JP2019137281A - Rubber composition for tire - Google Patents

Abstract

To provide a rubber composition for a tire that achieves both low rolling resistance and abrasion resistance under a high load.SOLUTION: A rubber composition comprises a filler containing silica blended to diene rubber 100 pts.mass composed of solution polymerization styrene-butadiene rubber 30-70 mass% having a terminal modification group with a glass-transition temperature of -30°C to -20°C, butadiene rubber of 10-30 mass%, and natural rubber of 10-40 mass%. A ratio (E'/Rb) of a kinetic storage elastic modulus E' of the rubber composition at -40°C to the rebound resilience ratio Rb (unit MPa) at 40°C is 20 or less.SELECTED DRAWING: None

Description

  The present invention relates to a rubber composition for tires that is compatible with both low rolling resistance and wear resistance under a high load.

  With the growing awareness of environmental conservation, it is required to reduce the rolling resistance of pneumatic tires and improve the fuel efficiency of the vehicle, and to improve the wear resistance and extend the tire life. In particular, pneumatic tires for commercial vehicles, including light trucks and vans, have a greater load on tires than passenger tires, and both wear resistance and low rolling resistance are achieved in such high load areas. There is a need to. In general, in order to improve the low rolling resistance, silica is compounded in the rubber composition for tires, but silica has a smaller reinforcing effect on the base rubber than carbon black, and wear resistance, particularly under high load. The wear resistance could not be improved sufficiently.

  Patent Document 1 discloses that a pneumatic tire having a tread manufactured using a rubber composition containing a predetermined amount of a specific oil-extended butadiene rubber, a specific styrene butadiene rubber, silica, and carbon black has low fuel consumption. It describes that it is excellent in abrasion resistance. However, the invention described in Patent Document 1 improves the wear resistance under high loads required for pneumatic tires for commercial vehicles even if the fuel efficiency and wear resistance of passenger car tires are improved. It was difficult to do.

International Publication No. 2015/040991

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

  The rubber composition for a tire of the present invention that achieves the above-mentioned object has a glass transition temperature of −30 ° C. to −20 ° C. and 30 to 70% by mass of a solution-polymerized styrene butadiene rubber having a terminal modified group, and 10 to A rubber composition in which a filler containing silica is blended with 100 parts by mass of a diene rubber comprising 30% by mass and 10 to 40% by mass of natural rubber, wherein the rubber composition is dynamic at −40 ° C. The ratio (E ′ / Rb) of the storage elastic modulus E ′ (unit MPa) and the rebound elastic modulus Rb (unit MPa) at 40 ° C. is 20 or less.

  The tire rubber composition of the present invention satisfies the above-described composition, and the ratio of the dynamic storage elastic modulus E ′ at −40 ° C. to the rebound elastic modulus Rb at 40 ° C. (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.

  80 parts by mass or less of the filler is blended with 100 parts by mass of the diene rubber, and the ratio of silica in the filler is preferably 80% by mass or more. The terminal modifying group can be selected from a hydroxy group, an alkoxysilyl group, a silicon-containing group having a siloxane bond, an aminosilyl group, an epoxy group, and an amino group.

  A pneumatic tire having the above-described tire rubber composition in the tire tread portion can achieve a balance between low rolling resistance and wear resistance under a high load at a higher level than before, and can be used for light trucks, light tires. Suitable for pneumatic tires for commercial vehicles including vans.

  The tire rubber composition has a glass transition temperature of −30 ° C. to −20 ° C. and 30-70% by mass of solution-polymerized styrene butadiene rubber having terminal modified groups, 10-30% by mass of butadiene rubber, and 10% of natural rubber. A filler containing silica is blended with 100 parts by mass of a diene rubber consisting of ˜40% by mass.

  The solution-polymerized styrene butadiene rubber having terminal modified groups is abbreviated as “solution-modified styrene butadiene rubber (hereinafter,“ modified S-SBR ”) having terminal modified groups reactive with silica at one or both ends of the polymer chain. There are things to do.) Examples of the terminal modifying group include a hydroxy group, a hydroxysilyl group, an alkoxy group, a carboxy group, and an amino group. The modified S-SBR may be produced by a normal method, or may be appropriately selected from commercially available products.

  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. When Tg is lower than −30 ° C., the wet performance is remarkably lowered. On the other hand, if Tg is higher than −20 ° C., rolling resistance increases. The Tg is a temperature at the midpoint of the transition zone by measuring a thermogram by differential scanning calorimetry (DSC) under a temperature increase rate condition of 20 ° C./min. Moreover, when modified | denatured S-SBR is an oil-extended article, it is set as the glass transition temperature of modified | denatured S-SBR in the state which does not contain an oil-extended component (oil).

  The modified S-SBR preferably does not contain an oil-extended component, and even if the filler is limited to 80 parts by mass or less, the rubber hardness can be increased at a temperature of normal temperature or higher. Further, the total amount of oil components contained in the rubber composition for tires is preferably small, and the total amount of oil components is preferably 0 to 25 parts by mass, more preferably 5 to 20 parts per 100 parts by mass of the diene rubber. It is good that it is a mass part.

  The content of the modified S-SBR is 30 to 70% by mass, preferably 40 to 50% by mass, in 100% by mass of the diene rubber. When the modified S-SBR is less than 30% by mass, the tensile strength at break and elongation at break of the rubber composition are lowered, so that the wear resistance is lowered. On the other hand, when the modified S-SBR exceeds 70% by mass, the dynamic storage elastic modulus E ′ at −40 ° C. of the rubber composition is increased and the wear resistance is inferior.

  As the butadiene rubber, those usually used in rubber compositions for tires can be used, and modified butadiene rubber may be used. Examples of the modifying group include the terminal modified groups of the modified S-SBR described above, and the types of the modifying groups may be the same or different. The content of butadiene rubber is 10 to 30% by mass, preferably 15 to 20% by mass, in 100% by mass of the diene rubber. When the butadiene rubber is less than 10% by mass, the dynamic storage elastic modulus E ′ at −40 ° C. is large and the wear resistance is inferior. On the other hand, if the butadiene rubber exceeds 30% by mass, the rebound resilience Rb at 40 ° C. of the rubber composition decreases and the rolling resistance increases.

  As the natural rubber, those usually used in tire rubber compositions can be used, and modified natural rubber may be used. An example of the modifying group is an epoxy group. Content of natural rubber is 10-40 mass% in 100 mass% of diene rubbers, Preferably it is 23-38 mass%. When the natural rubber is less than 10% by mass, the dynamic storage elastic modulus E ′ at −40 ° C. of the rubber composition is increased and the wear resistance is inferior. On the other hand, if the natural rubber exceeds 40% by mass, the rebound resilience Rb at 40 ° C. of the rubber composition becomes small and the rolling resistance cannot be improved.

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

  The rubber composition for tire contains a filler containing silica. The blending amount of the filler is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, further 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. . When the blending amount of the filler exceeds 80 parts by mass, the rolling resistance cannot be sufficiently reduced.

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

The CTAB adsorption specific surface area of silica is not particularly limited, but 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, the wear resistance of the tire rubber composition may not be sufficiently improved. If the CTAB adsorption specific surface area of silica exceeds 200 m ² / g, the low rolling resistance of the tire rubber composition may not 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, and mica. Carbon black is preferable. 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. In this specification, the nitrogen adsorption specific surface area of carbon black is a value measured according to JIS K6217-2.

  The rubber composition for a tire is good to mix | blend the silane coupling agent containing sulfur with a silica. By compounding a silane coupling agent containing sulfur, the dispersibility of silica in the diene rubber can be improved, and the action of improving wear resistance and low rolling resistance can be enhanced.

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

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

  To the rubber composition for a tire, a compounding agent other than the above can be added. As other compounding agents, vulcanization or crosslinking agents, vulcanization accelerators, anti-aging agents, liquid polymers, thermosetting resins, thermoplastic resins, tackifiers, etc. are generally used for rubber compositions for tires. Various compounding agents to be used can be exemplified. The compounding amounts of these compounding agents can be conventional conventional compounding amounts as long as they do not contradict the purpose of the present invention. Moreover, as a kneading machine, a normal rubber kneading machine, for example, a Banbury mixer, a kneader, a roll or the like can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, 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 composition shown in Table 1 as common compounding ingredients, and sulfur and a vulcanization accelerator. The components except for were kneaded with a 1.7 L hermetic Banbury mixer, and after a predetermined time had passed, they were discharged from the mixer and allowed to cool to room temperature. Then, the rubber composition for tires was prepared by returning to a 1.7 L closed Banbury mixer, adding sulfur and a vulcanization accelerator, and mixing. In addition, in the column of E-SBR in Table 1, in addition to the blending amount of the product, the blending amount of net E-SBR excluding the oil-extended component is shown in parentheses. Moreover, the compounding quantity of the compounding agent described in Table 2 was shown by the mass part with respect to 100 mass parts of diene rubber described in Table 1.

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

Dynamic storage elastic modulus E ′ and loss tangent tan δ
The dynamic viscoelasticity of the obtained test piece was measured with 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. The loss tangent tan δ at E ′ and a temperature of 60 ° C. was determined. The reciprocal of the obtained tan δ value was calculated, and an index with the standard value as 100 was shown in Table 1. The larger the index of tan δ (60 ° C.) at a temperature of 60 ° C., the smaller the exothermic property, and the smaller the rolling resistance when a pneumatic tire is made.

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

Ratio (E '/ Rb)
From the dynamic storage elastic modulus E ′ at −40 ° C. obtained above and the rebound elastic modulus Rb at 40 ° C., the ratio (E ′ / Rb) was calculated, and the “ratio (E ′ / Rb)” in Table 1 was calculated. It described in the column.

2. Abrasion resistance 1.53 kg (15 N) under a low load and under a high load using a lambone wear tester (manufactured by Iwamoto Seisakusho Co., Ltd.) according to JIS K6264 using the obtained rubber test piece. The wear amount under low load and high load was measured under the condition of 06 kg (30 N) and a slip rate of 25%. Reciprocals of the obtained results are calculated, and listed in the columns of “Abrasion resistance under low load” and “Abrasion resistance under high load” in Table 1 as an index for setting the reciprocal of the wear amount of the standard example to 100. did. The larger the index of wear resistance, the better the wear resistance.

In addition, the kind of raw material used in Table 1 is shown below.
S-SBR-1: Solution-polymerized styrene butadiene rubber having amine group / alkoxysilane group, HPR850 manufactured by JSR, Tg = −25 ° C., non-oil-extended product S-SBR-2: N-methylpyrrolidone (NMP) modification 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 made by KIRANA SAPTA
E-SBR: emulsion-polymerized styrene butadiene rubber, Nipol 9548 manufactured by Nippon Zeon Co., Ltd., Tg = −37 ° C., oil-extended product in which 37.5 parts by mass of an oil-extended component is blended with 100 parts by mass of styrene-butadiene rubber. Carbon black: Cabot Japan Show Black 339, Nitrogen adsorption specific surface area of 88 m ² / g
Silica: 9100GR manufactured by Evonik, CTAB specific surface area is 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 KK

The types of raw materials used in Table 2 are shown below.
・ Stearic acid: NOF beads stearic acid YR
・ Zinc flower: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. ・ Anti-aging agent: Santoflex 6PPD manufactured by Flexis
・ Vulcanization accelerator 1: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Vulcanization accelerator 2: Noxeller DG made by Ouchi Shinsei Chemical Co., Ltd.
・ Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd.

  As is clear from Table 1, it was confirmed that the rubber compositions for tires of Examples 1 to 3 were 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, blends NMP-modified S-SBR-2, and the ratio (E '/ Rb) exceeds 20, so that it has low rolling resistance and low load. Inferior wear resistance under and under high load.
Since the modified S-SBR exceeds 70 mass% and the ratio (E ′ / Rb) exceeds 20, the rubber composition of Comparative Example 2 is inferior in wear resistance under low load and high load.
Since the modified S-SBR is less than 30% by mass and the butadiene rubber is more than 30% by mass, the rolling resistance of the rubber composition of Comparative Example 3 is increased.
Since the rubber composition of Comparative Example 4 does not contain butadiene rubber and the ratio (E ′ / Rb) exceeds 20, the wear resistance under low load and high load is inferior.
In the rubber composition of Comparative Example 5, the natural rubber exceeds 40% by mass and the rebound resilience Rb becomes small, so that the rolling resistance increases.
Since the rubber composition of Comparative Example 6 does not contain natural rubber and the ratio (E ′ / Rb) exceeds 20, the wear resistance under low load and high load is inferior.
Since the rubber composition of Comparative Example 7 did not contain modified S-SBR and compounded unmodified E-SBR, the rolling resistance increased and the wear resistance under high load was inferior.

Claims (4)

  It consists of 30 to 70% by mass of solution-polymerized styrene butadiene rubber having a glass transition temperature of −30 ° C. to −20 ° C. and having terminal modified groups, 10 to 30% by mass of butadiene rubber, and 10 to 40% by mass of natural rubber. A rubber composition in which a filler containing silica is blended with 100 parts by mass of a diene rubber, wherein the rubber composition has a dynamic storage elastic modulus E ′ (unit MPa) at −40 ° C. and a rebound resilience at 40 ° C. A tire rubber composition having a ratio (E ′ / Rb) of a rate Rb (unit: MPa) of 20 or less.   The tire rubber composition according to claim 1, wherein 80 parts by mass or less of the filler is blended with 100 parts by mass of the diene rubber, and the ratio of silica in the filler is 80% by mass or more. object.   The tire rubber composition according to claim 1 or 2, wherein the terminal-modified group is selected from a hydroxy group, an alkoxysilyl group, a silicon-containing group having a siloxane bond, an aminosilyl group, an epoxy group, and an amino group.   The pneumatic tire which has the rubber composition for tires in any one of Claims 1-3 in a tire tread part.