Rubber composition for treads and tire

Abstract

The purpose of the present invention is to provide a rubber composition for treads that achieves an excellent sustainable material ratio without a reduction in other physical properties.　The present invention is a rubber composition that includes a rubber component, silica, recycled carbon black, and an antioxidant. The rubber composition is characterized in that the rubber component contains a high-purity natural rubber that has a nitrogen content of no more than 0.3 mass% and in that when the carbon black is evaluated on a grind gauge, there are at least three lines that have a length of at least 10 mm, and the particle size of the third largest particle among the particles that constitute the lines that have a length of at least 10 mm is no more than 20 μm.

Description

Tread rubber composition and tire

[0001] This invention relates to a rubber composition for treads and a tire.

[0002] Conventionally, in heavy-duty pneumatic tires for rough roads, methods to prevent a decline in heat generation performance, appearance, and wear resistance have included selecting the carbon black compounded into the tire tread rubber composition and optimizing its filling amount. In recent years, various tread rubbers for heavy-duty pneumatic tires have also been proposed that incorporate silica in addition to carbon black.

[0003] For example, Patent Documents 1 to 3 disclose a technology that improves wear resistance, cut resistance, and heat generation performance by incorporating silica together with carbon black into a rubber composition for the tread of pneumatic tires used for heavy loads such as construction vehicles.

[0004] Furthermore, in addition to the aforementioned performance characteristics such as wear resistance, cut resistance, and heat generation performance, from the perspective of social sustainability, there is a demand for the use of so-called sustainable materials, such as materials derived from biological resources (biomass resources) and recycled resources, for the various components used in tires. The development of technologies to increase the usage rate of sustainable materials (hereinafter sometimes referred to as the "sustainable material ratio") is also desired.

[0005] JP-A-1-311141 JP-A-3-65406 JP-A-4-226140

[0006] The technologies described in Patent Documents 1 to 3 all aim to improve the heat generation performance, appearance performance, and wear resistance after driving in rubber compositions for the treads of heavy-duty pneumatic tires. However, when recycled carbon black is used as the carbon black, sufficient performance cannot be obtained, and further improvements were desired.

[0007] Therefore, the present invention aims to provide a rubber composition for treads with an excellent sustainable material ratio without compromising other performance characteristics. Furthermore, the present invention aims to provide a tire with an excellent sustainable material ratio without compromising other performance characteristics.

[0008] The inventors of this invention have diligently researched rubber compositions containing rubber components, silica, and carbon black in order to solve the above problems. They have found that by using high-purity natural rubber with a nitrogen content of 0.3% by mass or less as the rubber component, and by using a specific recycled carbon black as the carbon black, it is possible to increase the rubber strength, maintain various physical properties well, and improve the sustainability rate.

[0009] In other words, the gist of the present invention is as follows: [1] A rubber composition comprising a rubber component, silica, and carbon black, wherein the rubber component contains high-purity natural rubber with a nitrogen content of 0.3% by mass or less, the carbon black 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. The rubber composition for treads of the present invention makes it possible to improve the sustainable material ratio without reducing other performance.

[0010] [2] A tire characterized by comprising the tread rubber composition of the present invention. The tire of the present invention is capable of improving the sustainable material ratio without reducing other performance.

[0011] According to the present invention, it is possible to provide a tread rubber composition with an excellent sustainable material ratio without compromising other performance characteristics. Furthermore, according to the present invention, it is possible to provide a tire with an excellent sustainable material ratio without compromising other performance characteristics.

[0012] This is an explanatory diagram illustrating an example of measurement results using a grind gauge.

[0013] The following describes an example embodiment of the tread rubber composition and tire of the present invention.

[0014] <Tread Rubber Composition> The tread rubber composition of the present invention comprises a rubber component, silica, and carbon black. The following describes each component constituting the tread rubber composition of the present invention.

[0015] (Rubber component) The rubber component contained in the tread rubber composition of the present invention contains high-purity natural rubber with a nitrogen content of 0.3% by mass or less. By containing the high-purity natural rubber, the natural rubber does not contain an excessive amount of protein, and gelation can be suppressed. As a result, even when recycled carbon black, which will be described later, is used, various properties such as the reinforcing properties of the rubber can be maintained in good condition. From a similar viewpoint, the nitrogen content in the natural rubber is preferably 0.25% by mass or less, and more preferably 0.2% by mass or less.

[0016] Here, the high-purity natural rubber is not particularly limited in terms of other requirements, as long as the nitrogen content is 0.3% by mass or less. For example, the high-purity natural rubber may be natural rubber from which proteins have been removed by a centrifugal separation process. The centrifugal separation process is a process of deproteinizing natural rubber latex, which is the raw material for natural rubber, by centrifugal separation. The conditions for the centrifugal separation (rotation speed, time, etc.) are not particularly limited, and the conditions can be changed as appropriate depending on the amount of protein to be removed. For example, if the nitrogen content in the natural rubber is 0.1% by mass or less, the centrifugal separation process can be performed several times at a rotation speed of about 7500 rpm. After the centrifugal separation process, high-purity natural rubber can be obtained by washing and drying.

[0017] The natural rubber latex used in the centrifugal separation process is not particularly limited. For example, field latex collected from rubber trees or concentrated natural rubber latex obtained by processing it can be used. The dry rubber content in the natural rubber latex is also not particularly limited, but from the viewpoint of obtaining better abrasion resistance, it is preferably 10% by mass or more, more preferably 30% by mass, and even more preferably 40% by mass or more.

[0018] Furthermore, the content of the high-purity natural rubber in the rubber component may be 100%, but other types of rubber may also be included as long as they do not impair the objective of the present invention. In addition, the natural rubber may be a mixture of high-purity natural rubber and ordinary natural rubber. In that case, the content of the high-purity natural rubber in the rubber component is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 90% by mass or more, from the viewpoint of further improving abrasion resistance. It should be noted that rubber other than the high-purity natural rubber may also be included.

[0019] Furthermore, the rubber component preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. 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.

[0020] 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.

[0021] 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.

[0022] As the rubber component, the rubber derived from the biological resources and the rubber derived from the recycled resources are preferred. Here, the proportion 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 proportion 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%.

[0023] 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 measurement value by gel permeation chromatography (GPC), for example.

[0024] As the rubber component, a diene rubber is preferred, and as the diene rubber, an isoprene rubber and a butadiene rubber are preferred.

[0025] 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, Russian dandelion, etc. Natural rubber may be modified or denatured, and 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.

[0026] Examples of the butadiene rubber include butadiene rubber and styrene-butadiene rubber. Here, butadiene as the raw material of the butadiene rubber is preferably derived from biological resources or recycled resources.

[0027] Examples of the styrene-butadiene rubber include, for example, emulsion polymerization styrene-butadiene rubber and solution polymerization styrene-butadiene rubber. <op>

[0028] The isoprene rubber and the butadiene rubber preferably have a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, yet more preferably 60% by mass or more, still more preferably 70% by mass or more, further preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0029] In addition, in order to make the sustainability 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 with a monomer component derived from biological resources or a monomer component derived from recycled resources as the monomer component. Note that in order to make the sustainability rate within the above range, mass balance certified synthetic rubber can also be used.

[0030] 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.

[0031] 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.

[0032] The rubber component may have functional groups introduced through modification that interact with fillers such as carbon black and silica, which will be described later. 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.

[0033] 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.

[0034] 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.

[0035] For example, the method described in Japanese Patent Publication No. 2022-179158 can be used to prepare rubber derived from biological resources.

[0036] 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.

[0037] (Silica) The rubber composition for tire treads of the present invention contains silica in addition to the rubber components described above. By including silica in the rubber composition, various properties such as abrasion resistance and fracture resistance can be enhanced.

[0038] Here, the silica content is preferably such that the total silica content, including carbon black (described later), is 50 parts by mass or more per 100 parts by mass of the rubber component. By setting the total silica and carbon black content to 50 parts by mass or more per 100 parts by mass of the rubber component, the reinforcing properties of the tire can be enhanced, and superior wear resistance can be achieved. From a similar viewpoint, the total silica and carbon black content is preferably 60 parts by mass or more, and more preferably 65 parts by mass or more, per 100 parts by mass of the rubber component. On the other hand, from the viewpoint of suppressing deterioration of the processability and low heat generation properties of the rubber composition, the total silica and carbon black content is preferably 80 parts by mass or less, more preferably 75 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of the rubber component.

[0039] Furthermore, while the silica content must satisfy the total content mentioned above, from the viewpoint of achieving fracture resistance, it is preferable that the silica content alone be 5 parts by mass or more per 100 parts by mass of the rubber component. By setting the silica content to 5 parts by mass or more per 100 parts by mass of the rubber component, the reinforcing properties of the tire can be enhanced and fracture resistance can be achieved. From a similar viewpoint, it is preferable that the silica content be 10 parts by mass or more per 100 parts by mass of the rubber component. On the other hand, from the viewpoint of suppressing deterioration of the processability of the rubber composition, it is preferable that the silica content be 25 parts by mass or less per 100 parts by mass of the rubber component.

[0040] Here, it is preferable that the silica has a CTAB specific surface area of ​​200 to 240 ml / 100g. When the CTAB specific surface area of ​​the silica is 200 ml / 100g or more, an improvement in fracture resistance can be obtained, and when the CTAB specific surface area of ​​the silica is 240 ml / 100g or less, dispersion defects and a decrease in processability can be suppressed. The CTAB specific surface area of ​​the silica can be measured, for example, in accordance with JIS K 6430:2008.

[0041] Furthermore, the BET specific surface area of ​​the silica is 100 m². ２ / g or more, 250m ２ It can be less than or equal to / g. The BET specific surface area is the specific surface area obtained by the BET method, and in this invention, it can be measured in accordance with ASTM D4820-93.

[0042] The type of silica is not particularly limited. Examples include wet silica, colloidal silica, calcium silicate, and aluminum silicate. 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.

[0043] Furthermore, from the viewpoint of reducing environmental impact, silica derived from silicate plants is preferred as the silica. These silicate plants include, for example, mosses, ferns, horsetails, plants of the Cucurbitaceae family, Urticaceae family, and grasses. Among these plants, grasses are preferred. Among grasses, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred from the viewpoint of availability. Other examples of silica include silicon wafer scraps used as raw materials for semiconductors, silica recycled from glass bottles, etc., and used in manufacturing.

[0044] (Carbon black, recycled carbon black) The rubber composition of the present invention further contains carbon black in addition to the rubber components and silica described above. This is because the reinforcing properties of the rubber composition are enhanced, and better abrasion resistance can be obtained.

[0045] Furthermore, the rubber composition of the present invention includes recycled carbon black. Since recycled carbon black is a material derived from recycled resources, including recycled carbon black improves the proportion of sustainable materials in the tread rubber composition. Applying this rubber composition to tires improves the proportion of sustainable materials in the tires and reduces the environmental impact.

[0046] In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials submitted for recycling. Examples of such waste materials include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only rubber generated from rubber products but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is fine rubber generated, for example, in the buffing process of retreading tires, where the tread portion remaining on the base tire is scraped off. Peeling rubber is long pieces of rubber, for example, 1 to 2 cm wide, that are peeled off from the surface of rubber products such as tires. Peeling rubber is generated by scraping the surface of rubber products such as tires using a U-shaped or V-shaped knife like a peeler. Furthermore, waste rubber includes not only cross-linked rubber but also unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, and rubber parts or components at the manufacturing stage of final products. Used tires may be retreaded, or they may be tires discarded for any reason, such as tires that have reached the end of their lifespan, tires that have been replaced or scrapped, or ELTs (End-of-Life Tires). 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 desirable. Furthermore, waste oil that is mixed with carbon black or rubber containing carbon black is desirable. The aforementioned "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.

[0047] 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 above-mentioned vulcanized rubber product containing carbon black. When a rubber product containing carbon black is thermally decomposed, solid residue and volatile components (oil) are obtained, and recycled carbon black can be recovered from either. When recovering carbon black from volatile components, it is possible to recover oil with a specific gravity suitable for producing carbon black and use it to produce carbon black using an existing carbon black production method (for example, Japanese Patent Publication No. 2015-520259). In this case, unlike carbon black recovered from solid residue, there are advantages such as the absence of impurities and the absence of mixtures of different grades. Furthermore, in the production of environmentally friendly carbon black, there are various options besides the oil obtained by recovering volatile components from the thermal decomposition of rubber mentioned above, such as using vegetable oil or oil derived from waste plastics. However, edible resources such as vegetable oil present challenges in securing sufficient quantities due to other uses such as food, and the environmental impact associated with the expansion of cultivated land must also be considered. Similarly, oil derived from waste plastics is used for other purposes such as horizontal recycling of plastics, so supply issues are also a concern. On the other hand, when using volatile components (oil) produced by the thermal decomposition of vulcanized rubber products, particularly tires, the tire industry has a system for continuing to use existing materials, making it possible to continue using existing materials and reduce the consumption of new materials in new tire manufacturing, thereby contributing to reducing the environmental burden on the industry. The grade of carbon black is not particularly limited, but examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.Furthermore, when the recycled carbon black of the present invention 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.

[0048] 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 (

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

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

[0049] 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 and / or carboxyl groups on its surface. In addition, in Japanese Patent 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.

[0050] 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.

[0051] 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.

[0052] 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. In addition, it may be possible to group by tire type and by 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.

[0053] Furthermore, the recycled carbon black is one in which, when measured with a grind gauge, there are three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles that produce such lines of 10 mm or more is 20 μm or less. By incorporating recycled carbon black into a rubber composition that, when measured with a grind gauge, has three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles that produce such lines of 10 mm or more is 20 μm or less, the dispersibility of the recycled carbon black in the rubber is improved, thereby increasing the sustainability rate while also improving the high-temperature crack propagation resistance of the rubber composition after degradation. Methods for evaluating the dispersibility of carbon black using a grind gauge are described in JIS K5101-1-5 (especially regarding the preparation of paste) and JIS K5400 (especially regarding the method of evaluation by the manner in which linear marks are generated).

[0054] In the evaluation method for recycled carbon black of this embodiment, as described later, 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. Note that 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 using it for other purposes (performance other than the durability of the rubber composition containing recycled carbon black), the range of the grind gauge to be used can be appropriately selected according to the purpose. 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, and in the recycled carbon black of this embodiment, the paste of the recycled carbon black is prepared in accordance with JIS K5101-1-5 as a measurement sample for measurement using a grind gauge. By preparing the recycled carbon black paste in accordance with JIS K5101-1-5, the evaluation accuracy of recycled carbon black can be further improved.

[0055] 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.

[0056] 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.

[0057] 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, especially the 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.

[0058] 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.

[0059] Furthermore, the recycled carbon black may contain one or more metal atoms selected from the group consisting of Zn, Cu, and Fe. Since recycled carbon black is obtained from recycled waste as raw material, it contains various elements other than carbon (C), and zinc (Zn), copper (Cu), and iron (Fe) are elements that are easily contained in recycled carbon black. Therefore, recycled carbon black containing at least one of the elements of Zn, Cu, and Fe does not require any special removal operations, and tread rubber compositions containing such recycled carbon black are easy to manufacture.

[0060] If the recycled carbon black contains Zn, the Zn content in the recycled carbon black is preferably 2.5% by mass or less. A lower Zn content in the carbon black is preferable, but if the Zn content is 2.5% by mass or less, the deterioration of the physical properties of the rubber composition can be suppressed. From the viewpoint of suppressing the deterioration of the physical properties of the rubber composition, the Zn content is more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, even more preferably 1.0% by mass or less, and particularly preferably 0.5% by mass or less. The Zn content may also be 0.01% by mass or more, or 0.05% by mass or more. The above upper and lower limits can be combined as appropriate. Methods for adjusting the Zn content in recycled carbon black to within the above range include, for example, pre-analyzing the amount of Zn contained in the raw rubber to be acid-treated and recycled, and applying some or all of the raw rubber with a low Zn content.

[0061] Furthermore, if the recycled carbon black contains Fe, the Fe content in the recycled carbon black is preferably 0% by mass or more and 0.1% by mass or less. A lower Fe content in the recycled carbon black is preferable, but if the Fe content is 0.1% by mass or less, the deterioration of the physical properties of the rubber composition can be suppressed. From the viewpoint of suppressing the physical properties of the rubber composition, the Fe content is more preferably 0.09% by mass or less, even more preferably 0.08% by mass or less, still preferably 0.07% by mass or less, even more preferably 0.06% by mass or less, even more preferably 0.05% by mass or less, particularly preferably 0.04% by mass or less, and most preferably 0.03% by mass or less. The Fe content may also be 0.01% by mass or more, or 0.02% by mass or more. The above upper and lower limits can be combined as appropriate.

[0062] If the recycled carbon black contains Cu, the Cu content in the recycled carbon black is preferably 0% by mass or more and 0.05% by mass or less. A lower Cu content in the recycled carbon black is preferable, but if the Cu content is 0.05% by mass or less, the deterioration of the physical properties of the rubber composition can be suppressed. From the viewpoint of suppressing the physical properties of the rubber composition, the Cu content is more preferably 0.04% by mass or less, even more preferably 0.03% by mass or less, even more preferably 0.02% by mass or less, and even more preferably 0.01% by mass or less. The Cu content may also be 0.01% by mass or more, or 0.02% by mass or more. The above upper and lower limits can be combined as appropriate.

[0063] Furthermore, the recycled carbon black may contain components other than Zn, Fe, and Cu as described above. "Components other than Zn, Fe, and Cu" refers to components other than Zn, Fe, and Cu in the ash. Examples of components other than Zn, Fe, and Cu in the ash include Si (silicon), S (sulfur), Ca (calcium), K (potassium), Br (bromine), Mg (magnesium), Cl (chlorine), P (phosphorus), Co (cobalt), Na (sodium), and Al (aluminum).

[0064] The recycled carbon black may contain silicon (Si). In that case, the Si content in the recycled carbon black is preferably 0% by mass or more and 1.0% by mass or less. A Si content of 1.0% by mass or less suppresses a decrease in the physical properties of the rubber composition. From a similar viewpoint, the Si content is more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less. It is also preferable that the Si content is 0% by mass, i.e., substantially Si-free. On the other hand, the Si content may be 0.01% by mass or more, or 0.05% by mass or more. The above upper and lower limits can be combined as appropriate.

[0065] The recycled carbon black may contain sulfur (S). In that case, the S content in the recycled carbon black is preferably 0.4% by mass or more, and more preferably 0.5% by mass or more. Furthermore, the S content is preferably 2.0% by mass or less, more preferably 1.8% by mass or less, and even more preferably 1.0% by mass or less. The above upper and lower limits can be combined as appropriate.

[0066] The recycled carbon black may contain Ca (calcium). In that case, the Ca content in the recycled carbon black is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and particularly preferably 0.8% by mass or more. Furthermore, the Ca content is preferably 1.5% by mass or less, more preferably 1.2% by mass or less, and even more preferably 1.1% by mass or less. The above upper and lower limits can be combined as appropriate.

[0067] The recycled carbon black preferably has an ash content of 0.5% by mass or more and 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. In other words, 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.

[0068] 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. The lower limit of the ash content of the recycled carbon black used in this embodiment may be 0.5% by mass. Hereinafter, the ash content of carbon black is determined according to ASTM D8474 / D1506.

[0069] Furthermore, 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.

[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 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.

[0081] 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.

[0082] The recycled carbon black content is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, more preferably 5 to 50 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 5 to 20 parts by mass, per 100 parts by mass of the rubber component. When the recycled carbon black content is 5 parts by mass or more per 100 parts by mass of the rubber component, it has a significant effect in improving the ratio of sustainable materials in the tread rubber to which the rubber composition is applied, and when it is 50 parts by mass or less, the low rolling resistance of the rubber composition can be well maintained.

[0083] Further, the rubber composition for tread of the present invention may also contain carbon black other than the recycled carbon black. By combining carbon black other than the recycled carbon black with the recycled carbon black, the crack growth resistance of the rubber composition can be further improved. As the carbon black other than the recycled carbon black, plant-derived carbon black is particularly preferable. Examples of plant-derived carbon black include those derived from castor oil and rosin oil.

[0084] There is no particular limitation on the carbon black other than the recycled carbon black. For example, SAF, ISAF, IISAF, N339, HAF, FEF, GPF, SRF grade carbon black of high, medium or low structure, particularly SAF, ISAF, IISAF, N339, HAF, FEF grade carbon black are preferably used. The nitrogen adsorption specific surface area (N ２ SA, measured in accordance with JIS K6217-2:2001) is preferably 20 m ２ / g or more, more preferably 30 m ２ / g or more, still more preferably 50 m ２ / g or more, even more preferably 70 m ２ / g or more, and preferably 250 m​​​​​​​​​​​Preferably, the proportion of recycled carbon black in the total amount of recycled carbon black and other carbon black (i.e., the total amount of carbon black) is 5 to 21% by mass. When the proportion of recycled carbon black in the total amount of carbon black is 5% by mass or more, it has a significant effect on improving the ratio of sustainable materials in the rubber composition and the tread rubber using it. When the proportion of recycled carbon black in the total amount of carbon black is 21% by mass or less, the reinforcing properties and handling stability of the rubber composition can be further improved.

[0087] Furthermore, the carbon black has a nitrogen adsorption specific surface area (N ２ SA) is 135m ２ It is preferable that the N of the carbon black is 1 / g or more. ２ SA is 135m ２ This is because a higher concentration of 1 / g or more provides superior wear resistance. Furthermore, the nitrogen adsorption specific surface area (N) of the carbon black is also important. ２ SA) is 180m ２ It is preferable that the N of the carbon black is less than or equal to / g. ２ SA is 180m ２ When the N content is less than / g, it is possible to suppress deterioration of productivity and low heat generation. From a similar viewpoint, the N content of the carbon black ２ SA is 140-170m ２ It is more preferable that the nitrogen adsorption specific surface area (N) of the carbon black is greater than the amount of nitrogen adsorption. ２ Regarding SA, if multiple types of carbon black are included, it is the average value of those values, and can be measured, for example, in accordance with JIS K 6217-7:2013.

[0088] Furthermore, it is preferable that the carbon black has a dibutyl phthalate (OAN) oil absorption capacity of 80 to 120 ml / 100 g. ２ When the amount is 1 / g or more, low heat generation and deterioration of productivity can be suppressed, and the N of the carbon black ２When SA is 120 ml / 100 g or less, gelation can be suppressed, and better wear resistance can be obtained. From a similar viewpoint, the OAN of the carbon black is 85 to 110 m ２ It is preferable that the value be / g, and 85 to 100 m ２ It is more preferable that the amount is / g. The amount of OAN supplied with carbon black can be measured in accordance with ASTM D2414.

[0089] The carbon black content is preferably such that the total content of carbon black and silica is 50 parts by mass or more per 100 parts by mass of the rubber component. Furthermore, the carbon black content alone is preferably 40 parts by mass or more, more preferably 46 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. This is because when the carbon black content is 40 parts by mass or more per 100 parts by mass of the rubber component, the reinforcing properties are enhanced and superior abrasion resistance is obtained. On the other hand, the carbon black content is preferably 60 parts by mass or less per 100 parts by mass of the rubber component, and more preferably 55 parts by mass or less. This is because when the carbon black content is 60 parts by mass or less per 100 parts by mass of the rubber component, the deterioration of low heat generation can be suppressed.

[0090] Furthermore, it is preferable that the mass ratio of the carbon black content to the total content of the silica (carbon black / (carbon black + silica)) is 0.80 or higher. By setting the mass ratio of the carbon black content to the total content of the carbon black and silica to 0.80 or higher, better wear resistance can be achieved. From the viewpoint of maintaining good low heat generation, it is more preferable that the mass ratio of the carbon black content to the total content of the carbon black and silica (described later) be 0.95 or lower, and even more preferable that be 0.85 or lower.

[0091] (Resin) The tread rubber composition of the present invention preferably contains a resin in addition to the rubber components, silica, and carbon black described above. By including a resin, the ice performance and fracture resistance of the rubber composition can be further enhanced.

[0092] Furthermore, the resin preferably has a softening point of 130°C or higher. A softening point of 130°C or higher improves the resistance to fracture. From the same viewpoint, a softening point of 140°C or higher is preferred, and 145°C or higher is more preferred. In this specification, the softening point of the resin is the temperature at which the sphere drops when the softening point specified in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring-type softening point measuring device.

[0093] Here, the type of resin is not particularly limited. For example, terpene resins, rosin resins, C ５ based resin, C ５ -C ９ based resin, C ９ Examples include cyclopentadiene resins, dicyclopentadiene resins, aromatic resins, coumarone resins, indene resins, coumarone-indene resins, olefin resins, polyurethane resins, and acrylic resins. These resins may be used individually or in combination of two or more. Among the resins mentioned above, the resin is preferably a cyclopentadiene resin, and more preferably a dicyclopentadiene resin, because it can achieve better fracture resistance. The dicyclopentadiene resin is, for example, AlCl ３ Ya BF ３ This refers to resins obtained by polymerizing dicyclopentadiene using Friedel-Crafts type catalysts such as the above. Dicyclopentadiene-based resins include homopolymers of dicyclopentadiene, copolymers of dicyclopentadiene and aromatic monomers, and copolymers of dicyclopentadiene and C ９ Copolymers with fractions (such as vinyltoluene and indene) are examples.

[0094] Furthermore, the resin content is preferably 1 part by mass or more, and more preferably 1.5 parts by mass or more, per 100 parts by mass of the rubber component. This is because the above-mentioned effect of improving fracture resistance can be more effectively achieved. However, from the viewpoint of suppressing deterioration of low heat generation, the resin content is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0095] (Anti-aging agent) The tread rubber composition of the present invention contains an anti-aging agent in addition to the rubber components, silica, carbon black, and resin described above, and it is preferable that the content of the anti-aging agent is 0.4 parts by mass or more per 100 parts by mass of the rubber components. By including an anti-aging agent of 0.4 parts by mass or more per 100 parts by mass of the rubber components in the tread rubber composition, the reinforcing properties and wear resistance of the tread rubber composition can be further enhanced. From a similar viewpoint, it is preferable that the content of the anti-aging agent is 1 part by mass or more per 100 parts by mass of the rubber components.

[0096] Furthermore, it is preferable that the content of the anti-aging agent be less than 3 parts by mass per 100 parts by mass of the rubber component. This is because superior fracture resistance can be obtained when the content of the anti-aging agent is less than 3 parts by mass per 100 parts by mass of the rubber component. From a similar viewpoint, it is preferable that the content of the anti-aging agent be less than 2 parts by mass per 100 parts by mass of the rubber component.

[0097] The type of anti-aging agent is not particularly limited. For example, amine-based anti-aging agents, phenol-based anti-aging agents, and other anti-aging agents can be used. Among these anti-aging agents, it is preferable to use at least an amine-based anti-aging agent from the viewpoint of obtaining better wear resistance.

[0098] The amine-based antioxidant is preferably at least one selected from the group consisting of N-(1,3-dimethylbutyl)-N'-phenyl-para-phenylenediamine, N-isopropyl-N'-p-phenylenediamine, N-(3-methacryloyloxy-2-hydroxypropyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine. Among these, N-(1,3-dimethylbutyl)-N'-phenyl-para-phenylenediamine is particularly preferred. The amine-based antioxidant may be used alone or in combination of two or more.

[0099] (Silane Coupling Agent) Furthermore, if the tread rubber composition of the present invention 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. Bioethanol can also be used as a raw material for the silane coupling agent.

[0100] (Other Components) In addition to the components described above, the tread rubber composition of the present invention may contain other components as appropriate, selected for the purpose or as necessary, within the limits that do not impair the effects of the present invention. Other components may include, for example, inorganic fillers other than silica and carbon black, liquid softeners such as oils and liquid polymers, antioxidants, zinc oxide, sulfur, vulcanization accelerators, waxes, fillers such as stearic acid, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica, organic peroxides, cellulose nanofibers, cellulose particles, solid fine particles such as eggshells, rice husks, and walnut powder, and rubber powder obtained by crushing used rubber products.

[0101] Examples of inorganic fillers other than silica and carbon black include aluminum hydroxide and clay. Among these inorganic fillers, aluminum hydroxide and the like are preferred because they have relatively high reinforcing properties, while clay and the like are effective because they can be used to obtain effects that take advantage of their shape characteristics.

[0102] (Manufacturing of Tread Rubber Composition) The method for manufacturing the tread rubber composition of the present invention is not particularly limited, but for example, the rubber composition can be manufactured by blending various components as needed with the rubber component, kneading, heating, extruding, etc. The obtained rubber composition can be vulcanized by vulcanization.

[0103] 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 include Banbury mixers, intermixes, kneaders, and rolls, which are commonly used for mixing rubber compositions.

[0104] 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.

[0105] 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.

[0106] There are no particular restrictions on the apparatus, method, and conditions for performing the vulcanization, and they can be appropriately selected according to the purpose. Examples of vulcanization apparatus include molding vulcanizers that use molds for vulcanizing rubber compositions. As for the vulcanization conditions, the temperature is, for example, around 100 to 190°C.

[0107] <Tire> The tire of the present invention is characterized by containing the tread rubber composition of the present invention described above. By including the tread rubber composition of the present invention as a tire material, an excellent sustainable material ratio can be achieved without degrading other physical properties. The tire of the present invention can be used, for example, as a heavy-duty tire, a truck / bus tire, an aircraft tire, or a passenger car tire, but among these, it is preferable to use it as a heavy-duty tire. This is because the tread rubber composition used as the material for the tread has excellent wear resistance, which offers significant advantages when used as a heavy-duty tire.

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

[0109] Furthermore, while the tread rubber composition of the present invention is required to be applied to the tread (base tread, cap tread, under tread) in the tire of the present invention, it can also be applied to various other components. For example, it can be used in cushion rubber, shoulder, sidewall, clinch, bead filler, carcass coating rubber, insulation, chafer, inner liner, etc., and can also be used in the side reinforcement layer of run-flat tires, etc. In addition, the tread rubber composition of the present invention can be applied to rubber tracks, seismic isolation rubber, etc., in addition to tires.

[0110] 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.

[0111] [Example 1] It is assumed that a sample of a tread rubber composition will be prepared by mixing each component according to the formulation shown in Table 1 and kneading it using a Banbury mixer. In addition, although not shown in Table 1, various processing aids, additives, vulcanizing chemicals, and vulcanization accelerators are added as appropriate during sample preparation, to the extent that they do not affect the effects of the present invention.

[0112] <Evaluation> For each tread rubber composition sample, it is assumed that the sample will be extruded into a sheet, and then vulcanized at 145°C for 90 minutes to produce a vulcanized rubber sample. The following evaluation will then be performed on the resulting vulcanized rubber sample.

[0113] (1) Evaluation of heat generation For each vulcanized rubber sample, it is assumed that the loss tangent (tanδ) will be measured using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.) under the conditions of a temperature of 23°C, an initial load of 1600 mN, a dynamic strain of 1%, and a frequency of 52 Hz. Using the measurement results of formulations not shown in the table, a simulation of the effect of changing the formulation was performed, and the loss tangent (tanδ) of the formulations listed in the table was predicted. For the evaluation, the reciprocal of the measured value of tanδ was taken and expressed as an index with the reciprocal value of the tanδ of the comparative example sample set to 100, and the larger the index value, the better the low heat generation performance. The evaluation results are shown in Table 1. If the index value is 90 or higher, there is no effect on the tire performance.

[0114] (2) Abrasion Resistance Evaluation For each vulcanized rubber sample, it was assumed that the abrasion rate would be measured by rolling it on a grinding wheel at a constant speed. Using the measurement results of formulations not shown in the table, a simulation of the effect of changing the formulation on performance was performed, and the abrasion rate of the formulations listed in the table was predicted. The evaluation was performed by calculating the reciprocal of the abrasion rate and expressing it as an index with the reciprocal of the abrasion rate of the vulcanized rubber made from the comparative example rubber composition set to 100. A larger index value indicates a slower abrasion rate and better abrasion resistance. The evaluation results are shown in Table 1.

[0115] (3) For each vulcanized rubber sample, it is assumed that the fracture strength will be measured after thermal degradation at 100°C for 24 hours. Using the measurement results of formulations not shown in the table, a simulation of the effect of changing the formulation will be performed to predict the fracture resistance of the formulations listed in the table. For evaluation, the value will be shown as an index value with the measurement results of the comparative example set to 100, and a larger index value will indicate superior fracture resistance.

[0116]

[0117] *1 TSR20 *2 High-purity natural rubber with a nitrogen content of 0.18% by mass, obtained by centrifugal separation *3 N ２ SA: 145m ２ / g, OAN oil supply rate: 99ml / 100g of carbon black *4 N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. "Nocrac 6C" *5 Manufactured by Tosoh Silica Co., Ltd. "Nipseal KQ"

[0118] Table 1 shows that the sample of tread rubber composition corresponding to the inventive example exhibits well-balanced and excellent results in terms of low heat generation, abrasion resistance, and fracture resistance. On the other hand, the sample of tread rubber composition corresponding to the comparative example is inferior to the inventive example in at least one of the evaluation items.

[0119] [Example 2] Two types of rubber compositions having the compound compositions shown in Table 2 were prepared, and vulcanized rubber test pieces were obtained by vulcanizing samples of these rubber compositions at 145°C for 33 minutes.

[0120] <Evaluation> (1) Breaking strength before and after thermal degradation The obtained vulcanized rubber test pieces were punched into JIS-3 dumbbells, and the resulting samples were subjected to tensile tests at room temperature according to JIS K 6251:2004, and the breaking strength (TB) before (initial) thermal degradation and after (100°C × 24 hours) thermal degradation was measured. The results are shown in Table 2. A higher value indicates better fracture resistance, i.e., better crack resistance.

[0121] (2) Sustainable Material Ratio For each sample of tread rubber composition, the total content of materials derived from biological resources (biomass resources) and recycled resources was measured, and the content per 100 parts by mass of rubber component (sustainable material content) and the mass ratio of the rubber composition (sustainable material ratio) were derived. The obtained sustainable material ratios are shown in Table 2. Note that a higher obtained sustainable material content and sustainable material ratio indicates a better sustainability rate.

[0122]

[0123] *6 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *7 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 *8 Recycled carbon black: Enrestec, product name "PB365", ash content = 17% by mass *9 Anti-aging agent: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrack 6C" *10 Anti-aging agent: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrack 224" *11 Oil: ENEOS, product name "A / Omix" *12 Fatty acid: Miyoshi Oil & Fat Co., Ltd., product name "MXST" *13 Other chemicals: Total amount of sulfur, vulcanization accelerator, resin, and wax, same ratio in each rubber composition

[0124] The results in Table 2 show that when carbon black (virgin carbon black) is simply replaced with recycled carbon black among the various materials contained in the rubber composition, the tensile strength before and after thermal degradation decreases.

[0125] [Example 3] <Evaluation of recycled carbon black> First, the physical properties of recycled carbon black 1 and 2 were measured using the following method.

[0126] (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 Huber Mahler (model: H3) under conditions of a load of 0.4536 kN and a glass plate rotation speed of 100 r / min. In accordance with JIS K5400, each sample paste was placed on a grind gauge and stretched with a scraper. A grind gauge with a range of 0 to 25 μm was used. It was confirmed that three or more continuous lines of 10 mm or more appeared, and the scale at the location where the line caused by the third largest particle among the particles that produced the continuous lines of 10 mm or more appeared was read, and this reading was taken as the particle size of the third largest particle. The average value of the particle size measured four times is shown in Table 3.

[0127] (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.

[0128] (3) Elemental analysis: The content of zinc (Zn), copper (Cu), and iron (Fe) was confirmed by X-ray fluorescence analysis (XRF).

[0129] (4) Ash content The ash content of the carbon black sample was measured according to ASTM D8474 and D1506.

[0130]

[0131] (Example 2 of Invention, Comparative Example 2) Rubber compositions were prepared using a standard Banbury mixer according to the formulations shown in Table 4. Other chemicals included antioxidants, oils, fatty acids, sulfur, and vulcanization accelerators, and the same types and amounts were added in both the comparative example and the example of invention. Commercially available chemicals commonly used in the preparation of rubber compositions were used. The amounts added were also the amounts commonly used when preparing rubber compositions.

[0132] <Evaluation> After vulcanization treatment, each obtained sample was subjected to the following evaluations (1), (2), and (3). (1) Sustainable material ratio The total content of materials derived from biological resources (biomass resources) and recycled resources (recycled resources) was measured for the rubber composition of each sample, and the content per 100 parts by mass of rubber component (sustainable material blending portion) and the mass ratio of the rubber composition (sustainable material ratio) were derived. The obtained sustainable material ratios are shown in Table 4. Note that a larger obtained sustainable material blending portion and sustainable material ratio indicates a better sustainability rate.

[0133] (2) Tensile strength after thermal degradation Each rubber composition was vulcanized at 145°C for 33 minutes to obtain vulcanized rubber. The obtained vulcanized rubber was thermally degraded 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. The tensile strength of the test piece of Invention Example 2 was set to 100, and 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 Invention Example 2) × 100 The larger the high-temperature tensile strength index after degradation, the less the vulcanized rubber is likely to break, indicating superior performance after degradation (fracture resistance).

[0134] (3) The rubber composition to be subjected to the post-thermal degradation crack resistance test 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. Using this test piece, a dc / dn test (using Shimadzu Corporation's "ServoPulsa") was performed, applying repeated fatigue with a strain of 30-100% at a frequency of 5 Hz and 80°C. The crack propagation rate was calculated when the common logarithm of the tear energy [J / m2] after 1950 cycles was 3.9. The crack propagation rate obtained by the above treatment was normalized by the reciprocal of the formulation data for each example, with the formulation data of Invention Example 2 used as a control (index value 100). A larger index value indicates a lower crack propagation rate and superior crack resistance.

[0135]

[0136] *14 Natural rubber: RSS#3 *15 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *16 New carbon black: Manufactured by Asahi Carbon, N550 *17 Recycled carbon black 1: Same as Table 3 *18 Recycled carbon black 2: Same as Table 3

[0137] Tables 3 and 4 show that even with rubber compositions containing recycled carbon black of the same ash content, the tensile strength and crack resistance after thermal degradation of the rubber composition are improved when the recycled carbon black, as measured by a grind gauge of the blended recycled carbon black, shows three or more lines of 10 mm or longer in length, and the third largest particle among those resulting in these lines has a particle size of 20 μm or less.

[0138] [Example 4] (Examples 3-4 of the Invention, Comparative Example 3) 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 3 to prepare rubber compositions for each sample.

[0139] <Evaluation> Each sample of the rubber composition was vulcanized at 145°C for 33 minutes to obtain vulcanized rubber, and then evaluated as follows. The evaluation results are shown in Table 5.

[0140] (1) The Zn and S content was measured by Zn-quantity X-ray fluorescence analysis.

[0141] (2) 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

[0142] (3) 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 the standard example as the control (index value 100): Tensile strength index = (Tensile strength of test specimens other than the standard example / Tensile strength of test specimen of the standard example) × 100 A higher index indicates that the rubber composition is less prone to fracture and has superior tensile strength.

[0143] (4) Viscoelasticity A viscoelasticity test was conducted using "ARES-G2" manufactured by TA Instruments Inc. under the conditions of a frequency of 15 Hz, shear strain of 10%, and temperature of 50°C, and the storage modulus (G') of the rubber composition was measured. The evaluation results were indexed with the 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.

[0144]

[0145] *19 SBR: Styrene-butadiene rubber, product name "#1500" *20 CB1: Carbon black, recycled carbon black equivalent to N330 *21 CB2: Carbon black, recycled carbon black equivalent to N330 *22 CB3: Carbon black, recycled carbon black equivalent to N330 *23 CB5: Carbon black, virgin (new) carbon black equivalent to N330

[0146] Table 5 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.

[0147] Furthermore, as shown in Examples 1 to 3 above, by using recycled carbon black as defined in this application and blending it with a rubber component containing high-purity natural rubber with a nitrogen content of 0.3% by mass or less, improvements in durability after thermal degradation can be expected. In addition, because recycled carbon black is used, it also contributes to improving the proportion of sustainable materials in the rubber composition.

[0148] According to the present invention, it is possible to provide a tread rubber composition with an excellent sustainable material ratio without compromising other performance characteristics. Furthermore, according to the present invention, it is possible to provide a tire with an excellent sustainable material ratio without compromising other performance characteristics.

[0149] 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 at the location where the line caused by the third largest particle appears [Contribution to the United Nations-led Sustainable Development Goals (SDGs)]

[0150] The SDGs have been proposed to realize a sustainable society. One embodiment of this invention is considered to be a technology that can contribute to "No. 12 - Responsible Consumption and Production" and "No. 13 - Climate Action," among others.

Claims

1. A rubber composition comprising a rubber component, silica, and carbon black, wherein the rubber component contains high-purity natural rubber with a nitrogen content of 0.3% by mass or less, the carbon black 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.

2. The tread rubber composition according to claim 1, characterized in that, 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 tread rubber composition according to claim 1, characterized in that, 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 adjusted.

4. Further comprising an anti-aging agent, wherein the total content of the silica and the carbon black is 50 parts by mass or more per 100 parts by mass of the rubber component, and the nitrogen adsorption specific surface area (N) of the carbon black. ２ SA) is 135m ２ The tread rubber composition according to claim 1 or 2, characterized in that the amount of the antioxidant is 0.4 parts by mass or more per 100 parts by mass of the rubber component.

5. The tread rubber composition according to claim 1 or 2, further comprising a resin, wherein the resin has a softening point of 130°C or higher, and its content is 1 part by mass or more per 100 parts by mass of the rubber component.

6. The tread rubber composition according to claim 1 or 2, characterized in that the mass ratio of the carbon black content to the total content of the carbon black and silica is 0.80 or more.

7. The tread rubber composition according to claim 1 or 2, characterized in that the high-purity natural rubber is obtained by removing proteins from natural rubber latex through a centrifugal separation process.

8. The tread rubber composition according to claim 1 or 2, characterized in that the content of the anti-aging agent is 0.7 parts by mass or more and less than 3 parts by mass per 100 parts by mass of the rubber component.

9. The tread rubber composition according to claim 1 or 2, characterized in that the carbon black content is 40 parts by mass or more per 100 parts by mass of the rubber component.

10. The tread rubber composition according to claim 1 or 2, characterized in that the silica content is 5 parts by mass or more and 25 parts by mass or less per 100 parts by mass of the rubber component.

11. The tread rubber composition according to claim 1 or 2, characterized in that the CTAB specific surface area of ​​the silica is 200 to 240 ml / 100g.

12. A tire characterized by comprising the tread rubber composition described in claim 1 or 2.

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