JP2014189694A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread having improved rubber hardness, elasticity modulus and rubber strength at a high temperature situation compared to conventional compositions while securing continuity of dry grip performance.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, 80 to 150 pts.wt. of carbon black having a nitrogen adsorption specific surface area of 200 to 400 m/g and 10 to 50 pts.wt. of an aromatic modified terpene, and 95 to 40 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

  TECHNICAL FIELD The present invention relates to a rubber composition for a tire tread, and more specifically, a rubber composition for a tire tread in which the rubber hardness, elastic modulus, and rubber strength at a high temperature state are improved to a conventional level while ensuring dry grip performance. Related to things.

  It is known that the grip performance of a pneumatic tire is greatly affected by the tire temperature, and sufficient grip performance cannot be obtained at low temperatures. In particular, in racing tires for circuit running, it is required that the rubber composition constituting the tread has a property of reaching a high temperature state as soon as possible after starting running. For this reason, a large amount of carbon black having a small particle diameter is blended in the rubber composition for tread. However, a rubber composition containing a large amount of carbon black tends to decrease in rubber hardness, elastic modulus, and rubber strength at high temperatures. For this reason, the wear resistance decreases and the wear state of the tread surface deteriorates when the high-speed driving is prolonged, and the dry grip performance gradually deteriorates due to the thermal sag phenomenon, and in some cases blowout may occur. there were.

  Patent Document 1 discloses that a rubber composition for a tire tread is blended with a styrene butadiene rubber having a high glass transition temperature and carbon black having a small particle size to suppress a decrease in rigidity due to heat generation during running, and to provide a dry grip performance and heat sag resistance. It is proposed to improve. However, the demand performance demanded by customers for racing tires will be higher, and the dry grip performance will be superior, and the rubber hardness, elastic modulus, and rubber strength at higher temperatures will be further improved to make the excellent dry grip performance longer. There is a need for a tire tread rubber composition that can be sustained.

JP 2007-246625 A

  An object of the present invention is to provide a rubber composition for a tire tread in which the rubber hardness, elastic modulus, and rubber strength in a high temperature state are improved to the conventional level or more while ensuring the dry grip performance. .

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 100 to 100 parts by weight of a total of 100% by weight of a rubber component is blended with 80 to 150 parts by weight of carbon black having a nitrogen adsorption specific surface area of 200 to 400 m ² / g and 10 to 50 parts by weight of an aromatic modified terpene resin. Of the styrene butadiene rubber, 95 to 40% by weight 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 is It is 1 to 1.8 million.

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 1 part by weight of a rubber component having a total of 100 to 100% by weight of 95 to 70% by weight of styrene butadiene rubber having 95 to 40% by weight of solution-polymerized styrene butadiene rubber S-SBR having a weight of 1 to 1.8 million. By blending 80 to 150 parts by weight of carbon black having a surface area of 200 to 400 m ² / g and 10 to 50 parts by weight of aromatic modified terpene resin, rubber hardness in a high temperature state while ensuring excellent dry grip performance, The elastic modulus and rubber strength can be improved over conventional levels, and the dry grip performance can be maintained longer.

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

  Pneumatic tires using the above-mentioned rubber composition in the tread have improved the rubber hardness, elastic modulus, and rubber strength at high temperatures over conventional levels while ensuring excellent dry grip performance. Can last long.

  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 styrene-diene-styrene copolymer, the rubber hardness, elastic modulus and rubber strength at high temperature are improved while ensuring large heat generation in the vulcanizable segment. can do. Thereby, the dry grip performance in a high temperature state can be maintained for a longer time while improving the dry 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 it does not have a vulcanizable segment, the heat generation cannot be increased and the dry grip performance cannot be improved. In addition, the elastic modulus of the rubber composition at a high temperature cannot be increased.

  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 at a high temperature while securing a large exothermic property to 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, the rubber hardness, elastic modulus, and rubber strength in a high temperature state 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 at a high temperature 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 exothermic property can be increased and the dry grip performance 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 at a high temperature 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 at a high temperature can be ensured. By setting the content of the styrene butadiene rubber to 95% by weight or less, the exothermic property can be increased and the dry grip performance 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 large exothermic property of the rubber composition and the rubber hardness, elastic modulus, and rubber strength at a high temperature can be further improved.

  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 in a high temperature state can be ensured. Further, by setting the content of the specific S-SBR to 95% by weight or less, the exothermic property can be increased and the dry grip performance can be improved.

  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. Grip performance can be ensured 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 in a high temperature state 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 50 parts by weight, preferably 20 to 45 parts by weight with respect to 100 parts by weight of the rubber component. Grip performance can be improved by setting the blending amount of the aromatic modified terpene resin to 10 parts by weight or more. By controlling the compounding amount of the aromatic modified terpene resin to 50 parts by weight or less, it is possible to suppress an increase in the adhesiveness of the rubber composition, suppress adhesion to the molding roll, and maintain good molding processability and handleability. Can do.

  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.

  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 80 to 150 parts by weight of carbon black having a nitrogen adsorption specific surface area of 200 to 400 m ² / g with respect to 100 parts by weight of the rubber component.

The carbon black used in the rubber composition of the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 200 to 400 m ² / g, preferably 250 to 390 m ² / g. Grip performance can be ensured by setting the N ₂ SA of carbon black to 200 m ² / g or more. Further, by the N ₂ SA of the carbon black below 400m ² / g, it is possible to maintain the abrasion resistance. The N ₂ SA of carbon black is determined according to JIS K6217-2.

  The compounding amount of carbon black is 80 to 150 parts by weight, preferably 90 to 140 parts by weight, based on 100 parts by weight of the rubber component. By setting the blending amount of carbon black to 80 parts by weight or more, it is possible to ensure rubber hardness, elastic modulus, and heat generation at a high temperature. Moreover, abrasion resistance can be maintained by making the compounding quantity of carbon black 150 parts by weight or less.

  The rubber composition for a tire tread of the present invention can contain other fillers other than carbon black. Examples of other fillers include silica, clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, and titanium oxide. Silica and clay 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 dry running on a circuit. Pneumatic tires that use this rubber composition in the tread part have improved the rubber hardness, elastic modulus, and rubber strength at higher temperatures than conventional levels while ensuring excellent dry grip performance, making the dry grip performance longer. Can last.

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

  15 kinds of rubber compositions for tire treads (Examples 1 to 4 and Comparative Examples 1 to 11) having the composition shown in Tables 1 and 2 with the compounding agents shown in Table 3 as common formulations, sulfur and a vulcanization accelerator. 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 15 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 a test piece. Rubber hardness, 300% modulus, tensile breaking strength and tan δ (100 ° C.) were evaluated.

Rubber hardness (100 ° C)
The rubber hardness of the obtained test piece was measured at a temperature of 100 ° C. with a durometer type A in accordance with JIS K6253. The obtained results are shown in the column of “Rubber hardness (100 ° 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 characteristics, and the better the steering stability and grip performance when the pneumatic tire runs for a long time at a high speed.

Tensile strength at break and 300% modulus (100 ° 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 100 ° C. and a tensile rate of 500 mm / min. 300% deformation stress) was measured. The obtained results are shown in the columns of “Break strength (100 ° C.)” and “300% Mod (100 ° C.)” in Tables 1 and 2 as indices with the value of Comparative Example 1 as 100, respectively. The larger these indices, the higher the tensile rupture strength and rigidity at high temperatures and the better the mechanical properties, and the better the steering stability, grip performance and wear resistance when the pneumatic tire runs at high speed for a long time. Means that.

Dry grip performance (tan δ at 100 ° C)
Using the obtained test piece, loss tangent tan δ (100 ° C.) was evaluated as an index of dry grip performance. Tan δ 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 100 ° C. The obtained results are shown in the column of “tan δ (100 ° C.)” in Tables 1 and 2 as an index with the value of Comparative Example 1 as 100. A larger index of tan δ (100 ° C.) means better dry grip 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 420,000, Tg −24 ° C., non-oil-extended product, NS116 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
・ Carbon black 1: CD2019 made by Colombian Carbon, N ₂ SA = 340 m ² / g
・ Carbon black 2: Sea 9 made by Tokai Carbon Co., N ₂ SA = 142 m 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 Co., Ltd. ・ Vulcanization accelerator: CBS accelerator, Nouchira CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

  As is clear from Tables 1 and 2, it was confirmed that the rubber compositions for tire treads of Examples 1 to 4 were high in rubber hardness, 300% modulus, rubber strength, and tan δ (100 ° C.) at high temperatures. Dry grip performance can be maintained longer.

  Since the rubber composition of Comparative Example 2 was blended with a styrene-butadiene-styrene copolymer (non-hydrogenated elastomer 1) without blending the partially hydrogenated elastomer 2, tan δ at 100 ° C., 300% modulus The tensile breaking strength (100 ° C.) is deteriorated.

  Since the rubber composition of Comparative Example 3 does not contain the partially hydrogenated elastomer 2, the tan δ at 100 ° C. deteriorates.

  In the rubber composition of Comparative Example 4, since the blended amount of the partially hydrogenated elastomer 2 exceeded 30 weight, the rubber hardness (100 ° C.) and the tensile strength at break (100 ° C.) deteriorate.

  Since the rubber composition of Comparative Example 5 was blended with the elastomer 3 in which the styrene-butadiene-styrene copolymer was completely hydrogenated without blending the partially hydrogenated elastomer 2, the tensile breaking strength (100 ° C.) and 100 ° C. Of tan δ deteriorates and the rubber hardness (100 ° C.) cannot be improved.

  In the rubber composition of Comparative Example 6, since the blending amount of S-SBR1 is less than 40% by weight, the rubber hardness, 300% modulus, rubber strength, and tan δ (100 ° C.) at high temperature (100 ° C.) are deteriorated.

  Since the rubber composition of Comparative Example 7 does not contain an aromatic modified terpene resin, the tan δ at 100 ° C. deteriorates.

  In the rubber composition of Comparative Example 8, since the aromatic modified terpene resin was blended in an amount exceeding 50 parts by weight, the rubber hardness (100 ° C.) deteriorated and the tensile strength at break (100 ° C.) cannot be improved.

  Comparative Example 9 In the rubber composition, since the blending amount of carbon black 1 is less than 80 parts by weight, tan δ at 100 ° C. is deteriorated.

  Comparative Example 10 In the rubber composition, since the compounding amount of carbon black 1 exceeds 150 parts by weight, the 300% modulus and the tensile strength at break (100 ° C.) are deteriorated.

In the rubber composition of Comparative Example 11, since N ₂ SA of carbon black 3 is less than 200 m ² / g, rubber hardness (100 ° C.), tensile breaking strength (100 ° C.), and tan δ at 100 ° C. are 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 2 and 3 was manufactured. When the obtained pneumatic tires are assembled on rims (size 15 x 6J), mounted on a test vehicle at an air pressure of 150 kPa, and the test driver travels 10 laps on a dry circuit course (about 2 km per lap) The lap time for each lap was measured. As the dry 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 the sustainability of the dry grip property was greatly improved by blending a specific partially hydrogenated elastomer.

  As for the pneumatic tire of Comparative Example 2, the average lap time was 0.6 seconds later than the reference time. Also, with this pneumatic tire, the lap time on the eighth lap had already deteriorated. Thus, it was confirmed that the sustainability of the dry grip property was significantly reduced by blending a styrene-butadiene-styrene copolymer (an elastomer that was not hydrogenated).

Claims (3)

Adsorption of nitrogen on 100 parts by weight of a rubber component comprising a total of 100% by weight of 5-30% by weight of an elastomer partially hydrogenated with styrene-diene-styrene copolymer and 95-70% by weight of styrene butadiene rubber. A rubber composition containing 80 to 150 parts by weight of carbon black having a specific surface area of 200 to 400 m ² / g and 10 to 50 parts by weight of an aromatic modified terpene resin, wherein 95 to 40 weights of the styrene butadiene rubber % Is a solution-polymerized styrene butadiene rubber S-SBR, 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. Composition.   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.