JP2009001721A - Rubber composition and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition having satisfactory wear resistance and fracture property and enabling wet skid resistance and dry gripping property to be considerably enhanced. <P>SOLUTION: The rubber composition is obtained by blending 100 parts by mass of a rubber component comprising 60-95 mass% of a styrene-butadiene copolymer (A) having a weight average molecular weight (expressed in terms of polystyrene) of 300,000-4,000,000 as measured by gel permeation chromatography and 5-40 mass% of a styrene-isoprene copolymer (B) having a weight average molecular weight (expressed in terms of polystyrene) of ≥200,000 as measured by gel permeation chromatography with 10-200 parts by mass of a liquid styrene-butadiene copolymer (C) having a weight average molecular weight (expressed in terms of polystyrene) of 5,000-200,000 as measured by gel permeation chromatography. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition and a pneumatic tire using the rubber composition, and particularly excellent wet skid resistance and dry grip properties without impairing wear resistance and fracture characteristics when used for a tire tread. It is related with the rubber composition which can provide.

  In recent years, requirements for high-speed driving stability of automobiles have become more severe, and in addition to the wear resistance and fracture characteristics conventionally required for rubber materials for automobile tire treads, wet skid resistance and dry grip characteristics There is a strong demand for rubber that excels in the quality. However, it is difficult to satisfy these characteristics, and in particular, wear resistance, wet skid resistance, and dry grip properties are in a mutually contradictory relationship. The grip properties depend on the hysteresis loss characteristics of the rubber composition, and various techniques have been disclosed in the past to improve the grip properties of the rubber composition.

  For example, Japanese Patent Laid-Open No. 63-101440 (Patent Document 1) discloses a technique for blending a styrene-butadiene copolymer rubber (SBR) with a styrene-butadiene copolymer having a low molecular weight and a high bond styrene content. ing. However, the rubber composition disclosed in Japanese Patent Application Laid-Open No. 63-101440 has a problem that some low molecular weight components form a cross-link with the rubber component of the matrix and are taken into the matrix, and sufficient hysteresis loss does not occur. It was.

  On the other hand, JP-A-61-203145 (Patent Document 2) discloses a low molecular weight aromatic vinyl compound-conjugated diene compound copolymer as a rubber composition having improved heat resistance, wear resistance and road surface grip. Although a rubber composition obtained by blending a coalescence with a diene rubber has been disclosed, there is still room for improvement with respect to wet grip resistance, dry grip resistance, and wear resistance.

  In addition, there is also known a technique in which a rubber composition highly filled with a resin is applied to a tread and the adhesive effect of the resin is utilized for a tire grip. There was a problem that the performance change with respect to temperature of the rubber composition applied to the tread became large. On the other hand, Japanese Patent Application Laid-Open No. 2004-59833 (Patent Document 3) discloses a high-molecular-weight styrene-butadiene copolymer and a low-molecular-weight styrene-isoprene copolymer as rubber compositions that can utilize the adhesive effect for grips. A rubber composition blended with is disclosed.

JP 63-101440 A JP-A-61-203145 JP 2004-59833 A

  However, as a result of investigation by the present inventor, it has been found that in a method in which a large amount of a low molecular weight styrene-butadiene copolymer or a styrene-isoprene copolymer is blended with a high molecular weight styrene-butadiene copolymer, such a copolymer is used. It has been found that since the weight average molecular weight of the coalescence is as low as about tens of thousands, the hysteresis loss of the rubber composition is increased and at the same time the wear resistance and fracture characteristics of the rubber composition are reduced.

  Accordingly, an object of the present invention is to provide a rubber composition that solves the above-mentioned problems of the prior art, has good wear resistance and fracture characteristics, and can greatly improve wet skid resistance and dry grip properties. There is. Another object of the present invention is to provide a pneumatic tire that significantly improves wet skid resistance and dry grip without impairing wear resistance and fracture characteristics by using such a rubber composition in a tread. It is to provide.

  As a result of intensive studies to achieve the above object, the present inventor has found that a low-molecular-weight liquid styrene-polymer is blended with a rubber component blended with a high-molecular-weight styrene-butadiene copolymer and a high-molecular-weight styrene-isoprene copolymer. In order to complete the present invention, it has been found that blending a butadiene copolymer can greatly improve wet skid resistance and dry grip properties while ensuring sufficient wear resistance and fracture characteristics of the rubber composition. It came.

  That is, the rubber composition of the present invention was measured by 60 to 95% by mass of a styrene-butadiene copolymer (A) having a polystyrene-equivalent weight average molecular weight of 300,000 to 4,000,000 measured by gel permeation chromatography and by gel permeation chromatography. The polystyrene-reduced weight average molecular weight measured by gel permeation chromatography is 5,000 with respect to 100 parts by mass of the rubber component consisting of 5 to 40% by mass of the styrene-isoprene copolymer (B) having a polystyrene-reduced weight average molecular weight of 200,000 or more. It is characterized by comprising 10 to 200 parts by mass of ˜200,000 liquid styrene-butadiene copolymer (C). Here, the liquid styrene-butadiene copolymer (C) is liquid at room temperature (25 ° C.).

  In the rubber composition of the present invention, the amount of bound styrene of the styrene-butadiene copolymer (A) is preferably 20 to 50% by mass.

  In the rubber composition of this invention, it is preferable that the vinyl bond amount of the butadiene part of the said styrene-butadiene copolymer (A) is 30 to 60%.

  In the rubber composition of the present invention, the amount of bound styrene of the liquid styrene-butadiene copolymer (C) is preferably 20 to 70% by mass.

  In the rubber composition of the present invention, the amount of the liquid styrene-butadiene copolymer (C) is preferably 20 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

  The pneumatic tire of the present invention is characterized by using the above rubber composition in a tread.

  According to the present invention, the specific molecular weight of the rubber component containing the styrene-butadiene copolymer (A) having a specific molecular weight and the styrene-isoprene copolymer (B) having a specific molecular weight in a specific ratio. By providing a liquid styrene-butadiene copolymer (C) having the above, a rubber composition having good wear resistance and fracture characteristics and capable of greatly improving wet skid resistance and dry grip properties is provided. can do. Further, by using such a rubber composition for a tread, a pneumatic tire can be provided in which wet skid resistance and dry grip properties are greatly improved without impairing wear resistance and fracture characteristics.

  The present invention is described in detail below. The rubber composition of the present invention comprises 60 to 95% by mass of a styrene-butadiene copolymer (A) having a polystyrene-converted weight average molecular weight of 300,000 to 4,000,000 measured by gel permeation chromatography and polystyrene measured by gel permeation chromatography. The polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography is 5,000-20 with respect to 100 parts by mass of the rubber component composed of 5-40% by mass of the styrene-isoprene copolymer (B) having an equivalent weight average molecular weight of 200,000 or more. It is characterized by comprising 10 to 200 parts by mass of 10,000 liquid styrene-butadiene copolymer (C).

  In the rubber composition of the present invention, the styrene-isoprene copolymer (B) having a weight average molecular weight of 200,000 or more has higher adhesiveness than the styrene-butadiene copolymer and increases the hysteresis loss of the rubber composition. be able to. For this reason, the rubber composition of the present invention contains the styrene-isoprene copolymer (B) in a specific ratio in the styrene-butadiene copolymer (A) having a weight average molecular weight of 300,000 to 4,000,000. Thus, wet skid resistance and dry grip properties can be improved while sufficiently ensuring wear resistance and fracture characteristics. In addition, since the liquid styrene-butadiene copolymer (C) having a weight average molecular weight of 5,000 to 200,000 has a large flow loss over time, the copolymer is used with respect to 100 parts by mass of the rubber component of the rubber composition of the present invention. When (C) is blended in an amount of 10 to 200 parts by mass, the hysteresis loss of the rubber composition further increases, and wet skid resistance and dry grip properties can be greatly improved. Moreover, even if it mix | blends the said copolymer (C) with respect to the rubber component which contains the said copolymer (A) and a copolymer (B) in a specific ratio, abrasion resistance and a fracture | rupture characteristic are enough. Can be secured. Therefore, by using the rubber composition of the present invention for a tread of a pneumatic tire, high clip performance (wet skid resistance) while sufficiently ensuring the wear resistance (economic efficiency) and fracture characteristics (safety) of the tire. Compatibility and dry grip performance). Moreover, since the rubber composition of this invention has the above characteristics, it can be suitably applied to belts and various industrial rubber articles.

  The styrene-butadiene copolymer (A) used in the rubber composition of the present invention needs to have a polystyrene equivalent weight average molecular weight of 300,000 to 4,000,000 as measured by gel permeation chromatography (GPC). When the weight average molecular weight of the copolymer (A) is less than 300,000, the fracture characteristics of the rubber composition are lowered. On the other hand, when it exceeds 4 million, the viscosity of the polymerization solution becomes too high and the productivity is lowered.

  The styrene-butadiene copolymer (A) preferably has a bound styrene content of 20 to 50% by mass. If the amount of bound styrene in the copolymer (A) is less than 20% by mass, the fracture characteristics of the rubber composition are lowered, and it is difficult to satisfy wet skid resistance and other characteristics at the same time. When it exceeds%, the wear resistance of the rubber composition is lowered.

  The styrene-butadiene copolymer (A) preferably has a vinyl bond content in the butadiene portion of 30 to 60%. If the amount of vinyl bonds in the butadiene part of the copolymer (A) is less than 30%, the wet skid resistance of the rubber composition may be insufficient. On the other hand, if it exceeds 60%, the wear resistance of the rubber composition may be insufficient. May decrease.

  In the rubber composition of the present invention, the styrene-butadiene copolymer (A) is used as a rubber component. When the total amount of the rubber component is the copolymer (A), wet skid resistance and dry grip properties are obtained. Since it cannot be improved sufficiently, the rubber component of the rubber composition of the present invention needs to contain 5 to 40% by mass of the styrene-isoprene copolymer (B). When the proportion of the copolymer (B) in the rubber component of the rubber composition of the present invention is less than 5% by mass, a sufficient increase in hysteresis loss cannot be obtained, while when it exceeds 40% by mass, Destructive properties are significantly reduced.

  The styrene-isoprene copolymer (B) used in the rubber composition of the present invention needs to have a polystyrene equivalent weight average molecular weight of 200,000 or more as measured by gel permeation chromatography (GPC). When the weight average molecular weight of the copolymer (B) is less than 200,000, the fracture characteristics, abrasion resistance, wet skid resistance and dry grip properties of the rubber composition are reduced.

  Furthermore, the rubber composition of the present invention comprises a liquid styrene-butadiene copolymer (C) having a polystyrene-equivalent weight average molecular weight of 5,000 to 200,000 measured by gel permeation chromatography (GPC) with respect to 100 parts by mass of the rubber component. 10 to 200 parts by mass, and preferably 20 to 100 parts by mass. If the content of the copolymer (C) is less than 10 parts by mass, sufficient strength and dry grip properties cannot be obtained. On the other hand, if it exceeds 200 parts by mass, the Mooney viscosity of the rubber composition becomes too low, and production Sexuality will deteriorate.

  The liquid styrene-butadiene copolymer (C) used in the rubber composition of the present invention is required to have a polystyrene equivalent weight average molecular weight of 5,000 to 200,000 as measured by gel permeation chromatography (GPC). When the weight average molecular weight of the copolymer (C) is less than 5000, the fracture characteristics, abrasion resistance, wet skid resistance and dry grip properties of the rubber composition are reduced. On the other hand, when it exceeds 200,000, the wet skid resistance is reduced. And dry grip properties are reduced.

  The liquid styrene-butadiene copolymer (C) preferably has a bound styrene content of 20 to 70% by mass. If the amount of bound styrene of the copolymer (C) is less than 20% by mass, the wet skid resistance and dry grip property of the rubber composition may be insufficient. On the other hand, if the amount exceeds 70% by mass, it becomes resinous. Therefore, the rubber composition becomes hard and wet skid resistance and dry grip properties tend to decrease.

  Further, in the liquid styrene-butadiene copolymer (C), it is preferable that 60% or more of the unsaturated bonds in the butadiene portion are hydrogenated. If the hydrogenation rate of the butadiene part of the copolymer (C) is 60% or more, the effect of improving the hysteresis loss of the rubber composition at room temperature or higher is increased. On the other hand, when the hydrogenation rate of the unsaturated bond in the butadiene portion of the copolymer (C) is less than 60%, the copolymer (C) is involved in crosslinking of the rubber composition, and sufficient grip properties are obtained. There may not be.

  In the rubber composition of the present invention, the styrene-butadiene copolymer (A), the styrene-isoprene copolymer (B), and the liquid styrene-butadiene copolymer (C) constitute, for example, the respective copolymers. The monomer to be obtained is copolymerized by anionic polymerization using a lithium polymerization initiator in the presence of ether or tertiary amine in a hydrocarbon solvent. Here, the hydrocarbon solvent is not particularly limited, but cycloaliphatic hydrocarbons such as cyclohexane, methylcyclopentane, cyclooctane, propane, butane, pentane, hexane, heptane, octane, decane, etc. Aliphatic hydrocarbons, aromatic hydrocarbons such as benzene, toluene, and ethylbenzene can be used. These hydrocarbons may be used alone or in combination of two or more. Of these hydrocarbons, aliphatic hydrocarbons and alicyclic hydrocarbons are preferred.

  The lithium-based polymerization initiator is preferably an organic lithium compound. Examples of the organic lithium compound include alkyl lithium such as ethyl lithium, propyl lithium, n-butyl lithium, sec-butyl lithium, and t-butyl lithium; phenyl Aryl lithium such as lithium and tolyl lithium; Alkenyl lithium such as vinyl lithium and propenyl lithium; Alkylene dilithium such as tetramethylene dilithium, pentamethylene dilithium, hexamethylene dilithium and decamethylene dilithium; 1,3-dilithio In addition to arylene lithium such as benzene and 1,4-dilithiobenzene; 1,3,5-trilithiocyclohexane, 1,2,5-trilithionaphthalene, 1,3,5,8-tetralithiodecane, 1 , 2,3,5-tetralithio-4-hexyl-anthracene, etc. It is below. Among these, n-butyllithium, sec-butyllithium, t-butyllithium and tetramethylenedilithium are preferable, and n-butyllithium is particularly preferable. The amount of the lithium-based polymerization initiator used is determined by the polymerization rate in the reaction operation and the molecular weight of the copolymer to be produced, and is usually preferably in the range of 0.02 to 5 mg as a lithium atom per 100 g of monomer, and 0.05 to 2 mg. A range is more preferred.

  The polymerization reaction for obtaining the copolymer (A), the copolymer (B) and the copolymer (C) can be carried out by either a batch polymerization method or a continuous polymerization method. The polymerization temperature in the polymerization reaction is preferably in the range of 0 to 130 ° C. Further, the polymerization reaction can be carried out by any polymerization method such as isothermal polymerization, temperature rising polymerization and adiabatic polymerization. Furthermore, when performing the polymerization, an allene compound such as 1,2-butadiene may be added in order to prevent the formation of a gel in the reaction vessel.

  Furthermore, when hydrogenating the unsaturated bond of the butadiene part of the liquid styrene-butadiene copolymer (C), hydrogenation is performed by using the obtained copolymer (C) as an organic carboxylate or organic carboxylate. , Hydrogenation catalyst comprising a group 1-3 organometallic compound; nickel, platinum, palladium, ruthenium, rhodium metal catalyst supported on carbon, silica, diatomaceous earth, etc .; one selected from cobalt, nickel, rhodium, ruthenium complex, etc. Can be carried out by hydrogenating under 1 to 100 atmospheres of pressurized hydrogen.

  In the rubber composition of the present invention, it is preferable to further add a filler. Here, as the filler, carbon black and silica are preferable. The carbon black is preferably FEF, SRF, HAF, ISAF, or SAF grade, and more preferably HAF, ISAF, or SAF grade. On the other hand, as silica, wet silica and dry silica are preferable, and wet silica is more preferable. These fillers may be used alone or in combination of two or more.

  In addition to the styrene-butadiene copolymer (A), styrene-isoprene copolymer (B), liquid styrene-butadiene copolymer (C), filler, the rubber composition of the present invention includes, for example, aging. Additives usually used in the rubber industry such as inhibitors, silane coupling agents, vulcanization accelerators, vulcanization accelerators, vulcanizers, etc., are selected as appropriate within the range that does not impair the purpose of the present invention. Can be blended. As these compounding agents, commercially available products can be suitably used.

  The rubber composition of the present invention is obtained by kneading using a kneader such as a roll or an internal mixer, and after molding, vulcanization is performed, and the tire tread rubber, under tread, carcass, sidewall In addition to tire applications such as beads, it can also be used in anti-vibration rubber, belts, hoses, and other industrial products, but is particularly suitable as a tread rubber for tires.

  The pneumatic tire of the present invention is characterized by using the rubber composition described above for a tread. A tire using the rubber composition as a tread has a high hysteresis loss at room temperature or higher, and thus has excellent wet skid resistance and dry grip properties while ensuring sufficient wear resistance and fracture characteristics. The pneumatic tire of the present invention is not particularly limited except that the above rubber composition is used for the tread, and can be produced according to a conventional method. Moreover, as gas with which this tire is filled, inert gas, such as nitrogen, argon, helium other than normal or the air which adjusted oxygen partial pressure, can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

  Copolymer (A), copolymer (B), and copolymer (C) were synthesized by the following method, and the obtained copolymer had a bound styrene content, a vinyl bond content, and a polystyrene equivalent weight average molecular weight (Mw). ) Was measured by the following method.

(1) Bound styrene amount The bound styrene amount of the synthesized copolymer was calculated from the integral ratio of ¹ H-NMR spectrum.

(2) Vinyl Bond Amount The vinyl bond amount of the butadiene portion of the synthesized copolymer was analyzed by an infrared method (Morello method).

(3) Polystyrene equivalent weight average molecular weight (Mw)
Gel permeation chromatography [GPC: 244 type GPC manufactured by Waters, column: GMH-3, GMH-6, G6000H-6 manufactured by Toyo Soda, detector: differential refractometer, mobile phase: tetrahydrofuran], and Waters as standard substance Using a monodispersed styrene polymer manufactured by the company, a calibration curve was created by previously determining the relationship between the molecular weight of the peak of the monodispersed styrene polymer and the GPC count, and using this, a polystyrene conversion of each polymer was made. The weight average molecular weight (Mw) was determined.

<Synthesis of styrene-butadiene copolymer (A)>
Cyclohexane 3000 g, tetrahydrofuran (THF) 12 g, 1,3-butadiene 200 g and styrene 100 g were introduced into a 5 liter autoclave with a stirring blade sufficiently purged with nitrogen, and the temperature in the autoclave was adjusted to 21 ° C. Next, 0.12 g of n-butyllithium was added and polymerization was carried out for 60 minutes under a temperature rising condition, and it was confirmed that the monomer conversion rate was 99%. Thereafter, 3.5 g of 2,6-di-t-butyl-p-cresol was added as an anti-aging agent to obtain a styrene-butadiene copolymer (A). The analytical values are shown in Table 1.

<Synthesis of Styrene-Isoprene Copolymer (B)>
Cyclohexane 3000 g, tetrahydrofuran (THF) 12 g, isoprene 150 g and styrene 150 g were introduced into a 5 liter autoclave with a stirring blade sufficiently purged with nitrogen, and the temperature in the autoclave was adjusted to 21 ° C. Next, 1.00 g of n-butyllithium was added and polymerization was carried out for 60 minutes under elevated temperature conditions, and it was confirmed that the monomer conversion was 99%. Thereafter, 3.5 g of 2,6-di-t-butyl-p-cresol was added as an anti-aging agent to obtain a styrene-isoprene copolymer (B). The analytical values are shown in Table 1.

<Synthesis of liquid styrene-butadiene copolymer (C)>
The synthesis was carried out in the same manner as the styrene-butadiene copolymer (A) except that the monomer charge ratio, the amount of the polymerization initiator used, and the like were changed. The analytical values are shown in Table 1.

  Next, using the above copolymer (A), copolymer (B) and copolymer (C), a rubber composition having the formulation shown in Table 2 was prepared according to a conventional method and added under normal conditions. The vulcanized rubber obtained by vulcanization was evaluated for dry grip properties, wet skid resistance, wear resistance and fracture strength by the following methods. The results are shown in Table 2.

(4) Dry grip property and wet skid resistance A wet skid surface and a dry road surface were reproduced and evaluated by a skid tester. The dry grip property and wet skid resistance of the rubber composition of Comparative Example 1 were each expressed as an index with the value of 100. It shows that it is excellent in dry grip property and wet skid resistance, so that an index value is large.

(5) Abrasion resistance The amount of wear at a slip rate of 60% at room temperature was measured using a Ramborn type wear tester, and the reciprocal of the amount of wear of the rubber composition of Comparative Example 1 was indicated as an index. The larger the index value, the better the wear resistance.

(6) Fracture strength A tensile test was performed at room temperature in accordance with JIS K 6301, the tensile strength (Tb) was measured, and the tensile strength of the rubber composition of Comparative Example 1 was expressed as an index. The larger the index value, the better the fracture characteristics.

* 1 N- (1,3- dimethylbutyl) -N ^'- phenyl -p- phenylenediamine.
* 2 Dibenzothiazyl disulfide.
* 3 N-t-butyl-2-benzothiazolylsulfenamide.

  As is apparent from Table 1, the rubber component containing the copolymer (A) having the molecular weight defined in the present invention and the copolymer (B) having the molecular weight defined in the present invention in a proportion defined in the present invention. From the comparison with the rubber compositions of Comparative Examples 1 to 4, the rubber compositions of Examples 1 to 3 blended with the copolymer (C) having the molecular weight specified in the present invention have sufficient wear resistance and fracture characteristics. It can be seen that the dry grip property and the wet skid resistance can be greatly improved.

  On the other hand, it can be seen from the results of Comparative Examples 1 to 3 that when the total amount of the rubber component is the copolymer (A), the wet skid resistance and the dry grip property of the rubber composition cannot be sufficiently improved. Further, from the results of Comparative Examples 2-3, when the blending amount of the copolymer (C) is increased, the dry grip property and the wet skid resistance of the rubber composition are improved, but the wear resistance and fracture characteristics are greatly improved. It turns out that it will fall. Furthermore, from the results of Comparative Example 4, it can be seen that the wet skid resistance and dry grip properties of the rubber composition cannot be sufficiently improved if the copolymer (B) is included but the copolymer (C) is not included. . Furthermore, it can be seen from the results of Comparative Example 5 that when the content of the copolymer (B) in the rubber component exceeds 40% by mass, the fracture characteristics of the rubber composition are significantly reduced.

Claims (6)

  Styrene-butadiene copolymer (A) having a polystyrene equivalent weight average molecular weight of 300,000 to 4,000,000 measured by gel permeation chromatography (A) 60 to 95% by mass and a polystyrene equivalent weight average molecular weight of 200,000 or more measured by gel permeation chromatography Liquid styrene-butadiene copolymer having a polystyrene-reduced weight average molecular weight of 5,000 to 200,000 measured by gel permeation chromatography with respect to 100 parts by mass of a rubber component consisting of 5 to 40% by mass of styrene-isoprene copolymer (B). A rubber composition comprising 10 to 200 parts by mass of the coalescence (C).   2. The rubber composition according to claim 1, wherein the styrene-butadiene copolymer (A) has a bound styrene content of 20 to 50 mass%.   The rubber composition according to claim 1, wherein the butadiene portion of the styrene-butadiene copolymer (A) has a vinyl bond content of 30 to 60%.   2. The rubber composition according to claim 1, wherein the liquid styrene-butadiene copolymer (C) has an amount of bound styrene of 20 to 70% by mass.   2. The rubber composition according to claim 1, wherein an amount of the liquid styrene-butadiene copolymer (C) is 20 to 100 parts by mass with respect to 100 parts by mass of the rubber component.   A pneumatic tire using the rubber composition according to claim 1 for a tread.