JP2007070451A - Rubber composition for pneumatic tire and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a pneumatic tire capable of improving wet performance and snow performance without impairing workability of rubber processing. <P>SOLUTION: A rubber component comprises 20-60 wt.% of a styrene-butadiene rubber (A) having a glass transition temperature of -35 to -25°C, a styrene content of 20-40 wt.% and a vinyl content of 20-60 wt.% in the butadiene segment and 80-40 wt.% of another diene rubber (B), the rubber component having a glass transition temperature of -70 to -55°C as the whole rubber component. The rubber composition comprises 100 pts.wt. of the rubber component, >100 pts.wt. and ≤200 pts.wt. of silica having a BET specific surface area of 210-300 m<SP>2</SP>/g and a silane coupling agent represented by the formula (2): (C<SB>n</SB>H<SB>2n+1</SB>O)<SB>3</SB>Si-C<SB>m</SB>H<SB>2m</SB>-S-CO-C<SB>k</SB>H<SB>2k+1</SB>(wherein n denotes an integer of 1-3; m denotes an integer of 1-5; and k denotes an integer of 5-9). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rubber composition for a pneumatic tire in which silica is blended, and a pneumatic tire using the same.

  In general, when a tire runs on a slippery road surface such as a wet road surface (wet road surface) or an icy / snow road surface (snow / ice road surface), the friction resistance between the road surface and the tire tread contact portion decreases, so that sufficient braking performance is achieved. Operability may not be obtained. Therefore, conventionally, various proposals have been made to improve braking performance and operability on wet road surfaces and icy and snowy road surfaces.

  For example, there is a method of reducing the resilience of tread rubber in order to improve wet performance, which is braking performance and operability on a wet road surface. More specifically, in a rubber composition for forming a tread, there is a method of using a polymer having a high glass transition point as a rubber component or increasing a blending amount of a filler and oil.

  There are also techniques for reducing the hardness of the tread rubber in a low temperature region or reducing the storage elastic modulus (E ′) in order to improve the snow performance, which is braking performance and operability on an icy and snowy road surface. More specifically, in a rubber composition for forming a tread, there is a method of using a polymer having a low glass transition point as a rubber component, using silica as a filler, and further combining a silane coupling agent (for example, , See Patent Documents 1 and 2 below).

  However, when a polymer having a high glass transition point is used, there is a problem that snow performance is lowered. Conversely, when a polymer having a low glass transition point is used, there is a problem that wet performance is lowered. In addition, when the amount of the filler is simply increased or when a polysulfide silane conventionally used as a coupling agent to be used with silica is used, the workability is greatly inferior, such as an increase in the number of mixing and a decrease in the extrusion speed. There is a problem.

Patent Document 3 listed below proposes a new protected mercaptosilane as a silane coupling agent used with silica in order to suppress unacceptable viscosity increase during processing and improve early curing (scorch). . However, the same document discloses that this protected mercaptosilane is particularly effective in achieving both wet performance and snow performance in a combination of a specific rubber component and small particle size silica. It has not been.
JP 2003-155383 A JP 2003-155384 A Special table 2001-505225 gazette

  The present invention has been made in view of the above points, and a rubber composition for a pneumatic tire that can improve wet performance and snow performance without impairing workability of rubber processing, and the same are used. An object is to provide a pneumatic tire.

  The present inventor uses a high styrene type styrene butadiene rubber as the rubber component, sets the glass transition point (Tg) of the rubber component as a whole in a relatively low specific range, and converts this into a large amount of small particle size silica. Further, by using a specific protected mercaptosilane as a silane coupling agent for bonding them, the effect of improving snow performance by a rubber component having a low Tg and a small particle size silica can be used without impairing workability. The inventors have found that the wet performance improvement effect can be brought out, and have completed the present invention.

That is, the rubber composition for a pneumatic tire according to the present invention has a glass transition point of −35 to −25 ° C., a styrene content of 20 to 40% by weight, and a vinyl content in the butadiene portion of 20 to 60% by weight. The styrene butadiene rubber (A) is 20 to 60% by weight and the other diene rubber (B) is 80 to 40% by weight, and the BET ratio is 100 parts by weight of the rubber component satisfying the following formula (1). Silica having a surface area of 210 to 300 m ² / g and a CTAB specific surface area of 160 to 300 m ² / g is blended more than 100 parts by weight and 200 parts by weight or less, and is a silane represented by the following general formula (2) A coupling agent is blended in an amount of 2 to 25 parts by weight with respect to 100 parts by weight of silica.

_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 (2)
In the formula, n is an integer of 1 to 3, m is an integer of 1 to 5, and k is an integer of 5 to 9.

  The pneumatic tire according to the present invention has a tread composed of these rubber compositions.

  According to the present invention, a rubber component having a low glass transition point including a specific styrene butadiene rubber is used, and the protected mercaptosilane represented by the above formula (2) is used as a silane coupling agent together with a small particle size silica. By doing so, wet performance and snow performance can be improved without impairing workability during rubber processing.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

In the rubber composition of the present invention, the styrene butadiene rubber (A) used as a rubber component is
−35 ° C. ≦ Glass transition point (Tg) ≦ −25 ° C.
20% by weight ≦ styrene content (St) ≦ 40% by weight
20% by weight ≦ vinyl content in the butadiene part (Vi) ≦ 60% by weight
Is a styrene-butadiene copolymer rubber (SBR) satisfying By using such a high styrene type SBR, the wet performance can be improved. If the styrene content is less than 20% by weight, it is difficult to ensure wet performance. Conversely, if the styrene content exceeds 40% by weight, the wear resistance decreases, which is not preferable. On the other hand, when the glass transition point is lower than −35 ° C., the wet performance tends to be reduced. On the other hand, if the vinyl content in the butadiene portion is less than 20% by weight, the wet performance tends to be lowered. Conversely, if it exceeds 60% by weight, the wear resistance is lowered, which is not preferable. Here, the glass transition point is a value (temperature increase rate 20 ° C./min) measured using differential scanning calorimetry (DSC) in accordance with JIS K7121.

  As long as the styrene-butadiene rubber (A) satisfies the above conditions, only one kind may be used, or two or more kinds may be blended and used. The rubber (A) may be one in which the end of the copolymer chain is treated with a tin-based, silicon-based or alkoxysilane-based coupling agent, and the terminal or main chain is a silanol having a silica chain. It may be modified with a functional group (for example, a hydroxyl group or an amino group) having interaction or chemical reactivity with the group.

  In the rubber composition of the present invention, the other diene rubber (B) used as a rubber component includes styrene butadiene rubber, butadiene rubber, natural rubber, isoprene rubber, styrene-isoprene other than the styrene butadiene rubber (A). Examples thereof include copolymer rubber and butadiene-isoprene copolymer rubber, and these may be used alone or in combination of two or more.

  The other diene rubber (B) is preferably glass transition point (Tg) ≦ −30 ° C. (more preferably Tg ≦ −40 ° C., particularly preferably Tg ≦ −55 ° C.), 0% by weight ≦ styrene content. Diene rubber satisfying (St) ≦ 25% by weight and 0% by weight ≦ vinyl content in the butadiene part (Vi) ≦ 60% by weight, one kind of diene rubber satisfying these conditions May be used alone or in combination of two or more. In addition, these other diene rubbers (B) may be tin-based, silicon-based, or alkoxysilane-based, and the terminal or main chain interacts with the silanol group of silica. Or may be modified with a functional group having chemical reactivity.

  In the rubber composition of the present invention, the rubber component is composed of 20 to 60% by weight of the styrene butadiene rubber (A) and 80 to 40% by weight of the other diene rubber (B), and The expression (1) is satisfied. The above formula (1) defines the glass transition point of the rubber component as a whole, and by setting the glass transition point of the rubber component as a whole as low as -70 ° C to -55 ° C, Snow performance can be improved. Here, when the glass transition point of the rubber component as a whole is less than −70 ° C., the wet performance deteriorates, and conversely when it exceeds −55 ° C., the snow performance deteriorates.

In the formula (1), the glass transition point of the rubber component as a whole is defined by a value obtained by adding the glass transition points of the respective polymers constituting the rubber component according to the weight ratio. For example, when both the styrene butadiene rubber (A) and the other diene rubber (B) are composed of a single polymer, the glass transition point of the rubber component as a whole is (t _A1 × m _A1 ) + (t _B1 × m _B1 ) (where t _A1 is the glass transition point of the styrene butadiene rubber (A), and m _A1 is the weight ratio of the styrene butadiene rubber (A) to the total rubber component (parts by weight of A / total rubber)). T _B1 is the glass transition point of the diene rubber (B), m _B1 is the weight ratio of the diene rubber (B) to the total rubber component (part by weight of B / weight of all rubber components). Part).

Silica (hydrous silicic acid) used in the rubber composition of the present invention has a colloidal characteristic of 210 ≦ BET specific surface area ≦ 300 m ² / g and 160 ≦ CTAB specific surface area (cetyltrimethylammonium bromide adsorption specific surface area) ≦ A small particle size of 300 m ² / g is used. Wet performance can be improved by using silica having such a small particle diameter. The BET specific surface area is more preferably 230 to 300 m ² / g. Moreover, CTAB specific surface area becomes like this. More preferably, it is 190-300 m < ² > / g, Most preferably, it is 190-210 m < ² > / g. Here, in the present invention, the BET specific surface area is a value measured according to JIS K6217. The CTAB specific surface area is a value measured according to ASTM D3765.

  The silica is blended in an amount exceeding 100 parts by weight and not more than 200 parts by weight based on 100 parts by weight of the rubber component. In this way, by combining the small particle size silica with a significantly increased amount compared to the conventional general silica compounding amount, together with the specification of the rubber component and the silane coupling agent, snow performance and Wet performance can be dramatically improved. The silica is preferably blended in an amount of 125 parts by weight or more in order to further improve the wet performance. Further, the upper limit of the blending amount is preferably 150 parts by weight or less from the viewpoint of rubber workability.

  Although not essential, carbon black may be blended with the rubber composition of the present invention together with silica, and the carbon black is blended in an amount of 0 to 100 parts by weight with respect to 100 parts by weight of the rubber component. Silica and carbon black are blended at a ratio of silica / carbon black = 1.2 / 1 to 1/0.

  The silane coupling agent used in the rubber composition of the present invention is a protected mercaptosilane represented by the general formula (2), in which a hydrogen atom of a mercapto functional group is substituted. Such protected mercaptosilane can be produced according to the method described in JP-T-2001-505225. The protected mercaptosilane is blended in an amount of 2 to 25 parts by weight with respect to 100 parts by weight of silica in order to sufficiently exhibit the effects of the present invention described above. The silane coupling agent may be preliminarily treated with silica, and the treated silica may be added to and mixed with the rubber component.

  In the rubber composition of the present invention, in addition to the components described above, various types of rubber compositions generally used in tires such as anti-aging agents, zinc white, stearic acid, softening agents, vulcanizing agents, and vulcanization accelerators are used. Additives can be blended. In addition, mixing of a rubber composition can be performed using a well-known mixer, In that case, the said rubber component, silica (it may contain carbon black depending on the case), and a silane coupling agent are 150-180 degreeC. Mixing is preferable in order to exhibit the effect of the present invention.

  By using a rubber component having a low Tg containing a specific styrene butadiene rubber (A) and using the protected mercaptosilane as a silane coupling agent together with a small particle size silica as a rubber composition comprising the above. In addition, both wet performance and snow performance can be achieved, and the workability of rubber processing can be improved. In particular, in the present invention, since the above-mentioned small particle size silica is used in a larger amount than before, wet performance and snow performance can be dramatically improved. Therefore, this rubber composition is preferably used as a rubber forming a tread of a pneumatic tire. In particular, since it is excellent in wet performance and snow performance, it is preferably used as a rubber constituting the tread in various winter tires including snow tires.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, a rubber composition was prepared according to the composition shown in Tables 1 and 2 below. At that time, the mixing temperature of the rubber composition was 160 ° C. Details of each component in Tables 1 and 2 are as follows.

SBR1: Asahi Kasei styrene butadiene rubber “Toughden E-50” (glass transition point = −34 ° C., styrene content = 35.5 wt%, vinyl content in butadiene portion = 33 wt%, rubber polymer 100 wt% Oil-extended rubber containing 37.5 parts by weight of oil with respect to parts)
SBR2: Styrene butadiene rubber “NS422” manufactured by ZEON (glass transition point = −35 ° C., styrene content = 40% by weight, vinyl content in butadiene part = 22% by weight, 100 parts by weight of rubber polymer Oil-extended rubber containing 37.5 parts by weight of oil)
SBR3: Styrene butadiene rubber “SL574” manufactured by JSR (glass transition point = −43 ° C., styrene content = 15 wt%, vinyl content in butadiene portion = 57 wt%)
BR: butadiene rubber “BR01” manufactured by JSR (glass transition point = −102 ° C.).

・ Carbon black: Carbon black N234 "Seast 7H" made by Tokai Carbon
Silica 1: “Ultrasil 7000GR” manufactured by Degussa (BET specific surface area = 170 m ² / g, CTAB specific surface area = 160 m ² / g)
Silica 2 and Silica 3: Silica produced by the method described in Japanese Patent No. 3304096. Silica 2 has a BET specific surface area of 220 m ² / g, CTAB specific surface area of 195 m ² / g, and silica 3 has a BET specific surface area. = 240 m ² / g, CTAB specific surface area = 200 m ² / g.

・ Oil: “JOMO Process X-140” manufactured by Japan Energy
General-purpose coupling agent: bis- (3-triethoxysilylpropyl) disulfide, “Si-75” manufactured by Degussa
Protected mercaptosilane: coupling agent represented by the above formula (2) (n = 2, m = 3, k = 7), “NXT” manufactured by GE Silicones.

  Moreover, in each rubber composition, as a common blend, 2 parts by weight of stearic acid (“Lunac S-20” manufactured by Kao) and zinc white (“Zinc Hana Class 1” manufactured by Mitsui Mining & Mining) are used for 100 parts by weight of the rubber component. ) 2 parts by weight, anti-aging agent (Sumitomo Chemical "Antigen 6C") 2 parts, wax (Ouchi Shinsei Chemical "Sannok N") 2 parts, vulcanization accelerator (diphenyl guanidine) 0.8 weight Parts, 1.2 parts by weight of a vulcanization accelerator (“Soxinol CZ” manufactured by Sumitomo Chemical) and 1.5 parts by weight of sulfur (“Powder Sulfur” manufactured by Tsurumi Chemical) were blended.

(Evaluation)
Each rubber composition obtained was evaluated for processability, and 195 / 65R15 pneumatic tires were vulcanized and molded according to a conventional method using each rubber composition as a tread rubber. Each tire obtained was evaluated for wet braking performance, snow braking performance, wet operability and snow operability. Each evaluation method is as follows.

Processability: Mooney viscosity was measured according to JIS K6300, and displayed as an index with the value of Comparative Example 1 being 100. A smaller index indicates a lower viscosity, that is, better workability.

・ Wet braking: Four 2,000cc domestic passenger cars are equipped with the above four pneumatic tires, run on a wet road with a depth of 2-3mm, and the ABS is operated at a speed of 90km / h to decelerate to 20km / h. The braking distance was measured. The value of Comparative Example 1 is expressed as an index, which is 100. The larger the index, the shorter the braking distance and the better the wet braking performance.

Snow braking performance: Four pneumatic tires were mounted on a 2000 cc domestic passenger car, running on an icy and snowy road surface, the ABS was operated at 60 km / h, and the braking distance when decelerating to 20 km / h was measured. The value of Comparative Example 1 is expressed as an index, which is 100. The larger the index, the shorter the braking distance and the better the snow braking performance.

-Wet operability and snow operability: It was a sensory (feeling) evaluation of steering stability by a test driver, and was evaluated by a 10-point method with Comparative Example 1 as 5 points. The higher the value, the better.

  The results are as shown in Tables 1 and 2. Compared to Comparative Example 1, Comparative Example 2 in which silica was simply replaced with small particle size silica, not only showed no improvement effect on wet performance, but also snow performance and Workability was greatly deteriorated. Further, in Comparative Example 3 in which the silane coupling agent was simply replaced with protected mercaptosilane as compared with Comparative Example 1, although the snow performance improvement effect was obtained, the wet performance improvement effect was not obtained. On the other hand, in Examples 1-4, snow performance and wet performance, particularly wet performance, were significantly improved with respect to Comparative Example 1 without impairing workability. Moreover, the wet performance was further improved as it was Examples 5-9.

  In Comparative Example 4, since the glass transition point of the entire rubber component is low, the effect of improving the wet performance cannot be obtained. In Comparative Example 5, the glass transition point of the entire rubber component is too high. The performance has deteriorated significantly. Further, in Comparative Examples 6 and 7, only the wet performance and snow performance equivalent to those of Comparative Example 1 were obtained because of the small amount of silica. Moreover, in the comparative example 8, since the specific styrene butadiene rubber (A) was not used, the improvement effect of wet performance was inadequate and especially operativity was insufficient.

  The rubber composition for a pneumatic tire of the present invention can be used as a rubber constituting a tread of a pneumatic tire, and is particularly suitable for various winter tires including a snow tire.

Claims (2)

Styrene butadiene rubber (A) having a glass transition point of −35 to −25 ° C., a styrene content of 20 to 40% by weight, and a vinyl content in the butadiene part of 20 to 60% by weight of 20 to 60% by weight, Containing 80 to 40% by weight of another diene rubber (B), and 100 parts by weight of a rubber component satisfying the following formula (1):
A silica having a BET specific surface area of 210 to 300 m ² / g and a CTAB specific surface area of 160 to 300 m ² / g is blended more than 100 parts by weight and 200 parts by weight or less,
And the rubber composition for pneumatic tires formed by mix | blending 2-25 weight part with the silane coupling agent represented by following General formula (2) with respect to 100 weight part of silica.

_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 (2)
(In the formula, n is an integer of 1 to 3, m is an integer of 1 to 5, and k is an integer of 5 to 9)   A pneumatic tire having a tread made of the rubber composition according to claim 1.