JP6539947B2 - Rubber composition for tire tread - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread, in which the balance between low rolling resistance and wet performance, and wear resistance is improved to the conventional level or more.

  In recent years, the performance required for pneumatic tires is diverse, and in order to improve the fuel efficiency of automobiles, the rolling resistance should be reduced, and the steering stability (wet performance) and abrasion resistance when traveling on a wet road surface should be increased. Etc. are required. In order to achieve both low rolling resistance and wet performance, it has been practiced to add silica to a rubber composition for a tire tread. However, when a large amount of silica is blended instead of carbon black, there is a problem that the tensile breaking property of the rubber composition is lowered and the abrasion resistance is deteriorated.

  Patent Document 1 proposes blending a specific silane coupling agent and an alkyltriethoxysilane together with silica into a rubber composition for a tire. Although this rubber composition can improve low rolling resistance and wet performance, it has not been able to improve the abrasion resistance.

Patent No. 4930661

  An object of the present invention is to provide a rubber composition for a tire tread, in which the balance between low rolling resistance and wet performance, and wear resistance is improved over conventional levels.

The rubber composition for a tire tread according to the present invention for achieving the above object comprises 3 to 20 parts by weight of carbon black, 60 to 150 parts by weight of silica, and 2 to 10 parts by weight of farnesene polymer based on 100 parts by weight of diene rubber. The present invention is characterized in that 0.5 to 8 parts by weight of alkyltriethoxysilane having an alkyl group having 3 to 20 carbon atoms and 5 to 15 parts by weight of the farnesene polymer and the alkyltriethoxysilane are blended. I assume.

  The rubber composition for a tire tread according to the present invention contains a carbon black, a silica, a farnesene polymer and an alkyltriethoxysilane in a diene rubber to limit the total of the farnesene polymer and the alkyltriethoxysilane. The abrasion resistance can be improved over conventional levels while achieving both low rolling resistance and high wet performance.

  The pneumatic tire using the rubber composition for a tire tread of the present invention in a cap tread can improve the abrasion resistance to a level higher than the conventional level while achieving both low rolling resistance and high wet performance.

  In the rubber composition for a tire tread of the present invention, the rubber component comprises a diene rubber. Examples of diene rubbers include natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber and the like. Among them, styrene butadiene rubber, butadiene rubber, natural rubber and isoprene rubber are preferable. These diene rubbers can be used alone or in any blend.

  It is preferable to use a styrene butadiene rubber as a main component as a diene rubber, and preferably 100 wt% or more, more preferably 60 to 100 wt%, of styrene butadiene rubber in 100 wt% of diene rubber. By using styrene butadiene rubber as a main component, it is possible to combine low rolling resistance and wet performance at a high level.

  As a styrene butadiene rubber, solution polymerization styrene butadiene rubber (S-SBR), emulsion polymerization styrene butadiene rubber (E-SBR), terminal-modified S-SBR etc. can be illustrated, for example.

  It is preferable that a butadiene rubber is contained as a diene rubber, and abrasion resistance can be made higher.

  Further, it is preferable to contain a natural rubber having a high affinity to the farnesene polymer as a diene rubber, and an isoprene rubber, so that the rubber strength can be increased.

  The rubber composition for a tire tread of the present invention has high abrasion resistance by blending carbon black. The compounding amount of carbon black is 3 to 20 parts by weight, preferably 5 to 15 parts by weight with respect to 100 parts by weight of the diene rubber. If the compounding amount of carbon black is less than 3 parts by weight, the reinforcing property of the rubber composition can not be sufficiently obtained, and the abrasion resistance is insufficient. When the amount of carbon black exceeds 20 parts by weight, rolling resistance increases.

The carbon black used in the present invention preferably has a nitrogen adsorption specific surface area N ₂ SA of 100 to 170 m ² / g, more preferably 130 to 160 m ² / g. If the N ₂ SA is less than 100 m ² / g, mechanical properties such as tensile fracture properties and dynamic modulus of the rubber composition may be reduced, and the abrasion resistance may be insufficient. When N ₂ SA exceeds 170 m ² / g, rolling resistance increases. N ₂ SA shall be measured in accordance with JIS K6217-2.

The rubber composition for a tire tread is compatible with low rolling resistance and wet performance by blending silica. The CTAB specific surface area of silica is preferably 140 to 210 m ² / g, more preferably 140 to 160 m ² / g. When the CTAB specific surface area is less than 140 m ² / g, the wet performance is insufficient. When the CTAB specific surface area exceeds 210 m ² / g, the dispersibility of the silica is deteriorated and the abrasion resistance is lowered. The CTAB specific surface area of silica is a value measured according to ISO 5794.

  In the present invention, the compounding amount of silica is 60 to 150 parts by weight, preferably 70 to 120 parts by weight, more preferably 70 to 100 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of silica is less than 60 parts by weight, the effect of reducing rolling resistance and improving wet performance can not be sufficiently obtained. When the amount of silica exceeds 150 parts by weight, wear resistance is lowered and rolling resistance is increased.

  In the present invention, the total amount of the inorganic filler containing carbon black and silica is not particularly limited, but preferably 65 to 160 parts by weight, more preferably 70 to 70 parts by weight per 100 parts by weight of diene rubber. It may be 130 parts by weight. If the total amount of the inorganic filler containing carbon black and silica is less than 65 parts by weight, abrasion resistance and wet performance may be insufficient. When the total amount of the inorganic filler containing carbon black and silica exceeds 160 parts by weight, rolling resistance may be increased.

  In the present invention, a silane coupling agent may be blended with silica. By blending a silane coupling agent, the dispersibility of silica in a diene rubber can be improved, and the action to improve low rolling resistance and wet performance can be enhanced.

  The type of silane coupling agent is not particularly limited as long as it can be used for a rubber composition containing silica, and, for example, bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3- (3-triethoxysilylpropyl) tetrasulfide, Sulfur-containing silane coupling agents such as triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane can be exemplified. .

  The blending amount of the silane coupling agent is preferably 3 to 15% by weight, more preferably 5 to 10% by weight, with respect to the weight of the silica. If the amount of the silane coupling agent is less than 3% by weight of the amount of the silica, the dispersion of the silica may not be sufficiently improved. When the compounding amount of the silane coupling agent exceeds 15% by weight of the silica compounding amount, the silane coupling agents are condensed with each other, and the desired hardness and strength in the rubber composition can not be obtained.

  The rubber composition for a tire tread of the present invention suppresses aggregation of silica and viscosity increase of the rubber composition by blending an alkyltriethoxysilane having an alkyl group having 3 to 20 carbon atoms, and low rolling resistance , Wet performance and abrasion resistance can be made more excellent.

  The alkyltriethoxysilane has an alkyl group having 3 to 20 carbon atoms, preferably 7 to 20 carbon atoms. As an alkyl group having 3 to 20 carbon atoms, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl Group, heptadecyl group, octadecyl group, nonadecyl group, icosyl group. Among them, from the viewpoint of compatibility with a diene rubber, an alkyl group having 8 to 10 carbon atoms is more preferable, and an octyl group and a nonyl group are more preferable.

  The compounding amount of the alkyltriethoxysilane is 0.5 to 8 parts by weight, more preferably 2 to 6 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of the alkyltriethoxysilane is less than 0.5 parts by weight, rolling resistance is increased and abrasion resistance is reduced. When the amount of the alkyltriethoxysilane exceeds 8 parts by weight, rolling resistance increases and wear resistance decreases.

  The rubber composition for a tire tread of the present invention can reduce rolling resistance and enhance abrasion resistance by blending a farnesene polymer. The farnesene polymer is highly compatible with the diene rubber and is liquid and excellent in permeability at normal temperature to the processing temperature of the rubber composition for a tire tread, so that the dispersibility of silica can be improved. In addition, since the farnesene polymer has a relatively high molecular weight and a crosslinkable structure, it can enhance the tensile breaking properties of the rubber composition for a tire tread beyond the conventional level after vulcanization and improve the wear resistance. .

  The farnesene polymer is a polymer of α-farnesene, a polymer of β-farnesene, or a copolymer of α-farnesene and β-farnesene, preferably a polymer of β-farnesene. In the polymer of farnesene, the structural unit derived from α-farnesene and / or β-farnesene is preferably 90% by weight or more, more preferably 95% by weight or more, more preferably 100% by weight, and butadiene, It may also contain constitutional units derived from other monomers such as isoprene.

  The compounding amount of the farnesene polymer is 2 to 10 parts by weight, preferably 2 to 7 parts by weight with respect to 100 parts by weight of the diene rubber. If the compounding amount of the farnesene polymer is less than 2 parts by weight, the effect of improving the low rolling resistance and the abrasion resistance can not be sufficiently obtained. When the amount of the farnesene polymer exceeds 10 parts by weight, the wet performance is reduced.

  The weight average molecular weight of the farnesene polymer is not particularly limited, but is preferably 2000 to 25,000, more preferably 2,500 to 20,000. When the weight average molecular weight of the farnesene polymer is less than 2000, the rubber hardness of the rubber composition is lowered, and it becomes easy to bleed out of the rubber composition. When the weight average molecular weight of the farnesene polymer exceeds 25,000, the processability is deteriorated.

  The molecular weight distribution (Mw / Mn; Mw is a weight average molecular weight, Mn is a number average molecular weight) of the farnesene polymer is preferably 1.0 to 2.0, more preferably 1.0 to 1.5, still more preferably 1 It is good that it is .0-1.3. When the molecular weight distribution of the farnesene polymer is in such a range, the variation in viscosity is reduced. In the present specification, the weight average molecular weight Mw and the number average molecular weight Mn of the farnesene polymer are determined by GPC (gel permeation chromatography) and determined by standard polystyrene conversion.

  The melt viscosity of the farnesene polymer is preferably 0.1 to 3.5 Pa · s, more preferably 0.1 to 2 Pa · s, and still more preferably 0.1 to 1.5 Pa · s. When the melt viscosity of the farnesene polymer is in such a range, kneading of the rubber composition is facilitated, and the dispersibility of the silica is improved. As used herein, the melt viscosity of the farnesene polymer is the melt viscosity at 38 ° C. as measured by a Brookfield viscometer.

  The farnesene polymer can be synthesized by a conventional method, for example, an emulsion polymerization method and a solution polymerization method can be exemplified, and it is preferable to synthesize by a solution polymerization method.

In the present invention, the total amount of the farnesene polymer A (parts by weight) and alkyl amounts of triethoxysilane B (parts by weight) (A + B) is against the 100 parts by weight of the diene rubber, 5 to 15 parts by weight It is. If the total (A + B) of the farnesene polymer and the alkyltriethoxysilane is less than 5 parts by weight, the effect of reducing the rolling resistance and increasing the abrasion resistance can not be sufficiently obtained. When the total (A + B) of both exceeds 15 parts by weight, the wet performance is reduced.

  The rubber composition for a tire tread according to the present invention includes various additives generally used for a tire rubber composition such as a vulcanizing or crosslinking agent, a vulcanization accelerator, various oils, an antioxidant, a plasticizer and the like. Such additives can be compounded in a conventional manner to give a rubber composition which can be vulcanized or crosslinked. The blending amounts of these additives can be conventional conventional blending amounts as long as the purpose of the present invention is not violated. The rubber composition for a tire tread of the present invention can be produced by mixing the above-mentioned respective components using a usual rubber kneading machine such as a Banbury mixer, a kneader, a roll and the like.

  The rubber composition for a tire tread according to the present invention can be suitably used for a cap tread in a pneumatic tire, and the balance between low rolling resistance and wet performance and abrasion resistance can be made excellent. .

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

In preparing 13 types of rubber compositions (Examples 3 to 5, Reference Examples 1 to 2, Comparative Examples 1 to 8) having the formulations shown in Tables 1 and 2 with the compounding agents shown in Table 3 as common formulations, The components other than sulfur and the vulcanization accelerator were weighed and kneaded for 5 minutes with a 1.8 L internal mixer, after which the masterbatch was discharged and cooled to room temperature. The masterbatch was subjected to a 1.8 L closed mixer, and sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition for a tire tread. In Tables 1 and 2, since the modified S-SBR and E-SBR are oil-extended products, the net rubber amount is shown in parentheses. Moreover, the compounding quantity of the common component of Table 3 was described as a weight part with respect to 100 weight part of diene based rubbers shown to Table 1,2.

  The resulting 13 types of rubber compositions were press-cured at 170 ° C. for 10 minutes in a predetermined mold to prepare a vulcanized rubber sample composed of the rubber composition for a tire tread. Using the obtained vulcanized rubber samples, rolling resistance (tan δ at 60 ° C.) was evaluated by the method shown below.

Rolling Resistance The rolling resistance of the obtained vulcanized rubber sample was evaluated by a loss tangent tan δ (60 ° C.) which is known to be an index of heat buildup. The tan δ (60 ° C.) was measured under conditions of an initial strain of 10%, an amplitude of ± 2%, a frequency of 20 Hz and a temperature of 60 ° C. using a visco-elastic spectrometer manufactured by Toyo Seiki Seisaku-sho. The obtained results are shown in Tables 1 and 2 as an index with the reciprocal of the value of Comparative Example 1 being 100. As the index of tan δ (60 ° C.) is larger, particularly when the index is 102 or more, the heat generation is small, which means that the rolling resistance is small and the fuel consumption performance is excellent when the tire is made into a pneumatic tire.

  The pneumatic tire of the size (225 / 40R18) which used 13 types of rubber compositions obtained for a cap tread was vulcanized and formed. Wet performance and abrasion resistance were evaluated by the methods shown below using each pneumatic tire.

Wet performance The obtained pneumatic tire is assembled on a wheel of rim size 18 × 8 JJ, mounted on a test vehicle of 2.5 liter class made in Japan, and a test course of 2.6 km per lap consisting of a wet road surface under the condition of 230 kPa air pressure. The vehicle was allowed to run and the steering stability at that time was scored by the sensitivity evaluation by three expert panelists. The obtained results are shown in Tables 1 and 2 as an index based on Comparative Example 1 being 100. The larger this index is, the more the index is 102 or more, the better the wet steering stability on a wet road surface.

Wear resistance The obtained pneumatic tire is assembled on a wheel of rim size 18 × 8 JJ, filled with air pressure 230 kPa, mounted on a test vehicle of 2.5 liter class made in Japan, and dried on a test road of 5 km around a circuit. Traveled 10 laps continuously at a speed of 80 km / h. Thereafter, the state of wear on the tread surface was visually observed, and Comparative Example 1 was rated as 100 and evaluated. The obtained results are shown in Tables 1 and 2. The larger the evaluation value, the better the abrasion resistance.

The types of raw materials used in Tables 1 and 2 are shown below.
Modified S-SBR: Terminally modified solution-polymerized styrene butadiene rubber, E581 manufactured by Asahi Kasei Chemicals, an oil-extended product E-SBR containing 37.5 parts by weight of an oil extending component with respect to 100 parts by weight of a net rubber component: emulsion-polymerized styrene Butadiene rubber, Nipol 1739, manufactured by Nippon Zeon Co., Ltd., an oil-extended product BR containing 37.5 parts by weight of an oil extending component with respect to 100 parts by weight of a net rubber component: Butadiene rubber, Nipol BR 1220 manufactured by Nippon Zeon
Carbon black: SEAST KH manufactured by Tokai Carbon Co., Ltd., nitrogen adsorption specific surface area 90 m ² / g
Silica: Rhodia Zeoxil 1165MP, CTAB specific surface area 160 m ² / g
Coupling agent: bis- (3-triethoxysilylpropyl) tetrasulfide, Si69 manufactured by Evonik Degussa
Farnesene 1: Polymer of β-farnesene polymerized according to the following synthesis example 1, weight average molecular weight 140 000, molecular weight distribution 1.2, melt viscosity 69 Pa · s
Alkylsilane: Octyltriethoxysilane, Shin-Etsu Chemical KBE-3083

Synthesis Example 1 (polymerization of farnesene 1)
In a pressure-resistant container purged with nitrogen and dried, 274 g of hexane and 1.2 g of n-butyllithium (17% by weight hexane solution) were charged, heated to 50 ° C., 272 g of β-farnesene was added, and polymerization was performed for 1 hour . After adding methanol to the obtained polymerization reaction solution, the polymerization reaction solution was washed with water. The water was separated, and the polymerization reaction solution was dried at 70 ° C. for 12 hours to obtain a polymer of β-farnesene (farnesene 1).

In addition, the kind of raw material used in Table 3 is shown below.
Aroma oil: Showa Shell Sekiyu KK extract No. 4 S
Stearic acid: Chiba fatty acid company beads stearic acid anti-aging agent: Sumitomo Chemical Co., Ltd. Antigen 6C
Wax: Sanochik zinc oxide manufactured by Ouchi Emerging Chemical Industry Co., Ltd. Zinc oxide manufactured by Shodomo Chemical Industry Co., Ltd. Three types of sulfur: Fine sulfur powder with gold oxide oil manufactured by Tsurumi Chemical Industry Co., Ltd. (sulfur content is 95.24% by weight)
Vulcanization accelerator 1: Noccellar CZ-G manufactured by Ouchi Emerging Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noccellar D manufactured by Ouchi emerging chemical industry

As apparent from Table 2, it was confirmed that the rubber compositions of Examples 3 to 5 improve the low rolling resistance, the wet performance and the abrasion resistance above conventional levels.

The rubber composition of Comparative Example 1 is a blending that is a standard not blending the farnesene polymer.
The rubber composition of Comparative Example 2 did not contain carbon black, so the wear resistance deteriorated.
In the rubber composition of Comparative Example 3, since the compounding amount of carbon black exceeds 20 parts by weight, the rolling resistance is increased and the abrasion resistance is deteriorated.

  In the rubber composition of Comparative Example 4, the wet performance was deteriorated because the blending amount of silica was less than 60 parts by weight. In the rubber composition of Comparative Example 5, since the compounding amount of silica exceeds 150 parts by weight, the rolling resistance is increased and the abrasion resistance is deteriorated.

In the rubber composition of Comparative Example 6, since the alkyltriethoxysilane was not blended, the rolling resistance increased and the abrasion resistance deteriorated.
In the rubber composition of Comparative Example 7, the rolling resistance increased because the compounding amount of the alkyltriethoxysilane exceeded 8 parts by weight, and the abrasion resistance deteriorated.
In the rubber composition of Comparative Example 8, the wet performance deteriorated because the compounding amount of the farnesene polymer exceeded 10 parts by weight .

Claims (2)

Alkyl triethoxysilane having 3 to 20 parts by weight of carbon black, 60 to 150 parts by weight of silica, 2 to 10 parts by weight of farnesene polymer, and 2 to 20 parts by weight of a farnesene polymer with respect to 100 parts by weight of diene rubber A rubber composition for a tire tread, comprising 0.5 to 8 parts by weight of the compound and 5 to 15 parts by weight of the farnesene polymer and the alkyltriethoxysilane in total.   A pneumatic tire comprising the rubber composition for a tire tread according to claim 1 as a cap tread.