Rubber composition and pneumatic tire using same

Abstract

Disclosed is a rubber composition characterized by containing: (A) a rubber component containing 30 parts by mass or more of a styrene-butadiene rubber (SBR) with respect to a total of 100 parts by mass of the rubber component; and (B) a high-density polyethylene in which the melt mass flow rate (MFR) measured at 190°C under a load of 2.16 kg is 6.0 g / 10 minutes or less. The rubber composition has excellent thermal strength and wear resistance.

Description

Rubber composition and pneumatic tire using the same

[0001] The present invention relates to a rubber composition and a pneumatic tire using the same, and more particularly to a rubber composition with excellent thermal strength and abrasion resistance and a pneumatic tire using the same.

[0002] In recent years, high toughness has been desired for pneumatic tires, and various proposals have been made to improve toughness. For example, Patent Document 1 proposes a rubber composition that achieves low heat generation, heat resistance, high hardness, and deformation resistance in a rubber composition, by blending 2 to 75 parts by weight of high-density polyethylene (HDPE) having a crosslinkable portion and a high-density polyethylene content of 35 to 70% by weight with 10 parts by weight of rubber component, and kneading at a temperature higher than the melting point of the blended resin. Patent Document 2 also proposes a rubber composition with a density of 0.94 to 0.98 g / cm³. ３ It has been proposed that by blending acid-modified polyethylene in parts 2 to 30 by mass per 100 parts by mass of diene rubber, the modulus at 100% elongation can be improved while maintaining the high low heat generation and elongation at break of the rubber composition. Furthermore, Patent Document 3 proposes that in order to achieve both cut resistance and abrasion resistance, a rubber composition containing rubber components and carbon black with a density of 0.910 g / cm³ is added. ３ 0.940g / cm or more ３ It has been proposed to incorporate low-density polyethylene (LDPE) of less than 1%.

[0003] On the other hand, it is known that conventionally, improving wet grip performance and reducing rolling resistance can be achieved by compounding silica with styrene-butadiene rubber (SBR), which has a high glass transition temperature (Tg), as a rubber component. However, silica has high cohesiveness and low affinity for SBR, resulting in insufficient dispersion of silica, which leads to problems such as inadequate strength properties, including abrasion resistance, after vulcanization compared to carbon black. Until now, there have been no attempts to provide a rubber composition that can provide a vulcanized rubber composition that balances abrasion resistance and strength properties at high temperatures by compounding high-density polyethylene with a rubber composition containing a relatively large amount of SBR.

[0004] Japanese Patent Publication No. 3657389, Japanese Patent Publication No. 6350508, International Publication No. 2019 / 013001

[0005] Therefore, an object of the present invention is to provide a rubber composition comprising styrene-butadiene rubber (SBR) and high-density polyethylene (HDPE) that can provide a vulcanized product with an excellent balance of abrasion resistance and thermal strength.

[0006] In order to solve the above problems and achieve the objectives of the present invention, the inventors investigated the effects of various HDPEs on the abrasion resistance and high-temperature strength properties of vulcanized rubber compositions using rubber components containing a relatively large amount of SBR. As a result, they found that when HDPEs with low fluidity, i.e., low melt mass flow rate (MFR), are used, a rubber composition can be obtained that provides a vulcanized product with an excellent balance of abrasion resistance and high-temperature strength properties, thus completing the present invention.

[0007] In other words, the present invention includes the following embodiments. [Embodiment 1] A rubber composition characterized by comprising the following: (A) a rubber component comprising 30 parts by mass or more of styrene-butadiene rubber (SBR) when the total amount is 100 parts by mass; and (B) high-density polyethylene having a melt mass flow rate (MFR) of 6.0 g / 10 min or less, measured at a temperature of 190°C and a load of 2.16 kg. [Embodiment 2] The rubber composition according to Embodiment 1, characterized in that the melting point of the high-density polyethylene (B) is 125°C or more and 140°C or less. [Embodiment 3] The rubber composition according to Embodiment 1 or 2, characterized in that the rubber composition comprises 1 to 60 parts by mass of high-density polyethylene (B) per 100 parts by mass of the rubber component (A). [Embodiment 4] The rubber composition according to any one of Embodiments 1 to 3, characterized in that the rubber composition further comprises 5 to 150 parts by mass of carbon black, silica powder, or a combination thereof per 100 parts by mass of the rubber component (A). [Embodiment 5] A pneumatic tire using the rubber composition described in any one of Embodiments 1 to 4.

[0008] The rubber composition of the present invention can provide a vulcanized rubber composition with an excellent balance of abrasion resistance and thermal strength, and is therefore useful as a rubber composition for tires, and especially as a rubber composition for tire treads.

[0009] The rubber composition of the present invention will be described in detail below.

[0010] The rubber composition of the present invention comprises the following: (A) a rubber component comprising 30 parts by mass or more of styrene-butadiene rubber (SBR) when the total amount is 100 parts by mass; and (B) high-density polyethylene having a melt mass flow rate (MFR) of 6.0 g / 10 min or less, measured at a temperature of 190°C and a load of 2.16 kg.

[0011] (A) Rubber component The rubber component (A) contains 30 parts by mass or more of styrene-butadiene rubber (SBR) when the total amount is 100 parts by mass. That is, the rubber component (A) consists only of SBR, or preferably consists of SBR and other rubbers such as natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), and acrylonitrile-butadiene rubber (NBR). Among these, a combination system of SBR and NR and / or BR is preferred from the viewpoint of improving the effects of the present invention.

[0012] When the total amount of the rubber component is 100 parts by mass, the lower limit of the amount of SBR in rubber component (A) can be 30 parts by mass, 35 parts by mass, 40 parts by mass, 45 parts by mass, or 50 parts by mass, and the upper limit can be 100 parts by mass, 95 parts by mass, 90 parts by mass, 85 parts by mass, 80 parts by mass, 75 parts by mass, 70 parts by mass, 65 parts by mass, or 60 parts by mass. Furthermore, when the total amount of the rubber component is 100 parts by mass, the range of the amount of SBR in rubber component (A) can be any combination of these lower and upper limits. When the total amount of the rubber component is 100 parts by mass, the range of the amount of SBR in rubber component (A) is preferably 30 parts by mass to 90 parts by mass, more preferably 30 parts by mass to 80 parts by mass, and even more preferably 40 parts by mass to 80 parts by mass. If the amount of SBR in rubber component (A) is less than 30 parts by mass, it is difficult to achieve sufficient improvement in thermal strength and abrasion resistance after vulcanization. When the amount of SBR in rubber component (A) is 40 to 80 parts by mass, the effect of improving the thermal strength and abrasion resistance of the vulcanized rubber composition obtained after vulcanization of the rubber composition in a well-balanced manner can be further enhanced.

[0013] Due to its high effectiveness in improving the thermal strength and abrasion resistance of the vulcanized rubber composition obtained after vulcanization of the rubber composition, when the rubber component (A) contains SBR and rubber other than SBR, it is preferable that the combination contains 30 to 80 parts by mass of SBR and 70 to 20 parts by mass of NR and / or BR, and more preferably 40 to 80 parts by mass of SBR and 60 to 20 parts by mass of NR and / or BR.

[0014] In this disclosure, thermal strength refers to the tensile strength at break (in MPa) measured by punching a JIS No. 3 dumbbell-shaped test piece out of a vulcanized rubber sheet obtained by vulcanizing the rubber composition of the present invention using a mold of a predetermined shape, as described later, and then performing a tensile test on the obtained test piece in accordance with JIS K6251:2017 at a tensile speed of 500 mm / min and a temperature of 100°C. In this disclosure, abrasion resistance refers to the abrasion resistance measured by taking a test piece of a predetermined shape from a vulcanized rubber sheet obtained by vulcanizing the rubber composition of the present invention using a mold of a predetermined shape, as described later, in accordance with JIS K6264-1, 2:2005, and measuring the amount of abrasion using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.) under conditions of a load of 15.0 kg (147.1 N) and a slip ratio of 25%. The reciprocal of each of the obtained results was calculated and used as an index for abrasion resistance, with standard example 1 set to 100.

[0015] (B) High-density polyethylene In the rubber composition of the present invention, high-density polyethylene (B) is a low-flow HDPE having a melt mass flow rate (MFR) of 6.0 g / 10 min or less, measured at a temperature of 190°C and a load of 2.16 kg in accordance with JIS K7210-1:2014. By incorporating such low-flow HDPE, the thermal strength and abrasion resistance after vulcanization of a rubber composition containing a rubber component with an SBR content of 30 parts by mass or more can be improved. The MFR of high-density polyethylene (B) is preferably 2.0 g / 10 min or less, more preferably 1.0 g / 10 min or less, and even more preferably 0.5 g / 10 min or less. The lower the MFR, the better the vulcanized rubber composition with superior thermal strength and abrasion resistance can be obtained. If the MFR is less than 6.0 g / 10 min, it is difficult to achieve sufficient improvement in thermal strength and abrasion resistance after vulcanization. While not bound by any particular theory, the reason why the high-density polyethylene having the above-mentioned predetermined MFR improves the thermal strength and abrasion resistance in the rubber composition of the present invention is thought to be that, under the mixing or kneading conditions when mixing or kneading the raw materials of the rubber composition using a mixing or kneading device such as a Banbury mixer or kneader, the SBR and high-density polyethylene are well compatible and exhibit a sea-island structure. In this disclosure, "high-density polyethylene" refers to 0.935 to 0.965 g / cm³. ３ This refers to polyethylene having a density of . As high-density polyethylene, polyethylene is preferred in which the MFR, measured in accordance with JIS K 7210-1:2014 at a temperature of 190°C and a load of 2.16 kg, is preferably 2.0 g / 10 min or less, more preferably 0.5 g / 10 min or less. High-density polyethylene (B) having the above-mentioned density and MFR is commercially available, for example, Novatec (trademark) HD ​​HJ363N manufactured by Nippon Polypropylene Co., Ltd. (MFR: 5 g / 10 min, melting point: 132°C, density: 0.953 g / cm³). ３ ), Novatec (trademark) HD ​​HY430 (MFR: 0.8 g / 10 min, melting point: 135°C, density: 0.954 g / cm³) ３ ), Novatec (trademark) HD ​​HY420 (MFR: 0.4 g / 10 min, melting point: 133°C, density: 0.956 g / cm³) ３), and Novatec (trademark) HD ​​HB420R (MFR: 0.2 g / 10 min, melting point: 133°C, density: 0.957 g / cm³) ３ ) and other such methods can be used.

[0016] Furthermore, it is preferable that the melting point of high-density polyethylene (B), as measured by differential scanning calorimetry (DSC) in accordance with JIS K7121:1987, is preferably between 125°C and 140°C, more preferably between 130°C and 140°C, and even more preferably between 130°C and 135°C. When the melting point of high-density polyethylene (B) is within the above range, the effect of balancing abrasion resistance and thermal strength is greater.

[0017] In the rubber composition of the present invention, the lower limit of the amount of high-density polyethylene (B) per 100 parts by mass of rubber component (A) can be 1, 3, 5, or 10 parts by mass, and the upper limit can be 60, 50, 40, 30, or 20 parts by mass. Furthermore, the range of the amount of high-density polyethylene (B) per 100 parts by mass of rubber component (A) can be any combination of these lower and upper limits. The range of the amount of high-density polyethylene (B) per 100 parts by mass of rubber component (A) is preferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass, even more preferably 3 to 40 parts by mass, and even more preferably 10 to 40 parts by mass. When the amount of high-density polyethylene (B) is within the above range, the effect of improving abrasion resistance and thermal strength in a well-balanced manner is particularly great.

[0018] (C) Carbon black, silica powder or combination thereof The rubber composition of the present invention further comprises, as a reinforcing agent (filler), 5 to 150 parts by mass of carbon black, silica powder or combination thereof per 100 parts by mass of rubber component (A). The lower limit of the total amount of carbon black, silica powder or combination thereof can be 5 parts by mass, 8 parts by mass, 10 parts by mass, 15 parts by mass, 20 parts by mass, 25 parts by mass, 30 parts by mass, 35 parts by mass, 40 parts by mass, 45 parts by mass, 50 parts by mass, 55 parts by mass, or 60 parts by mass, and the upper limit can be 150 parts by mass, 145 parts by mass, 140 parts by mass, 135 parts by mass, 130 parts by mass, 125 parts by mass, 120 parts by mass, 115 parts by mass, 110 parts by mass, 105 parts by mass, or 100 parts by mass. Furthermore, the range of the total amount of carbon black, silica powder or combination thereof can be any combination of these lower and upper limits. The total amount of carbon black, silica powder, or a combination thereof is preferably 15 to 115 parts by mass, more preferably 50 to 115 parts by mass. When the total amount of carbon black, silica powder, or a combination thereof is within the above range, the effect of improving abrasion resistance and thermal strength in a well-balanced manner can be further enhanced when combined with the rubber component (A) and high-density polyethylene (B) in the above-described ratio. The rubber composition of the present invention is preferable because by further including carbon black, silica powder, or a combination thereof in an amount within this range, a rubber composition with excellent mechanical properties, abrasion resistance, and / or low rolling resistance can be obtained. Furthermore, as mentioned above, silica has high cohesiveness and low affinity for SBR, resulting in insufficient dispersion of silica and consequently inadequate strength characteristics such as abrasion resistance after vulcanization compared to carbon black. However, the rubber composition of the present invention can achieve high thermal strength and abrasion resistance even when the amount of silica powder is relatively high (provided that the silica powder, either alone or in combination with carbon black, is in the range of 5 to 150 parts by mass per 100 parts by mass of rubber component (A)).

[0019] When the rubber composition of the present invention contains both carbon black and silica powder, with respect to 100 parts by mass of the rubber component (A), the lower limit of the blending amount of silica can be 3 parts by mass, 5 parts by mass, 10 parts by mass, 15 parts by mass, 20 parts by mass, 30 parts by mass, 40 parts by mass, 50 parts by mass, and the upper limit can be 140 parts by mass, 130 parts by mass, 120 parts by mass, 110 parts by mass, 100 parts by mass, 90 parts by mass, 80 parts by mass, 70 parts by mass, 60 parts by mass. Further, with respect to 100 parts by mass of the rubber component (A), the range of the blending amount of silica can be any combination of these lower limit and upper limit values. With respect to 100 parts by mass of the rubber component (A), the range of the blending amount of silica is preferably 3 to 110 parts by mass, more preferably 10 to 110 parts by mass, still more preferably 15 to 110 parts by mass, even more preferably 50 to 110 parts by mass. The lower limit of the blending amount of carbon black can be 2 parts by mass, 5 parts by mass, 10 parts by mass, 15 parts by mass, 20 parts by mass, 30 parts by mass, and the upper limit can be 50 parts by mass, 40 parts by mass, 35 parts by mass. Further, with respect to 100 parts by mass of the rubber component (A), the range of the blending amount of carbon black can be any combination of these lower limit and upper limit values. With respect to 100 parts by mass of the rubber component (A), the range of the blending amount of carbon black is preferably 5 to 40 parts by mass, more preferably 5 to 35 parts by mass. The less the blending amount of silica, the more likely the hot strength and abrasion resistance are to decrease. Conversely, if there is too much silica powder, the abrasion resistance and processability tend to decrease.

[0020] As the silica that can be used in the present invention, any silica known to be used in rubber compositions, such as dry silica, wet silica, colloidal silica, and precipitated silica, can be used alone or in combination of two or more. Among these, it is preferable to use wet silica mainly composed of hydrous silicic acid. There is no particular limitation on the specific surface area of silica, but the nitrogen adsorption specific surface area (N ２ SA) determined in accordance with ASTM D3037 is preferably 20 m ２ / g to 300 m ２ / g, more preferably 80 m ２ [[ID=​The value is / g, and more preferably 60 to 120m ２ This value is / g. Within this range, a rubber composition with excellent mechanical properties, wear resistance, and low rolling resistance can be obtained, making it preferable.

[0021] In this invention, carbon blacks that can be used include furnace black, acetylene black, thermal black, channel black, graphite, and any other carbon black that has been conventionally used in rubber compositions, either alone or in combination of two or more. There are no particular restrictions on the specific surface area of ​​the carbon black, but the nitrogen adsorption specific surface area required in accordance with ASTM D3037 is 90 m². ２ / g ~ 130m ２ It is preferable that the nitrogen adsorption specific surface area is within this range, as this provides excellent mechanical properties and wear resistance.

[0022] When the rubber composition for tires of the present invention contains silica as a reinforcing filler, the addition of a silane coupling agent is preferable because it further improves rolling resistance and abrasion resistance. Known silane coupling agents can be used, for example, alkoxysilanes such as vinyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, as well as sulfides such as bis[3-(triethoxysilyl)propyl]tetrasulfide, bis[3-(triethoxysilyl)propyl]disulfide, γ-trimethoxysilylpropyldimethylthiocarbamyltetrasulfide, and γ-trimethoxysilylpropylbenzothiazyltetrasulfide.

[0023] (D) Other Components In addition to the above components, the rubber composition of the present invention may contain various compounding agents and additives known in the art, such as sulfur and other vulcanizing or crosslinking agents, vulcanizing or crosslinking accelerators, zinc oxide, stearic acid, antioxidants, processing aids, and plasticizers.

[0024] The rubber composition of the present invention exhibits high levels of thermal strength and abrasion resistance after vulcanization, making it particularly useful for manufacturing tire components, especially tire treads.

[0025] The rubber composition of the present invention can be manufactured using a mixing or kneading apparatus such as a Banbury mixer or kneader, which are commonly used in the formulation of rubber compositions, under general mixing or kneading methods and operating conditions. After preparing the rubber composition by mixing various compounding agents, rubber components for tires, such as treads, can be formed by a general pressure molding method.

[0026] The present invention will be described in more detail with reference to the following examples and comparative examples, but it goes without saying that the technical scope of the present invention is not limited to these examples.

[0027] <Comparative Examples 1-4 and Examples 1-13> (1) Preparation of Rubber Compositions According to Table 1 below, raw materials other than the vulcanization accelerator and sulfur were mixed at 80°C for 5 minutes using a 1.7-liter sealed Banbury mixer. The highest temperature reached during this mixing was 150°C. Next, after releasing the mixture from the Banbury mixer, the vulcanization accelerator and sulfur were mixed in an open roll to obtain the unvulcanized rubber compositions of Comparative Examples 1-4 and Examples 1-13.

[0028] (2) Preparation of vulcanized rubber sheets for evaluation Each of the obtained rubber compositions (unvulcanized) was press-vulcanized at 160°C for 20 minutes using a mold (size of the internal space of the mold: 15 cm long x 15 cm wide x 2 mm high) to obtain vulcanized rubber sheets.

[0029]

[0030] The melting point and melt flow rate of high-density polyethylene were measured. The melt flow rate (MFR) of the raw material, high-density polyethylene, was measured in accordance with JIS K7210-1:2014 at a temperature of 190°C and a load of 2.16 kg. The melting point of the raw material, high-density polyethylene, was measured in accordance with JIS K7121:1987.

[0031] <Evaluation Method for Vulcanized Rubber Test Specimens> (1) Hot Strength Test A JIS No. 3 dumbbell-shaped test specimen (2 mm thick) obtained by punching out the vulcanized rubber sheet prepared as described above was subjected to a tensile test in accordance with JIS K6251:2017 at a tensile speed of 500 mm / min and a temperature of 100°C, and the tensile strength at break (MPa) was measured. In the examples and comparative examples, the measured tensile strength was converted to an index with the tensile strength of Comparative Example 1 set to 100. The obtained index values ​​are shown in Table 2 below. The higher the index value, the higher the breaking strength of the vulcanized rubber and the better the hot strength. If the index value of the hot strength is 100 or less, the rubber composition was evaluated as "unacceptable", if it is between 101 and 105, it was evaluated as "acceptable", if it is between 106 and 110, it was evaluated as "good", and if it is 110 or more, it was evaluated as "excellent". (2) Abrasion Resistance Test The amount of abrasion was measured from the vulcanized rubber sheet prepared as described above using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.) in accordance with JIS K6264-1, 2:2005, under the conditions of a load of 15.0 kg (147.1 N) and a slip ratio of 25%. The reciprocal of the measured amount of abrasion was calculated and converted into an index with the reciprocal of the amount of abrasion of Comparative Example 1 set to 100. The obtained index values ​​are shown in Table 2 below. The larger the index value, the less abrasion the vulcanized rubber has and the better its abrasion resistance. If the abrasion resistance index value is 100 or less, the rubber composition was evaluated as "unacceptable", if it is between 101 and 105, it was evaluated as "acceptable", if it is between 106 and 110, it was evaluated as "good", and if it is 110 or more, it was evaluated as "excellent".

[0032]

[0033] From the results in Table 2, comparing the rubber compositions of Comparative Examples 1 to 4 with those of Examples 1 to 13, it can be seen that the rubber compositions of Examples 1 to 13, which use HDPE having a predetermined MFR according to the present invention, with a rubber component containing 30 parts by mass or more of SBR when the total rubber component is 100 parts by mass, exhibit excellent thermal strength and abrasion resistance after vulcanization. Furthermore, comparing Comparative Example 3 with Examples 4 to 6 and 10, it can be seen that the effect of HDPE having a predetermined MFR and melting point according to the present invention (see Embodiment 2 above) improves thermal strength and abrasion resistance. Furthermore, comparing Comparative Example 3 with Examples 7 to 9, it can be seen that the effect of improving thermal strength and abrasion resistance is corresponding to the amount of HDPE having a predetermined MFR and melting point according to the present invention (see Embodiment 3 above). Furthermore, comparing Comparative Examples 2 and 3 with Examples 11 to 13, it can be seen that the effect of improving thermal strength and abrasion resistance is corresponding to the amount of filler according to the present invention (see Embodiment 4 above).

[0034] The rubber composition of the present invention can provide a vulcanized rubber composition with an excellent balance of abrasion resistance and thermal strength, and can therefore be suitably used as a rubber composition for tires, and particularly as a rubber composition for tire treads.

Claims

1. A rubber composition characterized by comprising the following: (A) a rubber component comprising 30 parts by mass or more of styrene-butadiene rubber (SBR) when the total amount is 100 parts by mass; and (B) high-density polyethylene having a melt mass flow rate (MFR) of 6.0 g / 10 min or less, measured at a temperature of 190°C and a load of 2.16 kg.

2. The rubber composition according to claim 1, characterized in that the melting point of the high-density polyethylene (A) is 125°C or higher and 140°C or lower.

3. The rubber composition according to claim 1, characterized in that the rubber composition contains 1 to 60 parts by mass of high-density polyethylene (B) per 100 parts by mass of the rubber component (A).

4. The rubber composition according to claim 1, characterized in that the rubber composition further comprises (C) 5 to 150 parts by mass of carbon black, silica powder, or a combination thereof, per 100 parts by mass of the rubber component (A).

5. A pneumatic tire using the rubber composition described in any one of claims 1 to 4.

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