Method for producing rubber composition

Abstract

The present invention addresses the problem of providing a method for producing a rubber composition by which it is possible to obtain a rubber composition that has exceptional low heat build-up properties and improves the ratio of sustainable materials in a rubber product. The solution to the aforementioned problem is a method for producing a rubber composition containing a rubber component (A) composed of at least one of natural rubber and synthetic diene rubber, a filler containing an inorganic filler (B), a silane coupling agent (C), and a compound (D) that promotes a reaction between silica and the silane coupling agent, wherein the method for producing a rubber composition is characterized in that: the inorganic filler (B) contains plant-derived silica (B1); the rubber composition is kneaded in a plurality of stages; and the rubber component (A), all or part of the inorganic filler (B), all or part of the silane coupling agent (C), and the compound (D) that promotes a reaction between silica and the silane coupling agent are kneaded in a first stage of kneading.

Description

Method for producing rubber composition

[0001] The present invention relates to a method for producing a rubber composition.

[0002] In response to the recent trend toward global carbon dioxide emission regulations due to growing interest in environmental issues, there is an increasing demand for improved fuel efficiency in automobiles. To meet this demand, tire performance needs to be improved in terms of fuel economy (i.e., reduced rolling resistance). While optimization of tire structure has been considered as a method for reducing tire rolling resistance, the most common method currently used is to use a rubber composition with lower heat buildup for tires. One known method for obtaining such a rubber composition with excellent low heat buildup is to use an inorganic filler such as silica as a filler. However, inorganic fillers (particularly silica) tend to aggregate in the rubber composition during compounding. To address this issue, silane coupling agents are generally used to prevent aggregation of inorganic fillers (particularly silica), and various attempts have been made to improve the coupling function of the silane coupling agents (see Patent Documents 1 to 4).

[0003] Special Table No. 2002-521515 Publication Special Publication No. 2002-521516 Publication Special Publication No. 2003-523472 Publication Special Publication No. 2003-530443

[0004] On the other hand, recently, from the viewpoint of social sustainability, there has been a demand for rubber products such as tires to contain an increased proportion of so-called sustainable materials, such as materials derived from biological resources (biomass resources) and materials derived from recycled resources, and there has also been a demand for an increased proportion of sustainable materials in the rubber compositions used in such rubber products. However, among the materials compounded in rubber compositions, the use of silica as a sustainable material has not been considered until now.

[0005] Therefore, an object of the present invention is to provide a method for producing a rubber composition that is capable of obtaining a rubber composition that not only has excellent low heat buildup but also increases the proportion of sustainable materials in rubber products.

[0006] The method for producing a rubber composition of the present invention, which solves the above problems, is outlined as follows.

[0007] [1] A method for producing a rubber composition comprising a rubber component (A) consisting of at least one of natural rubber and synthetic diene rubber, a filler including an inorganic filler (B), a silane coupling agent (C), and a compound (D) that accelerates the reaction between silica and the silane coupling agent, wherein the inorganic filler (B) includes plant-derived silica (B1), and the rubber composition is kneaded in multiple stages, and in a first stage of kneading, all or a part of the rubber component (A), all or a part of the inorganic filler (B), the silane coupling agent (C), and the compound (D) that accelerates the reaction between silica and the silane coupling agent are kneaded.

[0008] [2] The method for producing a rubber composition according to [1], wherein the compound (D) that promotes the reaction between silica and a silane coupling agent is at least one selected from the group consisting of guanidines, thiurams, dithiocarbamates, thioureas, xanthates, tertiary amine compounds, inorganic salt hydrates, 1,2-benzenediol, imidazole compounds, organic sulfonic acids, and water.

[0009] [3] The method for producing a rubber composition according to [1] or [2], wherein an organic acid compound (E) is further kneaded in the first stage of kneading, and the number of molecules X of the organic acid compound (E) in the rubber composition in the first stage is related to the number of molecules Y of the reaction accelerator compound (D) of silica and a silane coupling agent by the following formula (1): 0≦X≦1.5×Y (1).

[0010] [4] The method for producing a rubber composition according to any one of [1] to [3], wherein the maximum temperature of the rubber composition in the first stage of kneading is 120 to 190°C.

[0011] [5] The method for producing a rubber composition according to any one of [1] to [4], wherein the inorganic filler (B) is 30% by mass or more in the filler.

[0012] [6] The method for producing a rubber composition according to any one of [1] to [5], wherein the number of molecules of the reaction-accelerating compound (D) between the silica and the silane coupling agent in the rubber composition in the first stage of kneading is 0.1 to 1.0 times the number of molecules of the silane coupling agent (C).

[0013] [7] The method for producing a rubber composition according to any one of [2] to [6], wherein the guanidine is 1,3-diphenylguanidine.

[0014] [8] The method for producing a rubber composition according to any one of [2] to [6], wherein the thiuram is at least one compound selected from tetrakis(2-ethylhexyl)thiuram disulfide and tetrabenzylthiuram disulfide.

[0015] [9] The method for producing a rubber composition according to any one of [2] to [6], wherein the thioureas are at least one compound selected from N,N'-diethylthiourea, trimethylthiourea, N,N'-diphenylthiourea, and N,N'-dimethylthiourea.

[0016]

[10] The method for producing a rubber composition according to any one of [2] to [6], wherein the dithiocarbamate is at least one compound selected from zinc dibenzyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc dimethyldithiocarbamate, and copper dimethyldithiocarbamate.

[0017]

[11] The method for producing a rubber composition according to any one of [2] to [6], wherein the xanthogenate is zinc isopropylxanthogenate.

[0018]

[12] The tertiary amine compound is represented by the following general formula (i): [In the formula, R ａ , R ｂ and R ｃ may be the same or different, and each is any one of a methyl group, an alkyl group having 2 to 36 carbon atoms, an alkenyl group having 8 to 36 carbon atoms, a cyclohexyl group, and a benzyl group.].

[0019]

[13] The method for producing a rubber composition according to any one of [2] to [6], wherein the inorganic salt hydrate is sodium borate hydrate.

[0020]

[14] The imidazole compound is represented by the following general formula (ii): [In the formula, R ｄ , R ｅ , R ｆ and R ｇ may be the same or different and each represents a hydrogen atom or a monovalent organic group; ｄ , R ｅ , R ｆ and R ｇ and two or more of the above may be bonded to form a ring.].

[0021]

[15] The method for producing a rubber composition according to any one of [2] to [6], wherein the organic sulfonic acid is at least one compound selected from p-toluenesulfonic acid and benzenesulfonic acid.

[0022]

[16] The method for producing a rubber composition according to any one of [3] to

[15] , wherein 50 mol% or more of the organic acid compound (E) contained in the rubber composition in the first stage of kneading is stearic acid.

[0023]

[17] The method for producing a rubber composition according to any one of [3] to

[16] , wherein the rubber component (A) contains at least one selected from an emulsion-polymerized styrene-butadiene copolymer and a natural rubber, and 50 mol % or more of the organic acid compound (E) contained in the rubber composition in the first stage of kneading is at least one compound selected from a rosin acid and a fatty acid contained in the at least one selected from the emulsion-polymerized styrene-butadiene copolymer and the natural rubber.

[0024]

[18] The method for producing a rubber composition according to any one of [1] to

[17] , wherein in the first stage of the kneading, the rubber component (A), all or a part of the inorganic filler (B), and all or a part of the silane coupling agent (C) are kneaded, and then a reaction accelerator compound (D) for the silica and the silane coupling agent is added and further kneaded.

[0025]

[19] The method for producing a rubber composition according to any one of [1] to

[18] , wherein the plant-derived silica (B1) is silica derived from a grass plant.

[0026]

[20] The method for producing a rubber composition according to

[19] , wherein the plant-derived silica (B1) is silica derived from rice husks.

[0027] According to the present invention, it is possible to provide a method for producing a rubber composition that is capable of obtaining a rubber composition that not only has excellent low heat buildup but also increases the proportion of sustainable materials in rubber products.

[0028] The method for producing the rubber composition of the present invention will be described in detail below by way of example based on an embodiment thereof.

[0029] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0030] In this specification, the "proportion of sustainable materials" refers to the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from renewable resources (recycled resources) in a target rubber composition or rubber product (tire, etc.).

[0031] In this specification, the term "biological resources (biomass resources)" refers to carbon-neutral organic resources derived from living organisms, and includes, for example, materials stored in the form of starch or cellulose, the bodies of animals that grow by eating plants, and products obtained by processing plants or animals, and is a resource excluding fossil resources (petroleum, coal, natural gas, etc.). The biological resources may be edible or non-edible, but are preferably non-edible in order not to compete with food and from the viewpoint of effective resource utilization.

[0032] Specific examples of the biological resources include cellulosic crops (pulp, kenaf, wheat straw, rice straw, waste paper, papermaking residues, etc.), wood, charcoal, compost, food waste, vegetable oil residues, fishery residues, livestock excrement, food waste, wastewater sludge, natural rubber, cotton, oils and fats (palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, peanut oil, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, etc.), and the like. Examples of biological resources include: corn oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, coconut oil, etc.), carbohydrate crops (corn, wheat, rice, rice husks, rice bran, old rice, potatoes, buckwheat, cassava, sago palm, sugarcane, etc.), bagasse (i.e., the residue left after sugarcane juicing), soybeans, soybean pulp refuse, essential oils (pine oil, orange oil, eucalyptus oil, etc.), pulp black liquor, and algae. The biological resources may also be processed (i.e., biological resource-derived substances). Examples of processing methods include biological processing methods utilizing the activity of microorganisms, plants, animals, and their tissue cultures; chemical processing methods utilizing acids, alkalis, catalysts, thermal energy, light energy, etc.; and physical processing methods such as pulverization, compression, microwave treatment, and electromagnetic wave treatment. The biological resources may also be extracted and purified from the biological resources or biological resources that have undergone the above-described processing (i.e., biological resource-derived substances). For example, sugars, proteins, amino acids, fatty acids, fatty acid esters, etc., purified from the above-mentioned biological resources can also be used. Examples of the sugars include sucrose, glucose, trehalose, fructose, lactose, galactose, xylose, allose, talose, gulose, altrose, mannose, idose, arabinose, apiose, maltose, cellulose, starch, chitin, etc., derived from biological resources. Examples of the proteins include compounds derived from biological resources and formed by linking amino acids (preferably L-amino acids), including oligopeptides such as dipeptides. Examples of the amino acids include valine, leucine, isoleucine, arginine, lysine, asparagine, glutamine, phenylalanine, etc., derived from biological resources, with valine, leucine, isoleucine, arginine, and phenylalanine being preferred.The amino acids may be either L-amino acids or D-amino acids, but L-amino acids are preferred from the viewpoints of abundance in nature and ease of availability. Examples of the fatty acids include butyric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, etc., which are derived from biological resources. Examples of the fatty acid esters include modified products of vegetable oils, animal oils, and fats and oils derived from biological resources. These biological resources may contain various materials and impurities.

[0033] In this specification, the term "recycled resources" refers to resources obtained by regenerating (recycling) products that have been used once, or that have been collected without being used, or that have been discarded. For example, recycled resources include resources obtained by regenerating (recycling) used rubber products such as used tires.

[0034] <Method for Producing Rubber Composition> The method for producing a rubber composition of this embodiment is a method for producing a rubber composition comprising a rubber component (A) consisting of at least one of natural rubber and synthetic diene rubber, a filler including an inorganic filler (B), a silane coupling agent (C), and a compound (D) that accelerates the reaction between silica and the silane coupling agent. The method for producing a rubber composition of this embodiment is characterized in that the inorganic filler (B) includes plant-derived silica (B1), and the rubber composition is kneaded in multiple stages, and in the first stage of kneading, all or a portion of the rubber component (A), all or a portion of the inorganic filler (B), all or a portion of the silane coupling agent (C), and the compound (D) that accelerates the reaction between silica and the silane coupling agent are kneaded.

[0035] In the method for producing a rubber composition according to this embodiment, the reaction accelerator compound (D) for silica and a silane coupling agent is added and kneaded in the first stage of kneading in order to enhance the activity of the coupling function of the silane coupling agent (C). By enhancing the activity of the coupling function of the silane coupling agent (C), the low heat buildup of the resulting rubber composition can be improved. Furthermore, in the method for producing a rubber composition according to this embodiment, the plant-derived silica (B1) is a material derived from biological resources (biomass resources), and therefore the rubber composition obtained by this method for producing a rubber composition according to this embodiment has a high proportion of sustainable materials. Therefore, by applying the rubber composition obtained by this method for producing a rubber composition according to this embodiment to a rubber product, it is possible to increase the proportion of sustainable materials in the rubber product. Therefore, according to the method for producing a rubber composition according to this embodiment, a rubber composition can be obtained that not only has excellent low heat buildup but also increases the proportion of sustainable materials in the rubber product.

[0036] The maximum temperature of the rubber composition in the first stage of kneading is preferably 120 to 190° C. When the maximum temperature of the rubber composition in the first stage of kneading is 120 to 190° C., the activity of the coupling function of the silane coupling agent (C) can be more suitably increased, and the low heat buildup of the resulting rubber composition can be further improved.

[0037] The kneading process of the rubber composition in this embodiment includes at least two stages: a first stage of kneading that does not contain any vulcanization-related chemicals other than the reaction accelerator compound (D) between the silica and the silane coupling agent, and a final stage of kneading that contains vulcanization-related chemicals. If necessary, an intermediate stage of kneading that does not contain any vulcanization-related chemicals other than the reaction accelerator compound (D) between the silica and the silane coupling agent may be included. Here, the vulcanization-related chemicals refer to chemicals involved in vulcanization, specifically vulcanizing agents and vulcanization accelerators. The first stage of kneading in this embodiment refers to the initial stage of kneading the rubber component (A), the inorganic filler (B), and the silane coupling agent (C), but does not include the initial stage of kneading the rubber component (A) with fillers other than the inorganic filler (B) or the initial stage of pre-kneading only the rubber component (A). In this embodiment, the kneading stage before the final stage, such as the first stage or intermediate stage, is a process of blending and kneading raw materials other than vulcanization-related chemicals (vulcanizing agents and vulcanization accelerators), such as the rubber component (A), inorganic filler (B), and silane coupling agent (C), to disperse the inorganic filler (B) in the rubber composition and reinforce the rubber component (A). In this embodiment, the first stage is characterized by blending a reaction accelerator compound (D) between silica and the silane coupling agent, thereby improving the dispersion of the inorganic filler (B) in the rubber composition. Note that the rubber component, filler, etc. may be blended and kneaded in the intermediate stage.

[0038] In the method for producing the rubber composition of this embodiment, in the first stage of kneading, it is preferable to knead the rubber component (A), all or part of the inorganic filler (B), and all or part of the silane coupling agent (C), and then add the reaction accelerator compound (D) between the silica and the silane coupling agent and further knead. In the first stage of kneading, after kneading the rubber component (A), all or part of the inorganic filler (B), and all or part of the silane coupling agent (C), add the reaction accelerator compound (D) between the silica and the silane coupling agent and further knead, thereby further improving the activity of the coupling function of the silane coupling agent (C), and further improving the low heat buildup of the resulting rubber composition.

[0039] When an intermediate stage after the first stage of kneading and before the final stage is included, the maximum temperature of the rubber composition in the intermediate kneading stage is preferably 120 to 190°C, more preferably 130 to 175°C, and even more preferably 140 to 170°C. The kneading time is preferably 10 seconds to 20 minutes, more preferably 10 seconds to 10 minutes, and even more preferably 30 seconds to 5 minutes. When an intermediate stage is included, it is preferable to lower the temperature of the rubber composition after the first kneading stage by 10°C or more below the temperature after completion of the first kneading stage before proceeding to the next stage.

[0040] The final stage of kneading refers to the process of compounding and kneading vulcanization chemicals (vulcanizing agent, vulcanization accelerator). The maximum temperature of the rubber composition in this final stage is preferably 60 to 140°C, more preferably 80 to 120°C, and even more preferably 100 to 120°C. The kneading time is preferably 10 seconds to 20 minutes, more preferably 10 seconds to 10 minutes, and even more preferably 20 seconds to 5 minutes. When proceeding from the first stage or intermediate stage of kneading to the final stage, it is preferable to lower the temperature of the rubber composition by 10°C or more below the temperature at the end of the first stage before proceeding to the next stage.

[0041] In the method for producing the rubber composition of the present embodiment, various compounding ingredients, such as a vulcanization activator such as zinc oxide and an antioxidant, which are usually compounded in the rubber composition, are kneaded, as necessary, in the first or final stage of kneading, or in an intermediate stage between the first and final stages.

[0042] The kneading apparatus used in the method for producing a rubber composition of this embodiment may be a Banbury mixer, a roll, an intensive mixer, a kneader, a twin-screw extruder, etc. The kneading conditions are not particularly limited, and various conditions such as the input volume of the kneading apparatus, the rotation speed of the rotor, the ram pressure, and the type of kneading apparatus can be appropriately selected depending on the purpose.

[0043] The method for producing the rubber composition of the present embodiment is not particularly limited, and may include, in addition to the kneading described above, steps such as heating and extrusion. The obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0044] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0045] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0046] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of apparatuses for vulcanization include molding vulcanizers using molds used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0047] (Rubber Component (A)) The rubber composition obtained by the rubber composition production method of this embodiment contains a rubber component (A) consisting of at least one of natural rubber and synthetic diene rubber, and the rubber component (A) provides rubber elasticity to the composition. The rubber component (A) preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. Here, the "sustainability rate" of the rubber component (A) refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources (recycled resources) in the rubber component (A).

[0048] The rubber component (A) is preferably the rubber derived from biological resources and the rubber derived from recycled resources. Here, the proportion of the monomer component derived from biological resources in 100 mol% of the monomer components constituting the rubber derived from biological resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may even be 100 mol%. Furthermore, the proportion of the monomer component derived from recycled resources in 100 mol% of the monomer components constituting the rubber derived from recycled resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may even be 100 mol%.

[0049] The rubber component (A) is a component that contributes to crosslinking, and typically has a weight average molecular weight (Mw) of 10,000 or more, preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and preferably 5,000,000 or less, more preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,300,000 or less. In this specification, the weight average molecular weight (Mw) of the rubber component (A) can be determined in terms of standard polystyrene based on measurements obtained using, for example, a gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation).

[0050] The rubber component (A) is preferably a diene rubber, and the diene rubber is preferably an isoprene rubber or a butadiene rubber. Here, the isoprene rubber refers to a rubber containing units derived from isoprene as a monomer unit, and the butadiene rubber refers to a rubber containing units derived from butadiene as a monomer unit.

[0051] Examples of the isoprene-based rubber include natural rubber (NR), synthetic isoprene rubber (IR), modified natural rubber (modified NR), modified natural rubber (modified NR), and modified synthetic isoprene rubber (modified IR). Examples of natural rubber (NR) that can be used include those commonly used in the tire industry, such as RSS#3 and TSR20 (e.g., SIR20 and STR20). The origin of the natural rubber (NR) is not particularly limited, and examples include those derived from Hevea brasiliensis, guayule, and Russian dandelion. Examples of synthetic isoprene rubber (IR) are not particularly limited, and examples include those commonly used in the tire industry, such as IR2200. Examples of modified NR include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized synthetic isoprene rubber, hydrogenated synthetic isoprene rubber, and grafted synthetic isoprene rubber. These isoprene-based rubbers may be used alone or in combination of two or more. Among these, NR is preferred as the isoprene-based rubber.

[0052] The isoprene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. To achieve a sustainability rate within the above range, it is preferable to use natural rubber (NR) or a polymer synthesized using isoprene derived from biological resources or isoprene derived from recycled resources as a monomer component. In this case, the synthesized polymer may be a homopolymer of a monomer derived from biological resources, a homopolymer of a monomer derived from recycled resources, a copolymer of a monomer derived from biological resources and a monomer derived from recycled resources, or a copolymer of a monomer derived from biological resources and / or a monomer derived from recycled resources and a monomer derived from fossil resources (petroleum, etc.).

[0053] Examples of the butadiene-based rubber include butadiene rubber (BR), aromatic vinyl compound-butadiene copolymer rubber (for example, styrene-butadiene rubber (SBR)), etc. Here, butadiene, which is a raw material for butadiene-based rubber, is preferably derived from biological resources or recycled resources.

[0054] Examples of the butadiene rubber (BR) include high-cis butadiene rubber, low-cis butadiene rubber, and butadiene rubber containing syndiotactic polybutadiene crystals. Commercially available butadiene rubbers can be used as the butadiene rubber (BR), and examples of commercially available butadiene rubbers include products from UBE Elastomers Co., Ltd., ENEOS Materials Corporation, Asahi Kasei Corporation, and Zeon Corporation. These butadiene rubbers may be used alone or in combination of two or more.

[0055] Examples of the aromatic vinyl compound-butadiene copolymer rubber (e.g., SBR) include emulsion-polymerized aromatic vinyl compound-butadiene copolymer rubber (e.g., emulsion-polymerized styrene-butadiene rubber (E-SBR)) and solution-polymerized aromatic vinyl compound-butadiene copolymer rubber (e.g., solution-polymerized styrene-butadiene rubber (S-SBR)). In the aromatic vinyl compound-butadiene copolymer rubber, examples of the aromatic vinyl compound (aromatic vinyl monomer) include styrene, vinylnaphthalene, and divinylnaphthalene. These aromatic vinyl compounds may be used alone or in combination of two or more. Among these, styrene is preferred, and styrene derived from biological resources and styrene derived from recycled resources are particularly preferred. That is, SBR is preferred as the aromatic vinyl compound-butadiene copolymer rubber. The styrene may have a substituent. As the aromatic vinyl compound-butadiene copolymer rubber, commercially available products can be used, and examples of such commercially available products include products from Asahi Kasei Corporation, ENEOS Materials Corporation, Zeon Corporation, Sumitomo Chemical Co., Ltd. These aromatic vinyl compound-butadiene copolymer rubbers may be used alone or in combination of two or more.

[0056] The butadiene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. To achieve a sustainability rate within the above range, for example, a polymer synthesized using a bioresource-derived butadiene, a recycled resource-derived butadiene, a bioresource-derived aromatic vinyl compound (e.g., bioresource-derived styrene), or a recycled resource-derived aromatic vinyl compound (e.g., recycled resource-derived styrene) as a monomer component may be used. In this case, the synthesized polymer may be a homopolymer of a bioresource-derived monomer, a homopolymer of a recycled resource-derived monomer, a copolymer of a bioresource-derived monomer and a recycled resource-derived monomer, or a copolymer of a bioresource-derived monomer and / or a recycled resource-derived monomer and a fossil resource (e.g., petroleum)-derived monomer. Note that the butadiene rubber (B-BR) derived from biological resources (biomass resources) and aromatic vinyl compound-butadiene copolymer rubber derived from biological resources (for example, styrene-butadiene rubber (B-SBR) derived from biological resources (biomass resources)) include not only rubber obtained by polymerizing butadiene or the like according to conventional methods, but also rubber obtained by reactions involving microorganisms, plants, animals, and tissue cultures thereof (hereinafter also referred to as "microorganisms, etc.") or enzymatic reactions.

[0057] In order to set the sustainability rate of the entire rubber component (A) within the above range, it is preferable to use natural rubber (NR) as the rubber component (A) or a polymer synthesized using a monomer component derived from a biological resource or a monomer component derived from a recycled resource as a monomer component.

[0058] Generally, the raw materials for rubber compositions for tires (e.g., rubber and its monomers, fillers, resins, etc.) require large-scale manufacturing equipment for their production, and are therefore typically produced in large factories in specific regions, requiring significant amounts of energy for the storage and transportation of raw materials and products. In contrast, materials derived from biological resources (biomass resources) are derived from local agricultural products, forests, etc., and can be produced on a small scale through microbial fermentation and catalytic reactions. By utilizing local products and waste, the energy required for transporting and storing raw materials can be reduced, and the energy required for transporting and storing the produced materials to tire factories can also be reduced, making them environmentally friendly. Materials derived from recycled resources can be obtained, for example, by dismantling and pyrolyzing used tires to extract the tire-constituting materials, such as rubber, fillers, and steel cords. In addition, sulfur can be obtained from biological resources or processed products of biological resources by a method including a desulfurization step of desulfurizing biological resources or processed products of biological resources to remove sulfur-containing substances from the biological resources or processed products of biological resources, a recovery step of recovering sulfur from the desulfurization residue generated in the desulfurization step, and a processing step of processing the recovered sulfur into sulfur for vulcanization (for example, the method described in Japanese Patent Application No. 2022-140390), and raw materials for tire rubber compositions can be obtained from various waste products and used items. In this way, the use of sustainable materials (materials derived from biological resources or materials derived from recycled resources) can reduce the overall environmental impact of tire manufacturing, such as reducing carbon dioxide emissions (LCCO2) over the entire life cycle, reducing energy consumption (LCE) over the entire life cycle, reducing costs incurred over the entire life cycle (LCC), and reducing the use of fossil resources.

[0059] Furthermore, when producing the rubber composition, the ratios of monomer components derived from biological resources, monomer components derived from recycled resources, and monomer components derived from fossil resources can be appropriately selected depending on the supply situation of biological resources, recycled resources, and fossil resources (e.g., monomer components derived from fossil resources) and / or market demand (e.g., demand for biological resources as food). By polymerizing the monomer components derived from biological resources, monomer components derived from recycled resources, and monomer components derived from fossil resources, rubber derived from sustainable materials (materials derived from biological resources or materials derived from recycled resources) can be obtained that has performance equivalent to that of conventional synthetic rubber. When using monomer components derived from recycled resources, it may be difficult to separate them from monomer components derived from fossil resources due to the manufacturing process of the monomers. In such cases, the environmental impact can be evaluated by adopting the mass balance approach.

[0060] The ratio of each monomer unit (e.g., isoprene-derived unit, butadiene-derived unit, and aromatic vinyl compound-derived unit) in the entire rubber component (A) can be adjusted appropriately depending on the component to which it is applied. The ratio of each monomer unit in the entire rubber component can be adjusted, for example, by appropriately combining the above-mentioned isoprene-based rubber and butadiene-based rubber. The ratio of cis-bond units in the butadiene-derived units can also be adjusted appropriately depending on the component to which it is applied. In this specification, the term "monomer unit" refers to a structural unit of a polymer, the term "isoprene-derived unit" refers to a structural unit in a polymer formed based on the isoprene monomer (including isoprene units in natural rubber), the term "butadiene-derived unit" refers to a structural unit in a polymer formed based on the butadiene monomer, and the term "aromatic vinyl compound-derived unit" refers to a structural unit in a polymer formed based on the aromatic vinyl compound monomer. In this specification, the ratio of each monomer unit is measured by NMR.

[0061] The rubber component (A) may contain, in addition to the above-mentioned isoprene-based rubber, butadiene rubber (BR), and aromatic vinyl compound-butadiene copolymer rubber (e.g., SBR), synthetic diene-based rubbers such as acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), and ethylene-propylene-diene terpolymer rubber (EPDM). These rubber components may be used alone or in combination of two or more.

[0062] The rubber component (A) may be modified to have a functional group that interacts with fillers such as carbon black and silica. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups. These functional groups may have a substituent. These functional groups may be introduced into the rubber component either individually or in combination. Among these, an amino group, an alkoxy group, and an alkoxysilyl group are preferred, and a substituted amino group in which a hydrogen atom of an amino group is substituted with an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and an alkoxysilyl group having 1 to 6 carbon atoms are more preferred.

[0063] The functional group can be introduced, for example, by reacting a compound (modifier) ​​having the functional group with the rubber component (A). The functional group is a modified functional group that has interactivity with fillers such as silica and carbon black, and examples thereof include nitrogen-containing functional groups, silicon-containing functional groups, and oxygen-containing functional groups. Examples of compounds (modifiers) having nitrogen-containing functional groups include amino group-containing compounds, and examples of compounds (modifiers) having silicon-containing functional groups include silicon halides and hydrocarbyloxysilane compounds. Examples of compounds (modifiers) having oxygen-containing functional groups include alkoxy group-containing compounds, alkylene oxide group-containing compounds, and trialkylsilyloxy group-containing compounds. More specifically, examples of the compounds described in WO 2016 / 194316 and WO 2019 / 117256 include the compounds described in WO 2016 / 194316 and WO 2019 / 117256. These modifiers may be used alone or in combination of two or more.

[0064] The rubber derived from sustainable materials (materials derived from biological resources or materials derived from recycled resources) can be produced in the same manner as conventional methods for producing synthetic rubber derived from fossil resources, for example, by using monomer components derived from biological resources or monomer components derived from recycled resources, and, if necessary, monomer components derived from fossil resources. Furthermore, the rubber derived from sustainable materials (particularly rubber derived from biological resources) can also be obtained by reactions using microorganisms or enzyme reactions.

[0065] Regarding the method for preparing bioresource-derived rubber from the above-mentioned bioresources, for example, the method described in JP 2022-179158 A can be used. For example, by using butadiene obtained from a bioresource as the monomer component, it is possible to obtain a bioresource (biomass resource)-derived butadiene rubber (B-BR). Furthermore, by using styrene obtained from a bioresource and butadiene obtained from a bioresource as the monomer components, it is possible to obtain a bioresource (biomass resource)-derived styrene-butadiene rubber (B-SBR). Here, methods for obtaining B-BR and B-SBR from bioresources include artificial polymerization methods, in vivo polymerization methods, and polymerization methods using biological enzymes. The molecular weight, branching, microstructure, etc. of the obtained B-BR and B-SBR can be appropriately adjusted by changing the polymerization conditions according to known methods depending on the desired tire performance.

[0066] Suitable butadienes obtained from biological resources include butadienes derived from alkyl alcohols (preferably ethanol and butanol, more preferably butanol), butadienes derived from alkenes (preferably ethylene), and butadienes derived from unsaturated carboxylic acids (preferably tiglic acid). Two or more of these butadienes may be used in combination. Suitable styrenes obtained from biological resources include styrenes obtained from plants (preferably plants belonging to the Hamamelidaceae, Styraxaceae, and Apocynaceae families, more preferably plants belonging to the Liquidambar, Styrax, and Catharanthus roseus, and even more preferably sweetgum, Styrax rostrata, and Catharanthus roseus), and styrenes obtained from microorganisms (preferably microorganisms belonging to the Penicillium and Escherichia genera, more preferably P. citrinum, and transformed E. coli). Suitable styrenes may be used in combination.

[0067] Recently, biomass industrial complexes centered on bioethanol, bioethylene, and the like have been planned. However, bioethanol and bioethylene are produced primarily using sugars and / or cellulose as biological resources, and do not effectively utilize other biological resources such as proteins, lipids, and amino acids. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (e.g., demand for biomass resources as food), it is preferable to use multiple types of monomer components derived from biological resources as the biological resource-derived monomer component, or to use a combination of monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources, and further to appropriately adjust the ratios of these monomer components. This allows for the effective utilization of a wide range of biological resources, such as sugars, proteins, and lipids, as well as renewable resources, without relying on a single type of biological resource. It also allows for a stable supply of rubber derived from sustainable materials and further allows for environmental considerations depending on the production conditions. When multiple types of monomer components derived from biological resources are used, it is preferable to use monomer components derived from different biological resources, i.e., monomer components obtained from different biological resources. Specifically, it is preferable to use a mixture of butadienes derived from multiple types of biological resources with different origins as the biological resource-derived butadiene, and / or to use a mixture of styrenes derived from multiple types of biological resources with different origins as the biological resource-derived styrene. This allows for effective use of multiple types of biological resources.

[0068] (Filler) The rubber composition obtained by the method for producing a rubber composition according to this embodiment contains a filler including an inorganic filler (B). The inclusion of the filler improves the reinforcing properties of the rubber composition. The content of the filler is preferably in the range of 20 to 150 parts by mass per 100 parts by mass of the rubber component (A). An amount of 20 parts by mass or more is preferred from the viewpoint of improving the reinforcing properties of the rubber composition, and an amount of 150 parts by mass or less is preferred from the viewpoint of reducing rolling resistance.

[0069] The inorganic filler (B) is preferably present in an amount of 30% by mass or more in the filler. When the proportion of the inorganic filler (B) in the filler is 30% by mass or more, wet performance and low heat buildup can be achieved at the same time. From the viewpoint of wet performance and low heat buildup, the proportion of the inorganic filler (B) in the filler is more preferably 40% by mass or more, and even more preferably 70% by mass or more.

[0070] As the inorganic filler (B), silica and an inorganic compound represented by the following general formula (iii) can be used: dM.xSiO ｙ ・zH ２ O ... (iii) In the above general formula (iii), M is at least one selected from the group consisting of a metal selected from the group consisting of aluminum, magnesium, titanium, calcium, and zirconium, an oxide or hydroxide of these metals, a hydrate thereof, or a carbonate of these metals, and d, x, y, and z are, respectively, an integer of 1 to 5, an integer of 0 to 10, an integer of 2 to 5, and an integer of 0 to 10. Note that, in general formula (iii), when x and z are both 0, the inorganic compound becomes at least one metal, metal oxide, or metal hydroxide selected from aluminum, magnesium, titanium, calcium, and zirconium.

[0071] Examples of inorganic compounds represented by the general formula (iii) include alumina (Al2O3) such as γ-alumina and α-alumina; alumina monohydrate (Al2O3.H2O) such as boehmite and diaspore; aluminum hydroxide [Al(OH)3] such as gibbsite and bayerite; aluminum carbonate [Al2(CO3)3], magnesium hydroxide [Mg(OH)2], magnesium oxide (MgO), magnesium carbonate (MgCO3), talc (3MgO.4SiO2.H2O), attapulgite (5MgO.8SiO2.9H2O), titanium white (TiO2), titanium black (TiO 2n-1), calcium oxide (CaO), calcium hydroxide [Ca(OH)2], magnesium aluminum oxide (MgO.Al2O3), clay (Al2O3.2SiO2), kaolin (Al2O3.2SiO2.2H2O), pyrophyllite (Al2O3.4SiO2.H2O), bentonite (Al2O3.4SiO2.2H2O), aluminum silicate (Al2SiO5, Al4.3SiO4.5H2O, etc.), magnesium silicate (Mg2SiO4, MgSiO3, etc.), ke Examples of suitable inorganic compounds include calcium silicate (e.g., CaSiO), aluminum calcium silicate (e.g., AlO·CaO·2SiO), magnesium calcium silicate (CaMgSiO), calcium carbonate (CaCO), zirconium oxide (ZrO), zirconium hydroxide [ZrO(OH)·nH0], zirconium carbonate [Zr(CO)], and crystalline aluminosilicates containing hydrogen, alkali metal, or alkaline earth metal to compensate for charge, such as various zeolites. Furthermore, it is preferable that M in the general formula (iii) above is at least one selected from aluminum metal, aluminum oxide or hydroxide, and their hydrates, or aluminum carbonate. The inorganic compounds represented by the general formula (iii) above may be used alone or in combination. The average particle size of these inorganic compounds is preferably in the range of 0.01 to 10 μm, more preferably 0.05 to 5 μm, from the viewpoint of the balance between kneading workability, abrasion resistance, and wet grip performance.

[0072] Among the inorganic fillers (B), silica is preferred from the viewpoint of achieving both low heat generation and abrasion resistance. As the inorganic filler (B), silica may be used alone, or silica may be used in combination with one or more inorganic compounds represented by general formula (iii):

[0073] The inorganic filler (B) is preferably used in an amount of 20 to 120 parts by mass per 100 parts by mass of the rubber component (A). 20 parts by mass or more is preferred from the viewpoint of ensuring wet performance, and 120 parts by mass or less is preferred from the viewpoint of low heat buildup. Furthermore, 30 to 100 parts by mass is more preferred. When silica is used as the inorganic filler (B), the silica content in the filler is preferably 30% by mass or more, and more preferably 35% by mass or more.

[0074] -Silica- The inorganic filler (B) contains plant-derived silica (B1). The plant-derived silica (B1) is a material derived from biological resources (biomass resources). Therefore, the inclusion of the plant-derived silica (B1) increases the proportion of sustainable materials in the rubber composition. By applying the rubber composition to rubber products, the proportion of sustainable materials in the rubber products can be increased and the environmental load can be reduced.

[0075] From the viewpoint of reducing environmental impact, the plant-derived silica (B1) is preferably silica derived from silicic acid plants. Examples of such silicic acid plants include mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Poaceae plants. Among these plants, grasses are preferred, i.e., the plant-derived silica (B1) is preferably silica derived from grasses. Grass-derived silica can be procured locally near tire manufacturing plants, reducing the energy and costs required for transportation and storage, making it environmentally preferable from various viewpoints. Examples of such grasses include rice, bamboo grass, and sugarcane, with rice being preferred. Rice is widely cultivated for food, making it possible to obtain it locally over a wide area. Furthermore, rice husks are generated in large quantities as industrial waste, making it easy to secure a sufficient amount. Therefore, from the viewpoint of availability, rice husk-derived silica (hereinafter also referred to as "rice husk silica") is particularly preferred as the plant-derived silica (B1). The use of rice husk silica allows for the effective utilization of rice husks, which are industrial waste, and also allows for the local procurement of raw materials near tire manufacturing plants, thereby reducing the energy and costs of transportation and storage, making it environmentally advantageous from various perspectives. The rice husk silica may be rice husk charcoal powder obtained by carbonizing rice husks by heating, or may be precipitated silica produced by a wet process using an alkali silicate aqueous solution obtained by extracting rice husk ash, which is generated when rice husks are burned as fuel in a biomass boiler, with an alkali. The method for producing rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be obtained by pyrolyzing rice husks by steaming them in a kiln. The rice husk charcoal obtained in this manner can be pulverized using a known pulverizer (e.g., a ball mill), sorted, and classified into particles of a predetermined particle size range, to obtain rice husk charcoal powder. The precipitated silica derived from rice husks can be produced by the method described in JP-A-2019-38728.

[0076] The ratio of the plant-derived silica (B1) in the inorganic filler (B) is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 25% by mass or more, even more preferably 45% by mass or more, and most preferably 100% by mass. By making the ratio of the plant-derived silica (B1) in the inorganic filler (B) 5% by mass or more, the ratio of sustainable materials in the rubber composition is increased, and by applying the rubber composition to a rubber product, the ratio of sustainable materials in the rubber product can be further increased.

[0077] The inorganic filler (B) may contain silica other than the plant-derived silica (B1). Examples of such silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these, wet silica is preferred because it contains a large number of silanol groups. These silicas other than the plant-derived silica (B1) may be used alone or in combination of two or more. Commercially available silicas other than the plant-derived silica (B1) may be used, and examples of such commercially available silicas include products from Tosoh Silica Corporation, Evonik, Solvay, Solvay Japan, and Tokuyama Corporation.

[0078] From the viewpoint of reducing the environmental load, it is also preferable to use, as the silica, silica obtained by extracting silicic acid components from scraps of silicon wafers, which are raw materials for semiconductors, glass bottles, etc., and recycling the extracted silica for use in the production.

[0079] The plant-derived silica (B1) has a nitrogen adsorption specific surface area (N ２ SA) is 50m ２ / g or more, and ２ / g or more is more preferable, and 150m ２ / g or more, and ２ / g or less, and ２ / g or less is more preferable, and 230m ２ / g or less is more preferable, and 200m ２ / g or less. In this specification, the nitrogen adsorption specific surface area (N ２ SA) is a value measured by the BET method in accordance with ASTM D3037-93.

[0080] The content of the plant-derived silica (B1) can be adjusted appropriately depending on, for example, the tire category to which the rubber component (A) is applied, the tire component, the target performance, etc. For example, the content of the plant-derived silica (B1) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, more preferably 30 parts by mass or more, more preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, still more preferably 100 parts by mass or more, particularly preferably 110 parts by mass or more, and preferably 300 parts by mass or less, more preferably 200 parts by mass or less, even more preferably 180 parts by mass or less, and particularly preferably 150 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0081] - Carbon Black - The filler may contain carbon black in addition to the inorganic filler (B) described above. The carbon black reinforces the rubber composition and can improve the abrasion resistance of the rubber composition. As the carbon black, plant-derived carbon black and recycled carbon black (also called "recycled carbon black") are preferred. Examples of plant-derived carbon black include those derived from castor oil and pine oil. Recycled carbon black will be described in detail below.

[0082] From the viewpoint of further improving the abrasion resistance of the rubber composition and a tire using the same, the content of carbon black (total of recycled carbon black and carbon black other than recycled carbon black) in the rubber composition is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of rubber component (A). Also, from the viewpoint of workability of the rubber composition, the content of carbon black in the rubber composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of rubber component (A).

[0083] --Recycled Carbon Black-- In this specification, "recycled carbon black" refers to carbon black recovered from recycled waste raw materials. Examples of such waste include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only that generated from rubber products but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeled rubber. Buffing powder is fine rubber generated during the buffing process, for example, in tire retreading, where the tread portion remaining on the base tire is scraped off. Peeled rubber is a long piece of rubber, e.g., 1 to 2 cm wide, peeled from the surface of a rubber product such as a tire. Peeled rubber is generated by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Furthermore, waste rubber is not limited to crosslinked rubber but also includes unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, as well as rubber parts or components during the manufacturing process of final products. Used tires may be tires to be retreaded, or may be tires discarded for some reason, such as tires generated during tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their service life. Waste oils are not limited to those generated during the decomposition of plastics and rubber, but also include used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that contain no non-organic components, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils containing carbon black or rubber containing carbon black are desirable. "Recycled carbon black" differs from carbon black produced directly from hydrocarbons such as petroleum, natural gas, and coal, i.e., non-recycled carbon black. Note that "used" here refers not only to waste oils discarded after actual use, but also to waste oils that were produced but discarded without actually being used.

[0084] The recycled carbon black is preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by pyrolysis of a vulcanized rubber product containing carbon black is readily available because vulcanized rubber products containing carbon black are readily available and can be easily obtained by pyrolysis. Furthermore, the recycled carbon black is preferably obtained from the solid residue produced by the pyrolysis of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is pyrolyzed, a solid residue and a volatile component (oil) are obtained, and recycled carbon black can be recovered from either of them. When recovering carbon black from the volatile component, the oil component with a specific gravity suitable for producing carbon black can be recovered and used to produce carbon black using existing carbon black production methods (e.g., JP 2015-520259 A). Unlike carbon black recovered from solid residues, this method offers advantages such as no impurities and no mixing of different grades. In addition, in the production of environmentally friendly carbon black, various options are available, including oils obtained by recovering volatile components from rubber pyrolysis, as described above, as well as vegetable oils and oils derived from waste plastics. However, edible resources such as vegetable oils are needed for other uses, such as food, and there are challenges in securing sufficient quantities, as well as the environmental impact of expanding cultivated land. Furthermore, oils derived from waste plastics are also used for other purposes, such as horizontal plastic recycling, so supply issues are also a concern. On the other hand, using volatile components (oils) produced by the pyrolysis of vulcanized rubber products, particularly tires, allows for the continued use of existing materials due to the tire industry's ongoing system of using existing materials, thereby reducing the consumption of new materials in new tire production and contributing to a reduction in the industry's environmental impact. The grade of carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0085] Solid residues obtained by pyrolysis of waste materials such as used rubber and used tires contain ash in addition to carbon black. The ash is derived from non-volatile components contained in the rubber and tires. Therefore, recycled carbon black obtained from the solid residues has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, the higher the carbon content of the recycled carbon black, the better. The carbon content of the recycled carbon black is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content of the recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed moisture.

[0086] Specific examples of the ash include zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, and magnesium oxide. In the case of recycled carbon black produced from solid residue obtained by pyrolysis of waste, a certain amount of ash remains even after various processes for removing the ash. In this embodiment, the recycled carbon black is allowed to contain ash. In one embodiment, the lower limit of the ash content of the recycled carbon black may be 0.5% by mass.

[0087] The recycled carbon black can also be obtained from a pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3,427,975, citing "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, describes that recycled carbon black can be obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

[0027] ). Carbon black obtained from such pyrolysis processes typically lacks functional groups on its surface, as mentioned in paragraph

[0004] of Japanese Patent Publication No. 6,856,781 (Comparison of the Surface Morphology and Chemistry of Pyrolytic Carbon Black and Commercially Available Carbon Black, Powder Technology 160 (2005) pp. 190-193).

[0088] The recycled carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. The treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3,173,251, carbon black obtained by a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. Furthermore, in Japanese Patent Publication No. 6,856,781, carbon black obtained by a pyrolysis process is treated with an amino acid compound containing at least one thiol or disulfide group to obtain surface-activated carbon black. The recycled carbon black according to this embodiment also includes carbon blacks treated to include functional groups on their surfaces.

[0089] Furthermore, examples of thermal decomposition of crosslinked rubber products (vulcanized rubber products) such as used tires include thermal decomposition methods at temperatures of 650° C. or higher.

[0090] The crosslinked rubber products used for the decomposition may be grouped by the type of rubber component previously compounded, and then the decomposition step may be performed for each group. Alternatively, the crosslinked rubber products may be grouped by the type of filler previously compounded (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and then the decomposition step may be performed for each group. Furthermore, the crosslinked rubber products may be grouped by both type of rubber component and type of filler, and then the decomposition step may be performed for each group. When the decomposition step is performed for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when the recycled carbon black is compounded again into a rubber component, a rubber composition with better performance can be obtained.

[0091] Furthermore, when the crosslinked rubber product used in the degradation is derived from tires, the tires may be grouped in advance by type (e.g., for passenger cars, for trucks and buses, for large vehicles such as off-road vehicles, for aircraft, for agricultural vehicles, etc.), and the degradation step may be carried out for each group. Alternatively, the tires may be grouped in advance by tire component (e.g., tread rubber, sidewall rubber, bead rubber, steel cord-coated rubber, organic fiber-coated rubber, pad rubber, cushion rubber, etc.), and the degradation step may be carried out for each group. Furthermore, the tires may be grouped both by type and by tire component, and the degradation step may be carried out for each group. When the degradation step is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and therefore, when the recycled carbon black is blended again into a rubber component, a rubber composition with better performance can be obtained.

[0092] The recycled carbon black has a nitrogen adsorption specific surface area of ​​40 to 100 m as measured by the BET method. ２ / g, and 50 to 90m ２ / g, and more preferably 55 to 75m ２ In this specification, the nitrogen adsorption specific surface area of ​​recycled carbon black measured by the BET method is a statistical thickness specific surface area (STSA) determined in accordance with ASTM D6556.

[0093] The pH of the recycled carbon black is preferably 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. In this specification, the pH of the recycled carbon black is determined in accordance with ASTM D1512.

[0094] The recycled carbon black preferably has a toluene color transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, the toluene color transmittance of recycled carbon black is determined in accordance with ASTM D1618.

[0095] The recycled carbon black preferably has a heat loss of 3% by mass or less, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less at 125°C. Herein, the heat loss of recycled carbon black at 125°C is determined in accordance with ASTM D1509.

[0096] The recycled carbon black preferably has a sulfur content of 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less.

[0097] The recycled carbon black preferably has a 35 mesh sieve residue of 20 mass ppm or less, more preferably 15 mass ppm or less, and particularly preferably 10 mass ppm or less. Herein, the 35 mesh sieve residue of recycled carbon black is determined in accordance with ASTM D1514.

[0098] The recycled carbon black preferably has a 325 mesh (44 μm) sieve residue of 1000 mass ppm or less, more preferably 700 mass ppm or less, and particularly preferably 300 mass ppm or less. Herein, the 325 mesh (44 μm) sieve residue of the recycled carbon black is determined in accordance with ASTM D1514.

[0099] The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Herein, the pellet hardness of recycled carbon black is determined in accordance with ASTM D5230.

[0100] The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Herein, the pellet fine powder content of recycled carbon black is determined in accordance with ASTM D1508.

[0101] The particle size (D97) of the recycled carbon black is preferably 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Here, in this specification, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size distribution analyzer, assuming a refractive index of 1.33 for water and a refractive index of 1.75 for the filler.

[0102] The recycled carbon black preferably contains particles of 5 μm or less in a proportion of 50% by volume or more, more preferably 70% by volume or more, and particularly preferably 80% by volume or more.

[0103] The recycled carbon black preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the physical properties of the rubber product to which the rubber composition is applied can be improved. Herein, the ash content of the recycled carbon black is determined in accordance with ASTM D8474 and D1506.

[0104] The recycled carbon black preferably has a dibutyl phthalate (DBP) absorption of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, the DBP absorption of recycled carbon black is determined in accordance with ASTM D2414.

[0105] The recycled carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption capacity of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Herein, the 24M4DBP absorption capacity of the recycled carbon black is determined in accordance with ASTM D3493.

[0106] Commercially available recycled carbon black can be used. For example, Enrestec's product name "PB365" can be mentioned as such a commercially available product. PB365 is a recycled carbon black produced through the thermal decomposition of used tires, and has a nitrogen adsorption specific surface area of ​​73.6 m2 as measured by the BET method. ２ / g and contains about 17% by mass of ash.

[0107] The content of the recycled carbon black is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, still more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of the rubber component (A). When the content of the recycled carbon black is 5 parts by mass or more per 100 parts by mass of the rubber component (A), the effect of improving the proportion of sustainable materials in rubber products to which the rubber composition is applied is significant, and when the content is 50 parts by mass or less, the fracture resistance of the rubber composition can be more reliably maintained.

[0108] The proportion of silica in the total content of silica and carbon black is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which it is applied, the tire components, the target performance, etc. For example, in the case of tread rubber for passenger car tires, the proportion of silica in the total content of silica and carbon black is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. Furthermore, the proportion of silica in the total content of silica and carbon black may be 100% by mass, but is preferably 98% by mass or less.

[0109] Examples of the filler include calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, and the like, in addition to the above-mentioned silica and carbon black.

[0110] (Silane Coupling Agent (C)) The rubber composition obtained by the method for producing a rubber composition of this embodiment contains a silane coupling agent (C). The silane coupling agent (C) is preferably a compound represented by any one of the following general formulas (I) to (IV). By using these compounds as the silane coupling agent (C), workability during rubber processing is further improved and a rubber composition with better abrasion resistance can be produced.

[0111] (R １ O) ３－ｐ (R ２ ) ｐ Si-R ３ -S ａ -R ３ -Si(OR １ ) ３－ｒ (R ２ ) ｒ ... (I) In the above general formula (I), R １ When there are a plurality of R, they may be the same or different, and each represents a linear, cyclic or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxyalkyl group having 2 to 8 carbon atoms, or a hydrogen atom; ２ When there are a plurality of R, they may be the same or different, and each is a linear, cyclic or branched alkyl group having 1 to 8 carbon atoms; ３When there are a plurality of a, they may be the same or different and each is a linear or branched alkylene group having 1 to 8 carbon atoms. a has an average value of 2 to 6, and p and r may be the same or different and each has an average value of 0 to 3. However, both p and r cannot be 3.

[0112] Specific examples of the silane coupling agent (C) represented by the general formula (I) include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(3-methyldimethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(3-methyldimethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-trimethoxysilylpropyl)trisulfide, bis(3-methyldimethoxysilylpropyl)trisulfide, bis(2-monoethoxydimethylsilylpropyl) trisulfide, bis(2-triethoxysilylethyl) trisulfide, bis(3-monoethoxydimethylsilylpropyl) tetrasulfide, bis(3-monoethoxydimethylsilylpropyl) trisulfide, bis(3-monoethoxydimethylsilylpropyl) disulfide, bis(3-monomethoxydimethylsilylpropyl) tetrasulfide, bis(3-monomethoxydimethylsilylpropyl) trisulfide, bis(3-monomethoxydimethylsilylpropyl) disulfide, bis(2-monoethoxydimethylsilylethyl) tetrasulfide, bis(2-monoethoxydimethylsilylethyl) trisulfide, bis(2-monoethoxydimethylsilylethyl) disulfide, and the like.

[0113]

[0114] In the above general formula (II), R ４ is -Cl, -Br, R ９ O-, R ９ C(=O)O-, R ９ R １０ C=NO-, R ９ R １０CNO-, R ９ R １０ N- and -(OSiR ９ R １０ ) ｈ (OSiR ９ R １０ R １１ a monovalent group (R ９ , R １０ and R １１ may be the same or different, and each represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and h is an average value of 1 to 4; ５ is R ４ , a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R ６ is R ４ , R ５ , a hydrogen atom or -[O(R １２ O) ｊ ] ０．５ - group (R １２ is an alkylene group having 1 to 18 carbon atoms, and j is an integer of 1 to 4.), R ７ is a divalent hydrocarbon group having 1 to 18 carbon atoms, R ８ represents a monovalent hydrocarbon group having 1 to 18 carbon atoms, and x, y, and z are numbers that satisfy the relationship x+y+2z=3, 0≦x≦3, 0≦y≦2, and 0≦z≦1.

[0115] In the above general formula (II), R ８ , R ９ , R １０ and R １１ may be the same or different, and each is preferably a group selected from the group consisting of a linear, cyclic or branched alkyl group, an alkenyl group, an aryl group and an aralkyl group having 1 to 18 carbon atoms. ５ When R is a monovalent hydrocarbon group having 1 to 18 carbon atoms, it is preferably a group selected from the group consisting of a linear, cyclic, or branched alkyl group, an alkenyl group, an aryl group, and an aralkyl group. １２ R is preferably a linear, cyclic or branched alkylene group, and is particularly preferably a linear one. ７Examples of R include alkylene groups having 1 to 18 carbon atoms, alkenylene groups having 2 to 18 carbon atoms, cycloalkylene groups having 5 to 18 carbon atoms, cycloalkylalkylene groups having 6 to 18 carbon atoms, arylene groups having 6 to 18 carbon atoms, and aralkylene groups having 7 to 18 carbon atoms. The alkylene groups and alkenylene groups may be linear or branched, and the cycloalkylene groups, cycloalkylalkylene groups, arylene groups, and aralkylene groups may have a substituent such as a lower alkyl group on the ring. ７ As the alkylene group, an alkylene group having 1 to 6 carbon atoms is preferred, and particularly preferred examples include straight-chain alkylene groups such as methylene, ethylene, trimethylene, tetramethylene, pentamethylene, and hexamethylene.

[0116] R in the above general formula (II) ５ , R ８ , R ９ , R １０ and R １１ Specific examples of the monovalent hydrocarbon group having 1 to 18 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a cyclopentyl group, a cyclohexyl group, a vinyl group, a propenyl group, an allyl group, a hexenyl group, an octenyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, a phenethyl group, and a naphthylmethyl group. １２ Examples of the alkyl group include a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group, a decamethylene group, and a dodecamethylene group.

[0117] Specific examples of the silane coupling agent (C) represented by the general formula (II) include 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, 2-decanoylthioethyltriethoxysilane, 2-lauroylthioethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, and 2-lauroylthioethyltrimethoxysilane. Of these, 3-octanoylthiopropyltriethoxysilane (manufactured by General Electric Silicones, trademark: NXT Silane) is particularly preferred.

[0118] (R １３ O) ３－ｓ (R １４ ) ｓ Si-R １５ -S ｋ -R １６ -S ｋ -R １５ -Si(OR １３ ) ３－ｔ (R １４ ) ｔ ... (III) In the above general formula (III), R １３ When there are a plurality of R, they may be the same or different, and each represents a linear, cyclic or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxyalkyl group having 2 to 8 carbon atoms, or a hydrogen atom; １４ When there are a plurality of R, they may be the same or different, and each is a linear, cyclic or branched alkyl group having 1 to 8 carbon atoms; １５ When there are a plurality of R, they may be the same or different, and each is a linear or branched alkylene group having 1 to 8 carbon atoms. １６ is represented by the general formula (-S-R１７ -S-), (-R １８ -S ｍ１ -R １９ -) and (-R ２０ -S ｍ２ -R ２１ -S ｍ３ -R ２２ -) any one of the divalent groups (R １７ ~R ２２ are each a divalent hydrocarbon group having 1 to 20 carbon atoms, a divalent aromatic group, or a divalent organic group containing a heteroatom other than sulfur and oxygen, and m1, m2, and m3 each have an average value of 1 to less than 4. ) Multiple k's may be the same or different and each have an average value of 1 to 6, and s and t each have an average value of 0 to 3. However, both s and t cannot be 3.

[0119] Specific examples of the silane coupling agent (C) represented by the general formula (III) include: Average composition formula: (CH3CH2O)3Si-(CH2)3-S2-(CH2)6-S2-(CH2)3-Si(OCH2CH3)3, Average composition formula: (CH3CH2O)3Si-(CH2)3-S2-(CH2) 10 -S2-(CH2)3-Si(OCH2CH3)3, Average composition formula: (CH3CH2O)3Si-(CH2)3-S3-(CH2)6-S3-(CH2)3-Si(OCH2CH3)3, Average composition formula: (CH3CH2O)3Si-(CH2)3-S4-(CH2)6-S4-(CH2)3-Si(OCH2CH3)3, Average compositional formula: (CH3CH2O)3Si-(CH2)3-S-(CH2)6-S2-(CH2)6-S-(CH2)3-Si(OCH2CH3)3, Average compositional formula: (CH3CH2O)3Si-(CH2)3-S-(CH2)6-S 2.5 -(CH2)6-S-(CH2)3-Si(OCH2CH3)3, Average composition formula: (CH3CH2O)3Si-(CH2)3-S-(CH2)6-S3-(CH2)6-S-(CH2)3-Si(OCH2CH3)3, Average compositional formula: (CH3CH2O)3Si-(CH2)3-S-(CH2)6-S4-(CH2)6-S-(CH2)3-Si(OCH2CH3)3, Average compositional formula: (CH3CH2O)3Si-(CH2)3-S-(CH2)10 -S2-(CH2) 10 -S-(CH2)3-Si(OCH2CH3)3, Average composition formula: (CH3CH2O)3Si-(CH2)3-S4-(CH2)6-S4-(CH2)6-S4-(CH2)3-Si(OCH2CH3)3, Average composition formula: (CH3CH2O)3Si-(CH2)3-S2-(CH2)6-S2-(CH2)6-S2-(CH2)3-Si(OCH2CH3)3, Examples include compounds represented by the average compositional formula: (CH3CH2O)3Si-(CH2)3-S-(CH2)6-S2-(CH2)6-S2-(CH2)6-S-(CH2)3-Si(OCH2CH3)3.

[0120]

[0121] In the above general formula (IV), R ２３ is a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms, a plurality of G may be the same or different and each is an alkanediyl group or alkenediyl group having 1 to 9 carbon atoms, a plurality of Z ａ may be the same or different, each a functional group capable of bonding to two silicon atoms, and [—O—] ０．５ , [-O-G-] ０．５ and [-O-G-O-] ０．５ is a functional group selected from the group consisting of a plurality of Z ｂ may be the same or different, each a functional group capable of bonding to two silicon atoms, and [-O-GO-] ０．５ is a functional group represented by the formula: ｃ may be the same or different, and each represents —Cl, —Br, or —OR ２４ , R ２４ C(=O)O-, R ２４ R ２５ C=NO-, R ２４ R ２５ N-, R ２４ - and HO-GO- (where G is the same as above), and R ２４ and R ２５Each of m, n, u, v and w is a linear, branched or cyclic alkyl group having 1 to 20 carbon atoms. m, n, u, v and w are 1≦m≦20, 0≦n≦20, 0≦u≦3, 0≦v≦2, 0≦w≦1, and (u / 2)+v+2w=2 or 3. When there are a plurality of A moieties, Z in the plurality of A moieties ａ ｕ , Z ｂ ｖ and Z ｃ ｗ In the case where there are a plurality of B moieties, Z ａ ｕ , Z ｂ ｖ and Z ｃ ｗ Each of them may be the same or different.

[0122] Specific examples of the silane coupling agent (C) represented by the above general formula (IV) include the following structural formulas (V), (VI) and (VII).

[0123]

[0124] In structural formula (VII), each L is independently an alkanediyl group or an alkenediyl group having 1 to 9 carbon atoms, x=m, and y=n.

[0125] As a silane coupling agent represented by structural formula (V), a product manufactured by Momentive Performance Materials, Inc., under the trademark "NXT Low-V Silane" is commercially available. As a silane coupling agent represented by structural formula (VI), a product manufactured by Momentive Performance Materials, Inc., under the trademark "NXT Ultra Low-V Silane" is also commercially available. Furthermore, as a silane coupling agent represented by structural formula (VII), a product manufactured by Momentive Performance Materials, Inc., under the trademark "NXT-Z" can be mentioned.

[0126] The silane coupling agents represented by the general formula (II), structural formula (V) and structural formula (VI) have a protected mercapto group, which can prevent the occurrence of initial vulcanization (scorch) during processing prior to the vulcanization step, resulting in good processability.In addition, the silane coupling agents represented by structural formulas (V), (VI) and (VII) have a large number of alkoxysilane carbon atoms, which reduces the generation of volatile compounds (VOCs) (especially alcohols), making them preferable for the working environment.In addition, the silane coupling agent of structural formula (VII) is even more preferable because it achieves low heat buildup as tire performance.

[0127] Among the compounds represented by the general formulas (I) to (IV), the compound represented by the general formula (I) is particularly preferred as the silane coupling agent (C). This is because the reaction-accelerating compound (D) between silica and the silane coupling agent is likely to activate the polysulfide bond site that reacts with the rubber component (A). The silane coupling agent (C) may be used alone or in combination of two or more.

[0128] Bioethanol can also be used as a raw material for the silane coupling agent (C). Bioethanol is produced primarily using sugars and / or cellulose as biological resources, and does not effectively utilize other biological resources such as proteins, lipids, and amino acids. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (e.g., demand for biomass resources as food), it is preferable to use multiple types of ethanol (bioethanol) derived from biological resources as the raw material for the silane coupling agent (C), or to use a combination of ethanol (bioethanol) derived from biological resources, ethanol derived from renewable resources, and ethanol derived from fossil resources. This allows for the effective use of a wide range of biological resources and renewable resources, such as sugars, proteins, and lipids, without relying on a single type of biological resource, and also allows for environmental considerations depending on the production conditions.

[0129] The amount of the silane coupling agent (C) blended is preferably such that the mass ratio {silane coupling agent (C) / inorganic filler (B)} is from 1 / 100 to 20 / 100. A ratio of 1 / 100 or more more effectively improves the low heat buildup of the rubber composition, while a ratio of 20 / 100 or less reduces the cost of the rubber composition, improving economic efficiency. Furthermore, a mass ratio of 3 / 100 to 20 / 100 is more preferable, and a mass ratio of 4 / 100 to 10 / 100 is particularly preferable.

[0130] (Compound (D) for accelerating the reaction between silica and silane coupling agent) The rubber composition obtained by the method for producing a rubber composition of this embodiment contains a compound (D) for accelerating the reaction between silica and silane coupling agent. The compound (D) for accelerating the reaction between silica and silane coupling agent acts as a reaction catalyst for alkoxy groups and accelerates the reaction between silica and silane coupling agent in the first stage of kneading. Furthermore, the increased reactivity between silica and silane coupling agent enhances the reinforcing properties of silica and its dispersibility in rubber component (A), thereby improving the low heat buildup and wear resistance of the rubber composition.

[0131] The compound (D) that promotes the reaction between silica and a silane coupling agent is preferably at least one selected from the group consisting of guanidines, thiurams, dithiocarbamates, thioureas, xanthates, tertiary amine compounds, inorganic salt hydrates, 1,2-benzenediol, imidazole compounds, organic sulfonic acids, and water. These compounds have a high effect of promoting the reaction between silica and a silane coupling agent, further improving the low heat buildup of the resulting rubber composition.

[0132] Examples of the guanidines include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine. Among these, from the viewpoint of reactivity, 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, and 1-o-tolylbiguanide are preferred, with 1,3-diphenylguanidine being particularly preferred. By using 1,3-diphenylguanidine as the reaction accelerator compound (D) for the silica and silane coupling agent, the low heat buildup of the resulting rubber composition is further improved.

[0133] Examples of the thiurams include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrapropylthiuram disulfide, tetraisopropylthiuram disulfide, tetrabutylthiuram disulfide, tetrapentylthiuram disulfide, tetrahexylthiuram disulfide, tetraheptylthiuram disulfide, tetraoctylthiuram disulfide, tetranonylthiuram disulfide, tetradecylthiuram disulfide, tetradodecylthiuram disulfide, tetrastearylthiuram disulfide, tetrabenzylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetraisopropyl ... Examples include tetramethylthiuram monosulfide, tetraethylthiuram monosulfide, tetrapropylthiuram monosulfide, tetraisopropylthiuram monosulfide, tetrabutylthiuram monosulfide, tetrapentylthiuram monosulfide, tetrahexylthiuram monosulfide, tetraheptylthiuram monosulfide, tetraoctylthiuram monosulfide, tetranonylthiuram monosulfide, tetradecylthiuram monosulfide, tetradodecylthiuram monosulfide, tetrastearylthiuram monosulfide, tetrabenzylthiuram monosulfide, dipentamethylenethiuram tetrasulfide, etc. Among these, tetrakis(2-ethylhexyl)thiuram disulfide and tetrabenzylthiuram disulfide are preferred because of their high reactivity. By using at least one compound selected from tetrakis(2-ethylhexyl)thiuram disulfide and tetrabenzylthiuram disulfide as the compound (D) that promotes the reaction between silica and a silane coupling agent, the low heat buildup of the resulting rubber composition is further improved.

[0134] Examples of the dithiocarbamate salts include zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dipropyldithiocarbamate, zinc diisopropyldithiocarbamate, zinc dibutyldithiocarbamate, zinc dipentyldithiocarbamate, zinc dihexyldithiocarbamate, zinc diheptyldithiocarbamate, zinc dioctyldithiocarbamate, zinc di(2-ethylhexyl)dithiocarbamate, zinc didecyldithiocarbamate, zinc didodecyldithiocarbamate, zinc N-pentamethylene ... -ethyl-N-phenyldithiocarbamate, zinc dibenzyldithiocarbamate, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate, copper diisopropyldithiocarbamate, copper dibutyldithiocarbamate, copper dipentyldithiocarbamate, copper dihexyldithiocarbamate, copper diheptyldithiocarbamate, copper dioctyldithiocarbamate, copper di(2-ethylhexyl)dithiocarbamate, copper didecyldithiocarbamate, copper didodecyldithiocarbamate, N-pentamethylenedithiocarbamate Copper carbamate, copper dibenzyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, sodium dipropyldithiocarbamate, sodium diisopropyldithiocarbamate, sodium dibutyldithiocarbamate, sodium dipentyldithiocarbamate, sodium dihexyldithiocarbamate, sodium diheptyldithiocarbamate, sodium dioctyldithiocarbamate, sodium di(2-ethylhexyl)dithiocarbamate, sodium didecyldithiocarbamate, Sodium didodecyldithiocarbamate, sodium N-pentamethylenedithiocarbamate, sodium dibenzyldithiocarbamate, ferric dimethyldithiocarbamate, ferric diethyldithiocarbamate, ferric dipropyldithiocarbamate, ferric diisopropyldithiocarbamate, ferric dibutyldithiocarbamate, ferric dipentyldithiocarbamate, ferric dihexyldithiocarbamate, ferric diheptyldithiocarbamate, ferric dioctyldithiocarbamate, ferric di(2-ethylhexyl)dithiocarbamate,Examples of suitable compounds include ferric didecyldithiocarbamate, ferric didodecyldithiocarbamate, ferric N-pentamethylenedithiocarbamate, and ferric dibenzyldithiocarbamate. Among these, zinc dibenzyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc dimethyldithiocarbamate, and copper dimethyldithiocarbamate are preferred due to their high reactivity. By using at least one compound selected from zinc dibenzyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc dimethyldithiocarbamate, and copper dimethyldithiocarbamate as the compound (D) that promotes the reaction between silica and a silane coupling agent, the low heat buildup of the resulting rubber composition is further improved.

[0135] Examples of the thioureas include N,N'-diphenylthiourea, trimethylthiourea, N,N'-diethylthiourea, N,N'-dimethylthiourea, N,N'-dibutylthiourea, ethylenethiourea, N,N'-diisopropylthiourea, N,N'-dicyclohexylthiourea, 1,3-di(o-tolyl)thiourea, 1,3-di(p-tolyl)thiourea, 1,1-diphenyl-2-thiourea, 2,5-dithiobiurea, guanylthiourea, 1-(1-naphthyl)-2-thiourea, 1-phenyl-2-thiourea, p-tolylthiourea, o-tolylthiourea, etc. Among these, N,N'-diethylthiourea, trimethylthiourea, N,N'-diphenylthiourea, and N,N'-dimethylthiourea are preferred due to their high reactivity. By using at least one compound selected from N,N'-diethylthiourea, trimethylthiourea, N,N'-diphenylthiourea, and N,N'-dimethylthiourea as the compound (D) that accelerates the reaction between silica and a silane coupling agent, the low heat buildup of the resulting rubber composition is further improved.

[0136] Examples of the xanthogenates include zinc methylxanthogenate, zinc ethylxanthogenate, zinc propylxanthogenate, zinc isopropylxanthogenate, zinc butylxanthogenate, zinc pentylxanthogenate, zinc hexylxanthogenate, zinc heptylxanthogenate, zinc octylxanthogenate, zinc 2-ethylhexylxanthogenate, zinc decylxanthogenate, zinc dodecylxanthogenate, potassium methylxanthogenate, potassium ethylxanthogenate, potassium propylxanthogenate, potassium isopropylxanthogenate, potassium butylxanthogenate, potassium pentylxanthogenate, potassium hexylxanthogenate, Examples of suitable compounds include potassium heptyl xanthogenate, potassium octyl xanthogenate, potassium 2-ethylhexyl xanthogenate, potassium decyl xanthogenate, potassium dodecyl xanthogenate, sodium methyl xanthogenate, sodium ethyl xanthogenate, sodium propyl xanthogenate, sodium isopropyl xanthogenate, sodium butyl xanthogenate, sodium pentyl xanthogenate, sodium hexyl xanthogenate, sodium heptyl xanthogenate, sodium octyl xanthogenate, sodium 2-ethylhexyl xanthogenate, sodium decyl xanthogenate, and sodium dodecyl xanthogenate. Among these, zinc isopropyl xanthogenate is preferred due to its high reactivity. By using zinc isopropyl xanthogenate as the reaction accelerator compound (D) for the silica and silane coupling agent, the low heat buildup of the resulting rubber composition is further improved.

[0137] The tertiary amine compound is a compound represented by the following general formula (i): By using the tertiary amine compound represented by the general formula (i) as the compound (D) that accelerates the reaction between silica and a silane coupling agent, the low heat buildup of the resulting rubber composition is further improved.

[0138] In the above general formula (i), R ａ , R ｂ and R ｃmay be the same or different, and each represents one of a methyl group, an alkyl group having 2 to 36 carbon atoms, an alkenyl group having 8 to 36 carbon atoms, a cyclohexyl group, and a benzyl group. ａ , R ｂ and R ｃ It is more preferable that at least one of R is an alkyl group having 2 to 36 carbon atoms, an alkenyl group having 8 to 36 carbon atoms, a cyclohexyl group, or a benzyl group. ａ and R ｂ represents a methyl group, R ｃ Particularly preferred are dimethylalkylamines in which R represents an alkyl group having 12 to 36 carbon atoms, such as dimethylstearylamine, dimethylmyristylamine, dimethyloctadecenylamine, dimethylhexadecenylamine, and dimethyldodecylamine. Furthermore, a tertiary amine compound represented by the general formula (i) having a molecular weight of 180 or more is preferred because it can be reacted at room temperature. On the other hand, a tertiary amine compound having a molecular weight of less than 180 has a boiling point below room temperature, making it unable to react at room temperature and resulting in poor workability. In the first stage of kneading, it is preferred to knead 2 to 10 parts by mass, and more preferably 2 to 6 parts by mass, of the tertiary amine compound per 100 parts by mass of the rubber component (A). When the amount of the tertiary amine compound is 2 parts by mass or more, the desired improvements in dispersibility and abrasion resistance can be achieved. When the amount is 10 parts by mass or less, the silica dispersion-improving effect does not saturate, and conversely, the tertiary amine compound does not act unfavorably as a plasticizer, ensuring abrasion resistance, which is preferred.

[0139] As the inorganic salt hydrate, sodium borate hydrate (hydrated sodium borate) is preferred, and borax (Na ２ B ４ O ７ ・10H ２O) is particularly preferred. By using sodium borate hydrate as the reaction accelerator compound (D) for the silica and the silane coupling agent, the low heat buildup of the resulting rubber composition is further improved. In the first stage of kneading, it is preferable to knead 1 to 10 parts by mass, and more preferably 1 to 4 parts by mass, of the inorganic salt hydrate per 100 parts by mass of the rubber component (A). When the amount of the inorganic salt hydrate is 1 part by mass or more, the desired improvements in dispersibility and abrasion resistance can be achieved, and when it is 10 parts by mass or less, deterioration of kneading workability due to generation of moisture can be avoided, which is preferable.

[0140] The 1,2-benzenediol used as the reaction accelerator compound (D) for the silica and the silane coupling agent is preferably kneaded in an amount of 0.3 to 4 parts by mass, and more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the rubber component (A) in the first stage of kneading. When the amount of 1,2-benzenediol is 0.3 part by mass or more, the desired improvements in dispersibility and abrasion resistance can be achieved, and when the amount is 4 parts by mass or less, the vulcanization rate is not slowed, which is preferable.

[0141] The imidazole compound is a compound represented by the following general formula (ii): By using the imidazole compound represented by the general formula (ii) as the compound (D) that accelerates the reaction between silica and a silane coupling agent, the low heat buildup of the resulting rubber composition is further improved.

[0142] In the above general formula (ii), R ｄ , R ｅ , R ｆ and R ｇ may be the same or different and each represents a hydrogen atom or a monovalent organic group. ｄ , R ｅ , R ｆ and R ｇTwo or more of the above may be bonded to form a ring. Examples of the imidazole compound include imidazole, 4-ethylaminoimidazole, 2-mercapto-1-methylimidazole, 1-methylimidazole, 2,4,5-triphenylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-heptadecylimidazole, with imidazole being preferred. In the first stage of kneading, the imidazole compound is preferably kneaded in an amount of 0.3 to 4 parts by mass, and more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the rubber component (A). When the amount of the imidazole compound is 0.3 parts by mass or more, the desired improvements in dispersibility and abrasion resistance can be achieved, while when the amount is 4 parts by mass or less, scorch resistance is not impaired, which is preferable.

[0143] The organic sulfonic acid is preferably p-toluenesulfonic acid or benzenesulfonic acid. By using at least one compound selected from p-toluenesulfonic acid and benzenesulfonic acid as the reaction accelerator compound (D) for the silica and silane coupling agent, the low heat buildup of the resulting rubber composition is further improved. In the first stage of kneading, the organic sulfonic acid is preferably kneaded in an amount of 0.3 to 4 parts by mass, and more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the rubber component (A). When the amount of the organic sulfonic acid is 0.3 parts by mass or more, the desired improvements in dispersibility and abrasion resistance can be achieved, while when the amount is 4 parts by mass or less, the vulcanization rate is not slowed, which is preferable.

[0144] The water used as the reaction accelerator compound (D) for the silica and the silane coupling agent is preferably kneaded in an amount of 0.5 to 8 parts by mass per 100 parts by mass of the rubber component (A) in the first stage of kneading. When the amount of water is 0.5 part by mass or more, the desired improvements in dispersibility and abrasion resistance can be achieved, and when the amount is 8 parts by mass or less, the kneading efficiency of the kneader is not reduced, which is preferable.

[0145] The number of molecules (moles) of the silica-silane coupling agent reaction accelerator compound (D) in the rubber composition in the first stage of kneading is preferably 0.1 to 1.0 times the number of molecules (moles) of the silane coupling agent (C). A number of 0.1 times or more sufficiently activates the silane coupling agent (C), while a number of 1.0 times or less does not significantly affect the vulcanization rate. More preferably, the number of molecules (moles) of the silica-silane coupling agent reaction accelerator compound (D) is 0.2 to 0.6 times the number of molecules (moles) of the silane coupling agent (C). Since the silica-silane coupling agent reaction accelerator compound (D) is also used as a sulfur vulcanization accelerator (vulcanization accelerator), it may be blended in an appropriate amount, if desired, even in the final stage of kneading. When blending the silica-silane coupling agent reaction accelerator compound (D) in the final stage of kneading, it is not limited to the silica-silane coupling agent reaction accelerator compound (D) of the present invention, and known vulcanization accelerators can also be blended.

[0146] (Organic Acid Compound (E)) The rubber composition obtained by the method for producing a rubber composition of this embodiment preferably further contains an organic acid compound (E). In the method for producing a rubber composition of this embodiment, the organic acid compound (E) is further kneaded in the first stage of kneading, and the number of molecules X of the organic acid compound (E) in the rubber composition in the first stage preferably satisfies the relationship of the following formula (1) with respect to the number of molecules Y of the compound (D) for accelerating the reaction between silica and the silane coupling agent: 0≦X≦1.5×Y (1) By having the number of molecules X of the organic acid compound (E) in the rubber composition in the first stage satisfy the relationship of formula (1) with respect to the number of molecules Y of the compound (D) for accelerating the reaction between silica and the silane coupling agent, the activity of the coupling function is further enhanced, and the low heat buildup of the rubber composition can be further improved.

[0147] Examples of the organic acid compound (E) include organic acids such as saturated fatty acids and unsaturated fatty acids, such as stearic acid, palmitic acid, myristic acid, lauric acid, arachidic acid, behenic acid, lignoceric acid, capric acid, pelargonic acid, caprylic acid, enanthic acid, caproic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, and nervonic acid, and resin acids, such as rosin acid and modified rosin acid, and esters of the saturated fatty acids, unsaturated fatty acids, and resin acids.

[0148] It is preferable that 50 mol % or more of the organic acid compound (E) contained in the rubber composition in the first stage of kneading is stearic acid. When 50 mol % or more of the organic acid compound (E) contained in the rubber composition in the first stage of kneading is stearic acid, the function as a vulcanization accelerator aid is sufficiently exhibited.

[0149] When the rubber component (A) contains at least one selected from emulsion-polymerized styrene-butadiene copolymers and natural rubbers, it is preferable that 50 mol % or more of the organic acid compound (E) contained in the rubber composition in the first stage of kneading is at least one compound selected from rosin acid and fatty acid contained in the at least one selected from emulsion-polymerized styrene-butadiene copolymers and natural rubbers. The rosin acid (including modified rosin acid) and fatty acid contained in the emulsion-polymerized styrene-butadiene copolymer are derived from an emulsifier required for polymerizing the emulsion-polymerized styrene-butadiene copolymer. Furthermore, natural rubber typically contains a small amount of fatty acid. Therefore, in this case, the amount of organic acid compound (E) to be added can be reduced.

[0150] (Resin) The rubber composition obtained by the method for producing a rubber composition according to the present embodiment may contain a resin. Examples of the resin include terpene-based resins, rosin-based resins, C ５ based resin, C ５ -C ９ based resin, C ９Examples of suitable resins include cyclopentadiene-based resins, aromatic resins, coumarone resins, indene resins, coumarone-indene-based resins, olefin-based resins, polyurethane resins, and acrylic resins. These resins may be used alone or in combination of two or more. Among these resins, terpene-based resins, rosin-based resins, and C ５ based resin, C ５ -C ９ based resin, C ９ Preferred are cyclopentadiene-based resins, cyclopentadiene-based resins, and aromatic resins, with terpene-based resins and rosin-based resins being particularly preferred. Terpene-based resins and rosin-based resins are naturally derived, sustainable resins that can further reduce the environmental impact and can further improve tire performance, such as grip performance on various road surface conditions, including dry roads, wet roads, snow-covered roads, and frozen roads. ５ based resin, C ９ based resin, C ５ -C ９ The cyclopentadiene-based resin and the cyclopentadiene-based resin can improve abrasion resistance and fuel economy in a balanced manner, while the aromatic resin can improve grip performance, abrasion resistance, and rubber strength in a balanced manner.

[0151] The resin may be hydrogenated, i.e., may be a hydrogenated resin (hydrogenated resin). Furthermore, the resin may be modified to introduce a functional group that interacts with fillers such as carbon black and silica. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups.

[0152] The terpene resin is a solid resin obtained by blending turpentine, which is obtained simultaneously with the extraction of rosin from pine trees, or a polymerization component separated therefrom, and polymerizing the blend using a Friedel-Crafts catalyst. Examples of such resins include β-pinene resin and α-pinene resin. Terpene resins also include terpene-aromatic compound resins, representative examples of which include terpene-phenol resin and styrene-terpene resin. Terpene-phenol resins can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing the terpene with formalin. The styrene-terpene resin can be obtained by reacting styrene with terpenes using a Friedel-Crafts catalyst. The terpenes used as raw materials are not particularly limited; monoterpene hydrocarbons such as α-pinene and limonene are preferred, with those containing α-pinene being more preferred, and α-pinene being particularly preferred.

[0153] Examples of the rosin-based resin include natural resin rosins such as gum rosin, tall oil rosin, and wood rosin contained in raw pine resin and tall oil, and examples of modified rosins, rosin derivatives, and modified rosin derivatives include polymerized rosin and partially hydrogenated rosin thereof; glycerin ester rosin and partially hydrogenated rosin thereof and fully hydrogenated rosin thereof; pentaerythritol ester rosin and partially hydrogenated rosin thereof and polymerized rosin; and the like.

[0154] Said C ５ As a resin based on C, there is C obtained by thermal decomposition of naphtha in the petrochemical industry. ５ and aliphatic petroleum resins obtained by (co)polymerizing the distillate. ５ The fraction usually contains olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene.

[0155] Said C ５ -C ９ The C-based resin is ５ -C９ It refers to synthetic petroleum resin, ５ -C ９ Examples of the resin include petroleum-derived C ５ -C １１ The fraction was treated with AlCl ３ , B.F. ３ More specifically, copolymers containing styrene, vinyl toluene, α-methyl styrene, indene, etc. as the main component may be mentioned. ５ -C ９ As the resin, ９ Resins containing less of the above components are preferred from the viewpoint of compatibility with the rubber component. ９ "Low amount of the above components" means that the C ９ This means that the content of the above components is less than 50% by mass, preferably 40% by mass or less.

[0156] Said C ９ The C-based resin is ９ This refers to synthetic petroleum resins, such as AlCl ３ or BF ３ Using a Friedel-Crafts type catalyst such as C ９ It refers to a solid polymer obtained by polymerizing the fraction. ９ Examples of the resin include copolymers containing indene, α-methylstyrene, vinyltoluene, etc. as main components.

[0157] The cyclopentadiene-based resin refers to a resin containing a unit derived from a cyclopentadiene-based monomer as a monomer unit. Examples of the cyclopentadiene-based resin include a homopolymer of a cyclopentadiene-based monomer, a copolymer of two or more cyclopentadiene-based monomers, and a copolymer of a cyclopentadiene-based monomer and another monomer. Here, examples of the cyclopentadiene-based monomer include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene. Among these, dicyclopentadiene is preferred. That is, the cyclopentadiene-based resin is preferably a dicyclopentadiene-based resin. The dicyclopentadiene-based resin is, for example, a copolymer of AlCl ３ or BF ３The term "dicyclopentadiene-based resin" refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as Benzene, etc. Dicyclopentadiene-based resins include homopolymers of dicyclopentadiene, copolymers of dicyclopentadiene and aromatic monomers, copolymers of dicyclopentadiene and C ９ Examples include copolymers with distillates (vinyl toluene, indene, etc.).

[0158] The aromatic resin refers to a resin containing units derived from aromatic monomers as monomer units. Examples of the aromatic resin include homopolymers of aromatic monomers, copolymers of two or more aromatic monomers, and copolymers of aromatic monomers with other monomers. Examples of the aromatic monomer include styrene-based monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-phenylstyrene; phenol-based monomers such as phenol, alkylphenol, and alkoxyphenol; and naphthol-based monomers such as naphthol, alkylnaphthol, and alkoxynaphthol.

[0159] The softening point of the resin is preferably 30 ° C. or higher, more preferably 60 ° C. or higher, more preferably 80 ° C. or higher, more preferably higher than 110 ° C., more preferably 116 ° C. or higher, more preferably 120 ° C. or higher, more preferably 123 ° C. or higher, and even more preferably 127 ° C. or higher. From the viewpoint of processability, the softening point of the resin is preferably 160 ° C. or lower, more preferably 150 ° C. or lower, more preferably 145 ° C. or lower, more preferably 141 ° C. or lower, and even more preferably 136 ° C. or lower. In this specification, the softening point of the resin is the temperature at which the ball drops when the softening point as defined in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring and ball softening point tester.

[0160] Commercially available resins can be used, and examples of commercially available resins include products from ENEOS Corporation, Arakawa Chemical Industries, Ltd., ExxonMobil Corporation, Kraton Corporation, Yasuhara Chemical Co., Ltd., Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Kraton Polymers, Inc., Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., and Taoka Chemical Co., Ltd.

[0161] The content of the resin is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the resin is preferably in the range of 5 to 100 parts by mass, more preferably in the range of 10 to 60 parts by mass, per 100 parts by mass of the rubber component (A).

[0162] (Rubber Crumb) The rubber composition obtained by the rubber composition manufacturing method of this embodiment may contain rubber crumb. The rubber crumb may be obtained by pulverizing used rubber products such as used tires and, if desired, removing reinforcing materials such as steel and fibers, dust, glass, sand, stones, etc., or by preparing a new vulcanized rubber composition for the purpose of producing rubber crumb and pulverizing the resulting product. For example, rubber crumb can be obtained from vulcanized rubber by the method described in "Rubber Chemistry and Technology." The process of pulverizing vulcanized rubber to obtain rubber crumb may involve mechanical treatment or low-temperature treatment. For example, in mechanical treatment, various crushing devices such as a cracker mill or a granulator can be used to mechanically crush the vulcanized rubber into fine particles. In low-temperature treatment, the finely chopped vulcanized rubber is frozen at a cryogenic temperature and then crushed into fine particles. In addition, a magnetic separator or the like can be used to remove steel, and an air separator or the like can be used to remove fibers. The rubber powder may be a commercially available product, such as those from Global Corporation or Nantong Huili Rubber Corporation. From the viewpoint of reducing the environmental impact, it is preferable to use rubber powder obtained by crushing used rubber products such as used tires. The rubber powder may be used alone or in combination of two or more types.

[0163] The composition of the rubber crumb is not particularly limited and depends on the composition of the vulcanized rubber from used rubber products (used tires) or the like that serve as the raw material. In one embodiment, the rubber crumb contains a rubber component, carbon black, silica, etc. The rubber component, carbon black, silica, etc. contained in the rubber crumb may be the same as or different from the rubber component, carbon black, silica, etc. that can be contained in the rubber composition obtained by the above-described method for producing a rubber composition of this embodiment.

[0164] The rubber powder preferably has a volume average particle diameter of 1000 μm or less, more preferably 500 μm or less, even more preferably 200 μm or less, and even more preferably 100 μm or less. The smaller the volume average particle diameter of the rubber powder, the better, and there is no particular lower limit. In this specification, the volume average particle diameter is measured with a laser diffraction particle size distribution analyzer, for example, a "CAPA500" manufactured by Horiba, Ltd.

[0165] The rubber powder preferably has a 60-mesh sieve residue of less than 1% by mass, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, with no particular lower limit. The rubber powder preferably has an 80-mesh sieve residue of less than 10% by mass, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, with no particular lower limit. In this specification, the sieve residue is measured in accordance with ASTM D5644-01.

[0166] The rubber crumb has an acetone extractable content of preferably 12% by mass or less, more preferably 11% by mass or less, and even more preferably 10% by mass or less, and preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more. In this specification, the acetone extractable content in the rubber crumb refers to the acetone extractable content (%) determined by the acetone extraction method in accordance with JIS K6350.

[0167] The content of the rubber crumb is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber component is applied, the tire components, the target performance, etc. For example, the content of the rubber crumb is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, and is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, more preferably 100 parts by mass or less, more preferably 50 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0168] (Liquid Softener) The rubber composition obtained by the method for producing a rubber composition according to this embodiment may contain a liquid softener. Here, the "liquid softener" refers to a compounding agent that is liquid at 25°C (room temperature) and has the effect of softening the rubber composition. The liquid softener is not particularly limited, and examples thereof include oil and liquid polymer, among which oil is preferred. These liquid softeners may be used alone or in combination of two or more.

[0169] The oil is a general term for extender oils contained in rubber components and liquid oils added as compounding agents to rubber compositions. Examples include vegetable oils, process oils, oils obtained by recycling vegetable oils or process oils, and mixtures thereof. From the perspective of reducing environmental impact, vegetable oils and recycled oils are preferred. Examples of vegetable oils include palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, and coconut oil. Examples of process oils include paraffin-based process oils, aromatic process oils, and naphthenic process oils. As the oil, commercially available products can be used, and examples of commercially available oils that can be used include products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Oriso Corporation, H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Nisshin Oillio Group Co., Ltd., and the like. These oils may be used alone or in combination of two or more.

[0170] The liquid polymer is preferably a liquid diene-based polymer. Examples of the liquid diene-based polymer include liquid styrene-butadiene copolymer (liquid SBR), liquid polybutadiene (liquid BR), liquid polyisoprene (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), liquid styrene-butadiene-styrene block copolymer (liquid SBS block polymer), liquid styrene-isoprene-styrene block copolymer (liquid SIS block polymer), liquid polyfarnesene, and liquid farnesene-butadiene copolymer. These liquid polymers may be hydrogenated, or their terminals or main chains may be modified with functional groups (polar groups). These liquid polymers may be used alone or in combination of two or more.

[0171] The content of the liquid softener is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which it is applied, the tire components, the target performance, etc. For example, the content of the liquid softener is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, still more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0172] (Antiaging Agent) The rubber composition obtained by the method for producing a rubber composition of this embodiment may contain an antioxidant. Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), and 6-anilino-2,2,4-trimethyl-1,2-dihydroquinoline. Commercially available products can be used as the antioxidant, and examples of commercially available antioxidants that can be used include products from Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Co., Ltd., Flexis Co., Ltd., etc. These antioxidants may be used alone or in combination of two or more.

[0173] The content of the antioxidant is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which it is applied, the tire components, the target performance, etc. For example, the content of the antioxidant is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, and is preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of the rubber component (A).

[0174] (Wax) The rubber composition obtained by the rubber composition manufacturing method of this embodiment may contain a wax. Examples of the wax include natural waxes such as plant waxes and animal waxes; petroleum waxes such as paraffin wax and microcrystalline wax; and synthetic waxes such as ethylene polymers and propylene polymers. Commercially available waxes can be used, and examples of commercially available waxes include products from Seiko Chemical Co., Ltd., Nippon Seiro Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., and the like. These waxes may be used alone or in combination of two or more.

[0175] The content of the wax is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber component (A) is applied, the tire components, the target performance, etc. For example, the content of the wax is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, per 100 parts by mass of the rubber component (A).

[0176] (Stearic Acid) The rubber composition obtained by the method for producing a rubber composition according to the present embodiment may contain stearic acid. Commercially available stearic acid can be used, and examples of commercially available stearic acid include products from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Chiba Fatty Acid Co., Ltd., etc. These commercially available stearic acid products may be used alone or in combination of two or more.

[0177] The content of stearic acid is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber component (A) is applied, the tire component, the target performance, etc. For example, the content of stearic acid is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, per 100 parts by mass of the rubber component (A).

[0178] (Zinc Oxide) The rubber composition obtained by the rubber composition manufacturing method of this embodiment may contain zinc oxide (zinc white). The zinc oxide is preferably obtained not only from zinc metal but also from recycled zinc or zinc dross (i.e., obtained by recycling). Commercially available zinc oxide can be used, and examples of commercially available zinc oxide include products from Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., Mitsui Mining & Smelting Co., Ltd., and Toho Zinc Co., Ltd. These commercially available zinc oxide products may be used alone or in combination of two or more.

[0179] The content of the zinc oxide is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the zinc oxide is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, per 100 parts by mass of the rubber component (A).

[0180] (Sulfur) The rubber composition obtained by the rubber composition manufacturing method of this embodiment preferably contains sulfur. The sulfur may be derived from fossil resources, recycled resources, or sulfur obtained by processing biological resource-derived materials. From the viewpoint of reducing environmental impact, it is particularly preferable to use sulfur obtained from waste derived from biological resources. Examples of methods for obtaining sulfur from waste derived from biological resources include the method described in the aforementioned Japanese Patent Application No. 2022-140390. Furthermore, the sulfur may be powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, and the like, which are commonly used as crosslinking agents in the rubber industry. Commercially available sulfur products can be used, including those from Tsurumi Chemical Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, and the like. These sulfurs may be used alone or in combination of two or more.

[0181] The sulfur content is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber component (A) is applied, the tire components, the target performance, etc. For example, the sulfur content is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.8 parts by mass or more, and is preferably 8 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component (A).

[0182] (Vulcanization accelerator) The rubber composition obtained by the method for producing a rubber composition of this embodiment preferably contains a vulcanization accelerator. The vulcanization accelerator may be derived from fossil resources, recycled resources, or biological resources, but is preferably derived from biological resources from the viewpoint of reducing the environmental load. Vulcanization accelerators derived from biological resources can be obtained, for example, by the method disclosed in JP 2005-139239 A. The vulcanization accelerator partially overlaps with the reaction accelerator compound (D) between silica and a silane coupling agent described above. Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide, and N,N'-diisopropyl-2-benzothiazolesulfenamide; 1,3-diphenylguanidine (DPG), 1,3-diphenylguanidine (DPG), and 1,3-diphenylguanidine (1,3-diphenylguanidine). Examples of suitable vulcanization accelerators include guanidine-based vulcanization accelerators such as o-tolylguanidine and o-tolylbiguanidine; thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole (M) and di-2-benzothiazolyl disulfide (MBTS, DM); and thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrastearylthiuram disulfide, tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N). Commercially available vulcanization accelerators can be used, including those manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., and the like. These vulcanization accelerators may be used alone or in combination of two or more.

[0183] The content of the vulcanization accelerator is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the vulcanization accelerator is applied, the tire components, the target performance, etc. For example, the content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, and is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 5.5 parts by mass or less, relative to 100 parts by mass of the rubber component (A).

[0184] (Cellulose Nanofibers) The rubber composition obtained by the rubber composition manufacturing method of this embodiment may contain cellulose nanofibers (CNFs). The cellulose nanofibers can be blended into the rubber composition to reinforce the rubber composition. The cellulose nanofibers are preferably modified cellulose nanofibers, which are fine fibers made from modified cellulose. The fiber diameter of the cellulose nanofibers is not particularly limited, but is approximately 3 to 500 nm. The average fiber diameter and average fiber length of the cellulose nanofibers can be obtained by averaging the fiber diameters and fiber lengths obtained from the observation of each fiber using a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM). The cellulose nanofibers can be obtained by defibrating cellulose. The average fiber length and average fiber diameter of the fine fibers can be adjusted by oxidation treatment or defibration treatment.

[0185] The raw material for the cellulose nanofibers is not particularly limited as long as it contains cellulose, and examples thereof include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), bleached kraft pulp (BKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., ascidians), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc. These cellulose raw materials may be used alone or in combination of two or more.

[0186] The content of the cellulose nanofibers is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber component (A) is applied, the tire component, the target performance, etc. For example, the content of the cellulose nanofibers is preferably in the range of 1 to 100 parts by mass, more preferably in the range of 5 to 70 parts by mass, and even more preferably in the range of 10 to 40 parts by mass, per 100 parts by mass of the rubber component (A).

[0187] (Porous Cellulose Particles) The rubber composition obtained by the rubber composition manufacturing method of this embodiment may contain porous cellulose particles. The porous cellulose particles are preferably cellulose particles having a porous structure with a porosity of 75 to 95%, and by incorporating them into the rubber composition, performance on ice can be improved. When the porosity of the porous cellulose particles is 75% or more, the effect of improving performance on ice is excellent, and when the porosity is 95% or less, the strength of the particles can be increased. The porosity is more preferably 80 to 90%. The porosity of the porous cellulose particles can be calculated by measuring the volume of a certain mass of sample (i.e., porous cellulose particles) with a measuring cylinder, determining the bulk specific gravity, and using the following formula: Porosity (%) = {1 - [bulk specific gravity of sample (g / mL)] / [true specific gravity of sample (g / mL)]} × 100, where the true specific gravity of cellulose is 1.5.

[0188] The particle size of the porous cellulose particles is not particularly limited, but from the viewpoint of abrasion resistance, an average particle size of 1000 μm or less is preferred. The lower limit of the average particle size is not particularly limited, but it is preferably 5 μm or more. The average particle size is more preferably 100 to 800 μm, and even more preferably 200 to 800 μm. The porous cellulose particles are preferably spherical particles with a major axis / minor axis ratio of 1 to 2. The use of particles with such a spherical structure improves dispersibility in the rubber composition, contributing to improved performance on ice and the maintenance of abrasion resistance. The major axis / minor axis ratio is more preferably 1.0 to 1.5. The average particle size and major axis / minor axis ratio of the porous cellulose particles can be determined as follows. That is, porous cellulose particles are observed under a microscope to obtain an image, and this image is used to measure the long and short diameters of the particles (if the long and short diameters are the same, the length in a certain axis direction and the length in an axis direction perpendicular to it) for 100 particles, and the average particle size is obtained by calculating the average value, and the long diameter / short diameter ratio is obtained by averaging the values ​​obtained by dividing the long diameter by the short diameter.

[0189] The porous cellulose particles are commercially available from Rengo Co., Ltd. under the name "Viscopal" and are also described in JP-A Nos. 2001-323095 and 2004-115284, and can be suitably used.

[0190] The content of the porous cellulose particles is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber component (A) is applied, the tire component, the target performance, etc. For example, the content of the porous cellulose particles is preferably in the range of 0.3 to 20 parts by mass, more preferably in the range of 1 to 15 parts by mass, and even more preferably in the range of 3 to 15 parts by mass, per 100 parts by mass of the rubber component (A).

[0191] (Solid Particles) The rubber composition obtained by the rubber composition manufacturing method of this embodiment may contain solid particles. Blending the solid particles into the rubber composition can improve on-ice performance. The solid particles preferably have an average particle diameter of 1 μm or more, preferably 1000 μm or less, and more preferably 300 μm or less. Examples of the solid particles include plant-derived powders obtained from plants, such as rice husks, walnut flour, and walnut shells; animal-derived powders obtained from animals, such as eggshells (eggshell powder) and bone powder; powders derived from natural minerals, such as whitebait; inorganic particles, such as graphite and zinc oxide whiskers; water-soluble metal salt particles, such as magnesium sulfate and metal salts of lignosulfonic acid; and non-metallic fibers, such as glass fibers. Among these, rice husks, walnut shells, eggshells, and whitebait are preferred.

[0192] The content of the solid fine particles is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the solid fine particles is preferably in the range of 0.3 to 20 parts by mass, more preferably in the range of 1 to 15 parts by mass, and even more preferably in the range of 3 to 15 parts by mass, per 100 parts by mass of the rubber component (A).

[0193] (Others) In addition to the above-mentioned components, the rubber composition obtained by the method for producing a rubber composition of the present embodiment may further contain various additives commonly used in the tire industry, such as organic peroxides. The content of these additives is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber is applied, the tire components, the target performance, etc. For example, the content is preferably in the range of 0.1 to 200 parts by mass per 100 parts by mass of the rubber component (A).

[0194] (Applications) The rubber composition obtained by the method for producing a rubber composition of this embodiment can be applied to various constituent parts of a tire, for example, tread (cap tread, base tread, undertread), cushion rubber, shoulder, sidewall, clinch, bead filler, carcass coating rubber, insulation, chafer, inner liner, etc. It can also be used for side reinforcing layers of run-flat tires, etc. In addition to tires, the rubber composition of this embodiment can also be applied to rubber crawlers, seismic isolation rubber, hoses, etc.

[0195] For example, a tire can be manufactured by a conventional method using the above-mentioned rubber composition. Depending on the type of tire to be applied, the tire may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, or by molding a semi-vulcanized rubber that has been subjected to a pre-vulcanization step or the like and then further vulcanizing it. The tire is preferably a pneumatic tire, and the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0196] 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 in any way.

[0197] <Production and Evaluation of Rubber Compositions of Comparative Example 1 and Example 1> A rubber composition is produced using a conventional Banbury mixer, with the formulation shown in Table 1, by kneading in the first stage of kneading and then the final stage of kneading. The maximum temperature of the rubber composition in the first stage of kneading is 170°C, and the maximum temperature of the rubber composition in the final stage of kneading is 110°C. The total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources (recycled resources) is calculated for the rubber composition obtained in the final stage of kneading to calculate the sustainable material ratio, and the low heat buildup property is further evaluated using the method described below.

[0198] <Evaluation of Low Heat Buildup Property> The obtained rubber composition was vulcanized at 160°C for 20 minutes, and then tan δ was measured using a viscoelasticity measuring device (manufactured by Rheometrics) at a temperature of 60°C, a dynamic strain of 5%, and a frequency of 15 Hz, and the values ​​were expressed as reciprocal index values, with tan δ of Comparative Example 1 being set at 100. A larger index value indicates a smaller tan δ and better low heat buildup property.

[0199] <Production and Evaluation of Rubber Composition of Comparative Example 2> A rubber composition was produced using a conventional Banbury mixer, with the formulation shown in Table 1, by kneading in the first stage of kneading and then the final stage of kneading. The maximum temperature of the rubber composition in the first stage of kneading was 170°C, and the maximum temperature of the rubber composition in the final stage of kneading was 110°C. The total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources (recycled resources) was calculated for the rubber composition obtained in the final stage of kneading to calculate the sustainable material ratio, and the low heat buildup property was further evaluated by the following method.

[0200] <Evaluation of low heat buildup property> The obtained rubber composition was vulcanized at 160°C for 20 minutes, and then tan δ was measured using a viscoelasticity measuring device (manufactured by Rheometrics) at a temperature of 60°C, a dynamic strain of 5%, and a frequency of 15 Hz, and the value was expressed as an index number, with tan δ of Comparative Example 1 set to 100. A larger index value indicates a smaller tan δ and better low heat buildup property.

[0201]

[0202] * 1 SBR: Styrene-butadiene copolymer rubber, manufactured by Asahi Kasei Corporation, solution polymerization SBR, trade name "Tafden 2000" * 2 Aroma oil: Manufactured by Fuji Kosan Co., Ltd., trade name "Aromax # 3" * 3 Carbon black: Manufactured by Mitsubishi Chemical Corporation, trade name "Diablack N234", ISAF-HS * 4 Mineral-derived silica: Manufactured by Tosoh Silica Corporation, trade name "Nipsil AQ" * 5 Plant-derived silica: Rice husk silica * 6 Silane coupling agent: Manufactured by Degussa, trade name "Si69" * 7 Glycerin fatty acid ester: According to the method described in Production Example 1 of WO 2014 / 098155, the fatty acid was synthesized by changing the fatty acid from octanoic acid to an equal molar amount of palm-derived hardened fatty acid and further prepared by molecular distillation, glycerin fatty acid monoester content = 97% by mass, 54% by mass of the constituent fatty acids are stearic acid and 42% by mass are palmitic acid, 4% by mass are other fatty acids * 8 Antioxidant 6C: Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac 6C", N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine * 9 Diethylthiourea: Rhein Chemie Co., Ltd., trade name "Rhenogran ETU-80", N,N'-diethylthiourea * 10 Vulcanization accelerator DPG: Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccela D", 1,3-diphenylguanidine * 11 Vulcanization accelerator DM: Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccela DM", di-2-benzothiazolyl disulfide * 12 Vulcanization accelerator NS: Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccela NS-F", N-tert-butyl-2-benzothiazolyl sulfenamide

[0203] From Table 1, it can be seen that the rubber compositions of the examples produced by the method according to the present invention have excellent low heat buildup properties while also having an improved proportion of sustainable materials, and that by applying them to rubber products, the proportion of sustainable materials in the rubber products can be improved.

[0204] The rubber composition produced by the method of the present invention can be used for rubber products such as tires, rubber crawlers, and seismic isolation rubber.

Claims

1. A method for producing a rubber composition comprising a rubber component (A) consisting of at least one of natural rubber and synthetic diene rubber, a filler containing an inorganic filler (B), a silane coupling agent (C), and a compound (D) that promotes the reaction between silica and the silane coupling agent, wherein the inorganic filler (B) contains plant-derived silica (B1), and the rubber composition is kneaded in multiple stages, and in the first stage of kneading, all or a portion of the rubber component (A), the inorganic filler (B), all or a portion of the silane coupling agent (C), and the compound (D) that promotes the reaction between silica and the silane coupling agent are kneaded.

2. The method for producing a rubber composition according to claim 1, wherein the compound (D) that promotes the reaction between silica and a silane coupling agent is at least one member selected from the group consisting of guanidines, thiurams, dithiocarbamates, thioureas, xanthates, tertiary amine compounds, inorganic salt hydrates, 1,2-benzenediol, imidazole compounds, organic sulfonic acids, and water.

3. The method for producing a rubber composition according to claim 1, wherein an organic acid compound (E) is further kneaded in the first stage of kneading, and the number of molecules X of the organic acid compound (E) in the rubber composition in the first stage is related to the number of molecules Y of the reaction-accelerating compound (D) of the silica and the silane coupling agent by the following formula (1): 0≦X≦1.5×Y (1).

4. The method for producing a rubber composition according to claim 1, wherein the maximum temperature of the rubber composition in the first stage of kneading is 120 to 190°C.

5. The method for producing a rubber composition according to claim 1, wherein the inorganic filler (B) accounts for 30 mass % or more of the filler.

6. The method for producing a rubber composition according to claim 1, wherein the number of molecules of the reaction-accelerating compound (D) between the silica and the silane coupling agent in the rubber composition in the first stage of kneading is 0.1 to 1.0 times the number of molecules of the silane coupling agent (C).

7. The method for producing a rubber composition according to claim 2, wherein the guanidine is 1,3-diphenylguanidine.

8. The method for producing a rubber composition according to claim 2, wherein the thiuram is at least one compound selected from the group consisting of tetrakis(2-ethylhexyl)thiuram disulfide and tetrabenzylthiuram disulfide.

9. The method for producing a rubber composition according to claim 2, wherein the thioureas are at least one compound selected from the group consisting of N,N'-diethylthiourea, trimethylthiourea, N,N'-diphenylthiourea and N,N'-dimethylthiourea.

10. The method for producing a rubber composition according to claim 2, wherein the dithiocarbamate is at least one compound selected from the group consisting of zinc dibenzyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc dimethyldithiocarbamate, and copper dimethyldithiocarbamate.

11. The method for producing a rubber composition according to claim 2, wherein the xanthogenate is zinc isopropyl xanthogenate.

12. The tertiary amine compound is represented by the following general formula (i): [In the formula, R ａ , R ｂ and R ｃ may be the same or different, and each is one of a methyl group, an alkyl group having 2 to 36 carbon atoms, an alkenyl group having 8 to 36 carbon atoms, a cyclohexyl group, and a benzyl group.

13. The method for producing a rubber composition according to claim 2, wherein the inorganic salt hydrate is sodium borate hydrate.

14. The imidazole compound is represented by the following general formula (ii): [In the formula, R ｄ , R ｅ , R ｆ and R ｇ may be the same or different and each represents a hydrogen atom or a monovalent organic group; ｄ , R ｅ , R ｆ and R ｇ and two or more of the above may be bonded to form a ring.

15. The method for producing a rubber composition according to claim 2, wherein the organic sulfonic acid is at least one compound selected from the group consisting of p-toluenesulfonic acid and benzenesulfonic acid.

16. The method for producing a rubber composition according to claim 3, wherein 50 mol % or more of the organic acid compound (E) contained in the rubber composition in the first stage of kneading is stearic acid.

17. The method for producing a rubber composition according to claim 3, wherein the rubber component (A) contains at least one selected from emulsion-polymerized styrene-butadiene copolymer and natural rubber, and 50 mol % or more of the organic acid compound (E) contained in the rubber composition in the first stage of kneading is at least one compound selected from rosin acid and fatty acid contained in the at least one selected from emulsion-polymerized styrene-butadiene copolymer and natural rubber.

18. A method for producing a rubber composition according to claim 1, wherein in the first stage of the kneading, the rubber component (A), all or a part of the inorganic filler (B), and all or a part of the silane coupling agent (C) are kneaded together, and then a reaction-accelerating compound (D) for the silica and the silane coupling agent is added and further kneaded.

19. The method for producing a rubber composition according to claim 1, wherein the plant-derived silica (B1) is silica derived from a grass plant.

20. The method for producing a rubber composition according to claim 19, wherein the plant-derived silica (B1) is silica derived from rice husks.

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