JP2012188563A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread enhancing wet grip performance and abrasion resistance without aggravating rolling resistance and workability.SOLUTION: Silica having 120 to 180 m/g nitrogen adsorption specific surface area and carbon black are mixed to 100 pts.wt.diene based rubber including 60 to 90 wt.% modified solution polymerized styrene butadiene rubber having weight average molecular weight of 1,000,000 to 1,500,000, 30 to 60% vinyl bond amount and 30 to 50 wt.% styrene content, 5 to 30 wt.% butadiene rubber having molecular weight distribution Mw/Mn of 4.0 or below and 5 to 30 wt.% natural rubber or polyisoprene rubber so that filler total amounts may be 80% or less and the rate of silica to the filler total amounts may be 60 to 90% and 6 to 15% silane coupling agent to the silica is mixed.

Description

  The present invention relates to a rubber composition for tire treads, and more particularly to a rubber composition for tire treads that improves wet grip performance and wear resistance without deteriorating rolling resistance and workability.

  In general, a pneumatic tire is required to have low rolling resistance, excellent grip performance (wet grip performance) on a wet road surface, and excellent wear resistance. In order to reduce rolling resistance, the rubber composition for a tire tread constituting the tread portion includes, for example, a large amount of silica instead of carbon black, the total amount of silica and carbon black filler is reduced, or the glass transition point. For example, a polymer having a low (Tg) is blended. However, the rubber composition containing a large amount of silica instead of carbon black has deteriorated wear resistance, and the rubber composition having reduced filler total weight has deteriorated wet grip performance and wear resistance, and has a low Tg polymer. The rubber composition has a problem that wet grip performance deteriorates. In addition, when a large amount of silica is blended, the rubber viscosity of the rubber composition increases, and there is a problem that processability deteriorates.

  As a countermeasure, Patent Document 1 proposes a tire rubber composition in which silica is blended with a rubber component made of solution-polymerized styrene-butadiene rubber, emulsion-polymerized styrene-butadiene rubber, and butadiene rubber. This rubber composition has the effect of improving the three functions of low rolling resistance, wet grip performance and wear resistance. However, since the level of demand for these three functions by consumers is high, the above-mentioned rubber composition is not necessarily sufficient, and there is room for further improvement. Further, this rubber composition does not solve the problem of not deteriorating processability.

Japanese Patent Laid-Open No. 2005-23295

  An object of the present invention is to provide a rubber composition for a tire tread in which wet grip performance and wear resistance are improved without deteriorating rolling resistance and workability.

The rubber composition for a tire tread according to the present invention that achieves the above object comprises 60 to 90% by weight of a modified solution-polymerized styrene butadiene rubber, 5 to 30% by weight of butadiene rubber, and 5 to 30% by weight of natural rubber or polyisoprene rubber. A filler composed of carbon black and silica is added to 100 parts by weight of the diene rubber to be contained so that the total amount of the filler is 80 parts by weight or less and the proportion of silica in the total amount of the filler is 60 to 90% by weight. A silane coupling agent is blended in an amount of 6 to 15% by weight based on the amount of silica, and the modified solution polymerized styrene butadiene rubber has a weight average molecular weight of 1,000,000 to 1,500,000, a vinyl bond amount of 30 to 60%, The styrene content is 30 to 50% by weight, the molecular weight distribution (Mw / Mn) of the butadiene rubber is 4.0 or less, Nitrogen adsorption specific surface area of the serial silica characterized in that it is a 120~180m ² / g.

According to the rubber composition for a tire tread of the present invention, a diene system containing 60 to 90% by weight of a modified solution polymerized styrene butadiene rubber, 5 to 30% by weight of butadiene rubber, and 5 to 30% by weight of natural rubber or polyisoprene rubber. The total amount of filler consisting of carbon black and silica is 80 parts by weight or less with respect to 100 parts by weight of rubber, and the ratio of silica to the total amount of filler is 60 to 90% by weight, and the silane coupling agent is adjusted to the silica amount. On the other hand, since 6 to 15% by weight is blended, wet grip performance and wear resistance can be improved without deteriorating rolling resistance and workability. In particular, the blending amount of butadiene rubber having a molecular weight distribution (Mw / Mn) of 4.0 or less is 30% by weight or less, the filler is 80 parts by weight or less, and the silica ratio thereof is 90% by weight or less. The solution-polymerized styrene butadiene rubber has a weight average molecular weight of 1,000,000 to 1,500,000, a vinyl bond content of 30 to 60%, a styrene content of 30 to 50% by weight, and a butadiene rubber molecular weight distribution (Mw / Mn) of 4. 0.0 or less, and the nitrogen adsorption specific surface area of silica is 120 to 180 m ² / g, so that wet grip performance and wear resistance can be improved.

  In the present invention, the functional group of the modified solution-polymerized styrene butadiene rubber is preferably at least one selected from a hydroxyl group, an alkoxylyl group, an epoxy group, a carbonyl group, a carboxyl group, and an amino group. Thereby, wet performance and wear resistance can be achieved at a higher level without impairing rolling resistance and workability.

  In addition, the nitrogen adsorption specific surface area of silica shall be measured based on ISO9277.

  The pneumatic tire using the rubber composition for a tire tread of the present invention can improve wet grip performance and wear resistance while maintaining rolling resistance and workability.

  In the rubber composition for a tire tread of the present invention, the rubber component is a diene rubber, and the diene rubber is referred to as a modified solution-polymerized styrene butadiene rubber (hereinafter referred to as “modified S-SBR”) in 100% by weight of the diene rubber. ) 60 to 90 wt%, butadiene rubber (hereinafter referred to as “BR”) 5 to 30 wt%, natural rubber (hereinafter referred to as “NR”) or polyisoprene rubber (hereinafter referred to as “IR”). 5 to 30% by weight. The amount of rubber referred to here is the net amount of rubber excluding the amount of oil added.

  The modified S-SBR is a terminal-modified styrene butadiene rubber produced by solution polymerization so as to have a functional group at the molecular terminal. Examples of the functional group include a hydroxyl group, an alkoxyl group, an epoxy group, a carbonyl group, a carboxyl group, and an amino group. Such modified S-SBR can be produced by an ordinary method, for example, a method disclosed in Japanese Patent No. 3488926. Moreover, you may use it selecting suitably from a commercial item.

  In the present invention, by adding the modified S-SBR, the compatibility with silica is increased and the dispersibility is improved, so that both reduction of rolling resistance and securing of wear resistance can be achieved. The blending amount of the modified S-SBR in 100% by weight of the diene rubber is 60 to 90% by weight, preferably 55 to 85% by weight. If the blending amount of the modified S-SBR is less than 60% by weight, the effect of ensuring wet grip performance cannot be obtained. If the blending amount of the modified S-SBR is greater than 90% by weight, processability deteriorates due to an increase in viscosity.

  The modified S-SBR has a weight average molecular weight of 1,000,000 to 1,500,000, a vinyl bond content of 30 to 60%, and a styrene content of 30 to 50% by weight. By setting the characteristics of the modified S-SBR within such a range, wet grip performance and wear resistance can be improved while maintaining rolling resistance.

  In particular, the wear resistance can be improved by setting the weight average molecular weight of the modified S-SBR in the range of 1,000,000 to 1,500,000, preferably 1.1 million to 1,400,000. When the weight average molecular weight of the modified S-SBR is less than 1 million, the wear resistance is deteriorated. If the weight average molecular weight of the modified S-SBR is more than 1,500,000, processability deteriorates due to an increase in viscosity. The weight average molecular weight of the modified S-SBR is measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

  Moreover, wet grip performance and abrasion resistance can be improved by setting the vinyl bond content of the modified S-SBR in the range of 30 to 60%, preferably 33 to 57%. When the vinyl bond amount of the modified S-SBR is less than 30%, the wet grip performance is deteriorated. When the vinyl bond amount of the modified S-SBR is more than 60%, the wear resistance is deteriorated.

  Further, by setting the styrene content of the modified S-SBR in the range of 30 to 50% by weight, preferably 35 to 45% by weight, the rolling resistance is lowered and the rubber strength is increased to ensure the wear resistance. Can do. When the styrene content of the modified S-SBR is less than 20% by weight, the wet grip performance is deteriorated. When the styrene content of the modified S-SBR is larger than 60% by weight, rolling resistance or wear resistance is deteriorated.

  In addition, when unmodified styrene butadiene rubber is used, the silica dispersibility in the rubber is inferior compared with the modified styrene butadiene rubber, so that it is not possible to achieve both high performance such as rolling resistance and wet grip performance. . In addition, emulsion-polymerized styrene-butadiene rubber has poor microstructural selectivity in the rubber molecule compared to solution-polymerized styrene-butadiene rubber, and cannot achieve both high performance and high performance.

  In the present invention, the abrasion resistance of the rubber composition is ensured by blending BR. The blending amount of BR in 100% by weight of the diene rubber is 5 to 30% by weight, preferably 8 to 27% by weight. When the amount of BR is less than 5% by weight, the wear resistance of the rubber composition is deteriorated. When the blending amount of BR is larger than 30% by weight, the wet grip performance is deteriorated.

  Further, BR having a molecular weight distribution Mw / Mn of 4.0 or less, preferably 2.5 to 3.5 is used. In order to achieve both wet grip performance and workability, it is preferable that the BR molecular weight distribution Mw / Mn be in such a range. By keeping within the specified range, wet grip performance and workability can be improved. I can do it. In this specification, the molecular weight distribution Mw / Mn of BR is defined by the ratio of the weight average molecular weight Mw and the number average molecular weight Mn of BR. Moreover, the weight average molecular weight Mw and the number average molecular weight Mn of BR shall be measured by gel permeation chromatography (GPC) by standard polystyrene conversion.

  In the present invention, by adding NR or IR, it is possible to achieve both wear resistance and rolling resistance. The blending amount of NR or IR in 100% by weight of the diene rubber is 5 to 30% by weight, preferably 8 to 27% by weight. If the blending amount of NR or IR is less than 5% by weight, the rolling resistance cannot be maintained. When the blending amount of NR or IR is larger than 30% by weight, the wet grip performance is deteriorated.

  In the present invention, a filler composed of carbon black and silica is blended so that the total amount of the filler is 80 parts by weight or less, preferably 55 to 75 parts by weight with respect to 100 parts by weight of the diene rubber. Further, the ratio of silica in the total amount of filler composed of carbon black and silica is 60 to 90% by weight, preferably 65 to 85% by weight. By making the total amount of carbon black and silica within this range, it is possible to achieve both rolling resistance, wet grip performance and wear resistance of the rubber composition. In addition, the compounding of the modified S-SBR described above improves the affinity between silica and rubber and improves the dispersibility of silica, so that it is possible to achieve both workability, rolling resistance, wet grip performance and wear resistance. I can do it.

  When the total amount of filler relative to 100 parts by weight of the diene rubber is larger than 80 parts by weight, rolling resistance and workability deteriorate. Further, when the ratio of silica to the total amount of filler is less than 60% by weight, rolling resistance is deteriorated. If the ratio of silica to the total amount of filler is more than 90% by weight, the wear resistance and workability are deteriorated.

Silica having a nitrogen adsorption specific surface area (N ₂ SA) of 120 to 180 m ² / g is used. By using such specific silica, it is possible to achieve both wet grip performance, wear resistance and workability. When the nitrogen adsorption specific surface area (N ₂ SA) of silica is smaller than 120 m ² / g, the wear resistance is deteriorated. If the nitrogen adsorption specific surface area (N ₂ SA) of silica is larger than 180 m ² / g, processability deteriorates.

  Moreover, in this invention, by mix | blending a silica and a silane coupling agent together, it becomes possible to improve the dispersibility of a silica and to make compatible multiple performances, such as an improvement of workability and a fall of rolling resistance. A silane coupling agent is 6 to 15 weight% with respect to a silica compounding quantity, Preferably it is 7 to 10 weight%. When the blending amount of the silane coupling agent with respect to the blending amount of silica is less than 6% by weight, the wear resistance and workability deteriorate. Even if the blending amount of the silane coupling agent is 15% by weight or more, the desired improvement effect cannot be expected because the dispersibility improvement effect is small.

  Although it does not restrict | limit especially as a silane coupling agent, A sulfur containing silane coupling agent is preferable, for example, bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide. , 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and the like.

  In addition to the above-described carbon black and filler, the tire tread rubber composition includes a tire tread rubber composition such as a vulcanization or crosslinking agent, a vulcanization accelerator, an anti-aging agent, a plasticizer, and a processing aid. Various commonly used additives can be blended, and such additives can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. Such a rubber composition can be produced by mixing each of the above components using a known rubber kneading machine, for example, a Banbury mixer, a kneader, a roll or the like.

  The rubber composition for a tire tread of the present invention can be suitably used for a pneumatic tire. A pneumatic tire using the rubber composition for a tire tread can maintain a high level without deteriorating rolling resistance and workability, and can improve wet grip performance and wear resistance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  Nineteen types of rubber compositions for tire treads (Examples 1 to 6, Comparative Examples 1 to 13) having the formulations shown in Tables 1 to 3 were prepared so as to include the compounding agents shown in Table 4 as a common formulation. First, components other than sulfur and a vulcanization accelerator are kneaded for 5 minutes with a 1.8 L closed mixer and released. The master batch was allowed to cool at room temperature, and then subjected to an open roll and kneaded by adding sulfur and a vulcanization accelerator. In Tables 1 to 3, the total amount of filler represents the total amount of silica and carbon black, the silica ratio represents the weight ratio of silica in the total amount of filler, and the silane coupling agent ratio is the combination of silane coupling agent. The amount represents a ratio with respect to the amount of silica. In Tables 1 to 3, the compounding amounts of the modified S-SBR1 and 2, S-SBR1 and 2, and BR are shown in the upper stage, respectively, and the compounding amount of the net rubber component excluding the oil-extended oil is shown respectively. Shown in parentheses at the bottom. Further, for the modified S-SBR1 and 2 and S-SBR1 and 2 used, the type of the modifying group, styrene content, cis amount, trans amount, vinyl amount, weight average molecular weight, glass transition point (Tg), and oil addition The amounts are shown in Table 5.

  The Mooney viscosity was measured by the following method as an index of processability of the obtained 19 types of rubber compositions for tire treads.

Processability: Mooney viscosity The processability of the obtained rubber composition was evaluated by Mooney viscosity (ML _{1 + 4} ). As for Mooney viscosity (ML _{1 + 4} ), in accordance with JIS K6300, a Mooney viscometer uses an L-shaped rotor (38.1 mm diameter, 5.5 mm thickness), preheating time 1 minute, rotor rotation time 4 Measured at 100 ° C. and 2 rpm. The obtained results are shown in Table 1 as an index with the reciprocal of the value of Comparative Example 1 being 100. A larger index means a lower Mooney viscosity and better processability. If the index value is 98 or more, it is within the allowable range (conventional level).

  In addition, 19 kinds of obtained rubber compositions for tire treads were press vulcanized at 160 ° C. for 20 minutes in a mold having a predetermined shape to prepare a vulcanized rubber sample, and wet grip performance and rolling were performed by the following methods. Resistance and wear resistance were measured.

Wet grip performance; tan δ (0 ° C)
The wet grip performance of the obtained vulcanized rubber samples was evaluated by tan δ (0 ° C.), which is known to be an index of wet grip performance. tan δ (0 ° C.) is measured with a loss tangent tan δ (0 ° C.) at a temperature of 0 ° C. under the conditions of an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho. did. The obtained results are shown in Table 1 as an index with the value of Comparative Example 1 as 100. A larger index means better wet grip performance.

Rolling resistance; tan δ (60 ° C)
The rolling resistance of the obtained vulcanized rubber sample was evaluated by tan δ (60 ° C.), which is known to be an index of rolling resistance. tan δ (60 ° C.) is a loss tangent tan δ (60 ° C.) at a temperature of 60 ° C. measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz. did. The obtained results are shown in Table 1 as an index with the reciprocal of the value of Comparative Example 1 being 100. The larger this index, the smaller the tan δ (60 ° C.), and the lower the heat generation and the better the rolling resistance. If the index value is 98 or more, it is within the allowable range (conventional level).

Abrasion resistance The obtained vulcanized rubber sample was subjected to a load of 49 N, a slip rate of 25%, a time of 4 minutes, and room temperature in accordance with JIS K6264 using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho). The amount of wear was measured. The obtained results are shown in Table 1 as an index with the reciprocal of the wear amount of Comparative Example 1 as 100. Higher index means better wear resistance.

In addition, the kind of raw material used in Tables 1-3 and 5 is shown below.
NR: natural rubber, SIR20
Modified S-SBR1: terminal modified solution polymerized styrene butadiene rubber, E581 manufactured by Asahi Kasei Co., Ltd., and oil-extended modified S-SBR2: terminal modified solution polymerized styrene butadiene rubber containing 37.5 parts by weight of oil with respect to 100 parts by weight of rubber component, Japan NS530 manufactured by Zeon Co., Ltd., oil-extended product S-SBR1: solution polymerized styrene butadiene rubber containing 20.0 parts by weight of oil with respect to 100 parts by weight of rubber component, HP755B manufactured by JSR Co., Ltd. and 37.5 oils with respect to 100 parts by weight of rubber component Oil-extended S-SBR2 containing parts by weight: Solution-polymerized styrene-butadiene rubber, Toughden 1834 manufactured by Asahi Kasei Co., Ltd. Oil-extended product containing 37.5 parts by weight of oil with respect to 100 parts by weight of the rubber component BR1: Butadiene rubber, Nipol manufactured by Nippon Zeon BR1220, molecular weight distribution Mw / Mn = 2.9
BR2: butadiene rubber, Nipol BRX5000 manufactured by Nippon Zeon Co., Ltd., molecular weight distribution Mw / Mn = 6.4, silica containing 40 parts by weight of low molecular weight component with respect to 100 parts by weight of rubber component 1: ZEOSIL 115GR manufactured by Rhodia Silica, nitrogen adsorption ratio Surface area = 116 m ² / g
Silica 2: ZEOSIL PREMIUM 200MP manufactured by Rhodia Silica, nitrogen adsorption specific surface area = 204 m ² / g
Silica 3: ZEOSIL 1165MPGR manufactured by Rhodia Silica, nitrogen adsorption specific surface area = 162 m ² / g
CB: carbon black, show black N234 manufactured by Cabot Japan
Coupling agent: SI69 manufactured by EVONIK DEGUSSA
Aroma oil: Showa Shell Sekiyu Extract 4 S

The types of raw materials used in Table 4 are shown below.
Processing aid: Struktol A50P manufactured by SCHILL & SEILACHER
Zinc Hana: Zenda Chemical Co., Ltd. Zinc Oxide Type 3 Stearic Acid: Chiba Fatty Acid Co., Ltd. Beads Stearate Tungsten Anti-Aging Agent: Flexis Co., Ltd. SANTOFLEX 6PPD
Wax: Sunnock vulcanization accelerator made by Ouchi Shinsei Chemical Co., Ltd.
Sulfur: Kristex HS OT 20 manufactured by Akzo Nobel

  As is clear from the results of Tables 1 and 3, the rubber compositions for tire treads of Examples 1 to 6 all have wet grip performance and wear resistance while maintaining good processability and rolling resistance as compared with Comparative Example 1. I was able to improve the nature.

  On the other hand, as is clear from the results of Table 1, the rubber composition for tire tread of Comparative Example 2 used styrene butadiene rubber having a low Tg instead of natural rubber, but the wet grip performance deteriorated. Since the rubber composition for tire treads of Comparative Example 3 used butadiene rubber having a molecular weight distribution Mw / Mn of greater than 4.0, processability and wet grip performance were deteriorated.

Further, as is clear from the results in Table 2, the rubber composition for tire tread of Comparative Example 4 was deteriorated in wet grip performance and wear resistance because the weight average molecular weight of modified S-SBR2 was less than 1 million. Since the rubber composition for tire treads of Comparative Example 5 used unmodified S-SBR1 instead of modified S-SBR1, the wear resistance deteriorated. The rubber composition for tire tread of Comparative Example 6 was deteriorated in workability and wet grip performance because the modified S-SBR1 was less than 60% by weight and the BR was more than 30% by weight. The rubber composition for tire treads of Comparative Example 7 deteriorated wet grip performance because the modified S-SBR1 was less than 60% by weight and the NR was more than 30% by weight. In the rubber composition for tire treads of Comparative Example 8, since the nitrogen adsorption specific surface area of silica 1 was less than 120 m ² / g, wet grip performance and wear resistance were deteriorated. The rubber composition for tire treads of Comparative Example 9 deteriorated in workability because the nitrogen adsorption specific surface area of silica 2 exceeded 180 m ² / g.

  As is clear from the results in Table 3, the rubber composition for tire tread of Comparative Example 10 was deteriorated in workability and rolling resistance because the total amount of filler was larger than 80 parts by weight. The rubber composition for tire treads of Comparative Example 11 deteriorated in workability and wear resistance because the ratio of silica in all fillers was larger than 90% by weight. In the rubber composition for tire treads of Comparative Example 12, the rolling resistance was deteriorated because the ratio of silica in the total filler was smaller than 60% by weight. The rubber composition for tire treads of Comparative Example 13 deteriorated in workability and wear resistance because the amount of the silane coupling agent was smaller than 6% by weight of the amount of silica.

Claims (3)

It consists of carbon black and silica with respect to 100 parts by weight of a diene rubber containing 60 to 90% by weight of modified solution-polymerized styrene butadiene rubber, 5 to 30% by weight of butadiene rubber, and 5 to 30% by weight of natural rubber or polyisoprene rubber. A filler is blended so that the total amount of the filler is 80 parts by weight or less and the proportion of silica in the total amount of the filler is 60 to 90% by weight, and the silane coupling agent is 6 to 15% with respect to the silica amount. The modified solution polymerized styrene butadiene rubber has a weight average molecular weight of 1,000,000 to 1,500,000, a vinyl bond content of 30 to 60%, and a styrene content of 30 to 50% by weight. molecular weight distribution (Mw / Mn) of 4.0 or less, the nitrogen adsorption specific surface area of the silica is 120~180m ² / g der Tire tread rubber composition characterized by.   2. The tire according to claim 1, wherein the functional group of the modified solution-polymerized styrene butadiene rubber is at least one selected from a hydroxyl group, an alkoxylyl group, an epoxy group, a carbonyl group, a carboxyl group, and an amino group. Tread rubber composition.   A pneumatic tire using the rubber composition for a tire tread according to claim 1.