JP7483997B1 - Side reinforcement rubber for run-flat tires, and run-flat tires - Google Patents

Abstract

[Problem] To provide a side reinforcing rubber for run-flat tires that can contribute to improving sustainability. [Solution] The side reinforcing rubber for run-flat tires is characterized by using a rubber composition containing a rubber component and a filler containing recycled carbon black. [Selected Figure] Figure 1

Description

The present invention relates to side reinforcing rubber for run-flat tires and run-flat tires.

Run-flat tires, which have sidewall reinforcing rubber with a crescent-shaped cross section, are known as pneumatic tires. With such run-flat tires, even if the tire is punctured and the internal pressure drops, the side reinforcing rubber can take on the load, allowing the tire to be driven a considerable distance.

In addition, several studies have been conducted on this type of side reinforcing rubber in order to improve various characteristics, including run-flat durability (see, for example, Patent Document 1).

JP 2016-023207 A

Recently, from the perspective of social sustainability, there has been a demand for businesses and products to use so-called sustainable materials, such as materials derived from biological resources (biomass resources) and materials derived from recycled resources, and there is also a demand to increase the usage rate of sustainable materials (hereinafter sometimes referred to as the "sustainable rate" or "sustainable material ratio") in various components used in tires.

However, no attention or consideration has been given to the contribution of the side reinforcement rubber itself to sustainability.

Therefore, an object of the present invention is to provide a side reinforcing rubber for a run-flat tire that can contribute to improving sustainability.
Another object of the present invention is to provide a run-flat tire that uses such side reinforcing rubber and can contribute to improving sustainability.

In other words, the essential configuration of the side reinforcing rubber for run-flat tires and the run-flat tire of the present invention that solves the above problems is as follows:

[1] A side reinforcing rubber for run-flat tires, characterized in that a rubber composition containing a rubber component and a filler containing recycled carbon black is used.
Such a side reinforcing rubber for a run-flat tire according to the present invention can contribute to improving sustainability.

[2] The side reinforcing rubber according to [1], wherein the amount of the filler is more than 0 parts by mass and not more than 70 parts by mass per 100 parts by mass of the rubber component.
In this case, effects such as sufficiently low heat generation and low elasticity can be exhibited.

[3] The side reinforcing rubber according to [1] or [2], wherein the recycled carbon black is obtained by thermal decomposition of a vulcanized rubber product containing carbon black.
In this case, used rubber products can be effectively utilized, which can further contribute to reducing the environmental load.

[4] The side reinforcing rubber according to any one of [1] to [3], wherein the recycled carbon black has an ash content of 20 mass% or less.
In this case, the various physical properties required for tires and the quality of the recycled carbon black are improved.

[5] The side reinforcing rubber according to any one of [1] to [4], wherein the rubber component contains a modified diene rubber.
In this case, the resulting side reinforcing rubber generates less heat, and the gauge of the rubber can be made thinner, improving the rolling resistance without impairing run-flat running durability.

[6] A run-flat tire comprising: a carcass consisting of one or more carcass plies extending from a pair of bead portions through a sidewall portion to a tread portion; a pair of side reinforcing rubbers having a crescent cross section arranged on the inner side of the carcass in the tire width direction in the sidewall portion; and a bead filler arranged on the outer side in the tire radial direction of a bead core of the sidewall portion, wherein the side reinforcing rubber is the side reinforcing rubber according to any one of [1] to [5].
Such a run-flat tire of the present invention can contribute to improving sustainability.

According to the present invention, it is possible to provide a side reinforcing rubber for a run-flat tire that can contribute to improving sustainability.
Furthermore, according to the present invention, it is possible to provide a run-flat tire that uses such a side reinforcing rubber and can contribute to improving sustainability.

1 is a cross section of a half portion of a run-flat tire according to an embodiment of the present invention, taken along the tire axial direction.

The side reinforcing rubber for run-flat tires and the run-flat tire of the present invention will be described in detail below with reference to the embodiments.

<Definition>
The compounds described herein may be derived in whole or in part from fossil sources, from biological sources such as plant sources, from recycled sources such as used tires, or from a mixture of two or more of fossil sources, biological sources, and/or renewable sources.

In this specification, "sustainability rate" refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from renewable resources (recycled resources) in the target material.

In this specification, the biological resources (biomass resources) refer to carbon-neutral organic resources derived from living organisms, and include, for example, those 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 are resources other than fossil resources (petroleum, coal, natural gas, etc.). The biological resources may be edible or non-edible, but from the viewpoint of not competing with food and of effective resource utilization, it is preferable that they are non-edible.

Specific examples of the biological resources include, for example, cellulosic crops (pulp, kenaf, wheat straw, rice straw, waste paper, papermaking residues, etc.), wood, charcoal, compost, food waste, vegetable oil residues, fishery residues, livestock waste, 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 ... Examples of the 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, sugar cane, etc.), bagasse (i.e., the residue after squeezing juice from sugar cane), soybeans, soybean pulp, essential oils (pine oil, orange oil, eucalyptus oil, etc.), pulp black liquor, algae, etc. Examples of the biological resources include those that have been processed (i.e., biological resource-derived substances). Examples of the processing method include biological processing methods that utilize the functions of microorganisms, plants, animals, and tissue cultures thereof; chemical processing methods that utilize acids, alkalis, catalysts, thermal energy, light energy, etc.; physical processing methods such as micronization, compression, microwave processing, and electromagnetic wave processing; and the like. Examples of the biological resources include those that have been extracted and purified from the biological resources or the biological resources that have been processed (i.e., biological resource-derived substances). For example, sugars, proteins, amino acids, fatty acids, fatty acid esters, etc., purified from the biological resources can 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, and among these, valine, leucine, isoleucine, arginine, and phenylalanine are preferred. The amino acids may be 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.

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.

<Side reinforcement rubber for run-flat tires>
The side reinforcing rubber for run-flat tires according to one embodiment of the present invention (hereinafter, sometimes referred to as "side reinforcing rubber of this embodiment") is characterized by using a rubber composition (hereinafter, sometimes referred to as "rubber composition of this embodiment") containing a rubber component and a filler containing recycled carbon black. In other words, the side reinforcing rubber of this embodiment is characterized by containing a rubber component and a filler containing recycled carbon black. In this way, by using at least a filler containing recycled carbon black, the side reinforcing rubber can contribute to improving sustainability.

The side reinforcing rubber of this embodiment preferably has a dynamic storage modulus (E') of 10 MPa or less at 25°C with a dynamic strain of 1%, and also preferably has a Σ value of loss tangent tan δ of 5.5 or less at 28°C to 150°C. By having the dynamic storage modulus (E') of 10 MPa or less and the Σ value of 5.5 or less for the side reinforcing rubber, it is possible to achieve both high levels of durability and rolling resistance.

The side reinforcing rubber is typically a rubber member with a crescent-shaped cross section that is arranged on the inner side of the carcass in the tire width direction in the sidewall portion of a run-flat tire. Details of the structure of a run-flat tire to which the side reinforcing rubber of this embodiment can be applied will be described later.

(Rubber component)
The rubber composition of the present embodiment includes a rubber component that provides rubber elasticity to the composition. The rubber component preferably has a sustainability rate of 30 mass% or more, more preferably 40 mass% or more, more preferably 50 mass% or more, more preferably 60 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass% or more, even more preferably 90 mass% or more, and particularly preferably 100 mass%.

As the rubber component, rubber derived from biological resources and rubber derived from recycled resources are preferred.
Here, the proportion of the monomer components derived from biological resources in 100 mol% of the monomer components constituting the rubber derived from biological resources is preferably 10 mol% or more, more preferably 25 mol% or more, even more preferably 30 mol% or more, still more preferably 50 mol% or more, particularly preferably 80 mol% or more, and may be 100 mol%.
The proportion of the monomer components derived from recycled resources in 100 mol% of the monomer components constituting the rubber derived from recycled resources is preferably 10 mol% or more, more preferably 25 mol% or more, even more preferably 30 mol% or more, still more preferably 50 mol% or more, particularly preferably 80 mol% or more, and may be 100 mol%.

The rubber component is a component that contributes to crosslinking, and usually 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 can be determined, for example, by standard polystyrene conversion based on a measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

The rubber component is preferably a diene rubber, and the diene rubber is preferably an isoprene rubber or a butadiene rubber. Here, isoprene rubber refers to rubber that contains isoprene-derived units as monomer units, and butadiene rubber refers to rubber that contains butadiene-derived units as monomer units.

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) include those commonly used in the tire industry, such as RSS#3 and TSR20 (e.g., SIR20 and STR20). The origin of natural rubber (NR) is not particularly limited, and examples of the natural rubber include those derived from Hevea brasiliensis, guayule, and Russian dandelion. Examples of synthetic isoprene rubber (IR) are not particularly limited, and examples of the synthetic isoprene rubber (IR) include those commonly used in the tire industry, such as IR2200. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and the like. 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.

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, still more preferably 60% by mass or more, still 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.
In order to set the sustainability rate of the isoprene-based rubber 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 renewable 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 renewable resources, a copolymer of a monomer derived from biological resources and a monomer derived from renewable resources, or a copolymer of a monomer derived from biological resources and/or a monomer derived from renewable resources and a monomer derived from a fossil resource (petroleum, etc.).

The butadiene-based rubber may be butadiene rubber (BR), aromatic vinyl compound-butadiene copolymer rubber (e.g., styrene-butadiene rubber (SBR)), etc. Here, the butadiene that is the raw material for butadiene-based rubber is preferably derived from biological resources or recycled resources.

Examples of the butadiene rubber (BR) include high cis content butadiene rubber, low cis content butadiene rubber, and butadiene rubber containing syndiotactic polybutadiene crystals. Commercially available products can be used as the butadiene rubber (BR), and examples of commercially available butadiene rubber 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 types.

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)), solution-polymerized aromatic vinyl compound-butadiene copolymer rubber (e.g., solution-polymerized styrene-butadiene rubber (S-SBR)), and the like. In the aromatic vinyl compound-butadiene copolymer rubber, examples of the aromatic vinyl compound (aromatic vinyl monomer) include styrene, vinyl naphthalene, divinyl naphthalene, and the like. 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, Nippon Zeon Corporation, Sumitomo Chemical Co., Ltd., and the like. These aromatic vinyl compound-butadiene copolymer rubbers may be used alone or in combination of two or more.

The butadiene-based rubber has a sustainability rate of preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, still more preferably 60% by mass or more, still 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.
In order to set the sustainability rate of the butadiene-based rubber within the above range, for example, a polymer synthesized using butadiene derived from biological resources, butadiene derived from renewable resources, aromatic vinyl compounds derived from biological resources (e.g., styrene derived from biological resources), and aromatic vinyl compounds derived from renewable resources (e.g., styrene derived from renewable resources) as monomer components may be used. In this case, the synthesized polymer may be a homopolymer of a monomer derived from biological resources, a homopolymer of a monomer derived from renewable resources, a copolymer of a monomer derived from biological resources and a monomer derived from renewable resources, or a copolymer of a monomer derived from biological resources and/or a monomer derived from renewable resources and a monomer derived from a fossil resource (petroleum, etc.). In addition, butadiene rubber (B-BR) derived from biological resources (biomass resources), aromatic vinyl compound-butadiene copolymer rubber derived from biological resources (e.g., styrene-butadiene rubber (B-SBR) derived from biological resources (biomass resources)) includes not only rubber obtained by polymerizing butadiene, etc. according to a conventional method, but also rubber obtained by reaction or enzyme reaction by microorganisms, plants, animals, and tissue cultures thereof (hereinafter also referred to as "microorganisms, etc.").

In order to keep the sustainability rate of the entire rubber component within the above range, it is preferable to use natural rubber (NR) as the rubber component, or to use a polymer synthesized using monomer components derived from biological resources or monomer components derived from renewable resources as monomer components.

In general, the raw materials for rubber compositions for tires (rubber and its monomers, fillers, resins, etc.) require large-scale manufacturing equipment, so they are usually produced in large factories in specific regions, and a lot of energy is required for the storage and transportation of raw materials and products. In contrast, materials derived from biological resources (biomass resources) are derived from agricultural products, forests, etc. in each region, and can be produced on a small scale by fermentation of microorganisms 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 it environmentally friendly. In addition, materials derived from recycled resources (recycling resources) can be obtained, for example, by dismantling and pyrolyzing used tires to extract the materials that make up the tires, 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 materials for rubber compositions for tires can be obtained from various wastes and used items. In this way, by using sustainable materials (materials derived from biological resources or materials derived from renewable resources), it is possible to reduce the overall environmental burden in 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 (LCC) incurred over the entire life cycle, and reducing the amount of fossil resources used.

In addition, when producing the rubber composition, the ratio of monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources can be appropriately selected according to the supply situation of biological resources, renewable resources, and fossil resources (e.g., monomer components derived from fossil resources) and/or market demand (e.g., demand for biological resources as food), and the monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources can be polymerized to obtain rubber derived from sustainable materials (materials derived from biological resources or materials derived from renewable resources) that have the same performance as conventional synthetic rubber. Note that when using monomer components derived from renewable resources, it may be difficult to separate them from monomer components derived from fossil resources due to the manufacturing process of the monomer. In such cases, the impact on the environment can be evaluated by adopting the concept of mass balance.

The ratio of each monomer unit (e.g., unit derived from isoprene, unit derived from butadiene, unit derived from aromatic vinyl compound) in the entire rubber component can be adjusted appropriately depending on the member to which the rubber 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. In addition, the ratio of cis-bond units in the butadiene-based units can also be adjusted appropriately depending on the member to which the rubber is applied.
In this specification, the term "monomer unit" refers to a structural unit of a polymer, the term "unit derived from isoprene" refers to a structural unit in a polymer constituted based on the monomer isoprene (including the isoprene unit in natural rubber), the term "unit derived from butadiene" refers to a structural unit in a polymer constituted based on the monomer butadiene, and the term "unit derived from an aromatic vinyl compound" refers to a structural unit in a polymer constituted based on the monomer aromatic vinyl compound.
In this specification, the ratio of each monomer unit is measured by NMR.

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

The rubber component may be modified to introduce functional groups that interact 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 alone or in combination of two or more types. Among these, amino groups, alkoxy groups, and alkoxysilyl groups are preferred, and substituted amino groups in which the hydrogen atom of an amino group is substituted with an alkyl group having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and alkoxysilyl groups having 1 to 6 carbon atoms are even more preferred.

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

The rubber derived from sustainable materials (materials derived from biological resources or materials derived from renewable resources) can be produced in the same manner as conventional synthetic rubber derived from fossil resources, for example, by using monomer components derived from biological resources or monomer components derived from renewable resources, and, if necessary, monomer components derived from fossil resources. In addition, the rubber derived from sustainable materials (particularly rubber derived from biological resources) can also be obtained by reactions with microorganisms or enzyme reactions.

Regarding the method for preparing rubber derived from biological resources from the above-mentioned biological resources, for example, the method described in JP 2022-179158 A can be used. For example, by using butadiene obtained from biological resources as a monomer component, it is possible to obtain butadiene rubber (B-BR) derived from biological resources (biomass resources), and by using styrene obtained from biological resources and butadiene obtained from biological resources as monomer components, it is possible to obtain styrene-butadiene rubber (B-SBR) derived from biological resources (biomass resources). Here, methods for obtaining B-BR and B-SBR from biological resources include artificial polymerization methods, polymerization methods in vivo, 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 the target tire performance according to a known method.

As the butadiene obtained from the biological resources, butadiene derived from alkyl alcohols (preferably ethanol and butanol, more preferably butanol), butadiene derived from alkenes (preferably ethylene), and butadiene derived from unsaturated carboxylic acids (preferably tiglic acid) can be suitably used. Two or more of these butadienes may be used in combination.
As the styrene obtained from the biological resource, styrene obtained from a plant (preferably a plant belonging to the family Hamamelidaceae, Styracaceae, or Apocynaceae, more preferably a plant belonging to the genera Liquidamus, Styrax, or Catharanthus, and even more preferably Sweetgum, Styrax rosa, or Catharanthus roseus) or a microorganism (preferably a microorganism belonging to the genera Penicillium or Escherichia, more preferably P. citrinum or transformed E. coli) can be suitably used. Two or more of these styrenes may be used in combination.

Recently, biomass combinat mainly using bioethanol, bioethylene, etc., has been planned, but bioethanol and bioethylene are mainly produced using sugars and/or cellulose as biological resources, and other biological resources such as proteins, lipids, and amino acids cannot be effectively utilized. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, it is preferable to use multiple types of monomer components derived from biological resources as the monomer components derived from the biological resources, or to use monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources in combination, and further to appropriately adjust the ratio of these monomer components. This makes it possible to effectively utilize a wide range of biological resources and renewable resources such as sugars, proteins, and lipids without relying on one type of biological resource, and to stably supply rubber derived from sustainable materials, and further to consider the environment according to the situation at the time of production.
In addition, when using multiple types of monomer components derived from biological resources, 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 butadiene derived from multiple types of biological resources with different origins as the butadiene derived from biological resources, and/or to use a mixture of styrene derived from multiple types of biological resources with different origins as the styrene derived from biological resources. This allows multiple types of biological resources to be effectively utilized.

In the rubber composition of this embodiment, the rubber component preferably contains a modified diene rubber. In this case, the resulting side reinforcing rubber has low heat generation and can have a thin rubber gauge, improving rolling resistance without impairing run-flat running durability. In addition, from the viewpoint of fully obtaining the above effects, the proportion of the modified diene rubber in the rubber component is preferably 30% by mass or more, and more preferably 50% by mass or more. The modified diene rubber may be used alone or in combination of two or more types.

The modified diene rubber is preferably one in which a modifying functional group containing at least one of a tin atom, a nitrogen atom, and a silicon atom has been introduced into the molecule. Such modified diene rubber is obtained by modifying a diene rubber with a compound containing at least one of a tin atom, a nitrogen atom, and a silicon atom.

Examples of the compound containing a tin atom include tin tetrachloride, tributyltin chloride, dioctyltin dichloride, dibutyltin dichloride, and triphenyltin chloride.
Examples of the compound containing a nitrogen atom include an isocyanate compound, an aminobenzophenone compound, a urea derivative, 4-dimethylaminobenzylideneaniline, dimethylimidazolidinone, and N-methylpyrrolidone.
The functional group containing a silicon atom includes a silane group in which a hydrocarbyloxy group and/or a hydroxy group is bonded to a silicon atom.

The modified diene rubber is preferably an amine-modified diene rubber, more preferably one having an amine-based functional group, a protic amino group and/or an amino group protected by a removable group, introduced into the molecule as a modifying functional group, and even more preferably one having a silicon-containing functional group introduced therein.

Such modifying functional groups may be present at any of the polymerization initiation terminals, side chains, and polymerization active terminals of the diene rubber, but preferably at the polymerization terminals, more preferably at the same polymerization active terminals, they have an amino group protected by a protic amino group and/or a removable group, and a silicon atom bonded to a hydrocarbyloxy group and/or a hydroxy group, and particularly preferably a silicon atom bonded to one or two hydrocarbyloxy groups and/or hydroxy groups.

The modified diene rubber preferably has a Mooney viscosity (ML ₁₊₄ , 100° C.) of 10 to 150, more preferably 15 to 100. When the Mooney viscosity is 10 or more, sufficient rubber physical properties including fracture resistance can be obtained, and when it is 150 or less, good workability can be maintained.
The Mooney viscosity (ML ₁₊₄ , 130° C.) of the unvulcanized rubber composition containing the modified diene rubber is preferably 10-150, more preferably 30-100.
The modified diene rubber preferably has a ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn), i.e., a molecular weight distribution (Mw/Mn), of 1 to 3, and more preferably 1.1 to 2.7. By setting the molecular weight distribution (Mw/Mn) of the modified diene rubber within the above range, the workability of the rubber composition is not reduced, kneading is easy, and the physical properties of the rubber composition can be sufficiently improved.

The number average molecular weight (Mn) of the modified diene rubber is preferably 100,000 to 1,000,000, and more preferably 150,000 to 500,000. By setting the number average molecular weight of the modified diene rubber within the above range, it is possible to obtain excellent fracture resistance properties by suppressing the decrease in elastic modulus of the vulcanizate and the increase in hysteresis loss, and also to improve the workability of kneading the rubber composition.

(filler)
The rubber composition of the present embodiment contains a filler, and the filler is required to contain recycled carbon black.

Examples of fillers other than recycled carbon black include carbon black other than recycled carbon black (virgin carbon black), silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, etc. Examples of carbon black other than recycled carbon black include carbon black derived from plants. The rubber composition of this embodiment may further contain fillers other than these recycled carbon blacks.

The content of the filler in the rubber composition (side reinforcing rubber) of this embodiment is preferably more than 0 parts by mass and not more than 70 parts by mass per 100 parts by mass of the rubber component. If the content of the filler is not more than 70 parts by mass, sufficient effects such as low heat generation and low elasticity can be achieved. From the same viewpoint, the content of the filler per 100 parts by mass of the rubber component is more preferably not more than 60 parts by mass, and even more preferably not more than 55 parts by mass. In addition, from the viewpoint of maintaining the breaking strength and durability of the rubber well, the content of the filler per 100 parts by mass of the rubber component is preferably not less than 30 parts by mass, and more preferably not less than 40 parts by mass.

-Recycled carbon black-
In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials that have been recycled. Examples of the waste materials that have been recycled include rubber products (particularly vulcanized rubber products) that contain carbon black, such as used rubber and used tires, and waste oil. "Recycled carbon black" is different from carbon black that is produced directly from raw materials such as hydrocarbons, such as petroleum and natural gas, that is, carbon black that is not recycled. Note that "used" here includes not only carbon black that has been actually used and then discarded, but also carbon black that has been produced but not actually used and then discarded.

The recycled carbon black used in this embodiment is preferably obtained by thermal decomposition of a vulcanized rubber product containing carbon black. In this case, used rubber products can be effectively utilized, which can further contribute to reducing the environmental load. Furthermore, the recycled carbon black used in this embodiment is preferably obtained from a solid residue generated by thermal decomposition of the vulcanized rubber product containing the above carbon black. When a rubber product containing carbon black is thermally decomposed, a solid residue and a volatile component (oil) are obtained, and it is possible to recover recycled carbon black from either of them. However, it is preferable that the recycled carbon black used in this embodiment does not include carbon black recovered from oil.

The solid residue obtained by pyrolysis of waste materials such as used rubber and used tires contains ash in addition to carbon black. Ash is derived from non-volatile components contained in rubber and tires. For this reason, the recycled carbon black obtained from the solid residue 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 in the recycled carbon black, the better. In the recycled carbon black used in this embodiment, the carbon content is preferably 80% by mass or more, more preferably 85% by mass or more, more preferably 87% by mass or more, and even more preferably 89% by mass or more. The carbon content in the recycled carbon black used in this embodiment is preferably 97% by mass or less. Note that the above carbon content does not include adsorbed moisture.

Specific examples of ash include zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, magnesium oxide, and the like. 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. The lower limit of the ash content of the recycled carbon black used in this embodiment may be 0.5% by mass. On the other hand, in consideration of the various physical properties required for tires, the quality of the recycled carbon black, and the like, the ash content of the recycled carbon black is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 5.0% by mass or less.
In this specification, the ash content of carbon black is calculated from the mass of unburned components (ash content) obtained by burning carbon black at 550° C.±25° C. to convert it to incineration.

Recycled carbon black can also be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, referring to "Rubber Chemistry and Technology", Vol. 85, No. 3, pp. 408-449 (2012), in particular pp. 438, 440, and 442, describes that recycled carbon black is obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures ([0027]). Carbon black obtained from such pyrolysis processes usually lacks functional groups on its surface, as mentioned in [0004] of Japanese Patent No. 6856781 (Comparison of Surface Morphology and Chemistry of Pyrolytic Carbon Black and Commercial Carbon Black, Powder Technology 160 (2005) pp. 190-193).

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 the recycled carbon black can be carried out by a conventional method. For example, in European Patent Application Publication No. 3173251, carbon black obtained from a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black having hydroxyl and/or carboxyl groups on its surface. In Japanese Patent No. 6856781, carbon black obtained from a pyrolysis process is treated with an amino acid compound containing at least one thiol group or disulfide group to obtain carbon black with an activated surface. The recycled carbon black according to the present embodiment also includes carbon black that has been treated to include functional groups on its surface.

In addition, the thermal decomposition of crosslinked rubber products (vulcanized rubber products) such as used tires can be performed, for example, by a thermal decomposition method at a temperature of 650° C. or higher. The recycled carbon black used in this embodiment preferably has a nitrogen adsorption specific surface area N ₂ SA of 20 to 150 m ² /g and a DBP oil absorption of 50 to 150 ml/100 g. Note that, as the recycled carbon black in this embodiment, a commercially available product can be used, and an example of such a commercially available product is the product name "PB365" manufactured by Enrestec. PB365 is a recycled carbon black produced through the thermal decomposition of used tires, and has an N ₂ SA of 73.6 m ² /g. PB365 also contains about 17% by mass of ash.

The grade of the recycled carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available recycled carbon black can be used, and examples of commercially available recycled carbon black include products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Corporation, Nippon Steel Carbon Co., Ltd., Birla Carbon Co., Ltd., and the like. These recycled carbon blacks may be used alone or in combination of two or more types.

The nitrogen adsorption specific surface area (N ₂ SA) of the recycled carbon black is not particularly limited and can be appropriately adjusted depending on, for example, the target performance of the tire to which it is applied. For example, the nitrogen adsorption specific surface area (N ₂ SA) of the recycled carbon black is preferably 20 m ² /g or more, more preferably 50 m ² /g or more, more preferably 70 m ² /g or more, even more preferably 90 m ² /g or more, and preferably 200 m ² /g or less, more preferably 150 m ² /g or less, and even more preferably 130 m ² /g or less.
In this specification, the nitrogen adsorption specific surface area (N ₂ SA) of the recycled carbon black is determined in accordance with JIS K 6217-2:2017 (ISO 4652:2012).

The content of recycled carbon black in the rubber composition of this embodiment is preferably more than 0 parts by mass and not more than 70 parts by mass per 100 parts by mass of the rubber component. If the content of the recycled carbon black is not more than 70 parts by mass, sufficient effects such as low heat generation and low elasticity can be exhibited. From the same viewpoint, the content of recycled carbon black per 100 parts by mass of the rubber component is more preferably not more than 60 parts by mass, and even more preferably not more than 55 parts by mass. In addition, from the viewpoint of maintaining the breaking strength and durability of the rubber well, the content of recycled carbon black per 100 parts by mass of the rubber component is preferably not less than 30 parts by mass, and more preferably not less than 40 parts by mass.

- Carbon black other than recycled carbon black -
The rubber composition of the present embodiment may further contain, as a filler, a carbon black other than the recycled carbon black (virgin carbon black) in addition to the recycled carbon black. Examples of the carbon black other than the recycled carbon black include carbon black derived from plants, and examples of the plant-derived carbon black include those derived from castor oil and pine oil.

In addition, in the rubber composition of this embodiment, the proportion of recycled carbon black in the total of recycled carbon black and plant-derived carbon black (i.e., total carbon black) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass (i.e., the carbon black consists only of recycled carbon black) from the viewpoint of further improving sustainability.

-silica-
The rubber composition of the present embodiment may contain silica as a filler. Examples of the 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 has a large number of silanol groups. These silicas may be used alone or in combination of two or more. Commercially available products of the silica may be used, and examples of the commercially available silica products include products from Tosoh Silica Corporation, Evonik Corporation, Solvay Corporation, Solvay Japan Co., Ltd., and Tokuyama Corporation.

As the silica, silica derived from silicic acid plants is preferred from the viewpoint of reducing environmental load. The silicic acid plants are present, for example, in mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Gramineae plants. Among these plants, Gramineae plants are preferred. In addition, the Gramineae plants include rice, bamboo grass, sugarcane, and the like, among which rice is preferred. Since rice is widely cultivated for food, it can be procured locally in a wide area, and since rice husks are generated in large quantities as industrial waste, it is easy to secure the amount. Therefore, from the viewpoint of easy availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred as silica. By using the rice husk silica, rice husks that become industrial waste can be effectively utilized, and since the raw material can be procured locally near the tire manufacturing plant, the energy and cost of transportation and storage can be reduced, which is environmentally preferable from various viewpoints. The rice husk silica may be a powder of rice husk charcoal obtained by carbonizing rice husks by heating, or may be precipitated silica produced by a wet method using an aqueous alkali silicate solution, which is prepared by extracting rice husk ash generated when rice husks are burned in a biomass boiler using rice husks as fuel with an alkali. The method for producing the rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husks can be pyrolyzed by steaming them in a kiln to obtain rice husk charcoal. The rice husk charcoal thus obtained is pulverized using a known pulverizer (e.g., a ball mill), and then sorted and classified into a predetermined particle size range to obtain a powder of rice husk charcoal. The precipitated silica derived from rice husks can be produced by the method described in JP 2019-38728 A.
Further examples of the silica include silica produced by recycling silicon components from scraps of silicon wafers, which are raw materials for semiconductors, glass bottles, etc.

The silica preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 50 m ² /g or more, more preferably 100 m ² /g or more, and even more preferably 150 m ² /g or more, and preferably 350 m ² /g or less, more preferably 250 m ² /g or less, even more preferably 230 m ² /g or less, and even more preferably 200 m ² /g or less.
In this specification, the nitrogen adsorption specific surface area (N ₂ SA) of silica is a value measured by the BET method in accordance with ASTM D3037-93.

The content of the silica can be adjusted as appropriate, for example, depending on the target performance of the tire to which the rubber composition is applied. For example, the content of the silica 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, even 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.

(Silane coupling agent)
When the rubber composition of the present embodiment contains silica, in order to improve the effect of the silica, the rubber composition preferably contains a silane coupling agent. Examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N, Examples of the silane coupling agent include N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide, etc. As the silane coupling agent, commercially available products can be used, and examples of the commercially available silane coupling agent include products from Evonik, Momentive, Shin-Etsu Silicone Co., Ltd., Dow Corning Toray Co., Ltd., Tokyo Chemical Industry Co., Ltd., and Azumax Co., Ltd. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent can be adjusted as appropriate, for example, depending on the target performance of the tire to which it is applied. For example, the content of the silane coupling agent is preferably 1 part by mass or more, more preferably 6 parts by mass or more, and even more preferably 8 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the silica.

Bioethanol can also be used as a raw material for the silane coupling agent. Bioethanol is produced mainly using sugars and/or cellulose as biological resources, and other biological resources such as proteins, lipids, and amino acids cannot be effectively utilized. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, it is preferable to use multiple types of monomer components derived from biological resources as the monomer components derived from the biological resources, 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, depending on the supply situation of various biological resources, the supply situation of renewable resources, the supply situation of fossil resources, and market demands (for example, the demand for biomass resources as food). This makes it possible to effectively utilize 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 to take the environment into consideration depending on the situation at the time of production.

(resin)
The rubber composition of the present embodiment may contain a resin. Examples of the resin include terpene resins, rosin resins, _C5 resins, C5- _C9 resins, _C9 resins, cyclopentadiene resins, aromatic resins, coumarone resins, _indene resins, coumarone-indene resins, olefin resins, polyurethane resins, and acrylic resins. These resins may be used alone or in combination of two or more. Among these resins, terpene resins, rosin resins, _C5 resins, _C5 - _C9 resins, _C9 resins, cyclopentadiene resins, and aromatic resins are preferred, and terpene resins and rosin resins are particularly preferred. Terpene resins and rosin resins are naturally derived sustainable resins, and therefore can further reduce the environmental load and can further improve tire performance, such as grip performance on various road surface conditions such as dry road surfaces, wet road surfaces, snow-covered road surfaces, and frozen road surfaces. In addition, _C5 resin, _C9 resin, _C5 - _C9 resin, and cyclopentadiene resin can improve wear resistance and fuel economy in a well-balanced manner, while aromatic resin can improve grip performance, wear resistance, and rubber strength in a well-balanced manner.

The resin may be hydrogenated, i.e., may be a hydrogenated resin (hydrogenated resin). In addition, the resin may be modified to introduce a functional group that interacts with a filler such as carbon black or silica. Examples of the functional group 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.

The terpene resin is a solid resin obtained by blending turpentine, which is obtained at the same time when rosin is obtained from pine trees, or a polymerization component separated from the turpentine, and polymerizing it using a Friedel-Crafts catalyst, and examples of the terpene resin include β-pinene resin and α-pinene resin. Terpene resins also include terpene-aromatic compound resins, and representative examples of the terpene-aromatic compound resins include terpene-phenol resin and styrene-terpene resin. The terpene-phenol resin 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. There are no particular limitations on the terpenes used as raw materials, and monoterpene hydrocarbons such as α-pinene and limonene are preferred, those containing α-pinene are more preferred, and α-pinene is particularly preferred.

The rosin-based resins include natural resin rosins such as gum rosin, tall oil rosin, and wood rosin contained in raw pine resin and tall oil, and modified rosins, rosin derivatives, and modified rosin derivatives such as polymerized rosin and its partially hydrogenated rosin; glycerin ester rosin and its partially hydrogenated rosin and fully hydrogenated rosin; pentaerythritol ester rosin and its partially hydrogenated rosin and polymerized rosin.

The _C5 resin includes aliphatic petroleum resins obtained by (co)polymerizing _C5 fractions obtained by thermal cracking of naphtha in the petrochemical industry. The _C5 fractions usually include 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.

The _C5 - _C9 resin refers to _{a C5-C9 synthetic petroleum resin, and examples of the C5-C9 resin include solid polymers obtained by polymerizing petroleum-derived C5-C11 fractions using Friedel - Crafts} catalysts such as _AlCl3 and _BF3 , and more specifically, copolymers mainly composed of styrene, vinyltoluene, α-methylstyrene, indene, etc. As the _C5 - _C9 resin, a resin with a small amount of _C9 or more components is preferred from the viewpoint of compatibility with the rubber component. Here, "a small amount of _C9 or more components" means that the amount of _C9 or more components in the total amount of the resin is less than 50 mass%, preferably 40 mass% or less.

The _C9 resin refers to a _C9 synthetic petroleum resin, for example, a solid polymer obtained by polymerizing a _C9 fraction using a Friedel-Crafts type catalyst such as _AlCl3 or _BF3 . Examples of the _C9 resin include copolymers mainly composed of indene, α-methylstyrene, vinyltoluene, etc.

The cyclopentadiene resin refers to a resin containing a unit derived from a cyclopentadiene monomer as a monomer unit. Examples of the cyclopentadiene resin include a homopolymer of a cyclopentadiene monomer, a copolymer of two or more cyclopentadiene monomers, and a copolymer of a cyclopentadiene monomer and another monomer. Here, examples of the cyclopentadiene monomer include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene, and among these, dicyclopentadiene is preferred, that is, the cyclopentadiene resin is preferably a dicyclopentadiene resin. The dicyclopentadiene resin refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as _AlCl3 or _BF3 . Examples of the dicyclopentadiene resin include a homopolymer of dicyclopentadiene, a copolymer of dicyclopentadiene and an aromatic monomer, and a copolymer of dicyclopentadiene and a _C9 fraction (vinyl toluene, indene, etc.).

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 and other monomers. Examples of aromatic monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-phenylstyrene; phenolic monomers such as phenol, alkylphenol, and alkoxyphenol; and naphthol monomers such as naphthol, alkylnaphthol, and alkoxynaphthol.

The resin preferably has a softening point of 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 resin preferably has a softening point of 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 defined in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring and ball softening point tester.

The resin may be a commercially available product, and examples of the commercially available resin include products from ENEOS Corporation, Arakawa Chemical Industries, Ltd., ExxonMobil Corporation, Clayton, Yasuhara Chemical Co., Ltd., Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Clayton Polymers, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., and Taoka Chemical Co., Ltd.

The amount of the resin is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the rubber composition is applied. For example, the amount of the resin is preferably in the range of 5 to 100 parts by mass, and more preferably in the range of 10 to 60 parts by mass, per 100 parts by mass of the rubber component.

(rubber powder)
The rubber composition of the present embodiment may contain rubber powder. The rubber powder may be obtained by crushing used rubber products such as used tires, and removing reinforcing materials such as steel materials and fibers, dust, glass, sand, stones, etc., as desired, or by preparing a new vulcanized rubber composition to produce rubber powder and crushing it. For example, rubber powder can be obtained from vulcanized rubber by the method described in "Rubber Chemistry and Technology". In the process of crushing vulcanized rubber to obtain rubber powder, mechanical treatment or low-temperature treatment may be used. For example, in mechanical treatment, various crushing devices such as cracker mills and granulators can be used to mechanically crush vulcanized rubber into fine particles. In low-temperature treatment, finely chopped vulcanized rubber is frozen at extremely low temperatures and then crushed into fine particles. In addition, a magnetic separator or the like can be used to remove steel materials, and an air separator or the like can be used to remove fibers. The rubber powder may be a commercially available product, and examples of the commercially available rubber powder include products from Global Corporation or Nanton Huili Rubber Corporation. From the viewpoint of reducing the environmental load, 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 kinds.

The composition of the rubber powder is not particularly limited and depends on the composition of the vulcanized rubber of the raw material, such as used rubber products (used tires). In one embodiment, the rubber powder contains a rubber component, carbon black, silica, etc. The rubber component, carbon black, silica, etc. contained in the rubber powder may be the same as or different from the rubber component, carbon black, silica, etc. contained in the rubber composition of this embodiment described above.

The rubber powder has a volume average particle size of preferably 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 size of the rubber powder, the better, and there is no particular lower limit.
In this specification, the volume average particle size is measured by a laser diffraction particle size distribution measuring device, for example, "CAPA500" manufactured by Horiba, Ltd.

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

The rubber powder 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 extractables in the rubber crumb means the acetone extractables (%) determined by the acetone extraction method in accordance with JIS K6350.

The amount of the rubber powder is not particularly limited, and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the rubber powder is applied. For example, the amount of the rubber powder 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, even 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.

(Liquid softener)
The rubber composition of the present embodiment may contain a liquid softener. Here, the "liquid softener" is 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.

The oil is a general term for the extender oil contained in the rubber component and the liquid oil added as a compounding agent to the rubber composition, and examples thereof include vegetable oil, process oil, oil obtained by recycling vegetable oil or process oil, or a mixture thereof. From the viewpoint of reducing the environmental load, vegetable oil and oil obtained by recycling are preferred. Examples of the vegetable oil include palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, peanut 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, coconut oil, etc. Examples of the process oil include paraffin-based process oil, aromatic process oil, naphthenic process oil, etc. The oil can be a commercially available product, and examples of the commercially available oil include products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoi Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., and Nisshin Oillio Group Co., Ltd. These oils may be used alone or in combination of two or more types.

The liquid polymer is preferably a liquid diene polymer. Examples of the liquid diene 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 the ends 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.

The content of the liquid softener is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which it is applied. For example, the content of the liquid softener is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even 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.

(Anti-aging agent)
The rubber composition of the present 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), 6-anilino-2,2,4-trimethyl-1,2-dihydroquinoline, and the like. As the antioxidant, a commercially available product can be used, and examples of the commercially available antioxidant include products from Ouchi Shinko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Co., Ltd., Flexis Co., Ltd., and the like. These antioxidants may be used alone or in combination of two or more.

The content of the anti-aging agent is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which it is applied. For example, the content of the anti-aging agent 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, relative to 100 parts by mass of the rubber component.

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

The wax content is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the rubber is applied. For example, the wax content 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.

(stearic acid)
The rubber composition of the present embodiment may contain stearic acid. Commercially available stearic acid may be used, and examples of the commercially available stearic acid include products from NOF Corp., Kao Corp., FUJIFILM Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc. These commercially available stearic acid products may be used alone or in combination of two or more.

The content of the stearic acid is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the rubber composition is applied. For example, the content of the 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.

(Zinc Oxide)
The rubber composition of the present embodiment may contain zinc oxide (zinc white). The zinc oxide is preferably zinc oxide obtained by recycling. Commercially available products can be used as the zinc oxide, and examples of the commercially available zinc oxide include products from Hakusuitec Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., and the like. These commercially available zinc oxide products may be used alone or in combination of two or more. The zinc used in the zinc oxide may be not only zinc bullion, but also zinc obtained from recycled zinc or zinc dross.

The amount of zinc oxide is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the rubber composition is applied. For example, the amount of 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.

(sulfur)
The rubber composition of the present embodiment preferably contains sulfur. The sulfur may be derived from fossil resources, recycled resources, or materials derived from biological resources. From the viewpoint of reducing the environmental load, 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 methods described in the above-mentioned Japanese Patent Application No. 2022-140390. In addition, the sulfur may be powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, or the like, which are generally used as crosslinking agents in the rubber industry. As the sulfur, commercially available products can be used, and examples of commercially available sulfur products include products from Tsurumi Chemical Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., and Flexis Co., Ltd. These sulfurs may be used alone or in combination of two or more types.

The sulfur content is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the rubber composition is applied. 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, and more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

(Vulcanization accelerator)
The rubber composition of the present 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. The vulcanization accelerator derived from biological resources can be obtained, for example, by the method disclosed in JP-A-2005-139239.
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 (DPG). Examples of the vulcanization accelerator 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 products can be used as the vulcanization accelerator, and examples of the commercially available vulcanization accelerators include products from 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.

The content of the vulcanization accelerator is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which it is applied. 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.

(Cellulose nanofiber)
The rubber composition of the present embodiment may contain cellulose nanofibers (CNF). The cellulose nanofibers can be blended into the rubber composition to reinforce the rubber composition. The cellulose nanofiber is preferably a modified cellulose nanofiber, and the modified cellulose nanofiber is a fine fiber made from modified cellulose. The fiber diameter of the cellulose nanofiber is not particularly limited, but is about 3 to 500 nm. The average fiber diameter and average fiber length of the cellulose nanofiber can be obtained by averaging the fiber diameter and fiber length obtained from the results of observing each fiber using a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM). The cellulose nanofiber can be obtained by defibrating cellulose. The average fiber length and average fiber diameter of the fine fibers can be adjusted by oxidation treatment and defibration treatment.

The raw material for the cellulose nanofibers is not particularly limited as long as it contains cellulose, but 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.

The amount of the cellulose nanofiber is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the cellulose nanofiber is applied. For example, the amount of the cellulose nanofiber 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.

(Porous Cellulose Particles)
The rubber composition of the present 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 compounding them with the rubber composition, the performance on ice can be improved. When the porosity of the porous cellulose particles is 75% or more, the effect of improving the 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 a sample (i.e., the porous cellulose particles) with a measuring cylinder, calculating the bulk density, and using the following formula.
Porosity (%) = {1 - [bulk specific gravity of sample (g/mL)] / [true specific gravity of sample (g/mL)]} x 100
Here, the true specific gravity of cellulose is 1.5.

The particle size of the porous cellulose particles is not particularly limited, but from the viewpoint of abrasion resistance, the average particle size is preferably 1000 μm or less. 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 having a major axis/minor axis ratio of 1 to 2. By using particles having such a spherical structure, the dispersibility in the rubber composition is improved, which contributes to improving performance on ice and maintaining abrasion resistance, etc. The major axis/minor axis ratio is more preferably 1.0 to 1.5.
The average particle size and the long axis/short axis ratio of the porous cellulose particles are determined as follows: That is, the porous cellulose particles are observed under a microscope to obtain an image, and the long axis and short axis of the particles (when the long axis and short axis are the same, the length in a certain axis direction and the length in an axis direction perpendicular to the long axis) are measured for 100 particles using the image, and the average particle size is obtained by calculating the average value, and the long axis/short axis ratio is obtained by averaging the values obtained by dividing the long axis by the short axis.

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

The content of the porous cellulose particles is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the rubber is applied. 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.

(Solid fine particles)
The rubber composition of the present embodiment may contain solid fine particles. The solid fine particles can improve the performance on ice by blending them with the rubber composition. The solid fine particles preferably have an average particle diameter of 1 μm or more, and more preferably 1000 μm or less, and more preferably 300 μm or less. Examples of the solid fine particles include powders derived from plants, such as rice husks, walnut powder, and walnut shells; powders derived from animals, such as eggshells (eggshell powder) and bone powder; powders derived from natural minerals, such as whitebait; inorganic fine particles, such as graphite and zinc oxide whiskers; water-soluble metal salt fine particles, such as magnesium sulfate and metal salts of lignin sulfonate; non-metallic fibers, such as glass fibers; and the like. Among these, rice husks, walnut shells, eggshells, and whitebait are preferred.

The content of the solid fine particles is not particularly limited and can be adjusted as appropriate depending on, for example, the target performance of the tire to which the rubber is applied. 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.

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

(Method for producing rubber composition)
The method for producing the rubber composition of the present embodiment is not particularly limited, but for example, the rubber composition can be produced by blending the rubber component with a filler and various components appropriately selected as necessary, and kneading, heating, extruding, etc. The obtained rubber composition can be vulcanized to produce a vulcanized rubber.

There are no particular limitations on the conditions for the kneading, and the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, etc., as well as the conditions for the kneading temperature, kneading time, type of kneading device, etc., can be appropriately selected according to the purpose. Examples of kneading devices include Banbury mixers, intermixes, kneaders, rolls, etc., which are typically used for kneading rubber compositions.

There are no particular limitations on the conditions for the heat-in process, and the heat-in process temperature, heat-in process time, heat-in process equipment, and other conditions can be appropriately selected according to the purpose. Examples of the heat-in process equipment include a heat-in process roll machine typically used for heat-in process of rubber compositions.

There are no particular limitations on the extrusion conditions, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of extrusion devices include extruders that are typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

There are no particular limitations on the vulcanization device, method, conditions, etc., and these can be selected appropriately depending on the purpose. Devices for vulcanization include molding vulcanizers using molds that are typically used to vulcanize rubber compositions. As for vulcanization conditions, the temperature is, for example, about 100 to 190°C.

<Run-flat tires>
As shown in FIG. 1 , the run-flat tire of the present invention typically comprises a tread portion 1, a pair of sidewall portions 2 (only one side is shown) extending radially inward from each side of the tread portion 1, and a pair of bead portions 3 (only one side is shown) continuing to the radially inward of each sidewall portion 2.

The run-flat tire shown in FIG. 1 also includes a bead core 6 embedded in a pair of bead portions 3, a carcass 4 consisting of one or more carcass plies extending from the pair of bead portions 3 through the sidewall portion 2 to the tread portion 1, a bead filler 7 disposed radially outward of the bead core 6, a belt 5 disposed radially outward of the crown region of the carcass 4, and a tread rubber 11 disposed radially outward of the belt 5 to form the tread surface.

In the run-flat tire shown in FIG. 1, the carcass 4 is connected to the main body portion 4a that extends in a toroidal shape from the bead portion 3 through the sidewall portion 2 to the tread portion 1, and the main body portion 4a is anchored to the bead portion 3 by the folded portion 4b that is folded back around the bead core 6.

Furthermore, the run-flat tire of FIG. 1 includes a pair of side reinforcing rubbers 9 (only one side is shown) arranged on the inner side of the carcass 4 in the tire width direction in the sidewall portion 2. As shown in FIG. 1, the side reinforcing rubber 9 is gradually reduced in thickness toward the inner and outer sides in the tire radial direction in the cross section along the tire axial direction, and is crescent-shaped with a convex curve toward the outer side in the tire axial direction. By arranging the side reinforcing rubber 9 in this manner, even if the internal pressure of the tire is reduced due to a puncture or the like, the side reinforcing rubber 9 contributes to supporting the vehicle weight, making it possible to safely travel a certain distance. And, in the run-flat tire of the present invention, the side reinforcing rubber 9 is the side reinforcing rubber of the present embodiment described above. In this way, by using the side reinforcing rubber of the present embodiment, the obtained run-flat tire can contribute to improving sustainability.

As shown in FIG. 1, the run-flat tire of the present invention may also include an inner liner 8 arranged along the inner surface of the carcass 4 and made of a rubber material or the like that has excellent air impermeability.

The belt 5 located on the radially outer side of the carcass 4 can be configured by providing a belt layer 50 as shown in FIG. 1, and arranging a belt reinforcing layer 51 made of cords extending substantially in the tire circumferential direction on the radially outer side of the belt layer 50. The belt layer 50 can be configured by sequentially arranging an inner belt layer made of cords made of organic fibers or the like extending in a direction inclined to the tire circumferential direction and an outer belt layer made of cords extending in a direction intersecting the cords of the inner belt layer toward the radially outer side of the tire. However, the configuration, arrangement area, number of layers, etc. of the belt layers, etc. can be appropriately changed as necessary.

The run-flat tire of this embodiment can be manufactured by a normal method by applying the above-mentioned rubber composition to the side reinforcing rubber. For example, the tire of this embodiment may be obtained by molding and vulcanizing the unvulcanized rubber composition according to the type of tire to which it is applied, or by molding and then vulcanizing a semi-vulcanized rubber that has been subjected to a pre-vulcanization process or the like. The run-flat tire of this embodiment is preferably a pneumatic tire, and the gas to be filled in 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.

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 and can be modified as appropriate without departing from the spirit and scope of the invention.

Two types of rubber compositions having the compounding compositions shown in Table 1 are prepared, and these rubber compositions are arranged on the side reinforcing rubber 9 shown in FIG. 1, and a radial tire (run-flat tire) for passenger cars having a tire size of 215/45ZR17 is manufactured according to a conventional method.
The sustainable material ratio of the side reinforcing rubber in the manufactured tires was evaluated by calculating the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources (recycled resources). The results are shown in Table 1.

*1 Natural rubber: TSR20
*2 Modified butadiene rubber: Primary amine modified polybutadiene *3 Virgin carbon black: FEF grade carbon black (N550), Asahi Carbon Co., Ltd. "Asahi #60"
*4 Recycled carbon black: Recycled carbon black with an ash content of 17%, obtained by thermal decomposition of vulcanized rubber products containing carbon black. *5 Process oil: Aromatic oil, "Aromax #3" manufactured by Fuji Kosan Co., Ltd.
*6 Antioxidant: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
*7 Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazylsulfenamide, "Noccela CZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
*8 Vulcanization accelerator TOT: Tetrakis (2-ethylhexyl) thiuram disulfide, "Noccela TOT-N" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

From Table 1, it can be seen that the side reinforcement rubber of Example 1 has a higher ratio of sustainable materials than the side reinforcement rubber of Comparative Example 1, and can contribute to improving sustainability.

According to the present invention, it is possible to provide a side reinforcing rubber for a run-flat tire that can contribute to improving sustainability.
Furthermore, according to the present invention, it is possible to provide a run-flat tire that uses such a side reinforcing rubber and can contribute to improving sustainability.

Reference Signs List 1 Tread portion 2 Sidewall portion 3 Bead portion 4 Carcass 4a Main body portion of carcass 4b Turn-up portion of carcass 5 Belt 6 Bead core 7 Bead filler 8 Inner liner 9 Side reinforcing rubber 11 Tread rubber 50 Belt layer 51 Belt reinforcing layer

Claims (4)

A rubber composition containing a rubber component and a filler containing recycled carbon black ,
the rubber component is a diene-based rubber, the diene-based rubber contains a butadiene-based rubber, and the butadiene-based rubber consists solely of butadiene rubber,
The filler contains the recycled carbon black and optionally a carbon black other than the recycled carbon black, and consists solely of the recycled carbon black and any other carbon black than the recycled carbon black;
A side reinforcing rubber for run-flat tires, comprising the rubber composition, the filler content of which is more than 0 parts by mass and not more than 70 parts by mass per 100 parts by mass of the rubber component. The side reinforcement rubber according to claim 1 , wherein the recycled carbon black is obtained by pyrolysis of a vulcanized rubber product containing carbon black. The side reinforcement rubber according to claim 1 or 2, wherein the recycled carbon black has an ash content of 20% by mass or less. A run-flat tire comprising a carcass consisting of one or more carcass plies extending from a pair of bead portions through a sidewall portion to a tread portion, a pair of side reinforcing rubbers having a crescent cross section arranged on the inner side of the carcass in the tire width direction in the sidewall portion, and a bead filler arranged on the outer side of the bead core of the sidewall portion in the tire radial direction, the side reinforcing rubber being the side reinforcing rubber according to claim 1 or 2.

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