Tread rubber composition for two-wheeled vehicle tires, and two-wheeled vehicle tire

Abstract

The present invention addresses the problem of providing a tread rubber composition for two-wheeled vehicle tires, which is capable of increasing the proportion of sustainable materials while maintaining the physical properties acquired in the case where sustainable materials are not used. A solution to the problem is a tread rubber composition for two-wheeled vehicle tires, the composition comprising a rubber component and a filler. The filler contains recycled carbon black. When the recycled carbon black is measured using a grind gauge, three or more lines having a length of 10 mm or more are observed. 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 for motorcycle tire treads, and motorcycle tires

[0001] This invention relates to a rubber composition for the tread of a motorcycle tire, and to a motorcycle tire.

[0002] Conventionally, in motorcycle tire treads, a method has been developed that divides the tread into three sections in the tire width direction and uses two types of tread rubber to achieve a balance between the performance required for straight-line driving and the performance required for cornering.

[0003] For example, Patent Document 1 discloses a motorcycle tire comprising a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, wherein the tread portion is divided into three parts in the tire width direction by a center portion including the tire equator and a pair of shoulder portions including the tread ends, wherein the tread rubber of the center portion and the tread rubber of the shoulder portions both contain a rubber component including styrene-butadiene rubber and a modified conjugated diene polymer, and silica, and contain 40 to 120 parts by mass of filler per 100 parts by mass of the rubber component, and the silica content in the filler is 80% by mass or more. Furthermore, Patent Document 2 discloses a rubber composition for tires comprising a rubber component, a filler, and a softener, wherein the rubber component comprises at least one selected from styrene-butadiene rubber and butadiene rubber, the filler comprises silica and carbon black, the total content of silica and carbon black is 65 to 140 parts by mass per 100 parts by mass of the rubber component, and the softener comprises a liquid softener component and a hydrogenated resin, the proportion of the hydrogenated resin in the total content of the softener is 40% by mass or more, and the hydrogenated resin has a softening point exceeding 110°C and a weight-average molecular weight in polystyrene terms of 200 to 1600 g / mol, and a tire containing such a rubber composition.

[0004] International Publication No. 2017 / 204236, Japanese Patent Publication No. 2022-187976

[0005] Incidentally, in recent years, from the perspective of social sustainability, there has been a demand for the use of so-called sustainable materials in businesses and products, such as materials derived from biological resources (biomass resources) and materials derived from recycled resources. Furthermore, there is a demand to increase the usage rate of sustainable materials (hereinafter sometimes referred to as the "sustainability rate" or "sustainability ratio") in the various components used in tires. However, increasing the ratio of sustainable materials can, in some cases, lead to a decrease in physical properties compared to cases where sustainable materials are not used.

[0006] Therefore, the present invention aims to solve the problems of the above-mentioned prior art and provide a rubber composition for motorcycle tire treads that can increase the proportion of sustainable materials while maintaining the physical properties of a tire without sustainable materials. Furthermore, the present invention aims to provide a motorcycle tire in which the proportion of sustainable materials is increased while maintaining the physical properties of a tire without sustainable materials.

[0007] The gist of the present invention, which solves the above problems, is as follows.

[0008] [1] A rubber composition for the tread of a motorcycle tire, comprising a rubber component and a filler, wherein the filler contains recycled carbon black, and the recycled carbon black, when measured with a grind gauge, 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 the lines with a length of 10 mm or more is 20 μm or less.

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

[0010] [3] The rubber composition for tire treads of motorcycle tires according to [1] or [2], wherein, in the measurement of 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 to 90 to 110 r / min in accordance with JIS K5101-1-5, and the paste of recycled carbon black is prepared as the measurement sample.

[0011] [4] The rubber composition for motorcycle tire treads according to any one of [1] to [3], wherein the recycled carbon black contains one or more metal atoms selected from the group consisting of Zn, Cu, and Fe.

[0012] [5] The rubber composition for the tread of a motorcycle tire according to [4], wherein the recycled carbon black contains Zn.

[0013] [6] The rubber composition for motorcycle tire treads according to [5], wherein the recycled carbon black has a Zn content of 2.5% by mass or less.

[0014] [7] The recycled carbon black has an ash content of 20% by mass or less, the rubber composition for the tread of a motorcycle tire according to any one of [1] to [6].

[0015] [8] A tire comprising a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, wherein the tread portion is divided in the tire width direction by a center portion including the tire equatorial plane and a pair of shoulder portions including the tread ends, wherein at least one of the tread rubber of the center portion or the tread rubber of the shoulder portions is made of a motorcycle tire tread rubber composition described in any of [1] to [7], the rubber component of the rubber composition in the tread rubber of the center portion includes at least one selected from styrene-butadiene rubber and butadiene rubber, the rubber composition in the tread rubber of the center portion further includes a softener, the softener includes a resin, and the resin includes C5 resin and C5C9 resin.

[0016] [9] The tire according to [8], wherein the ratio of the storage modulus of the tread rubber in the center portion at 60°C to the storage modulus of the tread rubber in the shoulder portion at 60°C is greater than 1.72.

[0017] According to the present invention, it is possible to provide a rubber composition for motorcycle tire treads that can increase the proportion of sustainable materials while maintaining the physical properties of a tire without sustainable materials. Furthermore, according to the present invention, it is possible to provide a motorcycle tire with an increased proportion of sustainable materials while maintaining the physical properties of a tire without sustainable materials.

[0018] This is an explanatory diagram illustrating an example of measurement results using a grind gauge. This is a schematic cross-sectional view showing an example of a motorcycle tire according to the present invention.

[0019] The rubber composition for motorcycle tire treads and the motorcycle tire of the present invention will be described in detail below based on embodiments thereof.

[0020] 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.

[0021] In this specification, "sustainable material ratio" refers to the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources in the rubber composition and tire in question.

[0022] <Rubber Composition> The rubber composition for motorcycle tire treads of this embodiment (hereinafter also simply referred to as "rubber composition" and "rubber composition of this embodiment") is a rubber composition for motorcycle tire treads comprising a rubber component and a filler, wherein the filler includes recycled carbon black, 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. According to the above rubber composition for motorcycle tire treads, it is possible to increase the proportion of sustainable materials while maintaining the physical properties of a tire without sustainable materials. An example of a case where sustainable materials are not used is when new carbon black is used instead of recycled carbon black.

[0023] (Rubber component) The rubber composition for the tread of the motorcycle tire of this embodiment contains a 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.

[0024] 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.

[0025] In this specification, the 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.

[0026] As the rubber component, the rubber derived from the biological resources and the rubber derived from the recycled resources are preferred. Here, the ratio of the monomer component derived from the biological resources in 100 mol% of the monomer components constituting the rubber derived from the biological resources 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 resources in 100 mol% of the monomer components constituting the rubber derived from the recycled resources 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%.

[0027] The rubber component 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 1,5,000,000 or less. In this specification, the weight-average molecular weight (Mw) of the rubber component can be determined by standard polystyrene conversion based on the measurement value by gel permeation chromatography (GPC), for example.

[0028] As the rubber component, a diene rubber is preferred, and as the diene rubber, an isoprene rubber and a butadiene rubber are preferred.

[0029] Examples of the isoprene rubber include natural rubber and synthetic isoprene rubber. The origin of natural rubber is not particularly limited, and examples include those derived from Hevea brasiliensis, guayule, and Russian dandelion. The natural rubber may be modified or denatured, and the synthetic isoprene rubber may be denatured. These isoprene rubbers may be used alone or in combination of two or more. As the isoprene rubber, natural rubber is preferred.

[0030] Examples of the butadiene rubber include butadiene rubber and styrene-butadiene rubber. Here, the butadiene serving as a raw material for the butadiene rubber is preferably derived from biological resources or recycled resources.

[0031] Examples of the styrene-butadiene rubber include, for example, emulsion polymerization styrene-butadiene rubber and solution polymerization styrene-butadiene rubber.

[0032] The isoprene rubber and the butadiene rubber preferably have a sustainable rate of 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, still more preferably 60% by mass or more, still more preferably 70% by mass or more, still more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0033] In addition, in order to make the sustainable rate of the entire rubber component within the above range, it is preferable to use natural rubber as the rubber component, or a polymer synthesized using a monomer component derived from biological resources or a monomer component derived from recycled resources as the monomer component. In addition, in order to make the sustainable rate within the above range, mass balance certified synthetic rubber can also be used.

[0034] 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 can be appropriately adjusted depending on the member to which it is applied. The ratio of each monomer unit in the entire rubber component can be adjusted, for example, by appropriately combining the 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 as a monomer (including isoprene units in natural rubber), "unit derived from butadiene" means a constituent unit in a polymer composed of butadiene as a monomer, and "unit derived from aromatic vinyl compounds" means a constituent unit in a polymer composed of aromatic vinyl compounds as a monomer. In this specification, the ratio of each monomer unit is measured by NMR.

[0035] In addition to the isoprene-based rubber, butadiene rubber, and styrene-butadiene copolymer rubber mentioned above, the rubber component may also include diene-based rubbers such as acrylonitrile-butadiene rubber, chloroprene rubber, butyl rubber, and styrene-isoprene-butadiene copolymer rubber. These rubber components may be used individually or in combination of two or more.

[0036] The rubber component preferably contains at least one selected from styrene-butadiene rubber (SBR) and butadiene rubber (BR). More preferably, the rubber component contains both styrene-butadiene rubber and butadiene rubber. Styrene-butadiene rubber and butadiene rubber are relatively difficult to adhere to and have excellent fracture properties.

[0037] The rubber component may be unmodified, modified, or a blend of unmodified and modified rubber.

[0038] In the rubber components, the total proportion of styrene-butadiene rubber (SBR) and butadiene rubber (BR) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass.

[0039] -Styrene-butadiene rubber- The rubber component preferably contains styrene-butadiene rubber (SBR). From the viewpoint of improving handling stability, the rubber component preferably contains 50 parts by mass or more of styrene-butadiene rubber per 100 parts by mass of the rubber component, more preferably 60 parts by mass or more, and even more preferably 65 parts by mass or more. Furthermore, from the viewpoint of improving abrasion resistance, the rubber component preferably contains 90 parts by mass or less of styrene-butadiene rubber per 100 parts by mass of the rubber component, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less. Note that the styrene-butadiene rubber may be present in an amount of 100 parts by mass per 100 parts by mass of the rubber component, i.e., the rubber component may consist of styrene-butadiene rubber.

[0040] The styrene-butadiene rubber preferably has a styrene content of 5 to 50% by mass, and more preferably 8 to 45% by mass. If the styrene content of the styrene-butadiene rubber is 5% by mass or more, the abrasion resistance of the rubber composition is further improved. The styrene units can be determined by infrared spectroscopy (Morello method).

[0041] -Butadiene rubber- From the viewpoint of improving abrasion resistance, the rubber component preferably contains 10 parts by mass or more of butadiene rubber per 100 parts by mass of the rubber component, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more. Furthermore, from the viewpoint of improving handling stability, the rubber component preferably contains 50 parts by mass or less of styrene-butadiene rubber per 100 parts by mass of the rubber component, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less.

[0042] -Other Rubbers- The rubber component may contain other rubbers in addition to styrene-butadiene rubber and / or butadiene rubber. The content of other rubbers in the rubber component is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and may be 0% by mass. Examples of such other rubbers include natural rubber (NR), isoprene rubber (IR), chloroprene rubber (CR), styrene-isoprene rubber (SIR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), halogenated butyl rubber, etc. These other rubbers may be used individually or in mixtures of two or more.

[0043] The rubber component may be partially or entirely oil-distributed. When the rubber component is oil-distributed, the spreading oil is classified as a softening agent, as described later, and the amount of the spreading oil is included as part of the amount of the softening agent.

[0044] The 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 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.

[0045] 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.

[0046] 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.

[0047] For example, the method described in Japanese Patent Publication No. 2022-179158 can be used to prepare rubber derived from biological resources.

[0048] 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.

[0049] (Filler) The rubber composition for the tread of the motorcycle tire of this embodiment includes a filler. The filler includes recycled carbon black. The filler may also include at least one selected from silica and carbon black other than recycled carbon black, or it may include both silica and carbon black other than recycled carbon black. The filler can reinforce the rubber composition and improve the fracture properties of the rubber composition.

[0050] [Recycled Carbon Black] The rubber composition for the tread of the motorcycle tire of this embodiment contains recycled carbon black. Since recycled carbon black is a material derived from recycled resources, incorporating recycled carbon black into the rubber composition can improve the proportion of sustainable materials in the rubber product to which the rubber composition is applied.

[0051] 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 that generated from rubber products, but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and 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, rubber hoses, and rubber conveyor belts, as well as rubber parts or components at the manufacturing stage of final products. Used tires may include, for example, tires that have been retreaded, tires generated from tire replacement or vehicle scrapping, and End-of-Life Tires (ELTs) that have reached the end of their lifespan, or any other type of tire that has been discarded for any reason. 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 non-organic composition, such as those derived from silicone rubber or polyvinyl chloride, is preferable. Furthermore, waste oil that is mixed with carbon black or rubber containing carbon black is preferable. "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 actually used and then discarded, but also those that were manufactured but discarded without actually being used.

[0052] 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.

[0053] Furthermore, when recycled carbon black is recovered from solid residue, it is more preferably carbon black that has undergone surface treatment or surface modification. Examples of surface treatment or surface modification include hydrofluoric acid treatment, acid treatment such as hydrochloric acid or sulfuric acid, or treatment with peroxides. Surface treatment or surface modification may be carried out at room temperature, preferably at 70°C or higher, more preferably at 90°C or higher, and particularly preferably at 90°C to 100°C.

[0054] 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).

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] In the rubber composition of this embodiment, the recycled carbon black, 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 produce the lines of 10 mm or more is 20 μm or less. Measurement by grind gauge is related to the evaluation of the dispersibility of carbon black and is described in JIS K5101-1-5 (particularly concerning the preparation of paste) and JIS K5400 (particularly concerning the method of evaluation by the manner in which linear marks are generated).

[0060] From the viewpoint of the durability of the rubber composition, it is important whether the particle size of the third largest particle in the recycled carbon black being measured is 20 μm or less. 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. However, any grind gauge with an upper limit of the 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 (performance other than durability of the rubber composition containing recycled carbon black), the range of the grind gauge used can be appropriately selected according to the purpose.

[0061] 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 this embodiment, it is preferable to prepare the paste of recycled carbon black 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 evaluation accuracy of the recycled carbon black can be further improved.

[0062] 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.

[0063] Furthermore, when preparing the recycled carbon black paste in accordance with JIS K5101-1-5, it is preferable to apply a load of 0.4 to 0.5 kN and to rotate the glass plate at a speed of 90 to 110 r / min, from the viewpoint of improving evaluation accuracy.

[0064] 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.

[0065] 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.

[0066] The recycled carbon black preferably contains 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 special removal operations, and rubber compositions containing such recycled carbon black are easy to manufacture. Furthermore, among metal atoms, recycled carbon black preferably contains Zn (zinc). The Zn in recycled carbon black originates from, for example, zinc oxide used as a vulcanization aid. The presence of Zn in recycled carbon black can be expected to suppress the deterioration of the physical properties of the rubber composition. From the viewpoint of the durability of the rubber composition, the Zn content in recycled carbon black is usually 0.01 to 5% by mass, preferably 0.01 to 4% by mass, and more preferably 0.01 to 3% by mass. In one embodiment, the Zn content in the recycled carbon black is preferably 2.5% by mass or less. The Cu content in the recycled carbon black is usually 0 to 0.5% by mass, and preferably 0.01 to 0.1% by mass. The Fe content in the recycled carbon black is usually 0.01 to 0.5% by mass, and preferably 0.01 to 0.3% by mass.

[0067] The recycled carbon black may contain sulfur (S). Since sulfur (S) is an element that is readily found in recycled carbon black, recycled carbon black containing sulfur (S) does not require any special removal operations, and rubber compositions containing such recycled carbon black are easy to manufacture. The sulfur (S) content in the recycled carbon black is usually preferably 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less. The sulfur (S) content may also be 0.5% by mass or more, or 1% by mass or more.

[0068] 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.

[0069] The recycled carbon black 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] The recycled carbon black preferably has an ash content of 20% by mass or less. If the ash content in the recycled carbon black exceeds 20% by mass, it may not be possible to obtain a tire with sufficient reinforcement. Considering the reinforcement of the tire, the ash content is preferably 10% by mass or less, more preferably 6% by mass or less, more preferably 5% by mass or less, more preferably 4% by mass or less, more preferably 3% by mass or less, more preferably 2% by mass or less, and particularly preferably 1% by mass or less. On the other hand, the ash content may be 0.5% by mass or more. That is, the carbon black of the present invention preferably has an ash content of 0.5% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 6% by mass or less, even more preferably 0.5% by mass or more and 5% by mass or less, even more preferably 0.5% by mass or more and 4% by mass or less, even more preferably 0.5% by mass or more and 3% by mass or less, even more preferably 0.5% by mass or more and 2% by mass or less, and particularly preferably 0.5% by mass or more and 1% by mass or less.

[0080] 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. As described above, the lower limit of the ash content of the recycled carbon black used in this embodiment may be 0.5% by mass. Here, in this specification, the ash content of carbon black is determined according to ASTM D8474 / D1506.

[0081] The recycled carbon black 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. Hereinafter, the oil absorption rate (OAN) of the recycled carbon black is determined according to ASTM D2414.

[0082] The recycled carbon black preferably has an oil absorption rate (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. Hereinafter, the oil absorption rate (COAN) of the compressed sample of recycled carbon black is determined according to ASTM D3493.

[0083] The recycled carbon black content is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, even more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of rubber component. When the recycled carbon black content is 5 parts by mass or more per 100 parts by mass of rubber component, it has a significant effect in improving the ratio of sustainable materials in rubber products to which the rubber composition is applied, and when it is 50 parts by mass or less, the fracture resistance of the rubber composition can be maintained more reliably.

[0084] [Silica] In the rubber composition of this embodiment, the filler 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.

[0085] As the silica, from the viewpoint of reducing environmental impact, silica derived from silicate plants is preferable. Such silicate plants exist, for example, in mosses, ferns, toadstools, cucurbitaceae, nettle family, gramineae plants, etc. Among these plants, gramineae plants are preferable. Among gramineae plants, from the viewpoint of easy availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferable. As the silica, furthermore, end materials of silicon wafers that are raw materials for semiconductors, silica produced by recycling silicon components from glass bottles, etc., and the like can also be mentioned.

[0086] The silica is not particularly limited, but for example, silica with a CTAB specific surface area (cetyltrimethylammonium bromide adsorption specific surface area) of 70 m ２ / g or more and 250 m ２ / g or less can be used. The CTAB specific surface area means a value measured in accordance with ASTM D3765-92. However, taking the adsorption cross-sectional area per molecule of cetyltrimethylammonium bromide on the silica surface as 0.35 nm ２ , the specific surface area (m ２ / g) calculated from the adsorption amount of CTAB is taken as the CTAB specific surface area. Also, the BET specific surface area of the silica can be 100 m ２ / g or more and 250 m ２ / g or less. The BET specific surface area is the specific surface area determined by the BET method, and in the present invention, it can be measured in accordance with ASTM D4820-93.

[0087] From the viewpoint of improving wear resistance, the silica content in the rubber composition is preferably 70 parts by mass or more, more preferably 75 parts by mass or more, and even more preferably 80 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of balancing wear resistance and workability during tire manufacturing, the silica content in the rubber composition is preferably 110 parts by mass or less, and more preferably 100 parts by mass or less, per 100 parts by mass of the rubber component. In other words, the rubber composition of this embodiment preferably contains 70 parts by mass or more, more preferably 75 parts by mass or more, and even more preferably 80 parts by mass or more, of silica per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of balancing wear resistance and workability during tire manufacturing, the filler preferably contains 110 parts by mass or less, and more preferably 100 parts by mass or less, of silica per 100 parts by mass of the rubber component.

[0088] -Silane Coupling Agent- When the rubber composition 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.

[0089] Furthermore, bioethanol can also be used as a raw material for silane coupling agents.

[0090] [Carbon black other than recycled carbon black] In the rubber composition of this embodiment, the filler may further contain carbon black other than recycled carbon black.

[0091] Other than this recycled carbon black, there are no particular restrictions, but it is preferable to use carbon black of high, medium, or low structure grades such as SAF, ISAF, IISAF, N339, HAF, FEF, GPF, and SRF, and especially SAF, ISAF, IISAF, N339, HAF, and FEF grades. Nitrogen adsorption specific surface area (N ２ (Measured in accordance with SA, JIS K6217-2:2001), 20m ２ Preferably 30 m ２ More preferably 50 m ２ More preferably 70 m ２ More preferably 250m / g or more, and also 250m ２ Preferably less than / g, 200m ２ More preferably less than / g, and 150m ２ A value of less than / g is even more preferable. These carbon blacks may be used individually or in combination of two or more types.

[0092] 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 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. Furthermore, the content of carbon black other than the recycled carbon black 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, per 100 parts by mass of the rubber component.

[0093] The proportion of silica in the total content of the silica, recycled carbon black, and carbon black other than recycled 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. In addition, the proportion of silica in the total content of the silica, recycled carbon black, and carbon black other than recycled carbon black may 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.

[0094] [Other Fillers] In addition to recycled carbon black, carbon black other than recycled carbon black, and silica, the fillers may also include other fillers such as clay, talc, calcium carbonate, and aluminum hydroxide. The amounts of these other fillers can be appropriately changed as long as they do not interfere with the effects of the present invention.

[0095] (Softener) The rubber composition of this embodiment preferably contains a softener. The softener preferably contains a resin. It is even more preferable that the resin contains C5 resin and C5C9 resin. A softener is a compounding agent that has the effect of softening the rubber composition, and specific examples include resins and liquid plasticizers.

[0096] In the rubber composition of this embodiment, the content of the softener is preferably 40 parts by mass or more per 100 parts by mass of the rubber component. When the content of the softener is 40 parts by mass or more per 100 parts by mass of the rubber component, a higher level of compatibility between wear resistance and workability during tire manufacturing can be achieved. From a similar viewpoint, the content of the softener is more preferably 45 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of suppressing a decrease in wear resistance, the content of the softener is preferably 60 parts by mass or less, and more preferably 50 parts by mass or less, per 100 parts by mass of the rubber component. In this invention, the content of the softener includes not only the content of the softener blended together with the rubber component, but also the content of the stretching oil pre-blended in the rubber component.

[0097] [Resin] The rubber composition 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 or WO2019 / 116656 can be used.

[0098] 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).

[0099] In the rubber composition, it is preferable that the resin includes both C5-based resin and C5C9-based resin. By including both C5-based resin and C5C9-based resin, it is possible to achieve both wear resistance and workability in the tire.

[0100] The resin content is preferably 10 parts by mass or more and 25 parts by mass or less per 100 parts by mass of rubber component. From the viewpoint of achieving both wear resistance and workability of the tire, the resin content is preferably 15 parts by mass or more, and more preferably 20 parts by mass or less per 100 parts by mass of rubber component.

[0101] C5 resin refers to C5 synthetic petroleum resin, and as such, the C5 fraction obtained by the thermal decomposition of naphtha in the petrochemical industry is used as AlCl ３ BF ３Examples include aliphatic petroleum resins obtained by polymerization using Friedel-Crafts type catalysts such as [catalyst name missing]. The C5 fraction typically includes olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene. Commercially available products can be used as the C5 resins, for example, the "Escolets® 1000 series" aliphatic petroleum resin manufactured by ExxonMobil Chemical, "Quinton® 100 series" aliphatic petroleum resins manufactured by Nippon Zeon Corporation, specifically "A100, B170, M100, R100", and "T-REZ RA100" manufactured by Tonen Chemical Co., Ltd.

[0102] C5C9 resin refers to C5C9 synthetic petroleum resin, and as an example of a C5C9 resin, it is made by combining petroleum-derived C5 and C9 fractions into AlCl ３ BF ３ Examples include solid polymers obtained by polymerization using Friedel-Crafts type catalysts, and more specifically, copolymers mainly composed of styrene, vinyltoluene, α-methylstyrene, indene, etc. As for the C5C9 resin, a resin with a small amount of C9 or higher components is preferred from the viewpoint of compatibility with rubber components. Here, "small amount of C9 or higher components" means that the amount of C9 or higher components in the total amount of resin is less than 50% by mass, preferably 40% by mass or less. As the C5C9 resin, commercially available products can be used, for example, the trade name "Quinton (registered trademark) G100B" (manufactured by Nippon Zeon Co., Ltd.), the trade name "ECR213" (manufactured by ExxonMobil Chemicals), the trade name "T-REZ RD104" (manufactured by Tonen Chemical Co., Ltd.), etc.

[0103] In the rubber composition, the ratio of the content of C5 resin to the content of C5C9 resin is preferably 0.1 or more and 1.0 or less. A ratio of 0.1 or more and 1.0 or less for C5 resin to C5C9 resin results in excellent workability. From the viewpoint of workability, the ratio of the content of C5 resin to the content of C5C9 resin is more preferably 0.3 or more, even more preferably 0.5 or more, even more preferably 0.7 or less, and even more preferably 0.6 or less.

[0104] The resin may contain other resins in addition to C5 resins and C5C9 resins. Examples of other resins include C9 resins, dicyclopentadiene resins, terpene phenol resins, terpene resins, rosin resins, and alkylphenol resins.

[0105] C9 resins are resins obtained by polymerizing C9 aromatic compounds with 9 carbon atoms, primarily monomers such as vinyltoluene, alkylstyrene, and indene, which are by-products of the thermal decomposition of naphtha in the petrochemical industry, along with basic petrochemical raw materials such as ethylene and propylene. Specific examples of C9 fractions obtained by the thermal decomposition of naphtha include vinyltoluene, α-methylstyrene, β-methylstyrene, γ-methylstyrene, o-methylstyrene, p-methylstyrene, and indene. These C9 resins can be obtained by copolymerizing a mixture of C8 fractions such as styrene, C10 fractions such as methylindene and 1,3-dimethylstyrene, and even naphthalene, vinylnaphthalene, vinylanthracene, and p-tert-butylstyrene as raw materials, using, for example, a Friedel-Crafts type catalyst. Furthermore, the C9 resin may be a modified petroleum resin modified with compounds having hydroxyl groups, unsaturated carboxylic acid compounds, etc. Furthermore, commercially available products can be used as the C9 resin. For example, unmodified C9 petroleum resins include the product names "Nisseki Neopolymer (registered trademark) L-90", "Nisseki Neopolymer (registered trademark) 120", "Nisseki Neopolymer (registered trademark) 130", and "Nisseki Neopolymer (registered trademark) 140" (manufactured by JX Nippon Oil & Energy Corporation).

[0106] Dicyclopentadiene resin is a petroleum resin manufactured primarily from dicyclopentadiene, which is obtained by dimerizing cyclopentadiene. Commercially available dicyclopentadiene resins can be used, for example, "1105, 1325, and 1340" from the "Quinton® 1000 series," a alicyclic petroleum resin manufactured by Nippon Zeon Co., Ltd.

[0107] Terpene phenol resins can be obtained, for example, by reacting terpenes with various phenols using a Friedel-Crafts type catalyst, or by further condensation with formalin. There are no particular restrictions on the terpenes used as raw materials, but monoterpene hydrocarbons such as α-pinene and limonene are preferred, those containing α-pinene are more preferred, and α-pinene is particularly preferred. Commercially available terpene phenol resins can be used, for example, the trade names "Tamanol 803L" and "Tamanol 901" (manufactured by Arakawa Chemical Industries, Ltd.), the trade names "YS Polystar® U" series, "YS Polystar® T" series, "YS Polystar® S" series, "YS Polystar® G" series, "YS Polystar® N" series, "YS Polystar® K" series, and "YS Polystar® TH" series (manufactured by Yasuhara Chemical Co., Ltd.).

[0108] Terpene resins are solid resins obtained by polymerizing turpentine oil, which is obtained simultaneously when rosin is obtained from pine trees, or polymer components separated therefrom, using a Friedel-Crafts type catalyst. Examples include β-pinene resin and α-pinene resin. Commercially available terpene resins can be used, such as the "YS Resin" series (PX-1250, TR-105, etc.) manufactured by Yasuhara Chemical Co., Ltd., and the "PicoLite" series (A115, S115, etc.) manufactured by Hercules Corporation.

[0109] Rosin resin is the residue remaining after distilling turpentine essential oil from balsams such as pine resin (pine sap) collected from pine trees. It is a natural resin mainly composed of rosin acid (abietic acid, palastic acid, isopimal acid, etc.), as well as modified resins and hydrogenated resins obtained by processing these through modification, hydrogenation, etc. Examples include natural resin rosin, its polymerized rosin and partially hydrogenated rosin; glycerin ester rosin, its partially hydrogenated rosin, fully hydrogenated rosin and polymerized rosin; and pentaerythritol ester rosin, its partially hydrogenated rosin and polymerized rosin. Examples of natural resin rosin include gum rosin contained in raw pine resin and tall oil, tall oil rosin, and wood rosin. As the rosin resin, commercially available products can be used, for example, "NeoTol 105" (manufactured by Harima Chemicals Co., Ltd.), "SN Tack 754" (manufactured by Sunopco Co., Ltd.), "Lime Resin No. 1", "Pensel A" and "Pensel AD" (manufactured by Arakawa Chemical Industries, Ltd.), "Polypail" and "Pentalin C" (manufactured by Eastman Chemical Co., Ltd.), and "Hi-Rosin (registered trademark) S" (manufactured by Taisha Matsu Seiyu Co., Ltd.).

[0110] Alkylphenol resins can be obtained, for example, by a catalytic condensation reaction between alkylphenol and formaldehyde. Commercially available alkylphenol resins can be used, such as "Hitanol 1502P" (alkylphenol formaldehyde resin, manufactured by Hitachi Chemical Co., Ltd.), "Tackirol 201" (alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), "Tackirol 250-I" (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), "Tackirol 250-III" (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), and "R7521P", "SP1068", "R7510PJ", "R7572P", and "R7578P" (manufactured by SI GROUP INC.).

[0111] The resin contained in the rubber composition may be hydrogenated.

[0112] [Liquid Plasticizer] The softener preferably contains a liquid plasticizer. Preferably, the softener contains a liquid plasticizer in addition to the resin, and more preferably, the softener contains a liquid plasticizer in addition to the C5 resin and the C5C9 resin. The inclusion of a liquid plasticizer in the rubber composition improves workability during tire manufacturing. Here, the liquid plasticizer is liquid at 25°C (room temperature).

[0113] Examples of liquid plasticizers include oils. These oils are not limited to petroleum-based softeners such as aromatic oils, paraffinic oils, and naphthenic oils; and plant-based softeners such as palm oil, castor oil, cottonseed oil, and soybean oil. Among these, petroleum-based softeners such as aromatic oils, paraffinic oils, and naphthenic oils are preferred.

[0114] From the viewpoint of improving wear resistance, the liquid plasticizer content is preferably 5 parts by mass or more, and more preferably 9 parts by mass or more, per 100 parts by mass of rubber component. Furthermore, from the viewpoint of suppressing a decrease in handling stability, the liquid plasticizer content is preferably 30 parts by mass or less, and more preferably 26 parts by mass or less, per 100 parts by mass of rubber component.

[0115] (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, antioxidants, zinc oxide, sulfur, vulcanization accelerators, waxes, stearic acid, calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica and other fillers, 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.

[0116] (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 and each component including recycled carbon black using a kneader such as a Banbury mixer, roll mixer, or internal mixer. Alternatively, the 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 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.

[0117] (Applications) The rubber composition of this embodiment can be used for the treads of motorcycle tires.

[0118] <Motorcycle Tire> The motorcycle tire of this embodiment (hereinafter sometimes simply referred to as "tire") comprises a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, wherein the tread portion is divided in the tire width direction by a center portion including the tire equatorial plane and a pair of shoulder portions including the tread ends, wherein at least one of the tread rubber of the center portion or the tread rubber of the shoulder portions is made of the tread rubber composition of the motorcycle tire of this embodiment described above, the rubber component of the rubber composition in the tread rubber of the center portion includes at least one selected from styrene-butadiene rubber and butadiene rubber, the rubber composition in the tread rubber of the center portion further includes a softener, the softener includes a resin, and the resin includes C5 resin and C5C9 resin. The above motorcycle tire achieves both wear resistance and workability during tire manufacturing. Furthermore, because the above-mentioned motorcycle tires use the same rubber tread composition as the motorcycle tires described above, the proportion of sustainable materials has been improved.

[0119] In the above-described motorcycle tire, the rubber composition of the tread rubber in the center section contains at least one selected from styrene-butadiene rubber and butadiene rubber as a rubber component, thereby providing sufficient fracture characteristics. Furthermore, the inclusion of recycled carbon black in the rubber composition of at least one of the tread rubber in the center section or the tread rubber in the shoulder section improves wear resistance. Additionally, the rubber composition of the tread rubber in the center section contains a softening agent, and the softening agent contains both C5 resin and C5C9 resin, so that the C5 resin acts as an immiscibility with the polymer and migrates easily to the surface. Therefore, the motorcycle tire of this embodiment can achieve both wear resistance and ease of workability during tire manufacturing.

[0120] (Tire Structure) First, the structure of the motorcycle tire of this embodiment will be described with reference to Figure 2. The motorcycle tire 101 of this embodiment comprises a pair of bead portions 103, a pair of sidewall portions 104, and a tread portion 102 connected to both sidewall portions 104. The tread portion 102 is divided in the tire width direction by a center portion 109 including the tire equatorial plane 111 and a pair of shoulder portions 110 including the tread ends 112.

[0121] Each bead portion 103 typically has a bead core 105, and one or more carcass layers 106 are provided to extend in a toroidal shape between a pair of bead cores 105. The carcass layer 106 is made of multiple carcass cords covered with rubber.

[0122] The sidewall portion 104 extends radially outward from the bead portion 103 on the side of the tire, reinforcing and protecting the side.

[0123] The tread portion 102 extends across both sidewall portions 104. In the motorcycle tire 101 of this embodiment, the tread portion 102 uses a split tread which is divided into a center portion 109 and two shoulder portions 110 that sandwich the center portion 109. The split tread is divided into at least three parts by the center portion 109 which includes the tire equatorial plane 111 and a pair of shoulder portions 110 which include the tread end 112. The split tread may have further parts between the center portion 109 and the shoulder portions 110, or the center portion 109 may be divided into multiple parts. For example, the tread portion 102 may be divided into a first shoulder portion, a second shoulder portion, a first center portion, a second center portion, a third shoulder portion, and a fourth shoulder portion, starting from the tread end 112, with the center portion 19 and the shoulder portions 110 being divided accordingly. The segmented tread is preferably divided into three sections by a center section 109 and a pair of shoulder sections 110. The tire equator is the line of latitude of the tire passing through the center in the tire width direction, and the surface in the circumferential direction of the tire that includes the tire equator is called the tire equatorial surface 111.

[0124] The center portion 109 is more specifically defined as having a curved length (L) in the width direction of the tread surface of the center portion. Ｃ ) is the maximum length (L) of the curved length in the width direction of the entire tread surface. Ｔ (=L ｃ +L ｓ +L ｓ It is preferably 30-60% of the tread surface in the center section (L Ｃ ) is the maximum length (L) of the curved length in the width direction of the entire tread surface. Ｔ Abrasion resistance can be ensured if the ratio is 30% to 60% of the total.

[0125] The widthwise curve length (L) of the tread surface of the shoulder portion 110 Ｓ The shoulder portion 110 on one side may be different from the other shoulder portion 110, but it is generally preferable that they be the same, and the widthwise curve length of the shoulder portion 110 (one side) is L ＴIt is preferable that the concentration is (100 - Lc) / 2%.

[0126] Hereinafter, the rubber constituting the tread portion 102 may be referred to as the tread rubber. The tread rubber 108 of the shoulder portion is the rubber constituting the shoulder portion and may be simply referred to as the "shoulder rubber." The tread rubber 107 of the center portion is the rubber constituting the center portion and may be simply referred to as the "center rubber."

[0127] (Tread Rubber) In the motorcycle tire of this embodiment, at least one of the tread rubber in the center portion or the tread rubber in the shoulder portion is made of the above-described tread rubber composition for motorcycle tires.

[0128] In this embodiment, the storage modulus of the tread rubber in the center of the motorcycle tire is preferably 12 MPa or more, and more preferably 13 MPa or more, from the viewpoint of wear resistance. Furthermore, from the viewpoint of handling stability, the storage modulus of the tread rubber in the center is preferably 15 MPa or less, and more preferably 14 MPa or less. The range of the storage modulus of the tread rubber in the center at 60°C is preferably 12 MPa or more and 15 MPa or less, and more preferably 13 MPa or more and 14 MPa or less.

[0129] Furthermore, in the motorcycle tire of this embodiment, the storage modulus of the tread rubber in the shoulder portion at 60°C is preferably 5.0 MPa or more, and more preferably 7.0 MPa or more, from the viewpoint of wear resistance. Also, from the viewpoint of handling stability, the storage modulus of the tread rubber in the shoulder portion at 60°C is preferably 10 MPa or less, and more preferably 8.0 MPa or less. The range of the storage modulus of the tread rubber in the shoulder portion at 60°C is preferably 5.0 MPa or more and 10 MPa or less, and more preferably 7.0 MPa or more and 8.0 MPa or less.

[0130] Furthermore, the storage modulus of the tread rubber in the center section and the tread rubber in the shoulder section at 60°C can be measured using a viscoelasticity measuring device under the conditions of 60°C, a strain of 1.0%, and a frequency of 52 Hz.

[0131] In the motorcycle tire of this embodiment, it is preferable that the ratio of the storage modulus of elasticity of the tread rubber in the center section at 60°C to the storage modulus of elasticity of the tread rubber in the shoulder section at 60°C (storage modulus of elasticity of the tread rubber in the center section / storage modulus of elasticity of the tread rubber in the shoulder section) exceeds 1.72. When the ratio of the storage modulus of elasticity of the tread rubber in the center section at 60°C to the storage modulus of elasticity of the tread rubber in the shoulder section at 60°C exceeds 1.72, a tire with a higher degree of balance between wear resistance and workability is obtained. From a similar viewpoint, it is more preferable that the ratio of the storage modulus of elasticity of the tread rubber in the center section at 60°C to the storage modulus of elasticity of the tread rubber in the shoulder section at 60°C is 1.75 or higher, and even more preferable that it is 1.8 or higher. Furthermore, the upper limit of the ratio of storage moduli may be 2.0 or lower, for example, it is preferable that it is greater than 1.72 and 2.0 or lower, more preferable that it is 1.75 or higher and 2.0 or lower, and even more preferable that it is 1.8 or higher and 2.0 or lower.

[0132] (Rubber Composition) In the tire of this embodiment, the rubber composition constituting at least one of the tread rubber of the center portion or the tread rubber of the shoulder portion is the tread rubber composition for the motorcycle tire of this embodiment, wherein the rubber component of the rubber composition in the tread rubber of the center portion includes at least one selected from styrene-butadiene rubber and butadiene rubber, and the rubber composition in the tread rubber of the center portion further includes a softener, the softener includes a resin, and the resin includes C5 resin and C5C9 resin. The components that the rubber composition constituting at least one of the tread rubber of the center portion or the tread rubber of the shoulder portion includes and may include are the same as the rubber components, fillers, softeners, and other components that the tread rubber composition for the motorcycle tire described above includes and may include, and the descriptions in those sections of the tread rubber composition for the motorcycle tire described above are used with reference.

[0133] (Method for manufacturing motorcycle tires) The motorcycle tires of this embodiment are obtained by molding and vulcanizing a rubber composition. The method for manufacturing the rubber composition is not particularly limited, but for example, it can be manufactured by mixing the rubber components, fillers and softeners described above with various components as needed, and then kneading, heating, extruding, etc. Furthermore, the obtained rubber composition can be vulcanized to produce vulcanized rubber.

[0134] There are no particular restrictions on the mixing conditions, and various conditions such as the input volume of the mixing device, the rotation speed of the rotor, the ram pressure, as well as the mixing temperature, mixing time, and the type of mixing device can be appropriately selected according to the purpose. Examples of mixing devices typically used for mixing rubber compositions include Banbury mixers, intermixes, kneaders, and roll mixers.

[0135] There are no particular restrictions on the heat treatment conditions, and various conditions such as heat treatment temperature, heat treatment time, and heat treatment equipment can be appropriately selected according to the purpose. Examples of such heat treatment equipment include heat treatment roll machines commonly used for heat treatment of rubber compositions.

[0136] There are no particular restrictions on the extrusion conditions, and various conditions such as extrusion time, extrusion speed, extrusion equipment, and extrusion temperature can be appropriately selected according to the purpose. Examples of extrusion equipment include extruders typically used for extruding rubber compositions. The extrusion temperature can be determined as appropriate.

[0137] There are no particular restrictions on the equipment, methods, or conditions used for vulcanization, and they can be appropriately selected according to the purpose. Typical vulcanization equipment includes mold vulcanizers used for vulcanizing rubber compositions. The vulcanization temperature is typically around 100 to 190°C.

[0138] The motorcycle tire of this embodiment may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, depending on the type of tire to be applied, or by molding a semi-vulcanized rubber that has undergone a preliminary vulcanization process and then performing full vulcanization. The motorcycle 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.

[0139] (Applications) The motorcycle tire of this embodiment may be a front tire or a rear tire, but in this invention, wear resistance and workability during tire manufacturing can be achieved at a high level, so the effects of the present invention are particularly easily manifested when applied to a rear tire. The type of motorcycle is not particularly limited and can be appropriately selected according to the purpose. Examples of motorcycle types include racing motorcycles, motorcycles for general public roads, on-road motorcycles, and off-road motorcycles. Among these, motorcycles for general public roads and on-road motorcycles are preferred as motorcycles in which the effects of the present invention are particularly easily manifested, with motorcycles for general public roads being more preferred.

[0140] 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.

[0141] <Comparison of New Carbon Black and Recycled Carbon Black> Two types of rubber compositions having the compound compositions shown in Table 1 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 according to JIS K6251:2004, 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 1. A higher value indicates better fracture resistance, i.e., better crack resistance.

[0142]

[0143] *11 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *12 Carbon black: New carbon black, manufactured by Asahi Carbon, product name "N550", nitrogen adsorption specific surface area (N ２ SA) = 40m ２ / g, OAN (Oil Absorption) = 121 mL / 100 g *13 Recycled carbon black: Enrestec, product name "PB365", ash content = 17% by mass *14 Anti-aging agent: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrack 6C" *15 Anti-aging agent: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrack 224" *16 Oil: ENEOS, product name "A / Omix" *17 Fatty acid: Miyoshi Oil & Fat Co., Ltd., product name "MXST" *18 Other chemicals: Total amount of sulfur, vulcanization accelerator, resin, and wax, same ratio in each rubber composition

[0144] Table 1 shows that replacing virgin carbon black (new carbon black) with recycled carbon black among the various materials contained in the rubber composition reduces the tensile strength before and after thermal degradation.

[0145] <Evaluation of recycled carbon black (1)> The physical properties of carbon black were evaluated using the following method.

[0146] (Grind Gauge Measurement) A mixture was obtained by mixing 3.75 g of zinc oxide, 0.20 g of the carbon black under test, and 2.00 mL of epoxidized soybean oil. The obtained mixture was kneaded for 5 to 10 minutes to form a paste, and the sample paste was prepared. In accordance with JIS K5101-1-5, the paste was 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. The grind gauge used had a range of 0 to 25 μm. 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 2.

[0147] (Specific surface area of ​​nitrogen adsorption (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.

[0148] (Elemental Analysis) The content of zinc (Zn), copper (Cu), and iron (Fe) was confirmed by X-ray fluorescence analysis (XRF).

[0149] (Ash content) The ash content of the carbon black sample was measured according to ASTM D8474 and D1506.

[0150]

[0151] [Preparation and Evaluation of Rubber Compositions (1)] Rubber compositions were prepared using a standard Banbury mixer according to the formulations shown in Table 3. Other chemicals included antioxidants, oils, fatty acids, sulfur, and vulcanization accelerators, and the same types and amounts were added to rubber composition 3 and rubber composition 4. Commercially available chemicals commonly used in the preparation of rubber compositions were used. The amounts added were the amounts commonly used in the preparation of rubber compositions. The obtained rubber compositions were evaluated for post-degradation high-temperature tensile strength and post-thermal degradation crack resistance using the following methods.

[0152] (High-temperature tensile strength after degradation) Each rubber composition was vulcanized at 145°C for 33 minutes to obtain vulcanized rubber. The obtained vulcanized rubber was subjected to thermal degradation at 100°C for 48 hours in an air atmosphere. A tensile test was performed at 100°C in accordance with JIS K6251:2017, and the tensile strength was measured. With the tensile strength of the test piece of rubber composition 3 set to 100, the high-temperature tensile strength (fracture resistance) after degradation was expressed as an index using the following formula: High-temperature tensile strength index after degradation = (Tensile strength of the test piece / Tensile strength of the test piece of rubber composition 3) × 100 A higher high-temperature tensile strength index after degradation indicates that the vulcanized rubber is less prone to fracture and has superior post-degradation performance (fracture resistance).

[0153] (Crack resistance after thermal degradation) The rubber composition to be tested was pre-treated by thermal degradation at 100°C for 24 hours in an air atmosphere. A strip-shaped test piece was prepared from the rubber composition with a 0.5 mm hole drilled in the lengthwise direction in the center. A dc / dn test was performed using this test piece (using a Shimadzu Servopulsa, 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] after 1950 cycles was measured). ２ The crack propagation rate was calculated when the common logarithm of [ ] was 3.9. In the crack propagation rate obtained by the above process, the compounding data of rubber composition 3 was used as a control (index value 100), and the values ​​were normalized by the reciprocal of the compounding data for each example. A larger index value indicates a lower crack propagation rate and superior crack resistance.

[0154]

[0155] *31 Natural rubber: RSS#3 *32 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *33 New carbon black: Manufactured by Asahi Carbon, N550 *34 Recycled carbon black 1: Same as Table 1 *35 Recycled carbon black 2: Same as Table 1

[0156] Tables 2 and 3 show that rubber composition 3, which uses recycled carbon black with a particle size of 20 μm or less for the third largest particle, exhibits better high-temperature tensile strength after degradation compared to rubber composition 4, which uses recycled carbon black with a particle size of more than 20 μm for the third largest particle. Furthermore, rubber composition 3 also showed better crack resistance after thermal degradation compared to rubber composition 4.

[0157] Based on these evaluations, it can be seen that by using recycled carbon black in which the third largest particle size measured with a grind gauge is 20 μm or less, it is possible to contribute to improved sustainability while significantly suppressing adverse effects on tire rubber properties and maintaining performance.

[0158] <Evaluation of Recycled Carbon Black (2)> Carbon black (CB) and styrene-butadiene rubber with different ash content, Zn content, and S content were kneaded according to the formulations shown in Table 4 below to prepare rubber compositions for each example. Each rubber composition was evaluated using the evaluation method described below. The evaluation results are shown in Table 4.

[0159] (Amount of components in carbon black) The amounts of components such as Zn, Fe, and S in carbon black were measured by X-ray fluorescence analysis.

[0160] (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 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

[0161] (Tensile Strength) The rubber compositions of the standard example and each example were 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 tensile strength of the standard example specimen was set to 100, and the tensile strength was expressed as an index using the following formula: Tensile Strength Index = (Tensile Strength of Specimens Other Than the Standard Example / Tensile Strength of Specimen of the Standard Example) × 100 A larger index indicates that the vulcanized rubber is less prone to breakage and has superior tensile strength.

[0162] (Viscoelasticity) Viscoelasticity tests were conducted using TA Instruments' "ARES-G2" under the conditions of a frequency of 15 Hz, shear strain of 10%, and temperature of 50°C to measure the storage modulus (G') of the rubber composition. The evaluation results were indexed with a standard example 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.

[0163]

[0164] *41 SBR: Styrene-butadiene rubber, product name "#1500" *42 CB3: Carbon Black 3, recycled carbon black equivalent to N330 *43 CB4: Carbon Black 4, recycled carbon black equivalent to N330 *44 CB5: Carbon Black 5, recycled carbon black equivalent to N330 *45 CB6: Carbon Black 6, new carbon black equivalent to N330

[0165] Table 4 shows that when carbon black with reduced Zn content is applied to a rubber composition, the deterioration of the rubber composition's physical properties is suppressed.

[0166] <Tire Evaluation> (Preparation and Measurement of Rubber Composition in the Tread Rubber of the Shoulder Section) The rubber composition for the tread rubber of the shoulder section (shoulder rubber rubber composition) was prepared using a standard Banbury mixer according to the compound formulation shown in Table 5. In Table 5, "Total Amount of Softener" refers to the sum of the amount of softener as a compounding component and the oil spread amount of the rubber component.

[0167] [Measurement of Rubber Composition in the Tread Rubber of the Shoulder Section] -Storage Modulus- The storage modulus of the rubber composition in the tread rubber of the shoulder section was measured using a viscoelasticity measuring device (manufactured by Ueshima Seisakusho Co., Ltd.) at a temperature of 60°C, a frequency of 52 Hz, and a strain of 1.0%. The measurement results are shown in Table 5.

[0168]

[0169] *51 SBR: Styrene-butadiene rubber, manufactured by ENEOS Material, emulsion polymerized styrene-butadiene rubber, trade name "HP755B", containing 37.5 parts by mass of drawable oil per 100 parts by mass of rubber component, the middle section shows the content of the rubber component and the bottom section shows the content of the drawable oil. *52 BR: Butadiene rubber, manufactured by ENEOS Material, product name "BR01" *53 Carbon black, manufactured by Asahi Carbon Co., Ltd., product name "ASAHI #107" *54 Silica: manufactured by Tosoh Silica Co., Ltd., product name "NipSeal AQ" *55 Oil: manufactured by JX Nippon Oil & Energy Corporation, product name "A / O MIX" *56 C5C9 resin: manufactured by ENEOS, product name "T-REZ RD104" *57 Coupling agent: manufactured by Shin-Etsu Chemical Co., Ltd., product name "ABC-856" *58 Other chemicals: total amount including wax, anti-aging agent and workability improver *59 Vulcanization package: total amount including vulcanization accelerator, sulfur and stearic acid

[0170] (Preparation and Measurement of Rubber Composition in the Center Tread Rubber) The rubber compositions (center rubber rubber compositions) for the center tread rubber of Reference Examples 1 to 4 were prepared using a standard Banbury mixer according to the formulations shown in Table 6. The formulations and evaluation results are shown in Table 6. In Table 6, "Total Amount of Softener" refers to the sum of the amount of softener as a compounding component and the oil spread amount of the rubber component.

[0171] [Measurement of Rubber Composition in the Center Tread Rubber] -Storage Modulus- The storage modulus of the rubber composition in the center tread rubber was measured using a viscoelasticity measuring device (manufactured by Ueshima Seisakusho Co., Ltd.) at a temperature of 60°C, a frequency of 52 Hz, and a strain of 1.0%. Furthermore, from the measurement results of the storage modulus of the rubber composition in the shoulder tread rubber and the center tread rubber, the ratio of the storage modulus of the center tread rubber at 60°C to the storage modulus of the shoulder tread rubber at 60°C (storage modulus (center) / storage modulus (shoulder)) was calculated. The measurement results and calculation results are shown in Table 6.

[0172] (Tire Manufacturing) Using each of the prepared rubber compositions, a motorcycle tire (size: 180 / 55ZR17) was manufactured by conventional methods, comprising a pair of bead sections, a pair of sidewall sections, and a tread section connected to both sidewall sections, wherein the tread section is divided into three parts in the tire width direction by a center section including the tire equator and a pair of shoulder sections including the tread ends.

[0173] (Evaluation of manufactured tires) The workability and wear resistance during tire manufacturing were evaluated using the following method.

[0174] -Workability- The adhesion strength between the unvulcanized rubber composition and the metal at 90°C was measured using a tack meter and expressed as an index with the reciprocal of the adhesion strength in Reference Example 1 set to 100. A larger index indicates lower adhesion strength and better workability.

[0175] - Wear Resistance - On a paved test course, a test rider drove the vehicle for 3500 km at 80 km / h. After the run, the amount of tread remaining was measured, and the wear resistance of the tire was evaluated based on the amount of tread remaining. The evaluation results from Reference Example 1 are expressed as an index with 100. A higher index indicates better wear resistance.

[0176]

[0177] *60 C5 resin: Manufactured by ENEOS, product name “T-REZ RA100”

[0178] Table 6 shows that tires containing styrene-butadiene rubber and butadiene rubber, as well as C5C9 resin and C5 resin, can achieve both workability and wear resistance.

[0179] According to the present invention, it is possible to provide a rubber composition for motorcycle tire treads that can increase the proportion of sustainable materials while maintaining the physical properties of a tire without sustainable materials. Furthermore, according to the present invention, it is possible to provide a tire with an increased proportion of sustainable materials while maintaining the physical properties of a tire without sustainable materials.

[0180] 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 101: Motorcycle tire 102: Tread section 103: Bead section 104: Sidewall section 105: Bead core 106: Carcass layer 107: Center tread rubber 108: Shoulder tread rubber 109: Center section 110: Shoulder section 111: Tire equatorial plane 112: Tread edge

Claims

1. A rubber composition for motorcycle tire treads comprising a rubber component and a filler, wherein the filler contains recycled carbon black, and the recycled carbon black, when measured with a grind gauge, 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 the lines with a length of 10 mm or more is 20 μm or less.

2. The rubber composition for the tire tread of a motorcycle tire 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 for tire treads of motorcycle tires 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 for motorcycle tire treads according to claim 1, wherein the recycled carbon black contains one or more metal atoms selected from the group consisting of Zn, Cu, and Fe.

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

6. The rubber composition for motorcycle tire treads according to claim 5, wherein the recycled carbon black has a Zn content of 2.5% by mass or less.

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

8. A tire comprising a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, wherein the tread portion is divided in the tire width direction by a center portion including the tire equator and a pair of shoulder portions including the tread ends, wherein at least one of the tread rubber of the center portion or the tread rubber of the shoulder portions is made of the motorcycle tire tread rubber composition described in claim 1, the rubber component of the rubber composition in the tread rubber of the center portion includes at least one selected from styrene-butadiene rubber and butadiene rubber, the rubber composition in the tread rubber of the center portion further includes a softener, and the softener includes a resin, the resin including C5 resin and C5C9 resin, for a motorcycle tire.

9. The motorcycle tire according to claim 8, wherein the ratio of the storage modulus of the tread rubber in the center portion at 60°C to the storage modulus of the tread rubber in the shoulder portion at 60°C is greater than 1.72.

Images