Method for producing a rubber composition for a tire, rubber composition for a tire, and pneumatic tire

Abstract

To provide a method of producing a rubber composition for tires which has excellent fuel economy while maintaining or improving wear resistance, a rubber composition for tires, and a pneumatic tire.SOLUTION: There is provided a method of producing a rubber composition for tires containing: 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; and a crosslinking compounding agent. The method of producing a rubber composition for tires comprises: a first step of mixing 50-95 mass% out of 100 mass% of the hydrogenated copolymer and the whole amount of the silica; a second step of mixing the remaining hydrogenated copolymer with the mixture obtained in the first step; and a third step of mixing the crosslinking compounding agent with the mixture obtained in the second step.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a rubber composition for tires, a rubber composition for tires, and a pneumatic tire.

Background Art

[0002] In recent years, in response to the increasing environmental awareness, there has been a demand to reduce the rolling resistance of pneumatic tires in order to improve the fuel efficiency of automobiles.

[0003] As methods for producing rubber compositions for reducing rolling resistance, Patent Documents 1 and 2 describe a method of dividing and charging a filler, and Patent Documents 3 and 4 describe a method of dividing and charging a rubber component and a filler.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the rubber compositions described in Patent Documents 1 to 4 are all mainly composed of ordinary diene rubbers, and there is room for improvement in the rolling resistance and abrasion resistance of rubber compositions mainly composed of hydrogenated copolymers.

[0006] In view of the above points, an object of the present invention is to provide a method for producing a rubber composition for tires, a rubber composition for tires, and a pneumatic tire that have excellent low fuel consumption properties while maintaining or improving abrasion resistance.

Means for Solving the Problems

[0007] The method for producing a rubber composition for tires according to the present invention, in order to solve the above problems, is a hydrogenated copolymer obtained by hydrogenating an aromatic vinyl-conjugated diene copolymer, having a weight average molecular weight of 300,000 or more measured by gel permeation chromatography, and a hydrogenation rate of the conjugated diene part of 80 mol% or more. A method for producing a rubber composition for tires containing 70 to 100% by mass of a rubber component, silica, and a crosslinking compounding agent, comprising: a first step of mixing 50 to 95% by mass of 100% by mass of the hydrogenated copolymer and the total amount of silica; a second step of mixing the remaining hydrogenated copolymer with the mixture obtained in the first step; and a third step of mixing a crosslinking compounding agent with the mixture obtained in the second step.

[0008] The discharge temperature of the first step may be 120 to 160°C, and the discharge temperature of the second step may be 120 to 160°C.

[0009] The rubber composition for tires according to the present invention is obtained by the above production method.

[0010] The pneumatic tire according to the present invention is produced using the above rubber composition for tires.

Advantages of the Invention

[0011] According to the production method of the present invention, it is possible to provide a rubber composition for tires having excellent low fuel consumption while maintaining or improving wear resistance, and a pneumatic tire.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, matters related to the implementation of the present invention will be described in detail.

[0013] The manufacturing method of the rubber composition for tires according to this embodiment is a hydrogenated copolymer obtained by hydrogenating an aromatic vinyl-conjugated diene copolymer, having a weight average molecular weight measured by gel permeation chromatography of 300,000 or more, and a hydrogenation rate of the conjugated diene portion of 80 mol% or more. It is a manufacturing method of a rubber composition for tires containing 70 to 100% by mass of a rubber component, silica, and a crosslinking compounding agent, including a first step of mixing 50 to 95% by mass of the 100% by mass of the hydrogenated copolymer and the total amount of silica, a second step of mixing the remaining hydrogenated copolymer into the mixture obtained in the first step, and a third step of mixing a crosslinking compounding agent into the mixture obtained in the second step.

[0014] The manufacturing method of the rubber composition according to this embodiment can be carried out using a closed mixer such as a commonly used Banbury mixer.

[0015] In the first step, 50 to 95% by mass of the 100% by mass of the hydrogenated copolymer, the total amount of silica, and compounding agents excluding the crosslinking compounding agent are added, and kneaded while raising the temperature of the mixture.

[0016] The ratio of the hydrogenated copolymer compounded in the first step is not particularly limited as long as it is 50 to 95% by mass of the 100% by mass of the hydrogenated copolymer, but it is preferably 60 to 90% by mass.

[0017] The discharge temperature in the first step is not particularly limited, but it is preferably 120 to 160°C.

[0018] In the second step, the remaining hydrogenated copolymer is mixed. The discharge temperature in the second step is not particularly limited, but it is preferably 120 to 160°C.

[0019] When containing a rubber component other than the hydrogenated copolymer, it is preferable to knead the rubber component other than the hydrogenated copolymer in the first step. However, within a range not contrary to the object of the present invention, part or all of the rubber component other than the hydrogenated copolymer may be kneaded in the second step.

[0020] When compounding compounding agents other than silica and crosslinking compounding agents, it is preferable to knead in the first step, but within a range not contrary to the object of the present invention, it may be kneaded in the second step.

[0021] In the third step, a crosslinking compounding agent is added to the mixture obtained in the second step and kneaded. The discharge temperature at that time is not particularly limited, but it is preferably 80 to 120°C, more preferably 90 to 110°C.

[0022] The rubber component used in the method for producing the rubber composition according to this embodiment is a hydrogenated copolymer 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 the conjugated diene part of 80 mol% or more. Here, in this specification, the "weight average molecular weight measured by gel permeation chromatography (GPC)" means that a differential refractive index detector (RI) is used as a detector, tetrahydrofuran (THF) is used as a solvent, the measurement temperature is 40°C, the flow rate is 1.0 mL / min, the concentration is 1.0 g / L, the injection volume is 40 μL, and it is a value calculated in terms of polystyrene using commercially available standard polystyrene. Also, the hydrogenation rate is a value calculated from the spectral reduction rate of the unsaturated bond part of the spectrum obtained by measuring H 1 -NMR.

[0023] The aromatic vinyl constituting the above aromatic vinyl-conjugated diene copolymer is not particularly limited, and examples thereof include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, 2,4,6-trimethylstyrene, and the like. These may be used alone or in combination of two or more.

[0024] The conjugated diene constituting the above aromatic vinyl-conjugated diene copolymer is not particularly limited, and examples thereof include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, 1,3-hexadiene, and the like. These may be used alone or in combination of two or more.

[0025] The above aromatic vinyl-conjugated diene copolymer is not particularly limited, but is preferably a copolymer of styrene and 1,3-butadiene (styrene-butadiene copolymer). Therefore, as the hydrogenated copolymer, a hydrogenated styrene-butadiene copolymer is preferably used. The hydrogenated copolymer may be a random copolymer, a block copolymer, or an alternating copolymer.

[0026] The above hydrogenated copolymer can be synthesized, for example, by synthesizing an aromatic vinyl-conjugated diene copolymer and performing a hydrogenation treatment. The method for synthesizing the aromatic vinyl-conjugated diene copolymer is not particularly limited, and examples thereof include solution polymerization method, gas phase polymerization method, bulk polymerization method, etc., and the solution polymerization method is particularly preferred. Also, the polymerization mode may be either batch type or continuous type. It should be noted that commercially available aromatic vinyl-conjugated diene copolymers can also be used.

[0027] The hydrogenation method is not particularly limited, and hydrogenation may be carried out by known methods under known conditions. Usually, it is 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 arbitrarily selected by changing the amount of the hydrogenation catalyst, the hydrogen pressure during the hydrogenation reaction, the reaction time, etc. As the hydrogenation catalyst, usually, a compound containing any of the metals of Groups 4 to 11 of the periodic table can be used. For example, compounds containing Ti, V, Co, Ni, Zr, Ru, Rh, Pd, Hf, Re, Pt atoms can be used as the hydrogenation catalyst. More specific hydrogenation catalysts include metallocene compounds such as Ti, Zr, Hf, Co, Ni, Pd, Pt, Ru, Rh, Re, etc.; supported heterogeneous catalysts in which metals such as Pd, Ni, Pt, Rh, Ru, etc. are supported on carriers such as carbon, silica, alumina, diatomaceous earth, etc.; homogeneous Ziegler-type catalysts in which organic salts or acetylacetone salts of metal elements such as Ni, Co, etc. are combined with reducing agents such as organic aluminum; organometallic compounds or complexes such as Ru, Rh, etc.; and fullerenes or carbon nanotubes that have absorbed hydrogen, etc. can be mentioned.

[0028] The hydrogenation rate of the hydrogenated copolymer (the ratio of hydrogen added to the conjugated diene part 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%. When the hydrogenation rate is 80 mol% or more, the effect of improving the wear resistance due to the homogenization of crosslinking is excellent.

[0029] The weight average molecular weight of the hydrogenated copolymer is not particularly limited as long as it is 300,000 or more, but it 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.

[0030] The rubber component may contain a diene rubber other than the above hydrogenated copolymer. Examples of such diene rubbers include 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, and the like. Further, copolymers may be alternating copolymers, block copolymers, or random copolymers. These solid rubbers may be used alone or in combination of two or more.

[0031] The blending ratio of the above hydrogenated copolymer in the rubber component is preferably 70 to 100% by mass, more preferably 80 to 100% by mass.

[0032] The reinforcing filler contains silica, but carbon black may be used in combination. That is, the reinforcing filler may be silica alone or a combination of carbon black and silica. Preferably, it is a combination of carbon black and silica. The blending amount of the reinforcing filler is not particularly limited. For example, it is preferably 10 to 150 parts by mass, more preferably 20 to 100 parts by mass, and still more preferably 30 to 80 parts by mass with respect to 100 parts by mass of the rubber component.

[0033] The silica is not particularly limited, but wet silica such as wet precipitation method silica or wet gel method silica is preferably used. The blending amount of silica is preferably 10 to 150 parts by mass, more preferably 15 to 100 parts by mass with respect to 100 parts by mass of the rubber component from the viewpoints of the balance of tanδ of the rubber and the reinforcing property.

[0034] In addition to silica, a silane coupling agent such as sulfide silane or mercapto silane may be further blended. When the silane coupling agent is blended, the blending amount is preferably 2 to 20% by mass based on the blending amount of silica.

[0035] The carbon black is not particularly limited, and various known varieties can be used. The compounding amount of the carbon black is preferably 1 to 70 parts by mass, more preferably 1 to 30 parts by mass, based on 100 parts by mass of the rubber component.

[0036] Examples of the crosslinking compounding agents include vulcanizing agents and vulcanization accelerators. Examples of the vulcanizing agents include sulfur components such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersed sulfur. Although not particularly limited, the compounding amount is preferably 0.1 to 4 parts by mass, more preferably 0.2 to 3 parts by mass, based on 100 parts by mass of the rubber component.

[0037] Examples of the vulcanization accelerators include sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators. Among these, sulfenamide-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and guanidine-based vulcanization accelerators are preferred. Also, two or more of these may be used in combination. For example, it is preferably a combination of a dithiocarbamate-based vulcanization accelerator and a guanidine-based vulcanization accelerator. In this case, the blending ratio (guanidine-based vulcanization accelerator / dithiocarbamate-based vulcanization accelerator) is preferably 0.5 to 4.0 in terms of mass ratio.

[0038] Examples of the sulfenamide-based vulcanization accelerators include N-cyclohexyl-2-benzothiazolylsulfenamide (CZ), N-tert-butyl-2-benzothiazolylsulfenamide (NS), N-oxydiethylene-2-benzothiazolylsulfenamide (OBS), and N,N-diisopropyl-2-benzothiazolesulfenamide (DZ).

[0039] Examples of the guanidine-based vulcanization accelerators include 1,3-diphenylguanidine (D), di-O-tolylguanidine (DT), and the like.

[0040] 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), iron dimethyldithiocarbamate (FeMDC), and the like.

[0041] The compounding amount of the sulfenamide vulcanization accelerator is not particularly limited, but it is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 3 parts by mass, per 100 parts by mass of the rubber component.

[0042] The compounding amount of the guanidine vulcanization accelerator is not particularly limited, but it is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 3 parts by mass, per 100 parts by mass of the rubber component.

[0043] The compounding amount of the dithiocarbamate vulcanization accelerator is not particularly limited, but it is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 3 parts by mass, per 100 parts by mass of the rubber component.

[0044] The compounding amount of the vulcanization accelerator (the total amount when two or more are compounded) is preferably 0.1 to 7 parts by mass, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0045] As compounding agents excluding the crosslinking system compounding agents, compounding chemicals such as reinforcing fillers, process oils, processing aids, zinc oxide, stearic acid, softeners, plasticizers, resins, waxes, antioxidants, etc., which are used in the normal rubber industry, can be appropriately compounded within the normal range.

[0046] The rubber composition obtained by the production method according to this embodiment can be used for tires and can be applied to various parts of pneumatic tires such as treads and sidewalls of pneumatic tires for various applications and sizes, such as passenger car tires, large tires for trucks and buses. The rubber composition is formed into a predetermined shape by extrusion processing, for example, according to a conventional method, and after being combined with other parts, a pneumatic tire can be manufactured by vulcanization molding at, for example, 140 to 180°C.

[0047] The type of pneumatic tire according to this embodiment is not particularly limited, and various tires such as passenger car tires and heavy-duty tires used for trucks and buses can be mentioned.

[0048] <Impossible / unpractical things> The feature of the present invention is that in the first step, the hydrogenated copolymer is blended with the total amount of silica at a predetermined ratio, and in the second step, the mixture obtained in the first step and the remaining hydrogenated copolymer are mixed. The effect of the present invention is due to the microscopic difference in the dispersion state brought about by the characteristics of the manufacturing process, and the microscopic difference in the dispersion state cannot be distinguished by commonly used indicators such as composition and properties. Therefore, in the present invention, it can be said that "directly specifying the object by its structure or properties at the time of filing" is approximately impractical.

Examples

[0049] Examples of the present invention are shown below, but the present invention is not limited to these examples.

[0050] 〈Synthesis example of hydrogenated copolymer〉 In a nitrogen-substituted heat-resistant reaction vessel, 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 were added, and polymerization was carried out at a reaction temperature of 50 °C. After the polymerization was completed, 1.7 g of N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane was added and reacted for 1 hour. Then, hydrogen gas was supplied at a pressure of 0.4 MPa-gauge and stirred for 20 minutes. Next, the hydrogen gas supply pressure was set to 0.7 MPa-gauge and the reaction temperature was set to 90 °C, and the reaction was carried out using a catalyst mainly composed of titanocene dichloride until the desired hydrogenation rate was achieved. By removing the solvent, a hydrogenated copolymer was obtained.

[0051] The weight average molecular weight of the obtained hydrogenated copolymer was measured using "LC-10A" manufactured by Shimadzu Corporation as the measuring device, "PLgel-MIXED-C" manufactured by Polymer Laboratories as the column, a differential refractive index detector (RI) as the detector, THF as the 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. The measurement was carried out in terms of polystyrene conversion using standard polystyrene and was 350,000. The bound styrene content was 20% by mass, and the hydrogenation rate of the butadiene part was 90 mol%. The bound styrene content was determined from the spectral intensity ratio of the protons based on the styrene unit and the protons based on the butadiene unit (including the hydrogenated part) using H 1 -NMR.

[0052] <Examples and Comparative Examples> Using a Banbury mixer, according to the formulation (parts by mass) shown in Table 1 below, first, in the first step, the components excluding the vulcanization accelerator and sulfur were added and kneaded (discharge temperature = 160 °C), and the remaining hydrogenated copolymer was added and kneaded to the obtained mixture (discharge temperature = 160 °C). To the obtained mixture, in the third step, the vulcanization accelerator and sulfur were added and mixed (discharge temperature = 90 °C) to prepare a rubber composition.

[0053] The details of each component in Table 1 are as follows. ·SBR: "HPR350" manufactured by JSR Corporation · Hydrogenated SBR: The hydrogenated copolymer prepared according to the above synthesis example · Silica: "Ultrasil VN3" manufactured by Evonik Japan Co., Ltd. · Silane coupling agent: "Si69" manufactured by Evonik Japan Co., Ltd. · Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. · Aromatic oil: "Process NC140" manufactured by JXTG Energy Corporation · Zinc oxide: "Zinc Oxide No. 2" manufactured by Mitsui Mining & Smelting Co., Ltd. · Antioxidant: "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd. · Stearic acid: "Lunac S-20" manufactured by Kao Corporation · Wax: "OZOACE0355" manufactured by Nippon Seiro Co., Ltd. · Vulcanization accelerator 1: "Soxinol CZ" manufactured by Sumitomo Chemical Co., Ltd., a sulfenamide-based vulcanization accelerator · Vulcanization accelerator 2: "Nocceler-D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd., a guanidine-based vulcanization accelerator · Vulcanization accelerator 3: "Sancer ZBE" manufactured by Sanshin Chemical Industry Co., Ltd., a dithiocarbamate-based vulcanization accelerator · Sulfur: "Fine Powder Sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd.

[0054] For each of the obtained rubber compositions, the low fuel consumption performance and abrasion resistance were evaluated. The evaluation methods are as follows.

[0055] · Low fuel consumption performance: It was in accordance with JIS K6394. That is, for the test piece vulcanized at 160°C for 30 minutes, the loss factor tanδ was measured under the conditions of a temperature of 60°C, a static strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz using a viscoelasticity tester manufactured by Toyo Seiki Co., Ltd. For the reciprocal of tanδ, for Comparative Example 2, it was shown by an index with the value of Comparative Example 1 taken as 100, and for Examples 1 to 5 and Comparative Example 4, it was shown by an index with the value of Comparative Example 3 taken as 100. The smaller the index, the smaller the tanδ, and it was evaluated that the low fuel consumption property was excellent.

[0056] · Abrasion resistance: In accordance with JIS K6264, using a Lambourn abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd., the abrasion loss was measured under the conditions of a load of 40 N and a slip ratio of 30%. For the reciprocal of the abrasion loss, for Comparative Example 2, it was shown by an index with the value of Comparative Example 1 set to 100, and for Examples 1 to 5 and Comparative Example 4, it was shown by an index with the value of Comparative Example 3 set to 100. It was evaluated that the larger the index, the better the abrasion resistance.

[0057]

Table 1

[0058] The results are as shown in Table 1. From the comparison between Comparative Examples 1 and 2, in the formulation using styrene-butadiene rubber (SBR) as the rubber component, when the rubber component was divided and charged into the first step and the second step, the low fuel consumption performance and abrasion resistance deteriorated.

[0059] From the comparison between Examples 1 to 5 and Comparative Example 3, in the formulation using hydrogenated SBR as the rubber component, when the rubber component was divided and charged into the first step and the second step at a predetermined ratio, while maintaining or improving the abrasion resistance, the low fuel consumption performance was improved.

[0060] From the comparison between Comparative Examples 3 and 4, in the formulation using hydrogenated SBR as the rubber component, when the rubber component was divided and charged into the first step and the second step at a ratio outside the predetermined range, the low fuel consumption performance and abrasion resistance deteriorated.

Industrial Applicability

[0061] The method for manufacturing the rubber composition for tires of the present invention can manufacture a rubber composition that can be used for various tires such as passenger cars, light trucks, and buses.

Claims

1. A method for producing a rubber composition for tires, comprising a rubber component containing 70 to 100% by mass of a hydrogenated copolymer obtained by hydrogenating an aromatic vinyl-conjugated diene 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 portion of 80 mol% or more, silica, and a crosslinking compounding agent, wherein: a first step of mixing 50 to 95% by mass of the 100% by mass of the hydrogenated copolymer and the total amount of silica; a second step of mixing the remaining hydrogenated copolymer with the mixture obtained in the first step; and a third step of mixing a crosslinking compounding agent with the mixture obtained in the second step.

2. The method for producing a rubber composition for tires according to claim 1, wherein the discharge temperature in the first step is 120 to 160°C, and the discharge temperature in the second step is 120 to 160°C.

3. A rubber composition for tires obtained by the production method according to claim 1 or claim 2.

4. A pneumatic tire produced using the rubber composition for tires according to claim 3.

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