Rubber composition for tires

Abstract

To provide a rubber composition for tires capable of securing good extrusion processability while achieving both an improvement in wet performance and a reduction in rolling resistance.SOLUTION: A filler containing carbon black and silica is blended with a diene rubber containing 70 mass% or more of a styrene-butadiene rubber and 5 mass% or more and 30 mass% or less of a butadiene rubber synthesized with a titanium catalyst. The total blending amount of the carbon black and the silica is 70 pts.mass or more and 130 pts.mass or less based on 100 pts.mass of the diene rubber.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition for tires intended to be used primarily in the tread portion of pneumatic tires. [Background technology]

[0002] In general pneumatic tires other than winter tires (so-called normal tires and summer tires), excellent wet performance is required when running on wet road surfaces during rainfall, etc. In addition, low rolling resistance is required to improve fuel efficiency. In particular, a rubber composition for tires used in the tread portion that comes into contact with the road surface is required to achieve both of these performances.

[0003] For example, compounding a large amount of silica is known as a method for improving wet performance (see, for example, Patent Document 1). However, simply increasing the amount of silica does not necessarily reduce rolling resistance sufficiently. Therefore, compounding silica with a large specific surface area has been considered, but when silica with a large specific surface area is compounded, the viscosity of the unvulcanized compound increases, making it more likely to cause problems such as scorching during extrusion, and there is a concern that extrusion processability will deteriorate. Therefore, measures are required to ensure good extrusion processability while simultaneously improving wet performance and reducing rolling resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-196419 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a rubber composition for tires which can ensure good extrusion processability while simultaneously improving wet performance and reducing rolling resistance. [Means for solving the problem]

[0006] The rubber composition for tires of the present invention that achieves the above-mentioned object is characterized in that a filler containing carbon black and silica is blended with a diene rubber containing 70 mass% or more of styrene-butadiene rubber and 5 mass% to 30 mass% or less of butadiene rubber synthesized using a titanium catalyst, and the total blending amount of the carbon black and the silica per 100 mass parts of the diene rubber is 70 parts by mass or more and 130 parts by mass or less. Effect of the Invention

[0007] The rubber composition for tires of the present invention has the above-mentioned composition, and therefore can ensure good extrusion processability while improving wet performance and reducing rolling resistance. In particular, by appropriately compounding the filler containing carbon black and silica, it is possible to achieve a good balance between excellent wet performance and low rolling resistance. On the other hand, by using a butadiene rubber synthesized with a titanium catalyst, it is possible to achieve good extrusion processability without impairing the above-mentioned performance.

[0008] In the rubber composition for tires of the present invention, the styrene-butadiene rubber preferably contains 80% by mass or more of solution-polymerized styrene-butadiene rubber having a vinyl content of 35% by mass or less. By containing a large amount of styrene-butadiene rubber having a low vinyl content in this way, wet performance can be more effectively improved.

[0009] In the rubber composition for tires of the present invention, it is preferable to compound two kinds of silica having different BET specific surface areas as the silica. 2 / g or more 200m 2 / g or less. In addition, the BET specific surface area of ​​the other of the two types of silica is preferably 200 m 2 / g or more. This makes it possible to more highly improve wet performance and reduce rolling resistance at the same time. The BET specific surface area is measured in accordance with ISO 5794 / 1.

[0010] The rubber composition for tires of the present invention can be suitably used in the tread portion of a pneumatic tire. A pneumatic tire using the rubber composition for tires of the present invention in the tread portion can exhibit excellent wet performance and low fuel consumption performance due to the above-mentioned rubber physical properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In the rubber composition for tires of the present invention, the rubber component is a diene rubber, and necessarily includes styrene butadiene rubber and butadiene rubber. As the styrene butadiene rubber, solution-polymerized styrene butadiene rubber or emulsion-polymerized styrene butadiene rubber, which are usually used in rubber compositions for tires, can be exemplified, but in the present invention, it is particularly preferable to use solution-polymerized styrene butadiene rubber. On the other hand, the butadiene rubber must be synthesized using a titanium catalyst. In this way, by using a solution-polymerized styrene butadiene rubber and a butadiene rubber synthesized using a titanium catalyst in combination, it is possible to reduce rolling resistance while improving wet performance, and to exhibit good extrusion processability. Note that if the butadiene rubber is synthesized using a catalyst other than a titanium catalyst (for example, a cobalt catalyst, a nickel catalyst, a neodymium catalyst, etc.), even if wet performance and low rolling performance can be ensured, extrusion processability will deteriorate, and problems such as deterioration of the sheet surface and discoloration will easily occur when processed into a rubber sheet.

[0012] The amount of the styrene butadiene rubber is 70% by mass or more, preferably 70% by mass or more and 95% by mass or less, more preferably 75% by mass or more and 90% by mass or less, in 100 parts by mass of the diene rubber. The amount of the butadiene rubber synthesized by a titanium catalyst is 5% by mass or more and 30% by mass or less, preferably 10% by mass or more and 25% by mass or less, in 100 parts by mass of the diene rubber. When the styrene butadiene rubber and the butadiene rubber synthesized by a titanium catalyst are used in combination, setting the amount as described above is advantageous for achieving both improved wet performance and reduced rolling resistance while exhibiting good extrusion processability. If the amount of the styrene butadiene rubber is less than 70% by mass, the effect of improving wet performance cannot be sufficiently obtained. If the amount of the butadiene rubber synthesized by a titanium catalyst is less than 5% by mass, the effect of improving extrusion processability cannot be sufficiently expected. If the amount of the butadiene rubber synthesized by a titanium catalyst exceeds 30% by mass, the wet performance decreases.

[0013] The above-mentioned styrene butadiene rubber may contain a solution-polymerized styrene butadiene rubber (hereinafter referred to as low-vinyl-containing SBR) having a vinyl content of preferably 35% by mass or less, more preferably 10% by mass or more and 35% by mass or less. When such a low-vinyl-containing SBR is contained, the blending amount thereof is preferably 80% by mass or more, more preferably 80% by mass or more and 95% by mass or less, in the above-mentioned styrene butadiene rubber. By containing the above-mentioned low-vinyl-containing SBR, it is advantageous to exhibit good extrusion processability while simultaneously improving wet performance and reducing rolling resistance. When the vinyl content of the above-mentioned low-vinyl-containing SBR exceeds 35% by mass, the wet performance is deteriorated. When the blending amount of the above-mentioned low-vinyl-containing SBR is less than 80% by mass, the wet performance is deteriorated. When other styrene butadiene rubber is contained in addition to the above-mentioned low-vinyl-containing SBR, the vinyl content is not particularly limited. In addition, two or more kinds of styrene butadiene rubbers corresponding to the above-mentioned low-vinyl-containing SBR may be used in combination. In this case, the total amount of the two types of low vinyl content SBR is preferably 80% by mass or more, more preferably 80% by mass or more and 95% by mass or less. The vinyl content of the styrene-butadiene rubber is measured by infrared spectroscopy (Hampton method). The increase or decrease of the vinyl content in the styrene-butadiene rubber can be appropriately adjusted by a normal method using a catalyst or the like.

[0014] The rubber composition for tires of the present invention may contain other diene rubbers in addition to the above-mentioned butadiene rubber and styrene-butadiene rubber. As the other diene rubber, rubbers that can be generally used in rubber compositions for tires can be used. The other diene rubbers can be used alone or as an arbitrary blend.

[0015] In the rubber composition for tires of the present invention, a filler containing carbon black and silica is necessarily blended with the diene rubber. By blending the filler in this way, the rubber hardness of the rubber composition can be increased, and when the rubber composition is made into a pneumatic tire, the steering stability can be excellent. The filler necessarily contains the above-mentioned carbon black and silica, but other fillers other than carbon black and silica can also be blended. Examples of other fillers include calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, and calcium sulfate. These other fillers may be used alone or in combination of two or more.

[0016] In this way, when the filler is blended, the total amount of carbon black and silica is 70 parts by mass or more and 130 parts by mass or less, preferably 80 parts by mass or more and 120 parts by mass or less, relative to 100 parts by mass of the diene rubber. If the total amount of carbon black and silica is less than 70 parts by mass, the rubber hardness is low and the steering stability cannot be sufficiently ensured. If the total amount of carbon black and silica is more than 130 parts by mass, the filler is poorly dispersed in the rubber, making extrusion processing difficult, and as a result, the rolling resistance increases. The individual amounts of carbon black and silica are not particularly limited, but the carbon black is preferably blended in an amount of 1 part by mass to 50 parts by mass, more preferably 1 part by mass to 40 parts by mass, and the silica is preferably blended in an amount of 20 parts by mass to 129 parts by mass, more preferably 40 parts by mass to 119 parts by mass. In particular, by setting the amount of silica to be blended in the above range, it is advantageous to achieve good extrusion processability while simultaneously improving wet performance and reducing rolling resistance.

[0017] The carbon black used in the present invention has an iodine adsorption of preferably 100g / kg or more, more preferably 100g / kg to 150g / kg. By making the iodine adsorption of carbon black 100g / kg or more, the physical properties of the rubber composition can be improved, and both the steering stability and the ride comfort can be achieved. If the iodine adsorption of carbon black is less than 100g / kg, both the steering stability and the ride comfort cannot be achieved. The iodine adsorption of carbon black is a value measured in accordance with JIS K6217-1.

[0018] Examples of silica used in the present invention include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. Surface-treated silica that has been surface-treated with a silane coupling agent may also be used. These may be used alone or in combination of two or more. In particular, it is preferable to use two types of silica with different BET specific surface areas in combination.

[0019] When using silica alone, its BET specific surface area is preferably 150 m 2 / g~350m 2 / g, more preferably 150m 2 / g~300m 2 When using silica alone, setting the BET specific surface area of ​​the silica within the above range is advantageous for achieving both improved wet performance and reduced rolling resistance while exhibiting good extrusion processability. In this case, the BET specific surface area of ​​the silica is preferably 150 m 2 If the BET specific surface area of ​​the silica is less than 300 m 2 If it exceeds 1 / g, fuel economy performance will decrease.

[0020] When two types of silica with different BET specific surface areas are used in combination, the BET specific surface area of ​​one of the silicas is preferably 150 m 2 / g or more 200m 2 / g or less, more preferably 150m 2 / g or more 185m 2The BET specific surface area of ​​the other silica is preferably set to 200 m 2 / g or more, more preferably 200m 2 / g or more 300m 2 The difference in the BET specific surface area of ​​the two types of silica is preferably set to 5 m 2 / g or more 90m 2 / g or less, more preferably 15m 2 / g or more 75m 2 By setting the BET specific surface area of ​​each of the two types of silica within an appropriate range in this way, it is advantageous to achieve good extrusion processability while improving wet performance and reducing rolling resistance. 2 If the BET specific surface area of ​​one of the silicas (the silica having a relatively smaller BET specific surface area) is less than 200 m 2 If the BET specific surface area of ​​the other silica (the silica with a relatively larger BET specific surface area) exceeds 200 m 2 If it is less than 1 / g, the wet performance is reduced.

[0021] When two types of silica with different BET specific surface areas are used in combination, the ratio A:B of the blending amount A of one silica (the silica with a relatively smaller BET specific surface area) to the blending amount B of the other silica (the silica with a relatively larger BET specific surface area) is preferably 99:1 to 55:45, more preferably 95:5 to 65:35. By using two types of silica in a well-balanced manner in combination in this way, the effect of using two types of silica in combination can be more effectively exhibited.

[0022] When compounding silica as described above, it is preferable to use a silane coupling agent in combination. The dispersibility of silica can be improved by the silane coupling agent. The compounding amount of the silane coupling agent is preferably 4% by mass to 20% by mass, more preferably 4% by mass to 16% by mass, and further preferably 5% by mass to 15% by mass of the compounding amount of silica. If the compounding amount of the silane coupling agent is less than 4% by mass, the dispersibility of silica cannot be sufficiently improved. If the compounding amount of the silane coupling agent exceeds 20% by mass, the rubber composition is likely to undergo premature vulcanization, and there is a risk of deterioration in moldability.

[0023] The silane coupling agent is not particularly limited as long as it can be used in rubber compositions for tires, but examples thereof include sulfur-containing silane coupling agents such as bis-(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) disulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, γ-mercaptopropyl triethoxysilane, and 3-octanoylthiopropyl triethoxysilane. Among these, silane coupling agents having a mercapto group are preferred, as they can increase the affinity with silica and improve its dispersibility. These silane coupling agents may be blended alone or in combination.

[0024] In the rubber composition for tires of the present invention, oil can be blended with the diene rubber. Examples of oil include natural oil, synthetic oil, plasticizer, and other oils that are added when preparing the rubber composition. When blending oil, the blending amount is determined based on the total of the oil added at the time of preparation and the oil extender contained in the diene rubber (hereinafter referred to as the total of the oil components). Specifically, the total of the oil components is 45% or less, preferably 20% to 40%, of the total blending amount of the carbon black and silica. By containing an appropriate amount of oil in this way, wet performance, low rolling performance, and extrusion processability can be achieved in a well-balanced manner. If the total of the oil components exceeds 45%, the rubber hardness decreases and the dry performance (especially the steering stability on a dry road surface) deteriorates. The blending amount of oil (oil added at the time of preparation of the rubber composition) excluding the oil extender contained in the diene rubber can be set to, for example, 5 parts by mass to 20 parts by mass with respect to 100 parts by mass of the diene rubber.

[0025] The rubber composition for tires of the present invention may contain various additives that are generally used in rubber compositions for tires, such as vulcanizing or crosslinking agents, vulcanization accelerators, antioxidants, plasticizers, processing aids, liquid polymers, terpene resins, and thermosetting resins, within the range that does not impair the object of the present invention. Moreover, such additives can be kneaded by a general method to prepare a rubber composition, which can be used for vulcanization or crosslinking. The amount of these additives may be a conventional amount, as long as it does not go against the object of the present invention.

[0026] As described above, the rubber composition for tires of the present invention is excellent in wet performance and low rolling resistance, and exhibits good extrusion processability during production. Therefore, the rubber composition for tires of the present invention can be suitably used in the tread portion of pneumatic tires (particularly summer tires). A pneumatic tire using the rubber composition for tires of the present invention in the tread portion can exhibit excellent wet performance and low fuel consumption performance due to the above-mentioned rubber physical properties.

[0027] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. EXAMPLES

[0028] In preparing rubber compositions for tires (Standard Example 1, Comparative Examples 1-6, Examples 1-12) having the formulations shown in Tables 1-2, with the compounding ingredients shown in Table 3 as a common formulation, the components except for sulfur and vulcanization accelerator were kneaded in a 1.7 L internal Banbury mixer for 5 minutes, then discharged from the mixer and cooled at room temperature. The resulting mixture was charged into a 1.7 L internal Banbury mixer, and the sulfur and vulcanization accelerator were added and mixed to prepare rubber compositions for tires.

[0029] In the "SBR1", "SBR2", and "SBR3" columns in Tables 1 and 2, the net amount excluding oil extenders is shown in parentheses in addition to the amount of the product. "Total filler" in Tables 1 and 2 indicates the total amount of carbon black and silica.

[0030] The obtained rubber composition for tires was used to evaluate extrusion processability by the method described below. In addition, a pneumatic tire (tire size: 225 / 45R18) using the obtained rubber composition for tires as tread rubber was vulcanized and molded, and wet performance and fuel economy were evaluated by the methods described below.

[0031] Extrusion processability Each rubber composition for tires was used to prepare an extrusion sample using a Garvey die in accordance with ASTM D 2230-77, and the appearance of each extrusion sample (sharpness of edges and smoothness of surface skin) was evaluated visually. The evaluation results were indicated as "◯" when there were no abnormalities in appearance, and "×" when defects such as edge cuts or discoloration occurred.

[0032] Wet Performance The obtained pneumatic tire was mounted on a standard rim (rim size: 225 / 45R18), inflated to an air pressure of 250 kPa, mounted on a test vehicle, and driven on a wet road surface. The braking distance was measured when braking was applied at an initial speed of 40 km / h. The evaluation results were expressed as an index using the reciprocal of the measured value, with the value of Standard Example 1 being set at 100. The higher the index value, the shorter the braking distance and the better the wet performance.

[0033] Low fuel consumption Each test tire was mounted on a wheel with a rim size of 225 / 45R18, and the rolling resistance was measured in accordance with ISO28580 using a drum testing machine with a drum diameter of 1707.6 mm under conditions of an air pressure of 250 kPa, a load of 4.8 kN, and a speed of 80 km / h. The evaluation results were expressed as an index using the reciprocal of the measured value, with standard example 1 being 100. The higher the index value, the lower the rolling resistance and the more excellent the fuel efficiency performance.

[0034] [Table 1]

[0035] [Table 2]

[0036] [Table 3]

[0037] The types of raw materials used in Tables 1 to 3 are shown below. SBR1: Solution-polymerized styrene-butadiene rubber, Zeon Corporation's NIPOL NS560 (styrene content: 41% by mass, vinyl content: 31% by mass, oil-extended product containing 20% ​​by mass of oil per 100 parts by mass of rubber component) SBR2: Solution-polymerized styrene butadiene rubber, Zeon Corporation's NIPOL NS540 (styrene content: 42% by mass, vinyl content: 29% by mass, oil-extended product containing 25% by mass of oil per 100 parts by mass of rubber component) SBR3: Solution-polymerized styrene-butadiene rubber, Asahi Kasei TUFDENE F3420 (styrene content: 36% by mass, vinyl content: 41% by mass, oil-extended product containing 25% by mass of oil per 100 parts by mass of rubber component) BR1: Butadiene rubber synthesized using titanium catalyst, BR-1203 Ti manufactured by VORONEZHSYNTHEZKAUCHUK JSC BR2: Neodymium-catalyzed butadiene rubber, BR-1243 Nd produced by VORONEZHSYNTHEZKAUCHUK JSC BR3: Butadiene rubber synthesized using a cobalt catalyst, Zeon Corporation's NIPOL BR 1220 CB1: Carbon black, Cabot Japan VULCAN 7HJ Silica 1: Evonik ULTRASIL 7000GR (BET specific surface area: 160 m 2 / g) Silica 2: Solvay ZEOSIL PREMIUM 200MP (BET specific surface area: 210 m 2 / g) Silica 3: Evonic ZEOSIL 1165MP (BET specific surface area: 115 m 2 / g) Aroma oil: VIVATEC 500 by Klaus Dhleke KG Processing aid: Struktol A50P Anti-aging agent: LANXESS VULKANOX 4020 Wax: NIPPON SEIRO OZOACE-0015A Coupling agent: Silane coupling agent, Evonik Si69 Zinc oxide: ZM Silesia Zinc Oxide Stearic acid: PALMAC 1600 from IOI Acidchem Vulcanization accelerator: Sumitomo Chemical's Soxinol D-G (DPG) Sulfur: Hosoi Chemical Industry Co., Ltd. Oil refinery sulfur

[0038] As is clear from Table 1, the rubber compositions for tires of Examples 1 to 12 exhibited improved wet performance and fuel economy performance to the same or greater extent than that of Reference Example 1, while also exhibiting good extrusion processability, thereby achieving a high degree of compatibility between these performances.

[0039] On the other hand, in Comparative Example 1, the wet performance and extrusion processability were deteriorated because the compounding amount of butadiene rubber was large. In Comparative Example 2, the fuel economy performance was deteriorated because the compounding amount of butadiene rubber was small. In Comparative Example 3, the compounding amount of silica was small, and therefore the total filler (total compounding amount of carbon black and silica) was small, and therefore the wet performance was deteriorated. In Comparative Example 4, the compounding amount of silica was large, and therefore the total filler (total compounding amount of carbon black and silica) was large, and therefore the fuel economy performance and extrusion processability were deteriorated. In Comparative Example 5, the extrusion processability was deteriorated because a butadiene rubber with a different catalyst (BR2 synthesized by a neodymium catalyst) was used. In Comparative Example 6, the extrusion processability was deteriorated because a butadiene rubber with a different catalyst (BR3 synthesized by a cobalt catalyst) was used.

Claims

1. A rubber composition for tires, comprising: a diene rubber containing 70% by mass or more of styrene-butadiene rubber and 5% by mass or more and 30% by mass or less of butadiene rubber synthesized using a titanium catalyst; a filler containing carbon black and silica is blended with the diene rubber; the total amount of the carbon black and the silica blended per 100 parts by mass of the diene rubber is 70 parts by mass or more and 130 parts by mass or less; and the styrene-butadiene rubber contains 80% by mass or more of solution-polymerized styrene-butadiene rubber having a vinyl content of 35% by mass or less.

2. 2. The rubber composition for tires according to claim 1, wherein the silica is a mixture of two types of silica having different BET specific surface areas.

3. The BET specific surface area of ​​one of the two types of silica is 150 m 2 / g or more 200m 2 The rubber composition for tires according to claim 2, wherein the viscosity is 0.1 to 1000 MPa.

4. The other of the two types of silica has a BET specific surface area of ​​200 m 2 4. The rubber composition for tires according to claim 3, wherein the viscosity is 100 / g or more.

5. A pneumatic tire comprising a tread portion comprising the rubber composition for tires according to any one of claims 1 to 4.

Images