Rubber composition, tire, and run-flat tire

Abstract

This rubber composition is characterized by comprising a diene-based rubber component and a filler containing recycled carbon black, and is characterized in that: the diene-based rubber component includes a butadiene-based rubber; when the recycled carbon black is measured using a grind gauge, 3 or more lines having a length of 10 mm or more are observed; and, among particles forming the lines having a length of 10 mm or more, the particle size of particles having the third largest size is 20 µm or less.

Description

Rubber composition, tire, and run-flat tire

[0001] The present invention relates to a rubber composition, a tire, and a run-flat tire.

[0002] As a pneumatic tire, a run-flat tire having a side reinforcing rubber with a crescent cross-section in the sidewall portion and a bead filler disposed on the outer side in the tire diameter direction of the bead core is known. According to such a run-flat tire, for example, even when the tire is punctured and the internal pressure decreases, the side reinforcing rubber can substitute for the load, enabling travel for a considerable distance.

[0003] Also, regarding such side reinforcing rubber and bead filler, various studies have been made to improve various properties including run-flat durability. For example, Patent Document 1 discloses that a rubber composition prepared under predetermined conditions using a predetermined rubber component and carbon black can improve various properties of the side reinforcing rubber in a well-balanced manner.

[0004] On the other hand, recently, from the perspective of social sustainability, it is required to use so-called sustainable materials such as materials derived from biomass resources or recycled resources in businesses and products. For various members used in tires, an improvement in the usage rate of sustainable materials (hereinafter sometimes referred to as "sustainable rate" or "sustainable material ratio") is required. For example, as a material derived from recycled resources, recycled carbon black is known for carbon black.

[0005] Japanese Unexamined Patent Application Publication No. 2016-023207 <所定のゴム成分及びカーボンブラックを用い、ウェットマスターバッチを経る所定条件により作製されたゴム組成物が、サイド補強ゴムの各種特性をバランスよく改良することを開示している。

[0006] In order to improve the proportion of sustainable materials in rubber products, using conventional recycled carbon black instead of unused carbon black as a filler in rubber components such as side reinforcement rubber and bead filler may result in insufficient post-degradation high-temperature tear strength and post-degradation high-temperature tensile strength. Such post-degradation high-temperature tear strength and post-degradation high-temperature tensile strength are important functions required for run-flat tires.

[0007] Therefore, the object of the present invention is to provide a rubber composition that contributes to improved sustainability and exhibits excellent high-temperature tear strength and high-temperature tensile strength after degradation. Furthermore, the object of the present invention is to provide a tire and a run-flat tire using such a rubber composition that contribute to improved sustainability and exhibit excellent high-temperature tear strength and high-temperature tensile strength after degradation.

[0008] In other words, the gist of the present invention that solves the above problems is as follows.

[0009] [1] A rubber composition comprising a diene-based rubber component and a filler containing recycled carbon black, wherein the diene-based rubber component contains butadiene-based rubber, and the recycled carbon black is characterized in that, when measured with a grind gauge, three or more lines with a length of 10 mm or more are confirmed, and the particle size of the third largest particle among the particles that produce the lines with a length of 10 mm or more is 20 μm or less.

[0010] [2] The rubber composition according to [1], wherein, in the measurement of the recycled carbon black using a grind gauge, a paste of the recycled carbon black is prepared as a measurement sample in accordance with JIS K5101-1-5.

[0011] [3] The rubber composition according to [1] or [2], wherein, in the measurement of the recycled carbon black using a grind gauge, the applied load is set to 0.4 to 0.5 kN and the rotation speed of the glass plate is set to 90 to 110 r / min in accordance with JIS K5101-1-5, and the paste of the recycled carbon black is prepared.

[0012] [4] The rubber composition according to any one of [1] to [3], wherein the recycled carbon black comprises one or more selected from the group consisting of Zn, Fe, and Cu.

[0013] [5] The rubber composition according to [4], wherein the recycled carbon black comprises Zn.

[0014] [6] The rubber composition according to any one of [1] to [5], wherein the Zn content in the recycled carbon black is 0% by mass or more and 5% by mass or less.

[0015] [7] The rubber composition according to any one of [1] to [6], wherein the recycled carbon black has an ash content of 20% by mass or less.

[0016] [8] The rubber composition according to any one of [1] to [7], wherein the filler consists solely of carbon black.

[0017] [9] The rubber composition according to any one of [1] to [8], wherein the content of the filler is more than 0 parts by mass and 70 parts by mass or less per 100 parts by mass of the diene rubber component.

[0018]

[10] The rubber composition according to any one of [1] to [9], wherein the butadiene rubber comprises a modified butadiene rubber.

[0019]

[11] The rubber composition according to any one of [1] to

[10] , which is for use as a side reinforcement rubber for run-flat tires or as a bead filler for tires.

[0020] A tire characterized by using the rubber composition described in any of [1] to

[11] as a bead filler.

[0021]

[13] 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 crescent-shaped side reinforcing rubbers disposed on the inner side of the carcass in the tire width direction in the sidewall portion, and a bead filler disposed on the outer side of the bead core in the tire radial direction in the sidewall portion, wherein the side reinforcing rubber is made of the rubber composition described in any of [1] to

[10] .

[0022] According to the present invention, it is possible to provide a rubber composition that contributes to improved sustainability and exhibits excellent high-temperature tear strength and high-temperature tensile strength after degradation. Furthermore, according to the present invention, it is possible to provide a tire and a run-flat tire using such a rubber composition that contribute to improved sustainability and exhibit excellent high-temperature tear strength and high-temperature tensile strength after degradation.

[0023] This is an explanatory diagram illustrating an example of measurement results using a grind gauge. It shows a cross-section along the tire axis of one half of a run-flat tire according to one embodiment of the present invention.

[0024] Embodiments of the present invention will be described below. However, this description is for illustrative purposes only and does not limit the present invention in any way.

[0025] <Definitions> The compounds described herein may be derived in part or in whole from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, or recycled resources.

[0026] <Rubber Composition> A rubber composition according to one embodiment of the present invention (hereinafter sometimes referred to as "the rubber composition of this embodiment") contains at least a diene-based rubber component and a filler containing recycled carbon black. Furthermore, the rubber composition of this embodiment is characterized in that the diene-based rubber component contains butadiene-based rubber; and when measured with a grind gauge, the recycled carbon black shows three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles that produce such lines of 10 mm or more is 20 μm or less.

[0027] Thus, by using a filler containing at least recycled carbon black, the rubber composition of this embodiment can contribute to improved sustainability. Furthermore, the rubber composition of this embodiment uses recycled carbon black in which, when measured with a grind gauge, three or more lines with a length of 10 mm or more are confirmed, and the particle size of the third largest particle among the particles that produce such lines of 10 mm or more is 20 μm or less. By using such recycled carbon black, good dispersibility in the rubber composition is achieved, resulting in improved high-temperature tear strength and high-temperature tensile strength after degradation.

[0028] (Diene-based rubber component) The rubber composition of this embodiment contains a diene-based rubber component (hereinafter sometimes simply referred to as "rubber component"), which provides rubber elasticity to the composition. The sustainability rate of the rubber component is preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. Hereinafter, in this specification, "sustainability rate" refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources in the material in question.

[0029] In this specification, the term "biomass resources" refers to carbon-neutral organic resources of biological origin, excluding fossil resources (such as petroleum, coal, and natural gas). These biological resources may be edible or inedible, but are preferably inedible, as they do not compete with food resources and are considered to be resources that can be used effectively.

[0030] In this specification, the term "recycled resources" refers to resources obtained by recycling products that have been used, collected without being used, or discarded. For example, recycled resources include resources obtained by recycling used rubber products such as used tires.

[0031] The diene rubber component is preferably a diene rubber derived from biological resources and a diene rubber derived from recycled resources. Here, the proportion of the monomer component derived from biological resources in 100 mol% of the monomer component constituting the diene rubber derived from biological resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may also be 100 mol%. Furthermore, the proportion of the monomer component derived from recycled resources in 100 mol% of the monomer component constituting the diene rubber derived from recycled resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may also be 100 mol%.

[0032] The diene-based rubber component is a component that contributes to crosslinking, and typically has a weight-average molecular weight (Mw) of 10,000 or more, preferably 50,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, and also preferably 5,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. In this specification, the weight-average molecular weight (Mw) of the diene-based rubber component can be determined, for example, by converting it to standard polystyrene based on measurements obtained by gel permeation chromatography (GPC).

[0033] Furthermore, the diene-based rubber component in the rubber composition of this embodiment includes butadiene-based rubber. This effectively improves the durability of the rubber composition.

[0034] Examples of the butadiene-based rubber include butadiene rubber and styrene-butadiene rubber. In particular, in this embodiment, it is preferable that the butadiene-based rubber includes modified butadiene rubber. This effectively improves the durability of the rubber composition. From the viewpoint of contributing to improved sustainability, it is preferable that the butadiene used as a raw material for the butadiene-based rubber is derived from biological resources or recycled resources.

[0035] Examples of the butadiene rubber (BR) include butadiene rubber with a high cis content, butadiene rubber with a low cis content, and butadiene rubber containing syndiotactic polybutadiene crystals. Commercially available butadiene rubber can be used, and examples of such commercially available butadiene rubber include products from UBE Elastomer Co., Ltd., ENEOS Materials Corporation, Asahi Kasei Corporation, and Nippon Zeon Co., Ltd. These butadiene rubbers may be used individually or in combination of two or more types.

[0036] As described above, the butadiene-based rubber preferably contains modified butadiene rubber. In this case, the resulting side reinforcement rubber generates less heat, the rubber gauge can be made thinner, and rolling resistance can be improved without impairing run-flat driving durability. Furthermore, the proportion of the modified butadiene rubber in the rubber component is preferably 30% by mass or more, and more preferably 50% by mass or more, from the viewpoint of fully obtaining the above effects. The modified butadiene-based rubber may be used alone or in combination of two or more types.

[0037] The modified butadiene 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 is introduced into the molecule. Such a modified butadiene rubber can be obtained by modifying a diene rubber (butadiene rubber before modification) with a compound containing at least one of a tin atom, a nitrogen atom, and a silicon atom.

[0038] Examples of compounds containing the tin atom include tin tetrachloride, tributyltin chloride, dioctyltin dichloride, dibutyltin dichloride, and triphenyltin chloride. Examples of compounds containing the nitrogen atom include isocyanate compounds, aminobenzophenone compounds, urea derivatives, 4-dimethylaminobenzylideneaniline, dimethylimidazolidinone, and N-methylpyrrolidone. Examples of functional groups containing the silicon atom include silane groups, which are formed by bonding a hydrocarbyloxy group and / or a hydroxyl group to a silicon atom.

[0039] Of the modified butadiene rubbers, amine-modified butadiene rubbers are more preferred. Furthermore, of the modified butadiene rubbers, it is even more preferable that an amino group protected by a protic amino group and / or a detachable group, which is an amine-based functional group, is introduced into the molecule as a modifying functional group. Furthermore, of the modified butadiene rubbers, it is even more preferable that a functional group containing a silicon atom is introduced in addition to the above amino group.

[0040] Such modifying functional groups may be present at the polymerization initiation end, side chain, or polymerization active end of the butadiene rubber. The modified butadiene rubber preferably has at the polymerization end, more preferably at the same polymerization active end, an amino group protected by a protic amino group and / or a leaving group, and a silicon atom to which a hydrocarbyloxy group and / or a hydroxyl group is bonded, and particularly preferably a silicon atom to which one or two hydrocarbyloxy groups and / or hydroxyl groups are bonded.

[0041] The Mooney viscosity (ML1+4, 100°C) of the modified butadiene rubber is preferably 10 to 150, and more preferably 15 to 100. If the Mooney viscosity is 10 or higher, sufficient rubber properties, including fracture resistance, can be obtained, and if it is 150 or lower, good workability can be maintained. Furthermore, the Mooney viscosity (ML1+4, 130°C) of the rubber composition (unvulcanized rubber composition) containing the modified butadiene rubber is preferably 10 to 150, and more preferably 30 to 100. In addition, the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) (Mw / Mn), i.e., the molecular weight distribution (Mw / Mn), of the modified butadiene rubber is preferably 1 to 3, and more preferably 1.1 to 2.7. By setting the molecular weight distribution (Mw / Mn) of the modified butadiene rubber within the aforementioned range, the workability of the rubber composition is not reduced, mixing is easy, and the physical properties of the rubber composition can be sufficiently improved.

[0042] Further, the number average molecular weight (Mn) of the modified butadiene rubber is preferably from 100,000 to 1,000,000, and more preferably from 150,000 to 500,000. By setting the number average molecular weight of the modified butadiene rubber within the above range, it is possible to suppress a decrease in the elastic modulus of the vulcanizate and an increase in the hysteresis loss, thereby obtaining excellent fracture resistance characteristics, and also improving the kneading workability of the rubber composition.

[0043] Examples of the styrene-butadiene rubber include emulsion polymerization styrene-butadiene rubber, solution polymerization styrene-butadiene rubber, and the like.

[0044] The butadiene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0045] Further, the diene rubber component in the rubber composition of the present embodiment may contain other diene rubber components other than the butadiene-based rubber. Examples of such other diene rubber components include isoprene-based rubbers.

[0046] Examples of the isoprene-based rubber include natural rubber, synthetic isoprene rubber, and the like. The origin of the natural rubber is not particularly limited, and examples include those derived from Hevea brasiliensis, guayule, Russian dandelion, and the like. The natural rubber may be modified or denatured, and the synthetic isoprene rubber may also be denatured. These isoprene-based rubbers may be used alone or in combination of two or more. As the isoprene-based rubber, natural rubber is preferred.

[0047] The isoprene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0048] Furthermore, in order to keep the overall sustainability rate of the diene-based rubber component within the aforementioned range, it is preferable to use natural rubber as the rubber component, or to use polymers synthesized using monomer components derived from biological resources or recycled resources. In addition, mass balance certified synthetic rubber can also be used to keep the sustainability rate within the aforementioned range.

[0049] The ratio of each monomer unit (for example, units derived from isoprene, units derived from butadiene, and units derived from aromatic vinyl compounds) in the entire diene-based rubber component can be appropriately adjusted depending on the member to which it is applied. The ratio of each monomer unit in the entire diene-based rubber component can be adjusted, for example, by appropriately combining the isoprene-based rubber and butadiene-based rubber described above. The ratio of cis-bonded units in the butadiene-derived units can also be appropriately adjusted depending on the member to which it is applied. In this specification, "monomer unit" means a constituent unit of a polymer, "unit derived from isoprene" means a constituent unit in a polymer composed of isoprene, which is a monomer (including isoprene units in natural rubber), "unit derived from butadiene" means a constituent unit in a polymer composed of butadiene, which is a monomer, and "unit derived from aromatic vinyl compounds" means a constituent unit in a polymer composed of aromatic vinyl compounds, which are monomers. In this specification, the ratio of each monomer unit is measured by NMR.

[0050] The diene rubber component may include, in addition to the butadiene rubber and isoprene rubber mentioned above, other diene rubbers such as acrylonitrile-butadiene rubber, chloroprene rubber, butyl rubber, and styrene-isoprene-butadiene copolymer rubber. These diene rubber components may be used individually or in combination of two or more.

[0051] The diene-based rubber component may have functional groups that interact with fillers such as carbon black and silica introduced through modification. 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 also have substituents. These functional groups may be introduced into the diene-based rubber component individually or in combination of two or more. Among these, amino groups, alkoxy groups, and alkoxysilyl groups are preferred, and substituted amino groups in which the hydrogen atoms of the amino group are replaced by alkyl groups 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.

[0052] The functional group can be introduced, for example, by reacting a compound having the functional group (modifier) ​​with the rubber component. The compound having the functional group (modifier) ​​is a modifying functional group that interacts with fillers such as silica and carbon black, and can be a nitrogen-containing functional group, a silicon-containing functional group, or an oxygen-containing functional group. Examples of nitrogen-containing functional groups include amino group-containing compounds, examples of silicon-containing functional groups include silicon halides and hydrocarbyloxysilane compounds, and examples of oxygen-containing functional groups include alkoxy group-containing compounds, alkylene oxide group-containing compounds, and trialkylsilyloxy group-containing compounds. More specifically, examples include compounds described in WO2016 / 194316 and WO2019 / 117256. These modifiers may be used individually or in combination of two or more.

[0053] The aforementioned rubber derived from sustainable materials (materials derived from biological resources or materials derived from recycled resources) can be manufactured, for example, using monomer components derived from biological resources or monomer components derived from recycled resources, and, if necessary, monomer components derived from fossil resources, in the same manner as conventional methods for manufacturing synthetic rubber derived from fossil resources.

[0054] For example, the method described in Japanese Patent Publication No. 2022-179158 can be used to prepare rubber derived from biological resources.

[0055] As the butadiene obtained from the aforementioned 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 tigric acid) can be suitably used.

[0056] (Filler) The rubber composition of this embodiment contains a filler. The filler also contains recycled carbon black, and the recycled carbon black is required to produce at least three lines with a length of 10 mm or more when measured with a grind gauge, and the particle size of the third largest particle among the particles producing such lines of 10 mm or more is 20 μm or less. Recycled carbon black is also called recycled carbon black.

[0057] Other fillers besides recycled carbon black include other types of carbon black (virgin carbon black), silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, and the like. The rubber composition of this embodiment may further contain these other fillers. However, from the viewpoint of application as a side reinforcement rubber and / or bead filler for run-flat tires, it is preferable that the rubber composition of this embodiment consists only of carbon black (i.e., recycled carbon black and any virgin carbon black).

[0058] In the rubber composition of this embodiment, the filler content is preferably more than 0 parts by mass and 70 parts by mass or less per 100 parts by mass of the diene-based rubber component. If the filler content is 70 parts by mass or less, sufficient low heat generation and low elasticity effects can be achieved. From a similar viewpoint, the filler content per 100 parts by mass of the rubber component is more preferably 60 parts by mass or less, and even more preferably 55 parts by mass or less. Furthermore, from the viewpoint of maintaining good fracture strength and durability of the rubber, the filler content per 100 parts by mass is preferably 30 parts by mass or more, and more preferably 40 parts by mass or more.

[0059] Carbon black (recycled carbon black and carbon black other than recycled carbon black) can reinforce rubber compositions and improve their abrasion resistance. Examples of carbon black other than recycled carbon black include plant-derived carbon black. Examples of plant-derived carbon black include those derived from castor oil and pine resin oil.

[0060] From the viewpoint of further improving the wear resistance of the rubber composition and the tire to which it is applied, the carbon black content in the rubber composition of this embodiment is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the diene-based rubber component. Furthermore, from the viewpoint of the workability of the rubber composition, the carbon black content in the rubber composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of the diene-based rubber component.

[0061] -Recycled Carbon Black- In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials used for recycling. Examples of such waste materials include waste rubber, used tires, and waste oil. Waste rubber is not limited to that generated from rubber products, but refers to all discarded rubber, including unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is, for example, fine rubber generated in the buffing process that removes the tread portion remaining on the base tire during tire retreading. Peeling rubber is long pieces of rubber, for example, 1 to 2 cm wide, that are peeled off the surface of rubber products such as tires. Peeling rubber is generated by using a U-shaped or V-shaped knife like a peeler to scrape the surface of rubber products such as tires. Furthermore, waste rubber is not limited to cross-linked rubber, but also includes unvulcanized rubber. Rubber products include, for example, final products such as tires, rubber hoses, and rubber conveyor belts, as well as rubber parts or components used in the manufacturing process of these final products. Used tires may be retreaded, or they may be tires discarded for any reason, such as tires resulting from tire replacement or vehicle scrapping, or End-of-Life Tires (ELTs) that have reached the end of their lifespan. Waste oil is not limited to that generated when plastics and rubber are decomposed, but also includes used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that do not contain any composition other than organic matter, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils that contain carbon black or rubber containing carbon black are desirable. "Recycled carbon black" is different from carbon black that is directly manufactured using hydrocarbons such as petroleum, natural gas, and coal as raw materials, i.e., carbon black that is not recycled. Note that "used" here includes not only those that have been discarded after being actually used, but also those that were manufactured but discarded without actually being used.

[0062] Furthermore, it is preferable that the recycled carbon black is obtained by thermal decomposition of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by thermal decomposition of a vulcanized rubber product containing carbon black is readily available because a large amount of vulcanized rubber product containing carbon black exists and it can be easily obtained by thermal decomposition. Moreover, it is preferable that the recycled carbon black is obtained from the solid residue generated by the thermal decomposition of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is thermally decomposed, solid residue and volatile components (oil) are obtained, and recycled carbon black can be recovered from either. When recovering carbon black from volatile components, it is possible to recover oil with a specific gravity suitable for producing carbon black and use it to produce carbon black using an existing carbon black production method (for example, Japanese Patent Publication No. 2015-520259). In this case, unlike carbon black recovered from solid residue, there are advantages such as the absence of impurities and the absence of mixtures of different grades. Furthermore, in the production of environmentally friendly carbon black, there are various options besides the oil obtained by recovering volatile components from the thermal decomposition of rubber mentioned above, such as using vegetable oil or oil derived from waste plastics. However, edible resources such as vegetable oil present challenges in securing sufficient quantities due to other uses such as food, and the environmental impact associated with the expansion of cultivated land must also be considered. Similarly, oil derived from waste plastics is used for other purposes such as horizontal recycling of plastics, so supply issues are also a concern. On the other hand, when using volatile components (oil) produced by the thermal decomposition of vulcanized rubber products, particularly tires, the tire industry has a system for continuing to use existing materials, making it possible to continue using existing materials and reduce the consumption of new materials in new tire manufacturing, thereby contributing to reducing the environmental burden on the industry. The grade of carbon black is not particularly limited, but examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0063] The solid residue obtained by thermally decomposing waste materials such as used rubber and used tires contains ash in addition to carbon black. The ash originates from non-volatile components contained in rubber and tires. Therefore, the recycled carbon black obtained from this 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, a higher carbon content in recycled carbon black is preferable. In the recycled carbon black, the carbon content is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content in the recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed water.

[0064] The aforementioned ash content specifically includes 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 thermal decomposition of waste, a certain amount of ash remains even after various processes to remove it. In this embodiment, the presence of ash in recycled carbon black is permitted. In one embodiment, the lower limit of the ash content of the recycled carbon black may be 0.5% by mass.

[0065] Furthermore, the recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, states that it can be obtained by the pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

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

[0004] of Japanese Patent Publication No. 6856781 (Comparison of Surface Morphology and Chemistry of Pyrolysis Carbon Black and Commercial Carbon Black, Powder Technology 160 (2005) 190-193).

[0066] The recycled carbon black may lack functional groups on its surface, or it may have been treated to include functional groups on its surface. Treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3173251, carbon black obtained from a thermal decomposition process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl groups and / or carboxyl groups on its surface. In addition, in Japanese Patent Publication No. 6856781, carbon black obtained from a thermal decomposition 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 this embodiment also includes carbon black that has been treated to include functional groups on its surface.

[0067] Furthermore, for the thermal decomposition of cross-linked rubber products (vulcanized rubber products) such as used tires, one example is a thermal decomposition method at a temperature of 650°C or higher.

[0068] The cross-linked rubber products used in the aforementioned decomposition may be grouped by the type of rubber component they contain beforehand, and the decomposition process may be carried out for each group separately. Alternatively, they may be grouped by the type of filler they contain beforehand (for example, the type of carbon black, the type of silica, the mixing ratio of carbon black and silica, etc.), and the decomposition process may be carried out for each group separately. Furthermore, they may be grouped by both the type of rubber component and the type of filler, and the decomposition process may be carried out for each group separately. When the decomposition process is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when it is again incorporated into the rubber component, a rubber composition with better performance can be obtained.

[0069] Furthermore, if the cross-linked rubber product used in the decomposition is derived from a tire, it may be grouped in advance by tire type (for example, for passenger cars, trucks and buses, heavy vehicles such as off-road vehicles, aircraft, agricultural vehicles, etc.) and then the decomposition process may be carried out for each group. Alternatively, it may be grouped in advance by tire component (for example, tread rubber, sidewall rubber, bead rubber, steel cord coated rubber, organic fiber coated rubber, pad rubber, cushion rubber, etc.) and then the decomposition process may be carried out for each group. Moreover, it may be possible to group by both tire type and tire component and then carry out the decomposition process for each group. When the decomposition process is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when it is again blended into the rubber component, a rubber composition with better performance can be obtained.

[0070] Furthermore, the recycled carbon black used in this embodiment must, when measured with a grind gauge, show at least three lines with a length of 10 mm or more, and the particle size of the third largest particle among those particles that produce such lines of 10 mm or more must be 20 μm or less.

[0071] Methods for evaluating the dispersibility of carbon black using a grind gauge are described in JIS K5101-1-5 (particularly regarding paste preparation) and JIS K5400 (particularly regarding evaluation methods based on the manner in which linear traces are generated).

[0072] From the viewpoint of the durability of the rubber composition, the measurement using the grind gauge described above is important because it determines whether the particle size of the third largest particle in the recycled carbon black being measured is 20 μm or less. Therefore, the range of the grind gauge used is preferably 0 to 25 μm, from the viewpoint of accurately measuring particle sizes around 20 μm and from the viewpoint of ease of measurement. However, a grind gauge with an upper limit of the range greater than 20 μm can be used as it can determine whether the particle size of the third largest particle is 20 μm or less. Furthermore, when using grind gauge measurement for other purposes (evaluation of performance other than durability of rubber compositions containing recycled carbon black), the range of the grind gauge used can be appropriately selected according to the purpose.

[0073] As described above, JIS K5101-1-5 describes a method for preparing a paste of recycled carbon black as a measurement sample in grind gauge measurement. The paste of recycled carbon black can be prepared in accordance with JIS K5101-1-5 as a measurement sample for measurement using a grind gauge. By preparing the paste of recycled carbon black in accordance with JIS K5101-1-5, the accuracy of the evaluation of recycled carbon black (measurement using the grind gauge described above) can be further improved.

[0074] In one embodiment, the accuracy of grind gauge measurement can be further improved by appropriately adjusting the viscosity of the paste. In one embodiment, it is preferable to prepare a paste (measurement sample) containing recycled carbon black by blending recycled carbon black and zinc oxide with epoxidized soybean oil. Here, the blending ratio of the paste is not particularly limited, but it is preferable to use about 8 to 12 g of recycled carbon black and about 160 to 200 g of zinc oxide per 100 mL of epoxidized soybean oil.

[0075] Furthermore, in the measurement of recycled carbon black using a grind gauge, the paste of recycled carbon black can be prepared as a measurement sample by setting the applied load to 0.4 to 0.5 kN and the rotation speed of the glass plate to 90 to 110 r / min, in accordance with JIS K5101-1-5. In this case, the accuracy of the grind gauge measurement can be further improved.

[0076] When the recycled carbon black is measured with a grind gauge, three or more lines with a length of 10 mm or more can be observed. If the number of lines with a length of 10 mm or more is less than three, it is considered that the recycled carbon black being measured is too minute, and therefore cannot be sufficiently detected. In addition, while several lines caused by particles in the sample are observed when measuring with a grind gauge, in this embodiment, in accordance with JIS standards, lines with a length of 10 mm or more are not considered, and lines with a length of 10 mm or more are considered.

[0077] Furthermore, in this embodiment, in accordance with JIS standards, among the lines with a length of 10 mm or more, the line caused by the largest particle and the line caused by the second largest particle are judged to be abnormal values, and from the viewpoint of improving measurement accuracy, attention is paid to the line caused by the third largest particle and its particle size is confirmed. Here, the smaller the particle size of the third largest particle in the recycled carbon black, the better the dispersibility of the recycled carbon black in the rubber composition when the recycled carbon black is blended into the rubber composition, and the more likely it is that the durability of the rubber composition will improve. As described above, in the case of the recycled carbon black, if the particle size of the third largest particle among the particles that cause the line with a length of 10 mm or more is 20 μm or less, the dispersibility of the recycled carbon black in the rubber composition is improved, and the durability of the rubber composition can be effectively improved.

[0078] Figure 1 shows an explanatory diagram of an example of measurement results using a grind gauge. In the measurement using grind gauge 1, several lines attributable to particles in the measurement sample are observed. In this embodiment, in accordance with JIS standards, lines 2 with a length of less than 10 mm are not considered, and lines 3 with a length of 10 mm or more are considered. Furthermore, among the lines 3 with a length of 10 mm or more, line 31 attributable to the largest particle and line 32 attributable to the second largest particle are judged to be abnormal values, and in this embodiment, from the viewpoint of improving measurement accuracy, attention is focused on line 33 attributable to the third largest particle. The scale 4 at the location where line 33 attributable to the third largest particle appears is read, and this reading is taken as the particle size of the third largest particle. If the particle size of the third largest particle is 20 μm or less, the deterioration of the durability of the rubber composition, particularly its performance after degradation, can be suppressed even when recycled carbon black is added. In this specification, the measurement of recycled carbon black using a grind gauge is performed by the method described in the examples.

[0079] In this embodiment, recycled carbon black in which, when measured with a grind gauge, three or more lines with a length of 10 mm or more are observed, and the particle size of the third largest particle among the particles that produce such lines of 10 mm or more is 20 μm or less, can be manufactured by various methods. For example, recycled carbon black in which the particle size of the third largest particle is 20 μm or less can be manufactured by further grinding the recycled carbon black produced by a general method from recycled waste by a longer grinding process or by increasing the grinding intensity.

[0080] The recycled carbon black preferably contains one or more elements selected from the group consisting of Zn (zinc), Fe (iron), and Cu (copper). Such recycled carbon black can maintain the physical properties of the rubber composition while retaining components that may affect the deterioration of the rubber composition's properties, thus simplifying processing steps such as purification to completely remove components that may affect the deterioration of the rubber composition's properties.

[0081] Furthermore, the recycled carbon black may contain Zn (zinc). The Zn in the recycled carbon black originates from, for example, zinc oxide used as a vulcanization aid. If the Zn content in the recycled carbon black exceeds a certain amount, the physical properties of the rubber composition will deteriorate, but if it is below a certain amount, the deterioration of the physical properties of the rubber composition can be suppressed. However, the recycled carbon black may also not contain Zn.

[0082] If the recycled carbon black contains Zn, the Zn content in the recycled carbon black is preferably 0% by mass or more and 5% by mass or less. A lower Zn content in the carbon black is preferable, but if the Zn content is 5% by mass or less, the deterioration of the physical properties of the rubber composition can be suppressed. From the viewpoint of suppressing the deterioration of the physical properties of the rubber composition, the Zn content is more preferably 4.5% by mass or less, even more preferably 4% by mass or less, even more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less. The Zn content may also be 0.01% by mass or more, or 0.05% by mass or more. The above upper and lower limits can be combined as appropriate.

[0083] Methods to keep the Zn content in recycled carbon black within the above range include, for example, acid treatment and analyzing the amount of Zn contained in the raw rubber to be recycled in advance, and using some or all of the raw rubber with a low Zn content.

[0084] The recycled carbon black preferably has an ash content of 20% by mass or less, more preferably 19% by mass or less, and particularly preferably 18% by mass or less. When the ash content of the recycled carbon black is 20% by mass or less, the various physical properties of rubber products to which the rubber composition is applied can be improved. Herein, in this specification, the ash content of the recycled carbon black is determined according to ASTM D8474 / D1506.

[0085] The recycled carbon black has a nitrogen adsorption specific surface area of ​​40 to 100 m² obtained by the BET method. ２ It is preferable that the amount be / g, and 50 to 90 m ２ It is more preferable that the amount be / g, and 55 to 75 m ２ It is particularly preferable that the value be / g. Here, in this specification, the nitrogen adsorption specific surface area of ​​recycled carbon black by the BET method is the statistical thickness specific surface area (STSA), which is determined according to ASTM D6556.

[0086] The recycled carbon black preferably has a pH of 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. Herein, the pH of the recycled carbon black is determined according to ASTM D1512.

[0087] The recycled carbon black preferably has a toluene staining transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, in this specification, the toluene staining transmittance of recycled carbon black is determined according to ASTM D1618.

[0088] The recycled carbon black preferably has a heating loss of 3% by mass or less at 125°C, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less. Hereinafter, the heating loss of the recycled carbon black at 125°C is determined according to ASTM D1509.

[0089] The recycled carbon black preferably has a sulfur content of 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less.

[0090] The recycled carbon black preferably has a 35-mesh sieve residue of 20 ppm by mass or less, more preferably 15 ppm by mass or less, and particularly preferably 10 ppm by mass or less. Here, in this specification, the 35-mesh sieve residue of the recycled carbon black is determined according to ASTM D1514.

[0091] The recycled carbon black preferably has a 325-mesh (44 μm) sieve residue of 1,000 ppm by mass or less, more preferably 700 ppm by mass or less, and particularly preferably 300 ppm by mass or less. Here, in this specification, the 325-mesh (44 μm) sieve residue of the recycled carbon black is determined according to ASTM D1514.

[0092] The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Hereinafter, the pellet hardness of the recycled carbon black is determined according to ASTM D5230.

[0093] The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Hereinafter, the pellet fine powder content of the recycled carbon black is determined according to ASTM D1508.

[0094] The recycled carbon black preferably has a particle size (D97) of 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Hereinafter, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size analyzer, with the refractive index of water being 1.33 and the refractive index of the filler being 1.75.

[0095] The recycled carbon black preferably contains 50% or more by volume of particles 5 μm or smaller, more preferably 70% or more by volume, and particularly preferably 80% or more by volume.

[0096] The recycled carbon black preferably has an oil adsorption capacity (OAN) of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, in this specification, the OAN of the recycled carbon black is determined according to ASTM D2414.

[0097] The recycled carbon black preferably has a compressed oil adsorption capacity (COAN) of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Herein, in this specification, the COAN of the recycled carbon black is determined according to ASTM D3493.

[0098] The content of recycled carbon black in the rubber composition is preferably 1 to 100 parts by mass, more preferably 10 to 90 parts by mass, even more preferably 15 to 75 parts by mass, and particularly preferably 20 to 50 parts by mass, per 100 parts by mass of diene-based rubber component. When the content of recycled carbon black is 1 part by mass or more per 100 parts by mass of diene-based rubber component, it has a great effect in improving the ratio of sustainable materials in the rubber product to which the rubber composition is applied. When the content of recycled carbon black is 100 parts by mass or less per 100 parts by mass of diene-based rubber component, it is possible to improve the high-temperature tear strength and high-temperature tensile strength after degradation while improving the ratio of sustainable materials in the rubber product to which it is applied.

[0099] Furthermore, in the rubber composition of this embodiment, the proportion of recycled carbon black to the total of recycled carbon black and virgin carbon black (i.e., the total carbon black) is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of further improving sustainability. On the other hand, from the viewpoint of improving sustainability, the proportion of recycled carbon black to the total carbon black may be 100% by mass.

[0100] (Resin) The rubber composition of this embodiment may further contain a resin in addition to those described above. Examples of the resin include at least one resin selected from terpene resins, phenolic resins, coumarone-indene resins, xylene resins, rosin-based resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, polyurethane resins, acrylic resins, and the like. For the above resin, those described in Japanese Patent Application Publication No. 2022-132289 or WO2019116656 can be used.

[0101] The resin preferably has a softening point of 30°C or higher, more preferably 60°C or higher, more preferably 90°C or higher, more preferably higher than 110°C, and more preferably 120°C or higher. Furthermore, the resin preferably has a softening point of 160°C or lower, more preferably 150°C or lower, more preferably 145°C or lower, and more preferably 140°C or lower. The softening point of the resin is measured in accordance with JIS-K2207-1996 (ring-sphere method).

[0102] The content of the resin is not particularly limited, but is preferably in the range of 1 to 100 parts by mass, and more preferably in the range of 5 to 60 parts by mass, per 100 parts by mass of the diene rubber component.

[0103] (Other components) In addition to the components described above, the rubber composition of this embodiment may further contain various additives used in rubber products, especially tires, such as oils, liquid softeners such as liquid polymers, antioxidants, zinc oxide, sulfur, vulcanization accelerators, waxes, stearic acid, organic peroxides, cellulose nanofibers, cellulose particles, solid fine particles such as eggshells, rice husks, and walnut powder, and rubber powder obtained by crushing used rubber products.

[0104] (Method for producing the rubber composition) The method for preparing the rubber composition of this embodiment is not particularly limited, and known methods can be used. For example, it can be obtained by kneading a predetermined rubber component, carbon black, and other components using a kneader such as a Banbury mixer, roll mixer, or internal mixer. Alternatively, components other than the crosslinking accelerator and crosslinking agent may be mixed in a non-production (non-pro) stage, and the crosslinking accelerator and crosslinking agent may be added to the mixture and mixed in a production (pro) stage to prepare the rubber composition.

[0105] The rubber composition of this embodiment can be crosslinked or vulcanized. The conditions for crosslinking or vulcanizing the rubber composition can be adjusted as appropriate, for example, a temperature of 120 to 200°C and a heating time of 1 minute to 900 minutes.

[0106] (Applications) The rubber composition of this embodiment can be applied to various components of a tire, for example, the tread (cap tread, base tread, under tread), cushion rubber, shoulder, sidewall, bead filler, carcass coating rubber, belt coating rubber, insulation, chafer, inner liner, etc. It can also be used as side reinforcement rubber for run-flat tires. In addition to tires, the rubber composition of this embodiment can also be applied to hoses, rubber tracks, seismic isolation rubber, etc. Among these, the rubber composition of this embodiment is particularly suitable for side reinforcement rubber for run-flat tires or as bead filler for tires.

[0107] <Tire> A tire according to one embodiment of the present invention (hereinafter sometimes referred to as "the tire of this embodiment") is characterized by using the above-described rubber composition as a bead filler. Because the tire of this embodiment uses the above-described rubber composition, it contributes to improved sustainability and has excellent high-temperature tear strength and high-temperature tensile strength after degradation. The tire of this embodiment includes run-flat tires.

[0108] The tire of this embodiment can be manufactured by conventional methods using the rubber composition described above. For example, depending on the type of tire to be applied, the tire of this embodiment may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, or by molding a semi-vulcanized rubber that has undergone a pre-vulcanization process and then performing full vulcanization. The tire of this embodiment is preferably a pneumatic tire, and as the gas to fill the pneumatic tire, in addition to ordinary air or air with adjusted oxygen partial pressure, an inert gas such as nitrogen, argon, or helium can be used.

[0109] <Run-flat tires> Run-flat tires typically consist of a tread portion 101, a pair of sidewall portions 102 (only one side shown) extending radially inward from each side of the tread portion 101, and a pair of bead portions 103 (only one side shown) connected radially inward from each sidewall portion 102.

[0110] Furthermore, the run-flat tire shown in Figure 2 comprises a bead core 106 embedded in a pair of bead portions 103, a carcass 104 consisting of one or more carcass plies extending from the pair of bead portions 103 through the sidewall portion 102 to the tread portion 101, a bead filler 107 disposed on the radially outer side of the bead core 106, a belt 105 disposed on the radially outer side of the crown region of the carcass 104, and tread rubber 111 disposed on the radially outer side of the belt 105 to form the tread surface.

[0111] In the run-flat tire shown in Figure 2, the carcass 104 is connected to a main body portion 104a that extends in a toroidal shape from the bead portion 103 through the sidewall portion 102 to the tread portion 101, and the main body portion 104a is secured to the bead portion 103 by a folded portion 104b that is folded back around the bead core 106.

[0112] Furthermore, the run-flat tire in Figure 2 is provided with a pair of side reinforcing rubbers 109 (only one side is shown) disposed on the inside of the carcass 104 in the tire width direction in the sidewall portion 102. As shown in Figure 2, the side reinforcing rubber 109 has a crescent shape, with a cross-section shown along the tire axial direction, where the thickness gradually decreases toward the inside and outside in the tire radial direction, and is curved outward in a convex shape toward the outside in the tire axial direction. With the arrangement of such side reinforcing rubbers 109, even when the internal pressure of the tire decreases due to a puncture or the like, the side reinforcing rubbers 109 contribute to supporting the weight of the vehicle, making it possible to drive safely for a certain distance. In the run-flat tire of one embodiment of the present invention (hereinafter sometimes referred to as "the run-flat tire of this embodiment"), the rubber composition of this embodiment described above is used for the side reinforcing rubber 109. In this way, the run-flat tire obtained by using the rubber composition of this embodiment can contribute to improved sustainability.

[0113] Furthermore, as shown in Figure 2, the run-flat tire of this embodiment may include an inner liner 108 made of a rubber material or the like that has excellent air impermeability, which is arranged along the inner surface of the carcass 104.

[0114] Furthermore, the belt 105 located on the radially outer side of the carcass 104 can be configured, for example, as shown in Figure 2, by providing a belt layer 150 and arranging a belt reinforcement layer 151 consisting of cords extending substantially in the circumferential direction of the tire on the radially outer side of the belt layer 150. The belt layer 150 can be a layer in which an inner belt layer, consisting of cords made of organic fibers or the like, extends in a direction inclined with respect to the circumferential direction of the tire, and an outer belt layer, consisting of cords extending in a direction intersecting the cords of the inner belt layer, are sequentially arranged toward the radially outer side of the tire. However, the configuration, arrangement area, and number of layers of the belt layers can be changed as needed.

[0115] The run-flat tire of this embodiment can be manufactured by conventional methods by applying the above-mentioned rubber composition to the side reinforcement rubber. For example, depending on the type of tire to be applied, the tire of this embodiment may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, or by molding a semi-vulcanized rubber that has undergone a pre-vulcanization process, and then further vulcanizing it. The run-flat tire of this embodiment is preferably a pneumatic tire, and as the gas to fill the pneumatic tire, in addition to ordinary air or air with adjusted oxygen partial pressure, an inert gas such as nitrogen, argon, or helium can be used.

[0116] The present invention will be described in more detail below with reference to examples, but these examples are for illustrative purposes only and do not limit the present invention in any way.

[0117] <Evaluation 1> Recycled carbon black 1 and recycled carbon black 2 were prepared as test carbon blacks.

[0118] Next, 3.75 g of zinc oxide, 0.20 g of the carbon black under test, and 2.00 mL of epoxidized soybeans were mixed to obtain a mixture. The obtained mixture was kneaded for 5 to 10 minutes to form a paste, and sample pastes were prepared. In accordance with JIS K5101-1-5, pastes were prepared using a Toyo Seiki Co., Ltd. Huber Mahler (model: H3) under conditions of a load of 0.4536 kN and a glass plate rotation speed of 100 r / min. In accordance with JIS K5400, each sample paste was placed on a grind gauge and stretched with a scraper. A grind gauge with a range of 0 to 25 μm was used. It was confirmed that three or more continuous lines of 10 mm or more appeared, and the scale reading at the location where the line caused by the third largest particle among the particles that produced the continuous lines of 10 mm or more appeared was read, and this reading was taken as the particle size of the third largest particle. The same procedure was performed a total of four times, and the average particle size of the third largest particle from the four measurements was calculated. The results are shown in Table 1.

[0119] Furthermore, regarding the carbon black used in the test, the nitrogen adsorption specific surface area (N) was calculated according to ASTM D6556. ２ SA was measured. The results are shown in Table 1.

[0120] Furthermore, the Zn, Fe, and Cu content of the tested carbon black was measured by X-ray fluorescence analysis (XRF). The results are shown in Table 1.

[0121] Furthermore, the ash content of the tested carbon black was measured according to ASTM D8474 and D1506. The results are shown in Table 1.

[0122]

[0123] (Preparation of Rubber Compositions) Using the above-mentioned carbon black, rubber compositions were prepared according to the formulations shown in Table 2. Other chemicals included antioxidants, oils, fatty acids, sulfur, and vulcanization accelerators, and the same types and amounts were added in the reference comparative example and reference example. Commercially available chemicals commonly used in the preparation of rubber compositions were used. The amounts added were also the amounts commonly used in the preparation of rubber compositions. For each rubber composition prepared, the sustainable material ratio was evaluated by calculating the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources. The results are shown in Table 2.

[0124] (1) High-temperature tear strength after degradation For each example of rubber composition, the rubber composition to be tested was degraded in a nitrogen atmosphere at 100°C for 24 hours beforehand. Strip-shaped test pieces were prepared from the rubber composition with a 0.5 mm hole drilled in the lengthwise direction in the center. A DC / DC test (using Shimadzu Corporation's "ServoPulsa") was performed on the test pieces, and repeated fatigue was applied at a frequency of 5 Hz and 80°C with a strain of 30-100%, and the tear energy [J / m] at 1950 cycles was measured. ２ The crack propagation rate was calculated when the common logarithm of [ ] was 3.9. The calculated value for Example 1 was set to 100, and the reciprocal of the calculated value for Comparative Example 1 was indexed to evaluate the high-temperature tear strength after degradation. The results are shown in Table 2. A larger index value indicates a lower crack propagation rate and superior high-temperature tear strength after degradation.

[0125] (2) High-temperature tensile strength after degradation Furthermore, for each example of rubber composition, the rubber composition to be tested was degraded in advance at 100°C under a nitrogen atmosphere for 48 hours. Tensile tests were performed at 100°C in accordance with JIS K6251:2017, and the tensile strength was measured. The tensile strength of the test piece in Example 1 was set to 100, and the high-temperature tensile strength (fracture resistance) after degradation was expressed as an index using the following formula. The results are shown in Table 2. High-temperature tensile strength index after degradation = (Tensile strength of the test piece / Tensile strength of the test piece in Reference Example 1) × 100 The larger the index of high-temperature tensile strength after degradation, the more difficult the vulcanized rubber is to break, indicating superior post-degradation performance (fracture resistance).

[0126]

[0127] *1 Natural rubber: RSS#3 *2 Butadiene rubber: UBE Elastomers, "BR150L" *3 Virgin carbon black: Asahi Carbon, N550

[0128] Table 2 shows that the rubber composition of Example 1 contributes to a certain degree of improved sustainability, and that it exhibits better high-temperature tear strength and high-temperature tensile strength after degradation compared to the rubber composition of Comparative Example 1.

[0129] <Evaluation 2> (Tire Manufacturing) Two types of rubber compositions having the compound compositions shown in Table 3 are prepared, and these rubber compositions are placed on the side reinforcement rubber 109 shown in Figure 2, and a passenger car radial tire (run-flat tire) of tire size 215 / 45ZR17 is manufactured according to a standard method. The sustainable material ratio of the side reinforcement rubber in the manufactured tire is evaluated by calculating the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources. The results are shown in Table 3.

[0130]

[0131] *4 Modified butadiene rubber: Primary amine-modified polybutadiene *5 Process oil: Aromatic oil, "Aromax #3" manufactured by Fuji Kogyo Co., Ltd. *6 Anti-aging agent: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, "Nocrack 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *7 Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiadylsulfenamide, "Noxellar CZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *8 Vulcanization accelerator TOT: Tetrakis(2-ethylhexyl)thiuram disulfide, "Noxellar TOT-N" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0132] Table 3 shows that the side reinforcing rubber of Example 2 has a higher proportion of sustainable materials compared to the side reinforcing rubber of Comparative Example 2, and can contribute to improved sustainability.

[0133] <Evaluation 3> Using a standard Banbury mixer, rubber compositions were prepared by kneading with the formulations shown in Table 4. Each of the resulting rubber compositions was evaluated using the following evaluation method.

[0134] Furthermore, the Zn content of the carbon black used was measured by X-ray fluorescence analysis. The results are shown in Table 4.

[0135] Furthermore, the ash content of the carbon black used was measured by thermogravimetric analysis (TGA, RIGAKU Corporation) using the following procedure. The sample was heated from room temperature to 550°C under a nitrogen atmosphere, and then heated to maintain 550°C under an air atmosphere, and the loss on heating was measured. The loss on heating (mass%) when the sample was heated from room temperature to 550°C under a nitrogen atmosphere was defined as "Loss on heating 1," and the loss on heating (mass%) when heated to maintain 550°C under an air atmosphere was defined as "Loss on heating 2." The ash content was calculated using the following formula. The results are shown in Table 4. Ash content (mass%) = 100 - Loss on heating 1 - Loss on heating 2

[0136] (1) Tensile Strength Each example of rubber composition was vulcanized at 145°C for 33 minutes to obtain vulcanized rubber. Tensile tests were performed on each vulcanized rubber at room temperature in accordance with JIS K6301-1995 to measure its tensile strength. The evaluation results were expressed as an index using the following formula, with Reference Example 1 as the control (index value 100). The results are shown in Table 4. Tensile Strength Index = (Tensile strength of test specimens other than Reference Example 1 / Tensile strength of test specimen of Reference Example 1) × 100 A larger index indicates that the rubber composition is less prone to fracture and has superior tensile strength.

[0137] (2) Viscoelasticity Tests were conducted on each rubber composition using TA Instruments' "ARES-G2" under the conditions of a frequency of 15 Hz, a shear strain of 10%, and a temperature of 50°C to measure the storage modulus (G') of the rubber composition. The evaluation results were indexed with Reference Example 1 as the control (index value 100). The results are shown in Table 4. A higher index indicates a higher G', which in turn indicates superior rubber properties when applied to products such as tires.

[0138]

[0139] *12 SBR: Styrene-butadiene rubber, product name "#1500" *13 CB1: Carbon Black 1, recycled carbon black equivalent to N330 *14 CB2: Carbon Black 2, recycled carbon black equivalent to N330 *15 CB3: Carbon Black 3, recycled carbon black equivalent to N330 *16 CB4: Carbon Black 4, new carbon black equivalent to N330

[0140] Table 4 shows that when carbon black with reduced Zn content and ash content is applied, the deterioration of the physical properties of the rubber composition is suppressed.

[0141] <Evaluation 4> Two types of rubber compositions having the compound compositions shown in Table 5 were prepared, and these rubber compositions were vulcanized at 145°C for 33 minutes to obtain vulcanized rubber test pieces. The obtained vulcanized rubber test pieces were punched out into JIS-3 dumbbells, and the resulting samples were subjected to tensile tests at room temperature in accordance with JIS K 6251:2004, and the breaking strength (TB) before thermal degradation (initial) and after thermal degradation (100°C × 24 hours) was measured. The results are shown in Table 5. A higher value indicates better fracture resistance, i.e., better crack resistance.

[0142]

[0143] *17 Recycled carbon black: Enrestec, product name "PB365", ash content 17% by mass, OAN = 121 mL / 100 g *18 Anti-aging agent: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 6C", Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 224", same ratio in each rubber composition *19 Oil: ENEOS, product name "A / Omix" *20 Fatty acid: Miyoshi Oil & Fat Co., Ltd., product name "MXST" *21 Other chemicals: sulfur, vulcanization accelerator, resin, wax, same ratio in each rubber composition

[0144] Table 5 shows that replacing carbon black (virgin carbon black) with commercially available recycled carbon black among the various materials contained in the rubber composition reduces the tensile strength (TB) before and after thermal degradation, i.e., the crack propagation resistance.

[0145] Based on the evaluations in Tables 1 to 5, it can be expected that the rubber composition of the present invention will suppress the deterioration of its physical properties even when recycled carbon black is applied, and will also exhibit excellent high-temperature tear strength and high-temperature tensile strength after degradation, as well as contributing to improved sustainability.

[0146] According to the present invention, it is possible to provide a rubber composition that contributes to improved sustainability and exhibits excellent high-temperature tear strength and high-temperature tensile strength after degradation. Furthermore, according to the present invention, it is possible to provide a tire and a run-flat tire using such a rubber composition that contribute to improved sustainability and exhibit excellent high-temperature tear strength and high-temperature tensile strength after degradation.

[0147] 1 Grind gauge 2 Lines less than 10 mm in length 3 Lines 10 mm or longer 31 Line caused by the largest particle 32 Line caused by the second largest particle 33 Line caused by the third largest particle 4 Scale marking the location where the line caused by the third largest particle appears 101 Tread section 102 Sidewall section 103 Bead section 104 Carcass 104a Main body of the carcass 104b Folded section of the carcass 105 Belt 106 Bead core 107 Bead filler 108 Inner liner 109 Side reinforcement rubber 111 Tread rubber 150 Belt layer 151 Belt reinforcement layer

Claims

1. A rubber composition comprising a diene-based rubber component and a filler containing recycled carbon black, wherein the diene-based rubber component contains butadiene-based rubber, and the recycled carbon black is characterized in that, when measured with a grind gauge, three or more lines with a length of 10 mm or more are confirmed, and the particle size of the third largest particle among the particles that produce the lines with a length of 10 mm or more is 20 μm or less.

2. The rubber composition according to claim 1, wherein, in the measurement of the recycled carbon black using a grind gauge, a paste of the recycled carbon black is prepared as the measurement sample in accordance with JIS K5101-1-5.

3. The rubber composition according to claim 1, wherein, in the measurement of the recycled carbon black using a grind gauge, the applied load is set to 0.4 to 0.5 kN and the rotation speed of the glass plate is set to 90 to 110 r / min in accordance with JIS K5101-1-5, and the paste of the recycled carbon black is prepared as the measurement sample.

4. The rubber composition according to claim 1, wherein the recycled carbon black comprises one or more selected from the group consisting of Zn, Fe, and Cu.

5. The rubber composition according to claim 4, wherein the recycled carbon black contains Zn.

6. The rubber composition according to claim 3, wherein the Zn content in the recycled carbon black is 0% by mass or more and 5% by mass or less.

7. The rubber composition according to claim 1, wherein the recycled carbon black has an ash content of 20% by mass or less.

8. The rubber composition according to claim 1, wherein the filler consists solely of carbon black.

9. The rubber composition according to claim 1, wherein the content of the filler is more than 0 parts by mass and 70 parts by mass or less per 100 parts by mass of the diene-based rubber component.

10. The rubber composition according to claim 1, wherein the butadiene rubber comprises modified butadiene rubber.

11. The rubber composition according to claim 1, which is for use as a side reinforcement rubber for run-flat tires or as a bead filler for tires.

12. A tire characterized by using the rubber composition described in claim 1 as a bead filler.

13. 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 crescent-shaped side reinforcing rubbers disposed on the inner side of the carcass in the tire width direction within the sidewall portion; and a bead filler disposed on the outer side of the bead core in the tire radial direction within the sidewall portion, wherein the rubber composition described in claim 1 is used for the side reinforcing rubber.

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