JP2014189695A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread having excellent dry grip performance, steering stability and abrasion resistance in a wide temperature range.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, 50 to 120 pts.wt. of carbon black having a nitrogen adsorption specific surface area of 130 to 200 m/g and 2 to 10 pts.wt. of an aromatic modified terpene, and 60 to 40 wt.% of the styrene-butadiene rubber is an emulsification polymerized styrene butadiene rubber E-SBR, and the amount of the E-SBR is 40 wt.% or more.

Description

  The present invention relates to a rubber composition for a tire tread, and relates to a rubber composition for a tire tread that ensures excellent dry grip performance, steering stability and wear resistance in a wide temperature range.

  It is known that the grip performance of a pneumatic tire is greatly affected by the tire temperature, and that sufficient grip performance cannot be obtained at low temperatures, and that steering stability and wear resistance are reduced at high temperatures. In particular, rally racing tires are required to have high heat generation (tan δ) in a wide range of temperatures and excellent handling stability and wear resistance so as to be able to cope with changing road surface conditions and speed ranges. .

  For this reason, a rubber composition in which a large amount of carbon black is blended with an emulsion-polymerized styrene butadiene rubber (E-SBR) having a high glass transition temperature (Tg) has been proposed (for example, see Patent Document 1). However, the demanded performance demands of the tires for competition are higher, and the heat generation (tan δ) in a wide temperature range is further increased to improve the dry grip performance, and the rubber hardness and elasticity at high temperatures. There is a need for a rubber composition for a tread for a rally traveling tire that secures the rate and has excellent steering stability and wear resistance.

JP-A-63-191844

  An object of the present invention is to provide a rubber composition for a tire tread which ensures excellent dry grip performance, steering stability and wear resistance in a wide temperature range.

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 50 to 120 parts by weight of carbon black having a nitrogen adsorption specific surface area of 130 to 200 m ² / g and 2 to 10 parts by weight of an aromatic modified terpene resin. 60 to 40% by weight of the styrene butadiene rubber is emulsion-polymerized styrene butadiene rubber E-SBR, and the amount of styrene in the E-SBR is 40% by weight or more.

The rubber composition for a tire tread of the present invention is an emulsion-polymerized styrene butadiene rubber E having 5-30% by weight of an elastomer partially hydrogenated with a styrene-diene-styrene copolymer and 40% by weight or more of styrene. -Carbon black having a nitrogen adsorption specific surface area of 130 to 200 m ² / g is added to 100 parts by weight of a rubber component which is 100% by weight in total with 95 to 70% by weight of styrene butadiene rubber occupying 60 to 40% by weight of SBR. ~ 120 parts by weight, and by adding 2 to 10 parts by weight of the aromatic modified terpene resin, the exothermic property (tan δ) and the rubber hardness are further increased in a wide temperature range, and the dry grip performance and the handling stability are improved. The wear resistance at high temperature can be made excellent.

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

  Moreover, it is preferable to contain 10 to 55 weight% of solution polymerization styrene butadiene rubber S-SBR in 100 weight% of said rubber components.

  A pneumatic tire using the rubber composition described above in the tread portion can improve dry grip performance and steering stability in a wide temperature range, and can have excellent wear resistance in a high temperature state.

  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 the wide temperature range including a high temperature state can be made excellent. 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 emulsion polymerization styrene butadiene rubber E-SBR. By containing the specific emulsion polymerized styrene butadiene rubber E-SBR, the balance between the large exothermic property of the rubber composition and the rubber hardness, elastic modulus, and rubber strength in a high temperature state can be further improved.

  The content of the specific emulsion polymerized styrene butadiene rubber E-SBR is 60 to 40% by weight, preferably 55 to 45% by weight, in 100% by weight of the rubber component. By setting the content of the specific E-SBR to 40% by weight or more, it is possible to increase the rubber hardness in a high-temperature state and ensure the durability of steering stability and grip performance, and also improve the wear resistance. . In addition, by making the content of specific S-SBR 60% by weight or less, the elastic modulus at high temperature is increased to ensure steering stability, and the heat generation is increased to improve the grip performance. Can do.

  E-SBR is an emulsion-polymerized styrene butadiene rubber having a styrene content of 40% by weight or more. The amount of styrene in E-SBR is 40% by weight or more, preferably 40 to 45% by weight. By making the amount of styrene of E-SBR 40% by weight or more, the grip performance can be made excellent. The amount of styrene in E-SBR is measured by infrared spectroscopic analysis (Hampton method).

  The rubber composition for a tire tread of the present invention can optionally contain other styrene butadiene rubbers other than the specific E-SBR described above as the styrene butadiene rubber. Examples of other styrene butadiene rubbers include emulsion polymerized styrene butadiene rubber and solution polymerized styrene butadiene rubber having a styrene amount of less than 40% by weight. Among these, solution-polymerized styrene butadiene rubber is preferable, and grip and wear resistance are improved. The content of the other styrene butadiene rubber is preferably 55 to 10% by weight, more preferably 50 to 15% 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 2 to 10 parts by weight, preferably 5 to 10 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 2 parts by weight or more. By controlling the blending amount of the aromatic modified terpene resin to 10 parts by weight or less, the increase in the adhesiveness of the rubber composition is suppressed, the adhesion to the molding roll is suppressed, and good molding processability and handleability are maintained. 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 80 to 160 ° C., more preferably 85 to 140 ° C. may be used. If the softening point of the aromatic modified terpene resin is less than 80 ° 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 50 to 120 parts by weight of carbon black having a nitrogen adsorption specific surface area of 130 to 200 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 130 to 200 m ² / g, preferably 120 to 195 m ² / g. By making N ₂ SA of carbon black 130 m ² / g or more, grip performance can be ensured. Further, by the N ₂ SA of the carbon black below 200m ² / g, it is possible to ensure the wear resistance. The N ₂ SA of carbon black is determined according to JIS K6217-2.

  The compounding amount of carbon black is 50 to 120 parts by weight, preferably 60 to 110 parts by weight with respect to 100 parts by weight of the rubber component. By setting the blending amount of carbon black to 50 parts by weight or more, rubber hardness, elastic modulus, rubber strength, and heat generation can be ensured. Moreover, wear resistance can be ensured by making the compounding quantity of carbon black 120 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.

  16 types of rubber compositions for tire treads (Examples 1 to 4 and Comparative Examples 1 to 12) having the formulations shown in Tables 1 and 2 are combined with the compounding agents shown in Table 3 as 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 16 kinds of tire tread rubber compositions 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 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, the better the mechanical properties, and the better the steering stability even when the tire is at a high temperature.

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 pulling rate of 500 mm / min. 300% modulus (300% deformation stress) ) Was measured. The obtained results are shown in the column of “300% Mod (100 ° C.)” in Tables 1 and 2 as an index with the value of Comparative Example 1 as 100. The larger the index, the greater the rigidity at high temperature and the better the mechanical characteristics, and the better the steering stability and wear resistance when the pneumatic tire runs at high speed for a long time.

Dynamic viscoelasticity (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-SBR: 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
E-SBR1: emulsion-polymerized styrene butadiene rubber, an oil-extended product containing 33.5 parts by weight of oil with respect to 100 parts by weight of rubber component and 23.5% by weight of styrene, Nipol 1723 manufactured by Zeon Corporation
E-SBR2: emulsion-polymerized styrene-butadiene rubber, an oil-extended product containing 40% by weight of styrene and 37.5 parts by weight of oil with respect to 100 parts by weight of rubber component, Nipol 1739 manufactured by Nippon Zeon Co., Ltd.
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: Sea 9 made by Tokai Carbon Co., N ₂ SA = 142 m ² / g
Carbon black 2: Dia Black UX10 manufactured by Mitsubishi Chemical Corporation, N ₂ SA = 182 m ² / g
・ Carbon black 3: CD2019 made by Colombian Carbon, N ₂ SA = 340 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, the rubber compositions for tire treads of Examples 1 to 4 were confirmed to have high rubber hardness, 300% modulus, and tan δ (100 ° C.) at high temperatures (100 ° C.). The grip performance, steering stability and wear resistance can be made excellent.

  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, the rubber in a high temperature state (100 ° C.) Hardness, 300% modulus and tan δ (100 ° C.) cannot be improved.

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

  In the rubber composition of Comparative Example 3, since the blending amount of the partially hydrogenated elastomer 2 exceeds 30 weight, the rubber hardness (100 ° C.) is deteriorated.

In the rubber composition of Comparative Example 4, since the N ₂ SA of the carbon black 3 exceeds 200 m ² / g, the rubber hardness (100 ° C.) and the tan δ at 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 rubber hardness (100 ° C.) and 300% modulus were blended. (100 ° C.) gets worse.

  In the rubber composition of Comparative Example 6, since the styrene content of the emulsion-polymerized styrene butadiene rubber E-SBR1 is less than 40% by weight, the rubber hardness and the 300% modulus at high temperature (100 ° C.) deteriorate, and tan δ (100 ° C. ) Cannot be improved.

  In the rubber composition of Comparative Example 7, since the blending amount of the emulsion polymerization styrene butadiene rubber E-SBR2 is less than 40% by weight, the rubber hardness in a high temperature state (100 ° C.) is deteriorated.

  In the rubber composition of Comparative Example 8, since the blending amount of the emulsion-polymerized styrene butadiene rubber E-SBR2 exceeds 80% by weight, the rubber hardness and the 300% modulus at high temperature (100 ° C.) deteriorate, and tan δ (100 ° C.). Gets worse.

  Since the rubber composition of Comparative Example 9 does not contain an aromatic modified terpene resin, the 300% modulus in a high temperature state (100 ° C.) is deteriorated.

  In the rubber composition of Comparative Example 10, since the aromatic modified terpene resin was blended in an amount exceeding 10 parts by weight, the rubber hardness (100 ° C.) was deteriorated.

  In the rubber composition of Comparative Example 11, since the blending amount of the carbon black 1 is less than 50 parts by weight, the rubber hardness at high temperature (100 ° C.), the 300% modulus, and the tan δ at 100 ° C. are deteriorated. Since the compounding quantity of the carbon black 1 exceeds 120 weight part, the rubber hardness (100 degreeC) becomes too high for the rubber composition of the comparative example 12.

  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 2 was manufactured. Each of the pneumatic tires obtained was assembled on a rim (size 15 x 6J), mounted on a test vehicle at an air pressure of 150 kPa, and the test driver made 10 laps on a rally course (about 2 km per lap). Lap time was measured. As the continuous performance of the 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 2 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.

  The result of the pneumatic tire of Comparative Example 1 that the average lap time was 0.5 seconds later than the reference time was obtained. 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 (4)

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 50 to 120 parts by weight of carbon black having a specific surface area of 130 to 200 m ² / g and 2 to 10 parts by weight of an aromatic modified terpene resin, wherein 60 to 40 weights of the styrene butadiene rubber. % Is an emulsion-polymerized styrene butadiene rubber E-SBR, and the amount of styrene in the E-SBR is 40% by weight or more.   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.   The rubber composition for tire treads according to claim 1 or 2, wherein 10 to 55 wt% of solution-polymerized styrene butadiene rubber S-SBR is contained in 100 wt% of the rubber component.   A pneumatic tire using the tire tread rubber composition according to claim 1, 2 or 3.