Rubber composition containing cellulose nanofibers

Abstract

To provide a rubber composition, a rubber composite, and a rubber cured product, featuring superior dispersibility and orientation of cellulose nanofibers, and to provide a rubber cured product exhibiting superior physical properties (especially tensile properties and modulus) and surface smoothness.SOLUTION: A rubber composition contains cellulose nanofibers, a first rubber, and a second rubber, wherein the first rubber and the second rubber are liquid rubbers, and at 38°C, the viscosity η1 of the first rubber is smaller than the viscosity of the second rubber.SELECTED DRAWING: None

Description

Technical Field

[0001] One aspect of the present disclosure relates to a rubber composition containing cellulose nanofibers and the like.

Background Art

[0002] Conventionally, in rubber molded articles, it has been required to highly balance various properties such as mechanical strength, flexibility, abrasion resistance, and processability. For example, in order to improve the elastic modulus, hardness, abrasion resistance, etc., it is generally practiced to incorporate a filler into the rubber molded article. In order for such a rubber molded article containing a filler to exhibit desired properties, it is important that the filler is well dispersed in the rubber. In recent years, due to the increasing awareness of environmental issues, various attempts have been made to use cellulose, a low specific gravity and renewable material, as a filler to be incorporated into rubber molded articles. Among them, cellulose nanofibers are extremely promising as fillers for polymer molded articles because they have a good reinforcing effect per unit amount used on the polymer molded article when combined with various polymers to form a polymer molded article. If cellulose nanofibers can be used in rubber molded articles, it is possible to provide rubber molded articles that have a low specific gravity, are excellent in various physical properties, can be used in a variety of applications, and are also advantageous in terms of transportation costs and disposal costs. However, since cellulose nanofibers are essentially hydrophilic due to the contribution of hydroxyl groups in cellulose, it is generally difficult to mix them with rubber, which is a material with high hydrophobicity. Therefore, various attempts have been made to improve the miscibility between cellulose nanofibers and rubber.

[0003] For example, Patent Document 1 describes a rubber composition for tires containing a rubber component, microfibrillated plant fibers which may be cellulose fibers, and a modifier capable of covalently bonding to the microfibrillated plant fibers.

[0004] Further, Patent Document 2 describes a rubber composition for tires characterized in that 1 to 50 parts by mass of oxidized cellulose nanofibers are blended with 100 parts by mass of a diene-based rubber containing 5% by mass or more of a modified diene-based rubber having 0.1 mol% or more of polar groups.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technologies described in Patent Documents 1 and 2 are intended to disperse cellulose fibers in a rubber composition to improve the mechanical properties of the rubber composition. However, even with these technologies, the dispersibility of cellulose nanofibers in the rubber composition is still not sufficient, and there is still room for improvement in the mechanical properties. In addition, when blending cellulose nanofibers in various molded articles, good surface smoothness may be required from the viewpoints of the appearance, slidability, etc. of the molded article. In order to obtain good surface smoothness, it is advantageous to orient the cellulose nanofibers well in the molded article. However, the orientation of cellulose nanofibers has not been focused on in Patent Documents 1 and 2.

[0007] The present invention solves the above problems, and in one aspect, aims to provide a rubber composition, a rubber composite, and a rubber cured product excellent in the dispersibility and orientation of cellulose nanofibers, and in one aspect, aims to provide a rubber cured product exhibiting good physical properties (particularly, tensile properties and modulus) and surface smoothness.

Means for Solving the Problems

[0008] This disclosure includes the following items. [Item 1] A rubber composition comprising cellulose nanofibers, a first rubber, and a second rubber, wherein the first rubber and the second rubber are liquid rubbers, A rubber composition in which, at 38°C, the viscosity η1 of the first rubber is lower than the viscosity of the second rubber. [Item 2] The rubber composition according to Item 1, wherein, at 38°C, the viscosity η1 of the first rubber is 5,000 mPa·s to 100,000 mPa·s and the viscosity η2 of the second rubber is 100,000 mPa·s to 800,000 mPa·s. [Item 3] The rubber composition according to Item 1 or 2, wherein the number average molecular weight of the second rubber is 4,500 to 150,000. [Item 4] The rubber composition according to any one of Items 1 to 3, comprising 5 parts by mass to 300 parts by mass of the first rubber with respect to 100 parts by mass of the second rubber. [Item 5] The rubber composition according to any one of Items 1 to 4, comprising 5 parts by mass to 100 parts by mass of the first rubber with respect to 100 parts by mass of cellulose nanofiber. [Item 6] The rubber composition according to any one of Items 1 to 5, comprising 10 parts by mass to 300 parts by mass of the second rubber with respect to 100 parts by mass of cellulose nanofiber. [Item 7] The rubber composition according to any one of Items 1 to 6, comprising 5 mass% to 60 mass% of the second rubber. [Item 8] The rubber composition according to any one of Items 1 to 7, wherein the first rubber contains an aromatic vinyl monomer unit. [Item 9] The rubber composition according to any one of Items 1 to 8, wherein the second rubber is maleic anhydride-modified liquid polyisoprene. [Item 10] The rubber composition according to any one of Items 1 to 9, further comprising a dispersant. [Item 11] The rubber composition according to Item 10, wherein the dispersant is nonionic. [Item 12] The rubber composition according to Item 10 or 11, wherein the weight ratio of the dispersant to the second rubber is 0.01 to 2.0. [Item 13] The rubber composition according to any one of items 1 to 12, further comprising a third rubber. [Item 14] The rubber composition according to item 13, wherein the third rubber is natural rubber. [Item 15] The rubber composition according to any one of items 1 to 14, which is a dry body. [Item 16] The rubber composition according to item 15, wherein the median diameter of the crushed material is 10 μm to 8.0 mm. [Item 17] The bulk density of the loosened crushed material is 0.01 g / cm 3 ~0.80 g / cm 3 The rubber composition according to item 15 or 16. [Item 18] The rubber composition according to any one of items 1 to 17, wherein the degree of chemical bonding of the rubber composition is 0.01 to 4.0. [Item 19] A method for producing the rubber composition according to any one of items 1 to 18, comprising: a first step of mixing cellulose nanofibers and the first rubber to obtain a preliminary composition; and a second step of mixing the preliminary composition and the second rubber to obtain a rubber composition. A method comprising the above steps. [Item 20] A method for producing the rubber composition according to any one of items 1 to 18, comprising: a first step of mixing the first rubber and the second rubber to obtain a preliminary composition; and a second step of mixing the preliminary composition and the cellulose nanofibers to obtain a rubber composition. A method comprising the above steps. [Item 21] The method according to item 19 or 20, wherein in the second step, a third rubber is further mixed. [Item 22] A method for producing the rubber composition according to item 13 or 14, comprising: a step of mixing cellulose nanofibers and the first rubber to obtain a preliminary composition. A step of mixing the preliminary composition and the second rubber to obtain a dried body, and A step of mixing the dried body and a third rubber to obtain a rubber composition, A method comprising the above steps. [Item 23] A method for producing a rubber composition according to item 13 or 14, comprising: A step of mixing the first rubber and the second rubber to obtain a preliminary composition, A step of mixing the preliminary composition and the cellulose nanofiber to obtain a dried body, and A step of mixing the dried body and a third rubber to obtain a rubber composition, A method comprising the above steps. [Item 24] A dried body comprising the rubber composition according to any one of items 1 to 18. [Item 25] A method for producing a rubber composition, comprising: A step of mixing the dried body according to item 24 and a third rubber to obtain a rubber composition. [Item 26] The method according to item 21, wherein the third rubber is natural rubber. [Item 27] The method according to item 22, wherein the third rubber is natural rubber. [Item 28] The method according to item 23, wherein the third rubber is natural rubber. [Item 29] The method according to item 25, wherein the third rubber is natural rubber. [Item 30] A rubber composite which is a kneaded product of the rubber composition according to any one of items 1 to 18 and a fourth rubber. [Item 31] A rubber composite which is a kneaded product of the rubber composition according to item 13 and a fourth rubber. [Item 32] A method for producing a rubber composite, comprising: A method comprising mixing the rubber composition according to any one of items 1 to 18 and a fourth rubber. [Item 33] A method for producing a rubber composite, comprising: mixing the rubber composition according to item 13 with a fourth rubber. [Item 34] A rubber cured product which is a cured product of the rubber composite according to item 30. [Item 35] A tire comprising the rubber cured product according to item 34. [Item 36] A vibration isolator rubber comprising the rubber cured product according to item 34. [Item 37] A shoe outsole comprising the rubber cured product according to item 34. [Item 38] A conveyor belt comprising the rubber cured product according to item 34. [Advantages of the Invention]

[0009] According to the present invention, in one aspect, a rubber composition, a rubber composite, and a rubber cured product excellent in the dispersibility and orientation of cellulose nanofibers can be provided, and in one aspect, a rubber cured product exhibiting good physical properties (particularly, tensile properties and modulus) and surface smoothness can be provided. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, exemplary embodiments of the present invention (hereinafter abbreviated as "the present embodiment") will be described, but the present invention is not limited to these embodiments at all. It should be understood by those skilled in the art that the characteristic values of the present disclosure are values measured by the method described in the [Examples] section of the present disclosure or a method equivalent thereto unless otherwise specified.

[0011] ≪Rubber Composition≫ One aspect of the present disclosure provides a rubber composition comprising cellulose nanofibers, a first rubber, and a second rubber. The first rubber and the second rubber are liquid rubbers. While cellulose nanofibers are essentially hydrophilic due to their hydroxyl groups, rubbers are essentially hydrophobic, and it is usually difficult to uniformly disperse cellulose nanofibers in rubbers. As a result of various studies, the inventors have found that a specific combination of rubbers is useful for preparing a rubber composition having excellent dispersibility and orientation of cellulose nanofibers. The rubber composition can also be in the form of, for example, a masterbatch for rubber and kneaded with additional rubber to produce a rubber composite. The rubber composition, rubber composite, or rubber cured product of the present disclosure may exhibit good dispersibility and orientation of cellulose nanofibers. Thereby, in the rubber cured product of the present disclosure, good physical properties (particularly, tensile properties and modulus) and good surface smoothness can be achieved simultaneously.

[0012] In one aspect, at 38°C, the viscosity η1 of the first rubber is smaller than the viscosity η2 of the second rubber. In the present disclosure, the first rubber may also be referred to as a low-viscosity liquid rubber, and the second rubber as a high-viscosity liquid rubber. In various molded articles containing rubber, a rubber that is not a liquid rubber is used as a matrix rubber, and a liquid rubber is further used. By interposing the liquid rubber between the cellulose nanofibers and the matrix rubber, an improvement in the dispersibility of the cellulose nanofibers with respect to the matrix rubber is expected. However, according to the studies by the present inventors, it has been found that simply using a liquid rubber alone may not achieve the desired degree of improvement in the dispersibility of the cellulose nanofibers. Without being bound by theory, liquid rubbers that are useful from the viewpoint of improving the mechanical properties of rubber cured products tend to have a relatively high molecular weight and / or often have modified groups (more specifically, reactive groups). Such liquid rubbers having a high molecular weight and / or modified groups generally have a high viscosity. Although a high-viscosity liquid rubber may have good affinity with the matrix rubber, it is often difficult to uniformly and sufficiently mix with cellulose nanofibers. Further, when blending cellulose nanofibers in various molded articles, good surface smoothness may be required from the viewpoints of the appearance, slidability, etc. of the molded article. In order to obtain good surface smoothness, it is advantageous to orient the cellulose nanofibers well in the molded article. If the mobility of the cellulose nanofibers in the rubber composition or the rubber composite during the production of the molded article is good, it is easy to realize good orientation of the cellulose nanofibers. However, if the mixing of the cellulose nanofibers and the liquid rubber is insufficient or non-uniform, the desired movement of the cellulose nanofibers may be inhibited and the orientation may be reduced. Therefore, as a result of further studies by the present inventors, it has been found that the above problems can be solved by using at least two kinds of liquid rubbers having different viscosities, that is, a first rubber having a relatively low viscosity and a second rubber having a relatively high viscosity. The first rubber, being a low-viscosity liquid rubber, is excellent in fluidity and can favorably affinity with the second rubber by virtue of being a liquid rubber. Such a first rubber can easily penetrate between the second rubbers or between the second rubber and the cellulose nanofibers.In one aspect, the first rubber can well coat the cellulose nanofibers. On the other hand, the second rubber is a high-viscosity liquid rubber and has appropriate (i.e., not too high) fluidity, so that a considerable amount remains near the matrix rubber and can form a crosslink with the matrix rubber. Further, although the fluidity of the second rubber is not necessarily high, due to the intervention of the first rubber, it can appropriately approach the cellulose nanofibers. The cellulose nanofibers can achieve good dispersibility and orientation by being dispersed in the matrix rubber through such first and second rubbers.

[0013] Hereinafter, each component of the rubber composition will be described. Note that the amount of each component described as a value in the rubber composition components of this embodiment may be regarded as the amount of each component in the rubber composition of this embodiment.

[0014] <Cellulose Nanofibers> Cellulose nanofibers are fibers obtained by refining a cellulose fiber raw material through a defibrillation process or the like. As the cellulose fiber raw material, natural cellulose and regenerated cellulose can be used. As natural cellulose, wood pulp obtained from wood species (hardwood or softwood), non-wood pulp obtained from non-wood species (cotton, bamboo, hemp, bagasse, kenaf, cotton linter, sisal, straw, etc.), cellulose fiber aggregates produced by animals (e.g., tunicates), algae, and microorganisms (e.g., acetic acid bacteria) can be used. As regenerated cellulose, regenerated cellulose fibers (viscose, cupra, tencel, etc.), cellulose derivative fibers, regenerated cellulose or ultrafine filaments of cellulose derivatives obtained by the electrospinning method can be used.

[0015] In one aspect, fibrillation is a dry or wet mechanical treatment, preferably a wet treatment in which a mechanical treatment is applied to a slurry obtained by dispersing a cellulose fiber raw material in a liquid medium. A single device may be used one or more times for fibrillation, or a plurality of devices may each be used one or more times. The device used for fibrillation is not particularly limited, and examples include devices of types such as high-speed rotation type, colloid mill type, high-pressure type, roll mill type, ultrasonic type, etc., and high-pressure or ultra-high-pressure homogenizers, refiners, beaters, PFI mills, kneaders, dispersers, high-speed fibrillators, grinders (mortar type grinders), ball mills, vibration mills, bead mills, conical refiners, disk refiners, single-axis, two-axis or multi-axis kneading machines and extruders, etc. The cellulose fiber raw material may be subjected to a pretreatment before fibrillation. By the pretreatment, the fiber diameter, fiber length, fibrillation degree, etc. can be adjusted, or the content of components other than cellulose (acid-insoluble components such as lignin, alkali-soluble polysaccharides such as hemicellulose, etc.) can be adjusted, or the molecular weight, crystallinity, etc. can be adjusted. In one aspect, the pretreatment may be one or more selected from chemical treatment, pulverization, grinding, and classification, etc. Chemical treatment is a treatment using chemicals, and examples include cooking, bleaching, purification, hydrolysis treatment, enzyme treatment, regeneration of cellulose, and chemical modification. Pulverization is a treatment for dry-pulverizing a cellulose fiber raw material. Grinding is a treatment in which a pulverization treatment is applied to a slurry obtained by dispersing a cellulose fiber raw material in a liquid medium, and is distinguished from the above-mentioned pulverization in that it is wet. Classification is a separation operation for aligning the fiber lengths of a cellulose fiber raw material, and may be dry classification or wet classification.

[0016] Examples of the liquid medium include water and / or other media (for example, organic solvents, inorganic acids, bases, and / or ionic liquids), and may contain one type or two or more types of media.

[0017] Examples of the organic solvent include commonly used organic solvents such as alcohols (e.g., methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, t-butanol, ethylene glycol, diethylene glycol, glycerin, etc.); ethers (e.g., propylene glycol monomethyl ether, 1,2-dimethoxyethane, diisopropyl ether, tetrahydrofuran, 1,4-dioxane, etc.); carboxylic acids (e.g., formic acid, acetic acid, lactic acid, etc.); esters (e.g., ethyl acetate, vinyl acetate, etc.); ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, etc.); nitrogen-containing solvents (dimethylformamide, dimethylacetamide, acetonitrile, etc.); and sulfur-containing solvents (dimethyl sulfoxide). One or more of these can be used. In a typical embodiment, the liquid medium in the slurry is substantially only water.

[0018] [Specific surface area] From the viewpoint of obtaining a good effect of improving the physical properties by the cellulose nanofibers, the specific surface area of the cellulose nanofibers is preferably 2 m 2 / g or more, preferably 3 m 2 / g or more, preferably 5 m 2 / g or more, preferably 7 m 2 / g or more, preferably 10 m 2 / g or more, preferably 12 m 2 / g or more, preferably 15 m 2 / g or more, preferably 17 m 2 / g or more, preferably 20 m 2 / g or more, preferably 22 m 2 / g or more, preferably 25 m 2 / g or more, preferably 27 m 2 / g or more. Also, from the viewpoint of favorably dispersing the cellulose nanofibers in the rubber composition and the rubber cured product, it is preferably 400 m 2 / g or less, preferably 350 m 2 / g or less, preferably 300 m 2 / g or less, preferably 250 m 2 / g or less, preferably 200 m 2 / g or less, preferably 170 m 2 / g or less, preferably 150 m 2 / g or less, preferably 120 m 2 / g or less, preferably 100 m 2 / g or less.

[0019] The specific surface area of the cellulose nanofiber is measured using nitrogen gas with a specific surface area and pore size distribution measuring device (for example, Nova-4200e, manufactured by Quantachrome Instruments) for the porous sheet of the cellulose nanofiber. Specifically, after drying about 0.2 g of the porous sheet under vacuum at 105 °C for 5 hours, the adsorption amount of nitrogen gas at the boiling point of liquid nitrogen is measured at 5 points in the range where the relative vapor pressure (P / P0) is 0.05 or more and 0.2 or less (multi-point method), and the BET specific surface area (m 2 / g) is calculated by the device program. The porous sheet is produced by the method described in the section of [Porous Sheet] below.

[0020] The specific surface area of the cellulose nanofiber can be calculated from the following formula by assuming the cellulose nanofiber as a cylinder. Since the density of cellulose is 1.5 (g / cm 3 ), the volume per 1 g of cellulose is 6.67×10 -7 (m 3 / g). Assuming the converted fiber diameter of the cellulose nanofiber is r (m), the average outer perimeter of the cellulose nanofiber = πr, and the average cross-sectional area of the cellulose nanofiber = 0.25πr 2 . Therefore, per 1 g of the cellulose nanofiber, the total fiber length = 6.7×10 -7 (m 3 / g) / average cross-sectional area (= 0.25πr 2 ) Total surface area = specific surface area (m 2 / g)=6.67×10 -7 (m 3 / g) / average cross-sectional area (= 0.25πr 2 )×average outer perimeter (= πr)=6.67×10-7 (m 3 / g) / 0.25r = 26.68×10 -7 (m 3 / g) / r Therefore, The converted fiber diameter r (m) = 26.68×10 -7 (m 3 / g) / specific surface area (m 2 / g) That is, for example, when the BET specific surface area of the porous sheet is 40 m 2 The converted fiber diameter r of the cellulose nanofiber is calculated to be 66.7 nm.

[0021] In one aspect, the converted fiber diameter of the cellulose nanofiber is preferably 2 to 1000 nm from the viewpoint of obtaining a good effect of improving physical properties by the cellulose nanofiber. The converted fiber diameter of the cellulose nanofiber is more preferably 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, and more preferably 900 nm or less, or 800 nm or less, or 700 nm or less, or 600 nm or less, or 500 nm or less, or 400 nm or less, or 300 nm or less, or 200 nm or less.

[0022] [Number average fiber length] In one aspect, the number average fiber length L of the cellulose nanofiber is preferably 100 nm or more, or 500 nm or more, 1 μm or more, or 5 μm or more, or 10 μm or more, or 20 μm or more from the viewpoint of favorably expressing the effect of improving physical properties by the cellulose nanofiber, and preferably 1000 μm or less, or 800 μm or less, or 500 μm or less, or 400 μm or less, or 300 μm or less, or 200 μm or less from the viewpoint of favorably dispersing the cellulose nanofiber in the resin composition.

[0023] In one aspect, the number average fiber diameter D of the cellulose nanofibers is preferably 2 to 1000 nm from the viewpoint of obtaining a good physical property improvement effect by the cellulose nanofibers. The number average fiber diameter of the cellulose nanofibers is more preferably 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more, and more preferably 900 nm or less, or 800 nm or less, or 700 nm or less, or 600 nm or less, or 500 nm or less, or 400 nm or less, or 300 nm or less, or 200 nm or less.

[0024] The average fiber length (L) / fiber diameter (D) ratio of the cellulose nanofibers is preferably 30 or more, or 50 or more, or 80 or more, or 100 or more, or 120 or more, or 150 or more from the viewpoint of improving the mechanical properties of the rubber composite containing the cellulose nanofibers well with a small amount of cellulose nanofibers. The upper limit is not particularly limited, but is preferably 5000 or less, or 3000 or less, or 2000 or less, or 1000 or less from the viewpoint of handleability.

[0025] In the present disclosure, the fiber length, fiber diameter, and L / D ratio of the cellulose nanofibers are values measured by the following procedure using a scanning electron microscope (SEM). The aqueous dispersion of cellulose nanofibers is replaced with tert-butanol, diluted to 0.001 to 0.1 mass%, and dispersed using a high-shear homogenizer (for example, manufactured by IKA, trade name "Ultra Turrax T18") under the treatment conditions: rotation speed 15,000 rpm × 3 minutes, cast on an osmium-evaporated silicon substrate, and air-dried to obtain a measurement sample, which is measured with a high-resolution scanning electron microscope (SEM). Specifically, in an observation field with the magnification adjusted so that at least 100 cellulose nanofibers are observed, the lengths (L) and diameters (D) of 100 randomly selected cellulose nanofibers are measured, and the ratio (L / D) is calculated. Then, the respective number average values are taken as the number average fiber diameter L and the number average fiber diameter D, and the ratio (L / D) is calculated.

[0026] [Crystal polymorph] As crystal forms of cellulose, type I, type II, type III, type IV, etc. are known. Among them, type I and type II are particularly widely used. Although type III and type IV can be obtained on a laboratory scale, they are not widely used on an industrial scale. As the cellulose nanofibers of the present disclosure, the structural mobility is relatively high. By dispersing the cellulose nanofibers in rubber, a molded article with a lower linear expansion coefficient and more excellent strength and elongation during tensile and bending deformation can be obtained. Therefore, cellulose nanofibers containing cellulose type I crystals or cellulose type II crystals are preferred, and cellulose nanofibers containing cellulose type I crystals and having a crystallinity of 55% or more are more preferred.

[0027] [Crystallinity] The crystallinity of the cellulose nanofibers is preferably 55% or more. The higher the crystallinity, the higher the mechanical properties (strength, dimensional stability) of the cellulose itself. Therefore, when the cellulose nanofibers are dispersed in rubber, the strength and dimensional stability of the rubber composite tend to be high. The lower limit of the more preferred crystallinity is 60%, even more preferably 70%, and most preferably 80%. The upper limit of the crystallinity of the cellulose nanofibers is not particularly limited, and a higher value is preferred, but from the perspective of production, the preferred upper limit is 99%.

[0028] The crystallinity referred to here, when the cellulose nanofibers are cellulose type I crystals (derived from natural cellulose), is obtained by the Segal method from the diffraction pattern (2θ / deg. is 10 to 30) when the sample is measured by wide-angle X-ray diffraction, according to the following formula. Crystallinity (%) = [I (200) - I (amorphous) / I (200) ×100 I (200) : Diffraction peak intensity by the 200 plane (2θ = 22.5°) in cellulose type I crystals I (amorphous) : Halo peak intensity due to amorphous in cellulose type I crystals, which is the peak intensity on the low-angle side (2θ = 18.0°) 4.5° lower than the diffraction angle of the 200 plane

[0029] Also, when the crystallinity is such that the cellulose is cellulose type II crystal (derived from regenerated cellulose), in wide-angle X-ray diffraction, the crystallinity is determined by the following formula from the absolute peak intensity h0 at 2θ = 12.6° attributed to the (110) plane peak of the cellulose type II crystal and the peak intensity h1 of the baseline (a line connecting 2θ = 8° and 15°) at this plane spacing. Crystallinity (%) = (h0 - h1) / h0 × 100

[0030] [Degree of polymerization] Also, the degree of polymerization of the cellulose nanofiber is preferably 100 or more, more preferably 150 or more, more preferably 200 or more, more preferably 300 or more, more preferably 400 or more, more preferably 450 or more, and preferably 3500 or less, more preferably 3000 or less, more preferably 2000 or less, more preferably 1500 or less, more preferably 1200 or less, more preferably 1000 or less.

[0031] From the viewpoints of processability and manifestation of mechanical properties, it is desirable that the degree of polymerization of the cellulose nanofiber be within the above range. From the viewpoint of processability, it is preferable that the degree of polymerization is not too high, and from the viewpoint of manifestation of mechanical properties, it is desired that it is not too low.

[0032] The degree of polymerization of the cellulose nanofiber means the average degree of polymerization determined from the Staudinger viscosity rule using the limiting viscosity number measured by the copper ethylenediamine method in JIS P8215:1998 Cellulose dilute solution - Method for measuring limiting viscosity number.

[0033] In one aspect, the weight average molecular weight (Mw) of the cellulose nanofibers is 100,000 or more, more preferably 200,000 or more. The ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight (Mn) is 6 or less, preferably 5.6 or less, or 5.4 or less. A larger weight average molecular weight means fewer end groups of the cellulose molecules. Also, since the ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight represents the width of the molecular weight distribution, a smaller Mw / Mn means fewer ends of the cellulose molecules. Since the ends of the cellulose molecules serve as the starting points of thermal decomposition, when the weight average molecular weight of the cellulose molecules in the cellulose nanofibers is not only large but also the weight average molecular weight is large and at the same time the width of the molecular weight distribution is narrow, particularly highly heat-resistant cellulose nanofibers and rubber compositions containing cellulose nanofibers and rubber can be obtained. The weight average molecular weight (Mw) of the cellulose nanofibers may be, for example, 600,000 or less, or 500,000 or less, or 400,000 or less, from the viewpoint of the availability of the cellulose raw material. The number average molecular weight (Mn) of the cellulose nanofibers may be, for example, 200,000 or less, or 150,000 or less, or 100,000 or less, or 80,000 or less, or 60,000 or less, from the viewpoint of the availability of the cellulose fiber raw material. The ratio (Mw / Mn) of the weight average molecular weight to the number average molecular weight (Mn) may be, for example, 1.5 or more, or 1.7 or more, or 2 or more, from the viewpoint of the ease of manufacturing the cellulose nanofibers. Mw can be controlled within the above range by, for example, selecting a cellulose raw material having an Mw suitable for the purpose, appropriately performing physical treatment and / or chemical treatment on the cellulose raw material within an appropriate range, and the like. Mw / Mn can also be controlled within the above range by, for example, selecting a cellulose raw material having an Mw / Mn suitable for the purpose, appropriately performing physical treatment and / or chemical treatment on the cellulose raw material within an appropriate range, and the like. Each of the Mw and Mw / Mn of the cellulose raw material may be within the above range in one aspect.

[0034] The weight-average molecular weight and number-average molecular weight of the cellulose nanofibers referred to herein are values obtained by dissolving the cellulose nanofibers in N,N-dimethylacetamide with lithium chloride added, and then determining them by gel permeation chromatography using N,N-dimethylacetamide as a solvent.

[0035] [Alkali-soluble polysaccharides] Alkali-soluble polysaccharides that the cellulose nanofibers may contain include, in addition to hemicellulose, β-cellulose and γ-cellulose. Alkali-soluble polysaccharides are understood by those skilled in the art as components obtained as the alkali-soluble portion of holocellulose obtained by solvent extraction and chlorination treatment of plants (e.g., wood) (i.e., components obtained by removing α-cellulose from holocellulose). Alkali-soluble polysaccharides are polysaccharides containing hydroxyl groups and have poor heat resistance, which may cause disadvantages such as decomposition when heated, yellowing during heat aging, and a decrease in the strength of cellulose nanofibers. Therefore, it is preferable that the content of alkali-soluble polysaccharides in the cellulose nanofibers is low.

[0036] In one aspect, from the viewpoint of obtaining good dispersibility of the cellulose nanofibers, the average content rate of alkali-soluble polysaccharides in the cellulose nanofibers is preferably 20% by mass or less, or 18% by mass or less, or 15% by mass or less, or 12% by mass or less with respect to 100% by mass of the cellulose nanofibers. From the viewpoint of the ease of manufacturing the cellulose nanofibers, the above content rate may be 1% by mass or more, or 2% by mass or more, or 3% by mass or more.

[0037] The average content rate of alkali-soluble polysaccharides can be determined by the method described in a non-patent document (Wood Science Experiment Manual, edited by the Japanese Wood Research Society, pages 92 to 97, 2000), and is obtained by subtracting the α-cellulose content rate from the holocellulose content rate (Wise method). This method is understood in the art as a method for measuring the amount of hemicellulose. Calculate the alkali-soluble polysaccharide content rate three times for one sample, and use the number average of the calculated alkali-soluble polysaccharide content rates as the average alkali-soluble polysaccharide content rate.

[0038] [Acid-insoluble components] In one aspect, from the viewpoint of avoiding a decrease in the heat resistance of cellulose nanofibers and the accompanying discoloration, the average content rate of acid-insoluble components in cellulose nanofibers is preferably 10% by mass or less, or 5% by mass or less, or 3% by mass or less with respect to 100% by mass of cellulose nanofibers. From the viewpoint of the ease of manufacturing cellulose nanofibers, the above content rate may be 0.1% by mass or more, or 0.2% by mass or more, or 0.3% by mass or more.

[0039] The average content rate of acid-insoluble components is determined by quantifying the acid-insoluble components using the Klason method described in a non-patent document (Wood Science Experiment Manual, edited by the Japanese Wood Research Society, pages 92 to 97, 2000). This method is understood in the art as a method for measuring the amount of lignin. After stirring the sample in a sulfuric acid solution to dissolve cellulose, hemicellulose, etc., filter it with a glass fiber filter paper, and the obtained residue corresponds to the acid-insoluble components. Calculate the acid-insoluble component content rate from the weight of this acid-insoluble component. Then, measure the acid-insoluble component content rate three times for one sample, and use the number average thereof as the average acid-insoluble component content rate.

[0040] [Chemical modification] The cellulose nanofibers may be chemically modified cellulose nanofibers (also referred to as chemically modified cellulose nanofibers). Examples of the chemically modified cellulose nanofibers include inorganic esterified products such as nitrate esters, sulfate esters, phosphate esters, silicate esters, and borate esters, organic esterified products such as acetylation and propionylation, etherified products such as methyl ether, hydroxyethyl ether, hydroxypropyl ether, hydroxybutyl ether, carboxymethyl ether, and cyanoethyl ether, and TEMPO oxides formed by oxidizing the primary hydroxyl groups of cellulose. The chemically modified cellulose nanofibers may contain one or more types of modifying groups. In a preferred embodiment, the chemical modification is acylation using an esterifying agent, and particularly preferably acetylation. Preferred esterifying agents include acid halides, acid anhydrides, and vinyl carboxylates and carboxylic acids. Among these esterification reaction agents, in particular, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid, and among them, acetic anhydride and vinyl acetate are preferred from the viewpoint of reaction efficiency. The cellulose nanofibers may be chemically modified by a modifying agent, for example, at the stage of the cellulose fiber raw material, during the fibrillation process, or after the fibrillation process, or may be chemically modified during or after the preparation of the slurry as a dispersion, or during or after the drying process.

[0041] [Degree of acyl substitution (DS)] When cellulose nanofibers are chemically modified (e.g., by hydrophobization such as acylation), the dispersibility of the cellulose nanofibers in rubber tends to be good. On the other hand, for example, when combined with a dispersant, it is easy for cellulose nanofibers to show good dispersibility in rubber even if they are unsubstituted or have a low degree of substitution. When the cellulose nanofibers are esterified cellulose nanofibers, the acyl substitution degree (DS) is preferably 0.1 or more, or 0.2 or more, or 0.25 or more, or 0.3 or more, or 0.5 or more in terms of obtaining esterified cellulose nanofibers with a high thermal decomposition start temperature. Since an unmodified cellulose skeleton remains in the esterified cellulose nanofibers, it is possible to obtain esterified cellulose nanofibers having high tensile strength and dimensional stability derived from cellulose and a high thermal decomposition start temperature derived from chemical modification. Preferably, it is 2.0 or less, or 1.8 or less, or 1.5 or less, or 1.2 or less, or 1.0 or less, or 0.8 or less, or 0.7 or less, or 0.6 or less, or 0.5 or less.

[0042] When the modifying group of the chemically modified cellulose nanofibers is an acyl group, the acyl substitution degree (DS) can be calculated based on the peak intensity ratio between the peak derived from the acyl group and the peak derived from the cellulose skeleton from the reflection infrared absorption spectrum of the esterified cellulose nanofibers. The peak of the absorption band of C=O based on the acyl group appears at 1730 cm -1 and the peak of the absorption band of C-O based on the cellulose backbone chain appears at 1030 cm -1 The DS of the esterified cellulose nanofibers is defined as the DS obtained from the solid NMR measurement of the esterified cellulose nanofibers described later and the modification rate (IR index 1030) defined by the ratio of the peak intensity of the absorption band of C=O based on the acyl group to the peak intensity of the absorption band of C-O of the cellulose backbone chain. A correlation graph is prepared, and the calibration curve Substitution degree DS = 4.13 × IR index (1030) can be obtained by using this. IR index (1030) = H1730 / H1030 In the formula, H1730 and H1030 are 1730 cm -1 , 1030cm -1 (absorption band of CO stretching vibration of cellulose backbone chain) -1 and 1500cm -1 The line connecting the -1 and 1500cm -1 The line connecting these points is taken as the baseline, and the absorbance is calculated when this baseline is taken as 0.

[0043] The method for calculating the DS of esterified cellulose nanofibers using solid-state NMR is as follows: 13 C solid-state NMR measurements were performed to determine the carbon C from the pyranose ring of cellulose, which appears in the range from 50 ppm to 110 ppm. 1 -C 6 The intensity of the signal attributable to one carbon atom derived from the modifying group (Inf) relative to the total intensity of the signals attributable to the modifying group (Inp) can be calculated using the following formula: DS = (Inf) x 6 / (Inp) For example, if the modifying group is an acetyl group, -CH 3 The signal at 23 ppm assigned to the Use 13 The conditions for the C solid-state NMR measurement are, for example, as follows: Equipment:Bruker Biospin Avance500WB Frequency: 125.77MHz Measurement method: DD / MAS method Waiting time: 75sec NMR sample tube: 4mmφ Accumulation times: 640 times (approx. 14 hours) MAS: 14,500Hz Chemical shift reference: glycine (external reference: 176.03 ppm)

[0044] [Thermal decomposition onset temperature (T D ), temperature at 1% weight loss (T 1% ), 250℃ weight loss rate (T250℃ )] The thermal decomposition start temperature (T D ) of the cellulose nanofiber is preferably, in one aspect, 200 °C or higher, or 210 °C or higher, 220 °C or higher, or 230 °C or higher, or 240 °C or higher, or 250 °C or higher, or 260 °C or higher, or 270 °C or higher, or 275 °C or higher, or 280 °C or higher, or 285 °C or higher from the viewpoint of avoiding thermal degradation of the fine cellulose fibers during rubber kneading and curing and exhibiting excellent reinforcing properties. Although the higher the thermal decomposition start temperature is, the more preferable it is, from the viewpoint of the ease of manufacturing the cellulose nanofiber, it may be, for example, 320 °C or lower, or 310 °C or lower, or 300 °C or lower, or 290 °C or lower, or 280 °C or lower.

[0045] The temperature (T 1% ) at which the cellulose nanofiber has a 1 wt% weight loss is preferably, in one aspect, 230 °C or higher, or 240 °C or higher, or 250 °C or higher, or 260 °C or higher, or 270 °C or higher, or 275 °C or higher, or 280 °C or higher, or 285 °C or higher, or 290 °C or higher from the viewpoint of avoiding thermal degradation during rubber kneading and curing and exhibiting mechanical strength. The higher T 1% is, the more preferable it is, but from the viewpoint of the ease of manufacturing the cellulose nanofiber, it may be, for example, 330 °C or lower, or 320 °C or lower, or 310 °C or lower.

[0046] The weight loss rate (T 250℃ ) of the cellulose nanofiber at 250 °C is preferably, in one aspect, 15% or lower, or 12% or lower, or 10% or lower, or 8% or lower, or 6% or lower, or 5% or lower, or 4% or lower, or 3% or lower from the viewpoint of avoiding thermal degradation during rubber kneading and curing and exhibiting mechanical strength. The lower T 250℃ is, the more preferable it is, but from the viewpoint of the ease of manufacturing the cellulose nanofiber, it may be, for example, 0.1% or higher, or 0.5% or higher, or 0.7% or higher, or 1.0% or higher.

[0047] In the present disclosure, T DIt is a value obtained from a graph with temperature on the horizontal axis and weight retention rate (%) on the vertical axis in thermogravimetric (TG) analysis. Starting from the weight of cellulose nanofibers in a nitrogen flow at 150 °C (state where moisture is almost removed) (weight loss of 0 wt%), the temperature is further increased. The temperature (T 1% ) at 1 wt% weight loss and the temperature (T 2% ) at 2 wt% weight loss are used to obtain a straight line. The temperature at the point where this straight line intersects the horizontal line (baseline) passing through the starting point of 0 wt% weight loss is defined as T D .

[0048] The 1% weight loss temperature (T 1% ) is the temperature at 1 wt% weight loss starting from the weight at 150 °C when the temperature is continuously increased by the above method of T D . The specific measurement method is as follows: 10 mg of the porous sheet of microcrystalline cellulose fibers is heated from room temperature to 150 °C at a heating rate of 10 °C / min in a nitrogen flow of 100 ml / min, held at 150 °C for 1 hour, and then heated from 150 °C to 450 °C at a heating rate of 10 °C / min.

[0049] The 250 °C weight loss rate (T 250℃ ) of cellulose nanofibers is the weight loss rate when cellulose nanofibers are held at 250 °C for 2 hours under a nitrogen flow in TG analysis. 10 mg of the porous sheet of cellulose nanofibers is heated from room temperature to 150 °C at a heating rate of 10 °C / min in a nitrogen flow of 100 ml / min, held at 150 °C for 1 hour, then heated from 150 °C to 250 °C at a heating rate of 10 °C / min, and held at 250 °C for 2 hours as it is. Starting from the weight W0 at the time of reaching 250 °C, the weight after holding at 250 °C for 2 hours is taken as W1, and it is calculated from the following formula. 250 °C weight change rate (%): (W1 - W0) / W0 × 100

[0050] [Porous sheet] Various physical properties of cellulose nanofibers (specific surface area, crystallinity, crystal polymorph, degree of polymerization, Mw, Mn, Mw / Mn, average content rate of alkali-soluble polysaccharides, average content rate of acid-insoluble components, T D , T 1%, T 250℃ Measurements such as (...) may vary significantly depending on the form of the measurement sample. To obtain stable and reproducible measurements, a porous sheet without distortion is used as the measurement sample. The method for producing the porous sheet is as follows.

[0051] First, a concentrated cake of cellulose nanofibers with a solid content of 10% by mass or more, where the liquid medium is water, is added to tert-butanol and adjusted to a fine cellulose fiber solid content concentration of 0.5% by mass and a total weight of 100 g. Next, dispersion treatment is performed using a mixer or the like (for example, a high-shear homogenizer (for example, manufactured by IKA, product name "Ultra Turrax T18", treatment conditions: rotation speed 15,000 rpm × 3 minutes)) until there are no aggregates. It is adjusted so that the concentration is 0.5% by mass with respect to 0.5 g of the cellulose nanofiber solid content weight. 100 g of the obtained tert-butanol dispersion is filtered on filter paper. Without peeling the filtrate from the filter paper, it is sandwiched between two larger filter papers together with the filter paper, and while pressing the edges of the larger filter paper with weights, it is dried in an oven at 150 °C for 5 minutes. Then, the filter paper is peeled off to obtain a porous sheet with little distortion. The air permeability resistance R of this sheet is 100 sec / 100 ml or less per sheet basis weight of 10 g / m 2 Those with a value of 100 sec / 100 ml or less per sheet basis weight of 10 g / m are used as the porous sheet and used as the measurement sample.

[0052] The measurement of the air permeability resistance R is carried out by measuring the basis weight W (g / m 2 ) of a porous sheet sample left standing for 1 day in an environment of 23 °C and 50% RH, and then measuring the air permeability resistance R (sec / 100 ml) using a Wang-type air permeability resistance tester (for example, manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, according to the following formula, the value per basis weight is calculated. 2 Air permeability resistance per basis weight of 10 g / m Basis weight 10 g / m 2 Air permeability resistance (sec / 100 ml) per basis weight = R / W × 10

[0053] Various physical properties (number average fiber length, number average fiber diameter, L / D ratio, crystallinity, crystal polymorph, degree of polymerization, Mw, Mn, Mw / Mn, alkali-soluble content, average acid-insoluble component content, T D 、T 1% 、T 250℃ 、DS, etc.) of the cellulose nanofibers contained in the rubber composition, rubber composite, etc. are analyzed by the following method. Dissolve the polymer component in an organic or inorganic solvent that can dissolve the polymer component contained in the rubber composition, rubber composite, etc., separate the cellulose nanofibers, wash them thoroughly with the solvent, and then replace the solvent with tert-butanol. Then, analyze the cellulose nanofiber tert-butanol slurry using the same measurement method as the above method to calculate various physical properties of the cellulose nanofibers in the rubber composition and rubber composite.

[0054] In one aspect, the cellulose nanofibers may be provided in the form of a slurry containing a liquid medium or in the form of a dry body such as particles, films, or bulk. Examples of the liquid medium include water and / or an organic solvent having a boiling point, and it may contain one or more types of media. The slurry form has a liquid medium content of 50% by mass or more, and the liquid medium content in the dry body is less than 50% by mass. The liquid medium content is a value measured when heated at 180 °C using an infrared heating moisture meter (for example, manufactured by A&D Company, Limited, trade name "MX-50").

[0055] <The First Rubber and the Second Rubber> In one aspect, the first rubber and the second rubber are liquid rubbers. In one aspect, at 38°C, the viscosity η1 of the first rubber is smaller than the viscosity η2 of the second rubber. Throughout the present disclosure, a liquid rubber means a substance that has fluidity at 23°C and forms a rubber elastomer by crosslinking (more specifically, vulcanization) and / or chain extension. That is, the liquid rubber is an uncured product in one aspect. Also, having fluidity means that in one aspect, after putting the liquid rubber dissolved in cyclohexane into a vial with a body diameter of 21 mm and a total length of 50 mm at 23°C and then drying it, the liquid rubber is filled into the vial up to a height of 1 mm and sealed, and when the vial is placed upside down and left standing for 24 hours, a movement of the substance in the height direction of 0.1 mm or more can be confirmed. The liquid rubber may have a monomer composition of a general rubber, and is preferably of relatively low molecular weight from the viewpoints of ease of handling and good dispersibility of cellulose nanofibers. The liquid rubber exhibits a liquid shape in one aspect by having a number average molecular weight (Mn) of 150,000 or less. In the present disclosure, the molecular weight and molecular weight distribution of the rubber component are values obtained by measuring a chromatogram using gel permeation chromatography in which three columns filled with polystyrene-based gels are connected and using standard polystyrene to calculate by a calibration curve. Tetrahydrofuran is used as the solvent.

[0056] When curing the rubber composition to obtain a rubber cured product, from the viewpoint of improving the mechanical properties of the rubber cured product, it is desirable that the liquid rubber be vulcanized during curing. Alternatively, the liquid rubber may be cured by heat or the like.

[0057] Factors that increase or decrease the viscosity of the liquid rubber include the types of constituent monomers, molecular weight, presence or absence of a modifying group, type of modifying group, etc. Therefore, by adjusting these, a desired combination of the first rubber and the second rubber may be obtained. In one aspect, the modified liquid rubber may have a higher viscosity than the unmodified liquid rubber having the same constituent monomers and molecular weight due to the bonding or interaction of the modifying group with other groups. In one aspect, the difference in viscosity between the first rubber and the second rubber may be adjusted by the difference in molecular weight between the first rubber and the second rubber, or by the first rubber being an unmodified liquid rubber and the second rubber being a modified liquid rubber, or by a combination thereof.

[0058] The ratio of the number average molecular weight of the second rubber to the number average molecular weight of the first rubber may be greater than 1, and from the viewpoint of obtaining a good effect by the combined use of the first and second rubbers, it is preferably 1.1 or more, or 1.2 or more, or 1.3 or more. On the other hand, from the viewpoint of improving the mechanical properties of the rubber composition, rubber composite or rubber cured product, the above ratio is preferably 10.0 or less, or 9.0 or less, or 8.0 or less.

[0059] The number average molecular weight of the first rubber is preferably 1,000 or more, or 1,500 or more, or 2,000 or more from the viewpoint of obtaining good mechanical properties of the rubber composition, rubber composite or rubber cured product, and from the viewpoints of fluidity and obtaining a rubber cured product that does not become too hard and has good rubber elasticity, it is preferably 150,000 or less, or 145,000 or less, or 140,000 or less.

[0060] The number average molecular weight of the second rubber is preferably 4,500 or more, or 5,000 or more, or 5,500 or more from the viewpoint of obtaining good mechanical properties of the rubber composition, rubber composite or rubber cured product, and from the viewpoints of fluidity and obtaining a rubber cured product that does not become too hard and has good rubber elasticity, it is preferably 150,000 or less, or 140,000 or less, or 130,000 or less.

[0061] The viscosity η1 of the first rubber at 38°C is preferably 100,000 mPa·s or less, or 95,000 mPa·s or less, or 90,000 mPa·s or less from the viewpoints of fluidity and obtaining a rubber cured product having good rubber elasticity without becoming too hard, and is preferably 5,000 mPa·s or more, or 8,000 mPa·s or more, or 10,000 mPa·s or more from the viewpoint of obtaining good mechanical properties of the rubber composition, rubber composite, or rubber cured product.

[0062] The viscosity η2 of the second rubber at 38°C is preferably 800,000 mPa·s or less, or 700,000 mPa·s or less, or 600,000 mPa·s or less from the viewpoints of fluidity and obtaining a rubber cured product having good rubber elasticity without becoming too hard, and is preferably 100,000 mPa·s or more, or 120,000 mPa·s or more, or 140,000 mPa·s or more from the viewpoint of obtaining good mechanical properties of the rubber composition, rubber composite, or rubber cured product.

[0063] In the present disclosure, the viscosity is a value measured using a B-type viscometer.

[0064] At 38°C, the ratio η2 / η1 of the viscosity η2 of the second rubber to the viscosity η1 of the first rubber is greater than 1 in one aspect, preferably 1.2 or more, or 1.3 or more, or 1.4 or more, in terms of the first rubber being likely to penetrate between the second rubbers or between the second rubber and the cellulose nanofiber, and is preferably 160 or less, or 140 or less, or 120 or less, or 100 or less, or 80 or less, or 60 or less, or 40 or less, or 20 or less, or 15 or less from the viewpoint of obtaining good affinity between the first rubber and the second rubber.

[0065] The liquid rubber may be a conjugated diene polymer, a non-conjugated diene polymer, or a hydrogenated product thereof. The above polymer or its hydrogenated product may be an oligomer.

[0066] [Conjugated diene polymer] The conjugated diene polymer may be a homopolymer, or may be a copolymer of two or more conjugated diene monomers or a copolymer of a conjugated diene monomer and another monomer. The copolymer may be either random or block.

[0067] Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 3-methyl-1,3-pentadiene, 1,3-heptadiene, and 1,3-hexadiene, and these may be used alone or in combination of two or more.

[0068] In one aspect, the conjugated diene polymer is a copolymer of the above conjugated diene monomer and an aromatic vinyl monomer. The aromatic vinyl monomer is not particularly limited as long as it is a monomer copolymerizable with the conjugated diene monomer. For example, styrene, m- or p-methylstyrene, α-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinyl ethylbenzene, vinyl xylene, vinyl naphthalene, diphenylethylene, and divinylbenzene may be mentioned, and these may be used alone or in combination of two or more. From the viewpoints of the moldability of the rubber composition and the impact resistance of the molded article, styrene is preferred.

[0069] Examples of the random copolymer include butadiene-isoprene random copolymer, butadiene-styrene random copolymer, isoprene-styrene random copolymer, and butadiene-isoprene-styrene random copolymer. Examples of the composition distribution of each monomer in the copolymer chain include a perfect random copolymer close to a statistically random composition and a tapered (gradient) random copolymer with a gradient in the composition distribution. The bonding mode of the conjugated diene polymer, that is, the composition of 1,4-bond, 1,2-bond, etc., may be uniform or different between molecules.

[0070] The block copolymer may be a copolymer composed of two or more blocks. For example, a block A of an aromatic vinyl monomer and a block B which is a block of a conjugated diene monomer and / or a copolymer of an aromatic vinyl monomer and a conjugated diene monomer may form a block copolymer having a structure such as A-B, A-B-A, A-B-A-B, etc. Note that the boundary of each block does not necessarily have to be clearly distinguished. For example, when block B is a copolymer of an aromatic vinyl monomer and a conjugated diene monomer, the aromatic vinyl monomer in block B may be distributed uniformly or in a tapered shape. Also, in block B, there may be a plurality of portions where the aromatic vinyl monomer is uniformly distributed and / or portions where it is distributed in a tapered shape, respectively. Further, in block B, there may be a plurality of segments having different aromatic vinyl monomer contents. When there are a plurality of block A and block B in the copolymer, their molecular weights and compositions may be the same or different.

[0071] The block copolymer may also be a mixture of two or more kinds in which one or more of the bonding form, molecular weight, aromatic vinyl compound species, conjugated diene compound species, total amount of 1,2-vinyl content or 1,2-vinyl content and 3,4-vinyl content, aromatic vinyl compound component content, hydrogenation rate, etc. are different from each other.

[0072] The amount of vinyl bonds in the conjugated diene bond units in the conjugated diene polymer (for example, 1,2- or 3,4-bonds of butadiene) is preferably 5 mol% or more, or 10 mol% or more, or 13 mol% or more, or 15 mol% or more, and preferably 80 mol% or less, or 75 mol% or less, or 65 mol% or less, or 50 mol% or less, or 40 mol% or less. The amount of vinyl bonds in the conjugated diene bond units (for example, the amount of 1,2-bonds of butadiene) 13 can be determined by the C-NMR method (quantitative mode). That is, 13 By integrating the peak areas appearing below in C-NMR, a value proportional to the amount of carbon of each structural unit can be obtained, and as a result, it can be converted into mass% of each structural unit. Styrene 145 to 147 ppm Vinyl 110 - 116 ppm Diene (cis) 24 - 28 ppm Diene (trans) 29 - 33 ppm

[0073] In the copolymer of a conjugated diene monomer and an aromatic vinyl monomer, the amount of the aromatic vinyl monomer bonded to the conjugated diene monomer (also referred to as the aromatic vinyl bond amount in the present disclosure) is preferably 5.0% by mass or more and 70% by mass or less, or 10% by mass or more and 50% by mass or less with respect to the total mass of the conjugated diene polymer. The aromatic vinyl bond amount can be determined by the ultraviolet absorbance of the phenyl group, and based on this, the conjugated diene bond amount can also be determined.

[0074] The conjugated diene polymer may be partially hydrogenated or fully hydrogenated. From the viewpoint of suppressing thermal deterioration during processing, the hydrogenation rate of the hydrogenated product is preferably 50% or more, or 80% or more, or 98% or more, and from the viewpoint of low-temperature toughness, it is preferably 50% or less, or 20% or less, or 0% (i.e., non-hydrogenated product). Examples of the hydrogenated product of the conjugated diene polymer include the hydrogenated products of the conjugated diene polymers exemplified above, for example, hydrogenated products of butadiene homopolymer, isoprene homopolymer, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer.

[0075] [Non-conjugated diene polymer] The non-conjugated diene polymer may be a homopolymer, or a copolymer of two or more non-conjugated diene monomers or a copolymer of a non-conjugated diene monomer and other monomers. The copolymer may be random or block. Examples of the non-conjugated diene polymer include Olefin polymers such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-butene-diene rubber, ethylene-α-olefin copolymer, Examples include butyl rubber, brominated butyl rubber, acrylic rubber, fluororubber, silicone rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, α,β-unsaturated nitrile-acrylic acid ester-conjugated diene copolymer rubber, urethane rubber, polysulfide rubber, and the like.

[0076] In the ethylene-α-olefin copolymer, monomers copolymerizable with the ethylene unit include: aliphatic substituted vinyl monomers such as propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecene-1, eicosene-1, isobutylene; aromatic vinyl monomers such as styrene and substituted styrene; ester vinyl monomers such as vinyl acetate, acrylic acid ester, methacrylic acid ester, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl methacrylate; nitrogen-containing vinyl monomers such as acrylamide, allylamine, vinyl-p-aminobenzene, acrylonitrile; dienes such as butadiene, cyclopentadiene, 1,4-hexadiene, isoprene, and the like.

[0077] Preferably, it is a copolymer of ethylene and one or more α-olefins having 3 to 20 carbon atoms, more preferably a copolymer of ethylene and one or more α-olefins having 3 to 16 carbon atoms, and most preferably a copolymer of ethylene and one or more α-olefins having 3 to 12 carbon atoms. Further, from the viewpoint of expressing impact resistance, the number average molecular weight of the ethylene-α-olefin copolymer is preferably 10,000 or more, more preferably 10,000 to 100,000, still more preferably 10,000 to 80,000, and even more preferably 20,000 to 60,000. Also, from the viewpoint of achieving both fluidity and impact resistance, the molecular weight distribution (weight average molecular weight / number average molecular weight: Mw / Mn) is preferably 3 or less, and more preferably 1.8 to 2.7.

[0078] In addition, from the viewpoint of handleability during processing, the preferable ethylene unit content in the ethylene-α-olefin copolymer is 30 to 95% by mass based on the total amount of the ethylene-α-olefin copolymer.

[0079] These preferable ethylene-α-olefin copolymers can be produced by the production methods described in, for example, Japanese Patent Publication No. 4-12283, Japanese Unexamined Patent Application Publication No. 60-35006, Japanese Unexamined Patent Application Publication No. 60-35007, Japanese Unexamined Patent Application Publication No. 60-35008, Japanese Unexamined Patent Application Publication No. 5-155930, Japanese Unexamined Patent Application Publication No. 3-163088, U.S. Patent No. 5272236, and the like.

[0080] The liquid rubber is preferably at least one selected from the group consisting of styrene-butadiene rubber, natural rubber, butadiene rubber, farnesene rubber, and isoprene rubber.

[0081] In one aspect, the liquid rubber may be a modified liquid rubber. The modified liquid rubber may have a structure in which at least one type of modifying group is introduced into each of the polymers exemplified above. The modifying group may be one or more selected from the group consisting of an epoxy group, an acid anhydride group, a carboxy group, an aldehyde group, a hydroxy group, an alkoxy group, an amino group, an amide group, an imide group, a nitro group, an isocyanato group, a thio group, a mercapto group, and the like. The modifying group is preferably one or more selected from the group consisting of a maleic anhydride group and a succinic anhydride group, or a maleic anhydride group. Examples of the modified liquid rubber include epoxy-modified natural rubber, epoxy-modified butadiene rubber, epoxy-modified styrene-butadiene rubber, epoxy-modified isoprene rubber, carboxy-modified natural rubber, carboxy-modified butadiene rubber, carboxy-modified styrene-butadiene rubber, carboxy-modified isoprene rubber, acid anhydride-modified natural rubber, acid anhydride-modified butadiene rubber, acid anhydride-modified styrene-butadiene rubber, acid anhydride-modified isoprene rubber, and the like.

[0082] The modified liquid rubber may have reactive groups (for example, one or more selected from the group consisting of a hydroxyl group, a carboxy group, an isocyanato group, a thio group, an amino group, and a halo group) at both ends, and thus may be bifunctional. These reactive groups contribute to the crosslinking and / or chain extension of the modified liquid rubber.

[0083] The modified liquid rubber can have good fluidity due to being a liquid rubber and functionality due to having a modifying group. Such a modified liquid rubber is expected to exhibit an effect of improving the dispersibility of the cellulose nanofibers with respect to the third and / or fourth rubber of the present disclosure. However, excessive bonding or interaction may locally occur between the modifying groups of the modified liquid rubber or between the modifying group of the modified liquid rubber and the hydroxyl group of the cellulose nanofibers, and the modified liquid rubbers or the modified liquid rubber and the cellulose nanofibers may form a dense structure. In particular, in the case of a high-viscosity modified liquid rubber, there is a possibility that the modified liquid rubbers easily form a dense structure. Since such a dense structure can reduce the dispersibility or orientation of the cellulose nanofibers, it is desirable to be less.

[0084] In a preferred embodiment, the first rubber is an unmodified liquid rubber and the second rubber is a modified liquid rubber. The unmodified liquid rubber can substantially not cause bonding or interaction with the cellulose nanofibers. The unmodified liquid rubber has the advantage of not forming the above-mentioned dense structure. On the other hand, the modified liquid rubber can, in one embodiment, bond or interact with the cellulose nanofibers. When the first rubber having a low viscosity is an unmodified liquid rubber and the second rubber having a high viscosity is a modified liquid rubber, the first rubber can easily enter between the second rubbers or between the second rubber and the cellulose nanofibers, and it is possible to suppress the excessive approach of the functional groups of the second rubber and the cellulose nanofibers to other functional groups. Thereby, since the effect of improving the dispersibility of the cellulose nanofibers, which is an advantage of the second rubber, is favorably exhibited, it becomes easy to achieve good dispersibility and orientation of the cellulose nanofibers.

[0085] In the modified liquid rubber, the amount of the modifying group relative to 100 mol% of all monomer units is preferably 0.1 mol% or more, or 0.2 mol% or more, or 0.3 mol% or more in terms of the good dispersibility and orientation of the cellulose nanofibers due to the good affinity between the cellulose nanofibers and the modified liquid rubber. On the other hand, when the amount of the modifying group is excessive, the modified liquid rubbers or the modified liquid rubber and the cellulose nanofibers tend to form a dense structure, and the dispersibility and orientation of the cellulose nanofibers tend to decrease. In order to impart desired mechanical properties and surface smoothness to the rubber cured product, it is desirable to suppress the formation of such a dense structure. From the above viewpoints, the amount of the modifying group relative to 100 mol% of all monomer units is preferably 5 mol% or less, or 3 mol% or less. The amount of the modifying group can be confirmed by a method of calculating the molar ratio of the modifying group by combining infrared absorption spectroscopy, solid NMR (nuclear magnetic resonance), solution NMR, or quantification by elemental analysis of a monomer composition specified in advance and an element not contained in the unmodified rubber.

[0086] The modifying group content of the modified liquid rubber is preferably 0.5 mass% or more, or 0.8 mass% or more, or 1.0 mass% or more in terms of the good dispersibility and orientation of the cellulose nanofibers due to the good affinity between the cellulose nanofibers and the modified liquid rubber, and is preferably 20 mass% or less, or 15 mass% or less, or 10 mass% or less from the viewpoint of suppressing the formation of the above-mentioned dense structure. This modifying group content can be confirmed by NMR in one aspect.

[0087] The means for producing the modified liquid rubber is not particularly limited. For example, the method described in JP-A-2016-172859 can be used.

[0088] In one aspect, the modifying group of the modified liquid rubber can form a chemical bond (ionic bond, hydrogen bond, covalent bond, etc.), more preferably a covalent bond, with cellulose nanofibers and / or rubber during the production of a rubber composition, a rubber composite, or a rubber cured product, particularly during heat mixing. In particular, the covalent bond can be advantageous in further enhancing the reinforcing effect of the cellulose nanofibers. In one aspect, a chemical bond is formed between the modified liquid rubber and the cellulose nanofibers during the production of the rubber composition or the rubber composite, and a direct or chemical bond via another component (a vulcanizing agent in one aspect) between the modified liquid rubber and the third and / or fourth rubber can be formed during the production of the rubber cured product (i.e., during curing).

[0089] From the viewpoint of improving the mechanical properties of the rubber cured product, the first and / or second rubber may be chemically bonded to the rubber (specifically, the third and / or fourth rubber) via a vulcanizing agent during the curing of the rubber composition. Generally, when highly rigid cellulose nanofibers are included in a soft matrix rubber, the rigidity of the cellulose nanofibers propagates to the matrix rubber, improving the physical properties. Here, it is presumed that this propagation functions efficiently when the cellulose nanofibers and the matrix rubber are chemically bonded, expressing more excellent physical properties of the rubber cured product. Further, when kneading with the third and / or fourth rubber in a state where the cellulose nanofibers and the modified liquid rubber are chemically bonded, the modified liquid rubber grafted from the surface of the cellulose nanofibers penetrates into the third and / or fourth rubber, functioning as an anchor, effectively applying a shearing force to the adjacent cellulose nanofibers by drying, improving the dispersibility, and finally expressing excellent physical properties of the rubber cured product.

[0090] In one aspect, the presence of the chemical bond can be expressed as the degree of chemical bond by the following method. As one aspect, the degree of chemical bond is determined for the residue obtained by removing the rubber composition or the rubber composite with a solvent (e.g., hexane, cyclohexane, THF, etc.) 13 by C solid NMR analysis, and the ratio of the amount of components other than cellulose to the amount of cellulose components in the above residue is defined as the degree of chemical bond. Degree of chemical bonding = Amount of components other than cellulose in the residue / Amount of cellulose component in the residue

[0091] Specifically, the degree of chemical bonding is measured as follows. Put 1 g of the rubber composition or rubber composite and 50 ml of THF into a vial, perform a homogenizer treatment (manufactured by IKA, product name "Ultra Turrax T18", treatment conditions: rotation speed 15,000 rpm × 3 minutes), and then stir with a magnetic stirrer (200 rpm, 24 hours). Then, filter with a nylon mesh, wash the residue on the mesh with 20 ml or more of THF twice, and then perform vacuum drying (80 °C, 12 hours) to obtain a dry solid of cellulose nanofiber residue.

[0092] Subsequently, the dry solid of cellulose nanofiber residue is 13 Measured by solid-state 13C NMR, and the degree of chemical bonding is calculated by the following formula using the peak area (P1) at 100 - 110 ppm, the total peak area (P2) at 58 - 100 ppm, and the total peak areas (P3) at 110 ppm - 220 ppm and 0 ppm - 58 ppm. Degree of chemical bonding ={(P2 - P1×5)+P3} / (P1×6) 13 [13C solid-state NMR measurement conditions] (1) Sample tube: 7 mm diameter made of zirconia (2) Magnetic field strength: 11.75 T (3) Observed nucleus: 13 13C (4) Observation frequency: 125.8 MHz (5) Temperature: Room temperature (6) MAS rotation speed: 7 kHz (7) Pulse sequence: DD / MAS method (8) Pulse width: 5.6 microseconds (9) Acquisition time: 0.047 seconds (10) Waiting time: 1000 seconds (11) Number of integrations: 150 times (12) Measuring device: Avance500 (manufactured by Bruker Japan Co., Ltd.) (13) Chemical shift standard: Adamantane (external standard 29.5 ppm)

[0093] ​ The peaks at 58 - 110 ppm mainly originate from six carbon atoms derived from cellulose, and the peaks at 100 - 110 ppm are attributed to cellulose C1 carbon. Therefore, the value six times the peak area (P1) at 100 - 110 ppm is the total peak area of the six carbon atoms derived from cellulose (P1×6). On the other hand, since various compound - derived peaks frequently appear and overlap in the range of 58 - 100 ppm, the peak area of the five carbon atoms of cellulose in the range of 58 - 100 ppm is taken as five times the peak area at 100 - 110 ppm (P1×5), and the difference from the total peak area (P2) in the range of 58 - 100 ppm is taken as the peak area derived from carbon atoms other than cellulose. Also, since the peaks in the range of 110 ppm - 220 ppm and 0 ppm - 58 ppm all originate from carbon atoms other than cellulose, the sum of the total peak area (P3) in this range and the above - mentioned differential peak area is the peak area derived from all carbon atoms other than cellulose ((P2 - P1×5)+P3). From the above, the ratio of the peak area derived from all carbon atoms other than cellulose to the peak area of the six carbon atoms derived from cellulose described above is regarded as the ratio of the weight of components other than cellulose to the weight of the cellulose component in the residue, and is defined as the chemical bond degree.

[0094] The chemical bond degree is preferably 0.01 or more, or 0.03 or more, or 0.05 or more, or 0.1 or more, or 0.15 or more from the viewpoint that the reinforcing property by cellulose nanofibers is improved by chemical bonds. On the other hand, when producing a rubber cured product using the rubber composition and / or rubber composite, from the viewpoint of excellent dispersibility of cellulose nanofibers in the rubber cured product, the chemical bond degree is preferably 4.0 or less, or 3.6 or less, or 3.3 or less, or 3.0 or less, or 2.5 or less. When the chemical bond degree exceeds 4.0, it is presumed that excessive cross - linking occurs between the modified liquid rubbers and / or unmodified liquid rubbers bonded to the cellulose nanofibers, resulting in insolubilization, and there is a tendency that the cellulose nanofibers are difficult to disperse in the matrix rubber during kneading and the like.

[0095] In one aspect, the rubber cured product is analyzed by an electron microscope or an atomic force microscope (AFM). The presence of rubber bound to the cellulose nanofibers is confirmed by analysis using NMR, infrared absorption spectrum, or Nano-IR in one aspect as a phase existing in the vicinity of the cellulose nanofibers (in one aspect, as a region of a substance different from the third and / or fourth rubbers in the rubber cured product).

[0096] In one aspect, the presence of a covalent bond can be confirmed by the following method. In a rubber composition or a rubber composite, it is confirmed by analysis using Nano-IR on the residue obtained by removing the rubber with a solvent (for example, hexane or cyclohexane, etc.).

[0097] The first rubber is preferably included with an aromatic vinyl monomer unit in that the dispersibility and orientation of the cellulose nanofibers are good due to the good affinity with the cellulose nanofibers.

[0098] The second rubber is preferably maleic anhydride-modified liquid polyisoprene from the viewpoints of miscibility with the third rubber and / or the fourth rubber and affinity with the cellulose nanofibers.

[0099] In the rubber composition, the amount of the first rubber relative to 100 parts by mass of the second rubber is preferably 5 parts by mass or more, or 10 parts by mass or more, or 15 parts by mass or more from the viewpoint of favorably obtaining the advantages of the first rubber, and preferably 500 parts by mass or less, or 300 parts by mass or less, or 280 parts by mass or less, or 260 parts by mass or less from the viewpoint of not hindering the advantages of the second rubber.

[0100] In the rubber composition, the amount of the first rubber relative to 100 parts by mass of the cellulose nanofibers is preferably 1 part by mass or more, or 5 parts by mass or more, or 10 parts by mass or more from the viewpoint of favorably obtaining the advantages of the first rubber, and preferably 300 parts by mass or less, or 200 parts by mass or less, or 100 parts by mass or less, or 90 parts by mass or less, or 80 parts by mass or less from the viewpoint of maintaining good mechanical properties of the molded article.

[0101] In the rubber composition, the amount of the second rubber with respect to 100 parts by mass of the cellulose nanofiber is preferably 1 part by mass or more, or 5 parts by mass or more, or 10 parts by mass or more from the viewpoint of favorably obtaining the advantages of the second rubber, and is preferably 300 parts by mass or less, or 200 parts by mass or less, or 100 parts by mass or less from the viewpoint of suppressing excessive bonding or interaction between the second rubbers or between the second rubber and the cellulose nanofiber.

[0102] In the rubber composition, the content of the second rubber is preferably 1% by mass or more, or 5% by mass or more, or 7% by mass or more, or 10% by mass or more from the viewpoint of favorably obtaining the advantages of the second rubber, and is preferably 60% by mass or less, or 50% by mass or less, or 40% by mass or less from the viewpoint of suppressing excessive bonding or interaction between the second rubbers or between the second rubber and the cellulose nanofiber.

[0103] In the rubber composition, the total content of the first and second rubbers is 1% by mass or more, or 10% by mass or more, or 15% by mass or more, or 20% by mass or more from the viewpoint of improving the dispersibility and orientation of the cellulose nanofiber, and is preferably 90% by mass or less, or 80% by mass or less, or 70% by mass or less from the viewpoint of obtaining a desired amount of the cellulose nanofiber to obtain a good reinforcing effect.

[0104] <Dispersant> In one aspect, the rubber composition contains a dispersant. In one aspect, it is more preferable that the dispersant has a hydrophilic segment and a hydrophobic segment in the same molecule (that is, it is an amphiphilic molecule) from the viewpoint of more uniformly dispersing the cellulose nanofiber in the rubber composition.

[0105] [Amphiphilic molecule] In an amphiphilic molecule, the hydrophilic segment is a part that exhibits good affinity with cellulose nanofibers by containing a hydrophilic structure. Specific examples of the hydrophilic structure include hydroxyl groups, thiol groups, carboxy groups, sulfonic acid groups, sulfate ester groups, phosphate groups, boronic acid groups, silanol groups, groups derived from saccharides such as sorbitan and sucrose, groups derived from glycerin, -OM, -COOM, -SO 3 M, -OSO 3 M, -HMPO 4 , and -M 2 PO 4 (where M represents an alkali metal or an alkaline earth metal), and also has primary to tertiary amines and quaternary ammonium salts, etc. As the counter anion of the above quaternary ammonium salt, there are halide ions such as hydroxide ions, fluoride ions, chloride ions, bromide ions, iodide ions, and one or more hydrophilic groups selected from the group consisting of nitrate ions, formate ions, acetate ions, trifluoroacetate ions, p-toluenesulfonate ions, hexafluorophosphate, and tetrafluoroborate, etc.

[0106] Examples of the hydrophilic segment include segments of polyethylene glycol, segments containing repeating units including a quaternary ammonium salt structure, segments of polyvinyl alcohol, segments of polyvinylpyrrolidone, segments of polyacrylic acid, segments of carboxyvinyl polymer, segments of cationized guar gum, segments of hydroxyethyl cellulose, segments of methyl cellulose, segments of carboxymethyl cellulose, soft segments of polyurethane (specifically diol segments), etc. Nonionic polyoxyethylene derivatives are particularly preferred, and the polyoxyethylene chain length of the polyoxyethylene derivative may be 3 or more, or 5 or more, or 10 or more, or 15 or more. The longer the chain length, the higher the affinity with cellulose nanofibers, but from the perspective of the balance with the desired properties (such as mechanical properties) of the resin molded body, the polyoxyethylene chain length may be 60 or less, or 50 or less, or 40 or less, or 30 or less, or 20 or less.

[0107] Examples of the hydrophobic segment include a segment having a hydrocarbon, a segment having a fluorocarbon, a segment having an alkylene oxide unit with 3 or more carbon atoms (for example, a PPG block), a segment including a polymer structure, and the like. Examples of the segment having a hydrocarbon include an alkyl type, an alkenyl type, an alkyl ether type, an alkenyl ether type, an alkyl phenyl ether type, an alkenyl phenyl ether type, a rosin ester type, a bisphenol A type, a β-naphthyl type, a styrenated phenyl type, and a hydrogenated castor oil type, etc. The carbon number of the alkyl chain or alkenyl chain of the hydrophobic group (in the case of alkyl phenyl or alkenyl phenyl, the carbon number excluding the phenyl group) is preferably 2 or more, or 5 or more, or 10 or more, or 12 or more, or 16 or more. Examples of the segment having a fluorocarbon include a linear or branched alkyl type having 1 to 20 carbon atoms, etc. Examples of the segment including a polymer structure include an acrylic polymer, a styrene resin, a vinyl chloride resin, a vinylidene chloride resin, a polyolefin resin, an amino acid lactam including a ring-opening polymer of lactam, a polymer composed of a diamine and a dicarboxylic acid, a polyacetal resin, a polycarbonate resin, a polyester resin, a polyphenylene sulfide resin, a polysulfone resin, a polyether ketone resin, a polyimide resin, a fluorine resin, a silicone resin, a melamine resin, an epoxy resin, a phenol resin, etc. These hydrophobic segments may have either a linear structure or a branched structure. Further, the hydrophobic segment may have a single-chain structure or a structure of two or more chains. In the case of a structure of two or more chains, it may have a plurality of types of hydrophobic groups.

[0108] The structure of the amphiphilic molecule is not particularly limited. When the hydrophilic segment is A and the hydrophobic segment is B, linear copolymers such as AB-type block copolymers, ABA-type block copolymers, BAB-type block copolymers, etc., triblock copolymers containing A and B, tetrablock copolymers containing A and B, star copolymers containing A and B, monocyclic copolymers containing A and B, polycyclic copolymers containing A and B, cage-type copolymers containing A and B, graft copolymers containing A and B, etc. can be mentioned. When there are multiple hydrophilic segments in the molecule, the molecular structure of the hydrophilic segment may be a single type or a combination of two or more types. Similarly, when there are multiple hydrophobic segments in the molecule, the molecular structure of the hydrophobic segment may be a single type or a combination of two or more types.

[0109] [Surfactant] As the amphiphilic molecule, any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants can be used. The dispersant may be a polymer surfactant, a reactive surfactant, etc.

[0110] Examples of nonionic surfactants include fatty acid dialkanolamides (e.g., lauric acid diethanolamide), polyoxyalkylene fatty acid amides (e.g., polyoxyethylene stearic acid amide), polyoxyalkylene aryl ethers (e.g., polyoxyethylene phenyl ether), polyoxyalkylene alkylaryl ethers (e.g., polyoxyethylene octylphenyl ether), polyoxyalkylene alkyl or alkenyl ethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene stearyl ether), fatty acid esters of polyhydric alcohols (e.g., polyethylene glycol mono- or distearate, polyethylene glycol mono- or dilaurate, polyoxyethylene hydrogenated castor oil), glycerin fatty acid esters (e.g., glycerin monostearate, glycerin monooleate), sorbitan fatty acid esters (e.g., sorbitan monolaurate, sorbitan monostearate), polyoxyethylene-polyoxypropylene block polymers, etc.

[0111] Anionic surfactants (emulsifiers) may be carboxylates, sulfonates, sulfate esters, phosphate esters, etc. Examples of carboxylates include aliphatic monocarboxylic acids and alkyl ether carboxylates. Examples of sulfonates include dialkyl sulfosuccinates, alkane sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates. Examples of sulfate esters include alkyl sulfates and fatty oil sulfate esters. Examples of phosphate esters include alkyl phosphates and polyoxyethylene alkyl ether phosphates.

[0112] Examples of cationic surfactants include amine salts, amidoamine salts, quaternary ammonium salts, and imidazolinium salts. Specific examples include, but are not particularly limited to, amine salt type surfactants such as alkylamine salts, polyoxyethylene alkylamine salts, alkylamidoamine salts, amino alcohol fatty acid derivatives, polyamine fatty acid derivatives, and imidazolines; quaternary ammonium salt type surfactants such as alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkyldimethylbenzylammonium salts, alkylpyridinium salts, alkylisoquinolinium salts, and benzethonium chloride.

[0113] Examples of amphoteric surfactants include, for example, alkylamine oxides, alanines, imidazolinium betaines, amidobetaines, betaine acetates, etc. Specifically, long-chain amine oxides, lauryl betaine, stearyl betaine, lauryl carboxymethyl hydroxyethyl imidazolinium betaine, lauryl dimethylaminoacetate betaine, fatty acid amide propyl dimethylaminoacetate betaine, etc. may be mentioned.

[0114] [Hydrophilic polymer] In one aspect, the dispersant is preferably a hydrophilic polymer. In one aspect, the hydrophilic polymer is a polymer having a hydrophilic group selected from the group consisting of a hydroxyl group, a carboxy group, an amino group, an ammonium group, a sulfonic acid group, a phosphoric acid group, and the like. As the hydrophilic polymer, one or more selected from the group consisting of cellulose derivatives (hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, etc.), polyalkylene glycols, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, carboxyvinyl polymer, cationized guar gum, water-soluble polyurethane, polymers containing a quaternary ammonium salt structure, amides, amines, and the like can be used. Among them, cellulose derivatives and polyalkylene glycols are more preferable, and polyalkylene glycols are particularly preferable.

[0115] The amount of the dispersant in the rubber composition is preferably 1 part by mass or more, or 3 parts by mass or more, or 5 parts by mass or more, or 10 parts by mass or more with respect to 100 parts by mass of the cellulose nanofiber, and preferably 200 parts by mass or less, or 100 parts by mass or less, or 80 parts by mass or less, or 60 parts by mass or less, or 50 parts by mass or less.

[0116] In one aspect, the content of the dispersant in the rubber composition components may be 0.1% by mass or more, or 1% by mass or more, or 3% by mass or more, and in one aspect, may be 50% by mass or less, or 40% by mass or less, or 30% by mass or less.

[0117] In one aspect, the dispersant / second rubber weight ratio in the rubber composition components may preferably be 2.0 or less, or 1.0 or less, or 0.8 or less, or 0.75 or less, or 0.7 or less in order to form a chemical bond between the cellulose nanofibers and the second rubber. On the other hand, from the viewpoint of the dispersibility of the cellulose nanofibers, the presence of a certain amount or more of the dispersant is desirable, and the above weight ratio may preferably be 0.01 or more, or 0.03 or more, or 0.05 or more. Further, the dispersant contains a hydroxyl group or the like which is a hydrophilic functional group, or hydroxyl groups or the like may be newly formed by molecular cleavage during kneading. Since such hydroxyl groups or the like may react with the maleic anhydride groups of the second rubber and be consumed, reducing the degree of chemical bonding between the second rubber and the cellulose nanofibers, the above range is preferable.

[0118] <Third rubber> In one aspect, the rubber composition further comprises a third rubber. The third rubber may be one or more selected from the group consisting of natural rubber, conjugated diene polymers or non-conjugated diene polymers or hydrogenated products thereof. The above polymers or their hydrogenated products may be modified rubbers or may be oligomers. Examples of the third rubber also include thermoplastic elastomers. In one aspect, the third rubber is a rubber that is not the first and second rubbers of the present embodiment, more specifically, a rubber that does not have fluidity at 23°C (in other words, a solid rubber). The first and / or second rubber and the third rubber can be different from each other (heterogeneous) in one or more of the constituent monomer component species, constituent monomer component ratios, and molecular weights.

[0119] [Natural rubber] The natural rubber is not particularly limited. For example, from the viewpoint that it has many high molecular weight components and excellent breaking strength: RSS (Ribbed Smoked Sheet) Nos. 3 to 5 of the smoke-dried type; as TSR (Technically Specified Rubber) of mechanical drying, SIR (Standard Indonesian Rubber) (produced in Indonesia), STR (Standard Thai Rubber) (produced in Thailand), SMR (Standard Malaysian Rubber) (produced in Malaysia), etc.; and epoxidized natural rubber, etc. are mentioned.

[0120] [Conjugated diene polymer] The conjugated diene polymer may be a homopolymer, or may be a copolymer of two or more conjugated diene monomers or a copolymer of a conjugated diene monomer and another monomer. The copolymer may be either random or block.

[0121] Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 3-methyl-1,3-pentadiene, 1,3-heptadiene, and 1,3-hexadiene, and these may be used alone or in combination of two or more.

[0122] In one aspect, the conjugated diene polymer is a copolymer of the above conjugated diene monomer and an aromatic vinyl monomer. The aromatic vinyl monomer is not particularly limited as long as it is a monomer copolymerizable with the conjugated diene monomer. For example, styrene, m- or p-methylstyrene, α-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinyl ethylbenzene, vinyl xylene, vinyl naphthalene, diphenylethylene, and divinylbenzene are mentioned, and these may be used alone or in combination of two or more. From the viewpoints of the moldability of the rubber composite and the impact resistance of the molded body, styrene is preferable.

[0123] Examples of the random copolymer include a butadiene-isoprene random copolymer, a butadiene-styrene random copolymer, an isoprene-styrene random copolymer, and a butadiene-isoprene-styrene random copolymer. Examples of the composition distribution of each monomer in the copolymer chain include a perfect random copolymer close to a statistically random composition and a tapered (gradient) random copolymer having a gradient in the composition distribution. The bonding modes of the conjugated diene polymer, that is, the composition of 1,4-bond, 1,2-bond, etc. may be uniform or different between molecules.

[0124] The block copolymer may be a copolymer composed of two or more blocks. For example, it may be a block copolymer in which block A of an aromatic vinyl monomer and block B which is a block of a conjugated diene monomer and / or a copolymer of an aromatic vinyl monomer and a conjugated diene monomer form a structure such as A-B, A-B-A, A-B-A-B. Note that the boundary of each block does not necessarily have to be clearly distinguished. For example, when block B is a copolymer of an aromatic vinyl monomer and a conjugated diene monomer, the aromatic vinyl monomer in block B may be distributed uniformly or in a tapered shape. Also, block B may have a plurality of portions where the aromatic vinyl monomer is uniformly distributed and / or portions where it is distributed in a tapered shape, respectively. Further, block B may have a plurality of segments having different aromatic vinyl monomer contents. When there are a plurality of block A and block B in the copolymer, their molecular weights and compositions may be the same or different.

[0125] The block copolymer may also be a mixture of two or more kinds in which one or more of the bonding form, molecular weight, aromatic vinyl compound species, conjugated diene compound species, 1,2-vinyl content or the total amount of 1,2-vinyl content and 3,4-vinyl content, aromatic vinyl compound component content, hydrogenation rate, etc. are different from each other.

[0126] The amount of vinyl bonds in the conjugated diene bond units in the conjugated diene polymer (for example, the 1,2- or 3,4-bonds of butadiene) is preferably 5 mol% or more, or 10 mol% or more, or 13 mol% or more, or 15 mol% or more, and preferably 80 mol% or less, or 75 mol% or less, or 65 mol% or less, or 50 mol% or less, or 40 mol% or less. The amount of vinyl bonds in the conjugated diene bond units (for example, the amount of 1,2-bonds of butadiene) is 13 It can be determined by the 13C-NMR method (quantitative mode). That is, 13 By integrating the peak areas that appear below in 13C-NMR, a value proportional to the amount of carbon in each structural unit can be obtained, and as a result, it can be converted to mass% of each structural unit. Styrene 145 - 147 ppm Vinyl 110 - 116 ppm Diene (cis) 24 - 28 ppm Diene (trans) 29 - 33 ppm

[0127] In the copolymer of a conjugated diene monomer and an aromatic vinyl monomer, the amount of the aromatic vinyl monomer bonded to the conjugated diene monomer (also referred to as the aromatic vinyl bond amount in the present disclosure) may be preferably 5.0 mass% or more and 70 mass% or less, or 10 mass% or more and 50 mass% or less with respect to the total mass of the conjugated diene polymer. The aromatic vinyl bond amount can be determined by the ultraviolet absorbance of the phenyl group, and based on this, the conjugated diene bond amount can also be determined.

[0128] The conjugated diene polymer may be partially hydrogenated or fully hydrogenated. The hydrogenation rate of the hydrogenated product is preferably 50% or more, or 80% or more, or 98% or more from the viewpoint of suppressing thermal deterioration during processing, and preferably 50% or less, or 20% or less, or 0% (that is, non-hydrogenated product) from the viewpoint of low-temperature toughness. Examples of the hydrogenated product of the conjugated diene polymer include the hydrogenated products of the conjugated diene polymers exemplified above, for example, hydrogenated products of butadiene homopolymer, isoprene homopolymer, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer.

[0129] [Non-conjugated diene polymer] The non-conjugated diene polymer may be a homopolymer, or may be a copolymer of two or more non-conjugated diene monomers or a copolymer of a non-conjugated diene monomer and other monomers. The copolymer may be either random or block. Examples of the non-conjugated diene polymer include olefin polymers such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-butene-diene rubber, ethylene-α-olefin copolymer, butyl rubber, brominated butyl rubber, acrylic rubber, fluorine rubber, silicone rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, α,β-unsaturated nitrile-acrylic acid ester-conjugated diene copolymer rubber, urethane rubber, polysulfide rubber, etc.

[0130] In the ethylene-α-olefin copolymer, monomers copolymerizable with ethylene units include: aliphatic substituted vinyl monomers such as propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecene-1, eicosene-1, isobutylene; aromatic vinyl monomers such as styrene and substituted styrene; ester vinyl monomers such as vinyl acetate, acrylic acid ester, methacrylic acid ester, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl methacrylate; nitrogen-containing vinyl monomers such as acrylamide, allylamine, vinyl-p-aminobenzene, acrylonitrile; dienes such as butadiene, cyclopentadiene, 1,4-hexadiene, isoprene, etc.

[0131] Preferably, it is a copolymer of ethylene and one or more α-olefins having 3 to 20 carbon atoms, more preferably a copolymer of ethylene and one or more α-olefins having 3 to 16 carbon atoms, and most preferably a copolymer of ethylene and one or more α-olefins having 3 to 12 carbon atoms. Further, from the viewpoint of expressing impact resistance, the number average molecular weight of the ethylene-α-olefin copolymer is preferably 10,000 or more, more preferably 10,000 to 100,000, still more preferably 10,000 to 80,000, and even more preferably 20,000 to 60,000. Also, the molecular weight distribution (weight average molecular weight / number average molecular weight: Mw / Mn) is preferably 3 or less, more preferably 1.8 to 2.7, from the viewpoint of achieving both fluidity and impact resistance.

[0132] Also, the preferred ethylene unit content of the ethylene-α-olefin copolymer is 30 to 95% by mass based on the total amount of the ethylene-α-olefin copolymer, from the viewpoint of handleability during processing.

[0133] These preferred ethylene-α-olefin copolymers can be produced by the production methods described in, for example, Japanese Patent Publication No. 4-12283, Japanese Unexamined Patent Application Publication No. 60-35006, Japanese Unexamined Patent Application Publication No. 60-35007, Japanese Unexamined Patent Application Publication No. 60-35008, Japanese Unexamined Patent Application Publication No. 5-155930, Japanese Unexamined Patent Application Publication No. 3-163088, U.S. Patent No. 5272236, and the like.

[0134] [Modified Rubber] The third rubber may be a modified rubber. For example, in the conjugated diene polymer or non-conjugated diene polymer exemplified above, a modifying group such as an epoxy group, an acid anhydride group, a carboxy group, an aldehyde group, a hydroxyl group, an alkoxy group, an amino group, an amide group, an imide group, a nitro group, an isocyanate group, or a mercapto group may be introduced. Examples of the modified rubber include epoxy-modified natural rubber, epoxy-modified butadiene rubber, epoxy-modified styrene-butadiene rubber, carboxy-modified natural rubber, carboxy-modified butadiene rubber, carboxy-modified styrene-butadiene rubber, acid anhydride-modified natural rubber, acid anhydride-modified butadiene rubber, acid anhydride-modified styrene-butadiene rubber, and the like.

[0135] From the viewpoint of the affinity with cellulose nanofibers, the amount of the modifying group relative to 100 mol% of all monomer units is preferably 0.1 mol% or more, or 0.2 mol% or more, or 0.3 mol% or more, and is also preferably 5 mol% or less, or 3 mol% or less. The amount of the modifying group can be confirmed by a method of calculating the molar ratio of the modifying group by combining infrared absorption spectroscopy, solid NMR (nuclear magnetic resonance), solution NMR, or elemental analysis of a pre-specified monomer composition and an element not contained in the unmodified rubber.

[0136] [Thermoplastic elastomer] In one aspect, the third rubber can include a thermoplastic elastomer or be a thermoplastic elastomer. In the present disclosure, an elastomer is, in one aspect, a substance (specifically, a natural or synthetic polymer substance) that is an elastic body at room temperature (23°C). Also, being an elastic body means, in one aspect, that the storage elastic modulus at 23°C and 10 Hz measured by dynamic viscoelasticity measurement is 1 MPa or more and 100 MPa or less. The thermoplastic elastomer may be a conjugated diene polymer or a non-conjugated diene polymer, and is, in one aspect, a crosslinked product. A suitable monomer composition of the thermoplastic elastomer may be the same as that described above in the sections of (conjugated diene polymer) and (non-conjugated diene polymer).

[0137] From the perspective of achieving both impact strength and fluidity, the number average molecular weight (Mn) of the thermoplastic elastomer is preferably 10,000 to 500,000, or 40,000 to 250,000.

[0138] The thermoplastic elastomer may have a core-shell structure. Examples of elastomers having a core-shell structure include core-shell type elastomers having a core that is a particulate rubber and a shell that is a glassy graft layer formed outside the core. Preferred examples of the core include butadiene-based rubbers, acrylic-based rubbers, and silicone-acrylic composite rubbers. Preferred examples of the shell include glassy polymers such as styrene resins, acrylonitrile-styrene copolymers, and acrylic resins.

[0139] From the perspective of excellent compatibility with the first and / or second rubber, the thermoplastic elastomer is preferably at least one selected from the group consisting of styrene-butadiene block copolymers, styrene-ethylene-butadiene block copolymers, styrene-ethylene-butylene block copolymers, styrene-butadiene-butylene block copolymers, styrene-isoprene block copolymers, styrene-ethylene-propylene block copolymers, styrene-isobutylene block copolymers, hydrogenated products of styrene-butadiene block copolymers, hydrogenated products of styrene-ethylene-butadiene block copolymers, hydrogenated products of styrene-butadiene-butylene block copolymers, hydrogenated products of styrene-isoprene block copolymers, and homopolymers of styrene (polystyrene). More preferably, it is one or more selected from the group consisting of styrene-butadiene block copolymers, hydrogenated products of styrene-butadiene block copolymers, and polystyrene.

[0140] In one aspect, at least a part of the thermoplastic elastomer may have an acidic functional group. In the present disclosure, that the thermoplastic elastomer has an acidic functional group means that an acidic functional group is added through a chemical bond in the molecular backbone of the elastomer. Further, in the present disclosure, the acidic functional group means a functional group capable of reacting with a basic functional group or the like, and specific examples include a hydroxyl group, a carboxyl group, a carboxylate group, a sulfo group, an acid anhydride group, and the like.

[0141] From the viewpoint of affinity with a modified liquid rubber or the like, the addition amount of the acidic functional group in the elastomer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, still more preferably less than 1.5% by mass, based on 100% by mass of the elastomer. The number of acidic functional groups is a value obtained by measuring a sample for calibration curve in which an acidic substance has been mixed in advance with an infrared absorption spectrometer and measuring the sample based on a calibration curve prepared using the characteristic absorption band of the acid.

[0142] Examples of the elastomer having an acidic functional group include an elastomer having a core-shell structure having a layer formed using acrylic acid or the like as a copolymerization component as a shell, an ethylene-α-olefin copolymer containing acrylic acid or the like as a monomer, a polyolefin, an aromatic compound-conjugated diene copolymer, or an elastomer which is a modified product obtained by grafting an α,β-unsaturated dicarboxylic acid or a derivative thereof onto an aromatic compound-conjugated diene copolymer hydrogenated product in the presence or absence of a peroxide.

[0143] In a preferred aspect, the elastomer is an acid anhydride-modified elastomer.

[0144] Among these, modified products obtained by grafting α,β-unsaturated dicarboxylic acids or their derivatives onto polyolefins, aromatic compound-conjugated diene copolymers, or hydrogenated aromatic compound-conjugated diene copolymers in the presence or absence of peroxides are more preferable. Among them, in particular, modified products obtained by grafting α,β-unsaturated dicarboxylic acids and their derivatives onto ethylene-α-olefin copolymers or hydrogenated aromatic compound-conjugated diene block copolymers in the presence or absence of peroxides are particularly preferable.

[0145] Specific examples of the α,β-unsaturated dicarboxylic acids and their derivatives include maleic acid, fumaric acid, maleic anhydride, and fumaric anhydride. Among these, maleic anhydride is particularly preferable.

[0146] In one aspect, the elastomer may be a mixture of an elastomer having an acidic functional group and an elastomer not having an acidic functional group. When the total of both is 100% by mass, the mixing ratio of the elastomer having an acidic functional group and the elastomer not having an acidic functional group is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and most preferably 40% by mass or more from the viewpoint of maintaining good high toughness and physical property stability of the rubber cured product. The upper limit is not particularly limited, and substantially all the elastomers may be elastomers having an acidic functional group, but 80% by mass or less is desirable from the viewpoint of not causing problems in fluidity.

[0147] From the viewpoint of providing a rubber cured product excellent in mechanical strength, the third rubber is preferably at least one selected from the group consisting of styrene-butadiene rubber, natural rubber, and isoprene rubber, and more preferably natural rubber.

[0148] In the rubber composition components, the mass ratio [(total of cellulose nanofibers and the first and second rubbers) / third rubber] of the total amount of cellulose nanofibers and the first and second rubbers to the third rubber may be, in one aspect, 1 / 99 to 99 / 1, or 5 / 95 to 95 / 5, or 10 / 90 to 90 / 10, or 20 / 80 to 80 / 20, or 30 / 70 to 70 / 30.

[0149] For example, when a preliminary composition containing cellulose nanofibers and the first and second rubbers is used for the production of a rubber composition, the mass ratio (preliminary composition / third rubber) of the preliminary composition to the third rubber in the rubber composition components may be, in one aspect, 1 / 99 to 99 / 1, or 5 / 95 to 95 / 5, or 10 / 90 to 90 / 10, or 20 / 80 to 80 / 20, or 30 / 70 to 70 / 30.

[0150] In the rubber composition components, the content of the third rubber is preferably 10% by mass or more, or 20% by mass or more, and preferably 90% by mass or less, or 85% by mass or less, or 80% by mass or less.

[0151] In the rubber composition components, the total content of the first, second, and third rubbers is preferably 40% by mass or more, or 45% by mass or more, or 50% by mass or more, and preferably 99% by mass or less, or 95% by mass or less, or 90% by mass or less.

[0152] In the rubber composition components, the total content of the first and second rubbers with respect to 100 parts by mass in total of the first, second, and third rubbers is preferably 5 parts by mass or more, or 10 parts by mass or more, or 15 parts by mass or more, and preferably 70 parts by mass or less, or 65 parts by mass or less, or 60 parts by mass or less.

[0153] The amount of cellulose nanofibers in the rubber composition components is preferably 1 part by mass or more, or 2 parts by mass or more, or 3 parts by mass or more with respect to 100 parts by mass in total of the first, second, and third rubbers, and preferably 70 parts by mass or less, or 65 parts by mass or less, or 60 parts by mass or less.

[0154] The mass ratio of [cellulose nanofiber] / [total of the first, second, and third rubbers] in the rubber composition component is preferably 1 / 99 to 60 / 40, or 2 / 98 to 50 / 50, or 3 / 97 to 40 / 60.

[0155] [Vulcanizing agent, vulcanization accelerator] When the rubber composition component contains unvulcanized rubber, the rubber composition component typically contains a vulcanizing agent and may optionally contain a vulcanization accelerator. As the vulcanizing agent and vulcanization accelerator, conventionally known ones may be appropriately selected according to the type of unvulcanized rubber in the rubber composition component. As the vulcanizing agent, organic peroxides, azo compounds, oxime compounds, nitroso compounds, polyamine compounds, sulfur, sulfur compounds, etc. can be used. Examples of sulfur compounds include sulfur monochloride, sulfur dichloride, disulfide compounds, high molecular polysulfur compounds, etc.

[0156] The amount of the vulcanizing agent in the rubber composition component is preferably 0.01 part by mass to 20 parts by mass, or 0.1 part by mass to 15 parts by mass with respect to 100 parts by mass of the unvulcanized rubber in the rubber composition component.

[0157] Examples of the vulcanization accelerator include sulfenamide-based, guanidine-based, thiuram-based, aldehyde-amine-based, aldehyde-ammonia-based, thiazole-based, thiourea-based, dithiocarbamate-based vulcanization accelerators, etc. Zinc oxide, stearic acid, etc. may be used as a vulcanization aid. The amount of the vulcanization accelerator is preferably 0.01 part by mass to 20 parts by mass, or 0.1 part by mass to 15 parts by mass with respect to 100 parts by mass of the unvulcanized rubber in the rubber composition component.

[0158] [Additives for rubber] The rubber composition components may include various conventionally known additives for rubber (stabilizers, softeners, antioxidants, etc.). As the rubber stabilizer, one or more antioxidants such as 2,6-di-tert-butyl-4-hydroxytoluene (BHT), n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenyl) propionate, and 2-methyl-4,6-bis[(octylthio)methyl]phenol may be used. Further, as the rubber softener, one or more of process oil, extender oil, etc. may be used. However, the rubber composition of the present embodiment can form a flexible molded body in one aspect, and thus the rubber composition components can be free of a rubber softener in one aspect.

[0159] Note that the vulcanizing agent, vulcanization accelerator, and additives for rubber are typically added during the production of the rubber composite, but the mode of addition is not limited thereto.

[0160] <Additional Components of Rubber Composition Components> The rubber composition components may further include additional components. Examples of the additional components include additional polymers, organic or inorganic fillers, heat stabilizers, antioxidants, antistatic agents, colorants, etc. The content ratio of any additional component in the rubber composition components is appropriately selected within a range that does not impair the desired effects of the present invention, and may be, for example, 0.01 to 50% by mass, or 0.1 to 30% by mass.

[0161] <Production of Rubber Composition> The rubber composition can be produced by a method of mixing rubber composition components including cellulose nanofibers, a first rubber, and a second rubber. As the production method of the rubber composition, (1) A first step of mixing cellulose nanofibers and a first rubber which is a low-viscosity liquid rubber to obtain a preliminary composition, and A second step of mixing the preliminary composition and a second rubber which is a high-viscosity liquid rubber to obtain a rubber composition, (2) A first step of mixing a first rubber which is a low-viscosity liquid rubber and a second rubber which is a high-viscosity liquid rubber to obtain a preliminary composition, and, A method including a second step of mixing the preliminary composition and cellulose nanofibers to obtain a rubber composition. (3) A first step of drying a preliminary composition obtained by mixing cellulose nanofibers and a first rubber which is a low-viscosity liquid rubber to obtain a dried cellulose nanofiber body, and A method including a second step of mixing the dried cellulose nanofiber body and a second rubber which is a high-viscosity liquid rubber to obtain a rubber composition. (4) A method including a step of mixing cellulose nanofibers, a first rubber which is a low-viscosity liquid rubber, and a second rubber which is a high-viscosity liquid rubber to obtain a rubber composition. etc. can be mentioned.

[0162] The mixing conditions are not particularly limited. For example, the components constituting the rubber composition may be mixed using at least one selected from mixing means such as a rotating-revolving mixer, a planetary mixer, a stirring mixer, a stirring granulator, a propeller-type stirring device, a rotary stirring device, an electromagnetic stirring device, an open roll, a Banbury mixer, a kneader, a single-screw extruder, a twin-screw extruder, etc. to obtain a rubber composition. Further, stirring may be performed under heating in order to efficiently perform shearing.

[0163] In the method of (1) above, by combining the first rubber with cellulose nanofibers in advance, the contact opportunity between the cellulose nanofibers and the second rubber becomes more appropriate and uniform, so that the physical properties of the rubber composition, rubber composite or rubber cured product can be improved more favorably. After obtaining the rubber composition, it may be dried, and a powder may be formed by controlling the drying conditions. Further, in the method of (1) above, after obtaining the preliminary composition, the preliminary composition may be dried before mixing with the high-viscosity liquid rubber to produce a dried body (CNF-first rubber dried body described later), and then the high-viscosity liquid rubber may be mixed.

[0164] In one aspect, a dried body (in one aspect, a powder) of the rubber composition of the present disclosure is provided. In one aspect, a dried body (in one aspect, a powder) containing the rubber composition of the present disclosure is provided.

[0165] In one aspect, the rubber composition produced by the above method may include a crushing step. When the rubber composition discharged from the mixer is in the form of coarse particles or lumps, it may have an adverse effect on the dispersibility and workability of the cellulose nanofibers when producing the rubber composite and the rubber cured product, and it may be refined by the crushing step. For the crushing step, a coarse crusher, an intermediate crusher, a fine crusher, etc. can be used. Examples of the coarse crusher include a jaw crusher, an impact crusher, a cone crusher, etc. Examples of the intermediate crusher include a roll crusher, a hammer mill, etc. Examples of the fine crusher include a ball mill, a vibration mill, a pin mill, a stirring mill, a jet mill, etc. Also, a classifier may be used as necessary.

[0166] When the rubber composition contains a third rubber, in one aspect, the third rubber may be further mixed in the second step of the method of (1) or (2) above. The mixing conditions at this time are not particularly limited. For example, a kneader used in general rubber kneading such as a Banbury mixer, a kneader, an open roll, etc. can be used. The rotor of the kneader can use an intermeshing rotor, a tangential rotor, or a rotor designed for resin kneading. Examples of the intermeshing rotor include KIR-II manufactured by Kobe Steel, Ltd., EX7 type manufactured by Mitsubishi Heavy Industries, Ltd., etc. Examples of the tangential rotor include 5THR, 4WN, 4WH manufactured by Kobe Steel, Ltd., E type manufactured by Mitsubishi Heavy Industries, Ltd., etc. Examples of the rotor for resin kneading include roller-shaped R500B manufactured by Toyo Seiki Seisakusho, Ltd., etc.

[0167] Also, by the methods of (1) to (3) above, after the second step (after once preparing the rubber composition), the rubber composition and the third rubber may be mixed to obtain a rubber composition further containing the third rubber. The mixing conditions at this time may be the same as those described above for the case where the rubber composition contains the third rubber.

[0168] In particular, in the second step of the method (1) above, when further kneading a third rubber with a rubber kneader, the dispersion of the cellulose nanofibers can be particularly promoted. That is, in such a second step, since the viscosity of the kneaded product can be increased by the presence of the third rubber, the shearing force applied to the kneaded product can be increased. Further, according to the rubber kneader, even when using a high-viscosity rubber, the distribution proceeds well. Therefore, since the second rubber and the cellulose nanofibers come into contact with each other at an appropriate speed and sufficiently, the dispersion of the cellulose nanofibers can be promoted. All of the rubber compositions exemplified above can be suitably used, for example, as a masterbatch, and can be applied to the production of various rubber composites.

[0169] As a method of mixing the above-described cellulose nanofibers with the first rubber and / or the second rubber, in one aspect, the cellulose nanofibers may be added in the form of a dry cellulose nanofiber (also referred to as a CNF dry body in the present disclosure). In one aspect, the cellulose nanofibers may be mixed with the first rubber and / or the second rubber in the form of a slurry or a cake, the contained liquid medium may be dried and removed, and a preliminary composition or a rubber composition containing the cellulose nanofibers may be obtained.

[0170] <Drying step> In one aspect, a dried product containing cellulose nanofibers (which may be a cellulose nanofiber dried product, a preliminary composition containing cellulose nanofibers, or a rubber composition) can be produced by drying a cellulose nanofiber slurry or cake. The dried product containing cellulose nanofibers is, for example, a dried product containing cellulose nanofibers and a first rubber (also referred to as a "CNF-first rubber dried product" in the present disclosure.) (in one aspect, the dried product does not contain the second to fourth rubbers), a dried product containing cellulose nanofibers, a first rubber, and a second rubber (also referred to as a "CNF-first rubber-second rubber dried product" in the present disclosure.) (in one aspect, the dried product does not contain the third and fourth rubbers), or a dried product containing cellulose nanofibers, a first rubber, a second rubber, and a third rubber (also referred to as a "CNF-first rubber-second rubber-third rubber dried product" in the present disclosure.) (in one aspect, the dried product does not contain the fourth rubber). The dryer is not particularly limited, and examples include kneaders, planetary mixers, Henschel mixers, high-speed mixers, paddle dryers, propeller mixers, ribbon mixers, single-screw or twin-screw extruders, Banbury mixers, freeze dryers, shelf dryers, spray dryers, pneumatic dryers, fluidized bed dryers, drum dryers, and the like. The dryers may be used alone or in combination of at least two or more. In one aspect, when drying after mixing cellulose nanofibers with the first rubber and / or the second rubber, the mixing operation and the drying operation may be performed by the dryer alone, or each operation may be performed by a kneader and the dryer. The kneader is not particularly limited, and examples include at least one stirring means selected from mixing means such as rotating and revolving mixers, planetary mixers, stirring mixers, stirring granulators, propeller-type stirring devices, rotary stirring devices, electromagnetic stirring devices, open rolls, Banbury mixers, kneaders, single-screw extruders, and twin-screw extruders. Further, stirring may be performed under heating to efficiently perform the mixing.

[0171] The drying temperature may be, for example, 20°C or higher, or 30°C or higher, or 40°C or higher, or 50°C or higher, from the viewpoint of forming a dried body containing cellulose nanofibers having powder properties excellent in drying efficiency and dispersibility of cellulose nanofibers in the rubber composition and the rubber cured product. From the viewpoints of making it difficult for thermal degradation of the cellulose nanofibers and additional components to occur and avoiding excessive pulverization of the dried body containing cellulose nanofibers due to rapid drying of the slurry, it may be, for example, 600°C or lower, or 400°C or lower, or 300°C or lower, or 200°C or lower, or 180°C or lower, or 160°C or lower, or 140°C or lower, or 120°C or lower, or 100°C or lower. The drying temperature is the temperature of the heat source in contact with the slurry, and is defined, for example, as the surface temperature of the temperature control jacket of the drying device, the surface temperature of the heating cylinder, or the temperature of the hot air.

[0172] The pressure may be either atmospheric pressure or reduced pressure. From the viewpoint of forming a dried body containing cellulose nanofibers having powder properties excellent in drying efficiency and dispersibility of cellulose nanofibers in the rubber composition and the rubber cured product, it may be -1 kPa or lower, or -10 kPa or lower, or -20 kPa or lower, or -30 kPa or lower, or -40 kPa or lower, or -50 kPa or lower. From the viewpoint of avoiding excessive pulverization of the dried body containing cellulose nanofibers due to rapid drying of the slurry, it may be -100 kPa or higher, or -95 kPa or higher, or -90 kPa or higher. Atmospheric pressure drying may be in an air atmosphere or an inert atmosphere, and an air atmosphere is preferred from the viewpoint of economy. In one aspect, from the viewpoint of preventing oxidative degradation of the dried body containing cellulose nanofibers, it is preferably an inert atmosphere, more preferably a nitrogen atmosphere.

[0173] The concentration of cellulose nanofibers in the cellulose nanofiber slurry to be subjected to the drying process is preferably 1% by mass or more, or 2% by mass or more, or 3% by mass or more, or 5% by mass or more, or 10% by mass or more, or 15% by mass or more, or 20% by mass or more, or 25% by mass or more from the viewpoint of process efficiency during drying. From the viewpoints of uniform mixing of additives, avoiding excessive increase in the viscosity of the slurry, and maintaining good handleability by avoiding solidification due to aggregation, it is preferably 50% by mass or less, or 45% by mass or less, or 40% by mass or less, or 35% by mass or less. For example, the production of cellulose nanofibers is often carried out in a dilute dispersion, but the concentration of cellulose nanofibers in the slurry may be adjusted to the preferred range by concentrating such a dilute dispersion. For concentration, methods such as suction filtration, pressure filtration, centrifugal dewatering, and heating can be used. When the cellulose nanofiber concentration of the cellulose nanofiber slurry is 10% by mass or more, it is also referred to as a cellulose nanofiber cake.

[0174] In one aspect, the dried body containing cellulose nanofibers may contain the first rubber and / or the second rubber, and any additional components (for example, the dispersant described above), and may be added before, during, and / or after drying of the cellulose nanofiber slurry. In one aspect, the dried body containing cellulose nanofibers may be a dried body containing cellulose nanofibers and a dispersant (also referred to as a "CNF-dispersant dried body" in the present disclosure.) (The dried body does not contain the first to fourth rubbers in one aspect.) In one aspect, the first rubber and / or the second rubber, and / or any additional components may be added in a state of being dispersed or dissolved in water and / or an organic solvent. The organic solvent is not particularly limited, but a solvent in which the first rubber and the second rubber dissolve is preferred, and examples include non-aqueous solvents such as chloroform, toluene, hexane, and cyclohexane.

[0175] As a more specific example of the process sequence, the following can be exemplified. (i) Prepare a slurry containing cellulose nanofibers and optionally a dispersant → Dry to prepare a dried product (CNF dried product) → Prepare a preliminary composition containing the dried product and a first rubber (CNF-first rubber dried product) → Prepare a rubber composition containing the preliminary composition and a second rubber (CNF-first rubber-second rubber dried product) (ii) Prepare a slurry containing cellulose nanofibers and optionally a dispersant → Dry to prepare a dried product (CNF dried product) → Prepare a rubber composition containing the dried product, a first rubber, and a second rubber (CNF-first rubber-second rubber dried product) (iii) Prepare a slurry containing cellulose nanofibers, a first rubber, and optionally a dispersant → Dry to prepare a dried product (CNF-first rubber dried product) → Prepare a rubber composition containing the dried product and a second rubber (CNF-first rubber-second rubber dried product) (iv) Prepare a slurry containing cellulose nanofibers, a first rubber, a second rubber, and optionally a dispersant → Dry to prepare a rubber composition (CNF-first rubber-second rubber dried product)

[0176] [Liquid medium content] The liquid medium content of the dried product containing cellulose nanofibers is preferably 90% by mass or less, or 80% by mass or less, or 70% by mass or less, or 60% by mass or less, or 50% by mass or less, or 40% by mass or less, or 30% by mass or less, or 20% by mass or less, or 10% by mass or less from the viewpoints of workability during kneading when kneaded with a third rubber (when the dried product containing cellulose nanofibers does not contain the third rubber) and / or a fourth rubber and reduction of time and energy for vaporizing the liquid. The liquid medium content may be 0% by mass, but from the viewpoints of ease of manufacturing the dried product containing cellulose nanofibers and improvement of dispersibility in the rubber composition and / or rubber cured product due to the presence of the liquid, for example, it may be 0.1% by mass or more, or 1% by mass or more, or 1.5% by mass or more. The liquid medium content is a value measured at a heating temperature of 120 °C using an infrared heating type moisture meter. Examples of the liquid medium include water and / or other media (e.g., organic solvents, inorganic acids, bases, and / or ionic liquids), and may include one or more than two types of media, but preferably water.

[0177] [Average particle size] In one aspect, from the viewpoint of ease of production, the average particle size of the dried product containing cellulose nanofibers is preferably 1 μm or more, or 10 μm or more, 50 μm or more, or 100 μm or more, or 200 μm or more, or 500 μm or more. From the viewpoint that the dried product containing cellulose nanofibers can easily disintegrate in the rubber composition and / or rubber cured product and the cellulose nanofibers can be well dispersed, it is preferably 10,000 μm or less, or 5,000 μm or less, or 4,000 μm or less, or 3,000 μm or less, or 2,000 μm or less. The above average particle size is the value measured by a dynamic image analysis type particle size distribution measuring device (CAMSIZER X2 manufactured by Microtrac).

[0178] [Loose bulk density] In one aspect, from the viewpoint that the dried product containing cellulose nanofibers has good fluidity and excellent feedability, and from the viewpoint of suppressing the transfer of the dispersant to the rubber composition and / or rubber cured product, the loose bulk density of the dried product containing cellulose nanofibers is preferably 0.01 g / cm 3 or more, or 0.05 g / cm 3 or more, or 0.10 g / cm 3 or more, or 0.15 g / cm 3 or more, or 0.20 g / cm 3 or more, or 0.25 g / cm 3 or more, or 0.30 g / cm 3 or more, or 0.35 g / cm 3 or more, or 0.40 g / cm 3 or more, or 0.45 g / cm 3 or more, or 0.50 g / cm 3In the above, the dried body containing cellulose nanofibers can be easily disintegrated in the rubber composition and / or the rubber cured product, and the cellulose nanofibers can be well dispersed. Also, the dried body containing cellulose nanofibers is not too heavy, and poor mixing between the dried body containing cellulose nanofibers and the rubber composition and / or the rubber cured product can be avoided. Preferably, it is 0.85 g / cm 3 or less, or 0.80 g / cm 3 or less, or 0.75 g / cm 3 or less.

[0179] [Apparent bulk density] In one aspect, the apparent bulk density of the dried body containing cellulose nanofibers is useful for controlling the loose bulk density and the degree of compression within the scope of the present disclosure. The apparent bulk density of the dried body containing cellulose nanofibers is controlled from the point that the fine cellulose fiber dried body can be easily disintegrated in the rubber composition and the rubber cured product, and the fine cellulose fibers can be well dispersed. In one aspect, preferably, it is 0.01 g / cm 3 or more, or 0.1 g / cm 3 or more, or 0.15 g / cm 3 or more, or 0.2 g / cm 3 or more, or 0.3 g / cm 3 or more, or 0.4 g / cm 3 or more, or 0.5 g / cm 3 or more, or 0.6 g / cm 3 or more, and preferably, it is 0.95 g / cm 3 or less, or 0.9 g / cm 3 or less, or 0.85 g / cm 3 or less, or 0.80 g / cm 3 or less, or 0.70 g / cm 3 or less.

[0180] [Degree of compression] The degree of compression is a value calculated by degree of compression = (apparent bulk density - loose bulk density) / apparent bulk density. The loose bulk density and the apparent bulk density are values measured by the method described in the [Examples] section of the present disclosure. In one aspect, the degree of compaction represents the degree of volume reduction. In one aspect, the degree of compaction of the dry body containing cellulose nanofibers is preferably 1% or more, or 5% or more, or 10% or more, or 15% or more, or 20% or more, or 25% or more in that the fluidity of the dry body containing cellulose nanofibers is not too high. Also, in terms of the good fluidity and excellent feedability of the dry body containing cellulose nanofibers, and excellent handleability (specifically, it is difficult to cause scattering, floating, or dust formation), and in terms of well dispersing the dry body containing cellulose nanofibers in the rubber composition and / or rubber cured product, and suppressing the migration of the dispersant to the rubber, the degree of compaction is preferably 50% or less, or 45% or less, or 40% or less, or 35% or less, or 30% or less.

[0181] The above-mentioned loose bulk density, tapped bulk density, and degree of compaction are measured using a powder tester (model number: PT-X) manufactured by Hosokawa Micron Corporation. The number of tapping times for measuring the tapped bulk density is 180 times. When filling the powder into the cup, sieving with a sieve is not performed, and the powder is allowed to fall from the funnel with the distance between the upper surface of the cup and the end of the leg of the funnel being 10 - 20 cm apart.

[0182] [Median diameter of crushed material] In one aspect, the median diameter (50% diameter D of the crushed material of the dry body containing cellulose nanofibers 50, also referred to as the crushed material median diameter, is preferably 8.0 mm or less, or 7.0 mm or less, or 6.0 mm or less. When kneading the rubber composition with the third and / or fourth rubber, since the rubber composition is particulate and small, it is easy to be distributed throughout, which is excellent in that it can reduce manufacturing unevenness. On the other hand, the lower limit of the median diameter is preferably 10 μm or more, or 50 μm or more, or 100 μm or more for ease of manufacturing and reduction of dust explosiveness. The crushed material median diameter is the particle size of the crushed material of the dried product containing cellulose nanofibers that has undergone the crushing process by a planetary mixer. In one aspect, the dried product containing cellulose nanofibers is particulate but is a sticky solid because it contains liquid rubber, and may be a loose mass that can be crushed by hand. Therefore, it is preferable that the dried product containing cellulose nanofibers crushed through the crushing process is within the above range.

[0183] Crushing with a planetary mixer is carried out by stirring 200 g of the dried product containing cellulose nanofibers at 50 rpm and 25 °C for 15 minutes with a HIBIMIX (registered trademark) 2P-1 type (Primix Corporation). Subsequently, for the particle size distribution of this crushed material, first, a mini sieve shaker (manufactured by AS ONE, MVS-1N) is assembled and evaluated in the order of the opening sizes of the stainless steel sieves (75φ×20 mm, plain weave) from the lower stage: (1) 2.00 mm, (2) 3.35 mm, (3) 4.75 mm, (4) 6.7 mm, (5) 9.5 mm. Approximately 15 g of the dried product containing the crushed cellulose nanofibers is placed on a sieve with an opening size of 9.5 mm and vibrated for 3 minutes at the fastest vibration speed. Then, the weight of each sieve is measured, and the cumulative undersize distribution on each sieve is calculated from the difference in the individual weights. The crushed material median diameter (50% diameter D 50 ) is calculated from this cumulative undersize distribution. In addition, for those in which the weight of the powder passing through a sieve with an opening size of 2.00 mm among the dried product containing the crushed cellulose nanofibers exceeds 40 mass% of the total powder input for classification, it is measured with a dynamic image analysis type particle size distribution measuring device (CAMSIZER X2 manufactured by Microtrac), and the 50% diameter D in the cumulative distribution 50 is adopted as the crushed material median diameter.

[0184] [Bulk density of crushed material] In one aspect, the bulk density of the dried product containing the crushed cellulose nanofibers is preferably 0.01 g / cm 3 or more, or 0.05 g / cm 3 or more, or 0.1 g / cm 3 or more, or 0.15 g / cm 3 or more, or 0.20 g / cm 3 or more. When kneaded with the third and / or fourth rubber, it easily collapses and becomes bulky, so that the cellulose nanofibers can be well dispersed. Preferably, it is 0.80 g / cm 3 or less, or 0.7 g / cm 3 or less, or 0.6 g / cm 3 or less, or 0.55 g / cm 3 or less, or 0.5 g / cm 3 or less. The dried product with a low bulk density may have anisotropic particles and fuzz. Such a powder has a shearing force during kneading effectively applied to the dried product, improving the dispersibility of the cellulose nanofibers. The bulk density of the dried product containing the crushed cellulose nanofibers is the bulk density of the dried product containing the cellulose nanofibers that has undergone a crushing process by a planetary mixer. In one aspect, the dried product containing the crushed cellulose nanofibers is particulate but is a sticky solid because it contains a liquid rubber and may be a loose mass that can be crushed by hand. Therefore, it is preferable that the bulk density of the dried product containing the cellulose nanofibers crushed through the crushing process is within the above range. The bulk density is measured in accordance with JIS K 7365 (Plastics - Method for determining the apparent density of materials that can be poured from a specified funnel) for the crushed material obtained by the above method.

[0185] ≪Rubber composite, rubber cured product and molded product≫ One aspect of the present disclosure provides a rubber composite that is a kneaded product of the rubber composition of the present embodiment and a fourth rubber (base rubber), and a rubber cured product that is a cured product of the rubber composite. The mixing conditions of the rubber composition and the fourth rubber are not particularly limited, and for example, a kneader used in general rubber kneading such as a Banbury mixer, a kneader, or an open roll can be used.

[0186] <Fourth rubber> Specific embodiments of the fourth rubber may be the same as those of the third rubber. The total content of cellulose nanofibers, the first and second rubbers with respect to a total of 100 parts by mass of the third and fourth rubbers is preferably 1 part by mass or more, or 3 parts by mass or more, or 5 parts by mass or more, and preferably 50 parts by mass or less, or 45 parts by mass or less, or 40 parts by mass or less. In one aspect, the fourth rubber may be one or more selected from the group consisting of natural rubber, styrene-butadiene rubber, isoprene rubber, and butadiene rubber, and for example, may be natural rubber. When the rubber composition contains the third rubber, it is preferable that some or all of the constituent monomers of the third rubber and the fourth rubber are the same.

[0187] In one aspect, a rubber cured product can be obtained by a vulcanization press conforming to JIS K6299. A desired molded article may be manufactured by molding the rubber composite alone or together with other components into a desired shape. The combination method of the compounding components and the molding method are not particularly limited and may be selected according to the desired molded article. The molding method is not limited to these, but (1) A method of obtaining a molded article containing a rubber cured product by curing the uncured rubber before, during, and / or after molding when the third and / or fourth rubber contains uncured rubber and molding the rubber composite alone or together with additional components. (2) A method of obtaining a molded article by forming a rubber cured product obtained by curing the uncured rubber in the rubber composite and then molding this together with additional components. (3) A method of obtaining a molded article by melt-molding the rubber composite alone or together with additional components when the third and fourth rubbers are thermoplastic elastomers. Examples include the like. The molding may be performed by injection molding, extrusion molding, profile extrusion molding, blow molding, compression molding, or the like.

[0188] <Physical properties of rubber cured product> In one aspect, the tensile stress (modulus) (M100) at 100% elongation of the rubber cured product may be 2.0 MPa or more, or 3.0 MPa or more, or 4.0 MPa or more, and in one aspect, it may be 10.0 MPa or less, or 9.0 MPa or less, or 8.0 MPa or less.

[0189] In one aspect, the tensile stress (M300) at 300% elongation of the rubber cured product may be 3.0 MPa or more, or 5.0 MPa or more, or 6.0 MPa or more, and in one aspect, it may be 20.0 MPa or less, or 15.0 MPa or less, or 13.0 MPa or less.

[0190] In one aspect, the ratio (M300 / M100) of the tensile stress (M300) at 300% elongation to the tensile stress (M100) at 100% elongation of the rubber cured product may be 1.3 or more, or 1.4 or more, or 1.5 or more, and in one aspect, it may be 2.0 or less, or 1.8 or less.

[0191] In one aspect, the storage elastic modulus of the rubber cured product may be 2.0 MPa or more, or 2.5 MPa or more, and in one aspect, it may be 4.0 MPa or less, or 3.5 MPa or less, or 3.0 MPa or less.

[0192] The loss tangent of the rubber cured product being below a predetermined value is advantageous, for example, from the viewpoints of fuel consumption performance and low heat generation in tire applications. From this viewpoint, the loss tangent may be 0.18 or less, or 0.15 or less, or 0.10 or less in one aspect. On the other hand, the loss tangent of the rubber cured product being above a predetermined value is advantageous, for example, from the viewpoint of vibration damping performance in vibration damping rubber applications. From this viewpoint, the loss tangent may be 0.02 or more, or 0.03 or more, or 0.04 or more in one aspect. The above storage elastic modulus and loss tangent are values measured at 50°C and 10 Hz in a torsion mode using a rheometer.

[0193] The rubber cured product may form molded articles of various shapes. The molded articles can be used in a wide range of applications such as industrial machine parts, general machine parts, parts related to automobiles, railways, vehicles, ships, and aerospace, electronic and electrical parts, building and civil engineering materials, daily necessities, sports and leisure goods, housing members for wind power generation, container and packaging members, etc. Examples of applications include automotive parts (e.g., exterior parts such as tires, bumpers, fenders, door panels, various moldings, emblems, engine hoods, wheel caps, roofs, spoilers, various aeroparts, etc., and interior parts such as instrument panels, console boxes, trims, etc.), battery parts (in-vehicle secondary battery parts, lithium-ion secondary battery parts, fuel cases for solid methanol batteries, pipes for fuel cells, etc.), electronic and electrical equipment parts (e.g., parts of various computers and their peripheral devices, junction boxes, various connectors, various OA equipment, TVs, videos, disc players, chassis, refrigerators, air conditioners, liquid crystal projectors, etc.), and molded products such as daily necessities (shoe outsoles, etc.). One aspect of the present disclosure provides a tire, a vibration-proof rubber, a shoe outsole, or a conveyor belt containing the rubber cured product of the present disclosure.

Examples

[0194] Hereinafter, exemplary embodiments of the present invention will be further described with reference to examples, but the present invention is not limited to these examples at all.

[0195] ≪Evaluation method≫ <Cellulose nanofiber> [Production of porous sheet] A porous sheet of cellulose nanofibers was prepared to conduct the various evaluations described below. First, a concentrated cake was prepared by concentrating a cellulose nanofiber slurry with a Buchner funnel to a solid content of 10% by mass (a press was used if necessary). Subsequently, the concentrated cake was added to tert-butanol and adjusted to a fine cellulose fiber solid content concentration of 0.5% by mass and a total weight of 100 g. Next, a dispersion treatment was performed with a high-shear homogenizer (manufactured by IKA, trade name "Ultra Turrax T18", treatment conditions: rotation speed 15,000 rpm × 3 minutes) until there were no aggregates. 100 g of the obtained tert-butanol dispersion was filtered on filter paper. The filtrate was not peeled off from the filter paper, sandwiched between two larger filter papers together with the filter paper, and dried in an oven at 150 °C for 5 minutes while pressing the edges of the larger filter paper with weights. Thereafter, the filter paper was peeled off to obtain a porous sheet with little distortion. A porous sheet having an air permeability resistance of 100 sec / 100 ml or less per sheet basis weight of 10 g / m 2 was used as the porous sheet and as a measurement sample. After measuring the basis weight W (g / m 2 ) of the sample left standing for 1 day in an environment of 23 °C and 50% RH, the air permeability resistance R (sec / 100 ml) was measured using a Wangyan type air permeability resistance tester (manufactured by Asahi Seiko Co., Ltd., model EG01). At this time, according to the following formula, the value per 10 g / m 2 of the basis weight was calculated. Air permeability resistance per 10 g / m 2 of the basis weight (sec / 100 ml) = R / W × 10

[0196] [Specific surface area of cellulose nanofibers] The specific surface area of cellulose nanofibers was measured with a specific surface area and pore size distribution measuring device (Nova-4200e, manufactured by Quantachrome Instruments). Approximately 0.2 g of a porous sheet sample was dried at 105 °C for 5 hours under vacuum, and the nitrogen gas adsorption amount at the boiling point of liquid nitrogen was measured at 5 points in the range where the relative vapor pressure (P / P0) was 0.05 or more and 0.2 or less (multi-point method). Then, the BET specific surface area (m 2 / g) was calculated by the program of the same device.

[0197] [Degree of polymerization] The degree of polymerization of the microcrystalline cellulose fibers was calculated from Staudinger's viscosity law using the limiting viscosity number measured by the copper ethylenediamine method in accordance with JIS P8215:1998 Cellulose dilute solution - Method for measuring limiting viscosity number - Copper ethylenediamine method.

[0198] [Crystallinity] X-ray diffraction measurement of the porous sheet was performed, and the crystallinity was calculated from the following formula. Crystallinity (%) = [I (200) -I (amorphous) / I (200) ×100 I (200) : Diffraction peak intensity due to the 200 plane (2θ = 22.5°) in cellulose I-type crystal I (amorphous) : Halo peak intensity due to the amorphous phase in cellulose I-type crystal, which is the peak intensity on the low-angle side (2θ = 18.0°) 4.5° lower than the diffraction angle of the 200 plane (X-ray diffraction measurement conditions) Apparatus MiniFlex (manufactured by Rigaku Corporation) Operation axis 2θ / θ X-ray source CuKα Measurement method Continuous type Voltage 40 kV Current 15 mA Start angle 2θ = 5° End angle 2θ = 30° Sampling width 0.020° Scan speed 2.0° / min Sample: The porous sheet was attached onto the sample holder

[0199] [Average content rate of alkali-soluble polysaccharides] The average content rate of alkali-soluble polysaccharides was determined by subtracting the α-cellulose content rate from the holocellulose content rate (Wise method) for cellulose nanofibers by the method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pages 92 - 97, 2000). The alkali-soluble polysaccharide content rate was calculated three times for one sample, and the number average thereof was taken as the average content rate of alkali-soluble polysaccharides in cellulose nanofibers.

[0200] [Average content rate of acid-insoluble components] The quantification of acid-insoluble components was performed by the Klason method described in the non-patent literature (Wood Science Experiment Manual, edited by the Japanese Wood Research Society, pages 92-97, 2000) for microcrystalline cellulose fibers. The microcrystalline cellulose fibers dried to constant weight were precisely weighed, placed in a predetermined container, and 72 mass% sulfuric acid was added. After appropriately pressing with a glass rod so that the contents became uniform, it was autoclaved to dissolve cellulose and hemicellulose in the acid solution. After allowing to cool, the contents were filtered through glass fiber filter paper, and the acid-insoluble components were obtained as residues. The acid-insoluble component content rate was calculated from the weight of this acid-insoluble component, and the number average of the acid-insoluble component content rates calculated for 3 samples was defined as the average content rate of acid-insoluble components.

[0201] [Thermal decomposition start temperature (TD) of cellulose nanofibers] The T of cellulose nanofibers D The porous sheet was evaluated by the following measurement method. Apparatus: Thermo plus EVO2 manufactured by Rigaku Sample: A circular piece cut from the porous sheet was placed in an aluminum sample pan in a stack of 10 mg. Sample amount: 10 mg Measurement conditions: In a nitrogen flow of 100 ml / min, the temperature was raised from room temperature to 150 °C at a rate of 10 °C / min, held at 150 °C for 1 hour, and then the temperature was raised to 450 °C at a rate of 10 °C / min as it was. T D Calculation method: It was determined from a graph with the temperature on the horizontal axis and the weight retention rate (%) on the vertical axis. Starting from the weight at 150 °C (state where moisture was almost removed) of the porous sheet (weight reduction amount 0 wt%), the temperature was further raised, and a straight line passing through the temperature at 1 wt% weight reduction and the temperature at 2 wt% weight reduction was obtained. The temperature at the point where this straight line intersects the horizontal line (baseline) passing through the starting point of 0 wt% weight reduction amount was defined as the thermal decomposition start temperature (T D ).

[0202] [Rubber] [Viscosity at 38 °C] The viscosity of the rubber was measured using a B-type viscometer. The results are shown in Table 1.

[0203] [Number average molecular weight (Mn)] The values in the product catalog were shown.

[0204] <Rubber composition> Regarding the rubber composition, the following evaluations were conducted.

[0205] <Rubber composition containing the first and second rubbers> [Dispersibility of cellulose nanofibers] Regarding the rubber composition, optical microscope observation was performed under the following conditions. 1 mg of the sample was sandwiched between two cover glasses and crushed and spread to have a uniform thickness. The above sample was placed on the stage of a polarized light microscope BX51P manufactured by Olympus Corporation. A differential interference prism U-DICR manufactured by Olympus Corporation was inserted and differential interference observation was performed. The dispersibility of the cellulose nanofibers was evaluated according to the following criteria. A: Generally uniformly dispersed. B: Dispersed, but aggregation is observed. C: A large number of aggregations are confirmed.

[0206] [Cellulose nanofiber content] It was calculated according to the following formula. Cellulose nanofiber content (%) = weight of cellulose nanofibers / weight of rubber composition × 100 [Dispersant / second rubber weight ratio] It was calculated according to the following formula Dispersant / second rubber weight ratio = parts by mass of dispersant / parts by mass of second rubber

[0207] [Median particle size of crushed material] 200 g of the rubber composition was placed in a Hibiscus Mix (registered trademark) 2P-1 type (Primix Corporation), and stirred at 50 rpm and 25 °C for 15 minutes to obtain a crushed product. Subsequently, for the particle size distribution of this crushed product, first, a mini sieve shaker (manufactured by AS ONE, MVS-1N) was assembled with stainless steel sieves (75φ × 20 mm, plain weave) having mesh openings of (1) 2.00 mm, (2) 3.35 mm, (3) 4.75 mm, (4) 6.7 mm, and (5) 9.5 mm in this order from the bottom and evaluated. Approximately 15 g of the crushed rubber composition was placed on a sieve with a mesh opening of 9.5 mm, and vibrated at the fastest vibration speed for 3 minutes. Then, the weight of each sieve was measured, and the cumulative undersize distribution on each sieve was calculated from the difference in the individual weights. The median diameter (50% diameter D 50 ) of the crushed product was calculated from this cumulative undersize distribution. In addition, for those in which the powder weight passing through a 2.00 mm mesh opening after sieving exceeded 40 mass% of the total powder weight input to the shaker, it was measured with a dynamic image analysis type particle size distribution measuring device (CAMSIZER X2 manufactured by Microtrac), and 50% diameter D 50 was adopted as the median diameter of the crushed rubber composition.

[0208] [Bulk density of the crushed product] The crushed product obtained by the above method was measured according to JIS K 7365 (Method for obtaining the apparent density of materials that can be poured from a standard funnel for plastics).

[0209] [Degree of chemical bonding] 1 g of the rubber composition and 50 ml of THF were placed in a vial, and after performing a homogenizer treatment (manufactured by IKA, product name "Ultra Turrax T18", treatment conditions: rotation speed 15,000 rpm × 3 minutes), it was stirred with a magnetic stirrer (200 rpm, 24 hours). Then, it was filtered through a nylon mesh, and the residue on the mesh was washed twice with 20 ml or more of THF, and then vacuum dried (80 °C, 12 hours) to obtain a dry solid of cellulose nanofiber residue. Subsequently, the dry solid of cellulose nanofiber residue was 13Solid-state NMR measurement was performed, and the degree of chemical bonding was calculated using the following formula with the peak area (P1) at 100 to 110 ppm, the total peak area (P2) at 58 to 100 ppm, and the total peak areas (P3) at 110 ppm to 220 ppm and 0 ppm to 58 ppm. Degree of chemical bonding ={(P2 - P1×5)+P3} / (P1×6) 13 [13C solid-state NMR measurement conditions] (1) Sample tube: Made of zirconia, 7 mm in diameter (2) Magnetic field strength: 11.75 T (3) Observed nucleus: 13 13C (4) Observation frequency: 125.8 MHz (5) Temperature: Room temperature (6) MAS rotation speed: 7 kHz (7) Pulse sequence: DD / MAS method (8) Pulse width: 5.6 microseconds (9) Acquisition time: 0.047 seconds (10) Waiting time: 1000 seconds (11) Number of integrations: 150 times (12) Measuring device: Avance500 (manufactured by Bruker Japan Co., Ltd.) (13) Chemical shift standard: Adamantane (external standard 29.5 ppm)

[0210] [Rubber composition (masterbatch) further containing a third rubber] [Dispersibility of cellulose nanofibers] Regarding the rubber composition, in 10 randomly selected cross-sectional images of a 2 mm-sided cube observed by X-ray CT, the number of cellulose nanofiber aggregates with a size of 20,000 μm or more in each cross-section was counted, and the average number of aggregates per cross-section was calculated, and the cellulose nanofiber dispersion state was ranked according to the following criteria. 2 A: 5 or less A: 5 or less B: More than 5 and 10 or less C: More than 10 In Example 5, the following criteria were used S: 2 or less A: 3 to 5​ B: 5 to 8 pieces C: 9 to 10 pieces D: More than 10 pieces The measurement conditions of the X-ray CT are as follows. Device: Bruker X-CT Skyscan1272 Tube voltage: 40 kV, tube current: 100 μA Number of pixels: 2452×1640, pixel resolution: 1.2 μm, number of integrations: 8 times Scan: 0.2 degrees per step, 180-degree scan

[0211] <Rubber cured product> The following evaluations were performed on the rubber cured product. (1) Surface smoothness Small pieces were cut out from the rubber cured product sheet with scissors and placed on the stage of a confocal laser microscope (Keyence, VK-X250). Using a 10x objective lens, a surface unevenness image was obtained. The arithmetic mean height (Sa) was calculated according to ISO25178, and the result of the reference comparative example was set to 100 and indexed. The smaller the index, the better the surface smoothness.

[0212] (2) Tensile strength, tensile stress (modulus) According to the tensile test method of JIS K-6251, the tensile strength, the tensile stress at 100% elongation (100% modulus, M100), and the tensile stress at 300% elongation (300% modulus, M300) were measured, and the result of the reference comparative example was set to 100 and indexed. The larger the index, the better the tensile strength and tensile stress.

[0213] (3) Dispersion of cellulose nanofibers For the rubber cured product, among 10 randomly selected cross-sectional images of a 2 mm cube observed by X-ray CT, evaluation was performed in the same procedure as the above-mentioned [Dispersion of cellulose nanofibers] related to the rubber composition. The evaluation criteria used were the same as those in Example 5.

[0214] (4) Orientation of cellulose nanofibers Regarding the cellulose nanofibers observed by a transmission electron microscope, data processing was performed as follows to calculate the orientation degree of the cellulose nanofibers. When the roll kneading direction of the rubber cured sheet was defined as MD, the direction perpendicular to the roll kneading direction was defined as TD, and the sheet thickness direction was defined as ND, for the MD-ND plane of the sample, a section with a set thickness of 500 μm was taken using a cryomicrotome, observed at 1000 times magnification using a transmission electron microscope (JEOL JEM-1400), and images were obtained for 5 random fields of view. Regarding the observed cellulose nanofibers, binarization processing and particle analysis were performed using the image processing software ImageJ. In the particle analysis, the cellulose nanofibers were approximated as ellipses, and for each cellulose nanofiber, the angle θ formed by the major axis direction of the ellipse and MD was obtained. Regarding the cellulose nanofibers obtained from 5 TEM images, (3(cosθ)^2 - 1) / 2 was calculated, and the average value was taken as the orientation degree. The orientation of the cellulose nanofibers was evaluated according to the following criteria. A: Orientation degree is 0.7 or more B: Orientation degree is 0.5 or more and less than 0.7 C: Orientation degree is less than 0.5 In Example 6, the following criteria were used. S: Orientation degree is 0.8 or more A: Orientation degree is 0.7 or more and less than 0.8 B: Orientation degree is 0.6 or more and less than 0.7 C: Orientation degree is 0.5 or more and less than 0.6 D: Orientation degree is less than 0.5

[0215] ≪Materials Used≫ <Cellulose Nanofibers> [Cellulose Nanofiber A] 3 parts by mass of cotton linter pulp was immersed in 27 parts by mass of water and dispersed with a pulper. 170 parts by mass of water was added to 30 parts by mass of the cotton linter pulp slurry (including 3 parts by mass of cotton linter pulp) treated with the pulper and dispersed in water (solid content ratio: 1.5% by mass). Using an SDR14 type laboratory refiner (pressure type DISK type) manufactured by Aikawa Iron Works Co., Ltd. as a disk refiner device, with a clearance between disks of 1 mm, the aqueous dispersion was beaten for 30 minutes. Subsequently, beating was thoroughly performed under the condition that the clearance was reduced to a level close to almost zero, and a beaten aqueous dispersion (solid content concentration: 1.5% by mass) was obtained. The obtained beaten aqueous dispersion was directly subjected to 10 times of micronization treatment at an operating pressure of 100 MPa using a high-pressure homogenizer (NSO15H manufactured by Niro Soavi (Italy)), and a cellulose nanofiber A slurry (solid content concentration: 1.5% by mass) was obtained. Then, it was concentrated to a solid content ratio of 10% by mass with a dehydrator to obtain a cake of cellulose nanofiber A. Specific surface area: 53 m 2 / g Crystallinity: 82% Degree of polymerization: 1050 Average content rate of alkali-soluble polysaccharides: 3.6% Average content rate of acid-insoluble components: 0.9% T d : 260 °C

[0216] [Cellulose nanofiber B] To 200 g of dry weight of softwood pulp, 15 L of water, 25 g of sodium bromide, and 2.5 g of TEMPO were added, and after thoroughly stirring and dispersing, an aqueous solution of sodium hypochlorite (co-oxidizing agent) at 13 mass% was added so that the amount of sodium hypochlorite was 6.5 mmol / g, and the reaction was started. Since the pH decreased as the reaction proceeded, a 0.5 N aqueous sodium hydroxide solution was added dropwise to maintain the pH at 10 to 11, and the reaction was carried out until no change in pH was observed. After completion of the reaction, 0.1 N hydrochloric acid was added to adjust the pH to 7.0, and filtration and washing with water were repeated for purification to obtain cellulose fibers having a fiber surface oxidized with a carboxyl group content of 1.83 mmol / g. Next, the above cellulose fibers were diluted with pure water so that the solid content concentration became 1 wt%, and treated twice with an ultrahigh pressure homogenizer at a pressure of 140 MPa from a liquid temperature of 20 °C. After visually confirming the transparency of the treatment liquid, the fibrillation process of the cellulose fibers was terminated to obtain TEMPO-oxidized cellulose nanofibers. Specific surface area: 94 m 2 / g Crystallinity: 74% Degree of polymerization: 780 Average content rate of alkali-soluble polysaccharides: 12.9% Average content rate of acid-insoluble components: 1.5% T d : 205 °C

[0217] [Cellulose nanofiber C] Obtained from Sugino Machine Co., Ltd. (BinFis: BMa-10010) Specific surface area: 76 m 2 / g Crystallinity: 76% Degree of polymerization: 810 Average content rate of alkali-soluble polysaccharides: 12.6% Average content rate of acid-insoluble components: 3.2% T d : 220 °C

[0218] <Liquid rubber as the first rubber or the second rubber> Liquid rubber - 1: Ricon184 manufactured by Kray Valley (liquid butadiene-styrene random copolymer, Mn = 9,400) Liquid Rubber - 2: LIR - 30 manufactured by Kuraray Co., Ltd. (liquid polyisoprene, Mn = 28,000) Liquid Rubber - 3: LBR - 305 manufactured by Kuraray Co., Ltd. (liquid polybutadiene, Mn = 26,000) Liquid Rubber - 4: L - FR - 107 manufactured by Kuraray Co., Ltd. (liquid farnesene rubber, Mn = 130,000) Liquid Rubber - 5: Ricon153 manufactured by Kray Valley (liquid polybutadiene, Mn = 6,700) Liquid Rubber - 6: LIR - 403 manufactured by Kuraray Co., Ltd. (maleic anhydride - modified liquid polyisoprene, Mn = 34000, number of modified groups per molecular chain is 3) Liquid Rubber - 7: LIR - 410 manufactured by Kuraray Co., Ltd. (carboxy - modified liquid polyisoprene, Mn = 30,000, number of modified groups per molecular chain is 10) Liquid Rubber - 8: Ricon184MA6 manufactured by Kray Valley (maleic anhydride - modified liquid styrene - butadiene copolymer, Mn = 9,200, number of modified groups per molecular chain is 6) Liquid Rubber - 9: Ricon131MA20 manufactured by Kray Valley (maleic anhydride - modified liquid polybutadiene, Mn = 7,000, number of modified groups per molecular chain is 11) Liquid Rubber - 10: LIR - 50 manufactured by Kuraray Co., Ltd. (liquid polyisoprene, Mn = 54,000)

[0219] <The Third Rubber and the Fourth Rubber> Natural Rubber: RSS No.3 (Producer: UNIMAC RUBBER CO., LTD. (Thailand), Supplier: Marubeni Techno Rubber) Polyisoprene: IR2200 manufactured by JSR Corporation SBR - 1: Manufactured by the procedure described in the section [Manufacture of SBR - 1]. SBR - 2: Asaprene (registered trademark) Y031 manufactured by Asahi Kasei Corporation

[0220] [Manufacture of SBR - 1] An autoclave with an internal volume of 10 L, an internal height (L) to diameter (D) ratio (L / D) of 4.0, an inlet at the bottom, an outlet at the top, and a jacket for stirring and temperature control was used. In addition, a static mixer was connected to the reactor just before the raw material inlet. 1,3-butadiene, from which impurities such as moisture had been removed in advance, was mixed at 20.2 g / min, styrene at 16.8 g / min, and n-hexane at 137.6 g / min to obtain a mixed liquid. Just before this mixed liquid entered the first reactor, n-butyllithium for impurity inactivation treatment was supplied at 0.020 phm, mixed with the static mixer, and then continuously supplied to the bottom of the first reactor. Furthermore, 0.320 phm of 2,2-bis(2-oxolanyl)propane as a polar substance and 0.102 phm of NBL (normal butyl lithium) as a polymerization initiator were continuously fed to the bottom of the reactor, and the temperature inside the reactor was maintained at 82°C to obtain a rubber solution. The rubber solution produced in the reactor was fed from the top of the reactor to a static mixer, and a reaction was carried out immediately before the static mixer by continuously feeding M1 (1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) as a modifier in a ratio of 1.0 equivalent (however, the amount added was calculated assuming that 4 moles of NBL react with 1 mole of M1) to the lithium of NBL fed as a polymerization initiator, to obtain SBR-1.

[0221] <Dispersant> Nonionic dispersant: Sannix GL-3000 (polyoxyethylene polyoxypropylene triol) manufactured by Sanyo Chemical Industries, Ltd.

[0222] <Vulcanization aid> Zinc oxide: available from Fujifilm Wako Pure Chemical Industries, Ltd. Stearic acid: available from Fujifilm Wako Pure Chemical Industries, Ltd.

[0223] <Wax> Sunnock: Selected Special Wax (available from Ouchi Shinko Chemical Co., Ltd.)

[0224] <Anti-aging agent> No crack 6C: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (available from Ouchi Shinko Chemical Industrial Co., Ltd.)

[0225] <Vulcanization accelerator> Noxeller CZ: N-cyclohexyl-2-benzothiazolylsulfenamide (available from Ouchi Shinko Chemical Industrial Co., Ltd.) Noxeller D: 1,3-diphenylguanidine (available from Ouchi Shinko Chemical Industrial Co., Ltd.)

[0226] ≪Manufacture of rubber composition≫ <Rubber composition - 1 containing the first and second rubbers> [Examples 1-1 to 1-12] After putting 10% by mass of cellulose nanofiber cake A into a 200 ml PP cup, a low-viscosity liquid rubber and a dispersant were added so as to have the compounding ratio shown in Table 2, and as a final composition, an aqueous dispersion was prepared so that the concentration of cellulose nanofibers was 10% by mass. The 200 ml PP cup was set in a rotation-revolution mixer ARE-310 manufactured by Shinky Co., Ltd. and mixed in a stirring mode (revolution 2000 rpm, rotation 800 rpm) for 15 minutes. Next, a high-viscosity liquid rubber was added so as to have the compounding ratio shown in Table 2, and further mixed in a stirring mode (revolution 2000 rpm, rotation 800 rpm) for 15 minutes. The obtained composition was thinly spread on a release film and dried at 80 °C using SPH-201 manufactured by Espec Corporation, and then pulverized for 30 seconds using a mini speed mill MS-05 manufactured by Labonect Co., Ltd. to obtain a rubber composition. The obtained rubber composition was evaluated for dispersibility using an optical microscope.

[0227] [Example 1-13] In a beaker, 57.1 parts by mass of a liquid butadiene-styrene random copolymer (liquid rubber - 1) and 200 parts by mass of maleic anhydride-modified liquid polyisoprene (liquid rubber - 6) were dissolved in 2314 parts by mass of chloroform and stirred. Next, the liquid rubber solution was spread on a Teflon (registered trademark) bat and vacuum-dried at 80 °C to obtain a preliminary composition. After putting 10% by mass of cellulose nanofiber cake A into a 200 ml PP cup, a preliminary composition and a dispersant were added so as to obtain the compounding ratio shown in Table 2, and an aqueous dispersion was prepared as the final composition so that the concentration of cellulose nanofibers was 10% by mass. The 200 ml PP cup was set in a rotation-revolution mixer ARE-310 manufactured by Shinki Co., Ltd. and mixed in a stirring mode (revolution 2000 rpm, rotation 800 rpm) for 15 minutes. The obtained composition was thinly spread on a release film and dried at 80 °C using an SPH-201 manufactured by Espec Corporation, and then pulverized for 30 seconds using a mini speed mill MS-05 manufactured by Labo Net Co., Ltd. to obtain a rubber composition. The obtained rubber composition was evaluated for dispersibility using an optical microscope.

[0228] [Examples 1-14 to 1-22] A rubber composition was obtained in the same manner as in Example 1-12 except that the amount of chloroform was changed to 1414 parts by mass and the amounts and types of the low-viscosity liquid rubber and the high-viscosity liquid rubber were changed as shown in Table 2. The obtained rubber composition was evaluated for dispersibility using an optical microscope.

[0229] [Comparative Examples 1-1 to 1-10] After putting 10% by mass of cellulose nanofiber cake into a 200 ml PP cup, a low-viscosity liquid rubber or a high-viscosity liquid rubber and a dispersant were added so as to obtain the compounding ratio shown in Table 3, and an aqueous dispersion was prepared as the final composition so that the concentration of cellulose nanofibers was 10% by mass. The 200 ml PP cup was set in a rotation-revolution mixer ARE-310 manufactured by Shinki Co., Ltd. and mixed in a stirring mode (revolution 2000 rpm, rotation 800 rpm) for 15 minutes. The obtained composition was thinly spread on a release film and dried at 80 °C using an SPH-201 manufactured by Espec Corporation, and then pulverized for 30 seconds using a mini speed mill MS-05 manufactured by Labo Net Co., Ltd. to obtain a rubber composition. The obtained rubber composition was evaluated for dispersibility using an optical microscope.

[0230] <Rubber Composition (Masterbatch) Further Containing a Third Rubber - 1> [Examples 2-1 to 2-22, Comparative Examples 2-1 to 2-16] After placing 10% by mass of cellulose nanofiber cake in a 200 ml PP cup, a low-viscosity liquid rubber and a dispersant were added to obtain the compounding ratios shown in Tables 4 to 6, and an aqueous dispersion was prepared so that the concentration of cellulose nanofibers was 10% by mass as the final composition. The 200 ml PP cup was set in a rotation-revolution mixer ARE-310 manufactured by Shinki Co., Ltd. and mixed in the stirring mode (revolution 2000 rpm, rotation 800 rpm) for 15 minutes. The obtained composition was thinly spread on a release film and dried at 80 °C using SPH-201 manufactured by Espec Corporation, and then pulverized for 30 seconds using a mini speed mill MS-05 manufactured by Labo Net Co., Ltd. to obtain a preliminary composition.

[0231] Using a sealed kneader (internal volume 0.35 L) equipped with a temperature control device, at a filling rate of 65%, in accordance with the compositions shown in Tables 4 to 6, a third rubber, the preliminary composition, and a high-viscosity liquid rubber were added and kneaded at 140 °C for 5 minutes. The obtained kneaded product was recovered and passed through rolls to obtain a sheet-like rubber composition (masterbatch). A part was cut out from the sheet and evaluated for the dispersibility of cellulose nanofibers by X-ray CT. The results are shown in Tables 4 to 6.

[0232] [Example 2-23] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1 except that the kneading temperature was changed to 120 °C. A part was cut out from the sheet and evaluated for the dispersibility of cellulose nanofibers by X-ray CT. The results are shown in Table 5.

[0233] [Example 2-24] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1 except that the kneading temperature was changed to 130 °C. A part was cut out from the sheet and evaluated for the dispersibility of cellulose nanofibers by X-ray CT. The results are shown in Table 5.

[0234] [Example 2-25] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1, except that the kneading temperature was changed to 160°C. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0235] [Example 2-26] A preliminary composition was obtained in the same manner as in Example 2-1. Using a sealed kneader (internal volume 0.35 L) equipped with a temperature control device, as the first-stage kneading, at a filling rate of 65%, according to the composition shown in Table 5, the third rubber, the preliminary composition, and the modified liquid rubber were added and kneaded at 120°C for 5 minutes. Next, as the second-stage kneading, after cooling the obtained kneaded product to room temperature, it was kneaded again at 120°C for 3 minutes to improve the dispersion of cellulose nanofibers. The obtained kneaded product was recovered, and a sheet-like rubber composition (masterbatch) was obtained through a roll. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0236] [Example 2-27] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-26, except that the time for the second-stage kneading was changed to 5 minutes instead of 3 minutes. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0237] [Example 2-28] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-26, except that the temperatures for the first-stage and second-stage kneadings were changed to 140°C instead of 120°C. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0238] [Example 2-29] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-27, except that the kneading temperature of the first and second stages was changed from 120 °C to 140 °C. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0239] [Example 2-30] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1, except that the filling rate was changed to 55%. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0240] [Example 2-31] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1, except that the filling rate was changed to 75%. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0241] [Example 2-32] A preliminary composition was obtained in the same manner as in Example 2-1. Using a 1.6 L Banbury mixer, at a filling rate of 65%, according to the composition shown in Table 5, the third rubber, the preliminary composition, and the modified liquid rubber were added and kneaded at 120 °C for 5 minutes. The obtained kneaded product was recovered, and a sheet-like rubber composition (masterbatch) was obtained through rolls. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0242] [Example 2-33] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-32, except that the kneading temperature was changed to 140 °C. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0243] [Example 2-34] A preliminary composition was obtained in the same manner as in Example 2-1. Using a 0.5 L kneader, at a filling rate of 65%, according to the composition shown in Table 5, a third rubber, a preliminary composition, and a modified liquid rubber were added and kneaded at 120 °C for 5 minutes. The obtained kneaded material was recovered, and a sheet-like rubber composition (masterbatch) was obtained through a roll. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0244] [Example 2-35] A sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-34 except that the kneading temperature was changed to 140 °C. A part was cut out from the sheet, and the dispersibility of cellulose nanofibers was evaluated by X-ray CT. The results are shown in Table 5.

[0245] <Rubber cured product-1> [Examples 3-1 to 3-26, Comparative Examples 3-1 to 3-14] Using a sealed kneader (internal volume 0.35 L) equipped with a temperature control device, as the first-stage kneading, at a filling rate of 65%, according to the formulations shown in Tables 7 to 10, a rubber composition, a fourth rubber, zinc white, stearic acid, wax, and a stabilizer were added and kneaded at 140 °C for 3 minutes. Next, as the second-stage kneading, the obtained kneaded material was cooled to room temperature and then kneaded again at 140 °C for 3 minutes to improve the dispersion of cellulose nanofibers. After cooling, sulfur and a vulcanization accelerator were added and kneaded on an open roll set at 70 °C, and molded into a sheet. Then, the sheet-like kneaded material was vulcanized with a vulcanization press at 160 °C for 15 minutes using a mold with a thickness of 2.0 mm to obtain a rubber cured product sheet. Various evaluations were performed on the obtained rubber cured product sheet. The results are shown in Tables 7 to 10. The reference comparative examples are different for each fourth rubber type, and Comparative Examples 3-6, 3-12, and 3-14 correspond to them.

[0246] [Examples 4-1 to 4-47, Comparative Examples 4-1 to 4-16] A closed kneader (internal volume 0.35 L) equipped with a temperature control device was used. As the first-stage kneading, with a filling rate of 65%, according to the formulations shown in Tables 11 to 16, a masterbatch, the fourth rubber, zinc white, stearic acid, wax, and stabilizer were added and kneaded at 140 °C for 3 minutes. Next, as the second-stage kneading, the obtained kneaded material was cooled to room temperature and then kneaded again at 140 °C for 3 minutes to improve the dispersion of cellulose nanofibers. After cooling, sulfur and a vulcanization accelerator were added and kneaded on an open roll set at 70 °C, and formed into a sheet shape. Then, the sheet-shaped kneaded material was vulcanized with a vulcanization press at 160 °C for 15 minutes using a mold with a thickness of 2.0 mm to obtain a rubber cured sheet. Various evaluations were performed on the obtained rubber cured sheet. The results are shown in Tables 11 to 16. The reference comparative examples are different for each fourth rubber type, and Comparative Examples 4-6, 4-12, and 4-15 correspond to them.

[0247] <CNF-First Rubber-Second Rubber Dried Body> [Examples 5-1 to 5-4, 5-6 to 5-21, Comparative Examples 5-1 to 5-11] 10 mass% of cellulose nanofiber cake, the first rubber, and a dispersant were put into a 200 ml PP cup so as to have the formulation ratios shown in Tables 17 to 19, and then mixed in a rotation-revolution mixer (manufactured by Shinki Co., Ltd., ARE-310) in the stirring mode (revolution 2000 rpm, rotation 800 rpm). The obtained mixed cake was vacuum dried at 50 rpm and 80 °C using a planetary mixer (manufactured by Primix, Hibiscus Mix 2P-1) to obtain a CNF-first rubber dried body. Subsequently, according to the compositions shown in Tables 17 to 19, the CNF-first rubber dried body and the second rubber were kneaded in a closed kneader (internal volume 0.35 L) equipped with a temperature control device at a filling rate of 65% and a device temperature of 120 °C. While adjusting the rotation speed, the temperature of the material was raised to 160 °C over 10 minutes and then kneaded for an additional 5 minutes to obtain a CNF-first rubber-second rubber dried body (or, for the comparative example, a comparative dried body) as the rubber composition of the present disclosure. Note that the composition not containing the second rubber did not perform this step.

[0248] [Example 5-5] 15 g of the CNF - first rubber - second rubber dried product prepared in Example 5 - 4 was processed twice for 10 seconds using a tabletop mill (manufactured by Labo Netto, Mini Speed Mill MS - 05) to obtain a pulverized product. When compared with Example 5 - 4, both the median particle size and the loose bulk density decreased due to the pulverization treatment, and it became cottony.

[0249] In Example 5 - 1, when compared with Comparative Example 5 - 1, although a second rubber containing a maleic anhydride group was used, the first rubber was not used, and it was presumed that in the production of the CNF - first rubber - second rubber dried product or the comparative dried product, it was difficult for the second rubber to penetrate between the fibers of the cellulose nanofibers, resulting in a lower degree of chemical bonding. Also, Comparative Example 5 - 2 did not contain a second rubber having a maleic anhydride group, and no chemical bonding was present.

[0250] When comparing Examples 5 - 1 to 5 - 10, the higher the cellulose nanofiber content and the lower the dispersant / second rubber weight ratio, the higher the degree of chemical bonding. When the cellulose nanofiber content is high, the viscosities of the first rubber and the second rubber itself contained in the CNF - first rubber - second rubber dried product become high, and it becomes easier to apply a shearing force during kneading, resulting in excellent dispersibility. Also, because it became easier to apply a shearing force, it is presumed that the cellulose nanofibers that were close to each other during drying in the production of the CNF - first rubber dried product were loosened, making it easier for the second rubber to penetrate, and the degree of chemical bonding became high. On the other hand, it is considered that the dispersant has a hydroxyl group or that a hydroxyl group is newly formed by molecular cleavage during kneading. It is presumed that this hydroxyl group reacts with the maleic anhydride group of the second rubber and is consumed, leading to a decrease in the degree of bonding between the second rubber and the cellulose nanofibers. Therefore, the lower the dispersant / second rubber weight ratio, the higher the degree of chemical bonding tended to be. Also, when the cellulose nanofiber content is high, the median particle size of the pulverized product and the loose bulk density of the pulverized product are small. This is presumably because the high - viscosity liquid rubber functions as an adhesive, and the larger the amount (the lower the cellulose nanofiber content), the coarser the particles formed.

[0251] Comparing Example 5-3, Example 5-11, and Example 5-12, as the fiber diameter of the cellulose nanofiber species became smaller, the median particle size of the CNF - first rubber - second rubber dried body became smaller, and the loose bulk density became the largest. It is presumed that as the fiber diameter became smaller, the cohesive force of the cellulose nanofibers during drying became stronger, making them more likely to become fine powder and resulting in a larger loose bulk density. Furthermore, due to the strength of this cohesive force, it is presumed that the second rubber is less likely to penetrate between the fibers, resulting in a lower degree of chemical bonding. Also, for cellulose nanofiber B, it is TEMPO - oxidized cellulose nanofiber, and carboxyl groups are present at a high density on the fiber surface. In addition to the reduced contact probability between the maleic anhydride group of the second rubber and the hydroxyl group of the cellulose nanofiber due to the presence of this large number of carboxyl groups, it is presumed that the reactivity is low due to electrostatic repulsion, resulting in a lower degree of chemical bonding. Furthermore, as a reason for the low degree of chemical bonding, it is also presumed that there is a large amount of alkali - soluble component, which is a low - molecular polysaccharide contained in cellulose nanofibers B and C, and maleic anhydride is consumed and not directly bonded to the cellulose nanofibers.

[0252] Comparing Example 5-4 and Example 5-13, when the dispersant is not included, the hydrophobic first rubber is easily discharged from between the cellulose nanofiber fibers and agglomerates during drying. As a result, even when the second rubber is kneaded, it is difficult to penetrate between the cellulose nanofiber fibers, and it is presumed that the degree of chemical bonding becomes low. Also, since the highly viscous second rubber is difficult to penetrate between the fibers, it is presumed that there is a large amount of excess second rubber, the tackiness of the powder is high, the median particle size is also large, and it has an adverse tendency for the dispersion of cellulose nanofibers.

[0253] Comparing Example 5-4 with Examples 5-14 to 5-21 and Comparative Examples 5-3 to 5-10, although the first rubber species or the second rubber species are different, it is presumed that the tackiness of the powder increases due to the increase in the viscosity of the liquid rubber, and the median particle size and the loose bulk density increase. On the other hand, for Comparative Examples 5-3 to 5-6, since the cellulose nanofiber content was high, the crushed material median particle size and the loose bulk density were small. For Comparative Examples 5-7 to 5-10, since the cellulose nanofiber content was low, the crushed material median particle size and the loose bulk density became large. Compared with Examples 5-18 to 5-20, the degree of chemical bonding is low. This is presumably because the penetration of the second rubber is insufficient due to the absence of the first rubber, resulting in poor dispersibility and a low degree of chemical bonding. For Examples 5-18 and 5-21, the liquid rubbers used were carboxy-modified liquid polyisoprene and liquid polyisoprene. The former does not react with the hydroxyl group unless it is anhydrified by heating, so the degree of chemical bonding is low. The latter does not contain a modifying group, so it cannot bond with cellulose nanofibers and the degree of chemical bonding becomes 0.

[0254] In Comparative Example 5-11, the viscosity of the first rubber is greater than that of the second rubber. In the state where the extremely high-viscosity first rubber is contained between the cellulose nanofiber fibers in the comparative dried body, the low-viscosity second rubber is difficult to penetrate into the space between the fibers. Therefore, the degree of chemical bonding is low, the tackiness of the powder is high, the median particle size is also large, which is disadvantageous for the dispersion of cellulose nanofibers.

[0255] [Example 5-22] Kneading was started at a device temperature of 160 °C, and kneading was carried out for 15 minutes after reaching 160 °C. A CNF-first rubber-second rubber dried body was produced by the same method as in Example 5-20 except that a CNF-first rubber-second rubber dried body was obtained. Since kneading was carried out with a strong shearing force, the reaction was promoted and the degree of chemical bonding showed a high value.

[0256] [Example 5-23] According to the composition shown in Table 18, a CNF-first rubber dried body prepared in the same manner as in Example 5-1 and a second rubber were kneaded in a 1.6 L Banbury mixer at a filling ratio of 65% and an apparatus temperature of 120°C. After starting the kneading, the temperature of the material was raised to 160°C over 10 minutes while adjusting the rotation speed, and then kneaded for an additional 5 minutes to obtain a CNF-first rubber-second rubber dried body.

[0257] [Example 5-24] According to the composition shown in Table 18, a CNF-first rubber dried body prepared in the same manner as in Example 5-1 and a second rubber were kneaded in a 0.5 L kneader at a filling ratio of 65% and an apparatus temperature of 120°C. After starting the kneading, the temperature of the material was raised to 160°C over 10 minutes while adjusting the rotation speed, and then kneaded for an additional 5 minutes to obtain a CNF-first rubber-second rubber dried body.

[0258] [Example 5-25, Comparative Example 5-12] After putting 10 mass% of cellulose nanofiber cake A into a 200 ml PP cup, the first rubber and a dispersant were added so as to have the compounding ratios shown in Tables 18 and 19, and an aqueous dispersion was prepared so that the concentration of cellulose nanofibers became 10 mass% as the final composition. The 200 ml PP cup was set in a rotation-revolution mixer ARE-310 manufactured by Shinky Co., Ltd. and mixed in the stirring mode (revolution 2000 rpm, rotation 800 rpm) for 15 minutes. Next, the second rubber was added and further mixed in the stirring mode (revolution 2000 rpm, rotation 800 rpm) for 15 minutes. The obtained rubber composition was thinly spread on a release film and dried at 80°C using SPH-201 manufactured by Espec Corporation, and then pulverized for 30 seconds using a mini speed mill MS-05 manufactured by Labonekt Co., Ltd. to obtain a CNF-first rubber-second rubber dried body (Example 5-25) and a comparative dried body (Comparative Example 5-12). The second rubber has a maleic anhydride group, but it is presumed that it was ring-opened with water derived from cellulose nanofibers during the rotation-revolution mixer mixing, and the degree of chemical bonding was low and suppressed.

[0259] <CNF-first rubber-second rubber-third rubber dried body (masterbatch)> [Examples 5-26 to 5-37, Comparative Example 5-13] According to the composition shown in Table 20, the CNF-first rubber dried body or the CNF-first rubber-second rubber dried body and the second rubber and / or the third rubber were kneaded in a sealed kneader (internal volume 0.35 L) equipped with a temperature control device at a filling rate of 65% and a device temperature of 120 °C. After starting the kneading, the temperature of the material was raised to 160 °C over 10 minutes while adjusting the rotation speed, and then kneaded for another 5 minutes to obtain a CNF-first rubber-second rubber-third rubber dried body (masterbatch). The obtained dried body was in a lump shape and could not be crushed by a planetary mixer, and the particle size and bulk density could not be measured. Also, the degree of chemical bonding showed a considerably high value compared with Example 5-1, Example 5-25, Comparative Example 5-2, and Comparative Example 5-12. This is presumably because in addition to the chemical bonding between the second rubber and the cellulose nanofiber, a small amount of the third rubber itself crosslinked and became insoluble during the kneading of the third rubber. Further, in the evaluation of dispersibility by X-CT with the masterbatch, Example 5-26 was excellent, Example 5-30 was slightly excellent, and Example 5-34 was poor. This depends on the performance of the rubber compositions (CNF-first rubber-second rubber dried body, comparative dried body) used.

[0260] <Rubber cured product-2> [Examples 6-1 to 6-40, Comparative Examples 6-1 to 6-15] A sealed kneader (internal volume: 0.35 L) equipped with a temperature control device was used. As the first-stage kneading, at a filling rate of 65%, in accordance with the formulations shown in Tables 21 to 24, a CNF - first rubber - second rubber dried body (a dried body containing the rubber composition of the present disclosure) (or a comparative dried body) or a CNF - first rubber - second rubber - third rubber dried body (masterbatch), a fourth rubber, zinc white, stearic acid, wax, and a stabilizer were added and kneaded at 140°C for 3 minutes (so that the cellulose nanofibers in the rubber cured product were 5 parts by mass). Next, as the second-stage kneading, after cooling the obtained kneaded product to room temperature, it was kneaded again at 140°C for 3 minutes to improve the dispersion of the cellulose nanofibers. After cooling, sulfur and a vulcanization accelerator were added and kneaded on an open roll set at 70°C, and formed into a sheet shape. Then, the sheet-shaped kneaded product was vulcanized with a vulcanization press at 160°C for 15 minutes using a mold with a thickness of 2.0 mm to obtain a rubber cured product sheet. Various evaluations were performed on the obtained rubber cured product sheet. The results are shown in Tables 21 to 24. The reference comparative examples differ for each fourth rubber type, and Comparative Example 6-1, Comparative Examples 6-12 to 6-14 are applicable.

[0261] When comparing Example 6-1 and Comparative Example 6-1, Comparative Example 6-1 does not use the first rubber, and since the surface of the cellulose nanofibers cannot be coated with the first rubber during the production of the CNF - first rubber dried body, the cohesiveness is high. Also, the degree of chemical bonding is low, the reinforcing property is limited, and the improvement of the shear force by chemical bonding is also limited, and the dispersibility and orientation are insufficient. The same is true when comparing Examples 6-18 to 6-21 and Comparative Examples 6-7 to 6-10, Example 6-28 and Comparative Example 6-15, and Example 6-29 and Comparative Example 6-16.

[0262] When comparing Example 6-1 and Comparative Example 6-2, Comparative Example 6-2 does not use the second rubber and has no modifying groups for forming chemical bonds. Therefore, the degree of chemical bonding is low, the reinforcing property is limited, and the improvement of the shear force by chemical bonding is also limited, and the dispersibility and orientation are insufficient. The same is true when comparing Examples 6-14 to 6-17 and Comparative Examples 6-3 to 6-6.

[0263] Comparing Example 6-4 and Example 6-13, in Example 6-13 without a dispersant, the improvement in the physical properties of the cured product was limited. When producing a CNF dried body without adding a dispersant, it was presumed that it was difficult for the hydrophobic first rubber and second rubber to penetrate between the hydrophilic cellulose nanofiber fibers, resulting in a low degree of chemical bonding, easy aggregation, and a dried body that was disadvantageous for the dispersion of cellulose nanofibers. As described above, excellent physical properties were exhibited by including all of the first rubber, the second rubber, and the dispersant.

[0264] In Examples 6-1 to 6-10, the cured product using a CNF-first rubber-second rubber dried body with a high cellulose nanofiber content, a low dispersant / second rubber weight ratio, and a high degree of chemical bonding had excellent physical properties. When the cellulose nanofiber content was high and the degree of chemical bonding was high, the shearing force during kneading was easily applied, improving the dispersion of the cellulose nanofibers. Also, the mechanical properties were improved due to the presence of chemical bonds.

[0265] Comparing Example 6-4 and Example 6-5, by reducing the median particle size by pulverization and reducing the loose bulk density (fluffing), the shearing force during kneading was efficiently applied to the dried body, improving the dispersibility, orientation, and mechanical properties of the cellulose nanofibers.

[0266] Comparing Example 6-3, Example 6-11, and Example 6-12, even when the median particle size was small, the cured product properties of the fine powder CNF-first rubber-second rubber dried body with a large loose bulk density were limited in improvement. Also, due to the small fiber diameter of the cellulose nanofibers, the cohesiveness was high, and the fine powder dried body was considered hard particles and was disadvantageous for dispersion. Also, due to the low degree of chemical bonding, the improvement in the cured product properties was further limited.

[0267] Regarding Example 6-18 and Example 6-21, the liquid rubbers used were carboxy-modified liquid polyisoprene and liquid polyisoprene. The former had a low degree of chemical bonding, and the latter did not contain a modifying group, so it could not bond with cellulose nanofibers and was a dried product with a chemical bond degree of 0. This low degree of chemical bonding limited the improvement of the physical properties of the cured product compared to the other first and second rubber types.

[0268] In Comparative Example 6-11, due to the higher viscosity of the first rubber than the second rubber, the dried product had a low degree of chemical bonding, high tackiness of the powder, and a large median particle size. Therefore, the dispersion and orientation of cellulose nanofibers were poor, and the physical properties of the cured product were disadvantageous.

[0269] Comparing Example 6-20 and Example 6-22, Example 6-22 was a dried product with a significantly improved degree of chemical bonding due to kneading with strong shear force, but the dispersion and orientation of cellulose nanofibers tended to be poor, and the improvement of the physical properties of the cured product was limited. It is presumed that strong kneading partially caused cross-linking and insolubilization between the first rubber and / or the second rubber, inhibiting the dispersion and orientation during kneading with the fourth rubber.

[0270] Comparing Example 6-1 and Example 6-28, although the compositions were the same, the degree of chemical bonding in Example 6-28 was low and suppressed, so the dispersion and orientation of cellulose nanofibers tended to be poor, and the improvement of the physical properties of the cured product was limited. Regarding Comparative Example 6-15, it is presumed that the performance was low for the same reason when compared with Comparative Example 6-1.

[0271] In Examples 6-29 to 6-40 and Comparative Example 6-16, rubber cured products were prepared for four types of fourth rubbers using a masterbatch that was a CNF - first rubber - second rubber - third rubber dried body. Compared with the case of directly preparing from the CNF - first rubber - second rubber dried body (Examples 6-1 and Examples 6-25 to 6-27), the dispersion and orientation of cellulose nanofibers tended to be poor, and the improvement of the physical properties of the cured product was limited. It is considered that the dispersion and distribution during kneading were at a low level because it was in a lump form that could not be crushed. Also, the degree of chemical bonding showed a remarkably high value, and it is presumed that a small amount of the third rubber itself crosslinked and became insoluble during the kneading of the third rubber. It is considered that the insolubilization reduced the dispersion and orientation of the cellulose nanofibers to a low level. Furthermore, the dispersibility at the masterbatch stage differed depending on the type of the CNF - first rubber - second rubber dried body (comparative dried body in the comparative example) used to prepare the masterbatch. Compared with Example 5-1, Example 5-25 had a raw material with low dispersibility and a low degree of chemical bonding, and Comparative Example 5-2 had a raw material that did not contain the second rubber and had even lower dispersibility. Therefore, it is considered that it affected the physical properties of the final rubber cured product.

[0272]

Table 1

[0273]

Table 2

[0274]

Table 3

[0275]

Table 4

[0276]

Table 5

[0277]

Table 6

[0278]

Table 7

[0279]

Table 8

[0280]

Table 9

[0281]

Table 10

[0282]

Table 11

[0283]

Table 12

[0284]

Table 13

[0285]

Table 14

[0286]

Table 15

[0287]

Table 16

[0288]

Table 17

[0289]

Table 18

[0290]

Table 19

[0291]

Table 20

[0292]

Table 21

[0293]

Table 22

[0294]

Table 23

[0295]

Table 24

Industrial Applicability

[0296] Since the rubber composition according to the present disclosure can form a molded article having good physical properties, it can be suitably applied to a wide range of uses such as industrial machine parts, general machine parts, automobile, railway, vehicle, ship, and aerospace related parts, electronic and electrical parts, building and civil engineering materials, daily necessities, sports and leisure goods, housing members for wind power generation, container and packaging members, and the like.

Claims

1. A rubber composition comprising a cellulose nanofiber, a first rubber, and a second rubber, The first rubber and the second rubber are liquid rubbers, A rubber composition, wherein the viscosity η1 of the first rubber is smaller than the viscosity of the second rubber at 38°C.

2. 2. The rubber composition according to claim 1, wherein the viscosity η1 of the first rubber is 5,000 mPa·s to 100,000 mPa·s and the viscosity η2 of the second rubber is 100,000 mPa·s to 800,000 mPa·s at 38°C.

3. The rubber composition according to claim 1 or 2, wherein the second rubber has a number average molecular weight of 4,500 to 150,000.

4. The rubber composition according to claim 1 or 2, comprising 5 to 300 parts by mass of the first rubber per 100 parts by mass of the second rubber.

5. The rubber composition according to claim 1 or 2, comprising 5 to 100 parts by mass of the first rubber per 100 parts by mass of cellulose nanofibers.

6. The rubber composition according to claim 1 or 2, comprising 10 to 300 parts by mass of the second rubber per 100 parts by mass of cellulose nanofibers.

7. The rubber composition according to claim 1 or 2, comprising 5% by mass to 60% by mass of the second rubber.

8. The rubber composition according to claim 1 or 2, wherein the first rubber contains an aromatic vinyl monomer unit.

9. 3. The rubber composition of claim 1, wherein the second rubber is a maleic anhydride modified liquid polyisoprene.

10. The rubber composition according to claim 1 or 2, further comprising a dispersant.

11. The rubber composition of claim 10, wherein the dispersant is nonionic.

12. The rubber composition of claim 10, wherein the weight ratio of dispersant to second rubber is from 0.01 to 2.

0.

13. The rubber composition according to claim 1 or 2, further comprising a third rubber.

14. The rubber composition of claim 13, wherein the third rubber is a natural rubber.

15. The rubber composition according to claim 1 or 2, which is in a dry form.

16. The rubber composition according to claim 15, wherein the crushed product has a median diameter of 10 μm to 8.0 mm.

17. The loose bulk density of the crushed material is 0.01 g / cm ３ ~0.80g / cm ３ The rubber composition according to claim 15,

18. The rubber composition according to claim 1 or 2, wherein the degree of chemical bonding of the rubber composition is 0.01 to 4.

0.

19. A method for producing the rubber composition according to claim 1 or 2, A first step of mixing cellulose nanofibers and the first rubber to obtain a preliminary composition; and A second step of mixing the preliminary composition with the second rubber to obtain a rubber composition; A method comprising:

20. A method for producing the rubber composition according to claim 1 or 2, A first step of mixing the first rubber and the second rubber to obtain a preliminary composition; and A second step of mixing the preliminary composition with the cellulose nanofibers to obtain a rubber composition; A method comprising:

21. 20. The method of claim 19, further comprising mixing a third rubber in said second step.

22. A method for producing the rubber composition according to claim 13, A step of mixing cellulose nanofibers and the first rubber to obtain a preliminary composition; mixing the preliminary composition with the second rubber to obtain a dry mass; and A step of mixing the dried product with a third rubber to obtain a rubber composition; A method comprising:

23. A method for producing the rubber composition according to claim 13, mixing the first rubber with the second rubber to obtain a preliminary composition; A step of mixing the preliminary composition with the cellulose nanofibers to obtain a dry body; and A step of mixing the dried product with a third rubber to obtain a rubber composition; A method comprising:

24. A dried body comprising the rubber composition according to claim 1 or 2.

25. A method for producing a rubber composition, comprising the steps of: A rubber composition method comprising the step of mixing the dried product of claim 24 with a third rubber to obtain a rubber composition.

26. 22. The method of claim 21, wherein the third rubber is a natural rubber.

27. 23. The method of claim 22, wherein the third rubber is a natural rubber.

28. 24. The method of claim 23, wherein the third rubber is a natural rubber.

29. 26. The method of claim 25, wherein the third rubber is a natural rubber.

30. A rubber composite, which is a mixture of the rubber composition according to claim 1 or 2 and a fourth rubber.

31. A rubber composite, which is a mixture of the rubber composition according to claim 13 and a fourth rubber.

32. A method for producing a rubber composite, comprising the steps of: A method comprising mixing the rubber composition of claim 1 or 2 with a fourth rubber.

33. A method for producing a rubber composite, comprising the steps of: A method comprising mixing the rubber composition of claim 13 with a fourth rubber.

34. A cured rubber product, which is a cured product of the rubber composite of claim 30.

35. A tire comprising the rubber vulcanizate of claim 34.

36. A rubber vibration isolator comprising the cured rubber product according to claim 34.

37. A shoe outsole comprising the rubber vulcanized product of claim 34.

38. A conveyor belt comprising the vulcanized rubber according to claim 34.

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