JP2008088236A - Rubber composition for tire tread and pneumatic tire produced by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To lower the temperature dependence of wet braking of a rubber composition without lowering vulcanization rate while keeping low rolling resistance of a rubber composition. <P>SOLUTION: The rubber composition for tire tread contains (A) 100 pts.wt. of a rubber component containing (i) 5-30 pts.wt. of natural rubber (NR), (ii) 5-25 pts.wt. of polybutadiene rubber (BR), (iii) 5-85 pts.wt. of a styrene-butadiene copolymer rubber (SBR) having a glass transition temperature (Tg) of -50°C or over and below -30°C and (iv) 5-85 pts.wt. of a styrene-butadiene copolymer rubber (SBR) having a glass transition temperature (Tg) of -30 to -10°C, and (B) 55-90 pts.wt. of silica and has a tanδ(60°C) of ≤0.16 and a peak value of tanδ temperature dispersion of ≤1.0. The invention further provides a pneumatic tire produced by using the rubber composition as the tread part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire tread and a pneumatic tire using the same, and more particularly to a tire tread rubber composition in which the temperature dependency of wet braking is reduced while maintaining a low rolling resistance and the tread portion. It relates to a pneumatic tire used in the above.

  In recent years, silica has been used instead of carbon black as a reinforcing filler in order to achieve both wet performance and low fuel consumption of pneumatic tires (see Patent Document 1). However, when silica is used in combination with carbon black in the rubber composition or silica is used instead of carbon black, the wet performance of the resulting rubber composition is improved, and rolling resistance can be reduced. However, recently, the demand for fuel-efficient tires has become more severe, and extremely low rolling resistance is demanded while ensuring wet performance. In such cases, wet braking or μp (maximum in μ-S characteristics) There is a problem that the temperature dependency of the friction coefficient becomes large.

  When a rubber composition having a remarkably low rolling resistance is required while ensuring wet performance, silica is mainly used as the filler, and the total filler content of carbon black and silica is reduced as much as possible to increase heat generation. Techniques for reducing this are known. However, if the filler content is reduced, the performance of pure rubber is close, and the tan δ temperature dispersion peak shape becomes sharper from broader. In particular, when silica is blended, the shape becomes sharper than that of carbon black. The peak shape of the tan δ temperature dispersion is related to the temperature dependence of the wet braking performance, and the sharper the shape, the greater the temperature dependence of the wet braking performance.

JP-A-7-196850

  Accordingly, an object of the present invention is to provide a rubber composition in which the temperature dependence of wet braking is reduced without decreasing the vulcanization speed while maintaining low rolling resistance.

  According to the present invention, (A) (i) 5 to 30 parts by weight of natural rubber (NR), (ii) 5 to 25 parts by weight of polybutadiene rubber (BR), and (iii) glass transition temperature (Tg) of −50 ° C. Styrene-butadiene copolymer rubber (SBR) having a styrene-butadiene copolymer rubber (SBR) of less than -30 ° C and 5 to 85 parts by weight and (iv) a glass transition temperature (Tg) of -30 ° C to -10 ° C. 100 parts by weight of a rubber component containing 5 to 85 parts by weight and 55 to 90 parts by weight of (B) silica, tan δ (60 ° C.) is 0.16 or less, and the peak value of tan δ temperature dispersion is 1.0 or less. A rubber composition for a tire tread and a pneumatic tire using the rubber composition for a tread portion are provided.

  According to the present invention, by combining four kinds of rubber polymers having different Tg, the sharpening of tan δ temperature dispersion accompanying the reduction of the filler content mainly composed of silica is suppressed, and the wet performance of the rubber composition is suppressed. The temperature dependence of can be reduced.

  As a result of researches to solve the above problems, the present inventors have determined that in the rubber composition, in order to suppress the sharpening of tan δ temperature dispersion accompanying the reduction of the filler amount mainly composed of silica in the rubber composition. , And succeeded in reducing the temperature dependence of the wet performance of the rubber composition by blending four rubber polymers having different Tg in combination.

  In the rubber composition according to the present invention, as the rubber component (A), (i) 5 to 30 parts by weight (preferably 10 to 25 parts by weight) of natural rubber (NR), (ii) 5 to 5 parts of polybutadiene rubber (BR) 25 parts by weight (preferably 10 to 20 parts by weight) (preferably glass transition temperature (Tg) = − 90 ° C. or less), (iii) glass transition temperature (Tg) of −50 ° C. to less than −30 ° C. (preferably − 40 ° C to less than -30 ° C) styrene-butadiene copolymer rubber (SBR) 5 to 85 parts by weight (preferably 10 to 60 parts by weight) and (iv) glass transition temperature (Tg) of -30 ° C to -10 ° C 100 parts by weight in a total amount of 5 to 85 parts by weight (preferably 10 to 60 parts by weight) of styrene butadiene copolymer rubber (SBR) (preferably -30 to -20 ° C) is blended.

  According to the present invention, as described above, two kinds of SBR having different NR, BR and Tg ranges are blended as the rubber component (A). In this specification, the glass transition temperature Tg is a value measured by DSC (differential scanning calorimeter). These rubbers are all known and commercially available products can be used. According to the present invention, the above-mentioned object can be achieved by blending the four types of rubbers having different Tg in the above-described blending ratio and using them together with silica.

  In the rubber composition according to the present invention, silica as a component (B) is blended in an amount of 55 to 90 parts by weight, preferably 55 to 80 parts by weight, based on 100 parts by weight of the rubber component (A). If the blending amount is small, the reinforcing property of the rubber is lowered, which is not preferable. Conversely, if the blending amount is large, rolling resistance increases, which is not preferable. The silica used in the present invention may be any silica that can be used for tires, such as natural silica, synthetic silica, more specifically dry silica and wet silica. It is to be noted that any silane coupling agent can be blended together with the blending of silica in accordance with a conventional method, and the blending amount is not particularly limited, but is preferably 5 to 10% by weight based on the silica weight.

  The tire tread rubber composition according to the present invention has a value of tan δ (60 ° C.) (measured at 60 ° C. at an initial strain of 10%, an amplitude of 2%, and a frequency of 20 Hz using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho). It is 0.16 or less, preferably 0.15 or less, and the peak value of tan δ temperature dispersion (measured at an amplitude of 0.3% under the above-mentioned measuring instrument and measurement conditions, the measurement temperature is from −100 ° C. to 100 ° C. 2 Tan δ peak value obtained by measurement at every degree) is 1.0 or less, preferably 0.95 or less. If the value of tan δ (60 ° C.) is large, the rolling resistance increases, which is not preferable. If the peak value of tan δ temperature dispersion is large, the temperature dependency of μp increases, which is not preferable.

  In addition to the components described above, the rubber composition according to the present invention includes other reinforcing agents (fillers) such as carbon black, vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, various oils, anti-aging agents, plastics Various additives generally blended for tires such as additives and other rubber compositions can be blended, and these additives are kneaded by a general method to form a composition, which is then vulcanized or crosslinked. Can be used to do. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition of the present invention can be used for producing a pneumatic tire according to a conventional method for producing a pneumatic tire.

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

Examples 1-2 and Comparative Examples 1-5
Sample preparation In the formulation shown in Table I, the components other than the vulcanization accelerator and sulfur were kneaded for 5 minutes in a 1.5 liter closed mixer and released when the temperature reached 150 ° C to obtain a master batch. A vulcanization accelerator and sulfur were kneaded with this masterbatch with an open roll to obtain a rubber composition. Using this rubber composition, unvulcanized physical properties were evaluated by the following test methods. The results are shown in Table I.

  Next, the obtained rubber composition was vulcanized in a 15 × 15 × 0.2 cm mold at 150 ° C. for 20 minutes to prepare a vulcanized rubber sheet. The physical properties of the vulcanized rubber were measured by the following test methods. It was measured. The results are shown in Table I.

Rubber physical property evaluation test method T30 (min): Measured according to JIS K6300. The time (minutes) required to reach 30% vulcanization at a temperature of 160 ° C. was measured and designated as T30. Using Example 1 as a reference (100), the larger the index, the faster the vulcanization rate.
Hardness: Measured according to JIS K6253.

tan δ (0 ° C. and 60 ° C.): Measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. at an initial strain of 10%, an amplitude of ± 2%, a frequency of 20 Hz, and an ambient temperature of 0 ° C. and 60 ° C.
tan δ peak: Under the same conditions as described above, the atmospheric temperature was changed from −100 ° C. to 100 ° C., and the peak temperature of tan δ at that time was measured.

μp (15 ° C. and 25 ° C.): A tread rubber having the composition shown in Table 1 was produced, and a tire having a tire size of 185 / 65R15 was produced. The slip ratio was changed from 0 to 100% under the conditions of air pressure 200 KPa, rim 15 inch 6 JJ, speed 50 km / h, load 6 KN, road surface temperature 15 ° C. and 25 ° C., and the maximum friction coefficient (μp) at that time was measured.
Δμp: (μp measured at 15 ° C.) − (Μp measured at 25 ° C.).

  Rolling resistance: The resistance force of the tire produced above was measured when the drum diameter was 1707 mm, the load was 4 KN, and the speed was 50 km / h. The comparative example 1 is set as a reference (100), and the higher this index is, the smaller the rolling resistance is.

Table I Footnote * 1: Natural rubber STR20
* 2: Polyisoprene rubber IR2200 (Tg = −65 ° C.) manufactured by Nippon Zeon Co., Ltd.
* 3: Styrene butadiene copolymer rubber NS440 (Tg = −25 ° C.) manufactured by Nippon Zeon Co., Ltd.
* 4: Styrene butadiene copolymer rubber manufactured by Nippon Zeon Co., Ltd. Nipoi 1721 (Tg = -36 ° C)
* 5: Polybutadiene rubber Nipol BR 1220 manufactured by Nippon Zeon Co., Ltd. (Tg = −104 ° C.)
* 6: Silica Zeosil 165GR manufactured by Rhodia Silica Korea
* 7: Carbon black show black N339 manufactured by Cabot Japan Co., Ltd.
* 8: Three types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. * 9: Bead stearic acid manufactured by Nippon Oil & Fats Co., Ltd. * 10: Nocrack 6C manufactured by Ouchi Shinsei Chemical Co., Ltd.
* 11: Si69 manufactured by Degussa Corporation
* 12: Desolex No. 3 manufactured by Showa Shell Sekiyu K.K. * 13: Fine powdered sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd. * 14: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.
* 15: Ouchi Shinsei Chemical Co., Ltd. Noxeller D

  As described above, since the rubber composition of the present invention can reduce the temperature dependency of wet braking while maintaining low rolling resistance, it is useful as a tread rubber for fuel-efficient tires.

Claims (2)

  (A) (i) 5-30 parts by weight of natural rubber (NR), (ii) 5-25 parts by weight of polybutadiene rubber (BR), (iii) glass transition temperature (Tg) of −50 ° C. to less than −30 ° C. 5 to 85 parts by weight of styrene-butadiene copolymer rubber (SBR) and (iv) 5 to 85 parts by weight of styrene-butadiene copolymer rubber (SBR) having a glass transition temperature (Tg) of −30 ° C. to −10 ° C. A rubber composition for a tire tread comprising 100 parts by weight of a rubber component and 55 to 90 parts by weight of (B) silica, having a tan δ (60 ° C.) of 0.16 or less and a peak value of tan δ temperature dispersion of 1.0 or less. object.   A pneumatic tire using the rubber composition for a tire tread according to claim 1 in a tread portion.