JP2005220181A - Tire tread rubber composition and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire tread rubber composition which is suitable for tire tread for high-speed vehicles and simultaneously satisfies both excellent heat-resistance and fatigue characteristics, and to provide a high-performance pneumatic tire using the same. <P>SOLUTION: There is provided a cured tire tread rubber composition having carbon-carbon crosslinking in an amount of 20-60%, preferably 25-50%, based on the total crosslinking of the rubber. The amount of the total crosslinking is preferably 1.0×10<SP>-5</SP>to 1.0×10<SP>-4</SP>mol/cm<SP>3</SP>. The pneumatic tire is obtained by applying the tire tread rubber to the tread. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a tire tread rubber composition and a pneumatic tire using the same, and more particularly, to a tire tread rubber composition that is suitable for a tread for a high-speed vehicle tire and simultaneously satisfies excellent heat resistance and fatigue characteristics. And a high-performance pneumatic tire using the same.

  In a tread of a pneumatic tire, particularly a tread of a pneumatic tire for a high-speed competition vehicle, it is desired that the driving stability on a dry road surface during high speed running (hereinafter abbreviated as “dry grip performance”) is excellent. Patent Document 1 makes use of the high tan δ which is the merit of fine particle carbon black, and the grip performance is achieved by making the elastic modulus in the large deformation region, which is a demerit, and the elastic modulus E ′ in the high tan δ / small deformation region compatible. And a technology that achieves both ablation and wear resistance performance have been reported. In Patent Document 2, by specifying the ratio of the monosulfide bond amount to the total sulfur bond amount of the tread rubber for tires, the grip performance in a wide temperature range, the abrasion wear performance and the wear resistance performance are compatible. The technology that can be made to be reported is reported. However, the techniques reported in these patent documents have not achieved a high balance between heat resistance and fatigue characteristics.

  Further, conventionally, for the purpose of improving dry grip properties, an increase in oil components including resin and liquid polymer in tread rubber has been performed. However, since the heat generation component in the tread rubber increases when the oil component is increased, there is a problem that blow (foaming) due to high heat inside the tire and cracks due to deformation are likely to occur during running. In recent years, with the improvement in vehicle performance, the burden on the tire tread has been increasing more than ever, and it is necessary to achieve both higher heat resistance and fatigue characteristics than ever before.

If such coexistence can be achieved simply by improving the thermal stability of the crosslinking, it is possible to use a peroxide vulcanization system that provides only a thermally stable carbon-carbon crosslinking bond. As a result, fatigue characteristics are greatly reduced. In addition, the use of thiuram compounds, dithiocarbamic acid metal salts, dithiophosphoric acid metal salts, etc., that increase monosulfide as accelerators for sulfur vulcanization may be considered. It is insufficient for improving the heat resistance, which is the other characteristic required.
Japanese Patent Laid-Open No. 2003-221466 Japanese Patent Laid-Open No. 2003-213044

  As described above, in improving the dry grip property, there is currently no technology that provides both high heat resistance and fatigue properties.

  Accordingly, an object of the present invention is to provide a rubber composition for a tire tread that is suitable for a tire tread for a high-speed vehicle and satisfies both excellent heat resistance and fatigue characteristics and a high-performance pneumatic tire using the same. .

  The present inventors consider that it is not sufficient to focus on the amount of mesh of the monosulfide structure as in the prior art in order to achieve both heat resistance and fatigue characteristics at a higher level. A stable carbon-carbon cross-linking amount was measured, and the relationship between the cross-linking amount and heat resistance and fatigue characteristics was examined. It has been found that the above object can be achieved by the rubber composition, and the present invention has been completed.

  That is, the rubber composition for a tire tread of the present invention is a vulcanized rubber composition for a tire tread, wherein the ratio of the carbon-carbon cross-linking amount to the total cross-linking amount of the rubber is 20 to 60%. It is what. Here, the carbon-carbon cross-linking means that a cross-linking that cross-links the polymer chains of rubber is formed by at least one covalent bond between carbons.

The carbon-carbon cross-linking amount is preferably 25 to 50%. Moreover, it is preferable that the total amount of crosslinking is 1.0 × 10 ^{−5 to} 1.0 × 10 ⁻⁴ mol / cm ³ . Furthermore, it is preferable to contain 50 parts by weight or more of styrene-butadiene copolymer rubber and / or butadiene rubber having a vinyl bond amount of preferably 15% or more, more preferably 30% or more with respect to 100 parts by weight of the rubber component. Furthermore, the styrene content of the styrene butadiene copolymer rubber is preferably 20 to 60%.

  In addition, the present invention is a pneumatic tire characterized by applying the tire tread rubber to a tread.

  According to the present invention, a rubber composition that is suitable for a tire tread for a high-speed vehicle having excellent dry grip properties, and that can particularly improve heat resistance and improve tire durability without deteriorating dynamic fatigue characteristics. And a high-performance pneumatic tire using the same can be provided.

Hereinafter, specific modes for carrying out the present invention will be described.
(Rubber component)
Examples of the rubber component of the rubber composition of the present invention include diene rubbers such as styrene butadiene copolymer rubber (SBR), butadiene rubber (BR), natural rubber (NR), isoprene rubber (IR), chloroprene rubber (CR ), Ethylene-propylene-diene copolymer rubber (EPDM) and the like, and a styrene-butadiene copolymer having a vinyl bond amount of preferably 15% or more, more preferably 30% or more. The rubber and / or butadiene rubber is contained in an amount of 50 parts by weight or more based on 100 parts by weight of the rubber component. Thereby, heat resistance can be improved favorably.

  The rubber component according to the present invention preferably includes a styrene butadiene copolymer rubber having a styrene content of 20 to 60%. When the styrene content is less than 20%, it is difficult to obtain a desired grip force in a low temperature range and a high temperature range necessary for a high-performance tire, and when the styrene content exceeds 60%. The block rigidity is unnecessarily high, the rubber does not bite into the road surface, and the desired grip force cannot be obtained. In order to obtain the effect of the present invention remarkably, the styrene content is more preferably 30 to 45%. Such styrene-butadiene copolymer rubber may be synthesized by any synthesis method such as emulsion polymerization, solution polymerization, and the like.

  The rubber component according to the present invention includes an oil composed of an aromatic compound, a diene liquid styrene butadiene copolymer rubber or liquid butadiene rubber, a hydrogenated diene liquid styrene butadiene copolymer rubber, or a liquid butadiene rubber. What is oil-extended with at least 1 sort can be used conveniently. When the rubber component is oil-extended, it is advantageous in that kneading can be performed easily and reliably without slipping when kneading using a Banbury mixer or the like.

(Carbon-carbon cross-linking amount)
The rubber composition of the present invention has a carbon-carbon crosslinking amount of 20 to 60%, preferably 25 to 50%, and more preferably 30 to 40% with respect to the total crosslinking amount of the rubber. When the carbon-carbon cross-linking amount is less than 20%, a sufficient heat resistance level cannot be obtained. On the other hand, when the carbon-carbon cross-linking amount exceeds 60%, the fatigue characteristics are greatly deteriorated.

The total amount of crosslinking in the rubber is not particularly defined, but preferably 1.0 × 10 ⁻⁵ mol / cm ^{3 to} 1.0 × 10 ⁻⁴ mol in order to ensure flexibility and wear resistance as a tread rubber. / Cm ³ .

In the present invention, the carbon-carbon cross-linking amount (ν _c -c) and the total cross-linking amount (ν _T ) are values obtained by measurement by the following method as the cross-linking density (mol / cm ³ ). First, from a slab sheet molded and vulcanized to a thickness of 1 to 2 mm or a slice sheet of 1 to 2 mm thickness cut from a tire, a rubber piece of 2 mm in length, 2 mm in width, and 1-2 mm in height (depending on the sample thickness) And perform the following processing.

(1) A sample is put in a dry THF (tetrahydrofuran) / toluene (volume ratio 1/1) mixed solution and left to stand for 24 hours.

(2) A sample was put in a solution in which lithium aluminum hydride (LiAlH ₄ ) was excessively added to a dry THF / toluene (volume ratio 1/1) mixed solution and allowed to stand for 24 hours, and then the sample was dried in THF / toluene (volume ratio). 1/1) Wash several times with the mixed solution. The sample is again immersed in a dry THF / toluene (volume ratio 1/1) mixed solution, and an amount of methyl iodide equivalent to the solution is added. After leaving for 48 hours, the sample is washed several times with a dry THF / toluene (volume ratio 1/1) mixed solution, and then immersed in the dry THF / toluene (volume ratio 1/1) mixed solution again. The first treatment with lithium aluminum hydride (LiAlH ₄ ) breaks polysulfide bonds and disulfide bonds other than monosulfide bonds and carbon-carbon bridge bonds. Since only the monosulfide bond is cleaved by the subsequent methyl iodide treatment, the amount of the last remaining bond can be quantified as a carbon-carbon cross-linked bond.

Each of the samples (1) and (2) is subjected to a compression test of TMA in the height direction at 20 ° C. while being immersed in a solvent to obtain a compressive strain α with respect to the stress f. By substituting the obtained value into the following formula, the total cross-linking amount (ν _T ) from the network amount of the sample of (1) above, and the carbon amount from the network amount of the sample of (2) above. Carbon crosslinks (amount ν _cc ) are obtained as crosslink density (mol / cm ³ ), respectively.

  In the rubber composition of the present invention, the vulcanization accelerator is not particularly limited. However, if an example is given, a combination of a thiuram compound, a dithiocarbamate compound and a benzothiazole compound may be preferably mentioned. it can.

  Examples of the thiuram compound include tetrakis-2-ethylhexyl thiuram disulfide, tetrakis-2-isopropyl thiuram disulfide, tetrakis-dodecyl thiuram disulfide, tetrakis-benzyl thiuram disulfide and the like.

  Examples of the dithiocarbamate compound include zinc di-2-ethylhexyl dithiocarbamate, zinc dodecyldithiocarbamate, and benzyldithiocarbamate zinc.

  Furthermore, as the benzothiazole compound, 2-mercaptobenzothiazole, 4-methyl-2-mercaptobenzothiazole, dibenzothiazyl disulfide, 4,4′-dimethyldibenzothiazyl disulfide, N-cyclohexyl-2-benzothiazyl-sulfene Amide, N-cyclohexyl-4-methyl-2-benzothiazyl-sulfenamide, Nt-butyl-2-benzothiazyl-sulfenamide, Nt-butyl-4-methyl-2-benzothiazyl-sulfenamide, Nt-butyl-2-benzothiazyl-sulfenimide, Nt-butyl-4-methyl-2-benzothiazyl-sulfenimide, N, N′-dicyclohexyl-2-benzothiazyl-sulfenamide, etc. Can do.

  Among these vulcanization accelerators, a combination of a thiuram compound and a 2-mercaptobenzothiazole having a methyl group at the 4-position is preferable in that a high carbon-carbon cross-linking amount can be obtained with a relatively small amount. '-Dimethyldibenzothiazyl disulfide is most preferred.

  In the present invention, the amount of the vulcanization accelerator is not particularly specified, but even if the amount of addition is increased simply to increase the amount of carbon-carbon crosslinking, the scorch property and the bloom property at the time of unvulcanization are improved. Since there is a high possibility of problems, it should be selected as appropriate according to the type of problem.

(Carbon black)
The rubber composition for a tire tread of the present invention preferably contains carbon black having a nitrogen adsorption specific surface area of 80 to 280 m ² / g. If the nitrogen adsorption specific surface area of carbon black is less than 80 m ² / g, sufficient elastic modulus cannot be obtained and the wear resistance deteriorates. On the other hand, if it exceeds 280 m ² / g, the effect of improving grip strength and wear resistance can be expected. On the contrary, the kneading workability deteriorates, which is not preferable.

  Examples of carbon black that can be used include HAF, ISAF, SAF, and the like, and SAF is preferable from the viewpoint of coexistence of performance such as grip force on a wet road surface in a low temperature region and a wet road surface in a high temperature region or a semi-wet road surface. .

  Carbon black may be used individually by 1 type, may use 2 or more types together, and can also use a commercial item.

  As content in the rubber composition of carbon black, 70-200 weight part is preferable with respect to 100 weight part of rubber components, and 90-130 weight part is more preferable. When the content of carbon black is less than 70 parts by weight, the dry grip property and elastic modulus (E ′) of the rubber composition are not sufficient, and general characteristics such as strength are not sufficient, and the grounding property is poor. The lap time may also get worse. On the other hand, when it exceeds 200 parts by weight, the rubber composition becomes too hard, and on the contrary, the wear resistance is lowered, and the workability may be extremely deteriorated.

The rubber composition for a tire tread of the present invention preferably contains a C ₉ aromatic resin of petroleum resin and / or alkylphenol resin. Here, the C ₉ aromatic petroleum resin means a polymer of C ₉ aromatic monomer, examples of C ₉ aromatic monomer, vinyl toluene, alpha-methyl styrene, coumarone, indene, and the like. The C ₉ aromatic monomer may be used alone or in combination of two or more. Examples of the alkylphenol resins include alkylphenol-acetylene resins such as pt-butylphenol-acetylene and alkylphenol-formaldehyde resins including cresols, xylenols, pt-butylphenol, and pt-octylphenols. It is done. The softening point of these resins is preferably 60 to 150 ° C. If the softening point is less than 60 ° C, sufficient grip force on wet road surfaces and semi-wet road surfaces in a high temperature range cannot be obtained. On the other hand, if the softening point exceeds 150 ° C, the resin is not uniformly dispersed during kneading and the wear resistance is remarkably high. Since it falls, it is not preferable. It is used These C ₉ aromatic petroleum resin and alkylphenol resin alone or may be used two or more kinds.

  The compounding amount of these resins is preferably 3 to 50 parts by weight with respect to 100 parts by weight of the rubber component. When the blending amount of these resins is less than 3 parts by weight, the effect of adding the desired wet performance such as gripping force cannot be obtained. On the other hand, when the blending amount exceeds 50 parts by weight, the kneading workability is remarkably deteriorated. Therefore, it is not preferable. Moreover, it is preferable that the compounding quantity of resin is 5-40 weight part from the point that these effects become remarkable.

  Furthermore, in this invention, it is preferable that the acetone-chloroform extract of sulfuric acid is 30-270 weight part with respect to 100 weight part of rubber components. If this extract is less than 30 parts by weight or exceeds 270 parts by weight, it is not preferable because kneading workability deteriorates in spite of the fact that improvement in grip strength and wear resistance cannot be expected. Such an extracted amount is preferably 30 to 200 parts by weight from the viewpoint of both grip strength and wear resistance and kneading workability.

(Other ingredients)
Other components can be appropriately selected and used within the range not impairing the object of the present invention. For example, process oil, inorganic filler, softener, vulcanizing agent such as sulfur, vulcanizing aid, In addition to anti-aging agents, zinc oxide, stearic acid, anti-ozonants, colorants, antistatic agents, lubricants, antioxidants, coupling agents, foaming agents, foaming aids, and other additives, usually in the rubber industry The various compounding agents etc. which are used are mentioned. These can use a commercial item suitably.

  The oil content of process oil is not particularly limited and can be appropriately selected according to the purpose. Diene rubber and the like are preferred. If the rubber composition contains an oil such as process oil, the fluidity of the rubber composition can be controlled, the viscosity of the rubber composition before vulcanization is reduced, and the fluidity is increased. This is advantageous in that it can be extruded very well.

  The content of the oil component such as process oil in the rubber composition is 35 to 200 parts by weight with respect to 100 parts by weight of the rubber component including the oil extended part when the rubber component is oil extended. The amount is preferably 40 to 150 parts by weight. If the content of oil such as process oil is less than 35 parts by weight, processability may be deteriorated (Mooney viscosity of unvulcanized rubber will be extremely high), and dry grip properties may be deteriorated. On the other hand, if it exceeds 200 parts by weight, the processability may be deteriorated (the Mooney viscosity of the unvulcanized rubber composition may be extremely low), or the rubber may be too soft to deteriorate the wear resistance. is there.

(Manufacture of rubber composition)
The rubber composition of the present invention is obtained by kneading, heating, extruding, vulcanizing, etc., the rubber component, the resin, the carbon black, and the other components appropriately selected as necessary. Can be manufactured.

  The kneading conditions are not particularly limited, and various conditions such as the input volume to the kneading apparatus, the rotational speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of the kneading apparatus, and the like depend on the purpose. Can be selected as appropriate. Examples of the kneading apparatus include a Banbury mixer, an intermix, a kneader and the like that are usually used for kneading a rubber composition.

  The heating conditions are not particularly limited, and various conditions such as the heating temperature, the heating time, and the heating apparatus can be appropriately selected according to the purpose. As a heating apparatus, the roll machine etc. which are normally used for the heating of a rubber composition are mentioned, for example.

  Extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion apparatus, and extrusion temperature can be appropriately selected according to the purpose. As an extrusion apparatus, the extruder etc. which are normally used for extrusion of the rubber composition for tires are mentioned, for example. The extrusion temperature can be determined as appropriate.

  There is no restriction | limiting in particular about the apparatus, system, conditions, etc. which perform a vulcanization | cure, According to the objective, it can select suitably. Examples of the vulcanizing apparatus include a molding vulcanizer using a mold usually used for vulcanizing a rubber composition for tires. As a vulcanization condition, the temperature is usually about 100 to 190 ° C.

(Use)
The rubber composition of the present invention is suitable for high-performance tire treads, and can also be used for tire treads for high-speed racing vehicles such as circuit running, and is particularly preferably used for the tires of the present invention described below. it can.

(tire)
The tire of the present invention is obtained by using the rubber composition of the present invention for a tread. The tire of the present invention is not particularly limited except that the rubber composition of the present invention is used for a tread, and a known tire structure and material can be employed as it is.

  As an example of a tire, although not shown, a pair of bead cores, a carcass connected in a toroid shape between the bead cores, a belt for tightening a crown portion of the carcass, and a belt are disposed on the belt. Preferable examples include tires having tread rubber. The tire of the present invention may have a radial structure or a bias structure. In addition, nitrogen etc. are mentioned other than air as gas with which the tire of this invention is filled.

  The tread structure is not particularly limited, and may be a single-layer structure or a multi-layer structure. An upper cap portion that directly contacts the road surface and an inner side of the tire of the cap portion are adjacent to the tire. It is also possible to have a so-called cap-base structure composed of a lower-layer base portion disposed in a row. In this case, in the present invention, at least the cap portion is formed of the rubber composition of the present invention.

  The tire of the present invention is not particularly limited with respect to its production method. For example, first, the rubber composition of the present invention was prepared, and the obtained rubber composition was previously attached to the crown portion of the raw tire case. Affix on the unvulcanized base. Next, it can be produced by vulcanization molding with a predetermined mold under a predetermined temperature and pressure.

Hereinafter, the present invention will be described based on examples and comparative examples.
(Examples 1-9 and Comparative Examples 1-7)
Various rubber compositions for tire treads were kneaded and blended using a Banbury mixer according to the formulation (parts by weight) shown in Table 1 and Table 2 below. The resulting rubber composition for tire treads is vulcanized at 145 ° C. for 45 minutes, and then subjected to constant stress measurement with a flexometer described in JIS K6265. The fatigue time was measured. Further, the number of times of durability was measured by a dematcher test at room temperature. The values obtained by indexing the values of Comparative Example 1 and Comparative Example 5 as 100 are shown.

  Further, each rubber composition was subjected to network analysis by the above-described method to obtain a crosslinking density. The CC cross-linking ratio (carbon-carbon cross-linking amount) in Tables 1 and 2 was obtained according to the formula (network amount of carbon-carbon cross-linking / total cross-linking network amount) × 100.

  A JY tire (size: 225 / 40R18) was prototyped using a part of the rubber composition, and a tread for a competition tire was formed from the rubber composition. About the rubber composition used for the tread of each competition tire, heat fatigue resistance was evaluated as follows. The results are shown in Tables 1 and 2 below.

<Heat resistance fatigue>
The test tire was mounted on a competition vehicle and traveled on a circuit. After the circuit traveled, the inside and appearance of the tire were observed and evaluated according to the following criteria.
0 ... No blow chunks are generated.-1 ... Blow inside is observed within half the tread thickness.-2 ... Blow inside is half of the tread. State observed in the range exceeding -3 ... State where blow is observed inside and there is a crack of 0.5 mm or more -4 ... State where there is a crack outside

＊１ 日本合成ゴム（株）製 ０１２０（スチレン含有率３５％、ビニル結合量１６％、３５％アロマ油展）
＊２ 旭化成（株）製 タフデン４３５０（スチレン含有率３９％、ビニル結合量３８％、５０％アロマ油展）
＊３ ＳＡＦ（Ｎ₂ＳＡ １５０ｍ²／ｇ）
＊４ Ｃ₉芳香族樹脂 日本石油化学（株）製
＊５ アルキルフェノール樹脂
＊６ Ｎ−ｔ−ブチル−２−ベンゾチアジル−スルフェンアミド
＊７ テトラキス−２−エチルヘキシルチウラムジスルフィド
＊８ ビス（４−メチルジベンゾチアゾリル−２）−ジスルフィド

* 1 Nippon Synthetic Rubber Co., Ltd. 0120 (styrene content 35%, vinyl bond 16%, 35% aroma oil exhibition)
* 2 Toughden 4350 manufactured by Asahi Kasei Corporation (styrene content 39%, vinyl bond 38%, 50% aroma oil exhibition)
* 3 SAF (N ₂ SA 150m ² / g)
* 4 C ₉ aromatic resin * 5 Alkylphenol resin * 6 Nt-butyl-2-benzothiazyl-sulfenamide * 7 Tetrakis-2-ethylhexylthiuram disulfide * 8 Bis (4-methyldibenzo) Thiazolyl-2) -disulfide

  From the results shown in Tables 1 and 2, it can be seen that high heat resistance can be obtained while maintaining fatigue properties by increasing the amount of carbon-carbon crosslinks. Moreover, it can be seen from the test results of the heat fatigue resistance in an actual vehicle that the generation of blows is suppressed and the growth of cracks is suppressed as the amount of carbon-carbon cross-linking increases.

Claims (7)

  A rubber composition for a tire tread, which is a vulcanized tire tread, wherein the ratio of the carbon-carbon cross-linking amount to the total cross-linking amount of the rubber is 20 to 60%.   The rubber composition for a tire tread according to claim 1, wherein a ratio of the carbon-carbon cross-linking amount is 25 to 50%. Total amount of crosslinking is 1.0 × 10 ^-5 ~1.0 × 10 ^-4 mol / cm ³ in a claim 1 or 2 for a tire tread rubber composition.   The tire tread according to any one of claims 1 to 3, comprising 50 parts by weight or more of styrene-butadiene copolymer rubber and / or butadiene rubber having a vinyl bond amount of 15% or more with respect to 100 parts by weight of the rubber component. Rubber composition.   The rubber composition for a tire tread according to claim 4, wherein the vinyl bond amount is 30% or more.   The rubber composition for a tire tread according to claim 4 or 5, wherein the styrene-butadiene copolymer rubber has a styrene content of 20 to 60%.   A pneumatic tire, wherein the tire tread rubber according to any one of claims 1 to 6 is applied to a tread.