JP2008163113A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition having high gripping performance and good heat aging resistance without reducing modulus. <P>SOLUTION: The rubber composition for the tire tread comprises (A) 100 pts.wt. of a diene rubber having 350,000-2,000,000 weight average molecular weight, (B) 0.5-15 pts.wt. of a metal salt of acrylic acid or methacrylic acid, and (C) 3-100 pts.wt. of a low-molecular weigh diene rubber having 2,000-100,000 weight average molecular weight. The pneumatic tire uses the rubber composition at the tread part. <P>COPYRIGHT: (C)2008,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 suitable as a racing tire, which has a high grip and good heat aging resistance without lowering the modulus.

  In rubber compositions for racing tires, a technique is known in which a low molecular weight styrene-butadiene copolymer (SBR) is blended in order to improve gripping power. However, when low molecular weight SBR is blended, there is a problem that the modulus of the rubber composition is lowered.

Japanese Patent No. 2992102

  Accordingly, an object of the present invention is to obtain a rubber composition having high grip strength and good heat aging resistance without lowering the modulus.

  According to the present invention, (A) 100 parts by weight of a diene rubber having a weight average molecular weight of 350,000 to 2,000,000, (B) 0.5 to 15 parts by weight of a metal salt of acrylic acid or methacrylic acid, and ( C) A rubber composition for a tire tread comprising 3 to 100 parts by weight of a low molecular weight diene rubber having a weight average molecular weight of 2,000 to 100,000, and a pneumatic tire using the rubber composition for the tread part are provided.

  According to the present invention, by adding a metal salt of (meth) acrylic acid to a rubber composition containing a low molecular weight diene rubber such as low molecular weight SBR, the modulus is reduced without increasing the amount of sulfur. Thus, a rubber composition having a high grip and good heat resistance can be obtained.

  Low molecular weight diene rubbers such as low molecular weight SBR cause the lowering of the modulus, as with diene rubbers that are not low molecular weight, but react with sulfur, but due to the short molecular chain, it is difficult to obtain effective crosslinking, resulting in low molecular weight. In order to compensate for sulfur that becomes ineffective by reacting with a low molecular weight diene rubber such as SBR, a method of adjusting the modulus by increasing the amount of sulfur is generally used. However, an increase in the amount of sulfur causes another problem of deteriorating the heat aging resistance. In the case of racing tires, the deterioration in heat aging resistance leads to a decrease in grip during the race, while the decrease in modulus deteriorates the blow resistance, so that it is necessary to adjust the modulus.

  As a result of advancing research to solve the above problems, the present inventors have formulated a compound of sulfur by blending a metal salt of (meth) acrylic acid with a rubber composition blended with a low molecular weight rubber composition. The inventors succeeded in obtaining a rubber composition that suppresses the decrease in modulus without increasing the amount, has high grip strength, and has good heat aging resistance.

  In the present invention, (meth) acrylic acid (acrylic acid or methacrylic acid) is added to 100 parts by weight of a diene rubber having a weight average molecular weight of 350,000 to 2,000,000, preferably 380,000 to 1,800,000. Low molecular weight diene system having 0.5 to 15 parts by weight, preferably 0.6 to 12 parts by weight, and a weight average molecular weight of 2,000 to 100,000, preferably 2,500 to 80,000 A desired tire tread rubber composition can be obtained by blending 3 to 100 parts by weight, preferably 5 to 90 parts by weight of rubber.

  If the blending amount of the metal salt of (meth) acrylic acid is small, the desired effect cannot be obtained sufficiently. Conversely, if the blending amount is large, further improvement of the effect due to blending is not seen and the cost is increased, which is not preferable. As the metal salt (B) of (meth) acrylic acid, a salt such as zinc of acrylic acid or methacrylic acid, calcium salt of acrylic acid or methacrylic acid, magnesium salt of acrylic acid or methacrylic acid, etc. can be used. Most preferred is the use of zinc acid. These metal salts are known compounds and are widely commercially available.

If the molecular weight of the low molecular weight diene rubber is outside the above range, the effect of improving the grip force is insufficient, and if the amount of the low molecular weight diene rubber is small, the effect of improving the grip force is insufficient. This is not preferable because the properties deteriorate. As the low molecular weight diene rubber used in the present invention, the low molecular weight styrene-butadiene copolymer, polybutadiene, polyisoprene, styrene-isoprene copolymer, acrylonitrile-butadiene copolymer, and the like can be used. It is a known low molecular weight polymer and is widely available commercially. The low molecular weight diene rubber (C) has an average glass transition temperature T _g (measured at a heating rate of 20 ° C./min using a differential scanning calorimeter (DSC) and calculated by a midpoint method) of −45 ° C. It is preferably ˜0 ° C. If the _Tg is low, the grip may be lowered. Conversely, if the Tg is high, the rubber becomes hard and the grip in the initial stage of travel may be lowered.

Examples of the diene rubber (A) used in the present invention include natural rubber, styrene butadiene copolymer rubber, polybutadiene rubber, polyisoprene rubber, styrene-isoprene copolymer rubber, and acrylonitrile-butadiene copolymer rubber. Can do. The diene rubber preferably has an average glass transition temperature T _g (measured at a temperature increase rate of 20 ° C./min using a differential scanning calorimeter (DSC) and calculated by a midpoint method) at −45 ° C. to 0 ° C. is there. If the _Tg is low, the grip may be lowered. If the Tg is high, the rubber becomes hard, and the grip at the beginning of running may be lowered.

In a preferred embodiment of the present invention, carbon black and / or silica having a nitrogen adsorption specific surface area of 80 to 400 m ² / g (measured according to ASTM D3037) is 50 to 200 parts by weight per 100 parts by weight of the diene rubber (A). Preferably, 55 to 180 parts by weight are blended. If the nitrogen adsorption specific surface area is small, the grip may be lowered. Conversely, if the nitrogen adsorption specific surface area is large, the workability may be deteriorated. Further, when the total amount of carbon black and / or silica is small, the grip may be lowered, and when it is large, the workability may be deteriorated.

  In addition to the components described above, the rubber composition according to the present invention includes other reinforcing agents (fillers) other than carbon black and silica, vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, various oils, and anti-aging agents. Various additives generally blended for tires such as plasticizers and other rubber compositions can be blended, and these additives are kneaded by a general method to obtain a composition and vulcanized. Or it can be used to crosslink. 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.

  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.

Standard example, Examples 1-2 and Comparative Examples 1-2
Sample preparation In the formulation shown in Table I, the components other than the vulcanization accelerator and sulfur were kneaded in a 1.7 liter closed mixer for 5 minutes and released when the temperature reached 160 ° 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.

  Next, the resulting rubber composition was vulcanized in a 15 × 15 × 0.2 cm mold at 160 ° C. for 30 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 Durometer hardness: Measured according to JIS K 6253 (type A).

  Tensile test: M300 (300% modulus), TB (tensile strength) and EB (cut) before and after aging (100 ° C. × 48 hours or 120 ° C. × 24 hours) according to JIS K 6251 (JIS No. 3 dumbbell) Time elongation) was measured.

  Coefficient of friction: Measured on wet Alfart road surface using a dynamic friction tester according to ASTM E-1911. The results are shown as an index with the value of the standard example being 100. The larger this value, the greater the coefficient of friction and the higher the grip.

Table I Footnote * 1: SBR manufactured by Nippon Zeon Co., Ltd. (T _g = −31 ° C.)
* 2: Carbon black (N ₂ SA = 142 m ² / g) manufactured by Tokai Carbon Co., Ltd.
* 3: manufactured by Shodo Chemical Industry Co., Ltd. * 4: manufactured by Nippon Oil & Fats Co., Ltd. * 5: anti-aging agent manufactured by FLEXSYS * 6: low molecular weight SBR manufactured by SARTOMER (Mw = 4500, T _g = −18 ° C.)
* 7: Petroleum softener made by Japan Energy Co., Ltd. * 8: Made by Tsurumi Chemical Co., Ltd. * 9: Vulcanization accelerator made by Ouchi Shinsei Chemical Co., Ltd. * 10: Zinc monomethacrylate made by SARTOMER

  As described above, according to the present invention, by reducing the amount of sulfur without increasing the amount of sulfur, by adding a (meth) acrylic acid metal salt to a rubber composition containing a low molecular weight rubber, it is possible to prevent a decrease in modulus. In addition, since a rubber composition having high grip strength and good heat aging resistance can be obtained, it is useful for a tread portion of a pneumatic tire.

Claims (6)

  (A) 100 parts by weight of a diene rubber having a weight average molecular weight of 350,000 to 2,000,000, (B) 0.5 to 15 parts by weight of a metal salt of acrylic acid or methacrylic acid, and (C) a weight average molecular weight. A rubber composition for a tire tread, comprising 3 to 100 parts by weight of a low molecular weight diene rubber having a molecular weight of 2,000 to 100,000. The rubber composition for a tire tread according to claim 1, further comprising 50 to 200 parts by weight of carbon black and / or silica having a nitrogen adsorption specific surface area (N ₂ SA) of 80 to 400 m ² / g. The diene rubber average glass transition temperature T _g is a tire tread rubber composition according to claim 1 or 2, which is -45 ° C. ~0 ° C. of (A). The low molecular weight diene rubber average glass transition temperature T _g is a tire tread rubber composition according to claim 1, which is -45 ° C. ~0 ° C. of (C).   The rubber composition for a tire tread according to any one of claims 1 to 4, wherein the metal salt (B) of acrylic acid or methacrylic acid is zinc monomethacrylate.   A pneumatic tire using the rubber composition according to any one of claims 1 to 5 in a tread portion.