Rubber composition and crosslinked rubber product

Abstract

To provide a rubber composition that enables production of a crosslinked rubber product having a high modulus, a method for producing the rubber composition, and a crosslinked rubber product formed by crosslinking and molding the rubber composition.SOLUTION: A rubber composition comprises a rubber component, fine fibrous cellulose having a fiber width of 1,000 nm or less, and a nonionic water-soluble polymer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a crosslinked rubber product. [Background technology]

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

[0003] Fine fibrous cellulose, with an average fiber width of 1000 nm or less, is also known as fibrous cellulose. This type of cellulose has attracted attention as a new material with a wide range of applications. For example, development of sheets, resin composites, and thickeners containing fine fibrous cellulose is underway. Furthermore, composite materials incorporating fine fibrous cellulose with resin emulsions and / or rubber latex are also being considered.

[0004] Cited Document 1 discloses a method for producing a rubber composition, the method comprising: (a) treating pulp with an acid; (b) mechanically defibrating the acid-treated pulp to prepare microfibrillated plant fibers having an average fiber length of 1 to 20 μm, an average fiber diameter of 10 μm or less, and an aspect ratio of 2 to 1000; (c) mixing the microfibrillated plant fibers obtained in step (b) with rubber latex to disperse the microfibrillated plant fibers in the rubber latex; and (d) drying the dispersion obtained in step (c), with the aim of providing a rubber composition in which microfibrillated plant fibers are well dispersed in the rubber component and have improved breaking properties. Furthermore, Patent Document 2 discloses a polymer composition comprising (I) a polymer; (II) a nanocellulose dispersion composition (NDC) comprising: (i) a carbon black filler, an elastomer latex, a wax, or any combination thereof; and (ii) nanocellulose; and (III) a carbon black additive, with the aim of providing a method for significantly improving the dispersibility of nanocellulose in a polymer blend. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-025141 [Patent Document 2] Special Publication No. 2022-508946 Summary of the Invention [Problem to be solved by the invention]

[0006] Cited Documents 1 and 2 disclose compositions containing cellulose nanofibers and elastomers, base rubbers, etc. However, Cited Documents 1 and 2 require further improvement in the physical properties of the crosslinked rubber after crosslinking. In particular, other physical properties that do not lead to breakage, such as modulus, have not been considered, leaving room for improvement. An object of the present invention is to provide a rubber composition from which a crosslinked rubber product having a high modulus can be obtained, a method for producing the same, and a crosslinked rubber product obtained by crosslinking and molding the rubber composition. [Means for solving the problem]

[0007] The present inventors have found that the above problems can be solved by adding a nonionic water-soluble polymer to a rubber composition containing fine fibrous cellulose. The present invention provides the following <1> ~ <8> Regarding. <1> A rubber composition comprising a rubber component, fine fibrous cellulose having a fiber width of 1,000 nm or less, and a nonionic water-soluble polymer. <2> The nonionic water-soluble polymer is at least one selected from the group consisting of vinyl alcohol-based polymers, alkyl celluloses, hydroxyalkyl celluloses, and alkylhydroxyalkyl celluloses. <1> The rubber composition according to claim 1. <3> The nonionic water-soluble polymer is at least one selected from the group consisting of polyvinyl alcohol, vinyl alcohol / vinyl acetate copolymer, methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose; <1> or <2> The rubber composition according to claim 1. <4> The rubber composition contains 1 part by mass or more and 200 parts by mass or less of fine fibrous cellulose per 100 parts by mass of the rubber component. <1> ~ <3> The rubber composition according to any one of the above. <5> The composition contains 5 parts by mass or more and 150 parts by mass or less of a nonionic water-soluble polymer relative to 100 parts by mass of fine fibrous cellulose. <1> ~ <4> The rubber composition according to any one of the above. <6> <1> ~ <5> 1. A crosslinked rubber product obtained by crosslinking and molding a rubber compound containing the rubber composition according to any one of 1 to 8 above and a crosslinking agent. <7> The method comprises, in this order: preparing a mixed liquid containing a rubber component, fibrous cellulose, and a nonionic water-soluble polymer; and drying the mixed liquid to obtain a rubber composition. <1> ~ <5> 10. A method for producing the rubber composition according to any one of the above items. <8> <7> and crosslinking and molding a rubber compound containing the rubber composition and a crosslinking agent. [Effects of the Invention]

[0008] According to the present invention, there are provided a rubber composition from which a crosslinked rubber product having a high modulus can be obtained, a method for producing the same, and a crosslinked rubber product obtained by crosslinking and molding the rubber composition. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fine fibrous cellulose having phosphorus oxo acid groups and pH. [Figure 2] 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and pH. [Figure 3] FIG. 1 is a schematic side cross-sectional view of a double drum dryer, which is an example of a heating cylindrical dryer. [Figure 4] FIG. 1 is a side view schematic diagram of a double drum dryer, which is an example of a heating cylindrical dryer. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Rubber composition] The rubber composition of the present embodiment contains a rubber component, fine fibrous cellulose having a fiber width of 1,000 nm or less, and a nonionic water-soluble polymer. According to the rubber composition of this embodiment, a crosslinked rubber product having a high modulus can be obtained by adding a nonionic water-soluble polymer together with fine fibrous cellulose to the rubber component. In addition, crosslinked rubber products with high modulus tend to have lower elongation at break and are less likely to stretch, so they can maintain their shape even when subjected to strong stress, and are expected to have improved durability. This embodiment will be described in detail below.

[0011] [Rubber component] The rubber composition of the present 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), and polysulfide rubber (T). Nitrile rubbers include modified nitrile rubbers such as hydrogenated nitrile rubber, carboxyl-modified nitrile rubber, silicone-modified nitrile rubber, maleic acid-modified nitrile rubber, and hydroxyl-modified nitrile rubber, as well as hydrogenated versions of these; and acrylonitrile-butadiene-isoprene copolymers in which part of the butadiene has been 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 used alone or in combination of two or more. Furthermore, these rubber components may be pre-crosslinked raw materials that do not have a crosslinked structure, or may have a crosslinked structure.

[0012] Among these, the rubber component is preferably a diene rubber, and is preferably at least one selected from natural rubber, nitrile rubber, butadiene rubber, and styrene-butadiene rubber, more preferably at least one selected from natural rubber, nitrile rubber, and styrene-butadiene rubber, and even more preferably at least one selected from natural rubber, carboxylated nitrile rubber, and styrene-butadiene rubber. The rubber component may be a pre-crosslinked raw material. The rubber component is preferably a latex of the rubber component. Use of the rubber component latex improves the dispersibility of the fine fibrous cellulose, making it easier to obtain a composite material with excellent tensile properties. When a rubber component latex is used, a solid rubber component may be further mixed in. The solid rubber component may be added when the rubber composition is masticated or when the rubber compound is prepared, but is preferably added when the rubber compound is prepared.

[0013] [Fine fibrous cellulose] The rubber composition of the present embodiment contains fine fibrous cellulose. The fine fibrous cellulose is not particularly limited, and any known fine fibrous cellulose can be used. The upper limit of the fiber width of the fine fibrous cellulose is 1000 nm or less, preferably 100 nm or less, more preferably 50 nm or less, even more preferably 20 nm or less, and even more preferably 10 nm or less. As will be described later, the rubber composition may contain cellulose fibers having a fiber width exceeding 1 μm (1000 nm) (hereinafter also referred to as "coarse cellulose fibers").

[0014] The average fiber width of the fine fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and still more preferably 2 nm or more and 10 nm or less. The fine fibrous cellulose is, for example, single-filament cellulose.

[0015] The fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fine fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast onto glass may be observed. Next, electron microscope images are observed at magnifications of 1000x, 5000x, 10000x, or 50000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions. (1) Draw a line X at any point in the observed image, and 20 or more fibers intersect with the line X. (2) Draw a line Y that intersects the line perpendicularly within the same image, and 20 or more fibers intersect the line Y. For observation images that satisfy the above conditions, the widths of fibers intersecting with lines X and Y are visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the widths of fibers intersecting with lines X and Y are read. In this way, the widths of at least 20 fibers x 2 x 3 = 120 fibers are read. The average of the read fiber widths is then taken as the number-average fiber width of the fine fibrous cellulose.

[0016] The fiber length of the fine fibrous cellulose is not particularly limited, but is, for example, preferably 0.1 μm to 1000 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, destruction of the crystalline regions of the fine fibrous cellulose can be suppressed. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

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

[0018] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably 50 to 10,000, more preferably 100 to 1,000. By setting the axial ratio to the above lower limit or more, a rubber composition containing the fine fibrous cellulose can be easily formed. By setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when the fine fibrous cellulose is used as a dispersion, handling such as dilution becomes easier.

[0019] In this embodiment, the fine fibrous cellulose has, for example, both crystalline regions and amorphous regions. Fine fibrous cellulose having both crystalline regions and amorphous regions and having an axial ratio within the above range is realized by the method for producing fine fibrous cellulose described below.

[0020] In this embodiment, the fine fibrous cellulose preferably has an ionic substituent. The ionic substituent may include, for example, either an anionic group or a cationic group, or both. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. Furthermore, the ionic substituent is preferably a group that is introduced into the fine fibrous cellulose via an ester bond or an ether bond, and more preferably a group that is introduced into the fine fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation between the fine fibrous cellulose and a compound that becomes the ionic substituent.

[0021] Examples of anionic groups as ionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xanthate groups or substituents derived from xanthate groups (sometimes simply referred to as xanthate groups), phosphonic groups or substituents derived from phosphonic groups, phosphine groups or substituents derived from phosphine groups, sulfonic groups or substituents derived from sulfonic groups, and carboxyalkyl groups. Among these, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, a substituent derived from a sulfur oxoacid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group, more preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group, and even more preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as the anionic group, the dispersibility of the fine fibrous cellulose can be further improved, for example, even under alkaline or acidic conditions, and as a result, a sheet excellent in hardness, strength, and elongation can be easily obtained. Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, sulfonium groups, etc. Among these, the cationic group is preferably an ammonium group.

[0022] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0023] [ka] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of the n α and α' is O. - and the rest are R or OR. Note that all of α and α' are O - The n α's may all be the same or may be different. b+ is a cation of one or more valences consisting of organic or inorganic substances.

[0024] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. In formula (1), n ​​is preferably 1.

[0025] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, and n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl and t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl and cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl and allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl and 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl and cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl and naphthyl groups.

[0026] In addition, the derivative group in R is a carboxy group, a carboxylate group (-COO - ), a hydroxy group, an amino group, an ammonium group, or another functional group to which at least one functional group selected from the group consisting of hydroxy, amino, and ammonium groups is added or substituted, but is not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, which facilitates penetration into the fiber raw material and increases the yield of fine fibrous cellulose. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fine fibrous cellulose, the multiple Rs present may be the same or different.

[0027] β b+is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. It should be noted that in formula (1), β b+ When a plurality of β b+ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0028] More specifically, examples of the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group include a phosphate group (-POH), a salt of a phosphate group, a phosphorous acid (phosphonic acid) group (-POH), and a salt of a phosphite (phosphonic acid) group. The phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group may also be a group in which a phosphate group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), or an alkyl phosphonic acid group (e.g., a methylphosphonic acid group).

[0029] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

[0030] [ka]

[0031] In formula (2), b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, multiple p's may be the same number or different numbers. In formula (2), β b+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by formula (2) are introduced into the fine fibrous cellulose, the multiple β b+ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0032] The amount of ionic substituent introduced into the fine fibrous cellulose is, for example, preferably 0.10 mmol / g or more and 5.20 mmol / g or less, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, still more preferably 0.60 mmol / g or more, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, still more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, even more preferably 1.50 mmol / g or less, and even more preferably 1.00 mmol / g or less, per 1 g (mass) of fine fibrous cellulose. Here, the denominator in the unit mmol / g is the ratio of the counter ion of the ionic substituent to a hydrogen ion (H + By setting the amount of ionic substituent introduced within the above range, it is possible to easily refine the fiber raw material and improve the stability of the fine fibrous cellulose.

[0033] The amount of ionic substituents introduced into the fine fibrous cellulose can be measured, for example, by neutralization titration after the cellulose fibers have been subjected to a micronization treatment. In the measurement by neutralization titration, the amount introduced is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fine fibrous cellulose.

[0034] 1 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fine fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into the fine fibrous cellulose is measured, for example, as follows. First, ion-exchange water is added to the target cellulose fiber to prepare a slurry with a solids concentration of 0.2% by mass. This slurry is processed four times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. The fine fibrous cellulose dispersion is then treated with a strongly acidic ion-exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 1 is obtained. The titration curve shown in the upper part of Figure 1 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of Figure 1 plots the pH increment (derivative value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points of maximum increment (derivative value of pH with respect to the amount of alkali added) are confirmed on the curve plotting the measured pH against the amount of alkali added. 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 first dissociated acid from the fine fibrous cellulose contained in the slurry used for titration; the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid from the fine fibrous cellulose contained in the slurry used for titration; and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid from the fine fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid groups introduced (mmol / g). Note that the term "amount of phosphorus oxo acid groups introduced" (or "amount of phosphorus oxo acid groups") simply refers to the amount of first dissociated acid. In Figure 1, the region from the start of titration to the first endpoint is referred to as Region 1, and the region from the first endpoint to the second endpoint is referred to as Region 2. For example, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the apparent amount of weakly acidic groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) decreases, and the amount of alkali required in Region 2 is less than the amount required in Region 1. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the first dissociated acid amount) corresponds to the amount of phosphorus atoms regardless of whether condensation occurs. Furthermore, if the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weakly acidic groups, and the amount of alkali required in Region 2 is reduced or may even be zero. In this case, there is only one point on the titration curve where the pH increment is maximized.

[0035] The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fine fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)), since the denominator indicates the mass of the acid-form fine fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with an arbitrary cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups in the fine fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C form)) can be determined by converting the denominator to the mass of the fine fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Phosphorus oxoacid group content (C type) = Amount of phosphorus oxoacid groups (acid form) / {1+(W-1)×P / 1000} P [mmol / g]: total amount of anions derived from phosphorus oxoacid groups in fibrous cellulose (total amount of dissociated acid from phosphorus oxoacid groups) W: Formula weight per valence of cation C (e.g., Na is 23, Al is 9)

[0036] 2 is a graph showing the relationship between the amount of NaOH added dropwise to a dispersion of fine fibrous cellulose having carboxy groups as ionic substituents and pH. The amount of carboxy groups introduced into the fine fibrous cellulose is measured, for example, as follows. First, ion-exchange water is added to the target cellulose fiber to prepare a slurry with a solids concentration of 0.2% by mass. This slurry is processed four times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. The fine fibrous cellulose dispersion is then treated with a strongly acidic ion-exchange resin. Next, the change in pH was observed while adding aqueous sodium hydroxide solution, and a titration curve like that shown in the upper part of Figure 2 was obtained. The titration curve shown in the upper part of Figure 2 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of Figure 2 plots the pH increment (derivative value) (1 / mmol) against the amount of alkali added. In this neutralization titration, a single point was identified in the curve plotting the measured pH against the amount of alkali added, where the increment (derivative value of pH with respect to the amount of alkali added) reached a maximum. This maximum point is called the first endpoint. Here, the region from the start of the titration to the first endpoint in Figure 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the dispersion used for titration. The amount of alkali required in the first region of the titration curve (mmol) is then divided by the solids content (g) in the dispersion containing the fine fibrous cellulose to be titrated to calculate the amount of carboxyl groups introduced (mmol / g).

[0037] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups in the acid-form fine fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fine fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with any cation C so as to be charge equivalent, the amount of carboxy groups in the fine fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) can be determined by converting the denominator to the mass of the fine fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Carboxylic acid content (C type) = Carboxylic acid amount / {1 + (W-1) × (Carboxylic acid amount) / 1000} W: Formula weight per valence of cation C (e.g., Na is 23, Al is 9)

[0038] When measuring the amount of ionic substituents by titration, adding too much sodium hydroxide solution or titrating too quickly can result in lower ionic substituent levels than expected, leading to inaccurate results. For example, a suitable amount and interval is to titrate 10–50 μL of 0.1 N sodium hydroxide solution every 5–30 seconds. To eliminate the influence of carbon dioxide dissolved in the fine fibrous cellulose dispersion, it is also recommended to measure the amount of ionic substituents while blowing an inert gas such as nitrogen into the slurry from 15 minutes before the start of titration until the end of titration.

[0039] The amount of sulfate ester groups and sulfone groups introduced into the fine fibrous cellulose is determined by wet ashing the obtained fine fibrous cellulose using perchloric acid and concentrated nitric acid, then diluting it at an appropriate ratio and measuring the amount of sulfur by ICP atomic emission spectrometry. The amount of sulfur divided by the bone-dry mass of the fine fibrous cellulose used is taken as the amount of sulfur oxoacid groups and sulfonic acid groups (unit: mmol / g).

[0040] To obtain fine fibrous cellulose having an ionic substituent introduced therein, it is preferable to have an ionic substituent introduction step for introducing an ionic substituent into a cellulose-containing fiber raw material, a washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and an acid treatment step may be included instead of or in addition to the washing step. Examples of the ionic substituent introduction step include a phosphorus oxo acid group introduction step, a carboxy group introduction step, a sulfur oxo acid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. Each of these steps will be explained below.

[0041] <Fiber raw materials> The fiber raw material is a cellulose-containing fiber raw material. Examples of the fiber raw material include, but are not limited to, wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP); semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP); and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, bamboo, and bagasse. Examples of deinked pulp include, but are not limited to, deinked pulp made from recycled paper. The pulp raw material of this embodiment may be one of the above-mentioned materials, or two or more of them may be mixed and used. Among the above pulps, for example, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Furthermore, among wood pulps, for example, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoint of having a high cellulose content and a high yield of fine fibrous cellulose during defibration treatment, and of obtaining long-fiber fine fibrous cellulose with a large axial ratio due to little decomposition of cellulose in the pulp. Note that the use of long-fiber fine fibrous cellulose with a large axial ratio tends to increase viscosity.

[0042] <Phosphorus oxoacid group introduction step> When obtaining cellulose fibers having ionic substituents, it is preferable to carry out a step of introducing an ionic substituent before the microfiber treatment step. An example of the step of introducing an ionic substituent is a step of introducing a phosphorus oxo acid group. The step of introducing a phosphorus oxo acid group is a step of allowing the cellulose-containing fiber raw material to react with at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing a phosphorus oxo acid group by reacting with a hydroxyl group possessed by the cellulose-containing fiber raw material. This step results in the production of cellulose fibers having phosphorus oxo acid groups.

[0043] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material with compound A may be reacted in the absence of compound B.

[0044] One example of a method for reacting compound A with a fiber raw material in the presence of compound B is to mix compound A and compound B with a fiber raw material in a dry, wet, or slurry state. Among these methods, using a dry or wet fiber raw material is preferred because of the high uniformity of the reaction, and using a dry fiber raw material is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably a cotton-like or thin sheet form. Compound A and compound B may be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state heated to or above their melting point. Among these methods, adding compound A and compound B in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred because of the high uniformity of the reaction. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited. When compound A and compound B are in solution form, the fiber raw material may be immersed in the solution and allowed to absorb the liquid before being removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0045] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, and examples thereof include, but are not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acids of various purities can be used, such as 100% phosphoric acid (orthophosphoric acid) and 85% phosphoric acid. Phosphorous acids include 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acids are compounds in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphate groups, ease of further improving defibration efficiency in the defibration step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferred.

[0046] The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the yield improvement effect and costs.

[0047] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

[0048] The amount of compound B added relative to the fiber raw material (bone dry mass) is not particularly limited, but is, for example, preferably 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0049] In the reaction of a fiber raw material containing cellulose with compound A, the reaction system may contain, in addition to compound B, for example, amides or amines. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0050] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material and then heat-treat the fiber raw material. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower. Various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a stirring dryer, rotary dryer, disk dryer, roll-type heater, plate-type heater, fluidized-bed dryer, band-type dryer, filtration dryer, vibration fluidized dryer, flash dryer, reduced-pressure dryer, infrared heater, far-infrared heater, microwave heater, and high-frequency dryer.

[0051] In this embodiment, the heat treatment can be carried out by, for example, adding compound A to a thin sheet-like fiber raw material by impregnation or other methods, followed by heating, or by heating while kneading or stirring the fiber raw material and compound A in a kneader or the like. This can suppress unevenness in the concentration of compound A in the fiber raw material, making it possible to more uniformly introduce phosphorus oxoacid groups onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be due to the fact that, when water molecules move to the surface of the fiber raw material as it is dried, dissolved compound A is attracted to the water molecules by surface tension, preventing it from migrating to the surface of the fiber raw material in the same way (i.e., causing unevenness in the concentration of compound A).

[0052] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the device system, for example, the water retained in the slurry and the water generated in the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include an oven with a blower system. Constantly discharging the water from the device system can suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as the acid hydrolysis of sugar chains in the fiber. This makes it possible to obtain fine fibrous cellulose with a high axial ratio.

[0053] The heat treatment time is, for example, preferably from 1 second to 300 minutes, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds, after the water content has been substantially removed from the fiber raw material. In this embodiment, by setting the heating temperature and heating time within appropriate ranges, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range.

[0054] The phosphorus oxo acid group introduction step may be carried out at least once, but may also be carried out twice or more times. By carrying out the phosphorus oxo acid group introduction step twice or more, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material.

[0055] The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 0.10 mmol / g or more and 5.20 mmol / g or less, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, still more preferably 1.00 mmol / g or more, and more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, per gram (mass) of cellulose fiber. By keeping the amount of phosphorus oxoacid groups introduced within the above ranges, it is possible to facilitate the finening of cellulose fibers in the fine-finishing treatment step and to increase the stability of the fine fibrous cellulose.

[0056] <Carboxy group introduction step> The ionic substituent introduction step may include a carboxyl group introduction step, which is carried out by subjecting a cellulose-containing fiber raw material to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or by treating the cellulose-containing fiber raw material with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.

[0057] The compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Furthermore, the derivative of the compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include imidized products of acid anhydrides of compounds having carboxy groups, and derivatives of acid anhydrides of compounds having carboxy groups. The imidized products of acid anhydrides of compounds having carboxy groups are not particularly limited, but examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0058] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, the derivative of an acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of compounds having carboxy groups such as dimethyl maleic anhydride, diethyl maleic anhydride, diphenyl maleic anhydride, etc., in which at least some of the hydrogen atoms have been substituted with a substituent such as an alkyl group or a phenyl group.

[0059] When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of, for example, a pH of 6 or higher and 8 or lower. This type of treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as the fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as the catalyst, and sodium hypochlorite as the sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. The TEMPO oxidation treatment may also be carried out under conditions of a pH of 10 to 11. This type of treatment is also called alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material.

[0060] The amount of carboxy groups introduced into cellulose fibers varies depending on the type of substituent. For example, when carboxy groups are introduced by TEMPO oxidation, the amount is preferably 0.10 mmol / g or more and 3.65 mmol / g or less, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, even more preferably 0.60 mmol / g or more, and more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, even more preferably 1.50 mmol / g or less, and even more preferably 1.00 mmol / g or less. Alternatively, when the substituent is a carboxymethyl group, the amount of carboxy groups introduced may be 5.8 mmol / g or less per gram of cellulose fiber (mass). By keeping the amount of carboxy groups introduced within the above range, it is possible to facilitate the fine-fibrillation of cellulose fibers in the fine-fibrillation treatment step and improve the stability of the fine fibrous cellulose.

[0061] <Sulfonic group introduction step> The ionic substituent introduction step may include a sulfonic group introduction step, in which hydroxyl groups in a fiber raw material containing cellulose react with sulfur oxoacid to obtain cellulose fibers having sulfonic groups (sulfonic group-introduced fibers).

[0062] In the sulfonic acid group introduction step, instead of compound A in the above-described <Phosphorus Oxo Acid Group Introduction Step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfonic acid groups by reacting with hydroxyl groups in cellulose-containing fiber raw materials is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Sulfurous acid can be 5% aqueous sulfurous acid. Sulfates or sulfites include lithium, sodium, potassium, and ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Sulfamic acid or the like can be used as the sulfuric acid amide. In the sulfonic acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus Oxo Acid Group Introduction Step> in the same manner.

[0063] In the sulfonic acid introduction step, the cellulose raw material is preferably mixed with an aqueous solution containing a sulfur oxoacid and urea and / or a urea derivative, and then the cellulose raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that sulfonic acid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably 100°C or higher and 300°C or lower, more preferably 120°C or higher, even more preferably 150°C or higher, and more preferably 250°C or lower, even more preferably 200°C or lower.

[0064] In the heat treatment step, heating is preferably performed until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material and the amount of aqueous solution containing sulfur oxoacid and urea and / or a urea derivative added, but is preferably 10 seconds or more and 10,000 seconds or less. For the heat treatment, various devices having a heat medium can be used, such as a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, an airflow dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

[0065] The amount of sulfonic groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more and 5.00 mmol / g or less, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, still more preferably 0.40 mmol / g or more, even more preferably 0.50 mmol / g or more, and more preferably 3.00 mmol / g or less. By setting the amount of sulfonic groups introduced within the above range, it is possible to facilitate the fine pulverization of cellulose fibers in the fine pulverization treatment step and to increase the stability of the fine fibrous cellulose.

[0066] <Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)> The ionic substituent introduction step may include an oxidation step using a chlorine-based oxidizing agent, in which a chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0067] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or may be dissolved in an appropriate solvent and then added.

[0068] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent is, for example, converted into an effective chlorine concentration, preferably from 1 to 1,000% by mass, more preferably from 5 to 500% by mass, and even more preferably from 10 to 100% by mass. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably from 1 to 100,000 parts by mass, more preferably from 10 to 10,000 parts by mass, and even more preferably from 100 to 5,000 parts by mass.

[0069] The reaction time with the chlorine-based oxidizing agent in the oxidation step using a chlorine-based oxidizing agent varies depending on the reaction temperature, but is, for example, preferably 1 minute to 1,000 minutes, more preferably 10 minutes to 500 minutes, and even more preferably 20 minutes to 400 minutes. The pH during the reaction is preferably 5 to 15, more preferably 7 to 14, and even more preferably 9 to 13. At the start of the reaction and during the reaction, it is preferable to maintain the pH constant (for example, pH 11) by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0070] <Xanthate group introduction step> The process for producing fine fibrous cellulose may include a xanthate group introduction step as an ionic substituent introduction step. In the xanthate group introduction step, hydroxyl groups in a fiber raw material containing cellulose are substituted with xanthate groups represented by the following formula (3), thereby obtaining cellulose fibers having xanthate groups (xanthate group-introduced fibers). -OCSS - M + ...(3) where M + is at least one selected from the group consisting of a hydrogen ion, a monovalent metal ion, an ammonium ion, and an aliphatic or aromatic ammonium ion.

[0071] In the xanthate group introduction process, the cellulose-containing fiber raw material is first treated with an alkaline solution to obtain alkali cellulose. Examples of alkaline solutions include aqueous alkali metal hydroxides and aqueous alkaline earth metal hydroxides. Among these, the alkaline solution is preferably an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide, and more preferably an aqueous sodium hydroxide solution. When the alkaline solution is an aqueous alkali metal hydroxide solution, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 4% by mass or more to 9% by mass or less, more preferably 5% by mass or more. By setting the alkali metal hydroxide concentration at or above the lower limit, the cellulose mercerization can be sufficiently promoted, the amount of by-products generated during the subsequent xanthation can be reduced, and as a result, the yield of xanthate group-introduced fiber can be increased. This allows the defibration process described below to be performed more effectively. Furthermore, by setting the alkali metal hydroxide concentration to the above upper limit or less, it is possible to prevent the aqueous alkali metal hydroxide solution from penetrating into the crystalline regions of cellulose while allowing mercerization to proceed, which makes it easier to maintain the cellulose type I crystal structure and further increases the yield of fine fibrous cellulose.

[0072] The alkali treatment time is preferably 30 minutes to 6 hours, more preferably 1 hour to 5 hours. By setting the alkali treatment time within the above range, the final yield can be increased, and productivity can be improved.

[0073] The alkali cellulose obtained by the alkali treatment is preferably subjected to solid-liquid separation to remove as much aqueous solution as possible. This reduces the water content during the subsequent xanthate treatment, thereby accelerating the reaction. As a method for solid-liquid separation, a general dehydration method such as centrifugation or filtration can be used. The concentration of alkali metal hydroxide contained in the alkali cellulose after solid-liquid separation is preferably 3% by mass or more and 8% by mass or less based on the total mass of the alkali cellulose after solid-liquid separation.

[0074] In the xanthate group introduction step, a xanthate treatment step is carried out after alkali treatment. In the xanthate treatment step, alkali cellulose is reacted with carbon disulfide (CS2) to form (-O - Na + ) group (-OCSS - Na + ) group to obtain xanthate group-introduced fibers. In the above, the metal ions introduced into the alkali cellulose are typically Na + However, similar reactions occur with other alkali metal ions.

[0075] In the xanthation treatment, it is preferable to supply 10% by mass or more of carbon disulfide relative to the bone dry mass of cellulose in the alkali cellulose. Furthermore, in the xanthation treatment, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, more preferably 1 hour or more. Although the contact of carbon disulfide with alkali cellulose allows xanthation to proceed quickly, it takes time for carbon disulfide to penetrate into the interior of the alkali cellulose, so it is preferable to set the reaction time within the above range. On the other hand, the contact time between carbon disulfide and alkali cellulose can be 6 hours or less, which allows sufficient penetration into the alkali cellulose mass after dehydration, and allows reactive xanthation to be almost completed.

[0076] The reaction temperature in the xanthate treatment is preferably 46 ° C or less. By setting the reaction temperature within the above range, it is easy to suppress the decomposition of alkali cellulose. In addition, by setting the reaction temperature within the above range, it is easy to react uniformly, so it is possible to suppress the generation of by-products, and further, it is also possible to suppress the removal of the generated xanthate group.

[0077] The amount of xanthate group introduced in the xanthate group introduction step is preferably 0.60mmol / g or more and 5.00mmol / g or less per 1g (mass) of fiber raw material, more preferably 0.70mmol / g or more, even more preferably 0.80mmol / g or more, even more preferably 1.00mmol / g or more, even more preferably 1.20mmol / g or more, and more preferably 3.00mmol / g or less. By making the amount of xanthate group introduced within the above range, it is possible to facilitate the fine pulverization of the fiber raw material and improve the stability of the fine fibrous cellulose.

[0078] <Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step)> The ionic substituent introduction step may include a phosphonic or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phosphonic or phosphine group (compound E) is used as an essential component. A ), an optional alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce phosphonic or phosphine groups into the fiber raw material.

[0079] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E A Examples of suitable compounds include vinyl phosphonic acid, phenyl vinyl phosphonic acid, and phenyl vinyl phosphinic acid. From the viewpoints of the efficiency of introducing substituents, the defibration efficiency, cost, and ease of handling, Compound E A is preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0080] Compound E A When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0081] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0082] Compound E A The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0083] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0084] <Sulfonic Group Introduction Step (Sulfoalkylation Step) (Second Sulfonic Group Introduction Step)> The ionic substituent introduction step may include a sulfone group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfone group (compound E) is used as an essential component. B ) and, as an optional component, an alkali compound and a compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a sulfonic acid group into the fiber raw material.

[0085] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E B Examples of suitable olefin sulfonates include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is particularly preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. B is preferably sodium vinyl sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0086] Compound E B When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0087] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0088] Compound E B The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0089] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0090] <Carboxyalkylation step (third carboxy group introduction step)> The ionic substituent introduction step may include a carboxyalkylation step. As an essential component, a compound having a reactive group and a carboxy group (compound E C ), an optional alkaline compound, and compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

[0091] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E C As the chloroisothiazolinone, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the standpoints of efficiency in introducing substituents, and therefore defibration efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0092] Compound E C When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0093] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0094] Compound E CThe amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0095] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0096] <Cationic group introduction step (cationization step)> As an essential component, a compound having a reactive group and a cationic group (compound E D ), an optional alkaline compound, and a compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce cationic groups into the fiber raw material.

[0097] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, etc. Among these, the cationic group is preferably an ammonium group. Compound E D As the alkyl group, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> as an optional component in the same manner. The amount added is also preferably as described above.

[0098] Compound E DWhen adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0099] The reaction temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0100] Compound E D The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0101] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 5 minutes to 500 minutes, and even more preferably from 10 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0102] <Cleaning process> In the process of obtaining cellulose fibers having ionic substituents, a washing step can be carried out on the fibers having ionic substituents introduced therein, if necessary. The washing step is carried out by washing the fibers having ionic substituents introduced therein with, for example, water or an organic solvent. The washing step may be carried out after each of the steps described below, and the number of washing steps carried out in each washing step is not particularly limited.

[0103] <Alkali treatment process> In the process for obtaining cellulose fibers having ionic substituents, an alkali treatment step may be performed between the ionic substituent introduction step and the micronization step. The alkali treatment method is not particularly limited, but examples thereof include a method of immersing the ionic substituent-introduced fibers in an alkali solution.

[0104] The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of their high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility.

[0105] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5° C. to 80° C., more preferably from 10° C. to 60° C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5 minutes to 30 minutes, more preferably from 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the ionic substituent-introduced fiber.

[0106] In order to reduce the amount of alkaline solution used in the alkaline treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkaline-treated ionic substituent-introduced fiber with water or an organic solvent after the alkaline treatment step and before the micronization treatment step.

[0107] <Acid treatment process> In the process for obtaining cellulose fibers having an ionic substituent, an acid treatment step may be provided between the ionic substituent introduction step and the micronization treatment step. For example, the ionic substituent introduction step, acid treatment, alkali treatment, and micronization treatment may be performed in this order.

[0108] The acid treatment method is not particularly limited, but examples include a method of immersing the fiber raw material in an acid-containing acid solution. The concentration of the acid solution used is not particularly limited, but is preferably 10% by mass or less, more preferably 5% by mass or less. The pH of the acid solution used is also not particularly limited, but is preferably 0 to 4, more preferably 1 to 3. Examples of the acid contained in the acid solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, hydrochloric acid or sulfuric acid is particularly preferred.

[0109] The temperature of the acid solution in the acid treatment is not particularly limited, but is, for example, preferably from 5°C to 100°C, more preferably from 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is, for example, preferably from 5 minutes to 120 minutes, more preferably from 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the fiber raw material.

[0110] Counterion is NH4 + Process of replacing with> In this embodiment, the counter ions of the anionic groups of the fine fibrous cellulose are NH4 +When an anionic group is introduced into cellulose fibers by esterification using the above-mentioned compound B, the counter ion of the introduced anionic group is NH4 + Therefore, if the alkaline treatment step described above is not carried out, the counter ion will be NH4 + is maintained. On the other hand, when anionic groups are introduced by TEMPO oxidation, hypochlorous acid oxidation, carboxymethylation, etc., the counter ions of the anionic groups are NH4 + In this case, the anionic group-introduced cellulose fiber is subjected to an acid treatment process and a counter ion is replaced with NH4 + It is preferable to carry out a step of replacing the counter ion with NH4. + The step of replacing the cellulose with the cellulose syrup may be carried out before or after the defibration treatment step described below, but from the viewpoint of ease of production, it is preferably carried out before the defibration treatment step. Since the fine fibrous cellulose after the defibration treatment step has high water absorption and the slurry has high viscosity, the load on the washing step increases. Counterion is NH4 + The method for substitution is not particularly limited, but an example is a method in which the anionic group-introduced fiber that has been subjected to the acid treatment step described above is immersed in aqueous ammonia. The concentration of the aqueous ammonia used is not particularly limited, but is preferably 5N or more, more preferably 10N or more, and even more preferably 14N or more.

[0111] The temperature of the ammonia water is not particularly limited, but is, for example, preferably from 5° C. to 100° C., more preferably from 20° C. to 90° C. The immersion time in the ammonia water is not particularly limited, but is, for example, preferably from 5 minutes to 120 minutes, more preferably from 10 minutes to 90 minutes.

[0112] <Defibrillation process> Fine fibrous cellulose can be obtained by defibrating raw fiber material or ionic group-introduced fiber in a defibration treatment step. Defibration treatment is also called micronization treatment. In the defibration treatment step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include high-speed defibrators, grinders (stone mill-type grinders), high-pressure homogenizers, ultra-high-pressure homogenizers, high-pressure collision grinders, ball mills, bead mills, disk-type refiners, conical refiners, twin-screw kneaders, vibration mills, homomixers under high-speed rotation, ultrasonic dispersers, and beaters. Among the above defibration treatment devices, it is more preferable to use high-speed defibrators, high-pressure homogenizers, and ultra-high-pressure homogenizers, which are less affected by the grinding media and have less risk of contamination.

[0113] In the defibration process, for example, the fiber raw material or the ionic group-introduced fiber is preferably diluted with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0114] The solid content concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. In addition, the slurry obtained by dispersing the ionic group-introduced fibers in a dispersion medium may contain solids other than the ionic group-introduced fibers, such as urea having hydrogen bonding properties.

[0115] <Low polymerization treatment> In this embodiment, the method for producing fine fibrous cellulose may further include, in addition to the steps described above, a step of performing a polymerization degree reduction treatment to obtain fine fibrous cellulose with a desired degree of polymerization. Specifically, as described above, the method may include a step of subjecting cellulose fibers, into which preferably ionic groups, more preferably anionic groups, have been introduced, to a defibration treatment to obtain fine fibrous cellulose with a fiber width of 1000 nm or less, and a step of subjecting the fine fibrous cellulose to a polymerization degree reduction treatment. That is, the method for producing fine fibrous cellulose of this embodiment may include, for example, a step of subjecting cellulose fibers, into which anionic groups have been introduced, to a defibration treatment and then subjecting the fibers to a polymerization degree reduction treatment. Furthermore, since the amount of ionic substituents (preferably the amount of anionic substituents) in the fine fibrous cellulose hardly changes even after the polymerization reduction treatment, the amount of ionic substituents (preferably the amount of anionic substituents) in the microfibril cellulose before the polymerization reduction treatment can be approximated as the amount of ionic substituents (preferably the amount of anionic substituents) in the fine fibrous cellulose after the polymerization reduction treatment.

[0116] In this specification, the step of carrying out a polymerization degree reduction treatment is a step of carrying out a treatment to reduce the degree of polymerization of a dispersion containing fine fibrous cellulose to an appropriate range. Specifically, the polymerization degree reduction treatment is a step of reducing the degree of polymerization of the fine fibrous cellulose to preferably 50 or more and 500 or less.

[0117] Examples of the process for carrying out the polymerization degree reduction treatment include an ozone treatment process, an enzyme treatment process, a hypochlorous acid treatment process, and a subcritical water treatment process. The process for carrying out the polymerization degree reduction treatment is preferably at least one selected from an ozone treatment process, an enzyme treatment process, a hypochlorous acid treatment process, and a subcritical water treatment process, and more preferably at least one selected from an enzyme treatment process and an ozone treatment process. Note that the ozone treatment process, the enzyme treatment process, the hypochlorous acid treatment process, and the subcritical water treatment process have in common the reduction of the polymerization degree.

[0118] In the ozone treatment step, ozone is added to the fine fibrous cellulose dispersion (slurry). When adding ozone, it is preferable to add it as an ozone / oxygen mixed gas, for example. In this case, the ozone addition rate per 1 g of fine fibrous cellulose contained in the fine fibrous cellulose dispersion (slurry) is 1.0 × 10 -4 g or more, and 1.0 × 10 -3 The ozone addition rate per 1 g of fine fibrous cellulose is preferably 1.0 × 10 1 g or less, and 1.0 × 10 0 g or less, and more preferably 1.0 × 10 -1 g or less, and more preferably 3.0 × 10 -2 g or less, and more preferably 1.5 × 10 -2 g or less, and more preferably 1.0 × 10 -2 g or less, and more preferably 6.0 × 10 -3 After adding ozone to the fine fibrous cellulose dispersion (slurry), it is preferable to stir the mixture at a temperature of 10°C to 50°C for 10 seconds to 10 minutes, and then leave it to stand for 1 minute to 100 minutes.

[0119] In the enzyme treatment step, an enzyme is added to the fine fibrous cellulose dispersion (slurry). The enzyme used here is preferably a cellulase enzyme. Cellulase enzymes are classified into the carbohydrate hydrolase family based on the higher-order structure of the catalytic domain that functions to hydrolyze cellulose. Cellulase enzymes are broadly classified into endo-glucanases and cellobiohydrolases based on their cellulose degradation properties. Endo-glucanases have high hydrolytic activity against the amorphous portion of cellulose, soluble cellooligosaccharides, and cellulose derivatives such as carboxymethylcellulose, randomly cleaving the molecular chains from the inside and reducing the degree of polymerization. In contrast, cellobiohydrolases decompose the crystalline portion of cellulose to produce cellobiose. Cellobiohydrolases hydrolyze cellulose from the end of the molecule and are also called exo- or processive enzymes. While the enzyme used in the enzyme treatment step is not particularly limited, endo-glucanases are preferred.

[0120] In the enzyme treatment process, the enzyme addition rate was 1.0 × 10 per 1 g of fine fibrous cellulose. -7 g or more, and 1.0 × 10 -6 g or more, and more preferably 5.0 × 10 -6 g or more, and more preferably 1.0 × 10 -5 The enzyme addition rate is preferably 1.0×10 to 1 g of fine fibrous cellulose. -2 After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to stir the mixture at a temperature of 30°C to 70°C for 1 minute to 10 hours, and then place the mixture at a temperature of 90°C or higher to inactivate the enzyme.

[0121] In the hypochlorite treatment process, sodium hypochlorite is added to the fine fibrous cellulose dispersion (slurry). The sodium hypochlorite addition rate is 1.0 × 10 per 1 g of fine fibrous cellulose. -4 g or more, and 1.0 × 10-3 g or more, and more preferably 1.0 × 10 -2 The sodium hypochlorite addition rate is more preferably 1.0 × 10 per 1 g of fine fibrous cellulose. 2 g or less, and 1.0 × 10 1 g or less, and more preferably 3×10 0 After adding sodium hypochlorite to the fine fibrous cellulose dispersion (slurry), it is preferable to stir the mixture at a temperature of 10°C to 50°C for 1 minute to 10 hours.

[0122] In the subcritical water treatment step, a fine fibrous cellulose dispersion (slurry) is subjected to high-temperature and high-pressure treatment to bring it to a subcritical state. The fine fibrous cellulose is hydrolyzed in the subcritical state. Specifically, the fine fibrous cellulose dispersion (slurry) is placed in a reaction vessel, and the temperature is increased to 150°C to 500°C, preferably 150°C to 350°C, and the pressure inside the reaction vessel is increased to 10 MPa to 80 MPa, preferably 10 MPa to 20 MPa. The heating and pressurizing time is preferably 0.1 seconds to 100 seconds, more preferably 0.3 seconds to 50 seconds.

[0123] After the above-described polymerization degree reduction treatment, a second defibration treatment step may be further carried out. The second defibration treatment step may be the same as the above-described defibration treatment step for obtaining fine fibrous cellulose.

[0124] <Substituent removal treatment> The method for producing fine fibrous cellulose may include a substituent removal treatment step of removing at least a portion of the substituents from fine fibrous cellulose having a substituent and having a fiber width of 1000 nm or less. In this specification, the step of removing at least a portion of the substituents from the fine fibrous cellulose obtained by the above-mentioned step is also referred to as a substituent removal treatment step. When performing a polymerization reduction treatment, the substituent removal treatment step may be performed before or after the polymerization reduction treatment, but is preferably performed after the polymerization reduction treatment.

[0125] Examples of the substituent removal treatment step include a step of heat treating, enzyme treating, acid treating, alkali treating, etc. fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. These may be performed alone or in combination. Among these, the substituent removal treatment step is preferably a heat treating step or an enzyme treating step. By undergoing the above treatment steps, at least a portion of the substituents can be removed from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, and fine fibrous cellulose with an introduced substituent amount of less than 0.5 mmol / g can be obtained.

[0126] The substituent removal treatment step is preferably carried out in the form of a slurry. That is, the substituent removal treatment step is preferably a step of subjecting a slurry containing a substituent-containing fine fibrous cellulose having a fiber width of 1000 nm or less to a heat treatment, an enzyme treatment, an acid treatment, an alkali treatment, or the like. By carrying out the substituent removal treatment step in the form of a slurry, it is possible to prevent the residue of colored substances generated by heating or the like during the substituent removal treatment, as well as acids, alkalis, salts, and the like that are added or generated. This makes it possible to suppress the coloration of the fine fibrous cellulose. Furthermore, when a treatment is carried out to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to increase the efficiency of salt removal.

[0127] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and more preferably 15% by mass or less, and even more preferably 10% by mass or less. By controlling the concentration of the fine fibrous cellulose in the slurry within the above range, the substituent removal treatment can be performed more efficiently. Furthermore, by controlling the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of colored substances caused by heating or the like during the substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This can suppress coloration of the resulting fine fibrous cellulose. Furthermore, when a treatment is performed to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to increase the efficiency of salt removal.

[0128] When the substituent removal treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the heating temperature in the heat treatment step is preferably 40° C. or higher and 250° C. or lower, more preferably 50° C. or higher, even more preferably 60° C. or higher, more preferably 230° C. or lower, and even more preferably 200° C. or lower. In particular, when the substituent of the fine fibrous cellulose to be subjected to the substituent removal treatment step is a phosphorus oxo acid group or a sulfone group, the heating temperature in the heat treatment step is preferably 80° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher.

[0129] When the substituent removal treatment step is a heat treatment step, the heating device that can be used in the heat treatment step is not particularly limited, and examples that can be used include a hot air heater, a steam heater, an electric heater, a hydrothermal heater, a thermal heater, an infrared heater, a far-infrared heater, a microwave heater, a high-frequency heater, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, a flash dryer, and a reduced-pressure dryer. From the viewpoint of preventing evaporation, the heating is preferably carried out in a closed system, and from the viewpoint of further increasing the heating temperature, it is preferably carried out in a pressure-resistant device or container. The heat treatment may be a batch process, a batch continuous process, or a continuous process.

[0130] When the substituent removal treatment step is a step of enzymatically treating fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, it is preferable to use a phosphate ester hydrolase, a sulfate ester hydrolase, or the like in the enzymatic treatment step. In the enzyme treatment step, the enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 0.1 nkat or more and 100,000 nkat or less, more preferably 1.0 nkat or more, even more preferably 10 nkat or more, and more preferably 50,000 nkat or less, even more preferably 10,000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to treat it under conditions of 0°C or more and less than 50°C for 1 minute to 100 hours.

[0131] After the enzymatic reaction, a step of deactivating the enzyme may be carried out. Examples of methods for deactivating the enzyme include adding an acid or alkali component to the enzymatically treated slurry to deactivate the enzyme, and raising the temperature of the enzymatically treated slurry to 90°C or higher to deactivate the enzyme.

[0132] When the substituent removal treatment step is a step of acid treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, it is preferable to add an acid compound that can be used in the acid treatment step described above to the slurry in the acid treatment step.

[0133] When the substituent removal treatment step is a step of alkali treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, it is preferable to add an alkali compound that can be used in the alkali treatment step described above to the slurry in the alkali treatment step.

[0134] In the substituent removal treatment step, it is preferable that the substituent removal reaction proceeds uniformly. To proceed with the reaction uniformly, for example, the slurry containing the fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry may be increased. As a method for stirring the slurry, external mechanical shear may be applied, or self-stirring may be promoted by increasing the liquid feed rate of the slurry during the reaction.

[0135] In the substituent removal treatment step, spacer molecules may be added. The spacer molecules penetrate between adjacent fine fibrous cellulose particles, thereby acting as spacers to create fine spaces between the fine fibrous cellulose particles. Adding such spacer molecules in the substituent removal treatment step can suppress aggregation of the fine fibrous cellulose after the substituent removal treatment. This can more effectively improve the design properties and tensile properties of rubber compositions, crosslinked rubbers, and crosslinked rubber products containing fine fibrous cellulose.

[0136] The spacer molecule is preferably a water-soluble organic compound. Examples of water-soluble organic compounds include sugars, water-soluble polymers, urea, etc. Specifically, trehalose, urea, polyethylene glycol (PEG), polyethylene oxide (PEO), carboxymethyl cellulose, polyvinyl alcohol (PVA), etc. can be mentioned. Also, as water-soluble organic compounds, alkyl methacrylate·acrylic acid copolymers, polyvinyl pyrrolidone, sodium polyacrylate, propylene glycol, dipropylene glycol, polypropylene glycol, isoprene glycol, hexylene glycol, 1,3-butylene glycol, polyacrylamide, xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, pullulan, carrageenan, pectin, cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, amylose and other starches, glycerin, diglycerin, polyglycerin, hyaluronic acid, metal salts of hyaluronic acid can also be used.

[0137] Also, known pigments can be used as spacer molecules. For example, kaolin (including clay), calcium carbonate, titanium oxide, zinc oxide, amorphous silica (including colloidal silica), aluminum oxide, zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, styrene-based plastic pigment, hydrotalcite, urea resin-based plastic pigment, benzoguanamine-based plastic pigment, etc. can be mentioned.

[0138] <pH adjustment step> When the substituent removal treatment step is carried out in a slurry state, a step of adjusting the pH of the slurry containing microfibrillar cellulose may be provided before the substituent removal treatment step. For example, an anionic group is introduced into the cellulose fiber, and the counter ion of this anionic group is Na +In this case, the slurry containing the defibrated fine fibrous cellulose exhibits a weak alkaline pH. If the slurry is heated in this state, monosaccharides, which are one of the causes of coloration, may be generated due to the decomposition of cellulose, so the pH of the slurry is preferably adjusted to 8 or less, more preferably to 6 or less. Similarly, monosaccharides may be generated under acidic conditions, so the pH of the slurry is preferably adjusted to 3 or more, more preferably to 4 or more.

[0139] Furthermore, when the substituted fine fibrous cellulose is a phosphate-containing fine fibrous cellulose, it is preferable that the phosphorus of the phosphate group is susceptible to nucleophilic attack in order to improve the efficiency of removing the substituent. The phosphorus susceptible to nucleophilic attack is cellulose-OP(=O)(-O - H + )(-O - Na + To achieve this state, the pH of the slurry is adjusted to preferably 3 or more and 8 or less, more preferably 4 or more and 6 or less.

[0140] The means for adjusting the pH is not particularly limited, and for example, an acid component or an alkali component may be added to a slurry containing fine fibrous cellulose. The acid component may be either an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, and gluconic acid. The alkali component may be an inorganic alkali compound or an organic alkali compound. Examples of inorganic alkali compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. Examples of organic alkali compounds include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, and N,N-dimethyl-4-aminopyridine.

[0141] In addition, in the pH adjustment step, an ion exchange treatment may be performed to adjust the pH. A strong acid cation exchange resin or a weak acid ion exchange resin can be used in the ion exchange treatment. By treating with an appropriate amount of cation exchange resin for a sufficient time, a slurry containing fine fibrous cellulose with the desired pH can be obtained. Furthermore, in the pH adjustment step, the addition of an acid component or an alkali component may be combined with the ion exchange treatment.

[0142] <Salt removal treatment> After the substituent removal treatment step, it is preferable to carry out a treatment to remove salts derived from the removed substituents. Removing the salts derived from the substituents makes it easier to obtain fine fibrous cellulose that can suppress coloration. The means for removing the salts derived from the substituents is not particularly limited, and examples thereof include a washing treatment. The washing treatment is carried out, for example, by washing the fine fibrous cellulose that has aggregated in the substituent removal treatment with water or an organic solvent. From the viewpoint of more effectively suppressing yellowing, it is preferable to carry out the washing treatment by filtration dehydration, centrifugal dehydration, or centrifugation.

[0143] <Uniform dispersion processing> The method for producing fine fibrous cellulose may include a substituent removal treatment step of removing at least a portion of the substituents from fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, and a uniform dispersion treatment step after the substituent removal treatment. The uniform dispersion treatment step is a step of uniformly dispersing the fine fibrous cellulose obtained through the substituent removal treatment in the substituent removal treatment step. The state in which the fine fibrous cellulose is uniformly dispersed in the uniform dispersion treatment step refers to a state in which the fiber width of the fine fibrous cellulose is 100 nm or less. By undergoing the uniform dispersion treatment step, the number average fiber width of the fine fibrous cellulose can be easily adjusted to 100 nm or less, preferably 50 nm or less, even if the amount of introduced substituents is as low as less than 0.5 mmol / g.

[0144] In the uniform dispersion treatment step, for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure collision type grinder, ball mill, bead mill, disk type refiner, conical refiner, twin-screw kneader, vibration mill, homomixer under high-speed rotation, ultrasonic disperser or beater can be used. Among the above-mentioned uniform dispersion treatment devices, it is more preferable to use a high-speed defibrator or high-pressure homogenizer.

[0145] The treatment conditions for the uniform dispersion treatment step are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during treatment and the pressure during treatment. In a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fine fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In treatment with a high-pressure homogenizer, the pressure during treatment is preferably 1 MPa or more to 350 MPa, more preferably 10 MPa or more, even more preferably 50 MPa or more, still more preferably 100 MPa or more, and more preferably 300 MPa or less, and even more preferably 250 MPa or less.

[0146] In the uniform dispersion treatment step, the above-mentioned spacer molecules may be newly added. By adding such spacer molecules in the uniform dispersion treatment step, the fine fibrous cellulose can be more smoothly dispersed uniformly.

[0147] [Nonionic water-soluble polymer] The rubber composition of the present embodiment contains a nonionic water-soluble polymer. Here, the term "water-soluble" in "water-soluble polymer" means that the polymer has a solubility of 1 g or more in 100 g of water at any liquid temperature between 0 and 100° C. Furthermore, the term "polymer" refers to a compound having a molecular weight (weight average molecular weight when the molecular weight distribution is present) of 500 or more, preferably 1,000 or more, more preferably 3,000 or more, and even more preferably 5,000 or more. "Nonionic" means that it does not have an ionic group. The ionic group refers to both an anionic group and a cationic group. Specific examples include a carboxy group, a phosphate group, a sulfone group, and a phosphonate group. Although crosslinked rubber products obtained from rubber compositions containing an ionic water-soluble polymer as the water-soluble polymer have a high modulus, the resulting crosslinked rubber products have a high water absorption rate and do not have sufficient water resistance. By using a nonionic water-soluble polymer, crosslinked rubber products can be obtained that have lower water absorption than those using an ionic water-soluble polymer, resulting in excellent water resistance.

[0148] Examples of nonionic water-soluble polymers include natural polysaccharides, polyglycerin-based polymers, polyvinylpyrrolidone, vinylpyrrolidone / ethyl acetate copolymers, polyethyleneimine ethoxylate, polyacrylamide, polyhydroxyethylacrylamide, polyalkylene glycol, vinyl alcohol-based polymers, alkyl cellulose, hydroxyalkyl cellulose, and alkylhydroxyalkyl cellulose. Of these, at least one selected from the group consisting of vinyl alcohol-based polymers, alkyl cellulose, hydroxyalkyl cellulose, and alkylhydroxyalkyl cellulose is preferred.

[0149] Examples of natural polysaccharides, which are nonionic water-soluble polymers, include starch, guar gum, locust bean gum, glucomannan, and pullulan. Examples of polyglycerin-based polymers include polyglycerin, polyglycerin alkyl ethers, and polyglycerin alkyl esters. The polyalkylene glycol is preferably a polyalkylene glycol having an alkylene group having from 2 to 4 carbon atoms, and examples thereof include polyethylene glycol, polypropylene glycol, and polybutylene glycol. Examples of vinyl alcohol polymers include polyvinyl alcohol and vinyl alcohol / vinyl acetate copolymers. The polyvinyl alcohol may be modified or unmodified. Examples of alkyl cellulose include methyl cellulose, ethyl cellulose, and ethyl methyl cellulose. Examples of hydroxyalkyl cellulose include hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxypropyl ethyl cellulose. Examples of alkylhydroxyalkyl cellulose include hydroxyethyl methyl cellulose and hydroxypropyl methyl cellulose.

[0150] Among these, the nonionic water-soluble polymer is preferably at least one selected from the group consisting of polyvinyl alcohol, vinyl alcohol / vinyl acetate copolymer, methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose, more preferably at least one selected from the group consisting of polyvinyl alcohol and methyl cellulose, and even more preferably polyvinyl alcohol.

[0151] Examples of modified polyvinyl alcohol include acetoacetyl group-modified polyvinyl alcohol, ethylene oxide group-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol, and carboxy group-modified polyvinyl alcohol. As an example of acetoacetyl group modified polyvinyl alcohol, Gohsenx TM Z series (manufactured by Mitsubishi Chemical Corporation) is an example, and ethylene oxide group-modified polyvinyl alcohol is Gohsenx TM Examples of sulfonic acid group-modified polyvinyl alcohol include Gohsenx WO series (manufactured by Mitsubishi Chemical Corporation). TM Examples of carboxyl-modified polyvinyl alcohol include modified Poval D polymer (manufactured by Nippon Acetic Acid & Poval Co., Ltd.) and Kuraray Poval. TM An example is the K series (manufactured by Kuraray Co., Ltd.).

[0152] When the nonionic water-soluble polymer is polyvinyl alcohol, the saponification degree of the polyvinyl alcohol is preferably 50 mol% or more and 100 mol% or less, more preferably 70 mol% or more, even more preferably 80 mol% or more, and more preferably 99 mol% or less, from the viewpoint of improving the modulus of the crosslinked rubber product. A saponification degree within the above range is preferable because it improves the modulus of the crosslinked rubber product. The degree of saponification of polyvinyl alcohol is measured in accordance with JIS K 6726:1994.

[0153] Furthermore, when the nonionic water-soluble polymer is polyvinyl alcohol, the viscosity of a 4% aqueous solution of the polyvinyl alcohol at 20°C is preferably 1 mPa·s or more and 100 mPa·s or less, more preferably 2 mPa·s or more, and more preferably 70 mPa·s or less, and even more preferably 50 mPa·s or less. When the viscosity of a 4% aqueous solution of polyvinyl alcohol at 20°C is within the above range, a crosslinked rubber product having a high modulus and excellent handleability can be obtained, which is preferable. The viscosity of the aqueous polyvinyl alcohol solution is measured in accordance with JIS K 6726:1994.

[0154] In the rubber composition of this embodiment, the content of the fine fibrous cellulose per 100 parts by mass of the rubber component is preferably 1 part by mass or more and 200 parts by mass or less, more preferably 2 parts by mass or more, even more preferably 4 parts by mass or more, still more preferably 8 parts by mass or more, even more preferably 12 parts by mass or more, still more preferably 15 parts by mass or more, and preferably 150 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, still more preferably 60 parts by mass or less, even more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, from the viewpoint of ease of production of the rubber composition and obtaining a rubber composition that can give a crosslinked rubber product with a higher modulus. The content of fine fibrous cellulose per 100 parts by mass of the rubber component in the rubber composition of this embodiment may be different from the content of fine fibrous cellulose per 100 parts by mass of the rubber component when made into a crosslinked rubber product. Specifically, the content of fine fibrous cellulose in the rubber composition may be set high, and the rubber component may be added when preparing the rubber compound described below to adjust the content of fine fibrous cellulose per rubber component.

[0155] In the rubber composition of this embodiment, the content of the nonionic water-soluble polymer per 100 parts by mass of fine fibrous cellulose is, from the viewpoint of obtaining a crosslinked rubber product with a high modulus and from the viewpoint of ease of manufacturing the rubber composition, preferably 5 parts by mass or more and 150 parts by mass or less, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, still more preferably 20 parts by mass or more, even more preferably 40 parts by mass or more, and more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, and even more preferably 60 parts by mass or less.

[0156] The total amount of the rubber component, fine fibrous cellulose, and nonionic water-soluble polymer in the rubber composition is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and the upper limit is not particularly limited, but is 100% by mass or less.

[0157] In the present embodiment, the rubber composition may contain other components in addition to the above-described rubber component, fine fibrous cellulose, and nonionic water-soluble polymer. An example of such other component is coarse cellulose fiber having a fiber width exceeding 1 μm (1000 nm). The fiber width of the coarse cellulose fiber contained in the rubber composition of this embodiment is not particularly limited, but is, for example, preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more, even more preferably 10 μm or more, and more preferably 50 μm or less, and even more preferably 40 μm or less. The fiber width of the coarse cellulose fiber can be determined using a fiber length distribution measuring device (for example, FS5 manufactured by Valmet or L&W Fiber Tester Plus manufactured by ABB).

[0158] From the viewpoint of improving dispersibility in the rubber composition, the coarse cellulose fibers preferably have an ionic substituent, more preferably an anionic substituent. The preferred anionic substituents are the same as those for the fine fibrous cellulose, and the preferred ranges of the type and amount of the substituent are also the same.

[0159] When the rubber composition contains coarse cellulose fibers, the content of the coarse cellulose fibers per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more and 80 parts by mass or less, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, and more preferably 50 parts by mass or less, even more preferably 20 parts by mass or less. Furthermore, when the rubber composition contains coarse cellulose fibers, the content of the coarse cellulose fibers relative to 100 parts by mass of the total of the fine fibrous cellulose and the coarse cellulose fibers is preferably 1 part by mass or more and 95 parts by mass or less, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and preferably 90 parts by mass or less, more preferably 85 parts by mass or less. When the content of coarse cellulose fibers is within the above range, coarse cellulose fibers can be produced more cheaply than fine fibrous cellulose, and therefore, a rubber composition can be produced more cheaply, which is excellent in kneading properties and physical properties after crosslinking, and is therefore preferable.

[0160] The rubber composition of the present embodiment may contain other components such as zinc oxide, a vulcanization accelerator, an antioxidant, and a reinforcing agent, which may be added at any stage in the production process.

[0161] <Method of manufacturing rubber composition> The method for producing the rubber composition is not particularly limited, but it is preferable to produce the rubber composition by preparing a mixed liquid containing at least a rubber component, fine fibrous cellulose, and a nonionic water-soluble polymer, and removing the solvent from the mixed liquid. In the above-described production method, it is preferable to first prepare a mixed solution containing a rubber component, fine fibrous cellulose, and a nonionic water-soluble polymer. That is, the production method of the rubber composition of the present embodiment preferably includes the following steps (I) and (II). (I) A step of preparing a mixed liquid containing a rubber component, fibrous cellulose, and a nonionic water-soluble polymer. (II) A step of drying the mixed liquid to obtain a rubber composition

[0162] Specifically, in step (I), a rubber component, fine fibrous cellulose, and a nonionic water-soluble polymer are mixed and dispersed in an aqueous medium to obtain a dispersion of the mixture. Alternatively, a mixed liquid can be obtained by mixing an aqueous dispersion of the rubber component (rubber latex), an aqueous dispersion of fine fibrous cellulose, and an aqueous solution of the nonionic water-soluble polymer. Among these, it is preferable to mix an aqueous dispersion of the rubber component (rubber latex), a dispersion of fine fibrous cellulose, and an aqueous solution of the nonionic water-soluble polymer to obtain a dispersion (mixed liquid A) containing the rubber component, fine fibrous cellulose, and the nonionic water-soluble polymer. Mixing can be carried out using known devices such as a disperser, a three-one motor, a clearmix, a homomixer, a homogenizer, or a propeller agitator (e.g., a tornado agitator). The mixing temperature is not limited, but room temperature (20 to 30°C) is preferred. The mixing time can also be adjusted appropriately. When preparing a dispersion of the mixture, by thoroughly mixing the rubber component, the fine fibrous cellulose, and the nonionic water-soluble polymer, the physical properties after crosslinking tend to be improved.

[0163] The rubber latex is preferably a dispersion of a rubber component in an aqueous medium. The aqueous medium contains water as a main component, and the water content relative to the entire aqueous medium is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. The upper limit is not particularly limited, but is 100% by mass or less. In addition to water, the aqueous medium may contain known organic solvents and the like to the extent that the effects of the present disclosure are not impaired.

[0164] The solids concentration (by mass) of the mixed liquid is preferably 0.5% by mass or more and 50% by mass or less, more preferably 1% by mass or more, even more preferably 3% by mass or more, and more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the solids concentration of the mixed liquid is within the above range, the amount of energy required to remove solvents such as water can be reduced, and further, aggregation of fine fibrous cellulose particles in the resulting rubber composition is less likely to occur, resulting in excellent kneadability of the resulting rubber composition and excellent properties of the crosslinked product.

[0165] The solids concentration of the mixture dispersion can be calculated by the following formula (I) from the mass of the dried product obtained by drying a predetermined amount of the dispersion in a dryer at 105°C until it reaches a constant weight and the mass of the mixture dispersion subjected to drying. Solid concentration of the mixture dispersion (mass%) = Mass of dried material [g] / Mass of dispersion of mixture subjected to drying [g] × 100 (I)

[0166] The rubber composition is obtained by heating and drying the resulting mixture, as shown in the above-mentioned step (II). The heat drying method is not particularly limited, and examples thereof include a method of coating the mixed liquid on a substrate and a method of drying with a drum dryer. In the coating method, for example, a mixed liquid containing a rubber component, fine fibrous cellulose, and a nonionic water-soluble polymer is coated onto a substrate. Furthermore, by using a coating device and a long substrate, sheets can be produced continuously. The material of the substrate used in the coating method is not particularly limited, but a substrate with high wettability with the mixed liquid can suppress shrinkage of the sheet during drying, etc., and it is preferable to select a substrate from which the sheet formed after drying can be easily peeled off. Among these, resin films or plates or metal films or plates are preferred, but are not particularly limited. For example, resin films or plates such as acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polypropylene, polycarbonate, and polyvinylidene chloride, metal films or plates such as aluminum, zinc, copper, and iron plates, and those with their surfaces oxidized, stainless steel films or plates, brass films or plates, etc. can be used. In the coating method, if the viscosity of the mixture dispersion is low and it spreads on the substrate, a damming frame may be fixed to the substrate to obtain a sheet of the desired thickness and basis weight. Alternatively, a substrate with a batt-shaped damming frame may be used. The damming frame is not particularly limited, but it is preferable to select one that allows the edge of the sheet to be easily peeled off after drying. From this perspective, molded resin or metal plates are more preferable. In this embodiment, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polypropylene plates, polycarbonate plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and metal plates with their surfaces oxidized, stainless steel plates, brass plates, etc. may be used. The coater used to coat the mixed liquid on the substrate is not particularly limited, and examples thereof include a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. Die coaters, curtain coaters, and spray coaters are particularly preferred because they can make the thickness of the sheet more uniform.

[0167] The temperature of the mixed liquid and the ambient temperature when the mixed liquid is applied to a substrate (hereinafter, the temperature of the mixed liquid and the ambient temperature are collectively referred to as the "coating temperature") are not particularly limited, but are preferably, for example, from 5°C to 80°C, more preferably from 10°C to 60°C, even more preferably from 15°C to 50°C, and particularly preferably from 20°C to 50°C. If the coating temperature is at least the lower limit, the dispersion of the mixture can be applied more easily. If the coating temperature is at most the upper limit, evaporation of the dispersion medium during coating can be suppressed. The drying device to be used is not particularly limited, but examples thereof include an explosion-proof dryer. In the coating step, it is preferable to coat the dispersion of the mixture onto the substrate so that the finished basis weight and thickness of the sheet fall within the above-mentioned preferred ranges.

[0168] The mixed liquid may be heated and dried in a heating cylindrical dryer to obtain a rubber composition. FIG. 3 is a schematic cross-sectional side view of a double drum dryer 10, which is an example of a heating cylindrical dryer, and FIG. 4 is a schematic side view of the double drum dryer 10. As shown in FIG. First, a heat transfer medium (generally steam) is introduced into a rotating cylinder (drum) 1, and the mixed liquid is introduced into the feed section 2. The introduced mixed liquid adheres to the surface of the heated cylinder 1 as a sheet-like mixture 3, which is then quickly dried by heating. As the cylinder 1 rotates, the sheet-like mixture 3 is scraped off by a fixed scraper 4, and a rubber composition 5 (heat-dried product) is obtained.

[0169] The lower limit of the surface temperature of the heating cylindrical dryer is preferably 80° C. or higher, more preferably 90° C. or higher, and the upper limit of the surface temperature is preferably 250° C. or lower, more preferably 200° C. or lower. The surface temperature of the heated cylindrical dryer refers to the temperature of the cylinder surface that comes into contact with the mixed liquid. The surface temperature of the heated cylindrical dryer may be, for example, 80 to 250°C, 90 to 200°C, or 95 to 180°C. When the surface temperature of the heated cylindrical dryer is within the above range, production efficiency is good and a rubber composition that has excellent physical properties after crosslinking can be obtained.

[0170] The lower limit of the heat drying time in the heating cylindrical dryer is preferably 2 seconds or more, more preferably 4 seconds or more, and the upper limit of the heat drying time is preferably 1800 seconds or less, more preferably 600 seconds or less. The heat-drying time [sec] in the heating cylinder dryer refers to the time [sec] the mixture is in contact with the surface of the cylinder, and the heat-drying time may be, for example, 2 to 1800 seconds, 4 to 600 seconds, or 6 to 400 seconds. When the heat-drying time is within the above range, a dried product that is neither underdried nor overdried is obtained, and the product has excellent releasability from the drum.

[0171] The lower limit of the cylinder width w of the heating cylinder dryer is preferably 0.1 m or more, more preferably 0.2 m or more. The upper limit of the cylinder width w is not particularly limited, but is usually 7 m or less. The cylinder width w may be, for example, 0.1 to 7 m, or 0.2 to 5 m. When the cylinder width w is within the above range, a dried product with a uniform thickness can be obtained.

[0172] The lower limit of the cylinder rotation speed v of the heating cylinder dryer is preferably 0.001 m / sec or more, more preferably 0.002 m / sec. The upper limit of the cylinder rotation speed v is not particularly limited, but is usually 35 m / sec or less. The cylinder rotation speed v may be, for example, 0.001 to 3.5 [m / sec], or may be 0.002 to 0.2 [m / sec]. By keeping the cylinder rotation speed v within the above range, the time the mixture is in contact with the heated drum can be kept within an appropriate range, and a dried product with excellent kneadability and post-crosslinking physical properties can be obtained.

[0173] The heated cylindrical dryer used in the method for producing a rubber composition may be a conduction heating dryer in which a heat medium is introduced into the interior of a cylinder and the mixture is brought into contact with the surface of the heated cylinder to heat and dry. For example, a drum dryer such as a double drum dryer, a single drum dryer, or a twin drum dryer may be used, and a cylinder dryer, Yankee dryer, etc. may also be used. Among these, from the viewpoint of heat and drying efficiency, the heated cylindrical dryer is preferably a double drum dryer or a cylinder dryer.

[0174] [Rubber compound] In the present embodiment, the rubber compound refers to a composition obtained by kneading a rubber composition and before crosslinking. The rubber compound preferably contains at least a crosslinking agent, and may contain, in addition to the crosslinking agent, additives usable as additives in the rubber field, such as zinc oxide, vulcanization accelerators, fillers, softeners, fatty acids, antioxidants, peptizers, colorants, pH adjusters, curing resins, etc. Furthermore, in addition to the rubber components when preparing the rubber composition, a solid rubber may also be added. When solid rubber is newly added, the solid rubber is the same as that exemplified as the rubber component, but it is sufficient to add solid rubber (solid rubber) instead of adding it in latex form. Examples of crosslinking agents include sulfur-based crosslinking agents (e.g., powdered sulfur, sulfur flowers, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, and other sulfur; sulfur-containing compounds such as amine disulfide, polymer polysulfide, sulfur olefin adducts, sulfur chloride, and sulfur dichloride; and insoluble polymeric sulfur), peroxide-based crosslinking agents (e.g., dicumyl peroxide, dichlorobenzoyl peroxide, benzoyl peroxide, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, di-t-butylperoxy-di-isopropylbenzene, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane), and quinoid-based crosslinking agents (e.g., p-quinonedioxime and p,p'-dibenzoylquinonedioxime). Of these, sulfur-based crosslinking agents and peroxide-based crosslinking agents are preferred. The amount of the crosslinking agent added is not particularly limited, but is preferably 0.1 part by mass or more and 10 parts by mass or less, more preferably 0.5 part by mass or more, even more preferably 1.0 part by mass or less, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, relative to 100 parts by mass of the rubber component.

[0175] Furthermore, a crosslinking accelerator having the effect of accelerating crosslinking by a crosslinking agent may be contained, and when a sulfur-based crosslinking agent is used, it is preferable to contain a crosslinking accelerator (vulcanization accelerator). When a sulfur-based crosslinking agent (vulcanizing agent) is used as the crosslinking agent, it is preferable to use a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a thiuram-based vulcanization accelerator, a dithiocarbamate-based vulcanization accelerator, or the like as the crosslinking accelerator (vulcanization accelerator).

[0176] Examples of the filler include carbon black and silica. These fillers may be used alone or in combination of two or more. The content of the filler is not particularly limited and is preferably 10 parts by mass or more and 150 parts by mass or less, more preferably 20 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the rubber component.

[0177] The softener may include aromatic oils, paraffin oils, naphthenic oils, vegetable oils other than castor oil, low PCA oils such as MES, TDAE, and SRAE, and heavy naphthenic oils. Suitable low PCA oils include various plant-derived oils harvested from vegetables, nuts, and seeds. Plant-derived oils include soybean oil, sunflower oil, safflower oil, corn oil, linseed oil, cottonseed oil, rapeseed oil, cashew oil, sesame oil, camellia oil, jojoba oil, macadamia nut oil, coconut oil, and palm oil. The content of the softener, relative to 100 parts by mass of the rubber component, is preferably 1 part by mass or more and 35 parts by mass or less, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and more preferably 30 parts by mass or less, even more preferably 25 parts by mass or less.

[0178] Examples of the fatty acid include stearic acid, palmitic acid, arachidic acid, oleic acid, linoleic acid, arachidonic acid, etc. Among these, stearic acid is preferred. The content of the fatty acid is not particularly limited, and is preferably 0.1 parts by mass or more and 5 parts by mass or less, 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.

[0179] Examples of the antioxidant 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), 2-mercaptobenzimidazole (MBI), etc. The antioxidant may be used alone or in combination of two or more. The content of the antioxidants is not particularly limited and is preferably 0.1 to 5 parts by mass, more preferably 1 to 3 parts by mass, per 100 parts by mass of the rubber component. The total content of the antioxidants is preferably 0.2 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0180] The content of the zinc oxide (zinc white) is not particularly limited and is preferably 1 part by mass or more and 10 parts by mass or less, and more preferably 1.5 parts by mass or more and 8 parts by mass or less, per 100 parts by mass of the rubber component.

[0181] [Method for producing rubber compounds] The method for producing the rubber compound is not particularly limited, but it is preferable that the method includes at least a kneading step of kneading the rubber composition of the present embodiment. In the kneading step, it is preferable to masticate the rubber composition of the present embodiment, and then add at least a crosslinking agent and knead the mixture. In addition to the crosslinking agent, the additives described above may be blended. Furthermore, in the kneading step, a solid rubber may be blended in addition to the rubber component contained in the rubber composition. In this embodiment, in the rubber compound and the crosslinked rubber and crosslinked rubber product described below, the content of fine fibrous cellulose per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more and 50 parts by mass or less, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, and more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, from the viewpoint of improving water resistance and mechanical properties.

[0182] The method for producing the rubber compound is not particularly limited, but preferably includes a step of masticating the rubber composition of this embodiment. Mastication improves the dispersibility of the crosslinking agent and other components to be subsequently blended. Mastication may be performed by a conventional method, but may be low-temperature kneading using a roll machine such as an open roll, or high-temperature kneading using a Banbury mixer or the like. Among these, low-temperature kneading is preferred from the viewpoint of the dispersibility of the fine fibrous cellulose in the rubber composition. The temperature for low-temperature kneading is preferably 15°C or higher and 70°C or lower, more preferably 20°C or higher and 65°C or lower, and even more preferably 25°C or higher and 60°C or lower. The temperature for high-temperature kneading is preferably 80°C or higher and 200°C or lower. Furthermore, additives such as a crosslinking agent are added to the masticated rubber composition and kneaded to produce a rubber compound.

[0183] Kneading is a process of uniformly dispersing a crosslinking agent and other compounding ingredients in a rubber composition (preferably a masticated rubber composition). Kneading may be carried out in a known manner, for example, using a Banbury mixer, kneader, open roll, or the like. Examples of crosslinking agents include sulfur and peroxides. Examples of other compounding ingredients include the above-mentioned additives and solid rubbers.

[0184] [Crosslinked rubber, crosslinked rubber product and method for producing the same] The crosslinked rubber of this embodiment is obtained by crosslinking a rubber compound containing a crosslinking agent. Furthermore, by molding during crosslinking, a crosslinked rubber product can be obtained. That is, the method for producing a crosslinked rubber product preferably includes a step of crosslinking and molding a rubber compound containing a rubber composition and a crosslinking agent. The method for producing a crosslinked rubber product of the present invention may further include a step of molding the rubber compound obtained in the kneading step into an intended shape (molding step). Molding in this molding step can be carried out by various molding methods using an extruder, calendar roll, press, injection molding machine, transfer molding machine, blow molding machine, foam molding machine, etc. The molding method may be appropriately selected depending on the shape, application, and molding method of the final product. The kneading step and the molding step may be carried out separately or successively.

[0185] Regarding crosslinking, there are no particular limitations on the temperature as long as the crosslinking reaction proceeds, but generally, a crosslinked rubber is obtained by heating an uncrosslinked rubber compound obtained by kneading to crosslink (also called vulcanization when sulfur is contained). The heating temperature is preferably 140°C or higher, and preferably 200°C or lower, and more preferably 180°C or lower. Therefore, the heating temperature is preferably about 140 to 200°C, and more preferably about 140 to 180°C. For crosslinking, for example, a vulcanization device that performs mold vulcanization, can vulcanization, continuous vulcanization, etc. can be used.

[0186] In this embodiment, the water absorption rate of the crosslinked rubber and the crosslinked rubber product is preferably low, specifically, preferably 50.0% or less, more preferably 40.0% by mass or less, even more preferably 35.0% or less, and even more preferably 30.0% or less, with no particular lower limit, being 0% or more. Increasing the content of the nonionic water-soluble polymer tends to increase the water absorption rate, while increasing the content of the nonionic water-soluble polymer tends to increase the modulus, so it is preferable to select the content of the nonionic water-soluble polymer appropriately depending on the desired physical properties of the crosslinked rubber product. The water absorption rate is measured by the method described in the examples.

[0187] <Application> The crosslinked rubber product of this embodiment can be used for a variety of purposes, and is not particularly limited. For example, it is suitable for use in sealing materials, hoses, shoe soles, tire components, vibration-proof rubber, etc. Among these, the crosslinked rubber product is preferably a tire. [Example]

[0188] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0189] <Production Example 1> [Phosphorus oxo oxidation treatment] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 Sheet-type pulp with a Canadian Standard Freeness (CSF) of 700 mL when disintegrated and measured in accordance with JIS P 8121-2:2012 was used. This 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 (bone dry mass) of the raw pulp to adjust the total weight to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, to obtain a chemical-impregnated pulp. Next, the obtained chemical-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 a phosphorylated pulp.

[0190] The resulting phosphorylated pulp was then washed. 100 g (bone dry mass) of phosphorylated pulp was mixed with 10 L of ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then repeatedly filtered and dehydrated. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0191] Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little 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 a neutralized phosphorylated pulp. The washing treatment after the neutralization treatment was carried out in the same manner as the washing treatment for the phosphorylated pulp.

[0192] The infrared absorption spectrum of the obtained phosphorus oxyoxidized pulp was measured using FT-IR. -1Absorption due to P=O of phosphate groups was observed near the α-axis, confirming the addition of phosphate groups to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. The amount of phosphate groups (first dissociated acid amount, strong acid group amount) measured by the measurement method described below in [Measurement of phosphorus oxo acid group amount] was 1.45 mmol / g. The total dissociated acid amount was 2.45 mmol / g. The fiber width of the phosphorylated pulp was measured using a fiber length distribution analyzer and found to be 30 μm.

[0193] <Production Example 2> [Fiber defibration processing] Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example 1 to prepare a slurry with a solids concentration of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing phosphorylated fine fibrous cellulose. The fiber width of the phosphorylated fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm.

[0194] The average fiber width of fine fibrous cellulose was measured using, for example, an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.01% by mass or more and 0.1% by mass or less was prepared, and this suspension was cast onto a hydrophilized carbon film-coated grid to prepare a sample for TEM observation. When wide fibers were included, SEM images of the surface cast onto glass could also be observed. Next, electron microscope images were observed at magnifications 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 were adjusted to satisfy the following conditions. (1) A line X is drawn at any point in the observed image, and 20 to 100 fibers intersect with the line X. (2) Draw a line Y that intersects the line perpendicularly within the same image, and 20 to 100 fibers intersect the line Y. For observation images that satisfied the above conditions, the widths of the fibers intersecting with lines X and Y were calculated by comparing them with the scale bar set in the TEM image. In this way, three or more sets of observation images of at least the surface portions that did not overlap each other were obtained. Next, the widths of the fibers intersecting with lines X and Y were read for each image. This resulted in reading the widths of at least 20 fibers x 2 x 3 = 120 fibers. The average value of the read fiber widths was then used as the average fiber width of the fibrous cellulose.

[0195] X-ray diffraction confirmed that this phosphorylated fine fibrous cellulose maintained cellulose type I crystallinity. The amount of phosphate groups (amount of first dissociated acid groups, strong acid groups) measured by the method described below in [Measurement of amount of phosphorus oxoacid groups] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0196] Example 1 [Dilution process] The fine fibrous cellulose dispersion obtained in Production Example 2 was placed in a container so that the solid content of the fine fibrous cellulose was 20 parts by mass, and then ion-exchanged water was added to the container so that the solid content concentration of the fine fibrous cellulose was diluted to 1.0% by mass. A tornado agitator (general-purpose high-speed agitator, PM-202, manufactured by AS ONE Corporation) was used as the agitator, and a stirring blade with a diameter of 6 inches was attached, and the fine fibrous cellulose dispersion in the container was stirred with the agitator at 1000 rpm for 5 minutes.

[0197] [Preparation process of nonionic water-soluble polymer aqueous solution] Water was added to polyvinyl alcohol A (Gohsenex Z-300, acetoacetyl group-modified polyvinyl alcohol, saponification degree 98.0 to 99.0 mol%, manufactured by Mitsubishi Chemical Corporation, PVOH (A) in the table) and heated to 80°C to prepare a 15% aqueous solution of polyvinyl alcohol A.

[0198] [Mixing process] To the resulting 1.0% by mass fine fibrous cellulose dispersion, an aqueous dispersion of natural rubber latex (ULACOL, manufactured by Resitex Co., Ltd.) with a solids concentration of 61% by mass was added so that the solids content of the rubber component was 100 parts by mass. A tornado stirrer equipped with a 6-inch diameter stirring blade was used, and stirring was carried out at 1000 rpm for 5 minutes. Subsequently, 10 parts by mass of a solids content aqueous solution of polyvinyl alcohol A was added, and stirring was carried out at 1000 rpm for 3 minutes.

[0199] [Drying process] 50 mL of the resulting mixture was poured into a Teflon®-coated container with a base area of ​​540 cm 2 The dispersion was spread on a tray. The tray on which the dispersion was spread was placed in an explosion-proof dryer and dried at 40°C for 48 hours to obtain a sheet-like rubber composition. The thickness of the obtained rubber composition was 0.05 mm.

[0200] [Preparation of rubber compounds] The resulting rubber composition was masticated for 10 minutes without heating at 26 / 30 rpm using an open roll (a 6-inch two-roll mill manufactured by Daihan Co., Ltd.). Next, 2 parts by mass of a crosslinking agent (Percumyl D, dicumyl peroxide manufactured by NOF Corporation), 3 parts by mass of a vulcanization accelerator (zinc oxide A) (zinc oxide type 2 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.) were added to 100 parts by mass of the rubber component, and the mixture was kneaded for 6 minutes to obtain a rubber compound having a thickness of approximately 2 mm or more.

[0201] [Crosslinking process] The obtained rubber compound was placed in a mold and press-heated at 165°C for 20 minutes to produce a crosslinked rubber sheet having a thickness of 2 mm.

[0202] <Example 2> A crosslinked rubber sheet was obtained in the same manner as in Example 1, except that polyvinyl alcohol B (Kuraray Poval 5-74LLA (saponification degree 72.5 to 74.5 mol%, manufactured by Kuraray Co., Ltd.), PVOH (B) in the table) was used instead of polyvinyl alcohol A as the nonionic water-soluble polymer. An 8.6% aqueous solution of polyvinyl alcohol B was prepared and added so that the solid content of polyvinyl alcohol B was 10 parts by mass.

[0203] Example 3 A crosslinked rubber sheet was obtained in the same manner as in Example 1, except that methyl cellulose (Metolose 65SH-1500, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the nonionic water-soluble polymer instead of polyvinyl alcohol A. A 2% aqueous solution of methyl cellulose was prepared and added so that the solid content of methyl cellulose was 10 parts by mass.

[0204] Example 4 A crosslinked rubber sheet was obtained in the same manner as in Example 1, except that the amount of the aqueous solution of polyvinyl alcohol A added was reduced so that the solid content was 5 parts by mass.

[0205] <Example 5> A crosslinked rubber sheet was obtained in the same manner as in Example 1, except that the amount of the aqueous solution of polyvinyl alcohol A added was increased so that the solid content was 20 parts by mass.

[0206] Example 6 A crosslinked rubber sheet was obtained in the same manner as in Example 4, except that in the dilution step, the solid content of the fine fibrous cellulose was adjusted to 10 parts by mass.

[0207] Example 7 For a rubber composition obtained in the same manner as in Example 1, 1.5 parts by mass of insoluble sulfur (Mucron OT-20, manufactured by Shikoku Chemical Industry Co., Ltd.), 2 parts by mass of vulcanization accelerator A (Noccela MSA-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 2 parts by mass of zinc oxide A, 2 parts by mass of vulcanization accelerator aid (Stearic acid 50S, manufactured by Nisshin Rika Co., Ltd.), and 2 parts by mass of antioxidant (ANTAGE RD, manufactured by Kawaguchi Chemical Industry Co., Ltd.) were added per 100 parts by mass of the rubber component, and the mixture was kneaded for 10 minutes to obtain a rubber compound having a thickness of 2 mm. The obtained rubber compound was placed in a mold and press-heated at 150°C for 40 minutes to produce a crosslinked rubber sheet having a thickness of 2 mm.

[0208] <Comparative Example 1> A crosslinked rubber sheet was prepared in the same manner as in Example 1, except that polyvinyl alcohol A, a nonionic water-soluble polymer, was not added.

[0209] <Comparative Example 2> A crosslinked rubber sheet was prepared in the same manner as in Example 1, except that fine fibrous cellulose was not added.

[0210] <Comparative Example 3> A crosslinked rubber sheet was prepared in the same manner as in Example 6, except that polyvinyl alcohol A, a nonionic water-soluble polymer, was not added.

[0211] <Comparative Example 4> A crosslinked rubber sheet was prepared in the same manner as in Example 7, except that polyvinyl alcohol A, a nonionic water-soluble polymer, was not added.

[0212] <Comparative Example 5> A crosslinked rubber sheet was produced in the same manner as in Example 1, except that an ionic water-soluble polymer, sodium polymethacrylate (S-MA, manufactured by Asada Chemical Industry Co., Ltd., PMAA-Na in the table), was used instead of the nonionic water-soluble polymer, polyvinyl alcohol A.

[0213] [Measurement and Evaluation] <Water absorption test> For the crosslinked rubber sheets obtained in Examples 1 to 7 and Comparative Examples 1 to 5, test pieces were punched out to 2 cm square, and the masses were measured in an environment of 23°C and 50% RH according to Method A of JIS K 7209:2000, and then the pieces were immersed in ion-exchanged water at 70°C for 48 hours. The masses were measured after wiping off the surface moisture. The water absorption was calculated according to the following formula. Water absorption rate (%)=(W-Wo) / Wo×100 (Wo is the mass in a 23°C, 50% RH environment, and W is the mass after immersion in ion-exchanged water at 70°C for 48 hours).

[0214] <Tensile test under humidity controlled conditions> For the crosslinked rubber sheets obtained in Examples 1 to 7 and Comparative Examples 1 to 5, test pieces were punched into the shape of a dumbbell (dumbbell No. 6) as defined in JIS K 6251:2017. A tensile test was carried out in accordance with JIS K 6251:2017 using a universal testing machine (manufactured by Toyo Seiki Seisaku-sho, Ltd.) at 23±2°C, a gauge length of 25 mm, and a tensile speed of 500 mm / min, to measure the 100% modulus (σ100 (MPa)).

[0215] [Table 1]

[0216] The results in Table 1 show that the crosslinked rubbers (crosslinked rubber products) obtained in the examples had improved 100% modulus (σ100 (MPa)) compared to those not containing a nonionic water-soluble polymer or not containing fine fibrous cellulose. In addition, they had lower water absorption and better water resistance than those containing an ionic water-soluble compound. [Explanation of symbols]

[0217] 10...double drum dryer, 1...cylinder, 2...feed section, 3...sheet mixture, 4...scraper, 5...rubber composition

Claims

1. A rubber composition comprising a rubber component, fine fibrous cellulose having a fiber width of 1,000 nm or less, and a non-ionic water-soluble polymer. Rubber composition.

2. The rubber composition according to claim 1, wherein the nonionic water-soluble polymer is at least one selected from the group consisting of vinyl alcohol-based polymers, alkyl celluloses, hydroxyalkyl celluloses, and alkylhydroxyalkyl celluloses.

3. 2. The rubber composition according to claim 1, wherein the nonionic water-soluble polymer is at least one selected from the group consisting of polyvinyl alcohol, vinyl alcohol / vinyl acetate copolymer, methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose.

4. The rubber composition according to claim 1, comprising 1 part by mass or more and 200 parts by mass or less of fine fibrous cellulose per 100 parts by mass of the rubber component.

5. The rubber composition according to claim 1, comprising 5 parts by mass or more and 150 parts by mass or less of a nonionic water-soluble polymer per 100 parts by mass of the fine fibrous cellulose.

6. A crosslinked rubber product obtained by crosslinking and molding a rubber compound containing the rubber composition according to any one of claims 1 to 5 and a crosslinking agent.

7. A step of preparing a mixed liquid containing a rubber component, fibrous cellulose, and a nonionic water-soluble polymer; a step of drying the mixed liquid to obtain a rubber composition; in that order, A method for producing the rubber composition according to any one of claims 1 to 5.

8. A step of obtaining a rubber composition by the production method according to claim 7; and crosslinking and molding a rubber compound containing the rubber composition and a crosslinking agent. A method for manufacturing crosslinked rubber products.

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