JP2008297445A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire tread, increased in silica dispersibility so as especially to much improve wet performances, by compounding a predetermined amount of a carboxylic acid-modified liquid polyisoprene rubber to a cap tread compound compounded with much silica. <P>SOLUTION: The rubber composition for tire tread is provided by compounding 30-150 pts.wt. reinforcing filler containing ≥80 wt.% silica having 100-300 m<SP>2</SP>/g BET specific surface area, and 1-20 pts.wt. liquid polyisoprene having 2-10 carboxy groups per 1 molecule and 10,000-60,000 number-average molecular weight, per 100 pts.wt. diene-based rubber containing ≥50 pts.wt. high vinyl, high molecular weight styrene-butadiene copolymer rubber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition for tire treads, and more specifically, by adding a carboxylic acid-modified liquid polyisoprene rubber to a silica-rich compounded cap tread compound, the dispersibility of silica is improved, and particularly excellent wet performance. The present invention relates to a rubber composition for tire treads.

  Conventionally, cap tread compounds containing a large amount of silica have been challenged to improve the physical properties (wet performance, rolling resistance, etc.) of vulcanized rubber by avoiding the high cohesiveness of silica itself. . In order to improve the dispersibility of polar organic materials such as kneading adhesives and phenolic resins in tire rubber compositions made of general diene rubber, it is possible to improve the physical properties such as adhesion durability and elastic modulus. A technique for blending liquid polyisoprene into which an acid or a derivative thereof has been introduced is known from Patent Document 1 below, and in the rubber composition for tire treads, which is also made of a diene rubber, has excellent grip properties on frozen road surfaces and acceleration performance. A technique for blending liquid polyisoprene having a carboxyl group in order to obtain a studless tire having good braking performance is known from Patent Document 2 below. However, a technology for achieving such a high dispersibility of silica by blending such carboxylic acid-modified liquid polyisoprene rubber into a silica-rich rubber composition and improving the physical properties of the rubber composition has been proposed. Not.

Japanese Patent Laid-Open No. 2005-226016 Japanese Unexamined Patent Publication No. 7-118445

  Therefore, in the present invention, by adding a predetermined amount of the carboxylic acid-modified liquid polyisoprene rubber to the cap tread compound containing a large amount of silica, the dispersibility of silica is improved more than other silica processing aids, and particularly wet performance. An object of the present invention is to provide a rubber composition for a tire tread in which the rubber is highly improved.

According to the present invention, the silica having a BET specific surface area of 100 to 300 m ² / g is contained by 80% by weight or more with respect to 100 parts by weight of the diene rubber containing 50 parts by weight or more of high vinyl and high molecular weight styrene butadiene copolymer rubber. 30 to 150 parts by weight of a reinforcing filler and a rubber composition for a tire tread comprising 1 to 20 parts by weight of a liquid polyisoprene having 2 to 10 carboxyl groups per molecule and a number average molecular weight of 10,000 to 60,000. Things are provided.

  In the present invention, when a predetermined amount of a specific carboxylic acid-modified liquid polyisoprene is added as a processing aid to a rubber composition for a tire tread having a large amount of silica, silica can be highly dispersed, particularly wet performance. It has been found that a rubber composition for a tire tread excellent in the above can be obtained.

  As the diene rubber component used in the rubber composition for tire treads of the present invention, as a necessary component, a high vinyl, high molecular weight styrene butadiene copolymer rubber has a grip level and wear resistance required for a cap compound. Used to secure the sex. Here, the “high vinyl content” means that the proportion of the vinyl content in the butadiene component in the styrene-butadiene copolymer rubber is 35 to 85% by weight, preferably 35 to 75% by weight. If the vinyl content is less than 35% by weight, the grip performance is lowered, which is not preferable. Conversely, if it exceeds 85% by weight, the rubber becomes too hard at low temperatures, which is not preferable. Here, “high molecular weight” means that the weight average molecular weight of the styrene-butadiene copolymer rubber is 600,000 to 1,500,000, preferably 800,000 to 1,400,000. If the weight average molecular weight is less than 600,000, the wear becomes insufficient, which is not preferable. Conversely, if the weight average molecular weight exceeds 1,500,000, processing becomes difficult.

  The styrene-butadiene copolymer rubber component is used in an amount of 50 parts by weight or more, preferably 60 to 90 parts by weight with respect to 100 parts by weight of the entire rubber component in the rubber composition for a tire tread of the present invention. . If the amount is less than 50 parts by weight, the effect of the present invention is small, which is not preferable.

  Examples of other rubber components in the rubber composition for a tire tread of the present invention include natural rubber (NR), various butadiene rubbers (BR), polyisoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), Examples include chloroprene rubber, ethylene-propylene-diene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, and isoprene-butadiene copolymer rubber. These diene rubbers may be used alone or in two types within a predetermined range. It may be used as the above blend rubber.

The rubber composition for a tire tread of the present invention contains 80% by weight of fine silica having a BET specific surface area (measured by ISO 5794) of 100 to 300 m ² / g with respect to 100 parts by weight of the whole rubber component. The reinforcing filler contained above is blended in an amount of 30 to 150 parts by weight, preferably 40 to 120 parts by weight. As the reinforcing filler, silica may be used alone in the above blending amount, or a mixed system of silica and carbon black may be used. When the compounding amount of the reinforcing filler is less than 30 parts by weight, the desired effect of the present invention is not exhibited. Conversely, when it exceeds 150 parts by weight, the mixing processability is inferior, and the expected effect of the present invention is obtained. Since it is reduced, it is not preferable.

  In the tire tread rubber composition of the present invention, as a processing aid, 1 to 20 parts by weight of liquid polyisoprene having 2 to 10 carboxy groups per molecule and having a number average molecular weight of 10,000 to 60,000, Preferably it is mix | blended in the quantity of 1.2-10 weight part. If the blending amount of the processing aid is less than 1 part by weight, the desired effect cannot be exerted. Conversely, if it exceeds 20 parts by weight, the viscosity increases and the workability decreases. The liquid polyisoprene is commercially available as, for example, trade names “Claprene LIR403” and “Claprene LIR410” represented by the following general formulas (1) and (2).

  The rubber composition for a tire tread of the present invention is further compounded for general tires such as a vulcanization or cross-linking agent, a vulcanization or cross-linking accelerator, various oils, an anti-aging agent, a filler, a softener, and a plasticizer. These compounding agents can be compounded and kneaded by a general method to obtain a rubber composition, which can be vulcanized or crosslinked. The compounding amounts of these compounding agents can be set to conventional general compounding amounts as long as the object of the present invention is not violated.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, it cannot be overemphasized that the technical scope of this invention is not limited to these Examples.

Sample Preparation According to the formulation (parts by weight) shown in Table 1, each component such as rubber and silica excluding sulfur and vulcanization accelerator was loaded into a 1.7 L B-type Banbury mixer and mixed for 5 minutes. The master batch which was discharged to the outside of the mixer and cooled to room temperature was charged again into the Banbury mixer, and sulfur and a vulcanization accelerator were blended and mixed therewith to obtain a rubber composition. Next, this rubber composition was press vulcanized at 160 ° C. for 20 minutes in a predetermined mold to prepare a test sample (rubber sheet), which was subjected to the following test.

Test Method 1) Wet Performance: In accordance with JIS K6394, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho, tan δ under conditions of initial strain = 10%, amplitude = ± 2%, frequency = 20 Hz (0 ° C.) was measured, and wet performance was evaluated with this value. The results are shown as an index with Comparative Example 1 as 100. The larger the index, the better the wet performance.
2) Silica dispersibility: Using RPA2000 manufactured by Alpha Technology, the strain dependence of the storage modulus was measured under the conditions of a measurement temperature of 110 ° C. (preheating 1 minute), a frequency of 6 cpm, and an amplitude of 0.28 to 10%. The value of the storage elastic modulus when the strain amount was 0.56% was determined. The index was expressed as an index with Comparative Example 1 as 100. The larger the value, the smaller the number of defective dispersion and the better the dispersibility.

Examples 1-4 and Comparative Examples 1-4
The results are shown in Table 1 below.

  From the results of Table 1, in the rubber compositions of Examples 1 to 4, in which a predetermined amount of a specific carboxylic acid-modified liquid polyisoprene is blended with a silica-rich rubber composition, wet performance and silica dispersibility are extremely good. It turns out that it is.

  Therefore, the rubber composition of the present invention is extremely useful when used as a rubber composition for tire treads.

Claims (1)

Reinforcing filler 30 to 80% by weight of silica having a BET specific surface area of 100 to 300 m ² / g with respect to 100 parts by weight of diene rubber containing 50 parts by weight or more of high vinyl and high molecular weight styrene butadiene copolymer rubber A rubber composition for a tire tread comprising 150 parts by weight and 1 to 20 parts by weight of a liquid polyisoprene having 2 to 10 carboxyl groups per molecule and having a number average molecular weight of 10,000 to 60,000.