Rubber composition

Abstract

This rubber composition contains: 100 parts by mass of a rubber component (A) containing an ethylene propylene diene monomer (EPDM) and a butadiene rubber (BR); 26.5 to 69.5 parts by mass of a filler component (B) containing microfibrillated cellulose and carbon black; and 2-6 parts by mass of an organic peroxide crosslinking agent (C), in the rubber component (A), the EPDM is 65-88 parts by mass and the BR is 12-35 parts by mass, and in the filler component (B), the microfibrillated cellulose is 1.5-4.5 parts by mass and the carbon black is 25-65 parts by mass.

Description

Technical Field

[0001] This invention relates to a rubber composition in which anisotropy is suppressed. More specifically, it relates to a rubber composition that exhibits excellent strength and elongation not only in the grain direction oriented by the short reinforcing fibers of microfibrillated cellulose, but also in the transverse grain direction orthogonal to the fiber orientation direction. Background Technology

[0002] For rubber compositions incorporating reinforcing materials such as short fibers, pressure is applied to the uncrosslinked compound during extrusion or calendering during sheet forming. This causes the rubber molecules, polymer chains, and anisotropic granular reinforcing materials (as compounding agents) to orient themselves along the rolling direction. Consequently, tensile strength and elongation differ in the rolling direction (called the grain direction) and the direction perpendicular to it (called the transverse grain direction) within the molded body. This results in differences in the mechanical strength of the rubber molded body. The anisotropy of material properties is called texture phenomenon (also known as calendering texture).

[0003] The anisotropy of physical properties in the molded rubber composition (molded body) is utilized and applied in various ways depending on the purpose and environment of the rubber product. Patent Document 1 discloses a rubber structure mixed with short fibers, in which a specified amount of short fibers are oriented in three-dimensional directions (X-axis, Y-axis, Z-axis) and exhibit anisotropy for an elastic substrate in which a specified rubber is incorporated.

[0004] Patent document 2 discloses a rubber composition for tires, which contains short cellulose fibers with an average fiber length L of 1 mm to 3 mm and an average fiber diameter D of 70 nm to 1 μm, as well as diene rubber.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 4-166328

[0008] Patent Document 2: Japanese Patent Application Publication No. 2012-122019 Summary of the Invention

[0009] The significant anisotropy generated in rubber molded bodies formed from rubber compositions is an advantageous factor for achieving high modulus. However, if the orientation is incorrect during use, the desired strength cannot be achieved, and cracks may easily propagate along the grain direction, which can become disadvantages depending on the application. Furthermore, for rubber products used in sealing components such as rubber hoses, rubber rollers, rubber gaskets, washers, and seals, rubbers with low anisotropy are desirable. In addition, for products in the electronic field such as devices, batteries, electronic circuit boards, housing gaskets, and spacers, rubbers with low anisotropy are sometimes preferred.

[0010] The purpose of this invention is to provide a rubber composition that, when molded into a sheet, has a small difference in tensile properties between the texture direction and the transverse texture direction orthogonal to it, thereby suppressing anisotropy generated in the rubber molded body obtained through molding process.

[0011] The inventors have conducted in-depth research on rubber compositions that are suitable for increasing the modulus in the transverse grain direction while maintaining the modulus in the grain direction of rubber molded articles such as sheet rubber, and suppressing the anisotropy of the tensile properties of the rubber molded articles. As a result, the inventors discovered that by adding a filler component containing microfibrillated cellulose and carbon black, as well as an organic peroxide crosslinking agent, in a specific ratio to a rubber component containing ethylene propylene diene monomer (EPDM) rubber and butadiene rubber or styrene-butadiene rubber, the above-mentioned problems can be solved, thereby completing the present invention.

[0012] Specifically, the present invention relates to a rubber composition comprising:

[0013] Rubber component (A) 100 parts by weight contains ethylene propylene diene monomer (a1) rubber and butadiene rubber (a2a).

[0014] The filler component (B) consists of 26.5 to 69.5 parts by weight, containing microfibrillated cellulose (b1) and carbon black (b2).

[0015] Organic peroxide crosslinking agent (C) 2 to 6 parts by weight;

[0016] In the above rubber component (A),

[0017] Ethylene propylene diene monomer (a1) rubber is available in quantities of 65 to 88 parts by weight.

[0018] Butadiene rubber (a2a) is present in quantities of 12 to 35 parts by weight.

[0019] Of the above filler component (B),

[0020] Microfibrillated cellulose (b1) is present in quantities of 1.5 parts by weight to 4.5 parts by weight.

[0021] Carbon black (b2) is present in quantities of 25 to 65 parts by mass.

[0022] Additionally, the present invention relates to a rubber composition comprising:

[0023] Rubber component (A) 100 parts by weight contains ethylene propylene diene monomer (a1) rubber and styrene-butadiene rubber (a2b).

[0024] The filler component (B) consists of 26.5 to 69.5 parts by weight, containing microfibrillated cellulose (b1) and carbon black (b2).

[0025] Organic peroxide crosslinking agent (C) 2 to 6 parts by weight;

[0026] Of the above rubber component (A),

[0027] Ethylene propylene diene monomer (a1) rubber is available in quantities of 45 parts by weight to 82 parts by weight.

[0028] Styrene-butadiene rubber (a2b) is available in quantities of 18 to 55 parts by weight.

[0029] Of the above filler component (B),

[0030] Microfibrillated cellulose (b1) is present in quantities of 1.5 parts by weight to 4.5 parts by weight.

[0031] Carbon black (b2) is present in quantities of 25 to 65 parts by mass.

[0032] In this invention, the microfibrillated cellulose is preferably cellulose nanofiber (CNF) with a fiber diameter of 50 nm to 200 nm.

[0033] The rubber composition of the present invention, when formed into a sheet, exhibits a tensile property difference of less than 2 times between the grain direction and the transverse grain direction orthogonal to it, thus possessing low anisotropy. Therefore, the rubber composition of the present invention can reduce the anisotropy of properties generated in the molded rubber body after molding, and can obtain a rubber body with less anisotropy caused by molding. Detailed Implementation

[0034] The rubber composition of the present invention is characterized in that microfibrillated cellulose such as cellulose nanofibers, carbon black, and organic peroxide crosslinking agents are incorporated in a specific proportion as fillers in a rubber composition of a specific composition.

[0035] In the first rubber composition of the present invention, ethylene propylene diene monomer (EPDM) rubber (a1) and butadiene rubber (a2a) are included as rubber components. In addition, in the second rubber composition of the present invention, ethylene propylene diene monomer (EPDM) rubber (a1) and styrene-butadiene rubber (a2b) are included as rubber components.

[0036] In the first rubber composition of the present invention, ethylene propylene diene monomer (a1) comprises 65 to 88 parts by mass, and butadiene rubber (a2a) comprises 12 to 35 parts by mass. In the second rubber composition of the present invention, ethylene propylene diene monomer (a1) comprises 45 to 82 parts by mass, and styrene-butadiene rubber (a2b) comprises 18 to 55 parts by mass.

[0037] In the first rubber composition of the present invention, the microfibrillated cellulose (b1) is 1.5 to 4.5 parts by weight relative to 100 parts by weight of the rubber component. In the second rubber composition of the present invention, the microfibrillated cellulose (b1) is 1.5 to 4.5 parts by weight relative to 100 parts by weight of the rubber component. In both the first and second rubber compositions of the present invention, carbon black (b2) is 25 to 65 parts by weight relative to 100 parts by weight of the rubber component.

[0038] Specific examples of microfibrillated cellulose as a filler include nano-sized cellulose nanofibers (CNFs), with a fiber diameter preferably between 50 nm and 200 nm. More preferably, the fiber diameter of the CNF is between 50 nm and 150 nm (50 nm to 150 nm), and to obtain a higher reinforcing effect, the fiber length is preferably several micrometers or more.

[0039] In addition, carbon black, which is also used as a filler, is preferably of HAF to GPF grade from furnace-processed carbon black, based on the balance between dispersibility and reinforcement.

[0040] As an organic peroxide crosslinking agent, known crosslinking agents such as dicumyl peroxide (DCP) or 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (25B), which are capable of forming C-C bond crosslinking chains, can be used.

[0041] The rubber composition of the present invention may also contain any components such as anti-aging agents, oils or plasticizers.

[0042] <Examples of manufacturing rubber compositions>

[0043] A rubber composition is manufactured using the raw materials shown below.

[0044] Ethylene propylene diene monomer (EPDM): EPT-4021H manufactured by Mitsui Chemicals Co., Ltd.

[0045] Butadiene rubber (BR): UBE Elastomer Company's UBEPOL BR (registered trademark) BR 150B

[0046] Styrene-butadiene rubber (SBR): ESBR 1502 manufactured by ENEOS Materials

[0047] Nitrile butadiene rubber (NBR): Nipol (registered trademark) DN3350 manufactured by ZEON Corporation of Japan.

[0048] Natural Rubber (NR): Grade - RSS No. 3

[0049] Cellulose nanofibers (CNF): CELISH KY110N (average fiber diameter 100nm), manufactured by DAICEL Miraizu.

[0050] Carbon black (CB): SEAST (registered trademark) produced by Tokai Carbon Co., Ltd. SEAST V

[0051] Zinc oxide: The first type of zinc oxide manufactured by Sakai Chemical Co., Ltd.

[0052] Stearic acid: Powdered stearic acid (SAKURA) manufactured by Nippon Oil Company

[0053] Dicumyl peroxide (DCP): Manufactured by Nippon Oil Company, PERCUMYL (registered trademark).

[0054] To prevent cellulose nanofibers (CNF) and carbon black (CB) from agglomerating and to ensure their uniform dispersion, a high-concentration rubber masterbatch (MB and EPDM as the matrix) was prepared in advance and then added for mixing. Mixing.

[0055] EPDM masterbatch with cellulose nanofibers (rubber MB with CNF): Rubber MB with 20 phr CNF (KY110N) was prepared in PIGMOTEX CLEAR BB5045 and EPDM (EPT-4021H) manufactured by Sanyo Pigment Co., Ltd.

[0056] EPDM masterbatch with carbon black (rubber MB with CB): Rubber MB with 80 phr of CB (SEAST V) in EPDM (EPT-4021H) was prepared.

[0057] [Example 1]

[0058] The following ingredients are mixed using a two-roll mill (also known as a calender):

[0059] EPDM 20 parts (including MB portion, totaling 85 parts by weight; "parts" here means "parts by weight")

[0060] BR 15 copies,

[0061] It contains 18 parts of rubber MB with 20 phr CNF (15 parts EPDM and 3 parts CNF).

[0062] It is formulated with 90 parts of CB rubber MB (50 parts of EPDM and 40 parts of CB) containing 80 phr of CB.

[0063] 5 parts zinc oxide

[0064] 3 copies of DCP

[0065] 1 part stearic acid

[0066] The rubber is mixed at 50℃~60℃ for about 3 to 5 minutes (for orientation), and then four 0.6mm thick sheets with the same orientation direction are made. Next, the four 0.6mm thick sheets are overlapped in the same orientation direction, and cross-linking is performed by applying heat pressure at 170℃ for 20 minutes and 5MPa using a 2mm thick metal frame, resulting in a 2.0mm thick cross-linked rubber sheet [with orientation]. [Test piece of anisotropic embodiment 1].

[0067] [Comparative Example 1]

[0068] Unmixed Similar to Example 1, a cross-linked rubber sheet, "Comparative Example 1," was prepared by combining rubber components other than EPDM to serve as an evaluation benchmark (blank) for tensile strength (modulus) and anisotropy (orientation). Specifically, the following components were mixed using a two-roll mill:

[0069] 35 EPDM portions (100 portions in total, including MB portion).

[0070] BR 0 copies (not cooperating)

[0071] It is formulated with 18 parts of rubber MB containing 20 phr CNF (15 parts EPDM, 3 parts CNF).

[0072] It is formulated with 90 parts of CB (80 phr) of rubber MB (50 parts of EPDM and 40 parts of CB).

[0073] 5 parts zinc oxide

[0074] 3 copies of DCP

[0075] 1 part stearic acid

[0076] Similar to Example 1, after mixing at a specified temperature for a specified time, four sheets with a thickness of 0.6 mm and consistent orientation were prepared. Next, the four 0.6 mm thick sheets were overlapped in the same orientation, and crosslinking was performed using a 2 mm thick metal frame under heat pressure at 170°C for 20 minutes and a pressure of 5 MPa, resulting in a 2.0 mm thick crosslinked rubber sheet for testing, "Comparative Example 1". It should be noted that the crosslinked rubber sheet of Comparative Example 1, which does not contain rubber components other than EPDM, exhibits sufficient anisotropy due to the orientation (calendering texture) of the incorporated CNF.

[0077] The same procedures were followed as in Example 1, and test cross-linked rubber sheets for Examples 2 through 10 were produced. It should be noted that the total mass of the rubber material in each formulation was 100 parts by weight (PHR) in any example.

[0078] [Example 2]

[0079] In the preparation, 5 parts of EPDM (70 parts by mass including each MB portion) and 30 parts of BR were used. Otherwise, the same procedure as in Example 1 was followed to prepare the test crosslinked rubber sheet for Example 2.

[0080] [Example 3]

[0081] In the formulation, 25 parts of EPDM (85 parts of EPDM including each MB portion) and 12 parts of rubber MB with 20 phr CNF were prepared (10 parts of EPDM and 2 parts of CNF). Otherwise, the same procedure as in Example 1 was followed to prepare the test crosslinked rubber sheet of Example 3.

[0082] [Example 4]

[0083] The cross-linked rubber sheet for Example 4 was prepared by using 32.5 parts of EPDM (85 parts by mass including each MB portion) and 67.5 parts of rubber MB containing 80 phr of CB (37.5 parts of EPDM and 30 parts of CB). Otherwise, the same procedure as in Example 1 was followed.

[0084] [Example 5]

[0085] The cross-linked rubber sheet for Example 5 was prepared by using 7.5 parts of EPDM (85 parts by mass including each MB portion) and 112.5 parts of rubber MB containing 80 phr of CB (62.5 parts of EPDM and 50 parts of CB). Otherwise, the same procedure as in Example 1 was followed.

[0086] [Example 6]

[0087] The test crosslinked rubber sheet of Example 6 was prepared by using 5 parts of EPDM (85 parts by mass including each MB portion) and 135 parts of rubber MB containing 80 phr of CB (75 parts of EPDM and 60 parts of CB). Otherwise, the same procedure as in Example 1 was followed.

[0088] [Example 7]

[0089] The amount of dicumyl peroxide (DCP) was set to 5 parts (parts by weight), and otherwise the same procedure as in Example 1 was followed to prepare the test crosslinked rubber sheet for Example 7.

[0090] [Example 8]

[0091] Instead of “BR 15 parts”, 20 parts of styrene-butadiene rubber (SBR) and 15 parts of EPDM (including each MB part, totaling 80 parts by mass of EPDM) were used. Otherwise, the same procedure as in Example 1 was followed to produce the test crosslinked rubber sheet of Example 8.

[0092] [Example 9]

[0093] Instead of “BR 15 parts”, 30 parts of styrene-butadiene rubber (SBR) and 5 parts of EPDM (70 parts by mass including each MB part of EPDM) were used. Otherwise, the same procedure as in Example 1 was followed to produce the test crosslinked rubber sheet of Example 9.

[0094] [Example 10]

[0095] Instead of "rubber MB with 80 phr of CB", a rubber masterbatch with carbon black (rubber MB with CB) was prepared: a rubber MB with 120 phr of CB (SEAST V) in EPDM (EPT-4021H). Then,

[0096] Replace "BR15 copies" with:

[0097] Styrene-butadiene rubber (SBR) 50 parts,

[0098] 1.7 copies of EPDM (including each MB portion, totaling 50 copies of EPDM by mass).

[0099] It is formulated with 18 parts of rubber MB containing 20 phr CNF (15 parts EPDM, 3 parts CNF).

[0100] The rubber MB is formulated with 120 phr of CB and contains 73.3 parts (EPDM 33.3 parts, CB 40 parts).

[0101] In addition, the same procedure as in Example 1 was followed to produce the test cross-linked rubber sheet for Example 10.

[0102] The following procedures were performed in the same manner as in Example 1 or Comparative Example 1, and test crosslinked rubber sheets for Comparative Examples 2 to 11 were prepared. It should be noted that the total mass of the rubber material in each formulation was 100 parts by mass (PHR) for any comparative example.

[0103] [Comparative Example 2]

[0104] In the formulation, 25 parts of EPDM (90 parts by mass including each MB portion) and 10 parts of BR were used. Otherwise, the same procedure as in Example 1 was followed to produce the test crosslinked rubber sheet for Comparative Example 2.

[0105] [Comparative Example 3]

[0106] Instead of "rubber MB with 80 phr of CB", prepare a rubber masterbatch with carbon black (rubber MB with CB): a rubber MB with 120 phr of CB (SEAST V) in EPDM (EPT-4021H). Then, set it as:

[0107] EPDM 11.7 copies (60 mass copies including each MB portion).

[0108] BR 40 copies,

[0109] It is formulated with 18 parts of rubber MB containing 20 phr CNF (15 parts EPDM, 3 parts CNF).

[0110] The rubber MB is formulated with 120 phr of CB and contains 73.3 parts (EPDM 33.3 parts, CB 40 parts).

[0111] In addition, the same procedure was followed as in Example 1 to produce a test cross-linked rubber sheet for Comparative Example 3.

[0112] [Comparative Example 4]

[0113] Instead of "rubber MB with 80 phr of CB", prepare a rubber masterbatch with carbon black (rubber MB with CB): a rubber MB with 120 phr of CB (SEAST V) in EPDM (EPT-4021H). Then, set it as:

[0114] EPDM 1.7 copies (50 mass copies including each MB portion).

[0115] BR 50 copies,

[0116] It is formulated with 18 parts of rubber MB containing 20 phr CNF (15 parts EPDM, 3 parts CNF).

[0117] The rubber MB is formulated with 120 phr of CB and contains 73.3 parts (EPDM 33.3 parts, CB 40 parts).

[0118] In addition, the same procedure was followed as in Example 1 to produce a test cross-linked rubber sheet for Comparative Example 4.

[0119] [Comparative Example 5]

[0120] In the formulation, 30 parts of EPDM (85 parts of EPDM including each MB portion) and 6 parts of rubber MB with 20 phr CNF were prepared (5 parts of EPDM and 1 part of CNF). Otherwise, the same procedure as in Example 1 was followed to prepare the test crosslinked rubber sheet for Comparative Example 5.

[0121] [Comparative Example 6]

[0122] In the formulation, 10 parts of EPDM (85 parts of EPDM including each MB portion) and 30 parts of rubber MB with 20 phr CNF were prepared (25 parts of EPDM and 5 parts of CNF). Otherwise, the same procedure as in Example 1 was followed to prepare the test crosslinked rubber sheet for Comparative Example 6.

[0123] [Comparative Example 7]

[0124] The test crosslinked rubber sheet for Comparative Example 7 was prepared by using 45 parts of EPDM (85 parts by mass including each MB portion) and 45 parts of rubber MB containing 80 phr of CB (25 parts of EPDM and 20 parts of CB). Otherwise, the same procedure as in Example 1 was followed.

[0125] [Comparative Example 8]

[0126] The amount of dicumyl peroxide (DCP) was set to 1 part (parts by mass), and otherwise the same procedure was followed as in Example 1 to prepare the test crosslinked rubber sheet for Comparative Example 8.

[0127] [Comparative Example 9]

[0128] Instead of “BR 15 parts”, 15 parts of styrene-butadiene rubber (SBR) and 20 parts of EPDM (including each MB part, totaling 85 parts by mass of EPDM) were used. Otherwise, the same procedure as in Example 1 was followed to prepare the test crosslinked rubber sheet for Comparative Example 9.

[0129] [Comparative Example 10]

[0130] Instead of “BR 15 parts”, 30 parts of nitrile rubber (NBR) and 5 parts of EPDM (70 parts by mass including each MB part of EPDM) were used. Otherwise, the same procedure as in Example 1 was followed to prepare the test crosslinked rubber sheet for Comparative Example 10.

[0131] [Comparative Example 11]

[0132] Instead of "BR 15 parts", the sample was set to 15 parts natural rubber (NR) and 20 parts EPDM (85 parts by mass including all MB portions of EPDM). Otherwise, the same procedure as in Example 1 was followed to prepare the test crosslinked rubber sheet for Comparative Example 11. It should be noted that the test crosslinked rubber sheets of all the above examples and comparative examples are marked with a mark indicating the rolling direction (texture direction).

[0133] <Determination of physical properties of rubber compositions>

[0134] The cross-linked rubber sheets obtained in the examples and comparative examples were rolled in the grain direction, and the direction orthogonal to it was set as the transverse grain direction. Test pieces were prepared by punching the dumbbell-shaped No. 3 sheets according to JIS K 6251:2017, with the long side (test) aligned with either the grain or transverse grain direction. Using these test pieces, tensile tests were conducted according to the method specified in JIS K 6251:2017 at a test temperature of 23°C and a tensile speed of 500 mm / min. The tensile stress (50% modulus (M50)) at 50% elongation, the stress at tensile fracture (TB), and the elongation at tensile fracture (EB) were measured. Furthermore, the ratio of the M50 value in the grain direction to that in the transverse grain direction was calculated as an indicator of anisotropy.

[0135] The composition and formulation amounts of the rubber compositions of Examples 1-10 and Comparative Examples 1-11, as well as the tensile strength in the grain direction and transverse grain direction: TB (MPa), elongation at break: EB (%), 50% modulus: M50 (MPa), and the modulus ratio (50% modulus value in the grain direction / 50% modulus value in the transverse grain direction) indicating the magnitude (strength) of anisotropy are shown in Tables 1-3. The formulation amounts in the compositions of Tables 1-3 are in parts by mass [PHR, phr] (various compounding agents relative to 100% of the rubber mass). (Parts by mass of the material). It should be noted that sometimes the "mass" in the parts by mass of Tables 1 to 3 and below is omitted and simply referred to as "parts". In addition, "parts by mass" can also be called "parts by weight".

[0136]

[0137]

[0138]

[0139] According to Tables 1 and 2, when the rubber composition is EPDM and butadiene rubber, it can be determined from Examples 1, 2 and Comparative Examples 1 to 4 that if EPDM is 65 to 88 parts by mass and butadiene rubber is 12 to 35 parts by mass, the modulus M50 values ​​in the grain direction and transverse grain direction are equal to or greater than the M50 values ​​of Comparative Example 1, where the rubber composition is EPDM alone, and the modulus ratio (anisotropy index) is 2 or less.

[0140] For Comparative Examples 3 and 4, since the sheet broke before it could elongate, the modulus M50 value in the grain direction could not be measured. Furthermore, the modulus M50 value in the transverse grain direction could not be measured in Comparative Example 4.

[0141] Based on Tables 1 and 2, it can be determined that if the cellulose nanofibers (specific examples of microfibrillated cellulose) are 1.5 to 4.5 parts by mass, then the modulus M50 values ​​in the texture direction and transverse texture direction are equal to or greater than the M50 values ​​of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio (anisotropy index) is less than 2.

[0142] Based on Tables 1 and 2, it can be determined that if the carbon black content is 25 parts by mass or more, the M50 values ​​in both the grain direction and the transverse grain direction are equal to or greater than the M50 values ​​of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio (anisotropy index) is 2 or less. Furthermore, it is known that when attempting to increase the amount of carbon black to produce rubber sheets, it is possible to form sheets at 70 parts by mass; however, if the content exceeds 70 parts by mass, it becomes difficult to form sheets. The prototype sample with 70 parts by mass of carbon black exceeded the judgment benchmark in the physical property tests, but it was also found that problems may arise in terms of processability and reproducibility during future mass production. Therefore, it is determined that the preferred amount of carbon black in the rubber composition is 65 parts by mass or less.

[0143] Based on Tables 1 and 2, it can be determined that if the DCP (diisopropylbenzene peroxide) content is 2 to 6 parts by mass, the M50 values ​​of the texture direction and the transverse texture direction are equal to or greater than the M50 values ​​of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio (anisotropy index) is less than 2.

[0144] According to Table 3, it can be determined that when the rubber composition is EPDM and styrene-butadiene rubber (SBR), if the EPDM content is 45 to 82 parts by mass and the SBR content is 18 to 55 parts by mass, the modulus M50 values ​​in the grain direction and the transverse grain direction are equal to or greater than the M50 values ​​of Comparative Example 1, where the rubber composition is EPDM alone, and the modulus ratio (anisotropy index) is less than 2.

[0145] Table 3 confirms that when the rubber composition is EPDM and nitrile rubber (NBR) or EPDM and natural rubber (NR), even when the rubber composition is EPDM and butadiene rubber (BR) or EPDM and styrene-butadiene rubber (SBR) and is considered a suitable blending ratio, the modulus ratio (anisotropy index) is higher than that of Comparative Example 1.

[0146] It can be confirmed that by comprising 100 parts by mass of a rubber component (A) containing EPDM (a1) and butadiene rubber (a2a), 26.5 to 69.5 parts by mass of a filler component (B) containing microfibrillated cellulose (b1) and carbon black (b2), and 2 to 6 parts by mass of an organic peroxide crosslinking agent (C), wherein in the rubber component (A), EPDM (a1) is 65 to 88 parts by mass and butadiene rubber (a2a) is 12 to 35 parts by mass, and in the filler component (B), cellulose nanofibers (b1) is 1.5 to 4.5 parts by mass and carbon black (b2) is 25 to 65 parts by mass, when molded into a sheet, the modulus M50 values ​​in the grain direction and the transverse grain direction are equal to or greater than those of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio, as an indicator of anisotropy, is 2 or less.

[0147] Furthermore, it can be confirmed that by comprising 100 parts by mass of a rubber component (A) containing EPDM (a1) and styrene-butadiene rubber (a2b), 26.5 to 69.5 parts by mass of a filler component (B) containing microfibrillated cellulose (b1) and carbon black (b2), and 2 to 6 parts by mass of an organic peroxide crosslinking agent (C), wherein in the rubber component (A), EPDM (a1) is 45 to 82 parts by mass and styrene-butadiene rubber (a2b) is 18 to 55 parts by mass, and in the filler component (B), cellulose nanofibers (b1) is 1.5 to 4.5 parts by mass and carbon black (b2) is 25 to 65 parts by mass, when molded into a sheet, the modulus M50 values ​​in the grain direction and the transverse grain direction are equal to or greater than those of Comparative Example 1, where the rubber component is EPDM alone, and the modulus ratio, as an indicator of anisotropy, is 2 or less.

[0148] It should be noted that the microfibrillated cellulose used in the examples and comparative examples is cellulose nanofiber (CNF) with an average fiber diameter of 100 nm. However, when CNF with an average fiber diameter of 3 nm to 10 nm is used and cross-linked rubber sheets are prepared in the same manner as in Example 1, the modulus ratio (anisotropy index) is 1.0, indicating low orientation. In addition, the texture modulus M50 value is 4.3 MPa, which is lower than that of Comparative Example 1 (5.6 MPa).

[0149] Furthermore, when cellulose microfibers (CMF) with an average fiber diameter of a few micrometers (1μm to 9μm) were used to prepare the rubber sheet in the same manner as in Example 1, the modulus ratio (anisotropy index) was 1.1, indicating low orientation. In addition, the texture modulus M50 value was 4.5 MPa, which is lower than that of Comparative Example 1 (5.6 MPa).

[0150] Therefore, it is 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.

[0151] Industrial availability

[0152] The rubber composition of the present invention is useful for the manufacture of rubber products such as hoses, seals or vibration damping rubbers that require low anisotropy in rubber properties.

Claims

1. A rubber composition comprising: Rubber component (A) 100 parts by weight contains ethylene propylene diene monomer (a1) rubber and butadiene rubber (a2a). The filler component (B) consists of 26.5 to 69.5 parts by weight, containing microfibrillated cellulose (b1) and carbon black (b2). Organic peroxide crosslinking agent (C) 2 to 6 parts by weight; In the rubber component (A), Ethylene propylene diene monomer (a1) rubber is available in quantities of 65 to 88 parts by weight. Butadiene rubber (a2a) is present in quantities of 12 to 35 parts by weight. In the filler component (B), Microfibrillated cellulose (b1) is present in quantities of 1.5 parts by weight to 4.5 parts by weight. Carbon black (b2) is present in quantities of 25 to 65 parts by mass.

2. A rubber composition comprising: Rubber component (A) 100 parts by weight contains ethylene propylene diene monomer (a1) rubber and styrene-butadiene rubber (a2b). The filler component (B) consists of 26.5 to 69.5 parts by weight, containing microfibrillated cellulose (b1) and carbon black (b2). Organic peroxide crosslinking agent (C) 2 to 6 parts by weight; In the rubber component (A), Ethylene propylene diene monomer (a1) rubber is available in quantities of 45 parts by weight to 82 parts by weight. Styrene-butadiene rubber (a2b) is available in quantities of 18 to 55 parts by weight. In the filler component (B), Microfibrillated cellulose (b1) is present in quantities of 1.5 parts by weight to 4.5 parts by weight. Carbon black (b2) is present in quantities of 25 to 65 parts by mass.

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

Images