rubber composition

Abstract

To provide a rubber composition in which, when formed into a sheet, the difference in tensile properties between the grain direction and the antigravity direction perpendicular to it is small, and which can suppress anisotropy that occurs in the rubber molded article due to molding. [Solution] The rubber composition of the present invention comprises 100 parts by mass of a rubber component (A) containing ethylene propylene diene rubber (EPDM) and butadiene rubber (BR); 26.5 parts by mass or more and 69.5 parts by mass or less of a filler component (B) containing microfibrillated cellulose and carbon black; and 2 parts by mass or more and 6 parts by mass or less of an organic peroxide crosslinking agent (C), wherein the rubber component (A) consists of 65 parts by mass or more and 88 parts by mass or less of EPDM and 12 parts by mass or more and 35 parts by mass or less of BR, and the filler component (B) consists of 1.5 parts by mass or more and 4.5 parts by mass or less of microfibrillated cellulose and 25 parts by mass or more and 65 parts by mass or less of carbon black. When the rubber components are EPDM and styrene-butadiene rubber (SBR), the EPDM is 45 parts by mass or more and 82 parts by mass or less, the SBR is 18 parts by mass or more and 55 parts by mass or less, and the filler component (B) is microfibrillated cellulose, which is 1.5 parts by mass or more and 4.5 parts by mass or less.

Description

Technical Field

[0001] The present invention relates to a rubber composition with suppressed anisotropy. More specifically, the present invention relates to a rubber composition that is excellent not only in the strength and elongation in the direction of alignment in which the short fibers for reinforcing microfibrillated cellulose are oriented but also in the strength and elongation in the direction of anti-alignment perpendicular to the fiber orientation direction.

Background Art

[0002] In a rubber composition containing a reinforcing material such as short fibers, pressure is applied to the uncrosslinked kneaded product during extrusion during molding or calender rolling during sheet formation, and rubber molecules, polymer molecular chains, and anisotropic particulate reinforcing materials as compounding agents are oriented in the rolling direction, resulting in a difference in tensile strength and elongation between the rolling direction (referred to as the alignment direction) and the direction perpendicular thereto (referred to as the anti-alignment direction) in the molded body. Such anisotropy in the mechanical strength and physical properties of a rubber molded body is called the alignment phenomenon (also referred to as calender alignment).

[0003] "Anisotropy of physical properties" in the rubber composition (molded body) after molding is variously utilized and applied depending on the use and application environment of rubber products. Patent Document 1 discloses a short fiber-mixed rubber structure having anisotropy in which a predetermined amount of short fibers are oriented in three dimensions of the X-axis, Y-axis, and Z-axis with respect to an elastic base material of a predetermined rubber formulation.

[0004] Patent Document 2 discloses a rubber composition for tires containing cellulose short fibers having an average fiber length L of 1 mm to 3 mm and an average fiber diameter D of 70 nm to 1 μm and a diene-based rubber. [[ID=二十一]] [[ID=二十二]]

Prior Art Documents

Patent Documents

[0005] [[ID=二十九]] [[ID=三十]] [[ID=三十一]]

Patent Document 1

Patent Document 2

Disclosure of the Invention

[0006] The high anisotropy that occurs in molded rubber articles formed from rubber compositions is a desirable factor in generating a strong modulus. However, if used in the wrong direction, it can be a disadvantage depending on the application, as it may not achieve the desired strength and cracks may easily grow along the grain direction. Furthermore, for rubber products such as sealing components like rubber hoses, rubber rolls, rubber packings, gaskets, and seals, rubber with low anisotropy is preferred. In addition, for products in the electronics field, such as devices, batteries, electronic circuit boards, housing pads, and spacer blocks, the use of rubber with low anisotropy is sometimes preferred.

[0007] The present invention aims to provide a rubber composition that, when formed into a sheet, exhibits a small difference in tensile properties between the grain direction and the non-grain direction perpendicular to it, thereby suppressing anisotropy in the rubber molded article obtained by the molding process. [Means for solving the problem]

[0008] The inventors diligently continued their research on a rubber composition suitable for suppressing anisotropy in the tensile properties of a rubber molded article, such as a sheet of rubber, by increasing the modulus in the non-array direction while maintaining the modulus in the articulation direction. As a result, the inventors discovered that the above problem can be solved by blending a rubber component containing ethylene propylene diene rubber and butadiene rubber or styrene butadiene rubber with a filler component containing microfibrillated cellulose and carbon black and an organic peroxide crosslinking agent in specific proportions, thus completing the present invention.

[0009] Specifically, the present invention is: 100 parts by mass of rubber component (A) containing ethylene propylene diene rubber (a1) and butadiene rubber (a2a), A filler component (B) containing microfibrillated cellulose (b1) and carbon black (b2) in an amount of 26.5 parts by mass or more and 69.5 parts by mass or less, A rubber composition containing 2 to 6 parts by mass of an organic peroxide crosslinking agent (C), The aforementioned rubber component (A) is The ethylene propylene diene rubber (a1) is 65 parts by mass or more and 88 parts by mass or less. The butadiene rubber (a2a) is present in amounts of 12 parts by mass or more and 35 parts by mass or less. The aforementioned filler component (B) is The microfibrillated cellulose (b1) is present in an amount of 1.5 parts by mass or more and 4.5 parts by mass or less. The carbon black (b2) content is 25 parts by mass or more and 65 parts by mass or less. This relates to rubber compositions.

[0010] Furthermore, the present invention is 100 parts by mass of rubber component (A) containing ethylene propylene diene rubber (a1) and styrene butadiene rubber (a2b), A filler component (B) containing microfibrillated cellulose (b1) and carbon black (b2) in an amount of 26.5 parts by mass or more and 69.5 parts by mass or less, A rubber composition containing 2 to 6 parts by mass of an organic peroxide crosslinking agent (C), The aforementioned rubber component (A) is The ethylene propylene diene rubber (a1) is 45 parts by mass or more and 82 parts by mass or less. The styrene-butadiene rubber (a2b) is present in an amount of 18 parts by mass or more and 55 parts by mass or less. The aforementioned filler component (B) is The microfibrillated cellulose (b1) is present in an amount of 1.5 parts by mass or more and 4.5 parts by mass or less. The carbon black (b2) content is 25 parts by mass or more and 65 parts by mass or less. This relates to rubber compositions.

[0011] In the present invention, the microfibrillated cellulose is preferably cellulose nanofiber (CNF) with a fiber diameter of 50 nm or more and 200 nm or less. [Effects of the Invention]

[0012] The rubber composition of the present invention, when formed into a sheet, exhibits low anisotropy, with a difference of 2 or less in tensile properties between the grain direction and the non-grain direction perpendicular to it. Therefore, the rubber composition of the present invention can reduce the anisotropy of physical properties that occurs in the molded rubber article after molding, and makes it possible to obtain a molded rubber article with less anisotropy caused by the molding process. [Modes for carrying out the invention]

[0013] The rubber composition of the present invention is characterized by the addition of microfibrillated cellulose such as cellulose nanofibers, carbon black, and an organic peroxide crosslinking agent in specific proportions to a rubber composition of a specific composition.

[0014] The first rubber composition of the present invention contains ethylene propylene diene rubber (a1) and butadiene rubber (a2a) as rubber components. The second rubber composition of the present invention contains ethylene propylene diene rubber (a1) and styrene butadiene rubber (a2b) as rubber components.

[0015] The first rubber composition of the present invention contains 65 to 88 parts by mass of ethylene propylene diene rubber (a1) and 12 to 35 parts by mass of butadiene rubber (a2a). On the other hand, the second rubber composition of the present invention contains 45 to 82 parts by mass of ethylene propylene diene rubber (a1) and 18 to 55 parts by mass of styrene butadiene rubber (a2b).

[0016] The first rubber composition of the present invention contains 1.5 to 4.5 parts by mass of microfibrillated cellulose (b1) per 100 parts by mass of the rubber component. The second rubber composition of the present invention contains 1.5 to 4.5 parts by mass of microfibrillated cellulose (b1) per 100 parts by mass of the rubber component. The first and second rubber compositions of the present invention contain 25 to 65 parts by mass of carbon black (b2) per 100 parts by mass of the rubber component.

[0017] As a specific example of the microfibrillated cellulose as a filler, nano-sized cellulose nanofibers (CNF) are preferable, and the fiber diameter of the CNF is preferably 50 nm or more and 200 nm or less. Further, the fiber diameter of the CNF is more preferably 50 nm or more and 150 nm or less (50 nm to 150 nm), and its fiber length is preferably several μm or more in order to obtain a high reinforcing effect.

[0018] Also, the carbon black, which is also a filler, is preferably of the HAF to GPF grade of furnace black in terms of the balance between dispersibility and reinforcing property.

[0019] As the organic peroxide crosslinking agent, known crosslinking agents such as dicumyl peroxide (DCP) capable of forming a C-C bond crosslinked chain or 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (25B) can be used.

[0020] The rubber composition of the present invention may contain optional components such as an antioxidant, an oil or a plasticizer.

[0021] <Production Example of Rubber Composition> A rubber composition was produced using the raw materials shown below. · Ethylene propylene diene rubber (EPDM): EPT-4021H manufactured by Mitsui Chemicals · Butadiene rubber (BR): UBEPOL BR (registered trademark) BR 150B manufactured by UBE Elastomer · Styrene butadiene rubber (SBR): ESBR 1502 manufactured by ENEOS Material • Acrylonitrile butadiene rubber (NBR): Nipol (registered trademark) DN3350, manufactured by Nippon Zeon Corporation. • Natural rubber (NR): Grade - RSS No. 3 • Cellulose nanofiber (CNF): Celish® KY110N (average fiber diameter 100 nm) manufactured by Daicel Mirise Co., Ltd. • Carbon Black (CB): SEAST (registered trademark) manufactured by Tokai Carbon Co., Ltd. • Zinc oxide: Type 1 zinc oxide manufactured by Sakai Chemical Co., Ltd. • Stearic acid: Powdered stearic acid manufactured by NOF Corporation (Sakura brand) • Dicumyl peroxide (DCP): PERCUMYL® (registered trademark) manufactured by NOF Corporation.

[0022] To avoid aggregation and ensure uniform dispersion, a high-concentration rubber masterbatch (MB, EPDM-based) was prepared in advance, and then added to the mixture before mixing and kneading. • Cellulose nanofiber-reinforced EPDM masterbatch (CNF-reinforced rubber MB): We prepared a rubber MB containing 20 phr of CNF (KY110N) in EPDM (EPT-4021H) manufactured by Sanyo Shikko Co., Ltd., specifically PIGMOTEX CLEAR BB5045. • Carbon black-infused EPDM masterbatch (CB-infused rubber MB): A rubber MB was prepared by blending 80 phr of CB (Seast V) into EPDM (EPT-4021H).

[0023] [Example 1] 20 parts of EPDM (total of 85 parts by mass, including MB portion / hereafter, "parts" refers to "parts by mass") BR 15 copies, CNF20phr-containing rubber MB 18 parts (of which EPDM 15 parts and CNF 3 parts), 90 parts of CB80phr compound rubber MB (of which 50 parts are EPDM and 40 parts are CB), Zinc oxide 5 parts, DCP 3 parts, Stearic acid (part), Two roll mills (also called calenders) were used to mix the materials, which were then kneaded (oriented) at 50°C to 60°C for 3 to 5 minutes. Four sheets with a thickness of 0.6 mm were then prepared with the orientations aligned. Next, the four 0.6 mm thick sheets were stacked with the orientations aligned, and a 2 mm thick metal frame was used to perform a crosslinking treatment by hot pressing at 170°C for 20 minutes under a pressure of 5 MPa, thereby obtaining a 2.0 mm thick crosslinked rubber sheet [test piece of Example 1 with orientation and anisotropy].

[0024] [Comparative Example 1] Without mixing or blending any rubber components other than EPDM, a sample cross-linked rubber sheet, "Comparative Example 1," was prepared in the same manner as in Example 1 to serve as a blank for evaluating tensile strength (modulus) and anisotropy (orientation). Specifically, 35 parts of EPDM (total of 100 parts by mass, including MB portion), BR 0 parts (not included), CNF20phr-containing rubber MB 18 parts (EPDM 15 parts, CNF 3 parts), CB80phr compound rubber MB 90 parts (EPDM 50 parts, CB 40 parts), Zinc oxide 5 parts, DCP 3 parts, Stearic acid (part), Two roll mills were used to mix the materials, and after kneading at a predetermined temperature for a predetermined time, as in Example 1, four 0.6 mm thick sheets were prepared with their orientations aligned. Next, the four 0.6 mm thick sheets were stacked with their orientations aligned, and a 2 mm thick metal frame was used to perform a crosslinking treatment by hot pressing at 170°C for 20 minutes under a pressure of 5 MPa, yielding a 2.0 mm thick crosslinked rubber sheet for testing, "Comparative Example 1". It is considered that the crosslinked rubber sheet of Comparative Example 1, which does not contain any rubber components other than EPDM, exhibits sufficient "anisotropy" due to the orientation (calendering) of the blended CNF.

[0025] Cross-linked rubber sheets for Example 2 to Example 10 were prepared in the same manner as in Example 1. The total mass of rubber material in each compound was 100 parts by mass (PHR) in all examples.

[0026] [Example 2] The cross-linked rubber sheet for Example 2 was prepared in the same manner as in Example 1, except that the formulation consisted of 5 parts EPDM (70 parts by mass of EPDM including each MB portion) and 30 parts BR.

[0027] [Example 3] The cross-linked rubber sheet for Example 3 was prepared in the same manner as in Example 1, except that the formulation consisted of 25 parts EPDM (85 parts EPDM in total, including each MB component) and 12 parts CNF20phr-containing rubber MB (10 parts EPDM, 2 parts CNF).

[0028] [Example 4] The cross-linked rubber sheet for Example 4 was prepared in the same manner as in Example 1, except that it contained 32.5 parts of EPDM (85 parts by mass of EPDM including each MB) and 67.5 parts of CB80phr-containing rubber MB (37.5 parts of EPDM and 30 parts of CB).

[0029] [Example 5] The cross-linked rubber sheet for Example 5 was prepared in the same manner as in Example 1, except that it contained 7.5 parts of EPDM (85 parts by mass of EPDM including each MB) and 112.5 parts of CB80phr compounded rubber MB (62.5 parts of EPDM and 50 parts of CB).

[0030] [Example 6] The cross-linked rubber sheet for Example 6 was prepared in the same manner as in Example 1, except that it contained 5 parts of EPDM (85 parts by mass of EPDM including each MB portion) and 135 parts of CB80phr compounded rubber MB (75 parts of EPDM and 60 parts of CB).

[0031] [Example 7] A cross-linked rubber sheet for Example 7 was prepared in the same manner as in Example 1, except that the amount of dicumyl peroxide (DCP) added was 5 parts (parts by mass).

[0032] [Example 8] The cross-linked rubber sheet for Example 8 was prepared in the same manner as in Example 1, except that "BR 15 parts" was replaced with 20 parts of styrene-butadiene rubber (SBR) and 15 parts of EPDM (a total of 80 parts by mass of EPDM, including the MB portions of each).

[0033] [Example 9] The cross-linked rubber sheet for Example 9 was prepared in the same manner as in Example 1, except that "BR 15 parts" was replaced with 30 parts of styrene-butadiene rubber (SBR) and 5 parts of EPDM (70 parts by mass of EPDM including the MB portion of each).

[0034] [Example 10] Instead of "CB80phr compounded rubber MB," we have prepared CB120phr compounded rubber MB, which is made by compounding 120phr of CB (Seas V) into a carbon black compounded rubber masterbatch (CB compounded rubber MB): EPDM (EPT-4021H). Instead of "BR 15 units", use 50 units of styrene-butadiene rubber (SBR). 1.7 parts of EPDM (50 mass parts of EPDM in total, including each MB portion), CNF20phr-containing rubber MB 18 parts (EPDM 15 parts, CNF 3 parts), A cross-linked rubber sheet for Example 10 was prepared in the same manner as in Example 1, except that it contained 73.3 parts of CB120phr compounded rubber MB (33.3 parts of EPDM and 40 parts of CB).

[0035] Crosslinked rubber sheets for Comparative Examples 2 to 11 were prepared in the same manner as in Example 1 or Comparative Example 1. The total mass of rubber material in each compound was 100 parts by mass (PHR) for all comparative examples.

[0036] [Comparative Example 2] A cross-linked rubber sheet for Comparative Example 2 was prepared in the same manner as in Example 1, except that the formulation consisted of 25 parts EPDM (a total of 90 parts by mass of EPDM including each MB portion) and 10 parts BR.

[0037] [Comparative Example 3] Instead of "CB80phr compounded rubber MB," we have prepared CB120phr compounded rubber MB, which is made by compounding 120phr of CB (Seas V) into a carbon black compounded rubber masterbatch (CB compounded rubber MB): EPDM (EPT-4021H). EPDM 11.7 parts (total of 60 mass parts including each MB portion), BR 40 copies, CNF20phr-containing rubber MB 18 parts (EPDM 15 parts, CNF 3 parts), CB120phr compounded rubber MB73.3 parts (EPDM 33.3 parts, CB 40 parts), A cross-linked rubber sheet for Comparative Example 3 was prepared in the same manner as in Example 1, except for the aforementioned difference.

[0038] [Comparative Example 4] Instead of "CB80phr compounded rubber MB," we have prepared CB120phr compounded rubber MB, which is made by compounding 120phr of CB (Seas V) into a carbon black compounded rubber masterbatch (CB compounded rubber MB): EPDM (EPT-4021H). EPDM 1.7 parts (50 mass parts in total, including each MB portion), BR 50 copies, CNF20phr-containing rubber MB 18 parts (EPDM 15 parts, CNF 3 parts), CB120phr compounded rubber MB73.3 parts (EPDM 33.3 parts, CB 40 parts), A cross-linked rubber sheet for Comparative Example 4 was prepared in the same manner as in Example 1, except for the aforementioned difference.

[0039] [Comparative Example 5] A cross-linked rubber sheet for Comparative Example 5 was prepared in the same manner as in Example 1, except that the formulation consisted of 30 parts EPDM (85 parts EPDM including each MB component) and 6 parts CNF20phr-containing rubber MB (5 parts EPDM, 1 part CNF).

[0040] [Comparative Example 6] A cross-linked rubber sheet for Comparative Example 6 was prepared in the same manner as in Example 1, except that the formulation consisted of 10 parts EPDM (85 parts EPDM in total, including each MB component) and 30 parts CNF20phr-containing rubber MB (25 parts EPDM, 5 parts CNF).

[0041] [Comparative Example 7] A cross-linked rubber sheet for Comparative Example 7 was prepared in the same manner as in Example 1, except that it contained 45 parts of EPDM (85 parts by mass of EPDM including each MB component) and 45 parts of CB80phr-containing rubber MB (25 parts of EPDM and 20 parts of CB).

[0042] [Comparative Example 8] A cross-linked rubber sheet for Comparative Example 8 was prepared in the same manner as in Example 1, except that the amount of dicumyl peroxide (DCP) added was 1 part (parts by mass).

[0043] [Comparative Example 9] A cross-linked rubber sheet for Comparative Example 9 was prepared in the same manner as in Example 1, except that "BR 15 parts" was replaced with 15 parts of styrene-butadiene rubber (SBR) and 20 parts of EPDM (a total of 85 parts by mass of EPDM, including the MB portions of each).

[0044] [Comparative Example 10] A cross-linked rubber sheet for Comparative Example 10 was prepared in the same manner as in Example 1, except that "BR 15 parts" was replaced with 30 parts of acrylonitrile butadiene rubber (NBR) and 5 parts of EPDM (70 parts by mass of EPDM including MB portions of each).

[0045] [Comparative Example 11] A cross-linked rubber sheet for Comparative Example 11 was prepared in the same manner as in Example 1, except that "BR 15 parts" was replaced with 15 parts of natural rubber (NR) and 20 parts of EPDM (a total of 85 parts by mass of EPDM including the MB portions of each). All of the cross-linked rubber sheets for the above examples and comparative examples were marked to indicate the sheet-out rolling direction (row direction).

[0046] <Measurement of physical properties of rubber compositions> In the examples and comparative examples, the sheet-out rolling direction of the cross-linked rubber sheets was defined as the grain direction, and the direction perpendicular to it as the anti-grain direction. Test specimens were prepared by punching out dumbbell-shaped No. 3 sheets as described in JIS K 6251:2017, with the longitudinal (test) direction aligned with either the grain or anti-grain direction. Using these test specimens, tensile tests were performed according to the method specified in JIS K 6251:2017, under conditions of a measurement temperature of 23°C and a tensile speed of 500 mm / min. The tensile stress (50% modulus (M50)), stress at tensile fracture (TB), and elongation at tensile fracture (EB) were measured when the elongation was 50%. In addition, the ratio of the M50 values ​​in the grain direction and the anti-grain direction was calculated as an indicator of anisotropy.

[0047] Tables 1 to 3 show the composition and blending amounts of the rubber compositions for Examples 1 to 10 and Comparative Examples 1 to 11, as well as the tensile strength in the grain direction and anti-grain direction: TB (MPa), elongation at break: EB (%), 50% modulus: M50 (MPa), and modulus ratio (50% modulus value in the grain direction / 50% modulus value in the anti-grain direction) indicating the degree of anisotropy (strength / weakness). The unit of blending amounts in the compositions in Tables 1 to 3 is parts by mass [PHR, phr] (parts by mass of various compounding agents / materials per 100 units of rubber mass). Note that in Tables 1 to 3 and below, the term "mass" in "parts by mass" is sometimes omitted and simply written as "parts". Also, "parts by mass" can be replaced with "parts by weight" without any particular issue.

[0048] [Table 1]

[0049] [Table 2]

[0050] [Table 3]

[0051] From Tables 1 and 2, when the rubber components are EPDM and butadiene rubber, it was determined from Examples 1 and 2 and Comparative Examples 1 to 4 that if the EPDM is 65 parts by mass or more and 88 parts by mass or less, and the butadiene rubber is 12 parts by mass or more and 35 parts by mass or less, then the modulus M50 values ​​in the arranging direction and antiarranging direction are equal to or greater than the M50 value of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio (anisotropy index) is 2 or less.

[0052] In Comparative Examples 3 and 4, the modulus M50 value in the direction of the grain could not be measured because the sheet was cut without stretching. Furthermore, in Comparative Example 4, it was also impossible to measure the modulus M50 value in the direction opposite to the grain.

[0053] From Tables 1 and 2, it was determined that if the cellulose nanofiber (specific example of microfibrillated cellulose) is between 1.5 parts by mass and 4.5 parts by mass, the modulus M50 values ​​in the arranging direction and the antiarranging direction are equal to or greater than the M50 value of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio (anisotropy index) is 2 or less.

[0054] From Tables 1 and 2, it was determined that if the carbon black content is 25 parts by mass or more, the modulus M50 values ​​in the arranging direction and antiarranging direction are equal to or greater than the M50 value of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio (anisotropy index) is 2 or less. Furthermore, when attempts were made to produce rubber sheets by increasing the amount of carbon black, it was found that it was possible to mold it into a sheet at 70 parts by mass, but molding (sheet formation) became difficult when the amount exceeded 70 parts by mass. The prototype with 70 parts by mass of carbon black exceeded the judgment criteria in physical property tests, but it was also found that there is a possibility of problems with processability and reproducibility during future mass production. For this reason, it was determined that the amount of carbon black in the rubber composition should preferably be 65 parts by mass or less.

[0055] From Tables 1 and 2, it was determined that if the DCP (dicumyl peroxide) content is between 2 and 6 parts by mass, the modulus M50 values ​​in the arranging and antiarranging directions are equal to or greater than the M50 value of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio (anisotropy index) is 2 or less.

[0056] From Table 3, it was determined that when the rubber components are EPDM and styrene-butadiene rubber (SBR), if the amount of EPDM is 45 parts by mass or more and 82 parts by mass or less, and the amount of SBR is 18 parts by mass or more and 55 parts by mass or less, the modulus M50 values ​​in the arranging direction and antiarranging direction are equal to or greater than the M50 value of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio (anisotropy index) is 2 or less.

[0057] Table 3 shows that even when the rubber components are EPDM and acrylonitrile butadiene rubber (NBR), EPDM and natural rubber (NR), or EPDM and butadiene rubber (BR), or EPDM and styrene butadiene rubber (SBR), the modulus ratio (anisotropy index) is higher than that of Comparative Example 1.

[0058] Thus, the first rubber composition of the present invention is 100 parts by mass of rubber component (A) containing EPDM (a1) and butadiene rubber (a2a), A filler component (B) containing microfibrillated cellulose (b1) and carbon black (b2) in an amount of 26.5 parts by mass or more and 69.5 parts by mass or less, A rubber composition containing 2 to 6 parts by mass of an organic peroxide crosslinking agent (C), The rubber component (A) consists of EPDM (a1) in an amount of 65 parts by mass or more and 88 parts by mass or less. The butadiene rubber (a2a) is present in amounts of 12 parts by mass or more and 35 parts by mass or less. The filler component (B) is, The cellulose nanofiber (b1) is present in an amount of 1.5 parts by mass or more and 4.5 parts by mass or less. Because the amount of carbon black (b2) is between 25 parts by mass and 65 parts by mass, When formed into a sheet, it was confirmed that the modulus M50 values ​​in the grain direction and antigravity direction were equal to or greater than the M50 value of Comparative Example 1, in which the rubber component was EPDM alone, and that the modulus ratio, as an indicator of anisotropy, was 2 or less.

[0059] Furthermore, the rubber composition of the present invention is 100 parts by mass of rubber component (A) containing EPDM (a1) and styrene-butadiene rubber (a2b), A filler component (B) containing microfibrillated cellulose (b1) and carbon black (b2) in an amount of 26.5 parts by mass or more and 69.5 parts by mass or less, A rubber composition containing 2 to 6 parts by mass of an organic peroxide crosslinking agent (C), The rubber component (A) is, EPDM(a1) is 45 parts by mass or more and 82 parts by mass or less. The styrene-butadiene rubber (a2b) is present in an amount of 18 parts by mass or more and 55 parts by mass or less. The filler component (B) is, The cellulose nanofiber (b1) is present in an amount of 1.5 parts by mass or more and 4.5 parts by mass or less. Because the amount of carbon black (b2) is between 25 parts by mass and 65 parts by mass, When formed into a sheet, it was confirmed that the modulus M50 values ​​in the grain direction and antigravity direction were equal to or greater than the M50 value of Comparative Example 1, in which the rubber component was EPDM alone, and that the modulus ratio, as an indicator of anisotropy, was 2 or less.

[0060] In the examples and comparative examples, the microfibrillated cellulose used was cellulose nanofiber (CNF) with an average fiber diameter of 100 nm. However, when a cross-linked rubber sheet was prepared using CNF with an average fiber diameter of 3 nm to 10 nm in the same manner as in Example 1, the modulus ratio (anisotropy index) was 1.0, indicating low orientation. Furthermore, the modulus M50 value of the fibers was 4.3 MPa, which was lower than that of Comparative Example 1 (5.6 MPa).

[0061] Furthermore, when a rubber sheet was prepared using cellulose microfiber (CMF) with an average fiber diameter of several μm (1 μm to 9 μm) in the same manner as in Example 1, the modulus ratio (anisotropy index) was 1.1, indicating low orientation. In addition, the modulus M50 value of the fibers was 4.5 MPa, which was lower than that of Comparative Example 1 (5.6 MPa).

[0062] Based on these findings, it was determined that the microfibrillated cellulose used in the rubber composition of the present invention is preferably CNF with an average fiber diameter of 50 nm to 200 nm. [Industrial applicability]

[0063] The rubber composition of the present invention is useful in the manufacture of rubber products such as hoses, seals, or vibration-damping rubber, where low anisotropy of rubber properties is desired.

Claims

1. 100 parts by mass of rubber component (A) containing ethylene propylene diene rubber (a1) and butadiene rubber (a2a), A filler component (B) containing microfibrillated cellulose (b1) and carbon black (b2) in an amount of 26.5 parts by mass or more and 69.5 parts by mass or less, A rubber composition containing 2 to 6 parts by mass of an organic peroxide crosslinking agent (C), The aforementioned rubber component (A) is The ethylene propylene diene rubber (a1) is present in an amount of 65 parts by mass or more and 88 parts by mass or less. The butadiene rubber (a2a) is present in amounts of 12 parts by mass or more and 35 parts by mass or less. The aforementioned filler component (B) is The microfibrillated cellulose (b1) is present in an amount of 1.5 parts by mass or more and 4.5 parts by mass or less. The carbon black (b2) is present in amounts of 25 parts by mass or more and 65 parts by mass or less. Rubber composition.

2. 100 parts by mass of rubber component (A) containing ethylene propylene diene rubber (a1) and styrene butadiene rubber (a2b), A filler component (B) containing microfibrillated cellulose (b1) and carbon black (b2) in an amount of 26.5 parts by mass or more and 69.5 parts by mass or less, A rubber composition containing 2 to 6 parts by mass of an organic peroxide crosslinking agent (C), The aforementioned rubber component (A) is The ethylene propylene diene rubber (a1) is present in an amount of 45 parts by mass or more and 82 parts by mass or less. The styrene-butadiene rubber (a2b) is present in an amount of 18 parts by mass or more and 55 parts by mass or less. The aforementioned filler component (B) is The microfibrillated cellulose (b1) is present in an amount of 1.5 parts by mass or more and 4.5 parts by mass or less. The carbon black (b2) is present in amounts of 25 parts by mass or more and 65 parts by mass or less. Rubber composition.

3. The rubber composition according to claim 1 or 2, wherein the microfibrillated cellulose is cellulose nanofiber having a fiber diameter of 50 nm or more and 200 nm or less.

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