within the above range, the amount of energy required to remove solvents such as water can be reduced, and furthermore, aggregation of components (B) in the resulting rubber composite material becomes less likely to occur, resulting in excellent kneadability and crosslinking properties of the resulting rubber composite material.

[0071] The solid content concentration of the mixture can be calculated using the following formula (I) from the mass of the dried product obtained by drying a predetermined amount of the mixture in a 105°C dryer until a constant weight is reached, and from the mass of the mixture used for drying: Solid content concentration of the mixture (mass%) = 100 × mass of dried product [g] / mass of the mixture used for drying [g] (I)

[0072] [Solidification Process] The solidification process is a process of removing water from the mixture obtained in the mixing process to obtain a dried product. Water removal is preferably carried out by heating and drying. The heating and drying method is not particularly limited, and examples include coating the mixture onto a substrate and drying in a heated cylindrical dryer. In the coating method, for example, the mixture is coated onto the substrate. Furthermore, by using a coating device and a long substrate, sheets can be produced continuously.

[0073] The heated cylindrical dryer used in the method for manufacturing rubber composite materials can be any conduction-type dryer that introduces a heat transfer medium into the inside of a cylinder and heats and dries the mixture by bringing it into contact with the heated surface of the cylinder. For example, drum dryers such as double drum dryers, single drum dryers, and twin drum dryers may be used, and cylinder dryers, Yankee dryers, etc., can also be used. Among these, from the viewpoint of heating and drying efficiency, the heated cylindrical dryer is preferably a double drum dryer or a cylinder dryer.

[0074] [Washing Process] The washing process is a process of washing the dried material obtained in the solidification process with water to obtain a rubber composite material. Washing can be carried out, for example, by immersing the dried material in deionized water at room temperature for 10 to 60 hours. The method for manufacturing the rubber composite material of this embodiment may include a drying process after the washing process. The drying temperature is, for example, 25°C to 50°C.

[0075] The upper limit of the sodium element content in the rubber composite obtained by the rubber composite manufacturing method of the embodiment is preferably 0.20 mol / kg or less, more preferably 0.17 mol / kg or less, even more preferably 0.14 mol / kg or less, even more preferably 0.11 mol / kg or less, and even more preferably 0.08 mol / kg or less, from the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption. The lower limit is, for example, 0.01 mol / kg or more, from the viewpoint of ease of manufacturing the rubber composite.

[0076] The content of component (Cm) in the rubber composite obtained by the rubber composite manufacturing method of this embodiment is preferably 0.02 mol / kg or more and 1 mol / kg or less, more preferably 0.05 mol / kg or more, even more preferably 0.08 mol / kg or more, even more preferably 0.10 mol / kg or more, even more preferably 0.11 mol / kg or more, even more preferably 0.14 mol / kg or more, and more preferably 0.75 mol / kg or less, even more preferably 0.50 mol / kg or less, and even more preferably 0.30 mol / kg or less. From the viewpoint of improving the water resistance of the crosslinked rubber composition and suppressing the decrease in mechanical strength due to water absorption, the content of component (Cm) in the rubber composite obtained by the rubber composite manufacturing method of this embodiment is preferably above the lower limit, and from the viewpoint of ease of manufacturing the rubber composite, it is preferably below the upper limit. Preferably, the content of sodium element and components other than component (Cm) in the rubber composite obtained by the rubber composite manufacturing method of this embodiment is the same as the content of sodium element and components other than component (Cm) in the rubber composite of this embodiment.

[0077] [Rubber Compound] In this embodiment, "rubber compound" refers to a composite material obtained by kneading the rubber composite material of this embodiment or the rubber composite material obtained by the method for manufacturing the rubber composite material of this embodiment, in a state before crosslinking. The rubber compound preferably contains at least a crosslinking agent, and in addition to the crosslinking agent, it may also contain additives that can be used as additives in the field of rubber, such as zinc oxide, crosslinking accelerators (vulcanization accelerators), crosslinking accelerators (vulcanization accelerators), fillers, softeners, fatty acids, antioxidants, deconjugates, colorants, pH adjusters, and curing resins. Furthermore, solid rubber may be newly added in addition to the rubber components when preparing the rubber composite material. When newly adding solid rubber, the solid rubber may be the same as those exemplified as component (A): rubber component, but instead of adding it in latex form, solid rubber should be added. Examples of crosslinking agents include sulfur-based crosslinking agents (e.g., sulfur such as powdered sulfur, sulfurous salt, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur; sulfur-containing compounds such as disulfide amines, polymer polysulfides, sulfur olefin adducts, sulfur chloride, sulfur dichloride; insoluble polymer sulfur, etc.), peroxide-based crosslinking agents, and quinoid-based crosslinking agents, among which sulfur-based crosslinking agents or peroxide-based crosslinking agents are preferred. The amount of crosslinking agent added is not particularly limited, but is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 0.5 parts by mass or more, even more preferably 1.0 part by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, per 100 parts by mass of rubber component.

[0078] Furthermore, the crosslinking accelerator may be included, which has the effect of promoting crosslinking by the crosslinking agent. When a sulfur-based crosslinking agent is used, it is preferable to include a crosslinking accelerator (vulcanization accelerator). When a sulfur-based crosslinking agent (vulcanization 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 thiram-based vulcanization accelerator, a dithiocarbamate-based vulcanization accelerator, etc., as the crosslinking accelerator (vulcanization accelerator).

[0079] Examples of the fillers include carbon black and silica. These fillers may be used individually or in combination of two or more. There are no particular restrictions on the content of the fillers, but preferably it is 10 to 150 parts by mass, and more preferably 20 to 100 parts by mass, per 100 parts by mass of the rubber component.

[0080] Examples of the softening agent include aromatic oils, paraffin oil, naphthenic oil, vegetable oils other than castor oil, low PCA oils such as MES, TDAE, SRAE, and heavy naphthenic oil. Suitable low PCA oils include various plant-derived oils that can be 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 softening agent 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 even 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.

[0081] Examples of the aforementioned fatty acids include stearic acid, palmitic acid, arachidic acid, oleic acid, linoleic acid, and arachidonic acid. Among these, stearic acid is preferred. The content of the aforementioned fatty acids is not particularly limited, but is preferably 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 1 part by mass or more and 4 parts by mass or less, per 100 parts by mass of the rubber component.

[0082] Examples of the aforementioned antioxidants include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6C), 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). The content of the aforementioned antioxidants is not particularly limited, but is preferably 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 1 part by mass or more and 3 parts by mass or less, per 100 parts by mass of the rubber component. The total content of the antioxidants is preferably 0.2 parts by mass or more and 10 parts by mass or less, and more preferably 1 part by mass or more and 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0083] The content of the zinc oxide (zinc oxide) is not particularly limited, but is preferably 1 to 10 parts by mass, and more preferably 1.5 to 8 parts by mass, per 100 parts by mass of the rubber component.

[0084] [Method for Manufacturing Rubber Compound] The method for manufacturing the rubber compound is not particularly limited, but it is preferable to have a kneading step of kneading the rubber composite material of this embodiment or the rubber composite material obtained by the method for manufacturing the rubber composite material of this embodiment. In the kneading step, it is preferable to knead the rubber composite material and then add at least a crosslinking agent and knead it. In addition to the crosslinking agent, the additives mentioned above may also be added. Furthermore, in the kneading step, in addition to the rubber components contained in the rubber composite material, solid rubber may also be added. In this embodiment, in the rubber compound and the crosslinked rubber composition described later, the content of fibrous cellulose per 100 parts by mass of rubber components is preferably 0.1 parts by mass or more and 50 parts by mass or less, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, and more preferably 40 parts by mass or less, and even more preferably 25 parts by mass or less, from the viewpoint of improving water resistance and mechanical properties.

[0085] The method for manufacturing a rubber compound is not particularly limited, but it is preferable to include a step of kneading the rubber composite material. Kneading improves the dispersibility of crosslinking agents and other additives that are subsequently added. Kneading can be done by conventional methods, but it may also be done by low-temperature kneading using a roll machine such as an open roll, or by high-temperature kneading using a Banbury mixer or the like. Among these, low-temperature kneading is preferable from the viewpoint of dispersibility of fibrous cellulose in the rubber composite material. The temperature for low-temperature kneading is preferably 15°C to 70°C, more preferably 20°C to 65°C, and even more preferably 25°C to 60°C. The temperature for high-temperature kneading is preferably 80°C to 200°C. Furthermore, the rubber compound is manufactured by adding additives such as crosslinking agents to the kneaded rubber composite material and kneading them together.

[0086] Mixing is the process of uniformly dispersing crosslinking agents and other compounding agents in a rubber composite (preferably a pre-mixed rubber composite). Mixing may be carried out as is well known, for example, using a Banbury mixer, kneader, or open roll. Examples of crosslinking agents include sulfur and peroxides. Examples of other compounding agents include the additives mentioned above and solid rubber.

[0087] [Crosslinked Rubber Composition and Method for Manufacturing the Same] The crosslinked rubber composition of this embodiment is obtained by crosslinking a rubber compound containing a crosslinking agent. Furthermore, by molding during the crosslinking process, a crosslinked rubber composition (crosslinked rubber product) of a desired shape can be obtained. That is, the method for manufacturing the crosslinked rubber composition preferably includes the steps of crosslinking and molding a rubber compound containing a rubber composite material and a crosslinking agent. The method for manufacturing the crosslinked rubber composition of this embodiment may further include the step of molding the rubber compound obtained by the kneading step into the intended shape (molding step). Molding in this molding step can be carried out by various molding methods using an extrusion molding machine, calender roll, press, injection molding machine, transfer molding machine, hollow molding machine, foam molding machine, etc. The method should be appropriately selected according to the shape, application, and molding method of the final product. Note that the kneading step and the molding step may be carried out separately or continuously.

[0088] Regarding crosslinking, there are no particular restrictions on temperature as long as the conditions for the crosslinking reaction proceed, but generally, crosslinked rubber is obtained by heating the uncrosslinked rubber compound obtained by kneading to crosslink it (also called vulcanization if sulfur is included). The heating temperature is preferably 140°C or higher, preferably 200°C or lower, and more preferably 180°C or lower. Therefore, the heating temperature is preferably around 140 to 200°C, and more preferably around 140 to 180°C. For crosslinking, for example, a crosslinking apparatus that performs mold crosslinking, can crosslinking, continuous crosslinking, etc., can be used.

[0089] [Physical Properties of the Crosslinked Rubber Composition] <Water Absorption Rate> In this embodiment, it is preferable that the water absorption rate of the crosslinked rubber composition, as measured in accordance with JIS K 7209A method:2000, is low. Specifically, it is preferably 15% by mass or less, more preferably 13% by mass or less, even more preferably 11% by mass or less, and even more preferably 9% by mass or less. The lower limit is not particularly limited, and is 0% by mass or more. The water absorption rate is measured by the method described in the examples.

[0090] <Modulus> In this embodiment, it is preferable that the change in modulus before and after the water absorption test is small. The ratio of the 50% modulus of the crosslinked rubber composition after the water absorption test (measured in accordance with JIS K 6251:2017) to the 50% modulus of the crosslinked rubber composition before the water absorption test (measured in accordance with JIS K 6251:2017) (50% modulus after water absorption test / 50% modulus before water absorption test) is preferably 0.7 or more and 1.2 or less, more preferably 0.85 or more, more preferably 1.15 or less, even more preferably 1.10 or less, and even more preferably 1.05 or less. Water absorption test: A test piece of the crosslinked rubber composition (Type 6 dumbbell as described in JIS K 6251:2017) is immersed in ion-exchanged water at 70°C for 48 hours.

[0091] The ratio of the 100% modulus of the crosslinked rubber composition after the water absorption test to the 100% modulus of the crosslinked rubber composition before the water absorption test (100% modulus after water absorption test / 100% modulus before water absorption test) is preferably 0.5 or more and 1.1 or less, more preferably 0.55 or more, even more preferably 0.6 or more, even more preferably 0.65 or more, and most preferably 1.05 or less.

[0092] The ratio of the 300% modulus of the crosslinked rubber composition after the water absorption test to the 300% modulus of the crosslinked rubber composition before the water absorption test (300% modulus after water absorption test / 300% modulus before water absorption test) is preferably 0.4 or higher, and from the viewpoint of ease of manufacturing the crosslinked rubber composition, preferably 1.0 or lower, more preferably 0.55 or higher, and may also be 0.95, 0.9 or lower, or 0.85 or lower. The modulus is measured by the method described in the examples.

[0093] <Applications> The crosslinked rubber composition of this embodiment can be used for a variety of applications and is not particularly limited. For example, it is suitably used in sealing materials, hoses, shoe soles, tire components, vibration-damping rubber, etc. Among these, the crosslinked rubber composition is preferably used in tires.

[0094] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples.

[0095] <Manufacturing Example 1> [Phosphorus Oxo-Oxidation Treatment] As raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solids content 93% by mass, basis weight 245 g / m²) ２ A sheet-like material with a Canadian standard filtration capacity (CSF) of 700 mL, measured according to JIS P 8121-2:2012 after disintegration, was used.

[0096] The raw pulp was subjected to phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (oven-dry mass) of the raw pulp to adjust the mixture to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain chemically impregnated pulp. Next, the obtained chemically impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining phosphorylated pulp.

[0097] Next, the obtained phosphorylated pulp was subjected to a washing treatment. The washing treatment was carried out by repeatedly adding 10 L of deionized water to 100 g (dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the dispersion to ensure uniform pulp distribution, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate was 100 μS / cm or less.

[0098] Next, the washed phosphorylated pulp was subjected to neutralization treatment as follows. First, the washed phosphorylated pulp was diluted with 10 L of deionized water, and then a 1N sodium hydroxide aqueous solution was gradually added while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated and washed to obtain phosphorylated pulp that had undergone neutralization treatment.

[0099] The obtained phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed an absorption of 1,230 cm⁻¹. －１ Absorption based on the P=O of phosphate groups was observed in the vicinity, confirming that phosphate groups were added to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of Phosphorus Oxoacid Group Amount] below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0100] Deionized water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was processed twice at a pressure of 200 MPa using a wet atomizing device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fibrous cellulose dispersion containing phosphorylated microfibrous cellulose. The fiber width of the phosphorylated microfibrous cellulose was measured using a transmission electron microscope and found to be 3–5 nm. The degree of polymerization of the phosphorylated microfibrous cellulose was 630.

[0101] X-ray diffraction confirmed that this phosphorylated microfibrous cellulose maintained its type I cellulose crystal structure. The amount of phosphate groups (amount of first dissociated acid) measured by the method described in [Measurement of Phosphorus Oxoacid Groups] below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0102] [Measurement of Phosphorus Oxoacid Group Content] In measuring the amount of phosphorus oxoacid groups (phosphate groups) in cellulose fibers, first, ion-exchanged water was added to the target cellulose fibers to prepare a slurry with a solid content of 0.2% by mass. The obtained slurry was then treated with an ion-exchange resin, and the content was measured by titration using an alkali. The treatment with the ion-exchange resin was performed by adding 1 / 10 the volume of strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the slurry, shaking for 1 hour, and then pouring it onto a mesh with a mesh opening of 90 μm to separate the resin from the slurry. The titration using an alkali was performed by adding 10 μL of 0.1 N sodium hydroxide aqueous solution to the cellulose fiber-containing slurry after treatment with the ion-exchange resin at intervals of 5 seconds, and measuring the change in the pH value of the slurry. Nitrogen gas was blown into the slurry starting 15 minutes before the start of the titration. In this neutralization titration, two points are observed in the curve plotting the measured pH against the amount of alkali added, where the increment (the derivative of pH with respect to the amount of alkali added) is maximum. Of these, the first maximum increment obtained after starting to add alkali is called the first endpoint, and the next maximum increment obtained 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 the first dissociated acid in the slurry used for titration. Also, the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for titration. Note that the amount of phosphooxoacid groups (amount of first dissociated acid) (mol / g) was defined as the amount of alkali (mol / g) required from the start of titration to the first endpoint divided by the solid content (g) in the slurry being titrated. Similarly, the amount of alkali (mol / g) required from the start of titration to the second endpoint divided by the solid content (g) in the slurry being titrated was defined as the total amount of dissociated acid (mol / g).

[0103] <Example 1> To the phosphorylated microfibrous cellulose dispersion obtained in Production Example 1, ion-exchanged water was added so that the solid content concentration of phosphorylated microfibrous 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 6-inch diameter agitator blade was attached. The mixture was stirred at 1,000 rpm for 5 minutes to obtain the diluted phosphorylated microfibrous cellulose dispersion.

[0104] [Mixing Process] Natural rubber latex (HA-LATEX, manufactured by Resitex Co., Ltd., solid content concentration 61.5%) and a diluted phosphorylated fine fibrous cellulose dispersion were mixed so that each solid content was in parts by mass as shown in Table 1-1. A tornado stirrer was used as the agitator, and a 6-inch diameter agitator was attached, and the mixture was stirred at 1,000 rpm for 5 minutes to obtain mixture 1 (solid content concentration 5.6% by mass). To mixture 1, an aqueous solution of aluminum sulfate (aluminum sulfate 14-18 hydrate, manufactured by Kanto Chemical Co., Ltd.) with a solid content concentration of 10% by mass was mixed so that each solid content was in parts by mass as shown in Table 1-1. A tornado stirrer was used as the agitator, and a 6-inch diameter agitator was attached, and the mixture was stirred at 1,000 rpm for 3 minutes to obtain mixture 2 (solid content concentration 5.6% by mass).

[0105] [Solidification Process] The mixture 2 was spread on a tray (300 cm long, 21 cm wide) with a Teflon® coating on its surface, so that the thickness after drying would be 0.05 mm. It was then dried in a dryer at 40°C for 48 hours to obtain a sheet-like dried product.

[0106] [Washing Process] The above dried material was immersed in 20 times the amount of deionized water at room temperature and stirred for 24 hours to wash it. After 24 hours, it was removed from the deionized water, the water was lightly squeezed out, and then spread out on a tray and dried at 40°C for 24 hours to obtain a sheet-like rubber composite material.

[0107] [Preparation of Rubber Compound] The rubber composite material after the [washing process] was kneaded for 10 minutes at a rotation speed of 26 / 30 rpm without heating using an open roll mill (6-inch double roll mill, manufactured by Daihan Co., Ltd.). Next, 1.5 parts by mass of sulfur (Mukuron OT-20, manufactured by Shikoku Chemicals, Inc.), 2 parts by mass of vulcanization accelerator (zinc oxide, manufactured by Hayashi Pure Chemical Industries, Ltd.), 2 parts by mass of antioxidant (ANTAGE RD, manufactured by Kawaguchi Chemical Industries, Ltd.), 2 parts by mass of stearic acid (50S stearic acid, manufactured by Shin Nippon Rika Co., Ltd.), and 2 parts by mass of vulcanization accelerator (Noxellar MSA-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added to 100 parts by mass of rubber component, and kneaded for 6 minutes to obtain a rubber compound.

[0108] [Crosslinking Process] The obtained rubber compound was placed in a mold and pressed and heated at 150°C for 15 minutes to produce a sheet of crosslinked rubber composition with a thickness of 2 mm.

[0109] <Example 2> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 1, except that instead of an aqueous aluminum sulfate solution, an aqueous magnesium sulfate solution (magnesium sulfate heptahydrate, manufactured by Kanto Chemical Co., Ltd.) with a solid content concentration of 10% by mass was mixed with the mixture 1 so that each solid content was in the parts by mass shown in Table 1-1.

[0110] <Example 3> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 1, except that a mixture mainly composed of calcium 2-ethylhexanoate and calcium neodecanoate (5% Calcium Hydro-Cem, manufactured by Borchers, Milliken & Company) was added to mixture 1 instead of an aqueous aluminum sulfate solution, so that the respective solid components were in parts by mass as shown in Table 1-1.

[0111] <Example 4> The same procedure as in Example 1 was carried out to obtain a sheet of crosslinked rubber composition, except that an aqueous aluminum sulfate solution was mixed with the mixed solution 1 so that the respective solid components were in parts by mass as shown in Table 1-1.

[0112] <Example 5> The same procedure as in Example 1 was carried out to obtain a sheet of crosslinked rubber composition, except that an aqueous aluminum sulfate solution was mixed with the mixed solution 1 so that the respective solid components were in parts by mass as shown in Table 1-1.

[0113] <Example 6> [Mixing Step] A phosphorylated fine fibrous cellulose dispersion (solid content concentration 1.0% by mass) obtained in the same manner as in Example 1 was mixed with an aqueous solution of aluminum sulfate (aluminum sulfate 14-18 hydrate, manufactured by Kanto Chemical Co., Ltd.) with a solid content concentration of 10% by mass so that each solid content was in parts by mass as shown in Table 1-1. A tornado stirrer was used as the stirrer, and a 6-inch diameter stirring blade was attached, and the mixture was stirred at 1,000 rpm for 3 minutes to obtain mixture 3 (solid content concentration 1.2% by mass). Natural rubber latex (HA-LATEX, manufactured by Resitex Co., Ltd., solid content concentration 61.5% by mass) was mixed into mixture 3 so that each solid content was in parts by mass as shown in Table 1-1. A tornado stirrer was used as the stirrer, and a 6-inch diameter stirring blade was attached, and the mixture was stirred at 1,000 rpm for 5 minutes to obtain mixture 4 (solid content concentration 5.6% by mass). Except for using mixed liquid 4 in the [solidification process], adding 2 parts by mass of a crosslinking agent (Perkmill D, manufactured by NOF Corporation, dicumyl peroxide), 3 parts by mass of two types of zinc oxide (manufactured by Seido Chemical Industry Co., Ltd.), and 1.5 parts by mass each of antioxidants (ANTAGE MB, ANTAGE RD, manufactured by Kawaguchi Chemical Industry Co., Ltd.) per 100 parts by mass of rubber component in the [production of rubber compound], and pressing and heating at 165°C for 20 minutes in the [crosslinking process], the same process as in Example 1 was carried out to obtain a sheet of crosslinked rubber composition.

[0114] In Example 7, the same procedure as in Example 6 was followed to obtain a sheet of crosslinked rubber composition, except that in the [Preparation of Rubber Compound], 1.5 parts by mass of sulfur (Mukuron OT-20, manufactured by Shikoku Chemicals, Inc.), 2 parts by mass of vulcanization accelerator (zinc oxide, manufactured by Hayashi Pure Chemical Industries, Ltd.), 2 parts by mass of antioxidant (ANTAGE RD, manufactured by Kawaguchi Chemical Industries, Ltd.), 2 parts by mass of stearic acid (50S stearic acid, manufactured by Shin Nippon Rika Co., Ltd.), and 2 parts by mass of vulcanization accelerator (Noxellar MSA-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added per 100 parts by mass of rubber component, and in the [Crosslinking Process], the sheet was obtained by pressing and heating at 150°C for 15 minutes.

[0115] <Example 8> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 1, except that instead of an aqueous aluminum sulfate solution, an aqueous magnesium sulfate solution (magnesium sulfate heptahydrate, manufactured by Kanto Chemical Co., Ltd.) with a solid content concentration of 10% by mass was mixed with the mixture so that each solid content was in the parts by mass shown in Table 1-1.

[0116] <Example 9> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 1, except that instead of an aqueous aluminum sulfate solution, an aqueous magnesium sulfate solution (magnesium sulfate heptahydrate, manufactured by Kanto Chemical Co., Ltd.) with a solid content concentration of 10% by mass was mixed with the mixture so that each solid content was in the parts by mass shown in Table 1-1.

[0117] <Example 10> [Mixing Step] Mixture 1, obtained in the same manner as in Example 1, was mixed with an aqueous solution of octyldimethylethylammonium ethyl sulfate (Kachiogen ES-OW30, static surface tension: 62.0 mN / m, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) with a solid content concentration of 10% by mass, so that each solid content was in parts by mass as shown in Table 1-1. A tornado stirrer was used as the agitator, and a 6-inch diameter agitator was attached, and the mixture was stirred at 1,000 rpm for 5 minutes to obtain mixture 5. An aqueous solution of magnesium sulfate (magnesium sulfate heptahydrate, manufactured by Kanto Chemical Co., Ltd.) with a solid content concentration of 10% by mass was mixed into mixture 5 so that each solid content was in parts by mass as shown in Table 1-1. A tornado stirrer was used as the agitator, and a 6-inch diameter agitator was attached, and the mixture was stirred at 1,000 rpm for 3 minutes to obtain mixture 6. Mixture 6 was used in the [Solidification Step] and the same treatment as in Example 1 was carried out. The [washing process], [rubber compound preparation], and [crosslinking process] were carried out in the same manner as in Example 1 to obtain a sheet of crosslinked rubber composition.

[0118] <Example 11> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 10, except that a 10% by mass aqueous solution of polyoxyalkylene decyl ether (Neugen XL-80, static surface tension: 29.7 mN / m, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) with a solid content concentration of 10% by mass was mixed with the mixture 1 so that each solid content was in the parts by mass shown in Table 1-1.

[0119] <Example 12> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 10, except that a 10% by mass aqueous solution of polyoxyalkylene decyl ether (Neugen XL-80, static surface tension: 29.7 mN / m, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) with a solid content concentration of 10% by mass was mixed with the mixed solution 1 so that each solid content was in the parts by mass shown in Table 1-1.

[0120] <Example 13> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 10, except that a 10% by mass aqueous solution of polyoxyalkylene decyl ether (Neugen XL-80, static surface tension: 29.7 mN / m, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) with a solid content concentration of 10% by mass was mixed with the mixed solution 1 so that each solid content was in the parts by mass shown in Table 1-1.

[0121] <Example 14> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 10, except that instead of an aqueous solution of octyldimethylethylammonium ethyl sulfate, an aqueous solution of DTMACL (dodecyltrimethylammonium chloride, static surface tension: 35.2 mN / m) (manufactured by Tokyo Chemical Industry Co., Ltd.) with a solid content concentration of 10% by mass was mixed with the mixture so that each solid content was in the parts by mass shown in Table 1-1.

[0122] <Comparative Example 1> Mixture 1' was obtained in the same manner as in Example 1, except that an aqueous aluminum sulfate solution was not added in the [mixing step], the [washing step] was not performed, and natural rubber latex (ULACOL, manufactured by Resitex Co., Ltd.) was used. In the [immobilization step], mixture 1' was used instead of mixture 2, and a rubber compound was obtained in the same manner as in Example 1, except that 2 parts by mass of a crosslinking agent (Parkmill D, manufactured by NOF Corporation), 3 parts by mass of vulcanization accelerators (two types of zinc oxide, manufactured by Seido Chemical Industry Co., Ltd.), and 1.5 parts by mass each of anti-aging agents (ANTAGE MB, ANTAGE RD, manufactured by Kawaguchi Chemical Industry Co., Ltd.) were added per 100 parts by mass of rubber component. In the [crosslinking step], the obtained rubber compound was placed in a mold and pressed and heated at 165°C for 20 minutes to produce a sheet of crosslinked rubber composition with a thickness of 2 mm.

[0123] <Comparative Example 2> Except for the absence of aluminum sulfate aqueous solution in the [mixing step] and the [washing step], and the use of natural rubber latex (ULACOL, manufactured by Resitex Co., Ltd.), the same procedure was followed to obtain a sheet of crosslinked rubber composition.

[0124] <Comparative Example 3> The same procedure as in Example 1 was followed, except that the [washing step] was omitted, to obtain a sheet of crosslinked rubber composition.

[0125] <Comparative Example 4> The same procedure as in Example 2 was followed, except that the [washing step] was omitted, to obtain a sheet of crosslinked rubber composition.

[0126] <Comparative Example 5> The process was carried out in the same manner as in Example 3, except that the [washing step] was omitted, to obtain a sheet of crosslinked rubber composition.

[0127] <Comparative Example 6> The process was carried out in the same manner as in Example 6, except that the [washing step] was omitted, to obtain a sheet of crosslinked rubber composition.

[0128] <Comparative Example 7> The process was carried out in the same manner as in Example 7, except that the [washing step] was omitted, to obtain a sheet of crosslinked rubber composition.

[0129] <Comparative Example 8> A sheet of crosslinked rubber composition was obtained by the same procedure as in Example 7, except that instead of an aqueous aluminum sulfate solution in the [mixing step], an aqueous magnesium sulfate solution (magnesium sulfate heptahydrate, manufactured by Kanto Chemical Co., Ltd.) with a solid content concentration of 10% by mass was added, so that the amount of magnesium sulfate was 18 parts by mass (the concentration of magnesium element in the solid content was 0.58% by mass) per 500 parts by mass of rubber component, and the [washing step] was not performed.

[0130] <Comparative Example 9> A sheet of crosslinked rubber composition was obtained by performing the same procedure as in Example 1, except that instead of an aqueous solution of aluminum sulfate in the [mixing step], an aqueous dispersion of calcium stearate (LB Coat LBK-222, manufactured by Toho Chemical Industry Co., Ltd.) was added so that the amount of calcium stearate was 50 parts by mass per 500 parts by mass of rubber component, and natural rubber latex (ULACOL, manufactured by Resitex Co., Ltd.) was used.

[0131] <Comparative Example 10> Except that natural rubber latex (ULACOL, manufactured by Resitex Co., Ltd.) was used in the [mixing step], a 10% by mass sodium methacrylate aqueous solution (sodium methacrylate S-MA, manufactured by Asada Chemical Industries, Ltd.) was added instead of an aluminum sulfate aqueous solution in an amount of 79.5 parts by mass of sodium methacrylate per 500 parts by mass of rubber component, and the [washing step] was omitted, the same procedure as in Example 1 was performed to obtain mixed solution 2'. In the [solidification step], mixed solution 2' was used instead of mixed solution 2, and in the [production of rubber compound], 2 parts by mass of a crosslinking agent (Parkmill D, manufactured by NOF Corporation, dicumyl peroxide), 3 parts by mass of a vulcanization accelerator (two types of zinc oxide, manufactured by Seido Chemical Industry Co., Ltd.), and 1.5 parts by mass each of anti-aging agents (ANTAGE MB, ANTAGE RD, manufactured by Kawaguchi Chemical Industry Co., Ltd.) were added per 100 parts by mass of rubber component, the same procedure as in Example 1 was performed to obtain mixed solution 2'. In the [crosslinking process], the rubber compound obtained was placed in a mold and pressed and heated at 165°C for 20 minutes to obtain a sheet of crosslinked rubber composition with a thickness of 2 mm.

[0132] <Comparative Example 11> The process was carried out in the same manner as in Example 1, except that natural rubber latex (ULACOL, manufactured by Resitex Co., Ltd.) was used in the [mixing step], a 10% by mass sodium methacrylate aqueous solution (sodium methacrylate S-MA, manufactured by Asada Chemical Industries, Ltd.) was added instead of an aluminum sulfate aqueous solution to a total of 79.5 parts by mass of sodium methacrylate, and the [washing step] was omitted, to obtain a sheet of crosslinked rubber composition.

[0133] <Reference Example 1> Solid natural rubber obtained by drying natural rubber latex (ULACOL, manufactured by Regitex Co., Ltd.) was kneaded for 10 minutes at a rotation speed of 26 / 30 rpm without heating using an open roll mill (6-inch double roll mill, manufactured by Daihan Co., Ltd.). Next, 2 parts by mass of a crosslinking agent (Parkmill D, manufactured by NOF Corporation), 3 parts by mass of vulcanization accelerators (2 types of zinc oxide, manufactured by Seido Chemical Industry Co., Ltd.), and 1.5 parts by mass each of anti-aging agents (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 with a thickness of approximately 2 mm or more. The obtained rubber compound was placed in a mold and pressed and heated at 165°C for 20 minutes to produce a sheet of crosslinked rubber composition with a thickness of 2 mm.

[0134] <Reference Example 2> Solid natural rubber obtained by drying natural rubber latex (HA-LATEX, manufactured by Resitex Co., Ltd.) was kneaded for 10 minutes at a rotation speed of 26 / 30 rpm without heating using an open roll mill (6-inch double roll mill, manufactured by Daihan Co., Ltd.). Next, 2 parts by mass of a crosslinking agent (Parkmill D, manufactured by NOF Corporation), 3 parts by mass of vulcanization accelerators (2 types of zinc oxide, manufactured by Seido Chemical Industry Co., Ltd.), and 1.5 parts by mass each of anti-aging agents (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 with a thickness of approximately 2 mm or more. A sheet of the crosslinked rubber composition was obtained by performing the same heat press treatment as in Reference Example 1.

[0135] <Reference Example 3> Solid natural rubber obtained by drying natural rubber latex (ULACOL, manufactured by Regitex Co., Ltd.) was kneaded for 10 minutes at a rotation speed of 26 / 30 rpm without heating using an open roll mill (6-inch double roll mill, manufactured by Daihan Co., Ltd.). Next, 1.5 parts by mass of sulfur (Mucron OT-20, manufactured by Shikoku Chemicals, Inc.), 2 parts by mass of vulcanization accelerator, 2 parts by mass of antioxidant (ANTAGE RD), 2 parts by mass of stearic acid (Stearic Acid 50S, Shin Nippon Rika Co., Ltd.), and 2 parts by mass of vulcanization accelerator (Noxellar MSA-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added to 100 parts by mass of rubber component, and kneaded for 6 minutes to obtain a rubber compound with a thickness of approximately 2 mm or more. The obtained rubber compound was placed in a mold and pressed and heated at 150°C for 10 minutes to produce a sheet of crosslinked rubber composition with a thickness of 2 mm.

[0136] <Reference Example 4> Solid natural rubber obtained by drying natural rubber latex (HA-LATEX, manufactured by Resitex Co., Ltd.) was kneaded for 10 minutes without heating at a rotation speed of 26 / 30 rpm using an open roll mill (6-inch double roll mill, manufactured by Daihan Co., Ltd.). Next, 1.5 parts by mass of sulfur (Mukuron OT-20, manufactured by Shikoku Chemicals, Inc.), 2 parts by mass of vulcanization accelerator, 2 parts by mass of antioxidant (ANTAGE RD), 2 parts by mass of stearic acid (Stearic Acid 50S, manufactured by Shin Nippon Rika Co., Ltd.), and 2 parts by mass of vulcanization accelerator (Noxellar MSA-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added to 100 parts by mass of rubber component, and kneaded for 6 minutes to obtain a rubber compound with a thickness of approximately 2 mm or more. A sheet of crosslinked rubber composition was obtained by performing the same heat press treatment as in Reference Example 3.

[0137] [Method for measuring the amount of metallic elements] 0.01 to 0.5 g of the dried material or rubber composite obtained in Examples 1 to 14 and Comparative Example 9 was taken, 7 mL of nitric acid and 1 mL of hydrogen peroxide were added, and acid decomposition was carried out using a pressurized decomposition apparatus (ETHOS UP, manufactured by Milestone General (MG)). After confirming that there were no undecomposed materials, the volume was adjusted to 20 mL and diluted as appropriate. The amount of metallic elements was measured using ICP-OES (CIROS120, manufactured by Rigaku Corporation).

[0138] [Water Absorption Test] Test specimens were obtained by punching out dumbbells (Dumbbell No. 6 type) as described in JIS K 6251:2017 from the sheets of the cross-linked rubber compositions obtained in Examples 1-14, Comparative Examples 1-11, and Reference Examples 1-4. Based on JIS K 7209A method:2000, the mass of the test specimens was measured under a 23°C 50% RH environment, and then immersed in ion-exchanged water at 70°C for 48 hours. The mass was measured after wiping off the surface moisture. Water absorption rate (mass%) = 100 × (W - Wo) / Wo (where Wo is the mass under a 23°C 50% RH environment, and W is the mass after immersion in ion-exchanged water for 48 hours).

[0139] [Tensile Test] (Before water absorption test) Test specimens were obtained by punching out dumbbells (Dumbbell No. 6) as described in JIS K 6251:2017 from sheets of the crosslinked rubber composition obtained in Examples 1 to 14, Comparative Examples 1 to 11, and Reference Examples 1 to 4. Tensile tests were performed using a Strograph VG1F (manufactured by Toyo Seiki Seisakusho Co., Ltd.) according to JIS K 6251:2017 at 23±2℃, gauge length 20 mm, and tensile speed 500 mm / min, and the 50% modulus (σ50 (MPa)), 100% modulus (σ100 (MPa)), and 300% modulus (σ300 (MPa)) of the test specimens were measured.

[0140] (After water absorption test) Immediately after measuring the mass of the immersed test specimens used in the [water absorption test], a tensile test was performed using a Strograph VG1F (manufactured by Toyo Seiki Seisakusho Co., Ltd.) in accordance with JIS K 6251:2017 at 23±2℃, a gauge length of 20 mm, and a tensile speed of 500 mm / min, and the 50% modulus (σ50 (MPa)), 100% modulus (σ100 (MPa)), and 300% modulus (σ300 (MPa)) were measured. The closer the ratio of the modulus after the water absorption test to the modulus before the water absorption test (modulus after water absorption test / modulus before water absorption test) is to 1.0, the better the water resistance of the crosslinked rubber composition.

[0141]

[0142]

[0143] The results shown in Tables 1-1 and 1-2 indicate that the crosslinked rubber compositions obtained in the examples had lower water absorption and superior water resistance compared to the crosslinked rubber compositions of the comparative examples. Furthermore, the above effects were similar in both the case of peroxide crosslinking and sulfur crosslinking.

[0144] The crosslinked rubber composition of this embodiment has a low water absorption rate and does not easily decrease in mechanical strength after water absorption, so it is expected to be used in various tire components such as tire treads, sidewalls, and inner liners for passenger cars, small and medium-sized trucks, and large vehicles (large trucks, buses, construction vehicles, etc.), as well as exterior and interior materials, various rubber belts, various sealing materials, vibration isolation and damping materials, shoe soles, etc.

Claims

1. A rubber composite material containing the following components (A), (B), and (Cm), wherein component (A): rubber component, component (B): fibrous cellulose having anionic groups, component (Cm): metal element belonging to any of groups 2 to 14 of the periodic table, the content of component (Cm) in the rubber composite material is 0.02 mol / kg or more and 1 mol / kg or less, and the content of sodium element in the rubber composite material is 0.20 mol / kg or less.

2. The rubber composite material according to claim 1, wherein component (B) contains fine fibrous cellulose with a fiber width of 1 nm or more and 1,000 nm or less.

3. The rubber composite material according to claim 1 or 2, wherein the degree of polymerization of component (B) is 100 or more and 800 or less.

4. The rubber composite material according to any one of claims 1 to 3, wherein the content of component (B) in the rubber composite material is 0.1% by mass or more and 60% by mass or less.

5. A rubber compound containing the rubber composite material and crosslinking agent described in any one of claims 1 to 4.

6. A crosslinked rubber composition obtained by crosslinking the rubber compound described in claim 5.

7. A method for producing a rubber composite, comprising the following mixing, solidification, and washing steps: Mixing step: A step of obtaining a mixed solution containing the following components (A), (B), (Cs), (D) and water. Component (A): Rubber component. Component (B): Fibrous cellulose having anionic groups. Component (Cs): Inorganic salt of a metal belonging to any of groups 2 to 14 of the periodic table, and / or organic acid salt of a metal belonging to any of groups 2 to 14 of the periodic table, provided that the number of carbon atoms in the organic acid is 15 or less. Component (D): Sodium ion. Solidification step: A step of removing water from the mixed solution to obtain a dried product. Washing step: A step of washing the dried product with water to obtain a rubber composite. In the mixed solution, the mol ratio of component (D) to metal ions belonging to any of groups 2 to 14 of the periodic table derived from component (Cs) (component (D) / metal ions of component (Cs)) is 1 / 1 or more and 10 / 1 or less.

8. A method for producing a rubber composite material according to claim 7, wherein component (B) contains fine fibrous cellulose having a fiber width of 1 nm or more and 1,000 nm or less.

9. A method for producing a rubber composite material according to claim 7 or 8, wherein the degree of polymerization of component (B) is 100 or more and 800 or less.

10. A method for producing a rubber composite material according to any one of claims 7 to 9, wherein the content of component (D) in the total solid components contained in the mixed liquid is greater than 0.20 mol / kg.

11. A method for producing a rubber composite material according to any one of claims 7 to 10, wherein the sodium element content in the rubber composite material is 0.20 mol / kg or less.

12. A method for producing a rubber composite material according to any one of claims 7 to 11, wherein the content of component (B) in the total solid components contained in the mixed liquid is 0.1% by mass or more and 60% by mass or less.

13. A method for producing a rubber composite material according to any one of claims 7 to 12, wherein the content of component (Cs) in the total solid components contained in the mixed liquid is 0.03 mol / kg or more and 0.5 mol / kg or less.

14. A method for producing a rubber compound, comprising a kneading step of kneading a rubber composite material obtained by the method for producing a rubber composite material according to any one of claims 7 to 13 and a crosslinking agent.

15. A method for producing a crosslinked rubber composition, comprising the step of crosslinking a rubber compound obtained by the method for producing a rubber compound described in claim 14.

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