Rubber composition containing cellulose nanofibers

Abstract

The present invention provides: a rubber composition which is excellent in terms of dispersibility and orientation of cellulose nanofibers; a rubber composite; and a cured rubber product. One embodiment of the present invention provides a cured rubber product which exhibits good physical properties (in particular, tensile characteristics and modulus) and good surface smoothness. One embodiment of the present invention provides a rubber composition which contains cellulose nanofibers, a first rubber, and a second rubber, wherein: the first rubber is an unmodified liquid rubber; and the second rubber is a modified liquid rubber.

Description

Rubber composition containing cellulose nanofibers

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

[0002] Conventionally, rubber molded articles are required to have a high level of balance among various properties, such as mechanical strength, flexibility, abrasion resistance, and processability. For example, fillers are commonly incorporated into rubber molded articles to improve elastic modulus, hardness, abrasion resistance, etc. For such filler-containing rubber molded articles to exhibit the desired properties, it is important that the filler is well dispersed in the rubber. In recent years, with increasing awareness of environmental issues, various attempts have been made to use cellulose, a low-specific-gravity, renewable material, as a filler to be incorporated into rubber molded articles. Cellulose nanofibers, in particular, are highly promising fillers for polymer molded articles because of the excellent reinforcing effect they impart per used amount to polymer molded articles when combined with various polymers to form such articles. The use of cellulose nanofibers in rubber molded articles would enable the provision of rubber molded articles with low specific gravity, excellent physical properties, and advantages in a variety of applications, as well as transportation and disposal costs. However, cellulose nanofibers are inherently hydrophilic due to the hydroxyl groups in the cellulose, making them difficult to mix with rubber, which is generally a highly hydrophobic material. Therefore, various attempts have been made to improve the compatibility between cellulose nanofibers and rubber.

[0003] For example, Patent Document 1 describes a rubber composition for tires that includes a rubber component, microfibrillated plant fibers that may be cellulose fibers, and a modifier that can be covalently bonded to the microfibrillated plant fibers.

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

[0005] JP 2020-41076 A JP 2019-147877 A

[0006] The techniques described in Patent Documents 1 and 2 aim to improve the mechanical properties of a rubber composition by dispersing cellulose fibers in the rubber composition. However, even with these techniques, the dispersibility of cellulose nanofibers in the rubber composition is still insufficient, and there is still room for improvement in the mechanical properties. In addition, when incorporating cellulose nanofibers into various molded articles, good surface smoothness may be required from the standpoints of the appearance, sliding properties, 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, Patent Documents 1 and 2 do not pay attention to the orientation of the cellulose nanofibers.

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

[0008] The present disclosure includes the following items. [Item 1] A rubber composition comprising cellulose nanofibers, a first rubber, and a second rubber, wherein the first rubber is an unmodified liquid rubber and the second rubber is a modified liquid rubber. [Item 2] The rubber composition according to Item 1, wherein the ratio η2 / η1 of the viscosity η2 of the second rubber to the viscosity η1 of the first rubber at 38°C is 1.2 to 160. [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 100,000. [Item 4] The rubber composition according to any one of Items 1 to 3, wherein the first rubber is contained in an amount of 5 to 300 parts by mass per 100 parts by mass of the second rubber. [Item 5] The rubber composition according to any one of Items 1 to 4, wherein the first rubber is contained in an amount of 5 to 100 parts by mass per 100 parts by mass of cellulose nanofibers. [Item 6] The rubber composition according to any one of Items 1 to 5, comprising 10 to 300 parts by mass of the second rubber per 100 parts by mass of cellulose nanofibers. [Item 7] The rubber composition according to any one of Items 1 to 6, comprising 5 to 60% by mass of the second rubber. [Item 8] The rubber composition according to any one of Items 1 to 7, wherein the first rubber comprises aromatic vinyl monomer units. [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 any one of Items 1 to 11, further comprising a third rubber. [Item 13] The rubber composition according to Item 12, wherein the third rubber is natural rubber. [Item 14] The rubber composition according to any one of Items 1 to 11, in a dry form. [Item 15] A method for producing the rubber composition according to any one of items 1 to 14, comprising: a first step of mixing cellulose nanofibers with 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.[Item 16] A method for producing a rubber composition according to any one of items 1 to 14, 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 with the cellulose nanofibers to obtain a rubber composition. [Item 17] The method according to item 15 or 16, wherein a third rubber is further mixed in the second step. [Item 18] A method for producing a rubber composition according to item 12 or 13, comprising: a step of mixing cellulose nanofibers with the first rubber to obtain a preliminary composition, a step of mixing the preliminary composition with the second rubber to obtain a dried body, and a step of mixing the dried body with a third rubber to obtain a rubber composition. [Item 19] A method for producing a rubber composition according to item 12 or 13, comprising the steps of mixing the first rubber and the second rubber to obtain a preliminary composition, mixing the preliminary composition with cellulose nanofibers to obtain a dried body, and mixing the dried body with a third rubber to obtain a rubber composition. [Item 20] A dried body comprising the rubber composition according to any one of items 1 to 11. [Item 21] A method for producing a rubber composition, comprising the step of mixing the dried body according to item 20 with a third rubber to obtain a rubber composition. [Item 22] The method according to item 17, wherein the third rubber is natural rubber. [Item 23] The method according to item 18, wherein the third rubber is natural rubber. [Item 24] The method according to item 19, wherein the third rubber is natural rubber. [Item 25] The method according to item 21, wherein the third rubber is natural rubber. [Item 26] A rubber composite which is a kneaded product of the rubber composition according to any one of items 1 to 14 and a fourth rubber. [Item 27] ​​A cured rubber product which is a cured product of the rubber composite according to item 26. [Item 28] A tire comprising the cured rubber product according to item 27. [Item 29] A vibration-isolating rubber comprising the cured rubber product according to item 27. [Item 30] A shoe outsole comprising the cured rubber product according to item 27. [Item 31] A conveyor belt comprising the cured rubber product according to item 27.

[0009] According to one aspect of the present invention, it is possible to provide a rubber composition, a rubber composite, and a cured rubber product that exhibit excellent dispersibility and orientation of cellulose nanofibers, and in another aspect, it is possible to provide a cured rubber product that exhibits good physical properties (particularly tensile properties and modulus) and surface smoothness.

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

[0011] <Rubber Composition> One aspect of the present disclosure provides a rubber composition containing cellulose nanofibers, a first rubber, and a second rubber. In one aspect, the first rubber and the second rubber are liquid rubbers. Cellulose nanofibers are inherently hydrophilic due to their hydroxyl groups, while rubbers are inherently hydrophobic, making it generally difficult to uniformly disperse cellulose nanofibers in rubber. After extensive investigations, the present inventors have found that a specific combination of rubbers is useful for preparing a rubber composition with excellent cellulose nanofiber dispersibility and orientation. The rubber composition can also be made into, for example, a rubber masterbatch and kneaded with additional rubber to produce a rubber composite. The rubber composition, rubber composite, or cured rubber of the present disclosure can exhibit good cellulose nanofiber dispersibility and orientation. This allows the cured rubber of the present disclosure to achieve both good physical properties (particularly tensile properties and modulus) and good surface smoothness.

[0012] In one embodiment, the first rubber is an unmodified liquid rubber, and the second rubber is a modified liquid rubber. Typically, of the first and second rubbers, the second rubber can bond or interact with cellulose nanofibers, while the first rubber does not substantially bond or interact with them. The second rubber can have good fluidity due to being a liquid rubber and functionality due to having a modifying group. Such a second rubber is expected to improve the dispersibility of cellulose nanofibers in the third and / or fourth rubbers of the present disclosure. However, according to the inventors' studies, it has been found that the desired effect of improving the dispersibility of cellulose nanofibers may not be achieved simply by using the second rubber. Without being bound by theory, it is believed that one reason for this is that the modifying groups of the second rubber locally cause excessive bonding or interaction between the modifying groups of the second rubber or between the modifying groups of the second rubber and the hydroxyl groups of the cellulose nanofibers, resulting in the formation of a dense structure between the second rubbers or between the second rubber and the cellulose nanofibers. In particular, when the viscosity of the second rubber is relatively high, the second rubber may easily form a dense structure. Furthermore, when cellulose nanofibers are blended into various molded articles, good surface smoothness may be required from the standpoint of the appearance, sliding properties, etc. of the molded article. To achieve 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 rubber composite during the production of the molded article is good, good orientation of the cellulose nanofibers is easily achieved. However, if such a dense structure occurs, the orientation of the cellulose nanofibers may decrease. Therefore, the present inventors conducted further studies and found that the above-mentioned problems can be solved by using a first rubber in addition to the second rubber. The first rubber has the advantages of being a liquid rubber, which provides excellent fluidity, and not forming such a dense structure, which is due to the absence of a modifying group. The first rubber can penetrate between the second rubbers or between the second rubber and the cellulose nanofibers, thereby preventing the functional groups of the second rubber and the cellulose nanofibers from coming too close to other functional groups.This effectively demonstrates the advantage of the second rubber, which is the effect of improving the dispersibility of cellulose nanofibers, making it easier to achieve good dispersibility and orientation of the cellulose nanofibers.

[0013] Each component of the rubber composition will be described below. The amount of each component described as a value in the rubber composition of this embodiment may be considered as the amount of each component in the rubber composition of this embodiment.

[0014] <Cellulose nanofibers> Cellulose nanofibers are fibers obtained by pulverizing cellulose fiber raw materials through defibration treatment or the like. Natural cellulose and regenerated cellulose can be used as cellulose fiber raw materials. Examples of natural cellulose include wood pulp obtained from wood species (broadleaf or coniferous trees), non-wood pulp obtained from non-wood species (cotton, bamboo, hemp, bagasse, kenaf, cotton linter, sisal, straw, etc.), and cellulose fiber aggregates produced by animals (e.g., sea squirts), algae, and microorganisms (e.g., acetic acid bacteria). Examples of regenerated cellulose include regenerated cellulose fibers (viscose, cupra, Tencel, etc.), cellulose derivative fibers, and ultrafine threads of regenerated cellulose or cellulose derivatives obtained by electrospinning.

[0015] In one embodiment, defibration is a dry or wet mechanical treatment, preferably a wet treatment in which a slurry obtained by dispersing a cellulose fiber raw material in a liquid medium is mechanically treated. For defibration, a single device may be used once or more times, or multiple devices may each be used once or more times. The device used for defibration is not particularly limited, and examples include high-speed rotary, colloid mill, high-pressure, roll mill, and ultrasonic types of devices, such as high-pressure or ultra-high-pressure homogenizers, refiners, beaters, PFI mills, kneaders, dispersers, high-speed defibrators, grinders (stone-type grinders), ball mills, vibration mills, bead mills, conical refiners, disc refiners, and single-, twin-, or multi-screw kneaders / extruders. The cellulose fiber raw material may be subjected to pretreatment before defibration. Pretreatment can adjust the fiber diameter, fiber length, degree of fibrillation, etc., adjust the content of components other than cellulose (e.g., acid-insoluble components such as lignin, alkali-soluble polysaccharides such as hemicellulose, etc.), and adjust the molecular weight, degree of crystallinity, etc. In one embodiment, the pretreatment can be one or more selected from chemical treatment, pulverization, grinding, and classification. Chemical treatment is treatment using chemicals, and examples include cooking, bleaching, purification, hydrolysis, enzyme treatment, conversion to regenerated cellulose, and chemical modification. Grinding is a process in which a cellulose fiber raw material is dry-pulverized. Grinding is a process in which a slurry obtained by dispersing a cellulose fiber raw material in a liquid medium is subjected to a grinding treatment, and is distinguished from the above-mentioned grinding in that it is wet-pulverized. Classification is a separation operation to make the fiber length of the cellulose fiber raw material uniform, and can be dry classification or wet classification.

[0016] The liquid medium may include water and / or other media (eg, organic solvents, inorganic acids, bases, and / or ionic liquids), and may include one or more media.

[0017] Examples of the organic solvent include one or more 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). In a typical embodiment, the liquid medium in the slurry is substantially water alone.

[0018] [Specific surface area] The specific surface area of ​​the cellulose nanofibers is preferably 2 m² from the viewpoint of obtaining the effect of improving the physical properties of the cellulose nanofibers. 2 / g or more, preferably 3m 2 / g or more, preferably 5m 2 / g or more, preferably 7m 2 / g or more, preferably 10m 2 / g or more, preferably 12m 2 / g or more, preferably 15m 2 / g or more, preferably 17m 2 / g or more, preferably 20m 2 / g or more, preferably 22m 2 / g or more, preferably 25m 2 / g or more, preferably 27m 2 From the viewpoint of dispersing the cellulose nanofibers well in the rubber composition and the cured rubber, the cellulose nanofiber content is preferably 400 m / g or more. 2 / g or less, preferably 350m 2 / g or less, preferably 300m 2 / g or less, preferably 250m 2 / g or less, preferably 200m 2 / g or less, preferably 170m 2 / g or less, preferably 150m 2 / g or less, preferably 120m 2 / g or less, preferably 100m 2 / g or less.

[0019] The specific surface area of ​​cellulose nanofibers is measured by measuring the BET specific surface area of ​​a porous sheet of cellulose nanofibers with a specific surface area / pore size distribution measuring device (e.g., Nova-4200e, manufactured by Quantachrome Instruments) using nitrogen gas. Specifically, after drying approximately 0.2 g of the porous sheet at 120°C under vacuum for 5 hours, the amount of nitrogen gas adsorbed at the boiling point of liquid nitrogen is measured at 5 points in the range of relative vapor pressure (P / P0) of 0.05 to 0.2 (multipoint method), and the BET specific surface area (m 2 The porous sheet is produced by the method described in the section [Porous Sheet] below.

[0020] The specific surface area of ​​cellulose nanofibers can be calculated by assuming that the cellulose nanofibers are cylindrical, and the converted fiber diameter of the cellulose nanofibers can be calculated using the following formula: 3 ), so the volume per 1 g of cellulose is 6.7 × 10 -7 (m 3 When the converted fiber diameter of the cellulose nanofiber is r (m), the average circumferential length of the cellulose nanofiber is πr, and the average cross-sectional area of ​​the cellulose nanofiber is 0.25πr. 2 , so the total fiber length per 1 g of cellulose nanofiber is 6.7 × 10 -7 (m 3 / g) / average cross-sectional area (=0.25πr 2 ) Total surface area = specific surface area (m 2 / g) = 6.7 x 10 -7 (m 3 / g) / average cross-sectional area (=0.25πr 2 ) x average outer circumference length (=πr) = 6.7 x 10 -7 (m 3 / g) / 0.25r = 26.68 × 10 -7 (m 3 / g) / r Therefore, converted fiber diameter r (m) = 26.68 × 10 -7 (m 3 / g) / specific surface area (m 2 / g), and for example, the BET specific surface area of ​​the porous sheet is 40 m 2 The equivalent fiber diameter r of the cellulose nanofibers is calculated to be 66.7 nm.

[0021] In one aspect, the equivalent fiber diameter of the cellulose nanofibers is preferably 2 to 1,000 nm from the viewpoint of obtaining a favorable effect of improving physical properties by the cellulose nanofibers. The equivalent 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.

[0022] In one aspect, the number average fiber length L of the cellulose nanofibers is preferably 100 nm or more, or 500 nm or more, or 1 μm or more, or 5 μm or more, or 10 μm or more, or 20 μm or more, from the viewpoint of satisfactorily exhibiting the property-improving effect of the cellulose nanofibers, and is 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 satisfactorily dispersing the cellulose nanofibers in the resin composition.

[0023] In one aspect, the number average fiber diameter D of the cellulose nanofibers is preferably 2 to 1,000 nm, from the viewpoint of obtaining a favorable effect of improving physical properties due to the cellulose nanofibers. The number average fiber diameter D 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] From the viewpoint of satisfactorily improving the mechanical properties of a rubber composite containing cellulose nanofibers with a small amount of cellulose nanofibers, 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. There is no particular upper limit, but from the viewpoint of handleability, it is preferably 5,000 or less, or 3,000 or less, or 2,000 or less, or 1,000 or less.

[0025] In this disclosure, the fiber length, fiber diameter, and L / D ratio of cellulose nanofibers are values ​​measured using a scanning electron microscope (SEM) according to the following procedure. An aqueous dispersion of cellulose nanofibers is substituted with tert-butanol, diluted to 0.001 to 0.1% by mass, and dispersed using a high-shear homogenizer (e.g., IKA, product name "Ultra-Turrax T18") at 15,000 rpm for 3 minutes. The sample is then cast onto an osmium-deposited silicon substrate and air-dried. This sample is then measured using a high-resolution scanning electron microscope (SEM). Specifically, the length (L) and diameter (D) of 100 randomly selected cellulose nanofibers are measured in an observation field with a magnification adjusted so that at least 100 cellulose nanofibers are observed, and the ratio (L / D) is calculated. The respective number average values ​​are taken as the number average fiber diameter L and number average fiber diameter D, and the ratio (L / D) is calculated.

[0026] Known crystalline forms of cellulose include type I, type II, type III, and type IV, of which types I and II are particularly commonly used, while types III and IV are obtained on a laboratory scale but are not commonly used on an industrial scale. The cellulose nanofibers of the present disclosure are preferably cellulose nanofibers containing cellulose type I crystals or cellulose type II crystals, because they have relatively high structural mobility and, by dispersing the cellulose nanofibers in rubber, can produce molded articles with a lower linear expansion coefficient and superior strength and elongation during tensile and bending deformation. Cellulose nanofibers containing cellulose type I crystals and having a crystallinity of 55% or more are more preferred.

[0027] The crystallinity of the cellulose nanofibers is preferably 55% or higher. The higher the crystallinity, the higher the mechanical properties (strength, dimensional stability) of the cellulose itself, and therefore when the cellulose nanofibers are dispersed in rubber, the strength and dimensional stability of the rubber composite tend to be high. A more preferred lower limit for the crystallinity is 60%, even more preferably 70%, and most preferably 80%. There is no particular upper limit for the crystallinity of the cellulose nanofibers, and a higher value is preferable, but from the viewpoint of production, a preferred upper limit is 99%.

[0028] When the cellulose nanofiber is cellulose type I crystal (derived from natural cellulose), the crystallinity can be calculated by the Segal method from the diffraction pattern (2θ / deg. 10 to 30) obtained by measuring the sample by wide-angle X-ray diffraction, using 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 type I crystal (amorphous) : The halo peak intensity due to amorphous in cellulose type I crystal, which is the peak intensity at an angle 4.5° lower than the diffraction angle of the 200 plane (2θ = 18.0°)

[0029] When the cellulose is cellulose type II crystal (derived from regenerated cellulose), the crystallinity can be calculated from the absolute peak intensity h0 at 2θ=12.6° assigned to the (110) plane peak of cellulose type II crystal in wide-angle X-ray diffraction and the peak intensity h1 of the baseline (the line connecting 2θ=8° and 2θ=15°) at this interplanar spacing, using the following formula: Crystallinity (%) = (h0-h1) / h0 × 100

[0030] Furthermore, the degree of polymerization of the cellulose nanofibers 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 3300 or less, more preferably 3200 or less, more preferably 3100 or less, more preferably 3000 or less.

[0031] From the viewpoint of processability and mechanical property expression, it is desirable that the degree of polymerization of the cellulose nanofibers be within the above-mentioned range. From the viewpoint of processability, it is preferable that the degree of polymerization is not too high, and from the viewpoint of mechanical property expression, it is desirable that the degree of polymerization is not too low.

[0032] The degree of polymerization of cellulose nanofibers refers to the average degree of polymerization measured according to the reduced specific viscosity method using a copper ethylenediamine solution described in Verification Test (3) of the "15th Edition Japanese Pharmacopoeia Commentary (published by Hirokawa Shoten)."

[0033] In one embodiment, the weight-average molecular weight (Mw) of the cellulose nanofiber 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 higher weight-average molecular weight indicates a lower number of terminal groups in the cellulose molecule. Furthermore, 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 lower Mw / Mn indicates a lower number of terminals in the cellulose molecule. Since the terminals of cellulose molecules serve as the starting point for thermal decomposition, particularly high heat-resistant cellulose nanofibers and rubber compositions containing cellulose nanofibers and rubber can be obtained when the cellulose molecules of the cellulose nanofibers not only have a high weight-average molecular weight but also have a narrow molecular weight distribution. The weight-average molecular weight (Mw) of the cellulose nanofiber may be, for example, 600,000 or less, 500,000 or less, or 400,000 or less, from the viewpoint of the availability of cellulose raw materials. From the viewpoint of the ease of availability of cellulose fiber raw materials, the number average molecular weight (Mn) of 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 ease of production of cellulose nanofibers, the ratio of weight average molecular weight to number average molecular weight (Mn) (Mw / Mn) may be, for example, 1.5 or more, or 1.7 or more, or 2 or more. Mw can be controlled within the above range by selecting a cellulose raw material having an Mw appropriate for the purpose, or by appropriately performing physical and / or chemical treatments on the cellulose raw material within an appropriate range, etc. Mw / Mn can also be controlled within the above range by selecting a cellulose raw material having an Mw / Mn appropriate for the purpose, or by appropriately performing physical and / or chemical treatments on the cellulose raw material within an appropriate range, etc. In one embodiment, the Mw and Mw / Mn of the cellulose raw material may each be within the above range.

[0034] The weight average molecular weight and number average molecular weight of the cellulose nanofibers referred to here are values ​​determined by dissolving the cellulose nanofibers in N,N-dimethylacetamide containing added lithium chloride and then performing gel permeation chromatography using N,N-dimethylacetamide as a solvent.

[0035] Alkali-soluble polysaccharides that cellulose nanofibers may contain include hemicellulose, as well as 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 chlorine 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 can lead to disadvantages such as decomposition when heated, yellowing during thermal aging, and a decrease in the strength of cellulose nanofibers. Therefore, it is preferable that the content of alkali-soluble polysaccharides in cellulose nanofibers is low.

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

[0037] The average alkali-soluble polysaccharide content can be determined by the method described in a non-patent document (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000), by subtracting the α-cellulose content from the holocellulose content (Wise method). This method is understood in the art as a method for measuring hemicellulose content. The alkali-soluble polysaccharide content is calculated three times for each sample, and the number average of the calculated alkali-soluble polysaccharide contents is taken as the average alkali-soluble polysaccharide content.

[0038] In one aspect, the average content of acid-insoluble components in the cellulose nanofibers is preferably 10% by mass or less, or 5% by mass or less, or 3% by mass or less, relative to 100% by mass of the cellulose nanofibers, from the viewpoint of avoiding a decrease in the heat resistance of the cellulose nanofibers and the resulting discoloration. From the viewpoint of ease of production of the cellulose nanofibers, the content 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 acid-insoluble component content is determined by quantifying the acid-insoluble component using the Clason method described in the non-patent document (Wood Science Experiment Manual, edited by the Japan Wood Research Society, pp. 92-97, 2000). This method is recognized in the industry as a method for measuring lignin content. The sample is stirred in a sulfuric acid solution to dissolve cellulose, hemicellulose, etc., and then filtered through a glass fiber filter. The resulting residue corresponds to the acid-insoluble component. The acid-insoluble component content is calculated from the weight of this acid-insoluble component. The acid-insoluble component content is then measured three times for each sample, and the number average is taken as the average acid-insoluble component content.

[0040] [Chemical Modification] The cellulose nanofibers may be chemically modified cellulose nanofibers (also referred to as chemically modified cellulose nanofibers). Examples of chemically modified cellulose nanofibers include inorganic esters such as nitrate esters, sulfate esters, phosphate esters, silicate esters, and borate esters; organic esters such as acetylation and propionylation; ethers such as methyl ether, hydroxyethyl ether, hydroxypropyl ether, hydroxybutyl ether, carboxymethyl ether, and cyanoethyl ether; and TEMPO oxides obtained 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, with acetylation being particularly preferred. Preferred esterifying agents are acid halides, acid anhydrides, vinyl carboxylate esters, and carboxylic acids. Among these esterification reaction agents, at least one selected from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, vinyl butyrate, and acetic acid is particularly preferred from the standpoint of reaction efficiency. Acetic anhydride and vinyl acetate are particularly preferred. The cellulose nanofibers may be chemically modified with a modifying agent, for example, at the stage of raw cellulose fiber, during the defibration treatment, or after the defibration treatment, or may be chemically modified during or after the preparation of a slurry as a dispersion, or during or after the drying process.

[0041] [Degree of acyl substitution (DS)] When cellulose nanofibers are chemically modified (for example, by hydrophobization such as acylation), the cellulose nanofibers tend to have good dispersibility in rubber. On the other hand, when combined with a dispersant, for example, cellulose nanofibers can easily exhibit 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 degree of acyl substitution (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 order to obtain esterified cellulose nanofibers with a high thermal decomposition onset temperature. Since an unmodified cellulose skeleton remains in the esterified cellulose nanofibers, it is possible to obtain esterified cellulose nanofibers that combine the high tensile strength and dimensional stability inherent to cellulose with the high thermal decomposition onset temperature inherent to chemical modification. DS is preferably 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 nanofiber is an acyl group, the degree of acyl substitution (DS) can be calculated from the reflection infrared absorption spectrum of the esterified cellulose nanofiber based on the peak intensity ratio between the peak derived from the acyl group and the peak derived from the cellulose skeleton. The peak of the absorption band of C=O based on the acyl group is at 1730 cm -1 The peak of the absorption band of C—O based on the cellulose backbone appears at 1030 cm -1 The DS of the esterified cellulose nanofiber can be determined by creating a correlation graph between the DS obtained from the solid-state NMR measurement of the esterified cellulose nanofiber described below and the modification degree (IR index 1030), which is defined as 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 in the cellulose backbone chain, and using the calibration curve calculated from the correlation graph: Degree of substitution DS = 4.13 × IR index (1030). IR index (1030) = H1730 / H1030 In the formula, H1730 and H1030 are 1730 cm -1, 1030 cm -1 (absorption band of C-O stretching vibration of cellulose backbone chain). -1 and 1500 cm -1 The line connecting the -1 and 1500 cm -1 The line connecting these 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 by solid-state NMR is as follows: 13 C solid-state NMR measurement was performed, and carbon C derived from the pyranose ring of cellulose, which appeared in the range of 50 ppm to 110 ppm, was identified. １ -C ６ The DS can be calculated by the following formula, where the area intensity (Inf) of the signal attributed to one carbon atom derived from the modifying group is relative to the total area intensity (Inp) of the signals attributed to the carbon atom: DS = (Inf) x 6 / (Inp) For example, if the modifying group is an acetyl group, the signal at 23 ppm attributed to -CH3 can be used. 13 The conditions for C solid-state NMR measurement are, for example, as follows: Apparatus: Bruker Biospin Avance 500WB Frequency: 125.77 MHz Measurement method: DD / MAS method Waiting time: 75 sec NMR sample tube: 4 mmφ Number of accumulations: 640 (approximately 14 hours) MAS: 14,500 Hz Chemical shift reference: glycine (external reference: 176.03 ppm)

[0044] The thermal decomposition temperature of cellulose nanofiber (T D From the viewpoint of being able to exhibit the heat resistance and mechanical strength desired for in-vehicle applications and the like, in one aspect, the thermal decomposition onset temperature is preferably 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. The higher the thermal decomposition onset temperature, the more preferable, but from the viewpoint of ease of production of cellulose nanofibers, it may be, for example, 320°C or lower, or 310°C or lower, or 300°C or lower.

[0045] [Temperature at 1% weight loss (T 1% ), 250℃ weight loss rate (T 250℃ ) )] The temperature at which the cellulose nanofiber loses 1 wt% of its weight (T 1% In one aspect, from the viewpoint of avoiding thermal degradation during melt-kneading and being able to exhibit mechanical strength, the temperature is preferably 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. 1% The higher the temperature, the better, but from the viewpoint of ease of production of cellulose nanofibers, it may be, for example, 330°C or less, 320°C or less, or 310°C or less.

[0046] Weight loss rate of cellulose nanofiber at 250°C (T 250℃ From the viewpoint of avoiding thermal degradation during melt-kneading and being able to exhibit mechanical strength, in one aspect, T is preferably 15% or less, or 12% or less, or 10% or less, or 8% or less, or 6% or less, or 5% or less, or 4% or less, or 3% or less. 250℃ The lower the better, but from the viewpoint of ease of production of cellulose nanofibers, it may be, for example, 0.1% or more, 0.5% or more, 0.7% or more, or 1.0% or more.

[0047] In this disclosure, T D is a value obtained from a graph in thermogravimetry (TG) analysis, where the horizontal axis is temperature and the vertical axis is weight residual rate %. Starting from the weight of cellulose nanofiber at 150°C (a state in which moisture is almost completely removed) (weight loss of 0 wt%), the temperature is further increased, and the temperature at which the weight loss reaches 1 wt% (T 1% ) and the temperature at which the weight loss reaches 2 wt% (T 2% The temperature at the point where this line intersects with the horizontal line (baseline) that passes through the starting point of the weight loss of 0 wt% is called T D It is defined as:

[0048] 1% weight loss temperature (T 1% ) is the above T D The temperature is the temperature at which the weight loss reaches 1% by weight, starting from the weight at 150°C, when the temperature is continued to be increased by the method of (1).

[0049] Weight loss rate of cellulose nanofiber at 250°C (T 250℃ ) is the weight loss rate when cellulose nanofibers are held at 250°C under nitrogen flow for 2 hours in TG analysis. A porous sheet of cellulose nanofibers is heated from room temperature to 150°C at a temperature increase 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 temperature increase rate of 10°C / min, and held at 250°C for 2 hours. Starting with the weight W0 at the time when 250°C is reached, the weight after holding at 250°C for 2 hours is defined as W1, and is calculated using the following formula: Weight change rate at 250°C (%): (W1 - W0) / W0 x 100

[0050] [Porous Sheet] Various physical properties of cellulose nanofiber (specific surface area, crystallinity, crystalline polymorphism, degree of polymerization, Mw, Mn, Mw / Mn, alkali-soluble content, average acid-insoluble content, T D , T 1% , T 250℃ Measurements of materials such as cellulose, cellulose acetate, and cellulose nitrate may vary significantly depending on the shape of the sample. To ensure stable and reproducible measurements, a porous sheet without distortion is used as the measurement sample. The porous sheet is prepared as follows:

[0051] First, a concentrated cake of cellulose nanofibers with a solid content of 10% by mass or more, in which the liquid medium is water, is added to tert-butanol, and further dispersed using a mixer or the like (for example, a high-shear homogenizer (for example, IKA, trade name "Ultra Turrax T18", processing conditions: rotation speed 15,000 rpm x 3 minutes)) until no aggregates remain. The concentration is adjusted to 0.5% by mass per 0.5 g of cellulose nanofiber solids. 100 g of the resulting tert-butanol dispersion is filtered on filter paper. Without peeling the filtrate from the filter paper, it is sandwiched together with the filter paper between two larger pieces of filter paper, and dried in an oven at 150°C for 5 minutes while pressing down the edges of the larger filter paper with weights. The filter paper is then peeled off to obtain a porous sheet with little distortion. When the air resistance R of this sheet is 10 g / m2, the sheet has an average weight of 10 g / m2. 2A porous sheet having a flow rate of 100 sec / 100 ml or less is used as a measurement sample.

[0052] The air resistance R was measured by measuring the basis weight W (g / m) of a porous sheet sample left standing for one day in an environment of 23°C and 50% RH. 2 ) is measured, and then the air resistance R (sec / 100 ml) is measured using an Oken type air resistance tester (for example, manufactured by Asahi Seiko Co., Ltd., Model EG01). At this time, 10 g / m 2 Calculate the value per unit area. Unit area 10 g / m 2 Air resistance per unit area (sec / 100 ml) = R / W x 10

[0053] Various physical properties of cellulose nanofibers contained in rubber compositions, rubber composites, etc. (number average fiber length, number average fiber diameter, L / D ratio, crystallinity, crystalline polymorphism, degree of polymerization, Mw, Mn, Mw / Mn, alkali-soluble content, average acid-insoluble content, T D , T 1% , T 250℃ The cellulose nanofiber solubility (S), DS, etc., are analyzed by the following method. The polymer component contained in a rubber composition, rubber composite, etc. is dissolved in an organic or inorganic solvent capable of dissolving the polymer component, and the cellulose nanofiber is separated and thoroughly washed with the solvent. The solvent is then replaced with tert-butanol. The cellulose nanofiber tert-butanol slurry is then analyzed using the same measurement method as above, and various physical properties of the cellulose nanofiber in the rubber composition or rubber composite are calculated.

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

[0055] <First Rubber and Second Rubber> In one embodiment, the first rubber is an unmodified liquid rubber, and the second rubber is a modified liquid rubber. Throughout this disclosure, liquid rubber refers to a substance that has fluidity at 23°C and forms a rubbery elastomer through crosslinking (more specifically, vulcanization) and / or chain extension. That is, in one embodiment, the liquid rubber is an uncured product. In addition, having fluidity means, in one embodiment, that when liquid rubber dissolved in cyclohexane is placed in a vial having a body diameter of 21 mm and a total length of 50 mm at 23°C and then dried, the liquid rubber is filled into the vial to a height of 1 mm, sealed, and the vial is left upside down for 24 hours, a movement of the substance in the vertical direction of 0.1 mm or more can be confirmed. The liquid rubber may have a monomer composition similar to that of a typical rubber, and preferably has a relatively low molecular weight from the viewpoints of ease of handling and good dispersibility of cellulose nanofibers. In one embodiment, the liquid rubber has a number average molecular weight (Mn) of 150,000 or less, and is therefore in a liquid state. In this disclosure, the molecular weight and molecular weight distribution of the rubber component are values ​​obtained by measuring a chromatogram using gel permeation chromatography with three connected columns packed with polystyrene gel, and calculating the results using a calibration curve based on standard polystyrene. Tetrahydrofuran is used as the solvent.

[0056] When the rubber composition is cured to form a cured rubber, the liquid rubber is desirably vulcanized during curing in order to improve the mechanical properties of the cured rubber. Alternatively, the liquid rubber may be cured by heat or the like.

[0057] 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 cured rubber product, and is preferably 150,000 or less, or 145,000 or less, or 140,000 or less from the viewpoint of flowability and obtaining a cured rubber product that is not too hard and has good rubber elasticity.

[0058] 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 cured rubber product, and is preferably 100,000 or less, or 90,000 or less, or 80,000 or less, from the viewpoint of flowability and obtaining a cured rubber product that is not too hard and has good rubber elasticity.

[0059] 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 viewpoint of fluidity and from the viewpoint of obtaining a cured rubber product that is not too hard and has good rubber elasticity, 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 cured rubber product.

[0060] 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 viewpoint of fluidity and from the viewpoint of obtaining a cured rubber product that is not too hard and has good rubber elasticity, 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 cured rubber product.

[0061] In the present disclosure, viscosity is a value measured using a Brookfield viscometer.

[0062] At 38°C, the ratio η2 / η1 of the viscosity η2 of the second rubber to the viscosity η1 of the first rubber is preferably 1.2 or more, or 1.3 or more, or 1.4 or more, in order to facilitate the first rubber penetrating between second rubbers or between the second rubber and cellulose nanofibers, and is preferably 160 or less, or 140 or less, or 120 or less, in order to obtain good affinity between the first rubber and the second rubber.

[0063] The liquid rubber may be a conjugated diene polymer, a non-conjugated diene polymer, or a hydrogenated product thereof. The above polymer or hydrogenated product thereof may be an oligomer.

[0064] [Conjugated diene polymer] The conjugated diene polymer may be a homopolymer, 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.

[0065] 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.

[0066] In one embodiment, the conjugated diene polymer is a copolymer of the above-mentioned 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, and examples thereof include styrene, m- or p-methylstyrene, α-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinylethylbenzene, vinylxylene, vinylnaphthalene, diphenylethylene, and divinylbenzene, 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.

[0067] Examples of random copolymers include butadiene-isoprene random copolymers, butadiene-styrene random copolymers, isoprene-styrene random copolymers, and butadiene-isoprene-styrene random copolymers. The composition distribution of each monomer in the copolymer chain includes a completely random copolymer that is close to a statistically random composition, and a tapered (gradient) random copolymer with a gradient in composition distribution. The bonding mode of the conjugated diene polymer, i.e., the composition of 1,4-bonds, 1,2-bonds, etc., may be uniform or different between molecules.

[0068] The block copolymer may be a copolymer consisting of two or more blocks. For example, the block copolymer may have a structure such as A-B, A-B-A, or A-B-A-B, in which a block A of an aromatic vinyl monomer and a block B of a conjugated diene monomer and / or a copolymer of an aromatic vinyl monomer and a conjugated diene monomer constitute a block copolymer. The boundaries between the blocks do not necessarily need 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 manner. Furthermore, block B may have a plurality of portions where the aromatic vinyl monomer is distributed uniformly and / or a plurality of portions where the aromatic vinyl monomer is distributed in a tapered manner. Furthermore, block B may have a plurality of segments with different aromatic vinyl monomer contents. When a copolymer contains a plurality of blocks A and a plurality of blocks B, the molecular weights and compositions of the blocks A and B may be the same or different.

[0069] The block copolymer may be a mixture of two or more types that differ from each other in one or more of the bonding type, molecular weight, aromatic vinyl compound type, conjugated diene compound type, 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.

[0070] 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. 13 It can be determined by the C-NMR method (quantitative mode). 13By integrating the areas of the following peaks that appear in C-NMR, a value proportional to the carbon content of each structural unit can be obtained, which can then be converted into the mass % of each structural unit: Styrene 145-147 ppm Vinyl 110-116 ppm Diene (cis) 24-28 ppm Diene (trans) 29-33 ppm

[0071] In a 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% by mass or more and 70% by mass or less, or 10% by mass or more and 50% by mass or less, relative to the total mass of the conjugated diene-based polymer. The aromatic vinyl bond amount can be determined by the ultraviolet absorbance of the phenyl group, and the conjugated diene bond amount can also be determined based on this.

[0072] The conjugated diene polymer may be partially 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 degradation during processing, and is preferably 50% or less, or 20% or less, or 0% (i.e., a non-hydrogenated product) from the viewpoint of low-temperature toughness. Examples of the hydrogenated conjugated diene polymer include the hydrogenated products of the conjugated diene polymers exemplified above, and may be, for example, hydrogenated products of butadiene homopolymer, isoprene homopolymer, styrene-butadiene copolymer, or acrylonitrile-butadiene copolymer.

[0073] [Non-conjugated diene polymer] The non-conjugated diene polymer may be a homopolymer, a copolymer of two or more non-conjugated diene monomers, or a copolymer of a non-conjugated diene monomer and another monomer. 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, and ethylene-α-olefin copolymer, butyl rubber, brominated butyl rubber, acrylic rubber, fluororubber, silicone rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, α,β-unsaturated nitrile-acrylate-conjugated diene copolymer rubber, urethane rubber, and polysulfide rubber.

[0074] In the ethylene-α-olefin copolymer, examples of monomers that can be copolymerized 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, and isobutylene; styrene, substituted vinyl monomers; aromatic vinyl monomers such as substituted styrene; ester vinyl monomers such as vinyl acetate, acrylic esters, methacrylic esters, glycidyl acrylic esters, glycidyl methacrylic esters, and hydroxyethyl methacrylic esters; nitrogen-containing vinyl monomers such as acrylamide, allylamine, vinyl-p-aminobenzene, and acrylonitrile; and dienes such as butadiene, cyclopentadiene, 1,4-hexadiene, and isoprene.

[0075] 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. From the viewpoint of 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, more preferably 10,000 to 80,000, and even more preferably 20,000 to 60,000. 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 even more preferably 1.8 to 2.7.

[0076] The ethylene unit content of the ethylene-α-olefin copolymer is preferably 30 to 95% by mass based on the total amount of the ethylene-α-olefin copolymer, from the viewpoint of ease of handling during processing.

[0077] These preferred ethylene-α-olefin copolymers can be produced by the production methods described in, for example, JP-B-4-12283, JP-A-60-35006, JP-A-60-35007, JP-A-60-35008, JP-A-5-155930, JP-A-3-163088, U.S. Pat. No. 5,272,236, and the like.

[0078] 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.

[0079] Suitable examples of the unmodified liquid rubber as the first rubber are the polymers exemplified above. On the other hand, the modified liquid rubber as the second rubber may have a structure in which at least one modifying group is introduced into each of the polymers exemplified above. The modifying group may be one or more of 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 isocyanato group, a thio group, a mercapto group, etc. 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 modified liquid rubbers 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, and acid anhydride-modified isoprene rubber.

[0080] The modified liquid rubber may have reactive groups (e.g., one or more selected from the group consisting of hydroxyl, carboxyl, isocyanato, thio, amino, and halo groups) at both ends, and thus may be bifunctional. These reactive groups contribute to crosslinking and / or chain extension of the modified liquid rubber.

[0081] In the modified liquid rubber, the amount of modifying groups 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, because good affinity between the cellulose nanofibers and the modified liquid rubber results in good dispersibility and orientation of the cellulose nanofibers. On the other hand, if the amount of modifying groups is excessive, the modified liquid rubbers themselves or the modified liquid rubber and the cellulose nanofibers tend to form a dense structure, reducing the dispersibility and orientation of the cellulose nanofibers. In order to impart the desired mechanical properties and surface smoothness to the cured rubber, it is desirable to suppress the formation of such a dense structure. From this perspective, the amount of modifying groups relative to 100 mol% of all monomer units is preferably 5 mol% or less, or 3 mol% or less. The amount of modifying groups can be confirmed by infrared absorption spectroscopy, solid-state NMR (nuclear magnetic resonance), solution NMR, or a method of calculating the molar ratio of the modifying groups by combining a predetermined monomer composition with elemental analysis of elements not contained in the unmodified rubber.

[0082] The modifying group content of the modified liquid rubber is preferably 0.5% by mass or more, or 0.8% by mass or more, or 1.0% by mass or more, from the viewpoint of achieving good affinity between the cellulose nanofibers and the modified liquid rubber and thereby good dispersibility and orientation of the cellulose nanofibers, and is preferably 20% by mass or less, or 15% by mass or less, or 10% by mass or less, from the viewpoint of suppressing the formation of the above-mentioned dense structure. In one embodiment, this modifying group content can be confirmed by NMR.

[0083] The means for producing the modified liquid rubber is not particularly limited, but for example, the method described in JP 2016-172859 A can be used.

[0084] In one embodiment, the modifying group of the modified liquid rubber may form a covalent bond with the cellulose nanofiber and / or rubber during production of the rubber composition, rubber composite, or cured rubber, particularly during heating and mixing. The covalent bond may be advantageous in further enhancing the reinforcing effect of the cellulose nanofiber. In one embodiment, a covalent bond may be formed between the modified liquid rubber and the cellulose nanofiber during production of the rubber composition or rubber composite, and a covalent bond may be formed between the modified liquid rubber and the third and / or fourth rubber, either directly or via another component (a vulcanizing agent in one embodiment), during production of the cured rubber (i.e., during curing).

[0085] From the viewpoint of improving the mechanical properties of the cured rubber, the first and / or second rubber may be covalently bonded to a rubber (specifically, the third and / or fourth rubber) via a vulcanizing agent during curing of the rubber composition.

[0086] In one embodiment, the presence of covalent bonds can be confirmed by the following methods. In a rubber composition or rubber composite, the residue obtained by removing the rubber with a solvent (e.g., hexane or cyclohexane) is analyzed by nuclear magnetic resonance (NMR) or infrared absorption spectroscopy in one embodiment. In a cured rubber, the residue is analyzed by electron microscopy or atomic force microscopy (AFM in one embodiment). The presence of rubber bound to cellulose nanofibers is confirmed in one embodiment by analysis using NMR, infrared absorption spectroscopy, or Nano-IR as a phase present in the vicinity of the cellulose nanofibers (in one embodiment, as a region of a material different from the third and / or fourth rubber in the cured rubber).

[0087] The first rubber preferably contains aromatic vinyl monomer units, since they have good affinity with cellulose nanofibers, thereby providing good dispersibility and orientation of the cellulose nanofibers.

[0088] The second rubber is preferably maleic anhydride-modified liquid polyisoprene from the viewpoints of miscibility with the third rubber and / or fourth rubber and affinity with cellulose nanofibers.

[0089] In the rubber composition, the amount of the first rubber per 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 obtaining the advantages of the first rubber well, and is preferably 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 interfering with the advantages of the second rubber.

[0090] In the rubber composition, the amount of the first rubber per 100 parts by mass of cellulose nanofibers 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 obtaining the advantages of the first rubber well, and is preferably 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 body.

[0091] In the rubber composition, the amount of the second rubber per 100 parts by mass of cellulose nanofibers is preferably 10 parts by mass or more, or 15 parts by mass or more, or 20 parts by mass or more, from the viewpoint of obtaining the advantages of the second rubber well, and is preferably 300 parts by mass or less, or 280 parts by mass or less, or 260 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 nanofibers.

[0092] In the rubber composition, the content of the second rubber is preferably 5% by mass or more, or 7% by mass or more, or 10% by mass or more, from the viewpoint of obtaining the advantages of the second rubber well, and is preferably 60% by mass or less, or 55% by mass or less, or 50% 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 nanofibers.

[0093] In the rubber composition, the total content of the first and second rubbers is 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 nanofibers, and is preferably 90% by mass or less, or 85% by mass or less, or 80% by mass or less from the viewpoint of obtaining a good reinforcing effect by having the desired amount of cellulose nanofibers present.

[0094] <Dispersant> In one embodiment, the rubber composition contains a dispersant. In one embodiment, the dispersant preferably has a hydrophilic segment and a hydrophobic segment in the same molecule (i.e., is an amphiphilic molecule) from the viewpoint of dispersing the cellulose nanofibers more uniformly in the rubber composition.

[0095] [Amphiphilic Molecules] In amphiphilic molecules, the hydrophilic segment is a portion that exhibits good affinity with cellulose nanofibers due to the inclusion of a hydrophilic structure. Specific examples of the hydrophilic structure include hydroxyl groups, thiol groups, carboxyl groups, sulfonic acid groups, sulfate ester groups, phosphate groups, boronic acid groups, silanol groups, groups derived from sugars such as sorbitan and sucrose, groups derived from glycerin, groups represented by -OM, -COOM, -SOM, -OSOM, -HMPO, and -MPO (wherein M represents an alkali metal or alkaline earth metal), primary to tertiary amines, and quaternary ammonium salts. Examples of the counter anion of the quaternary ammonium salt include halide ions such as hydroxide ion, fluoride ion, chloride ion, bromide ion, and iodide ion, as well as one or more hydrophilic groups selected from the group consisting of nitrate ion, formate ion, acetate ion, trifluoroacetate ion, p-toluenesulfonate ion, hexafluorophosphate, and tetrafluoroborate.

[0096] Examples of hydrophilic segments include polyethylene glycol segments, segments containing repeating units having a quaternary ammonium salt structure, polyvinyl alcohol segments, polyvinylpyrrolidone segments, polyacrylic acid segments, carboxyvinyl polymer segments, cationized guar gum segments, hydroxyethyl cellulose segments, methyl cellulose segments, carboxymethyl cellulose segments, and polyurethane soft segments (specifically, diol segments). Nonionic polyoxyethylene derivatives are particularly preferred, and the polyoxyethylene chain length of the polyoxyethylene derivative may be 3 or more, 5 or more, 10 or more, or 15 or more. The longer the chain length, the higher the affinity with cellulose nanofibers. However, from the viewpoint of a balance with the desired properties (e.g., mechanical properties) of the resin molded article, the polyoxyethylene chain length may be 60 or less, 50 or less, 40 or less, 30 or less, or 20 or less.

[0097] Examples of hydrophobic segments include segments containing hydrocarbons, segments containing fluorocarbons, segments containing alkylene oxide units having 3 or more carbon atoms (e.g., PPG blocks), and segments containing polymer structures. Preferred hydrocarbon-containing segments include alkyl, alkenyl, alkyl ether, alkenyl ether, alkylphenyl ether, alkenylphenyl ether, rosin ester, bisphenol A, β-naphthyl, styrenated phenyl, and hydrogenated castor oil. The number of carbon atoms in the alkyl or alkenyl chain of the hydrophobic group (in the case of alkylphenyl or alkenylphenyl, the number of carbon atoms excluding the phenyl group) is preferably 2 or more, 5 or more, 10 or more, 12 or more, or 16 or more. Preferred fluorocarbon-containing segments include linear or branched alkyl groups having 1 to 20 carbon atoms. Examples of the polymer structure-containing segment include acrylic polymers, styrene resins, vinyl chloride resins, vinylidene chloride resins, polyolefin resins, amino acid lactams including lactam ring-opening polymerization products, polymers composed of diamines and dicarboxylic acids, polyacetal resins, polycarbonate resins, polyester resins, polyphenylene sulfide resins, polysulfone resins, polyether ketone resins, polyimide resins, fluorine-containing resins, hydrophobic silicone resins, melamine resins, epoxy resins, and phenolic resins. These hydrophobic segments may have either a linear or branched structure. The hydrophobic segment may have a single chain structure or two or more chain structures. When the hydrophobic segment has two or more chain structures, it may have multiple types of hydrophobic groups.

[0098] The structure of the amphiphilic molecule is not particularly limited, but examples thereof include linear copolymers such as AB block copolymers, ABA block copolymers, and BAB block copolymers, where A is the hydrophilic segment and B is the hydrophobic segment, tri-branched copolymers containing A and B, tetra-branched copolymers containing A and B, star copolymers containing A and B, monocyclic copolymers containing A and B, polycyclic copolymers containing A and B, cage copolymers containing A and B, and graft copolymers containing A and B. When multiple hydrophilic segments are present in a molecule, the molecular structure may be a single type or a combination of two or more types. Similarly, when multiple hydrophobic segments are present in a molecule, the molecular structure may be a single type or a combination of two or more types.

[0099] (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, or the like.

[0100] 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 alkyl aryl 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 esters, polyethylene glycol mono- or dilaurate esters, polyoxyethylene hydrogenated castor oil), glycerin fatty acid esters (e.g., glycerin monostearate, glycerin monooleate), sorbitan fatty acid esters (e.g., sorbitan monolaurate, sorbitan monostearate), and polyoxyethylene-polyoxypropylene block polymers.

[0101] The anionic surfactant (emulsifier) ​​may be a carboxylate, sulfonate, sulfate, phosphate, or the like. Examples of the carboxylate include aliphatic monocarboxylic acids and alkyl ether carboxylates; examples of the sulfonate include dialkyl sulfosuccinates, alkanesulfonates, alkylbenzenesulfonates, and alkylnaphthalenesulfonates; examples of the sulfate include alkyl sulfates and fat sulfate esters; and examples of the phosphate include alkyl phosphates and polyoxyethylene alkyl ether phosphates.

[0102] Examples of cationic surfactants include amine salts, amidoamine salts, quaternary ammonium salts, and imidazolinium salts. Specific examples include, but are not limited to, amine salt surfactants such as alkylamine salts, polyoxyethylene alkylamine salts, alkylamidoamine salts, aminoalcohol fatty acid derivatives, polyamine fatty acid derivatives, and imidazolines, and quaternary ammonium salt surfactants such as alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkyldimethylbenzylammonium salts, alkylpyridinium salts, alkylisoquinolinium salts, and benzethonium chloride.

[0103] Examples of amphoteric surfactants include alkylamine oxides, alanines, imidazolinium betaines, amidobetaines, and acetic acid betaine. Specific examples include long-chain amine oxides, lauryl betaine, stearyl betaine, lauryl carboxymethyl hydroxyethyl imidazolinium betaine, lauryl dimethylamino acetic acid betaine, and fatty acid amidopropyl dimethylamino acetic acid betaine.

[0104] [Hydrophilic Polymer] In one embodiment, the dispersant is preferably a hydrophilic polymer. In one embodiment, the hydrophilic polymer is a polymer having a hydrophilic group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, an ammonium group, a sulfonic acid group, a phosphate 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, polyvinylpyrrolidone, polyacrylic acid, carboxyvinyl polymers, cationized guar gum, water-soluble polyurethanes, polymers containing a quaternary ammonium salt structure, amides, amines, and the like can be used. Among these, cellulose derivatives and polyalkylene glycols are more preferred, and polyalkylene glycols are particularly preferred.

[0105] The amount of dispersant in the rubber composition is, per 100 parts by mass of cellulose nanofibers, 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, or 15 parts by mass or more, and preferably 200 parts by mass or less, or 150 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, or 70 parts by mass or less, or 60 parts by mass or less, or 50 parts by mass or less.

[0106] In one embodiment, the content of the dispersant in the rubber composition components may be 0.1% by mass or more, or 0.5% by mass or more, or 1% by mass or more, and in one embodiment, 40% by mass or less, or 35% by mass or less, or 30% by mass or less.

[0107] <Third Rubber> In one aspect, the rubber composition further contains a third rubber. The third rubber may be one or more selected from the group consisting of natural rubber, a conjugated diene polymer, a non-conjugated diene polymer, or a hydrogenated product thereof. The above polymer or its hydrogenated product may be a modified rubber or an oligomer. Examples of the third rubber include thermoplastic elastomers. In one aspect, the third rubber is a rubber other than the first and second rubbers of this embodiment, more specifically, a rubber that does not have fluidity at 23°C (in other words, a solid). The first and / or second rubber and the third rubber may differ (be heterogeneous) from each other in one or more of the constituent monomer component type, the constituent monomer component ratio, and the molecular weight.

[0108] [Natural Rubber] The natural rubber is not particularly limited, but examples thereof include, from the viewpoint of containing a large amount of high molecular weight components and having excellent breaking strength, smoke-dried RSS (Ribbed Smoked Sheet) Nos. 3 to 5; machine-dried TSR (Technically Specified Rubber) such as SIR (Standard Indonesian Rubber) (made in Indonesia), STR (Standard Thai Rubber) (made in Thailand), and SMR (Standard Malaysian Rubber) (made in Malaysia); and epoxidized natural rubber.

[0109] [Conjugated diene polymer] The conjugated diene polymer may be a homopolymer, 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.

[0110] 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.

[0111] In one embodiment, the conjugated diene polymer is a copolymer of the above-mentioned 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, and examples thereof include styrene, m- or p-methylstyrene, α-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinylethylbenzene, vinylxylene, vinylnaphthalene, diphenylethylene, and divinylbenzene, 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 article, styrene is preferred.

[0112] Examples of random copolymers include butadiene-isoprene random copolymers, butadiene-styrene random copolymers, isoprene-styrene random copolymers, and butadiene-isoprene-styrene random copolymers. The composition distribution of each monomer in the copolymer chain includes a completely random copolymer that is close to a statistically random composition, and a tapered (gradient) random copolymer with a gradient in composition distribution. The bonding mode of the conjugated diene polymer, i.e., the composition of 1,4-bonds, 1,2-bonds, etc., may be uniform or different between molecules.

[0113] The block copolymer may be a copolymer consisting of two or more blocks. For example, the block copolymer may have a structure such as A-B, A-B-A, or A-B-A-B, in which a block A of an aromatic vinyl monomer and a block B of a conjugated diene monomer and / or a copolymer of an aromatic vinyl monomer and a conjugated diene monomer constitute a block copolymer. The boundaries between the blocks do not necessarily need 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 manner. Furthermore, block B may have a plurality of portions where the aromatic vinyl monomer is distributed uniformly and / or a plurality of portions where the aromatic vinyl monomer is distributed in a tapered manner. Furthermore, block B may have a plurality of segments with different aromatic vinyl monomer contents. When a copolymer contains a plurality of blocks A and a plurality of blocks B, the molecular weights and compositions of the blocks A and B may be the same or different.

[0114] The block copolymer may be a mixture of two or more types that differ from each other in one or more of the bonding type, molecular weight, aromatic vinyl compound type, conjugated diene compound type, 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.

[0115] 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. 13 It can be determined by the C-NMR method (quantitative mode). 13 By integrating the areas of the following peaks that appear in C-NMR, a value proportional to the carbon content of each structural unit can be obtained, which can then be converted into the mass % of each structural unit: Styrene 145-147 ppm Vinyl 110-116 ppm Diene (cis) 24-28 ppm Diene (trans) 29-33 ppm

[0116] In a 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% by mass or more and 70% by mass or less, or 10% by mass or more and 50% by mass or less, relative to the total mass of the conjugated diene-based polymer. The aromatic vinyl bond amount can be determined by the ultraviolet absorbance of the phenyl group, and the conjugated diene bond amount can also be determined based on this.

[0117] The conjugated diene polymer may be partially 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 degradation during processing, and is preferably 50% or less, or 20% or less, or 0% (i.e., a non-hydrogenated product) from the viewpoint of low-temperature toughness. Examples of the hydrogenated conjugated diene polymer include the hydrogenated products of the conjugated diene polymers exemplified above, and may be, for example, hydrogenated products of butadiene homopolymer, isoprene homopolymer, styrene-butadiene copolymer, or acrylonitrile-butadiene copolymer.

[0118] [Non-conjugated diene polymer] The non-conjugated diene polymer may be a homopolymer, a copolymer of two or more non-conjugated diene monomers, or a copolymer of a non-conjugated diene monomer and another monomer. 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, and ethylene-α-olefin copolymer, butyl rubber, brominated butyl rubber, acrylic rubber, fluororubber, silicone rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, α,β-unsaturated nitrile-acrylate-conjugated diene copolymer rubber, urethane rubber, and polysulfide rubber.

[0119] In the ethylene-α-olefin copolymer, examples of monomers that can be copolymerized 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, and isobutylene; styrene, substituted vinyl monomers; aromatic vinyl monomers such as substituted styrene; ester vinyl monomers such as vinyl acetate, acrylic esters, methacrylic esters, glycidyl acrylic esters, glycidyl methacrylic esters, and hydroxyethyl methacrylic esters; nitrogen-containing vinyl monomers such as acrylamide, allylamine, vinyl-p-aminobenzene, and acrylonitrile; and dienes such as butadiene, cyclopentadiene, 1,4-hexadiene, and isoprene.

[0120] 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. From the viewpoint of 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, more preferably 10,000 to 80,000, and even more preferably 20,000 to 60,000. 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 even more preferably 1.8 to 2.7.

[0121] The ethylene unit content of the ethylene-α-olefin copolymer is preferably 30 to 95% by mass based on the total amount of the ethylene-α-olefin copolymer, from the viewpoint of ease of handling during processing.

[0122] These preferred ethylene-α-olefin copolymers can be produced by the production methods described in, for example, JP-B-4-12283, JP-A-60-35006, JP-A-60-35007, JP-A-60-35008, JP-A-5-155930, JP-A-3-163088, U.S. Pat. No. 5,272,236, and the like.

[0123] [Modified Rubber] The third rubber may be a modified rubber, and for example, the conjugated diene polymer or non-conjugated diene polymer exemplified above may have a modified 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 introduced therein. Examples of modified rubbers 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, and acid anhydride-modified styrene-butadiene rubber.

[0124] From the viewpoint of 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 preferably 5 mol% or less, or 3 mol% or less. The amount of the modifying group can be confirmed by infrared absorption spectroscopy, solid-state NMR (nuclear magnetic resonance), solution NMR, or a method of calculating the molar ratio of the modifying group by combining a predetermined monomer composition with quantification by elemental analysis of elements not contained in the unmodified rubber.

[0125] [Thermoplastic Elastomer] In one embodiment, the third rubber can include or be a thermoplastic elastomer. In the present disclosure, in one embodiment, an elastomer is a substance (specifically, a natural or synthetic polymer substance) that is elastic at room temperature (23°C). In addition, in one embodiment, being elastic means that the storage 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 in one embodiment, is a crosslinked product. The suitable monomer composition of the thermoplastic elastomer may be the same as that described above in the sections (Conjugated Diene Polymer) and (Non-Conjugated Diene Polymer).

[0126] The number average molecular weight (Mn) of the thermoplastic elastomer is preferably 10,000 to 500,000, or 40,000 to 250,000, from the viewpoint of achieving both impact strength and fluidity.

[0127] The thermoplastic elastomer may have a core-shell structure. Examples of elastomers having a core-shell structure include core-shell elastomers having a core made of particulate rubber and a shell made of a glassy graft layer formed on the outside of the core. Suitable core materials include butadiene rubber, acrylic rubber, and silicone-acrylic composite rubber. Suitable shell materials include glassy polymers such as styrene resin, acrylonitrile-styrene copolymer, and acrylic resin.

[0128] From the viewpoint of excellent compatibility with the first and / or second rubber, the thermoplastic elastomer is preferably at least one selected from the group consisting of a styrene-butadiene block copolymer, a styrene-ethylene-butadiene block copolymer, a styrene-ethylene-butylene block copolymer, a styrene-butadiene-butylene block copolymer, a styrene-isoprene block copolymer, a styrene-ethylene-propylene block copolymer, a styrene-isobutylene block copolymer, a hydrogenated product of a styrene-butadiene block copolymer, a hydrogenated product of a styrene-ethylene-butadiene block copolymer, a hydrogenated product of a styrene-butadiene-butylene block copolymer, a hydrogenated product of a styrene-isoprene block copolymer, and a homopolymer of styrene (polystyrene), and more preferably at least one selected from the group consisting of a styrene-butadiene block copolymer, a hydrogenated product of a styrene-butadiene block copolymer, and polystyrene.

[0129] In one embodiment, at least a portion of the thermoplastic elastomer may have an acidic functional group. In this disclosure, the term "thermoplastic elastomer having an acidic functional group" means that the acidic functional group is attached to the molecular backbone of the elastomer via a chemical bond. In this disclosure, the term "acidic functional group" refers to a functional group that can react with a basic functional group, and specific examples include a hydroxyl group, a carboxyl group, a carboxylate group, a sulfo group, and an acid anhydride group.

[0130] The amount of acidic functional groups added in the elastomer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and even more preferably less than 1.5% by mass, based on 100% by mass of the elastomer, from the viewpoint of affinity with the modified liquid rubber, etc. The number of acidic functional groups is a value obtained by measuring a calibration curve sample, in which an acidic substance has been mixed in advance, using an infrared absorption spectrometer and measuring the sample based on a calibration curve prepared using the characteristic absorption band of the acid.

[0131] Examples of the elastomer having an acidic functional group include an elastomer having a core-shell structure having a shell layer formed using acrylic acid or the like as a copolymerization component, and a modified elastomer obtained by grafting an α,β-unsaturated dicarboxylic acid or a derivative thereof onto an ethylene-α-olefin copolymer, polyolefin, aromatic compound-conjugated diene copolymer, or hydrogenated aromatic compound-conjugated diene copolymer containing acrylic acid or the like as a monomer, in the presence or absence of a peroxide.

[0132] In a preferred embodiment, the elastomer is an anhydride-modified elastomer.

[0133] Among these, modified products obtained by grafting an α,β-unsaturated dicarboxylic acid or a derivative thereof onto a polyolefin, an aromatic compound-conjugated diene copolymer, or a hydrogenated aromatic compound-conjugated diene copolymer in the presence or absence of a peroxide are more preferred, and among these, modified products obtained by grafting an α,β-unsaturated dicarboxylic acid or a derivative thereof onto an ethylene-α-olefin copolymer or a hydrogenated aromatic compound-conjugated diene block copolymer in the presence or absence of a peroxide are particularly preferred.

[0134] Specific examples of the α,β-unsaturated dicarboxylic acid and its derivatives include maleic acid, fumaric acid, maleic anhydride, and fumaric anhydride, with maleic anhydride being particularly preferred.

[0135] In one embodiment, the elastomer may be a mixture of an elastomer having an acidic functional group and an elastomer not having an acidic functional group. The mixing ratio of the elastomer having an acidic functional group and the elastomer not having an acidic functional group, when the total of both is taken as 100% by mass, 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 high toughness and stable physical properties of the cured rubber. The upper limit is not particularly limited, and substantially all of the elastomer may be an elastomer having an acidic functional group. However, from the viewpoint of avoiding problems with flowability, it is desirable for the upper limit to be 80% by mass or less.

[0136] From the viewpoint of providing a cured rubber product with excellent 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.

[0137] In the rubber composition component, the mass ratio of the total amount of the cellulose nanofibers and the first and second rubbers to the third rubber [(total amount of the cellulose nanofibers and the first and second rubbers) / third rubber] may be, in one embodiment, 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.

[0138] For example, when a preliminary composition containing cellulose nanofibers and first and second rubbers is used to produce a rubber composition, the mass ratio of the preliminary composition to the third rubber (preliminary composition / third rubber) in the rubber composition components may be, in one embodiment, 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.

[0139] 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.

[0140] 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.

[0141] In the rubber composition component, the total content of the first and second rubbers relative to 100 parts by mass of the 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.

[0142] The amount of cellulose nanofiber 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, and preferably 70 parts by mass or less, or 65 parts by mass or less, or 60 parts by mass or less, per 100 parts by mass of the total of the first, second, and third rubbers.

[0143] The mass ratio of [cellulose nanofiber] / [total of first, second and third rubbers] in the rubber composition components is preferably 1 / 99 to 60 / 40, or 2 / 98 to 50 / 50, or 3 / 97 to 40 / 60.

[0144] [Vulcanizing Agent, Vulcanization Accelerator] When the rubber composition components contain uncured rubber, the rubber composition components typically contain a vulcanizing agent and may optionally contain a vulcanization accelerator. Conventionally known vulcanizing agents and vulcanization accelerators may be appropriately selected depending on the type of uncured rubber in the rubber composition components. Examples of vulcanizing agents that can be used include organic peroxides, azo compounds, oxime compounds, nitroso compounds, polyamine compounds, sulfur, and sulfur compounds. Examples of sulfur compounds include sulfur monochloride, sulfur dichloride, disulfide compounds, and polymeric polysulfur compounds.

[0145] The amount of vulcanizing agent in the rubber composition components is preferably 0.01 to 20 parts by mass, or 0.1 to 15 parts by mass, per 100 parts by mass of uncured rubber in the rubber composition components.

[0146] Examples of vulcanization accelerators include sulfenamide-based, guanidine-based, thiuram-based, aldehyde-amine-based, aldehyde-ammonia-based, thiazole-based, thiourea-based, and dithiocarbamate-based vulcanization accelerators. Zinc oxide, stearic acid, and the like may also be used as a vulcanization aid. The amount of vulcanization accelerator is preferably 0.01 to 20 parts by mass, or 0.1 to 15 parts by mass, per 100 parts by mass of uncured rubber in the rubber composition components.

[0147] [Rubber Additives] The rubber composition components may contain various conventionally known rubber additives (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. Furthermore, as the rubber softener, one or more process oils, extender oils, etc. may be used. However, in one embodiment, the rubber composition of this embodiment is capable of forming a flexible molded article, and therefore, in one embodiment, the rubber composition components may not contain a rubber softener.

[0148] The vulcanizing agent, vulcanization accelerator, and rubber additives are typically added during the production of the rubber composite, but the manner of addition is not limited to this.

[0149] <Additional Components of Rubber Composition Components> The rubber composition components may further contain additional components. Examples of the additional components include additional polymers, organic or inorganic fillers, heat stabilizers, antioxidants, antistatic agents, colorants, etc. The content 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.

[0150] <Production of Rubber Composition> The rubber composition can be produced by mixing rubber composition components including cellulose nanofibers, a first rubber, and a second rubber. Examples of methods for producing the rubber composition include: (1) a method comprising: a first step of mixing cellulose nanofibers with the first rubber, which is an unmodified liquid rubber, to obtain a preliminary composition; and a second step of mixing the preliminary composition with the second rubber, which is a modified liquid rubber, to obtain a rubber composition; and (2) a method comprising: a first step of mixing the first rubber, which is an unmodified liquid rubber, with the second rubber, which is a modified liquid rubber, to obtain a preliminary composition; and a second step of mixing the preliminary composition with cellulose nanofibers to obtain a rubber composition. The mixing conditions are not particularly limited, and the rubber composition may be obtained by mixing the components constituting the rubber composition using a stirring means such as a rotation-revolution mixer, a planetary mixer, 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, or a twin-screw extruder. Furthermore, stirring may be performed under heating to efficiently perform shearing. In the above method (1), by combining the first rubber with the cellulose nanofibers in advance, the contact opportunity between the cellulose nanofibers and the second rubber becomes more moderate and uniform, which may result in better improvement in the physical properties of the rubber composition, rubber composite, or cured rubber. After the rubber composition is obtained, it may be dried, or a powder may be formed by controlling the drying conditions. Furthermore, in the above method (1), after the preliminary composition is obtained, the preliminary composition may be dried before mixing with the modified liquid rubber. In one aspect, a dried product (in one aspect, a powder) of the rubber composition of the present disclosure is provided. In one aspect, a dried product (in one aspect, a powder) containing the rubber composition of the present disclosure is provided.

[0151] When the rubber composition contains a third rubber, in one embodiment, the third rubber may be further mixed in the second step of the above method (1) or (2). The mixing conditions are not particularly limited, and for example, a kneader commonly used in rubber mixing, such as a Banbury mixer, kneader, or open roll mill, can be used. The kneader rotors can be either intermeshing or tangential, and rotors designed for resin mixing can also be used. Examples of intermeshing rotors include the KIR-II manufactured by Kobe Steel, Ltd. and the EX7 type manufactured by Mitsubishi Heavy Industries, Ltd. Examples of tangential rotors include the 5THR, 4WN, and 4WH manufactured by Kobe Steel, Ltd., and the E type manufactured by Mitsubishi Heavy Industries, Ltd. Examples of rotors for resin mixing include the Roller Type R500B manufactured by Toyo Seiki Seisakusho, Ltd. Alternatively, after preparing a rubber composition by the above method (1) or (2), the rubber composition may be mixed with a third rubber to obtain a rubber composition further containing a third rubber. The mixing conditions in this case may be the same as those described above when the rubber composition contains a third rubber. In particular, if a third rubber is further mixed in a rubber mixer in the second step of the above-mentioned method (1), the dispersion of the cellulose nanofibers can be particularly promoted. That is, in such a second step, the presence of the third rubber can increase the viscosity of the kneaded mixture, thereby increasing the shear force applied to the kneaded mixture. Furthermore, the use of a rubber mixer ensures good distribution even when a high-viscosity rubber is used. Therefore, the second rubber and the cellulose nanofibers come into sufficient contact at an appropriate speed, thereby promoting the dispersion of the cellulose nanofibers. All of the rubber compositions exemplified above can be suitably used, for example, as masterbatches and can be applied to the production of various rubber composites.

[0152] In one embodiment of the method for mixing the cellulose nanofibers with the first rubber and / or the second rubber, the cellulose nanofibers may be added in the form of dried cellulose nanofibers. In another embodiment, the cellulose nanofibers may be mixed with the first rubber and / or the second rubber in the form of a slurry, and the liquid medium contained therein may be dried and removed to obtain a preliminary composition or rubber composition containing the cellulose nanofibers.

[0153] <Drying Step> In one embodiment, a dried material containing cellulose nanofibers (which may be a dried cellulose nanofiber material, a preliminary composition containing cellulose nanofibers, or a rubber composition) can be produced by drying a cellulose nanofiber slurry. In one embodiment, the dried material containing cellulose nanofibers is a powder. The dryer is not particularly limited, but examples include a kneader, planetary mixer, Henschel mixer, high-speed mixer, propeller mixer, ribbon mixer, single- or twin-screw extruder, Banbury mixer, freeze dryer, shelf dryer, spray dryer, fluidized bed dryer, and drum dryer.

[0154] 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 drying efficiency and forming a dried body containing cellulose nanofibers with powder properties that are excellent in nano-dispersibility and macro-dispersibility of the cellulose nanofibers in the rubber composition, and may be, for example, 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 from the viewpoint of making thermal degradation of the cellulose nanofibers and additional components unlikely to occur and avoiding excessive pulverization of the dried body containing cellulose nanofibers due to rapid drying of the slurry. The drying temperature is the temperature of the heat source in contact with the slurry, and is defined, for example, by 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.

[0155] The pressure may be either atmospheric pressure or reduced pressure, but from the viewpoint of forming a dried body containing cellulose nanofibers with powder properties that are excellent in drying efficiency and in nano-dispersibility and macro-dispersibility of the cellulose nanofibers in the rubber composition, the pressure may be -1 kPa or less, or -10 kPa or less, or -20 kPa or less, or -30 kPa or less, or -40 kPa or less, or -50 kPa or less, and from the viewpoint of avoiding excessive pulverization of the dried body containing cellulose nanofibers due to rapid drying of the slurry, the pressure may be -100 kPa or more, or -95 kPa or more, or -90 kPa or more.

[0156] From the viewpoint of process efficiency during drying, the concentration of cellulose nanofibers in the cellulose nanofiber slurry to be subjected to the drying step 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 maintaining good handleability by avoiding an excessive increase in the viscosity of the slurry and solidification due to aggregation, the concentration 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, cellulose nanofibers are often produced in a dilute dispersion, and the cellulose nanofiber concentration in the slurry may be adjusted to the above-mentioned preferred range by concentrating such a dilute dispersion. Concentration can be achieved by methods such as suction filtration, pressure filtration, centrifugal deliquoring, and heating.

[0157] In one embodiment, the dried product containing cellulose nanofibers may contain a first rubber and / or a second rubber, and any additional components (e.g., the dispersant described above), which may be added before, during, and / or after drying of the cellulose nanofiber slurry. In one embodiment, the first rubber and / or the second rubber, and / or any additional components may be added in a dispersed or dissolved state in water and / or an organic solvent. The organic solvent is not particularly limited, but is preferably a solvent in which the first rubber and the second rubber dissolve, and examples of such non-aqueous solvents include chloroform, toluene, hexane, and cyclohexane.

[0158] [Liquid medium content] From the viewpoint of workability during kneading with the third rubber, the liquid medium content of the dried material containing cellulose nanofibers may be preferably 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. The liquid medium content may be 0% by mass, but from the viewpoint of ease of production of the dried material containing cellulose nanofibers, it may be, for example, 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 using an infrared heating moisture meter.

[0159] [Average particle size] In one embodiment, the average particle size of the dried material containing cellulose nanofibers is preferably 1 μm or more, or 10 μm or more, or 50 μm or more, or 100 μm or more, or 200 μm or more, or 500 μm or more from the viewpoint of ease of production, and 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 from the viewpoint of allowing the dried material containing cellulose nanofibers to easily disintegrate in the rubber composition and the cellulose nanofibers to be well dispersed in the rubber composition. The above average particle size is a value measured using a dynamic image analysis particle size distribution analyzer (CAMSIZER X2, manufactured by Microtrac).

[0160] [Loose bulk density] In one embodiment, the loose bulk density of the dried material containing cellulose nanofibers is preferably 0.01 g / cm from the viewpoints of good fluidity and excellent feedability of the dried material containing cellulose nanofibers and suppression of migration of the dispersant to the rubber composition. 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 3 The cellulose nanofiber-containing dry material is preferably 0.85 g / cm3 or more, in that the dry material containing cellulose nanofibers can be easily disintegrated in the rubber composition, allowing the cellulose nanofibers to be well dispersed in the rubber composition, and the dry material containing cellulose nanofibers is not too heavy, so that poor mixing of the dry material containing cellulose nanofibers with the rubber composition can be avoided. 3 or less, or 0.80 g / cm 3 or less, or 0.75 g / cm 3 The following is the result.

[0161] [Covered bulk density] In one embodiment, the compacted bulk density of the dried body containing cellulose nanofibers is controlled within a range useful for controlling the loose bulk density and compressibility within the ranges of the present disclosure, and in one embodiment, preferably 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, preferably 0.95 g / cm 3 or less, or 0.9 g / cm 3 or less, or 0.85 g / cm 3 The following is the result.

[0162] [Degree of compression] The degree of compression is a value calculated by the formula: Degree of compression = (tough bulk density - loose bulk density) / tough bulk density. The loose bulk density and tough bulk density are values ​​measured by the methods described in the [Examples] section of this disclosure. In one aspect, the degree of compression represents the degree of bulk loss. In one aspect, the degree of compression of the dried material 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, so that the fluidity of the dried material containing cellulose nanofibers is not too high. Furthermore, from the viewpoints of good fluidity and excellent feedability of the dried material containing cellulose nanofibers, excellent handleability (specifically, less scattering, floating, or dust formation), good dispersion of the dried material containing cellulose nanofibers in the rubber composition, and suppression of migration of the dispersant into the rubber, the degree of compression is preferably 50% or less, or 45% or less, or 40% or less, or 35% or less, or 30% or less.

[0163] The loose bulk density, compacted bulk density, and compressibility are measured using a powder tester (model number: PT-X) manufactured by Hosokawa Micron Corp. The compacted bulk density is measured by tapping 180 times.

[0164] More specific examples of the order of steps include the following: (i) preparing a slurry containing cellulose nanofibers and optionally a dispersant → drying to prepare a dried body → preparing a preliminary composition containing the dried body and a first rubber → preparing a rubber composition containing the preliminary composition and a second rubber (ii) preparing a slurry containing cellulose nanofibers and optionally a dispersant → drying to prepare a dried body → preparing a rubber composition containing the dried body, the first rubber, and the second rubber (iii) preparing a slurry containing cellulose nanofibers, the first rubber, and optionally a dispersant → drying to prepare a dried body → preparing a rubber composition containing the dried body and the second rubber (iv) preparing a slurry containing cellulose nanofibers, the first rubber, the second rubber, and optionally a dispersant → drying to prepare a rubber composition

[0165]

[0013] One aspect of the present disclosure provides a rubber composite that is a mixture of the rubber composition of the present embodiment and a fourth rubber (base rubber), and a cured rubber that is a cured product of the rubber composite. The mixing conditions for the rubber composition and the fourth rubber are not particularly limited, and for example, a kneading machine commonly used in rubber kneading, such as a Banbury mixer, a kneader, or an open roll, can be used.

[0166] <Fourth Rubber> A specific embodiment of the fourth rubber may be the same as that of the third rubber. The total content of the cellulose nanofibers, first rubber, and second rubber 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, relative to 100 parts by mass of the total of the third and fourth rubbers. In one embodiment, 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 may be, for example, 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.

[0167] In one embodiment, a cured rubber product can be obtained using a vulcanization press in accordance with JIS K6299. The desired molded product can be produced by molding the rubber composite, either alone or together with other components, into a desired shape. The method for combining the compounding components and the molding method are not particularly limited and may be selected depending on the desired molded product. Examples of molding methods include, but are not limited to, (1) a method in which the third and / or fourth rubber contains uncured rubber, and the uncured rubber is cured before, during, and / or after molding the rubber composite, either alone or together with additional components, to obtain a molded product containing a cured rubber product; (2) a method in which the third and / or fourth rubber contains uncured rubber, and the uncured rubber in the rubber composite is cured to form a cured rubber product, which is then molded together with additional components to obtain a molded product; and (3) a method in which the third and / or fourth rubber are thermoplastic elastomers, and the rubber composite is melt-molded alone or together with additional components to obtain a molded product. The molding may be carried out by injection molding, extrusion molding, extrusion profile molding, blow molding, compression molding, or the like.

[0168] <Physical Properties of Cured Rubber> The tensile stress (modulus) at 100% elongation (M100) of the cured rubber may, in one embodiment, be 2.0 MPa or more, or 3.0 MPa or more, or 4.0 MPa or more, and in another embodiment, may be 10.0 MPa or less, or 9.0 MPa or less, or 8.0 MPa or less.

[0169] The tensile stress at 300% elongation (M300) of the cured rubber may, in one embodiment, be 3.0 MPa or more, or 5.0 MPa or more, or 6.0 MPa or more, and in another embodiment, may be 20.0 MPa or less, or 15.0 MPa or less, or 13.0 MPa or less.

[0170] The ratio (M300 / M100) of the tensile stress at 300% elongation (M300) to the tensile stress at 100% elongation (M100) of the cured rubber may, in one aspect, be 1.3 or more, or 1.4 or more, or 1.5 or more, and in one aspect, may be 2.0 or less, or 1.8 or less.

[0171] The storage modulus of the cured rubber may be, in one embodiment, 2.0 MPa or more, or 2.5 MPa or more, and in another embodiment, 4.0 MPa or less, or 3.5 MPa or less, or 3.0 MPa or less.

[0172] It is advantageous for the loss tangent of the cured rubber to be a predetermined value or less, for example, in terms of fuel economy and low heat generation in tire applications. From this perspective, the loss tangent, in one aspect, may be 0.18 or less, or 0.15 or less, or 0.10 or less. On the other hand, it is advantageous for the loss tangent of the cured rubber to be a predetermined value or more, for example, in terms of vibration-damping performance in vibration-damping rubber applications. From this perspective, in one aspect, the loss tangent may be 0.02 or more, or 0.03 or more, or 0.04 or more. The storage modulus and loss tangent are values ​​measured using a rheometer in a torsional mode at 50°C and 10 Hz.

[0173] The cured rubber may be formed into molded articles of various shapes. The molded articles can be used in a wide range of applications, including industrial machine parts, general machine parts, automobile, railway, vehicle, ship, and aerospace-related parts, electronic and electrical parts, building and civil engineering materials, household goods, sports and leisure goods, wind power generation housing components, containers and packaging materials, etc. Examples of applications include automobile parts (e.g., exterior parts such as tires, bumpers, fenders, door panels, various moldings, emblems, engine hoods, wheel caps, roofs, spoilers, and various aero parts, and interior parts such as instrument panels, console boxes, and trim), battery parts (e.g., automotive secondary battery parts, lithium-ion secondary battery parts, solid methanol battery fuel cases, and fuel cell piping), electronic and electrical equipment parts (e.g., various computers and their peripherals, junction boxes, various connectors, various office automation equipment, televisions, videos, disc players, chassis, refrigerators, air conditioners, and LCD projectors), and household goods (e.g., shoe outsoles). One aspect of the present disclosure provides a tire, anti-vibration rubber, shoe outsole, or conveyor belt comprising the rubber vulcanized product of the present disclosure.

[0174] The following examples further illustrate exemplary embodiments of the present invention, but the present invention is not limited to these examples.

[0175] <Evaluation Methods> <Rubber> [Viscosity at 38° C.] The viscosity of the rubber was measured using a Brookfield viscometer. The results are shown in Table 1.

[0176] [Number average molecular weight (Mn)] The value shown is that in the product catalog.

[0177] <Rubber composition> The rubber compositions were evaluated as follows. <Rubber composition containing first and second rubbers> [Dispersibility of cellulose nanofibers] The rubber compositions were observed under an optical microscope under the following conditions. 1 mg of a sample was sandwiched between two cover glasses and crushed and spread to a uniform thickness. The sample was placed on the stage of an Olympus BX51P polarizing microscope. An Olympus U-DICR differential interference prism 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 was observed. C: Numerous aggregations were observed.

[0178] <Rubber composition (masterbatch) further containing a third rubber> [Dispersibility of cellulose nanofibers] The rubber composition was observed by X-ray CT, and 10 randomly selected cross-sectional images of a cube with a side length of 2 mm were taken. ２ The number of cellulose nanofiber aggregates of a size equal to or larger than this was counted, the average number of aggregates per cross section was calculated, and the cellulose nanofiber dispersion state was ranked according to the following criteria: A: 5 or less B: More than 5 and 10 or less C: More than 10 The X-ray CT measurement conditions were as follows: Apparatus: Bruker X-CT Skyscan 1272 Tube voltage: 40 kV, tube current: 100 μA Number of pixels: 2452 x 1640, pixel resolution: 1.2 μm, number of accumulations: 8 Scan: every 0.2 degrees, 180 degree scan

[0179] <Cured Rubber Product> The cured rubber product was evaluated as follows. (1) Surface Smoothness A small piece was cut from the cured rubber sheet with scissors and placed on the stage of a confocal laser microscope (Keyence Corporation, VK-X250), and a surface roughness image was obtained using a 10x objective lens. The arithmetic mean height (Sa) was calculated in accordance with ISO 25178, and indexed, with the result of the reference comparative example being set at 100. A smaller index indicates better surface smoothness.

[0180] (2) Tensile Strength, Tensile Stress (Modulus), and Tensile Elongation Tensile strength, tensile stress at 100% elongation (100% modulus, M100), tensile stress at 300% elongation (300% modulus, M300), and tensile elongation were measured according to the tensile testing method of JIS K-6251, and indexed based on the result of the reference comparative example being 100. A larger index indicates better tensile strength, tensile stress, and tensile elongation.

[0181] (3) Dispersibility of cellulose nanofibers The cured rubber was observed by X-ray CT, and 10 randomly selected cross-sectional images of a cube with sides of 2 mm were evaluated using the same procedure as in the above-mentioned [Dispersibility of cellulose nanofibers] for the rubber composition.

[0182] (4) Orientation of Cellulose Nanofibers The orientation degree of cellulose nanofibers was calculated by data processing as follows for cellulose nanofibers observed with a transmission electron microscope. The roll mixing direction of the cured rubber sheet was defined as MD, the direction perpendicular to the roll mixing direction as TD, and the thickness direction of the sheet as ND. Using a cryomicrotome, sections with a set thickness of 500 μm were taken from the MD-ND surface of the sample. These sections were observed at 1000x magnification using a transmission electron microscope (JEOL JEM-1400), and images were obtained from five randomly selected fields. The observed cellulose nanofibers were binarized and analyzed using the image processing software ImageJ. In the particle analysis, cellulose nanofibers were approximated as ellipses, and the angle θ between the major axis of the ellipse and the MD was calculated for each cellulose nanofiber. (3(cosθ)^2-1) / 2 was calculated for the cellulose nanofibers obtained from five TEM images, and the average value was used as the orientation degree. The orientation of the cellulose nanofibers was evaluated according to the following criteria: A: Degree of orientation is 0.7 or more; B: Degree of orientation is 0.5 or more and less than 0.7; C: Degree of orientation is less than 0.5.

[0183] <Materials Used> <First Rubber> Unmodified liquid rubber-1: Ricon 184 manufactured by Cray Valley (liquid butadiene-styrene random copolymer, Mn=9,400) Unmodified liquid rubber-2: LIR-30 manufactured by Kuraray (liquid polyisoprene, Mn=28,000) Unmodified liquid rubber-3: LBR-305 manufactured by Kuraray (liquid polybutadiene, Mn=26,000) Unmodified liquid rubber-4: L-FR-107 manufactured by Kuraray (liquid farnesene rubber, Mn=130,000) Unmodified liquid rubber-5: LIR-50 manufactured by Kuraray (liquid polyisoprene, Mn=54,000)

[0184] <Second Rubber> Modified liquid rubber-1: LIR-403 manufactured by Kuraray Co., Ltd. (maleic anhydride modified liquid polyisoprene, Mn = 34,000, number of modified groups per molecular chain: 3) Modified liquid rubber-1: LIR-410 manufactured by Kuraray Co., Ltd. (carboxy-modified liquid polyisoprene, Mn = 30,000, number of modified groups per molecular chain: 10) Modified liquid rubber-3: Ricon 184MA6 manufactured by Cray Valley Corporation (maleic anhydride modified liquid styrene butadiene copolymer, Mn = 9,200, number of modified groups per molecular chain: 6) Modified liquid rubber-4: Ricon 131MA20 manufactured by Cray Valley Corporation (maleic anhydride modified liquid polybutadiene, Mn = 7,000, number of modified groups per molecular chain: 11)

[0185] <Third Rubber> Natural rubber: RSS No. 3 (Producer: UNIMAC RUBBER CO., LTD. (Thailand), Supplier: Marubeni Techno Rubber) Polyisoprene: IR2200 manufactured by JSR Corporation SBR-1: Produced according to the procedure described in the section <<Production of SBR-1>> below.

[0186] <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: Produced according to the procedure described in the section "Production of SBR-1" below. SBR-2: Asaprene (registered trademark) Y031 manufactured by Asahi Kasei Corporation SBR-3: Nipol1 (registered trademark) 502 manufactured by Nippon Zeon Co., Ltd.

[0187] <Production of SBR-1> One autoclave was used, having 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 stirrer and a jacket for temperature control. Furthermore, one static mixer was connected just before the raw material inlet of the reactor. 1,3-butadiene, from which impurities such as water 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 solution. Just before this mixed solution entered the first reactor, n-butyllithium for impurity inactivation treatment was supplied at 0.020 phm, and the mixture was mixed in 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 supplied 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 supplied to a static mixer from the top of the reactor, and a reaction was carried out by continuously supplying M1 (1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) as a modifier at a ratio of 1.0 equivalent (however, the amount added was calculated assuming that 4 mol of NBL reacts per 1 mol of M1) to the lithium of NBL supplied as the polymerization initiator, and SBR-1 was obtained.

[0188] <Cellulose nanofibers> Three parts by mass of cotton linter pulp was immersed in 27 parts by mass of water and dispersed using a pulper. 30 parts by mass of the pulper-treated cotton linter pulp slurry (including 3 parts by mass of cotton linter pulp) was added to 170 parts by mass of water and dispersed in water (solid content: 1.5% by mass). The aqueous dispersion was beaten for 30 minutes using an SDR14 lab refiner (pressure type disc type) manufactured by Aikawa Iron Works Co., Ltd. as a disc refiner, with a clearance between discs of 1 mm. Subsequently, thorough beating was performed under conditions where the clearance was reduced to a level close to zero, yielding a beaten aqueous dispersion (solid content concentration: 1.5% by mass). The resulting beaten aqueous dispersion was then subjected to a high-pressure homogenizer (NSO15H manufactured by Niro Soavi (Italy)) for 10 passes at an operating pressure of 100 MPa to obtain a cellulose nanofiber slurry (solid content concentration: 1.5% by mass). The mixture was then concentrated to a solid content of 10% by mass using a dehydrator to obtain a cake of cellulose nanofibers.

[0189] <Dispersant> Nonionic dispersant: Sannix GL-3000 (polyoxyethylene polyoxypropylene triol) manufactured by Sanyo Chemical Industries, Ltd.

[0190] <Vulcanization aid> Zinc oxide: Available from Fujifilm Wako Pure Chemical Industries, Ltd. Stearic acid: Available from Fujifilm Wako Pure Chemical Industries, Ltd.

[0191] <Wax> Sunnock: Selected special wax (available from Ouchi Shinko Chemical Co., Ltd.)

[0192] <Antioxidant> Nocrac 6C: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (available from Ouchi Shinko Chemical Co., Ltd.)

[0193] <Vulcanization accelerator> Noccela CZ: N-cyclohexyl-2-benzothiazolylsulfenamide (available from Ouchi Shinko Chemical Co., Ltd.) Noccela D: 1,3-diphenylguanidine (available from Ouchi Shinko Chemical Co., Ltd.)

[0194] <<Production of Rubber Composition>> <Rubber Composition Comprising First and Second Rubbers> [Examples 1-1 to 1-11, 1-21 to 1-24] 10% by mass of cellulose nanofiber cake was placed in a 200 ml PP cup, and unmodified liquid rubber and dispersant were added to obtain the blending ratios shown in Tables 2 and 3. An aqueous dispersion was prepared so that the final composition had a cellulose nanofiber concentration of 10% by mass. The 200 ml PP cup was placed in a Thinky Planetary ... The resulting composition was thinly spread on a release film, 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 LabNect Co., Ltd. to obtain a rubber composition. The dispersibility of the resulting rubber composition was evaluated using an optical microscope.

[0195] [Examples 1-12] 57.1 parts by mass of liquid butadiene-styrene random copolymer (unmodified liquid rubber-1) and 200 parts by mass of maleic anhydride-modified liquid polyisoprene (modified liquid rubber-1) were dissolved in 2,314 parts by mass of chloroform in a beaker and stirred. Next, the liquid rubber solution was spread on a Teflon (registered trademark) tray and vacuum dried at 80°C to obtain a preliminary composition. A 10% by mass cellulose nanofiber cake was placed in a 200 ml PP cup, and the preliminary composition and dispersant were added to obtain the blending ratio shown in Table 2. An aqueous dispersion was prepared so that the final composition had a cellulose nanofiber concentration of 10% by mass. The 200 ml PP cup was placed in a Thinky Planetary ... The resulting composition was thinly spread on a release film, 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 LabNect Co., Ltd. to obtain a rubber composition. The dispersibility of the resulting rubber composition was evaluated using an optical microscope.

[0196] [Examples 1-13 to 1-20] Rubber compositions were obtained in the same manner as in Example 1-12, except that the amount of chloroform was changed to 1,414 parts by mass, and the amounts and types of the unmodified liquid rubber and modified liquid rubber were changed as shown in Table 2. The dispersibility of the obtained rubber compositions was evaluated using an optical microscope.

[0197] Comparative Examples 1-1 to 1-9: 10% by mass of cellulose nanofiber cake was placed in a 200 ml PP cup, and then unmodified liquid rubber or modified liquid rubber and a dispersant were added to obtain the blending ratios shown in Table 3. An aqueous dispersion was prepared so that the final composition had a cellulose nanofiber concentration of 10% by mass. The 200 ml PP cup was placed in a Thinky Corporation ARE-310 planetary centrifugal mixer and mixed for 15 minutes in stirring mode (revolution 2000 rpm, rotation 800 rpm). The resulting composition was thinly spread on a release film, dried at 80°C using an Espec Corporation SPH-201 mill, and then pulverized for 30 seconds using a LabNect Co., Ltd. Mini Speed ​​Mill MS-05 to obtain a rubber composition. The resulting rubber composition was evaluated for dispersibility using an optical microscope.

[0198] <Rubber Compositions (Masterbatches) Further Containing a Third Rubber> [Examples 2-1 to 2-21, 2-35 to 2-36, Comparative Examples 2-1 to 2-15] 10% by mass of cellulose nanofiber cake was placed in a 200 ml PP cup, and then unmodified liquid rubber and dispersant were added to obtain the blending ratios shown in Tables 4 to 6. An aqueous dispersion was prepared so that the cellulose nanofiber concentration was 10% by mass in the final composition. The 200 ml PP cup was placed in a Thinky Planetary ...

[0199] Using an internal mixer (capacity: 0.35 L) equipped with a temperature control device, the third rubber, preliminary composition, and modified liquid rubber were added according to the compositions shown in Tables 4 to 6 at a filling rate of 65%, and the mixture was mixed at 140°C for 5 minutes. The resulting mixture was collected and passed through a roll to obtain a sheet-like rubber composition (masterbatch). A portion was cut from the sheet, and the cellulose nanofiber dispersibility was evaluated using X-ray CT. The results are shown in Tables 4 to 6.

[0200] [Example 2-22] A sheet-shaped 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 portion 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.

[0201] [Example 2-23] A sheet-shaped 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 portion was cut out from the sheet, and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0202] [Example 2-24] A sheet-shaped 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 portion was cut out from the sheet, and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0203] [Example 2-25] A preliminary composition was obtained in the same manner as in Example 2-1. Using an internal mixer (capacity: 0.35 L) equipped with a temperature control device, the third rubber, preliminary composition, and modified liquid rubber were added according to the composition shown in Table 5 at a filling rate of 65% in the first stage of mixing, and the mixture was mixed at 120°C for 5 minutes. Next, in the second stage of mixing, the resulting mixture was cooled to room temperature and then mixed again at 120°C for 3 minutes to improve the dispersion of the cellulose nanofibers. The resulting mixture was collected and passed through a roll to obtain a sheet-like rubber composition (masterbatch). A portion was cut from the sheet, and the cellulose nanofiber dispersibility was evaluated using X-ray CT. The results are shown in Table 5.

[0204] [Example 2-26] A sheet-shaped rubber composition (masterbatch) was obtained in the same manner as in Example 2-25, except that the second-stage kneading time was changed from 3 minutes to 5 minutes. A portion was cut out from the sheet, and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0205] Example 2-27 A sheet-shaped rubber composition (masterbatch) was obtained in the same manner as in Example 2-25, except that the first-stage and second-stage kneading temperatures were changed from 120°C to 140°C. A portion was cut out from the sheet, and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0206] Example 2-28 A sheet-shaped rubber composition (masterbatch) was obtained in the same manner as in Example 2-26, except that the first-stage and second-stage kneading temperatures were changed from 120°C to 140°C. A portion was cut out from the sheet, and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0207] [Example 2-29] A sheet-shaped rubber composition (masterbatch) was obtained in the same manner as in Example 2-1, except that the filling rate was changed to 55%. A portion was cut out from the sheet and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0208] [Example 2-30] A sheet-shaped rubber composition (masterbatch) was obtained in the same manner as in Example 2-1, except that the filling rate was changed to 75%. A portion was cut out from the sheet, and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0209] [Example 2-31] 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%, the third rubber, preliminary composition, and modified liquid rubber were added according to the composition shown in Table 5, and the mixture was kneaded at 120°C for 5 minutes. The resulting kneaded product was collected and passed through a roll to obtain a sheet-like rubber composition (masterbatch). A portion was cut from the sheet, and the cellulose nanofiber dispersibility was evaluated using X-ray CT. The results are shown in Table 5.

[0210] [Example 2-32] A sheet-shaped rubber composition (masterbatch) was obtained in the same manner as in Example 2-31, except that the kneading temperature was changed to 140°C. A portion was cut out from the sheet and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0211] [Example 2-33] 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%, the third rubber, preliminary composition, and modified liquid rubber were added according to the composition shown in Table 5, and kneaded for 5 minutes at 120°C. The resulting kneaded product was collected and passed through a roll to obtain a sheet-like rubber composition (masterbatch). A portion was cut from the sheet, and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0212] [Example 2-34] A sheet-shaped rubber composition (masterbatch) was obtained in the same manner as in Example 2-33, except that the kneading temperature was changed to 140°C. A portion was cut out from the sheet and the cellulose nanofiber dispersibility was evaluated by X-ray CT. The results are shown in Table 5.

[0213] <Cured Rubber> [Examples 3-1 to 3-32, Comparative Examples 3-1 to 3-17] Using an internal mixer (capacity: 0.35 L) equipped with a temperature control device, the rubber composition, fourth rubber, zinc oxide, stearic acid, wax, and stabilizer were added according to the formulations shown in Tables 7 to 10 at a filling rate of 65% and kneaded for 3 minutes at 140°C. Next, in the second mixing stage, the resulting mixture was cooled to room temperature and then 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 using an open roll set at 70°C, and the mixture was molded into a sheet. The sheet-like mixture was then placed in a 2.0 mm-thick mold and vulcanized in a vulcanization press at 160°C for 15 minutes to obtain a cured rubber sheet. The resulting cured rubber sheet was then subjected to various evaluations. The results are shown in Tables 7 to 10.

[0214] Examples 4-1 to 4-48, Comparative Examples 4-1 to 4-15 Using an internal mixer (capacity: 0.35 L) equipped with a temperature control device, the first stage of mixing was performed at a filling rate of 65%. The masterbatch, fourth rubber, zinc oxide, stearic acid, wax, and stabilizer were added according to the formulations shown in Tables 11 to 17, and the mixture was mixed at 140°C for 3 minutes. Next, in the second stage of mixing, the resulting mixture was cooled to room temperature and then mixed 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 mixed using an open roll set at 70°C, and the mixture was molded into a sheet. The sheet-like mixture was then placed in a 2.0 mm-thick mold and vulcanized in a vulcanization press at 160°C for 15 minutes to obtain a cured rubber sheet. The resulting cured rubber sheet was then subjected to various evaluations. The results are shown in Tables 11 to 17.

[0215]

[0216]

[0217]

[0218]

[0219]

[0220]

[0221]

[0222]

[0223]

[0224]

[0225]

[0226]

[0227]

[0228]

[0229]

[0230]

[0231]

[0232] The rubber composition according to the present disclosure can be formed into a molded article having good physical properties, and therefore 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, construction and civil engineering materials, daily necessities, sports and leisure goods, housing components for wind power generation, and container and packaging components.

Claims

1. A rubber composition comprising cellulose nanofibers, a first rubber, and a second rubber, wherein the first rubber is an unmodified liquid rubber, and the second rubber is a modified liquid rubber.

2. The rubber composition according to claim 1, wherein the ratio η2 / η1 of the viscosity η2 of the second rubber to the viscosity η1 of the first rubber at 38° C. is 1.2 to 160.

3. The rubber composition according to claim 1 or 2, wherein the number average molecular weight of the second rubber is 4,500 to 100,000.

4. The rubber composition according to claim 1 or 2, comprising 5 to 300 parts by mass of said first rubber per 100 parts by mass of said 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. The rubber composition according to claim 1 or 2, wherein the second rubber is maleic anhydride modified liquid polyisoprene.

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

11. The rubber composition according to claim 10, wherein said dispersant is nonionic.

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

13. The rubber composition of claim 12, wherein said third rubber is a natural rubber.

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

15. A method for producing the rubber composition according to claim 1 or 2, comprising: a first step of mixing cellulose nanofibers with 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.

16. A method for producing a rubber composition according to claim 1 or 2, 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 with the cellulose nanofibers to obtain a rubber composition.

17. The method of claim 15, further comprising mixing a third rubber in said second step.

18. A method for producing a rubber composition according to claim 12, comprising the steps of: mixing cellulose nanofibers with the first rubber to obtain a preliminary composition; mixing the preliminary composition with the second rubber to obtain a dry body; and mixing the dry body with a third rubber to obtain a rubber composition.

19. A method for producing a rubber composition according to claim 12, comprising the steps of: mixing the first rubber with the second rubber to obtain a preliminary composition; mixing the preliminary composition with the cellulose nanofibers to obtain a dry body; and mixing the dry body with a third rubber to obtain a rubber composition.

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

21. A method for producing a rubber composition, comprising the step of mixing the dried product according to claim 20 with a third rubber to obtain a rubber composition.

22. The method of claim 17, wherein the third rubber is a natural rubber.

23. The method of claim 18, wherein the third rubber is a natural rubber.

24. The method of claim 19, wherein the third rubber is a natural rubber.

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

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

27. A cured rubber product, which is the cured product of the rubber composite of claim 26.

28. A tire comprising the rubber vulcanized product of claim 27.

29. A vibration-isolating rubber comprising the cured rubber product according to claim 27.

30. A shoe outsole comprising the rubber vulcanized product of claim 27.

31. A conveyor belt comprising the vulcanized rubber of claim 27.

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