JP7159566B2 - Rubber composition for tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a tire rubber composition that achieves both low rolling resistance and wear resistance under high load.

Due to the growing awareness of environmental conservation, it is required to reduce the rolling resistance of pneumatic tires to improve the fuel efficiency of vehicles, and to improve the wear resistance of pneumatic tires to extend the tire life. In particular, pneumatic tires for commercial vehicles, including light trucks and light vans, are subject to a greater load than passenger car tires. There is a need to. In general, silica is added to tire rubber compositions to improve low rolling resistance. The abrasion resistance could not be sufficiently improved.

Patent Document 1 discloses that a pneumatic tire having a tread made by using a rubber composition containing predetermined amounts of a specific oil-extended butadiene rubber, a specific styrene-butadiene rubber, silica, and carbon black has low fuel consumption. , to be excellent in wear resistance. However, in the invention described in Patent Document 1, even if the fuel efficiency and wear resistance of tires for passenger cars are improved, the wear resistance under high load required for pneumatic tires for commercial vehicles is improved. was difficult to do.

WO2015/040991

An object of the present invention is to provide a rubber composition for tires that achieves both low rolling resistance and wear resistance under high load.

The rubber composition for tires of the present invention, which achieves the above objects, has a glass transition temperature of −30° C. to −20° C. and contains 30 to 70% by mass of a solution-polymerized styrene-butadiene rubber having a terminal modifying group, and 10 to 10% by mass of a butadiene rubber. A rubber composition in which 50 to 90 parts by mass of a filler containing silica is blended with 100 parts by mass of diene rubber consisting of 30% by mass and 10 to 40% by mass of natural rubber, wherein the terminal modifying group is It is selected from hydroxyl group, alkoxysilyl group , aminosilyl group, epoxy group, and amino group, and is measured according to the dynamic storage modulus E' (unit MPa) of the rubber composition at -40°C and JIS K6255. The ratio (E'/Rb) of the rebound resilience modulus Rb (unit: %) at 40°C is 20 or less.

The rubber composition for tires of the present invention satisfies the above-mentioned composition, and the ratio (E'/Rb) of the dynamic storage modulus E' at -40°C and the rebound resilience modulus Rb at 40°C is 20 or less. , the balance between low rolling resistance and wear resistance under high load can be achieved at a higher level than before.

It is preferable that 50 to 80 parts by mass of the filler be blended with 100 parts by mass of the diene rubber, and the ratio of silica in the filler is 80% by mass or more. The diene rubber preferably contains 30 to 50% by mass of the solution-polymerized styrene-butadiene rubber, 10 to 30% by mass of the butadiene rubber, and 23 to 40% by mass of the natural rubber .

A pneumatic tire having the rubber composition for tires in the tire tread portion can achieve a higher level of balance between low rolling resistance and wear resistance under high load than ever before. Suitable for pneumatic tires for commercial vehicles including vans.

The rubber composition for tires contains 30 to 70% by mass of solution-polymerized styrene-butadiene rubber having a glass transition temperature of −30° C. to −20° C. and having a terminal modifying group, 10 to 30% by mass of butadiene rubber, and 10% of natural rubber. A filler containing silica is blended with 100 parts by mass of a diene-based rubber containing up to 40% by mass.

The solution-polymerized styrene-butadiene rubber having a terminal modification group is a solution-polymerized styrene-butadiene rubber having a terminal modification group reactive with silica at one or both ends of the polymer chain (hereinafter abbreviated as "modified S-SBR". sometimes.). Examples of terminal modified groups include a hydroxyl group, a hydroxysilyl group, an alkoxy group, a carboxyl group, an amino group and the like. Modified S-SBR may be produced by a conventional method, or may be used by appropriately selecting from commercially available products.

The modified S-SBR has a glass transition temperature (hereinafter sometimes abbreviated as "Tg") of -30°C to -20°C, preferably -27°C to -23°C. If the Tg is lower than -30°C, the wet performance is remarkably deteriorated. Also, when Tg is higher than -20°C, rolling resistance increases. Note that Tg is the temperature at the midpoint of the transition region, which is obtained by measuring a thermogram by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20°C/min. Further, when the modified S-SBR is an oil-extended product, the glass transition temperature of the modified S-SBR in a state not containing an oil-extending component (oil) is used.

Modified S-SBR preferably does not contain an oil extender, and even if the filler content is limited to 80 parts by mass or less, the rubber hardness can be increased at room temperature or higher. In addition, the total amount of oil components contained in the tire rubber composition is preferably small, and the total amount of the oil components compounded is preferably 0 to 25 parts by mass, more preferably 5 to 20 parts by mass, relative to 100 parts by mass of the diene rubber. It is good in it being a mass part.

The content of the modified S-SBR is 30 to 70% by mass, preferably 40 to 50% by mass, based on 100% by mass of the diene rubber. If the modified S-SBR is less than 30% by mass, the tensile strength at break and elongation at break of the rubber composition will be low, resulting in low abrasion resistance. On the other hand, when the modified S-SBR exceeds 70% by mass, the dynamic storage modulus E' of the rubber composition at -40°C increases and the wear resistance deteriorates.

As the butadiene rubber, those commonly used in rubber compositions for tires can be used, and modified butadiene rubbers may also be used. Examples of modifying groups include terminal modifying groups of modified S-SBR described above, and the types of modifying groups may be the same or different. The content of the butadiene rubber is 10 to 30% by mass, preferably 15 to 20% by mass, based on 100% by mass of the diene rubber. If the butadiene rubber content is less than 10% by mass, the dynamic storage elastic modulus E' at -40°C is large and the wear resistance is poor. If the butadiene rubber exceeds 30% by mass, the rebound resilience modulus Rb of the rubber composition at 40° C. becomes small and the rolling resistance becomes large.

As the natural rubber, those commonly used in rubber compositions for tires can be used, and modified natural rubbers may also be used. An epoxy group can be exemplified as the modifying group. The content of natural rubber is 10 to 40% by mass, preferably 23 to 38% by mass, based on 100% by mass of diene rubber. If the natural rubber content is less than 10% by mass, the dynamic storage elastic modulus E' at -40°C of the rubber composition increases and the wear resistance deteriorates. On the other hand, if the natural rubber exceeds 40% by mass, the rebound resilience modulus Rb of the rubber composition at 40° C. becomes small, and the rolling resistance cannot be improved.

The rubber composition for tires has a ratio (E'/Rb) of dynamic storage modulus E' (unit: MPa) at -40°C to rebound resilience modulus Rb (unit: % ) at 40°C of 20 or less. When the ratio (E'/Rb) is 20 or less, the balance between low rolling resistance and wear resistance under high load can be achieved at a higher level than before. The dynamic storage modulus E' at -40°C is an index of the elasticity of the rubber composition, and the smaller this value, the better the abrasion resistance of the rubber composition. The dynamic storage modulus E′ is determined according to JIS-K6394 using a viscoelastic spectrometer under the conditions of a frequency of 20 Hz, an initial strain of 10%, dynamic strain of ±2%, and a temperature of −40° C. E' (in MPa) is measured. The larger the rebound resilience modulus Rb at 40° C., the smaller the heat buildup of the rubber composition, and the better the low rolling resistance when made into a tire. The impact resilience Rb is measured according to JIS-K6255 at a temperature of 40° C. (unit: % ).

A rubber composition for tires contains a filler containing silica. The amount of the filler compounded is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 40 to 80 parts by mass, and particularly preferably 50 to 70 parts by mass with respect to 100 parts by mass of the diene rubber. . If the amount of the filler compounded exceeds 80 parts by mass, the rolling resistance cannot be sufficiently reduced.

The filler necessarily contains silica, and may contain fillers other than silica. The silica content is preferably 80% by mass or more, more preferably 80 to 95% by mass, still more preferably 80 to 92% by mass, based on 100% by mass of the filler. By setting the ratio of silica to 80% by mass or more, the rolling resistance can be further reduced.

Although the CTAB adsorption specific surface area of silica is not particularly limited, it is preferably 120 to 200 m ² /g, more preferably 170 to 195 m ² /g. If the CTAB adsorption specific surface area of silica is less than 120 m ² /g, there is a possibility that the abrasion resistance performance of the tire rubber composition cannot be sufficiently improved. If the CTAB adsorption specific surface area of silica exceeds 200 m ² /g, there is a possibility that the low rolling resistance of the rubber composition for tires cannot be sufficiently improved. In this specification, the CTAB adsorption specific surface area of silica is a value measured according to JIS K6217-3.

Examples of other fillers include carbon black, clay, calcium carbonate, talc, mica, and the like. Carbon black is preferred. The nitrogen adsorption specific surface area of carbon black is not particularly limited, but is preferably 60 to 160 m ² /g, more preferably 70 to 120 m ² /g. As used herein, the nitrogen adsorption specific surface area of carbon black is a value measured according to JIS K6217-2.

The rubber composition for tires preferably contains a sulfur-containing silane coupling agent together with silica. By blending a sulfur-containing silane coupling agent, the dispersibility of silica in the diene rubber can be improved, and the effect of improving wear resistance and low rolling resistance can be enhanced.

Examples of sulfur-containing silane coupling agents include bis-(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, and the like. can do.

The amount of the silane coupling agent compounded is preferably 3 to 15% by mass, more preferably 4 to 13% by mass, based on the mass of silica. If the compounded amount of the silane coupling agent is less than 3% by mass of the silica compounded amount, the dispersion of silica may not be sufficiently improved. If the compounded amount of the silane coupling agent exceeds 15% by mass of the silica compounded amount, the silane coupling agents may condense with each other, and the desired hardness and strength of the rubber composition may not be obtained.

Compounding agents other than those described above may be added to the rubber composition for tires. Other compounding agents include vulcanizing or cross-linking agents, vulcanization accelerators, anti-aging agents, liquid polymers, thermosetting resins, thermoplastic resins, tackifiers, etc., which are generally used in rubber compositions for tires. Various compounding agents used can be exemplified. The blending amount of these compounding agents can be a conventional general blending amount as long as it does not contradict the object of the present invention. As a kneader, a general rubber kneader such as a Banbury mixer, a kneader, or a roll can be used.

EXAMPLES The present invention will be further described with reference to examples below, but the scope of the present invention is not limited to these examples.

11 types of rubber compositions for tires (Examples 1 to 3, standard examples, and comparative examples 1 to 7) having the compounding agents shown in Table 2 as a common compounding compound shown in Table 1 were mixed with sulfur and a vulcanization accelerator. The ingredients except for were kneaded in a 1.7 L internal Banbury mixer, and after a predetermined period of time, the mixer was discharged and allowed to cool to room temperature. Then, the mixture was returned to the 1.7 L internal Banbury mixer, sulfur and vulcanization accelerator were added and mixed to prepare a rubber composition for tires. In the E-SBR column of Table 1, in addition to the blending amount of the product, the net blending amount of E-SBR excluding the oil extension component is shown in parentheses. The compounding amounts of the compounding agents shown in Table 2 are shown in parts by mass with respect to 100 parts by mass of the diene rubber shown in Table 1.

The obtained 11 types of rubber compositions were press-vulcanized in a predetermined mold at 160° C. for 30 minutes to prepare test pieces of tire rubber compositions. Using the obtained test piece, the dynamic storage modulus E′ at −40° C., the loss tangent tan δ (rolling resistance) at 60° C., the rebound resilience modulus Rb at 40° C., and the resistance under low load and high load. Abrasion resistance was evaluated by the method shown below.

dynamic storage modulus E′ and loss tangent tan δ
The dynamic viscoelasticity of the obtained test piece was measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. at an initial strain of 10%, an amplitude of ±2%, and a frequency of 20 Hz. E' and the loss tangent tan δ at a temperature of 60°C were determined. The reciprocals of the obtained tan δ values were calculated and shown in Table 1 as indices with the standard value being 100. The larger the index of tan δ (60°C) at a temperature of 60°C, the smaller the heat build-up, and the smaller the rolling resistance when made into a pneumatic tire.

Rebound Resilience Using the obtained test piece, rebound resilience Rb (unit: % ) at a temperature of 40°C was measured according to JIS K6255.

Ratio (E'/Rb)
From the dynamic storage modulus E' at -40°C and the rebound resilience modulus Rb at 40°C obtained above, the ratio (E'/Rb) was calculated, and the "ratio (E'/Rb)" in Table 1 was calculated. described in the column.

Abrasion Resistance Using the obtained rubber test piece, in accordance with JIS K6264, using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.), 1.53 kg (15 N) under a low load and 3.3 kg (15 N) under a high load. The amount of wear was measured under low load and high load under conditions of 06 kg (30 N) and a slip ratio of 25%. Calculate the reciprocal of each of the obtained results, and set the reciprocal of the wear amount of the standard example to 100 as an index in the columns of "wear resistance under low load" and "wear resistance under high load" in Table 1. did. It means that the larger the wear resistance index, the better the wear resistance.

The types of raw materials used in Table 1 are shown below.
・S-SBR-1: Solution-polymerized styrene-butadiene rubber having an amine group and an alkoxysilane group, HPR850 manufactured by JSR, Tg = -25°C, non-oil-extended product ・S-SBR-2: N-methylpyrrolidone (NMP)-modified solution polymerized styrene-butadiene rubber, NS116R manufactured by Nippon Zeon Co., Ltd., Tg = -24 ° C., non-oil extended product BR: Butadiene rubber, Nipol 1220 manufactured by Nippon Zeon Co., Ltd.
- NR: natural rubber, PT. SIR20 manufactured by KIRANA SAPTA
・E-SBR: Emulsion-polymerized styrene-butadiene rubber, Nipol 9548 manufactured by Nippon Zeon Co., Ltd., Tg = -37°C, an oil extended product obtained by blending 37.5 parts by mass of an oil extender with 100 parts by mass of styrene-butadiene rubber ・Carbon black: Cabot Japan Show Black 339 manufactured by Co., Ltd., nitrogen adsorption specific surface area is 88 m ² /g
・ Silica: 9100GR manufactured by Evonik, CTAB specific surface area of 190 m ² /g
Coupling agent: sulfur-containing silane coupling agent, bis(3-triethoxysilylpropyl) tetrasulfide, Si69 manufactured by Evonik Degussa
・Process oil: Extract No. 4 S manufactured by Showa Shell Sekiyu K.K.

The types of raw materials used in Table 2 are shown below.
・Stearic acid: Bead stearic acid YR manufactured by NOF Corporation
・ Zinc white: 3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. ・ Anti-aging agent: Santoflex 6PPD manufactured by Flexis Co., Ltd.
・ Vulcanization accelerator 1: Noxeler CZ-G manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
・Vulcanization accelerator 2: Noccellar DG manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
・Sulfur: Fine sulfur powder containing Kinkain oil manufactured by Tsurumi Chemical Industry Co., Ltd.

As is clear from Table 1, it was confirmed that the tire rubber compositions of Examples 1 to 3 are excellent in low rolling resistance and wear resistance under low load and high load.

The rubber composition of Comparative Example 1 does not contain modified S-SBR and contains NMP-modified S-SBR-2, and the ratio (E'/Rb) exceeds 20, so it has low rolling resistance and low load. Poor wear resistance under low and high loads.
The rubber composition of Comparative Example 2 has a modified S-SBR of more than 70% by mass and a ratio (E'/Rb) of more than 20, and is inferior in wear resistance under low load and high load.
The rubber composition of Comparative Example 3 has a modified S-SBR content of less than 30% by mass and a butadiene rubber content of more than 30% by mass, resulting in increased rolling resistance.
Since the rubber composition of Comparative Example 4 does not contain butadiene rubber and has a ratio (E'/Rb) of more than 20, it is inferior in wear resistance under low load and high load.
The rubber composition of Comparative Example 5 contains more than 40% by mass of natural rubber and has a low impact resilience Rb, resulting in high rolling resistance.
Since the rubber composition of Comparative Example 6 does not contain natural rubber and has a ratio (E'/Rb) of more than 20, it is inferior in wear resistance under low load and high load.
Since the rubber composition of Comparative Example 7 did not contain modified S-SBR and contained unmodified E-SBR, the rolling resistance increased and the wear resistance under high load was poor.

Claims (4)

30 to 70% by mass of solution-polymerized styrene-butadiene rubber having a glass transition temperature of −30° C. to −20° C. and having a terminal modifying group, 10 to 30% by mass of butadiene rubber, and 10 to 40% by mass of natural rubber. A rubber composition in which 50 to 90 parts by mass of a filler containing silica is blended with 100 parts by mass of diene rubber, wherein the terminal modification group is a hydroxy group, an alkoxysilyl group , an aminosilyl group, an epoxy group, an amino and the dynamic storage modulus E′ (unit MPa) of the rubber composition at −40° C. and the rebound resilience modulus Rb (unit %) at 40° C. measured according to JIS K6255 (E '/Rb) is 20 or less, a rubber composition for a tire. 2. The tire rubber according to claim 1, wherein 50 to 80 parts by mass of said filler is compounded with respect to 100 parts by mass of said diene rubber, and the ratio of silica in said filler is 80 mass % or more. Composition. 3. The diene rubber comprises 30 to 50% by mass of the solution-polymerized styrene-butadiene rubber, 10 to 30% by mass of the butadiene rubber, and 23 to 40% by mass of the natural rubber. The rubber composition for tires described. A pneumatic tire comprising the tire rubber composition according to any one of claims 1 to 3 in a tire tread portion.