JP2007246625A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread having excellent thermal drip resistance and excellent dry grip performance. <P>SOLUTION: This rubber composition for a tire tread comprises: (A) 100 parts by weight of a styrene-butadiene copolymer rubber having a glass transition temperature of more than -45°C; (B) 60 to 150 parts by weight of (1) carbon black having a nitrogen adsorption specific surface area (N<SB>2</SB>SA) of more than 250 m<SP>2</SP>/g or (2) a blend of (i) carbon black having N<SB>2</SB>SA of more than 250 m<SP>2</SP>/g and (ii) carbon black having N<SB>2</SB>SA of 100 to 150 m<SP>2</SP>/g, wherein the amount of the component (ii) is less than 50% by weight, based on the total amount of the components (i) and (ii); and (C) 5 to 150 parts by weight of a low molecular weight styrene-butadiene copolymer having a bonded styrene amount of 25% by weight or more and a weight average molecular weight of 2,000 to 50,000. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition for a tire tread having excellent heat sag resistance and dry grip performance.

In recent years, it has been required to improve the handling stability of pneumatic tires, and in particular, it is required to improve grip performance such as wet grip performance and dry grip performance of a tread portion. In order to improve the dry grip performance of the tread, it is effective to achieve high hysteresis loss, to suppress the reduction of hysteresis loss, or to control the glass transition temperature (Tg) of the rubber constituting the tread. It is known. For example, Patent Document 1 discloses a blend of a high molecular weight styrene-butadiene copolymer rubber (SBR) having a weight average molecular weight of 1,000,000 or more and a low molecular weight SBR having a weight average molecular weight of 2,000 to 50,000. It has been proposed to blend carbon black having an adsorption specific surface area (N ₂ SA) of 90 to 250 m ² / g. In Patent Document 2, a softener containing a diene homopolymer or a vinyl aromatic hydrocarbon-diene copolymer, which is a low molecular weight polymer having a weight average molecular weight of 2,000 to 100,000, is added to the rubber component. It has been proposed to do. Patent Document 3 includes a high molecular weight polymer component selected from a conjugated diene polymer having a polystyrene-equivalent weight average molecular weight of 30 × 10 ⁴ or more and a bound styrene content of 30% by weight or less, and a vinyl aromatic hydrocarbon-conjugated diene copolymer. It has been proposed to constitute a rubber composition from a blend with a low molecular weight polymer component having a polystyrene-reduced weight average molecular weight of 0.2 × 10 ⁴ to 8 × 10 ⁴ and a bound styrene content of 30% by weight or less. Patent Document 4 discloses a rubber component (A) composed of SBR having a styrene content of 40% or less, a vinyl content of 20 to 70%, and a weight average molecular weight of 60,000 to 3 million, and a glass transition temperature (Tg) of −45 ° C. or less. It has been proposed to combine a rubber component (B) comprising a diene rubber with a low molecular weight SBR having a styrene content of 1 to 60%, a vinyl content of 20 to 80% and a weight average molecular weight of 2,000 to 50,000. . Patent Document 5 discloses a copolymer of a conjugated diene having a high bonded styrene content and an aromatic vinyl compound, which has a glass transition temperature (Tg) higher than that of a rubber component and is semi-compatible or incompatible with the rubber component. It has been proposed to be blended with rubber components.

  However, as the carbon black having a smaller particle size is selected in order to further improve the grip performance or the blending amount of the carbon black is further increased, the heat generation during running becomes larger, so that the heat resistance sag decreases (that is, , The rigidity decreases during traveling), and stable traveling becomes impossible, and wear resistance also decreases as the rigidity decreases. On the other hand, in order to further improve the heat resistance drooping property, the grip performance is further lowered as the carbon black having a larger particle diameter is blended or the blending amount of the carbon black is decreased. Furthermore, as described in Patent Document 4, when the low molecular weight SBR is blended with the rubber composition in order to improve the grip performance, the Tg of the entire rubber composition usually increases. There is a problem that the temperature dependency becomes large. Further, even if a low molecular weight SBR having a low Tg is blended, or even if the blending amount of the softening agent is decreased in order to further improve the heat sag resistance, there is a problem that the grip performance is lowered accordingly.

  Thus, in the conventional rubber composition for a tire tread, the grip performance and the heat sag resistance are in a trade-off relationship that when one is improved, the other is reduced. In particular, in order to obtain a high dry grip performance, a rubber composition containing a larger amount of carbon black having a relatively small particle size and a softening agent is used. For example, a tread portion of a racing tire that requires stable grip performance at high speed In the case of use, the heat generation during traveling is large, so the degree of decrease in rigidity during traveling is larger, and there is a problem that traveling with a stable lap time becomes impossible.

JP-A-4-277537 JP 2000-289407 A JP-A-10-056771 JP 2002-322317 A JP 2005-325311 A

  Therefore, an object of the present invention is to provide a rubber composition for a tire tread that exhibits stable dry grip performance by suppressing a decrease in rigidity due to heat generation during traveling.

As a result of intensive studies to achieve the above object, the present inventor has unexpectedly found that SBR having a glass transition temperature exceeding −45 ° C., (1) carbon black having N ₂ SA exceeding 250 m ² / g; or ( 2) (i) with N ₂ SA is 250 meters ² / g greater than carbon black and (ii) N ₂ SA is a blend of carbon black is 100-150 ² / g, the amount of component (ii) is component ( A blend comprising less than 50% by weight of the total amount of i) and component (ii) and a low molecular weight styrene-butadiene copolymer having a bound styrene content of 25% by weight or more and a weight average molecular weight of 2,000 to 50,000 When the rubber composition obtained by doing so is used as a tire tread, it has been found that a decrease in rigidity due to heat generation during running is suppressed and dry grip performance is improved.

That is, the rubber composition for a tire tread of the present invention is
(A) a styrene-butadiene copolymer rubber having a glass transition temperature exceeding -45 ° C;
(B) 60 to 150 parts by weight of 100 parts by weight of the styrene-butadiene copolymer rubber (A)
(1) Carbon black N ₂ SA is more than 250m ² / g, or (2) (i) N ₂ SA is a carbon black of more than 250 meters ² / g (ii) N ₂ SA is at 100-150 ² / g A blend of carbon blacks, wherein the amount of component (ii) is less than 50% by weight of the total amount of components (i) and (ii);
(C) 5 to 150 parts by weight of a low molecular weight styrene-butadiene copolymer having a bound styrene amount of 25% by weight or more and a weight average molecular weight of 2,000 to 50,000, based on 100 parts by weight of the component (A),
Comprising.

  When the tire tread rubber composition is further blended with 5 to 50 parts by weight of a tackifying resin with respect to 100 parts by weight of SBR (A), the dry grip performance that does not depend on heat generation during running is further improved. Can be made.

  The styrene-butadiene copolymer rubber (A) used in the present invention has a glass transition temperature exceeding -45 ° C. The styrene-butadiene copolymer rubber (A) preferably has a bound styrene content of 5% by weight or more, more preferably 10 to 45% by weight, and a vinyl content of preferably 10 to 80%, more preferably 20 to 70%. %, And the glass transition temperature exceeds −45 ° C., preferably −40 to −5 ° C. If the glass transition temperature is −45 ° C. or lower, sufficient dry grip performance cannot be obtained, and if it is too high, the temperature dependence becomes large and the grip performance in the initial stage of travel becomes low. The styrene-butadiene copolymer rubber (A) used in the present invention may be any generally available.

The carbon black (B) used in the present invention is either (1) carbon black with N ₂ SA exceeding 250 m ² / g or (2) (i) N ₂ SA exceeding 250 m ² / g. A blend of carbon black and (ii) carbon black having N ₂ SA of 100 to 150 m ² / g, wherein the amount of component (ii) is less than 50% by weight of the total amount of component (i) and component (ii) Is a blend. The carbon black (B) preferably has a dibutyl phthalate oil absorption of 100 to 150 ml / 100 g. (B) When blending only carbon black with N ₂ SA of (1) exceeding 250 m ² / g, and (B) (2) (i) Carbon black with N ₂ SA exceeding 250 m ² / g (Ii) When blending with carbon black having N ₂ SA of 100 to 150 m ² / g, stable high dry grip performance independent of heat generation during running is achieved. Carbon black (B) is blended in an amount of 60 to 150 parts by weight with respect to 100 parts by weight of the styrene-butadiene copolymer rubber (A). If the carbon black (B) is less than 60 parts by weight relative to the styrene-butadiene copolymer rubber (A), sufficient improvement in dry grip performance cannot be achieved. On the other hand, when the carbon black (B) exceeds 150 parts by weight, the exothermic property of the resulting rubber composition increases, and as a result, the rigidity gradually decreases due to heat generation during running, resulting in a decrease in dry grip performance. When the N ₂ SA of the carbon black of (B) (1) and (B) (2) (i) is 250 m ² / g or less, sufficient improvement in dry grip performance cannot be achieved from the beginning of running. Examples of carbon black of carbon black (B) (2) (ii) include SAF and ISAF.

  The low molecular weight styrene-butadiene copolymer rubber (C) used in the present invention has a bound styrene content of 25% by weight or more and a weight average molecular weight of 2,000 to 50,000. The low molecular weight SBR (C) used in the present invention may be any generally available as long as the amount of bound styrene and the weight average molecular weight are within the above ranges. The amount of the low molecular weight styrene-butadiene copolymer rubber (C) is 5 to 150 parts by weight based on 100 parts by weight of the styrene-butadiene copolymer rubber (A). When the amount of bound styrene of the low molecular weight SBR (C) is less than 25% by weight, the effect of improving the grip performance is reduced. If the weight average molecular weight of the low molecular weight SBR (C) is less than 2,000, the effect of improving the grip performance is reduced, and if it exceeds 50,000, the grip performance is inferior. When the blending amount of the low molecular weight SBR (C) is less than 5 parts by weight with respect to 100 parts by weight of the styrene-butadiene copolymer rubber (A), the effect of improving the grip performance is reduced to 150 weights. If it exceeds the area, the grip performance is inferior, and the workability is remarkably deteriorated due to adhesion.

  As said tackifier resin (D) which can be mix | blended with the rubber composition for tire treads of this invention, what has a softening point of 60-150 degreeC is preferable. Specific examples of such tackifier resins include, for example, terpene resins such as YS resin PX800 manufactured by Yasuhara Chemical; aromatic modified terpene resins such as YS TO 85 manufactured by Yasuhara Chemical; aromatic resins such as Arizona Chemical And alpha-methylstyrene resins such as Sylvares SA85; aliphatic / aromatic resins such as coumarone-indene resins such as Escron G-90 manufactured by Nippon Steel Chemical Co., Ltd. The tackifying resin is preferably blended in an amount of 5 to 50 parts by weight with respect to 100 parts by weight of the styrene-butadiene copolymer rubber (A).

  The rubber composition for a tire tread of the present invention includes a vulcanizing agent and a vulcanization accelerator other than the rubber component and carbon black, a vulcanization accelerating aid such as stearic acid that is usually blended in the rubber composition, and various oils. Various compounding agents and additives such as fillers, softeners, plasticizers, surfactants, anti-aging agents, and the like can be compounded by general compounding methods in amounts generally used according to various applications. it can.

  The present invention will be further described below with reference to examples and comparative examples. Needless to say, the scope of the present invention is not limited to these examples.

Comparative Examples 1-6 and Examples 1-3
The formulations used for the preparation of the rubber compositions of Comparative Examples 1 to 6 and Examples 1 to 3 are as shown in Table 1 below.

註:
* 1: Emulsion polymerization SBR (NIPOL 9529 manufactured by Nippon Zeon Co., Ltd.), 50 phr oil extended, Tg = −20 ° C .;
* 2: Emulsion polymerization SBR (NIPOL 1712 manufactured by Nippon Zeon Co., Ltd.), 37.5 phr oil extended, Tg = −54 ° C .;
* 3: CD2019 manufactured by Colombian Chemicals Company, N ₂ SA = 390 m ² / g;
* 4: IP2000 manufactured by Cabot Japan, N ₂ SA = 192 m ² / g;
* 5: Tokai Carbon Seast 9, N ₂ SA = 142 m ² / g;
* 6: Ricon 100 manufactured by Sartomer, weight average molecular weight 4,500, amount of bound styrene 25% by weight;
* 7: Aromatic modified terpene resin TO85 manufactured by Yasuhara Chemical;
* 8: Process X-140 (manufactured by Japan Energy Co., Ltd.);
* 9: Antigen 6C (manufactured by Sumitomo Chemical Co., Ltd.);
* 10: 3 types of zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.);
* 11: Bead stearic acid YR (manufactured by NOF Corporation);
* 12: Sunseller DG (manufactured by Sanshin Chemical Industry Co., Ltd.);
* 13: Noxeller CZ-G (Ouchi Shinsei Chemical Co., Ltd.);
* 14: Fine powder sulfur with Jinhua seal oil (manufactured by Tsurumi Chemical Co., Ltd.);

  In accordance with the composition of Table 1 above, a vulcanization accelerator and components other than sulfur were mixed for 10 minutes using a 16 liter closed Banbury mixer, released from the mixer at 160 ° C., and vulcanization accelerator and Sulfur was mixed to obtain rubber compositions of comparative examples and examples.

  Next, a test tire of 195 / 55R15 size provided with a tread formed using the rubber composition prepared as described above was manufactured, and dry grip performance was determined according to the following test method. The results are shown in Table 2.

Test method
Dry grip performance In order to determine the stability of dry grip performance, dry grip performance was determined at the beginning and end of travel.
The dry grip performance at the beginning of running is a tire using 20 rounds of a circuit of 5.8 km per lap, obtaining an average value of lap times of the first 1 to 5 laps, and using the rubber composition of Comparative Example 1 as a tread portion. When the average value of the first 1-5 lap times obtained in step 1 was used as a reference, the evaluation was made in five stages as follows:
5: When 0.3 seconds or more faster than the reference standard,
4: When faster than the reference standard by 0.1 second or more and less than 0.3 second,
3: When it is less than ± 0.1 seconds with respect to the reference standard,
2: When it is slower than the reference standard by 0.1 second or more and less than 0.3 second,
1: When it is slower than the reference standard by 0.3 seconds or more.
The dry grip performance at the end of traveling was obtained by a tire using the rubber composition of Comparative Example 1 as a tread portion by calculating the average value of the last 15 to 20 laps of the 20 laps. When the average value of the lap times of the last 15 to 20 laps was used as a reference standard, the evaluation was made in five stages as follows:
5: When 0.3 seconds or more faster than the reference standard,
4: When faster than the reference standard by 0.1 second or more and less than 0.3 second,
3: When it is less than ± 0.1 seconds with respect to the reference standard,
2: When it is slower than the reference standard by 0.1 second or more and less than 0.3 second,
1: When it is slower than the reference standard by 0.3 seconds or more.
As for the above-mentioned dry grip performance at the beginning and end of traveling, the grip performance is better as the average value of the lap time is shorter (that is, faster) than the reference (Comparative Example 1).

  From the results of Table 2, it can be seen that in the rubber composition of the present invention, a decrease in rigidity due to heat generation during running is suppressed and a stable dry grip performance is provided.

Claims (2)

(A) a styrene-butadiene copolymer rubber having a glass transition temperature exceeding -45 ° C;
(B) 60 to 150 parts by weight of 100 parts by weight of the styrene-butadiene copolymer rubber (A)
(1) a nitrogen adsorption specific surface area (N ₂ SA) is more than 250 meters ² / g carbon black, or (2) (i) N ₂ SA is a carbon black of more than ^{250m 2 / g (ii) N} 2 SA is 100 A blend of carbon black that is ˜150 m ² / g, wherein the amount of component (ii) is less than 50% by weight of the total amount of component (i) and component (ii);
(C) 5 to 150 parts by weight of a low molecular weight styrene-butadiene copolymer having a bound styrene amount of 25% by weight or more and a weight average molecular weight of 2,000 to 50,000, based on 100 parts by weight of the component (A),
A rubber composition for tire treads comprising:   The rubber composition for a tire tread according to claim 1, wherein the rubber composition further comprises 5 to 50 parts by weight of (D) a tackifying resin with respect to 100 parts by weight of the component (A).