Rubber composition comprising cellulose nanofibrils

Abstract

The present application provides a rubber composition, a rubber composite, and a rubber cured product, each of which is excellent in dispersibility and orientation of cellulose nanofiber, and in one embodiment, the present application provides a rubber cured product which exhibits good physical properties (particularly, tensile properties and modulus) and surface smoothness. In one embodiment, the present application provides a rubber composition comprising cellulose nanofiber, a first rubber, and a second rubber, the first rubber being unmodified liquid rubber, and the second rubber being modified liquid rubber.

Description

Technical Field

[0001] One aspect of this disclosure relates to rubber compositions comprising cellulose nanofibers, etc. Background Technology

[0002] Traditionally, rubber molded articles require a high degree of balance between various properties such as mechanical strength, flexibility, wear resistance, and processability. For example, fillers are typically included in rubber molded articles to improve elastic modulus, hardness, and wear resistance. Good dispersion of the filler in the rubber is crucial for these filler-containing rubber molded articles to achieve the desired properties. In recent years, due to increased environmental awareness, various uses of cellulose as a low-gravity and renewable material for rubber molded articles are being explored. Cellulose nanofibers, in particular, show great promise as fillers for polymer molded articles because they provide excellent reinforcement per unit quantity when combined with various polymers. Using cellulose nanofibers in rubber molded articles could provide low-gravity articles with excellent physical properties, suitable for multiple applications, and advantageous in terms of transportation and waste costs. However, cellulose nanofibers are inherently hydrophilic due to the contribution of hydroxyl groups in cellulose, making them difficult to mix with rubber, which is highly hydrophobic. Therefore, various attempts have been made to improve the miscibility of cellulose nanofibers with rubber.

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

[0004] In addition, Patent Document 2 discloses a rubber composition for tires, characterized in that 1 to 50 parts by mass of oxidized cellulose nanofibers are mixed into 100 parts by mass of a diene rubber containing 5% or more of a modified diene rubber having 0.1 mol% or more of polar groups.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2020-41076

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-147877 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] The techniques described in Patent Documents 1 and 2 are methods for improving the mechanical properties of rubber compositions by dispersing cellulose fibers in them. However, according to these techniques, the dispersion of cellulose nanofibers in the rubber composition is still insufficient, and there is room for improvement in the mechanical properties. Furthermore, when cellulose nanofibers are blended into various molded articles, good surface smoothness is sometimes required from the viewpoint of the appearance and slip properties of the molded article. To obtain good surface smoothness, it is advantageous to have good orientation of the cellulose nanofibers in the molded article. However, Patent Documents 1 and 2 do not focus on the orientation of the cellulose nanofibers.

[0011] The present invention addresses the aforementioned problems. In one aspect, the objective is to provide rubber compositions, rubber composites, and rubber cured products with excellent dispersibility and orientation of cellulose nanofibers. In another aspect, the objective is to provide rubber cured products exhibiting good physical properties (particularly tensile properties and modulus) and surface smoothness.

[0012] Methods for solving problems

[0013] This disclosure includes the following items.

[0014] [Project 1]

[0015] 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.

[0016] [Project 2]

[0017] According to the rubber composition of Project 1, the ratio of the viscosity η2 of the second rubber to the viscosity η1 of the first rubber, η2 / η1, is 1.2 to 160 at 38°C.

[0018] [Project 3]

[0019] 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.

[0020] [Project 4]

[0021] The rubber composition according to any one of items 1 to 3, wherein, relative to 100 parts by weight of the second rubber, comprises 5 to 300 parts by weight of the first rubber.

[0022] [Project 5]

[0023] The rubber composition according to any one of items 1 to 4, wherein, relative to 100 parts by weight of cellulose nanofibers, comprises 5 to 100 parts by weight of the first rubber.

[0024] [Project 6]

[0025] The rubber composition according to any one of items 1 to 5, wherein, relative to 100 parts by weight of cellulose nanofibers, comprises 10 to 300 parts by weight of the aforementioned second rubber.

[0026] [Project 7]

[0027] The rubber composition according to any one of items 1 to 6 comprises 5% to 60% by mass of the second rubber.

[0028] [Project 8]

[0029] The rubber composition according to any one of items 1 to 7, wherein the first rubber comprises an aromatic vinyl monomer unit.

[0030] [Project 9]

[0031] The rubber composition according to any one of items 1 to 8, wherein the second rubber is maleic anhydride modified liquid polyisoprene.

[0032] [Project 10]

[0033] The rubber composition according to any one of items 1 to 9 further comprises a dispersant.

[0034] [Project 11]

[0035] The rubber composition according to Project 10, wherein the dispersant is nonionic.

[0036] [Project 12]

[0037] The rubber composition according to any one of items 1 to 11 further comprises a third rubber.

[0038] [Project 13]

[0039] According to the rubber composition of Project 12, wherein the third rubber is natural rubber.

[0040] [Project 14]

[0041] The rubber composition according to any one of items 1 to 11 is a dried body.

[0042] [Project 15]

[0043] A method for manufacturing the rubber composition according to any one of items 1 to 14, comprising: In the first step, cellulose nanofibers are mixed with the aforementioned first rubber to obtain a preparative composition; and In the second step, the above-mentioned preparative composition is mixed with the above-mentioned second rubber to obtain a rubber composition.

[0044] [Project 16]

[0045] A method for manufacturing a rubber composition according to any one of items 1 to 14, comprising: The first step involves mixing the first rubber with the second rubber to obtain a preparative composition; and In the second step, the preparative composition is mixed with the cellulose nanofibers to obtain a rubber composition.

[0046] [Project 17]

[0047] According to the method described in item 15 or 16, in the second step, a third rubber is further mixed.

[0048] [Project 18]

[0049] The method for manufacturing the rubber composition according to item 12 or 13 includes: The process of mixing cellulose nanofibers with the first rubber described above to obtain a preparative composition; The process of mixing the above-mentioned preparative composition with the above-mentioned second rubber to obtain a dried body; and The process of mixing the above-mentioned dried body with a third rubber to obtain a rubber composition.

[0050] [Project 19]

[0051] The method for manufacturing the rubber composition according to item 12 or 13 includes: The process of mixing the first rubber with the second rubber to obtain a preparative composition; The process of mixing the preparative composition with the cellulose nanofibers to obtain a dried body; and The process of mixing the above-mentioned dried body with a third rubber to obtain a rubber composition.

[0052] [Project 20]

[0053] A dried body comprising any one of items 1 to 11.

[0054] [Project 21]

[0055] A method for manufacturing a rubber composition, comprising the following steps: The dried body described in Project 20 is mixed with a third rubber to obtain a rubber composition.

[0056] [Project 22]

[0057] According to the method described in Project 17, the third rubber is natural rubber.

[0058] [Project 23]

[0059] According to the method described in Project 18, the third rubber is natural rubber.

[0060] [Project 24]

[0061] According to the method described in Project 19, the third rubber is natural rubber.

[0062] [Project 25]

[0063] According to the method described in Project 21, the third rubber is natural rubber.

[0064] [Project 26]

[0065] A rubber composite, which is a mixture of the rubber composition described in any one of items 1 to 14 and a fourth rubber.

[0066] [Project 27]

[0067] A cured rubber compound, which is a cured rubber composite as described in item 26.

[0068] [Project 28]

[0069] A tire comprising the rubber curing compound described in item 27.

[0070] [Project 29]

[0071] A vibration damping rubber comprising the rubber cured product described in item 27.

[0072] [Project 30]

[0073] A shoe outsole comprising the rubber curing material described in item 27.

[0074] [Project 31]

[0075] A conveyor belt comprising the rubber cured material described in item 27.

[0076] Invention Effects

[0077] According to the present invention, in one aspect, rubber compositions, rubber composites, and rubber cured products with excellent dispersibility and orientation of cellulose nanofibers can be provided; in another aspect, rubber cured products exhibiting good physical properties (particularly tensile properties and modulus) and surface smoothness can be provided. Detailed Implementation

[0078] Hereinafter, exemplary embodiments of the present invention (hereinafter referred to as "this embodiment") will be described, but the present invention is not limited to these embodiments in any way. It should be noted that, unless otherwise specified, the characteristic values ​​of this disclosure are values ​​measured by the method described in one of the [Examples] of this disclosure or by a method equivalent to that understood by those skilled in the art.

[0079] Rubber Compositions

[0080] One aspect of this disclosure provides a rubber composition comprising cellulose nanofibers, a first rubber, and a second rubber. In one aspect, the first and second rubbers are liquid rubbers. Cellulose nanofibers are inherently hydrophilic due to their hydroxyl groups, while rubber is inherently hydrophobic, making it generally difficult to uniformly disperse cellulose nanofibers in rubber. The inventors have conducted various studies and found that specific combinations of rubbers are useful for preparing rubber compositions with excellent dispersibility and orientation of cellulose nanofibers. This rubber composition can also be formulated, for example, as a rubber masterbatch, and compounded with additional rubber to produce a rubber composite. The rubber compositions, rubber composites, or cured rubbers of this disclosure exhibit good dispersibility and orientation of cellulose nanofibers. Furthermore, this allows for the combination of good physical properties (particularly tensile properties and modulus) and good surface smoothness in the cured rubbers of this disclosure.

[0081] In one embodiment, the first rubber is an unmodified liquid rubber, and the second rubber is a modified liquid rubber. Typically, in the first and second rubbers, the second rubber can bind to or interact with cellulose nanofibers, while the first rubber may substantially not produce such binding or interaction. The second rubber can possess the good flowability inherent in liquid rubber and the functionality inherent in having modified groups. Such a second rubber is expected to exhibit an effect of improving the dispersibility of cellulose nanofibers in the third and / or fourth rubbers of this disclosure. However, according to the research of the inventors, it has been found that using only the second rubber sometimes fails to achieve the desired level of improved dispersibility of cellulose nanofibers. While not bound by theory, one reason is believed to be that, depending on the modified groups of the second rubber, excessive binding or interaction may occur locally between the modified groups of the second rubber and each other, or between the modified groups of the second rubber and the hydroxyl groups of the cellulose nanofibers, resulting in a tight 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 rubbers may readily form a tight structure. Furthermore, when blending cellulose nanofibers into various molded articles, good surface smoothness is sometimes required from the viewpoint of the appearance and slip properties of the molded article. To obtain good surface smoothness, it is advantageous to have good orientation of the cellulose nanofibers in the molded article. If the cellulose nanofibers in the rubber composition or rubber composite used in manufacturing the molded article have good mobility, good orientation of the cellulose nanofibers can be easily achieved. However, if a dense structure as described above is formed, the orientation of the cellulose nanofibers may be reduced. Therefore, the inventors conducted further research and found that by using a first rubber in addition to a second rubber, the problems described above can be solved. The first rubber has the advantages of excellent flowability due to being a liquid rubber and the absence of modified groups, thus avoiding the formation of a dense structure as described above. By entering between the second rubbers or between the second rubbers and the cellulose nanofibers, the first rubber can suppress excessive proximity of the functional groups of the second rubbers and cellulose nanofibers to other functional groups. Therefore, the dispersibility-enhancing effect of the cellulose nanofibers, which is an advantage of the second rubber, is well exhibited, thus making it easy to achieve good dispersibility and orientation of the cellulose nanofibers.

[0082] The components of the rubber composition will now be described. It should be noted that the amounts of each component recorded as values ​​in the rubber composition of this embodiment can be considered as the amounts of each component in the rubber composition of this embodiment.

[0083] Cellulose nanofibers

[0084] Cellulose nanofibers are fibers obtained by micronizing cellulose fiber raw materials through processes such as defiberization. Natural cellulose and regenerated cellulose can be used as raw materials. Natural cellulose can be derived from wood pulp (broadleaf or coniferous trees), non-wood pulp (cotton, bamboo, hemp, bagasse, kenaf, cotton linters, sisal, rice straw, etc.), and aggregates of cellulose fibers produced by animals (e.g., tunicates), algae, or microorganisms (e.g., acetic acid bacteria). Regenerated cellulose can be derived from regenerated cellulose fibers (viscose, cuprammonium cellulose, Tencel, etc.), cellulose derivative fibers, and ultrafine threads of regenerated cellulose or cellulose derivatives obtained through electrospinning.

[0085] In one approach, defiberization is a dry or wet mechanical process, preferably a wet process that mechanically treats a slurry obtained by dispersing cellulose fiber raw materials in a liquid medium. Defiberization can be performed using a single device or multiple devices separately. The device used for defiberization is not particularly limited, and examples include high-speed rotary mills, colloid mills, high-pressure mills, roller mills, ultrasonic mills, high-pressure or ultra-high-pressure homogenizers, fine grinding mills, pulpers, PFI mills, kneaders, dispersers, high-speed defiberizers, grinders (mortar-type pulverizers), ball mills, vibratory mills, bead mills, conical fine grinding mills, disc fine grinding mills, single-screw, twin-screw, or multi-screw mixers / extruders, etc.

[0086] Cellulose fiber raw materials can be pre-treated before defiberization. Pre-treatment can be used to adjust fiber diameter, fiber length, degree of fibrillation, etc., or to adjust the content of components other than cellulose (such as acid-insoluble components like lignin, alkali-soluble polysaccharides like hemicellulose), or to adjust molecular weight, crystallinity, etc.

[0087] In one approach, pretreatment can be selected from one or more of chemical treatment, pulverization, milling, and classification. Chemical treatment is treatment using chemicals, such as cooking, bleaching, purification, hydrolysis, enzymatic treatment, regenerated cellulose, and chemical modification. Pulverization is a dry pulverization process of cellulose fiber raw materials. Milling is a process of pulverizing a pulp obtained by dispersing cellulose fiber raw materials in a liquid medium, distinguishing it from the above-mentioned pulverization in that it is a wet process. Classification is a separation operation used to make the fiber length of the cellulose fiber raw materials uniform, and can be dry classification or wet classification.

[0088] Examples of liquid media include water and / or other media (e.g., organic solvents, inorganic acids, bases and / or ionic liquids), and may include one or more media.

[0089] Examples of commonly used organic solvents include alcohols (e.g., methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, ethylene glycol, diethylene glycol, glycerol, 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) of one or more. In a typical configuration, the liquid medium in the slurry is essentially only water.

[0090] [Specific surface area]

[0091] From the perspective of obtaining the desired improvement in physical properties from cellulose nanofibers, the preferred specific surface area of ​​cellulose nanofibers is 2 m². 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 / g or more. Furthermore, from the viewpoint of ensuring good dispersion of cellulose nanofibers in the rubber composition and the cured rubber, 400m is preferred. 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.

[0092] Regarding the specific surface area of ​​cellulose nanofibers, the BET specific surface area of ​​porous sheets of cellulose nanofibers was measured using nitrogen gas using a specific surface area and pore size distribution measuring device (e.g., Nova-4200e, Quantachrome Instruments). Specifically, approximately 0.2 g of the porous sheet was dried under vacuum at 120°C for 5 hours, and the amount of nitrogen adsorbed at the boiling point of liquid nitrogen was measured at 5 points (multi-point method) within a relative vapor pressure (P / P0) range of 0.05 to 0.2. The BET specific surface area (m²) was calculated using the device program. 2 / g).

[0093] The porous sheet is prepared by the method described in the section on [Porous Sheets] which is described later.

[0094] Regarding the specific surface area of ​​cellulose nanofibers, the equivalent fiber diameter of cellulose nanofibers can be calculated by assuming that the cellulose nanofibers are cylindrical, according to the following formula.

[0095] Since the density of cellulose is 1.5 g / cm³ 3 Therefore, the volume of each 1g of cellulose is 6.7 × 10⁻⁶. -7 (m 3 / g).

[0096] If the equivalent fiber diameter of cellulose nanofibers is set as r (m), then the average outer perimeter of cellulose nanofibers = πr, and the average cross-sectional area of ​​cellulose nanofibers = 0.25πr. 2 Therefore, the total fiber length of each 1g of cellulose nanofibers is 6.7 × 10⁻⁶. -7 (m 3 / g) / average cross-sectional area (=0.25πr) 2 )

[0097] Total surface area = Specific surface area (m²) 2 / g)=6.7×10 -7 (m 3 / g) / average cross-sectional area (=0.25πr) 2 ) × average perimeter (=πr) = 6.7 × 10 -7 (m 3 / g) / 0.25r=26.68×10 -7 (m 3 / g) / r

[0098] Therefore, the converted fiber diameter r (m) = 26.68 × 10 -7 (m 3 / g) / Specific surface area (m²) 2 / g), for example, the BET specific surface area of ​​porous sheets is 40m². 2The converted fiber diameter r of the cellulose nanofiber is calculated to be 66.7 nm.

[0099] In one approach, from the viewpoint of effectively obtaining the property enhancement effect brought about by cellulose nanofibers, the equivalent fiber diameter of the cellulose nanofibers is preferably 2 to 1000 nm. More preferably, the equivalent fiber diameter of the cellulose nanofibers is 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more; even more preferably, it is 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.

[0100] In one embodiment, from the viewpoint of effectively exhibiting the property enhancement effect brought about by cellulose nanofibers, 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 ensuring good dispersion of the cellulose nanofibers in the resin composition, it 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.

[0101] In one embodiment, from the viewpoint of effectively obtaining the property enhancement effect brought about by cellulose nanofibers, the number-average fiber diameter D of the cellulose nanofibers is preferably 2 to 1000 nm. More preferably, the number-average fiber diameter of the cellulose nanofibers is 4 nm or more, or 5 nm or more, or 10 nm or more, or 15 nm or more, or 20 nm or more; even more preferably, it is 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.

[0102] From the viewpoint of effectively improving the mechanical properties of rubber composites containing cellulose nanofibers by utilizing 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 a processability viewpoint, it is preferably 5000 or less, or 3000 or less, or 2000 or less, or 1000 or less.

[0103] In this disclosure, the fiber length, fiber diameter, and L / D ratio of cellulose nanofibers are determined using a scanning electron microscope (SEM) according to the following steps. An aqueous dispersion of cellulose nanofibers is diluted to 0.001–0.1% by mass using tert-butanol, and dispersed using a high-shear homogenizer (e.g., IKA, trade name "ULTRA-TURRAX T18") at 15,000 rpm for 3 minutes. The dispersion is then cast onto an osmium-deposited silicon substrate. The air-dried material is used as the test sample, and measurements are performed using a high-resolution scanning electron microscope (SEM). Specifically, in an observation field adjusted to allow observation of at least 100 cellulose nanofibers, the length (L) and diameter (D) of 100 randomly selected cellulose nanofibers are measured, and the ratio (L / D) is calculated. Then, the number average of these values ​​is used as the number-average fiber length L and the number-average fiber diameter D, and the ratio (L / D) is calculated.

[0104] Cellulose crystals are known to be of types I, II, III, and IV, among which types I and II are commonly used, while types III and IV, although obtained on a laboratory scale, are not commonly used on an industrial scale. As for the cellulose nanofibers of this disclosure, from the perspective of high structural mobility and obtaining molded articles with lower coefficients of linear expansion and superior strength and elongation under tensile and flexural deformation by dispersing the cellulose nanofibers in rubber, cellulose nanofibers containing type I or type II cellulose crystals are preferred, and cellulose nanofibers containing type I cellulose crystals with a crystallinity of 55% or more are more preferred.

[0105] The crystallinity of cellulose nanofibers is preferably 55% or higher. Higher crystallinity results in higher mechanical properties (strength, dimensional stability) of cellulose itself, thus leading to a tendency for the rubber composite to exhibit high strength and dimensional stability when cellulose nanofibers are dispersed in rubber. A more preferred lower limit for crystallinity is 60%, further preferably 70%, and most preferably 80%. While there is no particular upper limit for the crystallinity of cellulose nanofibers, a higher limit is preferred; from a production standpoint, a preferred upper limit is 99%.

[0106] The crystallinity referred to here, when the cellulose nanofibers are cellulose type I crystals (derived from natural cellulose), is determined by the following formula using the Segal method, based on the diffraction pattern (2θ / deg. is 10~30) of the sample when measured by wide-angle X-ray diffraction.

[0107] Crystallinity (%) = [I (200) -I (amorphous) ] / I (200) ×100

[0108] I(200) The diffraction peak intensity of the 200 plane (2θ=22.5°) of cellulose type I crystals

[0109] I (amorphous) The peak intensity of the halo peak caused by amorphous inclusions in cellulose type I crystals, and the peak intensity at an angle 4.5° lower than the diffraction angle of the 200 plane (2θ=18.0°).

[0110] In addition, when the cellulose is cellulose type II crystal (from regenerated cellulose), the crystallinity is determined by the absolute peak intensity h0 at 2θ=12.6° of the (110) plane peak belonging to cellulose type II crystal in wide-angle X-ray diffraction and the peak intensity h1 of the baseline at the plane interval (the line connecting 2θ=8° and 15°) by the following formula.

[0111] Crystallinity (%) = (h0 - h1) / h0 × 100

[0112] In addition, the degree of polymerization of 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, preferably 3500 or less, more preferably 3300 or less, more preferably 3200 or less, more preferably 3100 or less, more preferably 3000 or less.

[0113] From the viewpoint of processability and mechanical properties, it is preferable that the degree of polymerization of cellulose nanofibers is within the aforementioned range. From the viewpoint of processability, it is preferable that the degree of polymerization is not too high; from the viewpoint of mechanical properties, it is desirable that the degree of polymerization is not too low.

[0114] The degree of polymerization of cellulose nanofibers refers to the average degree of polymerization determined by the concentration-to-viscosity method of copper ethylenediamine solution as described in the confirmation test (3) of the "Explanation of the Fifteenth Revision of the Japanese Pharmacopoeia (published by Hirokawa Shoten)".

[0115] In one embodiment, the weight-average molecular weight (Mw) of the cellulose nanofibers is 100,000 or more, more preferably 200,000 or more. The ratio of weight-average molecular weight to number-average molecular weight (Mn) (Mw / Mn) is 6 or less, preferably 5.6 or less or 5.4 or less. A higher weight-average molecular weight means fewer terminal groups in the cellulose molecules. Furthermore, the ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) represents the width of the molecular weight distribution; therefore, a smaller Mw / Mn means fewer terminal groups in the cellulose molecules. Since the terminals of cellulose molecules become the starting point for thermal decomposition, cellulose nanofibers with particularly high heat resistance and rubber compositions comprising cellulose nanofibers and rubber can be obtained when not only the weight-average molecular weight of the cellulose nanofibers is high, but also the width of the molecular weight distribution is narrow. From the viewpoint of the ease of obtaining cellulose raw materials, the weight-average molecular weight (Mw) of the cellulose nanofibers can be, for example, 600,000 or less, 500,000 or less, or 400,000 or less. From the viewpoint of ease of obtaining cellulose fiber raw materials, the number-average molecular weight (Mn) of cellulose nanofibers can 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 ease of manufacturing cellulose nanofibers, the ratio of weight-average molecular weight to number-average molecular weight (Mn) (Mw / Mn) can 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 cellulose raw materials with a Mw appropriate to the desired purpose, and by appropriately performing physical and / or chemical treatment on the cellulose raw materials within a suitable range. Mw / Mn can also be controlled within the above range by selecting cellulose raw materials with a Mw / Mn appropriate to the desired purpose, and by appropriately performing physical and / or chemical treatment on the cellulose raw materials within a suitable range. The Mw and Mw / Mn of the cellulose raw materials can each be within the above range in one manner.

[0116] The weight-average molecular weight and number-average molecular weight of cellulose nanofibers mentioned here refer to the values ​​obtained by gel permeation chromatography using N,N-dimethylacetamide as a solvent after dissolving cellulose nanofibers in N,N-dimethylacetamide with added lithium chloride.

[0117] Cellulose nanofibers may contain alkali-soluble polysaccharides, including not only hemicellulose but also β-cellulose and γ-cellulose. Alkali-soluble polysaccharides, as understood by those skilled in the art, refer to the alkali-soluble components obtained from whole cellulose (i.e., the components obtained by removing α-cellulose from whole cellulose) through solvent extraction and chlorination of plants (e.g., wood). Alkali-soluble polysaccharides are polysaccharides containing hydroxyl groups, exhibiting poor heat resistance, which may lead to decomposition upon heating, yellowing during heat aging, and reduced strength of cellulose nanofibers. Therefore, it is preferable that cellulose nanofibers contain a low content of alkali-soluble polysaccharides.

[0118] In one embodiment, from the viewpoint of obtaining good dispersibility of cellulose nanofibers, the average content of alkali-soluble polysaccharides in the cellulose nanofibers is preferably 20% by mass or less, or 18% by mass or less, or 15% by mass or less, or 12% by mass or less relative to 100% by mass of cellulose nanofibers. From the viewpoint of ease of manufacturing cellulose nanofibers, the above-mentioned content can be 1% by mass or more, or 2% by mass or more, or 3% by mass or more.

[0119] The average content of alkali-soluble polysaccharides can be determined using a method described in non-patent literature (Handbook of Wood Science Experiments, edited by the Japan Wood Science Society, pp. 92-97, 2000), by subtracting the α-cellulose content from the total cellulose content (Wise method). Furthermore, this method is understood in the art as a method for determining hemicellulose content. The alkali-soluble polysaccharide content is calculated three times for each sample, and the mean of the calculated alkali-soluble polysaccharide content is taken as the average alkali-soluble polysaccharide content.

[0120] In one approach, from the viewpoint of avoiding a decrease in the heat resistance of cellulose nanofibers and the associated discoloration, 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 ease of manufacturing cellulose nanofibers, the above-mentioned content can be 0.1% by mass or more, or 0.2% by mass or more, or 0.3% by mass or more.

[0121] The average content of acid-insoluble components was determined using the Claessen method described in non-patent literature (Handbook of Wood Science Experiments, edited by the Japan Wood Science Society, pp. 92-97, 2000). It should be noted that this method is understood in the art as a method for determining lignin content. After stirring the sample in sulfuric acid solution to dissolve cellulose and hemicellulose, it was filtered through glass fiber filter paper, and the resulting residue represented the acid-insoluble components. The content of acid-insoluble components was calculated from the weight of these components. Then, the content of acid-insoluble components was measured three times for each sample, and the average of these measurements was taken as the average content of acid-insoluble components.

[0122] [Chemical modification]

[0123] Cellulose nanofibers can be chemically modified cellulose nanofibers (also known as chemically modified cellulose nanofibers). Examples of chemically modified cellulose nanofibers include inorganic esters such as nitrates, sulfates, phosphates, silicates, and borates; organic esters such as acetylation and propionylation; ethers such as methyl ethers, hydroxyethyl ethers, hydroxypropyl ethers, hydroxybutyl ethers, carboxymethyl ethers, and cyanoethyl ethers; and TEMPO oxides formed by oxidizing the primary hydroxyl groups of cellulose. Chemically modified cellulose nanofibers can contain one or more modifying groups.

[0124] In a preferred embodiment, the chemical modification is acylation using an esterifying agent, particularly acetylation. As esterifying agents, acid halides, acid anhydrides, vinyl carboxylate, and carboxylic acids are preferred. From the viewpoint of reaction efficiency, at least one of the following groups is particularly preferred among acetic anhydride, propionic anhydride, butyric anhydride, vinyl acetate, vinyl propionate, butyric anhydride, and acetic acid, with acetic anhydride and vinyl acetate being preferred. Cellulose nanofibers can be chemically modified using a modifying agent at, for example, the stage of cellulose fiber raw material, during or after defibrillation, or during or after the preparation of a slurry as a dispersion, or during or after a drying process.

[0125] [Degree of acyl substitution (DS)]

[0126] When cellulose nanofibers are chemically modified (e.g., through hydrophobication such as acylation), they tend to exhibit good dispersibility in rubber. On the other hand, when combined with a dispersant, even if the cellulose nanofibers are unsubstituted or have a low degree of substitution, they readily exhibit good dispersibility in rubber. When the cellulose nanofibers are esterified cellulose nanofibers, from the perspective of obtaining esterified cellulose nanofibers with high thermal decomposition initiation temperatures, 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. From the perspective of obtaining esterified cellulose nanofibers that possess both high tensile strength and dimensional stability derived from cellulose and high thermal decomposition initiation temperatures derived from chemical modification due to the presence of unmodified cellulose backbone in the esterified cellulose nanofibers, the 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.

[0127] The degree of acyl substitution (DS) of chemically modified cellulose nanofibers, where the modifying group is an acyl group, can be calculated based on the reflectance infrared absorption spectrum of esterified cellulose nanofibers, using the peak intensity ratio between the peaks originating from the acyl group and those originating from the cellulose backbone. The absorption band of the C=O group based on the acyl group appears at 1730 cm⁻¹. -1 The CO absorption band based on the cellulose backbone chain shows a peak at 1030 cm⁻¹. -1 Regarding the DS of esterified cellulose nanofibers, a correlation graph was prepared between the DS obtained from solid-state NMR measurements of the esterified cellulose nanofibers (described later) and the modification rate (IR index 1030), defined as the ratio of the peak intensity of the absorption band of acyl-based C=O to the peak intensity of the absorption band of the CO backbone chain of cellulose. A standard curve was calculated from the correlation graph.

[0128] It can be calculated using the degree of substitution DS = 4.13 × IR index (1030).

[0129] IR index (1030) = H1730 / H1030

[0130] In the formula, H1730 and H1030 are 1730 cm. -1 1030cm -1 The absorbance at the absorption band of the CO stretching vibration of the cellulose backbone chain. Here, refers to the absorbance at 1900 cm⁻¹. -1 and 1500cm -1 The line and connection 800cm -1 and 1500cm -1 The line is used as the baseline, and the absorbance at which the absorbance is 0 is set.

[0131] The DS of esterified cellulose nanofibers based on solid-state NMR can be calculated as follows: The DS of the cryogenically pulverized esterified cellulose nanofibers is calculated... 13 The area intensity (Inf) of the signal attributable to a single carbon atom originating from a modifying group is determined by the following formula relative to the total area intensity (Inp) of the signal attributable to carbons C1 to C6 of the pyranose ring derived from cellulose appearing in the range of 50 ppm to 110 ppm.

[0132] DS = (Inf) × 6 / (Inp)

[0133] For example, when the modifying group is acetyl, a signal of 23 ppm belonging to -CH3 can be used.

[0134] Used 13 The conditions for C solid-state NMR measurements are as follows.

[0135] Device: Bruker Biospin Avance500WB

[0136] Frequency: 125.77MHz

[0137] Determination method: DD / MAS method

[0138] Waiting time: 75 seconds

[0139] NMR sample tube: 4mm Φ

[0140] Total number of times: 640 (approximately 14 hours)

[0141] MAS: 14,500Hz

[0142] Chemical shift reference: glycine (external reference: 176.03 ppm)

[0143] From the perspective of achieving the desired heat resistance and mechanical strength for applications such as automotive, the thermal decomposition initiation temperature (T0) of cellulose nanofibers is... D In one embodiment, the preferred temperatures are 200°C or higher, or 210°C or higher, or 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. Higher thermal decomposition initiation temperatures are preferred. From the viewpoint of ease of manufacturing cellulose nanofibers, temperatures can be, for example, below 320°C, or below 310°C, or below 300°C.

[0144] [Temperature at 1% weight loss (T)] 1% ), weight loss rate at 250℃ (T 250℃ )]

[0145] From the perspective of avoiding thermal degradation during melt mixing and maintaining mechanical strength, in one approach, the temperature at which 1 wt% weight of cellulose nanofibers decreases (T) is... 1% The preferred temperatures are above 230°C, or above 240°C, or above 250°C, or above 260°C, or above 270°C, or above 275°C, or above 280°C, or above 285°C, or above 290°C. 1% The higher the temperature, the better. From the perspective of ease of manufacturing cellulose nanofibers, the temperature can be, for example, below 330°C, below 320°C, or below 310°C.

[0146] From the perspective of avoiding thermal degradation during melt mixing and maintaining mechanical strength, in one approach, the weight loss rate (T) of cellulose nanofibers at 250°C is... 250℃ The preferred percentages are below 15%, below 12%, below 10%, below 8%, below 6%, below 5%, below 4%, or below 3%. 250℃ The lower the better, but from the viewpoint of ease of manufacturing cellulose nanofibers, it can be, for example, 0.1% or more, or 0.5% or more, or 0.7% or more, or 1.0% or more.

[0147] In this disclosure, T D The values ​​were derived from a thermogravimetric (TG) analysis chart where the horizontal axis represents temperature and the vertical axis represents the percentage of weight remaining. Starting with the weight of cellulose nanofibers at 150°C (with almost all moisture removed) (weight loss of 0 wt%), the temperature was further increased to obtain the temperature at which a 1 wt% weight loss was achieved (T). 1% ) and the temperature at which a 2wt% weight loss occurs (T) 2% The straight line. The temperature at the point where this straight line intersects the horizontal line (baseline) passing through the starting point of 0 wt% weight reduction is defined as T. D .

[0148] 1% weight reduction temperature (T) 1% ) is based on the above T D The method is to continuously increase the temperature at which 1% of the weight is reduced, starting from 150°C.

[0149] Weight loss rate of cellulose nanofibers at 250°C (T 250℃The weight loss of cellulose nanofibers after being held at 250°C under a nitrogen flow for 2 hours, as determined by TG analysis, is shown. Porous sheets of cellulose nanofibers were heated from room temperature to 150°C in a nitrogen flow at a rate of 10°C / min (100 ml / min), held at 150°C for 1 hour, and then heated from 150°C to 250°C at a rate of 10°C / min, held directly at 250°C for 2 hours. The weight W0 at the moment of reaching 250°C is taken as the starting point, and the weight after holding at 250°C for 2 hours is set as W1, calculated using the following formula.

[0150] Weight change rate at 250℃ (%): (W1-W0) / W0×100

[0151] [Porous sheet]

[0152] Various physical properties of cellulose nanofibers (specific surface area, crystallinity, crystal polymorphism, degree of polymerization, Mw, Mn, Mw / Mn, alkali-soluble content, average acid-insoluble content, T) D T 1% T 250℃ In measurements of (etc.), the values ​​sometimes vary significantly depending on the morphology of the sample. To ensure stable and reproducible measurements, porous sheets without deformation are used for the samples. The method for preparing porous sheets is described below.

[0153] First, a concentrated filter cake containing cellulose nanofibers with a solid content of 10% by mass or more and water as the liquid medium was added to tert-butanol. The mixture was then further dispersed using a mixer (e.g., a high-shear homogenizer, such as an IKA-manufactured ULTRA-TURRAX T18, processing conditions: 15,000 rpm × 3 minutes) until no aggregates were found. The concentration was adjusted to 0.5% by mass for a solid content of 0.5 g of cellulose nanofibers. 100 g of the resulting tert-butanol dispersion was filtered onto filter paper. Instead of peeling the filter paper off, the filter cake was sandwiched between two larger sheets of filter paper, and the edges of the larger sheets were pressed down with a weight while drying in an oven at 150°C for 5 minutes. The filter paper was then peeled off, yielding a porous sheet with minimal deformation. The air permeability R of this sheet was measured to be within 10 g / m². 2 Sheets with a unit area weight of less than 100 sec / 100 ml are classified as porous sheets and used as test samples.

[0154] The air permeability resistance R was determined as follows: the weight per unit area W (g / m²) of the porous sheet sample that had been left to stand for one day at 23℃ and 50%RH was measured. 2Afterwards, the air permeability resistance R (sec / 100ml) is measured using a Wangyan-type air permeability resistance tester (e.g., Asahi Seiko Co., Ltd., model EG01). Then, the air permeability resistance per 10g / m³ is calculated using the following formula. 2 The weight per unit area.

[0155] per 10g / m 2 Air permeability resistance per unit area (sec / 100ml) = R / W × 10

[0156] 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, crystal polymorphism, degree of polymerization, Mw, Mn, Mw / Mn, alkali-soluble component content, average acid-insoluble component content, T) D T 1% T 250℃ (DS, etc.) are analyzed using the following methods.

[0157] The polymer component is dissolved in an organic or inorganic solvent capable of dissolving polymer components contained in rubber compositions and rubber composites. Cellulose nanofibers are then separated, thoroughly washed with the solvent, and the solvent is replaced with tert-butanol. The tert-butanol slurry containing cellulose nanofibers is then analyzed using the same analytical method as described above to calculate various physical properties of the cellulose nanofibers in the rubber composition and rubber composite.

[0158] In one embodiment, cellulose nanofibers can be provided in the form of a slurry containing a liquid medium, or in the form of dried particles, membranes, or blocks. Examples of liquid media include water and / or organic solvents with boiling points, and one or more media may be included. The liquid medium content in the slurry form is 50% by mass or more, while the liquid medium content in the dried form is less than 50% by mass. The liquid medium content is measured using an infrared heating moisture meter (e.g., A&D Corporation, trade name "MX-50") after heating at 180°C.

[0159] <First Rubber and Second Rubber>

[0160] In one embodiment, the first rubber is an unmodified liquid rubber, and the second rubber is a modified liquid rubber. According to this disclosure, liquid rubber refers to a substance that is fluid at 23°C and forms a rubber elastomer through crosslinking (more specifically, vulcanization) and / or chain elongation. That is, in one embodiment, the liquid rubber is an uncured substance. Furthermore, being fluid means that, in one embodiment, by placing liquid rubber dissolved in cyclohexane into a vial with a main diameter of 21 mm × a total length of 50 mm at 23°C and allowing it to dry, thereby filling the vial to a height of 1 mm and sealing it, and then allowing it to stand for 24 hours with the vial inverted, movement of material at a height of 0.1 mm or more can be confirmed. The liquid rubber can have a typical rubber monomer composition, and from the viewpoint of ease of handling and obtaining good dispersibility of cellulose nanofibers, a lower molecular weight is preferred. In one embodiment, the liquid rubber is in liquid form by having a number average molecular weight (Mn) of 150,000 or less. It should be noted that, in this disclosure, the molecular weight and molecular weight distribution of the rubber component are values ​​obtained by determining the chromatogram using gel permeation chromatography with three columns connected together using polystyrene-based gel as the packing material, and calculated using a standard curve with standard polystyrene. Additionally, tetrahydrofuran is used as the solvent.

[0161] When a rubber composition is cured to produce a cured rubber product, from the viewpoint of improving the mechanical properties of the cured rubber product, it is preferable that the liquid rubber is vulcanized during curing. Alternatively, the liquid rubber may also be cured by heat or the like.

[0162] From the viewpoint of obtaining good mechanical properties of the rubber composition, rubber complex, or rubber cured product, 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 flowability and obtaining a rubber cured product that does not become too hard and has good rubber elasticity, it is preferably 150,000 or less, or 145,000 or less, or 140,000 or less.

[0163] From the viewpoint of obtaining good mechanical properties of the rubber composition, rubber complex, or rubber cured product, 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 flowability and obtaining a rubber cured product that does not become too hard and has good rubber elasticity, it is preferably 100,000 or less, or 90,000 or less, or 80,000 or less.

[0164] From the viewpoint of fluidity and to obtain a cured rubber that does not become too hard and has good rubber elasticity, 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 obtaining good mechanical properties of the rubber composition, rubber complex or cured rubber, it is preferably 5,000 mPa·s or more, or 8,000 mPa·s or more, or 10,000 mPa·s or more.

[0165] From the viewpoint of fluidity and to obtain a cured rubber that does not become too hard and has good rubber elasticity, 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 obtaining good mechanical properties of the rubber composition, rubber complex or cured rubber, it is preferably 100,000 mPa·s or more, or 120,000 mPa·s or more, or 140,000 mPa·s or more.

[0166] It should be noted that, in this disclosure, viscosity is a value measured using a type B viscometer.

[0167] From the viewpoint that the first rubber can easily penetrate between the second rubbers or between the second rubber and cellulose nanofibers, at 38°C, the ratio of the viscosity η2 of the second rubber to the viscosity η1 of the first rubber, η2 / η1, is preferably 1.2 or more, or 1.3 or more, or 1.4 or more. From the viewpoint of obtaining good affinity between the first rubber and the second rubber, it is preferably 160 or less, or 140 or less, or 120 or less.

[0168] The liquid rubber can be a conjugated diene polymer, a non-conjugated diene polymer, or their hydrides. The aforementioned polymers or their hydrides can be oligomers.

[0169] [Conjugated diene polymers]

[0170] Conjugated diene polymers can be homopolymers, copolymers of two or more conjugated diene monomers, or copolymers of conjugated diene monomers with other monomers. Copolymers can be random or block copolymers.

[0171] Examples of conjugated diene monomers 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, which can be used alone or in combination of two or more.

[0172] In one embodiment, the conjugated diene polymer is a copolymer of the aforementioned conjugated diene monomer and an aromatic vinyl monomer.

[0173] As an aromatic vinyl monomer, there are no particular limitations on any monomer that can copolymerize with a conjugated diene monomer. Examples include styrene, m-methylstyrene or p-methylstyrene, α-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinylethylbenzene, vinylxylene, vinylnaphthalene, diphenylethylene, and divinylbenzene. These can be used alone or in combination of two or more. From the viewpoint of the processability of the rubber composition and the impact resistance of the molded article, styrene is preferred.

[0174] Examples of random copolymers include butadiene-isoprene random copolymers, butadiene-styrene random copolymers, isoprene-styrene random copolymers, and butadiene-isoprene-styrene random copolymers. Regarding the compositional distribution of monomers within the copolymer chain, examples include completely random copolymers with near-statistically random compositions and gradient random copolymers with a progressively changing compositional distribution. The bonding modes of conjugated diene polymers, i.e., 1,4-bonds, 1,2-bonds, etc., can be uniform or different between molecules.

[0175] Block copolymers can be copolymers composed of two or more blocks. For example, they can be block copolymers with structures such as AB, ABA, ABAB, etc., formed by blocks A (aromatic vinyl monomers) and B (conjugated diene monomers) and / or blocks B (polymers of aromatic vinyl monomers and conjugated diene monomers). It should be noted that the boundaries between the blocks do not necessarily need to be clearly defined. For example, when block B is a copolymer of aromatic vinyl monomers and conjugated diene monomers, the aromatic vinyl monomers in block B can be uniformly or progressively distributed. Furthermore, block B can contain portions with uniformly distributed aromatic vinyl monomers and / or portions with progressively distributed aromatic vinyl monomers. Moreover, block B can contain segments with different amounts of aromatic vinyl monomers. When multiple blocks A and blocks B exist in the copolymer, their molecular weights and compositions can be the same or different.

[0176] Block copolymers can be mixtures of two or more different types of compounds, including but not limited to one type of bonding form, molecular weight, type of aromatic vinyl compound, type of conjugated diene compound, 1,2-vinyl content or the combined content of 1,2-vinyl and 3,4-vinyl, aromatic vinyl compound content, and hydrogenation rate.

[0177] The amount of vinyl bonds (e.g., 1,2- or 3,4- bonds of butadiene) in the conjugated diene polymer is preferably 5 mol% or more, or 10 mol% or more, or 13 mol% or more, or 15 mol% or more, 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.

[0178] The amount of vinyl bonds in the conjugated diene unit (e.g., the 1,2-bond amount in butadiene) can be determined by... 13 The result is obtained using C-NMR (quantitative model). That is, if... 13 By integrating the peak areas that appear in the following C-NMR, we can obtain a value proportional to the carbon content of each structural unit, and the result can be converted into the mass of each structural unit.

[0179] Styrene 145~147ppm

[0180] Vinyl 110~116ppm

[0181] Diene (cis) 24-28 ppm

[0182] Diene (trans) 29-33 ppm

[0183] In copolymers of conjugated diene monomers and aromatic vinyl monomers, the amount of aromatic vinyl monomers bonded to the conjugated diene monomers (also referred to herein as aromatic vinyl bonding amount) is preferably 5.0% to 70% by mass or 10% to 50% by mass relative to the total mass of the conjugated diene polymer. The aromatic vinyl bonding amount can be determined by the ultraviolet absorbance of the phenyl group, and the conjugated diene bonding amount can also be determined based on this.

[0184] Conjugated diene polymers can be partially or fully hydrogenated. From the viewpoint of suppressing thermal degradation during processing, the hydrogenation rate of the hydride is preferably 50% or more, or 80% or more, or 98% or more; from the viewpoint of low-temperature toughness, it is preferably 50% or less, or 20% or less, or 0% (i.e., non-hydrogenated). Examples of hydrides of conjugated diene polymers include those exemplified above, such as butadiene homopolymers, isoprene homopolymers, styrene-butadiene copolymers, and acrylonitrile-butadiene copolymers.

[0185] [Non-conjugated diene polymers]

[0186] Non-conjugated diene polymers can be homopolymers, or copolymers of two or more non-conjugated diene monomers, or copolymers of non-conjugated diene monomers with other monomers. Copolymers can be random or block copolymers. Examples of non-conjugated diene polymers include olefin polymers such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-butene-diene rubber, and ethylene-α-olefin copolymers; 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.

[0187] In ethylene-α-olefin copolymers, monomers capable of copolymerizing with ethylene units include: aliphatic substituted vinyl monomers such as propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, hepten-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecanene-1, eicosene-1, and isobutylene; aromatic vinyl monomers such as styrene and substituted styrene; ester vinyl monomers such as vinyl acetate, acrylate, methacrylate, glycidyl acrylate, glycidyl methacrylate, and hydroxyethyl methacrylate; nitrogen-containing vinyl monomers such as acrylamide, allylamine, vinyl-p-aminobenzene, and acrylonitrile; dienes such as butadiene, cyclopentadiene, 1,4-hexadiene, and isoprene; and so on.

[0188] The copolymer of ethylene with one or more α-olefins having 3 to 20 carbon atoms is preferred, more preferably a copolymer of ethylene with one or more α-olefins having 3 to 16 carbon atoms, and most preferably a copolymer of ethylene with one or more α-olefins having 3 to 12 carbon atoms. Furthermore, 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, even more preferably 10,000 to 80,000, and even more preferably 20,000 to 60,000. Additionally, from the viewpoint of balancing flowability 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.

[0189] Furthermore, from the viewpoint of operability during processing, the preferred content of ethylene units in the ethylene-α-olefin copolymer is 30 to 95% by mass relative to the total amount of the ethylene-α-olefin copolymer.

[0190] These preferred ethylene-α-olefin copolymers can be manufactured, for example, by the manufacturing methods described in Japanese Patent Application Publication No. 4-12283, Japanese Patent Application Publication No. 60-35006, Japanese Patent Application Publication No. 60-35007, Japanese Patent Application Publication No. 60-35008, Japanese Patent Application Publication No. 5-155930, Japanese Patent Application Publication No. 3-163088, and US Patent No. 5272236.

[0191] The liquid rubber is preferably selected from one or more of the group consisting of styrene-butadiene rubber, natural rubber, butadiene rubber, farnesene rubber, and isoprene rubber.

[0192] Preferred examples of the unmodified liquid rubber as the first rubber are the polymers illustrated above. On the other hand, the modified liquid rubber as the second rubber may have a structure in which at least one modifying group has been introduced into each of the polymers illustrated above. The modifying group may be one or more selected from epoxy, anhydride, carboxyl, aldehyde, hydroxyl, alkoxy, amino, amide, imide, nitro, isocyanate, thio, and mercapto groups. Preferably, the modifying group is one or more selected from the group consisting of maleic anhydride and succinic anhydride, or is maleic anhydride. Examples of modified liquid rubbers include epoxy-modified natural rubber, epoxy-modified butadiene rubber, epoxy-modified styrene-butadiene rubber, epoxy-modified isoprene rubber, carboxyl-modified natural rubber, carboxyl-modified butadiene rubber, carboxyl-modified styrene-butadiene rubber, carboxyl-modified isoprene rubber, anhydride-modified natural rubber, anhydride-modified butadiene rubber, anhydride-modified styrene-butadiene rubber, and anhydride-modified isoprene rubber.

[0193] Modified liquid rubbers can have reactive groups at both ends (e.g., selected from the group consisting of hydroxyl, carboxyl, isocyanate, thio, amino, and halogen groups), thus enabling them to be bifunctional. These reactive groups contribute to the crosslinking and / or chain elongation of the modified liquid rubber.

[0194] In modified liquid rubber, from the perspective of good affinity between cellulose nanofibers and modified liquid rubber, resulting in good dispersion and orientation of cellulose nanofibers, 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. On the other hand, if the amount of modifying groups is too large, the modified liquid rubber forms a dense structure with each other or with cellulose nanofibers, which tends to reduce the dispersion and orientation of cellulose nanofibers. In order to impart the desired mechanical properties and surface smoothness to the cured rubber, it is preferable to suppress the formation of such a dense structure. From the above viewpoint, 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 above-mentioned amount of modifying groups can be confirmed by infrared absorption spectroscopy, solid-state NMR (nuclear magnetic resonance), solution NMR, or by calculating the molar ratio of modifying groups by quantitatively combining a predetermined monomer composition with elements not included in the unmodified rubber based on elemental analysis.

[0195] From the perspective of good affinity between cellulose nanofibers and modified liquid rubber, resulting in good dispersibility and orientation of cellulose nanofibers, the content of modified groups in 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 suppressing the formation of the aforementioned dense structure, it is preferably 20% by mass or less, or 15% by mass or less, or 10% by mass or less. This content of modified groups can be confirmed by NMR in one embodiment.

[0196] There are no particular limitations on the means of manufacturing modified liquid rubber; for example, the method described in Japanese Patent Application Publication No. 2016-172859 can be used.

[0197] In one approach, the modifying groups of the modified liquid rubber can form covalent bonds with cellulose nanofibers and / or rubber during the manufacture of the rubber composition, rubber composite, or cured rubber, particularly during heat mixing. Covalent bonds are advantageous in further enhancing the reinforcing effect of the cellulose nanofibers. In one approach, covalent bonds between the modified liquid rubber and cellulose nanofibers can be formed during the manufacture of the rubber composition or rubber composite, and covalent bonds between the modified liquid rubber and a third and / or fourth rubber, either directly or via other components (in one approach, a vulcanizing agent), can be formed during the manufacture of the cured rubber (i.e., during curing).

[0198] From the viewpoint of improving the mechanical properties of cured rubber, the first and / or second rubbers can be covalently bonded to the rubber (specifically the third and / or fourth rubbers) during the curing of the rubber composition by means of a vulcanizing agent.

[0199] In one approach, the presence of covalent bonds can be confirmed by the following methods: In rubber compositions or rubber composites, for residues obtained after removing rubber with a solvent (e.g., hexane or cyclohexane), analysis is performed using nuclear magnetic resonance (NMR) or infrared absorption spectroscopy. In cured rubber, analysis is performed using electron microscopy or atomic force microscopy (AFM). For the presence of rubber bonded to cellulose nanofibers, as a phase present near the cellulose nanofibers (in one approach, as a region in the cured rubber that differs from the third and / or fourth rubber), analysis is performed using NMR, infrared absorption spectroscopy, or Nano-IR.

[0200] From the perspective of achieving good dispersibility and orientation of cellulose nanofibers through good affinity with them, the first rubber preferably contains aromatic vinyl monomer units.

[0201] From the viewpoint of miscibility with the third and / or fourth rubbers and affinity with cellulose nanofibers, the second rubber is preferably maleic anhydride-modified liquid polyisoprene.

[0202] In the rubber composition, from the viewpoint of obtaining the advantages of the first rubber well, the amount of the first rubber is preferably 5 parts by mass or more, or 10 parts by mass or more, or 15 parts by mass or more, relative to 100 parts by mass of the second rubber, and from the viewpoint of not hindering the advantages of the second rubber, it is preferably 300 parts by mass or less, or 280 parts by mass or less, or 260 parts by mass or less.

[0203] In the rubber composition, from the viewpoint of obtaining the advantages of the first rubber, the amount of the first rubber is preferably 5 parts by mass or more, or 10 parts by mass or more, or 15 parts by mass or more, relative to 100 parts by mass of cellulose nanofibers. From the viewpoint of maintaining the mechanical properties of the molded article well, it is preferably 100 parts by mass or less, or 90 parts by mass or less, or 80 parts by mass or less.

[0204] In the rubber composition, from the viewpoint of obtaining the advantages of the second rubber, the amount of the second rubber is preferably 10 parts by mass or more, or 15 parts by mass or more, or 20 parts by mass or more, relative to 100 parts by mass of cellulose nanofibers. From the viewpoint of suppressing excessive binding or interaction between the second rubbers or between the second rubbers and cellulose nanofibers, it is preferably 300 parts by mass or less, or 280 parts by mass or less, or 260 parts by mass or less.

[0205] From the viewpoint of obtaining the advantages of the second rubber 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 suppressing excessive binding or interaction between the second rubbers or between the second rubbers and cellulose nanofibers, it is preferably 60% by mass or less, or 55% by mass or less, or 50% by mass or less.

[0206] In the rubber composition, from the viewpoint of achieving good dispersibility and orientation of cellulose nanofibers, the combined 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, and from the viewpoint of achieving good reinforcing effect by having cellulose nanofibers present in a desired amount, it is preferably 90% by mass or less, or 85% by mass or less, or 80% by mass or less.

[0207] <Dispersant>

[0208] In one embodiment, the rubber composition includes a dispersant. In another embodiment, from the viewpoint of dispersing the cellulose nanofibers more uniformly in the rubber composition, it is further preferred that the dispersant has both hydrophilic and hydrophobic segments (i.e., amphiphilic molecules) within the same molecule.

[0209] [Amphiphilic molecules]

[0210] In amphiphilic molecules, the hydrophilic segment exhibits good affinity for cellulose nanofibers by containing a hydrophilic structure. Specifically, the hydrophilic structure includes groups such as hydroxyl, thiol, carboxyl, sulfonic acid, sulfate, phosphate, borate, silanol, groups derived from sugars such as sorbitan anhydride and sucrose, groups derived from glycerol, groups represented by -OM, -COOM, -SO3M, -OSO3M, -HMPO4, and -M2PO4 (where M represents an alkali metal or alkaline earth metal), as well as primary to tertiary amines and quaternary ammonium salts. As counter anions for the aforementioned quaternary ammonium salts, examples include halide ions selected from groups consisting of hydroxide ions, fluoride ions, chloride ions, bromide ions, iodide ions, nitrate ions, formate ions, acetate ions, trifluoroacetate ions, p-toluenesulfonate ions, hexafluorophosphate ions, and tetrafluoroborate ions, containing one or more hydrophilic groups.

[0211] Examples of hydrophilic segments include segments of polyethylene glycol, segments containing repeating units with quaternary ammonium salt structures, segments of polyvinyl alcohol, segments of polyvinylpyrrolidone, segments of polyacrylic acid, segments of carboxyvinyl polymers, segments of cationic guar gum, segments of hydroxyethyl cellulose, segments of methyl cellulose, segments of carboxymethyl cellulose, and soft segments of polyurethane (specifically, glycol segments). Nonionic polyoxyethylene derivatives are particularly preferred, and the polyoxyethylene chain length of the polyoxyethylene derivative can be 3 or more, or 5 or more, or 10 or more, or 15 or more. The longer the chain length, the higher the affinity for cellulose nanofibers; however, from the viewpoint of balancing with the desired properties (e.g., mechanical properties) of the resin molded body, the polyoxyethylene chain length can be 60 or less, or 50 or less, or 40 or less, or 30 or less, or 20 or less.

[0212] Examples of hydrophobic segments include segments containing hydrocarbons, segments containing fluorinated carbon, segments containing alkyl epoxide units with 3 or more carbon atoms (e.g., PPG blocks), and segments containing polymer structures.

[0213] As the hydrocarbon segment, alkyl, alkenyl, alkyl ether, alkenyl ether, alkylphenyl ether, alkenylphenyl ether, rosin ester, bisphenol A, β-naphthyl, styrenated phenyl, and hydrogenated castor oil types are preferred. The number of carbon atoms in the hydrophobic alkyl or alkenyl chain (in the case of alkylphenyl or alkenylphenyl, the number of carbon atoms after removing the phenyl group) is preferably 2 or more, 5 or more, 10 or more, 12 or more, or 16 or more.

[0214] As for the segments containing fluorinated carbon, linear or branched alkyl types with 1 to 20 carbon atoms are preferred.

[0215] Preferred polymer segments include acrylic polymers, styrene resins, vinyl chloride resins, vinylidene chloride resins, polyolefin resins, amino acid lactams of ring-opening polymers containing lactams, polymers composed of diamines and dicarboxylic acids, polyacetal resins, polycarbonate resins, polyester resins, polyphenylene sulfide resins, polysulfone resins, polyetherketone resins, polyimide resins, fluorine resins, hydrophobic silicone resins, melamine resins, epoxy resins, and phenolic resins.

[0216] These hydrophobic segments can be either straight-chain or branched-chain structures. Furthermore, the hydrophobic segments can be one chain or two or more chain structures; when they are two or more chain structures, they can possess a variety of hydrophobic groups.

[0217] There are no particular restrictions on the structure of amphiphilic molecules. When the hydrophilic segment is designated as A and the hydrophobic segment as B, examples of linear copolymers such as AB-type block copolymers, AB-A-type block copolymers, and BAB-type block copolymers can be given, as well as 3-branched copolymers containing A and B, 4-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 can be given.

[0218] When a molecule contains multiple hydrophilic segments, its molecular structure can be a single type or a combination of two or more types. Similarly, when a molecule contains multiple hydrophobic segments, its molecular structure can be a single type or a combination of two or more types.

[0219] (surfactant)

[0220] As an amphiphilic molecule, it can be any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. The dispersant can be a polymeric surfactant, a reactive surfactant, etc.

[0221] Examples of nonionic surfactants include: fatty acid dialkylolamides (e.g., lauric acid diethanolamide), polyoxyethylene fatty acid amides (e.g., polyoxyethylene stearamide), polyoxyethylene aryl ethers (e.g., polyoxyethylene phenyl ether), polyoxyethylene alkyl aryl ethers (e.g., polyoxyethylene octylphenyl ether), polyoxyethylene alkyl or alkenyl ethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene stearyl ether), fatty acid esters of polyols (e.g., polyethylene glycol mono- or distearate, polyethylene glycol mono- or dilaurate, polyoxyethylene hydrogenated castor oil), glycerol fatty acid esters (e.g., glyceryl monostearate, glyceryl monooleate), sorbitol fatty acid esters (e.g., sorbitol monolaurate, sorbitol monostearate), polyoxyethylene-polyoxypropylene block polymers, etc.

[0222] Anionic surfactants (emulsifiers) can be carboxylates, sulfonates, sulfates, phosphates, etc. For example, carboxylates can include aliphatic monocarboxylic acids and alkyl ether carboxylates; sulfonates can include dialkyl sulfosuccinates, alkane sulfonates, alkylbenzene sulfonates, and alkylnaphthalene sulfonates; sulfates can include alkyl sulfates and oil sulfates; and phosphates can include alkyl phosphates and polyoxyethylene alkyl ether phosphates.

[0223] Examples of cationic surfactants include amine salts, amide amine salts, quaternary ammonium salts, and imidazoline salts. Specific examples, without particular limitation, include alkyl amine salts, polyoxyethylene alkyl amine salts, alkyl amide amine salts, amino alcohol fatty acid derivatives, polyamine fatty acid derivatives, imidazoline and other amine salt surfactants, alkyl trimethylammonium salts, dialkyl dimethylammonium salts, alkyl dimethyl benzylammonium salts, alkyl pyridinium salts, alkyl isoquinolineium salts, benzyl chloride and other quaternary ammonium salt surfactants.

[0224] Examples of amphoteric surfactants include alkyl amine oxides, alanine oxides, imidazoline betaines, amide betaines, and acetate betaines. More specifically, examples include long-chain amine oxides, lauryl betaine, stearyl betaine, lauryl carboxymethyl hydroxyethyl imidazoline betaine, lauryl dimethyl aminoacetic acid betaine, and fatty acid amide propyl dimethyl aminoacetic acid betaine.

[0225] [Hydrophilic polymer]

[0226] In one embodiment, the dispersant is preferably a hydrophilic polymer. In another embodiment, the hydrophilic polymer is a polymer having a hydrophilic group selected from the group consisting of hydroxyl, carboxyl, amino, ammonium, sulfonic acid, and phosphate groups. As the hydrophilic polymer, one or more can be used selected from the group consisting of cellulose derivatives (hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, etc.), polyalkylene glycols, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, carboxyvinyl polymers, cationic guar gum, water-soluble polyurethane, polymers containing quaternary ammonium salt structures, amides, and amines. Cellulose derivatives and polyalkylene glycols are more preferred, and polyalkylene glycols are particularly preferred.

[0227] The amount of dispersant in the rubber composition relative to 100 parts by weight of cellulose nanofibers is preferably 1 part by weight or more, or 3 parts by weight or more, or 5 parts by weight or more, or 10 parts by weight or more, or 15 parts by weight or more, preferably 200 parts by weight or less, or 150 parts by weight or less, or 100 parts by weight or less, or 90 parts by weight or less, or 80 parts by weight or less, or 70 parts by weight or less, or 60 parts by weight or less, or 50 parts by weight or less.

[0228] In one embodiment, the content of the dispersant in the rubber composition may be 0.1% by mass or more, or 0.5% by mass or more, or 1% by mass or more; in another embodiment, it may be 40% by mass or less, or 35% by mass or less, or 30% by mass or less.

[0229] <Third Rubber>

[0230] In one embodiment, the rubber composition further comprises a third rubber. The third rubber may be one or more selected from the group consisting of natural rubber, conjugated diene polymers, or non-conjugated diene polymers, or their hydrides. The aforementioned polymers or their hydrides may be modified rubbers or oligomers. Thermoplastic elastomers may also be exemplified as the third rubber. In one embodiment, the third rubber is not the first or second rubber of this embodiment; more specifically, it is a rubber that is not flowable at 23°C (in other words, a solid). The first and / or second rubbers and the third rubber may differ from each other (be of different types) in one or more of the following aspects: the type of constituent monomer components, the ratio of constituent monomer components, and the molecular weight.

[0231] [Natural Rubber]

[0232] As for natural rubber, there are no particular limitations. For example, from the perspective of high molecular weight components and excellent breaking strength, examples include RSS (Ribbed Smoked Sheet) Nos. 3-5, which are gas-dried; SIR (Standard Indonesian Rubber), STR (Standard Thai Rubber), and SMR (Standard Malaysian Rubber), which are mechanically dried; and epoxidized natural rubber, etc.

[0233] [Conjugated diene polymers]

[0234] Conjugated diene polymers can be homopolymers, copolymers of two or more conjugated diene monomers, or copolymers of conjugated diene monomers with other monomers. Copolymers can be random or block copolymers.

[0235] Examples of conjugated diene monomers 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, which can be used alone or in combination of two or more.

[0236] In one embodiment, the conjugated diene polymer is a copolymer of the aforementioned conjugated diene monomer and an aromatic vinyl monomer.

[0237] As an aromatic vinyl monomer, there are no particular limitations on any monomer that can copolymerize with a conjugated diene monomer. Examples include styrene, m-methylstyrene or p-methylstyrene, α-methylstyrene, ethylstyrene, p-tert-butylstyrene, vinylethylbenzene, vinylxylene, vinylnaphthalene, diphenylethylene, and divinylbenzene. These can be used alone or in combination of two or more. From the viewpoint of the processability of the rubber composite and the impact resistance of the molded article, styrene is preferred.

[0238] Examples of random copolymers include butadiene-isoprene random copolymers, butadiene-styrene random copolymers, isoprene-styrene random copolymers, and butadiene-isoprene-styrene random copolymers. Regarding the compositional distribution of monomers within the copolymer chain, examples include completely random copolymers with near-statistically random compositions and gradient random copolymers with a progressively changing compositional distribution. The bonding modes of conjugated diene polymers, i.e., 1,4-bonds, 1,2-bonds, etc., can be uniform or different between molecules.

[0239] Block copolymers can be copolymers composed of two or more blocks. For example, they can be block copolymers with structures such as AB, ABA, ABAB, etc., formed by blocks A (aromatic vinyl monomers) and B (conjugated diene monomers) and / or blocks B (polymers of aromatic vinyl monomers and conjugated diene monomers). It should be noted that the boundaries between the blocks do not necessarily need to be clearly defined. For example, when block B is a copolymer of aromatic vinyl monomers and conjugated diene monomers, the aromatic vinyl monomers in block B can be uniformly or progressively distributed. Furthermore, block B can contain portions with uniformly distributed aromatic vinyl monomers and / or portions with progressively distributed aromatic vinyl monomers. Moreover, block B can contain segments with different amounts of aromatic vinyl monomers. When multiple blocks A and blocks B exist in the copolymer, their molecular weights and compositions can be the same or different.

[0240] Block copolymers can be mixtures of two or more different types of compounds, including but not limited to one type of bonding form, molecular weight, type of aromatic vinyl compound, type of conjugated diene compound, 1,2-vinyl content or the combined content of 1,2-vinyl and 3,4-vinyl, aromatic vinyl compound content, and hydrogenation rate.

[0241] The amount of vinyl bonds (e.g., 1,2- or 3,4- bonds of butadiene) in the conjugated diene polymer is preferably 5 mol% or more, or 10 mol% or more, or 13 mol% or more, or 15 mol% or more, 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.

[0242] The amount of vinyl bonds in the conjugated diene unit (e.g., the 1,2-bond amount in butadiene) can be determined by... 13 The result is obtained using C-NMR (quantitative model). That is, if... 13 By integrating the peak areas that appear in the following C-NMR, we can obtain a value proportional to the carbon content of each structural unit, and the result can be converted into the mass of each structural unit.

[0243] Styrene 145~147ppm

[0244] Vinyl 110~116ppm

[0245] Diene (cis) 24-28 ppm

[0246] Diene (trans) 29-33 ppm

[0247] In copolymers of conjugated diene monomers and aromatic vinyl monomers, the amount of aromatic vinyl monomers bonded to the conjugated diene monomers (also referred to herein as aromatic vinyl bonding amount) is preferably 5.0% to 70% by mass or 10% to 50% by mass relative to the total mass of the conjugated diene polymer. The aromatic vinyl bonding amount can be determined by the ultraviolet absorbance of the phenyl group, and the conjugated diene bonding amount can also be determined based on this.

[0248] Conjugated diene polymers can be partially or fully hydrogenated. From the viewpoint of suppressing thermal degradation during processing, the hydrogenation rate of the hydride is preferably 50% or more, or 80% or more, or 98% or more; from the viewpoint of low-temperature toughness, it is preferably 50% or less, or 20% or less, or 0% (i.e., non-hydrogenated). Examples of hydrides of conjugated diene polymers include those exemplified above, such as butadiene homopolymers, isoprene homopolymers, styrene-butadiene copolymers, and acrylonitrile-butadiene copolymers.

[0249] [Non-conjugated diene polymers]

[0250] Non-conjugated diene polymers can be homopolymers, or copolymers of two or more non-conjugated diene monomers, or copolymers of non-conjugated diene monomers with other monomers. Copolymers can be random or block copolymers. Examples of non-conjugated diene polymers include olefin polymers such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-butene-diene rubber, and ethylene-α-olefin copolymers; 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.

[0251] In ethylene-α-olefin copolymers, monomers capable of copolymerizing with ethylene units include: aliphatic substituted vinyl monomers such as propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, hepten-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecanene-1, eicosene-1, and isobutylene; aromatic vinyl monomers such as styrene and substituted styrene; ester vinyl monomers such as vinyl acetate, acrylate, methacrylate, glycidyl acrylate, glycidyl methacrylate, and hydroxyethyl methacrylate; nitrogen-containing vinyl monomers such as acrylamide, allylamine, vinyl-p-aminobenzene, and acrylonitrile; dienes such as butadiene, cyclopentadiene, 1,4-hexadiene, and isoprene; and so on.

[0252] The copolymer of ethylene with one or more α-olefins having 3 to 20 carbon atoms is preferred, more preferably a copolymer of ethylene with one or more α-olefins having 3 to 16 carbon atoms, and most preferably a copolymer of ethylene with one or more α-olefins having 3 to 12 carbon atoms. Furthermore, 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, even more preferably 10,000 to 80,000, and even more preferably 20,000 to 60,000. Additionally, from the viewpoint of balancing flowability 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.

[0253] Furthermore, from the viewpoint of operability during processing, the preferred content of ethylene units in the ethylene-α-olefin copolymer is 30 to 95% by mass relative to the total amount of the ethylene-α-olefin copolymer.

[0254] These preferred ethylene-α-olefin copolymers can be manufactured, for example, by the manufacturing methods described in Japanese Patent Application Publication No. 4-12283, Japanese Patent Application Publication No. 60-35006, Japanese Patent Application Publication No. 60-35007, Japanese Patent Application Publication No. 60-35008, Japanese Patent Application Publication No. 5-155930, Japanese Patent Application Publication No. 3-163088, and US Patent No. 5272236.

[0255] Modified rubber

[0256] The third type of rubber can be a modified rubber. For example, in the conjugated diene polymers or non-conjugated diene polymers exemplified above, modifying groups such as epoxy groups, acid anhydride groups, carboxyl groups, aldehyde groups, hydroxyl groups, alkoxy groups, amino groups, amide groups, imide groups, nitro groups, isocyanate groups, and mercapto groups can be introduced. Examples of modified rubbers include epoxy-modified natural rubber, epoxy-modified butadiene rubber, epoxy-modified styrene-butadiene rubber, carboxyl-modified natural rubber, carboxyl-modified butadiene rubber, carboxyl-modified styrene-butadiene rubber, acid anhydride-modified natural rubber, acid anhydride-modified butadiene rubber, and acid anhydride-modified styrene-butadiene rubber.

[0257] From the viewpoint of affinity with cellulose nanofibers, 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, and more preferably 5 mol% or less, or 3 mol% or less. The above-mentioned amount of modifying groups can be determined by infrared absorption spectroscopy, solid-state NMR (nuclear magnetic resonance), solution NMR, or by calculating the molar ratio of modifying groups by quantitatively combining a predetermined monomer composition with elements not present in the unmodified rubber based on elemental analysis.

[0258] [Thermoplastic elastomers]

[0259] In one embodiment, the third rubber may comprise or be a thermoplastic elastomer. In this disclosure, an elastomer, in one embodiment, refers to a substance that is elastic at room temperature (23°C) (specifically, a natural or synthetic polymer). In another embodiment, "elastic" means a storage modulus at 23°C and 10Hz, measured by dynamic viscoelasticity testing, that 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, it is a crosslinked polymer. The preferred monomer composition of the thermoplastic elastomer may be the same as described in either the (conjugated diene polymer) or (non-conjugated diene polymer) category above.

[0260] From the perspective of balancing impact strength and flowability, the number average molecular weight (Mn) of thermoplastic elastomers is preferably 10,000~500,000 or 40,000~250,000.

[0261] Thermoplastic elastomers can have a core-shell structure. Examples of core-shell elastomers include core-shell type elastomers having a core of granular rubber and a shell of glassy grafted layers formed on the outside of the core. Butadiene-based rubbers, acrylic rubbers, and silicone-acrylic composite rubbers are preferred as the core. Styrene resins, acrylonitrile-styrene copolymers, and acrylic resins are preferred as the shell.

[0262] From the viewpoint of excellent compatibility with the first and / or second rubber, the thermoplastic elastomer is preferably selected from at least one of the group consisting of styrene-butadiene block copolymers, styrene-ethylene-butadiene block copolymers, styrene-ethylene-butene block copolymers, styrene-butadiene-butene block copolymers, styrene-isoprene block copolymers, styrene-ethylene-propylene block copolymers, styrene-isobutylene block copolymers, hydrides of styrene-butadiene block copolymers, hydrides of styrene-ethylene-butadiene block copolymers, hydrides of styrene-butadiene-butene block copolymers, hydrides of styrene-isoprene block copolymers, and homopolymers of styrene (polystyrene), more preferably one or more of the group consisting of styrene-butadiene block copolymers, hydrides of styrene-butadiene block copolymers, and polystyrene.

[0263] In one embodiment, at least a portion of the thermoplastic elastomer may have acidic functional groups. In this disclosure, the presence of acidic functional groups in a thermoplastic elastomer means that acidic functional groups are chemically added to the molecular backbone of the elastomer. Furthermore, in this disclosure, acidic functional groups refer to functional groups capable of reacting with basic functional groups, etc. Specific examples include hydroxyl, carboxyl, carboxylic acid ester, sulfonyl, and anhydride groups.

[0264] From the viewpoint of affinity with modified liquid rubber, the amount of acidic functional groups added to the elastomer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, further preferably 0.2% by mass or more, preferably 5% by mass or less, more preferably 3% by mass or less, further preferably 2% by mass or less, and further preferably less than 1.5% by mass, based on 100% by mass of the elastomer. It should be noted that the number of acidic functional groups is a value obtained by measuring a standard curve sample premixed with an acidic substance using an infrared absorption spectroscopy apparatus, based on a standard curve prepared using the characteristic absorption bands of the acid.

[0265] Examples of elastomers with acidic functional groups include: elastomers with a core-shell structure having a shell formed by using acrylic acid or the like as a copolymer; and modified elastomers obtained by grafting α,β-unsaturated dicarboxylic acids or their derivatives onto ethylene-α-olefin copolymers, polyolefins, aromatic compound-conjugated diene copolymers, or aromatic compound-conjugated diene copolymer hydrides containing acrylic acid or the like as monomers, in the presence or absence of peroxides.

[0266] In a preferred embodiment, the elastomer is an anhydride-modified elastomer.

[0267] Among these, more preferred are modified products obtained by grafting α,β-unsaturated dicarboxylic acids or their derivatives onto polyolefins, aromatic compound-conjugated diene copolymers, or aromatic compound-conjugated diene copolymer hydrides in the presence or absence of peroxides. Particularly preferred are modified products obtained by grafting α,β-unsaturated dicarboxylic acids or their derivatives onto ethylene-α-olefin copolymers or aromatic compound-conjugated diene block copolymer hydrides in the presence or absence of peroxides.

[0268] Specific examples of α,β-unsaturated dicarboxylic acids and their derivatives include maleic acid, fumaric acid, maleic anhydride and fumaric anhydride, with maleic anhydride being particularly preferred.

[0269] In one embodiment, the elastomer can be a mixture of an elastomer having acidic functional groups and an elastomer without acidic functional groups. Regarding the mixing ratio of the elastomer having acidic functional groups to the elastomer without acidic functional groups, when the total of both is set to 100% by mass, from the viewpoint of maintaining the high toughness and physical property stability of the cured rubber, the elastomer having acidic functional groups 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. There is no particular upper limit, and substantially all elastomers can be elastomers having acidic functional groups, but from the viewpoint of not causing flowability issues, 80% by mass or less is preferred.

[0270] From the viewpoint of providing a rubber curing product with excellent mechanical strength, the third rubber is preferably one or more selected from the group consisting of styrene-butadiene rubber, natural rubber and isoprene rubber, and more preferably natural rubber.

[0271] In the rubber composition, the mass ratio of the total amount of cellulose nanofibers to the first rubber and the second rubber to the third rubber [(total amount of cellulose nanofibers to the first rubber and the second rubber) / third rubber] can be 1 / 99~99 / 1, or 5 / 95~95 / 5, or 10 / 90~90 / 10, or 20 / 80~80 / 20, or 30 / 70~70 / 30.

[0272] For example, when a preparatory composition comprising cellulose nanofibers and a first rubber and a second rubber is used in the manufacture of a rubber composition, the mass ratio of the preparatory composition to the third rubber (preparatory composition / third rubber) in the rubber composition composition can be 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 in one manner.

[0273] In the rubber composition, the content of the third rubber is preferably 10% by mass or more, or 20% by mass or more, preferably 90% by mass or less, or 85% by mass or less, or 80% by mass or less.

[0274] In the rubber composition, 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.

[0275] In the rubber composition, the total content of the first and second 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, relative to a total of 100 parts by mass of the first, second and third rubbers.

[0276] Relative to a total of 100 parts by mass of the first, second, and third rubbers, the amount of cellulose nanofibers in the rubber composition is preferably 1 part by mass or more, or 2 parts by mass or more, or 3 parts by mass or more, preferably 70 parts by mass or less, or 65 parts by mass or less, or 60 parts by mass or less.

[0277] The mass ratio of [cellulose nanofibers] to [the total of the first, second and third rubbers] in the rubber composition is preferably 1 / 99 to 60 / 40, or 2 / 98 to 50 / 50, or 3 / 97 to 40 / 60.

[0278] [Vulcanizing agent, vulcanization accelerator]

[0279] When a rubber composition contains uncured rubber, it typically includes a vulcanizing agent and may optionally include a vulcanization accelerator. The vulcanizing agent and vulcanization accelerator can be selected appropriately based on the type of uncured rubber in the rubber composition, using conventionally known vulcanizing agents and vulcanization accelerators. As vulcanizing agents, organic peroxides, azo compounds, oxime compounds, nitroso compounds, polyamine compounds, sulfur, sulfur compounds, etc., can be used. Examples of sulfur compounds include sulfur monochloride, sulfur dichloride, disulfide compounds, and high molecular weight polysulfide compounds.

[0280] The amount of vulcanizing agent in the rubber composition is preferably 0.01 to 20 parts by weight, or 0.1 to 15 parts by weight, relative to 100 parts by weight of uncured rubber in the rubber composition.

[0281] Examples of vulcanization accelerators include sulfenamide-based, guanidine-based, thiuram-based, aldehyde-amine-based, aldehyde-amine-based, thiazole-based, thiourea-based, and dithiocarbamate-based accelerators. Additionally, zinc oxide and stearic acid can be used as vulcanization aids. The amount of vulcanization accelerator is preferably 0.01 to 20 parts by weight, or 0.1 to 15 parts by weight, relative to 100 parts by weight of uncured rubber in the rubber composition.

[0282] [Additives for Rubber]

[0283] The rubber composition may contain various conventionally known rubber additives (stabilizers, softeners, anti-aging agents, etc.). As a 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. Additionally, as a rubber softener, one or more processing oils, extender oils, etc., may be used. However, since the rubber composition of this embodiment can form a soft molded body in one embodiment, the rubber composition may not contain a rubber softener in one embodiment.

[0284] It should be noted that vulcanizing agents, vulcanization accelerators, and rubber additives are typically added during the manufacture of rubber composites, but the manner of addition is not limited to this.

[0285] <Additional components to the rubber composition>

[0286] The rubber composition may further include additional components. Examples of additional components include polymers, organic or inorganic fillers, heat stabilizers, antioxidants, antistatic agents, colorants, etc. The proportion of any additional component in the rubber composition may be appropriately selected within a range that does not impair the desired effects of the present invention, for example, it may be 0.01 to 50% by mass or 0.1 to 30% by mass.

[0287] <Preparation of Rubber Compositions>

[0288] Rubber compositions can be manufactured by mixing rubber composition components comprising cellulose nanofibers, a first rubber, and a second rubber. Examples of methods for manufacturing rubber compositions include: (1) A method comprising a first step of mixing cellulose nanofibers with a first rubber as an unmodified liquid rubber to obtain a preparative composition; and a second step of mixing the preparative composition with a second rubber as a modified liquid rubber to obtain a rubber composition; and (2) A first step of mixing a first rubber, which is an unmodified liquid rubber, with a second rubber, which is a modified liquid rubber, to obtain a preparative composition; and a second step of mixing the preparative composition with cellulose nanofibers to obtain a rubber composition; etc.

[0289] There are no particular limitations on the mixing conditions. For example, the components constituting the rubber composition can be mixed using various mixing methods such as a rotary mixer, planetary mixer, propeller agitator, rotary mixer, electromagnetic agitator, open mill, Banbury mixer, kneader, single-screw extruder, and twin-screw extruder to obtain the rubber composition. Additionally, stirring under heat can be performed to effectively induce shearing.

[0290] In the method described in (1) above, by combining the first rubber with cellulose nanofibers in advance, the contact opportunities between the cellulose nanofibers and the second rubber become more moderate and uniform, thus the physical properties of the rubber composition, rubber composite or rubber cured product can be improved better.

[0291] The rubber composition can be dried after it is obtained, or it can be formed into powder by controlling the drying conditions. Alternatively, in the method described in (1) above, the pre-composition can be dried after it is obtained and before it is mixed with the modified liquid rubber.

[0292] In one embodiment, a dried body (in one embodiment, a powder) of the rubber composition of the present disclosure is provided. In another embodiment, a dried body (in one embodiment, a powder) comprising the rubber composition of the present disclosure is provided.

[0293] When the rubber composition contains a third rubber, in one manner, the third rubber may be further mixed in the second step of the method described in (1) or (2) above. The mixing conditions are not particularly limited at this time; for example, a mixing mill commonly used in rubber compounding, such as a Banbury mixer, kneader, or open mill, may be used. The rotor of the mixing mill may be a meshing rotor, a tangential rotor, or a rotor designed for resin compounding. Examples of meshing rotors include the KIR-II manufactured by Kobe Steel Corporation and the EX7 type manufactured by Mitsubishi Heavy Industries, Ltd. Examples of tangential rotors include the 5THR, 4WN, and 4WH manufactured by Kobe Steel Corporation and the E type manufactured by Mitsubishi Heavy Industries, Ltd. Examples of rotors for resin compounding include the roller-type R500B manufactured by Toyo Seiki Manufacturing Co., Ltd.

[0294] Alternatively, the rubber composition can be temporarily prepared using the method described in (1) or (2) above, and then mixed with a third rubber to obtain a rubber composition that also contains the third rubber. The mixing conditions in this case can be the same as those described for the case where the rubber composition contains the third rubber.

[0295] In particular, in the second step of the method described above (1), when a third rubber is further mixed using a rubber mixer, the dispersion of cellulose nanofibers can be particularly promoted. That is, in such a second step, the viscosity of the mixture can be increased due to the presence of the third rubber, thereby increasing the shear force applied to the mixture. In addition, according to the rubber mixer, even when using high-viscosity rubber, the distribution is well carried out. Therefore, the second rubber and the cellulose nanofibers come into sufficient contact at an appropriate speed, thus promoting the dispersion of cellulose nanofibers.

[0296] The rubber compositions exemplified above can all be suitably used as, for example, masterbatches and can be applied to the manufacture of various rubber composites.

[0297] As a method for mixing the aforementioned cellulose nanofibers with a first rubber and / or a second rubber, in one embodiment, the cellulose nanofibers can be added in the form of a dried cellulose nanofiber body. In another embodiment, the cellulose nanofibers can be mixed with the first rubber and / or the second rubber in the form of a slurry, and the contained liquid medium can be dried to remove it, thereby obtaining a preparative composition or a rubber composition containing cellulose nanofibers.

[0298] <Drying Process>

[0299] In one embodiment, the dried body containing cellulose nanofibers (which may be a dried cellulose nanofiber body, a preparative composition containing cellulose nanofibers, or a rubber composition) can be manufactured by drying a cellulose nanofiber slurry. In another embodiment, the dried body containing cellulose nanofibers is a powder.

[0300] As for dryers, there are no particular limitations; examples include kneaders, planetary mixers, Henschel mixers, high-speed mixers, propeller mixers, ribbon mixers, single-screw or twin-screw screw extruders, Banbury mixers, freeze dryers, shed dryers, spray dryers, fluidized bed dryers, and drum dryers.

[0301] From the viewpoint of forming a dried body of cellulose nanofibers with excellent powder properties including excellent nanodispersion and macrodispersion of cellulose nanofibers in the rubber composition and drying efficiency, the drying temperature can be, for example, above 20°C, or above 30°C, or above 40°C, or above 50°C. From the viewpoint of not easily generating thermal degradation of cellulose nanofibers and additional components, and from the viewpoint of avoiding excessive micronization of the dried body containing cellulose nanofibers due to rapid drying of the slurry, the drying temperature can be, for example, below 200°C, or below 180°C, or below 160°C, or below 140°C, or below 120°C, or below 100°C.

[0302] Drying temperature is the temperature of the heat source in contact with the slurry, such as the surface temperature of the temperature-regulating sleeve of the drying device, the surface temperature of the heating cylinder, or the temperature of the hot air.

[0303] The pressure can be either atmospheric pressure or reduced pressure. From the viewpoint of forming a dry body of cellulose nanofibers with excellent powder properties including drying efficiency and excellent nano-dispersion and macro-dispersion of cellulose nanofibers in the rubber composition, it can be below -1 kPa, or below -10 kPa, or below -20 kPa, or below -30 kPa, or below -40 kPa, or below -50 kPa. From the viewpoint of avoiding excessive micronization of the dry body containing cellulose nanofibers due to rapid drying of the slurry, it can be above -100 kPa, or above -95 kPa, or above -90 kPa.

[0304] From the viewpoint of process efficiency during drying, the concentration of cellulose nanofibers in the cellulose nanofiber slurry supplied for the drying process is preferably 1% by mass or more, or 2% by mass or more, or 3% by mass or more, or 5% by mass or more, or 10% by mass or more, or 15% by mass or more, or 20% by mass or more, or 25% by mass or more. From the viewpoint of avoiding excessive increase in slurry viscosity and maintaining good workability due to solidification caused by agglomeration, it is preferably 50% by mass or less, or 45% by mass or less, or 40% by mass or less, or 35% by mass or less. For example, the manufacture of cellulose nanofibers is mostly carried out in a dilute dispersion, but the concentration of cellulose nanofibers in the slurry can also be adjusted to the above-mentioned preferred range by concentrating such a dilute dispersion. Concentration can be achieved by methods such as vacuum filtration, pressure filtration, centrifugation, and heating.

[0305] In one embodiment, the dried body containing cellulose nanofibers may include a first rubber and / or a second rubber, and any additional components (such as the dispersant described above), which may be added before, during, and / or after drying the cellulose nanofiber slurry. In another 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. There are no particular limitations on the organic solvent, but solvents that dissolve the first and second rubbers are preferred, and examples include non-water-soluble solvents such as chloroform, toluene, hexane, and cyclohexane.

[0306] [Liquid medium content]

[0307] From the viewpoint of operability when compounding with a third type of rubber, the liquid medium content of the dried body containing cellulose nanofibers is 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 can be 0% by mass, but from the viewpoint of ease of manufacturing the dried body containing cellulose nanofibers, it can 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.

[0308] [Average Particle Size]

[0309] In one embodiment, from the viewpoint of ease of manufacture, the average particle size of the dried body containing cellulose nanofibers is preferably 1 μm or more, or 10 μm or more, 50 μm or more, or 100 μm or more, or 200 μm or more, or 500 μm or more. From the viewpoint of the dried body containing cellulose nanofibers readily disintegrating in the rubber composition, thereby enabling good dispersion of the cellulose nanofibers in the rubber composition, it is preferably 10000 μm or less, or 5000 μm or less, or 4000 μm or less, or 3000 μm or less, or 2000 μm or less. The above-mentioned average particle size is a value measured using a dynamic image analysis particle size distribution measuring device (CAMSIZER X2, Microtrac Corporation).

[0310] Loose bulk density

[0311] In one approach, from the viewpoint of good flowability and excellent feedability of the dried body containing cellulose nanofibers, and from the viewpoint of inhibiting the transfer of dispersant to the rubber composition, the loose bulk density of the dried body containing cellulose nanofibers is preferably 0.01 g / cm³. 3 Above, or 0.05g / cm 3 Above, or 0.10 g / cm 3 Above, or 0.15g / cm 3 Above, or 0.20 g / cm 3 Above, or 0.25g / cm 3 Above, or 0.30 g / cm 3 Above, or 0.35g / cm 3 Above, or 0.40 g / cm 3 Above, or 0.45g / cm 3 Above, or 0.50 g / cm 3Based on the above, considering that the dried body containing cellulose nanofibers readily disintegrates in the rubber composition, thus enabling good dispersion of the cellulose nanofibers in the rubber composition, and that the dried body containing cellulose nanofibers is not too heavy, thereby avoiding poor mixing between the dried body containing cellulose nanofibers and the rubber composition, the loose bulk density of the dried body containing cellulose nanofibers is preferably 0.85 g / cm³. 3 Below, or 0.80g / cm 3 Below, or 0.75g / cm 3 the following.

[0312] [Tap density]

[0313] In one embodiment, the tap density of the dried body containing cellulose nanofibers is controlled within a range useful for controlling the loose bulk density and compressibility within the scope of this disclosure, preferably 0.01 g / cm³ in one embodiment. 3 Above, or 0.1 g / cm 3 Above, or 0.15g / cm 3 Above, or 0.2g / cm 3 Above, or 0.3g / cm 3 Above, or 0.4 g / cm 3 Above, or 0.5g / cm 3 Above, or 0.6 g / cm 3 The above, preferably 0.95 g / cm³ 3 Below, or 0.9g / cm 3 Below, or 0.85g / cm 3 the following.

[0314] [Compression]

[0315] The compressibility is calculated as compressibility = (tap density - loose bulk density) / tap density. The loose bulk density and tap density are values ​​determined by the method described in one of the [Examples] of this disclosure.

[0316] In one embodiment, compressibility refers to the degree of volume reduction. In one embodiment, considering that the flowability of the dried body containing cellulose nanofibers is not too high, the compressibility of the dried body containing cellulose nanofibers is preferably 1% or more, or 5% or more, or 10% or more, or 15% or more, or 20% or more, or 25% or more. Furthermore, considering that the dried body containing cellulose nanofibers has good flowability and excellent feedability, excellent processability (specifically, it is not easy to generate scattering, floating or dust formation), good dispersion of the dried body containing cellulose nanofibers in the rubber composition, and suppression of the transfer of dispersant to rubber, the compression ratio is preferably 50% or less, or 45% or less, or 40% or less, or 35% or less.

[0317] The loose bulk density, tapped density, and compressibility were measured using a powder analyzer (model: PT-X) manufactured by Hosokawa Micron Co., Ltd. The tapped density was measured using 180 tapping cycles.

[0318] As a more specific example of the process sequence, the following can be provided.

[0319] (i) Preparation of a slurry comprising cellulose nanofibers and optionally a dispersant → drying to prepare a dried body → preparation of a preliminary composition comprising the dried body and a first rubber → preparation of a rubber composition comprising the preliminary composition and a second rubber.

[0320] (ii) Preparation of a slurry containing cellulose nanofibers and optionally a dispersant → drying to prepare a dried body → preparation of a rubber composition comprising the dried body, a first rubber, and a second rubber.

[0321] (iii) Preparation of a slurry comprising cellulose nanofibers, a first rubber, and an optional dispersant → drying to prepare a dried body → preparation of a rubber composition comprising the dried body and a second rubber.

[0322] (iv) Preparation of a slurry comprising cellulose nanofibers, a first rubber, a second rubber, and an optional dispersant → drying to prepare a rubber composition.

[0323] Rubber Composites, Cured Rubber Products and Molded Articles

[0324] One aspect of this disclosure provides a rubber composite, which is a mixture of the rubber composition and a fourth rubber (base rubber) according to this embodiment, and a cured rubber product, which is a cured product of the rubber composite. The mixing conditions for the rubber composition and the fourth rubber are not particularly limited; for example, a mixing mill commonly used in rubber compounding, such as a Banbury mixer, kneader, or open mill, can be used.

[0325] <Fourth Rubber>

[0326] The fourth rubber can be in the same manner as the third rubber. Relative to a total of 100 parts by mass of the third and fourth rubbers, the total content of cellulose nanofibers and the first and second rubbers is preferably 1 part by mass or more, or 3 parts by mass or more, or 5 parts by mass or more, preferably 50 parts by mass or less, or 45 parts by mass or less, or 40 parts by mass or less. In one embodiment, the fourth rubber can be one or more selected from the group consisting of natural rubber, styrene-butadiene rubber, isoprene rubber, and butadiene rubber, for example, natural rubber. When the rubber composition includes the third rubber, it is preferable that the third rubber and the fourth rubber have some or all of the same constituent monomers.

[0327] In one method, a cured rubber compound can be obtained by vulcanization pressing according to JIS K6299. The desired molded body can be manufactured by molding the rubber composite alone or together with other components into the desired shape. There are no particular limitations on the combination method of the compounding components and the molding method, which can be selected according to the desired molded body. As molding methods, examples include, but are not limited to: (1) a method in which the third and / or fourth rubbers contain uncured rubber, and the uncured rubber is cured before, during and / or after molding when molding the rubber composite alone or together with the additional components, thereby obtaining a molded body containing cured rubber; (2) a method in which the third and / or fourth rubbers contain uncured rubber, and the uncured rubber in the rubber composite is cured to form a cured rubber compound, and then it is molded together with the additional components to obtain a molded body; (3) a method in which the third and fourth rubbers are thermoplastic elastomers, and the rubber composite is molded alone or melt-molded together with the additional components to obtain a molded body; and so on. Molding can be carried out by injection molding, extrusion molding, extrusion molding, blow molding, compression molding, etc.

[0328] <Properties of Cured Rubber>

[0329] The tensile stress (modulus) (M100) of the cured rubber at 100% elongation can be above 2.0 MPa, above 3.0 MPa, or above 4.0 MPa in one embodiment, and below 10.0 MPa, below 9.0 MPa, or below 8.0 MPa in another embodiment.

[0330] The tensile stress (M300) at 300% elongation of the cured rubber can be above 3.0 MPa, above 5.0 MPa, or above 6.0 MPa in one embodiment, and below 20.0 MPa, below 15.0 MPa, or below 13.0 MPa in another embodiment.

[0331] The ratio (M300 / M100) of the tensile stress at 300% elongation to the tensile stress at 100% elongation of the cured rubber can be 1.3 or more, or 1.4 or more, or 1.5 or more in one embodiment, and 2.0 or less, or 1.8 or less in another embodiment.

[0332] The storage modulus of the cured rubber can be above 2.0 MPa or above 2.5 MPa in one method, and below 4.0 MPa, below 3.5 MPa, or below 3.0 MPa in another method.

[0333] From the perspective of fuel efficiency and low heat generation in applications such as tires, it is advantageous for the loss tangent of the cured rubber to be below a specified value. From this perspective, the loss tangent can be 0.18 or less, or 0.15 or less, or 0.10 or less in one embodiment. On the other hand, from the perspective of vibration damping performance in applications such as vibration-damping rubber, it is advantageous for the loss tangent of the cured rubber to be above a specified value. From this perspective, the loss tangent can be 0.02 or more, or 0.03 or more, or 0.04 or more in one embodiment. The storage modulus and loss tangent mentioned above are values ​​measured using a rheometer in a torsional manner at 50°C and 10Hz.

[0334] Cured rubber can be formed into molded bodies of various shapes. These molded bodies can be used in a wide range of applications, including industrial machinery parts, general machinery parts, automotive / railway / vehicle / ship / aerospace related parts, electronic / electrical parts, building / civil engineering materials, household goods, sports / leisure products, wind power generation shell components, and container / packaging components. For example, they can be formed into automotive parts (e.g., tires, bumpers, mudguards, door panels, various trim strips, car logos, engine hoods, wheel covers, roofs, spoilers, various aerodynamic kits, etc., as well as interior parts such as dashboards, console boxes, and decorative parts), battery parts (on-board secondary battery parts, lithium-ion secondary battery parts, fuel housings for solid methanol batteries, piping for fuel cells, etc.), electronic / electrical equipment parts (e.g., various computer and peripheral equipment, junction boxes, various connectors, various OA equipment, televisions, VCRs, CD players, chassis, refrigerators, air conditioners, LCD projectors, etc.), and household goods (shoe outsoles, etc.). One aspect of this disclosure is to provide tires, vibration-damping rubbers, shoe outsoles, or conveyor belts incorporating the rubber-cured material of this disclosure.

[0335] Example

[0336] The following examples further illustrate the illustrative aspects of the present invention, but the present invention is not limited to these examples in any way.

[0337] Evaluation Methods

[0338] Rubber

[0339] [Viscosity at 38℃]

[0340] The viscosity of the rubber was measured using a type B viscometer. The results are shown in Table 1.

[0341] [Number-average molecular weight (Mn)]

[0342] Show the values ​​in the product catalog.

[0343] <Rubber Composition>

[0344] The rubber composition was evaluated as follows.

[0345]

[0346] [Dispersibility of cellulose nanofibers]

[0347] For the rubber composition, optical microscopy observation was performed under the following conditions. A 1 mg sample was held between two coverslips, flattened and spread out to achieve a uniform thickness. The sample was placed on the stage of an Olympus BX51P polarizing microscope. Differential interference was observed by inserting an Olympus U-DICR differential interference prism. The dispersibility of the cellulose nanofibers was evaluated according to the following criteria.

[0348] A: Dispersed roughly evenly.

[0349] B: Dispersion, but cohesion was observed.

[0350] C: A large amount of agglomeration has been confirmed.

[0351] <Rubber compositions (masterbatches) further containing a third type of rubber>

[0352] [Dispersibility of cellulose nanofibers]

[0353] For the rubber composition, in 10 randomly selected cross-sectional images of a cube with one side of 2 mm observed by X-ray CT, the 20,000 μm in each cross-section was analyzed. 2 The number of cellulose nanofiber aggregates of the above dimensions was counted, the average number of aggregates per cross section was calculated, and the dispersion state of cellulose nanofibers was classified according to the following criteria.

[0354] A: Less than 5

[0355] B: More than 5 but less than 10

[0356] C: More than 10

[0357] The measurement conditions for X-ray CT are as follows.

[0358] Device: Bruker X-CT Skyscan 1272

[0359] Tube voltage: 40kV, tube current: 100μA

[0360] Number of pixels: 2452×1640, pixel resolution: 1.2μm, total number of times: 8

[0361] Scan: Scan every 0.2 degrees, 180 degrees

[0362] <Rubber cured products>

[0363] The following evaluation was performed on the cured rubber.

[0364] (1) Surface smoothness

[0365] Cut small pieces from the cured rubber sheet using scissors and place them on the stage of a confocal laser microscope (KEYENCE, VK-X250). Obtain an image of the surface unevenness using a 10x objective lens. Calculate the arithmetic mean height (Sa) according to ISO 25178, and exponentialize the result of the benchmark comparison example to 100. The smaller the exponent, the better the surface smoothness.

[0366] (2) Tensile strength, tensile stress (modulus), tensile elongation

[0367] Tensile strength, tensile stress at 100% elongation (100% modulus, M100), and tensile stress at 300% elongation (300% modulus, M300), as well as tensile elongation, were determined using the tensile test method of JIS K-6251. The results of the benchmark comparison example were indexed as 100. The larger the index, the better the tensile strength, tensile stress, and tensile elongation.

[0368] (3) Dispersibility of cellulose nanofibers

[0369] For the cured rubber, the evaluation was conducted using the same procedure as described above for the [dispersibility of cellulose nanofibers] in 10 randomly selected cross-sectional images of a cube with one side of 2 mm observed by X-ray CT.

[0370] (4) Orientation of cellulose nanofibers

[0371] For cellulose nanofibers observed using a transmission electron microscope, the following data processing is performed to calculate the orientation degree of the cellulose nanofibers.

[0372] When the rolling direction of the cured rubber sheet is set as MD, the direction perpendicular to the rolling direction is set as TD, and the thickness direction of the sheet is set as ND, for the MD-ND surface of the sample, a slice with a set thickness of 500 μm is collected using a cryogenic slicer. The slices are then observed at 1000x magnification using a transmission electron microscope (JEM-1400, NEC). Images are obtained from five randomly selected fields of view. The observed cellulose nanofibers are binarized and subjected to particle analysis using ImageJ image processing software. In the particle analysis, the cellulose nanofibers are approximated as ellipses, and the angle θ between the major axis of the ellipse and MD is obtained for each cellulose nanofiber. For the cellulose nanofibers obtained from the five TEM images, (3(cosθ)^2-1) / 2 is calculated, and its average value is taken as the orientation degree. The orientation of the cellulose nanofibers is evaluated according to the following criteria.

[0373] A: Orientation degree is 0.7 or higher.

[0374] B: Orientation degree is 0.5 or higher and less than 0.7

[0375] C: Orientation degree less than 0.5

[0376] Materials Used

[0377] First Rubber

[0378] Unmodified liquid rubber-1: Ricon184 (liquid butadiene-styrene random copolymer, Mn=9,400) manufactured by Cray Valley Corporation

[0379] Unmodified liquid rubber-2: LIR-30 (liquid polyisoprene, Mn=28,000) manufactured by Kuraray.

[0380] Unmodified liquid rubber-3: LBR-305 (liquid polybutadiene, Mn=26,000) manufactured by Kuraray.

[0381] Unmodified liquid rubber-4: L-FR-107 (liquid farnesene rubber, Mn=130,000) manufactured by Kuraray.

[0382] Unmodified Liquid Rubber-5: LIR-50 (liquid polyisoprene, Mn=54,000) manufactured by Kuraray.

[0383] <Second Rubber>

[0384] Modified liquid rubber-1: LIR-403 manufactured by Kuraray (maleic anhydride modified liquid polyisoprene, Mn=34,000, 3 modifying groups per molecule chain)

[0385] Modified Liquid Rubber-2: LIR-410 manufactured by Kuraray (carboxyl-modified liquid polyisoprene, Mn=30,000, 10 modifying groups per molecule chain)

[0386] Modified Liquid Rubber-3: Ricon184MA6 manufactured by Cray Valley (maleic anhydride modified liquid styrene-butadiene copolymer, Mn=9,200, with 6 modifying groups per molecule chain)

[0387] Modified Liquid Rubber-4: Ricon131MA20 manufactured by Cray Valley (maleic anhydride modified liquid polybutadiene, Mn=7,000, 11 modifying groups per molecule chain)

[0388] <Third Rubber>

[0389] Natural Rubber: RSS No. 3 (Producer: UNIMAC RUBBER CO., LTD. (Thailand), Supplier: MarubeniTechno Rubber Corporation)

[0390] Polyisoprene: JSR Corporation IR2200

[0391] SBR-1: Manufactured according to the steps described in the "Manufacturing of SBR-1" section below.

[0392] <Fourth Rubber>

[0393] Natural Rubber: RSS No. 3 (Producer: UNIMAC RUBBER CO., LTD. (Thailand), Supplier: MarubeniTechno Rubber Corporation)

[0394] Polyisoprene: JSR Corporation IR2200

[0395] SBR-1: Manufactured according to the steps described in the "Manufacturing of SBR-1" section below.

[0396] SBR-2: Asahi Kasei Corporation, Asaprene (registered trademark) Y031

[0397] SBR-3: Nipol1 (registered trademark) 502 manufactured by Zeon Corporation of Japan

[0398] The Manufacturing of SBR-1

[0399] A high-pressure reactor with an internal volume of 10L and an internal height (L) to diameter (D) ratio (L / D) of 4.0 is used. It has an inlet at the bottom and an outlet at the top, and is equipped with a stirrer and a jacket for temperature control. A static mixer is connected to the feed inlet of the reactor. Pre-treated 1,3-butadiene (with impurities such as moisture removed) is mixed at 20.2 g / min, styrene at 16.8 g / min, and n-hexane at 137.6 g / min to obtain a mixture. Just before this mixture enters the first reactor, n-butyllithium for impurity deactivation is supplied at 0.020 phm, mixed using the static mixer, and continuously supplied to the bottom of the first reactor. Then, 2,2-bis(2-tetrahydrofuranyl)propane, as a polar substance, is made up to 0.320 phm, and NBL (n-butyllithium), as a polymerization initiator, is made up to 0.102 phm. These are continuously supplied to the bottom of the reactor, and the temperature inside the reactor is maintained at 82°C to obtain a rubber solution.

[0400] The rubber solution produced in the reactor is supplied from the top of the reactor to a static mixer. In front of the static mixer, M1 (1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) as a modifier is continuously supplied at a ratio of 1.0 equivalent (wherein the amount added is calculated as 4 mol of NBL reacting with 1 mol of M1) relative to lithium supplied as a polymerization initiator, and the reaction is carried out to obtain SBR-1.

[0401] Cellulose nanofibers

[0402] Three parts by weight of cotton linter pulp were impregnated with 27 parts by weight of water and dispersed using a pulper. 170 parts by weight of water were added to 30 parts by weight of the pulped cotton linter pulp (containing 3 parts by weight of cotton linter pulp) to disperse it in water (solid content 1.5% by weight). The dispersion was then beating for 30 minutes using an Aikawa Tetsuko SDR14 laboratory refiner (pressure type DISK) with a disc refining device and a disc gap of 1 mm. Next, the dispersion was thoroughly beating was performed with the gap reduced to almost zero to obtain a beaten aqueous dispersion (solid content concentration: 1.5% by weight). The obtained beaten aqueous dispersion was then directly micronized 10 times using a high-pressure homogenizer (Niro Soavi NSO15H) at an operating pressure of 100 MPa to obtain a cellulose nanofiber pulp (solid content concentration: 1.5% by weight). Then, the solid content was concentrated to 10% by mass using a dehydrator to obtain a filter cake of cellulose nanofibers.

[0403] <Dispersant>

[0404] Nonionic dispersant: SANNIX GL-3000 (polyoxyethylene polyoxypropylene triol) manufactured by Sanyo Chemical Co., Ltd.

[0405] <Vulcanizing aids>

[0406] Zinc oxide: Available from Fujifilm and Kojun Chemical Co., Ltd.

[0407] Stearic acid: Available from Fujifilm and Kojun Chemical Co., Ltd.

[0408] Wax

[0409] Sunnoc: Selected special waxes (available from Ouchi Shinsei Chemical Co., Ltd.)

[0410] Anti-aging agents

[0411] Nocrac 6C: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (available from Ouchi Shinsei Chemical Co., Ltd.)

[0412] <Vulcanization Accelerator>

[0413] Nocceler CZ: N-cyclohexyl-2-benzothiazolyl sulfinamide (available from Ouchi Shinsei Chemical Co., Ltd.)

[0414] Nocceler D: 1,3-Diphenylguanidine (available from Ouchi Shinsei Chemical Co., Ltd.)

[0415] Manufacturing of Rubber Compositions

[0416]

[0417] [Examples 1-1 to 1-11, 1-21 to 1-24]

[0418] A 10% by weight cellulose nanofiber filter cake was placed in a 200ml PP cup. Unmodified liquid rubber and dispersant were then added in the proportions shown in Tables 2 and 3 to form the final composition, with the concentration of cellulose nanofibers being 10% by weight to prepare an aqueous dispersion. The 200ml PP cup was placed in a THINKY ARE-310 rotary mixer manufactured by THINKY Corporation and mixed for 15 minutes in stirring mode (2000 rpm revolution, 800 rpm rotation). Next, modified liquid rubber was added in the proportions shown in Tables 2 and 3, and the mixture was further mixed for 15 minutes in stirring mode (2000 rpm revolution, 800 rpm rotation).

[0419] The obtained composition was stretched thinly onto a release film, dried at 80°C using SPH-201 manufactured by ESPEC Corporation, and then pulverized for 30 seconds using Mini Speed ​​Mill MS-05 manufactured by LABONECT Corporation to obtain a rubber composition. The dispersibility of the obtained rubber composition was evaluated using an optical microscope.

[0420] [Examples 1-12]

[0421] In a beaker, 57.1 parts by weight of liquid butadiene-styrene random copolymer (unmodified liquid rubber-1) and 200 parts by weight of maleic anhydride modified liquid polyisoprene (modified liquid rubber-1) were dissolved in 2314 parts by weight of chloroform and stirred. Next, the liquid rubber solution was expanded in a Teflon (registered trademark) container and vacuum dried at 80°C to obtain the preliminary composition.

[0422] After placing 10% by mass of cellulose nanofiber filter cake into a 200ml PP cup, the prepared composition and dispersant were added in the proportions shown in Table 2 as the final composition, and an aqueous dispersion was prepared with the concentration of cellulose nanofibers being 10% by mass. The 200ml PP cup was placed in a THINKY ARE-310 rotary mixer manufactured by THINKY Co., Ltd., and mixed for 15 minutes in stirring mode (2000 rpm revolution, 800 rpm rotation).

[0423] The obtained composition was stretched thinly onto a release film, dried at 80°C using SPH-201 manufactured by ESPEC Corporation, and then pulverized for 30 seconds using Mini Speed ​​Mill MS-05 manufactured by LABONECT Corporation to obtain a rubber composition. The dispersibility of the obtained rubber composition was evaluated using an optical microscope.

[0424] [Examples 1-13~1-20]

[0425] Except that the amount of chloroform was 1414 parts by mass, and the amounts and types of unmodified and modified liquid rubber were changed as shown in Table 2, the rubber compositions were obtained in the same manner as in Examples 1-12. The dispersibility of the obtained rubber compositions was evaluated using an optical microscope.

[0426] [Comparative Examples 1-1 to 1-9]

[0427] After placing 10% by mass of cellulose nanofiber filter cake into a 200ml PP cup, unmodified or modified liquid rubber and dispersant were added in the proportions shown in Table 3 as the final composition, and an aqueous dispersion was prepared with the concentration of cellulose nanofibers being 10% by mass. The 200ml PP cup was placed in a THINKY ARE-310 rotary mixer manufactured by THINKY Corporation, and mixed for 15 minutes in stirring mode (2000 rpm revolution, 800 rpm rotation).

[0428] The obtained composition was stretched thinly onto a release film, dried at 80°C using SPH-201 manufactured by ESPEC Corporation, and then pulverized for 30 seconds using Mini Speed ​​Mill MS-05 manufactured by LABONECT Corporation to obtain a rubber composition. The dispersibility of the obtained rubber composition was evaluated using an optical microscope.

[0429] <Rubber compositions (masterbatches) further containing a third type of rubber>

[0430] [Examples 2-1 to 2-21, 2-35 to 2-36, Comparative Examples 2-1 to 2-15]

[0431] After placing 10% by mass of cellulose nanofiber filter cake into a 200ml PP cup, unmodified liquid rubber and dispersant were added in the proportions shown in Tables 4-6 as the final composition, and an aqueous dispersion was prepared with the concentration of cellulose nanofibers being 10% by mass. The 200ml PP cup was placed in a THINKY ARE-310 rotary mixer manufactured by THINKY Corporation, and mixed for 15 minutes in stirring mode (2000 rpm revolution, 800 rpm rotation).

[0432] The obtained composition was thinly stretched on a release film and dried at 80°C using SPH-201 manufactured by ESPEC Corporation. Then, it was pulverized for 30 seconds using Mini Speed ​​Mill MS-05 manufactured by LABONECT Corporation to obtain the prepared composition.

[0433] Using a closed mixer (0.35L capacity) equipped with a temperature control device, the third rubber, the preparatory composition, and the modified liquid rubber were added at a filler ratio of 65% according to the compositions shown in Tables 4-6, and mixed at 140°C for 5 minutes. The resulting mixture was recycled and passed through rollers to obtain a sheet-like rubber composition (masterbatch). A portion was cut from the sheet, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Tables 4-6.

[0434] [Example 2-22]

[0435] Except for changing the mixing temperature to 120°C, a sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0436] [Example 2-23]

[0437] Except for changing the mixing temperature to 130°C, a sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0438] [Example 2-24]

[0439] Except for changing the mixing temperature to 160°C, a sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0440] [Example 2-25]

[0441] The prepared composition was obtained in the same manner as in Example 2-1.

[0442] Using a closed mixer (0.35L capacity) equipped with a temperature control device, the first stage of mixing was performed with a filler ratio of 65%, according to the composition shown in Table 5, adding the third rubber, the preparatory composition, and the modified liquid rubber, and mixing at 120°C for 5 minutes. Next, as 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 cellulose nanofibers. The resulting mixture was recovered and passed through rollers to obtain a sheet-like rubber composition (masterbatch). A portion was cut from the sheet, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0443] [Example 2-26]

[0444] The mixing time for the second stage was set to 5 minutes instead of 3 minutes, and otherwise, sheet-like rubber compositions (masterbatches) were obtained in the same manner as in Examples 2-25. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0445] [Example 2-27]

[0446] Except for changing the mixing temperature of the first and second stages from 120°C to 140°C, sheet-like rubber compositions (masterbatches) were obtained in the same manner as in Examples 2-25. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0447] [Example 2-28]

[0448] Except for changing the mixing temperature of the first and second stages from 120°C to 140°C, sheet-like rubber compositions (masterbatches) were obtained in the same manner as in Examples 2-26. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0449] [Example 2-29]

[0450] Except for changing the filler content to 55%, a sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0451] [Examples 2-30]

[0452] Except for changing the filler content to 75%, a sheet-like rubber composition (masterbatch) was obtained in the same manner as in Example 2-1. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0453] [Example 2-31]

[0454] The prepared composition was obtained in the same manner as in Example 2-1.

[0455] Using a 1.6L Banbury internal mixer, with a filler ratio of 65%, the third rubber, the preparatory composition, and the modified liquid rubber were added according to the composition shown in Table 5, and mixed at 120°C for 5 minutes. The resulting mixture was recycled and passed through rollers to obtain a sheet-like rubber composition (masterbatch). A portion was cut from the sheet, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0456] [Example 2-32]

[0457] Except for changing the mixing temperature to 140°C, sheet-like rubber compositions (masterbatches) were obtained in the same manner as in Examples 2-31. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0458] [Examples 2-33]

[0459] The prepared composition was obtained in the same manner as in Example 2-1.

[0460] Using a 0.5L kneader, with a filler ratio of 65%, the third rubber, the preparatory composition, and the modified liquid rubber were added according to the composition shown in Table 5, and kneaded at 120°C for 5 minutes. The resulting mixture was recycled and passed through rollers to obtain a sheet-like rubber composition (masterbatch). A portion was cut from the sheet, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0461] [Examples 2-34]

[0462] Except for changing the mixing temperature to 140°C, sheet-like rubber compositions (masterbatches) were obtained in the same manner as in Examples 2-33. A portion of the sheet was cut off, and the dispersibility of the cellulose nanofibers was evaluated using X-ray CT. The results are shown in Table 5.

[0463] <Rubber cured products>

[0464] [Examples 3-1 to 3-32, Comparative Examples 3-1 to 3-17]

[0465] Using a closed mixing mill (0.35L capacity) equipped with a temperature control device, as the first stage of mixing, the rubber composition, fourth rubber, zinc oxide, stearic acid, wax, and stabilizer were added according to the formulations shown in Tables 7-10, with a filler ratio of 65%, and mixed at 140°C for 3 minutes. Next, as 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 cellulose nanofibers. After cooling, sulfur and a vulcanization accelerator were added and mixed using an open mill set to 70°C, and the mixture was shaped into sheets. Then, the sheet-shaped mixture was vulcanized at 160°C for 15 minutes using a vulcanization press with a 2.0mm thickness mold to obtain a cured rubber sheet. Various evaluations were performed on the obtained cured rubber sheets. The results are shown in Tables 7-10.

[0466] [Examples 4-1 to 4-48, Comparative Examples 4-1 to 4-15]

[0467] Using a closed mixing mill (0.35L capacity) equipped with a temperature control device, the first stage of mixing was performed with a 65% filler ratio. Following the formulations shown in Tables 11-17, the masterbatch, fourth rubber, zinc oxide, stearic acid, wax, and stabilizer were added and mixed at 140°C for 3 minutes. Next, as 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 cellulose nanofibers. After cooling, sulfur and a vulcanization accelerator were added and mixed using an open mill set to 70°C, forming a sheet. Then, the sheet mixture was vulcanized at 160°C for 15 minutes using a vulcanization press with a 2.0mm thickness mold to obtain a cured rubber sheet. Various evaluations were performed on the obtained cured rubber sheet. The results are shown in Tables 11-17.

[0468] [Table 1]

[0469] [Table 2]

[0470] [Table 3]

[0471] [Table 4]

[0472] [Table 5]

[0473] [Table 6]

[0474] [Table 7]

[0475] [Table 8]

[0476] [Table 9]

[0477] [Table 10]

[0478] [Table 11]

[0479] [Table 12]

[0480] [Table 13]

[0481] [Table 14]

[0482] [Table 15]

[0483] [Table 16]

[0484] [Table 17]

[0485] Industrial applicability

[0486] The rubber composition disclosed herein can form molded articles with good physical properties, and is therefore suitable for a wide range of applications, including industrial mechanical parts, general mechanical parts, automotive / railway / vehicle / ship / aerospace related parts, electronic / electrical parts, building / civil engineering materials, consumer goods, sports / leisure products, shell components for wind power generation, and container / 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, At 38°C, the ratio of the viscosity η2 of the second rubber to the viscosity η1 of the first rubber, η2 / η1, is 1.2~160.

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, wherein, The first rubber comprises 5 to 300 parts by weight relative to 100 parts by weight of the second rubber.

5. The rubber composition according to claim 1 or 2, wherein, The first rubber comprises 5 to 100 parts by weight relative to 100 parts by weight of cellulose nanofibers.

6. The rubber composition according to claim 1 or 2, wherein, The second rubber comprises 10 to 300 parts by weight relative to 100 parts by weight of cellulose nanofibers.

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

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

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, The dispersant is nonionic.

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

13. The rubber composition according to claim 12, wherein, The third type of rubber is natural rubber.

14. The rubber composition according to claim 1 or 2, wherein it is a dried body.

15. A method for manufacturing the rubber composition according to claim 1 or 2, comprising: The first step involves mixing cellulose nanofibers with the first rubber to obtain a preparative composition. as well as The second step involves mixing the prepared composition with the second rubber to obtain a rubber composition.

16. A method for manufacturing the rubber composition according to claim 1 or 2, comprising: The first step involves mixing the first rubber with the second rubber to obtain a preparative composition. as well as In the second step, the preparative composition is mixed with the cellulose nanofibers to obtain a rubber composition.

17. The method according to claim 15, wherein, In the second process, the third rubber is further mixed.

18. A method for manufacturing the rubber composition of claim 12, comprising: The process of mixing cellulose nanofibers with the first rubber to obtain a preparative composition; The process of mixing the preparative composition with the second rubber to obtain a dried body; as well as The process of mixing the dried body with a third rubber to obtain a rubber composition.

19. A method for manufacturing the rubber composition according to claim 12, comprising: The process of mixing the first rubber and the second rubber to obtain a preparative composition; The process of mixing the preparative composition with the cellulose nanofibers to obtain a dried body; and The process of mixing the dried body with a third rubber to obtain a rubber composition.

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

21. A method for manufacturing a rubber composition, comprising the following steps: The dried body of claim 20 is mixed with a third rubber to obtain a rubber composition.

22. The method according to claim 17, wherein, The third type of rubber is natural rubber.

23. The method according to claim 18, wherein, The third type of rubber is natural rubber.

24. The method according to claim 19, wherein, The third type of rubber is natural rubber.

25. The method according to claim 21, wherein, The third type of rubber is natural rubber.

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

27. A cured rubber compound, which is a cured rubber composite of claim 26.

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

29. A vibration-damping rubber comprising the cured rubber of claim 27.

30. A shoe outsole comprising the rubber cured material of claim 27.

31. A conveyor belt comprising the rubber cured material of claim 27.

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