Tire rubber composition, tire rubber material, and tire

Abstract

[Problem] To provide a tire rubber material that has an excellent balance of wear resistance, breaking strength, and fatigue crack resistance, a tire rubber composition that is suitable for production of the tire rubber material, and a tire that includes the tire rubber material. [Solution] A tire rubber composition according to the present invention includes 5–90 parts by mass of a hydrophilic fumed silica and 1.5–30 parts by mass of a silane coupling agent per 100 parts by mass of a synthetic rubber. The BET specific surface area Sf (m2 / g) of the hydrophilic fumed silica and the hydrophilic fumed silica content Cf (parts by mass) per 100 parts by mass of the synthetic rubber satisfy the following relationship. 4,500≤Sf×Cf≤35,000

Description

Rubber composition for tires, rubber material for tires, and tires

[0001] The present invention relates to a rubber composition for tires, a rubber material for tires, and tires. Specifically, the present invention relates to a rubber material for tires that is particularly excellent in breaking strength, abrasion resistance, and fatigue crack resistance, and a composition suitable for producing the rubber material for tires.

[0002] In recent years, with increasing interest in automobile safety, there has been an increasing demand for not only low fuel consumption but also driving stability. To meet this demand, there has been a demand for tires that satisfy the following performance requirements: low heat buildup with reduced rolling resistance, driving stability on both wet and dry road surfaces, and high wear resistance. In response to these demands, improvements have been made to reinforcing fillers and rubber components.

[0003] Carbon black has traditionally been used as a reinforcing filler because it can impart high abrasion resistance to rubber materials for tires. However, it is difficult to obtain rubber materials for tires that have a high level of balance between wet grip performance, abrasion resistance, and fuel economy by using carbon black alone. To address this problem, wet silica has been compounded in place of carbon black. However, it is known that when wet silica is used as a filler, the amount of carbon black compounded is relatively reduced, inevitably resulting in a decrease in the fracture strength and abrasion resistance of rubber materials for tires. In addition, wet silica has poor dispersibility in rubber, which increases the Mooney viscosity of rubber materials for tires during kneading, resulting in poor processability in extrusion molding.

[0004] Patent Documents 1 and 2 propose rubber materials for tires that contain a rubber component, carbon black and wet silica as fillers, and an inorganic compound powder, for the purpose of obtaining a rubber material for tires that is excellent in fuel economy and wet grip performance without reducing abrasion resistance.

[0005] However, the rubber materials for tires described in Patent Documents 1 and 2 need to be blended with a relatively large amount of inorganic compound powder in order to fully achieve the effects of improving wet grip performance and fuel economy. In such cases, abrasion resistance tends to be reduced. Therefore, a rubber material for tires having a better balance of abrasion resistance, fuel economy, and wet grip performance has not yet been obtained.

[0006] Patent Document 3 proposes a rubber material for tires that has improved abrasion resistance and wet grip performance by using, together with a diene rubber component and wet silica, carbon black with specified properties calculated from two-dimensional projection image analysis of aggregates and DBP, N2SA, etc. However, although abrasion resistance and wet grip performance are improved, fuel economy is not fully satisfactory.

[0007] Furthermore, tires used on automobiles are subjected to a certain load due to the weight of the vehicle, the load being transported, etc. Therefore, the tires are required to have sufficient breaking strength and fatigue crack resistance to withstand the applied load.

[0008] Patent Document 4 proposes a rubber composition in which the hydrogen content of carbon black as a reinforcing filler is reduced, and describes that this rubber composition can improve fatigue crack resistance.

[0009] JP 2005-213353 A JP 2018-150420 A JP 2012-158661 A WO 2016 / 024397

[0010] However, the rubber materials for tires described in Patent Documents 1 to 3 have not been evaluated at least with respect to fatigue crack resistance.

[0011] Furthermore, although the rubber material for tires described in Patent Document 4 has been evaluated for abrasion resistance and fatigue crack resistance, the present inventors have found that the abrasion resistance and fatigue crack resistance of the rubber material for tires are insufficient.

[0012] The present invention has been made in view of the above circumstances, and has an object to provide a rubber material for tires having an excellent balance of abrasion resistance, breaking strength, and fatigue crack resistance, a rubber composition for tires suitable for producing the rubber material for tires, and a tire including the rubber material for tires.

[0013] The aspects of the present invention are as follows.

[0014] [1] A rubber composition for a tire, comprising 5 parts by mass or more and 90 parts by mass or less of hydrophilic fumed silica and 1.5 parts by mass or more and 30 parts by mass or less of a silane coupling agent per 100 parts by mass of synthetic rubber, wherein the BET specific surface area Sf (m 2 / g) and the content Cf (parts by mass) of hydrophilic fumed silica per 100 parts by mass of synthetic rubber satisfy the following relationship: 4,500≦Sf×Cf≦35,000 [2] The BET specific surface area Sf of the hydrophilic fumed silica is 180 m 2 / g or more 500m 2 / g or less.

[0015] [3] A rubber material for a tire obtained by vulcanizing the rubber composition for a tire according to [1] or [2]. [4] The rubber material for a tire according to [3], which has a tear strength TS of 18 kN / m or more.

[0016] [5] A tire including a tire component made of the rubber material for a tire according to [3] or [4].

[0017] According to the present invention, it is possible to provide a rubber material for tires having an excellent balance of abrasion resistance, breaking strength, and fatigue crack resistance, a rubber composition for tires suitable for producing the rubber material for tires, and a tire including the rubber material for tires.

[0018] The present invention will be described in detail below based on specific embodiments in the following order: 1. Rubber composition for tires 1.1. Synthetic rubber 1.2. Hydrophilic fumed silica 1.3. Silane coupling agent 1.4. Other components 2. Method for producing rubber composition for tires 3. Rubber material for tires

[0019] (1. Rubber Composition for Tire) The rubber composition for tire according to the present embodiment is a kneaded product used to obtain a rubber material for tire, which will be described later. The rubber composition for tire contains synthetic rubber, hydrophilic fumed silica, and a silane coupling agent.

[0020] (1.1. Synthetic Rubber) Examples of synthetic rubbers contained in the rubber composition for tires according to this embodiment include isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). These synthetic rubbers may be used alone or in combination of two or more. In this embodiment, SBR and BR are preferred as synthetic rubbers.

[0021] The SBR is not particularly limited, and examples thereof include unmodified solution-polymerized SBR (S-SBR), unmodified emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR).

[0022] For example, the content of SBR in the synthetic rubber (100 parts by mass) contained in the rubber composition for tires is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, because this provides excellent processability during extrusion. Also, the content of SBR is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, because this can suppress heat generation in the rubber material for tires.

[0023] The BR is not particularly limited, and for example, BR containing syndiotactic polybutadiene crystals can be used. Examples of BR products containing syndiotactic polybutadiene crystals include high-cis BR such as BR1220 manufactured by Zeon Corporation and BR130B and BR150B manufactured by Ube Industries, Ltd., and VCR412 and VCR617 manufactured by Ube Industries, Ltd.

[0024] For example, the content of BR in the synthetic rubber (100 parts by mass) contained in the rubber composition for tires is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, because this improves abrasion resistance, and the content of BR is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, because this can suppress heat generation in the rubber material for tires.

[0025] (1.2. Hydrophilic fumed silica) Fumed silica is fine particle silicon dioxide produced by high-temperature hydrolysis of silicon tetrachloride in an oxyhydrogen flame. Therefore, the production method of fumed silica is different from that of wet silica, and the primary particle size of the primary aggregates (smallest constituents) is smaller than that of wet silica, and the nitrogen adsorption BET specific surface area is larger. The particles of fumed silica are aggregated and fused in a beaded shape, forming bulky aggregates. In other words, fumed silica is distinguished from wet silica.

[0026] Fumed silica is divided into hydrophilic and hydrophobic fumed silica based on its properties toward water. Fumed silica has silanol groups on its surface. These silanol groups are chemically active and particularly reactive with water. Therefore, surface treatment (hydrophobic treatment) is sometimes performed to reduce the reactivity with water by reacting the silanol groups with other substances. Hydrophobically treated fumed silica is called hydrophobic fumed silica, while untreated fumed silica is called hydrophilic fumed silica.

[0027] In this embodiment, hydrophobic fumed silica and hydrophilic fumed silica are distinguished by the degree of modified hydrophobicity (M value) shown below. The degree of modified hydrophobicity (M value) is a value obtained by a measurement method utilizing the fact that hydrophobic fumed silica floats in water but is completely suspended in methanol. The method described in the examples of WO 2004 / 099075 can be used to measure the M value. When hydrophobic fumed silica and hydrophilic fumed silica are represented by the M value, hydrophobic fumed silica has an M value of 1 or more, and hydrophilic fumed silica has an M value of less than 1.

[0028] The fumed silica contained in the rubber composition for a tire according to the present embodiment is hydrophilic fumed silica. As will be described later, it is believed that hydrophilic fumed silica is more likely to form a structure attributable to fumed silica than hydrophobic fumed silica. The presence of such a structure in the rubber material for a tire obtained by vulcanizing the rubber composition for a tire is believed to improve the abrasion resistance of the rubber material for a tire. On the other hand, hydrophobic fumed silica has less of such a structure, and the improvement in abrasion resistance tends to be insufficient.

[0029] In this embodiment, the tap density of the hydrophilic fumed silica may be, for example, 45 g / L or more and 400 g / L or less. From the viewpoint of the production cost of the rubber composition for a tire, it is preferable that the tap density of the hydrophilic fumed silica is relatively low, and from the viewpoint of productivity, it is preferable that the tap density of the hydrophilic fumed silica is relatively high.

[0030] When the tap density of the hydrophilic fumed silica is low, the hydrophilic fumed silica is bulky, so that in order to uniformly disperse it in the rubber composition for a tire, it is necessary to divide the compounding amount and add it multiple times, which tends to result in poor productivity.On the other hand, when the tap density of the hydrophilic fumed silica is high, a compression treatment is required to increase the tap density of the hydrophilic fumed silica, which requires an extra step and tends to increase the production cost.

[0031] In this embodiment, the BET specific surface area of ​​the hydrophilic fumed silica is 180 m or less in a range that satisfies the relationship described below. 2 / g or more, 200m 2 / g or more, 250m 2 / g or more, 300m 2 / g or more, 350m 2 / g or more. By ensuring that the BET specific surface area of ​​the hydrophilic fumed silica is within the above range, the number of silanol groups in the hydrophilic fumed silica that serve as reaction sites with synthetic rubber or a silane coupling agent can be sufficiently secured. As a result, the hydrophilic fumed silica and synthetic rubber can be well mixed.

[0032] The upper limit of the BET specific surface area of ​​the hydrophilic fumed silica is not particularly limited, but may be, for example, 500 m 2 / g. If the BET specific surface area of ​​the hydrophilic fumed silica is too small, the flame temperature during production of the fumed silica must be increased, which tends to result in the loss of the structure unique to fumed silica and the inability to produce fumed silica stably. If the BET specific surface area of ​​the hydrophilic fumed silica is too large, it tends to result in the inability to produce fumed silica stably.

[0033] In the rubber composition for tires, the content of hydrophilic fumed silica is 5 parts by mass or more and 90 parts by mass or less per 100 parts by mass of synthetic rubber, within the range that satisfies the relationship described below. By setting the content of hydrophilic fumed silica within the above range, a rubber material for tires having excellent abrasion resistance can be easily obtained.

[0034] In the rubber composition for tires, the content of hydrophilic fumed silica is more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of synthetic rubber, while the content of hydrophilic fumed silica is more preferably 90 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of synthetic rubber.

[0035] If the content of hydrophilic fumed silica is too low, the abrasion resistance of the resulting tire rubber material tends to be insufficient, whereas if the content of hydrophilic fumed silica is too high, the hydrophilic fumed silica is not sufficiently dispersed in the synthetic rubber, and a good kneaded product tends to be difficult to obtain.

[0036] In this embodiment, the BET specific surface area of ​​the hydrophilic fumed silica contained in the rubber composition for tires is Sf (m 2 / g), and the content of hydrophilic fumed silica per 100 parts by mass of synthetic rubber contained in the rubber composition for tires is Cf (parts by mass), Sf and Cf satisfy the following relationship: 4,500≦Sf×Cf≦35,000

[0037] When the hydrophilic fumed silica contained in the rubber composition for tires satisfies the above relationship, the above-mentioned effects are enhanced, and the rubber material for tires can achieve good breaking strength, abrasion resistance, and fatigue crack resistance all at the same time.

[0038] In this embodiment, Sf×Cf is preferably 6,000 or more and 25,000 or less, and more preferably 9,000 or more and 15,000 or less.

[0039] (1.3. Silane Coupling Agent) When a silane coupling agent is contained in a rubber composition for a tire, a crosslinked structure between the hydrophobic synthetic rubber and the hydrophilic fumed silica is easily formed via the silane coupling agent. As a result, the dispersibility of the hydrophilic fumed silica in the rubber composition for a tire can be improved, and the abrasion resistance of the rubber material for a tire can be improved.

[0040] The silane coupling agent is preferably a sulfur-containing silane coupling agent, such as bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and mercapto-thiocarboxylate oligomer.

[0041] In this embodiment, from the viewpoint of the fatigue crack resistance of the tire rubber material, the silane coupling agent is preferably a sulfide-based silane coupling agent such as bis-(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, or 3-trimethoxysilylpropylbenzothiazole tetrasulfide. Of these, bis-(3-triethoxysilylpropyl)tetrasulfide is preferred.

[0042] In the rubber composition for tires, the content of the silane coupling agent is 1.5 parts by mass or more and 30 parts by mass or less per 100 parts by mass of synthetic rubber. If the content of the silane coupling agent is too low, the dispersibility of the hydrophilic fumed silica in the rubber composition for tires tends to be insufficient. If the content of the silane coupling agent is too high, the silane coupling agents tend to condense with each other, and the resulting rubber material for tires tends to have insufficient wear resistance.

[0043] In the rubber composition for tires, the content of the silane coupling agent is more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, per 100 parts by mass of synthetic rubber, while the content of the silane coupling agent is more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of synthetic rubber.

[0044] Furthermore, within the range of the content of the silane coupling agent relative to 100 parts by mass of synthetic rubber, it is preferable to increase the content of the silane coupling agent relatively as the BET specific surface area of ​​the hydrophilic fumed silica increases. This is because sufficient reaction points with the hydrophilic fumed silica can be secured. Specifically, the silane coupling agent is added in an amount of 0.33 to 1 mg / m relative to the specific surface area of ​​the silica to be added. 2 It is particularly preferable to add it in the range of

[0045] In the rubber composition for tires, by satisfying the above-mentioned relationships and setting the contents of the synthetic rubber, hydrophilic fumed silica, and silane coupling agent within the above-mentioned ranges, it is possible to easily obtain a rubber material for tires that can achieve good fatigue crack resistance in addition to good abrasion resistance.

[0046] (1.4. Other Components) In this embodiment, the rubber composition for a tire may contain components that are blended into rubber compositions for a tire, in addition to the above-described components (synthetic rubber, hydrophilic fumed silica, and silane coupling agent). An example of such a component is a lubricant. When the rubber composition for a tire contains a lubricant, the kneadability of the rubber composition for a tire is improved.

[0047] Examples of lubricants include stearic acid and process oil. A lubricant may be used alone, or two or more types may be used in combination. Examples of process oils include aromatic oil, paraffin oil, naphthenic oil, etc. These may be used alone, or two or more types may be used in combination.

[0048] The amount of lubricant blended is not limited as long as the effects of the present invention can be obtained. For example, the amount of lubricant blended is preferably 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of synthetic rubber. Furthermore, the amount of lubricant blended is more preferably 2 parts by mass or more and even more preferably 3 parts by mass or more per 100 parts by mass of synthetic rubber. On the other hand, the amount of lubricant blended is more preferably 35 parts by mass or less and even more preferably 30 parts by mass or less per 100 parts by mass of synthetic rubber.

[0049] If the amount of lubricant is too small, the rubber composition for tires may have poor kneadability, and the abrasion resistance of the resulting rubber material for tires may not be sufficiently improved.If the amount of lubricant is too large, shear may not be applied during kneading, and the hydrophilic fumed silica may not be sufficiently dispersed in the synthetic rubber.

[0050] Furthermore, the rubber composition for a tire may contain a reinforcing filler other than hydrophilic fumed silica. Examples of reinforcing fillers include carbon black, wet silica, clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, and titanium oxide. From the viewpoint of the properties of the rubber material for a tire, it is preferable that the content of reinforcing fillers other than hydrophilic fumed silica in the rubber composition for a tire is small. On the other hand, since fumed silica is more expensive than other reinforcing fillers, from the viewpoint of cost, the rubber composition for a tire may contain other reinforcing fillers within a range in which the effects of the present invention can be obtained.

[0051] In the present embodiment, the rubber composition for a tire may contain at least one selected from carbon black and wet silica as a reinforcing filler other than hydrophilic fumed silica.

[0052] The contents of carbon black and wet silica may be set in consideration of costs within a range that achieves the effects of the present invention. When a reinforcing filler is blended, an appropriate amount of filler coupling agent may also be blended depending on the reinforcing filler to be blended.

[0053] Furthermore, the rubber composition for a tire may contain various additives such as zinc oxide, an antioxidant, a plasticizer, a processing aid, a liquid polymer, and a thermosetting resin. The amounts of these additives to be blended are not limited as long as the effects of the present invention can be obtained, and may be general amounts. On the other hand, the rubber composition for a tire according to this embodiment does not need to contain a diol.

[0054] (2. Method for producing rubber composition for tire) The rubber composition for tire according to the present embodiment is obtained by kneading the above-described synthetic rubber, the above-described hydrophilic fumed silica, the above-described silane coupling agent, and, if necessary, other components.

[0055] In this embodiment, the rubber composition for a tire can be obtained by simultaneously or sequentially adding and kneading the above-mentioned components into a known kneading device such as a Banbury mixer or a kneader. The kneading conditions may be set so that the components are sufficiently kneaded.

[0056] (3. Rubber Material for Tire) The rubber material for tire according to this embodiment is a material obtained by vulcanizing the above-mentioned rubber composition for tire. Therefore, the components contained in the rubber material for tire and their contents are the same as the types and contents of the components (synthetic rubber, hydrophilic fumed silica, silane coupling agent, etc.) contained in the above-mentioned rubber composition for tire.

[0057] A tire rubber material containing only carbon black or wet silica as a reinforcing filler has a structure in which the rubber component and the carbon black or silica are crosslinked via sulfur, or a structure in which the rubber component and the carbon black or silica are crosslinked via a silane coupling agent, or the like.

[0058] On the other hand, the rubber material for a tire according to this embodiment contains hydrophilic fumed silica derived from the above-mentioned rubber composition for a tire. In this rubber material for a tire, it is believed that a structure resulting from the hydrophilic fumed silica exists in addition to a structure in which synthetic rubber and hydrophilic fumed silica are crosslinked via sulfur and a structure in which synthetic rubber and hydrophilic fumed silica are crosslinked via a silane coupling agent.

[0059] It is believed that this structure breaks and reconnects when stress is applied to the tire rubber material, resulting in the stress being dispersed and the wear resistance of the tire rubber material being improved.

[0060] It should be noted that the present inventors have confirmed that the above-mentioned effect is reduced in the case of hydrophobic fumed silica.

[0061] The tear strength TS of the tire rubber material is preferably 18 kN / m or more, more preferably 21 kN / m or more, and even more preferably 30 kN / m or more. There is no particular upper limit to the tear strength, but it is, for example, 200 kN / m.

[0062] The tear strength TS can be measured in accordance with JIS K6252-1. The curve showing the change in tear force obtained by the measurement is analyzed in accordance with JIS K6274, and the tear strength TS can be calculated from the analysis results. The detailed measurement method will be described in the examples.

[0063] The A hardness of the rubber material for tires is preferably not less than 55 and not more than 72. When the A hardness of the rubber material for tires is within the above range, it can be suitably applied to various types of tires.

[0064] As described above, the rubber material for a tire according to the present embodiment can exhibit a high level of well-balanced breaking strength, abrasion resistance, and fatigue crack resistance, and therefore can be suitably used for various tire components, particularly for the tread, base tread, sidewall, clinch, etc.

[0065] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention.

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0067] (Preparation of Rubber Composition for Tire) The following components (A-1) to (D-4) were charged into a 0.6 L volume Plastomill (Model BR600 manufactured by Toyo Seiki Seisakusho) so that the compounding amounts per 100 parts by mass of the total of synthetic rubbers (A-1) and (A-2) were as shown in Table 1. After charging, the rotor rotation speed was adjusted to be in the range of 20 to 100 rpm, and the kneaded mixture was kneaded for about 15 minutes while the rotation speed was adjusted so that the temperature of the kneaded mixture was in the range of 140 to 170°C. After kneading was completed, the mixture was cooled to room temperature and removed to obtain a kneaded mixture.

[0068] (A) Synthetic rubber (A-1) SBR (HPR850, manufactured by ENEOS Materials Corporation) (A-2) BR (BR01, manufactured by ENEOS Materials Corporation) (B) Filler (B-1) Carbon black (SEAT 6, manufactured by Tokai Carbon Co., Ltd., nitrogen adsorption BET specific surface area: 119 m 2 / g, tap density: 400 g / L) (B-2) Wet silica (manufactured by Tosoh Silica Corporation, Nipsil AQ, nitrogen adsorption BET specific surface area: 200 m 2 / g, tap density: 300 g / L) (B-3) Hydrophilic fumed silica (Tokuyama Corporation, Reolosil QS-30C, nitrogen adsorption BET specific surface area: 300 m 2 / g, tap density: 100g / L) (C) Silane coupling agent (C-1) Bis-(3-triethoxysilylpropyl)tetrasulfide (Si69, manufactured by EVONIK Corporation) (D) Other components (D-1) Lubricant (Stearic acid: Beads Stearic Acid YR, manufactured by NOF Corporation) (D-2) Process oil (Aromax 3 (TDAE Oil), manufactured by Fuji Kosan Co., Ltd.) (D-3) Antioxidant (Ozonone 6C, manufactured by Seiko Chemical Co., Ltd.) (D-4) Lubricant (Zinc oxide: Zinc oxide type 3, manufactured by Seido Chemical Industry Co., Ltd.)

[0069] The nitrogen adsorption BET specific surface area of ​​each of the fillers (B-1) to (B-3) was measured by the nitrogen adsorption BET method using a BELSOP MINI X manufactured by Microtrac.

[0070] To the obtained kneaded mixture, (D-5) to (D-7) shown below were added in the amounts shown in Table 1 relative to a total of 100 parts by mass of synthetic rubbers (A-1) and (A-2), and the mixture was mixed using a 6-inch roll tester to obtain a rubber composition for a tire. The amount of sulfur added was set in consideration of the amount of sulfur contained in other added components.

[0071] (D) Other Components (D-5) Sulfur (Kinkaji Oil-Filled Fine Sulfur, manufactured by Tsurumi Chemical Industry Co., Ltd.) (D-6) Vulcanization Accelerator (N-Cyclohexyl-2-benzothiazolesulfenamide (CBS): manufactured by Sanshin Chemical Industry Co., Ltd., Suncerer CM-G) (D-7) Vulcanization Accelerator (1,3-Diphenylguanidine (DPG): manufactured by Sanshin Chemical Industry Co., Ltd., Suncerer D-G)

[0072] The BET specific surface area Sf of the hydrophilic fumed silica and the content Cf were used to calculate Sf×Cf. The results are shown in Table 1.

[0073]

[0074] (Preparation of tire rubber material) Subsequently, the obtained tire rubber composition was press-vulcanized at 170°C for about 20 minutes to obtain a tire rubber material. Test specimens for the following evaluations were prepared from the obtained tire rubber material. The obtained test specimens were used to evaluate the following physical properties.

[0075] (Shore A Hardness) For the test pieces of the obtained tire rubber material, the hardness (Shore A hardness) was measured using a durometer in accordance with JIS K6253 Type A. The results are shown in Table 1.

[0076] (Breaking Properties) The obtained test pieces were processed into the shape of No. 3 dumbbell-shaped test pieces, and a tensile test was carried out in accordance with JIS K6251 at a tensile speed of 500 mm / min. In the tensile test, the tensile breaking strength (MPa) was measured. The tensile breaking strength of Comparative Example 1 (Standard Example 1) was set to 100, and the breaking strength index was calculated for Example 1 and Comparative Example 2 using the following formula. The larger the index, the better the strength. The results are shown in Table 1. (Breaking strength index) = 100 × (tensile breaking strength of Examples and Comparative Examples) / (tensile breaking strength of Standard Example 1)

[0077] (Wear resistance performance: FPS abrasion volume) For the test pieces of the obtained rubber material for tires, the FPS abrasion volume was measured using an FPS abrasion tester (AB-2012 manufactured by Ueshima Seisakusho) under conditions of a temperature of 35°C, a load of 40 N, a slip ratio of 10%, and a test time of 2 minutes. Volume loss was calculated from the FPS abrasion volume, and the abrasion index was calculated for Example 1 and Comparative Example 2 using the following formula, with the loss volume for Comparative Example 1 (Standard Example 1) set at 100. The higher the index, the better the abrasion resistance performance. The results are shown in Table 1. (Wear index) = 100 × (loss volume for Standard Example 1) / (loss volume for Examples and Comparative Examples)

[0078] (Fatigue crack resistance: tear strength) Test pieces of the obtained rubber material were punched out into rectangular shapes with long sides of 130 mm and short sides of 40 mm, and a 70 mm long incision was made from the midpoint of the short side in the long side direction to obtain trouser-shaped test pieces. The thickness of the test pieces was 1 mm. A tensile test was conducted on the trouser-shaped test pieces in accordance with JIS K6252-1 at a pulling rate of 100 mm / min, and the tear strength until the test piece broke was measured. The measured tear strength was analyzed based on JIS K6274 to calculate the tear strength. The calculated tear strength TS of Comparative Example 1 (Standard Example 1) was set to 100, and the tear strength index was calculated for Example 1 and Comparative Example 2 using the following formula. The higher the index, the better the fatigue crack resistance. The results are shown in Table 1. (Tensile strength index) = 100 × (tear strength of Examples and Comparative Examples) / (tear strength of Standard Example 1)

[0079] From Table 1, it was confirmed that a tire rubber material in which the BET specific surface area and content of hydrophilic fumed silica satisfy the above-mentioned relationship has a better balance of abrasion resistance, breaking strength, and fatigue crack resistance than a tire rubber material that does not contain hydrophilic fumed silica.

Claims

1. A rubber composition for tires containing 5 to 90 parts by mass of hydrophilic fumed silica and 1.5 to 30 parts by mass of a silane coupling agent with respect to 100 parts by mass of synthetic rubber, wherein the BET specific surface area Sf (m 2 / g) of the hydrophilic fumed silica and the content Cf (parts by mass) of the hydrophilic fumed silica with respect to 100 parts by mass of the synthetic rubber satisfy the following relationship: 4,500 ≦ Sf × Cf ≦ 35,000 2. The BET specific surface area Sf of the hydrophilic fumed silica is 180 m 2 / g or more and 500 m 2 / g or less, and the rubber composition for tires according to claim 1.

3. A rubber material for a tire obtained by vulcanizing the rubber composition for a tire according to claim 1.

4. A rubber material for a tire obtained by vulcanizing the rubber composition for a tire according to claim 2.

5. The rubber material for a tire according to claim 3, wherein the tear strength TS is 18 kN / m or more.

6. The rubber material for a tire according to claim 4, wherein the tear strength TS is 18 kN / m or more.

7. A tire including a tire member made of the rubber material for a tire according to any one of claims 3 to 6.

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