Rubber composition

Abstract

The problem addressed by the present application is to provide a rubber composition having excellent vibration-proofing and sound-deadening properties. The rubber composition disclosed by the present application is a crosslinked rubber composition containing ethylene propylene diene rubber (EPDM), 110–190 parts by mass of carbon black per 100 parts by mass of the ethylene propylene diene rubber, 10–35 parts by mass of an aromatic modified terpene resin per 100 parts by mass of the ethylene propylene diene rubber, a crosslinking agent, and oil. The nitrogen adsorption specific surface area of the carbon black is 70–120 m2 / g, the iodine adsorption capacity is 70–125 mg / g, and the DBP oil absorption capacity is 50–100 cm3 / 100 g.

Description

rubber composition

[0001] The present invention relates to a rubber composition.

[0002] Rubber compositions have been used in a variety of applications. Various properties are required of rubber compositions depending on the application. When used as a material with excellent vibration damping properties, rubber compositions are required to have excellent sound-deadening properties against radiated sound caused by vibration.

[0003] 1 of Patent Document 1 (JP 2020-41684 A) discloses a torsional damper (see

[0017] ) that includes a boss attached to the front end of the crankshaft, a vibration ring disposed on the outside of the boss and around which a belt is wound, and a cavity formed along the front outer edge of the boss to use sound wave interference to damp radiated sound emitted from the front center of the boss through the crankshaft. However, the volume and opening area of ​​the cavity must be appropriately set according to the radiated sound from the crankshaft, and there is room for further improvement in terms of versatility.

[0004] Japanese Patent Application Laid-Open No. 2020-41684

[0005] The present invention has been made in view of the above circumstances, and the inventors have discovered a rubber composition having a specific relationship between rubber hardness Hs and sound pressure level, which can reduce sound pressure level and has excellent vibration-damping properties, and have completed the present invention. That is, the present invention provides a rubber composition having excellent vibration-damping properties and sound-deadening properties.

[0006] The gist of the present invention is as follows: [1] A rubber composition, the sound pressure level and rubber hardness measured under the following vibration conditions satisfy the following formula (1): (sound pressure level) (dB)≦0.045x ２-6.63x+351.33 (1) (In the above formula (1), x represents rubber hardness Hs°, and 45≦x≦85) [Vibration conditions] A sweep test is performed on a rubber composition at 55 to 65°C with a vibration amplitude of ±10G and a sweep frequency of 200 to 3000Hz. [2] The rubber composition is a crosslinked rubber composition comprising: ethylene propylene diene rubber (EPDM); 110 to 190 parts by mass of carbon black per 100 parts by mass of the ethylene propylene diene rubber; 10 to 35 parts by mass of aromatic modified terpene resin per 100 parts by mass of the ethylene propylene diene rubber; a crosslinking agent; and oil, wherein the nitrogen adsorption specific surface area of ​​the carbon black is 70 to 120 m ２ / g, iodine adsorption capacity 70-125 mg / g, DBP oil absorption capacity 50-100 cm ３ [3] The rubber composition according to [1] above, wherein the carbon black has a nitrogen adsorption specific surface area of ​​70 to 120 m. [4] A crosslinked rubber composition comprising: an ethylene propylene diene rubber (EPDM); 110 to 190 parts by mass of carbon black per 100 parts by mass of the ethylene propylene diene rubber; 10 to 35 parts by mass of an aromatic modified terpene resin per 100 parts by mass of the ethylene propylene diene rubber; a crosslinking agent; and an oil, wherein the carbon black has a nitrogen adsorption specific surface area of ​​70 to 120 m. ２ / g, iodine adsorption capacity 70-125 mg / g, DBP oil absorption capacity 50-100 cm ３ [5] The rubber composition according to the above [4], which is a rubber composition for a torsional damper.

[0007] A rubber composition having excellent vibration-proofing and sound-deadening properties can be provided.

[0008] 1 is a cutaway perspective view showing an example of a torsional damper having the rubber composition of the present invention; 2 is a diagram showing the relationship between the hardness of the rubber composition and the sound pressure level in formulas (1) to (3); 3 is a diagram showing a method for measuring the sound pressure level of a rubber composition of an embodiment; 4 is a diagram showing a torsional damper used for measuring the sound pressure level;

[0009] The rubber composition of the present invention has a sound pressure level and rubber hardness measured under the following vibration conditions, which satisfy the following formula (1): (sound pressure level) (dB)≦0.045× ２ -6.63x+351.33 (1) (In the above formula (1), x represents the rubber hardness Hs° (unit), and 45≦x≦85.) [Vibration conditions] A sweep test is performed on a rubber composition at 55 to 65°C with a vibration amplitude of ±10G and a sweep frequency of 200 to 3000Hz.

[0010] The above vibration conditions are achieved by vibrating the rubber composition using a vibrator. The rubber composition is integrated with a vibrating body to damp the vibration of the vibrating body and also to muffle sound emitted from the vibrating body. Therefore, the sound pressure level of the rubber composition is measured by fixing a structure in which the rubber composition and the vibrating body are integrated to a vibrator and vibrating the structure with the vibrator, thereby vibrating the rubber composition in the structure. For example, when a torsional damper containing the rubber composition of the present invention is used as the structure, the center of the torsional damper 1 is fixed to a vibrator 10 with a bolt 12, as described below with reference to FIG. 3 . Next, a sweep test is performed on the torsional damper and the rubber composition contained therein under the above vibration conditions, and the sound pressure level of the rubber composition is measured using a microphone 11 positioned 70 mm away from the fixing bolt 12 in the bolt axial direction. A free-field type 378A06 microphone manufactured by PCB Corporation can be used. The torsional damper used for measuring the sound pressure level of the rubber composition is a torsional damper having the shape and dimensions shown in Fig. 4. The hub 2 and vibration ring 4 of the torsional damper 1 in Fig. 4 are made of FC250 (cast iron), and the projected area of ​​the hub 2 is 6236 mm ２ , d １ (Outer diameter of torsional damper 1) = 147 mm, d ２ (Stay width) = 32mm, d ３ (Cast window outer diameter) = 95mm, d ４ (Casting window inner diameter) = 57 mm, d ５ (Boss width) = 29.5 mm, d ６(hub inner diameter) = 105 mm. The torsional damper 1 in Fig. 4 has the rubber composition of the present invention as the rubber ring 3.

[0011] The rubber composition of the present invention has a high tan δ (loss factor) and satisfies the relationship of the above formula (1), thereby achieving excellent vibration-proofing and sound-deadening properties. The rubber hardness Hs° can be measured using a Type A durometer under the conditions of JIS K6253. Formula (1) is represented by the line shown as Standard 3 in Figure 2, which will be described later.

[0012] The tan δ of the rubber composition is preferably 0.29 or more. When the tan δ of the rubber composition is within this range, the rubber composition can have excellent vibration-proofing properties and sound-deadening properties.

[0013] The rubber hardness Hs of the rubber composition can be adjusted by the component composition of the rubber composition. The rubber composition is preferably a thermosetting rubber composition containing ethylene propylene diene rubber (EPDM), carbon black, an aromatic modified terpene resin, a crosslinking agent, and oil, and crosslinked by the crosslinking agent. The rubber composition is also a crosslinked rubber composition containing ethylene propylene diene rubber (EPDM), 110 to 190 parts by mass of carbon black per 100 parts by mass of the ethylene propylene diene rubber, 10 to 35 parts by mass of the aromatic modified terpene resin per 100 parts by mass of the ethylene propylene diene rubber, the crosslinking agent, and oil, and the nitrogen adsorption specific surface area of ​​the carbon black is 70 to 120 m. ２ / g, iodine adsorption capacity 70-125 mg / g, DBP oil absorption capacity 50-100 cm ３ / 100g is more preferable.

[0014] The rubber hardness Hs of the rubber composition can be adjusted to a desired range of 45° to 85° by adjusting the content and type of carbon black, which has the property of hardening the rubber composition, and the content and type of oil, which has the property of softening the rubber composition. Oil may be incorporated into the ethylene propylene diene rubber in advance to form an oil-extended polymer type ethylene propylene diene rubber. The ethylene propylene diene rubber may be a non-oil-extended polymer type ethylene propylene diene rubber that does not contain oil, and the rubber composition may contain a non-oil-extended polymer type ethylene propylene diene rubber and oil. The rubber composition may also contain an oil-extended polymer type ethylene propylene diene rubber and oil. In the case of an oil-extended polymer type ethylene propylene diene rubber, the content of the ethylene propylene diene rubber in the rubber composition is the total content of the oil-extended polymer type ethylene propylene diene rubber minus the oil content. The Mooney viscosity ML1+4 (125°C) of the oil-extended polymer type ethylene propylene diene rubber (before crosslinking) is preferably 50 or higher.

[0015] When the ethylene propylene diene rubber contains ENB (5-ethylidene-2-norbornene) as a diene unit, the ENB content in the ethylene propylene diene rubber is preferably 4.0 to 9.0 mass%, more preferably 4.5 to 8.5 mass%. Commercially available ethylene propylene diene rubbers can be used. Examples of commercially available oil-extended polymer ethylene propylene diene rubbers include EP98 (trade name) manufactured by ENEOS and KELTAN4869C (trade name) manufactured by ARLANXEO. Examples of commercially available non-oil-extended polymer ethylene propylene diene rubbers include EP35 (trade name) manufactured by ENEOS and KELTAN2750 (trade name) manufactured by ARLANXEO.

[0016] The content of carbon black in the rubber composition is preferably 110 to 190 parts by mass, more preferably 120 to 180 parts by mass, per 100 parts by mass of ethylene propylene diene rubber. By having the carbon black content within the above range, the rubber composition can have excellent processability. The nitrogen adsorption specific surface area of ​​carbon black is 70 to 120 m ２ / g, and 80 to 110m ２ / g. The nitrogen adsorption specific surface area represents the specific surface area per unit weight of carbon black and can be measured in accordance with JIS K6217-2:2001. The iodine adsorption of carbon black is preferably 70 to 125 mg / g, more preferably 80 to 120 mg / g. The iodine adsorption can be measured in accordance with JIS K6217-1:2008. The DBP oil absorption of carbon black is 50 to 100 cm ３ / 100g, and 60 to 90cm ３ / 100g is more preferable. DBP oil absorption can be measured in accordance with JIS K6217-4:2017. Specific examples of carbon black include HAF-LS carbon black and ISAF-LS carbon black. When the nitrogen adsorption specific surface area, iodine adsorption amount, and DBP oil absorption amount of the carbon black are within the above ranges, the internal friction of the rubber composition can be increased while maintaining excellent processability. As a result, the tan δ of the rubber composition can be improved, thereby improving the sound deadening properties of the rubber composition.

[0017] The content of the aromatic-modified terpene resin in the rubber composition is preferably 10 to 35 parts by mass, more preferably 15 to 35 parts by mass, and even more preferably 15 to 30 parts by mass per 100 parts by mass of ethylene propylene diene rubber. When the content of the aromatic-modified terpene resin is within the above range, the rubber composition has excellent tackiness and good compatibility with the ethylene propylene diene rubber. Therefore, by shifting the glass transition temperature of the ethylene propylene diene rubber to a higher temperature, the tan δ of the rubber composition can be improved, thereby improving the sound deadening properties of the rubber composition. Examples of aromatic-modified terpene resins include those obtained by copolymerizing a terpene monomer such as α-pinene, β-pinene, or dipentene (limonene) with an aromatic monomer such as substituted or unsubstituted styrene, and can be used as an oligomer with a molecular weight of several hundred to several thousand.

[0018] The content of the crosslinking agent in the rubber composition is preferably 3 to 5 parts by mass, more preferably 3.3 to 4.5 parts by mass, per 100 parts by mass of ethylene propylene diene rubber. It is preferable to use at least an organic peroxide-based crosslinking agent, such as dicumyl peroxide (DCP). Sulfur can also be used as the crosslinking agent together with the organic peroxide-based crosslinking agent.

[0019] The content of oil in the rubber composition is preferably 45 to 80 parts by mass, and more preferably 55 to 70 parts by mass, per 100 parts by mass of ethylene propylene diene rubber. Mineral oil is preferably used as the oil, and examples of such mineral oil include paraffin oil. The rubber composition may contain, in addition to the ethylene propylene diene rubber, carbon black, aromatic-modified terpene resin, crosslinking agent, and oil, components such as zinc oxide, stearic acid, antioxidants, and co-crosslinking agents.

[0020] One embodiment is a crosslinked rubber composition comprising: ethylene propylene diene rubber (EPDM); 110 to 190 parts by mass of carbon black per 100 parts by mass of the ethylene propylene diene rubber; 10 to 35 parts by mass of aromatic modified terpene resin per 100 parts by mass of the ethylene propylene diene rubber; a crosslinking agent; and oil, wherein the carbon black has a nitrogen adsorption specific surface area of ​​70 to 120 m. ２ / g, iodine adsorption capacity 70-125 mg / g, DBP oil absorption capacity 50-100 cm ３ The rubber composition of this embodiment contains specific components in a specific composition, and therefore can achieve excellent vibration-proofing and sound-deadening properties due to the synergistic effects of the specific components.

[0021] The rubber composition of the present invention is preferably a rubber composition for a torsional damper. The rubber composition can effectively muffle noise emitted from a hub when the torsional damper is in use. FIG. 1 is a cutaway perspective view showing a portion of a torsional damper comprising the rubber composition of the present invention. As shown in FIG. 1, the torsional damper 1 is attached to the tip of the crankshaft of an automobile engine and transmits the rotation of the crankshaft to an alternator, power steering, or the like. The torsional damper 1 includes a hub 2 having a boss portion 2a, a stay 2b, and an outer peripheral portion 2c, a rubber ring 3 made of the rubber composition of the present invention, and a vibration ring 4. The boss portion 2a is fastened to the tip of the crankshaft and is driven to rotate about its central axis. The outer peripheral surface of the vibration ring 4 is provided with a pulley groove 4a through which a belt is fitted, forming a power transmission pulley.

[0022] The torsional damper 1 can suppress (absorb) the torsional resonance of the crankshaft by having the vibrating ring 4 resonate in the rotational direction and the rubber ring 3 provide vibration isolation. The rotational resonance frequency of the vibrating ring 4 is generally between 300 and 600 Hz. On the other hand, the vibrating ring 4 also resonates in the axial direction, with a frequency of several hundred Hz, similar to the torsional vibration. Since the local resonance of the hub 2 is the largest, radiated noise is emitted from the hub 2.

[0023] In the torsional damper 1, the radiated sound caused by the local resonance of the hub 2 is generated from the stay 2b and the outer peripheral portion 2c of the hub 2. Therefore, as will be shown below, the radiated sound can be reduced by increasing tan δ.

[0024] (i) The equation representing (hub axis direction vibration velocity) is shown as equation (4) below. As shown in equation (4) below, (hub axis direction vibration velocity) depends on (hub axis direction acceleration) and (hub axis direction frequency). (hub axis direction vibration velocity) = (hub axis direction acceleration) / (2 × π × hub axis direction frequency) (4) (ii) By increasing tan δ, (hub axis direction acceleration) decreases. (iii) By increasing tan δ, the local resonance frequency of the hub, which is (hub axis direction frequency), shifts to the higher frequency side.

[0025] From the above, by increasing the tan δ of the rubber composition that constitutes the rubber ring 3, the vibration velocity in the hub axle direction can be reduced, thereby making it possible to reduce radiated noise.

[0026] (Examples 1 to 3, Comparative Examples 1 to 3) Materials having the compositions shown in Table 1 below were kneaded using a kneader such as an Intermix, kneader, or Banbury mixer, or an open roll. Next, press crosslinking was performed at 180°C for 6.0 minutes to prepare rubber compositions for measuring rubber hardness Hs and tan δ. Separately, an annular rubber composition was prepared, and this annular rubber composition was press-fitted as a rubber ring 3 between the boss portion 2a and the metal members of the vibration ring 4 to prepare a torsional damper 1 for measuring sound pressure levels, as shown in FIG. 4. In the torsional damper 1 shown in FIG. 4, the hub 2 and the vibration ring 4 were made of FC250 (cast iron), and the projected area of ​​the hub 2 was 6236 mm ２ , d １ (Outer diameter of torsional damper 1) = 147 mm, d ２ (Stay width) = 32mm, d ３ (Cast window outer diameter) = 95mm, d ４ (Casting window inner diameter) = 57 mm, d ５ (Boss width) = 29.5 mm, d ６(Hub inner diameter) = 105 mm. In each example, the rubber hardness Hs was set to 55°, 65°, or 75° by adjusting the material composition.

[0027]

[0028] Note that each numerical value in Table 1 represents (parts by mass). Furthermore, the parts by mass of oil-extended EPDM1 and oil-extended EPDM2 represent the total parts by mass of EPDM and oil, and "oil in oil-extended EPDM1" and "oil in oil-extended EPDM2" represent the parts by mass of oil in oil-extended EPDM1 and oil-extended EPDM2, respectively. Therefore, the parts by mass of EPDM in oil-extended EPDM1 is (oil-extended EPDM1) - (oil in oil-extended EPDM1). Similarly, the parts by mass of EPDM in oil-extended EPDM2 is (oil-extended EPDM2) - (oil in oil-extended EPDM2).

[0029] The names of materials used in each example are shown below. Oil-extended EPDM1: ML1+4 (125°C) = 48, ENB content 8.7% by mass, C2 content 62% by mass Oil-extended EPDM2: ML1+4 (125°C) = 52, ENB content 4.5% by mass, C2 content 58% by mass Non-oil extended EPDM1: ML1+4 (125°C) = 65, ENB content 9.0% by mass, C2 content 44% by mass Non-oil extended EPDM2: ML1+4 (100°C) = 38, ENB content 5.8% by mass, C2 content 61% by mass Non-oil extended EPDM3: ML1+4 (125°C) = 87, ENB content 4.5% by mass, C2 content 59% by mass Carbon black A: SRF-HS carbon black, nitrogen adsorption specific surface area 32m ２ / g, iodine adsorption amount 30mg / g, DBP oil absorption amount 140cm ３ / 100g Carbon black B: HAF carbon black, nitrogen adsorption specific surface area 79 m ２ / g, iodine adsorption amount 80mg / g, DBP oil absorption amount 101cm ３ / 100g Carbon black C: HAF-LS carbon black, nitrogen adsorption specific surface area 84 m ２ / g, iodine adsorption amount 86mg / g, DBP oil absorption amount 75cm ３ / 100g Aromatic modified terpene resin: YS Resin TO-115 (trade name); ethylene vinyl acetate copolymer (compound name) Resin B: Ultrathene 750 (trade name) DCP: dicumyl peroxide Oil A: Diana Process Oil PW-380 (trade name)

[0030] For the rubber compositions obtained in each example, rubber hardness Hs, tan δ, and sound pressure level were measured by the following methods.

[0031] (Rubber Hardness Hs) For the rubber composition obtained in each example, the rubber hardness Hs was measured using a Type A durometer under the conditions of JIS K6253.

[0032] (tan δ) Using a Viscoelasticity Spectrometer (trade name) manufactured by UBM, tan δ of the rubber composition obtained in each example was measured under conditions of 60° C., a vibration frequency of 100 Hz, and a dynamic strain of 1%.

[0033] (Sound Pressure Level) To measure sound pressure levels, a torsional damper having a rubber ring made of the rubber composition obtained in each example was used. As shown in FIG. 3 , the center of the torsional damper 1 for measuring sound pressure levels, prepared as described above, was fixed to a vibrator 10 via a bolt 12. A high-frequency dynamic characteristics tester (product name) manufactured by Saginomiya Seisakusho Co., Ltd. was used as the vibrator. Using this tester, the torsional damper 1 and the rubber composition that constituted the rubber ring 3 included in the torsional damper 1 were heated to 55 to 65°C, and a sweep test was performed with a vibration amplitude of ±10 G and a sweep frequency of 200 to 3000 Hz. During the sweep test, the sound pressure level of the sound emitted from the torsional damper 1 having the rubber composition (rubber ring 3) was measured using a microphone 11 (manufactured by PCB Co., Ltd.; free-field type 378A06) positioned 70 mm away from the bolt 12 in the bolt axial direction.

[0034] The tan δ and sound pressure level measured for each example are shown in Table 2 below.

[0035]

[0036] In addition, when the rubber hardness Hs is between 45° and 85°, the formula (3) is 0.057x ２-7.88x+387.38, equation (2); 0.0593x ２ -8.2668x+399.46, formula (1); 0.045x ２ The relationship between sound pressure level and the formula -6.63 x +351.33 is shown in Figure 2. In Figure 2, formulas (3), (2), and (1) are shown as Standards 1, 2, and 3, respectively. Figure 2 also shows the sound pressure levels when the rubber hardness Hs is 55°, 65°, and 75° in Standards 1, 2, and 3 as points. Table 3 below shows the sound pressure levels when the rubber hardness Hs is 55°, 65°, and 75° in Standards 1, 2, and 3.

[0037]

[0038] It is clear that the rubber compositions of Examples 1 to 3 all have sound pressure levels below Standard 3, and therefore the rubber compositions of the present invention exhibit excellent sound deadening properties. In addition, the rubber compositions of Examples 1 to 3 have high tan δ of 0.29 or more compared to Comparative Examples 1 to 3, and therefore exhibit excellent vibration damping properties.

[0039] On the other hand, it is clear that the rubber compositions of Comparative Examples 1 to 3 do not exhibit sufficient sound deadening properties, as they exceed the sound pressure levels represented by Standards 2 and 3, although they are below the sound pressure level represented by Standards 1. Furthermore, it is clear that the rubber compositions of Comparative Examples 1 to 3 have low tan δ of 0.22 or less, and are inferior in vibration damping properties.

[0040] REFERENCE SIGNS LIST 1 Torsional damper 2 Hub 2a Boss portion 2b Stay 2c Outer periphery 3 Rubber ring 4 Vibration ring 4a Pulley groove

Claims

1. A rubber composition whose sound pressure level and rubber hardness measured under the following vibration conditions satisfy the following formula (1): (sound pressure level) (dB) ≦ 0.045 x ２ -6.63x+351.33 (1) (In the above formula (1), x represents rubber hardness Hs°, and 45≦x≦85.) [Vibration Conditions] A sweep test is performed on a rubber composition at 55 to 65° C. with a vibration amplitude of ±10 G and a sweep frequency of 200 to 3000 Hz.

2. The rubber composition is a crosslinked rubber composition comprising: ethylene propylene diene rubber (EPDM); 110 to 190 parts by mass of carbon black per 100 parts by mass of the ethylene propylene diene rubber; 10 to 35 parts by mass of aromatic modified terpene resin per 100 parts by mass of the ethylene propylene diene rubber; a crosslinking agent; and oil, wherein the nitrogen adsorption specific surface area of ​​the carbon black is 70 to 120 m. ２ / g, iodine adsorption 70-125mg / g, DBP oil absorption 50-100cm ３ The rubber composition according to claim 1, wherein the elastic modulus is 100 g / 100 g.

3. The rubber composition according to claim 1 or 2, which is a rubber composition for a torsional damper.

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