Rubber composition, tire internal member, and tire

Abstract

The present invention addresses the problem of providing a rubber composition that maintains air permeability resistance while improving the proportion of sustainable materials, the post-degradation high-temperature tensile strength, and the post-degradation crack propagation resistance. The means for solving the aforementioned problem is a rubber composition that contains a rubber component and recycled carbon black, the recycled carbon black having three or more lines that have a length of 10 mm or more as measured by a grinding gauge and being such that the particle size of the third-largest particle among the particles that yield the lines having a length of 10 mm or more is 20 μm or less, and the rubber component containing butyl rubber.

Description

Rubber composition, tire internal components, and tire

[0001] This invention relates to a rubber composition, an internal component of a tire, and a tire.

[0002] Conventionally, various rubber compositions have been used in rubber products such as tires, rubber tracks, and seismic isolation rubber. Furthermore, in order to ensure the strength of these rubber products, carbon black is usually added as a reinforcing filler to the rubber compositions that serve as their raw materials.

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

[0004] European Patent Application Publication No. 3427975

[0005] However, if recycled carbon black is used as a reinforcing filler instead of unused carbon black to increase the proportion of sustainable materials in rubber products, the physical properties of the rubber composition may deteriorate depending on the condition of the recycled carbon black. For example, in internal components of tires, high-temperature tensile strength after degradation, crack propagation resistance after degradation, and air permeability resistance are required, but these properties may deteriorate. Therefore, it is necessary to maintain air permeability while improving the proportion of sustainable materials, high-temperature tensile strength after degradation, and crack propagation resistance after degradation.

[0006] Therefore, the present invention aims to solve the problems of the above-mentioned prior art and provide a rubber composition in which the proportion of sustainable materials, high-temperature tensile strength after degradation, and crack propagation resistance after degradation are improved while maintaining air permeability resistance. Furthermore, the present invention aims to provide tire internal components and tires in which the proportion of sustainable materials, high-temperature tensile strength after degradation, and crack propagation resistance after degradation are improved while maintaining air permeability resistance.

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

[0008] [1] A rubber composition comprising a rubber component and recycled carbon black, wherein the recycled carbon black is such that, when measured with a grind gauge, it has three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles that give rise to the lines with a length of 10 mm or more is 20 μm or less, and the rubber component comprises butyl rubber.

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

[0010] [3] The rubber composition according to [1] or [2], wherein, in the measurement using the grind gauge, the applied load is set to 0.4 to 0.5 kN and the rotation speed of the glass plate is set to 90 to 110 r / min in accordance with JIS K5101-1-5, and the paste of the recycled carbon black is prepared.

[0011] [4] The rubber composition 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 according to [4], wherein the recycled carbon black comprises Zn.

[0013] [6] The rubber composition according to [5], wherein the recycled carbon black has a Zn content of 0% by mass or more and 3.0% by mass or less.

[0014] [7] The rubber composition according to any one of [1] to [6], wherein the recycled carbon black has an ash content of 20.0% by mass or less.

[0015] [8] The rubber composition according to any one of [1] to [7], wherein the rubber component further comprises isoprene rubber.

[0016] [9] The rubber composition according to any one of [1] to [8], wherein the butyl rubber content is 70 to 95 parts by mass per 100 parts by mass of the rubber component.

[0017]

[10] The rubber composition according to any one of [1] to [9], further comprising oil.

[0018]

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

[10] , further comprising a phenolic resin.

[0019]

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

[11] , further comprising 10 parts by mass or less of rubber powder and recycled rubber per 100 parts by mass of the rubber component.

[0020]

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

[12] , further comprising clay.

[0021]

[14] An internal tire component comprising the rubber composition described in any of [1] to

[13] .

[0022]

[15] A tire comprising the tire internal components described in

[14] .

[0023] According to the present invention, it is possible to provide a rubber composition in which the proportion of sustainable materials, high-temperature tensile strength after degradation, and crack propagation resistance after degradation are improved while maintaining air permeability resistance. Furthermore, according to the present invention, it is possible to provide tire internal components and tires in which the proportion of sustainable materials, high-temperature tensile strength after degradation, and crack propagation resistance after degradation are improved while maintaining air permeability resistance.

[0024] This is an explanatory diagram illustrating an example of measurement results using a grind gauge. This is a cross-sectional view of one embodiment of the tire of the present invention.

[0025] The rubber composition, tire internal components, and tire of the present invention will be described in detail below based on their embodiments.

[0026] 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.

[0027] 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.

[0028] <Rubber Composition> The rubber composition of this embodiment comprises a rubber component and recycled carbon black, wherein 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 give rise to the lines with a length of 10 mm or more is 20 μm or less, and the rubber component is characterized by containing butyl rubber. In the rubber composition of this embodiment, since the recycled carbon black is a material derived from recycled resources, by blending recycled carbon black into the rubber composition, the proportion of sustainable materials in the rubber product to which the rubber composition is applied can be improved. However, as described above, if recycled carbon black is blended instead of ordinary unused carbon black, the physical properties of the rubber composition may deteriorate. In the rubber composition of this embodiment, while suppressing and maintaining the decrease in air permeability resistance by using butyl rubber, the recycled carbon black is such that, when measured with a grind gauge, there are three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles that give rise to such lines is 20 μm or less. As a result, the dispersibility of the recycled carbon black in the rubber composition is good, and the durability of the rubber composition, in particular the high-temperature tensile strength after degradation and the crack propagation resistance after degradation, is improved. Therefore, the rubber composition of the present invention maintains air permeability resistance while improving the proportion of sustainable materials, high-temperature tensile strength after degradation, and crack propagation resistance after degradation.

[0029] (Rubber component) The rubber composition of this embodiment contains a rubber component, which provides rubber elasticity to the rubber 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.

[0030] 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.

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

[0032] As the rubber component, the rubber derived from the biomass resource and the rubber derived from the recycled resource are preferable. Here, the ratio of the monomer component derived from the biomass resource in 100 mol% of the monomer components constituting the rubber derived from the biomass resource is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%. Also, the ratio of the monomer component derived from the recycled resource in 100 mol% of the monomer components constituting the rubber derived from the recycled resource is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%.

[0033] 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 1,500,000 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 measured value by, for example, gel permeation chromatography (GPC).

[0034] In the rubber composition of the present embodiment, the rubber component includes butyl rubber. Butyl rubber is a rubber obtained by copolymerizing isobutylene with isoprene and is also called isobutylene-isobutylene copolymer (IIR). Butyl rubber has extremely low gas permeability and can contribute to maintaining air permeation resistance. The butyl rubber may be unmodified or modified. Examples of the modified butyl rubber (modified butyl rubber) include halogenated butyl rubbers such as chlorinated butyl rubber and brominated butyl rubber.

[0035] The content of butyl rubber is preferably 70 to 95 parts by mass in 100 parts by mass of the rubber component. Butyl rubber has extremely low gas permeability. When the rubber component contains 70 to 95 parts by mass of butyl rubber in 100 parts by mass of the rubber component, it can suppress the decrease in high-temperature tensile strength after deterioration and the crack growth resistance after deterioration, while maintaining the air permeability resistance of the rubber composition. From the viewpoints of elongation at break (EB) after heat deterioration and maintenance of air permeability resistance, the rubber component preferably contains 78 to 95 parts by mass of butyl rubber in 100 parts by mass of the rubber component, more preferably 80 to 95 parts by mass, and even more preferably 80 to 92 parts by mass.

[0036] The rubber component preferably further contains a diene rubber. As the diene rubber, an isoprene rubber and a butadiene rubber are preferable. In one embodiment of the present invention, it is preferable that the rubber component further contains an isoprene rubber in addition to butyl rubber. By including an isoprene rubber in the rubber component, the breaking strength of the rubber composition can be increased. As a result, the durability of the rubber product using the rubber composition can be further improved.

[0037] The rubber component preferably contains 5 to 25 parts by mass of isoprene rubber in 100 parts by mass of the rubber component. When the rubber component contains 5 to 25 parts by mass of isoprene rubber in 100 parts by mass of the rubber component, the breaking strength of the rubber composition can be increased. As a result, the durability of the rubber product using the rubber composition can be further improved. From the same viewpoint, the rubber component preferably contains 5 to 22 parts by mass of isoprene rubber in 100 parts by mass of the rubber component, more preferably 5 to 20 parts by mass, and even more preferably 8 to 20 parts by mass.

[0038] Examples of the isoprene rubber include natural rubber, synthetic isoprene rubber, etc. The origin of the natural rubber is not particularly limited, and examples include those derived from para rubber tree, guayule, Russian dandelion, etc. 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 preferable.

[0039] Examples of the butadiene-based rubber include butadiene rubber and styrene-butadiene rubber. Here, it is preferable that the butadiene used as a raw material for the butadiene-based rubber is derived from biological resources or recycled resources.

[0040] Examples of the styrene-butadiene rubber include emulsion-polymerized styrene-butadiene rubber and solution-polymerized styrene-butadiene rubber.

[0041] The isoprene-based rubber and the butadiene-based rubber preferably have a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0042] Furthermore, in order to keep the overall sustainability rate of the rubber component within the aforementioned range, it is preferable to use natural rubber as the rubber component, or to use polymers synthesized using monomer components derived from biological resources and monomer components derived from recycled resources as monomer components. It is also possible to use mass balance certified synthetic rubber to keep the sustainability rate within the aforementioned range.

[0043] 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 mentioned above. The ratio of cis-bonded units in the butadiene-derived units can also be appropriately adjusted depending on the member to which it is applied. In this specification, "monomer unit" means a constituent unit of a polymer, "unit derived from isoprene" means a constituent unit in a polymer composed of isoprene, which is a monomer (including isoprene units in natural rubber), "unit derived from butadiene" means a constituent unit in a polymer composed of butadiene, which is a monomer, and "unit derived from aromatic vinyl compounds" means a constituent unit in a polymer composed of aromatic vinyl compounds, which are monomers. In this specification, the ratio of each monomer unit is measured by NMR.

[0044] In addition to the butyl rubber and isoprene-based rubbers mentioned above, the rubber components may also include diene-based rubbers such as butadiene rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene rubber, chloroprene rubber, and styrene-isoprene-butadiene copolymer rubber. These rubber components may be used individually or in combination of two or more.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] For example, the method described in Japanese Patent Publication No. 2022-179158 can be used to prepare rubber derived from biological resources.

[0049] 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.

[0050] (Recycled Carbon Black) The rubber composition 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 rubber products 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] The solid residue obtained by thermally decomposing waste materials such as used rubber and used tires contains ash in addition to carbon black. The ash originates from non-volatile components contained in rubber and tires. Therefore, the recycled carbon black obtained from this solid residue has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, a higher carbon content in recycled carbon black is preferable. In the recycled carbon black, the carbon content is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content in the recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed water.

[0054] The aforementioned ash content specifically includes zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, magnesium oxide, and the like. In the case of recycled carbon black produced from solid residue obtained by thermal decomposition of waste, a certain amount of ash remains even after various processes to remove it. In this embodiment, the presence of ash in recycled carbon black is permitted. In one embodiment, the lower limit of the ash content of the recycled carbon black may be 0.5% by mass.

[0055] 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).

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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).

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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 0% by mass or more and 3% 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.

[0068] 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.

[0069] The recycled carbon black has a nitrogen adsorption specific surface area of ​​40 to 100 m² obtained by the BET method. ２It 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] The recycled carbon black preferably has an ash content of 25% by mass or less, and more preferably 20% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the various physical properties of the rubber product to which the rubber composition is applied can be improved. Herein, in this specification, the ash content of the recycled carbon black is determined according to ASTM D8474 / D1506.

[0081] The recycled carbon black preferably has an oil adsorption capacity (OAN) of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, in this specification, the oil adsorption capacity (OAN) of the recycled carbon black is determined according to ASTM D2414.

[0082] The recycled carbon black preferably has an oil adsorption capacity (COAN) of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Hereinafter, the oil adsorption capacity (COAN) of the compressed sample of recycled carbon black is determined according to ASTM D3493.

[0083] Commercially available recycled carbon black can be used. Examples of such commercially available products include "PB365" manufactured by Enrestec. PB365 is recycled carbon black produced by the thermal decomposition of used tires, and has a nitrogen adsorption specific surface area of ​​73.6 m² by the BET method. ２ It is 1 / g and also contains approximately 17% by mass of ash.

[0084] 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.

[0085] (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.

[0086] 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).

[0087] The resin content is not particularly limited, but for example, the resin is preferably in the range of 1 to 100 parts by mass, and more preferably in the range of 5 to 60 parts by mass, per 100 parts by mass of the rubber component.

[0088] [Phenolic Resin] The rubber composition of this embodiment preferably further contains a phenolic resin. By further containing a phenolic resin in the rubber composition, the various physical properties of the rubber product to which the rubber composition is applied can be improved.

[0089] The phenolic resin is not particularly limited and can be appropriately selected according to the required performance. For example, it can be produced by condensing phenols such as phenol, cresol, resorcinol, tert-butylphenol, or mixtures thereof with formaldehyde in the presence of an acid catalyst such as hydrochloric acid or oxalic acid. Furthermore, the phenolic resin may be unmodified or modified. In addition, the phenolic resin may be used alone or in combination of two or more types.

[0090] Examples of unmodified phenolic resins include phenolic resins and phenol-formaldehyde resins.

[0091] Examples of modified phenolic resins include those having a structure obtained by modifying an unmodified phenolic resin with oils such as rosin oil, tall oil, cashew oil, linoleic acid, oleic acid, and linolenic acid, and having substituents such as hydrocarbon groups (e.g., alkyl groups) on the phenolic skeleton of the phenolic resin.

[0092] The hydroxyl group equivalent of the phenol resin is preferably 100 g / eq to 300 g / eq, more preferably 100 g / eq to 200 g / eq, and even more preferably 100 g / eq to 150 g / eq. The above hydroxyl group equivalent is measured in accordance with JIS K0070:1992.

[0093] The content of the phenolic resin is not particularly limited and can be adjusted as appropriate depending on the tire category, tire components, target performance, etc. For example, the content of the phenolic resin is preferably 0.1 parts by mass or more, and preferably 3.5 parts by mass or less, per 100 parts by mass of the rubber component.

[0094] (Oil) The rubber composition of this embodiment preferably further contains oil. By further containing oil in the rubber composition, the various physical properties of the rubber product to which the rubber composition is applied can be improved.

[0095] The aforementioned oils refer to the drawstring oils contained in rubber components and the liquid oils added as compounding agents to rubber compositions. Examples include vegetable oils, process oils, oils obtained by recycling vegetable oils or process oils, or mixtures thereof. From the viewpoint of reducing environmental impact, vegetable oils and recycled oils are preferred as oils. Examples of vegetable oils include palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, peanut oil, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, and coconut oil. Examples of process oils include paraffinic process oils, aromatic process oils, and naphthenic process oils. Commercially available oils can be used as the aforementioned oils. Examples of commercially available oils that can be used include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Nisshin Oillio Group Ltd., etc. These oils may be used individually or in combination of two or more types.

[0096] The oil content is not particularly limited and can be adjusted as appropriate depending on the tire category, tire components, target performance, etc. For example, the oil content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, more preferably 3 parts by mass, more preferably 5 parts by mass or more, more preferably 7 parts by mass or more, more preferably 9 parts by mass or more, and also preferably 25 parts by mass or less, and more preferably 20 parts by mass or less, per 100 parts by mass of the rubber component.

[0097] (Rubber Powder and Recycled Rubber) The rubber composition of this embodiment preferably further contains at least one of rubber powder and recycled rubber. By including at least one of rubber powder and recycled rubber in the rubber composition, the proportion of sustainable materials in the rubber product can be further improved. Rubber powder and recycled rubber will be described in detail below. In this specification, rubber powder and recycled rubber are not included in the rubber components described above.

[0098] The rubber composition of this embodiment preferably contains at least one of rubber powder and recycled rubber in an amount of 10 parts by mass or less per 100 parts by mass of the rubber component. By containing at least one of rubber powder and recycled rubber in an amount of 10 parts by mass or less per 100 parts by mass of the rubber component, the proportion of sustainable materials in the rubber product can be further improved without degrading the properties of the rubber composition. The content of at least one of rubber powder and recycled rubber may be 8 parts by mass or less, or 7 parts by mass or less per 100 parts by mass of the rubber component. Alternatively, the content of at least one of rubber powder and recycled rubber may be 2 parts by mass or more per 100 parts by mass of the rubber component.

[0099] -Rubber Powder- The rubber powder may be obtained by crushing used rubber products such as used tires, and optionally removing reinforcing materials such as steel materials and fibers, dust, glass, sand, stones, etc., or by preparing a new vulcanized rubber composition for the production of rubber powder and crushing it. For example, rubber powder can be obtained from vulcanized rubber by the method described in "Rubber Chemistry and Technology". In the process of crushing vulcanized rubber to obtain rubber powder, mechanical treatment or low-temperature treatment may be used. For example, in mechanical treatment, various crushing equipment such as cracker mills and granulators can be used to mechanically crush the vulcanized rubber into fine particles. In low-temperature treatment, the finely chopped vulcanized rubber is frozen at an extremely low temperature and then crushed into fine particles. In addition, a magnetic separator can be used to remove steel materials, and an air separator can be used to remove fibers. The rubber powder can be a commercially available product, and examples of such commercially available rubber powders include those from Global Corporation or Nantong Huili Rubber Corporation. From the viewpoint of reducing environmental impact, it is preferable to use rubber powder obtained by crushing used rubber products such as used tires. The rubber powder may be used alone or in combination of two or more types.

[0100] The composition of the rubber powder is not particularly limited and depends on the composition of the vulcanized rubber used as a raw material, such as used rubber products (used tires). In one embodiment, the rubber powder includes rubber components, carbon black, silica, etc. The rubber components, carbon black, silica, etc. contained in the rubber powder may be the same as or different from the rubber components, carbon black, silica, etc. that may be contained in the rubber composition of this embodiment described above.

[0101] The rubber powder preferably has a volume-average particle diameter of 1000 μm or less, more preferably 500 μm or less, even more preferably 200 μm or less, and even more preferably 100 μm or less. Furthermore, the smaller the volume-average particle diameter of the rubber powder, the better, and there is no particular lower limit. In this specification, the volume-average particle diameter is measured using a laser diffraction particle size distribution analyzer, for example, the "CAPA500" manufactured by Horiba, Ltd.

[0102] The rubber powder preferably has a residue of less than 1% by mass after sieving through a 60-mesh sieve, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, with no particular lower limit. Furthermore, the rubber powder preferably has a residue of less than 10% by mass after sieving through an 80-mesh sieve, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, with no particular lower limit. In this specification, the sieve residue is measured according to ASTM D5644-01.

[0103] The rubber powder preferably has an acetone extract content of 12% by mass or less, more preferably 11% by mass or less, even more preferably 10% by mass or less, and preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more. In this specification, the acetone extract content in the rubber powder refers to the acetone extract content (%) obtained by an acetone extraction method in accordance with JIS K6350.

[0104] The content of the rubber powder is not particularly limited and can be adjusted as appropriate depending on the tire category to which it is applied, the internal components of the tire, the target performance, etc. For example, the content of the rubber powder is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and also preferably 200 parts by mass or less, more preferably 150 parts by mass or less, more preferably 100 parts by mass or less, more preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less.

[0105] -Recycled Rubber- The recycled rubber is obtained by recycling used rubber from rubber products such as tires. By including recycled rubber in the rubber composition, the proportion of sustainable materials in rubber products can be increased.

[0106] In the rubber composition of this embodiment, commercially available recycled rubber can be used as the recycled rubber. The recycled rubber can be, for example, recycled used rubber from automobile tires, tubes, and other rubber products as specified in JIS K6313-2012, or rubber having equivalent properties. The recycled rubber may also be desulfurized.

[0107] The type of recycled rubber can be selected from recycled tube rubber, recycled tire rubber, or other recycled rubber, and multiple types can be combined. Among these, recycled tire rubber is preferred. The method for manufacturing the recycled rubber is not particularly limited, and known methods such as the oil pan method and the liquemeter method can be used.

[0108] The rubber component in the recycled rubber preferably has a natural rubber content of 40% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass. The natural rubber content in the recycled rubber can be determined by measurement using pyrolysis gas chromatography (PyGC).

[0109] The recycled rubber content can be adjusted as appropriate depending on the tire category, tire components, target performance, etc. For example, the recycled rubber content is preferably 0.1 to 40 parts by mass, more preferably 0.5 to 20 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of rubber components.

[0110] (Clay) The rubber composition of this embodiment preferably further contains clay. Including clay in the rubber composition allows for a higher level of air permeability resistance to be maintained. The clay is preferably flat, and more preferably has an aspect ratio of 3 to 30. An aspect ratio of 3 or more of the clay can improve the air permeability resistance of the rubber composition, and an aspect ratio of 30 or less of the clay can maintain good processability of the rubber composition.

[0111] The clay used is not limited to any particular type, but examples include kaolin clay, sericite clay, calcined clay, and silane-modified clay with surface treatment. One type of clay may be used alone, or two or more types may be used in combination. Among these, kaolin clay is preferred from the viewpoint of maintaining resistance to air permeability.

[0112] The clay content is not particularly limited and can be adjusted as appropriate depending on the tire category, tire components, target performance, etc. For example, the clay content is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and preferably 50 parts by mass or less, and more preferably 40 parts by mass or less, per 100 parts by mass of the rubber component.

[0113] (Silica) The rubber composition of this embodiment may contain silica. The type of silica is not particularly limited. Examples include wet silica, colloidal silica, calcium silicate, aluminum silicate, etc. Among the above, wet silica is preferred, and precipitated silica is more preferred. These silicas may be used individually or in combination of two or more types.

[0114] From the perspective of reducing environmental impact, silica derived from silicate plants is preferred as the silica. Such silicate plants are present, for example, in mosses, ferns, toxics, cucurbitaceae, urticaceae, gramineae plants, etc. Among these plants, gramineae plants are preferred. Among gramineae plants, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred from the perspective of easy availability. As the silica, further examples include silica produced by recycling silicon components from the edge materials of silicon wafers used as raw materials for semiconductors, glass bottles, etc. and used in production.

[0115] The silica is not particularly limited. 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, assuming the adsorption cross-sectional area per molecule of cetyltrimethylammonium bromide on the silica surface is 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.

[0116] Also, the content of the silica is not particularly limited. For example, the content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, and still more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. On the other hand, the content of silica is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and still more preferably 100 parts by mass or less with respect to 100 parts by mass of the rubber component.

[0117] (Silane Coupling Agent) If 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.

[0118] Furthermore, bioethanol can also be used as a raw material for silane coupling agents.

[0119] (Carbon black other than recycled carbon black) The rubber composition of this embodiment may contain carbon black other than recycled carbon black.

[0120] 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. This carbon black may be used alone or in combination of two or more types.

[0121] 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.

[0122] 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.

[0123] (Other) 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 liquid softeners like liquid polymers, antioxidants, zinc oxide, sulfur, vulcanization accelerators, waxes, stearic acid, calcium carbonate, talc, alumina, aluminum hydroxide, mica and other fillers, organic peroxides, cellulose nanofibers, cellulose particles, eggshells, rice husks, walnut powder and other solid fine particles.

[0124] (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.

[0125] (Applications) The rubber composition of this embodiment can be applied to various components of a tire, for example, the tread (cap tread, base tread, under tread), cushion rubber, shoulder, sidewall, bead filler, carcass coating rubber, belt coating rubber, insulation, chafer, inner liner, etc. It can also be used as a side reinforcement layer for run-flat tires. In addition to tires, the rubber composition of this embodiment can also be applied to hoses, rubber tracks, seismic isolation rubber, etc.

[0126] <Tire Internal Components> The tire internal components of this embodiment are characterized by being made of the rubber composition described above. Because the tire internal components of this embodiment are made of the rubber composition described above, the proportion of sustainable materials, high-temperature tensile strength after degradation, and crack propagation resistance after degradation are improved while maintaining air permeability resistance.

[0127] <Tire> The tire of this embodiment is characterized by comprising the tire internal components described above. Because the tire of this embodiment comprises the tire internal components described above, the proportion of sustainable materials, the high-temperature tensile strength after degradation, and the crack propagation resistance after degradation are improved while maintaining air permeability resistance. The tire of this embodiment can be manufactured by a conventional method using the tire internal components made of the rubber composition described above. For example, the 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 pre-vulcanization process, and then further vulcanizing it. The tire of this embodiment is preferably a pneumatic tire, and as the gas to be filled into the pneumatic tire, in addition to ordinary air or air with adjusted oxygen partial pressure, inert gases such as nitrogen, argon, and helium can be used.

[0128] Next, an embodiment of the tire of the present invention will be described in detail with reference to the drawings. Figure 2 is a cross-sectional view of an embodiment of the tire of the present invention. The tire 21 of this embodiment shown in Figure 2 has a pair of bead portions 22, a pair of sidewall portions 23, and a tread portion 24 connected to both sidewall portions 23, and comprises a carcass 26 extending in a toroidal shape between bead cores 25 embedded in each of the pair of bead portions 22, and a belt 27 arranged on the radially outer side of the crown portion of the carcass 26. Furthermore, the tire 21 of this embodiment has side rubber 28 on the pair of sidewall portions 23, and an inner liner 29 made of rubber is arranged along the inner surface of the carcass 26.

[0129] The carcass 26 of the tire 21 shown in Figure 2 is composed of a single carcass ply made of multiple parallel-arranged cords covered with coating rubber, and the carcass 26 consists of a main body portion that extends in a toroidal shape between the pair of bead cores 25 and folded portions that are wound radially outward from the inside to the outside in the tire width direction around each bead core 25, but the number of plies and structure of the carcass 26 in the tire 21 of the present invention are not limited to this.

[0130] Furthermore, in the tire 21 shown in Figure 2, a belt 27 consisting of two belt layers is arranged on the radially outer side of the crown portion of the carcass 26. The belt layers typically consist of rubberized layers of cords (preferably steel cords) that extend at an angle to the tire's equatorial plane. The two belt layers are stacked so that the cords constituting the belt layers intersect each other with the tire's equatorial plane in between, thereby forming the belt 27. Although the belt 27 in the figure consists of two belt layers, in the tire 21 of the present invention, the number of belt layers constituting the belt 27 may be three or more.

[0131] 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.

[0132] <Evaluation of Carbon Black> The physical properties of carbon black were evaluated using the following method.

[0133] (1) Grind gauge measurement: 3.75 g of zinc oxide, 0.20 g of the test carbon black, and 2.00 mL of epoxidized soybean oil were mixed to obtain a mixture. The obtained mixture was kneaded for 5 to 10 minutes to form a paste, and the sample paste was prepared. In accordance with JIS K5101-1-5, paste was prepared using a Toyo Seiki Co., Ltd. Huber Mahler (model: H3) under conditions of load 0.4536 kN and glass plate rotation speed 100 r / min. In accordance with JIS K5400, each sample paste was placed on a grind gauge and stretched with a scraper. A grind gauge with a range of 0 to 25 μm was used. It was confirmed that three or more continuous lines of 10 mm or more appeared, and the scale at the location where the line caused by the third largest particle among the particles that produced the continuous lines of 10 mm or more appeared was read, and this reading was taken as the particle size of the third largest particle. The average value of the particle size measured four times is shown in Table 1.

[0134] (2) Nitrogen adsorption specific surface area (N ２ SA) In accordance with ASTM D6556, calculate the specific surface area (N) of nitrogen adsorption of the tested carbon black. ２ SA was measured.

[0135] (3) Elemental analysis: The content of zinc (Zn), copper (Cu), and iron (Fe) was confirmed by X-ray fluorescence analysis (XRF).

[0136] (4) Ash content The ash content of the carbon black sample was measured according to ASTM D8474 and D1506.

[0137]

[0138] <Preparation and Evaluation of Rubber Compositions (1)> Rubber compositions were prepared using a standard Banbury mixer according to the formulations shown in Table 2. For each rubber composition obtained, the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources was calculated to determine the sustainable material ratio. Other chemicals included antioxidants, oils, fatty acids, sulfur, and vulcanization accelerators, and the same types and amounts were added in Reference Examples 1 and 2. Commercially available chemicals commonly used in the preparation of rubber compositions were used. The amounts added were the amounts commonly used when preparing rubber compositions. The obtained rubber compositions were evaluated for post-degradation high-temperature tensile strength and post-degradation crack propagation resistance using the following methods.

[0139] (5) Evaluation method for 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 degraded at 100°C for 48 hours in an air atmosphere. A tensile test was performed at 100°C in accordance with JIS K 6251:2017 and the tensile strength was measured. The high-temperature tensile strength after degradation was expressed as an index using the following formula, with the tensile strength of the test piece in Reference Example 1 set to 100. High-temperature tensile strength index after degradation = (Tensile strength of the test piece / Tensile strength of the test piece in Reference Example 1) × 100 A larger index indicates better high-temperature tensile strength after degradation.

[0140] (6) Evaluation method for crack propagation resistance after degradation The rubber composition to be tested was degraded in an air atmosphere at 100°C for 24 hours beforehand. Strip-shaped test pieces were prepared from the rubber composition with a 0.5 mm hole drilled in the lengthwise direction in the center, and a dc / dn test was performed using the test pieces (using a Shimadzu "Servopulsa" at a frequency of 5 Hz and 80°C, repeated fatigue was applied with a strain of 30-100%, and the tear energy [J / m] at 1950 cycles was measured. ２ The crack propagation rate was calculated when the common logarithm of [ ] was 3.9. In the crack propagation rate obtained by the above process, the formulation data of Reference Example 1 was used as a control (index value 100), and the formula data of each example was normalized by the reciprocal of the formula data. A larger index value indicates a lower crack propagation rate and superior crack propagation resistance.

[0141]

[0142] *1 Natural rubber: RSS#3 *2 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *3 New carbon black: Manufactured by Asahi Carbon, N550 *4 Recycled carbon black 1: Same as Table 1 *5 Recycled carbon black 2: Same as Table 1

[0143] Table 2 shows that the rubber composition of Reference Example 1 is a recycled carbon black in which, when measured with a grind gauge, there are three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles that give rise to these lines of 10 mm or more is 20 μm or less. This improves the proportion of sustainable materials while also improving the high-temperature tensile strength and crack propagation resistance after degradation.

[0144] <Preparation and Evaluation of Rubber Compositions (2)> Rubber compositions were prepared using a standard Banbury mixer according to the formulations shown in Table 3. Each of the obtained rubber compositions was evaluated using the evaluation method described below.

[0145] (7) Ash Content The ash content of carbon black was measured by thermogravimetric analysis (TGA, RIGAKU Corporation). The sample was heated from room temperature to 550°C under a nitrogen atmosphere, and then heated to maintain 550°C under an air atmosphere, and the loss on heating (mass%) was measured. The loss on heating (mass%) when the sample was heated from room temperature to 550°C under a nitrogen atmosphere was defined as "Loss on Heating 1," and the loss on heating (mass%) when heated to maintain 550°C under an air atmosphere was defined as "Loss on Heating 2." The ash content was calculated using the following formula: Ash content (mass%) = 100 - Loss on Heating 1 - Loss on Heating 2

[0146] (8) Tensile Strength Tensile tests were conducted at room temperature in accordance with JIS K6301-1995, and the tensile strength of each rubber composition was measured. The evaluation results were expressed as an index using the following formula, with Reference Example 3 as the control (index value 100): Tensile Strength Index = (Tensile strength of test specimens other than Reference Example 3 / Tensile strength of test specimen of Reference Example 3) × 100 A larger index indicates that the rubber composition is less prone to fracture and has superior tensile strength.

[0147] (9) Viscoelasticity A viscoelasticity test was performed using "ARES-G2" manufactured by TA Instruments Inc. under the conditions of a frequency of 15 Hz, a shear strain of 10%, and a temperature of 50°C, and the storage modulus (G') of the rubber composition was measured. The evaluation results were indexed with Reference Example 3 as the control (index value 100). A larger index indicates a higher G', which in turn indicates superior rubber properties when applied to products such as tires.

[0148]

[0149] *6 SBR: Styrene-butadiene rubber, product name "#1500" *7 CB3: Carbon Black 3, recycled carbon black equivalent to N330 *8 CB4: Carbon Black 4, recycled carbon black equivalent to N330 *9 CB5: Carbon Black 5, recycled carbon black equivalent to N330 *10 CB6: Carbon Black 6, new carbon black equivalent to N330

[0150] Table 3 shows that when carbon black with a Zn content of 0% by mass or more and 3.0% by mass or less is applied, the deterioration of the physical properties of the rubber composition is suppressed.

[0151] <Preparation and Evaluation of Rubber Compositions (3)> Rubber compositions for Reference Example 7 and Reference Example 8 were prepared according to the formulations shown in Table 4. For each rubber composition obtained, the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources was calculated to determine the sustainable material ratio. Other chemicals included antioxidants, oils, fatty acids, sulfur, and vulcanization accelerators, and the same types and amounts were added in Reference Example 7 and Reference Example 8. Commercially available chemicals commonly used in the preparation of rubber compositions were used. The amounts added were the amounts commonly used when preparing rubber compositions. Furthermore, the air permeability resistance and elongation at break (EB) after thermal degradation were evaluated for the obtained rubber compositions using the following method. The evaluation results are shown in Table 4.

[0152] (10) Evaluation of Air Permeability Resistance As an evaluation of air permeability resistance, the obtained rubber composition was measured for air permeability at 60°C using an air permeability tester GTR-31ABSM (manufactured by GTR Tech Co., Ltd.). The air permeability (JIS K 6275-1:2009) is shown as an index, with the air permeability of Reference Example 7 set to 100. A smaller index value indicates better air permeability resistance.

[0153] (11) Evaluation of elongation at break (EB) after thermal degradation A vulcanized rubber test piece was prepared by vulcanizing the rubber composition. Next, the vulcanized rubber test piece was left at 100°C for 24 hours to allow thermal degradation to occur. A tensile test similar to that in JIS K 6251 was performed on the thermally degraded test piece at 100°C, and the elongation at break (EB) after thermal degradation was measured. The results are expressed as an index with the elongation at break (EB) after thermal degradation in Reference Example 7 set to 100. A larger index value indicates a larger elongation at break (EB) after thermal degradation.

[0154]

[0155] *11 NR: Natural rubber *12 IIR: Brominated butyl rubber, manufactured by Exxon, product name "Bromobutyl 2222" *13 Unused CB: Unused carbon black, manufactured by Asahi Carbon, product name "Asahi #55", nitrogen adsorption specific surface area (N ２ SA) = 26m ２ / g, OAN = 87 mL / 100 g *14 Recycled CB: Recycled carbon black, manufactured by Enrestec, product name "PB365", ash content = 17% by mass *15 Oil: manufactured by JX Corporation, product name "Super Oil Y22" *16 Phenolic resin: manufactured by Sumitomo Bakelite Co., Ltd., product name "DUREZ 19900"

[0156] Table 4 shows that the rubber composition of Reference Example 8, by using butyl rubber and recycled carbon black, has an improved proportion of sustainable materials while maintaining air permeability resistance.

[0157] Two types of rubber compositions having the compound compositions shown in Table 5 were prepared, and these rubber compositions were vulcanized at 145°C for 33 minutes to obtain vulcanized rubber test specimens. The obtained vulcanized rubber test specimens were punched out into JIS-3 dumbbells, and the resulting samples were subjected to tensile tests at room temperature in accordance with JIS K 6251:2004, and the breaking strength (TB) before thermal degradation (initial) and after thermal degradation (100°C × 24 hours) was measured. The results are shown in Table 5. A higher value indicates better fracture resistance, i.e., better crack resistance.

[0158]

[0159] *17 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *18 Carbon black: Manufactured by Asahi Carbon, product name "N550", nitrogen adsorption specific surface area (N ２ SA) = 40m ２ / g, OAN = 121 mL / 100 g *19 Recycled carbon black: Enrestec, product name "PB365", ash content 17% by mass *20 Anti-aging agent: product name "Nocrack 6C" (Ouchi Shinko Chemical Industry Co., Ltd.) and product name "Nocrack 224" (Ouchi Shinko Chemical Industry Co., Ltd.), same ratio in each rubber composition *21 Oil: ENEOS, product name "A / Omix" *22 Fatty acid: Miyoshi Oil & Fat Co., Ltd., product name "MXST" *23 Other chemicals: sulfur, vulcanization accelerator, resin, and wax, same ratio in each rubber composition

[0160] Table 5 shows that replacing carbon black (virgin (new) carbon black) with commercially available recycled carbon black among the various materials contained in the rubber composition reduces the tensile strength (TB) before and after thermal degradation, i.e., the crack propagation resistance.

[0161] Tables 2 to 5 show that the rubber composition of the present invention, when measured with a grind gauge, has three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles that give rise to these lines of 10 mm or more is 20 μm or less. By applying recycled carbon black, the proportion of sustainable materials is improved, and it is expected that the high-temperature tensile strength and high-temperature crack propagation resistance after degradation will be improved, while air permeability resistance will be maintained.

[0162] The rubber composition of the present invention can be used in rubber products such as tires, rubber tracks, seismic isolation rubber, and hoses, and is particularly suitable as an inner liner for tires.

[0163] 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 21: Tire 22: Bead area 23: Sidewall area 24: Tread area 25: Bead core 26: Carcass 27: Belt 28: Side rubber 29: Inner liner

Claims

1. A rubber composition comprising a rubber component and recycled carbon black, wherein 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 give rise to the lines with a length of 10 mm or more is 20 μm or less, and the rubber component comprises butyl rubber.

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

3. The rubber composition according to claim 1, wherein, in the measurement using the 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 the recycled carbon black is prepared.

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

6. The rubber composition according to claim 5, wherein the recycled carbon black has a Zn content of 0% by mass or more and 3.0% by mass or less.

7. The rubber composition according to claim 1, wherein the recycled carbon black has an ash content of 20.0% by mass or less.

8. The rubber composition according to claim 1, wherein the rubber component further comprises isoprene-based rubber.

9. The rubber composition according to claim 1, wherein the butyl rubber content is 70 to 95 parts by mass per 100 parts by mass of the rubber component.

10. The rubber composition according to claim 1, further comprising oil.

11. The rubber composition according to claim 1, further comprising a phenolic resin.

12. The rubber composition according to claim 1, further comprising at least one of rubber powder and recycled rubber in an amount of 10 parts by mass or less per 100 parts by mass of the rubber component.

13. The rubber composition according to claim 1, further comprising clay.

14. An internal tire component comprising the rubber composition described in claim 1.

15. A tire comprising the tire internal member described in claim 14.

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