JP2014189697A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread having improved dry grip performance, steering stability and abrasion resistance compared to conventional compositions.SOLUTION: There is provided a rubber composition manufactured by blending 100 pts.wt. of a rubber composition having total 100 wt.% of 5 to 30 wt.% of an elastomer to which a styrene-diene-styrene copolymer partially hydrogenated and 95 to 70 wt.% of a styrene-butadiene rubber, 90 to 170 pts.wt. of silica, and 10 to 30 pts.wt. of an aromatic modified terpene, and 95 to 60 wt.% of the styrene-butadiene rubber is a solution polymerized styrene butadiene rubber S-SBR, and the glass transition temperature of the S-SBR is -30°C to -5°C and the weight average molecular weight of 1,000,000 to 1,800,000.

Description

  The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition for a tire tread in which wet grip performance, steering stability and wear resistance are improved to a level higher than conventional levels.

  Pneumatic tires for high-performance automobiles require a wide range of performance, especially high-speed driving stability, wet road surface stability (wet performance), and excellent wear resistance. It is required to suppress changes in tire performance (wear skin and thermal sag) when traveling for a long time. For example, competition tires for running on wet roads not only have excellent wet performance, that is, handling stability and grip performance when running on wet roads, but also suppress wear skin and thermal sag that occur when driving at high speeds for a long time. Is required.

  Patent Document 1 includes a styrene-butadiene copolymer rubber having a glass transition temperature (Tg) of −30 ° C. to 0 ° C. or a blend having an average Tg of −30 ° C. to 0 ° C. mixed with two or more SBRs. Grip performance in a semi-wet state by a rubber composition in which 80 to 180 parts by weight of a filler containing 50 parts by weight or more of silica and 5 to 60 parts by weight of a resin having a softening point of 100 to 150 ° C. are blended with 100 parts by weight of SBR It is proposed to improve. However, adjusting the TBR Tg of SBR and adding a large amount of silica is not always sufficient to fully meet the demands of customers regarding wet grip performance, steering stability and wear resistance.

JP 2007-321046 A

  An object of the present invention is to provide a rubber composition for a tire tread in which wet grip performance, steering stability and wear resistance are improved to a level higher than that of the conventional level.

  The rubber composition for a tire tread of the present invention that achieves the above object comprises an elastomer partially hydrogenated with a styrene-diene-styrene copolymer in an amount of 5 to 30% by weight and a styrene butadiene rubber in an amount of 95 to 70% by weight. A rubber composition in which 90 to 170 parts by weight of silica and 10 to 30 parts by weight of an aromatic-modified terpene resin are blended with 100 parts by weight of a rubber component that is 100% by weight, ˜60 wt% is a solution-polymerized styrene butadiene rubber S-SBR, and the S-SBR has a glass transition temperature of −30 ° C. to −5 ° C. and a weight average molecular weight of 1,000,000 to 1,800,000.

  The rubber composition for a tire tread of the present invention comprises 5-30% by weight of an elastomer partially hydrogenated with a styrene-diene-styrene copolymer, a glass transition temperature of -30 ° C to -5 ° C, and a weight average molecular weight. Of 100 to 100 parts by weight of a rubber component having a total of 100% by weight of 95 to 70% by weight of styrene butadiene rubber having 95 to 60% by weight of a solution-polymerized styrene butadiene rubber S-SBR having a weight of 1 to 1.8 million. By blending ˜170 parts by weight and 10 to 30 parts by weight of the aromatic modified terpene resin, wet grip performance, steering stability and wear resistance can be improved to the conventional level or more.

  As the elastomer, an elastomer obtained by partially hydrogenating a styrene-butadiene-styrene copolymer is preferable.

  A pneumatic tire using the above-described rubber composition in the tread portion can improve wet grip performance, steering stability and wear resistance to a conventional level or more.

  In the rubber composition for a tire tread according to the present invention, the rubber component is composed of an elastomer (hereinafter referred to as “partially hydrogenated elastomer”) partially hydrogenated with a styrene-diene-styrene copolymer, and a styrene butadiene rubber. To 100% by weight.

  The partially hydrogenated elastomer is an elastomer obtained by partially hydrogenating a styrene-diene-styrene copolymer such as styrene-butadiene-styrene or styrene-isoprene-styrene. By partially hydrogenating the polydiene block of the styrene-diene-styrene copolymer, the wet performance (tan δ at 0 ° C.) is improved by the vulcanizable segment, and the rubber hardness, elastic modulus, and rubber strength are improved. It can be improved. As a result, it is possible to improve the steering stability and the wear resistance to the conventional level or more while improving the wet grip performance. On the other hand, a rubber composition containing an elastomer such as styrene-ethylene / butylene-styrene copolymer (SEBS) and styrene-ethylene / propylene-styrene (SEPS) completely hydrogenated with styrene-diene-styrene copolymer is Since there is no vulcanizable segment, the wet performance (tan δ at 0 ° C.), elastic modulus and rubber strength cannot be improved.

  In the present invention, partial hydrogenation of a styrene-diene-styrene copolymer means that 5-60% by weight, more preferably 8-60% by weight, of the polydiene segment is hydrogenated. By hydrogenating the polydiene segment in the above range, it is possible to improve the rubber hardness, elastic modulus and rubber strength while improving wet performance (tan δ at 0 ° C.) with the vulcanizable segment.

  As the partially hydrogenated elastomer contained in the tire rubber composition of the present invention, a partially hydrogenated elastomer of a styrene-butadiene-styrene copolymer is preferable.

  The partially hydrogenated elastomer to be blended in the present invention preferably has a number average molecular weight (hereinafter referred to as “Mn”) of 100,000 to 200,000, more preferably 100,000 to 150,000. By setting the Mn of the partially hydrogenated elastomer to 100,000 or more, rubber hardness, elastic modulus, and rubber strength can be secured at a high level. Further, when the Mn of the partially hydrogenated elastomer is 200,000 or less, the processability of the rubber composition can be maintained at a good level. In the present specification, Mn of the partially hydrogenated elastomer is measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

  The partially hydrogenated elastomer blended in the present invention preferably has a styrene content of 40 to 65% by weight, more preferably 45 to 60% by weight. By setting the amount of styrene in the partially hydrogenated elastomer to 40% by weight or more, rubber hardness, elastic modulus, and rubber strength can be ensured. Further, by setting the styrene content of the partially hydrogenated elastomer to 65% by weight or less, the rubber strength can be secured at a high level and the wear resistance can be maintained. The amount of styrene in the partially hydrogenated elastomer is measured by infrared spectroscopic analysis (Hampton method).

  In the present invention, the content of the partially hydrogenated elastomer is 5 to 30% by weight, preferably 7 to 15% by weight, in 100% by weight of the rubber component. By setting the content of the partially hydrogenated elastomer to 5% by weight or more, the wet performance (tan δ at 0 ° C.) can be improved. By setting the content of the partially hydrogenated elastomer to 30% by weight or less, rubber hardness, elastic modulus, and rubber strength can be ensured.

  In the rubber composition of the present invention, the rubber component comprises the above-mentioned partially hydrogenated elastomer and styrene butadiene rubber. The content of styrene-butadiene rubber is 95 to 70% by weight, preferably 93 to 85% by weight, in 100% by weight of the rubber component. By setting the content of styrene-butadiene rubber to 70% by weight or more, rubber hardness, elastic modulus, and rubber strength can be ensured. By setting the content of styrene-butadiene rubber to 95% by weight or less, wet performance (tan δ at 0 ° C.) can be improved.

  In the present invention, the styrene butadiene rubber necessarily includes a specific solution polymerized styrene butadiene rubber S-SBR. By containing the specific solution-polymerized styrene butadiene rubber S-SBR, the balance between the wet performance of the rubber composition (tan δ at 0 ° C.) and the rubber hardness, elastic modulus, and rubber strength can be improved. it can.

  The content of the specific solution polymerized styrene butadiene rubber S-SBR is 95 to 40% by weight, preferably 85 to 55% by weight, in 100% by weight of the rubber component. By setting the content of specific S-SBR to 40% by weight or more, rubber hardness and rubber strength can be ensured. Moreover, wet performance (tan (delta) of 0 degreeC) can be improved by making content of specific S-SBR into 95 weight% or less.

  The specific S-SBR described above is a solution-polymerized styrene having a glass transition temperature (hereinafter referred to as “Tg”) of −30 ° C. to −5 ° C. and a weight average molecular weight (hereinafter referred to as “Mw”) of 1 million to 1.8 million. Butadiene rubber.

  The Tg of S-SBR is -30 ° C to -5 ° C, preferably -25 to -10 ° C. Wet grip performance can be secured by setting the Tg of S-SBR to -30 ° C or higher. Moreover, wear resistance can be ensured by making Tg of S-SBR into -5 degreeC or less.

  The Mw of S-SBR is 1 million to 1.8 million, preferably 1.1 million to 1.5 million. By setting Mw of S-SBR to 1 million or more, rubber hardness, elastic modulus, and rubber strength can be secured at a high level. Moreover, the processability of a rubber composition is securable by Mw being 1.8 million or less.

  The rubber composition for a tire tread of the present invention can optionally contain other styrene butadiene rubbers other than the specific S-SBR described above as the styrene butadiene rubber. Examples of other styrene butadiene rubbers include solution polymerized styrene butadiene rubber having a Tg lower than −30 ° C., solution polymerized styrene butadiene rubber having an Mw of less than 1,000,000, and emulsion polymerized styrene butadiene rubber. The content of the other styrene-butadiene rubber is preferably 55 to 0% by weight, more preferably 40 to 0% by weight in 100% by weight of the rubber component.

  The rubber composition for a tire tread of the present invention improves grip performance by blending an aromatic modified terpene resin. The compounding amount of the aromatic modified terpene resin is 10 to 30 parts by weight, preferably 12 to 25 parts by weight with respect to 100 parts by weight of the rubber component. By setting the blending amount of the aromatic modified terpene resin to 10 parts by weight or more, the steering stability and the wet performance can be improved. In addition, by controlling the blending amount of the aromatic modified terpene resin to 30 parts by weight or less, an increase in the adhesiveness of the rubber composition is suppressed, adhesion to the molding roll is suppressed, and good molding processability and handleability are maintained. be able to.

  The aromatic modified terpene resin is obtained by polymerizing a terpene and an aromatic compound. Examples of terpenes include α-pinene, β-pinene, dipentene, and limonene. Examples of the aromatic compound include styrene, α-methylstyrene, vinyl toluene, indene and the like. Of these, a styrene-modified terpene resin is preferable as the aromatic-modified terpene resin. Such an aromatic modified terpene resin has good compatibility with the diene rubber, so that the tan δ at 0 ° C. of the rubber composition is increased and the wet grip performance is improved.

  As the aromatic modified terpene resin, one having a softening point of preferably 70 to 160 ° C., more preferably 85 to 150 ° C. may be used. When the softening point of the aromatic modified terpene resin is less than 70 ° C., the effect of improving the grip performance cannot be sufficiently obtained. Moreover, when the softening point of aromatic modified terpene resin exceeds 160 degreeC, there exists a tendency for abrasion resistance to deteriorate. In addition, the softening point of aromatic modified terpene resin shall be measured based on JISK6220-1 (ring ball method).

  The rubber composition for a tire tread of the present invention contains 90 to 170 parts by weight, preferably 100 to 150 parts by weight of silica with respect to 100 parts by weight of the rubber component. By setting the amount of silica to 90 parts by weight or more, tan δ (0 ° C.) can be increased and wet grip performance can be improved. Moreover, by making the compounding amount of silica 170 parts by weight or less, it is possible to secure the rubber strength and rigidity of the rubber composition, and to improve the steering stability and the wear resistance.

  In the present invention, a reinforcing filler other than silica can be blended. The total amount of silica and other reinforcing fillers is preferably 90 to 170 parts by weight, more preferably 100 to 150 parts by weight, based on 100 parts by weight of styrene butadiene rubber. When the total of silica and other reinforcing fillers is less than 90 parts by weight, wet grip performance is deteriorated. On the other hand, if the total amount of silica and other reinforcing fillers exceeds 170 parts by weight, the wear resistance deteriorates and the workability also deteriorates. Examples of other reinforcing fillers include carbon black, clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, and titanium oxide. Carbon black and clay are preferable.

  As the silica, silica usually used in a rubber composition for a tire tread, for example, wet method silica, dry method silica, or surface-treated silica can be used.

  In the rubber composition of the present invention, by adding a silane coupling agent together with silica, it is preferable to improve the dispersibility of the silica and enhance the reinforcement with the diene rubber. The silane coupling agent is preferably added in an amount of 2 to 20% by weight, more preferably 5 to 15% by weight, based on the amount of silica. When the compounding amount of the silane coupling agent is less than 2% by weight of the silica weight, the effect of improving the dispersibility of silica cannot be obtained sufficiently. On the other hand, when the silane coupling agent exceeds 20% by weight, the silane coupling agents are polymerized with each other, and a desired effect cannot be obtained.

  The silane coupling agent is not particularly limited, but is preferably a sulfur-containing silane coupling agent, such as bis- (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, Examples thereof include 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane. Of these, bis- (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide are preferable.

  The tire tread rubber composition generally includes a vulcanization or crosslinking agent, a vulcanization accelerator, an anti-aging agent, a plasticizer, a processing aid, a liquid polymer, a thermosetting resin, and the like. Various compounding agents used can be blended. Such a compounding agent can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. The compounding amounts of these compounding agents can be the conventional general compounding amounts as long as they do not contradict the purpose of the present invention. The rubber composition for a tire tread can be produced by mixing each of the above components using a known rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for a tire tread of the present invention can be suitably used for a pneumatic tire, particularly a racing pneumatic tire for wet running on a circuit. Pneumatic tires that use this rubber composition in the tread part have improved rubber hardness, elastic modulus, and rubber strength over conventional levels while ensuring excellent wet performance, and have improved handling stability and wear resistance to conventional levels. This can be improved.

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

  14 kinds of rubber compositions for tire treads (Examples 1 to 4 and Comparative Examples 1 to 10) having the composition shown in Tables 1 and 2 with the compounding agents shown in Table 3 as common formulations, sulfur and vulcanization accelerators The components except for were prepared by adding sulfur and a vulcanization accelerator to an open roll and kneading the master batch which was kneaded for 5 minutes at 160 ° C. with a 1.8 L closed mixer. In Tables 1 and 2, the net compounding amount of each rubber component is shown in parentheses for SBR containing oil-extended oil. Moreover, the addition amount of the common compounding agent described in Table 3 was expressed in parts by weight with respect to 100 parts by weight of the rubber component described in Tables 1 and 2 (net amount of rubber 100 parts by weight).

  The obtained 14 types of rubber compositions for tire treads were press vulcanized at 160 ° C. for 20 minutes in a mold having a predetermined shape to prepare test pieces, and the rubber hardness, 300% modulus, and tensile strength were measured by the following methods. The breaking strength and tan δ (0 ° C.) were evaluated.

Rubber hardness (20 ℃)
The rubber hardness of the obtained test piece was measured at a temperature of 20 ° C. with a durometer type A in accordance with JIS K6253. The obtained results are shown in the column of “Rubber hardness (20 ° C.)” in Tables 1 and 2 as an index with the value of Comparative Example 1 being 100. The larger the index, the higher the rubber hardness and the better the mechanical properties, and the better the steering stability when making a pneumatic tire.

Tensile strength at break and 300% modulus (20 ° C)
From the obtained test piece, a JIS No. 3 dumbbell-type test piece (thickness 2 mm) was punched out in accordance with JIS K6251 and tested at a temperature of 20 ° C. and a pulling speed of 500 mm / min. 300% deformation stress) was measured. The obtained results are shown in the columns of “Break Strength (20 ° C.)” and “300% Mod (20 ° C.)” in Tables 1 and 2 as indices with the value of Comparative Example 1 as 100 respectively. As these indexes are larger, it means that the tensile strength at break and rigidity are large and the mechanical properties are excellent, and the wear resistance and steering stability are excellent when a pneumatic tire is formed.

Wet performance (tan δ at 0 ℃)
Using the obtained test piece, loss tangent tan δ (0 ° C.) was evaluated as an index of wet performance. Tanδ was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho under the conditions of an initial strain of 10%, an amplitude of ± 2%, a frequency of 20 Hz, and a temperature of 0 ° C. The obtained results are shown in the column of “tan δ (0 ° C.)” in Tables 1 and 2 as an index with the value of Comparative Example 1 being 100. A larger index of tan δ (100 ° C.) means better wet performance.

The types of raw materials used in Tables 1 and 2 are shown below.
S-SBR1: Solution-polymerized styrene butadiene rubber, styrene content is 36% by weight, vinyl content is 64% by weight, Mw is 1,470,000, Tg is -13 ° C., oil component is 37.5 parts by weight with respect to 100 parts by weight of rubber component Oil exhibition products including Toughden E680 manufactured by Asahi Kasei Chemicals
S-SBR2: solution-polymerized styrene butadiene rubber, styrene content is 37% by weight, vinyl content is 42% by weight, Mw is 1.26 million, Tg is -27 ° C., and the oil content is 37.5 parts by weight with respect to 100 parts by weight of the rubber component. Oil exhibition products including Toughden E581 manufactured by Asahi Kasei Chemicals
S-SBR3: solution-polymerized styrene butadiene rubber, styrene content 23% by weight, vinyl content 70% by weight, Mw 490,000, Tg -23 ° C., non-oil-extended product, NS616 manufactured by Zeon Corporation
Elastomer 1: Styrene-butadiene-styrene copolymer, 48% by weight of styrene, 65800 Mn, Tufprene 126S manufactured by Asahi Kasei Chemicals
Elastomer 2: Elastomer partially hydrogenated styrene-butadiene-styrene copolymer, 57% by weight of styrene, 103,000 Mn, manufactured by Asahi Kasei Chemicals O. E. S1611
Elastomer 3: Elastomer completely hydrogenated with styrene-butadiene-styrene copolymer, styrene content 61% by weight, Mn 96700, manufactured by Asahi Kasei Chemicals O. E. L605
Silica: Rhodia Zeosil 1165MP, CTAB specific surface area of 1592 m ² / g
Coupling agent: Si69 manufactured by Evonik Degussa
Carbon black: Tokai Carbon Co. SEAST ^{_{9, N 2 SA = 142m 2}} / g
Terpene resin: Aromatic modified terpene resin having a softening point of 125 ° C., YS resin TO-125 manufactured by Yashara Chemical Co., Ltd.
・ Oil: Showa Shell Sekiyu Extract 4 S

The types of raw materials used in Table 3 are shown below.
-Zinc flower: Zinc oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd.-Stearic acid: Bead Stearic Acid YR manufactured by NOF Corporation
・ Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Industry Co., Ltd. ・ Vulcanization accelerator 1: Vulcanization accelerator DPG, Nouchira D
-Vulcanization accelerator 2: Vulcanization accelerator CBS, Nouchira CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

  The rubber compositions for tire treads of Examples 1 to 4 have steering stability (rubber hardness (20 ° C.), 300% modulus (20 ° C.) and tensile breaking strength (20 ° C.)), wet grip performance (tan δ at 0 ° C.). ) And wear resistance (tensile breaking strength (20 ° C.)) were confirmed to be improved.

  Since the rubber composition of Comparative Example 1 was blended with a styrene-butadiene-styrene copolymer (non-hydrogenated elastomer 1) without blending the partially hydrogenated elastomer 2, 300% modulus (20 ° C.), As in Example 2, it is not possible to improve the tensile strength at break (20 ° C.) and tan δ (0 ° C.).

  The rubber composition of Comparative Example 2 was blended with the elastomer 3 in which the styrene-butadiene-styrene copolymer was completely hydrogenated without blending the partially hydrogenated elastomer 2, so that it had a 300% modulus (20 ° C.) and a tensile fracture. Strength (20 ° C.) deteriorates.

  Since the rubber composition of Comparative Example 3 does not contain the partially hydrogenated elastomer 2, the tan δ at 0 ° C. deteriorates.

  In the rubber composition of Comparative Example 4, since the blending amount of the partially hydrogenated elastomer 2 exceeds 30 weight, the rubber hardness (20 ° C.) is deteriorated.

  In the rubber composition of Comparative Example 5, since the specific S-SBR content is less than 60% by weight, the rubber hardness (20 ° C.) and tan δ at 0 ° C. are deteriorated, and the tensile breaking strength (20 ° C.) is improved. I can't.

  In the rubber composition of Comparative Example 6, since the compounding amount of silica is less than 90 parts by weight, tan δ (0 ° C.) is deteriorated and (20 ° C.) cannot be improved.

  In the rubber composition of Comparative Example 7, since the amount of silica exceeds 170 parts by weight, the 300% modulus (20 ° C.) and the tensile strength at break (20 ° C.) are deteriorated.

  Since the rubber composition of Comparative Example 8 does not contain an aromatic modified terpene resin, the tan δ at 0 ° C. deteriorates.

  In the rubber composition of Comparative Example 9, since the aromatic-modified terpene resin was blended in an amount exceeding 30 parts by weight, the tensile strength at break (20 ° C.) deteriorates and the rubber hardness (20 ° C.) cannot be improved.

  Since the rubber composition of Comparative Example 10 does not contain specific S-SBR, tan δ at 0 ° C. is deteriorated.

  Further, a pneumatic tire having a tire size of 195 / 55R15 in which a tire tread portion was constituted by the rubber compositions of Example 2 and Comparative Examples 1 and 3 was manufactured. When the obtained pneumatic tires are assembled on rims (size 15 × 6J), mounted on a test vehicle at an air pressure of 150 kPa, and the test driver runs 10 laps on a circuit course under wet conditions (about 2 km per lap) The lap time for each lap was measured. As the wet grip performance, the average time of 8 to 10 laps in 10 consecutive laps was evaluated using the average time of 8 to 10 laps in the pneumatic tire of Comparative Example 3 as a reference time.

  In the pneumatic tire of Example 2, the average lap time was faster than the reference time by 1.0 second or more. Thus, it was confirmed that wet grip performance was greatly improved by blending a specific partially hydrogenated elastomer.

  The pneumatic tire of Comparative Example 1 showed that the average lap time was 0.6 seconds later than the reference time. In this pneumatic tire, it was confirmed that the wet grip performance sustainability was significantly reduced by blending a styrene-butadiene-styrene copolymer (an elastomer that was not hydrogenated).

Claims (3)

  Silica is added to 100 parts by weight of a rubber component that is 100% by weight in total of 5 to 30% by weight of an elastomer partially hydrogenated with a styrene-diene-styrene copolymer and 95 to 70% by weight of styrene butadiene rubber. 90 to 170 parts by weight, a rubber composition containing 10 to 30 parts by weight of an aromatic modified terpene resin, and 95 to 60% by weight of the styrene butadiene rubber is solution-polymerized styrene butadiene rubber S-SBR, A rubber composition for a tire tread, wherein the glass transition temperature of the S-SBR is -30 ° C to -5 ° C and the weight average molecular weight is 1,000,000 to 1,800,000.   The rubber composition for a tire tread according to claim 1, wherein the elastomer is an elastomer obtained by partially hydrogenating a styrene-butadiene-styrene copolymer.   A pneumatic tire using the rubber composition for a tire tread according to claim 1.