Rubber composition for sidewall rubber, and tire

Abstract

The present invention addresses the problem of providing a rubber composition for sidewall rubber, the rubber composition giving a tire having an improved sustainable-material proportion while retaining high-temperature crack propagation resistance after thermal deterioration and elongation at break after thermal deterioration. The rubber composition for sidewall rubber comprises a rubber component (A) and recycled carbon black (B), and is characterized in that the recycled carbon black (B), when examined with a grind gauge (1), shows three or more lines (3) each having a length of 10 mm or longer and the third largest particle among the particles which have caused the lines (3) each having a length of 10 mm or longer has a particle size of 20 μm or less.

Description

Rubber composition for side rubber and tire

[0001] This invention relates to a rubber composition for sidewalls and to tires.

[0002] Conventionally, various rubber compositions have been used for the side rubber installed in the sidewall portion of tires. Furthermore, in order to ensure the strength of the tire sidewall portion, carbon black is usually added as a reinforcing filler to the rubber composition that serves as its raw material.

[0003] On the other hand, in recent years, from the perspective of social sustainability, there has been a demand for the use of so-called sustainable materials, such as materials derived from biological resources (biomass resources) and recycled resources, for various components used in tires, and there is a demand for an increase in the proportion of sustainable materials in the rubber composition applied to such tires. For example, recycled carbon black is known as a material derived from recycled resources (see Patent Document 1 below).

[0004] European Patent Application Publication No. 3427975

[0005] However, when the inventors considered using recycled carbon black as a reinforcing filler instead of unused carbon black to improve the proportion of sustainable materials in tires, they found that the high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation of the rubber composition decreased, and the durability of rubber components to which this rubber composition was applied decreased after thermal degradation. In particular, the side rubber applied to the sidewall of a tire becomes hot during driving and requires high durability even after thermal degradation.

[0006] Therefore, the object of the present invention is to provide a rubber composition for side rubbers that can improve the proportion of sustainable materials in tires while maintaining high-temperature crack propagation resistance and elongation at break after thermal degradation. Furthermore, the object of the present invention is to provide a tire with an improved proportion of sustainable materials while maintaining durability after thermal degradation.

[0007] The rubber composition for side rubber and the gist of the tire of the present invention, which solves the above problems, are as follows.

[0008] [1] A rubber composition for side rubber comprising a rubber component (A) and recycled carbon black (B), wherein the recycled carbon black (B) is characterized in that, when measured with a grind gauge, there are 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 give rise to the lines with a length of 10 mm or more is 20 μm or less.

[0009] [2] The rubber composition for side rubber according to [1], wherein, in the measurement using the grind gauge, a paste of recycled carbon black (B) is prepared as the measurement sample in accordance with JIS K5101-1-5.

[0010] [3] The rubber composition for side rubber according to [1] or [2], wherein, in the measurement using the 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 as the measurement sample, and the paste of recycled carbon black (B) is prepared.

[0011] [4] A rubber composition for side rubber according to any one of [1] to [3], further comprising a quinoline-based antioxidant (C).

[0012] [5] A rubber composition for side rubber according to any one of [1] to [4], further comprising zinc oxide (D).

[0013] [6] The rubber composition for side rubber according to any one of [1] to [5], wherein the recycled carbon black (B) comprises one or more metal atoms selected from the group consisting of Zn, Cu, and Fe.

[0014] [7] A rubber composition for side rubber according to any one of [1] to [6], wherein the recycled carbon black (B) contains Zn.

[0015] [8] The rubber composition for side rubber according to any one of [1] to [7], wherein the recycled carbon black (B) has a Zn content of 0% by mass or more and 5.0% by mass or less.

[0016] [9] The rubber composition for side rubber according to any one of [1] to [8], wherein the recycled carbon black (B) has an ash content of 20.0% by mass or less.

[0017]

[10] A rubber composition for side rubber according to any one of [1] to [3] and [6] to [9], further comprising a quinoline-based antioxidant (C) and zinc oxide (D), wherein the mass ratio of zinc oxide (D) to the quinoline-based antioxidant (C) [zinc oxide (D) / quinoline-based antioxidant (C)] is greater than 0 and 3.0 or less.

[0018]

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

[10] , wherein the total amount of styrene in the rubber component (A) is 5% by mass or less.

[0019]

[12] A rubber composition for side rubber according to any one of [1] to

[11] , wherein the rubber component (A) contains natural rubber.

[0020]

[13] The rubber composition for side rubber according to

[12] , wherein the rubber component (A) further comprises butadiene rubber.

[0021]

[14] The rubber composition for side rubber according to [5] or

[10] , wherein the content of zinc oxide (D) is 4 parts by mass or less per 100 parts by mass of the rubber component (A).

[0022]

[15] A rubber composition for side rubber according to any one of [1] to

[14] , further comprising an antioxidant (E) other than a quinoline-based antioxidant.

[0023]

[16] The rubber composition for side rubber according to

[15] , wherein the antioxidant (E) other than the quinoline-based antioxidant is a phenylenediamine-based antioxidant.

[0024]

[17] A tire characterized by having a side rubber made of a rubber composition for side rubber described in any one of [1] to

[16] .

[0025] According to the present invention, it is possible to provide a rubber composition for side rubber that can improve the ratio of sustainable materials in a tire while maintaining the high-temperature crack growth resistance after thermal degradation and the elongation at break after thermal degradation. Further, according to the present invention, it is possible to provide a tire in which the ratio of sustainable materials is improved while maintaining the durability after thermal degradation.

[0026] It is an explanatory view of an example of the measurement result by a grind gauge. It is a cross-sectional view of one embodiment of the tire of the present invention.

[0027] Hereinafter, the rubber composition for side rubber and the tire of the present invention will be specifically illustrated and described based on their embodiments.

[0028] <Definition> The compounds described in this specification may be partially or entirely derived from fossil resources, may be derived from biological resources such as plant resources, or may be derived from recycled resources such as used tires. Further, it may be derived from a mixture of any two or more of fossil resources, biological resources, and recycled resources.

[0029] In this specification, the "ratio of sustainable materials" is the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources (recycled resources) in the target rubber composition for side rubber and tire.

[0030] In this specification, the biological resources (biomass resources) refer to carbon-neutral organic resources derived from organisms and are resources excluding fossil resources (such as petroleum, coal, and natural gas). The biological resources may be edible or inedible, but it is preferable that they do not compete with food and are inedible from the viewpoint of effective utilization of resources.

[0031] In this specification, the recycled resources (recycled resources) refer to resources obtained by recycling products that have been used once, collected without being used, or discarded. For example, recycled resources include resources obtained by recycling used rubber products such as used tires.

[0032] <Rubber Composition for Side Rubbers> The rubber composition for side rubbers of this embodiment comprises a rubber component (A) and recycled carbon black (B). In the rubber composition for side rubbers of this embodiment, the recycled carbon black (B) is characterized in that, when measured with a grind gauge, there are 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 give rise to the lines with a length of 10 mm or more is 20 μm or less.

[0033] In the rubber composition for side rubber of this embodiment, recycled carbon black (B) is a material derived from recycled resources, thus improving the proportion of sustainable materials in the rubber composition for side rubber of this embodiment. Therefore, by applying the side rubber made from the rubber composition for side rubber of this embodiment to a tire, it is possible to improve the proportion of sustainable materials in the tire. However, when general recycled carbon black is blended into a rubber composition, the high-temperature crack propagation resistance and elongation at break after thermal degradation of the rubber composition deteriorate. In contrast, in the rubber composition for side rubber of this embodiment, by blending recycled carbon black (B) that, when measured with a grind gauge, has 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 give rise to the lines with a length of 10 mm or more is 20 μm or less, it is possible to maintain the high-temperature crack propagation resistance and elongation at break after thermal degradation of the rubber composition. Therefore, according to the rubber composition for side rubber of this embodiment, it is possible to improve the proportion of sustainable materials in the tire while maintaining the high-temperature crack propagation resistance and elongation at break after thermal degradation.

[0034] "Rubber component (A)" The rubber composition for side rubber of the present embodiment contains a rubber component (A), and the rubber component (A) imparts rubber elasticity to the composition. It is preferable that the sustainable rate of the rubber component (A) is 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, further more preferably 60% by mass or more, still further 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. Here, the "sustainable rate" of the rubber component (A) is the total mass ratio of the components derived from biomass resources (biological resources) and the components derived from recycled resources (recycled resources) in the rubber component (A).

[0035] As the rubber component (A), the rubber derived from the biomass resource and the rubber derived from the recycled resource are preferable. Here, the ratio of the monomer component derived from the biomass resource in 100 mol% of the monomer components constituting the rubber derived from the biomass resource is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%. Also, the ratio of the monomer component derived from the recycled resource in 100 mol% of the monomer components constituting the rubber derived from the recycled resource is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%.

[0036] The rubber component (A) is a component that contributes to crosslinking. Usually, the weight average molecular weight (Mw) is 10,000 or more, preferably 50,000 or more, more preferably 150,000 or more, still more preferably 200,000 or more, and preferably 5,000,000 or less, more preferably 2,000,000 or less, still more preferably 1,500,000 or less. In this specification, the weight average molecular weight (Mw) of the rubber component (A) can be determined by standard polystyrene conversion based on the measurement value by gel permeation chromatography (GPC), for example.

[0037] In the rubber composition for side rubber of this embodiment, the total amount of styrene in the rubber component (A) is preferably 5% by mass or less, more preferably 3.0% by mass or less, and may be 0% by mass. When the total amount of styrene in the rubber component (A) is 5% by mass or less, the physical properties of the rubber composition are improved, and the high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation can be improved. Furthermore, when the total amount of styrene in the rubber component (A) is 3.0% by mass or less, the high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation of the rubber composition can be further improved. In this specification, the total amount of styrene in the rubber component (A) is the total content of the styrene portion contained in the total amount of rubber component (A) (unit: mass%), and can be calculated as Σ (content of each rubber component × amount of styrene in each rubber component / 100).

[0038] The rubber component (A) is preferably a diene-based rubber, and isoprene-based rubber and butadiene-based rubber are preferred as the diene-based rubber.

[0039] Examples of the isoprene-based rubber include natural rubber (NR) and synthetic isoprene rubber (IR). The origin of the natural rubber is not particularly limited, and examples include that derived from the Para rubber tree, guayule, or Russian dandelion. The natural rubber may be modified or altered, and the synthetic isoprene rubber may also be altered. These isoprene-based rubbers may be used individually or in combination of two or more types. Natural rubber is preferred as the isoprene-based rubber.

[0040] Examples of the aforementioned butadiene-based rubber include butadiene rubber (BR) and styrene-butadiene rubber (SBR). Here, it is preferable that the butadiene used as a raw material for the butadiene-based rubber is derived from biological resources or recycled resources.

[0041] Examples of the styrene-butadiene rubber include emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR).

[0042] The isoprene-based rubber and the butadiene-based rubber preferably have 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.

[0043] Furthermore, in order to keep the overall sustainability rate of the rubber component (A) within the aforementioned range, it is preferable to use natural rubber (NR) as the rubber component (A), or to use a polymer synthesized using monomer components derived from biological resources or recycled resources as monomer components. It is also possible to use mass balance certified synthetic rubber to keep the sustainability rate within the aforementioned range.

[0044] The rubber component (A) preferably contains natural rubber (NR). By including natural rubber in the rubber component (A), it is possible to further improve the proportion of sustainable materials and increase the fracture strength of the rubber composition. As a result, the proportion of sustainable materials and the durability of the tire using the rubber composition can be further improved.

[0045] The rubber component (A) preferably contains butadiene rubber (BR). Butadiene rubber can improve physical properties of the rubber composition, such as elongation at break (EB). Furthermore, it is particularly preferable that the rubber component (A) further contains butadiene rubber (BR) in addition to natural rubber (NR). By using natural rubber and butadiene rubber in combination as rubber component (A), the high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation of the rubber composition can be further improved.

[0046] 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 rubber component (A) can be adjusted as appropriate. The ratio of each monomer unit in the entire rubber component (A) 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 units derived from butadiene can also be adjusted as appropriate. In this specification, "monomer unit" means a constituent unit of a polymer, "unit derived from isoprene" means a constituent unit in a polymer composed based on the monomer isoprene (including isoprene units in natural rubber), "unit derived from butadiene" means a constituent unit in a polymer composed based on the monomer butadiene, and "unit derived from aromatic vinyl compounds" means a constituent unit in a polymer composed based on the monomer aromatic vinyl compound. In this specification, the ratio of each monomer unit is measured by NMR.

[0047] The rubber component (A) may include, in addition to the isoprene-based rubber, butadiene rubber (BR), and styrene-butadiene rubber (SBR) mentioned above, diene-based rubbers such as acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). These rubber components may be used individually or in combination of two or more.

[0048] The rubber component (A) may have functional groups that interact with fillers such as carbon black and silica introduced into it 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 rubber component (A) 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.

[0049] The functional group can be introduced, for example, by reacting a compound having the functional group (modifier) ​​with the rubber component (A). The functional group is a modifying functional group that interacts with fillers such as silica and carbon black, and examples include nitrogen-containing functional groups, silicon-containing functional groups, and oxygen-containing functional groups. Examples of compounds having nitrogen-containing functional groups (modifiers) include amino group-containing compounds, examples of compounds having silicon-containing functional groups (modifiers) include silicon halides and hydrocarbyloxysilane compounds, and examples of compounds having oxygen-containing functional groups (modifiers) include alkoxy group-containing compounds, alkylene oxide group-containing compounds, and trialkylsilyloxy group-containing compounds. More specifically, examples include compounds described in International Publication No. 2016 / 194316 and International Publication No. 2019 / 117256. These modifiers may be used individually or in combination of two or more.

[0050] 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.

[0051] For example, the method described in Japanese Patent Publication No. 2022-179158 can be used to prepare rubber derived from the above-mentioned biological resources.

[0052] 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.

[0053] "Recycled Carbon Black (B)" The rubber composition for the side rubber of this embodiment contains recycled carbon black (B). Since recycled carbon black (B) is a material derived from recycled resources, the inclusion of recycled carbon black (B) improves the proportion of sustainable materials in the rubber composition for the side rubber. By applying this rubber composition to a tire, the proportion of sustainable materials in the tire can be improved, thereby reducing the environmental impact.

[0054] In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials submitted for recycling. Examples of such waste materials include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only rubber generated from rubber products but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is fine rubber generated, for example, in the buffing process of retreading tires, where the tread portion remaining on the base tire is scraped off. Peeling rubber is long pieces of rubber, for example, 1 to 2 cm wide, that are peeled off from the surface of rubber products such as tires. Peeling rubber is generated by scraping the surface of rubber products such as tires using a U-shaped or V-shaped knife like a peeler. Furthermore, waste rubber includes not only cross-linked rubber but also unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, and rubber parts or components at the manufacturing stage of final products. Used tires may include, for example, those that have been retreaded, as well as tires that have been discarded for any reason, such as those resulting from tire replacement or vehicle scrapping, and 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 oil that does not contain any composition other than organic matter, such as those derived from silicone rubber or polyvinyl chloride, is desirable. Furthermore, waste oil that is mixed with carbon black or rubber containing carbon black is 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.

[0055] Furthermore, it is preferable that the recycled carbon black (B) 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 (B) is obtained from the solid residue generated by the thermal decomposition of the above-mentioned 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.

[0056] 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 (B), 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 (B) is preferably 97% by mass or less. Note that the carbon content does not include adsorbed water.

[0057] 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 inclusion of ash in recycled carbon black (B) is permitted. In one embodiment, the lower limit of the ash content of the recycled carbon black (B) may be 0.5% by mass.

[0058] Furthermore, the recycled carbon black (B) can be obtained from a 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).

[0059] The recycled carbon black (B) 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] In the rubber composition for side rubber of this embodiment, the recycled carbon black (B) is such that, when measured with a grind gauge, there are 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 the lines with a length of 10 mm or more is 20 μm or less. By incorporating recycled carbon black into the rubber composition, which is such that, when measured with a grind gauge, there are 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 the lines 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 high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation of the rubber composition can be maintained.

[0064] Methods for evaluating the dispersibility of carbon black using the aforementioned grind gauge are described in JIS K5101 (particularly regarding paste preparation) and JIS K5400 (particularly regarding evaluation methods based on the manner of linear mark formation). In the evaluation of recycled carbon black using a grind gauge, as described later, it is important whether the particle size of the third largest particle in the recycled carbon black being measured is 20 μm or less, from the viewpoint of high-temperature crack propagation resistance and elongation at break after thermal degradation of the rubber composition. Therefore, from the viewpoint of accurately measuring particle sizes around 20 μm and from the viewpoint of ease of measurement, it is preferable to use a grind gauge with a range of 0 to 25 μm. Note that any grind gauge with an upper limit of a range greater than 20 μm can be used, as it is possible to determine whether the particle size of the third largest particle is 20 μm or less. Furthermore, when used for other purposes (maintaining properties other than high-temperature crack propagation resistance and elongation at break after thermal degradation of rubber compositions containing recycled carbon black), the range of the grind gauge used can be appropriately selected according to the purpose.

[0065] 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. In evaluating the recycled carbon black used in the rubber composition of this embodiment, it is preferable to prepare the paste of recycled carbon black according to JIS K5101-1-5 as a measurement sample for measurement using a grind gauge. By preparing the paste of recycled carbon black according to JIS K5101-1-5, the evaluation accuracy of the recycled carbon black can be further improved. Furthermore, a rubber composition containing recycled carbon black evaluated using such a measurement sample can more reliably maintain high-temperature crack propagation resistance and elongation at break after thermal degradation. 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 mixing 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.

[0066] Furthermore, in the evaluation of recycled carbon black using the grind gauge, when preparing the paste of recycled carbon black in accordance with JIS K5101-1-5, it is preferable to apply a load of 0.4 to 0.5 kN and rotate the glass plate at a speed of 90 to 110 r / min, from the viewpoint of improving evaluation accuracy. A rubber composition containing recycled carbon black evaluated using a measurement sample prepared with the applied load and glass plate rotation speed within the above range can more reliably maintain high-temperature crack propagation resistance and elongation at break after thermal degradation.

[0067] 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, even if recycled carbon black is added, the durability of the rubber composition, in particular the high-temperature crack propagation resistance after thermal degradation and the decrease in elongation at break after thermal degradation can be suppressed. In this specification, the measurement of recycled carbon black (B) using a grind gauge is performed by the method described in the examples.

[0068] In this embodiment, recycled carbon black having three or more lines of 10 mm or longer in length, as measured by a grind gauge, and the particle size of the third largest particle among the particles that give rise to these lines of 10 mm or longer being 20 μm or less, can be produced by various methods. For example, recycled carbon black with a particle size of 20 μm or less can be produced by further grinding the recycled carbon black produced by a general method from recycled waste by extending the grinding process for a longer time or increasing the grinding intensity.

[0069] The recycled carbon black (B) may contain one or more metal atoms selected from the group consisting of Zn, Cu, and Fe. Since recycled carbon black is obtained from recycled waste as raw material, it contains various elements other than carbon (C), and zinc (Zn), copper (Cu), and iron (Fe) are elements that are easily contained in recycled carbon black. Therefore, recycled carbon black containing at least one of the elements of Zn, Cu, and Fe does not require any special removal operations, and rubber compositions for side rubbers containing such recycled carbon black are easy to manufacture.

[0070] The recycled carbon black (B) may contain Zn. As mentioned above, recycled carbon black is obtained from recycled waste as a raw material, and therefore contains various elements other than carbon (C). Zinc (Zn) is derived from, for example, zinc oxide used as a vulcanization aid, and is an element that is particularly likely to be found in recycled carbon black. Therefore, recycled carbon black containing Zn does not require any special removal operations, and rubber compositions for side rubbers containing such recycled carbon black are easy to manufacture.

[0071] The recycled carbon black (B) preferably has a Zn content of 0% by mass or more and 5.0% by mass or less. A rubber composition for side rubber containing recycled carbon black with a Zn content of 5.0% by mass or less is more likely to maintain high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation. From a similar viewpoint, the recycled carbon black (B) is more preferably 4.5% by mass or less, even more preferably 4.0% by mass or less, even more preferably 3.5% by mass or less, and particularly preferably 3.0% by mass or less. The Zn content in the recycled carbon black (B) may also be 0.01% by mass or more, or 0.05% by mass or more. The upper and lower limits can be combined as appropriate. The Cu content in the recycled carbon black (B) is usually 0 to 0.5% by mass, and preferably 0.01 to 0.1% by mass. Furthermore, the Fe content in the recycled carbon black (B) is usually 0.01 to 0.5% by mass, and preferably 0.01 to 0.3% by mass.

[0072] The recycled carbon black (B) 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.

[0073] The recycled carbon black (B) preferably has a pH of 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. Herein, in this specification, the pH of the recycled carbon black is determined according to ASTM D1512.

[0074] The recycled carbon black (B) preferably has a toluene color transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, in this specification, the toluene color transmittance of recycled carbon black is determined according to ASTM D1618.

[0075] The recycled carbon black (B) 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. Here, in this specification, the heating loss of recycled carbon black at 125°C is determined according to ASTM D1509.

[0076] The recycled carbon black (B) may contain sulfur. Since sulfur is an element that is readily found in recycled carbon black, recycled carbon black containing sulfur does not require any special removal operations, and rubber compositions containing such recycled carbon black are easy to manufacture. The recycled carbon black (B) preferably contains 5% by mass or less sulfur, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less.

[0077] The recycled carbon black (B) 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.

[0078] The recycled carbon black (B) 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.

[0079] The recycled carbon black (B) preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Here, in this specification, the pellet hardness of the recycled carbon black is determined according to ASTM D5230.

[0080] The recycled carbon black (B) 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.

[0081] The recycled carbon black (B) preferably has a particle size (D97) of 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Here, in this specification, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size analyzer, with the refractive index of water being 1.33 and the refractive index of the filler being 1.75.

[0082] The recycled carbon black (B) 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.

[0083] The recycled carbon black (B) preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the various physical properties of the side rubber to which the rubber composition is applied can be improved. Furthermore, the recycled carbon black (B) preferably has an ash content of 20.0% by mass or less. A rubber composition for side rubber containing recycled carbon black with an ash content of 20.0% by mass or less is more likely to maintain high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation. Hereinafter, the ash content of the recycled carbon black is determined according to ASTM D8474 / D1506.

[0084] The recycled carbon black (B) preferably has an oil absorption rate (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.

[0085] The recycled carbon black (B) preferably has an oil absorption rate (COAN) of 50 to 110 mL / 100 g of compressed sample, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Hereinafter, the COAN of the recycled carbon black is determined according to ASTM D3493.

[0086] The content of the recycled carbon black (B) is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, still more preferably 5 to 50 parts by mass, even more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass with respect to 100 parts by mass of the rubber component (A). When the content of the recycled carbon black (B) is 5 parts by mass or more with respect to 100 parts by mass of the rubber component (A), the effect of improving the ratio of the sustainable material of the side rubber to which the rubber composition is applied is great. When it is 50 parts by mass or less, the high-temperature crack growth resistance after heat deterioration of the rubber composition and the elongation at break (EB) after heat deterioration can be more reliably maintained.

[0087] "Carbon black other than recycled carbon black" The rubber composition for side rubber of the present embodiment preferably contains carbon black other than the recycled carbon black. By combining carbon black other than the recycled carbon black with the recycled carbon black (B), the high-temperature crack growth resistance after heat deterioration of the rubber composition and the elongation at break (EB) after heat deterioration can be further improved. As the carbon black other than the recycled carbon black, carbon black derived from plants is particularly preferable. Examples of the carbon black derived from plants include those derived from castor oil and rosin oil.

[0088] There is no particular limitation on the carbon black other than the recycled carbon black. For example, carbon black of SAF, ISAF, IISAF, N339, HAF, FEF, GPF, SRF grades with high, medium or low structure, particularly SAF, ISAF, IISAF, N339, HAF, FEF grades of carbon black are preferably used. Nitrogen adsorption specific surface area (N ２ SA, measured in accordance with JIS K6217-2:2001) is preferably 20 m ２ / g or more, more preferably 30 m ２ / g or more, more preferably 50 m ２ / g or more, still more preferably 70 m ２ / g or more, and preferably 250 m ２ / g or less, more preferably 200 m ２ / g or less, and more preferably 150 m２ A value of less than / g is even more preferable. This carbon black may be used alone or in combination of two or more types.

[0089] The content of carbon black other than the recycled carbon black is not particularly limited, but is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component (A). Also, is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 90 parts by mass or less.

[0090] From the viewpoint of improving the sustainable material ratio, the proportion of recycled carbon black (B) in the total amount of recycled carbon black (B) and carbon black other than recycled carbon black (i.e., the total amount of carbon black) is preferably 1% by mass or more, more preferably 5% by mass, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 100% by mass. Furthermore, from the viewpoint of improving the durability of the rubber composition (high temperature crack propagation resistance and elongation at break after thermal degradation (EB)), it is preferably 100% by mass or less, more preferably 80% by mass or less, even more preferably 50% by mass or less, and particularly preferably 25% by mass or less. These upper and lower limits can be arbitrarily combined according to the required physical properties.

[0091] "Quinoline-based anti-aging agent (C)" The rubber composition for side rubber of this embodiment preferably further contains a quinoline-based anti-aging agent (C). The quinoline-based anti-aging agent (C) is an anti-aging agent having a quinoline portion or a derivative portion thereof (such as a dihydroquinoline portion). The quinoline-based anti-aging agent has the effect of improving the heat degradation resistance of the rubber composition and improving the high-temperature crack propagation resistance and elongation at break (EB) after heat degradation. Therefore, the rubber composition for side rubber containing the quinoline-based anti-aging agent (C) has improved high-temperature crack propagation resistance and elongation at break (EB) after heat degradation.

[0092] The quinoline-based antioxidant (C) preferably has a dihydroquinoline moiety, and more preferably has a 1,2-dihydroquinoline moiety. Specific examples of the quinoline-based antioxidant (C) include polymers of 2,2,4-trimethyl-1,2-dihydroquinoline (antioxidant TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), and 6-anilino-2,2,4-trimethyl-1,2-dihydroquinoline. Commercially available products can be used as the quinoline-based antioxidant (C), and examples of commercially available products of this antioxidant include those from Ouchi Shinko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Corporation, Flexis, and others. These antioxidants may be used individually or in combination of two or more. The quinoline-based antioxidant (C) preferably contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antioxidant TMDQ). A quinoline-based antioxidant containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline has a high effect in improving the heat resistance degradation of the rubber composition and also has the advantage of being less likely to cause discoloration of the rubber composition. Examples of polymers of 2,2,4-trimethyl-1,2-dihydroquinoline include dimers, trimers, tetramers, etc.

[0093] The content of the quinoline-based antioxidant (C) is preferably in the range of 0.1 to 5 parts by mass per 100 parts by mass of the rubber component (A). When the content of the quinoline-based antioxidant (C) is 0.1 parts by mass or more per 100 parts by mass of the rubber component (A), the heat degradation resistance of the rubber composition can be sufficiently ensured, and the high-temperature crack propagation resistance and elongation at break (EB) after heat degradation can be sufficiently improved. Furthermore, when the content of the quinoline-based antioxidant (C) is 5 parts by mass or less per 100 parts by mass of the rubber component (A), the influence on other rubber properties such as heat generation is reduced, making it suitable for tire sidewall rubber applications. From the viewpoint of heat degradation resistance, the content of the quinoline-based antioxidant (C) is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component (A), and from the viewpoint of affecting other rubber properties, it is preferably 4 parts by mass or less, more preferably 3 parts by mass or less, per 100 parts by mass of the rubber component (A).

[0094] "Anti-aging agent other than quinoline-based anti-aging agent (E)" The rubber composition for the side rubber of this embodiment preferably further contains an anti-aging agent other than quinoline-based anti-aging agent (E). By including an anti-aging agent other than quinoline-based anti-aging agent (E) together with the quinoline-based anti-aging agent (C), the anti-aging effects of each are complemented, and the high-temperature crack propagation resistance after thermal degradation and the elongation at break (EB) after thermal degradation are further improved.

[0095] Other antioxidants (E) besides the quinoline-based antioxidant include phenylenediamine-based antioxidants, diphenylamine-based antioxidants, phenol-based antioxidants, quinone-based antioxidants, carbamate-based antioxidants, imidazole-based antioxidants, and among these, phenylenediamine-based antioxidants are preferred. The phenylenediamine-based antioxidant has a phenylenediamine moiety (-NH-C ６ H ４The antioxidant has a -NH-) or a derivative thereof. By including a phenylenediamine-based antioxidant together with a quinoline-based antioxidant (C), the anti-aging effects of each antioxidant are complemented, and the high-temperature crack propagation resistance after thermal degradation and the elongation at break (EB) after thermal degradation are further improved. Examples of the phenylenediamine-based 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), and N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine. Commercially available phenylenediamine-based antioxidants can be used, and examples of such commercially available antioxidants include those from Ouchi Shinko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Corporation, Flexis Co., Ltd., and others. These antioxidants may be used individually or in combination of two or more.

[0096] The content of the antioxidant (E) other than the quinoline-based antioxidant is not particularly limited, but is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, even more preferably 2 parts by mass or more, and also preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of the rubber component (A).

[0097] "Zinc Oxide (D)" The rubber composition for side rubber of this embodiment preferably further contains zinc oxide (D). Since zinc oxide (D) has the effect of facilitating the vulcanization of the rubber composition, the rubber composition for side rubber containing zinc oxide (D) is easy to vulcanize.

[0098] The zinc oxide (D) can be any zinc ingot, or preferably zinc oxide obtained from recycled zinc or zinc dross (i.e., obtained through recycling). Commercially available zinc oxide (D) can be used, and examples of commercially available zinc oxide (D) include products from Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., Mitsui Mining & Smelting Co., Ltd., and Toho Zinc Co., Ltd. These commercially available zinc oxide (D) products may be used individually or in combination of two or more types.

[0099] The content of zinc oxide (D) is not particularly limited, but is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, even more preferably 1.8 parts by mass or more, and preferably 10 parts by mass or less, more preferably 6 parts by mass or less, even more preferably 4 parts by mass or less, and particularly preferably 2.2 parts by mass or less, per 100 parts by mass of rubber component (A). When the content of zinc oxide (D) is 4 parts by mass or less per 100 parts by mass of rubber component (A), the high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation of the rubber composition are further improved. Furthermore, when the zinc oxide (D) content is in the range of 1.5 to 4 parts by mass per 100 parts by mass of the rubber component (A), the vulcanization properties of the rubber composition are improved, while the high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation are further improved. When the content is in the range of 1.8 to 2.2 parts by mass, the vulcanization properties of the rubber composition are further improved, while the high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation are further improved.

[0100] The rubber composition for the side rubber of this embodiment preferably contains both the quinoline-based antioxidant (C) and the zinc oxide (D). Here, the mass ratio of the zinc oxide (D) to the quinoline-based antioxidant (C) [zinc oxide (D) / quinoline-based antioxidant (C)] is preferably greater than 0 and 3.0 or less, more preferably 0.01 or more and 2.5 or less, even more preferably 0.1 or more and 2.0 or less, more preferably 0.1 or more and 1.5 or less, and particularly preferably 0.1 or more and 1.0 or less. When the mass ratio of zinc oxide (D) / quinoline-based antioxidant (C) is 3.0 or less, the high-temperature crack propagation resistance after thermal degradation and the elongation at break (EB) after thermal degradation can be sufficiently improved. Furthermore, if the mass ratio of zinc oxide (D) to quinoline-based antioxidant (C) is 0.1 or higher, the vulcanization properties of the rubber composition are improved, and if it is 1.5 or lower, the high-temperature crack propagation resistance after thermal degradation and the elongation at break (EB) after thermal degradation can be further improved.

[0101] The mass ratio [zinc oxide (D) / total amount of antioxidants] of the zinc oxide (D) and the total amount of the quinoline-based antioxidant (C) and the antioxidant other than the quinoline-based antioxidant (E) (i.e., the total amount of antioxidants) is preferably greater than 0 and 0.80 or less, more preferably 0.1 to 0.70, even more preferably 0.2 to 0.60, and particularly preferably 0.25 to 0.55. When the mass ratio of zinc oxide (D) / total amount of antioxidants is 0.80 or less, the high-temperature crack propagation resistance after thermal degradation and the elongation at break (EB) after thermal degradation can be further improved. Also, when the mass ratio of zinc oxide (D) / total amount of antioxidants is 0.1 or more, the vulcanization properties of the rubber composition are improved.

[0102] "Resin" The rubber composition for the side rubber of this embodiment may contain a resin. 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 and International Publication No. 2019 / 116656 can be used.

[0103] 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).

[0104] The content of the resin is not particularly limited, but for example, it 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 rubber component (A).

[0105] "Silica" The rubber composition for the side rubber of this embodiment may contain silica. The type of silica is not particularly limited. Examples include wet silica, colloidal silica, calcium silicate, aluminum silicate, etc. Among the above, wet silica is preferred, and precipitated silica is more preferred. These silicas may be used individually or in combination of two or more types.

[0106] From the viewpoint of reducing environmental impact, silica derived from silicate plants is preferred. These silicate plants include, for example, mosses, ferns, horsetails, cucurbitaceae, nettleaceae, and grasses. Among these plants, grasses are preferred. Among grasses, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred from the viewpoint of availability. Further examples of silica include silica recycled from silicon wafer scraps used as raw materials for semiconductors, glass bottles, etc.

[0107] The silica is not particularly limited, but for example, if its CTAB specific surface area (cetyltrimethylammonium bromide adsorption specific surface area) is 70 m² ２ / g or more, 250m ２ Silica of 0.35 nm or less can be used. The CTAB specific surface area refers to the value measured in accordance with ASTM D3765-92. However, the adsorption cross-section per molecule of cetyltrimethylammonium bromide on the silica surface is 0.35 nm. ２ The specific surface area (m²) is calculated from the amount of adsorption of CTAB. ２ The CTAB specific surface area is defined as ( / g). The BET specific surface area of ​​the silica is 100 m². ２ / g or more, 250m ２ It can be less than or equal to / g. The BET specific surface area is the specific surface area obtained by the BET method, and in this invention, it can be measured in accordance with ASTM D4820-93.

[0108] Furthermore, the silica content is not particularly limited. For example, it is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the rubber component (A). On the other hand, it is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less.

[0109] The proportion of silica in the total content of the silica and carbon black is not particularly limited, but is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. It may also be 100% by mass, but is preferably 98% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, even more preferably 80% by mass or less, and particularly preferably 70% by mass or less.

[0110] "Silane Coupling Agent" When the rubber composition for the side rubber of this embodiment contains silica, it is preferable that the rubber composition contains a silane coupling agent in order to improve the effect of the silica. 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- Examples include N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and dimethoxymethylsilylpropylbenzothiazolyl tetrasulfide. These silane coupling agents may be used individually or in combination of two or more.

[0111] Furthermore, bioethanol can also be used as a raw material for the silane coupling agent.

[0112] "Other" In addition to the components described above, the rubber composition for the side rubber of this embodiment may further contain various additives used in rubber products, especially tires, such as liquid softeners like oil and liquid polymers, fillers such as sulfur, vulcanization accelerators, wax, stearic acid, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica, 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.

[0113] "Method for Producing a Rubber Composition for Side Rubbers" The method for preparing the rubber composition for side rubbers of this embodiment is not particularly limited, and known methods can be used. For example, it can be obtained by kneading each component, including rubber component (A) and recycled carbon black (B), 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. The rubber composition for side rubbers of this embodiment can be crosslinked or vulcanized. The conditions for crosslinking or vulcanizing the rubber composition can be adjusted as appropriate, for example, the temperature can be 120 to 200°C and the heating time can be 1 minute to 900 minutes.

[0114] <Tire> The tire of this embodiment is characterized by having a side rubber made of the rubber composition for side rubber described above. Because the tire of this embodiment has a side rubber made of the rubber composition for side rubber described above, the proportion of sustainable materials is improved while maintaining durability after thermal degradation.

[0115] Next, an embodiment of the tire of the present invention will be described in detail with reference to the drawings. Figure 2 is a cross-sectional view of an embodiment of the tire of the present invention. The tire 11 of this embodiment shown in Figure 2 has a pair of bead portions 12, a pair of sidewall portions 13, and a tread portion 14 connected to both sidewall portions 13, and comprises a carcass 16 extending in a toroidal shape between bead cores 15 embedded in each of the pair of bead portions 12, and a belt 17 arranged on the radially outer side of the crown portion of the carcass 16.

[0116] The carcass 16 of the tire 11 shown in Figure 2 is composed of a single carcass ply made of multiple parallel-arranged cords covered with coating rubber. The carcass 16 consists of a main body that extends in a toroidal shape between the pair of bead cores 15 and folded-over portions that are wound radially outward from the inside to the outside in the tire width direction around each bead core 15. However, the number of plies and structure of the carcass in the tire of the present invention are not limited to this.

[0117] Furthermore, in the tire 11 shown in Figure 2, a belt 17 consisting of two belt layers is arranged on the radially outer side of the crown portion of the carcass 16. These belt layers typically consist of rubberized layers of cords (preferably steel cords) that extend at an inclination with respect to the tire's equatorial plane. The two belt layers are stacked so that the cords constituting the belt layers intersect each other with the tire's equatorial plane in between, thereby forming the belt 17. Although the belt 17 in the figure consists of two belt layers, in the tire of the present invention, the number of belt layers constituting the belt may be three or more.

[0118] Furthermore, the tire 11 of this embodiment is provided with side rubber 18 on a pair of sidewall portions 13, and the rubber composition of this embodiment described above is used for the side rubber 18. As a result, the tire 11 of this embodiment maintains durability after thermal degradation while improving the proportion of sustainable materials.

[0119] The tire of this embodiment can be manufactured by conventional methods using the above-described rubber composition for the side 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 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, inert gases such as nitrogen, argon, and helium can be used.

[0120] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0121] <Evaluation of Recycled Carbon Black> The physical properties of recycled carbon black 1 and 2 were evaluated using the following method.

[0122] (1) Grind gauge measurement: 3.75 g of zinc oxide, 0.20 g of the carbon black under test, and 2.00 mL of epoxidized soybean oil 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 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 average value of the particle size measured four times is shown in Table 1.

[0123] (2) Nitrogen adsorption specific surface area (N ２ SA) In accordance with ASTM D6556, the specific surface area (N) of nitrogen adsorption of the tested carbon black. ２ SA was measured.

[0124] (3) Elemental analysis: The content of zinc (Zn), copper (Cu), and iron (Fe) was confirmed by X-ray fluorescence analysis (XRF).

[0125] (4) Ash content The ash content of the carbon black sample was measured according to ASTM D8474 and D1506.

[0126]

[0127] <Preparation and Evaluation of Rubber Compositions in Example 1 and Comparative Example 1> Rubber compositions for side rubbers were prepared using a standard Banbury mixer 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 Example 1 and Comparative Example 1. Commercially available chemicals commonly used when preparing rubber compositions for side rubbers were used. The amounts added were the amounts commonly used when preparing rubber compositions for side rubbers. The total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources (recycled resources) was calculated for the rubber composition to determine the sustainable material ratio. Furthermore, the high-temperature crack propagation resistance after thermal degradation was evaluated for the obtained rubber compositions using the following method.

[0128] (5) Evaluation method for high-temperature crack propagation resistance after thermal degradation Each sample was degraded in a nitrogen atmosphere at 100°C for 24 hours beforehand. Strip-shaped test pieces were prepared from the degraded rubber composition with a 0.5 mm hole drilled in the lengthwise direction in the center. A dc / dn test was performed using these test pieces (using a Shimadzu "Servopulsa" at a frequency of 5 Hz and 80°C, applying repeated fatigue with a strain of 30-100%), and the tear energy [J / m] at 1950 cycles was determined. ２ The crack propagation rate when the common logarithm of [ ] is 3.9 was calculated, and the high-temperature crack propagation resistance after degradation was evaluated. The reciprocal of the crack propagation rate was expressed exponentially, with the value of Comparative Example 1 set to 100. A larger exponential value indicates a lower crack propagation rate and superior high-temperature crack propagation resistance after thermal degradation.

[0129] (6) Evaluation method for tensile strength after thermal degradation Each sample was degraded in advance at 100°C under a nitrogen atmosphere for 48 hours. The rubber composition after degradation was subjected to a tensile test at 100°C in accordance with JIS K 6251:2017 and its tensile strength was measured. The tensile strength of the test piece in Reference Example 1 was set to 100 and expressed as an index. A larger index value indicates stronger tensile strength and superior high-temperature tensile strength after degradation.

[0130]

[0131] *1 Natural rubber: RSS#3 *2 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *3 New carbon black: Manufactured by Asahi Carbon, N550 *4 Recycled carbon black 1: Same as Table 1 *5 Recycled carbon black 2: Same as Table 1 *6 Anti-aging agent: Manufactured by Ouchi Shinko Chemical Industry, product name "Nocrac 224", 2,2,4-trimethyl-1,2-dihydroquinoline polymer

[0132] Tables 1 and 2 show that even with rubber compositions containing recycled carbon black of the same ash content, the high-temperature crack propagation resistance after thermal degradation of the rubber composition varies greatly depending on the particle size of the third largest particle measured by the grind gauge of the incorporated recycled carbon black. It can be seen that incorporating recycled carbon black in which the third largest particle size measured by the grind gauge is 20 μm or less improves the high-temperature crack propagation resistance after thermal degradation.

[0133] <Preparation and Evaluation of Rubber Compositions for Reference Examples 1 to 4> Rubber compositions for Reference Examples 1 to 4 were prepared according to the formulations shown in Table 3. For each rubber composition obtained, the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources was calculated to determine the sustainable material ratio. Furthermore, the elongation at break (EB) after thermal degradation was evaluated for the obtained rubber compositions using the following method. The results are shown in Table 3.

[0134] (7) Evaluation of elongation at break (EB) after thermal degradation A vulcanized rubber test piece was prepared by vulcanizing the rubber composition. Next, the vulcanized rubber test piece was left at 100°C for 24 hours to allow thermal degradation to occur. A tensile test similar to that in JIS K 6251 was performed on the thermally degraded test piece at 100°C, and the elongation at break (EB) after thermal degradation was measured. The results are expressed as an index with the elongation at break (EB) after thermal degradation in Reference Example 1 set to 100. A larger index value indicates a larger elongation at break (EB) after thermal degradation.

[0135]

[0136] *7 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *8 Unused carbon black: Manufactured by Asahi Carbon, product name "N550", nitrogen adsorption specific surface area (N ２ SA) = 40m ２ / g, OAN = 121 mL / 100 g *9 Recycled carbon black: Enrestec, product name "PB365", ash content = 17% by mass *10 Quinoline-based antioxidant: Seiko Chemicals, Ltd., product name "Nonflex RD", 2,2,4-trimethyl-1,2-dihydroquinoline polymer *11 Phenylenediamine-based antioxidant: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 6C", N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine *12 Other chemicals: Total amount of sulfur, vulcanization accelerator, resin, oil, and wax, Reference Examples 1 to 4 are in the same ratio

[0137] The results from Reference Examples 1 to 4 in Table 3 show that by appropriately adjusting the amounts of quinoline-based antioxidants and zinc oxide while maintaining the proportion of sustainable materials, the elongation at break (EB) after thermal degradation can be improved.

[0138] <Preparation and Evaluation of Rubber Compositions for Reference Examples 5-8> Rubber compositions were prepared using a standard Banbury mixer according to the compounding methods shown in Table 4. Each of the obtained rubber compositions was evaluated using the evaluation methods described below.

[0139] (8) The zinc (Zn) content was confirmed by Zn content X-ray fluorescence analysis (XRF).

[0140] (9) Ash Content The ash content of carbon black was measured by thermogravimetric analysis (TGA, RIGAKU Corporation). 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 (mass%) 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: Ash content (mass%) = 100 - Loss on Heating 1 - Loss on Heating 2

[0141] (10) Evaluation of Tensile Strength Tensile tests were conducted at room temperature in accordance with JIS K6301-1995, and the tensile strength of each rubber composition was measured. The evaluation results were expressed as an index using the following formula, with Reference Example 5 as the control (index value 100): Tensile Strength Index = (Tensile strength of test specimens other than Reference Example 5 / Tensile strength of test specimen of Reference Example 5) × 100 A larger index indicates that the rubber composition is less likely to break and has superior tensile strength.

[0142] (11) Evaluation of Viscoelasticity A viscoelasticity test was performed using "ARES-G2" manufactured by TA Instruments, Inc., under the conditions of a frequency of 15 Hz, shear strain of 10%, and temperature of 50°C, and the storage modulus (G') of the rubber composition was measured. The evaluation results were indexed with Reference Example 5 as the control (index value 100). A higher index indicates a higher G', which in turn indicates superior rubber properties when applied to products such as tires.

[0143]

[0144] *13 SBR: Styrene-butadiene rubber, manufactured by ENEOS Material Co., Ltd., product name "#1500" *14 CB1: Carbon Black 1, recycled carbon black equivalent to N330 *15 CB2: Carbon Black 2, recycled carbon black equivalent to N330 *16 CB3: Carbon Black 3, recycled carbon black equivalent to N330 *17 CB4: Carbon Black 4, new carbon black equivalent to N330

[0145] Table 4 shows that when carbon black with a Zn content of 5.0% by mass or less, or an ash content of 20.0% by mass or less, is used, the deterioration of the physical properties of the rubber composition is suppressed.

[0146] <Preparation and Evaluation of Rubber Compositions in Reference Examples 9 and 10> 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 specimens. The obtained vulcanized rubber test specimens were punched out into JIS-3 dumbbells, and the obtained 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.

[0147]

[0148] *1 Natural rubber: RSS#3 *2 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *8 Unused carbon black: Manufactured by Asahi Carbon, product name "N550", nitrogen adsorption specific surface area (N ２ SA) = 40m ２ / g, DBP oil absorption = 121 mL / 100 g *9 Recycled carbon black: Enrestec, product name "PB365", ash content = 17% by mass *18 Anti-aging agent (phenylenediamine type): Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 6C" *19 Anti-aging agent (quinoline type): Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 224" *20 Oil: ENEOS, product name "A / Omix" *21 Fatty acid: Miyoshi Oil & Fat Co., Ltd., product name "MXST" *22 Other chemicals: sulfur, vulcanization accelerator, resin, wax, same ratio in each rubber composition

[0149] Table 5 shows that replacing unused 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.

[0150] From the results shown in Tables 2 and 3 above, it can be seen that by incorporating recycled carbon black in which, when measured with a grind gauge, there are 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 is 20 μm or less, the proportion of sustainable materials can be improved while maintaining the high-temperature crack propagation resistance and elongation at break (EB) after thermal degradation of the rubber composition.

[0151] 1: Grind gauge 2: Line less than 10 mm in length 3: Line 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 mark where the line caused by the third largest particle appears 11: Tire 12: Bead area 13: Sidewall area 14: Tread area 15: Bead core 16: Carcass 17: Belt 18: Side rubber

Claims

1. A rubber composition for side rubber comprising a rubber component (A) and recycled carbon black (B), wherein the recycled carbon black (B) is characterized in that, when measured with a grind gauge, there are 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 give rise to the lines with a length of 10 mm or more is 20 μm or less.

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

3. The rubber composition for side rubber according to claim 1, wherein, in the measurement using the 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 recycled carbon black (B) is prepared as the measurement sample.

4. The rubber composition for side rubber according to claim 1, further comprising a quinoline-based antioxidant (C).

5. The rubber composition for side rubber according to claim 1, further comprising zinc oxide (D).

6. The rubber composition for side rubber according to claim 1, wherein the recycled carbon black (B) contains one or more metal atoms selected from the group consisting of Zn, Cu, and Fe.

7. The rubber composition for side rubber according to claim 1, wherein the recycled carbon black (B) contains Zn.

8. The rubber composition for side rubber according to claim 1, wherein the recycled carbon black (B) has a Zn content of 0% by mass or more and 5.0% by mass or less.

9. The rubber composition for side rubber according to claim 1, wherein the recycled carbon black (B) has an ash content of 20.0% by mass or less.

10. The rubber composition for side rubber according to claim 1, further comprising a quinoline-based antioxidant (C) and zinc oxide (D), wherein the mass ratio of zinc oxide (D) to the quinoline-based antioxidant (C) [zinc oxide (D) / quinoline-based antioxidant (C)] is greater than 0 and 3.0 or less.

11. The rubber composition for side rubber according to claim 1, wherein the total amount of styrene in the rubber component (A) is 5% by mass or less.

12. The rubber composition for side rubber according to claim 1, wherein the rubber component (A) includes natural rubber.

13. The rubber composition for side rubber according to claim 12, wherein the rubber component (A) further comprises butadiene rubber.

14. The rubber composition for side rubber according to claim 5 or 10, wherein the content of zinc oxide (D) is 4 parts by mass or less per 100 parts by mass of the rubber component (A).

15. The rubber composition for side rubber according to claim 1, further comprising an antioxidant (E) other than a quinoline-based antioxidant.

16. The rubber composition for side rubber according to claim 15, wherein the antioxidant (E) other than the quinoline-based antioxidant is a phenylenediamine-based antioxidant.

17. A tire characterized by comprising a side rubber made of the rubber composition for side rubber described in claim 1.

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