Rubber composition for tires

Abstract

To provide a rubber composition for tires which has excellent hardness while maintaining wear resistance without reducing the content of sulfur.SOLUTION: A pneumatic tire contains: a rubber component containing 70-100 mass% of a hydrogenated copolymer which is obtained by hydrogenating an aromatic vinyl-conjugated diene copolymer and has a weight average molecular weight measured by gel permeation chromatography of 300,000 or more and a hydrogenation rate of a conjugated diene moiety of 80 mol% or more; silica; a silane coupling agent; and sulfur. The content of the silane coupling agent is 9-14 mass% based on the silica.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition for a tire. [Background technology]

[0002] If a pneumatic tire does not have sufficient hardness, the handling of the vehicle will be reduced, and therefore, hardness is required of a rubber composition for a tire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 143111 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-138198 Summary of the Invention [Problem to be solved by the invention]

[0004] One method for increasing the hardness of a rubber composition for tires is to increase the amount of a silane coupling agent. However, when the amount of a silane coupling agent is increased in a rubber composition mainly containing a diene rubber, although the hardness increases, crosslinking points tend to be concentrated at one point, and abrasion resistance tends to deteriorate.

[0005] To address this problem, Patent Document 1 reduces the sulfur content when increasing the amount of silane coupling agent to prevent deterioration in wear resistance. However, if the amount of sulfur is reduced, high hardness cannot be maintained, and handling performance may be reduced.

[0006] In view of the above, an object of the present invention is to provide a rubber composition for tires that can provide excellent hardness while maintaining abrasion resistance without reducing the sulfur content.

[0007] Incidentally, Patent Document 2 describes that by blending a predetermined silica and a predetermined silane coupling agent, an increase in Mooney viscosity can be suppressed and a rubber composition having good processability, abrasion resistance, and mechanical strength can be obtained, but the rubber composition does not contain a hydrogenated copolymer. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the rubber composition for tires according to the present invention contains a rubber component containing 70 to 100 mass% of a hydrogenated copolymer obtained by hydrogenating an aromatic vinyl-conjugated diene copolymer, the hydrogenated copolymer having a weight-average molecular weight of 300,000 or more as measured by gel permeation chromatography and a hydrogenation rate of the conjugated diene moiety of 80 mol% or more, silica, a silane coupling agent, and sulfur, wherein the content of the silane coupling agent is 9 to 14 mass% relative to the silica. [Effects of the Invention]

[0009] According to the present invention, a rubber composition for tires having excellent hardness while maintaining abrasion resistance can be obtained without reducing the sulfur content. DETAILED DESCRIPTION OF THE INVENTION

[0010] Matters relating to the implementation of the present invention will be described in detail below.

[0011] The rubber composition for tires according to this embodiment contains a rubber component containing 70 to 100 mass% of a hydrogenated copolymer obtained by hydrogenating an aromatic vinyl-conjugated diene copolymer, the hydrogenated copolymer having a weight-average molecular weight of 300,000 or more as measured by gel permeation chromatography and a hydrogenation rate of the conjugated diene moiety of 80 mol% or more; silica; a silane coupling agent; and sulfur, wherein the content of the silane coupling agent is 9 to 14 mass% relative to the silica.

[0012] The rubber component is a hydrogenated copolymer of an aromatic vinyl-conjugated diene copolymer, and includes a hydrogenated copolymer having a weight-average molecular weight of 300,000 or more as measured by gel permeation chromatography, and a hydrogenation rate of the conjugated diene moiety of 80 mol% or more. Here, in this specification, "weight-average molecular weight measured by gel permeation chromatography (GPC)" refers to a value calculated in terms of polystyrene using a refractive index detector (RI) as a detector, tetrahydrofuran (THF) as a solvent, a measurement temperature of 40°C, a flow rate of 1.0 mL / min, a concentration of 1.0 g / L, and an injection amount of 40 μL, using commercially available standard polystyrene. The hydrogenation rate is calculated using H 1 The value is calculated from the spectral reduction rate of the unsaturated bond portion of the spectrum obtained by measuring NMR.

[0013] The aromatic vinyl constituting the aromatic vinyl-conjugated diene copolymer is not particularly limited, but examples thereof include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, 2,4,6-trimethylstyrene, etc. These may be used alone or in combination of two or more.

[0014] The conjugated diene constituting the aromatic vinyl-conjugated diene copolymer is not particularly limited, but examples thereof include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, 1,3-hexadiene, etc. These may be used alone or in combination of two or more.

[0015] The aromatic vinyl-conjugated diene copolymer is not particularly limited, but is preferably a copolymer of styrene and 1,3-butadiene (styrene-butadiene copolymer). Therefore, the hydrogenated copolymer is preferably a hydrogenated styrene-butadiene copolymer. The hydrogenated copolymer may be a random copolymer, a block copolymer, or an alternating copolymer.

[0016] The hydrogenated copolymer can be synthesized, for example, by synthesizing an aromatic vinyl-conjugated diene copolymer and subjecting it to a hydrogenation treatment. The method for synthesizing the aromatic vinyl-conjugated diene copolymer is not particularly limited, but examples thereof include solution polymerization, gas phase polymerization, and bulk polymerization, with solution polymerization being particularly preferred. The polymerization method may be either a batch method or a continuous method. It is also possible to use commercially available aromatic vinyl-conjugated diene copolymers.

[0017] The hydrogenation method is not particularly limited, and hydrogenation may be carried out by a known method under known conditions. It is usually carried out at 20 to 150°C under a hydrogen pressure of 0.1 to 10 MPa in the presence of a hydrogenation catalyst. The hydrogenation rate can be freely selected by changing the amount of hydrogenation catalyst, the hydrogen pressure during the hydrogenation reaction, the reaction time, etc. A compound containing any of the metals in Groups 4 to 11 of the Periodic Table can usually be used as the hydrogenation catalyst. For example, a compound containing a Ti, V, Co, Ni, Zr, Ru, Rh, Pd, Hf, Re, or Pt atom can be used as the hydrogenation catalyst. More specific examples of the hydrogenation catalyst include metallocene compounds of Ti, Zr, Hf, Co, Ni, Pd, Pt, Ru, Rh, Re, etc.; supported heterogeneous catalysts in which a metal such as Pd, Ni, Pt, Rh, Ru, etc. is supported on a carrier such as carbon, silica, alumina, or diatomaceous earth; homogeneous Ziegler-type catalysts in which an organic salt or acetylacetone salt of a metal element such as Ni or Co is combined with a reducing agent such as organoaluminum; organometallic compounds or complexes of Ru, Rh, etc.; and fullerenes and carbon nanotubes that have absorbed hydrogen.

[0018] The hydrogenation rate of the hydrogenated copolymer (the hydrogenated ratio relative to the conjugated diene portion of the aromatic vinyl-conjugated diene copolymer) is 80 mol% or more, preferably 80 to 95 mol%, more preferably 85 to 95 mol%, and even more preferably 90 to 95 mol%. A hydrogenation rate of 80 mol% or more provides an excellent effect of improving abrasion resistance due to homogenized crosslinking.

[0019] The weight average molecular weight of the hydrogenated copolymer is not particularly limited as long as it is 300,000 or more, but is preferably 300,000 to 2,000,000, more preferably 300,000 to 1,000,000, and even more preferably 300,000 to 600,000.

[0020] The rubber component may contain diene rubbers other than the above hydrogenated copolymers, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, etc. These diene rubbers may be used alone or in a blend of two or more.

[0021] The content of the hydrogenated copolymer in the rubber component is not particularly limited, but is preferably 70 to 100 mass %, more preferably 80 to 100 mass %. When the content of the hydrogenated copolymer in the rubber component is within the above range, wear resistance is easily maintained even when a high amount of silane coupling agent is compounded without reducing the sulfur content.

[0022] The rubber composition for a tire according to the present embodiment contains silica and a silane coupling agent. The silica is not particularly limited, but wet silica such as wet precipitation silica or wet gel silica is preferably used. The content of silica is 30 to 100 parts by mass, preferably 50 to 80 parts by mass, per 100 parts by mass of the rubber component.

[0023] The reinforcing filler contains silica, but carbon black may also be used in combination with silica. That is, the reinforcing filler may be silica alone or a combination of silica and carbon black. A combination of silica and carbon black is preferred. The content of the reinforcing filler is not particularly limited, but is preferably 30 to 150 parts by mass, more preferably 30 to 100 parts by mass, and even more preferably 50 to 80 parts by mass, per 100 parts by mass of the rubber component.

[0024] The carbon black is not particularly limited, and various known types can be used. The content of carbon black is preferably 1 to 70 parts by mass, and more preferably 1 to 30 parts by mass, per 100 parts by mass of the rubber component.

[0025] The silane coupling agent is not particularly limited, but sulfide silane, mercapto silane, etc. are preferably used. The content of the silane coupling agent is 9 to 14 mass % relative to the silica content, and preferably 9 to 12 mass %. When the content of the silane coupling agent is within the above range, excellent hardness is likely to be obtained while maintaining wear resistance.

[0026] The rubber composition for tires according to the present embodiment contains, as the vulcanizing agent, a sulfur component such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, or highly dispersible sulfur, and the content thereof is preferably 0.5 to 4 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of the rubber component.

[0027] The rubber composition for a tire according to the present embodiment contains a silane coupling agent in a predetermined content, thereby achieving excellent hardness while maintaining abrasion resistance. The mechanism behind this is unclear, but can be assumed as follows. When the amount of silane coupling agent is increased in a compound primarily containing a normal diene rubber, crosslinking points are concentrated at one point, resulting in a deterioration in abrasion resistance. On the other hand, when the amount of silane coupling agent is increased in a compound primarily containing a hydrogenated copolymer, the hydrogenated copolymer has a small amount of double bonds, so crosslinking points are not concentrated at one point but are spread throughout the polymer chain, and it can be assumed that this allows for an increase in hardness while maintaining abrasion resistance.

[0028] In addition to the above-mentioned components, the rubber composition for a tire according to the present embodiment may contain compounding chemicals such as processing aids, zinc oxide, stearic acid, softeners, plasticizers, liquid rubbers, resins, waxes, antioxidants, and vulcanization accelerators, which are generally used in the rubber industry, within normal ranges.

[0029] Examples of the vulcanization accelerator that can be used include sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, dithiocarbamate vulcanization accelerators, thiuram vulcanization accelerators, thiazole vulcanization accelerators, and thiourea vulcanization accelerators. Among these, sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, and dithiocarbamate vulcanization accelerators are preferred.

[0030] Examples of sulfenamide vulcanization accelerators include N-cyclohexyl-2-benzothiazolylsulfenamide (CZ), N-tert-butyl-2-benzothiazolylsulfenamide (NS), N-oxydiethylene-2-benzothiazolylsulfenamide (MBS), and N,N-diisopropyl-2-benzothiazolesulfenamide (DZ).

[0031] Examples of the guanidine vulcanization accelerator include 1,3-diphenylguanidine (D) and di-O-tolylguanidine (DT).

[0032] Examples of dithiocarbamate vulcanization accelerators include zinc dibenzyldithiocarbamate (ZnBzDTC), zinc dimethyldithiocarbamate (ZnMDC), zinc diethyldithiocarbamate (ZnEDC), zinc di-n-butyldithiocarbamate (ZnBDC), zinc N-pentamethylenedithiocarbamate (ZnPDC), zinc ethylphenyldithiocarbamate (ZnEPDC), sodium dimethyldithiocarbamate (NaMDC), sodium diethyldithiocarbamate (NaEDC), sodium di-n-butyldithiocarbamate (NaBDC), tellurium diethyldithiocarbamate (TeEDC), copper dimethyldithiocarbamate (CuMDC), and iron dimethyldithiocarbamate (FeMDC).

[0033] When a sulfenamide vulcanization accelerator is contained, its content is not particularly limited, but is preferably 0.1 to 3 parts by mass, and more preferably 0.2 to 2 parts by mass, per 100 parts by mass of the rubber component.

[0034] When a guanidine vulcanization accelerator is contained, its content is not particularly limited, but is preferably 0.1 to 3 parts by mass, and more preferably 0.2 to 2 parts by mass, per 100 parts by mass of the rubber component.

[0035] When a dithiocarbamate vulcanization accelerator is contained, its content is not particularly limited, but is preferably 0.1 to 3 parts by mass, and more preferably 0.2 to 2 parts by mass, per 100 parts by mass of the rubber component.

[0036] Among these vulcanization accelerators, it is preferable to use a dithiocarbamate vulcanization accelerator and a guanidine vulcanization accelerator in combination, and the blending ratio (guanidine vulcanization accelerator / dithiocarbamate vulcanization accelerator) is preferably 0.5 to 3.0 in mass ratio.

[0037] When two or more types of vulcanization accelerators are used in combination, the total content of the vulcanization accelerators is preferably 0.1 to 9 parts by mass, and more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the rubber component.

[0038] The rubber composition according to the present embodiment can be prepared by kneading in a conventional manner using a commonly used mixer such as a Banbury mixer, kneader, roll, etc. That is, in the first mixing stage, additives other than the vulcanizing agent and vulcanization accelerator are added and mixed with the rubber component, and then in the final mixing stage, the vulcanizing agent and vulcanization accelerator are added and mixed with the resulting mixture to prepare the rubber composition.

[0039] The rubber composition thus obtained can be used for tires, and can be applied to various parts of tires, such as the tread and sidewall of pneumatic tires of various uses and sizes, such as passenger cars, large tires for trucks and buses, etc. The rubber composition can be molded into a rubber member of a predetermined shape according to a conventional method, for example, by extrusion processing, combined with other parts, and then vulcanized and molded at, for example, 140 to 180°C, to produce a pneumatic tire.

[0040] The type of pneumatic tire according to this embodiment is not particularly limited, and examples include various types of tires such as tires for passenger cars and heavy-duty tires used for trucks, buses, etc. [Example]

[0041] Examples of the present invention will be shown below, but the present invention is not limited to these examples.

[0042] <Synthesis example of hydrogenated copolymer 1> A nitrogen-purged heat-resistant reactor was charged with 2.5 L of cyclohexane, 50 g of tetrahydrofuran (THF), 0.12 g of n-butyllithium, 100 g of styrene, and 400 g of 1,3-butadiene, and the mixture was polymerized at 50°C. After polymerization was complete, 1.7 g of N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane was added and the mixture was allowed to react for 1 hour. Hydrogen gas was then introduced at a pressure of 0.4 MPa (gauge) and the mixture was stirred for 20 minutes. The hydrogen gas supply pressure was then increased to 0.7 MPa (gauge), the reaction temperature was increased to 90°C, and the mixture was reacted using a catalyst primarily consisting of titanocene dichloride until the desired hydrogenation rate was achieved. The solvent was then removed to obtain hydrogenated copolymer 1.

[0043] The weight average molecular weight of the obtained hydrogenated copolymer 1 was measured using a Shimadzu Corporation "LC-10A" measuring device, a Polymer Laboratories "PLgel-MIXED-C" column, a differential refractive index detector (RI) as a detector, THF as a solvent, a measurement temperature of 40°C, a flow rate of 1.0 mL / min, a concentration of 1.0 g / L, and an injection volume of 40 μL, and was 350,000 in polystyrene equivalent terms using standard polystyrene. The bound styrene content was 20 mass% and the hydrogenation rate of the butadiene moiety was 90 mol%. The bound styrene content was measured using H 1 The NMR was used to determine the spectral intensity ratio of the protons based on the styrene unit and the protons based on the butadiene unit (including the hydrogenated portion).

[0044] Examples and Comparative Examples Using a Banbury mixer, according to the formulation (parts by mass) shown in Tables 1 and 2 below, first, in the first mixing stage (non-pro kneading process), components excluding the vulcanization accelerator and sulfur were added and mixed (discharge temperature = 160°C), and then, in the final mixing stage (pro kneading process), the vulcanization accelerator and sulfur were added and mixed (discharge temperature = 90°C) to the obtained mixture, thereby preparing a rubber composition.

[0045] Details of each component in Tables 1 and 2 are as follows: SBR: JSR Corporation "HPR350" Hydrogenated SBR: Hydrogenated copolymer 1 prepared according to the synthesis example above Silica: Evonik Japan "Ultrasil VN3" Silane coupling agent: Evonik Japan "Si69" Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. Aromatic oil: JXTG Nippon Oil & Energy Corporation "Process NC140" Zinc oxide: "Zinc oxide type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent: "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd. Stearic acid: Kao Corporation's "Lunac S-20" Wax: Nippon Seiro Co., Ltd. "OZOACE0355" Vulcanization accelerator 1: Sumitomo Chemical Co., Ltd.'s "Soxinol CZ", a sulfenamide vulcanization accelerator Vulcanization accelerator 2: "Noccera-D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a guanidine vulcanization accelerator Vulcanization accelerator 3: Sansera ZBE manufactured by Sanshin Chemical Industry Co., Ltd., a dithiocarbamate vulcanization accelerator Sulfur: Tsurumi Chemical Industry Co., Ltd. "Fine powder sulfur"

[0046] The rubber compositions thus obtained were evaluated for abrasion resistance and hardness. The measurement and evaluation methods were as follows, and the evaluation results are shown in Tables 1 and 2.

[0047] Abrasion resistance: In accordance with JIS K6264, a Lambourn abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd. was used to measure the abrasion loss under conditions of a load of 40 N and a slip ratio of 30%, and the reciprocal of the abrasion loss was expressed as an index, with the value for Comparative Example 1 set to 100.

[0048] Hardness: Measured at 23°C using a type A durometer conforming to JIS K6253, and expressed as an index with the value of Comparative Example 1 being 100.

[0049] [Table 1]

[0050] [Table 2]

[0051] The results are shown in Tables 1 and 2. Comparing Comparative Example 1 with Comparative Examples 2 to 4, when the content of silane coupling agent was increased without reducing the sulfur content in a formulation mainly composed of styrene butadiene rubber (SBR), the hardness increased but the abrasion resistance deteriorated.

[0052] On the other hand, a comparison between Comparative Example 5 and Examples 1 to 3 shows that when the content of the silane coupling agent was increased without reducing the content of sulfur in a formulation mainly composed of a hydrogenated copolymer, the hardness could be increased while maintaining the wear resistance. [Industrial Applicability]

[0053] The rubber composition for tires of the present invention can be used for various tires for passenger cars, light trucks, buses, etc.

Claims

[Claim 1] The rubber composition for a tire contains a rubber component containing 70 to 100 mass % of a hydrogenated copolymer obtained by hydrogenating an aromatic vinyl-conjugated diene copolymer, the hydrogenated copolymer having a weight average molecular weight of 300,000 or more as measured by gel permeation chromatography and a hydrogenation rate of the conjugated diene moiety of 80 mol % or more, silica, a silane coupling agent, sulfur, and a vulcanization accelerator, the content of the silane coupling agent being 9 to 14 mass % relative to the silica, and the vulcanization accelerator including a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, and a dithiocarbamate-based vulcanization accelerator.

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